JP4345969B2 - Pencil lead, manufacturing method thereof, and carbon powder used therefor - Google Patents

Description

  The present invention relates to a pencil lead such as a wood-axis pencil lead and a mechanical pencil lead, a method for producing the same, and a carbon powder suitable as a constitutional material thereof.

  Conventionally, in a thermal power plant, an exciter is used to supply a generator and a magnetic force to the generator. Slip rings and the like are used for generators and exciters, and the carbon brush used for these slip rings and the like is in sliding contact with the outer peripheral surface of the current collector ring fixed to the rotating shaft via an insulator. Therefore, the brush is replaced when it is worn down to the limit of use of the brush, that is, to the position of the specified use length. Since generators and exciters are operated according to the operation of thermal power plants, brush replacement is performed once or twice a year, and used brushes are discarded at the expense of disposal. The current situation is landfill disposal or incineration disposal.

  In recent years, however, manufacturers have been required to collect and recycle used household electrical appliances.・ Various recycling technologies have been implemented, such as using crude ash for roadbed materials and cement materials. Therefore, how to effectively use waste carbon brushes has become a major issue.

  By the way, the brushes used in generators include natural graphite brushes and metal graphite brushes, but natural graphite brushes with low smoothness and aggressiveness are frequently used for high voltage devices. Yes. This natural graphite brush is obtained by mixing a carbon black powder or graphite powder and a binder made of a synthetic resin and the like, solidifying and molding, and cutting it into a predetermined shape and size.

  On the other hand, a pencil lead or the like is well known as a product using carbon such as graphite. The pencil lead is formed by kneading an organic compound that carbonizes when fired at a high temperature, such as natural resin, synthetic resin, coal tar pitch, etc., with an extender such as graphite, carbon black, and coke powder, and then extruding it into a desired shape. The resin is carbonized by firing at a high temperature, and the pores of the obtained sintered body are impregnated with oils and fats such as liquid paraffin to obtain a finished core (see Patent Document 1). As another type, it is produced by mixing and kneading an extender such as graphite or carbon black, clay, surfactant, etc., and firing at a high temperature after molding to obtain a sintered body, which is impregnated with fats and oils. There are also things.

  Regarding graphite for pencil cores, there are other types of graphite other than natural graphite, such as quiche graphite in which a large amount of carbon is deposited in molten iron when melting a blast furnace or coke, and has the same physical properties as natural graphite. Although it is often used, it has a problem that the supply amount fluctuates because it depends on the operation status of the blast furnace.

  In addition, by using graphite having a methacrylic acid ester polymerized on its surface, a technique for improving the strength without impairing the pencil core concentration and writing quality (see Patent Document 2), and further, the polyimide film is heat-treated and graphitized. A method of performing the above has also been proposed (see Patent Document 3).

JP-A-7-179806 (paragraph number 0012, etc.) JP-A-61-95084 JP-A-3-279207

  The present invention aims to make effective use of the carbon brush that has been disposed of, and by using graphite recycled from the carbon brush, the pencil core has a good balance of strength, concentration, and writing performance, and uses a core made of natural graphite. It is an object of the present invention to provide a pencil lead having a quality (strength, concentration) equal to or higher than that and a manufacturing method thereof. Another object of the present invention is to provide a fine carbon powder suitable as an extender for a pencil lead.

  In order to solve the above-mentioned problems, the present inventor has paid attention to the common points of the composition and manufacturing method of the carbon brush and the pencil lead, and as a result of intensive study, the pencil powder is obtained by finely pulverizing the pencil lead and the carbon brush. By applying it, it was found that a pencil lead having a good balance of pencil core strength, concentration, and writing performance was obtained, and that it was possible to recycle a carbon brush that had been disposed of in the past, leading to the present invention. .

  That is, the present invention provides a pencil lead comprising carbon powder obtained by finely pulverizing a carbon brush.

  In the pencil lead, the carbon brush is preferably a waste carbon brush. The carbon brush is preferably a graphite brush.

  The present invention also relates to a pencil core comprising a body material and a binder as main materials, kneaded and molded at a high temperature, and then a carbon powder obtained by pulverizing a carbon brush as part or all of the body material It is intended to provide a pencil lead characterized by containing.

