Method for producing ABS plastics having improved properties
10731031 ยท 2020-08-04
Assignee
Inventors
Cpc classification
C08L55/02
CHEMISTRY; METALLURGY
C08L2205/03
CHEMISTRY; METALLURGY
C08L55/02
CHEMISTRY; METALLURGY
C08F6/008
CHEMISTRY; METALLURGY
International classification
Abstract
The invention relates to a method for producing thermoplastic molding materials based on acrylonitrile-butadiene-styrene copolymers (ABS) having improved surface properties, in particular improved resistance of the surface quality to storage in a warm, humid environment, and having a reduced content of residual monomers. The invention further relates to the use of a fluid bed dryer and/or a flash dryer in the production of thermoplastic ABS molding materials in order to improve the surface quality. The invention further relates to the use of a fluid bed dryer and/or a flash dryer in the production of thermoplastic ABS molding materials having a reduced content of residual monomers. The invention further relates to ABS molding materials that can be produced by means of the method according to the invention and to molded parts (e.g., molded bodies, films, and coatings) that can be produced from the thermoplastic molding materials according to the invention.
Claims
1. A process for the production of a thermoplastic molding composition comprising: A: from 5 to 95% by weight of at least one thermoplastic copolymer A produced from: A1: from 50 to 95% by weight, based on the copolymer A, of a monomer A1 selected from styrene, -methylstyrene, and mixtures of styrene and at least one other monomer selected from -methylstyrene, p-methylstyrene, and C.sub.1-C.sub.8-alkyl (meth)acrylate, A2: from 5 to 50% by weight, based on the copolymer A, of a monomer A2 selected from acrylonitrile and mixtures of acrylonitrile and at least one other monomer selected from methacrylonitrile, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids, B: from 5 to 95% 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 styrene, -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 total quantity of B11+B12 is exactly 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 styrene and mixtures of styrene and at least one other monomer selected from -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 acrylonitrile and mixtures of acrylonitrile and at least one other monomer selected from methacrylonitrile, anhydrides of unsaturated carboxylic acids, and imides of unsaturated carboxylic acids; where the total quantity of graft base B1 and graft shell B2 is exactly 100% by weight; and K: from 0 to 90% by weight of at least one other component K, comprising the following steps: a) precipitation of the at least one graft copolymer B after the emulsion polymerization reaction via addition of a precipitation solution comprising at least one salt and/or at least one inorganic acid; b) mechanical dewatering of the precipitated graft copolymer B, where a graft copolymer B with water content smaller than or equal to 50% by weight is obtained; c) drying of the dewatered graft copolymer B with use of a drying gas, where the graft copolymer B is caused to move in the drying gas and the temperature of the drying gas is in the range from 50 to 160 C.; and d) mixing of the thermoplastic copolymer A, of the at least one dried graft copolymer B, and optionally of the other component(s) K.
2. The process of claim 1, wherein the drying of the dewatered graft copolymer B in step c) takes place with use of a fluidized-bed drier and/or of a pneumatic drier.
3. The process of claim 1, wherein the median particle diameter d.sub.50 of the graft base B1 is in the range from 100 to 1000 nm.
4. 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 which has a median particle diameter d.sub.50 in the range from 230 to 330 nm and of a graft base B1-B which has a median particle diameter d.sub.50 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 which has a median particle diameter d.sub.50 in the range from 10 to 220 nm.
5. The process of claim 4, wherein in step a) the graft copolymers B-I and B-II are mixed and the mixture of the graft copolymers is precipitated via addition of the precipitation solution comprising at least one salt.
6. The process of claim 1, wherein the drying in step c) is carried out by means of a drying gas selected from air and/or nitrogen, where: the drying is carried out with use of a fluidized-bed drier and the temperature of the drying gas is in the range from 50 to 100 C.; or the drying is carried out with use of a pneumatic drier and the temperature of the drying gas is in the range from 100 to 160 C.
