METHOD FOR THE PRODUCTION OF REDUCED DISCOLORATION ASA OR ABS GRANULE COPOLYMERS

Description

[0001] The present invention relates to a process for producing graft copolymers with reduced discoloration, in particular reduced yellowing, based on acrylonitrile styrene acrylate (ASA) or acrylonitrile butadiene styrene (ABS) graft copolymers, and to graft copolymers obtained by this process. The invention further relates to a process for producing a thermoplastic molding compound containing ABS or ASA graft copolymers obtained by the process according to the invention, and to molding compounds obtained thereby.

[0002] ABS copolymers and ASA copolymers have been used in large quantities for decades as thermoplastic molding compounds for the production of various types of molded parts. It is known that styrene-acrylonitrile (SAN) and / or α-methylstyrene-acrylonitrile (AMSAN) copolymers can be modified to improve their impact strength by incorporating one or more graft rubbers (hereinafter also referred to as graft copolymers), such as grafted polybutadiene rubbers or grafted, cross-linked polyacrylates. These impact-modified SAN molding compounds can be produced by polymerizing styrene and acrylonitrile in the presence of, for example, a polybutadiene rubber and / or by subsequently mixing a graft copolymer with a separately prepared styrene-acrylonitrile matrix.

[0003] The property profiles of molding compounds and the molded parts produced from them can vary considerably. Particularly important properties of ABS and ASA molding compounds include advantageous mechanical properties such as high toughness and impact strength, good processability, relatively high heat resistance, and a light base color (low yellow value) so that the material can be colored in a wide range of hues.

[0004] Typically, graft rubber copolymers are produced by synthesizing cross-linked polyacrylate latices or polybutadiene latices as graft bases via emulsion polymerization. Subsequently, one or more graft shells are formed by grafting a mixture of, for example, styrene and acrylonitrile, and optionally other monomers, onto these shells via graft emulsion polymerization. After emulsion polymerization, the graft copolymer latex is usually precipitated, separated from the suspension, washed, and dried (e.g., WO 2015 / 078751).

[0005] WO 2015 / 000873 describes graft copolymer latexes in which the precipitation step is followed by a sintering step in which the precipitated graft copolymer latex, in particular an ABS graft copolymer latex, is agglomerated into larger particles at a temperature of 100° to 125°C.

[0006] Processes for producing ASA or ABS graft copolymers comprising a precipitation and a sintering step are further described in WO 2020 / 043690 and WO 2020 / 020869. In a first step, the graft copolymer latex is mixed with the precipitation solution at a temperature T1 (precipitation temperature) in the range of 30 to 80 °C, and then, in a second step, the precipitation mixture is maintained at a temperature T2 (sintering temperature) in the range of 70 to 140 °C for a period of preferably 2 to 90 minutes.

[0007] The production of ASA graft copolymers with one or two graft shells is described as an example. The latter are obtained by graft emulsion polymerization in two stages, whereby styrene is first grafted onto a cross-linked polybutyl acrylate rubber latex, and then a mixture of styrene and acrylonitrile is grafted onto this first graft shell. After completion of the monomer addition, post-polymerization takes place at 65°C for 60 minutes. The resulting ASA graft copolymer latex (Dw 500 nm) is then precipitated at 60°C or 70°C using MgSO₄ and subsequently sintered at 92°C or 130°C for 5 minutes.

[0008] WO 2020 / 020831 also discloses ASA graft copolymers comprising a two-layer styrene-acrylonitrile copolymer graft shell, wherein the first layer was formed by emulsion polymerization of styrene onto a polyacrylate latex, and the second layer – obtained by emulsion polymerization of styrene and acrylonitrile – was grafted onto the polystyrene-grafted latex. The resulting graft copolymers were processed by precipitation at 88°C, brief heating to 99°C, filtration, washing, and drying.

[0009] A disadvantage is that the graft copolymers obtained according to the prior art methods exhibit discoloration after the sintering step, in particular yellowish to reddish discoloration, i.e. a high yellow value.

[0010] WO 03 / 010214 describes the production of ABS graft copolymers with low residual styrene and acrylonitrile monomer content by emulsion polymerization, wherein a mixture of styrene and acrylonitrile is added to a diene rubber base and polymerized to a conversion of 95%, and then a third monomer (boiling point < 120°C), preferably methyl methacrylate, is added and polymerized.

[0011] The temperatures during polymerization, post-polymerization, and precipitation are a maximum of 93°C. After precipitation, the material is insulated and dried. There is no sintering step.

[0012] WO 2015 / 7165810 A1 describes a process for producing styrene graft copolymers with an optimized residual monomer content, as well as graft copolymers produced thereby and molding compounds containing them. The process comprises (i) providing and agglomerating the graft base B present in an emulsion; (ii) adding styrene monomers A1 and vinyl cyanide monomers A2 to the graft base B over a defined period of monomer addition; and (iii) the simultaneous graft copolymerization of the added styrene monomers A1 and the vinyl cyanide monomers A2 onto the agglomerated graft base B, wherein step (ii) integrates the mass ratio of styrene monomers A1 to vinyl cyanide monomers A2 of the monomer addition at the end of the monomer addition period as the mass ratio of the components of the monomer addition over the entire monomer addition period.

[0013] Well-known ASA and ABS graft copolymers often have an excessively high residual acrylonitrile monomer content, which does not meet today's market requirements, as acrylonitrile is a health hazard and has an unpleasant odor.

[0014] An object of the present invention is to provide a process for producing ASA or ABS graft copolymers that yields ASA or ABS graft copolymers with a low residual acrylonitrile monomer content. Furthermore, the ASA or ABS graft copolymers should exhibit no or only minimal discoloration after sintering, and thus a white or nearly white color, i.e., a low yellowness index (YI).

[0015] It has now been surprisingly shown that the residual acrylonitrile monomer content of ASA or ABS graft copolymers can be significantly reduced, and less discolored graft rubbers are obtained after sintering, if, during the production of the graft shell, further vinyl aromatic monomer is added following the simultaneous addition of vinyl aromatic and nitrile monomer, and the resulting reaction mixture of rubber graft base and added monomers is allowed to polymerize.

[0016] An object of the invention is a process for producing at least one graft copolymer B containing (preferably consisting of): B1: 40 to 90 wt.%, preferably 45 to 85 wt.%, particularly preferably 50 to 70 wt.%, based on the graft copolymer B, of at least one, preferably one, graft base B1, obtained by emulsion polymerization of: B11 50 to 100 wt.%, preferably 80 to 100 wt.%, particularly preferably 90 to 99.9 wt.%, based on the graft base B1, of at least one monomer B11 selected from C1-C8 alkyl(meth)acrylate, preferably n-butyl acrylate, and butadiene; B12 0 to 10 wt.%, preferably 0 to 5 wt.%, often 0.1 to 5 wt.%, particularly preferably 0 to 2.5 wt.%, often 1 to 2.5 wt.%, based on the graft base B1, of at least one multifunctional crosslinking monomer B12, preferably selected from allyl (meth)acrylate, divinylbenzene, diallyl maleate, diallyl fumarate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate and dihydrodicyclopentadienyl acrylate (DCPA); B13 0 to 50 wt.%, preferably 0 to 20 wt.%, particularly preferably 0 to 10 wt.%.-%, based on the graft base B1, of at least one further monomer B13 selected from styrene, alpha-methylstyrene, C1-C4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, chloroprene, methyl methacrylate, alkylene glycol di(meth)acrylate and vinyl methyl ether; wherein the sum of B11, B12 and B13 is 100 wt%; and B2: 10 to 60 wt.%, preferably 15 to 55 wt.%, particularly preferably 30 to 50 wt.%, based on the graft copolymer B, at least one, preferably one or two, particularly preferably two, graft shell(s) B2, which - in the presence of the at least one graft base B1 - is obtained by emulsion polymerization of: B21 50 to 100 wt.%, preferably 50 to 95 wt.%, particularly preferably 65 to 85 wt.%, most preferably 70 to 85 wt.%, based on the graft shell B2, at least one vinylaromatic monomer B21 selected from styrene and alpha-methylstyrene; and B22 0 to 50 wt.%, preferably 5 to 50 wt.%, particularly preferably 15 to 35 wt.%.-%, most preferably 15 to 30 wt.%, based on the graft shell B2, of at least one monomer B22 selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, anhydrides of unsaturated carboxylic acids (e.g. maleic anhydride or phthalic anhydride) and imides of unsaturated carboxylic acids (e.g. N-substituted maleimide such as N-cyclohexyl maleimide or N-phenyl maleimide); wherein the sum of B21 and B22 is 100 wt.%; and wherein at least one graft shell B2 is obtained by emulsion polymerization of 50 to 95 wt.%, preferably 65 to 85 wt.%, particularly preferably 70 to 85 wt.%, of at least one monomer B21 and 5 to 50 wt.%, preferably 15 to 35 wt.%, particularly preferably 15 to 30 wt.%, of at least one monomer B22; wherein the sum of the at least one graft base B1 and the at least one graft shell B2 yields 100 wt.%; and wherein . The procedure includes the following steps: a) Production of a latex comprising at least one graft copolymer B: a1) a aqueous latex containing at least one, preferably one, graft base B1; a2) optionally production of a first graft shell B2 or B2' by: a2-1) addition and emulsion polymerization of a first part - based on the total amount of B21 - of the at least one monomer B21 or B21', preferably styrene, to the graft base B1; a2-2) post-polymerization of the latex obtained in a2-1); a3) Production of a first graft shell B2 or, if steps a2-1) and a2-2 are present, production of a second graft shell B2 or B2" by: a3-1) simultaneous addition and emulsion polymerization of a first or further part of the at least one monomer B21 or B21" - based on the total amount of B21 - and the total amount of the at least one monomer B22 or B22" to the latex from step a1) or a2-2) ...a2-2); a3-2) immediately after completion of the addition of the monomers in step a3-1), addition and emulsion polymerization of the remaining part of the at least one monomer B21 or B21" - based on the total amount of B21 - to the latex obtained in step a3-1); a3-3) post-polymerization of the latex of the graft copolymer B obtained in step 3-2), preferably for at least 15 minutes.

