What is Surface Energy of Materials & Why Does it Matter?

First Published: June 25, 2023
Channel: Technology

In packaging, the surface energy of materials can be the difference between success and failure. But what is it exactly? And why does it matter so much?

For those of us in the packaging world, the surface energy of materials can determine if print sticks to the substrate, if a label successfully adheres to the product and if seals on packages have the correct level of integrity.

Surface energy, simply put, is the level of attraction between a material’s molecules and molecules of other materials around it. Molecules in the main bulk of a material have a lot of surrounding molecules to bond with; those at the surface, not so many, making them capable of bonding with molecules in other materials, such as inks and adhesives.

The higher a material’s surface energy, the easier it generally is to bond to other materials.

Why is this concept so important in industries like packaging and printing?

Adhesion: In printing and packaging, different materials need to stick together. Higher surface energy materials tend to be easier to adhere to because they’re more willing to interact with other substances (they want to find dance partners!). For example, water (a high surface energy substance) wets glass (another high surface energy substance) but beads up on waxed paper (a low surface energy material).

Ink Dispersion: Surface energy also affects how ink spreads over a material. In printing, it’s crucial that ink evenly disperses over the material to ensure a clear, high-quality print. If the surface energy of the printing substrate is too low compared to the ink, the ink may not spread evenly, resulting in poor print quality and a lack of durability.

Packaging Integrity: Ensuring a good seal between different packaging materials is crucial to maintaining product quality and safety. This seal often depends on the surface energy compatibility of the materials used. The seal may fail if the surface energies are not well-matched, leading to packaging integrity issues.

In summary, surface energy, while an invisible and often overlooked property, is vital in the packaging and printing industries. Understanding and manipulating surface energy can improve adhesion, enhance print quality, and ensure packaging integrity – ultimately resulting in better products. So next time you see a beautifully printed brochure or an excellently sealed package, remember there’s a dance of surface energy behind the scenes.

Which packaging materials have high or low surface energy?

This table shows some common packaging materials that would be classed as high or low in surface energy.

This could change, as surface treatments can adjust a material’s surface energy – indeed these methods are often used to treat materials.

High Surface Energy MaterialsLow Surface Energy Materials
GlassPolyethylene
AluminumPolypropylene
Stainless SteelPTFE (Teflon)
Polyvinyl Chloride (PVC)Silicone
PolystyreneLow Density Polyethylene (LDPE)
Polyethylene Terephthalate (PET)Fluoropolymers
PolycarbonatePolyvinylidene Fluoride (PVDF)
Paper
Corrugated Packaging
Table Showing Materials That Have High or Low Surface Energy

Techniques Used to Change the Surface Energy of Materials

Absolutely! Surface treatment is a common way to manipulate surface energy and make materials more compatible with inks and adhesives, ultimately improving the printing quality.

Corona Treatment: One of the most common methods is corona treatment, typically used on plastics. This involves exposing the surface to a high-voltage electrical discharge or corona. The high energy discharge breaks the molecular bonds on the surface of the plastic, creating more opportunities for bonding with ink or adhesive. This effectively increases the surface energy of the plastic, making it more receptive to printing or adhesion.

This method is often used to treat plastic films to make them suitable for printing n packaging applications.

Flame Treatment: Flame treatment is another useful method for treating three-dimensional objects. The flame’s heat oxidizes the material’s surface, increasing its surface energy and improving its adhesive properties. This is commonly used for objects like bottles before labeling, to ensure the labels correctly adhere to the glass surface.

Plasma Treatment: In plasma treatment, the material’s surface is exposed to a glow-discharge plasma that changes the surface properties. This can be used to clean surfaces, remove contaminants, and increase surface energy, making bonding easier for inks and adhesives. This ensures the best print quality and durability.

Chemical Treatment: Certain chemicals can be applied to a surface to alter its surface energy. A common example is applying a primer to a surface before painting. The primer has a high surface energy and provides a better surface for the paint to adhere to.

Mechanical Abrasion: Techniques like sanding or blasting a surface with particles can increase the surface area and create more opportunities for the ink or adhesive to bond with the surface.

All of these methods aim to increase the surface energy of the material, improving its compatibility with inks or adhesives. By choosing the most appropriate method based on the specific material and application, industries can greatly enhance the quality of their printing and packaging processes.

When it comes to packaging, adhesion – the ability of two different materials to stick together – is paramount. The effectiveness of adhesion depends on the surface energy of the materials involved. The general rule is that for good adhesion, the surface energy of the adhesive (like glue or ink) should be lower than the substrate’s surface energy (like the package surface).

Measuring Surface Energy

Surface energy is usually quantified in terms of dynes/cm or mJ/m^2. One way to measure it is using contact angle measurements. This involves placing a droplet of liquid onto a solid’s surface and measuring the angle which the liquid, solid, and vapor (usually air) meet. The smaller the angle, the higher the surface energy of the solid material. This measurement provides crucial information for applications like adhesion, where the surface energy of the substrate material needs to be known.

A drop of Ink on Low Surface Energy Material (Left) & High Surface Energy (Right)

Conclusion

In essence, surface energy is like the invisible hand that guides how materials behave and interact with each other, especially in the field of packaging.

Without proper understanding and control of surface energy, we would face numerous challenges in ensuring that labels stick, packages remain sealed, and print quality remains high.

So, the next time you see a beautifully printed and well-packaged product, remember the role of surface energy. It truly is a case of small details and big differences.

Further Reading

3M Science of Adhesion

Wikipedia Surface Energy

You May Also Like…