7. The process of claim 1, wherein the drying in step c) is carried out by means of a drying gas selected from air and/or nitrogen, where: the drying is carried out with use of a fluidized-bed drier, the temperature of the drying gas is in the range from 50 to 100 C., and the average residence time of the graft copolymer B in the fluidized-bed drier is from 10 to 60 min; or the drying is carried out with use of a pneumatic drier, the temperature of the drying gas is in the range from 100 to 160 C., and the average residence time of the graft copolymer B in the pneumatic drier is from 1 to 300 seconds.
8. The process of claim 1, wherein the drying in step c) is carried out by means of a drying gas selected from air and/or nitrogen, where: the drying is carried out with use of a fluidized-bed drier which has one or more heat exchangers integrated into the fluidized bed, the temperature of the drying gas is in the range from 50 to 100 C., and the heat exchanger is operated at a temperature in the range from 50 to 100 C.
9. The process of claim 1, wherein the dried graft copolymer B obtained in step c) has water content in the range from 0.05 to 0.8% by weight and total residual monomer content smaller than or equal to 2,000 ppm.
10. The process of claim 1, wherein a fluidized-bed drier and/or of a pneumatic drier is used in the production of a thermoplastic molding composition for the drying of the graft copolymer B, the water content of which is less than or equal to 50% by weight, after the emulsion polymerization reaction, precipitation, and mechanical dewater of the graft copolymer B, in order to improve the surface quality of the thermoplastic molding composition.
11. The process of claim 9, wherein the drying of the graft copolymer B is carried out in a fluidized-bed drier and/or a pneumatic drier by means of a drying gas selected from air and/or nitrogen, and the temperature of the drying gas is in the range from 50 to 160 C.
12. The process of claim 9, wherein the improvement of the surface quality of the thermoplastic molding composition comprises a reduced number of surface defects after storage of the molding composition at a temperature in the range from 30 to 100 C. and relative humidity in the range from 65 to 100% and/or direct action of liquid water at a temperature in the range from 30 to 100 C. on the surface of the molding composition.
13. The process of claim 1, wherein a fluidized-bed drier and/or of a pneumatic drier is used in the production of a thermoplastic molding composition for the drying of the graft copolymer B, the water content of which is smaller than or equal to 50% by weight, after emulsion polymerization, precipitation, and mechanical dewatering of the graft copolymer B, in order to reduce total residual monomer content in the graft copolymer B.
14. A thermoplastic molding composition obtained by a process of claim 1, where the thermoplastic molding composition comprises salt inclusions and where the size of at least 80% of the salt inclusions, based on the total number of the salt inclusions, is smaller than 0.3 mm.
15. A molding produced from a thermoplastic molding composition of claim 14.
Description
DESCRIPTION OF THE FIGURES
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(5) The examples and claims below provide further explanation of the invention.
EXAMPLES
Example 1Production of the Components
(6) 1.1 Production of the ABS Rubbers ABS1 and ABS2 (Component B)
(7) Graft Copolymer B-I
(8) 30 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex (graft base B1-A) with median particle diameter d.sub.50 299 nm and 60% by weight gel content and 30 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex (graft base B1-B) with median particle diameter d.sub.50 371 nm and 82% by weight gel content were mixed with deionized water to give about 27% by weight solids content. The respective polybutadiene lattices were produced by free-radical emulsion polymerization from a polybutadiene seed latex with median particle diameter d.sub.50 113 nm. The median particle diameter d.sub.50 is the diameter at which 50% by volume of the particles (e.g. of the polybutadiene latex) are smaller than, and the other 50% by volume are larger than, the d.sub.50 diameter.
(9) The mixture was then heated to 60 C., and 0.25 part by weight of potassium peroxodisulfate (dissolved in water) was admixed therewith.
