There are two main printing technologies on the market today for printing devices: piezoelectric and thermal inkjet.
Piezoelectric printing technology is developed on the ability of piezoelectric crystals to deform under the influence of electricity. Due to the use of this technology, it became possible to control printing, namely: to monitor the size of the drop, the speed of its exit from the nozzles, as well as the thickness of the jet, etc. One advantage of such a system is that the droplet size can be controlled. This ability allows you to get better images.
To date, experts have proven that the reliability of such systems is much higher than other systems. inkjet printing.
When using this technology, the print quality is very high. Even universal and inexpensive models allow you to get images of the highest quality and high resolution. Also, the most important advantage of PU with a piezo system is high color rendering, which allows the image to look bright and saturated.
Epson technologies - time-tested quality
The printheads of EPSON inkjet printers are high-quality development, which is precisely what explains them. high price. If you use a piezoelectric printing system, then you are guaranteed reliable operation of the printing device, and the print head does not dry out or clog due to the fact that it has minimal contact with air. The piezoelectric printing system was developed and implemented by EPSON, and only EPSON holds a patent for this system.
The thermal inkjet printing principle is used in Canon, HP, Brother printers. By heating the ink, they are transferred to the paper. By means of an electric current, liquid ink is proportionally heated, which is the reason for the name this method printing - thermal jet. An increase in temperature reproduces a heating element, which is located inside the thermal structure. With a strong increase in temperature, the main part of the paint evaporates, the pressure in the structure quickly rises, and a small drop of paint comes out of the heat chamber through a precision nozzle. This process is repeated repeatedly after one second.
The main disadvantage of the thermal inkjet method is that with such a printing technology, enough a large number of precipitation, which over time can disable it. Also, this scale clogs the nozzles over time, which leads to a loss in quality and print speed of the printer.
Also, devices that use thermal inkjet printing, due to constant temperature fluctuations, the print heads deteriorate, as it corny burns out under the influence of enormous temperature. This is the main disadvantage of such devices. The period of operation of the Epson PG MFP is absolutely identical to the service life of the device itself. This was made possible thanks to the high-quality materials from which the print head was developed. Customers who use thermal inkjet printing will often need to change the print head, as the high temperature will often cause it to burn out, which will greatly increase financial costs. The quality of the print head will also make a huge difference if users are using remanufactured cartridges.
Using an Epson inkjet printer in conjunction with refillable cartridges is very beneficial, as it improves the quality of the printer and reduces the cost of each printed image.
The print head of EPSON printers is of great importance not only for the stable operation of the printer. PG Quality allows you to increase print quality and print speed. Also, if the print head does not come into contact with air and dries out, the user will not have to change it, and therefore spend money in vain. Devices that use the thermal inkjet principle of operation can overheat greatly, and, accordingly, the print head can also overheat, which, if overheated, can simply burn out and get out of the standing.
As numerous checks and tests show, in order to print as economically as possible and at the same time be bright and effective, engineers recommend using EPSON printers with CISS. EPSON devices work much longer and more efficiently with the LF system than other similarly priced remote control units from other manufacturing companies.
Epson is a trusted manufacturer of quality products that make your job easier and more productive.
Inkjet technology appeared in the mid-1980s as a result of an attempt to get rid of the shortcomings of the two dominant printing methods at the time: dot matrix and laser (electrographic). laser printing was unacceptably expensive, and color was not yet dreamed of (and even now, although color lasers have become available, they have no chance of getting around inkjet in the field of photo prints). And inkjet printing emerged as a cheap alternative for printing office documents, devoid of the disadvantages of dot-matrix printers - slow, noisy and producing low-quality prints.
The idea, which, apparently, almost simultaneously (around 1985) came to the minds of engineers from Hewlett-Packard and Canon, was to replace the needle that hits the paper in dot-matrix printers through the ink layer on the ribbon with a drop of liquid ink. The volume of the drop should be calculated so that it does not spread and creates a point of a certain diameter. This technology got real life when they came up with a convenient way to form a dosed drop - thermal.
The thermal inkjet printing method is actually monopolized by Canon and Hewlett-Packard, which own most of the patents for this technology, the rest of the companies only license it, making their own small changes. While HP uses the term "thermal inkjet" (thermal ink-jet) printing method, and Canon prefers the term "bubble-jet" (bubble-jet).
