Water-based ink composition for writing implements and writing implements using the same

Abstract

To provide a water-based ink composition for writing instruments that is excellent in the low temperature stability and the scratch resistance of handwritten characters and the like, and to provide a writing instrument including the same.SOLUTION: A water-based ink composition for writing instruments contains a colorant, a water-soluble oxolane compound with a boiling point of 100°C or higher, an aqueous resin, and water. There is also provided a writing instrument including the same.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] It has been known for some time that water-soluble organic solvents are used in aqueous ink compositions for writing instruments, such as ink compositions for ballpoint pens, for the purpose of improving the dry-up resistance and stability of the ink composition over time. Glycol-based solvents such as propylene glycol are known as water-soluble organic solvents suitable for such purposes. These glycol-based solvents have relatively low volatility, which results in improved dry-up resistance by suppressing water evaporation at the pen tip, improved ink stability over time by suppressing evaporation from the ink tank, improved ink penetration onto paper and improved writing drying, and the solvent contained in the ink composition causes freezing point depression, thereby suppressing freezing at low temperatures.

[0003] However, even ink compositions containing such glycol-based solvents may not have sufficient ink fluidity when placed at a low temperature, such as -10°C, even after being returned to room temperature, and further improvement is desired. In addition, ink compositions containing glycol-based solvents have poor permeability, and when written on, for example, a resin film, the handwriting does not dry sufficiently, and rubbing the handwriting immediately after writing can cause problems such as fading, and improvement is also desired in this regard. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 62-241977 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a water-based ink composition for a writing instrument that has both low-temperature stability and good writing drying properties. [Means for solving the problem]

[0006] The water-based ink composition for a writing instrument according to the present invention is characterized by comprising a colorant, a water-soluble oxolane compound having a boiling point of 100° C. or higher, and water.

[0007] The water-based ballpoint pen according to the present invention contains the ink composition described above. [Effects of the Invention]

[0008] According to the present invention, by using a specific water-soluble oxolane compound as a solvent, there is provided an aqueous ink composition for a writing instrument which exhibits little fluctuation in performance even after exposure to low-temperature conditions, dries handwritten characters quickly even when written on a non-permeable writing surface, is resistant to smearing even when rubbed, and has excellent low-temperature stability, handwriting drying properties, and handwriting rub-off resistance. DETAILED DESCRIPTION OF THE INVENTION

[0009] <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") comprises a colorant, a specific water-soluble oxolane compound, and water.

[0010] <Coloring agent> The colorant used in the present invention is not particularly limited and may be a dye, pigment, or the like, and may be appropriately selected and used.

[0011] The dyes that can be used in the present invention are not particularly limited as long as they are soluble or dispersible in an aqueous medium. Examples include various dyes such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes, and food dyes, which can be used alone or in combination of two or more. The content of the dye is preferably 0.1 to 20% by mass, more preferably 0.1 to 10% by mass, based on the total mass of the ink composition.

[0012] Specifically, acid dyes include CI Acid Red 18, CI Acid Red 51, CI Acid Red 52, CI Acid Red 87, CI Acid Red 92, CI Acid Red 289, CI Acid Orange 10, CI Acid Yellow 3, CI Acid Yellow 7, CI Acid Yellow 23, 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, and CI Acid Violet 49. , CI Acid Black 1, CI Acid Black 2; 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; direct dyes include CI Direct Red 28, CI Direct Yellow 44, CI Direct Blue 86, CI Direct Blue 87, CI Direct Violet 51, CI Direct Black 19; and food colorings include CI Food Yellow 3 and CI Food Black 2.

[0013] Pigments that can be used in the present invention include inorganic, organic, and processed pigments, including 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, pearlescent pigments, fluorescent pigments, phosphorescent pigments, and complementary color pigments. Other examples include microencapsulated pigments in which a colored resin particle, consisting of a pigment dispersed in a medium, is encapsulated or solidified within a shell made of a resin wall-forming substance using known microencapsulation methods. Microencapsulated pigments encapsulating functional materials such as liquid crystals, reversible thermochromic compositions, and photochromic materials may also be used. Furthermore, colored resin particles in which a pigment is coated with a transparent or translucent resin, or colored or colorless resin particles colored with a pigment or dye, may also be used. These dyes and pigments may be used alone or in combination of two or more. The content of the colorant is preferably 1 to 30% by mass based on the total mass of the ink composition.

[0014] Furthermore, conventionally, pigments are dispersed in ink compositions, which tend to have poorer penetration into the writing surface compared to ink compositions containing dyes, making it difficult to improve the drying properties of written lines. However, in the present invention, by using a water-soluble oxolane compound, a water-based resin, or a surfactant in combination as described below, the drying properties of written lines can be further improved even when a pigment is used as a colorant. Furthermore, pigments have excellent water resistance and light resistance, and can produce good color development. For these reasons, it is preferable to use a pigment as a colorant.

