Thermal inkjet and piezoelectric printing - pros and cons. Inkjet Printing Types: Thermal Inkjet and Piezoelectric

Inkjet printers are among the most popular among consumers today. Moreover, in most cases, such a printer is bought as a peripheral to a home computer. There are reasons for that, and first of all, the low price and the ability to print color documents. Meanwhile, according to the sellers of a number of salons of computer equipment, most users have more than a vague idea about the principles of inkjet printing. If everything is more or less clear to their owners with the work of dot-matrix or laser printers, then, as a rule, they can only say about inkjet printers that the picture is formed there by spraying small drops of ink on the paper.

To begin with, it is probably worth explaining what is such an indicator as dpi, which, it turns out, is more important than, for example, print speed. DPI (dot per inch, that is, dots inch) is the so-called number of drops per inch, a function of the frequency with which drops are ejected and the speed at which the printer's print head moves along the horizontal axis. A controlled nozzle at certain moments discretely ejects drops of ink and thus draws a line. The main challenge for a printer manufacturer is the combination of quality (maximum droplet per line) and speed (minimum droplet per line to achieve higher speed). Droplet ejection speed is from 10 to 20 thousand per second. By varying this frequency, or the speed at which the printhead carriage moves, it is possible to achieve optimal horizontal droplet density and hence print quality.

Resolution is a parameter determined by the size of the ink droplets. When applying smaller droplets, the clarity of the image will be higher when compared with an equal surface area filled with a smaller number of larger droplets. It is clear that in this case, a higher quality will require a lower print speed, and vice versa.

Inkjet printers differ in the way they print.

Three main printing methods are quite widespread.

Thermal inkjet printing

The development of thermal inkjet printing technology began in 1984. The pioneers then were HP and Canon. But things went slowly, and for a long time it was not possible to come to the necessary results. Only in the 90s was it possible to finally achieve an acceptable level of quality, speed and cost. Lexmark later joined HP and Canon to further develop thermal printers, leading to today's high-resolution printers.

As the name implies, the thermal (more correctly, electrothermal) formation of a jet is based on an increase in the temperature of liquid ink under the action of an electric current. This temperature increase is provided by a heating element which is located in the ejection chamber. When heated, some of the ink evaporates, excess pressure quickly builds up in the chamber, and a small drop of ink is ejected from the ejection chamber through a precision nozzle. Within one second, this process is repeated many times. The most important thing for the success of this technology. this is to select the configuration of the ejection chamber, as well as the diameter and accuracy of the nozzle as accurately as possible. The behavior of the ink during heating and ejection from the nozzle, along with the characteristics of the ink itself (its viscosity, surface tension, ability to evaporate, etc.), is also influenced by the characteristics of the channel leading to the nozzle and the exit point to the nozzle. Of great importance for ensuring the correct ejection of ink from the nozzle are also the nature of the change in the ink meniscus in the nozzle after ejection and the refilling of the ejection chamber. Let us consider in more detail the stages of formation and ejection of a drop. The formation of a thermal ink jet begins in the print head of the cartridge. An electrical impulse generates a heat flux on the heating elements equivalent to more than two billion watts per square meter. This is about 10 times greater than the flux on the surface of the Sun. However, since the duration of the thermal pulse is only 2 millionths of a second, although the temperature at this time increases at a rate of 300 million degrees per second, the surface of the heating element only has time to heat up to about 600°C during this time. Since the heating is extremely fast, in reality the temperature at which the ink can no longer exist as a liquid is reached only in a layer with a thickness of less than one millionth of a millimeter. At this temperature (approximately 330°C), a thin layer of ink begins to evaporate and the bubble is forced out of the nozzle. The vapor bubble is formed at a very high temperature, and therefore the vapor pressure in it is about 125 atmospheres, i.e. four times the pressure generated in modern gasoline internal combustion engines. Such a bubble, which has tremendous energy, acts like a piston, ejecting ink from a nozzle onto the page at a speed of 500 inches per second. The resulting drop weighs only 18 billionths of a gram. By commands from the printer driver, several hundred nozzles can be activated simultaneously in any combination. The reservoirs from which ink is supplied to the print head can be divided into two constructive types. Firstly, a monoblock system is widely used, combining an integrated ink tank and an ejection unit. It has the advantage that the print head is replaced every time the ink tank is changed, helping to maintain high print quality. In addition, it is simpler in design and easier to carry out replacements. In the second, more complex system, the print head is separated from the ink reservoir, and only this reservoir is replaced when it is empty. The foam in the ink reservoir acts as a sponge to soak up liquid ink so that ink is continuously supplied to the print head, and there is neither unwanted gravity leakage from the cartridge nor ink leakage from the print head itself. On the basis of a monoblock cartridge there are electrical contacts and a print head. a key element of the entire inkjet printing process; ink is supplied to the print head through a set of channels coming from the reservoir. Printhead manufacturing. it is a complex process carried out at the microscopic level, where the accuracy of measurements is determined by microns. The main materials used for the ejection chamber, ink channel, electronic control circuit and heating elements are similar to those used in the semiconductor industry, where the thinnest conductive metal and insulating layers are precision laser processed. This technology requires large investments in both development and production, and this is one of the main reasons that very few companies venture into this area. The printhead is a collection of many micro-sets, consisting of ejection chambers and associated nozzles, arranged in a checkerboard pattern in order to increase the vertical density of the nozzles. With this arrangement of nozzles, the number of nozzles at a distance of about 1.27 cm can reach 208, as is the case, for example, in the black cartridges of the Lexmark Z models, so that a resolution of 1.44 million dots can be achieved. Print quality is determined by many factors, but the main ones are. these are the dot size, the vertical density of the dots, and the frequency of droplet ejection through the nozzle; it is these indicators that are the main criteria for further work on printheads, whether they are thermal or piezoelectric heads. Thermal heads have some advantages over electromechanical ones, since the key technology for their manufacture is similar to that used in the manufacture of microprocessor chips and other semiconductor electronic products. Rapid progress in these areas is benefiting thermal technology, and even higher resolutions and faster print speeds can be expected in the coming years. Thermal inkjet printing has several advantages over competing piezo technology. For example, simplicity of design and close analogy with semiconductor manufacturing: this means that the marginal cost of production here will be lower than for a competing technology. The configuration of the ejection chambers allows the nozzles to be located closer together, which makes it possible to achieve higher resolution.

