Thermochromic ink composition for writing instruments and writing instruments containing the same

Abstract

The present invention provides a thermochromic ink composition for writing instruments that offers excellent re-writing properties, allowing for the formation of clear writing without interruption or smudging, even when writing again on an area where the ink has been erased by friction heat using thermochromic ink, and a writing instrument incorporating this composition. [Solution] A thermochromic ink composition for writing instruments comprising a microcapsule pigment containing a thermochromic composition, water, and core-shell type cerium oxide particles, and a writing instrument containing the same. Furthermore, the core-shell type cerium oxide particles have an average particle diameter in the range of 10 to 200 nm.

Description

[Technical Field]

[0001] This invention relates to a thermochromic ink composition for writing instruments. Furthermore, it relates to a thermochromic ink composition and writing instrument that allows rewriting on ink that has been erased by frictional heat. [Background technology]

[0002] In recent years, ballpoint pens and marking pens that use friction heat to heat and erase writing on paper have become widely popular. These writing instruments use microcapsule pigments containing a thermochromic composition as a coloring agent. In addition to normal writing, rubbing the area where an error occurred causes the microcapsule pigment to discolor due to the friction heat, erasing the writing. When writing again on the erased area, depending on the type of additives such as resins mixed into the ink, the writing may become interrupted or streaky, making it impossible to rewrite. Therefore, a technique has been disclosed in which a specific polyether-modified silicone is added to a thermochromic ink with the aim of forming a clear handwriting without smudging or other issues when writing again on handwriting that has been erased (see, for example, Patent Documents 1 and 2).

[0003] The aforementioned patent document describes a technology that improves the leveling properties of water-based inks by adding a specific polyether-modified silicone to thermochromic inks, thereby improving the ability to rewrite on erased areas and to overwrite on unerased writing. This technology resolves the problems of conventional thermochromic inks, making it possible to create more practical products. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-004022 [Patent Document 2] Japanese Patent Publication No. 2015-036391 [Overview of the project] [Problems that the invention aims to solve]

[0005] This invention, in response to further research into improving the re-writing properties of thermochromic inks for writing applications, found that suppressing the aggregation of microcapsule pigments that occurred during writing friction improves re-writing properties, leading to the provision of a more effective thermochromic ink composition for writing instruments and a writing instrument containing it. [Means for solving the problem]

[0006] The present invention requires a thermochromic ink composition for writing instruments comprising a microcapsule pigment containing a thermochromic composition, water, and core-shell type cerium oxide particles. Furthermore, the requirements are that the core-shell type cerium oxide particles have an average particle diameter in the range of 10 to 200 nm and are included in the total amount of the ink composition in the range of 0.1 to 5% by mass. Furthermore, the core-shell type cerium oxide particles must have a core-shell structure consisting of a core portion made up of secondary particles formed by the spherical aggregation of primary cerium oxide particles, and a shell portion made up of a layer of polymer material located on the surface of the secondary particles; the diameter of the primary cerium oxide particles must be 1 to 4 nm; and the polymer material must be one of the following: polyvinylpyrrolidone, hydroxypropyl cellulose, hydroxypropyl methylcellulose, or polyethylene glycol. Furthermore, the requirements include a writing instrument containing a thermochromic ink composition for writing instruments as described in any of the above, and that it be a ballpoint pen with a ball of 0.5 mm or less at the pen tip. Furthermore, the requirements are that the device includes a friction member that discolors the writing marks made by the writing instrument due to frictional heat, that the friction member has an abrasive portion whose durometer hardness measurement value (Type D) according to JIS K 6253-3 is in the range of 30 to 59, and that the friction member has an abrasive portion whose durometer hardness measurement value (Type A) according to JIS K 6253-3 is in the range of 80 to 99. [Effects of the Invention]

[0007] The present invention provides a highly practical thermochromic ink composition for writing instruments, and a writing instrument containing this water-based ink, which allows for clear writing without interruption or smudging, even when writing again on an area where writing with thermochromic ink has been erased by friction heat. [Modes for carrying out the invention]

