Non-fired pencil lead and method for manufacturing the same

Abstract

This invention provides a non-fired pencil lead that offers sufficient writing strength even when the tip is sharpened, is less susceptible to deterioration due to moisture absorption, is erasable, and simultaneously achieves improved opacity and fixation of the written line—qualities not achievable with conventional methods. [Solution] A non-fired pencil lead characterized by containing a carboxymethylcellulose salt, a high-molecular-weight organic acid, and a powder.

Description

[Technical Field]

[0001] This invention relates to a non-fired pencil lead with a writing surface that is black to dark in color. [Background technology]

[0002] Conventionally, it has been known that for displays intended for visually impaired persons such as those with low vision, white text on a black background is more effective than the usual display of black text on a white background (Patent Document 1). Furthermore, an image receiving device that converts images to grayscale display for colorblind individuals has been disclosed (Patent Document 2). These types of displays are known to be gentle and effective not only for visually impaired people but also for the general public with normal vision.

[0003] The applicant has been conducting research and development on writing instruments that can make such markings by hand on black or dark-colored notebooks. In an attempt to produce white or gray colored leads, for example, it is possible to produce a general white or gray colored lead by forming the lead body by extrusion molding after mixing and dispersing castor wax, titanium dioxide whiskers, talc, etc. With general colored pencil leads that have been sold in the past, although it is possible to draw white lines, they do not slide well on the writing surface and have high writing resistance when worn down, so it is not possible to write sufficiently on black or dark-colored notebooks. When writing thin, dark letters, the tip of the lead body does not have sufficient strength, so the tip frequently breaks.

[0004] Furthermore, since the aforementioned general colored leads cannot be erased with an eraser, the applicant has also been conducting research and development on erasable colored leads manufactured by firing. A lead body mainly composed of boron nitride can be obtained by kneading boron nitride powder with a binder such as polyvinyl chloride resin, extruding it into a wire, firing it in a nitrogen atmosphere, and impregnating it with oil (Patent Document 4). This document describes the case in which carbon black is used for hue adjustment along with boron nitride and graphite. In that case, it is described that spherical carbon black is sandwiched between plate-like particles such as boron nitride and graphite, resulting in a lead body with low bending strength and poor writing performance.

[0005] Therefore, the applicant has developed and completed a non-fired pencil lead that is erasable while simultaneously improving the density and fixation of the written line (Patent Document 5). The invention is a non-fired pencil lead characterized by comprising 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. In this invention, a very large amount of graphite and binder material is added. However, this document does not disclose that by blending multiple types of white powder, a lead can be obtained that has sufficient opacity (density) and erasability when writing on a black or dark colored writing surface, while also having tip strength that is less likely to break even when strong writing pressure is applied. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Utility Model Registration No. 3178191 (Abstract, Claims for Utility Model Registration, Detailed Description of the Invention) [Patent Document 2] Japanese Patent Publication No. 2009-15438 (Abstract, Claims, Detailed Description of the Invention) [Patent Document 3] Japanese Patent Publication No. 3-106976 (Examples, etc.) [Patent Document 4] Japanese Patent Publication No. 7-258594 (Claims, Summary of Invention) [Patent Document 5] International Publication WO2022 / 264643A1 (Abstract, Claims, Detailed Description of the Invention) [Overview of the project] [Problems that the invention aims to solve]

[0007] Each embodiment of this application aims to provide a non-fired pencil lead that has sufficient writing strength even when the tip is sharpened, exhibits minimal deterioration due to moisture absorption, is erasable, and simultaneously achieves improved opacity of the written line even when writing on a black or dark-colored writing surface, which could not be achieved by conventional methods. [Means for solving the problem]

[0008] The non-fired pencil lead of the first embodiment of the present application is characterized by comprising a water-soluble resin containing a carboxymethylcellulose salt, an acid, and a white powder.

[0009] The non-fired pencil lead of the second embodiment of the present application is characterized in that, in addition to the configuration of the first embodiment, the white powder is both a filler and a pigment.

[0010] Furthermore, it is preferable that the non-fired pencil lead of the present invention is characterized in that the acid is an organic acid. Furthermore, it is preferable that the non-fired pencil lead of the present invention is characterized in that the organic acid is a polymer acid.

[0011] The third aspect of the present invention, a non-fired pencil lead, is characterized in that, in addition to the configuration of the first aspect, the molded lead body is porous.

