Baking lead and manufacturing method of baking lead

Abstract

To provide a baked lead in which bending strength and writing smoothness are improved.SOLUTION: Provided is a baked lead in which graphite is contained, R value by Raman spectroscopy is 0.15 or more and 0.55 or less, and the size La (nm) in the a-axis direction and the size Lc (nm) in the c-axis direction of the graphite, which are determined by X-ray diffraction measurement, satisfy formula (1). 2La +3Lc≤280 -- Formula (1).SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Baked leads used in writing instruments such as pencils and mechanical pencils are manufactured by mixing and kneading graphite with a binder such as resin, molding the mixture, and baking it to form a baked body, and then impregnating the pores in the baked body with oil, wax, or the like as needed. Required properties of baked leads used in writing instruments include bending strength and smooth writing. However, bending strength and smooth writing are mutually exclusive properties, and various methods have been investigated to find a favorable correlation (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, in the prior art, there was room for further improvement in bending strength and smooth writing feel.

[0006] An object of the present invention is to provide a baking lead and a method for manufacturing the baking lead that can improve bending strength and smooth writing feel. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides "1. Contains graphite, The R value by Raman spectroscopy is 0.15 or more and 0.55 or less, 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 determined by X-ray diffraction measurement satisfy formula (1); 232≦ 2La+3Lc≦280 ···Formula (1) Baking core. 2. The size La (nm) in the a-axis direction and the size Lc (nm) in the c-axis direction of the graphite determined by X-ray diffraction measurement satisfy formula (2), 232≦2La+3Lc≦260 ···Formula (2) 1. The baking core described in paragraph 1. 3 The size Lc of the graphite in the c-axis direction is 15 nm or more and 40 nm or less. Section 1 or Section 2 The baking core described in . 4 By mixing, molding, crushing, and firing the raw material mixture at least twice, The graphite contains graphite, and the R value measured by Raman spectroscopy is 0.15 or more and 0.55 or less, and 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 determined by X-ray diffraction measurement satisfy formula (1). A method for manufacturing a baking lead, comprising: manufacturing a baking lead; 232≦2La+3Lc≦280 ···Formula (1) " [Effects of the Invention]

[0008] The present invention can improve bending strength and smooth writing feel. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] (baking core) The sintered lead of this embodiment contains graphite, has an R value by Raman spectroscopy of 0.15 or more and 0.55 or less, and 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 determined by X-ray diffraction measurement satisfy the following formula (1):

[0011] 2La+3Lc≦280 ···Formula (1)

[0012] The baked lead of this embodiment has an R value measured by Raman spectroscopy that satisfies the specific range described above, and the graphite size La (nm) and size Lc (nm) satisfy the specific relationship described above. Therefore, the baked lead of this embodiment can improve bending strength and smooth writing. This will be explained in detail below.

[0013] (R value) 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.

[0014] 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 firing lead, and the G band (1580 cm -1 ) peak indicates the presence of crystalline graphite.

[0015] 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.

[0016] The baking lead of this embodiment has an R value of 0.15 or more and 0.55 or less by Raman spectroscopy, and preferably has an R value of 0.20 or more and 0.50 or less.

[0017] The measurement conditions for Raman spectroscopy are not particularly limited as long as a Raman spectrum can be obtained by measuring the fired 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 the measurement may also be performed using a microscopic laser Raman spectrometer equipped with a microscope.

[0018] For example, the Raman shift can be determined using a microscopic laser Raman spectrometer under the following measurement conditions.

[0019] -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

[0020] (graphite) The graphite contained in the sintered lead of this embodiment has a crystallite size La (nm) in the a-axis direction and a crystallite size Lc (nm) in the c-axis direction that satisfy the relationship of the above formula (1), 2La + 3Lc ≦ 280. It is more preferable that the crystallite size La (nm) in the a-axis direction and a crystallite size Lc (nm) in the c-axis direction of the graphite contained in the sintered lead of this embodiment satisfy the following formula (2), and particularly preferable that they satisfy the following formula (3).

[0021] 100≦2La+3Lc ···Formula (2) 100≦2La+3Lc≦260 ···Formula (3)

[0022] 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.

[0023] 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).

[0024] Scherrer's formula: L = Kλ / βcosθ Equation (A)

[0025] In formula (A), L, K, λ, and β each represent the following.

[0026] 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)

[0027] The size La and size Lc of the graphite crystallites contained in the firing lead of this embodiment may each be within a range that satisfies the above formula (1), and can be adjusted appropriately.

