JPH0820743A - Production of pencil lead - Google Patents

Abstract

PURPOSE:To produce a pencil lead which has practical strengths, has luster lower than that of a graphite-based lead, gives bluish black written lines, and provides the feel of smooth writing. CONSTITUTION:In this process for producing a pencil lead by mixing a boron nitride powder as the body with a binder, kneading and molding the mixture, baking it at a high temp., and impregnating the resultant sintered product with a suitable oil or fat, a part or all of the boron nitride powder is pretreated with a silane coupling agent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a pencil lead, and in particular, a pure black obtained by heat treatment at high temperature using boron nitride powder as an extender and synthetic or natural resin as a binder. The present invention relates to a method for producing a pencil lead having a drawn line, excellent strength, and improved writing quality.

[0002]

2. Description of the Related Art A conventional burned pencil lead is formed by mixing and kneading an inorganic substance such as graphite, boron nitride, talc, mica, carbon black, etc. with clay and water as a surfactant or a plasticizer. After that, a clay type product obtained by firing at a high temperature to obtain a sintered body and impregnated with fats and oils, a binder such as the above inorganic body material and pitches such as synthetic resin or natural resin or asphalt, If necessary, the required solvent and / or plasticizer, lubricant, etc. are added, and these are mixed and kneaded,
This kneaded product is extruded into a linear body, then fired at a high temperature to carbonize the resin, and is roughly classified into a carbon type in which fats and oils are impregnated in the pores of the fired body using carbon as a binder. . Basically, the clay type pencil lead is used for wood axis pencils and the carbon type pencil lead is used for mechanical pencils because of its practical strength and cost.

It has been generally known to use various coupling agents for modifying the surface characteristics of coloring materials, etc., as one means for improving the strength of carbon type pencil leads. Various methods have been devised. For example, in the method described in JP-A-63-156873, carbon materials such as graphite and carbon black are added to a composition containing an aluminate coupling agent effective for surface modification. In some methods, an aluminate-based coupling agent is coated on the surface of a carbon material as a coloring material in advance to improve the strength and concentration of a pencil lead using the carbon material. Further, in the method described in Japanese Patent Publication No. 64-7632, there is a method in which a silane coupling agent is compounded with a resin to modify the resin and improve the strength.

[0004]

The drawing line color of a pencil lead obtained when graphite is used as an extender causes the problem that black gray, which is the hue of graphite, occurs and that light is reflected in the drawing line. Had. Therefore, for the purpose of improving the problem of writing color, conventionally, it was studied in the form of simply replacing the graphite as an extender material with a heat-resistant inorganic powder such as boron nitride, the pencil lead obtained by these methods is However, there is a problem in that strength and concentration are insufficient as compared with those using graphite. Among these problems, it is generally known to use various coupling agents to improve the strength, and various methods have been devised, but they have the following problems. .

For example, in the method described in JP-B-63-156873, a carbon material such as graphite or carbon black is added to a composition containing an aluminate coupling agent effective for surface modification. In this method, the strength and the density of the pencil lead using the carbon material are improved by coating the surface of the carbon material as the coloring material with the aluminate coupling agent in advance. However, according to this method, although the strength and the density of the pencil lead using the carbon material are improved, the line color cannot be improved.
Further, it is described that the silane coupling agent and the titanate coupling agent have almost no effect on the coloring material of these carbon materials. Further, in the method described in Japanese Patent Publication No. 64-7632, there is a method in which a resin is modified by combining a silane coupling agent with the resin to improve the strength. However, according to this method, the strength is improved. Improves but the writing feels worse.

Generally, a silane coupling agent has the following formula

Embedded image The property of improving the affinity and bondability of the interface by forming a siloxane film at the interface between the organic substance and the inorganic substance by having a molecular structure represented by In some cases, the effect of the silane coupling agent cannot be effectively exerted by simply mixing it in the composition. This is because the reaction from the hydrolysis of the silane coupling agent to the dehydration polymerization does not proceed sufficiently and most of them remain in an unreacted state, and even when a part of them reacts to form a siloxane bond, the siloxane component remains It does not disperse uniformly at the interface between the organic substance and the inorganic substance and segregates in the composition, so that it does not act effectively for improving the affinity and binding property at the interface. When the amount of silane coupling agent added is relatively small (less than 10% of the inorganic substance), the former unreacted silane coupling agent is large, and when the amount is relatively large (more than 10% of the inorganic substance), the latter. Segregation of siloxane occurs.

