Porous black fired pencil lead containing graphite

Abstract

To provide a pencil lead which highly satisfies both concentration improvement of writing lines and fixability improvement, and which avoids soiling, for example, a hand used for writing.SOLUTION: A pencil lead is obtained by impregnation of a wax having a melting point of 45-80°C. Alternatively, a pencil lead is obtained by impregnation at normal temperature (25°C) of a solid oily composition including 50 mass% or more of a wax having a melting point of 45-80°C, and 10 mass% or more of a tackifier resin.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention achieves a high degree of balance between improved ink density and fixation, and is less likely to smudge onto the hands while writing. Porous black firing containing graphite Regarding pencil lead. [Background technology]

[0002] Conventional calcined pencil leads use graphite as a coloring agent, resulting in a writing surface where the ab-side of the graphite covers the paper. This ab-side reflects light, making the writing difficult to see as black. Therefore, various techniques have been employed to improve the density of the writing produced by pencil leads. When aiming to increase the density of handwriting, a large amount of graphite, as a coloring agent, is transferred to the writing surface. Therefore, a related performance aspect is fixation (resistance to smudging when the lines are rubbed). In other words, aiming to increase the density of handwriting will result in poor fixation, and conversely, improving fixation will result in difficulties with the density of handwriting.

[0003] Therefore, in the field of pencil leads, diligent research has been conducted to achieve a balance between these performance characteristics. For example, in a pencil lead formed by impregnating the pores of a fired pencil lead with an oily substance, the oily substance is a solid at room temperature, such as silicone oil, and an oily substance that is incompatible with the solid oily substance and is liquid at room temperature, and the reflectance density of the drawn line and the fixation of the drawn line have been investigated (see, for example, Patent Document 1). In this case, "good fixation" means that the amount of smudging due to abrasion, which was estimated to be over 20%, was suppressed to around 10%, which was not sufficient.

[0004] Furthermore, in a pencil lead obtained by impregnating a porous material with an impregnation component, the impregnation component is a silicone oil or the like and carbon atoms with 14 to 50 carbon atoms (C 14 ~C 50There are known pencil leads that attempt to achieve both dark writing and good line fixation by impregnating the pores of a calcined pencil lead with an organic substance having a polar group (see, for example, Patent Document 2). In this case as well, "good fixation" means that smudging due to abrasion, which was estimated to be over 20% at worst, is suppressed to about 20%, which is still not sufficient.

[0005] Furthermore, a "lead core" is disclosed which is composed of a sintered body made of boron nitride and carbon, and an adhesive filling the pores of the sintered body, wherein the peel strength between the adhesive and the drafting film on which it is written is 50 g / 2.5 cm or more, and the adhesive (adhesive wax, a mixture of wax and resin) is blended into the pores of the fired core, resulting in a high-strength, high-concentration "lead core" with excellent adhesion to the drafting film (see, for example, Patent Document 3). This "lead core" has excellent adhesion to the drafting film, but is considered to be too adhesive to the paper surface.

[0006] Furthermore, a pencil lead has been disclosed in which a fired core containing dispersed graphite and an oily substance impregnated into the pores of the fired core are impregnated with a wax and a compatible substance with rosin resin and / or petroleum resin as at least a portion of the oily substance, thereby achieving both improved density on the paper surface and improved fixability (see, for example, Patent Document 4). However, the "improved fixability" referred to here is estimated to suppress smudging due to abrasion by about 10%, which is considered insufficient. Furthermore, the applicant has disclosed a pencil lead with excellent color development, line density, drawing feel, lightfastness, and mechanical strength, in which a specific pigment and jojoba oil, etc., are impregnated into the pores of a white or monochromatic porous fired core (see, for example, Patent Document 5). This pencil lead does not use graphite, and no disclosure or consideration has been made regarding its ability to adhere to paper. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 5-271604 (Detailed Description of the Invention, Examples, etc.) [Patent Document 2] Japanese Patent Publication No. 2005-314620 (Claims, Detailed Description of the Invention, etc.) [Patent Document 3] Japanese Patent Publication No. 60-105598 (Detailed Description of the Invention, Examples, etc.) [Patent Document 4] Japanese Patent Publication No. 3-31377 (Claims, Detailed Description of the Invention, etc.) [Patent Document 5] Japanese Patent Publication No. 2002-179975 (Claims, Detailed Description of the Invention, etc.) [Overview of the project] [Problems that the invention aims to solve]

[0008] In view of the problems of the prior art described above, this invention aims to solve them by achieving a high degree of balance between improved ink density and improved ink fixation, and by preventing smudging on the hands while writing. Porous black firing containing graphite The purpose is to provide pencil lead. [Means for solving the problem]

[0009] In view of the above-mentioned conventional problems, the present inventors aim to resolve them by impregnating the material with one component having a melting point above a specific temperature, or with two or more components including this component and a component with specific physical properties, thereby achieving the above objective. Porous black firing containing graphite We discovered that pencil lead could be obtained, and thus completed the present invention.