Although there are differences between them, they are fundamentally identical.
On fig. 1 shows the process of thermal inkjet printing in the form of a conditional cinegram of the cycle of the nozzle (sometimes called ejectors). A miniature heating element is built into the chamber wall (highlighted in red in the top frame), which heats up very quickly to a high temperature (500 °C). The ink boils (second frame), a large vapor bubble forms in them (the next two frames) and the pressure rises sharply - up to 120 atmospheres, which causes the ink to be pushed out through the nozzle at a speed of more than 12 m / s in the form of a drop with a volume of about 2 picolitres (this is two thousandths from a billionth of a litre). The heating element is switched off by this moment, and the bubble collapses due to pressure drop (bottom frames). Everything happens very quickly - in a few microseconds. The ink is fed into the nozzle due to capillary forces (which is much slower), and after filling the nozzle with a new portion, the system is ready to work. The entire cycle takes approximately 100 ms, that is, the frequency of drops is 10 kHz, and in modern printers - twice as much.
Such an autonomously controlled nozzle is part of the print head located on a carriage moving across the sheet, similar to the print unit of a dot matrix printer. With a nozzle diameter of 10 microns, the placement density is 2500 nozzles per inch; in one head there can be from several hundred to several thousand nozzles. In modern high-speed devices, fixed heads began to be used - in order to eliminate the slowest stage in the entire process of the transverse movement of the carriage. For example, HP produces high-performance photo kiosks in which the heads are arranged in blocks across the entire width of the sheet.
On Canon printers, the thermal element is located on the side of the camera (as in Fig. 1), while on HP (and Lexmark) it is on the back. Perhaps this difference is due to the original ideas: according to corporate legend, a Canon engineer dropped a soldering iron on a paint syringe (that is, the syringe heated up from the side), and HP researchers borrowed the principle from an electric kettle, which is heated from the end. Like it or not, the lateral arrangement allows Canon to mount two thermal elements per nozzle, which improves performance and manageable droplet size, but complicates and increases the cost of design.
Canon's more expensive "bubble" heads are reusable and built into the printer. HP heads are easier to manufacture, because they were traditionally built directly into the cartridge and thrown away with it. This is much more convenient, as it guarantees print quality (the head simply does not have time to work out the resource) and high reliability of the assembly. However, with this approach, improving the heads leads to a rise in the cost of cartridges, so many modern HP printers have separate heads, like Epson or Canon. For example, the Photosmart Pro B9180, today's flagship of HP's "home" photo printers, has replaceable individual heads, while its cheaper analogue, the Photosmart Pro B8353, has cartridge-integrated heads.
What are the technologies?
Photo printers have almost universally replaced conventional inkjet models. This is quite natural and is a consequence of technological progress, because all modern A4 inkjet photo printers easily perform the function of universal printing devices, easily coping with both text and work schedule, and with photo printing, the quality is not inferior to the products of a photo lab.
In order to understand how the numerous models of photo printers available in stores differ from each other, and which one is more likely to satisfy your need for high-quality photographs, we will talk about the principles of imprint formation in such devices.
Currently, two fundamentally different types of home photo printers are being produced: inkjet and sublimation.
Inkjet photo printing
The first inkjet printer appeared in 1984, and we owe it to the American company Hewlett-Packard. The printing technology of such printers is hidden in the name: the image on paper is formed by jets of ink that are ejected from the print head. By the way, it was inkjet printers that made multi-color printing available, since black ink could be replaced or supplemented with inks of other colors. There are three inkjet printing technologies: Epson and Brother use piezoelectric technology, Canon use bubble technology, Lexmark and Hewlett-Packard use thermal inkjet technology. Each technology has its own zest, but in principle they are all extremely close, and the differences come down to how the ejection of ink drops from the nozzles onto the paper is organized.
