Four new silicone polymers that Wacker has developed facilitate cost savings in the coating process and ensure that the label laminate can easily be processed on high-speed equipment.

Pressure-sensitive adhesive (PSA) labels consist of two layers: the release paper or film and an adhesive material – the actual label. The skill of a laminate manufacturer lies in adjusting the desired release force so that both matrix peeling and labeling run smoothly. However, this is not an easy task: firstly, because the matrix peeling and labeling take place at different speeds and, secondly, because the viscoelastic properties of the adhesive and the release properties of the silicone layer change with increasing peel rate.

This is where the novel, solvent-free silicone polymers come into play which the Munich-based chemical group Wacker has developed for its new Dehesive SFX line. The products yield high-quality release layers that feature a flat release force profile and can be used on the highest speed coating equipment.

Unlike conventional silicone release agents, the new silicone polymers have a starlike structure. They are highly branched and have a three-dimensional molecular architecture. Several silicone branches extend out in different directions from a central building block. At the end of every branch, there is a vinyl group. This star-like structure significantly influences the properties of the new polymers. Their molecular structure gives rise to a flat release force profile, a major advantage, especially for use on high-speed coating equipment.

Since the new star polymers contain so many crosslinkable groups, they are extremely reactive. They cure considerably faster than conventional silicone polymers with the same viscosity. This high reactivity can be used to save on platinum, which catalyses the curing of the release coating. 

The new star polymers are tailor-made for various substrates and yield different release force profiles. They differ in their viscosity and curing rate, in particular.

Dehesive SFX 250 is the most reactive of the four new polymers. It has a relatively low viscosity of 200 mPa-s, ideal for non-porous backing material.  It cures extremely quickly – an advantage for use on high-speed coating equipment.

Liner manufacturers can also make use of Dehesive SFX 250’s high reactivity to reduce the amount of platinum catalyst or lower the curing temperature, both leading to cost reductions. 

Where a fast-curing silicone is to be used on porous substrates and a low release force at high peel rates is required, Dehesive SFX 380 with its viscosity of 400 mPa-s is a good choice. 

On non-porous, smooth substrates, the applied silicone remains almost entirely on the surface and spreads out evenly. This is the case for film substrates and high-quality glassine papers. For such substrates, Wacker has developed Dehesive SFX 195, which has a low viscosity of 190 mPa-s. 

The fourth polymer, Dehesive SFX 280 has a viscosity of 220 mPa-s. It is equally suitable for both non-porous and porous substrates. 

Since a disruptive mist can form at high coating speeds, Wacker also offers its star polymers an integrated anti-misting additive.