Non-calcined pencil lead

Abstract

A non-calcined pencil lead includes a body material, a pigment, a water-soluble resin, a cross-linking agent, and polycaprolactone.

Description

Technical Field

[0001] The present invention relates to non-calcined pencil leads. Background Art

[0002] Traditionally, fired pencil leads have been manufactured by kneading graphite and clay to form a core, sintering the clay at a high temperature of approximately 1000°C to obtain a core body, and then impregnating the pores of the core body with oil or the like. These fired pencil leads are widely used because the impregnated oil fixes the graphite to the paper surface, making them easy to erase with an eraser (e.g., Japanese Patent Application Publication No. 2007-138031). However, fired pencil leads require heating to approximately 1000°C to sinter the clay binder, which consumes a lot of energy.

[0003] Conventional unfired pencil leads are manufactured by mixing wax or resin as a binder with various inorganic or organic pigments, forming the lead into a core shape using an extruder, and then drying it as needed (e.g., Japanese Patent Application Publication No. 2012-52109). These unfired pencil leads, made of wax or resin as a binder, sometimes lack strength. Consequently, when the tip is sharpened, sufficient tip strength may not be achieved during writing. Furthermore, they are virtually non-erasable.

[0004] On the other hand, there is a technology that uses carboxymethylcellulose salt as a binder to achieve a non-calcined pencil lead without compromising writing quality and colorability even under high humidity, and without causing lead expansion due to moisture absorption (Japanese Patent Application Laid-Open No. 11-335617). However, there is a problem in that moisture absorption easily causes a decrease in strength. Summary of the Invention

[0005] Problems to be solved by the invention

[0006] The object of each embodiment of the present application is to provide a non-calcined pencil lead that has sufficient strength for writing even when the tip is sharpened, suppresses strength reduction due to moisture absorption, and achieves both improved density of written lines and improved fixability, which is not achievable by conventional methods.

[0007] Solutions for solving problems

[0008] The first embodiment of the non-calcined pencil lead of the present application includes a base material, a pigment, a water-soluble resin, a crosslinking agent, and polycaprolactone.

[0009] The unburned pencil lead according to the second aspect of the present application has the configuration of the first aspect, wherein the water-soluble resin contains sodium carboxymethylcellulose, and the cross-linking agent is polyacrylic acid.

[0010] The non-calcined pencil lead according to the third aspect of the present application has the structure of the first or second aspect, and further has the lead body impregnated with grease.

[0011] Effects of the Invention

[0012] Each embodiment of the present application is constructed as described above, and therefore can provide a non-calcined pencil lead that has not been achieved by conventional methods, has sufficient strength for writing even when the tip is sharpened, suppresses the reduction in strength due to moisture absorption, and achieves both improved density of the written line and improved fixability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a perspective view schematically showing the appearance of a non-calcined pencil lead according to an embodiment. DETAILED DESCRIPTION

[0014] The non-calcined pencil lead according to the embodiment of the present application comprises: a body material, a pigment, a water-soluble resin, a cross-linking agent and polycaprolactone.

[0015] The base material is not particularly limited as long as it is used in existing unfired pencil leads; any material can be used. For example, white base materials such as boron nitride, kaolin, talc, mica, and calcium carbonate can be used. Depending on the color tone of the solid drawing material, colored base materials such as graphite can also be used. Of course, mixtures of multiple types of these can also be used. Graphite, talc, boron nitride, and kaolin are particularly preferred due to their physical properties and shape.

[0016] Examples of the pigment 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, 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, and Green No. 3. These pigments can be used alone or in combination of two or more.

[0017] Water-soluble resin is used as a binder, and water-soluble organic polymers such as sodium carboxymethylcellulose, ammonium carboxymethylcellulose, polyvinyl alcohol, and methylcellulose can be used. In addition, starch can also be used as a raw material for the water-soluble resin.

[0018] Sodium carboxymethylcellulose in the water-soluble resin is a cellulose derivative, and refers to carboxymethylcellulose in which the hydrogen (-H) of some hydroxyl groups of the glucopyranose monomers constituting the cellulose skeleton is replaced by carboxymethyl (-CH2COOH) groups, and the hydrogen ions at the carboxymethyl terminals are replaced by sodium ions.

