Porous non-fired pencil lead and method for manufacturing a porous non-fired pencil lead

Abstract

This non-baked pencil lead comprises a water soluble polymer, a crosslinking agent, and a powder, and is characterized in that the water soluble polymer is selected from the group consisting of carboxymethylcellulose salts, starches, polyvinyl alcohols, and xanthan gums, and that the crosslinking agent is selected from the group consisting of acids, polyamide epoxies, polyacrylamides, titanium alkoxides, and glyoxals.

Description

Technical Field

[0001] The present invention relates to Porous non-fired pencil leads body and a method for manufacturing the same.

Background Art

[0002] Conventionally, fired pencil leads are generally manufactured by kneading graphite and clay to form a core, sintering the clay at a high temperature near 1,000°C to obtain a core body, and then impregnating pores generated in the core body with oil or the like. Such fired pencil leads are widely used because the graphite is fixed to the paper surface by the impregnated oil and the erasability with an eraser is good (for example, Japanese Patent Application Laid-Open No. 2007-138031). However, fired pencil leads require heating near 1,000°C to sinter the clay as a binder, which consumes energy.

[0003] In addition, conventional non-fired pencil leads use wax or resin as a binder, knead with various inorganic or organic pigments, and are manufactured by forming into a core shape using an extrusion molding machine or the like and performing a drying process as necessary (for example, Japanese Patent Application Laid-Open No. 2012-52109). Such non-fired pencil leads have a binder of wax or resin and may have poor strength. Therefore, when the tip is sharpened, sufficient tip strength may not be obtained during writing. Also, there is almost no erasability with an eraser.

[0004] On the other hand, there is also a technique that by using carboxymethyl cellulose salt as a binder, non-fired pencil leads do not impair writing feel and coloring property even under high humidity, and core expansion due to moisture absorption does not occur (Japanese Patent Application Laid-Open No. 11-335617). However, there is a problem that strength reduction due to moisture absorption is likely to occur.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Each embodiment of this application aims to provide a non-fired pencil lead that, unlike conventional methods, has sufficient writing strength even when the tip is sharpened, is less susceptible to deterioration due to moisture absorption, is erasable, and simultaneously achieves improved density of the written line and improved fixation. [Means for solving the problem]

[0006] The non-fired pencil lead of the first embodiment of the present application comprises a water-soluble polymer, a crosslinking agent, and a powder, wherein the water-soluble polymer is selected from the group consisting of carboxymethylcellulose salt, starch, polyvinyl alcohol, and xanthan gum, and the crosslinking agent is selected from the group consisting of acid, polyamide epoxy, polyacrylamide, titanium alkoxide, and glyoxal.

[0007] The non-fired pencil lead of the second aspect of the present application is characterized in that the water-soluble polymer is a carboxymethylcellulose salt and the crosslinking agent is an acid.

[0008] The non-fired pencil lead of the third aspect of the present application is characterized in that, in addition to the configuration of the second aspect, the acid is an organic acid.

[0009] The non-fired pencil lead of the fourth aspect of the present application is characterized in that, in addition to the configuration of the third aspect, the organic acid is a polymer acid.

[0010] The fifth aspect of the present invention, a non-fired pencil lead, is characterized in that, in addition to the configuration of any of the first to fourth aspects, the powder is at least one of a extender and a pigment.

[0011] The sixth aspect of the present invention is characterized by further containing cellulose in addition to any of the components of the first to fifth aspects.

[0012] The seventh aspect of the present invention, a non-fired pencil lead, is characterized in that, in addition to any of the configurations of the first to sixth aspects, the molded lead body is porous.

[0013] A method for manufacturing a non-fired pencil lead according to the eighth aspect of the present application includes the steps of preparing a mixture of a water-soluble polymer, a crosslinking agent, and a powder, and molding the mixture into a lead body, characterized in that the water-soluble polymer and the crosslinking agent are reacted and crosslinked in the molding step.

