JP4627563B2 - Pencil lead and method for manufacturing the same - Google Patents

Description

  The present invention relates to a pencil lead such as a pencil lead for a mechanical pencil and a pencil lead for a wooden shaft, and more specifically, a pencil lead that has a strong strength, a smooth writing feeling, a dark drawn line, and a vivid black. Regarding the method.

In general, important properties required for a pencil lead are good writing feeling, good color development of drawn lines, and high mechanical strength.
The applicant of the present application increases the effective pore volume and surface area that can be impregnated with oil in a solid drawing material such as a pencil lead, further improves the compressive strength, has a smooth writing, and has sufficient color development and line density. Solid drawing material containing at least a nanomaterial (nanoparticle) in order to provide a solid drawing material having a small amount of wear, good erasability, and difficult to get dirty even if the drawn line is rubbed by hand Proposing a solid drawing material characterized by forming a solid drawing material core obtained by firing or non-baking a blended composition for use, and filling the pores of the solid drawing material core with a lubricant (For example, refer to Patent Document 1).

  Further, for the purpose of providing a method for producing a pencil core which is an extruded core that can form a thick film containing fine particles at a high concentration by writing, a part or all of the fine particles having an average particle size of 100 nm or less are obtained. Also known is a manufacturing method of a core body (for example, refer to Patent Document 2) that is preliminarily adhered to the surface of a plate-like body material to form a particulate-attached plate-like body material, mixed with a core body material, kneaded, and then molded by extrusion. This technique includes the disclosure of Patent Document 1 above. Note that the thickness of the film described in Patent Document 2 is merely a numerical representation of the power for hiding the base, and is not related to the visual color (density) or writing quality.

  By the way, the evaluation item referred to as “writing taste” or “writing feeling” in Patent Document 1 has the following drawbacks. That was because the subjects did not change mechanical pencils by writing in a short time, and evaluated based on the feeling when drawing with the side that was reduced in the posture at the start of the test. . Since the reduced surface is a worn and smooth surface, it is written on the smooth surface that is almost worn from the beginning to the end of drawing.

For this reason, when applied to a product by the applicant of the present application that has been recently released and gaining popularity (mechanical pencil, trade name “Kurtoga”, manufactured by Mitsubishi Pencil Co., Ltd., WO 2007/142135 (Patent No. 4240417)), When the test is performed by applying the core to be tested to the mechanical pencil of the type where the core rotates every time it is written and is always written by a new part, the writing feeling as before is reproduced. It was found that there was a problem of not being done.
That is, even if nanoparticles are simply mixed and a solid drawing material is formed by the technique described in Patent Document 1 or the like, it is a better drawing line density, writing quality in actual writing, and a typical index thereof. A favorable evaluation of the static / dynamic friction coefficient could not be obtained. When measuring static and dynamic friction coefficients in a solid drawing material simply mixed with nanoparticles, depending on the evaluation method referred to as `` writing taste '' or `` writing feeling '', depending on the core manufacturing method, configuration, etc. The problem of not necessarily reproducing was discovered.

  As described above, in the pencil lead using nanomaterials (nanoparticles), in addition to the case where it is used for conventional mechanical pencils, wood spindles, etc., the core rotates every time it is written, so it is always a new part. The pencil lead used for a mechanical pencil or the like of the type written by the pencil lead, which has a better smooth writing feeling, high strength, dark drawn lines and vivid black, and its At present, the manufacturing method is eagerly desired.

JP 2007-138031 A (claims, examples, etc.) JP 2008-115221 A (Claims, Examples, etc.)

  The present invention is to solve this problem in view of the above-mentioned problems and the current state of the prior art, and in the case of using a pencil lead using nanoparticles for normal mechanical pencils, wooden axes, etc. In addition, even if the pencil core is used for mechanical pencils of the type where the core rotates every time it is written and is always written by a new part, it has a better smooth writing feeling and higher It aims at providing the pencil lead used as the vivid black which has a drawn line density, and its manufacturing method.

  As a result of intensive studies in view of the above-described conventional problems, the present inventors have formed a core of a pencil core with graphite or the like, and then a nanoparticle having a specific particle diameter and sphericity in a specific liquid Is uniformly dispersed and impregnated to produce a pencil lead, the pencil lead having a lower drawing density, writing quality, and static / dynamic friction coefficient than the pencil lead disclosed in Patent Document 1 and the like, and a method for producing the same As a result, the present invention has been completed.