[0012] The non-fired pencil lead of the fourth aspect of the present application is characterized by being impregnated with oil, in addition to the configuration of the third aspect.

[0013] The non-fired pencil lead of the fifth aspect of the present application is characterized in that, in addition to the configuration of the second aspect, the extender contains boron nitride.

[0014] The non-fired pencil lead of the sixth aspect of the present application is characterized in that, in addition to the configuration of the fifth aspect, the extender further contains graphite.

[0015] The non-fired pencil lead of the seventh aspect of the present application is characterized in that, in addition to the configuration of the second aspect, the pigment contains titanium oxide or carbon black.

[0016] The method for manufacturing the non-fired pencil lead of the eighth aspect of the present application includes a step of preparing a mixture of a water-soluble resin containing carboxymethylcellulose salt, an acid, and a white powder, and a step of molding the mixture onto a core body. In the molding step, the water-soluble resin containing carboxymethylcellulose salt is reacted with the acid to cause crosslinking.

Advantages of the Invention

[0017] Since each embodiment of the present application is configured as described above, it is possible to provide a non-fired pencil lead that has sufficient strength during writing even when the tip is sharpened, has little deterioration due to moisture absorption, has erasability, and achieves both improved concealment of the writing line even when writing on a black or dark writing surface, which could not be obtained by conventional methods.

Brief Description of the Drawings

[0018] [Figure 1] It is a perspective view schematically showing the appearance of the non-fired pencil lead of the embodiment.

Modes for Carrying Out the Invention

[0019] The non-fired pencil lead of the embodiment of the present application contains a water-soluble resin containing carboxymethylcellulose salt, an acid, and a white powder.

[0020] Carboxymethylcellulose salts are derivatives of cellulose in which a hydrogen atom (-H) in some of the hydroxyl groups of the glucopyranose monomer that constitutes the cellulose backbone is replaced with a carboxymethyl group (-CH2COOH), and the terminal hydrogen ion of this carboxymethyl group is replaced with a metal ion. Examples of such metal ions include sodium ions and potassium ions. For example, sodium carboxymethylcellulose, represented by the structural formula of formula (1) below, is an example of a carboxymethylcellulose salt. Examples of water-soluble resins include starch, polyvinyl alcohol, and polyvinyl acetate.

[0021] [ka]

[0022] The acid can be either an organic or inorganic acid. When the sodium ions of carboxymethylcellulose sodium are replaced by the acid, it becomes acid-type carboxymethylcellulose, which becomes insoluble and suppresses moisture absorption.

[0023] In this embodiment, the white powder is both a filler and a pigment.

[0024] As for the binder material, there are no particular limitations as long as it is the same as that used in conventional non-fired pencil leads, and any of them can be used. For example, white binder materials such as boron nitride, kaolin, talc, mica, and calcium carbonate can be used, and depending on the hue of the solid drawing material, colored binder materials such as graphite can also be used, and of course mixtures of several of these can also be used. Particularly preferred are boron nitride, kaolin, talc, and graphite, due to their physical properties and shape.

[0025] Examples of pigments include titanium dioxide, iron black, carbon black, Prussian blue, ultramarine blue, Blue No. 1, red iron oxide, yellow iron oxide, chromium oxide, chromium hydroxide, zinc oxide, zirconium oxide, cobalt oxide, fish scale foil, bismuth oxychloride, titanium mica, 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, etc. These can be used individually or in mixtures of two or more.

[0026] The acid in this embodiment may be either an inorganic acid or an organic acid, but an organic acid is more preferable.

[0027] 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, and acrylic acid. In this embodiment, among these carboxylic acids, unsaturated carboxylic acids such as acrylic acid, which have one or more double bonds in their hydrocarbon chain, are preferred as organic acids.

[0028] The organic acid described above is preferably a polymeric acid. That is, this polymeric acid is formed by the polymerization of multiple unsaturated carboxylic acid monomers at the double bond portion of the organic acid described above. For example, polyacrylic acid, represented by the structural formula of formula 2 below, is formed by the polymerization of acrylic acid (CH2=CHCOOH) to a molecular weight of approximately 25,000.

