Piezoelectric inkjet printing physical basis of piezoelectronics. Piezoelectric printing

What kind of technology?

Photo printers have almost everywhere replaced ordinary 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 graphics printing, as well as photo printing, with a quality that is not inferior to darkroom products.

In order to understand how the numerous models of photo printers presented 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 print formation in such devices.

There are currently two fundamentally different types of home photo printers available: 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 accessible, since black ink could be replaced or supplemented with ink 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 peculiarity, but in principle they are all extremely similar, and the differences boil down to the way in which the ejection of ink drops from the nozzles onto the paper is organized.

Piezoelectric printing technology

Piezoelectric technology is based on the property of piezocrystals to deform when an electric current is applied to them. Piezocrystals act as mini-pumps that release a strictly defined amount of ink onto the paper. Among the advantages of such a system is the possibility of flexible control of the droplet size, which is carried out at the electrical level, which simplifies the production of 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 downside of the advantages is the comparative high cost of the print head, so it is usually installed in the printer and is not part of a replaceable cartridge. Unfortunately, the piezoelectric head is very susceptible to air or counterfeit ink getting into the nozzles. In both cases, you can get clogged nozzles with subsequent head replacement, the price of which can be comparable to the price of the printer itself. In addition, to maintain the nozzles in working condition, 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 drawback. A new generation of Epson DURAbrite pigment ink has also appeared, in which microscopic, homogeneous coloring particles are contained in a liquid polymer. Such ink practically does not smear on any paper, which allows increasing print resolution and has 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 advantage of Epson printers is the naturalness of color rendering, which is especially critical when printing photographs. The only “but”: all these advantages are realized only when using branded ink, and there are a huge number of master-made fakes on the Russian market. There is only one way out - to buy ink exclusively from large companies that 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 used in the world's first serial inkjet printer, the HP ThinkJet, is distinguished by the fact that ink is heated for printing: part of the ink is heated, and part, due to excess pressure, is ejected through the nozzle. The heating and cooling process 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 color printing speed.

The quality of thermal inkjet printing is very close to the quality of piezoelectric printing, in addition, the manufacturing technology of the print head is close to the technology of producing microcircuits, 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 damage the printer.

Bubble printing technology

Canon's bubble technology is a special case of thermal inkjet printing, in which ink is ejected solely due to the formation of gas bubbles that arise 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. It’s not in vain that Canon specialists 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 constant volume are applied to the paper every second with the highest precision. Unlike traditional inkjet technology, printing applies more ink to the page in less time, which makes it possible to print edge-to-edge (borderless) photos up to A4 size at high speed.

Sublimation printing

A common drawback of all inkjet photo printers, caused by technological reasons, is print banding, which manifests itself in different models to varying degrees. At best, it is invisible or barely noticeable, but if some of the nozzles become clogged or the printer's mechanics malfunction, the print becomes divided into unattractive horizontal stripes. Sublimation printers belonging to the class of thermal printing devices are completely free from this drawback.

Sublimation printing technology comes from the Latin word sublimare ("to lift") 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 arrives, 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 three main dyes must be transferred to the paper in the correct combinations: magenta, turquoise and yellow.

Since pixelation and banding due to the printing technology itself are completely absent in this case, 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 is, of course, up to you. 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 that is 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 what the vast majority of inkjet photo printers are aimed at. But for the rest, both are good.

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Unlike the thermal inkjet method of ejecting ink onto a sheet of paper by heating the ink to a high temperature and creating excess steam pressure, with piezo printing the ink is ejected through the use of force - a short-term impact.

The operating principle of printers with piezoprinting technology: the impact of a piezoelectric crystal on ink in a limited volume of the print head leads to the release of a dosed portion of ink to the desired location on a sheet of paper. Modern print heads use piezocrystals, to which you can apply different current levels and change the period of application of the current to the crystal. This makes it possible to change the size of the ink drop within the specified parameters, the force of the projection and the thickness of the jet. Drops of ink fall into a strictly planned place in a strictly planned order and in a strictly planned volume.

Thermal inkjet and piezoelectric technologies use different physical principles to spray ink onto paper, causing the ink to have different viscosity, electrical conductivity, chemical and physical composition and therefore are not interchangeable.

