Aqueous ink composition for writing instrument and writing instrument using the same

Abstract

To provide an aqueous ink composition for writing instruments having excellent anti-drip performance and capable of giving excellent calligraphy and, a writing instrument using the same.SOLUTION: An aqueous ink composition for writing instruments includes a colorant, a surfactant, and water, wherein at 20°C, the surface tension of the ink composition is γ (mN / m), and when the dynamic advancing contact angle with respect to the pen nib of the ink composition is θa, the ink composition satisfies the following formula (1): θa≤2.0γ-36.0 (1). This ink composition can be suitably combined with writing instruments that have a comb-like ink reservoir.SELECTED DRAWING: Figure 1

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] Some writing implements have a structure in which the pen tip is attached to the end of a barrel via an ink flow regulator (hereinafter sometimes referred to as a pen core) that regulates the ink flow rate, and an ink reservoir that contains an ink composition is provided inside the barrel. When this type of writing implement is changed from a tip-up position or a horizontal position to a tip-down position for writing, the ink composition contained in the ink reservoir flows down the inner wall of the ink reservoir toward the pen tip and moves to the paper surface via the pen core, making writing possible. The ease with which the ink composition moves when it is guided to the pen tip via the pen core has a significant effect on the writing performance of the writing implement, and this is called ink mobility.

[0003] If the ink mobility is not properly adjusted in a writing instrument, the ink composition may not be guided and may remain in the ink reservoir, or may drip from the pen tip, causing so-called dripping. In addition, if the ink composition foams due to shaking or the like, the ink mobility may be impaired, and therefore it is also desirable to suppress foaming.

[0004] The ink mobility within the pen core and the ink reversibility within the ink reservoir depend on the surface tension and viscosity of the ink composition, and are therefore often adjusted by using surfactants, but adding an excessive amount of surfactant can make the ink composition more susceptible to foaming. Suppressing the ink mobility and foaming of the ink composition within the ink reservoir has also been studied, and an ink composition is known in which the ink reversibility was studied while focusing on the foaming property and defoaming rate of the ink composition (Patent Document 1).

[0005] However, when the ink composition drips, it unintentionally stains the surroundings, and therefore it is very important to prevent the ink composition from dripping. For this reason, there has been a demand for an ink composition that can suppress dripping while maintaining sufficient ink mobility. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-015875 A Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a water-based ink composition for a writing instrument that is capable of forming excellent handwriting and is suppressed from dripping, and a writing instrument using the same. [Means for solving the problem]

[0008] According to the present invention, the following inventions are provided. [1] A water-based ink composition for a writing instrument comprising a colorant, a surfactant, and water, wherein when the surface tension of the ink composition at 20° C. is γ (mN / m) and the dynamic advancing contact angle of the ink composition with a pen core is θa, the following formula (1) is satisfied: θa≦2.0γ-36.0 (1) The aqueous ink composition for a writing instrument satisfies the above requirements. [2] The ink composition comprises a compound represented by formula (2): θa≧ 1.8γ-53.0 (2) The ink composition according to [1], further satisfying the above. [3] The ink composition according to [1] or [2], wherein the surface tension γ of the ink composition at 20° C. is 35 mN / m to 65 mN / m. [4] The ink composition according to any one of [1] to [3], wherein the surfactant has a polyoxyalkylene glycol structure. [5] The ink composition according to any one of [1] to [4], wherein the viscosity of the ink composition at 20°C is 10.0 mPa s or less. [6] The ink composition according to any one of [1] to [5], wherein the content of the surfactant based on the total mass of the ink composition is 0.001 to 1.0 mass %. [7] A writing instrument comprising a comb-shaped ink retaining portion and containing the ink composition according to any one of [1] to [6]. [8] The writing instrument according to [7], wherein the ink retaining portion is made of acrylonitrile styrene resin or acrylonitrile butylene styrene resin. Effect of the Invention

[0009] According to the present invention, it is possible to provide a water-based ink composition for a writing instrument that is sufficiently suppressed from dripping and that can produce good handwriting, and a writing instrument using the same. [Brief description of the drawings]

[0010] [Figure 1] 1 is a graph showing the relationship between surface tension and dynamic advancing contact angle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described in detail. In this specification, unless otherwise specified, "parts", "%", "ratio" and the like indicating the composition are based on mass, and the content is the mass% of the constituent component based on the mass of the ink composition.

[0012] <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 an ink composition) comprises a colorant, a surfactant, and water, and has specific physical properties.

