Imagine cast biaxially oriented polypropylene films made at lower temperatures and higher speeds with improved shrink capability. ``Designer catalysts should be able to produce resins meeting almost any reasonable set of performance criteria,'' James J. McAlpin, Michael C. Chen and Aspy K. Mehta, researchers at Exxon Chemical, claim in a paper they are scheduled to present Sept. 25 at the SPO '96 conference.
Their presentation will provide details on their development of isotactic PP resins using Houston-based Exxon's metallocene catalyst technology, and the potential uses of those resins in cast BOPP films.
``If low stretching temperature and broadened BOPP processing window is the goal, the catalyst/ product designer must broaden the molecular-weight distribution, and tacticity or composition distribution of the resins,'' the paper added.
According to the paper, Exxon achieved the development through catalyst technology devised in conjunction with Hoechst AG of Frankfurt, Germany.
SPO '96, an international business forum on specialty polyolefins, is being held Sept. 25-27 in Houston.
The Exxon researchers said they have found that the processing window for resins with broadened molecular weights compares favorably to standard PP resins made with Ziegler-Natta catalysts.
According to the researchers, the metallocene resins can be processed at temperatures as much as 27§ F lower than conventional resins.
``This suggests the possibility of a resin with step-out processability allowing significantly higher line speed and much-improved manufacturing economics,'' the researchers said.
The metallocene BOPP films survived stretching tests at temperatures nearly 36§ F below their melting points and at 54§ F below the processing temperatures of comparable conventional resins, according to the group of researchers.
However, they also noted some deficits in the resins' performance.
``It is clear that the single-site Exxpol resin is deficient in high-speed stretchability to the Ziegler-Natta control [resin],'' they said.
``This confirms the expectation that its narrow melting point and narrow molecular-weight distribution would be negative influences in some conditions,'' they added.
However, they said, tailoring resins by using the metallocene technology produces resins that provide the desired performance in stretching.