JP7358233B2 - Ballpoint pens and ballpoint pen refills - Google Patents

Description

The present invention relates to a ballpoint pen and a ballpoint pen refill.

Ballpoint pens are widely used for writing addresses, etc., and the width of the handwriting can be adjusted by changing the outer diameter of the ball provided at the pen tip.

Ballpoint pens enable writing by utilizing the principle that as the ball rotates, the ink at the nib is ejected onto the paper from the gap between the ball and the ball gripping part, and the ink is supplied from the ink storage part to the nib. There is.

Ink used in ballpoint pens, for example, is required to have high handwriting drying properties. As a technique related to handwriting dryness, for example, Patent Document 1 discloses a technique for controlling the SP value and vapor pressure of a water-soluble organic solvent, and Patent Document 2 discloses a technique for controlling the SP value and vapor pressure of a water-soluble organic solvent, and Patent Document 2 discloses a technique for controlling the SP value and vapor pressure of a water-soluble organic solvent. A technique for doing so has been disclosed.

Japanese Patent Application Publication No. 2012-21045 JP2001-271020A

Among ballpoint pens, those with large-diameter balls have a wide gap between the ball and the ball gripping part, and ink can easily be ejected from this gap, making it possible to form wide, clear handwriting. It is. Therefore, it is suitable, for example, when writing an address in relatively large letters, and because the visibility is improved, it is also suitable for use by elderly people with reduced eyesight.
However, since a ballpoint pen equipped with a large diameter ball ejects a large amount of ink, even if the handwriting drying property is good, the ink may bleed onto the back side of the paper.
In addition, when a ballpoint pen with a large diameter ball needs to continuously eject a large amount of ink during shorthand, the ink supply to the pen tip cannot keep up and the ball and ball gripping part Air may enter the pen tip through the gap, causing writing defects such as broken handwriting or thin handwriting.

Further, in a ballpoint pen refill equipped with an ink storage tube, the rear end of the stored ink is sealed with a liquid stopper and/or a solid stopper. Liquid stoppers and solid stoppers (hereinafter sometimes referred to as "stoppers") prevent ink from leaking from the ballpoint pen refill and evaporation of moisture, etc. When the ink is consumed by writing, the inside of the ballpoint pen refill is As the ink decreases, it moves toward the tip of the ballpoint pen refill.
However, if a ballpoint pen is stored for a long period of time, the stopper may become hard. In that case, even if the ink is consumed, the stopper may have difficulty moving inside the ballpoint pen refill, and a gap may form between the inner wall of the ballpoint pen refill and the stopper, causing water in the ink to evaporate and reduce the viscosity of the ink. It can be expensive. Therefore, when a ballpoint pen is stored for a long period of time, the amount of ink ejected during writing may decrease, resulting in poor writing.

The present invention was made in view of the above circumstances, and its main purpose is to provide clear handwriting with less chance of ink ejection failure even during shorthand writing, and to prevent ink set-off to the back side of the paper. To provide a ballpoint pen with a large diameter ball that is small in number and has excellent storage stability, and a ballpoint pen refill housed in the ballpoint pen.

Aspect 1 of the present invention is
A water-based ink composition containing water, a colorant, a surfactant, an antioxidant, and a spinnability imparting agent,
The surfactant consists of a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkenylsulfosuccinic acid. one or more selected from the group;
The spinnability imparting agent incorporates an aqueous ink composition containing polyacrylamide having a weight average molecular weight of 50,000 to 4,500,000,
The viscosity of the aqueous ink composition at 20° C. measured at 20 rpm using an EL viscometer is 1 to 20 mPa·s,
the aqueous ink composition has a shear thinning index n of 0.80 to 1.00 at 20°C;
This is a ballpoint pen having a ball in the pen tip with an outer diameter of more than 0.7 mm and less than 2.0 mm.

Aspect 2 of the present invention is a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkylsulfosuccinic acid. The ballpoint pen according to aspect 1, wherein a mass ratio of the content of the antioxidant to the total content of the antioxidant is 0.05 or more and 0.50 or less.

Aspect 3 of the present invention is the aspect 1 or 2, wherein the surfactant contains one or more selected from the group consisting of a metal salt or amine salt of dialkyl sulfosuccinic acid and a metal salt or amine salt of dialkenyl sulfosuccinic acid. This is the ballpoint pen described.

Aspect 4 of the present invention provides a ballpoint pen refill comprising the pen tip and an ink storage tube, the ink storage tube containing the water-based ink composition, and an end surface of the water-based ink composition filled with an ink backflow preventer. The ballpoint pen according to any one of aspects 1 to 3, wherein the ballpoint pen is housed in a barrel.

Aspect 5 of the present invention is the ballpoint pen according to any one of aspects 1 to 4, which is a knock type.

Aspect 6 of the present invention is the ballpoint pen according to any one of aspects 1 to 5, wherein the pen tip has a pipe tip structure.

Aspect 7 of the present invention is that the aqueous ink composition comprises a branched monohydric alcohol substituted with an alkyl group and/or an alkyloxy group, a branched dihydric alcohol substituted with an alkyl group, an alkylene glycol monoalkyl ether, 7. The ballpoint pen according to any one of aspects 1 to 6, containing one or more co-solvents selected from the group consisting of alkylene glycol dialkyl ethers and γ-lactams.

Aspect 8 of the present invention is a ballpoint pen refill comprising a pen nib and an ink storage tube, an aqueous ink composition built into the ink storage tube, and an ink backflow preventer filled in an end surface of the aqueous ink composition. hand,
The aqueous ink composition contains water, a colorant, a surfactant, an antioxidant, and a spinnability imparting agent,
The surfactant consists of a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkenylsulfosuccinic acid. one or more selected from the group;
The spinnability imparting agent contains polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less,
The viscosity of the aqueous ink composition at 20° C. measured at 20 rpm using an EL viscometer is 1 to 20 mPa·s,
the aqueous ink composition has a shear thinning index n of 0.80 to 1.00 at 20°C;
This ballpoint pen refill has a ball having an outer diameter of more than 0.7 mm and less than 2.0 mm in the pen tip.

Aspect 9 of the present invention provides a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkylsulfosuccinic acid. The ballpoint pen refill according to aspect 7, wherein a mass ratio of the content of the antioxidant to the total content of the antioxidant is 0.05 or more and 0.50 or less.

Aspect 10 of the present invention is in aspect 8 or 9, wherein the surfactant contains one or more selected from the group consisting of a metal salt or amine salt of dialkyl sulfosuccinic acid and a metal salt or amine salt of dialkenyl sulfosuccinic acid. This is the ballpoint pen refill described.

Aspect 11 of the present invention is the ballpoint pen refill according to any one of aspects 8 to 10, wherein the pen tip has a pipe tip structure.

Aspect 12 of the present invention is that the aqueous ink composition comprises a branched monohydric alcohol substituted with an alkyl group and/or an alkyloxy group, a branched dihydric alcohol substituted with an alkyl group, an alkylene glycol monoalkyl ether, The ballpoint pen refill according to any one of aspects 8 to 11, containing one or more co-solvents selected from the group consisting of alkylene glycol dialkyl ethers and γ-lactams.