[0028] Specifically, the graphite crystallite size Lc is preferably 15 nm or more and 40 nm or less, and more preferably 20 nm or more and 35 nm or less.

[0029] The graphite crystallite size La is preferably 50 nm or more and 75 nm or less, and more preferably 55 nm or more and 70 nm or less.

[0030] (Porosity and pore size) Although the detailed manufacturing method will be described later, the firing lead of this embodiment is manufactured by performing a manufacturing process including a firing step. Therefore, the firing lead of this embodiment has pores. The pores may also be called pores.

[0031] The porosity of the firing lead of this embodiment is preferably 10% or more and 30% or less, and more preferably 20% or more and 30% or less.

[0032] 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.

[0033] The pore size of the baking lead of this embodiment is preferably 0.005 μm or more and 0.1 μm or less, more preferably 0.01 μm or more and 0.1 μm or less, and particularly preferably 0.01 μm or more and 0.05 μm or less.

[0034] 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.

[0035] The porosity and pore size are factors that affect the strength of the burned lead. By setting at least one of the porosity and pore size of the burned lead of this embodiment within the above range, it is possible to further improve the bending strength. Furthermore, by setting at least one of the porosity and pore size of the burned lead within the above range, it is thought that the oily substance impregnated into the burned body during the manufacture of the burned lead can be more easily impregnated, further improving the smoothness of the writing experience.

[0036] (writing density and hardness) The hardness and writing density of the baked lead of this embodiment are not limited.

[0037] Baked leads used in writing implements such as pencils and mechanical pencils come in a variety of hardnesses. The hardness of leads used in writing implements is expressed, for example, by hardness symbols such as HB. In the JIS standard, a lead with a writing density D of 0.25 to 0.45 measured using the method specified in JIS S 6006:2020 or JIS S 6005:2019 is considered to have a hardness of HB. The writing density D and hardness of the baked lead of this embodiment are not limited to a writing density D of 0.25 to 0.45 and a hardness of HB.

[0038] The sintered lead of this embodiment may have any writing density D and hardness specified in the JIS standard, as long as the R value satisfies the above-mentioned specific range and the size La and size Lc of the contained graphite satisfy the above formula (1).

[0039] 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.

[0040] As described above, the baked lead of this embodiment contains graphite, has an R value of 0.15 or more and 0.55 or less by Raman spectroscopy, and 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 determined by X-ray diffraction measurement satisfy the above formula (1). The inventors have found that when the R value of the baked lead satisfies the above range and the size of the contained graphite satisfies the above formula (1), it is possible to improve bending strength and smooth writing feel.

[0041] The reason why the above-mentioned effect is exhibited is not clear, but is speculated as follows: However, the present invention is not limited to the speculation below.

[0042] The baked lead of this embodiment has an R-value in the range of 0.15 to 0.55, and is therefore presumed to achieve a smooth and pleasant writing experience. Furthermore, the size of the graphite contained in the baked lead of this embodiment satisfies the above formula (1), and is therefore presumed to achieve a good bending strength. Furthermore, since the baked lead of this embodiment has an R-value in the above-mentioned specific range, it is not necessary to make the size of the graphite contained smaller than necessary, and it is presumed that it can be made within the range of formula (1). Therefore, it is presumed that the baked lead of this embodiment can improve the smoothness of writing without compromising bending strength.

[0043] To improve the smoothness of writing, it is believed that using graphite powder with excellent lubricity and increasing its proportion is effective. However, graphite powder that does not have self-bonding properties does not contribute to strength, and increasing the content of graphite powder to improve the smoothness of writing does not provide the bending strength required for writing. For this reason, in the prior art, there was room for improvement in improving both bending strength and smoothness of writing, which are contradictory properties.

[0044] On the other hand, the baked lead of this embodiment has an R-value within the above range and the size of the contained graphite satisfies the relationship of the above formula (1), so it is presumed that both the bending strength and the smoothness of writing, which are contradictory properties, can be improved. Furthermore, in addition to the above effects, it is presumed that the baked lead of this embodiment can achieve various performance improvements required of a baked lead for a writing instrument, such as smoothness of writing and writing distance, without compromising bending strength and writing density.

[0045] (Manufacturing method of baking lead) An example of a method for manufacturing a firing lead according to the present embodiment will be described. Note that the method for manufacturing a firing 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.

