Ink composition and writing instrument

Abstract

To provide an erasable ink composition and writing instrument which have good quality and erasability of handwriting even when viscosity is low, and have good discharge property with time.SOLUTION: An ink composition having erasability contains colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less, a binder resin, a solvent, and polyoxyethylene hardened castor oil, wherein a difference between specific gravity of the colored resin particles and specific gravity of the total component other than the colored resin particles is 0.07 or more and 0.7 or less, and a film in which the binder resin wraps the colored resin particles is formed on a discharged paper surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to ink compositions and writing instruments. [Background technology]

[0002] Ink compositions have been proposed that allow handwriting to be erased with an eraser or the like (that is, have erasability).

[0003] For example, Patent Document 1 discloses a writing instrument eraser-erasable aqueous ink composition that uses pigment particles (colored resin particles) with an average particle size in the range of 2 to 30 μm as a colorant. This ink composition contains a polymer flocculant to create a bridge structure between the pigment particles, preventing them from settling on the paper surface or separating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-143381 Summary of the Invention [Problem to be solved by the invention]

[0005] Ink compositions for marking pens generally have lower viscosities than ink compositions for ballpoint pens, etc. In erasable ink compositions containing colored resin particles (colorants) with a relatively large average particle size, the colored resin particles tend to settle in the ink composition if the viscosity of the ink composition is low due to the large specific gravity of the colored resin particles. When such an ink composition is used in a marking pen, the colored resin particles that have settled in the ink composition become viscous over time, which can reduce the ejection performance from the nib of the writing instrument and deteriorate the writing performance.

[0006] In view of the above circumstances, at least one embodiment of the present invention aims to provide an erasable ink composition and writing implement that have good handwriting quality and erasability even when the viscosity is low, and that also have good ejection properties over time. [Means for solving the problem]

[0007] The ink composition according to at least one embodiment of the present invention comprises: An erasable ink composition, colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less; A binder resin, a solvent; Polyoxyethylene hydrogenated castor oil, Contains the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less; On the surface of the paper onto which the ink is discharged, the binder resin envelops the colored resin particles to form a film.

[0008] Furthermore, a writing instrument according to at least one embodiment of the present invention comprises: an ink reservoir in which the ink composition is stored; a writing unit configured to receive the ink composition from the ink reservoir; Equipped with. [Effects of the Invention]

[0009] According to at least one embodiment of the present invention, there is provided an erasable ink composition and writing implement that have good writing quality and erasability even when the viscosity is low, and that also have good jetting properties over time. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a writing implement (marking pen) according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present invention.

[0012] (Ink composition) The ink composition according to some embodiments is an erasable ink composition, and contains colored resin particles having an average particle size of 5 μm or more and 15 μm or less, a binder resin, a solvent, and polyoxyethylene hydrogenated castor oil, wherein the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less. When the ink composition is ejected onto a paper surface, the binder resin envelops the colored resin particles to form a film.

[0013] The ink composition having the above-described configuration contains colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less, and a binder resin, and the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less, so that a writing instrument with good handwriting quality and erasability can be obtained. That is, since the average particle diameter of the colored resin particles in the ink composition is 5 μm or more, the ink composition ejected onto the paper surface is less likely to penetrate between the paper fibers and settle on the paper surface. Therefore, the ink composition that has dried on the paper surface can be easily removed by peeling it off with an eraser. Furthermore, since the average particle diameter of the colored resin particles in the ink composition is 15 μm or less, the handwriting density is less likely to decrease, resulting in good handwriting quality. Furthermore, since the ink composition contains a binder resin with adhesive properties, a film in which the colored resin particles are encapsulated by the binder resin is formed on the paper surface onto which the ink composition has been ejected. Therefore, the ink composition is less likely to penetrate between the paper fibers and settle on the paper surface, so the ink composition that has dried on the paper surface can be easily removed by peeling it off with an eraser. Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.07 or more, so the content of polyoxyethylene hydrogenated castor oil is not too high and the viscosity of the ink composition is not too high, thereby preventing deterioration of the ink composition's ejection properties in a writing instrument. Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.7 or less, so the specific gravity of the colored resin particles is not too high relatively, preventing the colored resin particles from settling on the paper surface before forming a film on the paper surface onto which the ink composition has been ejected. Therefore, when erasing handwriting made with the ink composition, it is difficult for unerased marks to remain. Furthermore, since the ink composition having the above-mentioned configuration contains polyoxyethylene hydrogenated castor oil, the polyoxyethylene hydrogenated castor oil is adsorbed onto the surfaces of the colored resin particles, thereby suppressing adhesion and aggregation of the colored resin particles, and improving the redispersibility of the colored resin particles. Therefore, even if the colored resin particles settle in the ink composition, the sediment is less likely to become viscous, and deterioration of the ejection properties over time can be suppressed. As described above, according to the ink composition having the above-mentioned constitution, it is possible to obtain an erasable ink composition that has good writing quality and erasability, and also has good dischargeability over time, even if it has a low viscosity.

[0014] The average particle size of the colored resin particles described above is measured by dynamic light scattering for the representative diameter, the particle size distribution is expressed in volumetric conversion, and the average particle size is calculated as the median diameter.

[0015] The colored resin particles contained in the ink composition may be particles in which a pigment serving as a colorant is dispersed in a resin material, or particles in which a pigment serving as a colorant is coated with a resin material. The former colored resin particles can be produced, for example, by a melt-kneading method or a suspension polymerization method. In the melt-kneading method, a pigment component is blended with a resin material, and the resulting mixture is melt-kneaded and then pulverized to obtain colored resin particles. In the suspension polymerization method, a pigment component is mixed and dispersed in a polymerizable monomer, and the resulting mixture is subjected to suspension polymerization in an aqueous medium to obtain colored resin particles. The colored resin particles may be hollow.

