A method of making a pencil or a crayon by triple extrusion,...

B - Operations – Transporting – 43 – K

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B43K 19/16 (2006.01)

Patent

CA 2362775

The method of continuously manufacturing pencils or crayons consists in coextruding a filled first thermoplastic material referred to as "lead" material, and around it both an intermediate "protective" layer of a thermoplastic material having no expanding agent and a second thermoplastic material containing an expanding agent and referred to as "wood" material, and in cooling said coextruded thermoplastic materials. According to the invention, the thermoplastic material constituting the protective layer is determined so that during cooling it remains deformable while the lead material shrinks. The pencil is constituted by superposing a core of a filled first thermoplastic material referred to as "lead" material, a protective layer of a non-expanded thermoplastic material, and a layer of an expanded second thermoplastic material referred to as "wood" material. According to the invention, the thermoplastic material constituting the protective layer has a solidification point which is lower than that of the thermoplastic material constituting the lead material.

Le procédé de fabrication en continu de crayons à écrire ou à colorier consiste à co-extruder une première matière thermoplastique chargée, dénommée matière mine, et autour de celle-ci une couche intermédiaire dite de protection dans une matière thermoplastique exempte d'agent d'expansion et une seconde matière thermoplastique contenant un agent d'expansion, dénommée matière bois, et à refroidire lesdites matières thermoplastiques co-extrudées. Selon l'invention la matière thermoplastique constitutive de la couche de protection est déterminée en sorte de rester déformable pendant le retrait de la matière mine, lors du refroidissement. Le crayon (1) est constitué par la superposition d'une âme (1) en une première matière thermoplastique chargée dénommée matière mine, d'une couche de protection (2) d'une matière thermoplastique non-expansée et d'une couche (3) d'une deuxième matière thermoplastique expansée dénommé matière bois. Selon l'invention, la matière thermoplastique constitutive de la couche de protection (2) a un point de solidification qui est inférieur à celui de la matière thermoplastique constitutive de la matière mine (1).

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