The invention relates to a process for the preparation of light-weight ABS (acrylonitrile- butadiene-styrene) molding compositions having a low density and high strength, ABS molding compositions obtained by said process and their use in various applications.

Current industrial practice is to reinforce ABS resins by glass fibers, mineral fillers or in some cases with carbon fibers. This provides good enhancements of mechanical prop erties of ABS resins but the density of the ABS composition is considerably increased.

CN-A 102746606 discloses modified ABS materials filled with hollow glass microbeads comprising: 50 to 80 wt.-% of ABS resin (no details about composition), 3 to 5 wt.-% of a compatibilizer, 5 to 10 wt.-% of a toughener (e.g. hydrogenated SBS styrene-based thermoplastic elastomer), 3 to 5 wt.-% of a silane coupling agent, 1 to 3 wt.-% of a rein- forcing agent (ultrafine silica) , 5 to 30 wt.-% of hollow glass beads (i.e. soda lime boro- silicate), and 1 to 3 wt.-% of plastic processing assistants. As compatibilizer, a styrene maleic anhydride graft copolymer (S-g-MAH) is used. The ABS material is obtained by first premixing the ABS resin, compatibilizer and coupling agent in a blender or mixer, then all other components (including the hollow glass beads) are added and mixing is continued, and the obtained mixed material is melt-blended in a twin-screw extruder. The ABS material is used for instruments and household-applications; light weight applica tions are not mentioned.

WO 2015/162242 discloses a foamed light weight styrene polymer composition for au- tomotive applications comprising: A) 40 to 88% by weight of an ABS and/or ASA resin, B) 5 to 30% by weight of hollow glass microspheres (i.e. soda lime borosilicate, particle size (diameter) 5 to 50 pm), C) 0.1 to 2.5% by weight of a chemical foaming agent, D) 1 to 5% by weight of a compatibilizer (e.g. a styrene-acrylonitrile grafted maleic anhydride copolymer), E) 5 to 20% by weight of an impact modifier, and F) optionally 0.1 to 3% by weight of a plastic processing aid. Preferably the ABS resin is a mixture of graft copoly mer A1) - a diene based rubber onto which a copolymer of styrene and acrylonitrile is grafted - with 40 to 85 wt.-% of a rubber free styrene-acrylonitrile copolymer A2). The material is obtained by melt mixing all components, except of the hollow glass beads, in a twin-screw extruder, and then the hollow glass beads are added by a side-feeder in a zone of the extruder after the kneading section.

Said prior art processes have the disadvantage that often crushing of the hollow glass beads occurs during the mixing and melt-blending steps. Thus the afore-mentioned pro cesses for the preparation of light weight polymer compositions are still in need of im- provement. One object of the invention is to provide a process for the preparation of light weight thermoplastic molding compositions which allows a trouble-free feeding and minimizes the crushing of the hollow-glass beads. It was surprisingly found that the problem can be solved by the process according to the claims.

One aspect of the invention is a process for the preparation of a thermoplastic molding composition (TP) comprising (or consisting of) components (A), (B), (C), (D) and, if pre sent, (E):

(A) 10 to 65 wt.-% of at least one graft copolymer (A) consisting of 15 to 60 wt.-% of a graft sheath (A2) and 40 to 85 wt.-% of a graft substrate - an agglomerated buta diene rubber latex - (A1), where (A1) and (A2) sum up to 100 wt.-%, obtained by emulsion polymerization of styrene and acrylonitrile in a weight ratio of 95:5 to 50:50 to obtain a graft sheath (A2), it being possible for styrene and/or acrylonitrile to be replaced partially (less than 50 wt.-%) by alpha-methylstyrene, methyl methacrylate or maleic anhydride or mixtures thereof, in the presence of at least one agglomerated butadiene rubber latex (A1) with a median weight particle diameter D50 of 200 to 800 nm; where the agglomerated rubber latex (A1) is obtained by agglomeration of at least one starting butadiene rubber latex (S-A1) having a median weight particle diameter D50 of equal to or less than 120 nm;

(B) 30.5 to 80 wt.-% of at least one copolymer (B) of styrene and acrylonitrile in a weight ratio of from 81:19 to 65:35, it being possible for styrene and/or acrylonitrile to be partially (less than 50 wt.-%) replaced by methyl methacrylate, alpha-methyl styrene and/or 4-phenylstyrene, preferably alpha-methyl styrene; wherein copoly mer (B) has a weight average molar mass M _w of 90,000 to 145,000 g/mol;

(C) 1.5 to 9.5 wt.-% of at least one copolymer (C) - as compatibilizing agent - with at least one functional group selected from epoxy, maleic anhydride and maleic im- ide;

(D) 3 to 29 wt.-% of hollow glass microspheres (D);

(E) 0 to 15 wt.-%, preferably 0.01 to 10 wt.-%, of further additives, except from fibers and fillers, and/or processing aids - different from (D) - as component (E); where the components A, B, C, D and, if present E, sum to 100 wt.-%; which process comprises the following steps:

(i) Premixing of a portion of 2 to 10 wt.-%, preferably 3 to 8 wt.-%, of component (A) with the hollow glass microspheres (D); (ii) Mixing and melting of the remaining portion of component (A), components (B), (C) and, if present, (E), in the feeding section of an extruder, preferably a twin-screw extruder;

(iii) Addition of the pre-mixture obtained in step (i) to the melt obtained in step (ii) by a side-feeder in a zone of the extruder after the kneading section to obtain the thermoplastic molding composition (TP) by melt mixing.