[0016] The resin constituting the colored resin particles may be, for example, an acrylic resin or a urethane resin.

[0017] The pigment constituting the colored resin particles may include, for example, carbon black, an azo pigment, a phthalocyanine pigment, an anthraquinone pigment, a quinacridone pigment, an indigo pigment, a dioxazine pigment, a perylene pigment, a perinone pigment, an isoindolinone pigment, an isoindoline pigment, a metal complex pigment, a quinophthalone pigment, a diketopyrrolopyrrole pigment, or a titanium oxide pigment.

[0018] The content of the colored resin particles in the ink composition may be 10% by weight or more and 22% by weight or less. When the content of the colored resin particles is within the above range, an ink composition having good writing density, ejection properties, and erasability can be obtained.

[0019] The binder resin contained in the ink composition may be, for example, acrylonitrile butadiene rubber (NBR), styrene butadiene rubber, or urethane rubber.

[0020] In one embodiment, the binder resin may contain acrylonitrile butadiene rubber (NBR). In this case, a good balance can be maintained between the fixability of the ejected ink composition to the paper surface and the erasability of handwriting made with the ink composition using an erasing member. When the ink composition has good fixability to the paper surface, the paper surface is less likely to be contaminated even when handwriting on the paper surface is rubbed with a finger.

[0021] The content of the binder resin in the ink composition may be 19% by weight or more and 27% by weight or less. If the content of the binder resin is 19% by weight or more, the binding strength between the colored resin particles will not be too low, and a decrease in the erasability of the handwriting formed from the ink composition can be suppressed. On the other hand, if the content of the binder resin is 27% by weight or less, the solids concentration in the ink composition will not be too high, and the viscosity of the ink composition will not be too high, and a deterioration in the jetting ability can be suppressed.

[0022] The ink composition contains water as a solvent. The water in the ink composition may be mineral water, tap water, ion-exchanged water, purified water, distilled water, or pure water.

[0023] 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.

[0024] In one embodiment, the ink composition may contain ethylene glycol as a high-boiling point solvent, which can improve the stability of the ink composition in a low-temperature environment.

[0025] 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 written marks are not excessively reduced, and the ink composition can have appropriate cap-off properties.

[0026] Polyoxyethylene hydrogenated castor oil is a substance used as a nonionic surfactant and can be adsorbed onto the surface of colored resin particles. In the ink composition, polyoxyethylene hydrogenated castor oil functions as a dispersant, and by being adsorbed onto the surface of the colored resin particles, adhesion and aggregation of the colored resin particles are suppressed.

[0027] Examples of commercially available polyoxyethylene hydrogenated castor oils include NIKKOL HCO-30 (average number of moles of ethylene oxide added: 30), NIKKOL HCO-40 (average number of moles of ethylene oxide added: 40), NIKKOL HCO-50 (average number of moles of ethylene oxide added: 50), NIKKOL HCO-60 (average number of moles of ethylene oxide added: 60), and NIKKOL HCO-80 (average number of moles of ethylene oxide added: 80) (all manufactured by Nikko Chemicals Co., Ltd.).

[0028] The average number of moles of ethylene oxide added in the polyoxyethylene hydrogenated castor oil contained in the ink composition may be 40 or more and 60 or less. When the average number of moles of ethylene oxide added in the polyoxyethylene hydrogenated castor oil is 40 or more, the redispersibility of the colored resin particles in the ink composition is good, and the sediment of the colored resin particles in the ink composition particles is less likely to become viscous. When the average number of moles of ethylene oxide added in the polyoxyethylene hydrogenated castor oil is 60 or less, the affinity of the polyoxyethylene hydrogenated castor oil for both water and the resin particles is not too strong, and a three-dimensional structure in which the polyoxyethylene hydrogenated castor oil is adsorbed to the surface of the colored resin particles is easily formed. This makes it easier to suppress adhesion between the colored resin particles, and the sediment of the colored resin particles in the ink composition is less likely to become viscous.

[0029] The content of polyoxyethylene hydrogenated castor oil in the ink composition may be 1.2% by weight or more and 17.0% by weight or less.

[0030] The ratio of the content of polyoxyethylene hydrogenated castor oil to the content of colored resin particles in the ink composition may be 15% or more and 25% or less on a weight basis, and more preferably 18% or more and 22% or less.

[0031] If the ratio of the polyoxyethylene hydrogenated castor oil content to the colored resin particle content is 15% or more or 18% or more by weight, the redispersibility of the colored resin particles in the ink composition is good, and the sediment of the colored resin particles in the ink composition is less likely to become viscous.If the ratio of the polyoxyethylene hydrogenated castor oil content to the colored resin particle content is 25% or less or 22% or less by weight, the content of the colored resin particles in the ink composition is not too small, and therefore the handwriting density is less likely to decrease, resulting in good handwriting quality.

[0032] In some embodiments, the ink composition may contain silica nanoparticles or platelet-like clay mineral particles.

[0033] In this specification, silica nanoparticles refer to silica particles having an average particle size of 100 nm or less.

[0034] By including silica nanoparticles or plate-like clay mineral particles in the ink composition, the silica nanoparticles or plate-like clay mineral particles function as an anti-aggregation agent, improving the redispersibility of the colored resin particles.

