Pencil lead and pencil

Abstract

To provide a pencil lead in which both smooth writing and resistance to breakage are achieved.SOLUTION: Provided is a pencil lead in which the tip strength / lead bending strength is 0.6 or more and 1.5 or less and the writing resistance value is 65 N or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pencil lead and a pencil. [Background technology]

[0002] The pencil lead used in pencils is manufactured by mixing and kneading graphite with a binder such as resin, molding the mixture, and firing it to form a fired body, and then impregnating the pores in the fired body with oil, wax, or the like as needed. Required properties of pencil leads include smooth writing and resistance to breakage. However, smooth writing and resistance to breakage are mutually exclusive properties, and various methods have been investigated to find a favorable correlation between them (see, for example, Patent Document 1 and Patent Document 2).

[0003] Patent Document 1 discloses a baked pencil lead in which the crystallite size Lc of the graphite contained therein is 15 to 60 nm. Patent Document 2 discloses a baked pencil lead in which the size Lc of the graphite crystallite in the c-axis direction, the size La of the graphite crystallite in the a-axis direction, and the ratio between these are within specific ranges. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-127055 A [Patent Document 2] JP 2017-222787 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, with conventional techniques, there is still room for further improvement in achieving both smooth writing and resistance to breakage.

[0006] An object of the present invention is to provide a pencil lead and a pencil that can improve the smoothness of writing and the resistance to breakage. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides "1. A pencil lead that is clamped by a wooden shaft and configured as a pencil, Tip strength / core bending strength is 0.6 8 That's it. 0 5 or less, The writing resistance is 65N or less. the law of nature , The pore diameter is 0.005 μm or more and 0.05 μm or less, The porosity is 10% or more and 30% or less, The core bending strength is 116 MPa or more and 188 MPa or less, The tip strength is the strength of the pencil lead having a truncated cone shape with an angle of 13±1° at the tip in the extension direction and a tip diameter of 0.35 mm, The tip strength is 121.4 MPa or more and 127.5 MPa or less, The diameter is 2 mm, Pencil lead. 2. Contains graphite, The crystallite size of the graphite in the c-axis direction is 25.3 nm or more 31.2 nm or less, 2. The pencil lead according to claim 1. 3 .Section 1 or No. In item 2 Pencil lead as described a wooden shaft portion that holds the pencil lead; "A pencil equipped with..." [Effects of the Invention]

[0008] The present invention can achieve both smooth writing and resistance to breakage. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an example of a pencil according to this embodiment. [Figure 2] FIG. 2 is a schematic diagram of an example of a cross section perpendicular to the drawing direction of a pencil. [Figure 3] FIG. 3 is a schematic diagram showing an example of a pencil in a state where one end in the extension direction is sharpened. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE INVENTION In the present specification, the terms "parts", "%", "ratio" and the like indicating the composition are based on mass unless otherwise specified.

[0011] (pencil lead) The pencil lead of this embodiment has a tip strength / lead bending strength of 0.6 or more and 1.5 or less, and a writing resistance of 65 N or less.

[0012] The pencil lead of this embodiment has tip strength / lead bending strength and writing resistance that satisfy the specific ranges described above. Therefore, the pencil lead of this embodiment can achieve both smooth writing and resistance to breakage, which are contradictory properties.

[0013] Furthermore, the pencil lead of this embodiment is able to achieve both smooth writing and resistance to breakage, which are characteristics required of a pencil lead. Therefore, it is possible to provide users who use pencils for long periods of time for reasons such as occupation or hobby with a pencil lead and pencil that is resistant to breakage, smooth writing, and reduces fatigue, thereby effectively reducing stress associated with writing.

[0014] This will be explained in detail below.

[0015] (Tip strength / lead bending strength and writing resistance) The tip strength / lead bending strength of the pencil lead of this embodiment is 0.6 or more and 1.5 or less.

[0016] The tip strength / lead bending strength of the pencil lead of this embodiment is in the range of 0.6 to 1.5, with the lower limit of this range preferably being 0.65 or more, more preferably 0.70 or more, even more preferably 0.75 or more, and particularly preferably 0.80 or more. The upper limit of the above range of tip strength / lead bending strength of the pencil lead of this embodiment is preferably 1.4 or less, more preferably 1.3 or less, and even more preferably 1.2 or less.

[0017] The tip strength of a pencil lead refers to the strength of the tip, which is one end of the pencil lead in the extension direction. The tip strength of a pencil lead is measured under the following conditions.