[0008] In this invention, by adding core-shell type cerium oxide particles to an aqueous ink composition for writing instruments that uses microcapsule pigments containing a thermochromic composition as a coloring agent, which can be erased using the frictional heat generated by rubbing the paper surface with a friction member, the aggregation of microcapsule pigments that occurred during friction of writing can be suppressed, thereby improving the ability to rewrite. The problem during rewriting is thought to be that when erasing, the friction material rubs against the writing on the paper surface, causing the microcapsule pigments, which were uniformly distributed in the colored state, to decolorize due to heat. At the same time, the microcapsule pigments aggregate together, forming clumps (aggregates) and uneven areas on the paper surface. As a result, areas with different wettability than the paper surface appear as islands, and when rewriting, the water-based ink does not form a uniform writing line, causing line breakage and other problems. To suppress the above-mentioned problems, it is presumed that during writing, core-shell type cerium oxide particles penetrate between microcapsule pigments, forming handwriting while maintaining good visibility, and when the handwriting is rubbed, the particles prevent direct contact between the microcapsule pigments, thereby suppressing aggregation. As a result, no uneven areas caused by aggregates are formed on the paper surface, creating a state with excellent re-writing properties. Furthermore, even in water-based inks, the presence of core-shell type cerium oxide particles dispersed between microcapsule pigments suppresses contact between the microcapsule pigments, making aggregation of the microcapsule pigments over time less likely, thus resulting in excellent ink stability.

[0009] Microcapsule pigments containing thermochromic compositions are used as colorants. Any type of thermochromic composition encapsulated in microcapsules can be applied, regardless of whether the effect is reversible or irreversible. By heating the handwriting, the hue of the handwriting can be changed, or the color can be altered, faded, or colored. By encapsulating the thermochromic composition in microcapsules, this change in handwriting can be achieved stably over a long period without any change in composition.

[0010] In particular, as the thermochromic composition encapsulated in the microcapsule pigment, a reversible thermochromic composition comprising (a) an electron-donating color-changing organic compound, (b) an electron-accepting compound, and (c) a reaction medium that determines the temperature at which the color reaction between the two occurs is preferred, from the viewpoint of repeated use and accuracy of temperature changes. Specifically, as microcapsule pigments containing the reversible thermochromic composition, we can use heat-decolorizing microcapsule pigments containing a reversible thermochromic composition, as described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, Japanese Patent Publication No. 1-29398, etc., which changes color before and after a predetermined temperature (color change point), exhibiting a decolorized state in the temperature range above the high-temperature color change point and a colored state in the temperature range below the low-temperature color change point, where only one of the two states exists in the room temperature range, and the other state is maintained as long as the heat or cold required to bring about that state is applied, but returns to the state exhibited in the room temperature range when the application of heat or cold is stopped, and which have a relatively small hysteresis width (ΔH=1~7℃). Furthermore, there are those exhibiting relatively large hysteresis characteristics (ΔH=8~50℃) as described in Japanese Patent Publication No. 4-17154, Japanese Patent Publication No. 7-179777, Japanese Patent Publication No. 7-33997, Japanese Patent Publication No. 8-39936, etc., and those exhibiting large hysteresis characteristics as described in Japanese Patent Publication No. 2006-137886, Japanese Patent Publication No. 2006-188660, Japanese Patent Publication No. 2008-45062, Japanese Patent Publication No. 2008-280523, etc. In other words, the shape of the curve plotting the change in color intensity due to temperature changes follows a significantly different path depending on whether the temperature is raised from a temperature below the color change temperature range or lowered from a temperature above the color change temperature range. This means that the color development state at low temperatures below the complete color development temperature, or the decolorization state at high temperatures above the complete decolorization temperature, can be determined by using a reversible thermochromic composition that has color memory properties in a specific temperature range, and heat-decolorizing microcapsule pigments can also be applied. Furthermore, as a reversible thermochromic composition having color memory properties that can be applied to writing instrument inks, the complete color development temperature is set to a temperature that can only be obtained in a freezer, a cold region, etc., i.e., -50 to 0°C, preferably -40 to -5°C, more preferably -30 to -10°C, and the complete decolorization temperature is set to a temperature that can be obtained from frictional heat from a friction body, a hair dryer, or other readily available heating source, i.e., 50 to 95°C, preferably 50 to 90°C, more preferably 60 to 80°C, and the ΔH value is set to 40 to 100°C, thereby enabling it to effectively maintain the color exhibited under normal conditions (daily living temperature range).

