New Developments in the Field of Labels
From production efficiency to printing quality, from environmental requirements to cost control, label printing places higher demands on flexographic plates and printing technology. To meet these requirements, suppliers of flexographic plates and equipment continuously innovate. We are pleased to see that over the past decade, flexographic technology has developed rapidly. Even during the three years of the COVID-19 pandemic, the research and promotion of flexographic plates and platemaking equipment did not stop. Through continuous analysis and research of customer needs, new products for flexographic plates and platemaking equipment have been launched, many of which have been applied in label printing production and have received positive market feedback. In this article, the author combines the latest platemaking technology and equipment launched by their company to explain the innovative applications of flexographic platemaking technology in the field of label printing for readers.
1. Application of Improved Flat-Top Dot Plates in Label Printing
Since the emergence of flat-top dot plates that do not rely on equipment, this type of product has been widely used. Users can produce flat-top dot plates using existing platemaking equipment with plates that have built-in flat-top dots. Currently, the main flexographic plate suppliers on the market have launched flat-top dot plates and continue to innovate. Taking DuPont's new generation EasyR series plates launched in 2021 as an example, these plates, while retaining the original performance of Easy plates, further enhance the plate's print durability and printing quality, as shown in Figure 1.
Figure 1 Comparison of halftone dots on Easy Thermo-sensitive Plate EFXR before and after improvement
A scratch test was conducted on the Easy Thermo-sensitive Plate EFXR67 shown in Figure 1 before and after the improvement. It can be seen that the flat-top halftone plate before improvement showed dot loss after multiple scratches, whereas the improved Easy Thermo-sensitive Plate EFXR67 maintained stable and intact halftone dots under the same testing conditions. In further production tests, some users also reported that the print run length of the new generation flat-top halftone plates increased by 50% or more compared to before. In addition, in a large number of printing tests, the improved new generation EasyR series plates also demonstrated excellent print quality. Figure 2 shows sample prints produced by domestic label printing companies using the new generation EasyR series plates.
Enlarging the area marked by the red rectangle in Figure 2, it can be seen that the fine highlight halftone dots are fully uniform and meet the market's plate-making requirements for high-end flexo labels. The effect of the enlarged highlight halftone dots is shown in Figure 3.
Figure 2 Narrow-web printing sample of the new generation thermal plate
Figure 3: Locally magnified highlight dot effect
In the label printing process, highlight areas that gradient down to zero often exhibit many incomplete and unstable dots. These unstable small dots deform under printing pressure, causing the dots to not only receive ink at the top but also transfer the ink accumulated on the shoulders under pressure, forming streak-like dots in the highlight area. This makes the highlight areas that gradient down to zero appear relatively harsh, resulting in breakage issues. As shown in Figure 4, the linear ultra-high highlight areas without dot compensation show sudden enlargement of dots.
A magnified view of this gradient area in Figure 4 shows that the dots in the highlight area are irregularly formed, as illustrated in Figure 5.
Figure 4 Common flexographic gradient to zero break issues
Figure 5 Irregular highlight effects cause hard edges to appear
It is precisely because these issues have persisted for a long time that flexography finds it extremely difficult to reproduce highlight effects. Especially in prepress retouching, color separation, and plate-making stages, there are corresponding countermeasures. Making flexographic highlights appear more natural has almost become an important long-term goal for flexography.
The upgraded flat-top dot plates have more stable small dots, which can produce better highlight effects (as shown in Figure 6). From the perspective of the plate material, they solve common problems in highlight gradation and also reduce some of the prepress workload. In addition, the latest EasyR thermal plates can stably support 15μm dots, which correspond to 1% dot size at 190 lpi, breaking through the conventional 1% dot size at 175 lpi. Stable dots can deliver good repeatability and high stability in printing performance. As shown in Figure 7, the dots printed with this plate have a diameter of 23μm, which is only 2% dot size at 175 lpi.
Figure 6 Printing performance of EFXR highlight dots on the improved flat-top dot plate
Figure 7 The latest thermal plate EFXR can produce dots with a diameter of less than 20 μm and stably complete label printing.
2. Application of Specialized Plates for LED (Light Emitting Diode) Exposure Units
The continuous development of LED technology has driven the ongoing progress in flexible plate-making technology. LED exposure technology features stable energy output, which can completely solve the energy fluctuation problem of traditional exposure units. However, for various reasons, the current mainstream LED exposure units still use a platform-scanning method for exposure. As shown in Figure 8, a comparison is made between the exposure of the same type of flexible plate using an LED system and a traditional exposure unit. It can be seen that the LED light source is installed on a movable light strip, and under the drive of the motor, the light strip reciprocates on the platform. The advantage of a scanning-type exposure unit is that it greatly reduces the cost of LED exposure units, but it also brings other issues, such as the setting of exposure parameters. Figure 8 shows the amount of UV light exposure received by specific graphic positions on the plate in each process. Because LED systems usually use scanning exposure, the graphic areas are exposed multiple times during the exposure process, and the UV energy intensity of each exposure is much higher than that of traditional exposure units.
