Baked pencil lead

Abstract

To provide a fired pencil lead that offers a light and smooth writing feel, suppresses the spread of lead powder when rubbed, and produces a writing style that is less likely to smudge the paper. [Solution] A fired pencil lead is made in which a liquid that satisfies a specific relationship between the kinematic viscosity value at 40°C and the kinematic viscosity value at 100°C is impregnated into the pores of the fired core.

Description

[Technical Field]

[0001] This invention relates to a fired pencil lead. [Background technology]

[0002] Traditionally, writing instruments using fired pencil leads, such as pencils and mechanical pencils, have been widely used.

[0003] Firing pencil leads are obtained by mixing raw materials such as graphite, boron nitride, and binders, followed by molding, firing, and impregnation of the pores formed by firing with an oil or the like. While they have high lead strength and produce dark writing, rubbing such writing can cause lead powder to spread and stain the paper, so improvements are being considered. (See, for example, Patent Document 1)

[0004] Patent Document 1 describes a fired pencil lead in which an impregnation liquid containing oil-soluble smectite is impregnated into the pores. This pencil lead is designed to reduce paper contamination caused by rubbing by suppressing the movement of abrasion particles from writing using the oil-soluble smectite.

[0005] While the aforementioned conventional fired pencil lead technology is indeed capable of suppressing some degree of smudging when writing is rubbed, its effect is not sufficient, and it does not easily provide a light and smooth writing feel. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-77329 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a fired pencil lead that provides a light and smooth writing feel, suppresses the spreading of lead powder when rubbed, and produces a writing surface that is less likely to smudge. [Means for solving the problem]

[0008] To solve the above problems, the present invention "1. A fired pencil lead in which a liquid satisfying the following general formula (1) is impregnated into the pores of a fired core body." 0.80 ≤ 1 - (kinematic viscosity at 100°C / kinematic viscosity at 40°C) ≤ 0.90 (1) 2. The calcined pencil lead according to paragraph 1, wherein the weight-average molecular weight of the liquid is 200 g / mol or more and 5000 g / mol or less. 3. The calcined pencil lead according to item 1 or 2, wherein the number average molecular weight of the liquid is 200 g / mol or more and 2000 g / mol or less. 4. A fired pencil lead according to any one of paragraphs 1 to 3, wherein the dispersion degree of the liquid is 3 or less. [Effects of the Invention]

[0009] According to the present invention, a fired pencil lead is provided that provides a light and smooth writing feel, suppresses the spreading of lead powder when rubbed, and produces a writing result that is less likely to smudge the paper surface. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described in detail below. In this specification, unless otherwise specified, "parts," "%," "ratio," etc., indicating the composition are based on mass.

[0011] The fired pencil lead of the present invention is formed by impregnating the pores of the fired lead body with a specific liquid.

[0012] The liquid impregnated into the pores of the calcined core satisfies the following general formula (1). 0.80 ≤ 1 - (kinematic viscosity at 100°C / kinematic viscosity at 40°C) ≤ 0.90 (1) By applying this liquid, a light and smooth writing feel can be achieved, and the adhesion of the lead powder contained in the writing is improved, preventing the lead powder from spreading and smudging the paper when the writing is rubbed. In this application, the kinematic viscosity of the impregnating liquid is measured in accordance with ISO23581 and calculated by applying the following general formula (2). Kinematic viscosity (mm 2 / s) = Viscosity (mPa·s) / Density (g / cm 3 ) (2) For the measuring instrument of kinematic viscosity, for example, a kinematic viscosity measuring device (manufactured by Anton Paar, trade name: SVM3001) can be used.

[0013] In addition, the liquid to be impregnated into the pores preferably has a kinematic viscosity at 40°C of 30 mm 2 / sec or more and 550 mm 2 / sec or less, more preferably 50 mm 2 / sec or more and 550 mm 2 / sec or less, even more preferably 80 mm 2 / sec or more and 550 mm 2 / sec or less. Further preferably, the kinematic viscosity at 100°C is 5.0 mm 2 / sec or more and 100 mm 2 / sec or less, preferably 7.5 mm 2 / sec or more and 100 mm 2 / sec or less, more preferably 7.5 mm 2 / sec or more and 80 mm 2 / sec or less, even more preferably 10 mm 2 / sec or more and 50 mm 2 / sec or less, which can further enhance the stain resistance when the handwriting is erased.

[0014] Considering that the liquid to be impregnated into the pores enhances the stain resistance when the handwriting is erased, the weight average molecular weight (Mw) is, for example, 200 g / mol or more and 5000 g / mol or less, 4000 g / mol or less, 3000 g / mol or less, 2000 g / mol or less, 1000 g / mol or less, 300 g / mol or more. Considering obtaining a light and smooth writing feeling, it is, for example, 400 g / mol or more.