[0015] <Water-soluble oxolane compound> The ink composition according to the present invention contains a water-soluble oxolane compound having a boiling point of 100° C. or higher. Because oxolane compounds with low boiling points tend to volatilize easily from the ink composition, the boiling point must be 100° C. or higher, preferably 110° C. or higher, and more preferably 120° C. or higher, in order to maintain the stability of the ink composition. Furthermore, in order to be present uniformly and stably in the aqueous ink composition, it is preferable that the compound be water-soluble. Here, water-soluble means that the required amount can be uniformly dissolved in the aqueous ink composition. More specifically, the solubility in water at 20°C is preferably 5 g / 100 ml or more, more preferably 10 g / 100 ml or more, and even more preferably 20 g / 100 ml or more.

[0016] The oxolane compound used in the present invention is a derivative of oxolane or dioxolane. Oxolane or dioxolane cannot be used because of their low boiling points. Furthermore, the boiling point tends to increase as the substituent group becomes bulkier, but water solubility tends to decrease if only hydrophobic groups are present. From this perspective, the oxolane compound used in the present invention is preferably one represented by the following formula (1): [ka] where: X is O or CR2; Each R is independently hydrogen, alkyl having 1 to 3 carbon atoms, hydroxyalkyl having 1 to 3 carbon atoms, aminoalkyl having 1 to 3 carbon atoms, or alkoxy having 1 to 3 carbon atoms. Preferably, one or two R's are alkyl having 1 to 3 carbon atoms, and more preferably, one or two R's are hydroxyalkyl having 1 to 3 carbon atoms or aminoalkyl having 1 to 3 carbon atoms.

[0017] Also preferred water-soluble oxolane compounds are: 2,2-Dimethyl-4-hydroxymethyl-1,3-dioxolane (bp 188-189°C) 2,2-Dimethyl-4-hydroxyethyl-1,3-dioxolane 2,2-Dimethyl-4,5-dihydroxyethyl-1,3-dioxolane 2-Methyl-2-ethyl-1,3-dioxosolane (bp 116-117°C) 2-Methoxy-1,3-dioxolane (bp 129-130°C) 2-Chloromethyl-1,3-dioxolane (bp 157-158°C) 2,2-Dimethyl-1,3-oxolane-4-methanamine Tetrahydrofurfurylamine Tetrahydrofurfuryl alcohol

[0018] Of these, the following are more preferred: 2,2-Dimethyl-4-hydroxymethyl-1,3-dioxolane 2,2-Dimethyl-4-hydroxyethyl-1,3-dioxolane 2,2-Dimethyl-4,5-dihydroxyethyl-1,3-dioxolane

[0019] Similar to conventionally used glycol-based solvents, such water-soluble oxolane compounds can prevent freezing by lowering the freezing point, and they also exhibit little deterioration in performance even after storage under low-temperature conditions or after freezing, thereby achieving excellent low-temperature stability.

[0020] The content of the water-soluble oxolane compound in the ink composition according to the present invention is preferably 1 to 30 mass %, more preferably 5 to 20 mass %, and even more preferably 10 to 20 mass %, based on the total mass of the ink composition.

[0021] <Water-based resin> The ink composition according to the present invention preferably further contains an aqueous resin. By combining the ink composition according to the present invention with an aqueous resin, the fixation of handwriting can be improved, and as a result, the abrasion resistance can be improved.

[0022] In the present invention, the term "waterborne resin" refers to a resin that is highly hydrophilic to water. Examples of such waterborne resins include water-soluble resins that have hydrophilic groups and can be uniformly dissolved in water, and water-dispersible resins that can be uniformly dispersed in water in the form of fine particles.

[0023] The water-soluble resin is a polymer having hydrophilic groups such as hydroxyl groups and carboxyl groups. Specific examples of the water-soluble resin include acrylic resins, alkyd resins, polyvinylpyrrolidone, and polyvinyl alcohol. These water-soluble resins also have the function of uniformly dispersing pigment particles, water-insoluble water-dispersible resins, and hydrophobic organic resin particles contained in the ink composition.

[0024] The content of the water-soluble resin is preferably 0.1 to 10 mass %, and more preferably 0.5 to 5 mass %, based on the total mass of the ink composition.

[0025] A water-dispersible resin is a resin that is poorly soluble in water and can be uniformly dispersed in water in the form of fine particles. Specific examples of such resins include acrylic resins, urethane resins, styrene-butadiene resins, polyester resins, and vinyl acetate resins. Such water-dispersible resins are generally blended in the form of a dispersion into an ink composition.

[0026] The water-dispersible resin has an average particle size of 0.2 μm or less, more specifically, 0.01 to 0.2 μm. When the average particle size is 0.2 μm or less, there is little sedimentation of the resin particles in the ink composition, and the ink dispersion stability is good.

[0027] The water-dispersible resin used in the present invention preferably has a minimum film-forming temperature of 40° C. or less, more preferably 20° C. or less. When the minimum film-forming temperature is 40° C. or less, a film is easily formed in the room temperature range, and the drying and abrasion resistance of handwriting improves not only on permeable surfaces but also on non-permeable surfaces, and the ability to prevent ink from dripping from the pen tip also tends to improve.

