Pencil lead and method for manufacturing the same, and pencil

Abstract

The present invention provides a pencil lead capable of achieving both bending strength and writing density even when graphite is used as the filler material, a method for manufacturing the same, and a pencil equipped with the pencil lead. [Solution] The pencil lead of the present invention has an apparent density (g / cm³). 3 The value obtained by dividing ) by the volume-average particle size (μm) is 0.040 (g / cm³). 3 It contains graphite particles that are spheroidal graphite or scaly graphite and are larger than or equal to ( / μm).

Description

[Technical Field]

[0001] This invention relates to pencil lead, a method for manufacturing the same, and pencils. [Background technology]

[0002] Generally, pencil lead (fired pencil lead) is manufactured by kneading a compound material mainly consisting of a filler material and a binder, extruding the kneaded material into a fine wire shape, heat-treating it to a firing temperature, and then impregnating the pores of the resulting fired lead body with oils and fats as needed.

[0003] Binding materials used include graphite, mica, talc, and boron nitride. Among these binding materials, graphite is suitable for drawing because it exhibits a black to steel-gray color and has high lubricity.

[0004] Pencil leads can be manufactured by selecting various lead diameters during extrusion molding to obtain a lead body of the desired diameter, and by changing the compounding materials or firing temperature to obtain a lead body of the desired hardness or writing density. However, generally, increasing the bending strength tends to result in a pencil lead that is less prone to wear during writing, possessing high bending strength but low writing density. Conversely, increasing the writing density tends to result in a lead body with low bending strength that is easily broken by the force applied during writing. Thus, there is a negative correlation between bending strength and writing density.

[0005] Therefore, various techniques have been proposed to achieve both bending strength and writing density. For example, Patent Document 1 proposes a pencil lead that uses both graphite and synthetic fluorphlogopite. Patent Document 2 also proposes a pencil lead that uses both graphite and inorganic plate-like particles (such as plate-like alumina) that have an aspect ratio of 5 or more and a particle size of 1 μm or more and contain oxygen atoms. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-81715 [Patent Document 2] Japanese Patent Publication No. 2015-10157 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the conventional technologies described in Patent Documents 1 and 2, etc., aim to achieve both bending strength and writing density by using graphite in combination with other binders, and binders other than graphite were considered essential.

[0008] Therefore, the object of the present invention is to provide a pencil lead that can achieve both bending strength and writing density even when graphite is used as the filler material, a method for manufacturing the same, and a pencil equipped with the pencil lead. [Means for solving the problem]

[0009] The following embodiments are specific means for solving the above problems. <1> Apparent density (g / cm 3 The value obtained by dividing ) by the volume-average particle size (μm) is 0.040 (g / cm³). 3 A pencil lead containing graphite particles that are larger than or equal to ( / μm) and are spheroidal graphite or scaly graphite. <2> The volume-average particle size of the graphite particles is 1 to 15 μm. <1> The pencil lead described. <3> The graphite particle content is 10 to 90% by mass. <1> or <2> The pencil lead described. <4> Apparent density (g / cm 3 The value obtained by dividing ) by the volume-average particle size (μm) is 0.040 (g / cm³). 3 A method for manufacturing pencil lead, comprising kneading a compound material containing graphite particles that are spheroidal graphite or scaly graphite and have a diameter of 1 / μm or more, and a binder, molding the mixture, and then firing it. <5> <1> ~ <3> A pencil having the lead described in any one of the items. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a pencil lead capable of achieving both bending strength and writing density even when only graphite is used as a filler material, a method for manufacturing the same, and a pencil provided with the pencil lead.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, specific embodiments to which the present invention is applied will be described in detail. In this specification, the notation "x to y" using numerical values x and y means "x or more and y or less" unless otherwise specified. When a unit is attached only to the numerical value y in such notation, the unit is also applied to the numerical value x.

[0012] <Pencil Lead> The pencil lead according to this embodiment has, as a filler material, a value obtained by dividing the apparent density (g / cm 3 ) by the volume average particle diameter (μm) of 0.040 (g / cm 3 / μm) or more, and includes graphite particles that are spherical graphite or flaky graphite (hereinafter also referred to as "specific graphite particles").