[0035] That is, when the ink composition contains silica nanoparticles, the silica nanoparticles form a three-dimensional network structure (stereoscopic structure) in the ink composition. Furthermore, when the ink composition contains plate-like clay mineral particles, the negatively charged layer surfaces and positively charged end surfaces of the plate-like clay mineral particles attract each other in the ink composition, forming a house-of-card structure (stereoscopic structure), which is a three-dimensional association structure of layer surface-end surface bonds. In this way, a three-dimensional structure of silica nanoparticles or plate-like clay mineral particles is formed in the ink composition, and this three-dimensional structure suppresses the settling of the colored resin particles and also suppresses adhesion and aggregation between the colored resin particles. Therefore, the redispersibility of the colored resin particles in the ink composition is improved.

[0036] The silica nanoparticles may be surface-treated with dimethylsilyl, trimethylsilyl, polydimethylsiloxane, alkylsilyl, methacrylsilyl, aminosilane hydrophobizing treatment, or other hydrophobic treatments.

[0037] The average particle size of the silica nanoparticles may be 5 nm or more and 40 nm or less, more preferably 10 nm or more and 20 nm or less. When the average particle size of the silica nanoparticles is within the above range, a three-dimensional network structure is easily formed in the ink composition, and the three-dimensional network structure formed in the ink composition easily suppresses the settling of the colored resin particles.

[0038] Examples of commercially available silica nanoparticles include Aerosil R976 (average particle size 7 nm), Aerosil R974 (average particle size 12 nm), Aerosil R972 (average particle size: 16 nm), Aerosil 130 (average particle size: 16 nm), and Aerosil 50 (average particle size 30 nm) (all manufactured by Nippon Aerosil Co., Ltd.). The average particle size was measured by dynamic light scattering for the representative diameter, the particle size distribution was expressed on a volume basis, and the average particle size was calculated using the median diameter.

[0039] The content of silica nanoparticles in the ink composition may be 0.05% by weight or more and 1.0% by weight or less, or may be 0.05% by weight or more and 0.5% by weight or less.

[0040] If the content of silica nanoparticles in the ink composition is 0.05% by weight or more, a three-dimensional network structure of silica nanoparticles is appropriately formed in the ink composition, which makes it easy to suppress the settling of colored resin particles and the adhesion and aggregation of colored resin particles.If the content of silica nanoparticles in the ink composition is 1.0% by weight or less or 0.5% by weight or less, the viscosity of the ink composition does not become too high.

[0041] Plate-like clay mineral particles are layered (plate-like) particles. When these clay mineral particles are dispersed in water and left to stand, the negatively charged layer surfaces and positively charged edge surfaces attract each other, forming a house-of-cards structure, a three-dimensional association structure of layer surface-edge surface bonds.

[0042] The plate-like clay mineral particles include silicate minerals such as bentonite, smectite, montmorillonite, beidellite, saponite, stevensite, and hectorite.

[0043] Examples of commercially available plate-like clay mineral particles include bentonite such as Kunipia-F, Kunipia-G, Kunipia-G4, Kunipia-G10, and Moistonite-S (all manufactured by Kunimine Industries Co., Ltd.).

[0044] The content of the plate-like clay mineral particles in the ink composition may be 0.01% by weight or more and 0.1% by weight or less.

[0045] If the content of the plate-like clay mineral particles in the ink composition is 0.01% by weight or more, the card-house structure of the plate-like clay mineral particles is appropriately formed in the ink composition, which makes it easy to suppress the settling of the colored resin particles and the adhesion and aggregation of the colored resin particles.If the content of the plate-like clay mineral particles in the ink composition is 0.1% by weight or less, the viscosity of the ink composition does not become too high.

[0046] The ink composition according to some embodiments may further include various additives. For example, the ink composition may include a preservative. The preservative may include, for example, zinc pyrithione. The content of additives such as preservatives in the ink composition may be 0.5 wt % or less.

[0047] The ink composition according to some embodiments may have a viscosity at 23° C. of 5 mPa·s or more and 50 mPa·s or less, and more preferably 10 mPa·s or more and 40 mPa·s or less.

[0048] If the viscosity of the ink composition is within the above range, suitable ejection properties can be obtained when the ink composition is applied to a marking pen.

[0049] In some embodiments, the ink composition does not contain polysaccharides (such as gum arabic, gum tragacanth, or xanthan gum), proteins (such as casein or gelatin), or cellulose derivatives (such as hydroxyethyl cellulose) as thickeners.

[0050] The ink composition according to some embodiments contains colored resin particles having an average particle size of 5 μm or more and 15 μm or less, a binder resin, a solvent, and polyoxyethylene hydrogenated castor oil, and the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less, so that the viscosity of the ink composition can be easily adjusted to the above-mentioned range without using the above-mentioned thickener.

[0051] (Writing instrument configuration) Next, a writing instrument according to some embodiments will be described. The writing instrument according to some embodiments includes an ink reservoir that contains the ink composition described above, and a writing part configured to receive the ink composition from the ink reservoir.

[0052] Note that the writing instrument described below with reference to the figures is a direct ink marking pen, but the writing instrument in some embodiments may be a cotton-filled marking pen, or may be a writing instrument other than a marking pen (such as a felt-tip pen, marker, or brush pen).

[0053] FIG. 1 is a schematic cross-sectional view of a marking pen, which is a writing implement according to one embodiment. As shown in FIG. 1, the marking pen 1 (writing implement) includes a barrel 10, a cartridge 30 housed in the barrel 10, and a cap 20 attached to the tip of the barrel 10. The cap 20 shown in the figure includes an outer cap 22 and an inner cap 24 attached to the outer cap 22. As shown in the figure, an erasing member 12 for erasing marks made by the marking pen 1 may be detachably provided at the rear end of the barrel 10. In the example shown in the figure, the erasing member 12 functions as a tail plug. By removing the erasing member 12, a used cartridge 30 can be removed from the rear end of the barrel 10 and replaced.

