Baked pencil lead

Abstract

To provide fired pencil lead that can maintain writing line density while improving bending strength, and offers a smooth writing feel, and a method for producing the same.SOLUTION: Fired pencil lead is prepared by sintering a mixture containing a body material, an organic binder, organic modified silicone, and silica oxide nanoparticles.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a fired pencil lead containing at least a filler and an organic binder.

Background Art

[0002] Conventionally, as fired pencil leads, fillers such as graphite and boron nitride, organic binders such as vinyl chloride resin, vinylidene chloride resin, vinyl acetate resin, chlorinated polyethylene, polyvinyl alcohol, acrylamide resin, chlorinated paraffin resin, phenol resin, furan resin, urea resin, and butyl rubber, clay binders such as bentonite and kaolin clay, plasticizers such as phthalic esters, solvents such as methyl ethyl ketone and water, stabilizers such as stearates, lubricants such as stearic acid, and fillers such as carbon black are mixed, dispersed, kneaded, extruded into a thin wire shape, and heat-treated to a firing temperature. After that, a fired pencil lead impregnated with oily substances or waxes such as silicone oil, liquid paraffin, spindle oil, squalane, and α-olefin oligomers is known.

[0003] Generally, there is an inverse correlation between the bending strength of a fired pencil lead and the density of the writing line. When trying to improve the bending strength, the fired pencil lead becomes difficult to wear, and as a result, the density of the writing line decreases. Conversely, if the fired pencil lead is made easy to wear in order to improve the density of the writing line, the bending strength decreases. Therefore, various inventions for improving this inverse correlation have been disclosed. As an example of a material for improving the characteristics of a fired pencil lead, as shown in the following patent documents, by adding a silicon compound to a filler and an organic binder and heat-treating at a firing temperature, a fired pencil lead and a manufacturing method thereof that exhibit effects such as improvement in bending strength while maintaining the density of the writing line and suppression of appearance defects are disclosed. In addition, as a performance of a fired pencil lead, a technique for impregnating a lubricating component into the pores of the core body after heat treatment has been disclosed in order to obtain a smooth writing feeling.

[0004] Patent Document 1 discloses a method for producing a fired pencil lead with high bending strength by using silicon oxide and / or silicon organic compounds as compounding materials for the fired pencil lead and firing them under specific temperatures and atmospheres. Furthermore, Patent Document 2 discloses a method for manufacturing a fired pencil lead that does not produce defects in appearance and has an excellent balance between bending strength and the density of the writing line, by using hydrophobic amorphous silica as a compounding material for the fired pencil lead. Patent Document 3 discloses a method for manufacturing a fired pencil lead that, by using silsesquioxane as a compounding material for the fired pencil lead, does not cause any defects in appearance in the fired pencil lead, and exhibits higher bending strength and darker writing than that of Patent Document 2. Patent Document 4 discloses a method for manufacturing a fired pencil lead that exhibits a smooth writing feel because carbon nanoparticles or silicon oxide ceramic nanoparticles dispersed in an oily substance impregnated into the lead body after heat treatment, rather than being used as a compounding material for the fired pencil lead, act as bearings during writing. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 63-35672 [Patent Document 2] Japanese Patent Publication No. 2004-175900 [Patent Document 3] Japanese Patent Publication No. 2011-68796 [Patent Document 4] International Publication No. WO2010 / 123070 [Overview of the project] [Problems that the invention aims to solve]

[0006] Generally, when the bending strength of a fired pencil lead is improved, it results in a scratchy writing feel. This is because the bonding of the binder material with resin carbides is one of the factors that improves bending strength. These resin carbides are formed by heat-treating an organic binder at firing temperatures, but because the process of expansion and contraction occurs during heat treatment, the expansion and condensation due to the decomposition and volatilization of organic matter occur irregularly, causing the entire lead to complex volume contraction. As a result, the surface of the resin carbides becomes uneven, and the bonding between the uneven resin carbides and the binder material becomes dense and aggregated in some areas, and uneven in others with large voids. Therefore, these uneven and aggregated areas of the resin carbides cause scratching during writing, which impairs the smooth writing feel. While inventions have been disclosed that achieve both bending strength and line density by adding silicon compounds, the effects of conventionally known silicon compounds were to obtain the effect of the silicon compound itself as a reinforcing agent for bending strength, and not to act on the resin carbide. Therefore, the problem that the writing quality deteriorates when bending strength and line density are improved remained unresolved.

[0007] The silicon oxide shown in Patent Document 1 has no affinity for organic binders and plays a role in binding the binder materials together independently of the resin carbide. However, although heat treatment at firing temperatures improves the strength of the core, the dispersion is not uniform, and the bonding area with the binder material is coarse and dense, resulting in insufficient improvement in bending strength and a rough writing feel. Patent documents 2 and 3 disclose that by using silicon compounds with surface treatments or molecular structures that can improve dispersion uniformity with respect to organic binders, the density of the writing line can be maintained and the bending strength improved. However, as the bending strength improved, the writing feel deteriorated, and it was not possible to obtain a smooth writing experience without snagging. In the method of impregnating the pencil lead with an oily substance containing dispersed nanoparticles, as described in Patent Document 4, the nanoparticles block the openings of the pores effective for impregnation that exist in the core after heat treatment, reducing the number of pores effective for impregnation. As a result, the amount of impregnated oily substance retained in the fired pencil lead decreases, preventing it from fully exerting its lubricating effect and impairing the smooth writing experience.