[0013] Specifically, when the surface tension of the ink composition at 20° C. is γ (mN / m) and the dynamic advancing contact angle of the ink composition with a pen core is θa, the ink composition according to the present invention satisfies the following formula (1): θa≦2.0γ-36.0 (1) Furthermore, the ink composition according to the present invention satisfies the following requirements: θa≧ 1.8γ-53.0 (2) It is preferable that the following is satisfied.

[0014] The ink composition according to the present invention preferably has a surface tension γ of 35 mN / m to 65 mN / m at 20°C.

[0015] Here, the surface tension γ and the dynamic advancing contact angle θa were measured by the following method. [Surface tension γ] The surface tension is measured in an environment of 20° C. by a surface tension meter, for example, DY-200 (product name) manufactured by Kyowa Interface Science Co., Ltd., using a platinum plate by a vertical plate method. [Dynamic advancing contact angle θa] The dynamic advancing contact angle is measured in an environment of 20° C. using a contact angle measuring instrument, for example, DMo-602 (trade name) manufactured by Kyowa Interface Science Co., Ltd., by an extension method.

[0016] Here, the surface tension γ is generated by the mutual attraction of liquid molecules due to intermolecular forces at the interface between the liquid ink composition and the air in contact with it. In other words, the surface tension γ is a force generated at the gas-liquid interface. The dynamic advancing contact angle θa is the contact angle formed at the front side with respect to the moving direction of a droplet of the liquid ink composition when the droplet moves or spreads on the solid substrate surface. In other words, the dynamic advancing contact angle θa depends on the force generated at the solid-liquid interface. It was unexpected that the dripping resistance of the ink composition could be improved by linking the phenomenon at the gas-liquid interface with the phenomenon at the solid-liquid interface in this way.

[0017] Both the surface tension γ and the dynamic advancing contact angle θa are related to the wettability of the writing implement, but there have been no reports on the correlation between them and the mobility of the ink composition in the writing implement or the resistance to dripping. The present inventors have conducted extensive research into this point and have found that excellent mobility and resistance to dripping of the ink composition can be obtained when the relationship shown in the above formula (1) is satisfied. Furthermore, by satisfying such a relationship, the ink composition is ejected from the pen tip onto the paper surface at an appropriate flow rate during writing, making it easier to obtain good handwriting, and furthermore, the permeability into the paper surface can be properly maintained, making it easier to obtain good handwriting with little bleeding or show-through.

[0018] The mobility and drip-proofing properties of the ink composition according to the present invention are particularly exhibited when used in a writing instrument having a comb-shaped ink reserve member as an ink flow regulator. In a writing instrument having a comb-shaped ink reserve member as an ink flow regulator, when the internal pressure of the ink reservoir increases, the excess ink that is blown out is taken in and held in the comb-shaped structure, thereby preventing ink leakage (dripping). In order for this comb-shaped ink reserve member to function effectively, the ink composition needs to have appropriate wettability.

[0019] Here, if the wettability is improved by simply lowering the surface tension of the ink composition, the resistance of the ink composition due to the surface tension will be insufficient, the ink composition will not be retained in the comb-like structure, and the ink may leak out from the pen tip. Conversely, if the wettability is insufficient, the ink composition will not flow smoothly into the ink retaining member, and in this case too, the ink retaining member may not function effectively, causing the ink composition to leak out.

[0020] In contrast, in the ink composition of the present invention, by satisfying the relationship of formula (1) as described above, appropriate wettability can be achieved, and it is believed that excellent ink composition mobility and resistance to dripping can be obtained.

[0021] The ink composition according to the present invention may be contained in a writing instrument equipped with an ink reservoir or an ink flow regulator. In this case, if the surface tension of the ink composition is high, the ink composition is less likely to enter the gaps of the comb-shaped structures, and the ink that cannot be held tends to leak out and drip. Furthermore, the ink mobility tends to deteriorate, and smearing tends to occur easily. On the other hand, if the surface tension of the ink composition is low, the ink composition is more likely to excessively enter the gaps of the comb-shaped structures, and the ink that cannot be held tends to leak out and drip. For this reason, the surface tension γ of the ink composition according to the present invention is preferably 35 mN / m to 65 mN / m, preferably 35 to 60 mN / m, more preferably 35 to 55 mN / m, and particularly preferably 40 to 55 mN / m.

[0022] Furthermore, the ink composition according to the present invention preferably has an ink viscosity of 10 mPa s or less, measured using a B-type rotational viscometer at a rotation speed of 60 rpm and 20° C. If the viscosity of the ink composition is within the above numerical range, the ink discharge property from the pen tip and the ink transfer property can be improved, and good handwriting can be obtained.