[0015] Furthermore, considering the need to enhance resistance to smudging when the ink is rubbed, the number-average molecular weight (Mn) of the impregnating liquid should be, for example, 200 g / mol to 2000 g / mol, 1500 g / mol or less, 1000 g / mol or less, and 250 g / mol or more. Considering the need to obtain a light and smooth writing feel, it should be, for example, 300 g / mol or more. The value obtained by dividing the weight-average molecular weight of the liquid by the number-average molecular weight (dispersion: Mw / Mn) should be, for example, 3 or less, 2.5 or less, 2 or less, and 1.5 or less, so that a light and smooth writing feel and resistance to smudging when the ink is rubbed can be achieved. In this application, the weight-average molecular weight and number-average molecular weight of the liquid are measured by gel permeation chromatography (GPC) and are expressed as weight-average molecular weight or number-average molecular weight converted to standard polystyrene, in accordance with JIS K7252-1~4:2016. For measuring instruments, for example, GPC measuring instruments manufactured by Tosoh Corporation (product name: HLC-8320GPC) or GPC measuring instruments manufactured by the same company (product name: HLC-8420GPC) can be used.

[0016] The impregnation liquid may be a liquid composed of a single substance or a liquid composed of multiple substances in combination, and is not limited to any liquid that satisfies general formula (1). Examples of applicable substances include hydrocarbon oils such as paraffin oil and naphthenic oil, silicone oils such as dimethyl silicone oil, diphenyl silicone oil, methylphenyl silicone oil, amino-modified silicone oil, polyether-modified silicone oil, and fatty acid-modified silicone oil, animal and vegetable oils such as whale oil, lard, rapeseed oil, and soybean oil, and spindle oil.

[0017] Furthermore, surfactants with an HLB value of 8 or higher, such as polyoxyethylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene polyoxypropylene alkyl ethers, and polyoxyethylene alkylphenyl ethers, as well as glycol ethers with a boiling point of 160°C or higher, can also be used as impregnation liquids. The substances applicable to the impregnation liquid are not limited to those described above, and one or more substances may be used. The HLB value is determined by the Griffin method.

[0018] To achieve both a light and smooth writing feel and resistance to smudging when the writing is rubbed, the substances applied to the impregnation liquid are preferably silicone oil, paraffin oil, and naphthenic oil, with diphenyl silicone oil and methylphenyl silicone oil being preferred as silicone oils. The impregnation liquid may contain colorants such as dyes and pigments, resins, surfactants other than those mentioned above, etc.

[0019] The fired core can be manufactured by conventionally known methods. Specifically, it is manufactured by mixing and kneading raw materials containing graphite, boron nitride, talc, mica, etc., and a binder, followed by molding and firing processes.

[0020] Natural graphite, synthetic graphite, quiche graphite, expanded graphite, and expanded graphite can all be used as graphite.

[0021] Any conventionally known binder, such as resins or clay minerals, can be used. Examples of resins include water-soluble resins, thermoplastic resins, and thermosetting resins. In addition, pitch-like substances such as coal tar and asphalt can also be used. Furthermore, they can be used in combination with solvents and plasticizers.

[0022] Examples of clay minerals include kaolinite, halosite, montmorillonite, sericite, and bentonite minerals.

[0023] Furthermore, ceramics, zeolites, diatomaceous earth, activated clay, silica, aluminum phosphate, silicone resins, and silicone rubber can also be used as binders.

[0024] The porosity of the fired pencil lead is not particularly limited, but it is preferably in the range of 10 to 40%. A porosity of 10 to 40% results in darker lines, a smoother writing feel, and maintains the strength of the fired pencil lead. For even greater consideration of line darkness and maintaining the strength of the fired pencil lead, a porosity of 20 to 40% is more preferable.

[0025] The porosity of the fired core is measured by the mercury intrusion method. Porosity is the value relative to the volume when mercury is pressed into a void with a diameter of 330 μm. The measurement conditions are set to an initial pressure of 4 kPa, a mercury contact angle of 130 degrees, and a mercury surface tension of 485 dyns / cm.

[0026] The impregnation rate of the liquid into the pores according to the present invention is preferably 5% or more, and more preferably 10% or more, considering the formation of a dark handwriting line. Furthermore, the liquid impregnation rate into the pores is calculated using the following general formula (3) from the weight of the fired core before and after immersion in the liquid at 100°C for 24 hours. Impregnation rate (%)=(X1 / X2)×100 (3) Here, X1 = weight of the fired core after immersion - weight of the fired core before immersion, and X2 = weight of the fired core after immersion.

[0027] An example of the method for manufacturing the fired pencil lead of the present invention is as follows.

