JP6281700B2 - Firing pencil lead and method for producing the same - Google Patents

Description

  The present invention relates to a pencil lead obtained by firing and a method for producing the same.

  A general baked pencil lead is based on graphite and synthetic and / or natural resin, and if necessary, a plasticizer such as phthalate ester, a solvent such as methyl ethyl ketone, a lubricant such as stearic acid, boron nitride, It was obtained by using pigments and extenders such as talc, mica, carbon black, and amorphous silica together, dispersing and kneading these blended materials, extruding them into fine wires, and then heat-treating them to the firing temperature. The pores of the fired core are obtained by impregnating oily substances such as liquid paraffin and silicone oil.

  Graphite as the main material is a black coloring component, has a cleavage property, and has an inert surface. Therefore, when used as a baked pencil lead, it has little connection with surrounding organic matter, and the core Since it is easy to detach from the body, high lubricity can be obtained as a writing feeling. However, in the handwriting, since the basal plane of graphite is arranged in parallel with the paper surface, there is a problem in that it becomes a black-gray handwriting with strong light reflection.

  Therefore, various attempts have been made to bring the handwriting color closer to black (handwriting with low reflectivity), and one of the means for replacing graphite with another material has been studied. However, for example, when cleaved boron nitride is used in place of graphite, light reflected by the basal surface with a structure similar to graphite, the combined with the white of the particles, the writing lines still reflect light. Exhibits a black-gray color. In addition, talc, mica, etc. are also cleaved particles, but since these have low heat resistance, they lose their cleaveability due to structural changes such as desorption and sintering of crystal water when fired. Since it is surface active, it is strongly bonded to the surrounding resin carbide, and the core is difficult to collapse and cannot be practically used.

  Graphite and boron nitride are heat resistant and do not lose their cleaving property even when fired, but there is a problem of reflection on the basal surface. Attempts have also been made to make it closer to black. However, if a pigment that does not have cleavage or surface slip is used, the core body will not easily collapse due to binding with the binder resin carbide, so that only a light writing line with a low concentration can be obtained, and the blackness of the writing line cannot be felt. turn into.

Therefore, various methods for applying surface coating to graphite and boron nitride have been reported. For example, the invention described in Japanese Patent Application Laid-Open No. 11-256091 (Patent Document 1) discloses a fired pencil lead containing graphite and boron nitride coated with ultrafine particles, and aluminum, magnesium, nickel, cobalt as ultrafine particles are disclosed. Iron, titanium boride, zirconium boride, silicon carbide, titanium carbide, boron carbide, boron nitride, aluminum nitride, silicon nitride, titanium nitride, aluminum oxide, magnesium oxide, silicon oxide, and titanium oxide.
The invention described in Japanese Patent Application Laid-Open No. 08-27407 (Patent Document 2) discloses a fired pencil lead formed by using an inorganic material coated with a carbon thin film by a carbon vapor deposition method or a residual carbon resin, Examples of inorganic extenders include boron nitride, talc, mica, and molybdenum disulfide.

Japanese Patent Laid-Open No. 11-256091 Japanese Patent Laid-Open No. 08-27407

In the invention described in Patent Document 1, the unevenness of the surface covered with any of the exemplified ultrafine particles does not have a structure that absorbs light waves, and is not sufficient to obtain a black writing line. .
If only a carbon thin film is formed as described in Patent Document 2, reflected light of various phases is generated when interference occurs at the crystallite grain boundary, so that the effect of reducing reflection is small. In addition, the carbon thin film is integrated with the surrounding binder resin carbide by heat treatment at the time of core production, and the bond between the binder resin carbide and the binder is stronger than the bond between the inorganic extender and the carbon thin film. The carbon thin film is easily peeled off from the surface, and the coloring effect is difficult to obtain. Therefore, it is not sufficient to obtain a black writing line with a high density and low reflection.

  The gist of the present invention is a fired pencil lead containing composite particles in which low-order titanium oxide is adhered to the surface of hexagonal boron nitride.