[0023] As described above, when the ink composition of the present invention is used in a writing instrument in which a comb-shaped ink retaining member is arranged as an ink flow regulator, the function of the comb-shaped ink retaining member can be fully utilized, and therefore the ink composition can be suitably used in the above writing instrument, and in this case, in order to obtain excellent resistance to dripping and good ink dischargeability from the pen tip, the ink viscosity is preferably 10.0 mPa·s or less, more preferably 5.0 mPa·s or less, and particularly preferably 2.0 mPa·s or less. In the present invention, the viscosity can be measured using a B-type rotational viscometer (model: BLII, rotor: BL adapter, manufactured by Toki Sangyo Co., Ltd.).

[0024] The pH of the ink composition of the present invention is preferably 6 to 11, and more preferably 7 to 10. If the pH of the ink composition is within the above range, each component in the ink composition can be present stably, and furthermore, corrosion of metal parts of a writing instrument, such as a pen tip, with which the ink composition comes into contact, can be prevented. In the present invention, the pH value can be measured at 20°C, for example, using a HM-30R pH meter (manufactured by DKK-TOA Corporation).

[0025] The components of the ink composition of the present invention will be described in detail below. <Surfactant> The surfactant used in the present invention is not particularly limited as long as it can adjust the surface tension of the ink composition and provide good wettability to the writing implement member, and various surfactants can be used. For example, ionic surfactants such as anionic surfactants, cationic surfactants, and amphoteric surfactants, and nonionic surfactants can be used. In addition, surfactants having an acetylene bond in the structure, silicone surfactants, fluorine surfactants, etc. may also be used.

[0026] In the present invention, in consideration of compatibility with other components in the ink composition and in consideration of obtaining a sufficient effect of the surfactant, it is preferable to use a nonionic surfactant. In addition, as described later, when the ink composition is contained in a glass ink container, it is necessary to consider the prevention of the generation of precipitates due to reactions with metal ions, and in view of the prevention of the generation of precipitates, it is preferable to use a nonionic surfactant in the present invention.

[0027] Examples of the nonionic surfactant include ether type, ether ester type, ester type, and nitrogen-containing type, and examples of the compounds include the following: (1) Ether-type nonionic surfactants Polyoxyethylene polyoxypropylene alkyl ethers, Polyoxyethylene polyoxypropylene aryl ether, Polyoxyethylene polyoxypropylene alkyl aryl ethers, Polyoxyethylene alkyl ether, Polyoxyethylene aryl ether, Polyoxyethylene alkyl aryl ethers, and polyoxyalkylene alkyl ethers such as polyoxyethylene tristyryl phenyl ether; Polyoxyalkylene aryl ethers, polyoxyalkylene alkyl aryl ethers, and polyoxyalkylene glycols such as polyoxyethylene polyoxypropylene glycol; Aliphatic alcohol polyglycol ether, etc. (2) Ether ester type nonionic surfactants Polyoxyalkylene sorbitan fatty acid esters such as polyoxyethylene sorbitan monolaurate; Polyoxyethylene tristyryl phenyl phosphate diester, Polyoxyethylene polyoxypropylene tristyryl phenyl phosphate diester, Polyoxyethylene fatty acid esters, Fatty acid esters of polyoxyethylene polyoxypropylene block polymers, etc. (3) Ester-type nonionic surfactants polyoxyalkylene vegetable oils such as polyoxyethylene castor oil; Polyoxyalkylene hydrogenated vegetable oils such as polyoxyethylene hydrogenated castor oil, Polyoxyethylene polyoxypropylene vegetable oils such as polyoxyethylene polyoxypropylene castor oil, Sorbitan Monostearate, sorbitan fatty acid esters such as sorbitan tristearate; Glycerol fatty acid esters, etc. (4) Nitrogen-containing nonionic surfactants Polyoxyethylene fatty acid amides, Polyoxyethylene alkylamines and the like.

[0028] Furthermore, in the present invention, among nonionic surfactants, it is preferable to use an ether-type nonionic surfactant, and among them, it is preferable to use a polyoxyalkylene glycol.

[0029] Among the polyoxyalkylene glycols, it is preferable to use polyoxyethylene polyoxypropylene glycol. Among the polyoxyethylene polyoxypropylene glycols, it is more preferable to use a polyoxyethylene polyoxypropylene block polymer as represented by the formula (a). HO(CH2CH2O) x (CH(CH3)CH2O) y (CH2CH2O) z H(a) In the formula, x, y, and z are positive numbers.

