Fired core

Abstract

To attain compatibility between high strength and high density.SOLUTION: A fired core includes boron nitride powder having an average particle diameter of 1 μm or more and 20 μm or less and a specific surface area of 10 m2 / g or less, and a binder.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a fired core.

Background Art

[0002] Conventionally, as a pencil lead or a core for a mechanical pencil, a fired core containing an organic binder and a filler is known. For example, in order to achieve high strength and high density, a fired core containing a filler such as boron nitride having an average particle diameter of less than 5 μm and a large specific surface area of 100 to 300 m 2 / g or more is disclosed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, since the smaller the average particle diameter of the particles used, the larger the specific surface area of the particles, in the prior art, more binder is required. As the content of the binder increases, high strength can be achieved, but the writing density decreases. For this reason, it has been difficult in the prior art to achieve both high strength and high density.

[0005] An object of the present invention is to provide a fired core that achieves both high strength and high density.

Means for Solving the Problems

[0006] In order to solve the above problems, the present invention provides "1. A fired core containing boron nitride powder having an average particle diameter of 1 μm or more and 20 μm or less and a specific surface area of 10 m 2 / g or less, and a binder. 2. The specific surface area of the boron nitride powder is 1 m 2above / g The fired core according to claim 1. 3. The content of the binder with respect to the total amount of the fired core is 1% by mass or more and 20% by mass or less. The fired core according to claim 1. 4. The ratio of the content of the boron nitride powder and the binder with respect to the total amount of the fired core is in the range of 1:99 to 45:65 by mass ratio. The fired core according to claim 1. 5. The fired core according to claim 1, containing graphite. 6. The specific surface area is 1 m 2 / g or more and 50 m 2 / g or less, the fired core according to claim 1.

Advantages of the Invention

[0007] The present invention can achieve both high strength and high concentration.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described in detail. In this specification, "parts", "%", "ratio", etc. indicating the formulation are based on mass unless otherwise specified.

[0009] (Fired core) The fired core of this embodiment contains boron nitride powder having an average particle diameter of 1 μm or more and 20 μm or less and a specific surface area of 10 m 2 / g or less, and a binder.

[0010] The fired core of this embodiment contains a binder. Therefore, the fired core of this embodiment can achieve high strength. Further, the fired core of this embodiment contains boron nitride powder having an average particle diameter of 1 μm or more and 20 μm or less and a specific surface area of 10 m 2 / g or less. Therefore, the fired core of this embodiment can hold the boron nitride powder with a minimum amount of binder, promote wear during writing without impairing the lubricating properties of the boron nitride powder, and as a result, it is considered that a dark handwriting can be obtained. Therefore, the fired core of this embodiment can achieve both high strength and high concentration.

[0011] Hereinafter, each component constituting the fired core of the present embodiment will be described in detail.

[0012] (Boron nitride powder) The boron nitride powder contained in the fired core of the present embodiment has an average particle diameter of 1 μm or more and 20 μm or less and a specific surface area of 10 m 2 / g or less.

[0013] The average particle diameter of the boron nitride powder must be 1 μm or more and 20 μm or less, preferably 2 μm or more and 20 μm or less, more preferably 5 μm or more and 15 μm or less, and particularly preferably 5 μm or more and 10 μm or less.

[0014] The specific surface area of the boron nitride powder must be 10 m 2 / g or less, preferably 1 m 2 / g or more and 10 m 2 / g or less, more preferably 2 m 2 / g or more and 10 m 2 / g or less, and particularly preferably 2 m 2 / g or more and 9 m 2 / g or less.

[0015] By containing boron nitride powder with an average particle diameter and specific surface area within the above ranges, the fired core of the present embodiment can hold the boron nitride powder with a minimum necessary binder, promote wear during writing without impairing the lubricating properties of the boron nitride powder, and as a result, it is considered that a dark handwriting can be obtained. Therefore, the fired core of the present embodiment can achieve both high strength and high density.

[0016] The average particle diameter of the boron nitride powder in the present embodiment is the value of the 50% particle diameter of the measurement result obtained by the laser diffraction / scattering method. This average particle diameter can be measured, for example, with a SALD series (manufactured by Shimadzu Corporation) or a Microtrac BlueRaytrac (manufactured by Nikkiso Co., Ltd.).

