Water-based ink composition for writing instruments, and writing instruments using 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] This invention relates to an aqueous ink composition for writing instruments and a writing instrument using the same. [Background technology]

[0002] When writing with a writing instrument filled with ink, the ink usually penetrates the paper surface, resulting in a flat, two-dimensional writing surface. However, by making this writing surface three-dimensional, it is possible to enjoy a different kind of writing experience. One proposed method for forming three-dimensional handwriting involves adding heat-expandable microcapsules to an ink composition. The resulting handwriting is then treated with a heat source such as an iron or hair dryer, causing the microcapsules to expand and produce three-dimensional handwriting. (For example, Patent Document 1) However, conventional ink compositions have problems such as insufficient three-dimensionality in the resulting handwriting, or even when three-dimensional handwriting is obtained, the handwriting does not expand uniformly, resulting in unevenness in the three-dimensionality, or the handwriting does not adhere sufficiently to the writing surface and peels off, leaving room for improvement. Furthermore, the ink ejection from the pen tip is unstable, making it difficult to leave a uniform writing pattern, and it is challenging to leave fine details such as letters in a three-dimensional form. Solving these problems is also required. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-191962 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present invention solves the above-mentioned problems and provides an aqueous ink composition for writing instruments and a writing instrument using the same that can form handwriting with excellent three-dimensionality and fixation. [Means for solving the problem]

[0005] To solve the above problems, the present invention "1. It comprises water, a coloring agent, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a shear viscosity reducing agent." The content of the total content of the foaming agent and the water-dispersible resin relative to the content of the shear viscosity reducing agent is , solids The ratio is based on mass. 67 ~ 93.3 That is, A water-based ink composition for writing instruments characterized by the following. 2 The first foaming agent is a heat-sensitive foaming agent. In the section The ink composition described. 3 The heat-sensitive blowing agent is a heat-expanding blowing agent. 2 The aqueous ink composition for writing instruments described in the section. 4 The content of the foaming agent is 1% by mass to 20% by mass, based on the total mass of the ink composition, according to item 1 to item 2. 3 A water-based ink composition for writing instruments as described in any one of the items. 5 The content of the water-dispersible resin is 1% by mass to 50% by mass, based on the total mass of the aqueous ink composition for writing instruments, according to paragraphs 1 to 2. 4 A water-based ink composition for writing instruments as described in any one of the items. 6 The solid content ratio of the aqueous ink composition for writing instruments is 10% by mass to 50% by mass, according to item 1 to item 2. 5 A water-based ink composition for writing instruments as described in any one of the items. 7 The viscosity of the aforementioned aqueous ink composition for writing instruments is as follows: 20°C, shear rate 1.92 sec -1 Under these conditions, the pressure is 500 mPa·s or higher, item 1 to item 2 6 A water-based ink composition for writing instruments as described in any one of the items. 8 Articles 1 through 1 7A writing instrument containing the aqueous ink composition according to any one of the items. 9 . It is a pressure-type writing instrument, the writing instrument according to item 8 .」 shall be used.

Effect of the Invention

[0006] According to the present invention, it is possible to provide an aqueous ink composition for a writing instrument and a writing instrument using the same, which can obtain a handwriting with excellent three-dimensional effect, and the obtained handwriting is difficult to peel off from the writing surface and has excellent fixing property.

Brief Description of the Drawings

[0007] [Figure 1] It is a longitudinal sectional view of an example of a cap-type pressure ballpoint pen. [Figure 2] It is a longitudinal sectional view of the ballpoint pen of FIG. 1 with the cap removed. [Figure 3] It is an explanatory view showing a writing instrument in a state where a cap is fitted to the rear end portion of a shaft cylinder (pressurized state).

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described in detail. In this specification, "parts", "%", "ratio", etc. indicating formulation are based on mass unless otherwise specified, and the content rate is the mass % of the constituent components based on the mass of the ink composition.

[0009] <Aqueous Ink Composition for Writing Instruments> The aqueous ink composition for a writing instrument according to the present invention (hereinafter, sometimes referred to as an ink composition) contains 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 to use a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a thickener in the ink composition of the present invention. By using these components, it is possible to obtain handwriting that allows for visual confirmation of three-dimensionality, and that is resistant to peeling from the writing surface, exhibiting excellent three-dimensionality and adhesion. The constituent 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 brushstrokes appear larger, resulting in a three-dimensional effect. Foaming agents are foaming agents that foam in response to external stimuli such as heat or light. Specifically, these 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 a three-dimensional effect when subjected to heat treatment. Furthermore, examples of heat-sensitive foaming agents include thermal expansion foaming agents (also called physical foaming agents) and thermal decomposition foaming agents (also called chemical foaming agents). In this application, however, it is preferable to use a thermal expansion foaming agent, which tends to have a high volume expansion ratio.