Wt.-% means percent by weight.

The median weight particle diameter D ₅₀ , also known as the D ₅₀ value of the integral mass distribution, is defined as the value at which 50 wt.-% of the particles have a diam eter smaller than the D ₅₀ value and 50 wt.-% of the particles have a diameter larger than the D ₅₀ value.

In the present application the weight-average particle diameter D _w , in particular the me dian weight particle diameter D50, is determined with a disc centrifuge (e.g.: CPS Instru ments Inc., DC 24000 with a disc rotational speed of 24000 rpm). The weight-average particle diameter D _w is defined by the following formula (see G. Lagaly, O. Schulz and R. Ziemehl, Dispersionen und Emulsionen: Eine Einfuhrung in die Kolloidik feinverteilter Stoffe einschlieBlich der Tonminerale, Darmstadt: Steinkopf-Verlag 1997, ISBN 3-7985 -1087-3, page 282, formula 8.3b):

D _w = sum ( n, * di ⁴ ) / sum( n, * d, ³ ) n, is number of particles of diameter d,.

The summation is performed from the smallest to largest diameter of the particles size distribution. It should be mentioned that for a particles size distribution of particles with the same density which is the case for the starting rubber latices and agglomerated rub ber latices the volume average particle size diameter Dv is equal to the weight average particle size diameter Dw.

The weight average molar mass M _w is determined by GPC (solvent: tetrahydrofuran, polystyrene as polymer standard) with UV detection according to DIN 55672-1:2016-03.

Preferably - in an optional step prior to step (ii) of the process according to the invention - a mixture of the remaining portion of component (A), components (B), (C) and, if pre sent, (E) is prepared and premixed - for example in a high speed mixer or extruder - to obtain a uniformly mixed material. Preferably - in an optional step subsequent to step (iii) of the process according to the invention - the molding composition obtained in step (iii) is extruded via a die plate and the extruded polymer strands are cooled, preferably water cooled, and pelletized.

Preferably in step (i) of the process according to the invention, a portion of 3 to 8 wt.-% of component (A), more preferably a portion of 4 to 6 wt.-% of component (A), - based on the total component (A) - is used.

In step (i) the hollow microspheres (D) are premixed with the portion of component (A) with the aid of a mixer. Premixing means said components are dry-blended (= physically mixed in solid state).

Preferably in step (i) the used components are mixed for 1 to 5 minutes, more preferably 2 minutes, at an average speed of 250 to 1000 rpm, more preferably 450 to 550 rpm, in particular 500 rpm, to obtain a pre-mixture.

Due to this premixing in step (i) of the process according to the invention the crushing of the hollow glass microspheres (D) is minimized during the melt mixing in step (iii).

The melt mixing in steps (ii) and (iii) is generally done at temperatures in the range of from 160°C to 300°C, preferably from 180°C to 280°C, more preferably 215°C to 250°C.

Said temperatures ensure the complete melting of the entire component (A) and a trou ble-free feeding.

In the process according to the invention preferably a twin-screw extruder is used. More preferably a twin screw extruder having high channel depth conveying elements is used to avoid breaking of the hollow glass beads (D). The high channel depth defined by the OD/ID ratio is preferably 1.3 to 1.8 more preferably approximately 1.55. A particular suit able extruder has 9 heating zones, usually in zones 1 , 2, 5, 6 and 8 are the high channel width/volume conveying elements, and usually in zones 3 and 4, in particular in more than half of zones 3 and 4, are kneading sections. In zone 1 (feeding section), the re maining portion of component (A), components (B), (C) and, if present, (E) is fed and passed through a set of kneading blocks to ensure its complete melt mixing.

The pre-mixture obtained in step (i) is supplied by a side feeder in a zone after the knead ing section, which is usually in one of zones 4 to 6, preferably in zone 5 or 6. Zones 7 and 9 are having toothed blocks to aid distributive mixing, in particular zone 7 is having conveying elements and toothed blocks. A further aspect of the invention is a thermoplastic molding composition (TP) obtained by the process according to the invention. It is preferable that the thermoplastic molding composition (TP) comprises (or consists of):

12 to 57 wt.-% component (A),

35 to 80 wt.-% component (B),

2 to 8 wt.-% component (C),

5 to 25 wt.-% component (D),

0.01 to 10 wt.-% component (E).