According to the present invention, a ballpoint pen and a ballpoint pen equipped with a large diameter ball have clear handwriting that is unlikely to cause ink discharge failure even when shorthand, has little ink set-off to the back side of the paper, and has excellent storage stability. A ballpoint pen refill is provided.

In order to solve the above problems, the present inventors conducted intensive studies and controlled the viscosity and shear thinning index of the water-based ink composition within a predetermined range, and also controlled the composition of the water-based ink composition as follows. I thought of doing it. That is, the surfactant consists of a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkenylsulfosuccinic acid. The composition of the aqueous ink composition was controlled so as to contain one or more selected from the group, polyacrylamide having a weight average molecular weight of 50,000 to 4,500,000 as a spinnability imparting agent, and an antioxidant. As a result, the present inventors have found that a ballpoint pen can be obtained that is less prone to ink discharge failure, has clear handwriting, has less ink set-off to the back side of the paper, and has excellent storage stability.

In this specification, the fact that ink discharge failure is unlikely to occur and the handwriting is clear is sometimes referred to as excellent writing performance, and the fact that there is little ink set-off to the back side is sometimes referred to as excellent bleed-through performance. .
Below, details of a ballpoint pen and a ballpoint pen refill according to an embodiment of the present invention will be explained.

1. Water-based ink composition Ballpoint pens and ballpoint pen refills according to embodiments of the present invention include:
Contains water, a colorant, a surfactant, an antioxidant, and a spinnability imparting agent,
A group in which the surfactant consists of a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkenylsulfosuccinic acid. including one or more selected from;
The spinnability imparting agent contains an aqueous ink composition containing polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less.
In addition, the water-based ink composition is
The viscosity at 20°C measured at 20 rpm using an EL viscometer is 1 to 20 mPa s,
The aqueous ink composition has a shear thinning index n of 0.80 to 1.00 at 20°C.
Each configuration will be explained in detail below.

(1) Water Water is not particularly limited, but preferably distilled water or ion-exchanged water with few impurities. The water content may be appropriately controlled in consideration of the component composition so as to obtain desired properties, but is usually 20% by mass or more and 97% by mass or less.

(2) Colorant Examples of the colorant include dyes and pigments.

Since dyes instantly permeate from the paper surface to form handwriting when writing, they tend to dry quickly compared to pigments, which do not easily permeate the paper surface.
As the dye, acidic dyes, basic dyes, direct dyes, etc. that can be dissolved in an aqueous medium can be used.
Acidic dyes include New Coccin (C.I. 16255), Tartrazine (C.I. 19140), Acid Blue Black 10B (C.I. 20470), Guinea Green (C.I. 42085), Brilliant Blue FCF (C.I.42090), Acid Violet 6B (C.I.42640), Soluble Blue (C.I.42755), Naphthalene Green (C.I.44025), Eosin (C.I.45380), Phloxin (C.I.45410), erythrosine (C.I.45430), nigrosine (C.I.50420), acidflavin (C.I.56205), etc. are used.
Basic dyes include chrysoidine (C.I. 11270), methyl violet FN (C.I. 42535), crystal violet (C.I. 42555), malachite green (C.I. 42000), Victoria Blue FB ( C.I.44045), Rhodamine B (C.I.45170), Acridine Orange NS (C.I.46005), Methylene Blue B (C.I.52015), etc. are used.
Direct dyes include Congo Red (C.I.22120), Direct Sky Blue 5B (C.I.24400), Violet BB (C.I.27905), Direct Deep Black EX (C.I.30235), and Kaya. Rus Black G Conch (C.I. 35225), Direct Fast Black G (C.I. 35255), Phthalocyanine Blue (C.I. 74180), etc. 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 fluorescent pigments.
Specifically, for example, C. I. Pigment Blue 15:3B [Product name: Sandye Super Blue GLL-E, pigment content 24%, manufactured by Sanyo Shiki Co., Ltd.], C.I. I. Pigment Red 146 [Product name: Sandye Super Pink FBL, pigment content 21.5%, manufactured by Sanyo Shiki Co., Ltd.], C.I. I. Pigment Yellow 81 [Product name: TC Yellow FG, pigment content approximately 30%, manufactured by Dainichiseika Kagyo Co., Ltd.], C.I. I. Pigment Red 220/166 [Product name: TC Red FG, pigment content approximately 35%, manufactured by Dainichiseika Kagyo Co., Ltd.].
In addition, for example, white pigments such as titanium oxide, metal powders 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, gold or Examples include silver metallic pigments, phosphorescent pigments, and cholesteric liquid crystal type glitter pigments.
As the fluorescent pigment, fluorescent pigments in the form of synthetic resin fine particles in which various fluorescent dyes are made into a solid solution in a resin matrix can be used.
Furthermore, it is also possible to use a microcapsule pigment containing a thermochromic composition and/or a photochromic composition and, if necessary, a fragrance, a pigment, and/or a dye.

The thermochromic composition is a reversible composition comprising (a) an electron-donating color-forming organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction of both of the above occurs. Thermochromic compositions are preferred, which can be encapsulated in microcapsules and used as reversible thermochromic microcapsule pigments.
As a reversible thermochromic composition, for example, a characteristic having a relatively small hysteresis width ΔH (ΔH 1 to 7° C.). The reversible thermochromic composition changes color before and after a predetermined temperature (color change point), and exhibits a decolorized state at a temperature above the high temperature discoloration point and a colored state at a temperature below the low temperature discoloration point. Among the above two states, only one specific state exists in the normal temperature range, and the other state is maintained as long as the heat or cold necessary for that state to occur is applied, When such heat or cold is no longer applied, it returns to the state it exhibits at room temperature.
Furthermore, for example, relatively large hysteresis characteristics (ΔH=8 ~50°C), or as described in JP-A No. 2006-137886, JP-A No. 2006-188660, JP-A No. 2008-45062, and JP-A No. 2008-280523, etc. Examples include reversible thermochromic compositions that exhibit large hysteresis characteristics. In the reversible thermochromic composition, the shape of the curve plotting the change in color density due to temperature change is such that the shape of the curve is such that the temperature increases from a temperature lower than the discoloration temperature range, and vice versa. Depending on the temperature, the color changes following a very different route, and the color development state at a low temperature below the complete color development temperature, or the discoloration state at a high temperature range above the complete color discoloration temperature, changes color memory in a specific temperature range. have Specifically, the reversible thermochromic composition having such color memory properties is produced at a temperature that allows complete color development only in a freezing room or a cold region, that is, from -50 to 0°C, preferably from -40 to 0°C. -5°C, more preferably -30 to -10°C, and the complete color erasure temperature is the temperature obtained from frictional heat from a friction body or a familiar heating element such as a hair dryer, that is, 50 to 95°C, preferably 50 to By specifying the range of 90°C, more preferably 60 to 80°C, and specifying the ΔH value to 40 to 100°C, it is possible to effectively maintain the color exhibited under normal conditions (daily living temperature range). can.
The reversible thermochromic composition as described above can be used as a heat-decolorable microcapsule pigment in which it is encapsulated in microcapsules.