Piezoelectric technology

The piezoelectric system, created on the basis of an electromechanical device and brought to commercial readiness by Epson, was first used in Epson inkjet printers not so long ago. in 1993. Piezotechnology is based on the property of some crystals, called piezocrystals (an example is quartz crystals in common quartz watches), to deform under the influence of an electric current; thus, the term defines an electromechanical phenomenon. This physical property allows some materials to be used to create a miniature "ink pump" in which a positive to negative voltage change will cause a small volume of ink to be compressed and vigorously ejected through an open nozzle. As with the formation of an ink jet due to thermal effects, the drop size here is determined by the physical characteristics of the ejection chamber and the pressure created in this chamber due to the deformation of the piezocrystal. The droplet size is changed by changing the amount of current flowing through the ejection mechanism. As with thermal printers, the frequency of the piezoelectric ejection depends on the potential frequency of the electrical impulses, which in turn is determined by the time it takes the camera to return to its “quiet” state, when it is filled with ink and ready for the next work cycle. Piezo technology is highly reliable, which is very important because the print head, for purely economic reasons, cannot be part of a replaceable ink cartridge, as in thermal systems, but must be rigidly connected to the printer. For both thermal and piezoelectric systems, the performance is determined by many factors. The ability to change the size of the dot gives piezo technology certain advantages. On the other hand, piezo technology faces some purely physical limitations. For example, the large size of the electromechanical ejection chamber means that the vertical density of the nozzles must be less than that of thermal counterparts. Not only does this limit the prospects for further development, but it also means that to achieve higher resolution and uniformity in high quality printing, multiple passes of the print head over the same page are required.

A stationary printhead is somewhat cost-effective because it does not have to be replaced. However, this advantage is partially offset by the risk of air entering the system when changing the cartridge. This clogs the nozzles, reduces print quality, and requires several cleaning cycles to restore normal system performance. Another limitation so far for piezo systems concerns the use of dye-based inks: when using color (pigment) inks, which are of higher quality, but also have a higher density, there is also a risk of clogging of the nozzles. The piezoelectric printhead, based on prior technology, has lower development costs, but is noticeably more expensive to manufacture. At present, the advantages of piezoelectric heads, such as high reliability and the ability to change the size of the drop, are very significant and make it possible to manufacture products of very high quality. However, as the price of thermal inkjet printers continues to decline and they increasingly capture the entry-level printer market, there remains a market for mid-range and high-end products for piezo systems.

