JP2015044893A - Fired pencil lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fired pencil lead capable of suppressing contamination of a paper surface (scattering of abrasion powders) while acquiring high writing density for improving performance of the fired pencil lead, and capable of breaking conventional inverse correlation of fixability of the abrasion powders to a paper surface and writing density, because when writing density is improved, an amount of the abrasion powders increases, so that the paper surface is easily contaminated due to scratch by hand.SOLUTION: Provided is the fired pencil lead comprising at least graphite and synthetic resin, and the mixture of graphite and synthetic resin N is mixed and subjected to extrusion molding into a filament state, and then the mixture is subjected to heat treatment to firing temperature, for obtaining the fired pencil lead. In a fine hole of the fired pencil lead, a substance whose melting point is 30-45°C, whose surface tension at 50°C is 21 mN/m or lower and whose dynamic viscosity is 230 mm/s or lower is disposed.

Description

  The present invention relates to a fired pencil lead obtained by blending at least graphite and a synthetic resin, kneading and extruding into a fine wire, and then heat-treating to a firing temperature.

  General fired pencil lead is mainly composed of graphite and synthetic resin such as vinyl chloride resin, plasticizer such as phthalate ester, solvent such as methyl ethyl ketone and water, stearate, stearic acid, carbon black, etc. If necessary, these materials are dispersed, mixed and kneaded, extruded into fine wires, and then heat treated up to the firing temperature. Silicone oil, liquid paraffin, spindles are formed in the pores formed by firing. It is manufactured by appropriately impregnating oils such as oil, squalane and α-olefin oligomer, and waxes.

  It is known that a high concentration of writing lines can be obtained depending on the substance disposed in the core pores. However, the higher the writing line concentration, the greater the number of abrasion powders placed on the paper surface. Become. On the other hand, if the stains due to scratches such as hands are made inconspicuous, the number of abrasion powders arranged on the paper surface must be reduced, and a writing line having a sufficient density cannot be obtained.

  In order to improve this, as a method of improving the fixability of the writing line by devising the impregnating component arranged in the core pores, a highly viscous substance or a substance having high chemical affinity with the paper surface is used. It is known to be used for impregnating agents. For example, Patent Document 1 reports an example using an extreme pressure additive, and Patent Document 2 reports an example using a water-soluble polymer organic solvent solution.

JP 2001-207103 A Japanese Patent No. 4815794

Extreme pressure additives and organic solvent solutions of water-soluble polymers increase the kinematic viscosity and surface tension due to the strong electrical interaction of hydrophilic functional groups between molecules, resulting in fine particles in the core pores. It is difficult to enter a gap.
In addition, organic solvent solutions of extreme pressure additives and water-soluble polymers have hydrophilic functional groups such as hydroxyl groups, ester groups, and sulfone groups in their molecules, so hydrophobic graphite particles, resin carbides, etc. Chemical repulsion with the constituent material of the core body, and penetration into fine spaces will be suppressed.
In addition, the extreme pressure additive and the hydrophilic functional group of the water-soluble polymer interact strongly with the hydroxyl group on the paper surface, but chemically repel the hydrophobic abrasive powder. For this reason, rubbing with a hand or the like makes it easy for the wear powder to separate from the extreme pressure additive and the water-soluble polymer, and the wear powder spreads on the paper surface. Therefore, the fixability of the wear powder on the paper surface is not satisfactory. It was.
Accordingly, there has been a need for a fired pencil lead that is sufficiently impregnated into the core pores and impregnated with a component that can achieve both a high writing concentration and a high fixability of the wear powder.

In the present invention, at least graphite and a synthetic resin are blended, kneaded, extruded into a fine wire, and then subjected to heat treatment up to the firing temperature. A fired pencil lead in which a substance having a surface tension of 21 mN / m or less and a kinematic viscosity at 50 ° C. of 230 mm ² / s or less is disposed.

