US3262904A - Pencil leads - Google Patents

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US3262904A
US3262904A US135067A US13506761A US3262904A US 3262904 A US3262904 A US 3262904A US 135067 A US135067 A US 135067A US 13506761 A US13506761 A US 13506761A US 3262904 A US3262904 A US 3262904A
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writing
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graphite
styrene
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Dennis L Ripley
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Dow Chemical Co
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D13/00—Pencil-leads; Crayon compositions; Chalk compositions
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L25/00—Compositions of, homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Compositions of derivatives of such polymers
    • C08L25/02—Homopolymers or copolymers of hydrocarbons
    • C08L25/04—Homopolymers or copolymers of styrene
    • C08L25/08—Copolymers of styrene
    • C08L25/12—Copolymers of styrene with unsaturated nitriles
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/06—Polyethene

Definitions

  • the present invention relates to an improved composition for and a method of manufacturing Writing cores. More specifically, it relates to plastic bonded graphite writing core compositions and a method of their manufacture for use as pencil leads.
  • Commercial pencil lead is composed of four principal ingredients: graphite, clay, gums and waxes.
  • powdered graphite is combined with purified, wet clay and mixed for several days in ball mills or revolving drums. Water is removed and the mixture is compressed under hydraulic pressure through an extrusion die having orifices the size of the desired leads.
  • the extruded lead is cut into lengths of about seven inches and dried at elevated temperatures for several days.
  • the leads are then baked at approximately 1600 F. for several hours. Losses due to warpage and breakage plus extensive handling requirements add to the cost of the time consuming procedures.
  • FIGURE 1 is a representation of a writing. core 10 in accordance with the invention.
  • FIGURE 2 is a longitudinal cross sectionalvie-w of a pencil 11 comprising a wood case 12 containing a generally centrally disposed groove 13 having a writing core 10.
  • FIGURE 3 is a side elevation of a pencil 15 comprising a casing 16 with a tapered end 17 and a pointed end writing core 10.
  • the improved composition consists of amorphous, natural flake graphite which is finely dispersed in organic thermoplastic resins selected to provide a writing lead with the desired strength and writing qualities.
  • Leads containing less than 20 percent thermoplastic resin become objectionably weak while those containing more than 45 percent thermoplastic resin tend to become overly waxy.
  • Maximum strength is not obtained with the 45 percent thermoplastic composition.
  • the flexural strength increases as this percentage is decreased from 45 percent until a point of maximum strength is reached at a composition of approximately 30 percent thermoplastic resins and 70 percent (graphite.
  • the thermoplastic resinous material comprises two components utilized in a ratio which is varied according to the physical properties desired in the writing core.
  • One of the components employed is a rigid thermoplastic resin such as styrene polymer or a copolymer of styrene and acrylonitrile having a flexural strength over 10,000 psi.
  • the other component is a softer, low melt viscosity resin such as branched, high pressure polyethylene.
  • the improved compositions for writing cores are suitable for use in a continuous extrusion process utilizing conventional plastic processing techniques.
  • the lead produced in this manner is ready for immediate use; a valuable property which makes possible continuous process methods of manufacture.
  • the appropriate amounts of thermoplastic resins and graphite are intimately blended in conventional plastic processing techniques such as dry blending and mill mixing, extrusion mixing and graphite dispersion in a resin solution followed by evaporation of the volatile component of the dispersion.
  • the mixture is then fabricated into desired shapes by extrusion, molding or similar means.
  • Flexural strengths of compositions in accordance with the invention were determined by placing writing core samples on supports spaced two inches apart and deflecting the midpoints of these spans at a rate of onehalf inch per minute until the breaking point was reached and the result, expressed as flexural strength in p.s.i., calculated from the following modulus of rupture formula:
  • Flexural strength of the writing core is influenced by factors other than the composition. Generally, the strength increases with intensive mixing and increased compacting prior to extrusion.
  • the extrusion temperature also influences the fiexural strength of the writing core.