Piezoelectric printing technology
Piezoelectric technology is based on the property of piezoelectric crystals to deform when an electric current is applied to them. Piezocrystals act as mini-pumps that eject a strictly defined amount of ink onto paper. Among the advantages of such a system is the possibility flexible management droplet size, which is carried out at the electrical level, which makes it easier to obtain high-resolution prints. It is believed that the reliability of such a system is significantly higher than that of all other inkjet printing systems. The reverse side of the advantages is the comparative high cost of the print head, so it is usually installed in the printer, and not part of a replaceable cartridge. Unfortunately, piezoelectric head very afraid of air or counterfeit ink getting into the nozzles. In both cases, you can get clogged nozzles, followed by head replacement, the cost of which can be comparable to the price of the printer itself. In addition, to keep the nozzles in working order, it is necessary to periodically print at least something on such a printer, otherwise ink residues can also clog the nozzles.
However, the new generation of Epson branded ink allows you to forget about this shortcoming. A new generation of Epson DURAbrite pigment inks has also appeared, in which microscopic homogeneous coloring particles are in a liquid polymer. Such ink practically does not blur on any paper, which allows to increase print resolution and have high light and moisture resistant properties.
The quality of piezoelectric printing is extremely high: even inexpensive universal models can produce prints of almost photographic quality with high resolution. Another merit Epson printers is the naturalness of color reproduction, which is especially critical when printing photographs. The only "but": all these advantages are realized only when using branded inks, and master fakes on Russian market great amount. There is only one way out - to buy ink exclusively in large firms, which are official dealers of the manufacturer. Do not forget that a broken printer with a "left" cartridge is automatically removed from the warranty.
Thermal inkjet printing technology
Thermal inkjet technology, which, by the way, was also used in the world's first mass-produced HP ThinkJet inkjet printer, differs in that ink heating is used for printing: in this case, part of the ink is heated, and part, due to excess pressure, is ejected through a nozzle. The process of heating and cooling is repeated several thousand times within one second, the heating temperature is up to 600°C, and the time of the thermal pulse itself does not exceed two millionths of a second. All modern HP models feature proprietary PhotoREt hardware and software technology, which is responsible for the most realistic color reproduction and high speed color printing.
The quality of thermal inkjet printing is very close to the quality of piezoelectric printing, besides, the manufacturing technology of the print head is close to the technology of manufacturing microchips, so the heads are cheaper than piezoelectric ones and, as a rule, are built into a replaceable ink cartridge. Naturally, such a cartridge is somewhat more expensive than just a sealed ink container, but a "non-original" cartridge will no longer be able to completely disable the printer.
Bubble printing technology
Canon bubble technology is special case thermal inkjet printing, in which the ejection of ink is carried out solely due to the formed gas bubbles that occur when the ink is heated, while the heating element is located on the side of the nozzle, and not behind it, as in classic thermal inkjet printers. Canon specialists knowingly invested a lot of money in the development of a proprietary print head using FINE technology (Full-photolithography Inkjet Nozzle Engineering), which means “photolithographic production of ink nozzles”: it provides not only high-quality, but also high-speed color photo printing.
The FINE print head uses a micro nozzle system: millions of microscopic ink droplets of a constant volume are applied to the paper every second with the highest precision. Unlike traditional inkjet technology, more ink is applied to the page in less time, which makes it possible to high speed print photos “edge-to-edge” (borderless) up to A4 format.
sublimation printing
A common drawback of all inkjet photo printers, caused by technological reasons, is the banding of the print, which manifests itself in different models to varying degrees. At best, it is imperceptible or barely noticeable, however, if part of the nozzles become clogged or the printer mechanics fail, the print becomes divided into unattractive horizontal stripes. Sublimation printers belonging to the class of thermal printers are completely free from this drawback.
Sublimation printing technology comes from the Latin word sublimare ("lift up") and represents the transition of a substance when heated from a solid state to a gaseous state, bypassing the liquid state.
The principle of operation of a sublimation printer is as follows: when a print job is received, the printer heats the film with the dye applied to it, as a result of which the dye evaporates from the film and is applied to special paper. As a result of the same heating, the pores of the paper open and the dye is clearly fixed on the print, after which the surface of the paper again becomes smooth and glossy. Printing is carried out in several passes, since the three main dyes must be transferred to the paper in the correct combinations: magenta, cyan and yellow.
