A METHOD OF MAKING A PENCIL OR A CRAYON BY TRIPLE EXTRUSION, AND A PENCIL OR A CRAYON INCLUDING AN INTERMEDIATE PROTECTIVE LAYER

摘要

The method of continuously manufacturing pencils orcrayons consists in coextruding a filled firstthermoplastic material referred to as "lead" material,and around it both an intermediate "protective" layer ofa thermoplastic material having no expanding agent and asecond thermoplastic material containing an expandingagent and referred to as "wood" material, and in coolingsaid coextruded thermoplastic materials. According tothe invention, the thermoplastic material constitutingthe protective layer is determined so that during coolingit remains deformable while the lead material shrinks.The pencil is constituted by superposing a core of afilled first thermoplastic material referred to as "lead"material, a protective layer of a non-expandedthermoplastic material, and a layer of an expanded secondthermoplastic material referred to as "wood" material.According to the invention, the thermoplastic materialconstituting the protective layer has a solidificationpoint which is lower than that of the thermoplasticmaterial constituting the lead material.