In his Zagreb workshop, Slavoljub Penkala patented the invention, which is still used around the world - a mechanical pencil. This doctor of organic chemistry has changed life for anyone who has ever been able to write. His first mechanical pencil Penkala patented under his name in 1906, and only a year later he did the same with his first solid ink pencil.

Owner of numerous inventions and patents, Penkala has been trying to produce his inventions and thus gain value for use. Thus, having met Edmund Moster and his brother Mavro in 1906, he entered into a contract with them to found Penkala-Edmund Moster & Co. The company built a factory in Zagreb and began producing automatic pencils, fountain pens and other print accessories according to Penkala's patents. This factory soon became one of the world's largest manufacturers of stationery, and the mechanical pencil achieved a great market success in 70 countries. That is why the name of Penkala, under which it was sold, became popular in the style of the pen of this kind, and in some countries it is still used today.

Slavoljub Penkala emphasized his great love for Croatia. Although Eduard Penkala was born in today's Slovakia, when he came to Zagreb he changed his name to Slavoljub to highlight his love and affiliation to the Croatian people. He decided to change the name at the time of intensive pursuit of Hungarisation, and change of name was his way of showing resistance. He died on February 5, 1922 in Zagreb.