Process for producing ABS graft copolymers

Abstract

The invention relates to a process for producing graft copolymers based on acrylonitrile-butadiene-styrene copolymers (ABS), wherein the graft copolymers may be dewatered particularly readily after production and precipitation and have a low residual moisture content after centrifugation. The invention further relates to a process for producing thermoplastic molding materials using the thus obtained ABS graft copolymers.

Claims

1. A process for the production of a graft copolymer composition comprising: B: from 90 to 100% by weight of at least one graft copolymer B comprising: B1: from 40 to 85% by weight, based on the graft copolymer B, of at least one graft base B1 which is obtained via emulsion polymerization of: B11: from 50 to 100% by weight, based on the graft base B1, of butadiene, B12: from 0 to 50% by weight, based on the graft base B1, of at least one other monomer B12 selected from the group consisting of styrene, α-methylstyrene, acrylonitrile, methacrylonitrile, isoprene, chloroprene, C.sub.1-C.sub.4-alkylstyrene, C.sub.1-C.sub.8-alkyl (meth)acrylate, alkylene glycol di(meth)acrylate, and divinylbenzene; where the entirety of B11+B12 provides precisely 100% by weight; and B2: from 15 to 60% by weight, based on the graft copolymer B, of a graft shell B2 which is obtained via emulsion polymerization, in the presence of the at least one graft base B1, of: B21 from 50 to 95% by weight, based on the graft shell B2, of a monomer B21 selected from the group consisting of styrene and mixtures of styrene with at least one other monomer selected from the group consisting of α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8-alkyl (meth)acrylate; B22 from 5 to 50% by weight, based on the graft shell B2, of a monomer B22 selected from the group consisting of acrylonitrile and mixtures of acrylonitrile with at least one other monomer selected from the group consisting of methacrylonitrile, anhydrides of unsaturated carboxylic, acids and imides of unsaturated carboxylic acids; where the entirety of graft base B1 and graft shell B2 provides precisely 100% by weight; and K1: from 0 to 10% by weight of at least one other component K1, comprising the steps of: a) production of the graft copolymer B comprising emulsion polymerization of the graft shell B2 in the presence of the at least one graft base 131, where the graft copolymer B is obtained in the form of a latex L; b) precipitation of the latex L of the at least one graft copolymer B after emulsion polymerization via addition of at least one precipitation solution F comprising at least one salt and/or at least one acid, where a precipitation solution F1 and a portion of the latex L1 are mixed in a first container H1 at a temperature T.sub.1 in the range from 30 to 80° C., and the mixture of latex L1 and precipitation solution F1 is passed into at least two further containers H2 and H3 with temperatures T.sub.2 and T.sub.3 in the range from 60 to 130° C., where optionally further portions of the latex L2 and/or L3 and optionally further precipitation solutions F2 and/or F3 are added, where the volume V.sub.1 of the first container H1 is less than or equal to 30% of the volume V.sub.2 of the second container H2; c) mechanical dewatering of the precipitated graft copolymer B from step b), where an extracted serum S and a graft copolymer B are obtained, where the residual moisture content of the graft copolymer B is less than or equal to 25% by weight; and d) optionally drying of the dewatered graft copolymer B from step c).

2. The process of claim 1, wherein the process comprises the step of: d) drying of the dewatered graft copolymer B from step c), where a graft copolymer powder is obtained with residual moisture content less than or equal to 5% by weight.

3. The process of claim 1, wherein the volume V.sub.1 of the first container H1 is from 0.1 to 10% of the volume V.sub.2 of the second container H2.

4. The process of claim 1, wherein the first container H1 is a flow tube.

5. The process of claim 1, wherein the temperature T.sub.2 in container H2 is higher than the temperature T.sub.1 in container H1 by at least 10° C.

6. The process of claim 1, wherein the temperature T.sub.2 in container H2 is lower than the temperature T.sub.3 in container H3 by at least 10° C.

7. The process of claim 1, wherein the temperature T.sub.1 in container H1 is in the range from 40 to 60° C., the temperature T.sub.2 in container H2 is in the range from 61 to 84° C., and the temperature T.sub.3 in container H3 is in the range from 85 to 100° C.

8. The process of claim 1, wherein the precipitation solution F comprises at least one salt selected from the group consisting of magnesium sulfate, calcium chloride, and sodium chloride, and/or at least one inorganic acid.

9. The process of claim 1, wherein the precipitation solution F comprises a portion S.sub.R of the serum S extracted in step c).

10. The process of claim 1, wherein the average residence time t.sub.1 of the mixture of latex L and precipitation solution F in container H1 is in the range from 1 to 1000 seconds.

11. The process of claim 1, wherein the average residence time of the mixture of latex L and precipitation solution F in the containers H2 and H3 is respectively in the range from 5 to 60 min.