Since pixelization and banding are completely absent in this case due to the printing technology itself, sublimation printers working with a seemingly modest resolution of 300x300 dpi are capable of producing photographs that are not inferior in quality to prints of inkjet models with a much higher resolution. The main disadvantages of sublimation models are the high cost of consumables and the lack of household models that work with A4 sheets.
Conclusion
Which printer to choose, of course, you decide. For our part, we can suggest that a self-respecting inkjet photo printer works with a resolution of at least 4800x1200 dpi, sublimation - at least 300x300 dpi. Consumables for inkjet photo printers are cheaper than sublimation ones, but the latter allow you to get a print with a quality much higher than inkjet ones. All modern sublimation photo printers for home printing are still compact models, and cannot boast of printing photos in A4 format, which is aimed at the vast majority of inkjet photo printers. Other than that, both are good.
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Technology thermal inkjet printing based on the property of ink to expand in volume when heated. The heated ink, increasing in volume, pushes microscopic ink droplets into the nozzles of the print head of the printer, which form an image on paper. AT general view thermal inkjet printing technology is shown below.
Thermal Inkjet Technology
Thermal inkjet printing is the most popular inkjet printing technology and is used in 75% of inkjet printers.
Share of printers using thermal inkjet printing technology
The largest contribution to the development of thermal inkjet printing technology was made by corporations Canon and HP, who independently developed two printing technologies in the 1970s: Bubble Jet (Canon) and Thermal Inkjet(H.P.).
Thermal Inkjet Technologies
Bubble Jet thermal inkjet technology was introduced to the public in 1981 at the Grand Fair. In 1985 using innovative technology The legendary Canon BJ-80 monochrome printer was released, in 1985 - the first Canon BJC-440 color printer.
Schematic representation of Bubble Jet inkjet printing technology
The essence of technology Inkjet Bubble Jet is as follows. A thermistor (heater) is built into each nozzle of the print head for instant heating of the ink, which at temperatures above 500 ° C, evaporating, form a bubble that pushes the ink drop out. Then the thermistor turns off, the ink cools and the bubble disappears, and the low pressure zone draws in a new portion of ink.
Interestingly, the ink heats up to a temperature of 500°C in just 3 microseconds, and drops fly out of the nozzle at a speed of 60 km/h. Every second in each nozzle of the print head, the ink heating and cooling cycle is repeated 18,000 times.
The second inkjet technology - Thermal Inkjet - began to be developed by HP in 1984, but the first ThinkJet printer based on this printing technology was introduced into mass production much later.
Schematic representation of Thermal Inkjet technology
Thermal Inkjet Technology is based on the same printing principle as Bubble Jet technology, with the only difference being that in printers using Bubble Jet technology, thermistors are located in the microscopic nozzles of the print head, while in printers using Thermal Inkjet technology, they are located directly behind the nozzle.
Thus, Bubble Jet and Thermal Inkjet technologies differ only in details.
The main advantages of thermal inkjet printing over piezo inkjet printing are the absence of moving mechanisms and stable operation. Along with this, thermal inkjet printing has one significant drawback: it does not allow you to control the size and shape of ink droplets. In addition, when ink drops fly out of the print head nozzle, satellite drops (satellites) that form when the ink boils escape with them. The appearance of such "satellites" can be triggered by the unstable vibration of the ink mass during its ejection from the nozzle. It is the satellite drops that cause the formation of an undesirable contour (“ink fog”) around the print and mixing colors in graphic files.
The operation of various piezoelectronic devices is based on piezoelectric effect , which was discovered in 1880 by the French scientists brothers P. Curie and J. Curie. The word "piezoelectricity" means "electricity from pressure". direct piezoelectric effect or simply piezo effect consists in the fact that under pressure on some crystalline bodies, called piezoelectrics, electric charges of equal magnitude, but different in sign, arise on opposite faces of these bodies. If you change the direction of deformation, i.e., do not compress, but stretch the piezoelectric, then the charges on the faces will change sign to the opposite.
Piezoelectrics include some natural or artificial crystals, such as quartz or Rochelle salt, as well as special piezoelectric materials, such as barium titanate. In addition to the direct piezoelectric effect, it is also used reverse piezo effect , which consists in the fact that under the influence of an electric field, the piezoelectric contracts or expands depending on the direction of the field strength vector. In crystalline piezoelectrics, the intensity of the direct and inverse piezoelectric effect depends on how the mechanical force or electric field strength is directed relative to the axes of the crystal.
