JPH061941A - Pencil lead and its production - Google Patents

Abstract

PURPOSE:To obtain a pencil lead having excellent flexural strength in high efficiency by kneading a specific graphite with a binder, forming and baking the mixture and impregnating an oil and fat into the formed product. CONSTITUTION:Graphite is hydrophilized by oxidizing a part or total of graphite by air-oxidation process or Hummers-Offeman process using sulfuric acid, sodium nitrate and potassium permanganate and fluorinating the oxidized product under a fluorine pressure of <=500mmHg preferably at <=200 deg.C. The hydrophilized graphite is kneaded with a binder such as clay and the mixture is formed and baked at a high temperature to obtain a sintered compact. The objective pencil lead can be produced by impregnating an oil and fat into the sintered compact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving the strength of a pencil lead manufactured by using clay, a water-soluble synthetic resin or the like as a binder.

[0002]

2. Description of the Related Art A conventional pencil lead is formed by mixing and kneading graphite, clay, water as a surfactant and a plasticizer, and molding.
After firing at high temperature to obtain a sintered body, a clay type that is manufactured by impregnating oils and fats, graphite, synthetic resin and plasticizer, foaming agent, lubricant, etc. are mixed and kneaded and molded. After that, it is roughly classified into a carbon type one obtained by firing at a high temperature to carbonize the resin, and impregnating a burning body using carbon as a binder with fats and oils. Further, in the carbon type pencil lead, the resin used is classified into water-soluble one and water-insoluble one.

Among these, in a carbon type pencil lead using a clay type pencil lead and a water-soluble resin, water is used as a plasticizer for the clay or the water-soluble resin, but graphite is a typical hydrophobic substance. Therefore, the adhesion between graphite and clay or water-soluble resin is poor, and the strength is low.
Therefore, the strength has been improved by a method of adding a surfactant or a coupling agent to improve the adhesiveness. However, the surfactant and the coupling agent are not sufficiently improved in strength because they depolymerize or sublime during firing to form a peeling layer at the interface with improved adhesiveness.

[0004]

DISCLOSURE OF THE INVENTION An object of the present invention is to produce a pencil lead by using clay or a water-soluble resin as a binder for graphite which is a main raw material and water as a plasticizer. When it is attempted to enhance the adhesiveness between graphite and a binder and further strengthen the adhesiveness by using a conventional surfactant or coupling agent, a peeling layer is formed at the interface during firing to achieve the desired adhesiveness. It is to provide a pencil lead excellent in strength by improving the fact that it was not improved.

[0005]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the above problems. The fact that the strength of the pencil lead cannot be increased is due to poor adhesion between graphite and clay or water-soluble resin, and basically it is because the graphite does not get wet with water. As a result of research based on the idea that the strength of the pencil lead may be enhanced by subjecting graphite to a surface treatment, the objective was achieved by oxidizing the graphite surface and then fluorinating it. The present invention has been completed by finding out what can be done.

[0006] That is, the present invention is as follows: (1) Calcination by kneading, molding and firing kneading, shaping and firing of graphite, which is obtained by subjecting part or all of graphite to oxidation treatment and then fluorination treatment to make it hydrophilic. A pencil lead consisting of a bound body and oils and fats impregnated into its pores,

(2) A part or all of graphite is subjected to an oxidation treatment, and then graphite that has been hydrophilized by fluorination is kneaded with a binder, molded, sintered at high temperature, and sintered. A method for producing a pencil lead, characterized in that a body is obtained and the sintered body is impregnated with fats and oils,

(3) A method for producing a pencil lead according to the above item (2), wherein a part or all of graphite is oxidized, and then fluorinated at a fluorine pressure of 500 mmHg or less.

(4) The method for producing a pencil lead according to the above (2) or (3), wherein a part or all of graphite is subjected to an oxidation treatment, and then a fluorination treatment is performed at a temperature of 200 ° C. or lower.

(5) The oxidation treatment is carried out by air oxidation or by the Hummers-Offemann method using sulfuric acid, sodium nitrate and potassium permanganate (2), (3),
The method for producing a pencil lead according to any one of (4).

The present invention will be described in detail. The surface treatment of graphite has been carried out with a surfactant or a coupling agent for the purpose of improving the wetting of the graphite powder with water.The surfactant and the coupling agent are relatively large molecules. Moreover, a delamination layer or pores are formed at the interface due to depolymerization or sublimation during firing.

When graphite is reacted with fluorine at a temperature of 650 ° C. or higher, fluorinated graphite (CF) _n is formed. Also 450 ° C
It is known that (C ₂ F) _n can be similarly formed by treating with a certain degree. (CF) _n and (C ₂ F) _n are water-repellent, and when used in a pencil lead, the strength is low due to insufficient adhesion of the interface layer, which is considered to be due to the water repellency. In addition, fluorine is desorbed during firing, and highly toxic fluorine gas and hydrogen fluoride are released, which is not preferable. Furthermore, it was very expensive and not suitable for practical use.