[0011] Microencapsulation of the aforementioned thermochromic composition can be carried out by interfacial polymerization, interfacial polycondensation, in situ polymerization, liquid curing coating, phase separation from aqueous solutions, phase separation from organic solvents, melt-dispersion cooling, air suspension coating, spray drying, etc., and can be appropriately selected depending on the application. Furthermore, depending on the purpose, a secondary resin film can be applied to the surface of the microencapsulated pigment to provide durability or modify the surface properties for practical use. The aforementioned microcapsule pigment is applied with an average particle diameter in the range of about 0.1 to 4.0 µm, and in particular, to achieve high density of handwriting, those with an average particle diameter of 0.5 µm or more are preferable. Furthermore, in consideration of dispersibility in ink and low tendency to aggregate when erased by rubbing, those with an average particle diameter of less than 3.0 µm, preferably 2.9 µm or less, are advantageous and suitable for achieving the object of the constitution of the present invention. Furthermore, the measurement of the average particle diameter is performed as follows: particle regions are determined using image analysis-type particle size distribution measurement software "Mac-View" manufactured by Mountech Co., Ltd., the projected area equivalent circle diameter (Heywood diameter) is calculated from the area of the particle regions, and the value is measured as the average particle diameter of particles equivalent to equal-volume spheres based on said value. In addition, when the particle diameter of all or most of the particles exceeds 0.2 µm, the average particle diameter of particles equivalent to equal-volume spheres can also be measured by the Coulter method using a particle size distribution analyzer (manufactured by Beckman Coulter Inc., product name: Multisizer 4e).

[0012] The aforementioned microcapsule pigment may be used alone or in an appropriate mixture of two or more kinds, and is used in an amount of 10 to 38% by weight, preferably 15 to 35% by weight, in the ink composition. Since the individual concentration of the microcapsule pigment is lower than that of general-purpose colorants, use within the aforementioned range is preferable from the practical perspective of ink concentration. As a result, the ink has high solid content and tends to aggregate, which makes the constitution of the present invention effective.

[0013] Furthermore, in order to impart a desired hue without thermochromic change to handwriting, a colorant (dye and general pigment) that can be dissolved or dispersed in an aqueous medium can be used. For example, as dyes, acid dyes, basic dyes, direct dyes and the like can be used; as general pigments, in addition to inorganic pigments such as carbon black and ultramarine blue, and organic pigments such as copper phthalocyanine blue and benzidine yellow, water-dispersed pigment products that are finely and stably dispersed in an aqueous medium in advance using a surfactant or the like are used. Furthermore, metallic luster pigments such as metal powder and pearl pigments, fluorescent pigments, phosphorescent pigments, and white pigments such as titanium dioxide can also be applied. It should be noted that these can also be encapsulated in the microcapsule pigment.

[0014] Core-shell cerium oxide particles have high dispersibility in water and are chemically inert, so they exist in a dispersed state between microcapsule pigments in ink, and handwriting is formed while entering between the microcapsule pigments during writing. Accordingly, when the water-based ink is stored for a long period of time or when the handwriting is rubbed, the particles prevent direct contact between the microcapsule pigments, thereby suppressing aggregation. Furthermore, due to its high transmittance, it does not affect the hue of the handwriting formed on the paper surface, does not cause residual color when the handwriting is decolored, and can be used without impairing the function as a thermochromic writing instrument.

[0015] The core-shell cerium oxide particles are core-shell particles composed of cerium oxide as a core portion and a shell portion formed of a layer of a polymer substance. The core portion is preferably composed of secondary particles obtained by spherically aggregating and assembling primary particles of cerium oxide. In this case, the diameter of the primary particles of cerium oxide is preferably 1 to 4 nm. The particle size of the primary particles refers to the crystallite size (primary particle size) obtained from Hall's equation using the half-width of a diffraction peak measured by an X-ray diffraction (XRD) apparatus. Secondary particles are aggregates of primary particles, and are sometimes referred to as primary aggregates. Each individual spherical cerium oxide particle of the core portion is a secondary particle, not a primary particle. Further, the cerium oxide particles may have monovalent to pentavalent metal ions added thereto, examples of which include Na, Ca, Y, Gd, Zr, Hf, Nb and the like.

[0016] The shell portion is a layer of a polymer substance located on the surface of the secondary particles of the core portion, and the polymer substance is composed of polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), hydroxypropyl methyl cellulose, polyethylene glycol (PEG), and related polymers thereof. Related polymers include cross-linked structures of the above polymers such as polymers formed by cross-linking PVP molecules with each other and polymers formed by cross-linking HPC molecules with each other, polymers formed by cross-linking PVP or HPC with polyols, polymers formed by cross-linking polyol molecules with each other, and products obtained by reaction of the foregoing with cerium oxide, and the polymer includes various types of these polymers.