[0008] In view of the above circumstances, at least one embodiment of the present invention aims to provide a fired pencil lead that can achieve both improved bending strength and maintenance of line density, as well as a smooth writing feel. [Means for solving the problem]

[0009] A fired pencil lead according to at least one embodiment of the present invention is obtained by firing a mixture containing a filler material, an organic binder, an organically modified silicone, and silicon oxide nanoparticles. In some embodiments, the organically modified silicone is polyglycerin-modified silicone. In some embodiments, the silicon oxide nanoparticles are hydrophobic silica nanoparticles.

[0010] A method for manufacturing a fired pencil lead according to at least one embodiment of the present invention is: At a minimum, the process involves mixing a binder, an organic binder, an organically modified silicone, and silicon oxide nanoparticles to obtain a mixture. The steps include: molding the mixture to obtain a molded body, The steps include firing the molded body to obtain a fired pencil lead, It is equipped with. [Effects of the Invention]

[0011] According to at least one embodiment of the present invention, a fired pencil lead is provided that can achieve both improved bending strength and maintenance of line density, while also having a smooth writing feel. [Modes for carrying out the invention]

[0012] Several embodiments of the present invention will be described below. However, the embodiments described below are not intended to limit the scope of the present invention, but are merely illustrative examples.

[0013] In some embodiments, the fired pencil lead is obtained by firing a mixture containing a filler material, an organic binder, an organically modified silicone, and silicon oxide nanoparticles. In some embodiments, the fired pencil lead is obtained by kneading a mixture containing a filler material, an organic binder, an organically modified silicone, and silicon oxide nanoparticles, extruding the resulting molded body, and then heat-treating it to a firing temperature.

[0014] A method for manufacturing a fired pencil lead according to several embodiments includes the steps of: mixing a binder, an organic binder, an organically modified silicone, and silicon oxide nanoparticles to obtain a mixture; molding the mixture to obtain a molded body; and firing the molded body to obtain a fired pencil lead. It is equipped with.

[0015] Organically modified silicones are compounds in which some of the methyl groups of dimethylpolysiloxane are replaced with organic functional groups, and these organic functional groups exhibit affinity for organic binders. Furthermore, silicon oxide nanoparticles exhibit affinity for the siloxane bonds of the organically modified silicone. Therefore, during mixing or kneading, at the interface between the organic binder and the silicon oxide nanoparticles, the organically modified silicone adsorbs onto the organic binder, and the siloxane bonds adsorb onto the silicon oxide nanoparticles, forming an adsorption layer. Subsequently, through heat treatment (sintering), the siloxane bonds in the organically modified silicone adsorption layer are thought to become a resin carbide coating, consisting of compounds such as silicon oxides and carbides. The resin carbide with the coating has higher strength compared to the case without the coating, thus improving flexural strength. Also, because compounds such as silicon oxides and carbides have low thermal expansion coefficients, they can suppress the formation of surface irregularities due to the expansion and contraction of the organic binder, resulting in a smoother surface. Silicon oxide nanoparticles form interconnected pores that gently release decomposition products generated during heat treatment (firing) of the organic binder, allowing thermal decomposition to proceed slowly and further suppressing the formation of uneven surfaces on the organic binder. As a result, a smooth writing feel is obtained, and the adhesion area of ​​the resin carbide to the binder material is smaller compared to when no coating is formed, thus not hindering wear during writing. When erasing the writing line with an eraser, the contact area between the wear powder containing the smooth surface resin carbide and the eraser is larger than the contact area between the wear powder containing the uneven surface resin carbide and the eraser, resulting in good erasability even for dark and clear writing. Therefore, it is possible to obtain a fired pencil lead that achieves both improved bending strength and maintenance of writing line density, and reduces friction during writing, resulting in a smooth writing feel with reduced snagging.

[0016] As classifications of organically modified silicones, there may be mentioned, but not limited to, polyglycerin-modified silicones, polyether-modified silicones, amino-modified silicones, amino-polyether-modified silicones, diol-modified silicones, carbinol-modified silicones, carboxyl-modified silicones, higher fatty acid ester-modified silicones, higher fatty acid amide-modified silicones, acrylic-modified silicones, long-chain alkyl-modified silicones, phenyl-modified silicones, etc.

[0017] Examples of polyglycerin-modified silicones include KF-6100, KF-6104, KF-6105, KF-6106, and KF-6115 manufactured by Shin-Etsu Chemical Co., Ltd.

[0018] Examples of polyether-modified silicones include KF-6017, KF-6028, KF-6038, KF-6048, KF-6123 manufactured by Shin-Etsu Chemical Co., Ltd., and FZ-2203, FZ-2222 manufactured by Dow Corning Toray Co., Ltd.

[0019] Examples of amino-modified silicones include KF-8004, KF-8005S, KF-8015, and KF-867S manufactured by Shin-Etsu Chemical Co., Ltd.