[0028] The content of the water-dispersible resin is preferably 0.1 to 5.0% by mass based on the total mass of the ink composition. By including 0.1% by mass or more of the water-dispersible resin, desired effects such as improved scratch resistance of handwriting can be easily achieved. On the other hand, if the content is too high, an excessively strong film may be formed on the pen tip, impairing dry-up resistance or saturating the improvement effect, so a content of 5.0% by mass or less is preferred.

[0029] Specific examples of the acrylic resin emulsion include Neocryl XK-190, Neocryl A1127 (trade names, manufactured by DSM Neoresin), Joncryl 390, Joncryl 74J, Joncryl PDX-7630A, and Joncryl 7600 (all trade names, manufactured by BASF Japan Ltd.).

[0030] When the ink composition according to the present invention contains a water-based resin, it is preferable to contain a combination of both a water-soluble resin and a water-dispersible resin. By using this combination in an ink composition for a ballpoint pen, it is possible to simultaneously improve rub resistance, water resistance, and resistance to dry-up.

[0031] <Water> The water used in the present invention is not particularly limited, and examples thereof include ion-exchanged water, ultrafiltered water, and distilled water. The ink composition of the present invention contains water as the main solvent. The water content is 50 to 90% by mass, preferably 60 to 80% by mass, based on the total mass of the ink composition.

[0032] <Other additives> In addition to the above components, the ink composition according to the present invention may contain other additives as required.

[0033] The ink composition according to the present invention may further contain a phosphate ester surfactant. The phosphate ester surfactant not only improves the dispersibility of the ink composition, but also acts as a lubricant when the ink composition is used in a ballpoint pen. The lubricant improves the lubricity between the ball and ballpoint pen tip of the ballpoint pen, thereby smoothing the ball's rotation and suppressing wear on the ball seat, thereby improving the writing feel. The phosphate ester surfactant used in the present invention has a phosphate group that is easily adsorbed to metal, which improves lubricity, suppresses wear on the ball seat, and improves the writing feel. Therefore, when the ink composition according to the present invention is applied to a ballpoint pen, a particularly excellent writing feel can be achieved. Furthermore, the inclusion of a phosphate ester surfactant can also improve the drying properties of the writing. This is thought to be because the phosphate ester surfactant smooths the ball's rotation and prevents excess ink from forming at the tip. Since this surfactant not only improves lubricity but also dispersibility, it is effective when the ink composition is used in writing instruments other than ballpoint pens.

[0034] Examples of the phosphate ester surfactant include linear alcohol-based, styrenated phenol-based, nonylphenol-based, and octylphenol-based phosphate ester surfactants. Among these, it is preferable to use linear alcohol-based and styrenated phenol-based phosphate ester surfactants.

[0035] In the present invention, the phosphate ester surfactant preferably has an HLB value of 5 to 15, and more preferably 6 to 13. Furthermore, the number of carbon atoms in the alkyl or alkylaryl group of the phosphate ester surfactant is preferably 6 to 30, more preferably 8 to 18, and particularly preferably 10 to 14. This is because linear phosphate ester surfactants having a specific HLB value and carbon number provide excellent writing stability, such as stable production of good handwriting with reduced line skipping and blurring, and can also synergistically improve the dispersion effect together with the dispersant used in the present invention and simultaneously provide a lubricating effect.

[0036] In the present invention, the HLB value of a phosphate ester surfactant means the HLB value of a raw material nonionic surfactant used to produce the phosphate ester surfactant, and is a value calculated by the Kawakami method using the following formula: HLB = 7 + 11.7 log (Mw / Mo), (Mw: molecular weight of hydrophilic group, Mo: molecular weight of lipophilic group)

[0037] Specific examples of phosphate ester surfactants include the Plysurf series (Dai-ichi Kogyo Seiyaku Co., Ltd.), examples of linear alcohol phosphate ester surfactants include Plysurf A212C, A208B, A213B, A208F, A215C, A219B, and A208N, examples of styrenated phenol phosphate ester surfactants include Plysurf AL, examples of nonylphenol surfactants include Plysurf 207H, A212E, and A217E, and examples of octylphenol surfactants include Plysurf A210G.

[0038] When the ink composition according to the present invention contains a phosphate ester surfactant, the content thereof is preferably 0.1 to 2.0 mass %, more preferably 0.5 to 1.5 mass %, based on the total mass of the ink composition.

[0039] The above-mentioned phosphate ester surfactants can also be used after being neutralized appropriately with alkaline substances such as amines or alkali metals.

[0040] The ink composition according to the present invention may further contain a shear thinning agent, which imparts to the ink composition the property of reducing its viscosity when shear stress is applied thereto.

