Reactive hotmelt polyurethane adhesive formulations; introduction and basic formula

Reactive hotmelt polyurethane adhesives (RHPUA) are a type of adhesive that is formulated by combining polyurethane (PU) resins and reactive hotmelt (RHM) technology. These adhesives offer a number of benefits over traditional hotmelt adhesives, including superior strength and flexibility, as well as improved resistance to temperature and chemical exposure.

The formulation of RHPUA typically begins with the selection of the appropriate PU resin. This can include polyether, polyester, or polycarbonate-based resins, depending on the specific properties and performance requirements of the adhesive. The PU resin is then combined with a reactive hotmelt (RHM) agent, which is typically a polyisocyanate or polyamine.

Once the PU resin and RHM agent have been mixed together, additional ingredients can be added to the formulation to enhance specific properties of the adhesive. For example, fillers such as talc or clay can be added to increase the strength and stiffness of the adhesive, while plasticizers can be added to improve flexibility and reduce brittleness.

In addition to these ingredients, various catalysts and stabilizers may also be included in the formulation to control the curing process and improve the stability of the adhesive. For example, catalysts such as tertiary amines or tin compounds can be used to speed up the curing process, while stabilizers such as antioxidants can be added to prevent the adhesive from degrading over time.

Once the formulation is complete, the adhesive is typically extruded or injection-molded into the desired shape, such as a film or a bead. The adhesive can then be applied to the surfaces to be bonded using various methods, such as coating, laminating, or spraying.

Overall, the formulation of RHPUA is a complex process that requires careful selection of ingredients and precise control of the curing process. However, the resulting adhesive offers a number of benefits over traditional hotmelt adhesives, including superior strength, flexibility, and resistance to temperature and chemicals.

Typical RHPUA formulation:

Ingredients:

• Polyurethane prepolymer (100 parts)
• Isocyanate curing agent (5-10 parts)
• Wax (2-5 parts)
• Pigment (1-3 parts)
• Stabilizer (0.5-1 part)
• Additive (optional, 0.5-1 part)

Instructions:

1. Mix the polyurethane prepolymer and curing agent in a mixing vessel.
2. Slowly add the wax and stir until fully incorporated.
3. Add the pigment and stabilizer and continue to stir until well mixed.
4. If desired, add any additional additives such as UV stabilizers or flame retardants.
5. Heat the mixture to a temperature of around 120-150°C and continue to stir until the adhesive becomes a homogeneous liquid.
6. Allow the adhesive to cool and solidify before use.
7. The adhesive can be applied to surfaces using a hot melt applicator or roller.
8. The adhesive will cure and harden as it cools, forming a strong bond between the surfaces.

Note: The exact formulation may vary depending on the specific polyurethane prepolymer and curing agent used, and the desired properties of the final adhesive. It is important to consult the manufacturer's instructions and conduct thorough testing before using the adhesive in any applications.

Formulating RHMPU or want to improve existing adhesive formulation, do not forget to accee the experts recommended online training on reactive PU hotmelts