[0017] The inventive method as described above may further comprise one or more of the following steps b) to g) (in the order mentioned): b) Precipitation of the graft copolymer B latex obtained in step a) at a temperature of 30 to 95°C, preferably 40 to 90°C, particularly preferably 50 to 90°C, most preferably 60 to 88°C, wherein the graft copolymer B latex is mixed with at least one precipitation solution PS, resulting in a precipitation mixture; c) Sintering of the precipitation mixture obtained in step b) at a temperature of 85 to 150°C, preferably 90 to 145°C, particularly 90 to 140°C, most preferably 92 to 135°C, preferably for 15 to 90 minutes, particularly preferably 15 to 75 minutes, particularly 20 to 60 minutes, wherein the temperature in step c) is at least 5°C, preferably at least 10°C, particularly preferably 15°C, higher than in step b); d) optionally cooling the sintered precipitation mixture from step c), preferably to a temperature of 20 to 90°C;e) mechanical dewatering of the sintered precipitate mixture obtained in step c) or d), wherein a graft copolymer B with a water content equal to or less than 50 wt.%, preferably equal to or less than 40 wt.%, particularly preferably 10 to 35 wt.%, in each case based on the moist graft copolymer B, is obtained; f) optionally washing the graft copolymer B obtained in step e); g) optionally drying the graft copolymer B obtained in step e) or f).

[0018] A preferred method according to the invention as described above comprises steps a), b), c) and e), and optionally steps d), f) and / or g).

[0019] The term 'latex' refers to a polymer dispersion, i.e., a mixture of polymer particles and an aqueous liquid. Graft copolymer B

[0020] Preferably, the graft copolymer B is selected from ASA graft copolymers and ABS graft copolymers; ASA graft copolymers are particularly preferred.

[0021] ASA graft copolymers typically contain a cross-linked polyalkyl(meth)acrylate rubber, in particular a cross-linked polybutyl acrylate graft base B1, as graft base B1.

[0022] ABS graft copolymers typically contain one or more polybutadiene rubbers and / or one or more styrene-butadiene rubbers as the graft base B1.

[0023] Typically, the graft base B1 consists of a polymer, preferably an at least partially cross-linked polymer, with a glass transition temperature (Tg) below 0°C, preferably below -20°C, particularly preferably below -40°C, wherein the glass transition temperature Tg is measured by dynamic mechanical analysis (DMA) using a frequency of 1 Hz.

[0024] The at least one graft shell B2 typically consists of monomers that copolymerize to form a polymer with a glass transition temperature of more than +20°C, preferably more than +60°C.

[0025] Preferred monomers of graft shell B2 (monomers B21 and B22) are styrene and / or (alpha)-methylstyrene and (meth)acrylonitrile, in particular styrene and acrylonitrile, and optionally methyl(meth)acrylate, ethyl acrylate, N-phenylmaleimide and maleic anhydride.

[0026] Preferred monomers B11 for the preparation of the graft base B1 are butadiene, alkyl acrylates and / or alkyl methacrylate (also referred to as alkyl(meth)acrylates) with 1 to 8, preferably 4 to 8, carbon atoms in the alkyl group.

[0027] Preferably, the monomer B11 is at least a monomer selected from C 4 -C 8 -alkyl acrylates, preferably selected from butyl acrylate, ethylhexyl acrylate and cyclohexyl acrylate.

[0028] Frequently, n-butyl acrylate and / or 2-ethylhexyl acrylate are used as monomer B11; n-butyl acrylate alone or in mixture with other monomers B11 is particularly preferred.

[0029] To achieve crosslinking of the C1-C8 alkyl(meth)acrylate monomers B11 and thus crosslinking of the graft base B1, the monomers B11 are polymerized in the presence of 0.1 to 10 wt.%, preferably 0.1 to 5 wt.%, particularly preferably 0.5 to 4 wt.%, most preferably 1 to 3 wt.%, in particular 1 to 2.5 wt.%, based on the graft base B1, of one or more polyfunctional, crosslinking monomer(s) B12.

[0030] Suitable monomers B12 are in particular polyfunctional, crosslinking monomers that can be copolymerized with the aforementioned monomers, especially B11 and B13.

[0031] Suitable polyfunctional, crosslinking monomers B12 contain two or more, preferably two or three, particularly preferably exactly two ethylenic double bonds, which are preferably not 1,3-conjugated.

[0032] Examples of suitable polyfunctional, crosslinking monomers B12 are allyl(meth)acrylate, divinylbenzene, diallyl esters of carboxylic acids, such as diallyl maleate, diallyl fumarate, and diallyl phthalate. The acrylic acid ester of tricyclodecenyl alcohol (tricyclodecenyl acrylate, dihydrodicyclopentadienyl acrylate, DCPA) – as described in DE-A 1 260 135 – is also a preferred polyfunctional, crosslinking monomer B12.

[0033] In particular, the polyfunctional crosslinking monomer B12 (which is preferably used for crosslinking polyalkyl(meth)acrylate rubber) is at least one monomer selected from allyl(meth)acrylate (AMA), divinylbenzene, diallyl maleate, diallyl fumarate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate and dihydrodicyclopentadienyl acrylate (DCPA), preferably allyl(meth)acrylate, divinylbenzene, diallyl maleate, diallyl fumarate, diallyl phthalate and DCPA, preferably allyl(meth)acrylate and DCPA.

[0034] In a preferred embodiment, 1 to 2.5 wt.%, preferably 1.5 to 2.2 wt.%, based on the graft base B1, dihydrodicyclopentadienyl acrylate (DCPA) alone or in mixture with at least one further of the above-mentioned monomers B12, in particular in mixture with allyl(meth)acrylate, is used as monomer B12.

[0035] Furthermore, the at least one graft base B1 may optionally contain one or more copolymerizable, monoethylene unsaturated monomers B13 that are different from B11 and B12.

[0036] Monomers B13 can be selected, for example, from styrene, alpha-methylstyrene, C 1 -C 4 -alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, chloroprene, methyl methacrylate, alkylene glycol di(meth)acrylate and vinyl methyl ether.

[0037] Preferably, the further monomer B13 is at least a monomer selected from styrene, (alpha)-methylstyrene, acrylonitrile, methacrylonitrile, methyl(meth)acrylate, isoprene, chloroprene and C1-C4-alkylstyrene.

[0038] In a preferred embodiment, the vinylaromatic monomer is styrene and / or (alpha)-methylstyrene, and the monomer B22 is acrylonitrile or a mixture of acrylonitrile and at least one monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, maleic anhydride, phthalic anhydride, N-cyclohexyl maleimide, and N-phenylmaleimide. If B22 is a mixture of acrylonitrile and at least one monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, maleic anhydride, phthalic anhydride, N-cyclohexyl maleimide, and N-phenylmaleimide, the proportion of acrylonitrile, based on the total amount of B22, is at least 50 wt.%, preferably at least 80 wt.%, and particularly preferably at least 90 wt.%.

[0039] Acrylonitrile is particularly preferred as the monomer B22.

[0040] Particularly preferred are the monomers B21 and B22 used for the emulsion polymerization of graft copolymer B, mixtures of styrene and acrylonitrile with a weight ratio of styrene to acrylonitrile in the range of 95:5 to 50:50, preferably in the range of 90:10 to 65:35, particularly preferably in the range of 85:15 to 70:30.

[0041] In a preferred embodiment, the at least one graft base B1 is obtained by emulsion polymerization of: B11: 80 to 99.9 wt.%, preferably 90 to 99.5 wt.%, particularly preferably 90 to 99.0 wt.% based on the graft base B1, of at least one C1-C8 alkyl(meth)acrylate, preferably n-butyl acrylate and / or 2-ethylhexyl acrylate, as monomer B11; B12: 0.1 to 10 wt.%, preferably 0.5 to 4 wt.%, particularly preferably 1 to 2.5 wt.%, based on the graft base B1, of at least one polyfunctional crosslinking monomer B12; preferably selected from allyl(meth)acrylate, divinylbenzene, diallyl maleate, diallyl fumarate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate and dihydrodicyclopentadienyl acrylate (DCPA); B13: 0 to 19.9 wt.%, preferably 0 to 9.5 wt.%, particularly preferably 0 to 9.0 wt.%, based on the graft base B1, of at least one further monomer, preferably selected from styrene, alpha-methylstyrene, C1-C4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, chloroprene, methyl methacrylate, alkylene glycol di(meth)acrylate and vinyl methyl ether; where the sum of B11, B12 and B13 equals 100% by weight.

[0042] In a further preferred embodiment, the at least one graft base B1 is obtained by emulsion polymerization of: B11: 90 to 99.9 wt.%, preferably 97 to 99.5 wt.%, particularly preferably 97.5 to 99 wt.%, based on the graft base B1, of at least one C1-C8 alkyl(meth)acrylate, preferably at least one C4-C8 alkyl(meth)acrylate, particularly preferably n-butyl acrylate and / or 2-ethylhexyl acrylate, most preferably n-butyl acrylate, as monomer B11; and B12: 0.1 to 10 wt.%, preferably 0.5 to 3 wt.%, particularly preferably 1 to 2.5 wt.%, based on the graft base B1, of at least one multifunctional, crosslinking monomer B12; selected from allyl(meth)acrylate, divinylbenzene, diallyl maleate, diallyl fumarate, diallyl phthalate and dihydrodicyclopentadienyl acrylate (DCPA), in particular from allyl(meth)acrylate and / or dihydrodicyclopentadienyl acrylate (DCPA); where the sum of B11 and B12 is 100 wt% (based on all monomers of the graft base B1).

[0043] In particular, further suitable compositions of the graft base B1, containing the monomers B11, B12 and optionally B13, as well as the general process for their preparation are described, for example, in DE-A 28 26 925, DE-A 31 49 358 and DE-A 34 14 118.

[0044] In a preferred embodiment, the at least one graft shell B2 is obtained by emulsion polymerization in the presence of the at least one graft base B1 from: B21: 50 to 95 wt.%, preferably 65 to 90 wt.%, particularly preferably 70 to 85 wt.%, based on the graft shell B2, at least one vinylaromatic monomer B21, wherein the monomer B21 is selected from styrene and (alpha)-methylstyrene, in particular styrene; and B22: 5 to 50 wt.%, preferably 10 to 35 wt.%, particularly preferably 15 to 30 wt.%, based on the graft shell B2, at least one ethylene-unsaturated monomer B22, wherein the monomer B22 is selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, anhydrides of unsaturated carboxylic acids (e.g., maleic anhydride, phthalic anhydride), and imides of unsaturated carboxylic acids (e.g., N-substituted maleimide, such as...). N-cyclohexyl maleimide and N-phenyl maleimide), preferably selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile.

