Process for preparing graft rubber compositions with improved dewatering

Abstract

A process for the production of a graft copolymer composition is presented, which is based on acrylonitrile-styrene-acrylate (ASA) or acrylonitrile-butadiene-styrene (ABS) graft copolymers. The graft copolymers obtained by emulsion polymerization and precipitation show improved dewatering behavior after precipitation. Based on this method ASA and ABS graft copolymers with low residual humidity can be obtained. Furthermore, the invention relates to a process for the production of a thermoplastic molding composition comprising at least one thermoplastic styrene copolymer, in particular a styrene-acrylonitrile copolymer, the graft copolymer obtained by the process, and optional further components.

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: 50 to 90% by weight, based on the graft copolymer B, of at least one graft base B1, obtained by emulsion polymerization of: B11: 50 to 100% by weight, based on the graft base B1, of at least one monomer B11 selected from C.sub.1-C.sub.8 alkyl(meth)acrylate and butadiene; B12: 0 to 10% by weight, based on the graft base B1, of at least on poly-functional cross-linking monomer B12; and B13 0 to 50% by weight, based on the graft base B1, of at least one further monomer B13 selected from styrene, α-methylstyrene, C.sub.1-C.sub.4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, chloroprene, methyl(meth)acrylate, alkylenglycol-di(meth)acrylate, and vinylmethylether; where the sum of B11, B12, and B13 equals 100% by weight; and B2: 10 to 50% by weight, based on the graft copolymer B, of at least one graft shell B2, which is obtained via emulsion polymerization in the presence of the at least one graft base B1 of: B21: 50 to 100% by weight, based on graft shell B2, of at least one monomer B21 selected from styrene, α-methylstyrene or mixtures of styrene and at least one further monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8 alkyl(meth)acrylate; and B22: 0 to 50% by weight, based on graft shell B2, of at least one monomer B22 selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer chosen from methacrylonitrile, acrylamide, vinylmethyl ether, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids; where the total sum of graft base B1 and graft shell B2 equals 100% by weight; and K1: from 0 to 10% by weight of at least one other component K1; comprising the following steps: a) preparation of the at least one graft copolymer B encompassing emulsion polymerization of the monomers B21 and B22 in the presence of at least one graft base B1 to form the at least one graft shell B2, wherein the graft copolymer B is obtained in the form of a latex; b) precipitation of the at least one graft copolymer B after its emulsion polymerization in step a), wherein the graft copolymer B latex is mixed with at least one precipitation solution PS resulting in a precipitation mixture, wherein the at least one precipitation solution PS comprises at least one alkaline-earth metal salt, and wherein the precipitation mixture has a solid content of more than 10.2% by weight; c) mechanical dewatering of the precipitated graft copolymer B, where a graft copolymer B having a water content equal or less than 40% by weight is obtained, and wherein the molar ratio of alkaline metal ions to alkaline-earth metal ions in the graft copolymer B is equal or less than 0.16; d) optionally washing of the dewatered graft copolymer B; e) optionally drying of the dewatered graft copolymer B obtained in step c) or d); and f) optionally addition of one or more optional components K1.

2. The process of claim 1, wherein the at least one graft base B1 is obtained by emulsion polymerization of: B11: 70 to 99.9% by weight, based on the graft base B1, of at least one C.sub.1-C.sub.8 alkyl(meth)acrylate as monomer B11; B12: 0.1 to 10% by weight, based on the graft base B1, of at least on poly-functional cross-linking monomer B12; and B13 0 to 29.5% by weight, based on the graft base B1, of at least one further monomer, selected from styrene, α-methylstyrene, C.sub.1-C.sub.4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, chloroprene, methyl(meth)acrylate, alkylenglycol-di(meth)acrylate, and vinylmethylether; where the sum of B11, B12, and B13 equals 100% by weight.

3. The process of claim 1, wherein the graft copolymer B comprises: B1: 50 to 70% by weight, based on the graft copolymer B, of exactly one, graft base B1; and B2: 30 to 50% by weight, based on the graft copolymer B, of exactly one graft shell B2, obtained by emulsion polymerization, in the presence of the graft base B1, of: B21: 50 to 95% by weight, based on the graft shell B2, of at least one vinylaromatic monomer B21 selected from styrene, α-methylstyrene or mixtures of styrene with α-methylstyrene or methyl(meth)acrylate; and B22: 5 to 50% by weight, based on the graft shell B2, of at least one ethylenically unsaturated monomer B22 selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile; wherein the total sum of graft base B1 and graft shell B2 is 100% by weight, and wherein the graft copolymer latex obtained in step a) has a particle size in the range of 60 to 140 nm.