[0017] Further, the core-shell cerium oxide particles may be surface-modified with at least one of a silane compound represented by the following general formula (1) and a silane coupling agent represented by the following general formula (2). This facilitates the production of the particles, and when applied to writing instrument ink, exhibits the same effects as those described above. R 1 n ―Si―(OR 2 ) 4-n (1) [In the formula, R 1 and R 2 are each independently R 1 represents an alkyl group having 1 to 18 carbon atoms, an aryl group, or a vinyl group, R 2 represents an alkyl group having 1 to 5 carbon atoms, an alkoxyalkyl group having 2 to 8 total carbon atoms, or a hydrogen atom, and n is 1 or 2.]] X―R 3 ―Si(CH3) q ―(OR 4 ) 3-q (2) [In the formula, X represents a vinyl group, a glycidoxy group, a 3,4-epoxycyclohexyl group, a styryl group, a methacryl group, an acryl group, an amino-containing group, an isocyanate group, or a ureido group, R 3 and R 4 are each independently R 3This represents an alkylene group having 1 to 5 carbon atoms, or, if X is a glycidoxy group, an alkylene or phenylene group with a total of 2 to 5 carbon atoms containing one oxygen atom in the form of an ether bond, and R 4 [where q represents an alkyl group having 1 to 5 carbon atoms, an alkoxyalkyl group having a total of 2 to 8 carbon atoms, or a hydrogen atom, and q is 0 or 1.] In this case, it is preferable to pre-treat the core-shell type cerium oxide with a carboxylic acid to improve the reactivity of the silane compound. Preferred carboxylic acids are monocarboxylic acids having 1 or 2 carbon atoms, or hydroxycarboxylic acids. Examples of monocarboxylic acids are not particularly limited, but include formic acid and acetic acid. Examples of hydroxycarboxylic acids are not particularly limited, but include hydroxyacetic acid, lactic acid, malic acid, and citric acid.

[0018] Core-shell type cerium oxide particles preferably have an average particle diameter in the range of 10 to 200 nm, and particularly preferably in the range of 20 to 100 nm, considering their dispersion stability and the efficiency of rewriting. The aforementioned particle size is determined by scanning electron microscopy (SEM) observation. In this case, it represents the average size of 50 or more particles captured in the SEM image. It can also be determined by dynamic light scattering (DLS). Dynamic light scattering requires the refractive index and viscosity of the dispersion medium. The refractive index of the dispersion medium can be obtained from literature, and the viscosity of the dispersion medium can be set to be the same as the viscosity of the dispersion being measured, and the viscosity of the dispersion can be measured and used.

[0019] In this invention, the average particle diameter is determined by selecting a suitable measurement method from the approximate particle diameter. In the core-shell type cerium oxide particles (including primary particles in the core) and microcapsules used in the following examples and comparative examples, the values ​​obtained by measuring using a suitable method from the aforementioned measurement methods based on the approximate particle diameter are described.

[0020] Core-shell type cerium oxide particles are preferably added in an amount of 0.1 to 5% by mass, more preferably 0.1 to 3% by mass, of the total amount of the ink composition. At concentrations below 0.1% by mass, sufficient effects are difficult to obtain, and no improvement in effect is observed even when added at concentrations exceeding 5% by mass; therefore, further addition is unnecessary.

[0021] There are no particular restrictions on the type of water used in water-based inks; for example, tap water, deionized water, ultrafiltered water, and distilled water are examples. The water content relative to the total mass of the ink composition is not particularly limited, but is preferably in the range of 35 to 95% by mass, and more preferably in the range of 40 to 90% by mass.

[0022] In addition to the essential components described above, the ink composition of the present invention may contain optional components as long as they do not impair the effects of the present invention. For example, conventional water-soluble organic solvents that are compatible with water can be used. Specifically, examples include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, hexylene glycol, 1,3-butanediol, neoprene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monoethyl ether, 2-pyrrolidone, and N-methyl-2-pyrrolidone. Furthermore, the aforementioned water-soluble organic solvent may be used individually or in combination of two or more types, and is used in an amount of 2 to 60% by mass, preferably 5 to 35% by mass, in the ink composition.

