Oil-based ink composition for writing instruments and writing instrument using the same

Abstract

An object of the present invention is to obtain an oil-based ink composition for a writing instrument which maintains a good writing feeling while suppressing ink leakage, and a writing instrument using the same.SOLUTION: The oil-based ink composition for writing utensils comprises a colorant, an organic solvent and titanium phosphate having an average primary particle diameter of ≤ 5 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an oil-based ink composition for a writing instrument and a writing instrument using the same. [Background technology]

[0002] Conventionally, in the case of oil-based ink compositions for writing instruments, in order to prevent ink leakage from the gap at the writing tip (ink leakage from the gap between the ball and the tip tip) in the case of ballpoint pens, and to prevent ink leakage from the writing tip in the case of marking pens and felt-tip pens, various technologies have been proposed for oil-based ink compositions for writing instruments, such as using a solvent with a vapor pressure of 0.001 mmHg or more at 25°C, using silica or terpene phenol resin as an ink leakage inhibitor, or using a gelling agent to set the ink viscosity high.

[0003] As such oil-based ink compositions for writing instruments, techniques using alcohols, polyhydric alcohols, and glycol ether solvents having a vapor pressure of 0.001 mmHg or more at 25°C are disclosed in JP 2004-107591 A, entitled "Oil-based ink composition for writing instruments," techniques using ink leakage inhibitors are disclosed in JP 10-195365 A, entitled "Oil-based ink for ballpoint pens," which uses silica having an average primary particle size of 7 to 40 nm, and JP 2007-126528 A, entitled "Oil-based ink for ballpoint pens," which uses a terpene phenol resin having an OH value of 150 or more, and JP 7-196972 A, entitled "Oil-based ink composition for ballpoint pens," which uses hydrogenated castor oil or fatty acid amide wax as a shear thinning agent. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] "JP 2004-107591 A" [Patent Document 2] "Unexamined Japanese Patent Publication No. 10-195365" [Patent Document 3] "JP 2007-126528 A" [Patent Document 4] "Unexamined Japanese Patent Publication No. 7-196972" [Patent Document 5] "JP 2019-131628 A" Summary of the Invention [Problem to be solved by the invention]

[0005] However, while Patent Document 1 is effective in suppressing ink leakage to a certain extent, when the ink viscosity is reduced, the solvent used in Patent Document 1 alone is unable to sufficiently suppress ink leakage. Furthermore, Patent Document 2 discloses that silica with a primary average particle size of 7 to 40 nm has poor dispersion stability in oil-based ink due to its small particle size and high specific gravity. Furthermore, Patent Document 3 discloses that terpene phenol resin with an OH value of 150 or more has poor solubility in oil-based ink due to its high OH value, and therefore fails to exhibit sufficient effectiveness. Furthermore, Patent Document 4 discloses that hydrogenated castor oil and fatty acid amide wax can suppress ink leakage to a certain extent, but they increase the ink viscosity when stationary, tend to deteriorate ink tracking, and can cause smearing of handwriting, affecting the writing experience.

[0006] Furthermore, in recent years, in order to achieve a smooth writing feel, the viscosity of oil-based inks for writing instruments has been reduced, which has resulted in an increased amount of ink being ejected, making it more likely for ink to leak from the gap at the writing tip, which can be a problem.

[0007] Therefore, in order to suppress ink leakage, Patent Document 5 proposes a solution in which an organotitanium compound and polyvinyl butyral are used, and the organotitanium compound forms a three-dimensional crosslinked structure in the ink by crosslinking resins together, making it possible to provide ink viscosity expression, thereby making it possible to set a high ink viscosity when stationary, and by suppressing the flow of ink, ink leakage from the gap at the writing tip (in the case of a ballpoint pen, ink leakage from the gap between the ball and the tip) can be suppressed.

[0008] An object of the present invention is to provide an oil-based ink composition for a writing instrument that suppresses ink leakage while maintaining a good writing feel, and a writing instrument using the same. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention "1. An oil-based ink composition for a writing instrument, comprising a colorant, an organic solvent, and titanium phosphate having an average primary particle size of 5 μm or less. 2. The oil-based ink composition for writing instruments according to item 1, wherein the content of the titanium phosphate is 0.01% by mass or more and 2.0% by mass or less based on the total amount of the ink composition. 3. The oil-based ink composition for a writing instrument according to item 1 or 2, characterized in that the oil-based ink composition for a writing instrument contains a shear thinning agent. 4. The oil-based ink composition for a writing instrument according to item 1 or 2, wherein the shear thinning agent is acrylic acid. 5. The oil-based ink composition for a writing instrument according to item 1 or 2, wherein the organic solvent is selected from the group consisting of alkylene glycol alkyl ether solvents, amide solvents, and alkylene oxide derivatives of glycerin. 6. The oil-based ink composition for a writing instrument according to item 1 or 2, wherein the solubility parameter of the organic solvent is 8 or more and 13 or less. 7. A writing instrument containing the oil-based ink composition for a writing instrument according to item 1 or 2. 8. A ballpoint pen containing the oil-based ink composition for a writing instrument according to item 1 or 2. [Effects of the Invention]

[0010] Titanium phosphate particles having an average primary particle diameter of 5 μm or less create a physical barrier in the gap at the writing tip (the gap between the ball and the inner wall of the tip end), thereby suppressing ink leakage and maintaining a good writing feel, and a writing instrument using the same can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention is characterized in that it contains titanium phosphate having an average primary particle diameter of 5 μm or less, thereby making it possible to suppress ink leakage while maintaining a good writing feel.

