JPH05179189A - Pencil lead - Google Patents

Abstract

PURPOSE:To provide a baked pencil lead highly durable to chuck and is suitable in lead collapse on the area of contact with a paper surface. CONSTITUTION:The title lead comprises graphite and carbon obtained by baking a binder. The porosity is 10-40%, and the volume fraction of pores of a pore diameter of 0.003-0.2mum is at least 80%.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art A baking type pencil lead having a skeleton obtained by subjecting it to high temperature heat treatment combines graphite and synthetic resin with other skeletons such as oxides using graphite and clay. It is used as a material and is roughly classified into one that is used as a fired core body by carbonization.

With a pencil lead made of graphite, clay, etc., it was not possible to make a lead which requires high strength like a lead for a mechanical pencil. The one having a fired core by carbonization is more excellent in strength and concentration than a pencil core made of graphite and clay, and is generally used as a thin core for mechanical pencils and the like.

The carbonized and baked pencil lead is generally used as a binder such as asphalt, coal tar pitch, polyvinyl chloride resin, polyvinyl alcohol or furan resin, and an extender typified by graphite and a plastic used as required. A mixture of agents, solvents, stabilizers, etc., is uniformly dispersed in a kneader, etc., and then extruded, then subjected to high temperature heat treatment, and the firing core has pores, so if necessary, silicone oil, spindle It is obtained by impregnating an oily substance such as oil.

[0005]

When writing normally with a knock type mechanical pencil, especially a pencil for a plotter, there is a problem that core breakage occurs in a thread cutting chuck and stains on the paper surface due to core powder. Various studies have been made on this problem, such as improving the strength and the like by using a binder or a manufacturing method, and trying to solve the problem by using an impregnated oily substance, but none of them is a drastic solution.

[0006]

In view of the above problems, the present inventor has conducted a thorough analysis of the pores of a pencil lead.
That is, it was found that a pencil lead excellent in overall quality can be obtained by carefully studying the three conditions of the amount of pores, the diameter of pores, and the distribution of pores and controlling the conditions. That is, although various studies have been made on the porosity and the oily substance, the pore diameter has not been studied much. This time, the problem could be solved by satisfying the three conditions including the pore diameter.

The pencil lead of the present invention is a pencil lead whose main component is carbon obtained by firing graphite and a binder. The pencil lead has a porosity of 10 to 40% and a pore diameter of 0.003. ~ 0.
In the range of 2 μm, the gist is a pencil lead having a volume ratio of pores of 80% or more and impregnated with an oily substance.

As a result of diligent studies on the pores, the present inventor has found that the range of the pore diameter is preferably 0.003 to 0.2 μm. When it is 0.003 μm or less, impregnation with an oily substance becomes difficult, and core collapse during writing hardly occurs, making it difficult to obtain a practical concentration. On the other hand, when it is 0.2 μm or more, it is difficult to obtain sufficient bending strength, and the amount of core powder generated during writing becomes large.
However, the pore volume ratio is 0.00
If 80% or more of those in the range of 3 to 0.2 μm can obtain the pencil lead targeted by the present invention, 20% of those having a pore diameter of 0.003 μm or less and / or 0.2 μm or more are obtained. When the amount is below, a good pencil lead can be obtained without impairing the object of the present invention.

Furthermore, it is ideal that the pencil lead, which is the object of the present invention, has 100% pores within the above range, but in reality it is impossible to achieve 100% due to variations. Then, as a result of diligent examination, 8 within the above range
It has been clarified that if the content is 0% or more, the pencil lead targeted by the present invention can be achieved. If it is 80% or less, the strength of the pencil lead is liable to be deteriorated, and the core powder is likely to come out at the same time.
The writing quality and the density vary greatly, and it is difficult to obtain the pencil lead targeted by the present invention.

Further, it is necessary that the pencil lead has a porosity of 10 to 40% within the above range of the pore diameter and the pore volume ratio. In other words, a core having a porosity of more than 40% has a low bending strength, and the core is easily broken on the chuck. At the same time, when writing on the paper, the core collapses on the contact surface with the paper, and the core powder The large number of marks makes the handwriting unclear and stains the paper surface. Further, in the case of a core having a porosity of 10% or less, the amount of oil impregnated is small, and further, the core collapse of the contact surface with the paper surface is unlikely to occur, resulting in poor writing quality 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, both of the above problems occur, and it is difficult to obtain a product with 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 immersed in oil. It is difficult to control the amount of pores and the diameter of pores, and they slightly change depending on kneading conditions, extrusion conditions, firing conditions, and raw materials.

In the present invention, various conditions were changed to prepare samples having various pore amounts and pore distributions, and the relations with the characteristics were earnestly studied. The amount of pores and pore diameter can be controlled by kneading conditions, that is, kneading temperature, kneading time, kneading atmosphere, kneading pressure, extrusion conditions, that is, extrusion temperature, extrusion speed, and high-temperature heat treatment conditions, that is, maximum temperature and heating rate. , Heating pattern,
It is obtained by changing and combining the atmosphere. Therefore, the molding of the pencil lead may be performed by a method well known in the art, that is, by kneading selected materials and molding such as extrusion.

[0013]

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

[0014]

[Table 1]

The method of measuring each physical property in the present invention will be described below. 1. Porosity Porosity is expressed as a percentage by allowing a liquid having good permeability (for example, benzyl alcohol) to be absorbed by the pores of the core and dividing the volume of the absorbed liquid by the bulk volume of the core. Porosity (apparent porosity) = (total volume of liquid absorbed in core) / (bulk volume of core) × 100 = (W3-W1) /
(W3−W2) × 100 where W1 is the dry weight of the core before absorbing the liquid. W2
Is the weight of the wick that has absorbed the liquid in its pores. W3 is the weight of the core after the liquid is absorbed in the pores of the core. 2. Pore volume ratio A pore size and its pore volume ratio were measured using a mercury injection type auto scan 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. Handwriting test Handwriting and automatic drafting machine (FP- by Graphtec Co., Ltd.)
7000), tracing paper made by Kimoto (KG
T-55) was used to write straight in a straight line for 10 m under a load of 500 g, and the core breakage by the screw cutting chuck, the appearance of core powder, and the stain on the paper surface were observed.

[0016]

From the above, it can be seen from Table 1 that the sample numbers C, E, F and I, which are within the scope of the present invention, are the most comprehensively evaluated. The pencil lead of the present invention is particularly suitable for pencil leads. When used in a plotter pencil, etc., core breakage on the screw cutting chuck and stains on the paper surface due to core powder are unlikely to occur, and core collapse on the contact surface with the paper surface is suitable, so the writing feeling is good and practical It has an excellent feature that the concentration can be obtained and the variation is small at the same time.

Claims (1)

[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.
A pencil lead having a pore volume ratio of m of 80% or more.