The main advantage of Epson print head technology is the achievement of very high resolution (5760x1440 dpi with an ink droplet size of 3 picoliters) and photographic print quality. The compression of the ceramic and the fact that the ink does not heat up results in smoother droplets compared to the explosive ejection of ink from a thermal head nozzle. The droplet size is better controlled with a piezoelectric head. Epson print head nozzles are smaller than thermal heads (10-15 microns compared to 20-25 for Canon and 30-50 for HP and Lexmark). And it works faster: 50 kHz versus 20 kHz.

An additional advantage of the piezoelectric head is the ability to print with inks based on various solvents: oil, sublimation, solid ink, etc. Due to this advantage, piezo technology plays an important role in the field of printing on special substrates such as non-porous materials, fabrics, etc.

The disadvantages of using a piezo head are its high cost and demands on ink quality. In addition, the relatively large mass of the piezo head causes large vibrations in printers during high-speed printing and requires increased attention to the development of the drive and positioning system.

All major inkjet printer manufacturers use thermal inkjet technology. Only Seiko Epson Corporation uses piezoelectric printing technology. This technology is protected by more than 4,000 patents in all countries.

Epson designs its devices according to the following principle: the print head is built into the device, and ink cartridges are supplied in the form of ink tanks of different volumes from 10 to 50 ml. This allows you to slightly reduce the cost of daily printing, because other manufacturers supply cartridges along with print heads. In addition, the user can connect a CISS (continuous ink supply system) to his device for even better business printing. However, when choosing a CISS, you must carefully select the manufacturer, because The market is saturated with cheap goods and low-quality inks.

Epson closely monitors the inkjet printing market and captures its trends and changes. Most recently, the company introduced the Epson L800 device with a CISS of its own design. The line of these models with low printing costs is called Print Factory. Users of such devices can independently refill ink containers.

To summarize, we note that technology does not stand still and inkjet printing is by no means dying, as some experts in the field of printing predicted it 3-4 years ago. It's safe to say that inkjet printing can provide relatively inexpensive, high-quality, high-resolution prints.

Epson cartridges and consumables can be easily refilled with toner. Our company carries out Epson, taking into account all the features of their configuration.

There are two main printing technologies common in the inkjet printing market: piezoelectric and thermal inkjet.

The differences between these systems are in the method of depositing a drop of ink onto the paper.

Piezoelectric technology was based on the ability of piezocrystals to deform when exposed to electric current. Thanks to the use of this technology, complete control of printing is achieved: the size of the drop, the thickness of the jet, the speed of drop ejection onto the paper, etc. are determined. One of the many advantages of this system is the ability to control the droplet size, which allows for high-resolution prints.

The reliability of the piezoelectric system has been proven to be significantly higher compared to other inkjet printing systems.

The print quality when using piezoelectric technology is extremely high: even universal, inexpensive models allow you to get prints with almost photographic quality and high resolution. Another advantage of printing devices with a piezoelectric system is the naturalness of color rendering, which becomes really important when printing photographs.

The print heads of EPSON inkjet printers have a high level of quality, which explains their high cost. With a piezoelectric printing system, reliable operation of the printing device is ensured, and the print head rarely fails and is installed on the printer, and is not part of replaceable cartridges.

The piezoelectric printing system was developed by EPSON, it is patented and its use is prohibited by other manufacturers. Therefore, the only printers that use this printing system are EPSON.

Thermal inkjet printing technology is used in Canon, HP, Brother printers. Ink is supplied to paper by heating it. The heating temperature can be up to 600°C. The quality of thermal inkjet printing is an order of magnitude lower than piezoelectric printing, due to the inability to control the printing process due to the explosive nature of the drop. As a result of such printing, satellites (satellite drops) often appear, which interfere with obtaining high quality and clarity of prints, leading to distortion. This drawback cannot be avoided, since it is inherent in the technology itself.

Another disadvantage of the thermal inkjet method is the formation of scale in the print head of the printer, since ink is nothing more than a combination of chemicals dissolved in water. The resulting scale clogs the nozzles over time and significantly deteriorates the print quality: the printer begins to streak, color rendition deteriorates, etc.

Due to constant temperature changes in devices using thermal inkjet printing technology, the print head is gradually destroyed (burns out under the influence of high temperature when the thermoelements overheat). This is the main disadvantage of such devices.
The service life of the print head of EPSON printers is the same as the device itself, thanks to the high quality of manufacturing of the PG. Users of devices with thermal inkjet printing will have to buy a new print head each time and replace it, which not only reduces the durability of the printer, but also significantly increases printing costs.
The quality of the print head also matters when using non-original consumables, in particular CISS.

