JPH1036747A - Pencil lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a pencil lead that has color deepness improving effect on handwriting and smooth writing touch, and can be sufficiently fixed on paper by impregnating polydimethylsiloxane into fine pores of the lead. SOLUTION: This pencil lead comprises a calcined lead whose fine pores are impregnated with polydimethylsiloxane which has preferably a kinematic viscosity of 5-1000cSt at 25 deg.C by such an impregnation process as vacuum impregnation, high-pressure impregnation or normal-pressure impregnation, at temperature of 70-200 deg.C, thereby developing noticeable effects as a lead for a mechanical pencil and for a plotter owing to its constant color deepness in handwriting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a pencil lead.

[0002]

2. Description of the Related Art Conventionally, a pencil lead is obtained by kneading a material such as graphite and a binder such as a resin, kneading, extruding, and firing to impregnate oil into pores of a fired lead to obtain a finished lead. Here, the oil impregnated into the pores is for increasing the writing concentration and smoothing the writing taste. Examples of the oil include animal and vegetable oils such as whale oil, lard, rapeseed oil, soybean oil, spindle oil, and liquid paraffin. And other mineral oils, and waxes, etc., which are used alone or in combination.

[0003]

However, each of the above conventional fats and oils has a problem. That is, animal and vegetable oils and waxes cannot significantly increase handwriting density even when impregnated in a baked wick, and when used in a mechanical pencil wick, the wick retention by the chuck is considerably higher than that of mineral oils. Inferior. Next, although mineral oils are excellent in core retention by the chuck, the writing density is not so much improved. Still another problem, which is common to any of the above materials, is that when the humidity is high, handwriting does not easily fall on paper and becomes thin. Also, in writing with a plotter, since writing is performed at high speed on the paper surface, frictional heat is generated between the paper surface and the sintering core, the kinematic viscosity of the impregnated oil is reduced or deteriorated, and the handwriting density when writing at low speed, There is a problem that a difference occurs in handwriting density when writing at high speed.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been completed as a result of intensive studies on the above-mentioned problems. By impregnating the pores with polydimethylsiloxane, the effect of improving the handwriting density is large and the writing quality is improved. The result is a pencil lead that is smooth and has very good fixation to the paper surface.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The structure of polydimethylsiloxane impregnated into pores of a sintering core is represented by (CH)
₃ ) ₃ SiO ((CH ₃ ) ₂ SiO) _n Si (CH ₃ )
It is a kind of silicone oil indicated by ₃ and its characteristics are non-toxic and extremely stable with time. Silicone oil itself has relatively good stability over time as compared with other oils, but the present invention has found that polydimethylsiloxane has even better performance as a core among silicone oils.

[0006]

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[0007] The polydimethylsiloxane is easily and completely filled into the pores of the fired core, and after impregnation, the degree of improvement in the density of handwriting is extremely large as compared with before impregnation. When the core collapses, it helps uniform and smooth collapse and smoothes brush strokes. Further, when used as a mechanical pencil lead, it has a core retention force equal to or higher than that of the fired core before impregnation when the core is drawn out from the mechanical pencil and subjected to a vertical load. In addition, when the humidity is high, the handwriting is difficult to be put on the paper and it is easy to be thin, but the above material has a small kinematic viscosity change due to temperature and also has a hygroscopic property, so it becomes dense even when the humidity is high. In other words, it has a feature that the density of the handwriting does not change due to the humidity at the time of writing.

The polydimethylsiloxane preferably has a kinematic viscosity at 25 ° C. of 5 to 1000 cST, and most preferably, a range of 10 to 300 cSt. Within the range of the kinematic viscosity, the above characteristics are most easily obtained. When the kinematic viscosity is 5 or less, the initial performance is good, but polydimethylsiloxane evaporates with time, and the handwriting density decreases and the handwriting density decreases. It is easy for a change in writing taste to occur. On the other hand, if it is 1,000 or more, it becomes difficult to impregnate the pores of the fired core, and it is difficult to improve the handwriting density and to obtain a smooth writing taste. In addition,
Kinematic viscosity is the absolute viscosity reduced by density.

The porosity of the sintering core used in the present invention is arbitrary, but preferably 10 to 50%. 10
% Or less, the effect of impregnation cannot be obtained, and if it is 50% or more, the impregnation amount increases, the writing taste tends to be heavy, and the strength deteriorates.

In the present invention, polydimethylsiloxane alone may be used alone, or may be used in combination with other known substances such as other fats and oils and waxes.
It can be appropriately selected and used according to the intended use such as strength.

The method for producing the pencil lead of the present invention is briefly described as follows: graphite, carbon black, boron nitride, talc,
Add binders such as clay, natural polymer compound, synthetic polymer compound, pitch, asphalt, etc. to body material such as mica, add solvent, plasticizer, heat-resistant pigment, etc. if necessary, knead and extrude I do. This extrusion core is generally
It is fired at a temperature of 1500 ° C., and the pores of the obtained fired core are impregnated with polydimethylsiloxane to obtain a finished core.
As a method for impregnating polydimethylsiloxane, similarly to general fats and oils, impregnation is performed while maintaining the temperature at 70 to 200 ° C. using normal pressure impregnation or reduced pressure, pressure impregnation. After sufficient impregnation, excess polydimethylsiloxane adhering to the surface is removed by centrifugation or spray washing.

[0012]

【Example】

Example 1 60 parts by weight of graphite, 40 parts by weight of polyvinyl chloride, and 100 parts by weight of methyl ethyl ketone were kneaded to prepare a kneaded product, and the kneaded product was extruded to prepare an extruded core.
Calcination was carried out at a temperature of 2 ° C. for 2 hours to obtain a calcination core having an outer diameter of 0.57 mmφ and a porosity of 32%. 25 ° C. in the pores of the fired core
Kinematic viscosity at 15 cSt polydimethylsiloxane,
It was impregnated at 90 ° C. for 4 hours under normal pressure to obtain a finished core.

Example 2 A core similar to that of Example 1 was used as a sintering core, and impregnated with polydimethylsiloxane having a kinematic viscosity of 200 cSt at 25 ° C. in the pores in the same process as in Example 1. Core.

Comparative Example 1 Polymethylhydrogensiloxane was impregnated into the pores of the same fired core as in Example 1 in the same manner as in Example 1.

Comparative Example 2 The same fired core as in Example 1 was impregnated with polymethylphenylsiloxane in the same pores as in Example 1.

Comparative Example 3 Spindle oil was impregnated into the pores of the same fired core as in Example 1 in the same process as in Example 1.

Next, the above Examples 1 and 2 and Comparative Example 1,
Table 1 shows the performance of the cores obtained in 2, 3. The concentration (D) in the test was determined according to JIS-S6005.
The higher the value, the darker it is. In addition, the plotter speed in high-speed writing is 80 cm / sec,
The plotter speed for low speed writing is 10 cm / sec.

[0018]

As is clear from the test results of the above examples, the pencil lead of the present invention has a large effect of improving the density of handwriting before and after impregnation, and has a very good and smooth writing taste. It has an effect on a normal pencil lead and a lead for a mechanical pencil, and particularly has a remarkable effect as a lead for a mechanical pencil. It also has the feature that the handwriting density is constant depending on the writing speed, and in particular, has a remarkable effect as a plotter core.

Claims (2)

[Claims] 1. A pencil lead comprising at least polydimethylsiloxane impregnated in pores of a fired lead. 2. The kinematic viscosity of polydimethylsiloxane is 2
The pencil lead according to claim 1, wherein the pencil lead temperature is 5 to 1000 cSt at 5C.