Fired pencil lead

Abstract

This baked pencil lead is obtained by baking a mixture including an extender, an organic binding material, and a polyether-modified silicone.

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, butyl rubber, clay binders such as bentonite and kaolin clay, plasticizers such as phthalic acid esters, solvents such as methyl ethyl ketone and water, stabilizers such as stearates, lubricants such as stearic acid, fillers such as carbon black, etc. are mixed, dispersed, kneaded, and extruded into a thin wire shape, and then heat-treated to the 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 oligomer 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 a fired pencil lead that is easy to wear is used 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 the filler and the organic binder and heat-treating at the firing temperature, a fired pencil lead and its manufacturing method that exhibit effects such as improvement in bending strength while maintaining the density of the writing line and suppression of appearance defects are disclosed. Also, 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 to obtain a smooth writing feeling.

[0004] Patent Document 1 discloses a method for manufacturing a fired pencil lead with high flexural strength by performing a firing process at a specific temperature and atmosphere using an oxide of silicon and / or an organic compound of silicon as a blending material for the fired pencil lead. Also, Patent Document 2 discloses a method for manufacturing a fired pencil lead with excellent balance between flexural strength and writing line density without causing appearance defects by using hydrophobic amorphous silica as a blending material for the fired pencil lead. Patent Document 3 discloses a method for manufacturing a fired pencil lead that shows a darker writing trace with higher flexural strength than Patent Document 2 without causing appearance defects in the fired pencil lead by using silsesquioxane as a blending material for the fired pencil lead. Patent Document 4 discloses a method for manufacturing a fired pencil lead that exhibits a smooth writing feel by having carbon nanoparticles or silicon oxide ceramic nanoparticles dispersed in an oily substance impregnated into the core body after heat treatment, rather than as a blending material for the fired pencil lead, and these nanoparticles exert a bearing effect during writing.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] Generally, when the bending strength of a fired pencil lead is improved, it results in a snaggy writing feel. This is because the adhesion of the matrix materials by the resin carbide is one of the factors improving the bending strength. The resin carbide is formed by heat-treating an organic binder at the firing temperature. However, since it undergoes the processes of expansion and contraction during heat treatment, expansion and condensation due to the decomposition and volatilization of the organic matter occur irregularly, and the entire core body undergoes complex volume shrinkage. As a result, the surface of the resin carbide becomes uneven, and there are parts where the adhesion between the uneven resin carbide and the matrix material is dense and aggregated, and uneven parts with large voids are generated. Therefore, the unevenness and aggregated parts of this resin carbide cause snags during writing, which is a factor deteriorating the smooth writing feel. Although inventions have been disclosed that achieve both bending strength and the density of the writing line by adding a silicon compound, the effects of the conventionally known silicon compounds are for obtaining the effect as a reinforcing agent for the bending strength of the silicon compound itself and do not act on the resin carbide. Therefore, the problem that the writing feel deteriorates when the bending strength and the density of the writing line are improved has not been solved.

[0007] The silicon oxide and / or the organic compound of silicon shown in Patent Document 1 has no affinity with the organic binder and plays a role of binding the matrix materials independently of the resin carbide. Although the strength of the core body is improved when heat-treated at the firing temperature, it is difficult to achieve uniform dispersion, and the adhesion part with the matrix material is coarse and dense, so the improvement in bending strength is also insufficient, and it has a snaggy writing feel. Patent Documents 2 and 3 disclose that by using a silicon compound having a surface treatment or a molecular structure that can improve the dispersion uniformity with respect to the organic binder, the density of the writing line is maintained and the bending strength is improved. However, as the bending strength is improved, the writing feel deteriorates, and a snag-free smooth writing feel cannot be obtained. In the method of impregnating an oily substance in which nanoparticles are dispersed, as disclosed in Patent Document 4, the pores effective for impregnation existing in the core body after heat treatment are blocked at the openings of the pores by the nanoparticles, and the number of pores effective for impregnation decreases. Therefore, the amount of the impregnated oily substance retained in the fired pencil lead decreases, the effect as a lubricant cannot be fully exhibited, and the smooth writing feeling is impaired.

[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 an improvement in bending strength and a maintenance of the density of the writing line, and has a smooth writing feeling.