  Furthermore, the present invention provides a method for producing a pencil lead, characterized in that a material mainly composed of carbon powder obtained by finely pulverizing a carbon brush and a binder is subjected to high-temperature firing after kneading and molding. .

  Furthermore, the present invention provides a carbon powder used as a material for a pencil lead, which is obtained by pulverizing a carbon brush.

  In the carbon powder, the carbon brush is preferably a waste carbon brush. The carbon brush is preferably a graphite brush.

  According to the present invention, a material suitable as an extender for a pencil lead can be obtained by pulverizing a carbon brush such as a graphite brush. Moreover, by using this, a high-strength, high-performance wood spindle pencil lead and a mechanical pencil lead can be obtained. Further, since the waste carbon brush can be recycled, resources can be secured.

  The pencil lead of the present invention contains carbon powder obtained by finely pulverizing a carbon brush. The pencil lead referred to in the present invention includes both a wood pencil lead and a mechanical pencil lead.

  The carbon brush used in the present invention is not particularly limited, and a conventionally known carbon brush can be used regardless of size and type. From the viewpoint of effective use of resources, it is preferable to use a waste carbon brush. Various types of carbon brushes have been put into practical use depending on the type of raw material carbon, the molding method, the type of additives, and the like. For example, a raw material powder such as carbon black powder or graphite powder added with a binder made of a synthetic resin or the like and compressed and solidified, or the above-mentioned solidified material is electrically conductive to give desired conductivity as required. There are those obtained by mixing and sintering a conductive metal powder, or those obtained by sintering a carbon black powder or graphite powder subjected to metal plating such as copper plating, and these can be appropriately selected and used.

  Among these, a graphite brush using graphite powder as a raw material is preferably used from the viewpoint of good crushability, high concentration of the prepared pencil lead, and excellent writing quality. The graphite may be either natural graphite or artificial graphite.

  The carbon brush used in the present invention may be added with carbon fibers, carbon nanotubes, graphite whiskers, other reinforcing materials, and the like as long as the object of the present invention is not impaired.

  When carbon powder is pulverized to obtain carbon powder, collect the carbon brushes used for generators and exciters, remove the attached conductors, roll crusher, hammer mill, pin mill, atomizer, classifier mill, Although it can obtain by grind | pulverizing with grinders, such as a brown mill and a jet mill, it is not limited to this. The pulverized carbon powder preferably has an average particle diameter (D50) in the range of 1 μm to 200 μm. If the average particle size is too large, the bending strength of the pencil lead will not be exhibited, whereas if the average particle size is too small, the writing quality will be poor. In addition, since the bending strength of the pencil lead tends to decrease when the width of the average particle size range is widened, from the viewpoint of preparing a pencil lead having a good balance of strength, concentration and writing performance, the average particle size of the carbon powder is The range of 2 to 50 μm is more preferable, and the range of 5 to 30 μm is more preferable.

  In the pencil lead of the present invention, the carbon powder is used as all or part of the extender. The blending amount of the extender depends on the purpose and hardness, but is 10 to 90% by mass, preferably 20 to 80% by mass of the entire pencil lead. If it exceeds 90% by mass, the blending amount of the binder is excessively reduced, and the balance as a pencil lead is lost. On the other hand, when the amount is less than 10% by mass, the strength of the pencil lead becomes too high, the writing quality becomes poor, and the density also decreases.

  When the carbon powder of the present invention is used in combination with another extender, the other extender is selected from at least one selected from natural graphite, artificial graphite, quiche graphite, carbon black, graphitized carbon black, coke powder, and the like. An average particle diameter of 50 μm or less, preferably 1 μm to 15 μm is used. The combination ratio is not particularly limited, and the ratio can be appropriately determined according to the purpose and application.

  Among other constitutional materials, the combined use of carbon powder and graphite is preferable. In this case, the combination ratio is arbitrary, but it is preferable to use both in a ratio (mass ratio) of graphite / carbon powder = 99/1 to 1/99. By using together, the bending strength of a pencil lead (especially a mechanical pencil lead) is improved as compared with the case where both are used alone. Examples of graphite include natural graphite, artificial graphite, and quiche graphite.