[0017] The specific surface area of the boron nitride powder is the BET specific surface area determined by the BET method. This BET specific surface area can be measured, for example, with a FlowSorb III 2305 (manufactured by Shimadzu Corporation) or a MACSORB (manufactured by Mountech Co., Ltd.).

[0018] Note that boron nitride powder generally contains B2O3 as a surface oxide film and metal elements such as Fe, Al, and Ca as impurities. Since the melting point of B2O3 is 450 °C, when a large amount of B2O3 is contained in the boron nitride powder, it may melt during firing and the core material may deform. In addition, there is a disadvantage that the boron nitride powder binds to the carbide of the binder and gives a snagging feeling during writing. Also, when a large amount of metal impurities are contained, although the reason is not clear, as a result, the bending strength of the fired core tends to decrease. Therefore, from the viewpoint of avoiding these problems, the purity of the boron nitride powder is preferably 98% or more.

[0019] From the viewpoints of the strength and wear of the core, the content of the boron nitride powder with respect to the total amount of the fired core is preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less.

[0020] (Graphite) The fired core of the present embodiment may be configured to contain graphite together with the above boron nitride powder in addition to the boron nitride powder.

[0021] The average particle diameter and specific surface area of the graphite are not limited.

[0022] For example, the average particle diameter of the graphite is preferably 1 μm or more and 30 μm or less, and more preferably 2 μm or more and 25 μm or less.

[0023] The specific surface area of the graphite is preferably 1 m 2 / g or more and 20 m 2 / g or less, and more preferably 2 m 2 / g or more and 15 m 2 / g or less.

[0024] The content of graphite is not limited. For example, the content of graphite relative to the total amount of the fired core in this embodiment is preferably 1% by mass or more and 50% by mass or less, and more preferably 5% by mass or more and 40% by mass or less.

[0025] By including both boron nitride powder and graphite in the fired core, the glossiness of the handwriting can be suppressed.

[0026] (Binder) The binder contained in the fired core of this embodiment is not limited as long as it can hold and solidify the boron nitride powder and graphite, which are the extender materials contained in the fired core.

[0027] For example, as the binder, residues after heat-treating clays, ceramics, zeolite, diatomaceous earth, activated clay, silica, aluminum phosphate, silicone resin, silicone rubber, thermoplastic resin, thermosetting resin, natural polymer substances, petroleum asphalt, coal tar, pitches such as naphtha cracked pitch under vacuum or in an inert atmosphere can be used.

[0028] Examples of the above thermoplastic resins include vinyl chloride resin, chlorinated vinyl chloride resin, polyvinyl alcohol, etc., examples of the thermosetting resins include furan resin, phenol resin, epoxy resin, etc., and examples of the natural polymer substances include lignin, cellulose, tragacanth gum, etc. Thermoplastic resins, thermosetting resins, and natural polymer substances can also be used as molding aids during the production of the fired core.

[0029] Among these, from the viewpoint of whiteness after heat treatment, it is preferable to use silica as the binder.

[0030] The content of the binder relative to the total amount of the fired core is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 20% by mass or less, and particularly preferably 5% by mass or more and 20% by mass or less.

[0031] Since the fired core of the present embodiment contains boron nitride powder having the above specific specific surface area and average particle diameter, the binder can hold the boron nitride powder even when the content of the binder is within the above range. Therefore, when the content of the binder is within the above range, the boron nitride powder can be held with the minimum necessary amount of binder, and the wear during writing is promoted without impairing the lubricating properties of the boron nitride powder, and as a result, a dark handwriting can be obtained. Therefore, the fired core of the present embodiment can achieve both high strength and high density.

[0032] (Content ratio of binder and extender) The ratio of the content of the binder to the total amount of the fired core with respect to the above boron nitride powder is preferably in the range of 1:99 or more and 45:65 or less, more preferably in the range of 5:95 or more and 30:70 or less, and particularly preferably in the range of 10:90 or more and 25:75 or less in terms of mass ratio (binder:boron nitride powder).