Means for Solving the Problems

[0009] A fired pencil lead according to at least one embodiment of the present invention is obtained by firing a mixture containing a filler, an organic binder, and a polyether-modified silicone. In some embodiments, the fired pencil lead is obtained by at least blending a filler, an organic binder, and a polyether-modified silicone, kneading, extrusion molding, and then heat-treating to the firing temperature. In some embodiments, the content of the polyether-modified silicone in the mixture is 0.5% by weight or more and 3% by weight or less with respect to the content of the organic binder in the mixture. In some embodiments, the polyether-modified silicone is a polyether-modified silicone having a molecular structure with a branched silicone chain as the main chain. In some embodiments, the kinematic viscosity of the polyether-modified silicone at 25°C is 100 mm 2 / s or more and 10,000 mm 2 / s or less.

[0010] A method for manufacturing a fired pencil lead according to at least one embodiment of the present invention includes at least a step of mixing at least a filler, an organic binder, and a polyether-modified silicone to obtain a mixture, a step of molding the mixture to obtain a molded body, a step of firing the molded body to obtain a fired pencil lead, and comprises.

Effects of the Invention

[0011] According to at least one embodiment of the present invention, there is provided a fired pencil lead that can achieve both an improvement in bending strength and a maintenance of the density of writing lines, and has a smooth writing feel.

Mode for Carrying Out the Invention

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

[0013] The fired pencil lead according to some embodiments is obtained by firing a mixture containing a extender, an organic binder, and a polyether-modified silicone. In some embodiments, the fired pencil lead is obtained by kneading a mixture containing a extender, an organic binder, and a polyether-modified silicone, extruding the kneaded mixture to obtain a formed body, and heat-treating the formed body to a firing temperature.

[0014] The manufacturing method of the fired pencil lead according to some embodiments includes at least the steps of mixing at least a extender, an organic binder, and a polyether-modified silicone to obtain a mixture, forming the mixture to obtain a formed body, and firing the formed body to obtain a fired pencil lead. comprises.

[0015] Polyether-modified silicone is a compound in which some of the methyl groups of dimethylpolysiloxane are substituted with at least polyoxyalkylene groups. Since the polyoxyalkylene groups show an affinity for organic binders, an adsorption layer in which the polyether-modified silicone is adsorbed onto the organic binder is formed at the interface between the organic binder and other compounding materials during mixing or kneading. Thereafter, it is considered that, by heat treatment (firing), the siloxane bond part of the polyether-modified silicone adsorption layer becomes a compound such as an oxide or carbide of silicon as a coating of resin carbide. The resin carbide with the coating formed has higher strength compared to the case without the coating, so the flexural strength is improved. In addition, since compounds such as oxides and carbides of silicon have a low coefficient of thermal expansion, generation of uneven surface shapes due to expansion and contraction of the organic binder can be suppressed, and a smooth surface is likely to be obtained. For this reason, a smooth writing feel can be obtained, and since the adhesion area of the resin carbide to the extender is smaller compared to the case without the coating, wear during writing is not hindered. Therefore, it is possible to obtain a fired pencil lead with a smooth writing feel, which achieves both an improvement in flexural strength and maintenance of the density of the writing line, and has reduced snagging due to a decrease in friction during writing.

[0016] Typical examples of the classification of polyether-modified silicone include a side-chain type in which a polyoxyalkylene group is introduced into the side chain of the silicone chain serving as the main chain, a single-end type in which a polyoxyalkylene group is introduced into one end of the silicone chain, a double-end type in which polyoxyalkylene groups are introduced into both ends of the silicone chain, and an (AB)n type in which the main chain structure consists of an alternating copolymer of a silicone chain and a polyoxyalkylene group. Furthermore, the side-chain type is classified into a linear type and a branched type according to the molecular structure of the main chain. Also, as the polyoxyalkylene group, those containing at least a polyoxyethylene group and / or a polyoxypropylene group are more preferable because they have a high flexural strength and a small writing resistance value.

