JP7523344B2 - Friction member and thermochromic writing material including same - Google Patents

Description

The present invention relates to a friction member and a thermochromic writing material that includes the same.

Friction members that cause writing marks formed with a thermochromic writing material to fade and/or change color due to frictional heat, and thermochromic writing materials that contain such friction members, have been widely known for some time. Examples of such friction members include those made of styrene-butylene-styrene (SBS) copolymer or styrene-ethylene-butylene-styrene (SEBS) copolymer, as described in Patent Document 1.

JP 2006-123324 A

In recent years, thermochromic cursive writing materials have come to be used together with non-thermochromic cursive writing materials, and it has become common for handwriting made with thermochromic cursive writing materials to coexist with handwriting made with non-thermochromic cursive writing materials on the same paper.
In the above-mentioned cases, when the handwriting of the thermochromic cursive material is erased by rubbing with a conventional friction member, the handwriting of the nearby non-thermochromic cursive material is also rubbed at the same time, and as a result, the handwriting of the non-thermochromic cursive material may spread (or be scattered) to the periphery, thereby impairing the appearance (appearance) of the handwriting.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a friction member that can erase the handwriting of a thermochromic cursive body when the handwriting of a non-thermochromic cursive body is rubbed against the thermochromic cursive body together with the handwriting of a non-thermochromic cursive body, and a thermochromic cursive body that includes the friction member, and can adequately maintain the appearance of the handwriting of the non-thermochromic cursive body.

Aspect 1 of the present invention is
A friction member that thermally discolors handwriting formed with a thermochromic writing material by frictional heat,
The hardness measured by a type D durometer is 55 to 90;
The friction member has a dynamic friction coefficient of 0.25 to 0.50.

Aspect 2 of the present invention is the friction member according to aspect 1, in which the hardness is 65 to 80 and the dynamic friction coefficient is 0.25 to 0.35.

Aspect 3 of the present invention is the friction member according to aspect 1 or 2, in which the friction member includes an organic polymer material.

Aspect 4 of the present invention is the friction member according to aspect 3, in which the organic polymer material includes a polyethylene resin.

Aspect 5 of the present invention is a thermochromic writing material that includes the friction member described in any one of aspects 1 to 4.

According to an embodiment of the present invention, it is possible to provide a friction member that can erase the handwriting of a thermochromic cursive body when the handwriting of a non-thermochromic cursive body is rubbed against the thermochromic cursive body together with the handwriting of a non-thermochromic cursive body, and a thermochromic cursive body including the friction member, and can adequately maintain the appearance of the handwriting of the non-thermochromic cursive body.

1 is a color density-temperature curve of a reversible thermochromic composition. 1 is an image showing the results of evaluation 1 of Example 1. 13 is an image showing the results of evaluation 1 in Example 2. 13 is an image showing the results of evaluation 1 in Example 3. 13 is an image showing the result of evaluation 1 of Comparative Example 1. 13 is an image showing the result of evaluation 1 of Comparative Example 2. 1 is an image showing the results of evaluation 2 in Example 1. 13 is an image showing the results of evaluation 2 of Example 2. 13 is an image showing the results of evaluation 2 in Example 3. 13 is an image showing the result of evaluation 2 of Comparative Example 1. 13 is an image showing the result of evaluation 2 of comparative example 2.

The present inventors have conducted extensive research to solve the above problems, and as a result, have found that by controlling the hardness and dynamic friction coefficient of the friction member within an appropriate range, it is possible to obtain a friction member that can erase the handwriting of a thermochromic writing body and can adequately maintain the appearance of the handwriting of a non-thermochromic writing body when the handwriting of a thermochromic writing body is rubbed against the thermochromic writing body together with the handwriting of a non-thermochromic writing body, and a thermochromic writing body including the friction member.
Hereinafter, the friction member and the thermochromic writing material including the same according to the embodiment of the present invention will be described in detail.

1. Friction Member The friction member according to the embodiment of the present invention is a member for thermally discoloring handwriting formed with a thermochromic writing material by frictional heat, and has a hardness of 55 to 90 as measured with a type D durometer hardness meter, and a dynamic friction coefficient of 0.25 to 0.50. By setting the hardness and dynamic friction coefficient within the above ranges, when the handwriting of a non-thermochromic writing material is rubbed together with the handwriting of the thermochromic writing material, the handwriting of the thermochromic writing material can be erased, and the appearance of the handwriting of the non-thermochromic writing material can be sufficiently maintained.

If the hardness is less than 55, the writing will be easily deformed along the depression on the paper surface formed along with the handwriting when rubbed, and the ink on the writing of the non-thermochromic cursive will be easily moved, resulting in the writing of the non-thermochromic cursive spreading out (or scattering). Preferably, the hardness is 65 or more. On the other hand, if the hardness is more than 90, it will be difficult to erase the writing of the thermochromic cursive, and it will be necessary to rub it many times (or strongly) to erase it, resulting in the writing of the non-thermochromic cursive spreading out (or scattering). Preferably, the hardness is 80 or less.

If the kinetic friction coefficient is less than 0.25, it becomes difficult to erase the handwriting of the thermochromic cursive, and as a result of repeatedly (or strongly) rubbing in an attempt to erase it, the handwriting of the non-thermochromic cursive also spreads (or scatters). On the other hand, if the kinetic friction coefficient is more than 0.50, the ink on the handwriting of the non-thermochromic cursive is easily shifted when rubbed, and as a result, the handwriting of the non-thermochromic cursive spreads (or scatters). Preferably, the kinetic friction coefficient is 0.35 or less.

The hardness is measured as follows using a D-type durometer (Durometer manufactured by Techlock Corporation, Model: GS-720G). First, the core tip of the durometer is placed above the tip of the friction member so that the normal line of the core tip and the normal line of the tip of the friction member (corresponding to the tip (abrasion part) of the friction member in the longitudinal direction of the writing body when attached to the writing body) roughly coincide with each other. Then, the peak value of the durometer when the core tip is pressed against the friction member under an environment of 25°C and 50% RH with a load of 5.0 kgf and a speed of 3 mm/sec is defined as the hardness of the friction member.
In order to measure as described above, for example, when the longitudinal direction of the writing body to which the friction member is attached roughly coincides with the normal line of the tip of the friction member, the writing body to which the friction member is attached may be cut so that the cut surface is roughly perpendicular to the longitudinal direction of the writing body, and then, with the cut surface facing down, the part including the friction member may be placed on a durometer hardness meter so that the tip of the core of the durometer hardness meter is positioned above the tip of the friction member, and the tip of the core may be pressed against the friction member to measure the hardness of the friction member. In this case, when the tip of the friction member is a flat surface, the part including the friction member may be placed so that the tip of the core of the durometer hardness meter is positioned above the center of the flat surface.

