JPH04168096A - Manufacture of pencil lead - Google Patents

Abstract

PURPOSE:To improve the inverse correlationship between the density and strength of a pencil lead by specifying an average particle diameter for pore forming material and using the material whose depolymerization starting temperature is higher than the substantial ending temperature of lead contraction. CONSTITUTION:A pencil lead uses a pore forming material whose average particle diameter ranges from 0.03 to 0.10mum and depolymerization temperature is higher than the substantial ending temperature of lead contraction. It is recommended that a pore forming material selectively used have a depolymerization temperature of 350 deg.C or higher. In addition, the average particle diameter of 0.03 to 0.10mum means that the particle suited for the purpose is extremely small as a particle of normal concept. If a pore forming material of this fine particle is used it is not susceptible of deformation or crushing, when it is kneaded using a roll or a kneader. Therefore, the pore distribution of a baked lead after pore formation is stable. Further, if the material has a depolymerization temperature of 350 deg.C, it can well maintain its baked form leaving an adequate number of pores intact after depolymerization process.

Description

[Detailed Description of the Invention] (Industrial Application Field) When manufacturing a pencil lead by using an organic binder and an extender as main materials, kneading, molding, and firing, the depolymerized pores It relates to a product made by using a forming material in combination.

(Prior art) The above-mentioned pencil lead is generally called an organic fired lead, and usually consists of a binder such as polyvinyl chloride resin, polyvinyl alcohol, or furan resin, and a body material such as graphite or boron nitride, and a plasticizer. , using solvents, stabilizers, etc. as necessary, and forming a uniform dispersion using a kneader such as a kneader with 13 rolls into an appropriate size, heat-treating at high temperature, and baking to form a skeleton due to carbonization of the binder. Obtain a core body, and further,
It is obtained by impregnating it with an oily substance such as silicone oil, spindle oil, liquid paraffin, montan wax, or microcrystalline wax as necessary. Here, the reason why the oily substance can be impregnated is that the fired core has pores.

It is known that a pore-forming material is used as one of the means to artificially form these pores6.
Japanese Patent No. 26849 discloses a material in which pores are formed by depolymerization.

(Problem to be Solved by the Invention) Artificially forming pores in the fired core by using a pore-forming material is often helpful in improving concentration, but on the other hand, it often results in a decrease in strength. .

That is, even if a pore-forming material is used, it has not been possible to improve the inverse correlation between the concentration and strength of the resulting pencil lead.

(Means for solving the problem) As a pore-forming material, the average particle size is 0.03 to 0.10 μm.
A material whose depolymerization initiation temperature is equal to or higher than the substantial end temperature of core shrinkage is used. That is, the present invention uses an organic binder and an extender as main materials, and when producing a pencil lead by kneading, molding, and firing, a depolymerizable pore-forming material is also used. A method for producing a pencil lead in which the pore-forming material has an average particle size of 0.03 to 0.10 μm and a depolymerization initiation temperature equal to or higher than the substantial end temperature of core shrinkage. This is the summary.

This will be explained below.

Examples of substances that are depolymerized include polyethylene, polypropylene, polyisobutylene, polystyrene, polymethacrylate, polytetrafluoroethylene, nylon, and polymethmethylstyrene. Among these, those having a depolymerization initiation temperature of 350° C. or higher are selected and used.

Of course, it's a derivative.

It may also be one that has undergone degeneration due to radiation. It may be a copolymer, a mixture, or a so-called polymer alloy.

Furthermore, the depolymerization initiation temperature differs depending on the molecular weight and polymerizability. Here, the depolymerization initiation temperature is.

What is generally known as the thermal decomposition temperature can be used. This is because the depolymerization does not have to completely reduce the carbon yield to zero; for example, carbon black or other powders may be dispersed therein. In addition, the shape may be arbitrary, such as irregular shape, spherical shape, fibrous shape, or flat shape.

The average particle size of 0.03 to 0.10 μm means that the particles are extremely small in the conventional concept. If such a fine-particle pore-forming material is used, it will hardly be deformed or crushed during kneading with a roll or kneader, but the pore distribution of the fired core after pore formation is stable. Become something. However, if the average particle size is so small, if the core continues to shrink due to the progress of carbonization of the binder even after depolymerization starts during heat treatment, it will not function as a pore-forming material.