It is particularly preferable that the thermoplastic molding composition (TP) comprises (or consists of):

21 to 49.95 wt.-% component (A),

42 to 70 wt.-% component (B),

3 to 5 wt.-% component (C),

5 to 15 wt.-% component (D),

0.05 to 5 wt.-% component (E).

It is most preferable that the thermoplastic molding composition (TP) comprises (or con sists of):

30 to 48.95 wt.-% component (A),

42 to 60 wt.-% component (B),

3 to 5 wt.-% component (C),

6 to 11 wt.-% component (D),

0.05 to 4 wt.-% component (E).

Component (A)

Graft copolymer (A) (component (A)) is known and described in WO 2012/022710. Graft copolymer (A) consists of 15 to 60 wt.-% of a graft sheath (A2) and 40 to 85 wt.-% of a graft substrate - an agglomerated butadiene rubber latex - (A1), where (A1) and (A2) sum up to 100 wt.-%.

Preferably graft copolymer (A) is obtained by emulsion polymerization of styrene and acrylonitrile in a weight ratio of 80:20 to 65:35 to obtain a graft sheath (A2), it being possible for styrene and/or acrylonitrile to be replaced partially (less than 50 wt.-%, pref erably less than 20 wt.-%, more preferably less than 10 wt.-%, based on the total amount of monomers used for the preparation of (A2)) by alpha-methylstyrene, methyl methac rylate or maleic anhydride or mixtures thereof, in the presence of at least one agglomer ated butadiene rubber latex (A1). This rubber latex has a median weight particle diameter Dsoof 200 to 800 nm, preferably 225 to 650 nm, more preferably 250 to 600 nm, most preferred 280 to 350 nm, in par ticular 300 to 350 mm.

Preferably the at least one, preferably one, graft copolymer (A) consists of 20 to 50 wt.-% of a graft sheath (A2) and 50 to 80 wt.-% of a graft substrate (A1).

More preferably graft copolymer (A) consists of 30 to 45 wt.-% of a graft sheath (A2) and 55 to 70 wt.-% of a graft substrate (A1).

Preferably graft copolymer (A) consists of 35 to 45 wt.-% of a graft sheath (A2) and 55 to 65 wt.-% of a graft substrate (A1).

Preferably the obtained graft copolymer (A) has a core-shell-structure; the graft substrate (a1) forms the core and the graft sheath (A2) forms the shell.

Preferably for the preparation of the graft sheath (A2) styrene and acrylonitrile are not partially replaced by one of the above-mentioned co-monomers; preferably styrene and acrylonitrile are polymerized alone in a weight ratio of 95:5 to 50:50, preferably 80:20 to 65:35.

The at least one, preferably one, starting butadiene rubber latex (S-A1) preferably has a median weight particle diameter D50 of equal to or less than 110 nm, particularly equal to or less than 87 nm.

The term “butadiene rubber latex” means polybutadiene latices produced by emulsion polymerization of butadiene and less than 50 wt.-% (based on the total amount of mon omers used for the production of polybutadiene polymers) of one or more monomers that are copolymerizable with butadiene as comonomers.

Examples for such monomers include isoprene, chloroprene, acrylonitrile, styrene, al pha-methylstyrene, Ci-C4-alkylstyrenes, Ci-Cs-alkylacrylates, Ci-Cs-alkylmethacrylates, alkyleneglycol diacrylates, alkylenglycol dimethacrylates, divinylbenzol; preferably, buta diene is used alone or mixed with up to 30 wt.-%, preferably up to 20 wt.-%, more pref erably up to 15 wt.-% styrene and/or acrylonitrile, preferably styrene.

Preferably the starting butadiene rubber latex (S-A1) consists of 70 to 99 wt.-% of buta diene and 1 to 30 wt.-% styrene. More preferably the starting butadiene rubber latex (S- A1) consists of 85 to 99 wt.-% of butadiene and 1 to 15 wt.-% styrene. More preferably the starting butadiene rubber latex (S-A1) consists of 85 to 95 wt.-% of butadiene and 5 to 15 wt.-% styrene.

The agglomerated rubber latex (graft substrate) (A1) is obtained by agglomeration of the above-mentioned starting butadiene rubber latex (S-A1) with preferably at least one acid anhydride, more preferably acetic anhydride or mixtures of acetic anhydride with acetic acid, in particular acetic anhydride.

The preparation of graft copolymer (A) is described in detail in WO 2012/022710. It can be prepared by a process comprising the steps: a) synthesis of starting butadiene rubber latex (S-A1) by emulsion polymerization, b) agglomeration of latex (S-A1) to obtain the agglomerated butadiene rubber latex (A1) and y) grafting of the agglomerated butadiene rubber latex (A1) to form a graft copolymer (A). The synthesis (step a) of starting butadiene rubber latices (S-A1) is described in detail on pages 5 to 8 of WO 2012/022710.

Preferably the starting butadiene rubber latices (S-A1) are produced by an emulsion polymerization process using metal salts, in particular persulfates (e.g. potassium persulfate), as an initiator and a rosin-acid based emulsifier.