A substance used in the present invention having a melting point of 30 to 45 ° C., a surface tension at 50 ° C. of 21 mN / m or less and a kinematic viscosity of 230 mm ² / s or less (hereinafter referred to as an impregnation component of the present invention) Since it is 30-45 degreeC, it liquefies by the frictional heat which generate | occur | produces between a core and a paper surface at the time of writing. Furthermore, since the surface tension at 50 ° C. (liquid state) is 21 mN / m or less, it easily penetrates into the pores, and at the same time, the kinematic viscosity at 50 ° C. (liquid state) is 230 mm ² / s or less. Since it is easily deformed and moved by external force, it penetrates between core structures (between resin carbide structures, between resin carbide and graphite particle surfaces, etc.), and surface functional groups between core structures Weakens the electrical interaction due to the stress, and the stress applied to the core during writing can easily desorb constituents such as graphite particles from the core, increasing the number of wear powders placed on the paper. be able to. In addition, since the surface of the detached graphite particles becomes wet with the substance, the lead color luster peculiar to the graphite particle basal surface can be reduced by disturbing the reflected light, and the wear powder becomes blacker. Since it can be shown, the writing line density is improved.

  Furthermore, since the impregnating component of the present invention penetrates into the paper surface and falls in temperature, it solidifies and the abrasion powder is fixed on the paper surface, so that the abrasion powder spreads on the paper surface and the fixing is suppressed as much as possible. A good writing line is obtained.

Hereinafter, the present invention will be described in detail.
In the fired pencil lead of the present invention, the core body before the impregnation component of the present invention is disposed in the pores can be obtained by firing a kneaded and molded product of at least graphite and a synthetic resin.
Examples of graphite include scaly graphite, scaly graphite, earthy graphite, and artificial graphite. These graphites may be used alone or in combination of two or more. Moreover, the compounding quantity of graphite is not particularly limited, but by setting it to 40% by weight or more of the entire composition, sufficient graphite particles are present in the core after the heat treatment, and a sufficient writing line concentration is obtained. In addition, even if graphite is added in an amount exceeding 80% of the total amount, there is no problem in the effect of the present invention, but the ratio of the resin carbide that binds the graphite particles in the core is reduced, and the core has a brittle structure. Since it becomes a body, it becomes a core which is difficult to write, and there is a problem in practical use.

  Moreover, as long as the synthetic resin which can be used for preparation of a core is a commercially available synthetic resin, all the synthetic resins can be used. Examples thereof include polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, chlorinated polyethylene resin, polyvinyl alcohol resin, polyacrylamide resin, chlorinated paraffin resin, furan resin, urea resin, and butyl rubber. These synthetic resins may be used alone or as a mixture of two or more synthetic resins. In addition, the blending amount of the synthetic resin is not particularly limited, but pores are formed in the core body due to removal of components that vaporize during the heat treatment. An amount of pores are formed in the core body, and the surface of the core body constituent material can be sufficiently wetted by allowing more impregnated components of the present invention to penetrate into the core body. The interaction of the present invention can be sufficiently weakened and the wear powder can be sufficiently coated, so that the effects of the present invention are easily obtained. If the synthetic resin exceeds 70% of the total formulation, there is no problem in the effect of the present invention, but the amount of pores in the core increases too much, and the mixing ratio of the graphite particles also decreases. Since the existence ratio of the graphite particles in the core body is reduced and the core body has a low density, the core body is difficult to write, and there is a problem in practical use.

  Conventionally known materials can be used as materials other than the above graphite and synthetic resin. For example, if a plasticizer such as dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, dipropylene glycol dibenzoate, dioctyl adipate, propion carbonate, or a solvent such as methyl ethyl ketone or water is used, the amount of synthetic resin is small However, since these substances are vaporized during heat treatment and more cores are formed, more impregnating components of the present invention are permeated into the core to sufficiently wet the surface of the core constituent material. Since the electrical interaction by the surface functional groups between the core components can be sufficiently weakened and the wear powder can be sufficiently covered, the effects of the present invention can be easily obtained. However, if the above plasticizer or solvent is added in an amount exceeding 40% by weight of the total amount, there is no problem in the effect of the present invention, but the amount of pores in the core is excessive, and the addition of graphite particles Since the ratio is also lowered, the existence ratio of the graphite particles in the core body is reduced, and the core body has a low density, so that the core body is difficult to write and there is a problem in practical use.

