IOTA CORPORATION LTD.
Hits: 808 img
The automotive invisible car wrap mainly consists of three layers: the coating layer, the substrate, and the adhesive layer. The coating layer is located on the top, followed by the substrate, which together primarily serve to resist external damage. The adhesive layer, at the bottom, plays a pivotal role in connecting the car paint and the substrate.
Based on the type of solvent, PSAs are divided into water-based and oil-based (also known as solvent-based) categories. Water-based PSAs can be further subdivided into water-dispersible and water-emulsion types, depending on the dispersion method of the solute.
Water-based polyurethane PSA is a type of adhesive sensitive to pressure, featuring high peel strength and peel adhesion, suitable for bonding materials such as foam and paper.
However, water-based PSAs contain surfactants. If used in car wrap films, they may come into contact with water during use, thereby affecting their adhesive performance. Furthermore, water-based PSAs lack transparency and weatherability, especially when car wrap films come into contact with water. Therefore, pure water-based PSAs struggle to meet the requirements of car wrap films.
Car wraps have strict requirements for peel strength, including high peel force, initial tack, and cohesion. Besides light exposure, temperature resistance and aging performance are also challenges that most pure water-based PSAs cannot overcome. Additionally, factors such as the adhesive's aging performance, adhesion to the substrate, and non-residual glue need to be considered.
Compared to many other PSA tapes, car wrap films have a significant difference in their application scenario: they are frequently exposed to sunlight and rain. Moreover, the substrates of car wrap films often have high transparency, and the car paint surface is very smooth. Therefore, when removing the car wrap film, no residual glue should be left behind, which is a higher requirement than for PVC advertising stickers.
(1) Peel force: Peel strength refers to the force required to peel the adhesive layer off a standard substrate at a constant rate and angle. The specific peel strength required for car wraps depends on actual conditions.
(2) Initial tack: Initial tack is the adhesive strength formed by the rapid "wetting" of the PSA on the substrate under low pressure. It is mainly determined by the mobility of the polymer chains. Only when the chains are highly mobile, able to form good wetting with the rough substrate surface, and achieve molecular-level contact with the substrate molecules, can sufficient bonding strength be generated through intermolecular interactions. Initial tack determines whether construction personnel can repeatedly apply the film and achieve a perfect application effect.
(3) Cohesion: Cohesion refers to the internal strength of the adhesive. As the adhesive for protective films, its cohesion must be very high. Otherwise, when peeling off the film, internal cracking of the adhesive may occur, leading to residual glue.
(4) Testing standards for aging performance include xenon arc lamp aging resistance, heat aging resistance, and humidity aging resistance.
(5) Adhesion to the substrate: This refers to the bonding force between the adhesive and the substrate.
Reasons for residual glue: Adhesion and cohesion are the key factors determining whether glue will be left on the car paint surface or take away the car paint when peeling off the film. Once the adhesion is less than the cohesive force, residual glue will remain on the car paint surface. Conversely, if the cohesive force is less than the adhesive force, peeling the film will also cause the breaking of bonds between adhesive molecules, ultimately leading to glue residue.
Typically, to ensure that both adhesion and cohesion are greater than the adhesive force, there are certain requirements for the texture of the adhesive. Currently, PSAs on the market can meet this requirement. Generally, for PSAs, the adhesive force is less than the cohesion, and the cohesion is less than the adhesion to the substrate. Using PSAs to make invisible car wraps can greatly reduce the phenomenon of glue residue on car paints. Among PSAs, oil-based PSAs best meet the requirements of car wrap films. Therefore, most car wrap films on the market currently use oil-based acrylic adhesives.