[0054] The cartridge 30 includes an ink reservoir 32 that forms an ink reservoir 34 (ink tank), and a writing part 36 to which ink stored in the ink reservoir 34 is supplied. The writing part 36 may be formed from a fiber core, a plastic nib, or a metal nib. When the writing part 36 is formed from a fiber core, the fiber core preferably has a void ratio of 60% or more. When the writing part 36 is formed from a plastic nib or a metal nib, the nib preferably has an ink flow passage with a diameter of 80 μm or more.

[0055] In the illustrated exemplary embodiment, a valve member 42 is provided at the tip of the ink reservoir 32 to switch between a supply state and a non-supply state of the ink composition from the ink reservoir 34 to the writing part 36. The valve member 42 is supported by a valve support member 40 attached to the tip of the ink reservoir 32. The valve member 42 includes a valve stem 44 that passes through the tip opening of the valve support member 40 and a valve body 46 that can seat on a valve seat formed by the valve support member 40. A lead-receiving hole 43 is provided at the tip of the valve stem 44 along the axial direction, and the writing part 36 is fitted into the lead-receiving hole 43. A biasing member 47 is provided between the valve member 42 and the valve support member 40 to bias the valve member 42 in a valve-closing direction (toward the tip in the axial direction). The cartridge 30 may include a sleeve 38 for guiding axial movement of the writing part 36. The ink reservoir 34 may be provided with a stirrer 48 for stirring the ink composition in the ink reservoir 34 .

[0056] When the axial rearward force applied to the writing part 36 of the marking pen 1 from the paper surface or the like is small, the biasing force of the biasing member 47 causes the valve element 46 to seat on the valve seat, resulting in a closed valve state, and the supply path for supplying the ink composition from the ink reservoir 34 to the writing part 36. On the other hand, when the axial rearward force applied to the writing part 36 of the marking pen 1 from the paper surface or the like becomes greater than the biasing force of the biasing member 47, the valve element 46 separates from the valve seat, resulting in an open valve state, and the supply path for supplying the ink composition from the ink reservoir 34 to the writing part 36 is opened. In this way, the ink composition is ejected from the ink reservoir 34 and supplied to the writing part 36. [Example]

[0057] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0058] Dispersions A to AB having the compositions shown in Tables 1 to 3 were used to prepare ink compositions of Examples 1 to 31 and Comparative Examples 1 to 6 shown in Tables 4 to 9. The materials used are as follows. Tables 1 to 3 show the content (wt%) of each material in the dispersion, and Tables 4 to 9 show the content (wt%) of each material in the ink composition.

[0059] In the examples, the average particle diameter was measured by dynamic light scattering for representative diameters, particle size distribution was expressed by volume conversion, and the average particle diameter was calculated as a median diameter.

[0060] <Colored resin particles> Acrylic resin particles (1): FUJI 022 (pigment: carbon black, manufactured by Fuji Pigment Co., Ltd.), average particle size: 0.235 μm, specific gravity: 1.8 Acrylic resin particles (2): Labcolor 224 (SMD) (pigment: carbon black, manufactured by Dainichiseika Chemicals Co., Ltd.), average particle size: 3 μm, specific gravity: 1.12 Acrylic resin particles (3): Art Pearl G-800BK (pigment: carbon black, manufactured by Negami Chemical Industries, Ltd.), average particle size: 6 μm, specific gravity: 1.12 Acrylic resin particles (4): Labcolor 224 (11F) (pigment: carbon black, manufactured by Dainichi Seika Chemicals Co., Ltd.), average particle size: 11 μm, specific gravity: 1.12 Acrylic resin particles (5): Art Pearl G-400BK (pigment: carbon black, manufactured by Negami Chemical Industries, Ltd.), average particle size: 15 μm, specific gravity: 1.12 Acrylic resin particles (6): average particle size: 18 μm, specific gravity: 1.12 Urethane resin particles (1): Art Pearl C-800BK (pigment: carbon black, manufactured by Negami Chemical Industries, Ltd.), average particle size: 6 μm, specific gravity: 1.26 Urethane resin particles (2): Urethane colored resin particles (CuPc) (pigment: copper phthalocyanine), average particle size: 6 μm, specific gravity: 1.7 Urethane resin particles (3): (urethane colored resin particles (CuPc) (pigment: copper phthalocyanine), average particle size: 15 μm, specific gravity: 1.7

[0061] <Dispersant> Polyoxyethylene (POE) hydrogenated castor oil (1): NIKKOL HCO-30 (manufactured by Nikko Chemicals Co., Ltd.), average number of ethylene oxide moles added: 30 Polyoxyethylene (POE) hydrogenated castor oil (2): NIKKOL HCO-40 (manufactured by Nikko Chemicals Co., Ltd.), average number of ethylene oxide moles added: 40 Polyoxyethylene (POE) hydrogenated castor oil (3): NIKKOL HCO-50 (manufactured by Nikko Chemicals Co., Ltd.), average number of moles of ethylene oxide added: 50 Polyoxyethylene (POE) hydrogenated castor oil (4): NIKKOL HCO-60 (manufactured by Nikko Chemicals Co., Ltd.), average number of ethylene oxide moles added: 60 Polyoxyethylene (POE) hydrogenated castor oil (5): NIKKOL HCO-80 (manufactured by Nikko Chemicals Co., Ltd.), average number of ethylene oxide moles added: 80 Acrylic Dispersant

[0062] Water (Tables 1 to 3): Ion-exchanged water

[0063] <Binder resin> NBR emulsion (water dispersion of acrylonitrile butadiene rubber, solid content 48.5%)

[0064] <Solvent> ethylene glycol

[0065] <Anti-aggregating agent> Clay mineral particles (plate-like clay mineral particles): Bentonite Silica fine particles (silica nanoparticles): dimethylsilyl-treated silica nanoparticles

[0066] Water (Tables 4 to 9): Ion-exchanged water

[0067] The ink compositions were prepared as follows: Colored resin particles, water, and a dispersant (polyoxyethylene hydrogenated castor oil) listed in Tables 1 to 3 were stirred with a propeller stirrer to prepare dispersions (Dispersions A to AB in Tables 1 to 3). Binder resins, solvents, anti-aggregating agents, and water listed in Tables 4 to 9 were stirred with a propeller stirrer, and the above-mentioned dispersions were further added and stirred with the propeller stirrer to obtain ink compositions.