[0020] Examples of amino-polyether-modified silicones include X-22-3939A manufactured by Shin-Etsu Chemical Co., Ltd., and DOWSIL SILSTYLE 104, DOWSIL SILSTYLE 201 manufactured by Dow Corning Toray Co., Ltd.

[0021] Examples of diol-modified silicones include X-22-176DX, X-22-176F, and X-22-176GX-A manufactured by Shin-Etsu Chemical Co., Ltd.

[0022] Examples of carbinol-modified silicones include X-22-4039, X-22-4015, KF-6000, KF-6001, KF-6002, KF-6003, X-22-170BX, and X-22-170DX manufactured by Shin-Etsu Chemical Co., Ltd.

[0023] Examples of carboxyl-modified silicones include X-22-3701E, X-22-162C, and X-22-3710, all manufactured by Shin-Etsu Chemical Co., Ltd.

[0024] An example of a high-grade fatty acid ester-modified silicone is X-22-715 manufactured by Shin-Etsu Chemical Co., Ltd.

[0025] An example of a high-grade fatty acid amide-modified silicone is KF-3935 manufactured by Shin-Etsu Chemical Co., Ltd.

[0026] An example of acrylic-modified silicone is X-22-2445 manufactured by Shin-Etsu Chemical Co., Ltd.

[0027] Examples of long-chain alkyl-modified silicones include KF-412, KF-413, KF-414, KF-415, KF-4003, KF-4701, KF-4917, KF-7235B, and X-22-7322, all manufactured by Shin-Etsu Chemical Co., Ltd.

[0028] Examples of phenyl-modified silicones include KF-50-100CS, KF-50-300CS, KF-50-1,000CS, KF-50-3,000CS, KF-53, KF-54, and X-21-3265, all manufactured by Shin-Etsu Chemical Co., Ltd.

[0029] The content of organically modified silicone is preferably 0.5% by weight or more and 3.0% by weight or less relative to the content of the organic binder. This content is sufficient to coat the organic binder, and the thickness of the coating is appropriate for the baked pencil lead to wear easily during writing. It also suppresses the formation of uneven surfaces on the resin carbide, resulting in a baked pencil lead that exhibits a smooth writing feel. Furthermore, a content of 0.8% by weight or more and 2.0% by weight or less is particularly preferable.

[0030] Among these, polyglycerin-modified silicones having polyglycerin groups as organic functional groups, or polyether-modified silicones having polyether groups as organic functional groups, are preferred because they have high affinity for organic binders and excellent adsorption properties, thus effectively smoothing the organic binder during heat treatment (sintering). Furthermore, in addition to the above effects, polyglycerin-modified silicones are particularly preferred because, due to the high hydrogen bonding properties of the hydroxyl groups, which are part of the polyglycerin group, and the bulkiness of their molecular structure, silicon oxide nanoparticles can be uniformly dispersed.

[0031] Silicon oxide nanoparticles are particles composed of silicon oxides, with an average particle diameter of 1 nm or more and less than 1 μm when observed using an electron microscope. Examples include silicon oxide nanoparticles composed of silica (silicon dioxide) (hereinafter referred to as silica nanoparticles) and silicon oxide nanoparticles composed of silsesquioxane.

[0032] Silica is classified into synthetic silica and natural silica. Synthetic silica is further classified into dry silica and wet silica based on its manufacturing method. Wet silica is further subdivided into precipitated silica, silica gel, colloidal silica, etc. Furthermore, silica nanoparticles are classified into hydrophilic silica nanoparticles (untreated particle surface) and hydrophobic silica nanoparticles (hydrophobic silica nanoparticles) (hydrophobic particle surface).

[0033] Hydrophilic silica nanoparticles synthesized by the dry method include Aerosil OX50 (average particle size 40 nm), Aerosil 50 (average particle size 30 nm), Aerosil 90G (average particle size 20 nm), Aerosil 130 (average particle size 16 nm), Aerosil 150 (average particle size 14 nm), Aerosil 200 (average particle size 12 nm), and Aerosil 300 (average particle size 7 nm), all manufactured by Nippon Aerosil Co., Ltd. Examples include Aerosil 380 (average particle size 7 nm), and Rheoroseal QS-09 (average particle size 22 nm), Rheoroseal QS-10 (average particle size 15 nm), Rheoroseal QS-102 (average particle size 12 nm), Rheoroseal QS-20 (average particle size 12 nm), Rheoroseal QS-30 (average particle size 7 nm), and Rheoroseal QS-40 (average particle size 7 nm) from Tokuyama Corporation.

[0034] Hydrophobic silica nanoparticles synthesized by the dry method include Aerosil R972 (average particle size 16nm), Aerosil R972V (average particle size 16nm), Aerosil R972CF (average particle size 16nm), Aerosil R974 (average particle size 12nm), Aerosil R202 (average particle size 14nm), Aerosil R805 (average particle size 12nm), Aerosil R812 (average particle size 7nm), and Aerosil R812S (average particle size 7nm) from Nippon Aerosil Co., Ltd., and Rheoroseal MT-10 (average particle size 15nm), Rheoroseal DM-10 (average particle size 15nm), and Rheoroseal DM-2 from Tokuyama Corporation. Examples include 0S (average particle size 12nm), Rheoroseal DM-30 (average particle size 7nm), Rheoroseal DM-30S (average particle size 7nm), Rheoroseal KS-20SC (average particle size 12nm), Rheoroseal HG-09 (average particle size 22nm), Rheoroseal HM-20L (average particle size 12nm), Rheoroseal HM-30S (average particle size 7nm), Rheoroseal ZD-30ST (average particle size 7nm), Rheoroseal PM-09 (average particle size 22nm), Rheoroseal PM-20 (average particle size 12nm), Rheoroseal X-20 (average particle size 12nm), and Rheoroseal X-30 (average particle size 7nm).