[0014] The method for manufacturing a non-fired pencil lead according to the ninth aspect of this application is characterized in that, in addition to the configuration of the eighth aspect, the water-soluble polymer is a carboxymethylcellulose salt and the crosslinking agent is an acid. [Effects of the Invention]

[0015] Since each embodiment of the present invention is configured as described above, it is possible to provide a non-fired pencil lead that has sufficient writing strength even when the tip is sharpened, has less deterioration due to moisture absorption, is erasable, and achieves both improved density of the written line and improved fixation, which could not be obtained by conventional methods. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic perspective view showing the appearance of the non-fired pencil lead of the embodiment. [Modes for carrying out the invention]

[0017] The non-fired pencil lead of the embodiment of the present invention comprises a water-soluble polymer, a crosslinking agent, and a powder, wherein the water-soluble polymer is selected from the group consisting of carboxymethylcellulose salt, starch, polyvinyl alcohol, and xanthan gum, and the crosslinking agent is selected from the group consisting of acid, polyamide epoxy, polyacrylamide, titanium alkoxide, and glyoxal. Preferably, the water-soluble polymer is a carboxymethylcellulose salt and the crosslinking agent is an acid.

[0018] Carboxymethyl cellulose salt is a derivative of cellulose. In carboxymethyl cellulose where a part of the hydroxy groups of the glucopyranose monomers constituting the cellulose skeleton has hydrogen (-H) substituted with a carboxymethyl group (-CH2COOH), it refers to a substance in which the hydrogen ion at the end of this carboxymethyl group is substituted with a metal ion. Examples of this metal ion include sodium ion and potassium ion. For example, sodium carboxymethyl cellulose represented by the structural formula of the following formula (1) can be cited as an example of carboxymethyl cellulose salt.

[0019]

Chemical formula

[0020] The acid may be either an organic acid or an inorganic acid. When the sodium ion of sodium carboxymethyl cellulose is substituted with an acid, it becomes acid-type carboxymethyl cellulose and is insolubilized to suppress moisture absorption.

[0021] The powder in this embodiment is at least one of a extender and a pigment.

[0022] The extender is not particularly limited as long as it is used in conventional non-fired pencil leads, and any of them can be used. For example, white extenders such as boron nitride, kaolin, talc, mica, calcium carbonate, etc., and depending on the hue of the solid drawing material, colored extenders can also be used, and of course mixtures of several of these can also be used. Particularly preferably, boron nitride, kaolin, and talc can be cited from their physical properties and shapes.

[0023] Examples of pigments include, for example, titanium oxide, iron black, carbon black, ultramarine blue, ultramarine, Blue No. 1, bengara, iron oxide yellow, chromium oxide, chromium hydroxide, zinc oxide, zirconium oxide, cobalt oxide, fish scale foil, bismuth oxychloride, mica titanium, Blue No. 2, Blue No. 404, Red No. 2, Red No. 3, Red No. 102, Red No. 104, Red No. 105, Red No. 106, DPP red, Yellow No. 4, Yellow No. 5, Green No. 3, and other pigments. These can be used alone or in combination of two or more.

[0024] The acid in this embodiment may be either an inorganic acid or an organic acid, but an organic acid is more desirable.

[0025] Organic acids are a general term for organic compounds that exhibit acidity, and most of them are carboxylic acids such as formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, acrylic acid, etc. Among these carboxylic acids, unsaturated carboxylic acids such as acrylic acid, which have one or more double bonds in the hydrocarbon chain, are preferred as the organic acid in this aspect.

[0026] The above organic acid is preferably a polymer acid. That is, this polymer acid is a polymerized product of multiple molecules of unsaturated carboxylic acid monomers at the double bond portion among the above organic acids. For example, polyacrylic acid represented by the structural formula of Formula (2) below, in which acrylic acid (CH2=CHCOOH) is polymerized and the molecular weight is about 25000, can be mentioned.

[0027] [-CH2CH(COOH)-] n ···Formula (2)

[0028] Here, the molecular weight of the polymer acid is not particularly limited, but it is preferably 5000 or more and 1000000 or less. When the sodium ions of the individual monomers constituting the carboxymethylcellulose acid salt are substituted with an acid due to the molecular weight being 5000 or more, the polymers are crosslinked at many locations, and the stability of the bond is improved. On the other hand, when the molecular weight is 1000000 or less, it becomes easy to mix with the powder.

[0029] The above-mentioned non-fired pencil lead can be manufactured by the following manufacturing method. Specifically, the method includes the steps of preparing a mixture of carboxymethylcellulose salt, acid, and powder, and molding the mixture into a lead body, wherein in the molding step, the carboxymethylcellulose salt and the acid are reacted to form a crosslink.

