Water-based ink composition for writing instruments, and writing instrument including the same

Abstract

To provide a water-based ink composition for writing instruments that can form handwritten characters having an excellent stereoscopic appearance and excellent fixability, and a writing instrument including the same.SOLUTION: A water-based ink composition for writing instruments contains water, a colorant, a foamer, a water-dispersible resin with a glass transition temperature of lower than 100°C, and a thickener.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] When writing with a writing instrument filled with an ink composition, the ink usually penetrates the paper surface, resulting in a flat handwriting. However, by making this handwriting three-dimensional, it is possible to enjoy a different handwriting from the usual one. As one method for forming three-dimensional handwriting, an ink composition has been proposed in which thermally expandable microcapsules are added and the resulting handwriting is treated with a heater such as an iron or a hairdryer, causing the thermally expandable microcapsules to expand, resulting in a three-dimensional handwriting (for example, Patent Document 1). However, conventional ink compositions have problems such as the resulting handwriting not having a sufficient three-dimensional effect, or even if a three-dimensional handwriting is obtained, the handwriting does not expand uniformly, resulting in uneven three-dimensional effect, or the handwriting does not adhere sufficiently to the surface on which it is written, causing it to peel off, leaving room for improvement. Furthermore, the ink ejection from the writing tip is unstable, making it difficult to leave uniform handwriting and to leave fine handwriting such as letters in a three-dimensional form, and there is a need to solve these problems. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-191962 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention solves the above-mentioned problems and provides a water-based ink composition for a writing instrument, which is capable of forming handwriting that has excellent three-dimensional effect and fixation properties, and a writing instrument using the same. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides "1. An aqueous ink composition for a writing instrument, characterized in that it is an aqueous ink composition for a writing instrument comprising water, a colorant, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickener. 2. The ink composition according to item 1, wherein the foaming agent is a heat-sensitive foaming agent. 3. The ink composition according to item 1 or 2, wherein the heat-sensitive foaming agent is a thermal expansion foaming agent. 4. The ink composition according to any one of items 1 to 3, wherein the thickener is a shear thinning agent. 5. The ink composition according to any one of items 1 to 4, wherein the content of the foaming agent is 1% by mass to 20% by mass based on the total mass of the ink composition. 6. The ink composition according to any one of items 1 to 5, wherein the content of the water-dispersible resin is 1% by mass to 50% by mass based on the total mass of the ink composition. 7. The ink composition according to any one of items 1 to 6, wherein the solid content of the ink composition is 10% by mass to 50% by mass. 8. The viscosity of the ink composition is 20°C and the shear rate is 1.92 sec -1 8. The ink composition according to any one of items 1 to 7, wherein the viscosity of the ink composition is 500 mPa·s or more under the conditions below. 9. A writing instrument containing the composition described in any one of items 1 to 8. 10. The writing instrument according to claim 9, which is a pressure-type writing instrument. " [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a water-based ink composition for a writing instrument, which can produce handwriting with excellent three-dimensional effect, and further, the resulting handwriting is not easily peeled off from the surface on which it is written, and has excellent fixability, and a writing instrument using the same. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a vertical cross-sectional view of an example of a cap-type pressure ballpoint pen. [Figure 2] 2 is a vertical cross-sectional view of the ballpoint pen of FIG. 1 with the cap removed. [Figure 3] FIG. 2 is an explanatory diagram showing the writing instrument in a state where the cap is fitted onto the rear end of the barrel (pressurized state). DETAILED DESCRIPTION OF THE INVENTION

[0008]

[0023] In the present specification, unless otherwise specified, the terms "parts," "%," "ratio," and the like that indicate the composition are based on mass, and the content is the mass % of the constituent component based on the mass of the ink composition.

[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 the ink composition) comprises water, a colorant, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickener. It is particularly important that the ink composition of the present invention contains a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100° C., and a thickener. By using these components, a three-dimensional effect can be visually confirmed, and handwriting that is difficult to peel off from the writing surface and has excellent three-dimensional effect and fixability can be obtained. The components of the ink composition of the present invention will be described in detail below. <Foaming agent> The ink composition according to the present invention comprises a foaming agent. The foaming agent makes the handwriting expand, giving it a three-dimensional feel. The foaming agent is a foaming agent that foams in response to an external stimulus such as heat or light, and specific examples thereof include heat-sensitive foaming agents that foam in response to heat and photosensitive foaming agents that foam in response to light. Among these, in the present invention, it is preferable to use a heat-sensitive foaming agent that can produce handwriting with a three-dimensional feel by heat treatment. Furthermore, examples of the heat-sensitive foaming agent include a thermal expansion foaming agent (also called a physical foaming agent) and a thermal decomposition foaming agent (also called a chemical foaming agent). In the present application, it is preferable to use a thermal expansion foaming agent, which tends to have a high volume expansion ratio.

[0010] In the present application, the thermally expandable foaming agent is not particularly limited, but it is preferable to use thermally expandable microcapsules, because when used together with a water-dispersible resin having a glass transition temperature of less than 100°C, which will be described later, it is easy to form handwriting with excellent three-dimensional effect and the three-dimensional effect is easily maintained. Thermally expandable microcapsules are particles with a core-shell structure in which a volume-expanding compound is encapsulated in a thermoplastic resin. When heated, the thermoplastic resin in the outer shell begins to soften, and the vapor pressure of the encapsulated volume-expanding compound increases, reaching a pressure sufficient to deform the particles, causing the thermoplastic resin in the outer shell to stretch and expand.