The dynamic friction coefficient is measured by measuring the force F (load parallel to the paper) applied to the friction member when the friction member is run on the paper so that the tip of the friction member rubs against the paper using a HEIDON friction wear tester (manufactured by Shinto Scientific Co., Ltd., Tribogear Type: 14). The force F and the load N (200 gf) applied to the friction member (perpendicular to the paper) are applied to F = μ (dynamic friction coefficient) × N to calculate the dynamic friction coefficient μ. Sampling of the force F is performed at 0.001 second intervals, and the force F measured from the start of measurement to 0.3 seconds after the start of measurement is not used to calculate the dynamic friction coefficient. The paper surface is the front side of NPi Form <55> (manufactured by Nippon Paper Industries Co., Ltd.), the measurement environment is 23°C, 42% RH, the running speed is 4 m/min, the running distance is 10 cm, and the angle between the normal to the tip of the friction body and the paper surface is 90°. In addition, three measurement samples are prepared for each friction member, one measurement is performed for each measurement sample, and the average value of the measurements for the three measurement samples is regarded as the dynamic friction coefficient of the friction member.

The friction member preferably contains an organic polymer material. This makes it easier to adjust the hardness and dynamic friction coefficient to the above ranges. The friction member preferably contains more than 50% by mass of an organic polymer material, more preferably contains 75% by mass or more of an organic polymer material, even more preferably contains 90% by mass or more of an organic polymer material, and even more preferably is made of an organic polymer material.

The organic polymer material preferably contains at least one selected from the group consisting of relatively hard synthetic resins such as polyolefin resin, polycarbonate, polyethylene terephthalate, polyacetal, acrylic, nylon, acrylonitrile-styrene copolymer resin (AS resin) and acrylonitrile-butadiene-styrene copolymer resin (ABS resin), styrene-based, olefin-based, polystyrene and polyolefin block copolymer, urethane-based, polyester-based, polyamide-based, 1,2-polybutadiene-based, vinyl chloride-based and fluorine-based thermoplastic elastomers, blends of polypropylene and ethylene-propylene-based rubber, blends of butadiene and acrylonitrile copolymer, and blends of chlorinated polyethylene and nylon, rubber elastomers such as silicone rubber, and natural rubber. This makes it easier to adjust the hardness and dynamic friction coefficient to the above ranges. Among them, the inclusion of polyethylene makes it easier to adjust the hardness and dynamic friction coefficient to the above preferred ranges. Examples of polyolefin resins include polyethylene resins such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and high-pressure low-density polyethylene; polypropylene resins such as isotactic polypropylene and syndiotactic polypropylene; poly-1-butene, poly-4-methyl-1-pentene, poly-3-methyl-1-butene, ethylene/α-olefin copolymer, propylene/α-olefin copolymer, 1-butene/α-olefin copolymer, cyclic olefin copolymer, and chlorinated polyolefin.
Among these, polyethylene resin has the advantages of being less susceptible to oxidation and having good weather resistance, and of not losing strength even at low temperatures, making it less susceptible to deterioration even with long-term use and suitable for use in cold regions, as compared with, for example, polypropylene resin, etc. Preferably, the friction member contains more than 50% by mass of polyethylene resin, more preferably contains 75% by mass or more of polyethylene resin, even more preferably contains 90% by mass or more of polyethylene resin, and even more preferably is made of polyethylene resin.

The friction member preferably has a convex curved shape. The convex curved shape makes it easy to rub the handwriting appropriately without peeling it off. In addition, a constant contact area is obtained regardless of the contact angle with the handwriting, and only the desired area can be rubbed without rubbing a wide area. Furthermore, the abrasion of the friction member itself can be reduced, heat generation efficiency can be increased, and scraping debris is less likely to be produced, making it possible to accurately and easily discolor the area to be discolored. The radius of curvature of the convex curved surface is preferably set in the range of 1 mm to 10 mm. By setting it in the above range, narrow handwriting formed by cursive writing can be accurately and easily discolored.

The friction member may contain various additives within the scope of the present invention. For example, a colorant selected from general-purpose dyes and pigments may be added to the friction member to improve the design, or a color display part may be made to match the color of the handwriting. Furthermore, various additives such as fillers may be added to the friction member as necessary.

There are no particular limitations on the method for producing the friction member, and any known method can be used. For example, the friction member can be produced by kneading the material and molding it into a desired shape.

2. Thermochromic Writing Body The thermochromic writing body according to the embodiment of the present invention includes the above-mentioned friction member. In consideration of portability, for example, the friction member may be fixed to the thermochromic writing body. The location where the friction member is fixed is not particularly limited, and examples thereof include the tip portion (top) of the cap, the rear end portion of the barrel (the portion where the writing tip portion is not provided), etc.

The thermochromic writing material can incorporate a thermochromic ink composition. The thermochromic ink composition contains a reversible thermochromic microencapsulated pigment (hereinafter sometimes referred to as "microencapsulated pigment" or "MC pigment" (Micro Capsule pigment)) as a colorant. The microencapsulated pigment is a microcapsule in which the reversible thermochromic composition is encapsulated. The reversible thermochromic composition contains an electron-donating color-forming organic compound, an electron-accepting compound, and a reaction medium that determines the temperature at which the color reaction of the electron-donating color-forming organic compound and the electron-accepting compound occurs. The microencapsulated pigment loses color when exposed to heat, i.e., it changes from colored to, for example, white or light colored.

As the reversible thermochromic composition contained in the microencapsulated pigment, those described in JP-B-51-44706, JP-B-51-44707, JP-B-1-29398, JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, and JP-A-8-39936 can be used. The reversible thermochromic composition changes color around a certain temperature boundary, exhibiting a colored or decolored state, and the color change has hysteresis. The hysteresis characteristics in the color density-temperature curve of the reversible thermochromic composition are explained with reference to Figure 1.

1, the vertical axis represents color density, the horizontal axis represents temperature, and the change in color density due to temperature change progresses along the arrows. A is a point indicating the density at temperature _t4 (hereinafter referred to as complete decolorization temperature) at which the completely decolorized state is reached, B is a point indicating the density at temperature _t3 (hereinafter referred to as decolorization onset temperature) at which decolorization starts, C is a point indicating the density at temperature _t2 (hereinafter referred to as color development onset temperature) at which color development starts, and D is a point indicating the density at temperature _t1 (hereinafter referred to as complete color development temperature) at which the completely colored state is reached.

