JP6167696B2 - Firing pencil lead - Google Patents

Description

  The present invention relates to a pencil lead obtained by firing.

General fired pencil lead requires graphite, boron nitride, talc, etc., synthetic resin, plasticizer such as phthalate ester, solvent such as methyl ethyl ketone, stearate, stearic acid, carbon black, amorphous silica, etc. Depending on the combination, these compounded materials are dispersed and mixed, kneaded, extruded into a thin line, heat treated up to the firing temperature, and an oily substance is added in the pores of the obtained fired core as necessary. Complete by impregnation.
Among graphite, boron nitride, talc, and the like, which are main materials, graphite is suitable for drawing because it has black to steel gray color, and has high lubricity, so it is preferably used as a main material for pencil cores.

A pencil core can be obtained by selecting various core diameters at the time of extrusion molding, and a core body having a desired handwriting concentration and hardness can be obtained by changing the blending and firing temperature. In general, when trying to increase the bending strength, it becomes difficult to wear during writing, and the bending strength is large, but the handwriting concentration tends to be thin, and conversely, when trying to increase the handwriting concentration The bending strength is small, and the core is easy to break due to the force applied at the time of writing or the impact when dropped. Thus, there is a negative correlation between bending strength and handwriting density.
Various inventions for breaking this negative correlation have been reported, and some of them use inorganic plate-like particles. The invention described in Japanese Patent Application Laid-Open No. 2004-262984 (Patent Document 1) relates to a pencil lead containing plate-like alumina in a compounded material, and is described in Japanese Patent Application Laid-Open No. 2003-313485 (Patent Document 2). The present invention relates to a pencil lead containing flat titanium diboride, and the invention described in Japanese Patent Application Laid-Open No. 2008-081715 (Patent Document 3) relates to a pencil lead using a so-called synthetic fluorine phlogopite. It is.

JP 2004-262984 A JP 2003-313485 A JP 2008-081715 A

  The invention described in Patent Document 1 is intended to improve the handwriting concentration by attaching resin carbide to the surface of plate-like alumina, and the invention described in Patent Document 2 is based on the blackness of flat titanium diboride particles. However, in such a method of increasing the handwriting concentration simply by the color of the inorganic plate-like particles, it is necessary to add approximately 10 wt% or more with respect to graphite. When such an amount is blended, the hard inorganic plate-like particles collide with each other in the kneading process by a roll mill or the like, so that the particle size at the time of blending is not retained, and many fine powders are generated by pulverization. Since this fine powder is not large enough to form a skeleton with graphite, the core strength is the strength of the graphite alone skeleton, and it easily adheres to and aggregates with inorganic plate-like particles of the same composition, reducing the surface smoothness. This prevents the orientation of the inorganic plate-like particles. Therefore, the core strength does not actually increase and is not sufficient to break the negative correlation between the bending strength and the handwriting density. The invention described in Patent Document 3 uses a flake-shaped synthetic fluorophlogopite to make a dense core body that is oriented in the same direction as graphite at the time of extrusion molding, and is a core body that is hard to break with improved handwriting concentration due to attached carbides. However, simply increasing the orientation of the core does not function as a skeleton because the bond between the synthetic fluorophlogopite and graphite is weak, so it is not sufficient to break the negative correlation between bending strength and handwriting concentration. It was.

The present invention relates to a pencil core obtained by firing, and at least graphite and an inorganic plate-like particle having an oxygen atom aspect ratio of 5 or more and a particle size of 1 μm or more in the core of 0.1 wt% to 0.45 wt% and It is contained in an amount of 0.15 wt% to 0.75 wt% with respect to graphite , the aspect ratio is 5 or more, the particle size is 1 μm or more, and the number ratio of inorganic plate-like particles having oxygen atoms is 90% or more and the flatness is 500 nm or less The gist of the present invention is a fired pencil lead that is characterized.

