JPH0978022A - Production of black pencil lead - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a black pencil lead having smooth writing touch, excellent density of the written line and high strength of the lead. SOLUTION: A black pencil lead is produced by using clay powder composed of >=97wt.% of a fraction having diameter of <=3μm and <=1wt.% of a fraction having particle diameter of >=10μm measured by Andreasen method, compounding the clay powder with a 1st additive consisting of a sodium salt of a condensation product of β-naphthalenesulfonic acid and formaldehyde, optionally further compounding with a 2nd additive consisting of one or more kinds of water-soluble sugars and/or sugar-alcohols (the water-soluble sugar is preferably a starch graft-polymerized with gum arabic and/or polyvinyl alcohol and the sugar-alcohol is preferably sorbitol), adjusting the amount of water to be added to the compounded composition to <=35 pts.wt. based on 100 pts.wt. of the compounded composition and performing the compounded material by charging the material in a cylinder of a performing machine and evacuating the cylinder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a black pencil lead used for pencils.

[0002]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a black pencil lead which has a smooth writing quality and is excellent in drawing line density and strength.

[0003]

[Means for Solving the Problems] As a result of earnest research for solving the above problems, the present inventor has found that graphite powder, clay powder, a first additive and a second additive which is added as necessary. Water is added to the compounding composition to disperse and mix using a vertical axis high-speed mixer, and after adjusting the water content, preforming is performed and extrusion molding is performed with a ram type extrusion molding machine, followed by drying and firing to obtain a fired product. In the method for producing a black pencil lead impregnated with oils and fats, the clay powder comprises 97% by weight or more of particles having a particle size of 3 μm or less and 1% by weight or less of particles having a particle size of 10 μm or more as measured by the Andriazen method. In addition, a sodium salt of a β-naphthalenesulfonic acid formalin condensate is blended as the first additive, and the second additive is preferably a starch in which the water-soluble saccharide is graft-polymerized with gum arabic and / or polyvinyl alcohol, Water is added to the blended composition in an amount of 35 parts by weight or less based on 100 parts by weight of the blended composition. The adjusted moisture has a hardness of HB to 9H of 13.5 to 17.0% by weight,
The hardness of B to 6B is 17.5 to 23.0% by weight, and it is optimal to perform preforming after depressurizing and deaerating the inside of the cylinder after charging the compounding material into the cylinder of the preforming machine. Was discovered and the present invention was completed.

Next, the compounded composition and the manufacturing process of the present invention will be specifically described. The graphite powder is used as a colorant / constituent, but one normally used for a pencil lead can be used. Graphite is natural graphite or artificial graphite by the manufacturing method, it is classified into scaly graphite or earthy graphite due to the difference in crystallinity, it may be appropriately selected depending on the physical properties of the desired black pencil lead, in the present invention, regarding the type of graphite It is not particularly limited. Also,
If necessary, carbon black may be added to increase the blackness.

The graphite powder used in the present invention has an average particle size of 15 μm or less, preferably 10 μm, since it is dispersed and mixed in a vertical axis high speed mixer using clay powder and additives in a limited amount of water. The following is desirable.

Clay powder is used as a core binder. As the clay species, kaolinite-based hydrohalloysite and montmorillonite-based bentonite, which are usually used for pencil lead, can be used, but graphite powder and additives together with a limited amount of water are used for the vertical axis high speed mixer. 3 μm as measured by Andriazen's method
The following particles must be 97% by weight or more, and the particles having a size of 10 μm or more must be 1% by weight or less. 3 μm
When the amount of the following particles is less than 97% by weight and the amount of the particles of 10 μm or more exceeds 1% by weight, the core produced through the production process of the present invention has a reduced strength and the writing quality is not smooth. Such disadvantages occur.

The blending ratio of the graphite powder and the clay powder depends on the required hardness and the physical properties of the core, and the hardness becomes harder as the clay content is increased, and the core having a softer hardness is obtained if the clay content is decreased. Examples of graphite-clay ratios for several hardnesses are shown in Table 1. The unit of Table 1 is% by weight.

[0008]

[Table 1]

In the present invention, a sodium salt of β-naphthalenesulfonic acid formalin condensate is used as the first additive. The sodium salt of β-naphthalene sulfonic acid formalin condensate is usually obtained as an easily water-soluble fine powder, which acts as a wetting agent for graphite powder and clay to improve the dispersion efficiency, and leaves a carbide after firing to give strength and writing comfort. Contribute to improvement.

The amount of the first additive added is 0.5 to 3.0 parts by weight based on 100 parts by weight of the total amount of graphite powder and clay powder,
It is preferably 1.5 to 2.0 parts by weight. If the amount is less than 0.5 parts by weight, no effect is obtained, and if the amount exceeds 3.0 parts by weight, the amount of carbides is too large and the brush feels undesirably.