Furthermore, a pigment dispersion in which a pigment is previously dispersed in an aqueous medium using a surfactant and/or a resin may be used.
Examples of resins for dispersing pigments include polyamide resins, polyurethane resins, polyester resins, epoxy resins, melamine resins, phenol resins, silicone resins, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetate, polyvinyl chloride, polyvinylidene chloride, and polystyrene. , acrylic acid resin, maleic acid resin, gum arabic, cellulose, dextran, casein, derivatives thereof, and copolymers of the above resins.

The colorant may be one type or a mixture of two or more types.
Since dyes instantly permeate from the paper surface to form handwriting when writing, they tend to dry quickly compared to pigments, which do not easily permeate the paper surface. Therefore, the coloring agent is preferably a dye, and pigments may be used in addition to the dye as long as the quick-drying properties are not impaired.

The content of the colorant may be appropriately controlled in consideration of the component composition so as to obtain desired properties, but is usually 1% by mass or more and 15% by mass or less.

(3) Surfactant Surfactants include metal salts or amine salts of monoalkylsulfosuccinic acid, metal salts or amine salts of monoalkenylsulfosuccinic acid, metal salts or amine salts of dialkylsulfosuccinic acid, and metal salts of dialkenylsulfosuccinic acid. or amine salts. This improves the ink discharge performance and/or the paper surface permeability of the ink. Furthermore, the metal salt or amine salt of monoalkylsulfosuccinic acid, the metal salt or amine salt of monoalkenylsulfosuccinic acid, the metal salt or amine salt of dialkylsulfosuccinic acid, and the metal salt or amine salt of dialkenylsulfosuccinic acid is selected from the group consisting of By containing one or more of these, even when a ballpoint pen is stored for a long period of time, it is possible to suppress a decrease in the ejectability of the water-based ink composition. Defects are less likely to occur.

The surfactant preferably contains one or more selected from the group consisting of a metal salt or amine salt of dialkyl sulfosuccinic acid and a metal salt or amine salt of dialkenyl sulfosuccinic acid. Thereby, any one or more of the ink discharge properties before long-term storage, the ink discharge properties after long-term storage, and/or the paper permeability of ink can be improved more easily.

The metal salt or amine salt of monoalkylsulfosuccinic acid preferably has an alkyl group having 6 to 12 carbon atoms in its structure. When the metal salt or amine salt of monoalkyl sulfosuccinic acid has an alkyl group having 6 to 12 carbon atoms in its structure, the ink dischargeability and/or the paper surface permeability of the ink will be better.
It is preferable that the alkyl group has a branched structure. If the alkyl group has a branched structure, the ink discharge properties and/or the paper surface permeability of the ink will be better.
In particular, it is most preferable that the metal salt or amine salt of monoalkylsulfosuccinic acid has a 2-ethylhexyl group as an alkyl group in its structure.

The metal salt or amine salt of monoalkenyl sulfosuccinic acid preferably has an alkylene group having 6 to 12 carbon atoms in its structure. When the metal salt or amine salt of monoalkenyl sulfosuccinic acid has an alkylene group having 6 to 12 carbon atoms in its structure, the ink dischargeability and/or the paper surface permeability of the ink will be better.
It is preferable that the alkylene group has a branched structure. When the alkylene group has a branched structure, the ink discharge properties and/or the paper surface permeability of the ink will be better.

The metal salt or amine salt of dialkylsulfosuccinic acid preferably has an alkyl group having 6 to 12 carbon atoms in its structure. When the metal salt or amine salt of dialkyl sulfosuccinic acid has an alkyl group having 6 to 12 carbon atoms in its structure, the ink dischargeability and/or the paper surface permeability of the ink will be better.
It is preferable that the alkyl group has a branched structure. If the alkyl group has a branched structure, the ink discharge properties and/or the paper surface permeability of the ink will be better.
In particular, the metal salt or amine salt of dialkylsulfosuccinic acid most preferably has a 2-ethylhexyl group as an alkyl group in its structure.

The metal salt or amine salt of dialkenyl sulfosuccinic acid preferably has an alkylene group having 6 to 12 carbon atoms in its structure. When the metal salt or amine salt of dialkenyl sulfosuccinic acid has an alkylene group having 6 to 12 carbon atoms in its structure, the ink dischargeability and/or the paper surface permeability of the ink will be better.
It is preferable that the alkylene group has a branched structure. When the alkylene group has a branched structure, the ink discharge properties and/or the paper surface permeability of the ink will be better.

Examples of metal salts of monoalkylsulfosuccinic acid include disodium lauryl sulfosuccinate.

Examples of the metal salt or amine salt of dialkyl sulfosuccinic acid include sodium di(2-ethylhexyl) sulfosuccinate, sodium dilauryl sulfosuccinate, dioctyl sulfosuccinate, dinonyl sulfosuccinate, didecyl sulfosuccinate, and diundecyl sulfosuccinate. acid salts, dimyristyl sulfosuccinate, dipalmityl sulfosuccinate, distearyl sulfosuccinate, and diarachidylsulfosuccinate.

Examples of the metal salt or amine salt of dialkenyl sulfosuccinate include dioctenyl sulfosuccinate, dinonenyl sulfosuccinate, didecenyl sulfosuccinate, diundecenyl sulfosuccinate, and didodecenyl sulfosuccinate. salt, dioleyl sulfosuccinate.

Total content of metal salt or amine salt of monoalkyl sulfosuccinic acid, metal salt or amine salt of monoalkenyl sulfosuccinic acid, metal salt or amine salt of dialkyl sulfosuccinic acid, and metal salt or amine salt of dialkenyl sulfosuccinic acid. The amount is preferably 0.01% by weight or more, more preferably 0.05% by weight or more, and preferably 5% by weight or less, more preferably 1% by weight or less. When the total content is 0.01% by mass or more and 5% by mass or less, it becomes easier to achieve both ink dischargeability and paper surface permeability of the ink.

The surfactant may be one type or a mixture of two or more types.

The surfactant includes anions other than metal salts or amine salts of monoalkylsulfosuccinic acid, metal salts or amine salts of monoalkenylsulfosuccinic acid, metal salts or amine salts of dialkylsulfosuccinic acid, and metal salts or amine salts of dialkenylsulfosuccinic acid. The surfactant may include a surfactant, a nonionic surfactant, and/or an amphoteric surfactant.

Examples of anionic surfactants include fatty acid soaps, n-acyl amino acid salts, alkyl ether carboxylates, carboxylic acid salts such as acylated peptides, alkyl sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, Sulfonic acid salts such as α-olefin sulfonate and N-acyl sulfonate, sulfuric acid salts such as sulfated oil, alkyl sulfate, alkyl ether sulfate, alkyl allyl ether sulfate, and alkyl amide sulfate, alkyl phosphorus Examples include phosphate ester salts such as acid salts, alkyl ether phosphates, and alkyl allyl ether phosphates.
Examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene fatty acid ester, polyoxyethylene alkyl allyl ether, sorbitan esters, alkyl sulfosuccinate, and alkyl phosphorus. Acid ester, alkyl sulfate ester, polyoxyethylene hydrogenated castor oil, decaglyceryl monolaurate, sucrose stearate, sucrose palmitate, sucrose myristate, sucrose oleate, sucrose laurate , and polyether-modified alkylsiloxane.
Examples of amphoteric surfactants include carboxybetaine type, aminocarboxylic acid type, imidazolium betaine, lecithin, and alkylamine oxide.

