Overall Working Principle of the Printer
Since the invention of continuous inkjet technology by a professor at Stanford University in the 1960s, the development history of inkjet printers has been rapid. Today in the 21st century, common inkjet printers now have thermal foaming inkjet printers and piezoelectric inkjet printers, so common inkjet printheads are mainly divided into two categories: thermal foaming inkjet printheads and piezoelectric inkjet printheads.
Whether it is a thermal foaming inkjet printer or a piezoelectric inkjet printer, it is inseparable from the print head. It can be said that the print head is the core component of the inkjet printer. In addition, there are paper feeding/paper feeding components, precise positioning components, ink-absorbing cleaning components, and electronic signal control components.
When the printer motherboard receives the print job from the computer, it immediately converts it into various signal pulses through its own decoding. It first enters the paper by controlling the paper feeder. So how to judge whether the paper has entered? There is a paper sensor in the paper feed channel of the inkjet printer, which is controlled by a time pulse signal. If it is not triggered within the specified time, the mainboard determines that the paper feed fails and continues to the next paper feed. If the paper feed fails twice in a row, It will feedback to the computer a signal that the printer is out of paper. If the sensor is successfully triggered within the specified time, the mainboard will record this data and then accurately control the step signal through the grating disk sensor. Subsequently, the ink cart where the print head is located is positioned according to the transverse grating sensor. At this time, the motherboard has obtained the X and Y axis data of the print head and paper and then can calculate the precise coordinates based on the X and Y axis data. When the print head reaches the coordinates with print data, the motherboard immediately gives a pulse signal to control the print head to eject ink droplets, which repeatedly form patterns on the paper.
When cleaning is required, the ink truck moves to the ink stack position according to the signal from the grating sensor. At this time, the ink capping station assy is lifted up to completely seal the print head nozzle. The cleaning pump starts to work and forms a negative pressure in the sealing area to draw out the ink and start using the ink to flush the nozzle. After flushing is completed, the ink stack descends and the wiper bounces up to scrape off the remaining ink from the print head. Then the ink carriage is reset and cleaning is completed.
Thermal Foaming Inkjet Printing Technology
Having talked about the overall working principle of the printer, now let’s talk about thermal foaming inkjet printing technology.
Inkjet printing technology is a new contactless, pressureless, and plateless printing technology that can print information stored in an electronic computer by inputting it into an inkjet printer. According to the working principle, inkjet printing technology can be divided into two types: solid inkjet and liquid inkjet. The main working method of solid inkjet is dye sublimation, but the cost is high; while the main working method of a liquid inkjet printer is divided into thermal foaming type and micro piezoelectric type, and these two technologies are still the most popular inkjet technology today in the printing market, in this article we mainly introduce thermal inkjet printing technology.
At present, the thermal foaming inkjet printing technology is mainly used by companies such as Canon and HP. Thermal foaming inkjet printing technology heats the nozzle to generate bubbles in the ink, and the bubbles squeeze the ink and spray it onto the printing substrate. It is a high-temperature and high-pressure printing technology.
The working principle of thermal foaming inkjet printing technology is to use thin film resistors to instantly heat ink with a volume of less than 5uL to more than 300°C in the ink ejection area, forming countless tiny bubbles. The bubbles move at an extremely fast speed (less than 10 us) gather into large bubbles and expand, forcing the ink droplets to be ejected from the nozzle. After the bubble continues to grow for a few microseconds, it disappears back onto the resistor. As the bubble disappears, the ink in the nozzle also retracts. Then the suction force generated by the surface tension of the ink will pull new ink to the ink ejection area to prepare for the next cycle of printing.
Since the ink near the nozzle is continuously heated and cooled, the accumulated temperature continues to rise to 30~50°C. Therefore, it is necessary to use the ink circulation cooling in the upper part of the ink cartridge. However, during a long printing process, the ink in the entire ink cartridge will still remain at 40°C. ~50℃ or so. Since thermal bubble inkjet printing is performed under higher temperature conditions, the ink must have low viscosity (approximately less than 1.5mPa.s) and high surface tension (approximately greater than 40mN/m) to ensure long-term printing. Continuously print at high speeds.
Advantages of Thermal Foaming Inkjet Printing Technology
Thermal foaming inkjet printing technology generally uses an ink system that is a mixture of water-based and oil-based dyes. It can achieve good printing quality whether it is used on a home printer or a commercial printer. By reducing the ink droplet ejection area and integrating circuit circulation technology, future inkjet printers using thermal foaming inkjet printing technology will have smaller ink droplets, eject ink droplets more frequently, and produce richer harmonized colors and smoother mesh tones. Thermal foaming inkjet printing technology meets the basic elements such as low operating frequency, high nozzle count, and single printing resolution required for high-speed printing. It can improve printing speed and printer work efficiency. Integrated circuit technology can also continue to reduce printing costs.
In addition, the print head using thermal foaming inkjet printing technology requires that the ink cartridge and the nozzle form an integrated structure because the ink cartridge and ink will generate pressure under the action of thermal bubbles. When the ink cartridge is replaced, the print head must be updated at the same time so that users no longer have to worry about print head clogging. However, this also results in relatively expensive consumable costs.
Disadvantages of Thermal Foaming Inkjet Printing Technology
Nozzles that use thermal foaming inkjet printing technology have been working in high-temperature and high-pressure environments for a long time. The nozzles are seriously corroded and can easily cause ink droplets to splash and nozzle clogging.
In terms of printing quality, since the ink needs to be heated during use, the ink is prone to chemical changes at high temperatures and is unstable in nature, and the color authenticity will be affected to a certain extent; on the other hand, since the ink is ejected through bubbles, the directionality and volume of ink droplets are difficult to control, and the edges of printed lines are easily uneven, which affects the printing quality to a certain extent.
In terms of application, thermal foaming inkjet printing technology has certain restrictions on inks. It can only use high-tension and low-viscosity water-based inks with water as the main medium. Organic solvents cannot be used. Therefore, solvent-based inks cannot be used for printing production of outdoor large-format advertising.
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