[0010] Furthermore, in this application, there are no particular restrictions on the thermally expanding foaming agent, but it is preferable to use thermally expanding microcapsules because using them together with a water-dispersible resin having a glass transition temperature of less than 100°C, as described later, makes it easier to form handwriting with excellent three-dimensionality and to maintain that three-dimensionality. 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 of the outer shell begins to soften, and the vapor pressure of the encapsulated volume-expanding compound increases, creating a pressure sufficient to deform the particle, causing the thermoplastic resin of the outer shell to stretch and expand.

[0011] As the thermoplastic resin constituting the outer shell, for example, polymers of (meth)acrylonitrile and copolymers with a high (meth)acrylonitrile content are preferably used. In the case of such copolymers, other monomers (comonomers) that can be used include vinyl halides, vinylidene halides, styrene monomers, (meth)acrylate monomers, vinyl acetate, butadiene, vinylpyridine, and chloroprene. The above thermoplastic resin may be made crosslinkable with crosslinking agents 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, triacrylic formal, and triallyl isocyanurate. While uncrosslinked is preferred, partial crosslinking is also permitted to the extent that it does not impair the properties of the thermoplastic resin. Furthermore, as volume-expanding compounds, substances that vaporize under realistic temperature conditions, such as low-boiling point solvents and water, can be used. Examples of low-boiling point solvents 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] Commercially available products can be used as thermally expandable microcapsules. Examples of such commercially available products include the Advancell series from Sekisui Chemical Co., Ltd., the Expancell series from AkzoNovel (distributed in Japan by Nippon Philite Co., Ltd.), the Matsumoto Microsphere series from Matsumoto Oil & Fat Pharmaceutical Co., Ltd., and the Kureha Microsphere series from Kureha Corporation. These can be used individually or in combination of two or more.

[0013] On the other hand, examples of pyrolytic blowing agents include organic pyrolytic blowing agents and inorganic pyrolytic blowing agents. Examples of organic pyrolysis-type blowing agents include azosicarbonamide 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'-disulfone hydrazide diphenylsulfone, toluenedisulfonyl hydrazine, p-toluenedisulfonyl hydrazide, p-toluenesulfonyl semicarbazide, and diethylazodicarboxylate. Examples of inorganic pyrolysis-type blowing agents include sodium bicarbonate and other bicarbonates, carbonates, and combinations of bicarbonates and organic acid salts. Furthermore, the foaming agent may be used alone or in combination of two or more types.

[0014] As described above, in this 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 microcapsule size is 1μ or larger, it is easier to obtain handwriting with excellent three-dimensionality. If it is 50μ or smaller, the dispersion stability of the thermally expandable microcapsules can be improved, and ink ejection can be improved and stabilized, making it easier to obtain handwriting with uniform and continuous three-dimensionality. In addition, the long-term stability of the ink can also be improved. To further improve the above effects, the average particle size of the thermally expanded microcapsules is more preferably 5 μm or more, even more preferably 10 μm or more, even 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 start 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, also 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, 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 numerical range, unintended foaming and expansion are less likely to occur under normal storage and usage conditions, general-purpose equipment can be easily used for heat treatment, and three-dimensional handwriting can be easily obtained.

[0016] The foaming agent content is preferably 1 to 20% by mass, and more preferably 2 to 10% by mass, based on the total mass of the ink composition. If the foaming agent content is within the above range, the ink's ejection from the writing tip improves, resulting in a writing style with superior three-dimensionality. Furthermore, the ink's stability over time can also be improved.

[0017] <Water dispersible resin> The ink composition according to the present invention comprises a water-dispersible resin (hereinafter sometimes referred to as a water-dispersible resin) having a glass transition temperature (Tg) of less than 100°C. 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, preferably in an emulsified dispersion in an aqueous medium, and also exists in particulate form without dissolving in the ink composition.

