Process for producing a thermoplastic moulding compound comprising a thermoplastic copolymer A and a graft copolymer B
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 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 in of the fluidized bed ( 5 ) on feeding ( 9 ) of the dewatered graft copolymer B ( 4 ) is measured, ii. a finish temperature T 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 ΔT act between the finish temperature T out and the starting temperature T in is formed and the difference ΔT act is compared with a target value ΔT target , and iv. the finish temperature T out is adjusted by—increasing a mass flow rate of drying gas ( 3 ) supplied and/or the feed temperature T G,feed of the drying gas ( 3 ) when the difference ΔT act is smaller than the target value ΔT target or—reducing a mass flow rate of drying gas ( 3 ) supplied and/or the feed temperature T G,feed of the drying gas ( 3 ) when the difference ΔT act is greater than the target value ΔT target .
1 . 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, based on the total dewatered graft copolymer B;
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 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 in of the fluidized bed is measured in the inflow of the dewatered graft copolymer B,
ii. an end temperature T out of the fluidized bed is measured in the outflow of the dried graft copolymer B and/or of the offgas,
iii. a difference ΔT meas between the measured end temperature T out and the measured starting temperature T in is calculated and the difference ΔT meas compared with a nominal value ΔT nom , which is at least 2° C., and
iv. the end temperature T out is adjusted by
increasing a mass flow of supplied drying gas and/or the inflow temperature T G,in of the drying gas when the difference ΔT meas is smaller than the nominal value ΔT nom , or
decreasing a mass flow of supplied drying gas and/or the inflow temperature T G,in of the drying gas when the difference ΔT meas is greater than the nominal value ΔT nom ; and
d) mixing together the thermoplastic copolymer A, the dried graft copolymer B, optionally further polymeric component(s) C, and optionally further component(s) K, selected from fillers, additives, and auxiliaries.
2 . The process of claim 1 , wherein a fluid-bed dryer is employed for the drying in step c).
3 . The process of claim 1 , wherein the fluidized bed is divided into at least two subzones.
4 . The process of claim 1 , 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 out is measured.
5 . The process of claim 1 , wherein the nominal value ΔT nom is at least 5° C.
6 . The process of claim 1 , wherein the starting temperature T in ranges from 20° C. to 50° C.
7 . The process of claim 1 , wherein the dewatered graft copolymer B is supplied in step c) with a variable mass flow.
8 . The process of claim 1 , wherein the dewatered graft copolymer B is supplied in step c) with a variable water content.
9 . The process of claim 1 , wherein the nominal value ΔT nom is constant over time.
10 . The process of claim 1 , 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.
11 . The process of claim 1 , wherein the graft copolymer B is based on an acrylic ester-styrene-acrylonitrile copolymer or on a polybutadiene.
12 . The process of claim 1 , 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 acrylonitrile-butadiene-styrene (ABS) copolymer 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.
13 . The process of claim 1 , wherein the dewatered graft copolymer B obtained in step c) is cooled.
14 . The process of claim 1 , wherein the step b) of dewatering the precipitated graft copolymer B is performed by centrifugation, filtration, or a combination thereof.
15 . The process of claim 1 , wherein the fluidized bed is divided into at least two subzones by at least one weir.
16 . The process of claim 4 , wherein the end temperature T out is measured at the outlet.
17 . The process of claim 1 , wherein the nominal value ΔT nom ranges from 5° C. to 50° C.
18 . The process of claim 1 , wherein the starting temperature T in ranges from 25° C. to 40° C.
19 . The process of claim 1 , 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.