ABS molding composition having improved crack and chemical resistance and its use Description The invention is directed to ABS molding compositions that exhibit improved environmental stress crack resistance properties in the presence of olefinic unsaturated blowing agents, such as hydrofluoro olefins (HFO). The invention further deals with their use in hydrofluoro olefin containing areas and as inner liner in cooling apparatuses. For thermoformed equipment liners e.g. of refrigerators, styrene copolymers and in particular ABS resins are often the material of choice for the balance of properties: strength, toughness (impact resistance), appearance (gloss and color), chemical resistance, processability, and price. Sheet extrusion grades of ABS provide deep draw capability for thermoforming operations, strength and toughness for durability in as- sembly and use, high gloss, stain and chemical resistance to items such as food.

The refrigeration industry uses polyurethane foam for heat insulation between the outer metal cabinet and the inner plastic liner. The polyurethane requires a blowing agent to generate the foam. The choice of a blowing agent is a complicated matter that depends on many factors including thermal conductivity, cost, flammability, toxicity, and envi- ronmental factors such as ozone depletion and global warming potential.

When used as refrigerator liners, the ABS resin is also exposed to foamed-in-place insulation during assembly. Foamed-in-place insulation typically generates a rush of chemical blowing agent (one chemical or mixtures of different chemicals) so as to foam the insulating material (e.g. polyurethane). As ABS liners are exposed to the blowing agent, the ABS resin has to be designed and composed in a way that it provides chemical resistance against the applied blowing agent. Otherwise it will degrade the ABS material, when getting in contact with the liner, causing it to crack.

To date, several ABS compositions were invented that show good stress cracking re- sistance against commonly used foam blowing agents such as chlorofluorocarbons (CFC), hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC), and hydrocarbons (e.g. cyclopentane). US 2008/0093578 discloses a thermoplastic resin composition for a refrigeratorcom- prising an ABS graft copolymer resin (A) obtained by emulsion polymerization, a styrenic copolymer (B) comprising (b1 ) a copolymer prepared by copolymerizing poly- butadiene with acrylonitrile and styrene and (b2) a copolymer prepared by copolymeriz- ing polybutadiene with styrene, and a SAN-copolymer (C). Said resin composition is stress crack resistant against HCFC.

In regard to the environmental factors, particularly global warming potential, a new class - the "Fourth Generation" - of blowing agents was developed that contains olefinic unsaturation. The unsaturation in the structure of these so-called HFOs (hydrofluoro olefins, e.g. trans-1-chloro-3,3,3-trifluoropropene, trade name Solstice ^® LBA, Honeywell or Forane ^® 1233zd, Arkema as well as (Z)-1 ,1 , 1- 4,4,4-hexafluorobutene, FHO- 1336mzz-Z trade name Formacel ^® 1 100, Chemours) cause them to readily decompose in the atmosphere in a matter of days rather than hundreds of years, thereby minimizing harmful global warming. However, although these HFO blowing agents have some appealing advantages, they appear to be more susceptible to cause environmental stress cracks and damage to the ABS material comprised in the inner liner of a refrigerator.

For application of this new type of blowing agent, an ABS resin (acrylonitrile-butadien- styrene-copolymer composition) is needed that provides most of the favorable proper- ties known for ABS material like strength, toughness (impact resistance), appearance (gloss and color), processability and price but in particular shows a high stress crack resistance against olefinic blowing agents or mixtures containing these blowing agents.

US 2014/019090978 describes refrigerators which are insulated with a polyurethane foam in which the blowing agent comprises substantially 1 -chloro-3,3,3- trifluoropropene. Preferably the inner liner of the refrigerator is formed in large part from High Impact Polystyrene (HIPS). Further suitable materials from which the liner may be formed at least partly are GPPS, styrene copolymers, such as styrene-butadiene block copolymers, ASA, ABS, polyolefins, (meth)acrylates such as PMMA, PC, PVC, PET and mixtures of these. In all examples only HIPS alone has been used. WO 2000/36010 discloses thermoplastic molding compositions comprising 5 to 98 wt- % ABS graft copolymer (A), 1 to 90 wt.-% SAN-copolymer (B) and 1 to 70 wt.-%, preferably 0,1 to 15 wt.-%, of a styrene-butadiene block copolymer (C) composed of at least one polystyrene hard block S and at least one elastomeric styrene/butadiene- copolymer block (S/B), preferably a linear S-SB-S blockcopolymer.

