EXTRUSION METHOD FOR PRODUCING A THERMOPLASTIC MOLDING COMPOUND, AND DEVICE FOR CARRYING OUT THE METHOD

Abstract

Method for producing a thermoplastic molding compound (F) in an extruder, which has at least one screw having an outside diameter (D), wherein a thermoplastic component (TP) containing at least one thermoplastic polymer, a component (C) containing a graft polymer based in particular on butadiene and/or acrylate, and optionally a component (Z) containing additives are heated to a temperature of 200° C. to 280° C., melted and mixed by supplying thermal energy in a melting section (S) and/or in at least one mixing section (M) such that the thermoplastic molding compound (F) is formed, and the thermoplastic molding compound is subsequently degassed in a degassing zone (E) of the extruder, wherein an absolute pressure (P1) of less than 2 bar is set in this zone, and after the degassing the molding compound (F) is conveyed to a melt pump (SP) by screw elements, wherein the total length of the screw elements of a conveying path (FS) from the degassing opening (O) to the melt pump (SP) is less than five times the outside diameter (D) of the at least one screw.

Claims

1-16. (canceled)

17. A process for the production of a thermoplastic molding composition (F) in an extruder, which has at least one screw with an external diameter (D), where a thermoplastic component (TP), comprising at least one thermoplastic polymer, component (C), comprising a graft polymer based on butadiene and/or on acrylate, and optionally component (Z), comprising additives, are heated by introduction of thermal energy and/or mechanical energy in a melting section (S) of the extruder and/or in at least one mixing section (M) of the extruder to a temperature of 200° C. to 280° C., melted, and mixed, thus forming the thermoplastic molding composition (F), and the thermoplastic molding composition (F) is then devolatilized in a devolatilization zone (E) of the extruder, said zone having at least one devolatilization aperture (O), where an absolute pressure (P1) below 2 bar is established in the devolatilization zone (E) of the extruder, and after the devolatilization, the thermoplastic molding composition (F) is conveyed by means of screw elements to a melt pump (SP), where the total length of the screw elements of a region of conveying (FS) from the at least one devolatilization aperture (O) to the melt pump (SP) is less than five times the external diameter (D) of the at least one screw.

18. The process of claim 17, wherein the absolute pressure (P2) of the thermoplastic molding composition (F) during conveying from the at least one devolatilization aperture (O) to the melt pump (SP) is below 40 bar.

19. The process of claim 17, wherein the absolute pressure (P3) of the thermoplastic molding composition (F) is increased in the melt pump (SP) to at least 50 bar.

20. The process of claim 17, wherein the temperature of the thermoplastic molding composition (F) during conveying from the at least one devolatilization aperture (O) to the melt pump (SP) is below 280° C.

21. The process of claim 17, wherein the thermoplastic molding composition (F) is introduced, from the melt pump (SP), into a melt-pelletization procedure.

22. The process of claim 17, wherein the thermoplastic molding composition (F) is conveyed via at least one melt filter (SF) after the melt pump (SP) in conveying direction.

23. The process of claim 17, wherein the thermoplastic component (TP) comprises a component (A), comprising a thermoplastic polymer, and a component (B), comprising a styrene copolymer.

24. The process of claim 17, wherein the thermoplastic component (TP) comprises, as a component (A), a polymethyl methacrylate (PMMA), a polyamide, and/or a polycarbonate (PC), and comprises, as a component (B), a styrene-acrylonitrile copolymer (SAN) or an alpha-methyl-styrene-acrylonitrile copolymer (AMSAN), and comprises, as the component (C), a butadiene-containing graft rubber.