In the case of the pencil lead composition, the unreacted silane coupling agent does not contribute to the improvement of the strength at all, and may evaporate during firing to cause cracks or swelling in the core. In addition, the segregated siloxane component does not contribute to the improvement of strength, and causes a feeling of dryness during writing, which hinders smooth writing. That is, when the addition amount of the silane coupling agent is small, the strength is hardly improved, and when the addition amount is large, the strength is lowered and the writing quality is deteriorated. For the reason described above, in the method described in Japanese Patent Publication No. 64-7632, to produce a pencil lead having a pure black drawing line, which is the object of the present invention, and which has excellent strength and improved writing quality. I can't.

[0008]

Means for Solving the Problems As a result of intensive studies by the present inventors in order to improve the above-mentioned problems, the silane coupling agent suitably selected on the surface of boron nitride powder used as an extender. The present invention has been completed by discovering that by treating the composition with a suitable amount, the composition has a pure black line, is excellent in strength, and can improve writing quality.

[0009]

The function of the present invention is as follows. (1) Kneading boron nitride powder as a body material with a binder
A sintered body is obtained by molding and firing at a high temperature, and when manufacturing a pencil lead impregnated with oil or the like, a part or all of the boron nitride powder as an extender is preliminarily a silane coupling agent. It is a method for producing a pencil lead, which is a treated boron nitride powder. (2) The method for producing a pencil lead according to claim 1, wherein a silane coupling agent having a carbon residue rate of 10% or more when used at a high temperature of 1,000 ° C or higher in a non-oxidizing atmosphere is used. . (3) The method for producing a pencil lead according to claim 1, wherein the method for treating the silane coupling agent is a wet treatment method. (4) The method for producing a pencil lead according to claim 1, wherein the treatment amount of the silane coupling agent is 0.1 to 5.0% with respect to the weight of the extender.

The mechanism by which the silane coupling agent of the present invention is used, which has a pure black line, is excellent in strength, and can improve writing quality is as follows. (1) Kneading boron nitride powder as a body material with a binder
The boron nitride powder used as an extender in the production of a pencil lead obtained by molding and firing at high temperature to obtain a sintered body and appropriately impregnating fats and oils is one produced by a known method. Good, but the average particle size is 0.1 ~ 20μm, especially 1 ~
It is preferably 8 μm. If it is less than 0.1 μm,
The strength of the core may be significantly reduced. On the other hand, if it exceeds 20 μm, it may not be possible to uniformly mix it with the organic binder, and practical strength as a core may not be exhibited. Further, it is preferable that the boron nitride powder is well-crystallized, and the Lc value measured by the Gakshin Carbon Material 117 Committee method is 500 Å or more, particularly 700 Å or more. If it is less than 500Å, a part of the crystal structure of boron nitride becomes amorphous, and sufficient strength of the core may not be obtained.

(2) A silane coupling agent as a surface treatment agent has almost no effect on carbon materials such as graphite and carbon black, whereas boron nitride powder has an effect on it. Since the surface of the powder has active hydrogen capable of reacting with the silane coupling agent, the silane coupling agent may be subjected to a dry treatment or a wet treatment, preferably a wet treatment to obtain a boron nitride powder having a By forming a siloxane coating on the surface, it is possible to improve the affinity with organic binders and bondability, and by using a silane coupling agent with a residual carbon ratio of 10% or more, the pencil lead is By firing at a high temperature of 1,000 ° C or higher in an oxidizing atmosphere, the organic binder and silane coupling agent are each carbonized, and the carbon components are assimilated and bonded, resulting in excellent strength. It is possible to obtain the body.

