JPS585950B2 - Enpitsu Shinno Seizouhou - Google Patents

Description

[Detailed description of the invention] The present invention relates to a novel method for producing a pencil lead.

Traditionally, the method of producing pencil lead is at 1000℃.
There is a known method for producing pencil leads that involves heat treatment at a nearby high temperature, but this high temperature heat treatment method has the drawbacks of complicating the process and making it difficult to achieve uniform quality and continuous production.

Recently, a method that allows continuous production has been researched and developed.The method uses a synthetic resin as a binder, kneads it at a temperature slightly exceeding the melting temperature of the resin, and after evaporating most of the volatile matter, it is made into a screw type. It is produced using an extruder.

For example, a method of kneading pigments with polyethylene, polybutene, etc. and extrusion molding (Japanese Patent Publication No. 46-36684), a method of kneading pigments with metal soap, polyvinyl alcohol, CMC, and extrusion molding (Japanese Patent Publication No. 47-48564),
A method of graft polymerizing vinyl chloride to vinyl acetate copolymer, kneading it with pigment, and extrusion molding (Japanese Patent Publication No. 18900/1989
), a method of mixing pigments into polystyrene, copolymers of acrylic acid and styrene, polycarbonate, polymethyl methacrylate, etc. (Japanese Patent Publication No. 49-12302), thermoplastic resins such as polyethylene, vinyl chloride, furan, epoxy resins, etc. Although there are methods such as kneading curable resin and pigment (Japanese Patent Publication No. 49-12300), the breakage strength of the pencil lead is still low in both methods, and in order to increase the breakage strength, it is necessary to reduce the amount of resin used as a binder. If the number of pens increases, the density of the handwriting becomes thinner.

As a result of various studies to solve these drawbacks, the present inventor has developed a reaction product obtained by reacting a compound represented by the following general formula (1) with an organic polyisocyanate in an amount equal to or less than the reaction equivalent. Pigments and fatty acid metal salts are added to the mixture, and if necessary, substances such as clays, waxes, plasticizers, and solvents are added and kneaded, and this is extruded while heating at 80 to 300°C, resulting in excellent breakage strength and The present invention was completed by discovering that a pencil lead with dark handwriting can be obtained.

Next, a specific manufacturing method of the present invention will be described in detail. Compounds represented by the general formula (1) include polyethylene terephthalate, polypropylene terephthalate, polyisopropylene terephthalate, polybutylene terephthalate, and the like.

Furthermore, if n is less than 500, that is, the average degree of polymerization is less than 500, sufficient hardness and strength of the pencil lead cannot be obtained, so n is set to be more than 500.

Organic polyisocyanates that can react with these compounds having hydroxyl groups include tetramethylene diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, 3,3 bitrylene 4,4 diincyanate, and 3,3 dimethyl diphenyl. Methane 4,4 diisocyanate, 1 mediphenylmethane 2.4,4,4 triisocyanate, triphenylmethane 4,4,4 triisocyanate, etc., and the reaction conditions are based on the reaction equivalent of -〇H group. On the other hand, it is desirable to use 0.5 to 1.3 reaction equivalents, preferably 0.8 to 1.1 reaction equivalents of organic incyanate.

In addition, the reaction temperature is 20 to 100°C, preferably 40 to 80°C.
It is best to react for 3 hours or more at

At this time, if necessary, the reaction may be carried out in an organic solvent such as xylol, toluene, benzol, ethyl acetate, methyl acetate, or butyl acetate.

The reaction products thus obtained include inorganic and organic substances such as carbon black, oil smoke, graphite, iron black, bad lead powder, silicon carbide, yellow lead, Hansa yellow, toluidine red, bat orange, Victoria blue, and phthalocyanine blue. pigment, and as a lubricant, zinc stearate, magnesium stearate, aluminum stearate, zinc oleate, magnesium oleate, aluminum oleate, zinc palmitate, magnesium palmitate, aluminum palmitate, calcium stearate, calcium oleate, A fatty acid metal salt such as calcium palmitate is added and kneaded.

At this time, if necessary, substances such as clay, calcium carbonate, waxes such as paraffin and wood wax, or organic solvents such as methyl ethyl ketone, ethyl acetate, and xylol, or dioctyl phthalate, dibutyl phthalate, and glyceryl adipate may be used. If a plasticizer is added, kneading becomes easier.

To describe the kneading conditions, when these pigments and organic metal salts, as well as substances such as clay, calcium carbonate, and waxes are added, the above-mentioned general formula ( 5 to 140 parts by weight, preferably 10 to 100 parts by weight of a reaction product obtained by reacting the compound shown in 1) with an organic polyisocyanate are added and thoroughly kneaded.

When the thus obtained kneaded product is extruded using an extrusion molding machine at an extrusion temperature of 80 to 300°C, preferably 120 to 250°C, a pencil lead having excellent breaking strength and writing density is obtained.

The extrusion molding machine used in the present invention can be either a screw type or a piston type.

Furthermore, the pencil lead of the present invention can also be used as a pencil lead for synthetic resin-shafted pencils manufactured in a continuous manner.

Example 1 10 parts by weight of polyethylene tere-7talate 10 parts by weight of xylene were added to a reaction vessel, the temperature was raised to 50°C to form a solution, and 2 parts by weight of tetramethylene diisocyanate were added.
After reacting at a temperature of 50° C. for 3 hours, the solvent was separated and removed.

Next, 5 parts by weight of carbon black and 20 parts by weight of graphite were added to 30 parts by weight.
After kneading the mixture for a minute, 10 parts by weight of aluminum stearate was added and kneaded for 1 hour.

The product thus obtained was processed by an extruder for 1
It was extruded to a thickness of 2 m in diameter while heating at 80°C±10°C.

The core thus obtained has a black color and a breakage strength of 3
The reflectance at 2500g/mm2 was 56%.

(However, the smaller the reflectance value, the darker the handwriting.

) Example 2 Polypropylene terephthalate 10 parts by weight Methyl ethyl ketone 5 parts by weight Xylol
Add 5 parts by weight to the reaction vessel, raise the temperature to 60°C to make a sufficient solution, then add 2 parts by weight of tolylene diisocyanate,
After reacting at a temperature of 40° C. for 3 hours, the solvent was separated and removed.

Next, this reaction product was transferred to three rolls, and 2 parts by weight of dioctyl phthalate (plasticizer)
After adding 15 parts by weight of Hansa Yellow (pigment) and kneading the mixture for 30 minutes, adding 10 parts by weight of calcium stearate,
Kneaded for hours.

Thereafter, it was extruded using an extruder at a temperature of 150° C.±10° C. to a thickness of one hole in diameter.

The core obtained in this way has a breakage strength of It was a yellow core with a value of 31000 g/mm2.

The reflectance was 75%.

Claims (1)

[Claims] 1. A method for producing a pencil lead which is made of at least a binder and a coloring agent as main materials and is formed by cross-wiring and extrusion molding, in which the binder is a reaction between a compound represented by the following general formula (1) and an organic polyisocyanate. A method for producing a pencil lead characterized by using the product.