[0033] When the ratio of the content of the binder to the total amount of the fired core with respect to the above boron nitride powder is within the above range, the effect of excellent lubricating properties during writing can be obtained.

[0034] (Specific surface area of fired core) The specific surface area of the fired core is preferably 1 m 2 / g or more and 50 m 2 / g or less, more preferably 2 or more and 50 or less, and particularly preferably 5 or more and 45 or less.

[0035] When the specific surface area of the fired core is within the above range, it is possible to reduce the writing tip debris.

[0036] The specific surface area of the fired core is determined by the BET multipoint method using a sintered body obtained by mixing and dispersing the constituent materials of the fired core, extrusion molding, heat treatment for solidification (drying), and then firing.

[0037] (Other additives) In the fired core of the present embodiment, for the purpose of improving the dispersibility during kneading in the manufacturing process and / or improving the fluidity and moldability during extrusion molding, at least one of plasticizers or solvents such as water (purified water), dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, dioctyl adipate, diallyl isophthalate, propylene carbonate, alcohols, ketones, and esters can be added as needed.

[0038] (Method for manufacturing a fired core) The fired core of the present embodiment is obtained by, for example, mixing and dispersing the above boron nitride powder, or boron nitride powder and graphite, the above binder, and the above solvent and / or plasticizer added as needed using a Henschel mixer, kneading with a pressure kneader or two-roll mill and extruding into a linear shape, then heat-treating in air to remove the remaining plasticizer and solidifying (drying), and then firing at a temperature around 1000 °C in a non-oxidizing atmosphere or inert atmosphere such as a nitrogen atmosphere to obtain a sintered body, and manufacturing the sintered body as a fired core.

[0039] Moreover, a core that does not contain graphite in the fired core body can obtain a white core body by further firing at a temperature around 800 °C in an oxidizing atmosphere.

[0040] Furthermore, by impregnating the pores of the obtained fired core, which is a sintered body, with ink containing oils and fats or coloring materials, a core body for a pencil lead or a mechanical pencil lead can be manufactured.

[0041] Examples of coloring materials include oil-soluble dyes, acid dyes, basic dyes, and metal-containing dyes. Also, as salt-forming dyes of these dyes, salt-forming dyes of acid dyes and basic dyes, salt-forming dyes of basic dyes and organic acids, salt-forming dyes of acid dyes and organic amines, etc. can be mentioned.

[0042] The solvent used together with the dye can be arbitrarily selected in consideration of the solubility and other properties of the coloring agent to be used. Depending on the difference in boiling point, both high-boiling organic solvents and low-boiling solvents can be used.

[0043] Specific examples of the high-boiling solvent include diethylene glycol monophenyl ether (phenyl diglycol, 283 °C), diethylene glycol monobenzyl ether (302 °C), triethylene glycol monobutyl ether (butyl triglycol, 271 °C), ethylene glycol monobenzyl ether (256 °C), and the like.

[0044] Examples of the low-boiling organic solvents include triethylene glycol monomethyl ether (249 °C), phenyl cellosolve (247 °C), propylene glycol monomethyl ether (243 °C), benzyl alcohol (205 °C), 3-methoxy-3-methyl-1-butanol (174 °C), xylene (139 °C), toluene (111 °C), isopropyl alcohol (82 °C), methyl ethyl ketone (79 °C), ethyl alcohol (78 °C), ethyl acetate (77 °C), acetone (56 °C), and the like. The dye and the solvent can be arbitrarily combined to form an ink.

[0045] Examples of the oils and fats include, but are not limited to, silicone oil, spindle oil, and the like.

Examples

[0046] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the following examples.

[0047] (Examples 1 to 14, Comparative Examples 1 to 12) The raw materials of the extender, binder, and solvent shown in the table were kneaded in the compounding amounts shown in the table, extruded into a thin line shape, dried in the air, and fired by heating to 1000 °C in a nitrogen atmosphere to obtain a sintered body. By impregnating the sintered body with an impregnating material, a fired core having a diameter of 0.7 mm and a comparative fired core were produced. The content of each material shown in the table is expressed in mass% based on the total amount of the fired core or the comparative fired core.