[0045] In particular, the graft copolymer B comprises a graft base B1, preferably a cross-linked polyalkyl(meth)acrylate rubber as described above, and one or more graft shell(s) B2, in particular one or two graft shells B2, which differ in the selection and quantity of the monomers B21 and B22 and are obtained by stepwise graft emulsion polymerization of the monomers B21 and / or B22 in the presence of graft base B1 or in the presence of already grafted graft base based on B1.

[0046] In a preferred embodiment, the graft copolymer B comprises at least one graft base B1, preferably a cross-linked polybutyl acrylate rubber as described above, and exactly one graft shell B2, obtained by emulsion polymerization of the monomers B21 and B22 as described above, in particular styrene and acrylonitrile, in the presence of the graft base B1 (one-step grafting).

[0047] In a further preferred embodiment, the graft copolymer B comprises at least one graft base B1, preferably a cross-linked polybutyl acrylate rubber as described above, and two different graft shells B2, designated as graft shells B2' and B2", wherein B2' is obtained by emulsion polymerization of the monomer B21 (designated as B21'), in particular styrene, in the presence of the graft base B1, and the graft shell B2" is obtained by subsequent emulsion polymerization of the monomers B21 and B22 (designated as B21" and B22") as described above, in particular styrene and acrylonitrile, in the presence of the graft base B1 grafted with B2' (two-stage grafting).

[0048] In a preferred embodiment (one-stage grafting), the graft copolymer B contains: B1: 50 to 70 wt.%, preferably 55 to 65 wt.%, particularly preferably 58 to 65 wt.%, based on the graft copolymer B, at least one, preferably one, graft base B1 as described above, wherein the at least one graft base B1 preferably has a particle size (in particular mean particle diameter D v ) in the range of 50 to 190 nm, preferably 60 to 150 nm, particularly preferably 60 to 100 nm; B2: 30 to 50 wt.%, preferably 35 to 45 wt.%, particularly preferably 35 to 42 wt.%, based on the graft copolymer B, a graft shell B2, obtained by emulsion polymerization in the presence of at least one graft base B1 of: B21: 50 to 95 wt.%, preferably 65 to 85 wt.%, particularly preferably 70 to 85 wt.%, based on the graft shell B2, at least one vinylaromatic monomer B21, wherein the monomer B21 is selected from styrene and (alpha)-methylstyrene, in particular styrene; and B22: 5 to 50 wt.%, preferably 15 to 35 wt.%.-%, particularly preferably 15 to 30 wt%, based on the graft shell B2, of at least one ethylene-unsaturated monomer B22, wherein the monomer B22 is selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, anhydrides of unsaturated carboxylic acids (e.g. maleic anhydride, phthalic anhydride) and imides of unsaturated carboxylic acids (e.g. N-substituted maleimide such as N-cyclohexyl maleimide and N-phenyl maleimide), preferably selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile; . wherein the total amount of graft base B1 and graft shell B2 is 100 wt.% and wherein the latex of the graft copolymer B obtained in step a) has a particle size (in particular mean particle diameter D) v ) in the range of 60 to 200 nm, preferably from 80 to 150 nm.

[0049] According to a further embodiment, in the previously described single-stage grafting process, the graft base B1, which preferably has a particle size (in particular mean particle diameter Dv) in the range of 80 to 150 nm, can be agglomerated by known agglomeration processes (e.g., WO 2012 / 022710 and WO 2014 / 170406 or WO 2014 / 170406). The agglomerated graft base B1 is then grafted with a graft shell B2 as described above, wherein the latex obtained in step a) contains graft copolymers B with particle sizes (in particular mean particle diameter Dv) in the range of 200 to 600 nm, preferably 250 to 500 nm, and particularly preferably 300 to 400 nm. The latex obtained by means of an agglomerated graft base B1 is often bimodal and often exhibits bimodal particle size distributions with particle sizes (especially mean particle diameter Dv) in the range of 60 to 200 nm, often 60 to 150 nm, and 300 to 600 nm.

[0050] Typically, the particle size of latices in graft copolymer B can be expressed as the volume-mean average particle diameter, Dv value. The volume-mean particle diameter Dv (or the mean particle diameter according to De Broucker), also called mean particle diameter Dv, is an average value based on the unit volume of the particles. For example, the volume-mean particle diameter Dv can be determined by light scattering (laser diffraction) (e.g., with a Beckman Coulter instrument).

[0051] Furthermore, the particle size can be specified as the mean particle size D50. The mean particle diameter D50 represents the value on the particle size distribution curve at which 50 vol% of the particles (e.g., polyacrylate latex particles) have a diameter smaller than the D50 value and the other 50 vol% have a diameter larger than the D50 value. Similarly, the D90 value, for example, indicates the particle diameter at which 90 vol% of all particles have a smaller diameter.

[0052] According to the present invention, the particle size mentioned in connection with the graft copolymer B preferably means the volume-average particle diameter Dv, which was determined by means of light scattering.

[0053] In another preferred embodiment (two-stage grafting B2' and B2"), the graft copolymer B contains: B1: 50 to 70 wt.%, preferably 55 to 65 wt.%, based on the graft copolymer B, of at least one, preferably exactly one, graft base B1 as described above, wherein the at least one graft base B1 preferably has a particle size (in particular mean particle diameter Dv) in the range of 200 to 700 nm, preferably 300 to 600 nm, particularly preferably 350 to 550 nm; B2': 5 to 25 wt.%, preferably 5 to 20 wt.%, particularly preferably 5 to 15 wt.%, based on the graft copolymer B, of at least one graft shell B2' obtained by emulsion polymerization, in the presence of graft base B1, of: B21' 100 wt.%, based on graft shell B2', of at least one vinylaromatic monomer B21' selected from styrene and (alpha)-methylstyrene, in particular styrene; and B2": 20 to 40 wt.%, preferably 20 to 35 wt.%.-%, based on the graft copolymer B, at least one graft shell B2", obtained by emulsion polymerization, in the presence of graft base B1, grafted with B2', of: B21": 50 to 95 wt.%, preferably 65 to 90 wt.%, particularly preferably 70 to 85 wt.%, based on the graft shell B2", at least one vinylaromatic monomer B21", selected from styrene and (alpha)-methylstyrene, in particular styrene; and B22": 5 to 50 wt.%, preferably 10 to 35 wt.%, particularly preferably 15 to 30 wt.%, based on the graft shell B2", at least one monomer B22" selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, anhydrides of unsaturated carboxylic acids (e.g. maleic anhydride, phthalic anhydride) and imides of unsaturated carboxylic acids (e.g.N-substituted maleimide, such as N-cyclohexyl maleimide and N-phenyl maleimide), preferably selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile; wherein the total of graft base B1, graft shell B2' and graft shell B2" is 100 wt.%, and wherein the latex of the graft copolymer B obtained in step a) has a particle size (in particular, mean particle diameter Dv in the range of 300 to 800 nm, preferably 350 to 700 nm).

[0054] According to another embodiment, the graft copolymer B is a mixture of the embodiments of one-stage graft copolymer B and two-stage graft copolymer B described above (including graft B2' and B2").

[0055] Particularly preferred are the monomers B21, B21' and B21" styrene or mixtures of styrene and alpha-methylstyrene. The proportion of styrene, based on the total amount of B21 (or B21' and B21"), is preferably at least 50 wt.%, particularly preferably at least 80 wt.%, and most preferably at least 90 wt.%.

[0056] Particularly preferred are the monomers B22 and B22" acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, maleic anhydride, N-cyclohexyl maleimide, N-phenyl maleimide, and especially acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile and maleic anhydride. In the aforementioned mixtures of acrylonitrile, the proportion of acrylonitrile, based on the total amount of monomers B22 or B22", is at least 50 wt.%, preferably at least 80 wt.%, and particularly preferably 90 wt.%.

[0057] In a particularly preferred embodiment of the invention, the monomers B21, B21' and B21" are styrene and the monomers B22 and B22" are acrylonitrile.

[0058] In another embodiment, the graft copolymer B can be an ABS graft copolymer containing: B1: 40 to 80 wt.%, preferably 45 to 70 wt.%, particularly preferably 45 to 65 wt.%, based on the graft copolymer B, of at least one graft base B1 obtained by emulsion polymerization of butadiene as monomer B1; and B2: 20 to 60 wt.%, preferably 30 to 55 wt.%, particularly preferably 35 to 55 wt.%, based on the graft copolymer B, of at least one graft shell B2 as described above, preferably obtained by emulsion polymerization of 65 to 85 wt.%, based on the graft shell B2, of styrene as monomer B21 and 15 to 35 wt.%, based on the graft shell B2, of acrylonitrile as monomer B22, in the presence of the at least one graft base B1; wherein the total of graft base B1 and graft shell B2 is equal to 100 wt. %; and wherein the latex of the ABS graft copolymer B has a particle size (in particular mean particle diameter Dv) in the range of 100 to 500 nm.

[0059] In a further embodiment of the invention, the inventive method comprises the synthesis of at least two, preferably two, three or four different graft copolymers B, wherein the graft copolymers B (e.g. graft copolymers BI and B-II) differ in their particle size.

[0060] In the aforementioned embodiment, graft copolymer B comprises in particular at least two graft copolymers BI and B-II, preferably based on crosslinked C1-C8 alkyl(meth)acrylate graft bases B1 as described above, wherein: Graft copolymer BI (fine-grained ASA rubber) has a particle size (in particular mean particle diameter Dv) in the range of 60 to 200 nm, preferably from 80 to 150 nm, and graft copolymer B-II (coarse-grained ASA rubber) has a particle size (mean particle diameter Dv) in the range of 300 to 800 nm, preferably 350 to 700 nm.

