JP7447336B1 - Ink compositions and writing instruments - Google Patents

Abstract

The present invention provides an ink composition having sufficient handwriting density, appropriate ejection properties, and good erasability, and a writing instrument equipped with such an ink composition. [Solution] The ink composition 30 is an ink composition 30 having erasability, and includes at least colored resin particles having an average particle diameter of 5 to 15 μm, a binder resin, and a solvent, and has a specific gravity of the colored resin particles. The difference between the binder resin and the specific gravity of the components other than the colored resin particles is 0.06 or more and 0.7 or less, and the binder resin envelops the colored resin particles to form a film on the ejected paper surface. [Selection diagram] Figure 1

Description

The present invention relates to an ink composition and a writing instrument.

BACKGROUND ART Ink compositions having erasability that allow handwriting to be erased with an eraser or the like have been proposed. For example, Patent Document 1 discloses a writing instrument eraser erasable aqueous ink composition using pigment particles (colored resin particles) having an average particle diameter in the range of 2 to 30 μm as a colorant. By adding a polymer flocculant to this ink composition, a bridging structure is developed between the pigment particles, thereby preventing the pigment particles from settling and separating on the paper surface.

Japanese Patent Application Publication No. 2004-143381

However, the ink composition of Patent Document 1 tends to have a high viscosity because a relatively large amount of a polymer flocculant that forms a bridge structure is added to suppress sedimentation and separation of colored resin particles. Furthermore, when the amount of colored resin particles added is increased, the viscosity of the ink composition becomes higher and the ejectability deteriorates, making it difficult to obtain sufficient handwriting density. On the other hand, if the particle diameter of the pigment particles added is made as small as possible in order to obtain good ejection properties and sufficient handwriting density, there is a risk that the pigment particles will enter the paper surface and the erasing performance will deteriorate.

The present invention was created in view of the above points, and provides an ink composition having sufficient handwriting density, appropriate ejection properties, and good erasability, and a writing instrument equipped with such an ink composition. The purpose is to

In order to solve the above problems, the present inventors conducted intensive research and found that when the colored resin particles contained in the ink composition and components other than the colored resin particles satisfy a predetermined relationship, the ink composition can be ejected. It has been found that sedimentation of the ink on the paper surface can be suppressed, and that the ink ejected onto the paper surface forms a predetermined film and exhibits excellent erasability.

That is, the ink composition of the present invention is an ink composition having erasability, and includes at least colored resin particles having an average particle diameter of 5 to 15 μm, a binder resin, and a solvent, and the specific gravity of the colored resin particles is The difference between the binder resin and the specific gravity of components other than the colored resin particles is 0.06 or more and 0.7 or less, and the binder resin envelops the colored resin particles to form a film on the ejected paper surface.

Moreover, the writing instrument of the present invention is filled with the above-mentioned ink composition.

According to the present invention, it is possible to provide an ink composition having sufficient handwriting density, appropriate ejection properties, and good erasability, and a writing instrument equipped with such an ink composition.

FIG. 2 is a schematic diagram showing the appearance of a ballpoint pen according to an embodiment, in which (a) shows a state with a cap attached, and (b) shows a state with a cap removed.

(First embodiment)
The ink composition according to the first embodiment of the present invention will be described below. The ink composition according to this embodiment includes at least colored resin particles, a binder resin, and a solvent. The ink composition discharged onto the paper surface does not settle on the paper surface (in other words, without getting between the fibers of the paper), and the handwriting made of the ink composition forms a film on the paper surface. The ink composition according to the present embodiment forms a predetermined film on the paper surface upon which it is ejected, and exhibits excellent erasability by using a common eraser or the like. In other words, the handwriting made of the film formed on the paper surface with the ink composition of the present embodiment is effectively erased by being rubbed off with an eraser or the like, while generating eraser debris (film peeling debris). be done.

The ink composition according to this embodiment is used, for example, by being filled inside a ballpoint pen. FIGS. 1A and 1B are schematic diagrams showing the appearance of a cap-type ballpoint pen 10 including an ink composition 30 according to an embodiment. As shown in FIGS. 1A and 1B, the ink composition 30 is filled in an ink tank of a refill (not shown) housed inside the case 12 of the ballpoint pen 10. The ink composition 30 is ejected from the pen tip 10a of the ballpoint pen 10 housed in the cap 14.

