894 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS :•: ' 11 • : •' :' ......... - .... :•.. '....--•f':-:•,:•: •!•' .' •' •:• ... ::,. :• .&"- : '• . .-i ß . -•:: . •- - . -•. •., .. ..... ,:,•:- .. •..•', ..• •. : ...... ..:. • ß • • - .•..•.:,• ..... .? ' '• •. :' •' . ....: '. •. -'• , • •-' . .":. '2:- - ::..-.::...•:• ...• ... •.• •:.--....:•: •... ..•.........:.--.r-:-: :.•.-.•:•,•....?- •..• .. .--•,.....•...• ..•.• :• .•:•.•'•-•- •. .....• ':}.... .... ..:•":'.' . '..•..•.' .... '• :• ,:•: ß . ........ •.. - ..,:½: ..• •:4•. ?- •:.:.• :•}..,:-.-•:...:• :...... • .... :• . ....•. ,....•:..:..: ..... .• .• o • ...... :• -,.• •T' ..•.j•½: •' -• .•. ß •" -•4' ':' • ' '• • i• ' ".:..•:•. : •.•: . -•,, . . ,•...:•. ....... • .... ::• ....... Figure 1. Lead extruder, Fr. Erhardt, Nurnberg, West Germany The first system could be considered ideal in that it is completely pressure-dependent that is, when a given pressure is applied to the mass it will extrude through the die. This type of system would not usually be of a wax base. The second system has properties of a thixotropic nature that is, on the application of pressure the system experiences an isothermal-revers- ible sol-gel transformation. This is usually observed in wax-oil systems such as carnauba wax and mineral oil combination. The final system is one that is frequently encountered in cosmetic lead manufacturing. This system is such that it will not flow when initially put under pressure, but rather it will compress until the internal friction has generated enough heat to lower the viscosity, and the mass will flow through the die. This system is both temperature- and pres- sure-dependent. The various systems that are encountered in cosmetic lead manu- facturing require an extrusion apparatus that can be regulated for both pressure and rate. Hydraulic units for lead manufacturing are rare and in most cases they cannot attain the pressure required for all formula- tions. The lead industry, both graphite and cosmetic, has relied on an extruder that attains high pressures by the use of gears and a screw mechanism. The equipment shown in Fig. 1 is a specially adapted lead extruder for cosmetic use.

EXTRUSION OF COSMETIC PRODUCTS 895 '•.. • . i .:: • .. ::- ..... •X': .... .i•:::':. • {• •..' '•.., ß •' . .5::.:..:::a,..:.•. %%.., ß :y. .y.•- • ..:'• '•v:'. . -• . ,:.., . .::- -.:---. ...... ß . ß .... '. .'•:,..,4 ....•,:•:•.:...... Figure 2. Hydraulic lead extruder, Red Cedar Pencil Company, Lewisburg, Tenn. This machine is a constant-pressure, variable-rate extruder. The large box at the base of the control panel contains a gear system to regu- late the rate of extrusion. The ram is a large screw, turned by a series of gears, that has a force of 90 tons. The lead is extruded through the die, picked up by the belt, and cut to the size of the boards. The cut lead travels on the belt until it is pushed onto the board. It is then cut to the required length and packed. Two cylinders are used in this operation one is being filled while the other is extruded. This type of equipment is satisfactory for most cosmetic leads. For a system that is pressure-dependent, the extruder shown in Fig. 2 has been used. This is an oil hydraulic system that can attain pressures of 75,000 psi. The rate of extrusion is regulated by the amount of oil allowed into the cylinder. In this case, the lead is ex- truded through the bottom of the cylinder and put on lead boards by hand. The preparation of the material prior to extrusion is similar to that of lipstick manufacturing. The waxes are melted and the pigments are dispersed by means of a triple-roll mill. An important difference, how- ever, is the removal of air prior to extrusion. Figure 3 shows the result of air in cosmetic leads. This type of air is easily observable and the lead can be discarded by the operator. In some cases, air does not ap- pear on the surface of the lead but remains in the body of the wax. Results of this type of air are shown in Fig. 4.