Using Epson CISS allows the user to increase print volumes by 50%.
The print head of EPSON printers, as has been mentioned more than once in this article, is of high quality, due to which an increase in print volumes does not negatively affect the operation of the printer, but on the contrary allows the user to get maximum savings without compromising print quality.

Due to the characteristics of printing devices using thermal inkjet technology, an increase in printing volumes can lead to the failure of the PG printer.

As observations show, to obtain maximum savings with perfect print quality, it is more advisable to use EPSON printing devices with CISS. EPSON printers operate with a continuous ink supply system more consistently than printing devices from other manufacturers.

Some of the discoveries or inventions, which have long ago become commonplace, over time acquire a variety of beautiful myths and legends.
One such story tells the story of an employee at a small research laboratory owned by a large computer company. After a sleepless night spent working on a new capricious design for some electronic contraption, this employee inadvertently placed a soldering iron next to a syringe filled with rosin (I would like to attribute that it contained ink, but it did not). Naturally, in the end the workwear was ruined, but most importantly, the idea of ​​thermal inkjet printing arose. A white coat with a stain went to the dry cleaner, and inkjet technology, through the efforts of Canon, Hewlett-Packard, Epson, Lexmark and other companies, came to offices and homes, striking in its accessibility and colorfulness.

Why jet?

Over the past few years, the computer industry has been experiencing a real ink boom. For many users, inkjet printers are the most affordable and versatile printing devices. The images they produce in many cases are superior in quality to printed prints, and the maximum print speed has already come very close to the performance indicators of junior models of laser printers. Comparable to amateur photographs from mini-labs, full-color photorealistic inkjet printing has become the main trump card of inkjet printer manufacturers in the struggle to attract new customers.

In pursuit of customers and to the envy of competitors, the droplet size is constantly decreasing and new technologies are being developed to improve color rendering. The new names and logos are already making my head spin. Naturally, the most inquisitive ones have a question: are all the principles and ideas that each manufacturer is proud of really unique?

In proud loneliness

For quite some time now, two camps have formed in this market sector. In one, Epson with piezoelectric technology alone rules the show, and in the other, an entire alliance of “boiling ink” adherents has gathered.

The piezoelectric printing method is based on the property of some crystalline substances to change their physical dimensions under the influence of electric current.

The most striking example is quartz resonators, used in many electronic devices. This phenomenon was used to create a miniature pump in which a change in voltage causes a small volume of ink to be compressed in a narrow capillary channel and instantly ejected through a nozzle.

The print head of a piezoelectric inkjet printer must be highly reliable, since due to its fairly high cost, it is almost always built into the printer and does not change when installing a new ink cartridge, as is the case with thermal inkjet printing. This design of the piezoelectric head has certain advantages, but there is a constant danger of printer failure due to an air bubble entering the ink supply system (which can happen when changing the cartridge) or normal downtime for several weeks. In this case, the nozzles become clogged, print quality deteriorates, and restoring normal operation requires qualified maintenance, which is often impossible to carry out outside a service center.

Without breaking away from the team

While Epson was going its own way, periodically surprising the computer community with another breakthrough, other players in the inkjet printing market were no less successfully using a print head of a different design. Most of them consider their developments unique, although their essence is banal and simple, and the difference often lies only in the name.

Thermal inkjet printers work like a geyser: inside a chamber with a limited amount of ink, a miniature heating element creates a bubble of steam, which instantly increases in volume, pushing a drop of ink onto the paper.

Using this technology, it is not difficult to obtain miniature printing elements arranged with high density, which promises developers a potential increase in resolution with a significant margin for the future. However, there is a downside to thermal inkjet printing. Due to constant temperature changes, the print head is gradually destroyed, and as a result it has to be replaced along with the ink cartridge.

More names - loud and different!

Bubbles are bubbles, but simple pictures have long ceased to surprise anyone. So we have to fight for every picoliter in a drop, for every shade on paper.

But there really aren’t that many ways to improve the quality of the final image. The most obvious and accessible option was to increase the number of ink colors. To the four basic colors (black, blue, crimson and yellow), many manufacturers have added two more - light blue and light crimson.

