Ink composition and writing instrument

Abstract

The present invention provides an ink composition and writing instrument that allows for proper erasure of handwriting immediately after writing, while allowing the handwriting to adhere to the paper surface relatively quickly. [Solution] An erasable ink composition comprising a colorant, nitrile rubber, and a solvent. The ink composition contains an antioxidant for suppressing the aging of the nitrile rubber in an amount of less than 1.0 phr, or the ink composition contains a radical generator capable of generating radicals that act on the double bonds of the nitrile rubber.

Description

Technical Field

[0001] The present disclosure relates to an ink composition and a writing instrument.

Background Art

[0002] As an erasable ink that can be erased after writing with a writing instrument, a type of erasable ink has been used that erases handwriting on paper by peeling the film forming the handwriting off the paper surface when rubbed with an eraser.

[0003] Patent Document 1 describes an erasable ink composition that includes colored resin particles, a binder resin such as acrylonitrile butadiene rubber (nitrile rubber), and a solvent, and forms a film on the paper surface in which the binder resin encapsulates the colored resin particles when discharged from a writing instrument.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] Incidentally, although an erasable ink composition containing nitrile rubber as a binder resin has erasability, it does not fix on paper for a long period of time (that is, it is erased when rubbed), and thus may be unsuitable for use depending on the application, such as use in official documents, for example.

[0006] In view of the foregoing circumstances, at least one embodiment of the present invention aims to provide an ink composition and a writing instrument in which handwriting can be appropriately erased immediately after writing, while the handwriting easily fixes on the paper surface in a relatively short period of time.

Means for Solving the Problem

[0007] An ink composition according to at least one embodiment of the present invention, An ink composition having erasability, Coloring agents and, Nitrile rubber and Solvent and, It contains, The content of the antioxidant for suppressing the aging of the nitrile rubber is less than 1.0 phr.

[0008] An ink composition according to at least one embodiment of the present invention, An ink composition having erasability, Coloring agents and, Nitrile rubber and Solvent and, A radical generator capable of generating radicals that act on the double bonds of the nitrile rubber, It contains.

[0009] Furthermore, a writing instrument according to at least one embodiment of the present invention is An ink storage section in which the above-mentioned ink composition is contained, A writing section configured to receive the ink composition from the ink storage section, It is equipped with. [Effects of the Invention]

[0010] According to at least one embodiment of the present invention, an ink composition and writing instrument are provided that allow the writing to be properly erased immediately after writing, while the writing is easily fixed to the paper surface in a relatively short period of time. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of one side of a ballpoint pen, which is a writing instrument according to one embodiment. [Figure 2] Figure 1 is a schematic diagram showing the refill that makes up the ballpoint pen. [Figure 3] Figure 2 shows a cross-sectional view of the refill. [Modes for carrying out the invention]

[0012] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements and the like of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the present invention thereto, and are merely illustrative examples.

[0013] (Ink composition) An ink composition according to some embodiments is an erasable ink composition that contains a colorant, a nitrile rubber, and a solvent, wherein the content of an anti-aging agent for suppressing aging of the nitrile rubber is less than 1.0 phr.

[0014] In the above-described embodiment, the ink composition contains nitrile rubber functioning as a binder in addition to the colorant and the solvent, so when the ink composition is discharged from the writing instrument, a film of the ink composition is formed on the paper surface. Therefore, immediately after writing with the writing instrument, the handwriting on the paper surface can be erased by rubbing with an eraser, whereby the film forming the handwriting is peeled off from the paper surface and erased. Here, in the ink composition, the nitrile rubber functioning as a binder resin undergoes oxidative degradation due to cleavage of intramolecular double bonds caused by light or the like. For this reason, nitrile rubber is generally distributed in a state where an anti-aging agent for suppressing such oxidative degradation (aging) is blended. In contrast, in the above-described embodiment, the content of the anti-aging agent is less than 1.0 phr, which is lower than that in typical nitrile rubber. Therefore, the effect of the anti-aging agent on preventing oxidative degradation of the nitrile rubber is suppressed, and the nitrile rubber becomes prone to oxidative degradation. For this reason, the ink composition discharged from the writing instrument and forming a handwriting (film) on the paper surface will be depolymerized into low-molecular-weight substances due to oxidative degradation of the nitrile rubber within a relatively short period of time, penetrate into the interior of the paper surface, and be fixed on the paper surface. Therefore, according to the above-described embodiment, immediately after writing, the handwriting can be appropriately erased, and the handwriting (ink composition) can be fixed on the paper surface in a relatively short period of time.