4. The process of claim 1, wherein the graft copolymer B comprises: B1: 50 to 70% by weight, based on the graft copolymer B, of at least one graft base B1; B2′: 10 to 20% by weight, based on the graft copolymer B, of at least one graft shell B2′, which is obtained by emulsion polymerization, in the presence of graft base B1, of: B21′ 100% by weight, based on graft shell B2′, of at least one vinylaromatic monomer B21′ selected from styrene, α-methylstyrene or a mixture of styrene and at least one further monomer selected from a-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.4-alkyl(meth)acrylate; and B2″: 20 to 30% by weight, based on the graft copolymer B, of at least one graft shell B2″, which is obtained by emulsion polymerization, in the presence of graft base B1 grafted with B2′, of: B21″: 70 to 80% by weight, based on the graft shell B2″, of at least one vinylaromatic monomer B21″ selected from styrene, α-methylstyrene or mixtures of styrene and α-methylstyrene or methyl(meth)acrylate; and B22″: 20 to 30% by weight, based on the graft shell B2″, of at least one ethylenically unsaturated monomer B22″ selected from acrylonitrile or mixtures of acrylonitrile an methacrylonitrile; wherein the total sum of graft base B1, graft shell B2′, and graft shell B2″ is 100% by weight, and wherein the graft copolymer latex obtained in step a) has a particle size in the range of 400 to 700 nm.

5. The process of claim 1, wherein the solid content of the precipitation mixture obtained in step b) is in the range from 10.3 to 20% by weight.

6. The process of claim 1, wherein the graft copolymer B latex is mixed with the at least one precipitation solution PS in step b) at a temperature T.sub.1 in the range of 30 to 70° C. and afterwards the precipitation mixture is kept for at least 5 minutes at a temperature T.sub.2 in the range of 70 to 120° C.

7. The process of claim 1, wherein the precipitation mixture obtained in step b) comprises more than 0.8% by weight of the at least one alkaline-earth metal salt, based on the total mass of the precipitation mixture.

8. The process of claim 1, wherein the pH of the precipitation mixture obtained in step b) is equal to or less than 10.

9. The process of claim 1, wherein the dewatered graft copolymer B obtained in step c) has a water content in the range from 20 to 38% by weight.

10. The process of claim 1, wherein the molar ratio of alkaline metal ions to alkaline-earth metal ions in the dewatered graft copolymer B obtained in step c) is in the range of 0.01 to 0.1.

11. A process for the production of a thermoplastic molding composition comprising: A: 5 to 95% by weight of at least one thermoplastic copolymer A produced from: A1: 50 to 95% by weight, based on the copolymer A, of a monomer A1 selected from styrene, α-methylstyrene and mixtures of styrene and at least one other monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8-alkyl (meth)acrylate; and A2: 5 to 50% by weight, based on the copolymer A, of at least one monomer A2 selected from acrylonitrile and mixtures of acrylonitrile and at least one other monomer selected from methacrylonitrile, acrylamide, vinylmethyl ether, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids; B: 5 to 95% by weight of at least one graft copolymer B as defined in claim 1; C: 0 to 90% by weight of at least one further polymeric component C; and K2: 0 to 10% by weight of at least one further component K2; comprising the following steps: a) to c) and optionally d) to f) as described in claim 1; g) mixing the thermoplastic copolymer A, the at least one graft copolymer B, and optionally one or more further polymeric component C and/or optionally one or more further components K2.

12. The process of claim 11, wherein the thermoplastic copolymer A is produced from: A1: 64 to 95% by weight, based on the copolymer A, of monomer A1 selected from styrene and mixtures of styrene and at least one other monomer selected from α-methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8-alkyl (meth)acrylate; and A2: 5 to 36% by weight, based on the copolymer A, of monomer A2 selected from acrylonitrile.

13. The process of claim 11, wherein the thermoplastic molding composition comprises: C: 20 to 60% by weight, based on the total molding composition, of at least one further polymer component C selected from polycarbonates, polyamides, and polyesters.

14. The process of claim 11, wherein the mixing in step g) is carried out at a temperature in the range of 180 to 300° C.

15. A graft copolymer composition obtained by the process of claim 1.

16. A thermoplastic molding composition obtained by the process of claim 11.

Description

EXAMPLES

(1) 1. Step a: Preparation of Styrene-Co-Acrylonitrile Grafted Polybutylacrylate Latices (Graft Copolymer B Latex)

(2) The following graft copolymers latices B-1 and B-2 were prepared:

(3) a. Preparation of Graft Copolymer B-1 Latex (Basic Rubber Latex L1: Graft Rubber Latex L2:)

(4) The reaction vessel was charged with 90.2 parts of demineralized water, 0.61 parts of the sodium salt of a C.sub.12-C.sub.18 paraffin sulfonic acid and 0.23 parts sodium bicarbonate. When the temperature in the reaction vessel reached 59° C. 0.16 parts of sodium persulfate, dissolved in 5 parts of demineralized water, were added. A mixture of 59.51 parts butyl acrylate and 1.21 parts tricyclodecenylacrylate was added within a period of 210 min. Afterwards the reaction was continued for 60 min. Finally the polymer dispersion (graft base B1-1) had a total solid content of 39.6% and the latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 75 nm.

