Patent GB-704063-A (GB)
Title: Improvements in or relating to the manufacture of writing means
IPC: C09D13/00
Filed: 1949-06-22
Abstract: Writing means such as pencils or crayons, with or without coatings, or parts thereof, such as leads, writing cores or sheaths for writing cores, are manufactured by extrusion or injection moulding using a mixture consisting of (a) a large quantity of "suitable material" which forms the basic material determining the character of the finished article, (b) a quantity of natural or synthetic wax small in proporation to the quantity of said suitable material and (c) a quantity of a thermoplastic synthetic resin or cellulose derivative which is always less than the quantity of said suitable material, the individual constituents being mixed before moulding either initially in groups or altogether so as to give ultimately a homogeneous mixture, this mixture being moulded under pressure in a dry and hot condition.  "Suitable material" means substances such as wood flour or dust, bone powder, cotton, cork, finely divided paper, straw meal, kaolin, graphite or dyestuffs, whose grain size influences the properties of the finished article.  The wax may be paraffin wax, synthetic hard wax or lamp black (which contains wax).  The thermoplastic synthetic resin includes such substances as polyvinyl chloride, polyamides or polythene, singly or in admixture, and mixtures with cellulose derivatives may be used. Plasticisers and lubricants, both small in quantity compared with the quantity of thermoplastic synthetic resin or cellulose derivative, may be added, also small quantities of fats. Colouring substances, e.g. zinc white, titanium white or ochre, may be added.  The thermoplastic synthetic resin or cellulose derivative, which acts as a binding agent, may have added to it, as an additional binding agent, thermoplastic natural resin or thermosetting synthetic resin.  The core and sheath may be extruded together with a coating composition, or the core alone may be extruded with a similar coating.  One machine may produce several pencils simultaneously.  The materials used in one example for making a sheath are wood dust, straw meal, rice flour, dibutyl phthalate, paraffin wax, zinc stearate and titanium white. In another example two compositions are mixed together, the first composition comprising polyvinylchloride, colophony powder, wood dust and tricresyl phosphate and the second comprising wax, calcium stearate, zinc white and casein.  An example of a composition for making a core comprises graphite, lamp black, ethyl cellulose and Kongo resin, plasticized with castor oil.  An example of a coating composition comprises polyvinyl chloride, tricresyl phosphate, ochre and titanium white.  To the composition for the core or sheath may be added a substance which liberates gas upon heating, e.g. ammonium carbonate or bicarbonate.  The Specification as open to inspection under Sect. 91 comprises also the addition of perfumes or tasty materials, or luminescent substances.  This subject-matter does not appear in the Specification as accepted.ALSO:Pencils and crayons are moulded by extrusion or injection from a suitable mixture (see Group IV (a)) under pressure in a dry and hot condition.  With extrusion moulding a continuous rod is cut into suitable lengths.  The cores (or leads) may be moulded separately, and so may the sheaths, or a complete pencil may be extruded through a common nozzle at the end of the machine.  The cores and sheaths may be coated.  One machine may produce several pencils simultaneously.