Many different materials are used as a base for silicone coated release liner, including various types of papers, papers with a polyolefin layer on their surface, or plastic films. Papers represent the largest share of these substrates, and in particular of those used by the industrial producers of silicone coated release liner.
The function of the paper substrate is to act as material carrier for the release coating, normally represented by silicone. The combination of the substrate and the release coating forms the release liner, sometimes also referred to as “backing”, for an adhesive or tacky material.
In general, paper is a material composed for its largest part of cellulose fibers, which are turned into web format in a water based process. In this process, smaller or larger amounts of other components or ingredients are added to the fibers, and – depending on the needs – surface treatments are added on one or both sides of the paper web. These surface treatments are sometimes referred to as “finish”.
Papers developed as a substrate for release liner have a surface designed to provide a good barrier to silicone (a property also referred to as “holdout”) in order to enable a sufficient coverage with a controlled silicone quantity, and to ensure chemical compatibility with the silicone coating process, in order not inhibit silicone anchorage and curing.
Several other physical and mechanical characteristics play an important role in the design of release base papers, with specific properties added in order to ensure good performance not only through silicone coating but also through further specific converting and end use in a variety of different segments of use.
Paper types most frequently used as substrates for release liners, are:
Glassine / SCK Papers:
These represent the single largest type of papers substrates and are smooth , glossy and dense papers obtained through the pressure of nips between pairs of cylinders which press the paper web going through them. Lightweight super-calandered papers are also characterized by high transparency. These papers are mostly used in release liners for Label or Tape application, but also for Industrial and Medical applications.
Clay Coated Papers:
These papers have one or both surfaces coated with a clay coating. The function of the coating is to provide a suitable barrier to silicone, but also dimensional stability and lay-flatness.
These papers are mostly used in release liners for large format Self-Adhesive Graphics laminates, but also for label, Industrial, and Envelope applications.
Other types of release base papers include Poly-coated papers, where the surface is coated with a polyolefin layer, and Machine glazed or Machine finished papers, which do not go through a process of coating or calandering, but whose surface is finished on the paper machine through the smoothing effect of large metal cylinders.
Images courtesy of Ahlstrom-Munksjö