Bubble jet printing

The Canon Bubble-Jet bubble-jet printing principle, invented in the late 70s, is ingeniously simple. In each nozzle, the thinnest channel in which droplets of ink are formed, there is a microscopic heater. Electrical pulses applied to it cause the ink to boil with the formation of air bubbles, and these bubbles push equal volumes of ink out of the nozzle with each pulse. Heating stops, the bubble disappears, a new portion of ink is drawn into the nozzle, and it is ready for a new cycle!

However, it took about 8 years for the first bubble inkjet printer to become available to users. In 1981, the promising Canon Bubble-Jet technology was first presented at the Canon Grand Fair and immediately attracted the attention of specialists. But it was not until 1985 that the first commercial model of the Canon BJ-80 monochrome printer appeared, and the first full-color BJ printer BJC-440 (A2 format, 400 dpi) appeared in 1988.

Until a certain period, the word “printing” was associated either with the work of a printing house, or with laser regulars in large offices. Inkjet printing was different in that it was a process of transferring an image or text using a nozzle plate and liquid dye.

It would seem that the concept of inkjet printing began to come into use only recently, after inkjet printers became available to the average user. However, the history of their development covers almost 200 years.

The figure below illustrates the evolution of inkjet printing from its inception to the present.

Stages of development of inkjet printing

Theoretical developments

The theoretical foundations of inkjet printing technology originate in 1833. It was then that Felix Savard, a French physicist and inventor, revealed an interesting pattern: as a result of liquid spraying through holes with a microscopic diameter (nozzles), perfectly even drops are formed. And only 45 years later, in 1878, this phenomenon was mathematically described by Lord Reilly, Nobel Prize winner.

However, earlier, in 1867, William Thompson patented the idea of ​​a continuous ink supply (Continuous Ink Jet). He used electrostatic forces to control the spraying of ink and liquid dye onto paper. Based on this principle, William Thompson designed the recorders necessary for the operation of electric telegraphs.

Continuous printing

Significant for inkjet printing technology was 1951 - Siemens received a patent for an inkjet printer, the first of its kind. It was based on the technology of continuous ink supply. A little later, many global manufacturers of printing equipment adopted this technology and continued to improve it.

The forerunners of modern inkjet printers were rather bulky, equipped with various cylinders, pumps and other moving parts, whimsical to use and, moreover, cost a lot of money. Such printers worked very slowly, and not without drawbacks: they could leak ink when printing, which was not very convenient and safe.

Print on demand

The process originated in the 60s of this century, when a professor from Stanford University managed to obtain ink drops of the same volume and equally spaced from each other. To do this, he used pressure waves produced due to the movement of a piezoceramic element. Such a system was called “Drop-on-demand”, translated from English as “drops on demand”. The technology made it possible to move away from the use of a complex ink recycling system, a charging system, and also to eliminate droplet deflection.

For the first time, on-demand printing was used in 1977 in Siemens PT-80 printers, and some time later (1978) in Silonics printers. Later, this printing method continued its evolution: the technology developed and became the basis of more and more new models of inkjet printers for commercial use.

The most expensive part in a printer was, and still is, the print head. It was impossible to “painlessly” replace it, as it happened with the cartridge. Therefore, users found new interaction algorithms. For example, to prevent clogging of the nozzles of the print head with air bubbles or dried ink residues, they tried to use the printer even when it was not particularly necessary. And all in order to prevent a long downtime of the printing device.

Back in the 70s of the twentieth century, the prerequisites for color printing appeared. The Swedish professor Herz has found a way to reproduce all sorts of shades of gray thanks to the method of regulating the density of the droplets. This made it possible to print not only text, but also various images, transmitting gray gradations.

bubble seal

We owe the technology of bubble printing to Canon. In the late 70s, its specialists showed the world the technology of inkjet printing, previously unknown - "Bubble Jet" or "bubble printing". The principle of operation of these inkjet printers is as follows: a microscopic thermoelement is placed in the nozzle, which instantly heats up to 500 ° C as soon as a current acts on it. When heated, the ink boils, air bubbles (bubbles) are formed inside the chamber, under the influence of which equal volumes of ink are pushed out of the nozzle onto the paper. As soon as the ink stops heating and cools to its previous temperature, the bubbles burst, and the next portion of ink is drawn into the nozzle. This ensures uninterrupted printing.