12. The process of claim 1, wherein the graft copolymer B is a mixture of at least two graft copolymers B-I and B-II, where graft copolymer B-I is obtained via emulsion polymerization of a mixture of the monomers B21 and B22 in the presence of a graft base B1-A, the average particle diameter D.sub.50 of which is in the range from 230 to 330 nm, and of a graft base B1-B, the average particle diameter D50 of which is in the range from 340 to 480 nm; and graft copolymer B-II is obtained via emulsion polymerization of a mixture of the monomers B21 and B22 in the presence of a graft base B1-C, the average particle diameter D50 of which is in the range from 10 to 220 nm; where the mixture of the graft copolymers B-I and B-II is used in step b) as latex L and is precipitated via the addition of the at least one precipitation solution F.

Description

DESCRIPTION OF THE FIGURE

(1) FIG. 1 is a flow diagram of a possible embodiment of the invention. A precipitation solution F1′ and a portion L1 of the graft copolymer latex are added to the first precipitation container H1 with volume V.sub.1 and temperature T.sub.1.

(2) The mixture from container H1 (precipitated or preprecipitated graft copolymer latex) is passed into the second precipitation container H2 with volume V.sub.2 and temperature T.sub.2. The mixture from container H2 (precipitated graft copolymer latex) is passed into the third precipitation container H3 with volume V.sub.3 and temperature T.sub.3.

(3) A portion S.sub.A of the serum (or mother liquor) extracted during the dewatering in step c) is discharged, and a portion S.sub.R of said serum is returned. Various fractions S1, S2 and S3 of the returned fraction of the serum S.sub.R can be introduced into the containers H1, H2 and/or H3. It is moreover possible to add fresh electrolyte solution (precipitation solution) F1′, F2′ or F3′ comprising at least one acid and/or one salt into the containers H1, H2 and/or H3. It is moreover possible first to mix the returned serum portion S1 with the fresh precipitation solution F1′ (broken-line arrow) before adding same to the latex L1 in container H1. This applies equally to S2/F2′ and S3/F3′ and to the containers H2 and H3.

(4) The portion L1 is preferably at least 90% by weight of the total quantity of the latex L (graft copolymer B after the emulsion polymerization). It is equally preferable that the portion L1 is 90% by weight and that L2 is 10% by weight of the total quantity of the latex L.

(5) The invention is explained further via the examples and claims that follow.

EXAMPLES

Example 1—Production of the ABS Rubbers (Graft Copolymer B)

(6) 1.1 Emulsion Polymerization

(7) Graft Polymer B-I-a

(8) 30 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex with average particle diameter D.sub.50 299 nm and gel content 60% by weight, produced with use of a polybutadiene seed latex with average particle diameter D.sub.50 113 nm via free-radical emulsion polymerization, and 30 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex with average particle diameter D.sub.50 371 m and gel content 82% by weight, produced with use of a polybutadiene seed latex with average particle diameter D.sub.50 113 nm via free-radical emulsion polymerization were mixed and brought to solids content about 27% by weight with deionized water.

(9) The mixture of the polybutadiene latices was heated to 60° C. and 0.5 part by weight of potassium peroxodisulfate (dissolved in water) was admixed therewith. 40 parts by weight of a monomer mixture made of 73% by weight of styrene, 27% by weight of acrylonitrile and 0.1 part by weight of tert-dodecyl mercaptan were then added uniformly within 6 hours. In parallel with the above, 1 part by weight (calculated as solid substance) of the sodium salt of a resin acid mixture (dissolved in alkalinified water) was added over a period of 6 hours. During the course of the 6 hours, the reaction temperature was raised from 60° C. to 80° C. Once all of the additions had ended, reaction was continued for 2 hours at 80° C. The graft latex was then cooled to room temperature. The solids content of the graft copolymer latex was 34.9% by weight, determined gravimetrically (drying in convection drying oven at 180° C. for 23 minutes).

(10) Graft Copolymer B-I-b

(11) A mixture of polybutadiene latices was produced as described for B-I-a.

(12) 40 parts by weight of a monomer mixture of 75% by weight of styrene and 25% by weight of acrylonitrile was added within a period of 4 hours to the mixture of polybutadiene latices. With start of the monomer addition, 0.14 part by weight of tert-butyl hydroperoxide and 0.14 part by weight of sodium ascorbate were added as initiator over a period of 9 hours; at the same time, 1.7 parts by weight (calculated as solid substance) of the sodium salt of a resin acid mixture (dissolved in alkalinified water) were added over a period of 6 hours. Over the course of the first 6 hours the reaction temperature was raised from 60° C. to 80° C.

(13) After the end of initiator addition, the reaction was continued for one hour at 80° C. The graft latex was then cooled to room temperature. The solids content of the graft copolymer latex was 35.0% by weight, determined gravimetrically (drying in convection drying oven at 180° C. for 23 minutes).

(14) Graft copolymer B-II

(15) 50 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex with average particle diameter D.sub.50 113 nm and with gel content 91% by weight, produced with use of a polybutadiene seed latex with average particle diameter D.sub.50 49 nm via Free-radical seed polymerization, were brought to about 27% by weight solids content with deionized water.