[0010] In other words, the present invention Porous black firing containing graphite The pencil lead is characterized by being impregnated with a wax having a melting point of 45 to 80°C, and is further characterized by being impregnated with an oily composition that is solid at room temperature (25°C) and contains 50% or more by mass of wax having a melting point of 45 to 80°C and 10% or more by mass of a tackifying resin. The wax with a melting point of 45-80°C is preferably a glycerin fatty acid ester. It is preferable that the tackifying resin is at least one selected from the following Group A. Group A: terpene phenol resin, rosin ester resin, ketone resin, petroleum resin, polybutene Furthermore, it is preferable to contain an oil that is liquid at room temperature. It is preferable that the tackiness of the wax having a melting point of 45 to 80°C or the oily composition that is solid at room temperature is 10 gf or more. It is preferable that the tackiness of the wax having a melting point of 45 to 80°C or the oily composition that is solid at room temperature is 40 gf or more, and the viscosity at 50°C is 40 to 200 mPas. When the pencil lead is written by the method of JIS S 6006:2020, the wear amount is preferably 2.0 mm / 6 m or more, and the dirtiness defined by the concentration of the portion where the dirt spreads after 4 reciprocating rubbings so that the written line protrudes from the line drawn with a felt having a vertical load of 500 g is 0.60 or less. It is preferable that the value of the dirtiness / the wear amount is 0.025 or less.

Advantages of the Invention

[0011] According to the present invention, it is possible to highly achieve both an improvement in the density of the written line and an improvement in the fixing property, and it is difficult for dirt to adhere to the hand while writing. Porous black firing containing graphite A pencil lead is provided. The objects and effects of the present invention are recognized and obtained by using the components and combinations particularly pointed out in the claims. Both the above general description and the following detailed description are exemplary and explanatory, and do not limit the present invention described in the claims.

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, note that the technical scope of the present invention is not limited to each of the embodiments described in detail below, and extends to the invention described in the claims and its equivalents.

[0013] The pencil lead of the present invention is characterized in that, in the first invention, it is impregnated with a wax having a melting point of 45 to 80°C, and in the second invention, it is impregnated with an oily composition that is solid at room temperature (25°C, the same hereinafter) and contains 50% by mass or more of a wax having a melting point of 45 to 80°C and 10% by mass or more of an adhesion-imparting resin. Hereinafter, when referring to the present invention, it includes both the first invention and the second invention.

[0014] In the present invention, as the pencil lead body to be impregnated with the wax having a melting point of 45 to 80°C, or the oily composition that is solid at room temperature and contains 50% by mass or more of a wax having a melting point of 45 to 80°C and 10% by mass or more of an adhesion-imparting resin, a black porous fired core body can be mentioned. This black porous fired core body can be obtained by conventional compounding materials and manufacturing methods, etc. As long as it is a black porous fired core body containing at least graphite, the types of compounding materials and manufacturing methods are not particularly limited. For example, when the pencil lead is for a mechanical pencil, the compounding material contains at least graphite. In the case of a black porous fired core body such as a pencil lead other than a mechanical pencil, it is preferable to contain at least graphite, a extender material, a ceramic binder, etc. In addition, for the porous fired core body for a mechanical pencil, as other components, as a binder, polyvinyl chloride, polyvinyl alcohol, phenol resin, pitch, cellulose, polyacrylonitrile, as nanoparticles, metal nanoparticles with an average particle size of 100 nm or less, diamond nanoparticles, coated nanoparticles obtained by coating a base material composed of these nanoparticles, etc. with amorphous carbon, graphite, diamond, and ceramic materials, carbon particles such as fullerenes, as stabilizers, calcium-zinc stearate, sodium stearate, magnesium stearate, as plasticizers, dioctyl phthalate, dioctyl adipate, diisobutyl phthalate, in the case of a fired pencil lead, as other components, coloring materials, lubricants, binder components, various silicone oils, lard, acrylic resins, epoxy resins, celluloid, and other thermoplastic resins, organic solvents, etc. can be used.

