Electrophotography (EP)

Electrophotography, or EP, is the oldest of the non-impact printing technologies, having been invented in the mid 1930's by Chester Carlson. Electrophotographic printing is also often referred to as Xerography (meaning dry writing) and/or laser printing. Technically the term "laser" refers to the specific light exposure technology used in the process, but more often than not, the term laser printer is generically used to describe any electrophotographic printing system (such as an LED printer, regardless of its exposure technology.

Electrophotography is the most complex digital printing technology, consisting of two critical materials and seven process steps.

Electrophotographic (EP) Printing Materials

• Toner
• Photoconductor (Often referred to as the photoreceptor)

Seven Process Steps:

1. Charge
2. Expose
3. Development
4. Transfer
5. Fuse
6. Clean
7. Erase

The principal advantages of Electrophotography, or EP, over other non-impact printing or digital printing technologies are:

• Excellent print quality for text, graphics, and pictorials
• Large speed range - products from 4 PPM to 1,000 PPM

The technologies and technical disciplines utilized in the development of an EP system include: Mechanical Engineering (Mechanism Design, Machine Design, Paper Handling Design, Fusing System Design, Heat Transfer), Electrical Engineering (Digital Hardware Design, Analog Design), Firmware Development, Software Engineering, Physics (Electrostatics), Material Science, and Paper Handling.

Torrey Pines Research (TPR) is the leading independent technical authority in electrophotographic printing technology and the product development of electrophotographic printing system products and sub-systems. 

In recent years, TPR has been called upon to extend the technologies associated with Electrophotography to other industries requiring controlled precision material deposition of dry powders and liquids. 

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Toner Development Sub-system

The process of creating the toner image on the surface of the photoreceptor is referred to as the toner development process. While each of the seven steps of the EP process are critical to the proper function of the system as a whole, it is often said that the most critical step is the toner development step. Proper development of the latent electrostatic image on the surface of the photoconductor requires the careful integration of materials, electrostatics, mechanics, and electronics.  

The primary dry powder development technologies include the following Dual Component Development (DCD) and Single Component Development (SCD). The primary differences between these dry powder development technologies are as follows:

• Dual Component Development (DCD) - Characterized by the fact that the materials associated with the development process are comprised of two constituents, the toner and the carrier. The combination of the toner and carrier is referred to as the developer material. The toner is the material that ultimately comprises the final image, and is typically 5 microns to 10 microns in size and is composed of a thermal plastic resin material with a colorant added together with a number of other material additives used to optimize its performance. The carrier is typically magnetically permeable, approximately 4 to 10 times larger than the toner, and is used to charge the toner via Tribo-electrification, and transport the toner via its magnetic properties.
  
• Single Component Development (SCD) - characterized by the fact that the material associated with the development process only consist of the toner, the material that ultimately comprises the final image.

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