Surface Energy Explained: Will a Security Label Bond and Void Correctly?

When using a tamper-evident tape or security label, it is important to know that the adhesive will bond properly and that the tamper-evident feature will activate as intended.

This can sometimes be a challenge. One tamper-evident material may adhere securely to one surface but lift away easily from another, even when both surfaces look and feel very similar.

The key difference is often surface energy.

What is surface energy?

Surface energy describes how readily the molecules on the surface of a material interact with themselves and with other molecules, such as liquids or adhesives.

This affects how easily an adhesive can spread across, or “wet out”, the surface.

Surface energy is particularly important for tamper-evident security labels because the adhesive must create a strong enough bond for the VOID, transfer or destructible mechanism to work correctly.

In adhesive applications, a higher-energy surface generally allows the adhesive to spread more easily and make close contact.

A lower-energy surface is more likely to resist that interaction.

Tamper-evident technology and surface energy: a quick answer

Higher-energy surfaces are generally easier to bond.

Low-surface-energy plastics such as polyethylene and polypropylene can be more difficult and may require a specialist adhesive.

Cleanliness, texture, temperature, pressure and dwell time can also affect the final result.

What does wet-out mean?

Wet-out describes how well a liquid, such as a pressure-sensitive adhesive, spreads across and conforms to the application surface.

Although the adhesive appears solid, application pressure helps it flow into microscopic irregularities and create a larger effective contact area.

Good wet-out does not automatically guarantee a successful security application, but poor wet-out can prevent the label from developing enough surface contact for the tamper-evident mechanism to work consistently.

How a water droplet can provide a useful guide

A simple water-drop check can give a quick visual indication on a smooth, non-porous surface.

Choose a representative area of the actual application surface, place a small droplet of clean water on it, and observe whether the droplet spreads or forms a pronounced bead.

A flatter droplet suggests better wetting, while strong beading may indicate a lower-energy or contaminated surface.

An inconsistent result across the same item may point to variations in the finish or surface cleanliness.

Better wetting

A flatter, spreading droplet suggests that the surface is easier to wet.

Poorer wetting

A pronounced bead suggests a lower-energy or potentially contaminated surface.

Use this as an indication, not an approval test

The result can be influenced by contamination, texture, coatings and temperature.

It is also unsuitable for porous materials such as paper and cardboard, where water absorption can obscure the result.

Testing the actual security material on the production surface remains essential.

Why adhesion matters to tamper evidence

An ordinary product label mainly needs to stay attached.

A security label has an additional role: it must provide a visible and preferably irreversible indication when removal is attempted.

Depending on its construction, a security label may leave a VOID message on the protected item, reveal a message within the label, separate into layers or break into fragments.

These effects rely on a controlled relationship between the adhesive, the label construction and the application surface.

If the surface bond is too weak, the whole label may lift before the tamper mechanism activates.

The label may appear to be faulty when the real issue is poor surface contact or an unsuitable adhesive.

Surface type and bonding behaviour

Higher surface energy materials include glass, stainless steel, aluminium and some polar plastics such as nylon. These are usually easier for adhesives to wet out and bond to.

Medium or variable surfaces include painted metals, ABS, cardboard and coated materials. Performance depends heavily on the finish, texture and adhesive.

Lower surface energy materials include polyethylene, polypropylene and some non-stick or silicone-treated surfaces. These are more difficult to wet out and may require a specialist adhesive.

These are broad categories rather than guarantees.

An adhesive bonds to the surface it actually touches, not necessarily the material underneath.

Paint, powder coating, varnish, mould-release agents and other treatments can therefore change the behaviour of the base material.

How surface contact affects different security materials

Different security constructions need the adhesive bond to behave in different ways.

Residue security labels are designed to leave a VOID, OPEN or transfer message on the protected item. If the surface bond is weak, the complete label may lift before the transfer layer separates.

No-residue security labels are designed to reveal a message within the label without leaving sticky residue. If the surface bond is weak, the internal VOID mechanism may not activate reliably.

