The problem of QR code printing on cigarette packs has been solved; this well-known cigarette pack printing company has taken action!
Variable QR codes represent a further extension and enhancement of QR code technology in packaging applications. By applying variable QR codes to packaging, every smallest unit of product can have a unique QR code, truly realizing "one item, one code." "One Item, One Code" will not only further strengthen anti-counterfeiting traceability for products, allowing precise tracking down to every smallest unit, but also enable enterprises to collect data from users down to the individual, truly realizing personalized marketing for products.
With the development of new technologies and processes, the application of QR codes on cigarette packs continues to expand. To continuously optimize and solve various printing suitability issues (such as QR code glue, string lines, grade deviations, etc.), industry scholars have conducted extensive research and analysis, aiming to improve product quality while ensuring the stability of QR code quality. My company conducts multi-dimensional and comprehensive testing and exploration of printing equipment parameters during the QR code printing process, aiming to set key nodes for output equipment parameters, ensuring the effectiveness, standardization, and uniformity of production control and testing from the source, effectively improving QR code printing quality, providing customers with higher-quality products and services, and offering the industry more effective research methods and ideas.
Printing equipment and working principle
The printing equipment used this time is a sheet-fed inkjet printer, which consists of a mechanical platform (paper feeding mechanism, paper feed platform, paper rewinding mechanism), printing system, curing mechanism, and online inspection system; The core is the printing system, which consists of the print head module, CNC system, and ink supply system. The core of the printing system is the industrial control computer controlling the ink supply system. First, the printing software sets the printing parameters, then the industrial control computer (main control board) and the digital-analog system process or convert the data, directly controlling the print head for printing.
The piezoelectric inkjet printing technology used in inkjet printers belongs to the room temperature and pressure printing technology. It places many tiny piezoelectric ceramics near the printhead nozzle. Because the piezoelectric ceramics exhibit bending and deformation under voltage changes at both ends, when the image information voltage is applied to the piezoelectric ceramic, the expansion and vibration deformation of the ceramic changes with the image information voltage, ensuring that the ink in the print head is ejected evenly and accurately under stable conditions at normal temperature and pressure.
Ink temperature parameter test
In this experiment, with the printhead fixed, the test variable was ink temperature, while other printing parameters remained unchanged. The changes in the printed sample were measured on the substrate, and ink temperature, droplet formation, flowability, and diffusion on the substrate were observed. To more conveniently test and estimate the dimensional changes under different ink temperatures, and simultaneously print square blocks to test their variability.
Based on the above tests, it can be concluded that changes in ink temperature parameters can directly affect printing results. As shown in Figure 1, as ink temperature increases, ink viscosity decreases and ink fluidity improves, allowing better spread to the substrate surface, resulting in fewer surface defects (white spots, string lines). As shown in Figure 2, as ink temperature increases, the dot area or line diffusion of the printed sample changes little, but the chamfers and burrs at the edges increase, visually making the area appear thicker.
Figure 1 Printing effects at different ink temperatures
Figure 2 Changes in square area at different ink temperatures
Voltage, vehicle speed, and printhead height parameter tests
This test was conducted with a fixed printhead, where the test variables were voltage, vehicle speed, and printhead height, while other printing parameters remained unchanged. The changes in printed samples on the substrate were measured. Through these tests, it can be determined that voltage affects the aggregation of primary ink droplets, the diffusion of "satellite ink droplets," and the deformation of printed graphics and text.
Under a vehicle speed of 120 m/min and an ink temperature of 46°C, adjusting the voltage led to printing changes as shown in Figure 3. From the figure, it can be seen that voltage has little effect on the printing shape. However, according to principle analysis, under normal circumstances, the ink forms a normal plane inside the printhead. When voltage is applied, the ink begins to flow outward, forming a long ink filament. Under the action of surface tension, the ink filament forms droplets. Through the interaction of droplets and viscosity, the filament breaks to create inkjet formation. If the filament is too long, satellite dots are easily formed. When the voltage is high, the ink amount is larger, the initial speed is higher, and the velocity is faster, resulting in smaller particles. The Brownian motion of the particles is stronger, and the formed ink filament is shorter, making it easier for the primary ink to aggregate. The printing effect is better, and the thickness will also be relatively higher.
Figure 3 Voltage Variation Printing Effect
Under a voltage of 32V and a temperature of 48°C, different vehicle speeds were adjusted to test the ink drop coalescence at the normal printhead height, as shown in Figure 4; a comparison of flying ink during coding under different vehicle speeds, normal printhead height, and printhead height lowered by 3mm, as shown in Figure 5; QR code printing effects under different vehicle speeds and printhead heights are shown in Figure 6.
Figure 4 Droplet coalescence under the same voltage, same temperature, same nozzle height, and different vehicle speeds
Figure 5 Comparison of ink splashing of the printhead at different vehicle speeds, normal printhead height (h), and printhead height lowered by 3mm (h-3)
Figure 6 QR code printing effects under different vehicle speeds and different printhead heights
From Figures 4 to 6, it can be seen that both vehicle speed and printhead height affect the convergence of the main ink droplets, directly influencing the thickness and deformation of the printed graphics, thereby affecting the quality grade and appearance of the QR code printing. The higher the printhead, the longer the formed ink threads, making it more difficult for the main ink to converge. The greater the vehicle speed, the more dispersed the ink droplets are when they land on the paper, resulting in poorer effects. Based on the above process experiments, four main process parameters were summarized and verified: ink temperature, printhead voltage, printhead height, and paper speed, all affecting printing quality. The ink temperature and voltage determine the printing effect (white spots, stringing), while vehicle speed and printhead height determine ink droplet convergence and flight trajectory (splashing, thickness).