The color change temperature range is the temperature range between _t1 and _t4 , where the material can exhibit either a colored state or a decolored state, and the temperature range between _t2 and _t3 , where the difference in color density is large, is the temperature range where the material substantially maintains two phases.

The length of line segment EF is a measure of the contrast of the discoloration, and the length of line segment HG passing through the midpoint of line segment EF is the temperature width (hereinafter sometimes referred to as the "hysteresis width ΔH") that indicates the degree of hysteresis. If the hysteresis width is large, the color density changes along significantly different paths when the temperature is increased from the lower side of the discoloration temperature range, and conversely, when the temperature is decreased from the higher side of the discoloration temperature range. If this ΔH value is small, only one specific state of both the states before and after discoloration will exist in the room temperature range, while if the ΔH value is large, it is easier to maintain both states before and after discoloration.

The above-mentioned JP-B-51-44706, JP-B-51-44707, and JP-B-1-29398, etc., describe reversible thermochromic compositions of the heat-discoloring type (discolored by heating and colored by cooling) with a relatively small hysteresis width ΔH of 1.5°C to 3.8°C. In addition, the above-mentioned JP-B-4-17154, JP-A-7-179777, JP-A-7-33997, and JP-A-8-39936, etc., describe reversible thermochromic compositions of the heat-discoloring type with a relatively large hysteresis width ΔH of 8°C to 70°C. In other words, the shape of the curve plotting the change in color density with temperature changes follows a path that is significantly different when the temperature is increased from a lower temperature side than the discoloration temperature range than when the temperature is decreased from a higher temperature side than the discoloration temperature range.

For example, the reversible thermochromic composition has a complete color development temperature t ₁ of a freezer or a cold region (for example, -50 ° C. or more and 0 ° C. or less, preferably -40 ° C. or more, more preferably -30 ° C. or more, preferably -5 ° C. or less, more preferably -10 ° C. or less), a complete decolorization temperature t ₄ of frictional heat by a friction body or heat from a heating body such as a hair dryer (for example, 45 ° C. or more and 95 ° C. or less, preferably 50 ° C. or more, more preferably 60 ° C. or more, preferably 90 ° C. or less, more preferably 80 ° C. or less), and a ΔH value of 40 ° C. or more and 100 ° C. or less, so that the composition can function effectively by maintaining the color exhibited in normal conditions (daily living temperature range). In addition, from the viewpoint of functioning more effectively by maintaining the color exhibited in normal conditions, the color development initiation temperature of the reversible thermochromic composition is preferably -10 ° C. or less. In addition, the complete color development temperature is preferably lower than the color development initiation temperature.

The method for encapsulating the reversible thermochromic composition in the microcapsules is not particularly limited, and examples thereof include the interfacial polymerization method, the interfacial polycondensation method, the in situ polymerization method, the liquid hardening coating method, the phase separation method from an aqueous solution, the phase separation method from an organic solvent, the melt dispersion cooling method, the air suspension coating method, and the spray drying method, and may be appropriately selected depending on the application.

Materials for the microcapsules include organic resins, such as epoxy resins, urea resins, urethane resins, and isocyanate resins.

By providing a secondary resin coating on the surface of the microcapsules according to the purpose, durability can be imparted, and the surface properties can be modified for practical use.

The mass ratio of the microcapsule (i.e., the microcapsule wall portion not encapsulating the reversible thermochromic composition) to the reversible thermochromic composition is preferably 1 part by mass or more, more preferably 1 part by mass or more, and preferably 7 parts by mass or less, more preferably 6 parts by mass or less, of the reversible thermochromic composition per part by mass of the microcapsule. By making the reversible thermochromic composition 7 parts by mass or less per part by mass of the microcapsule, it becomes easy to make the microcapsule wall have an appropriate wall thickness without becoming too thin, and it becomes easy to improve the heat resistance and pressure resistance of the microcapsule pigment. In addition, by making the reversible thermochromic composition 1 part by mass or more per part by mass of the microcapsule, it becomes easy to improve the color density and clarity when the microcapsule pigment develops color.

After being decolorized by heat, the microencapsulated pigment remains on the writing surface (paper surface, etc.) in a white or lightly colored state. Therefore, it is preferable that the traces left after the handwriting is decolorized by heat are not noticeable (hereinafter, this may be referred to as "excellent thermal decolorization property"). It is also preferable that the microencapsulated pigment is more inhibited from falling off when the handwriting is rubbed with a friction member and decolorized by frictional heat (hereinafter, this may be referred to as "excellent non-falling property").

From the viewpoint of further improving one or more of thermal decolorization and non-detachment, the content of the microcapsule pigment is preferably 50% by mass or less, more preferably 35% by mass or less, and even more preferably 10% by mass or less. The number of decolorized microcapsule pigments contained in the trace after the writing of the thermochromic writing body is decolorized by heat can be reduced, so that the trace is less noticeable. In addition, since the number of microcapsule pigments attached to the writing body is small, when the writing of the thermochromic writing body and the writing of the non-thermochromic writing body are rubbed with a friction member, the detachment of the microcapsule pigments accompanying the writing of the non-thermochromic writing body from the writing body can be more suppressed, and the writing of the non-thermochromic writing body becomes less likely to be interrupted.
Furthermore, by setting the content of the microencapsulated pigment to preferably 50% by mass or less, more preferably 35% by mass or less, and even more preferably 10% by mass or less, the ink ejection properties become better and a smooth writing feel can be more easily obtained when using a thermochromic writing material.
There is no particular lower limit to the content of the microencapsulated pigment, but from the viewpoint of more easily increasing the visibility of the handwriting of the thermochromic cursive material, the content of the microencapsulated pigment is preferably 1 mass % or more, and more preferably 5 mass % or more.
The microcapsule pigment may be used alone or in combination of two or more kinds.