[0012] (Titanium phosphate) In the present invention, it has been found that ink leakage can be suppressed by including titanium phosphate particles with an average primary particle diameter of 5 μm or less in an ink composition for oil-based ballpoint pens. This is because titanium phosphate particles of a specific size create physical barriers in the gap between the ball and the inner wall of the tip, thereby suppressing ink leakage. Furthermore, the titanium phosphate particles adhere to each other, creating a structure formed by weak aggregation, which forms a structure in the ink that is highly resistant to ink leakage when left stationary, thereby enabling high ink leakage suppression. Meanwhile, because the structure is formed by weak aggregation, the aggregated structure is broken down by physical actions such as the rotation of the ball during writing. This allows for smooth writing without impeding ink fluidity, thereby reducing writing resistance and achieving a good writing feel. Furthermore, titanium phosphate particles with an average primary particle diameter of 5 μm or less are preferably used because they are stably dispersed even in organic solvents, thereby maintaining ink stability over time.

[0013] The average particle size of titanium phosphate having an average primary particle size of 5 μm or less is preferably 3 μm or less, more preferably 2 μm or less, because a smaller average particle size allows the particles to adhere to each other, filling gaps at the writing tip, and also makes it easier to form a weakly aggregated structure and suppress ink leakage. Furthermore, taking into consideration the dispersion stability of titanium phosphate in the ink (ink stability over time), 1 μm or less is preferred, and even more preferably 0.5 μm or less. On the other hand, if the average particle size is too small, the effect of suppressing ink leakage due to physical obstructions caused by the titanium phosphate particles is likely to be poor, so the average particle size is preferably 0.01 μm or more, more preferably 0.1 μm or more.

[0014] Furthermore, in consideration of dispersibility in ink, the average thickness of the titanium phosphate is preferably 0.01 μm or more and 4 μm or less, more preferably 0.01 μm or more and 2 μm or less, and even more preferably 0.02 μm or more and 0.3 μm or less. The primary particle diameter (D50) and thickness (D50) of titanium phosphate can be determined by taking multiple SEM images at randomly selected positions using a scanning electron microscope (SEM) at a magnification sufficient to capture 50 to 100 particles. The resulting SEM images are then analyzed using Mountech's image analysis software, Mac-View ver. 4. 100 to 200 particles are measured to determine the longest diameter in the plane direction of each particle. The longest diameter in the plane direction of each particle is then used to calculate D50, the value at which the cumulative frequency of the smaller particle size in the volume-based cumulative particle size distribution is 50%. The resulting D50 is the primary particle diameter of the plate-like particles. 100 to 200 plate-like particles are measured to determine the thickness of each plate-like particle. Then, using the thickness of each plate-like particle, D50, which is the value at which the cumulative frequency from the small particle size side in the volume-based cumulative particle size distribution becomes 50%, is calculated, and the obtained D50 is taken as the thickness of the plate-like particle.

[0015] Furthermore, the aspect ratio, which is the value obtained by dividing the average primary particle diameter by the average thickness, is preferably 3 or more, more preferably 5 or more and 15 or less, more preferably 5 or more and 12 or less, and more preferably 6 or more and 10 or less.

[0016] The titanium phosphate may be in the form of plate-like particles, spherical particles, etc., but in consideration of the effects of suppressing ink leakage and dispersion stability, plate-like particles are preferred. Furthermore, it is preferable that the structural formula is represented by Ti(HPO4)2·H2O or the like and that it is a crystalline titanium phosphate.

[0017] Furthermore, the content of the titanium phosphate is more preferably 0.01% by mass or more and 2.0% by mass or less of the total amount of the ink composition, taking into consideration ink leakage prevention and writing feel. Furthermore, taking into consideration ink stability over time, writing feel, and write-through performance, the content is preferably 0.01% by mass or more and 1% by mass or less, more preferably 0.01% by mass or more and 0.5% by mass or less, and even more preferably 0.05% by mass or more and 0.2% by mass or less.

[0018] (organic solvent) Examples of organic solvents include alkylene oxide derivatives of glycerin such as polyoxyalkylene glyceryl ether, polyoxyalkylene alkyl glucoside, and polyoxypropylene alkyl ether; alkylene glycol alkyl ethers such as alkylene glycol monoalkyl ether and alkylene glycol dialkyl ether; amide solvents of β-alkoxypropionamides such as 3-methoxy-N,N-dimethylpropanamide, 3-butoxy-N,N-dimethylpropanamide, and 3-ethoxy-N,N-dimethylpropanamide; glycol solvents such as diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, and ethylene glycol; and alcohol solvents such as benzyl alcohol, methanol, ethanol, 1-propanol, 2-propanol, isopropanol, isobutanol, t-butanol, propargyl alcohol, allyl alcohol, 3-methyl-1-butyn-3-ol, ethylene glycol monomethyl ether acetate, and other higher alcohols.

[0019] Among these organic solvents, alkylene glycol alkyl ethers, amide solvents, and alkylene oxide derivatives of glycerin are preferred, and alkylene glycol alkyl ethers or amide solvents are more preferred, considering that they are more likely to stably disperse with the titanium phosphate in the ink and therefore more likely to exhibit the effects of the present invention.Furthermore, alkylene glycol alkyl ethers or amide solvents of β-alkoxypropionamides are preferred, and from this perspective, alkylene glycol monoalkyl ethers are even more preferred.

[0020] Furthermore, in the case of alkylene glycol monoalkyl ethers, the number of carbon atoms in the alkylene glycol moiety of the alkylene glycol monoalkyl ether is preferably 3 or more and 8 or less, in consideration of stability with the titanium phosphate. In consideration of greater stability and easier achievement of the effects of the present invention, the number of carbon atoms is preferably 4 or more and 6 or less. Regarding the number of carbon atoms in the alkyl ether moiety of the alkylene glycol monoalkyl ether, in consideration of stability with the titanium phosphate, the shorter the alkyl ether moiety, the better. Therefore, the number of carbon atoms is preferably 1 to 6, and in consideration of easier stability and easier effect, it is preferably 1 to 4, and more preferably 1 to 2.

