The principle of the most popular inkjet coding te

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The principle of inkjet coding technology in the operation of inkjet printer

"inkjet coding" refers to many related technologies. We use these technologies to make very small ink droplets eject from the nozzle, the ink droplets pass through the air, and finally fall on the surface of the printed object to form a printing pattern

valve type printing

this method is the easiest to realize. In the past 20 years, it has been mainly used for printing on the outer packaging box. Basically, a valve printing device includes a low-pressure ink system, an electronic control box and a nozzle connected to the box with a flexible conduit. The ink in the ink system is sent to the nozzle in the nozzle through the simple opening/closing valve in 2012 (a nozzle usually has 7 to 18 nozzles with a diameter of 200 microns or more). When an ink drop needs to be ejected, the electronic component opens the corresponding on/off valve, and the ink drop is ejected

due to the simple mechanical structure, the valve type printing system is easy to establish. Customers usually select suppliers by comparing the user interface (i.e. whether the operation is easy), printing ability/printing diversity/quality and applicable ink series

the printing quality of valve type printing is unstable. This is because the ink stays in the nozzle before being ejected. If the ink dries in the pipe, it will cause blockage. The system uses water-based ink for printing on permeable surfaces. Many manufacturers of valve type printing systems produce non permeable surface inks that dry faster than water-based ink. At this time, blocking will occur from time to time, and the drying time is still quite long - about 15 ~ 30 seconds

in general, if the requirements for printing quality are not high and the nozzle is cleaned frequently, the valve type printing system can perform well. Although the purchase cost is low, the use cost of the valve type inkjet printing system after oneortwo years has been invited by Indian Prime Minister modi to calculate that it is high, so this technology is gradually replaced by the pulse type inkjet printing technology. Pulse printing technology is mainly divided into two types: piezoelectric printing and bubble printing - the realization of these two technologies is very different. The pulse printing nozzle is developed from the office printing field - pulse printing is now widely accepted in the office printing field and has good results

pulse printing

although pulse printing is simple in concept, it is worth noting that no one obtained the initial patent until the 1970s, and although canon, Hewlett Packard and other companies did a lot of research, no cheap and reliable products were put on the market until the 1990s, so pulse printing is not as simple as it seems, There are still many things to be done, from printing on clean paper at a fixed printing distance in the office to completing inkjet coding in the harsh environment of the factory

piezoelectric jet printing

the first appearance of pulse jet printing technology is piezoelectric jet printing. In short, the ink pressure in the nozzle must be low enough (or negative pressure), because it is the surface tension of the ink that keeps the ink in the nozzle. When printing is required, a pulse electric pressure is applied to the piezoelectric crystal, which deforms and reduces the volume of the nozzle ink cavity. In this way, a drop of ink is ejected from the nozzle, and then the piezoelectric crystal returns to its original state. Due to the surface tension, new ink enters the nozzle. By arranging a large number of nozzles side by side, the ideal printing width and resolution (general point/mm) can be obtained. Although the printing resolution can be improved by tilting the nozzle (which will sacrifice the printing height), the printing resolution is fundamentally determined by the nozzle spacing. More precise improvements can make each piezoelectric crystal drive more nozzles (say 8), and 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 sprayed surface

because the system is not continuous, the ink must remain fluid in the nozzle and dry on the surface to be sprayed. The ink used in piezoelectric printing is usually oil-based or paraffin based. These two types of ink will not dry in the nozzle, but can be absorbed by the printing surface. Piezoelectric inkjet printing also uses some quick drying inks, which still take a long time (about 10 seconds) to dry. When the product needs to be treated quickly after printing and no stains are allowed, the use of quick drying ink will cause problems. In order to avoid the ink drying in the nozzle, we can also add a low pulse voltage to the piezoelectric crystal, which will slightly disturb the ink in the nozzle, and the ink in the nozzle will not dry. This method depends on the change of ink composition or more precise mechanical improvement

another way to realize piezo jet printing is to heat the nozzle and use heat-soluble ink at the same time. In this way, the ink kept as a fluid in the nozzle will solidify on the colder surface of the printed object. This piezoelectric printing system can get good results on many sprayed surfaces, but it is easy to be scratched off in the process of touching. In addition to the problem that the ink dries in the nozzle, another problem that needs to be paid attention to is that the nozzle is very sensitive to vibration. The vibration can make the ink vibrate out of the nozzle and the ink cavity, so that the surface tension can not make the ink fill the nozzle of the channel. At this time, the system must be restarted. Obviously, when the vibration problem is found, the printing quality has been affected

bubble printing

bubble printing technology is an updated technology and is still widely used in the office field