Low-order titanium oxide is composed of titanium atoms that are electron-deficient and oxygen atoms that are electron-rich, and the basal plane of hexagonal boron nitride is electron-deficient and boron-rich. It consists of a certain nitrogen atom. Therefore, when hexagonal boron nitride and low-order titanium oxide are brought into close contact with each other by the compounding process, titanium atoms are strongly bonded to nitrogen atoms and oxygen atoms to boron atoms, so hexagonal boron nitride and low-order oxidation are applied by the force applied during writing. There is no separation between the titanium and the writing line is presumed to have a black color tone with little reflection from low-order titanium oxide.
In addition, hexagonal boron nitride is easy to peel off from the core because it is cleaved. If composite particles with low-order titanium oxide attached to the hexagonal boron nitride surface are used for the fired pencil core, they will collapse during writing. As a result, the black particles become a core fixed on the paper surface, and a black writing line with a high density and less reflection can be obtained.

Hereinafter, the present invention will be described in detail.
Hexagonal boron nitride used as a base material has a hexagonal crystal structure similar to graphite (h-BN), and what is called cubic boron nitride (c-BN) which has a cubic crystal structure. Different. Hexagonal boron nitride is composed of layers of alternating nitrogen and boron atoms arranged at the apex of a regular hexagon, and the layers are connected by weak van der Waals forces and cleaved. Can be preferably used.
The particle color of hexagonal boron nitride itself is white, and stably exists up to a temperature of about 1000 ° C. in air and over 2000 ° C. in an inert atmosphere. Commercial products of hexagonal boron nitride include Denkaboron nitride SGP, MGP, GP, HGP, SP-2, SGPS (manufactured by Denki Kagaku Kogyo Co., Ltd.), Shoubiu UHP, UHP-1K, UHP- 2, UHP-S1 (above, manufactured by Showa Denko KK), FS-1, HP-P1, HP-60, HP-2, HP-4W, HP-6, HP-1 (above, Mizushima Alloy Iron ( Etc.).

Low-order titanium oxide is in a state in which oxygen atoms have escaped from the crystal lattice of titanium dioxide, resulting in lattice defects. The chemical formula is represented by titanium oxide represented by TiO _x (0 <x <2). The It is obtained by reducing titanium dioxide by heating it at high temperature in hydrogen gas or ammonia gas, and the crystal has a regular octahedral crystal lattice structure in which six oxygen atoms are coordinated around one titanium atom. It is inferred that oxygen deficiency occurred from titanium and the electrons shared with titanium were left, and the particles had a black color without reflection.
At the interface with the binder resin carbide, low-order titanium oxide becomes more reactive due to heat generated by high-temperature firing such as 1100 ° C. to 1300 ° C., and is reduced to carbon in the resin carbide, resulting in a blacker color with more oxygen lattice defects. It is inferred that it will become low-order titanium oxide or titanium carbide, and a blacker writing line is obtained. When the temperature exceeds 1300 ° C., the reduction reaction also converges, and the influence of the core being hard and baked becomes large.
If the particle size of the low-order titanium oxide adhered to the hexagonal boron nitride is less than 1 μm, it can be preferably used because the color is good and the appearance at the time of molding is not affected.
Commercially available low-order titanium oxides include Titanium Black 12S, 13M, 13M-C (manufactured by Mitsubishi Materials Electronics Chemical Co., Ltd.), TILACK D fine particle type, ultrafine particle type (above, Ako Kasei Co., Ltd.) ))).