[0068] The ink compositions of the examples and comparative examples were subjected to the following tests and evaluations. The evaluation results are shown in Tables 4 to 9.

[0069] (Dischargeability) Each ink composition was filled into a marker (marking pen 1) shown in Figure 1, and the marker was used to write a handwritten mark on a piece of paper (a base paper for writing inside in accordance with JIS-S-5504). The handwritten mark and the state of the ink being discharged were evaluated. The evaluation criteria were as follows: A: Continuously ejected onto the paper regardless of density B: Slight smearing occurs during dispensing, but does not affect handwriting at all C: Some smearing occurs during dispensing, but handwriting can be written. D: The handwriting was so faded that it was not possible to write it on the paper.

[0070] (Density of application area (writing area)) Each ink composition was ejected onto the paper using a bar coater (No. 7 manufactured by Imoto Manufacturing Co., Ltd.) to form a film of a certain thickness on the paper. The optical density of the film formed on the paper was then measured using a fluorescence spectrodensitometer (FD-5 manufactured by Konica Minolta, Inc.). The evaluation criteria were as follows: A: Optical density is 1.0 or more B: Optical density less than 1.0, 0.9 or more C: Optical density less than 0.9, 0.8 or more D: Optical density was less than 0.8

[0071] (Erase area density) Each film used to evaluate the density of the applied area was rubbed and erased with an erasing material (injection molded product: styrene-based thermoplastic elastomer resin blended with 10 to 30% by weight of polypropylene resin) under a load of 1 kg, and the optical density of the erased trace was measured using the above-mentioned fluorescence spectrodensitometer. The evaluation criteria are as follows: A: 0.012 or less B: Greater than 0.12 and less than or equal to 0.18 C: greater than 0.18 and less than or equal to 0.02 D: Greater than 0.02

[0072] (Redispersibility) Three markers (marking pens 1) shown in Figure 1 were prepared for each example, and each marker was filled with an ink composition. They were then left to stand for one month in an environment of 25°C and 65% relative humidity, with one facing upward, one facing downward, and one facing sideways. After that, the markers were turned with the tip facing downward and vibrated (knocked) up and down, and the number of knocks until the stirring ball (stirrer 48) in the ink tank (ink storage section 34) began to move was counted, and the average number of knocks for the three markers was calculated. The evaluation criteria were as follows: A: Within 1 time B: 2 to 5 times C: 6 to 20 times D: More than 20 times

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3]

[0076] [Table 4]

[0077] [Table 5]

[0078] [Table 6]

[0079] [Table 7]

[0080] [Table 8]

[0081] [Table 9]

[0082] The ink compositions of Examples 1 to 31 contain colored resin particles having an average particle size of 5 μm or more and 15 μm or less, a binder resin, a solvent, and polyoxyethylene hydrogenated castor oil, and the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less.

[0083] These ink compositions have an average particle diameter of 5 μm or more, which makes it difficult for the ink composition ejected onto the paper surface to penetrate between the paper fibers and settle on the paper surface, presumably resulting in good erasability (erased area density). Furthermore, because the average particle diameter of the colored resin particles is 15 μm or less, the handwriting density is unlikely to decrease, which is presumably resulting in good handwriting quality (applied area density). Furthermore, because the ink compositions described above contain a binder resin with adhesive properties, a film is formed on the paper surface onto which the ink composition is ejected, in which the colored resin particles are encapsulated by the binder resin. This makes it difficult for the ink composition to penetrate between the paper fibers and settle on the paper surface, which is presumably resulting in good erasability (erased area density). Furthermore, because the difference in specific gravity between the colored resin particles and all other components of the ink compositions described above is 0.07 or more, the content of polyoxyethylene hydrogenated castor oil is not too high, which prevents the viscosity of the ink composition from becoming too high, which is presumably preventing deterioration of the ink composition's ejectability in a writing instrument (ejectability). Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.7 or less, so the specific gravity of the colored resin particles is not too high, and the colored resin particles are prevented from settling on the paper surface before a film is formed on the paper surface onto which the ink composition is ejected. This is thought to be why the erasability of handwriting made by the ink composition was good (erasability). Furthermore, since these ink compositions contain polyoxyethylene hydrogenated castor oil, the polyoxyethylene hydrogenated castor oil is adsorbed onto the surfaces of the colored resin particles, thereby suppressing adhesion and aggregation of the colored resin particles, which is thought to have resulted in good redispersibility of the colored resin particles (redispersibility). Therefore, even if the colored resin particles settle in the ink composition, the sediment is unlikely to become viscous, and it is thought that deterioration in ejection properties over time is suppressed.

[0084] Therefore, it is believed that the ink compositions of Examples 1 to 31 were able to provide erasable ink compositions that had good handwriting quality and erasability, and also had good jetting properties over time, even though they had low viscosity.

[0085] In addition, in the ink compositions of Examples 1 to 20 and 23 to 31, the average number of moles of ethylene oxide added to the polyoxyethylene hydrogenated castor oil is 40 or more and 60 or less.