[0046] The sintered lead is manufactured by mixing and kneading raw materials containing graphite and a binder such as resin, extruding the mixture into a molded body, then sintering the molded body to form a sintered body, and impregnating the pores of the sintered body with an oily substance such as oil or wax as necessary. The sintered lead of this embodiment can also be manufactured by any method similar to this manufacturing method.

[0047] In the method for producing a sintered lead of this embodiment, it is preferable to produce the sintered lead by performing each of the mixing, molding, pulverization, and firing of the raw material mixture two or more times. In detail, the method for producing a sintered lead of this embodiment includes a primary mixing and kneading step, a pre-firing step, a pre-pulverization step, a secondary mixing and kneading step, a pre-forming step, a re-pulverization step, an extrusion molding step, a firing step, and an oil immersion step.

[0048] (1) Primary mixing and kneading process In the primary mixing and kneading step, primary mixing and kneading are performed. Specifically, raw materials are first blended, and then mixed and kneaded. The raw materials include graphite and a binder.

[0049] 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.

[0050] 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.

[0051] Of these, only graphite and resin are blended to form a compound, which is then subjected to primary mixing and primary kneading. A Henschel mixer, kneader, three-roller mixer, etc. can be used for mixing and kneading. Any kneader can be selected, such as a pressure kneader, ordinary kneader, or continuous kneader.

[0052] (2) Pre-baking process In the pre-firing step, the primary mixture obtained in the primary mixing and kneading step is pre-fired. Specifically, in the pre-firing step, the primary mixture obtained in the primary mixing and kneading step is first coarsely pulverized to a pulverizable degree. The pulverized product obtained by the coarse pulverization is then subjected to a firing treatment (pre-firing). The firing treatment is carried out under vacuum or in an inert gas atmosphere. The firing temperature is not particularly limited, but a temperature in the range of 600°C to 800°C is sufficient. This firing treatment carbonizes the contained binder and impairs the lubricity of the graphite, making it easier to pulverize and finely pulverize.

[0053] (3) Pre-crushing process In the pre-pulverization step, the primary mixture pre-fired in the pre-firing step is finely pulverized (pre-pulverized) to obtain a pulverized product of the primary mixture.

[0054] The particle size after pre-milling affects the quality performance of the resulting firing lead. Therefore, it is important to ensure that the desired particle size is achieved. The particle size after pre-milling is D 50 The thickness is preferably 1 μm or more and 30 μm or less, and more preferably 5 μm or more and 10 μm or less.

[0055] The size and distribution of the pre-pulverized particles can be measured using a particle size distribution analyzer based on the laser diffraction / scattering method. In this embodiment, the particle size after pre-pulverization is determined based on the so-called D 50 (Median diameter measured on a volume basis) is used. Note that although the particle size distribution can be measured using either a dry method or a wet method, when measuring the size of relatively small particles, it is preferable to use the simpler dry method.

[0056] A general crusher can be used for crushing. Specifically, (i) examples of coarse crushers include hammer crushers, jaw crushers, gyratory crushers, cone crushers, and impact crushers. (ii) Examples of medium crushers include roll crushers, cutter mills, stamp mills, millstone-type sloot mills, and ring mills. (iii) Examples of fine crushers include roller mills, jet mills, hammer mills, and pin mills.

[0057] A coarse pulverizer is used for the coarse pulverization carried out in the preliminary calcination step, and a fine pulverizer is used for the fine pulverization carried out in the preliminary pulverization step. These may be used alone or in combination.

[0058] (4) Secondary mixing and kneading process In the secondary mixing and kneading step, the graphite powder obtained in the preliminary pulverization step is blended with raw materials other than the graphite powder, and these are mixed and kneaded again. The raw materials other than the graphite powder include a binder. Examples of the binder include the same binder as used in the primary mixing and kneading step.

[0059] (5) Preforming process In the preforming step, the mixture obtained in the secondary mixing and kneading step is further mixed and preformed into thin wires using an extruder or the like.

[0060] (6) Re-grinding process In the re-grinding step, the thin linear compact obtained in the pre-molding 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.

[0061] The size and distribution of the reground 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.

[0062] (7) Extrusion molding process In the extrusion molding step, the kneaded material re-pulverized in the re-pulverization step 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.

[0063] (8) 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.

[0064] (9) 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.

[0065] By going through the above steps, the firing lead of this embodiment is manufactured.