  The method of adhering low-order titanium oxide particles to hexagonal boron nitride to form a composite is not particularly limited as long as it is a conventionally known method capable of attaching low-order titanium oxide to the hexagonal boron nitride surface. For example, a dry process in which hexagonal boron nitride and low-order titanium oxide are put into a high-speed air flow stirrer to give impact to each other, or put into an automatic mortar and attached while applying compression shear force, Wet treatment in which hexagonal boron nitride is placed in a volatile organic solvent in which low-order titanium oxide is dispersed and the solvent is evaporated by heating while stirring, and volatile organic solvent in which low-order titanium oxide is dispersed is hexagonal. It can be used regardless of whether it is dry or wet, such as a semi-wet process that is deposited by spraying on crystalline boron nitride. In addition, it is possible to obtain composite particles by lowering titanium oxide to lower titanium oxide, such as by immersing hexagonal boron nitride in a colloidal solution of titanium oxide and then drying and heat-treating in a reducing atmosphere. Among them, a method of obtaining composite particles while applying a compressive shearing force with an automatic mortar is preferable from the viewpoint of adhesive strength.

  The amount of the composite particles used is preferably 20 wt% or more, since a sufficient coloring effect can be exerted on the writing line when the amount used is 20 wt% or more with respect to the total amount of the blend composition excluding the solvent. More preferably, it is desirable to set it as 40 wt% or more.

  Further, it is desirable that the coverage of the hexagonal boron nitride of the low-order titanium oxide by the composite is 70% or more with respect to the area of the basal plane. The measurement of the coverage is based on the SEM image obtained by photographing the hexagonal boron nitride basal surface in the composite particles from directly above, the area (A) of the hexagonal boron nitride obtained using an image analyzer and the low-order titanium oxide. The coverage (%) = (B) / (A) × 100 is used, and the average value calculated in the same manner for 50 particles is defined as the coverage of the composite particles. As the image analysis device, for example, Luzex (manufactured by Nireco Corporation) can be used. If the result of coverage by such a measurement is 70% or more, the gloss produced by reflecting light from the hexagonal boron nitride basal surface can be greatly reduced, so the reflectance of the handwriting (Y value) Handwriting of 20% or less can be easily obtained, and the handwriting can be recognized as black by visual observation. In addition, the reflectance (Y value) of the handwriting (Pentel Co., Ltd. product, Rolly, product code | symbol BP127-A) by a black ball-point pen ink is about 15% in general.

As materials other than the above, as long as the effect of the fired pencil lead according to the present invention is not impaired, conventionally used constituent materials of the fired pencil lead can be used without limitation, and the conventionally known production methods are limited. It can be manufactured without using.
For example, inorganic particles such as graphite, talc, and mica can be used in combination. Polyvinyl chloride, polyvinylidene chloride, chlorinated polyvinyl chloride, chlorinated polyethylene, and chlorinated paraffin resins can be used as synthetic resins for the binder. , Furan resin, polyvinyl alcohol, styrene resin, acrylic resin, urea resin, melamine resin, polyester resin, styrene-butadiene copolymer, polyvinyl acetate, polyacrylamide resin, butyl rubber, lignin, cellulose, tragacanth gum, gum arabic, etc. Natural resins can be used alone or in combination of two or more as required. Further, conventionally known plasticizers such as dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diallyl isophthalate, tricresyl phosphate, dioctyl adipate, ketones such as methyl ethyl ketone and acetone, ethanol and the like Solvents such as alcohols, solvents such as water, fatty acids such as stearic acid and behenic acid and fatty acid amides, and stabilizers such as stearate may be used in combination. Also, fillers for shaping purposes such as iron, aluminum, titanium, zinc and other metal oxides and nitrides, amorphous silica, small amounts of colorants such as carbon black and fullerene, carbon nanotubes, carbon fibers, fibrous titanic acid A filler such as potassium may be used in combination.

  These blended materials are uniformly dispersed with a kneader, a Henschel mixer, three rolls, etc., and then formed into a thin wire shape, appropriately heat-treated according to the resin used, and finally 800 ° C. or higher, preferably 1100 in a non-oxidizing atmosphere. A baking pencil core is obtained by performing a baking process at a temperature of from 1 to 300C. Then, if necessary, α-olefin oligomer, silicone oil, liquid paraffin, spindle oil, synthetic oil such as ester oil, animal and vegetable oil such as squalane, castor oil, paraffin wax, microcrystalline wax, polyethylene wax, montan wax, carnauba It is manufactured by impregnating a waxy material such as wax.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited only to an Example.