The ABS graft copolymer (A) is advantageously prepared by emulsion polymerization. The graft base is preferably a pure polybutadiene latex. Preferred compositions are composed of 24 to 29.4 wt.-% (A), 56 to 68.4 wt.-% (B) and 2 to 20 wt.-% C. The mold- ing compositions can be used in electrical devices, such as kitchen machinery, shavers, telephones, vacuum cleaners, monitor casings, keyboards, electric lawnmowers, toy railroads, washing machines, dishwashers and refrigerators. The reference is silent about the application as inliner of refrigerators and about its resistance against chemicals.

WO 2009/004018 describes thermoplastic molding compositions comprising 75 to 99 % of a SAN-copolymer A, 0 to 60 wt.-%, preferably 1 to 30 wt.-%, of a ABS graft rubber copolymer B and 1 to 10 wt.-%, preferably 1 to 5 wt.-%, of a thermoplastic SBS block copolymer C. Suitable polymerization processes of the graft copolymers B are emul- sion polymerization, solution polymerization, suspension polymerization, or bulk polymerization, aqueous emulsion polymerization being preferred. Blends composed of Terluran ^® (SAN/ABS) and Styroflex ^® (elastomer SBS block copolymer) treated with cyclopentane show an improved environmental stress crack resistance (ESCR). The molding compositions can be used for refrigerator inliners. The reference is silent about HFO blowing agents.

The formation of environmental stress cracks due to the presence of HFO against ABS resins and its potential to reduce the lifetime of ABS resin inner liners in cooling apparatuses is the problem addressed by the present invention.

It is an object of the invention to provide ABS resin compositions suitable for inner liners of cooling apparatuses that show most of the favorable properties known for ABS materials and in particular exhibit improved environmental stress crack resistance (ESCR) properties in presence of olefinic unsaturated blowing agents, in particular in presence of hydrofluoro olefins (HFO). One aspect of the invention is a thermoplastic molding composition for use in hydro- fluoro olefin containing areas comprising (or consisting of) components A, B, C and D: (A) 10 to 35% by weight of a graft rubber copolymer A obtained by emulsion polymerization and built up from

(ai) 30 to 90% by weight, based on (A), of at least one graft base (a^ made from

(an) 70 to 98% by weight, based on (a^, of at least one diene, in particular 1 ,3-butadiene, and

(a ₁₂ ) 2 to 30% by weight, based on (a^, of at least one monomer selected from the group consisting of: styrene, α-methylstyrene, acry- lonitrile, methacrylonitrile and methyl methacrylate, in particular styrene; and

(a ₂ ) 10 to 70% by weight, based on (A), of a graft (a ₂ ), grafted onto the graft base and built up from

(a ₂ i) 65 to 95% by weight, based on (a ₂ ), of at least one vinylaro- matic monomer, in particular styrene,

(a ₂₂ ) 5 to 35% by weight, based on (a ₂ ), acrylonitrile and/or methac- rylonitrile, preferably acrylonitrile, and

(a ₂₃ ) 0 to 20% by weight, based on (a ₂ ), of at least one monomer selected from the group consisting of: Ci-C ₄ - alkyl(meth)acrylates, maleic anhydride, N-phenyl maleimide, N- cyclohexyl maleimide and (meth)acrylamide;

(B) 50 to 70 % by weight of at least one copolymer B made from

(b^ 50 to 95% by weight, based on (B), of at least one vinylaromatic monomer, preferably styrene or a-methylstyrene, more preferred styrene, and (b ₂ ) 5 to 50% by weight, based on (B), acrylonitrile and/or methacryloni- trile, preferably acrylonitrile, and

(b ₃ ) 0 to 20% by weight, based on (B), of one or more of the monomers as described for (a ₂ 3);

(C) 4 to 20% by weight of at least one elastomeric block copolymer C made from (c-ι) 15 to 65% by weight, based on (C), of at least one diene, preferably butadiene, and

(c ₂ ) 35 to 85% by weight, based on (C), of at least one vinylaromatic monomer, preferably styrene,

which block copolymer C comprises

i) at least two blocks S which have polymerized units of vinylaromatic monomer c ₂ , a glass transition temperature T _g above 25°C and form a hard phase, and

ii) at least one elastomeric block B/S (soft phase) which contains both polymerized units of vinylaromatic monomer c ₂ and diene c-i, has a random structure, a glass transition temperature Tg of from -50 to +25°C and forms a soft phase,

and the amount of the hard phase formed from the blocks S accounting for from 5 to 40% by volume, based on the total block copolymer;

4 to 20% by weight of at least one graft rubber copolymer D obtained by mass polymerization and built up from

(d 10 to 25% by weight, based on (D), of at least one graft base (d^ made from

(dn) 75 to 100% by weight, based on (d-,), of at least one diene, in particular 1 ,3-butadiene, and

(d ₁₂ ) 0 to 25% by weight, based on (di), of at least one vinylaromatic monomer, preferably styrene or a-methylstyrene, more preferred styrene, and

