Inkjet v Laser

Inkjet printers are generally characterised as cheap to buy but expensive to run. Some inkjet manufacturers are challenging this with inkjets they claim have a lower ownership cost than laser printers.

There might not be much to choose between inkjets and laser printers in principle. Inkjets deliver a colourant to the page in a water / isopropyl mix. Laser printers deliver a colourant in a dry styrene / wax mix.

The colourants might be pretty similar delivered either way. The mechanisms are very different.

A laser printer holds the styrene-colour mix in a powder of microscopic dry particles. The toner is transferred between a set of drums and the paper using a series of electrostatic fields (high voltages) controlled by a fine laser beam. Laser printers are fairly expensive to make because:

• They need half a dozen precision rollers mounted over the paper transport mechanism.
• The page-image needs to be complete in printer RAM before the print mechanism starts.

An inkjet cartridge holds the suspension of colourant as liquid in a tank. The liquid is sprayed in microscopic droplets by a printhead. Printheads normally scan back and forth across the paper transport mechanism.

• The printhead itself is complicated, the other physical hardware need not be.
• Printhead scanning is not particularly rapid and can stop at the end of a line, so a users computer can feed the page-image a line at a time.

Inkjets and Cost Compromise

Cheap printers normally use a thermal inkjet mechanism. An inkjet has a series of microscopic nozzles which squirt droplets of liquid ink at the page. All sorts of mechanisms can be used to control the droplets but the two favourites are piezoelectric crystals used by Epson and Xerox - in big printers - and thermal printheads used by HP, Canon, Lexmark and almost everyone else. For some information on how printheads work see this page .

The manufacturing complexity of a basic inkjet is similar to that for a CD player or a remote-control toy, a lightweight plastic chassis with a couple of motors and a simple microprocessor control.  Inkjet printheads can be complicated but the rest of a basic printer mechanism need not be. A typical home printer with a set of starter cartridges (and printheads) sells in a supermarket for about £30.

Inkjet printers can be designed many different ways. There used to be such a thing as a monochrome inkjet but it costs very little extra to make a colour machine so no-one bothers with black-only print. The interesting point is how the ink cartridges are designed to fit into the machine.

Tricolour and black cartridges. - Tricolour cartridges share a single cartridge and head, there is usually a black cartridge alongside to print text. This design is only suitable where the cartridges are small because when one colour runs out the whole thing is replaced and the remaining ink is wasted. This kind of printer suits student essays largely in black with just the odd spot of colour and the occasional small photograph. Tricolour printing is usually slow because a single head is shared amongst the colours. Printers like this are intended for an average use of just a couple of pages per day. Avoid printing full-colour pages and photographs because such pages will prove expensive.

Separate cartridges - have an ink tank and probably a print head for each of the colours. This kind of machine may be slightly more expensive to make because the carriage is bigger and slightly more complicated to accomodate the individual tanks. The advantage to the user is that it doesn't waste so much ink. Such printers are usually more economical to use but a bit more expensive to buy than their tricolour competitors. They tend to use cheap disposable printheads so the printer isn't likely to be very fast. Most faults will be fixed by changing the cartridge involved. Since the head is part of the cartridge part of its life may be wasted when the ink is used up.

Separate Heads and Cartridges. This technique doesn't waste heads or cartridges but the mechanism is still more expensive to make. Because the printheads won't be wasted they can be big devices with hundreds of nozzles so the printer can be quite fast. The separate heads do tend to be expensive to buy when they fail - they should generally last about four cartridges. The net cost of four cartridges and a head should be lower than the cost of four cartridges each with integral heads.

Large separate cartridges - in the printer base. Putting ink in big cartridges is the most economical way to distribute it (short of using bottles). However the whole printer is more complicated because a heavy cartridge can't sit on the printer carriage. There are tubes running from the cartridges to the printheads and they need to be primed. Priming the tubes and cleaning the printheads usually needs to be some kind of pump or pressure mechanism acting on the ink. Printhead maintenance can have quite elaborate scrapers, suction pumps and droplet detection. Printers built this way have low ink supply costs and big fast printheads so they are suited to office use and may be cost-competitive with laser printers. Furthermore each new generation of printers is an advance on the last.

Printers that cost least to buy use the tricolour cartridges that cost most to replace per millilitre of ink. There is an additional benefit; tricolour cartridges are easiest to deal with in some ways because almost every problem is answered with "get a new cartridge".

Separate cartridges with integrated disposable heads suit some people. It is easy to fix faults - the answer is try a new cartridge. At least the waste is lower.

Another benefit for those who enjoy experimenting is that this scheme suits refilling cartridges. If it all goes horribly wrong and the cartridge won't come back to life just a bit of ink is wasted. Experimenting with separate printheads is more risky because if the ink is inappropriate the head will be damaged.

There are inkjet printers that are intended to be cheap to run and reliable - but they don't sell in supermarkets for £30. They sell through specialist computer shops and on-line and prices run from £200 upwards.

Business quality inkjet printers like the Epson B-310 claim "colour printing now" costs up to 50% less than competitive lasers". By "competitive" they mean small, sub £299 expensive to run laser printers that aren't very competitive. There is an interesting point though, inkjet technology is now capable of undercutting laser printers.

Pagewidth printheads. A new generation of inkjet based printers are available which are much faster than their predecessors because they use pagewidth heads. These machines typically have a throughput towards 60 pages per minute - as fast as the paper handling mechanisms in current printers can provide the paper. Some manufacturers hope these fast inkjets will replace the laser printer. At the moment the purchase cost is equal to that of a comparable laser printer but things are expected to change in 2011. There doesn't seem to be any specific reason why we aren't seeing 60 ppm colour inkjets in supermarkets for £299 with litre bottles of ink for £20. That just isn't how the industry works at the moment.

Inkjet cartridges are usually a little more than a plastic tank with ink in. There is either a printhead with a limited life, or there is a valve coupling the tank to the printhead. There will be a pressure relief labyrinth or some way to pressurize the ink inside the cartridge. And on many cartridges there will be a memory chip that records when the tank is empty and then refuses to print, even if the cartridge is refilled.

Manufacturers (and supermarkets) don't put warning notices on their lowest cost offerings saying "not suited to photographers and office use". Get the manufacturer's brochure PDF from their website and see what cartridge configuration they are using. Have a look at cartridge costs before buying. Buyers need to make an educated guess about how much printing they will do and fit their expectations to the ownership costs of the printer.