[0061] The graft copolymer BI (fine-grained ASA rubber) is preferably obtained by emulsion polymerization of the monomers B21 and B22 as described above, in particular of styrene as B21 and acrylonitrile as B22, in the presence of the previously prepared graft base B1 as described above, as an example of a one-stage graft copolymer B.

[0062] Preferably, the graft copolymer B-II (coarse ASA rubber) should have a narrow particle size distribution, wherein the particle size distribution Q = (D 90 -D 10 ) / D 50 is less than 0.3, preferably less than 0.2.

[0063] According to a further preferred embodiment, the graft copolymer B is a graft copolymer produced by emulsion polymerization with a core-shell structure, comprising an inner core BK1 and three layers BK2, BH1 and BH2, in the order BK1, BK2, BH1, BH2 from the inside out (for example, as described in WO 2020 / 020834 A1). In the previously described graft copolymer B with a core-shell structure, the graft base B1 described above comprises an inner core BK1 and an outer core shell BK2, and the graft shell B2 or B2' and B2" comprises the layers BH1 and BH2.

[0064] According to another preferred embodiment, the graft copolymer B is a graft copolymer produced by emulsion polymerization with a core-shell structure comprising an inner core BS and four layers BK1, BK2, BH1 and BH2, in the order BS, BK1, BK2, BH1, BH2 from the inside out.

[0065] In the previously described graft copolymer B with a core-shell structure, the graft base B1 described above comprises an inner core BS, a first core shell BK1 and a second (outer) core shell BK2, and the graft shell B2 or B2' and B2" comprises the layers BH1 and BH2.

[0066] Often, such graft copolymers B with a core-shell structure are composed of: BS: 0 to 5 wt% of an inner core BS consisting of at least one copolymer of: BK21: 95.0 to 99.0 wt% of at least one C2-C8 alkyl acrylate; BK22: 1.0 to 5.0 wt% of one or more bi- or polyfunctional crosslinking monomers; BK1: 0 to 19 wt% of an inner core BK1, or - if BS is present - a core shell BK1, consisting of at least one copolymer of: BK11: 95.0 to 99.9 wt% of at least one vinylaromatic monomer and BK12: 0.1 to 5.0 wt% of at least one bi- or polyfunctional crosslinking monomer; BK2: 40 to 61 wt% of a core shell BK2 consisting of at least one copolymer of: BK21: 95.0 to 99.0 wt% of at least one C2-C8 alkyl acrylate; BK22: 1.0 to 5.0 wt.% of one or more bi- or polyfunctional crosslinking monomers; BH1: 1 to 19 wt.% of a first graft shell layer BH1, consisting of at least one vinylaromatic polymer; and BH2: 21 to 39 wt.%.-% of a second graft shell layer BH2 ​​consisting of at least one copolymer containing at least one vinylaromatic monomer BH21 and at least one nitrile monomer BH22; wherein the sum of BS, BK1, BK2, BH1 and BH2 equals 100 wt%; and wherein the mean particle diameter Dv of the graft copolymer B is in the range of 300 to 600 nm.

[0067] Suitable crosslinked C1-C8 alkyl(meth)acrylate polymer graft bases B1 of the graft copolymer B-II (designated as B1-II) can be prepared according to known methods for the production of coarse dispersions, expediently by seed polymerization, as described in DE 1 911 882 for the production of ASA polymers.

[0068] According to this process, a finely divided, cross-linked acrylate latex or a finely divided, cross-linked polystyrene latex with a particle size (in particular, mean particle diameter Dw) of 50 to 180 nm, preferably 50 to 120 nm, is used as seed latex. The seed latex, obtained by emulsion polymerization of C1-C8 alkyl(meth)acrylates and cross-linking monomers or by emulsion polymerization of styrene and cross-linking monomers (see, for example, BK1 as described above), is subjected to a further polymerization reaction. In particular, the reaction conditions are adjusted such that only further growth of the existing seed latex particles is permitted, without forming new latex particles (described in Journal of Applied Polymer Science, Vol. 9 (1965), pages 2929 to 2938). An initiator is typically used in this process.

[0069] The particle size of the resulting graft copolymer B-II (coarse rubber) can be adjusted by varying the ratio of seed latex to monomers. Graft copolymer B-II is preferably obtained by emulsion polymerization of monomers B21 and B22 as described above, in particular styrene or α-methylstyrene as B21 and acrylonitrile as B22, in the presence of the previously prepared graft base B1-II.

[0070] Preferably, the graft copolymers BI and B-II described above are prepared separately in steps a) to c), optionally d), and e), and optionally f) and g), precipitated, sintered, optionally cooled, dehydrated and optionally washed and dried.

[0071] It is also possible to mix the graft copolymer latices BI and B-II after their separate preparation in step a) and precipitate them together in step b). Subsequent steps such as sintering in step c), cooling in step d), dewatering in step e), washing in step f), and drying in step g) can be carried out as described.

[0072] The weight ratio of the graft copolymers BI and B-II can be varied over a wide range.

[0073] Preferably, the graft copolymer B is a mixture of graft copolymer BI and B-II, wherein the weight ratio of BI: B-II is from 90 : 10 to 10 : 90, preferably 80 : 20 to 20 : 80.

[0074] Graft copolymers B with different particle sizes, in particular bimodal particle size distributions of 60 to 200 nm and 300 to 600 nm, can also be obtained using known agglomeration processes.

[0075] Graft copolymers with large and small particles are described, for example, in DE-A 36 15 607.

[0076] Furthermore, graft copolymers B with two or more different graft shells B2 can be used as described above. Other graft copolymers with multilayer graft shells are described, for example, in EP-A 0111260 and WO 2015 / 078751. Step a) - Preparation of the graft copolymer B by emulsion polymerization

[0077] The production of a latex of at least one graft copolymer B in step a) of the process according to the invention comprises: a1) A supply of aqueous latex containing at least one, preferably one, graft base B1; a2) optionally, preparation of a first graft shell B2 or B2' by: a2-1) addition and emulsion polymerization of a first part – based on the total amount of B21 – of the at least one monomer B21 or B21', preferably styrene, to the graft base B1; a2-2) post-polymerization of the latex obtained in a2-1); a3) preparation of a first graft shell B2 or – if steps a2-1) and a2-2 are present – ​​preparation of a second graft shell B2 or B2' by: a3-1) simultaneous addition and emulsion polymerization of a first or further part of the at least one monomer B21 or B21' – based on the total amount of B21 – and the total amount of the at least one monomer B22 or B22' to the latex from step a1) or B22'.a2-2); a3-2) immediately after completion of the addition of the monomers in step a3-1), addition and emulsion polymerization of the remaining part of the at least one monomer B21 or B21" - based on the total amount of B21 - to the latex obtained in step a3-1); a3-3) post-polymerization of the latex of the graft copolymer B obtained in step 3-2).

[0078] Typically, the graft copolymer B is produced in the form of a latex (rubber) by emulsion polymerization in step a), wherein first one or more graft base(s) B1 are obtained by emulsion polymerization of the monomers B11, B12 and optionally B13 as described, and subsequently one or more graft shell(s) B2 are obtained by emulsion graft polymerization of the monomers B21 and B22 as described in the presence of one or more of the graft bases B1.

[0079] Preferably, the latex of the graft copolymer B is polymerized by aqueous radical emulsion polymerization. The reaction is typically initiated via water-soluble or oil-soluble radical polymerization initiators, e.g., inorganic or organic peroxides such as peroxodisulfate or benzoyl peroxide, or with the aid of redox initiator systems (see WO 2002 / 10222, DE-A 28 26 925, and EP-A 022 200). Preferably, an inorganic peroxide salt, in particular an inorganic peroxodisulfate salt, preferably sodium peroxodisulfate and / or potassium peroxodisulfate, is used in the emulsion polymerization of the graft copolymer B.

[0080] Conventional anionic emulsifiers may be used as emulsifiers in the preparation of graft base B1 and / or in the emulsion polymerization for the production of the at least one graft copolymer B. Preferably used as emulsifiers are: alkyl sulfates, alkyl sulfonates, alkyl sulfonic acids, aryl sulfonates, soaps of saturated or unsaturated fatty acids, as well as alkaline disproportionated or hydrogenated abiic or talloleic acids or mixtures thereof. For the production of butadiene-based graft bases, emulsifiers with carboxyl groups are preferably used (e.g., disproportionated abiic acid, salts of C10-C18 fatty acids). Furthermore, alkali soaps of sodium and potassium salts of disproportionated and / or dehydrated and / or hydrogenated and / or partially hydrogenated resins (rosin) with at least 30 wt.% dehydroabiatic acid content and at most 1 wt.% are preferably used as emulsifiers for butadiene-based graft bases.-% content of abiotic acid is used.

[0081] For the production of graft bases based on C 1 -C 8 -alkyl(meth)acrylates, C 10 -C 20 -alkylsulfonic acids and / or C 10 -C 20 -alkylsulfonates, for example a C 12 -C 18 -alkylsulfonic acid, are preferably used as emulsifiers.

[0082] Furthermore, salts, acids and bases can be used in the emulsion polymerization of the graft base B1 and the graft shell B2, especially to adjust the pH value or to buffer the reaction mixture.

[0083] For example, sulfuric acid, phosphoric acid, solutions of sodium hydroxide, potassium hydroxide, sodium salts and potassium salts of carbonates, bicarbonates, sulfates and / or phosphates (e.g. tetrasodium pyrophosphate) can be used.

[0084] In a preferred embodiment, at least one carbonate and / or bicarbonate salt, such as sodium bicarbonate, is used as a buffer.

[0085] The polymerization temperature during the emulsion polymerization of the graft copolymer B in step a), i.e. a2) and a3), of the process according to the invention is generally 25 to 95°C, preferably 40 to 90°C, particularly preferably 50 to 80°C, and especially 55 to 70°C.

[0086] Conventional temperature control, e.g. isothermal, can be used here; however, the graft polymerization reaction is preferably carried out such that the temperature difference between the beginning and end of the reaction is at least 2°C, preferably at least 3°C, often 2 to 3°C (i.e., the temperature is correspondingly higher at the end of the reaction).

[0087] According to the invention, the graft copolymer B is produced by means of emulsion polymerization. Common embodiments of the emulsion polymerization reaction in batch or continuous operation are known to those skilled in the art.

