Thermochromic writing instruments

Abstract

To chemically and physically erase marks of thermochromic ink containing a metallic luster pigment.SOLUTION: The thermochromic ink contains a metallic luster pigment, the thermochromic writing instrument is provided with a mounting hole 2 for mounting a friction body 3, the friction body 3 includes a mounting portion 5 inserted into the mounting hole 2 and a friction portion 32 having a convex curved surface that protrudes from the mounting hole 2, a volume Ve of the friction portion 32 and a volume Vp of the metallic luster pigment satisfy 5≤Ve / Vp≤35, a maximum outer diameter D and protruding length L of the friction portion 32 satisfy 0.1≤L / D≤1.5, and the material of the friction body 3 has a Shore A hardness measured in accordance with JIS K 7215 of the Japanese Industrial Standards immediately after the start of indenter contact in the range of 60 to 85, and a Shore A hardness value (ΔHS) defined by the following formula is greater than or equal to 0 and less than 5: ΔHS=(Shore A hardness immediately after the start of indenter contact)-(Shore A hardness 15 seconds after the start of indenter contact).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a writing instrument. More specifically, it relates to a writing instrument provided with a friction body for thermally discoloring the writing of thermochromic ink.

Background Art

[0002] In recent years, thermochromic writing instruments have become widely popular. Thermochromic writing instruments incorporate thermochromic ink. The writing of thermochromic ink can be discolored or erased by heating. Thermochromic writing instruments are provided with a friction body that generates frictional heat for erasing or discoloring the writing of thermochromic ink. Note that "discoloration" of thermochromic ink means changing from one color to another color. "Erasure" is a form of discoloration and means changing from a colored state to a colorless state.

[0003] For example, International Publication No. 2018 / 116767 discloses a writing instrument incorporating thermochromic ink to which a metallic luster pigment has been added. This thermochromic writing instrument is provided with a friction body containing a viscoelastic body. This friction body can chemically and physically erase thermochromic ink to which a metallic luster pigment has been added. That is, the friction body containing a viscoelastic body erases the thermochromic ink by frictional heat and adsorbs the metallic luster pigment by viscoelasticity and peels it off the paper surface. Thus, the friction body containing a viscoelastic body disclosed in International Publication No. 2018 / 116767 has both chemical erasability for erasing thermochromic ink by frictional heat and physical erasability for peeling off the metallic luster pigment by viscoelasticity.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, friction materials containing viscoelastic materials have a problem in that the amount of deformation of the friction material gradually increases due to the reciprocating motion (hereinafter referred to as "friction motion") when rubbing against the ink markings of thermochromic ink. In other words, viscoelastic materials have the property that the amount of deformation increases over time when a constant external force is applied. For this reason, friction materials containing viscoelastic materials gradually deform larger and larger as the friction motion is repeated. When the amount of deformation of the friction material becomes large, it may not be possible to generate the frictional heat necessary to change or erase the ink markings of thermochromic ink.

[0006] On the other hand, by gradually reducing the force required to cause friction, the amount of deformation of the friction body can be kept constant. However, if the force required to cause friction becomes too small, it may not generate the frictional heat necessary to change or erase the ink's markings. In particular, the elastic modulus of a friction body made of synthetic resin is temperature-dependent. Therefore, if the temperature of the friction body itself rises due to frictional heat, or if the friction body is used in a high-temperature environment, the friction body becomes more susceptible to deformation.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a thermochromic writing instrument that enables the chemical and physical erasure of ink marks written with thermochromic ink to which metallic luster pigments are added, and that allows the friction material to exhibit desired frictional performance by suppressing deformation of the friction material. [Means for solving the problem]

[0008] (1) To achieve the above objective, the thermochromic writing instrument of the present invention comprises a thermochromic ink and a friction body for causing the ink to change color by frictional heat, wherein a metallic luster pigment is added to the thermochromic ink, the thermochromic writing instrument is provided with a mounting hole for attaching the friction body, the friction body includes a mounting portion inserted into the mounting hole and a convex curved friction portion protruding from the mounting hole, the volume Ve of the friction portion and the volume Vp of the metallic luster pigment satisfy 5 ≤ Ve / Vp ≤ 35, the maximum outer diameter D of the friction portion and the protruding length L satisfy 0.1 ≤ L / D ≤ ​​1.5, and the material of the friction body is JIS K The Shore A hardness value measured in accordance with 7215 immediately after the start of indentation contact is in the range of 60 to 85, and the value of Shore A hardness defined by the following formula (ΔHS) is 0 or greater and less than 5. ΔHS = (Shore A hardness value immediately after indenter contact begins) - (Shore A hardness value 15 seconds after indenter contact begins)

[0009] The friction element provided in the thermochromic writing instrument described in (1) above can chemically change or eliminate the color of the ink by frictional heat, and can also physically remove the metallic luster pigment added to the thermochromic ink. On the other hand, by setting the ΔHS of the friction element material to less than 5, it is possible to provide sufficient rigidity to the friction part against frictional action. This suppresses deformation of the friction part when frictional action is performed, and allows the friction part to exhibit the desired frictional performance.

[0010] (2) Preferably, in the thermochromic writing instrument of (1) above, the material of the friction body has a product value (Tb × Eb) of tensile strength Tb at break and elongation Eb at break, measured in accordance with the Japanese Industrial Standard JIS K 6251, which is 5000 or more and 18000 or less.

[0011] By setting the product of the tensile strength Tb at break and the elongation Eb at break (Tb × Eb) of the friction material to be between 5000 and 18000, the friction material generates an appropriate amount of wear debris when rubbing against a writing surface. This makes it possible to attach and encapsulate the metallic luster pigment added to the thermochromic ink with the wear debris.

[0012] (3) Preferably, in the thermochromic writing instrument of (1) or (2) above, the mounting hole is provided so as to penetrate the rear end of the barrel or the top of the cap constituting the thermochromic writing instrument along the vertical central axis, and has an inner circumferential surface between two openings located at the upper and lower ends, and an inward projection is formed on the inner circumferential surface of the mounting hole that protrudes toward the inside of the mounting hole, and an outward projection is formed on the outer circumferential surface of the mounting portion that protrudes toward the outside of the mounting portion, and when the mounting portion is inserted into the mounting hole, the outward projection overcomes the inward projection so that the outward projection and the inward projection are locked together, and the friction body is provided with a straight inner hole that opens at least at the lower end of the mounting portion along the vertical central axis, and the inner hole A rod-shaped core is inserted into the inner hole, having a length that fits within the inner hole and an outer surface that contacts the inner surface of the inner hole. When the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the core is held in a position corresponding to the inner surface of the mounting hole, so that the mounting portion is held in a position corresponding to the outer surface of the core and the mounting hole. Inside It is configured to be held between the directional projections.

[0013] The mounting portion of the friction element is sandwiched between the outer surface of the core and the inward projection of the mounting hole, and is firmly fixed in the mounting hole. This increases the overall rigidity of the friction element, suppresses deformation of the friction element when friction is performed, and makes it possible to achieve the desired friction performance. In particular, even if the friction element is made of a low-hardness material, the desired rigidity can be given to the entire friction element. This makes it possible to efficiently change the color of the writing with thermochromic ink. Furthermore, the core is inserted into the inner hole of the friction element after the inward projection of the mounting hole and the outward projection of the mounting portion are locked together. This makes it possible to easily attach the friction element to a thermochromic writing instrument without requiring a large amount of force.

[0014] (4) Preferably, in the thermochromic writing instrument of (3) above, when the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the core has a length from the opening at the lower end of the inner hole to the opening at the upper end of the mounting hole.

[0015] Since the core has a length from the opening at the lower end of the inner hole to the opening at the upper end of the mounting hole, when the friction part wears down, the core will not be exposed from the friction part and damage the paper surface.

[0016] (5) Preferably, in the thermochromic writing instrument of (3) or (4) above, when the mounting portion is inserted into the mounting hole and the core is inserted into the inner hole, the lower end of the core is at the same position as the lower end of the mounting portion, or higher than the lower end of the mounting portion.

[0017] By positioning the lower end of the core at the same position as the lower end of the mounting part, or above the lower end of the mounting part, insertion of the core into the friction body becomes easier, improving assembly efficiency.

[0018] (6) Preferably, in any of the thermochromic writing instruments described in (3) to (5) above, the inner hole is a hole that opens at the lower end of the mounting portion and is closed at the upper end of the friction portion, and a vent is provided in the core to discharge air from the inner hole during the process of inserting the core into the inner hole.

[0019] During the process of the refill being inserted into the inner hole, the air inside the inner hole is not compressed by the refill and is discharged to the outside. As a result, the insertion of the refill into the friction body becomes easy, and the refill can be reliably attached to the inner hole.

[0020] (7) Preferably, in the thermochromic writing instrument of (6) above, the ventilation part is a through hole penetrating from one end to the other end of the refill along the longitudinal central axis of the refill.

[0021] During the process of the refill being inserted into the inner hole, the air inside the inner hole is not compressed by the refill and is reliably discharged to the outside through the through hole. As a result, the insertion of the refill into the friction body becomes easy, and the refill can be reliably attached to the inner hole.

[0022] (8) Preferably, in the thermochromic writing instrument of (6) above, the ventilation part is at least one groove or protrusion continuous from one end to the other end of the refill along the outer peripheral surface of the refill.

[0023] During the process of the refill being inserted into the inner hole, the groove or protrusion of the refill forms a gap between the outer peripheral surface of the refill and the inner peripheral surface of the inner hole. As a result, the air inside the inner hole is not compressed by the refill and is reliably discharged to the outside through the gap formed by the groove or protrusion. As a result, the insertion of the refill into the friction body becomes easy, and the refill can be reliably attached to the inner hole.

[0024] (9) Preferably, in the thermochromic writing instrument of any one of (3) to (8) above, the refill has a symmetric shape in the vertical direction.

[0025] Since the refill has a symmetric shape in the vertical direction, the distinction between the upper and lower parts of the refill disappears. As a result, the refill can be inserted into the inner hole from either the upper or lower part of the refill, and the operation of inserting the refill into the inner hole becomes easy.