(5) An amount of 151.9 parts of the graft base B1-1 as described above was added to the reaction vessel together with 92.2 parts of demineralized water and 0.14 parts of sodium persulfate, dissolved in 3.22 parts of demineralized water. Within a period of 190 min a mixture of 31.18 parts of styrene and 9.31 parts of acrylonitrile was added at a temperature of 61° C., followed by a post polymerization time of 60 min at 65° C. A graft copolymer latex B-1 (polymer dispersion) with a total solid content of 35.5% was obtained. The latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 87 nm.

(6) b. Preparation of Graft Copolymer B-2 Latex (Basic Rubber Latex L3/Graft Rubber Latex L4)

(7) The reaction vessel was charged with 70.66 parts of demineralized water, 0.3 parts of the graft base B1-1 (obtained as described above having a particle diameter of 75 nm) and 0.23 parts of sodium bicarbonate. After heating the reaction vessel to 60° C., 0.16 parts of sodium persulfate, dissolved in 5 parts demineralized water, were added to the reaction mixture. A mixture of 59.51 parts butyl acrylate and 1.21 parts tricyclodecenylacrylate was added within a period of 210 min. In parallel to the first feed a solution of 0.36 parts of the sodium salt of a C.sub.12-C.sub.18 paraffin sulfonic acid in 16.6 parts demineralized water was also added over a period of 210 min. After 200 min, from starting the feed, the temperature was ramped to 65° C. Afterwards the reaction was continued for 60 min at 65° C. Finally the polymer dispersion (graft base B1-2) had a total solid content of 39.4% and the latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 440 nm (determined by turbidity).

(8) An amount of 154 parts of the graft base B1-2 as described above was added to the reaction vessel together with 88.29 parts of demineralized water, 0.11 parts of the sodium salt of a C.sub.12-C.sub.18 paraffin sulfonic acid and 0.14 parts of sodium persulfate, dissolved in 5.61 parts of demineralized water. The reaction mixture was heated to 61° C. Within a period of 60 min 13.16 parts styrene were added at a temperature of 61° C., followed by a post polymerization time of 90 min, where the temperature was increased from 61° C. to 65° C. Then a mixture of 20.5 parts of styrene and 6.83 parts of acrylonitrile were added to the reaction over a period of 150 min. The reaction was continued at 65° C. for another 60 min. A polymer dispersion with a total solid content of 35.2% was obtained. The latex particles had a mean particle diameter D.sub.w (determined by turbidity) of 500 nm (determined by turbidity).

(9) 2. Step b: Precipitation of the Graft Copolymer Latex B (Step b)

(10) The graft copolymer latices B-1 and B-2, which were prepared as described above, were precipitated using MgSO.sub.4 solution as precipitation solution PS using different precipitation conditions (e.g. temperature, MgSO.sub.4 concentration, ratio of sodium to potassium).

(11) The precipitated graft copolymers B (graft copolymer B slurries) were obtained as described in the following. The resulting slurries were transferred to a centrifuge, having a diameter of 400 mm, and centrifuged for 60 s at 1650 rpm, which results centripetal force of 614 G. The dewatered graft copolymer B was obtained in form of a wet powder.

(12) Residual humidity of the dewatered graft copolymers was determined by Mettler Toledo HR73 Halogen Moisture Analyzer. Sodium and magnesium content were determined by ICP-OES using the dried graft copolymer B powder, i.e. after drying the dewatered graft copolymers in a lab oven at 70° C. for 2 days.

(13) The influence of different precipitation conditions on residual humidity after centrifugation was investigated and the results are summarized in table 1 below.

Example E-1 (Comparative)

(14) 112.5 g of a MgSO.sub.4 solution (19.9 wt.-%) were mixed with 2143.1 g demineralized water. 451.1 g of this solution were used as pre-charge and heated to 60° C. 900 g of graft copolymer B-1 latex and 1804.5 g of the remaining diluted MgSO.sub.4 solution were added separately within 10 min, while the temperature was kept at 60° C. Then the resulting mixture was heated to 92° C. for 5 min (sintering)

(15) The resulting slurry was processed as described in the general procedure above.

Example E-2 (Inventive)

(16) 147.9 g of a MgSO.sub.4 solution (20 wt.-%) were mixed with 1358.8 g demineralized water. 301.3 g of this solution was used as pre-charge and heated to 60° C. 900 g of graft copolymer B-1 latex and 1205.3 g of the remaining diluted MgSO4 solution were added separately within 10 min, while the temperature was kept at 60° C. Then the resulting mixture was heated to 92° C. for 5 min (sintering).