[0086] In these ink compositions, the average number of moles of ethylene oxide added is 40 or more, which is believed to have resulted in good redispersibility of the colored resin particles in the ink composition, and the colored resin particle sediment in the ink composition was less likely to become viscous (redispersibility). Furthermore, the average number of moles of ethylene oxide added is 60 or less, which is believed to have resulted in the polyoxyethylene hydrogenated castor oil not having an excessively strong affinity with both water and the resin particles, and therefore the polyoxyethylene hydrogenated castor oil is likely to form a three-dimensional structure in which it is adsorbed to the surface of the colored resin particles. This likely contributes to the prevention of adhesion between the colored resin particles, and the colored resin particle sediment in the ink composition was less likely to become viscous (redispersibility). This likely contributes to more effectively suppressing the deterioration of jettability (jettability).

[0087] In addition, in the ink compositions of Examples 1 to 9 and 12 to 22, the ratio of the content of polyoxyethylene hydrogenated castor oil to the content of colored resin particles in the ink composition is 15% or more and 25% or less on a weight basis.

[0088] In these ink compositions, the above-mentioned content ratio is 15% or more by weight, so the redispersibility of the colored resin particles in the ink composition is good (redispersibility), which is thought to have prevented the sediment of colored resin particles from becoming viscous in the ink composition particles. Also, because the above-mentioned content ratio is 25% or less by weight, the content of the colored resin particles in the ink composition does not become too small, so the handwriting density is unlikely to become low (applied area density), which is thought to have resulted in good handwriting quality.

[0089] Furthermore, the ink compositions of Examples 23 to 31 contain silica nanoparticles (Examples 25 to 27, 30 to 31) or plate-like clay mineral particles (Examples 23 to 24, 28 to 29).

[0090] The ink compositions of Examples 25 to 27 and 30 to 31 contain silica nanoparticles, which form a three-dimensional network structure (stereostructure) of silica nanoparticles in the ink composition, and this steric structure is thought to have suppressed the settling of the colored resin particles and the adhesion and aggregation of the colored resin particles with each other, which is thought to have resulted in good redispersibility of the colored resin particles in the ink composition (redispersibility).

[0091] The ink compositions of Examples 23-24 and 28-29 contain plate-like clay mineral particles, and therefore form a house-of-card structure (three-dimensional structure) of the plate-like clay mineral particles in the ink composition, which is thought to have suppressed the settling of the colored resin particles and the adhesion and aggregation of the colored resin particles to each other. Therefore, it is thought that the redispersibility of the colored resin particles in the ink composition was good (redispersibility).

[0092] Therefore, it is believed that the ink compositions of Examples 23 to 31 make it easier to obtain erasable ink compositions that have good handwriting quality and erasability, and also have good jetting properties over time, even if they have a low viscosity.

[0093] In addition, the ink compositions of Examples 25 to 27 have a content of silica nanoparticles in the ink composition of 0.05% by weight or more and 0.5% by weight or less.

[0094] In these ink compositions, the content of silica nanoparticles is 0.05 wt% or more, which allows a three-dimensional network structure of silica nanoparticles to be appropriately formed in the ink composition, which is thought to facilitate the suppression of settling of colored resin particles and adhesion and aggregation between colored resin particles, resulting in good redispersibility (redispersibility).Furthermore, the content of silica nanoparticles is 0.5 wt% or less, which is thought to prevent the viscosity of the ink composition from becoming too high, resulting in good jetting properties (jetting properties).

[0095] In addition, the ink compositions of Examples 23 and 24 have a content of plate-like clay mineral particles in the ink composition of 0.01% by weight or more and 0.1% by weight or less.

[0096] In these ink compositions, the content of plate-like clay mineral particles is 0.01% by weight or more, so the card-house structure of the plate-like clay mineral particles is appropriately formed in the ink composition, which is thought to easily suppress the settling of the colored resin particles and the adhesion and aggregation of the colored resin particles, resulting in good redispersibility (redispersibility).Furthermore, because the content of plate-like clay mineral particles is 0.1% by weight or less, the viscosity of the ink composition does not become too high, which is thought to result in good ejection properties (ejection properties).

[0097] The ink compositions of Comparative Examples 1 and 3 had an average particle size of less than 5 μm for the colored resin particles, and therefore the ink compositions ejected onto the paper surface were likely to get between the paper fibers and settle on the paper surface, which is thought to be why the erasability was poor (erased area density).

[0098] It is believed that the ink composition of Comparative Example 2 had a low handwriting density (applied area density) because the average particle size of the colored resin particles was greater than 15 μm.

[0099] In the ink composition of Comparative Example 3, the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles was greater than 0.7. Therefore, the specific gravity of the colored resin particles was large, and the colored resin particles settled to the paper surface before a film was formed on the paper surface onto which the ink composition was ejected, which is thought to have resulted in incomplete erasure when erasing the handwriting made with the ink composition (erasability).

[0100] In the ink compositions of Comparative Examples 4 and 5, the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles was less than 0.07, which is thought to have resulted in a high content of dispersant in the ink composition and an increase in the viscosity of the ink composition, which in turn resulted in a deterioration in the ejection properties of the ink composition (ejection properties).

[0101] The ink composition of Comparative Example 6 did not contain polyoxyethylene hydrogenated castor oil, and therefore was unable to sufficiently suppress adhesion and aggregation of the colored resin particles, which is thought to be why the redispersibility was not good (redispersibility).

[0102] The contents described in each of the above embodiments can be understood, for example, as follows.

[0103] [1] The ink composition according to at least one embodiment of the present invention comprises: An erasable ink composition, colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less; A binder resin, a solvent; Polyoxyethylene hydrogenated castor oil, Contains the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less; On the surface of the paper onto which the ink is discharged, the binder resin envelops the colored resin particles to form a film.

