Electrophotographic (EP) Imaging, also known as xerography, has been around for about 80 years, originally invented by Chester Carlson and later it became the seed from which Xerox developed copiers, printers, and ultimately digital presses. According to IS&T, “Electrophotography is based on two natural phenomena: materials of opposite electrical charge attract, and some materials become better conductors of electricity when exposed to light.” The basic technology overview is that of a photoreceptor coated onto a conducting drum surface which gets electrically charged and then exposed by a laser which neutralizes the unwanted image areas. The areas not neutralized attract the toner to the still charged areas of the image on the drum which then gets transferred and then fused to the substrate for final adhesion.

This is a very “simple” explanation and there are many more steps to the process, but it is the basic core technology for almost all of the EP imaging in use today. Depending on the manufacturer’s implementation, there are many significant methods of enhancements to the process. For example, the original toner was metallic, but is now composed of photopolymers, which requires even more technology to support the process. Other methods actually transfer the charged image to a belt and then the image is transferred and fused to the substrate—think “offset.” 

EP has been a very significant technology for printing, although the complexity of the process has created certain barriers to productivity. Over the years process refinements have been able to improve productivity. The first Xerox photocopier imaged at 7.5 ppm, many EP presses today are now producing 100–120 ppm or ~100 fpm. This is admirable performance for commercial printing, but packaging demands high productivity. Flexo is the predominant packaging print technology, and that can reach up to 2,000 fpm, although average production speeds are 300–1,000 fpm. Even production inkjet is now achieving 600 fpm, which is why it is starting to become a niche player in short to medium run package printing. As the demands for shorter runs to support mass customization of FMCG (Fast Moving Consumer Goods) has grown, HP Indigo has developed a niche supporting those requirements with their EP technology. Until recently, they have been operating at about 85 fpm successfully in short run label and recently flexible packaging, but it still doesn’t approach the productivity of production inkjet and not even close to flexo speeds.