Furthermore, an eraser 20 for erasing handwriting written on a paper surface using an ink composition 30 is fixed to the case 12 of the pen end 10b of the ballpoint pen 10 on the opposite side from the pen tip 10a. The eraser 20 is fixed to the case 12 so that it does not come off from the case 12 during a scratching operation. Note that the eraser 20 may not only be fixed to the case 12, but may also be attached to or covered with the case 12. Further, the part of the ballpoint pen 10 to which the eraser 20 is attached is not limited to the case 12, but may be any exterior member that is exposed to the outside of the ballpoint pen 10. Examples of the exterior member here include a cap, a tip member (tip metal), a barrel shaft (case), a tail plug, a grip member (grip portion), and an operating member (knock portion).

The eraser 20 is made of a predetermined elastomer, and is a viscoelastic body that has ink erasing properties with respect to the ink composition 30. The eraser 20 is made of a material such that the difference in SP (Solubility Parameter) value ((cal/cm ³ ) ^1/2 ) with the binder resin contained in the ink composition 30 described later is 0.1 or more. Preferably, it is made of a material. The SP value here is calculated from the square root of the heat of evaporation required to evaporate 1 cm ³ of liquid. If the difference in the above SP values is 0.1 or more, the affinity between the eraser 20 and the binder resin blended in the ink composition 30 will be low (it will be difficult to dissolve), and the When the handwriting created by the ink composition is rubbed off and erased, the binder resin is prevented from spreading on the paper surface.

Further, the eraser 20 is preferably formed of a material that provides a contact angle of less than 60° when the ink composition 30 is dropped onto its surface. The contact angle here refers to a static contact angle, and is measured, for example, by the θ/2 method. If the contact angle is less than 60°, when erasing handwriting, it becomes difficult to slip between the eraser 20 and the film forming the handwriting made of the ink composition 30 (it becomes difficult to slide over the handwriting), and the eraser 20 The film that makes up the handwriting becomes easier to adhere to, making it easier to erase the handwriting.

Specifically, the material of the eraser 20 is preferably one of natural rubber, synthetic rubber, and synthetic resin, which are used as materials for general erasers. Examples of the synthetic rubber include styrene-butadiene rubber, chloroprene rubber, butyl rubber, acrylonitrile-butadiene rubber, acrylic rubber, urethane rubber, silicone rubber, and fluorine rubber. Examples of the synthetic resin include polyvinyl chloride, polyethylene, polypropylene, thermoplastic elastomers (polyurethane-based, styrene-based, olefin-based, polyethylene-based), and the like. By comparing the difference in SP value with the binder resin blended in the ink composition 30, an appropriate material can be selected from the above materials.

Next, the ink composition 30 according to this embodiment will be described in detail. The ink composition 30 includes colored resin particles having an average particle diameter of 5 to 15 μm and containing a pigment such as carbon black. The preferred average particle diameter of the colored resin particles is about 6 μm. If the average particle diameter of the colored resin particles is smaller than 5 μm, the ink composition 30 ejected onto the paper surface tends to settle on the paper surface and easily enters between the fibers of the paper. On the other hand, if the average particle diameter of the colored resin particles is larger than 15 μm, the handwriting density will decrease. When the average particle diameter of the colored resin particles is within the above range, the ink composition 30 can prevent the ink composition 30 from penetrating into the paper fibers, and can provide a practical handwriting density. Note that the average particle diameter of the colored resin particles can be measured by dispersing the colored resin particles in water and using a laser rotation type particle size distribution measuring device.

Further, the ink composition 30 includes a binder resin having adhesive properties to provide binding properties between the colored resin particles, and a solvent. The solvent includes a dispersant for dispersing colored resin particles, a high boiling point solvent for imparting so-called cap-off properties to the ink composition 30, a liquid component in an aqueous thickener solution, water, etc. Contains all liquid ingredients.

Further, in the ink composition 30, the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles including the solvent is set to be 0.06 or more and 0.7 or less. If the specific gravity difference is larger than 0.7, the colored resin particles will settle on the paper surface before a film is formed on the paper surface on which the ink composition 30 is ejected, and when erasing the handwriting created by the ink composition 30, There will be some unerased parts. In addition, the formulation in which the specific gravity difference is smaller than 0.06 is a composition that contains a large amount of other components having a large specific gravity such as a dispersant, and as a result, the viscosity of the ink composition 30 increases and the ejection properties deteriorate. . By setting the above specific gravity difference to 0.06 or more and 0.7 or less, the colored resin particles are prevented from settling on the paper surface before a film is formed on the paper surface, and the adhesive binder resin is colored. A film is formed on the paper surface while enveloping the resin particles. That is, the ink composition 30 forms a film in which the binder resin envelops the colored resin particles on the paper surface on which it is ejected. The erasability of handwriting by the ink composition 30 can be improved.

