Updated November 19th,
When deciding what kind of adhesive to use for your manufacturing, packaging and labeling needs, you may consider a moisture-curing polyurethane hot melt adhesive (PUR). With their high bond strength, polyurethane hot melts can be an attractive option for many different kinds of adhesive applications. However, polyurethane hot melts are not without their disadvantages as well. Let’s take a closer look at the pros and cons of using polyurethane hot melts for your particular adhesive needs.
PUR hot melt draws moisture from the substrates and the atmosphere and cures to form a bond that is stronger than most other adhesives, including water-based adhesives as well as other hot melt adhesive formulations.
Because polyurethane hot melt adhesives are applied like other hot melt adhesives, using glue guns or similar equipment, operators can quickly get up to speed on applying best practices without having to learn all new processes and equipment.
Polyurethane hot melt works quickly to form an extremely strong bond, with a fast set time. This allows you to quickly and confidently move through the manufacturing or packaging process with less concern about weak bonds or shifting substrates.
Include strength, flexibility, temperature and chemical resistance. PUR can be used in a wide range of industries and has many applications.
Unlike water-based adhesives that soak into the substrate, polyurethane hot melt adhesives stay on the surface of the materials. Because of this, a bond line can be created, which may be aesthetically unappealing or may even affect the product or packaging itself. This bond line needs to be accounted for in the production process.
Because PUR hot melt adhesive bonds quickly, it’s imperative to get the application right the first time. Less “forgiving” than other types of adhesives, polyurethane hot melt gives you a short window of time to apply the adhesive and make adjustments. Once that window is closed, the substrates aren’t going anywhere, so if you don’t get the exact result you want the first time you may need to start over.
PUR equipment is considered very specialized and comes with an additional cost, and the maintenance on the production line must be adhered to – they are not very forgiving.
PUR glue typically has a shelf life of about one year after the bottle is opened. It’s important to note that this is an average estimate and can vary based on storage conditions and specific product formulations.
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PUR glue is known for its waterproof properties. It is designed to withstand exposure to water and other liquids without losing its strength, making it an ideal choice for applications requiring moisture resistance.
The best way to clean PUR glue is to use a specific solvent designed to dissolve the adhesive. Common solvents used for this purpose include methyl ethyl ketone (MEK) and acetone
PUR glue is made by reacting two separate components: an isocyanate and a polyol. The isocyanate is usually made from either methylene diphenyl diisocyanate (MDI) or toluene diisocyanate (TDI), and the polyol can vary in chemical makeup, often being a blend of polyester or polyether.
Polyurethane glue is effective on almost all types of materials, whether porous or non-porous. However, it may not perform well on polyethylene, polypropylene, or substances like silicone or Teflon
Reactive polyurethanes – or PUR adhesives – hit the market close to a decade ago and have transformed the adhesive industry. PUR’s abbreviated moniker is PURfect for these ultra pure adhesives. Created without the use of animal byproduct or formaldehyde, PUR adhesives champion science’s ability to enhance existing elements for (literally) purer and cleaner alternatives. PUR adhesives are also stronger than many of their predecessors and are favored for their tackiness, flexibility, bond strength, ability to unite unlike substrates, and long shelf life. Many artisans prefer PUR products in the bookbinding, woodworking, packaging and electronics industries to name a few.
But what makes PUR adhesives special? Thanks to their unique synthetic makeup, PUR products tend to be more expensive than traditional hot melt adhesives. PUR hot melts are also applied in much the same way you would expect to apply traditional adhesives. PUR Glue Guns such as the 3M PUR 250 Polyurethane Glue Gun or Titebond HiPURformer PUR Glue Gun deliver the adhesive from their nozzle at a variety of temperatures, the melt cools, and you’re in business.
The real magic happens after application. PUR adhesives draw moisture from the air and substrates to create a substantially stronger bond. PUR’s unique ability to wick moisture from its surroundings gives the adhesive greater flexibility and durability. PUR products can also bond unlike surfaces and deliver superior results under a variety of temperatures or conditions. These tighter bonds are especially useful in the woodworking and bookbinding industries and many factories and craftsman now list PUR products as their adhesive of choice.
The only real drawback – if it can be called that – of PUR glues is the longer, 24-hour curing time. Although PUR adhesives become tacky shortly after application (the same way you would expect a traditional hot melt to behave), maximum strength can’t be accelerated as the glue wicks moisture away. For this reason, you might need to wait a little longer for your finished product – but the bond will be worth the wait. For this same reason, it’s important to keep PUR glues in an airtight container prior to application because contact with the air can interfere with the adhesive’s properties.
Aside from your cure time, there’s no reason to wait. PUR technology can take your adhesive projects to the next level, adding new strength and agility to your work. Because we know you won’t settle for anything less than purely the best.