[0026] (10) Preferably, in any of the thermochromic writing instruments described in (3) to (9) above, the outer surface of the core is the inner hole A protrusion is provided that contacts the inner circumferential surface.

[0027] The protrusions on the outer surface of the core securely hold the core within the inner hole. This reliably prevents the core from falling out of the inner hole.

[0028] (11) To achieve the above objective, the thermochromic writing instrument of the present invention comprises a thermochromic ink and a friction body for causing the writing made with the thermochromic ink to change color by frictional heat, wherein the thermochromic ink contains at least one of a fluorescent pigment, a phosphorescent pigment, and titanium dioxide, the thermochromic writing instrument is provided with a mounting hole for attaching the friction body, the friction body includes a mounting portion inserted into the mounting hole and a convex curved friction portion protruding from the mounting hole, and the material of the friction body has a product value (Tb × Eb) of tensile strength at break Tb and elongation at break Eb, measured in accordance with the Japanese Industrial Standard JIS K 6251, which is 5000 or more and 18000 or less.

[0029] By setting the product of the tensile strength Tb at break and the elongation Eb at break (Tb × Eb) of the friction material to be between 5000 and 18000, the friction material generates an appropriate amount of wear debris when rubbing against a writing surface. This makes it possible to attach and encapsulate at least one of the fluorescent pigments, phosphorescent pigments, and titanium dioxide added to the thermochromic ink to the wear debris. [Effects of the Invention]

[0030] The thermochromic writing instrument of the present invention makes it possible to chemically and physically erase the writing marks of thermochromic ink to which metallic luster pigments have been added, and suppresses deformation of the friction body, thereby enabling the friction body to exhibit desired friction performance.

[0031] Herein, in this specification, "front" for thermochromic writing instruments means the direction of the pen tip, and "rear" for thermochromic writing instruments means the direction opposite to the pen tip. Furthermore, "up" for mounting holes means the direction of the rear end of the barrel or the top of the cap, and "down" for mounting holes means the direction opposite to these. In addition, "up" for friction bodies means the direction of the friction part, and "down" for friction bodies means the direction of the mounting part. Moreover, unless otherwise specified, the content of multiple components constituting a composition described herein means the total amount of the substance corresponding to each component. Furthermore, the term "metallic gloss pigment" broadly includes pigments that can impart gloss to the writing of thermochromic inks. For example, transparent metallic gloss pigments and metal vapor-deposited resin pigments are both included in the term "metallic gloss pigment". [Brief explanation of the drawing]

[0032] [Figure 1] This is a cross-sectional view showing the main parts of a thermochromic writing instrument according to the first embodiment of the present invention, before the friction body mounting portion is inserted into the mounting hole of the barrel. [Figure 2] This is a cross-sectional view showing the temporary insertion state during the process of inserting the friction body mounting portion into the mounting hole of the shaft cylinder. [Figure 3] This is a cross-sectional view showing the friction element mounting portion inserted into the mounting hole of the shaft cylinder. [Figure 4] This is a cross-sectional view showing the core inserted into the inner bore of the friction body. [Figure 5] This is a cross-sectional view showing a thermochromic writing instrument according to a second embodiment of the present invention. [Figure 6] This is an external view showing a writing set comprising a thermochromic writing instrument and a friction element according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0033] Hereinafter, a thermochromic writing instrument according to an embodiment of the present invention will be described with reference to the drawings.

[0034] 1. Overview Figures 1 to 4 show the main parts of a thermochromic writing instrument according to the first embodiment of the present invention. In Figures 1 to 4, the entire thermochromic writing instrument is not shown; only the rear end of the barrel 1 constituting the thermochromic writing instrument is shown. The thermochromic writing instrument of this embodiment comprises a barrel 1, a friction element 3, and a core 7. A mounting hole 2 is provided at the rear end of the barrel 1. The friction element 3 is attached to the mounting hole 2. An inner hole 31 is provided in the friction element 3 along its vertical central axis. The core 7 is inserted into the inner hole 31.

[0035] 2. Mounting holes As shown in Figure 1, a mounting hole 2 is provided at the rear end of the shaft cylinder 1. The mounting hole 2 penetrates the rear end of the shaft cylinder 1 along the vertical central axis. The mounting hole 2 has an inner circumferential surface between two openings located at the upper and lower ends. Below the inner circumferential surface of the mounting hole 2, an annular inward projection 21 is formed. A guide surface 21a, which is an inverted conical tapered surface, is formed on the inner circumferential surface of the inward projection 21. The diameter of the guide surface 21a gradually decreases from top to bottom. The lower end of the guide surface 21a is continuous with the vertical inner circumferential surface of the smallest diameter portion 21b, which is the opening at the lower end of the mounting hole 2. The lateral cross-sectional shape of such a mounting hole 2 is a circle with different diameters.

[0036] Here, the barrel 1 is manufactured by injection molding of a synthetic resin (for example, polypropylene). The mounting hole 2 and the inward projection 21 are integrally molded to the rear end of the barrel 1 by injection molding. Note that the mounting hole 2 is not limited to the rear end of the barrel 1, but may also be provided, for example, on the top of the cap that constitutes a thermochromic writing instrument.

[0037] 3.Friction body As shown in Figure 1, the friction body 3 of this embodiment has a bullet-shaped friction portion 32 (large diameter portion 4) and a mounting portion 5 (small diameter portion) with a smaller diameter than the friction portion 32 integrally molded below it. The friction portion 32 is used to change the color of thermochromic ink adhering to the paper surface by frictional heat. Furthermore, the friction portion 32 of this embodiment has the function of adsorbing and peeling off metallic luster pigments added to the thermochromic ink from the paper surface. The mounting portion 5 is used to attach the friction body 3 to the mounting hole 2 of the shaft 1.

[0038] 3.1 Friction area (large diameter section) The outer circumferential surface of the friction portion 32 has a convex curved shape that allows it to contact the paper surface at various angles of inclination. The diameter of the lower end of the friction portion 32 is larger than the diameter of the opening at the upper end of the mounting hole 2, and preferably smaller than the diameter of the rear end surface of the shaft cylinder 1. An annular surface 41 is formed at the boundary between the friction portion 32 and the mounting portion 5, which abuts against the rear end surface of the shaft cylinder 1. When the mounting portion 5 is attached to the mounting hole 2, the friction portion 32 protrudes above the rear end surface of the shaft cylinder 1.

[0039] As shown in Figure 1, the maximum outer diameter D of the friction portion 32 and the protruding length L of the friction portion 32 satisfy 0.1 ≤ L / D ≤ ​​1.5, preferably 0.5 ≤ L / D ≤ ​​1.1. The ratio L / D of the maximum outer diameter D to the protruding length L of the friction portion 32 serves as an indicator of the size of the portion exposed to the outside of the friction portion 32 and the rigidity of the friction portion 32. If the L / D value is 0.1 or greater, the friction portion 32 has sufficient rigidity to rub away handwriting on the paper. On the other hand, if the L / D value is 1.5 or less, the friction portion 32 has an exposed portion of sufficient size to erase a large amount of handwriting. In this embodiment, the friction portion 32 has a maximum outer diameter D = 6.1, a protruding length L = 6.3, and L / D ≈ 1.0.

[0040] Furthermore, if the friction portion 32 has a convex curved shape, it is preferable to make the thickness of the top of the friction portion 32 the thickest. This increases the rigidity of the top and the area near the top that is used when rubbing the handwriting on the paper, allowing the friction action to be performed smoothly.

[0041] 3.2 Mounting section The mounting portion 5 consists of a cylindrical wall portion and has a diameter smaller than the diameter of the lower end of the friction portion 32, and is large enough to be inserted into the mounting hole 2. An annular outward projection 51 is formed in the center of the outer circumferential surface of the mounting portion 5. An annular bulge 52 is formed above the outward projection 51 on the outer circumferential surface of the mounting portion 5. Below the outward projection 51 on the mounting portion 5 is a cylindrical portion 53.

[0042] A guide surface 51a, which is an inverted conical tapered surface, is formed on the outer circumferential surface of the outward projection 51. The diameter of the guide surface 51a gradually increases from bottom to top. The upper end of the guide surface 51a is continuous with the vertical outer circumferential surface of the maximum outer diameter portion 51b of the outward projection 51. The upper end of the vertical outer circumferential surface of the maximum outer diameter portion 51b is continuous with the horizontal annular upper end surface.

[0043] Here, the diameter of the largest outer diameter portion 51b of the outward-facing projection 51 is larger than the diameter of the smallest inner diameter portion 21b of the inward-facing projection 21 of the mounting hole 2 described above, and smaller than the diameter of the opening at the upper end of the mounting hole 2. For example, the dimensional difference between the largest outer diameter portion 51b and the smallest inner diameter portion 21b is in the range of 0.5 mm to 2.0 mm, preferably in the range of 0.5 mm to 1.0 mm. This dimensional difference allows the outward-facing projection 51 to pass smoothly over the inward-facing projection 21 during the process of inserting the mounting portion 5 into the mounting hole 2, making it possible to easily lock the outward-facing projection 51 and the inward-facing projection 21 together (see Figures 2 and 3).

[0044] The bulging portion 52 contacts the inner circumferential surface of the opening at the upper end of the mounting hole 2 when the mounting portion 5 is fully inserted into the mounting hole 2 (see Figure 3). This suppresses radial wobbling of the friction body 3. The diameter of the bulging portion 52 is approximately the same as the diameter of the opening at the upper end of the mounting hole 2. Furthermore, the diameter of the bulging portion 52 is smaller than the diameter of the lower end of the friction portion 32, and larger than the diameter of the maximum outer diameter portion 51b of the outward projection 51.

[0045] The diameter of the cylindrical portion 53 is smaller than the diameter of the smallest inner diameter portion 21b of the inward projection 21 of the mounting hole 2 described above. The cylindrical portion 53 is for temporarily inserting the mounting portion 5 into the mounting hole 2. This temporary insertion state is shown in Figure 2. Such a cylindrical portion 53 makes the installation of the friction body 3 easier. That is, by dropping the friction body 3 toward the mounting hole 2, it can be placed in the temporary insertion state shown in Figure 2. Then, by pushing the friction body 3 toward the mounting hole 2, the mounting portion 5 is fully inserted into the mounting hole 2, and at the same time, the outward projection 51 and the inward projection 21 are locked together (see Figure 3). Note that the outer circumferential surface below the outward projection 51 of the mounting portion 5 is not limited to the circumferential surface of the cylindrical portion 53, but may be, for example, an inverted conical tapered surface.