That is, the present invention resides in the following (1) to (7).
(1) In a pencil core containing scaly graphite having an a-axis or b-axis and c-axis aspect ratio of 5 or more having an ab surface with a flatness of 2 μm or less, the volume average diameter (mv value) of the graphite is 100 A pencil lead characterized in that nanoparticles having an mv value of 0.05 to 2 and a sphericity of 0.1 to 20 nm are in contact with the ab surface of the graphite.
(2) The pencil lead according to (1) above, wherein the nanoparticles used for the pencil lead are carbon nanoparticles.
(3) The pencil lead as described in (2) above, wherein the carbon nanoparticles are diamond.
(4) The pencil lead according to any one of claims 1 to 3, wherein the volume average diameter (mv value) of the nanoparticles is 4 to 100 nm.
(5) The total coefficient of friction obtained by dividing the average value (n = 10) of the total friction force in the image line in the image line method using the image line machine defined in JIS S 6005: 2007 by the writing load is 0. The pencil lead according to any one of (1) to (5) above, which is 191 to 0.218.
(6) When the polished cross section of the pencil lead is observed at 5 μm × 5 μm using FE-SEM (acceleration voltage 5 kV), 1 to 300 of the nanoparticles are observed. The pencil lead according to any one of (1) to (5).
(7) After forming a pencil core containing at least an a-axis having an ab surface with a flatness of 2 μm or less and a flake graphite having an aspect ratio of 5 or more between the b-axis and the c-axis, the nanoparticles are made to have a refractive index A method for producing a pencil lead, wherein the pencil lead is impregnated after being dispersed in a liquid having a viscosity of 1.3 to 1.5 and a viscosity at 25 ° C. of 7 to 200 mm ² / s.
The drawing machine defined in “JIS S 6005: 2007” defined in the present invention is such that the core body is tilted at an angle of 75 degrees and is drawn while rotating. When writing a mechanical pencil of the type in which the body rotates and is always written by a new part, it is close to the mode at the time of drawing. Therefore, in the present invention, a value (n = 10) obtained by dividing the average value of the total frictional force in the image line in the image line method using the image line machine defined in JIS S 6005: 2007 by the writing load, The value obtained by dividing the “dynamic friction coefficient” and the initial frictional force by the written load was referred to as “static friction coefficient” and used as an evaluation item.

  According to the present invention, in addition to the case where the pencil core using nanoparticles is used for a normal mechanical pencil, a wooden shaft, etc., the core rotates every time it is written and is always written by a new part. Even a pencil lead used for a type of mechanical pencil or the like is provided with a pencil lead that has a better smooth writing feeling and a bright black color having a higher line density and a method for producing the pencil lead. .

It is explanatory drawing based on the electron microscope (SEM) image for measuring the flatness etc. of scale-like natural graphite.

Hereinafter, embodiments of the present invention will be described in detail.
The pencil lead of the present invention is a pencil lead containing scaly graphite having an a-axis or b-axis and c-axis aspect ratio of 5 or more having an ab surface with a flatness of 2 μm or less. (mv value) 100 having a mv value of 0.05 to 2 and having a sphericity of 0.1 to 20 nm is in contact with the ab surface of the graphite.
Further, the method for producing a pencil lead of the present invention comprises a pencil lead core containing scaly graphite having an a-axis or a-b plane with a flatness of 2 μm or less and an aspect ratio of b-axis to c-axis of 5 or more. After forming, the nanoparticles are dispersed in a liquid having a refractive index of 1.3 to 1.5 and a viscosity at 25 ° C. of 7 to 200 mm ² / s, and then impregnated into the pencil core. It is.
Hereinafter, “the present invention” includes both the pencil lead and the manufacturing method thereof.

The flake graphite used in the present invention needs to have an a-axis or ab-axis and c-axis aspect ratio of 5 or more having at least an ab surface with a flatness of 2 μm or less, preferably writing taste, writing resistance From this point, it is desirable that the aspect ratio of the a-axis or b-axis and c-axis having an ab surface with a flatness of 0.05 to 2 μm is 5 to 100.
If the flatness of the scaly graphite used exceeds 2 μm, or the aspect ratio of the a-axis or b-axis and c-axis having the ab surface of the scaly graphite is less than 5, the result is a disadvantageous condition for lubrication. Friction increases, which is not preferable.

The scaly graphite that can be used in the present invention is a scaly graphite that has the above-mentioned characteristics and has an a-axis with an ab surface having a flatness of 2 μm or less or an aspect ratio of the b-axis to the c-axis of 5 or more. For example, it can be selected from natural graphite, artificial graphite, quiche graphite, expanded graphite, expanded graphite, etc. having the above characteristics, and these may be used alone or in combination of two or more. It is.
In addition, the scaly graphite in the present invention preferably has a volume average diameter (mv value) of 4 to 10 μm from the viewpoint of strength and writing quality.
In addition, the volume average diameter (mv value) in the present invention (including examples and the like to be described later) refers to an average diameter weighted by volume from the measurement result in the laser diffraction / scattering method. The dry measurement can be performed using a microtrack (manufactured by Nikkiso Co., Ltd., 3100II), and the nanoparticle described later can be measured using a nanotrack [manufactured by Nikkiso Co., Ltd., UPA-EX150 (internal probe type)].

In the present invention, a core for forming a pencil core is formed using the above scaly graphite. The core for forming the pencil lead can be formed by baking or non-baking the pencil lead blend composition containing the scaly graphite.
In the present invention, the core for forming the pencil lead uses a pencil lead blending composition containing scaly graphite having the above-mentioned characteristics, but the components other than the scaly graphite depend on the type of the pencil lead and the like. Each component such as a binder component such as a lubricant and a thermoplastic synthetic resin, and an organic solvent can be appropriately selected and used.
For example, if the pencil lead is a calcined pencil lead for a mechanical pencil, it can contain at least carbon black and amorphous carbon in addition to flake graphite, and the non-fired pencil lead contains at least oils and fats and waxes. Furthermore, the fired pencil lead can contain at least an extender and a ceramic binder.