<Preparation of Composite Particles A to D>
50 parts by weight of hexagonal boron nitride (average particle size 10 μm, HP-1, manufactured by Mizushima Alloy Iron Co., Ltd.) and low-order titanium oxide (average particle size 1 μm, Tilac D, manufactured by Ako Kasei Co., Ltd.) 20 parts by weight 40 parts by weight, 30 parts by weight, and 10 parts by weight were put into an automatic mortar and stirred for 1 hour to obtain composite particles A to D in which low-order titanium oxide was adhered to the surface of hexagonal boron nitride. The coverage was 50%, 90%, 70% and 30%, respectively.

<Preparation of composite particle E>
By introducing 50 parts by weight of hexagonal boron nitride and 35 parts by weight of low-order titanium oxide into a hybridization system (manufactured by Nara Machinery Co., Ltd.) and dispersing and mixing them in a high-speed air stream, low-order oxidation is performed on the surface of hexagonal boron nitride. Composite particles E to which titanium was adhered were obtained. The coverage was 50%.

<Preparation of composite particle F>
The immersion of 50 parts by weight of hexagonal boron nitride in a 10% strength aqueous titanium oxide colloid solution for 1 hour and then drying at 100 ° C. was repeated three times to obtain hexagonal boron nitride having titanium oxide adhered to the surface. The obtained particles were heat-treated at 900 ° C. in a reducing atmosphere with ammonia gas to reduce the titanium oxide, thereby obtaining composite particles F in which low-order titanium oxide was adhered to the surface of hexagonal boron nitride. The coverage was 50%.

<Example 1>
Polyvinyl chloride 25 parts by weight Composite particles A 30 parts by weight Stearic acid 2 parts by weight Dibutyl phthalate 10 parts by weight Methyl ethyl ketone 20 parts by weight The above materials were dispersed and mixed by a Henschel mixer, and kneaded by 3 rolls for 10 minutes. Extruded into a thin line with a single screw extruder, heated from room temperature to 300 ° C. in air over about 10 hours, held at 300 ° C. for about 1 hour, and further heated in a sealed container to 1000 A baking treatment at the highest temperature was performed, and after cooling, liquid paraffin was impregnated to obtain a pencil lead having a nominal diameter of 0.5.

<Examples 2 to 4>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particles B to D were used instead of A.

<Example 5>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the amount of the composite particles A was changed from 30 parts by weight to 55 parts by weight.

<Example 6>
A pencil having a nominal diameter of 0.5 in the same manner as in Example 1 except that the amount of the composite particles A was changed from 30 parts by weight to 15 parts by weight and 15 parts by weight of hexagonal boron nitride was added. I got a wick.

<Example 7>
A pencil having a nominal diameter of 0.5 in the same manner as in Example 1 except that the amount of the composite particles A was changed from 30 parts by weight to 7 parts by weight and 23 parts by weight of hexagonal boron nitride was added. I got a wick.

<Example 8>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle E was used instead of the composite particle A.

<Example 9>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle F was used instead of the composite particle A.

<Examples 10 to 12>
In Example 2, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 2, except that the firing temperature was changed to 1000 ° C. and fired at 1200 ° C., 1100 ° C., and 900 ° C., respectively.

<Preparation of Composite Particle G Coated with Ultrafine Particles of 0.1 μm or Less>
Composite particles G in which 0.08 μm of alumina is coated on the surface of hexagonal boron nitride by applying 50 parts by weight of hexagonal boron nitride to a thermal plasma coating apparatus using alumina as a coating material and performing coating treatment. Got. The coverage was 100%.

<Preparation of Composite Particle H Formed with Carbon Thin Film Using Residual Carbon Resin>
50 parts by weight of hexagonal boron nitride and 40 parts by weight of polyvinyl chloride are put into an automatic mortar and stirred for 1 hour to attach polyvinyl chloride to the surface of hexagonal boron nitride, and then in a non-oxidizing atmosphere. The resulting fired product was finely pulverized by heat treatment at 800 ° C. to obtain composite particles H having a carbon thin film formed on the surface of hexagonal boron nitride. The coverage was 100%.