Therefore, although carbonization of the binder progresses as the temperature rises, it is required that depolymerization begins at a temperature higher than the temperature at which shrinkage of the core itself actually ends. Although it depends on the type of binder and the rate of temperature increase during heat treatment, shrinkage of the core actually ends when the treatment atmosphere temperature exceeds 300°C. For example, the dehydrochloric acid reaction in a chlorinated resin such as polyvinyl chloride, which is one of the typical binding materials,
It starts when the temperature exceeds 300°C and almost completes at 300°C. Therefore, for example, if it has a depolymerization initiation temperature of 350°C, it can sufficiently maintain its shape.
Sufficient pores can be left after depolymerization. By the way,
Commercially available materials such as Microgel (trade name) manufactured by Nippon Paint ■ and MP series manufactured by Soken Kagaku ■ can also be used.

Except for using such a pore-forming material, the conventionally known methods described above can be used as they are. Note that the amount of pore-forming material used is appropriate depending on the type of binding material, etc.
A ratio of about 2 to 40% by weight relative to the binder is generally good.

(Example) Hereinafter, parts simply indicate parts by weight, and particle diameters indicate average particle diameters.

Large polyvinyl chloride 50 parts graphite
50 parts dioctyl phthalate
15 parts stearate 2
50 parts methyl ethyl ketone 10 parts pore-forming material (three-dimensionally crosslinked polymethyl methacrylate fine particles with a particle size of 0.03 μm and a thermal decomposition temperature of 360°C) The above mixture was kneaded with three rolls and extruded into a fine wire shape. , gradually heated in air to 300℃ over about 8 hours,
Furthermore, heat treatment was performed to 1000° C. in an inert atmosphere to obtain a fired core having a diameter of about 0.5 part m, and this was impregnated with spindle oil.

In Example 1, the particle size of the pore-forming material was 0.05 μm.
Everything was the same as in Example 1 except that 0.10 μm (Example 2) and 0.10 μm (Example 3) were used.

In Example 1, the amount of pore forming material used was 10 parts.
Everything was the same as in Example 1 except that the amounts were changed to 1 part (Example 4), 5 parts (Example 5), 15 parts (Example 6), and 20 parts (Example 7).

In Example 1, the particle size of the pore-forming material was 0.08 μm.
The same procedure as in Example 1 was carried out except that polyamide fine particles having a thermal decomposition temperature of 380''C were used.

In the main example 1, the particle size was 0.10 μm as the pore forming material.
The same procedure as in Example 1 was carried out except that acrylic fine particles having a thermal decomposition temperature of 330°C were used.

In Example 1, except that no pore-forming material was used,
Everything was the same as in Example 1.

In the main example 1, the particle size was 0.02μ as the pore-forming material.
Everything was the same as in Example 1 except that 0.12 μm (Comparative Example 2) and 0.12 μm (Comparative Example 3) were used.

In the planar clay Example 1, a particle size of 0.03 μm was used as the pore forming material.
The same procedure as in Example 1 was carried out except that polystyrene fine particles having a thermal decomposition temperature of 270° C. were used.

JIS bending strength and density for each side above.
Table 1 shows the results measured according to S6005.

(Hereinafter, blank space) Table 1 (Effects of the invention) In Table 1, the density values of Example 1 and Comparative Example 4 are both 0.33, but the bending strength value is higher in Example 1. . Further, although there is almost no difference in the bending strength value uN (approximately 360 MPa) between Example 1 and Comparative Example 2, the concentration value of Example 1 is larger. As can be seen from these examples, according to the present invention, it is possible to produce a pencil lead with an improved concentration-strength inverse relationship when pores are actively formed using a pore-forming material. .

Claims (1)

[Claims] A depolymerizable pore-forming material is used in conjunction with a depolymerizable pore-forming material in producing a pencil lead using an organic binder and an extender as main materials, kneading, molding, and firing. As, the average particle size is 0.03-0.10μm
A method for producing a pencil lead using a pencil lead whose depolymerization initiation temperature is equal to or higher than the substantial end temperature of core shrinkage.