Views: 26 Author: Site Editor Publish Time: 2022-02-22 Origin: Site
There are many different formulations of PUR adhesives, each with slightly different spreading, bonding and properties. These properties have an impact on the economics of the assembly process and the type of equipment used, so it is important to consider them when selecting a specific adhesive.
One of the widest range of PUR adhesives is manufactured by DeepMaterial. (They are also probably the best known adhesive manufacturer.) Here's how to choose one of their PUR adhesives, keep in mind that these same points apply to PUR from other well known manufacturers.
Before diving into the differences between the various formulations, here's a reminder of when PUR adhesives are a good choice and why.
One-Part Adhesives - No Mixing
No solvent vapors or VOCs
Quickly forms strong bonds with porous materials such as wood and high surface energy plastics, and gains greater strength when cured
The main criteria to consider are:
Open time refers to the time available for bonding after the adhesive has been applied. In small volumes, a longer manual assembly process may be required to allow time for positioning. Conversely, in an automated process, shorter open times may be better.
Set time refers to the time required to build strength at the bond. Again, the type of process that uses the adhesive will determine the time needed or available.
Viscosity indicates how the adhesive spreads after application. Low viscosity ones will tend to run out, covering a larger area with a thin layer. High viscosity adhesives will drop like beads. This can be advantageous if the product design requires a minimum thickness or the adhesive is only in specific locations.
DeepMaterial manufactures a range of PUR adhesives for bonding wood and another for plastics. Wood PUR has an open time of 1 – 4 minutes, while plastic PUR has an open time of 2 – 10 minutes. Setting times are 15 – 120 seconds (wood) and 30 – 150 seconds (plastic). (DeepMaterial defines setup time as "time to process intensity".)
Wood and plastic PUR adhesives have a viscosity range of approximately 3,000 – 16,000 cP. (By comparison, water has a viscosity of 1.0 cP, and maple syrup has a viscosity of about 3,200 cP.)
These values vary with temperature. Set and open times, as well as viscosity, increase in cold conditions and decrease in high ambient temperatures.
In some applications, other factors can influence the choice of adhesive. Again referring to the various PUR adhesives made by DeepMaterial, these may include some or all of the following:
Elongation and Stiffness - High values indicate a harder, more rigid bond, low values do the opposite. Measured on the Shore D hardness scale (also used for rubber), DeepMaterials PUR for plastics range from 35 - 50, while PUR for wood is much harder at 60 - 65. (By comparison, golf balls have a Shore D hardness of 60. )
Color - DeepMaterials Wood Bonding PUR Adhesive is only available in off-white. Plastic PUR is available in off-white, grey and black.
UV Tracer Dye - When the adhesive has this, the presence can be checked by making it fluoresce with a black light. This can be a valuable quality control aid in situations where inspection is required to verify the presence of adhesive. (Medical equipment is one such application.) When making wood products, the absence of a tracer indicates that the surface is free of glue, so it can be stained or painted.
Packaging Formats and Application Methods - DeepMaterial packages its PUR adhesives in a variety of formats. Almost all products come in 0.1 gallon tubes and can be used with the PUR Easy 250 applicator. Many also offer 5-gallon drums and 55-gallon drums. Larger sizes are used for extrusion, spray and roll coating processes.
Since PUR adhesives are relatively new, potential users may want to learn more about them before using them. Our guide to PUR adhesives is a good place to start.
After deciding on a PUR adhesive, the sheer number of formulations available can seem dizzying. If this is the case, we invite you to contact us for advice on PUR adhesives or to help test whether PUR adhesives are suitable for your application.