JPH1017307A - Boron nitride powder for fired pencil lead and fired pencil lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain pure black color and small glossiness and to improve writing feeling and flexural strength by using a specific born nitride powder as an inorganic extender of a fired pencil lead. SOLUTION: The boron nitride powder 1-5μm in average particle diameter, 25-50m<2> /g in specific surface area, >=700Å in the size of crystallite and >=97% in purity is dispersed, mixed and kneaded as the inorganic extender with an organic binder and if necessary, a plasticizer, a stabilizer or the like. Next, a lead body obtained by extruding into fine line state to form, drying and firing at 800-1,400 deg.C in a gaseous nitrogen atmosphere is impregnated with oils and fats.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fired pencil lead having a pure black line, a low gloss, and a high bending strength, and more particularly to a mechanical pencil lead.

[0002]

2. Description of the Related Art Conventionally, a pencil lead is formed by mixing, kneading and mixing inorganic materials such as graphite, boron nitride, talc, mica, and carbon black with water and a surfactant and a plasticizer. A clay type manufactured by impregnating the fired body with oils and fats by firing at a high temperature, and the inorganic substance and an organic binder of pitches such as resin or asphalt, if necessary, a plasticizer, After adding an agent, mixing, kneading, and molding, the mixture is fired in a nitrogen gas at 800 to 1400 ° C. to carbonize an organic binder such as a resin, thereby obtaining a fired body using carbon as a binder. These are roughly classified into two types: carbon types manufactured by impregnating oils and fats. Due to the relationship between the practical strength and the manufacturing cost, the former can be used as a wooden pencil lead and the latter can be used as a mechanical pencil lead.

[0003] In general, graphite is used as a core material and a coloring material for a pencil lead, and its physical properties have been improved by adjusting the orientation, the composition, and the like. However, when graphite is used, there is a problem in that light is reflected on the drawn line, making it difficult to read depending on the viewing angle, and the drawn line color is black-gray. The reason is considered to be that graphite contains π electrons due to SP ₂ hybrid orbital, and the π electrons have properties close to free electrons of a metal, so that they exhibit a metallic luster and reflect light.

Therefore, as a countermeasure, hexagonal boron nitride (hereinafter referred to as BN) powder having a crystal structure similar to that of graphite, having no π electrons, and having excellent heat resistance and lubricating properties is used to reduce the carbon content of the organic binder. A method of obtaining a pure black core material by expressing the color of the compound has been considered for a long time. However, when BN powder is used in place of graphite, the core material strength tends to be lower than when graphite is used. For example, Tokiko 3-60
In the case of JP-A-352 or 5-9472,
Flexural strength of core material using BN powder is 190-230M
It is about Pa, and there is a problem that the bending strength is still insufficient as compared with a core material using graphite. That is, although BN powder has been conventionally used as an inorganic base material of a pencil lead, BN powder for expressing the required characteristics of a fired pencil lead such as bending strength, blackness, and smooth brush feeling in a large and well-balanced manner. The properties have not been sufficiently studied,
Therefore, none of the prototype fired pencil cores was satisfactory in characteristics.

[0005]

In view of the above-mentioned problems of the prior art, the inventors of the present invention have found that the most suitable B for satisfying the required characteristics of a fired pencil lead, especially a mechanical pencil lead.
As a result of intensive studies on N powder properties, the present invention has been completed.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that the average particle diameter is
5 μm, specific surface area 25-50 m ² / g, crystallite size 7
BN with a purity of at least 00 Å and a purity of at least 97%
By using the powder as an inorganic substance of the fired pencil lead, it was found that a fired pencil lead having high bending strength, exhibiting a pure black color, and having a smooth brush feeling was obtained, and the present invention was completed. Was. Therefore, the present invention provides an average particle size of 1 to 5
μm, specific surface area 25-50 m ² / g, crystallite size 70
BN powder for a baked pencil lead (Claim 1), characterized by having a purity of at least 0 Å and a purity of at least 97%, and a baked pencil lead (Claim 2) using this BN powder as an inorganic substance, particularly sharp. This is a pencil lead (claim 3).

Hereinafter, the manufacturing process of the fired pencil lead and the physical properties of the fired pencil lead to which the characteristics of the BN powder for a fired pencil lead according to the present invention contribute will be described.
A detailed description is given in relation to four characteristics of crystallite size and purity.

The BN powder and the organic binder are added, if necessary, with a plasticizer, a stabilizer and the like, dispersed, mixed and kneaded. Next, it is extruded into a fine wire and dried in the air. Next, it is fired in a nitrogen gas at 800 to 1400 ° C., and the obtained core body is impregnated with fats and oils such as spindle oil, whereby a fired pencil lead is manufactured.

