Degassing method, degassing device and use of screw elements

Devolatilisation apparatus comprising at least one extruder which has:

• a barrel and n barrel holes Bn having the associated hole diameters Dn where n is an integer, preferably an integer from 1 to 16, particularly preferably from 1 to 12, very particularly preferably from 2 to 8 and even more preferably 2, and the barrel holes in the case of n being greater than 1 preferably pass through opposite one another and are likewise preferably arranged parallel to one another,
• one or more screws Wn which can be driven so as to rotate and are in each case arranged concentrically in one of the barrel holes Bn, have an axis of rotation An and are equipped with treatment elements whose cross-sectional profile in the circumferential direction has
• m relative maxima Rmmax n in respect of the radial dimension of the cross-sectional profile to the axis of rotation An of the screw Wn, where m is an integer from 1 to 8, preferably from 1 to 4, particularly preferably 1, 2 or 3, very particularly preferably 1 or 2 and even more preferably 2,
• a maximum value Rmax n in respect of the radial dimension of the cross-sectional profile to the axis of rotation An of the screw Wn, where Rmax n fulfils:
• Rmax n<=(Dn/2)
• at least one feed zone,
• one or more devolatilisation zones comprising in each case at least one devolatilisation opening which is suitable for discharge of volatile constituents from a polymer-containing medium from the extruder,
• at least one discharge zone,
• where the extruder has screw elements SE having a pitch t as treatment elements, which are configured so that at least two of the following three conditions are met:
• S1) the cross-sectional profile has at least one relative maximum Rmmax n based on the radial dimension of the profile curve, for which:
• 0.420 Dn<Rmmax n<0.490 Dn, preferably 0.430 Dn>=Rmmax n<0.485 Dn, particularly preferably 0.440 Dn<Rmmax n<0.482 Dn and particularly preferably 0.450 Dn<Rmmax n<0.480 Dn,
• S2) 1.38 Dn<t<5.00 Dn, preferably 1.60 Dn<t<3.00 Dn, particularly preferably 1.80 Dn<t<2.50 Dn and very particularly preferably 1.90 Dn<t<2.40 Dn,
• S3) the cross-sectional profile of the respective screw element has no tangential angle β greater than 30°, preferably greater than 25°, particularly preferably 22°, very particularly preferably 15° and very particularly preferably 10°, on the active flanks located at the front in the direction of rotation in the range of the radial dimension from 0.95 Rmax to Rmax, preferably from 0.90 Rmax to Rmax, particularly preferably from 0.80 Rmax to Rmax, very particularly preferably from 0.50 Rmax to Rmax and even more preferably in the entire range from 0 to Rmax, where the tangential angle β is defined as
• the smaller of the two angles formed on drawing the tangents at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile cannot be continually differentiated
• and is 0° at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile can always be differentiated.