Degassing method, degassing device and use of screw elements

1. A devolatilisation apparatus comprising at least one extruder, the extruder comprising:

a barrel and n barrel holes B n having associated hole diameters D n where n is an integer,

one or more screws W n arranged concentrically in each of the barrel holes B n and configured to be rotatable within the barrel holes, wherein each screw has an axis of rotation A n and is equipped with treatment elements, the treatment elements having a cross-sectional profile orthogonal to the axis of rotation, wherein the cross-sectional profile in a circumferential direction has:

m relative maxima R m max n in respect of a radial dimension of the cross-sectional profile to the axis of rotation A n of the screw W n , where m is an integer from 1 to 8,

a maximum value R max n in respect of radial dimension of the cross-sectional profile to the axis of rotation A n of the screw W n , where R max n fulfils:

R max n <=( D n /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, and

wherein the treatment elements comprise screw elements having a pitch t, and the screw element are configured so that each of the following three conditions are met:

S1) the cross-sectional profile has at least one relative maximum R m max n based on the radial dimension of the profile curve, for which:

0.420 D n <R m max n <0.490 D n ,

S2) 1.38 D n <t<5.00 D n , and

S3) the cross-sectional profile of the respective screw element has no tangential angle β greater than 30°, on the active flanks located at the front in the direction of rotation in the range of the radial dimension from 0.95 R max to R max , where the tangential angle β is defined as

a smaller of the two angles formed on drawing 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.

2. The devolatilisation apparatus according to claim 1 , wherein:

the extruder comprises at least one of a single-screw extruder and a multiscrew extruder; and

the screw elements SE have a modular construction and comprise a core shaft and screw elements which have an accommodation opening for the core shafts or are configured as screws having a solid construction or as screws comprising individual subsegments and produced in solid construction.

3. The devolatilisation apparatus according to claim 1 , wherein n=2 to 8, and the barrel holes pass through opposite one another and are arranged parallel to one another.

4. The devolatilisation apparatus according to claim 1 , wherein n=2, and the barrel holes B n pass through and are arranged parallel to one another.

5. The devolatilisation apparatus according to claim 1 , wherein:

for R m max n , m is 2,

for S1), 0.450 D n <R m max n <0.480 D n ,

for S2), 1.90 D n <t<2.40 D n , and

for S3), the cross-sectional profile of the respective screw element has no tangential angle β greater than 10° on the active flanks located at the front in the direction of rotation in the entire range of the radial dimension from 0 to R max .

6. The devolatilisation apparatus according to claim 1 , wherein:

the extruder has at least one dispersing zone; and

the devolatilisation apparatus comprises 1 to 20 devolatilisation zones, the devolatilisation zones, in the transport direction of the extruder, define a last devolatilisation zone, and at least the last devolatilisation zone is equipped with screw elements SE.

7. The devolatilisation apparatus according to claim 6 , wherein the devolatilisation apparatus comprises 2 to 8 devolatilisation zones, at least one devolatilisation zone is located upstream of the teed zone of the extruder, and ail of the devolatilization zones are equipped with screw elements SE.

8. The devolatilisation apparatus according to claim 1 , wherein the devolatilisation openings comprise devolatilisation domes, and the devolatilisation openings and devolatilisation domes are configured for preventing or reducing exit of polymer-containing medium therethrough.

9. The devolatilisation apparatus according to claim 1 , wherein surfaces within the devolatilisation openings comprise coatings which reduce or prevent adhesion of material being devolatilised to the surface.

10. The devolatilisation apparatus according to claim 1 , wherein the extruder comprises:

one or more feed openings for the introduction of additives; and

at least one depressurisation element located upstream of at least some of the devolatilisation zones of the extruder.

11. The devolatilisation apparatus according to claim 10 , wherein the depressurisation elements comprise perforated plates, and the perforated plates are made up of a plurality of parts so that they can be taken from the barrel without removal of the screws from the barrel.

12. The devolatilisation apparatus according to claim 1 , wherein;

the screw elements SE are two-flighted or three-flighted; and

the screw elements SE have a cross-sectional profile represented completely by a profile curve which can he continually differentiated.

13. The devolatilisation apparatus according to claim 12 , wherein the screw elements SE are unsymmetrical or symmetrical.

14. The devolatilisation apparatus according to claim 1 , wherein the screw elements SE have

a longitudinal axis M*,

a core radius Rj and an outer radius R a in which each have the longitudinal axis M* as midpoint,

an outer contour A(φ)running around the longitudinal axis M*, where φ is the angle around the longitudinal axis M*, and

R j <D A ((P)<R a for a spacing D A ((p) of the outer contour A (φ) from the longitudinal axis M,

and further wherein

the outer contour A(φ) has at least one outer contour section A(Δφ) which runs along an angular section Δφ and has a continually changing spacing D A (Δφ) from the longitudinal axis M*, where Rj<D A (Δφ)<R a , and

has an associated evolute E,

which is a number of n points P(i) where i=1 to n and n>3,

where each of the points P(i) is located outside the longitudinal axis M* and within the outer radius R a , and

each two adjacent points P(i)and P(i+1) have a spacing Δr(i) from one another which is less than R j /2.

15. The devolatilisation apparatus according to claim 1 , wherein the screw elements SE are made of steel or powder-metallurgically produced metallic composites based on iron, nickel or cobalt.

16. The devolatilisation apparatus according to claim 1 , further comprising;

one or more concentrator units located upstream of the extruder; and

a devolatilisation extruder or devolatilisation kneader located upstream of the extruder.

17. The devolatilisation apparatus according to claim 16 , further comprising a transfer zone connecting the devolatilising preextruder or devolatilising prekneader and the extruder, wherein the transfer zone has at east one depressurisation element.

18. The devolatilisation apparatus according to claim 17 , wherein the transfer zone has one depressurisation element and further comprises at least one pressure regulating unit.