[0104] The ink composition having the above-mentioned configuration [1] contains colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less, and a binder resin, and the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less, so that a writing instrument having good handwriting quality and erasability can be obtained. That is, since the average particle diameter of the colored resin particles in the ink composition is 5 μm or more, the ink composition ejected onto the paper surface is less likely to penetrate between the paper fibers and settle on the paper surface. Therefore, the ink composition that has dried on the paper surface can be easily removed by peeling it off with an eraser. Furthermore, since the average particle diameter of the colored resin particles in the ink composition is 15 μm or less, the handwriting density is less likely to decrease, resulting in good handwriting quality. Furthermore, since the ink composition contains a binder resin with adhesive properties, a film in which the colored resin particles are encapsulated by the binder resin is formed on the paper surface onto which the ink composition has been ejected. Therefore, the ink composition is less likely to penetrate between the paper fibers and settle on the paper surface, so the ink composition that has dried on the paper surface can be easily removed by peeling it off with an eraser. Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.07 or more, so the content of polyoxyethylene hydrogenated castor oil is not too high and the viscosity of the ink composition is not too high, thereby preventing deterioration of the ink composition's ejection properties in a writing instrument. Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.7 or less, so the specific gravity of the colored resin particles is not too high relatively, preventing the colored resin particles from settling on the paper surface before forming a film on the paper surface onto which the ink composition has been ejected. Therefore, when erasing handwriting made with the ink composition, it is difficult for unerased marks to remain. Furthermore, since the ink composition having the configuration of [1] above contains polyoxyethylene hydrogenated castor oil, the polyoxyethylene hydrogenated castor oil is adsorbed onto the surfaces of the colored resin particles, thereby suppressing adhesion and aggregation of the colored resin particles, and improving the redispersibility of the colored resin particles. Therefore, even if the colored resin particles settle in the ink composition, the sediment is less likely to become viscous, and deterioration of the dischargeability over time can be suppressed. As described above, according to the above-mentioned configuration [1], it is possible to obtain an erasable ink composition that has good handwriting quality and erasability, and also has good dischargeability over time, even if it has a low viscosity.

[0105] [2] In some embodiments, in the configuration of [1] above, The polyoxyethylene hydrogenated castor oil has an average number of moles of ethylene oxide added of 40 or more and 60 or less.

[0106] In the above-mentioned configuration [2], since the average number of moles of ethylene oxide added in the polyoxyethylene hydrogenated castor oil is 40 or more, the colored resin particles have good redispersibility in the ink composition, and the colored resin particles do not easily settle out of the ink composition particles, resulting in a viscous deposit. Furthermore, in the above-mentioned configuration [2], since the average number of moles of ethylene oxide added in the polyoxyethylene hydrogenated castor oil is 60 or less, the affinity of the polyoxyethylene hydrogenated castor oil for both water and the resin particles is not too strong, and a three-dimensional structure in which the polyoxyethylene hydrogenated castor oil is adsorbed onto the surface of the colored resin particles is easily formed. This makes it easier to suppress adhesion between the colored resin particles, and the colored resin particles do not easily settle out of the ink composition, resulting in a viscous deposit. Therefore, the above-mentioned configuration [2] can more effectively suppress a decrease in jetting performance.

[0107] [3] In some embodiments, in the configuration of [1] or [2] above, The ratio of the content of the polyoxyethylene hydrogenated castor oil to the content of the colored resin particles in the ink composition is 15% or more and 25% or less on a weight basis.

[0108] In the above-mentioned configuration [3], the ratio of the polyoxyethylene hydrogenated castor oil content to the colored resin particle content is 15% or more by weight, so the colored resin particles have good redispersibility in the ink composition, and the colored resin particle sediment is less likely to become viscous in the ink composition particles. In the above-mentioned configuration [3], the ratio of the polyoxyethylene hydrogenated castor oil content to the colored resin particle content is 25% or less by weight, so the content of the colored resin particles in the ink composition does not become too small, and the handwriting density is less likely to decrease, resulting in good handwriting quality. Therefore, the above-mentioned configuration [3] makes it possible to more effectively suppress a decrease in ejection performance while obtaining good handwriting quality.

[0109] [4] In some embodiments, in any of the configurations [1] to [3] above, The ink composition comprises It further contains silica nanoparticles or plate-like clay mineral particles.

[0110] According to the above configuration [4], since the ink composition further contains silica nanoparticles or plate-like clay mineral particles, the redispersibility of the colored resin particles is improved. That is, when the ink composition contains silica nanoparticles, the silica nanoparticles form a three-dimensional network structure (stereoscopic structure) in the ink composition. Furthermore, when the ink composition contains plate-like clay mineral particles, the negatively charged layer surfaces and positively charged end surfaces of the plate-like clay mineral particles attract each other in the ink composition, forming a house-of-card structure (stereoscopic structure), which is a three-dimensional association structure of layer surface-end surface bonds. In this way, a three-dimensional structure of silica nanoparticles or plate-like clay mineral particles is formed in the ink composition, and this three-dimensional structure suppresses the settling of the colored resin particles and also suppresses adhesion and aggregation between the colored resin particles. Therefore, the redispersibility of the colored resin particles in the ink composition is improved. Therefore, according to the above feature [4], it becomes easier to obtain an erasable ink composition that has good handwriting quality and erasability, and also has good dischargeability over time, even if the viscosity is low.

[0111] [5] In some embodiments, in the configuration of [4] above, The content of the silica nanoparticles in the ink composition is 0.05% by weight or more and 0.5% by weight or less.