[0015] According to some embodiments, the ink composition is an erasable ink composition, comprising: a colorant; nitrile rubber; a solvent; and a radical generator capable of generating radicals that act on double bonds of the nitrile rubber.

[0016] In the above embodiment, since the ink composition contains nitrile rubber functioning as a binder in addition to the colorant and the solvent, when the ink composition is ejected from the writing instrument, a film of the ink composition is formed on the paper surface. Therefore, immediately after writing with the writing instrument, by rubbing the handwriting on the paper surface with an eraser, the film forming the handwriting can be peeled off from the paper surface and erased. In addition, the ink composition according to the above embodiment contains a radical generator capable of generating radicals that act on double bonds of the nitrile rubber, whereby radicals generated from the radical generator act on the double bonds of the nitrile rubber to promote oxidative degradation of the nitrile rubber. For this reason, the ink composition ejected from the writing instrument that forms handwriting (a film) on the paper surface is depolymerized into low-molecular-weight compounds due to oxidative degradation of the nitrile rubber within a relatively short period of time, penetrates into the paper, and is fixed on the paper surface. Therefore, according to the above embodiment, the handwriting can be appropriately erased immediately after being formed, and the handwriting (the ink composition) can be fixed on the paper surface within a relatively short period of time.

[0017] The above ink composition contains a particulate colorant. The colorant may be colored resin particles. The colored resin particles may be particles in which a pigment as a colorant is dispersed in a resin material, or particles obtained by coating a pigment as a colorant with a resin material.

[0018] In some embodiments, the average particle diameter of the colorant is 5 μm or more and 15 μm or less. Here, the measurement method for the average particle diameter of the colored resin particles uses dynamic light scattering for the representative diameter, the particle size distribution is expressed on a volume basis, and the average particle diameter is calculated as the median diameter.

[0019] If the average particle size of the colorant contained in the ink composition is 5 μm or larger, the ink composition dispensed onto the paper surface is less likely to penetrate between the paper fibers and less likely to settle on the paper surface. Therefore, the dried ink composition on the paper surface can be easily peeled off and erased with an eraser. Furthermore, if the average particle size of the colorant contained in the ink composition is 15 μm or smaller, the density of the writing does not tend to decrease, resulting in good writing quality. Thus, according to the above embodiment, it is possible to achieve both good writing quality and erasability, and the writing (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0020] Colored resin particles can be produced, for example, by a melt-kneading method or a suspension polymerization method. In the melt-kneading method, colored resin particles are obtained by blending pigment components into a resin material and then pulverizing it after melt-kneading. In the suspension polymerization method, colored resin particles are obtained by mixing and dispersing pigment components in a polymerizable monomer and then carrying out suspension polymerization in an aqueous medium. The colored resin particles may be hollow.

[0021] The resin constituting the colored resin particles may be, for example, an acrylic resin or a urethane resin.

[0022] The pigments constituting the colored resin particles may include, for example, carbon black, azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, indigo pigments, dioxazine pigments, perylene pigments, perinone pigments, isoindolinone pigments, isoindoline pigments, metal complex pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, or titanium dioxide pigments.

[0023] The content of colored resin particles in the ink composition may be 10% by weight or more and 22% by weight or less. By having the content of colored resin particles within the above range, an ink composition with good ink density, ejection properties, and erasability can be obtained.

[0024] Nitrile rubber (NBR: nitril-butadiene rubber) is a copolymer of acrylonitrile and butadiene (acrylonitrile-butadiene rubber) and functions as a binder that binds the components in the ink composition. As a result, when the ink composition is dispensed from the writing instrument, a film of the ink composition is formed on the paper surface. Therefore, the film that forms the writing can be peeled off the paper surface and erased by rubbing the writing with an eraser.

[0025] The nitrile rubber content in the ink composition may be 19% by weight or more and 27% by weight or less. If the binder resin content is 19% by weight or more, the binding between colored resin particles will not become too low, and a decrease in the erasability of the writing formed from the ink composition can be suppressed. On the other hand, if the binder resin content is 27% by weight or less, the solid content concentration in the ink composition will not become too high, so the viscosity of the ink composition will not become too high, and a deterioration in discharge performance can be suppressed.

[0026] Nitrile rubber is usually available in the form of an emulsion containing solid nitrile rubber. Commercially available nitrile rubber emulsions often contain 1.0 phr or more of an antioxidant to suppress oxidative degradation (aging) of the nitrile rubber.

