JPH04198283A - Manufacture of pencil lead - Google Patents

Abstract

PURPOSE:To obtain a pencil lead which can be greatly improved in the inverse correlation between strength and density by using a specified graphite in the method of producing a pencil lead wherein a material consisting mainly of graphite and an organic binder is subjected to a specified treatment. CONSTITUTION:In the method of obtaining a pencil lead wherein a material consisting mainly at least graphite and an organic binder (e.g. PVC) is kneaded, molded and then baked, use is made of a graphite which has a particle diameter of 5mu or smaller and has, formed thereon, a film of an organic material giving less carbonaceous residue than that of the organic binder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for producing a pencil lead, which uses graphite and an organic binder as at least the main materials, and which is kneaded, molded, and then fired.

(Prior art) The pencil lead produced by the method described above is generally called a fired resin lead, and graphite is an extremely popular material because it provides a smooth writing feel and high strength. .

In order to improve the inverse relationship between strength and concentration (if you try to make something with high strength, it will have inferior density, and if you try to make something with excellent density, it will have low strength), Various studies have been made on this graphite.

Forming a film on the surface is one such method; for example, Japanese Patent Application Laid-Open No. 61-95084 discloses the use of graphite in which polymethacrylic acid ester is polymerized on the surface. Aiming to improve strength without impairing density or writing feel, polymethacrylate ester is compatible with the binder and depolymerizes during heat treatment, improving the adhesion between graphite and binder after kneading. In addition, after firing, it is expected to have the effect of forming uniform microbores inside, and the resulting effects.

(Problem M to be solved by the invention) Graphite is extremely surface inactive, and if it is easily crushed, it is also likely to cause delamination. Therefore, even if a film as described above is formed on the surface, it cannot be maintained stably.

That is, shearing force is inevitably applied to the material during the kneading process using a suitable device such as a kneader or roll, and this shearing force causes the graphite to be crushed or delaminated, and also because the graphite is surface inert.

The film peels off from the graphite. In the end, the result is not much different from simply using the coating material together with graphite.

(Means for Solving the Problems) There are two methods for obtaining a stable film that can withstand the shearing force during kneading treatment.

One is to use graphite with a particle size of 5 μm or less, and the other is to form a film with a material having rubber elasticity. That is, the present invention provides (1) a method for producing a pencil lead in which graphite and an organic binder are used as at least the main materials, and after kneading and forming, a firing treatment is performed, as the graphite;
A method for producing a pencil lead characterized by using a pencil lead having a particle size of 5 μm or less and having an organic film formed on the surface thereof with a carbon residue smaller than that of the organic binder (2) Graphite and organic In the method for manufacturing a pencil lead using a binder as at least the main material, kneading, shaping, and firing, the graphite has a carbon residual amount smaller than that of the organic binder on the surface. The gist of the present invention is a method for producing a pencil lead, which is characterized by using an organic substance having rubber elasticity and forming a film thereon.

The details will be explained below.

If the particle size of graphite is reduced to 5 μm or less, the influence of shearing force on crosstalk will be reduced. Such particles having a small particle size can be obtained by an appropriate pulverization method such as jet pulverization. You may also ask a powder supplier. Expanded graphite can also be crushed or exfoliated, and some artificial graphite originally has this particle size. Note that the particle size has variations, and in the present invention, means the average value. In terms of homogeneity, it is preferable that the distribution be as small as possible.

Furthermore, if the film is formed of a material having rubber elasticity, the film will restore its shape due to its rubber elasticity even if it is subjected to shearing force during kneading. That is, peeling from the graphite surface can be suppressed.

These two means can be used together. That is, the particle size is 5 μm.
From the point of view of (1) to select graphite below, the film materials include polyethylene, polypropylene, polyisobutylene, polystyrene, polymethacrylate,
A depolymerized resin such as polytetrafluoroethylene, nylon, or polymethmethylstyrene can be used depending on the material used for the binding material.
From the point of view of point (2) of selecting a coating material with rubber elasticity, graphite with a particle size larger than 5 μm can be used, but
Graphite having a particle size of 5 μm or less on which a film having rubber elasticity is formed can also be used, and these methods can also be used in combination. Here, examples of the material of the film having rubber elasticity include polychloroprene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, ethylene vinyl acetate, and the like. In addition, the formation of the film is
It may be a method of polymerization on the graphite surface, a method of immersing graphite in a coating material that has been made into a solution, or a method of immersing graphite in a coating material that has been made into a solution. It is appropriate to adopt a film forming method using It can also be formed into a multi-layered film or a film containing dispersed materials used for other purposes. The amount of coating is also appropriate depending on the type of material, but in general, the weight ratio to the amount of graphite is 5 to 5.
It is best to set it to about 40%.

Conventionally known methods can be used as they are except for the graphite on which a film has been formed. That is, for example, polyvinyl chloride,
Polyvinylidene chloride, chlorinated rubber, chlorinated polyethylene,
Appropriate binders and film-forming graphite represented by chlorinated resins such as chlorinated polyvinyl chloride or copolymers thereof, and plasticizers such as phthalate esters, solvents, and stabilizers used as necessary.

Reinforcing materials such as various whiskers are kneaded using an appropriate device such as a Henschel mixer or a pressure kneader with 13 rolls, formed into a fine wire shape by extrusion molding, etc., and then subjected to a firing process to obtain a fired core. , liquid paraffin, wax, or other oily substances as necessary.