25. The process of claim 17, wherein the thermoplastic molding composition (F) comprises a first mixture of: component (A): 25 to 69% by weight, based on the entirety of components (A), (B), and (C), of a methyl methacrylate polymer obtainable by polymerization of a second mixture consisting of: (A1) 90 to 100% by weight, based on (A), of methyl methacrylate, and (A2) 0 to 10% by weight, based on (A), of a C.sub.1-C.sub.8-alkyl ester of acrylic acid, component (B): 30 to 69% by weight, based on the entirety of components (A), (B), and (C), of a copolymer obtainable by polymerization of a third mixture of: (B1) 65 to 88% by weight, based on (B), of a vinylaromatic monomer, and (B2) 12 to 35% by weight, based on (B), of a vinyl cyanide, component (C): 1 to 40% by weight, based on the entirety of components (A), (B), and (C), of a graft copolymer obtainable from: (C1) 40 to 90% by weight, based on (C), of a core obtainable by polymerization of a first monomer mixture consisting of: (C11) 65 to 99.9% by weight, based on (C1), of a 1,3-diene, (C12) 0 to 34.9% by weight, based on (C1), of vinylaromatic monomers, and (C13) 0.1 to 5% by weight, based on (C1), of an agglomeration polymer, (C2) 5 to 40% by weight, based on (C), of a first graft shell obtainable by polymerization of a second monomer mixture consisting of: (C21) 30 to 39% by weight, based on (C2), of a vinylaromatic monomer, (C22) 61 to 70% by weight, based on (C2), of a C.sub.1-C.sub.8-alkyl ester of methacrylic acid, and (C23) 0 to 3% by weight, based on (C2), of a crosslinking monomer, and (C3) 5 to 40% by weight, based on (C), of a second graft shell obtainable by polymerization of a third monomer mixture consisting of: (C31) 70 to 98% by weight, based on (C3), of a C.sub.1-C.sub.8-alkyl ester of methacrylic acid, and (C32) 2 to 30% by weight, based on (C3), of a C.sub.1-C.sub.8-alkyl ester of acrylic acid, and optionally component (Z), comprising additives, in quantities of 0 to 20% by weight, based on the entirety of components (A), (B), and (C), with the proviso that the ratio by weight of (C2) to (C3) is in the range of 2:1 to 1:2, where: the core (C1) has a monomodal particle size distribution, the median particle size D.sub.50 of the core (C1) is in the range of 300 to 400 nm, and the absolute value of the difference calculated from refractive index (n.sub.D-C) of the entire component (C) and the refractive index (n.sub.D-AB) of an entire matrix of components (A) and (B) is below 0.01.

26. The process of claim 17, wherein the thermoplastic molding composition (F) comprises no more than 5% by weight of water, based on the entire composition of the thermoplastic molding composition (F).

27. A thermoplastic molding composition (F) produced by the process of claim 17.

28. The thermoplastic molding composition (F) of claim 27, wherein the thermoplastic molding composition (F) comprises no more than 5 ppm of monomeric butadiene, based on the entire composition of the thermoplastic molding composition (F).

29. A device for conducting the process of claim 17, comprising an extruder, which comprises at least one screw with an external diameter (D), an addition section (DA), at least one mixing section (M), at least one devolatilization zone (E), and a melt pump (SP) with an entry aperture, wherein the devolatilization zone (E) has at least one devolatilization aperture (O) and the arrangement of the devolatilization zone (E) and the melt pump (SP) is such that the total length of the screw elements of a region of conveying (FS) between the at least one devolatilization aperture (O) of the devolatilization zone (E) and the entry aperture of the melt pump (SP) is less than five times the external diameter (D) of the screw.

30. The device of claim 29, wherein there is at least one melt filter (F) arranged after the melt pump (SP) in conveying direction and/or the melt pump (SP) has connection to a device for underwater pelletization procedure (UW).

31. The device of claim 29, wherein the extruder has two screws rotating in the same direction.

32. The device of claim 29, wherein the at least one melting section (S) and one mixing section (M) are combined in a section of the extruder.

33. The process of claim 21, wherein the melt-pelletization procedure is an underwater pelletization procedure (UW).

Description

[0121] The thermoplastic molding composition (F) can be used to produce moldings, primarily by injection molding or by blow molding. Further, the thermoplastic molding compositions (F) can also be pressed, calendered, extruded or vacuum-formed. Comparative examples and inventive examples of the invention are presented in the drawings and are explained in more detail in the description below and in the claims.

[0122] FIG. 1 shows an extruder of the invention with melt filter,

[0123] FIG. 2 shows an extruder of the invention without melt filter,

[0124] FIG. 3 shows an extruder of the invention with combined melting and mixing zone,

[0125] FIG. 4 shows an extruder with combined melting and mixing zone according to the prior art and

[0126] FIG. 5 shows an embodiment of an extruder without further conveying elements (FE) and an embodiment with further conveying elements (FE).

[0127] FIG. 1 shows an extruder of the invention comprising an addition section (DA), a melting section (S), a first mixing section (M1), a second mixing section (M2) and a devolatilization zone (E) with a devolatilization aperture (O), and also a melt pump (SP), which has an adapter (AD). There is a melt filter (SF) arranged after the melt pump (SP) in conveying direction, followed by a device for the underwater pelletization procedure (UW).

[0128] FIG. 2 shows an extruder of the invention which in essence corresponds to the extruder depicted in FIG. 1, but has no melt filter (SF).