[0011] The thermoplastic resin constituting the shell is preferably, for example, a (meth)acrylonitrile polymer or a copolymer with a high (meth)acrylonitrile content, and in the case of such a copolymer, other monomers (comonomers) such as vinyl halide, vinylidene halide, styrene-based monomers, (meth)acrylate-based monomers, vinyl acetate, butadiene, vinylpyridine, and chloroprene are used. The thermoplastic resin may be made crosslinkable with a crosslinking agent such as divinylbenzene, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, allyl (meth)acrylate, triacrylformal, triallyl isocyanurate, etc. As for the crosslinked form, non-crosslinking is preferred, but partial crosslinking may be possible to the extent that the properties as a thermoplastic resin are not impaired. The volume expansion compound may be a substance that vaporizes under realistic temperature conditions, such as a low-boiling point solvent or water. Examples of the low-boiling point solvent include hydrocarbons such as n-pentane, isopentane, neopentane, butane, isobutane, hexane, and petroleum ether; and chlorinated hydrocarbons such as methyl chloride, methylene chloride, dichloroethylene, trichloroethane, and trichloroethylene.

[0012] As the thermally expandable microcapsules, commercially available products can be used, such as the Advancell series manufactured by Sekisui Chemical Co., Ltd., the Expancell series manufactured by AkzoNovel (sold in Japan by Nippon Phillite Co., Ltd.), the Matsumoto Microsphere series manufactured by Matsumoto Yushi Seiyaku Co., Ltd., and the Kureha Microsphere series manufactured by Kureha Corporation. These may be used alone or in combination of two or more.

[0013] On the other hand, examples of the thermally decomposable foaming agent include organic thermally decomposable foaming agents and inorganic thermally decomposable foaming agents. Examples of organic thermally decomposable blowing agents include azocarbonamide complexes (ADCA), azobisisobutyronitrile (AIBN), dinitrosopentamethylenetetramine (DPT), N,N'-dimethyl-N,N'-dinitrosoterephthalamide, benzenesulfonyl hydrazide (BSH), p-toluenesulfonyl hydrazide (TSH), 4,4'-oxybis(benzenesulfonyl hydrazide) (OBSH), 3,3'-disulfonehydrazide diphenyl sulfone, toluenedisulfonyl hydrazine, p-toluenedisulfonyl hydrazide, p-toluenesulfonyl semicarbazide, and diethyl azodicarboxylate. Examples of inorganic thermal decomposition type foaming agents include hydrogen carbonates such as sodium hydrogen carbonate, carbonates, and combinations of hydrogen carbonates and organic acid salts. The foaming agent may be used alone or in combination of two or more.

[0014] As described above, in the present application, it is particularly preferable to use thermally expandable microcapsules as the foaming agent, and the average particle size of the thermally expandable microcapsules is preferably 1 μm to 50 μm. If the diameter is 1 μm or more, handwriting with excellent three-dimensional effect is easily obtained, and if the diameter is 50 μm or less, the dispersion stability of the thermally expandable microcapsules can be improved, and the ink discharge property can be improved and stabilized, making it easier to obtain handwriting with uniform and continuous three-dimensional effect.In addition, the ink stability over time can be improved. Taking further consideration of improving the above effects, the average particle size of the thermally expandable microcapsules is more preferably 5 μm or more, even more preferably 10 μm or more, and more preferably 40 μm or less, even more preferably 30 μm or less, and even more preferably 20 μm or less.

[0015] Furthermore, the foaming initiation temperature (Ts) of the thermally expandable microcapsules is preferably 60°C or higher, more preferably 70°C or higher, even more preferably 80°C or higher, and preferably 150°C or lower, more preferably 140°C or lower, even more preferably 120°C or lower, and particularly preferably 110°C or lower. Furthermore, the maximum expansion temperature (Tm) of the thermally expandable microcapsules is preferably 100°C or higher, more preferably 110°C or higher, and preferably 200°C or lower, more preferably 180°C or lower, even more preferably 150°C or lower, and particularly preferably 140°C or lower. If the foaming initiation temperature and maximum expansion temperature are within the above-mentioned ranges, unintended foaming and expansion are unlikely to occur under normal storage and usage environments, general-purpose equipment can be easily used for the heat treatment, and three-dimensional handwriting can be easily obtained.

[0016] The content of the foaming agent is preferably from 1 to 20 mass %, more preferably from 2 to 10 mass %, based on the total mass of the ink composition. If the content of the foaming agent is within the above range, the ink can be ejected well from the tip of the pen, resulting in handwriting with excellent three-dimensional effect. In addition, the ink's stability over time can be improved.

[0017] <Water dispersible resin> The ink composition according to the present invention comprises a water-dispersible resin having a glass transition temperature (Tg) of less than 100°C (hereinafter sometimes referred to as water-dispersible resin). The water-dispersible resin used in the present invention is a resin that is poorly soluble in water but can be uniformly dispersed in water, and is preferably one that is emulsified and dispersed in an aqueous medium, and is present in the ink composition in a particulate form without being dissolved.