[0046] 3.3 Formation of a ring-shaped space The outer diameter of the intermediate portion of the mounting part 5 (the portion between the bulging portion 52 and the outward projection 51) is smaller than the inner diameter of the portion near the entrance of the mounting hole 2 (the portion above the inward projection 21). As a result, in the temporary insertion state shown in Figure 2, an annular space 6 is formed between the mounting part 5 and the mounting hole 2. This annular space 6 prevents the intermediate portion of the mounting part 5 from being pressed against the inner circumferential surface near the entrance of the mounting hole 2. That is, after the temporary insertion state shown in Figure 2, the outward projection 51 of the mounting part 5 overcomes the inward projection 21 of the mounting hole 2. At this time, the outward projection 51 is strongly pressed against the inward projection 21, causing the intermediate portion of the mounting part 5 to elastically deform and bulge radially outward. If the intermediate portion of the mounting part 5 were to be pressed against the inner circumferential surface near the entrance of the mounting hole 2, frictional resistance would be generated that would hinder the insertion of the mounting part 5. The annular space 6 accommodates the intermediate portion of the mounting portion 5, which bulges radially outward, thereby preventing the intermediate portion of the mounting portion 5 from being pressed against the inner circumferential surface near the entrance of the mounting hole 2.

[0047] 3.4 Axial clearance As shown in Figure 1, the length A from the upper end of the mounting portion 5 to the upper end of the outward projection 51 is slightly greater than the length B from the upper end of the mounting hole 2 to the lower end of the inward projection 21. This ensures that the entire outward projection 51 passes over the inward projection 21. In other words, if lengths A and B were the same, frictional resistance between the outward projection 51 and the inward projection 21 could prevent the upper end surface of the maximum outer diameter portion 51b of the outward projection 51 from passing over the inward projection 21. By making the length A of the mounting portion 5 slightly larger than the length B of the mounting hole 2, the entire outward projection 51 can pass over the inward projection 21 even after the annular surface 41 of the large diameter portion 4 contacts the rear end of the shaft cylinder 1. This ensures that the entire outward projection 51 passes over the inward projection 21 even if frictional resistance occurs between the outward projection 51 and the inward projection 21. Here, the dimensional difference between lengths A and B manifests as a clearance C between the outward projection 51 and the inward projection 21, as shown in Figure 3. The clearance C is preferably in the range of 0.05 mm to 1.0 mm, and more preferably in the range of 0.1 mm to 0.5 mm. With such a small clearance C, the friction body 3 will not move in the direction of the central axis, nor will the locking between the outward projection 51 and the inward projection 21 loosen.

[0048] 3.5 Internal bore An inner hole 31 is provided inside the friction body 3. The inner hole 31 is a straight hole provided along the central axis of the friction body 3 and opens at least at the lower end of the friction body 3. In this embodiment, the inner hole 31 extends from the lower end of the mounting portion 5 to the center of the friction portion 32, and is closed on one side that does not open at the upper end of the friction portion 32. The inner hole 31 is provided from the lower end of the mounting portion 5 to a position that reaches at least the upper end of the outward projection 51. Such an inner hole 31 makes it easier for the outward projection 51 to deform radially inward. This makes it easy to lock the outward projection 51 and the inward projection 21 together. Furthermore, a core 7, which will be described later, is inserted into the inner hole 31.

[0049] In this embodiment, the inner hole 31 opens at the lower end of the mounting portion 5 of the friction body 3, but not at the upper end of the friction portion 32. If the inner hole 31 were to open at the upper end of the friction portion 32, it would become impossible to rub the writing with the upper end of the friction portion 32, and the friction performance of the friction portion 32 would decrease.

[0050] Furthermore, because the inner hole 31 does not open at the upper end of the friction portion 32, the rigidity of the friction portion 32 is increased, improving its frictional performance. In addition, when attaching the friction body 3 to the mounting hole 5, the deflection of the entire friction body 3 is suppressed, making the installation work easier.

[0051] 3.6 Hardness and viscosity of the friction material The material constituting the friction body 3 is preferably an elastic synthetic resin (rubber, elastomer), such as silicone resin, SBS resin (styrene-butadiene-styrene copolymer), SEBS resin (styrene-ethylene-butylene-styrene copolymer), fluororesin, chloroprene resin, nitrile resin, polyester resin, ethylene propylene diene rubber (EPDM), etc.

[0052] In this embodiment, the friction element 3 has a lower hardness than conventional friction elements in order to physically erase the metallic luster pigment added to the thermochromic ink (described later) from the paper surface. The low hardness of the friction element 3 allows it to penetrate into the depressions of handwriting formed on the paper surface.

[0053] The hardness of the material of friction body 3 is expressed by the Shore A hardness value, measured in accordance with the "Durometer Hardness Test Method for Plastics" specified in the Japanese Industrial Standard JIS K 7215-1986. The durometer used to measure the Shore A hardness value is equipped with a spring-driven indenter, and the amount of indentation the indenter is pressed into the object being measured is displayed as the Shore A hardness value. The Shore A hardness value decreases as the object being measured becomes softer and increases as the object becomes harder.

[0054] It is preferable that the Shore A hardness value of the material of friction body 3, measured by a test method compliant with JIS K 7215-1986, satisfies the following conditions i) and ii). i) The Shore A hardness value immediately after the start of contact with the indenter is between 60 and 85. ii) The value of ΔHS, as defined by the following formula, is between 0 and 5. ΔHS = (Shore A hardness value immediately after indenter contact begins) - (Shore A hardness value 15 seconds after indenter contact begins) In addition, "immediately after the start of indenter contact" in i) and ii) above means the time within 1 second after the indenter contacts the object being measured.

[0055] In i) above, the Shore A hardness value immediately after the start of needle contact is preferably 60 to 80, and more preferably 65 to 75. A friction body 3 made of a material that satisfies the conditions in i) above has a higher efficiency in generating frictional heat compared to conventional friction bodies. As a result, the friction body 3 can easily thermally discolor the writing of thermochromic ink. Furthermore, a friction body 3 made of a material that satisfies the conditions in i) above is softer than conventional friction bodies and can penetrate into the depressions of writing formed on the paper surface. In addition, by the material of the friction body 3 satisfying the ΔHS value in ii) above, it becomes possible to adsorb and peel off metallic luster pigment from within the depressions of writing.

[0056] The value of ΔHS in ii) above indicates the relaxation time of stress relaxation (stress change over time) when a certain strain is applied to the material of the friction body 3. The stress relaxation time serves as a criterion for distinguishing whether a substance is an elastic, viscoelastic, or viscous substance. A material of the friction body 3 that satisfies the value of ΔHS in ii) above can be said to be an elastic substance with appropriate viscosity that enables the adsorption of metallic luster pigments. On the other hand, a substance with a ΔHS value of 5 or more can be said to be a viscous or viscoelastic substance. If the friction body 3 is a viscous or viscoelastic substance, the amount of deformation when rubbing the writing of thermochromic ink will be too large, and sufficient friction performance cannot be obtained. In particular, the elastic modulus of the friction body 3 made of synthetic resin depends on temperature. Therefore, if the temperature of the friction body 3 itself rises due to frictional heat, and if the friction body 3 is used in a high-temperature environment, the friction body 3 will be more prone to deformation. Accordingly, it is preferable that the value of ΔHS of the material of the friction body 3 is 0 or more and less than 5. Here, the value of ΔHS in ii) above can be arbitrarily set depending on the type and / or composition of one or more comonomers contained in the polymer material.

[0057] Furthermore, the Shore A hardness values ​​in i) and ii) above may be obtained by converting the Shore D hardness value of the material of friction body 3, measured by a test method compliant with JIS K 7215-1986, to a Shore A hardness value.

[0058] 3.7 Amount of wear on the friction material To physically remove the metallic luster pigment added to the thermochromic ink from the paper surface, it is preferable that the friction body 3 abrades by rubbing against the paper surface, generating a small amount of wear debris (eraser debris). The friction body 3 removes the metallic luster pigment from the paper surface by abrading itself and causing the metallic luster pigment to adhere to and encase in the wear debris.

[0059] The amount of wear of the friction element 3 is expressed by the tensile strength Tb at break and elongation Eb at break, which are calculated in accordance with the "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties" specified in the Japanese Industrial Standard JIS K 6251:2017. The tensile strength Tb at break is the value obtained by dividing the tensile force recorded when the object is cut by the cross-sectional area of ​​the object before testing. The elongation Eb at break is the elongation of the object when it is cut, and is expressed as a ratio (%) to the length of the object before testing.

[0060] The inventors have found that the amount of wear of the friction element 3 is inversely proportional to Tb × Eb. That is, the amount of wear of the friction element 3 is affected by the mechanical strength and elongation of the material. By setting the tensile strength Tb at break and elongation Eb at break to appropriate values, the amount of wear of the friction element 3 can be controlled. The value of Tb × Eb represents the energy required to wear down the friction element 3. Therefore, the value of Tb × Eb becomes smaller as the object being measured wears down more easily, and larger as the object being measured wears down less easily.

[0061] It is preferable that the Tb × Eb value of the material of friction body 3, calculated according to the method in accordance with JIS K 6251:2017, satisfies the following condition iii). iii) 5000 ≤ Tb × Eb ≤ 18000 Note that in iii) above, the unit of tensile strength Tb at break is "MPa" and the unit of elongation Eb at break is "%", but these may be converted to other units.

[0062] In iii) above, 8000 ≤ Tb × Eb ≤ 16000 is preferred, and 10000 ≤ Tb × Eb ≤ 14000 is more preferred. By satisfying the conditions in iii) above, the material of the friction body 3 will generate an appropriate amount of wear debris through normal friction action by human hands. This makes it possible to attach and encase the metallic luster pigment added to the thermochromic ink to the wear debris.