<Preparation of composite particle I>
50 parts by weight of hexagonal boron nitride and 10 parts by weight of carbon black (average primary particle size of 24 nm, MA100, manufactured by Mitsubishi Chemical Corporation) were put in an automatic mortar and stirred for 1 hour, and the surface of hexagonal boron nitride Composite particles A to D having carbon black adhered thereto were obtained. The coverage was 50%.

<Preparation of composite particle J>
50 parts by weight of hexagonal boron nitride and 15 parts by weight of diamond nanoparticles (primary particle average diameter 50 nm, manufactured by Sumiishi Materials Co., Ltd.) were put into an automatic mortar and stirred for 1 hour. Composite particles A to D having carbon black adhered to the surface were obtained. The coverage was 50%.

<Preparation of composite particle K>
50 parts by weight of hexagonal boron nitride and 20 parts by weight of titanium dioxide (average particle size: 0.25 μm, JR-403, manufactured by Teika Co., Ltd.) were placed in an automatic mortar and stirred for 1 hour. Composite particles A to D having carbon black adhered to the surface were obtained. The coverage was 50%.

<Preparation of Composite Particle L>
By putting 50 parts by weight of cubic boron nitride (particle size: 8-12 μm, BN-B, manufactured by Showa Denko KK) and 20 parts by weight of low-order titanium oxide into a hybridization system and dispersing and mixing them with a high-speed air stream, Composite particles L in which low-order titanium oxide was adhered to the surface of hexagonal boron nitride were obtained. The coverage was 50%.

<Comparative Example 1>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example except that the composite particle A was changed to scaly graphite (average particle size: 10 μm).

<Comparative example 2>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example except that the composite particle A was replaced with talc (average particle size 12 μm, SW, manufactured by Nippon Talc Co., Ltd.).

<Comparative Example 3>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particles A were replaced with low-order titanium oxide.

<Comparative Example 4>
In Example 1, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particles A were replaced with hexagonal boron nitride.

<Comparative Example 5>
In Example 1, a pencil core having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particles A were replaced with 19 parts by weight of hexagonal boron nitride and 11 parts by weight of low-order titanium oxide.

<Comparative Example 6>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle A was replaced with the composite particle G in Example 1.

<Comparative Example 7>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle A was replaced with the composite particle H in Example 1.

<Comparative Example 8>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle A was replaced with the composite particle I in Example 1.

<Comparative Example 9>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle A was replaced with the composite particle J in Example 1.

<Comparative Example 10>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle A was replaced with the composite particle K in Example 1.

<Comparative Example 11>
A pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Example 1 except that the composite particle A was replaced with the composite particle K in Example 1.

<Comparative Examples 12-14>
In Comparative Example 4, a pencil lead having a nominal diameter of 0.5 was obtained in the same manner as in Comparative Example 4, except that firing was performed at 1200 ° C., 1100 ° C., and 900 ° C. instead of the firing temperature of 1000 ° C.

  As mentioned above, about the pencil lead obtained by each Example and the comparative example, the bending strength and density | concentration were evaluated according to JISS6005 about the darkness of a writing line. The darker the black, the higher the value, but it is easier to obtain a high value even with glossy writing lines. Therefore, as a reflectance measurement of the writing line, the Y value of the XYZ color system was measured with a spectrocolorimeter on the drawing paper whose surface was filled by changing the drawing interval from the density measurement condition to 0.3 mm. A smaller Y value results in less reflection and lower brightness. The higher the density value and the smaller the Y value, the better the black writing line with darkness and less reflection.