[0027] Examples of the aforementioned anti-aging agents include phenolic and amine-based anti-aging agents. Examples of phenolic anti-aging agents include 4,4'-butylidenebis(6-tert-butyl-m-cresol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,2'-methylenebis(6-tert-butyl-4-ethylphenol), 4,4'-thiobis(6-tert-butyl-m-cresol), or 2,4-bis(octylthiomethyl)-6-methylphenol. Examples of amine-based antioxidants include N-isopropyl-N'-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine, poly(2,2,4-trimethyl-1,2-dihydroquinoline), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline, 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, nickel(II) dibutyldithiocarbamate, or tris(nonylphenyl)phosphate. One or more of these antioxidants may be included in the ink composition.

[0028] In some embodiments, as described above, the content of the anti-aging agent in the ink composition is less than 1.0 phr. In some embodiments, the content of the anti-aging agent in the ink composition may be less than 0.5 phr. In some embodiments, the ink composition may not contain an anti-aging agent (or the content of the anti-aging agent in the ink composition may be 0.0 phr or less). Note that phr (parts per hundred rubber) is a unit that represents the weight of a component per 100 units of rubber weight.

[0029] If the amount of antioxidant is less than 1.0 phr, less than 0.5 phr, or 0.0 phr or less, the amount of antioxidant is lower than that of typical nitrile rubber. As a result, the effect of the antioxidant in preventing oxidative degradation of the nitrile rubber is suppressed, and the nitrile rubber becomes more susceptible to oxidative degradation. Consequently, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes smaller in molecular weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and becomes fixed to the paper surface.

[0030] The radical-generating agent contained in the ink composition is a substance that can generate radicals that act on the double bonds of nitrile rubber when activated by, for example, light (ultraviolet light, etc.) or heat. The radical-generating agent may also be one that is commonly used as a polymerization initiator.

[0031] When an ink composition contains a radical generator, the radicals generated by the radical generator act on the double bonds of the nitrile rubber, accelerating the oxidative degradation of the nitrile rubber. As a result, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes smaller in molecular weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and becomes easier to fix to the paper surface.

[0032] Examples of polymerization initiators include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 2-hydroxy-2-methylpropiophenone, oligomer of 2-hydroxy-1-(4-isopropenylphenyl)-2-methylpropan-1-one, mesityl(phenyl)ketone, 4-methylbenzophenone, ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate, 2-hydroxy-2-methylpropiophenone, and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. Examples include sid, 2,2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-(dimethylamino)-1-(4-morpholinophenyl)-2-benzyl-1-butanone, and 1-[4-(phenylthio)phenyl]octane-1,2-dione=2-(O-benzoyloxime). Product names include IM-TT01 (manufactured by KSM Corporation), TPO-L (manufactured by IGM Resins BV), Omnirad1173 (manufactured by IGM Resins BV), and Omnirad819 (manufactured by IGM Resins BV). These may be used individually or in combination of two or more types.

[0033] The radical generating agent content is preferably 0.1% to 10.0% by weight, more preferably 0.1% to 5.0% by weight, and even more preferably 0.1% to 2.0% by weight, of the total amount of the ink composition.

[0034] If the radical generator content in the ink composition is 0.1% by weight or more, the radicals generated by the radical generator can more effectively promote the oxidative degradation of the nitrile rubber. If the radical generator content in the ink composition is 10.0% by weight or less, 5.0% by weight or less, or 2.0% by weight or less, the viscosity of the ink composition will not become excessively high, resulting in good dispensing performance when applied to a writing instrument. Therefore, if the radical generator content in the ink composition is within the above range, it is possible to achieve good ink dispensing performance while promoting the oxidative degradation of the nitrile rubber, thereby fixing the writing (ink composition) to the paper surface in a relatively short period of time.

[0035] Some ink compositions according to certain embodiments may contain, in addition to a radical generator, a sensitizer to promote the generation of radicals in the radical generator. In this case, since the sensitizer promotes the generation of radicals in the radical generator, the action of the radicals generated from the radical generator on the double bonds of the nitrile rubber can be promoted, and the oxidative degradation of the nitrile rubber can be promoted more effectively.

[0036] Examples of photosensitizers include benzoxazole photosensitizers, pyrazoline photosensitizers, coumarin photosensitizers, 2,2-bis[[(3-mercaptopropionyl)oxy]methyl]trimethylene bis[3-mercaptopropionate], 3-mercaptopropionate of dipentaerythritol, methoxybutyl-β-mercaptopropionate, pentaerythritol tetrakis(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptobutyrate), 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinan-2,4,6-trione, 1,4-bis(3-mercaptobutyryloxy)butane, and polyfunctional thiols. These may be used individually or in combination of two or more types.

