JP2022171313A - Water-based ink composition for ballpoint refills and ballpoint refill containing the same - Google Patents

Abstract

To provide a water-based ink composition for ballpoint refills that prevents bubbles from occurring and remaining over the long term, and also retains excellent initial writing performance without changing over the long term.SOLUTION: A water-based ink composition for ballpoint refills is contained in a ballpoint refill, the ballpoint refill having a ballpoint chip and an ink storage tube, where the ink storage tube stores ink, and the end face of the ink is filled with an ink backflow inhibitor. The ink composition comprises a colorant, a shear-thinning tackifier, a substance represented by formula (1) and/or a salt thereof, and water, where X and Y each denote a functional group selected from -H, -R, -OH, -OR, -NH2, -NHR and -NR2, and R is an alkyl group, excluding the case where both of X and Y are hydrogen.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an aqueous ink composition for ballpoint pen refills and a ballpoint pen refill containing the same.

Conventionally, refillable ballpoint pens containing shear-thinning ink have been widely used.
Shear-thinning ink maintains its viscosity in a state where no shearing force is applied to the ink when it is stationary, and when writing, when a strong shearing force is applied from a ball rotating at high speed, the viscosity quickly decreases and the ink is expelled from the pen tip. Since it exhibits a viscosity behavior in which the viscosity recovers quickly afterward, a ballpoint pen using such ink is excellent in operability, and it is possible to suppress ink leakage during storage and sedimentation and aggregation of insoluble components in the ink while writing. exhibits good ink ejection properties, and can form clear handwritings with less bleeding.

However, refills containing shear-thinning ink are susceptible to air bubbles in the ink, and the air bubbles may reduce writing performance.
For example, with shear-thinning ink, dissolved air in the ink becomes bubbles due to low pressure near the ball rotating at high speed, and air mixed in from the pen tip when impacted by knocking or dropping, etc. When air bubbles form in the ink, the air bubbles accumulate on the pen tip side, and the ink does not follow the ink during writing, resulting in blurred handwriting or inability to write. Further, in ballpoint pen refills, it is inevitable that air bubbles are mixed in the ink when the ink storage tube is filled with the shear-thinning ink, and the remaining air bubbles may cause the above-described writing problems. Furthermore, when the ink backflow preventer (liquid plug) that follows the consumption of ink is filled in contact with the trailing end surface of the ink, the bubbles accumulate between the ink and the ink backflow preventer and expand over time. As a result, there is a risk of causing backflow.

Therefore, methods for chemically removing the gas in the ink have been investigated, and for example, a technique for adding α-tocopherol or the like has been disclosed (see, for example, Patent Document 1).

Patent Document 1 discloses water-based inks in which α-tocopherol is applied as a gas scavenger. Since α-tocopherol is water-insoluble in this ink, a solubilizer is used in combination, and air bubbles in the water-based ink can be absorbed.
However, the ink of this prior art does not have sufficient stability in dissolution of α-tocopherol, and α-tocopherol precipitates over time, making it difficult to maintain the bubble suppressing effect. In addition, in order to dissolve α-tocopherol in water-based ink, it is necessary to add a large amount of a surfactant, which is a solubilizer, and such ink has the disadvantage that the degree of freedom in blending adjustment is likely to be limited. was

JP-A-10-330672

The present invention provides a water-based ink composition for ball-point pen refills, which can suppress the formation and retention of air bubbles over a long period of time, and can provide good writing performance equivalent to that at the initial stage over a long period of time.

式中、ＸとＹは－Ｈ、－Ｒ、－ＯＨ、－ＯＲ、－ＮＨ_２、－ＮＨＲおよび－ＮＲ_２から選ばれる官能基であり、Ｒはアルキル基である。ただし、Ｘ、Ｙ双方が水素である場合を除く。
２．前記ＸとＹは、－Ｈ、－ＯＨおよび－ＮＨ_２から選ばれる官能基である（ただし、Ｘ、Ｙ双方が水素である場合を除く）、第１項に記載の水性インキ組成物。
３．２０℃において、せん断速度３．８４ｓｅｃ^－１で測定される粘度が、２０～２０００ｍＰａ・ｓであり、せん断速度３８４ｓｅｃ^－１で測定される粘度が、１～１００ｍＰａ・ｓであり、剪断減粘指数ｎが０．１５以上、０．７未満である、第１項または第２項に記載の水性インキ組成物。
４．式（１）に示される物質及び／又はその塩の含有量が水性インキ組成物全質量に対して０．０５～５質量％である、第１項～第３項に記載の水性インキ組成物。
５．前記着色材が顔料である、第１項～第４項のいずれか１項に記載の水性インキ組成物。
６．ボールペンチップと、インキ収容管とを備え、前記インキ収容管に第１項～第５項のいずれか１項に記載の水性インキ組成物が収容され、前記水性インキ組成物の端面にインキ逆流防止体が充填されてなるボールペンレフィル。
７．第６項に記載のボールペンレフィルが内蔵されてなるボールペン。」とする。 In order to solve the above problems, the present invention
"1. A ball-point pen refill comprising a ball-point pen tip and an ink storage tube, ink is stored in the ink storage tube, and an ink backflow prevention member is filled in the end surface of the ink. A water-based ink composition for ballpoint pen refills, comprising a material, a shear thinning agent, a substance represented by formula (1) and/or a salt thereof, and water.

