JPH055075A - Production of pencil lead - Google Patents

Abstract

PURPOSE:To improve the inverse relationship between strength and concentration and to impart sufficient strength to a pencil lead by producing a resin-baked pencil lead using a graphite having a low carbon-residue film. CONSTITUTION:Graphite particles having particle diameter of >=5mum are coated with a film-forming graphite produced by dispersing graphite particles having particle diameter of <=1mum in a low carbon-residue organic substance such as depolymerized resin. The coated graphite is used as a raw material for the objective pencil lead.

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, which comprises using graphite and an organic binder at least as main materials, kneading, molding, and then firing treatment.

[0002]

2. Description of the Related Art A pencil lead produced by the above-mentioned method is generally called a resin-fired lead, but graphite is extremely popular as a material because it brings a smooth writing taste and high strength. For the purpose of further improvement of the inverse correlation between strength and concentration (the relation where the higher the strength, the poorer the concentration, the better the strength, the lower the strength). Various studies have been made on this graphite.

Forming a film is one of them. For example, JP-A-61-95084 discloses the use of graphite obtained by polymerizing polymethacrylic acid ester on the surface. Polymethacrylic acid ester, which is compatible with the binder and depolymerizes during heat treatment, improves the adhesion between the graphite and the binder after kneading, and the action of forming uniform micropores inside after firing, And, it is expected that the effect of the strength improvement by this is obtained.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to develop the idea of using film-formed graphite and to further improve the above-described inverse correlation between strength and concentration. I will explain the consideration.

The size of graphite used has a great relationship with strength and concentration. The strength is higher when a relatively large one is used. However, the size of the graphite on the writing line also increases correspondingly, and the covering state on the writing surface becomes non-uniform, resulting in poor density. However, this may be because the graphite is crushed or delaminated by the shearing force that is inevitably applied in the kneading treatment with an appropriate material such as a kneader or a roll. Even if used, no improvement in strength can be expected.

The opposite is true when a relatively small one is used. However, if it is too small, it will be substantially integrated with the binder after firing and carbonization, but if it becomes small to some extent, even if smaller graphite is used, the concentration due to the uniform coating state on the writing line No improvement can be expected.

The formation of a film on graphite is believed to potentially have the advantage of contributing to both of these sides.
The coating can protect the graphite from being directly subjected to shearing forces that cause crushing and delamination, and if the coating has a carbon residual amount smaller than that of the binder, the coating is integrated with the binder. This is because it is considered that the protection from

However, merely forming a film on graphite cannot exert its advantages effectively. For many minutes, graphite is prone to crushing and delamination, and even if small graphite is thinly covered with a low carbon residual amount film (in consideration of the ratio of the film to graphite used), the graphite and binder after firing carbonization Unable to prevent the integration with. It is necessary to examine the size of graphite used and the relationship between graphite and film.

[0009]

According to the present invention, in a method for producing a pencil lead, which comprises using graphite and an organic binder at least as main materials, kneading, molding, and then firing treatment, the graphite is 5 μm or more. An organic material film having a carbon residual amount smaller than that of the organic binder on graphite having a particle size of 1
A method for producing a pencil lead is characterized in that a method is used in which graphite particles having a particle size of μm or less are dispersedly contained.

The details will be described below. Graphite having a particle size of 5 μm or more is referred to as “mother graphite”, and graphite having a particle size of 1 μm or less is referred to as “child graphite”.

As the sub-graphite, it is possible to use an ordinary graphite having a large particle size, which is pulverized by a jet mill or the like and appropriately classified, and a commercially available product generally called colloidal graphite or a conductive coating composition is used. It is also possible to use commercially available agents and the like. An example of the product is HAG-150 manufactured by Nippon Graphite Co., Ltd., Super Coro Height # 16, Pro Height 15Z, Oil Height G3.
07, Vannie-Height BP-4, Hitachisol Metallurgy Co., Ltd. Hitasol GP-60S, AB-1 and the like.

The mother graphite is suitable as long as it has a particle size of 5 μm or more, but it is not necessary to select one that is too large, as can be seen from the foregoing, but rather, considering the ease of kneading, etc. It may be appropriately selected from those up to about μm. In the present invention, the particle size means the average particle size, but it is preferable that the distribution range is small.

The organic substances used for the film include polyethylene, polypropylene, polyisobutylene, polystyrene, polymethacrylic acid ester, polytetrafluoroethylene, nylon, depolymerizable resins such as polymethamethylstyrene, and low carbon residue. As long as it is quantitative, an appropriate material can be used in relation to the material used for the binder. Examples thereof are those having rubber elasticity such as polychloroprene, butadiene / styrene copolymers, butadiene / acrylonitrile copolymers, and ethylene vinyl acetate. However, it is desirable that the material used for this film has poor compatibility with the binder, if possible. When they are compatible with each other, the film properties of the corners are often impaired by kneading or the like. The formation of the film on the mother graphite may be carried out by immersing the mother graphite in a solution film material in which the child graphite is dispersed, by a spray-dry method, or by other methods such as, for example, Hybridase manufactured by Nara Machinery Co., Ltd. A suitable method can be used, such as employing a film forming method using a machine called a system. It is also possible to form a multi-layer or to form a film containing other substances used for purposes other than the child graphite. The coating amount is appropriate depending on the type of material, but it is generally preferable to set the coating amount to about 5 to 40% by weight with respect to the mother graphite. Also, depending on the amount used, the amount of child graphite used with respect to the organic substance used for the coating can be appropriately set to, for example, about 5% by weight or about 70% by weight.