From the viewpoint of further improving one or more of thermal decolorization and non-detachment, the average particle size of the microcapsule pigment is preferably 50 μm or less, more preferably 5.0 μm or less, and even more preferably 1.0 μm or less. The decolorized microcapsule pigment contained in the trace after the handwriting of the thermochromic writing body is thermally decolorized is small, and the transparency of the decolorized microcapsule pigment is high, so that the trace is less noticeable. In addition, since the microcapsule pigment attached to the writing body is small, when the handwriting of the thermochromic writing body and the handwriting of the non-thermochromic writing body are rubbed with a friction member, the desorption of the microcapsule pigment accompanying the handwriting of the non-thermochromic writing body from the writing body can be more suppressed, and the handwriting of the non-thermochromic writing body is less likely to be interrupted.
Furthermore, by setting the average particle size of the microencapsulated pigment to preferably 50 μm or less, more preferably 5.0 μm or less, and even more preferably 1.0 μm or less, the ink ejection properties become better, and a smooth writing feel can be more easily obtained when using a thermochromic writing material.
Although the lower limit of the average particle size of the microencapsulated pigment is not particularly limited, from the viewpoint of more easily increasing the color density and clarity when the microencapsulated pigment develops color, the average particle size of the microencapsulated pigment is preferably 0.01 μm or more, more preferably 0.1 μm or more, and even more preferably 0.5 μm or more. In addition, by setting the average particle size of the microencapsulated pigment within the above range, the penetration of the microencapsulated pigment into the fibers of the writing object, for example, paper, can be more suppressed, so that when the handwriting of the thermochromic writing object is rubbed with a rubbing member to erase the color, the erasure becomes easier.

The average particle diameter of the microcapsule pigment may be determined, for example, by using Mountech's image analysis particle size distribution measurement software "MacView" to determine the particle area, calculating the projected area circle equivalent diameter (Heywood diameter) from the area of the particle area, and measuring the average particle diameter of the particles equivalent to a sphere of equal volume using this value.

In addition, when the particle diameter of all or most of the particles exceeds 0.2 μm, the average particle diameter of the microencapsulated pigment may be measured as the average particle diameter of particles equivalent to an equal volume sphere by the Coulter method using, for example, a particle size distribution measuring device "Multisizer 4e" manufactured by Beckman Coulter, Inc. In addition, the volume-based particle diameter and average particle diameter (median diameter) of the microencapsulated pigment may be measured using, for example, a laser diffraction/scattering type particle size distribution measuring device "LA-300" manufactured by Horiba, Ltd., calibrated based on values measured using a standard sample or a measuring device using the Coulter method (electrical detection zone method).

The thermochromic ink composition may be oil-based or water-based, but for example, taking into consideration the ink ejection properties, etc., a water-based thermochromic ink composition may be used.

When the thermochromic ink composition is aqueous, it contains water as the main solvent. The water is not particularly limited and may be, for example, ion-exchanged water, ultrafiltered water, or distilled water. The water content may be appropriately controlled in consideration of the component composition so as to obtain the desired characteristics.

Below, we will explain other components that may be included in the thermochromic ink composition, using the example of a water-based thermochromic ink composition.

The thermochromic ink composition may contain polysaccharides. Polysaccharides have various effects, mainly imparting shear thinning properties (shear thinning agent), improving resistance to drying up, and adjusting the ink viscosity (thickener).

Here, the shear thinning property is a property that the ink composition has a high viscosity when left at rest and decreases when a shear force is applied. Examples of ballpoint pens include those that contain an ink composition generally called gel ink. The gel ink has a high viscosity when left at rest without shear stress and is stably held in the writing body, and when writing, the ink near the ball becomes less viscous due to the high shear force generated by the high speed rotation of the ball, and as a result, the ink is discharged from the gap between the ball and the ball housing and adheres to the writing object. By containing polysaccharides, the thermochromic ink composition can be made into a gel ink.
Furthermore, for example, when the thermochromic ink composition is used in a ballpoint pen or a marking pen, particularly a knock-type ballpoint pen, the pen tip is placed in a state where it is easily dried out, and as a result, the writing tool may become unable to write with the pen, which is called a dry-up state.

Examples of polysaccharides include succinoglycan, xanthan gum, welan gum, guar gum, locust bean gum, carrageenan, diutan gum, and derivatives thereof, as well as cellulose derivatives, glycomannan, gelling polysaccharides extracted from seaweed such as agar and carrageenin, and dextrin. Examples of cellulose derivatives include methylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and salts thereof.

By using dextrin or a cellulose derivative, it may be possible to simultaneously obtain effects such as imparting shear thinning properties, improving resistance to drying up, and adjusting the ink viscosity. Dextrin is preferred because it is highly effective in improving resistance to drying up.

The dextrin is preferably, for example, a sugar mixture containing starch saccharification products of 8 or more sugars and/or reduced products thereof. The sugar mixture preferably contains 30% by mass or more of starch saccharification products of 8 or more sugars, etc., more preferably 50% by mass or more, and even more preferably 70% by mass or more. Dextrin is preferable because it has excellent film-forming properties and is highly effective in suppressing water evaporation from the pen tip when the thermochromic ink composition is applied to a cursive writing instrument.

The polysaccharides may be used alone or in combination of two or more kinds.
When the thermochromic ink composition contains a polysaccharide, the content of the polysaccharide is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and is preferably 1.0% by mass or less, more preferably 0.5% by mass or less.

When the thermochromic ink composition contains succinoglycan and/or xanthan gum, the total content of succinoglycan and/or xanthan gum is preferably 0.01% by mass or more and 1.0% by mass or less. This makes it easy to maintain a high level of ink ejection characteristics from the pen tip and easily suppress aggregation of the microencapsulated pigment. The content of succinoglycan or xanthan gum is more preferably 0.1% by mass or more, and more preferably 0.5% by mass or less.

When the thermochromic ink composition contains dextrin or a cellulose derivative, the content of dextrin or cellulose derivative is preferably 0.1% by mass or more and 5% by mass or less. This makes it easy to maintain a high level of ink ejection characteristics from the pen tip, and also makes it easy to suppress ink dripping from the pen tip and water evaporation.

The thermochromic ink composition may contain polyvinylpyrrolidone (hereinafter sometimes referred to as "PVP"), which is a polymer of N-vinyl-2-pyrrolidone. This has the effects of improving the dry-up resistance, adjusting the ink viscosity (thickening agent), suppressing the aggregation of microencapsulated pigments, improving the adhesion and tackiness of the ink components to paper, etc., and by using PVP, it is sometimes possible to obtain all of these effects at the same time.

The degree of polymerization of PVP is preferably from 2 to 20, more preferably from 10 to 6. By making the degree of polymerization from 2 to 20, it is possible to easily suppress an increase in the ink viscosity and aggregation of the microencapsulated pigment when the water in the thermochromic ink composition evaporates.

When the thermochromic ink composition contains PVP, the PVP content is preferably 1% by mass or more, more preferably 2% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less.