[0015] Examples of graphite that can be used include natural graphite such as flaky natural graphite, artificial graphite, quiche graphite, expanded graphite, and expanded graphite. Examples of ceramic binders include crystalline or amorphous SiO2, Si3N4, Al2O3, ZrO, MgO, boron nitride, B2O3, and AlN, and these may be used individually or in combination of two or more. In this invention (including the examples described later), the average particle size refers to the volume-weighted average diameter (mv value) obtained from the measurement results of the laser diffraction-scattering method. For example, in the case of nanoparticles, it can be measured using NanoTrack [Nikkiso Co., Ltd., UPA-EX150 (internal probe type)].

[0016] The binder material is not particularly limited to those used in conventional pencil leads; any of them can be used. For example, white binder materials such as boron nitride, kaolin, talc, mica, and calcium carbonate can be used, and depending on the hue of the pencil lead, colored binder materials can also be used. Naturally, mixtures of several types of these can also be used. Particularly preferred are boron nitride, kaolin, and talc, due to their physical properties and shape.

[0017] The binder component is not particularly limited to those used in conventional pencil leads; any of them can be used. Examples include celluloses such as carboxymethylcellulose, polyvinyls such as polyvinylpyrronidone, polyethers such as polyoxyethylene, acrylic acids such as polyacrylic acid, inorganic polymers such as tetraethyl orthosilicate (TEOS) condensate, clays such as montmorillonite, and ceramic glass. These can be used individually or in combination of two or more.

[0018] Examples of thermoplastic resins include polyvinyl alcohol, polyvinyl chloride, polychlorinated vinyl chloride, polyamide, polyethylene, polypropylene, and polyetheretherketone. The organic solvent used is preferably one that acts as a plasticizer capable of dissolving the thermoplastic resin. Specifically, dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, dioctyl adipate, diallyl isophthalate, propylene carbonate, alcohols, ketones, esters, and the like can be used.

[0019] In the present invention, the fired pencil lead can be obtained by kneading, molding, drying, and firing in a non-oxidizing atmosphere the various components (graphite, carbon black, nanoparticles, extender, surfactant, fragrance, thermoplastic resin, organic solvent, etc.) used in each type of pencil lead, such as fired pencil lead for mechanical pencils or fired pencil lead other than for mechanical pencils.

[0020] For example, in the manufacture of pencil lead for mechanical pencils, preferably, from the viewpoint of strength, density, and writing feel, the pencil lead composition is composed of (a) 30-70% by mass of the above-mentioned graphite or carbon black, (b) 0.01-1% by mass of nanoparticles, and other components such as (c) 30-60% of thermoplastic synthetic resin and (d) 0-30% of an organic solvent capable of dissolving the thermoplastic synthetic resin. These are dispersed and mixed in a Henschel mixer, kneaded with a pressure kneader and a double roll, molded in an extruder, dried in an electric furnace at 110-250°C to form the lead body for pencil lead formation before firing, and then fired in an inert gas atmosphere such as nitrogen at 800-1400°C for 20-40 hours to produce the pencil lead body.

[0021] In the present invention, as described above, a pencil lead can be obtained by impregnating the pores of a black porous fired core containing at least graphite with a wax having a melting point of 45 to 80°C, or by impregnating the pores of a solid oily composition at room temperature containing 50% by mass or more of a wax having a melting point of 45 to 80°C and 10% by mass or more of a tackifying resin.

[0022] Examples of waxes with a melting point of 45 to 80°C used in the present invention include waxes such as glycerin fatty acid esters, lacquer wax (melting point 52°C), Japanese wax (melting point 53°C), montan wax (melting point 78 to 80°C), paraffin wax (melting point 48 to 75°C), and sawtooth wax (melting point 52°C), as well as thermoplastic resins such as ethylene-vinyl acetate copolymers (melting point 75 to 80°C or lower) and ethylene-acrylic copolymers (melting point 65 to 80°C or lower), and cured palm oil (melting point 45 to 59°C), at least one of these (each individually or in mixtures of two or more, the same applies hereinafter).