(d ₂ ) 75 to 90% by weight, based on (D), of a graft (d ₂ ), grafted onto the graft base and built up from

(d ₂ i) 68 to 82%, preferably 70 to 80%, by weight, based on (d ₂ ), of at least one vinylaromatic monomer, preferably styrene or a- methylstyrene, more preferred styrene,

(d ₂₂ ) 18 to 32%, preferably 20 to 30%, by weight, based on (d ₂ ), acrylonitrile or methacrylonitrile, preferably acrylonitrile, and (d ₂₃ ) 0 to 20% by weight, based on (d ₂ ), of one or more of the monomers as described for (a ₂₃ ); wherein the sum of components A, B, C and D totals 100% by weight.

The volume fraction of the two phases of block copolymer C can be measured by means of high-contrast electron microscopy or solid-state NMR spectroscopy.

In the context of the invention the term "diene" refers to a 1 ,3-diene, in particular 1 ,3- butadiene and/or isoprene, often butadiene. According to the invention the term "mass polymerization" means a bulk or a solution polymerization or a suspension polymerization in which the polymerization is started as before mentioned as bulk or solution polymerization and is then continued after suspension in water to final conversion. The term "wt.-%" is identical to "% by weight". The term "pbw" is identical to "parts by weight".

If in said thermoplastic molding composition the amounts of components A, C and/or D are further specified, the amount of component B is set within the given range, provid- ed that the amounts of components A to D add up to 100% by weight.

The thermoplastic molding composition according to the invention can further comprise optional components E and/or F. Component E is at least one inorganic additive E selected from phyllosilicates (E1 ) and nano calcium carbonate (E2). Component E can be used in amounts of from 0.01 to 10 parts by weight, based on 100 parts by weight of the composition consisting of components A, B, C and D. Component F is at least one further additive and/or processing aid F. Component F can be used in amounts of from 0.01 to 20 parts by weight, based on 100 parts by weight of the composition consisting of components A, B, C and D. If in said thermoplastic molding composition optional components E and/or F are present, the minimum amount of each of components E and F preferably is 0.05, more preferred 0.10 parts by weight, based on 100 parts by weight of the composition consisting of components A, B, C and D.

Preferred are thermoplastic molding compositions in accordance with the invention comprising (consisting of) components A, B, C and D in the following amounts:

(A) : 15 to 28 wt.-%;

(B) : 53 to 70 wt.-%;

(C): 6 to 15 wt.-%;

(D): 6 to 15 wt.-%;

wherein components A, B, C and D have the meaning as described for the use before.

More preferred are thermoplastic molding compositions in accordance with the inven- tion comprising (consisting of) components A, B, C and D in the following amounts:

(A) : 18 to 28 wt.-%;

(B) : 55 to 70 wt.-%;

(C) : 6 to 15 wt.-%;

(D) : 6 to 15 wt.-%;

wherein components A, B, C and D have the meaning as described before.

Most preferred are thermoplastic molding compositions in accordance with the invention comprising (consisting of) components A, B, C and D in the following amounts: (A): 18 to 25 wt.-%;

(B): 55 to 65 wt.-%;

(C) : 6 to 15 wt.-%;

(D) : 6 to 15 wt.-%;

wherein components A, B, C and D have the meaning as described before. In particular preferred are molding composition consisting of components A, B, C and D in the amounts as hereinbefore defined. Furthermore preferred are molding compositions in accordance with the invention consisting of components A, B, C, D and 1 to 20, preferably 1 to 15 parts by weight of component F, based on 100 parts by weight of the composition consisting of components A, B, C and D. Furthermore preferred are molding compositions in accordance with the invention consisting of components A, B, C, D, and 0.01 to 10, preferably 0.01 to 8, more preferably 0.01 to 5 parts by weight of component E, based on 100 parts by weight of the compo- sition consisting of components A, B, C and D.

Furthermore preferred are molding compositions used in accordance with the invention consisting of components A, B, C, D and, based on 100 parts by weight of the composition consisting of components A, B, C and D, 1 to 20, preferably 1 to 15 parts by weight of component F, and 0.01 to 10, preferably 0.01 to 8, more preferably 0.01 to 5 parts by weight of component E.

Even more preferred are thermoplastic molding compositions in accordance with the invention comprising (or consisting of):

(A): 18 to 25 wt.-%;

(B) : 55 to 64.9 wt.-%;

(C) : 6 to 15 wt.-%;

(D) : 6 to 15 wt.-%;

wherein the sum of components A, B, C and D totals 100% by weight,

and which further comprise 0.1 to 15 parts by weight of component F, based on 00 parts by weight of the composition consisting of components A, B, C and D.

