PROCESS FOR PRODUCING A THERMOPLASTIC MOULDING COMPOUND COMPRISING A THERMOPLASTIC COPOLYMER A AND A GRAFT COPOLYMER B

Abstract

The invention relates to a process for producing a thermoplastic moulding compound comprising a thermoplastic copolymer A and a graft copolymer B (4), comprising: continuously drying the dewatered graft copolymer B (4) by supplying a drying gas (3) and the dewatered graft copolymer B (4), by moving the dewatered graft copolymer B (4) through the drying gas (3) and forming a fluidized bed (5), the drying gas (3) having a feed temperature T.sub.G,feed in the range from 50? C. to 160? C., and by removing dried graft copolymer B (4) and an offgas (7), wherein i. a starting temperature T.sub.in of the fluidized bed (5) on feeding (9) of the dewatered graft copolymer B (4) is measured, ii. a finish temperature T.sub.out of the fluidized bed (5) on removal (11) of the dried graft copolymer B (4) and/or of the offgas (7) is measured, iii. a difference ?T.sub.act between the finish temperature T.sub.out and the starting temperature T.sub.in is formed and the difference ?T.sub.act is compared with a target value ?T.sub.target, and iv. the finish temperature T.sub.out is adjusted byincreasing a mass flow rate of drying gas (3) supplied and/or the feed temperature T.sub.G,feed of the drying gas (3) when the difference ?T.sub.act is smaller than the target value ?T.sub.target orreducing a mass flow rate of drying gas (3) supplied and/or the feed temperature T.sub.G,feed of the drying gas (3) when the difference ?T.sub.act is greater than the target value ?T.sub.target.

Claims

1-15. (canceled)

16. A process for producing a thermoplastic molding compound comprising at least one thermoplastic copolymer A and at least one graft copolymer B, comprising the following steps: a) precipitating the at least one graft copolymer B after an emulsion polymerization, by adding a precipitation solution; b) dewatering the precipitated graft copolymer B, affording a dewatered graft copolymer B having a water content of less than or equal to 50% by weight; c) continuously drying the dewatered graft copolymer B, wherein a drying gas and the dewatered graft copolymer B are supplied, the dewatered graft copolymer B is moved by the drying gas and a fluidized bed forms, the drying gas has an inflow temperature T.sub.G,in ranging from 50? C. to 160? C., and dried graft copolymer B and an offgas are discharged, wherein i a starting temperature T.sub.in of the fluidized bed is measured in the inflow of the dewatered graft copolymer B, ii. an end temperature T.sub.out of the fluidized bed is measured in the outflow of the dried graft copolymer B and/or of the offgas, iii. a difference ?T.sub.meas between the measured end temperature T.sub.out and the measured starting temperature T.sub.in is calculated and the difference ?T.sub.meas compared with a nominal value ?T.sub.nom, which is at least 2? C., and iv. the end temperature T.sub.out is adjusted by increasing a mass flow of supplied drying gas and/or the inflow temperature T.sub.G,in of the drying gas when the difference ?T.sub.meas is smaller than the nominal value ?T.sub.nom, or decreasing a mass flow of supplied drying gas and/or the inflow temperature T.sub.G,in of the drying gas when the difference ?T.sub.meas is greater than the nominal value ?T.sub.nom; and d) optionally mixing together the thermoplastic copolymer A, the dried graft copolymer B, optionally further polymeric component(s) C, and optionally further component(s) K.

17. The process of claim 16, wherein a fluid-bed dryer is employed for the drying in step c).

18. The process of claim 16, wherein the fluidized bed is divided into at least two subzones.

19. The process of claim 16, wherein the fluidized bed moves from an inlet of the dewatered graft copolymer B to an outlet of the dried graft copolymer B and that the end temperature T.sub.out is measured.

20. The process of claim 16, wherein the nominal value ?T.sub.nom is at least 5? C.

21. The process of claim 16, wherein the starting temperature T.sub.in ranges from 20? C. to 50? C.

22. The process of claim 16, wherein the dewatered graft copolymer B is supplied in step c) with a variable mass flow.

23. The process of claim 16, wherein the dewatered graft copolymer B is supplied in step c) with a variable water content.

24. The process of claim 16, wherein the nominal value ?T.sub.nom is constant over time.

25. The process of claim 16, wherein the dewatered graft copolymer B is supplied in step c) with a water content ranging from 5% by weight to 45% by weight, based on the dewatered graft copolymer B.

26. The process of claim 16, wherein the graft copolymer B is based on an acrylic ester-styrene-acrylonitrile copolymer or on a polybutadiene.

27. The process of claim 16, wherein the dried graft copolymer B obtained in step c) is based on an acrylic ester-styrene-acrylonitrile copolymer (ASA) and has a water content ranging from 0.05% by weight to 0.6% by weight, a total content of styrene of less than 500 ppm, and a total content of acrylonitrile of less than 100 ppm, in each case based on the dry graft copolymer B, or the dried graft copolymer B obtained in step c) is based on a polybutadiene (ABS) and has a water content ranging from 0.05% by weight to 0.8% by weight and a total content of styrene of less than or equal to 2000 ppm, in each case based on the dry graft copolymer B.

28. The process of claim 16, wherein the dewatered graft copolymer B obtained in step c) is cooled.

29. The process of claim 16, wherein the step b) of dewatering the precipitated graft copolymer B is performed by centrifugation, filtration, or a combination thereof.

