EP0048571B2 - Pencil lead, and methods and apparatus for its manufacture - Google Patents
Pencil lead, and methods and apparatus for its manufacture Download PDFInfo
- Publication number
- EP0048571B2 EP0048571B2 EP19810304138 EP81304138A EP0048571B2 EP 0048571 B2 EP0048571 B2 EP 0048571B2 EP 19810304138 EP19810304138 EP 19810304138 EP 81304138 A EP81304138 A EP 81304138A EP 0048571 B2 EP0048571 B2 EP 0048571B2
- Authority
- EP
- European Patent Office
- Prior art keywords
- lead
- microns
- pencil lead
- method defined
- range
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims description 23
- 238000004519 manufacturing process Methods 0.000 title claims description 5
- 239000002245 particle Substances 0.000 claims description 42
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 34
- 229910002804 graphite Inorganic materials 0.000 claims description 30
- 239000010439 graphite Substances 0.000 claims description 30
- 239000000126 substance Substances 0.000 claims description 23
- 239000000463 material Substances 0.000 claims description 18
- 239000011230 binding agent Substances 0.000 claims description 16
- 239000007787 solid Substances 0.000 claims description 14
- 238000010438 heat treatment Methods 0.000 claims description 7
- 229920003002 synthetic resin Polymers 0.000 claims description 7
- 239000000057 synthetic resin Substances 0.000 claims description 7
- 238000005304 joining Methods 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 4
- 239000002131 composite material Substances 0.000 description 8
- 239000011162 core material Substances 0.000 description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 3
- 229910052786 argon Inorganic materials 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000001125 extrusion Methods 0.000 description 2
- 230000002093 peripheral effect Effects 0.000 description 2
- 206010016322 Feeling abnormal Diseases 0.000 description 1
- 238000005056 compaction Methods 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 229920006350 polyacrylonitrile resin Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000002310 reflectometry Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 238000009751 slip forming Methods 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B43—WRITING OR DRAWING IMPLEMENTS; BUREAU ACCESSORIES
- B43K—IMPLEMENTS FOR WRITING OR DRAWING
- B43K19/00—Non-propelling pencils; Styles; Crayons; Chalks
- B43K19/16—Making non-propelling pencils
- B43K19/18—Making pencil writing-cores
Definitions
- the present invention generally relates to a pencil lead and, more particularly, to an improved pencil lead, as well as to methods of and apparatus for making the pencil lead.
- pencil lead for a variety of forms of pencils including wood-sheathed ordinary pencils and especially spare leads for propelling-type pencils be thinner and stronger, i.e. stiffer and of greater strength to resist breaking, in addition to satisfying their general requisites of lower friction coefficient or greater smoothness to write, suitable wear resistance, highly reflectivity or darkness (e.g. blackness) and less dispersion of powder on writing.
- the present invention seeks to provide a novel and improved pencil lead suitable for a wide variety of pencils including wood-sheathed pencils and especially for a propelling pencil, which lead is greater in strength than the conventional pencil lead and can be much reduced in diameter while exhibiting a strength equivalent to or even higher than that of the conventional pencil lead.
- the present invention also seeks to provide a novel and improved pencil lead which is thin and stiff, and yet presents a sufficiently soft feeling on writing.
- the present invention seeks to provide a method of making the improved pencil lead-and to provide an apparatus for carrying out that method.
- a pencil lead constituted by a plurality of (preferably three or more) lead elements of a solid marking substance individually having a thick ranging between 10 and 250 microns, preferably between 10 and 100 microns and optimally between 30 and 50 microns, and bundled and joined together with a binder material.
- the solid marking substance may consist at least in part of finely divided graphite
- the binder material may consist at least in part of finely divided graphite and may contain a synthetic resin.
- the pencil led or the bundle of the lead elements when joined may advantageously have a thickness ranging between 0.1 and 0.5 mm.
- the solid marking substance may advantageously consist of a mixture essentially of graphite particles and at least one synthetic resin uniformly mixed and heat-treated.