Without additional tricks and significant changes in the technological process, only Epson could achieve such an effect. The fact is that the operating principle of the piezoelectric head allows you to control the size of the drop by changing the amount of control voltage applied to the piezoelectric element. This technology is called Variable Dot Size. Well, adherents of bubble printing had to seriously work on changing the design of the nozzles. In each of them several heating elements of different power were placed.

By turning them on one at a time or all at the same time, you can get droplets of different sizes, as is the case in modern thermal inkjet printers. Canon dubbed its developments in this area Drop Modulation, and HP used a ready-made name with additional indices - PhotoREt II and PhotoREt III. In addition to the ability to control the drop size, it became possible to sequentially apply several drops to the same point on the surface of a sheet of paper.

But print quality depends not only on the technical perfection of the design of the printer itself, but also on other, no less significant factors.

Behind the jet front

With the increase in resolution and printing speed, it became clear that the pursuit of improving these characteristics in itself cannot provide significant gains unless the image carrier, that is, the paper, is improved. It would seem that what could be simpler than paper? But it was not there! Any “cunning” technologies will be powerless if you put plain office paper in the printer tray.

A beautiful A4 sheet, the sight and smell of which makes any laser printer hum with pleasure, turns out to be completely unprepared for the streams of multi-colored ink spewed at it from hundreds of nozzles.

The surface of ordinary paper has a fibrous structure, which is due to its production technology. As a result, miniature drops, strictly calculated in size, begin to spread over the surface in the most unpredictable way. In this case, it does not matter at all what kind of printing is used - thermal or piezoelectric. One solution to this problem is to use pigment ink, which is a suspension of dispersed particles in a colorless liquid carrier, since solid particles cannot penetrate the inner layers and spread along the fibers of the paper.

Pigment-based ink allows you to obtain bright and rich shades, but they also have certain disadvantages, in particular low resistance to external influences.

Inkjet printing technology is such that the best results can only be achieved when using special paper. Photos on plain paper appear faded and less clear. Unlike regular paper, specially coated paper and so-called photo paper have several special layers. Its printouts are virtually indistinguishable from photographs produced using a chemical photo process.

Simple budget paper for inkjet printing, as a rule, has a density of 90-105 g/m2, a relatively small thickness and an excellent whiteness indicator. Due to the special treatment of the front or both sides, such paper is more resistant to the vagaries of ink and prevents it from spreading and penetrating deep into the sheet.

Special photo paper with a glossy or matte surface usually has a density of up to 200 g/m 2 and is a multi-layered product of modern technology.

Each layer performs specific functions.

The bottom layer is the base that provides strength and rigidity to the document.

The next layer acts as an optical reflector, giving the image brightness and whiteness. Next is the main bonding ceramic or plastic layer, which makes up many vertical channels without long fibrous formations along the surface of the sheet and provides the necessary ink density at the printed point. A final, glossy or matte protective layer is applied to the absorbent, giving the surface strength and protecting it from external influences.

During the printing process, ceramic particles absorb ink, preventing it from spreading over the surface. As a result, the shape of the points and their orientation remain unchanged.

In addition, there is no need to be afraid of accidental ingress of moisture, since deep and strictly vertical microcapillaries reduce the likelihood of spreading to a minimum.

In drop matrix printing, the heating elements (thermistors) built into the head serve as a “projectile” that causes drops to be ejected from the nozzles of the print head. When a short-term voltage is applied, the temperature of the heating element sharply (within a few microseconds) increases to several hundred degrees and causes instant boiling and evaporation of the ink in contact with it. The bubble of steam that appears in this case acts as “gunpowder”, causing the ink to “shoot” out of the nozzle. Then the voltage is removed from the thermistor, it cools down, the ink vapor condenses, the bubble collapses and a zone of reduced pressure is formed in the nozzle, under the influence of which a new portion of ink is sucked in. An important feature of such a printing device is the simplicity of the nozzle design. Moreover, in addition to the low manufacturing cost, such devices have a number of other advantages:

The high reliability of each nozzle simplifies the design and, therefore, reduces the size of the printing unit, since it is not necessary to provide the ability to replace nozzles;

The nozzles can be placed much closer to each other, which increases print resolution;

Quiet operation of the print head.