If necessary, one or more water-soluble saccharides and / or sugar alcohols are added to the compounding composition as a second additive. The water-soluble saccharide may be any of monosaccharide, disaccharide, and polysaccharide, and may be a derivative thereof if it is water-soluble. Preferably, the water-soluble saccharide is selected from starch obtained by graft-polymerizing gum arabic and / or polyvinyl alcohol, and the sugar alcohol is sorbit, which gives good results.
By adding the second additive to the composition, the dispersion
Prevents the evaporation of water in the compounding material from the mixing process to the molding process, improves the moldability in the molding process, improves the green strength of the molded product, and miniaturizes the open pores and porosity caused by thermal decomposition during firing. It is possible to increase the number of open pores and increase the porosity to improve the impregnation rate of oils and fats after firing, and to give a smoother writing feel. The second additive may be omitted depending on the physical properties of the core.

The total amount of the second additive added is 0.5 to 7.0 parts by weight, preferably 1.0 to 5.0 parts by weight, based on 100 parts by weight of the total amount of graphite powder and clay powder. If the amount is less than 0.5 parts by weight, the effect is not exerted. If the amount is more than 7.0 parts by weight, the recycling of defective cores and cutting margins generated in the molding process may occur, the core may be bent in the drying process, and the fired product may be produced. There are drawbacks such as reduced strength, which is not preferable.

When the above-mentioned compounded composition is dispersed and mixed by using a vertical axis high speed mixer, first, graphite powder, clay powder and, if necessary, a high molecular weight powdery second additive are placed in a tank. Add and mix at high speed by dry method. Examples of the high molecular weight powdery second additive include polysaccharides such as gum arabic and starch, and derivatives thereof. As the vertical axis high speed mixer, a Henschel mixer equipped with a cooler mixer is preferable from the viewpoint of mixing / dispersion efficiency and water content adjustment described later.

Next, water, the first additive and, if necessary, the low-molecular-weight second additive are dissolved in water, put into a tank, and wet-mixed at high speed for dispersion. Examples of the second additive having a low molecular weight include monosaccharides, secondary compounds, and sugar alcohols such as sorbit. The total amount of water used at this time is 35 parts by weight or less with respect to 100 parts by weight of the composition. If the amount exceeds 35 parts by weight, the material in the tank is close to a slurry state, and the dispersion efficiency is undesirably reduced. The minimum amount of water used varies depending on the clay ratio of the blended composition, but in order to efficiently wet the clay and the additives, it is advisable to add water in an amount of 5% by weight or more based on the adjusted water content before preforming.

After the dispersion and mixing, the water content of the material is adjusted. To adjust the water content, the inside of the tank is heated during the mixing to evaporate the water, and when the water content is close to the predetermined water content, the material is moved to a cooler mixer and the remaining water to be volatilized is evaporated while cooling and stirring. The adjusted water content is 13.5% to 17.0% by weight for HB-9H with a high clay ratio, and 17.5 to 23.0% by weight for the hardness with a low clay ratio B-6B. If the water content is too low, not only will the clay's binding force decrease and the green strength will be weaker, but the hardness of the final product will shift to a lesser degree, and if the water content is too high, the green strength will be weak and the hardness of the final product will be low. Shifts softly. Also, there is a drawback that the diameter of the core deviates from the target when there is too much water or too little water.

The material whose water content has been adjusted is discharged from the mixer into a container for preforming. It is preferable to use a water vapor impermeable substance for the container of the material whose water content is adjusted so that the water content does not evaporate from the material until the extrusion molding is completed. Here, the preforming is a diameter of 50 to 150 mm and a length of 1 as a pre-process of extrusion molding in order to give the extrudate a denseness.
Forming into a columnar shape of 50 to 400 mm is referred to. As a means of preforming, there is a method of colliding the piston with the material in the cylinder at high speed, or taking out a compressed product after compression molding using a hydraulic piston, but in the present invention, after depressurizing the inside of the cylinder and degassing The method of compression molding using a hydraulic piston is adopted.

By degassing, not only the density of the extruded product is improved and the product strength is improved, but also cavities and cracks can be prevented. The degree of vacuum is preferably 10 mmHg or less.

Next, the preform is molded into a desired sectional shape by a gear type or hydraulic type ram type extruder.
Usually, the cross section of the pencil lead is circular, but other shapes may be used if necessary. Since the pencil lead according to the present invention causes volumetric shrinkage due to evaporation of water in a drying step and sintering of clay in a firing step which will be described later, an extruded product can be produced in anticipation of volumetric shrinkage depending on water content and the amount of clay. It is necessary to determine the cross-sectional dimensions. The molded product is preferably cut to a desired length before drying.