- the graphite particles may be particles of a uniform particle size in a range between 10 and 100 or 200 microns and preferably between 30 and 50 microns, but preferably should include particles of a relatively small, uniform particle size (e.g. between 1 and 10 microns) and particles of a relatively large, uniform particle size (e.g. between 10 and 100 microns or between 150 and 200 microns).
- the invention also provides, in a second aspect thereof, a method of making a pencil lead, comprising the steps of: (a) preparing a semi-soft solid marking substance; (b) extruding the said substance to prepare a plurality of lead elements of the said substance individually having a thickness ranging between 10 and 250 microns and preferably between 10 and 100 microns; and (c) bundling the said lead elements and joining them with a binder material to form the said pencil lead.
- the method advantageously further comprises the step (d) of heating the said lead elements at least one temperature between 800 and 3500°C subsequent to step (b) and prior to step (c), and further the step (e) subsequent to step (c), of heating the said bundled lead elements at a temperature between 1000 and 2000°C.
- each of steps (d) and (e) is carried out in an inert atmosphere (e.g. argon) or in a graphite powder to prevent the lead elements from being oxidized.
- the invention also provides, in a third aspect thereof, an apparatus for making a pencil lead, comprising: a vessel for retaining a semi-soft solid marking substance; means for extruding the said substance in the said vessel to prepare a plurality of lead elements of the said core material having a thickness ranging between 10 and 250 microns; and means for bundling the said lead elements and joining them with a binder material to form the said pencil lead.
- US patent specification 2149905 discloses a lead pencil whose lead is produced from a number of strands. However, the lead is in the form of such strands only during an intermediate step in the manufacturing process, and not in the final product, merged to form the final lead.
- the conventional single graphite-based pencil lead is in the form of a circular rod having a diameter D of 0.2 to 0.5 mm, and electronmicro- graphical observation has revealed that it has a texture generally as illustrated in Fig. 1. It has been observed that the texture has fine graphite grains shown by fine gathers 11 closer to the peripheral surface S of the core 1 and coarse graphite grains shown by coarse gathers 12 deeper inside the core 1. It has been found that as the diameter of such a graphite-based lead 1 is reduced, the grains 11 closer to the peripheral surface approach in size and appearance the grains 12 deeper inside the core 1. It has thus been assumed that the finer the core 1, the greater its strength (i.e. breaking force per cross-sectional area). This has been experimentally confirmed as shown by the graph of Fig.
- the novel pencil lead according to the invention has been devised with this discovery in mind and, as shown in Figs. 3, 4 and 5 by way of example, example, comprises a plurality of lead elements 10 of a solid marking substance individually having a thickness ranging between 10 and 250 microns, preferably between 10 and 100 microns, and bundled and firmly joined together with a binder material 13.
- a binder material 13 Three, seven and five lead elements 10 are used in the embodiments of Figs. 3, 4 and 5, respectively.
- the lead elements 10 circular in section may have a diameter and hence a thickness of 30 to 50 microns. This makes a composite pencil lead having an overall thickness of 0.1 mm in Fig. 3 and composite pencil leads having an overall thickness of 0.3 mm in Figs. 4 and 5.
- Electron-micrographical observation shows that a graphite-based pencil lead or elements lead of such a thickness has a uniform graphite grain distribution throughout its body. Measurements show also that each of the composite leads of Figs. 3, 4 and 5 has a strength approaching or even greater than 10 tons/cm 2 (i.e. 99.64 x 10 7 N/m 2 ). This represents five times or more increase in strength than conventional single leads of 0.2 mm diameter which have at most a strength of 2 tons/cm 2 (i.e. 19.928 x 10 7 N/ m 2 ). It has been found that the composite lead of Fig. 3 of 0.1 mm in diameter constituted with three lead elements 10 has a strength of 28 tons/ cm 2 (i.e. 278 .99 x 10 7 N/m 2 ), thus being 14 times stronger than the conventional single lead structure of the same diameter.
- raw solid marking substance 2 retained in a receptacle 3 is forced through a plurality of small extrusion dies or spinneret openings 4 (e.g. individually circular in cross-section) to produce a plurality of continuously formed lead elements 10 and of material individually having a uniform thickness as described.