As resin or rosin acid-based emulsifiers, those are being used in particular for the production of the starting rubber latices by emulsion polymerization that contain alkaline salts of the rosin acids. Salts of the resin acids are also known as rosin soaps. Examples include alkaline soaps as sodium or potassium salts from disproportionated and/or dehydrated and/or hydrated and/or partially hydrated gum rosin with a content of dehydro- abietic acid of at least 30 wt.-% and preferably a content of abietic acid of maximally 1 wt.-%. Furthermore, alkaline soaps as sodium or potassium salts of tall resins or tall oils can be used with a content of dehydroabietic acid of preferably at least 30 wt.-%, a content of abietic acid of preferably maximally 1 wt.-% and a fatty acid content of preferably less than 1 wt.-%.

Mixtures of the aforementioned emulsifiers can also be used for the production of the starting rubber latices. The use of alkaline soaps as sodium or potassium salts from disproportionated and/or dehydrated and/or hydrated and/or partially hydrated gum rosin with a content of dehydroabietic acid of at least 30 wt.-% and a content of abietic acid of maximally 1 wt.-% is advantageous.

Preferably the emulsifier is added in such a concentration that the final particle size of the starting butadiene rubber latex (S-A1) achieved is from 60 to 110 nm (median weight particle diameter D50). Polymerization temperature in the preparation of the starting rubber latices (S-A1) is generally 25°C to 160°C, preferably 40°C to 90°C. Further details to the addition of the monomers, the emulsifier and the initiator are described in WO 2012/022710. Molecular weight regulators, salts, acids and bases can be used as described in WO 2012/022710. Then the obtained starting butadiene rubber latex (S-A1) is subjected to agglomeration (step b)) to obtain an agglomerated rubber latex (A1). The agglomeration may be carried out as described on pages 8 to 12 of WO 2012/022710, said method is preferred.

Preferably acetic anhydride, more preferably in admixture with water, is used for the ag glomeration. Preferably the agglomeration step b) is carried out by the addition of 0.1 to 5 parts by weight of acetic anhydride per 100 parts of the starting rubber latex solids.

The agglomerated rubber latex (A1) is preferably stabilized by addition of further emul sifier while adjusting the pH value of the latex (A1) to a pH value (at 20°C) between pH 7.5 and pH 11, preferably of at least 8, particular preferably of at least 8.5, in order to minimize the formation of coagulum and to increase the formation of a stable agglomer ated rubber latex (A1) with a uniform particle size. As further emulsifier preferably rosin- acid based emulsifiers as described above in step step a) are used. The pH value is adjusted by use of bases such as sodium hydroxide solution or preferably potassium hydroxide solution.

The obtained agglomerated latex rubber latex (A1) has a median weight particle diame ter Dsoof generally 200 to 800 nm, preferably 225 to 650 nm, more preferably 250 to 600 nm, most preferred 280 to 350 nm, in particular 300 to 350 nm. The obtained agglomer ated latex rubber latex (A1) preferably is mono-modal.

In step y) the agglomerated rubber latex (A1) is grafted to form the graft copolymer (A). Suitable grafting processes are described in detail on pages 12 to 14 of WO 2012/022710.

Graft copolymer (A) is obtained by emulsion polymerization of styrene and acrylonitrile - optionally partially replaced by alpha-methylstyrene, methyl methacrylate and/or ma leic anhydride - in a weight ratio of 95:5 to 50:50 to obtain a graft sheath (A2) (in partic ular a graft shell) in the presence of the above-mentioned agglomerated butadiene rub ber latex (A1).

Preferably graft copolymer (A) has a core-shell-structure.

The grafting process of the agglomerated rubber latex (A1) of each particle size is pref erably carried out individually. Preferably the graft polymerization is carried out by use of a redox catalyst system, e.g. with cumene hydroperoxide or tert.-butyl hydroperoxide as preferable hydroperoxides. For the other components of the redox catalyst system, any reducing agent and metal component known from literature can be used.

According to a preferred grafting process which is carried out in presence of at least one agglomerated butadiene rubber latex (A1) with a median weight particle diameter Dsoof preferably 280 to 350 nm, more preferably 300 to 330 nm, in an initial slug phase 15 to 40 wt.-%, more preferably 26 to 30 wt.-%, of the total monomers to be used for the graft sheath (A2) are added and polymerized, and this is followed by a controlled addition and polymerization of the remaining amount of monomers used for the graft sheath (A2) till they are consumed in the reaction to increase the graft ratio and improve the conversion. This leads to a low volatile monomer content of graft copolymer (A) with better impact transfer capacity.

Further details to polymerization conditions, emulsifiers, initiators, molecular weight reg ulators used in grafting step y) are described in WO 2012/022710. Component (B)

In the thermoplastic molding composition (TP) copolymer (B) (= matrix polymer) is gen erally comprised in an amount of 30.5 to 80 wt.-%, preferably 35 to 80 wt.-%, more pref erably 40 to 70 wt.-%, most preferably 42 to 60 wt.-%, particularly most preferred 43 to 55 wt.-%.