The content of the surfactant is preferably 0.01% by mass or more and 5% by mass or less.

Total content of metal salt or amine salt of monoalkyl sulfosuccinic acid, metal salt or amine salt of monoalkenyl sulfosuccinic acid, metal salt or amine salt of dialkyl sulfosuccinic acid, and metal salt or amine salt of dialkenyl sulfosuccinic acid. The mass ratio of the content of the antioxidant to the amount is preferably 0.05 or more and 0.50 or less, and storage stability and/or strike-through performance can be further improved. The mass ratio is more preferably 0.10 or more, and more preferably 0.40 or less.

(4) Antioxidant By containing an antioxidant, even when air enters through the gap between the ball and the ball gripping part during shorthand writing and mixes with the water-based ink composition, the air disappears due to the antioxidant. Therefore, handwriting defects such as broken handwriting and faded handwriting are less likely to occur. In addition, by containing an antioxidant, even when a ballpoint pen is stored for a long period of time, it is possible to suppress a decline in the ejectability of the water-based ink composition. Poor handwriting is less likely to occur.

Examples of antioxidants include sulfurized fatty acids and their salts, mercaptothiadiazole, alkylhydroxylamines, ascorbic acid, ascorbic acid derivatives, α-tocopherol, catechin, catechin derivatives, synthetic polyphenols, phosphonates, phosphinates, and sulfites. , sulfoxylate, dithionite, thiosulfate, thiourea dioxide, formamidine sulfinic acid, thiosulfate, and glutathione.

The antioxidant preferably includes mercaptothiadiazole, sulfurized fatty acid, sulfurized fatty acid salt, or alkylhydroxylamine, and more preferably mercaptothiadiazole. Mercaptothiadiazole is highly effective in suppressing poor handwriting.
Furthermore, by containing the sulfurized fatty acid or its salt, corrosive components in the ink are prevented from directly acting on the ball surface, and corrosion phenomena on the ball surface accompanied by metal elution can be easily suppressed.

Examples of mercaptothiadiazole include 2,5-dimercapto-1,3,4-thiadiazole, 2-methyl-5-mercapto-1,3,4-thiadiazole, and 2-amino-5-mercapto-1,3,4 -thiadiazole, and their alkali metal, ammonium, alkanolamine, cyclohexylamine and cyclohexylalkanolamine salts. 2,5-dimercapto-1,3,4-thiadiazole is highly effective in suppressing poor handwriting.

Examples of sulfurized fatty acids include sulfides of fatty acids having 8 to 20 carbon atoms, and specific examples include sulfurized pelargonic acid, sulfurized lauric acid, sulfurized palmitic acid, sulfurized oleic acid, sulfurized stearic acid, and sulfurized nonadecane. Examples include acids, sulfurized linolenic acid, sulfurized linoleic acid, and the like. Furthermore, a hydrocarbon group having 8 to 20 carbon atoms having at least one carboxyl group or a salt thereof, such as sulfurized distearic acid, has one or more (specifically an integer of 1 to 8) sulfur atom chain (hydrocarbon group). Examples include difatty acids that bind to both ends of the fatty acids (including those interposed), and one or more of these may be selected and used.
Examples of the sulfurized fatty acid salts include alkali metal salts such as lithium, sodium, and potassium, amine salts such as alkanolamines and ammonia, alkaline earth metal salts, Zn salts, Al salts, Sn salts, and Sb salts.
When containing sulfurized fatty acids and/or salts thereof, the total content is preferably 0.1% by mass or more, preferably 10% by mass or less, and more preferably 5% by mass or less.

Examples of alkylhydroxylamines include N,N-diethylhydroxylamine.

The antioxidant may be one kind or a mixture of two or more kinds.
The content of the antioxidant is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and preferably 5% by mass or less, more preferably 2.0% by mass or less. When the content of the antioxidant is 0.05% by mass or more and 5% by mass or less, the aqueous ink composition can be easily supplied from the ink accommodating part to the nib during ink discharge, so that the ink dischargeability is improved. is likely to improve.

(5) Threadability imparting agent The spinnability imparting agent contains polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less. This makes it easy to supply ink from the ink accommodating part to the pen tip when discharging ink, resulting in good ink discharging properties, and does not impart excessive stringiness to the water-based ink composition, so it can last for a long time. It exhibits stable solubility across the board. Further, by containing polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less, the strike-through performance can be improved. Furthermore, by containing polyacrylamide with a weight average molecular weight of 50,000 or more and 4,500,000 or less, it is possible to suppress a decrease in the ejectability of the water-based ink composition even when the ballpoint pen is stored for a long period of time. This makes writing defects less likely to occur even after long-term storage.

The weight average molecular weight of polyacrylamide is the weight average molecular weight measured by gel permeation chromatography (GPC) using a tetrahydrofuran solution as a developing solvent and calculated using polystyrene as a standard substance.

The weight average molecular weight of the polyacrylamide is preferably 400,000 or more, more preferably 500,000 or more, and preferably 2,500,000 or less, more preferably 2,000,000 or less.

The content of polyacrylamide having a weight average molecular weight of 50,000 to 4,500,000 is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and preferably 1% by mass or less, more preferably 0. .1% by mass or less. When the content of polyacrylamide having a weight average molecular weight of 50,000 to 4,500,000 is 0.001% by mass to 1% by mass, ink dischargeability is likely to be improved.

An example of the polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less includes Sunfloc NOP (manufactured by Sanyo Chemical Industries, Ltd., weight average molecular weight: 2,000,000).

The stringability imparting agent may be one type or a mixture of two or more types.

The spinnability imparting agent may include a spinnability imparting agent other than polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less.

Examples of other spinnability imparting agents include water-soluble synthetic polymers such as polyvinyl alcohol, sodium polyacrylate, alkyl acid-alkyl methacrylate copolymers, polyethylene oxide, carboxymethyl cellulose, methyl cellulose, ethyl cellulose, cellulose and its derivatives. Molecules, polysaccharides derived from microorganisms such as welan gum, alkasealan, alkase gum, and zeta sea gum; seaweed polysaccharides of alginic acid and its derivatives; seed polysaccharides such as guar gum, locust bean gum and its derivatives; and resin polysaccharides such as taragant gum. It will be done.

The content of the stringability imparting agent is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and preferably 1% by mass or less, more preferably 0.1% by mass or less.

(6) Thickener The aqueous ink composition may contain a thickener.
Examples of thickeners include carrageenan, xanthan gum, welan gum, zeta sea gum, diutan gum, succinoglycan (average molecular weight of about 1 million to 8 million), which is an organic acid-modified heteropolysaccharide whose constituent monosaccharides are glucose and galactose, and Examples include guar gum. Particularly, λ-carrageenan is preferable because the viscosity can be adjusted without imparting excessive thixotropy to the aqueous ink composition.

The thickener may be one type or a mixture of two or more types.
When containing a thickener, the content of the thickener is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass. It is as follows. When the content of the thickener is 0.05% by mass or more and 5% by mass or less, ink can be easily discharged.