wherein X and Y are functional groups selected from -H, -R, -OH, -OR, -NH ₂ , -NHR and -NR ₂ , and R is an alkyl group. However, the case where both X and Y are hydrogen is excluded.
2. 2. The water-based ink composition according to item 1, wherein X and Y are functional groups selected from -H, -OH and _-NH2 (except when both X and Y are hydrogen).
3. At 20 ° C., the viscosity measured at a shear rate of 3.84 sec ⁻¹ is 20 to 2000 mPa s, the viscosity measured at a shear rate of 384 sec ⁻¹ is 1 to 100 mPa s, and the shear reduction 3. The water-based ink composition according to item 1 or 2, wherein the viscosity index n is 0.15 or more and less than 0.7.
4. The aqueous ink composition according to any one of items 1 to 3, wherein the content of the substance represented by formula (1) and/or a salt thereof is 0.05 to 5% by mass based on the total mass of the aqueous ink composition. .
5. 5. The water-based ink composition according to any one of items 1 to 4, wherein the coloring material is a pigment.
6. A ball-point pen tip and an ink storage tube, wherein the aqueous ink composition according to any one of items 1 to 5 is accommodated in the ink storage tube, and an ink backflow prevention is provided on an end surface of the aqueous ink composition. A ballpoint pen refill filled with a body.
7. A ballpoint pen containing the ballpoint pen refill according to item 6. ”.

According to the present invention, there is provided a water-based ink composition for ballpoint pen refills and a ballpoint pen refill containing the same, which can suppress the formation and residue of air bubbles over a long period of time, and can obtain good writing performance equivalent to that at the initial stage over a long period of time. is provided.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. In the present specification, "parts", "%", "ratios" and the like indicating the composition are based on mass unless otherwise specified.

The water-based ink composition according to the present invention (hereinafter sometimes referred to as "ink composition" or "composition") comprises a coloring agent, a shear-thinning agent, and the formula (1). It contains a substance and/or its salt and water. Each component constituting the ink composition according to the present invention will be described below.

(colorant)
As the coloring material, all dyes and pigments that can be dissolved or dispersed in an aqueous medium can be used, and specific examples are given below.
Acid dyes, basic dyes, direct dyes, and the like can be used as the dyes.
Acid dyes include New Coccine (CI 16255), Tartrazine (CI 19140), Acid Blue Black 10B (CI 20470), Guinea Green (CI 42085), Brilliant Blue FCF. (CI 42090), Acid Violet 6B (CI 42640), Soluble Blue (CI 42755), Naphthalene Green (CI 44025), Eosin (CI 45380), Phloxine (CI 45410), erythrosine (CI 45430), nigrosine (CI 50420), acid flavin (CI 56205) and the like.
Basic dyes include chrysoidine (CI 11270), methyl violet FN (CI 42535), crystal violet (CI 42555), malachite green (CI 42000), Victoria Blue FB ( CI 44045), rhodamine B (CI 45170), acridine orange NS (CI 46005), methylene blue B (CI 52015) and the like are used.
Direct dyes include Congo Red (CI 22120), Direct Sky Blue 5B (CI 24400), Violet BB (CI 27905), Direct Deep Black EX (CI 30235), Kaya Las Black G Conch (CI 35225), Direct Fast Black G (CI 35255), Phthalocyanine Blue (CI 74180) and the like are used.