[0018] In the present invention, by using a water-dispersible resin having a glass transition temperature of less than 100°C, it is possible to obtain handwriting with excellent three-dimensional effect due to the effect of the foaming agent, and also to obtain handwriting with excellent fixation to the writing surface. The glass transition temperature of the water-dispersible resin used in the present invention is preferably 80°C or lower, more preferably 50°C or lower, even more preferably 20°C or lower, particularly preferably 10°C or lower, and preferably -10°C or higher, more preferably 0°C or higher. The glass transition temperature (Tg) can be determined by differential scanning calorimetry.

[0019] Examples of the water-dispersible resin include acrylic resins, urethane resins, vinyl resins, and styrene resins. Among these, in the present application, it is preferable to select and use one or more of acrylic resins, styrene resins, and vinyl resins, and it is more preferable to use styrene resins or vinyl resins, because the effect of the foaming agent is obtained, and handwriting with excellent three-dimensional effect and excellent fixability is easily obtained. As the styrene-based resin, a styrene-olefin-based polymer composed of styrene and an olefin such as butadiene, isoprene, ethylene-butylene, or ethylene-propylene is preferably used. As the vinyl resin, vinyl acetate resin is preferably used. Furthermore, it is preferable to use a styrene-olefin polymer, and it is more preferable to use a styrene-butadiene polymer, because it is easy to improve the above effects, the resulting handwriting has elasticity (flexibility) to the touch, and it is easy to obtain handwriting with a continuous three-dimensional feel. The reason for this is unclear, but is thought to be as follows: When a styrene-olefin polymer is used, the film formed on the handwriting surface tends to have excellent elasticity. This allows the handwriting to fully receive the force of the foaming agent without being affected by the film on the handwriting surface. Furthermore, the elasticity of the film is maintained, and the handwriting itself becomes an elastic, flexible foam after foaming. Therefore, the resulting handwriting is continuous, has a sufficient three-dimensional feel, and is highly elastic (flexible). In consideration of improving the above effects, the styrene-butadiene polymer preferably has a styrene content of 60 mol % or less, and more preferably 50 mol % or less, relative to the total amount constituting the styrene-butadiene polymer.

[0020] The weight-average molecular weight of the water-dispersible resin is preferably 10,000 to 10,000,000, more preferably 30,000 to 3,000,000, and even more preferably 100,000 to 1,000,000. In the present invention, the weight-average molecular weight can be measured by a conventional method using gel permeation chromatography. The same applies to the weight-average molecular weights described below.

[0021] Furthermore, the water-dispersible resin preferably has an average particle size of 500 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less. When the average particle size is 500 nm or less, the dispersion stability of the resin particles is improved, and ink dischargeability is improved and stabilized, making it easier to obtain excellent three-dimensional effect and uniform, continuous handwriting. In addition, sedimentation of the resin particles is suppressed, resulting in good ink dispersion stability. The average particle size can be measured by dynamic light scattering.

[0022] When producing the ink composition according to the present invention, the water-dispersible resin may be added in the form of a dispersion, for example, an emulsion, in which the resin is dispersed in water (using a dispersant as necessary). Adding the water dispersion in the form of an emulsion to the ink composition is also a preferred embodiment.

[0023] Examples of commercially available emulsions containing water-dispersible resins include emulsions of acrylic resins such as Movinyl 718A (trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), emulsions of vinyl acetate resins such as Vinyblanc 1002 and 1008 (trade name, manufactured by Nissin Chemical Industry Co., Ltd.), and emulsions of styrene-butadiene polymers such as L-1924 and L-1432 (trade name, manufactured by Asahi Kasei Chemicals Corporation).

[0024] The content of the water-dispersible resin is preferably 1 to 50% by mass based on the total mass of the ink composition. When the content of the water-dispersible resin is within the above range, the ink dischargeability can be improved, and handwriting with excellent three-dimensional effect and excellent fixation can be obtained. In addition, the ink stability over time can be improved. Furthermore, in consideration of improving the above effects, the content is more preferably 5 to 40% by mass, even more preferably 10 to 30% by mass, and particularly preferably 15 to 30% by mass. It is also possible to use a combination of multiple water-dispersible resins.

[0025] <Thickener> The ink composition of the present invention comprises a thickener. The thickener makes it easy to suppress the settling and aggregation of the foaming agent and water-dispersible resin in the ink when it is left to stand, thereby achieving excellent dispersibility of the foaming agent, water-dispersible resin, etc. As a result, unevenness is less likely to occur in the three-dimensional effect of handwriting after the foaming treatment, and handwriting with excellent three-dimensional effect and fixation can be obtained. Although conventionally known substances can be used as the thickener, it is preferable to use a substance that can impart shear thinning properties to the ink composition (shear thinning agent). By using such a substance, the ink composition can be easily made low-viscosity when subjected to external force, while maintaining an ink viscosity that is less likely to cause the foaming agent, water-dispersible resin, etc. to settle or aggregate when left standing. This makes it possible to further improve the ink dischargeability from the writing tip during writing, while suppressing ink settling and aggregation when left standing. This allows for the production of handwriting with even greater three-dimensionality. In particular, when such an ink composition is used in a pressure-sensitive writing instrument, a strong shear force is applied to the ink when pressure is applied, which tends to further reduce the viscosity of the ink, thereby improving the ink dischargeability from the writing tip, ensuring a sufficient amount of ink in the handwriting before the foaming treatment, and resulting in handwriting with even more excellent three-dimensionality after the foaming treatment. Furthermore, when used in a pressure-sensitive ballpoint pen, among other pressure-sensitive writing implements, a strong shear stress is easily applied to the ink as the ball rotates, making it easier to achieve the above-mentioned effects. Furthermore, since the ink discharge amount can be stabilized, uniform, continuous, and three-dimensional handwriting can be easily obtained, and even fine handwriting such as letters can be easily left three-dimensional.