[0017] The kinematic viscosity of the polyether-modified silicone at 25°C is 100 mm 2 / s or more and 10,000 mm 2When it is below / s, dispersion into the organic binder during kneading becomes easy and uniformity is improved, and during heat treatment, detachment from the organic binder due to viscosity reduction can be effectively suppressed. Furthermore, the kinematic viscosity described above is 500 mm 2 / s or more and 4500 mm 2 / s or less is particularly preferable. Also, the ratio of the content of polyether-modified silicone in the mixture to the content of the organic binder in the mixture is preferably 0.5% by weight or more and 3% by weight or less. When the above ratio is 0.5% by weight or more and 3% by weight or less, it becomes a sufficient content for forming a film, and an appropriate film thickness is obtained such that the fired pencil lead is easily worn during writing, and a fired pencil lead excellent in the balance between bending strength and writing line density can be obtained. More preferably, the above ratio is 0.8% by weight or more and 2% by weight or less.

[0018] Examples of the both-end type polyether-modified silicone include X-22-4952 (kinematic viscosity at 25°C: 100 mm 2 / s), X-22-4272 (kinematic viscosity at 25°C: 270 mm 2 / s), KF-6123 (kinematic viscosity at 25°C: 420 mm 2 / s), and KF-6004 (solid at normal temperature) manufactured by Shin-Etsu Chemical Co., Ltd.

[0019] Examples of the (AB)n type polyether-modified silicone include DOWSIL FZ-2203 (kinematic viscosity at 25°C: 4100 mm 2 / s), DOWSIL FZ-2222 (kinematic viscosity at 25°C: 20000 mm 2 / s), DOWSIL FZ-2233 (kinematic viscosity at 25°C: 5000 mm 2 / s) manufactured by Dow Corning Toray Co., Ltd., Silsoft860 (kinematic viscosity at 25°C: 170 mm 2 / s), Silsoft870 (kinematic viscosity at 25°C: 220 mm 2 / s), and Silsoft900 (kinematic viscosity at 25°C: 250 mm 2 / s) manufactured by Momentive Performance Materials Japan LLC.

[0020] Examples of straight-chain polyether-modified silicones include KF-351A (kinematic viscosity at 25°C: 70 mm 2 / s), KF-352A (kinematic viscosity at 25°C: 1600 mm 2 / s), KF-353 (kinematic viscosity at 25°C: 430 mm 2 / s), KF-354L (kinematic viscosity at 25°C: 200 mm 2 / s), KF-355A (kinematic viscosity at 25°C: 150 mm 2 / s), KF-615A (kinematic viscosity at 25°C: 920 mm 2 / s), KF-945 (kinematic viscosity at 25°C: 130 mm 2 / s), KF-640 (kinematic viscosity at 25°C: 20 mm 2 / s), KF-642 (kinematic viscosity at 25°C: 50 mm 2 / s), KF-643 (kinematic viscosity at 25°C: 19 mm 2 / s), KF-644 (kinematic viscosity at 25°C: 38 mm 2 / s), KF-6020 (kinematic viscosity at 25°C: 180 mm 2 / s), KF-6204 (kinematic viscosity at 25°C: 70 mm 2 / s), X-22-4515 (kinematic viscosity at 25°C: 4000 mm 2 / s), KF-6011 (kinematic viscosity at 25°C: 130 mm 2 / s), KF-6011P (kinematic viscosity at 25°C: 140 mm 2 / s), KF-6012 (kinematic viscosity at 25°C: 1600 mm 2 / s), KF-6015 (kinematic viscosity at 25°C: 150 mm 2 / s), KF-6017 (kinematic viscosity at 25°C: 600 mm 2 / s), KF-6017P (kinematic viscosity at 25°C: 850 mm 2 / s), KF-6043 (kinematic viscosity at 25°C: 400 mm 2 / s), KF-6048 (copolymerized with an alkyl group, kinematic viscosity at 25°C: 2700 mm 2 / s), X-22-2516 (covariance with alkyl and aralkyl groups, kinematic viscosity at 25°C: 70 mm 2 / s), X-22-3939A (covariance with amino group, kinematic viscosity at 25°C: 3300 mm 2 / s), X-22-4741 (covariance with epoxy group, kinematic viscosity at 25°C: 350 mm 2 / s), KF-1002 (covariance with epoxy group, kinematic viscosity at 25°C: 4500 mm 2 / s), and DOWSIL ES-5612 Formulation Aid manufactured by Dow Corning Toray Co., Ltd. (kinematic viscosity at 25°C: 1000 mm 2 / s), DOWSIL BY25-337 (kinematic viscosity at 25°C: 3000 mm 2 / s), DOWSIL BY22-008M (kinematic viscosity at 25°C: 2500 mm 2 / s), DOWSIL ES-5373 Formulation Aid (kinematic viscosity at 25°C: 660 mm 2 / s), DOWSIL FZ-2123 (kinematic viscosity at 25°C: 90 mm 2 / s), DOWSIL SS-2804 (kinematic viscosity at 25°C: 390 mm 2 / s), DOWSIL SH3771 M Fluid (kinematic viscosity at 25°C: 300 mm 2 / s), DOWSIL 5200 Formulation Aid (covariance with alkyl group, kinematic viscosity at 25°C: 2000 mm 2 / s), TSF4440 manufactured by Momentive Performance Materials Japan Co., Ltd. (kinematic viscosity at 25°C: 160 mm 2 / s), SF1188A (kinematic viscosity at 25°C: 1100 mm 2 / s), SF1288 (kinematic viscosity at 25°C: 400 mm 2 / s), Silsoft840 (kinematic viscosity at 25°C: 420 mm 2 / s), Silsoft875 (kinematic viscosity at 25°C: 400 mm 2 / s), Silsoft880 (kinematic viscosity at 25°C: 600 mm 2 / s) may be mentioned.