The thermochromic ink composition may contain a thickener other than polysaccharides. Examples of the thickener include alginic acid alkyl esters, polymers having a molecular weight of 100,000 to 150,000, mainly composed of alkyl esters of methacrylic acid, benzylidene sorbitol, benzylidene xylitol, and derivatives thereof, as well as nonionic surfactants having an HLB value of 8 to 12, such as crosslinkable acrylic acid polymers, inorganic fine particles, polyglycerin fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene castor oil, polyoxyethylene lanolin, lanolin alcohol, and beeswax derivatives, polyoxyethylene alkyl ethers, polyoxypropylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and fatty acid amides, and further include salts of dialkyl sulfosuccinic acid or salts of dialkenyl sulfosuccinic acid.
The thickeners other than polysaccharides may be used alone or in combination of two or more kinds.

The thermochromic ink composition may contain a surfactant. Examples of surfactants include phosphate ester surfactants, silicone surfactants, surfactants having an acetylene bond in the structure, and fluorine-based surfactants. These surfactants can be appropriately selected depending on the components and applications of the thermochromic ink composition. For example, when the thermochromic ink composition is used in a ballpoint pen, a phosphate ester surfactant is preferred.

The surfactant may be used alone or in combination of two or more kinds.
When the thermochromic ink composition contains a surfactant, the content of the surfactant is preferably 0.1 mass % or more, more preferably 0.3 mass % or more, and is preferably 2.0 mass % or less, more preferably 1.5 mass % or less.

The thermochromic ink composition may contain a pH adjuster. In order to adjust the pH of the thermochromic ink composition to an appropriate range, various acids or bases can be used as pH adjusters. Examples of pH adjusters include inorganic salts such as ammonia, sodium carbonate, sodium phosphate, sodium hydroxide, and sodium acetate, organic basic compounds such as water-soluble amine compounds such as triethanolamine and diethanolamine, lactic acid, and citric acid.

The pH adjusters may be used alone or in combination of two or more.
When the thermochromic ink composition contains a pH adjuster, the content of the pH adjuster is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and is preferably 5.0% by mass or less, more preferably 2.0% by mass or less.

In addition, when the thermochromic ink composition is incorporated in a ballpoint pen, the thermochromic ink composition may contain a lubricant to easily prevent wear of the ball seat. Examples of the lubricant include higher fatty acids such as oleic acid, nonionic surfactants having a long-chain alkyl group, polyether-modified silicone oils, thiophosphite triesters such as thiophosphite tri(alkoxycarbonylmethyl ester) and thiophosphite tri(alkoxycarbonylethyl ester), polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphoric acid monoesters, polyoxyethylene alkyl ether or polyoxyethylene alkylaryl ether phosphoric acid diesters, their metal salts, ammonium salts, amine salts, and alkanolamine salts.
The lubricant may be used alone or in combination of two or more kinds.

If necessary, a resin such as an acrylic resin, a styrene-maleic acid copolymer, or a polyvinyl alcohol may be added to the thermochromic ink composition to impart adhesion and viscosity to the paper surface.
The resins may be used alone or in combination of two or more kinds.

The thermochromic ink composition may contain a rust inhibitor such as, for example, benzotriazole, tolyltriazole, dicyclohexylammonium nitrite, diisopropylammonium nitrite, and saponin.
The rust inhibitors may be used alone or in combination of two or more kinds.

The thermochromic ink composition may contain a preservative or antifungal agent, such as, for example, carbolic acid, the sodium salt of 1,2-benzthiazolin-3-one, sodium benzoate, sodium dehydroacetate, potassium sorbate, propyl paraoxybenzoate, and 2,3,5,6-tetrachloro-4-(methylsulfonyl)pyridine.
The preservatives and antifungal agents may each be used alone or in combination of two or more kinds.

The thermochromic ink composition may contain humectants such as, for example, urea, reduced or non-reduced starch hydrolysates, and oligosaccharides such as trehalose, sucrose, glucose, sorbitol, mannitol, sodium pyrophosphate, and the like.
The wetting agent may be used alone or in combination of two or more kinds.

The thermochromic ink composition may contain a defoamer, a dispersant, a specific gravity adjuster, etc., each of which may be used alone or in combination of two or more kinds.

The thermochromic ink composition may contain a water-soluble organic solvent that is compatible with water in order to improve the quick-drying property. Examples of the water-soluble organic solvent include ethanol, propanol, butanol, glycerin, sorbitol, triethanolamine, diethanolamine, monoethanolamine, ethylene glycol, diethylene glycol, thiodiethylene glycol, polyethylene glycol, propylene glycol, butylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, sulfolane, 2-pyrrolidone, and N-methyl-2-pyrrolidone.
The water-soluble organic solvent may be used alone or in combination of two or more kinds.

The method for producing the thermochromic ink composition is not particularly limited, and a commonly known method may be used. For example, the thermochromic ink composition may be produced by stirring a mixture of the above-mentioned components with a stirrer such as a propeller stirrer, homodisper or homomixer, or by dispersing the mixture with a disperser such as a bead mill.

Examples of thermochromic writing media include ballpoint pens, marking pens, brush pens, fountain pens, and calligraphy pens. In one embodiment, the thermochromic writing media is a ballpoint pen refill or a marking pen refill (hereinafter, these may be collectively referred to as "refills").

When the thermochromic writing object is a ballpoint pen, the structure and shape of the ballpoint pen itself are not particularly limited, and examples include ballpoint pens in which the thermochromic ink composition is directly contained inside the barrel, an ink flow rate control member in the shape of a comb groove or an ink flow rate control member made of a fiber bundle is interposed, and the ballpoint pen tip with a ball attached to the tip and the ink flow rate control member are connected directly or via a holder.

In addition, when the thermochromic writing body is a ballpoint pen, for example, a ballpoint pen having an ink reservoir filled with a thermochromic ink composition in the barrel, the ink reservoir fluidly connected to the ballpoint pen tip can be mentioned. In addition, a ballpoint pen having a structure in which the thermochromic ink composition is directly stored in the barrel, a grease-like follower that follows the ink as it is consumed is filled in the rear of the barrel, a press-in part of a tail plug having an air flow passage (vent hole) that communicates between the inside and outside of the barrel is press-fitted into the rear end of the barrel, and a ballpoint pen tip with a ball attached to the tip is attached directly or via a holder can be mentioned. In one embodiment, the thermochromic writing body is a ballpoint pen refill having an ink reservoir filled with a thermochromic ink composition and a ballpoint pen tip that is in communication with the ballpoint pen tip.