Examples of the pigment include inorganic pigments such as carbon black and ultramarine blue, organic pigments such as copper phthalocyanine blue and benzidine yellow, and water dispersions finely and stably dispersed in an aqueous medium in advance using a surfactant or resin. Pigment products and the like are used, for example, C.I. I. Pigment Blue 15:3B [product name: Sandye Super Blue GLL, pigment content 24%, manufactured by Sanyo Color Co., Ltd.], C.I. I. Pigment Red 146 [product name: Sandye Super Pink FBL, pigment content 21.5%, manufactured by Sanyo Color Co., Ltd.], C.I. I. Pigment Yellow 81 [product name: TC Yellow FG, about 30% pigment content, manufactured by Dainichiseika Kogyo Co., Ltd.], C.I. I. Pigment Red 220/166 [product name: TC Red FG, about 35% pigment content, manufactured by Dainichiseika Kogyo Co., Ltd.] and the like.
Examples of the resin for dispersing the pigment include polyamide resin, polyurethane resin, polyester resin, epoxy resin, melamine resin, phenol resin, silicone resin, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, Examples include polystyrene, acrylic acid resin, maleic acid resin, gum arabic, cellulose, dextran, casein, derivatives thereof, copolymers of the above resins, and the like.
As the fluorescent pigment, a fluorescent pigment in the form of synthetic resin fine particles, in which various fluorescent dyes are dissolved in a resin matrix, can be used.
In addition, white pigments such as titanium oxide, metal powder pigments such as aluminum, natural mica, synthetic mica, alumina, pearl pigments in which the surface of a core material selected from glass pieces is coated with metal oxides such as titanium dioxide, cholesteric liquid crystal type Bright pigments and the like can also be used.

Further, examples of coloring agents that can be applied to the ink composition include coloring agents that change color due to frictional heat.

The coloring material that changes color due to frictional heat is selected regardless of whether it is reversible or irreversible, if the handwriting changes color (hue change, transparency, or color disappearance) when the handwriting is rubbed with a friction body or the like and heated. can be applied In addition to the colorant itself that changes hue, it is also possible to change the hue by using a transparent (decolorized) colorant and a general-purpose colorant such as the above-described dyes and pigments.
Examples of the heat-discoloring coloring material include, for example, reversible types disclosed in JP-A-2012-219160 and JP-A-2014-5422, which are exemplified as cited documents, and JP-A-2010-229332. The irreversible types disclosed are applicable.
In particular, by encapsulating the thermochromic composition in microcapsules, the change in handwriting can be achieved stably for a long period of time without causing a change in composition, which is suitable. As the thermochromic composition encapsulated in the microcapsule pigment, from the viewpoint of repeated usability, accuracy of temperature change, etc., (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound and (c) a reversible thermochromic composition comprising a reaction medium that determines the temperature at which the two color reactions occur.

Examples of the reversible thermochromic composition include those described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc. It changes color before and after, exhibits a discolored state in a temperature range above the high-temperature side color change point, and a colored state in a temperature range below the low-temperature side color change point. The other state is maintained as long as the heat or cold required to develop that state is applied, but returns to the state exhibited at room temperature when the heat or cold is no longer applied, and the hysteresis width is Heat-discolorable microcapsule pigments, in which a reversible thermochromic composition having relatively small characteristics (ΔH=1 to 7° C.) is encapsulated in microcapsules, can be applied.
Furthermore, relatively large hysteresis characteristics (ΔH = 8 to 50 ° C.), and exhibits large hysteresis characteristics described in JP-A-2006-137886, JP-A-2006-188660, JP-A-2008-45062, JP-A-2008-280523, etc. That is, the shape of the curve plotting the change in color density due to temperature change is greatly different when the temperature is increased from the lower temperature side than the discoloration temperature range and when the temperature is decreased from the higher temperature side than the discoloration temperature range. A reversible thermochromic composition that changes color along a path and retains color in a specific temperature range in a colored state in a low temperature range below the complete color development temperature or in a colorless state in a high temperature range above the complete color disappearance temperature. A heat-erasable microcapsule pigment containing is also applicable.
Specifically, the reversible thermochromic composition having color memory properties, which is applied to the ink for writing instruments, is a temperature at which the complete color development temperature can be obtained only in a freezer, a cold region, etc., that is, -50 to 0 ° C. , preferably -40 to -5 ° C., more preferably -30 to -10 ° C., and the temperature obtained from a familiar heating body such as a frictional heat by a friction body, a hair dryer, that is, 50 to 95 ° C. , preferably 50 to 90 ° C., more preferably 60 to 80 ° C., and specifying the ΔH value to 40 to 100 ° C., effectively maintaining the color exhibited in the normal state (daily life temperature range) can function.

Microencapsulation of the thermochromic composition includes interfacial polymerization method, interfacial polycondensation method, in situ polymerization method, in-liquid curing coating method, phase separation method from aqueous solution, phase separation method from organic solvent, melting dispersion cooling method, aerial suspension coating method, spray drying method, etc., which are appropriately selected according to the application. Furthermore, depending on the purpose, the surface of the microcapsule pigment may be further provided with a secondary resin film to impart durability, or the surface characteristics may be modified for practical use.