[0066] As described above, in the method for producing a sintered lead of this embodiment, the mixing, molding, pulverization, and firing of the raw material mixture are each performed at least twice. That is, in the method for producing a sintered lead of this embodiment, the mixing, molding, pulverization, and firing of the raw material mixture are each performed at least twice by performing the following steps in this order: (1) primary mixing and kneading step, (2) pre-firing step, (3) pre-pulverization step, (4) secondary mixing and kneading step, (5) pre-forming step, (6) re-pulverization step, (7) extrusion molding step, (8) firing step, and (9) oil immersion step.

[0067] In the method for producing a sintered lead of this embodiment, the sintered lead may be produced by carrying out a series of steps, including (2) a pre-sintering step, (3) a pre-pulverizing step, (4) a secondary mixing and kneading step, (5) a pre-molding step, (6) a re-pulverizing step, (7) an extrusion molding step, and (8) a sintering step, N times, followed by (9) an oil immersion step, where N is an integer of 1 or more, preferably an integer of 1 to 5, and more preferably an integer of 1 to 3.

[0068] Thus, the method for manufacturing a burned lead of this embodiment manufactures the burned lead of this embodiment by mixing, molding, pulverizing, and firing the raw material mixture at least twice each. Therefore, the method for manufacturing a burned lead of this embodiment manufactures a burned lead whose R value satisfies the specific range described above and whose graphite size La and size Lc satisfy formula (1) described above. Therefore, the burned lead of this embodiment can achieve improved bending strength and smooth writing feel.

[0069] The reason why the method for manufacturing the sintered lead of this embodiment can obtain a sintered lead in which the R value satisfies the specific range and the graphite size La and size Lc satisfy the formula (1) above, and the above-mentioned effects are achieved, is not fully understood, but is presumed as follows. However, the present invention is not limited by the following presumption.

[0070] In the method for producing the sintered lead of this embodiment, as described above, the mixing of the raw material mixture, molding, pulverization, and sintering are each performed two or more times. By performing each of these two or more times, the adhesion between the graphite and the binder is increased, the graphite is hardly separated from the binder, and the binder and graphite are firmly adhered to each other, which is thought to result in a sintered lead having a strong and uniform structure. Note that the above production method is one example, and the sintered lead of this embodiment can also be produced by other methods.

[0071] However, rather than simply performing each of the mixing, molding, crushing, and heat treatment (firing) steps more than twice, it is possible to efficiently manufacture a fired lead with better properties by adjusting various conditions and optimizing the raw materials.

[0072] For example, the density of the sintered core can be improved by adjusting the pressure in the preforming step (5) to increase the adhesion between the graphite particles in the mixture and the binder, or by adjusting the drawing ratio when preforming into thin wires. The drawing ratio refers to the ratio of the diameter of the material inlet of the extruder to the diameter of the compact extrusion part.

[0073] (writing implements) The baked lead of this embodiment is applicable to various writing instruments that use a baked lead as a writing lead. For example, the baked lead of this embodiment can be used as a pencil lead that is clamped by a pencil shaft made of wood or the like, or as a lead for a mechanical pencil that allows the lead to be inserted, removed, and replaced, for example, by extending the lead.

[0074] The structure and shape of a writing instrument, which is an example of an application target of the baked lead of this embodiment, are not particularly limited. [Example]

[0075] 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.

[0076] Example 1 The firing lead of Example 1 was manufactured by the following steps.

[0077] The following raw material A1 was prepared as the raw material to be used in the primary mixing and kneading step.

[0078] -Raw material A1- Natural graphite 60 parts by weight Vinyl acetate resin 25 parts by weight Ethanol 15 parts by mass

[0079] The above raw material A1 was mixed in a Henschel mixer, and further mixed and kneaded again using a three-roll mill (primary mixing and kneading step). Next, the amount of ethanol was adjusted and the kneaded product was coarsely crushed using a hammer crusher, and the crushed product was heat-treated at a maximum temperature of 800°C in a non-oxidizing atmosphere (pre-calcination step), and further finely crushed using a jet mill (pre-crushing step), to obtain D, which is composed of graphite and a small amount of carbonaceous material derived from vinyl acetate resin. 50 = 5 μm finely ground material was obtained as the grinding material of the primary mixture.

[0080] Next, the following raw material B1 was prepared as the raw material to be used in the secondary mixing and kneading step. The pulverized product of the primary mixture contained in raw material B1 was the finely pulverized product obtained in the above step using raw material A1.