[0026] As the shear thinning agent, a crosslinked acrylic acid polymer, an associative thickener, a polysaccharide, or the like can be used. Associative thickeners include polyesters, polyethers, urethane-modified polyethers, polyaminoplasts, alkali-swelling associative thickeners, nonionic associative thickeners, etc., depending on the associative hydrophobic group, and polysaccharides include xanthan gum, welan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, diutan gum, etc. These shear thinning agents can be used alone or in combination of two or more. Among these, it is preferable to use polysaccharides or cross-linked acrylic acid polymers, and more preferably polysaccharides. This is because they are resistant to the shear of a mixer, allow stable ink preparation, and are compatible with water-dispersible resins and blowing agents, making it easy to prepare inks with excellent stability over time. Furthermore, among polysaccharides, succinoglycan is more preferable because it has a higher viscosity in a static state (low shear) than other polysaccharides, making it easier to stably disperse water-dispersible resins and blowing agents, resulting in an ink composition with excellent dispersion stability.

[0027] The content of the thickener is preferably 0.01 to 5% by mass, more preferably 0.05 to 1% by mass, and even more preferably 0.1 to 0.8% by mass, based on the total mass of the aqueous ink composition. When the content of the thickener is within the above range, excellent dispersibility of the foaming agent and water-dispersible resin can be obtained, ink discharge from the writing tip can be improved, handwriting with excellent three-dimensional effect and fixation can be easily obtained, and the ink stability over time can also be improved.

[0028] In addition, in consideration of obtaining excellent ink stability over time, improved and stabilized ink dischargeability, uniform and continuous three-dimensional effect, and excellent fixability of handwriting, the ratio of the total content of the foaming agent and water-dispersible resin to the content of the thickener is preferably 50 to 120, more preferably 60 to 100, by mass.

[0029] <Coloring agent> The ink composition of the present invention contains a colorant, and any of the conventionally known pigments and dyes can be used.

[0030] The dye is not particularly limited, and examples thereof 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.

[0031] 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.

[0032] The pigment is not particularly limited. Examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine pigments, azo pigments, quinacridone pigments, quinophthalone pigments, styrene pigments, triphenylmethane pigments, perinone pigments, perylene pigments, dioxazine pigments, and further luster pigments, microcapsule pigments, colored resin pigments, etc. The pigment may be a water-dispersed pigment product that has been dispersed in a medium in advance using a pigment dispersant such as a surfactant.

[0033] In the present invention, the colorant is preferably a pigment, as this allows for good color development and facilitates the production of handwriting with excellent three-dimensional effect. Among pigments, it is preferable to use colored resin pigments. Colored resin pigments tend to have excellent heat resistance and weather resistance, and therefore tend to maintain good color development even after the handwriting has been foamed. Furthermore, they tend to provide stable ink discharge from the writing tip, making it easy to obtain uniform, continuous handwriting with excellent three-dimensional effect. Furthermore, the ink's stability over time is also likely to be improved. In the present invention, the colored resin pigment refers to resin particles colored with a coloring agent. The coloring agent is not particularly limited as long as it can color the resin particles, and any pigment or dye can be used. The resin particles are preferably styrene-acrylonitrile resin particles (hereinafter sometimes referred to as SA resin particles) because they have excellent alkali resistance, acid resistance, and heat resistance, and are highly stable even in the presence of various additives. Specific examples of commercially available products containing colored resin particles include the Shinroihi Color series (manufactured by Shinroihi Co., Ltd.), the Lumicol series (manufactured by Nippon Fluorescent Chemical Co., Ltd.), the LM series (manufactured by Fuji Dye Co., Ltd.), and the Epocolor series (manufactured by Nippon Shokubai Co., Ltd.). Specific examples of the Lumicol series include NKW-2317H, NKW-6307H, NKW-2308H, NKW-2302H, NKW-2305H, and NKW-6305H. Other products in the Shinrohi Color series include Shinrohi Color Base SW-11, SW-12, SW-13, SW-14, SW15, SW-16, SW-17, SW-18, SW-27, SW-37, SW-47, SF-1012, SF-1013, SF-1014, SF-1015, SF-1017, SF-1027, SF-1038, and SF-5015.