[0041] As the shear thinning agent, a substance that is soluble or dispersible in water is effective. Specific examples include xanthan gum, welan gum, succinoglycan (average molecular weight approximately 1 to 8 million), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, cellulose derivatives such as methylcellulose and hydroxyethylcellulose, thickening polysaccharides such as diutan gum, alginate alkyl esters, polymers with a molecular weight of 100,000 to 150,000 whose main component is an alkyl ester of methacrylic acid, glucomannan, carbohydrates with gelling properties extracted from seaweed such as agar and carrageenan, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, poly-N-vinylcarboxylic acid amide, inorganic fine particles, nonionic surfactants with an HLB value of 8 to 12, metal salts and amine salts of dialkyl sulfosuccinic acid, and the like. Furthermore, stable shear thinning properties can be imparted to the ink composition even when N-alkyl-2-pyrrolidone and anionic surfactants are added in combination. These shear thinning agents may be used alone or in combination of two or more. These shear thinning agents also have the effect of improving the dispersion stability of pigments and the like.

[0042] Among these, thickening polysaccharides are preferably used because they are expected to improve the stability of the ink composition over time. In particular, when the colorant is a pigment, xanthan gum, succinoglycan, alkaloid gum, zeta sea gum, diutan gum, and welan gum are more preferred because they form a three-dimensional network structure in an aqueous medium and can achieve a higher level of pigment dispersibility.

[0043] When the ink composition according to the present invention contains a shear thinning agent, its content is preferably 0.05 to 0.5% by mass based on the total mass of the ink composition. In general, a larger amount of shear thinning agent tends to improve the dispersibility of the pigment, while a smaller amount tends to reduce blurring of handwriting.

[0044] The ink composition according to the present invention may contain various additives other than those described above, such as water-soluble organic solvents, humectants, surfactants, lubricants, polysaccharides, pH adjusters, rust inhibitors, preservatives, organic resin particles, and water-soluble resins, for the purpose of improving the ink properties and functions, as long as the performance of the present invention is not impaired.

[0045] The ink composition of the present invention may contain a water-soluble organic solvent other than the water-soluble oxolane compound to achieve dissolution stability, prevent water evaporation, and prevent drying, to the extent that the effects of the present invention are not impaired. Examples of such water-soluble organic solvents include (i) glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, and glycerin, and (ii) alcohols such as methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, and other higher alcohols. The content of the water-soluble organic solvent other than the water-soluble oxolane compound is preferably 0.1 to 30% by mass, more preferably 0.1 to 20% by mass, and even more preferably 0.1 to 10% by mass, based on the total mass of the ink composition.

[0046] The ink composition according to the present invention may contain a humectant such as urea or sorbitol in addition to the water-soluble organic solvent described above in order to prevent water evaporation. In this specification, the water-soluble organic solvent described above is not included in the humectant. The content of the humectant is preferably 0.1 to 10% by mass, more preferably 0.1 to 5% by mass, based on the total mass of the ink composition.

[0047] The ink composition according to the present invention may contain various surfactants other than phosphate ester surfactants, such as nonionic, anionic, and cationic surfactants, as well as surfactants having an acetylene bond in their structure and silicone surfactants.

[0048] A surfactant having an acetylene bond in its structure or a silicone surfactant may be included to further improve the drying properties of the writing.

[0049] The surfactant having an acetylene bond in its structure used in the ink composition according to the present invention is preferably one having ethylene oxide added thereto. The number of moles of ethylene oxide added is preferably 10 or less, more preferably 8 or less. The number of moles of ethylene oxide added is preferably 4 or more. Examples of such surfactants include acetylene glycol surfactants and acetylene alcohol surfactants, each having 10 or less moles of ethylene oxide added. Of these, acetylene glycol surfactants are preferred because they tend to improve the penetrability into the writing surface and improve the drying properties of the writing.

[0050] Such surfactants can significantly improve the penetrability into the writing surface, allowing the ink composition containing the surfactant to quickly penetrate into paper, thereby shortening the time it takes for the handwriting formed on the surface of the writing surface to completely dry. Furthermore, the ink composition has excellent handwriting drying properties, and when the handwritten area is rubbed, the composition is prevented from adhering to areas where there was no handwriting or from being removed from the handwritten area.

[0051] Although the reason for this is unclear, it is believed that such surfactants exhibit a suitable balance of hydrophobicity and hydrophilicity for achieving a penetrating effect. In consideration of the improved effect of surfactants having an acetylene bond in their structure, the number of moles of ethylene oxide added is preferably 8 or less. In addition, in consideration of the stability over time of the ink composition, it is preferably 4 or more.

[0052] Furthermore, surfactants having an acetylene bond in their structure improve the drying properties of written marks and also have the effect of improving the writing feel by providing a smooth writing feel, etc. This is because when the surfactant is combined with an ink composition for a ballpoint pen, the inclusion of a surfactant having an acetylene bond in its structure improves the lubricity between the ball and ballpoint pen tip of the ballpoint pen and can suppress wear of the ball seat.

[0053] The ink composition according to the present invention, which contains a surfactant having an acetylene bond in its structure, can contain other lubricants, but it is particularly preferable to use it in combination with the above-mentioned phosphate ester surfactant, among other lubricants.