Pigment ink is more susceptible to air bubbles than dye ink because air bubbles tend to be adsorbed on the pigment surface. However, since the ink of the present invention suppresses the formation and retention of air bubbles over time by the air bubble suppressor described later, good writing performance can be maintained for a long period of time even when a pigment is used as a coloring material. be done.

The above-mentioned coloring materials can be used singly or in admixture of two or more, and used within the range of, for example, 0.1 to 40% by mass, preferably 3 to 30% by mass, in the ink composition.

(Shear thinning agent)
Water-soluble or dispersible substances are effective as shear-thinning agents, such as xanthan gum, welan gum, zeta-sea gum, diutan gum, macrohomopsis gum, and organic acid-modified heteropolysaccharides whose constituent monosaccharides are glucose and galactose. Polymers with a molecular weight of 100,000 to 150,000 mainly composed of succinoglycan (average molecular weight of about 100,000 to 8,000,000), guar gum, locust bean gum and derivatives thereof, alginic acid alkyl esters, methacrylic acid alkyl esters, Glucomannan, carrageenan and other carbohydrates with gelling ability extracted from seaweed, poly N-vinyl-carboxylic acid amide cross-linked product, benzylidene sorbitol and benzylidene xylitol or derivatives thereof, cross-linkable acrylic acid polymer, inorganic fine particles, HLB Examples include nonionic surfactants having a value of 8 to 12, and metal salts and amine salts of dialkylsulfosuccinic acid. Furthermore, an N-alkyl-2-pyrrolidone and an anionic surfactant may be added in combination to the ink composition.
The shear thinning agent can be used in the range of 0.1 to 20% by mass in the ink composition.

式中、ＸとＹは－Ｈ、－Ｒ、－ＯＨ、－ＯＲ、－ＮＨ_２、－ＮＨＲおよび－ＮＲ_２から選ばれる官能基であり、Ｒはアルキル基である。ただし、Ｘ、Ｙ双方が水素である場合を除く。
前記式（１）に示される物質の塩としては、アルカリ金属塩、アンモニウム塩、モノエタノールアミン、ジエタノールアミン、トリエタノールアミン等のアルカノールアミン塩等が挙げられる。
前記気泡抑制剤は水性インキ組成物中で還元作用を呈することから、良好な酸素吸収能を長期間に亘って発現するものである。従って、インキ中の酸素を含む気体が集まって気泡となることを長期的に抑制でき、さらには、前記気泡抑制剤はインキ中の気泡の残留を抑制することもできる。このため、本発明のインキ組成物は初期と同等の良好な筆記性が長期に亘って維持される。
また、前記気泡抑制剤はインキ中で親水性基であるスルホ基と疎水性を有するナフタレン環を併せ持つため、疎水性を有し、水中で分散をさせにくい有機顔料やカーボンブラック等における水性インキ中の分散性を良好にする効果をも奏する。
式（１）に示される物質とその塩は併用しても良い。 (foam suppressor)
A substance represented by the following formula (1) or a salt thereof is applied to the ink composition as an antifoaming agent.

wherein X and Y are functional groups selected from -H, -R, -OH, -OR, -NH ₂ , -NHR and -NR ₂ , and R is an alkyl group. However, the case where both X and Y are hydrogen is excluded.
Examples of the salt of the substance represented by formula (1) include alkali metal salts, ammonium salts, alkanolamine salts such as monoethanolamine, diethanolamine and triethanolamine.
Since the foam inhibitor exhibits a reducing action in the water-based ink composition, it exhibits good oxygen absorption capacity over a long period of time. Therefore, it is possible to prevent the gas containing oxygen in the ink from collecting and forming air bubbles over a long period of time, and furthermore, the air bubble suppressing agent can suppress the remaining air bubbles in the ink. Therefore, the ink composition of the present invention maintains for a long period of time the same good writability as in the initial stage.
In addition, since the foam inhibitor has both a sulfo group, which is a hydrophilic group, and a naphthalene ring, which has hydrophobicity, in ink, it has hydrophobicity and is difficult to disperse in water. It also has the effect of improving the dispersibility of
The substance represented by Formula (1) and its salt may be used in combination.

Considering bubble suppression performance, X and Y in Formula (1) are functional groups selected from -H, -OH and _-NH2 , except when both X and Y are hydrogen. is preferred, one of X and Y is a functional group selected from —H, —OH and _—NH2 and the other is more preferably _—NH2 , and one of X and Y is —OH and , the other is more preferably —NH ₂ .