[0030] Among these, in the present invention, in consideration of improving ink mobility and drip resistance, and further obtaining good handwriting with little bleeding or strike-through, the weight average molecular weight of the polyoxyethylene polyoxypropylene block polymer represented by the above formula (a) is preferably 1000 or more, and more preferably 1200 or more. Moreover, the weight average molecular weight of the polyoxyethylene polyoxypropylene block polymer represented by the formula (a) is preferably 20000 or less, more preferably 15000 or less, and even more preferably 10000 or less. In the formula (a), the number of oxyethylene groups (x+z) is preferably 20-300, and the number of oxypropylene groups (y) is preferably 30-65. Furthermore, in the polyoxyethylene polyoxypropylene block polymer represented by the formula (a), the content of oxyethylene groups based on the total number of oxyalkylene groups is more preferably 5% or more and 60% or less.

[0031] Specific examples of polyoxyalkylene glycols that can be used in the present invention include the Pronon series (manufactured by NOF Corporation), the Unilube series (manufactured by NOF Corporation), and the Newpol series (manufactured by Sanyo Chemical Industries, Ltd.).

[0032] The content of the surfactant is preferably 0.001 to 1 mass %, more preferably 0.005 to 0.5 mass %, further preferably 0.005 to 0.3 mass %, and particularly preferably 0.01 to 0.1 mass %, based on the total mass of the ink composition. If the content of the surfactant is within the above range, the effect of the surfactant is fully exerted, and excellent ink mobility and dripping resistance are maintained in a well-balanced manner.

[0033] <Coloring agent> Colorants that can be used in the present invention include any dye or pigment, and are not particularly limited.

[0034] The dye is not particularly limited, and examples thereof include acid dyes, basic dyes, direct dyes, disperse dyes, oil-soluble dyes, reactive dyes, metal-containing dyes, food dyes, and various salt-forming dyes.

[0035] Specific examples of 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, CI Acid Violet 49, CI Acid Black 1, CI Acid Black 2 etc. Examples include:

[0036] Specific examples of basic dyes include: CI Basic Orange 2, CI Basic Orange 14, CI Basic Green 4, CI Basic Blue 9, CI Basic Blue 26, CI Basic Violet 1, CI Basic Violet 3, CI Basic Violet 10 etc. Examples include:

[0037] Specifically, 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 etc. Examples include:

[0038] Specific examples of disperse dyes include: CI Disperse Yellow 82, CI Disperse Yellow 3, CI Disperse Yellow 54, CI Disperse Red 191, CI Disperse Red 60, CI Disperse Violet 57, etc. Examples include:

[0039] Specifically, food colourings include: CI Food Yellow 3, CI Food Black 2 etc. Examples include:

[0040] In addition, the pigment that can be used in the present invention is not particularly limited. For example, inorganic pigments, organic pigments, processed pigments, etc. can be mentioned. Specifically, carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, aluminum pigments, pearl pigments, fluorescent pigments, phosphorescent pigments, complementary color pigments, etc. can be mentioned. In addition, colored resin particles such as resin particles colored with dyes, and microcapsule pigments in which a colored body formed by dispersing a coloring material in a medium is encapsulated or solid-dissolved in a shell made of a resin wall-forming material by a known microencapsulation method can also be used.

[0041] In the present invention, it is preferable to use dyes, and among them, it is preferable to use acid dyes and basic dyes, and it is particularly preferable to use acid dyes.

[0042] As the colorant, the above pigments and dyes may be used alone or in combination of two or more kinds.

[0043] The content of the colorant in the ink composition of the present invention is preferably 0.1 to 10% by mass based on the total mass of the ink composition. When the content of the colorant is within the above range, excellent ink mobility and dripping resistance can be obtained.

[0044] <Water> The water is not particularly limited, and for example, tap water, ion-exchanged water, ultrafiltered water, distilled water, or the like can be used.

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

[0046] The ink composition according to the present invention preferably contains a chelating agent for sequestering metals present in the ink composition. The ink composition according to the present invention can be suitably used in a writing instrument having an ink flow regulator such as a comb-shaped ink retaining member, for example, a fountain pen. It is considered that such a writing instrument is used by a user by repeatedly refilling the ink composition. In such a case, it is assumed that the ink composition is stored in a glass ink container such as a glass bottle and used. Glass bottles are easy to mold, inexpensive, and readily available, and furthermore, the desired strength can be easily obtained from them. On the other hand, when an ink composition is stored in a glass bottle for a long period of time, particularly when inexpensive and versatile soda-lime glass is used, there is a high possibility that alkaline components in the glass will elute into the ink composition, and these eluted alkaline components may react with components of the ink composition to form a precipitate. For this reason, the use of a chelating agent in the present invention is effective because, when the ink is stored in a glass ink container, it supplements the eluted alkaline components and prevents the alkaline components from reacting with the components in the ink composition to form water-insoluble precipitates, thereby preventing the ink flow path from being blocked by the precipitates, causing the writing to fade or becoming impossible to write with.