[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-dimensionality due to the effect of the foaming agent, and also to obtain handwriting with excellent adhesion 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 also preferably -10°C or higher, and more preferably 0°C or higher. The glass transition temperature (Tg) can be determined by differential scanning calorimetry.

[0019] Examples of water-dispersible resins include acrylic resins, urethane resins, vinyl resins, and styrene resins. In particular, in this application, it is preferable to select and use one or more from acrylic resins, styrene resins, and vinyl resins, and it is more preferable to use styrene resin or vinyl resin. This is because the effect of the foaming agent makes it easier to obtain handwriting with excellent three-dimensionality, and furthermore, it is easier to obtain handwriting with excellent fixation. As the styrene-based resin, a styrene-olefin polymer composed of styrene and olefins such as butadiene, isoprene, ethylene-butylene, and ethylene-propylene is preferably used. Vinyl acetate resin is preferably used as the vinyl resin. Furthermore, it is preferable to use a styrene-olefin polymer, and more preferable to use a styrene-butadiene polymer, because it is easier to improve the above effects, the resulting handwriting has elasticity (flexibility), and it is easier to obtain handwriting with a continuous three-dimensional feel. The reason for this is unclear, but it is thought to be as follows: When styrene-olefin polymers are used, the film formed on the surface of the handwriting tends to have excellent elasticity. Therefore, the handwriting can fully receive the force of the foaming agent without being affected by the film on the surface of the handwriting, and furthermore, the elasticity of the film is maintained, so the handwriting itself after foaming becomes an elastic and flexible foam. Thus, the resulting handwriting is continuous and has sufficient three-dimensionality, while also being highly elastic (flexible). Considering the improvement of 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 of styrene constituting the styrene-butadiene polymer.

[0020] Furthermore, the mass-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. Here, in the present invention, the mass-average molecular weight can be measured by a conventional method using gel permeation chromatography. The same applies to the mass-average molecular weights described thereafter.

[0021] Furthermore, the water-dispersible resin is preferably one with an average particle diameter of 500 nm or less, more preferably 300 nm or less, and even more preferably 200 nm or less. When the average particle diameter is 500 nm or less, the dispersion stability of the resin particles is improved, the ink discharge performance is enhanced and stabilized, resulting in excellent three-dimensionality and a uniform, continuous writing style. In addition, the sedimentation of resin particles is suppressed, and the ink dispersion stability is also good. The average particle size can be measured using dynamic light scattering.

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

[0023] Examples of commercially available emulsions containing water-dispersible resins include acrylic resin emulsions such as Movinyl 718A (trade name, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), vinyl acetate resin emulsions such as Vinibran 1002 and 1008 (trade names, manufactured by Nisshin Chemical Industry Co., Ltd.), and styrene-butadiene polymer emulsions such as L-1924 and L-1432 (trade names, 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 ejection performance can be improved, resulting in handwriting with excellent three-dimensionality and excellent fixation. Furthermore, the long-term stability of the ink can also be improved. Furthermore, considering the improvement of the above effects, it is more preferably 5 to 40% by mass, even more preferably 10 to 30% by mass, and particularly preferably 15 to 30% by mass. Furthermore, multiple types of water-dispersible resins can be combined.

[0025] <Thickening agent> The ink composition of the present invention comprises a thickening agent. The thickening agent helps to suppress the sedimentation and aggregation of foaming agents and water-dispersible resins in the ink during standing, resulting in excellent dispersibility of foaming agents and water-dispersible resins. Therefore, unevenness in the three-dimensional effect of the handwriting after foaming treatment is less likely to occur, resulting in handwriting with excellent three-dimensionality and fixation. While conventionally known substances can be used as thickeners, it is preferable to use a substance that can impart shear-thinning properties to the ink composition (a shear-thinning agent). By using such a substance, the ink viscosity can be maintained such that foaming agents and water-dispersible resins are less likely to settle and aggregate when left standing, while the ink composition can be easily reduced in viscosity when external force is applied. Therefore, while suppressing ink settling and aggregation when left standing, the ink discharge performance from the tip of the pen during writing can be further improved. As a result, it is possible to obtain handwriting with even better three-dimensionality. In particular, when such an ink composition is used in a pressurized writing instrument, a strong shear force is applied to the ink during pressurization, making it easier for the ink to become lower in viscosity. As a result, the ink discharge from the tip of the pen is improved, making it possible to ensure a sufficient amount of ink in the writing before foaming, and the writing after foaming becomes even more three-dimensional. Furthermore, when used in pressurized ballpoint pens, a strong shear stress is easily applied to the ink as the ball rotates, making it easier to obtain the above effects. In addition, because the ink output can be stabilized, it is easier to obtain uniform, continuous, and three-dimensional handwriting, and even fine handwriting such as letters can be easily preserved in three dimensions.