The cut molded product is dried using a dryer to evaporate the water content. In order to increase the straightness of the dried product, it is preferable to use a cylindrical container having a hole in the side surface and to dry the product while rotating it around the axis of the container. Drying conditions vary depending on the composition of the composition, but from room temperature to 110 to 160 ° C
The temperature is raised to and held for 2 to 10 hours. It is necessary to avoid a rapid rise in temperature in order to prevent the occurrence of cracks.

The dried molded product is packed in a heat-resistant crucible or the like and fired in a non-oxidizing atmosphere. Firing is performed from room temperature to 950 to 1200 ° C. over 1 to 3 hours, and after cooling, the fired product is taken out.

Next, the baked product is impregnated with oils and fats to obtain a product. As a type of fats and oils, lard normally used for black lead for pencils,
One or more kinds of whale oil, fish oil, carnauba wax, etc. can be selected. For the impregnation operation, the burned material is 150-18
It is put into the impregnated oil heated to 0 ° C., kept for 2 to 6 hours and taken out, and then the fats and oils attached to the core surface are removed using a centrifuge or the like to complete the process.

[0022]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0023]

[Example 1] Natural scaly graphite powder [Nippon Graphite Industry Co., Ltd. CSP] 67 parts by weight Natural clay graphite powder [Nippon Graphite Industry Co., Ltd. ASSP-E] 12 parts by weight Particles of 3 μm or less measured by Andriazen's method German clay powder containing 98.5% by weight and 0.2% by weight of particles having a size of 10 μm or more 21 parts by weight Arabic gum powder 4 parts by weight The above-mentioned blended composition was put into a Henschel mixer to prepare 15
High speed stirring for minutes. Sodium salt of β-naphthalenesulfonic acid formalin condensate [Demol N manufactured by Kao ■] 1.7 parts by weight is dissolved in 5 parts by weight of water 27 parts by weight of water The above composition is added and the latter 10 minutes are heated. The mixture was stirred at high speed for 20 minutes, and the blended material was transferred to a cooler mixer to adjust the water content to 22.5% by weight and taken out.
Then put this into the cylinder of the ram hydraulic preformer,
After degassing to 1 mmHg and applying pressure of 45 kg / cm ² , compression molding was carried out to obtain a preform, which was then made into a circular shape with a cross section of 3.20 using a gear type ram type extruder. Extruded and cut to a length of 191 mm, inserted into a cylindrical container with holes on the side, put in a dryer and rotate from the room temperature to 150 ° C in 30 minutes while rotating around the axis of the container, 150 It was kept at ℃ for 2.5 hours to dry the water.
Next, the dried product is inserted into a silicon carbide heat-resistant crucible whose inside is covered with a graphite plate, heated from room temperature to 1150 ° C in 1.5 hours and baked, then slowly cooled and the baked core is taken out. , 160 ℃
Immerse the lard in the heated lard for 5 hours to impregnate it with oil, shake off the lard adhering to the core surface with a centrifuge, and
A considerable amount of black lead for pencil was obtained.

[0024]

[Example 2] 58 parts by weight of natural scaly graphite powder [CSP manufactured by Nippon Graphite Industry Co., Ltd.] 58 parts by weight of natural clay-like graphite [ASSP-E manufactured by Nippon Graphite Industry Co., Ltd.] 7 parts by weight 21 parts by weight of German clay powder of Example 1 polyvinyl alcohol 3.0 parts by weight of starch graft-polymerized with [PETROSIZE L-2B manufactured by Nippon Starch Chemical Co., Ltd.] 15
High speed stirring for minutes. Sodium salt of β-naphthalene sulfonic acid formalin condensate [Demol N manufactured by Kao] 1.5 parts by weight is dissolved in 5 parts by weight of water 25 parts by weight of water The above composition is further added to adjust the water content to 20.0% by weight. Except that the extruded product had a circular cross-sectional diameter of 2.93 mm and the heat-resistant crucible was made of crystallized glass, oil impregnation was carried out under the same conditions as in Example 1 to obtain a black lead for pencil equivalent to 3B.

[0025]

[Example 3] Natural scaly graphite powder [Nippon Graphite Industry Co., Ltd. CSP] 68 parts by weight German clay powder of Example 1 32 parts by weight Starch graft-polymerized with polyvinyl alcohol 3.0 parts by weight [Nippon Kagaku Co., Ltd. Petrosize] L-2B] The above blended composition was put into a Henschel mixer and
High speed stirring for minutes. Sodium salt of β-naphthalene sulfonic acid formalin condensate [Demol N manufactured by Kao ■] 1.3 parts by weight is dissolved in 5 parts by weight of water 25 parts by weight of water The above composition is further added to adjust the water content to 16.5% by weight. A black core for pencils equivalent to HB was obtained by performing oil impregnation under the same conditions as in Example 1 except that the diameter of the circular cross section of the extruded product was 2.18 mm.