[0021] Examples of branched polyether-modified silicones include KF-6028 (kinematic viscosity at 25°C: 900 mm 2 / s) and KF-6028P (kinematic viscosity at 25°C: 900 mm 2 / s) manufactured by Shin-Etsu Chemical Co., Ltd., and KF-6038 (copolymerization with an alkyl group, kinematic viscosity at 25°C: 700 mm 2 / s).

[0022] Among these, branched polyether-modified silicones, particularly KF-6028 or KF-6028P, are preferred. Being branched weakens the intermolecular interaction between polyether-modified silicones, making it easier to obtain uniformity during kneading and enabling the formation of a highly smooth film. From the above, a fired pencil lead that exhibits a smooth writing feel with significantly reduced friction during writing compared to conventional fired pencil leads can be obtained without causing snagging during writing.

[0023] The polyether-modified silicone may be used alone or in combination of two or more. It can also be used in combination with other silicone compounds. Examples include, but are not limited to, dimethylpolysiloxane, polyglycerin-modified silicone, amino-modified silicone, and methylphenyl-modified silicone.

[0024] Examples of the matrix material include graphite, boron nitride, mica, talc, etc. As for graphite, either natural graphite or artificial graphite can be used, but it is preferable to use natural graphite with well-developed crystals and good cleavage. More preferably, flake graphite among natural graphite is used. Flake graphite has well-developed crystals, and the developed crystals are stacked to have a high aspect ratio and a smooth surface. Therefore, when forming a core into a thin wire shape by extrusion molding, flake graphite can be oriented in the extrusion direction to improve the bending strength of the core, and also, due to its excellent cleavage, a smooth writing feel and a high density of writing lines can be obtained. Commercially available products of flake graphite include the BF series, CPB series, SC series manufactured by Nakagoshi Graphite Industry Co., Ltd., and the FT series, MF series manufactured by Fuji Graphite Industry Co., Ltd. As for boron nitride, hexagonal boron nitride (h-BN) is mentioned. Crystals are developed in which boron atoms and nitrogen atoms alternately occupy the vertices of regular hexagons, and the crystals are stacked in multiple layers to form one particle of hexagonal boron nitride (h-BN). Therefore, the particles of hexagonal boron nitride (h-BN) have a plate shape similar to graphite. Also, since the layers are bonded by weak van der Waals forces, hexagonal boron nitride (h-BN) is rich in lubricity. Due to such properties, hexagonal boron nitride (h-BN) is suitable as a material for fired pencil leads like graphite, and the fired pencil leads obtained using hexagonal boron nitride (h-BN) will have high bending strength and writing line density. Commercially available products include Denka Boron Nitride SGP, Denka Boron Nitride GP, Denka Boron Nitride HGP, Denka Boron Nitride SP-2 manufactured by Denka Co., Ltd., and SHP-3, SHP-5, SHP-7, HP-1, HP-2, HP-4W, HP-6, HP-60, HP-P1, FS-1 manufactured by Mizushima Alloy Steel Co., Ltd., etc.