[0081] -Raw material B1- 36 parts by mass of crushed primary mixture Vinyl acetate resin 28 parts by mass Coal pitch 16 parts by mass Ethanol 20 parts by weight

[0082] The raw material B1 was mixed using a Henschel mixer in the same manner as in the production of the pulverized primary mixture using raw material A1, and then mixed and kneaded again using a three-roll mill while adjusting the amount of ethanol (secondary mixing and kneading process).

[0083] Next, the mixture was preformed into thin wires using a single-screw extruder (preforming step) to obtain a thin wire-shaped molded product. The obtained molded product was pulverized using a pin mill (re-pulverizing step), and D 50 This pulverized material was again molded into thin wires of the desired size using a single-screw extruder (extrusion molding step).

[0084] The obtained molded body was heat-treated in air up to 250°C for 10 hours, and then further heat-treated in a non-oxidizing atmosphere at a maximum temperature of 1300°C, and cooled to obtain the fired body of Example 1 (firing step).

[0085] The obtained sintered body of Example 1 was impregnated with spindle oil by holding it at 100°C for 2 hours (oil immersion process), and after removing excess oil from the surface of the sintered body, a sintered lead of Example 1 for a pencil having a diameter of 2.00 mm was obtained.

[0086] Example 2 The firing lead of Example 2 was produced by the following steps.

[0087] The following raw material A2 was prepared as the raw material to be used in the primary mixing and kneading step.

[0088] -Raw material A2- Natural graphite 60 parts by weight Vinyl acetate resin 25 parts by weight Ethanol 15 parts by mass

[0089] The raw material A2 was mixed in a Henschel mixer, and then mixed and kneaded again using a three-roll mill (primary mixing and kneading process). Next, the amount of ethanol was adjusted and the kneaded product was coarsely crushed using a hammer crusher. The crushed product was heat-treated at a maximum temperature of 800°C in a non-oxidizing atmosphere (pre-calcination process), and then finely crushed using a jet mill (pre-crushing process). D, which consisted of graphite and a small amount of carbonaceous material derived from vinyl acetate resin, was obtained. 50 = 10 μm finely ground material was obtained as the grinding material of the primary mixture.

[0090] Next, the following raw material B2 was prepared as the raw material to be used in the secondary mixing and kneading step. The pulverized product of the primary mixture contained in raw material B2 was the finely pulverized product obtained in the above step using raw material A2.

[0091] -Raw material B2- Crushed primary mixture: 42 parts by mass Vinyl acetate resin 30 parts by weight Coal pitch 8 parts by weight Ethanol 20 parts by weight

[0092] The raw material B2 was mixed using a Henschel mixer in the same manner as in producing the pulverized primary mixture using raw material A2, and then mixed and kneaded again using a three-roll mill (secondary mixing and kneading step).

[0093] Next, the mixture was preformed into thin wires using a single-screw extruder (preforming step) to obtain a thin wire-shaped molded product. The obtained molded product was pulverized using a pin mill (re-pulverizing step), and D 50 This pulverized material was again molded into thin wires of the desired size using a single-screw extruder (extrusion molding step).

[0094] The obtained molded body was heat-treated in air up to 250°C for 10 hours, and then further heat-treated in a non-oxidizing atmosphere at a maximum temperature of 1000°C, and cooled to obtain a fired body of Example 2 (firing step).

[0095] The obtained sintered body of Example 2 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, a sintered lead of Example 2 for a pencil having a diameter of 2.00 mm was obtained.

[0096] Example 3 The firing lead of Example 3 was produced by the following steps.

[0097] In Example 3, the raw material A2 used in Example 2 was used, and a pulverized product of the primary mixture was obtained in the same manner as in Example 2.

[0098] Next, the following raw material B3 was prepared as the raw material to be used in the secondary mixing and kneading step. The pulverized product of the primary mixture contained in raw material B3 was the pulverized product of the primary mixture obtained in the same manner as in Example 2 using raw material A2.

[0099] -Raw material B3- Crushed primary mixture: 41 parts by mass Vinyl acetate resin 27 parts by weight Coal pitch 12 parts by weight Ethanol 20 parts by weight

[0100] The above raw material B3 was mixed using a Henschel mixer in the same manner as when producing the pulverized product of the primary mixture using raw material A2, and then mixed and kneaded again using a three-roll mill while adjusting the amount of ethanol (secondary mixing and kneading process).

[0101] Next, the mixture was preformed into thin wires using a single-screw extruder (preforming step) to obtain a thin wire-shaped molded product. The obtained molded product was pulverized using a pin mill (re-pulverizing step), and D 50 This pulverized material was again molded into thin wires of the desired size using a single-screw extruder (extrusion molding step).