[0023] As for the glycerin fatty acid ester used as the "wax component," any glycerin fatty acid ester with a melting point of 45-80°C (between 45°C and 80°C) that is generally classified as such can be used without any particular limitations. For example, palmitic acid glyceride, stearate glyceride, etc., with a melting point of 45-80°C, and monoglycerides, diglycerides, and triglycerides can all be used. Furthermore, in addition to these, any natural products such as the above-mentioned waxes such as Japanese wax and Japanese lacquer wax, and sumac waxes such as Japanese lacquer wax and Japanese lacquer wax, which have glycerin fatty acid esters as their main component, can be used. If commercially available waxes with a melting point of 45-80°C are available, they can be used. Preferred waxes with a melting point of 45-80°C include glycerin fatty acid esters, lacquer wax, Japanese lacquer wax, Japanese wax, and Japanese wax, which are used as "wax components."

[0024] In the present invention, in the first invention, the desired pencil lead is obtained by impregnating the above-mentioned fired pencil lead body with the above-mentioned wax (100% by mass) having a melting point of 45 to 80°C, and in the second invention, the desired pencil lead is obtained by impregnating the body with an oily composition that is solid at room temperature and contains 50% by mass or more of the wax having a melting point of 45 to 80°C and 10% by mass or more of a tackifying resin.

[0025] Examples of tackifier resins used in the second invention include at least one of terpene phenol resins, rosin ester resins, ketone resins, petroleum resins, and polybutenes, which are generally considered to be amorphous oligomers with molecular weights ranging from several hundred to several thousand. Other terpene resins besides terpene phenol resins include terpene resins, aromatically modified terpene resins, and hydrogenated terpene resins. These tackifying resins, particularly in terms of improving adhesion, use a predetermined amount of at least one selected from terpene phenol resin, rosin ester resin, ketone resin, petroleum resin, and polybutene in addition to the aforementioned wax with a melting point of 45 to 80°C.

[0026] The terpene phenol resins that can be used are obtained by copolymerizing terpene compounds and phenols by cationic polymerization under a Friedel-Crafts catalyst. The above terpene compounds are generally polymers of isoprene (C5H8) and monoterpenes (C5H8). 10 H 16 ), sesquiterpenes (C 15 H 24 ), diterpene (C 20 H 32 These compounds are classified into categories such as ), and are based on these as their basic skeletons. Among these, monoterpenes, sesquiterpenes, and diterpenes are preferred in the present invention, with sesquiterpenes and monoterpenes being more preferred. Examples of these terpene compounds include myrcene, allocimene, ocimene, and α-p Nene, β-pinene, dipentene, limonene, α-phellandrene, α-terpinene, γ- Terpinene, terpinolene, 1,8-cineole, 1,4-cineole, α-terpineole β-terpineol, γ-terpineol, camphene, tricyclene, sabinene Examples include paramentadienes and karenes. Among these, α-pinene, β-pinene, limonene, myrcene, allocimene, α- Terpinene is preferred.

[0027] Examples of phenols include phenol, cresol, xylenol, and propyl phenol. Phenolic acid, hydroxyphenol, hydroquinone, resorcinol, methoxyphenol, bromine Examples include mophenol, bisphenol A, and bisphenol F. Among these, phenol and cresol are preferred. Terpene phenol resins are a type of tackifier (adhesion-imparting resin) and are generally considered to be amorphous oligomers with molecular weights ranging from several hundred to several thousand. Other terpene resins include terpene resins, aromatically modified terpene resins, and hydrogenated terpene resins. In this invention, hydrogenated terpene phenol resins obtained by hydrogenating terpene phenol resins may also be used. In this second invention, commercially available terpene phenol resins can be used, for example, those manufactured by Yasuhara Chemical Co., Ltd. under product names such as the Polystar series and Mighty Ace series, which are readily available. Specifically, examples include YS Polystar T30, YS Polystar T80, YS Polystar T115, and YS Polystar T160 (all manufactured by Yasuhara Chemical Co., Ltd.).