Preferably copolymer (B) (= component (B)) is a copolymer of styrene and acrylonitrile in a weight ratio of from 77:23 to 68:32, more preferably 76:24 to 70:30, most preferably 74:26 to 72:28, it being possible for styrene and/or acrylonitrile to be partially (less than 50 wt.-%, preferably less than 20 wt.-%, more preferably less than 10 wt.-%, based on the total amount of monomers used for the preparation of (B)) replaced by alpha-methyl styrene and/or 4-phenylstyrene, preferably alpha-methyl styrene.

It is preferred that styrene and acrylonitrile are not partially replaced by one of the above- mentioned comonomers. Component (B) is preferably a copolymer of styrene and acry lonitrile.

Copolymer (B) has preferably a melt flow index (MFI) of 60 to 70 g/10 min (ASTM D1238). The weight average molar mass M _w of copolymer (B) generally is 90,000 to 145,000 g/mol, preferably 95,000 to 130,000 g/mol, more preferably 100,000 to 115,000 g/mol.

Details relating to the preparation of such copolymers are described, for example, in DE- A 2420358, DE-A 2724360 and in Kunststoff-Handbuch ([Plastics Handbook], Vieweg- Daumiller, volume V, (Polystyrol [Polystyrene]), Carl-Hanser-Verlag, Munich, 1969, pp. 122 ff. , lines 12 ff.). Such copolymers prepared by mass (bulk) or solution polymeri- zation in, for example, toluene or ethylbenzene, have proved to be particularly suitable.

Component (C)

In the thermoplastic molding composition (TP) copolymer (C) is generally comprised in an amount of 1.5 to 9.5 wt.-%, preferably 2 to 8 wt.-%, more preferably 3 to 5 wt.-%, most preferably 4 to 5 wt.-%.

Preferably copolymer (C) comprises structural units derived from maleic imide, in partic ular N-phenyl maleic imide, and/or maleic anhydride. Copolymers (C) often comprise structural units derived from maleic imide and/or maleic anhydride in an amount of from 1 to 30 wt.-%, preferably 6 to 12 wt.-%, more preferably 8 to 10 wt.-%.

Copolymer (C) functions as a compatibilizing agent between the glass reinforcing agents (components D and E) and the matrix polymer by improving the bonding of the hollow glass beads and the glass fibers to the matrix polymer phase.

More preferably copolymer (C) is selected from the group consisting of: styrene-maleic anhydride copolymers, styrene-acrylonitrile-maleic anhydride-terpolymers, styrene-N- phenyl maleic imide-copolymers and styrene-acrylonitrile-N-phenyl maleic imide-terpol- ymers.

In particular preferred are styrene-acrylonitrile-maleic anhydride terpolymers.

More preferred are styrene-acrylonitrile-maleic anhydride terpolymers comprising struc- tural units derived from maleic anhydride in an amount of 8 to 10 wt.-%.

The preparation of copolymer (C) is commonly known. It can be advantageously pre pared by mass (bulk) or solution polymerization by a continuous free radical polymeriza tion process. Copolymer (C) has preferably a melt flow index (MFI) in the range of 90 to 110 g/10 min (ASTM D1238). The weight average molar mass M _w of copolymer (C) is generally in the range of from 80,000 to 145,000 g/mol, preferably in the range of from 90,000 to 100,000 g/mol.

Component D

In the thermoplastic molding composition (TP) (D) (= hollow glass microspheres or hol low glass beads) is generally comprised in an amount of 5 to 29 wt.-%, preferably 5 to 25 wt.-%, more preferably 5 to 15 wt.-%, most preferably 6 to 11 wt.-%.

The hollow glass microspheres or hollow glass beads (HGB) used as component (D) comprise inorganic materials which are typically used for glasses such as e.g. silica, alumina, zirconia, magnesium oxide, sodium silicate, soda lime, borosilicate etc.

Preferably the hollow glass beads comprise soda lime borosilicate, which is commercially available.

The hollow glass beads are preferably mono-modal.

Generally the hollow glass beads have a particle size (median weight particle diameter D50) in the range of from 15 to 60 pm, preferably 18 to 40 pm, more preferably 18 to 25 pm.

Furthermore it is preferred that the glass beads are of the thin wall type having preferably a wall thickness of 0.5 to 1.5 pm.

The hollow glass microspheres generally have a true density of from 0.40 to 0.60 g/cm ³ , preferably 0.40 to 0.50 g/cm ³ . Their bulk density is preferably in the range of from 0.25 to 0.35 g/cm ³ , in particular 0.25 to 0.30 g/cm ³ . The hollow glass microspheres preferably have a compressive strength in the range of 100 to 140 MPa, in particular 105 to 120 MPa.

Component (E)

If component (E) is present, its minimum amount is 0.01 wt.-%, based on the entire ther moplastic molding composition (TP).