Figure 8 Comparison between Traditional Exposure Machines and LED Exposure Machines
Under the two exposure modes, the photosensitive resin undergoes two completely different cross-linking processes. Traditional exposure machines involve continuous exposure, while LED exposure machines using platform scanning use intermittent exposure. During the exposure process, once the LED light has passed, the curing of the graphic areas is affected. Compared to continuous exposure, the exposure time of most LED platemaking machines needs to be extended, so flexible plate suppliers and equipment manufacturers invest significant resources to optimize plate-making parameters for LED exposure, so that the performance of plates made with LED exposure can reach or exceed that of plates made with traditional exposure. The most common issues involve adjusting exposure settings, such as the output energy of the exposure machine, scanning speed, and the number of scans.
Additionally, although using high-energy UV output can shorten the exposure time, it may come at the cost of plate quality. The combination of high output and short exposure times often causes the smallest dots to enlarge, the angles of line and text shoulders to widen, and the dot surfaces to become recessed-all of which can reduce printing exposure latitude and print quality. Therefore, to avoid these problems, longer LED exposure times are often required. These challenges are akin to making the surface of a steak crispy while ensuring the inside remains fully cooked. In technical terms, it means achieving fine print elements and surface microstructures while allowing most of the resin to fully undergo photopolymerization, creating plates that can print stably.
If the photosensitive resin formulation is optimized for LED exposure from the start, fewer compromises need to be made in production efficiency and quality. Optimized flexible plates, combined with experienced application support staff, can achieve the best results. In the second half of 2021, DuPont specifically adjusted and optimized plate formulations for LED-UV exposure and launched a new series of photosensitive resin plates, Cyrel® Lightning. This series addresses a variety of issues that ordinary flexible plates encounter under LED exposure.
These plates feature custom LED UV sensitivity, allowing a balance between surface curing and overall curing. This innovation enables rapid surface curing and effectively reduces the inhibition of resin polymerization by oxygen during LED exposure intervals. At the same time, by fine-tuning the UV absorption characteristics of the plates, the series can achieve full overall curing. The recently launched Cyrel® LSH plates have an exposure time reduced by 42% compared to DPR plates, while retaining DPR plates' fine highlights and excellent mid-tone reproduction. For LED exposure technology, our company continues to introduce the LED exposure-specific plate LFH suitable for solventless systems. This plate inherits many advantages of LSH and, combined with solventless plate processing technology, is expected to gain more user favor.
3. Application of Thermal Plate-Making Equipment
As environmental awareness among printing companies in China increases, the efficiency, safety, and environmental advantages of solventless systems are increasingly recognized in the industry, and their installed capacity in China is growing. As shown in Figure 9, the successful installation of DuPont Cyrel® 2000TD equipment worldwide has validated the high quality and reliability of the latest generation of solventless plate-making systems. Currently, in addition to common narrow-web label printing, users in developed flexographic markets increasingly use wide-web flexo presses for label printing.
Figure 9: The widely praised 2000TD and the 3000TD launched in 2022 have elevated the quality level of thermal plate-making to that of solvent-based plate-making.
The solvent-free plate-making system 3000TD, launched in 2022, has brought solvent-free plate-making technology to a new height in both efficiency and quality. The maximum plate size that the plate-making machine can handle has reached 1270×2032mm, which can meet most users' demands for large-format plates. Due to the use of numerous new technologies, compared with the previous generation of large-format thermal plate-making systems, the latest 3000TD plate-making machine has made a significant improvement in quality. When paired with the latest thermal plates, the solvent-free technology can completely match traditional solvent plate-making in terms of quality. Additionally, the 3000TD plate-making machine features an ergonomically designed control panel and has seen considerable improvements in temperature and pressure control, exhaust emissions, and environmental noise. Moreover, according to DuPont's updated product lifecycle assessment report, this thermal plate-making system can save 56% of non-renewable energy consumption and reduce greenhouse gas emissions by 38% compared to solvent plate-making.
4. Application of Automated Plate-Making Equipment
To address common safety, efficiency, and accuracy issues in flexographic plate cutting, automatic plate cutters have gradually attracted the attention of many users in recent years. As shown in Figure 10, the Kongsberg X20E is an example. This automatic plate cutter not only shortens plate cutting time but can also simulate the printing effect of seamless sleeves, enhancing the stability of high-speed printing, as shown in Figure 11.
Figure 10 Kongsberg X20E installed at DuPont Shanghai Customer Technology Center in September 2022
Figure 11 shows an interlaced cutting plate completed by the automatic plate cutter, which can simulate the printing effect of a seamless sleeve while also improving the stability of high-speed printing.
5. More Environmentally Friendly Plate Cleaning Solvents
For solvent users, the company I work for has upgraded the formula of the eco-friendly solvent Flexosol-i and launched the latest generation of eco-friendly solvent, Flexosol-X, which is more environmentally friendly and has overall better performance. Compared with the eco-friendly solvent Flexosol-i, Flexosol-X has better usage and recycling stability, requires less time for plate cleaning and drying, and can further reduce energy consumption. At the same time, the VOC emissions of eco-friendly solvent Flexosol-X are reduced by 57%, fully meeting the stricter European environmental standards for solvent use.
Technological development will not stop. It is believed that more flexographic plate and equipment suppliers will continue to work on improving flexographic quality, increasing plate-making efficiency, and enhancing product sustainability, providing better products and technology for flexographic label users and supporting the long-term development of Chinese label printing enterprises.