- the material 2 may be a semi-soft sdolid or solution of a synthetic resin R (e.g. polyacrylonitrile resin monomer) in which graphite particles G are uniformly distributed and as conventionally is heated, say, at a temperature of 200°C during extrusion.
- a synthetic resin R e.g. polyacrylonitrile resin monomer
- the graphite particles may be of a uniform particle size of, say, 30 to 50 microns but, according to a preferred feature of the invention, should preferably include particles of a relatively small, uniform particle size of around 5 microns, e.g. 1 to 10 microns, and particles of a relatively large, uniform particle size of 10 to 100 microns or 150 to 200 microns.
- the lead elements 10 continuously extruded through the openings 4 in parallel with one another are passed as a group 5 through a heating stage 6 comprising a primary baking heater 6a and a further heater 6b, then through a joining stage 7 and a final heating stage 8, and are finally squeezed between a pair of compression rollers 9a and 9b which serve to apply a sufficient tension to each of the lead elements 10 being drawn from the receptacle 3.
- the die openings 4 are formed spaced apart from one another with a suitable spacing in a bottom wall of the receptacle 3.
- the heater 6a is provided to heat the lead elements 10 being drawn from the openings 4 at a temperature of, say, 1000°C thereby baking the lead elements 10.
- the heater 6b is used to heat-treat the baked lead elements 10 at a temperature of, say, 3000°C, thereby homogenizing graphite crystallization.
- the parallel-running filaments are bundled in the joining stage 7 which includes an opening 7a, typically circular in section, defined by the wall of a metal frame 7b and an outlet nozzle 7c of an injector 7d.
- the latter includes a hopper 7e for feeding a binder material 13, e.g. a mixture of graphite particles and 10% by weight stylene solutioned in toluene, into a chamber 7f in which a plunger 7g formed with a screw 7h extends toward the nozzle opening 7c and is rotationally driven by a motor 7m.
- a binder material 13 e.g. a mixture of graphite particles and 10% by weight stylene solutioned in toluene
- the binder material 13 is continuously fed into the nozzle 7c and in turn to opening 7a to distribute itself around the individual lead elements 10 and to fill the interstices therein.
- a roughly jointed composite lead 20' with a cross-section as shown in Fig. 7 is formed.
- the coarse lead 20' is then passed through the heater 8 and baked there at a temperature of, say, 1200°C, and thereafter squeezed between the compression rollers 9a and 9b rotating in the directions shown by arrows to yield a densified or finished composite core 20.
- Such a composite pencil lead made in the manner so far described has practically the same appearance as a conventional single lead and yet has much greater strength, as described already.
- the finished lead 20 is cut by a blade 15 disposed downstream of the compaction stage 9 and intermittently operated by a motor 16 to provide successive pieces of the finished lead of a desired length.
- graphite particles in the solid marking substance 2 have particles of a smaller uniform particle size around 5 microns and a larger uniform particle size between 10 and 100 microns or 150 to 200 microns. With these different size grades of particles mixed uniformly to constitute the solid marking substance 2, it has been found that a composite pencil lead excellent in strength and yet relatively soft and smooth to write with is provided.
Landscapes
- Inks, Pencil-Leads, Or Crayons (AREA)
Description
- The present invention generally relates to a pencil lead and, more particularly, to an improved pencil lead, as well as to methods of and apparatus for making the pencil lead.
- It is desirable that pencil lead for a variety of forms of pencils including wood-sheathed ordinary pencils and especially spare leads for propelling-type pencils be thinner and stronger, i.e. stiffer and of greater strength to resist breaking, in addition to satisfying their general requisites of lower friction coefficient or greater smoothness to write, suitable wear resistance, highly reflectivity or darkness (e.g. blackness) and less dispersion of powder on writing.
- The present invention seeks to provide a novel and improved pencil lead suitable for a wide variety of pencils including wood-sheathed pencils and especially for a propelling pencil, which lead is greater in strength than the conventional pencil lead and can be much reduced in diameter while exhibiting a strength equivalent to or even higher than that of the conventional pencil lead.
- The present invention also seeks to provide a novel and improved pencil lead which is thin and stiff, and yet presents a sufficiently soft feeling on writing.