[0047] Chelating agents include: Ethylenediaminetetraacetic acid (EDTA), Hydroxyethylenediaminetriacetic acid (HEDTA), Glycol ether diamine tetraacetic acid (GEDTA), Nitrilotriacetic acid (NTA), Hydroxyethyliminodiacetic acid (HIDA), Dihydroxyethylglycine (DHEG), Diethylenetriaminepentaacetic acid (DTPA), Triethylenetetramine hexaacetic acid (TTHA) and their alkali metal salts, ammonium salts or amine salts.

[0048] Considering the fact that the alkaline components can be sufficiently supplemented, that there is little tendency for the chelating agent to have a significant effect on the physical properties of the ink composition before and after the incorporation of the chelating agent, and also the compatibility with the surfactant used in the present invention, it is preferable to use aminocarboxylic acids such as EDTA, HEDTA, and GEDTA and salts thereof among the above chelating agents, and of these, it is preferable to use ethylenediaminetetraacetic acid (EDTA) and salts thereof.

[0049] The content of the chelating agent in the ink composition of the present invention is preferably 0.01 to 1 mass% based on the total mass of the ink composition. If it is 1 mass% or less, it is unlikely to adversely affect the performance and physical properties of the ink composition, such as discoloration of the ink. Also, if it is 0.01 mass% or more, it is possible to supplement the alkali components eluted from the glass and suppress the occurrence of precipitation.

[0050] The ink composition of the present invention preferably contains an amine. Examples of the amine include alkylamines, alkanolamines, and heterocyclic amines. Among them, it is more preferable to use alkanolamines.

[0051] Alkanolamines have conventionally been used as pH adjusters, but in the present invention, they not only properly adjust the pH of the ink composition, but also tend to improve ink mobility and drip resistance.

[0052] Alkanolamines are compounds having a hydroxy group and an amino group in an alkane skeleton. In the present invention, it is preferable to use alkanolamines represented by the following formula (b). R 2 R 3 NR 1 -OH (b) In the formula, R 1 represents an ethylene group, a trimethylene group, or a propylene group; R 2 and R 3 each independently represents a hydrogen atom, a methyl group, an ethyl group, or -R 1 Indicates the -OH group.

[0053] Specific examples of such alkanolamines include methylethanolamine, monoisopropanolamine, diethylethanolamine, monoethanolamine, propanolamine, methyldiethanolamine, diethanolamine, and triethanolamine.

[0054] In the present invention, taking into consideration the stability over time of the ink composition, it is preferable to use, among the above-mentioned alkanolamines, triethanolamine, which is a weak base, because even when movement occurs in the ink composition, triethanolamine is likely to exhibit excellent wettability to the ink reservoir and ink flow regulator, and excellent ink mobility and excellent resistance to dripping can be stably obtained over time.

[0055] In addition, triethanolamine has excellent moisture absorption properties and therefore tends to improve the dry-up resistance of the ink composition, and therefore the use of triethanolamine in the present invention is effective because it tends to improve the ink mobility and dripping resistance as well as the writing performance when the ink composition dries up.

[0056] The content of alkanolamine in the ink composition of the present invention is preferably 0.1 to 10% by mass based on the total mass of the ink composition. If the content of alkanolamine is within the above range, it is possible to adjust the ink composition to an appropriate pH value, and further excellent dripping resistance and ink mobility can be obtained. Furthermore, in consideration of improvement of dry-up resistance and color development of handwriting, it is more preferably 0.1 to 5% by mass, and even more preferably 0.5 to 3% by mass.

[0057] In addition, the ink composition of the present invention may contain additives such as a water-soluble organic solvent, a polysaccharide, a water-soluble resin, a pH adjuster, a rust inhibitor, a preservative, a moisturizer, a penetrant, and a lubricant for the purpose of further improving the ink properties and functions.

[0058] Examples of water-soluble organic solvents include: (i) glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, or glycerin; (ii) Alcohols such as methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate and other higher alcohols; (iii) Glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 3-methoxybutanol, and 3-methoxy-3-methylbutanol.

[0059] Of these, it is preferable to use diethylene glycol, ethylene glycol, glycerin, etc., which have excellent stability in the ink composition.

[0060] The content of the water-soluble organic solvent in the ink composition is preferably 0.1 to 10 mass % based on the total mass of the ink composition.

[0061] Examples of polysaccharides include xanthan gum, welan gum, succinoglycan (average molecular weight approximately 1 to 8 million), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, guar gum, locust bean gum and its derivatives, alginic acid alkyl esters, polymers with a molecular weight of 100,000 to 150,000 whose main component is an alkyl ester of methacrylic acid, glycomannan, agar, pullulan, carrageenan, etc.