[0030] For example, a mixture is prepared by kneading a carboxymethylcellulose salt, an acid, and a powder. A solvent may be added as needed. The mixture obtained is extruded into the shape of a pencil lead using a plunger-type or screw-type extruder. If a solvent is used, it is then removed by drying (approximately 40°C, 24 hours). This molding process yields a non-fired pencil lead 10 having a roughly cylindrical core body 11, as shown in Figure 1. The molded core body is porous, having pores derived from the microscopic structure of the powder. These pores may be left as they are, or they may be heated at 60-80°C for 12 hours and then impregnated with oils and / or waxes as needed. As a solvent, a lower alcohol such as methanol or ethanol, or water may be used.

[0031] Suitable oils and fats include oils that are liquid at room temperature, such as liquid paraffin, spindle oil, silicone oil, α-olefin oligomer, and squalane. Among these, silicone oil is particularly good, with examples including dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil, cyclic dimethyl silicone oil, polyether-modified silicone oil, methyl styryl-modified silicone oil, and alkyl-modified silicone oil.

[0032] In addition to the above, various water-soluble organic polymer binders such as polyvinyl alcohol and methylcellulose can be used as auxiliary binders. Furthermore, in addition to the above components, cellulose may also be included.

[0033] By using the manufacturing method described above, a non-fired pencil lead is produced by kneading and molding at least a carboxymethylcellulose salt, an acid, and a powder, thereby suppressing the deterioration of strength due to moisture absorption and producing a non-fired pencil lead with erasability. In addition, it is possible to achieve both improved line density and improved fixation. [Examples]

[0034] The following describes each example and comparative example. In each of the following examples and comparative examples, CSP (Nippon Graphite) was used as graphite, and Highmicron HE5 (Takehara Chemical Industry) was used as talc.

[0035] [A] Examples 1 to 9 (1) Raw materials The raw materials for the non-fired pencil leads of Examples 1 to 9 and Comparative Examples 1 and 2 had the following composition.

[0036] (1-1) Example 1 In Example 1, the powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. The content of sodium carboxymethylcellulose salt (Sunrose F20LC, Nippon Paper Industries) relative to the total amount was 8% by mass. The content of polyacrylic acid (Aqualic HL-415, Nippon Shokubai) as the acid relative to the total amount was also 8% by mass. The 1% viscosity of Sunrose F20LC at 25°C was 150-250 mPa·m, and the degree of etherification was 0.55-0.65.

[0037] (1-2) Example 2 In Example 2, the powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. The content of sodium carboxymethylcellulose salt (Sunrose F10MC, Nippon Paper Industries) relative to the total amount was 8% by mass. The content of polyacrylic acid (Aqualic HL-415, Nippon Shokubai) as an acid relative to the total amount was also 8% by mass. The 1% viscosity of Sunrose F10MC at 25°C was 50-150 mPa·m, and the degree of etherification was 0.65-0.75.

[0038] (1-3) Example 3 In Example 3, the powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. The content of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 8% by mass. The content of polyacrylic acid (Aqualic HL-415, Nippon Shokubai) as the acid relative to the total amount was also 8% by mass. The 1% viscosity of Sunrose F30MC at 25°C was 250-350 mPa·m, and the degree of etherification was 0.65-0.75.

[0039] (1-4) Example 4 In Example 4, the powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. The content of sodium carboxymethylcellulose salt (Sunrose F120MC, Nippon Paper Industries) relative to the total amount was 8% by mass. The content of polyacrylic acid (Aqualic HL-415, Nippon Shokubai) as the acid relative to the total amount was also 8% by mass. The 1% viscosity of Sunrose F120MC at 25°C was 850-1,200 mPa·m, and the degree of etherification was 0.65-0.75.

[0040] (1-5) Example 5 In Example 5, the powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. The content of sodium carboxymethylcellulose salt (Sunrose F20HC, Nippon Paper Industries) relative to the total amount was 8% by mass. The content of polyacrylic acid (Aqualic HL-415, Nippon Shokubai) as the acid relative to the total amount was also 8% by mass. The 1% viscosity of Sunrose F20HC at 25°C was 150-250 mPa·m, and the degree of etherification was 0.80-1.00.

[0041] (1-6) Example 6 In Example 6, the powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. The content of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 8% by mass. Furthermore, the content of polyacrylic acid (Aqualic AS-58, Nippon Shokubai) as the acid relative to the total amount was also 8% by mass.

[0042] (1-7) Example 7 In Example 7, the powder content relative to the total amount was 70% by mass of graphite and 20% by mass of talc. The content of sodium carboxymethylcellulose salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 5% by mass. The content of citric acid as an acid relative to the total amount was also 5% by mass.