Various additives and/or processing aids (E) (= component (E)), except from fibers and fillers, may be used for the thermoplastic molding composition (TP) in amounts of from 0.01 to 15 wt.-%, preferably 0.05 to 10 wt.-%, more preferably 0.05 to 5 wt.-%, as assis tants and processing additives. Suitable additives and/or processing aids (E) include, for example, dyes, pigments, col orants, antistats, antioxidants, stabilizers for improving thermal stability, stabilizers for increasing photostability, stabilizers for enhancing hydrolysis resistance and chemical resistance, anti-thermal decomposition agents, dispersing agents, flow modifiers and surface energy enhancer, and in particular external/internal lubricants that are useful for production of molded bodies/articles.

These additives and/or processing aids are admixed in step (ii) of the process according to the invention, in order to profit early from the stabilizing effects (or other specific ef fects) of the added substance.

Suitable lubricants/glidants and demolding agents include stearic acids, stearyl alcohol, stearic esters, amide waxes (bisstearylamide, in particular ethylenebisstearamide), pol yolefin waxes and/or generally higher fatty acids, derivatives thereof and corresponding fatty acid mixtures comprising 12 to 30 carbon atoms.

Examples of suitable antioxidants include sterically hindered monocyclic or polycyclic phenolic antioxidants which may comprise various substitutions and may also be bridged by substituents. These include not only monomeric but also oligomeric compounds, which may be constructed of a plurality of phenolic units.

Hydroquinones and hydroquinone analogs are also suitable, as are substituted compounds, and also antioxidants based on tocopherols and derivatives thereof.

It is also possible to use mixtures of different antioxidants. It is possible in principle to use any compounds which are customary in the trade or suitable for styrene copolymers, for example antioxidants from the Irganox range. In addition to the phenolic antioxidants cited above by way of example, it is also possible to use so-called costabilizers, in particular phosphorus- or sulfur-containing costabilizers. These phosphorus- or sulfur- containing costabilizers are known to those skilled in the art.

Suitable flow modifiers and surface energy enhancer comprise at least one oligomeric or polymeric compound having at least one functional group selected from the group consisting of ester groups, siloxane groups, epoxy groups, anhydride groups, carboxyl groups, acrylate groups, and nitrile groups. A preferred flow modifier and surface energy enhancer is for example a mixture of a di ester of sebacic acid and glycidyl epoxy alkoxy siloxane. Examples of pigments are titanium dioxide, phthalocyanines, ultramarine blue, iron ox ides, and carbon black, and the entire class of organic and inorganic pigments.

Dyes are any of the dyes which can be used for the transparent, semitransparent, or non-transparent coloring of polymers, in particular those dyes which are suitable for coloring styrene copolymers. Dyes of this type are known to the skilled worker. Said pigments and dyes may be used in amounts up to 10 wt.-%, preferably up to 5 wt.-%.

One preferred pigment is carbon black (e.g. from Cabot Corp., USA).

Preferably component (E) is at least one lubricant, antioxidant, flow modifier and surface energy enhancer and/or pigment.

For further additives and/or processing aids, see, for example, "Plastics Additives Hand book", Hans Zweifel, 6th Ed., Hanser Publ., Munich, 2009.

A further aspect of the invention are shaped articles produced from the thermoplastic molding composition (TP) obtained by the process according to the invention. Said shaped articles can be obtained by known processes for thermoplastic processing, in particular preferred is injection molding.

The thermoplastic molding compositions (TP) obtained by the process according to the invention are lightweight compositions having a reduced specific gravity and good me chanical properties such as tensile and flexural properties.

A further aspect of the invention is the use of the thermoplastic molding composition (TP) obtained by the process according to the invention or of shaped articles produced there from for various applications, in particular in the auto-(mobile), white goods or - in espe cially - electronic industry. Preferred is the use of the thermoplastic molding composition (TP) or of shaped articles produced therefrom for electronic devices where a high endur ance and fatigue resistance is required (e.g. fan blades).

The invention is further illustrated by the examples, figures and claims.

Examples

Test Methods

Particle Size Dw/ D50

For measuring the weight average particle size Dw (in particular the median weight par ticle diameter D50) with the disc centrifuge DC 24000 by CPS Instruments Inc. equipped with a low density disc, an aqueous sugar solution of 17.1 ml_ with a density gradient of 8 to 20% by wt. of saccharose in the centrifuge disc was used, in order to achieve a stable flotation behavior of the particles. A polybutadiene latex with a narrow distribution and a mean particle size of 405 nm was used for calibration. The measurements were carried out at a rotational speed of the disc of 24,000 r.p.m. by injecting 0.1 ml_ of a diluted rubber dispersion into an aqueous 24% by wt. saccharose solution. The calcula tion of the weight average particle size Dw was performed by means of the formula

D _w = sum ( n, * di ⁴ ) / sum( n, * d, ³ ) n,: number of particles of diameter d,.

Molar Mass M _w : The weight average molar mass M _w is determined by GPC (solvent: tetrahydrofuran, polystyrene as polymer standard) with UV detection according to DIN 55672-1 :2016-03.