  Also, stabilizers such as stearate to prevent thermal degradation of synthetic resin during the manufacturing process, fatty acids such as stearic acid and behenic acid and fatty acid amides to improve moldability and releasability A lubricating material or the like can also be blended. Furthermore, clay minerals such as metal oxides and nitrides such as silicon, iron, aluminum, titanium, and zinc, mica, and talc in order to improve the core appearance quality such as the diameter roundness of the core and the chuck pressure resistance of the mechanical pencil. Further, inorganic additives such as fullerene, carbon nanotube, carbon black, and carbon fiber can be used in combination.

  These raw materials are dispersed and mixed with a Henschel mixer or the like, kneaded with a kneader, three rolls, etc., then extruded into a thin wire shape, and subjected to heat treatment from room temperature to around 300 ° C. in air to produce a pencil core.

The impregnation component of the present invention needs to have a melting point of 30 to 45 ° C., a surface tension at 50 ° C. of 21 mN / m or less, and a kinematic viscosity of 230 mm ² / s or less. They may be obtained from a single substance or a mixture of two or more substances, but the melting point, surface tension, and kinematic viscosity values represent the intrinsic physical properties of a single substance, In the case of a mixture of a plurality of substances, it refers to the value of the impregnated component as a whole.
The surface tension at 50 ° C. is preferably low in order to penetrate into the fine pores, but if it is too low, the electrical interaction between the molecules of the impregnating component when placed on the paper with the wear powder. Is less than 10 mN / m, and the volatility becomes high and it becomes difficult to fix the abrasion powder on the paper surface. Similarly, the kinematic viscosity at 50 ° C. is preferably low in order to penetrate into the fine pores, but if it is too low, the impregnated component does not cover the graphite particles and easily moves to the paper by gravity. Therefore, it is preferably 100 mm ² / s or more. As an example, there is a silicon alkyl copolymer obtained by converting a part of methyl groups of dimethyl silicone oil into a linear or branched alkyl group having 15 to 30 carbon atoms. Examples of commercially available products include SF1632 (manufactured by Momentive Performance Materials, USA, melting point: 30 ° C., kinematic viscosity (50 ° C.): 212 mm ² / s, surface tension: 20.3 mN / m), XF42-B1183 (Momentive Performance Materials, melting point: 30 ° C., kinematic viscosity (50 ° C.): 202 mm ² / s, surface tension: 20.5 mN / m), XF42-C4696 (Momentive Performance Materials) Manufactured by the United States, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20.6 mN / m), and the like.

Any substance that can be mixed with the impregnation component can be any substance as long as the impregnation component as a whole has a melting point of 30 to 45 ° C., a surface tension at 50 ° C. of 21 mN / m or less, and a kinematic viscosity of 230 mm ² / s or less. Can be used. For example, hydrocarbon oils such as liquid paraffin and α-olefin oligomers, various waxes such as synthetic waxes and plant waxes, various fatty acids such as linolenic acid and arachidic acid, non-polyoxyethylene alkyl ethers and polyglycerin fatty acid esters, etc. Examples thereof include ionic surfactants and various modified silicone oils such as dimethyl silicone oil. These substances may be mixed alone, or two or more substances may be selected and mixed.

  The melting point can be determined by differential scanning calorimetry (DSC) or the like. For example, it can be measured using XDSC-7000 (manufactured by Hitachi High-Tech Science Co., Ltd.) or DSC-60Plus series (manufactured by Shimadzu Corporation). Further, the surface tension can be determined using the Wilhelmy method (plate method, vertical plate method). For example, it can be measured using DY-300, DY-500, DY-700 (manufactured by Kyowa Interface Chemical Co., Ltd.). Furthermore, the kinematic viscosity can be measured using an automatic kinematic viscosity measuring device PVS VAS (manufactured by Lauda), but the kinematic viscosity may be calculated by dividing the absolute viscosity by the density (specific gravity).

  Examples of the method for disposing the impregnation component of the present invention in the pores of the core include, but are not particularly limited to, an impregnation method by dipping, a pressure impregnation method, and a vacuum impregnation method.

