JP2000160092A - Manufacture of core of pencil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To break inverse relationship between tenacity and concentration by using a linear polyester resin as a part of a binder in case of kneading a material containing at least the binder and a filler, extruding and heat-treating thereof up to a firing temperature. SOLUTION: A linear polyester resin to be used as a binder preferably includes a co-polymerized polyester having a polyalkylene terephthalate as a main chain, concretely a polyethylene terephthalate or a polyglycol-modified polyethylene terephthale. The binder is kneaded with necessitated materials including a filler such as graphite, a plasticizer and a stabilizer and the mixture is extruded to produce a formed item which is dried, heat-treated up to firing temperature, cooled and taken out, followed by being immersed in an oily material containing one or more appropriate compounds selected from liquid paraffin, spindle oil, microcrystalline wax, low molecular weight polyethylene wax, paraffin wax, squalene and the like.

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 obtained by kneading, extruding, and heat-treating at least a binder and a material containing a body material to a firing temperature.

[0002]

2. Description of the Related Art Conventionally, in a method of manufacturing a fired pencil lead, various kinds of binders have been used, starting with clay, natural resins, synthetic resins, and the like. A solvent type using a chlorine-containing resin such as vinyl and an aqueous type using a water-soluble resin such as gum arabic and polyvinyl alcohol. However, the water-based type is inefficient in its production process because it requires a long drying time to remove water in its production process.
In addition, because of the problem of low strength in terms of quality, recently, mainly solvent type using chlorine-containing resin,
It is widely used due to its good workability.

[0003]

The above-mentioned binder has the function of increasing the strength of the pencil lead by binding the materials such as graphite and boron nitride by carbonization by heat treatment. The balance between the size and the amount of pores generated along with the volatilization of the plasticizer during the process, that is, the pores are small, and as the amount decreases, the strength decreases and the concentration decreases. In recent years, in the above-mentioned conventional binder, the inverse correlation between the strength and the concentration has been improved, but it is still not enough. However, the present inventor has found that the use of a specific material for at least a part of the binder can break the inverse correlation between the strength and the concentration, and has completed the present invention. .

[0004]

According to the present invention, there is provided a method for producing a pencil lead comprising kneading, extruding, and heat-treating at least a binder and a material containing a body material to a firing temperature. The present invention provides a method for producing a pencil lead, wherein a linear polyester resin is used for the part.

The details will be described below. Examples of the linear polyester resin include maleic acid, fumaric acid, metaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid,
Succinic acid, abipic acid, sebacic acid, malonic acid, maleic acid, anhydrides or lower alkyl esters of these acids, dimers of linolenic acid, other divalent organic acid monomers, , 4-benzenetricarboxylic acid,
1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-
Hexanetricarboxylic acid, 1,3-dicarboxyl-2
-Methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, empoletrimer acid, anhydrides of these acids, and other trivalent or higher polyvalent compounds Carboxylic acid monomer, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,
Diols such as 2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, and other dihydric alcohol monomers;
Sorbitol, 1,2,3,6-hexanetetrol,
1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose,
1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylprotantriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,
3,5-trihydroxylmethylbenzene, other 3
And an alcohol monomer having a valency or higher.

Examples of commercial products already on the market as these linear polyester resins include "Kemit" (a copolymer polyester having a polyalkylene terephthalate as a main chain, manufactured by Toray Industries, Inc.) and "Stafix" (a polyglycol). Modified polyethylene terephthalate, manufactured by Fuji Photo Film Co., Ltd., "Elitel" (copolyester having polyalkylene terephthalate as main chain, Unitika Ltd.)
And the like, and these may be used alone or in combination. It can also be used in combination with a conventional binder. When used in combination with the conventional binder, if the content is less than 3% by weight, the effect of improving the strength and concentration of the linear polyester resin is difficult to be exhibited, so the usage amount is 3% by weight or more based on the total amount of the binder. Preferably, there is.

[0007] The above-mentioned binder is kneaded, extruded, and dried together with a body material such as graphite, and materials used as necessary such as a plasticizer and a stabilizer. After taking out, add liquid paraffin,
The oil is impregnated with one or more suitable oils such as spindle oil, microcrystalline wax, low molecular weight polyethylene wax, paraffin wax, and squalane.

