JPH01193379A - Production of pencil lead - Google Patents

Abstract

PURPOSE:To practically obtain a pencil lead having a low porosity, hardly any abrasion loss and excellent in flexural strength, by carrying out heat treatment at the decomposition starting temperature of a thermoplastic resin or below under reduced pressure and removing a softener of the thermoplastic resin. CONSTITUTION:The aimed pencil lead, obtained by kneading (A) a thermoplastic resin with (B) an extender material and (C) a softener (e.g., dioctyl phthalate), extrusion molding the resultant kneaded material and subjecting the molded material to calcining treatment at the decomposition starting temperature of the component (A) or below, e.g., 180-300 deg.C under <=1/10<2>Torr, using a far infrared heater.

Description

[Detailed Description of the Invention] (Industrial Application Field) The main ingredients are at least a thermoplastic resin as a binder, an extender, and a softener for the thermoplastic resin, and after kneading and extrusion molding, a baking treatment is performed. The present invention relates to a method for producing an organic fired pencil lead.

(Prior art and problems to be solved) When producing organic fired pencil lead, it is necessary to ensure that the thermoplastic resin as a binder is sufficiently kneaded with the body material and other materials used as necessary. Therefore, softeners for thermoplastic resins are generally used.

As this softening agent, in the present inventor's opinion.

It is better to use one with a relatively high boiling point. Of course, it is not possible to use materials with relatively low boiling points, but from the viewpoint of workability, kneading with an appropriate kneading machine such as a roll, kneader, or mixer, or extrusion molding with an appropriate molding machine such as a screw type or piston type is recommended. However, this is because these processes are usually carried out under heated conditions, and it is better to leave a sufficient amount of softener in these steps.

Examples of preferred high-boiling softeners include dioctyl phthalate, dibutyl phthalate, and dibutyl phthalate. Examples include butylphthalyl butyl glycolate, dioctyl sebacate, dioctyl adipate, propylene carbonate, ethylene glycol, and the like.

The problem is that this softener often remains at unnecessarily high temperatures during the firing process. That is, specifically, the thermoplastic resin as a binder starts to decompose at a relatively low temperature stage of firing, and this affects the carbonization after step 7. If such a large amount remains, the resulting pencil lead will have a low density and weak strength.

By the way, the idea of removing the softener beforehand in order to increase the density is not entirely unknown;
The claim of Publication No. 6 states, ``A coloring material and a binder are kneaded together with a plasticizer or a solvent for the binder, and then only the plasticizer or solvent in the kneaded material is extracted and removed with a solvent. A method for producing a pencil lead characterized by forming a plasticizer or solvent-free mixed product, followed by extrusion molding and firing at a high temperature." But this.

As mentioned above, extrusion molding becomes extremely difficult. Either the extrusion molding should be done at a very high extrusion pressure, the diameter should be made very thick so that the extrusion pressure can be lowered, or the extrusion molding should be done at a very high temperature and the viscosity of the material reduced. However, when considering the performance of actual extrusion molding machines, the fact that some extrusion molding machines have extremely small diameters such as 0.3 m, and the stable temperature of thermoplastic resins, their uses are extremely limited. do not have.

Therefore, it is important to know how to remove the softener, and the present invention aims to provide one means for doing so.

(Means for solving the problem) By performing heat treatment in a temperature range below the decomposition start temperature of the thermoplastic resin under reduced pressure.

Remove the softener. That is, one aspect of the present invention is to use at least a thermoplastic resin as a binding material, an extender, and a softener for the thermoplastic resin as main materials, and to form a cross wire.

In the method for producing an organic fired pencil lead which is subjected to a firing treatment after extrusion molding, the softening agent is removed by performing heat treatment in a temperature range below the decomposition start temperature of the thermoplastic resin under reduced pressure. The gist of this paper is a method for manufacturing a pencil lead characterized by the following.

Preferred softeners include dioctyl phthalate, dibutyl phthalate, butylphthalyl butyl glycolate, dioctyl sebacate, dioctyl adipate, propylene carbonate, ethylene glycol, and the like, as described above.

The decomposition start temperature of thermoplastic resins depends on the type, for example, polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, chlorinated polyethylene, polyvinyl butyral, polyvinyl acetate or copolymers thereof, acrylonitrile-styrene copolymer. Although it varies depending on the product, acrylonitrile-butadiene-styrene copolymer, etc., it is generally about 180 to 300'C. It is sufficient to set an appropriate temperature at which the softening material can be removed within a range not exceeding this range. Incidentally, as a heating means, a drying oven or the like may be used as appropriate, but if a far-infrared heater is used, uneven heating can be easily avoided.

