The principle of inkjet coding technology in the operation of printer
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"Inkjet coding" refers to a number of related techniques that we use to cause very small droplets of ink to be ejected from the nozzle, the droplets of ink passing through the air, and finally falling onto the surface of the substrate to form a print pattern.
Valve printing
This method is the easiest to implement. In the past 20 years, it has been mainly used in the outer packaging. Basically, a valve printing device includes a low pressure ink system, an electronic control cabinet and a flexible conduit connected to the chassis. Nozzle. The ink in the ink system is sent to the nozzles in the nozzle through a simple open/close valve (one nozzle typically has 7 to 18 nozzles of 200 microns diameter or more). When an ink droplet needs to be ejected, the electronic component opens the corresponding open/close valve, and the ink droplet is ejected.
Due to the simple mechanical structure, the valve printing system is easy to set up. Customers typically select suppliers by comparing the user interface (ie, ease of operation), printability/printing diversity/quality, and applicable ink series.
The quality of the jet printing is unstable. This is because the ink stays in the nozzle until it is ejected, and if the ink dries in the pipe, it will block. The system uses water-based inks to print best on permeable surfaces. Many valve-type printing system manufacturers produce non-permeable surface inks that dry faster than water-based inks. The time is still quite long—about 15 to 30 seconds.
In general, the valve printing system can perform well if the quality of the printing is not high and the nozzle is cleaned frequently. Although the acquisition cost is lower, the cost of using the valve printing system is higher after one or two years, so this technology has gradually been replaced by pulse printing technology. Pulse jet printing technology is mainly divided into two types: piezoelectric printing and bubble printing - the realization of these two technologies is very different, pulse jet printing nozzle developed from the field of office printing - pulse printing It is now widely accepted in the field of office printing and has a good effect.
Pulse jet printing
Although pulse jet printing is conceptually simple, it is worth noting that it was not until the 1970s that someone got the initial patent, and even though companies such as Canon and Hewlett-Packard did a lot of research until the 1990s. Cheap and reliable products are put on the market, so pulse printing is not as simple as it seems, from inkjet printing at a fixed printing distance to clean paper in the office to inkjet coding in the harsh environment of the factory. There are many things to do.
Piezoelectric printing
Pulse jet printing technology first appeared in piezoelectric printing. In short, the ink pressure in the nozzle must be low enough (or negative pressure) because the surface tension of the ink keeps the ink in the nozzle and needs to be printed. When a pulse voltage is applied to the piezoelectric crystal, the piezoelectric crystal is deformed to reduce the volume of the nozzle ink chamber. Thus, a drop of ink is ejected from the nozzle, and then the piezoelectric crystal is restored to its original shape, and new ink enters the nozzle due to surface tension. By arranging a large number of nozzles side by side, the desired print width and resolution (typically 8-6 dots/mm) can be obtained. Although it is possible to increase the print resolution by tilting the print head (which would sacrifice the print height), the print resolution is fundamentally determined by the nozzle pitch. More precise improvements can make each piezoelectric crystal drive more nozzles (say 8), 32 piezoelectric crystals can drive the ink in 256 nozzles, which will have a larger printing range, of course There are only 32 programmable landing points on the surface being printed.
Because the system is not continuous, the ink must remain fluid in the nozzle and dry on the surface being printed. The inks used in piezoelectric printing are typically oil-based or paraffin-based. These two types of inks do not dry out in the nozzle but are absorbed by the printing surface. Piezo printing also uses some fast-drying inks, which still take a long time (about 10 seconds) to dry out. The use of fast-drying inks creates problems when the product needs to be processed quickly after printing and smudges are prohibited. In order to prevent the ink from drying out in the nozzle, we can also add a lower pulse voltage to the piezoelectric crystal, which will cause a slight disturbance to the ink in the nozzle, and the ink in the nozzle will not dry out. This method relies on changes in ink composition or mechanically more sophisticated improvements.
Another method of achieving piezoelectric printing is to heat the nozzle while using a hot soluble ink. Thus, the ink that remains fluid in the nozzle solidifies on the surface of the colder print. This piezoelectric printing system produces good results on many printed surfaces, but is easily scraped off during touches. In addition to the problem that the ink will dry out in the nozzle, another problem to be aware of is that the nozzle is sensitive to vibration. The vibration causes the ink to be shaken out of the nozzle and the ink chamber so that the surface tension does not allow the ink to fill the nozzle, and the system must be restarted. Obviously, when the vibration problem is found, the print quality has been affected.
Bubble printing
Bubble jet printing technology is an updated technology that is still widely used in the office sector.