[0018] Using a pencil sharpener, one end of the pencil lead in the extension direction is sharpened into a cone shape with an angle of 13±1°, resulting in a truncated cone-shaped tip with a tip diameter of 0.35 mm. The pencil lead with the truncated cone-shaped tip is then fixed with a jig at an angle of 60° with the surface of a piece of paper placed on a horizontal surface. The pencil lead is then moved with a vertical force applied at a speed of 10 mm per minute, and the normal force value at the time of breakage is measured. This measurement is performed on five pencil leads with similar truncated cone-shaped tips, and the average normal force value at the time of breakage is calculated as strength F (kgf). Furthermore, the tip strength I (MPa) can be calculated from the obtained strength F (kgf) using the following formula (α):

[0019] I=(F×9.81) / A formula (α)

[0020] In formula (α), I represents the tip strength (Mpa). F represents the strength F (kgf). A represents the tip area of ​​the pencil lead. The tip area of ​​the pencil lead is calculated by 0.175 mm x 0.175 mm x 3.14.

[0021] The lead bending strength is measured using the method specified in JIS S6006:2020, with a fulcrum distance of 40 mm, and the average bending strength value measured for 10 pencil leads is calculated as the lead bending strength.

[0022] Writing resistance is measured by measuring the horizontal resistance when writing using the method specified in JIS S6006:2020, and the average resistance from 1 second onwards, excluding the period less than 1 second from the start of writing, can be calculated as the writing resistance value for one line.

[0023] By setting the tip strength / lead bending strength and writing resistance of the pencil lead within the above ranges, it is believed that it is possible to achieve both smooth writing and resistance to breaking. Furthermore, the pencil lead of this embodiment, which has the tip strength / lead bending strength and writing resistance within the above ranges, is not only resistant to breaking when writing, but also resistant to breaking when sharpening the tip, and tends to be able to sharpen the tip to a sharper angle. For this reason, the pencil lead of this embodiment is also preferred by users who want to use pencils as sharp as possible for professional or hobby reasons.

[0024] (graphite) The pencil lead of this embodiment contains graphite.

[0025] The size Lc of the graphite crystallites in the c-axis direction contained in the pencil lead of this embodiment is preferably 15 nm or more and 40 nm or less, and more preferably 20 nm or more and 35 nm or less.

[0026] There are no particular limitations on the size La of the graphite crystallite in the a-axis direction. For example, the size La of the graphite crystallite is preferably 50 nm or more and 75 nm or less, and more preferably 55 nm or more and 70 nm or less.

[0027] The graphite contained in the pencil lead of this embodiment preferably has a crystallite size La (nm) in the a-axis direction and size Lc (nm) in the c-axis direction that satisfy the following formula (1), more preferably the following formula (2), and particularly preferably the following formula (3):

[0028] 2La+3Lc≦280 ···Formula (1) 100≦2La+3Lc ···Formula (2) 100≦2La+3Lc≦260 ···Formula (3)

[0029] The size La represents the width (nm) of the graphite crystallite in the a-axis direction. The size Lc represents the thickness (nm) of the graphite crystallite in the c-axis direction. Both the size La and the size Lc are volume-weighted average sizes.

[0030] The graphite crystallite size La and size Lc can be calculated as follows. First, based on an XRD profile measured using an X-ray diffractometer, the half-width of the diffraction line corresponding to the (110) plane for size La and the half-width of the diffraction line corresponding to the (002) plane for size Lc are calculated. Then, from these calculated diffraction lines and half-widths, the size La and size Lc can be calculated using the following Scherrer formula (A).

[0031] Scherrer's formula: L = Kλ / βcosθ Equation (A)

[0032] In formula (A), L, K, λ, and β each represent the following.

[0033] L: Crystallite size [nm] K: Scherrer constant (apply K=1) λ: X-ray wavelength [nm] β: Half-width (diffraction line width at an intensity equivalent to 50% of the peak intensity) θ: X-ray irradiation angle (radian)

[0034] (Porosity and pore size) Although the detailed manufacturing method will be described later, the pencil lead of this embodiment is manufactured by a manufacturing process that includes a baking step. Therefore, the pencil lead of this embodiment has pores. The pores are sometimes called pores.

[0035] The porosity of the pencil lead of this embodiment is preferably 10% or more and 30% or less, and more preferably 20% or more and 30% or less.

[0036] The porosity is the percentage of the volume of pores in the external volume of the pencil lead, assuming that the external volume is 1. The porosity can be determined, for example, by measurements in accordance with JIS R1634:1998 or by measurements using a pore distribution measuring device.

[0037] The pore diameter of the pencil lead of this embodiment is preferably 0.005 μm or more and 0.05 μm or less, more preferably 0.01 μm or more and 0.03 μm or less, and particularly preferably 0.01 μm or more and 0.026 μm or less.