[0026]

[Example 4] Natural scaly graphite powder [CSP from Nippon Graphite Industry Co., Ltd.] 59 parts by weight German clay powder of Example 1 41 parts by weight The above-mentioned compounded composition was put into a Henschel mixer to prepare 15 parts by weight.
High speed stirring for minutes. Sodium salt of β-naphthalenesulfonic acid formalin condensate [DEMO N manufactured by Kao ■] 2.0 parts by weight dissolved in 5 parts by weight of water D-sorbit liquid preparation 4.0 parts by weight [Foodle-70 manufactured by Towa Kasei Co., Ltd.] Water 24 parts by weight The above composition was further added, the adjusted water content was adjusted to 15.5% by weight, and the diameter of the cross-section of the extruded product was changed to 2.11 mm. A considerable amount of black lead for pencil was obtained.

[0027]

Example 5 8 parts by weight of natural scaly graphite powder [CPM-2 manufactured by Nippon Graphite Industry Co., Ltd.] 40 parts by weight of natural scaly graphite powder [■ CPF-3 manufactured by Chuetsu Graphite Industry Co., Ltd.] 52 parts by weight of Totoku Kibushi clay powder containing 98.5% by weight of particles and 0.2% by weight of particles having a size of 10 μm or more.
High speed stirring for minutes. Sodium salt of β-naphthalenesulfonic acid formalin condensate [DEMO N manufactured by Kao ■] 2.0 parts by weight dissolved in 5 parts by weight of water D-sorbit liquid preparation 4.0 parts by weight [Foodle-70 manufactured by Towa Kasei Co., Ltd.] Water 23 parts by weight The above composition was further added, the adjusted water content was 14.0% by weight, and the diameter of the circular cross section of the extruded product was 2.19 mm. A considerable amount of black lead for pencil was obtained.

[0028]

[Example 6] 10 parts by weight of natural scaly graphite powder [CPM-2 manufactured by Nippon Graphite Industry Co., Ltd.] 26 parts by weight of natural scaly graphite powder [■ CPF-3 manufactured by Chuetsu Graphite Industry Co., Ltd.] 15 parts by weight The above composition is added to a Henschel mixer and
High speed stirring for minutes. Sodium salt of β-naphthalenesulfonic acid formalin condensate [Demol N manufactured by Kao] 2.0 parts by weight dissolved in 5 parts by weight of water D-sorbit liquid preparation 4.0 parts by weight [Foodle-70 manufactured by Towa Kasei Kogyo Co., Ltd.] Water 23 parts by weight The above composition was further added, the adjusted water content was 14.0% by weight, and the diameter of the circular cross section of the extruded product was 2.21 mm. To obtain a black lead for pencil.

Examples 1 to 6 JIS of black lead for pencil obtained
Table 2 shows the measurement results of the diameter and bending strength according to -S-6005, and the determination results of hardness and writing quality by a trained inspector.

[0030]

As is apparent from the above test results shown in Table 2, the black lead for pencils according to the method of the present invention has a smooth writing quality and is excellent in line density and strength. Can be provided.

[0031]

[Table 2]

Claims (3)

[Claims] 1. Water is added to a compounding composition comprising graphite powder, clay powder, a first additive and a second additive optionally added, and dispersed and mixed using a vertical axis high speed mixer, After adjusting the water content, preforming, extrusion molding with a ram type extruder, drying, firing, and impregnation of fats and oils in the fired product, in the method of producing a black pencil lead, clay powder is Andriazen 3 μm as measured by the method
The following particles are 97% by weight or more, and the particles having a diameter of 10 μm or more are particles of 1% by weight or less. A sodium salt of β-naphthalenesulfonic acid formalin condensate is blended as a first additive, and added as necessary. One or more water-soluble sugars and / or sugar alcohols are blended as the second additive to be added, and the amount of water added to the blended composition is 35 parts by weight or less based on 100 parts by weight of the blended composition. The adjusted water content of 13. has a hardness of HB to 9H.
5 to 17.0 wt%, hardness of B to 6B is 17.5 to 2
It is 3.0% by weight, and the pre-molding is performed by charging the compounding material into a cylinder of a pre-molding machine, depressurizing the inside of the cylinder, and degassing, and then molding. 2. The method for producing a black pencil lead according to claim 1, wherein the water-soluble saccharide as the second additive is starch obtained by graft-polymerizing gum arabic and / or polyvinyl alcohol. 3. The method for producing a black pencil lead according to claim 1, wherein the sugar alcohol as the second additive is sorbit.