Due to its ultra-thin thickness, low tensile strength (120-150MPa), and elongation of less than 3%, 0.006mm aluminum foil is prone to defects such as tensile deformation, wrinkling, and interlayer slippage during flexible packaging lamination if tension control is improper. These defects directly affect the barrier properties and appearance qualification rate of packaging products. Based on the mechanical properties of 0.006mm aluminum foil and the lamination process flow, this paper systematically analyzes the mechanism of tension loss control, proposes a core control strategy of “stage-specific precise control + dynamic compensation”, covering tension parameter setting, equipment configuration, and collaborative optimization schemes for the entire process of unwinding, conveying, and winding. Combined with enterprise application cases, the effectiveness of the technology is verified, providing a practical professional solution for tension control of 0.006mm aluminum foil in flexible packaging lamination production.
0.006mm aluminum foil; flexible packaging lamination; tension control; stage-specific control; dynamic compensation; tensile deformation
In high-end flexible packaging lamination fields such as food and pharmaceuticals, 0.006mm aluminum foil serves as the core barrier layer in multi-layer composite structures (e.g., PET/Al0.006/PE) due to its excellent oxygen barrier properties (oxygen transmission rate < 0.1 cm³/(m²·24h·0.1MPa)) and light-shielding performance. However, its ultra-thin thickness results in mechanical properties characterized by “low tensile resistance and high sensitivity” — its longitudinal tensile strength is only 60%-70% of that of conventional 0.01mm aluminum foil, its transverse wrinkle resistance is even weaker, and it exhibits significant anisotropy (15%-20% difference in mechanical properties between longitudinal and transverse directions).
During the lamination process, aluminum foil undergoes four key stages: unwinding, guide roller conveying, pressure roller lamination, and winding. If the tension in any stage exceeds its mechanical tolerance threshold or exhibits instantaneous fluctuations, quality issues may arise: excessive unwinding tension causes “pre-stretching” of the aluminum foil, leading to uneven dimensional shrinkage after lamination; fluctuations in conveying tension trigger local stress concentration, forming wavy wrinkles; improper winding tension results in uneven winding or residual interlayer internal stress, leading to rebound wrinkling during subsequent processing. According to industry research, the defect rate of 0.006mm aluminum foil lamination caused by tension control failure accounts for over 60% of the total defect rate. Therefore, establishing a scientific tension control system is crucial for ensuring production stability.
The elastic modulus of 0.006mm aluminum foil is approximately 70GPa, much lower than that of PET film (2.8GPa). Under the same tension, the elastic deformation rate of aluminum foil is more than 25 times that of PET. If tension is set with reference to conventional substrates (e.g., PET), aluminum foil easily exceeds its elastic limit, resulting in irreversible plastic stretching. Meanwhile, the smooth surface of aluminum foil (surface roughness Ra < 0.1μm) leads to low friction with guide rollers, and even minor tension fluctuations can cause conveying deviation, further exacerbating local tension imbalance.
During lamination, tension is transmitted from the unwinding end to the winding end through the guide roller system. Improper tension connection between stages leads to a “tension accumulation effect”: for example, excessive unwinding tension → superimposed tension in the conveying stage → aluminum foil stretching; or winding tension lower than conveying tension → aluminum foil slack before winding, causing wrinkling. Additionally, changes in lamination speed (e.g., acceleration, deceleration) generate inertial tension. When the speed increases from 30m/min to 50m/min, inertial tension can increase by 0.8-1.2N/m, exceeding the tolerance range of 0.006mm aluminum foil (maximum safe tension ≤ 3.0N/m).
Guide roller parallelism errors (>0.01mm/m) cause uneven transverse stress on aluminum foil, forming a “unilateral tension difference” and triggering transverse stretching or edge wrinkling; insufficient tension sensor precision (error > ±0.3N) fails to capture minor tension fluctuations in real time, leading to delayed response of the control system and missed adjustment windows.
Unwinding is the “source” of tension control, requiring prevention of initial stretching of aluminum foil during unwinding. The core solutions are as follows:
Based on the tensile strength of 0.006mm aluminum foil, the unwinding tension should be controlled within 1.5-2.5N/m, with fine adjustments based on actual mechanical test data of the aluminum foil — if the tensile strength of a batch of aluminum foil is only 120MPa, the upper tension limit should be reduced to 2.2N/m; if the tensile strength reaches 150MPa, it can be increased to 2.5N/m. Meanwhile, the unwinding tension should be 0.3-0.5N/m lower than the conveying stage tension to form a “tension gradient”, preventing slack at the junction of unwinding and conveying.