[0021] Among the alkylene glycol alkyl ethers described above, triethylene glycol alkyl ethers, compounds having a butylene glycol alkyl ether structure, propylene glycol alkyl ethers, and diethylene glycol alkyl ethers are preferred, considering that they are easily dissolved in the titanium phosphate, maintain a good writing feel, and are likely to suppress blurred handwriting and skipped lines. From a further consideration, compounds containing triethylene glycol monomethyl ether, compounds having a butylene glycol monomethyl ether structure, propylene glycol monomethyl ether, and diethylene glycol monobutyl ether are more preferred, and from a further consideration, compounds having a butylene glycol monomethyl ether structure are more preferred.

[0022] Amide solvents are also preferred because they are more easily dispersed stably with the titanium phosphate and can more easily exert the effects of the present invention. Specifically, the physical obstruction of titanium phosphate can more effectively suppress ink leakage, and titanium phosphate particles are more likely to form a structure formed by weak aggregation in which they adhere to each other, forming a structure in the ink that has high resistance to ink leakage when left standing, making it easier to exert a higher ink leakage suppression effect. Furthermore, among amide solvents, β-alkoxypropionamides such as 3-methoxy-N,N-dimethylpropanamide (boiling point 215°C), 3-butoxy-N,N-dimethylpropanamide (boiling point 252°C), and 3-ethoxy-N,N-dimethylpropanamide are preferred. This is because titanium phosphate tends to form weak aggregate structures in amide solvents, which are more easily broken down by physical actions such as the rotation of the ball during writing. This allows for a better writing feel while reducing writing resistance and without impairing ink fluidity during writing. From this perspective, 3-methoxy-N,N-dimethylpropanamide and 3-butoxy-N,N-dimethylpropanamide are preferred, with 3-methoxy-N,N-dimethylpropanamide being even more preferred.

[0023] Furthermore, with regard to alkylene oxide derivatives of glycerin, polyoxyalkylene glyceryl ethers are preferred in view of the fact that they further improve lubricity, thereby suppressing line skipping and blurred handwriting and improving the writing feel, and from this perspective, it is even more preferable to use polyoxyalkylene diglyceryl ethers.

[0024] In addition, the solubility parameter (SP value) of organic solvents is between 8 and 13 (cal / cm 3 ) 1 / 2 This is because the effect of the present invention is easily exhibited due to the compatibility with the titanium phosphate. From a more detailed consideration, the solubility parameter (SP value) is preferably 9 or more and 12 or less (cal / cm 3 ) 1 / 2 Further, if considered, the solubility parameter (SP value) is preferably 10 or more and 11 or less (cal / cm 3 ) 1 / 2 It is preferable that: The solubility parameter (SP value) of a solvent used in this invention is a value expressed as the square root of the molecular cohesive energy, and is described in Chapter IV, Solubility Parameter Values, of the Polymer Handbook (Second Edition). The SP value is expressed in units of (cal / cm3)1 / 2 and refers to the value at 25°C. For those for which no data is given, the values ​​can be calculated by the method described in RF Fedors, Polymer Engineering Science, 14, p. 147 (1967).

[0025] Furthermore, it is preferable that the boiling point of the organic solvent is 170°C or higher. This is because if the boiling point is lower than 170°C, the organic solvent will easily evaporate, the ink viscosity will easily increase, it will be difficult to suppress line skipping and handwriting smearing, and the writing feel will be affected, so from further consideration, it is preferable that the boiling point is 200°C or higher. On the other hand, if the boiling point is higher than 300°C, the organic solvent will be difficult to evaporate, which will likely affect the suppression of ink leakage, so it is preferable that the boiling point is 300°C or lower, and from further consideration, it is preferable that the boiling point is 280°C or lower.

[0026] Furthermore, in consideration of improving solubility, strike-through, handwriting drying properties, bleeding, etc., the content of the organic solvent is preferably 10% by mass or more and 90% by mass or less, and more preferably 25% by mass or more and 80% by mass or less, of the total amount of the ink composition.

[0027] In the present invention, the blending ratio of the titanium phosphate to the organic solvent (organic solvent / titanium phosphate) is preferably 50 to 8,000 times, in order to facilitate stable dispersion of the titanium phosphate in the organic solvent and to facilitate the exertion of the effects of the present invention, and more preferably 150 to 8,000 times, in order to maintain a good writing feel and to prevent blurred handwriting and skipped lines. Furthermore, the blending ratio is preferably 350 to 1,600 times, in order to maintain a good writing feel and to prevent blurred handwriting and skipped lines.