[0028] The rosin ester resin used in the present invention is a resin obtained by esterifying a rosin resin mainly composed of abietic acid, disproportionated rosin resin, hydrogenated rosin resin, or a dimer of resin acids such as abietic acid (polymerized rosin resin) with alcohol. A portion of the hydroxyl groups of the alcohol used in esterification are not used in the esterification process and are instead contained within the resin, thereby adjusting the hydroxyl value to the above range. Examples of alcohols include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol. Furthermore, a resin obtained by esterifying rosin resin is called a rosin ester resin, a resin obtained by esterifying disproportionated rosin resin is called a disproportionated rosin ester resin, a resin obtained by esterifying hydrogenated rosin resin is called a hydrogenated rosin ester resin, and a resin obtained by esterifying polymerized rosin resin is called a polymerized rosin ester resin. In the present invention, any of these can be used. Examples of the rosin ester resins mentioned above include Ester Gum HP manufactured by Arakawa Chemical Industries, Ltd., and Haritac F85 manufactured by Harima Chemicals, Ltd.

[0029] The ketone resins that can be used are commercially available products, such as ketone resin K-90 (manufactured by Arakawa Chemical Industries, Ltd.). Examples of rosin-modified phenolic resins that can be used include: a rosin-modified phenolic resin obtained by dissolving p-alkylphenols such as p-octylphenol and p-nonylphenol with paraformaldehyde and rosin in toluene, reacting them under an acid or alkali catalyst, then adding glycerin, pentaerythritol, or rosin at 200°C, reacting with a resol resin, and then esterifying with glycerin; a rosin-modified phenolic resin obtained by reacting a glycerin ester of rosin with a resol resin; or a rosin-modified phenolic resin obtained by reacting a rosin-modified alkyd resin with a phenolic resin. Commercially available products include Tamanol 135, Tamanol 350, and Tamanol 354 manufactured by Arakawa Chemical Industries, Ltd.

[0030] The polybutenes that can be used are not particularly limited, and examples include homopolymers of isobutene and copolymers of isobutene and n-butene. Commercially available polybutenes can be used. Examples of commercially available products include INEOS' "Indopol H-100," NOF's "PB200N," Nippon Oil & Energy's "Nisseki Polybutene," and Nippon Oil & Energy's "Tetrax."

[0031] Examples of petroleum resins include aromatic hydrocarbon resins and saturated or unsaturated aliphatic hydrocarbon resins. Examples include C5 petroleum resins (aliphatic petroleum resins polymerized from fractions such as isoprene, 1,3-pentadiene, cyclopentadiene, methylbutene, and pentene), C9 petroleum resins (aromatic petroleum resins polymerized from fractions such as α-methylstyrene, o-vinyltoluene, m-vinyltoluene, and p-vinyltoluene), and C5C9 copolymer petroleum resins. Commercially available products such as Petrotac 100V (manufactured by Tosoh Corporation) can be used.

[0032] The oily composition, which is solid at room temperature and comprises 50% by mass or more, preferably 50-90% by mass, of a wax with a melting point of 45-80°C, and 10% by mass or more, preferably 10-30% by mass, of a tackifying resin, may further contain an oil that is liquid at room temperature, from the viewpoint of improving line density and writing lubricity. Examples of oils that can be used that are liquid at room temperature include at least one of jojoba oil, ester oil, higher alcohol, and liquid paraffin.

[0033] In this second invention, if the content of wax with a melting point of 45-80°C is less than 50% by mass, the effects of the present invention cannot be achieved. Furthermore, by using 10% by mass or more of tackifying resin, the oil tackiness is increased, and the fixing of drawn lines can be improved. The amount of the liquid oil at room temperature is preferably 10 to 30% by mass relative to the total amount of the oily composition.

[0034] The tackiness of the wax having a melting point of 45 to 80°C or the oily composition that is solid at room temperature is preferably 10 gf or more, and more preferably 40 to 120 gf, from the viewpoint of line fixing. In the present invention (including the embodiments described later), the above-mentioned tackiness is a value calculated by measurement using the "TAC1000" tacking test machine manufactured by Lesca Corporation.

[0035] More preferably, the wax having a melting point of 45 to 80°C or the oily composition that is solid at room temperature has an adhesiveness of 40 gf or more and a viscosity of 40 to 200 mPas at 50°C. In the present invention (including the examples described later), the viscosity at 50°C is a value calculated by measurement using the MCR102 rheometer manufactured by Anton Paar.

[0036] In this invention, by impregnating the pores of the black porous fired core described above with a wax having a melting point of 45-80°C, or an oily composition that is solid at room temperature and contains 50% by mass or more of a wax having a melting point of 45-80°C and 10% by mass or more of a tackifying resin, the desired pencil lead can be obtained, achieving an even higher level of balance between improved density of the writing line and improved fixability, and moreover, a pencil lead that is less likely to stain the hands of the person writing with it can be obtained.