[0035] Examples of hydrophobic silica nanoparticles synthesized by the wet process include QSG-10 (average particle size 15 nm), QSG-30 (average particle size 30 nm), QSG-80 (average particle size 80 nm), QSG-90 (average particle size 90 nm), QSG-100 (average particle size 110 nm), and QSG-170 (average particle size 170 nm), all manufactured by Shin-Etsu Chemical Co., Ltd.

[0036] Among silica nanoparticles, silica synthesized by the dry method is non-porous, making it suitable for releasing decomposition products generated by the organic binder during heat treatment (firing) to the outside of the core. This suppresses the formation of uneven surfaces on the resin carbide during heat treatment (firing), resulting in a smoother writing experience, which is preferable. Furthermore, it is preferable to use hydrophobic silica nanoparticles whose surfaces have been hydrophobicized. Hydrophobic silica nanoparticles have weak interactions between silica nanoparticles, making uniform dispersion in the mixture easy. This suppresses the formation of uneven surfaces on the resin carbide during heat treatment (firing), resulting in a smoother writing experience, which is particularly preferable.

[0037] Examples of silicon oxide nanoparticles composed of silsesquioxane include SP-1120 water-dispersible type (average particle size 20 nm, organic functional group of constituent units is a methyl group), SP-6120 water-dispersible type (average particle size 20 nm, organic functional group of constituent units is a vinyl group), SP-1120 organic solvent-dispersible type (average particle size 20 nm, organic functional group of constituent units is a methyl group), and SP-6120 organic solvent-dispersible type (average particle size 20 nm, organic functional group of constituent units is a vinyl group), all manufactured by Konishi Chemical Industry Co., Ltd.

[0038] The silicon oxide nanoparticle content is preferably 1.0% to 7.0% by weight relative to the organic binder content. When it is 1.0% to 7.0% by weight, sufficient pores for releasing decomposition products are formed in relation to the organic binder and it does not hinder adhesion with graphite. Furthermore, it is particularly preferable when it is 2.0% to 6.0% by weight. When the average particle size of the silicon oxide nanoparticles is 3 nm to 40 nm, decomposition products generated by the organic binder during heat treatment (firing) can be gently released, and the formation of uneven shapes on the resin carbide surface can be suppressed, resulting in a fired pencil lead that exhibits a smooth writing feel. Furthermore, it is particularly preferable when it is 5 nm to 25 nm.

[0039] When the content of organically modified silicone relative to the organic binder is 0.5% by weight or more and 3.0% by weight or less, and the content of silicon oxide nanoparticles relative to the organic binder is 1.0% by weight or more and 7.0% by weight or less, the content of organically modified silicone and silicon oxide nanoparticles are in a mutually suitable ratio, and the content of organically modified silicone is sufficient for uniform adsorption to the silicon oxide nanoparticles, resulting in a fired pencil lead that suppresses the uneven shape of the resin carbide and exhibits a smooth writing feel. Furthermore, it is particularly preferable when the content of organically modified silicone relative to the organic binder is 0.8% by weight or more and 2.0% by weight or less, and the content of silicon oxide nanoparticles relative to the organic binder is 2.0% by weight or more and 6.0% by weight or less.

[0040] Examples of filler materials include graphite, boron nitride, mica, and talc. Both natural and synthetic graphite can be used, but it is preferable to use natural graphite with well-developed crystals and good cleavage. Even more preferable is the use of flaky graphite among natural graphites. Flaky graphite has well-developed crystals, and these developed crystals are stacked, resulting in a high aspect ratio and a smooth surface. Therefore, when forming the lead into a fine wire shape by extrusion molding, flaky graphite can be oriented in the extrusion direction, improving the bending strength of the lead. Furthermore, its excellent cleavage allows for a smooth writing feel and high line density. Commercially available flaky graphite products include the BF series, CPB series, and SC series from Chuetsu Graphite Industry Co., Ltd., and the FT series and MF series from Fuji Graphite Industry Co., Ltd. As for boron nitride, hexagonal boron nitride (h-BN) is used. A crystal structure has developed in which boron and nitrogen atoms alternately occupy the vertices of a regular hexagon. These crystals are stacked in multiple layers to form a single particle of hexagonal boron nitride (h-BN), and thus, like graphite, hexagonal boron nitride (h-BN) particles have a plate-like shape. Furthermore, the layers are bound together by weak van der Waals forces, making hexagonal boron nitride (h-BN) highly lubricating. Due to these properties, hexagonal boron nitride (h-BN) is suitable as a material for calcined pencil lead, just like graphite, and calcined pencil lead obtained using hexagonal boron nitride (h-BN) has high bending strength and dense writing lines. Commercially available products include Denka Boron Nitride SGP, Denka Boron Nitride GP, Denka Boron Nitride HGP, and Denka Boron Nitride SP-2 from Denka Co., Ltd., and SHP-3, SHP-5, SHP-7, HP-1, HP-2, HP-4W, HP-6, HP-60, HP-P1, and FS-1 from Mizushima Iron Alloy Co., Ltd.