[0037] The sensitizer content is preferably 0.1% by weight or more and 10.0% by weight or less, more preferably 0.1% by weight or more and 5.0% by weight or less, and even more preferably 0.1% by weight or more and 2.0% by weight or less, based on the total amount of the ink composition.

[0038] If the sensitizer content in the ink composition is 0.1% by weight or more, the sensitizer can effectively promote the generation of radicals in the radical generator, thereby more effectively accelerating the oxidative degradation of the nitrile rubber. If the sensitizer content in the ink composition is 10.0% by weight or less, 5.0% by weight or less, or 2.0% by weight or less, the viscosity of the ink composition will not become excessively high, resulting in good dispensing performance when applied to a writing instrument. Therefore, if the sensitizer content in the ink composition is within the above range, it is possible to achieve good ink dispensing performance while accelerating the oxidative degradation of the nitrile rubber, thereby fixing the writing (ink composition) to the paper surface in a relatively short period of time.

[0039] The ink composition may contain a high-boiling point solvent as a solvent to impart cap-off properties to the ink composition. Examples of high-boiling point solvents that can be used include glycerin, ethylene glycol, diethylene glycol, and propylene glycol.

[0040] In one embodiment, the ink composition may contain ethylene glycol as a high-boiling point solvent. In this case, the stability of the ink composition in low-temperature environments can be improved.

[0041] The content of the high-boiling point solvent in the ink composition may be 3.0% by weight or more and 15.0% by weight or less. If the content of the high-boiling point solvent in the ink composition is within the above range, the drying properties of the writing will not decrease excessively, and the ink composition will have appropriate cap-off properties.

[0042] The ink composition may contain a dispersant to improve the dispersibility of components in the ink composition, such as colorants. The dispersant may contain a surfactant that has affinity for the colorant. The surfactant may be a nonionic surfactant. The content of the dispersant in the ink composition may be 0.5% by weight or more and 3.0% by weight or less.

[0043] Some ink compositions according to certain embodiments may further contain various additives.

[0044] In some embodiments, the ink composition may contain a preservative. The preservative may include, for example, zinc pyrithione. The amount of preservative in the ink composition may be 0.04% by weight or more and 0.5% by weight or less.

[0045] In some embodiments, the ink composition may contain a thickening agent to adjust the viscosity of the ink composition. The thickening agent may include, for example, polysaccharides (such as gum arabic, tragacanth gum, or xanthan gum), proteins (such as casein or gelatin), or cellulose derivatives (such as hydroxyethylcellulose). The content of the thickening agent in the ink composition may be 0.05% by weight or more and 2.0% by weight or less.

[0046] (Writing instrument composition) Next, a writing instrument according to several embodiments will be described. A writing instrument according to several embodiments comprises an ink storage section in which the above-mentioned ink composition is contained, and a writing section configured to receive the ink composition from the ink storage section.

[0047] In the following description with reference to the figures, the writing instrument is a ballpoint pen, but in some embodiments, the writing instrument may be a writing instrument other than a ballpoint pen (for example, a felt-tip pen, marker, or brush pen or other marking pen).

[0048] Figure 1 is a schematic one-sided cross-sectional view of a ballpoint pen, which is a writing instrument according to one embodiment. Figure 2 is a schematic diagram showing the refill that makes up the ballpoint pen shown in Figure 1, and Figure 3 is a cross-sectional view of the refill shown in Figure 2.

[0049] The ballpoint pen S (writing instrument) shown in Figure 1 comprises a barrel including a front barrel 5 and a rear barrel 6, and a refill R housed in the barrel. The front barrel 5 and the rear barrel 6 are fastened together by screws.

[0050] A cap 1 is attached to the front barrel 5, covering the tip 11 of the refill R (see Figures 2 and 3). A crown 2 is fitted onto the cap 1, and the clip 3 is held in place by the fitting of the cap 1 and the crown 2, preventing it from coming off.

[0051] A packing 4 is fitted to the inner top surface of the cap 1. In the illustrated example, the packing 4 is disc-shaped. Also, in the illustrated example, the packing 4 is positioned coaxially with the axial direction of the cap 1. When the cap 1 is fitted and inserted onto the front shaft 5, the packing 4 positioned on the inner top surface of the cap 1 deforms and makes contact with the tip side of the tip 11. This keeps the tip of the tip 11 in a sealed state.