However, in recent years, it has been found that when graphite is treated at a temperature of 200 ° C. or less at a very low fluorine pressure, wettability with water is improved. It has not yet been clarified why water wettability is improved, but 2
It has been found that graphite treated with a fluorine pressure of 00 ° C or less and / or 500 mmHg or less has good wettability with water, and is at a level that can be sufficiently used as a pencil lead. It was found that the wettability is further improved by the chemical treatment. In addition, it is relatively inexpensive because it requires only a small amount of expensive fluorine gas,
Less fluorine is released during firing. Since the fluorine component that is released during firing is released in the form of an atom or a very small molecule, it is possible to extremely reduce the peeling layer at the interface, which is a problem when a surfactant or coupling agent is used. .

Further, in the case of a clay type pencil lead, the desorbed fluorine component is dissolved in silica or alumina in the clay,
A decrease in the sintering temperature, which is considered to be due to the formation of flux components, is observed, and it also acts as a sintering aid.

In the present invention, the surface of graphite is oxidized prior to this light fluorine treatment. Examples of the oxidation treatment include air oxidation, for example, air oxidation at 500 ° C. for 30 minutes, or Hummers-Offeman (Hummers-Offeman) using sulfuric acid, sodium nitrate or potassium permanganate.
Method).

As the fluorination treatment, light surface fluorination is performed under the conditions of a temperature of 200 ° C. or lower and a fluorine pressure of 500 mmHg or lower. Over 200 ℃ and / or 500mmHg
In order to improve the wettability with water, the treatment in a short time is conceivable, but the graphite to be treated is a powder, and the treatment time can be controlled by the treatment under such conditions. Practically difficult. Further, if the fluorination treatment is performed under such extreme conditions after the oxidation treatment, the possibility of explosion is high and it is dangerous.

[0017]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Graphite oxidized by the following method is placed on a nickel boat with a thickness of about 3 mm, and SUS3
After being housed in a 16-made reactor, it was heated to 120 ° C. and kept at 10 ⁻³ mmHg or less for 12 hours to remove adsorbed water and the like. It was left to cool to the treatment temperature while maintaining the vacuum state, fluorine gas was introduced to the following pressure, and the treatment was performed by contacting for the following time.

(Example 1) Natural scaly graphite (average particle size 5 micron, fixed carbon content 99.5%) was subjected to air oxidation at 500 ° C. for 30 minutes and then treated with fluorine gas at a pressure of 10 mmHg for 10 minutes at room temperature. 70 parts by weight Kaolinite-based clay 30 parts by weight Water 20 parts by weight The above blended composition is mixed and granulated with a Henschel mixer,
After extrusion molding, it is dried at 180 ° C for 12 hours, then heated to 1100 ° C in a reducing atmosphere to have a diameter of 2.00
mm sintered body was obtained and impregnated with lard to obtain a pencil lead. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Example 2) After air-oxidizing at 500 ° C for 30 minutes, at room temperature and at a pressure of 50 mmHg, fluorinated graphite was used for 30 minutes. I got a pencil lead. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

Example 3 All were the same except that graphite was treated with fluorine in the same manner as in Example 1 after oxidizing the graphite by the Hummers-Offemann method using sulfuric acid, sodium nitrate and potassium permanganate. Diameter 2.0mm under the condition
Got a pencil lead. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Example 4) Graphite used in Example 1 60 parts by weight Polyvinyl alcohol 20 parts by weight Tragant gum 15 parts by weight Vanillin 5 parts by weight Water 80 parts by weight Ethylene glycol 20 parts by weight After mixing the above composition with a Henschel mixer , Fully kneaded with three rolls and extruded, then 250 ℃
After drying for 12 hours, the mixture was heated to 1000 ° C. in a nitrogen atmosphere to obtain a sintered body having a diameter of 0.57 mm, which was impregnated with spindle oil to obtain a pencil lead. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Example 5) A diameter of 0.57 was obtained in the same manner as in Example 4 except that the graphite used in Example 2 was used.
I got a pencil lead of mm. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Example 6) A diameter of 0.57 was obtained in the same manner as in Example 4 except that the graphite used in Example 3 was used.
I got a pencil lead of mm. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Comparative Example 1) A pencil lead was obtained in the same manner as in Examples 1 to 3 except that the graphite used in Examples 1 to 3 was used without being treated. The strength of the obtained pencil lead and the result of the writing test are shown in Table 1.

(Comparative Example 2) A pencil lead was obtained in the same manner as in Examples 4 to 6 except that the graphite used in Examples 4 to 6 was used without being treated. The strength of the obtained pencil lead and the result of the writing test are shown in Table 1.

(Comparative Example 3) In the graphite of Example 1, 1 at a pressure of 10 mmHg at room temperature except that air oxidation was not performed.
A pencil lead was obtained in the same manner as in Example 1 including 0 minute fluorine gas treatment. The strength of the obtained pencil lead and the result of the writing test are shown in Table 1.