Besides the graphite having such a film formed thereon, a conventionally known method can be used as it is. That is, for example, polyvinyl chloride, polyvinylidene chloride, chlorinated polyethylene, urea resin, melamine resin, furan resin, polyvinyl alcohol, polyacrylamide, an appropriate binder such as butyl rubber, and film-forming graphite, and if necessary, used Will be
Knead a plasticizer such as phthalate ester, a solvent, a stabilizer, a filler, etc. with an appropriate material such as a kneader or a triple roll,
After being formed into a fine wire by extrusion molding or the like, it is subjected to a firing treatment to obtain a fired core, and further an oily substance such as liquid paraffin, spindle oil, microcrystalline wax, montan wax, polyethylene wax, carnauba wax, etc. Impregnate.

The reason why the inverse correlation between strength and concentration can be improved by the present invention is presumed to be as follows.

The graphite used in the present invention is obtained by coating the mother graphite with a film having a low residual carbon content containing dispersed child graphite. The child graphite helps protect the mother graphite from the shearing force that causes pulverization and delamination, and the mother graphite is a binder containing a considerable amount of the child graphite present in the film on the surface. Helps prevent integration with. As described above, it is considered that the advantages of each graphite are effectively exhibited by the mutual utilization of the child graphite and the mother graphite.

[0017]

EXAMPLES In the following, "part" means "part by weight" and "%"
"%" Means "% by weight".

Example 1 Polyvinyl chloride 30 parts Film-forming graphite 50 parts (Mother graphite having a particle size of 10 μm and 30% of child graphite having a particle size of 0.5 μm is coated with nylon at a ratio of 22.5%. Dioctyl phthalate (plasticizer) 15 parts Stearate (stabilizer) 2 parts Methyl ethyl ketone (solvent) 30 parts After thoroughly kneading the above mixture with a pressure kneader and three rolls , Extruded into a thin wire, heated to 300 ° C in air, and further heated to 1000 ° C in an inert atmosphere,
After cooling, it was impregnated with spindle oil to obtain a pencil lead of 0.5 mm.

<Examples 2 and 3> In Example 1, as the film-forming graphite, the particle size of the mother graphite was 10 μm to 50 μm.
m was the same as in Example 1 except that the thickness was changed to 6 μm.

<Examples 4 and 5> In Example 1, as the film-forming graphite, the coating amount of the film was 20% to 10%, 3
All were the same as in Example 1 except that the one changed to 0% was used.

Example 6 In Example 1, as film-forming graphite, styrene was polymerized at a rate of 5% on mother graphite having a particle size of 6 μm, and then 10% of child graphite having a particle size of 7 μm was added to the mother graphite. The same procedure as in Example 1 was carried out, except that the above-mentioned hybridization system was used in a proportion and polyvinyl alcohol was coated on the mother graphite in a proportion of 5%.

Example 7 Furan resin 50 parts Film-forming graphite 40 parts (Mother graphite having a particle size of 10 μm, vinyl acetate containing 40% of child graphite having a particle size of 0.3 μm, is coated at a ratio of 20%. ) Paraffin wax 5 parts After thoroughly kneading the above mixture with a pressure kneader and three rolls, extrusion molding into a fine wire form, curing treatment at 110 ° C for 20 hours, and further inert atmosphere It was heated to 1000 ° C. in the inside, cooled, and then impregnated with spindle oil to obtain a pencil lead of 0.5 mm.

<Comparative Examples 1 and 2> In Examples 1 and 7,
The same procedure as in each of the examples was performed except that graphite without film formation (mother graphite) was used in place of the film-formed graphite.

Comparative Example 3 In Example 1, 40 parts of graphite having a particle size of 10 μm and a particle size of 0.5 were used in place of the film-forming graphite.
Other than simply using 3 parts of μm graphite and 7 parts of nylon,
All were the same as in Example 1.

<Comparative Example 4> The same procedure as in Example 1 was carried out except that, in Example 1, the film-forming graphite was changed from 10 μm to 1 μm in particle diameter of the mother graphite.

<Comparative Example 5> The same procedure as in Example 1 was carried out except that, in Example 1, the film-forming graphite used had a particle size of child graphite changed from 0.5 μm to 2 μm.

Regarding the products obtained in each of the above examples, JIS S
The results of measuring the bending strength and the density according to 6005 are shown in Table 1.

[0028]

[Table 1]

[0029]

As can be seen from Table 1, according to the present invention, it is possible to sufficiently improve the inverse correlation between strength and concentration by using surface-coated graphite.

Claims (1)

Claim: What is claimed is: 1. A method for producing a pencil lead, which comprises using graphite and an organic binder at least as main materials, and kneading, molding, and then performing a firing treatment, wherein the graphite has a particle size of 5 μm or more. A pencil lead, characterized in that a graphite film having a particle size, which is formed of an organic material film having a carbon residual amount smaller than that of the above-mentioned organic binder, containing graphite particles having a particle size of 1 μm or less dispersed therein is used. Manufacturing method.