(7) Wax emulsion, resin emulsion The water-based ink composition may contain a wax emulsion and/or a resin emulsion. Thereby, when the ballpoint pen is stored, it is easy to prevent ink from leaking from the gap between the ball and the ball gripping part. Therefore, it is preferably used in aqueous ink compositions incorporated in knock-type ballpoint pens.

Examples of wax emulsions include olefin wax emulsions such as polyethylene, polypropylene, polyethylene oxide, and polypropylene oxide, fatty acid amide-modified polyethylene wax emulsions, ethylene-vinyl acetate copolymer wax emulsions, and ethylene-acrylic copolymers and styrene-acrylic copolymers. and acrylic wax emulsions such as acrylic copolymers. Particularly, oxidized polyethylene wax emulsion is preferable because it is easy to form a film at room temperature, so handwriting easily dries, and since the film of oxidized polyethylene is soft, handwriting does not easily get rubbed.

Examples of resin emulsions include polyolefins, urethane resins, nylon resins, vinyl acetate resins, acrylic ester resins, acrylic ester copolymer resins, acrylic polyol resins, vinyl chloride-vinyl acetate copolymer resins, maleic acid resins, and polyesters. Resin, styrene resin, styrene copolymer resin, polyethylene resin, polycarbonate resin, epoxy resin, styrene-butadiene copolymer resin, acrylonitrile-butadiene copolymer resin, methyl methacrylate-butadiene copolymer resin, butadiene resin, chloroprene resin, melamine resin , polyvinyl alcohol and polyvinylpyrrolidone emulsions. In particular, acrylic resin emulsion is preferable because it is easy to form a film at room temperature, so handwriting is easy to dry, and polyethylene oxide film is soft, so handwriting is difficult to scratch.

The average diameter of the wax emulsion and resin emulsion is preferably 0.05 μm or more, more preferably 0.1 μm or more, and preferably 2.0 μm or less, more preferably 0.5 μm or less.

The average diameter of the wax emulsion and the resin emulsion can be measured by a dynamic light scattering method using, for example, a dynamic scattering particle size measuring device "Nanotrac NANO-flex" manufactured by Microtrac Bell Co., Ltd.

The wax emulsion and/or resin emulsion may be one type or a mixture of two or more types.

When containing a wax emulsion and/or a resin emulsion, the total content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 10% by mass or less in terms of solid content. , more preferably 5% by mass or less. When the content is 0.1% by mass or more and 10% by mass or less, ink leakage can be easily suppressed.

When the aqueous ink composition contains an oxidized polyethylene wax emulsion and/or an acrylic resin emulsion, it preferably contains an oligomer or polymer of N-vinyl-2-pyrrolidone having a K value of less than 40. This makes it easier to prevent ink from leaking from the gap between the ball and the ball gripping part when the ballpoint pen is stored. The K value is a viscosity characteristic value that correlates with molecular weight, and is a numerical value calculated by applying the relative viscosity value (25° C.) measured by a capillary viscometer to the Fikentscher equation below.

K= (1.5 logη _rel -1)/(0.15+0.003c)+(300clogη _rel +(c+1.5clogη _rel ) ² ) ^1/2 /(0.15c+0.003c ² )

Here, η _rel is the relative viscosity of the oligomer or polymer aqueous solution of N-vinyl-2-pyrrolidone to water, and c is the relative viscosity of the N-vinyl-2-pyrrolidone oligomer or polymer aqueous solution. Pyrrolidone oligomer or polymer concentration (% by mass).

(8) Auxiliary Solvent In order to improve the quick drying properties of the water-based ink composition, a water-soluble organic solvent that is compatible with water can be used as an auxiliary solvent. By using an auxiliary solvent, the permeability of the aqueous ink composition into the paper surface is further improved, handwriting drying properties are improved, and ink set-off can be further suppressed.

As co-solvents, for example, monoethanolamine, diethanolamine, triethanolamine, ethylene glycol monomethyl ether acetate, ethanol, propanol, butanol, glycerin, sorbitol, propane-1,2-diol, butane-1,3-diol, phenyl glycol and linear alkylene glycols such as ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, and butylene glycol.
More preferable co-solvents include, for example:
A branched monohydric alcohol substituted with an alkyl group and/or an alkyloxy group such as 2-ethylhexanol and 3-methoxy-3-methylbutanol (more preferably an alkyl group having 1 or 2 carbon atoms and/or a carbon (branched monohydric alcohol having a total of 3 to 8 carbon atoms, substituted with 1 to 4 alkyloxy groups);
A branched dihydric alcohol substituted with an alkyl group such as 2-methylpentane-2,4-diol and 2-methylpentane-1,3-diol (more preferably a branched dihydric alcohol substituted with an alkyl group having 1 or 2 carbon atoms) (branched dihydric alcohol with a total number of carbon atoms of 5 to 12);
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol-2-ethylhexyl ether, ethylene glycol isopropyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, diethylene glycol monomethyl ether, Alkylene glycol monoalkyl ethers (more preferably , alkylene glycol monoalkyl ether having a total number of carbon atoms of 3 or more and 15 or less);
Alkylene glycol dialkyl ethers such as diethylene glycol ethyl methyl ether and triethylene glycol butyl methyl ether (more preferably alkylene glycol monoalkyl ethers having a total number of carbon atoms of 3 to 15); and 2-pyrrolidone and N-methyl- Examples include γ-lactams such as 2-pyrrolidone.

One type of auxiliary solvent may be used alone, or two or more types may be used in combination.
When containing an auxiliary solvent, the content of the auxiliary solvent is preferably 0.5% by mass or more, more preferably 1% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less. When the content of the auxiliary solvent is 0.5% by mass or more and 15% by mass or less, the quick drying properties of the aqueous ink composition can be easily improved.

(9) Other components If necessary, pH adjusters such as inorganic salts such as sodium carbonate, sodium phosphate, and sodium acetate, and organic basic compounds such as water-soluble amine compounds, benzotriazole, tolyltriazole, saponin, etc. rust inhibitors, carbolic acid, sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate and 2,3,5,6-tetrachloro-4- Preservatives or fungicides such as (methylsulfonyl)pyridine, wetting agents such as urea, sorbitol, mannitol, sucrose, glucose, reduced starch hydrolyzate and sodium pyrophosphate, antifoaming agents, and ink permeability. Enhancing fluorosurfactants may also be used.
Furthermore, lubricants can be added, such as metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-added cationic surfactants, phosphoric acid ester surfactants, N-acyl amino acid surfactants, and dicarboxylic acid surfactants. , 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, dimethyl Dithiocarbamates, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine, salts thereof, and the like may be used.
In addition, oligomers of N-vinyl-2-pyrrolidone, oligomers of N-vinyl-2-piperidone, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, and N-vinyl-ε-caprolactam are also available. Addition of thickening inhibitors such as oligomers can also enhance functionality in the retractable form.

The aqueous ink composition can be prepared by mixing and stirring the above-mentioned components according to a conventional method.

