JP2012116946A - Fired pencil lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fired pencil lead with smaller dispersion of bending strength, thereby solving the following problems: since a plasticizer, which is conventionally used so far in the fired pencil lead, makes the structure of the fired core uneven due to problems of its compatibility and migration with a synthetic resin, which results in the dispersion of bending strength.SOLUTION: This fired pencil lead is obtained by: using a compounding material of at least graphite and a copolymer containing ethylene and vinyl chloride in the structure; kneading the material; extrusion-molding the material into a fine line; and heat-treating the line up to the firing temperature.

Description

  The present invention relates to a fired pencil lead obtained by blending at least graphite and a synthetic resin, kneading and extruding into a thin wire, and then heat-treating to a firing temperature.

  General fired pencil lead is used in combination with graphite and synthetic resin, plasticizer such as phthalate ester, solvent such as methyl ethyl ketone, stearate, stearic acid, carbon black, amorphous silica, etc. After being mixed and kneaded and extruded into a thin wire, heat treatment is performed up to the firing temperature, and the pores of the obtained fired core are impregnated with oil as necessary to complete.

  By selecting various core diameters at the time of extrusion molding, a core body having a target core diameter can be obtained, and by changing the blending and firing temperature, a core body having a target writing concentration can be obtained. While satisfying the target writing density (hardness), it is required to have both strength that is not broken by the force applied during writing and the impact when dropped, that is, the bending strength.

As described above, the main material of the fired pencil core is graphite and synthetic resin. However, the synthetic resin becomes a carbide by heat treatment, and serves as a binder for fixing graphite as a core. Among synthetic resins, chlorinated resins such as vinyl chloride resin and vinyl chloride-vinyl acetate copolymer are easy to use such as moldability and cost, and also bind graphite when carbonized by firing. Therefore, it is also preferred because it has a good yield of carbides, and is used as a material for a fired pencil lead (Patent Document 1).
However, when the synthetic resin as the binder is a vinyl chloride resin or a vinyl chloride-vinyl acetate copolymer, these resins are poor in plasticity alone and cannot be processed as a pencil core, such as phthalate esters. The plasticizer is used to improve the processability such as molding (Patent Document 2). The plasticizer also has a role of forming pores in which the oily substance enters the fired pencil core by being decomposed during the heat treatment. In general, if there are few pores in the core, the amount of oil impregnated as a lubricant is reduced, it becomes difficult to wear during writing, and the bending strength is high, but it tends to be a fired pencil core with a low writing concentration, and there are many pores If this is the case, the amount of oil impregnated as a lubricant will increase and the amount of wear during writing will increase, so the bending strength will be small, but it will tend to be a fired pencil lead with a high writing concentration.
In addition, as a binder that is easy to mold without using a plasticizer, a vinyl chloride copolymer, an acrylic ester-vinyl chloride copolymer, which is a combination of a vinyl chloride resin and a softer resin than the vinyl chloride resin. Polymerization is also used as a material for a fired pencil lead (Patent Document 3).

JP 2008-189873 A Japanese Patent Laid-Open No. 7-18213 Japanese Patent Laid-Open No. 2005-60666

As disclosed in Patent Documents 1 and 2, a fired pencil core containing a plasticizer moves between molecular chains of the resin even after being kneaded and molded with graphite or resin in the core composition before firing. , Because plasticizers gather, ooze out on the core surface, or move between graphite particles, the plasticizer distribution in the core becomes non-uniform, and the plasticizer is thermally decomposed The pores of the core body have a large distribution and size variation. As a result, the structure of the fired pencil core becomes non-uniform, which may cause a variation in bending strength.
In the case of using a soft resin as disclosed in Patent Document 3, molding is possible without using a plasticizer, but there are few pores formed in the core, and a pencil with a desired writing concentration. Problems such as inability to create a lead.

  The present invention provides a calcined pencil lead obtained by subjecting at least graphite and a copolymer containing an ethylene part and a vinyl chloride part in the structure, kneading and extruding into a thin wire, and then heat-treating to a calcining temperature. The gist.

