In recent months, the tobacco industry has conducted in-depth analysis of volatile organic compounds (VOCs) found in cigarette packaging. Based on current findings, they are planning to revise the VOCs limit standards for these packages. Each individual compound must not exceed the set threshold, and this new regulation is already being tested in certain regions. With this change, ensuring that gravure-printed cigarette packs meet the updated VOCs standards has become a top priority for printing companies.
According to material testing data, both the solvents used to dilute ink and the ink itself significantly affect VOCs levels in the final product. However, the ink plays the most critical role, as it directly determines the overall VOC content. Therefore, improving the VOCs performance of inks is essential to address the issue of excessive VOCs in cigarette packaging.
In real-world production, multiple factors influence VOCs levels in cigarette packs. For clarity and research purposes, we selected a typical traditional solvent-based gravure cigarette pack (7-color printing with 3 large solid color blocks) as our focus. The packaging material was aluminum-coated paper, and the ink used was solvent-based. Table 1 shows the VOCs detection data before improvement. The total over-standard ratio of the 15 compounds was 18.9. After 10–15 days of storage, this dropped to between 7 and 10, meeting the less-than-15-times requirement but still failing some individual indicators. Further improvements were needed, leading us to develop two different strategies.
Option 1: Improve the formulation of solvent-based ink
This approach involves modifying the ink formula while keeping the solvent system unchanged. The goal is to reduce the VOCs content of specific compounds that exceeded the standard. Since large solid color areas have the greatest impact, we focused on the three main colors used in those areas. The reformulation involved adjusting the solvent structure and proportions based on the limit values, while maintaining ink performance. Through repeated trials, we determined the optimal ink formula. According to Table 1, the improved ink achieved an over-standard multiple of 4.4. After 13–15 days of storage, all individual compounds met the required limits, successfully achieving the intended goal.
Although improving ink formulation is crucial, full success requires collaboration across all aspects of production. First, the choice of solvent used to dilute the ink greatly affects VOCs levels. Different solvents have varying dissolving power and evaporation rates, so their amounts should be adjusted accordingly. For example, higher-limit solvents like ethanol and n-propyl acetate can be increased, while lower-limit ones like n-butyl acetate and isopropyl alcohol should be reduced. During printing, the primary solvents used are ethanol and ethyl acetate, with isopropyl alcohol as a supplement. For line text printing, n-propyl acetate and n-butyl acetate are used, along with a small amount of propylene glycol methyl ether for slow drying.
During the printing process, it's important to control drying temperature and airflow to ensure complete solvent evaporation. Strengthening VOCs monitoring helps prevent unexpected variations during production. Also, closely observing ink performance during the improvement phase is vital—any issues must be addressed promptly. Small-scale trials before mass production are necessary to avoid errors.
When mixing inks from different manufacturers, special attention must be given to VOCs content, especially benzene, which has a very low limit and is easily exceeded. In practice, we encountered a case where mixed inks caused benzene to exceed the standard, highlighting the need for strict monitoring.
Additionally, VOCs levels in cigarette packs are influenced by post-press processing, storage conditions, and time. Die-cutting, good ventilation, and longer storage times tend to reduce VOCs levels. Most customers require at least 15 days between production and delivery, so scheduling production to allow sufficient time for VOCs to evaporate ensures compliance with individual standards.
Option 2: Switch to water-based ink
Building on the first option, this strategy aims to achieve better VOCs control with minimal changes to the production process. In practice, only one color sequence was switched to water-based ink. The results showed that all 15 compounds met the standard requirements.
However, this transition is more than just introducing water-based ink—it requires coordination between ink, plate-making, and printing. For instance, selecting one of the three solid colors for the switch ensures minimal disruption to existing processes. The printing plates must also be re-made to suit water-based inks, with cell depth adjusted from 45–55 μm (for solvent-based inks) to 15–25 μm.
To compensate for the slower drying of water-based inks, the drying equipment needs upgrades—increasing power, air volume, and oven length improves drying efficiency. Monitoring the performance of water-based inks during production is essential, particularly for adhesion, dryness, color, and gloss. If drying issues arise, adjusting the water-to-ethanol ratio or adding quick-drying agents may help. If problems persist, the ink formula may need further adjustments.
It’s also important to understand the characteristics of water-based inks and follow proper usage guidelines. Mixing with solvent-based inks is strictly prohibited. Production procedures must be standardized, including timely cleaning of printing plates when idle to prevent drying and maintain print quality.
Finally, additives such as dispersants, defoamers, leveling agents, and cross-linking agents can be used as needed to enhance the performance of water-based inks.
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