[0023] Furthermore, a water-soluble resin can be added to provide adhesion to the paper surface. Examples of water-soluble resins include alkyd resins, acrylic resins, styrene-maleic acid copolymers, cellulose derivatives, polyvinylpyrrolidone, polyvinyl alcohol, and dextrin. One or more water-soluble resins can be used in combination, and they are used in an amount of 1 to 20% by mass in the ink composition, provided that they do not impair drying resistance.

[0024] In addition, if necessary, pH adjusters such as organic basic compounds, rust inhibitors such as benzotriazole, toltriazole, and saponins, preservatives or fungicides such as carbolic acid, sodium salt of 1,2-benzthiazolin 3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl parahydroxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine, wetting agents such as urea, sorbitol, mannitol, sucrose, glucose, and sodium pyrophosphate, defoamers, and fluorinated or nonionic surfactants to improve ink penetration may be used. Furthermore, lubricants can be added, and examples include metal soaps, polyalkylene glycol fatty acid esters, ethylene oxide-additive cationic surfactants, phosphate ester surfactants, N-acyl amino acid surfactants, dicarboxylic acid-type surfactants, β-alanine-type surfactants, 2,5-dimercapto-1,3,4-thiadiazole and its salts or oligomers, 3-amino-5-mercapto-1,2,4-triazole, thiocarbamate, dimethyldithiocarbamate, α-lipoic acid, condensates of N-acyl-L-glutamic acid and L-lysine and their salts. Furthermore, shear-reducing agents such as xanthan gum, gellan gum, succinoglycan, and guar gum can also be added. Furthermore, the functionality of the retractable ballpoint pen form can be enhanced by adding thickening inhibitors such as N-vinyl-2-pyrrolidone oligomer, N-vinyl-2-piperidone oligomer, N-vinyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, ε-caprolactam, and N-vinyl-ε-caprolactam oligomer.

[0025] The thermochromic ink composition of the present invention is filled into marking pens and ballpoint pens equipped with a fiber tip, felt tip, plastic tip, or ballpoint pen tip at the writing end. The marking pens and ballpoint pens may be of the cap type, which has a cap that covers the pen tip, or they may be of the retractable type, which has a retractable mechanism such as a push-button type, twist-button type, or slide-button type, and the pen tip can be stored inside the barrel.

[0026] When filling a marking pen, the structure and shape of the marking pen itself are not particularly limited. For example, a marking pen tip (bullet-shaped, chisel-shaped, brush-pen-shaped, etc.) such as a fiber tip, felt tip, or plastic tip, or a fountain pen-type metal tip, can be attached to the writing tip, and ink can be impregnated into an ink-absorbing body made of fiber bundles housed inside the barrel, supplying ink to the writing tip. Another example is a marking pen in which ink is directly housed inside the barrel, and a predetermined amount of ink is supplied to the writing tip via a comb-shaped ink flow rate adjustment member or an ink flow rate adjustment member made of fiber bundles. Yet another example is a marking pen in which ink is directly housed inside the barrel, and a predetermined amount of ink is supplied to the writing tip via a valve mechanism. In addition to a cap type, a retractable type can be created by providing an airtight opening and closing lid on the pen tip retraction hole, or by using an ink component with a highly moist composition. In addition to pens with a single nib, there may also be double-ended pens with nibs of different thicknesses and shapes at both ends of the barrel (one end of which may be a ballpoint pen), or double-ended pens with the same nib shape but containing different colored inks.

[0027] When filling a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited. Examples include a structure in which ink is impregnated into an ink-absorbing material made of fiber bundles housed inside the barrel and supplied to the writing tip; a structure in which ink is directly housed inside the barrel and an ink flow rate adjustment member with comb-shaped grooves or an ink flow rate adjustment member made of fiber bundles is interposed; and a ballpoint pen having an ink-retaining tube filled with an ink composition inside the barrel, the ink-retaining tube communicating with a tip to which a ball is attached, and a liquid stopper to prevent backflow closely attached to the end face of the ink. A solid stopper can also be used in combination with the liquid stopper.

