The delamination rate of cigarette pack gum in folding cartons has dropped below 1%-these 4 key factors cannot be ignored!
Cigarette packs have the functions of brand display, product protection and anti-counterfeiting traceability, and their process accuracy and quality standards are much higher than those of ordinary packaging. As the last core process of cigarette pack molding, the strength of the adhesive layer directly determines the structural stability of cigarette packs in the whole process of warehousing, transportation and sales. According to the 2024 survey data of the Tobacco Packaging Professional Committee of the China Packaging Federation, the scrap rate of finished products caused by the problem of gluing boxes in domestic tobacco packaging enterprises will reach an average of 5.7%, and some small and medium-sized enterprises will exceed 15%, with an annual direct economic loss of more than 200 million yuan.
At present, there are three major pain points in the viscose control of cigarette pack glue boxes: first, the adhesive selection depends on experience, and there is a lack of systematic matching with special papers for cigarette packs such as water loose paper and transfer aluminized paper; second, there is no quantitative standard for process parameters such as glue application, speed, and uniformity; Third, the setting of pressure curing parameters is unreasonable, resulting in the adhesive not fully penetrating the paper fibers. Based on this, this paper takes the problem of adhesive failure of cigarette pack glue boxes as the starting point, and proposes a quantifiable and practical viscose control scheme from four dimensions: adhesive selection, gluing process parameter optimization, pressure curing condition control and whole process quality control, aiming to solve common problems in the industry and improve the production quality of cigarette packs.
Analysis of the core causes of the failure of cigarette pack glue adhesive
01/ Insufficient adhesive performance and paper adaptability
The surface properties of the paper are a key factor affecting the bonding effect. The physical and chemical properties of the adhesive are the basis of the adhesive effect, and its insufficient adaptability to the cigarette pack paper is the primary cause of adhesive failure. The surface properties and fiber structure of different papers are significantly different, and the requirements for wettability, permeability, and curing characteristics of adhesives are completely different, and the compatibility of different papers and adhesives is shown in Table 1.
02/ The gluing process parameters are out of control
The gluing process is the core link of adhesive control, and the loss of control of the three parameters of glue application, glue uniformity and glue application speed is an important reason for the failure of adhesive.
(1) The amount of glue applied is unreasonable
When the amount of glue is insufficient, the adhesive cannot fully cover the adhesive surface of the paper, the bonding points between the fibers are reduced, and the adhesive strength is significantly reduced. Excessive glue application will lead to "glue overflow", pollute the appearance of the cigarette pack, and the excess adhesive is easy to produce bubbles when curing, but reduce the adhesive fastness, taking 232g/m² laser transfer paper as an example, the relationship between the amount of glue and the peel strength is shown in Table 2.
Table 2 Relationship between glue amount and peel strength
(2)Glue Coating Uniformity Does Not Match the Speed
The uniformity of glue coating directly affects the stress distribution of the adhesive layer. If there are 'missed glue spots' on the coated surface, the adhesion strength in that area is zero, making it a weak point prone to delamination. Taking 232g/m² laser transfer paper with a glue coating of 7g/m² as an example, the effect of coating speed on process indicators is shown in Table 3.
Table 3 Effect of Glue Coating Speed on Process Indicators
03/ Pressurization and curing conditions not up to standard
Pressurization and curing after folding the carton is a key step for the adhesive to form a stable bonding layer. Insufficient pressure or too short pressurization time can lead to the adhesive not fully penetrating the fibers or expelling air bubbles, resulting in microscopic voids in the bonding layer and ultimately causing delamination.
04/ Indirect effects of environmental factors
The temperature and humidity of the production environment can indirectly affect the adhesive's effectiveness. Too low a temperature (<18°C) reduces the adhesive's fluidity and slows down the curing process; too high a humidity (>65%) causes the paper to absorb moisture, fiber expansion, increased difficulty for adhesive penetration, and prolonged curing time; too low a humidity (<40%) causes the adhesive surface to dry quickly while the interior is not fully cured, resulting in a "false tack" phenomenon. Changes in the delamination rate of cigarette cartons under different temperature and humidity conditions are shown in Figure 1.
Optimization scheme for viscose control of cigarette pack glue box
01/ Adhesive selection strategy based on paper properties
The core principle of adhesive selection is to achieve "wettability adaptation, permeability adaptation, and curing characteristics adaptation", while taking into account the requirements of the use environment, cost and environmental protection, and constructing a scientific selection system, the specific selection strategy is as follows.