[0088] The optional step a2) includes the production of a first graft casing B2 or B2' by: a2-1) Addition and emulsion polymerization of a first part of the at least one monomer B21 or B21', preferably styrene, to the graft base B1, wherein a latex of a graft base B1 grafted with B2' is obtained, and a2-2) Postpolymerization of the latex obtained in a2-1).

[0089] The temperature in step a2) is chosen as described above and is preferably 50 to 80°C, particularly 55 to 70°C.

[0090] The post-polymerization in step a2-2) preferably takes place over a period of 15 to 45 minutes, preferably 20 to 35 minutes.

[0091] Step a3) of the inventive method comprises the production of a first graft shell B2 or - if steps a2-1) and a2-2) are present - the production of a second graft shell B2 or B2" as previously described.

[0092] The temperature in step a3) is selected as described above and is preferably 50 to 80°C, particularly 50 to 70°C. Preferably, the temperature in step a3) is at least 2°C, preferably 3 to 4°C, higher than the temperature in step a2).

[0093] In step a3-1), the monomers B21 or B21" and B22 or B22" are added individually or as a monomer mixture in the specified quantities and ratios continuously to the latex from step a1) or a2-2) and polymerized.

[0094] The addition of the monomers preferably takes place over a period of 60 to 250 minutes, particularly preferably 100 to 200 minutes, most preferably 120 to 180 minutes.

[0095] In step a3-2), the remaining part of the at least one monomer B21 or B21", preferably styrene, is added, generally over a period of 5 to 45 minutes, preferably 10 to 35 minutes, particularly preferably 15 to 35 minutes, and especially 20 to 30 minutes.

[0096] In step a3-2), the "remaining part" of the at least one monomer B21 or B21" generally means up to 5 wt.%, preferably 1 to 4.5 wt.%, based on the graft copolymer B.

[0097] In step a3-3), the latex of the graft copolymer B obtained in step 3-2) is post-polymerized preferably for at least 15 minutes, particularly preferably for 20 to 90 minutes, and most preferably for 30 to 60 minutes.

[0098] The method according to the invention can further comprise steps b) to g) as described above. Preferably, a method according to the invention as described above comprises steps a), b), c) and e), and optionally steps d), f) and / or g). Step b) Precipitation of the latex of the graft copolymer B

[0099] Step b) of the process according to the invention comprises precipitating the graft copolymer B obtained in step a), wherein the latex of the graft copolymer B is mixed with at least one precipitation solution PS, thereby forming a precipitation mixture, wherein preferably the at least one precipitation solution PS contains at least one salt and / or acid. In particular, the precipitation solution PS contains at least one alkaline earth metal salt, preferably at least one salt of magnesium and / or calcium; particularly preferably at least one magnesium salt.

[0100] In particular, the at least one alkaline earth metal salt is selected from alkaline earth metal halides such as chlorides, alkaline earth metal sulfates, alkaline earth metal phosphates such as orthophosphates or pyrophosphates, alkaline earth metal acetates, and alkaline earth metal formates. Preferably, the at least one alkaline earth metal salt is selected from chlorides and sulfates.

[0101] Preferred alkaline earth metal salts are magnesium sulfate (such as kieserite (Mg[SO₄] · H₂O), pentahydrite (Mg[SO₄] · 5H₂O), hexahydrite (Mg[SO₄] · 6H₂O) and epsomite (Mg[SO₄] · 7H₂O, Epsom salt)), magnesium chloride, calcium chloride, calcium formate, magnesium formate or mixtures thereof. The use of magnesium sulfate is particularly preferred.

[0102] In particular, the solids content of the precipitation mixture obtained in step b) is in the range of 5 to 20 wt.%, preferably 7 to 18 wt.%, more preferably 10 to 18 wt.%, also preferably 12 to 20 wt.%.

[0103] Preferably, the pH of the precipitate mixture obtained in step b) is in the range of 5 to 10, more preferably in the range of 6 to 9, and particularly preferably in the range of 8 to 9. For example, the pH can be adjusted by adding buffer salts, acids and / or bases, wherein, for example, sulfuric acid, phosphoric acid, solutions of sodium hydroxide, potassium hydroxide, sodium salts and potassium salts of carbonates (e.g., sodium carbonate Na₂CO₃ and / or sodium bicarbonate NaHCO₃ or mixtures thereof), sulfates or phosphates (e.g., tetrasodium pyrophosphate) are used.

[0104] For example, at least one buffer salt selected from sodium salts, in particular selected from sodium carbonates, sodium sulfates and sodium phosphates, preferably selected from sodium carbonate Na 2 CO 3 and sodium hydrogen carbonate NaHCO 3, is preferably added.

[0105] The addition of the buffer salts, acids and / or bases can take place during steps a) and / or b), preferably during the preparation of the at least one graft copolymer B (emulsion polymerization, step a).

[0106] Typically, in step b), the precipitation solution PS and the graft copolymer B-latex are mixed for a period of time ranging from 5 to 40 minutes, preferably 5 to 35 minutes.

[0107] The precipitation in step b) is carried out at a temperature (= T1) of 30 to 95°C, preferably 40 to 90°C, particularly preferably 50 to 90°C, and most preferably 60 to 88°C. Preferably, the latex of the graft copolymer B is mixed with the at least one precipitation solution PS at a temperature (= T1) of 30 to 95°C, preferably 40 to 90°C, and particularly preferably 50 to 90°C. The precipitation is preferably carried out in a precipitation vessel (e.g., a precipitation kettle). Step c) Sintering of the precipitation mixture

[0108] In step c) of the process according to the invention, the precipitation mixture obtained in step b) is sintered at a temperature (= T2) of 85 to 150°C, preferably 90 to 145°C, in particular 90 to 140°C, most preferably 92 to 135°C.

[0109] The temperature (= T2) in step c) is generally at least 5°C, preferably at least 10°C, particularly preferably 15°C, higher than the temperature (= T1) in step b).

[0110] During sintering, the precipitation mixture is generally held at this temperature T2 for at least 15 minutes, preferably for a period of 15 to 90 minutes, particularly preferably 15 to 75 minutes, and most preferably 20 to 60 minutes.

[0111] Sintering causes the graft copolymer particles contained in the precipitation mixture to agglomerate, resulting in larger particles.

[0112] The precipitation in step b) and the sintering in step c) of the process according to the invention can be carried out in different containers or in the same container. Precipitation and sintering in the same container are particularly possible when the process is operated batchwise, since in this case the graft copolymer latex is first mixed with the precipitation solution at a lower temperature and then the graft copolymer particles are sintered at a higher temperature. It is therefore preferred if a precipitation container is used for step (b) and a sintering container for step (c), wherein the sintering container and the precipitation container are two different containers. Step d) - Cooling the sintered precipitation mixture

[0113] It has proven advantageous to cool the sintered precipitation mixture obtained in step c) of the process according to the invention before mechanical dewatering in step e), preferably to a temperature of 20 to 90°C, often 20 to 80°C, and often 20 to 70°C. A heat exchanger can be used, for example, to cool the sintered precipitation mixture. Step e) - Mechanical dewatering of the sintered precipitation mixture

[0114] In step e) of the process according to the invention, a mechanical dewatering of the sintered precipitation mixture obtained in step c) or d) is carried out, whereby a graft copolymer B with a water content of 50 wt.% or less, preferably 40 wt.% or less, particularly preferably 10 to 35 wt.% is obtained.

[0115] The water content (also referred to as residual moisture) of the graft copolymer B after dehydration is the water content in weight percent, based on the moist graft copolymer B obtained after dehydration.

[0116] The water content is determined, in particular, using suitable analytical instruments (e.g., drying and weighing equipment), whereby the sample is dried until a constant weight is achieved over a defined period. For example, the water content of graft copolymer B can be determined in a Mettler Toledo HR73 halogen moisture analyzer at 180°C until a constant weight is achieved for 30 seconds.

[0117] In particular, the water content of the dehydrated graft copolymer B obtained in step e) is in the range of 10 to 50 wt.%, preferably 10 to 40 wt.%, particularly preferably 10 to 35 wt.% (based on the total dehydrated graft copolymer B).

[0118] Typically, step e) of the process according to the invention comprises the mechanical dewatering of the sintered graft copolymer B by means of continuous or discontinuous centrifugation and / or filtration.

[0119] Preferably, the mechanical dewatering of the sintered graft copolymer B is achieved by continuous centrifugation.

[0120] The sintered graft copolymer B is typically centrifuged with a centripetal acceleration of 200 to 2200 g (where g is the acceleration due to gravity (1 g = 9.81 m / s²)), preferably of 500 to 1500 g, for a period of 1 second to 5 minutes, preferably 1 to 120 seconds. Step f) - Optional washing of the dehydrated graft copolymer B

[0121] The mechanical dehydration of the graft copolymer B in step e) can be combined with a washing step (e.g. on a centrifuge) or can be followed by a washing step (step f)), wherein the dehydrated graft copolymer B is preferably treated with water.

[0122] It is also possible to use a mixture of water and a polar, water-miscible organic solvent, such as alcohols.

[0123] Preferably, the water or the aforementioned water mixture is removed after treatment of the graft copolymer B by filtration and / or centrifugation. Preferably, in a subsequent washing step f), a graft copolymer B with a water content in the range of 10 to 50 wt.%, preferably 10 to 40 wt.%, and particularly preferably 10 to 35 wt.%, is obtained.

[0124] It is also preferred that a graft copolymer B is obtained with a water content as described above for step e). Step g) - Optional drying of the dehydrated graft copolymer B

[0125] The process according to the invention optionally also includes drying (step g) of the graft copolymer B obtained in step e) or f) - dehydrated and optionally washed - in a known manner.

[0126] For example, the dehydrated and optionally washed graft copolymer B can be dried by hot drying gas, e.g., air, or by means of a pneumatic dryer. The drying can be carried out, for example, in a cabinet dryer or other commonly known drying equipment such as a flash dryer or fluidized bed dryer. Typically, the optional drying step is carried out at a temperature of the drying equipment or the drying gas in the range of 50 to 180°C, preferably from 55 to 155°C, and particularly preferably from 60 to 150°C.

[0127] Typically, the resulting dried graft copolymer B has a water content of less than 5 wt.%, preferably less than 1 wt.%, preferably in the range of 0.05 to 0.8 wt.%, preferably 0.1 to 0.8 wt.%.

