JP2006265299A - Fired pencil lead - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fired pencil lead which scratches little, presents a smooth feel of writing and rarely breaks irrespective of the differences in quality of paper such as high quality paper, medium quality paper and straw paper. <P>SOLUTION: The fired pencil lead is composed at least of graphite and obtained by kneading graphite and a binder such as a resin and clay, extrusion-molding the mixture and firing it at ≥600°C. In the crystal structure of the graphite of the fired lead as determined by X-ray diffraction, the ratio of the diffraction intensity I<SB>r</SB>of the rhombohedron structure at (100) plane and (110) plane to the diffraction intensity I<SB>h</SB>of the hexagonal structure at (100) plane and (101) plane: I<SB>r</SB>/I<SB>h</SB>is 0-0.40. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fired pencil lead having almost no broken core and good writing performance regardless of paper quality.

Conventionally, a fired pencil lead used for pencils and mechanical pencils is made by using a binder such as clay or resin for a material such as graphite or carbon black, kneading and extruding this, and firing at a temperature of 600 ° C. or higher. The pores of the obtained fired core are impregnated with fats and oils to obtain a finished core. Here, in the normal fired pencil lead, the center of the material is graphite, and examples of the type include scaly, earthy, and scaly, and a lubricant that provides a smooth writing texture while exhibiting black as a coloring material. It also has a role as. By the way, a general core used in the past shows a smooth writing taste if the paper quality is good, such as fine paper, but if the paper quality becomes rough and inferior, it will avoid catching and roughening. It becomes difficult, and the core breakage is affected by good or bad sliding regardless of paper quality. In particular, since the bending strength has to be increased as the diameter of the mechanical pencil core becomes smaller, such as 0.5 mm, 0.4 mm, and 0.3 mm, the above-described tendency becomes more prominent. This problem is influenced by the amount and type of carbon obtained from the clay and resin that bear the strength of the core, or the production method, but the graphite itself has a great influence because of its high content. Under such circumstances, for example, expanded graphite, fluorinated graphite, ultra flat graphite, or the definition of impurities in graphite have been studied as types of graphite aiming at performance improvement (see Patent Document 1) (Patent Document 1) 2) (see Patent Document 3) (see Patent Document 4).
Japanese Patent Laid-Open No. 57-14666 JP-A-6-293874 JP-A-6-1941 Japanese Patent Laid-Open No. 2-92973

  However, even if any graphite is used in Patent Documents 1, 2, and 3, a slight improvement in bending strength is recognized, but conversely, writing performance such as writing taste tends to be deteriorated. Such phenomena are hardly solved. Patent Document 4 aims to reduce the occurrence of anomalous friction coefficient by removing impurities in graphite, but is different from improving writing quality. As described above, various attempts have been made to improve various performances with a focus on bending strength and writing quality as graphite. However, in the present situation, ordinary graphite and other conventional graphites that have been used in the past are used in many cases. .

It is a fired pencil core composed of at least graphite, and has a rhombohedral structure diffraction intensity I _r = r (100) + r (110) and a hexagonal structure diffraction intensity I _h = h (100 in X-ray diffraction of graphite. ) + H (101) and the diffraction intensity ratio I _r / I _h is 0 to 0.40.

  The fired pencil lead of the present invention has a very smooth writing taste, almost no breakage of the lead at the time of writing, and is less rough and caught even on paper having a rough paper quality and inferior surface condition, and further the diameter of the lead is thin. It has a good writing performance that the above-mentioned feature becomes remarkable.

  The fired pencil core of the present invention is characterized in that the rhombohedral structure portion in the crystal structure of graphite has a specific range.

