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AssigneeConte
InventorsJacques Bachelet, Philippe Chavatte, Guy Chochoy, Jose Duez, Claude Fouble, Didier Lange
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According to the invention, the writing or coloring pencil is obtained by tri-extrusion of three thermoplastic materials forming the lead material, the expanded wood material and an intermediate protective layer, containing no expanding agent, which is compatible with the lead material and the wood material and has a melting point which is equal to or higher than the melting points of the lead material and the wood material. The three co-extruded materials all contain in particular the same basic component, such as for example a polystyrene-methacrylate copolymer. The protective layer can be of a different color from the other two layers. The writing or coloring pencil with protective casing between the lead and the expanded wood, all three being in thermoplastic material, is, in particular a pencil with soft or extra-soft lead.
A method for continuously manufacturing a writing or coloring pencil, consisting in coextruding in one coextrusion head a lead material which is a first thermoplastic material containing a filler, and covering said lead material with a layer of wood material which is a second coextruded thermoplastic material containing an expanding agent, wherein the coextruded lead material is, prior to receiving its casing of the wood material, enveloped in an intermediate protective layer produced by coextruding a further thermoplastic material which contains no expanding agent, and is compatible with the lead material and the wood material and has a melting point which is equal to or higher than both the melting points of the lead material and of the wood material, such that the thermoplastic material constituting the protective layer is less fluid than the lead and wood materials at the temperature of the coextrusion.
A writing or coloring pencil, constituted in a coextrusion processing by the superposition of a core of a lead material which is a first thermoplastic material containing a filler and of a layer of wood material which is a second thermoplastic material containing an expanding agent, said pencil comprising an intermediate protective layer between the lead material and the wood material, intermediate layer including non-expanded thermoplastic material, being compatible with the lead material and the wood material and having a melting point which is equal to or higher than both the melting points of the lead material and of the wood material, such that the thermoplastic material constituting the protective layer is less fluid than the lead and wood materials at the temperature of the coextrusion.
Dependencies are inferred from the claim text.