[0128] Another object of the invention is a graft copolymer B obtained by the process according to the invention. Graft copolymers B obtained by the process according to the invention are characterized - in comparison to graft copolymers not according to the invention (without step a3-2, i.e. without B21 post-dosage) - by a white or almost white color even after the sintering step and have a low, significantly reduced, yellowness index (measured according to ASTM E313-10).

[0129] A further object of the invention is a method for producing a thermoplastic molding compound comprising at least one graft copolymer B obtained according to the inventive method, and at least one thermoplastic vinyl aromatic copolymer A, optionally at least one further polymeric component C selected from polycarbonates, polyamides and polyesters, and optionally one or more additives and / or auxiliaries D, by mixing the components, preferably in the melt.

[0130] Preferably, the at least one thermoplastic vinyl aromatic copolymer A is a rubber-free polymer.

[0131] Preferably, the at least one thermoplastic vinyl aromatic copolymer A is a copolymer made from: A1: 50 to 95 wt.%, preferably 60 to 90 wt.%, more preferably 60 to 85 wt.%, based on copolymer A, of a monomer A1 selected from styrene, alpha-methylstyrene and mixtures of styrene and at least one further monomer selected from o-methylstyrene, p-methylstyrene and C1-C8-alkyl(meth)acrylate; A2: 5 to 50 wt.%, preferably 10 to 40 wt.%, particularly preferably 15 to 40 wt.%, based on 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, vinyl methyl ether, anhydrides of unsaturated carboxylic acids (e.g. maleic anhydride or phthalic anhydride) and imides of unsaturated carboxylic acids (e.g. N-substituted maleimides, such as N-cyclohexyl maleimide or N-phenyl maleimide).

[0132] The thermoplastic copolymer A is preferably prepared from mixtures of styrene with other comonomers A2. Particularly preferred is A1 styrene and A2 acrylonitrile, i.e., the thermoplastic copolymer A is a styrene-acrylonitrile copolymer (SAN). Furthermore, particularly preferred is A1 (alpha)-methylstyrene and A2 acrylonitrile, i.e., the thermoplastic copolymer A is an (alpha)-methylstyrene-acrylonitrile copolymer (AMSAN).

[0133] As thermoplastic copolymer A, in general any SAN and / or AMSAN copolymer known to those skilled in the art can be used within the scope of the present invention.

[0134] In particular, the thermoplastic copolymer A is selected from SAN and / or AMSAN copolymers containing less than 36 wt.% acrylonitrile as monomer A2, based on the copolymer A. Preferably, the thermoplastic copolymer A contains at least one vinylaromatic monomer A1, preferably styrene, in an amount of 50 to 99 wt.%, more preferably 60 to 95 wt.%, particularly preferably 65 to 90 wt.%, and most preferably 65 to 70 wt.%, and at least one (meth)acrylonitrile monomer A2, more preferably acrylonitrile, in an amount of 1 to 50 wt.%, more preferably 5 to 40 wt.%, more preferably 10 to 35 wt.%, and most preferably 30 to 35 wt.%.

[0135] In particular, the weight-average molecular weight (Mw) of the thermoplastic copolymer A is in the range of 15,000 to 200,000 g / mol, preferably in the range of 30,000 to 150,000 g / mol. Typically, the number-average molar mass (Mn) of the thermoplastic copolymer A is 15,000 to 100,000 g / mol.

[0136] Preferably, the mean molecular weight can be determined by gel permeation chromatography (GPC) relative to polystyrene as a standard and using, for example, UV detection.

[0137] Preferably, the thermoplastic copolymer A has a viscosity number VZ (determined according to DIN 53726 at 25°C, 0.5 wt.% in dimethylformamide) of 50 to 120 ml / g, preferably of 50 to 100 ml / g, particularly preferably of 55 to 85 ml / g.

[0138] In a preferred embodiment, the thermoplastic copolymer A is a SAN (styrene-acrylonitrile copolymer) or AMSAN (alpha-methylstyrene-acrylonitrile copolymer) having a medium molecular weight and / or medium viscosity in the above-mentioned ranges.

[0139] Copolymer A can be produced by all known methods, for example bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization or mixed methods, e.g. bulk / suspension polymerizations, with or without other components.

[0140] The synthesis of thermoplastic copolymers A is possible by thermal initiation or by the addition of initiators, especially radical initiators, such as peroxides.

[0141] Thermoplastic copolymers A are preferably produced by bulk or solution polymerization.

[0142] The thermoplastic copolymer A is particularly preferably produced from the components acrylonitrile and styrene and / or alpha-methylstyrene by bulk polymerization or in the presence of one or more solvents, for example toluene or ethylbenzene.

[0143] A polymerization process is described, for example, in the Plastics Handbook, Vieweg-Daumiller, Volume V, (Polystyrene), Carl-Hanser-Verlag, Munich 1969, pages 122 ff.

[0144] Optionally, the thermoplastic molding compound contains 0 to 90 wt.%, preferably 0 to 60 wt.%, often 0 to 30 wt.%, based on the total molding compound, of at least one further polymer component C. Preferably, the optional polymer component C is selected from polycarbonates (including aromatic polycarbonates and aromatic polyester carbonates), polyamides and polyesters, particularly preferably from polycarbonates and polyamides.

[0145] Preferably, the at least one further polymer component C is at least an aromatic polycarbonate and / or at least an aromatic polyester carbonate.

[0146] Suitable aromatic polycarbonates and / or aromatic polyester carbonates are described in the prior art and can be produced using known methods. Particularly suitable aromatic polycarbonates and aromatic polyester carbonates and their production are described in DE-A 2 714 544, DE-A 3 000 610, DE-A 3 832 396 and DE-A 3 077 934.

[0147] Preferably, the aromatic polycarbonate used as component C is a polycarbonate based on bisphenol A and phosgene, which also includes polycarbonates produced from corresponding precursors or synthesis building blocks of bisphenol A and phosgene.

[0148] Preferably, the at least one further polymer component C can be at least one polyamide selected from homo-polyamides, co-polyamides, and mixtures of such polyamides. Suitable polyamides and processes for their preparation are known from the prior art. Particularly suitable semi-crystalline polyamides are polyamide-6, polyamide-6,6, mixtures, and corresponding copolymers of these components.

[0149] In particular, the thermoplastic molding compound obtained according to the inventive method can contain 0 to 10 wt.%, preferably 0 to 5 wt.%, often 0.1 to 5 wt.%, based on the total thermoplastic molding compound, at least one additive and / or auxiliary agent D.

[0150] Particularly preferred is the inclusion of at least one additive and / or auxiliary agent D in an amount of 0.001 to 10 wt.%, particularly preferably 0.01 to 5 wt.%, based on the total thermoplastic molding compound.

[0151] In particular, additive and / or auxiliary agent D is not a polymeric compound.

[0152] The optional additive and / or auxiliary agent D can be selected from commonly known additives and / or auxiliaries for plastic materials. For examples of common auxiliaries and auxiliaries, reference is made to "Plastics Additives Handbook", Ed. Gächter and Müller, 4th edition, Hanser Verlag, Munich, 1996. For instance, at least one additive and / or auxiliary agent D can be selected from fillers, reinforcing agents, colorants, pigments, lubricants or mold release agents, stabilizers (especially light and heat stabilizers), antioxidants, UV absorbers, plasticizers, antistatic agents, flame retardants, bactericides, fungicides, optical brighteners, and blowing agents.

[0153] The optional additive and / or auxiliary D is preferably selected from dyes, pigments, lubricants or demolding agents, stabilizers, in particular light stabilizers, antistatic agents, flame retardants and fillers, in particular mineral fillers.

[0154] The invention preferably relates to a method for producing a thermoplastic molding compound comprising (preferably consisting of): A: 5 to 95 wt.%, preferably 30 to 95 wt.%, particularly preferably 40 to 90 wt.% of at least one thermoplastic copolymer A prepared from: A1: 50 to 95 wt.%, preferably 60 to 90 wt.%, more preferably 60 to 85 wt.%, based on the copolymer A, of a monomer A1 selected from styrene, alpha-methylstyrene and mixtures of styrene and at least one further monomer selected from o-methylstyrene, p-methylstyrene and C1-C8-alkyl(meth)acrylate; A2: 5 to 50 wt.%, preferably 10 to 40 wt.%, particularly preferably 15 to 40 wt.%, based on 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, vinyl methyl ether, anhydrides of unsaturated carboxylic acids (e.g. maleic anhydride or phthalic anhydride) and imides of unsaturated carboxylic acids (e.g. N-substituted maleimides, such as N-cyclohexyl maleimide or N-phenyl maleimide).B: 5 to 95 wt.%, preferably 5 to 70 wt.%, particularly preferably 10 to 60 wt.% of at least one graft copolymer B as defined above; C: 0 to 90 wt.%, preferably 0 to 80 wt.%, often 0 to 30 wt.% of at least one further polymeric component C; and D: 0 to 10 wt.%, preferably 0 to 5 wt.%, frequently 0.1 to 5 wt.% of at least one additive and / or auxiliary D; and . wherein the process comprises the following steps: a), preferably a), b), c), e) and optionally d), f) and / or g) as described above, and h) mixing the thermoplastic copolymer A and the at least one graft copolymer B, and optionally at least one further polymeric component C and / or optionally at least one additive and / or auxiliary D.

[0155] Methods and devices for mixing the graft copolymer B with the thermoplastic polymer A and optionally the further polymer component C and / or additive and / or auxiliary D are known to those skilled in the art.

[0156] Possible mixing devices for carrying out compounding include, for example, discontinuously operating heated internal mixers with or without a piston, continuous kneaders such as continuous internal mixers, screw kneaders with axially oscillating screws, Banbury mixers, continuous extruders and rolling mills, mixing mills with heated rollers and calenders.

[0157] Typically, mixing step h) includes melt compounding and / or melt extrusion and can typically be carried out using one or more kneaders, extruders, and / or twin-screw extruders. For melt extrusion, for example, single- or twin-screw extruders are particularly suitable.

[0158] The use of a twin-screw extruder is preferred.

[0159] The mixing in step h) can be done sequentially or simultaneously.

