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 Doc Toner explains: laser toner and copier toner

Toner: what is it?

Toner is a complex powder that a laser printer or copier uses to form an image. Laser printers and copiers force toner powder to form the image you want on paper and as a final step, the toner image is melted onto the paper. What started off as a powder then passes through being a fluid and ends up as a solid - toner bonded to your page.

If you're daft enough to call yourself Doc Toner, you'll probably spend a lot of time answering questions about toner. I'm often asked will the toner for some laser printer work in some other laser printer. Frankly, it's a miracle that a toner will work at all, even in its own printer, let alone in another machine it wasn't specifically designed for. Toners don't just happen. Like cars, they're designed down to the smallest part. And as we're going to see, for toner, those parts are getting pretty small.

Every time you print a page with your laser printer, toner walks a tight-rope. A long list of technical compromises that designers of the laser printer implemented as they saw fit at the time. Toner to refill an empty cartridge has to walk that same tight-rope just like the original toner did. As a company that survives by encouraging an army of do-it-yourself toner tight-rope walkers, we take the design of each individual toner seriously.

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Toner chemistry

Toner at the chemical level is a blend of plastic resins, colouring pigments and other ingredients needed to make those resins and colours react to the electrostatic bombardment they're going to get on their roller coaster ride through a laser printer.

The resins give toner its overall physical ability to be first a fine powder, then melt at a relatively low temperature, then form a permanent plastic solid capable of bonding with paper fibres. No prizes for guessing that the colouring pigments give toner its colour. Up until recently, when colour laser printers were invented, that colour was always black, but now we're getting familiar with cyan toner, magenta toner and yellow toner. In the case of magnetic toner, the main "other ingredient" is normally magnetic iron oxide. A complex cocktail of charge control agents is also served up to help the toner particles respond correctly to the electrostatic hurricane inside the printer.

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Toner particles: size matters

When laser printers first started to be used widely around 1990 and the Hewlett Packard LaserJet 2 was the latest thing, toner particles were an average of 12 microns in diameter. 12 microns is about half the width of a human hair. In the LaserJet 4, around two years later, the average toner particle size was down to about 8 microns. Customers were asking me, "Is your refill toner microfine?". Well we had to sell something that would get across that tight-rope and produce prints of the same quality as the original. The only way to do that was to have a toner powder of the right formulation. That involved not just the particle size, but the fact that HP 4 toner has a much lower resin content and a much higher iron oxide content than HP 2 toner.

8 micron toner coincided with 600dpi print resolution. 600 dpi refers to a laser beam diameter capable of making 600 dots per inch. Half the diameter of the 300pdi printers before.

The last thing a laser printer does to our toner particle as it leaves the printer is melt it and squash it. The relative improvement of a 600 dpi machine printing with 8 micron toner does make sense. Your laser dots are half the size. Then you fill those half-size dots with toner particles that are two-thirds the size. Xerox, the originators of this whole xerography bandwagon and Canon, designers of the first desktop laser printer engines that reached a mass market, both think this results in finer print. I'm with them on this one.

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The Hewlett Packard LaserJet 1010 / 1012 / 1015 printer, released in 2003, uses "traditional" pulverized toner. We launched our toner refill kit for it early in 2004. The machine has been printing our invoices and delivery notes ever since.

Toner manufacture: back to the grind

The advent of chemically produced toners (see "Toner then and toner now") is changing the name of the toner game. But the majority of toners are still manufactured using a melt mixing or hot compounding process. The resins, carbon black, magnetic iron oxides, waxes and charge control agents are blended while molten to form a hot paste the consistency of cake mix. This viscous mixture is then cooled either by slabbing it out, by extruding it onto a cooling belt or by pelletizing it and cooling the pellets. This raw toner is then ground to a powder by jet mills or air-swept hammer mills. These processes produce a wide variety of particle sizes. The over-size and under-size toner particles are sifted out in a 1 to 3 pass process.

The pulverized, sifted toner powder is then blended with additives to adjust flow and electrostatic properties. This final blending is critical and hard to control, especially when the additive particle size is a lot different from the toner particle size.

For toner produced this way, an average toner particle of about 8 microns is about as small as you can get without astronomical costs.

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Toner then and toner now: chemical toner

So if smaller laser beam dots and smaller toner particles give better print. Where are we going next?

1200dpi laser printers have been around for a while, but until very recently they must have been using whacking great lumps of toner 8 microns across to fill their tiny 21 micron dots.

It's time to genuflect and make way for chemically manufactured toner. This approach to making toner involves growing the particles from the molecular level in an emulsion made from all the ingredients dissolved or suspended in a liquid.

Toner manufacturers aren't slow to present us with a laundry list of benefits inherent in the chemical toner approach. Smaller particles can be made precisely - down to 4 microns. Half the size of the smallest particle that can feasibly be produced by the traditional milling process, it takes one hundred 4 micron toner particles to make your average full-stop.

Chemically made toner particles are round or "potato" shaped, not the jagged grit of pulverized toner. Smooth particles flow better in the powder state and hold a more uniform electrostatic charge in the laser printer.

Last but not least, page yield is higher for smaller toner particles. A lot higher. You need 40% less 4 micron toner than 8 micron toner to print the same thing.

Chemical toners first started to be seen in desktop laser printers with Hewlett Packard's Color LaserJet 4500. Interestingly this machine has conventionally pulverized magnetic black toner and chemically produced non-magnetic coloured toners. Anyone still want to ask me if the toner from one laser printer will work in another?

Doc Toner

Our refill kit and refill toner for the Hewlett Packard HP Color LaserJet 1500/ 2500, launched in May 2004, uses chemically manufactured toner.
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