Although the volume impregnation rate in the core of the impregnation component of the present invention is not particularly limited, it is preferably 1% or more. When the volume impregnation ratio of the impregnating component of the present invention in the core is 1% or more, the impregnating component of the present invention sufficiently weakens the electrical interaction due to the surface functional groups of the core components, and wear Since the powder can be sufficiently covered, the effects of the present invention are easily obtained.
In addition, since the pores of the fired pencil core are distributed in a region smaller than the micropores of 1 μm or less, the impregnated component that has entered the pores is made into a thin film and is in contact with the pore wall (wall surface in the core). It arrange | positions in a pore in the state. Therefore, the surface area in the core with which the impregnating component disposed in the pores contacts can be considered by substituting the intruding volume of the impregnating component.
The volume impregnation rate of the core of the impregnation component of the present invention is a percentage obtained by dividing the volume at 25 ° C. of the substance impregnated in the core pores by the total pore volume of the core. Is. The pore volume of the core can be determined by using a mercury intrusion method and the pore distribution of the core can be measured using Pore Kaiser 9320 (Shimadzu Corporation).

  EXAMPLES Next, although an Example is given and this invention is demonstrated further, this invention is not limited to these Examples.

<Example 1>
Vinyl chloride resin 30 parts by weight Graphite 50 parts by weight Dioctyl phthalate 10 parts by weight Stearic acid 2 parts by weight Methyl ethyl ketone 8 parts by weight The above materials are blended sufficiently with a kneader and three rolls, then extruded into a thin line, and in air The mixture was heated to 300 ° C. and further heated to 1100 ° C. in an inert atmosphere to obtain a fired core having a nominal diameter of 0.5 mm. XF42-C4696 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20.6 mN / m heated to 100 ° C. ) For 10 hours to remove the excess impregnated component adhering to the core surface, and the volume impregnation rate of the impregnated component was impregnated with 44.5% by volume of all pores in the core. A fired pencil lead was obtained.

<Example 2>
In Example 1, XF42-C4696 heated to 100 ° C. (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20. 6 mN / m) A fired pencil lead was obtained in the same manner as in Example 1 except that the immersion time of the fired core was changed to 1 hour. The volume impregnation rate of the impregnation component was 10.2% by volume in all pores in the core.

<Example 3>
In Example 1, XF42-C4696 heated to 100 ° C. (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20. A fired pencil lead was obtained in the same manner as in Example 1 except that the immersion time of the fired core in 6 mN / m) was changed to 0.5 hour. The volume impregnation rate of the impregnation component was 1.0% by volume in all pores in the core.

<Example 4>
In Example 1, XF42-C4696 heated to 100 ° C. (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20. A fired pencil lead was obtained in the same manner as in Example 1 except that the immersion time of the fired core in 6 mN / m) was changed to 0.4 hour. The volume impregnation rate of the impregnation component was 0.9% by volume in all pores in the core.

<Example 5>
In Example 1, instead of XF42-C4696, XF42-B1183 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 30 ° C., kinematic viscosity (50 ° C.): 202 mm ² / s, surface tension: 20 0.5 mN / m) was used to obtain a fired pencil lead in the same manner as in Example 1. The volume impregnation rate of the impregnation component was 46.7% by volume in all pores in the core.

<Example 6>
In Example 1, instead of XF42-C4696, SF1632 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 30 ° C., kinematic viscosity (50 ° C.): 212 mm ² / s, surface tension: 20.3 mN / M) was used to obtain a fired pencil lead in the same manner as in Example 1. The volume impregnation rate of the impregnation component was 47.5% by volume in all pores in the core.

<Example 7>
In Example 1, instead of XF42-C4696, XF42-C4696 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20.6 mN / m) 70 parts by weight, XF42-B1183 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 30 ° C., kinematic viscosity (50 ° C.): 202 mm ² / s, surface tension: 20 0.5 mN / m) Same as Example 1 except that a mixture with 30 parts by weight (melting point: 40 ° C., kinematic viscosity (50 ° C.): 221 mm ² / s, surface tension: 20.6 mN / m) was used. A fired pencil lead was obtained. The volume impregnation ratio of the impregnation component was 45.6% by volume in all pores in the core.