(10) 40 parts by weight of a mixture of 74.5% by weight of styrene; 25.5% by weight of acrylonitrile and 0.12 part by weight of tert-dodecyl mercaptan were then uniformly metered into the mixture within a period of 5 hours. In parallel therewith, 1.3 parts by weight (calculated as solid substance) of the sodium salt of a resin acid mixture (Burez DRS S70 E, Lawter BVBA, B-9130 Kallo, Belgium, dissolved in alkalinified water) were metered into the mixture over a period of 5 hours, and 0.25 part by weight of potassium peroxodisulfate (dissolved in deionized water) was likewise metered into the mixture over a period of 5 hours. During the course of the first three hours the reaction temperature was raised from 60 C. to 81 C. After all of the metered additions had ended, there followed two hours of postreaction time at 81 C., and the graft copolymer B-I was then cooled to room temperature. The gravimetrically determined solids content of the graft copolymer B-I (drying in a convection oven at 180 C., 23 minutes) was 34.9% by weight.
(11) Graft Copolymer B-II
(12) 51.5 parts by weight (calculated as solid) of an anionically emulsified polybutadiene latex (graft base B1-C) with median particle diameter d.sub.50 113 nm and 91% by weight gel content were mixed with deionized water to give about 27% by weight solids content.
(13) The polybutadiene latex was produced by free-radical seed polymerization from a polybutadiene seed latex with median particle diameter d.sub.50 49 nm.
(14) The mixture was then heated to 60 C., and 0.25 part by weight of potassium peroxodisulfate (dissolved in water) was admixed therewith.
(15) 48.5 parts by weight of a mixture of 74.5% by weight of styrene; 25.5% by weight of acrylonitrile and 0.10 part by weight of tert-dodecyl mercaptan were then uniformly metered into the mixture within a period of 5 hours. In parallel therewith, one part by weight (calculated as solid substance) of the sodium salt of a resin acid mixture (Burez DRS S70 E, Lawter BVBA, B-9130 Kallo, Belgium, dissolved in alkalinified water) were metered into the mixture over a period of 5 hours, and 0.25 part by weight of potassium peroxodisulfate (dissolved in deionized water) was metered into the mixture over a period of 5 hours.
(16) During the course of the first three hours the reaction temperature was raised from 60 C. to 81 C. After all of the metered additions had ended, there followed two hours of postreaction time at 81 C., and the graft copolymer B-II was then cooled to room temperature. The gravimetrically determined solids content of the graft copolymer B-II (drying in a convection oven at 180 C., 23 minutes) was 34.2% by weight.
(17) Precipitated Graft Copolymer B
(18) The graft copolymers B-I and B-II as described above were mixed by stirring in a ratio by weight of 60:40 (calculated as solid). 1.0% by weight of a phenolic antioxidant (Irganox 1076, BASF SE), based on the solid of the graft copolymers B-I and B-II, was added in the form of a dispersion to said mixture, and the resultant mixture was mixed.
(19) A magnesium sulfate/sulfuric acid solution was then used for continuous coagulation. For this, the mixture of the graft copolymers B-I and B-II, a magnesium sulfate solution (18% by weight) and sulfuric acid (15% by weight) were metered continuously into a stirred precipitation container I which was maintained at 94 C. by introduction of steam. The following concentrations were maintained here in the precipitation container I: 2.6% by weight of magnesium sulfate, based on the mixture of the graft copolymers B-I and B-II, calculated as solid, 0.4% by weight of sulfuric acid (calculated as 100% strength material), based on the mixture of the graft copolymers B-I and B-II, calculated as solid, 18% by weight of mixture of the graft copolymers B-I and B-II, calculated as solid, based on all of the metered substances in the precipitation container.
(20) The average residence time in the precipitation container was 15 minutes. In order to complete the precipitation, the contents of the precipitation container I were metered continuously into the precipitation container II. The average residence time in the precipitation container II was 15 minutes, and the temperature was maintained at about 92 to 94 C. After cooling of the precipitated mixture of the graft copolymers B-I and B-II from precipitation container II to 70 C., said mixture was isolated from the aqueous phase by centrifuging with centripetal acceleration of 320 g for 10 seconds. This gave a water-moist graft copolymer B with 30% by weight residual moisture content (ABS1).
(21) Another sample of the precipitated graft copolymer B was cooled to 70 C. and then isolated from the aqueous phase by centrifuging with centripetal acceleration of 650 g for 60 seconds, to give a water-moist graft copolymer B with 16.2% by weight residual moisture content (ABS2).
