Friction Coefficient, Surface Roughness, and Slipperiness of Plastic Films
The relationship between the surface friction coefficient, roughness, and slipperiness of plastic films is interrelated and crucial for various applications.
The evaluation of slipperiness is often based on the magnitude of the friction coefficient. Both dynamic and static friction coefficients play a significant role in assessing slipperiness. When slipperiness improves, there is a corresponding change in both dynamic and static friction coefficients. To better align with end-user requirements, it is advisable to simulate variations in the friction coefficient under different temperature and humidity conditions.
Surface Friction Coefficient of Plastic Films
The friction coefficient of films is a critical technical parameter in production. It serves as a quantitative assessment criterion for the opening performance of plastic films, alongside anti-adhesive properties. Additionally, it provides reference data for the operation speed of automatic packaging machines, tension adjustment, and wear during film operation. In processes like printing, lamination, bag-making, and packaging, the surface friction coefficient of the film is linearly related to its surface roughness. Under certain conditions, as surface roughness increases, the friction coefficient decreases. Lowering the friction coefficient is advantageous for printing, lamination, and aluminum coating, enhancing the bonding between the film and these materials. The magnitude of the friction coefficient is adjusted through the addition of additives.
Surface Roughness of Plastic Films
Surface roughness is a comprehensive evaluation of the microscopic geometric features of small peaks and valleys on the film's surface. Appropriate surface roughness benefits ink printing, lamination, and vacuum aluminum coating. Excessive roughness may prevent ink, adhesives, or aluminum molecules from filling the surface recesses, leading to reduced adhesion and potential delamination during printing.
Generally, plastic film surfaces are smooth, causing adhesion during winding and difficulties in unwinding. Smooth film surfaces are also disadvantageous for ink printing, lamination, and vacuum aluminum coating, as they significantly reduce the adhesion between ink, adhesives, and the film surface. To introduce a certain level of roughness to the film surface (aside from corona treatment), anti-adhesive additives are incorporated during the film's formation. The control of surface roughness is crucial for the smooth production and downstream usage of films.
Slipperiness of Plastic Films
Slipperiness is primarily influenced by the type and amount of additives, as well as corona treatment. Moreover, the film's usage environment, downstream customer processing conditions, and production environment can impact slipperiness. Controlling slipperiness in the film production process is essential to provide suitable slipperiness without causing adverse effects on downstream customer use due to additive migration.
Lubricants, also known as slip agents, are categorized into internal and external lubrication. When processing CPP (IPP) and CPE (IPE) films, amide-type slip agents are typically added to the heat-sealing layer, while processing BOPP films involves adding slip agents to the core layer. These agents migrate to the film's surface ("external migration"), forming an oily surface that improves surface properties, reduces the friction coefficient, and enhances slipperiness. The amount added depends on the film thickness and the desired friction coefficient specified by the customer. Amide-type slip agents are generally unnecessary in the processing of BOPET and BOPA films.