Examples of the carbon black that can be used include oil furnace black, gas furnace black, channel black, thermal black, acetylene black, lamp black, and graphitized carbon black obtained by graphitizing these.
Moreover, as an extender, if it is used for the conventional pencil lead, it will not specifically limit, All can be used. For example, white based materials such as boron nitride, kaolin (kaolinite, halloysite), montmorillonite, talc, mica, calcium carbonate, and other colored materials can be used, and naturally several types of these materials can also be used. Particularly preferred are boron nitride, kaolin and talc because of their physical properties and shape.

Examples of the ceramic binder include crystalline or amorphous SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , ZrO ₂ , MgO, BN, B ₂ O ₃ , AlN, and the like. More than one species may be used.
Examples of the thermoplastic synthetic resin include polyvinyl alcohol, polyvinyl chloride, polychlorinated vinyl chloride, polyamide, polyethylene, polypropylene, polyether ether ketone, and the like.
As the organic solvent, those capable of dissolving the thermoplastic synthetic resin are preferable, and specifically, dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, dioctyl adipate, diallyl isophthalate, propylene carbonate, alcohols, ketones, Esters can be used.

  In the pencil lead for mechanical pencils, α-olefin oligomer, fatty acid ester, spindle oil, waxes, boron nitride, talc, silicone oil, silica fine particles, metal soap, etc. can be used as other components. In the fired pencil lead or the fired pencil lead, silicone oil, lard, acrylic resin, epoxy resin, celluloid, and other thermoplastic resins can be used as other components.

In the present invention, each component (extension material, thermoplastic resin, organic solvent, etc.) used for the above-mentioned composition for pencil lead, for example, a pencil lead for mechanical pencils, a non-fired pencil lead, and a fired pencil lead is kneaded and molded. A core for a pencil lead formed by firing in a dry and non-oxidizing atmosphere or non-firing treatment (low temperature drying at 50 to 120 ° C.) can be formed.
The content of the scaly graphite having the above characteristics used for forming the core for the pencil lead is 20 to 80% by mass (hereinafter simply referred to as “%”) with respect to the total amount of the composition for the pencil lead. Preferably, it is desirable to set it to 30 to 70%, but the optimum value varies depending on the hardness.
If the content of the flaky graphite is less than 20% or exceeds 80%, the balance of hardness, writing quality and strength is lost, which is not preferable.

  In the present invention, for example, in the production of a baked pencil lead for mechanical pencils, preferably, from the viewpoint of strength, concentration, and writing quality, the total amount of the pencil lead blend composition is (a) flaky graphite 20 to 20 having the above characteristics. 80%, (b) 30-60% thermoplastic synthetic resin, (c) 0-30% organic solvent capable of dissolving the thermoplastic synthetic resin is dispersed and mixed with a Henschel mixer, with a pressure kneader and two rolls. After kneading and molding with an extrusion molding machine, drying is performed at 110 to 250 ° C. in an electric furnace, and then 800 to 1400 ° C. and 20 to 40 in a non-oxidizing atmosphere (nitrogen gas atmosphere and inert gas atmosphere). A core for forming a pencil core can be formed by firing over time.

The pencil lead of the present invention is obtained by dispersing nanoparticles in a liquid having a refractive index of 1.3 to 1.5 and a viscosity at 25 ° C. of 7 to 200 mm ² / s in the pencil lead formed above. It is obtained by impregnating the pencil core.

The liquid used in the present invention has a structure in which nanoparticles are impregnated into the pores of the pencil core, and the nanoparticles are brought into contact with the ab surface of the scaly graphite constituting the pencil core, and for the purpose of increasing the concentration, It is used to act as a lubricant, and has a refractive index of 1.3 to 1.5 and a kinematic viscosity at 25 ° C. of 7 to 200 mm ² / s from the viewpoint of easy penetration into pores and light reflectance. What will be mentioned.
The liquid that can be used is not particularly limited as long as it has the above characteristics, and dimethylsilicone, dimethylsilicone oil, carboxymethylcellulose (CMC) liquid, trimethylpentaphenyltrisiloxane, liquid paraffin, and fatty acid ester having the above characteristics. Etc., or a mixture of two or more of them. Specifically, the high call M series by Kaneda, the KF-96 series by Shin-Etsu Chemical, etc. which are marketed are mentioned.
The refractive index in the present invention (including examples and the like to be described later) refers to the absolute refractive index, and the kinematic viscosity is a unit [mm ² / s] based on the viscosity measurement method of JIS K 2283 and JIS Z 8803. For example, it can be directly measured by “Canon Fenceke” or “Ubellode”.

When the refractive index of these liquids is less than 1.3 or more than 1.5, the contribution to the reduction of the reflectance is low, and when the viscosity is less than 7 mm ² / s, the liquid is put into the core. On the other hand, when the viscosity exceeds 200 mm ² / s, the liquid does not penetrate uniformly into the pores, which is not preferable.

  In the present invention, the nanoparticles to be used are not particularly limited as long as they are generally classified as nanoparticles, and any of them can be used. For example, diamond nanoparticles, composite particles of carbon nanotubes, and Carbon nanoparticles such as composite particles of fullerene and ceramics such as oxide ceramics, nitride ceramics, phosphate ceramics, carbide ceramics, silicate ceramics and boride ceramics of metals such as silicon, titanium, zirconium, aluminum and cerium Nanoparticles can be used.