The ink reservoir tube for containing the thermochromic ink composition may be, for example, a molded article made of a thermoplastic resin such as polyethylene, polypropylene, polyethylene terephthalate, or nylon.
The ballpoint pen tip may be directly connected to the ink reservoir, or the ink reservoir and the ballpoint pen tip may be connected via a connecting member.

The rear end of the thermochromic ink composition contained in the ink reservoir tube is preferably filled with an ink backflow prevention body. Examples of ink backflow prevention bodies include liquid plugs and solid plugs.

Examples of liquid stoppers include non-volatile or difficult-to-volatile liquids, such as petrolatum, spindle oil, castor oil, olive oil, refined mineral oil, liquid paraffin, polybutene, α-olefins, α-olefin oligomers and co-oligomers, dimethyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, and fatty acid-modified silicone oil, and these may be used alone or in combination of two or more kinds.

It is preferable to thicken the non-volatile liquid and/or the difficult-to-volatile liquid to a suitable viscosity by adding a thickener. Examples of the thickener include clay-based thickeners such as silica with a hydrophobic surface treatment, fine silica particles with a methylated surface, aluminum silicate, swellable mica, bentonite and montmorillonite that have been hydrophobically treated, fatty acid metal soaps such as magnesium stearate, calcium stearate, aluminum stearate and zinc stearate, tribenzylidene sorbitol, fatty acid amides, amide-modified polyethylene wax, hydrogenated castor oil, and dextrin-based compounds such as fatty acid dextrin, and cellulose-based compounds.

Examples of solid plugs include solid plugs made of resin, such as polyethylene, polypropylene, and polymethylpentene. Liquid plugs and solid plugs made of resin may be used in combination as ink backflow prevention bodies.

Examples of ballpoint pen tips include ballpoint pen tips in which the ball is held in a ball-holding section formed by pressing the area near the tip of a metal pipe inwards from the outside (pipe-type ballpoint pen tip), ballpoint pen tips in which the ball is held in a ball-holding section formed by cutting a metal material with a drill or the like, ballpoint pen tips in which a resin ball receiving seat is provided inside a metal or plastic tip, and ballpoint pen tips in which the ball held in the tip is biased forward by a spring body.

The ballpoint pen tip may be a pipe-type ballpoint pen tip having at least a metal pipe whose tip is a straight cylindrical body (straight tubular cylinder). Examples of the shape of the pipe-type ballpoint pen tip include a ballpoint pen tip made of a metal pipe whose entire tip is a straight cylindrical body, and a ballpoint pen tip having a straight metal pipe at the tip and a shape whose outer diameter and inner diameter expand behind the pipe. The latter is preferred because it has good ink ejection properties.
Furthermore, by combining the thermochromic ink composition with a pipe-type ballpoint pen tip equipped with a ball having a diameter of, for example, 0.25 mm or more and 0.5 mm or less, a ballpoint pen having excellent ink ejection properties and resistance to drying up can be obtained.

Balls are generally made of cemented carbide, stainless steel, ruby, ceramic, resin, rubber, etc. The ball diameter is generally 0.2 mm or more and 3.0 mm or less.

When the thermochromic writing object is a marking pen, the structure and shape of the marking pen itself are not particularly limited, and examples include a marking pen having a structure in which the thermochromic ink composition is directly stored inside the barrel, a comb-groove-shaped ink flow rate control member or an ink flow rate control member made of a fiber bundle is interposed, and a marking pen tip made of a fiber processed body or a resin molded body with a capillary gap is connected to the ink flow rate control member, and a marking pen having a structure in which the marking pen tip and an ink reservoir tube are arranged via a valve body that opens when the marking pen tip is pressed, and the thermochromic ink composition is directly stored in the ink reservoir tube.

In addition, when the thermochromic writing material is a marking pen, for example, the marking pen has an ink occlusion body made of a fiber bundle impregnated with a thermochromic ink composition built into the barrel, and the marking pen tip is attached to the barrel directly or via an intermediate member, so that the ink occlusion body and the tip are in fluid communication. In one embodiment, the thermochromic writing material is a marking pen refill in which the ink occlusion body impregnated with the thermochromic ink composition is in communication with the marking pen tip.

The marking pen tip is a porous member having interconnected pores and a porosity in the range of approximately 30% to 70%, such as a resin-processed fiber body, a fused heat-fusible fiber body, or a felt body, or an extrusion-molded synthetic resin body having a plurality of ink outlet holes extending in the axial direction, with one end processed into a shape suitable for the purpose, such as a bullet shape, a rectangle, or a chisel shape.
The ink occlusion body is made by bundling crimped fibers in the longitudinal direction, and is placed inside a plastic cylinder or a covering such as a film, with the porosity adjusted to the range of approximately 40 to 90%.

The valve body may be a conventional, general-purpose pumping type, and is preferably set to a spring pressure that can be pressed and released by the pressure of the pen.

Thermochromic writing elements may be provided with a cap to protect the writing tip and prevent it from drying out.

The thermochromic writing body may be a retractable writing body in which a refill is housed in a barrel and the writing tip protrudes from the barrel opening by the operation of a retraction mechanism. Examples of the operation method of the retraction mechanism include a knock type, a rotation type, and a slide type. One example of a retractable writing body is a composite type retractable ballpoint pen in which multiple ballpoint pen refills are housed in a barrel and the writing tip of one of the ballpoint pen refills protrudes from the barrel front end opening by the operation of the retraction mechanism.

A non-thermochromic writing material incorporating a non-thermochromic ink composition can be used together with a thermochromic writing material according to an embodiment of the present invention.

The non-thermochromic ink composition is not particularly limited, and may contain a general pigment and/or dye as a colorant.
Examples of pigments include inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, fine particle fluorescent pigments of synthetic resins in which various fluorescent dyes are solid-dissolved in a resin matrix, and white pigments such as pearl pigments, metal powder pigments, and titanium dioxide.
Examples of the dye include acid dyes, basic dyes, and direct dyes.

The non-thermochromic ink composition may be oil-based or water-based.

When the non-thermochromic ink composition is aqueous, the non-thermochromic ink composition may contain, for example, the components described above in "Other components that may be contained in the thermochromic ink composition" for the thermochromic aqueous ink composition, as appropriate.

As with thermochromic writing materials, examples of non-thermochromic writing materials include ballpoint pens, marking pens, brush pens, fountain pens, and calligraphy pens, as well as ballpoint pen refills and marking pen refills. The details of these are the same as those described above for thermochromic writing materials, and non-thermochromic writing materials can be obtained by using a non-thermochromic ink composition.