[0028] The aforementioned ballpoint pen tip can be a straight metal pipe or a metal pipe with a tapered shape that narrows the inner diameter of the front part that serves as the writing section, with a ball held in a ball-holding portion formed by pressing the tip of the pipe inward from the outer surface; or a ball held in a ball-holding portion formed by cutting a metal material with a drill or the like; or a ball held in such a metal pipe or tip formed by cutting a metal material is biased forward by a spring. Furthermore, the balls used are those made of cemented carbide, stainless steel, ruby, ceramic, etc., with an outer diameter of 0.1 to 2.0 mm, preferably 0.2 to 1.2 mm, and more preferably 0.28 to 1.0 mm. In particular, the ink composition of the present invention enables reliable and vivid color formation through rewriting, even when the amount of ink dispensed during writing is small. Therefore, its effect is particularly pronounced in ballpoint pen form, and is especially useful in ballpoint pens with a ball diameter of 0.5 mm or less and a small amount of ink dispensed.

[0029] The barrel containing the ink composition is preferably made of a thermoplastic resin such as polyethylene, polypropylene, or polyethylene terephthalate, as this offers advantages in terms of low ink evaporation and productivity. The tip can be directly connected to the barrel, or it can be connected to the barrel and tip via a connecting member. Furthermore, it can be configured as a replaceable cartridge type. When the ink composition is low viscosity, the ink composition can be contained within the barrel by either attaching an ink retaining member to the front of the barrel and directly containing the ink composition within the barrel, or by impregnating a porous body or a fibrous material with the ink composition and then containing it.

[0030] Furthermore, by using a transparent, colored transparent, or translucent molded body for the barrel, the ink color and ink level can be checked. In the form of a ballpoint pen, the barrel may be in the form of a ballpoint pen refill, with the refill housed inside the outer barrel, or the barrel itself, with a tip attached to the end, may be used as the ink reservoir, with ink directly filled into the barrel.

[0031] Furthermore, the ballpoint pen using the aforementioned barrel can be either a capped or retractable type. As for retractable ballpoint pens, any structure in which the writing tip provided on the ballpoint pen refill is housed inside the outer barrel while exposed to the outside air, and the writing tip protrudes from the opening of the outer barrel when the retractable mechanism is activated, can be used. Examples of operating methods for the retraction mechanism include knocking, rotating, and sliding mechanisms. A retractable pen may have a retractable mechanism at the rear end or side of the outer barrel, and pressing the retractable mechanism causes the writing tip of the ballpoint pen refill to extend and retract from the opening at the front end of the outer barrel. Alternatively, pressing a clip on the outer barrel may cause the writing tip of the ballpoint pen refill to extend and retract from the opening at the front end of the outer barrel. Furthermore, a part of the barrel, such as the front barrel, may also serve as the retractable mechanism. A rotary type can be exemplified by having a rotating part (such as a rear shaft) on the outer shaft, and by rotating this part, the writing tip of the ballpoint pen refill extends and retracts from the opening at the front end of the outer shaft. A sliding type may be exemplified by having a sliding part on the side of the barrel, which allows the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the outer barrel by operating the slide, or by sliding a clip part provided on the outer barrel, which allows the writing tip of the ballpoint pen refill to extend and retract from the opening at the front of the outer barrel. Furthermore, a retractable ballpoint pen may be a composite type that houses multiple ballpoint pen refills in addition to one that houses a single ballpoint pen refill within the outer barrel. Also, the ink reservoir that makes up the ballpoint pen refill may be made of resin or metal.

[0032] An ink backflow prevention device can also be filled into the trailing end of the ink contained in the ballpoint pen refill. The ink backflow prevention body can be either liquid or solid. Examples of liquid ink backflow prevention bodies include non-volatile media such as polybutene and silicone oil. If desired, silica, aluminum silicate, etc., can be added to the media. Furthermore, resin molded products can be used as solid ink backflow prevention bodies. Furthermore, the liquid and solid ink backflow prevention devices can be used in combination.

[0033] Furthermore, along with the writing instrument, a friction member can be used to erase or change the color of the writing by generating frictional heat. The friction member is preferably one containing an elastomer or elastic resin that is highly elastic and can generate appropriate friction and frictional heat during friction. Although it is also possible to rub the ink marks with an eraser, eraser residue is generated during friction, so the aforementioned friction member is preferably used. The materials used to constitute the friction member include silicone resin, resins containing styrene copolymers, polyester resins, etc., and hard and soft materials can be mixed and used while considering the balance between friction and moldability. While the aforementioned friction member can be combined with a separate, arbitrarily shaped component (friction body) from the writing instrument to create a writing instrument set, fixing the friction member to the writing instrument's exterior results in a form that is highly portable and convenient. In the case of capped writing instruments, there are no particular limitations on where the friction element can be provided. For example, the cap itself may be formed from the friction element, the barrel itself from the friction element, the clip itself may be formed from the friction element if a clip is provided, or the friction element may be provided at the tip (top) of the cap or the rear end of the barrel (the part opposite the cap side where the writing tip is not provided). In the case of retractable writing instruments, the location where the friction element is provided is not particularly limited. For example, the barrel itself may be formed from the friction element, or if a clip is provided, the clip itself may be formed from the friction element, or a friction element may be provided near the barrel opening (pen tip side), at the rear end of the barrel (the part without the writing tip), or at the knock mechanism (operating part). Furthermore, the operating part itself may be made of a friction element.