The principle of bubble inkjet printing technology

As soon as Canon introduced bubble jet technology at the Grand Fair in 1981, it immediately caught the public's attention. And already in 1985, the Canon BJ-80 saw the light, the first monochrome bubble printer. Three years later, the Canon BJC-440 appeared, the first large format printer to use the same technology. He could already print in color at 400 dpi.

The cost of printing with bubble inkjet technology is relatively low. However, the cost of maintaining the printer increases because the print head is built into the ink cartridges and not the printer. But there is a downside to the coin: the device remains operational if a non-original cartridge is used.

Thermal printing

The era of thermal printing began towards the end of the 90s, although HP and Canon began developing it as early as 1984. The thing is that it was not possible to achieve the necessary combination of quality and cost of printing, as well as the speed of work. A little later, Lexmark joined the giants of the industry. In this tandem, these major companies have achieved high resolution printing and created a semblance of modern printers.

The resulting technology became known as "thermal printing" (thermal inkjet). This technology was used by HP's first line of inkjet printers, the ThinkJet.

HP THinkJet Inkjet Printers

The principle of thermal printing is to increase the volume of ink when heated. The temperature of the heating element inside the print head was raised by the heating element. Ink located close to the heating element begins to evaporate when heated. Bubbles are formed, which push out a certain amount of them from the nozzle. The pressure drop causes the same volume of ink to enter the print head. This process is repeated with a high cyclicity of up to 12,000 refuelings per second. The printhead based on thermal inkjet technology consists of a large number of microscopic nozzles and ejection chambers.

HP has chosen an unusual course - it has made a replacement print head, which is part of the cartridge and is thrown away with it without much regret. This step solved the printer's durability problem.

The principle of operation of a thermal printer

Bubble and thermal inkjet printers were affordable, compact, quiet, and provided a wide color range, which flooded the market for affordable printers and almost drove dot-matrix printers out of the market.

Piezoelectric seal

The technology of the piezoelectric printing system (Piezoelectric Ink Jet) appeared in 1993 thanks to Epson, which was the first to use it in their printers. The principle of piezoelectric printing is based on the property of piezocrystals to change their volume and shape under the influence of current. In the structure of the cartridge, one of the walls is a piezoelectric plate. It bends under the influence of current and thereby reduces the volume of the ink chamber. As a result, a certain amount of ink is pushed out of the nozzle.

The principle of piezoelectric printing technology

The advantage of a stationary print head is its efficiency, because it does not have to be changed as often as cartridges. However, there is a small chance that when you change the cartridge, air may get into the print head and clog the nozzles, affecting print quality.

Modern traditions

The development of technology has now made inkjet printers even more popular. They are purchased for both office and home use due to their affordable price and compactness. Sometimes users buy color inkjet printers as a complement to monochrome laser printers. There is an opinion that laser devices can print text documents faster and cheaper, while inkjet devices can print color photographs.

Currently, 4600x1200 dpi is considered the print resolution standard for modern inkjet printers. But there are already devices that surpass this indicator. Other features of inkjet printers include borderless printing, as well as a built-in LCD display or a port for reading memory cards.

Benefits of inkjet printers

The most basic trump card of inkjet printers is the high quality of color printing. You can recreate bright and realistic photos with excellent rendering of fine details and midtones. In addition, inkjet printers are practically silent, do not require a long warm-up time, are presented in a wide range of models and are available in various modifications.

Disadvantages of inkjet printers

The main reason for refusing to use an inkjet is the high cost of original cartridges, the fragility of prints due to fading or spreading of ink when liquid enters, and clogged print heads. Although the solutions to all these shortcomings are very simple. Clogs can be overcome with standard head cleaning, and prints can be made more durable using pigment ink. But to avoid overpaying for original cartridges, alternative consumables and ink, which at the moment have reached high quality indicators, will help. The difference from the original ink is no more than 2-5%, due to which the difference in print results is indistinguishable to the naked eye.