- In addition, the present invention seeks to provide a method of making the improved pencil lead-and to provide an apparatus for carrying out that method.
- In accordance with the present invention, there is provided, in a first aspect thereof, a pencil lead constituted by a plurality of (preferably three or more) lead elements of a solid marking substance individually having a thick ranging between 10 and 250 microns, preferably between 10 and 100 microns and optimally between 30 and 50 microns, and bundled and joined together with a binder material. Specifically, the solid marking substance may consist at least in part of finely divided graphite, and the binder material may consist at least in part of finely divided graphite and may contain a synthetic resin. The pencil led or the bundle of the lead elements when joined may advantageously have a thickness ranging between 0.1 and 0.5 mm. The solid marking substance may advantageously consist of a mixture essentially of graphite particles and at least one synthetic resin uniformly mixed and heat-treated. The graphite particles may be particles of a uniform particle size in a range between 10 and 100 or 200 microns and preferably between 30 and 50 microns, but preferably should include particles of a relatively small, uniform particle size (e.g. between 1 and 10 microns) and particles of a relatively large, uniform particle size (e.g. between 10 and 100 microns or between 150 and 200 microns).
- The invention also provides, in a second aspect thereof, a method of making a pencil lead, comprising the steps of: (a) preparing a semi-soft solid marking substance; (b) extruding the said substance to prepare a plurality of lead elements of the said substance individually having a thickness ranging between 10 and 250 microns and preferably between 10 and 100 microns; and (c) bundling the said lead elements and joining them with a binder material to form the said pencil lead.
- The method advantageously further comprises the step (d) of heating the said lead elements at least one temperature between 800 and 3500°C subsequent to step (b) and prior to step (c), and further the step (e) subsequent to step (c), of heating the said bundled lead elements at a temperature between 1000 and 2000°C. Preferably, each of steps (d) and (e) is carried out in an inert atmosphere (e.g. argon) or in a graphite powder to prevent the lead elements from being oxidized.
- The invention also provides, in a third aspect thereof, an apparatus for making a pencil lead, comprising: a vessel for retaining a semi-soft solid marking substance; means for extruding the said substance in the said vessel to prepare a plurality of lead elements of the said core material having a thickness ranging between 10 and 250 microns; and means for bundling the said lead elements and joining them with a binder material to form the said pencil lead.
- US patent specification 2149905 discloses a lead pencil whose lead is produced from a number of strands. However, the lead is in the form of such strands only during an intermediate step in the manufacturing process, and not in the final product, merged to form the final lead.
- These and other features of the present invention as well as advantages thereof will become more readily apparent from the following description made with reference to the accompanying drawings in which:
- Fig. 1 is a cross-sectional view diagrammatically illustrating a texture of a single conventional graphite pencil lead;
- Fig. 2 is a graph illustrating the relationship between the thickness of the single graphite pencil lead and the strength thereof;
- Figs. 3, 4 and 5 are cross-sectional views diagrammatically illustrating pencil leads embodying the present invention;
- Fig. 6 is a diagrammatic view, essentially in elevational or longitudinal section, illustrating an apparatus for making a pencil lead according to the present invention; and
- Fig. 7 is a cross-sectional view diagrammatically illustrating a semi-finished lead which develops in the process utilizing the apparatus of Fig. 6.