[0025] Examples of the organic binder 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, and natural resins such as lignin, cellulose, tragacanth gum, and gum arabic. These organic binders may be used alone or in combination of two or more. In particular, thermoplastic resins such as polyvinyl chloride are preferred because they are highly processable, inexpensive, and have stable supply. Examples of polyvinyl chloride include the TH series, TU series, TE series, TG series manufactured by Ocean PVC Co., Ltd., the Kanebinyl S series, Kanebinyl KS series, Kanebinyl K series, Kanebinyl M series, Kanebinyl HM series manufactured by Kaneka Corporation, the Leuron Paste manufactured by Toray Industries, Inc., and the ZEST series manufactured by Shin Daiichi Vinyl Co., Ltd.

[0026] In some embodiments, the fired pencil lead may be obtained by firing a mixture containing a filler, an organic binder, and polyether-modified silicone, as well as other materials such as a clay binder and / or various additives.

[0027] Examples of the clay binder include bentonite and kaolin clay. Examples of the plasticizer include dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diallyl isophthalate, tricresyl phosphate, dioctyl adipate, etc. Examples of the solvent include ketones such as methyl ethyl ketone and acetone, alcohols such as ethanol, and water. Examples of the stabilizer include stearates, organotin compounds, barium-zinc compounds, calcium-zinc compounds, etc. Examples of the lubricant include fatty acids such as stearic acid and behenic acid, and fatty acid amides. Examples of the filler include metals such as iron, aluminum, titanium, and zinc and their alloys, oxides and nitrides of these metals and alloys, silicon oxides such as silicon dioxide (silica) and silsesquioxane, carbon black, fullerenes, etc. These fillers can be appropriately used in the form of spherical, amorphous granular, needle-shaped, fibrous, plate-shaped, etc. Also, one kind or a combination of two or more kinds may be used. Among these, plate-shaped particles are preferable because they are oriented in the extrusion direction and arranged in the core body in the same manner as graphite during extrusion molding. For example, plate-shaped silica and plate-shaped alumina can be mentioned. As plate-shaped silica, amorphous exfoliated plate-shaped silica obtained by subjecting vermiculite to an expansion treatment, followed by acid treatment, washing with water, drying, pulverization, and classification can be mentioned. Vermiculite is a mineral mainly composed of hydrous mica classified into the vermiculite group clay minerals or the mica group clay minerals, and is also called vermiculite. The chemical composition of vermiculite varies depending on the production area, etc., but a typical composition is as follows. SiO2 35 - 45 wt% Al2O3 10 - 20 wt% MgO 37 - 30 wt% Fe2O3 5 - 22 wt% CaO 0 - 3 wt% Na2O 0 - 1 wt% K2O 0 - 10 wt% Heavy metal content other than Fe (Pb, Cr, Cd, etc.) 0.2 wt% or less Ignited raw material (1050 °C) 3 - 25 wt% By treating vermiculite with sulfuric acid, hydrochloric acid, nitric acid, etc., colored components such as MgO3 and Fe2O3 are removed, resulting in plate-like silica (amorphous cleavage plate-like silica) that maintains the layer structure of vermiculite. Since the layers of this plate-like silica (amorphous cleavage plate-like silica) are bonded by hydrogen bonds due to hydroxyl groups, it can be easily cleaved by simply applying a slight shearing force to the plate-like silica. Also, since the layer structure of the plate-like silica (amorphous cleavage plate-like silica) does not change even when heat-treated up to 1100°C, it can be suitably used for fired pencil leads. Examples of commercially available products include Sylleaf manufactured by Mizusawa Chemical Industry Co., Ltd. Examples of plate-like alumina include α-Al2O3, γ-Al2O3, θ-Al2O3, etc. Since the particle surface of plate-like alumina is smooth, the lubricity between particles is good, and it is less likely to impair the density and writing feel of the writing line. Examples of commercially available products include Seraph FYA00610, FYA02025, FYA10030 manufactured by Kinsai Matech Co., Ltd., and the Cerasure BMM series manufactured by Kawai Lime Industry Co., Ltd. Also, silsesquioxane is represented by the compositional formula [R(SiO 1.5 ) n and is called [sil-sesqui-oxane] in the sense of a siloxane having 1.5 oxygen atoms (= sesqui) in the unit composition. Examples of silsesquioxane include octakis(dimethylsilyloxy)octasil silsesquioxane (R: OSi(CH3)2H) manufactured by Tokyo Chemical Industry Co., Ltd., octavinyl octasil silsesquioxane (R: CH3-CH=CH2), and its derivatives, etc.

