JPH02284972A - Pencil lead - Google Patents

Abstract

PURPOSE:To obtain a pencil lead, composed of a calcined lead body containing graphite and a calcined covering containing boron nitride and capable of improving susceptibility of scripts to fouling based on the use of the graphite without deteriorating advantages of strength and writing performance. CONSTITUTION:The objective pencil lead composed of a calcined lead body containing graphite and a calcined covering, containing boron nitride and arranged on the outer periphery of the above-mentioned lead body.

Description

[Detailed description of the invention] (Industrial application field) Regarding sintered type pencil lead.

(Prior art and its problems) Pencil leads are roughly divided into two types depending on how they are obtained. A sintered type in which a sintered (fired) skeleton of the binder is formed through high-temperature heat treatment, and a non-sintered type in which the heat treatment is at most a low temperature for purposes such as drying. It is. Here, the sintered type generally has better strength than the non-sintered type.

In order to obtain this sintered type pencil lead, resins such as polyvinyl chloride resin, polyvinyl alcohol, and furan resin, and clay minerals such as bentonite and sericron are usually used as binding materials, and the A homogeneous dispersion is formed using a kneader, etc. together with plasticizers, solvents, stabilizers, excipients, etc. used in the process, and then formed into an appropriate diameter.Then, the binder is sintered (fired) to form a skeleton. It is obtained by subjecting it to high-temperature heat treatment and, if necessary, impregnating it with an oily substance such as silicone oil or spindle oil.

Some of them are impregnated with ink, and some are further treated to form a metallic color film.

Graphite is very commonly used in this sintered type of pencil lead. Although there are other substitutes for graphite, such as boron nitride, and there are some exceptions, graphite is currently the most preferred material when considering strength and writing quality.

However, sintered pencil lead inherently leaves handwriting easily smudged, and the use of graphite has the disadvantage that handwriting becomes even more smudged. It is thought that this is because when writing, the graphite is not sufficiently peeled off between the eyebrows, and this delamination progresses due to the abrasion of the handwriting.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a sintered pencil lead that is less likely to smudge handwriting due to the use of graphite.

(Means for solving the problem) By using materials other than graphite together with graphite,
In addition, depending on how they are used in combination, the disadvantages of graphite can be improved more than the advantages of graphite are diminished.The present invention was made based on this knowledge. Place around the outer periphery. That is, the present invention includes a sintered core containing graphite and an outer periphery of the core. The gist is a pencil lead consisting of a sintered outer shell containing boron nitride.

The details will be explained below. Note that, hereinafter, the sintered core and the sintered outer skin will be simply referred to as the "core" and the "outer skin", respectively.

As mentioned above, boron nitride has been conventionally used as a substitute for graphite, and if boron nitride is used as a complete substitute for graphite, it will not provide the strength improvement or smoothness of writing that graphite provides. Further, even if graphite and boron nitride are simply used as a mixture, the effect will not be improved. However, when boron nitride is contained in the outer cover, the ease with which handwriting is smudged by graphite is improved more than the strength and writing feel are reduced. When worn, the outer skin rubs against the core handwriting (in the case of vertical writing,
No matter which direction you write, the outer shell will follow the stroke of the core. Also.

In the case of diagonal writing, it depends on the direction of writing, but there is always a direction of scratching. ).

Further, in obtaining the pencil lead of the present invention, there are no major problems in terms of composition and manufacturing method. For example, it is possible to obtain a sintered pencil lead using graphite and a sintered pencil lead using boron nitride. , the procedure for extrusion molding of wire coating can be used as is. The resulting product has an appropriate shape and size relationship, such as one in which the core and the outer skin are concentric circles, and one in which the core has a polygonal cross section such as a triangle or square, and the outer skin has a circular cross section.

Here, sintered type pencil leads may be further classified into two types depending on whether the binding material forms a carbonized skeleton or not. In the present invention, we will refer to these as "resin sintered core" and "clay sintered core", borrowing the expressions and expressions of "resin" and "clay", which are representative respectively, for convenience. There are four combinations available depending on whether the core is a resin sintered core or a clay sintered core. That is, the combinations are resin fired core-resin fired core, resin fired core-clay sintered core, clay sintered core-resin fired core, and clay sintered core-clay sintered core. Any combination may be used as appropriate. Also,
For example, various materials can be selected and used for both the core and the outer skin, such as containing boron nitride for other purposes. However, considering that resin fired cores generally have better strength than clay sintered cores, it is preferable to use an organic fired core as the core for small diameter cores. Furthermore, as mentioned above, the outer skin is arranged primarily to suppress the ease with which handwriting is smudged by the core, so taking this into account, it does not necessarily exhibit visible "handwriting". You don't have to.