(10) Viscosity properties The water-based ink composition has a viscosity of 1 to 20 mPa·s at 20°C, measured at 20 rpm using an EL viscometer. As a result, the thixotropy of the water-based ink composition is weakened and the ink fluidity is improved, so that the ink dischargeability is improved, and the paper surface permeability is improved, so that the handwriting drying property is improved. The viscosity is preferably 2 mPa·s or more, more preferably 5 mPa·s or more, and preferably 18 mPa·s or less, more preferably 15 mPa·s or less. In addition, by setting the above viscosity to 1 to 20 mPa・s, even when a ballpoint pen is stored for a long period of time, it is possible to suppress a decrease in the ejectability of the water-based ink composition. However, writing errors are less likely to occur.

Further, the aqueous ink composition has a shear thinning index n expressed by the following formula (1) measured at 20° C. from 0.80 to 1.00.

T=Kj ⁿ (1)
Here, T is shear stress [N/m ² ], K is viscosity coefficient (constant), and J is shear rate [s ⁻¹ ].

As a result, when writing, the ink at the pen tip is ejected without accumulating in the gap between the ball and the ball gripping part, so that it is possible to reduce the occurrence of smudges and creases and form clear handwriting. The shear thinning index is preferably 0.85 or more, more preferably 0.90 or more.

The shear thinning index n can be measured using, for example, a rheometer "DHR-2" manufactured by TA Instruments, and the values of 3.84 s ^-1 , 38.4 s ^-1 and 384 s ^-1 are measured. The shear rate and the shear stress (shear stress) obtained at each shear rate are applied to the above equation (1) to find n.

(11) pH
The pH of the aqueous ink composition is preferably 6 or more and 10 or less. Thereby, precipitation and decomposition of additives and the like can be further suppressed, the storage stability of the aqueous ink composition can be further improved, and ball corrosion can be further suppressed. The pH is preferably 7 or higher, and preferably 9 or lower.

(12) Surface tension The surface tension of the aqueous ink composition is preferably 20 mN/m or more and 45 mN/m or less. This makes it possible to further suppress handwriting blurring, making it easier to form clear handwriting, and increasing the permeability of the ink to the paper surface, thereby improving drying properties. The surface tension of the aqueous ink composition is preferably 25 mN/m or more, and preferably 40 mN/m or less.

2. Ballpoint Pen and Ballpoint Pen Refill A ballpoint pen according to an embodiment of the present invention contains a water-based ink composition and has a ball having an outer diameter of more than 0.7 mm and less than 2.0 mm at the pen tip. By providing such a large diameter ball, ink ejection performance can be improved.
Further, a ballpoint pen refill according to an embodiment of the present invention includes a pen nib having a ball with an outer diameter of more than 0.7 mm and no more than 2.0 mm, and an ink storage tube, and contains an aqueous ink composition in the ink storage tube, The end face of the aqueous ink composition is filled with an ink backflow preventer.

The structure and shape of the ballpoint pen itself are not particularly limited, except that the pen tip is equipped with a ball having an outer diameter of more than 0.7 mm and less than 2.0 mm. For example, there is a ballpoint pen in which a ballpoint pen refill according to an embodiment of the present invention is housed in a barrel. Further, the ballpoint pen may be a retractable type having a retractable mechanism such as a knock type, a rotary type, or a sliding type, and the pen tip can be retracted and retracted from the tip hole of the barrel.

The structure of the pen tip is not particularly limited. For example, it may have a structure in which a ball receiving seat and an ink outlet are formed inside by cutting metal, or a plurality of (for example, four) inward protrusions may be formed on the inner surface near the tip of a metal pipe on the outer surface. It may be a structure in which an ink outflow gap is formed between the inward protrusions and extends radially outward from the center, that is, a pipe tip structure. In particular, the pipe tip structure has a relatively small contact area with the rear end of the ball, so it can provide a smooth writing feeling with low writing pressure, and it can also improve ink ejection performance, so it is suitable for ballpoint pen tips. is preferably of pipe tip structure.

The ball held in the pen tip may be made of cemented carbide, stainless steel, ruby, ceramic, or the like. The present invention is particularly effective in embodiments in which the nib includes a larger ball, for example, an outer diameter of 0.8 mm or more or 1.0 mm or more. That is, as the outer diameter of the ball increases, the amount of ink ejected increases, which tends to cause problems with poor writing such as ink set-off and broken handwriting, but the ballpoint pen according to the embodiment of the present invention Even when the pen tip has a ball with a larger outer diameter, it is possible to reduce ink set-off and improve writing performance. Therefore, the ballpoint pen according to the embodiment of the present invention can be suitably used as a bold ballpoint pen having a ball with a large outer diameter at the pen tip. In addition, from the viewpoint of further reducing ink set-off and writing defects while increasing the ink discharge amount and obtaining a lighter and smoother writing feeling, the outer diameter of the ball of the pen tip is preferably 0.8 mm or more, or more. Preferably it is 1.0 mm or more, preferably 1.6 mm or less.
The movable distance in the radial direction between the inner diameter of the ball holding part of the pen tip and the ball is preferably 10 μm or more, preferably 50 μm or less, and the axial movable distance of the ball is preferably 10 μm or more, Preferably it is 30 μm or less.

The pen tip has an elastic member inside the tip that bounces the rear end of the ball forward, and when not writing, the ball is pressed against the inner edge of the tip to create a close contact state, and when writing, the ball is pushed back by pressure. It is preferable to allow the ink to flow out, thereby suppressing ink leakage when not in use.

Examples of elastic members include springs made of thin metal wires, springs made of thin metal wires with a straight part (rod part) at one end, linear plastic processed bodies, etc. It is configured to be able to be pressed by force.

The ink storage tube, which is connected directly to the pen tip or via a connecting member, is made of a general-purpose cylindrical molded member, for example, a molded member of thermoplastic resin such as polyethylene, polypropylene, or polyethylene terephthalate. Suitable for use in terms of productivity. Furthermore, by using a transparent, colored transparent or semi-transparent molded body as the ink storage tube, it is possible to check the ink color, the amount of ink remaining, etc.

An ink backflow preventer is filled at the rear end of the ink stored in the ink storage tube. Examples of the ink backflow prevention body include liquid stoppers and solid stoppers.

The liquid stopper is made of, for example, a non-volatile liquid and/or a hardly volatile liquid (base oil). Specifically, petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefin, α-olefin oligomer or cooligomer, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyester Examples include ether-modified silicone oil and fatty acid-modified silicone oil, which may be used alone or in combination of two or more.

A gelling agent may be added to the non-volatile liquid and/or the slightly volatile liquid to thicken it to a suitable viscosity. Examples of gelling agents include silica with a hydrophobically treated surface, fine particle silica with a methylated surface, aluminum silicate, swelling mica, clay thickeners such as hydrophobically treated bentonite or montmorillonite, and magnesium stearate. , fatty acid metal soaps such as calcium stearate, aluminum stearate, and zinc stearate, tribenzylidene sorbitol, fatty acid amide, amide-modified polyethylene wax, hydrogenated castor oil, dextrin compounds such as fatty acid dextrin, and cellulose compounds.
Polybutene or silicone oil is preferably used as the base oil of the ink backflow preventer, and fatty acid amide or silica is preferably used as the thickener.

Examples of the solid stopper include solid stoppers made of resin, such as polyethylene, polypropylene, and polymethylpentene.

As the ink backflow prevention body, a liquid stopper and a solid stopper made of resin may be used together.