[0038] The pore size can be measured using a mercury intrusion porosimetry device with an initial pressure of 7 kPa and mercury parameters of 130 degrees mercury contact angle and 485 dyns / cm mercury surface tension, and the mode diameter (most frequent value) can be determined as the pore size.

[0039] Porosity and pore size are factors that affect the strength of a pencil lead. By setting at least one of the porosity and pore size of the pencil lead of this embodiment within the above range, it is possible to further improve bending strength. Furthermore, by setting at least one of the porosity and pore size of the pencil lead within the above range, it is thought that the oily substance that is impregnated into the baked body during the manufacture of the pencil lead can be more easily impregnated, further improving the smoothness of writing.

[0040] It is also presumed that by adjusting the porosity and pore size of the pencil lead within the above ranges, the tip strength / bending strength and writing resistance can be adjusted to fall within the above ranges of this embodiment.

[0041] (R value) The pencil lead of this embodiment preferably has an R value of 0.15 or more and 0.55 or less, as measured by Raman spectroscopy. Furthermore, it is even more preferable that the R value of the pencil lead of this embodiment is within the above range, and that the size La (nm) of the graphite in the a-axis direction and the size Lc (nm) of the graphite in the c-axis direction satisfy the above formula (1).

[0042] Raman spectroscopy, as defined in JIS K 0137:2010, is a method for analyzing the molecular-level structure of a substance from the Raman spectrum obtained by dispersing the Raman scattered light that occurs when a substance is irradiated with light.

[0043] When carbon materials are measured by Raman spectroscopy, the D band peak appears at 1360 cm when the symmetry is disturbed by the introduction of defects. -1 The G band peak due to the graphite structure is observed around 1580 cm -1 That is, the D band (1360 cm-1 ) peak indicates the presence of amorphous carbon or amorphous carbon contained in the pencil lead, and the G band (1580 cm -1 ) peak indicates the presence of crystalline graphite.

[0044] The R value is 1580 cm -1 The G-band peak intensity (I G ) and 1360cm -1 The peak intensity of the D band near D ) and the ratio (I D / I G ) The R value is sometimes called the Raman R value. The R value is inversely proportional to the crystallite size determined by X-ray diffraction, with a smaller R value indicating higher crystallinity and a larger R value indicating lower crystallinity.

[0045] The pencil lead of this embodiment preferably has an R value measured by Raman spectroscopy of 0.15 or more and 0.55 or less, and more preferably 0.20 or more and 0.50 or less.

[0046] The measurement conditions for Raman spectroscopy are not particularly limited as long as a Raman spectrum can be obtained by measuring the pencil lead of this embodiment, and a Raman spectrometer equipped with a laser light source, a spectrometer, and a detector can be used. For example, the Raman shift by laser Raman spectroscopy can be measured under the following conditions. Note that measurement may also be performed using a microscopic laser Raman spectrometer equipped with a microscope.

[0047] For example, the Raman shift can be determined using a microscopic laser Raman spectrometer under the following measurement conditions.

[0048] -Measurement conditions- Laser wavelength: 532[nm] Laser output: 10mW Objective lens: 10x Exposure time: 10 seconds Number of times accumulated: 2 times ·Number of marking lines: 1200[gr / mm] Slit width: 100 μm Filter: Unused Detector: CCD (Charge-Coupled Device) semiconductor element

[0049] It is estimated that if the R value measured by Raman spectroscopy falls within the specific range described above and the graphite size La (nm) and size Lc (nm) satisfy the above formula (1), further improvements in bending strength and smooth writing feel can be achieved.

[0050] (writing density and hardness) The hardness and writing density of the pencil lead of this embodiment are not limited.

[0051] Pencil leads used in pencils come in various hardnesses. The hardness of pencil leads is expressed by hardness symbols such as HB. In the JIS standard, a pencil lead with a writing density D of 0.25 to 0.45 measured according to the method specified in JIS S 6006:2020 or JIS S 6005:2019 is defined as having a hardness of HB. The writing density D and hardness of the pencil lead of this embodiment are not limited to a writing density D of 0.25 to 0.45 and a hardness of HB.

[0052] The pencil lead of this embodiment may have any writing density D and hardness specified by the JIS standard, as long as the tip strength / lead bending strength is 0.6 or more and 1.5 or less and the writing resistance is 65 N or less.

[0053] The writing density D is measured according to the method specified in JIS S 6006:2020 or JIS S 6005:2019. The Kent paper used is manufactured by Oji Paper Co., Ltd. and has a basis weight of 126 g / m. 2 , Thickness: 0.150mm, Density: 0.85g / cm 3 , one having quality characteristics of the ratios of surface roughness: 81a, smoothness: 81S, sizing: 110S, whiteness: 99.4%, and opacity: 92.7% is used.

