JP3009004B2 - Pencil lead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a graphite as a main component,
The present invention relates to a pencil lead made of carbon obtained by firing a binding material, which has high durability against a chuck and is particularly effective for a pencil written on a severe condition such as a plotter.

[0002]

2. Description of the Related Art A fired pencil lead having a skeleton obtained by performing a high-temperature heat treatment is obtained by combining graphite and a synthetic resin with another skeleton such as an oxide using graphite and clay. It is roughly divided into those which are used as materials and are made into a fired core by carbonization.

[0003] A pencil lead made of graphite, clay, or the like, could not produce a lead that required high strength like a pencil lead. A core having a fired core by carbonization is superior in strength and concentration as compared with a pencil core made of graphite and clay, and is generally used as a small diameter core for a mechanical pencil or the like.

[0004] The carbonized and fired pencil lead is generally used as a binder such as asphalt, coal tar pitch, polyvinyl chloride resin, polyvinyl alcohol, and furan resin as a filler material and a plastic material used as necessary. The mixture is extruded using a kneader or the like, and then subjected to high-temperature heat treatment.Since the fired core has pores, if necessary, silicone oil, spindle It is obtained by impregnating an oily substance such as oil.

[0005]

When writing with a knocking mechanical pencil, especially a plotter pencil, there is a problem in that the core is broken by a screw cutting chuck or the paper surface is stained by core powder. Various studies have been made on this problem, such as improving the strength and the like by using a binder and a manufacturing method, and trying to solve the problem by using an impregnated oily substance. However, none of these studies is a drastic solution.

[0006]

In view of the above problems, the present inventors have conducted a thorough analysis on the pores of a pencil lead.
That is, the present inventors have found that three conditions of the pore volume, the pore size, and the pore distribution are intensively studied, and a pencil lead having excellent performance as an overall quality can be obtained by controlling the conditions. That is, various studies have been made on the porosity and the oily substance, but the pore diameter has not been studied much. This time, the problem was solved by satisfying three conditions including the pore diameter.

[0007] The pencil lead of the present invention is a pencil lead mainly composed of carbon obtained by firing graphite and a binder, and has a porosity of 10 to 40% and a pore diameter of 0.003. ~ 0.
The gist of the present invention is a pencil lead having a pore volume occupying 80% or more in a range of 2 μm and impregnated with an oily substance.

As a result of intensive studies on the pores, the present inventors have found that the pore diameter is preferably in the range of 0.003 to 0.2 μm. When the thickness is 0.003 μm or less, it is difficult to impregnate the oily substance, and it is difficult for the core to collapse during writing, and it is difficult to obtain a practical concentration. On the other hand, if the thickness is 0.2 μm or more, it is difficult to obtain a sufficient bending strength, and the amount of core powder generated during writing increases.
However, as described below, the pore volume ratio is 0.00
From the viewpoint that the pencil lead intended for the present invention can be obtained if 80% or more in the range of 3 to 0.2 μm is used, 20% or less have pore diameters of 0.003 μm or less and / or 0.2 μm or more. In the following case, a good pencil lead can be obtained without impairing the object of the present invention.

Furthermore, the pencil lead intended for the present invention ideally has 100% of pores in the above range, but in reality, 100% is impossible due to variations and the like. Therefore, as a result of intensive study, it was found that 8
It became clear that if it is 0% or more, the pencil lead aimed at by the present invention can be achieved. If it is less than 80%, the strength of the pencil lead is likely to be deteriorated, and the core powder is more likely to come out.
A great variation occurs in writing taste and density, and it is difficult to obtain a pencil lead intended for the present invention.

In addition, the porosity of the pencil lead needs to be 10 to 40% within the range of the pore diameter and the pore volume ratio described above. In other words, a core having a porosity of more than 40% has a low bending strength and is likely to be broken at the chuck, and at the same time, when writing on a paper surface, the contact surface with the paper surface is liable to collapse. The large amount of blemishes makes the handwriting unclear and stains the paper. Further, in the case of a core having a porosity of 10% or less, the amount of impregnated oil is small, and the core in contact with the paper hardly collapses, so that the writing quality is poor and a practical concentration cannot be obtained. However, even if the porosity is in the range of 10 to 40%, if the pore diameter and the pore volume ratio are not appropriate, any of the above problems occur, and it is difficult to obtain a product having sufficient overall quality.

The pencil lead of the present invention is made based on a general manufacturing method in which an organic binder and graphite are kneaded, extruded, fired, and oil-immersed. It is difficult to control the amount of pores and the diameter of pores, and they vary subtly depending on kneading conditions, extrusion conditions, firing conditions, and raw materials.

In the present invention, by changing many of these conditions, samples having various pore volumes and pore distributions were prepared, and the relationship between the samples and the characteristics was intensively studied. The control of the amount of pores and the pore diameter is based on kneading conditions, ie, kneading temperature, kneading time, kneading atmosphere, kneading pressure, extrusion conditions, ie, extrusion temperature, extrusion speed, and high-temperature heat treatment conditions, ie, maximum temperature, and heating rate. , Heating pattern,
It can be obtained by changing and combining atmospheres. Therefore, the pencil lead may be formed by a method well known in the art, that is, by kneading a material selected and then performing molding such as extrusion.

[0013]

EXAMPLES The sample numbers of the pencil leads obtained as described above were designated as A to L, and Table 1 shows the physical properties and performance of the pores.

[0014]

[Table 1]

The method for measuring each physical property in the present invention will be described below. 1. Porosity The porosity is a percentage in which a liquid having good permeability (for example, benzyl alcohol) is absorbed into the pores of the core, and the volume of the absorbed liquid is divided by the bulk volume of the core. Porosity (apparent porosity) = (total volume of liquid absorbed in wick) / (bulk volume of wick) × 100 = (W3-W1) /
(W3-W2) × 100 where W1 is the dry weight of the wick before absorbing the liquid. W2
Is the weight in the liquid of the wick that has absorbed the liquid in the pores. W3 is the weight of the wick after absorbing the liquid into the pores of the wick. 2. Pore volume ratio The pore diameter and the pore volume ratio were measured using a mercury intrusion type autoscan porosimeter (pore distribution measuring device AUTOSCAN-60 / QUANTACHROME). 3. Bending strength test and concentration test The method described in JIS-S-6005-1989 was used. 4. Written test Handwriting and an automatic drafting machine (FP-
7000), Kimoto tracing paper (KG
T-55), a vertical stroke of 10 m was linearly written with a load of 500 g in a straight line, and the thread breakage of the core by the screw chuck, the appearance of the core powder, and the stain on the paper surface were observed.

[0016]

As can be seen from Table 1, the sample numbers C, E, F and I in the category of the present invention are the most excellent in the overall evaluation. The pencil lead of the present invention is When used for pencils for plotters, it is difficult for the thread to be broken by the threading chuck or stains on the paper surface due to the core powder. It has an excellent feature that the concentration is obtained and the variation is small.

Claims (1)

(57) [Claims] 1. A pencil lead comprising graphite as a main component and carbon obtained by firing a binder, wherein the pencil lead has a porosity of 10 to 40% and a pore diameter of 0.003 to 0.2 μm.
m. A pencil lead characterized by having a pore volume ratio of 80% or more.