For practical purposes, piezoelectrics of various shapes are used: rectangular or round plates, cylinders, rings. Such piezoelectric elements are cut out of crystals in a certain way, while maintaining orientation relative to the axes of the crystal. The piezoelectric element is placed between metal plates or metal films are applied to opposite faces of the piezoelectric element. Thus, a capacitor with a piezoelectric dielectric is obtained.
If we bring to such a piezoelectric element AC voltage, then the piezoelectric element, due to the inverse piezoelectric effect, will shrink and expand, i.e., perform mechanical vibrations. In this case, the energy of electrical vibrations is converted into the energy of mechanical vibrations with a frequency equal to the frequency of the applied alternating voltage. Since the piezoelectric element has a certain natural frequency, a resonance phenomenon can be observed. The greatest amplitude of oscillations of the plate of the piezoelectric element is obtained when the frequency of the external EMF coincides with the natural frequency of the oscillations of the plate. It should be noted that there are several resonant frequencies that correspond to different types of plate vibrations.
Under the influence of an external variable mechanical force, an alternating voltage of the same frequency arises on the piezoelectric element. In this case, mechanical energy is converted into electrical energy and the piezoelectric element becomes a variable EMF generator. We can say that the piezoelectric element is an oscillatory system in which electromechanical oscillations can occur. Each piezo element is equivalent to an oscillatory circuit. In an ordinary oscillating circuit, composed of a coil and a conder, the energy of the electric field concentrated in the conder is periodically transferred to the energy of the magnetic field of the coil and vice versa. In a piezoelectric element, mechanical energy is periodically converted into electrical energy. Let's look at the equivalent circuit of the piezoelectric element:
Rice. 1 - Equivalent circuit of the piezoelectric element
The inductance L reflects the inertial properties of the piezoelectric plate, the capacitance C characterizes the elastic properties of the plate, the active resistance R is the energy loss during vibrations. Capacitance C 0 is called static and is the usual capacitance between the plates of the piezoelectric element and is not related to its oscillatory properties.
Piezoelectric inkjet heads for printers were developed in the seventies. In most piezoelectric inkjet printers, overpressure in the ink chamber is created using a piezoelectric disc that changes its shape - bends when an electrical voltage is applied to it. Curving, the disk, which is one of the walls of the chamber with ink, reduces its volume. Under the action of excess pressure, liquid ink is emitted from the nozzle in the form of a drop. The pioneer of piezoelectric technology, Epson, was unable to successfully compete in sales volume with its competitors Canon and Hewlett-Packard due to the relatively high technological cost of piezoelectric printheads - they are more expensive and more complex than bubble printheads.
The main disadvantage of Epson inkjet printers is that the head costs the same as the printer. And if it dries up, then it is advisable to simply throw out the printer.
For other printers, the downside is the cost of consumables.
3. The principle of operation of laser printers. Laser and led printers. Main characteristics, advantages and disadvantages.
The impetus for the creation of the first laser printers was the emergence of a new technology developed by Canon. Specialists of this company, specializing in the development of copiers, created the LBP-CX printing mechanism. Hewlett-Packard, in collaboration with Canon, began developing controllers that make the print engine compatible with PC and UNIX computer systems.
Initially competing with petal and dot matrix printers, the laser printer quickly gained popularity around the world. Other copier companies soon followed Canon's lead and began research into laser printers. Another important development was the emergence color laser printers. XEROX and Hewlett-Packard introduced a new generation of printers that used the PostScript Level 2 page description language, which supports color representation of the image and allows you to increase print performance, and color accuracy. Laser printers form an image by positioning dots on paper (raster method). Initially, the page is formed in the printer's memory and only then transferred to the printing engine. Raster representation of symbols and graphic images is produced under the control of the printer controller. Each image is formed by the appropriate arrangement of points in the cells of the grid or matrix.