Furthermore, in addition to the average particle diameter of the colored resin particles in the ink composition 30 being within the above range, the difference in specific gravity between the colored resin particles and components other than the colored resin particles is 0.06 or more and 0.7 or less. By doing so, while ensuring a practical writing density, when the ink composition 30 is ejected onto the paper surface, it is prevented from entering the paper fibers, and furthermore, the binder resin wraps around the colored resin particles, thereby improving erasability. It can be made good.

In the ink composition 30, it is even more preferable that the difference in specific gravity between the colored resin particles and components other than the colored resin particles is 0.25 or less or 0.11 or less. By reducing the above-mentioned specific gravity difference, sedimentation of the colored resin particles on the paper surface is further suppressed. Thereby, when erasing handwriting with the ink composition 30, erasability of the handwriting can be made even better.

Further, it is preferable that the ink composition 30 forms a film having fixability on the paper surface onto which it is ejected. As described above, since the ink composition 30 forms a film on the paper surface in a skin-like manner, the film becomes difficult to peel off from the paper surface. That is, since a film having fixability is formed on the paper surface, the film will not be peeled off from the paper surface unless it is intentionally erased. In this way, by forming a film having fixability, even when the surface of the film is rubbed with a finger or the like, part of the film is prevented from peeling off from the paper surface and sliding on the paper surface. Therefore, it is possible to realize the ink composition 30 that does not stain the paper surface.

Further, the thickness of the film formed on the paper surface by the ejected ink composition 30 is preferably within the range of 1 to 100 μm. Since the minimum particle diameter of the colored resin particles contained in the ink composition 30 is about 1 μm, the thickness of the film is at least 1 μm or more. On the other hand, if the thickness of the film is larger than 100 μm, when the ink composition 30 is ejected onto the paper surface, it takes time for the solvent component of the ink composition 30 to be absorbed by the paper surface and volatilized into the atmosphere, resulting in extremely slow drying. This makes it difficult to erase the handwriting created by the ink composition 30. When the thickness of the film is within the above range, when the handwriting made of the film is rubbed off and erased with the eraser 20, it can be easily erased (easily rubbed off ). Note that if the ink composition 30 contains a material with a large particle diameter, such as glitter, the thickness of the film may be increased by the thickness of the material.

Further, the binder resin contained in the ink composition 30 is preferably acrylonitrile butadiene rubber (NBR). This is because when the binder resin is acrylonitrile butadiene rubber, the balance between the fixability of the ejected ink composition 30 to the paper surface and the erasability of handwriting by the ink composition 30 with an eraser is maintained optimally. In other words, because it has fixability, it does not contaminate the paper surface even when rubbed with a finger, and it remains fixed on the paper surface unless the film is intentionally erased. Examples of binder resins other than acrylonitrile butadiene rubber include styrene butadiene rubber and urethane rubber.

Further, the acrylonitrile butadiene rubber as a binder resin contained in the ink composition 30 is preferably contained in an amount of 19 to 26 parts by weight based on the total amount of the ink composition 30. If the amount of acrylonitrile butadiene rubber blended is less than 19 parts by weight, the binding property between the colored resin particles will decrease, and the erasability of handwriting by the ink composition 30 will decrease. On the other hand, if the blending amount of acrylonitrile butadiene rubber is more than 26 parts by weight, the solid content concentration in the ink composition 30 increases, which increases the viscosity of the ink composition 30 and deteriorates the ejection properties. By setting the blending amount of acrylonitrile butadiene rubber within the above range, the erasability of handwriting by the ink composition 30 can be improved.

Colored resin particles are made by dispersing and blending various pigments such as carbon black into various resin materials.The manufacturing method is to blend the pigment components into resin materials, melt-knead them, and then crush them to produce colored resin particles. Examples include a melt-kneading method for producing particles, and a suspension polymerization method for producing colored resin particles by dispersing and blending a pigment component in a polymerizable monomer and carrying out suspension polymerization in an aqueous medium. Alternatively, it may be colored resin particles in which a pigment is coated with a resin material. Further, the resin material used for the colored resin particles included in the ink composition 30 is preferably acrylic resin particles or urethane resin particles. Note that the colored resin particles may be hollow.

Pigments to be dispersed and blended into the resin material are not particularly limited, but include azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, indigo pigments, dioxazine pigments, perylene pigments, perinone pigments, and isoindolinone pigments. , isoindoline pigments, metal complex pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, titanium oxide pigments, and the like can be used.