[0048] (Evaluation) For each of the fired cores of the prepared examples and the comparative fired cores of the comparative examples, the following evaluations were carried out using the cores impregnated with the impregnating materials shown in the table.

[0049] (Bending strength) For the fired cores of the examples and the comparative fired cores of the comparative examples, the bending strength (MPa) was measured according to JIS S6005 (2019). The measurement results are shown in the table.

[0050] (Writing density) The writing density was measured using a fluorescence spectrophotometer (FD-7) of Konica Minolta, Inc. for the drawn lines written with a writing load of 1.96 N (200 g load) by the method specified in JIS S 6005:2019 (core for mechanical pencils), and the measured value under the following setting conditions was taken as the density value. The measurement results are shown in the table.

[0051] (Settings of the densitometer) ·Measurement function: Density ·Display format: Absolute value ·Density filter: Auto ·Reference color selection: Auto

[0052] As for other setting functions, the following functions are not used. ·Density measurement conditions: Density illumination conditions, density white reference, density status ·Color measurement conditions: Color illumination conditions, observation light source, field of view, color system, color difference formula

[0053] The Kent paper used was manufactured by Oji Paper Co., Ltd., with a basis weight of 126 g / m2, a thickness of 0.150 mm, a density of 0.85 g / cm 3 and having quality characteristics in the ratio of surface roughness: 81a, smoothness: 81S, sizing degree: 110S, whiteness: 99.4%, and opacity: 92.7%.

[0054] (Specific surface area of the fired core and the comparative fired core) For the fired cores of the examples and the comparative fired cores of the comparative examples, the specific surface area of the sintered body before infiltrating the infiltrant was measured by the BET multi-point method using a device named TriStarII manufactured by Micromeritics. The measurement results of the specific surface area are shown in a table.

[0055] [Table 1]

[0056] [Table 2]

[0057] [Table 3]

[0058] [Table 4]

[0059] As shown in Tables 1 to 4, it was confirmed that the fired cores of the examples can achieve both an improvement in flexural strength and handwriting density compared to the comparative fired cores. Specifically, when comparing Examples 1 to 3, 13 and Comparative Examples 1 to 3, which were impregnated with the same impregnating material, it was confirmed that the fired cores of Examples 1 to 3, 13 can achieve both an improvement in flexural strength and handwriting density compared to the comparative fired cores of Comparative Examples 1 to 3. Similarly, when comparing Examples 4 to 6, 14 and Comparative Examples 4 to 6, which were impregnated with the same impregnating material, it was confirmed that the fired cores of Examples 4 to 6, 14 can achieve both an improvement in flexural strength and handwriting density compared to the comparative fired cores of Comparative Examples 4 to 6. Similarly, when comparing Examples 7 to 9 and Comparative Examples 7 to 9, which were impregnated with the same impregnating material, it was confirmed that the fired cores of Examples 7 to 9 can achieve both an improvement in flexural strength and handwriting density compared to the comparative fired cores of Comparative Examples 7 to 9. Similarly, when comparing Examples 10 to 12 and Comparative Examples 10 to 12, which were impregnated with the same impregnating material, it was confirmed that the fired cores of Examples 10 to 12 can achieve both an improvement in flexural strength and handwriting density compared to the comparative fired cores of Comparative Examples 10 to 12.

Industrial Applicability

[0060] The fired core of the present invention can be used as a core for a pencil lead or a mechanical pencil lead.

Claims

1. A fired core comprising boron nitride powder having an average particle diameter of 1 μm or more and 20 μm or less and a specific surface area of 10 m ２ / g or less, and a binder.

2. The specific surface area of the boron nitride powder is 1 m ２ / g or more, The fired core according to claim 1.

3. The content of the binder with respect to the total amount of the fired core is 1% by mass or more and 20% by mass or less. The fired core according to claim 1.

4. The ratio of the content of the boron nitride powder and the binder with respect to the total amount of the fired core is in the range of 1:99 or more and 45:65 or less by mass ratio. The fired core according to claim 1.

5. The fired core according to claim 1, containing graphite.

6. The specific surface area is 1 m ２ / g or more and 50 m ２ / g or less, the fired core according to claim 1.

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