Writing or coloring pencil

Abstract

A writing or coloring pencil has three layers obtained by co-extrusion, including an unexpanded polymer-based lead, an unexpanded intermediate protective layer surrounding the lead and comprising an ethylene (C1-C4 alkyl) acrylate copolymer, alone or as a blend with a styrene polymer, and an expanded styrene polymer-based synthetic wood material surrounding the intermediate protective layer.

Claims

1. A writing or coloring pencil comprising the following three layers obtained by co-extrusion: an unexpanded polymer-based lead; an unexpanded intermediate protective layer surrounding the lead and comprising an ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer, alone or as a blend with a styrene polymer; and an expanded styrene polymer-based synthetic wood material surrounding the intermediate protective layer.

2. The writing or coloring pencil according to claim 1, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer is at least one copolymer selected from the group consisting of ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer and ethylene butyl acrylate copolymer.

3. The writing or coloring pencil according to claim 2, wherein be ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer is ethylene butyl acrylate copolymer.

4. The writing or coloring pencil according to claim 1, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer is in a sheath and has a content of the sheath that is in the range 20% to 100% by weight, with respect to a total weight of a composition of the sheath.

5. The writing or coloring pencil according to claim 4, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer content of the sheath is in the range 30% to 55% by weight, with respect to the total weight of the composition of the sheath.

6. The writing or coloring pencil according to claim 1, wherein the unexpanded polymer-based lead comprises a styrene polymer or a polyolefin.

7. The writing or coloring pencil according to claim 6, wherein the unexpanded polymer-based lead is acrylonitrile butadiene styrene or polypropylene.

8. The writing or coloring pencil according to claim 1, wherein the unexpanded intermediate protective layer has a thickness that is in the range 0.11 mm to 0.31 mm.

9. The writing or coloring pencil according to claim 8, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer is in a sheath and has a content of the sheath that is in the range 25% to 50% by weight, with respect to the total weight of a composition of the sheath.

10. The writing or coloring pencil according to claim 9, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer content of the sheath is in the range 30% to 40% by weight, with respect to the total weight of the composition of the sheath.

11. The writing or coloring pencil according to claim 8, wherein the thickness of the unexpanded protective intermediate layer is in the range 0.14 mm to 0.17 mm.

12. A writing or coloring pencil according to claim 1, wherein the unexpended intermediate protective layer has a thickness in the range 0.05 mm to 0.10 mm.

13. The writing or coloring pencil according to claim 12, wherein the thickness of the unexpanded protective intermediate layer is in the range 0.07 mm to 0.09 mm.

14. The writing or coloring pencil according to claim 12, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer is in a sheath and has a content of the sheath that is in the range 25% to 100% by weight, with respect to the total weight of a composition of the sheath.

15. The writing or coloring pencil according to claim 14, wherein the ethylene (C.sub.1-C.sub.4 alkyl) acrylate copolymer content of the sheath is in the range 45% to 55% by weight, with respect to the total weight of the composition of the sheath.

16. The writing or coloring pencil according to claim 1, wherein the unexpanded polymer-based lead has a diameter that is in the range 2 mm to 3.8 mm.

17. The writing or coloring pencil according to claim 1, wherein the unexpended protective intermediate layer is of a color that is different from a color of the unexpanded polymer-based lead and from a color of the synthetic wood material or the unexpended protective intermediate layer is of a color that is that is the same as that of the lead or as that of the synthetic wood material.

18. The writing or coloring pencil according to claim 1, wherein the styrene polymer of the synthetic wood material is polystyrene.

19. The writing or coloring pencil according to claim 1, which is a graphite pencil, wherein the unexpanded polymer-based lead comprises graphite.

20. The writing or coloring pencil according to claim 1, which is a colour pencil.

21. The writing or coloring pencil according to claim 1, further comprising: a supplemental decorative layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a cross section of an example of a graphite pencil of the invention with a section that is hexagonal.

(2) FIG. 2 is a perspective view of the example of a graphite pencil of the invention with a section that is hexagonal.

DETAILED DESCRIPTION OF THE DISCLOSURE

(3) The example of the graphite pencil 4 of the invention with a section that is hexagonal and shown in FIGS. 1 and 2 therefore comprises four layers, the lead (1) with a circular section, the protective intermediate layer (2) with a circular section that concentrically surrounds the lead (1), the expanded synthetic wood material (3) with a hexagonal section that concentrically surrounds the protective intermediate layer, and a decorative layer (5) with a hexagonal section that concentrically surrounds the synthetic wood material.