[0054] Furthermore, the surfactant having an acetylene bond in its structure used in the present invention may further contain propylene oxide in addition to ethylene oxide. In the present invention, by selecting and using a surfactant having an acetylene bond in its structure to which ethylene oxide and propylene oxide have been added, further improvement in the drying properties of handwriting and stability over time of the ink composition tend to be obtained. This is because such a surfactant having both ethylene oxide and propylene oxide added thereto maintains a more favorable balance between hydrophobicity and hydrophilicity. This effect is easily achieved when the ratio of the number of moles of ethylene oxide added to the number of moles of propylene oxide added is 1:1 to 5:1.

[0055] Furthermore, in consideration of the arrangement of surfactant molecules at the gas-liquid interface, it is preferable that the total number of moles of ethylene oxide added and the number of moles of propylene oxide added is 10 or less. If the number of moles added is too large, the surfactant molecules become too long and tend to be prone to steric hindrance when arranged at the gas-liquid interface. A total number of moles added of 10 or less is particularly preferable, since it maintains a good balance between the hydrophobicity and hydrophilicity of the surfactant and also provides an effect that takes into consideration the influence of steric hindrance when arranged at the gas-liquid interface.

[0056] Furthermore, in consideration of improving the drying properties of the ink composition and the stability over time, it is more preferable to use a surfactant having an acetylene bond in its structure in which the number of moles of ethylene oxide added is 5 and the number of moles of propylene oxide added is 2.

[0057] The HLB value of the surfactant having an acetylene bond in its structure is preferably 3 to 14, more preferably 6 to 12, and particularly preferably 7 to 9. When the surfactant having an acetylene bond in its structure has an HLB value of 3 or more, it can exist stably without remaining dissolved in water as a solvent, and can exhibit its effects both initially and over time, which is preferable, and when the surfactant has an HLB value of 14 or less, it is likely to be arranged near the gas-liquid interface due to its hydrophobicity, and the effects of the surfactant, such as improved handwriting drying, can be obtained instantly with a small amount, which is preferable.

[0058] Specific examples of surfactants having an acetylene bond in the structure include the Olfine series (manufactured by Nissin Chemical Industry Co., Ltd.), the Surfynol series, and the Dynol series (all manufactured by Air Products Japan Co., Ltd.).

[0059] By balancing the silicon skeleton, hydrophobic groups such as propylene oxide, and hydrophilic groups such as ethylene oxide within the structure, silicone surfactants are stable in the ink composition while allowing the surfactant molecules to quickly align at the gas-liquid interface. This allows for rapid control of the surface tension of the ink composition during writing, improving penetration and achieving both excellent writing drying and long-term stability of the ink composition. Among silicone surfactants, those with a mass-average molecular weight of 500 to 3,000 are preferred. This is because, with regard to the surfactant's ability to align at the gas-liquid interface, if the mass-average molecular weight exceeds 3,000, the silicone surfactant molecules become too large, tending to slow their alignment at the gas-liquid interface, which can result in insufficient writing drying. On the other hand, if the mass-average molecular weight is 3,000 or less, the silicone surfactant molecules become relatively small, which tends to allow the surfactant molecules to align at the gas-liquid interface quickly, thereby improving writing drying. Furthermore, if the mass-average molecular weight is less than 500, it is difficult to achieve the desired writing drying. Taking the above effects into consideration, the mass average molecular weight is preferably 500 to 3,000, more preferably 500 to 2,000, and even more preferably 1,000 to 2,000.

[0060] Furthermore, silicone surfactants improve the writing experience by improving the drying properties of ink while also providing a smooth writing feel. This effect is effectively achieved when the ink composition of the present invention is combined with a ballpoint pen. This is thought to be because the ink composition contains a silicone surfactant, which improves the lubrication between the ball and ballpoint pen tip of the ballpoint pen and suppresses wear of the ball seat. The ink composition according to the present invention, which contains a silicone surfactant, can contain other lubricants. However, it is particularly preferable to use the silicone surfactant in combination with the above-mentioned phosphate ester surfactant among other lubricants.

[0061] Regarding the solubility parameter (hereinafter referred to as SP value) of the silicone surfactant, taking into consideration the drying property of the ink, an SP value of 8 to 13 is preferable, and from a more particular consideration, an SP value of 9 to 12 is preferable, and an SP value of 10 to 11 is particularly preferable. The SP value of water, which is the main component of the solvent, is 23.4, and if the SP value of the silicone surfactant is close to this value, it will be more likely to be stable in a uniformly dissolved state. On the other hand, if the SP value is within the above range, the difference with the SP value of water is large, which makes it easier for the surfactant molecules to align quickly at the gas-liquid interface and also ensures stability in the ink composition, which is preferable.

[0062] Specific examples of silicone surfactants include the Silface series (manufactured by Nissin Chemical Industry Co., Ltd.), the BYK series (manufactured by BYK-Chemie Co., Ltd.), the Silsoft Spread series, and the Coatosil series (all manufactured by Momentive Performance Materials, Inc.), which may be used alone or in combination of two or more.