The compositions of the aqueous ink compositions of Examples and Comparative Examples are shown in Tables 1 to 3 below, but the present invention is not limited to these Examples. Note that the units of composition in Tables 1 to 3 are mass %.

The contents of the raw materials in Tables 1 to 5 will be explained.
(1) Manufactured by Orient Chemical Industry Co., Ltd., product name: Water Black 191L (solid content: 15%)
(2) Manufactured by Sumitomo Chemical Co., Ltd., product name: Acid Blue PG
(3) Manufactured by Fuji Color Co., Ltd., product name: Fuji SP Black 8065 (solid content: 25%)
(4) Dai-ichi Kogyo Seiyaku Co., Ltd., Plysurf AL, polyoxyethylene distyrenated phenyl ether phosphate ester (5) Lonza Japan Co., Ltd., product name: Proxel XL-2, benzisothiazolin-3-one (6) λ-Carrageenan (7) Manufactured by Rohm and Haas, product name: Primal DR-72
(8) Triethanolamine (9) Propylene glycol monopropyl ether (10) Ethylene glycol monobutyl ether (11) 2-methylpentane-1,3-diol (12) Ethylene glycol (13) Daicel, N,N- Diethylhydroxylamine (14) 2,5-dimercapto-1,3,4-thiadiazole (15) Manufactured by Sanyo Chemical Industries, Ltd., trade name: Sanmorin OT-70, sodium di(2-ethylhexyl) sulfosuccinate (16) Toho Chemical Manufactured by Kogyo Co., Ltd., product name: Kohacool L-40, disodium lauryl sulfosuccinate (17) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Neocol P, sodium dioctyl sulfosuccinate (18) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Plysurf DBS, sodium alkyl (C4) phosphate (19) Polyacrylamide A (weight average molecular weight: 10,000)
(20) Polyacrylamide B (weight average molecular weight: 100,000)
(21) Polyacrylamide C (weight average molecular weight: 500,000)
(22) Manufactured by Sanyo Chemical Industries, Ltd., product name: Sunfloc NOP, polyacrylamide D (weight average molecular weight: 2 million)
(23) Polyacrylamide E (weight average molecular weight: 4 million)
(24) Polyacrylamide F (weight average molecular weight: 5 million)
(25) Manufactured by Kusumoto Kasei Co., Ltd., product name: NeoCryl A-1091 (acrylic resin emulsion, solid content: 45%)
(26) Manufactured by BASF Japan, product name: Joncryl 537J (acrylic resin emulsion, solid content: 46%)
(27) Manufactured by Meisei Chemical Industry Co., Ltd., product name: Meikatex PENO (oxidized polyethylene wax emulsion, solid content: 25%)
(28) Manufactured by ASHLAND, USA, product name: PVP K-12 polymer (polymer of N-vinyl-2-pyrrolidone, K value: 10-14)
(29) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., trade name: Pitzcor K-17L (polymer of N-vinyl-2-pyrrolidone, K value: 15-19)

The "ratios" in Tables 1 to 3 are: metal salt or amine salt of monoalkyl sulfosuccinic acid, metal salt or amine salt of monoalkenyl sulfosuccinic acid, metal salt or amine salt of dialkyl sulfosuccinic acid, and dialkenyl sulfosuccinic acid. It means the mass ratio of the content of the antioxidant to the total content of the metal salt or amine salt. The mass ratio is the amount of antioxidant A (13) and antioxidant B (14) relative to the total content of surfactant A (15), surfactant B (16), and surfactant C (17). ) is the mass ratio of the total content.

Polyacrylamides A to C, E and F were prepared as follows.
The acrylamide aqueous solution was placed in a reaction vessel and sealed with nitrogen. Immediately, a redox initiator was added to the acrylamide aqueous solution in the order of an oxidizing agent and a reducing agent, and then a polymerization reaction was carried out at 95°C while stirring the acrylamide aqueous solution to form an acrylamide hydrogel. I got it. After the reaction was completed, the reaction vessel was cooled, and the obtained acrylamide hydrogel was dried with hot air to obtain polyacrylamide. Note that the obtained polyacrylamide was used after being ground.
Ammonium persulfate, potassium persulfate, and hydrogen peroxide were used as appropriate as the oxidizing agent for the redox initiator. In addition, as reducing agents for the redox initiator, inorganic salts (ferrous sulfate, ferrous ammonium sulfate, sodium hydrogen sulfite) and trimethylamine were used as appropriate.

The weight average molecular weights of polyacrylamides A to F were measured. The weight average molecular weight of polyacrylamide is the weight average molecular weight measured by GPC using a tetrahydro solution as a developing solvent and calculated using polystyrene as a standard substance.
A 0.5% by mass tetrahydrofuran solution of polyacrylamide was prepared, and the solution was analyzed using a Tosoh column "TSK gel GMH6" and a Tosoh GPC device "HLC-802A" equipped with a refractive index detector. GPC measurements were performed under conditions of a measurement temperature of 40° C. and a solution injection volume of 200 μl.

The K value of the N-vinyl-2-pyrrolidone polymer was calculated by applying the relative viscosity value (25° C.) measured by a capillary viscometer to the Fikentscher equation below.

K= (1.5 logη _rel -1)/(0.15+0.003c)+(300clogη _rel +(c+1.5clogη _rel ) ² ) ^1/2 /(0.15c+0.003c ² )

Here, η _rel is the relative viscosity of the oligomer or polymer aqueous solution of N-vinyl-2-pyrrolidone to water, and c is the relative viscosity of the N-vinyl-2-pyrrolidone oligomer or polymer aqueous solution. Pyrrolidone oligomer or polymer concentration (% by mass).

1. Preparation of water-based ink composition and evaluation of viscosity Raw materials were mixed in the amounts of Examples and Comparative Examples, stirred at 20° C. in a disper for 1 hour, and then filtered to obtain a water-based ink composition. For those containing a thickener, a water-based ink composition was obtained by mixing the raw materials excluding the thickener and stirring under the above conditions, then adding the thickener and stirring for an additional hour.

The viscosity of the water-based ink composition at 20° C. was measured at 20 rpm using an EL viscometer “RE-85L” manufactured by Toki Sangyo Co., Ltd.

For the aqueous ink composition, the shear thinning index n at 20° C., expressed by the following formula (1), was measured using a rheometer “DHR-2” manufactured by TA Instruments. Specifically, by applying the shear rates of 3.84 s ^-1 , 38.4 s ^-1 and 384 s ^-1 and the shear stress (shear stress) obtained at each of these shear rates to the following equation (1), The shear thinning index n was determined.

T=Kj ⁿ (1)
Here, T is shear stress [N/m ² ], K is viscosity coefficient (constant), and J is shear rate [s ⁻¹ ].

The results of the viscosity evaluation are shown in Tables 6 to 10 below.

2. Production of a ballpoint pen A water-based ink composition was filled into a ballpoint pen refill in which a stainless steel tip (pipe tip structure) holding a cemented carbide ball with a diameter of 1.0 mm was fitted to one end of a transparent polypropylene pipe. After arranging an ink backflow preventer at the rear end, a ballpoint pen refill was assembled into the barrel to produce a knock-type ballpoint pen. The ink backflow preventer was prepared by adding 1.5 parts of fatty acid amide as a thickener to 98.5 parts of polybutene, and then kneading the mixture with a three-roll mill.