  • the optimum extrusion temperature determined for various compositions in the following examples, increased as the proportion of rigid thermoplastic resin component in the mixture was increased. This temperature always remained below the decomposition temperatures of the thermoplastic resinous components.
  • Example 1 20 percent styrene-acrylonitrile copolymer (prepared by the polymerization of about 70 percent styrene and 30 percent acrylonitrile) with a flexural strength of about 17,000 to 19,000 psi. and a melt viscosity of about 14,600 poises when a shearing force of 700,000 dynes/ cm. at 227 C. is applied, 10 per-cent branched, high pressure polyethylene with a melt viscosity of about 375 poises at 450 F. and 700,000 dynes/cm. and 70 percent natural flake, amorphous, Mexican graphite (99 percent passing 325 mesh U.S.
  • the resulting writing core had a flexural strength of about 8,000 p.s.i. and a hardness, as determined by multiple comparisons with commercial writing lead samples bearing numerical designations, equivalent to No. 3.
  • Example 2 A mixture of 25 percent styrene-acrylonitrile copolymer, percent branched, high pressure polyethylene and 70 percent graphite, all as defined in Example 1, was blended, densified and extruded as in Example 1 with the extrusion temperature changed to approximately 225 C.
  • the resulting writing core possessed a flexural strength of about 11,500 p.s.i. and a hardness equivalent to No. 4 as determined by multiple comparisons with commercial samples bearing numerical designations.
  • Example 3 A mixture of percent styrene-acrylonitrile copolymer, 15 percent branched, high pressure polyethylene and 70 percent graphite, all as defined in Example 1, was blended, densified and extruded as in Example 1 with the extrusion temperature changed to approximately 170 C.
  • the resulting writing core possessed a flexural strength of about 7,300 p.s.i. and a hardness equivalent to No. 2% determined as in the previous examples.
  • Example 4 A mixture of percent styrene-acrylonitrile copolymer, 12 /2 percent branched, high pressure polyethylene and 62 /2 percent graphite, all as defined in Example 1, was blended, densified and extruded as in Example 1, with the extrusion temperature changed to approximately 220 C.
  • the resulting writing core possessed a flexural strength of about 6,800 p.s.i.
  • the flexural strength of the product writing core decreases. Reducing the graphite component from approximately 70 percent towards a minimum of 55 percent also results in lower flexural strength. In both cases, the flexural strength may be increased by increasing the ratio of rigid to soft
  • a method for making writing cores, in a form ready for use in pencils which consists essentially in dry blending a mixture of ten to thirty percent of a rigid thermoplastic resin selected from the group consisting of polystyrene and styrene-acrylonitrile copolymers, 1 to 20 percent of a branched, high pressure polyethylene material and 65 to percent natural flake graphite, compacting the mixture at a temperature above the softening point of the rigid thermoplastic resinous material, extruding the so densified mixture through a die with orifices of appropriate diameter and severing the extrudate into required lengths for use in pencils.
  • a rigid thermoplastic resin selected from the group consisting of polystyrene and styrene-acrylonitrile copolymers, 1 to 20 percent of a branched, high pressure polyethylene material and 65 to percent natural flake graphite
  • a composition for writing cores which consists of 65 to 75 percent graphite, 10 to 30 percent styreneacrylonitrile copolymer and 1 to 20 percent branched, high pressure polyethylene.
  • a composition for writing cores consisting essentially of (a) 55 to percent flake graphite and (b) 20 to 45 percent of organic thermoplastic resinous material consisting of (l) predominantly styrene linear thermoplastic polymer with a flexural strength above 10,000 p.s.i. and (2) a branched, high pressure polyethylene with a melt viscosity of about 300 to 500 poises at 450 F. under a shearing force of 700,000 dynes/cmf 4.
  • a composition for writing cores consisting essentially of (a) 55 to 80 percent flake graphite and (b) 20 to 45 percent of organic thermoplastic resinous material consisting of (1) a branched, high pressure polyethylene with a melt viscosity of about 300 to 500 poises at 450 F. and 700,000 dynes/cm. and (2) a copolymer of styrene and acrylonitrile with a melt viscosity of about 10,000 to 20,000 poises at 227 C. and 700,000 dynes/cm.
  • a composition for writing cores which consists essentially of from 55 to 80 percent graphite, 10 to 30 percent of an organic thermoplastic resin selected from the group consisting of styrene polymers and styrene-acrylonitrile copolymers, and 0 to 20 percent branched, high pressure polyethylene.
  • a composition for writing cores which consists of 65 to 75 percent graphite, 10 to 30 percent styrene polymer, and 1 to 20 percent branched, high pressure polyethylene.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Wood Science & Technology (AREA)
  • Inks, Pencil-Leads, Or Crayons (AREA)