A lot of news from the development of modern printers, MFPs and plotters can be read.

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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. In general, the technology of thermal inkjet printing is presented 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 is heated 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 stability of 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.

Rapidly developing, inkjet printing is developing new segments and applications. In the fight for market prospects, R&D in printheads, inks and specialty formulations is crucial. A big plus when choosing an inkjet printing device will be basic knowledge about manufacturers and printhead technologies.

Any jet head works on the principle of electronically controlled spraying of liquid droplets onto the desired surface. The two main classes are continuous feed heads and piezoelectric pulsed (Drop on Demand, DOD) heads, each divided into subclasses.

In continuous inkjet printing, droplets are sprayed non-stop, either on the media or in a container for recycling and reuse. In DOD equipment, the ejection of droplets depends on certain conditions, and they are formed using a pulse in the ink supply chamber. Varieties of inkjet DOD printers are determined by the characteristics of the pulse generation. There are three main categories of technologies on the market: thermal, piezo and continuous flow (electrostatic).

Thermal inkjet printing

The first thermal inkjet printing technology was proposed in 1977 by Canon design engineer Ichiro Endo. Thermal printheads have come a long way since the first desktop printers of this type were released.

Regardless of the design features, thermal printheads are united by a concept: small droplet size with high speed and density of nozzles.

In a compact ink chamber, droplets are formed by rapidly heating a resistive element. Rapidly heating up to several hundred degrees, it causes the ink molecules to evaporate. A bubble (pressure pulse) forms in the boiling liquid, which forces the ink out of the chamber. As a result, a drop appears at the other end of the nozzle. Once pushed out, the vacuum in the chamber is filled with fresh ink from the reservoir and the process is repeated.

The disadvantage of the technology is the limited range of compatible fluids: thermal inkjet inks need to be designed with evaporation and resistance to high local temperatures. In addition, thermal printheads are adversely affected by the process of so-called cavitation: bubbles constantly form and burst on the surface of the heating element, from which it wears out. However, modern materials provide thermal inkjet heads with a sufficiently long service life.

To reduce droplet size and increase print speed, high-precision technologies are needed to increase the number of nozzles per surface width. Canon FINE printheads offer an impressive 2,560 nozzles per color (15,360 nozzles per printhead). Nozzles vary in diameter because thermal technology is unable to produce droplets of different sizes. In each head, nozzles of 1, 2 and 5 squares are combined in a special way.

Hewlett Packard has achieved impressive nozzle density in the Edgeline printhead. The design with a print width of 10.8 cm consists of five silicon chips arranged in a checkerboard pattern.

The physical resolution reaches 1200 dpi at an operating frequency of 48 kHz. The dual row of nozzles (10,560 per die) allows the Edgeline to apply two colors. When printing in one color, the second row remains as a backup. Each head, designed to work with water-based or latex ink, has 5 matrices - a total of 52,800 nozzles.

Edgeline is installed in latex printers and roll presses from HP. The 77 cm print width T300 comes with 70 printheads for each side of the printed web. Thus, in duplex mode, 7,392,000 nozzles function, and the machine applies 148 billion drops to the printed material every second with high accuracy. All thermal printheads are consumables and their life depends on the amount of ink passing through them.

Thermal printheads for desktop inkjet printers are also available from Kodak and Lexmark. Some of the models they completed have already been discontinued.

In the wide format water-based inkjet market, the battle is between Canon and HP, the only supplier of latex printers with thermal printheads. And no one but HP has yet offered a thermal printhead in a single pass configuration.

Thermal inkjet technologies are quite confident in their niche, but most large and extra large format roll and flatbed printers are now represented by models with piezo inkjet printheads.

Piezo technology: drop on demand

Piezoelectric printheads combine the principle of spraying drops. Thanks to a wide range of modifications for different materials and applications, they are very popular with manufacturers of inkjet printers.

The principle of drop-on-demand technology is based on the change in the shape of certain crystals when voltage is applied. As a result, the chamber is deformed, generating an impulse. Piezoelectric inkjet heads from more than a dozen manufacturers are on the market.

Inkjet technologies have a lot of applications, printing is just one of them. Inkjet printheads are used for marking and coding, postcode and address printing, document processing, textile printing and marking, engraving, photovoltaics, material deposition, and high-precision liquid dispersion.