[0037] In the present invention, the method for impregnating the pores of the porous fired core having the above configuration is not particularly limited, but for example, the porous fired core, which is black and contains at least graphite, can be immersed in a solution of an oily composition that is solid at room temperature, either as is or diluted with a solvent such as ethylene glycol, ethanol, 2-ethylhexanol, butyl cellsolve, dipropylene glycol monomethyl ether, isopropanol, or propylene glycol, and then, if necessary, heated and immersed, and after sufficient impregnation using reduced pressure and increased pressure, the solvent can be removed (dried).

[0038] In the impregnation treatment described above, the amount of the oily composition, which is solid at room temperature and contains at least graphite and is black, impregnated into the pores of the porous fired core body, which is black in color, is not particularly limited, but varies depending on the type of pencil, porosity, etc. However, an amount of about 0.1 to 30% by mass relative to the weight of the pencil core is preferable to sufficiently exhibit the effects of the present invention, and more preferably 0.5 to 15% by mass.

[0039] In the pencil lead of the present invention, preferably, from the standpoint of writing hardness and line density, the wear amount when writing by the method of JIS S 6006:2020 is 2.0 mm / 6 m or more, and the staining ability, defined by the density of the area where the stain spreads when the written line is rubbed back and forth four times with a felt with a vertical load of 500 g so as to extend beyond the line, is 0.60 or less. More preferably, the ratio of fouling to wear is 0.025 or less, and particularly preferably 0.005 to 0.020. To achieve a fouling level of 0.60 or less, and further to reduce the fouling level / abrasion rate to 0.025 or less, this can be done by selecting a suitable wax type with a melting point of 45-80°C or higher, depending on the type of pencil lead, or by using a suitable combination such as 50% by mass or more of a wax type with a melting point of 45-80°C and 10% by mass or more of a tackifying resin type.

[0040] In the present invention, as described above, by impregnating the pores of a black porous fired core with the above-mentioned wax with a melting point of 45-80°C, or an oily composition that is solid at room temperature and contains 50% by mass or more of the above-mentioned wax with a melting point of 45-80°C and 10% by mass or more of a tackifying resin, the composition penetrates and breaks down easily when the core is worn, and the wear particles adhere more easily to the paper surface. This allows for dark writing on smooth paper surfaces, achieving a high degree of both improved line density and improved adhesion. As a result, a pencil lead is obtained that is superior to conventional pencils in terms of adhesion, and is less likely to stain the hands of the person writing. [Examples]

[0041] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0042] (Example 1: Mechanical pencil lead) A black porous fired core (fired pencil core) was prepared using the following method. 40 parts by mass of flaky natural graphite Nanoparticles: Diamond nanoparticles (particle size: mv value 50 nm) 0.4 parts by mass Polyvinyl chloride 40 parts by mass Sodium stearate 1 part by mass 15 parts by mass of dioctyl phthalate The above nanoparticles and dioctyl phthalate were dispersed in a bead mill for 180 minutes, and the other above materials were mixed and dispersed in a Henschel mixer (mixing and dispersion time 20 minutes, the same applies hereafter). After kneading with a pressure kneader and rolls, and molding, the dioctyl phthalate was dried, and then the mixture was fired in a nitrogen (N2) atmosphere at 1000°C for 10 hours to produce a fired pencil lead (mechanical pencil lead) with a diameter of 0.565 mm and a length of 60 mm. Next, the fired pencil lead was immersed in 100% by mass of urushirou (manufactured by Cerarica NODA Co., Ltd.) and impregnated at 150°C for 24 hours to produce a pencil lead. By weight measurement, it was confirmed that the amount of impregnation in the lead was 15.2% by mass relative to the weight of the lead.

[0043] (Examples 2-8 and Comparative Examples 1-3) The fired pencil lead obtained in Example 1 above was immersed in a wax + tackifying resin with the composition shown in Table 1 below, and impregnated in the same manner as in Example 1 above to produce pencil leads. As in Example 1 above, the amount of impregnation in each lead is indicated in Table 1 below by weight measurement. The ingredients used in Table 1 were from the following products, etc. Paraffin wax (Paraffin wax 150F, manufactured by Nippon Seiro Co., Ltd.) Terpene phenol resin A (YS Polystar T30, manufactured by Yasuhara Chemical Co., Ltd.) Terpene phenol resin B (YS Polystar T115, manufactured by Yasuhara Chemical Co., Ltd.) Terpene phenol resin C (YS Polystar T160, manufactured by Yasuhara Chemical Co., Ltd.) Terpene phenol resin D (YS Polystar T80, manufactured by Yasuhara Chemical Co., Ltd.) Rosin ester resin (ester gum HP, manufactured by Arakawa Chemical Co., Ltd.) Polybutene (Polybutene SV7000, manufactured by ENEOS Corporation) Dimethyl silicone oil (KF96-30cs, manufactured by Shin-Etsu Chemical Co., Ltd.) Laurylamine (Amine BB, manufactured by NOF Corporation) Myristylamine (Amine MB, manufactured by NOF Corporation)