(1) Accurately select according to the type of paper
The surface structure, physical and chemical properties of different cigarette pack papers are significantly different, and the type and parameters of the adhesive need to be matched in a targeted manner.
(1) Coated paper: smooth surface and dense ink layer, preferably choose modified water-based adhesive with a viscosity of 1800~2000mPa·s. The surfactant it contains can reduce the contact angle from 45° to 28° to improve wettability; The added penetrant can break through the barrier of the ink layer, increase the penetration depth from 52μm to 75μm, and the adhesive strength reaches 2.65N/cm, which is significantly higher than that of conventional water-based adhesives.
(2) Transfer laser aluminum plating cardboard: the surface metal coating leads to poor wettability, and a special water-based adhesive containing a coupling agent should be selected, through which the chemical bond between the metal coating and the adhesive is formed to enhance the bonding force, so that the contact angle is reduced from 78° to 32°, and the penetration depth is increased to 68μm; If adhesives are used, the temperature should be controlled at 90~100°C to ensure the wetting effect of the coating.
(3) Water loose paper: loose fibers, easy to absorb moisture, preferential choice of adhesive with a melting point of 120~130°C, its curing speed is fast, can avoid moisture absorption and deformation of the paper, the penetration depth can reach more than 48μm, and the adhesive strength is ≥ 3.0N/cm. The experimental data showed that the adhesive strength of the adhesive at 160°C was 3.2N/cm, which was much higher than that of 2.1N/cm at 140°C.
(4) Corrugated cigarette pack lining: porous structure, large thickness, high permeability adhesive is selected, and the curing speed is controlled at 3~5s to ensure that the adhesive layer fully penetrates into the corrugated gap and forms a stable bonding structure.
(2) Combined use of environment adaptation selection
During the storage and transportation of cigarette packs, it may face high temperature and high humidity environments, and the adhesive needs to have corresponding weather resistance.
(1) High temperature and high humidity areas in the south: select moisture-resistant modified water-based adhesive and add mildew inhibitors to ensure that the adhesive strength retention rate is ≥ 90% under the condition of humidity of 80% and temperature of 35°C, so as to avoid degumming caused by water absorption and softening of the adhesive layer.
(2) Dry and low-temperature areas in the north: choose low-crystalline adhesives, optimize the molecular structure design, avoid brittleness and cracking of the adhesive layer at low temperature, and maintain the adhesive strength at -10°C at ≥85% to ensure the structural stability in the low-temperature environment.
(3) Cigarette packs that need to be laminated at high temperature: choose a high-temperature resistant adhesive (temperature resistance ≥ 120°C) to prevent the softening and failure of the adhesive layer caused by the lamination process, and ensure long-term stability of the adhesive performance.
(3) Balance cost and environmental protection
On the premise of meeting the quality requirements, establish a dual evaluation system of "cost performance and environmental protection":
(1) Environmental protection index control: the VOCs content of water-based adhesives needs to be ≤ 50g/L, which complies with GB 38508-2020 "Volatile Organic Compound Content Limits of Cleaning Agents"; Halogen-free and low-smoke products are preferred for adhesives to avoid toxic gases generated during the production process and ensure the safety of the working environment.
(2) Comprehensive cost optimization: Although the unit price of special modified adhesives is about 15% higher than that of conventional products, it can significantly reduce the degumming rate and reduce rework losses. The practical application of an enterprise shows that after the use of special modified water-based adhesives, the comprehensive production cost is reduced by 8%, achieving a win-win situation of quality and efficiency.
02/ Quantitative optimization of gluing process
(1) Determine the optimal glue application interval
Precise gluing volume standards are formulated for different papers, and the "critical glue application" (the minimum amount of glue applied when the peel strength begins to stabilize) and the "optimal amount of glue" of each paper are determined through experiments.
(1) Coated paper: the critical gluing amount is 5g/m², and the optimal range is 5~7g/m². In this range, the adhesive can fully cover the adhesive surface, form a uniform adhesive layer, the peel strength is stable at 2.4~2.65N/cm, and the overflow rate is controlled below 0.5%.
(2) Transfer aluminized cardboard: critical gluing amount 6g/m², optimal range 6~8g/m². Experimental data showed that when the glue amount of the paper was 3~6g/m², the peel strength increased linearly with the increase of the glue application, from 1.2N/cm to 2.5N/cm. The peeling strength in the range of 6~8g/m² tended to be stable, between 2.5~2.65N/cm. After exceeding 8 g/m², the peel strength decreased slightly and the overflow rate increased significantly, from 0.5% to 8%.