(16) The polybutadiene latex was heated to 60° C., and 0.5 part by weight of potassium peroxodisulfate (dissolved in water) was admixed therewith. 50 parts by weight of a mixture of 73% by weight of styrene, 27% by weight of acrylonitrile and 0.1 part by weight of tert-dodecyl mercaptan were added uniformly within 6 hours. In parallel with the above, 1 part by weight (calculated as solid substance) of the sodium salt of a resin acid mixture (dissolved in alkalinified water) was added over a period of 6 hours. During the course of the 6 hours, the reaction temperature was raised from 60° C. to 80° C. Once all of the additions had ended, reaction was continued for 2 hours at 80° C. The graft latex was then cooled to room temperature. The solids content of the graft copolymer latex was 35.2% by weight, determined gravimetrically (drying in convection drying oven at 180° C. for 23 minutes).

(17) Graft Copolymer B-III

(18) 60 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex with average particle diameter D.sub.50 330 nm and with gel content 85% by weight were brought to about 28% by weight solids content with deionized water and heated to 60° C.

(19) 40 parts by weight of a monomer mixture consisting of 74% by weight of styrene and 26% by weight of acrylonitrile, and also 0.4 part by weight of tert-dodecyl mercaptan and 0.4% by weight of the sodium salt of a resin acid mixture (dissolved in alkalinified water) were uniformly added within 3 hours. The graft polymerization of the monomers onto the graft base was carried out by using 0.005 part by weight of iron(II) sulfate heptahydrate, 0.22 part by weight of dextrose, 0.17 part by weight of sodium diphosphate decahydrate, and also 0.11 part by weight of cumene hydroperoxide. The temperature here was raised within 4 hours from 60° C. to 72° C., and kept at 70° C. for a further 2 hours. The reaction mixture was then cooled to 55° C. within 1.5 hours. The graft latex was then cooled to room temperature. The solids content of the graft copolymer latex was 35.1% by weight, determined gravimetrically (drying in convection drying oven at 180° C. for 23 minutes). 0.25% by weight of phenolic antioxidant and 0.25% by weight of thiolic antioxidant were admixed with the dispersion.

(20) 1.2 Precipitation of the Graft Copolymers B after Emulsion Polymerization by Mixing of the Precipitate Solution F (Electrolyte Solution) with the Graft Copolymer Latices L.

Example 1A (of the Invention)

(21) The graft copolymers B-I-a and B-II (in the form of latices) were mixed by stirring in the ratio 60%:40%, calculated as solid. 1.0% by weight of a phenolic antioxidant (Irganox 1076, BASF SE), based on the total solids of the graft copolymer mixture B-I-a and B-II, was added in the form of a dispersion to the said mixture, and mixed.

(22) This mixture and a precipitation solution F (electrolyte solution) described below were continuously mixed in the container H1 at a temperature of from 45 to 50° C. The temperature of the graft copolymer mixture here is about 30 to 35° C. and the temperature of the electrolyte solution here is about 60 to 68° C. The following streams were continuously added here to the container H1 and thus mixed: 100 parts by weight per hour of the graft copolymer mixture B-I and B-II in the form of 35.0% by weight latex precipitation solution F-I (electrolyte solution) consisting of a mixture of 75 parts by weight per hour of returned serum fraction S-I (cf. S1 in FIG. 1); 2.8 parts by weight per hour of an 18% by weight aqueous magnesium sulfate solution and 0.51 part by weight per hour of a 15% by weight aqueous sulfuric acid solution

(23) The mixture from container H1 was passed into a second container H2. The temperature in the precipitation container H2 was kept at 94° C. (product temperature of the precipitated graft copolymer dispersion) by feeding steam into the precipitation container H2. No further precipitation solution and no further latex L were passed into container H2. The mixture from container H2 was passed into a third container H3. The temperature in the precipitation container H3 was 92° C. No substances other than the continuous feed from the precipitation container H2 were added to the precipitation container H3.

(24) The volume of the container H1, configured as tube, was 2.0% of the volume of the precipitation container H2; the container H1 was 100% filled.

(25) The average residence time t.sub.1 in the container H1 was 30 seconds (s). The average residence time in the containers H2 and H3 was respectively 21 minutes; each of the containers was 85% filled.

(26) There was a further container H4 downstream, which comprised a continuously operated circuit with a spiral heat exchanger, with the aid of which the product temperature of the precipitated graft copolymer dispersion was kept at 70° C. The average residence time in the container H4 was 21 minutes (min).

(27) The containers H2 to H4 had stirrers with which the contents were continuously mixed.

(28) The precipitated graft copolymer was isolated from the serum S by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 511 g (where g is average acceleration due to gravity) for a period of 26 seconds, thus giving a water-moist graft copolymer B with residual moisture content 21.2% by weight.

(29) Residual moisture content is defined as the proportion of water in a water-moist mixture. Residual moisture content RMC was determined gravimetrically by drying a sample weighing about 2.5 g at 180° C. to constant weight, or at most for 10 minutes.

(30) The water-moist graft copolymer was dried in a pneumatic dryer. Grain size D.sub.50 [mm], bulk density [kg/L] and residual moisture content after drying were determined. Grain size D.sub.50 was measured by sieve analysis in accordance with ISO 3310-1 with the following sieves 63, 100, 150, 200, 300, 500, 800 and 2000 μm.