[0034] As the aforementioned friction member, those having a friction portion with a durometer hardness measurement value (Type D) in accordance with JIS K 6253-3 in the range of 30 to 59, or those having a friction portion with a durometer hardness measurement value (Type A) in accordance with JIS K 6253-3 in the range of 80 to 99, are particularly useful. The durometer hardness measurement range provided allows for easy generation of frictional heat with moderate force when erasing handwriting by friction, thus minimizing damage to the paper surface and preventing the handwriting from peeling off. This ensures that the area where the handwriting was erased is not roughened, and the ability to rewrite on the erased area, which is the objective of this invention, is easily maintained. [Examples]

[0035] Examples are described below, but the present invention is not limited to these examples. Table 1 shows the composition of the thermochromic aqueous inks of the examples, and Table 2 shows the composition of the comparative examples. The numerical values ​​of the compositions in the tables represent parts by mass.

[0036] [Table 1]

[0037] [Table 2]

[0038] The contents of the raw materials listed in the table are explained according to the footnote numbers. (1) A microcapsule pigment containing a reversible thermochromic composition consisting of (a) 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluorane as component (b) 4.5 parts of 1,1-bis(4′-hydroxyphenyl)n-decane and 7.5 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane as component (c) 50.0 parts of 4-benzyloxyphenylethyl caprate (color development temperature: -20℃, decolorization temperature: 57℃, ΔH: 63℃, average particle size: 1.0 μm, changes color from black to colorless) (2) A microcapsule pigment containing a reversible thermochromic composition consisting of (a) 2.0 parts of 3-(4-diethylamino-2-hexyloxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide as component (a), 8.0 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane as component (b), and 50.0 parts of 4-benzyloxyphenylethyl caprate as component (c), which changes color from blue to colorless). (3) A microcapsule pigment containing a reversible thermochromic composition consisting of (a) 2.0 parts of 4-[2,6-bis(2-ethoxyphenyl)-4-pyridinyl]-N,N-dimethylbenzeneamine, (b) 6.0 parts of 2,2-bis(4′-hydroxyphenyl)-hexafluoropropane, and (c) 5.0 parts of 4-benzyloxyphenylethyl caprate (color development temperature: -20°C, decolorization temperature: 61°C, ΔH: 66°C, average particle size: 2.3 μm, changes color from yellow to colorless). (4) Average particle size 40 nm (primary particle size of cerium oxide: 2-3 nm), shell: PVP, aqueous dispersion with 10% solid content by weight. (5) Average particle size 20 nm (primary particle size of cerium oxide: 2-3 nm), shell: PVP, aqueous dispersion with 10% solid content by weight. (6) Average particle size 70 nm (primary particle size of cerium oxide: 2-3 nm), shell: PVP, aqueous dispersion with 10% solids by weight. (7) Average particle size 90 nm (primary particle size of cerium oxide: 2-3 nm), shell: HPC, aqueous dispersion with 10% solids by weight. (8) Manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name: Prysurf AL (9) Manufactured by Arcsarda Japan, Product name: Proxel XL-2 (10) Sigma-Aldrich, trade name: Cerium(IV) Oxide Dispersion, 20% by weight colloidal dispersion in 2.5% acetic acid, average particle size 30-50 nm (11) Nissan Chemical Corporation, product name: Snowtex 30, silica sol with 20% by weight of active ingredient, average particle size 40-50 nm (12) Nippon Shokubai Co., Ltd., Product name: Seahostar KE-W10, Aqueous dispersion with 15% solids by weight, Average particle size 100 nm

[0039] Preparation of marking pen ink The raw materials were mixed in the proportions specified in Examples 1-4 and Comparative Examples 1-4, stirred at 2000 rpm for 1 hour in a disperser at 20°C, and then filtered to obtain a marking pen ink composition.