In the case of producing a pencil lead, carbon nanoparticles are preferable from the viewpoint of suppressing hue change, and diamond nanoparticles are particularly preferable from the viewpoint of obtaining economical efficiency and smooth writing property.
Examples of the diamond nanoparticles that can be used include diamond nanoparticles prepared by an explosion method, a static pressure method, an impact compression method, an EACVD method, a gas phase synthesis method, and a liquid phase growth method. Examples include polycrystalline diamond particles, single crystal diamond particles, and cluster diamond.
Specifically, the product name “Nanoamand B” manufactured by Nano Carbon Research Institute, MD series manufactured by Tomei Diamond Industrial Co., Ltd., SCM Nanodiamond manufactured by Sumiishi Materials, SCM Fine Diamond, and CD (Cluster Diamond manufactured by Nanotech Systems) ), CDS (Cluster Diamond Slurry), GCD (Graphite Cluster Diamond), GCDS (graphite Cluster Diamond slurry), JETRO artificial diamond, and the like can be used.

The range of the sphericity of the nanoparticles used is such that the sphericity is 0.1 to 20 nm, preferably 0.1 to 10 nm, and more preferably 0.1 to 5 nm. In the present invention (including examples and the like to be described later), “sphericity” refers to the equivalent of what is defined in JIS B 1501 as a method for measuring ball balls for ball bearings. According to this, the sphericity is measured by measuring the contour of the surface of a steel ball on two or three equator planes that form 90 ° of each steel ball with a roundness measuring machine. Although it is calculated as the maximum value of the distance in the radial direction to the surface, since the nanoparticles of the present invention are too small and cannot be measured by this method, measurement based on JIS was performed. For only one equatorial plane of 10 particles observed on the SEM or TEM screen, the roundness is measured by image processing as the maximum value of the radial distance from the minimum circumscribed circle to the particle surface. Value.
Nanoparticles with a sphericity of less than 0.1 nm are not preferred from the standpoints of raw material procurement, cost, handleability, etc. On the other hand, if nanoparticles with a sphericity of more than 20 nm are used, the nanoparticles themselves This increases the probability of the shape being unsuitable as a solid lubricant, resulting in steric hindrance and increased friction.

In the present invention, the volume average particle diameter (mv value) of the nanoparticles used is such that the pores (closed cells) and pores (closed cells) in the pencil core are connected at the time of production, and open pores (open cells) are connected. Furthermore, from the point of forming, in nanoparticles such as nanoparticles made of the ceramic material and carbon nanoparticles including diamond nanoparticles, the volume average diameter (mv value) 100 of graphite having the above characteristics is 0.01-2. It is necessary to have an mv value, and it is desirable to have an mv value of 0.1 to 1.
The volume average diameter (mv value) of the nanoparticles used is preferably 4 to 100 nm, more preferably 5 to 40 nm, and particularly preferably 5 to 30 nm.
The volume average diameter of nanoparticles such as nanomaterials made of the ceramic material or carbon particles including diamond nanoparticles is less than 0.05 with respect to the volume average diameter (mv value) 100 of graphite having the above characteristics, or the volume average of nanoparticles. When the diameter (mv value) is less than 4 nm, it is difficult to monodisperse as particles and is easy to aggregate, or the reactivity is high and unstable, resulting in a negative effect on the slip of graphite. When the volume average diameter (mv value) of graphite of the characteristic graphite exceeds 2 or the volume average diameter (mv value) of the nanoparticles exceeds 100 nm, the structure as a pencil core collapses and the strength decreases. Absent.
The diamond nanoparticles contain a small amount of impurities, most of which are sp3 surface functional groups derived from the diamond structure, and are components removed when dispersed in oil. Since the other impurities are about 0.2%, the effects of the present invention are not adversely affected. Diamonds with a diamond purity of 99% or higher are solid lubricants with a low coefficient of friction. Generally, impurities that are not solid lubricants in solid lubricants degrade the lubrication characteristics when they exceed 1%. To start doing.

As the content of the nanoparticles having these characteristics in the liquid, the content of the nanoparticles in the pencil lead obtained by the impregnation treatment is preferably 0.001 to 5%, more preferably 0.002. It is adjusted to ˜1%, particularly preferably 0.01 to 0.5%.
In order to make the content of the above-mentioned range of nanoparticles in the obtained pencil lead, it varies depending on the size of the pencil lead, the pore diameter and the pore volume, etc., but in the total amount of the liquid to be impregnated, the nanoparticles are contained. Preferably, it is 0.01 to 10%, more preferably 0.02 to 2%, and particularly preferably 0.05 to 0.5%.
When the content of the nanoparticles in the pencil lead is less than 0.001%, the effective pore volume hardly changes and no difference from the pencil lead not added appears. On the other hand, in order to make the core having a nanoparticle content exceeding 5%, the effective pore volume has to be increased, but this leads to a significant decrease in the strength of the pencil core. Further, although it is necessary to increase the concentration of nanoparticles in the dispersion liquid to be impregnated, this causes a variation in the amount of nanoparticles mixed in the core, which is not preferable.

  In the present invention, the pencil core is immersed as it is in a dispersion liquid in which nanoparticles having the above characteristics are dispersed in a liquid having the above characteristics, or under pressure (for example, 0.5 to 5 MPa) and / or under heating ( For example, by subjecting it to immersion treatment or the like at a liquid temperature of 60 to 200 ° C., the target pencil lead, that is, the pencil lead containing scaly graphite having the above characteristics, has a volume average diameter (mv value) of 100 of the graphite. Thus, a pencil lead is obtained in which nanoparticles having an mv value of 0.05 to 2 and a sphericity of 0.1 to 20 nm are in contact with the ab surface of the graphite.

