JP-2026076117-A - Thermochromic ink composition for writing instruments and writing instruments containing the same

Abstract

[Problem] To provide a thermochromic ink composition for writing instruments and a writing instrument containing it, which can achieve dispersion stability without increasing viscosity, even when using a poorly dispersible material such as microcapsule pigments as a coloring agent in an aqueous ink with excellent drying properties using a sugar mixture. [Solution] A thermochromic ink composition for writing instruments comprising a microcapsule pigment containing a thermochromic composition, water, sugar A which is a sugar mixture containing 30% by mass or more of a starch saccharified product of 8 or more sugars and/or its reduced product, and sugar B which is 3 or less sugar, wherein the mass ratio of sugar A to sugar B incorporated in the ink is in the range of B/A ≥ 2, and a writing instrument containing the same. [Selection Diagram] None

Inventors

• 山田 亮

Assignees

• 株式会社パイロットコーポレーション

Dates

Publication Date

20260511

Application Date

20251003

Priority Date

20241023

Claims (9)

1. It consists of a microcapsule pigment containing a thermochromic composition, water, sugar A which is a sugar mixture containing 30% by mass or more of starch saccharified products and/or reduced products thereof of 8 or more sugars, and sugar B which contains 3 or fewer sugars. A thermochromic ink composition for writing instruments in which the mass ratio of sugar A and sugar B blended in the ink is in the range of B/A ≥ 2.
2. The thermochromic ink composition for writing instruments according to claim 1, wherein the aforementioned sugar A is contained in the ink composition in an amount of 0.5 to 5.0% by mass.
3. The thermochromic ink composition for writing instruments according to claim 1, wherein the sugar B is one or more selected from trehalose, palatinose, and fructose.
4. The thermochromic ink composition for writing instruments according to claim 1, wherein the microcapsule pigment is added in an amount of 10 to 35% by mass of the total ink composition.
5. A thermochromic ink composition for writing instruments according to claim 1, containing hollow particles.
6. The thermochromic ink composition for writing instruments according to claim 5, wherein the particle size of the hollow particles is in the range of 0.1 to 1 times the particle size of the microcapsule pigment.
7. A thermochromic ink composition for writing instruments according to claim 1, wherein the viscosity at 20°C is in the range of 1 to 30 mPa·s.
8. A writing instrument containing the thermochromic ink composition for writing instruments described in any one of claims 1 to 7.
9. The writing instrument according to claim 8, comprising a friction member that changes the color of the writing produced by the aforementioned writing instrument due to frictional heat.

Description

This invention relates to a thermochromic ink composition for writing instruments. Furthermore, it relates to a thermochromic ink composition and writing instrument with excellent dispersion stability. In recent years, ballpoint pens and marking pens that use frictional heat to erase or change the color of the writing have become widely popular. These writing instruments use microcapsule pigments containing a thermochromic composition as a coloring agent. However, since these pigments have poor dispersibility in aqueous media, shear-reducing agents and thickeners are added to increase the viscosity of the ink and ensure dispersion stability in the ink. In ballpoint pens using the aforementioned microcapsule pigment along with a shear viscosity reducing agent, there is a drawback that drying (dry-up) is likely to occur due to moisture evaporation from the pen tip. Therefore, a technique has been disclosed in which a sugar mixture containing 30% by mass or more of a starch saccharified product of eight or more sugars and/or its reduced product is used in combination with the shear viscosity reducing agent (see, for example, Patent Documents 1 and 2). The aforementioned sugar mixture is useful because, when the ballpoint pen tip is exposed to air for a long period of time, it forms a brittle film that suppresses moisture evaporation from the pen tip. When writing again, the film easily breaks down when the pen tip is brought into contact with the paper surface, resulting in good writing from the start. Furthermore, since its addition can increase ink viscosity, more stable pigment dispersion can be obtained by adjusting the amount added, making it a highly versatile material for gel inks. However, increasing the amount of additive to the ink to increase its viscosity can cause smudging in the writing, so the amount of additive needs to be adjusted. Furthermore, because it is necessary to use a shear viscosity reducer in combination with the microcapsule pigment to achieve dispersion stability, its application was limited to refillable ballpoint pens. Japanese Patent Publication No. 2011-174030Japanese Patent Publication No. 2011-178979 In this invention, we have found that, in a water-based ink with excellent drying properties using the aforementioned sugar mixture, even when using a material that tends to settle, such as microcapsule pigments, as a coloring agent, the dispersion stability of the microcapsule pigments can be maintained without increasing the viscosity of the ink by using sugars of three saccharides or less in combination with the sugar mixture in a specific ratio. Therefore, this invention is not limited to refillable ballpoint pens with a pipe in the ink reservoir, but can be widely applied to general-purpose writing instruments. This results in a thermochromic writing instrument ink with excellent drying properties and dispersion stability, enabling the formation of superior handwriting in various types of writing instruments. Microcapsule pigments containing thermochromic compositions are used as colorants. Any type of thermochromic composition encapsulated in microcapsules, regardless of whether the change is reversible or irreversible, can be applied. By heating or cooling the handwriting, the hue of the writing can be changed, or the writing can be decolorized or colored. This change in the handwriting can be achieved stably over a long period without compositional changes by encapsulating the thermochromic composition in microcapsules. 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 to 7°C). Furthermore, there are those exhibiting relatively large hysteresis