[0043] (1-8) Example 8 In Example 8, the powder content relative to the total amount was 70% by mass of graphite and 20% by mass of talc. The content of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 5% by mass. The content of oxalic acid as an acid relative to the total amount was also 5% by mass.

[0044] (1-9) Example 9 In Example 9, the powder content relative to the total amount was 70% by mass of graphite and 20% by mass of talc. The content of sodium carboxymethylcellulose salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 5% by mass. The content of hydrochloric acid as the acid relative to the total amount was also 5% by mass.

[0045] (1-10) Comparative Example 1 The powder content relative to the total amount was 70% by mass of graphite and 22% by mass of talc. The content of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 5% by mass. Note that no acid was included in Comparative Example 1.

[0046] (1-11) Comparative Example 2 The powder content relative to the total amount was 70% by mass of graphite and 14% by mass of talc. In addition, the content of sodium carboxymethylcellulose salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 5% by mass. In Comparative Example 2, sodium polyacrylate (Aqualic DL-522) was used instead of acid, and its content relative to the total amount was 8% by mass.

[0047] (2) Manufacturing of non-fired pencil lead After kneading the raw materials for each of the above Examples 1 to 9 and Comparative Examples 1 and 2, they were extruded into the shape of a pencil lead using a plunger-type or screw-type extruder to obtain non-fired pencil leads.

[0048] (3) Measurement of bending strength The bending strength of the unfired pencil leads of Examples 1 to 9 and Comparative Examples 1 and 2 described above was measured. Specifically, for each unfired pencil lead, the bending strength at three points was measured at a temperature of 23°C with a support distance of 40 mm, and the pressure at which it broke (unit: MPa) was determined. Measurements were taken twice: immediately after manufacturing and after 72 hours after manufacturing, when left in an environment of 35°C and 80% humidity. The results are shown in Table 1 below. In Table 1 below, the "strength reduction rate" is the value Z (%) calculated by the following formula (3), where X is the bending strength immediately after manufacturing and Y is the bending strength 3 days after manufacturing.

[0049] Z=(XY) / X×100...Equation (3)

[0050] [Table 1]

[0051] First, in Comparative Example 1, which did not use acid as a raw material, the strength reduction rate was 57.7%, resulting in a strength that was less than half of the bending strength immediately after manufacturing. Furthermore, in Comparative Example 2, which used salt (sodium polyacrylate) instead of acid as a raw material, the strength reduction rate was even more significant at 83.5%.

[0052] In contrast, the non-fired pencil leads in Examples 1 to 9 all showed a lower rate of strength reduction than the comparative examples. In particular, Example 5 had a strength reduction rate of 7.0%, maintaining almost the same bending strength as immediately after manufacturing.

[0053] Based on the above results, it is presumed that in Examples 1 to 9, the carboxymethylcellulose salt was insoluble by the acid, becoming acid-type carboxymethylcellulose, thereby suppressing its reaction with moisture in the air. Furthermore, when a polymeric acid was used as the acid (Examples 1 to 5), it is presumed that in addition to the insolubilization of the carboxymethylcellulose salt by the acid, the acid-type carboxymethylcellulose was stabilized by crosslinking with the linear portion of the polymer.

[0054] [B] Examples 10 to 18 (4) Raw materials The raw materials for the non-fired pencil leads of Examples 10 to 18 and Comparative Examples 3 to 5 had the following compositions. The mass percentages shown below represent the content relative to the total amount.

[0055] (4-1) Example 10 Example 10 had a composition containing 60% by mass of graphite as powder, 5% by mass of starch (NSP-EA, Nippon Denko Co., Ltd.; the same applies hereinafter) and 5% by mass of polyvinyl alcohol (PVA-105, Kuraray Co., Ltd.; the same applies hereinafter) as water-soluble polymers, 5% by mass of polyacrylic acid (Aqualic HL-415, Nippon Shokubai Co., Ltd.; the same applies hereinafter) as a high-molecular-weight organic acid as a crosslinking agent, and 25% by mass of carbon black (MA-100, Mitsubishi Chemical Corporation; the same applies hereinafter) as a pigment.