  The binder used in the present invention includes clay minerals such as kaolinite, halloysite, bentonite and montmorillonite, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, vinyl chloride-vinyl acetate copolymer, ethylene-vinyl acetate copolymer. Polymer, Acrylic ester-vinyl acetate copolymer, Acrylic ester-vinyl chloride copolymer, Thermoplastic resin such as acrylic ester polymer, Natural polymer such as carboxymethylcellulose, lignin, tragacanth gum, Polyethylene glycol, etc. It is preferable to use at least one selected from pitches such as synthetic polymers, coal tar pitch, naphtha decomposition pitch, petroleum asphalt, and synthetic resin dry distillation pitch.

  The blending amount of the binder is 10 to 90% by mass, preferably 20 to 80% by mass of the entire pencil lead. When it exceeds 90% by mass, the writing quality becomes poor, and when it is less than 10% by mass, the bending strength of the pencil lead is not sufficient.

  Furthermore, plastics such as water, dioctyl phthalate, dibutyl phthalate, tricresyl phosphate, dioctyl adipate, diallyl isophthalate, propylene carbonate are used for the purpose of improving dispersibility during kneading and / or improving fluidity and moldability during extrusion molding. And at least one selected from stabilizers such as agents, solvents such as alcohols, ketones, esters, stearates, chlorinated products of higher aliphatic hydrocarbons or higher fatty acid esters, if necessary. Also good.

  In the present invention, the above-mentioned extender and binder are used as main materials, and the above-mentioned solvent and / or plasticizer and / or stabilizer (surfactant) are added as necessary, and mixed with a Henschel mixer or a pressure kneader. Dispersed and kneaded with three rolls, etc., extruded with a normal extruder into a line with the desired core thickness, heat treated at a temperature of 80 to 120 ° C., and then combined as necessary The material is pyrolyzed and fired at a high temperature of 900 ° C. or higher, preferably about 900 to 1300 ° C. in a non-oxidizing atmosphere. Furthermore, you may add a coloring material as needed.

  After firing, the pores of the obtained sintered body are impregnated with at least one selected from animal oils such as lard, spindle oil, liquid paraffin, and silicone oil and vegetable oils. In the impregnation operation, the sintered body is put into impregnated oil heated to 100 to 150 ° C., held and removed for 2 to 8 hours, and then the oils and fats adhering to the core surface are removed using a centrifuge or the like. Thus, a pencil lead is obtained.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only the following Examples.

(Production Example 1)
About 30 kg of natural graphite carbon brushes (NCC634 and NCC634R manufactured by National Carbon Company) from which lead wires were removed were coarsely pulverized as a pretreatment with a hammer mill (CONDUX CHM23 type, Φ3 mm screen, throughput of about 138 kg / h). The coarsely pulverized carbon brush was finely pulverized by supplying it to a classifier mill (CUX260, CONDUX) at a speed of about 18 kg / h. The pulverization conditions were a mill rotation speed of 4200 rpm and a classification section rotation speed of 2200 rpm, and collection was performed with a cyclone. The recovered amount of carbon powder was about 20 kg (the rest was collected by the bag filter part), and the average particle size (D50) was 27 μm.

  Next, using the obtained carbon powder (hereinafter referred to as recycled graphite), a wood axis pencil lead (Examples 1-2 and Comparative Examples 1-2) and a mechanical pencil lead (Examples 3-5) Comparative Examples 3 to 5) were produced.

Example 1
German clay 30 parts by weight Recycled graphite 70 parts by weight Carboxymethylcellulose (CMC) l. 6 parts by mass Polyethylene glycol (PEG) 2.5 parts by mass

  The above blended composition was put into a Henschel mixer and stirred at high speed for 15 minutes. Next, 0.3 part by weight of a dispersant, 0.9 part by weight of a wetting agent and 30 parts by weight of water were added and stirred for 10 minutes. Then, after heating and stirring for 10 minutes, the mixture was stirred for 10 minutes while cooling and the granulated product was taken out. Next, roll processing was performed in order to make a granulated material into a film form. The number of times was four. Subsequently, the film was put in a preforming machine and compressed to prepare a preform. The preform was packed in a cylinder of a molding machine and extruded using a 2.16 mm die. The core was dried in a dryer at 110 ° C. for about 6 hours. The dried core was packed in a graphite crucible and fired under conditions of holding at 1200 ° C. for 1 hour in an inert atmosphere. Then, fats and oils (paraffin oil) were impregnated into the fired product to obtain a finished core having a diameter of 2 mm.

