Removing odorous formaldehyde from stabilized shaped polyoxymethylenes
OwnerHelmut Doerfel, Franz Schmidt +3inventors
InventorsHelmut Doerfel, Franz Schmidt, Wilhelm Schuette, Claus Cordes, Wolfgang Schenk
Life of this patent
Estimating the term…
Abstract
Method of removing odorous formaldehyde from stabilized shaped polyoxymethylenes in which an inert gas is caused to flow over stabilized and shaped solid polyoxymethylenes at elevated temperatures not high enough to cause sticking or fusion of the polyoxymethylene, until substantially all of the volatile formaldehyde has been removed.
Claims5
In a method for removing odorous monomeric formaldehyde from stabilized polyoxymethylenes wherein a polyoxymethylene copolymer is prepared by copolymerizing formaldehyde or trioxane with comonomers selected from 1,3-dioxolane, ethyleneoxide, 1,3-dioxepane or polydioxolane, said copolymer is subjected to stabilization by incorporating antioxidants and thermostabilizers in extruders and the copolymers are converted to granules or particulate shaped articles containing from 50 to 1000 ppm of monomeric formaldehyde, the improvement comprising:
- causing an inert gas to flow over the stabilized and shaped solid polyoxymethylene at a temperature of from about 110.degree. to 140.degree. C, but more than 25.degree. C below the melting point of the polymer until the volatile formaldehyde content of the copolymer is lowered to less than 60 ppm.
Dependencies are inferred from the claim text.