2. Characteristic Test of Ballpoint Pen The following tests were conducted using the obtained ballpoint pen.

-Writing Performance Two 5-fold swirls with a maximum diameter of about 10 cm were handwritten in succession on JIS P3201 writing paper A, and the condition of the handwriting was visually confirmed. When writing down the swirls, it took about 2 seconds for each swirl. The writing performance test was conducted at a room temperature of 20° C. and a relative humidity of 65%.
A writing performance test was also conducted under the same conditions as above for ballpoint pens that were kept at 50° C. for 60 days to simulate long-term storage.
The evaluation criteria were as follows, with ○ and △ being passed, and × being failing.
○: There are no gaps or gaps in the handwriting. △: There are slight gaps or gaps in the handwriting. ×: There are obvious gaps or gaps in the handwriting, or there are breaks in the handwriting.

-Bleed-through performance The word "Ei" was handwritten on JIS P3201 writing paper A, and the back side of the writing surface was visually confirmed. The strike-through performance test was conducted at a room temperature of 20° C. and a relative humidity of 65%.
The evaluation criteria were as follows, with ○ and △ being passed, and × being failing.
○: No bleed-through is observed. △: bleed-through is observed only at the "stop" part of the characters.
×: See-through is confirmed throughout

- Drying performance The word "ei" was handwritten on JIS P3201 writing paper A, and after 3 seconds, the handwriting was traced with a finger, and the handwriting was visually confirmed. Further, the drying performance test was conducted at a room temperature of 20° C. and a relative humidity of 65%.
The evaluation criteria were as follows, with ○ and △ being passed, and × being failing.
〇: No stretching or staining of the handwriting is observed. △: Slight stretching or staining is observed only at the "stop" part. ×: Stretching or staining is observed throughout the letters.

- Ink leakage test The ballpoint pen was left standing for 20 hours at a room temperature of 20° C. and a relative humidity of 90% with the tip of the ballpoint pen facing vertically downward. Thereafter, the tip of the chip was visually observed.
The evaluation criteria were as follows, with 〇 and △ as passing, and × as failing.
〇: No ink leakage at tip tip △: Slight ink leakage at tip tip ×: Ink droplets generated at tip tip

The test results are shown in Tables 6 to 10 below.

Claims (12)

A water-based ink composition containing water, a colorant, a surfactant, an antioxidant, and a spinnability imparting agent,
The surfactant consists of a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkenylsulfosuccinic acid. one or more selected from the group;
The spinnability imparting agent incorporates an aqueous ink composition containing polyacrylamide having a weight average molecular weight of 50,000 to 4,500,000,
The viscosity of the aqueous ink composition at 20° C. measured at 20 rpm using an EL viscometer is 1 to 20 mPa·s,
the aqueous ink composition has a shear thinning index n of 0.80 to 1.00 at 20°C;
The pen tip has a ball with an outer diameter of more than 0.7 mm and less than 2.0 mm,
the antioxidant comprises mercaptothiadiazole,
Total content of metal salt or amine salt of monoalkyl sulfosuccinic acid, metal salt or amine salt of monoalkenyl sulfosuccinic acid, metal salt or amine salt of dialkyl sulfosuccinic acid, and metal salt or amine salt of dialkenyl sulfosuccinic acid. A ballpoint pen , wherein a mass ratio of the content of the antioxidant to the amount is 0.05 or more and 0.50 or less . The ballpoint pen according to claim 1, further comprising an oxidized polyethylene wax emulsion and/or an acrylic resin emulsion and an oligomer or polymer of N-vinyl-2-pyrrolidone having a K value of less than 40. The ballpoint pen according to claim 1 or 2, wherein the surfactant contains one or more selected from the group consisting of a metal salt or amine salt of dialkyl sulfosuccinic acid and a metal salt or amine salt of dialkenyl sulfosuccinic acid. A ballpoint pen refill comprising the pen tip and an ink storage tube, the ink storage tube containing the water-based ink composition, and an end face of the water-based ink composition filled with an ink backflow preventer is stored in the barrel. The ballpoint pen according to any one of claims 1 to 3, comprising: The ballpoint pen according to any one of claims 1 to 4, which is a knock type. The ballpoint pen according to any one of claims 1 to 5, wherein the pen tip has a pipe tip structure. The aqueous ink composition contains a branched monohydric alcohol substituted with an alkyl group and/or an alkyloxy group, a branched dihydric alcohol substituted with an alkyl group, an alkylene glycol monoalkyl ether, an alkylene glycol dialkyl ether, and γ - Ballpoint pen according to any one of claims 1 to 6, containing one or more co-solvents selected from the group consisting of lactams. A ballpoint pen refill comprising a pen tip and an ink storage tube, an aqueous ink composition built into the ink storage tube, and an ink backflow preventer filled in an end surface of the aqueous ink composition,
The aqueous ink composition contains water, a colorant, a surfactant, an antioxidant, and a spinnability imparting agent,
The surfactant consists of a metal salt or amine salt of monoalkylsulfosuccinic acid, a metal salt or amine salt of monoalkenylsulfosuccinic acid, a metal salt or amine salt of dialkylsulfosuccinic acid, and a metal salt or amine salt of dialkenylsulfosuccinic acid. one or more selected from the group;
The spinnability imparting agent contains polyacrylamide having a weight average molecular weight of 50,000 or more and 4,500,000 or less,
The viscosity of the aqueous ink composition at 20° C. measured at 20 rpm using an EL viscometer is 1 to 20 mPa·s,
the aqueous ink composition has a shear thinning index n of 0.80 to 1.00 at 20°C;
The pen tip has a ball with an outer diameter of more than 0.7 mm and less than 2.0 mm,
the antioxidant comprises mercaptothiadiazole,
Total content of metal salt or amine salt of monoalkyl sulfosuccinic acid, metal salt or amine salt of monoalkenyl sulfosuccinic acid, metal salt or amine salt of dialkyl sulfosuccinic acid, and metal salt or amine salt of dialkenyl sulfosuccinic acid. A ballpoint pen refill , wherein the mass ratio of the content of the antioxidant to the amount is 0.05 or more and 0.50 or less . The ballpoint pen refill according to claim 8, further comprising an oxidized polyethylene wax emulsion and/or an acrylic resin emulsion and an oligomer or polymer of N-vinyl-2-pyrrolidone having a K value of less than 40. The ballpoint pen refill according to claim 8 or 9, wherein the surfactant contains one or more selected from the group consisting of a metal salt or amine salt of dialkyl sulfosuccinic acid and a metal salt or amine salt of dialkenyl sulfosuccinic acid. The ballpoint pen refill according to any one of claims 8 to 10, wherein the pen tip has a pipe tip structure. The aqueous ink composition contains a branched monohydric alcohol substituted with an alkyl group and/or an alkyloxy group, a branched dihydric alcohol substituted with an alkyl group, an alkylene glycol monoalkyl ether, an alkylene glycol dialkyl ether, and γ - Ballpoint pen refill according to any one of claims 8 to 11, containing one or more co-solvents selected from the group consisting of lactams.