Identifying HSE & LSE Substrates – Part II
When searching for the appropriate adhesive system to create the best bond to your substrate, one of the most critical issues to determine is the surface energy of the substrate. Most substrates are classified as either High Surface Energy (HSE) or Low Surface Energy (LSE) and are categorized by their dyne levels.
To understand the concept of surface energy, simply, if you have a substrate with a slippery, heavily coated surface, adhesives have a difficult time flowing into that substrate, therefore not creating a solid bond. These substrates are considered Low Surface Energy or LSE.
If you have a non-coated, clean, or coarse surface the adhesive can flow into that substrate, therefore creating a solid bond. These substrates are considered to be High Surface Energy or HSE.
Unfortunately, this simple guide is not always enough to make a substrate determination and further testing is needed.
Determining the surface energy can be easily achieved by use of Surface Energy Test Pens and Inks also called dyne level testing.
Dyne Test Pens are a cost-effective, quick and simple method to measure surface wetting or surface energy. Dyne Pens are also called Corona Test Pens or Sherman Pens. When the Dyne level test fluid is applied to the surface, the liquid will either form a continuous film on the surface or pull back into small droplets.
HOW TO CONDUCT A DYNE PEN TEST
1. Choose a Dyne pen that you believe will be lower than the test sample
2. Press the pen tip firmly onto the sample until the tip is saturated with test fluid
3. Lightly draw the pen over the surface in 3 parallel passes each about 4 inches long, disregard the first 2 passes as they are used to flush the pen tip. Evaluate only the 3rd pass.
4. Within 3 seconds you will know if the substrate has a lower or higher level of dyne, than the pen. If the marker dissipates, into droplets, within 3 seconds the dyne level is lower.
5. If a solid line remains you have achieved a higher level of dyne.
6. The higher the dyne level, the higher the surface energy.
7. Materials with a surface energy below 36 dynes/cm are considered low surface energy and are usually more difficult to bond.
The exact surface energy, or Dyne level, can be determined by applying a range of increasing or decreasing values of Dyne Pen. Dyne Test Pens are generally available in a range of values from 30 to 72 Dynes/cm.
Dyne test fluids perform well on most non-absorbent materials. It is critical that the test fluid does not alter the surface properties of the substrate. For example, if the test fluid permeates a fiber substrate (e.g. paper) and causes swelling, results will indicate unrealistically easy wetting. A chemical reaction between the test fluid and the substrate invalidates results altogether.
TIPS TO REMEMBER
- Never use pens that are out of date or if the tip has been contaminated.
- Store your test pens at room temperature.
- Conduct your tests in a clean and level test area.
- Conduct your tests at room temperature and not in a very humid environment.
- Test in at least three different clean locations of the material sample.
- Don’t touch the area to be tested
- Never re-test in the same area