(22) 1.2 Production of the ABS Rubber ABS3 (Component B)
(23) The ABS rubber ABS3 (graft copolymer B) was produced in accordance with WO 2012/022710, page 28, Graft rubber polymer 15 example. After precipitation with sulfuric acid, the water-moist graft copolymer ABS3 was isolated from the aqueous phase by centrifuging; residual moisture content was 31.8% by weight.
(24) 1.3 Production of the ABS Rubber ABS4 (Component B)
(25) The ABS rubber ABS4 (graft copolymer B) was produced in accordance with WO 2014/170407 A1, pages 31-32, Graft copolymer B-1 example. After precipitation with a magnesium sulfate solution, the water-moist graft copolymer B-IV was isolated from the aqueous phase by centrifuging; residual moisture content was 26.2% by weight.
(26) Thermoplastic Copolymer A
(27) Free-radical solution polymerization with peroxidic initiation was used to produce a random styrene/acrylonitrile copolymer (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. The molar masses M.sub.w and M.sub.n were determined by gel permeation chromatography with tetrahydrofuran as solvent and polystyrene calibration. Content of oligomer with molar mass below 1 000 g/mol was 1.0% by weight, likewise determined by gel permeation chromatography with tetrahydrofuran as solvent and polystyrene calibration. Determination of oligomer content in random styrene/acrylonitrile copolymers is 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).
Example 2: Drying of the Graft Copolymer B
Example 2A: Drying of the Graft Copolymer B (ABS1) by a Pneumatic Drier
(28) The water-moist graft copolymer B (coprecipitated graft copolymers B-I and B-II, as described in Example 1.1 above) with 30% by weight residual moisture content (ABS1) was dried in a pneumatic drier with a nitrogen/air mixture with a proportion of less than 1% by volume of oxygen as carrier gas. The residence time required by the graft copolymer B to reach its final residual moisture content was typically from 5 to 10 seconds. The temperature of the carrier gas was 145 C. and the product temperature was 85 C. Residual moisture content after drying was 0.7% by weight. The material was obtained in the form of a fine-particle powder with median grain size d.sub.50 0.4 m. The grain size d.sub.50 was determined by sieve analysis in accordance with ISO 3310-1 with the following sieves: 63, 100, 150, 200, 300, 500, 800 and 2000 m.
Example 2B: Drying of the Graft Copolymer B (ABS1) by a Fluidized-Bed Drier
(29) The water-moist graft copolymer B (coprecipitated graft copolymers B-I and B-II, as described in Example 1.1 above) with 30% by weight residual moisture content (ABS1) was dried in a fluidized-bed drier with air as carrier gas. The residence time was 35 minutes. The temperature of the air was 80 C. and the product temperature was 48 C. Residual moisture content after drying was 0.5% by weight. The material was obtained in the form of a fine-particle powder with median grain size d.sub.50 0.4 m (by means of sieve analysis in accordance with ISO 3310-1).
Example 2C: Drying of the Graft Copolymer B in a Convection Oven
(30) The water-moist graft copolymer B (coprecipitated graft copolymers B-I and B-II, as described in Example 1.1 above) with 30% by weight residual moisture content (ABS1) was dried in a convection oven for 2 days at 70 C. until residual moisture content was 0.7% by weight. The material was obtained in the form of a fine-particle powder with median grain size d.sub.50 0.4 m (by means of sieve analysis in accordance with ISO 3310-1).
Example 2D: Drying of the Graft Copolymer B in an Extruder with Simultaneous Processing to Give Moldings
(31) Drying of the water-moist graft copolymer B (coprecipitated graft copolymers B-I and B-II with 30% by weight residual moisture content as described above) (ABS1) was carried out in accordance with the patent application EP-A 0734825.
(32) For this, the graft copolymer B was dewatered mechanically in a twin-screw extruder. The thermoplastic copolymer A and silicone oil were introduced as melt into the twin-screw extruder and mixed with the graft copolymer B, and after extrusion the ABS molding compositions F4 here were obtained as pellets by way of a die plate and pelletizer.