[0063] In the above iii), if the value of Tb × Eb exceeds 18000, it becomes difficult to wear down the friction body 3 by normal friction action performed by a human hand. Therefore, it is not possible to wear down the friction body 3 while simultaneously adhering the metallic luster pigment to and encasing the wear debris.

[0064] On the other hand, in iii) above, if the value of Tb × Eb is less than 5000, the friction body 3 will easily wear away due to normal friction action by human hands. As a result, the frictional heat generated by the friction body 3 is lost along with the wear debris, making it difficult to efficiently thermally change the color of the thermochromic ink.

[0065] 4. Core The core 7 is formed from a synthetic resin or metal that is harder than the friction body 3. The materials constituting the core 7 will be described later. In this embodiment, the core 7 is a small cylindrical component having an outer diameter that is approximately the same as the inner diameter of the inner hole 31. Such a core 7 is inserted into the inner hole 31 of the friction body 3. The outer circumferential surface of the core 7 contacts the inner circumferential surface of the inner hole 31, thereby firmly fixing the friction body 3 to the mounting hole 2 of the shaft cylinder 1. This increases the overall rigidity of the friction part 32 and suppresses deformation of the friction part 32. As a result, even if the hardness of the material of the friction body 3 is reduced, good friction performance can be achieved.

[0066] Furthermore, the contact between the outer surface of the core 7 and the inner surface of the inner hole 31 increases the rigidity of the outward projection 51 provided on the mounting portion 5 of the friction body 3, thereby suppressing inward deformation of the outward projection 51. As a result, the outward projection 51 and the inward projection 21 are strongly locked together, preventing the friction body 3 from falling out of the mounting hole 2.

[0067] Furthermore, it is preferable that the outer surface of the core 7 is pressed against the inner surface of the inner hole 31 rather than merely in contact with it. In order to press the outer surface of the core 7 against the inner surface of the inner hole 31, the outer diameter of the core 7 should be made larger than or equal to the inner diameter of the inner hole 31. By pressing the outer surface of the core 7 against the inner surface of the inner hole 31, the rigidity of the friction portion 32 and the outward projection 51 is increased, and the detachment of the core 7 and the friction body 3 is more reliably prevented.

[0068] Here, "rigidity" of the friction part 32 refers to the deformation resistance of the friction part 32 to external forces, and includes tensile rigidity, compressive rigidity, bending rigidity, shear rigidity, torsional rigidity, etc. External forces are mainly the forces applied to the friction part 32 during frictional operation. It is preferable that the friction part 32 has sufficient rigidity to prevent buckling due to external forces during frictional operation.

[0069] 4.1 Core Material The core 7 is formed from a synthetic resin or metal that is harder than the friction body 3. Examples of synthetic resins that can be used include polypropylene, polyethylene, polystyrene, polycarbonate, polyethylene terephthalate, polyacetal, acrylic, nylon, acrylonitrile-styrene copolymer (AS resin), acrylonitrile-butadiene-styrene copolymer (ABS resin), etc. Alternatively, a rubber or elastomer harder than the friction body 3 may be used. Examples of rubber or elastomers that can be used include silicone resin, SBS resin (styrene-butadiene-styrene copolymer), SEBS resin (styrene-ethylene-butylene-styrene copolymer), fluororesin, chloroprene resin, nitrile resin, polyester resin, and ethylene propylene diene rubber (EPDM). The synthetic resin core 7 can be manufactured by cutting or injection molding. Furthermore, examples of metals that can be used include aluminum alloy, stainless steel, brass, etc. On the other hand, the metal core 7 can be manufactured by cutting or plastic deformation, for example.

[0070] 4.2 Core Shape The core 7 is preferably symmetrical vertically with respect to its lateral central axis, as shown in Figure 4. By making the core 7 symmetrical vertically, there is no distinction between the top and bottom of the core 7, and it can be inserted into the inner hole 31 from either the top or bottom. Conversely, the core 7 may also be asymmetrical vertically. For example, at least the upper edge portion of the core 7 may be chamfered to facilitate insertion into the inner hole 31.

[0071] 4.3 Ventilation In this embodiment, the inner hole 31 is a hole that opens at the lower end of the mounting portion 5 and is closed at the upper end of the friction portion 32. On the other hand, the core 7 is a small cylindrical component with an outer diameter greater than or equal to the inner diameter of the inner hole 31. When such a core 7 is inserted into the inner hole 31, which is closed at one end, the air inside the inner hole 31 is compressed by the core 7, and it may not be possible to smoothly insert the core 7 into the inner hole 31. Therefore, a ventilation portion 71 is provided in the core 7. The ventilation portion 71 in this embodiment is a through hole that penetrates from one end to the other of the core 7 along the vertical central axis of the core 7. During the process of inserting the core 7 into the inner hole 31, the air inside the inner hole 31 is discharged to the outside by passing through the ventilation portion 71. With such a ventilation portion 71, the work of inserting the core 7 into the inner hole 31 becomes easier, and it becomes possible to perform the insertion work of the core 7 by an automatic assembly machine.

[0072] The ventilation portion 71 is not limited to the configuration shown in Figure 4. For example, the cross-sectional shape of the ventilation portion 71 is not limited to a circle, but may be a shape other than a circle. Also, the ventilation portion 71 may be provided offset from the central axis of the core 7. Furthermore, the ventilation portion 71 is not limited to a through hole, but may be, for example, at least one groove or projection provided on the outer circumferential surface of the core 7. Alternatively, for example, the ventilation portion 71 may be a spiral groove or projection provided along the outer circumferential surface of the core 7. The spiral groove or projection provides an anti-slip effect that prevents the core 7 from falling out of the inner hole 31. Furthermore, instead of providing the ventilation portion 71 on the core 7, the groove or projection described above may be provided on the inner circumferential surface of the inner hole 31.

[0073] 4.4 Upper core and lower core In this embodiment, the upper half of the core 7 is called the upper core portion 72, and the lower half of the core 7 is called the lower core portion 73. As already mentioned, the core 7 is cylindrical with the same outer diameter along its entire length. However, the core 7 may also be tapered, with the outer diameter of the lower core portion 73 being larger than the outer diameter of the upper core portion 72. This makes it easier to insert the core 7 into the inner hole 31. In addition, the larger outer diameter of the lower core portion 73 increases the rigidity of the outward projection 51, suppressing inward deformation of the outward projection 51. As a result, the outward projection 51 and the inward projection 21 are strongly locked together, preventing the friction body 3 from falling off.

[0074] 4.5 Retention of the core To prevent the core 7 inserted into the inner hole 31 from easily coming out, an anti-slip surface can be provided on the outer surface of the core 7. As an anti-slip surface, for example, the outer surface of the core 7 may be processed to be rough to increase the frictional resistance against the inner surface of the inner hole 31. Alternatively, minute protrusions may be provided on the outer surface of the core 7 to provide an anti-slip surface. Furthermore, by making the outer diameter of the core 7 significantly larger than the inner diameter of the inner hole 31, the core 7 may be prevented from easily coming out of the inner hole 31.

[0075] 5. Method of mounting the friction element Next, the mounting method for the friction body 3 according to this embodiment will be explained with reference to Figures 1 to 4.

[0076] As shown in Figure 1, the friction body 3 is positioned above the mounting hole 2 at the rear end of the shaft cylinder 1, and then drops down towards the mounting hole 2. Then, as shown in Figure 2, the cylindrical portion 53 of the mounting part 5 enters the smallest inner diameter portion 21b of the mounting hole 2, and the mounting part 5 is temporarily inserted into the mounting hole 2. At this time, the guide surface 51a of the mounting part 5 comes into contact with the guide surface 21a of the mounting hole 2, thereby stably maintaining the temporarily inserted state of the mounting part 5.

[0077] Next, the friction body 3, which is in a temporarily inserted state, is pushed into the mounting hole 2. This causes the outward projection 51 of the mounting portion 5 to overcome the inward projection 21 of the mounting hole 2. At this time, the outward projection 51 is strongly pressed against the inward projection 21, causing the middle portion of the mounting portion 5 to elastically deform and bulge radially outward. The radially outward-bulging middle portion of the mounting portion 5 is then housed in the annular space 6 within the mounting hole 2. As a result, the middle portion of the mounting portion 5 does not press against the inner circumferential surface near the entrance of the mounting hole 2, thus not hindering the insertion of the mounting portion 5. Therefore, the outward projection 51 passes smoothly over the inward projection 21, and the outward projection 51 and the inward projection 21 become locked together. This completes the insertion of the mounting portion 5 into the mounting hole 2 (see Figure 3).

[0078] Subsequently, as shown in Figure 4, the core 7 is inserted into the inner hole 31 of the friction body 3. During the process of inserting the core 7 into the inner hole 31, the air inside the inner hole 31 is discharged to the outside through the ventilation section 71. This ventilation section 71 allows the core 7 to be easily inserted into the inner hole 31. Once inserted into the inner hole 31, the core 7 presses the mounting section 5 outward, strengthening the locking between the outward projection 51 and the inward projection 21. This completes the attachment of the friction body 3 to the rear end of the shaft cylinder 1.

[0079] According to this mounting method for the friction body 3, before inserting the core 7 into the inner hole 31, the highly flexible mounting part 5 can be inserted into the mounting hole 2, allowing the outward projection 51 and the inward projection 21 to be easily locked together. Subsequently, by inserting the core 7 into the inner hole 31, inward and outward forces act on the mounting part 5, firmly maintaining the locking between the outward projection 51 and the inward projection 21. Furthermore, since the core 7 is inserted into the inner hole 31 after the mounting part 5 has been inserted into the mounting hole 2, the mounting work of the friction body 3 shown in Figures 1 to 4 does not require much force.

[0080] 6. Thermochromic ink The thermochromic ink incorporated in the thermochromic writing instrument of this embodiment may be water-based, oil-based, or gel ink, as long as it can form thermochromic writing. Furthermore, the form of the thermochromic ink is not limited to liquid, but may also be solid, such as pencil lead. The thermochromic ink will be described in detail below.

