Color of the cigarette pack lining paper

Do you know the main reasons why the lining paper of cigarette packs frequently shows color differences?

Cigarette pack liner paper is a type of packaging paper used to line the inner layer of cigarette small boxes. Its function is to reduce water loss from cigarettes, preserve the original aroma and taste, and also enhance the shape and appearance of the cigarettes.



During the inspection and use of liner paper in major cigarette pack companies, there have been frequent reports of color difference issues. This is also the most critical physical indicator in the production and quality control process of cigarette pack liner paper, and the industry defines it as a Class A indicator.



Causes of color differences in the liner paper of cigarette packs



From years of work experience, color differences in cigarette pack liner paper are influenced by multiple factors, mainly including raw materials, production processes, equipment, and environment.



01/ Raw material factors



The base paper for cigarette pack liner paper is generally produced using bleached wood pulp. Different batches of pulp vary in fiber type, whiteness, and purity content, which affect the Lab value and directly cause color deviation in the base paper substrate.



When coating semi-finished base paper, the content of pigments such as titanium dioxide in the coating deviates, causing color differences between pigment batches and directly resulting in overall color differences on the base paper.



02/ Production process factors



(1) Composite Stage



When laminating the liner paper of cigarette packs, factors such as adhesive concentration, hardness, lamination pressure, and drying temperature affect the thickness and brightness of the base paper, which in turn causes color deviations in the lining paper.



(2) Printing Stage



During printing, fluctuations in ink viscosity, uneven printing pressure, and wear of the mesh cavities on the anilox roller lead to inconsistent ink transfer amounts, resulting in color differences in the same batch of products; Incomplete cleaning of the color-changing printing plate, residual old ink, and contamination of new ink can also cause color shifts.



(3) Embossing stage



To improve the molding degree of cigarette pack liner paper packaging, over 90% of lining paper products use embossing technology. Embossing methods include steel roll-to-nylon, steel roll-to-wool paper roll, and steel roll-to-steel roll. Regardless of the embossing method, the deeper the embossing, the lower the brightness value L, but the color values a and b vary irregularly-sometimes higher, sometimes lower.



03/ Equipment and environmental factors



(1) Equipment accuracy issues



Wear of coating and printing rollers causes cavities to become shallower, reducing ink accumulation, and the amount of transferred printing ink changes accordingly, directly affecting the semi-finished product's color values a and b.



(2) Tension control issues



An unstable tension control system causes inconsistent stretch rates of the lining paper during winding, changing the pigment coating thickness per unit area and causing color differences.



(3) Environmental fluctuation



Fluctuations in production workshop temperature and humidity will affect the moisture content of the base paper and ink viscosity, thereby affecting the transfer performance of coatings and inks. High humidity can also cause pigment clumping, reducing coating uniformity and causing color differences.



Measures for controlling color difference in cigarette pack liner paper



To address the sources of color differences in cigarette pack liner paper, a closed-loop control system must be established throughout the entire process, from raw material entry, production process control, to finished product inspection. The specific control measures are as follows.



01/ Control of color differences at the source of raw materials



Stabilizing raw material quality from the source is the foundation for controlling color differences.



(1) Fixed raw material suppliers and product specifications



Core raw materials such as wood pulp, titanium dioxide, ink, and aluminum foil are supplied at designated points, requiring suppliers to maintain consistency of core ingredients and strictly controlling hue and whiteness deviations in each batch. For example, wood pulp whiteness deviation is controlled within ±2%, color difference ∆ Eab in ink batches is controlled within 0.8, and non-compliant raw materials are strictly prohibited from entering warehousing.



(2) Establish a mixed batch system for raw material preparation



For multiple batches of the same type of raw material, mix and use them evenly in certain proportions to reduce the impact of single batch deviations on the overall color. For example, during base paper production, 3~5 batches of the same specification wood pulp are mixed and pulped according to the ratio, effectively reducing whiteness differences between batches.



(3) Conduct trial testing in advance



After each batch of new raw materials is stored, a pilot production is conducted. After testing that the finished product color difference meets requirements, it is then put into mass use, avoiding issues with batch color difference defects in large production batches.



02/ Color difference stability control during the production process



Stable production processes are the core part of controlling color differences, requiring targeted control requirements for different processes.



(1) Base paper production stage



Stabilize process parameters and keep pulp concentration, pulping degree, and sizing volume fluctuating within a minimal range. For example, pulp concentration fluctuations should be controlled within ±0.2%, drying temperature fluctuations within ±2°C, ensuring uniformity and whiteness of the base paper. A grading system is implemented for base paper, removing base paper with color deviation exceeding standards to prevent unqualified raw and auxiliary materials from entering the next process.



(2) Printing Stage



Establish unified ink mixing standards, fix the ratio of ink, solvent, and additives, use automatic ink mixing equipment instead of manual ink mixing, and improve ink mixing accuracy; Monitor ink viscosity in real time during printing, automatically add solvent, and maintain stable viscosity; Regularly clean the ink system and printing roller patterns to prevent old ink residue from contaminating new ink; Regularly calibrate the pressure of printing equipment to ensure uniform and consistent printing pressure, avoiding differences in ink transfer caused by pressure deviations.



03/ Online inspection and process correction control



Introducing an online color difference detection system to achieve real-time monitoring and automatic correction of the production process is the core method for controlling color difference in modern cigarette pack liner paper production. Online colorimeters are installed at key locations on the production line (after coating, printing, and before slitting) to detect color difference in each process step in real time according to the set standard color parameters. When the color difference exceeds the set threshold, the system automatically alarms and adjusts process parameters. For example, when the color difference is too dark, it automatically reduces the coating amount; when it is lighter, it automatically increases the coating amount, achieving dynamic closed-loop control; The online system can also automatically mark areas with color difference that are not conforming, and subsequent slitting processes remove it, preventing nonconforming products from entering the market.



04/ Daily control of environment and equipment



Maintain stable production environment conditions, control workshop temperature between 20~25°C and relative humidity at 50%~65%, and avoid process parameter changes caused by large temperature and humidity fluctuations.



Perform daily equipment maintenance, regularly calibrate and clean roller surfaces, tension systems, and inspection systems to ensure equipment accuracy meets requirements. For example, calibrate the online colorimeter daily, clean the printing anilox rollers as needed, check the wear of coating rollers once a week, and promptly eliminate color differences caused by equipment factors.



05/ Finished product inspection and batch control



A comprehensive finished product color difference testing system has been established, using standard color samples as a reference in accordance with industry standards, using standard light sources (D65 standard light source) and benchtop colorimeters to detect finished product color differences. At least five samples are randomly selected per batch for testing. Batches with excessive color differences are deemed unqualified.



Establish a batch color traceability system so that products from the same batch maintain consistent production processes and raw materials. Retain production samples from each batch; next time, compare with standard samples first, then with products from the previous batch, to control batch color differences and avoid excessive color differences between batches.



For color difference issues reported by cigarette packaging printing companies, promptly trace production processes and record parameters, identify the causes of color differences, and continuously optimize control plans.



Controlling color difference in cigarette pack liner paper requires attention to three key details: First, standardize monitoring conditions, which must be evaluated under standard light sources and observation angles to avoid human judgment errors caused by ordinary light sources or different observation angles; Second, distinguish between batch color difference and storage color difference. During storage, cigarette pack liner paper may experience slight color aging due to light and oxidation, so standard samples must be sealed and stored away from light, with regular replacement to avoid judgment deviations caused by sample aging; Third, balancing cost and quality, reasonably setting color difference control thresholds while meeting industry standards and customer requirements to avoid excessive control that increases production costs. ...