[0063] Furthermore, the total content of surfactants having an acetylene bond in their structure or silicone surfactants is more preferably 0.01 to 3.0% by mass, based on the total mass of the ink composition. This is because if the total content of surfactants having an acetylene bond in their structure or silicone surfactants is less than 0.01% by mass, it is difficult to achieve the desired writing drying properties, and if it exceeds 3.0% by mass, the ink composition's stability over time is likely to be affected. From further considerations, a content of 0.05 to 2.0% by mass is more preferable, and 0.1 to 1.5% by mass is particularly preferable.

[0064] In addition to the surfactants described above, lubricants that can be used include alkylbenzenesulfonic acid, amino acids, N-acylamino acids, aliphatic amide alkylene oxide adducts, terpenoid acid derivatives, and salts thereof. More specifically, oleic acid, stearic acid, linoleic acid, linolenic acid, ricinoleic acid, dodecylbenzenesulfonic acid, alanine, glycine, lysine, threonine, serine, proline, sarcosine, N-acylsarcosine, polyoxyethylene fatty acid amides, and salts thereof.

[0065] The ink composition according to the present invention may contain a polysaccharide. Some polysaccharides function as the shear thinning agent described above, but polysaccharides without such a function may also be used depending on the purpose. Specific examples of polysaccharides that provide effects such as adjusting ink viscosity and improving dry-up resistance include dextrin and λ-carrageenan. Furthermore, examples of polysaccharides that provide an effect of improving dispersion stability include cellulose derivatives such as methyl cellulose and hydroxyethyl cellulose.

[0066] When an ink composition contains components that can exist in a water-insoluble state, such as pigments, at the nib of a writing instrument containing the ink, water may evaporate, causing the ink to dry and solidify, clogging the ink flow passages. This phenomenon can affect ink discharge, potentially rendering the writing instrument unable to write again despite remaining ink. For this reason, improving dry-up resistance is desirable. Therefore, it is also necessary to consider improving dry-up resistance at the tip of a ballpoint pen, for example. Dextrin forms a coating on the nib, which prevents the solvent in the ink from evaporating. Therefore, using dextrin is effective because it can produce an ink composition with excellent dry-up resistance.

[0067] The mass-average molecular weight of the dextrin is preferably 5,000 to 120,000. If it is 120,000 or more, the coating formed on the pen tip is hard, and handwriting tends to be easily smudged when starting to write after drying up. On the other hand, if it is less than 5,000, it is difficult to impart viscosity changes sufficient to improve dispersion stability over time, and the dextrin tends to become more hygroscopic, resulting in a soft coating formed on the pen tip that is difficult to maintain stably at the pen tip, making it difficult to suppress evaporation of the solvent in the ink. In further consideration of improving the above effects, it is preferable to use dextrin with a mass-average molecular weight of 20,000 to 100,000.

[0068] The content of dextrin is preferably 0.1 to 5% by mass based on the total mass of the ink composition. This is because if it is less than 0.1% by mass, the effect of improving dry-up resistance tends to be insufficient, and if it exceeds 5% by mass, it tends to be difficult to dissolve in the ink. In consideration of better dissolution stability in the ink, 0.1 to 3% by mass is preferable, and in consideration of better improvement in dry-up resistance, 1 to 3% by mass is most preferable.

[0069] The ink composition according to the present invention may contain two or more types of polysaccharides.

[0070] Examples of pH adjusters include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide, and sodium acetate, organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine, lactic acid, and citric acid. The content of the pH adjuster in the ink composition is preferably 0.1 to 25% by mass, and more preferably 0.5 to 10% by mass.

[0071] Examples of the rust inhibitor include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, and dialkylthiourea.

[0072] Examples of preservatives include 2-methyl-4-isothiazolin-3-one (hereinafter sometimes referred to as MIT), 2-n-octyl-4-isothiazolin-3-one (hereinafter sometimes referred to as OIT), 1,2-benzisothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, N-(n-butyl)-1,2-benzisothiazolin-3-one, 2-pyridinethiol-1-oxide sodium, 3-iodo-2-propynyl butylcarbamate sodium benzoate, benzotriazole, and phenol. The content of these preservatives is preferably 20 to 200 ppm based on the total mass of the ink composition. Furthermore, using MIT and OIT in combination is preferred because it improves antibacterial properties. In this case, the content of OIT is preferably 1 to 50 ppm based on the total mass of the ink composition, and the blending ratio of OIT to MIT is preferably 1:1 to 10:1 based on mass.

[0073] The ink composition of the present invention can use organic resin particles other than the water-dispersible resins described above, which have relatively poor affinity for water. The use of such organic resin particles can suppress ink dripping. Examples of organic resin particles that can be used in the present invention include olefin-based resin particles such as polyethylene resin and polypropylene resin, and nitrogen-containing resin particles containing nitrogen atoms in their chemical structure, such as melamine-formaldehyde resin, benzoguanamine-formaldehyde resin, benzoguanamine-melamine-formaldehyde resin, urea-formaldehyde resin, and nylon resin. These organic resin particles can be used alone or in combination.