[0019] A crosslinking agent is used to crosslink polymers of a water-soluble resin such as sodium carboxymethylcellulose to stabilize its physical and chemical properties. For example, polyacrylic acid can be used. Polyacrylic acid is represented by the structural formula 1 below and is a polymerized form of acrylic acid (CH2=CHCOOH) with a molecular weight of approximately 25,000.

[0020] [-CH2CH(COOH)-] n Formula (1)

[0021] The molecular weight of the polyacrylic acid is not particularly limited, but is preferably 5,000 to 1,000,000. A molecular weight of 5,000 or greater allows the sodium ions of the monomers constituting the carboxymethylcellulose salt to be replaced with an acid, resulting in cross-linking of the polymers at numerous locations, improving bonding stability. On the other hand, a molecular weight of 1,000,000 or less facilitates mixing with powders.

[0022] Polycaprolactone is a polymer obtained by polymerization of ε-caprolactone and is used to improve the water resistance of unfired pencil leads. An example of this is polycaprolactone diol (chemical formula: C4H8O3(C6H 10 O2) n ) and polycaprolactone triol (chemical formula: C2H5C[CH2O[CO(CH2)5O] n H]3).

[0023] The uncalcined pencil lead can be produced by the following method. Specifically, the method comprises the steps of preparing a mixture of a base material, a pigment, a water-soluble resin, a crosslinking agent, and PTFE; and molding the mixture into a core body. During the molding step, the carboxymethyl cellulose salt and the crosslinking agent react to cause crosslinking.

[0024] For example, when a physical material, a pigment, a water-soluble resin, a cross-linking agent and polycaprolactone are kneaded to prepare a mixture, a solvent may be added as needed. As a solvent, lower alcohols such as methanol and ethanol or water are used. Then, the obtained mixture is extruded into the shape of a pencil lead using a plunger-type or screw-type extruder. It should be noted that when a solvent is used, the solvent is then dried (at about 40°C for 24 hours) to remove it. By this molding, a pencil lead is obtained. Figure 1 The unfired pencil lead 10 shown has a roughly cylindrical core 11. The formed core 11 is porous, with pores derived from the powder's microstructure. These pores can remain as is, but it is desirable to heat them at 60-80°C for 12 hours and then impregnate them with a fat.

[0025] As the oils and fats, those that are liquid at room temperature, such as liquid paraffin, spindle oil, silicone oil, α-olefin oligomers, squalane, etc., can be suitably used. Among these, silicone oil is particularly good, and examples thereof include dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil, cyclic dimethyl silicone oil, polyether-modified silicone oil, methylstyrene-modified silicone oil, and alkyl-modified silicone oil.

[0026] By the above-described production method, a non-calcined pencil lead is formed by kneading and molding at least a base material, a pigment, a water-soluble resin, a crosslinking agent, and polycaprolactone, thereby producing a non-calcined pencil lead with suppressed moisture deterioration in strength. Specific embodiments

[0028] (1) Raw materials

[0029] The raw materials commonly used in the non-calcined pencil leads of each example and comparative example are as follows. Graphite (MCP-10, Nippon Graphite) was used as the base material. Carbon black (MA-100, Mitsubishi Chemical) was used as the pigment. A water-soluble resin was a mixture of equal weights of sodium carboxymethylcellulose (SUNROSE F20LC, Nippon Paper), starch (STARCH TK, Nippon Starch Chemical Co., Ltd.), and polyvinyl alcohol (PVA-217, Kuraray). Polyacrylic acid (AQUALIC HL-415, Nippon Shokubai) was used as the crosslinking agent. Silicone oil (KF-96-100CS, Shin-Etsu Chemical) was used as the oil impregnated into the lead.

[0030] (2) Example

[0031] (2-1) Example 1

[0032] In Example 1, 45% by mass of a base material, 30% by mass of a pigment, 15% by mass of a water-soluble resin, 5% by mass of a crosslinking agent, and 5% by mass of a high molecular weight polycaprolactone having a melting point of 60° C. (PLACCEL H1P, DAICEL) were mixed.