Next, the fired pencil lead of the present invention will be specifically described. The graphite composed of the fired pencil core has a diffraction intensity ratio I _r / I _h = (r (100) + r (110)) / (h (100) + h (101)) obtained by X-ray diffraction of 0 to 0. It is characterized by 0.40, preferably in the range of 0 to 0.30, particularly in the range of 0 to 0.25. Here, I _r = r (100) + r (110) is the (100) plane, the diffraction intensity of the rhombohedral structure at the (110) plane, I _h = h (100) + h (101) is the (100) plane, The diffraction intensity of the hexagonal structure in the (101) plane is shown, and in the crystal structure of graphite, when I _r / I _h indicating the ratio of the diffraction intensity of the rhombohedral structure to the hexagonal structure is 0 to 0.40, A fired pencil lead having a good writing quality without roughness and catching can be obtained regardless of the paper quality. When the diffraction intensity ratio is 0, the rhombohedral structure on the (100) plane and the (110) plane is 0, so that the writing performance is most preferable. When it is 0.40 or more, although the degree varies depending on the difference in paper quality, the writing performance is deteriorated such as roughening or catching and easy core breakage. This becomes more prominent as the core diameter becomes smaller.

  The reason for this is not clear. However, one of the important factors for writing quality is the crystal structure and delamination of graphite. Focusing on the crystal structure, the graphite in the core is composed of hexagonal mesh lattices. It is composed of a hexagonal structure and a rhombohedral structure. In the rhombohedral structure, the positional displacement between the carbon network surfaces to be laminated is small compared to the hexagonal structure, and the interlaminar interlaminar force is strong. Therefore, delamination and slipping between layers becomes more difficult than the hexagonal structure, and as a result, exfoliation when writing is not smooth, and as a whole it is thought that the writing feel becomes rough or gets caught, and as a result, it tends to break. It is assumed that the tendency becomes more noticeable as the paper becomes rougher.

  The fired pencil lead of the present invention is composed of carbon or graphite obtained by firing clay or resin in addition to the above graphite, and examples of the clay include clay minerals such as kaolinite, halloysite, montmorillonite, and bentonite. Moreover, conventionally well-known thing is used as resin used as a binder at the time of manufacture, for example, synthetic polymer substances, such as polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, furan resin, phenol resin, epoxy resin, lignin, cellulose And natural polymeric substances such as tragacanth gum and gum arabic, and pitches such as petroleum asphalt, coal tar pitch, and resin dry distillation pitch.

  In addition to the above materials, other constitutional materials may be added. Examples of the extender include mica, talc, boron nitride, and carbon black. The porosity of the fired pencil lead used in the present invention is arbitrary, but is preferably in the range of 5 to 40% in order to improve slipping by impregnating with oils and fats. If it is 5% or less, the effect of impregnation cannot be obtained, and if it is 40% or more, the amount of impregnation increases, the writing quality tends to be heavy, and the bending strength also deteriorates. As the fats and oils, any conventionally known oils may be used, and examples thereof include spindle oil, liquid paraffin, silicone oil, modified silicone oil and the like. Preferably, modified silicone oil is used, particularly polyether. Of these, modified silicone oils are preferred. That is, since the concentration improving effect is excellent, a core having high bending strength and high concentration can be obtained.

  The production method of the fired pencil lead of the present invention will be described. Addition of graphite as a colorant and resin or clay as a binder, and constitutional materials such as talc and mica, solvent, plasticizer and the like as necessary. Kneading and extrusion molding. The extruded core is baked at a temperature of approximately 600 ° C. or higher in a non-oxidizing atmosphere such as a nitrogen atmosphere, and pores of the obtained baked core are impregnated with fats and oils to obtain a baked pencil core.