[0160] Furthermore, it is suitable to mix some or all components at a temperature of 15 to 40 °C, for example at room temperature, in a first step and then - in a second step - to increase the temperature to 200 to 300 °C, if necessary by adding further components.

[0161] Preferably, the mixing in step h) is carried out at temperatures in the range of 100 to 400°C, preferably 180 to 300°C. Typically, this temperature depends on the chemical and physical properties of the components. It should typically be selected to achieve a substantially molten polymer mixture. In this context, "molten" means that all components, particularly the polymeric components, are molten, except for those that are not intended to be molten, such as glass fibers or pigment particles. On the other hand, the temperature should not be unnecessarily high to avoid thermal damage to the polymer mixture. The mixing apparatus is usually operated at temperatures of 150 to 400°C, preferably 180 to 300°C, and typically has different temperature zones, as is known to those skilled in the art.

[0162] The mixing of the thermoplastic copolymer A, the at least one graft copolymer B, and optionally further components C and D can be carried out sequentially or simultaneously in a known manner. Furthermore, it is possible to first mix some components at temperatures of 15 to 40°C, particularly at room temperature (approx. 20°C), and then to increase the temperature to 200 to 300°C, optionally with the addition of other components.

[0163] Furthermore, the invention relates to a thermoplastic molding compound and molded bodies produced therefrom, wherein the thermoplastic molding compound is obtained by the inventive method for producing a thermoplastic molding compound containing the graft copolymer B as described and at least one thermoplastic vinyl aromatic copolymer A.

[0164] The thermoplastic molding compounds can be used to produce molded parts such as sheets or semi-finished products, films, fibers, or foams. Processing can be carried out according to known thermoplastic processing methods; in particular, production can be carried out by deep drawing, extrusion, injection molding, calendering, blow molding, pressing, press sintering, or sintering, preferably by injection molding.

[0165] The molding compounds according to the invention can be used to produce molded parts of any kind. These can be manufactured using injection molding, extrusion, and blow molding processes. Another processing method is the production of molded parts by thermoforming from previously produced sheets or films and by film overmolding.

[0166] Examples of these molded parts include films, profiles, housing parts of all kinds, e.g. for household appliances such as juicers, coffee machines, mixers; for office equipment such as monitors, printers, copiers; exterior and interior parts of motor vehicles; sheets, pipes, electrical installation ducts, windows, doors and other profiles for the construction sector (interior and exterior applications) as well as parts for electrical and electronic applications such as switches, plugs and sockets.

[0167] In particular, the molding compounds according to the invention can be used, for example, to produce the following molded parts: parts for the interior fittings of rail vehicles, ships, aircraft, buses and other motor vehicles, body parts for engines and vehicles, housings for electrical devices with small transformers, housings for devices for processing and transmitting information, housings and covers for medical devices, massage devices and housings therefor, toy vehicles for children, flat wall elements, housing molded parts for safety devices, thermally insulated transport containers, devices for keeping or caring for small animals, molded parts for sanitary and bathroom facilities, protective grilles for ventilation openings, molded parts for garden sheds and tool sheds, housings for garden tools.

[0168] The invention is described in more detail by the following examples and claims. In the following, "parts" refers to parts by weight unless otherwise specified. Examples Example 1 (according to the invention, subsequent dosing of styrene (incl. step a3-2)) Production of styrene-co-acrylonitrile-grafted polybutylacrylate latices (graft copolymer B-1)

[0169] The following graft copolymer B latex was prepared as follows: Seed latex BS

[0170] The reaction vessel was charged with 132 parts demineralized water, 1.0 part of the sodium salt of a C12-C18 alkylsulfonic acid, and 0.41 parts sodium bicarbonate. When the temperature in the reaction vessel reached 59°C, 0.30 parts potassium persulfate, dissolved in 9.7 parts demineralized water, were added.

[0171] A mixture of 98 parts butyl acrylate and 2 parts tricyclodecenyl acrylate was added and polymerized over 210 minutes. The polymerization was then continued for a further 60 minutes.

[0172] The polymer dispersion obtained had a total solids content of 38.8% and the latex particles had a mean particle diameter Dv (volume mean (determined by light scattering (LS) using Beckman Coulter)) of 87 nm. Graft base B1-1

[0173] The reaction vessel was charged with 60.1 parts demineralized water, 0.3 parts of the previously described seed latex (particle diameter 87 nm) and 0.21 parts sodium bicarbonate.

[0174] After heating the reaction vessel to 61°C, 0.18 parts potassium persulfate, dissolved in 5.8 parts demineralized water, were added to the reaction mixture. A mixture of 58.9 parts butyl acrylate and 1.1 parts tricyclodecenyl acrylate was then added and polymerized over a period of 210 minutes.

[0175] In parallel with the first inflow, a solution of 0.38 parts of the sodium salt of a C 12 -C 18 -alkylsulfonic acid in 21.9 parts fully demineralized water was added over a period of 210 minutes.

[0176] The reaction was then continued for 60 minutes at 61 °C.

[0177] The polymer dispersion obtained (butyl acrylate rubber latex, graft base B1-1) had a total solids content of 39.3% and the mean particle diameter Dv (determined by LS Beckmann Coulter) of the latex particles was 440 nm. (a) Production of the graft casing B2 (2-stage B2' and B2")

[0178] The reaction vessel was filled with 180 parts by weight of demineralized water, 59.9 parts by weight of graft base B1-1, and 0.11 parts by weight of the sodium salt of a C12-C18 paraffinic acid. After heating the reaction vessel to 61°C, 0.16 parts by weight of potassium persulfate, dissolved in 5.2 parts by weight of demineralized water, were added to the reaction mixture. Over 60 minutes, 8.67 parts by weight of styrene were added at a temperature of 61°C, followed by a post-polymerization period of 30 minutes at 61°C. A mixture of 18.9 parts by weight of styrene and 8.10 parts by weight of acrylonitrile was then added over a period of 150 minutes, during which time the temperature was continuously increased to 65°C. Subsequently, 4.33 parts by weight of styrene were added over a period of 30 minutes. The reaction was continued at 65°C for a further 60 minutes. A dispersion of a graft copolymer B-1 was obtained.

[0179] The latex particles B-1 had a mean diameter Dv of 556 nm (determined by LS Beckman Coulter). An aliquot was taken to determine the residual acrylonitrile (AN) monomer content directly after the post-polymerization time at 65 °C. b) Precipitation of the graft copolymer B-latex

[0180] 110 g of a MgSO4 solution (20.3 wt%) were mixed with 1850 g of demineralized water. 390 g of this solution was used as a pre-charge and heated to 70 °C. 800 g of the polymer latex from step a2) and the remaining diluted MgSO4 solution were added separately over 10 minutes while maintaining a temperature of 70 °C. c) Sintering of the precipitation mixture and d) Cooling

[0181] The precipitation mixture obtained in step b) was heated to a temperature of 124°C within 30 minutes (sintering) and after reaching a temperature of 124°C the heating was stopped and the precipitation mixture was allowed to cool to room temperature. e) Drainage, f) Washing and g) Drying

[0182] The resulting (sintered and cooled) precipitate mixture was centrifuged. The dehydrated, washed graft copolymer B was dried in a laboratory oven at 70°C for 2 days, yielding a powder of graft copolymer B. The dried graft copolymer B had a water content of < 1 wt%. Comparison example C1 Production of a graft copolymer B-C1 (without post-dosing of styrene)

[0183] The preparation of a graft copolymer B with a two-stage graft shell B2' and B2" was carried out analogously to Example 1, however, no styrene was added in step a), i.e., step a3-2) is omitted. The reaction vessel was filled with 180 parts by weight of demineralized water, 59.9 parts by weight of graft base B1-1, and 0.11 parts by weight of the sodium salt of a C12-C18 paraffinic acid. After heating the reaction vessel to 61°C, 0.16 parts by weight of potassium persulfate, dissolved in 5.2 parts by weight of demineralized water, were added to the reaction mixture. Within 60 minutes, 13.0 parts by weight of styrene were added at a temperature of 61°C, followed by a post-polymerization time of 30 minutes at 61°C. Then, a mixture of 18.9 parts by weight of styrene and 8.10 Acrylonitrile by weight was added over a period of 150 minutes, with the temperature being continuously increased to 65 °C during this time.The reaction was continued at 65°C for a further 60 minutes. A dispersion of a graft copolymer B-C1 was obtained. The latex particles B-C1 had a mean diameter of 558 nm (determined by LS Beckman Coulter). An aliquot was taken to determine the residual AN monomer content directly after the post-polymerization time at 65°C. The remaining steps b) to g) were carried out analogously to Example 1. Comparison example C2 Production of a B-C2 graft copolymer (comparison, MMA re-dosage)

[0184] The preparation of a graft copolymer B with a 2-stage graft shell B2' and B2" was carried out analogously to Example 1, however, in step a3-2) methyl methacrylate (MMA) was added instead of styrene. The reaction vessel was filled with 180 parts by weight of demineralized water, 59.9

[0185] The reaction vessel was filled with 0.11 parts by weight of graft base B1-1 and 0.11 parts by weight of the sodium salt of a C12-C18 paraffinic acid. After heating the reaction vessel to 61°C, 0.16 parts by weight of potassium persulfate, dissolved in 5.2 parts by weight of demineralized water, were added to the reaction mixture. Over 60 minutes, 8.67 parts by weight of styrene were added at a temperature of 61°C, followed by a post-polymerization time of 30 minutes at 61°C. A mixture of 18.9 parts by weight of styrene and 8.10 parts by weight of acrylonitrile was then added over a period of 150 minutes, during which time the temperature was continuously increased to 65°C. Subsequently, 4.33 parts by weight of methyl methacrylate were added over a period of 30 minutes. The reaction was continued at 65°C for a further 60 minutes.

[0186] A dispersion of a graft copolymer B-C2 was obtained. The latex particles B-C2 had a mean diameter of 554 nm (determined by LS Beckman Coulter). An aliquot was taken to determine the residual AN monomer content directly after the post-polymerization time at 65 °C.

[0187] The remaining steps b) to g) were carried out analogously to Example 1.

[0188] The acrylonitrile (AN) residual monomer (REMO) content (see Table 1) was determined by headspace gas chromatography with flame ionization detector (GC-FID) with external calibration using mesitylene and propionitrile as internal standard (= IS) solution in DMSO.