[0029] [-CH2CH(COOH)-]n...Formula (2)

[0030] Here, there are no particular limitations on the molecular weight of the polymeric acid, but it is desirable that it be between 5,000 and 1,000,000. When the molecular weight is 5,000 or more, when the sodium ions of the individual monomers constituting the carboxymethylcellulose salt are substituted with the acid, the polymers are cross-linked at many points, improving the stability of the bond. On the other hand, when the molecular weight is 1,000,000 or less, mixing with powders becomes easier.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] In addition to the above, various water-soluble organic polymer binders such as polyvinyl alcohol and methylcellulose can also be used as auxiliary binders.

[0035] By using the manufacturing method described above, a non-fired pencil lead is produced by kneading and molding a water-soluble resin containing 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 simultaneously improve the opacity of the writing line on black or dark-colored writing surfaces.

[0036] The white or gray non-fired pencil lead produced in this way has a lightness (L) of the lines drawn on white paper. * w) and the brightness of the lines drawn on black paper (L * The difference from (b) is very small, and even when writing on black paper, it completely conceals and maintains brightness, so even when writing on a black writing surface, the difference in brightness due to the increase or decrease in black pigment is easily noticeable. ΔL * =L * wL * b Of course, the black writing surface (L * On page 28), writing with the white, non-fired pencil lead of the present invention will produce clear and eye-friendly characters. [Examples]

[0037] (1) Raw materials The raw materials for the non-fired pencil lead in each example and comparative example had the following composition.

[0038] (1-1) Example 1 In Example 1, the powder content relative to the total amount was 20% by mass of boron nitride and 48% by mass of talc. Titanium dioxide was used as the pigment at 20% by mass. Furthermore, the content of carboxymethylcellulose sodium salt (Sunrose F20LC, Nippon Paper Industries) was 3% by mass, similarly, starch was 3% by mass, and polyvinyl alcohol (PVA) was 3% by mass. Additionally, polyacrylic acid (Aqualic HL-415, Nippon Shokubai) was used as the acid at 3% by mass.

[0039] (1-2) Example 2 The powder content of Example 2 was the same as in Example 1, except that boron nitride was 15% by mass and graphite was added separately at 5% by mass.

[0040] (1-3) Example 3 The powder content of Example 3 was formulated in the same manner as in Example 1, except that boron nitride was 10% by mass and graphite was added separately at 10% by mass.

[0041] (1-4) Example 4 The powder content of Example 4 was formulated in the same manner as in Example 1, except that boron nitride was 5% by mass and graphite was added separately at 15% by mass.

[0042] (1-5) Example 5 The powder content in Example 5 was the same as in Example 1, except that boron nitride was not included (0% by mass) and graphite was included at 20% by mass.

[0043] (1-6) Comparative Example 1 The powder content relative to the total amount was 50% by mass of talc and 20% by mass of titanium dioxide. In addition, the content of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries) relative to the total amount was 5% by mass. In Comparative Example 1, no acid was included, and the mixed wax was 25% by mass.

[0044] (1-7) Comparative Example 2 The powder content relative to the total amount was 70% by mass of talc. In addition, 30% by mass of clay was added.

[0045] (2) Manufacturing of non-fired pencil lead After kneading the raw materials for each of the above Examples 1 to 5 and Comparative Examples 1 and 2, they were extruded into the shape of a pencil lead using a plunger-type or screw-type extruder. Silicone oil was then impregnated into the unfired pencil lead by 12 parts by weight for Examples 1 to 5 and 10 parts by weight for Comparative Example 2, per 100 parts by weight of the unfired lead body. No silicone oil was impregnated into Comparative Example 1.

[0046] (3) Measurement of tip strength (φ0.6) The tip strength was measured for each of the non-fired pencil leads in Examples 1 to 5 and Comparative Examples 1 and 2 described above. Specifically, for each non-fired pencil lead, the tip shape was corrected by sharpening the lead into a cone shape at an angle of 17±1°, and then forming a 0.6±0.1mm cone-shaped base, ensuring that 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 chipped was measured and defined as the tip strength value.

[0047] (4) Measurement 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.

[0048] (5) Measurement of the coefficient of dynamic friction The coefficient of dynamic friction between the pencil lead and the writing surface during writing was measured. Specifically, the tip of a non-fired pencil lead, mounted on a regular pencil's wooden shaft, was sharpened to a conical shape at an angle of 17±1°, and then the tip was sharpened to a circle with a diameter of 0.6±0.1 mm, resulting in an overall frustoconical shape. The pencil shaft with the tip shaped in this way was held at a 60° angle with the tip facing downwards using a special fixing jig, and then fixed to a dynamic friction measuring machine (TRIBOGEAR, Shinto Kagaku). In this state, a load of 300g was applied, and the coefficient of dynamic friction was measured when writing at a speed of 10 mm / sec.

