Polyurethane (PU) adhesives are those adhesive contains -NHCOO- and/or isocyanate group (-NCO-) in molecular chain. Polyurethane adhesives have many polar groups, which can form covalent and hydrogen bonds with materials contains active hydrogen.
What are application features of polyurethane adhesives?
1. Polyurethane adhesives many polar groups, which can form covalent and hydrogen bonds with materials contains active hydrogen. That’s why it has excellent chemical adhesion with foam plastics, leather, fabric, metal, rubber, plastic and other smooth surface products.
2. By controlling the proportion of soft and hard segments in the PU molecular chain, adhesives with different hardness and elongation can be made.
3. The bonding process is simple and easy to use: it can be cured by heating or at room temperature.
4. Curing without by-products, so the adhesive layer rarely appears defects.
5. Excellent low and ultra low temperature performance. Its adhesive layer can withstand -196℃ to -253℃ low temperature environment.
6. It has good water resistance, solvent resistance and mould resistance.
What are the main categories of polyurethane adhesives? How is this adhesive made?
Single-component polyurethane adhesive:
Its main material contains isocyanate groups which can react with water in the air to form a high strength solid sealant. This process is generally called moisture curing. Although the using of single-component adhesive is convenient, but it cures slow, and there are bubbles in the curing process, which leads to decreasing of the bonding strength.
Two-component polyurethane adhesive:
It belongs to reactive curing type, which is composed of A and B components. Component A: component B = 10:1. Two-component polyurethane adhesive has the advantages of fast curing, excellent wear resistance and good weather resistance. However, this kind of polyurethane adhesive don’t have ideal heat resistance. The light polyurethane adhesive is prone to photo-aging, yellowing and fading when used in outdoor conditions.
Applications of polyurethane adhesive:
For shoe materials:
The focus of shoe industry is to reduce solvent toxicity and develop Eco-friendly PU adhesives with fast curing and high peel strength.
Automobile industry:
A large number of lightweight metals, composite materials and plastics are used into the new automobile structure. In high-grade automobiles, single-component polyurethane sealant are mainly used for Auto windshield, structural adhesive for bonding composite materials.
Building adhesives:
Two - component adhesive is mainly used in building steel plate and insulation material bonding. The bonding layer is firm and hard to deform.
How to improve the heat resistance and anti-yellowing of polyurethane adhesive?
Hindered phenolic main antioxidant & phosphite auxiliary antioxidant:
The main antioxidant mainly acts as a free radical chain termination. OMNISTAB AN1135 and OMNISTAB AN1076 can effectively improve the thermal stability of adhesives at high temperatures.
The auxiliary antioxidant mainly consists of phosphite ester and thioester compounds, which decompose hydroperoxides. OMNISTAB AN626 and OMNISTAB AN9228 are widely used as hydrolysis resistant auxiliary antioxidant in polyurethane adhesives.
UV absorbers:
In atmospheric UV light, the most sensitive wavelength of PU chain is 330-400nm. The UV energy will lead to the photooxidation degradation reaction of PU. Then the polyurethane adhesive will turn yellow and become discolored, and its mechanical properties also greatly reduce.
OMNISTAB UV571 and OMNISTAB UV326 can effectively absorb the sensitive band of polyurethane, and convert it into heat energy, thus inhibiting photooxidation degradation from the source.
If you are interested in above additives, welcome to contact our sales staff. Sincerely looking forward to your inquiry!