A closed-loop control system consisting of a “magnetic powder brake + dancer roller” is adopted: the magnetic powder brake provides basic braking force, and the dancer roller detects the tightness of the aluminum foil in real time through a displacement sensor. When the aluminum foil roll diameter decreases from the maximum (e.g., 600mm) to the minimum (e.g., 150mm), the system automatically adjusts the braking force according to the roll diameter calculation formula (T=K×D, where T is tension, K is the coefficient, and D is the roll diameter), ensuring the unwinding tension fluctuation range is ≤ ±0.3N/m. For example, for every 50mm decrease in roll diameter, the braking force is reduced by 0.1-0.15N, preventing sudden tension increases caused by reduced roll diameter.
A “pre-stretching roller” is added to the unwinding frame, with a surface micro-convex texture (convex height 0.05mm, spacing 2mm) to slightly stretch the aluminum foil, eliminating interlayer stress generated during winding; meanwhile, a “low-friction unwinding bushing” is used to reduce the friction coefficient between the aluminum foil and the core to below 0.1, preventing local tension concentration caused by excessive friction resistance during unwinding.
The conveying stage is the most complex in terms of aluminum foil stress, requiring precise stage-specific tension matching based on the process characteristics of “unlaminated → pressed → cured”:
The tension is set to 2.0-3.0N/m, slightly higher than the unwinding tension, ensuring the aluminum foil fits closely to the guide roller and preventing deviation caused by slack. A “tension buffer roller group” (composed of 3-4 guide rollers with a diameter of 80mm and spacing of 300mm) is configured in this stage to disperse local tension and reduce stretching risk by increasing the contact area between the aluminum foil and guide rollers.
During pressure roller lamination, the bonding between aluminum foil and substrate (e.g., PET) generates additional friction, requiring the tension to be reduced to 1.8-2.5N/m to prevent aluminum foil stretching caused by superimposed friction and tension. Meanwhile, the tension must be coordinated with the pressure roller pressure (0.3-0.5MPa) and lamination speed (30-50m/min): when the speed increases to 50m/min, the tension should be synchronously reduced by 0.2-0.3N/m to avoid enhanced tension effects from inertial force; when the pressure increases to 0.5MPa, the tension can be appropriately increased by 0.1-0.2N/m to ensure the discharge of interface air bubbles.
During adhesive curing, aluminum foil is prone to internal stress due to thermal shrinkage, requiring the tension to be controlled within 1.8-2.2N/m and adopting “progressive tension adjustment” — the tension is gradually reduced by 0.2N/m from the pressure roller outlet to before winding to alleviate internal stress accumulation. A “tension sensor” (precision ±0.1N) is installed at the oven outlet in this stage to monitor tension changes in real time. When fluctuations exceed ±0.2N, the system automatically adjusts the servo motor speed to achieve dynamic compensation.
Winding tension directly affects the flatness of the aluminum foil roll and subsequent processing performance, with the core goal of preventing “excessive late-stage tension” and “interlayer slippage”:
At the initial winding stage (roll diameter 150mm), the tension is set to 2.5-3.0N/m to ensure close bonding between the aluminum foil and substrate; as the roll diameter increases, the tension is reduced by 0.2-0.3N/m for every 100mm increase in roll diameter. When the roll diameter reaches 600mm, the tension is reduced to 1.8-2.2N/m. This gradient is implemented through a preset PLC algorithm, such as an “exponential decay model” (T=T0×e^(-kD), where T0 is the initial tension, k is the decay coefficient, and D is the roll diameter increment), preventing tension mutations caused by linear decay.
A “pneumatic pressure roller” is configured outside the winding roller, applying an auxiliary pressure of 0.1-0.15MPa to ensure tight interlayer bonding of the aluminum foil. Meanwhile, the pressure is adjusted in real time through a pressure sensor — as the roll diameter increases, the pressure roller pressure is synchronously reduced by 0.02MPa per 100mm roll diameter increase, preventing compressive stress on the inner layer from the outer aluminum foil.
A “CCD visual correction system” (precision ±0.2mm) is used to detect the edge position of the aluminum foil in real time. When the deviation exceeds 0.5mm, the system drives the winding frame to move horizontally, ensuring the edge alignment of the aluminum foil roll is ≤0.3mm and preventing local tension concentration caused by misaligned edges.