[0028] Graphite and resin are added, and if necessary, solvents, plasticizers, etc. are added, kneaded, and extruded. This extruded product is fired at a high temperature of 600°C or higher to obtain a fired core body having pores. The liquid according to the present invention is impregnated into the pores of the fired core body to form a fired pencil lead. As a method of impregnation with the liquid, an atmospheric pressure impregnation method or a reduced pressure / pressure impregnation method can be applied.

[0029] Furthermore, the fired pencil lead of the present invention can also be manufactured by the following manufacturing method.

[0030] Boron nitride, graphite, and an inorganic binder are added, and if necessary, solvents, plasticizers, etc. are added, kneaded, and extruded. This extruded product is fired at a high temperature of 600°C or higher to obtain a fired core body with pores. A liquid containing a polyoxyethylene surfactant, a glycol ether with a boiling point of 160°C or higher, and a dye is impregnated into the pores of the fired core body to form a fired colored pencil lead. As a method of impregnation with the liquid, atmospheric pressure impregnation or reduced pressure / pressure impregnation can be applied. After sufficient impregnation with the liquid, excess ink adhering to the surface is removed by centrifugation or spray washing. [Examples]

[0031] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0032] In this embodiment, kinematic viscosity was measured in accordance with ISO 23581, and calculated by applying general formula (2). A kinematic viscosity analyzer (manufactured by Anton Paar, product name: SVM3001) was used as the measuring instrument.

[0033] The weight-average molecular weight and number-average molecular weight were measured according to paragraph 0015.

[0034] The porosity of the fired core was measured using the mercury intrusion method under the conditions described in paragraph 0025.

[0035] Furthermore, the liquid impregnation rate of the fired pencil lead was determined by the procedure described in paragraph 0026.

[0036] (Example 1) Natural graphite 36 parts by mass Vinyl acetate resin 28 parts by mass Petroleum pitch 16 parts by mass Ethanol 20 parts by mass The above raw materials were mixed in a Henschel mixer, and then further mixed and kneaded using a three-roll mixer. The kneaded material was then molded into a fine wire shape using a single-screw extruder. The resulting molded body was heat-treated at a maximum temperature of 1000°C in a non-oxidizing atmosphere to obtain a fired body with a porosity of 25% and a nominal diameter of 0.5 mm. A hydrocarbon oil obtained by heating a calcined body to 100°C (manufactured by ENEOS Corporation, product name: Super Oil M100, paraffin oil, kinematic viscosity value at 40°C: 97.82 mm²). 2 kinematic viscosity value at 100°C ( / sec): 11.14 mm 2 After immersion for 24 hours in a solution of 0.89 (value of general formula (1)), excess oil was removed from the lead surface to obtain the pencil lead. The liquid impregnation rate of the pencil lead was 12.9%.

[0037] (Example 2) A pencil lead was obtained in the same manner as in Example 1, except that a silicone oil (Shin-Etsu Chemical Co., Ltd., product name: KF-54, methylphenyl silicone oil) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0038] (Example 3) Instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1, a hydrocarbon oil (product name: M46, paraffin oil, kinematic viscosity at 40°C: 47.58 mmHg, manufactured by ENEOS Corporation) was used. 2 kinematic viscosity at 100°C ( / sec): 6.958 mm² 2 ( / sec) and hydrocarbon oil (manufactured by ENEOS Corporation, product name: M460, paraffin oil, kinematic viscosity value at 40℃: 468.2 mm) 2 kinematic viscosity at 100°C ( / sec): 31.45 mm² 2 A pencil lead was obtained in the same manner as in Example 1, except that a mixture of ( / sec) and was used in a weight ratio of 50:50.

[0039] (Example 4) A pencil lead was obtained in the same manner as in Example 1, except that instead of the hydrocarbon oil (manufactured by ENEOS Corporation, Super Oil M100) used in Example 1, a mixture of hydrocarbon oil (manufactured by ENEOS Corporation, product name: M46, paraffin oil) and alkyl methacrylate copolymer (manufactured by Toho Chemical Industry Co., Ltd., product name: LeBlanc 6-860 (the former 6 is the Roman numeral 6)) was used in a weight ratio of 70:30.

[0040] (Example 5) A pencil lead was obtained in the same manner as in Example 1, except that a hydrocarbon oil (product name: Pure Safety 68, paraffin oil, manufactured by Cosmo Oil Lubricants Co., Ltd.) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0041] (Example 6) A pencil lead was obtained in the same manner as in Example 1, except that a silicone oil (Shin-Etsu Chemical Co., Ltd., product name: HIVAC F-5, methylphenyl silicone oil) was used instead of the hydrocarbon oil (manufactured by ENEOS Corporation, product name: Super Oil M100) used in Example 1.

