For our purposes, and in the woodworking industry, PUR adhesive is a short way of saying the more descriptive term polyurethane reactive hot melt glue, it's an acronym derived from the primary ingredient and its hardening process, PolyUrethane Reactive. PUR was first used in Sweden in the 1980s and has grown in popularity over the past 30 years, starting in Europe, and then into the USA.
It is being used more and more in industries around the world to bond a wide variety of materials to each other. PUR is used to make everything from shoes, to flooring, to furniture. For Laminate Works, we'll be using it very soon in our new lamination line and edgebander. In preparation of those two capabilities coming online, we thought we'd do an in-depth look at this non-toxic, quick setting and versatile adhesive.
What's PUR made out of?
As stated above, PUR is made from polyurathane, and is a string of polymers that share similar chemistry, typically linked together by urethane (the reaction product of an isocyante and alcohol).
How does PUR work?
PUR is a reactive hot melt adhesive that's heated before processing and applied in a molten state creating an instant bond between materials as it cools. Over the next 24 hours, it builds up its green strength through a chemical reaction process. Water molecules (from the substrate and the air) then trigger the chemical reaction which transforms the adhesive into a thermosetting polymer. After complete cross-linking, reactive hot melt adhesives provide a stronger bond with a superior resistance against moisture, heat and chemicals.
The reactive groups in the adhesive will also form strong (covalent) chemical bonds with suitable reactive partners on the surface of the substrate, which significantly expands the range of adhesion.
Manufacturers provide reactive hot melt adhesives in different supply forms depending on the application and required use.
Characteristics of PUR
- It works with materials that are different from each other and achieves a high-quality bond with products that typically are difficult to bond, including nonporous materials
- It creates a strong and long-lasting bond, especially compared to water based glues or traditional hot melt glues
- It has high green strength, and depending on the type used, can bond almost instantly
- It is flexible for different uses—it can set hard or remain rubbery
- It is thermosetting and tolerates a wide temperature range and will not delaminate in extreme usage conditions or during storage
- It's easy to use and requires no mixing or measuring
- It will not shrink or curl after being set
- PUR is very efficient, using less adhesive for a strong bond over other options such as PVA
- Comes in a variety of specialized forms including 100% transparent
Advantages of PUR to a lamination based manufacturer
- Perfectly smooth application layer removes any telegraphing from the surface of the bonded material
- Dramatically increases the variety of materials that can be bonded including non-porous materials such as metal, plastic, styrofoam and even stone and marble
- Superior bond is significantly stronger than PVA or EVA glues and is nearly impossible to separate or de-laminate
- Can be used with transparent and semi-transparent materials or coatings
- Can be machined immediately, increasing manufacturing efficiency and flexibility
The future is PUR
Given the performance characteristics above and the potential materials PUR can work with, we're convinced that this technology is a superior solution for bonding panels of all types. In addition, we see PUR as a great solution for edgebanding in many cases as well. We're investing heavily in both technologies and are excited to be on the cutting edge in working with them both. We can't wait to see where it takes us as we work with our customers to develop new products and solutions for their business.