Non-baked pencil lead and method for producing same

Abstract

This non-baked pencil lead comprises a carboxymethyl cellulose salt, a polymeric organic acid, and a powder.

Description

Non-baked pencil lead and its manufacturing method

[0001] The present invention relates to a non-baked pencil lead for writing on a black to dark colored surface.

[0002] It has been known that white text on a black background is more effective than the usual black text on a white background when it comes to displays for people with visual impairments such as low vision (Utility Model Registration No. 3178191). Also, an image reception device that converts images into a grayscale display for color-blind people has been disclosed (Japanese Patent Laid-Open No. 2009-15438). It is known that such displays are gentle on the eyes and effective not only for the visually impaired but also for the general population with normal vision.

[0003] The present applicant has continued research and development into writing instruments that allow such markings to be handwritten on black or dark-colored notebooks. To produce a white or gray colored lead, for example, castor wax, titanium dioxide whiskers, talc, etc. are blended and dispersed, and then extrusion-molded to form a lead body, producing a typical white or gray colored lead (Japanese Patent Laid-Open Publication No. 3-106976). While typical colored pencil leads sold in the past are capable of drawing white lines, they are difficult to slide on the writing surface and experience high writing resistance as they wear, making them inadequate for writing adequately on black or dark-colored notebooks. When writing thin, dark characters, the tip of the lead lacks strength, resulting in frequent breakage.

[0004] Furthermore, because the aforementioned common colored leads cannot be erased with an eraser or the like, the present applicant has also conducted research and development into erasable colored leads manufactured by firing. Boron nitride powder is mixed with a binder such as vinyl chloride resin, extruded into a linear shape, fired in a nitrogen atmosphere, and then impregnated with oil to obtain a lead primarily composed of boron nitride (Japanese Patent Laid-Open Publication No. 7-258594). This publication describes the use of carbon black in conjunction with boron nitride and graphite to adjust the hue. It also describes the problem that in this case, spherical carbon black becomes sandwiched between plate-like particles of boron nitride or graphite, resulting in a lead with low bending strength and poor writing performance.

[0005] Therefore, the present applicant has developed and perfected a non-baked pencil lead that not only has erasability but also improves the density and fixability of written lines (WO 2022 / 264643 A1). The non-baked pencil lead is characterized by comprising a water-soluble polymer, a crosslinker, and a powder, the water-soluble polymer being selected from the group consisting of carboxymethylcellulose salt, starch, polyvinyl alcohol, and xanthan gum, and the crosslinker being selected from the group consisting of acid, polyamide epoxy, polyacrylamide, titanium alkoxide, and glyoxal. Here, a large amount of graphite and a filler material are added. However, this document does not disclose that a lead can be obtained by blending multiple types of white powder to achieve sufficient hiding power (density) and erasability when written on black or dark-colored surfaces, while also having tip strength that is less likely to break even when subjected to strong writing pressure.

[0006] The objective of each embodiment of the present application is to provide a non-baked pencil lead that has sufficient strength during writing even when the tip is sharpened, is less susceptible to deterioration due to moisture absorption, has erasability, and also provides improved concealment of written lines even when writing on black or dark-colored surfaces, something that could not be achieved by conventional methods.

[0007] The non-baked pencil lead of a first aspect of the present application is characterized by including a water-soluble resin containing a carboxymethyl cellulose salt, an acid, and a white powder.

[0008] A non-baked pencil lead according to a second aspect of the present application is characterized in that, in addition to the configuration of the first aspect, the white powder is both an extender and a pigment.

[0009] In addition, the non-baked pencil lead of the present application is preferably characterized in that the acid is an organic acid.In addition, the non-baked pencil lead of the present application is preferably characterized in that the organic acid is a polymeric acid.

[0010] The non-baked pencil lead of the third aspect of the present application is characterized in that, in addition to the configuration of the first aspect, the lead body after molding is porous.

[0011] The non-baked pencil lead of a fourth embodiment of the present application is characterized in that, in addition to the configuration of the third embodiment, it is impregnated with oil.

[0012] A non-baked pencil lead according to a fifth aspect of the present application is characterized in that, in addition to the configuration of the second aspect, the filler material contains boron nitride.

[0013] A sixth aspect of the present invention provides a non-baked pencil lead that, in addition to the configuration of the fifth aspect, further contains graphite in the filler material.

[0014] A seventh aspect of the present invention provides a non-baked pencil lead that, in addition to the configuration of the second aspect, is characterized in that the pigment contains titanium oxide or carbon black.

[0015] The eighth aspect of the present application provides a method for producing a non-baked pencil lead, which includes the steps of preparing a mixture of a water-soluble resin containing a carboxymethyl cellulose salt, an acid, and a white powder, and molding the mixture into a pencil lead, wherein the water-soluble resin containing a carboxymethyl cellulose salt and the acid are reacted with each other to crosslink the pencil lead during the molding step.

