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"Inkjet coding" refers to a number of related technologies, and we use these techniques to eject very small ink droplets from the nozzles, the ink droplets passing through the air, and finally falling on the surface of the printed material to form a printing pattern. All of these related technologies have the following characteristics:
Non-contact: Because only the ink droplets touch the surface of the printed object, the moving surface and the fragile surface can be successfully printed.
Changed information: The information can be continuously changed, so the time, date, lot number and similar data can be changed online and in real time.
Speed: With inkjet coding technology, objects with a travel speed of no more than 6 m/s can be printed - this is sufficient for most production processes.
Like all things, there may be some technologies that are particularly applicable in specific situations, but in terms of the absolute breadth of the application, inkjet coding technology is still unmatched.
The technology needed for inkjet coding is not new. As early as the 19th century, people were able to break the ink flow and charge and deflect the ink drop. Also, piezoelectric materials have existed for some time, for example, they are used in sonar, cigarette lighters. However, what actually promotes the development of inkjet coding technology is:
The need to print date and lot numbers on the product (valve inkjet encoders and continuous inkjet encoders)
Â·Development of computer printers (pulse inkjet encoders)
Â· Development and application of microprocessors Since the 1960s, many amazing technologies have emerged and blossomed. The technologies that can survive and develop today are mainly divided into three types: valve-type printing, pulse-type printing and continuous printing. Type printing.
These three major technologies will overlap when applied, and each has its own strengths and weaknesses. To a large extent, it is these strengths and weaknesses that determine their most suitable range of applications. The original intention of this article is to introduce each technology to the reader and help the user to choose the best solution for himself.
This method of valve printing is the easiest to implement. In the past 20 years, it has been mainly used in outer packaging.
Basically, a valve print apparatus includes a low pressure ink system, an electronically controlled cabinet, and a showerhead attached to the cabinet with a flexible conduit. The ink in the ink system is sent through a simple opening/closing valve to the nozzles in the spray head (a spray head typically has 7 to 18 200 micron diameter nozzles or more). When an ink droplet needs to be ejected, the electronic component opens the corresponding opening/closing valve and the ink droplet is ejected. (Figure 1 shows:)
Due to the simple mechanical structure, the valve type printing system is easy to establish. Customers typically select suppliers by comparing the user interface (ie, whether the operation is easy), the print capability/print diversity/quality, and the applicable ink series.
The print quality of valve printing is not stable. This is because the ink stays in the nozzle until it is ejected. If the ink dries in the pipe, it will block. The system works best with water-based inks that print on osmotic surfaces. Many valve-type printing system manufacturers produce non-permeable surface inks that dry faster than water-based inks. Blocking occurs and the drying time is still quite longâ€”about 15 to 30 seconds.
In general, if the print quality requirements are not high and the nozzles are frequently cleaned, the valve printing system can perform well. Although the cost of acquisition is relatively low, the cost of the use of the valve jet printing system is higher after one or two years, so this technology has gradually been replaced by pulse jet printing technology.
Pulse jet printing The jet printing technology is mainly divided into two types: piezoelectric jet printing and bubble jet printing - the realization of these two technologies is very different. Pulsed inkjet printheads have evolved from the field of office printing - pulsed printing is now widely accepted in office printing and has excellent results.
Although pulsed jet printing is conceptually simple, it is worth noting that it was not until the 1970s that some people obtained the initial patent, and although Canon, Hewlett-Packard and other companies did a lot of research until the 1990s, What is cheaper? So pulse printing is not as simple as it seems. There is still a lot to be done in the office to print at a fixed print distance to clean paper and to complete inkjet coding in the harsh environment of the factory.
Piezoelectric jet printing The first type of jet printing technology is piezoelectric printing (Figure 2 shows:)
Simply put, the pressure of the ink in the nozzle must be sufficiently low (or negative pressure) because the surface tension of the ink keeps the ink in the nozzle. When printing is needed, a pulse voltage is applied to the piezoelectric crystal. The piezoelectric crystal Deformation occurs, reducing the volume of the nozzle ink chamber. In this way, a drop of ink is ejected from the nozzle. Then, the piezoelectric crystal returns to its original state, and new ink enters the nozzle due to surface tension. By arranging a large number of nozzles side by side, the ideal print width and resolution (typically 8-6 dots/mm) can be achieved. Although the print resolution can be increased by tilting the print head (which sacrifices print height), the print resolution is fundamentally determined by the nozzle pitch. More sophisticated improvements will allow each piezo crystal to drive more nozzles (say, 8), and 32 piezo crystals will drive 256 nozzles of ink, which will have a larger print range, of course. There are only 32 programmable placement points on the printed surface.
Because the system is not continuous, the ink must remain fluid in the nozzle and dry on the printed surface. The inks used in piezoelectric ink jet printing are usually oil-based or paraffin-based. These two types of inks do not dry out in the nozzles, but they can be absorbed by the printing surface. Piezoelectric jet printing also uses some quick-drying inks. Fast-drying inks still take a long time (about 10 seconds) to dry out. When the product needs to be processed quickly and printing is prohibited after the printing, the use of quick-drying ink can cause problems. In order to prevent the ink from drying out in the nozzle, we can also apply a lower pulse voltage to the piezoelectric crystal. This will cause slight disturbance to the ink in the nozzle and the ink in the nozzle will not dry out. This method relies on changes in the ink composition or mechanically more sophisticated improvements.
Another method to achieve piezoelectric printing is to heat the print head while using a hot melt ink. In this way, the ink remaining fluid in the nozzle solidifies on the surface of the colder printed object. The piezoelectric print system can achieve good results on many printed surfaces, but it is easily scraped off during touch.
In addition to the problem of the ink drying out in the nozzle, another problem that needs attention is that the nozzle is sensitive to vibrations. The vibration can cause the ink to be ejected out of the nozzle and the ink chamber so that the surface tension cannot cause the ink to fill the nozzle. The system must then be restarted. Obviously, the print quality has been affected when vibration problems are discovered. (To be continued)
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