[0028] The fired pencil lead according to some embodiments of the present invention is obtained by firing a mixture containing a filler, an organic binder, and a polyether-modified silicone. Here, the "fired pencil lead" is obtained through a heat treatment called "firing". Generally, when a composition containing an organic substance (organic binder) such as a synthetic resin or a natural resin is heat-treated to the firing temperature, the resin molecules are intricately intertwined with a filler such as graphite, and decomposition and condensation of the organic substances occur irregularly, resulting in a complex volume shrinkage of the entire core. Therefore, the skeletal structure of the core after heat treatment becomes extremely complex at the microscopic level, and the degree and size of the bonding of the individual compositions after heat treatment also vary. It is not practical to conduct systematic measurements and analyses that are dominant in relation to the above effects, as it requires conducting a large number of experiments. It is considered that there are circumstances where it is impossible or approximately impractical to directly identify the object based on its structure or properties.

[0029] As the oil to be impregnated into the pores of the core after heat treatment, conventionally known oils can be used. For example, oily substances such as liquid paraffin, α-olefin oligomer, squalane, spindle oil, silicone oil, fatty acid ester, and castor oil, and waxes such as paraffin wax, microcrystalline wax, and carnauba wax can be mentioned, but it is not limited thereto.

Example

[0030] Hereinafter, the present invention will be described based on examples, but the present invention is not limited only to the examples. For the measurement of kinematic viscosity, an automatic kinematic viscosity measuring device PVS VAS manufactured by Lauda, Canon Fenske, Ubbelohde, etc. manufactured by Shibata Scientific Co., Ltd. can be used, or it may be calculated by dividing the absolute viscosity by the density (specific gravity).

[0031] <Example 1> KF-6028 (branched polyether-modified silicone) 0.45 parts by weight Scaly graphite (filler: volume average diameter 15 μm) 45 parts by weight Polyvinyl chloride (organic binder) 30 parts by weight 20 parts by weight of dioctyl phthalate (plasticizer) 15 parts by weight of methyl ethyl ketone (solvent) 1.5 parts by weight of stearate (stabilizer) 0.5 parts by weight of stearic acid (lubricant) 1 part by weight of carbon black (filler) The addition amount of polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight. After subjecting the above compounded materials to dispersion mixing treatment with a Henschel mixer and kneading treatment with a three-roll mill, they were extruded into a thin wire shape with a single-screw extruder, heated from room temperature to 350 °C in air over about 10 hours, and heat-treated by holding at 350 °C for about 1 hour. Further, a firing treatment with a maximum of 1100 °C was performed in a sealed container to obtain a core body after heat treatment with a nominal diameter of 0.5. After immersing this core body after heat treatment in molten paraffin heated to 100 °C for 10 hours, the excess components on the surface were removed to obtain a fired pencil lead.

[0032] <Example 2> A fired pencil lead was obtained in the same manner as in Example 1, except that the compounding amount of KF-6028 was changed from 0.45 parts by weight to 0.06 parts by weight. The addition amount of polyether-modified silicone is 0.2% by weight based on the addition amount of the organic binder. That is, the ratio of the content of polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 0.2% by weight.

[0033] <Example 3> A fired pencil lead was obtained in the same manner as in Example 1, except that the compounding amount of KF-6028 was changed from 0.45 parts by weight to 0.15 parts by weight. The addition amount of polyether-modified silicone is 0.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 0.5% by weight.

[0034] <Example 4> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the compounding amount of KF-6028 was changed from 0.45 parts by weight to 0.24 parts by weight. The addition amount of the polyether-modified silicone is 0.8% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 0.8% by weight.

[0035] <Example 5> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the compounding amount of KF-6028 was changed from 0.45 parts by weight to 0.9 parts by weight. The addition amount of the polyether-modified silicone is 3% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 3% by weight.