  By using a copolymer containing ethylene and vinyl chloride in the structure as a compounding material, vaporization of the ethylene part and carbonization of the vinyl chloride part proceed almost simultaneously due to the copolymer during firing of the compounding composition. Vaporized material is released before carbonization of vinyl chloride is completed and a hard skeleton is formed, and pores are reduced or biased by subsequent contraction, or vaporized after a hard skeleton is formed. Since it does not swell and destroy the skeleton or form cracks, it is presumed that uniform pores are formed, and a fired pencil lead with small variation in bending strength is obtained.

Hereinafter, the present invention will be described in detail.
As the copolymer containing ethylene and vinyl chloride in the present invention, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate-vinyl chloride copolymer, ethylene-vinyl chloride-vinylidene chloride, ethylene-vinyl chloride-acrylic Examples include acid esters, ethylene-vinyl acetate-carbon monoxide-vinyl chloride copolymers, and ethylene-acrylic acid ester-carbon monoxide-vinyl chloride copolymers. In addition, the structure is not particularly limited as long as ethylene and vinyl chloride are contained in the structure. Also, the form of copolymerization is not particularly limited by alternating copolymers, random copolymers, block copolymers, graft copolymers, and the like.
Commercially available products include VE-T (produced by Sekisui Chemical Co., Ltd.) as an ethylene-vinyl chloride copolymer, and Sekisui PVC-TG (ethylene-vinyl acetate-vinyl chloride graft) as an ethylene-vinyl acetate-vinyl chloride copolymer. Copolymer resin, manufactured by Sekisui Chemical Co., Ltd.).

  The composition ratio of the ethylene part and the vinyl chloride part of the copolymer containing the ethylene part and the vinyl chloride part used in the present invention affects the hardness of the fired core. That is, the vinyl chloride portion forms a carbide that binds graphite in the fired core, so if the relative amount is large, the amount of carbide increases and the core becomes hard and difficult to wear. If the vinyl chloride portion is small, the fired core becomes soft and wears easily. Since the ethylene part becomes pores after firing, if the relative amount of the ethylene part is large, the core part has a lot of pores and becomes a soft core, and is easily worn. If there are few pores, the core will be hard and difficult to wear. Pencil cores range from soft and dark writing lines such as 4B and 3B to hard and thin writing lines such as 3H and 4H. However, by adjusting the blend ratio, the desired writing density (hardness) ) Can be obtained.

  In addition, the blending amount of the copolymer containing the ethylene portion and the vinyl chloride portion in the structure with respect to the graphite is not particularly limited, and the molding temperature at the time of extrusion molding into a thin line shape when producing a fired pencil core and In view of the above, it may be set as appropriate in consideration of the flexibility of the molded body. If the amount of the copolymer containing an ethylene part and a vinyl chloride part in the structure relative to graphite is too small, the function as a resin that fixes and bonds graphite as a core is weakened and molding cannot be performed, or the amount is too large. If it is too much, it may become a core that is difficult to wear.

As materials used other than the above, conventionally used constituent materials of a fired pencil lead can be used without limitation.
Specifically, examples of graphite include scaly graphite, scaly graphite, soil graphite, and artificial graphite. Boron nitride, talc, mica, flake silica, amorphous silica, carbon black, etc. can be used as inorganic substances other than graphite. In addition to chlorine-containing resins such as vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinylidene chloride resin, synthetic resins include polyvinyl acetate, furan resin, polyvinyl alcohol, polyacrylamide, urea resin, etc. as required. Can be used together. Furthermore, in addition to conventionally known plasticizers such as dioctyl phthalate (DOP) and dibutyl phthalate (DBP), stearic acid, stearates, alcohols, ketones, esters, aromatic hydrocarbons and the like can be used in combination.
Moreover, it can manufacture using a conventionally well-known manufacturing method without limitation.
For example, the compound is uniformly dispersed with a kneader, a Henschel mixer, three rolls, etc., then formed into a thin wire shape, heat treated up to about 300 ° C. in air, and further 800 ° C. to 1300 ° C. in a non-oxidizing atmosphere. A baking treatment is performed to obtain a baking pencil lead. Thereafter, if necessary, it is impregnated with an oil or wax such as silicone oil, liquid paraffin, spindle oil, paraffin wax, microcrystalline wax, polyethylene wax, montan wax, carnauba wax.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to these Examples.
<Example 1>
VE-T (ethylene-vinyl chloride copolymer (vinyl chloride ratio 92%), manufactured by Sekisui Chemical Co., Ltd.) 30 parts by weight Graphite 55 parts by weight stearate (lubricant) 2 parts by weight stearic acid (lubricant) 2 parts by weight Part methyl ethyl ketone (solvent) 30 parts by weight The above materials were dispersed and mixed with a Henschel mixer, kneaded with three rolls, then extruded into a thin wire and heated from room temperature to 300 ° C in air over about 10 hours. And then heat-treating at 300 ° C. for about 1 hour, further subjecting it to firing at a maximum of 1000 ° C. in a sealed container, and after cooling, impregnating with liquid paraffin to obtain a fired pencil having a nominal diameter of 0.7. I got a wick.