Description

July 26, 1966 D. L. RIPLEY 3,262,904
PENCIL LEADS Filed Aug. 30, 1961 INVENTOR. Benn/Ls L. R/p/ey IQGENT United States Patent 3,262,904 PENCIL LEADS Dennis L. Ripley, Bartlesville, Okla, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Aug. 30, 1961, Ser. No. 135,067 7 Claims. (Cl. 260-41) The present invention relates to an improved composition for and a method of manufacturing Writing cores. More specifically, it relates to plastic bonded graphite writing core compositions and a method of their manufacture for use as pencil leads.
Commercial pencil lead is composed of four principal ingredients: graphite, clay, gums and waxes. In a typical method of preparing leads according to the art, powdered graphite is combined with purified, wet clay and mixed for several days in ball mills or revolving drums. Water is removed and the mixture is compressed under hydraulic pressure through an extrusion die having orifices the size of the desired leads. The extruded lead is cut into lengths of about seven inches and dried at elevated temperatures for several days. The leads are then baked at approximately 1600 F. for several hours. Losses due to warpage and breakage plus extensive handling requirements add to the cost of the time consuming procedures.
It is an object of the present invention to provide an improved composition and method of manufacture for Writing cores which would obviate the costly pro cedural and handling problems involved in present day pencil lead production while yielding a commercially advantageous writing lead. Other objects of the present invention will become apparent from the following specifications and claims.
It has now been discovered that the qualities of present commercial writing leads are readily reproduced, and in many instances superior properties provided, by an improved composition, which comprises graphite bonded with organic thermoplastic resinous materials. This improved composition possesses properties which enables an improved method of manufacture to be utilized resulting in greatly increased production economy.
For the purpose of facilitating an understanding of the invention, there are shown in the drawings certain forms which are to be understood as not limiting the invention to the precise arrangements and instrumentalities illustrated.
FIGURE 1 is a representation of a writing. core 10 in accordance with the invention.
FIGURE 2 is a longitudinal cross sectionalvie-w of a pencil 11 comprising a wood case 12 containing a generally centrally disposed groove 13 having a writing core 10.
FIGURE 3 is a side elevation of a pencil 15 comprising a casing 16 with a tapered end 17 and a pointed end writing core 10. i
The improved composition consists of amorphous, natural flake graphite which is finely dispersed in organic thermoplastic resins selected to provide a writing lead with the desired strength and writing qualities. Leads containing less than 20 percent thermoplastic resin become objectionably weak while those containing more than 45 percent thermoplastic resin tend to become overly waxy. Maximum strength, however, is not obtained with the 45 percent thermoplastic composition. The flexural strength increases as this percentage is decreased from 45 percent until a point of maximum strength is reached at a composition of approximately 30 percent thermoplastic resins and 70 percent (graphite.
In a preferred embodiment, the thermoplastic resinous material comprises two components utilized in a ratio which is varied according to the physical properties desired in the writing core. One of the components employed is a rigid thermoplastic resin such as styrene polymer or a copolymer of styrene and acrylonitrile having a flexural strength over 10,000 psi. The other component is a softer, low melt viscosity resin such as branched, high pressure polyethylene.
The improved compositions for writing cores are suitable for use in a continuous extrusion process utilizing conventional plastic processing techniques. The lead produced in this manner is ready for immediate use; a valuable property which makes possible continuous process methods of manufacture. In this improved method of writing core production the appropriate amounts of thermoplastic resins and graphite are intimately blended in conventional plastic processing techniques such as dry blending and mill mixing, extrusion mixing and graphite dispersion in a resin solution followed by evaporation of the volatile component of the dispersion. The mixture is then fabricated into desired shapes by extrusion, molding or similar means.
Flexural strengths of compositions in accordance with the invention were determined by placing writing core samples on supports spaced two inches apart and deflecting the midpoints of these spans at a rate of onehalf inch per minute until the breaking point was reached and the result, expressed as flexural strength in p.s.i., calculated from the following modulus of rupture formula:
M C S I where S=the modulus of rupture M =the moment at the break point C=the distance from the centroid to the outer surface and I==the moment of inertia.
Flexural strength of the writing core is influenced by factors other than the composition. Generally, the strength increases with intensive mixing and increased compacting prior to extrusion. The extrusion temperature also influences the fiexural strength of the writing core. The optimum extrusion temperature determined for various compositions in the following examples, increased as the proportion of rigid thermoplastic resin component in the mixture was increased. This temperature always remained below the decomposition temperatures of the thermoplastic resinous components.
Beneficially, the rigid plastic component used in this invention is a polymer prepared from a vinyl aromatic compound of the formula AR-OR=OH wherein R is selected from the group consisting of hydrogen and methyl, AR is an aromatic group containing up to ten carbon atoms, and the group CR=OH is attached directly to a carbon atom of the aromatic ring, which may have chemically combined in the polymer molecule a minor proportion of such substituents as acrylonitrile.