Graphite and inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle size of 1 μm or more are extruded in the form of fine wires in a state of being mixed with other blends, respectively. There is a high probability that the ab surfaces (basal surfaces) are oriented in the same direction, and the surfaces are easily bonded to each other. Since the surface of this inorganic plate-like particle has an oxygen atom, it binds to the surface of graphite having a reducing action and becomes a skeleton in the core to support the core, and because of its ab surface, it supports the core against bending. It is easy to assume that high bending strength can be realized.
If the particle size of the inorganic plate-like particles is 1 μm or more, the aggregation action due to the intermolecular force between the particles is weak, so the intermolecular force does not hinder the orientation. On the other hand, when the particle size of the inorganic plate-like particles is less than 1 μm, the aggregation action due to the intermolecular force between the particles becomes strong, and the orientation of other graphite, which lowers its orientation, is hindered.
And at the time of writing, the edge surface, which is the edge of the inorganic plate-like particles arranged in an aligned state, is rubbed against the paper surface, coupled with the fact that the particles are somewhat large, the effect of wrinkles works, the ab surface bond is easily peeled off and the graphite It is inferred that the core can be separated from the core, and the core is worn to obtain a high handwriting density.
As described above, by containing inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle size of 1 μm or more, a pencil core that breaks the negative correlation between the bending strength and the handwriting density is obtained.

  Further, when the inorganic plate-like particles are cleaved plate-like particles, it is assumed that the particles themselves are cleaved and broken at the time of writing, so that the core is easily broken and becomes a core having a high handwriting density.

  Further, when the cleaving plate-like particles are amorphous, the surface activity is high, so that the bond between graphite and particles can be strengthened, and a core body with higher bending strength can be obtained.

Hereinafter, the present invention will be described in detail.
Graphite that is preferably used as the main material of the pencil lead can be broadly divided into artificial graphite and natural graphite. For use as a pencil lead, natural graphite having a good growth and cleavage is generally used. ing. Natural graphite is generally classified into scaly graphite and scaly graphite with developed crystals, and low crystalline earthy graphite with low purity. The flake graphite with a smooth surface improves the strength of the core by orienting in the extrusion direction when forming the core into a thin line shape, and also has a smooth hand feeling and high handwriting due to its excellent cleavage. Since the density can be obtained, it is preferably used for obtaining the bending strength and the handwriting density.

In the present invention, the particle size is defined as the minimum value of the a-axis length or the b-axis length among the a-axis, b-axis, and c-axis of the particles photographed with an electron microscope. The aspect ratio is defined as (particle size / c-axis length).
Examples of the inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle size of 1 μm or more include plate-like materials such as metal oxides, silicates, and phosphates. Specifically, plate-like alumina, plate-like silica as metal oxide, mica, talc, vermiculite as silicate, plate-like apatite as phosphate, and the like can be mentioned. Generally, if the aspect ratio (minimum value of a-axis length or b-axis length / c-axis length) is 5 or more, it is said to be a plate shape. When the aspect ratio is 5 or more, the orientation during molding is good, and when the aspect ratio is less than 5, it is difficult to obtain the effect of bonding between the faces due to the decrease in orientation, and the orientation of the graphite is disturbed. It has a negative effect on the bending strength. In addition, many particles with high ab surface flatness (maximum value of the line parallel to the line connecting the particle long axis ends in the SEM photograph observed with the ab surface being perpendicular) are included. Therefore, it can be said that it is advantageous to obtain a bonding effect between the surfaces, and it is preferable that 90% or more of particles having a flatness of 500 nm or less are present in number ratio.
When such inorganic plate-like particles are contained in the core body, the carbon in the graphite having a reducing action deprives or attracts oxygen atoms in the particles, so that the charge on the particle surface moves, and the contact between the particles and the graphite occurs. Bonding force between carbon and oxygen works on the surface, and sintering that reduces the surface energy occurs on the contact surface between the inorganic plate-like particles, and a skeleton can be formed.
The orientation and wrinkle action acting on the inorganic plate-like particles are hardly affected by the number of particles and can be effective even in a small amount. The inorganic plate-like particles are contained in the core at 0.1 wt% or more with respect to graphite. A core body having the effects of the present invention can be obtained in an amount of 0.15 wt% or more.
In addition, since the step of kneading the material leads to fineness due to collision between particles in the compound, the core contains 0.1 wt% to 0.45 wt% and 0.15 wt% to 0.75 wt% with respect to graphite. If it is made to do, since the particle size of the added initial state is maintained, it is more preferable.

Commercially available inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle size of 1 μm or more include Seraph 05025, 05070, 07070, and 10030 (made by Kinsei Matec Co., Ltd.) as plate-like alumina, Plate-like HAP (made by Iwase Cosfa Co., Ltd.) as plate-like apatite, Y-1800, Y-3000, SA-310, FA-450 (made by Yamaguchi Mica Co., Ltd.) as cleaved silicate mica , Talc as CT-35, CT-250 (above manufactured by Yamaguchi Mica Co., Ltd.), P-8, P-6, P-4, P-3, P-2, MS-P, MSW, MS (above Japan) Sylleaf (manufactured by Mizusawa Chemical Co., Ltd.) and the like are exemplified as cleaved inorganic amorphous plate-like particles.
In addition, it does not prevent that the inorganic particle which is less than 1 micrometer is used together in the pencil core of this invention.