[0054] (Pencil lead manufacturing method) An example of a method for manufacturing a pencil lead according to this embodiment will be described. Note that the method for manufacturing a pencil lead broadly encompasses all embodiments that incorporate the specific features of the invention, and should not be construed as being limited to the embodiment described below.

[0055] Pencil leads are produced by mixing and kneading raw materials containing graphite and a binder such as resin, extruding the mixture to form a compact, and then firing the compact to form a fired body. The pores in the fired body are then impregnated with oily substances such as oil or wax as necessary.

[0056] The pencil lead of this embodiment can also be manufactured by any method similar to this manufacturing method. For example, the manufacturing method of the pencil lead of this embodiment includes a mixing step, a preforming step, a crushing step, an extrusion molding step, a baking step, and an oil immersion step.

[0057] (1)Mixing process First, the raw materials are blended, mixed, and kneaded. The raw materials include graphite and a binder.

[0058] It is preferable to use graphite with a small crystallite size rather than one with a large crystallite size, but since graphite with a small crystallite size is difficult to obtain and the size varies depending on the crushing or pulverization process in the manufacturing process, the size of the graphite is not necessarily limited.

[0059] Any conventionally known binder can be used. Typical binders include various resins. Examples of resins that can be used include water-soluble resins, thermoplastic resins, and thermosetting resins, but pitch-like substances such as coal tar and asphalt can also be used. Furthermore, solvents and plasticizers can also be blended as raw materials.

[0060] These ingredients are blended to form a raw material blend, and after primary mixing as necessary, further mixing and kneading are carried out. A Henschel mixer, kneader, three-roller mixer, etc. can be used for mixing and kneading. Here, any kneader can be selected, such as a pressure kneader, ordinary kneader, or continuous kneader.

[0061] (2) Preforming process In the preforming step, the mixture obtained in the mixing step is further mixed and preformed into thin wires using an extruder or the like. By performing such preforming and the subsequent grinding step, in other words, by mixing and forming the raw material mixture and grinding it twice or more times, it becomes easier to produce pencil leads containing smaller crystallites.

[0062] However, rather than simply mixing, molding, and grinding the materials two or more times, it is possible to efficiently manufacture pencil leads with superior properties by adjusting the various conditions and optimizing the raw materials.

[0063] For example, the density of the pencil lead can be improved by adjusting the pressure during preforming to increase the adhesion between the graphite particles and the binder in the mixture, or by adjusting the drawing ratio during preforming into a thin wire. Here, the drawing ratio refers to the ratio of the diameter of the material inlet and the diameter of the compact extrusion part of the extruder.

[0064] (3) Crushing process In the pulverization step, the thin linear compact obtained in the preforming step is pulverized. The particle size after pulverization is not particularly limited, but may be D 50 The particle size is preferably 10 μm or more and 500 μm or less, and more preferably 50 μm or more and 400 μm or less. Small particles are preferable to facilitate the formation of a fine, dense structure. Furthermore, to prevent particles from scattering after pulverization, to facilitate handling, and to shorten the pulverization time, it is preferable that the particles are somewhat large.

[0065] The size and distribution of the crushed particles can be measured using a particle size distribution analyzer based on the laser diffraction and scattering method, as described above. As described above, the particle size is measured using the so-called D 50 (Median diameter measured on a volume basis) Particle size distribution can be measured by either a dry method or a wet method, but when measuring the size of relatively small particles, it is preferable to measure by the simpler dry method.

[0066] A general crusher can be used for crushing. Specifically, (i) examples of coarse crushers include jaw crushers, gyratory crushers, cone crushers, and impact crushers; (ii) examples of medium crushers include roll crushers, cutter mills, stamp mills, stone mills, and ring mills; and (iii) examples of fine crushers include roller mills, jet mills, hammer mills, and pin mills. These may be used alone or in combination.

[0067] (4) Extrusion molding process In the extrusion molding process, the kneaded material pulverized in the pulverization process is heated as necessary and extruded into thin wires. Any extruder can be used. The extrusion speed of the kneaded material during extrusion molding is, for example, 0.1 m / s or more and 15 m / s or less.

[0068] (5) Firing process In the firing step, the kneaded material extruded in the extrusion step is fired. The firing atmosphere preferably has a low oxygen content, and is carried out in a vacuum or inert gas atmosphere. The firing temperature is not particularly limited, but is preferably 800°C or higher and 1500°C or lower, and more preferably 1000°C or higher and 1400°C or lower.