The following provides a more detailed explanation of the embodiments of the present invention, using examples. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the intent described above and below, and all such modifications are within the technical scope of the embodiments of the present invention.

The friction member of Example 1 was obtained by molding polyethylene resin (manufactured by Mitsubishi Chemical Corporation, product name: Novatec LJ809A) into the same shape as the friction member included with Friction Ball Knock 05 using a known method. The friction member included with Friction Ball Knock 05 has a tip (abrasion part) with a convex curved shape (radius of curvature 2.5 mm).

The friction member of Example 2 was obtained by molding polyethylene resin (manufactured by Mitsubishi Chemical Corporation, product name: Novatec HJ260) into the same shape as the friction member included with Friction Ball Knock 05 using a known method.

The friction member of Example 3 was obtained by molding polyethylene resin (manufactured by Mitsubishi Chemical Corporation, product name: Novatec MG2TA) into the same shape as the friction member included with Friction Ball Knock 05 using a known method.

As a comparative example, a friction member of Comparative Example 1 was obtained by molding an SEBS copolymer (manufactured by Aron Chemical Industries, Ltd., product name: AR-885C) into the same shape as the friction member included with Friction Ball Knock 05 by a known method. In addition, a friction member included with a commercially available thermochromic writing material was used as the friction member of Comparative Example 2. The normal line of the tip of the friction member of Comparative Example 2 and the longitudinal direction of the thermochromic writing material were roughly aligned.

The hardness and dynamic friction coefficient of the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 were measured.
The hardness was measured as follows using a D-type durometer hardness tester (Durometer manufactured by Techlock Corporation, Model: GS-720G). First, the friction members of Examples 1 to 3 and Comparative Example 1 were attached to a thermochromic writing body (Friction Ball Knock 05) so that the longitudinal direction of the thermochromic writing body and the normal line of the tip (convex curved surface shape) of the friction member were approximately aligned. The thermochromic writing bodies to which the friction members of Examples 1 to 3 and Comparative Examples 1 to 2 were attached were cut so that the cut surface was approximately perpendicular to the longitudinal direction of the thermochromic writing body. Then, with the cut surface facing down, the portion including each friction member was placed on a durometer hardness tester so that the tip of the durometer hardness tester was located above the tip of each friction member. The tip of the core was pressed against each friction member under a load of 5.0 kgf at a speed of 3 mm/sec in an environment of 25° C. and 50% RH, and the peak value displayed on a durometer hardness meter was taken as the hardness of each friction member.

The dynamic friction coefficient was measured by using a HEIDON friction and wear tester (tribogear type: 14, manufactured by Shinto Scientific Co., Ltd.) to measure the force F (load parallel to the paper surface) applied to each friction member when each friction member of Examples 1 to 3 and Comparative Examples 1 to 2 was run on the paper surface so that the tip of each friction member rubbed against the paper surface. The friction member of Comparative Example 2 was removed from a commercially available thermochromic writing material and used for the measurement. The dynamic friction coefficient μ was calculated by applying the force F and the load N (200 gf) applied to each friction member (perpendicular to the paper surface) to F = μ (dynamic friction coefficient) × N. The force F was sampled at 0.001 second intervals, and the force F measured from the start of the measurement until 0.3 seconds after the start of the measurement was not used to calculate the dynamic friction coefficient. The paper surface was the front side of NPi Foam <55> (manufactured by Nippon Paper Industries Co., Ltd.), the measurement environment was 23°C, 42% RH, the running speed was 4 m/min, the running distance was 10 cm, and the angle between the normal to the tip of each friction member and the paper surface was 90°. In addition, three measurement samples were prepared for each friction member, and one measurement was performed for each measurement sample, and the average value of the measurement values of the three measurement samples was taken as the dynamic friction coefficient of each friction member.

The thermochromic writing materials used to evaluate the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 were prepared as follows:

First, the microcapsule pigment contained in the thermochromic ink composition was prepared as follows. A suspension of a reversible thermochromic microcapsule pigment MC1 was obtained, which contains a reversible thermochromic composition consisting of 4.5 parts of 2-(2-chloroanilino)-6-di-n-butylaminofluoran as an electron donor color-developing organic compound, 4.5 parts of 1,1-bis(4-hydroxyphenyl)n-decane as an electron acceptor compound, and 7.5 parts of 2,2-bis(4-hydroxyphenyl)hexafluoropropane as an electron acceptor compound, and 50.0 parts of decanoic acid-4-benzyloxyphenylethyl as a reaction medium. The suspension was centrifuged to isolate MC1. MC1 had an average particle size of 2.0 μm, and exhibited behavior with hysteresis characteristics of t1: -20°C, t2: -9°C, t3: 40°C, t4: 57°C, and △H63°C, and reversibly changed color from black to white and from white to black. The average particle size of the microcapsule pigment was measured as the average particle size (median size) based on volume using a HORIBA, Ltd. laser diffraction/scattering particle size distribution analyzer "LA-300" that was calibrated based on values measured using a measuring device that uses the Coulter method (electrical detection zone method).

A thermochromic ink composition was obtained by mixing 8.0 parts by mass of the above MC1, 5.0 parts by mass of glycerin as a water-soluble organic solvent, 0.5 parts by mass of polyoxyethylene distyrenated phenyl ether phosphate ester (trade name: Plysurf AL, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a surfactant, 0.5 parts by mass of triethanolamine as a pH adjuster, 0.2 parts by mass of benzoisothiazolin-3-one (trade name: Proxel XL-2, manufactured by Lonza Japan Co., Ltd.) as a preservative, 0.3 parts by mass of xanthan gum (trade name: Kelzan, manufactured by Sansho Co., Ltd.) as a polysaccharide, and 85.5 parts by mass of water.

The thermochromic ink composition was filled into a ballpoint pen (manufactured by Pilot Corporation, product name: Friction Ball Knock 05) to produce a thermochromic writing material. The ballpoint pen contains a ballpoint pen refill that can be filled with the thermochromic ink composition in an ink reservoir tube with a ballpoint pen tip (ball diameter 0.5 mm) fitted into one end of a polypropylene pipe, and can also be filled by placing an ink backflow prevention body in close contact with the rear end surface of the ink.