[0074] Examples of materials for the olefin resin particles include polyolefins such as polyethylene, polypropylene, and polybutene, as well as mixtures thereof. Among these, polyethylene is preferred in terms of suppressing ink leakage and improving writing feel. Specific examples include low-density polyethylene, high-density polyethylene, low-molecular-weight polyethylene, modified polyethylene, and modified high-density polyethylene. Among these, low-density polyethylene, low-molecular-weight polyethylene, and modified polyethylene are preferred in terms of ink leakage suppression. Low-density polyethylene is particularly preferred because it has a lower melting point and is softer than other types of polyethylene, making it easier for polyethylene particles to adhere to each other and less likely to form gaps between the particles, reducing ink leakage. Furthermore, low-density polyethylene is soft, making it suitable for use in improving writing feel, etc. The olefin resin particles may contain materials other than polyolefins as needed.

[0075] Regarding the shape of the organic resin particles, spherical or irregular shapes can be used, but spherical resin particles are preferred in view of reducing frictional resistance. The spherical resin particles referred to here are not limited to true spheres, but may also be approximately spherical resin particles or approximately oval spherical resin particles.

[0076] Furthermore, the content of organic resin particles is more preferably 0.01 to 10.0% by mass relative to the total amount of the ink composition. This is because if the content of organic resin particles is less than 0.01% by mass, it is difficult to prevent ink leakage, and if it exceeds 10.0% by mass, the aggregate structure tends to become stronger, which can affect the writing feel and dry-up performance. From further consideration, the content is preferably 0.02 to 5.0% by mass, particularly preferably 0.03 to 1.0%, and most preferably 0.05 to 0.5% by mass.

[0077] The ink composition of the present invention has a suitable viscosity, which satisfies the requirements for ink drooping, ink leakage, and bleeding of handwriting. Specifically, the viscosity of the ink composition of the present invention is 1.92 sec. at a shear rate of 1.92 sec. under an environment of 20°C. -1Preferably, the viscosity is 100 to 5000 mPa·s, more preferably 1000 to 3500 mPa·s, and even more preferably 1500 to 3000 mPa·s. When the viscosity of the ink composition is within the above range, the ink composition has excellent dispersion stability, good ink dischargeability, and can produce good handwriting without bleeding.

[0078] <Writing instruments> The structure and shape of the writing instrument to be filled with the aqueous ink composition for a writing instrument of the present invention are not particularly limited, and conventional general-purpose ones can be applied, and the ink composition can be used for various writing instruments such as ballpoint pens with ballpoint pen tips, marking pens and felt-tip pens with fiber tips, felt tips, plastic tips, etc., and fountain pens with metal tips. Of these, the ink composition of the present invention is preferably used in ballpoint pens, and can also be applied to pressure-type ballpoint pens.

[0079] Furthermore, the writing instrument in which the ink composition of the present invention can be used may be one that is directly filled with the ink composition, or one that includes an ink reservoir or ink occlusion body that can be filled with the ink composition.Furthermore, the writing instrument may be an ink cartridge type writing instrument in which the ink reservoir or ink occlusion body is structured to be detachably replaceable from the main body of the writing instrument.

[0080] In addition, writing instruments that can use the ink composition of the present invention include cap-type writing instruments that have a cap that covers the pen tip, and retractable ballpoint pens that can store the pen tip in a barrel, such as knock-type, rotary-type, and slide-type.

[0081] Furthermore, the supply mechanism of a writing instrument in which the ink composition of the present invention can be used is not particularly limited, and examples include (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 ink composition to the pen tip, (mechanism 2) a mechanism that has a comb-shaped ink flow rate adjusting member and supplies the ink composition to the pen tip through this, (mechanism 3) a mechanism that has an ink flow rate adjusting member with a valve mechanism and supplies the ink composition to the pen tip, and (mechanism 4) a mechanism that supplies the ink composition directly to the pen tip without an ink flow rate adjusting member.

[0082] When the specifications of a ballpoint pen filled with the aqueous ink composition for a writing instrument of the present invention were examined, it was found that, where A (mg) is the ink consumption per 100 m of the aqueous ballpoint pen and B (mm) is the ball diameter, the relationship is preferably 110≦A / B≦600, more preferably 120≦A / B≦500, and even more preferably 150≦A / B≦450. This is because, by keeping the relationship within the above ranges, the ink consumption is appropriate relative to the ball diameter, improving ink fluidity and suppressing blurring of handwriting, making it easier to obtain good handwriting.

[0083] The ink consumption is measured by conducting a spiral writing test using five test samples at a writing speed of 4 m / min on JIS P3201 writing paper at a writing angle of 65° and a writing load of 100 g at 20°C. The average ink consumption per 100 m is defined as the ink consumption per 100 m. There are no particular restrictions on the ball diameter, but balls of approximately 0.1 to 2.0 mm are generally used.

[0084] As for the specifications of the ballpoint pen tip, the amount of movement of the ball in the ballpoint pen tip in the vertical axis direction (clearance) is preferably 20 to 50 μm, and more preferably 30 to 45 μm. This is because, within this range, the ink ejection volume can be appropriately adjusted, suppressing blurring of the handwriting and making it easier to obtain good handwriting, and furthermore, if the clearance is within this range, the ratio A / B can also be easily adjusted.