(3) Water loose paper: the critical glue amount is 5g/m², and the optimal range is 5~7g/m², which can ensure that the adhesive strength is ≥ 3.0N/cm, and at the same time avoid rubber overflow pollution.
During the production process, the amount of glue is accurately controlled by adjusting the gap of the gluing roller (accuracy ± 0.01mm), equipped with an online glue amount detector, real-time monitoring and feedback data, and automatically alarming when the deviation exceeds ±0.5g/m² to ensure that the amount of glue is always in the optimal range.
(2) Optimize the gluing speed and uniformity
The application speed and uniformity directly affect the wetting and penetration effect of the adhesive on the paper surface, and precise control is required through process matching and equipment optimization.
(1) Glue application speed matching: According to the type of adhesive, the speed standard is formulated, and the water-based adhesive application speed is controlled at 50~70m/min, and the adhesive application speed is controlled at 60~80m/min to ensure that the adhesive has sufficient wetting time on the paper surface (≥0.5s). The field test data shows that when the gluing speed of water-based adhesive is increased from 60m/min to 90m/min, the qualified rate of gluing uniformity decreases from 98% to 75%, and the degumming rate increases from 1.2% to 5.8%, which verifies the importance of speed matching.
(2) Optimization of gluing rollers: Adopt anilox roller gluing technology, select the number of mesh according to the type of paper, improve the amount of glue and permeability, and ensure that there is no leakage or accumulation on the glued surface.
(3) Cleaning and maintenance: Formulate a strict cleaning cycle for the gluing roller, and thoroughly clean it after each shift of production to prevent the dry formation of the glue layer from affecting the subsequent gluing effect. After cleaning, standard specimens are used to verify the uniformity of gluing, and the pass rate ≥ 98% before starting production, ensuring the stability of the process from the level of equipment maintenance.
03/ Standardization of the pressure curing process
Pressure curing is a key step in the formation of a stable adhesive layer by adhesives, and it is necessary to establish a three-dimensional standard system of "pressure-time-temperature", while optimizing the curing environment to ensure the quality of bonding.
(1) Standardization of pressurization parameters
Based on laboratory verification data, a general standard for the pressurization process of cigarette pack glue is formulated, and it is flexibly adjusted according to the thickness of the paper.
(1) Pressure: The standard pressure range is 0.4~0.6MPa, the upper limit (0.5~0.6MPa) for thick paper (such as corrugated paper lining) and the lower limit (0.4~0.5MPa) for thin paper (such as transfer aluminized paper) to ensure that the adhesive fully penetrates the fiber. Experiments show that when the pressure is increased from 0.3MPa to 0.5MPa, the shear strength increases from 4.1N/mm² to 5.2N/mm², and the improvement effect is significant.
(2) Pressurization time: water-based adhesive pressurized for 3~5s, adhesive pressurized for 2~3s, and the core requirement is pressurization time ≥3s. The data show that at 0.5MPa pressure, when the pressurization time increases from 1s to 3s, the shear strength jumps from 2.1N/mm² to 5.2N/mm², an increase of 147.6%. The shear strength growth slowed down in the range of 3~5s, indicating that 3s could meet the basic curing needs.
③ Pressing Temperature: Water-based adhesives are pressed at room temperature, with the adhesive pressing temperature controlled between 40–50°C. Moderate heating accelerates the curing process and improves bonding efficiency.
High-precision pressure sensors and timers are installed on the production line to monitor the pressing process of each carton in real-time, ensuring parameters meet standards and preventing delamination caused by improper pressing.
(2) Curing Environment Control
The glued cigarette packs are placed in a temperature- and humidity-controlled room (temperature 20–25°C, humidity 50%–60%) for curing. The curing time should be no less than 24 hours for water-based adhesives or 12 hours for other adhesives. After curing, the adhesive strength is tested on samples, and only qualified packs can proceed to the next process. The testing standards are: coated paper and transfer-metallized paper peel strength ≥ 2.5 N/cm, wood-free paper peel strength ≥ 3.0 N/cm, and shear strength ≥ 5.0 N/mm².
Glue control for cigarette pack folding is a systematic process involving raw material selection, process parameter optimization, environmental control, and quality inspection. Its core lies in achieving precise matching of the "adhesive-paper-process". The adhesive selection strategy based on paper characteristics, quantified gluing process parameters, standardized pressing and curing conditions, and full-process quality control system proposed in this paper have been industrially verified to effectively reduce cigarette pack delamination rates to below 1%, significantly improving the stability of product quality.