Polyurethane adhesives are widely used in electronic potting, industrial assembly, automobile manufacturing and other fields due to their excellent adhesion, flexibility and weather resistance. However, in actual applications, some users may encounter problems such as brittle and easy cracking of the surface after curing, which not only affects the use effect but also may reduce the life of the product. This article will analyze the common reasons that cause polyurethane adhesives to become brittle from the aspects of formula, process and environment, and provide corresponding solutions.
Analysis of common causes
Formula design issues
the amount of component B added is too high, the cross-linking density increases, the hardness of the cured product increases, but the flexibility decreases significantly, which can easily cause the colloid to become brittle.
Improper use of catalysts
In order to speed up the curing process, some manufacturers will add catalysts such as organic tin. However, excessive use of catalysts will lead to too fast a reaction, and the molecular chains will begin to cross-link before they are fully extended, resulting in a rigid structure and eventually a “fast hardening and brittle” phenomenon.
Construction and environmental factors
Curing temperature is too high
High temperature environment will greatly increase the reaction speed of polyurethane, but it will also sacrifice the flexibility of the molecular chain. Especially when the recommended temperature is exceeded (such as >70°C), the colloid is prone to form a high cross-linking density structure, thus becoming brittle.
Improper surface treatment of the substrate
If there are impurities such as oil, moisture or dust on the surface of the substrate, it will not only affect the adhesion of the colloid, but may also form microbubbles or stress concentration areas during the curing process, resulting in local brittleness, falling off or cracking.
Suggestions for countermeasures
Adjust the recipe ratio
Optimizing the A/B ratio
can appropriately reduce the amount of component B, or increase the proportion of component A accordingly, thereby reducing the cross-linking density and making the cured colloid more flexible.
Optimize the catalyst system
and select catalysts with mild reaction rates (such as organic amines), or reasonably reduce the catalyst concentration and extend the curing time to allow the molecular chains to fully react to form a stable but flexible network structure.
Improve process and environmental control
Reasonable control of curing temperature
is recommended to be cured within the range of room temperature to 60°C. If the temperature is too high, cooling measures should be taken to avoid embrittlement caused by excessive reaction.
Improve the quality of surface treatment.
Before applying glue, the substrate should be thoroughly cleaned to ensure that there is no oil, moisture or dust. If necessary, surface treatment agent or plasma pretreatment can be used to enhance adhesion and avoid embrittlement and peeling caused by poor adhesion in the later stage.
Conclusion
Although surface embrittlement of polyurethane adhesive is common, it can be avoided through reasonable formula design and rigorous construction technology. Factors such as formula ratio, catalyst selection, and curing environment need to be controlled throughout the entire process to ensure the stability and reliability of product performance. If you encounter similar problems in the application of polyurethane adhesive, please feel free to contact our technical team and we can provide you with customized solutions.