[0049] (6) Brightness measurement For each example and each comparative example, hand-drawn lines and machine-drawn lines were measured using a colorimeter (SC-P, Suga Test Instruments Co., Ltd.).

[0050] (7) 60° gloss measurement For each example and comparative example, the glossiness at 60° was measured for both hand-drawn and machine-drawn lines using a UGV-5 digital angle-shifting gloss meter (manufactured by Suga Test Instruments Co., Ltd.).

[0051] (8) Measurement of opacity (black drawing paper) The solid drawing materials obtained in each of the above examples and comparative examples were each used as they were to fill in a black drawing paper with a size of 50 mm × 50 mm vertically and horizontally, and the state of the writing surface at that time was evaluated according to the following four evaluation criteria: ◎, ○, △, and ✕. Evaluation criteria: ◎: The black color of the base is completely concealed and cannot be seen. ○: The black color of the base is almost concealed and cannot be seen unless one pays attention. △: The black color of the base can be seen faintly. ✕: The black color of the base can be clearly seen.

[0052] (9) Measurement of character erasability (According to the test of writing density specified in JIS S 6005:2007, a ruled line was written. Specifically, a non-fired pencil lead was set in a line drawing machine, and on a Kent paper with a basis weight of 128 ± 5 g / m 2 of black a ruled line was written under the conditions of a writing load of 2.94 N (300 g weight), a writing angle of 75°, a writing speed of 50 mm / second, and a writing distance of 6 m. For this ruled line, first, the value measured with a densitometer (PDA-65, Konica Minolta) was taken as the pre-erasure ruled line density (D0). Next, after applying a load of 11.76 N (1,200 g weight) to this ruled line with a rubber eraser piece and rubbing it back and forth 4 times, the value measured with the above densitometer was taken as the post-erasure ruled line density (D1). Then, the rubber eraser erasure rate (E R ) was obtained by the following formula. E R (%) = (D1 - D0) / D1 × 100 ◎: 90% or more ○: 80% or more and less than 90% △: 30% or more and less than 80% ✕: Less than 30%

[0053]

Table 1

[0054] In contrast, all of the non-fired pencil leads in the examples showed high tip strength values. Furthermore, the values ​​for wear rate, dynamic friction coefficient, brightness, and gloss were good, resulting in high opacity in all cases. Additionally, all exhibited good eraserability.

[0055] Thus, the non-fired pencil lead of the present invention can contain a large amount of pigment and white filler material, allowing for easy adjustment of the hue from white to gray while maintaining high opacity. Because it is non-fired, these hues do not change, and even when writing on a black or dark-colored writing surface, it can draw clear, eye-friendly lines while maintaining high opacity and line brightness, and the lines have good erasability. [Industrial applicability]

[0056] This invention can be used as a non-fired pencil lead for writing on writing surfaces such as black or dark-colored notebooks. It can also be used as a temporary correction tool, with the erased portion being removable with an eraser. [Explanation of symbols]

[0057] 10 Non-fired pencil lead 11 Lead body

Claims

1. A non-fired pencil lead characterized by containing a water-soluble resin containing a carboxymethylcellulose salt, a high-molecular-weight organic acid, and a white powder.

2. The non-fired pencil lead according to claim 1, characterized in that the white powder is both a filler and a pigment.

3. The non-fired pencil lead according to claim 1, characterized in that the core body after molding is porous.

4. The non-fired pencil lead according to claim 3, characterized by being impregnated with oil.

5. The non-fired pencil lead according to claim 2, characterized in that the aforementioned body material contains boron nitride.

6. The non-fired pencil lead according to claim 5, characterized in that the aforementioned body material further contains graphite.

7. The non-fired pencil lead according to claim 2, characterized in that the aforementioned pigment contains titanium dioxide or carbon black.

8. A step of preparing a mixture of a water-soluble resin containing a carboxymethylcellulose salt, a high-molecular-weight organic acid, and a white powder, and The process includes molding the mixture into a core, A method for producing a non-fired pencil lead according to claim 1, characterized in that, in the molding step, the water-soluble resin containing the carboxymethylcellulose salt is reacted with the acid to cause crosslinking.

Images