Release liners can be classified by coated and uncoated types, or by the type of release agent used.
Coated release liners
Release agents have a certain degree of permeability. Without adequate barrier protection, the release agent will penetrate into the paper substrate, leading to problems such as poor curing and excessive consumption of release agent (resulting in high costs). Therefore, a plastic coating treatment (commonly known as extrusion coating) is required on the paper surface. In China, polyethylene (PE) pellets are generally used for extrusion coating, with a required melt flow index (MFI) of around 7. Domestic PE pellets are typically selected from Yanshan Petrochemical’s grade 1C7A. Coated release liners are further divided into single-side coated and double-side coated release liners.
Uncoated release liners
Mainly include glassine paper, CCK paper, and other special-treated release liners.
Selection of Release Liner
The coating weight of the release agent directly affects the compatibility with adhesives. Water-based adhesives require a relatively low silicone coating weight, while solvent-based adhesives and hot melt adhesives demand a higher silicone coating weight due to their strong permeability and destructive effect, which usually necessitates heavy coating.
Adhesive coating plants generally choose heavy-coated release liners.
Lamination plants usually opt for medium-coated release liners; for thermal lamination processes, however, heavy-coated release liners are required.
Protective films using water-based adhesives only need light-coated release liners.
Medium-coated release liners are suitable for solvent-based adhesive protective films, while heavy-coated release liners are not recommended for protective film applications.
Due to climatic factors, die-cutting plants should select release liners with higher peel force in winter and those with lower peel force in summer.
For tapes with special requirements, the release liners used in the die-cutting process need to be discussed with release coating suppliers. In-depth testing and comparison must be conducted before mass production; otherwise, a large number of defective products will be generated.
Off-spec release liners (with mismarked specifications) are not entirely unusable. They can still be applied in low-demand scenarios, which explains the presence of numerous off-spec release liner suppliers in the domestic market.