Destructible vinyl labels are designed to break into fragments when removal is attempted. If the surface bond is weak, the label may peel away in one piece rather than fragmenting.

Residue security tape is designed to transfer a visible security message along a sealed surface. If the surface bond is weak, the transfer may be incomplete or inconsistent across the seal.

Security tape can be particularly demanding because one length may cross printed board, an unprinted panel and a carton seam.

Differences across those areas can affect both adhesion and the consistency of the transferred message.

What else affects security label adhesion?

Surface energy is important, but it should be considered alongside several practical factors.

Cleanliness matters because dust, oil, condensation, fingerprints and mould-release agents can prevent direct adhesive contact.

Texture can also affect performance. On a rough surface, the adhesive initially touches only the highest points, reducing the effective bonding area.

Coatings such as printing inks, varnishes, wax treatments, paint and powder coating can behave differently from the material beneath them.

Temperature is another important factor. Many pressure-sensitive adhesives become firmer when cold and may not wet out readily during application.

Application pressure also matters. Firm, even pressure across the whole label helps develop contact, particularly at the edges.

Dwell time should also be considered because the bond can continue developing after application. An immediate peel test may not represent later performance.

Curves can also create problems, as labels wrapped around small diameters experience a continuous lifting force at the edges.

Cardboard is especially variable. Recycled fibres, dust, printing, protective coatings and the strength of the outer paper layer can all influence the result.

In some cases, removal pulls away carton fibres rather than producing a clean VOID transfer. This may still provide visible evidence of interference, but it is a different tamper response.

How should an application be tested?

For unusual or security-critical applications, testing should be carried out on the exact production surface rather than a generic sample of the same material.

Apply the label to a clean, representative surface using firm, even pressure.

Test at the lowest expected application temperature where relevant.

Allow a realistic dwell period before attempting removal, ideally 24 hours where possible.

Expose samples to the expected storage or service conditions.

Remove the label at different speeds and angles.

Check whether the intended VOID, residue or fragmentation effect is clear and difficult to conceal.

The assessment should consider the complete tamper response, not simply whether the label feels sticky or is difficult to peel.

Choosing the right security label or tape

The strongest adhesive is not automatically the best choice.

A very aggressive construction may be unsuitable for a delicate or reusable surface, while a clean-removal adhesive may be inappropriate where permanent residue is required.

The correct material must balance initial tack, developed adhesion, surface compatibility, temperature, flexibility and the required tamper response.

Universeal supplies specialist adhesive formulations and bespoke security constructions for more challenging plastics, coatings, textures and operating conditions.

Need help matching a security material to your surface?

Tell Universeal about the substrate, application conditions and required tamper response.

The team can help identify suitable materials and provide samples for assessment.

Frequently asked questions

Will security labels adhere to polypropylene or polyethylene?

Security labels can be used on some polypropylene and polyethylene surfaces, but these plastics are generally more difficult to bond.

A specialist adhesive may be required, and the proposed label should be tested on the actual item.

Do security labels work on cardboard?

Yes, security labels and tapes are widely used on cardboard cartons.

However, recycled fibres, dust, inks, varnishes, water-resistant coatings and surface strength can all affect the result.

Testing should use the actual carton specification.

Why does my VOID label peel off without showing a message?

Possible causes include poor adhesive wet-out, surface contamination, insufficient application pressure, low application temperature, inadequate dwell time or an adhesive that is not compatible with the substrate.

How long should I wait before testing a security label?

The appropriate dwell time depends on the adhesive, surface and temperature.

An immediate peel test is unlikely to represent the fully developed bond.

As a minimum, allow at least 30 minutes. Ideally, leave the label for 24 hours where possible to allow the adhesive bond to develop fully.

For comparative testing, apply all samples consistently and assess them after the same realistic period.

Can a water droplet accurately measure surface energy?

A water droplet can provide a simple visual indication of wetting on a smooth, non-porous surface, but it does not provide a reliable numerical measurement.

Testing the actual security label remains the best way to assess application performance.

For more information on Surface Energy Explained: Will a Security Label Bond and Void Correctly? talk to Universeal (UK) Ltd