These range from viscosity and adhesion to many different substrates, to application properties, such as pot life and cure times.
Polyurethane adhesives (PU adhesives) are polymer-based glues generally used in high strength bonding applications. Polyurethane systems used for adhesives can be separated into two main classifications, 1K (one-part) and 2K (two-part) systems, which share many similarities. All polyurethane adhesives use the same fundamental chemical reaction, this being a reaction between an isocyanate and a polyol.
For two-part systems the isocyanate and the polyol will be manufactured and supplied as separate components. For the chemical reaction to take place and fully crosslink, just prior to application, the components must be combined in the correct ratio with sufficient mixing.
For a one-part system, water needs to be present to crosslink and this can be from moisture in the atmosphere. However, for some adhesives this will be from the application of a water mist prior to the second substrate being bonded.
There are many advantages to polyurethane adhesives, and these include the following:
- Excellent adhesion to a wide range of substrates
- Cure time and pot life can be varied by formulation changes
- Good flexibility can be achieved in the cured product
- Good resistance to solvents when cured
- High resistance to water so can be used for immersed or exterior projects
- Application methods include roller, bead or spray, by manual or automatic systems
- Although they can be solvent borne, they can also be supplied solvent-free
- Heat is not required for cure, but can be used to speed up the process once both substrates are present
- Remain bonded through a wide range of operating temperatures
Advantages of a One-Part PU System
Of course, there are differences between one and two-part systems. One-component adhesives require no mixing, so application is easy. Also, they offer excellent chemical resistance. They can be solvented or solvent-free, depending on the application.
Most substrates that bond with a one-part system will also adhere with a two-part system and vice versa. Consequently, the choice of whether a user chooses a one-part or a two-part adhesive is best made by considering advice from the adhesive manufacturer and knowing the advantages and limitations of each system for a specific application.
Two-part systems are guaranteed to achieve full through-cure in a specified time, but the two components will need to be properly mixed in the correct ratio. In contrast, a one-part system may be easier to apply and require no mixing; but could require water-misting. It is important to remember that the cure time will be more affected by ambient conditions. Therefore, the desired application method of the adhesive along with any time constraints will influence which system to use.
Applications - What is Polyurethane Adhesive Used For?
Polyurethane adhesives from Chemique have been formulated to provide specific bonding properties. For example, grades are available for bonding substrates where more flexibility is necessary, right through to formulations where a harder bond line is required.
Polyurethane adhesives can be used to bond a wide variety of substrates, including metal, plastic, wood, foam and is a popular choice for panel bonding applications. This is particularly true for the manufacture of composite panels, including aluminium honeycomb panels, truck panels, cladding, SIPs panels and insulation.
Polyurethane adhesives also have a high resistance to water, making them ideal for exterior or immersed applications.
The Solfre range of laminating adhesives includes several controlled open time and cure rates to suit a variety of bonding processes.