In the present invention, the confirmation of inorganic plate-like particles having an oxygen atom-containing aspect ratio of 5 or more and a particle size of 1 μm or more in the core is performed by heat-treating the pencil core after firing in an oxidizing atmosphere, such as graphite. It is good to confirm by observing the ash content of the inorganic plate-like particles obtained by eliminating the carbonaceous matter from oxidation exhaustion. Generally, graphite and carbides in an oxidizing atmosphere start to be oxidized and consumed from about 400 ° C. to 500 ° C. Therefore, heat treatment at 800 ° C. to 900 ° C. is performed to obtain ash. Judgment of ash content is based on the disappearance of the lead color of graphite. If the heat treatment takes a long time, the inorganic plate-like particles may be oxidized and consumed. Therefore, the treatment for about 2 to 3 hours is preferable.
In the present invention, the baked pencil lead to be observed is placed on a magnetic dish, held in an oxidizing atmosphere furnace maintained at 900 ° C. for 2 hours, and then cooled and confirmed to be ash with an optical microscope (magnification 100 times). The aspect ratio, particle size, and flatness are confirmed by observing from the side of the core with a scanning electron microscope (magnification 5000 times) (average value of n = 10). The confirmation of the content of the inorganic plate-like particles in the core may be calculated from the weight before and after ash treatment.

As a material other than the above, a conventionally used constituent material of a fired pencil core can be used without limitation, and a conventionally known production method can be used without limitation.
For example, inorganic particles such as boron nitride that do not have oxygen atoms can be used in combination, such as polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, chlorinated polyethylene, chlorinated paraffin resin, furan resin, polyvinyl chloride. Synthetic resins such as alcohol, styrene resin, acrylic resin, urea resin, melamine resin, polyester resin, styrene-butadiene copolymer, polyvinyl acetate, polyacrylamide resin, and butyl rubber are used in combination of one or more as required. You can also Further, conventionally known plasticizers such as dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diallyl isophthalate, tricresyl phosphate, dioctyl adipate, ketones such as methyl ethyl ketone and acetone, ethanol and the like Solvents such as alcohols, solvents such as water, fatty acids such as stearic acid and behenic acid and fatty acid amides, and stabilizers such as stearate may be used in combination. In addition, oxides or nitrides of metals such as iron, aluminum, titanium, and zinc, amorphous silica, carbon black, fullerene, carbon nanotubes, and carbon fibers may be used in combination.
These compounded materials are uniformly dispersed with a kneader, a Henschel mixer, three rolls, etc., then formed into a thin wire shape, and appropriately heat-treated according to the resin used, and finally at 800 ° C. to 1300 ° C. in a non-oxidizing atmosphere. A fired pencil core is obtained by performing a baking treatment. In order to prevent the inorganic plate-like particles from being pulverized and becoming a fine powder of less than 1 μm at the time of kneading, for example, the amount of inorganic plate-like particles is suppressed or inorganic in the middle of the roll. A plate-like particle may be added to reduce the load on the particle.
After that, if necessary, α-olefin oligomer, silicone oil, liquid paraffin, spindle oil, synthetic oil such as ester oil, animal and vegetable oil such as squalane, castor oil, paraffin wax, microcrystalline wax, polyethylene wax, montan wax, carnauba It is manufactured by impregnating a waxy material such as wax.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited only to an Example.