[0028] (coloring agent) The colorant used in the present invention is not particularly limited and may be a dye, a pigment, or the like, and may be appropriately selected and used. The combined use of a dye and a pigment is preferred because it is easier to obtain the following effects. Examples of dyes include oil-soluble dyes, acid dyes, basic dyes, metal-containing dyes, and various salt-forming dyes thereof, such as salt-forming dyes formed between an acid dye and a basic dye, salt-forming dyes formed between an organic acid and a basic dye, and salt-forming dyes formed between an acid dye and an organic amine. These dyes may be used alone or in combination of two or more. Considering the stability over time due to compatibility with titanium phosphate having an average primary particle size of 5 μm or less, it is preferable to use at least a salt-forming dye. Furthermore, considering that the stability over time can be maintained due to the stable salt-forming bond, it is preferable to use a salt-forming dye formed between a basic dye and an organic acid, a salt-forming dye formed between an acid dye and a basic dye, or a salt-forming dye formed between an acid dye and an organic amine.Specific examples of dyes include Balifast Black 1802, Balifast Black 1805, Balifast Black 1807, Balifast Violet 1701, Balifast Violet 1704, Balifast Violet 1705, Balifast Blue 1601, Balifast Blue 1605, Balifast Blue 1613, Balifast Blue 1621, Balifast Blue 1631, Balifast Red 1320, Balifast Red 1355, Balifast Red 1360, Balifast Yellow 1101, Balifast Yellow 1151, Nigrosine Base EXBP, Nigrosine Base EX, BASE OF BASIC DYES ROB-B, BASE OF BASIC DYES RO6G-B, BASE OF BASIC DYES VPB-B, BASE OF BASIC DYES VB-B, and BASE OF BASIC DYES MVB-3 (all manufactured by Orient Chemical Industry Co., Ltd.), Aizen Spiron Black GMH-Special, and Aizen Spiron Violet C-RH, Aizenspiron Blue GNH, Aizenspiron Blue 2BNH, Aizenspiron Blue C-RH, Aizenspiron Red C-GH, Aizenspiron Red C-BH, Aizenspiron Yellow C-GNH, Aizenspiron Yellow C-2GH, SPT Blue 111, SPT Blue GLSH-Special, SPT Red 533, SPT Orange 6, SBN Violet 510, SBN Yellow 530, SRC-BH (all manufactured by Hodogaya Chemical Co., Ltd.), and the like.

[0029] Furthermore, examples of pigments include inorganic, organic, and processed pigments, and specific examples include carbon black, aniline black, ultramarine, yellow lead, titanium oxide, iron oxide, phthalocyanine-based, azo-based, quinacridone-based, diketopyrrolopyrrole-based, quinophthalone-based, threne-based, triphenylmethane-based, perinone-based, perylene-based, dioxazine-based, metallic pigments, pearl pigments, fluorescent pigments, and phosphorescent pigments.

[0030] It is preferable to use a pigment as the colorant, because the use of pigment particles creates physical obstacles in the gap at the writing tip (the gap between the ball and the tip tip), making it easier to suppress ink leakage. Furthermore, in the present invention, the use of titanium phosphate with an average primary particle diameter of 5 μm or less creates a synergistic effect due to the physical obstacles created by the titanium phosphate particles and the pigment at the writing tip, resulting in a higher ink leakage suppression effect and simultaneously achieving a pigment dispersion effect, which is preferable. Furthermore, pigments are preferable because they provide excellent handwriting fastness, particularly excellent light resistance.

[0031] The content of the colorant is preferably 5% by mass or more and 30% by mass or less relative to the total amount of the ink composition. This is because if it is less than 5% by mass, it tends to be difficult to obtain thick handwriting, and if it exceeds 30% by mass, it tends to affect the solubility in the ink. Taking these tendencies into consideration, the content is preferably 7% by mass or more and 25% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less.

[0032] (shear thinning agent) In the present invention, it is also preferable to include a shear thinning agent. This is because the inclusion of a shear thinning agent can increase the ink viscosity, making it easier to achieve dispersion stability over time and suppress ink leakage. Examples of shear thinning agents include acrylic acid resins (polyacrylic acid resins), cellulose derivatives, polysaccharides, fatty acid amides, and hydrogenated castor oil. Among these, it is preferable to use an acrylic acid resin, which can disperse and stabilize the titanium phosphate and make it easier to obtain the effects of the present invention, and taking into consideration stability with organic solvents.Furthermore, cross-linked acrylic acid resins are preferred, because by forming a three-dimensional network structure, a stable thickening effect can be obtained while further stabilizing the dispersion of the titanium phosphate, and this is effective in suppressing ink leakage.

[0033] Acrylic acid resins (polyacrylic acid resins) are preferred because they have affinity with alkylene glycol alkyl ethers and amide solvents, among other organic solvents, and swelling and dispersion facilitate the formation of pseudoplastic and stable thickening properties, making it easier to achieve the effects of the present invention. Furthermore, considering the writing feel and writing performance (reduction of smearing and blobbing of handwriting), crosslinked polyacrylic acid resins are preferred. This is because crosslinked polyacrylic acid resins themselves have a crosslinked structure, and alkylene glycol alkyl ethers and amide solvents are more likely to form a more three-dimensional network structure. Therefore, the formation of a denser crosslinked structure makes it easier to impart pseudoplasticity, which reduces the ink viscosity during writing and improves the writing feel and writing performance (reduction of smearing and blobbing). Carboxyvinyl polymers are particularly preferred.

[0034] Furthermore, for acrylic acid resins (polyacrylic acid resins), the carboxyl group content in the acrylic acid resin (polyacrylic acid resin) is preferably 40% by mass or more and 80% by mass or less, in order to obtain a stable thickening effect together with organic solvents. Even more preferably, it is 50% by mass or more and 70% by mass or less. In particular, when alkylene glycol alkyl ethers or amide solvents are used, polyacrylic acid resins with a carboxyl group content of 55% by mass or more and 65% by mass or less are preferred, as they have excellent swelling and dispersibility and impart pseudoplasticity, thereby lowering the ink viscosity during writing and improving the writing feel. Furthermore, alkylene glycol monoalkyl ethers and β-alkoxypropionamides are even more preferred.

[0035] Furthermore, the bulk density (g / ml) of the acrylic acid resin (polyacrylic acid resin) is preferably 0.5 (g / ml) or less. This is because the effects of the present invention are more readily exhibited by having excellent swelling and dispersibility in organic solvents and water, and from a more particular perspective, it is preferably 0.3 (g / ml) or less. On the other hand, if the bulk density (g / ml) of the acrylic acid resin (polyacrylic acid resin) is less than 0.01 (g / ml), swelling and dispersion are difficult, and the acrylic acid resin (polyacrylic acid resin) is more likely to aggregate. For this reason, it is preferably 0.01 (g / ml) or more, and from a more particular perspective, it is preferably 0.1 (g / ml) or more. The bulk density can be measured, for example, by a bulk density measuring device (Scott volume meter, manufactured by Tsutsui Rikagaku Kikai Co., Ltd.).