[0069] (6) Oil immersion process The fired body obtained by the firing step contains pores. In the oil-impregnation step, these pores are impregnated with an oily substance. Any known oil component may be used as the oily substance. The oil-impregnation step can improve the writing feel, etc., when writing. The oil-impregnation method is not particularly limited, and can be carried out by any known method.

[0070] The pencil lead of this embodiment is manufactured through the above-described steps. Note that the above manufacturing method is one example, and the pencil lead of this embodiment can also be manufactured by other methods.

[0071] (pencil) The pencil lead of this embodiment is applicable to various writing instruments that use a pencil lead as a writing lead. For example, the pencil lead of this embodiment can be used as a writing lead for a pencil.

[0072] Fig. 1 is a schematic diagram of an example of a pencil 10 according to this embodiment. Fig. 2 is a schematic diagram of an example of a cross section perpendicular to the extension direction X of the pencil 10.

[0073] The pencil 10 includes a pencil lead 12 of this embodiment and a wooden shaft 14. The pencil lead 12 is sandwiched by the wooden shaft 14, which is long in the extension direction X of the pencil lead 12. The wooden shaft 14 is made of, for example, wood.

[0074] A paint layer 16 may be provided on the outer circumferential surface of the wooden shaft 14 of the pencil 10. The paint layer 16 is a layer that protects the outer circumferential surface of the wooden shaft 14.

[0075] The coating layer 16 is composed of three layers, for example, a base layer 16A, an intermediate coating layer 16B, and a surface layer 16C laminated in this order on the outer circumferential surface of the wooden shaft portion 14. The coating layer 16 may be composed of one layer, two layers, or four or more layers, and is not limited to a three-layer configuration.

[0076] The base layer 16A is a layer that compensates for the shortcomings of the wooden shaft portion 14 as a coating base and creates a smooth coating base surface. The base layer 16A is a layer made of, for example, a sealing agent. There are no particular restrictions on the sealing agent, and known sealers, water-based sealing agents, etc. can be used as appropriate.

[0077] The intermediate coating layer 16B is a layer that is further coated on the base layer 16A to make it even smoother. There are no limitations on the materials that make up the intermediate coating layer 16B. The surface layer 16C is a layer that is further coated on the surface of the intermediate coating layer 16B to make it smoother. Any known finishing paint can be used for the surface layer 16C. There are no particular limitations on the finishing paint, and for example, enamel paint, clear paint, etc. can be used as appropriate.

[0078] At least one layer constituting the coating layers 16 preferably has a color corresponding to the hardness of the pencil lead 12. In other words, at least one layer constituting the coating layers 16 preferably has a color corresponding to the hardness of the pencil lead 12. For example, a color corresponding to the hardness of the pencil lead 12 is set in advance. Then, at least one layer constituting the coating layers 16 may be set to a color according to the hardness of the pencil lead 12 held by the wooden shaft portion 14.

[0079] FIG. 2 shows an example in which the intermediate coating layer 16B is a layer having a color corresponding to the hardness of the pencil lead 12.

[0080] FIG. 3 is a schematic diagram showing an example of a state in which one end of the pencil 10 in the extension direction X has been sharpened using a pencil sharpener or the like. As shown in FIG. 3, when one end of the pencil 10 is sharpened using a pencil sharpener or the like, a portion of the intermediate coating layer 16B is exposed on the sharpening surface of the pencil 10. In other words, the intermediate coating layer 16B, which has a color corresponding to the pencil lead 12, becomes easily visible from the outside. Therefore, a user can easily identify the hardness of the pencil lead 12 of the pencil 10 by visually checking the color of the intermediate coating layer 16B on the sharpening surface.

[0081] Furthermore, for example, even if the surface layer 16C on which the hardness is indicated is scraped off, or the pencil 10 is placed in a pen stand or the like so that the hardness indication is hidden, the user can easily identify the hardness of the pencil lead 12 by visually checking the color of the intermediate layer 16B without relying on the hardness indication on the surface layer 16C. Therefore, in addition to the above effects, the pencil 10 of this embodiment can eliminate the inconvenience and hassle caused by having the hardness indication written on the surface layer 16C.

[0082] Returning to Figure 2, the explanation will continue. The shape of the cross section of the pencil 10 perpendicular to the extension direction X is not limited. Figures 1 to 3 show an example in which the cross section of the pencil 10 perpendicular to the extension direction X is hexagonal. However, the shape of the cross section of the pencil 10 perpendicular to the extension direction X may be either a circle or a polygon, and is not limited to a hexagon.

[0083] When the cross section of the pencil 10 perpendicular to the extension direction X has a polygonal shape, it is preferable that the vertices of each side constituting the polygon have rounded corners, that is, rounded corners.