- Referring now to the drawings:
- The conventional single graphite-based pencil lead is in the form of a circular rod having a diameter D of 0.2 to 0.5 mm, and electronmicro- graphical observation has revealed that it has a texture generally as illustrated in Fig. 1. It has been observed that the texture has fine graphite grains shown by fine gathers 11 closer to the peripheral surface S of the core 1 and coarse graphite grains shown by coarse gathers 12 deeper inside the core 1. It has been found that as the diameter of such a graphite-based lead 1 is reduced, the grains 11 closer to the peripheral surface approach in size and appearance the
grains 12 deeper inside the core 1. It has thus been assumed that the finer the core 1, the greater its strength (i.e. breaking force per cross-sectional area). This has been experimentally confirmed as shown by the graph of Fig. 2 in which the thickness (diameter 0) of the lead or graphite element in microns (u) is plotted along the abscissa and the strength thereof in tons/cm2 (alternatively Newtons/m2) plotted along the ordinate. Each of the abscissa and the ordinate is plotted in logarithmic scale. The graph of Fig. 2 shows that the logarithm of strength varies in inverse proportion to the logarithm of thickness. - The novel pencil lead according to the invention has been devised with this discovery in mind and, as shown in Figs. 3, 4 and 5 by way of example, example, comprises a plurality of
lead elements 10 of a solid marking substance individually having a thickness ranging between 10 and 250 microns, preferably between 10 and 100 microns, and bundled and firmly joined together with abinder material 13. Three, seven and fivelead elements 10 are used in the embodiments of Figs. 3, 4 and 5, respectively. In each example, thelead elements 10 circular in section may have a diameter and hence a thickness of 30 to 50 microns. This makes a composite pencil lead having an overall thickness of 0.1 mm in Fig. 3 and composite pencil leads having an overall thickness of 0.3 mm in Figs. 4 and 5. Electron-micrographical observation shows that a graphite-based pencil lead or elements lead of such a thickness has a uniform graphite grain distribution throughout its body. Measurements show also that each of the composite leads of Figs. 3, 4 and 5 has a strength approaching or even greater than 10 tons/cm2 (i.e. 99.64 x 107 N/m2). This represents five times or more increase in strength than conventional single leads of 0.2 mm diameter which have at most a strength of 2 tons/cm2 (i.e. 19.928 x 107 N/ m2). It has been found that the composite lead of Fig. 3 of 0.1 mm in diameter constituted with threelead elements 10 has a strength of 28 tons/ cm 2 (i.e. 278.99 x 107 N/m2), thus being 14 times stronger than the conventional single lead structure of the same diameter. - Referring to Fig. 6 which shows an apparatus for making a novel pencil lead according to the invention, raw solid marking
substance 2 retained in areceptacle 3 is forced through a plurality of small extrusion dies or spinneret openings 4 (e.g. individually circular in cross-section) to produce a plurality of continuously formedlead elements 10 and of material individually having a uniform thickness as described. Thematerial 2 may be a semi-soft sdolid or solution of a synthetic resin R (e.g. polyacrylonitrile resin monomer) in which graphite particles G are uniformly distributed and as conventionally is heated, say, at a temperature of 200°C during extrusion. The graphite particles may be of a uniform particle size of, say, 30 to 50 microns but, according to a preferred feature of the invention, should preferably include particles of a relatively small, uniform particle size of around 5 microns, e.g. 1 to 10 microns, and particles of a relatively large, uniform particle size of 10 to 100 microns or 150 to 200 microns. - The
lead elements 10 continuously extruded through theopenings 4 in parallel with one another are passed as agroup 5 through aheating stage 6 comprising aprimary baking heater 6a and afurther heater 6b, then through a joiningstage 7 and afinal heating stage 8, and are finally squeezed between a pair ofcompression rollers 9a and 9b which serve to apply a sufficient tension to each of thelead elements 10 being drawn from thereceptacle 3. - The
die openings 4 are formed spaced apart from one another with a suitable spacing in a bottom wall of thereceptacle 3. Theheater 6a is provided to heat thelead elements 10 being drawn from theopenings 4 at a temperature of, say, 1000°C thereby baking thelead elements 10. Theheater 6b is used to heat-treat the bakedlead elements 10 at a temperature of, say, 3000°C, thereby homogenizing graphite crystallization. - The parallel-running filaments are bundled in the joining
