How to Select a Release Liner for Butyl Tape
A release liner protects the adhesive surface of butyl tape during production, storage and transport. It should then peel away easily and predictably during application. Its role, however, extends well beyond that of a disposable separator. The liner affects lamination, rewinding, roll stability, converting, die-cutting, automated feeding and the behaviour of the finished product at the point of use.
An unsuitable liner can create excessive or insufficient separation force, compound transfer, butyl deformation and unstable slip-stick peeling. The useful question is therefore not which release liner is universally best. It is which liner matches a particular butyl compound, tape construction and manufacturing process.
Research published in 2026 by a scientific team working with Almara confirms that nominal release level alone cannot reliably predict performance. The study compared three double-sided silicone-coated PET liners with seven real butyl materials. Individual liner–butyl pairs behaved differently during separation even though the liners belonged to the same general material category.
What a release liner is made of
A typical release liner should be evaluated as a system with at least two components:
- a carrier such as paper, PET, PE or PP,
- a release coating, most commonly silicone.
The carrier influences dimensional stability, stiffness and behaviour during rewinding, die-cutting and feeding. The release coating largely determines the interaction between the liner surface and the adhesive compound.
Two PET liners can therefore perform very differently. They may use different silicone chemistries, degrees of cure, coating weights, coating uniformity or release modifiers. The inner and outer sides may also have different properties. A specification such as “50 μm PET, silicone-coated on both sides” does not provide enough information to qualify a liner.
Paper PET PE or PP
No carrier material is optimal for every butyl tape. Selection should reflect both product requirements and the operating conditions of the production line.
Paper liners
Paper can be cost-effective and may convert well. Its response to humidity must nevertheless be considered because moisture can change its dimensions, stiffness and mechanical stability. Variations in storage conditions may therefore affect the behaviour of the finished roll.
PET liners
PET offers high dimensional stability and close thickness control. It is especially useful when the process requires precise geometry, consistent die-cutting, repeatable feeding or reliable operation at higher speeds.
PE and PP liners
Polyolefin liners can offer greater flexibility and different winding behaviour from paper or PET. Their suitability depends on tape construction, liner thickness, web tension, temperature and the intended application method.
The same principle applies to every carrier: the carrier material alone does not determine release force. Performance depends on the complete release-surface–butyl interface.
Why datasheet release force is not enough
ISO 29862:2024 includes a separate method for measuring the adhesion of a release liner to adhesive tape at a 180-degree angle. The standard distinguishes this measurement from tape peel adhesion to steel and from peel adhesion to the tape’s own backing. That distinction also matters in practical material qualification.
The value stated on a liner datasheet may have been measured with a specified tape or reference adhesive system. A real butyl compound has its own rheological profile, tack, cohesion and capacity to deform. These properties can influence the test result as strongly as the silicone surface.
In the 2026 study by Almara and the collaborating scientific team, the test geometry was inspired by FINAT FTM 10, but the standard tape was replaced with real butyl specimens. The authors therefore describe the result as apparent or effective separation force, rather than a standard datasheet release force. For production decisions, the relevant unit of assessment is the actual pair: the selected liner and the specific butyl compound.
Slip-stick and peel stability
Two liners can produce a similar average separation force and still perform very differently. One may deliver a smooth, stable force trace. The other may show repeated sharp rises and drops in force. This unstable pattern is known as slip-stick.
Slip-stick can cause:
- jerking during automatic liner removal,
- local deformation of the butyl compound,
- uneven material feeding,
- fibrillation and string formation,
- unstable final application.
The 2026 study evaluated the number of slip-stick peaks in addition to average separation force. Peak count is not a universal pass-or-fail limit, but it is a useful comparative indicator. It can identify liner–butyl combinations whose average force appears acceptable even though separation is unstable. For quality control, this means that a single average value does not describe the whole peel event.
Why slip-stick occurs
A butyl compound is viscoelastic. During peeling, energy is not used solely to separate two surfaces. The material may stretch, deform and form strings. When the separation front becomes unstable, stress builds and is followed by a sudden slip. Repetition of this cycle produces the characteristic force peaks.
Relevant factors include:
- cohesion and modulus of the butyl compound,
- the proportion of low-molecular-weight PIB components,
- tack and surface characteristics,
- material and ambient temperature,
- peel speed and geometry,
- silicone chemistry and degree of cure.
Studies of butyl formulations show that a composition change can affect viscosity, MVR, cohesion and peel at the same time. A liner problem should therefore not be analysed independently of the compound formulation. Changing the liner may improve performance, but in some cases the better response is to adjust the compound or process settings.
Are both sides of the liner the same
With a double-sided silicone-coated liner, identical performance on both sides should not be assumed. The 2026 study found side-to-side differences for some liner–butyl combinations. One tested liner showed high symmetry, while the performance of other liners depended on the butyl material with which they were paired.
If both sides are used in the finished roll, each side should be included in qualification. The liner orientation should also be clearly defined in process documentation so that the material is not accidentally reversed during production.
The effect of ageing and storage
A tape may perform well one day after manufacture and behave differently several months later. During storage, the interface can evolve through changes in contact, material relaxation, migration of low-molecular-weight components, changes to the silicone surface or mechanical stabilisation of the construction.
Qualification should therefore include an initial measurement and testing after controlled ageing. Comparing storage at room temperature with storage at elevated temperature is particularly useful. Test conditions should reflect the expected shelf life, logistics route and potential storage temperatures of the product.
How to qualify a liner for a new butyl tape
A practical qualification programme combines laboratory measurements with trials under real process conditions.
1 Initial screening
Test several candidate liners with the same butyl compound. Compare average separation force, stability of the force trace, the number or intensity of slip-stick events and the failure mode. Record temperature, peel speed, peel angle and contact time so that results remain comparable.
2 Test both sides
Evaluate each side of a double-sided silicone-coated liner separately. A result from one side does not demonstrate the performance of the other.
3 Ageing
Repeat the measurement after a defined time and under specified temperature conditions. The programme may include natural and accelerated ageing when their correlation has been established for the construction.
4 Surface inspection
After separation, check for compound transfer, fibrillation, migration marks, local damage and changes in the butyl surface. A force curve alone cannot reveal every failure mechanism.
5 Process validation
The final trial should use the actual application speed, web tension and product geometry. A laboratory peel test is valuable for comparing options, but it cannot reproduce every effect encountered during rewinding, die-cutting or automatic liner removal.
The lowest release force is not always best
It may seem logical to select the liner that peels away most easily. Release that is too low can cause accidental delamination during rewinding, difficulties in die-cutting, loss of construction stability and uncontrolled lifting during transport. Release that is too high can deform the compound, promote fibrillation and disrupt application.
The optimum is therefore process-specific. The liner must hold the construction securely during production and storage while still allowing stable removal under the intended conditions of use.
Conclusion
A release liner should be qualified as part of the complete material system. The most reliable approach is to test the specific butyl compound, specific liner and actual process conditions together. A datasheet is useful for selecting candidates, but it cannot replace testing of the real pair or validation on the production line.
Almara research and development support
Do you manufacture butyl tapes and experience release problems, slip-stick, compound transfer or unstable unwinding? Almara’s R&D team can help assess a specific compound in the actual liner–butyl system and develop material parameters for the requirements of your production process.