We manufacture prepolymers with an isocyanate content of 15-20% NCO using a variety of diphenylmethane-based isocyanates and polyether polyols. Business has recently picked up, and we have been asked to produce prepolymers with a low isocyanate content (~ 3%). Unfortunately, we are having problems with reproducibility. What might be causing this problem?
Since your company is making isocyanate prepolymers, you already have a fundamental understanding of the typical issues of controlling the mix ratio of isocyanate to polyol and the normal reaction temperatures used. But manufacturing low-isocyanate prepolymers (LNCO) presents special challenges. In general, it is necessary to more tightly control the entire production process. LNCOs are often used in applications that require flexibility and are frequently based on high-molecular-weight (> 4,000) difunctional polyether polyols. Raw material quality needs to be closely examined for the production of this class of isocyanate prepolymers. It is recommended that critical properties of the raw materials should be examined just before use, even if they are received within specification.