JPH061942A - Pencil lead and its production - Google Patents

Abstract

PURPOSE:To obtain a pencil lead having stable quality and excellent wettability and flexural strength 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 carrying out the oxidative fluorination of a part or total of graphite with a mixed gas consisting of fluorine and an oxygen-containing gas and having a fluorine partial pressure of <=500mmHg at a reaction temperature of preferably <=200 deg.C. The hydrophilized graphite is kneaded with clay and a binder such as a water-soluble synthetic resin (e.g. PVA) and the mixture is formed and baked at a high temperature to obtain a sintered compact. The objective pencil lead can be produced by properly 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 prepared by mixing and kneading graphite, clay, water as a surfactant and a plasticizer, molding and firing at a high temperature to obtain a sintered body, and then impregnating fats and oils. A clay type product manufactured by mixing with graphite, a synthetic resin, a plasticizer, a foaming agent, a lubricant, etc. are mixed and kneaded, molded, and then baked at a high temperature to carbonize the resin, and a baked body using carbon as a binder. It is roughly classified into the carbon type that is obtained by impregnating oils and fats. 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 release layer at the interface where the adhesiveness is improved.

Therefore, the inventors of the present invention previously improved the wettability by fluorinating graphite and using graphite having improved wettability with water, and by subjecting oxidized graphite to fluorination. A method using graphite is proposed. However, the fluorinated graphite after the oxidation treatment has two drawbacks: the quality is difficult to stabilize and the price is high, and the pencil lead obtained is similarly unstable in quality and expensive. It was

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a pencil lead having substantially the same quality as the pencil lead using the graphite fluorinated after the oxidation treatment previously proposed by the present inventors. To provide stable and inexpensive
Even when using a surfactant or a coupling agent to improve the adhesion between graphite and a binder, it is necessary to eliminate the interfacial peeling layer formed during firing and to provide a pencil lead with even greater strength. Is.

[0006]

The poor adhesion between graphite and clay or water-soluble resin is basically because graphite does not wet with water. Therefore, surface treatment of graphite has been performed with a surfactant or a coupling agent for the purpose of improving the wetting of the graphite powder with water, but the surfactant and coupling agent are relatively large molecules. In addition, a delamination layer or pores are formed at the interface due to depolymerization or sublimation during firing.

It has been found that when graphite is oxidized and then fluorinated, it is softened in terms of concentration and wear as compared with the case where only fluorine is treated. However, the treatment becomes two steps and the quality is difficult to stabilize. There was a difficulty. Therefore, it was thought that the quality could be stabilized and the processing cost could be reduced by further processing, and as a result of research, it was found that this problem could be solved by further carrying out oxidative fluorination, and the present invention was completed.

That is, the present invention is as follows: (1) A graphite obtained by kneading, molding and firing graphite oxyfluorinated with a mixed gas of a part or all of graphite and oxygen and a binder. A pencil lead consisting of a bound body and oils and fats impregnated in the sintered body,

(2) Oxidative fluorination treatment is carried out with a mixed gas of a gas containing oxygen in part or all of graphite and fluorine.
A method for producing a pencil lead, characterized in that the hydrophilized graphite is kneaded and molded with a binder, fired at a high temperature to obtain a sintered body, and the sintered body is appropriately impregnated with fats and oils.

(3) The method for producing a pencil lead according to the above item (2), wherein an oxidative fluorination treatment is carried out with a gas containing fluorine having a fluorine partial pressure of 500 mmHg or less and a fluorine mixed gas,

(4) The method for producing a pencil lead according to the above item (2) or (3), wherein the fluorine oxide treatment is performed at a temperature of 200 ° C. or less.

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 for a pencil lead, the strength is low due to insufficient adhesion of the interface layer, which is considered to be due to water repellency. In addition, fluorine is desorbed during firing to release highly toxic fluorine gas and hydrogen fluoride, 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
The graphite fluorinated at a fluorine partial pressure of 00 ° C. or lower and / or 500 mmHg or lower had good wettability with water, and was at a level that was sufficiently usable as a pencil lead.

The inventors of the present invention have conducted further research to improve the wettability to water and to obtain a high quality pencil lead by oxidizing graphite and then fluorinating it as compared with the case of treating only fluorine. Revealed. However, there is a drawback that the quality is not stable because the treatment for graphite is a two-step treatment of oxidation and fluorination.

Therefore, the inventors of the present invention have the same quality as when the fluorination is carried out after the oxidation treatment, even if the oxidation fluorination treatment is carried out in one step by treating with the mixed gas of the gas containing oxygen and fluorine. The present invention has been completed by confirming that a pencil lead of stable quality can be obtained. In addition, it is relatively inexpensive because the treatment is done in one stage and only a small amount of expensive fluorine gas is used, and the amount of fluorine desorbed during firing is also small, so hygiene is also considered. Are better.

Since the fluorine component released during firing is released in the form of an atom or a very small molecule, the peeling layer at the interface, which is a problem when a surfactant or a coupling agent is used, is extremely reduced. You can Furthermore, in the case of a clay-type pencil lead, the desorption of the fluorine component dissolves in silica or alumina in the clay, and a decrease in the sintering temperature, which is considered to form a flux component, is observed. It is thought that it also acts as.

It is conceivable that a short time treatment is carried out in order to perform the oxidative fluorination treatment at a fluorine partial pressure of more than 200 ° C. and / or more than 500 mmHg and to improve the wettability with water, but the graphite to be treated is a powder. Therefore, it is practically difficult to control the processing time with the processing under the conditions. Also,
Highly explosive, not practical.