[0052] As shown in Figures 2 and 3, the refill R includes a pipe 13 (ink reservoir) in which ink is contained, and a holder 12 and a tip 11 (writing part) attached to the end of the pipe 13. The holder 12 may be press-fitted into the pipe 13. The tip 11 may be press-fitted into the holder 12. The tip 11 is provided with a ball located at its tip and held rotatably.

[0053] The inside of the pipe 13 is filled with ink 14 (ink composition). Furthermore, grease 15 and a float 16 are inserted behind the ink 14 inside the pipe 13.

[0054] The ink 14 contained in the pipe 13 is supplied to the tip 11 through a passage formed inside the holder 12. When writing with the ballpoint pen S, the ink 14 is ejected onto the paper surface through the ball at the tip of the tip 11, forming a line on the paper.

[0055] Furthermore, the ink composition according to the above embodiment contains nitrile rubber to provide erasable functionality, and at the same time, the oxidative degradation of the nitrile rubber is accelerated compared to conventional methods in order to fix the writing marks to the paper surface after writing. In this regard, as described above, when the cap 1 is attached, the tip of the tip 11 is kept in a sealed state by the packing 4. Therefore, when the writing instrument is not in use (during storage, etc.), the ink composition contained inside the writing instrument is less likely to come into contact with ultraviolet rays and oxygen in the air, thus suppressing the oxidative degradation of the nitrile rubber. Alternatively, by using a material that can block light (ultraviolet rays, etc.) as the material forming the pipe 13 and barrel of the refill R in which the ink composition is contained, the oxidative degradation of the nitrile rubber in the ink composition when the writing instrument is not in use (during storage, etc.) can be suppressed. [Examples]

[0056] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0057] As shown in Table 1, ballpoint pens containing the ink compositions of Examples 1-8 and Comparative Example 1 were prepared. The materials used are as follows. Table 1 also shows the content (weight %) of each material in the ink composition.

[0058] In the examples, the average particle diameter was measured using dynamic light scattering for the representative diameter, the particle size distribution was expressed on a volume basis, and the average particle diameter was calculated using the median diameter.

[0059] <Coloring agent> Colored resin particles (1):

[0060] <Surfactants> Nonionic surfactant (1): Black colored resin particles, average particle size 6 μm

[0061] <Nitrile rubber> NBR Emulsion (1): Aqueous dispersion of acrylonitrile butadiene rubber, solids content 48.5%, phenolic antioxidant content relative to nitrile rubber 1.0 phr NBR Emulsion (2): Aqueous dispersion of acrylonitrile butadiene rubber, solids content 48.5%, phenolic antioxidant content relative to nitrile rubber 0 phr

[0062] <Radical Generating Agent> Radical generator (1): Ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate

[0063] <Sensitizer> Sensitizer (1): Benzoxazole photosensitizer Sensitizer (2): Polyfunctional thiol sensitizer

[0064] Zinc pyrithione Ethylene glycol Propylene glycol Xanthan gum Water: Ion-exchanged water

[0065] The procedure for preparing the ink composition is as follows: A dispersion was prepared by stirring the colorant, surfactant, and water listed in Table 1 using a propeller stirrer. Other materials, including nitrile rubber, listed in Table 1 were stirred using a propeller stirrer, and then the above dispersion was added and stirred using a propeller stirrer to obtain the ink composition.

[0066] The following tests and evaluations were performed on the ink compositions of each example and comparative example. The evaluation results are shown in Table 1.

[0067] (Handwriting retention) Each ink was filled into a ballpoint pen refill with a φ0.8 tip, and ballpoint pen writing was obtained by writing on high-quality paper. For the purpose of irradiating the aforementioned writing with light, a xenon arc lamp was used with a relative humidity of 50±5% and an irradiance of 50 W / m². 2 The samples were exposed to a specific environment (300-400 nm) for a set period of time. Afterward, the handwriting was rubbed five times back and forth with an eraser under a 500 gf load, and it was observed whether the handwriting could be erased. The exposure time required until the handwriting could no longer be erased by rubbing (i.e., until the handwriting became fixed to the paper) was counted. The evaluation criteria are as follows: A+: Less than 5 hours A: 5 hours or more but less than 10 hours B: 10 hours or more but less than 15 hours C: 15 hours or more

[0068] (Ink ejection properties) Each ink composition was filled into a ballpoint pen refill with a φ0.8mm ballpoint tip, and the ink ejection performance was checked when writing on high-quality paper at writing speeds of 7cm / sec and 10cm / sec. The evaluation criteria are as follows. A+: Regardless of whether writing speed was 7cm / sec or 10cm / sec, the ink flow was extremely stable with no smudging. A: When writing at 7cm / sec, the ink flow was stable and the writing did not skip or fade. Even when writing at a speed of 7cm / sec, the ink flow was inconsistent, resulting in streaking and uneven ink release.