[0036] If the content of the acrylic acid resin (polyacrylic acid resin) is less than 0.1% by mass relative to the total amount of the ink composition, the swelling property is insufficient and pseudoplasticity is difficult to obtain, and if it exceeds 5.0% by mass, the swelling and dispersibility in the ink tends to deteriorate, so the content is preferably 0.1% by mass or more and 5.0% by mass or less relative to the total amount of the ink composition. Even more particularly, the content is preferably 0.3% by mass or more and 3.0% by mass or less, and even more particularly, the content is preferably 0.6% by mass or more and 1.8% by mass or less.

[0037] In the present invention, the blending ratio of the organic solvent to the acrylic acid resin (polyacrylic acid resin) (organic solvent / acrylic acid resin (polyacrylic acid resin)) is preferably 5 to 150 times by mass in consideration of swelling and dispersibility. In consideration of more stable swelling and dispersibility, it is more preferably 10 to 120 times, and from further consideration, it is more preferably 20 to 100 times.

[0038] Furthermore, in the present invention, when an acrylic acid resin (polyacrylic acid resin) is used, it is preferable that the ink contains water. The reason for this is unclear, but water has excellent affinity with the acrylic acid resin (polyacrylic acid resin), and by further stabilizing the swelling dispersion with the acrylic acid resin (polyacrylic acid resin), a stable thickening effect is easily obtained. Furthermore, water improves the slipperiness of the ball, improves ink ejection, and suppresses blobbing and smearing, thereby improving writing performance. It can be used particularly effectively when used in ballpoint pens. Furthermore, water has excellent affinity with alkylene glycol alkyl ethers or amide solvents, and is stable, making it preferable. As the water, conventional water such as ion-exchanged water, distilled water, and tap water can be used.

[0039] If the water content is less than 0.1% by mass of the total ink composition, it is likely to affect the ball's sliding properties and writing performance, and if it exceeds 30% by mass, it is likely to deteriorate the solubility in the ink, so the water content is preferably 0.1% by mass or more and 30% by mass or less of the total ink composition. Further, from consideration, 2% by mass or more and 20% by mass or less is more preferable, and from consideration, 3% by mass or more and 15% by mass or less is even more preferable.

[0040] (resin) In order to further improve the ink leakage suppression effect, it is preferable to use a resin as an ink viscosity adjuster. Examples of resins include polyvinyl butyral resin, ketone resin, polyacetal resin, polyvinyl alcohol resin, cellulose resin, terpene resin, alkyd resin, phenoxy resin, polyvinyl acetate resin, etc., but among these, it is preferable to use a polyvinyl butyral resin or a ketone resin, as this makes it easier to improve the ink leakage suppression effect.

[0041] Furthermore, when considering the ink leakage suppression effect and the improvement of writing feel, it is preferable to use polyvinyl butyral resin. This is because the coating formed by the polyvinyl butyral resin on the outside of the tip tip makes it easier to improve ink leakage. In particular, as described above, the inclusion of titanium phosphate is preferable because it acts as a physical barrier and forms a weak cohesion structure from the inside of the tip tip, thereby suppressing ink leakage from both the inside and outside of the ballpoint pen tip tip, thereby expecting a higher ink leakage suppression effect. Polyvinyl butyral resin is also preferred because it forms a constantly elastic ink layer between the ball and ball seat, making direct contact less likely and improving the writing feel. Furthermore, when a pigment is used as the colorant, polyvinyl butyral resin is also preferred because it provides a pigment dispersion effect. Here, the polyvinyl butyral resin is obtained by reacting polyvinyl alcohol (PVA) with butyraldehyde (BA), and has a structure having butyral groups, acetyl groups, and hydroxyl groups.

[0042] Furthermore, the polyvinyl butyral resin preferably has a hydroxyl group content of 20 mol% or more. This is because polyvinyl butyral resins with a hydroxyl group content of less than 20 mol% are insufficient in organic solvents, making it difficult to achieve sufficient lubrication and ink leakage suppression. Furthermore, considering the writing performance due to moisture absorption, it is preferable to use a polyvinyl butyral resin with a hydroxyl group content of 20 mol% or more. Furthermore, considering ink leakage suppression, the hydroxyl group content is preferably 28 mol% or more, and more preferably 32 mol% or more. Furthermore, using a polyvinyl butyral resin with a hydroxyl group content of more than 45 mol% tends to increase moisture absorption, which can affect the stability over time of the ink components. Therefore, polyvinyl butyral resins with a hydroxyl group content of 45 mol% or less are preferred, and polyvinyl butyral resins with a hydroxyl group content of 40 mol% or less are more preferred. The amount of hydroxyl groups (mol %) of the polyvinyl butyral resin refers to the content of hydroxyl groups (mol %) relative to the total molar amount of butyral groups (mol %), acetyl groups (mol %), and hydroxyl groups (mol %).

[0043] Furthermore, when used in combination with the titanium phosphate, the ketone resin is expected to synergistically provide a higher ink leakage suppression effect, and is also preferable because it has the effect of suppressing bleeding. Furthermore, ketone resins are preferred because they improve lubricity under high writing pressure (writing loads of 300 gf to 500 gf). Among ketone resins, it is preferable to use ketone resins with cyclic structures such as aromatic ring skeletons (having a benzene ring, such as a phenyl group, an acetophenone group, or a naphthalene group) or cyclohexane skeletons (having a cyclohexane ring, such as a cyclohexane group or a cyclohexanone group). This is because the ketone resins with cyclic structures provide a cushioning effect, improving lubricity under high writing pressure (writing loads of 300 gf to 500 gf). Ketone resins with aromatic ring skeletons are more preferred because they have many double bond structures, making them more likely to provide a stronger cushioning effect, resulting in effective lubrication under high writing pressure (writing loads of 300 gf to 500 gf).