(31) A portion of the serum (returned serum S.sub.R) was returned as described above to the process. The serum comprised 768 mg/L of total organic carbon (TOC). The serum fraction S.sub.A not returned to the precipitation process was sent for disposal as wastewater and requires treatment to reduce the TOC loading.

Example 1B (not of the Invention)—without Container H1

(32) The precipitation of a mixture of the graft copolymer latices B-I-a and B-II (60:40) was carried out in a manner similar to that of example 1A, but without the container H1. The precipitation solution F-I and the graft copolymer latices were added separately by way of separate lines to the precipitation container H2. All of the other precipitation parameters, for example temperatures, flow rates and residence times, were the same as in example 1A.

(33) The precipitated graft copolymer was substantially isolated from the serum S by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 581 g (where g is average acceleration due to gravity) for a period of 67 seconds, thus giving a water-moist graft copolymer B with residual moisture content 27.1% by weight. This material was dried as described in example 1A in a pneumatic dryer.

Example 1C (of the Invention)

(34) The precipitation was carried out fundamentally in the same way as in example 1A, but with a higher temperature of from 50 to 55° C. in precipitation container H1, a lower temperature in precipitation container H2 (86° C.) and a higher temperature in precipitation container H3 (94° C.). The further treatment likewise took place as described in example 1A.

Example 1D (of the Invention)

(35) The precipitation was carried out fundamentally in the same way as in example 1A, but with a higher temperature in the precipitation container H1 (50-55° C.), a lower temperature in precipitation container H2 (78° C.) and a higher temperature in precipitation container H3 (94° C.). The further treatment likewise took place as described in example 1A.

Example 1E (of the Invention)

(36) The precipitation was carried out fundamentally in the same way as in example 1A, but with a higher temperature in precipitation container H1 (50-55° C.), a lower temperature in precipitation container H2 (70° C.) and a higher temperature in precipitation container H3 (94° C.). The further treatment likewise took place as described in example 1A.

Example 1F (of the Invention)

(37) The precipitation was carried out fundamentally in the same way as in example 1A, but 0.23 part by weight per hour of a 50% by weight aqueous acetic acid solution (precipitation solution F-II) was used instead of 0.51 part by weight per hour of a 15% by weight aqueous sulfuric acid solution. The further treatment likewise took place as described in example 1A.

(38) The graft copolymer is substantially isolated from the serum by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 581 g (where g is average acceleration due to gravity) for a period of 33 seconds, thus giving a water-moist graft copolymer B with residual moisture content 21.0% by weight.

(39) The water-moist graft copolymer is dried in a pneumatic dryer. Grain size D.sub.50 [mm], bulk density [kg/L] and residual moisture content after drying were determined.

(40) The serum S comprised 1220 mg/L of total organic carbon (TOC). The serum fraction S.sub.A not returned to the precipitation process was sent for disposal as wastewater and requires treatment to reduce the TOC loading.

Example 1G (not of the Invention): Higher Temperature in Precipitation Container H1 (94° C.)

(41) The graft copolymers B-I and B-II (latices) were mixed by stirring in the ratio 60:40, calculated as solids. The method was analogous to that of example 1A. The graft copolymer mixture B-I and B-II and the precipitation solution F-I (electrolyte solution) were mixed continuously in the container H1 at a temperature of 94° C. For this it was necessary to heat the graft copolymer mixture to a temperature of about 94° C. and likewise to heat the precipitation solution to a temperature of about 94° C. However, this procedure proved to be disadvantageous because heating of the graft copolymer mixture produced small quantities of coagulate which rapidly led to latex-metering problems and to instability in conduct of the experiment and finally to termination of the experiment. The measured values presented in table 1 were determined on samples taken before termination. Instead of drying in the pneumatic dryer, the moist powder obtained before termination was dried for 2 days at 70° C. in a laboratory drying oven. The significantly larger grain size D.sub.50, 0.8 mm, proved to be disadvantageous in comparison with the example 1A; this size, and the longer drying time associated therewith, are rather unsuitable for drying in a pneumatic dryer.

Example 1H (not of the Invention)—Nature and Size of Container H1

(42) The method was analogous to that of example 1A, but a container H1 was used which was the same as container H2 in form and function, i.e. container H1 in this case was a stirred container with fill level 85% and average residence time 21 minutes. The temperature in the container H1 was 50° C.

(43) The temperatures at which the graft copolymer mixture and the precipitation solution were used were the same as in example 1A. However, this procedure proved to be very disadvantageous because after only a very short period of operation a large quantity of coagulate accumulated on the stirrer of the container H1, and led to termination of the experiment. It was impossible to obtain any representative examples for analyses.

Example 1I (not of the Invention)—Graft Polymer B-III/without Container H1

(44) 42.8 parts by weight of the graft copolymer latex B-III were precipitated with 57.2 parts by weight of precipitation solution F-III consisting of 0.78% by weight sulfuric acid.