[0062] Examples of the water-soluble resin include cellulose derivatives, polyvinyl alcohol, polyvinylpyrrolidone, and polyvinyl butyral. Examples of the cellulose derivatives include hydroxyethyl cellulose, carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, and hydroxypropyl methyl cellulose.

[0063] Examples of pH adjusters include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide, and sodium acetate, basic organic compounds, lactic acid, and citric acid. These pH adjusters may be used alone or in combination of two or more.

[0064] The rust inhibitors include benzotriazole and its derivatives, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, sodium thiosulfate, saponin, and dialkylthiourea.

[0065] Preservatives include phenol, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, 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, and propynyl iodide butylcarbamate.

[0066] Examples of the moisturizing agent include polyhydric alcohol solvents, urea, sorbitol, and N,N,N-trialkylamino acids such as trimethylglycine, triethylglycine, and tripropylglycine.

[0067] <Method of producing ink composition> The ink composition according to the present invention can be produced by any conventionally known method. Specifically, the ink composition can be produced by blending the required amounts of the above-mentioned components and mixing them with various stirrers such as a propeller stirrer, a homodisper, or a homomixer, or various dispersing machines such as a bead mill.

[0068] <Writing implements> The ink composition of the present invention can be used in various writing instruments, such as marking pens and ballpoint pens with a fiber tip, felt tip, plastic tip, or ballpoint pen tip, and fountain pens with a metal writing tip.

[0069] The ink composition of the present invention can also be used in devices that are directly filled with the ink composition, or devices that are provided with an ink reservoir that can be filled with the ink composition.

[0070] The ink composition of the present invention can be suitably used in a writing instrument equipped with an ink reservoir (ink cartridge) that can be freely attached and detached to the main body of the writing instrument, or an ink reservoir (ink inhaler) that has the function of directly sucking ink into the ink reservoir from an ink container such as an ink bottle.

[0071] Since the ink reservoir as described above may be provided inside the barrel of a writing instrument, the inner diameter of the ink reservoir is likely to be restricted. For this reason, the ink composition generally does not flow easily inside the ink reservoir, and special consideration must be given to the ink mobility inside the ink reservoir. Since the ink composition of the present invention has excellent ink mobility inside the ink reservoir, it can be suitably used in a writing instrument equipped with an ink reservoir.

[0072] In particular, when the material of the ink reservoir is made of a resin material, the ink reservoir tends to have poor wettability with the ink composition, and it is necessary to take into consideration the ink mobility within the ink reservoir in particular. The ink composition of the present invention can suppress the decrease in wettability when the ink moves with respect to the resin material, and therefore can be suitably used in a writing instrument having a resin ink reservoir.

[0073] In addition, it is desirable for the ink reservoir to be made of a semi-transparent or transparent material that allows the remaining amount of ink to be seen. Examples of such materials include thermoplastic resins such as polyethylene, polypropylene, polymethylpentene, polyethylene terephthalate, polycyclohexane terephthalate, polycarbonate, and nylon. In addition, since the ink reservoir stores the ink composition for a long period of time, it is preferable to use a crystalline resin that has excellent chemical resistance, and therefore it is more preferable to use a crystalline olefin resin such as polyethylene, polypropylene, or polymethylpentene.

[0074] The ink composition of the present invention can provide good ink reversibility even for ink reservoirs using the resin materials described above. In particular, when the surface tension of the ink composition is set to 35 mN / m to 65 mN / m, even when the ink moves, it is likely to wet the resin, and the ink reversibility in the ink reservoir is likely to be improved. Furthermore, among the above resins, polymethylpentene has particularly excellent transparency while also having excellent chemical resistance, and also has moderate flexibility, so it is suitable for use in ink reservoirs (ink cartridges) that can be freely attached and detached to the writing instrument body as described above, and ink reservoirs (ink inhalers) that have the function of directly sucking ink into the ink reservoir from an ink container such as an ink bottle.

[0075] However, polymethylpentene has a low surface tension, and the ink composition tends to have insufficient wettability to polymethylpentene. For this reason, in a writing instrument using an ink reservoir containing polymethylpentene, it is necessary to particularly consider the ink reversibility. However, the ink composition of the present invention exhibits excellent wettability even to an ink reservoir containing polymethylpentene when the ink moves, and therefore excellent ink reversibility can be obtained. Therefore, the ink composition of the present invention can be suitably used for an ink reservoir containing polymethylpentene. Furthermore, when the surface tension of the ink composition is set to 35 mN / m to 60 mN / m, it is effective and preferable because it is easy to obtain good wettability to polymethylpentene and easy to further improve the ink reversibility.

