In recent times, the tobacco industry has conducted a thorough analysis of volatile organic compounds (VOCs) found in cigarette packaging. Based on these findings, they are planning to revise the VOC limit standards for cigarette packages. Each individual compound within the limit index must not exceed the set standard, and this requirement has already been implemented in pilot regions. Faced with this new challenge, ensuring that gravure-printed cigarette packs meet the updated VOCs standards has become a top priority for printing companies.
According to raw material testing data, solvents used to dilute ink and the ink itself are the main contributors to VOC content in cigarette packaging. Among these, the ink plays the most critical role, as it directly determines the level of VOCs present. Therefore, improving the VOC content of inks is essential to address the issue of excessive VOC levels in cigarette packaging.
In real-world production, numerous factors influence the VOC content of cigarette packs. For the purpose of discussion and research, we have selected a typical traditional solvent-based gravure cigarette pack (7-color printing, with 3 large solid color blocks) printed on aluminized paper using solvent-based gravure ink as the subject for improvement analysis. The VOC detection data before the improvement is shown in Table 1. The total over-standard ratio of the 15 compounds was 18.9, and after 10–15 days of storage, the total over-standard ratio dropped to between 7 and 10, which meets the less than 15 times requirement but still fails some individual indicators, requiring further improvements. To address this, two different strategies were developed based on actual production conditions.
Option 1: Improve the formulation of solvent-based ink
This approach involves modifying the ink formulation while keeping the solvent system unchanged, aiming to reduce the levels of specific VOCs that previously exceeded the limits. Since large solid color areas have the greatest impact on VOC content, the inks used for the three main solid colors were targeted for improvement. The reformulation focused on adjusting the solvent structure and proportions, maintaining ink performance while meeting the required VOC limits. After several trials and adjustments, the optimal ink formula was determined. According to the real-time sampling test results in Table 1, the over-standard multiple was reduced to 4.4. After 13–15 days of storage, all individual VOCs met the requirements, achieving the desired outcome.
Although improving the ink formulation is crucial, effective VOC control also requires close coordination across all aspects of the production process.
(1) In practice, the choice of solvent used to dilute the ink significantly affects VOC detection results. Based on the limit values of different solvents, their usage should be adjusted according to their dissolving power and evaporation rate. For example, higher-limit solvents like ethanol and n-propyl acetate can be increased, while lower-limit solvents such as n-butyl acetate and isopropyl alcohol should be reduced. The primary solvents used during printing are ethanol and ethyl acetate, with isopropyl alcohol as a supplement. For line text printing, n-propyl acetate and n-butyl acetate are added, along with an appropriate amount of propylene glycol methyl ether for slow drying.
(2) During the printing process, it's important to adjust and control the drying temperature and air volume to ensure full solvent evaporation and minimize residue. Strengthening VOC monitoring helps prevent any uncertainties from affecting the final product.
(3) Throughout the improvement phase, it's essential to closely monitor ink performance and conduct regular checks to identify and resolve issues promptly. Small-scale trials should be conducted before mass production to avoid unexpected problems.
(4) When mixing inks from different manufacturers during color mixing, special attention must be paid to VOC content, especially benzene, which often exceeds limits due to its low threshold. The author has encountered benzene overruns caused by mixed inks, so continuous monitoring is necessary to prevent such incidents.
(5) VOC levels in cigarette packaging are influenced by various factors, including post-press processing, storage environment, and duration. Die-cutting, good ventilation, and longer storage times tend to result in lower VOC content.
(6) Most customers require at least 15 days between production and delivery. This allows time for VOCs to evaporate naturally, helping meet individual indicator requirements.
Option 2: Switch to water-based ink
This option builds upon the first, aiming for better VOC control with minimal process changes. In practice, only one color sequence was changed to water-based ink. The improved VOC content data from this approach is shown in Table 1. All 15 compound limits were met.
The implementation of this option goes beyond simply introducing water-based ink—it involves coordinating ink, plate-making, and printing to achieve the desired results.
(1) Considering that the excess multiple in the first option was relatively low, one of the three solid colors was chosen for the switch to water-based ink. The selection was based on minimizing changes to the existing production process and equipment without compromising product performance.
(2) With the change in the ink system, a new printing plate suitable for water-based ink was created. The depth of the printing cells was adjusted to 15–25 μm, compared to 45–55 μm for solvent-based inks.
(3) To compensate for the slower drying time of water-based inks, the drying device of the corresponding color set was modified. Increasing the power, air volume, and oven length improved drying efficiency, ensuring complete drying of the ink.
(4) Close attention must be given to the printing performance of water-based inks. Key indicators such as adhesion, dryness, color, and gloss should be monitored regularly. If drying issues occur, the water-to-ethanol ratio can be adjusted, or a quick-drying agent may be added. If the problem persists, the ink formulation may need to be re-evaluated.
(5) It’s important to understand the characteristics and proper usage of water-based inks. Mixing with solvent-based inks is strictly prohibited. Production operations must be standardized, and printing plates should be cleaned promptly if the press is shut down to prevent ink from drying and affecting print quality.
(6) Additives such as dispersants, defoamers, leveling agents, slip agents, and cross-linking agents can be used as needed to enhance the performance of water-based inks.
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