Laminating film is widely used in the printing and packaging industries to protect paper and printed materials. However, many customers find that laminating film is prone to wrinkling, edge curling, and curling under high temperatures.
As a professional laminating film manufacturer, YIDU, with 32 years of production experience, analyzes the causes of wrinkling at high temperatures and provides solutions.
1. Main Causes of Wrinkling in Laminating Film at High Temperatures
Uneven Thermal Shrinkage
Most laminating films are made from PET base film, which undergoes slight thermal shrinkage when heated.
If the hot-pressing temperature or speed is uneven, the film layer will shrink faster in some areas than others, forming wrinkles.
Excessively High Temperature Setting
If the laminating machine temperature exceeds the film material's heat resistance range, it will cause the film surface to soften or even locally melt.
Uneven expansion of the film material at high temperatures easily leads to wrinkling and edge curling.
Uneven Pressure Distribution:
Uneven roller pressure during hot pressing can lead to unbalanced stress on the film material, resulting in wrinkles.
This is especially common when laminating large sheets or when paper thickness is uneven, as localized excessive pressure is a frequent issue.
Substrate Moisture Absorption or Expansion:
Paper, cardboard, or printing materials expand when damp, and the laminating film, lacking sufficient rigidity at high temperatures, will expand and contract with the substrate, forming wrinkles.
This is particularly prone to occur in environments with high humidity or significant seasonal changes.
Film Thickness or Quality Issues:
The film becomes more flexible at high temperatures, making it prone to thermal wrinkling.
Inconsistent thermal expansion coefficients between different layers of low-quality films or composite films can also exacerbate wrinkling.
2. Practical Methods for Solving High-Temperature Wrinkling Problems
High-temperature wrinkling is one of the most common problems encountered during the use of laminating film. By scientifically adjusting processing parameters, selecting suitable materials, and optimizing the substrate condition, the wrinkling rate can be effectively reduced. The following are detailed operating recommendations:
2.1 Controlling Hot-Sealing Temperature
Adjust the temperature according to the heat resistance of the film material.
BOPP film generally has a heat resistance temperature between 100–130℃, while PET film has a heat resistance temperature between 110–150℃.
Excessive hot-sealing temperature can cause the film to soften or partially melt, forming wrinkles; insufficient temperature will result in weak adhesion and bubbling.
Temperature Uniformity
The heating rollers of the heat sealing machine or laminating machine must maintain a uniform temperature to avoid overheating or undercooling in certain areas.
An infrared thermometer or thermal imager can be used to detect the temperature distribution of the heating rollers, ensuring a temperature error ≤ 3℃.
2.2 Adjusting Pressure and Speed
Roller Pressure
Roller pressure should be uniform. Excessive pressure can easily cause wrinkles, while insufficient pressure may prevent complete adhesion.
It is recommended to adjust the pressure in sections for large-format or thick substrates to ensure balanced force in each section.
Lamination Speed
The lamination speed must be matched with the hot-pressing temperature. Too high a speed may result in insufficient heating of the film material, while too low a speed will concentrate heat, leading to localized wrinkling.
For films of different thicknesses and substrates, the optimal speed can be determined experimentally: 0.5–1 m/min is recommended for small-format paper, and 0.3–0.7 m/min for medium-format paper.
2.3 Selecting Suitable Thickness and Quality Film
Film Thickness
Thin films (20–25 microns) soften and wrinkle easily, suitable for small office documents; thick films (35–50 microns) are more stable and suitable for large-format printing or packaging materials.
Film Quality
High-quality films have uniform stretch and a stable coefficient of thermal shrinkage, with consistent thermal expansion between different layers, significantly reducing wrinkling rates.
Functional Film Selection
For high-temperature lamination, heat-resistant or wrinkle-resistant films can be selected. These films incorporate a low-heat-shrinkage layer or a tensile-resistant coating during hot pressing to reduce localized wrinkles.
2.4 Keeping the Substrate Dry and Flat
Substrate Moisture Control
Moisture absorption and expansion of paper or cardboard are common causes of wrinkling at high temperatures.
It is recommended to control the substrate moisture content within the range of 4–6%. Drying should be performed before lamination if necessary.
Substrate Flatness
For corrugated or warped paper, pre-press or clamp it to ensure a flat surface before entering the hot press.
2.5 Preheating and Segmented Processing
Preheating Treatment
For thicker or larger sheets of paper, preheat at a low temperature for 20–30 seconds to allow the substrate and film to heat up simultaneously, reducing thermal stress.
Segmented Processing
For large packaging or brochures, lamination can be performed in segments, covering smaller areas each time to reduce wrinkles caused by differences in thermal expansion.
2.6 Using Functional Coated Films
Anti-Wrinkle Coating
YIDU offers films with an anti-wrinkle, low-shrinkage coating to maintain film flatness and reduce wrinkling during high-temperature processing.
High-Temperature Resistant Coating
For high-temperature heat-sealing environments, the selected heat-resistant coating film can withstand processing temperatures above 150℃ without deformation.
Environmentally Friendly Coating
Using environmentally friendly water-based coating film materials, it not only has excellent wrinkle resistance but also meets green packaging requirements.