In addition to the colored resin particles and the binder resin, the ink composition 30 of the present embodiment includes a dispersant such as an acrylic dispersant for dispersing the colored resin particles, and a dispersant such as an acrylic dispersant for imparting so-called cap-off properties to the ink composition 30. It may also contain a high boiling point solvent, a thickener for adjusting viscosity, water, and the like. As the dispersant, various surfactants, water-soluble polymers, etc. that have an affinity for colored resin particles are used. The amount of water blended is adjusted depending on the ejection properties (viscosity) of the ink composition 30. Regarding the ejection properties of the ink composition 30, it is preferable that the ink composition 30 continues to be ejected onto the paper surface without blurring, and it is more preferable that the ink composition 30 continues to be ejected onto the paper surface without distinguishing between darkness and lightness.

If too much of the high boiling point solvent is added, the drying properties of handwriting will deteriorate, so it is preferable to limit the amount to the minimum necessary so as not to interfere with other components. Examples of high boiling point solvents include glycerin, ethylene glycol, diethylene glycol, propylene glycol, and the like. In the ink composition 30 of this embodiment, it is more preferable to mix ethylene glycol as a high boiling point solvent. By incorporating ethylene glycol, the stability of the ink composition 30 in a low-temperature environment can be improved.

Examples of thickeners include polysaccharides such as gum arabic, gum tragacanth, and xanthan gum, proteins such as casein and gelatin, cellulose derivatives such as methylcellulose and hydroxyethylcellulose, ethylene-propylene copolymers, polyvinyl alcohol, and bentonite. In the ink composition 30 of this embodiment, it is more preferable to mix xanthan gum as a thickener. Thickeners other than xanthan gum may be used as long as they impart shear thinning properties.

Furthermore, in the present invention, additives such as 3-methoxybutanol, 3-methyl-3-methoxybutanol, 3-methyl- 1,3-butanediol, 1,3-butanediol, hexylene glycol (2-methylpentane-2,4-diol), urea, ethylene urea, thiourea as a wetting agent, phenoxyethanol as a preservative, benzothiazoline type, Omazine type agents, anti-mold agents, anti-corrosion agents, lubricants, anti-foaming agents, pH adjusters, gloss-imparting agents, and perfumes may also be added.

In the ink composition 30 of this embodiment, the amount of colored resin particles added is preferably 10 to 20% by weight, and the amount of thickener added is preferably 0.4% by weight or less. When the amount of colored resin particles added is within the above range, sufficient handwriting density, appropriate ejection properties, and good erasability can be achieved. Further, by adding the thickener in an amount within the above range, appropriate ejection properties can be achieved.

The ink composition 30 according to the present embodiment configured as described above is an ink composition having erasability, and includes colored resin particles having an average particle diameter of 5 to 15 μm, a binder resin, and a solvent. The difference between the specific gravity of the colored resin particles and the specific gravity of components other than the colored resin particles is 0.06 or more and 0.7 or less, and the binder resin wraps the colored resin particles on the paper surface to be discharged. form.

That is, in the ink composition 30 of the present embodiment, the colored resin particles and components other than the colored resin particles satisfy the above relationship, so that settling of the colored resin particles on the paper surface is suppressed, and the colored resin particles are prevented from settling on the paper surface after being ejected. A film having fixing properties as described above is formed. Therefore, by rubbing off the handwriting made of the film formed on the paper surface with an eraser or the like, the handwriting can be easily erased while generating peeling debris of the film. In this way, it is possible to realize an ink composition 30 with excellent erasability while suppressing the settling of colored resin particles onto the paper surface.

Furthermore, since the handwriting made with the ink composition 30 of the present embodiment is composed of the film in the above-described manner, it has excellent light resistance and temperature resistance compared to handwriting made with conventional thermochromic ink. , erased handwriting will not be restored due to changes in environmental temperature. Furthermore, because the colored resin particles are prevented from settling on the paper surface, the density of the handwriting is higher than that of conventional thermochromic inks, and the writing experience is also excellent.

In addition, the handwriting made with the ink composition 30 of the present embodiment is composed of the film in the above-described manner, and the fixation of the film on the paper surface is also ensured. will not contaminate. Furthermore, since the colored resin particles are prevented from settling on the paper surface, the density of the handwriting can be higher than that of a pencil, and the width of the handwriting can be made constant. As described above, in this embodiment, a novel ink composition 30 has sufficient handwriting density, appropriate ejection properties, and good erasability, and overcomes the disadvantages of conventional thermochromic inks and disadvantages of pencils. can be provided.

Further, the ballpoint pen 10 according to the present embodiment is filled with the above-mentioned ink composition 30. Thereby, a specific configuration for writing handwriting by discharging the ink composition 30 onto a paper surface can be provided.