stage 7 which includes an opening 7a, typically circular in section, defined by the wall of a metal frame 7b and anoutlet nozzle 7c of an injector 7d. The latter includes ahopper 7e for feeding abinder material 13, e.g. a mixture of graphite particles and 10% by weight stylene solutioned in toluene, into achamber 7f in which aplunger 7g formed with ascrew 7h extends toward the nozzle opening 7c and is rotationally driven by amotor 7m. As theplunger 7g is rotated by themotor 7m, thebinder material 13 is continuously fed into thenozzle 7c and in turn to opening 7a to distribute itself around theindividual lead elements 10 and to fill the interstices therein. Thus, through the opening 7a, a roughly jointed composite lead 20' with a cross-section as shown in Fig. 7 is formed. The coarse lead 20' is then passed through theheater 8 and baked there at a temperature of, say, 1200°C, and thereafter squeezed between thecompression rollers 9a and 9b rotating in the directions shown by arrows to yield a densified or finishedcomposite core 20. Such a composite pencil lead made in the manner so far described has practically the same appearance as a conventional single lead and yet has much greater strength, as described already. - The finished
lead 20 is cut by ablade 15 disposed downstream of the compaction stage 9 and intermittently operated by amotor 16 to provide successive pieces of the finished lead of a desired length. - It is desirable to conduct heat-treatment at each of the
stages lead elements 10 or the core 20' from being oxidized. The course or finishedpencil lead 20' or 20 may be further subjected to impregnation with paraffine to improve its quality. - As mentioned previously, it is desirable that graphite particles in the solid marking
substance 2 have particles of a smaller uniform particle size around 5 microns and a larger uniform particle size between 10 and 100 microns or 150 to 200 microns. With these different size grades of particles mixed uniformly to constitute the solid markingsubstance 2, it has been found that a composite pencil lead excellent in strength and yet relatively soft and smooth to write with is provided.
Claims (35)
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP13166880A JPS5757696A (en) | 1980-09-24 | 1980-09-24 | Lead of pencil and its manufacture |
JP131668/80 | 1980-09-24 |
Publications (4)
Publication Number | Publication Date |
---|---|
EP0048571A2 EP0048571A2 (en) | 1982-03-31 |
EP0048571A3 EP0048571A3 (en) | 1982-06-09 |
EP0048571B1 EP0048571B1 (en) | 1984-08-01 |
EP0048571B2 true EP0048571B2 (en) | 1988-06-15 |
Family
ID=15063429
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP19810304138 Expired EP0048571B2 (en) | 1980-09-24 | 1981-09-10 | Pencil lead, and methods and apparatus for its manufacture |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0048571B2 (en) |
JP (1) | JPS5757696A (en) |
DE (1) | DE3165243D1 (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4545983A (en) * | 1981-08-26 | 1985-10-08 | Plough, Inc. | Method for making cosmetic pencils |
JPS61132628A (en) * | 1984-11-27 | 1986-06-20 | Inoue Japax Res Inc | Production of graphite fiber |
FR2693634B1 (en) * | 1992-07-17 | 1994-10-07 | Bsn | Food product in particular of the biscuit or pastry type and its manufacturing process. |
JP5025368B2 (en) * | 2007-07-26 | 2012-09-12 | 三菱鉛筆株式会社 | Solid drawing material |
JP6358795B2 (en) * | 2013-11-11 | 2018-07-18 | 三菱鉛筆株式会社 | Composite plate and manufacturing method thereof |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
DE126851C (en) * | ||||
GB191308351A (en) * | 1913-04-09 | 1914-03-19 | John Abbet Walls | Improvements in Pencils. |
US2149905A (en) * | 1936-05-30 | 1939-03-07 | Firm Koh I Noor Tuzkarna L & C | Lead for pencils, color pencils, copying pencils, or the like and process for manufacturing the same |
GB575868A (en) * | 1943-05-19 | 1946-03-08 | M A Ferst Ltd | Improvements in pencil leads and the like graphite marking elements |
GB1171634A (en) * | 1965-11-10 | 1969-11-26 | Dainihon Bungu Kabushiki Kaish | A method of preparing pencil leads |
-
1980
- 1980-09-24 JP JP13166880A patent/JPS5757696A/en active Pending
-
1981
- 1981-09-10 EP EP19810304138 patent/EP0048571B2/en not_active Expired
- 1981-09-10 DE DE8181304138T patent/DE3165243D1/en not_active Expired
Also Published As
Publication number | Publication date |
---|---|
DE3165243D1 (en) | 1984-09-06 |
EP0048571A2 (en) | 1982-03-31 |
EP0048571A3 (en) | 1982-06-09 |
JPS5757696A (en) | 1982-04-06 |
EP0048571B1 (en) | 1984-08-01 |
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