[0056] (4-2) Example 11 Example 11 contained 48% by mass of graphite as a powder, 4% by mass of polyvinyl alcohol and 4% by mass of xanthan gum (Echo Gum, Gokyo Food & Chemical) as water-soluble polymers, and 4% by mass of polyacrylic acid as a crosslinking agent. In addition, it contained 35% by mass of carbon black as a pigment and 5% by mass of stearic acid soap (LI-ST, Nitto Chemical Industries; the same applies hereinafter) as a metal soap.

[0057] (4-3) Example 12 Example 12 had a composition containing 47% by mass of graphite as powder, 6% by mass of starch and 6% by mass of polyvinyl alcohol as water-soluble polymers, 6% by mass of polyamide epoxy (Smirez Resin 650, Taoka Chemical Industry) as a crosslinking agent, and 35% by mass of carbon black as a pigment.

[0058] (4-4) Example 13 Example 13 had a composition containing 45% by mass of graphite and 10% by mass of talc as powder, 3% by mass of sodium carboxymethylcellulose salt (Sunrose F30MC, Nippon Paper Industries) as a water-soluble polymer, 4% by mass of starch and 4% by mass of polyvinyl alcohol, 4% by mass of polyacrylic acid as a crosslinking agent, and 30% by mass of carbon black as a pigment.

[0059] (4-5) Example 14 Example 14 contained 45% by mass of graphite and 10% by mass of talc as powders, 1% by mass of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) as a water-soluble polymer, 4% by mass of starch and 4% by mass of polyvinyl alcohol, and 4% by mass of polyacrylic acid as a crosslinking agent. In addition, it contained 30% by mass of carbon black and 2% by mass of cellulose nanofiber (TC-02X, Nippon Paper Industries) as pigments.

[0060] (4-6) Example 15 Example 15 contained 45% by mass of graphite and 10% by mass of talc as powders, 1% by mass of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) as a water-soluble polymer, 4% by mass of starch and 4% by mass of polyvinyl alcohol, and 4% by mass of polyacrylic acid as a crosslinking agent. In addition, it contained 30% by mass of carbon black and 2% by mass of cellulose powder (KC Floc W-400G, Nippon Paper Industries) as pigments.

[0061] (4-7) Example 16 Example 16 contained 47% by mass of graphite as powder, 6% by mass of starch and 6% by mass of polyvinyl alcohol as water-soluble polymers, 6% by mass of polyacrylamide (Hermid PY, Harima Chemicals) as a crosslinking agent, and also contained 30% by mass of carbon black and 5% by mass of stearic acid soap as a metal soap.

[0062] (4-8) Example 17 Example 17 contained 50% by mass of graphite and 6% by mass of talc as powders, 2% by mass of sodium carboxymethylcellulose salt (Sunrose F30MC, Nippon Paper Industries) as a water-soluble polymer, 5% by mass of starch and 5% by mass of polyvinyl alcohol, and 2% by mass of titanium alkoxide (Orgatic TA-10, Matsumoto Fine Chemicals) as a crosslinking agent, and also contained 30% by mass of carbon black as a pigment.

[0063] (4-9) Example 18 Example 18 contained 50% by mass of graphite and 6% by mass of talc as powders, 2% by mass of sodium carboxymethylcellulose salt (Sunrose F30MC, Nippon Paper Industries) as a water-soluble polymer, 5% by mass of starch and 5% by mass of polyvinyl alcohol, and 2% by mass of glyoxal (reagent, Fujifilm Wako Pure Chemical Industries) as a crosslinking agent, and also contained 30% by mass of carbon black as a pigment.

[0064] (4-10) Comparative Example 3 Comparative Example 3 had a composition containing 60% by mass of graphite and 10% by mass of talc as powder, 5% by mass of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) as a water-soluble polymer, and 25% by mass of carbon black as a pigment.

[0065] (4-11) Comparative Example 4 Comparative Example 4 consists of 60% by mass of graphite and 10% by mass of talc as powders, and a crosslinking agent. Tepo The composition contains 5% by mass of acrylic acid and 25% by mass of carbon black as a pigment.

[0066] (4-12) Comparative Example 5 Comparative Example 5 had a composition containing 55% by mass of graphite and 10% by mass of talc as powders, 5% by mass of starch and 5% by mass of polyvinyl alcohol as water-soluble polymers, and 25% by mass of carbon black as a pigment.

[0067] (5) Manufacturing of non-fired pencil lead After kneading the raw materials for each of the above Examples 10 to 18 and Comparative Examples 3 to 5, they were extruded into the shape of a pencil lead using a plunger-type or screw-type extruder to obtain non-fired pencil leads.