(3) The method of treating the surface of the boron nitride powder with a suitable amount of the silane coupling agent suitably selected as the surface treating agent is carried out in a machine capable of high speed stirring such as a Henschel mixer. Add boron nitride powder, add silane coupling agent slowly to it, stir after stirring, and dry it by reacting with moisture in the air, or prepare an aqueous solution of silane coupling agent. Among them, there is a wet treatment method in which a boron nitride powder is treated and then dried. However, it is preferable to use the wet treatment method because the dispersibility of the coupling agent is better and the effect of the invention is further enhanced.

The silane coupling agent is used to treat the boron nitride powder in order to impart a bonding force to the interface between the organic binder and the boron nitride powder. The bondability between the organic functional group of the ring agent and the organic binder must be taken into consideration. That is, in order to further enhance the effect of the invention, for example, when the organic binder is vinyl chloride resin or phenol resin, it is better to use an amino group or an epoxy group. The treatment amount of the silane coupling agent at this time may be appropriately adjusted according to the specific surface area of the boron nitride powder, but is usually in the range of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the boron nitride powder. If the amount of treatment is outside this range, the effect of the invention cannot be obtained as described above. This optimum amount of treatment makes it possible to obtain a boron nitride powder having a siloxane coating formed by a silane coupling agent on the surface of the boron nitride powder. That is, a pencil lead having excellent strength and improved writing quality can be produced by this treatment method.

[0014]

EXAMPLES Examples and comparative examples of the present invention and quality measurement data thereof are shown in Table 1 below, but the present invention is not limited to these examples. Example 1 Boron nitride [manufactured by Shin-Etsu Chemical Co., Ltd .; average particle size: 2 μm] 100 parts by weight vinyl chloride resin 100 parts by weight Dioctyl phthalate・ ・ ・ ・ ・ ・ ・ ・ ・ 40 parts by weight zinc stearate ・ ・ ・ ・ ・ ・ 4 parts by weight

First, γ-methacryloxypropylmethoxysilane / KBM503 as a silane coupling agent.
[Shin-Etsu Chemical Co., Ltd. product name] 3 parts by weight is dissolved in 50 parts by weight of methanol, 150 parts by weight of water and 20 parts by weight of 60% acetic acid aqueous solution are added, and ultrasonic vibration is performed for 1 hour. A silane aqueous solution was prepared. Next, 100 parts by weight of the above boron nitride powder was added to 223 parts by weight of this aqueous solution, and the mixture was stirred at high speed and mixed, and then dried in a vacuum at about 120 ° C for 10 hours, and the powder surface was treated with a silane coupling agent. To produce boron nitride. Next, after thoroughly mixing and kneading with the other above-mentioned compounded composition, extruding into a fine wire, heating and drying in air, and heating and firing to about 1,000 ° C in a non-oxidizing atmosphere to obtain a core body. A pencil lead with a core diameter of 0.57 mm was obtained by impregnating with spindle oil. The results of the bending strength test and the writing characteristic test conducted on the obtained pencil lead are shown in Table 1 below.

Example 2 The silane coupling agent used in Example 1 was N-β (aminoethyl) γ-aminopropyltrimethoxysilane.
Change to KBM603 [Shin-Etsu Chemical Co., Ltd. product name],
3 parts by weight of this coupling agent was dissolved in 200 parts by weight of water, and ultrasonic vibration was performed for 1 hour to prepare an aqueous silane solution.
Others were the same as in Example 1 to obtain a pencil lead having a core diameter of 0.57 mm. The results of the bending strength test and the writing characteristic test conducted on the obtained pencil lead are shown in Table 1 below.

Example 3 The silane coupling agent used in Example 2 was first added to the boron nitride powder of Example 1 and subjected to high speed stirring,
Aged for 10 days to prepare a boron nitride powder having the surface of the powder treated with a silane coupling agent. Next, it is thoroughly mixed and kneaded with the other above-mentioned compounded composition, extruded into a fine wire, dried by heating in air, and then dried in a non-oxidizing atmosphere.
The core body obtained by heating and firing to 1,000 ° C. was impregnated with spindle oil to obtain a pencil lead having a core diameter of 0.57 mm. The results of the bending strength test and the writing characteristic test conducted on the obtained pencil lead are shown in Table 1 below.