[0042] (Example 7) A pencil lead was obtained in the same manner as in Example 1, except that a hydrocarbon oil (Sankyo Yuka Kogyo Co., Ltd., product name: SNH46, naphthenic oil) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0043] (Example 8) A pencil lead was obtained in the same manner as in Example 1, except that a hydrocarbon oil (product name: M46, paraffin oil, manufactured by ENEOS Corporation) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0044] (Comparative Example 1) A pencil lead was obtained in the same manner as in Example 1, except that a hydrocarbon oil (product name: Chrysef Oil F150, naphthenic oil, manufactured by ENEOS Corporation) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0045] (Comparative Example 2) A pencil lead was obtained in the same manner as in Example 1, except that a silicone oil (Shin-Etsu Chemical Co., Ltd., product name: KF-96-50cs, dimethyl silicone oil) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0046] (Comparative Example 3) A pencil lead was obtained in the same manner as in Example 1, except that a silicone oil (Shin-Etsu Chemical Co., Ltd., product name: KF-50-100cs, methylphenyl silicone oil) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0047] (Comparative Example 4) A pencil lead was obtained in the same manner as in Example 1, except that a hydrocarbon oil (Sankyo Yuka Kogyo Co., Ltd., product name: SNH220, naphthenic oil) was used instead of the hydrocarbon oil (Super Oil M100, manufactured by ENEOS Corporation) used in Example 1.

[0048] The pencil leads obtained from each of the above examples were evaluated for their stain resistance and writing feel. The results are shown in Table 1.

[0049] Table 2 shows the weight-average molecular weight (Mw), number-average molecular weight (Mn), and degree of dispersion (Mw / Mn) of the liquid impregnated into the pencil lead in the examples. Furthermore, the measurement conditions for Mw and Mn of hydrocarbon oil are as described in Condition 1 below. (Condition 1) Measuring instrument: GPC measuring instrument manufactured by Tosoh Corporation, product name (HLC-8320GPC) Column: Tosoh TSKgel G4000H xL (7.8mm I.D. × 30cm) and Tosoh TSKgel G2000H xL (7.8mm I.D. × 30cm) connected together Detector: Differential refractometer (RI) Eluent:THF Flow rate: 1.0mL / min Concentration: 1mg / mL Injection volume: 100μL Column temperature: 40℃

[0050] Furthermore, the measurement conditions for Mw and Mn of the silicone oil are as follows (condition 2 below). (Condition 2) Measuring instrument: GPC measuring instrument manufactured by Tosoh Corporation, product name (HLC-8420GPC) Column: Two Tosoh TSKgel GMHHR-H (7.8mm I.D. × 30cm) columns connected together. Detector: Differential refractometer (RI) Eluent: Toluene Flow rate: 1.0mL / min Concentration: 1mg / mL Injection volume: 100μL Column temperature: 40℃

[0051] [Table 1] In the table, * indicates values ​​obtained by applying the kinematic viscosity of the impregnating liquid at 40°C and 100°C to the general formula (1) [1-(kinematic viscosity at 100°C / kinematic viscosity at 40°C)]. The unit of kinematic viscosity is mm. 2 It is / sec.

[0052] [Table 2] In the table, the units for weight-average molecular weight and number-average molecular weight are g / mol.

[0053] (Evaluation of stain resistance) A line drawn using the method specified in JIS 6005:2019 was rubbed four times back and forth with a tissue under a vertical load of 500g, so as to extend beyond the line. The whiteness of the area where the lead powder spread from the line due to the rubbing was measured using a densitometer (FD-7, Konica Minolta, Inc.). The degree of soiling was calculated from the measured whiteness using the following general formula (4). Degree of soiling = 100 - [(X1 / X2) × 100] (4) However, X1 = whiteness after rubbing, and X2 = whiteness before rubbing. The above general formula (4) indicates that a higher value means a greater degree of soiling.

[0054] When the test papers were visually observed after the whiteness measurement, the areas where the core powder had spread due to rubbing were clearly visible in Comparative Examples 2 and 3, while the areas where the core powder had spread were lighter in color and less noticeable in Examples 1-8 and Comparative Examples 1 and 4.

[0055] (Evaluation of writing feel) Each pencil lead was used to repeatedly write the same short sentence on test paper (KOKUYO Co., Ltd.: Campus Notebook A-ruled), and the writing feel was evaluated according to the following criteria. A: Lightweight and smooth B: Heavy

Claims

1. A fired pencil lead having a liquid satisfying the following general formula (1) impregnated into the pores of a fired core. 0.80 ≤ 1 - (kinematic viscosity at 100°C / kinematic viscosity at 40°C) ≤ 0.90 (1)

2. The calcined pencil lead according to claim 1, wherein the weight-average molecular weight of the liquid is 200 g / mol or more and 5000 g / mol or less.

3. The fired pencil lead according to claim 1, wherein the number average molecular weight of the liquid is 200 g / mol or more and 2000 g / mol or less.

4. The fired pencil lead according to claim 1, wherein the dispersion degree of the liquid is 3 or less.

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