[0081] The thermochromic ink used in thermochromic writing instruments is one that changes color or disappears when heated. As the colorant added to the thermochromic ink, it is preferable to use a reversible thermochromic composition containing an electron-donating color-developing organic compound, an electron-accepting compound, and a reaction medium for determining the temperature at which the color reaction of these compounds occurs. In particular, microcapsule pigments, in which the reversible thermochromic composition is encapsulated in microcapsules, are more preferable.

[0082] Examples of the first reversible thermochromic composition include those described in Japanese Patent Publication No. 51-44706, Japanese Patent Publication No. 51-44707, and Japanese Patent Publication No. 1-29398. The reversible thermochromic compositions described in these publications have discoloration points on both the high-temperature and low-temperature sides. The discoloration point refers to a predetermined temperature that marks the boundary where discoloration occurs. The first reversible thermochromic composition becomes decolorized in the temperature range above the high-temperature discoloration point and becomes colored in the temperature range below the low-temperature discoloration point. At room temperature, either the decolorized state or the colored state is maintained. The other state is maintained only while the temperature reaches the high-temperature or low-temperature discoloration point. Once the temperature is no longer at the high-temperature or low-temperature discoloration point, it returns to the other state. In other words, the first reversible thermochromic composition has a relatively small hysteresis characteristic width ΔH (for example, ΔH is between 1°C and 7°C).

[0083] As a second type of reversible thermochromic composition, for example, Japanese Patent Publication No. 4-17154, Japanese Unexamined Patent Publication No. 7-179777, Japanese Unexamined Patent Publication No. 7-33997, Japanese Unexamined Patent Publication No. 8-39936, Japanese Unexamined Patent Publication No. 2006-137886, Japanese Unexamined Patent Publication No. 2006-188660, Japanese Unexamined Patent Publication No. 2008-45062, and Japanese Unexamined Patent Publication No. 2008-280523 describe a reversible thermochromic composition with a large hysteresis characteristic width ΔH (for example, a ΔH value of 8°C or more and 50°C or less).

[0084] Here, the magnitude of the width ΔH of the hysteresis characteristic is indicated by the shape of the curve plotted between the color density of the reversible thermochromic composition and temperature. For example, suppose a reversible thermochromic composition becomes completely decolorized in the temperature range above the high-temperature color change point and becomes fully colored in the temperature range below the low-temperature color change point. The temperature at which it becomes completely decolorized is called the "complete decolorization temperature," and the temperature at which it becomes fully colored is called the "complete color development temperature." In the curve plotted between the color density of this reversible thermochromic composition and temperature, if the path of the curve from the low-temperature complete decolorization temperature to the high-temperature complete color development temperature and the path of the curve from the high-temperature complete color development temperature to the low-temperature complete decolorization temperature are significantly different, the width ΔH of the hysteresis characteristic will be large. Furthermore, such a reversible thermochromic composition has color memory properties that maintain a colored or decolorized state in a specific temperature range, for example, the room temperature range (everyday living temperature range).

[0085] In a reversible thermochromic composition having color memory properties, it is preferable to set the complete color development temperature to a low temperature outside the room temperature range, and the complete decolorization temperature to a temperature of frictional heat that can be generated by a friction body. The complete color development temperature is, for example, in the range of -50°C to 0°C, preferably -40°C to -5°C, and more preferably -30°C to -10°C. On the other hand, the complete decolorization temperature is, for example, in the range of 50°C to 95°C, preferably 50°C to 90°C, and more preferably 60°C to 80°C. Furthermore, by setting the width ΔH of the hysteresis characteristic to 40°C to 100°C, the color development state or decolorization state is well maintained in the room temperature range.

[0086] By encapsulating the aforementioned reversible thermochromic composition within microcapsules, a heat-decolorizing microcapsule pigment can be manufactured. The average particle size of the microcapsule pigment is, for example, in the range of 0.05 μm to 5.0 μm, preferably 0.1 μm to 4.0 μm, and more preferably 0.5 μm to 3.0 μm. This results in good writing performance and ink density for thermochromic writing instruments. Furthermore, when the average particle size of the microcapsule pigment is 2.0 μm or larger, it becomes possible not only to chemically decolorize the ink but also to physically erase it from the paper surface. That is, microcapsule pigments with an average particle size of 2.0 μm or larger are physically peeled off the paper surface by adsorption onto a friction material, and are irreversibly erased.

[0087] The average particle size of the microcapsule pigment is measured using "Mac-View," image analysis-based particle size distribution measurement software manufactured by MOUNTECH Co., Ltd. First, the region of the microcapsule pigment particles is identified, then the projected area circle equivalent diameter (Heywood diameter) is calculated from the area of ​​the particle region, and finally, the average particle size of the particles equivalent to an equivolute sphere is measured based on the value of the projected area circle equivalent diameter.

[0088] Furthermore, if the particle size of all or most of the microcapsule pigments contained in the thermochromic ink exceeds 0.2 μm, it is possible to measure them using the "Multisizer® 4e" particle size distribution analyzer manufactured by Beckman Coulter, Inc. In this case, the equivalent diameter of the equivolute spheres of the microcapsule pigments is measured using the Coulter method, and the average particle size is determined based on this measurement.

[0089] Furthermore, general dyes or pigments that do not exhibit thermal discoloration may be added as coloring components. This makes it possible to impart a desired color that does not change with heat to the writing of thermally discolored inks. Examples of general dyes include acid dyes, basic dyes, and direct dyes. Examples of general pigments include inorganic pigments such as carbon black and ultramarine, organic pigments such as copper phthalocyanine blue and benzidine yellow, and dispersed pigment products that have been finely and stably dispersed in a medium using a surfactant beforehand. In addition, metallic pigments such as metal powders and pearl pigments, fluorescent pigments, phosphorescent pigments, and special pigments such as titanium dioxide can also be used. These coloring components may be used in combination with the microcapsule pigments described above, or they may be encapsulated within the microcapsule pigments.

[0090] 6.1 Metallic Luster Pigments By adding a metallic luster pigment to a thermochromic ink, the ink becomes metallic, and glossy handwriting is formed. Preferably, a transparent metallic luster pigment is added to the thermochromic ink. The transparent metallic luster pigment gives gloss to the handwriting of the thermochromic ink, and when the handwriting of the thermochromic ink is chemically erased, it appears to be completely erased without any gloss.

[0091] As a transparent metallic luster pigment, a luminous pigment in which the core material is coated with a metal oxide, or a cholesteric liquid crystal type luminous pigment may be used. As the core material, materials selected from, for example, natural mica, synthetic mica, flattened glass flakes, or flaky aluminum oxide can be used.

[0092] Effective luminous pigments using natural mica as the core material include those coated with titanium dioxide on its surface, and those coated with iron oxide or non-thermochromic dye pigments on top of the titanium dioxide. Examples of luminous pigments using natural mica as the core material include "Iriodin®" from Merck KGaA and "Lumina®" from BASF SE.

[0093] For luminous pigments using synthetic mica as the core material, those coated with a metal oxide such as titanium dioxide are effective. Examples of metal oxides that can be used include titanium, zirconium, chromium, vanadium, and iron oxides, with titanium dioxide being the main component. As a luminous pigment with a synthetic mica surface coated with a metal oxide, for example, the product "ULTIMICA®" manufactured by Nippon Koken Kogyo Co., Ltd. can be used.

[0094] For luminous pigments using flattened glass fragments as the core material, those in which the surface is coated with a metal oxide such as titanium dioxide are effective. As an example of a luminous pigment in which the surface of flattened glass fragments is coated with a metal oxide, the product name "MetaShine®" manufactured by Nippon Sheet Glass Co., Ltd. can be used.

[0095] For luminous pigments using flaky aluminum oxide as the core material, those coated with a metal oxide such as titanium oxide are effective. Examples of metal oxides that can be used include titanium, zirconium, chromium, vanadium, and iron oxides, with titanium oxide being the main component. As a luminous pigment with a metal oxide coating on the surface of flaky aluminum oxide, for example, Merck KGaA's trade name "Xirallic®" can be used.

[0096] Liquid crystal polymers used as cholesteric liquid crystal pigments have the property of reflecting some of the light in a broad spectral range while transmitting all of the light in the other ranges due to the interference effect of light. Cholesteric liquid crystal pigments have excellent metallic luster, color flop properties where the hue changes depending on the viewpoint, and transparency. As the cholesteric liquid crystal pigment, for example, the trade name "HELICONE(registered trademark)HC" manufactured by Wacker Chemie AG can be used.

[0097] Additionally, a glossy material manufactured by vacuum deposition can be used. This glossy material is produced by vacuum deposition of metals such as gold and silver onto a film to form a foil, and then peeling the foil from the film and finely crushing it. As such a glossy material, the product name "LG neo®" manufactured by Oike Kogyo Co., Ltd. can be used.

[0098] The average particle size of the metallic luster pigment described above is set to be within the range of 0.1 μm to 50 μm, preferably 2 μm to 40 μm, and more preferably 10 μm to 40 μm. This ensures good writing performance and handwriting brightness for the thermochromic writing instrument. As a method for measuring the average particle size of the metallic luster pigment, for example, the particle size distribution is measured using the particle size distribution analyzer "LA-300" manufactured by Horiba, Ltd., and the average particle size (median diameter) is calculated on a volume basis based on the measured particle size distribution.

[0099] 6.2 Physical Removal of Metallic Luster Pigments Metallic pigments do not easily penetrate the paper surface. Therefore, when writing with thermochromic ink containing metallic pigments is rubbed, the metallic pigments scatter on the paper, resulting in a poor appearance after erasing. This is especially true on black paper, where the metallic pigment's shine is more pronounced, making the erased writing look even worse.

[0100] Therefore, the material of the friction element 3 in this embodiment satisfies the condition i) above, which is that the Shore A hardness value immediately after the start of contact with the indenter is 60 or more and 85 or less. This allows the friction element 3 to penetrate into the depressions of the handwriting formed on the paper surface. Furthermore, the material of the friction element 3 in this embodiment satisfies the condition ii) above, which is that the ΔHS value is 0 or more and less than 5. This allows the friction element 3 to adsorb and peel off the metallic luster pigment from within the depressions of the handwriting. In other words, according to the friction element 3 of this embodiment, it is possible to physically erase the metallic luster pigment added to the thermochromic ink without scattering it on the paper surface. In addition, the handwriting of the thermochromic ink is chemically erased by frictional heat.

