Reflective paint, also known as premixed retro-reflective paint, was invented by the 3M company in 1949. The invention was called “Highway Marking Paint Containing Glass Beads” and basically consisted of reflective glass spheres mixed with white or yellow paint. This liquid traffic paint was designed to be sprayed onto road surfaces and, when dry, would create a reflective stripe. The key innovation was the incorporation of reflective glass spheres into the paint mixture, allowing for a one-step application process.
Prior to this invention, the traditional method of creating reflective markings involved applying glass beads over wet paint, known as the “drop-on method.” Paint was applied to a highway, and glass beads were applied right after the paint application, followed by allowing the paint to dry. The results were generally good with this method; however, this two-step process had its challenges, particularly with the tendency of glass beads to settle below the paint surface, reducing their reflectivity. So, 3M set out to create a better process and product.
The 3M invention attempted to solve the problems of the drop-on method by mixing the reflective glass spheres directly into the paint. This premixed paint and bead mix was then sprayed onto roads in the form of striping. As the paint wore over time, new glass beads would be exposed, ensuring consistent reflectivity. While this invention was successful, it did not replace the drop-on method.
In 1956, American Marietta filed for a patent on their version of premixed reflective paint. They first used crushed glass to achieve specular reflectivity and stripe longevity. Light hitting the stripes would scatter, but enough would return to the viewer for the stripes to light up. Later, American Marietta added micro glass spheres to this mix, which added a retroreflective element to the paint. The results were good, but like 3M’s invention, this product never actually replaced the simple drop-on method.
Credit to the Inventor of Glass Microspheres – It is important to note that reflective paint relies on two primary components: a liquid binder or paint and reflective glass beads. The invention of perfectly round glass beads that could reflect light was a crucial development in the early 1900s. These spheres were invented by Rudolph Potters in 1914. Without these glass beads, reflective paint, as well as the drop-on method, would not have been possible. Reflective tape can also be added to this list as not possible without the micro beads.
Of note is that today, the drop-on method is used almost exclusively. The problem of the beads sinking has been solved by adjusting the viscosity of the paint, varying the size of the glass spheres or beads, and using a larger volume of beads. In short, the drop-on method was just too successful and too convenient of a process to abandon. Also, spraying paint without beads requires basic spray equipment, but spraying paint with glass beads intermixed requires different equipment and is more difficult to do.
For more information on the history and development of reflective paint, you can visit the following link: Reflective Paint History
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