[0036] <Example 6> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that the compounding amount of KF-6028 was changed from 0.45 parts by weight to 1.2 parts by weight. The addition amount of the polyether-modified silicone is 4% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 4% by weight.

[0037] <Example 7> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to KF-6017 (linear polyether-modified silicone). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0038] <Example 8> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to KF-6038 (branched polyether-modified silicone, covariant with an alkyl group). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0039] <Example 9> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to KF-6048 (linear polyether-modified silicone, covariant with an alkyl group). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0040] <Example 10> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to FZ-2203 ((AB)n-type polyether-modified silicone). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0041] <Example 11> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to FZ-2123 (linear polyether-modified silicone). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0042] <Example 12> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to FZ-2222 ((AB)n type polyether-modified silicone). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0043] <Example 13> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to Silsoft 900 ((AB)n type polyether-modified silicone). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0044] <Example 14> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to FZ-2233 ((AB)n type polyether-modified silicone). The addition amount of the polyether-modified silicone is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the polyether-modified silicone in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0045] <Comparative Example 1> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to KF-96-1,000 cs (dimethylpolysiloxane, kinematic viscosity at 25°C: 1000 mm 2 / s, manufactured by Shin-Etsu Chemical Co., Ltd.). The addition amount of the dimethylpolysiloxane is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the silicon compound in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0046] <Comparative Example 2> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to Aerosil R972 (hydrophobic amorphous silica (surface group: (CH3)2), manufactured by Nippon Aerosil Co., Ltd.). The addition amount of Aerosil R972 is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the silicon compound in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0047] <Comparative Example 3> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to Aerosil R202 (hydrophobic amorphous silica surface-treated with silicone oil, manufactured by Nippon Aerosil Co., Ltd.). The addition amount of Aerosil R202 is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the silicon compound in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0048] <Comparative Example 4> In Example 1, a fired pencil lead was obtained in the same manner as in Example 1, except that KF-6028 was changed to octakis(dimethylsilyloxy)octasilsesquioxane (manufactured by Tokyo Chemical Industry Co., Ltd.). The addition amount of the silsesquioxane is 1.5% by weight based on the addition amount of the organic binder. That is, the ratio of the content of the silicon compound in the mixture of the above materials to the content of the organic binder is 1.5% by weight.

[0049] <Comparative Example 5> In Example 1, after kneading and extrusion molding with a formulation without adding polyether-modified silicone (KF-6028), heat treatment was performed up to the firing temperature, and diamond nanoparticles (specific surface area 450m 2 / g, volume average diameter mv value 10 nm, manufactured by Diamond Material Co., Ltd.) were dispersed in dimethyl silicone oil KF96-30CS (kinematic viscosity at 25°C: 30 mm 2In / s, with a refractive index of 1.401 (manufactured by Shin-Etsu Chemical Co., Ltd.) at a temperature of 100 °C, after immersing for 10 hours, the excess components on the surface were removed to obtain a fired pencil lead.

[0050] Regarding the fired pencil leads obtained in Examples 1 to 14 and Comparative Examples 1 to 5 above, the bending strength, the density of the writing line, and the writing resistance value were measured by the following methods.

[0051] (Test method for bending strength) The measurement of the bending strength was carried out according to JIS S 6005.

[0052] (Test method for the density of the writing line) The measurement of the density of the writing line was carried out according to JIS S 6005.

[0053] (Test method for writing resistance value) The measurement of the writing resistance value was carried out using a friction and wear tester TriboGear Type: 40 manufactured by Shinto Kagaku Co., Ltd. The measurement environment was set at a temperature of 23 °C ± 2 °C and a humidity of 65% ± 5%. For the mechanical pencil, P205 manufactured by Pentel Co., Ltd. was used and fixed to the friction and wear tester using a dedicated writing instrument holder. On the measurement stage, a stainless steel plate lining and the test paper shown in JIS S 6039 were fixed, and the frictional force when writing a straight line with the mechanical pencil was measured. The test paper was previously left standing in a constant temperature and humidity chamber at a temperature of 23 °C and a humidity of 65% for 24 hours or more. The apparatus conditions were: writing angle: 75 degrees, vertical load: 200 g, moving speed: 1 cm / second, sampling speed: 1 KHz, measurement time: 10 seconds. Among the 10 seconds of measurement time, the average value of the frictional force from 1.5 seconds to 9.5 seconds was taken as the dynamic frictional force, and the writing resistance value (coefficient of dynamic friction) was calculated by dividing the dynamic frictional force by the vertical load. Note that the calculation of the writing resistance value is automatically calculated by the dedicated software Tribosoft6 attached to the apparatus.

