Polyurethane hot melt, commonly called PUR hot melt, is an adhesive that is heated and dispensed from a cartridge or slug using a heated gun or piece of bulk dispensing equipment. In comparison, traditional hot melt comes in stick or pellet form. PUR is also unique because it solidifies through moisture in the air to form a strong bond that will not re-melt.
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Because of its strength, durability, and fast set time, PUR is ideal for a wide variety of applications in woodworking, finish carpentry, shoe repair, furniture repair, broken glassware repair, laminate countertops, construction and remodeling, and more. It is also simple to dispense, cost effective and bonds to a lot of different substrates.
Polyurethane hot melt uses expand into a lot of manufacturing and product assembly applications across the world. Applications for PUR adhesives often involve strong bonds to wood, plastics, fabrics, leather and many other materials. They 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.
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, it would become 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.
PUR hot melt is different than traditional hot melt in the bonds that it forms. It is dispensed in the same way with the adhesive being heated to a liquid state for application. But 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:
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 melts 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 airtight 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).
To modify a quote from Spiderman, “With great bonds comes great responsibility.” And this responsibility is a more difficult cleaning process. Large equipment used to dispense PUR must be cleaned and purged regularly with PUR hot melt cleaner because after the adhesive sets, it is very difficult to remove. This is not as big of a problem with cartridge-based adhesives as there are disposable nozzles that eliminate the need to purge and clean them.
PUR hot melt can be dispensed either from PUR cartridge guns or from bulk equipment.Choosing what system is best for you will depend on your application and the volume being dispensed.
More popular than ever is dispensing PUR from smaller, less expensive cartridge guns. These easy-to-use dispensing systems are affordable 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.
The 50 gram PUR hot melt cartridges offer a low cost and simple way to dispense PUR. These systems are often used for woodworking, light product assembly and repairs.
10 Ounce Cartridge Systems
10 ounce PUR cartridge systems allow for higher output and more adhesive choices. The adhesive applicators are more expensive but still more affordable than large bulk dispensing systems. These applicators also connect to an air compressor allowing for effortless air-powered dispensing. They are available in both bead dispensing and spray dispensing options.
Bulk PUR hot melt adhesives require large, industrial equipment.Theyare 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 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
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For Bulk PUR Dispensing Systems
We hope this overview has been helpful and you now better understand PUR hot melts applications as well as how they are dispensed.
Polyurethane hot melts are being used more and more in industries from high volume manufacturing to DIY and home repair. This is because PUR hot melts have some amazing characteristics that appeal to a huge set of users. PUR hot melts are non-toxic, quick setting, offer great temperature and weather resistance and are affordable at any volume requirement. Here is the Complete Guide to Polyurethane PUR hot melts to answer any questions you may have about this exciting adhesive technology.
Discovered in the s in Switzerland, the PUR hot melt technology has enjoyed increasingly popularity, first across Europe, and then across the Atlantic in the U.S.A.
- A 24-hour period of curing allows the moisture in the air to react with the PUR hot melt to create the strong bond.
- PUR eliminates VOCs. The advanced technology and its chemical reaction with moisture free PUR hot melt from the need for solvents or formaldehyde—ensuring both a safer work experience and final product.
Following are key characteristics and benefits of using PUR hot melt as your go-to adhesive.
Many industries now incorporate hot melt technology into their processes. Everything from footwear to mattresses to boat construction has pivoted to gluing with PUR hot melt in order to maximize ease of use and flexibility, take advantage of temperature and moisture tolerances, and reduce labor time. Below are brief descriptions of the top four applications for PUR holt melt.
The website Canadian Woodworking & Home Improvement suggests that you “Stack and hot-glue many pieces to save time in the shop,” and “When working with small parts, use hot melt glue to fasten them to larger pieces to make machining them safer.”
The blog, Woodworking Hot Melt Essentials, helps guide you through the experience of selecting the right adhesive or the job at hand. Two top PUR products for use in woodworking are available here and here.
As our blog, How Hot Metal Molding Can Replace Traditional Epoxy in Manufacturing, states, “The advantages of low pressure hot melt molding over traditional epoxy include ease of application, the elimination of curing times and an environmentally friendly process. Hot melt molding is particularly useful within the automotive and medical device industries which require the preparation of connectors and switches that need to be sealed and protected from water and dust.”
A top PUR product for general assembly use may be found here.
The PUR hot melt technology, with its chemical reaction with moisture, has reduced or eliminated heat-related disadvantages of traditional hot melt.
PUR’s flexibility, along with its wide temperature tolerance, and water and chemical resistance ensure its effectiveness in a wide range of both indoor and outdoor environments.
Check out this tensile strength test between traditional hot melt adhesives and PUR hot melt:
Looking for a replacement for the discontinued Titebond HighPURformer line? Our Infinity PUR offers you the same formula and cartridges for ease of transition.
Your success is our business: please contact us with any questions about our products or applications.
Related Products: Infinity Bond Flex 50 PUR Hot Melt Applicator