The resulting pencil lead contains nanoparticles in the above range, and when produced by the above production method, it becomes a pencil lead having suitable wear characteristics and the like, and more preferably defined in JIS S 6005: 2007. The total friction coefficient (dynamic friction coefficient) obtained by dividing the average value (n = 10) of the total friction force in the drawing line by the drawing load in the drawing method using the drawing machine is 0.191 to 0.218. It is desirable that a core body can be obtained in which a smooth writing can be felt even with a sharp core in which the core body rotates.
Moreover, when a 5 μm × 5 μm observing of the polished cross section of the pencil core using a FE-SEM (manufactured by Hitachi High-Tech, S-4700 type, acceleration voltage 5 kV—current value 10 μA), 1 to 300 nanoparticles are observed. It is preferable that 2 to 100 particles are observed when the above-mentioned “more preferable range” nanoparticles are added, and 5 to 50 particles are observed when the “particularly preferable range” is added.
The total coefficient of friction and the number of nanoparticles are the physical properties such as the flatness and aspect ratio of the flaky graphite used, the content thereof, the sphericity of the nanoparticles, the volume average diameter (mv value) and the content thereof. It can be adjusted by suitably combining (impregnation amount) and the kind of oil.

In the present invention configured as described above, a pencil lead compounding composition containing at least flake graphite having an a-axis or a-axis or b-axis and c-axis aspect ratio of 5 or more having an ab surface with a flatness of 2 μm or less. After the calcination treatment, the above characteristics are obtained by impregnating with a liquid having a sphericity of 0.1 to 20 nm and containing nanoparticles having a volume average diameter (mv value) in a specific range with respect to graphite having the above characteristics. Of the porous structure of the pencil core in a state where the nanoparticles are infiltrated into the pores of the porous body composed of flaky graphite (the state where the nanoparticles are in contact with the ab surface of the flaky graphite) Therefore, a changed property can be obtained from a normal one. Specifically, since the nanoparticles contained in the liquid having the above characteristics exhibit the effect of a suspension or a bearing, the lubrication of the core is significantly improved as compared with the case where no nanoparticles are added. This greatly improves the lubrication of the pencil lead. In addition, when the nanoparticles enter the core body, the smooth drawn line causes irregular reflection, so that the so-called “shine” disappears, resulting in a dark color. In addition, due to the action of the flake graphite itself having the above characteristics, the friction between the paper, the flake graphite particles, and the flake graphite particles is reduced, and the erasability is improved. Furthermore, since the nanoparticles can be uniformly dispersed without interfering with the orientation of the flake graphite having the above characteristics, the effect as an extender is added, the compressive strength is improved, and the wear of the core is also improved. Since the amount is small, the amount of graphite on the drawn line is also small and the hands are difficult to get dirty.
Furthermore, in the present invention, in addition to the above-described effects, the pencil lead has a lower drawn line density, writing quality, and static / dynamic friction coefficient than the pencil lead disclosed in Patent Document 1 mentioned above. Even if the pencil core is used for mechanical pencils, etc., where the core rotates every time it is written and is always written by a new part, it has a better and smoother writing feeling and a higher stroke. A pencil core that has a vivid black color and a method for producing the same can be obtained (this point will be described in more detail in Examples and Comparative Examples described later).

  The pencil lead of the present invention is not limited to the above embodiment, and can be implemented with various modifications within the scope of the technical idea of the present invention. For example, before forming the core obtained in the above embodiment, that is, the pencil core formed by baking or non-baking the blended composition for a pencil core containing at least the scaly graphite having the above characteristics, for example, graphite Nanoparticles may be adhered to the ab surface of the particles and filled with a liquid containing nanoparticles having the above characteristics after firing. In this case, since the nanoparticles in the pencil core and the nanoparticles in the liquid are completely independent, the same or different nanoparticles may be used in different contents. In this case, the preferable content of the nanoparticles is desirably a maximum of 10% in the pencil lead.

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

[Examples 1-6, Reference Examples and Comparative Examples 1-7]
The flatness of the scale-like natural graphite to be used, the physical properties such as the aspect ratio, and the sphericity of the nanoparticles were measured by the following measuring methods.
(Measurement method of flatness)
The maximum value of a line parallel to a line segment that connects the particle long axis ends to each other as shown in FIG. (N = 10)
The aspect ratio was calculated by measuring the c-axis length from FIG. 1, measuring the ab plane from the observed image, and calculating the ratio.
(Measurement method of sphericity)
It was determined as the maximum value of the radial distance from the minimum circumscribed circle of 10 particles observed on the SEM or TEM screen to the particle surface.