<Example 8>
In Example 1, instead of XF42-C4696, XF42-C4696 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20.6 mN / m) 95 parts by weight and liquid paraffin (hydrocarbon oil, melting point: −50 ° C. or less, kinematic viscosity (50 ° C.): 25 mm ² / s, surface tension: 26.4 mN / m) 5 parts by weight A sintered pencil lead was obtained in the same manner as in Example 1 except that a mixture (melting point: 43 ° C., kinematic viscosity (50 ° C.): 220 mm ² / s, surface tension: 20.6 mN / m) was used. The volume impregnation rate of the impregnation component was 44.7% by volume in all pores in the core.

<Example 9>
In Example 1, instead of XF42-C4696, XF42-B1183 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 30 ° C., kinematic viscosity (50 ° C.): 202 mm ² / s, surface tension: 20.5 mN / m) 95 parts by weight, Loxiol G22 (paraffin wax, manufactured by Henkel, Germany, melting point: 55-62 ° C., kinematic viscosity (100 ° C.): 4.1 mm ² / s, surface tension (100 ° C. ): 28.5 mN / m) Example 1 except that a mixture with 5 parts by weight (melting point: 38 ° C., kinematic viscosity (50 ° C.): 208 mm ² / s, surface tension: 20.5 mN / m) was used. In the same manner, a fired pencil lead was obtained. The volume impregnation rate of the impregnation component was 45.9% by volume in all pores in the core.

<Comparative Example 1>
In Example 1, instead of XF42-C4696, TSF451-10 (silicone oil, manufactured by Momentive Performance Materials, USA, melting point: −60 ° C. or lower, kinematic viscosity (50 ° C.): 8 mm ² / s, surface A fired pencil lead was obtained in the same manner as in Example 1 except that the tension was 20.5 mN / m. The volume impregnation ratio of the impregnation component was 52.1% by volume in all pores in the core.

<Comparative example 2>
In Example 1, instead of XF42-C4696, TSF451-300 (silicone oil, manufactured by Momentive Performance Materials, USA, melting point: −50 ° C. or less, kinematic viscosity (50 ° C.): 205 mm ² / s, surface A fired pencil lead was obtained in the same manner as in Example 1 except that the tension was 20.5 mN / m. The volume impregnation ratio of the impregnation component was 43.2% by volume in all pores in the core.

<Comparative Example 3>
In Example 1, instead of XF42-C4696, XF42-C4696 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20.6 mN / m) 85 parts by weight, Loxiol G22 (paraffin wax, manufactured by Henkel, Germany, melting point: 55-62 ° C., kinematic viscosity (100 ° C.): 4.1 mm ² / s, surface tension (100 ° C. ): 28.5 mN / m) Example 1 except that a mixture with 15 parts by weight (melting point: 45 ° C., kinematic viscosity (50 ° C.): 232 mm ² / s, surface tension: 20.8 mN / m) was used. In the same manner, a fired pencil lead was obtained. The volume impregnation rate of the impregnation component was 41.5% by volume in all pores in the core.

<Comparative Example 4>
In Example 1, instead of XF42-C4696, XF42-C4696 (silicone wax, manufactured by Momentive Performance Materials, USA, melting point: 45 ° C., kinematic viscosity (50 ° C.): 230 mm ² / s, surface tension: 20.6 mN / m) 90 parts by weight, liquid paraffin (hydrocarbon oil, melting point: −50 ° C. or less, kinematic viscosity (50 ° C.): 25 mm ² / s, surface tension: 26.4 mN / m) 5 parts by weight (Melting point: 43 ° C., kinematic viscosity (50 ° C.): 220 mm ² / s, surface tension: 20.6 mN / m) and 10 parts by weight (melting point: 41 ° C., kinematic viscosity (50 ° C.): 208 mm ² / S, surface tension: 22.3 mN / m) was used in the same manner as in Example 1 to obtain a fired pencil lead. The volume impregnation rate of the impregnation component was 40.2% by volume in all pores in the core.