In accordance with the invention the afore-mentioned molding compositions are preferably used for the preparation of inliners for cooling apparatuses, in particular refrigera- tors.

Component A (Graft rubber copolymer A)

The at least one graft rubber copolymer A is used as an impact modifier and forms a soft phase having a glass transition temperature T _g of < 0°C, preferably < -20°C, particularly preferably < -40°C The glass transition temperature T _g is measured by dynamic mechanical analysis (DMA) using a frequency of 1 Hz.

Preferably at least one graft copolymer A according to the invention is used which is built up from:

40 to 90 wt.-%, preferably 45 to 85 wt.-%, particularly preferably 45 to 75 wt.-% of at least one graft base a based on (A), made from:

80 to 98 wt.-%, preferably 85 to 97 wt.-%, based on (a^, of at least one diene (an), preferably 1 ,3-butadiene,

2 to 20 wt.-%, preferably 3 to 15 wt.-%, based on (a-ι), of at least one monomer (a ₁₂ ), preferably styrene; and

a ₂ : 10 to 60 wt.-%, preferably 15 to 55 wt.-%, particularly preferably 25 to 55 wt.-%, based on (A), of a graft a ₂₎ grafted onto the graft base and built up from:

65 to 80 wt.-%, in particular 65 to 75 wt.-%, based on (a ₂ ), of at least one vinylaromatic monomer (a ₂ i), in particular styrene, and

20 to 35 wt.-%, in particular 25 to 35 wt.-%, based on (a ₂ ), of acrylonitrile and/or methacrylonitrile (a ₂₂ ), preferably acrylonitrile, and

0 to 20% by weight, based on (a ₂ ), of at least one monomer (a ₂₃ ).

The diene a^ is preferably 1 ,3-butadiene and/or isoprene, more preferably 1 ,3- butadiene. Comonomer a ₁₂ is preferably styrene.The vinylaromatic monomer a ₂₁ is preferably styrene and/or a-methylstyrene, more preferred styrene. Comonomer a ₂₂ is acrylonitrile and/or methacrylonitrile, preferably acrylonitrile. Further comonomer a ₂ 3 is at least one monomer selected from the group consisting of: C C^ alkyl(meth)acrylates, maleic anhydride, N-phenyl maleimide, N-cyclohexyl maleimide and (meth)acrylamide, preferably C ₁ -C ₄ -alkyl(meth)acrylates and maleic anhydride. Preferably comonomer a ₂₃ is not present.

The weight average particle diameter D _w of the at least one graft base a-, of the graft copolymer A is generally 0.15 pm to 0.80 pm, preferably 0.15 to 0.50 pm, particularly preferably 0.20 pm to 0.50 pm, most preferably 0.25 to 0.40 pm.

One or more graft copolymers A with uni-, bi-, tri- or multimodal particle size distribu- tions can be used.

The weight average particle diameter D _w can be determined by a measurement with an ultracentrifuge (see W. Scholtan, H. Lange: Kolloid Z. u. Z. Polymere 250, pp. 782 to 796 (1972)) or a disc centrifuge DC 24000 by CPS Instruments Inc. at a rotational speed of the disc of 24,000 r.p.m. The particle diameter can also be determined by static light scattering (see A. Schmidt in Houben- Weyl, Methoden der Organischen Chemie, Georg Thieme Verlag, Stuttgart, 1987, volume E20, pp. 238-248.) wherein with this method in opposite to the two first no information about the particles size dis- tribution is obtained. For definition of the weight average particle size D _w see: G.

Lagaly, 0. Schulz, R. Zimehl: Dispersionen und Emulsionen: Eine Einftihrung in die Kolloidik feinverteilter Stoffe βϊηεοϊιΝββΙίοΐΊ der Tonminerale, Darmstadt: Steinkopf- Verlag 1997, ISBN 3-7985-1087-3, page 282, formula 8.3b. Preferred diene rubbers (graft bases a^ and graft copolymers A are described in EP-B 0993476, in WO 01/62848 and in WO 2012/022710 (in particular pages 23-28).

Processes for the preparation of the graft copolymers A are known to a person skilled in the art and described in the literature. According to the invention the graft base (a^ and the graft copolymers A are obtained from free-radical emulsion polymerization (EP 993476 B, WO 01/62848 and WO 2012/022710).