[0076] In addition, in a writing instrument equipped with an ink reservoir (ink aspirator) that has a function of directly aspirating ink from an ink container such as an ink bottle into the ink reservoir, the ink mobility in the ink reservoir may be insufficient with a conventional ink composition as described above. However, since the ink composition of the present invention has excellent ink reversibility, it is easy to fill the ink aspirator with ink. Therefore, from the above point of view, it can be said that the ink composition of the present invention can be suitably used in a writing instrument equipped with an ink aspirator as an ink reservoir.

[0077] In addition, some of the ink inhalers have a movable body that can move back and forth within the ink inhaler as a weight to make it easier to move the ink in the ink inhaler toward the pen tip, or as a stopper to retain the ink sucked up from the ink bottle within the ink inhaler when inhaling ink.

[0078] In such an ink suction device having a moving body disposed therein, the ink mobility within the ink suction device may be deteriorated depending on the material of the moving body.

[0079] In particular, when the moving body is made of a resin material, the ink composition has poor wettability to the moving body, and ink mobility tends to be suppressed. However, the ink composition of the present invention exhibits excellent wettability to the moving body made of the resin material, and can suppress the deterioration of ink reversibility. Therefore, the ink composition of the present invention can be suitably used in a writing instrument equipped with an ink inhaler in which a moving body, particularly a moving body made of a resin material, is arranged.

[0080] Furthermore, the writing instrument in which the ink composition of the present invention can be used may be a cap type having a cap covering the writing tip, or a retractable type in which the writing tip can be housed in a barrel such as a knock type, a rotating type, or a sliding type. In particular, in a retractable writing instrument, measures against ink leakage from the pen tip are considered more important, so the ink composition of the present invention, which has excellent leakage resistance, can be suitably used in a retractable writing instrument.

[0081] The ink supply mechanism of a writing instrument in which the ink composition of the present invention can be used is not particularly limited, and examples include (mechanism 1) a mechanism having a comb-shaped ink retaining member as an ink flow regulator and supplying the ink composition to the pen tip, (mechanism 2) a mechanism having an ink guide core made of a fiber bundle or the like as an ink flow regulator and supplying the ink composition to the pen tip through this, (mechanism 3) a mechanism having an ink flow regulator with a valve mechanism and supplying the ink composition to the writing tip, and (mechanism 4) a mechanism that supplies the ink composition directly to the pen tip without an ink flow regulator.

[0082] Among them, the ink composition of the present invention can be particularly suitably used in (Mechanism 1) a mechanism that has a comb-shaped ink retaining member as an ink flow rate regulator and supplies the ink composition to the pen tip. This is because, as described above, the ink composition of the present invention has excellent ink composition mobility and can provide particularly excellent dripping resistance.

[0083] In addition, when a resin material is used for the ink flow regulator, the wettability of the ink composition may be affected by the type of the resin. The ink composition of the present invention can be suitably used for commonly used resin materials, but is particularly effective when used in combination with an ink flow regulator using an acrylonitrile-styrene resin or an acrylonitrile-butylene-styrene resin. For this reason, the ink composition of the present invention is preferably used for a writing instrument having an ink reservoir made of an acrylonitrile-styrene resin or an acrylonitrile-butylene-styrene resin.

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. It is not something that is done.

[0085] <Examples E1 to E17 and Comparative Examples R1 to R5> The following ingredients were mixed to prepare an ink composition of Example E1. CI Acid Yellow 23 0.10% by mass CI Acid Red 289 0.10% by weight Diethylene glycol 2.00% by mass Triethanolamine 1.00% by mass 1,2-Benzisothiazolin-3-one 0.05% by mass Pronon #204 (surfactant a) 0.05% by mass EDTA 0.10% by mass PVP (not mixed) Ion exchange water Residual Total 100.00% by mass

[0086] Furthermore, the type of surfactant and the amount of polyvinylpyrrolidone (PVP) added were changed as shown in Table 1 to prepare ink compositions of each example. The physical properties and dripping resistance of the resulting ink compositions were evaluated as follows. The results are also shown in Table 1. Furthermore, the relationship between surface tension and dynamic advancing contact angle is shown in Figure 1.

[0087] <Viscosity> The viscosity of the resulting ink composition was measured using a B-type rotational viscometer (model: BLII, rotor: BL adapter, manufactured by Toki Sangyo Co., Ltd., sample amount: 20 ml) at 20° C. and a rotation speed of 60 rpm.

[0088] <density> The density of the resulting ink composition was measured using a density meter (model: DMA4501, manufactured by Anton Paar) at 20°C.