[0068] (6) Measurement of bending strength The bending strength of the non-fired pencil leads of each of the above Examples 10 to 18 and Comparative Examples 3 to 5 was measured in the same manner as in (3) above. The results are shown in Table 2 below.

[0069] [Table 2]

[0070] First, in Comparative Example 3, which did not contain a crosslinking agent as a raw material, the strength reduction rate was 52.5%, resulting in a strength that was less than half of the bending strength immediately after manufacturing. Similarly, in Comparative Example 5, which also did not contain a crosslinking agent, the strength reduction rate was 30.0%, resulting in a strength that was reduced to 70% of the bending strength immediately after manufacturing. Furthermore, in Comparative Example 4, which did not contain a water-soluble polymer as a raw material, the strength reduction rate was 66.9%, resulting in a strength that was reduced to about 30% of the bending strength immediately after manufacturing.

[0071] In contrast, the non-fired pencil leads of Examples 10 to 18 all showed significantly lower strength reduction rates than the comparative examples. 11 The strength reduction rate was 0.3%, meaning it maintained almost the same bending strength as immediately after manufacturing.

[0072] Based on the above results, it is presumed that in Examples 10 to 18, the water-soluble polymer was insolubilized by the crosslinking agent, thereby suppressing its reaction with moisture in the air and thus preventing a decrease in strength. Furthermore, when a polymeric organic acid was used as the acid (Examples 10, 11, and 13 to 15), it is presumed that the water-soluble polymer was stabilized not only by the insolubilization of the water-soluble polymer by the acid, but also by crosslinking with the linear portion of the polymer.

[0073] (7) Tip strength The lead tip shape was determined by sharpening the lead into a cone shape at an angle of 17±1°, and then creating a 0.6±0.1mm cone-shaped base to ensure the tip shape was not irregular. The pencil shaft with the tip shaped in this way was held at 60° using a special fixing jig. A load was then applied at a speed of 10 mm / min, and the load at which the tip broke was measured and defined as the tip strength value. If the load decreased rapidly by 0.7N or more, it was determined that the lead had broken.

[0074] (8) Amount of mechanical writing wear A record-type mechanical writing measurement was performed according to JIS S 6006 8.7 writing density, and the amount of mechanical writing wear of non-fired lead was calculated.

[0075] (9) Line density The density of the drawing lines was measured using a colorimeter in accordance with the method specified in JIS S 6006 8.7 Writing Density.

[0076] (10) Results The measurement results for tip strength, mechanical writing wear, and line density are shown in Table 3 below.

[0077] [Table 3]

[0078] The results shown in Table 3 above indicate that each example's formulation achieves practically acceptable tip strength, writing quality, and line density. [Industrial applicability]

[0079] This invention can be used as a non-fired pencil lead.

Claims

1. A porous, non-fired pencil lead containing a water-soluble polymer reacted with a crosslinking agent, and a powder, and free of wax, The water-soluble polymer is selected from the group consisting of carboxymethylcellulose salt, starch, polyvinyl alcohol, and xanthan gum. The aforementioned crosslinking agent is selected from the group consisting of acids, polyamide epoxy, polyacrylamide, titanium alkoxide, and glyoxal, resulting in a porous, non-fired pencil lead.

2. The porous, non-fired pencil lead according to claim 1, characterized in that the water-soluble polymer is a carboxymethylcellulose salt and the crosslinking agent is an acid.

3. The porous, non-fired pencil lead according to claim 2, characterized in that the acid is an organic acid.

4. The porous, non-fired pencil lead according to claim 3, characterized in that the organic acid is a polymer acid.

5. The porous, non-fired pencil lead according to any one of claims 1 to 4, characterized in that the powder is at least one of a filler material and a pigment.

6. A porous, non-fired pencil lead according to any one of claims 1 to 5, further characterized by containing cellulose.

7. A step of preparing a mixture of a water-soluble polymer, a crosslinking agent which is an acid, and a powder without adding wax, The process includes molding the mixture into a core, A method for producing a porous, non-fired pencil lead, characterized in that, in the molding step, the water-soluble polymer and the crosslinking agent are reacted to form a crosslink.

8. The method for producing a porous, non-fired pencil lead according to claim 7, characterized in that the water-soluble polymer is a carboxymethylcellulose salt and the crosslinking agent is a polymeric acid with a molecular weight of 5,000 to 1,000,000.

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