[0102] The obtained molded body was heat-treated in air up to 250°C for 10 hours, and then further heat-treated in a non-oxidizing atmosphere at a maximum temperature of 1150°C, and cooled to obtain a fired body of Example 3 (firing step).

[0103] The obtained sintered body of Example 3 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, a sintered lead of Example 3 for a pencil having a diameter of 2.00 mm was obtained.

[0104] Example 4 The firing lead of Example 4 was produced by the following steps.

[0105] In Example 4, raw material A1 was used as in Example 1, and a pulverized product of the primary mixture was obtained in the same manner as in Example 1.

[0106] Next, the following raw material B4 was prepared as the raw material to be used in the secondary mixing and kneading step. The pulverized product of the primary mixture contained in raw material B4 was the pulverized product of the primary mixture obtained in the same manner as in Example 1 using raw material A1.

[0107] -Raw material B4- 39 parts by weight of crushed primary mixture Vinyl acetate resin 28 parts by mass Coal pitch 13 parts by weight Ethanol 20 parts by weight

[0108] The raw material B4 was mixed using a Henschel mixer in the same manner as in the production of the pulverized primary mixture using raw material A1, and then mixed and kneaded again using a three-roll mill while adjusting the amount of ethanol (secondary mixing and kneading process).

[0109] Next, the mixture was preformed into thin wires using a single-screw extruder (preforming step) to obtain a thin wire-shaped molded product. The obtained molded product was pulverized using a pin mill (re-pulverizing step), and D 50 This pulverized material was again molded into thin wires of the desired size using a single-screw extruder (extrusion molding step).

[0110] The obtained molded body was heat-treated in air up to 250°C for 10 hours, and then further heat-treated in a non-oxidizing atmosphere at a maximum temperature of 1300°C, and cooled to obtain a fired body of Example 4 (firing step).

[0111] The obtained sintered body of Example 4 was impregnated with spindle oil by holding it at 100°C for 2 hours (oil immersion process), and after removing excess oil from the surface of the sintered body, a sintered lead of Example 4 for a mechanical pencil having a nominal diameter of 0.35 mm was obtained.

[0112] (Comparative Example 1) A comparative sintered lead of Comparative Example 1 was produced in the same manner as in Example 1, except that the production of a pulverized product of the primary mixture using raw material A1 in Example 1 was not carried out, and raw material B1 containing graphite powder was used instead of the pulverized product of the primary mixture. That is, in Comparative Example 1, the primary mixing and kneading step, pre-firing step, and pre-pulverization step using raw material A1 in Example 1 were not carried out, and raw material B1 containing graphite powder was used instead of the pulverized product of the primary mixture obtained by undergoing these steps.

[0113] (Comparative Example 2) A pulverized product of the primary mixture was produced using raw material A2 in Example 2, and the comparative firing lead of Comparative Example 2 was produced in the same manner as Example 2, except that the pre-molding process and re-pulverizing process were not performed in the subsequent processes, including the secondary mixing and kneading process using raw material B2.

[0114] That is, in Comparative Example 2, raw material B2 was mixed and kneaded in the secondary mixing and kneading process, and then subjected to the extrusion molding process without performing the preforming process and re-grinding process, thereby producing a comparative baking lead for Comparative Example 2.

[0115] (Comparative Example 3) A comparative sintered lead for Comparative Example 3 was produced in the same manner as in Example 1, except that the production of a pulverized product of the primary mixture using raw material A1 in Example 1 was not carried out, and instead of the pulverized product of the primary mixture, raw material B1 containing graphite for Comparative Example 3 described below was used. That is, in Comparative Example 3, the primary mixing and kneading step, pre-firing step, and pre-pulverization step using raw material A1 in Example 1 were not carried out, and instead of the pulverized product of the primary mixture obtained by undergoing these steps, raw material B1 containing graphite for Comparative Example 3 described below was used.

[0116] The graphite for Comparative Example 3 was D, which was made by finely pulverizing natural graphite using a jet mill. 50 = 5 μm finely ground material was used.

[0117] Comparative Example 4 In Comparative Example 4, raw material A1 was used as in Examples 1 and 4, and a pulverized product of the primary mixture was obtained in the same manner as in Examples 1 and 4.

[0118] Next, the following raw material B14 was prepared as the raw material to be used in the secondary mixing and kneading step. The pulverized product of the primary mixture contained in raw material B14 was the pulverized product of the primary mixture obtained in the same manner as in Example 1 using raw material A1.