<Example 1>
Polyvinyl chloride 30 parts by weight Graphite 25 parts by weight Plate-like alumina (average particle size 5 μm, manufactured by Kinsei Matec Co., Ltd.) 0.25 parts by weight Zinc stearate 0.5 parts by weight Stearic acid 2 parts by weight Dibutyl phthalate 10 parts by weight 20 parts by weight of methyl ethyl ketone The above material was dispersed and mixed with a Henschel mixer, kneaded with a three roll for 10 minutes, then extruded into a thin line with a single screw extruder (pressure 500 MPa), and from room temperature to 300 ° C. in air. The temperature is increased over about 10 hours, and heat treatment is performed at 300 ° C. for about 1 hour. Further, a baking treatment is performed to achieve a maximum of 1000 ° C. in a sealed container, and after cooling, liquid paraffin is impregnated. A pencil lead with a nominal diameter of 0.5 was obtained.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 2 μm, and the aspect ratio was 7. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 2>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the plate-like alumina used in Example 1 was replaced with an average particle size of 10 μm (manufactured by Kinsei Matec Co., Ltd.).
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 3 μm and the aspect ratio was 8. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 3>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1, except that the plate-like alumina to be used was replaced with an average particle size of 10 μm and added after 5 minutes of the kneading treatment with three rolls. .
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 4 μm and the aspect ratio was 8. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 4>
A pencil lead with a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the plate-like alumina used in Example 1 was replaced with an average particle size of 2 μm (manufactured by Kinsei Matec Co., Ltd.).
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 1 μm and the aspect ratio was 5. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 5>
0.25 parts by weight of alumina fine particles having an average particle size of 0.4 μm (AHP200, manufactured by Nippon Light Metal Co., Ltd.) were previously stirred together with a small amount of dibutyl phthalate in a mixer to prepare alumina aggregates.
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the alumina aggregate was replaced with the plate-like alumina in Example 1.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 3 μm and the aspect ratio was 5. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. Incidentally, 90% of particles having a flatness of 500 nm or less were present.

< Comparative Example 1 >
In Example 5, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 5, except that the prepared alumina aggregate was added after 5 minutes of the kneading treatment with three rolls.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 4 μm and the aspect ratio was 5. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. In addition, 80% of particles having a flatness of 500 nm or less were present.