30. The process of claim 16, wherein the fluidized bed is divided into at least two subzones by at least one weir.

31. The process of claim 19, wherein the end temperature T.sub.out is measured at the outlet.

32. The process of claim 16, wherein the nominal value ?T.sub.nom ranges from 5? C. to 50? C.

33. The process of claim 16, wherein the starting temperature T.sub.in ranges from 25? C. to 40? C.

34. The process of claim 16, wherein the dewatered graft copolymer B is supplied in step c) with a water content ranging from 15% by weight to 40% by weight, based on the dewatered graft copolymer B.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0240] Example embodiments of the invention are shown in the drawing and are elucidated in more detail in the description that follows.

[0241] In the FIGURE:

[0242] FIG. 1 shows a schematic representation of continuous drying in a fluid-bed dryer.

[0243] FIG. 1 shows in schematic form a continuous drying of a dewatered graft copolymer B 4 in a fluid-bed dryer 13. A drying gas 3 and the dewatered graft copolymer B 4 are supplied to the fluid-bed dryer 13, wherein the dewatered graft copolymer B 4 is moved in the fluid-bed dryer 13 by the drying gas 3 and a fluidized bed 5 forms. The angled inflow of the drying gas 3 in the illustrated embodiment results in the transport of the fluidized bed 5 in the fluid-bed dryer 13 in a horizontal direction of conveyance 27 and the discharge of an offgas 7 from the fluidized bed 5. The fluidic behavior of the fluidized bed 5 means that a vertical inflow of the drying gas 3 is alternatively also possible.

[0244] A starting temperature T.sub.in of the fluidized bed 5 is measured in an inflow 9 of the dewatered graft copolymer B 4 at an inlet 21 into the fluidized bed 5. In addition, an end temperature T.sub.out of the fluidized bed 5 is measured in the outflow 11 of the dried graft copolymer B 4 at an outlet 23 from the fluidized bed 5. The difference ?T.sub.meas between the end temperature T.sub.out and the starting temperature T.sub.in is calculated and serves as a control variable for continuous drying. The difference ?T.sub.meas is compared with a defined nominal value ?T.sub.nom and the mass flow of the supplied drying gas 3 and/or an inflow temperature T.sub.G,in of the drying gas 3 are set in accordance therewith.

[0245] In the illustrated embodiment, the fluidized bed 5 is divided into a first subzone 15 and a second subzone 17 by a weir 19. In addition, in the illustrated embodiment the second subzone 17 is adjoined by a cooling area in which a cooling gas 25 is supplied instead of the drying gas 3.

[0246] The invention is not limited to the example embodiments described herein. Rather, a large number of modifications is possible within the range specified by the claims. The invention is elucidated further by the examples, FIGURE, and claims that follow:

Examples

[0247] For the continuous drying of an ASA graft copolymer B, a fluid-bed dryer having a perforated base area of 0.24 m.sup.2 was used, to which the dewatered graft copolymer B was supplied. A drying gas having a volume flow of 8 m.sup.3/min was supplied. The average residence time of the graft copolymer B in the fluidized bed was 20 minutes. A temperature measurement was carried out in the fluidized bed both at the start and at the end of the fluid bed, i.e. at the inlet and at the outlet of the graft copolymer B.

[0248] Six examples (E) and three comparative examples (CE) are shown in Table 1. A first graft copolymer B I having a median particle diameter of 98 nm had a residual monomer content of 808 ppm before drying. A second graft copolymer B II having a median particle diameter of 550 nm had a residual monomer content of 821 ppm before drying.

TABLE-US-00001 TABLE 1 Graft copolymer B Water content Inlet Inlet T.sub.in T.sub.G, in Example [kg/h] [% by wt.] [? C.] [? C.] CE I.1 15 31 36 80 CE I.2 18 31 36 80 E I.1 15 34 36 90 E I.2 15 31 36 87 E I.3 15 31 36 93 CE II 15 36 35 85 E II.1 15 36 35 92 E II.2 15 36 35 96 Residual monomer Water content content T.sub.out ?T.sub.meas Outlet Outlet Example [? C.] [? C.] [% by wt.] [ppm] CE I.1 36 0 2 192 CE I.2 36 0 5 510 E I.1 41 5 1 <20 E I.2 41 5 1 <20 E I.3 50 14 0.7 <20 CE II 36 1 3 212 E II.1 40 5 1 <20 E II.2 50 15 0.6 <20

[0249] Unlike in the comparative examples, the content of residual monomers in the dried graft 5 copolymer B was consistently reduced to less than 20 ppm with an adequately large ?T.sub.meas, irrespective of the water content of the supplied dewatered graft copolymer B. A ?T.sub.meas here of at least 5? C. resulted in a significant reduction in the content of residual monomers and to a consistently low water content in the graft copolymer B at the outlet.

[0250] The graft copolymer B advantageously dried in this way is used with a SAN matrix, for example, to produce thermoplastic molding compounds and molded articles that have good mechanical and optical properties and no disagreeable odor.

LIST OF REFERENCE SIGNS

[0251] 3 Drying gas [0252] 4 Graft copolymer B [0253] 5 Fluidized bed [0254] 7 Offgas [0255] 9 Inflow [0256] 11 Outflow [0257] 13 Fluid-bed dryer [0258] 15 First subzone [0259] 17 Second subzone [0260] 19 Weir [0261] 21 Inlet [0262] 23 Outlet [0263] 25 Cooling gas [0264] 27 Direction of conveyance