The non-thermochromic writing materials used to evaluate the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 above were prepared as follows:

A non-thermochromic ink composition was obtained by mixing 10.0 parts by weight of a black dye (product name: Water Black 191L, solid content: 15%) manufactured by Orient Chemical Industry Co., Ltd. as a dye, 10.0 parts by weight of ethylene glycol as a water-soluble organic solvent, 1.0 part by weight of an ether of acetylene glycol and polyoxyethylene (product name: Acetylenol E100, manufactured by Kawaken Fine Chemical Co., Ltd.) as a surfactant, 0.5 parts by weight of polyoxyethylene distyrenated phenyl ether phosphate (product name: Plysurf AL, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), 0.5 parts by weight of triethanolamine as a pH adjuster, 0.2 parts by weight of benzoisothiazolin-3-one (product name: Proxel XL-2, manufactured by Lonza Japan Co., Ltd.) as a preservative, 0.2 parts by weight of xanthan gum (product name: Kelzan, manufactured by Sansho Co., Ltd.) as a polysaccharide, and 77.6 parts by weight of water.

The non-thermochromic ink composition was filled into a ballpoint pen (manufactured by Pilot Corporation, product name: V-Ball RT05) to prepare a non-thermochromic writing material. The ballpoint pen contains a ballpoint pen refill that can be filled with the thermochromic ink composition in an ink reservoir tube having a ballpoint pen tip (ball diameter 0.5 mm) fitted into one end of a polypropylene pipe, and can also be filled by bringing an ink backflow prevention body into close contact with the rear end surface of the ink.

The following evaluations 1 and 2 were performed on the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 using the thermochromic writing material and non-thermochromic writing material.

(Rating 1)
The handwriting "old" formed with the thermochromic cursive and the non-thermochromic cursive on a test paper (KOKUYO resume paper (large quantity) B5 JIS format compliant 10 sheets Shin-51J) in a 25°C 50% RH environment was rubbed at an angle of 60 degrees, a load of 300 g, and a speed of 10 cm/sec using the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 three seconds after the handwriting of the non-thermochromic cursive was formed, and the ink spread of the handwriting formed with the non-thermochromic cursive after the handwriting of the thermochromic cursive was erased was visually confirmed.

(Rating 2)
The handwriting of "Nagoya" was formed by tracing the handwriting formed with the thermochromic cursive material on a test paper (KOKUYO resume paper (large quantity) B5, 10 sheets in accordance with JIS format, Shin-51J) in an environment of 25°C and 50% RH, with the non-thermochromic cursive material. 10 seconds after the handwriting of the non-thermochromic cursive material was formed, the test paper was rubbed with the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 at an angle of 60 degrees, a load of 300 g, and a speed of 10 cm/sec to visually confirm the ink spread of the handwriting formed with the non-thermochromic cursive material after the handwriting of the thermochromic cursive material was erased.

The hardness, dynamic friction coefficient, and results of evaluations 1 and 2 of the friction members of Examples 1 to 3 and Comparative Examples 1 and 2 are summarized in Table 1. In addition, images showing the results of evaluations 1 and 2 of Examples 1 to 3 and Comparative Examples 1 to 2 are shown in Figures 2A to 2E and 3A to 3E, respectively, as follows.
Figure 2A: Results of evaluation 1 in Example 1 Figure 2B: Results of evaluation 1 in Example 2 Figure 2C: Results of evaluation 1 in Example 3 Figure 2D: Results of evaluation 1 in Comparative Example 1 Figure 2E: Results of evaluation 1 in Comparative Example 2 Figure 3A: Results of evaluation 2 in Example 1 Figure 3B: Results of evaluation 2 in Example 2 Figure 3C: Results of evaluation 2 in Example 3 Figure 3D: Results of evaluation 2 in Comparative Example 1 Figure 3E: Results of evaluation 2 in Comparative Example 2 The results of evaluations 1 and 2 in Table 1 were judged as follows.
A: No evidence of ink spreading around the handwriting is observed. B: Slight evidence of ink spreading around the handwriting is observed. C: Clear evidence of ink spreading around the handwriting is observed.

From the results in Table 1, the following can be considered. All of Examples 1 to 3 in Table 1 are examples that satisfy all of the requirements stipulated in the embodiments of the present invention, and were rated A or B in Evaluations 1 and 2. When the handwriting of the thermochromic cursive body was rubbed against the handwriting of the non-thermochromic cursive body together with the handwriting of the thermochromic cursive body, the handwriting of the thermochromic cursive body could be erased while the appearance of the handwriting of the non-thermochromic cursive body was sufficiently maintained. In particular, Example 2, unlike Examples 1 and 3, satisfied the preferable requirements of a hardness of 65 to 80 and a dynamic friction coefficient of 0.25 to 0.35, and therefore showed particularly excellent results (rated A) in Evaluations 1 and 2.
On the other hand, Comparative Example 1 in Table 1 is an example that does not satisfy the requirements defined in the embodiment of the present invention, and since the hardness was less than 55 and the dynamic friction coefficient exceeded 0.50, it was rated C in the evaluations 1 and 2. Comparative Example 2 in Table 2 is also an example that does not satisfy the requirements defined in the embodiment of the present invention, and since the dynamic friction coefficient exceeded 0.50, it was rated C in the evaluations 1 and 2.

The embodiments of the present invention may include the following applications:
(1) A set of the above-mentioned thermochromic writing medium (ballpoint pen) and the above-mentioned non-thermochromic writing medium (ballpoint pen) (a retractable ballpoint pen set).
(2) A set of a capped ballpoint pen containing a refill filled with the thermochromic ink composition and having the friction body (e.g., Example 2) attached to the tip of the cap, and a capped ballpoint pen containing a refill filled with the non-thermochromic ink composition. (3) A composite type retractable ballpoint pen containing a refill filled with the first thermochromic ink composition (e.g., an ink that reversibly changes from black to white as described in the Examples of the present application), a refill filled with the second thermochromic ink composition (an ink that reversibly changes from a color other than black (e.g., pink) to white), and a refill filled with the non-thermochromic ink, and having the friction body (e.g., Example 2) attached to the rear end of the barrel.

t1: Complete color development temperature of the heat-discoloring type microencapsulated pigment t2: Color development start temperature of the heat-discoloring type microencapsulated pigment t3: Coloring start temperature of the heat-discoloring type microencapsulated pigment t4: Complete coloring temperature of the heat-discoloring type microencapsulated pigment ΔH: Hysteresis width

Claims (4)

A friction member that thermally discolors handwriting formed with a thermochromic writing material by frictional heat,
The hardness measured by a type D durometer is 65 to 80 ;
A friction member having a dynamic friction coefficient of 0.25 to 0.35 . The friction member of claim 1 , wherein the friction member comprises an organic polymeric material. The friction member according to claim 2 , wherein the organic polymeric material comprises a polyethylene resin. A thermochromic writing material comprising the friction member according to any one of claims 1 to 3 .

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