A PSA Primer
What you need to know about pressure-sensitive adhesives
Let’s talk about PSAs! Pressure-sensitive adhesive (PSA) is a non-reactive glue that bonds to a surface when pressure is applied. With PSAs, there is no need for additional agents like solvents to activate the adhesive.
When it comes to PSA options, there are so many, but it all depends on your specific needs. Before you get into the sticky of it, there’s several factors you need to consider when looking for a PSA based on your end goal. The application, substrate, desired performance, and application environment will guide which PSA option will work best for you.
Ranging from permanent to medium to removable, PSAs are sticky all the time – it is just the level of stickiness that varies.
Something else to consider when assessing PSAs are their shear and peel strength.
Shear strength refers to the weight that the adhesive can withstand in a direction parallel to the face of the substrate material. It’s the maximum shear stress that the PSA can withstand without failure. Peel strength is the average force required to separate two bonded materials. PSAs range from high to low shear and high to low peel.
A Closer Look at Permanent, Medium and Removable PSAs
Permanent PSAs are commonly used for product or packaging assembly. For example, protective packaging with foam inserts affixed to wood or corrugated containers. Tape and label manufacturers use permanent hot melt pressure-sensitive adhesive attached to a liner. Permanent PSAs have a high shear and high peel.
Medium-strength PSAs are often used for retail applications. For example, manufacturers who ship products in containers that are also used for display on the shelf want to ensure that the product labels are positioned outward. They will use a medium PSA to affix the product in the container to ensure it is correctly oriented when opened and put on display. Similarly, a multi-pack product with an outer wrapper may use a medium PSA to adhere the items together so that products don’t shift during wrapping.
Direct mail and gift card holders frequently use removable PSA. Commonly called booger glue, removable PSAs are the visible bead of glue that affixes a gift card to the card carrier. There is a wide array of removable PSA options depending on the paper and what coating is on that paper. For example, if your paper has a shiny varnish or an aqueous coating you will need a more aggressive adhesive. On the other hand, in the case of digital printing on paper with loser fibers where the ink is sitting on top of the paper, you will want a light peel.
With removable PSAs you also need to think about staining. Booger glue – hehe! – contains oil which allows the adhesive to release from the paper. If the oil seeps into the paper this results in staining. If this is a concern, have no fear! There are unique low-staining removable PSAs available.
Permanent, medium, removable. Shear and Peel. There are a LOT of variables to think about when it comes to PSAs. The experts at Chicago Glue and Machine are always here to help you find the right adhesives to meet your needs!