[0026] As shear-reducing agents, cross-linked acrylic acid polymers, associated thickeners, polysaccharides, and the like can be used. Examples of associated thickeners include polyester-based, polyether-based, urethane-modified polyether-based, and polyaminoplast-based thickeners, as well as alkali-swelling associated thickeners and nonionic associated thickeners, depending on the associated hydrophobic group. Examples of polysaccharides include xanthan gum, gellan gum, succinoglycan, guar gum, locust bean gum, λ-carrageenan, cellulose derivatives, and dieutan gum. These shear-reducing agents can be used individually or in combination of two or more. Of these, polysaccharides or cross-linked acrylic acid polymers are preferred, and polysaccharides are more preferred. This is because they are resistant to the shear of a stirrer, allowing for stable ink production, and they have good compatibility with water-dispersible resins and foaming agents, making it easy to adjust them into inks with excellent long-term stability. Furthermore, among polysaccharides, succinoglycans are more preferred because, compared to others, they have a higher viscosity in a static state (at low shear), making it easier to stably disperse water-dispersible resins and foaming 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. If the thickening agent content is within the above numerical range, excellent dispersibility of foaming agents and water-dispersible resins can be obtained, improving ink discharge from the writing tip and making it easier to obtain writing lines with excellent three-dimensionality and fixation. Furthermore, the long-term stability of the ink can also be improved.

[0028] Furthermore, considering the need to obtain a writing style with excellent ink stability over time, improved and stable ink discharge, a uniform and continuous three-dimensional feel, and excellent fixation, 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 by mass, and more preferably 60 to 100.

[0029] <Coloring agent> The ink composition according to the present invention comprises a colorant. Any conventionally known pigment or dye can be used.

[0030] There are no particular restrictions on the dyes used. Examples include various dyes such as acid dyes, basic dyes, reactive dyes, direct dyes, disperse dyes, and food colorings, which can be used individually or in combination of two or more.

[0031] Specifically, the 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. Examples of basic dyes include CI Acid Black 1, CI Acid Black 2, basic dyes such as 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, and CI Basic Violet 10, direct dyes such as CI Direct Red 28, CI Direct Yellow 44, CI Direct Blue 86, CI Direct Blue 87, CI Direct Violet 51, and CI Direct Black 19, and food colorings such as CI Food Yellow 3 and CI Food Black 2.

[0032] The pigments used are not particularly limited. Examples include carbon black, aniline black, ultramarine, lead yellow, titanium dioxide, iron oxide, phthalocyanine pigments, azo pigments, quinacridone pigments, quinophthalone pigments, styrene pigments, triphenylmethane pigments, perinone pigments, perylene pigments, dioxazine pigments, as well as luminescent pigments, microcapsule pigments, and colored resin pigments. Alternatively, the pigments may be pre-dispersed in a medium using a pigment dispersant such as a surfactant, or other water-dispersible pigment products may be used.

[0033] In this application, it is preferable that the coloring agent be a pigment, as this makes it easier to obtain brushstrokes with good color development and excellent three-dimensionality. Furthermore, among pigments, it is preferable to use colored resin pigments. Colored resin pigments tend to have excellent heat resistance and weather resistance, making it easier to maintain good color development even after the handwriting has been foamed. In addition, they tend to provide stable ink discharge from the tip of the pen, making it easier to obtain handwriting with a uniform, continuous, and excellent three-dimensional effect. Moreover, the ink's stability over time is also easily improved. In this invention, a colored resin pigment refers to resin particles that have been colored with a colorant. The colorant 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. Examples of commercially available products containing colored resin particles include the Shinloihi Color series (manufactured by Shinloihi Co., Ltd.), the Lumicol series (manufactured by Nippon Fluorescent Chemicals Co., Ltd.), the LM series (manufactured by Fuji Pigment Co., Ltd.), and the Epocolor series (manufactured by Nippon Shokubai Co., Ltd.). Specifically, examples of the Lumicol series include NKW-2317H, NKW-6307H, NKW-2308H, NKW-2302H, NKW-2305H, and NKW-6305H. Other products in the Shinlohi Color series include Shinlohi Color Base SW-11, SW-12, SW-13, SW-14, SW-15, 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] Furthermore, using reversible thermochromic microcapsule pigments as colorants is also a preferred form. By using reversible thermochromic microcapsule pigments as colorants, it is possible not only to obtain three-dimensional handwriting, but also to achieve both a three-dimensional change in shape and a change in color of the handwriting, making the handwriting even more enjoyable. Reversible thermochromic microcapsule pigments include those containing a reversible thermochromic composition comprising at least (a) an electron-donating color-changing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction between the two occurs.