As is clear from the results in Table 1 above, the fired pencil lead of Examples 1 to 12 within the scope of the present invention can obtain a black writing line that is darker and less reflective than the pencil lead of Comparative Examples 1 to 14. found.
Example 1 is a core obtained by using 45 wt% of hexagonal boron nitride / low-order titanium oxide composite particles having a coverage of 50% with respect to the total amount, and using graphite, which is a conventional inorganic material particle. Compared to Comparative Example 1 and Comparative Example 2 using talc, the concentration is high and the Y value is small. Further, even when compared with Comparative Example 5 in which hexagonal boron nitride and low-order titanium oxide were simply used in the proportion of composite particles A, Example 1 has a high concentration and a small Y value. The effect of becoming a black writing line with little reflection is obtained. In Comparative Example 3 using titanium black, the writing line is thin and the writing line is thin, and the Y value is large because the writing line is thin. In Comparative Example 4 using hexagonal boron nitride, there is reflection due to the basal plane. The value has not improved. The comparative example 6-11 which uses a conventionally well-known composite particle has a density | concentration and a small Y value, and a composite particle is obtained by compounding a hexagonal boron nitride and a low-order titanium oxide, compared with comparative examples 6-11. An effect that was not possible has been obtained.
Examples 2 to 4 are examples in which composite particles having a different coverage from that of Example 1 were used, and the effect was obtained as the coverage increased. From this, it is presumed that the lower the titanium oxide is coated, the lower the reflection of hexagonal boron nitride and the lower titanium oxide coloring effect. In particular, the effects of Examples 2 and 3 having a coverage of 70% or more are high, and it can be said that it is preferable to use a composite particle having a coverage of 70% or more.
Examples 5-7 are the examples which changed the usage-amount of composite particle | grains from Example 1, and the core with less reflection is obtained, so that the usage-amount increases. This is presumed that sufficient wear powder is obtained by the good collapsibility of the composite particles, and the coloring effect is increased. In particular, the effects are obtained in Examples 1, 5, and 6 in which the usage amount is 20% or more, and in particular, good effects are obtained in Examples 1 and 5 in which the usage amount is 40% or more. % Or more, and more preferably 40 wt% or more.
Examples 8 and 9 are examples in which the production method of the composite particles was changed from Example 1, and also in Example 8 produced using a high-speed air stream and Example 9 produced using a titanium oxide colloidal solution. Compared with the comparative example, a thick and less reflective core is obtained. In comparison with Example 1, it can be inferred that the better effect of Example 1 was obtained because the compressive shear force by the automatic mortar resulted in strong adhesive force.
Examples 10 to 12 are examples in which the firing temperature was changed from Example 2, and Examples 12 and 2 performed at the firing temperatures of 900 ° C. and 1000 ° C. were Comparative Examples 14 and Comparative Examples fired at the same temperature. In Example 11 and Example 10 carried out at firing temperatures of 1100 ° C. and 1200 ° C., the concentration was 0.28D deeper than 4, respectively, and the Y value was reduced by 19.6% and 19.7%. Compared to Comparative Examples 12 and 13 fired at a temperature of 0.30D, the concentrations were 0.30D deeper, the Y values were reduced by 21.0% and 21.1%, and the difference was widened. When the temperature becomes 1100 ° C. or higher, the reactivity of the low-order titanium oxide is increased at the interface with the binder resin carbide, and it is reduced to carbon in the resin carbide, so that the black low-order titanium oxide having many oxygen lattice defects, The formation of titanium carbide is considered to suppress the decrease in concentration and increase in reflection even when the firing temperature is raised and the core becomes hard.
As described above, by containing composite particles in which low-order titanium oxide is adhered to the surface of hexagonal boron nitride, a black writing line fired pencil core with a high concentration and low reflection is obtained.

Claims (3)

A fired pencil lead containing composite particles in which low-order titanium oxide is adhered to the surface of hexagonal boron nitride. 2. The fired pencil core according to claim 1, wherein the composite particles are composite particles in which 70% or more of the hexagonal boron nitride surface is covered with the attached low-order titanium oxide. The manufacturing method of the baking pencil lead of Claim 1 or Claim 2 baked at 1100 degreeC or more.