Example 1
Scale-like natural graphite A (ab surface with flatness 0.2 μm, mv value 8 μm, c-axis thickness 1 μm, aspect ratio 8) 40 parts by weight Polyvinyl chloride 40 parts by weight Sodium stearate 1 part by weight Dioctyl phthalate 19 parts by weight Above The material was mixed and dispersed with a Henschel mixer, kneaded with a pressure kneader and a roll, and after molding, the dioctyl phthalate was dried and baked at 1000 ° C. for 10 hours in a nitrogen gas atmosphere. A fired pencil core having a length of 60 mm was produced.
Next, in the liquid A (liquid temperature 100 ° C., the same applies hereinafter) in which nanoparticles A (0.1% by mass) described below are dispersed, the fired pencil core is impregnated under pressure at 1 MPa (impregnation time 180 minutes, The same applies hereinafter) to obtain a nanodiamond-containing fired pencil lead.
Liquid A: dimethyl silicone oil KF96-30CS (kinematic viscosity 30 mm ² / s, refractive index 1.401, manufactured by Shin-Etsu Chemical Co., Ltd.)
Nanoparticle A: Diamond nanoparticle (sphericity 3 nm, mv value 10 nm, manufactured by Sumitomo Materials)
The nanoparticle A had an mv value of 0.125 with respect to the volume average diameter (mv value) 100 of the scaly natural graphite A.

(Example 2)
Liquid B: CMC-Na 1 wt% distilled water (7 mm ² / s, refractive index 1.345)
Nanoparticle A: Diamond nanoparticle (sphericity 3 nm, mv value 10 nm, manufactured by Sumitomo Materials)
The liquid pencil B obtained by dispersing the nanoparticles A (0.1% by mass) described above was impregnated under pressure at 1 MPa with the fired pencil core obtained in Example 1 to obtain a nanodiamond-containing fired pencil core.

(Example 3)
Liquid C: trimethylpentaphenyltrisiloxane (kinematic viscosity 175 mm ² / s, refractive index 1.580, manufactured by Toray Industries, Inc.)
Nanoparticle A: Diamond nanoparticle (sphericity 3 nm, mv value 10 nm, manufactured by Sumitomo Materials)
The liquid pencil C in which the nanoparticles A (0.1% by mass) described above were dispersed was impregnated at 1 MPa with the fired pencil core obtained in Example 1 to obtain a nanodiamond-containing fired pencil core.

Example 4
Liquid D: Dimethyl silicone: KF-96L-5cs (kinematic viscosity 5 mm ² / s, refractive index 1.396, manufactured by Shin-Etsu Chemical Co., Ltd.)
Nanoparticle A: Diamond nanoparticle (sphericity 3 nm, mv value 10 nm, manufactured by Sumitomo Materials)
The liquid D in which the nanoparticles A (0.1% by mass) described above were dispersed was pressure impregnated with the fired pencil core obtained in Example 1 at 1 MPa to obtain a nanodiamond-containing fired pencil core.

(Example 5)
Liquid E: Dimethyl silicone: KF-96-500 cs (kinematic viscosity 500 mm ² / s, refractive index 1.403, manufactured by Shin-Etsu Chemical Co., Ltd.)
Nanoparticle A: Diamond nanoparticle (sphericity 3 nm, mv value 10 nm, manufactured by Sumitomo Materials)
In the liquid E in which the nanoparticles A (0.1% by mass) described above were dispersed, the fired pencil core obtained in Example 1 was pressure impregnated at 1 MPa to obtain a nanodiamond-containing fired pencil core.

(Example 6)
Scale natural graphite A (ab surface with flatness 0.2 μm, mv value 8 μm, c-axis thickness 1 μm, aspect ratio 8) 70 parts by weight Kaolinite clay 15 parts by weight Halloysite clay 15 parts by weight Water 30 parts by weight Mix and disperse with a Henschel mixer and knead with two rolls until the water content is about 18 parts by mass. After the resulting kneaded product was extruded into a linear body using an extrusion die, it was heat-treated in air at 120 ° C. for 20 hours to remove residual moisture, and in a nitrogen atmosphere to 1,200 ° C. for 10 hours. Firing was performed at 1,200 ° C. for 1 hour.
Subsequently, it immersed in the liquid F of the following description which disperse | distributed the nanoparticle A (0.1 mass%) of the following description, and was immersed in oil, and obtained the wood-axis pencil lead of diameter 2.05mm.
Liquid F: Miyoshi adjustment lard (manufactured by Miyoshi Yushi Co., Ltd.)
Nanoparticle A: Diamond nanoparticle (sphericity 3 nm, mv value 10 nm, manufactured by Sumiishi Materials)
In addition, with respect to the volume average diameter (mv value) 100 of the scaly natural graphite A, the nanoparticles had an mv value of 0.125.

(Reference example, nanoparticles A are mixed and dispersed in the material)
Scale-like natural graphite A (ab surface with a flatness of 0.2 μm, mv value of 8 μm, c-axis thickness of 1 μm, aspect ratio of 8) 40 parts by mass Diamond nanoparticles (sphericity of 3 nm, mv value of 10 nm, manufactured by Sumitomo Materials) )
0.1 parts by weight Polyvinyl chloride 40 parts by weight Sodium stearate 1 part by weight Dioctyl phthalate 19 parts by weight The above materials are mixed and dispersed with a Henschel mixer, kneaded with a pressure kneader and a roll, and after molding, after dioctyl phthalate is dried, A fired pencil core having a diameter of 0.565 mm and a length of 60 mm was manufactured by firing at 1000 ° C. for 10 hours in a nitrogen gas atmosphere.
Next, the fired pencil core was pressure impregnated at 1 MPa in the liquid A used in Example 1 to obtain a nanodiamond-containing fired pencil core.