[0016] Since each embodiment of the present application is configured as described above, it is possible to provide a non-baked pencil lead that has sufficient strength when writing even when the tip is sharpened, is less susceptible to deterioration due to moisture absorption, has erasability, and also has improved concealment of written lines even when writing on black or dark-colored surfaces, something that could not be achieved by conventional methods.

[0017] FIG. 1 is a perspective view schematically illustrating the appearance of a non-baked pencil lead according to an embodiment.

[0018] The non-baked pencil lead of the present embodiment includes a water-soluble resin containing a carboxymethyl cellulose salt, an acid, and a white powder.

[0019] Carboxymethyl cellulose salts are derivatives of cellulose in which hydrogen (-H) is replaced by a carboxymethyl group (-CH) in some of the hydroxyl groups of the glucopyranose monomers that make up the cellulose backbone. ２This refers to carboxymethyl cellulose in which the hydrogen ion at the end of the carboxymethyl group is substituted with a metal ion. Examples of such metal ions include sodium ions and potassium ions. For example, sodium carboxymethyl cellulose represented by the structural formula (1) below is an example of a carboxymethyl cellulose salt. Examples of water-soluble resins include starch, polyvinyl alcohol, and polyvinyl acetate.

[0020]

[0021] The acid may be either an organic acid or an inorganic acid. When the sodium ions of sodium carboxymethylcellulose are substituted with an acid, the resulting carboxymethylcellulose becomes acid-type, insoluble, and is thus inhibited from absorbing moisture.

[0022] The white powder in this embodiment is both an extender and a pigment.

[0023] The filler may be any of those used in conventional non-baked pencil leads, and is not particularly limited. For example, white fillers such as boron nitride, kaolin, talc, mica, and calcium carbonate can be used, and depending on the hue of the solid drawing material, colored fillers such as graphite can also be used. Naturally, mixtures of several of these can also be used. In particular, boron nitride, kaolin, talc, and graphite are preferred due to their physical properties and shape.

[0024] Examples of pigments include titanium oxide, iron black, carbon black, Prussian blue, ultramarine, Blue No. 1, red iron oxide, yellow iron oxide, 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, and Green No. 3, and these can be used alone or in combination of two or more.

[0025] The acid in this embodiment may be either an inorganic acid or an organic acid, but is more preferably an organic acid.

[0026] Organic acid is 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, the organic acid in this embodiment is preferably an unsaturated carboxylic acid having one or more double bonds in the hydrocarbon chain, such as acrylic acid.

[0027] The organic acid is preferably a polymeric acid. That is, the polymeric acid is obtained by polymerizing a plurality of molecules of unsaturated carboxylic acid monomers from the organic acid at the double bond portion. For example, acrylic acid (CH ２ ═CHCOOH) is polymerized to have a molecular weight of about 25,000, and is represented by the following structural formula 2:

[0028] [-CH ２ CH(COOH)-] ｎ ...Formula (2)

[0029] Here, the molecular weight of the polymeric acid is not particularly limited, but is preferably 5,000 or more and 1,000,000 or less. When the molecular weight is 5,000 or more, when the sodium ions of the individual monomers constituting the carboxymethyl cellulose acid salt are substituted with the acid, the polymers are crosslinked at multiple sites, improving the stability of the bond. On the other hand, when the molecular weight is 1,000,000 or less, mixing with powder becomes easy.

[0030] The non-baked pencil lead can be produced by the following method, which includes the steps of preparing a mixture of a carboxymethyl cellulose salt, an acid, and a powder, and molding the mixture into a pencil lead, in which the carboxymethyl cellulose salt and the acid are reacted with each other to crosslink the pencil lead.

[0031] For example, a mixture is prepared by kneading a carboxymethyl cellulose salt, an acid, and a powder. A solvent can be added at this time, if necessary. The mixture obtained by this preparation is extruded into the shape of a pencil lead using a plunger-type or screw-type extruder. If a solvent is used, the solvent is then removed by drying (approximately 40°C, 24 hours). This molding process results in a non-baked pencil lead 10 having a roughly cylindrical core 11, as shown in Figure 1. The core after molding is porous, with pores derived from the microscopic structure of the powder. These pores may be left as they are, or may be heated at 60 to 80°C for 12 hours and then impregnated with oils, fats, and / or waxes, if necessary. The solvent used may be a lower alcohol such as methanol or ethanol, or water.

[0032] As the oils and fats, oily substances that are liquid at room temperature, such as liquid paraffin, spindle oil, silicone oil, α-olefin oligomer, squalane, etc. Of these, silicone oils are particularly preferable, and examples thereof include dimethyl silicone oil, methyl phenyl silicone oil, methyl hydrogen silicone oil, cyclic dimethyl silicone oil, polyether-modified silicone oil, methyl styryl-modified silicone oil, and alkyl-modified silicone oil.