Despite the fact that Canon, Hewlett-Packard and Lexmark printers share the same technology, they have their own design features. In devices from Hewlett-Packard and Lexmark, the ink enters, relatively speaking, a separate chamber, where a thermistor is installed. As you can see in the figure, the drop is “shot” in the same direction in which the gas bubble is formed.

Canon took a slightly different path. In Canon Bubble-Jet printers, bubbles are formed in the direction perpendicular to the ejection of droplets from the nozzles. This solution is cheaper to manufacture and theoretically provides lower accuracy of “serial shots” (although in practice the latter is difficult to notice). In modern models of printers using drop matrix printing technology, the frequency of drop generation is tens of kilohertz, and microscopic doses form drops with a minimum volume of 1 pl. At the same time, print heads manufactured by photolithography can contain over six thousand nozzles. It is worth noting that companies have different approaches to the question of how exactly the print head should be made. In Lexmark products, the print head is part of the cartridge, and therefore its resource is short (the nozzles only need to produce the amount of ink contained in the cartridge), but the problems are also small if the head, for example, dries out - the user simply changes the cartridge and continues working. A similar design is used in most Hewlett-Packard printers (the exception is the latest models with SPT technology). A number of Canon devices are designed differently, in which the print head is a separate (and quite expensive) block with a long resource, easily replaced by another if necessary, and the ink comes from cartridges installed in this block.

Color inkjet printers

Since cartridges can contain ink of various colors, modern inkjet printers at a relatively low cost can easily cope with the task of color printing, which is their main advantage over their main competitors - laser printers.

Most color inkjet printers use the CMYK color scheme: Cyan, Magenta, Yellow and Black, i.e. There is a color ink cartridge containing cyan, magenta and yellow ink, and a black ink cartridge. Due to the mutual superposition of drops of different colors in inkjet printers, it is possible to obtain an almost complete color gamut. In theory, all three colors should be combined to produce a pitch black color, but in reality they produce a muddy brown color and must be supplemented with black (K) ink to achieve a pitch black color.

For high-quality and color-correct printing, the atomizer (print head) must be as accurate as possible. Its characteristics are print resolution and droplet sizes, and it must be able to create droplets of different sizes. Today, each manufacturer has found its own approach to this task, but the essence of proprietary technologies remains unchanged - the sprayer must be flexible and precise. An example of this: the creation of 6-color printers (two more colors are added to the CMYK scheme: Light Cyan and Light Magenta), i.e. such printing devices create images using a CMYKLcLm scheme. With these printers, you can achieve more accurate color and halftone reproduction. In particular, the pink color, which dominates the color of human skin, can be printed more naturally, and accordingly, the printing of amateur photographs becomes an order of magnitude better. Seiko Epson printer line, first using this scheme, received the corresponding name - Stylus Photo.

Another problem with color printing is the mismatch between the color representation on the screen (RGB scheme) and the color representation on the printer (CMYK scheme). Color conversions from CMYK to RGB or vice versa will never be reversible, i.e. If you create an image in RGB, convert it to CMYK, and then back again, the colors will not be displayed correctly. To solve this problem, new drivers are being created that automatically create a transition between RGB and CMYK just before printing. But this cannot completely solve the problem. The similarity of colors on the screen and on the printer will only be relative.

LASER PRINTING

A laser printer is a device that forms an image received from a computer on paper or other media (transparent film, envelope, fabric, etc.) using electrophotography, i.e., using the ability of some materials to change their electrical charge under the influence of light radiation.

Xerography

Xerography was invented in 1936. American scientist. Xerox- it's dry and xerography - This is a type of dry image printing. Xerography uses a plate of selenium, a semiconductor material, to store graphic information. A layer of semiconductor - selenium - is applied to the metal base of the plate made of a good conductor (copper and its alloys). The plate is polished and has a high class of purity - a mirror surface. The xerographic printing process can be divided into several stages.

First stage- charger semiconductor selenium plate with a uniform electrical charge using a corona discharge. The process takes place in the dark.

Second phase -exposure- projection of an image onto a charged selenium plate. Photons of light knock out electrons in selenium. These points acquire electronic conductivity, and the potential of the plate “drains” onto the conducting base. “Potential” holes are formed. As a result, a potential image relief is formed on the surface of the plate when the image is exposed.

Third stage- manifestation Images. Coloring powder is poured onto the potential relief, which is attracted to the potential peaks.

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Fourth stage -pouring powder that is not attracted to potential holes under the influence of gravity.