[0101] Furthermore, when a metallic luster pigment is added to the thermochromic ink, it is preferable that the volume Vp of the metallic luster pigment and the volume Ve of the friction portion 32 satisfy the condition in iv) below. iv) 5 ≤ Ve / Vp ≤ 35

[0102] The volume Vp of the metallic luster pigment indicates the amount of metallic luster pigment that gives the writing a glossy appearance. The volume Ve of the friction part 32 indicates the amount of friction part 32 that physically erases the metallic luster pigment through wear. By keeping the Ve / Vp value within the range of 5 to 35, a balance is maintained between the amount of metallic luster pigment added to the thermochromic ink and the amount of friction part 32 required to erase this amount of metallic luster pigment. That is, when Ve / Vp is at the upper limit of 35, the amount of metallic luster pigment is the minimum amount that gives the writing a visible glossy appearance. In this case, the friction part 32 is the maximum amount that can erase 100% of the minimum amount of metallic luster pigment. On the other hand, when Ve / Vp is at the lower limit of 5, the amount of metallic luster pigment is the maximum amount that gives the writing a high glossy appearance. In this case, the friction part 32 is the minimum amount that can erase 30% of the maximum amount of metallic luster pigment. The Ve / Vp value is preferably between 8 and 26, and more preferably between 10 and 20.

[0103] 6.3 Other Additives Various conventionally known additives may be added to the thermochromic ink. If the thermochromic ink is water-based, for example, pH adjusters, rust inhibitors, preservatives, fungicides, wetting agents, defoaming agents, surfactants, lubricants, fixing agents such as resins, shear viscosity reducing agents, pen tip drying inhibitors, and drip prevention agents may be added. If the thermochromic ink is oil-based, for example, viscosity modifiers, preservatives, rust inhibitors, defoaming agents, lubricants, dispersants, anti-streaking agents, anti-leakage agents, and surfactants may be added.

[0104] 7. Thermochromic writing instruments The type of thermochromic writing instrument in this embodiment is not particularly limited and may be any of the following: a fountain pen, a marking pen, a ballpoint pen, a retractable solid writing instrument, etc. Furthermore, the thermochromic writing instrument may be either a capped type or a retractable type. A capped thermochromic writing instrument has a cap to cover the pen tip. A retractable thermochromic writing instrument has a retractable mechanism that allows the pen tip to be extended from the barrel and retracted into the barrel. The retractable mechanism may be any of the following: a knock type, a twist type, a slide type, etc. Furthermore, a retractable thermochromic writing instrument may have two or more refills and be configured to selectively extend any one of the two or more refills. In this case, the two or more refills may have different types of pen tips and / or different colors of thermochromic ink.

[0105] The tip of the marking pen may be, for example, a fiber tip, a felt tip, a plastic tip, a metal tip, etc. The thermochromic ink used in the marking pen may be impregnated with an ink-absorbing body made of fiber bundles. The ink-absorbing body is housed inside the barrel. The thermochromic ink impregnated in the ink-absorbing body is supplied to the pen tip. Alternatively, the thermochromic ink used in the marking pen may be housed directly inside the barrel. In this case, the barrel is provided with an ink flow rate adjustment member made of comb grooves or fiber bundles. The thermochromic ink housed directly inside the barrel is supplied to the pen tip via the ink flow rate adjustment member. Instead of an ink flow rate adjustment member, the barrel may be provided with a valve mechanism that supplies a predetermined amount of ink to the pen tip.

[0106] The thermochromic ink used in the ballpoint pen is filled, for example, into an ink reservoir tube fitted with a ballpoint pen tip. In this case, an ink backflow prevention body is placed at the rear end of the thermochromic ink within the ink reservoir tube. Alternatively, the thermochromic ink used in the ballpoint pen may be directly contained within the barrel. In this case, an ink backflow prevention body is placed at the rear end of the thermochromic ink within the barrel. Furthermore, the thermochromic ink used in the ballpoint pen may be impregnated with an ink-absorbing material consisting of fiber bundles. The barrel may be provided with an ink flow rate adjustment member consisting of comb grooves or fiber bundles. A predetermined amount of thermochromic ink is supplied to the pen tip via the ink flow rate adjustment member.

[0107] In the various types of thermochromic writing instruments described above, the friction element 3 of this embodiment is integrated with the thermochromic writing instrument by being attached to any of the components constituting the thermochromic writing instrument (see Figure 5). For example, the friction element 3 is attached to the cap, clip, top cap, tip, barrel, end cap, grip, and the operating part for extending and retracting the pen tip, etc., which constitute the thermochromic writing instrument. The friction part 32 may also be covered by a cover to prevent soiling.

[0108] Furthermore, the friction element 3 in this embodiment may not be attached to any of the components constituting the thermochromic writing instrument, and may be a separate component from the thermochromic writing instrument (see Figure 6). The separate friction element 3 may be made solely of the low-hardness synthetic resin material described above. Alternatively, the separate friction element 3 may be attached to other components made of a high-hardness material.

[0109] 8. Effects The friction element 3 of this embodiment, like conventional friction elements, can discolor or erase the ink marks of thermochromic ink by generating frictional heat. Furthermore, the low-hardness friction portion 32 penetrates into the depressions of the ink marks, adsorbing the metallic luster pigment added to the thermochromic ink and peeling it off the paper surface. The metallic luster pigment adsorbed by the friction portion 32 becomes entangled in the wear debris of the friction portion 32 and is completely removed from the paper surface. In this way, the friction element 3 of this embodiment can chemically and physically erase ink marks of thermochromic ink containing metallic luster pigment.

[0110] By using the friction element 3 of this embodiment, it is possible to erase the writing of thermochromic ink containing metallic luster pigments without leaving any color residue. As a result, the appearance of the paper surface after erasing the writing is improved. In particular, metallic luster pigments with an average particle size of 10 μm or more can give high luster to the writing of thermochromic inks and are easily adsorbed by the friction element 32.

[0111] Conventional friction materials have a Shore A hardness value that is too high, making them unable to erase pencil lead marks. To erase pencil lead marks, it is necessary to use an eraser with a low Shore A hardness value. In contrast, the friction material 3 of this embodiment has a lower Shore A hardness value than conventional friction materials. Furthermore, the friction material 3 has properties similar to an eraser, as it wears down by rubbing against the paper surface, producing a small amount of wear debris. Therefore, it is possible to erase both thermochromic ink marks and pencil lead marks with a single friction material 3.

[0112] The friction element 3 in this embodiment may be separate from the thermochromic writing instrument (see friction element 201 in Figure 6). The friction element 3, separate from the thermochromic writing instrument, is preferably attached to a support for gripping with the fingers. The support is formed, for example, from a hard synthetic resin or metal. The friction element 3, separate from the thermochromic writing instrument, is combined with the thermochromic writing instrument to form a single writing set. [Examples]

[0113] The following describes examples of the thermochromic writing instrument of the present invention with reference to Figures 5 and 6. In the first and second examples described below, the numerical values ​​indicating the composition content are in parts by mass. The average particle size of the thermochromic pigment was measured using the "Multisizer® 4e" particle size distribution analyzer manufactured by Beckman Coulter, Inc. The equivalent diameter of an isovolume sphere of the thermochromic pigment was measured using the Coulter method, and the average particle size was calculated from this measurement. The average particle size of the metallic luster pigment was measured using the "LA-300" particle size distribution analyzer manufactured by Horiba, Ltd. The particle size distribution of the metallic luster pigment was measured, and the average particle size (median diameter) was calculated on a volume basis based on this measurement. The Shore A hardness of the friction material was measured according to the test method conforming to the Japanese Industrial Standard JIS K 7215. A sample of a predetermined shape, thickness, and size was prepared using the same material as the friction material. The Shore A hardness of this sample was measured by pressurizing it with a manual durometer.

[0114] • First embodiment In the first embodiment, the thermochromic writing instrument 103 of the second embodiment shown in Figure 5 was used. A friction element 101 is attached to the rear end of the barrel 182 of the thermochromic writing instrument 103.

[0115] The friction body 101 is formed of a polyester elastomer that satisfies the conditions i) to iv) above. The Shore A hardness value of the polyester elastomer immediately after the start of indentation contact was 70, and the Shore A hardness value 15 seconds after the start of indentation contact was 69. Therefore, the ΔHS value of the polyester elastomer is 1.

[0116] The tensile strength Tb and elongation Eb at break of the polyester elastomer were measured according to the test method compliant with JIS K 6251:2017. The measurement results showed a tensile strength Tb of 14 MPa and an elongation Eb of 890%. Therefore, the Tb × Eb value of the polyester elastomer is 12460.

[0117] By injection molding the polyester elastomer described above, a milky white friction body 101 with the shape shown in Figure 5 was obtained. The friction body 101 comprises a convex curved friction portion 111 and a cylindrical mounting portion 112. A stepped locking portion is formed at the lower end of the mounting portion 112. By making the friction portion 111 a convex curved shape, the friction action is stabilized and it becomes easier to rub against handwriting on the paper surface.

[0118] The mounting portion 112 of the friction body 101 is inserted into a mounting hole 181 provided at the rear end of the shaft cylinder 182. Two ring beads are formed on the inner circumferential surface of the mounting hole 181. The mounting portion 112 is sandwiched between the two ring beads within the mounting hole 181. Furthermore, the locking portion of the mounting portion 112 is locked to the lower end of the mounting hole 181. The maximum outer diameter D of the friction portion 111 is 6, and the protrusion length L from the mounting hole 181 is also 6. Therefore, the L / D value of the friction portion 111 is 1.

[0119] The thermochromic writing instrument 103 is a retractable ballpoint pen. The pen tip (ballpoint pen tip) 105 of the thermochromic writing instrument 103 can be extended or retracted by sliding the operating part 184 forward. The operating part 184 protrudes outward from the side of the barrel 182. Inside the barrel 182 is a retractable mechanism for extending and retracting the pen tip 105. The retractable mechanism mainly consists of a sliding body 18 4 a) It consists of a refill holder 185, a coil spring 183, and a locking member 186. The refill 104 is housed in front of the refill holder 185 inside the barrel 182.