(Example 2)
British clay 30 parts by weight Recycled graphite 70 parts by weight Carboxymethylcellulose (CMC) l. 6 parts by mass Polyethylene glycol (PEG) 2.5 parts by mass

  A black pencil lead was obtained in the same manner as in Example 1 except that the blending composition used in Example 1 was changed to the blending composition.

(Comparative Example 1)
German clay 30 parts by weight Natural graphite 70 parts by weight Carboxymethylcellulose (CMC) l. 6 parts by mass Polyethylene glycol (PEG) 2.5 parts by mass

  A black pencil lead was obtained in the same manner as in Example 1 except that the blending composition used in Example 1 was changed to the blending composition.

(Comparative Example 2)
British clay 30 parts by weight Natural graphite 70 parts by weight Carboxymethylcellulose (CMC) l. 6 parts by mass Polyethylene glycol (PEG) 2.5 parts by mass

  A black pencil lead was obtained in the same manner as in Example 1 except that the blending composition used in Example 1 was changed to the blending composition.

  About the black pencil lead of Examples 1-2 and Comparative Examples 1-2, bending strength (MPa) and density | concentration (d) were measured based on JIS-S-6005. The results are shown in Table 1.

  As is clear from Table 1, the pencil lead using the recycled graphite of the present invention has the same concentration but superior bending strength as compared with the conventional pencil lead using natural graphite.

(Example 3)
Polyvinyl chloride resin 50 parts by weight Recycled graphite 50 parts by weight Stearate 5 parts by weight Dioctyl phthalate 20 parts by weight Methyl ethyl ketone 10 parts by weight

  The above blended composition was mixed with a kneader, sufficiently kneaded with three rolls, and then formed into a core with an extruder. This was treated at 110 ° C. for 24 hours and 200 ° C. for 12 hours, and then fired at 1200 ° C. for 1 hour in an inert atmosphere. The pores of the fired core were impregnated with fats and oils (silicone oil) to obtain a finished core having a diameter of 0.5 mm.

(Example 4)
Polyvinyl acetate resin 50 parts by mass Recycled graphite 50 parts by mass Stearate 3 parts by mass Chlorinated paraffin 18 parts by mass Methyl ethyl ketone 10 parts by mass

  A mechanical pencil lead was obtained in the same manner as in Example 3 except that the blending composition used in Example 3 was changed to the blending composition.

(Example 5)
Polyvinyl chloride-polyvinyl acetate copolymer 50 parts by mass Recycled graphite 50 parts by mass Stearate 3 parts by mass Chlorinated paraffin 5 parts by mass Methyl ethyl ketone 10 parts by mass

  A mechanical pencil lead was obtained in the same manner as in Example 3 except that the blending composition used in Example 3 was changed to the blending composition.

(Comparative Example 3)
Polyvinyl chloride resin 50 parts by mass Natural graphite 50 parts by mass Stearate 3 parts by mass Dioctyl phthalate 15 parts by mass Methyl ethyl ketone 10 parts by mass

  A mechanical pencil lead was obtained in the same manner as in Example 3 except that the blending composition used in Example 3 was changed to the blending composition.

(Comparative Example 4)
Polyvinyl acetate resin 50 parts by weight Natural graphite 50 parts by weight Stearate 3 parts by weight Chlorinated paraffin 18 parts by weight Methyl ethyl ketone 10 parts by weight

  A mechanical pencil lead was obtained in the same manner as in Example 3 except that the blending composition used in Example 3 was changed to the blending composition.

(Comparative Example 5)
Polyvinyl chloride-polyvinyl acetate copolymer 50 parts by mass Natural graphite 50 parts by mass Stearate 3 parts by mass Chlorinated paraffin 5 parts by mass Methyl ethyl ketone 10 parts by mass

  A mechanical pencil lead was obtained in the same manner as in Example 3 except that the blending composition used in Example 3 was changed to the blending composition.

  For the mechanical pencil cores of Examples 3 to 5 and Comparative Examples 3 to 5, bending strength (MPa) and concentration (d) were measured in accordance with JIS-S-6005. The results are shown in Table 2.

  As is apparent from Table 2, the mechanical pencil lead using the recycled graphite of the present invention is superior in concentration and bending strength compared to the conventional mechanical pencil lead using natural graphite.