(Comparative Example 1, conforming to Example 11 of JP2007-138031A)
Flatness 3 μm, mv value 10 μm, c-axis thickness 1 μm, flaky natural graphite with aspect ratio 10 49 parts by weight Diamond nanoparticles (single crystal diamond, sphericity 1.5 nm, mv value 5 nm) 1 part by weight polyvinyl chloride 50 parts by weight Sodium stearate 1 part by weight Dioctyl phthalate 20 parts by weight The above materials are mixed and dispersed with a Henschel mixer, kneaded with a pressure kneader and two rolls and extruded into a linear body, and then the remaining plasticizer is removed. After heat treatment in air as much as possible, solidify (dry), calcinate in a nitrogen gas atmosphere at 1000 ° C., and finally immerse in α-olefin oligomer (Lion Corporation, Lipoloop 20) and soak in oil. A mechanical pencil lead HB having a thickness of 0.570 mm was obtained.

(Comparative Example 2)
Liquid A: dimethyl silicone oil KF96-30CS (kinematic viscosity 30 mm ² / s, refractive index 1.401, manufactured by Shin-Etsu Chemical Co., Ltd.)
Nanoparticle B: Diamond nanoparticle (sphericity 25 nm, mv value 50 nm, manufactured by Sumitomo Materials)
In the liquid B (liquid temperature 100 ° C.) in which the nanoparticles B (0.1% by mass) described above are dispersed, the fired pencil core obtained in Example 1 is pressure impregnated at 1 MPa (impregnation time 180 minutes). And a nanodiamond-containing fired pencil lead was obtained.

(Comparative Example 3)
Scale-like natural graphite A of Example 1 (ab surface with a flatness of 0.2 μm, mv value of 8 μm, c-axis thickness of 1 μm, aspect ratio of 8) and the same amount of scaly natural graphite B (ab surface with a flatness of 3 μm) A nanodiamond-containing fired pencil lead was obtained in the same manner as in Example 1 except that the mv value was 10 μm, the c-axis thickness was 1 μm, and the aspect ratio was 10).

(Comparative Example 4)
The same amount of scaly natural graphite A (with a flatness of 0.2 μm) (the ab surface with a flatness of 0.2 μm, mv value of 8 μm, c-axis thickness of 1 μm, aspect ratio of 8) of Example 1 above. A nanodiamond-containing fired pencil lead was obtained in the same manner as in Example 1, except that the ab surface, mv value was 3 μm, c-axis thickness was 1 μm, and aspect ratio was 3).

(Comparative Example 5)
The pencil core obtained in Example 1 above was impregnated under pressure in the same manner as in Example 1 above in the liquid A used in Example 1 containing no nanoparticles A, to obtain a nanodiamond-containing fired pencil core.

(Comparative Example 6, conforming to Example 11 of JP2007-138031A)
Flatness 3 μm, mv value 10 μm, c-axis thickness 1 μm, flaky natural graphite with an aspect ratio 10 69 parts by weight Diamond nanoparticles (single crystal diamond, sphericity 1.5 nm, mv value 5 nm) 1 part by weight Kaolinite clay 15 parts by weight Halloysite clay 15 parts by weight Water 30 parts by weight The above materials are mixed and dispersed with a Henschel mixer, and sufficiently heated and kneaded with two rolls until the water content is about 18 parts by weight. After the resulting kneaded product was extruded into a linear body using an extrusion die, it was heat-treated in air at 120 ° C. for 20 hours to remove residual moisture, and in a nitrogen atmosphere to 1,200 ° C. for 10 hours. Firing was performed at 1,200 ° C. for 1 hour.
Subsequently, it was immersed in the liquid F (Miyoshi adjustment lard) used in Example 6, and was immersed in oil, and the wood-axis pencil lead of diameter 2.05mm was obtained.

(Comparative Example 7)
The pencil core obtained in Example 6 was immersed in the liquid F (Miyoshi adjustment lard) used in Example 6 that does not contain nanoparticles A in the same manner as in Example 6 above, and the wood shaft with a diameter of 2.05 mm. I got a pencil lead.

About each baking pencil lead (a pencil lead for mechanical pencils, a wood spindle pencil lead) obtained in Examples 1 to 6, Reference Examples and Comparative Examples 1 to 7, bending strength and compressive strength (N) are as follows. Abrasion amount (mm), concentration, erasure rate (%), coefficient of friction (static, dynamic), number of nanoparticles, writing feeling by sensory evaluation, difficulty of soiling, and initial slip were evaluated.
These results are shown in Table 1 below.

(Measurement method of bending strength)
For the pencil cores for mechanical pencils of Examples 1 to 5, Reference Examples and Comparative Examples 1 to 6, the bending strength was measured by the bending strength test defined in JIS S 6005: 2007. (N = 100) In addition, the bending strength was measured in the bending strength test defined in JIS S 6006: 2007 (n = 100) for the wood spindle pencil cores of Example 6 and Comparative Examples 6 and 7.

(Measurement method of compressive strength)
The core was placed horizontally and fixed on a plane, and the breaking strength was measured by a compression test from above with a compression jig having a width of 2 mm and a width of 5 mm with Tensilon (ORIENTEC RTC-1150A) (n = 100).
In addition, since the compressive strength which is this evaluation item is an index which shows that it is hard to crush with the chuck | zipper of the pencil lead for mechanical pencils, it does not measure with the wood-axis pencil lead of Example 6 and Comparative Examples 6 and 7, and evaluation is carried out. “−”.

