JPS5840595B2 - Enpitsu Shin no Seizou Hohou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a pencil lead, and more particularly to a method for obtaining a pencil lead having a desired hardness by using a crosslinkable resin as a binder.

Conventionally, pencil leads have been produced using clay as a binder, but these have had the drawbacks of low cohesive strength, low bending strength, and insufficient performance such as abrasion resistance.

Furthermore, since firing is performed at around 1000° C., it is economically disadvantageous in terms of securing firing equipment and heat sources.

Another method that does not use clay is to use a polymeric substance as a binder and fire it (pyrolyze it), but it is difficult to adjust the firing conditions and quality maintenance is difficult, and it is economically disadvantageous in terms of the heat source. Met.

Furthermore, Japanese Patent Publication No. 49-12302 describes a method of molding a core from graphite and a thermoplastic resin, but it is difficult to obtain cores with desired hardnesses using this method, and it is difficult to obtain cores with different hardnesses using this method. Since it is necessary to use a large amount of thermoplastic resin, the disadvantage is that the writing quality becomes poor.

As a result of various studies on methods for solving the above-mentioned problems, the present invention has been made by selecting various resins that cause crosslinking,
The present invention was completed based on the fact that depending on the degree of crosslinking, a pencil lead having a desired hardness can be obtained while maintaining various properties such as breakage strength and abrasion.

The method of the present invention involves mixing a composition in which graphite and carbon black are blended with a polyvinyl chloride resin or a copolymer resin thereof with one or more selected from zinc oxide, antimony oxide, and mercaptoimidacillin. It consists of producing pencils by heating, molding, and crosslinking.

That is, the resin used in the present invention is a polyvinyl chloride resin or a copolymer resin thereof.

As the copolymer resin, resins copolymerized with vinyl acetate, ethylene, propylene, etc. are useful.

It is known that polyvinyl chloride resin is dehydrochlorinated by heating at about 120°C or higher, and it is also known that dehydrochlorination is completely completed at about 300°C.

In this state, it is not strong enough to be used as a pencil lead, and for practical purposes, as stated in the Japanese Patent Publication No. 37-1970, 1000℃ is required.
It is necessary to process and carbonize at a high temperature of about 100 ml.

As a result of diligent efforts, the present inventors added a crosslinking agent at a temperature of up to 200°C to crosslink the resin, aiming to improve the strength, and made it practical.

For example, it is estimated that the following crosslinking reaction occurs, and a very strong reaction product is obtained.

This reactant is a stable substance that does not dissolve in any solvent.

Therefore, pencil leads having various hardnesses can be freely produced depending on the degree of polymerization of the resin used, the copolymerization rate, and the amount of crosslinking agent.

The production of the pencil lead in the present invention involves sufficiently dissolving polyvinyl chloride resin or its copolymer resin in a solvent using a high-speed mixer, and then adding graphite, carbon, a crosslinking agent, if necessary, a physical constitution, a plasticizer, a fat and oxidation binder, etc. etc., are kneaded with three rolls while cooling, most of the solvent is evaporated, and the mixture is formed into a rod shape and heated and extruded.

In this manufacturing method, the content of resin in the core is preferably 20 or less, and if it increases more than this, the writing quality becomes poor.

Examples are shown below.

Example 1 Graphite 40.0 parts by weight Carbon black 5. O〃Magnesium stearate 18.0//Zinc oxide
1.5 PVC-vinyl acetate copolymer resin
12.0//(vinyl #1000AS polymerization degree 3
201 86% PVC, 14% PVC (manufactured by Denki Kagaku Kogyo Co., Ltd.) Methyl ethyl ketone 50. First, add the resin to Ott methyl ethyl ketone and completely dissolve it with a high-speed mixer, then add the other ingredients one after another, knead with three rolls while cooling, evaporate most of the solvent, and form it into a rod shape.
Fill this into an extruder and extrude the core at 180°C.
A continuous core with a diameter of 2X was obtained and cut into regular lengths.

The obtained core has a hardness of HB and a bending strength of 20,00.0
,! i' 7m1 (JIS6005-1971), the coefficient of friction was 0.20, both excellent, and the writing was extremely smooth.

In addition, the resulting core was added to methyl ethyl ketone and a dissolution test was conducted. As a result, it was found that the core was insolubilized, which confirmed that the resin was crosslinked.

In addition, the core made from the formulation excluding zinc oxide from the example,
The results of the dissolution test of methyl ethyl ketone show that it dissolves well.
Moreover, its bending strength was 13,000 g/mA, which was lower than that crosslinked with zinc oxide.

Example 2 Graphite 35.0 parts by weight Carbon black 5. o Magnesium stearate 16. O//antimony oxide
6. o Dioctyl stalate
10.0//vinyl chloride resin
13. O // (SH-250 degree of polymerization 2500, manufactured by Denki Kagaku Kogyo Co., Ltd.) Methyl ethyl ketone 50.0 // The above composition was kneaded in the same manner as in Example 1, most of the solvent was evaporated, and the extruder was filled with 200 The core was extruded at 0.degree. C. to obtain a continuous core with a diameter of 2X, which was cut to length.

The resulting core has a hardness of 2H and a bending strength of 21,500 g.
/ma, the friction coefficient was excellent at 0.19, and the writing was extremely smooth.

Further, as in Example 1, the results of the dissolution test revealed that the resin was insolubilized, which confirmed that it was crosslinked.

In addition, in a formulation that does not cause a crosslinking reaction by excluding antimony oxide from the example, the bending strength is 12,500 g/m4
So it was weak.

Example 3 Graphite carbon black Magnesium stearate 2-mercaptoimidacillin Ethylene-vinyl chloride copolymer resin (Z-550 Degree of polymerization 550 Dioctyl stalate Methyl ethyl ketone Antimony oxide 50.0 parts by weight 5, Q tt 18.0 tt 1.5 〃 12.0// Manufactured by Nichiryo Kagaku Co., Ltd.) 8.0 〃 50.0 〃 0.5〃 The above composition was kneaded in the same manner as in Example 1, most of the solvent was evaporated, and the mixture was filled into an extruder. The core was extruded at 200° C. to form a bottom shape to obtain two continuous cores, which were cut into regular lengths.

The obtained core has a hardness of 2B and a bending strength of 20,000 jj
/mi, the friction coefficient was 0.21, which was excellent, and the writing was extremely smooth.

Further, as in Example 1, the results of the dissolution test revealed that the resin was insolubilized, which confirmed that it was crosslinked.

In addition, in the formulation in which 2-mercaptoimidapurine and antimony oxide were removed from the examples and did not cause a crosslinking reaction, the bending strength was weak at 10.00 (1/ma).

As is clear from the above examples, the present invention makes it possible to obtain cores with different hardness by causing a dechlorination reaction of chlorine in the polymer chain by heating at a low temperature, and by adding a crosslinking agent to crosslink the resin. In addition, a product with sufficiently satisfactory breaking strength and abrasion resistance was obtained.

Moreover, it had good penability and was excellent in practical use.

Furthermore, the present invention enables continuous production and can greatly contribute to improving productivity and reducing costs.

Claims (1)

[Claims] 1. Graphite and carbon black, and a composition in which polyvinyl chloride resin or its copolymer resin is blended with one or more selected from zinc oxide, antimony oxide, and mercaptoimidacillin are kneaded and heated. A method for producing a pencil lead characterized by crosslinking.