[0119] -Raw material B14- 39 parts by weight of crushed primary mixture Vinyl acetate resin 28 parts by mass Coal pitch 13 parts by weight Ethanol 20 parts by weight

[0120] A comparative baking lead of Comparative Example 4 was produced in the same manner as in Example 4, except that the preforming step and re-pulverizing step were not performed in the subsequent steps including the secondary mixing and kneading step using raw material B14.

[0121] That is, in Comparative Example 4, raw material B14 was mixed and kneaded in the secondary mixing and kneading process, and then subjected to the extrusion molding process without performing the preforming process and re-grinding process, thereby producing a comparative baked lead of Comparative Example 4 for a mechanical pencil.

[0122] The obtained compact was heat-treated in air up to 250°C for 10 hours, and then further heat-treated in a non-oxidizing atmosphere at a maximum temperature of 1300°C, and cooled to obtain a comparative fired body of Comparative Example 4.

[0123] The comparative sintered body of Comparative Example 4 obtained was impregnated with spindle oil by holding it at 100°C for 2 hours, and after removing excess oil from the surface of the comparative sintered body, a comparative sintered lead of Comparative Example 4 for a mechanical pencil having a nominal diameter of 0.35 mm was obtained.

[0124] (evaluation) The physical properties and performance were evaluated for the baking leads of Examples 1 to 3 and the comparative baking leads of Comparative Examples 1 to 3. The results obtained are shown in Table 1. The evaluation conditions were as follows.

[0125] -R value- The R values ​​of the fired bodies of Examples 1 to 3 and the comparative fired bodies of Comparative Examples 1 to 3 were measured, and the values ​​shown in Table 1 were obtained.

[0126] The R value was measured using a microscopic laser Raman spectrometer (Horiba Ltd., product name XploRA Plus) at 1580 cm under the following measurement conditions: -1 The G-band peak intensity (I G ) and 1360cm -1 The peak intensity of the D band near D ) was measured.

[0127] -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

[0128] For each of the fired bodies of Examples 1 to 3, the peak intensity of the G band (I G ) and D band peak intensity (I D ) was measured twice, and the ratio of these peak intensities (I D / I G ) was calculated as the R value of each of the fired bodies of Examples 1 to 3. The calculated R values ​​are shown in Table 1.

[0129] Similarly, for each of the comparative fired bodies of Comparative Examples 1 to 3, the peak intensity of the G band (I G ) and D band peak intensity (I D ) was measured twice, and the ratio of these peak intensities (I D / I G ) was calculated as the R value of each of the comparative fired bodies of Comparative Examples 1 to 3. The calculated R values ​​are shown in Table 1.

[0130] -Crystallite size “2La+3Lc”- The size La (nm) and 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 3 were measured, and the value of 2La + 3Lc was calculated. The calculated values ​​are shown in Table 1.

[0131] The graphite crystallite size was measured under the following measurement conditions.

[0132] 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 3 was measured. c (002 face) and size L a The surface roughness (110) of each sample was measured. One fired sample or one comparative fired sample was used for each measurement.

[0133] 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.

[0134] 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°.

[0135] The background was removed (using a fifth-order Chebyshev polynomial) from the diffraction lines near 26.4° or 77.5°, corresponding to the (002) or (110) planes in the obtained XRD profile, and the X-ray absorption factors were corrected and profile fitting was performed. The crystallite size La and size Lc were 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.

[0136] -Bending strength evaluation- The bending strength was evaluated for the baking leads of Examples 1 to 3 and the comparative baking leads of Comparative Examples 1 to 3. The bending strength was evaluated using the measured value of bending strength (MPa) and writing density.

[0137] The bending strength (MPa) was measured according to the method specified in JIS S 6006:2020 or JIS S 6005:2019. When JIS S 6006:2020 was used, the distance between supports was 40 mm, and when JIS S 6005:2019 was used, the distance between supports was 20 mm. For each of the baking leads of Examples 1 to 3 and the comparative baking leads of Comparative Examples 1 to 3, the average of the values ​​measured for 10 pieces was used as the bending strength (MPa). The measurement results are shown in Table 1.

[0138] The writing density was measured by measuring lines written according to the method specified in JIS S 6006:2020 or JIS S 6005:2019 using a densitometer (Sakura Densitometer PDA65 (product name, Konishiroku Photo Industry Co., Ltd.)). The measurement results are shown in Table 1.