[0034] In addition, it is also a preferred embodiment to use a reversible thermochromic microencapsulated pigment as the colorant. By using a reversible thermochromic microencapsulated pigment as the colorant, not only can a three-dimensional handwriting be obtained, but it is also possible to achieve both a three-dimensional change in shape and color of the handwriting, making it possible to enjoy the handwriting even more. In addition, examples of reversible thermochromic microcapsule pigments include those that encapsulate a reversible thermochromic composition consisting of at least (i) an electron-donating color-forming organic compound, (ii) an electron-accepting compound, and (iii) a reaction medium that determines the temperature at which the color-forming reaction between the two occurs.

[0035] The content of the colorant varies depending on the type, but is preferably 0.1 to 30 mass %, more preferably 1 to 20 mass %, and even more preferably 2 to 10 mass %, based on the total mass of the ink composition. The colorants may be used alone or in combination of two or more types as appropriate.

[0036] <Water> The ink composition according to the present invention contains water. The water is not particularly limited, and examples thereof include tap water, ion-exchanged water, ultrafiltered water, and distilled water. The content of water is preferably 10 to 90 mass % based on the total mass of the ink composition.

[0037] <Other additives> The ink composition of the present invention essentially contains the above-mentioned components (foaming agent, water-dispersible resin, thickener, colorant, and water), but may contain other components as needed.

[0038] <Constitution agent> The ink composition according to the present invention may further contain an extender. By using the extender, the shape of handwriting before the foaming treatment is easily maintained, and handwriting with excellent three-dimensional effect is easily obtained after the foaming treatment. Examples of the extender include inorganic extenders such as calcium carbonate, kaolin, talc, silica, aluminum silicate, alumina, and barium sulfate, as well as organic extenders such as resin particles. The content of the extender is preferably 0.1 to 20% by mass based on the total mass of the ink composition, and is more preferably 1 to 10% by mass, since the effect of the extender is utilized to easily obtain handwriting with excellent three-dimensional effect, and taking into consideration the ink stability over time, ink discharge stability, and maintenance of good color development of handwriting.

[0039] <Water-soluble organic solvent> The ink composition of the present invention preferably further contains a water-soluble organic solvent. Generally, when the ink composition contains components that can exist in a water-insoluble state in the main solvent, such as a foaming agent, a water-dispersible resin, or even a pigment, the water evaporates from the nib of a writing instrument filled with the ink, causing the ink to dry and solidify, resulting in clogging of the ink flow path. When this occurs, it is difficult to clear the clogging with additional ink, and the writing instrument may become unable to write again, even though there is ink remaining. For this reason, it is preferable to improve the dry-up resistance. The ink composition of the present invention contains the above-mentioned components, and since the ink composition contains these components at high concentrations, there is a strong need to improve the dry-up resistance. For this reason, the ink composition of the present invention preferably further contains a water-soluble organic solvent that can improve the dry-up resistance. Examples of water-soluble organic solvents include polyhydric alcohols and glycol ethers, and among these, it is preferable to select and use polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin. These solvents have little effect on the blowing agent and water-dispersible resin, do not significantly affect the dispersion stability of the ink composition, and can impart the moisture absorption effect of polyhydric alcohols to the ink composition, thereby improving dry-up resistance. Among these, it is preferable to use glycerin in the present application.

[0040] The content of the water-soluble organic solvent is preferably 0.1 to 20% by mass based on the total mass of the ink composition, and is preferably 1 to 10% by mass in order to improve resistance to dry-up and to facilitate the production of handwritten lines with a three-dimensional feel.

[0041] The ink composition of the present invention may also contain various additives such as a pH adjuster, a rust inhibitor, a preservative, and a chelating agent for the purpose of improving the ink properties and functions.

[0042] Examples of pH adjusters include basic inorganic compounds such as ammonia, sodium carbonate, sodium phosphate, and sodium hydroxide; basic organic compounds such as sodium acetate, triethanolamine, and diethanolamine; lactic acid, acetic acid, and citric acid.

[0043] Examples of preservatives include phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, sodium 2-pyridinethiol-1-oxide, 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, orthophenylphenol or its salts.

[0044] Examples of the rust inhibitor include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, and dialkylthiourea.

[0045] Examples of chelating agents include ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), glycol ether diaminetetraacetic acid (GEDTA), nitrilotriacetic acid (NTA), hydroxyethyliminodiacetic acid (HIDA), dihydroxyethylglycine (DHEG), diethylenetriaminepentaacetic acid (DTPA), triethylenetetraminehexaacetic acid (TTHA), and alkali metal salts, ammonium salts, or amine salts thereof.

[0046] In the present invention, the composition may further contain a moisturizing agent other than the water-soluble organic solvent, such as urea, sorbitol, dextrin, N,N,N-trialkylamino acids such as trimethylglycine, and hyaluronic acids.

[0047] Furthermore, nonionic surfactants, anionic surfactants, cationic surfactants, surfactants having an acetylene bond in the structure, fluorine-containing surfactants, and the like can also be added. Antifoaming agents can also be added. Lubricants such as phosphate ester surfactants and fatty acids can also be added. Water-soluble resins that have hydrophilic groups and can be uniformly dissolved in water can also be added.