(45) The streams were mixed continuously in the container H2 at a temperature of 70° C. Two further containers H3 and H4 (with the same shape and size as H2) were installed downstream. The temperature in the precipitation container H3 was 81° C., and the temperature of the container H4, through which the product finally passed, was 82° C. No substances other than the continuous feed from the precipitation container H2 were added to the precipitation container H3. The average residence time in the containers H2, H3 and H4 was respectively 15 minutes, the containers being respectively 85% filled.

(46) There was a further container H5 installed downstream which comprised a continuously operated circuit with a spiral heat exchanger, with the aid of which the temperature of the precipitated graft copolymer dispersion was kept at 70° C.

(47) The graft copolymer was substantially isolated from the serum by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 447 g (where g is average acceleration due to gravity) for a period of 46 seconds, thus giving a water-moist graft copolymer B with residual moisture content 31.4% by weight. The water-moist graft copolymer B was dried in a pneumatic dryer. Grain size D.sub.50 [mm], bulk density [kg/L] and residual moisture content after drying were determined.

Example 1J (of the Invention)

(48) The precipitation is carried out as in example 11, but the streams of the graft copolymer latex B-III and of the precipitation solution F-III were mixed in the container H1, which was configured as tube. The volume of the container H1 was 0.8% of the volume of the precipitation container H2; the container H1 was 100% filled. The temperature in precipitation container H1 was 60° C. The average residence time t.sub.1 in H1 was 9 seconds, and in H2 to H4 it was respectively 15 minutes.

(49) The precipitated graft copolymer was substantially isolated from the serum by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 447 g (where g is average acceleration due to gravity) for a period of 46 seconds, thus giving a water-moist graft copolymer B with residual moisture content 20.1% by weight. The water-moist graft copolymer B was dried in a pneumatic dryer. Grain size D.sub.50 [mm], bulk density [kg/L] and residual moisture content after drying were determined.

Example 1K (of the Invention)

(50) The precipitation was carried out as in example 1J, except that the temperature in precipitation container H1 is 50° C.

(51) The precipitated graft copolymer B was substantially isolated from the serum by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 447 g (where g is average acceleration due to gravity) for a period of 46 seconds, thus giving a water-moist graft copolymer B with residual moisture content 20.1% by weight. The water-moist graft copolymer B was dried in a pneumatic dryer. Grain size D.sub.50 [mm], bulk density [kg/L] and residual moisture content after drying were determined.

Example 1L (of the Invention)

(52) The graft copolymers B-I-a and B-I-b (in the form of latices) were mixed by stirring in the ratio 25%:75%, calculated as solid. 1.0% by weight of a phenolic antioxidant (Irganox 1076, BASF SE), based on the total solids of the graft copolymer mixture B-I-a and B-I-b, was added in the form of a dispersion to said mixture, and mixed.

(53) This mixture and the precipitation solution F-IV (electrolyte solution) described below were continuously mixed in the container H1 at a temperature of from 45 to 50° C. The temperature of the graft copolymer mixture here is about 30 to 35° C. and the temperature of the electrolyte solution here is about 60 to 68° C. The following streams were continuously added here to the container H1 and thus mixed: 100 parts by weight per hour of the graft copolymer mixture B-I-a and B-I-b in the form of 35.0% by weight latex precipitation solution F-IV (electrolyte solution) consisting of a mixture of 45 parts by weight per hour of returned serum fraction S-IV (cf. S1 in FIG. 1); 3.0 parts by weight per hour of an 18% by weight aqueous magnesium sulfate solution and 0.65 part by weight per hour of a 15% by weight aqueous sulfuric acid solution

(54) The mixture from container H1 was passed into a second container H2. The temperature in the precipitation container H2 was kept at 94° C. (product temperature of the precipitated graft copolymer dispersion) by feeding steam into the precipitation container H2. The mixture from container H2 was passed into a third container H3.

(55) The temperature in the precipitation container H3 was 92° C. No substances other than the continuous feed from the precipitation container H2 were added to the precipitation container H3.

(56) The volume of the container H1, configured as tube, was 2.0% of the volume of the precipitation container H2; the container H1 was 100% filled. The average residence time t.sub.1 in the container H1 was 30 seconds (s). The average residence time in the containers H2 and H3 was respectively 21 minutes; each of the containers was 85% filled.

(57) There was a further container H4 downstream, which comprised a continuously operated circuit with a spiral heat exchanger, with the aid of which the product temperature of the precipitated graft copolymer dispersion was kept at 70° C. The average residence time in the container H4 was 21 minutes.

(58) The containers H2 to H4 had stirrers with which the contents were continuously mixed.

(59) The precipitated graft copolymer was isolated from the serum S by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 378 g (where g is average acceleration due to gravity) for a period of 32 seconds, thus giving a water-moist graft copolymer B with residual moisture content 22.6% by weight.

(60) The water-moist graft copolymer was dried in a pneumatic dryer. Grain size D.sub.50 [mm], bulk density [kg/L] and residual moisture content after drying were determined.

Example 1M (not of the Invention)—without Container H1

(61) The precipitation of a mixture of the graft copolymer latices B-I-a and B-I-b (25:75) was carried out in a manner similar to that for example 1L, but without the container H1. The precipitation solution F-IV and the graft copolymer latices were added separately by way of separate lines to the precipitation container H2. All of the other precipitation parameters, for example temperatures, flow rates and residence times, were the same as in example 1L.