[0013] Generally, as types of graphite used in pencil leads, flaky (lumpy) graphite (vein graphite), amorphous graphite, etc. are known. Among flaky graphite, those with a relatively thin thickness are also referred to as flake graphite. In addition to the above, as types of graphite, there are expandable graphite, spherical graphite, etc., which are mainly obtained by processing flake graphite. As a result of the inventors' study on various graphite particles, it has been found that when using graphite particles that are spherical graphite or flaky graphite and have a value obtained by dividing the apparent density (g / cm 3 ) by the volume average particle diameter (μm) of 0.040 (g / cm 3 / μm) or more, it is possible to achieve both bending strength and writing density.

[0014] Note that the specific graphite particles have an apparent density (g / cm 3The value obtained by dividing 3 it by the volume average particle diameter (μm) is 0.040 (g / cm

[0015] / μm) or more, and as long as it has the same properties as spherical graphite or flaky graphite, so-called artificial graphite particles may be used.

[0016] The apparent density (g / cm 3 ) of the specific graphite particles divided by the volume average particle diameter (μm) is preferably 0.040 to 0.090 g / cm 3 / μm, more preferably 0.043 to 0.085 g / cm 3 / μm, and even more preferably 0.047 to 0.080 g / cm 3 / μm.

[0017] The apparent density of the specific graphite particles is preferably 0.240 to 0.800 g / cm 3 more preferably 0.​​​​​​​​​​​​​​​In this specification, the median diameter (D50) measured using a laser diffraction particle size distribution analyzer (SALD-2200, manufactured by Shimadzu Corporation) shall be used as the volume-average particle size of graphite particles.

[0021] The content of specific graphite particles is preferably 10-90% by mass, more preferably 20-80% by mass, and even more preferably 30-70% by mass, depending on the hardness of the pencil lead. By setting the content of specific graphite particles within the above range, a good balance between bending strength and writing density tends to be achieved.

[0022] The pencil lead according to this embodiment may contain binders other than specified graphite particles. However, the proportion of specified graphite particles in the total binder is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass (i.e., it does not contain binders other than specified graphite particles).

[0023] The pencil lead according to this embodiment includes, in addition to the filler material, a fired product of a binder, which will be described later. The content of the fired binder is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and even more preferably 30 to 70% by mass. By setting the content of the fired binder within the above range, a good balance between bending strength and writing density tends to be achieved.

[0024] Furthermore, the pencil lead according to this embodiment may have oils and fats impregnated into the pores of the fired lead body. Examples of oils and fats include lard, vegetable oil, spindle oil, liquid paraffin, and silicone oil.

[0025] The pencil lead according to this embodiment can be used as a lead for wooden pencils or as a lead for mechanical pencils. When used as a lead for wooden pencils, the wooden pencil has a structure in which, for example, the pencil lead according to this embodiment is placed in the center of the wooden shaft.

[0026] <Manufacturing method for pencil lead> The pencil lead according to this embodiment can be manufactured, for example, by kneading a compound material containing specific graphite particles and a binder, molding it, and then firing it.

[0027] Examples of binders include clay minerals such as kaolinite, halloysite, bentonite, and montmorillonite; thermoplastic resins such as polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, acrylic acid ester-vinyl acetate copolymer, acrylic acid ester-vinyl chloride copolymer, and acrylic acid ester polymer; thermosetting resins such as furan resin; natural polymers such as carboxymethylcellulose, lignin, and tragacanth gum; synthetic polymers such as polyethylene glycol; and pitches such as coal tar pitch, naphtha decomposition pitch, petroleum asphalt, and synthetic resin carbonization pitch. A single binder may be used alone, or two or more may be used in combination.

[0028] The compounding materials may contain, from the viewpoint of improving dispersibility during kneading and improving fluidity or moldability during extrusion molding, water; plasticizers such as dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, dioctyl adipate, diallyl isophthalate, and propylene carbonate; solvents such as alcohols, ketones, and esters; stabilizers such as stearates, higher aliphatic hydrocarbons, and chlorinated higher fatty acid esters; and so on.