The following examples are illustrative of the present invention but are not to be construed as limiting thereof.
Example 1 20 percent styrene-acrylonitrile copolymer (prepared by the polymerization of about 70 percent styrene and 30 percent acrylonitrile) with a flexural strength of about 17,000 to 19,000 psi. and a melt viscosity of about 14,600 poises when a shearing force of 700,000 dynes/ cm. at 227 C. is applied, 10 per-cent branched, high pressure polyethylene with a melt viscosity of about 375 poises at 450 F. and 700,000 dynes/cm. and 70 percent natural flake, amorphous, Mexican graphite (99 percent passing 325 mesh U.S. sieve size) were dry blended and densified by milling on rolls at a temperature of 210 C. The mixture was extruded through a inch screw extruder at an extrusion temperature of approximately 180 C. The resulting writing core had a flexural strength of about 8,000 p.s.i. and a hardness, as determined by multiple comparisons with commercial writing lead samples bearing numerical designations, equivalent to No. 3.
Example 2 A mixture of 25 percent styrene-acrylonitrile copolymer, percent branched, high pressure polyethylene and 70 percent graphite, all as defined in Example 1, was blended, densified and extruded as in Example 1 with the extrusion temperature changed to approximately 225 C. The resulting writing core possessed a flexural strength of about 11,500 p.s.i. and a hardness equivalent to No. 4 as determined by multiple comparisons with commercial samples bearing numerical designations.
Example 3 A mixture of percent styrene-acrylonitrile copolymer, 15 percent branched, high pressure polyethylene and 70 percent graphite, all as defined in Example 1, was blended, densified and extruded as in Example 1 with the extrusion temperature changed to approximately 170 C. The resulting writing core possessed a flexural strength of about 7,300 p.s.i. and a hardness equivalent to No. 2% determined as in the previous examples.
Example 4 A mixture of percent styrene-acrylonitrile copolymer, 12 /2 percent branched, high pressure polyethylene and 62 /2 percent graphite, all as defined in Example 1, was blended, densified and extruded as in Example 1, with the extrusion temperature changed to approximately 220 C. The resulting writing core possessed a flexural strength of about 6,800 p.s.i.
Tests of the writing cores described in the preceding examples, both as wood cased pencils and as mechanical pencil leads, demonstrated qualities of writing smoothness, uniformity and visibility of line markings, and core flexural strength that in many instances were superior to commercially available products. The preparation of writing cores in accordance with the invention is completed in a few hours while typical, present day, commercial methods require a week or longer to produce finished leads.
In general, as the graphite component is increased from 70 percent towards a maximum of 80 percent the flexural strength of the product writing core decreases. Reducing the graphite component from approximately 70 percent towards a minimum of 55 percent also results in lower flexural strength. In both cases, the flexural strength may be increased by increasing the ratio of rigid to soft While the foregoing examples and illustrations describe certain embodiments of the invention in considerable detail for the purpose of facilitating full and clear understanding, it will be understood that many modifications can be made therein without departing from the scope of the invention.
I claim:
1. A method for making writing cores, in a form ready for use in pencils, which consists essentially in dry blending a mixture of ten to thirty percent of a rigid thermoplastic resin selected from the group consisting of polystyrene and styrene-acrylonitrile copolymers, 1 to 20 percent of a branched, high pressure polyethylene material and 65 to percent natural flake graphite, compacting the mixture at a temperature above the softening point of the rigid thermoplastic resinous material, extruding the so densified mixture through a die with orifices of appropriate diameter and severing the extrudate into required lengths for use in pencils.
2. A composition for writing cores which consists of 65 to 75 percent graphite, 10 to 30 percent styreneacrylonitrile copolymer and 1 to 20 percent branched, high pressure polyethylene.
3. A composition for writing cores consisting essentially of (a) 55 to percent flake graphite and (b) 20 to 45 percent of organic thermoplastic resinous material consisting of (l) predominantly styrene linear thermoplastic polymer with a flexural strength above 10,000 p.s.i. and (2) a branched, high pressure polyethylene with a melt viscosity of about 300 to 500 poises at 450 F. under a shearing force of 700,000 dynes/cmf 4. A composition for writing cores consisting essentially of (a) 55 to 80 percent flake graphite and (b) 20 to 45 percent of organic thermoplastic resinous material consisting of (1) a branched, high pressure polyethylene with a melt viscosity of about 300 to 500 poises at 450 F. and 700,000 dynes/cm. and (2) a copolymer of styrene and acrylonitrile with a melt viscosity of about 10,000 to 20,000 poises at 227 C. and 700,000 dynes/cm.
5. The method of claim 1 wherein the ratio of rigid thermoplastic resin to polyethylene material is from about 1:1 to 5:1, respectively.
6. A composition for writing cores which consists essentially of from 55 to 80 percent graphite, 10 to 30 percent of an organic thermoplastic resin selected from the group consisting of styrene polymers and styrene-acrylonitrile copolymers, and 0 to 20 percent branched, high pressure polyethylene.
7. A composition for writing cores which consists of 65 to 75 percent graphite, 10 to 30 percent styrene polymer, and 1 to 20 percent branched, high pressure polyethylene.
References Cited by the Examiner UNITED STATES PATENTS 2,988,784 6/ 1961 Lorenian 83 XR FOREIGN PATENTS 704,063 2/ 1954 Great Britain.
OTHER REFERENCES Smith, Vinyl Resins, Reinhold Plastics Application Series, Reinhold Pub. Corp., New York, 1958, page 72.
MORRIS LIEBMAN, Primary Examiner.
LAWRENCE CHARLES, Examiner.
R. R. RATH, K. B. CLARKE, I. s. WALDRON,
Assistant Examiners.