[0129] FIG. 3 shows an extruder of the invention which in essence corresponds to the extruder depicted in FIG. 2. The melting section and a mixing section are combined here in one section (SM1).

[0130] FIG. 4 shows an extruder according to the prior art which, in contrast to the extruder depicted in FIG. 3, has further conveying elements (FE) between the devolatilization zone (E) and the melt pump (SP), and therefore the length of the region of conveying (FS) between the devolatilization aperture (O) and the melt pump (SP), where this means the total length of the screw elements of the region of conveying (FS), is more than five times the external diameter of the extruder screw.

[0131] FIG. 5 shows, in the upper image, an extruder of the invention which, in contrast to the extruder depicted in the lower image, has no further conveyor elements (FE) between the devolatilization zone (E) and the melt pump (SP). Accordingly, according to the upper image there is a short region of conveying (FS) present, in contrast to the region of conveying (FS) according to the lower image of FIG. 5.

COMPARATIVE EXAMPLE 1

[0132] 500 kg/h of thermoplastic molding composition were produced at a rotation rate of 500 rpm in an extruder which had two screws rotating in the same direction with an external diameter (D) of 65 mm, a devolatilization section, comprising a devolatilization aperture (O), and a discharge zone following same. This was an extruder analogous to the lower image of FIG. 5, but without a melt pump (SP).

[0133] The thermoplastic molding composition (TP) in the examples consisted of: [0134] A) 28.60% by weight of polymethyl methacrylate, VN 53 ml/g (0.5% by weight in DMF at 25° C.), [0135] B) 35.10% by weight of styrene-acrylonitrile copolymer, VN 100 ml/g (0.5% by weight in DMF at 25° C.), comprising 81% by weight of styrene, 19% by weight of acrylonitrile, [0136] C) 36.10% by weight of butadiene-methyl methacrylate-styrene-graft rubber (MBS product Paraloid 2668 from Dow Chemical), and also [0137] Z) 0.20% by weight of calcium stearate.

[0138] The discharge zone, in which the pressure was increased to 60 bar, comprised conveying elements. The extruder comprised no melt pump (SP), and the length of the region of conveying FS between the devolatilization aperture O and the melt pump SP was 5.25 D.

[0139] The temperature of the thermoplastic molding composition measured by a commercially available insertion thermometer on the pellet strand discharged from the start-up diverter of the underwater pelletization system, which had been switched to “floor”, was 295° C. at the end of the discharge zone. Content of residual monomers was determined by means of gas chromatography, where the sample was produced by placing 1 g of the fully cooled resultant thermoplastic molding composition in 5 g of a solvent mixture produced from 78.048 g of dimethyl sulfoxide, 7.2 mg of mesitylene, 4.32 g of toluene and 0.432 g of propionitrile and shaking at 40° C. for 24 hours. A liquid sample of the mixture cooled to room temperature was injected into a gas chromatograph.

[0140] The content of residual butadiene determined in the thermoplastic molding composition produced was 5.5 ppm, based on the entire composition of the thermoplastic molding composition. This is disadvantageous for some applications.

COMPARATIVE EXAMPLE 2

[0141] The extruder used in comparative example 2, based on FIG. 4, differed from the extruder according to comparative example 1 in that the pressure was increased from 10 bar to 60 bar by a melt pump following the discharge zone. The length of the region of conveying (FS) between the devolatilization aperture (O) and the melt pump (SP) was 5.25 D. The temperature of the thermoplastic molding composition after the melt pump was 285° C. The residual butadiene content determined in the resultant thermoplastic molding composition was 3.5 ppm, based on the entire composition of the thermoplastic molding composition. This is disadvantageous for some applications.

INVENTIVE EXAMPLE 3

[0142] The extruder used, corresponding to FIG. 3, differed from the extruder according to comparative example 2 in that the length of the region of conveying (FS) between the devolatilization aperture (O) and the melt pump (SP) was only 1.25 D.

[0143] The temperature of the thermoplastic molding composition after the melt pump was 256° C. The residual butadiene content determined in the resultant thermoplastic molding composition was below 1 ppm, based on the entire composition of the thermoplastic molding composition.

[0144] The effect of the low level of build-up of residual monomer with the process of the invention could also be confirmed with other styrene-copolymer molding compositions comprising graft polymer, for example the ABS compositions according to WO 2017/093468 (e.g. with molding compositions comprising at least 60% by weight of SAN and at least one polybutadiene-based graft copolymer).