[0041] Examples of organic binders include synthetic resins such as polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, chlorinated polyethylene, chlorinated paraffin, furan resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, urea resin, melamine resin, polyester, styrene-butadiene copolymer, polyvinyl acetate, polyacrylamide, and butyl rubber, as well as natural resins such as lignin, cellulose, tragacanth gum, and gum arabic. These organic binders may be used individually or in combination of two or more. Thermoplastic resins such as polyvinyl chloride are particularly preferred because they are highly processable, inexpensive, and have a stable supply. Examples of polyvinyl chloride include the TH series, TU series, TE series, and TG series from Taiyo Vinyl Co., Ltd., the Kanevinyl S series, Kanevinyl KS series, Kanevinyl K series, Kanevinyl M series, and Kanevinyl HM series from Kaneka Corporation, Ryuron Paste from Tosoh Corporation, and the ZEST series from Shin-Daiichi Vinyl Co., Ltd.

[0042] In some embodiments, the fired pencil lead may be obtained by firing a mixture that includes a binder, an organic binder, an organically modified silicone, and silicon oxide nanoparticles, as well as other materials such as a clayey binder and / or various additives.

[0043] Examples of clayey binders include bentonite and kaolin clay. Examples of plasticizers include dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diallyl isophthalate, tricresyl phosphate, and dioctyl adipate. Examples of solvents include ketones such as methyl ethyl ketone and acetone, alcohols such as ethanol, and water. Examples of stabilizers include stearates, organotin compounds, barium-zinc compounds, and calcium-zinc compounds. Examples of lubricants include fatty acids such as stearic acid and behenic acid, and fatty acid amides. Examples of fillers include metals such as iron, aluminum, titanium, and zinc, and their alloys, as well as oxides and nitrides of these metals and alloys, carbon black, and fullerenes. These fillers can be used in various shapes such as spherical, amorphous granules, needle-shaped, fibrous, and plate-shaped as appropriate. One or more types may be used in combination. Among these, plate-like particles are preferred because, during extrusion molding, they are oriented in the extrusion direction and positioned within the core, similar to graphite. Examples include plate-like silica and plate-like alumina. As an example of plate-like silica, amorphous cleavable plate-like silica obtained by expanding vermiculite, followed by acid treatment, washing, drying, crushing, and classification is mentioned. Vermiculite is a mineral mainly composed of hydrated mica, classified as a vermiculite group clay mineral or mica group clay mineral, and is also called vermiculite. The chemical composition of vermiculite varies depending on the source, but typical compositions are as follows. SiO235~45wt% Al2O310~20wt% MgO37~30% by weight Fe2O35~22wt% CaO 0~3wt% Na2O 0~1wt% K2O 0~10wt% Content of heavy metals other than Fe (Pb, Cr, Cd, etc.) is 0.2% by weight or less. Burning raw material (1050℃) 3~25% by weight By treating vermiculite with sulfuric acid, hydrochloric acid, or nitric acid, colored components such as MgO3 and Fe2O3 are removed, resulting in plate-like silica (amorphous cleavable plate-like silica) that retains the layered structure of vermiculite. Since the layers of this plate-like silica (amorphous cleavable plate-like silica) are connected by hydrogen bonds via hydroxyl groups, it can be easily cleaved by applying only a light shear force. Furthermore, the layered structure of the plate-like silica (amorphous cleavable plate-like silica) does not change even after heat treatment up to 1100°C, making it suitable for use in calcined pencil leads. A commercially available example is Silleaf manufactured by Mizusawa Chemical Industries, Ltd. Examples of plate-like alumina include α-Al2O3, γ-Al2O3, and θ-Al2O3. Because the particle surface of plate-like alumina is smooth, it has good interparticle lubrication, which does not impair the density of the writing line or the writing feel. Commercially available products include Ceraph FYA00610, FYA02025, and FYA10030 from Kinsei Matec Co., Ltd., and the Cerasure BMM series from Kawai Lime Industry Co., Ltd.

[0044] In some embodiments of the present invention, fired pencil leads are obtained by firing a mixture containing a binder, an organic binder, an organically modified silicone, and silicon oxide nanoparticles. Here, "fired pencil lead" is obtained through a heat treatment called "firing." Generally, when a composition containing organic substances (organic binders) such as synthetic resins or natural resins is heat-treated to a firing temperature, the resin molecules become intricately intertwined with the binder, such as graphite, and the decomposition and condensation of the organic substances occur irregularly, causing a complex volume contraction of the entire lead. As a result, the skeletal structure of the lead after heat treatment becomes extremely complex in its fine details, and the degree and size of bonding of individual components after heat treatment vary. Therefore, it is considered that there are circumstances in which it is impossible or utterly impractical to directly identify the object by its structure or properties, requiring systematic measurements and analyses that are predominantly related to the above effects, and thus impossible or utterly impractical to perform experiments.

