Understanding the Treatment Level in Metallized Cast Polypropylene (VMCPP) and Metallized Polyethylene Terephthalate (VMPET) Films in Lamination.

In the flexible packaging industry, it is common to assess the treatment level of materials using dyne inks and dyne pens. However, there are significant differences in how treatment levels behave in different types of metallized films, particularly between Metallized Cast Polypropylene (VMCPP) and Metallized Polyethylene Terephthalate (VMPET) films. This article provides insights into checking treatment levels in these films and the key differences that affect their performance in packaging applications.

Importance of Treatment Levels in Metallized Films

For metallized films, treatment levels indicate the surface energy of the material, which influences its ability to bond with adhesives during lamination. Typically, for chemical-treated VMPET films, the required dyne level is between 52 to 56 dynes, depending on the optical density (OD) of the film. Optical density refers to the opacity or thickness of the metallized coating, and it is categorized into three levels:

- Low optical density (OD < 2.2)

- Medium optical density (2.2 < OD < 2.8)

- High optical density (OD > 2.8)

Across all these levels, VMPET films must achieve the required dyne levels to ensure proper lamination performance.

Metal Bond Strength and Particle Distribution

?To further understand why VMPET and VMCPP behave differently, it is essential to examine the metal bond strength and particle distribution within these films:

?- VMPET has a much stronger metal bond, typically around 600 gm/mm, ensuring a tight arrangement of aluminum particles on the film’s surface. This tight configuration allows for stronger adhesion and less flexibility when handled.

- VMCPP, on the other hand, has a weaker metal bond strength of only 50 gm/mm, making the aluminum particles more loosely arranged. This weaker bond allows the metal coating to be easily removed, even with slight touches, and gives VMCPP a unique flexibility.

An analogy can help visualize the difference: Imagine filling two containers with 10 grams of glass balls—one with large balls and the other with small ones. If you fill both containers with water, the container with large balls will hold more water because the larger balls leave more space between them. In this analogy, VMPET acts like the container with small particles, leaving little room for adhesive penetration. VMCPP, however, is like the container with large particles, allowing for greater adhesive penetration during lamination.

Adhesion in Lamination: VMCPP’s Advantage

?When it comes to lamination, the differences in metal bond strength and particle distribution directly impact the adhesive used. VMCPP tends to require more adhesive (higher GSM) during the lamination process because of the larger spaces between aluminum particles, making it easier for adhesive to penetrate the polymer film.

?However, this also means that treatment levels become less critical for VMCPP at higher and medium optical densities. The treatment level merely indicates the wetting ability of the outermost surface, which doesn't play as significant a role in the adhesion process for VMCPP because of its natural capacity to absorb adhesive.

?In contrast, VMPET’s tightly packed aluminum particles do not allow for as much adhesive penetration, so the treatment level plays a more significant role in ensuring proper adhesion.?

Moisture and Surface Tension: Key Factors for VMCPP

?While the treatment level is less critical for VMCPP in terms of adhesion, other factors must be considered when laminating VMCPP films. The most important factor is moisture. VMCPP’s outermost surface, especially the metal side, can trap moisture, which interferes with adhesive penetration.

?To ensure successful lamination, it is essential to control the moisture level on the outer surface of VMCPP, as well as the environmental moisture during the lamination process. High moisture levels can disrupt the adhesive’s ability to penetrate the film, resulting in weaker bonds. Surface tension between the film and the adhesive also plays a crucial role in ensuring strong adhesion.

Now you know the VMPET and VMCPP are both widely used in flexible packaging, their treatment levels and lamination behaviors differ significantly. For VMPET, maintaining high treatment levels across all optical densities is crucial for ensuring adhesion due to its tightly packed metal particles and strong bond strength. VMCPP, on the other hand, benefits from its loosely arranged particles, which allow for better adhesive penetration, making treatment levels less important in certain cases, especially at higher optical densities.

However, careful attention must be paid to moisture levels when working with VMCPP, as trapped moisture can hinder adhesive performance. Understanding these differences helps packaging companies optimize their processes and choose the right materials for their applications.

Praneeth Madarasingha