The content of the foam inhibitor is preferably 0.05 to 5% by mass, more preferably 0.1 to 3% by mass, more preferably 0.1 to 2% by mass, relative to the total mass of the ink composition. is more preferable. When the content is 0.05% or more, the bubble suppressing performance of the bubble suppressing agent is sufficiently exhibited, and when the content exceeds 5% by mass, the corrosiveness of the ball-point pen tip increases, and the ink ejection property tends to decrease.

Conventional general-purpose water-soluble organic solvents that are compatible with water can also be used in the ink composition. - butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol mono Ethyl ether, 2-pyrrolidone, N-methyl-2-pyrrolidone and the like.
The water-soluble organic solvent can be used alone or in combination of two or more, and is used in the range of 2 to 60% by weight, preferably 5 to 35% by weight in the ink composition.

Further, it is preferable to use a pH adjuster to adjust the pH to a desired value according to the characteristics of the ink composition.
As the pH adjuster, conventionally known acidic substances and basic substances can be applied. Examples of acidic substances include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, carbonic acid, boric acid, lactic acid, citric acid, tartaric acid, malic acid, and the like. Examples of basic substances include strong alkalis such as sodium hydroxide and potassium hydroxide, and weak alkalis such as ammonia, sodium carbonate, sodium hydrogen phosphate and potassium hydrogen phosphate. Alkanolamines such as monoethanolamine, diethanolamine and triethanolamine are also applicable as the basic substance.

In addition, if necessary, rust inhibitors such as benzotriazole, tolyltriazole, saponin, phenolic acid, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, paraoxybenzoic acid Preservatives or fungicides such as propyl, 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, urea, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolysate, sodium pyrophosphate Wetting agents such as antifoaming agents, fluorine-based surfactants and nonionic surfactants for improving ink permeability may also be used. Furthermore, the basic substance described above can also be used as a neutralizing agent for the substance represented by the formula (1).
Furthermore, lubricants can be added, such as metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide addition type cationic surfactants, phosphoric acid ester surfactants, N-acyl amino acid surfactants, dicarboxylic acid type surfactants. agent, β-alanine-type surfactant, 2,5-dimercapto-1,3,4-thiadiazole and its salts and oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, Dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine, and salts thereof are used.
In addition, N-vinyl-2-pyrrolidone oligomer, N-vinyl-2-piperidone oligomer, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, N-vinyl-ε-caprolactam Addition of thickening inhibitors such as oligomers can also enhance functionality in the hive-and-recess form.

One or two or more water-soluble resins such as alkyd resins, acrylic resins, styrene-maleic acid copolymers, polyvinylpyrrolidone, polyvinyl alcohol, dextrin, etc. may be added as long as the drying resistance is not impaired.

The ink composition preferably has a viscosity of 20 to 2000 mPa·s measured at a shear rate of 3.84 sec ⁻¹ and a viscosity of 1 to 100 mPa·s measured at a shear rate of 384 sec ⁻¹ . More preferably, the ink composition has a viscosity of 100 to 1500 mPa·s measured at a shear rate of 3.84 sec ⁻¹ and a viscosity of 1 to 60 mPa·s measured at a shear rate of 384 sec ⁻¹ . When the viscosity of the ink composition is within the above range, leakage of ink from the tip of the ball-point pen and sedimentation and agglomeration of the pigment in a stationary state are sufficiently suppressed, and ink discharge from the tip of the ball-point pen during writing is improved. , easy to form clear handwriting. The viscosity of the ink composition can be adjusted to a desired range by appropriately selecting the ink composition, such as the content of the coloring agent and the content of the shear thinning agent.
The viscosity is measured with the ink composition at 20° C., and a rheometer “Discovery HR-2” manufactured by TA Instruments Co., Ltd. can be used as the measuring device.

The water-based ink composition preferably has a shear thinning index n represented by the following formula (2) measured at 20° C. of 0.15 or more and less than 0.7, and preferably 0.2 to 0.6. is more preferable.
T=KJn (2)
Here, T is the shear stress [N/m ² ], K is the viscosity coefficient (constant), and J is the shear rate [sec ⁻¹ ].
As a result, leakage of ink from the tip of the ballpoint pen and sedimentation and aggregation of the pigment in a stationary state are sufficiently suppressed, and the ink of the tip of the ballpoint pen is discharged without accumulating in the gap between the ball and the ball gripping portion during writing. Therefore, it becomes easy to form clear handwriting.