[0054] The results are shown in Table 1. As is clear from Table 1, the fired pencil leads of Examples 1 to 14 have the same density of the writing line and improved bending strength compared to the fired pencil leads of Comparative Examples 1 to 5, and can obtain a smoother writing feel.

[0055]

Table 1

[0056] In Examples 1 to 14, since polyether-modified silicone is blended, the writing resistance value is low, and while a smooth writing feeling with reduced snagging can be obtained, high writing density and improved bending strength are observed. Furthermore, in Examples 1, 3 to 5, and 7 to 14 where the content of polyether-modified silicone is 0.5% by weight or more and 3% by weight or less based on the content of the organic binder, fired pencil leads with excellent balance between bending strength and writing line density and a smooth writing feeling are obtained.

[0057] In Examples 1 to 6, since polyether-modified silicone having a molecular structure with a branched silicone chain as the main chain is blended, fired pencil leads showing particularly smooth writing feeling are obtained.

[0058] The kinematic viscosity of the polyether-modified silicone is 100 mm 2 / s or more and 10,000 mm 2 / s or less. In Examples 1 to 10 and 13 to 14, fired pencil leads with excellent balance between bending strength and writing line density and a smooth writing feeling are obtained.

[0059] In Comparative Example 1, dimethylpolysiloxane having no polyoxyalkylene group is added. Although the bending strength is improved, the writing resistance value is high, resulting in a writing feeling with many snags.

[0060] In Comparative Example 2, hydrophobic amorphous silica with its surface hydrophobized by methyl groups is added. Although the bending strength is improved, the writing resistance value is high, resulting in a writing feeling with many snags.

[0061] In Comparative Example 3, hydrophobic amorphous silica with its surface treated with silicone oil is added. Although the bending strength is improved, the writing resistance value is high, resulting in a writing feeling with many snags.

[0062] In Comparative Example 4, silsesquioxane was added, and although the flexural strength was improved, the writing resistance value was high, resulting in a writing feel with many catches.

[0063] In Comparative Example 5, the pores effective for impregnation present in the fired pencil lead were blocked at the pore openings by nanodiamond, and the number of pores effective for impregnation decreased. Therefore, the lubricity of the oily substance cannot be fully exhibited, and a smooth writing feel has not been achieved.

[0064] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

[0065] In this specification, expressions indicating that things such as "identical", "equal", and "homogeneous" are in an equal state represent not only a strictly equal state, but also a state in which there are tolerances or differences to the extent that the same function can be obtained. Also, in this specification, the expressions "comprising", "including", or "having" for a component are not exclusive expressions excluding the existence of other components.

Claims

1. A fired pencil lead obtained by firing a mixture containing a filler, an organic binder, and a polyether-modified silicone.

2. Obtained by heat-treating a molded body obtained by kneading and extrusion-molding the mixture to the firing temperature The fired pencil lead according to Claim 1.

3. The fired pencil lead according to Claim 1 or 2, characterized in that the content of the polyether-modified silicone in the mixture is 0.5% by weight or more and 3% by weight or less based on the content of the organic binder in the mixture.

4. The fired pencil lead according to any one of Claims 1 to 3, characterized in that the polyether-modified silicone is a polyether-modified silicone having a molecular structure with a branched silicone chain as the main chain.

5. The kinematic viscosity at 25 °C of the polyether-modified silicone is 100 mm ２ / s or more and 10,000 mm ２ / s or less, and the fired pencil lead according to any one of claims 1 to 4, characterized in that.

6. At least, a step of mixing a filler, an organic binder, and a polyether-modified silicone to obtain a mixture, A step of molding the mixture to obtain a molded body, A step of firing the molded body to obtain a fired pencil lead, A method for manufacturing a fired pencil lead comprising the steps.

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