What are two-component Polyurethane Adhesives?
Unlike one-component polyurethane adhesives, two-component solutions are comprised of a resin and a hardener, such as polyols and poly-isocyanate polymers, that must be mixed together prior to application. While the ratios of each component may vary, proper mix ratio and complete mixing are vital to causing a chemical reaction and reaching suitable properties for a specific application. 2KPU have the advantages of single component polyurethane adhesives but are able to cure more quickly through larger gaps and are not dependent on moisture or heat to cure.
Advantages of two-component polyurethane adhesives
When considering an adhesive technology, it’s important to know the advantages two-component polyurethane adhesives bring to manufacturing processes:
- Strong bonding to heighten durability.
- Better chemical resistance compared to one-component polyurethane adhesive.
- Automatic dispensing capabilities and quick cure speed to improve production efficiencies.
- Ability to cure quickly and in a definite time for an application adapted to your lean manufacturing needs.
- High versatility and optimization of mechanical properties for enhanced performance.
- Multi-substrates adhesion to increase design options.
- Environmental compatibility with recyclable or partially bio-based adhesives.
What are Bostik's innovations about two-part Polyurethane Adhesives?
Our extensive technology portfolio includes the following sustainable innovations:
Improved Recyclability Levels
We develop adhesives that promote the recyclability of packaging. For example, our innovative SF10M (A+B), dedicated to mono-material PE packaging and has Recyclass approval.
Reduced Harmful Substances
We manufacture products without harmful substances, such as BPA, Glymo and PAA (primary aromatic amines). Our aliphatic, solvent-free adhesive system, Herberts 2K-LF 760 - retortable grade, is also PAA-free.
Decreased Isocyanate Emissions and Waste Production
We also formulate innovative products that yield low isocyanate emissions to reduce environmental impact. Further, these easy-to-use and durable products enable thermoplastic and composite bonding with limited surface treatment to improve production efficiencies and reduce material usage. They also help repair plastic so that it doesn’t have to be discarded as waste.
Applications of two-component polyurethane adhesives
Two-part polyurethane is commonly used in flexible packaging. For this application, very fluid products must be laminated to film rollers. They are applied in thin layers in minimal quantities and are heated to increase their viscosity.
Herberts 2K-LF 520 with Hardener 107 is a two-component, solvent-free adhesive used in the flexible packaging market. It is designed for medium-performance applications with high bond on aluminium foil and metallized films.
Building & Construction
We also use PU2K for panels in buildings Materials. There are many formulations of polyurethane foam to optimize the density for insulation, structural sandwich panels, or architectural components. In building materials, PU2K is appreciated for its low viscosity, no solvent, and fire-retardant properties.
PU2K is widely used in general transportation and is generally mixed with a static mixer in a ratio of 1:1 (as many -OH functions as -NCO). 2KPU is often used in sandwich panels as well as mounting adhesive. In marine, they are used for the deck to hull bonding. They are appreciated for their very well-defined reactivity and their very high mechanical properties.
The main attractive features of two-component polyurethane adhesives for automotive are that they give the assembly high resistance to impacts and vibrations. They are also a great solution to bond dissimilar substrates and assemble various materials, notably metals, glass, and many thermoplastic materials and composites.
Polyurethane bi-component adhesives are mainly used for liquefied natural gas tankers. These adhesives are used for insulation layers. Their outstanding versatility and easy adjustment of mechanical properties make them ideal for this application. They are resistant to cryogenic temperatures of -170°C.
Frequently Asked Questions about 2-part Polyurethane Adhesives
Why use 3 part polyurethane adhesive instead of 2 part polyurethane adhesive in sandwich panels?
PU3K consists of 3-components with different reactivity: 2 components A (two resins with different reactivities), and one component B (hardener). An automatic system ensures ideal proportions when mixing these three components, so the reactivity of the adhesive can be regulated. PU3K is widely used for sandwich panels. It solves problems of open time control, which PU2K cannot solve. Indeed, the issue of PU2K for buildings is the dependence on panel temperature, shed temperature, humidity, etc.
PU3K adhesive is ideal for complex panels, which require multiple layers. As the layers are added, the reactivity of the adhesive can be modified. For example, you can start with the slow formula and enrich your mix with the fast formula over time. This process give you enough time to apply all the layers, guarantees a homogeneous and simultaneous crosslinking at pressing, and prevents the adhesive from crosslinking before the panel is pressed.
What are the differences in terms of applications of solvent-based 2KPU compared to solvent-free 2 part polyurethane adhesive in flexible lamination?
- For the PU2K solvent range, we use an engraved cylinder to apply the adhesive on the first substrate. This cylinder rotates in a solvent glue bath at room temperature. The filling of the engravings is done by capillarity. Then it is heated in an oven to evaporate the solvent before laminating the second substrate.
- For the PU2K solvent-free range, the adhesive is heated (from 40°C to 60°C) and applied between two rubber rollers. The adhesive is applied by transfer on the first substrate, the second substrate is applied directly (no oven required).
What are the advantages of 2-part polyurethane adhesive compared to epoxy for Liquefied Natural Gas (LNG)?
PU2Ks are less brittle than epoxy adhesives, have easily adjustable structures and mechanical properties, and have good resistance to very low temperatures.