PAPER PENCIL LEAD

Abstract

The present invention concerns an extrudable, unexpanded paper pencil lead, comprising, by weight relative to the total weight of the lead, between 40 and 60%, and advantageously between 44 and 50%, of graphite; between 15 and 40%, and advantageously between 20 and 35%, of a polyolefin; between 5 and 15%, and advantageously between 6 and 10%, of a colourless mineral filler; between 5 and 20%, and advantageously between 5 and 15%, of carbon black coated with or mixed with a polyolefin wax or a polyolefin; between 0 and 16%, and advantageously between 5 and 15%, of an additive. It further concerns the paper pencil comprising a lead according to the invention.

Claims

1. A non-expanded, extrudable paper pencil lead, comprising, on a weight basis relative to the total weight of the lead: between 40 and 60% of graphite; between 15 and 40% of a polyolefin; between 5 and 15% of a colorless mineral filler; between 5 and 20% of carbon black coated with or mixed with a polyolefin wax or a polyolefin; between 0 and 16% of an additive.

2. The paper pencil lead as claimed in claim 1, wherein the polyolefin is polypropylene.

3. The paper pencil lead as claimed in claim 1, wherein the colorless mineral filler is chosen in the group consisting of a clay, talc, boron nitride, silica, calcium carbonate, mica, steatite powder, and mixtures thereof.

4. The paper pencil lead as claimed in claim 3, wherein the colorless mineral filler is a lamellar mineral filler.

5. The paper pencil lead as claimed in claim 1, wherein the carbon black content of the carbon black coated with or mixed with a polyolefin wax or a polyolefin is between 25 and 65%, relative to the total weight of the carbon black coated with or mixed with a polyolefin wax or a polyolefin.

6. The paper pencil lead as claimed in claim 1, wherein the carbon black is coated with a polyolefin wax.

7. The paper pencil lead as claimed in claim 14, wherein the polyolefin wax is a polyethylene wax.

8. The paper pencil lead as claimed in claim 1, wherein the additive is chosen in the group consisting of glidants, processing agents, coupling agents, dispersants, lubricants, and mixtures thereof.

9. The paper pencil lead as claimed in claim 14, which does not comprise any plasticizer.

10. The paper pencil lead as claimed in claim 14, which is extruded.

11. The paper pencil lead as claimed in claim 1, wherein the graphite has a volume-based particle size D50 measured by laser particle size analysis of between 15 and 20 μm.

12. A paper pencil comprising a lead as claimed in claim 1.

13. A non-expanded, extrudable paper pencil lead as claimed in claim 1, which comprises, on a weight basis relative to the total weight of the lead: between 44 and 50% of graphite; between 20 and 35% of a polyolefin; between 6 and 10% of a colorless mineral filler; between 5 and 15% of carbon black coated with or mixed with a polyolefin wax or a polyolefin; between 5 and 15% of an additive.

14. The paper pencil lead as claimed in claim 4, wherein the colorless mineral filler is a clay.

15. The paper pencil lead as claimed in claim 14, wherein the clay is chosen in the group consisting of montmorillonite, bentonite and kaolin.

16. The paper pencil lead as claimed in claim 15, wherein the clay is kaolin.

17. The paper pencil lead as claimed in claim 5, wherein the carbon black content of the carbon black coated with or mixed with a polyolefin wax or a polyolefin is between 30 and 60% by weight, relative to the total weight of the carbon black coated with or mixed with a polyolefin wax or a polyolefin.

18. The paper pencil lead as claimed in claim 6, wherein the carbon black content is between 40 and 65% by weight, relative to the total weight of the carbon black coated with a polyolefin wax.

19. The paper pencil lead as claimed in claim 8, wherein the additive is chosen in the group consisting of stearates, an amide, waxes, fatty acids, glycerol and derivatives thereof, siloxane grafted onto polypropylene, maleic anhydride-grafted polypropylene and mixtures thereof.

Description

EXAMPLE 1

[0053] The two tables below collate examples of lead compositions according to the present invention for obtaining the characteristics of improving the erasability, good darkness and sufficient chemical properties to be used in paper pencils.

TABLE-US-00001 TABLE 1 Composition No. No. No. No. No. (weight %)/example 1 2 3 4 5 Polypropylene 26 26 26 24 26 Kaolin 8 6 10 Talc 8 Silica 8 Carbon black coated with 9 9 9 9 polyethylene wax Carbon black/low-density 9 polyethylene base masterbatch Graphite 47 47 47 47 47 Additive 10 12 10 10 10 Total 100 100 100 100 100

TABLE-US-00002 TABLE 2 Composition No. No. No. (weight%)/example 6 7 8 Polypropylene 30 24.8 26 Kaolin 8 7.5 Bentonite 8 Carbon black coated with 9 8.5 9 polyethylene wax Graphite 45 44.8 47 Additive 8 14.4 10 Total 100 100 100