(Second embodiment)
Next, an ink composition according to a second embodiment of the present invention will be described. The ink composition according to the second embodiment has the difference between the particle diameter of the colored resin particles contained in the components and the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles as in the first embodiment. It is different from The other components in the ink composition, the structure of the colored resin particles, the manufacturing method, and the like are the same as those of the ink composition 30 of the first embodiment, so the explanation thereof will be omitted.

The ink composition of the present embodiment contains colored resin particles having an average particle diameter of less than 5 μm and containing a pigment such as carbon black inside, and the specific gravity of the colored resin particles and the above-mentioned solvent-containing colored resin particles. The difference between the specific gravity of all components is 0.05 or less. If the average particle diameter is less than 5 μm but the specific gravity difference is greater than 0.05, the colored resin particles will settle before a film is formed on the paper surface, resulting in poor erasability. In addition, when the difference in specific gravity is 0.05 or less, but the average particle diameter of the colored resin particles is 5 μm or more (in this case, the formulation is a composition that contains a large amount of other components with high specific gravity such as dispersants) By containing a large amount of other components having a large specific gravity, the viscosity of the ink composition increases, resulting in poor ejection properties.

From the above, by setting the average particle diameter of the colored resin particles to less than 5 μm, and setting the difference between the specific gravity of the colored resin particles and the specific gravity of all components other than the colored resin particles containing the solvent to 0.05 or less. , the colored resin particles are prevented from settling on the paper surface before a film is formed on the paper surface, and a film is formed on the paper surface while the adhesive binder resin wraps around the colored resin particles, resulting in good erasing. Characteristics are achieved, and appropriate ejection performance is also achieved. Note that the resin material used for the colored resin particles included in the ink composition of this embodiment is preferably polystyrene resin particles, polyethylene resin particles, or polypropylene resin particles.

In this way, for example, by producing colored resin particles using polystyrene, polyethylene, polypropylene, etc., or by producing colored resin particles themselves with a hollow structure, they can be precipitated in a solvent mainly composed of acrylonitrile butadiene rubber. Never. Furthermore, the acrylonitrile butadiene rubber emulsion forms an adhesive layer on the paper surface, and the resin pigment is fixed on it, making it possible to maintain erasability and further reduce the particle size, making it possible to increase the density of handwriting. can also be maintained.

The ink composition according to the present embodiment configured as described above is an ink composition having erasability, and includes at least colored resin particles having an average particle diameter of less than 5 μm, a binder resin, and a solvent. , the difference between the specific gravity of the colored resin particles and the specific gravity of components other than the colored resin particles is 0.05 or less, and a film formed by the binder resin surrounding the colored resin particles is formed on the ejected paper surface. Therefore, similarly to the ink composition 30 of the first embodiment, by rubbing off the handwriting made of a film formed on the paper surface with an eraser or the like, the handwriting can be easily erased while generating scraps of the film. be able to. Therefore, in this embodiment as well, it is possible to realize an ink composition having sufficient handwriting density, appropriate ejection properties, and good erasability.

Although each embodiment of the present invention has been described above, the present invention is not limited to each of the above embodiments, and various changes can be made without departing from the gist thereof. For example, in the first embodiment, a ballpoint pen filled with an ink composition is illustrated, but the writing instrument filled with an ink composition is not limited. For example, it may be a fountain pen or marker filled with an ink composition, or it may be a brush filled with an ink composition.

(First example)
Hereinafter, the present invention will be explained in detail with reference to Examples. In the first example, an optimal composition for an ink composition was investigated. Specifically, we created ink compositions in which the type of colored resin particles to be blended, the average particle diameter of the colored resin particles, the amount of binder resin blended, and the difference in specific gravity between the colored resin particles and components other than the colored resin particles. 31 samples (25 types of example samples and 6 types of comparative example samples) were prepared. Each of the 31 samples of ink compositions was evaluated for ejection properties, handwriting density (represented as applied area density using an experimental method), and handwriting erasability (represented as erased area density using an experimental method).

(1) Composition of each ink composition Regarding the average particle diameter of the colored resin particles, the colored resin particles with different average particle diameters within the range of 0.02 to 18 μm are mixed with an acrylic dispersant with a solid content of 45%. Twenty-one types of dispersion liquids were used. Regarding the types of colored resin particles, there are 11 types of dispersions (dispersions A to F, H, I, L to N) in which acrylic colored resin particles are dispersed, and 4 types in which urethane colored resin particles are dispersed. (Dispersions G, J, K, O) and six types of dispersions in which polystyrene-based colored resin particles were dispersed (Dispersions P to U) were used. The compositions of Dispersions A to G are shown in Table 1 below, the compositions of Dispersions H to N are shown in Table 2 below, and the compositions of Dispersions O to U are shown in Table 3 below. The unit of blending amount for each dispersion composition is weight % (total amount 100 weight %). In addition, the average particle diameter here is the value of D50 calculated on a volume basis in a laser diffraction method.