The shear thinning index n can be measured, for example, using a rheometer “Discovery HR-2” manufactured by TE Instruments Co., Ltd. 3.84 sec ⁻¹ , 38.4 sec ⁻¹ and 384 sec ⁻¹ The shear rate and the shear stress (shear stress) obtained at each shear rate are applied to the above equation (2) to obtain n.

A ball-point pen refill to be filled with the ink composition will be described. A ball-point pen refill comprises an ink containing tube containing an ink composition, and a ball-point pen tip which is attached to the ink containing tube directly or via a connecting member and rotatably holds a ball.
The tip of the ballpoint pen, which serves as the writing tip, is, for example, machined from metal to form a ball receiving seat and an ink outlet inside, or a metal pipe with a plurality of inward projections on the inner surface near the tip. It is possible to apply an ink outflow gap which is formed by press deformation and which extends radially outward in the radial direction from the central portion between the inwardly protruding portions. The contact area is relatively small, and a smooth writing feeling can be given with a low writing pressure.

The ball held in the ballpoint pen tip is made of cemented carbide, stainless steel, ruby, ceramic, etc., and has an outer diameter of 0.1 to 2.0 mm, preferably 0.2 to 1.2 mm, more preferably 0.28 to 0.28 mm. A 0.7 mm ball is effective. When using a ball of 0.7 mm or less, the tip clearance is increased for the purpose of increasing the ink ejection amount and for the purpose of stably ejecting microcapsule pigments (especially 0.1 μm or more) that have a larger particle diameter than ordinary coloring materials. Therefore, it is easy for air to enter due to impact such as writing or knocking. Therefore, the ink of the present invention acts more effectively.
In the ballpoint pen tip, an elastic member is arranged in the tip to spring the rear end of the ball forward, and when writing is not performed, the ball is pressed against the inner edge of the tip of the tip so as to be in a close contact state, and when writing, the pen pressure is applied. The ball can be retracted to allow the ink to flow out, thereby suppressing ink leakage when not in use.
Examples of the resilient member include a thin metal wire spring, a spring having a straight portion (rod portion) at one end, a linear plastic processed body, etc., which can be pressed with a resilient force of 5 to 40 g. applied as

For the ink storage tube, for example, a molding made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon, or a metal tubular body is used. In addition to directly connecting the ballpoint pen tip to the ink containing tube, the ink containing tube and the tip may be connected via a connecting member (tip holder).
Furthermore, by using a transparent, colored transparent, or translucent molded body as the ink storage tube, the ink color, remaining amount of ink, etc. can be checked.

The trailing end of the ink contained in the ball-point pen refill is filled with an ink backflow prevention member.
The ink backflow preventive composition comprises a non-volatile liquid or a low-volatility liquid.
Specifically, petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or co-oligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, Polyether-modified silicone oil, fatty acid-modified silicone oil and the like can be mentioned, and one or more of them can be used in combination.

It is preferable to add a gelling agent to the non-volatile liquid or the hardly volatile liquid to increase the viscosity to a suitable viscosity. Hydrophobic mica, clay-based thickeners such as bentonite and montmorillonite with hydrophobic treatment, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate, and zinc stearate, tribenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax , hydrogenated castor oil, dextrin-based compounds such as fatty acid dextrin, and cellulose-based compounds.
Further, the liquid ink backflow preventive composition and the solid ink backflow preventer can be used together.

A ballpoint pen containing a ballpoint refill will be described.
The ballpoint pen may be a retractable ballpoint pen. As a retractable ballpoint pen, the writing tip provided on the ballpoint pen refill is stored in the outer shaft in a state where it is exposed to the outside air, and the writing tip protrudes from the outer shaft opening by the operation of the retracting mechanism. You can use all of them if you have them.
Methods of operating the retractable mechanism include, for example, a knock type, a rotating type, a sliding type, and the like.
The knock type has a knock portion on the rear end of the outer shaft or on the side surface of the outer shaft, and by pressing the knock portion, the writing tip of the ballpoint pen refill is projected or retracted from the front end opening of the outer shaft. A configuration can be exemplified in which the writing tip of the ballpoint pen refill protrudes and retracts from the outer shaft front end opening by pressing the provided clip portion.
The rotary type can be exemplified by a configuration in which the outer shaft has a rotating portion (rear shaft, etc.), and the writing tip of the ballpoint refill is projected and retracted from the front end opening of the outer shaft by rotating the rotating portion.
The slide type has a slide part on the side surface of the barrel, and by operating the slide, the writing tip of the ballpoint pen refill can be retracted from the front end opening of the outer shaft, or the clip part provided on the outer shaft is slid. A configuration can be exemplified in which the writing tip of the ball-point pen refill protrudes and retracts from the front end opening of the outer shaft.
Incidentally, the retractable ball-point pen may be a composite type retractable ball-point pen in which a plurality of ball-point refills are stored in addition to one in which one ball-point pen refill is stored in the outer shaft. Further, the ink containing tube constituting the ball-point pen refill may be made of resin, or may be made of metal.