(1) Average Particle Size When manufacturing a fired pencil lead, the organic binder should uniformly coat the surface of the BN powder in the dispersing and mixing steps, and the fired lead must be somewhat dense and sufficiently dense. It is necessary to have a sufficient bending strength and to have pores enough to absorb oil in the oil impregnation step. Here, when the average particle diameter of the BN powder is less than 1 μm, the agglomerated particles increase and the mixing with the organic binder tends to be insufficient. As a result, the surface of the BN that is not coated with the organic binder remains, and the surface has no bonding force even at the time of sintering, which causes cracks or lowers the core material strength even if no cracks are formed. Further, when the BN surface comes out on the drawing line, there is no colorant component in that portion, which is a factor of lowering the blackness. On the other hand, when the average particle size exceeds 5 μm, the pore size of the core material becomes too large, and the bending strength is reduced. Therefore, the average particle size of the BN powder is 1 to 5
It needs to be μm.

(2) Specific surface area The BN powder needs to have an appropriate surface area for coating the surface with the organic binder in the dispersion and mixing steps.
When the specific surface area is less than 25 m ² / g, the amount of the organic binder is excessive, segregation occurs in the core material structure, and local cracking or deformation may occur in the firing step. Further, when the amount of the organic binder is reduced in order to prevent the phenomenon, the degree of blackness is reduced because the amount of the carbonized component acting as a coloring material is reduced in proportion. On the other hand, when the specific surface area exceeds 50 m ² / g, the organic binder cannot coat the entire surface of the BN powder, and therefore, the same disadvantages as in the case where the average particle diameter is less than 1 μm occur. Further, when the amount of the organic binder is increased so as to coat the entire surface of the BN powder, disadvantages such as distortion occurring during extrusion molding and excessive shrinkage during firing occur. Therefore, the specific surface area of the BN powder is 25 to 50.
It needs to be m ² / g.

(3) Crystallite Size In order to impart sufficient bending strength to the core material, it is necessary to sufficiently orient the BN powder at the time of extrusion molding so that the internal structure has a micro-honeycomb structure. Further, in order to have a smooth writing feel during writing, it is necessary that the BN powder has excellent lubricity. For this purpose, the shape of the BN powder must be plate-like. In general, the particle shape of BN powder depends on the degree of crystal growth, and crystalline BN powder has a plate shape, and amorphous BN powder has an amorphous shape. As an index indicating the degree of crystal growth, there is a crystallite size measured by the Gakushin Carbon Materials 117 Committee method. The crystallite size is the size in the C-axis direction (Lc value)
And the size in the A-axis direction (La value), but the peak of (002) is the sharpest in the X-ray diffraction.
Expressing with the c value is more accurate. Although there is no clear numerical boundary between the crystalline and amorphous BN crystals, the L _c value is 700 Å or more in order to satisfy the required properties of the fired pencil lead as an inorganic material. It is necessary. Further, if the crystallite size exceeds 1000 angstroms, the error is large and the true value is unknown, so the Gakushin Carbon Materials 117 Committee Law stipulates that the crystallite size is simply indicated as "> 1000 angstroms". Therefore, the upper limit of the crystallite size cannot be specified in the present invention.

(4) Purity BN powder generally contains B ₂ O ₃ or F
Metal elements such as e, Al, and Ca are contained as impurities. Since the melting point of B ₂ O ₃ is 450 ° C., if a large amount of B ₂ O ₃ is contained in the BN powder, it melts at the time of firing and deforms the core material or binds to the carbonized organic binder. This causes a problem of giving a feeling of being caught when writing. The reason is not clear when a large amount of metal impurities is contained, but as a result, the bending strength of the core tends to decrease. Therefore, in order to avoid the above problems, the purity of the BN powder needs to be 97% or more.

The average particle diameter satisfying the above conditions is 1 to 5 μm.
m, specific surface area 25-50 m ² / g, crystallite size 700
BN powder having a purity of 97% or more and a purity of 97% or more is used as an inorganic substance.
By passing the above-mentioned process as a starting material together with an organic binder such as epoxy resin and asphalt pitch, and various plasticizers and stabilizers as necessary, the bending strength is high, a pure black color and a smooth brush are obtained. A pencil lead having a feeling is obtained. Therefore, the core can be suitably used as a mechanical pencil core.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to examples.