[0048] <Water-based ink composition for writing instruments> The viscosity of the ink composition of the present invention is 20°C at a shear rate of 1.92 sec -1 Under the conditions of (0.5 rpm), the viscosity is preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, even more preferably 2000 mPa·s or more, and is preferably 10000 mPa·s or less, more preferably 5000 mPa·s or less. If the viscosity is within the above range, the ink has excellent dispersion stability and excellent ink ejection properties, and handwriting with excellent three-dimensional effect and fixation can be stably obtained. The solid content of the ink composition is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and even more preferably 20 to 40% by mass, based on the total mass of the ink composition. If the solid content ratio is within the above range, 20°C, shear rate 1.92 sec -1 The ink viscosity under these conditions can be easily set within the above range, and handwriting with excellent three-dimensional effect and fixation can be formed. From the above, it is preferable that the ink composition according to the present invention tends to have a higher viscosity and a higher solid content ratio than ink compositions for writing instruments that are commonly used as described above, in order to obtain handwriting that has excellent three-dimensional effect and excellent fixation.

[0049] The ink composition according to the present invention is used in a writing instrument, and a preferred embodiment of the present invention is a pressure-sensitive writing instrument, and more particularly a pressure-sensitive ballpoint pen. In this case, it is preferable that good ink ejection properties are obtained during writing. Therefore, the viscosity of the ink composition is 20°C, shear rate 76.8 sec -1 Under the condition of (20 rpm), the viscosity is preferably 500 mPa·s or less, more preferably 400 mPa·s or less, and even more preferably 300 mPa·s or less. Furthermore, in consideration of the dispersion stability of the ink when left to stand and good ink ejection from the writing tip, which allows for stable and uniform handwriting with a three-dimensional feel, it is preferable that the viscosity gradient between the ink composition when stationary and when flowing is at least a certain level, in other words, the viscosity ratio of the ink composition when subjected to high shear and when subjected to low shear is at least a certain level. Therefore, the viscosity ratio of the ink composition at high shear and low shear (20°C, shear rate 1.92 sec -1 Viscosity under the conditions (0.5 rpm) / 20 °C shear rate 76.8 sec -1 The viscosity under the condition of (20 rpm) is preferably 5 or more, more preferably 10 or more, and preferably 20 or less.

[0050] <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 in a variety of stirrers such as a magnetic hot stirrer, a propeller stirrer, a homogenizer stirrer, a homodisper, a homomixer, or a planetary stirrer, or in a variety of dispersers such as a bead mill.

[0051] <Writing implements> The writing implement according to the present invention contains the ink composition described above. The structure and shape of the writing implement to be filled with the ink composition of the present invention are not particularly limited, and conventional general-purpose implements can be used, but a pressure-sensitive writing implement is particularly preferred. This is because the ink composition of the present invention tends to have a high viscosity and a high solids content, and when used in a pressure-sensitive writing implement, the ink discharge properties can be improved. This makes it possible to ensure a sufficient amount of ink in the handwriting before the foaming treatment, and the handwriting after the foaming treatment has a more three-dimensional feel and excellent fixation. Furthermore, it is preferable that the ink be used in a pressurized ballpoint pen with a ballpoint pen tip. By using a pressurized ballpoint pen, the ink discharge property is easily stabilized, and uniform, three-dimensional handwriting can be easily obtained. Furthermore, it is possible to make even fine handwriting three-dimensional. Examples of pressurized ballpoint pens include pressurized ballpoint pens in which pressurized gas is sealed inside an ink reservoir and the pressure of this pressurized gas pressurizes the ink composition toward the tip end of the tip; knock-type pressurized ballpoint pens in which the space at the rear end of the ink composition is compressed by knocking, attaching a cap, or moving the pen tip due to writing pressure when writing, and the ink composition is pressed toward the tip end by the pressure caused by this compression; cap-type pressurized ballpoint pens equipped with a cap that covers the pen tip; and pen pressure pressurized ballpoint pens. Since the ink composition according to the present invention tends to have a high solid content ratio, and taking into consideration resistance to dry-up, a cap-type pressure ballpoint pen capable of sealing the pen tip is more preferred.

[0052] The pressure applied to the ink composition filled inside the ink reservoir from the rear end side by pressurization is preferably greater than atmospheric pressure, specifically, preferably greater than atmospheric pressure but not greater than 1.5 times. More specifically, if atmospheric pressure is 1000 hPa, the pressure is preferably greater than 1000 hPa and not greater than 1500 hPa, and more preferably greater than 1000 hPa and not greater than 1200 hPa. This makes it possible to suppress ink leakage from the tip end while optimizing ink consumption, thereby achieving a sufficient three-dimensional effect and improving handwriting quality and handwriting density.