Furthermore, a friction member for erasing or discoloring handwriting by frictional heat can be used together with the ballpoint pen.
As the friction member, an elastic body such as an elastomer, a plastic foam, or the like, which is rich in elasticity and capable of generating moderate friction during friction and generating frictional heat, is suitable. An eraser can also be used to rub the handwriting, but since eraser shavings are generated during rubbing, the aforementioned friction member is preferably used.
Examples of materials for the friction member include styrene thermoplastic elastomers such as silicone resin, SEBS resin (styrene ethylene butadiene styrene block copolymer), SBS resin (styrene butylene styrene copolymer), polyester resin, polypropylene resin and styrene. A mixture of a thermoplastic elastomer, a mixture of a polypropylene resin and a thermoplastic polypropylene elastomer, and the like are used.
The friction member can be a combination of a ballpoint pen and a separate member of arbitrary shape (friction body) to obtain a writing instrument set.
In the case of a cap-type ballpoint pen, the place where the friction member is provided is not particularly limited. The friction member itself can be formed of a friction member, or the friction member can be provided at the tip end (top) of the cap or the rear end of the barrel (the portion where the writing tip is not provided).
In the case of a retractable ballpoint pen, the place where the friction member is provided is not particularly limited. A friction member can be provided in the vicinity of the opening of the barrel, the rear end of the barrel (the portion where the writing tip is not provided), or the knock portion.

Examples are described below, but the present invention is not limited to these examples.
Table 1 shows the compositions, ink viscosities, and ink shear thinning indices of the water-based inks for writing instruments of Examples and Comparative Examples. The numerical values of the composition in the table indicate % by mass, and the unit of viscosity is mPa·s.
The viscosity was measured using a rheometer “Discovery HR-2” manufactured by TE Instruments Co., Ltd. when the ink composition was at 20°C. In addition, the shear thinning index n was measured using a rheometer “Discovery HR-2” manufactured by TE Instruments Co., Ltd., at shear rates of 3.84 sec ⁻¹ , 38.4 sec ⁻¹ and 384 sec ⁻¹ , and the shear stress (shear stress) obtained at each of these shear rates were applied to the above equation (2) to obtain n.

The content of raw materials in the table will be explained along with the note numbers.
(1) Pigment: carbon black (product name: Mitsubishi Carbon Black MA-100, manufactured by Mitsubishi Chemical Corporation)
(2) Shear thinning agent: xanthan gum (product name: Kelzan, manufactured by Sansho)
(3) substance represented by formula (1) (X: —OH, Y: —NH ₂ )
(4) a substance represented by formula (1) (both X and Y —OH)
(5) substance represented by formula (1) (X: -OH, Y: -H)
(6) Solubilizer for dl-α-tocopherol: Sodium oleoyl sarcosinate (7) Phosphate ester surfactant: Polyoxyethylene styrylphenyl ether phosphate (product name: Plysurf AL, Daiichi Kogyo Seiyaku Co., Ltd.) made)
(8) Water-soluble resin: polyvinylpyrrolidone (product name: Rubitec K-17, manufactured by BASF Japan)

Preparation of Ballpoint Pen Ink Among the materials listed in Table 1, polyvinylpyrrolidone, carbon black, and a portion of water were mixed using a three-roll mill to obtain a processed pigment. The processed pigment and the remaining materials except for the shear thinning agent in the blending amounts of the above Examples and Comparative Examples are mixed, stirred at 20 ° C. with a disper at 400 rpm for 1 hour, and then the shear thinning agent is mixed. was added and further stirred for 1 hour to obtain a ballpoint pen ink composition.

Preparation of Ink Backflow Preventer To 98.5 parts of polybutene as a base oil, 1.5 parts of a fatty acid amide as a thickening agent was added, followed by kneading with a triple roll to obtain an ink backflow preventer.

Preparation of ballpoint pen Each ballpoint pen ink composition was filled into a ballpoint pen refill in which a stainless steel cutting tip holding a cemented carbide ball with a diameter of 0.5 mm was fitted to one end of a transparent polypropylene ink storage tube. After arranging the ink backflow prevention member at the rear end, a sample ball-point pen was produced by attaching a cap.