[0089] <Surface tension> The surface tension γ of the resulting ink composition was measured using a surface tension meter (model: DY-200, manufactured by Kyowa Interface Science Co., Ltd., platinum plate, vertical plate method). The measurement was performed under conditions of 20°C.

[0090] <Dynamic advancing contact angle> The dynamic advancing contact angle θa of the obtained ink composition against a resin plate (an acrylonitrile styrene resin plate (AS) or an acrylonitrile butylene styrene resin plate (ABS). Hereinafter, this may be referred to as a pen core plate depending on the case) of the same material and surface condition as the pen core that supplies the ink composition to the pen tip was measured using a contact angle measuring device (model: DMo-602, manufactured by Kyowa Interface Science Co., Ltd., the above pen core plate, expansion method, discharge level 150, liquid speed 6.00 μL / s, analysis method: perfect circle fitting method, no curvature correction). The measurement was performed under conditions of 20° C. The measured value was the average value from 100 to 4700 ms.

[0091] <Drip-resistant performance> The ink composition obtained was poured into a polyethylene ink cartridge, and attached to a retractable fountain pen (Pilot Corporation fountain pen, FCN-1MR-M) equipped with a comb-shaped ink reserve portion (pen core) made of the same material and with the same surface condition as the pen core plate used in the measurement of the dynamic forward contact angle, to obtain a writing instrument containing the ink composition of Example E1. The writing instrument was knocked to extend the pen tip, and the pen tip was placed facing downward in a vacuum desiccator, and the pressure was reduced from atmospheric pressure to 70 mmHg for 5 minutes and then reduced from atmospheric pressure to 80 mmHg for 10 minutes. The presence or absence of ink dripping was confirmed, and dripping resistance was evaluated on a 6-level scale from A to F according to the following evaluation criteria (n=5). A: No ink dripping was observed within 10 minutes of the start of decompression. B: No ink dripping was observed within 5 minutes of the start of decompression. C: One ink drop was observed within 5 minutes of the start of decompression. D: Two ink drops were observed within 5 minutes of the start of decompression. E: Three ink drops were observed within 5 minutes of the start of decompression. F: Five ink drops were observed within 5 minutes of the start of decompression.

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] Surfactant a: A surfactant having a polyoxyalkylene glycol structure with an average number of moles of ethylene oxide added of 30 and an average number of moles of propylene oxide added of 35 (product name: Pronon #204, manufactured by NOF Corporation). The amounts added in the table are calculated as the active ingredient. Surfactant b: a surfactant having a polyoxyalkylene glycol structure with an average number of moles of ethylene oxide added of 150 and an average number of moles of propylene oxide added of 35 (product name: Pronon #208, manufactured by NOF Corporation). The amounts added in the table are calculated as the active ingredient. Surfactant c: A surfactant having a polyoxyalkylene glycol structure with an average number of moles of ethylene oxide added of 390 and an average number of moles of propylene oxide added of 70 (product name: Newpol PE-128, manufactured by Sanyo Chemical Industries, Ltd.) The amounts added in the table are calculated as the active ingredient. Surfactant d: A surfactant having a polyoxyalkylene glycol structure with an average number of moles of ethylene oxide added of 200 and an average number of moles of propylene oxide added of 70 (product name: Unilube 70DP-950B, manufactured by NOF Corporation). The amounts added in the table are calculated as the active ingredient.

[0096] The results show that ink compositions having a θa of 2.0γ-36.0 or less exhibit excellent dripping resistance.

Claims

1. A water-based ink composition for a writing instrument comprising a colorant, a surfactant, and water, wherein when the surface tension of the ink composition at 20° C. is γ (mN / m) and the dynamic advancing contact angle of the ink composition with a pen core is θa, the following formula (1): θa≦2.0γ-36.0 (1) The aqueous ink composition for a writing instrument satisfies the above requirements.

2. The ink composition comprises a compound represented by formula (2): θa≧1.8γ−53.0 (2) The ink composition according to claim 1 , further comprising:

3. 3. The ink composition according to claim 1, wherein the surface tension γ of the ink composition at 20° C. is 35 mN / m to 65 mN / m.

4. The ink composition according to claim 1 or 2, wherein the surfactant has a polyoxyalkylene glycol structure.

5. 3. The ink composition according to claim 1, wherein the viscosity of the ink composition at 20°C is 10.0 mPa·s or less.

6. 3. The ink composition according to claim 1, wherein the content of the surfactant is 0.001 to 1.0 mass % based on the total mass of the ink composition.

7. A writing implement comprising a comb-shaped ink retaining portion and containing the ink composition according to claim 1 or 2.

8. 8. The writing implement according to claim 7, wherein the ink retaining portion is made of acrylonitrile styrene resin or acrylonitrile butylene styrene resin.

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