Talking about the Application of Different Printing Methods in Inkjet Printing (I)

Valve type printing

This method is the easiest to implement. In the past 20 years, it has been mainly used in 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. Sprinklers. 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.

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 for printing on osmotic surfaces. Many valve-jet printer manufacturers produce non-permeable surface inks that dry faster than water-based inks, which can happen when blocking occurs. The time is still quite long — it takes 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the cost of the use of the valve jet printing system is higher after one or two years, so this technology has gradually been replaced by pulse jet printing technology. Pulsed jet printing technology is mainly divided into two types: piezoelectric jet printing and bubble jet printing - the realization of these two kinds of technology is very different, the pulse jet printing nozzle developed from the field of office printing - pulsed printing Now it is widely accepted in the field of office printing and has good results.

Pulse printing

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 companies such as Canon and Hewlett-Packard did a lot of research until the 1990s, Cheaper and more reliable products are put on the market, so pulsed printing is not as simple as it seems, from jet printing in the office at a fixed printing distance to clean paper to inkjet coding in the harsh environment of the factory. There are many things to do.

Piezoelectric printing

First of all, pulsed printing technology is piezoelectric printing. In simple terms, the ink pressure in the nozzle must be sufficiently low (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 and the volume of the nozzle ink chamber is reduced. In this way, a drop of ink is ejected from the nozzle, and 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 the 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.