(62) The precipitated graft copolymer was substantially isolated from the serum S by batch centrifuging by a scraper centrifuge at a temperature of 70° C. and with centripetal acceleration a.sub.z 567 g (where g is average acceleration due to gravity) for a period of 85 seconds, thus giving a water-moist graft copolymer B with residual moisture content 27.5% by weight. This material was dried as described in example 1L in a pneumatic dryer.

(63) Table 1 collates the experimental conditions, and also the values of grain size D.sub.50 [mm], the bulk densities [kg/L] and the residual moisture contents after drying and after centrifuging for examples 1A to 1K. The following symbols are used here:

(64) TABLE-US-00001 V1 Volume of container H1 in % relative to V.sub.2 (volume of container H2) T1 Temperature in container H1 T2 Temperature in container H2 T3 Temperature in container H3 T4 Temperature in container H4 T5 Temperature in container H5 t.sub.1/t.sub.2/t.sub.3/t.sub.4/t.sub.5 Average residence times in the containers H1/H2/H3/H4/H5 F-I Precipitation solution in example 1A F-II Precipitation solution in example 1F F-III Precipitation solution in example 1I F-IV Precipitation solution in example 1L RMC Residual moisture content in % by weight D.sub.50 Grain size D.sub.50 of graft copolymer B after drying in mm BD Bulk density of graft copolymer B after drying in kg/L a.sub.z Centripetal acceleration G Average acceleration due to gravity t.sub.c Centrifuging time n.p. Not present n.d. Not determinable

(65) From table 1 it can be seen that examples 1A of the invention with use of a first precipitation container H1 with T.sub.1 below 80° C. in the form of a flow tube with a volume of 2% of the volume of the subsequent container H2 (i.e. V.sub.1=0.02*V.sub.2) exhibits significantly lower residual moisture content after centrifuging than example 1B without container H1.

(66) Although example 1B not of the invention was centrifuged at higher rotation rate and with longer centrifuging time than example 1A, the graft copolymer 1A exhibits significantly lower residual moisture content.

(67) A particularly low residual moisture content after centrifuging is obtained when the temperature T.sub.1 in precipitation container H1 rises and the temperature T.sub.2 in the second precipitation container H2 falls, see examples 1C to 1E. A temperature T.sub.1 above 90° C. in the first container (example 1G) proved to be disadvantageous.

(68) Comparison of example 1F with example 1A reveals that the result obtained using acetic acid in the precipitation solution is good and comparable with that obtained using sulfuric acid. However, use of sulfuric acid in the precipitation is more advantageous than use of acetic acid, because sulfuric acid gives rise to a significantly lower TOC value in the wastewater, while being equally suitable for the purpose.

(69) If the volume V.sub.1 of the first container H1 is selected to be exactly the same as the volume V.sub.2 of the subsequent container H2 (example 1H), disadvantageous results are obtained, i.e. it is impossible to carry out the precipitation.

(70) From table 1 it can moreover be seen that the examples 1J and 1K of the invention (precipitation of graft copolymer B-III) have lower residual moisture content after centrifuging and are therefore more amenable to dewatering than the comparable example 1I not of the invention.

(71) From table 1 it can moreover be seen that the example 1L of the invention (precipitation of graft copolymer B-I-a/B-I-b) has lower residual moisture content after centrifuging and is therefore more amenable to dewatering than the comparable example 1M not of the invention.

(72) TABLE-US-00002 TABLE 1 Summary of results of examples 1A to 1F Example 1A 1B 1C 1D 1E 1F Unit Of the Of the Of the Of the Of the invention Comparison invention invention invention invention V.sub.1 [% relative to 2 n.p. 2 2 2 2 V.sub.2] T.sub.1 [° C.] 45-50 n.p. 50-55 50-55 50-55 45-50 T.sub.2 [° C.] 94 94 86 78 70 94 T.sub.3 [° C.] 92 92 94 94 94 92 T.sub.4 [° C.] 70 70 70 70 70 70 t.sub.1 [s] 30 n.p. 30 30 30 30 t.sub.2/t.sub.3/t.sub.4 [min] 21 21 21 21 21 21 Graft copolymer B-I-a/ B-I-a/ B-I-a/ B-I-a/ B-I-a/ B-I-a/ B-II B-II B-II B-II B-II B-II Precipitation F-I F-I F-I F-I F-I F-II solution a.sub.z [g] 511 581 511 511 511 581 t.sub.c [s] 26 67 26 26 26 33 RMC (after [% by 21.1 27.1 20.4 19.8 19.2 21.0 centrifuging) wt.] D.sub.50 [mm] 0.4 0.4 0.4 0.4 0.4 0.4 BD [kg/L] 0.42 0.40 0.43 0.43 0.44 0.42 RMC (after [% by 0.95 0.87 0.75 0.82 0.66 0.8 drying) wt.] Summary of results of examples 1G to 1K Example 1G 1H 1I 1J 1K 1L 1M Unit Of the Of the Of the Comparison Comparison Comparison invention invention invention Comparison V.sub.1 [% 2 100 n.p. 0.8 0.8 2 n.p. relative to V.sub.2] T.sub.1 [° C.] 94 50 n.p. 50 60 45-50 n.p. T.sub.2 [° C.] 94 94 70 70 70 94 94 T.sub.3 [° C.] 92 92 81 81 81 92 92 T.sub.4 [° C.] 70 70 82 82 82 70 70 T.sub.5 [° C.] n.p. n.p. 70 70 70 n.p. n.p. t.sub.1 [s] 30 21 n.p. 9 9 30 30 t.sub.2/t.sub.3/t.sub.4 [min] 21 21 15 15 15 21 21 Graft copolymer B-I-a/ B-I-a/ B-III B-III B-III B-I-a/ B-I-a/ B-II B-II B-I-b B-I-b Precipitation F-I F-I F-III F-III F-III F-IV F-IV solution a.sub.z [g] 511 n.d. 707 707 707 378 567 t.sub.c [s] 26 n.d. 46 46 46 32 85 RMC (after [% by 21.0 n.d. 31.4 20.1 20.3 22.6 27.5 centrifuging) wt.] D.sub.50 [mm] 0.8 n.d. 0.35 0.32 0.33 0.4 0.4 BD [kg/L] 0.43 n.d. 0.37 0.41 0.40 0.37 0.29 RMC (after [% by n.d. n.d. 0.92 0.88 0.87 0.9 0.9 drying) wt.]