[0040] Making a marking pen The marking pen ink composition is impregnated into an ink-absorbing body made of polyester sliver coated with a synthetic resin film, housed in a barrel made of polypropylene resin, and assembled to connect a processed tip (bullet-shaped plastic pen) with numerous ink guide holes formed in polyester resin to the tip of the barrel via a holder, and a cap is attached to obtain a marking pen. A friction member (durometer hardness type A: 90) made of an elastic material containing styrene-based elastomer is provided on the top of the cap.

[0041] Preparation of ballpoint pen ink The raw materials, excluding succinoglycan, were mixed in the proportions specified in Examples 5-8 and Comparative Examples 5-8. The mixture was stirred at 2000 rpm for 1 hour at 20°C using a disper, then a thickener was added and the mixture was stirred for another hour. The mixture was then filtered to obtain a ballpoint pen ink composition.

[0042] Preparation of an ink backflow prevention device An ink backflow prevention body was obtained by adding 1.5 parts of fatty acid amide as a thickening agent to 98.5 parts of polybutene as a base oil, and then kneading the mixture using a three-roller system.

[0043] Making a ballpoint pen A ballpoint pen was manufactured by filling a ballpoint pen refill, in which a stainless steel tip (containing a spring that presses the ball toward the writing section) holding a 0.4 mm diameter cemented carbide ball was fitted to one end of a transparent polypropylene pipe, with the aforementioned ink compositions, and then placing an ink backflow prevention body at the rear end of the refill. Finally, the ballpoint pen refill was assembled into the barrel and a cap was attached. A friction member (durometer hardness type D: 40) made of an elastic material containing styrene-based elastomer was provided at the rear end of the barrel.

[0044] The following tests were conducted using each of the writing instruments obtained. Written exam Each writing instrument, confirmed to be capable of writing, was used to handwrite the letters A through J on JIS P3201 writing paper A at a temperature of 25°C. The letters were then erased by friction heat generated by rubbing them with the friction element attached to each writing instrument. Subsequently, the condition of the handwriting was visually inspected when spiral circles were continuously written over the erased areas. The results of each test are shown below.

[0045] [Table 3]

[0046] The evaluation of the test results is as follows: Written exam ○: Good handwriting was obtained even on the erased text, and rewriting was possible. ×: Fading or smudging is visible in the handwriting on the erased text.

Claims

1. A thermochromic ink composition for writing instruments comprising microcapsule pigments containing a thermochromic composition, water, and core-shell type cerium oxide particles.

2. The thermochromic ink composition for writing instruments according to claim 1, wherein the core-shell type cerium oxide particles are in the range of an average particle diameter of 10 to 200 nm.

3. The thermochromic ink composition for writing instruments according to claim 1, wherein the core-shell type cerium oxide particles have a core-shell structure comprising a core portion consisting of secondary particles formed by the spherical aggregation and aggregation of primary cerium oxide particles, and a shell portion consisting of a layer of polymer material located on the surface of the secondary particles.

4. The thermochromic ink composition for writing instruments according to claim 3, wherein the diameter of the primary particles of cerium oxide is 1 to 4 nm.

5. The thermochromic ink composition for writing instruments according to claim 3, wherein the polymer substance is one of polyvinylpyrrolidone, hydroxypropylcellulose, hydroxypropylmethylcellulose, or polyethylene glycol.

6. The thermochromic ink composition for writing instruments according to claim 1, wherein core-shell type cerium oxide particles are contained in an amount of 0.1 to 5% by mass of the total amount of the ink composition.

7. A writing instrument containing the thermochromic ink composition for writing instruments described in any one of claims 1 to 6.

8. The writing instrument according to claim 7, which is a ballpoint pen equipped with a ball of 0.5 mm or less at the tip.

9. The writing instrument according to claim 7, further comprising a friction member that changes the color of the writing made by the aforementioned writing instrument due to frictional heat.

10. The writing instrument according to claim 9, wherein the friction member has a friction portion having a durometer hardness measurement value (Type D) in accordance with JIS K 6253-3 in the range of 30 to 59.

11. The writing instrument according to claim 9, wherein the friction member has a friction portion having a durometer hardness measurement value (Type A) in accordance with JIS K 6253-3 in the range of 80 to 99.

Images