[0045] Conventional known oils can be used to impregnate the pores of the core after heat treatment. Examples include, but are not limited to, oily substances such as liquid paraffin, α-olefin oligomers, squalane, spindle oil, silicone oil, fatty acid esters, and castor oil, as well as waxes such as paraffin wax, microcrystalline wax, and carnauba wax. [Examples]

[0046] The present invention will be described below based on examples, but the present invention is not limited to these examples. The average particle diameter was calculated as the arithmetic mean of the individual diameters of 100 arbitrary particles observed using a scanning electron microscope JSM-IT800 manufactured by JEOL Ltd.

[0047] <Example 1> KF-6106 (Polyglycerin-modified silicone) 0.45 parts by weight Aerosil R972 (hydrophobic silica nanoparticles synthesized by dry process, average particle size 16 nm) 1.2 parts by weight Scale-like graphite (body material: average volume diameter 15 μm) 45 parts by weight Polyvinyl chloride (organic binder) 30 parts by weight Dioctyl phthalate (plasticizer) 20 parts by weight Methyl ethyl ketone (solvent) 15 parts by weight Stearate (stabilizer) 1.5 parts by weight Stearic acid (lubricant) 0.5 parts by weight The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight. The above-mentioned materials were dispersed and mixed using a Henschel mixer, then kneaded using a three-roll mill. After that, they were extruded into a fine wire shape using a single-screw extruder, and then heated in air from room temperature to 350°C over approximately 10 hours, and held at 350°C for approximately 1 hour. Furthermore, they were subjected to a firing process in a sealed container to a maximum temperature of 1100°C to obtain a heat-treated core with a nominal diameter of 0.5. This heat-treated core was then immersed in liquid paraffin heated to 100°C for 10 hours, and excess components on the surface were removed to obtain a fired pencil lead.

[0048] <Example 2> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 added was changed from 0.45 parts by weight to 0.21 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.7% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0049] <Example 3> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 added was changed from 0.45 parts by weight to 0.27 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.9% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0050] <Example 4> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 added was changed from 0.45 parts by weight to 0.54 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.8% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0051] <Example 5> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 added was changed from 0.45 parts by weight to 0.75 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 2.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0052] <Example 6> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.45 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is also 1.5% by weight.

[0053] <Example 7> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.66 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 2.2% by weight.

[0054] <Example 8> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of Aerosil R972 was changed from 1.2 parts by weight to 1.65 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 5.5% by weight.

[0055] <Example 9> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of Aerosil R972 was changed from 1.2 parts by weight to 1.95 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 6.5% by weight.

[0056] <Example 10> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 was changed from 0.45 parts by weight to 0.21 parts by weight, and the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.45 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.7% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 1.5% by weight.

[0057] <Example 11> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 added was changed from 0.45 parts by weight to 0.12 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.4% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0058] <Example 12> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 added was changed from 0.45 parts by weight to 0.96 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 3.2% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0059] <Example 13> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.24 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 0.8% by weight.

[0060] <Example 14> A fired pencil lead was obtained in the same manner as in Example 1, except that the amount of Aerosil R972 was changed from 1.2 parts by weight to 2.16 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 7.2% by weight.

[0061] <Example 15> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 was changed from 0.45 parts by weight to 0.12 parts by weight, and the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.45 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.4% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 1.5% by weight.

[0062] <Example 16> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 was changed from 0.45 parts by weight to 0.21 parts by weight, and the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.24 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.7% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 0.8% by weight.

[0063] <Example 17> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the amount of KF-6106 was changed from 0.45 parts by weight to 0.12 parts by weight, and the amount of Aerosil R972 was changed from 1.2 parts by weight to 0.24 parts by weight. The polyglycerin-modified silicone content relative to the organic binder is 0.4% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 0.8% by weight.

[0064] <Example 18> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-6115 (polyglycerin-modified silicone). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0065] <Example 19> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-6104 (polyglycerin-modified silicone). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0066] <Example 20> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil R202 (hydrophobic silica nanoparticles synthesized by the dry method, with an average particle size of 14 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0067] <Example 21> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil R812 (hydrophobic silica nanoparticles synthesized by the dry method, with an average particle size of 7 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0068] <Example 22> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with QSG-10 (hydrophobic silica nanoparticles synthesized by a wet process, with an average particle size of 15 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0069] <Example 23> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with QSG-30 (hydrophobic silica nanoparticles synthesized by a wet process, with an average particle size of 30 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0070] <Example 24> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil 300 (hydrophilic silica nanoparticles synthesized by a dry method, with an average particle size of 7 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophilic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0071] <Example 25> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil 130 (hydrophilic silica nanoparticles synthesized by a dry method, with an average particle size of 16 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophilic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0072] <Example 26> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil 90G (hydrophilic silica nanoparticles synthesized by a dry method, with an average particle size of 20 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophilic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0073] <Example 27> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil 50 (hydrophilic silica nanoparticles synthesized by a dry method, with an average particle size of 30 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophilic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0074] <Example 28> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Aerosil OX50 (hydrophilic silica nanoparticles synthesized by the dry method, with an average particle size of 40 nm). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophilic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0075] <Example 29> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-6017 (polyether-modified silicone). The polyether-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0076] <Example 30> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-6028 (polyether-modified silicone). The polyether-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0077] <Example 31> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with FZ-2203 (polyether-modified silicone). The polyether-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0078] <Example 32> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-3939A (amino-polyether modified silicone). The content of amino-polyether modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0079] <Example 33> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-8004 (amino-modified silicone). The content of amino-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0080] <Example 34> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-176F (diol-modified silicone). The content of diol-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0081] <Example 35> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-4015 (carbinol-modified silicone). The content of carbinol-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0082] <Example 36> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-3701E (carboxyl-modified silicone). The carboxyl-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica nanoparticle content relative to the organic binder is 4.0% by weight.