Regarding the blending amount of the binder resin, acrylonitrile butadiene rubber (NBR) was used as the binder resin blended in each ink composition. Specifically, an NBR emulsion with a solid content of 48.5% was used. For each ink composition, the blending amount of acrylonitrile butadiene rubber (hereinafter referred to as "NBR blending amount") was varied within the range of 19 to 27% by weight. Regarding the specific gravity difference between colored resin particles and components other than colored resin particles, the specific gravity difference is 0.05, 0.07, 0.1, 0.11, 0.13, 0.25, 0.26, 0. An ink composition of 7.0.79 was prepared.

For each ink composition, components other than colored resin particles (dispersions A to G) and binder resin (acrylonitrile butadiene rubber) include ethylene glycol as a high boiling point solvent, a 3% xanthan gum aqueous solution as a thickener, and water. was blended. For samples in which the difference in specific gravity between colored resin particles and components other than colored resin particles is 0.06 or more, Table 4 below shows each composition of Examples 1 to 10, and Table 5 below shows each composition of Examples 11 to 20. The compositions of Comparative Examples 1 to 6 are shown in Table 6 below. For samples in which the difference in specific gravity between colored resin particles and components other than colored resin particles is 0.05 or less, the compositions of Comparative Examples 4 and 5 are shown in Table 6 below, and the compositions of Examples 21 to 25 are shown in Table 7 below. and the composition of Comparative Example 6 are shown below. Note that the units of the amounts shown in Tables 4 to 7 are weight % (total amount 100 weight %).

For comparative study of the average particle size of the colored resin particles to be blended, each sample of the ink composition of Examples 1 to 20 was mixed with dispersions C, D, and D in which the average particle size of the colored resin particles was 6 μm, 11 μm, and 15 μm. E, G, H, I, J, K, and N (see Tables 4 and 5), and each sample of the ink composition of Examples 21 to 25 was prepared with the colored resin particles having an average particle diameter of 0. 02 μm, 0.1 μm, 0.3 μm, 1 μm, and 3 μm dispersions P, Q, R, S, and T were prepared, respectively (see Table 7). On the other hand, the samples of the ink compositions of Comparative Examples 1 to 5 were dispersions A, B, F, L, M, and O in which the average particle diameter of colored resin particles was 0.235 μm, 3 μm, 6 μm, 15 μm, and 18 μm. A sample of the ink composition of Comparative Example 6 was prepared using dispersion U in which the average particle diameter of colored resin particles was 6 μm (see Table 7).

Regarding the comparative study of the blending amount of binder resin, the ink composition sample of Example 17 was prepared with an NBR blending amount of 1% by weight, and the ink composition sample of Example 6 was prepared with an NBR blending amount of 17% by weight. The ink composition samples of Examples 1, 10, and 11 were prepared with an NBR content of 19% by weight, and the ink composition samples of Examples 12 and 13 were prepared with an NBR content of 21% by weight. %, the ink composition sample of Example 20 was prepared with an NBR content of 22% by weight, and the ink composition sample of Example 18 was prepared with an NBR content of 23% by weight. Each sample of the ink composition of Examples 2, 4, 5, 8, 9, 14-16, 21-25 was prepared with an NBR loading of 24% by weight, and the sample of the ink composition of Example 19 was prepared with an NBR loading of 24% by weight. The sample of the ink composition of Example 3 was prepared with a blending amount of 25% by weight, and the sample of the ink composition of Example 7 was produced with a blending amount of NBR of 27% by weight. (See Tables 6 and 7).

On the other hand, each sample of the ink composition of Comparative Examples 4 and 5 was prepared with an NBR content of 19% by weight, and each sample of the ink composition of Comparative Examples 1 to 3 and 6 was prepared with an NBR content of 24% by weight. % by weight (see Tables 6 and 7).

A comparative study of the specific gravity difference between the colored resin particles and components other than the colored resin particles was conducted using Example 8 so that the specific gravity difference was 0.11 for each sample of the ink compositions of Examples 1 to 7 and 14 to 16. The samples of the ink compositions of Examples 10 and 11 were prepared such that the difference in specific gravity was 0.25 for the sample of the ink composition of Example 9, and the difference of specific gravity was 0.26 for the sample of the ink composition of Example 9. The difference in specific gravity was 0.07 for the sample of the ink composition of Example 17, and the difference in specific gravity of the sample of the ink composition of Example 17 was 0.7. 1, the specific gravity difference for each sample of the ink compositions of Examples 21 to 25 was 0.05, and the specific gravity difference was 0.13 for each sample of the ink compositions of Examples 18 to 20. They were prepared by adjusting each one so that it became (see Table 4, Table 5, and Table 7).