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

[0036] <Water> The ink composition according to the present invention comprises water. There are no particular restrictions on the water used; for example, tap water, deionized water, ultrafiltered water, or distilled water can be used. The water content is preferably 10 to 90% by mass, based on the total mass of the ink composition.

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

[0038] <Constitutional preparation> The ink composition according to the present invention may further contain a binder. By using a binder, the shape of the handwriting before foaming is more easily maintained, and after foaming, it is easier to obtain handwriting with excellent three-dimensionality. Examples of binders include inorganic binders such as calcium carbonate, kaolin, talc, silica, aluminum silicate, alumina, and barium sulfate, as well as organic binders 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. A content of 1 to 10% by mass is more preferable, considering that the effect of the extender makes it easier to obtain handwriting with excellent three-dimensionality, as well as the long-term stability of the ink, ink ejection stability, and maintenance of good color development of the handwriting.

[0039] <Water-soluble organic solvents> The ink composition according to the present invention preferably further contains a water-soluble organic solvent. Generally, when an ink contains components that can exist in an insoluble state in water, which is the main solvent, such as foaming agents, water-dispersible resins, and pigments, the water may evaporate at the nib of a writing instrument filled with the ink, causing the ink to dry and solidify, and potentially clogging the ink channels. When this phenomenon occurs, it is difficult to clear the clog with subsequent ink, and the writing instrument may become unable to write again, even though there is still ink remaining. For this reason, it is preferable to improve the resistance to drying up. The ink composition of the present invention contains the above-mentioned components, and furthermore, their content is high, so there is a strong need to improve the resistance to drying up. For this reason, the ink composition of the present invention preferably further contains a water-soluble organic solvent that can improve the resistance to drying up. Examples of water-soluble organic solvents include polyhydric alcohols and glycol ethers, but among these, it is preferable to select and use polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin. This is because these solvents have little effect on foaming agents and water-dispersible resins, do not significantly affect the dispersion stability of the ink composition, and can impart the hygroscopic effect of polyhydric alcohols to the ink composition, thereby improving its resistance to drying up. In particular, in this application, it is preferable to use glycerin.

[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. Furthermore, considering the need to improve drying resistance while also easily obtaining handwriting with a three-dimensional feel, it is preferably 1 to 10% by mass.

[0041] Furthermore, the ink composition of the present invention may contain various additives such as pH adjusters, rust inhibitors, preservatives, and chelating agents for the purpose of improving the ink's physical 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] Rust inhibitors include benzotriazole and its derivatives, toltriazole, dicyclohexylammonium nitride, diisopropylammonium nitride, sodium thiosulfate, saponin, or dialkylthiourea.

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

[0046] Furthermore, the present invention may further contain humectants other than the water-soluble organic solvent. Examples include urea, sorbitol, dextrin, N,N,N-trialkyl amino acids such as trimethylglycine, and hyaluronic acid derivatives, which can be suitably used.

[0047] Furthermore, nonionic surfactants, anionic surfactants, cationic surfactants, surfactants containing acetylene bonds in their structure, and fluorinated surfactants can also be added. Furthermore, defoaming agents can be added. Lubricants such as phosphate ester surfactants and fatty acids can also be added. In addition, water-soluble resins that have hydrophilic groups and can dissolve uniformly in water can also be added.