Despite the offensive inkjet printers, the dominance of laser devices in workplaces in the office is now unquestioned. There are many reasons behind the popularity of laser printers. They use a proven technology that has proven to be highly reliable: printing is fast, silent and quite affordable, its quality in most cases is close to printing. Manufacturers of laser printers have not stood still either, continuing to increase print speed and quality while pushing prices down. In 1994, a typical laser printer had a nominal speed of 4 ppm, a resolution of 300 dpi, and a price of $800. In 1995, we saw an increase in the number of products that print at 6 ppm at 600 dpi and have a real retail price of $350.
Every two to three years, manufacturers increase print speeds by 1 or 2 ppm, and by the end of the decade, personal laser printers had reached speeds of 12-15 ppm. In addition, they decrease dimensions of laser printers- thus, manufacturers achieve a reduction in price and the possibility of installing their products on a cramped desktop. One of the consequences of this is often limited means for handling paper compared to large-sized models. The input containers usually hold no more than 100 sheets, and the paper pocket is often designed for manual feeding of sheets at the same time - for this, you must first remove a stack of paper from it. The capacity of output trays is also limited - if the printer is equipped with such a device at all. Some printers have a paper path that is so convoluted that vendors do not recommend using sticky label machines.
The most widely used laser printers use photocopying technology, also called electrophotography, which consists in precisely positioning a dot on a page by changing the electrical charge on a special film made of a photoconductive semiconductor. A similar printing technology is used in copiers.
The most important structural element of a laser printer is a rotating photoconductor, which transfers the image to paper. The photoconductor is a metal cylinder coated with a thin film of a photoconductive semiconductor (usually zinc oxide). A static charge is evenly distributed over the surface of the drum. With the help of a thin wire or grid, called corona wire, a high voltage is applied to this wire, causing a luminous ionized region, called corona, to appear around it. A microcontroller-controlled laser generates a thin beam of light that reflects off a rotating mirror. This beam, falling on the photodrum, illuminates elementary areas (points) on it, and as a result of the photoelectric effect, the electric charge changes at these points.
For some types of printers, the drum surface potential decreases from -900 to -200 V. Thus, a copy of the image appears on the photoconductor in the form of a potential relief.
In the next working step, with the help of another drum, called the developer (developer), on the photoconductor is applied toner- the smallest coloring dust. Under the action of a static charge, small particles of toner are easily attracted to the surface of the drum at the points exposed, and form an image on it.
A sheet of paper from the input tray is moved by a roller system to the drum. Then the sheet is given a static charge, opposite in sign to the charge of the illuminated dots on the drum. When the paper contacts the drum, toner particles from the drum are transferred (attracted) to the paper. To fix the toner on paper, the sheet is charged again and it is passed between two rollers, which heat it up to a temperature of about 180° - 200°C. After the actual printing process, the drum is completely discharged, cleaned of adhering toner particles and ready for a new printing cycle.
The described sequence of actions is very fast and provides high quality printing. When printing on color laser printer two technologies are used. In accordance with the first, widely used until recently, a corresponding image was formed on the drum for each individual color (Cyan, Magenta, Yellow, Black), and the sheet was printed in four passes, which naturally affected the speed and quality of printing. In modern models, as a result of four successive passes, toner of each of the four colors is applied to the drum unit. Then, when the paper comes into contact with the drum, all four colors are transferred to it at the same time, forming the desired color combinations on the print. The result is smoother color reproduction, almost the same as thermal transfer color printers.
Printers of this class are equipped with a large amount of memory, a processor and, as a rule, their own hard drive. The hard drive contains a variety of fonts and special programs that manage the work, control the status and optimize printer performance. colored laser printers are quite large and heavy. The technology of the color laser printing process is very complex and the price of color laser printers is still very high.
LED printer: principle of operation, similarities with laser printers and differences from it
LED and laser digital printing technology have in common the use in both cases of the electrographic process to obtain the final print. In fact, these are devices of the same class: in both cases, the light source, controlled by the printer processor, forms a surface charge on the photosensitive drum corresponding to the required image.
Further, to put it simply, the rotating drum passes by the toner hopper, attracts particles of toner to the `illuminated` places and transfers the toner to the paper. Then the toner is fixed on the paper with a thermoelement (oven) and we get a finished print at the output. ¶Now let's go back and take a closer look at the design of the light source that illuminates the drum. It is in the type of light source used that the difference between a laser and LED printer lies: unlike a laser unit, in the latter case a ruler consisting of thousands of LEDs is used. Accordingly, the LEDs through the focusing lenses illuminate the surface of the photosensitive drum across its entire width.