[0069] [Table 1]

[0070] The ink compositions of Examples 1-6 and 8 contain a colorant, nitrile rubber, and a solvent, and contain less than 1.0 phr of an anti-aging agent to suppress the aging of the nitrile rubber.

[0071] These ink compositions contain nitrile rubber in addition to colorants and solvents. Therefore, when written on with a writing instrument, a film of the ink composition is formed on the paper surface. Immediately after writing, the film forming the writing mark could be removed by rubbing the paper with an eraser. Furthermore, these ink compositions contain less than 1.0 phr of antioxidant, or more specifically, no antioxidant at all. Therefore, because the antioxidant content is lower than that of typical nitrile rubber, the effect of the antioxidant in preventing oxidative degradation of the nitrile rubber is suppressed, and as a result, the nitrile rubber is more susceptible to oxidative degradation. Consequently, it is thought that the ink composition, which was dispensed from the writing instrument and formed a writing mark (film) on the paper surface, became low-molecular-weight due to oxidative degradation of the nitrile rubber in a relatively short period of time, penetrated into the paper surface, and became fixed to the paper surface.

[0072] Furthermore, the ink compositions of Examples 2 to 8 contain a colorant, nitrile rubber, a solvent, and a radical generator capable of generating radicals that act on the double bonds of the nitrile rubber.

[0073] These ink compositions contain nitrile rubber in addition to colorants and solvents. Therefore, when written on with a writing instrument, a film of the ink composition is formed on the paper surface. Immediately after writing, the film forming the writing can be removed by rubbing the paper with an eraser. Furthermore, these ink compositions contain a radical generator capable of generating radicals that act on the double bonds of nitrile rubber. Therefore, it is thought that the radicals generated from the radical generator act on the double bonds of nitrile rubber, accelerating the oxidative degradation of the nitrile rubber. Consequently, it is thought that the ink composition, which was dispensed from the writing instrument and formed a writing mark (film) on the paper surface, became low-molecular-weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrated into the paper surface, and became fixed to the paper surface.

[0074] Therefore, it is considered that the ink compositions of Examples 1 to 8 have the effect of allowing the writing to be properly erased immediately after writing, and fixing the writing (ink composition) to the paper surface in a relatively short period of time.

[0075] In contrast, the ink composition of Comparative Example 1 contains a colorant, nitrile rubber, and a solvent, but contains an antioxidant to suppress the aging of the nitrile rubber of 1.0 phr or more, and does not contain a radical generator capable of generating radicals that act on the double bonds of the nitrile rubber.

[0076] The ink composition of Comparative Example 1 contains nitrile rubber in addition to a colorant and solvent. Therefore, when written on with a writing instrument, a film of the ink composition is formed on the paper surface. Immediately after writing, the film forming the writing mark can be removed by rubbing the paper with an eraser. On the other hand, the ink composition of Comparative Example 1 contains an antioxidant of 1.0 phr or more and does not contain a radical generator that promotes the oxidative degradation of nitrile rubber. Therefore, it is thought that the oxidative degradation of nitrile rubber was suppressed. As a result, the nitrile rubber in the ink composition that was dispensed from the writing instrument and formed a writing mark (film) on the paper surface did not undergo oxidative degradation and become smaller in molecular weight, and did not penetrate into the paper surface. Therefore, it is thought that the writing mark did not adhere to the paper surface.

[0077] Furthermore, the ink compositions of Examples 2 to 7 contain a radical generator in an amount of 0.1% to 10.0% by weight. Therefore, by promoting the oxidative degradation of the nitrile rubber contained in the ink composition that forms the writing, the writing can be fixed to the paper surface in a relatively short period of time. Additionally, the viscosity of the ink composition does not become excessively high, resulting in particularly good dispensing performance when applied to a writing instrument.

[0078] The contents described in each of the above embodiments can be understood, for example, as follows:

[0079] [1] An ink composition according to at least one embodiment of the present invention, An ink composition having erasability, Coloring agents and, Nitrile rubber and Solvent and, It contains, The content of the antioxidant for suppressing the aging of the nitrile rubber is less than 1.0 phr.