(Examples 6 to 14)
A mechanical pencil lead was obtained in the same manner as in Example 3 except that the compounding composition used in Example 3 was changed to the following compounding composition. As fats and oils to be impregnated in the pores of the fired core, Examples 6, 9, and 12 used paraffin oil, and Examples 7, 8, 10, 11, 13, and 14 used silicone oil.

(Example 6)
Polyvinyl chloride resin 50 parts by weight Recycled graphite 25 parts by weight Natural graphite 25 parts by weight Stearate 5 parts by weight Dioctyl phthalate 20 parts by weight Methyl ethyl ketone 10 parts by weight

(Example 7)
Polyvinyl acetate resin 50 parts by weight Recycled graphite 25 parts by weight Natural graphite 25 parts by weight Stearate 3 parts by weight Chlorinated paraffin 18 parts by weight Methyl ethyl ketone 10 parts by weight

(Example 8)
Polyvinyl chloride-polyvinyl acetate copolymer 50 parts by weight Recycled graphite 25 parts by weight Natural graphite 25 parts by weight Stearate 3 parts by weight Chlorinated paraffin 5 parts by weight Methyl ethyl ketone 10 parts by weight

Example 9
Polyvinyl chloride resin 50 parts by weight Recycled graphite 25 parts by weight Artificial graphite 25 parts by weight Stearate 5 parts by weight Dioctyl phthalate 20 parts by weight Methyl ethyl ketone 10 parts by weight

(Example 10)
Polyvinyl acetate resin 50 parts by weight Recycled graphite 25 parts by weight Artificial graphite 25 parts by weight Stearate 3 parts by weight Chlorinated paraffin 18 parts by weight Methyl ethyl ketone 10 parts by weight

Example 11
Polyvinyl chloride-polyvinyl acetate copolymer 50 parts by weight Recycled graphite 25 parts by weight Artificial graphite 25 parts by weight Stearate 3 parts by weight Chlorinated paraffin 5 parts by weight Methyl ethyl ketone 10 parts by weight

Example 12
Polyvinyl chloride resin 50 parts by weight Recycled graphite 30 parts by weight Artificial graphite 10 parts by weight Natural graphite 10 parts by weight Stearate 5 parts by weight Dioctyl phthalate 20 parts by weight Methyl ethyl ketone 10 parts by weight

(Example 13)
Polyvinyl acetate resin 50 parts by weight Recycled graphite 30 parts by weight Artificial graphite 10 parts by weight Natural graphite 10 parts by weight Stearate 3 parts by weight Chlorinated paraffin 18 parts by weight Methyl ethyl ketone 10 parts by weight

(Example 14)
Polyvinyl chloride-polyvinyl acetate copolymer 50 parts by weight Recycled graphite 30 parts by weight Artificial graphite 10 parts by weight Natural graphite 10 parts by weight Stearate 3 parts by weight Chlorinated paraffin 5 parts by weight Methyl ethyl ketone 10 parts by weight

  For the mechanical pencil cores of Examples 6 to 14, the bending strength (MPa) and the concentration (d) were measured according to JIS-S-6005. The results are shown in Table 3.

  As is apparent from Table 3, a high strength and high concentration mechanical pencil core was obtained by using graphite brush recycled graphite, which is recycled graphite, and natural graphite or artificial graphite.

Claims (9)

A pencil lead comprising carbon powder obtained by finely pulverizing a carbon brush. The pencil lead according to claim 1, wherein the carbon brush is a waste carbon brush. The pencil lead according to claim 1 or 2, wherein the carbon brush is a graphite brush. A pencil core made of an extender and a binder as main ingredients, kneaded and molded at a high temperature, and contains carbon powder obtained by finely pulverizing a carbon brush as part or all of the extender And pencil lead. The pencil lead according to claim 4, wherein the extender contains carbon powder obtained by finely pulverizing a carbon brush and graphite in a ratio of 99/1 to 1/99. A method for producing a pencil lead, characterized in that a material mainly composed of carbon powder obtained by finely pulverizing a carbon brush and a binder is baked at high temperature after kneading and molding. A carbon powder used as a material for building up a pencil lead, which is obtained by finely pulverizing a carbon brush. The carbon powder according to claim 7, wherein the carbon brush is a waste carbon brush. The carbon powder according to claim 7 or 8, wherein the carbon brush is a graphite brush.