<Comparative Example 5>
In Example 1, instead of XF42-C4696, TSF451-500 (silicone oil, manufactured by Momentive Performance Materials, USA, melting point: −50 ° C. or lower, kinematic viscosity (50 ° C.): 350 mm ² / s, surface A fired pencil lead was obtained in the same manner as in Example 1 except that the tension was 20.8 mN / m. The volume impregnation ratio of the impregnation component was 38.9% by volume in all pores in the core.

<Comparative Example 6>
In Example 1, instead of XF42-C4696, liquid paraffin (hydrocarbon oil, melting point: −50 ° C. or lower, kinematic viscosity (50 ° C.): 25 mm ² / s, surface tension: 26.4 mN / m) was used. Except for the above, a fired pencil lead was obtained in the same manner as in Example 1. The volume impregnation rate of the impregnation component was 45.8% by volume in all pores in the core.

<Comparative Example 7>
In Example 1, instead of XF42-C4696, Hexaglyn PR-15 (polyglycerin fatty acid picture ester, manufactured by Nikko Chemicals Co., Ltd., melting point: 30 ° C., kinematic viscosity (50 ° C.): 285 mm ² / s, surface tension: A fired pencil lead was obtained in the same manner as in Example 1 except that 49.6 mN / m) was used. The volume impregnation rate of the impregnation component was 35.8% by volume in all pores in the core.

<Comparative Example 8>
In Example 1, instead of XF42-C4696, Loxiol G22 (paraffin wax, manufactured by Henkel, Germany, melting point: 55-62 ° C., kinematic viscosity (100 ° C.): 4.1 mm ² / s, surface tension (100 ° C): A fired pencil lead was obtained in the same manner as in Example 1 except that 28.5 mN / m) was used. The volume impregnation rate of the impregnation component was 25.6% by volume in all pores in the core.

<Comparative Example 9>
In Example 1, in place of XF42-C4696, 95 parts by weight of Wako primary ethylene glycol (ethylene glycol, manufactured by Wako Pure Chemical Industries, Ltd.) and 5 weights of PVA UMR-10M (polyvinyl alcohol, manufactured by Unitika) A calcined pencil in the same manner as in Example 1 except that a mixture with a part (melting point: −10 ° C. or lower, kinematic viscosity (50 ° C.): 9.8 mm ² / s, surface tension: 35.9 mN / m) was used. I got a wick. The volume impregnation rate of the impregnation component was 9.8% by volume in all pores in the core.

<Comparative Example 10>
In Example 1, instead of XF42-C4696, 90 parts by weight of Wako primary ethylene glycol (ethylene glycol, manufactured by Wako Pure Chemical Industries, Ltd.) and 10 parts by weight of PVA UMR-10M (polyvinyl alcohol, manufactured by Unitika Ltd.) A baked pencil lead in the same manner as in Example 1 except that a mixture (melting point: −10 ° C. or lower, kinematic viscosity (50 ° C.): 25.6 mm ² / s, surface tension: 39.6 mN / m) is used. Got. The volume impregnation rate of the impregnation component was 6.9% by volume in all pores in the core.

<Comparative Example 11>
In Example 1, instead of XF42-C4696 heated to 100 ° C., Polyvan A (molybdenum dithiocarbamate, manufactured by Vanderbilt, USA, melting point: 258 ° C.) heated to 260 ° C. was used. A fired pencil lead was obtained in the same manner, but the impregnating component was not impregnated at all in the pores in the core.

<Comparative Example 12>
In Example 1, instead of XF42-C4696, 10 parts by weight of Polyvan A (molybdenum dithiocarbamate, manufactured by Vanderbilt, USA, melting point: 258 ° C.) and spindle oil (hydrocarbon oil, melting point: −40 ° C. or less, dynamic Viscosity (50 ° C.): 25 mm ² / s, surface tension: 26.9 mN / m) (melting point: −20 ° C. or less, kinematic viscosity: 6.6 mm ² / s, surface tension: 29.7 mN / m) A fired pencil lead was obtained in the same manner as in Example 1 except that was used. The volume impregnation ratio of the impregnation component was 42.8% by volume in all pores in the core.