<Example 6 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the blending amount of the plate-like alumina was changed to 0.20 parts by weight.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 4 μm and the aspect ratio was 9. Moreover, content in a core is 0.5 wt%, and content with respect to graphite is 0.80 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 7 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the compounding amount of the plate-like alumina was changed to 0.03 parts by weight.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 5 μm and the aspect ratio was 10. Moreover, content in a core is 0.07 wt%, and content with respect to graphite is 0.12 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 8 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the blending amount of the plate-like alumina was changed to 0.15 parts by weight.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 5 μm and the aspect ratio was 10. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 9 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the blending amount of the plate-like alumina was changed to 0.19 parts by weight.
The particle diameter of the plate-like alumina in confirming the ash content of the core was 5 μm and the aspect ratio was 10. Moreover, content in a core is 0.45 wt%, and content with respect to graphite is 0.75 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 10 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the amount of the plate-like alumina was changed to 0.10 parts by weight.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 5 μm and the aspect ratio was 10. Moreover, content in a core is 0.25 wt%, and content with respect to graphite is 0.40 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 11 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the amount of the plate-like alumina was changed to 0.04 parts by weight.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 5 μm and the aspect ratio was 10. Moreover, content in a core is 0.10 wt%, and content with respect to graphite is 0.15 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 12 >
In Example 1, the plate-like alumina is replaced with talc (cleavable, crystalline, MICRO ACE P-3, average particle size 5.0 μm, manufactured by Nippon Talc Co., Ltd.), and the blending amount is 0.15 parts by weight. A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except for the change.
The particle diameter of talc as determined by checking the ash content of the core was 5 μm, and the aspect ratio was 10. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 13 >
In Example 1, plate-like alumina was replaced with mica (with cleaving property, crystalline, SJ-005, average particle size 5.0 μm, manufactured by Yamaguchi Mica Co., Ltd.), and the blending amount was changed to 0.15 parts by weight. Otherwise, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1.
The particle diameter of mica obtained by confirming the ash content of the core was 5 μm, and the aspect ratio was 10. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 14 >
In Example 1, plate-like alumina was replaced with mica (with cleaving property, crystalline, A-11, average particle size 3.0 μm, manufactured by Yamaguchi Mica Co., Ltd.), and the blending amount was changed to 0.15 parts by weight. Otherwise, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1.
The particle diameter of mica obtained by confirming the ash content of the core was 3 μm, and the aspect ratio was 7. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 15 >
In Example 1, plate-like alumina was replaced with mica (cleavable, crystalline, SJ-010, average particle size 10.0 μm, manufactured by Yamaguchi Mica Co., Ltd.), and the blending amount was changed to 0.15 parts by weight. Otherwise, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1.
The particle diameter of mica obtained by confirming the ash content of the core was 10 μm, and the aspect ratio was 15. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 16 >
In Example 1, the plate-like alumina is replaced with plate-like silica (with cleaving, amorphous, silleaf, average particle size 5.0 μm, manufactured by Mizusawa Chemical Co., Ltd.), and the blending amount is 0.15 parts by weight. A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except for the change.
The particle diameter of the platy silica obtained by confirming the ash content of the core was 5 μm, and the aspect ratio was 10. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 17 >
In Example 1, plate-like alumina was pulverized with a pulverizer (Starburst, manufactured by Sugino Machine Co., Ltd.) to replace plate-like silica with a particle size of 3 μm, and the blending amount was changed to 0.15 parts by weight. Obtained a pencil lead having a nominal diameter of 0.5 in the same manner as in Example 1.
The particle diameter of the platy silica obtained by confirming the ash content of the core was 3 μm, and the aspect ratio was 8. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 18 >
A pencil having a nominal diameter of 0.5 in the same manner as in Example 1, except that the plate-like alumina was replaced with 0.15 parts by weight of plate-like silica and added after 5 minutes of the kneading treatment with the three rolls. I got a wick.
The particle diameter of the plate-like silica obtained by confirming the ash content of the core was 8 μm, and the aspect ratio was 14. Moreover, content in a core is 0.37 wt%, and content with respect to graphite is 0.60 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 19 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the plate-like alumina was changed to plate-like silica and the blending amount was changed to 0.05 parts by weight.
The particle diameter of the platy silica obtained by confirming the ash content of the core was 5 μm, and the aspect ratio was 10. Moreover, content in a core is 0.12 wt%, and content with respect to graphite is 0.20 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Example 20 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that 25 parts by weight of graphite was replaced with 20 parts by weight and 5 parts by weight of boron nitride (average particle size: 13 μm) was added. It was.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 2 μm, and the aspect ratio was 7. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.25 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Comparative Example 2 >
A pencil lead having a nominal diameter of 0.5 in the same manner as in Example 1 except that the plate-like alumina was replaced with alumina having an average particle diameter of 0.6 μm (LS-500, manufactured by Nippon Light Metal Co., Ltd.). Got.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 0.6 μm, and the aspect ratio was 2. The core content is 0.61 wt%, and the content with respect to graphite is 1.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Comparative Example 3 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the blending amount of the plate-like alumina was changed to 3.0 parts by weight.
The particle diameter of the plate-like alumina obtained by confirming the ash content of the core was 0.5 μm and the aspect ratio was 8. Moreover, content in a core is 7.38 wt%, and content with respect to graphite is 12.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Comparative example 4 >
In Example 1, except that the plate-like alumina was replaced with synthetic fluorine phlogopite (average particle size 6 μm, PDM-5B, manufactured by Topy Industries Co., Ltd. ), and the blending amount was changed to 3.0 parts by weight. In the same manner, a pencil lead having a nominal diameter of 0.5 was obtained.
The particle diameter of the synthetic fluorine phlogopite obtained by confirming the ash content of the core was 0.6 μm and the aspect ratio was 7. Moreover, content in a core is 7.38 wt%, and content with respect to graphite is 12.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Comparative Example 5 >
In Example 1, except that the plate-like alumina was replaced with flat titanium diboride (average particle diameter of 4 μm, TiB2-N, manufactured by Nippon Shin Metal Co., Ltd. ), the nominal diameter of 0. A pencil lead of 5 was obtained.
The particle diameter of the flat titanium diboride obtained by confirming the ash content of the core was 4 μm and the aspect ratio was 8. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. Incidentally, 100% of the particles having a flatness of 500 nm or less were present.

<Comparative Example 6 >
A pencil lead having a nominal diameter of 0.5 in the same manner as in Example 1 except that the plate-like alumina was replaced with spherical alumina (average particle size 5 μm, DAM-05, manufactured by Denki Kagaku Kogyo Co., Ltd.) . Got.
The particle diameter of the spherical alumina obtained by confirming the ash content of the core was 5 μm. Moreover, content in a core is 0.61 wt%, and content with respect to graphite is 1.0 wt%. There are no particles having a flatness of 500 nm.

<Comparative Example 7 >
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that plate-like alumina was not used.
None of the resulting core ash remained.

  As described above, the bending strength and the concentration were evaluated in accordance with JIS S 6005 for the pencil lead obtained in each example and comparative example.