[0018]

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. [Method for oxidative fluorination of graphite] After placing graphite in a boat made of nickel with a thickness of about 3 mm and storing it in a reactor made of SUS316, the graphite was heated to 120 ° C and kept at 10 ^-3 mmHg or less for 12 hours. Adsorbed water and the like were removed. While maintaining the vacuum state, the mixture was allowed to cool to the treatment temperature, a mixed gas of oxygen and fluorine was introduced to an arbitrary pressure, and contact was conducted for an arbitrary time for treatment.

(Example 1) Natural scaly graphite treated with a mixed gas of oxygen and fluorine (1: 1) at a pressure of 20 mmHg for 10 minutes at room temperature (average particle size: 5 microns, fixed carbon content: 99.5%) 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) 3 at a pressure of 100 mmHg at room temperature
A pencil lead having a diameter of 2.0 mm was obtained in the same manner as in Example 1 except that graphite treated with a mixed gas of oxygen and fluorine (1: 1) for 0 minutes was used. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

(Example 3) The same procedure as in Example 1 except that graphite treated with a mixed gas of oxygen and fluorine (1: 1) at 100 ° C and a pressure of 100 mmHg for 30 minutes was used. A 0 mm pencil lead was obtained. 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 After thoroughly kneading with a three-roll mill, extrusion molding, drying at 250 ° C for 12 hours, then heating to 1000 ° C in a nitrogen atmosphere to obtain a sintered body with a diameter of 0.57mm, impregnated with spindle oil. 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 5) A diameter of 0.5 was obtained in the same manner as in Example 4 except that the graphite used in Example 2 was used.
A 7 mm pencil lead was obtained. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

Example 6 A pencil lead having a diameter of 0.57 mm was obtained under the same conditions as in Example 4, except that the graphite used in Example 3 was used. 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 having a diameter of 2.0 mm was obtained in the same manner as in Example 1 except that the graphite used in Examples 1 to 6 was used untreated. 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 having a diameter of 0.57 mm was obtained in the same manner as in Example 4, except that the graphite used in Examples 1 to 6 was used untreated. The strength of the obtained pencil lead and the result of the writing test are shown in Table 1.

(Comparative Example 3) Graphite used in Comparative Example 2 55 parts by weight Polyvinyl chloride (polymerization degree 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 After thoroughly kneading with a three-roll mill, extrusion molding, drying at 200 ° C for 12 hours, then heating to 1000 ° C in a nitrogen atmosphere to obtain a sintered body with a diameter of 0.57 mm, impregnated with spindle oil. 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.

Comparative Example 4 The same procedure as in Example 4 was repeated except that graphite was air-oxidized at 500 ° C. for 30 minutes and then treated with 10 mmHg of fluorine gas for 10 minutes.
A 57 mm pencil lead was obtained. Table 1 shows the results of the strength test and the writing property test performed on the obtained pencil lead.

[0029]

[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 JIS S6005 test method.

As is clear from Table 1, the pencil lead of the present invention has strength significantly exceeding that of conventional pencil leads,
It can be seen that it softens the wear. That is, it is shown that the strength is far superior to that of the conventional pencil lead if the composition and the like are adjusted so as to give the same concentration and wear.
Further, in Comparative Example 4 and Example 4, the oxidation treatment was performed before the fluorination treatment and the oxidation treatment was performed at the same time, but the quality of the pencil lead is almost the same. However, the variation in strength of Example 4 was about one half of the variation in Comparative Example 4. Therefore, according to the present invention, it can be said that the quality is more stable than when the fluorination treatment is performed after the oxidation treatment.

The results of the carbon type pencil lead using a water-insoluble synthetic resin are shown in Comparative Example 3, but the pencil lead of the present invention exhibited strength exceeding this, and therefore the conventional water-soluble resin was used. It is considered that the problem of interfacial peeling, which has been a problem in the pencil lead used, is solved and an interface having excellent adhesiveness is formed as compared with the case of using a water-insoluble resin. This is because the wettability with water improved by the oxidative fluorination treatment is due to the addition of polar components to the graphite surface energy, and as a result, electrostatic attraction acts on the interfacial adhesion between graphite and clay or water-soluble resin. However, it is considered that the adhesive force at the graphite-water-insoluble resin interface, which is only the Van der Waals force, was exceeded.

[0032]

EFFECTS OF THE INVENTION The pencil lead of the present invention has a strength that greatly exceeds conventional pencil leads, but also softens the concentration and wear. Therefore, if the composition is adjusted to give the same concentration and wear,
It has a strength far exceeding that of a conventional pencil lead. Although the quality is the same as that obtained by performing oxidation and fluorination in two steps, the variation in strength is half and the quality is stable. Even when a water-soluble resin was used as the binder, the strength was significantly improved, and the problem of interfacial peeling could be solved.

Claims (4)

[Claims] 1. A sintered body obtained by kneading, molding and firing graphite oxidatively fluorinated with a mixed gas of a part or all of graphite containing oxygen and fluorine, and the sintered body. A pencil lead consisting of oils and fats impregnated in the body. 2. A graphite is partly or wholly subjected to an oxidative fluorination treatment with a mixed gas of a gas containing oxygen and fluorine, and the hydrophilized graphite is kneaded and shaped with a binder and fired at a high temperature. A method for producing a pencil lead, comprising obtaining a bound body and impregnating the sintered body with oils and fats as appropriate. 3. The method for producing a pencil lead according to claim 2, wherein the oxidative fluorination treatment is performed with a gas containing oxygen and a fluorine partial pressure of 500 mmHg or less and a fluorine mixed gas. 4. The method for producing a pencil lead according to claim 2, wherein the fluorine oxide treatment is performed at a temperature of 200 ° C. or lower.