[0029] When manufacturing pencil lead, first, the above-mentioned blending materials are mixed and dispersed in a Henschel mixer or pressure kneader, kneaded with a three-roll machine, and then extruded into a fine wire of the desired diameter. Next, the molded body is heat-treated at 80-120°C, followed by thermal decomposition of the binder as needed, and then fired in an inert atmosphere at a high temperature of 900°C or higher, preferably 900-1300°C, to obtain a fired lead body.

[0030] The resulting sintered core can be used as a pencil lead as is, but it is preferable to impregnate the pores of the sintered core with oils and fats. This impregnation can be carried out by immersing the sintered core in oils and fats heated to 100-150°C and holding it for 2-8 hours. After impregnation, the sintered core can be removed, and any oils and fats adhering to the core surface can be removed using a centrifuge or the like. [Examples]

[0031] The present invention will be described more specifically below with reference to examples, but the present invention is not limited to these examples.

[0032] <Examples 1-5 and Comparative Examples 1-13> Examples 1-5 and Comparative Examples 1-13 used compound materials with the following compositions. Various types of graphite shown in Table 1: 66 parts by mass Clay: 34 parts by mass Carboxymethylcellulose: 2 parts by mass Polyethylene glycol: 3 parts by mass

[0033] The above-mentioned ingredients were placed in a Henschel mixer and stirred at high speed for 15 minutes. Next, 0.3 parts by mass of dispersant, 0.9 parts by mass of wetting agent, and 30 parts by mass of water were added and stirred for 10 minutes. After that, heat was applied and the mixture was stirred for 10 minutes, then stirred for 10 minutes while cooling to extract the granules. Next, the granules were rolled about four times to form a film, and the film was placed in a pre-molding machine and compressed to produce a pre-molded product. The pre-molded product was packed into the cylinder of the molding machine and extruded using a die with a hole diameter of 2.16 mm. The molded body was dried in a 110°C dryer for about 6 hours. The dried molded body was packed into a graphite crucible and fired under conditions of 900-1300°C for 1 hour in an inert atmosphere. After that, the fired core was impregnated with oils and fats (paraffin oil, etc.) to obtain a pencil lead with a length of 180 mm and a diameter of 2 mm.

[0034] The obtained pencil lead was then used to create a pencil shaft using pencil slats (shaft plates) made of incense cedar wood, resulting in a hexagonal pencil with a length of 175 mm and a shaft diameter of 8 mm.

[0035] <Rating> [Bending strength and writing density] The bending strength (MPa) and writing density of the pencil leads of each example and comparative example were measured in accordance with JIS S 6006:2020. The record method (Method A) was used to measure the writing density. The results are shown in Table 1.

[0036] [Writing resistance] For each example and comparative example pencil, the horizontal resistance force was measured using a load cell when writing according to the method specified in JIS S 6006:2020. The average resistance force (gf) from 1 second onward, excluding the period less than 1 second from the start of writing, was used as the writing resistance value for one pencil. The same test was then performed on each of the five pencils to determine their writing resistance values, and the average value was used as the writing resistance of each example and comparative example pencil. The results are shown in Table 1.

[0037] [Table 1]

[0038] As shown in Table 1, apparent density (g / cm³) 3 The value obtained by dividing ) by the volume-average particle size (μm) is 0.040 (g / cm³). 3 When graphite particles with a diameter of 1 / μm or more and that are spheroidal or scaly graphite are used, the value obtained by multiplying the bending strength (MPa) by the writing density is large, demonstrating that a balance between bending strength and writing density can be achieved.

Claims

1. Apparent density (g / cm ３ The value obtained by dividing ) by the volume-average particle size (μm) is 0.040 (g / cm³). ３ A pencil lead containing graphite particles that are spheroidal graphite or scaly graphite and are larger than or equal to ( / μm).

2. The pencil lead according to claim 1, wherein the volume-average particle size of the graphite particles is 1 to 15 μm.

3. The pencil lead according to claim 1, wherein the content of the graphite particles is 10 to 90% by mass.

4. Apparent density (g / cm ３ The value obtained by dividing ) by the volume-average particle size (μm) is 0.040 (g / cm³). ３ A method for manufacturing pencil lead, comprising kneading a compound material containing graphite particles that are spheroidal graphite or scaly graphite and have a diameter of 1 / μm or more, and a binder, molding the mixture, and then firing it.

5. A pencil comprising the pencil lead described in any one of claims 1 to 3.

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