Example 2: Production of ABS Molding Compositions and ABS Moldings

(73) 2.1 Thermoplastic Copolymer A

(74) The thermoplastic copolymer A used was a random styrene/acrylonitrile copolymer A-IV (styrene: acrylonitrile ratio by weight 73:27) with weight-average molar mass M.sub.w 106 000 g/mol and number-average molar mass M.sub.n 15 000 g/mol.

(75) The thermoplastic copolymer A-IV was obtained via free-radical solution polymerization with peroxidic initiation. The content of oligomer with molar mass below 1000 g/mol in the thermoplastic copolymer A-IV was 1.0% by weight. The molar masses M.sub.w and M.sub.n and the oligomer content were determined by gel permeation chromatography with tetrahydrofuran as solvent and polystyrene calibration. Determination of oligomer content in random styrene/acrylonitrile copolymers is moreover described in K. Kirchner, H. Schlapkohl, Makromol. Chem. 177 (1976) 2031-2042, “The formation of oligomers in the thermal copolymerisation of the styrene/acrylonitrile system”.

(76) 2.2. Linear Polycarbonate K2

(77) Component K2 used was a linear polycarbonate based on bisphenol A with weight-average molar mass M.sub.w 27 500 (determined by gel permeation chromatography in methylene chloride at 25° C.).

(78) 2.3 Thermoplastic Molding Compositions 2A to 2F and 2I to 2K

(79) The dried graft copolymer B from examples 1A to 1F and 1I to 1K and the thermoplastic copolymer A-IV were mixed in proportions as in table 2 (data in % by weight) together with 2.0 parts by weight of ethylenebisstearylamide, 0.3 part by weight of magnesium stearate and 0.15 part by weight of a polydimethylsiloxane with viscosity 1000 centistokes at from 200 to 250° C. in a ZSK 25 extruder (manufacturer: Coperion), and after palletization processed to give moldings.

(80) The molding compositions 2A to 2F and 2I to 2K, and moldings produced therefrom, were obtained. The moldings comply with the requirements of the respective test standards.

(81) The following properties were determined on the molding compositions and, respectively, the moldings: Notched impact resistance at room temperature (ak RT) and at −20° C. (ak-20° C.) in accordance with ISO 180/1A (unit: kJ/m.sup.2) Thermoplastic flowability (MVR (220/10) for 220° C. and 10 kg load in accordance with ISO 1133, unit: cm.sup.3/10 min) Gloss at 20° in accordance with DIN 67530 Yellowness Index in accordance with ASTM method E313-96

(82) Table 2 collates the test results. From the test results it is seen that the molding compositions 2A to 2E and 2I to 2K have comparable mechanical and optical properties. However, the molding compositions 2A, 2C to 2E and 2J and 2K of the invention can be produced at lower cost, because the corresponding graft copolymers are more amenable to dewatering and have lower residual moisture content after centrifuging.