On the other hand, Comparative Example 4, Samples of ink compositions Nos. 5 and 6 were prepared by adjusting the specific gravity difference to be 0.05 (see Tables 6 and 7).

(2) Evaluation of each ink composition Regarding the evaluation of the ejectability of each ink composition, each ink composition filled in a ballpoint pen was ejected onto a paper surface (inner base paper compliant with JIS-S-5504) and handwriting was evaluated. A rating of ◎ is given if the paper continues to be dispensed on the paper surface without distinction of density or lightness, and a rating of 〇 is given if the paper is slightly blurred while being dispensed but has no effect on the handwriting at all. If the handwriting was blurred but the handwriting could be written, it was rated △, and if it was blurred and the handwriting could not be written on the paper, it was rated ×.

To evaluate the concentration of each ink composition in the coated area, each ink composition was discharged onto the above paper surface using a bar coater (manufactured by Imoto Manufacturing Co., Ltd.: No. 7) to form a film of a constant thickness on the paper surface. did. Then, the optical density of the film formed on the paper surface was measured using a fluorescence spectrodensitometer (manufactured by Konica Minolta, Inc.: FD-5). Regarding the measurement results, those that were 1.0 or more were evaluated as ◎, those that were less than 1.0 and 0.9 or more were evaluated as ○, and those that were less than 0.9 and 0.8 or more. was evaluated as △, and those that were less than 0.8 were evaluated as ×.

Regarding the evaluation of the erased area density of each ink composition, each film used for the evaluation of the applied area density was compared with a general eraser (PVC: 30-40%, plasticizer: 40-50%, others: 10-30%). %) under a load of 1 kg, and the optical density was measured using the fluorescence spectrodensitometer mentioned above. Regarding the measurement results, those that are 0.012 or less are evaluated as ◎, those that are greater than 0.12 and 0.18 or less are evaluated as ○, and those that are greater than 0.18 and 0.02 or less. Those that were larger than 0.02 were evaluated as △, and those that were larger than 0.02 were evaluated as ×.

(3) Evaluation results The evaluation results of ejection properties, applied area density, and erased area density for each ink composition are shown in Table 8 below for Examples 1 to 20 and Comparative Examples 1 to 5, and Table 8 below for Examples 1 to 20 and Comparative Examples 1 to 5. and Comparative Example 6 are shown in Table 9 below.

First, the evaluation results of Examples 1 to 20 and Comparative Examples 1 to 6 will be discussed. As shown in Table 8, regarding the comparative study of ejection properties, it was confirmed that all the ink compositions of Examples 1 to 20 and Comparative Examples 1 and 3 were rated ◎, 〇, or △. Ta. Regarding the comparative study of coating area density, all the ink compositions of Examples 1 to 20 and all comparative examples of Comparative Examples 1 to 6 except Comparative Example 2 were evaluated as ◎, 〇, or △. I was able to confirm something. Regarding the comparative study of erased area density, all the ink compositions of Examples 1 to 20 and Comparative Examples 1 to 5 except Comparative Examples 1 and 3 were evaluated as ◎, 〇, or △. I was able to confirm that it was an evaluation.

By giving a rating of △ or higher for all evaluation items of ejectability, coating area density, and erasing area density, a practically usable writing density is ensured, and when the ink composition 30 is ejected onto the paper surface, the ink is In addition, the binder resin envelops the colored resin particles, making it possible to improve erasability.

In the evaluation study of Examples 1 to 20 and Comparative Examples 1 to 6, Comparative Examples 1 to 6 were evaluated as × in at least one evaluation item. On the other hand, Examples 1 to 8, 10, 11, 14 to 16, and 19, which had better evaluation results in which all the evaluation items were rated ○ or higher, had colored pigment particles and colored It was found that the difference in specific gravity with components other than resin particles was 0.25 or less. The ink compositions of Examples 1 to 5, 8, 10, 11, 14, and 16, which had even better evaluation results, had acrylic colored resin particles or urethane colored resin particles whose average particle diameter was 5. A dispersion liquid with a particle diameter of ~15 μm is blended, an amount of NBR is blended within a range of 19 to 26% by weight, and the difference in specific gravity between colored resin particles and components other than colored resin particles is 0. It was found to be less than .25.