At this time, the graphite used as the raw material is graphite prepared so that the diffraction intensity ratio I _r / I _h is 0.40 or less in the crystal structure. In other words, since the rhombohedral structure in graphite is produced in large quantities by cleavage of graphite, it was prepared by suppressing the pulverization and micronization of graphite to some extent so that the diffraction intensity ratio I _r / I _h is 0.40 or less. Or a powder having a rhombohedral structure adjusted by heat treatment of graphite powder. As pulverization and micronization progress, the rhombohedral structure increases and eventually the crystal structure changes greatly, and the performance as a core improves in strength, but the concentration decreases and writing performance such as writing taste increases. It will deteriorate. Further, when manufacturing the core, it is necessary to carefully carry out kneading with a kneader or a three-roller. For example, when the mixed materials are kneaded strongly at high pressure for a long time, the dispersibility of the graphite is improved, but the cleavage of the graphite is promoted by pulverization and micronization, leading to an increase in the rhombohedral structure, resulting in extrudability. Is good and the strength is high, but it is hard and the writing quality is deteriorated. Next, examples and comparative examples of the present invention will be shown and described in more detail. “Parts” is “parts by weight”.

Graphite (flaky graphite with I _r / I _h adjusted to 0.10) 60 parts Polyvinyl chloride 40 parts Methyl ethyl ketone 100 parts Dioctyl phthalate 20 parts The above ingredients are kneaded to produce a kneaded product, and this kneaded product is extruded. After forming and forming an extruded core, the temperature was raised to 1000 ° C. at a rate of temperature increase of 50 ° C./hour in an argon gas atmosphere, fired at 1000 ° C. for 2 hours, a diameter of 0.38 mm, and a porosity of 12%. A fired core was obtained. This fired core is composed of graphite having a diffraction intensity ratio I _r / I _h of 0.10 and carbon obtained by firing polyvinyl chloride, and a modified silicone oil (polyether) is placed in the pores of this fired core. System) was impregnated to obtain a fired pencil lead.

(Comparative Example 1)
Instead of the graphite of Example 1, a scaly graphite having a diffraction intensity ratio I _r / I _h of 0.45 that was conventionally used was used as a fired pencil lead in the same process as in Example 1.

(Comparative Examples 2-3)
The crystal structure of graphite was measured by X-ray diffraction using a commercially available A and B mechanical pencil core with a nominal size of 0.3 mm as Comparative Examples 2 and 3, respectively. The diffraction intensity ratio I _r / I _h was 0.90 for Company A and 1.15 for Company B.

  For Example 1 and Comparative Examples 1, 2, and 3, the paper quality, bending strength, hardness, and number of core breaks were compared. As for the writing taste by paper quality, high quality paper, medium quality paper, and straw half paper are used as paper, and the writing taste is a sensory test when actually written. ◎ is very smooth without being caught, ○ is slightly stuck but smooth, △ is somewhat stuck and slightly rough, and x is rough and rough. The bending strength (MPa) is measured based on JIS-S6005, and the hardness indicates HB. The number of core breaks indicates the number of core breaks when 400 kanji characters are written on the horizontal rule in the KOKUYO campus notebook. The average number of breaks for each sample was tested for 10 people. . The results are shown in Table 1. The X-ray diffraction intensity ratio of the core is measured by using a measurement sample that is lightly pulverized and granulated to such an extent that the graphite crystals are not changed, and irradiated with X-rays to the (100) plane of the rhombohedral structure ( The ratio of integral intensities by X-ray diffraction in the (110) plane and the (100) plane and (101) plane of the hexagonal structure was determined.

  As is clear from Table 1, the fired pencil lead of the present invention has no catch, smooth writing and almost no broken core, and there is no change in writing taste regardless of the difference in paper quality, and smooth and stable writing. It can be seen that it has excellent characteristics such as having performance.

  There is almost no core breakage, writing can be performed smoothly without selecting paper quality, and stable use is possible even if the diameter of the core is reduced.

Claims (1)

It is a fired pencil core composed of at least graphite, and has a rhombohedral structure diffraction intensity I _r = r (100) + r (110) and a hexagonal structure diffraction intensity I _h = h (100 in X-ray diffraction of graphite. ) + H (101) and the diffraction intensity ratio I _r / I _h is 0 to 0.40.