Historical facts
The idea behind the inkjet printing is not so new. Already in 1867 William Thomson obtained a patent for a self-recording unit designed for the electric telegraph. It used electrostatics to control spraying ink and paint drops on paper. In 1951 Siemens produced the first jet printer for business. In the 1960's other manufacturers were successfully introducing their own modifications. The inkjet printer had a reputation of an expensive, dirty and unreliable device. With its pumps, tanks and other moving parts it was not capable of providing high-quality printing.
The contemporary inkjet printer has not completely resolved these issues of separate print heads, cartridges, spray nozzles and control precision. In the 1970's some studies around piezoelectric printing were carried out. Some special crystals are used. They vibrate when a charge is made to squeeze some ink. Thermo-jet printing was one of the most achievements.
Types of inkjet printers
A print head is the key element of an inkjet printer. The print head consists of a large number of nozzles linked to ink. Ink is fed to the nozzles by capillary properties and prevented from leaking due to the surface tension of the liquid. The head has a special built-in mechanism to eject microscopic ink droplets from nozzles. Depending on the configuration of this mechanism different printers are referred to as one or another class.
Ink jet printers use one of the two ink drops ejection methods, piezoelectric (Epson) or gas bubbles (Canon, HP).
The idea behind the piezoelectric technology is that a piezoelectric element deforms influenced by the electric field. Each nozzle of the print head has a built-in flat membrane made of a piezoelectric crystal. The membrane is deformed under the influence of the electric pulse, and microscopic droplets of ink are ejected from the nozzle under pressure.
With the gas-bubble method a small amount will be rapidly heated to the boiling point. The heating rate is so high that it is like explosion. The resulting steam emits a microscopic ink drop from the nozzle. A microscopic heating element is built in each nozzle to apply this method.
Each of these two methods has pros and cons.
The piezoelectric technology is the cheapest one and is more reliable since high temperature is not involved. Compared to heating this method is less inertial which improves the print rate.
The bubble technology requires a high temperature. At high temperatures, the heater will be covered by a soot layer over time, so this technology can make print heads run out of order quickly.
Inkjet heads
Inkjet heads can be divided into two groups, fixed heads and disposable heads. A fixed head is built into the printer and is designed for the same lifetime as the printer. Fixed head are believed to be better than the low-cost disposable heads. Ink cartridges for the printers with fixed heads will be cheaper as there is no need for replacement. But if something goes wrong with such a head, it is needed to change the printer.
A disposable head is built into the cartridge. It is replaced every time when we fill the cartridge. This makes the price of such cartridges higher and the print quality becomes worse after refilling the cartridge several times.
Types of ink
The type of ink for jet printing can be different depending on the application. For example, the pigmented ink which represents a suspension of fine dye particles in a certain way. The solvent ink uses soluble dyes. The basis for the ink used is so different. Methods of fixing are also different, soaking, drying and UV fixation.
Scope of application
Application of inkjet printers is various. At home and in offices inkjet printers provide the colourful and monochrome printing. Advertising agencies use large-format printers to produce POS-materials, indoor and outdoor advertising. The printers with the width of up to 6 m are different. They are mainly used to make outdoor advertising. There is also large-format inkjet printing for the thick-sheet materials which are generally used for decoration of the sales outlets. There are dedicated digital colour proof systems based on the continuous inkjet technology.
Pros and cons
To sum up, it can be presented as follows.
The advantages of inkjet printers
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Low price;
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High-quality printing, the ability to clearly print small details;
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Printing in bright colours suitable for printing images;
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Easy to operate;
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Relatively good print speed and they are more quiet than matrix printers;
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Time is not needed to warm up before start.
The disadvantages of inkjet printers
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Print head have limited life period and are fragile;
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High maintenance cost (the price of ink cartridges);
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Not suitable for printing in high volumes;
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Print speed is not as high as laser printers;
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Possible ink leakage on paper; The inks are very sensitive to water, even a small drop of water may smudge the ink on paper;
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Inability to use markers when editing texts.
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