[0044] If the total content of the resins is less than 1% by mass relative to the total amount of the ink composition, the amount of resin film formed may be insufficient and ink leakage prevention performance may be poor, while if it exceeds 40% by mass, solubility in the ink may be poor, so it is preferably 1% by mass or more and 40% by mass or less relative to the total amount of the ink composition. Furthermore, in consideration of ink leakage prevention performance, it is preferably 5% by mass or more, and if it exceeds 30% by mass, the ink viscosity may become too high, which may affect the writing feel and writing performance, so it is preferably 5% by mass or more and 30% by mass or less.

[0045] (surfactant) In the present invention, it is preferable to use a surfactant because improving lubricity improves the writing feel, and furthermore, when the tip end is left in the air and the tip end dries, it suppresses smearing, improving writing performance. This is because the lubricating layer formed by the surfactant facilitates improving lubricity, and further, the surfactant softens the coating formed when the tip end dries, suppressing smearing, and improving writing performance. Examples of surfactants include fatty acids, silicone-based surfactants, fluorine-based surfactants, phosphate ester-based surfactants, and fatty acid esters. Among these, considering the above effects, it is preferable to use one or more of fatty acids, phosphate ester-based surfactants, and fatty acid esters. In particular, when used in a ballpoint pen, it is preferable to use a phosphate ester surfactant because the phosphate group makes it easy for the surfactant to be adsorbed to the ballpoint pen tip or ball, such as metal, and therefore makes it easy to obtain a lubricating effect.

[0046] Regarding the HLB value of the surfactant, in consideration of stability with the titanium phosphate, lubricity, and good writing performance (start-up performance), the HLB value is preferably 5 or more and 17 or less. From this perspective, the HLB value is more preferably 6 or more and 14 or less. Furthermore, in consideration of lubricity, the HLB value is preferably 12 or less, and more preferably 6 or more and 12 or less. The HLB value used in the present invention can be determined by the Griffin method, Kawakami method, etc. In particular, in retractable writing implements such as knock-type writing implements and rotary-extending writing implements, unlike cap-type writing implements, the pen tip is always exposed to the outside, so it is easy to affect the writing performance when the writing tip is dry, so it is more preferable to use a surfactant with the above HLB value.In particular, when used in a ballpoint pen, it is easy to affect the writing performance when the ballpoint pen tip is dry, so it is effective and preferable.

[0047] Specific examples of the surfactant include fatty acids such as oleic acid, stearic acid, and linoleic acid; silicone surfactants such as dimethyl silicone, methylphenyl silicone, polyether-modified silicone, and higher fatty acid ester-modified silicone; fluorine-based surfactants such as perfluorobutyl sulfonate, perfluorogroup-containing carboxylate, perfluorogroup-containing phosphate, perfluorogroup-containing phosphate ester-type compound, perfluoroalkyl betaine, and perfluoroalkylamine oxide compound; and phosphate surfactants such as polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate monoester, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate diester, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphate triester, alkyl phosphate ester, alkyl ether phosphate ester, and derivatives thereof.

[0048] The content of the surfactant is more preferably 0.1% by mass or more and 5% by mass or less of the total amount of the ink composition. This is because if it is less than 0.1% by mass, it tends to be difficult to obtain the desired lubricity, and if it exceeds 5.0% by mass, the ink tends to become unstable over time. Taking this tendency into consideration, the content is preferably 0.3% by mass or more and 3% by mass or less of the total amount of the ink composition, and even more preferably 0.5% by mass or more and 3% by mass or less.

[0049] (organic amine) In the present invention, the use of an organic amine is preferred because neutralizing and stabilizing the acrylic acid resin with the organic amine allows for sufficient swelling and dispersion, resulting in a stable thickening effect. Furthermore, even when a phosphate ester surfactant is used, neutralizing and stabilizing the ink and stabilizing it in the ink are preferred because they are more likely to improve the writing feel and writing performance. Examples of organic amines include amines containing ethylene oxide, such as oxyethylene alkylamines and polyoxyethylene alkylamines; alkylamines, such as laurylamine and stearylamine; aliphatic amines, such as dimethyl alkylamines, distearylamine, dimethyl laurylamine, dimethyl stearylamine, and dimethyl octylamine; and alkanolamines, such as diethanolamine and triethanolamine. Among these, amines containing ethylene oxide are preferred in terms of stability with the acrylic acid resin and surfactant.

[0050] The HLB value of the organic amine is preferably 5 or more and 17 or less. This is because a stable thickening effect can be obtained by neutralizing and stabilizing the acrylic acid resin and stabilizing the swelling and dispersion with the organic solvent. In consideration of further stabilizing the neutralization and improving the swelling and dispersion properties, the HLB value is preferably 6 or more and 17 or less, and further taking into consideration the above, the HLB value is preferably 7 or less and 16 or less.

[0051] The content of the organic amine is preferably from 0.1% by mass to 10% by mass of the total amount of the ink composition, taking into consideration the neutralization stability with the acrylic acid resin and the surfactant, and furthermore, from 0.1% by mass to 5% by mass, taking into consideration the neutralization with the surfactant, and more preferably from 0.5% by mass to 3% by mass.

[0052] The content of the organic amine is preferably from 0.1% by mass to 10% by mass of the total amount of the ink composition, taking into consideration the neutralization stability with the acrylic acid resin and the surfactant, and furthermore, from 0.1% by mass to 5% by mass, taking into consideration the neutralization with the surfactant, and more preferably from 0.5% by mass to 3% by mass.

[0053] Additionally, colorant stabilizers, plasticizers, chelating agents, stringiness imparting agents, etc. may be used as appropriate. These may be used alone or in combination of two or more.