Conveying guide rollers adopt “high-precision seamless steel pipes” (material: 45# steel, quenched and tempered), precision-ground by a centerless grinder to ensure radial runout ≤0.008mm and parallelism ≤0.01mm/m; the surface is chrome-plated (thickness 5-10μm) and mirror-polished to achieve a surface roughness Ra ≤0.1μm, reducing the friction coefficient between the aluminum foil and guide rollers (≤0.15) and minimizing local tension fluctuations.
“High-precision tension sensors” (range 0-5N, resolution 0.01N) are installed at three key stages (unwinding, conveying, winding) to form a “three-point linked detection”; sensor signals are transmitted to the PLC in real time via the Profinet protocol (response time ≤0.05s). When the tension in any stage exceeds the set range, the system immediately triggers an alarm and adjusts, ensuring closed-loop tension control.
An “electromagnetic induction heating pressure roller” is adopted (surface temperature uniformity ±2℃) to avoid aluminum foil thermal shrinkage differences caused by uneven temperature; the pressure roller crown error is controlled within ≤0.02mm to ensure uniform transverse pressure distribution and prevent local tension imbalance caused by uneven pressure.
Before lamination, 0.006mm aluminum foil undergoes “chromate passivation treatment” (passivation solution concentration 20-30g/L, temperature 40℃, treatment time 3s), forming a dense passivation film (thickness 50-100nm) on the surface. This not only improves the surface tension (from 30mN/m to 45-50mN/m) and enhances bonding strength with the adhesive but also improves the tensile toughness of the aluminum foil, increasing the tension tolerance upper limit by 5%-8%.
PET substrates laminated with aluminum foil require “preheating and dewatering” (oven temperature 45℃, time 10s, moisture content controlled ≤0.1%) and “corona treatment” (surface tension ≥50mN/m) to reduce interface resistance between the substrate and aluminum foil during lamination and prevent tension superimposition caused by excessive resistance.
A large-scale pharmaceutical packaging enterprise produces three-layer composite films of “PET/Al0.006/PE”. Previously, due to improper tension control, the aluminum foil tensile deformation rate reached 3.5%-5.0% and the wrinkling defect rate reached 12%-15%. After adopting the tension control scheme proposed in this paper, the specific implementation measures are as follows:
After 30 consecutive days of production following implementation, the statistical data are as follows:
Meanwhile, the barrier properties of the composite film significantly improved: the oxygen transmission rate decreased from 0.12-0.15 cm³/(m²·24h·0.1MPa) (before transformation) to 0.08-0.10 cm³/(m²·24h·0.1MPa), meeting the strict requirements of pharmaceutical packaging. The enterprise reduced monthly waste losses by approximately 320,000 yuan and increased production efficiency by 18%.
In the future, an “AI visual tension prediction system” will be introduced, which captures micro-deformations on the aluminum foil surface (e.g., wrinkle precursors, stretching lines) in real time through cameras, establishes a prediction model based on historical tension data, and adjusts tension parameters 0.5-1s in advance to achieve “predictive control” and further reduce the defect rate.
For new high-tensile 0.006mm aluminum foils (e.g., adding Mg and Mn elements to achieve a tensile strength of over 180MPa), a “variable tension algorithm” needs to be developed to dynamically adjust tension thresholds based on the real-time mechanical properties of the aluminum foil (obtained via online tensile testing machines), realizing precise “material-process” matching.
An integrated control platform for the four parameters of “tension-temperature-pressure-speed” will be built, using digital twin technology to simulate tension changes during the lamination process and optimize parameter combinations through virtual simulation, reducing the actual debugging cycle and improving production stability.
Tension control for 0.006mm aluminum foil during lamination must focus on the three cores of “material property adaptation, stage-specific precise control, and equipment-process collaboration”. Through roll diameter dynamic compensation in the unwinding stage, stage-specific tension matching in the conveying stage, gradient decreasing control in the winding stage, combined with equipment precision upgrading and material pretreatment, defects such as stretching and wrinkling can be effectively solved. The three newly added tables clearly sort out parameters for each stage, equipment precision requirements, and pretreatment processes, providing more intuitive technical references for practical production. Practical applications show that the optimized tension control scheme can control the aluminum foil tensile deformation rate within 1.5% and the wrinkling defect rate below 3%, significantly improving product quality and production efficiency. In the future, with the integration of intelligent technologies, tension control for 0.006mm aluminum foil will move toward “predictive and adaptive” development, providing stronger support for high-quality production in the flexible packaging lamination industry.