[0080] In the configuration described in [1] above, the ink composition contains a nitrile rubber that functions as a binder in addition to a colorant and a solvent, so when the ink composition is dispensed from the writing instrument, a film of the ink composition is formed on the paper surface. Therefore, immediately after writing with the writing instrument, the film that forms the writing can be peeled off the paper surface and erased by rubbing the writing on the paper surface with an eraser. In this ink composition, the nitrile rubber, which functions as a binder resin, undergoes oxidative degradation due to the cleavage of intramolecular double bonds caused by light, etc. For this reason, nitrile rubber is usually distributed with an antioxidant added to suppress such oxidative degradation (aging). In contrast, in the composition described in [1] above, the amount of antioxidant is less than 1.0 phr, and since the amount of antioxidant is lower than that of typical nitrile rubber, the effect of the antioxidant in preventing oxidative degradation of the nitrile rubber is suppressed, making the nitrile rubber more susceptible to oxidative degradation. As a result, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes low-molecular-weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and fixes to the paper surface. Therefore, according to the configuration described in [1] above, the handwriting can be properly erased immediately after writing, and the handwriting (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0081] [2] In some embodiments, in the configuration of [1] above, The aforementioned ink composition does not contain the aforementioned anti-aging agent.

[0082] In the configuration described in [2] above, since the ink composition does not contain an anti-aging agent, the effect of the anti-aging agent in preventing oxidative degradation of the nitrile rubber is more effectively suppressed, making the nitrile rubber more susceptible to oxidative degradation. As a result, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes smaller in molecular weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and easily adheres to the paper surface. Therefore, with the configuration described in [2] above, the mark can be properly erased immediately after writing, and the mark (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0083] [3] In some embodiments, in the configuration of [1] or [2] above, The aforementioned ink composition, The material further contains a radical generating agent capable of generating radicals that act on the double bonds of the nitrile rubber.

[0084] According to the configuration described in [3] above, the ink composition contains a radical generator capable of generating radicals that act on the double bonds of the nitrile rubber. The radicals generated from the radical generator act on the double bonds of the nitrile rubber, thereby accelerating the oxidative degradation of the nitrile rubber. As a result, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes smaller in molecular weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and easily adheres to the paper surface. Therefore, according to the configuration described in [3] above, the mark can be properly erased immediately after writing, and the mark (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0085] [4] An ink composition according to at least one embodiment of the present invention, An ink composition having erasability, Coloring agents and, Nitrile rubber and Solvent and, A radical generator capable of generating radicals that act on the double bonds of the nitrile rubber, It contains.

[0086] In the configuration described in [4] above, the ink composition contains a nitrile rubber that functions as a binder in addition to a colorant and a solvent, so when the ink composition is dispensed from the writing instrument, a film of the ink composition is formed on the paper surface. Therefore, immediately after writing with the writing instrument, the film that forms the writing can be peeled off the paper surface and erased by rubbing the writing on the paper surface with an eraser. Here, the nitrile rubber, which functions as a binder resin in the ink composition, undergoes oxidative degradation when its intramolecular double bonds are broken by light, etc. For this reason, nitrile rubber is usually distributed with an anti-aging agent added to suppress such oxidative degradation (aging). The ink composition described in [4] above contains a radical generator capable of generating radicals that act on the double bonds of the nitrile rubber. Therefore, the radicals generated from the radical generator act on the double bonds of the nitrile rubber, accelerating the oxidative degradation of the nitrile rubber. As a result, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes low-molecular-weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and fixes to the paper surface. Therefore, according to the configuration described in [4] above, the handwriting can be properly erased immediately after it is formed, and the handwriting (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0087] [5] In some embodiments, in the configuration of [3] or [4] above, The radical generator contains a sensitizer for promoting the generation of radicals.

[0088] According to the configuration described in [5] above, the ink composition contains a sensitizer that can promote the generation of radicals in the radical generator, thereby promoting the action of radicals generated from the radical generator on the double bonds of the nitrile rubber, and more effectively accelerating the oxidative degradation of the nitrile rubber. As a result, the ink composition, which is dispensed from the writing instrument and forms a mark (film) on the paper surface, becomes low-molecular-weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and fixes to the paper surface. Therefore, according to the configuration described in [5] above, the mark can be properly erased immediately after writing, and the mark (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0089] [6] In some embodiments, in any of the configurations described in [1] to [5] above, The average particle size of the coloring agent is 5 μm or more and 15 μm or less.