[0084] When the shape of the cross section orthogonal to the extension direction X of the pencil 10 is polygonal, by making the vertices of each side of the polygon rounded, the pencil 10 can be made easy to grip and less tiring to use even when writing for a long time.

[0085] Furthermore, although there are no limitations on the thickness of the coating layer 16, it is preferable that the thickness be 0.05 mm or more, and more preferably 0.06 mm or more. By making the coating layer 16 have the above thickness, it is possible to make the writing surface smooth to the touch of the fingers.

[0086] (Pencil manufacturing method) An example of a method for manufacturing the pencil 10 of this embodiment will be described. Note that the method for manufacturing the pencil 10 broadly encompasses all embodiments that include the specific features of the invention, and should not be construed as being limited to the embodiment described below.

[0087] The pencil 10 is manufactured through, for example, a woodworking process, a painting process, a printing process, a cutting process, and the like.

[0088] (A) Woodworking process In the woodworking process, for example, a groove for the pencil lead 12 is formed in the center of two boards used as the wooden shaft 14, and the pencil lead 12 is placed in the groove, and the two boards are then glued together to obtain plywood. The plywood is then processed into a hexagonal cross section to obtain the wooden shaft 14 with the pencil lead 12 sandwiched between them.

[0089] (B) Painting process The painting process includes, for example, a surface preparation process, an undercoat process, and a finishing process.

[0090] In the priming process, the surface of the wooden shaft 14 manufactured in the woodworking process is painted with a filler or the like to form a base layer 16A on the wooden shaft 14. In the intermediate coating process, an intermediate coating layer 16B is formed on the base layer 16A. In the finishing process, a finishing paint is applied on the intermediate coating layer 16B to form a surface layer 16C on the intermediate coating layer 16B. The painting method in the painting process may be a known method such as an ironing method.

[0091] (C) Printing process In the printing process, characters or designs indicating the hardness of the pencil lead 12 are printed on the surface of the pencil 10 depending on the intended use of the pencil 10. Any known printing method may be used, such as hot stamp printing, dry offset printing, or thermal transfer printing.

[0092] (D) Small cutting process The cutting step is a step of cutting the end of the pencil 10 in the extension direction X to make it flat.

[0093] The pencil 10 of this embodiment is manufactured through these steps. Note that the manufacturing method described above is an example, and the pencil 10 of this embodiment can also be manufactured by other methods. Furthermore, various post-processing steps may be carried out as appropriate after the above steps. [Example]

[0094] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to the following examples.

[0095] Example 1 The pencil lead of Example 1 was manufactured by the following process.

[0096] -Raw material A1- Natural graphite 45 parts by weight Vinyl acetate resin 30 parts by weight Coal pitch 15 parts by mass Ethanol 20 parts by weight

[0097] The above-mentioned raw material A1 was prepared as a raw material. The above-mentioned raw material A1 was mixed using a Henschel mixer, and further mixed and kneaded again using a three-roll mill. Next, it was preformed into a thin wire using a single-screw extruder to obtain a thin wire-like molded body. The obtained molded body was pulverized using a pin mill to obtain a pulverized product. This pulverized product was then molded into a thin wire again using a single-screw extruder to obtain a desired dimension. The obtained molded body was heat-treated in air up to 250°C for 10 hours, and then further heat-treated at a maximum temperature of 1000°C in a non-oxidizing atmosphere, and cooled to obtain the sintered body of Example 1.

[0098] The obtained sintered body of Example 1 was impregnated with spindle oil by holding it at 100°C for 2 hours, and after removing excess oil from the surface of the sintered body, it was cut to a length of 180 mm to obtain the pencil lead of Example 1. The diameter of the obtained pencil lead of Example 1 was 2 mm, and the writing density D was 0.35.

[0099] The obtained pencil lead of Example 1 was sandwiched between two plates with grooves formed therein and processed into a hexagonal cross section to obtain a wooden shaft holding the pencil lead of Example 1. The obtained wooden shaft was then subjected to a painting process using a water-based filler, a paint for the intermediate coat, and an enamel paint, to obtain the pencil of Example 1.

[0100] Example 2 -Raw material A2- Natural graphite 45 parts by weight Vinyl acetate resin 15 parts by mass Vinyl chloride resin 20 parts by mass Coal pitch 10 parts by mass Methyl ethyl ketone 15 parts by mass Dioctyl phthalate 0.5 parts by mass

[0101] The pencil lead of Example 2 was obtained in the same manner as in Example 1, except that raw material A2 was used instead of raw material A1 of Example 1. The diameter of the pencil lead of Example 2 obtained was 2 mm, and the writing density D was 0.51. Furthermore, a pencil of Example 2 was obtained in the same manner as in Example 1 using the pencil lead of Example 2 obtained.