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0054] Example 1 The following materials, excluding the thickener, were mixed in the amounts shown below using a magnetic stirrer while heating and stirring at room temperature to prepare a base ink. Then, the following thickener was added to the base ink in the amounts shown below, and the mixture was thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was achieved, thereby obtaining the ink composition of Example 1. Foaming agent (thermal expandable foaming agent (thermal expandable microcapsules), product name: EXPANCEL031 WUF40, Nippon Ferrite Co., Ltd., average particle size: 10 to 16 μm, foaming start temperature: 80 to 95°C, maximum expansion temperature: 120 to 135°C, solid content: 76% by mass), 5.0 parts by mass Water-dispersible resin (styrene-butadiene copolymer emulsion, product name: L1924, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature 5°C, solid content 46% by mass, styrene content: 45 mol%, average particle size: 150 nm) 50.0 parts by mass Thickener (succinoglycan) 0.3 parts by mass Colorant (44% by mass water dispersion of colored resin particles (pink), product name: Lumicol NKW-2317H, manufactured by Nippon Fluorescent Chemical Co., Ltd.) 10.0 parts by mass Water-soluble organic solvent (glycerin) 5.0 parts by mass ·Water 29.7 parts by mass

[0055] <Examples 2 to 11 and Comparative Examples 1 to 3> In Examples 2 to 11 and Comparative Examples 1 to 3, water-based ink compositions were obtained in the same manner as in Example 1, except that the types and amounts of components contained in the ink compositions were changed to the compositions shown in the table. The numerical values ​​for the compositions in the table indicate parts by mass.

[0056] [Table 1]

[0057] [Table 2]

[0058] The explanation follows the note numbers for the materials in the table. (1) Product name: Advancell EMH204, manufactured by Sekisui Chemical Co., Ltd., average particle size: 36 to 44 μm, foaming start temperature: 110 to 130°C, maximum expansion temperature: 160 to 180°C (2) Product name: EXPANCEL031 WUF40, Nippon Ferrite Co., Ltd., average particle size: 10 to 16 μm, foaming start temperature: 80 to 95°C, maximum expansion temperature: 120 to 135°C, solid content: 76% by mass (3) 4,4'-oxybis(benzenesulfonylhydrazide), trade name: Neo Celvon #5000, manufactured by Eiwa Chemical Industry Co., Ltd. (4) Product name: Cell Paste 101, manufactured by Eiwa Chemical Industry Co., Ltd. (5) Product name: L1924, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature: 5°C, solid content: 46% by mass, styrene content: 45% by mol, average particle size: 150 nm (6) Product name: L1432, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature: 18°C, solid content: 46% by mass, styrene content: 50 mol%, average particle size: 200 nm (7) Product name: Vinyblan 1008, manufactured by Shin-Etsu Chemical Co., Ltd., glass transition temperature 30°C, solid content 46% by mass (8) Product name: Movinyl 718A, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., glass transition temperature: -6°C, solid content: 46% by mass (9) Product name: Movinyl 972, manufactured by Nippon Synthetic Chemical Industry Co., Ltd., glass transition temperature 100°C, solid content 50% by mass (10) Product name: Hivis Wako 104, manufactured by Wako Pure Chemical Industries, Ltd. (11) Product name: SG-95, manufactured by Nippon Talc Co., Ltd. (12) Product name: BF-40E, manufactured by Sakai Chemical Industry Co., Ltd. (13) Product name: Lumicol NKW-2317H, manufactured by Nippon Fluorescent Chemical Co., Ltd., solid content 44% (14) Product name: Water Yellow 6C, manufactured by Orient Chemical Industry Co., Ltd.

[0059] Preparation of reversible thermochromic microcapsule pigment 1 A reversible thermochromic microcapsule pigment 1 was prepared by encapsulating in microcapsules a reversible thermochromic composition having color memory properties, which was composed of an electron-donating color-forming organic compound and 1.0 part of 3,6-bis(diphenylamino)fluoran as components, 3.0 parts of 1,1-bis(4-hydroxyphenyl)-2-ethylhexane and 5.0 parts of 2,2-bis(4'-hydroxyphenyl)-hexafluoropropane as electron-accepting compounds, and 50.0 parts of 4-benzyloxyphenylethyl caprate as a reaction medium. The average particle size of Microcapsule Pigment 1 was 1.8 μm, the temperature at which it completely faded was 55° C., the temperature at which it completely developed color was −20° C., and it changed color from blue to colorless with temperature change.

[0060] <Evaluation> The ink compositions of the Examples and Comparative Examples were filled into ballpoint pen refill 7 of cap-type pressure ballpoint pen 1, and writing was performed under pressure, and it was possible to write. For the following handwriting evaluation, writing was performed using the above pressure ballpoint pen, and the obtained handwriting was evaluated.

[0061] Here, a cap-type pressure ballpoint pen 1 is shown in FIGS. The cap-type pressure ballpoint pen 1 has a front barrel 2 with a grip member 14 attached to the grip portion and a rear barrel 3 connected together, and a ballpoint pen refill 7 disposed in the barrel body. Furthermore, in the cap-type pressure ballpoint pen 1, a translucent cap 4 obtained by injection molding PP resin is detachably attached by fitting a fitting protrusion formed on the inner wall of the cap 4 over a fitting protrusion formed on the side wall of the front barrel 2. When the cap is attached to the front barrel 2, the ballpoint pen tip 10 is sealed by a sealing member provided inside the cap.

[0062] A ballpoint pen tip 10 rotatably holding a ball with a diameter of 1.0 mm is attached to the front end of an ink reservoir 8 provided in the ballpoint pen refill 7 via a tip holder 9 . At the rear end of the ink reservoir 8, a tail plug 11 having an air hole for communicating the inside and outside is attached. The ink reservoir 8 is filled with a water-based ink composition 12 for a writing instrument having the above-mentioned ink formulation and an ink follower 13 . Although not shown, a coil spring is provided behind the ball to constantly press the ball against the inner wall of the front end of the tip.