Suitable temperatures for the emulsion polymerization process are generally from 20 to 100 °C, preferably 30 to 90 °C. As emulsifiers there may be used conventional emulsi- fiers for example, alkali metal salts of alkyl- or alkylarylsulfonic acids, alkyl sulfates, salts of higher fatty acids having 10 to 30 carbon atoms, sulfosuccinates, ether sulfonates or rosin soaps from different natural raw materials. Preference is given to alkali metal salts, in particular the sodium and potassium salts, of alkylsulfonates or fatty acids having 10 to 18 carbon atoms. Further preference is given to resin or rosin acid-based emulsifiers, in particular 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 dehydroabietic acid of at least 30 wt.-% and preferably a content of abietic acid of max- imally 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 wt.-% and a content of abietic acid of maximally wt.-% is advantageous.

In general, the emulsifiers are used in amounts of 0.5 to 5 wt.-%, in particular from 0.5 to 4 wt.-%, based on the monomers used for the preparation of the graft base a^

Preferably for the preparation of the dispersion so much water is used that the finished dispersion has a solids content of 20 to 50 wt.-%.

For initiating the polymerization radical initiators are suitable, which decompose at the selected reaction temperature, i.e. those which decompose by heat alone, as well as those decomposing in the presence of a redox system. The polymerization initiators used are preferably those forming free-radicals, such as peroxides, preferably peroxo- sulphates (as sodium or potassium persulfate) and azo compounds such as azodiiso- butyronitrile. Redox systems can also be used, in particular those based on hydroperoxides, such as cumene hydroperoxide or tert-butyl hydroperoxide together with a reducing agent, e.g. succrose, dextrose and ferrous iron.

In general, the polymerization initiators are used in an amount of 0.05 to 1 wt.-%, preferred 0.1 to 1 wt.-%, based on the graft base monomers a _1t and a ₁₂ .

The polymerization initiators and also the emulsifiers can be added to the reaction mix- ture, either discontinuously as the total amount at the beginning of the reaction, or, continuously divided into several portions intermittently at the beginning and at one or more later time points during a specified time interval. Continuous addition may also follow a gradient, which can for example rise or decline and can be linear or exponential, or stepwise.

Further, molecular weight regulators such as, e.g. ethylhexylthioglycolate, n- or t- dodecyl mercaptan and other mercaptans, terpinols and dimeric alpha-methyl styrene or other suitable compounds for regulating the molecular weight can be used. The molecular weight regulators can be added to the reaction mixture batch-wise or continuously, as described for the polymerization initiators and emulsifiers before.

To maintain a constant pH-value which is preferably from 6 to 12.5, preferred 7 to 12.0, buffer substances such as Na ₂ HP0 ₄ NaH ₂ P0 ₄ , sodium hydrogen carbonate, sodium carbonate or buffers based on citric acid/citrate, can be used additionally. Regulators and buffer substances are used in the usual amounts.

In a particular preferred embodiment, during the grafting of the graft base with the monomers a ₂ i and a ₂₂ and optionally a ₂₃ a hydroperoxide and a reducing agent are added together with ferrous iron.

The person skilled in the art selects the polymerization conditions, in particular the type, quantity and dosage of the emulsifier and of the other polymerization auxiliaries so that the resultant rubber latex (graft base) a1 of the graft copolymer A has an average particle size, defined by the weight average particle diameter D _w of from 0.15 pm to 0.80, preferably 0.15 to 0.60 pm, particularly preferably 0.20 μιτι to 0.50 pm, most preferably 0.25 to 0.40 pm. In case of a monomodal particle size distribution the resultant particle diameter D _w of the polymer particles of the graft base a-ι is preferably from 0.20 pm to 0.50 pm, more preferably 0.25 to 0.40 pm. One can also select the polymerization conditions so, that the polymer particles of the graft base a1 have a bi-, tri- or polymodal particle size distribution in the afore-mentioned ranges. A bi-, tri- or polymodal particle size distribution can be achieved by a (partially) agglomeration of the graft base particles a-i .

Furthermore and preferred in accordance with the invention, to achieve a bi-, tri- or polymodal particle size distribution of the graft rubber copolymer (A), it is possible to prepare, separately from one another in the usual manner, two or more different graft bases a^ ₎ , a _1-2) etc. differing in their weight average particle size D _w , and to mix said graft bases a- ), a _-2) etc. in the desired mixing ratio. Advantageously first a graft base ai is prepared in the usual manner, which is then separately agglomerated in two or more batches to obtain two or more different graft bases a _M) , a _{1 2)} etc. differing in their particle size D _w . Afterwards the graft a ₂ is grafted onto the mixture of said (agglomerated) graft bases

Preferred is the use of a graft rubber copolymer (A) having a bimodal particle size dis- tribution which is prepared from a mixture of a(n) (agglomerated) graft base a^ ₎ of fine particles having a particle size D _w of from 0.15 to 0.30 pm, preferably 0.15 to 0.25 μηι and a(n) (agglomerated) graft base a-^ _j of coarse particles having a particle size D _w of from 0.40 to 0.80 pm, preferably 0.45 to 0.60 pm. The mixing ratio of graft bases a^ to a _1-2) is preferably from 50/50 to 90/10.