Among Examples 1 to 20, the ink compositions of Examples 1, 2, and 10, which were rated ◎ in all evaluation items of ejectability, applied area density, and erased area density, and showed the best evaluation results, were colored. It was confirmed that the average particle diameter of the resin particles was 6 μm, the NBR content was 19 to 24% by weight, the difference in specific gravity between the colored resin particles and the solvent was 0.06 to 0.11, and the average particle diameter was 5 to 24% by weight. For an ink composition containing colored resin particles of 15 μm, this was found to be the optimal composition as an ink composition.

Next, the evaluation results of Examples 21 to 25 and Comparative Example 6 will be discussed. As shown in Table 9, in the comparative study of ejection properties, it was confirmed that all the ink compositions of Examples 21 to 25 and Comparative Example 7 were rated ◎. Regarding the comparative study of the concentration of the coated area, it was confirmed that only Comparative Example 7 was evaluated as ×, and Examples 21 to 25 were evaluated as ◎ or ○. Regarding the comparative study of erased area density, it was confirmed that all the ink compositions of Examples 21 to 25 and Comparative Example 7 were evaluated as ◎, ○, or △.

In the evaluation study of Examples 21 to 25 and Comparative Example 7, Examples 24 and 25, which had better evaluation results with all evaluation items being rated ○ or higher, had components other than colored pigment particles and colored resin particles. It was found that the difference in specific gravity between the two was 0.05. The ink composition of Example 25, which had even better evaluation results, contained a dispersion of polystyrene-based colored resin particles with an average particle diameter of 3 μm, and the NBR content was 24% by weight. It was confirmed that the difference in specific gravity between colored resin particles and components other than colored resin particles was 0.05, and in an ink composition containing colored resin particles with an average particle diameter of less than 5 μm, this It was found that the composition was optimal.

(Second example)
In the second example, the thickness of the film formed by the ink composition discharged onto the paper surface was measured. The ink composition used in the measurement was the ink composition of Example 2 shown in Table 2 above. Further, the ink composition was discharged from a ballpoint pen, and the paper surface on which the ink composition was discharged was a base paper compliant with JIS-S-5504.

Specifically, the film thickness was measured as follows. First, an ink composition was discharged onto a paper surface to draw five straight lines. Next, the vicinity of the center of each straight line was erased using the general eraser used in the first example. Next, the thickness of each straight line was measured at a portion where the ink composition had not been erased and a portion where the ink composition had been erased. Then, the difference between the area where the ink composition was not erased and the area where the ink composition was erased was calculated, and this was taken as the film thickness. This eliminates the effect of dents on the paper surface caused by pen pressure.

The film thickness was measured using a level difference meter (Keyence: VR-3000) at two locations per straight line (one location where the ink composition was not erased and one where the ink composition was erased). A total of 10 areas (area 1 to area 10) were measured. The measurement results are shown in Table 10 below.

As shown in Table 10, it was confirmed that the film thickness formed by the ink composition discharged onto the paper surface was within the range of 16 to 56 μm. Also, take into consideration that the minimum particle size of the colored resin particles blended into the ink composition is about 1 μm, and that particles other than colored resin particles such as glitter (average particle size 100 μm) may be mixed in. As a result, it was estimated that the film formed by the ink composition would have a thickness within the range of 1 to 100 μm.

10 ballpoint pen 10a pen tip 10b pen end 12 case 14 cap 20 character eraser 30 ink composition

Claims (9)

An ink composition having erasability,
Containing at least colored resin particles having an average particle diameter of 5 to 15 μm, a binder resin, and a solvent,
The difference between the specific gravity of the colored resin particles and the specific gravity of components other than the colored resin particles is 0.06 or more and 0.7 or less,
Forming a film in which the binder resin envelops the colored resin particles on the paper surface to be discharged without the colored resin particles settling on the paper surface to be discharged;
Ink composition. The ink composition according to claim 1, wherein the difference between the specific gravity of the colored resin particles and the specific gravity of components other than the colored resin particles is 0.25 or less. The ink composition according to claim 2, which forms a film having fixability on the paper surface onto which it is ejected. The ink composition according to claim 3, wherein the thickness of the film is within the range of 1 to 100 μm. The ink composition according to claim 1, wherein the binder resin is acrylonitrile butadiene rubber. The ink composition according to claim 4, comprising 19 to 26 parts by weight of the acrylonitrile butadiene rubber. The ink composition according to claim 1, wherein the colored resin particles are acrylic resin particles or urethane resin particles. The ink composition according to claim 1, wherein the added amount of the colored resin particles is 10 to 20% by weight, and the added amount of the thickener is 0.4% by weight or less. A writing instrument filled with the ink composition according to any one of claims 1 to 7.

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