[0120] The barrel 182 is composed of a front barrel 182b and a rear barrel 182a. An opening 182c is provided at the tip of the front barrel 182b. The opening 182c has a diameter that allows the pen tip 105 of the refill 104 to protrude or retract. The rear barrel 182a is screwed onto the rear end of the front barrel 182b. The retractable mechanism described above is housed inside the rear barrel 182b. To house the sliding body 184a, which is integrally molded with the operating part 184, the rear barrel 182a is composed of first and second parts that can be separated in the front-rear direction. A sliding hole extending in the front-rear direction is formed in the second part that constitutes the rear of the rear barrel 182a. When the sliding body 184a is housed inside the rear barrel 182a, the operating part 184 protrudes outward from the sliding hole.

[0121] The sliding body 184a is a substantially cylindrical resin molded product integrally molded with the operating part 184. Multiple sawtooth-shaped protrusions are formed at the tip of the sliding body 184a. A refill holder 185 is positioned in front of the sliding body 184a within the rear shaft 182a. The refill holder 185 is a substantially cylindrical resin molded product that fits onto the rear end of the refill 104. Multiple stepped portions are formed at the rear end of the refill holder 185. These stepped portions engage with the sawtooth-shaped protrusions of the sliding body 184a. In addition, multiple ribs extending in the axial direction are formed at equal intervals on the outer circumferential surface of the refill holder 185. On the other hand, multiple grooves are formed at equal intervals on the inner surface of the first component that constitutes the front of the rear shaft 182a. These grooves guide the multiple ribs of the refill holder 185 in the axial direction.

[0122] The front end of the refill holder 185 has a smaller outer diameter than the rest of the unit and is inserted into the rear end of the coil spring 183. The front end of the coil spring 183 is locked to a locking member 186 fixed inside the rear shaft 182a. The coil spring 183 biases the refill holder 185 and the refill 104 backward.

[0123] When the operating part 184 is slid forward with the pen tip 105 fully retracted, the multiple ribs of the refill holder 185 are guided into the multiple grooves in the rear barrel 182a, causing the refill holder 185 to move forward. As the multiple ribs pass through the multiple grooves, the sawtooth-shaped protrusions of the sliding body 184a engage with the stepped portion of the refill holder 185, causing the refill holder 185 to rotate by a predetermined angle. As a result, the end faces of the multiple ribs come into contact with the end faces of the multiple grooves, fixing the refill holder 185 in the forward position. Consequently, the pen tip 105 of the refill 104 remains protruding from the opening 182c of the front barrel 182b.

[0124] When the operating part 184 is slid forward with the pen tip 105 in the protruding position, the sawtooth-shaped protrusion of the sliding body 184a engages with the stepped portion of the refill holder 185, causing the refill holder 185 to rotate by a predetermined angle. This releases the contact between the end faces of the multiple ribs and the end faces of the multiple grooves, and the multiple ribs of the refill holder 185 are guided into the multiple grooves in the rear shaft 182a. The refill holder 185 moves backward due to the biasing force of the coil spring 183. As a result, the pen tip 105 of the refill 104 becomes retracted into the opening 182c of the front shaft 182b.

[0125] The refill 104 consists of a pen tip 105, an ink reservoir 106, and a connecting member 107. A ball is rotatably held at the front end of the pen tip 105. The ink reservoir 106 is a metal pipe with open front and rear ends. The connecting member 107 is made of transparent synthetic resin. The pen tip 105 is connected to the opening at the front end of the ink reservoir 106 via the connecting member 107. The refill 104 contains a thermochromic ink composition 161 and an ink-following body composition 162.

[0126] The components of the thermochromic ink composition 161 are: reversible thermochromic pigment (11 parts), transparent metallic luster pigment (3 parts), metal vapor deposition resin pigment (2 parts), shear viscosity reducing agent (0.3 parts), urea (10 parts), glycerin (10 parts), nonionic penetration agent (0.6 parts), hydrophobic silica-based defoaming agent (0.1 parts), preservative (0.1 parts), and water (62.9 parts).

[0127] The reversible thermochromic pigment consists of a reversible thermochromic composition that changes color from pink to colorless, encapsulated in microcapsules. The reversible thermochromic pigment has a color development temperature of -10°C, a decolorization temperature of 65°C, and an average particle size of 2.5 μm.

[0128] As the transparent metallic luster pigment, we used "Iriodin® 6103 Icy White," a product manufactured by Merck KGaA. This transparent metallic luster pigment consists of silver-colored particles with a metal oxide coating on the surface of synthetic mica. The average particle size of the transparent metallic luster pigment is 25 μm. As the metal vapor deposition resin pigment, we used "LG neo® Silver #325," a product manufactured by Oike Kogyo Co., Ltd. The particles of this metal vapor deposition resin pigment are silver in color, and the average particle size is 35 μm. The ratio Ve / Vp of the volume of the friction portion 111 to the total volume Vp of the transparent metallic luster pigment and the metal vapor deposition resin pigment is 15.

[0129] Xanthan gum was used as a shear viscosity reducing agent. "SN Wet 366," manufactured by Sunopco Co., Ltd., was used as a nonionic penetration agent. "Nopco 8034," manufactured by Sunopco Co., Ltd., was used as a hydrophobic silica-based defoaming agent. "Proxel (registered trademark) XL2," manufactured by Lonza Japan Co., Ltd., was used as a preservative.

[0130] The components of the ink-following body composition 162 are polybutene (98.5 parts) as a base oil and fatty acid amide (1.5 parts) as a thickener. The ink-following body composition 162 was obtained by kneading a mixture of polybutene and fatty acid amide using a three-roll press.

[0131] Using a thermochromic writing instrument 103, writing marks of thermochromic ink composition 161 were formed on the surface of "Writing Paper A" (100% chemical pulp, whiteness 75.0 or higher) conforming to the Japanese Industrial Standard JIS P3201. A pink thermochromic pigment formed the base of the writing marks, and a silver transparent metallic luster pigment and a metal vapor deposition resin pigment were dispersed within these marks. As a result, the writing marks of thermochromic ink composition 161 exhibited a metallic pink color on the white paper surface. Writing marks of thermochromic ink composition 161 were also formed on a black paper surface. As a result, the hue of the writing marks formed on the black paper surface was the same as that of the white paper surface. However, the luster of the writing marks formed on the black paper surface was particularly higher than that of the white paper surface.

[0132] The markings formed on the white and black paper can be chemically and physically erased by the friction element 101 attached to the thermochromic writing instrument 103. Specifically, the friction element 111 repeatedly rubs against the markings formed on the paper. This generates frictional heat, causing the thermochromic pigment in the markings to change from pink to colorless and transparent. Furthermore, the low-hardness friction element 111 penetrates into the depressions of the markings, adsorbing the silvery transparent metallic pigment and metal vapor-deposited resin pigment and peeling them off the paper. In addition, the transparent metallic pigment and metal vapor-deposited resin pigment adsorbed by the friction element 111 are enveloped in the wear debris of the friction element 111 and completely removed from the paper. In this way, the friction element 101 cleanly erases the markings of the thermochromic ink composition 161 without staining the paper. In particular, the metallic pigment and metal vapor-deposited resin pigment remaining on black paper emit a shine depending on the viewing angle, which poses a visually noticeable problem. This problem is solved by using friction element 101.

[0133] Table 1 below shows the results of evaluation tests for each of the friction bodies in Examples 1-4 and Comparative Examples 1-4. The friction bodies of Examples 1-4 satisfy both the conditions for Shore A hardness and Ve / Vp of the present invention. The friction bodies of Comparative Examples 1-4 do not satisfy either one of the conditions for Shore A hardness and Ve / Vp of the present invention. Each of the friction bodies in Examples 1-4 and Comparative Examples 1-4 has the same shape as the friction body 101 shown in Figure 5 and is attached to the rear end of the barrel 182 of the thermochromic writing instrument 103. The refill 104 of the thermochromic writing instrument 103 contains a thermochromic ink composition 161 and an ink-following body composition 162 consisting of the above-mentioned components. The pen tip 105 of the refill 104 is a ballpoint pen tip.

[0134] [Table 1]

[0135] The friction bodies of Examples 1 to 4 are all made of polyester elastomers. By mixing polyester elastomers with different hardnesses, the hardness of the friction bodies of Examples 1 to 4 was made different for each. The friction bodies of Examples 1 to 4 all satisfy the conditions of the present invention, with a Shore A hardness value of 60 to 85 immediately after the start of indentation contact, a ΔHS value of 0 to less than 5, and a Ve / Vp value of 5 to 35.

[0136] The friction material of Comparative Example 1 is made of a polyester elastomer with the same hardness as that of Example 1. The friction material of Comparative Example 1 has a Ve / Vp value of 4. In this respect, the friction material of Comparative Example 1 does not satisfy the conditions of the present invention, which require a Ve / Vp value of 5 or more and 35 or less.

[0137] The friction material of Comparative Example 2 consists of 40% α-polyolefin copolymer, 40% styrene elastomer, and 20% crystalline polypropylene. The friction material of Comparative Example 2 has a Shore A hardness value of 90 immediately after the start of indenter contact and a ΔHS value of 18. In these respects, the friction material of Comparative Example 2 does not satisfy the conditions of the present invention, which are a Shore A hardness value of 60 or more and 85 or less immediately after the start of indenter contact and a ΔHS value of 0 or more and less than 5.

[0138] The friction material of Comparative Example 3 is made of styrene elastomer (product name "AR-885C" of Aron Kasei Co., Ltd.). The Shore A hardness value of the friction material of Comparative Example 3 is 88 immediately after the start of indentation contact. In this respect, the friction material of Comparative Example 3 does not satisfy the conditions of the present invention, which state that the Shore A hardness value immediately after the start of indentation contact is between 60 and 85.