According to a particular embodiment, the graft base a- _! can be prepared by polymerizing the monomers a to a ₁₂ in the presence of a finely divided latex (so-called "seed latex" polymerization). This latex is provided and can be made of elastomeric polymers forming monomers or from other monomers such as those mentioned above. Suitable seed latices consist for example of polybutadiene or polystyrene.

In the seed polymerization usually first a finely divided polymer, preferably a polybutadiene, is produced as seed latex and then this seed latex is further polymerized with monomers comprising butadiene into larger particles (see Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, Part 1 , p. 339 (1961 ), Thieme Verlag, Stuttgart). It is preferably carried out using the seed batch process or using the seed- feed process.

Preferred graft bases a-ι and graft copolymers A may be obtained by the seed polymer- ization technology described in the document WO 2012/022710.

In another preferred embodiment, the graft base a-ι is produced in a so-called feed process. In this method, a certain proportion of the monomers a _t1 and a ₁₂ is provided and the polymerization is started, after which the remainder of the monomers a„ and a ₁₂ ("feed portion") is added as a feed during the polymerization.

The feed parameters (gradient shape, amount, duration, etc.) depend on the other polymerization conditions. The addition of the radical initiator and emulsifier is as described before. Preferably in the feed process, the proportion of the monomers first provided is up to 50 wt-%, preferably up to 40 wt.-%, based on a-,). Preferably the remainder of the monomers an to a ₁₂ is fed within 1 to 18 hours, in particular 2 to 16 hours, more preferred 4 to 12 hours.

In the second stage, the rubber latex is agglomerated. This can be done by adding a dispersion of an acrylic ester copolymer as agglomeration agent. Preferably dispersions of copolymers made from (C1-C4 alkyl)esters of acrylic acid, preferably of ethyl acrylate, and 0.1 to 10 wt.-% monomers forming polar polymers such as acrylic acid, methacrylic acid, acrylamide or methacrylamide, N-methylol methacrylamide or N-vinyl pyrrolidone, are used. Particularly preferred is a copolymer made from 96% ethyl acrylate and 4% of methacrylamide. The agglomerating dispersion may optionally contain one or more of the above acrylic ester copolymers. The concentration of the acrylate copolymers in the dispersion used for the agglomeration is generally between 3 and 40 wt.-%. For the agglomeration from 0.2 to 20, preferably 1 to 5 parts by weight of the agglomerating dispersion are used based on 100 parts of the rubber latex, in each case calculated on the solids content. The agglomeration is carried out by adding the agglomerating dispersion to the rubber. The addition rate usually is not critical, in general it takes about 1 to 30 minutes at a temperature between 20 and 90°C, preferably between 30 and 75°C.

Particular preference is given to the agglomeration of the rubber latex (graft base a^ with an acid, preferably with an acid anhydride and more preferably acetic anhydride (see WO 2012/022710, p. 9-10). Preferably the rubber latex a-, is mixed with said acid, and after agglomeration is complete, preferably restabilization with a base, preferably a potassium hydroxide solution, alone or in combination with an emulsifier solution such as Sodium or Potassium naphthalene sulfonate formaldehyde condensates or rosin soap is carried out. Preferred for the restabilization is a combination of potassium hy- droxide solution with sodium or potassium naphthalene sulfonate formaldehyde condensates or rosin soap.

Preferably, acetic anhydride is used for this agglomeration. However, other organic anhydrides can also be used. It is also possible to use mixtures of acetic anhydride with acetic acid or mixtures of organic anhydrides with acetic acid or other carboxylic acids.

Once the agglomeration is complete, the agglomerated rubber latex is preferably restabilized with a base such as potassium hydroxide solution alone, or, preferably in combination with an emulsifier solution such as sodium or potassium naphthalene sulfonate formaldehyde condensates or rosin soap, so that the result is a pH value of preferably more than pH 7.5. Other alkaline solutions, such as, e.g., sodium hydroxide solution, can be used, albeit this is less preferred.

According to a preferred embodiment first, the starting rubber latex is provided, where- in, in a preferred form, the solid content of the solid of this latex is adjusted to from 25 to 45 wt.-% by the addition of water. The temperature of the starting rubber latex, optionally mixed with water, can be adjusted in a broad range of from 0°C to 70°C, preferably of from 0°C to 60°C, and particularly preferably of from 5°C to 50°C. Preferably at this temperature, a mixture of preferably acetic anhydride and water, which was pre- pared by mixing, is added to the starting rubber latex under good mixing. The addition of the acetic anhydride-water mixture and the mixing with the starting rubber latex should take place within a time span of two minutes at most in order to keep the coagulate formation as small as possible. The coagulate formation cannot be avoided completely, but the amount of coagulate can be limited advantageously by this measure to significantly less than 1 wt.-%, generally to significantly less than 0.5 wt.-% based on the solids of the starting rubber latex used.