[0189] For this purpose, 1.00 g of latex dispersion B1, B-C1, or B-C2 was mixed with approximately 5.00 g of IS solution. The resulting mixture was shaken, and the REMO AN content was measured using headspace GC-FID.

[0190] REMO-AN after 300 minutes based on tsc ppm = m AN / m Latex × tsc / 100 × 1000000 m(AN): Mass AN in the latex sample, calculated by internal calibration with mesitylene and propionitrile; m(Latex): Total amount of latex used for analysis; tsc (total solid content): Total solids content

[0191] The yellowness index (YI) was determined for the obtained graft copolymers B1, B-C1 and B-C2 according to ASTM E313-10 (see Table 1). For this purpose, the respective graft copolymer powder was fixed between two microscope slides. Table 1 graft copolymer B-C1 B-1 B-C2 reaction without re-dosing Styrene re-dosage MMA re-dose YI (powder) after sintering 3.29 1.89 2.35 tsc (%) after 300 min 34.34 34.30 34.06 REMO ON [ppm] after 300 min 6049 2564 5217

[0192] The examples (see Table 1) show that the residual acrylonitrile monomer (REMO AN) content of the graft copolymer B-1 obtained according to the inventive process is much lower than the REMO AN content of the comparative examples B-C1 and B-C2.

[0193] Furthermore, the yellow value (YI) of the graft copolymer powder decreases significantly (see example graft copolymer B-1) when, according to the inventive process, a portion of the styrene used to produce the graft shell is added only after the addition of the styrene-acrylonitrile mixture.

[0194] This is particularly surprising, since such a pronounced effect is not found when MMA is redosed (see comparative example B-C2).

[0195] The higher the yellow value of a polymeric material, the more difficult it is to dye the material a specific color.

[0196] The graft copolymers according to the invention or the molding compounds containing them have a light, often white or almost white, base color, which makes them easy to color in a wide range of colors and allows them to be used in a variety of ways.

[0197] Various ASA copolymers were produced and tested according to the inventive process; they had improved color properties.

[0198] Molded parts made from the ASA copolymers were also produced and tested according to the inventive process; they had, among other things, improved color properties.

Claims

1. Process for the preparation of at least one graft copolymer B comprising: B1: 40 to 90% by weight, preferably 45 to 85% by weight, particularly preferably 50 to 70% by weight, based on the graft copolymer B, of at least one, preferably 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 C1-C8 alkyl (meth)acrylate and butadiene; B12 0 to 10% by weight, based on the graft base B1, of at least one multifunctional crosslinking monomer B12, preferably selected from allyl (meth)acrylate, divinylbenzene, diallyl maleate, diallyl fumarate, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate and dihydrodicyclopenta-dienyl acrylate (DCPA); B13 0 to 50% by weight, based on the graft base B1, of at least one further monomer B13 selected from styrene, alpha-methylstyrene, C1-C4-alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, chloroprene, methyl methacrylate, alkylene glycol di(meth)acrylate and vinyl methyl ether; wherein the sum of B11, B12 and B13 is 100% by weight; and B2: 10 to 60% by weight, based on the graft copolymer B, of at least one graft shell B2 which - in the presence of the at least one graft base B1 - is obtained by emulsion polymerization of: B21 50 to 100% by weight, based on the graft shell B2, of at least one vinylaromatic monomer B21 selected from styrene and alpha-methylstyrene; and B22 0 to 50% by weight, based on the graft shell B2, of at least one monomer B22 selected from acrylonitrile or mixtures of acrylonitrile and at least one further monomer selected from methacrylonitrile, acrylamide, vinyl methyl ether, anhydrides of unsaturated carboxylic acids and imides of unsaturated carboxylic acids; wherein the sum of B21 and B22 is 100% by weight; and wherein at least one graft shell B2 is obtained by emulsion polymerization of 50 to 95% by weight of at least one monomer B21 and 5 to 50% by weight of at least one monomer B22; wherein the sum of the at least one graft base B1 and the at least one graft shell B2 is 100% by weight; and wherein the process comprises the following steps: a) preparation of a latex of at least one graft copolymer B comprising: a1) presentation of an aqueous latex containing at least one graft base B1; a2) optionally preparation of a first graft shell B2 or B2' by: a2-1) addition and emulsion polymerization of a first part of the at least one monomer B21 or B21', preferably styrene, to the graft base B1; a2-2) post-polymerization of the latex obtained in a2-1); a3) preparation of a first graft shell B2 or, if steps a2-1) and a2-2 are present, preparation of a second graft shell B2 or B2" by: a3-1) simultaneous addition and emulsion polymerization of a first or a further portion of the at least one monomer B21 or B21" and the total amount of the at least one monomer B22 or B22" to the latex from step a1) or a2-2); a3-2) immediately after completion of the addition of the monomers in step a3-1), addition and emulsion polymerization of the remaining part of the at least one monomer B21 or B21" to the latex obtained in step a3-1); a3-3) post-polymerization of the latex of graft copolymer B obtained in step 3-2).

2. Process according to claim 1, further comprising the following steps b) to g): b) precipitation of the graft copolymer B latex obtained in step a) at a temperature of 30 to 95 °C, wherein the graft copolymer B latex is mixed with at least one precipitation solution PS, thereby forming a precipitation mixture; c) sintering of the precipitation mixture obtained in step b) at a temperature of 85 to 150 °C, preferably for 15 to 90 minutes, wherein the temperature in step c) is at least 5 °C higher than in step b); d) optionally cooling the sintered precipitation mixture from step c), preferably to a temperature of 20 to 90 °C; e) mechanical dewatering of the sintered precipitation mixture obtained in step c) or d), wherein a graft copolymer B with a water content equal to or less than 50% by weight is obtained; f) optionally washing the graft copolymer B obtained in step e); g) optionally drying the graft copolymer B obtained in step e) or f).

3. Process according to claim 1 or 2, characterized in that the at least one graft base B1 is obtained by emulsion polymerization of: B11: 80 to 99.9% by weight, based on the graft base B1, of at least one C1-C8 alkyl (meth)acrylate as monomer B11; B12: 0.1 to 10% by weight, based on the graft base B1, of at least one polyfunctional crosslinking monomer B12; B13: 0 to 19.9% by weight, based on the graft base B1, of at least one further monomer selected from styrene, alpha-methylstyrene, C1-C4 alkylstyrene, acrylonitrile, methacrylonitrile, isoprene, chloroprene, methyl methacrylate, alkylene glycol di(meth)acrylate and vinyl methyl ether; wherein the sum of B11, B12 and B13 is equal to 100% by weight.

4. Process according to one of claims 1 to 3, characterized in that the at least one graft copolymer B contains: B1: 50 to 70% by weight, based on the graft copolymer B, of exactly one graft base B1; und 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 and (alpha)-methylstyrene; and B22: 5 to 50% by weight, based on the graft shell B2, of at least one 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 latex of the graft copolymer B obtained in step a) has a particle size in the range from 60 to 200 nm as determined by light scattering.

5. Process according to one of claims 1 to 3, characterized in that the graft copolymer B contains: B1: 50 to 70% by weight, based on the graft copolymer B, of at least one graft base B1; and B2': 5 to 25% by weight, based on the graft copolymer B, of at least one graft shell B2', 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 and (alpha)-methylstyrene; and B2": 20 to 40% by weight, based on the graft copolymer B, of at least one graft shell B2", obtained by emulsion polymerization - in the presence of graft base B1 grafted with B2' - of: B21": 65 to 90% by weight, based on the graft shell B2", of at least one vinylaromatic monomer B21" selected from styrene and (alpha)-methylstyrene; and B22": 10 to 35% by weight, based on the graft shell B2", of at least one monomer B22" selected from acrylonitrile or mixtures of acrylonitrile and methacrylonitrile; wherein the total sum of graft base B1, graft shell B2' and graft shell B2" is 100% by weight, and wherein the latex of the graft copolymer B obtained in step a) has a particle size in the range from 300 to 800 nm as determined by light scattering.

6. Process according to any one of claims 1 to 5, characterized in that the monomer B21 or B21' and B21" is styrene, and the monomer B22 or B22" is acrylonitrile.

7. Process according to any one of claims 1 to 6, characterized in that in step a3-2) the addition of the remaining part of the at least one monomer B21 or B21", preferably styrene, generally takes place over a period of 5 to 45 minutes, preferably 10 to 35 minutes.

8. Process according to one of claims 1 to 6, characterized in that in step a3-3) the post-polymerization of the latex of the graft copolymer B obtained in step 3-2) takes place for at least 15 minutes, preferably for 20 to 90 minutes, most preferably for 30 to 60 minutes.

9. Process according to one of claims 1 to 7, characterized in that in step a3-2) the remaining part of the at least one monomer B21 or B21" is up to 5% by weight, preferably 1 to 4.5% by weight, based on the graft copolymer B.

10. Process according to one of claims 1 and 2 and 4 to 8, characterized in that step a2) is present and in step a3) a second graft shell B2" is prepared.

11. Process according to one of claims 1 to 9, characterized in that in step a3) the temperature is 40 to 90 °C, preferably 50 to 80 °C, and preferably at least 2 °C, preferably 3 to 4 °C, higher than the temperature in step a2).

12. Process according to one of claims 2 to 11, characterized in that in step b) the precipitation of the graft copolymer B latex takes place at a temperature of 40 to 90 °C, preferably 50 to 90 °C.

13. Process according to one of claims 2 to 12, characterized in that in step c) the precipitation mixture is sintered at a temperature of 90 to 145°C, in particular 90 to 140°C, for 15 to 90 minutes, preferably 15 to 75 minutes.

14. Graft copolymer B obtained by a process according to any one of claims 1 to 13.

15. Process for preparing a thermoplastic molding composition - comprising at least one graft copolymer B according to claim 14, and at least one, preferably rubber-free, thermoplastic vinylaromatic copolymer A, optionally at least one further polymeric component C selected from polycarbonates, polyamides and polyesters, and optionally one or more additives and / or auxiliaries D - by mixing the components, preferably in the melt.

16. Thermoplastic molding composition obtained by a process according to claim 15.

17. Molding made of a thermoplastic molding composition according to claim 16.