In other words, since the core contains graphite, it will naturally exhibit handwriting, but the outer skin does not need to actively contain a coloring material. Although there may be some doubts about the expression ``'', it also means that boron nitride can be made into a white sintered body, partly because the apparent color of boron nitride is whitish.

This is done in consideration of the fact that paper, which is a normal writing surface, is white.Of course, the same effect can be achieved by changing the color to match the color of the writing surface, but if you do this, Smudges on handwriting caused by "type pencil lead" become visually invisible, and, for example, if the overall diameter is 0.
Although it can be used with a 5nm mechanical pencil, it is also possible to make handwriting 0.3 mm thick (by the way, if you wet-copy this handwriting, it will be 0.5 mm thick).
(It is also possible to use the handwriting of "no".) and,
At this time, the strength is superior due to the presence of the outer skin compared to the case where the pencil lead is simply a small diameter pencil lead used in a 0.3 No. sharp pencil. Taking this into consideration, the outer cover may be a sintered pencil lead, but since there are cases where writing is done on a special writing surface such as a plotter that uses special paper, It is often preferable to keep the material ``colorless in appearance.''

(Example) Hereinafter, parts simply refer to parts by weight.

[Example 1] Akuyo Kikki vinyl chloride lrM resin 30 parts graphite
50 parts carbon black
5 parts stearate 1 part dioctyl phthalate 10 parts methyl ethyl ketone 15 parts 9 parts Bentonite 30 parts boron nitride
40 parts Polymethyl methacrylate (excipient) 20 parts Dioctyl phthalate 10 parts Methyl ethyl ketone 80 parts The above ingredients were kneaded using a Henschel mixer with 3 rolls, and then molded into 2 rolls using 2 screw extruders. 270℃
Heat treated in air until 900°C in an inert atmosphere.
A heat treatment was performed to raise the temperature to .degree. C., and after cooling, the pencil lead was impregnated with mineral oil to obtain a pencil lead having an outer diameter of about 0.5 nxn and a core diameter of about 0.3 ffI11, in which the outer shell and the core were concentric circles.

[Example 2 Go-Kinichi Megudo Skin-stopping test same as Example 1 Chlorinated vinyl chloride resin 40 parts Furan resin
30 parts boron nitride
50 parts stearate 2 parts dioctyl phthalate 10 parts methyl ethyl ketone
20 parts A pencil lead was obtained in the same manner as in Example 1 except that the above compounded materials were used.

[Comparative Example 1] In Example 1, only the core composition was used without using the outer shell composition, and a pencil lead having a diameter of about 0.5n++n was simply obtained.

[Comparative Example 2] In Example 1, the amount of graphite used in the core compound was halved, and boron nitride was used accordingly, without using the outer shell compound.
A pencil lead with a diameter of was obtained.

[Comparative Example 3] In Example 1, only the outer shell composition was used without using the core composition, and a sintered body with a diameter of about 0.5 mm was simply obtained, and instead of impregnating it with mineral oil, a black ballpoint pen was used. A pencil lead was obtained by impregnating it with commercial ink.

[Comparative Example 4] In Example 2, only a shell formulation was used without using a core formulation to obtain a pencil lead with a diameter of only about 0.5 nlT+.

The results of the characteristic evaluations obtained on each side above are shown in the table below.
Shown in 1. The bending strength (unit: gf/mm") and friction coefficient were measured according to JIS S 60o5.Furthermore, the fixing property (unit: 2%) was measured by applying a load of 400 to baryta paper.
When the reflectance of the handwriting written vertically in g is α, and the reflectance of the dirt generated outside the handwriting by rubbing this handwriting is β.

(100-β): Calculated as (100-a)X100, and the smaller the value, the less likely the handwriting is to get dirty.

Table 1 (Effects of the invention) It is possible to obtain a pencil lead that improves the ease with which handwriting is smeared due to the use of graphite, without substantially reducing the strength and writing feel of a sintered type pencil lead that uses graphite. can.

Claims (1)

[Claims] A sintered core containing graphite, arranged around the outer periphery of the core,
A pencil lead consisting of a sintered outer shell containing boron nitride.