4. The principle of operation of sublimation printers. Main characteristics, advantages and disadvantages.
Sublimation printers appeared about ten years ago. Then they were considered exotic, highly professional equipment. Inkjet printers were originally aimed at the mass user, which means that these two product groups did not compete with each other. The image quality of sublimation printers of a decade ago was incomparably superior to that which inkjet machines could provide. But the cost of printing on the latter was almost an order of magnitude lower.
A common drawback of all inkjet photo printers, caused by technological reasons, is the banding of printing, which manifests itself in different models to varying degrees. At best, it is imperceptible or barely noticeable, however, if part of the nozzles become clogged or the printer mechanics fail, the print becomes divided into unattractive horizontal stripes. Sublimation printers belonging to the class of thermal printers are completely free from this drawback.
Sublimation printing technology comes from the Latin word sublimare ("lift up") and represents the transition of a substance when heated from a solid state to a gaseous state, bypassing the liquid state.
The principle of operation of a sublimation printer is as follows: when a print job is received, the printer heats the film with the dye applied to it, as a result of which the dye evaporates from the film and is applied to special paper. As a result of the same heating, the pores of the paper open and the dye is clearly fixed on the print, after which the surface of the paper again becomes smooth and glossy. Printing is carried out in several passes, since the three main dyes must be transferred to the paper in the correct combinations: magenta, cyan and yellow.
Since pixelization and banding are completely absent in this case due to the printing technology itself, sublimation printers working with a seemingly modest resolution of 300x300 dpi are capable of producing photographs that are not inferior in quality to prints of inkjet models with a much higher resolution. The main disadvantages of sublimation models are the high cost of consumables and the lack of household models that work with A4 sheets.
A conventional inkjet printer prints on plain paper, while a sublimation printer requires special paper and a dye cartridge (ink ribbon), which is usually sold in a set. The cost of a set of 20 photos of a standard format 10 x 15 cm can be from $5 to $15. Thus, printing on a sublimation printer costs 3-4 times more than on an inkjet printer, and ten times more expensive than developing and printing conventional (analogue) films in the laboratory. This is clearly shown in the figure. 
5. The principle of operation of thermal printers. Main characteristics, advantages and disadvantages.
Color laser printers are not yet perfect. Thermal printers or, as they are also called, high-end color printers are used to obtain a color image with a quality close to photographic or to produce prepress color samples.
At present, three color thermal printing technologies have become widespread: inkjet transfer of molten dye (thermoplastic printing); contact transfer of molten dye (thermowax printing); thermal dye transfer (sublimation printing).
Common to the last two technologies is heating the dye and transferring it to paper (film) in the liquid or gaseous phase. The multicolor dye is usually applied to a thin lavsan film (5 µm thick). The film is moved by means of a tape transport mechanism, which is structurally similar to that of a needle printer. The matrix of heating elements forms a color image in 3-4 passes.
Thermal wax printers transfer the dye dissolved in the wax to the paper by heating a ribbon of colored wax. As a rule, paper with a special coating is required for such printers. Thermal wax printers are commonly used for business graphics and other non-photographic printing.
Sublimation printers are the best choice for printing an image almost indistinguishable from a photograph and making prepress samples. According to the principle of operation, they are similar to thermal wax, but only the dye (which does not have a wax base) is transferred from the tape to the paper.
Printers using inkjet transfer of molten ink are also called solid ink wax printers. When printed, colored wax blocks are melted and splattered onto the media, creating vibrant, saturated colors on any surface. The "photos" obtained in this way look slightly grainy, but satisfy all the criteria for photographic quality. This printer is not suitable for making transparencies because the wax drops are hemispherical after drying and create a spherical effect.
There are thermal printers that combine the technology of sublimation and thermal wax printing. Such printers allow you to print both draft and finishing prints on one device.
The print speed of thermal printers due to the inertia of thermal effects is low. For sublimation printers from 0.1 to 0.8 pages per minute, and for thermal wax printers - 0.5-4 pages per minute.