Marking carbonized pencil leads using sulfonated lignin or an aqueous sodium salt of lignin as binder
Abstract
Abstract PENCIL LEAD IS MADE BY MIXING 40 TO 50 PARTS OF SULFONATED LIGNIN OR AN AQUEOUS SODIUM SALT LIGNIN SOLUTION WITH 30 TO 40 PARTS GRAPHITE AND 5 TO 10 PARTS OF CARBON BLACK, KNEADING THE MIXTURE AND HEATING TO REDUCE THE MOISTURE CONTENT TO BELOW 20% AFTER EXTRUDING THE MIXTURE INTO THE FORM OF PENCIL LEAD AND DRYING THE FORMED ARTICLES THEY ARE HEATED TO ABOUT 500*C. AT A VERY SLOW RATE OF 5-10*C. PER HOUR. ONCE 500*C. HAS BEEN REACHED THE ARTICLES ARE FURTHER HEATED TO ABOVE 1000*C. AT A FASTER RATE OF 30-50*C. PER HOUR IN A GASEOUS PHASE ATMOSPHERE THAT IS INERT TO THE ARTICLES, SUCH AS NITROGEN. THE VERY SLOW HEATING RATE UP TO 500*C. IS ESSENTIAL TO GOOD STRENGTH OF THE CARBONIZED PENCIL LEAD. SUPPLEMENTARY BINDERS AND PLASTICIZERS SUCH AS POLYVINYL ALCOHOL, TRAGACANTH GUM, SODIUM ALGINATE AND CARBOXYMETHYLCELLULOSE CAN BE ADDED TO PREVENT PREMATURE THERMAL DECOMPOSITON OF THE LIGNIN.
Inventors
- 👤 Takamasa Kawakubo
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