Melt Flow Index (MFI) or Melt Volume Flow Rate (MFR): MFI/MFR test (ASTM D1238, 220 °C, 10 kg load) was performed on pellets using a MFI-machine of CEAST, Italy.

Impact test: Izod impact tests were performed on notched specimens (ASTM D 256 standard) using an instrument of CEAST (part of Instron’s product line), Italy.

Tensile test: carried out at 23°C (ASTM D 638, 5 mm/min and 50 mm/min) using a Uni versal testing Machine (UTM) of Instron, UK.

Flexural test: Flexural test was carried out at 23°C (ASTM D 790, 5 mm/min) using a UTM of Instron, UK.

Heat deflection temperature (HDT): test was performed on injection molded specimen (ASTM D 648, at 1.82 MPa, annealed) using a Zwick Roell machine, Germany.

VICAT Softening Temperature (VST): VST test was performed on injection molded test specimen (ASTM D 1525-09 standard) using a Zwick Roell machine, Germany. Test was carried out at a heating rate of 120°C/h (Method B) at 50 N load.

Rockwell Hardness: test was performed on injection molded test specimen according to ASTM D 785 by use of a test equipment from FIE Private Ltd., India.

Specific gravity: The measurement was done on a specific gravity (ASTM D 792) bal ance from Mettler Toledo. Materials used in the examples:

Component (A)

Fine-particle butadiene rubber latex (S-A1)

The fine-particle butadiene rubber latex (S-A1) which is used for the agglomeration step was produced by emulsion polymerization using tert-dodecyl-mercaptan as chain trans- fer agent and potassium persulfate as initiator at temperatures from 60° to 80°C. The addition of potassium persulfate marked the beginning of the polymerization. Finally the fine-particle butadiene rubber latex (S-A1) was cooled below 50°C and the non reacted monomers were removed partially under vacuum (200 to 500 mbar) at temperatures below 50°C which defines the end of the polymerization. Then the latex solids (in % per weight) were determined by evaporation of a sample at 180°C for 25 min. in a drying cabinet. The monomer conversion is calculated from the measured latex solids. The bu tadiene rubber latex (S-A1) is characterized by the following parameters, see table 1.

Latex S-A1-1 No seed latex is used. As emulsifier the potassium salt of a disproportionated rosin (amount of potassium dehydroabietate: 52 wt.-%, potassium abietate: 0 wt.-%) and as salt tetrasodium pyrophosphate is used.

Table 1 : Composition of the butadiene rubber latex S-A1 K = W* ( 1 -1 .4 * S ) * Dw

W = decomposed potassium persulfate [parts per 100 parts rubber]

S = salt amount in percent relative to the weight of solids of the rubber latex Dw = weight average particle size (= median particle diameter D50) of the fine-particle butadiene rubber latex (S-A1)

Production of the coarse-particle, agglomerated butadiene rubber latices (A1)

The production of the coarse-particle, agglomerated butadiene rubber latices (A1) was performed with the specified amounts mentioned in table 2. The fine-particle butadiene rubber latex (S-A1) was provided first at 25°C and was adjusted if necessary with deionized water to a certain concentration and stirred. To this dispersion an amount of acetic anhydride based on 100 parts of the solids from the fine-particle butadiene rubber latex (S-A1) as fresh produced aqueous mixture with a concentration of 4.58 wt.-% was added and the total mixture was stirred for 60 seconds.

After this the agglomeration was carried out for 30 minutes without stirring. Subsequently KOH was added as a 3 to 5 wt.-% aqueous solution to the agglomerated latex and mixed by stirring. After filtration through a 50 pm filter the amount of coagulate as solid mass based on 100 parts solids of the fine-particle butadiene rubber latex (B) was determined. The solid content of the agglomerated butadiene rubber latex (A), the pH value und the median weight particle diameter D50 was determined.

Table 2: Production of the coarse-particle, agglomerated butadiene rubber latices (A1)

Production of graft copolymer (A) 59.5 wt.-parts of mixtures of the coarse-particle, agglomerated butadiene rubber latices A1-1 and A1-2 (ratio 50 : 50, calculated as solids of the rubber latices (A1)) were diluted with water to a solid content of 27.5 wt.-% and heated to 55°C. 40.5 wt.-parts of a mixture consisting of 72 wt.-parts styrene, 28 wt.-parts acrylonitrile and 0.4 wt.-parts tert-dodecyl- mercaptan were added in 3 hours 30 minutes. At the same time when the monomer feed started the polymerization was started by feeding 0.15 wt.-parts cumene hydroperoxide together with 0.57 wt.-parts of a potassium salt of disproportionated rosin (amount of potassium dehydroabietate: 52 wt.-%, potassium abietate: 0 wt.-%) as aqueous solution and separately an aqueous solution of 0.22 wt.-parts of glucose, 0.36 wt.-% of tetraso- dium pyrophosphate and 0.005 wt.-% of iron-(ll)-sulfate within 3 hours 30 minutes. The temperature was increased from 55 to 75°C within 3 hours 30 minutes after start feeding the monomers. The polymerization was carried out for further 2 hours at 75°C and then the graft rubber latex (= graft copolymer A) was cooled to ambient temperature. The graft rubber latex was stabilized with ca. 0.6 wt.-parts of a phenolic antioxidant and precipi- tated with sulfuric acid, washed with water and the wet graft powder was dried at 70°C (residual humidity less than 0.5 wt.-%).