[0083] <Example 37> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-715 (higher fatty acid ester modified silicone). The content of higher fatty acid ester-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0084] <Example 38> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-3935 (higher fatty acid amide modified silicone). The content of higher fatty acid amide-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0085] <Example 39> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-2445 (acrylic-modified silicone). The content of acrylic-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0086] <Example 40> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with X-22-415 (long-chain alkyl-modified silicone). The content of long-chain alkyl-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0087] <Example 41> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-50-1,000CS (phenyl-modified silicone). The content of phenyl-modified silicone relative to the organic binder is 1.5% by weight, and the content of hydrophobic silica nanoparticles relative to the organic binder is 4.0% by weight.

[0088] <Example 42> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with SP-1120 organic solvent dispersion type (silicon oxide nanoparticles composed of silsesquioxane, average particle size 20 nm). The SP-1120 organic solvent dispersion type was left to stand at room temperature, and the organic solvent was dried before being used as a compounding material. The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the silicon oxide nanoparticles composed of silsesquioxane content relative to the organic binder is 4.0% by weight.

[0089] <Comparative Example 1> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-96-1,000CS (dimethylpolysiloxane) and Aerosil R972 was omitted. The content of dimethylpolysiloxane relative to the organic binder is 1.5% by weight, and the content of silicon oxide nanoparticles relative to the organic binder is 0% by weight.

[0090] <Comparative Example 2> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was omitted. The organic binder contains 0% by weight of organic-modified silicone, and the organic binder contains 4.0% by weight of hydrophobic silica nanoparticles.

[0091] <Comparative Example 3> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was omitted and Aerosil R972 was replaced with SP-1120 organic solvent dispersion type (silicon oxide nanoparticles composed of silsesquioxane, average particle size 20 nm). The SP-1120 organic solvent dispersion type was left to stand at room temperature, and the organic solvent was dried before being used as a compounding material. The organic binder contains 0% by weight of organic-modified silicone, and the organic binder contains 4.0% by weight of silicon oxide nanoparticles composed of silsesquioxane.

[0092] <Comparative Example 4> A fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-96-1,000CS (dimethylpolysiloxane). The organic binder contains 1.5% by weight of dimethylpolysiloxane and 4.0% by weight of hydrophobic silica nanoparticles.

[0093] <Comparative Example 5> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-96-1,000CS (dimethylpolysiloxane) and Aerosil R972 was replaced with Aerosil R202 (hydrophobic silica nanoparticles synthesized by the dry method, average particle size 14 nm). The organic binder contains 1.5% by weight of dimethylpolysiloxane and 4.0% by weight of hydrophobic silica nanoparticles.

[0094] <Comparative Example 6> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6106 was replaced with KF-96-1,000CS (dimethylpolysiloxane) and Aerosil R972 was replaced with SP-1120 organic solvent dispersion type (silicon oxide nanoparticles composed of silsesquioxane, average particle size 20 nm). The SP-1120 organic solvent dispersion type was left to stand at room temperature, and the organic solvent was dried before being used as a compounding material. The organic binder contains 1.5% by weight of dimethylpolysiloxane, and the organic binder contains 4.0% by weight of silicon oxide nanoparticles composed of silsesquioxane.

[0095] <Comparative Example 7> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with TMS-05DCA (hydrophobic silica nanoparticles synthesized by a wet process, average particle size 5 μm, manufactured by Teika Co., Ltd.). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the hydrophobic silica particle content relative to the organic binder is 4.0% by weight.

[0096] <Comparative Example 8> In Example 1, a calcined pencil lead was obtained in the same manner as in Example 1, except that Aerosil R972 was replaced with Tospearl 120A (silicon oxide particles composed of silsesquioxane whose constituent organic functional group is a methyl group, with an average particle size of 2 μm, manufactured by Momentive Performance Materials Japan LLC). The polyglycerin-modified silicone content relative to the organic binder is 1.5% by weight, and the silicon oxide particles composed of silsesquioxane content relative to the organic binder is 4.0% by weight.

[0097] <Comparative Example 9> In Example 1, a compound without KF-6106 (polyglycerin-modified silicone) and Aerosil R972 (hydrophobic silica nanoparticles) was kneaded, extruded, and then heat-treated to the firing temperature to obtain a heat-treated core. Dimethyl silicone oil KF96-30CS (kinematic viscosity at 25°C: 30 mm) was then used to disperse diamond nanoparticles (average particle size 10 nm, manufactured by Dia Material Co., Ltd.). 2 A fired pencil lead was obtained by immersing a material (manufactured by Shin-Etsu Chemical Co., Ltd., with a refractive index of 1.401, at a temperature of 100°C) for 10 hours, followed by removal of excess components from the surface.