[0015]

EXAMPLES (Example 1) 100 parts by weight of BN powder having an average particle diameter of 1.3 μm, a specific surface area of 48.5 m ² / g, a crystallite size of 755 Å, and a purity of 97.2% 100 parts by weight of vinyl chloride resin 100 parts by weight of phthalic acid Dioctyl 30 parts by weight Zinc stearate 2 parts by weight The above raw materials are kneaded, extruded into a thin wire, dried in the air, heated to 1000 ° C. in a nitrogen atmosphere, and fired to obtain a core. Impregnated with spindle oil, with a diameter of 0.
A 57 mm pencil lead was obtained. Table 1 shows the characteristics of the core.

Example 2 The same procedure as in Example 1 was carried out except that BN powder having an average particle size of 2.8 μm, a specific surface area of 31.2 m ² / g, a crystallite size of 985 Å, and a purity of 98.0% was used. Prototype and evaluation were performed. The results are shown in Table 1.

Example 3 Same as Example 1 except that BN powder having an average particle size of 3.9 μm, a specific surface area of 29.5 m ² / g, a crystallite size of> 1000 Å, and a purity of 98.7% was used. The prototype was evaluated. The results are shown in Table 1.

Example 4 Same as Example 1 except that BN powder having an average particle diameter of 4.7 μm, a specific surface area of 26.8 m ² / g, a crystallite size of> 1000 Å, and a purity of 99.1% was used. The prototype was evaluated. The results are shown in Table 1.

Comparative Example 1 The same as Example 1 except that BN powder having an average particle diameter of 5.8 μm, a specific surface area of 4.3 m ² / g, a crystallite size of> 1000 Å, and a purity of 99.5% was used. The prototype was evaluated. The results are shown in Table 1.

Comparative Example 2 The same procedure as in Example 1 was carried out except that BN powder having an average particle diameter of 0.7 μm, a specific surface area of 44.3 m ² / g, a crystallite size of 433 Å, and a purity of 97.1% was used. Prototype and evaluation were performed. The results are shown in Table 1.

Comparative Example 3 A BN powder having an average particle diameter of 1.4 μm, a specific surface area of 44.7 m ² / g, a crystallite size of 851 Å, and a purity of 95.7% was used in the same manner as in Example 1. Prototype and evaluation were performed. The results are shown in Table 1.

Comparative Example 4 The same procedure as in Example 1 was conducted except that BN powder having an average particle diameter of 1.0 μm, a specific surface area of 53.8 m ² / g, a crystallite size of 502 Å, and a purity of 97.0% was used. Prototype and evaluation were performed. The results are shown in Table 1.

Comparative Example 5 A prototype was produced and evaluated in the same manner as in Example 1 except that natural graphite having an average particle diameter of 3.7 μm and a specific surface area of 12.8 m ² / g was used. The results are shown in Table 1.

[0024]

[Table 1]

In the table, bending strength is a result of a three-point bending test performed in accordance with JIS S6005. Blackness: An automatic writing tester was used to write on a high-quality paper with a load of 3N, and the luminous reflectance Y of the written lines was measured by a spectrophotometer. Writing feel: By sensory writing.

As shown in Table 1, the case of the embodiment which satisfies the conditions of the present invention has a bending strength which is not inferior to that of the case of the comparative example 5 of a graphite core, and has improved blackness and smoothness. A good brush feeling was obtained. On the other hand, the cases of Comparative Examples 1 to 4 which deviate from the conditions of the present invention have at least one characteristically insufficient point in bending strength, blackness, and brush feeling, and all are inferior to the examples. Was the result. This confirmed the effect of the present invention.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and any structure having substantially the same configuration as the technical idea described in the claims of the present invention and exerting the same function and effect will be described. It is included in the technical scope of the invention. For example, in the above embodiment, an example was described in which the diameter of the mechanical pencil core was 0.57 mm.
The present invention is not limited to this, and it goes without saying that the same effects can be obtained even when applied to a thinner pencil lead, a thicker pencil lead, or a wooden pencil lead.

[0028]

According to the present invention, a fired pencil lead having high bending strength, exhibiting a pure black color, and having a smooth brush feel can be obtained.

Continuing from the front page (72) Inventor Toshihiko Shindo 2-13-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Industry Co., Ltd.

Claims (3)

[Claims] An average particle diameter of 1 to 5 μm and a specific surface area of 25 to
A boron nitride powder for a fired pencil lead, having a particle size of 50 m ² / g, a crystallite size of 700 Å or more, and a purity of 97% or more. 2. A fired pencil lead using the boron nitride powder according to claim 1 as an inorganic substance. 3. The fired pencil lead according to claim 2, which is a lead for a mechanical pencil.