[0048] <Water-based ink composition for writing instruments> The viscosity of the ink composition according to the present invention is determined at 20°C and a shear rate of 1.92 sec. -1 Under the condition of (0.5 rpm), the pressure is preferably 500 mPa·s or more, more preferably 1000 mPa·s or more, even more preferably 2000 mPa·s or more, also preferably 10000 mPa·s or less, and more preferably 5000 mPa·s or less. If the viscosity is within the above range, it is possible to consistently obtain handwriting with excellent dispersion stability, excellent ink discharge, and superior three-dimensionality and fixation. Furthermore, the solid content ratio 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, then at 20°C and a shear rate of 1.92 sec, -1 Under these conditions, the ink viscosity can be easily set within the range of the above values, allowing for the formation of handwriting with excellent three-dimensionality and fixation. Therefore, in order to obtain writing with excellent three-dimensionality and excellent fixation, the ink composition according to the present invention preferably tends to have a higher viscosity and solid content ratio than the ink compositions for writing instruments that are commonly used, as described above.

[0049] The ink composition according to the present invention is used in writing instruments, and a preferred embodiment of the present invention is a pressurized writing instrument, and more particularly, a pressurized ballpoint pen. In this case, it is preferable to obtain good ink discharge performance during writing. Therefore, the viscosity of the ink composition is determined at 20°C and a shear rate of 76.8 sec. -1 Under the conditions of (20 rpm), the pressure is preferably 500 mPa·s or less, more preferably 400 mPa·s or less, and even more preferably 300 mPa·s or less. Furthermore, considering the dispersion stability of the ink when stationary and the ability to obtain good ink discharge from the writing tip, resulting in stable and uniform handwriting with a three-dimensional feel, it is preferable that the viscosity gradient between the static viscosity and the flowing viscosity of the ink composition is above a certain level, that is, that the viscosity ratio of the ink composition under high shear and low shear is above a certain level. Therefore, the viscosity ratio of the ink composition under high shear and low shear conditions (20°C, shear rate 1.92 sec) -1 Viscosity under these conditions (0.5 rpm) / 20°C / shear rate 76.8 sec -1 The viscosity (under the condition of 20 rpm) is preferably 5 or higher, more preferably 10 or higher, and also preferably 20 or lower.

[0050] <Method for manufacturing ink composition> The ink composition according to the present invention can be manufactured by any conventionally known method. Specifically, it can be manufactured by blending the required amounts of each component and mixing them using various stirrers such as magnetic hot stirrers, propeller stirrers, homogenizer stirrers, homodispersers, homomixers, and planetary stirrers, as well as various dispersers such as bead mills.

[0051] <Writing instruments> The writing instrument according to the present invention contains the above-mentioned ink composition. The structure and shape of the writing instrument used to fill the ink composition according to the present invention are not particularly limited, and conventional, general-purpose writing instruments can be used, but a pressurized writing instrument is particularly preferred. This is because the ink composition according to the present invention tends to have a high viscosity and solid content ratio, and by using it in a pressurized writing instrument, the ink discharge performance can be improved. As a result, it becomes possible to ensure a sufficient amount of ink in the writing before foaming, and the writing after foaming has better three-dimensionality and excellent fixation. Furthermore, it is preferable to use it in a pressurized ballpoint pen with a ballpoint pen tip. By using a pressurized ballpoint pen, ink ejection is more easily stabilized, and uniform, three-dimensional writing is more easily obtained. In addition, it becomes possible to create three-dimensional lines even with fine writing. Examples of pressurized ballpoint pens include those that seal pressurized gas in the ink reservoir and use the pressure of this gas to push the ink composition toward the tip, those that compress the space on the rear end of the ink composition through actions such as clicking, attaching a cap, or the movement of the pen tip due to writing pressure, and use the resulting pressure to push the ink composition toward the tip, those that use a click mechanism, those that use a cap to cover the pen tip, and those that use writing pressure to pressurize. Since the ink composition according to the present invention tends to have a high solid content ratio, a pressurized ballpoint pen with a cap that can seal the pen tip is more preferable, considering its resistance to drying out.

[0052] The pressure applied to the ink composition filled inside the ink container from the rear end of the ink container by pressurization is preferably greater than atmospheric pressure, specifically, it is preferably greater than atmospheric pressure and 1.5 times or less. More specifically, if atmospheric pressure is 1000 hPa, it is preferably higher than 1000 hPa and 1500 hPa or less, and more preferably higher than 1000 hPa and 1200 hPa or less. This allows for optimal ink consumption while suppressing ink leakage from the tip, and improves handwriting quality and density, such as achieving sufficient three-dimensionality.