Claims (1)

1. A MAKING FOR MAKING WRITING CORES, IN A FORM READY FOR USE IN PENCILS, WHICH CONSISTS ESSENTIALLY IN DRY BLENDING A MIXTURE OF TEN TO THIRTY PERCENT OF A RIGID THERMOPLASTIC RESIN SELECTED FROM THE GROUP CONSISTING OF POLYSTYRENE ANS STYRENE-ACRYLONITRILE COPOLYMERS, 1 TO 20 PERCENT OF A BRANCHED, HIGH PRESSURE POLYETHYLENE MATERIAL AND 65 TO 75 PERCENT NATURAL FLAKE GRAPHITE, COMPACTING THE MIXTURE AT A TEMPERATURE ABOVE THE SOFTENING POINT OF THE RIGID THERMOPLASTIC RESINOUS MATERIAL, EXTRUDING THE SO DENSIFIED MIXTURE THROUGH A DIE WITH ORIFICES OF APPROPRIATE DIAMETER AND SEVERING THE EXTRUDATE INTO REQUIRED LENGTHS FOR USE IN PENCILS.
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3409574A (en) * 1964-07-10 1968-11-05 Mead Corp Marking materials comprising low-pressure polyethylene, high-pressure polyethylene and plasticizer
US3446878A (en) * 1964-12-08 1969-05-27 Dainihon Bungu Co Ltd Method of producing pencil lead
US3928520A (en) * 1971-08-19 1975-12-23 Pilot Kiko Kk Black lead and production thereof
JPS5421775B1 (en) * 1971-03-29 1979-08-02
DE3827968C1 (en) * 1988-08-17 1989-12-28 Solmex Ag, Weggis, Ch Pencil lead composition and process for its preparation
EP3042937A1 (en) * 2015-01-09 2016-07-13 Faber- Castell AG Lead or chalk containing graphite and a polymer binding agent and pencil with a graphite lead
US11550442B2 (en) * 2019-03-22 2023-01-10 Wacom Co., Ltd. Electronic pen

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB704063A (en) * 1949-06-22 1954-02-17 Zareh Lorenian Improvements in or relating to the manufacture of writing means
US2988784A (en) * 1948-06-28 1961-06-20 Lorenian Zareh Manufacture of pencils and other shaped articles

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2988784A (en) * 1948-06-28 1961-06-20 Lorenian Zareh Manufacture of pencils and other shaped articles
GB704063A (en) * 1949-06-22 1954-02-17 Zareh Lorenian Improvements in or relating to the manufacture of writing means

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3409574A (en) * 1964-07-10 1968-11-05 Mead Corp Marking materials comprising low-pressure polyethylene, high-pressure polyethylene and plasticizer
US3446878A (en) * 1964-12-08 1969-05-27 Dainihon Bungu Co Ltd Method of producing pencil lead
JPS5421775B1 (en) * 1971-03-29 1979-08-02
US3928520A (en) * 1971-08-19 1975-12-23 Pilot Kiko Kk Black lead and production thereof
DE3827968C1 (en) * 1988-08-17 1989-12-28 Solmex Ag, Weggis, Ch Pencil lead composition and process for its preparation
EP3042937A1 (en) * 2015-01-09 2016-07-13 Faber- Castell AG Lead or chalk containing graphite and a polymer binding agent and pencil with a graphite lead
US11550442B2 (en) * 2019-03-22 2023-01-10 Wacom Co., Ltd. Electronic pen
US11803286B2 (en) 2019-03-22 2023-10-31 Wacom Co., Ltd. Electronic pen

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