[0139] The friction body of Comparative Example 4 was made using a commercially available eraser made of polyvinyl chloride resin (product number "ER-F6" from Pilot Corporation) as the material. The friction body of Comparative Example 4 had a Shore A hardness value of 50 immediately after the start of indentation contact and a ΔHS value of 25. In these respects, the friction body of Comparative Example 4 does not satisfy the conditions of the present invention, which require a Shore A hardness value of 60 or more and 85 or less immediately after the start of indentation contact, and a ΔHS value of 0 or more and less than 5.

[0140] Using the friction bodies of Examples 1-4 and Comparative Examples 1-4, the erasability, wear debris, continuous erasability, and erasable amount were evaluated by erasing the writing on the thermochromic writing instrument 103.

[0141] <Evaluation of extinction properties> Eight sheets of white paper and eight sheets of black paper were prepared. The white paper is "Writing Paper A" (100% chemical pulp, whiteness 75.0 or higher) conforming to the Japanese Industrial Standard JIS P3201. The black paper is black paper made from 100% chemical pulp. The thickness of both the white and black paper is 0.09 mm, and the basis weight is 80 g / m². 2 The thermochromic writing instrument 103 was used to form the thermochromic ink composition 161 on the surfaces of white and black paper, respectively. The forms were circular spiral patterns. Ten spiral patterns were handwritten on one line on one sheet of paper. Then, the ten spiral patterns formed on the white and black paper were erased using the respective friction bodies of Examples 1-4 and Comparative Examples 1-4. The condition of the paper after erasing was visually confirmed.

[0142] The evaluation of extinction in Table 1 is as follows: A: The handwriting was erased without leaving any trace of color. B: A faint pink color from the thermochromic pigment or a silver color from the metallic pigment remained. C: The pink color of the thermochromic pigment or the silver color of the metallic pigment was not erased.

[0143] <Evaluation of wear debris> In the evaluation of erasability described above, ten spiral patterns formed on the surfaces of white and black paper were erased using the respective friction bodies of Examples 1-4 and Comparative Examples 1-4. After erasing, the condition of the wear debris generated from each friction body was visually inspected.

[0144] The evaluation of the wear debris in Table 1 is as follows: A: There were no practical problems. B: Wear debris adhered to the friction surface, causing practical problems. C: A large amount of wear debris was generated, causing practical problems.

[0145] <Evaluation of continuous elimination properties> Eight sheets of blank paper were prepared. The blank paper conforms to the Japanese Industrial Standard JIS P3201, "Writing Paper A" (100% chemical pulp, whiteness 75.0 or higher). The thickness of the blank paper is 0.09 mm, and the basis weight is 80 g / m². 2 The following was done. Using a thermochromic writing instrument 103, a mark of the thermochromic ink composition 161 was formed on a blank sheet of paper. The mark was a circular spiral pattern. Ten spiral patterns were handwritten in each of the 30 lines on one sheet of paper, for a total of 300 spiral patterns. Then, using the respective friction bodies of Examples 1-4 and Comparative Examples 1-4, the 30 lines of spiral patterns formed on each of the eight blank sheets of paper were erased continuously. During the process of erasing the 30 lines of spiral patterns, it was confirmed how many lines the friction performance of the friction body was maintained immediately after the start of erasing. In this evaluation of continuous erasability, the erasability of the metallic luster pigment and the state of wear debris were not considered.

[0146] The evaluation of continuous erasure in Table 1 is as follows: A: The frictional performance immediately after the erasing process began was maintained until 30 lines of the spiral pattern were erased. B: The frictional performance immediately after the erasing process began was maintained until 20 lines of the spiral pattern were erased. C: The frictional performance immediately after the erasure process began was maintained until 10 lines of the spiral pattern were erased.

[0147] <Evaluation of erasable amount> In the evaluation of continuous erasability described above, all 30 lines of spiral patterns were erased for each friction body of Examples 1-4 and Comparative Examples 1-4. Subsequently, the amount of thermochromic ink composition 161 consumed to handwrite 30 lines of spiral patterns and the amount of wear on the friction body to erase 30 lines of spiral patterns were measured. Based on these measurements, the weight of thermochromic ink composition 161 that could be erased before the friction part of each friction body of Examples 1-4 and Comparative Examples 1-4 was completely worn down (erasable amount) was calculated. The percentage of the ink weight contained in one refill 104 that this erasable amount represents was determined, and the practicality of the friction body was evaluated.

[0148] The evaluation of the erasable amount in Table 1 is as follows: A: It can erase more than 30% of the ink weight of one refill, so there are no practical issues. C: It cannot erase more than 30% of the ink weight of one refill, which poses a practical problem.

[0149] • Second embodiment The second embodiment used the friction element 201 of the third embodiment shown in Figure 6 and a thermochromic writing instrument 203. The configuration of the thermochromic writing instrument 203 is the same as that of the thermochromic writing instrument 103 of the first embodiment described above. The friction element 201 is separate from the thermochromic writing instrument 203. The combination of the friction element 201 and the thermochromic writing instrument 203 constitutes one writing set 209.

[0150] The friction element 201 is fitted to the tip of a support 202 made of rigid PP resin (polypropylene). The portion of the friction element 201 protruding from the tip of the support 202 becomes the friction portion 211. The friction portion 211 is used to chemically and physically erase thermochromic ink containing metallic luster pigments. The cross-sections of both the friction element 201 and the support 202 are elliptical in shape. Seven friction elements 201 were injection molded using the same materials as in Examples 1-4 and Comparative Examples 1-3 in Table 1 above.

[0151] On the other hand, the components of the thermochromic ink composition 161 used in the thermochromic writing instrument 203 are the same as those of the first embodiment described above. Specifically, the components of the thermochromic ink composition 161 are reversible thermochromic pigment (11 parts), transparent metallic luster pigment (3 parts), metal vapor deposition resin pigment (2 parts), shear viscosity reducing agent (0.3 parts), urea (10 parts), glycerin (10 parts), nonionic penetration agent (0.6 parts), hydrophobic silica-based defoaming agent (0.1 parts), preservative (0.1 parts), and water (62.9 parts).

[0152] However, the reversible thermochromic pigment consisted of a reversible thermochromic composition that changes color from blue to colorless encapsulated in microcapsules. Furthermore, the transparent metallic luster pigment used was "Iriodin® 6107 Icy White Lightning," a product of Merck KGaA. This transparent metallic pigment consists of silver particles with an average particle size of 25 μm.

[0153] Similar to the first embodiment described above, the thermochromic ink composition 161 is housed in the refill 104 of the thermochromic writing instrument 203. The tip of the refill 104 is a ballpoint pen tip. By sliding the operating part 184 forward, the tip 105 of the refill 104 can be extended or retracted.

[0154] Using a thermochromic writing instrument 203, writing marks of thermochromic ink composition 161 were formed on the surface of "Writing Paper A" (100% chemical pulp, whiteness 75.0 or higher) conforming to the Japanese Industrial Standard JIS P3201. A blue thermochromic pigment formed the base of the writing marks, and a silver transparent metallic luster pigment and a metal vapor deposition resin pigment were dispersed within these marks. As a result, the writing marks of thermochromic ink composition 161 exhibited a metallic blue color on the white paper surface. Writing marks of thermochromic ink composition 161 were also formed on the black paper surface. As a result, the hue of the writing marks formed on the black paper surface was the same as that of the white paper surface. However, the luster of the writing marks formed on the black paper surface was particularly higher than that of the white paper surface.

[0155] As described above, seven friction bodies 201 were injection molded using the same materials as in Examples 1-4 and Comparative Examples 1-3 in Table 1. Seven writing sets 209 were constructed by combining each of the seven friction bodies 201 with a thermochromic writing instrument 203. Each of the seven writing sets 209 was evaluated for erasability, wear debris, continuous erasability, and erasable amount. The evaluation results were the same as those for Examples 1-4 and Comparative Examples 1-3 in Table 1.

[0156] Four friction bodies 201 made of the same material as Examples 1-4 in Table 1 all showed good erasure test results. The friction body 211 repeatedly rubbed against the writing of the thermochromic ink composition 161. As a result, the friction body 211 generated frictional heat, and the thermochromic pigment in the writing changed color from blue to colorless and transparent. In addition, the low hardness of the friction body 211 penetrated into the depressions of the writing, adsorbing the silvery transparent metallic luster pigment and the metal vapor-deposited resin pigment and peeling them off the paper surface. Furthermore, the transparent metallic luster pigment and metal vapor-deposited resin pigment adsorbed by the friction body 211 were enveloped in the wear debris of the friction body 211 and completely removed from the paper surface. In this way, the friction body 201 cleanly erased the writing of the thermochromic ink composition 161 without staining the paper surface. In particular, the transparent metallic luster pigment and metal vapor-deposited resin pigment remaining on black paper emit a shine depending on the viewing angle, which is a problem as it is visually recognizable. This problem is solved by using friction material 201. [Explanation of Symbols]

[0157] 1 shaft cylinder 2 mounting holes 21 Introvert process 21a Guide surface 21b Minimum inner diameter 3 Friction body 31 Internal bore 32 Friction part 4. Large diameter section 41 Annular surface 5. Mounting section (small diameter section) 51 External process 51a Guide surface 51b Maximum outer diameter 52 Bulge 53 Lower extension 6. Ring space 7 Core 71 Ventilation section 72 Upper core 73 Lower core section A. Axial length from the upper end of the mounting part to the upper end of the outward projection B. Axial length from the upper end of the mounting hole to the lower end of the inward projection C. Clearance between the inward-facing and outward-facing processes.

Claims

[Claim 1] A thermochromic writing instrument comprising a thermochromic ink and a friction element for causing the ink to change color due to frictional heat, The aforementioned thermochromic ink contains a metallic luster pigment. The material of the friction body has a product value (Tb × Eb) of tensile strength Tb at break and elongation Eb at break, measured in accordance with the Japanese Industrial Standard JIS K 6251, which is between 5000 and 18000. The material of the friction body is a thermochromic writing instrument in which the Shore A hardness value immediately after the start of indentation contact, measured in accordance with the Japanese Industrial Standard JIS K 7215, is in the range of 60 to 85, and the value (ΔHS) of Shore A hardness as defined by the following formula is 0 or more and less than 5. ΔHS = (Shore A hardness value immediately after indenter contact begins) - (Shore A hardness value 15 seconds after indenter contact begins)

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