[0112] In the above-mentioned configuration [5], the content of silica nanoparticles in the ink composition is 0.05 wt% or more, and therefore a three-dimensional network structure of silica nanoparticles is appropriately formed in the ink composition, which makes it easy to suppress the settling of colored resin particles and the adhesion and aggregation of colored resin particles. Furthermore, in the above-mentioned configuration [5], the content of silica nanoparticles in the ink composition is 0.5 wt% or less, so the viscosity of the ink composition does not become too high. Therefore, the above-mentioned configuration [5] makes it easy to improve the redispersibility of colored resin particles in an ink composition with a relatively low viscosity.

[0113] [6] In some embodiments, in the configuration of [4] or [5] above, The content of the plate-like clay mineral particles in the ink composition is 0.01% by weight or more and 0.1% by weight or less.

[0114] In the above-mentioned configuration [6], the content of the plate-like clay mineral particles in the ink composition is 0.01% by weight or more, and therefore the card-house structure of the plate-like clay mineral particles is appropriately formed in the ink composition, which makes it easy to suppress the settling of the colored resin particles and the adhesion and aggregation of the colored resin particles. Furthermore, in the above-mentioned configuration [6], the content of the plate-like clay mineral particles in the ink composition is 0.1% by weight or less, so the viscosity of the ink composition does not become too high. Therefore, the above-mentioned configuration [6] makes it easy to improve the redispersibility of the colored resin particles in an ink composition with a relatively low viscosity.

[0115] [7] At least one embodiment of the writing instrument (e.g., marking pen 1) of the present invention comprises: An ink reservoir (34) in which the ink composition according to any one of [1] to [6] above is accommodated; a writing section (36) configured to receive the ink composition from the ink reservoir; Equipped with.

[0116] The ink composition in the writing instrument having the configuration [7] above contains colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less, and a binder resin, and the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less, so that a writing instrument with good handwriting quality and erasability can be obtained. That is, since the average particle diameter of the colored resin particles in the ink composition is 5 μm or more, the ink composition ejected onto the paper surface is less likely to penetrate between the paper fibers and settle on the paper surface. Therefore, the ink composition that has dried on the paper surface can be easily removed by peeling it off with an eraser. Furthermore, since the average particle diameter of the colored resin particles in the ink composition is 15 μm or less, the handwriting density is less likely to decrease, resulting in good handwriting quality. Furthermore, since the ink composition contains a binder resin with adhesive properties, a film in which the colored resin particles are encapsulated by the binder resin is formed on the paper surface onto which the ink composition has been ejected. Therefore, the ink composition is less likely to penetrate between the paper fibers and settle on the paper surface, so the ink composition that has dried on the paper surface can be easily removed by peeling it off with an eraser. Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.07 or more, so the content of polyoxyethylene hydrogenated castor oil is not too high and the viscosity of the ink composition is not too high, thereby preventing deterioration of the ink composition's ejection properties in a writing instrument. Furthermore, in the ink composition described above, the difference in specific gravity between the colored resin particles and all other components is 0.7 or less, so the specific gravity of the colored resin particles is not too high relatively, preventing the colored resin particles from settling on the paper surface before forming a film on the paper surface onto which the ink composition has been ejected. Therefore, when erasing handwriting made with the ink composition, it is difficult for unerased marks to remain. Furthermore, the ink composition in the writing instrument having the configuration [7] above contains polyoxyethylene hydrogenated castor oil, which adsorbs to the surfaces of the colored resin particles, thereby suppressing adhesion and aggregation of the colored resin particles, thereby improving the redispersibility of the colored resin particles. Therefore, even if the colored resin particles settle in the ink composition, the sediment is less likely to become viscous, and deterioration of the ejection properties over time can be suppressed. As described above, according to the configuration [7] above, even if the viscosity is low, it is possible to obtain a writing implement that has good writing quality and erasability, and that has good ejection properties over time.

[0117] The above describes an embodiment of the present invention, but the present invention is not limited to the above-described embodiment, and also includes forms in which the above-described embodiment is modified, or forms in which these forms are appropriately combined.

[0118] In this specification, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement strictly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent rectangular shapes or cylindrical shapes in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components. [Explanation of symbols]

[0119] 1 marking pen 10 shaft cylinder 12 Erasing material 20 caps 22 Outer cap 24 Inner cap 30 cartridges 32 Ink reservoir 34 Ink reservoir 36 Writing section 38 Sleeve 40 Valve support member 42 Valve member 43 Core receiving hole 44 Valve stem 46 Valve body 47 biasing member 48 Stirrer

Claims

1. An erasable ink composition, colored resin particles having an average particle diameter of 5 μm or more and 15 μm or less; A binder resin, a solvent; Polyoxyethylene hydrogenated castor oil, Contains a difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles is 0.07 or more and 0.7 or less; The binder resin envelops the colored resin particles and forms a film on the discharged paper surface. Ink composition.

2. The polyoxyethylene hydrogenated castor oil has an average number of moles of ethylene oxide added of 40 or more and 60 or less. The ink composition according to claim 1.

3. The ratio of the content of the polyoxyethylene hydrogenated castor oil to the content of the colored resin particles in the ink composition is 15% or more and 25% or less on a weight basis. The ink composition according to claim 1 or 2.

4. Further containing silica nanoparticles or plate-like clay mineral particles The ink composition according to claim 1 or 2.

5. The content of the silica nanoparticles in the ink composition is 0.05% by weight or more and 0.5% by weight or less. The ink composition according to claim 4.

6. The content of the plate-like clay mineral particles in the ink composition is 0.01% by weight or more and 0.1% by weight or less. The ink composition according to claim 4.

7. an ink reservoir that accommodates the ink composition according to claim 1 or 2; a writing unit configured to receive the ink composition from the ink reservoir; A writing instrument comprising:

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