Cling Films Provide Adhesion without Adhesives

The term "cling film" is commonly used to refer to a film that can cling to a substrate without the use of adhesives. Cling films have been used to produce products that are intended to be removed or repositioned such as decorative wall coverings, temporary labels, protective surfaces, writing surfaces and so forth. Cling films are generally divided into two major types: cling vinyl films and electrostatic cling films.

Cling vinyl film is simply ultra-conformable, highly plasticized vinyl film that is calendered into a very smooth film. It can be painted and printed upon and sticks by making intimate contact with the substrate.

These films are made from thin flexible PVC films that contain plasticizers and/or tackifiers. Cling vinyl films adhere to substrates primarily by capillary forces rather than electrostatic forces. As a result cling vinyl films are typically adhered to smooth, rigid surfaces such as glass windows. They do not adhere well to porous, rough, or contaminated surfaces.

Electrostatic cling films are films that have an electrostatic charge. These are made from materials that are technically referred to as electrets. A dielectric material is called electret if it exhibits a quasi-permanent electric field, which is either caused by trapping of electrostatic charges or by macroscopically oriented dipoles. Electrets have been used in acoustic parts, filters, and medical devices. More recently they have been used as cling films. The adhesion strength will depend on the electret charge density.

Real electrostatic charges can be injected into the material by various methods. Among other processes, corona charging is the most common technique because it is fast, easy to perform, and cost-efficient. Electrostatic cling films will adhere to a wider variety of substrates than the vinyl cling films described above.

The electret behavior of commercial high performance polymer films depends strongly on the chemical structure and cannot be easily predicted. Useful thermoplastic polymeric materials that can maintain an electret charge include, for example, fluorinated polymers, polyolefins, copolymers of olefins and other monomers, polyesters, polyamides, polycarbonates, polysulfones, non-plasticized polyvinyl chloride, and combinations thereof. Polypropylene (PP) is considered a good electret material and in addition it is an inexpensive commodity polymer that is easy to process.

Both vinyl and electrostatic cling films lose their ability to adhere over time due to environmental factors such as humidity, temperature, and secondary processes (e.g., printing). It is common practice, therefore, to fabricate and store electrets products in a place where there is minimum moisture and dust. This loss of bonding capability with time is undesirable for applications requiring long term adhesion for months or years.

To increase adhesion and durability, various activatable adhesives have been used in combination with electrostatic cling films. These adhesives include pressure sensitive adhesives, hot melt adhesives and microencapsulated adhesives. Depending on the activatable adhesives, these cling products can be temporarily repositionable and then become permanently attached with time.

The commercial possibilities for removable / repositionable cling films appear to be very large. Removable labels, temporary signs and banners, attaching credit cards to mailers, postable notes, and bookmarks are only some of the possible applications. Future uses of these products may include applications such as easy disassembly of parts for reuse or recycling, removable electronic parts, and advanced delatching and deployment mechanisms.