[0085] The amount of movement (clearance) of the ball in the ballpoint pen tip in the vertical direction indicates the distance the ball can move in the vertical direction of the ballpoint pen tip body.

[0086] <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 each component and mixing them using a mixer such as a propeller mixer, a homodisper, or a homomixer, or a disperser such as a bead mill. [Example]

[0087] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0088] <Examples 1 to 2 and Comparative Examples 1 to 5> Ink compositions were prepared according to the formulations shown in Table 1. The prepared ink compositions were evaluated for low temperature stability and handwriting drying properties (rubbing resistance of handwriting) under the following conditions.

[0089] Low temperature stability An ink container was prepared, having at its tip a ballpoint pen tip (ball longitudinal movement (clearance) of 30 μm) that rotatably held a 0.5 mm diameter cemented carbide ball. The ink container was filled with the prepared ink composition to prepare a refill, which was then attached to a gel ink ballpoint pen (trade name: Juice) manufactured by Pilot Corporation to obtain a ballpoint pen. The resulting ballpoint pen was used as a test ballpoint pen. The test ballpoint pen was stored at −10°C or −20°C for 3 days, and the ink flow was measured before and after storage, and evaluated according to the rate of change. (standard) S: within ±10% A: Within ±20% B: Within ±40% C: Within ±60% D: Within ±70%

[0090] How to measure ink flow Ink flow was measured by conducting a spiral writing test using five test samples on JIS P3201 writing paper at a writing angle of 65°, a writing load of 100 g, and a writing speed of 4 m / min in an environment of 25°C, and the average ink consumption per 10 m was calculated.

[0091] Drying of writing (rubbing resistance of writing) Using the prepared ink composition, a test ballpoint pen was prepared in the same manner as above. After writing on the surface of an impermeable resin film using the test ballpoint pen, the writing was rubbed off with tissue paper after 120 seconds and evaluated according to the following criteria. (standard) A: It's dry enough that the brush strokes won't rub off. B: Generally dry, with very little brushstrokes removed. C: Not dry and brush marks rub off.

[0092] The results obtained are shown in Table 1.

[0093] [Table 1]

[0094] The content in the table is the content of the solid content of each component relative to the total mass of the ink composition, and does not include the solvent or dispersion medium. *1: Joncryl HPD196 (product name, manufactured by BASF, concentration 36%) *2: Neocryl XK-190 (product name, manufactured by Neoresin, concentration 45%, MFT 0℃) *3: Plysurf A215C (product name, Daiichi Kogyo Seiyaku Co., Ltd., HLB value 11.5) *4: Surfynol 2502 (product name, manufactured by Air Products Japan Co., Ltd.) *5: Xanthan gum (concentration 2.4%) *6: Mass average molecular weight 30,000, Sandec series (product name, Sanwa Starch Co., Ltd.) *7: Metrolose SM-15 (product name, manufactured by Shin-Etsu Chemical Co., Ltd.) *8: Proxel XL2 (product name, manufactured by Lonza Japan Co., Ltd., concentration 10%) *9: Chemipearl M200 (product name, manufactured by Mitsui Chemicals, Inc., concentration 40%)

Claims

1. a colorant, a water-soluble oxolane compound having a boiling point of 100°C or higher, a water-based resin, a shear thinning agent, and water; the aqueous resin is a mixture of a water-soluble resin and a water-dispersible resin, the shear thinning agent is selected from the group consisting of xanthan gum, succinoglycan, alkaloid gum, zeta sea gum, diutan gum, and welan gum; and 20℃, shear rate 1.92sec －１ The aqueous ink composition for a ballpoint pen has a viscosity measured by a method of 100 to 5000 mPa·s.

2. The water-soluble oxolane compound is represented by the following formula (1): 【Chemical 1】 (where, X is O or CR ２ and Each R is independently hydrogen, alkyl having 1 to 3 carbon atoms, hydroxyalkyl having 1 to 3 carbon atoms, aminoalkyl having 1 to 3 carbon atoms, or alkoxy having 1 to 3 carbon atoms. The ink composition according to claim 1, wherein the ink composition is represented by the formula:

3. The ink composition according to claim 1 or 2, further comprising a phosphate ester surfactant.

4. The ink composition according to any one of claims 1 to 3, further comprising a surfactant having an acetylene bond in its structure, or a silicone surfactant.

5. A ballpoint pen containing the ink composition according to any one of claims 1 to 4.

6. 6. The ballpoint pen according to claim 5, wherein the ballpoint pen has a ballpoint pen tip, and the ball in the ballpoint pen tip has a movable amount in the longitudinal direction of the ball of 20 to 50 μm.

7. 7. The ballpoint pen according to claim 5, wherein the relationship of 110≦A / B≦600 is satisfied, where A (mg) is the ink consumption per 100 m of the ballpoint pen and B (mm) is the ball diameter in the ballpoint pen tip.

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