[0033] In addition to the above, various water-soluble organic polymer binders such as polyvinyl alcohol and methyl cellulose can also be used as auxiliary binders.

[0034] By using the above-described manufacturing method, a non-baked pencil lead can be produced by kneading and molding a water-soluble resin containing a carboxymethyl cellulose salt, an acid, and a powder, thereby suppressing deterioration of strength due to moisture absorption and providing erasability.In addition, this method also improves the concealment of written lines on black or dark-colored surfaces.

[0035] The white to gray non-baked pencil lead thus produced is characterized by the lightness (L ＊ w) and the lightness (L ＊The difference with b) is very small, and even when written on black paper, it provides good concealment and maintains brightness, so even when written on a black surface, the difference in brightness due to an increase or decrease in the amount of black pigment is easily noticeable. ＊ =L ＊ W-L ＊ b Of course, the writing surface is black (L ＊ If you write on the paper (p. 28) with the white non-baked pencil lead of the present invention, you can display clear characters that are easy on the eyes.

[0036] (1) Raw Materials The raw materials for the non-baked pencil leads of each Example and Comparative Example had the following composition.

[0037] (1-1) Example 1 In Example 1, the powder contents relative to the total amount were 20% by mass of boron nitride and 48% by mass of talc. Titanium oxide was used as the pigment at 20% by mass. Furthermore, the contents of carboxymethylcellulose sodium salt (Sunrose F20LC, Nippon Paper Industries Co., Ltd.) relative to the total amount were 3% by mass, as were starch and polyvinyl alcohol (PVA) at 3% by mass. Furthermore, the contents of polyacrylic acid (Aqualic HL-415, Nippon Shokubai Co., Ltd.) relative to the total amount were 3% by mass.

[0038] (1-2) Example 2 The powder contents of Example 2 were the same as those of Example 1, except that boron nitride was 15 mass % and graphite was 5 mass % relative to the total amount.

[0039] (1-3) Example 3 The powder content of Example 3 was 10 mass % for boron nitride and 10 mass % for graphite, relative to the total amount, and the mixture was blended in the same manner as in Example 1, except that the powder content of Example 3 was 10 mass % for boron nitride and 10 mass % for graphite.

[0040] (1-4) Example 4 The powder contents of Example 4 were the same as those of Example 1, except that boron nitride was 5 mass % and graphite was 15 mass % relative to the total amount.

[0041] (1-5) Example 5 The powder content of Example 5 was the same as that of Example 1, except that boron nitride was not blended (0 mass %) and graphite was blended in an amount of 20 mass % relative to the total amount.

[0042] (1-6) Comparative Example 1 The powder contents relative to the total amount were 50% by mass for talc and 20% by mass for titanium oxide. The content of carboxymethylcellulose sodium salt (Sunrose F30MC, Nippon Paper Industries Co., Ltd.) relative to the total amount was 5% by mass. In Comparative Example 1, no acid was added, and the mixed wax was 25% by mass.

[0043] (1-7) Comparative Example 2 The powder content relative to the total amount was 70 mass % for talc and 30 mass % for clay.

[0044] (2) Production of non-baked pencil leads After kneading the raw materials of each of the above Examples 1 to 5 and Comparative Examples 1 and 2, the mixture was extruded into the shape of a pencil lead using a plunger or screw extruder, and 12 parts by weight of silicone oil was impregnated per 100 parts by weight of the non-baked lead in Examples 1 to 5, and 10 parts by weight in Comparative Example 2, to obtain non-baked pencil leads. No silicone oil was impregnated in Comparative Example 1.

[0045] (3) Tip Strength (φ0.6) Measurement The tip strength was measured for each of the non-baked pencil leads of Examples 1 to 5 and Comparative Examples 1 and 2. Specifically, for each non-baked pencil lead, the lead was sharpened into a cone with an angle of 17±1°, and the tip was then cut into a truncated cone of 0.6±0.1 mm, and it was confirmed that the tip shape was not distorted. The pencil shaft with the tip thus trimmed was held at 60° using a dedicated fixture. A load was then applied at a rate of 10 mm / min, and the load at which the tip chipped was measured and used as the tip strength value.

[0046] (4) Measurement of Amount of Abrasion Due to Mechanical Writing A record-type mechanical writing measurement specified in JIS S 6006 8.7 writing density was carried out, and the amount of abrasion due to mechanical writing of the non-baked lead was calculated.