Component (B) Statistical copolymer (B) from styrene and acrylonitrile with a ratio of polymerized sty rene to acrylonitrile of 72:28 with a weight average molecular weight Mw of 110,000 g/mol, and a MFI at 220°C/10kg of 61 g/10 minutes, produced by free radical solution polymerization. Component (C)

Fine-Blend ^® SAM-010 (terpolymer of styrene, acrylonitrile and maleic anhydride, with 8±2 wt.-% maleic anhydride, Mw 90,000 to 100,000 g/mol) from Fine-blend Compatilizer Jiangsu Co., LTD, China.

Component (D)

Hollow glass microspheres - having a true density of 0.46 g/cm ³ , a bulk density of 0.28 g/cm ³ and a compressive strength of 110 MPa, particle diameter (D50) 20 pm - com- mercially available as iM16K from 3M India.

Component (E)

Various additives were used, e.g. the following components:

Preparation of thermoplastic compositions

All components were weighed and used in amounts according to the compositions given in Table 1. The batch size for all the compounding and extrusion trials was 10 kg.

At first (step (i) of the inventive process), a portion of 5 wt.-% of component (A) was premixed with the hollow glass microspheres (HGS, component (D)) for 2 minutes at an average speed of 500 rpm in a mixer. Then, the remaining portion (95 wt.-%) of compo- nent (A), components (B), (C) and (E) were premixed for 2 to 3 minutes at an average speed of 2200 rpm in a high speed mixer to obtain a uniform pre-mixture.

Then, the uniform pre-mixture of components (A), (B), (C) and (E) prepared was extruded through a twin-screw extruder. The extruder has co-rotating screws and has a separating feeding hopper (side feeder) after the kneading section, for feeding the pre-mixture with the HGS obtained in step (i). The pre-mixture of components (A), (B), (C) and (E) was melt blended in said twin-screw extruder at a screw speed of 350 rpm and using an incremental temperature profile from 215° C to 250° C for the different barrel zones. The pre-mixture with the HGS obtained in step (i) was separately fed during compounding through said side feeder of the extruder. The extruded reinforced polymer blend strands were water cooled, air-dried and pelletized.

This was followed by injection moulding to mould the standard test specimens. The tem perature profile of the injection moulding machine barrel was 220 to 240°C incremental.

The preparation of comparative example 1 was carried out as afore-mentioned but with out step (i) wherein component (D) with a portion of component (A) is mixed and dry- blended. Component (D) was added to the side-feeder solely (without a portion of component (A)). Table 1 : Reinforced ABS compositions The test data of the obtained ABS compositions are shown on Table 2.

Table 2: Properties of ABS compositions

The data according to Table 2 prove that the reinforced ABS compositions (Examples 1 to 3) obtained by the process according to the invention have a reduced specific gravity without compromising the mechanical properties in comparison to non-inventive ABS compositions.

The mechanical properties, especially tensile strength and flexural strength, of the light weight thermoplastic molding compositions obtained by the process according to the invention, show better results. By the process according to the invention with a lower loading of hollow glass microspheres (HGS) also, a better reduction in density is achieved (cp. specific gravity).

It was also observed that the process according to the invention gives a very high con sistency in the product with a uniform HGS distribution. This can be observed in the standard deviation (STDEV) of the ash content of samples S-1 to S-5 of inventive example 2 and comparative example 1, respectively (Table 3).

Table 3

The STDEV of the example according to the invention is insignificant and proves a bet ter distribution and consistency of the hollow glass microspheres (HGS) in the molding composition compared to comparative example 1 which STDEV is significantly higher and which properties are probably impaired due to the improper distribution of the HGS filler.

Also the surface quality of molding compositions obtained by the process according to the invention is improved (cp. Figures 1 and 2). Figure 1 shows on the left the surface of a sample according to example 2 and on the right the surface of a sample according to comparative example 1.

Figure 2 shows a microscopic image (scale-up 12.5 times) of a sample according to example 2. Figure 3 shows a microscopic image (scale-up 12.5 times) of a sample ac cording to comparative example 1.

The visual observation (cp. Figure 1) and microscope images (cp. Figures 2 and 3) clearly showed the better surface quality of the ABS sample of example 2 which surface was smooth due to a better dispersion of the hollow glass microspheres (HGS) in the molding composition compared to the sample of comparative example 1 which surface was found as rough.

The products made from such thermoplastic molding compositions, e.g. by injection molding, have improved physical properties.