Preferably the mixing ratio of the acetic anhydride-water mixture used in the agglomeration step is 1 :7.5 to 1 :40, preferably 1 :10 to 1 :30, more preferably 1 :15 to 1 :30. When the acetic anhydride-water mixture is added, agglomeration of the fine-particle rubber particles within the starting rubber latex to form larger rubber particles starts and is finished after 5 to 60 minutes according to the adjusted temperature. The rubber latex is not stirred or mixed in this phase. The agglomeration, the increase in size of the rubber particles, comes to a standstill when the entire amount of acetic anhydride is hydro- lyzed and the pH value of the rubber latex does not drop any further. For re-stabilization, again preferably potassium hydroxide solution or, preferably in combination with an emulsifier solution as before mentioned, is carefully added to the rubber latex and mixed with the rubber latex, so that a pH value of the rubber latex of at least pH 7.5 results. According to a further preferred embodiment, the agglomeration step is carried out by the addition of 0.1 to 5 parts by weight of acetic acid anhydride per 100 parts of the starting rubber latex solids. The starting rubber latex solids means here a solid content of preferably 25 to 45 wt.-% (evaporation sample at 180°C for 25 min. in drying cabinet), more preferably 30 to 45 wt.-%, particularly preferably 35 to 45 wt.-%. Furthermore agglomeration by pressure or freezing (pressure or freeze agglomeration) is possible. Said methods mentioned are known to a person skilled in the art.

The gel contents of the graft base a^ may in principle be adjusted in a manner known per se by employing suitable reaction conditions (e.g. high reaction temperature and/or polymerization up to a high conversion, as well as optionally the addition of crosslinking substances in order to achieve a high gel content, or for example low reaction temperature and/or termination of the polymerization reaction before too high a degree of crosslinking has occurred, as well as optionally the addition of molecular weight regulators, such as for example n-dodecyl mercaptan or t-dodecyl mercaptan in order to achieve a low gel content).

Usually, the polymerization of the graft base a-i is performed by selecting the reaction conditions, so that a graft base a^ with a specific crosslinking state is obtained. Essential parameters therefor are inter alia the reaction temperature and time, the ratio of monomers, regulators, free-radical initiators and, for example in the feed process, the feed rate and the amount and time of addition of regulator and initiator.

The crosslinking state of the graft base a- _\ can be measured by the gel content which is the product portion, which is crosslinked and thus not soluble in a particular solvent. The values given for the gel content relate to the determination by the wire cage method in toluene (see Houben-Weyl, Methoden der Organischen Chemie, Makromoleku- lare Stoffe, Part 1 , p. 307 (1961 ), Thieme Verlag Stuttgart). Usual gel contents of the graft bases ^ used in the invention are in the range from 60 to 98%, preferably 65 to 98%, more preferably 70 to 97%, most preferably 75 to 95%.

Preferably the gel content of the graft base a-ι is 70 to 97%, preferred 75 to 95% and the swelling degree of the gel in toluene is in the range of 15 to 35, preferably in the range of 18 to 33.

The preparation of the graft a ₂ grafted onto the graft base 3 can be performed under the same conditions as the preparation of the grafting base a-ι, in doing so it being pos- sible to produce the graft a ₂ in one or more process steps. Further details for the preparation of graft copolymers A are described in DE 12 60 135 and WO 2012/0227 0.

The graft polymerization of the monomers a ₂ i , a ₂₂ and a ₂₃ is also carried out in a free- radical emulsion polymerization technique. It may be carried out in the same system as the polymerization of the graft base a-,, and further emulsifier and initiator may be added. These need not be identical with the emulsifiers or initiators used for preparing the graft base a^. For the selection of emulsifier, initiator, regulator etc. the same remarks apply as for the preparation of the graft base a^ The monomer mixture to be grafted can be added to the reaction mixture all at once, batchwise in several stages, or pref- erably, continuously during the polymerization.

As far as during the grafting of the graft base a-i non-grafted polymers of the monomers a ₂₁ to a ₂₂ are obtained, their amounts are assigned to the weight of component A. Said amounts are generally in the range of from 10 to 50%, based on a ₂ .

