Car horn buttons made of PLEXIGLAS® Molding Compounds

© Evonik Industries AG, Konzernarchiv Hanau

A revolution in plastic processing

Soon after PLEXIGLAS® reached market maturity in the 1930s, chemists at Röhm & Haas were working on developing PLEXIGLAS® Molding Compounds for use in injection molding processes.

In a nutshell, injection molding processes involve materials that are liquefied and injected under pressure into a die. The finished product can then be removed from the die. The advantage of this process is that large quantities of highly precise molded parts can be produced cost-efficiently in a single step. For instance, molded components made of PLEXIGLAS® have become a staple in automotive pillar panels. This success story took its course in the 1930s.

Breaking new ground in PLEXIGLAS® research

In addition to successfully investigating the production of sheets, tubes and rods made of PLEXIGLAS®, the chemists at Röhm & Haas were also developing molding compounds for use in injection molding processes. While the injection molding of cellulose acetate and polystyrene had been possible since the end of the 1920s, the researchers had to tread new paths and develop a method for producing the PLEXIGLAS® granulate required for injection molding.

Numerous methods for producing PLEXIGLAS® granulate

First, they tried to produce vesicular and foam-like blocks that could be easily processed to granulate. Then, they developed the bead polymerization process, which was easier to control and thus better suited to industrial production. Adding low quantities of water-insoluble, powdery substances, the starting material was polymerized by stirring in water. After washing and drying, the result was a powder consisting of tiny beads. The chemists then worked on a new bulk polymerization process. They succeeded in creating crystal-clear blocks with highly uniform compositions, breaking them down mechanically and granulating them using extrusion machines. Today, the granulate is mainly produced in a continuous bulk polymerization process and marketed under the brand name PLEXIGLAS® Molding Compounds.

Spritzgießmaschine von Eckert & Ziegler

The right machine

To be able to process the PLEXIGLAS® Molding Compounds, the researchers also had to develop a suitable machine. They first tried hot-pressing in dies, then started using an extruder in 1934 and finally a small manual injection molding machine (see photo) by Eckert & Ziegler. The first fully automatic machine then came in the form of the “Isoma-Automat”, which was developed in the 1930s.

© Evonik Industries AG, Konzernarchiv Hanau

First applications

The first potential application of injection-molded PLEXIGLAS® Molding Compounds then presented itself when a company from Wuppertal tried to produce zippers with the material in the mid-1930s. However, their endeavor failed because the heat deflection temperature and the high-temperature stability of the injection molding compounds were insufficient.

The first series-produced components made of PLEXIGLAS® Molding Compounds were approx. 5-millimeter-long rods with a diameter of approx. 2 millimeters and a flat and a concave base. A microfilm with a souvenir picture was attached to the flat base. Viewed from the concave side, the picture was enlarged. Also referred to as “Stenops”, these lenses were inserted in pens and sold as souvenirs. Other products from the early days of injection molding include yellow reflective strips for bicycle pedals, which, due to their more precise design, had better reflective properties than strips made of glass. In addition, the molding compounds were ideal for producing emblems and badges (see cover photo), and later fountain pens and other writing and drawing instruments.

Today, Evonik offers an extensive product portfolio of PLEXIGLAS® Molding Compounds for all kinds of injection molding and extrusion applications. Products include pillar panels, headlight lenses and taillight covers, window profiles, efficient supermarket lamps and high-quality housing surfaces.