[0054] The ink viscosity of the oil-based ink composition for writing instruments of the present invention is not particularly limited, but is preferably 20°C at a shear rate of 0.18 sec -1 If the ink viscosity (at rest) exceeds 30,000 mPa·s, the writing performance and writing feel tend to deteriorate. -1 The ink viscosity (at rest) is preferably 30,000 mPa·s or less. -1 If the ink viscosity (when stationary) is less than 1000 mPa·s, it is difficult to prevent ink leakage, so if ink leakage is taken into consideration, it is preferably 1000 mPa·s or more. If consideration is given to further improving ink leakage prevention, writing feel, ink tracking performance, and writing start performance, the ink viscosity is more preferably 1500 mPa·s or more and 25000 mPa·s or less, and even more preferably 2000 mPa·s or more and 20000 mPa·s or less, and more preferably 2000 mPa·s or more and 15000 mPa·s or less. Furthermore, in retractable oil-based ballpoint pens such as knock-type oil-based ballpoint pens and rotary-type oil-based ballpoint pens, it is necessary to give more consideration to suppressing ink leakage, and therefore this is effective and preferable.

[0055] (ballpoint pen) Furthermore, the ink consumption of a ballpoint pen per 100 m is preferably 20 mg to 100 mg. This is because if the ink consumption per 100 m is less than 20 mg, it is difficult to obtain thick handwriting or a good writing feel, and if the ink consumption per 100 m exceeds 100 mg, the gap between the ball and the tip end is likely to affect ink leakage prevention, and writing performance and blobbing are likely to occur. Therefore, in consideration of the balance of the above effects, the ink consumption is preferably 30 mg to 80 mg, and in consideration of achieving both thicker handwriting and ink leakage prevention, it is preferably 40 mg to 70 mg. Regarding ink consumption, a spiral writing test was conducted using five test samples at a writing speed of 4 m / min on JIS P3201 writing paper at a writing angle of 70° and a writing load of 200 g at 20°C, and the average ink consumption per 100 m was defined as the ink consumption per 100 m.

[0056] Furthermore, the amount of movement of the ball in the ballpoint pen tip used in the present invention in the longitudinal direction is preferably 3 μm or more and 25 μm or less. This is because if it is less than 3 μm, it becomes difficult to obtain thick handwriting or a good writing feel, and if it exceeds 25 μm, it is likely to have an effect on suppressing ink leakage. From a more detailed consideration, it is preferably 5 μm or more and 22 μm or less, and more preferably 7 μm or more and 20 μm or less. In the present invention, the amount of movement of the ball of the ballpoint pen tip in the vertical axis direction is the shape of the ballpoint pen tip of the ballpoint pen in its initial state before writing begins.

[0057] Furthermore, in order to improve ink leakage suppression, it is effective not only to set the movement amount (μm) of the ball in the ballpoint pen tip in the vertical axis direction but also to consider the relationship with the average primary particle diameter (μm) of titanium phosphate. Specifically, the ratio of the movement amount (μm) of the ball in the ballpoint pen tip in the vertical axis direction to the average primary particle diameter (μm) of titanium phosphate (movement amount of ball in the vertical axis direction / average primary particle diameter of titanium phosphate) is preferably 1 to 100 times, since this makes it easier to suppress ink leakage. From a more specific perspective, a ratio of 3 to 70 times is preferable, and 5 to 60 times is more preferable.

[0058] The arithmetic mean roughness (Ra) of the ball surface of the ballpoint pen tip used in the present invention is preferably 0.1 nm or more and 12 nm or less. This is because if the arithmetic mean roughness (Ra) is less than 0.1 nm, ink does not adhere sufficiently to the ball surface, making it difficult to obtain thick handwriting, and line skips and smears are likely to occur in the handwriting. If the arithmetic mean roughness (Ra) is more than 12 nm, the ball surface is too rough, resulting in high rotational resistance between the ball and the ball seat, which tends to deteriorate the writing feel and further affects writing performance, such as smears, line skips, and uneven lines. Furthermore, an arithmetic mean roughness (Ra) of 0.1 nm or more and 10 nm or less is more preferable because it allows ink to adhere easily to the ball surface, and a value of 2 nm or more and 8 nm or less is even more preferable. Surface roughness can be measured using a Seiko Epson SPI3800N (model number).

[0059] The material used for the balls is not particularly limited, but examples include cemented carbide balls mainly composed of tungsten carbide, metal balls such as stainless steel, ceramic balls such as silicon carbide, silicon nitride, alumina, silica, and zirconia, and ruby ​​balls.

[0060] In addition, materials for ballpoint pen tips include metals such as stainless steel, nickel silver, brass, aluminum bronze, and aluminum, and resins such as polycarbonate, polyacetal, and ABS.However, in consideration of writing feel and workability such as cutting, a tip body made of nickel silver is preferred, and in consideration of wear of the ball seat and stability over time, a tip body made of stainless steel is preferred.

[0061] Example 1 The ink composition for an oil-based ballpoint pen in Example 1 was prepared by weighing out the following ink components in predetermined amounts, heating them to 60°C, and thoroughly stirring them using a Disper stirrer. The specific blending amounts were as follows:

[0062] Example 1 (ink formulation) Colorant (salt-forming dye of acid dye and basic dye) 10.0% by mass Colorant (salt-forming dye of basic dye and organic acid) 10.0% by mass 3-Methoxy-N,N-dimethylpropanamide (boiling point: 215°C) 70.9% by mass Water 5.0% by mass Titanium phosphate (plate-shaped particles, average primary particle diameter: 0.3 μm, average thickness: 0.35 μm, aspect ratio 8.5) 0.1% by mass Acrylic acid (crosslinked polyacrylic acid resin) 0.95% by mass Phosphate ester surfactant (HLB value: 11.5) 1.0% by mass Organic amine (polyoxyethylene alkylamine, HLB value: 15.4) 1.0% by mass Fatty acid ester 1.0% by mass

[0063] Testing and Evaluation The ink compositions (0.27 g) for oil-based ballpoint pens prepared in Example 1 and Comparative Example 1 were filled into oil-based ballpoint pen refills equipped with ink reservoirs (polypropylene) and ballpoint pen tips (ball movement distance in the longitudinal direction: 10 μm, arithmetic mean roughness (Ra) of the ball surface: 6 nm) that rotatably hold a ball with a ball diameter of φ0.5 mm.