[0033] (2-2) Example 2

[0034] In Example 2, 45% by mass of a base material, 30% by mass of a pigment, 15% by mass of a water-soluble resin, 5% by mass of a crosslinking agent, and 5% by mass of polycaprolactone diol (PLACCEL 240, DAICEL) having a melting point of 48 to 58° C. as polycaprolactone were mixed.

[0035] (2-3) Example 3

[0036] In Example 3, 45% by mass of a base material, 30% by mass of a pigment, 15% by mass of a water-soluble resin, 5% by mass of a crosslinking agent, and 5% by mass of polycaprolactone triol (PLACCEL 312, DAICEL) having a melting point of 33 to 37° C. as polycaprolactone were mixed.

[0037] (3) Comparative Example

[0038] (3-1) Comparative Example 1

[0039] As Comparative Example 1, 50% by mass of a base material, 30% by mass of a pigment, 15% by mass of a water-soluble resin, and 5% by mass of a crosslinking agent were mixed.

[0040] (3-2) Comparative Example 2

[0041] As Comparative Example 2, 45% by mass of a base material, 30% by mass of a pigment, 15% by mass of a water-soluble resin, 5% by mass of a crosslinking agent, and 5% by mass of a lacquer wax (SmackWax, Shinwa Health Industry) having a melting point of 52° C. were blended.

[0042] (3-3) Comparative Example 3

[0043] As Comparative Example 3, 45% by mass of a base material, 30% by mass of a pigment, 15% by mass of a water-soluble resin, 5% by mass of a crosslinking agent, and 5% by mass of silicone oil (KF-96-100CS, Shin-Etsu Chemical) were blended.

[0044] (4) Manufacture of non-calcined pencil leads

[0045] The raw materials of Examples 1 to 3 and Comparative Examples 1 to 3 were kneaded and then extruded into a pencil lead using a plunger or screw extruder. The water was then evaporated to produce an unfired pencil lead. The resulting lead was then immersed in silicone oil for impregnation. The proportion of silicone oil in the resulting unfired pencil lead was 16.3% by mass in Example 1, 16.7% by mass in Example 2, and 19.4% by mass in Example 3, as well as 21.0% by mass in Comparative Example 1, 20.0% by mass in Comparative Example 2, and 18.3% by mass in Comparative Example 3.

[0046] (5) Bending strength measurement

[0047] The bending strength of each unfired pencil lead from Examples 1 to 3 and Comparative Examples 1 to 3 was measured. Specifically, the bending strength of each unfired pencil lead was measured at 23°C with a 40 mm distance between the supporting points. The pressure at breakage (unit: MPa) was determined. The measurements were performed twice: immediately after production and 24 hours after standing in an environment at 35°C and 100% humidity. Furthermore, the strength reduction rate was calculated as the value Z (%) using the following formula (2), where the bending strength immediately after production is X and the bending strength 24 hours after production is Y.

[0048] Z=(XY) / X×100···Formula (2)

[0049] (6) Top strength measurement

[0050] The tip strength of each unfired pencil lead from Examples 1 to 3 and Comparative Examples 1 to 3 was measured. Specifically, the tip of the unfired pencil lead, attached to a conventional wooden pencil shaft, was cut into a conical shape with an angle of 17±1°. The tip was then rounded to a diameter of 0.6±0.1 mm, resulting in a truncated cone shape. The pencil shaft, with the tip adjusted in this manner, was held at a 60° angle with the tip facing downward using a dedicated fixture. In this state, a load was applied at a rate of 10 mm / minute, and the load at which the tip failed was measured (specifically, a sudden decrease in load of approximately 0.7 N or more was considered a tip failure).

[0051] (7) Wear measurement

[0052] The wear of each of the non-calcined pencil leads of Examples 1 to 3 and Comparative Examples 1 to 3 was measured when subjected to machine writing. Specifically, the wear of the lead was measured using a recording measuring machine specified in JIS S 6006 under the measurement conditions specified in the same standard.