(83) TABLE-US-00003 TABLE 2 Composition and test data for molding compositions 2A to 2F Molding compositions 2A 2C 2D 2E 2F Of the 2B Of the Of the Of the Of the invention Comparison invention invention invention invention Composition Graft [% by 34.2 — — — — — copolymer 1A wt.] Graft [% by — 34.2 — — — — copolymer 1B wt.] Graft [% by — — 34.2 — — — copolymer 1C wt.] Graft [% by — — — 34.2 — — copolymer 1D wt.] Graft [% by — — — — 34.2 — copolymer 1E wt.] Graft [% by — — — — — 34.2 copolymer 1F wt.] Copolymer [% by 63.4 63.4 63.4 63.4 63.4 63.4 A-IV wt.] Ethylene- [% by 2.0 2.0 2.0 2.0 2.0 2.0 bisstearylamide wt.] Magnesium [% by 0.3 0.3 0.3 0.3 0.3 0.3 stearate wt.] Polydimethylsiloxane [% by 0.1 0.1 0.1 0.1 0.1 0.1 wt.] Test results Notched impact [kJ/m.sup.2] 21.2 21.0 21.3 21.1 21.0 21.1 resistance at room temperature (ak RT) Notched impact [kJ/m.sup.2] 15.3 15.2 15.3 15.2 15.2 15.2 resistance at −20° C. (ak −20° C.) MVR (220/10) [cm.sup.3/ 31.1 29.3 29.5 30.9 32.0 30.6 10 min] Gloss at 20° 88.9 88.4 88.3 88.7 89.1 88.7 Yellowness Index 33.5 33.7 33.9 33.5 33.5 33.6 Composition and test data for molding compositions 2I to 2K Molding compositions 2I 2J 2K Not of the Of the Of the invention invention invention Composition Graft copolymer 1I [% by wt.] 27.3 — — Graft copolymer 1J [% by wt.] — 27.3 — Graft copolymer 1K [% by wt.] — — 27.3 Copolymer A-IV [% by wt.] 70.3 70.3 70.3 Ethylenebisstearylamide [% by wt.] 2.0 2.0 2.0 Magnesium stearate [% by wt.] 0.3 0.3 0.3 Polydimethylsiloxane [% by wt.] 0.1 0.1 0.1 Test results Notched impact resistance [kJ/m.sup.2] 21.4 21.3 21.4 at room temperature (ak RT) Notched impact resistance [kJ/m.sup.2] 15.9 15.8 15.8 at −20° C. (ak −20° C.) MVR (220/10) [cm.sup.3/10 min] 34.8 35.0 34.8 Gloss at 20° 94.2 94.5 94.2 Yellowness Index 38.5 38.2 39.0

(84) 2.4 Thermoplastic Molding Compositions 2L and 2M

(85) The dried graft copolymers B from examples 1L and 1M and the thermoplastic copolymer A-IV were mixed at 260° C. in proportions as in table 3 together with 43 parts by weight of linear polycarbonate K2; 0.75 part by weight of pentaerythritol tetrastearate; 0.12 part by weight of Irganox B900; 0.10 part by weight of Irganox 1076 and 0.02 part by weight of citric acid in a ZSK 25 extruder (manufacturer: Coperion), and after palletization processed to give moldings. This gave the molding compositions 2L and 2M, and moldings produced therefrom. The shape of the moldings complied with the requirements of the respective test.

(86) The following properties were determined on the molding compositions and, respectively, the moldings: Notched impact resistance at room temperature (ak RT) and at −20° C. (ak-20° C.) in accordance with ISO 180/1A (unit: kJ/m.sup.2) Thermoplastic flowability (MVR (260-5) for 260° C. and 5 kg load in accordance with ISO 1133, unit: cm.sup.3/10 min) Vicat softening point B/120 in accordance with DIN EN ISO 306 Ball indentation hardness (Hc) [N/mm.sup.2] EN ISO 2039-1 (test weight 358 N, time 30 s) Processing stability: The processing stability measure used for the molding compositions produced is the change (in percent) of MVR measured in accordance with ISO 1133 at 260° C. for non-flame-retardant polycarbonate/ABS compositions with RAM load 5 kg and residence time of the melt 15 minutes at a temperature of 300° C. with exclusion of air. The resultant value ΔMVR(proc.) is calculated from the formula:
ΔMVR(proc.)=[(MVR after melt aging−MVR before aging)/MVR before aging]*100%

(87) Table 3 collates the test results.

(88) The molding compositions 2L and 2M have comparable mechanical properties. However, the molding composition 2L of the invention can be produced at lower cost because it is more amenable to dewatering and because the graft copolymer 1L has lower residual moisture content after centrifuging.

(89) TABLE-US-00004 TABLE 3 Composition and test data for molding compositions 2L and 2M 2L 2M Molding compositions Invention Comparison Composition Graft copolymer 1L [pts. by wt.] 25.25 — Graft copolymer 1M [pts. by wt.] — 25.25 Copolymer A-IV [pts. by wt.] 31.19 31.19 Linear polycarbonate K2 [pts. by wt. 42.58 42.58 Pentaerythritol tetrastearate [pts. by wt.] 0.74 0.74 IrganoxB900 [pts. by wt.] 0.12 0.12 Irganox 1076 [pts. by wt.] 0.10 0.10 Citric acid [pts. by wt.] 0.02 0.02 Test results Notched impact resistance at [kJ/m.sup.2] 43.1 43.1 room temperature (ak RT) Notched impact resistance at [kJ/m.sup.2] 40.1 40.1 −20° C. (ak −30° C.) MVR (260/10) [cm.sup.3/10 min] 9.0 15.0 Vicat B/120 [° C.] 107.4 107.2 Ball indentation hardness (Hc) [N/mm.sup.2] 91.7 94.0 ΔMVR(proc.) [%] 165 283