Revisiting Control Challenges and Practical Solutions in Aluminum Foil Lamination

Aluminum foil lamination is a challenging structure in solvent-free lamination processes. We have previously provided a brief introduction to its control methods. This article will offer a more detailed explanation from a practical operational perspective, based on years of experience.

I. Basic Process Methods for Aluminum Foil Lamination

Tongze has been conducting experiments related to solvent-free aluminum foil lamination since 2008, accumulating extensive experience. Practice shows that batch production of aluminum foil lamination is achievable, but the reliability for widespread adoption still needs further improvement.

The core reason why aluminum foil lamination is difficult to master lies in: aluminum foil is a rigid substrate and extremely thin, while the initial tack of adhesives is relatively low, making it hard to achieve good initial bonding.

Aluminum foil lamination typically involves a three-layer or four-layer structure. Based on practical experience, we recommend two process methods to users: the Step-by-Step Method and the One-Step Method.

1. Step-by-Step Method

The Step-by-Step Method involves laminating only two layers at a time. A three-layer structure is completed in two steps, and a four-layer structure in three steps. Between the two lamination steps, either full curing or partial curing can be used.

We strongly recommend using the partial curing method—performing the next lamination within 2-4 hours after the first. This method, pioneered by Tongze, effectively reduces adhesive penetration (“bleed-through”) faults while shortening the production cycle and improving efficiency.

2. One-Step Method

The One-Step Method refers to completing the three-layer or four-layer lamination in a single pass, which requires corresponding specialized equipment.

Different process methods lead to variations in the problems prone to occur in aluminum foil lamination. Based on years of collaborative experience with users, the following sections provide specific operational solutions for several common challenges.

II. Practical Operational Solutions for Common Challenges

(1) Composite White Spots

This issue is more common in PET (printed film)/aluminum foil lamination. Adhesives for aluminum foil generally have higher viscosity compared to other flexible packaging adhesives. ဒီ, combined with uneven ink thickness distribution in multi-color printing, can cause the adhesive to fail to completely fill the ink depressions during curing, resulting in white spots on the appearance (see Figure 1).

Main Solutions:

1. Select suitable ink:​ Prefer inks with finer particles. This allows for appropriate reduction of adhesive application amount, lowering the probability of white spots.
2. Appropriately reduce machine speed:​ Control the machine speed between 100-150 m/min to allow sufficient time for the adhesive to fill the ink depressions.
3. Set steel roller temperatures appropriately:​ Control the metering roller temperature at 40-45°C, the coating steel roller at 50-55°C, and the lamination steel roller at 45-55°C. Specific settings can be flexibly adjusted based on adhesive characteristics.

(2) Adhesive Penetration and Reverse Tack (Bleed-Through)

This issue is common in standard aluminum foil lamination. The core reason is: aluminum foil itself has a certain number of pinholes, and the adhesive curing process is relatively slow. Under the pressure within the roll, the adhesive can easily penetrate through these pinholes, causing reverse tack, commonly known as “bleed-through.”

Main Solutions:

1. Choose aluminum foil with fewer pinholes:​ အလူမီနီယံသတ္တုပြား thickness is directly related to pinhole count. ယေဘုယျအားဖြင့်, thicker foil has fewer pinholes and is easier to laminate. It is recommended to use Grade A or better aluminum foil (အယ်လ်) with a thickness of 6.5μm-7μm.
2. Use high-viscosity adhesives:​ Examples include polyurethane retort-grade adhesives or specialized high-viscosity adhesives for aluminum foil. Aluminum foil lamination speeds are often controlled between 100-150 m/min. Lower lamination speeds require high-viscosity adhesives—these have higher molecular weight and more stable leveling properties, making them less prone to penetrating aluminum foil pinholes, which can significantly reduce reverse tack.
3. Reasonably control the interval between lamination steps:​ For PET/aluminum foil lamination, the intermediate interval time before laminating the inner layer should be controlled within 2-4 hours after the first lamination is complete, to prevent penetration due to incomplete adhesive curing.

(3) Winding Slip (Core Slippage)

This issue is more prone to occur in aluminum foil/PE lamination (see Figure 2). The main reasons are the low initial tack of the adhesive and reduced friction between substrates when the adhesive application amount is increased. Combined with trapped air between layers, relative slippage can easily occur under high pressure or tension.

Main Solutions:

1. Reasonably control adhesive application amount:​ Adhesive application amount is the most sensitive factor causing winding slip in solvent-free lamination. ပထမ, determine the critical point of adhesive application for each material combination. ဥပမာအားဖြင့်:
   • For aluminum foil/PE lamination, the adhesive amount is generally controlled at 1.3-1.5 g/m² and can be adjusted based on PE film thickness (thicker PE requires more adhesive). When reducing speed, control the amount at 1.1-1.2 g / m².
   • For PET/AL/PE structures, when laminating the PE layer via solvent-free process, the critical adhesive amount is about 1.3 g / m². It is recommended to set the amount between 1.1-1.2 g / m².
2. Adjust winding nip roller pressure and face:​ Controlling the winding nip roller is crucial. It regulates the tightness of the wound material to prevent slippage, specifically meeting two points: ပထမ, the nip roller must maintain balance with the wound material; second, air pressure should be controlled around 0.05 MPa. တစ်ပြိုင်နက်တည်း, use the nip roller adjustment screws to ensure the nip roller face is parallel to the core tube face.
3. Properly control winding tension:​ Higher winding tension makes the roll tighter and more prone to slip. ဥပမာအားဖြင့်, in a PE/PE structure, with initial winding tension set at 13 kg and adhesive at 1.3 g/m² causing slip, changing the adhesive to 1.1 g/m² may still occasionally cause slip. ဒါဆိုရင်, try to minimize the winding tension as much as possible while ensuring no core wrinkles.

(4) Soft Wrinkles in the Wound Roll

This problem often occurs at the core and splice areas (see Figure 3). The main solutions are as follows:

1. Use high-quality core tubes, or use printing plate cylinders as core tubes. During equipment operation, closely observe the winding nip roller to ensure no bouncing occurs.
2. Reasonably control winding tension and taper: It is recommended that for a substrate width of 1000 မီလီမီတာ, the winding tension be controlled at 40-50 Kg/full width, and the taper be controlled between 60%-80%.