[0090] In the configuration described in [6] above, the average particle size of the colorant contained in the ink composition is 5 μm or larger, so the ink composition dispensed onto the paper surface does not easily get into the fibers of the paper and does not easily settle on the paper surface. For this reason, the ink composition that has dried on the paper surface can be easily peeled off and erased with an eraser. In addition, in the configuration described in [6] above, the average particle size of the colorant contained in the ink composition is 15 μm or smaller, so the density of the writing does not easily decrease, and for this reason, the quality of the writing is good. Thus, with the configuration described in [6] above, it is possible to achieve both good writing quality and erasability, and the writing (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0091] [7] A writing instrument (e.g., a ballpoint pen S) according to at least one embodiment of the present invention is An ink storage section (e.g., pipe 13) in which the ink composition described in any one of the above items [1] to [6] is contained, A writing section (e.g., tip 11) configured to receive the ink composition from the ink storage section, It is equipped with.

[0092] In the configuration described in [7] above, the ink composition contains a nitrile rubber that functions as a binder in addition to a colorant and a solvent, so when the ink composition is dispensed from the writing instrument, a film of the ink composition is formed on the paper surface. Therefore, immediately after writing with the writing instrument, the film that forms the writing can be peeled off the paper surface and erased by rubbing the writing on the paper surface with an eraser. In this context, nitrile rubber, which functions as a binder resin in ink compositions, undergoes oxidative degradation due to the cleavage of intramolecular double bonds caused by light, etc. Therefore, nitrile rubber is typically distributed with an anti-aging agent added to suppress this oxidative degradation (aging). In contrast, in the configuration described in [7] above, the amount of antioxidant is less than 1.0 phr, and since the amount of antioxidant is lower than that of typical nitrile rubber, the effect of the antioxidant in preventing oxidative degradation of nitrile rubber is suppressed, making the nitrile rubber more susceptible to oxidative degradation. Alternatively, the ink composition described in [7] above contains a radical generator capable of generating radicals that act on the double bonds of nitrile rubber, and the radicals generated from the radical generator act on the double bonds of nitrile rubber, thereby accelerating the oxidative degradation of the nitrile rubber. Therefore, the ink composition, which is ejected from the writing instrument and forms a mark (film) on the paper surface, becomes smaller in molecular weight due to the oxidative degradation of the nitrile rubber in a relatively short period of time, penetrates into the paper surface, and fixes to the paper surface. Therefore, according to the configuration described in [7] above, the handwriting can be properly erased immediately after writing, and the handwriting (ink composition) can be fixed to the paper surface in a relatively short period of time.

[0093] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0094] In this specification, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" shall not only describe such arrangements strictly, but also describe states of relative displacement with tolerances or angles or distances that allow for the same function to be achieved. For example, expressions such as "identical," "equal," and "homogeneous" that describe things being in an equal state not only describe a state of being strictly equal, but also describe a state in which there is a tolerance or a difference that is sufficient to achieve the same function. Furthermore, in this specification, expressions describing shapes such as quadrilaterals and cylindrical shapes shall not only represent geometrically precise quadrilaterals and cylindrical shapes, but also shapes that include uneven surfaces, chamfered surfaces, etc., to the extent that the same effect can be achieved. Furthermore, in this specification, the expressions “equipment,” “includes,” or “possess” of a component are not exclusive expressions that exclude the existence of other components. [Explanation of Symbols]

[0095] 1 cap 2 crown 3 clips 4. Packing 5 Front axle 6 rear axle 11 chips 12 holders 13 pipes 14 Ink 15 Grease 16 floats R Refill S Ballpoint Pen

Claims

1. An ink composition having erasability, Coloring agents and, Nitrile rubber and Solvent and, It contains, The content of the antioxidant for suppressing the aging of the nitrile rubber is less than 1.0 phr. Ink composition.

2. Does not contain the aforementioned anti-aging agent. The ink composition according to claim 1.

3. The present invention further contains a radical generator capable of generating radicals that act on the double bonds of the nitrile rubber. The ink composition according to claim 1.

4. An ink composition having erasability, Coloring agents and, Nitrile rubber and Solvent and, A radical generator capable of generating radicals that act on the double bonds of the nitrile rubber, Contains Ink composition.

5. The radical generator contains a sensitizer for promoting the generation of radicals in the aforementioned radical generator. The ink composition according to claim 3 or 4.

6. The average particle size of the coloring agent is 5 μm or more and 15 μm or less. The ink composition according to claim 1 or 4.

7. An ink storage section in which the ink composition according to claim 1 or 4 is contained, A writing section configured to receive the ink composition from the ink storage section, A writing instrument equipped with [a specific feature].

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