[0102] Example 3 -Raw material A3- Natural graphite 47 parts by weight Vinyl acetate resin 20 parts by weight Vinyl chloride resin 15 parts by mass Coal pitch 8 parts by weight Methyl ethyl ketone 10 parts by mass Ethanol 5 parts by mass Dioctyl phthalate 0.5 parts by mass

[0103] The pencil lead of Example 3 was obtained in the same manner as in Example 1, except that raw material A3 was used instead of raw material A1 of Example 1. The diameter of the pencil lead of Example 3 obtained was 2 mm, and the writing density D was 0.63. Furthermore, a pencil of Example 3 was obtained in the same manner as in Example 1 using the pencil lead of Example 3 obtained.

[0104] (Comparative Example 1) As Comparative Example 1, a pencil manufactured by Kutsuwa Corporation under the trade name of Hokusine and having a hardness of HB was prepared as a comparative pencil for Comparative Example 1.

[0105] (Comparative Example 2) As Comparative Example 2, a pencil manufactured by Kutsuwa Corporation under the trade name of Hokusine and having a hardness of 2B was prepared as a comparative pencil for Comparative Example 2.

[0106] (Comparative Example 3) As Comparative Example 3, a pencil manufactured by Mitsubishi Pencil Co., Ltd., trade name: Hi-Uni, hardness HB, was prepared as a comparative pencil for Comparative Example 3.

[0107] Comparative Example 4 As Comparative Example 4, a pencil manufactured by Mitsubishi Pencil Co., Ltd., trade name: Hi-Uni, hardness 2B, was prepared as a comparative pencil for Comparative Example 4.

[0108] (evaluation) The physical properties were evaluated for the pencils of Examples 1 to 3 and the comparative pencils of Comparative Examples 1 to 4. The results obtained are shown in Table 1. The evaluation conditions were as follows.

[0109] -Crystallite size Lc- The size Lc (nm) of the graphite contained in each of the sintered bodies of Examples 1 to 3 and the comparative sintered bodies of Comparative Examples 1 to 4 was measured. The measurement results are shown in Table 1.

[0110] The graphite crystallite size Lc was measured under the following measurement conditions.

[0111] Using an X-ray diffractometer (manufactured by Bruker AXS, product name: D8 ADVANCE), the size L of the graphite crystallites contained in each of the sintered bodies of Examples 1 to 3 and the comparative sintered bodies of Comparative Examples 1 to 4 was measured. c The (002 plane) was measured. One fired body or one comparative fired body was used for each measurement.

[0112] Although crushed powder is generally used for X-ray diffraction measurements, crushing was not performed in this evaluation to avoid shape changes. The measurement was performed using the parallel beam method with a Goebel mirror.

[0113] Size L c The measurement was carried out by irradiating the fired body and the comparative fired body with X-rays parallel to the extrusion axis direction, and scanning the azimuth angle 2θ in the range of 20° to 30°. a The measurement was carried out by irradiating the fired body and the comparative fired body with X-rays (CuKα rays) perpendicular to the direction of the extrusion axis, and scanning the azimuth angle 2θ in the range of 70° to 80°.

[0114] The background was removed (using a fifth-order Chebyshev polynomial) from the diffraction line near 26.4° corresponding to the (002) plane in the obtained XRD profile, and the X-ray absorption factor was corrected and profile fitting was performed. The crystallite size, Lc, was then calculated using the Scherrer equation expressed by equation (A) above. The fundamental parameter (FP) method was used for fitting and to calculate the crystallite size.

[0115] -Porosity, pore diameter- The pencil leads of Examples 1 to 3 and the comparative pencil leads provided in each of the comparative pencils of Comparative Examples 1 to 4 were subjected to heat treatment at 600°C in a baking furnace under a vacuum or inert gas atmosphere. Then, for each of the pencil leads of Examples 1 to 3 and the comparative pencil leads provided in each of the comparative pencils of Comparative Examples 1 to 4 after this heat treatment, the percentage of the volume of the pores in the pencil leads was determined, assuming the external volume to be 1. Specifically, the porosity was measured using a mercury intrusion AutoScan porosimeter (pore distribution measuring device AutoPore V 9620, manufactured by Meritics Corporation) to measure the pore diameter and the porosity, which is the pore volume ratio.

[0116] The pore size was measured using the above-mentioned pore size distribution analyzer at an initial pressure of 7 kPa, with the mercury parameters being a mercury contact angle of 130 degrees and a mercury surface tension of 485 dyns / cm, and the mode diameter (most frequent value) was determined as the pore size. The measurement results for porosity and pore size are shown in Table 1.