[0053] (8) Line density measurement

[0054] The line density of each of the non-calcined pencil leads of Examples 1 to 3 and Comparative Examples 1 to 3 was measured. Specifically, the density was measured at four locations along the line based on the line density measurement method for recording measuring machines specified in JIS S 6006.

[0055] (9) Wipe concentration measurement

[0056] The rubbing density of each non-calcined pencil lead of Examples 1 to 3 and Comparative Examples 1 to 3 was measured. Specifically, the line (8) was rubbed back and forth four times with a felt loaded with 500 g, and the density at the turning point was measured.

[0057] (10) Determination of dynamic friction coefficient

[0058] The coefficient of kinetic friction between the unfired pencil leads of Examples 1 to 3 and Comparative Examples 1 to 3 and the writing surface during writing was measured. Specifically, the tip of the unfired pencil lead, attached to a conventional wooden pencil shaft, was cut into a conical shape with an angle of 17±1°. This tip was then rounded to a diameter of 0.6±0.1 mm, resulting in a truncated cone shape. The pencil shaft, with the tip adjusted in this manner, 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). A load of 300g was applied in this state, and the coefficient of kinetic friction was measured while drawing at a speed of 10 mm / second.

[0059] (11) Results

[0060] The measurement results in (5) to (10) are shown in Table 1. The values other than "density" and "rubbing density" in Table 1 are the average values of the values measured on 10 unfired pencil leads in each of the Examples and Comparative Examples.

[0061] [Table 1]

[0062] Examples / Comparative Examples Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Strength immediately after manufacture (MPa) 45.8 38.6 36.2 39.7 23.1 23.6 Strength after 24 hours (MPa) 40.1 34.6 32.2 32.9 19.1 19.8 Strength reduction rate (%) 12.4 10.5 11.1 17.1 17.2 16.0 Top strength (N) 6.0 6.4 5.8 5.1 4.7 4.4 Wear amount (mm) 1.84 1.80 2.06 2.10 2.56 2.44 concentration 0.466 0.510 0.548 0.559 0.626 0.632 Wipe concentration 0.053 0.058 0.068 0.090 0.080 0.090 Dynamic friction coefficient 0.193 0.188 0.191 0.190 0.201 0.202

[0063] First, the unfired pencil leads containing polycaprolactone in Examples 1, 2, and 3 exhibited strength reductions of 12.4%, 10.5%, and 11.1%, respectively. In contrast, the strength reductions in Comparative Example 1, which contained no polycaprolactone, Comparative Example 2, which contained lacquer wax instead of polycaprolactone, and Comparative Example 3, which contained silicone oil instead of polycaprolactone, were all higher than those in the Examples, at 17.1%, 17.2%, and 16.0%, respectively. This demonstrates that even when the unfired pencil leads in the Examples were left in a high-humidity environment for 24 hours immediately after production, the strength reduction was suppressed compared to the Comparative Examples.

[0064] Furthermore, the tip strength measurements were as follows: the unfired pencil leads of Examples 1, 2, and 3 were 6.0 N, 6.4 N, and 5.8 N, respectively. In contrast, the unfired pencil leads of Comparative Examples 1, 2, and 3 all showed lower strengths, at 5.1 N, 4.7 N, and 4.4 N, respectively. This demonstrates that the unfired pencil lead containing polycaprolactone exhibits improved tip strength.

[0065] It should be noted that the results of wear amount, concentration, wiping concentration and dynamic friction coefficient are as follows: each example is better than each comparative example, which also shows that the compounding of polycaprolactone does not have an adverse effect on the concentration and fixability of the written line.

[0066] Industrial applicability

[0067] The present invention can be utilized as a non-calcined pencil lead.

Claims

1. A non-calcined pencil lead comprising: a body material, a pigment, a water-soluble resin, a cross-linking agent and polycaprolactone.

2. The non-calcined pencil lead according to claim 1, wherein The water-soluble resin comprises sodium carboxymethyl cellulose, and The cross-linking agent is polyacrylic acid.

3. The non-calcined pencil lead according to claim 1 or claim 2, characterized in that: The core is impregnated with grease.

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