In addition, in order to lower the temperature at which the softening material can be removed, the higher the degree of pressure reduction, the better;
If it is less than orr, there is not much difference.

In addition, the materials and processes to be used may be according to those conventionally known. For example, as the extender material, graphite, talc, boron nitride, mica, bentonite, etc. can be selected as appropriate, and other materials can be used as necessary. As, carbon black, a silicon oxide.

Examples include fillers such as stearate, low boiling point solvents such as methyl ethyl ketone, and after baking, an oil immersion process using spindle oil, paraffin wax, silicone oil, etc. can be performed as necessary. .

(Example) Hereinafter, "parts" simply refer to "parts by weight."

<Example 1> Polyvinyl chloride resin 35 parts graphite
50 parts carbon black 5 parts dioctyl phthalate
18 parts stearic acid
2 parts methyl ethyl ketone 100
Thoroughly mix the above ingredients in a Henschel mixer (5
0℃), and then cross-wired (100℃) using a three-roll machine.
It was extruded into a thin wire shape (100°C) using a piston extruder. After wrapping this into a frame, put it in a decompression furnace and reduce it to 1/1.
The pressure was reduced to 0” Torr, and the temperature was gradually raised from room temperature to 80°C over 2 hours and from 80°C to 120°C over 8 hours.
It was further kept warm at 120°C for 3 hours. By the way, the heat source is a far-infrared ceramic heater (wavelength: 2°, 5-10 μm).
)It was used. After cooling and taking out, the temperature was raised from room temperature to 270°C in air over 10 hours, and after cooling and taking out, treatment was performed at 1000°C for 5 hours in a non-oxidizing atmosphere, and after cooling and taking out, spindle oil was impregnated. did. The diameter of the obtained product is 0.57 nn.

<Example 2> Polyvinyl chloride-vinyl acetate copolymer 25 parts Polyvinyl acetate 10 parts Graphite
60 parts silicon oxide fine powder
5-part stearate
Part 2 dibutyl phthalate 14
Part propylene carbonate 2 parts Methyl ethyl ketone 100 parts The above compounded materials were mixed in the same manner as in Example 1, and then extruded into a thin wire (110°C) using a screw extruder. After wrapping this into a frame, it was placed in a vacuum furnace, the pressure was reduced to 1/10" Torr, and the temperature was gradually raised from room temperature to 80°C over 2 hours, then from 80°C to 110°C over 8 hours, and then heated to 110°C. The temperature was further kept for 3 hours.The heat source was the same as in Example 1.After cooling and taking out the
The temperature was raised from room temperature to 270°C in air over 8 hours, and then cooled and taken out, heated to 1000°C in a non-oxidizing atmosphere.
- 2 hours of treatment was applied. The diameter of the obtained one is 2.05o
It is n.

Comparative Example 1> Everything was the same as in Example 1, except that the heat treatment in a vacuum furnace was performed without reducing the pressure.

Comparative Example 2> In Example 2, everything was the same as in Example 2 except that the heat treatment in a reduced pressure furnace was performed without reducing the pressure.

<Comparative Example 3> In Example 1, after cross-mixing and before extrusion molding, heat treatment in a reduced pressure furnace was performed in the same manner as in Example 1, and then the product was placed in a piston type extruder. Although I tried to extrude this, I was unable to extrude it, and even though I tried increasing the temperature, the inside of the extruder only became abnormally high temperature.

(Effects of the Invention) Table 1 shows the results of examining the porosity, wear amount 1 bending strength, and hardness of the samples obtained on each side (excluding Comparative Example 3). The porosity was determined by immersing the fired sample in benzyl alcohol for 1 hour (20°C) under ultrasonic vibration conditions.In other words, the volume of the sample was V, and the The weight is W□, W2. When the density of benzyl alcohol is D, the porosity (%) = (w, -W,) The amount of wear was determined when a vertical load of 300 g was applied to 1166 g/e) and the paper was written for 10 m.

1. As is well known, bending strength and hardness are determined by JI
It is a sub-chamber according to S 56005, a sub-chamber based on sensuality.

Table 1 As can be seen from Table 1, according to the present invention, it is possible to practically obtain a pencil lead with low porosity, less wear, and excellent bending strength.

Patent applicant: Pentel Co., Ltd.

Claims (1)

[Claims] A method for producing an organic sintered pencil lead comprising at least a thermoplastic resin as a binder, an extender, and a softener for the thermoplastic resin, and subjected to kneading, extrusion molding, and sintering treatment, wherein the thermoplastic A method for producing a pencil lead, characterized in that the softening agent is removed by heat treatment in a temperature range below the decomposition start temperature of the resin under reduced pressure.