Comparative Example 1 A pencil lead having a core diameter of 0.57 mm was obtained in the same manner as in Example 1 except that the boron nitride powder used in Example 1 was used as it was. The results of the bending strength test and the writing characteristic test conducted on the obtained pencil lead are shown in Table 1 below.

Comparative Example 2 A pencil lead having a core diameter of 0.57 mm was prepared in the same manner as in Example 1 except that the boron nitride powder used in Example 1 was replaced with a natural scaly graphite powder and used as it was. Got Table 1 shows the results of the bending strength test and the writing property test performed on the obtained pencil lead.

Comparative Example 3 The silane coupling agent used in Example 2 was first added to the vinyl chloride resin, thoroughly mixed and kneaded with the other compounded compositions of Example 1, and extruded into a fine wire. After heating and drying in air, the core obtained by heating and firing to about 1,000 ° C in a non-oxidizing atmosphere was impregnated with spindle oil to give a core diameter of 0.
I got a 57mm pencil lead. The results of the strength test and the writing characteristic test conducted on the obtained pencil lead are shown in Table 1 below.

[0021]

[Table 1]

The values of the concentration and wear in the bending strength test and the writing test shown in Table 1 are the results of the test according to JIS S 6005 test method. The oil absorption value is the result of expressing the difference between the weight of the core after oil absorption and the weight of the core before oil absorption as a percentage.
Glossiness is a 3 cm square piece of high-quality paper that is hand-painted repeatedly in the left-right direction and the top-bottom direction so that the surface of the paper is uniformly painted.
It is a result measured at an angle of 45 ° using 5D. The hue is the result of measuring the test piece used for the glossiness test using a multi-source spectrophotometer MSC-5N manufactured by Suga Test Instruments.

Comparing Example 1, Example 2 and Example 3 treated with the silane coupling agent with Comparative Example 1 which was not treated, the flexural strength was maintained and the oil absorption rate and the abrasion degree were increased. Writing is improved. In addition, the wet processing method of Example 2 provides a smoother writing quality than the dry processing method of Example 3. The reason for this is that the silane coupling agent is effective in increasing the amount of wear and the oil absorption rate by applying the silane coupling agent treatment. It is more preferable to use a wet treatment method so that the dispersibility of the silane coupling agent can be made more uniform, and uniform wear can be obtained, so that the writing feel becomes very smooth.

According to the treatment method of Comparative Example 3, the vinyl chloride resin is modified by the treatment with the silane coupling agent to cause voids, cracks and the like in the core, and the strength is lowered due to the influence of this portion, and segregation occurs. Due to the influence of the silane coupling agent described above, a feeling of being caught during writing is felt and the writing quality is significantly impaired. Compared with the case where the graphite of Comparative Example 2 is used as the extender material and the case where the boron nitride powder in the other examples is used as the extender material, it is apparent that the latter has a lower glossiness. Regarding the hue as well, when boron nitride powder is used in the same manner, it is black, but a so-called bluish black that exhibits a bluish purple hue is obtained, whereas the core using graphite is reddish black.

[0025]

As described above, according to the present invention, while satisfying the practical strength, the glossiness is smaller than that in the case of using graphite, and the drawing line showing a bluish black color is provided, and the writing feeling is smooth. It is possible to obtain an ideal pencil lead that gives strength.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomokazu Washio 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory (72) Toshihiko Shindo Annaka, Gunma Prefecture 2-13-1 Isobe Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory

Claims (4)

[Claims] 1. A method for producing a pencil lead obtained by kneading and molding boron nitride powder as an extender with a binder and firing at high temperature to obtain a sintered body, and appropriately impregnating fats and oils A method for producing a pencil lead, characterized in that a part or all of the boron nitride powder as an extender is a boron nitride powder which has been previously treated with a silane coupling agent. 2. The method for producing a pencil lead according to claim 1, wherein a silane coupling agent having a residual carbon rate of 10% or more when fired at a high temperature of 1,000 ° C. or more in a non-oxidizing atmosphere is used. 3. The method for producing a pencil lead according to claim 1, wherein the treatment method of the silane coupling agent is a wet treatment method. 4. The method for producing a pencil lead according to claim 1, wherein the amount of the silane coupling agent treated is 0.1 to 5.0% with respect to the weight of the extender.