(Example) Hereinafter, "part" simply indicates parts by weight, and "%" indicates weight %.

<Example 1> Polyvinyl chloride 30 parts Film-forming graphite 50 parts (10% styrene monomer polymerized on the surface of natural graphite with a particle size of 3 μm) Dioctyl phthalate (plasticizer) 15 parts Stearate ( Stabilizer) 2 parts Methyl ethyl ketone (solvent) 30 parts The above product was sufficiently kneaded using a pressure kneader and three rolls, extruded into a fine wire shape, heated to 300°C in air, and further heated in an inert atmosphere. 10 inside
It was heated to 00°C. After cooling.

A 0.5-yen pencil lead was obtained by impregnating it with spindle oil.

<Examples 2 to 4> Everything was the same as in Example 1, except that the film-forming graphite in Example 1 was obtained by polymerizing styrene monomer at a ratio of 5%, 20%, and 30% to graphite. did.

<Example 5> As the film-forming graphite of Example 1, one obtained by polymerizing styrene monomer and further polymerizing acrylonitrile monomer at a ratio of 5% to graphite on the surface was used. I did the same thing.

<Example 6> Furan resin 30 parts Film-forming graphite 40 parts (10% vinyl acetate hetamine polymerized on the surface of artificial graphite with a particle size of 2 μm) Paraffin wax 5 parts The above mixture was pressed After thorough kneading with a kneader and three rolls, the mixture was extruded into a thin wire, hardened at 110°C for 20 hours, and further heated to 1000°C in an inert atmosphere.

After cooling, it was impregnated with spindle oil to obtain a 0.5an pencil lead.

<Examples 7 and 8> Examples were repeated, except that as the film-forming graphite of Example 6, synthetic graphite with a particle size of 5 μm was polymerized with a listed vinyl monomer at a ratio of 5% and 20%. Same as 6.

<Example 9> As the film-forming graphite of Example 1, natural graphite with a particle size of 20 μm was immersed in a styrene-butadiene thermoplastic elastomer dissolved in a solvent and taken out to form a 10% film. The same procedure as in Example 1 was carried out.

<Example 10> Everything was the same as in Example 9, except that as the film-forming graphite in Example 9, a film formed with a styrene-isoprene-based thermoplastic elastomer was used instead of the styrene-butadiene-based thermoplastic elastomer. .

<Example 11> As the film-forming graphite of Example 9, after polymerizing 10% vinyl acetate monomer on the surface of artificial graphite with a particle size of 12 μm, a 5% ethylene vinyl acetate film was further formed. Everything was the same as in Example 9 except for the following.

<Example 12> As the film-forming graphite of Example 9, a film was formed using 20% styrene resin (containing silicone rubber powder with a particle size of 3 μm dispersed at a 30% ratio) on natural graphite with a particle size of 5 μm. Everything was the same as in Example 9, except that the same material was used.

<Example 13.14> Everything was the same as in Example 9, except that as the film-forming graphite of Example 9, a styrene-butadiene thermoplastic elastomer film was formed on artificial graphite with particle sizes of 4 μm and 2 μm. I made it.

<Comparative Examples 1 to 3> In Examples 1 and 6.9, all the procedures were the same as in each Example except that graphite without a film formation was used instead of the film-formed graphite.

Comparative Examples 4 and 5> As the film-forming graphite of Example 1, particle sizes of 7 μm and 20 μm were used.
The same procedure as in Example 1 was carried out except that a polystyrene film was used.

Comparative Example 6 The same procedure as in Example 6 was carried out except that the film-formed graphite used in Example 6 was a graphite with a particle size of 12 μm on which a polyvinyl acetate film was formed.

Comparative Example 7 In Comparative Example 1, everything was the same as in Comparative Example 1 except that 5 parts of polystyrene was also used in the formulation.

<Comparative Example 8> Comparative Example 2 was carried out in the same manner as in Comparative Example 2 except that 5 parts of polyvinyl acetate was also used in the formulation.

<Comparative Example 9> Comparative Example 3 was carried out in the same manner as in Comparative Example 3 except that 5 parts of a styrene-butadiene thermoplastic elastomer was used in combination with the formulation.

The bending strength and density of the samples obtained on each side were measured according to JIS 56005, and the results are shown in Table 1.

(Hereinafter, blank spaces) Table 1 (Effects of the Invention) As can be seen from Table 1, according to the present invention, the inverse correlation between strength and concentration using surface-coated graphite can be greatly improved.

Patent applicant: Pentel Co., Ltd.

Claims (2)

[Claims] (1) In a method for producing a pencil lead using graphite and an organic binder as at least the main materials, kneading, shaping, and firing, the graphite has a particle size of 5 μm or less, and the surface of the graphite has a particle size of 5 μm or less. A method for producing a pencil lead, characterized in that a pencil lead is formed with a film of an organic substance having a smaller residual carbon content than the residual carbon content of a binding material. (2) In a method for producing a pencil lead using graphite and an organic binder as at least the main materials, kneading, shaping, and then firing, the graphite is formed on the surface of the pencil lead by a carbon residue of the organic binder. 1. A method for producing a pencil lead, characterized in that an organic material having a small residual carbon content and having rubber elasticity is used.