[0117] -Corner R- The corner radius of each vertex of the hexagonal cross section was measured for each of the pencils of Examples 1 to 3 and the comparative pencils of Comparative Examples 1 to 4. The measurement results are shown in Table 1.

[0118] -Tip strength / lead bending strength, writing resistance value- (tip strength) Using a pencil sharpener (ein cms110 / manufactured by CARL Office Machines) with fine sharpening specifications, one end of the pencil lead in the extension direction was sharpened into a cone shape with an angle of 13±1°, resulting in a truncated cone-shaped tip with a tip diameter of 0.35 mm. The pencil lead with the truncated cone-shaped tip was then fixed with a jig at an angle of 60° with the surface of a paper placed on a horizontal surface. The pencil lead was then moved with a vertical force applied at a speed of 10 mm per minute, and the normal force value at the time of breakage was measured. This measurement was then performed on five pencil leads with similar truncated cone-shaped tips, and the average normal force value at breakage was calculated as strength F (kgf). Furthermore, the tip strength (MPa) was calculated from the obtained strength F (kgf) using the above formula (α). The results are shown in Table 1.

[0119] The tip strength (Mpa) of each of the pencils of Examples 2 and 3 and the comparative pencils of Comparative Examples 1 to 4 was determined in the same manner as for the pencil of Example 1. The results are shown in Table 1.

[0120] (core bending strength) The lead bending strength (MPa) was determined by measuring the bending strength of 10 pencil leads in Example 1 using the method specified in JIS S 6006:2020 with a fulcrum distance of 40 mm. The results are shown in Table 1.

[0121] The lead bending strength (MPa) of each of the pencil leads of Examples 2 and 3 and the comparative pencil leads of Comparative Examples 1 to 4 was determined in the same manner as for the pencil lead of Example 1. The results are shown in Table 1.

[0122] (Tip strength (Mpa) / Core bending strength (MPa)) The tip strength (Mpa) / core bending strength (MPa) value was calculated from the tip strength (Mpa) and core bending strength (MPa) obtained above for each of Examples 1 to 3 and Comparative Examples 1 to 4. The calculation results are shown in Table 1.

[0123] -Writing resistance- The writing resistance of the pencil of Example 1 was measured by measuring the horizontal resistance when writing according to the method specified in JIS S 6006:2020, and the average value of the resistance from 1 second onwards, excluding periods less than 1 second from the start of writing, was calculated as the writing resistance value for one pencil. The writing resistance values ​​of each of the five pencils of Example 1 were then calculated by the same test, and the average value was taken as the writing resistance of the pencil of Example 1. The resulting writing resistances are shown in Table 1.

[0124] The writing resistance of each of the pencils of Examples 2 and 3 and the comparative pencils of Comparative Examples 1 to 4 was determined in the same manner as for the pencil of Example 1. The results are shown in Table 1.

[0125] -Writing density- The writing density was measured by measuring lines written according to the method specified in JIS S 6006:2020 using a densitometer (Sakura densitometer PDA65 (product name, Konishiroku Photo Industry Co., Ltd.)). The measurement results are shown in Table 1.

[0126] [Table 1]

[0127] As shown in Table 1, the pencil leads of Examples 1 to 3 had a tip strength / lead bending strength of 0.6 or more and 1.5 or less, and a writing resistance of 65 N or less. On the other hand, the comparative pencil leads of Comparative Examples 1 to 4 did not satisfy the above ranges for at least one of the tip strength / lead bending strength and the writing resistance. Therefore, it was confirmed that the pencil leads of Examples 1 to 3, compared to the comparative pencil leads of Comparative Examples 1 to 4, achieved both smoother writing and less breakage. [Industrial Applicability]

[0128] The pencil lead according to the present invention can be used as a writing lead for a pencil. [Explanation of symbols]

[0129] 10 pencils 12 pencil lead

Claims

1. A pencil lead that is clamped by a wooden shaft and configured as a pencil, The tip strength / core bending strength is 0.68 or more and 1.05 or less, The writing resistance is 65N or less, The pore diameter is 0.005 μm or more and 0.05 μm or less, The porosity is 10% or more and 30% or less, The core bending strength is 116 MPa or more and 188 MPa or less, The tip strength is the strength of the pencil lead having a truncated cone shape with an angle of 13±1° at the tip in the extension direction and a diameter of 0.35 mm at the tip, The tip strength is 121.4 MPa or more and 127.5 MPa or less, The diameter is 2 mm, Pencil lead.

2. Contains graphite, The crystallite size of the graphite in the c-axis direction is 25.3 nm or more and 31.2 nm or less. The pencil lead according to claim 1.

3. A pencil comprising the pencil lead according to claim 1 or 2 and a wooden shaft portion that holds the pencil lead.

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