Inkjet printheads can be classified by:

• compatibility with liquids (compositions water, oil, solvent, UV, acid);
• operating temperature;
• number of nozzles;
• physical permission;
• print width;
• construction material;
• fixed or variable drop;
• the smallest droplet size;
• environmental friendliness.

The main difference between inkjet printheads is fixed or variable droplet size. Fixed drop printers are called binary printers. It is important to understand the differences between technologies and how they work.

Binary printheads produce droplets of a standard size. Sea options - from 1 pl to 200 pl or more (picoliter - one trillionth of a liter). The main advantage of the technology is that large drops cover the printed material faster. Another feature of printheads with a fixed drop size is reduced resolution. Therefore, they are better suited for large format printing, textile printing and other segments where resolution is not of paramount importance.

The smallest drop is provided by the Durst Rho P10 wide format printers: Quadro Array printheads with 10 pl offer up to 1000 dpi resolution. Inkjet heads with a drop size of 1 pl are not designed for graphics, but for the deposition of liquids and printed electronics.

Fixed drop printheads compare favorably with the spray rate, measured in kilohertz (1000 cycles per second). Inkjet printers based on this technology come in 4- and 6-color configurations. When working with large volumes, do not forget that the print speed of 4 colors is higher than that of 6 colors, and if several print heads are responsible for one color, the printer will generally “fly”.

Now there is an active debate on which technology is better and why - with a fixed or with a variable droplet size. But first of all, you need to take into account practical aspects: manufactured products, the cost of the printer, economically justified speed.

Variable drop size printheads are able to adjust the print resolution on the fly. To increase the drop, the system combines several drops of the base size.

Take for example a printer with a base drop of 6 pl. To get a drop of 12 pl, the system sends two pulses to the ink chamber at once: the drops meet in the air and merge into one. The drop sizes available for a particular printhead are called "levels".

The 8-level head forms drops of seven sizes. The piezoelectric head with support for 16 levels will give 15 droplet sizes. With a base drop size of 6 pl, the available options are obtained by simply multiplying the base drop: 6, 12, 18, 24, 30, 36, 42 pl.

If we analyze the frequency of spraying, it turns out that the formation of variable droplets takes more time, which is quite logical. For a 16-level piezo jet head, the base drop spray rate will be about 28 kHz. If you activate 8 droplet options for it, the spray rate will drop to 6.2 kHz. If all 16 options are involved, the speed is only 2.8 kHz. As you can see, when moving from the base level to the maximum possible 16 levels, the number of droplets formed is an order of magnitude less. Variable drop size printheads consistently print slower than fixed drop sizes. But they increase the resolution of small text and print quality in general.

To increase the performance of variable drop inkjet heads, printer makers increase the number of channels per color. An ink channel is a series of nozzles dedicated to a specific ink color, a typical option for scanning and printing systems in one run.

Scanning printing here refers to an inkjet printing method in which the carriage with the print head moves back and forth over the surface of the printed material, and it is fed in a start-stop mode. In some flatbed printers, the image is formed differently: the material reciprocates under a group of print heads that cover the entire width of the print.

Continuous Inkjet - High Speeds

Continuous inkjet technology is a non-contact version of high-speed printing that is used to print variable information onto moving material. Initially designed for adding dates, texts and barcodes, the modules now offer multi-color printing on roll materials. It's hard to believe, but Lord Kelvin was the first to patent this idea in 1867.

The principle of the technology is as follows: the pump delivers liquid ink from the tank to many tiny nozzles, forming a continuous stream of drops at a very high speed. The rate of droplet formation and spraying is controlled by a vibrating piezoelectric crystal. The speed of its vibration is called the frequency, which in this case varies from 50 to 175 kHz. Each nozzle delivers between 50,000 and 175,000 drops per second. They fly through an electrostatic field and, already charged, fall into a deflection field, which directs them to the material or to the collection tank for reuse. The bulk of the drops goes to processing, and only a small part forms an image on the print. One of the main advantages of this type of inkjet printheads is their high speed.

Kodak Stream is an example of continuous inkjet hybrid printing technology. Periodic pulses in the heating modules near each print head nozzle form tiny ink drops. By adjusting the size and shape of the pulse, the system changes the size of the dot and the speed of spraying drops. Stream technology generates droplets at 400 kHz, as fast as traditional web offset presses. Moreover, Kodak is sure that it is possible to increase the frequency of pulses.