[0008]

The reason why a pencil lead obtained by using a linear polyester as a binder can break the inverse correlation between strength and concentration is presumed to be as follows. The linear polyester resin used in the present invention is a liquid-phase carbonized binder that is once liquefied by heat treatment in air and then carbonized. By heat-treating this linear polyester in a state in which it is mixed with another compound,
The liquefied linear polyester is carbonized while uniformly contacting the surface of the body material such as graphite. Therefore, continuous pores formed when the liquefied linear polyester is carbonized are formed close to the body material, and the body material is easily detached from the core during writing, so that the handwriting density is increased. Is considered to be darker. Furthermore, compared to the conventional liquid phase carbonized binder, the linear polyester resin of the present invention has the specificity that the molecular structure is linear and an appropriate arrangement of functional groups is provided. Therefore, it is considered that since the strength of the carbide and the binding force with the constitutional material are large, the strength is higher than that of the conventional binder which is liquid phase carbonized. It is presumed that these two factors have made it possible to achieve both high concentration and high intensity, which were conventionally inversely correlated.

[0009]

<Example 1> 28 parts of vinyl chloride resin Linear polyester resin (Stafix P-LC, manufactured by Fuji Photo Film Co., Ltd.) 2 parts Graphite 50 parts Dioctyl phthalate 17 parts Stearic acid 3 parts Methyl ethyl ketone (solvent) 30 parts As a compound, the above materials were kneaded sufficiently by a kneader and a three-roll mill, and then extruded into a thin wire, and then air-blended in air.
C. and further heated to 1100.degree. C. in an inert atmosphere, and after cooling, impregnated with spindle oil to obtain a 0.5 mm pencil lead.

<Example 2> Vinyl chloride resin 15 parts Linear polyester resin 20 parts Graphite 50 parts Dioctyl phthalate 17 parts Stearic acid 3 parts Methyl ethyl ketone 30 parts After kneading thoroughly with a kneader and a three-roll mill, the above materials were blended. , Extruded into a thin wire, 300 in air
C. and further heated to 1100.degree. C. in an inert atmosphere, and after cooling, impregnated with spindle oil to obtain a 0.5 mm pencil lead.

Example 3 Linear polyester resin (Elitel UE3600 (manufactured by Unitika)) 20 parts Linear polyester resin 10 parts Graphite 50 parts Dioctyl phthalate 17 parts Stearic acid 3 parts Methyl ethyl ketone 30 parts After sufficiently kneading with a kneader and three rolls, extruding into a fine wire form,
C. and further heated to 1100.degree. C. in an inert atmosphere, and after cooling, impregnated with spindle oil to obtain a 0.5 mm pencil lead.

Comparative Example 1 The procedure of Example 1 was repeated except that the linear polyester resin (Stafix P-LC, manufactured by Fuji Photo Film Co., Ltd.) was not used and the vinyl chloride resin was 30 parts. A pencil lead of 0.5 mm was obtained in the same manner as in Example 1.

<Comparative Example 2> In Example 2, the same procedure as in Example 1 was repeated except that 30 parts of vinyl chloride resin and 32 parts of dioctyl phthalate were used, without using Staxix P-LC. A pencil lead of 5 mm was obtained.

For the pencil lead obtained in each of the above examples, JI
Table 1 shows the results of measuring the bending strength and the concentration based on S S 6005. (Bending strength: MPa, concentration:
D)

[0015]

[Table 1]

[0016]

As can be seen from Table 1, according to the present invention, it is possible to obtain a pencil lead having a higher strength and an improved inverse correlation between the density and the strength, as compared with the comparative example having a similar density. Things.

Claims (4)

[Claims] 1. A method for producing a pencil lead comprising kneading, extruding, and heat-treating at least a binder and a material containing a body material to a firing temperature, wherein a linear polyester resin is added to at least a part of the binder. A method for producing a pencil lead, which is used. 2. The method for producing a pencil lead according to claim 1, wherein a copolymer polyester having polyalkylene terephthalate as a main chain is used as the linear polyester resin. 3. The method for producing a pencil lead according to claim 2, wherein polyethylene terephthalate is used as said polyalkylene terephthalate. 4. The method according to claim 3, wherein the copolymerized polyester resin having polyethylene terephthalate as a main chain is polyglycol-modified polyethylene terephthalate.