(Test method for wear test)
The wear length of the core when writing at a writing angle of 75 °, a load of 300 gf, and a writing distance of 5 m was measured (n = 10).
(Measurement method of concentration)
It is the value which measured the drawn line written by the abrasion test with the densitometer (sakura DENSI TO METER PDA65) (n = 10x4 place).
(Erasing rate measurement method)
The stroke erasure rate after the stroke drawn by the abrasion test was reciprocated 5 times with an eraser (EP-105E) was determined (n = 10).

(Friction coefficient measurement method)
The value (n = 10) obtained by dividing the average value of the total frictional force in the image line in the image line method using the image line stipulated in JIS S 6005: 2007 and JIS S 6006: 2007 by the writing load is “ The value obtained by dividing the maximum value of friction by the written load was defined as the “dynamic friction coefficient”.
(Measurement method of the number of nanoparticles)
The number of nanoparticles when the polished cross section of each pencil lead was observed at 5 μm × 5 μm was measured using FE-SEM (manufactured by Hitachi High-Tech, S-4700 type, acceleration voltage 5 kV—current value 10 μA). .

[Writing feeling, resistance to soiling of soiled hands (difficulty in soiling), initial slip evaluation method]
Ten subjects repeatedly wrote a 400-character-packed manuscript paper as “Mitsubishi Pencil”, and compared with our existing product (“SHU” 0.5 mm-HB, manufactured by Mitsubishi Pencil Co., Ltd.). went.
The writing feeling was evaluated according to the following evaluation criteria by comparing whether or not it felt smooth.
The stain resistance was evaluated according to the following evaluation criteria by comparing stains on the hand after writing 400 characters.
The initial slip was evaluated according to the following evaluation criteria by comparing whether or not each stroke was smooth.
Evaluation criteria (average value):
◎: Very good ○: Better than existing product △: Equivalent to existing product ×: Worse than existing product

As is clear from the results of Table 1 above, each pencil lead for mechanical pencils 1 to 5 within the range of the present invention, and the wood spindle pencil core of Example 6 are comparative examples 1 to 5 and reference that are outside the range of the present invention. Compared to the pencil lead for each of the mechanical pencils of the examples, and the wood spindle pencil lead of Comparative Examples 6 and 7, it has excellent bending strength and compressive strength, has sufficient color developability and drawing density, and is less worn and erased. It was found that the results were good, initial slip, good writing feeling (writing taste), and difficult to get dirty.
On the other hand, when the comparative examples are viewed individually, Comparative Example 1 is a case where nanoparticles outside the scope of the present invention based on Example 11 of Japanese Patent Laid-Open No. 2007-138031 are used. Examples 3 and 4 are cases where scaly graphite that is outside the scope of the present invention is used, and Comparative Example 5 is a case where nanoparticles are not used. It turned out that it was not obtained. Comparative Example 6 is a wood-axis pencil lead that conforms to Example 11 of JP 2007-138031 A, and Comparative Example 7 is a wood-axis pencil lead that does not use nanoparticles. It was found that the target pencil lead could not be obtained with the lead.

  In addition to the pencil lead used for mechanical pencils, pencils for wooden axes, etc., it is a pencil lead used for mechanical pencils of the type where the core rotates at every writing and is always written by a new part. However, it is possible to obtain a pencil core having a better smooth writing feeling and a bright black color having a higher drawing density and a method for producing the same.

Claims (7)

In a pencil core containing scaly graphite having an a-axis or ab-axis having an ab surface with a flatness of 2 μm or less and an aspect ratio of c-axis of 5 or more, the volume average diameter (mv value) of the graphite is 100 Nanoparticles selected from carbon nanoparticles and ceramic nanoparticles having a mv value of 0.05 to 2 and a sphericity of 0.1 to 20 nm are in contact with the ab surface of the graphite in the pores of the pencil core. A pencil lead characterized by that.   The pencil lead according to claim 1, wherein the nanoparticles used for the pencil lead are carbon nanoparticles.   The pencil lead according to claim 2, wherein the carbon nanoparticles are diamond.   4. The pencil lead according to claim 1, wherein the nanoparticles have a volume average diameter (mv value) of 4 to 100 nm.   The total friction coefficient obtained by dividing the average value (n = 10) of the total friction force in the image line in the image line method using the image line machine defined in JIS S 6005: 2007 by the writing load is 0.191 to It is 0.218, The pencil lead as described in any one of Claims 1-4 characterized by the above-mentioned.   6. The nanoparticle is observed in an amount of 1 to 300 when the polished cross section of the pencil core is observed at 5 μm × 5 μm using FE-SEM (acceleration voltage 5 kV). Pencil lead as described in one. After forming a core of a pencil core containing scaly graphite having an a-axis or b-axis and c-axis having an ab surface with a flatness of 2 μm or less and an aspect ratio of 5 or more, the volume average diameter of the graphite (mv value) ) Nanoparticles selected from carbon nanoparticles and ceramic nanoparticles having an mv value of 0.05 to 2 with respect to 100 and a sphericity of 0.1 to 20 nm are 25 with a refractive index of 1.3 to 1.5. A method for producing a pencil lead, wherein the pencil lead is impregnated after being dispersed in a liquid having a viscosity at 7 ° C. of 7 to 200 mm ² / s.