(Comparative Example 4) In the graphite of Example 2, except that air oxidation was not carried out, 3 at a pressure of 50 mmHg at room temperature was used.
A pencil lead was obtained in the same manner as in Example 2 including 0 minute fluorine gas treatment. The strength of the obtained pencil lead and the result of the writing test are shown in Table 1.

(Comparative Example 5) Graphite used in Example 4 55 parts by weight Polyvinyl chloride (degree of polymerization 1000) 45 parts by weight Dioctyl phthalate 20 parts by weight Zinc stearate 2 parts by weight After mixing the above composition with a Henschel mixer , Fully kneaded with three rolls, extruded, then 200 ℃
After drying for 12 hours, the mixture was heated to 1000 ° C. in a nitrogen atmosphere to obtain a sintered body having a diameter of 0.57 mm, which was impregnated with spindle oil to obtain a pencil lead. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Comparative Example 6) In the graphite of Example 4, 1 at a pressure of 10 mmHg at room temperature was used except that air oxidation was not performed.
A pencil lead was obtained in the same manner as in Example 4 except that graphite that had been treated with fluorine gas for 0 minutes was used. The strength of the obtained pencil lead and the result of the writing test are shown in Table 1.

[0030]

[Table 1] The strength test result and the concentration / wear value in the writing test shown in Table 1 are the results of the test according to the test method of JIS S 6005.

As is clear from Table 1, the pencil lead of the present invention has a strength far superior to that of a conventional pencil lead that is neither oxidized nor fluorinated, while softening the concentration and wear. . That is, it shows that it has a much improved strength at the same concentration and wear. Comparing Comparative Examples 3 and 4 and Examples 1 and 2 only with fluorine treatment without oxidation, the strength is the same or slightly higher, but the concentration and wear are significantly softened. It suggests that the strength is much improved at the same concentration and wear.

The results of carbon type pencil lead using a water-insoluble synthetic resin are shown in Comparative Example 5. Examples 4 and 5 are as follows.
Since the pencil lead of developed the strength exceeding this, it solves the problem of interfacial peeling, which was a problem in the pencil lead using the conventional water-soluble resin, compared to the case of using the water-insoluble resin. It is considered to form an interface having excellent adhesiveness. It is considered that the reason why the wettability with water is improved by the fluorination treatment is that the polar component is added to the graphite surface energy, and the oxidation treatment is introduced to further improve the polarity. It is considered that the electrostatic attractive force acts on the interfacial adhesion between the clay and the water-soluble resin, and exceeds the adhesive force of the graphite-water-insoluble resin interface, which is only the van der Waals force.

Comparative Example 6 shows the result when no oxidation treatment was carried out in Example 4, but in the case of a carbon type pencil lead, when an oxidation treatment was added, in terms of strength, the strength was better than that of the fluorine treatment alone. Although it slightly decreases, the concentration and wear are almost the same. Throughout Examples 1 to 6, the concentration and wear are increased as compared with the case where the fluorination treatment is not performed, and it is considered that the oxidation treatment exerts the softening effect. When only oxidation treatment without applying
Since such an effect was not exhibited, it is considered to be a combined effect.

[0034]

EFFECTS OF THE INVENTION The pencil lead of the present invention is obtained by subjecting the surface of graphite to an oxidization treatment and then a fluorination treatment, so that the bending strength is greatly improved and the pencil lead is softened in terms of concentration and wear. Even the carbon type pencil lead using the water-soluble resin exhibited stronger strength than the case using the water-insoluble resin. The strength of the graphite is similar to that of just fluorinated graphite, and it is softened in terms of concentration and wear. It shows that the strength is much improved if the same concentration and wear are mixed. .

Claims (5)

[Claims] 1. A sintered body obtained by kneading, molding and firing graphite, which is obtained by subjecting a part or all of graphite to an oxidation treatment and then a fluorination treatment to make it hydrophilic, and a binder to impregnate the pores thereof. A pencil lead consisting of oils and fats. 2. Graphite obtained by subjecting a part or all of graphite to an oxidation treatment and then a fluorination treatment to render it hydrophilic.
A method for producing a pencil lead, which comprises kneading and forming a binder and firing at a high temperature to obtain a sintered body, and impregnating the sintered body with fats and oils. 3. The method for producing a pencil lead according to claim 2, wherein a part or all of the graphite is subjected to an oxidation treatment, and then subjected to a fluorination treatment at a fluorine pressure of 500 mmHg or less. 4. The method for producing a pencil lead according to claim 2, wherein a part or all of the graphite is subjected to an oxidation treatment and then subjected to a fluorination treatment at a temperature of 200 ° C. or lower. 5. The method for producing a pencil lead according to claim 2, wherein the oxidation treatment is carried out by air oxidation or by the Hummers-Offemann method using sulfuric acid, sodium nitrate and potassium permanganate.