(17) The resulting slurry was processed as described in the general procedure above.

Example E-3 (Inventive)

(18) 147.9 g of a MgSO.sub.4 solution (20.4 wt.-%) were mixed with 1207.8 g demineralized water. 271.1 g of this solution was used as pre-charge and heated to 60° C. 900 g of graft copolymer B-1 latex and 1084.5 of the remaining diluted MgSO4 solution were added separately within 10 min, while the temperature was kept at 60° C. Then the resulting mixture was heated to 92° C. for 5 min (sintering).

(19) The resulting slurry was processed as described in the general procedure above.

Example E-4 (Inventive)

(20) 147.9 g of a MgSO.sub.4 solution (20.4 wt.-%) were mixed with 905.9 g demineralized water. 210.7 g of this solution was used as pre-charge and heated to 50° C. 900 g of graft copolymer B-1 latex and 843 g of the remaining diluted MgSO.sub.4 solution were added separately within 10 min, while the temperature was kept at 50° C. Then the resulting mixture was heated to 92° C. for 5 min (sintering).

(21) The resulting slurry was processed as described in the general procedure above.

Example E-5 (Comparative)

(22) 87.5 g of a MgSO.sub.4 solution (19.9 wt.-%) were mixed with 2121.4 g demineralized water. 441.8 g of this solution was used as pre-charge and heated to 88° C. 900 g of graft copolymer B-2 latex and 1767.1 g of the remaining diluted MgSO.sub.4 solution are added separately within 10 min, while the temperature is kept at 88° C. Then the resulting mixture is heated to 99° C. for 5 min (sintering).

(23) The resulting slurry was processed as described in the general procedure above.

Example E-6 (Inventive)

(24) 133 g of a MgSO.sub.4 solution (20.4 wt.-%) were mixed with 1207.1 g demineralized water. 268 g of this solution was used as pre-charge and heated to 70° C. 900 g of graft copolymer B-2 latex and 1072.1 g of the remaining diluted MgSO.sub.4 solution were added separately within 10 min, while the temperature was kept at 70° C. Then the resulting mixture is heated to 130° C. for 5 min (sintering).

(25) The resulting slurry was processed as described in the general procedure above.

(26) The precipitation conditions and the results are summarized in the following table 1.

(27) TABLE-US-00001 TABLE 1 Graft copolymer compositions E1 E5 Example (comp.) E2 E3 E4 (comp.) E6 Graft copolymer B latex B-1 B-1 B-1 B-1 B-2 B-2 solid polymer [parts] 100 100 100 100 100 100 solid MgSO.sub.4.sup.1 [parts] 7 10 10 10 5.5 9 DM water.sup.1 [parts] 667 450 400 300 670 400 Precipitation temp. [° C.] 60 60 60 50 88 70 Sintering temp. [° C.] 92 92 92 92 99 130 Total solid content.sup.2 [%] 10.2 12.7 13.6 15.7 10.2 13.6 MgSO.sub.4 concentration.sup.3 0.8 1.4 1.5 1.8 0.6 1.4 [%] residual humidity after 43 33 30 29 54 35 centrifugation [%] Na [ppm] 220 — 52 96 380 90 Mg [ppm] 1300 — 1500 1800 1600 1600 molar ratio Na/Mg 0.179 — 0.037 0.056 0.251 0.059 .sup.1solid MgSO.sub.4 and demineralized water (DM) are given as part of weights based on 100 parts solid content of graft copolymer B. .sup.2The solid content was determined based on the amount of the components used. .sup.3MgSO.sub.4 concentration is given in % by weight based on the total weight of the precipitation mixture.

(28) It is clearly shown that a high alkaline to earth alkaline ratios (ratio Na/Mg) are unfavor-able due to the higher residual humidity. Above a molar Na/Mg ratio of 0.16 dewatering of the precipitated graft copolymer latex is significantly worse.

(29) 3. Test Procedures a. The particle size of the graft base B1 and the graft copolymer B latices were determined as mean particle diameter D.sub.w determined by turbidity as described in Lange, Kolloid-Zeitschrift und Zeitschrift für Polymere, Band 223, Heft 1. b. Residual humidity of the graft copolymers B after centrifugation was determined by Mettler Toledo HR73 Halogen Moisture Analyzer. c. Sodium and magnesium content in the graft copolymers B was determined by atom emission spectroscopy with inductive coupled plasma (ICP-AES) after chemical digestion. The dewatered graft copolymers B were dried in a lab oven at 70° C. for 2 days. Afterwards 200 mg of the polymer sample was dissolved in 5 ml nitric acid (microwave assisted at about 200 bar (total pressure of the digestion mixture) and about 220° C.).

(30) The solution obtained was diluted with Millipore water and determined via ICP-AES. A calibration series is obtained by dilution of certified reference material.