[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> A base ink was prepared by heating and stirring the following materials, excluding the thickener, in the following proportions using a magnetic stirrer at room temperature. Then, the following thickener was added to the prepared base ink in the following proportions, and the mixture was thoroughly mixed and stirred using a homogenizer stirrer until a uniform state was achieved to obtain the ink composition of Example 1. • Foaming agent (thermally expandable foaming agent (thermally expandable microcapsules), product name: EXPANCEL031 WUF40, Nippon Ferrite Co., Ltd., average particle size: 10-16 μm, foaming start temperature: 80-95°C, maximum expansion temperature: 120-135°C, solid content: 76% by mass) 5.0 parts by mass • Water-dispersible resin (styrene-butadiene copolymer emulsion, trade name: L1924, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature 5°C, solids content 46% by mass, styrene content: 45 mol%, average particle size: 150 nm) 50.0 parts by mass • Thickening agent (succinoglycan) 0.3 parts by mass • Coloring agent (44% by mass aqueous dispersion of colored resin particles (pink), product name: Lumicol NKW-2317H, manufactured by Nippon Fluorescent Chemicals 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 2-11 and Comparative Examples 1-3> Examples 2-11 and Comparative Examples 1-3 were prepared using the same method as in Example 1, except that the types and amounts of components in the ink composition were changed to those shown in the table. The numerical values ​​for composition in the table represent 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: 36-44 μm, foaming start temperature: 110-130°C, maximum expansion temperature: 160-180°C (2) Product name: EXPANCEL031 WUF40, Nippon Ferrite Co., Ltd., Average particle size: 10-16 μm, Foaming start temperature: 80-95°C, Maximum expansion temperature: 120-135°C, Solids content: 76% by mass (3) 4,4'-Oxybis(benzenesulfonylhydrazide), trade name: Neocerbon #5000, manufactured by Eiwa Chemical Industries Co., Ltd. (4) Product name: Cell Paste 101, manufactured by Eiwa Kasei Kogyo Co., Ltd. (5) Product name: L1924, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature: 5°C, solids content: 46% by mass, styrene content: 45 mol%, average particle size: 150 nm (6) Product name: L1432, manufactured by Asahi Kasei Chemicals Corporation, glass transition temperature: 18°C, solids content: 46% by mass, styrene content: 50 mol%, average particle size: 200 nm (7) Product name: Vinibran 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℃, solid content 50% by mass (10) Product name: Hibiscus 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 Chemicals Co., Ltd., solids 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 a reversible thermochromic composition with color memory properties in microcapsules. The composition consisted of an electron-donating chromogenic organic compound, 1.0 part of 3,6-bis(diphenylamino)fluorane as a component, 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 capric acid as a reaction medium. The average particle size of microcapsule pigment 1 was 1.8 μm, the complete decolorization temperature was 55°C, and the complete color development temperature was -20°C. It changed color from blue to colorless with temperature changes.

[0060] <Rating> The ink compositions of the examples and comparative examples were filled into the ballpoint pen refill 7 of a cap-type pressurized ballpoint pen 1, and writing was performed under pressure. The results were able to write. For subsequent handwriting evaluation, writing was performed using the above-mentioned pressurized ballpoint pen, and the resulting handwriting was evaluated.

[0061] Figures 1 to 3 show a cap-type pressurized ballpoint pen 1. The cap-type pressurized ballpoint pen 1 has a front barrel 2 with a grip member 14 attached to the grip portion, and a rear barrel 3 connected to a barrel body into which a ballpoint pen refill 7 is disposed. Furthermore, the cap-type pressurized ballpoint pen 1 has a translucent cap 4, obtained by injection molding PP resin, which is detachably attached to the front barrel 2 by fitting a fitting projection formed on the inner wall of the cap 4 over a fitting projection 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] At the front end of the ink reservoir 8 of the ballpoint pen refill 7, a ballpoint pen tip 10, which rotatably holds a 1.0 mm diameter ball, is attached via a tip holder 9. Furthermore, a tail plug 11 with an air vent that connects the inside and outside is attached to the rear end of the ink reservoir cylinder 8. The inside of the ink reservoir 8 is filled with a water-based ink composition 12 for writing instruments consisting of the ink mixture described above, and an ink-following body 13. Although not shown in the diagram, a coil spring is installed behind the ball to constantly press the ball against the inner wall of the front end of the tip.

[0063] Furthermore, the rear end of the ink reservoir 8 of 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-following body 13 is in communication with the outside air only through the communication hole 3A provided at the rear end of the rear barrel 3, which connects the inside and outside of the writing instrument.

