Let's Start with the PUR Hot Melt Basics
If you're a PUR hot melt connoisseur, sorry to bore you but we're going to start simply. Polyurethane hot melt, commonly called PUR hot melt, is an adhesive that is heated and dispensed from a cartridge or slug using a heated glue gun or piece of bulk dispensing equipment.
PUR hot melts offer a number of benefits (and some drawbacks) and are used in a huge range of manufacturing and assembly applications across the world. The best way to think of a PUR hot melt is like a traditional hot melt on steroids. It is simple to dispense, cost effective and bonds to a lot of different substrates.
Where PUR Hot Melt Adhesives Are Used
Polyurethane (PUR) hot melts are used in tons of manufacturing and product assembly applications across the world and gaining steam every year. You'll find PUR adhesives in applications that require strong bonds to wood, plastics, fabrics, leather and many other materials. PUR hot melts are becoming increasingly popular because of how versatile they are. PUR can be applied as a bead or sprayed for covering large surface areas. These adhesives also come in a wide range of open times and viscosities allowing them to cater to specific application needs.
Common Applications for PUR Hot Melt
The Difference Between PUR Hot Melt and Regular Hot Melt
Traditional Hot Melt Bonds
The biggest difference between PUR hot melt and traditional hot melt is the type of bond they create. Think of a traditional hot melt bond as a wax bond. You heat it up until it becomes liquid, apply it and stick your two parts together. If you were to heat the parts back up, the hot melt would be come liquid again and you could easily take the substrates apart. This isn't to say there aren't some very strong hot melt adhesives out there, this is just how the chemistry works.
Polyurethane (PUR) Hot Melt Bonds
PUR hot melt is different than traditional hot melt. It is dispensed in very much the same way, the adhesive is heated to a liquid state and applied to your materials and cools to 'stick' them together. But...this is where PUR hot melt is special. As it cools, PUR hot melt reacts with moisture in the air and changes chemically to create an incredibly strong bond. This bond then continues to strengthen over 24-48 hours until it is fully cured and super strong.
Check out this tensile strength test between traditional hot melt adhesives and PUR hot melt adhesives:
Benefits of PUR Adhesives
Drawbacks of PUR Hot Melt
Up until this point it's been all roses and unicorns but we're here to tell you there are some drawbacks to PUR hot melts. Remember that chemical change we talked about that gives PUR its strength and durability? Well, that chemical change that makes PUR the "Andre the Giant" of hot melt adhesives also comes with some downsides.
Because PUR hot melt reacts with moisture in the air, it must also be protected from moisture before it is used. This means it has to be packaged in air tight cartridges or foil and cannot be exposed before use. It also means that PUR hot melt carries a shelf life of around 12 months (traditional hot melts have none).
PUR Hot Melt: Better Keep it Clean...
To quote Spiderman, with great bonds comes great responsibility...and a more difficult cleaning process. Large equipment used to dispense PUR must be cleaned and purged regularly with PUR cleaning material because after the adhesive sets, it is very difficult to remove. This is not as big of a problem with cartridge based PUR adhesives as there are disposable nozzles that eliminate the need to purge and clean PUR glue guns.
Drawbacks of PUR Adhesives
Using Cartridge PUR Adhesive Systems
Bulk PUR hot melt adhesives require large, industrial equipment that is expensive and difficult to maintain. More popular than ever is dispensing PUR adhesives from smaller, less expensive PUR cartridge guns. These easy to use dispensing systems are affordable, easy-to-use and aren’t tethered to bulky melters that hinder movement and application freedom. Infinity PUR cartridges are available in 50 gram and 10 ounce sizes and work with all standard cartridge guns.
50 Gram Cartridge Systems
The 50 gram cartridge system offers a low cost and simple way to dispense PUR hot melt. These systems are often used for woodworking, light product assembly and repairs.
50 Gram PUR System Benefits
10 Ounce Cartridge Systems
10 ounce PUR cartridge systems allow for higher output and more adhesive choices. The PUR applicators are more expensive but still more affordable than large bulk dispensing systems. These applicators almost connect to an air compressor allowing for effortless air-powered dispensing. 10 ounce PUR glue guns are available in both bead dispensing and spray dispensing options.
10 Ounce PUR System Benefits
Using Bulk PUR Adhesive Systems
Bulk PUR is a great option for automated or extremely high volume dispensing applications. There are equipment drawbacks in terms of cost and maintenance but also cost savings using PUR in bulk sizes. The two most common bulk PUR sizes are HOLZ-HER slugs used in edgebanding equipment and foil wrapped slugs used in high volume and automated PUR equipment. Bulk PUR can also allow for more formulation options as it is less difficult to manufacture and pack.
For HOLZ-HER Edgebanding Machines
Bulk PUR Slugs
For Bulk PUR Dispensing Systems
Just a Little More PUR Information
Congratulations on getting to the end of our complete guide to PUR hot melt adhesives. We hope this overview has been helpful and you now better understand the chemistry of PUR hot melts, applications where they are used and the benefits and drawbacks of the technology.
As always, the experts at Hotmelt.com are available to answer any questions you have on PUR hot melt adhesives. We're happy to provide product recommendations, discuss applications or provide a custom quotation based on your needs.
Related Products: Infinity Bond Flex 50 PUR Hot Melt Applicator