[dlmiller]

Developer loses its charge over time. You have to replace it.

Every laser copier/printer still uses developer. If you can show me a model of laser printer that does not, I'm all ears.

There is also a transfer roller in each copier, maybe that's what you're talking about?

I could be mistaken, but as recently as 2020, every commercial copier I worked on, still uses developer. I have never worked on, or heard of a laser copier without developer.

[l8rlump]

"Mono-component" toner is toner that is magnetic in its own rite, so it doesn't need separate developer (iron powder) to make it magnetic. I believe the original mono-component toners had magnetite in them, but I believe now there's non-magnetic mono-component toner too.

[Animats]

Xerography is electrostatic, not magnetic.

Magnetic printers, with magnetic toner, have been built [1] but never really caught on. It was one of those dead ends from the early years of trying to build a faster printer.

Somehow I managed to encounter, early in my career, the first CRT phototypesetter prototype (Harris-Intertype), the first electrostatic liquid printer prototype (Clevite-Brush), the Data Interface Magnetic Printer, the Teletype Inktronic (swept a beam of ink dots with deflection plates, like a CRT), and a Corning Glass display that used photochromic glass (write with UV, view in green, erase with IR).

None were successful products, although for a decade or so, electrostatic liquid printers from Versatek [2] were a thing. They used "dark juice", toner particles in a liquid suspension. A row of electrodes charged the paper, which passed over a liquid surface where the paper picked up toner particles. Then a heating station fused the toner and evaporated the liquid. Required special paper. Print quality was mediocre, but the devices were quiet and fast.

[1] http://archive.computerhistory.org/resources/text/DataInterf...

[2] https://archive.org/details/TNM_Electrostatic_Printers__Plot...

[l8rlump]

Interesting stuff.

In classic xerography, yes, the toner is moved around electrostatically. But it also needs to have magnetic properties (either intrinsically or by means of developer) to form a magnetic “brush” which is presented to the drum. Think of iron filings mixed with toner on a piece of paper and a magnet on the other side. The right static charge will be able to pull the toner out while leaving the iron filings behind.