what makes a self-adhesive label stick?

Our guide to choosing the best adhesive for any surface

WHAT MAKES A LABEL STICK?

WHEN LABELING, THE SURFACE MAKES ALL THE DIFFERENCE...

We talk about polar surfaces like metal and glass, and non-polar surfaces like PE and PP plastic.

TWO SURFACE TYPES

When atoms bond together as molecules, they often share electrons unequally – this creates an electric dipole. More dipoles mean greater polarity or surface energy.

WHAT DETERMINES POLARITY?

We measure surface-energy in dynes/cm.Low-energy surfaces make it harder to achieve good adhesive wet-out.

MEASURING SURFACE ENERGY

TYPICAL SURFACE ENERGIES(dynes/cm)

High-energy polar surfacesAluminium 840, Glass 250-500, Stainless steel 700-1000

Low-energy non-polar surfacesAcrylic 38, Polyethylene (PE) 31, Polypropylene (PP) 29

Wet-out is a measure of how well an adhesive flows over a surface. Successful wet-out occurs when the surface has a higher attraction to the adhesive than the adhesive has to itself.

WHAT IS WET-OUT?

GOOD ADHESIVES NEED BALANCE

Getting optimal adhesion requires an adhesive with an appropriate balance of stickiness (tack and peel) and sufficiently low surface energy relative to the surface to be labelled.

Adhesives can be modified for optimal adhesion to high- or low-energy surfaces. The adhesives we use also resist heat, water, UV light, and are environmentally friendly.

ENGINEERING ADHESIVES

MODIFICATION DEPENDS ON THE SURFACE

Labels for high-energy surfaces like glass require little adhesive modification.

Labels for low-energy surfaces like PE plastic require more adhesive modification, such as additional tackifiers and additives.

BUT IT’S NOT THAT SIMPLE...

The additives that lower the surface energy of adhesives for PE plastic also reduce cohesion.

Cohesion describes the internal strength of an adhesive – or how resistant they are to chemicals, oils, heat, and exposure to water.

To regain the internal strength (cohesion) we lose from using additives, we cross-link the polymers in the adhesive.

This locks the polymers together, increasing the adhesive’s resistance to heat, chemicals, UV-light, and water.

CROSS-LINKING INCREASES COHESION

Before

After

UV light starts a cross-linking reaction in our RC adhesives.

Our RX adhesives are catalyst activated. This results in an exceptionally high density of cross-links, which increases resistance to chemicals, UV light, and temperature.

UV AND CATALYST-ACTIVATED CROSS-LINKING

So what does this all mean when choosing an adhesive?

Durable labels require long-term resistance to heat, oils, chemicals, and mechanical stress.

That means cross-linking technology is a good choice to improve adhesive strength even when labeling a high-energy surface like metal or glass.

ADHESIVES FOR POLAR SURFACES

Non-polar surfaces like PE and PP plastic demand a more complex formulation (additives, tackifiers, and cross-linking) to ensure good bonding.

ADHESIVES FOR NON-POLAR SURFACES

UPM Raflatac offers the optimal adhesive for your labeling needs, whatever the surface.

Check www.upmraflatac.com or contact us for more information.

WE CAN HELP YOU MAKE THE BEST CHOICE