<Example 2>
In Example 1, VE-T (ethylene-vinyl chloride copolymer) was changed to Sekisui PVC-TG (ethylene-vinyl acetate-vinyl chloride copolymer (vinyl chloride ratio 60%), manufactured by Sekisui Chemical Co., Ltd.). A pencil lead having a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except for the change.

<Example 3>
In Example 1, VE-T (ethylene-vinyl chloride copolymer) was changed from 30 parts by weight to 15 parts by weight, and Sekisui PVC-TG (ethylene-vinyl acetate-vinyl chloride copolymer), (Sekisui Chemical Co., Ltd.) A pencil lead having a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except that 15 parts by weight of Kogyo Co., Ltd. was added.

<Example 4>
In Example 1, a pencil lead having a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except that the amount of VE-T (ethylene-vinyl chloride copolymer) was changed from 30 parts by weight to 25 parts by weight. .

<Example 5>
In Example 1, a pencil lead with a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except that the amount of VE-T (ethylene-vinyl chloride copolymer) was changed from 30 parts by weight to 35 parts by weight. .

<Example 6>
In Example 1, a pencil lead having a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except that 3 parts by weight of phthalate was added.

<Example 7>
In Example 1, a pencil lead having a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except that 5 parts by weight of phthalate was added.

<Comparative Example 1>
Polyvinyl chloride 30 parts by weight Graphite 55 parts by weight Phthalate ester (plasticizer) 10 parts by weight Stearic acid salt (lubricant) 2 parts by weight Stearic acid (lubricant) 2 parts by weight Methyl ethyl ketone (solvent) 30 parts by weight In the same manner as in Example 1, a pencil lead having a nominal diameter of 0.7 was obtained.

<Comparative example 2>
In Comparative Example 1, a pencil lead having a nominal diameter of 0.7 was obtained in the same manner as Comparative Example 1, except that dipropylene glycol dibenzoate (benzoic acid and glycol ester: plasticizer) was used instead of phthalic acid ester. .

<Comparative Example 3>
In Example 1, a pencil lead having a nominal diameter of 0.7 was obtained in the same manner as in Example 1 except that VE-T (ethylene-vinyl chloride copolymer) was changed to vinyl chloride-acrylic acid ester copolymer. It was.

As described above, the bending strength and the handwriting density were measured according to JIS S 6005 for each of the 100 pencil leads obtained in each of the examples and comparative examples. For the bending strength, a standard deviation σ was also calculated as an evaluation of variation. The results are shown in Table 1.
By using a copolymer containing ethylene and vinyl chloride in the structure as a compounding material, it is possible to reduce variation in the bending strength of the fired pencil lead.

  Since the fired pencil lead of Examples 1 to 7 uses a copolymer containing ethylene and vinyl chloride in the structure as the material, the fired pencil has a uniform fired core structure and small variation in bending strength. A wick was obtained.

  Moreover, since Examples 1-5 were the baking pencil lead which does not use the plasticizer conventionally used at all, the baking pencil lead with smaller bending strength was obtained.

On the other hand, the fired pencil cores of Comparative Examples 1 and 2 do not use a copolymer containing ethylene and vinyl chloride in the structure, and use a plasticizer that has been used conventionally. The variation of is large.
The fired pencil lead of Comparative Example 3 uses a vinyl chloride-acrylic acid ester copolymer that does not contain ethylene in the structure, so the fired pencil lead has little effect of reducing variation in bending strength and has a low writing concentration. It became.

Claims (1)

A fired pencil lead obtained by blending at least graphite and a copolymer containing an ethylene part and a vinyl chloride part in the structure, kneading, extruding into a thin wire, and then heat-treating to a firing temperature.