[0064] Examples 2 to 18 As shown in Table 1, ink compositions for oil-based ballpoint pens of Examples 2 to 18 were obtained in the same manner as in Example 1, except that the ink components and tip specifications were changed. The table shows the measurement and evaluation results.

[0065] Comparative Examples 1 to 3 As shown in the table, except that the ink components and tip specifications were changed, ink compositions for oil-based ballpoint pens of Comparative Examples 1 to 3 were obtained in the same manner as in Example 1. The measurement and evaluation results are shown in the table. [Table 1] [Table 2]

[0066] In addition, the ink consumption per 100 m was measured by a spiral writing test using an oil-based ballpoint pen, and was 50 mg / 100 m for Example 1, 42 mg / 100 m for Example 11, and 60 mg / 100 m for Example 12. The ink viscosities of Examples 1, 11, and 12 were measured using a Brookfield Viscometer RVDVII+Pro CP-52 spindle at a temperature of 20°C and a shear rate of 0.18 sec. -1 Example 1: ink viscosity = 9000 mPa·s, Example 11: ink viscosity = 20000 mPa·s, Example 12: ink viscosity = 4000 mPa·s.

[0067] Ink leakage prevention test: The pen was left in an environment of 30°C and 85% RH with the tip facing downwards for 7 days, and ink leakage from the tip was confirmed. ◎ No ink droplets at the tip ○ The ink droplet at the tip end is within 1 / 4 of the tapered section △: The ink droplet at the tip end is between 1 / 4 and 1 / 2 of the tapered section ×...The ink droplet at the tip end is more than half the size of the tapered part.

[0068] Writing feel: After leaving the pen at room temperature for 7 days, a sensory test was conducted by handwriting on a writing test sheet to evaluate the writing feel. ◎ Very smooth ○ Smooth △: Slightly less smooth ×Heavy items

[0069] Writing test: A spiral writing test was carried out and evaluated at 20°C on JIS P3201 writing paper, with a writing angle of 70°, a writing load of 200 g, and a writing speed of 4 m / min. 〇···Written out △ Ink is stubborn, but the writing is complete ×...Things I couldn't finish writing

[0070] In Examples 1 to 18, good performance was obtained in the ink leakage suppression test, the writing feel test, and the writing completion test.

[0071] In Comparative Examples 1 to 3, titanium phosphate with an average primary particle size of 5 μm or less was not used, and therefore the ink leakage suppression was poor. In Comparative Example 3, titanium phosphate with an average primary particle size of 7 μm was used, and therefore writing was not completed in the writing test.

[0072] Furthermore, when using a retractable oil-based ballpoint pen (retractable ballpoint pen), such as a knock-type oil-based ballpoint pen or a twist-and-pull type oil-based ballpoint pen, ink leakage suppression performance is one of the most important performance characteristics. Therefore, it is effective to use an ink composition for an oil-based ballpoint pen, such as the present invention, which contains titanium phosphate having an average primary particle size of 5 μm or less, and which can suppress ink leakage from the gap at the writing tip (ink leakage from the gap between the ball and the tip tip) and achieve good ink leakage suppression performance.

[0073] In addition, in this example, for convenience, an oil-based ballpoint pen is exemplified in which an oil-based ballpoint pen refill is housed in which an oil-based ink composition for a writing instrument (ink composition for an oil-based ballpoint pen) is directly housed in the barrel, but the writing instrument of the present invention may also be a direct-fill type writing instrument or oil-based ballpoint pen in which the barrel serves as an ink storage tube and the oil-based ink composition for a writing instrument (ink composition for an oil-based ballpoint pen) is directly housed in the barrel. In addition, in this example, for convenience, a ballpoint pen tip formed by cutting a wire material is exemplified, but a ballpoint pen tip formed by pressing a pipe material may also be used. [Industrial Applicability]

[0074] INDUSTRIAL APPLICABILITY The present invention can be used as a writing instrument (oil-based ballpoint pen), and more specifically, can be widely used as a writing instrument (oil-based ballpoint pen) of a cap type, a retractable type, or the like.

Claims

1. An oil-based ink composition for a writing instrument, comprising a colorant, an organic solvent, and titanium phosphate having an average primary particle size of 5 μm or less.

2. 2. The oil-based ink composition for a writing instrument according to claim 1, wherein the content of the titanium phosphate is 0.01% by mass or more and 2.0% by mass or less based on the total amount of the ink composition.

3. 3. The oil-based ink composition for a writing instrument according to claim 1, further comprising a shear thinning agent.

4. 3. The oil-based ink composition for a writing instrument according to claim 1, wherein the shear thinning agent is acrylic acid.

5. 3. The oil-based ink composition for a writing instrument according to claim 1, wherein the organic solvent is selected from the group consisting of alkylene glycol alkyl ether solvents, amide solvents, and alkylene oxide derivatives of glycerin.

6. 3. The oil-based ink composition for a writing instrument according to claim 1, wherein the organic solvent has a solubility parameter of 8 or more and 13 or less.

7. A writing instrument containing the oil-based ink composition for writing instruments according to claim 1 or 2.

8. A ballpoint pen containing the oil-based ink composition for a writing instrument according to claim 1 or 2.

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