[0044] (Example 9: Pencil lead) A black porous fired core (fired pencil core) was prepared using the following method. 70 parts by mass of flaky natural graphite Natural clay powder 30 parts by mass Sodium polycarboxylate 4 parts by mass Grafted starch 4 parts by mass Water (purified water) 20 parts by mass The above materials were mixed and dispersed in a Henschel mixer (mixing and dispersion time 30 minutes, the same applies hereafter), molded, dried, and then fired in a nitrogen (N2) atmosphere at 1000°C for 10 hours to produce a fired pencil lead (pencil lead) with a diameter of 2.0 mm and a length of 180 mm. Next, the fired pencil lead was immersed in 100% by mass of urushirou (manufactured by Cerarica NODA Co., Ltd.) and impregnated at 150°C for 24 hours to produce a pencil lead. By weight measurement, it was confirmed that the amount of impregnation in the lead was 16.1% by mass relative to the weight of the lead.

[0045] (Examples 10-15 and Comparative Examples 4-6) The fired pencil lead obtained in Example 9 above was immersed in a mixture of wax + tackifying resin + liquid oil at room temperature, as shown in Table 2 below, and impregnated in the same manner as in Example 9 above to produce pencil lead. As in Example 9 above, the amount of impregnation in each lead was measured by weight and is shown in Table 2 below. The ingredients used in Table 2 were obtained from the following products, etc. Note that those listed in Table 1 are omitted. Glyceryl stearate (NIKKOL MGS-F50SEV, manufactured by Nikko Chemical Co., Ltd.) Hardened palm oil (extremely hardened palm oil, manufactured by Yokozeki Oil Co., Ltd.) Jojoba oil (NIKKOL Jojoba Oil S, manufactured by Nikko Chemicals Co., Ltd.) Ketone resin (Ketone resin K-90, manufactured by Arakawa Chemical Co., Ltd.) Petroleum resin (Petrotac 100V, manufactured by Tosoh Corporation) Carnauba wax (Carnauba wax #2, manufactured by Kato Yoko Co., Ltd.)

[0046] For each pencil lead (mechanical pencil lead, pencil lead) obtained in Examples 1-8, Examples 9-15, Comparative Examples 1-3, and Comparative Examples 4-6, the density of the writing line, abrasion, abrasion density, staining properties, abrasion density / abrasion, tackiness, and viscosity at 50°C were evaluated using the following evaluation methods. These results are shown in Tables 1 and 2 below.

[0047] (Method for evaluating the density of handwritten lines) The mechanical pencil leads of Examples 1-8 and Comparative Examples 1-3 were loaded into a Mitsubishi Pencil Co., Ltd. mechanical pencil (M5-450 1P), and the lines drawn by the pencil leads were measured using a densitometer (Konica Minolta DENSITOMETER PDA65) in a density test specified in JIS S 6005:2019. The leads were then evaluated according to the following evaluation criteria (average value, n=10). Furthermore, the pencil leads of Examples 9-15 and Comparative Examples 4-6 were evaluated using a densitometer (Konica Minolta DENSITOMETER PDA65) to measure the lines drawn by the pencil leads in a density test specified in JIS S 6006:2020, and were evaluated according to the following evaluation criteria (average value, n=10). Evaluation criteria: ○: Similar hardness △: Thin, about half-hard ×: 1 or more in hardness, too thin

[0048] (Method for evaluating wear) The lead of the mechanical pencils in Examples 1-8 and Comparative Examples 1-3 was loaded into a Mitsubishi Pencil Co., Ltd. mechanical pencil (M5-450 1P), and the length of the lead wear was measured when writing at a writing angle of 75°, with a load of 300gf, and a writing distance of 5m (average value, n=10). In addition, the lead of the pencils in Examples 9-15 and Comparative Examples 4-6 was sharpened into a cone shape at an angle of 17°, and the tip diameter of the pencil shaft was made into a 0.6mm cone shape. The length of the lead wear was measured when writing at a writing angle of 75°, with a load of 300gf, and a writing distance of 6m (average value, n=10).