(33) The molding composition F4 was obtained as pellets in a single step and then processed to give moldings. Table 1 below gives the constitution of the ABS molding composition F4.
Example 3: Production of ABS Molding Compositions and ABS Moldings
(34) The graft copolymers B described above in Examples 2A to 2C were mixed in a ZSK 25 (Coperion) extruder with the thermoplastic copolymer A and 0.10 part by weight of a polydimethylsiloxane with viscosity 1000 centistokes, and pelletized. Table 1 below gives the proportions.
(35) The resultant pellets were used to produce plaques (75502.5 mm) in an injection mold with polished surface at 240 C. melt temperature and 70 C. mold temperature.
Example 4: Testing of Surface Homogeneity
(36) In order to simulate hot moist environmental conditions, the plaques (75502.5 mm) were stored at 80 C. in deionized water for 8 hours. The plaques were dried, and then visible surface defects were counted by the naked eye at a viewing distance of about 30 to 40 cm; the number of surface defects (specks) is stated.
(37) Four plaques were tested from each molding composition. The test evaluated only the polished area. The number of surface defects on a test area totaling 150 cm.sup.2 was therefore counted, and is stated in Table 1 below.
(38) TABLE-US-00001 TABLE 1 Constitution of, and test data for, molding compositions F1 to F4 Molding compositions F1 F2 F3 F4 inventive inventive noninventive noninventive Graft % by wt. 48.2 copolymer of example 2A Graft % by wt. 48.2 copolymer of example 2B Graft % by wt. 48.2 copolymer of example 2C Graft % by wt. 48.2 copolymer of example 2D Copolymer A % by wt. 51.7 51.7 51.7 51.7 Polydimethyl- % by wt. 0.1 0.1 0.1 0.1 siloxane Sum % by wt. 100 100 100 100 Number of number 0 4 21 22 surface defects
(39) The molding compositions F1 and F2 are molding compositions of the invention, i.e. molding compositions comprising graft copolymers B dried in the invention. The molding compositions F3 and F4 are comparative examples comprising graft copolymers B not dried in the invention.
(40) From the test results on the molding compositions F1 to F4 it can be seen that the molding compositions produced by the process of the invention, and, respectively, moldings produced therefrom, exhibit a small number of surface defects (specks) and therefore better surface homogeneity after storage in a hot moist environment, while the resultant number of surface defects is significantly higher for the molding compositions not of the invention. It is possible that drying in the fluidized-bed drier or in a pneumatic drier results in particularly rapid and uniform drying, leading to small dimensions of salt inclusions (e.g. salt crystals), which cause few surface defects visible to the naked eye.
Example 5: Testing for Residual Monomer Content
(41) Residual monomer content as a function of drying in the fluidized-bed drier was tested as described above on the following ABS graft copolymers (component B): ABS2 Graft copolymer B produced as described in Example 1.1, with 16.2% by weight residual moisture content; ABS3 Graft copolymer B produced as described in Example 1.2, with 31.8% by weight residual moisture content; ABS4 Graft copolymer B produced as described in Example 1.3, with 26.2% by weight residual moisture content; 2A Graft copolymer B produced as described in Example 1.1 and dried in the pneumatic drier as in Example 2A with 0.7% by weight residual moisture content.
(42) In each case, styrene (Sty) content and 4-vinylcylohexene (VCH) content were determined by means of headspace gas chromatography with external calibration with use of para-xylene as internal standard. For this, in each case 1 g of the graft copolymer powder was dispersed by shaking in 5 g of dimethyl sulfoxide with added internal standard and subjected to headspace gas chromatography measurement at a sample temperature of 94 C. The temperature of the injection needle was 98 C., and the temperature of the transfer line between the headspace autosampler and the gas chromatograph was 135 C. The headspace autosampler used was a PerkinElmer HS-40 and the gas chromatograph used was a Hewlett Packard 5890 Series II. The total content of styrene and 4-vinylcyclohexene is also stated in ppm, the reference variable here being the input weight of the graft copolymer powder.