A voltage is applied to the two terminals, and the ink is heated due to the impedance between the terminals, thereby forming a vapor bubble, and a droplet of ink is ejected from the nozzle due to the expansion of the chlorine bubble. When the voltage between the terminals is removed, the bubbles disappear and a new ink fills the nozzles due to surface tension. Like piezoelectric printing, a series of nozzles are aligned to give a larger print range. The resolution is largely determined by the intensity of the nozzle arrangement.
Ink characteristics are especially important for the proper functioning of bubble jet systems. In the office, you can control the surface of the printed matter to match the ink, but in the production environment is completely another matter. For this reason, the impact of bubble jet printing technology in the field of product coding has been limited. However, in the case of bubble jet printing ink, we can get excellent printing results.
Continuous inkjet coding has a wide range of applications, and it is perhaps the most diverse technology. From the mid-1970s to the end of the 1970s, early continuous inkjet encoders were complicated to operate and frequently failed. This impression still exists, but the situation has changed, just as we no longer leak oil when driving. The latest continuous inkjet coding system requires only one operator to press on/off and weekly routine maintenance, and maintenance requires much less maintenance than other desperate devices. There are two types of continuous inkjet coding techniques that are related but different: slanted jet printing, binary jet printing.
Deflection printing
Deflection printing technology has been commercialized since the early 1970s, and it may be one of the most developed technologies in the production environment. Although the principle is quite simple, for many years, a large number of control circuits have been combined to ensure reliability and ease of use.
The ink is pressurized and sent to the nozzle to form an ink stream of about 20 M/s. There is a piezoelectric device behind the nozzle. When the voltage is applied, the device will generate displacement. This displacement will disturb the ink flow. If the frequency of the electrical signal applied to the piezoelectric device resonates with the ink jet frequency, the ink flow will break. Ink droplets of the same size and spacing. At the location where the continuous stream of ink breaks into a series of ink drops, there is a charging electrode. If the frequency of the pulse voltage on the charging electrode is the same as the frequency at which the ink stream breaks, each ink droplet will carry a corresponding charge. The ink droplets continue to move past a pair of deflector plates. The voltage on the deflection plate is a fixed value (for example, +/-5KV), forming an electrostatic field. Under the action of the electrostatic field, the charged ink droplets are corresponding to one of the deflection plates according to the amount of charge The amount of deflection. Eventually, the ink droplets pass through the air and land on the surface of the object that passes through the printhead. The uncharged ink droplets are not deflected and are recovered by a recovery tank installed at the bottom of the spray head, and finally recirculated to the nozzle through an ink reservoir.
Continuous printing
Thus, approximately, the mode of ink drop printing corresponds to the pulse voltage applied to the charging electrode. The actual process is not so simple. We must break the ink droplets in synchronism with charging the charging plate, and must consider the mutual repulsion between the charged ink droplets and even the aerodynamic problem of the ink droplets in flight. Users of continuous inkjet encoders do not feel these problems, but it is these issues that make designing continuous inkjet encoders interesting.
Because ink jetting is continuous, continuous inkjet encoders can use many types of inks, especially those that dry very quickly (within 1 second). Continuous ink jet coding techniques are therefore ideal for printing products that have a non-permeable surface (such as cans and plastics) that require rapid processing after printing. In addition, pigment inks with more vivid colors can be used.
Since continuous printing has a relatively high jetting speed, the printing distance of continuous printing is usually much longer than that of pulse printing (generally more than 10 mm), and the printing quality does not decrease. The placement of the nozzle position allows for a greater choice.
Binary printing
The concept of binary continuous printing technology is as long as the deflection printing technology, which was developed early in the commercial field of high-speed (high-cost), large-scale printing. With the advancement of technology, binary printing will be put into practical use in a short time.
The ink is ejected from a series of closely-arranged nozzles with a print resolution of 4 - 8 dots per mm. The ink flow is broken by the piezoelectric device into ink droplets. The fracture is similar to the deflection printing (although the binary printing has More ink flow). The dots that do not need to be printed are charged, deflected, and then recovered by the recovery tank. The ink dots that need to be printed are not charged, and are not deflected, and are directly hit on the surface of the object to be printed. Thus, the width of the print pattern is determined by the number of nozzles or the number of ink streams. Of course, we can also use inkjet inkjet printing to recover uncharged ink droplets.
Binary prints have a smaller print footprint than deflected prints, but are still much larger than valve prints. In principle, a wide variety of inks for deflection printing can be applied to binary printing. In the future, the choice of whether to use binary or defensive printing will depend on whether the printing is focused on the number of lines of information or speed and cost. When printing more than 3 lines of information at the same time, binary printing is undoubtedly faster than deflection printing. However, binary printing is more expensive and requires more manual work in early applications—especially when using different inks of the opposite sex. Basically, binary and slanted jets will co-exist because they currently offer customers the most versatile and efficient solution in the field of online printing.