[0064] The pressurizing mechanism, which is activated by the fitting of cap 4, is 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-following body 13. Specifically, when the rear end of the rear shaft 3 is inserted into the open end of the cap body 5 in the direction of arrow F in the diagram, the inner wall 5A of the cap body 5 and the side wall 3B of the rear shaft 3 first come into contact. At this time, the spaces inside the cap body 5, the rear shaft 3, and the ink reservoir 8 are connected in a sealed state through a communication hole 3A provided at the rear end of the rear shaft 3 that connects the inside and outside. Furthermore, when the cap 4 is advanced in the direction of arrow F in the figure, the sealed space is compressed until the fitting is complete. As a result, pressure can be applied to the water-based ink composition for writing instruments filled in the ballpoint pen refill 7 via the ink-following body 13. The pressure was 1050 hPa.

[0065] <Handwriting Analysis> 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 with a dryer (1200 watts) for 10 minutes. The three-dimensionality, fixation, and elasticity of the resulting writing were evaluated. The evaluation criteria are as follows. The results are shown in the table. Three-dimensional feeling ○: Visual inspection confirmed the raised areas of the handwriting. △: Visual inspection revealed some raised areas in the handwriting, but they were somewhat faint. ×: Visual inspection did not reveal any raised areas in the handwriting. Fixation ○: The writing did not peel off the surface even when touched. △: When the handwriting was touched, part of the handwriting peeled off the surface it was written on. ×: When the handwriting was touched, it peeled off the surface on which it was written. Elasticity ○: The handwriting has elasticity (flexibility). △: The handwriting has some elasticity (flexibility), but is somewhat lacking. ×: The handwriting lacks elasticity (flexibility).

[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 observed visually, no aggregation or separation was observed, indicating good ink stability over time.

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

[0068] [Viscosity ratio] Also, the viscosities of the obtained ink compositions of Example 1 and Example 8 were measured using an E-type rotational viscometer (model: DV-II+Pro, rotor: CPE-42, manufactured by Brookfield) under the conditions of a 20°C environment and a shear rate of 76.8 sec -1 (rotation speed 20 rpm). The viscosity at the above shear rate of 1.92 sec -1 (0.5 rpm) and the viscosity at a shear rate of 76.8 sec -1 (20 rpm) were calculated, and the viscosity ratio (0.5 rpm / 20 rpm) was determined to be 14 in both cases.

[0069] From the above, 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 has sufficient three-dimensionality and can form a writing trace with excellent fixing property. It was found that a writing instrument using this ink composition is excellent as a writing instrument.

Explanation of Signs

[0070] 1 Cap-type pressurized ballpoint pen 2 Front shaft 3 Rear shaft ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

Claims

1. It comprises water, a coloring agent, a foaming agent, a water-dispersible resin having a glass transition temperature of less than 100°C, and a shear viscosity reducing agent. The ratio of the solid content to the total content of the foaming agent and the water-dispersible resin to the content of the shear viscosity reducing agent is 67 to 93.3 by mass. A water-based ink composition for writing instruments characterized by the following.

2. The aqueous ink composition for writing instruments according to claim 1, wherein the foaming agent is a heat-sensitive foaming agent.

3. The aqueous ink composition for writing instruments according to claim 2, wherein the heat-sensitive foaming agent is a heat-expanding foaming agent.

4. The aqueous ink composition for writing instruments according to any one of claims 1 to 3, wherein the content of the foaming agent is 1% by mass to 20% by mass, based on the total mass of the aqueous ink composition for writing instruments.

5. The aqueous ink composition for writing instruments according to any one of claims 1 to 4, wherein the content of the water-dispersible resin is 1% by mass to 50% by mass, based on the total mass of the aqueous ink composition for writing instruments.

6. The aqueous ink composition for writing instruments according to any one of claims 1 to 5, wherein the solid content ratio of the aqueous ink composition for writing instruments is 10% by mass to 50% by mass.

7. The viscosity of the aforementioned aqueous ink composition for writing instruments is 20°C and the shear rate is 1.92 sec. －１ An aqueous ink composition for writing instruments according to any one of claims 1 to 6, wherein the pressure is 500 mPa·s or higher under the specified conditions.

8. A writing instrument comprising a water-based ink composition for writing instruments according to any one of claims 1 to 7.

9. The writing instrument according to claim 8, which is a pressurized writing instrument.

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