(4) The protective intermediate layer 2 is of a color that is different from that of the lead and the synthetic wood material and it is therefore visible both on the cross section of the pencil (FIG. 1), but also on the sharpened portion of the pencil (FIG. 2).

Example 1: Polyolefin-Based Lead

(5) A graphite pencil of the invention with a section that is hexagonal as illustrated in FIGS. 1 and 2 or with a section that is triangular was produced by co-extrusion.

(6) The compositions of the various layers were as follows: lead: polypropylene (PP, 25-35%), graphite (40-50%)+additives/pigments; protective intermediate layer: polystyrene or ABS (50-70%), ethylene butyl acrylate (EBA) (30-50%)+pigments. synthetic wood material (3): polystyrene (90-95%)+additives/pigments/colorless mineral filler.

(7) The thickness of the protective intermediate layer was 0.15 mm and that of the lead was 2.3 mm.

(8) A visual inspection was carried out after the pencil sharpening step.

(9) Good adhesion and very good sharpenability were observed.

(10) When this pencil was compared with a pencil obtained under the same conditions but with a sheath comprising: polystyrene or ABS (60-80%), EVA (20-40%)+pigments, better adhesion of the sheath with the lead was observed with the pencil of the present invention.

Example 2: Polyolefin-Based Lead

(11) A graphite pencil of the invention with a section that is hexagonal as illustrated in FIGS. 1 and 2 or with a section that is triangular was produced by co-extrusion.

(12) The compositions of the various layers were as follows: lead: polypropylene (PP, 25-35%), graphite (40-50%)+additives/pigments; protective intermediate layer: polystyrene (60%), ethylene butyl acrylate (EBA) (35%)+masterbatch (5%); synthetic wood material (3): polystyrene (90-95%)+additives/pigments/colorless mineral filler.

(13) The thickness of the protective intermediate layer was in the range 0.07 to 0.09 and that of the lead was 2.3 mm.

(14) A visual inspection was carried out after the pencil sharpening step.

(15) Good adhesion and very good sharpenability were observed.

(16) When this pencil was compared with a pencil obtained under the same conditions but with a sheath comprising: polystyrene (60%), EVA (35%)+masterbatch (5%), better adhesion of the sheath with the lead was observed with the pencil of the present invention, even though the sheath was very thin.

Example 3: Styrene-Polymer-Based Lead

(17) A colour pencil of the invention with a section that is hexagonal as illustrated in FIGS. 1 and 2 or with a section that is triangular was produced by co-extrusion.

(18) The compositions of the various layers were as follows: lead: ABS (35-40%), kaolin (10-15%), calcium stearate (25-30%)+additives/plasticizer/pigments (20-30%); protective intermediate layer: ABS (40-60%), ethylene butyl acrylate (EBA) (40-60%)+pigments; synthetic wood material (3): polystyrene (90-95%)+additives/pigments/colorless mineral filler.

(19) The thickness of the protective intermediate layer was 0.08 mm and that of the lead was 3.2 mm.

(20) This pencil was compared with a pencil obtained under the same conditions but with a sheath comprising: polystyrene (40-60%), EVA (40-60%)+pigments in a falling out lead test.

(21) This test served to verify that the lead did not become detached from the wood material.

(22) Test Equipment

(23) TCM 201M CHATILLON AMETEK dynamometer or equivalent force meter

(24) Sample Used in the Test:

(25) 50 pencils at t=0

(26) minimum of 10 pencils after one cycle, 24 h at 0 C., 24 h at 40 C. for 21 days.

(27) Test Method:

(28) The set up was positioned vertically in a support and lowered at 50 millimeters per minute (ram/min) in order to come into contact with a metal plate.

(29) Test Results:

(30) The result was the measurement of the force necessary to push in the lead, expressed in daN.

(31) None of the leads was considered to be falling out if the value was higher than 4 daN.

(32) None of the test samples of the pencil of the present invention exhibited a falling out lead.

(33) In contrast, the percentage of leads which fell out for the comparative pencils with an EVA-based sheath was approximately 30%, with half of them having a value of less than 4 daN and so considered to be falling out.

(34) The pencil of the present invention, with a sheath comprising EBA instead of EVA, therefore exhibits better adhesion between the lead and the wood material; this avoids any possible problems with loss of cohesion during the pencil sharpening operation.