one voltage is applied to the two terminals. Due to the resistance between the terminals, the ink is heated to form a vapor bubble. Due to the expansion of the chlorine bubble, a drop of ink is sprayed out of the nozzle. When the voltage between the terminals is removed, the bubbles disappear. Due to the surface tension, new ink is filled into the row nozzle. Just like the piezoelectric printing technology, a series of nozzles are arranged together to obtain a larger printing range. The resolution is largely determined by the dense arrangement of nozzles

ink characteristics are particularly important for the normal operation of bubble printing system. In the office, you can control the surface of the print to match the ink, but in the production environment, it is totally another matter. For this reason, the influence of bubble printing technology in the field of product coding is limited. However, in the application of bubble inkjet printing ink, we can get excellent inkjet printing effect

continuous inkjet coding has a wide range of applications, and it may be the most diverse technology. From the mid-1970s to the late 1970s, the early continuous inkjet coders had complex operation and frequent failures. This impression still exists, but the situation has changed, just as the car no longer leaks oil when we drive. The latest continuous inkjet coding system only requires the operator to press the on/off key and perform routine maintenance once a week, and the maintenance is much less than that of other ill fated equipment. There are two kinds of continuous ink-jet coding technologies that are related but different: deflection inkjet printing and binary inkjet printing

deflection jet printing

deflection jet printing technology has been commercialized since the early 1970s. It may be the most developed technology applied 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 simple use

the ink is pressurized and sent to the nozzle to form an ink flow of about 20m/s. There is a piezoelectric device behind the nozzle. When the voltage is applied, the device will generate displacement, which will disturb the ink flow. If the frequency of the electric signal applied to the piezoelectric device resonates with the ink jet frequency, the ink flow will break into ink droplets of the same size and spacing. At the position where the continuous ink flow breaks into a series of ink drops, there is a charging electrode. For example, due to aging and creep, the frequency of the pulse voltage on the charging electrode is the same as that of the ink flow fracture, and each ink drop will carry a corresponding charge. The ink drops move on and pass through a pair of deflection plates. The voltage on the deflection plate is a fixed value (for example, +/-5kv), forming an electrostatic field. Under the action of this electrostatic field, the charged ink drops will deflect towards one of the deflection plates according to their own charged amount. Finally, the ink drops pass through the air and fall on the surface of the printed object passing through the nozzle. The uncharged ink drops will not deflect and will be recycled in the recovery tank at the bottom of the nozzle. Finally, they will be recycled to the nozzle through an ink reservoir

continuous spray printing

in this way, approximately, the ink drop printing mode corresponds to the pulse voltage applied to the charging electrode. The actual process is not so simple. We must synchronize the breaking of ink drops with the charging of the charging plate, and we must consider the mutual repulsion between charged ink drops, even the aerodynamic problem of ink drops in flight. Users of continuous inkjet coders will not feel these problems, but it is these problems that make the design of continuous inkjet coders interesting

because the ink jet is continuous, the continuous inkjet coder can use many types of inks, especially those with very fast drying speed. Due to the hydraulic universal testing machine, they are classified as fine instrument equipped inks (within 1 second). Therefore, the continuous inkjet coding technology is very ideal for the printing of products with impermeable surfaces (such as cans and plastics) that need to be processed quickly after printing. In addition, pigment inks with more vivid colors can be used

due to the relatively high spraying speed of continuous printing, the printing distance of continuous printing is usually much farther than that of pulse printing (generally more than 10mm), but the printing quality will not decline, so there is a large choice for the placement of the nozzle

binary ink jet printing

the concept of binary continuous ink jet printing technology is as old as the deflection ink jet printing technology. In the early days, this technology developed towards the commercial field of high-speed (high cost) and large-scale ink jet printing. With the development of technology, binary ink jet printing will be applied in a very short time

the ink is ejected from a series of closely arranged nozzles. The printing resolution is 4 - 8 points/mm. The ink flow is broken into ink drops by the piezoelectric device. The breaking mode is similar to the deflection printing (but the binary printing has more ink flow). Ink dots that do not need to be sprayed are charged, deflected, and then recycled by the recycling tank. The ink dots to be sprayed are not charged and deflected, but directly hit the surface of the object to be sprayed. In this way, the width of the printing pattern is determined by the number of nozzles or ink flow. Of course, we can also use charged ink droplets for printing and recycle the uncharged ink droplets

the printing distance of binary printing is smaller than that of deflection printing, but it is still much larger than that of valve printing. In principle, all kinds of inks used for deflection printing can be used for binary printing. In the future, whether to use binary printing or deflection printing will depend on whether printing focuses on the number of information lines 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 inkjet printing is more expensive and requires more manual operations in early applications - especially when different foreign inks are used. Basically, binary printing and deflection printing will coexist, because at present, they provide customers with the most diverse and effective solutions in the printing field