The closest competitor to the Prosper CPM is HP's inkjet roll-to-roll CPM. The theoretical maximum frequency for it is declared at the level of 100 kHz. And for piezoelectric inkjet printers, the standard frequency is 25-40 kHz.

Stream technology is based on MEMS microelectromechanical systems (they were also used in HP Edgeline printheads). Modern MEMS manufacturing technology is similar in principle to integrated circuit fabrication techniques that are used to create ultra-miniature inkjet structures on silicon. The nozzle plate is a mechanical element combined with electronics on a common silicon base.

choose any

Printheads are just one component of complex printing systems. To select technologies that are optimal for a particular company, be sure to take into account technological differences. Given the widest selection of offers on the market today, it is important to arm yourself with as much information as possible.

About the author: Jeff Burton ([email protected]), SGIA Digital Print Analyst and Consultant for Digital Print Production, Color Management and Product Portfolio, Digital Equipment and Manufacturers. For more than 20 years in the industry, he has worked as a production manager, an association consultant, and a trainer. Author of numerous technical articles and speaker at industry events.

* SGIA Journal. March-April 2013. Reprinted with permission from the SGIA. (c) 2013.

On the same topic:

Among all imaging technologies, inkjet printing has gained its popularity.

It is used in printers, including large format ones.

The advantage of this technology is that the drop of ink is formed only at the right moment, which allows you to get high-quality images.

What is thermal inkjet printing

In this article, we will tell you what thermal inkjet printing is, its advantages, the principle of operation, and in what cases it is used.

The finished image consists of a large number of microscopic ink dots of various colors (color inkjet thermal printing).

At the moment when you need to apply the image, there is ink in the microscopic chamber of the nozzle, which must somehow be pushed onto the surface of the printed material (for example, paper).

The thermal method of printing consists in the fact that there is a heating element in the chamber, to which current is supplied at the time of printing. The duration of a momentary switching on of the current is a short period, up to 2 millionths of a second.

Under its action, the element heats up, the temperature of the paint increases to 500º, the volume of paint in the nozzle increases, which increases the pressure in the chamber, and a portion of the dye is pushed out of it. There is information that in the chamber, at the moment of heating, a pressure of more than 100 atmospheres is formed, which is quite a lot.

After that, a vacuum is formed, which contributes to the retraction of a new portion of paint. This process is repeated several thousand times per second.

Thermal Inkjet Equipment

This method of printing is used in the vast majority of inkjet printers. The technology was introduced to the market in the early 1980s. The leading manufacturers are Canon, HP, Lexmark.

Modern equipment makes it possible to form drops up to 35-40 microns in size, which makes it possible to obtain a high-quality and detailed image.

Typically, thermal printers have two printheads. One is for printing with black ink, and the other is for printing in color (cyan, magenta, and yellow).

There can be up to several hundred nozzles in one printhead, depending on the model.

Depending on the model, the heads can be inseparably connected to cartridges or built into the printer, that is, reusable. The latter option makes it possible to be more confident in the quality of printing, because this element does not have time to work out its resource. But in this way the price of printing becomes more.

Advantages and disadvantages of thermal printing

Thermal inkjet printing is widely used in printing technology, thanks to:

• quiet operation of the equipment,
• ensures high quality and resolution of printing,
• thermal inkjet printing technology allows you to get reliable print heads,
• stability of printers on this technology,
• high printing speed.

Disadvantages of thermal printing:

It is not always possible to accurately control the size of the resulting droplets,

During operation, satellite drops may form, which degrade the quality of the resulting image,

The print head sometimes needs to be cleaned,

It is advisable to choose a special paper that will reduce ink bleeding and paper warping,

Expensive ink cartridges. Although some take the risk and order non-original ones, which are a little cheaper.

Conclusion

Thermal inkjet printing gives you the opportunity to get professional printing at a low cost. The quality of the resulting image depends on the accuracy of the nozzle manufacturing, the structure of the ejection chamber. Also, the characteristics of the dye used (viscosity, surface tension, heat and evaporation capacity) affect the image acquisition.

We hope you were interested in this article, which gave an answer to the question: what is thermal inkjet printing and in what cases it is used.