(43) The ABS graft copolymers were dried in a fluidized-bed drier in a manner similar to that described in Example 2B
(44) 5.1 Drying of ABS2
(45) The water-moist ABS2 with 16.2% by weight residual moisture content was dried in a fluidized-bed drier with air as carrier gas. Total residence time was 65 min. Air temperature was 80 C. Table 2 collates the temperature profile of the graft polymer powder B (product temperature or fluidized bed temperature), the residual moisture content, and also the total content of residual monomers styrene and 4-vinylcyclohexene.
(46) TABLE-US-00002 TABLE 2 Drying of the graft copolymer ABS2 by a fluidized-bed drier Fluidized bed Drying time temperature Residual moisture content Sty + VCH [min] [ C.] [% by wt.] [ppm] 0 25 16.2 n.d. 5 33 14.5 n.d. 10 31 11.9 n.d. 20 30 6.1 n.d. 30 36 1.2 n.d. 35 48 0.5 1809 40 57 0.4 1335 45 62 0.3 933 50 65 0.3 n.d. 55 67 0.3 451 60 68 0.3 n.d. 65 69 0.3 235 n.d.: not determined
(47) Product temperature after the first 35 min was 48 C. After this first drying phase, after 35 min, residual moisture content was 0.5% by weight and the content of styrene and 4-vinylcyclohexene was 1 809 ppm. The material was obtained in the form of a fine-particle powder with d.sub.50 median grain size 0.4 m.
(48) Drying in the fluidized-bed drier was then carried out for a further 30 minutes, with unchanged air temperature of 80 C. The quantities of the volatile compounds styrene and 4-vinylcyclohexene decreased here from a total of 1 809 ppm to 235 ppm.
(49) The results are also depicted in
(50) 5.2 Drying of ABS3
(51) The water-moist ABS3 with 31.8% by weight residual moisture content was dried in a fluidized-bed drier with air as carrier gas. Total residence time was 85 min.
(52) Air temperature was 80 C. Table 3 collates the temperature profile of the graft polymer powder B (product temperature or fluidized bed temperature), the residual moisture content, and also the total content of residual monomers styrene and 4-vinylcyclohexene.
(53) TABLE-US-00003 TABLE 3 Drying of the graft copolymer ABS3 by a fluidized-bed drier Fluidized bed Drying time temperature Residual moisture content Sty + VCH [min] [ C.] [% by wt.] [ppm] 0 29 31.8 n.d. 5 29 30.3 n.d. 10 29 29.2 n.d. 15 29 27.1 n.d. 20 29 24.5 n.d. 30 29 15.5 n.d. 40 29 13.2 n.d. 50 29 7.2 n.d. 55 30 2.5 6946 60 39 0.9 6481 65 57 0.7 4623 70 63 0.6 n.d. 75 66 0.5 1743 80 68 0.4 n.d. 85 69 0.3 677 n.d.: not determined
(54) Product temperature after the first 60 min was 39 C. After this first drying phase, after 60 min, residual moisture content was 0.9% by weight and the content of styrene and 4-vinylcyclohexene was 6 481 ppm. The material was obtained in the form of a fine-particle powder with d.sub.50 median grain size 0.54 m (determined by means of sieve analysis in accordance with ISO 3310-1).
(55) Drying in the fluidized-bed drier was then carried out for a further 25 minutes, with unchanged air temperature of 80 C. The quantities of the volatile compounds styrene and 4-vinylcyclohexene decreased here from a total of 6 481 ppm to 677 ppm.
(56) The results are also depicted in
(57) 5.3 Drying of ABS4
(58) The water-moist graft copolymer ABS4 with 26.2% by weight residual moisture content was dried in a fluidized-bed drier with air as carrier gas. Total residence time was 75 min. Air temperature was 80 C. Table 4 collates the temperature profile of the graft polymer powder B (product temperature or fluidized bed temperature), the residual moisture content, and also the total content of residual monomers styrene and 4-vinylcyclohexene.