[0139] The bending strength of the baking leads of Examples 1 to 3 and the comparative baking leads of Comparative Examples 1 to 3 was evaluated using the measured bending strength (Mpa) and writing density. The evaluation criteria for bending strength are shown below. The evaluation results are also shown in Table 1.

[0140] --Bending strength evaluation criteria-- ○: High bending strength Bending strength (MPa) of 230 MPa or more in the range of writing density 0.21 to 0.23 Bending strength (MPa) of 170 MPa or more in the range of writing density 0.38 to 0.40 Bending strength (MPa) of 100 MPa or more in the range of writing density 0.60 to 0.62 Bending strength (MPa) of 70 MPa or more in the range of writing density 0.64 to 0.66 Bending strength (MPa) of 50 MPa or more in the range of writing density 0.74 to 0.76 Bending strength (MPa) of 40 MPa or more in the range of writing density 0.79 to 0.81 ×: Low bending strength Bending strength (MPa) of less than 230 MPa in the range of writing density 0.21 to 0.23 Bending strength (MPa) is less than 170 MPa in the range of writing density 0.38 to 0.40 Bending strength (MPa) is less than 100 MPa in the range of writing density 0.60 to 0.62 Bending strength (MPa) is less than 70 MPa in the range of writing density 0.64 to 0.66 Bending strength (MPa) is less than 50 MPa in the range of writing density 0.74 to 0.76 Bending strength (MPa) of less than 40 MPa in the range of writing density 0.79 to 0.81

[0141] -Evaluation of smoothness of writing- The smoothness of writing was evaluated for the baked leads of Examples 1 to 3 and the comparative baked leads of Comparative Examples 1 to 3. The smoothness of writing was evaluated by evaluating the writing feel and pen handling. Writing feel refers to whether writing was smooth and easy. Pen handling refers to whether writing was smooth and easy without any snags.

[0142] As Reference Example 1, a commercially available baked lead with a lead diameter of 2.0 mm (manufactured by Mitsubishi Pencil Co., Ltd., product name "uni2.0-210 1P", refill lead (HB)) was prepared.

[0143] Thirty subjects then wrote the same short sentence repeatedly over five pages of a commercially available Campus notebook with A-ruled lines (manufactured by Kokuyo Co., Ltd.) without using an underlay, for each of the baked leads of Examples 1 to 3, the comparative baked leads of Comparative Examples 1 to 3, and the baked pencil lead of Reference Example, and evaluated them relative to the baked pencil lead of Reference Example 1. The evaluation criteria for writing feel and penmanship are shown below. The evaluation results are also shown in Table 1.

[0144] --Evaluation criteria for writing feel and penmanship-- ◎: Relatively very good ○: Relatively good △: Relatively poor ×: Relatively the worst

[0145] [Table 1]

[0146] As shown in Table 1, it was confirmed that the baked leads of Examples 1 to 3 were improved in both bending strength and smooth writing feel compared to the comparative baked leads of Comparative Examples 1 to 3.

[0147] The bending strength and smooth writing feel were also evaluated for the baked lead of Example 4 and the comparative baked lead of Comparative Example 4. As a result, the baked lead of Example 4 had improved bending strength and smooth writing feel compared to the comparative baked lead of Comparative Example 4. [Industrial Applicability]

[0148] The baked lead according to the present invention can be used as a writing lead for writing implements such as pencils and mechanical pencils.

Claims

1. Contains graphite, The R value measured by Raman spectroscopy is 0.15 or more and 0.55 or less, 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 determined by X-ray diffraction measurement satisfy formula (1), 232≦2La+3Lc≦280...Formula (1) Baking core.

2. The size La (nm) in the a-axis direction and the size Lc (nm) in the c-axis direction of the graphite determined by X-ray diffraction measurement satisfy formula (2). 232≦2La+3Lc≦260...Formula (2) The baking lead according to claim 1 .

3. The size Lc of the graphite in the c-axis direction is 15 nm or more and 40 nm or less. The baking lead according to claim 1 or claim 2.

4. A method for producing a sintered lead, in which a raw material mixture is mixed, molded, pulverized, and fired at least twice each to produce a sintered lead that contains graphite, has an R value of 0.15 or more and 0.55 or less by Raman spectroscopy, and has a size La (nm) in the a-axis direction and a size Lc (nm) in the c-axis direction of the graphite determined by X-ray diffraction measurement that satisfy formula (1). 232≦2La+3Lc≦280...Formula (1)

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