[0063] In addition, the rear end of the ink reservoir 8 provided in the ballpoint pen refill 7 is press-fitted into the rear end of the rear barrel 3, and the space following the portion of the ink reservoir 8 filled with the ink composition 12 and the ink follower 13 is only connected to the outside air by a communication hole 3A provided in the rear end of the rear barrel 3, which connects the inside and outside of the writing instrument.

[0064] The pressurizing mechanism that operates when the cap 4 is fitted will be described in detail below. By fitting the cap 4 onto the rear barrel 3 of the writing instrument body, pressure can be applied to the ink composition 12 filled in the ballpoint pen refill 7 via the ink follower 13. Specifically, when the rear end of rear barrel 3 is inserted into the open end of cap body 5 in the direction of arrow F in the figure, inner wall 5A of cap body 5 and side wall 3B of rear barrel 3 first come into contact. At this time, the spaces inside the cap body 5, the rear barrel 3 and the ink reservoir 8 are communicated in a sealed state through a communication hole 3A provided at the rear end of the rear barrel 3, which communicates the inside and outside. Further, when the cap 4 is advanced in the direction of arrow F in the figure, the sealed space is compressed until the fitting is completed. As a result, pressure can be applied to the water-based ink composition for a writing instrument filled in the ballpoint pen refill 7 via the ink follower 13. The pressure was 1050 hPa.

[0065] <Handwriting evaluation> The ink compositions of the Examples and Comparative Examples were written on writing paper (JIS P 3201 Writing Paper A), left overnight, and then heated for 10 minutes in a hair dryer (1200 watts). The handwriting was then evaluated for three-dimensional effect, fixation, and elasticity. The evaluation criteria were as follows. The results are shown in the table below. Three-dimensional feeling ○: The raised handwriting was clearly visible. △: The raised handwriting was visually confirmed, but was somewhat weak. ×: No raised handwriting was visually observed. Fixation ○: When touched with handwriting, it did not peel off from the surface on which it was written. △: When the handwriting was touched, part of the handwriting peeled off from the surface being written on. ×: When touched with handwriting, the mark peeled off from the surface being written on. Elasticity ○: The writing is elastic (flexible). △: The handwriting has some elasticity (flexibility), but is somewhat lacking. ×: No elasticity (flexibility) in the writing.

[0066] The ink composition of Example 1 was placed in a 15 mm diameter airtight glass test tube and left at room temperature for 3 days. When the state of the ink composition was visually observed, no aggregation or separation was observed, and the ink had good stability over time.

[0067] The viscosity of the ink compositions of Examples 1 and 8 was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) at a shear rate of 1.92 sec in an environment of 20°C. -1 The ink viscosity was measured under the conditions of rotation speed 0.5 rpm and was found to be 3020 mPa·s and 3328 mPa·s.

[0068] [Viscosity ratio] The viscosity of the ink compositions of Examples 1 and 8 was measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) at a shear rate of 76.8 sec in an environment of 20°C. -1 The ink viscosity was measured under the condition of 20 rpm. The shear rate above is 1.92 sec -1 Viscosity at shear rate of 76.8 sec (0.5 rpm) -1 The viscosity at 20 rpm was calculated, and the viscosity ratio (0.5 rpm / 20 rpm) was calculated, which was 14 for both.

[0069] From the above, it has been found that an ink composition containing water, a colorant, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickener can produce handwriting that has sufficient three-dimensionality and excellent fixation, and that a writing instrument using this ink composition is an excellent writing instrument. [Explanation of symbols]

[0070] 1 Cap-type pressurized ballpoint pen 2 front axle 3 rear axle 3A communication hole 3B Side wall 4 Cap 5 Cap body 5A Inner wall 6 Sealing material 7 Ballpoint pen refills 8 Ink reservoir 9 Chip holder 10 Ballpoint Pen Tips 11 tail plug 11A Air vent 12. Ink compositions for writing instruments 13 Ink follower 14 Grip

Claims

1. A water-based ink composition for a writing instrument, comprising water, a colorant, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickener.

2. 2. The ink composition according to claim 1, wherein the blowing agent is a heat-sensitive blowing agent.

3. 3. The ink composition according to claim 1, wherein the heat-sensitive foaming agent is a thermal expansion foaming agent.

4. The ink composition according to any one of claims 1 to 3, wherein the thickener is a shear thinning agent.

5. The ink composition according to any one of claims 1 to 4, wherein the content of the foaming agent is 1% by mass to 20% by mass based on the total mass of the ink composition.

6. The ink composition according to any one of claims 1 to 5, wherein the content of the water-dispersible resin is 1% by mass to 50% by mass based on the total mass of the ink composition.

7. The ink composition according to any one of claims 1 to 6, wherein the solid content of the ink composition is 10% by mass to 50% by mass.

8. The viscosity of the ink composition is 20°C, the shear rate is 1.92 sec －１ The ink composition according to any one of claims 1 to 7, wherein the viscosity of the ink composition is 500 mPa·s or more under the conditions of

9. A writing instrument containing the composition according to any one of claims 1 to 8.

10. 10. The writing instrument of claim 9, which is a pressure-sensitive writing instrument.

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