(59) TABLE-US-00004 TABLE 4 Drying of the graft copolymer ABS4 by a fluidized-bed drier Fluidized bed Drying time temperature Residual moisture content Sty + VCH [min] [ C.] [% by wt.] [ppm] 0 30 26.3 n.d. 5 30 23.8 n.d. 10 30 21 n.d. 20 30 15.2 n.d. 25 30 12.2 n.d. 30 30 9.6 n.d. 35 30 6.6 n.d. 40 32 3.4 n.d. 45 41 1.3 2133 50 54 0.6 1766 55 61 0.4 1249 60 65 0.3 n.d. 65 67 0.4 536 70 68 0.3 n.d. 75 69 0.3 235 n.d.: not determined
(60) Product temperature after the first 45 min was 41 C. After this first drying phase, after 45 min, residual moisture content was 1.3% by weight and the content of styrene and 4-vinylcyclohexene was 2 133 ppm.
(61) The material was obtained in the form of a fine-particle powder with d.sub.50 median grain size 0.37 m. Drying in the fluidized-bed drier was then carried out for a further 30 minutes, with unchanged air temperature of 80 C. The quantities of the volatile compounds styrene and 4-vinylcyclohexene decreased here from a total of 2 133 ppm to 235 ppm.
(62) The results are also depicted in
(63) 5.4 Combination of Pneumatic Drier and Fluidized-Bed Drier
(64) The graft copolymer 2A dried in the pneumatic drier with 0.7% by weight residual moisture content and d.sub.50 median grain size 0.4 m and 5 147 ppm content of styrene and 4-vinylcyclohexene (Example 2A above) was dried in a fluidized-bed drier with air as carrier gas. Residual monomer content (total of styrene and 4-vinylcyclohexene) is collated in Table 5.
(65) Residence time in the fluidized-bed drier was 20 minutes. Average product temperature was 70 C. The total quantities of the volatile compounds styrene and 4-vinylcyclohexene decreased here from a total of 5 147 ppm to 255 ppm. The residual moisture content of the dried graft copolymer 2A was 0.3% by weight.
(66) TABLE-US-00005 TABLE 5 Drying of the graft copolymer 2A by a fluidized-bed drier Drying time Sty + VCH [min] [ppm] 0 5147 2.5 3750 5 2524 7.5 1760 10 1280 12.5 878 15 606 17.5 379 20 255
5.5 Production of Thermoplastic Molding Compositions and Moldings, and Testing of Surface Homogeneity
(67) The ABS graft copolymer powders dried in Examples 5.1 to 5.4 were used as component B for the production of ABS molding compositions and ABS moldings. For this, the dried graft copolymers 5.1 to 5.4 were, as described in Example 3, mixed with the thermoplastic copolymer A and polydimethylsiloxane with viscosity 1000 centistokes in a ZSK 25 extruder (Coperion) and pelletized. Table 6 below gives the proportions.
(68) The resultant pellets were used to produce plaques in an injection mold with polished surface as described in Example 3. The surface homogeneity of the plaques in a hot moist environment was tested as described in Example 4. Table 6 below gives the results.
(69) TABLE-US-00006 TABLE 6 Constitution of, and test data for, molding compositions F5 to F8 Molding compositions F5 F6 F7 F8 Comment inventive inventive inventive inventive Graft % by ABS2, dried 48.2 copolymer 5.1 wt. Graft % by ABS3, dried 46.7 copolymer 5.2 wt. Graft % by ABS4, dried 46.7 copolymer 5.3 wt. Graft % by 2A, dried 48.2 copolymer 5.4 wt. (combination of pneumatic drier and fluidized-bed drier) Copolymer A % by 51.7 53.225 53.225 51.7 wt. Polydimethyl- % by 0.1 0.075 0.075 0.1 siloxane wt. Total % by 100 100 100 100 wt. Number of number 0 7 11 0 surface defects
(70) It was found that the molding compositions F5 to F8 of the invention, produced from a graft copolymer B with lower residual monomer content and lower water content (dried to a greater extent) than the molding compositions F1 and F2 (Table 1) of the invention have similarly good surface homogeneity. The molding compositions F5 to F8 of the invention additionally feature reduced residual monomer content, in particular of styrene and 4-vinylcyclohexene, in comparison with the molding compositions F1 to F4.