As is clear from the results of Table 1 above, the pencil cores of Examples 1 to 20 within the scope of the present invention were found to be superior in bending strength and handwriting density as compared with the pencil cores of Comparative Examples 1 to 7 .
Example 1 is obtained by containing a core plate-like alumina having a particle size of 2μm an aspect ratio of 7, Comparative Example 2 having a particle size of 0.6μm in Comparative Example 7 and aspect ratio 2 of unformulated, grain aspect ratio 8 The comparative example 3 having a diameter of 0.5 μm, the comparative example 5 using flat titanium dioxide having no oxygen atom, the bending strength is high and the concentration is equal to or higher than that of the plate-like alumina having an oxygen atom. The effect is obtained by the particle size. In addition, the particle diameter of Example 1 is changing from the particle diameter of 5 micrometers at the time of a mixing | blending, and it is guessed that the refinement | miniaturization has occurred by the collision of the particles in a compounding.
In Examples 1 to 4, the size of the plate-like alumina to be blended and the kneading conditions were changed to change the obtained particle size in the range of 1 to 4 μm, and Example 4 having a particle size of 1 μm was a comparative example. Compared to 3 , the bending strength and concentration are improved, and an effect can be obtained with a particle size of 1 μm or more. Further, since the bending strength is improved as the particle size is increased and the concentration decrease is small, it is presumed that the larger the particle size, the easier the adhesive action and wrinkle action work.
Example 5 and Comparative Example 1 were obtained by pre-aggregating alumina fine particles to obtain plate-like alumina in the core, and the contents of particles having a flatness of 500 nm or less were 90% and 80%, respectively. . Comparative Example 1 having a particle size of 4 μm has a larger particle size than that of Example 5 and Example 2 having a particle size of 3 μm, but the bending strength is reduced. It is advantageous to obtain, and it can be said that 90% or more of particles having a flatness of 500 nm or less are preferably present.
In Examples 6 to 11 , the content of the plate-like alumina in the core was changed in the range of 0.07 to 0.50 wt%, and the content relative to the graphite was changed in the range of 0.12 to 0.80 wt%. Example 6 having a body content of 0.50 wt% and a content of 0.80 wt% relative to graphite, Example 7 having a core content of 0.07 wt% and a content based on graphite of 0.12 wt%, and a core content There is a large difference in bending strength from Examples 8 to 11 in which the content is 0.15% to 0.45% by weight and the content with respect to graphite is 0.15% to 0.75% by weight. The amount is 0.1 wt% to 0.45 wt% and the content with respect to graphite is 0.15 wt% to 0.75 wt%. Note particle size in Examples 8-11 has not changed from the particle size 5μm in formulation, miniaturization due to collision among particles in the formulation is estimated to have been avoided.
Examples 12 to 15 are those using crystalline mica or talc having cleaving property as the inorganic plate-like particles, and the concentration is higher than those in Examples 8 to 11 using crystalline plate-like alumina having no cleaving property. The core is easy to collapse due to the cleavage of the particles, and a high concentration can be obtained. In addition, as with the plate-like alumina, the larger the particle size, the better the bending strength and the less the decrease in concentration. Therefore, it is assumed that the larger the particle size, the easier the action of adhesion and wrinkle.
Examples 16 to 19 use cleaved amorphous plate-like silica as inorganic plate-like particles, and the bending strength is higher than those of Examples 12 to 15 containing crystalline cleaved plate-like particles. It is speculated that the high surface activity of the amorphous material strengthens the bond between graphite and particles, and provides a higher bending strength.
Example 20 is a combination of plate-like alumina and boron nitride which is an inorganic particle having no oxygen atom. The same effect as in Example 1 was obtained, and an inorganic particle having no oxygen atom was used in combination. Even in this case, the effect of the present invention can be obtained.
As described above, by containing inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle diameter of 1 μm or more, a fired pencil lead having excellent bending strength and handwriting density is obtained.

Claims (3)

In the pencil core obtained by firing, at least graphite and inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle size of 1 μm or more are 0.1 wt% to 0.45 wt% in the core and 0 to graphite. .15 wt% to 0.75 wt% , the aspect ratio is 5 or more, the particle diameter is 1 μm or more, and the number ratio of the inorganic plate-like particles having oxygen atoms is 90% or more and the flatness is 500 nm or less. A fired pencil lead. The fired pencil lead according to claim 1, wherein the inorganic plate-like particles having an oxygen atom aspect ratio of 5 or more and a particle size of 1 µm or more are cleaved plate-like particles. The fired pencil lead according to claim 2, wherein the cleaved plate-like particles are cleaved inorganic amorphous plate-like particles.