Using the inks and ballpoint pens prepared as described above, the following evaluations 1 to 4 were performed.

1. Appearance of ink 1
Using a syringe, 10 μml of air was injected into the ballpoint pen refill to form air bubbles in the ink. Then, after this ballpoint pen refill was allowed to stand at 25° C. for one week, the ballpoint pen refill was visually observed. As for the evaluation criteria, A was accepted and B was rejected.
A: No bubbles confirmed B: Bubbles confirmed

2. Handwriting formation 1
Renmaru was written twice by hand, and the handwriting was visually observed. The diameter of one circle was 3 cm, and 12 circles were formed per writing. As the writing paper, trade name: NPi Form <55> (manufactured by Nippon Paper Industries Co., Ltd.) was used. The writing speed was the speed of writing 3 circles per second.
The evaluation criteria were A passed and B and C failed.
A: From the first stroke to the end of writing, clear handwriting without faintness or discontinuity is formed.
B: Blurred handwriting or broken handwriting is observed in 1 to 11 circles.
C: Blurred handwriting or broken handwriting is observed in 12 or more circles.

3. Appearance of ink 2
After the ballpoint pen was stored at 40° C. for 90 days with the ballpoint pen tip facing downward, the ballpoint pen refill was visually observed. The evaluation criteria were A passed and B and C failed.
A: No bubbles were observed at the interface between the ink backflow preventive and the ink.
B: Air bubbles were observed at the interface between the backflow preventive and the ink, but the backflow preventive and the ink were partially in contact with each other.
C: Air bubbles were observed between the ink backflow prevention member and the ink, and the ink backflow prevention member and the ink were completely dissociated.

Four. Handwriting formation 2
The ball-point pen confirmed to be writable was stored at 40° C. for 90 days with the ball-point pen tip facing upward. After returning the ball-point pen to room temperature (25° C.), writing was performed in the same manner as in the above “Handwriting Formability 1”, and the handwriting was visually observed. The evaluation criteria were A passed and B and C failed.
A: From the first stroke to the end of writing, clear handwriting without faintness or discontinuity is formed.
B: Blurred handwriting or broken handwriting is observed in 1 to 11 circles.
C: Blurred handwriting or broken handwriting is observed in 12 or more circles.
Table 2 shows the results of the above evaluation.

(summary)
The inks of Examples 1 to 5 were found to be excellent in air bubble suppressing performance from observation of the appearance of the inks and the ability to form good handwriting, and were able to form good handwriting from the initial stage over a long period of time.
The ink of Comparative Example 1 was inferior in air bubble control performance, and although it was possible to form good handwriting in the initial stage, the handwriting formability deteriorated due to the influence of air bubbles after a long period of time.
- Although the ink of Comparative Example 2 was superior to the ink of Comparative Example 1 in bubble suppression performance, the handwriting formability deteriorated due to the influence of bubbles after long-term aging.

Claims (7)

A ball-point pen refill comprising a ball-point pen tip and an ink storage tube, wherein ink is stored in the ink storage tube, and an end surface of the ink is filled with an ink backflow preventer, the ink being contained in the ball-point pen refill, the ink comprising: An aqueous ink composition for ballpoint pen refills, comprising a shear thinning agent, a substance having a structure of formula (1) and/or a salt thereof, and water.

wherein X and Y are functional groups selected from -H, -R, -OH, -OR, -NH ₂ , -NHR and -NR ₂ , and R is an alkyl group. However, the case where both X and Y are hydrogen is excluded. 2. The aqueous ink composition according to claim 1, wherein said X and Y are functional groups selected from -H, -OH and _-NH2 (except when both X and Y are hydrogen). At 20 ° C., the viscosity measured at a shear rate of 3.84 sec ^-1 is 20 to 2000 mPa s, the viscosity measured at a shear rate of 384 sec ^-1 is 1 to 100 mPa s, and the shear thinning index 3. The aqueous ink composition according to claim 1, wherein n is 0.15 or more and less than 0.7. The aqueous ink composition according to any one of claims 1 to 3, wherein the content of the substance represented by formula (1) and/or a salt thereof is 0.05 to 5% by mass with respect to the total mass of the aqueous ink composition. ink composition. The water-based ink composition according to any one of claims 1 to 4, wherein the coloring material is a pigment. A ballpoint pen tip and an ink containing tube, wherein the aqueous ink composition according to any one of claims 1 to 5 is contained in the ink containing tube, and an ink backflow preventer is provided on an end face of the aqueous ink composition. A filled ballpoint pen refill. A ball-point pen containing the ball-point pen refill according to claim 6.