  About the baked pencil lead obtained by each said example, the bending strength was measured according to JIS S6005, and the density | concentration was measured according to JIS S6005. In addition, the fixing property is α, where the density of the part written and drawn by density measurement is superimposed on the written part and tissue paper is superimposed on the written part, and the written part is rubbed under a certain condition of reciprocating 10 times with tissue paper at a vertical load of 500 g. Β / α was obtained as a percentage, where β was the concentration after rubbing of the same portion as the portion where the concentration α was measured. Larger values indicate better fixability.

In Examples, at least graphite and a synthetic resin are blended, kneaded, extruded into a thin wire, and then subjected to heat treatment up to the firing temperature. By placing a substance having a surface tension at 50 ° C. of 21 mN / m or less and a kinematic viscosity of 230 mm ² / s or less, higher than when impregnated with the conventional impregnating agent in Comparative Examples 10 to 13 A writing line is obtained in which the concentration and the contamination of the paper surface are suppressed as much as possible.
In Examples 1 to 4, when the volume impregnation ratio of the impregnation component used in the present invention into the core was changed, when the impregnation component was present in the core in an amount of 1% by volume or more, high concentration writing was obtained. And soiling the paper surface is suppressed as much as possible.
Further, in Examples 1, 5 and 6, three kinds of impregnation having a melting point of 30 to 45 ° C., a surface tension at 50 ° C. of 21 mN / m or less and a kinematic viscosity of 230 mm ² / s or less. Ingredients are placed in the core. With each impregnation component, there is a slight difference in the fixability of the writing line due to the difference between the melting point and the kinematic viscosity, but a higher concentration than when impregnating the conventional impregnating agent in Comparative Examples 10 to 13, and A writing line in which the contamination of the paper surface is suppressed as much as possible is obtained.
In Examples 7 to 10, a mixture of two types of impregnation components is disposed in the core. Even when the mixture is placed in the core, the characteristics of the mixture are that the melting point is 30 to 45 ° C., the surface tension at 50 ° C. is 21 mN / m or less and the kinematic viscosity is 230 mm ² / s or less. The effect of the invention is obtained, and a writing line that has a higher concentration and that suppresses the soiling of the paper as much as possible is obtained as compared with the case where the conventional impregnating agent in Comparative Examples 10 to 13 is impregnated.
Furthermore, as in Example 9, when a slight amount of a material having a melting point of about 50 to 60 ° C. is mixed, solidification of the impregnated component on the paper surface is promoted, and a writing line in which the paper surface is further prevented from being stained is obtained. Can do.
The impregnated components of Comparative Example 1 and Comparative Example 2 have a melting point of 30 ° C. or lower and are not solidified on the paper surface. Further, the impregnation component of Comparative Example 8 has a kinematic viscosity at 50 ° C. of 230 mm ² / s or more, and the impregnation component of Comparative Example 9 has a surface tension at 50 ° C. of 21 mN / m. Since the penetration between the constituents is insufficient, a high-concentration writing line is not obtained. Furthermore, since the impregnation component of Comparative Example 10 used in the conventional impregnation component has a high surface tension and does not sufficiently penetrate between the core constituent materials, it is presumed that a high-concentration writing line was not obtained. The Further, since the impregnation component of Comparative Example 12 did not penetrate into the core, the writing line concentration improvement effect and the fixability improvement effect could not be obtained. In the impregnation component of Comparative Example 13, the extreme pressure additive was dissolved in the spindle oil. At that time, the structure of the extreme pressure additive was broken, and the structure of the extreme pressure additive did not return to its original state even after time passed, and solidification (or semi-solidification) of the impregnation component did not occur. It seems that the fixability of the writing lines on the paper is insufficient.

Claims (1)

At least graphite and a synthetic resin are blended, kneaded, extruded into a fine wire, and then subjected to heat treatment up to the firing temperature. The melting point is 30 to 45 ° C., and the melting point is 50 to 50 ° C. A fired pencil lead obtained by disposing a substance having a surface tension of 21 mN / m or less and a kinematic viscosity of 230 mm ² / s or less.