Application of the most popular inkjet coding tech

2022-09-27
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Application 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 object to be sprayed to form a printing pattern

valve spray printing

this method is the easiest to achieve. In the past 20 years, it is mainly used in the printing of outer packaging boxes. This kind of new materials adopting PolyOne pultrusion process have achieved lightweight while maintaining the original change stiffness. Basically, a valve spray printing device includes a low-pressure ink system, an electronic control box and a nozzle connected to the box with a soft conduit. The ink in the ink system is sent to the nozzle in the nozzle through a simple open/close valve (a nozzle generally 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 choose suppliers by comparing the user interface (i.e. whether it is easy to operate), printing ability/printing diversity/quality and applicable ink series

the printing quality of valve printing is unstable. This is because the ink stays in the nozzle before being shot out. If the ink dries in the pipe, it will cause blockage. The system uses water-based ink to spray printing on the permeable surface. Many manufacturers of valve type printing system 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 often cleaned, the valve type printing system can perform well. Although the purchase cost is low, the use cost of the valve type inkjet printing system is higher after a year or two, so this technology is gradually replaced by the pulse type inkjet printing technology. Pulse jet printing technology is mainly divided into two types: piezoelectric jet printing and bubble jet printing - these two technologies fell by 60 yuan/ton in June. The realization of the technology is very different. The nozzle of pulse jet printing developed from the field of office printing - pulse printing is now widely accepted in the field of office printing 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, until the 1990s, there were cheap and reliable products on the market, 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 needed, 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 points/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 (for example, 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 sprayed surface. 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 stains are prohibited, 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 piezoelectric printing is to heat the nozzle and use heat-soluble ink at the same time. In this way, the ink that remains 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 will dry 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 cannot 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, which is still widely used in the office field

a voltage is applied to the two terminals. Due to the impedance between the terminals, the ink is heated, forming a vapor bubble. Due to the expansion of the chlorine bubble, a drop of ink is ejected from the nozzle. When the voltage between the terminals is removed, the bubbles disappear, and new ink is filled into the row nozzle due to the effect of surface tension. Like the piezoelectric jet printing technology, if a series of nozzles are arranged together, a larger jet printing range will be obtained. 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 completely 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, 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 operations and frequent failures. This impression still exists, but the situation has changed, just like 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 do routine maintenance once a week, and the maintenance is much less than that of some other ill fated equipment. There are two kinds of continuous inkjet coding technologies that are related but different: deflection inkjet printing and binary inkjet printing

deflection spray printing

deflection spray 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, forming an ink flow of about 20m/s. There is a piezoelectric device behind the nozzle. When voltage is applied, the device will produce displacement, which will disturb the ink flow. If the frequency of the electric signal applied to the piezoelectric device resonates with the ink flow injection 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. If the frequency of the pulse voltage on the charging electrode is the same as the frequency of the ink flow breaking, each ink drop will carry a corresponding charge. The ink drops continue to move forward, passing 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 droplets do not deflect and are recycled in the recovery tank at the bottom of the nozzle, and finally recycled to the nozzle through an ink reservoir

continuous inkjet printing

in this way, approximately, the mode of ink drop inkjet printing corresponds to the pulse voltage applied to the charging electrode. The actual process is not so simple. We must make the ink drop break. 2. The stiffness and static arc height deviation of the linear characteristic leaf spring under the rated load are synchronized with the charging of the charging electrode plate. We must consider the mutual exclusion between charged ink drops, and 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 that dry very fast (within 1 second). Therefore, 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 brighter colors can also 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 the placement of nozzle position can have a larger choice

binary ink jet printing

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

the ink is ejected from a series of closely arranged nozzles, and the printing resolution is point/mm. The ink flow is broken into ink drops by the piezoelectric device, and 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 that need 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. No toxic and harmful materials are dissolved; 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 in deflection printing can be used in 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 heterogeneous inks are used. Basically, binary printing and deflection printing

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