[0049] [Method for evaluating the adhesion (staining) concentration through scrubbing] For the mechanical pencil leads of Examples 1-8 and Comparative Examples 1-3, the lines drawn with the pencil lead were subjected to a density test as specified in JIS S 6005:2019. For the pencil leads of Examples 9-15 and Comparative Examples 4-6, the lines drawn with the pencil lead were subjected to a density test as specified in JIS S 6006:2020. The pencil leads were rubbed back and forth four times with a felt pad under a vertical load of 500g, so as to extend beyond the line. The area where the staining spread was measured using a densitometer (Konica Minolta, DENSITOMETER PDA65), and evaluated according to the following evaluation criteria (average value, n=10). Evaluation criteria: ◎: 1 hardness or higher, stain resistant ○: Approximately 1 hardness, stain-resistant △: Stain-resistant due to its semi-hardness ×: Same hardness level

[0050] (Calculation of abrasion concentration / wear) The values ​​for abrasion concentration and wear obtained above were used for the calculation.

[0051] (Method for evaluating adhesiveness) Using the tacking tester "TAC1000" manufactured by Reska, after pushing in at a probe temperature of 40°C and a load of 500 g for 5 seconds and then pulling up, the integrated value of the adhesive force was measured (average value, n = 10) for evaluation.

[0052] (Evaluation method for viscosity @ 50°C) Using the rheometer "MCR102" manufactured by Anton Paar, at a plate temperature of 50°C and a shear rate of 100 s -1 viscosity @ 50°C (mPas: average value, n = 10) was measured.

[0053]

Table 1

[0054]

Table 2

[0055] As is clear from the results of Table 1 and Table 2 above, the mechanical pencil leads of Examples 1 to 8 and the pencil leads of Examples 9 to 15 within the scope of the present invention can highly achieve both an improvement in the density of the writing stroke and an improvement in the fixing property, have good viscosity, and are found to be pencil leads that are difficult to get dirty on the hand while writing, as compared with Comparative Examples 1 to 3 and Comparative Examples 4 to 6 outside the scope of the present invention.

Industrial Applicability

[0056] The pencil lead of the present invention can be suitably used for wooden shaft pencil leads, mechanical pencils, etc.

Claims

1. A porous, black, fired pencil lead containing graphite, characterized by being impregnated with an oily composition that is solid at room temperature (25°C), comprising 50% by mass or more of a wax selected from group A below, having an adhesiveness of 10 gf or more, a viscosity at 50°C of 40 to 200 mPa·s, and a melting point of 45 to 80°C, and 10% by mass or more of a tackifying resin selected from group B below. Group A: Glycerin fatty acid ester, Japanese lacquer tree, Japanese lacquer tree, Japanese wax tree Group B: Terpene phenol resins, rosin ester resins, ketone resins, petroleum resins, polybutene

2. Furthermore, the porous black fired pencil lead containing graphite according to claim 1 is characterized by containing an oil that is liquid at room temperature, selected from group C below. Group C: Jojoba oil, ester oil, higher alcohol, liquid paraffin

3. The porous black fired pencil lead containing graphite according to claim 1 or 2, characterized in that the wax selected from group A is a glycerin fatty acid ester.

4. A porous black calcined pencil lead containing graphite according to claim 1 or 2, characterized in that the wax having a melting point of 45 to 80°C and an adhesiveness of 10 gf or more, and a viscosity of 40 to 200 mPa·s at 50°C, or the oily composition that is solid at room temperature, has an adhesiveness of 40 gf or more.

5. A porous black fired pencil lead containing graphite, as described in any one of items 1 to 4, characterized in that the amount of wear when writing by the method of JIS S 6006:2020 is 2.0 mm / 6 m or more, and the fouling ability, as defined by the concentration of the area where the fouling spreads when the written line is rubbed back and forth four times with a felt with a vertical load of 500 g so as to extend beyond the line, is 0.60 or less.

6. The porous black fired pencil lead containing graphite according to claim 5, characterized in that the ratio of the aforementioned staining rate to the aforementioned wear rate is 0.025 or less.

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