[0098] The bending strength, line density, and writing resistance values ​​of the fired pencil leads obtained in Examples 1 to 42 and Comparative Examples 1 to 9 were measured using the following methods.

[0099] (Test method for bending strength) The bending strength was measured in accordance with JIS S 6005.

[0100] (Test method for the density of writing lines) The density of the writing lines was measured in accordance with JIS S 6005.

[0101] (Test method for writing resistance) The writing resistance was measured using a Tribogear Type:40 friction and wear tester manufactured by Shinto Kagaku Co., Ltd. The measurement environment was set to a temperature of 23°C ± 2°C and a humidity of 65% ± 5%. A Pentel P205 mechanical pencil was used and fixed to the friction and wear tester using a dedicated writing instrument holder. A stainless steel plate underlay and test paper specified in JIS S 6039 were fixed on the measurement stage, and the frictional force was measured when writing on a straight line with the mechanical pencil. The test paper was pre-treated by leaving it in a constant temperature and humidity chamber at 23°C and 65% humidity for at least 24 hours. The apparatus conditions were: writing angle: 75 degrees, vertical load: 200g, movement speed: 1cm / sec, sampling speed: 1KHz, and measurement time: 10 seconds. During a 10-second measurement period, the average frictional force from 1.5 seconds to 9.5 seconds was defined as the kinetic friction force. The writing resistance value (kinetic friction coefficient) was calculated by dividing the kinetic friction force by the vertical load. The writing resistance value is automatically calculated using the dedicated software Tribosoft6 included with the device.

[0102] The results are shown in Tables 1 and 2. As is clear from Tables 1 and 2, the fired pencil leads of Examples 1 to 42 have the same density of writing lines as the fired pencil leads of Comparative Examples 1 to 9, but with improved bending strength and a smoother writing feel.

[0103] [Table 1]

[0104] [Table 2]

[0105] Examples 1-42 incorporate organically modified silicone and silicon oxide nanoparticles, resulting in low writing resistance and a smooth, snag-free writing experience, while also exhibiting high line density and improved bending strength. Among these, Examples 1-32, which incorporate polyglycerin-modified silicone or polyether-modified silicone, yield a particularly smooth-writing fired pencil lead.

[0106] Examples 1 to 10 yield baked pencil leads that exhibit a smooth writing feel because the polyglycerin-modified silicone content relative to the organic binder is 0.5% to 3.0% by weight and the hydrophobic silica nanoparticle content relative to the organic binder is 1.0% to 7.0% by weight. Among these, Examples 1, 3, 4, 7, and 8 yield baked pencil leads that exhibit a particularly smooth writing feel because the polyglycerin-modified silicone content relative to the organic binder is 0.8% to 2.0% by weight and the hydrophobic silica nanoparticle content relative to the organic binder is 2.0% to 6.0% by weight.

[0107] In Comparative Example 1, dimethylpolysiloxane in which the methyl groups are not substituted with organic functional groups is added, and silicon oxide nanoparticles are not added. As a result, the bending strength is improved, but the writing resistance is high, resulting in a rough writing feel with a lot of scratching.

[0108] In Comparative Example 2, hydrophobic silica nanoparticles were added instead of organically modified silicone, which improved bending strength, but resulted in high writing resistance and a rough writing feel.

[0109] In Comparative Example 3, instead of adding organically modified silicone, silicon oxide nanoparticles composed of silsesquioxane were added. While this improved bending strength, it resulted in high writing resistance and a rough, scratchy writing experience.

[0110] In comparative examples 4-6, dimethylpolysiloxane in which the methyl groups are not substituted with organic functional groups was added. While this improved bending strength, it resulted in high writing resistance and a rough, scratchy writing experience.

[0111] In comparative examples 7 and 8, silicon oxide particles other than nanoparticles were added, which improved bending strength, but resulted in high writing resistance and a rough writing feel.

[0112] In Comparative Example 9, the pores effective for impregnation present in the fired pencil lead are blocked by nanodiamonds, reducing the number of pores effective for impregnation. As a result, the lubricating properties of the oily substance cannot be fully utilized, and a smooth writing experience is not achieved.

[0113] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0114] In this specification, expressions such as "identical," "equal," and "homogeneous" that describe things being in an equivalent state shall not only describe a state of being strictly equal, but also describe a state in which tolerances or differences exist to the extent that the same function can be obtained. Furthermore, in this specification, the expressions “equipment,” “includes,” or “possess” of a component are not exclusive expressions that exclude the existence of other components.

Claims

1. A fired pencil lead obtained by firing a mixture containing a binder, an organic binder, an organically modified silicone, and silicon oxide nanoparticles.

2. The fired pencil lead according to claim 1, characterized in that the organically modified silicone is a polyglycerin-modified silicone.

3. The fired pencil lead according to claims 1 and 2, characterized in that the silicon oxide nanoparticles are hydrophobic silica nanoparticles.

4. At a minimum, the process involves mixing a binder, an organic binder, an organically modified silicone, and silicon oxide nanoparticles to obtain a mixture. The steps include: molding the mixture to obtain a molded body, The steps include firing the molded body to obtain a fired pencil lead, A method for manufacturing fired pencil lead, comprising the features described above.

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