[0047] (5) Measurement of Dynamic Friction Coefficient The dynamic friction coefficient between the writing surface and the pencil was measured during writing. Specifically, the tip of a non-baked pencil lead attached to the wooden shaft of a normal pencil was sharpened into a conical shape with an angle of 17±1°, and the tip was then sharpened into a circle with a diameter of 0.6±0.1 mm, giving the entire pencil a truncated conical shape. The pencil shaft with the tip shaped in this way was held at an angle of 60° with the tip facing downward using a dedicated fixture and fixed to a dynamic friction measuring machine (TRIBOGEAR, Shinto Scientific). In this state, a load of 300 g was applied, and the dynamic friction coefficient was measured when writing at a speed of 10 mm / sec.

[0048] (6) Measurement of Brightness For each of the Examples and Comparative Examples, hand-drawn lines and instrument-drawn lines were measured using a color meter (SC-P, Suga Test Instruments Co., Ltd.).

[0049] (7) 60° Gloss Measurement For each of the Examples and Comparative Examples, the gloss at 60° to the hand-drawn line and the machine-drawn line was measured using a digital variable angle gloss meter UGV-5 (manufactured by Suga Test Instruments Co., Ltd.).

[0050] (8) Measurement of hiding power (black drawing paper) Each of the solid drawing materials obtained in the above examples and comparative examples was used as is to fill in a 50 mm x 50 mm area of ​​black drawing paper vertically and horizontally, and the appearance of the written surface was evaluated using the following four evaluation criteria A, B, C, and D. Evaluation criteria: A: The black color of the base is completely hidden and cannot be seen. B: The black color of the base is almost hidden and cannot be seen unless you are careful. C: The black color of the base is faintly visible. D: The black color of the base is clearly visible.

[0051] (9) Character erasability measurement (A line was drawn in accordance with the test for writing density specified in JIS S 6005:2007. Specifically, a non-baked pencil lead was set in the drawing machine, and a line was drawn on a paper with a basis weight of 128±5 g / m ２ A line was drawn on a black Kent paper sheet of 100 mm in diameter 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 / sec, and a writing distance of 6 m. The drawn line was first measured with a densitometer (PDA-65, Konica Minolta), and the obtained value was designated as the drawn line density before erasure (D ０Next, the drawn line was rubbed four times with a rubber eraser under a load of 11.76 N (1,200 g weight), and the resulting value was measured with the densitometer and recorded as the drawn line density after erasure (D １ ) and the eraser erasure rate (E Ｒ ) was obtained. Ｒ (%) = (D １ -D ０ ) / D １ x 100 A: 90% or more B: 80% or more but less than 90% C: 30% or more but less than 80% D: Less than 30%

[0052]

[0053] First, in Comparative Example 1, which contained wax as a raw material, the tip strength was 3.8, which was lower than the tip strength of the Examples, and the erasability was extremely poor. Also, in Comparative Example 2, which used clay instead of boron nitride as a raw material, the gloss level increased significantly, making it "unpleasant to the eyes," and there was a significant decrease in the amount of wear and hiding power.

[0054] In contrast, the non-baked pencil leads of the Examples all had high tip strength values. Furthermore, the values ​​for wear, dynamic friction coefficient, brightness, and glossiness were good, resulting in high hiding power. Furthermore, the eraser erasability was also good.

[0055] In this way, the non-baked pencil lead of the present invention can contain a large amount of pigment and white extender, and can easily adjust the hue from white to gray while maintaining high hiding power. Because it is non-baked, these hues do not change, and even when writing on a black or dark surface, it is possible to obtain a non-baked pencil lead that can draw clear lines that are easy on the eyes while maintaining high hiding power and line lightness, and that draws lines that are easily erasable with an eraser.

[0056] The present invention can be used as a non-baked pencil lead for writing on a writing surface such as a black or dark colored notebook, and can also be used as a temporary correction tool that allows the erased portion to be removed with an eraser.

Claims

1. A non-baked pencil lead comprising a water-soluble resin containing a carboxymethyl cellulose salt, a polymeric organic acid, and a white powder.

2. The non-baked pencil lead according to claim 1, wherein the white powder is both a filler and a pigment.

3. The non-baked pencil lead according to claim 1, wherein the lead body after molding is porous.

4. The non-baked pencil lead according to claim 3, characterized in that it is impregnated with oil.

5. The non-baked pencil lead according to claim 2, wherein the filler material includes boron nitride.

6. The non-baked pencil lead according to claim 5, wherein the filler further contains graphite.

7. The non-baked pencil lead according to claim 2, wherein the pigment comprises titanium oxide or carbon black.

8. A method for producing a non-baked pencil lead according to claim 1, comprising the steps of: preparing a mixture of a water-soluble resin containing a carboxymethyl cellulose salt, a polymeric organic acid, and a white powder; and molding the mixture into a pencil lead; wherein in the molding step, the water-soluble resin containing a carboxymethyl cellulose salt and the organic acid are reacted to crosslink each other.

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