Preferably at least one graft copolymer A is used obtained by emulsion polymerization of

a^ 40 to 90 wt.-%, preferably 45 to 85 wt.-%, based on (A), particularly preferably 45 to 75 wt.-% of at least one graft base a ₁ made from:

(a1 1 ) 80 to 98 wt.-%, preferably 85 to 97 wt.-%, based on a of 1 ,3-butadiene,

(a12) 2 to 20 wt.-%, preferably 3 to 15 wt.-%, based on a,, of styrene; and a ₂ : 10 to 60 wt.-%, preferably 15 to 55 wt.-%, based on (A), particularly preferably 25 to

55 wt.-% of a graft a ₂ , grafted onto the graft base a^ and built up from: a ₂₁ : 65 to 80 wt.-%, in particular 65 to 75 wt.-%, based on a ₂ , of styrene; and a ₂₂ : 20 to 35 wt.-%, in particular 25 to 35 wt.-%, based on a ₂ , of acrylonitrile.

Component B

Component B forms a hard phase having a glass transition temperature T _g of > 20°C, measured by dynamic mechanical analysis (DMA) using a frequency of 1 Hz.

Preferably component B is at least one copolymer B obtained by polymerization of styrene or α-methylstyrene (b^ and acrylonitrile (b ₂ ), a so-called SAN-copolymer or AMSAN copolymer. SAN-copolymers are even more preferred.

Said SAN and AMSAN copolymers generally are made from 18 to 40 wt.-%, preferably 22 to 33 wt.-%, particularly preferably 25 to 31 wt.-% of acrylonitrile, and 82 to 60 wt.- %, preferably 78 to 67 wt.-%, particularly preferably 75 to 69 wt.-% styrene or a- methylstyrene, wherein the sum of styrene or a-methylstyrene and acrylonitrile totals 100 wt.-%.

Component B, in particular said at least one SAN- or AMSAN-copolymer, preferably has a weight average molar mass M _w of from 85,000 to 300,000 g/mol, more preferably from 120,000 to 250,000 g/mol and most preferably from 140,000 to 230,000 g/mol, measured by gel permeation chromatography and using polystyrene for calibration. Preferably component B is a mixture of at least two, preferably two, three, four or five, SAN-copolymers having different weight average molar masses M _w in the aforementioned ranges.

Copolymers B are obtained in a known manner by bulk, solution, suspension, precipitation or emulsion polymerization, bulk, suspension and solution polymerization are preferred. Details of these processes are described, for example in "Kunststoffhandbuch, Eds. R. Vieweg and G. Daumiller, Vol. 4 "Polystyrol", Carl Hanser Verlag, Munich 1996, p 104 ff and in "Modern Styrenic Polymers: Polystyrenes and Styrenic copolymers" (Eds., J. Scheirs, D. Priddy, Wiley, Chichester, UK, (2003), pages 27 to 29) and in GB-A 1 ,472,195. The melting volume rate (MVR, measured according to ISO 1 133 at 220°C and 10 kg load) of component B, in particular of the at least one SAN-copolymer as defined above, is preferably at least 3 mL/10 min, more preferably in the range of from 3 to 20 mL/10 min.

Preferably component B is a mixture of at least two, preferably two, three, four or five, copolymers B, preferably SAN-copolymers B, with different MVRs in the range of from 3 to 90 mL/10 min. The ratio of said at least two, preferably two, three, four or five, copolymers B, preferably SAN-copolymers B, with different MVR is chosen so, that the resulting MVR of the mixture is preferably in the range of from 3 to 20 mL/10 min.

Component C

Block copolymer C can be represented, for example, by one of the formulae 1 to 12:

(I ) S-B/S-S;

(2) (S-B/S)n;

(3) (S-B/S)n-S;

(4) B/S-(S-B/S)n;

(5) X-[(S-B/S)n]m+1 ;

(6) X-[(B/S--S)n]m+1 ;

(7) X-[(S-B/S)n-S]m+1 ;

(8) X-[(B/S-S)n-B/S]m+1 ;

(9) Y-[(S-B/S)n]m+1 ;

(10) Y-[(B/S--S)n]m+1 ;

(I I ) Y-[(S-B/S)n-S]m+1 ;

(12) Y-[(B/S-S)n-B/S]m+1 ; where S is the hard phase and B/S is the soft phase, ie. the block built up randomly from diene units and vinylaromatic monomer units, X is the radical of an n-functional initiator, Y is the radical of an m-functional coupling agent and m and n are natural numbers from 1 to 10.

Styrene, a-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene or mixtures thereof can be used as vinylaromatic monomers c ₂ both for the hard blocks S and for the soft blocks B/S. Styrene is preferably used. Butadiene, isoprene, 2,3-dimethylbutadiene, 1 ,3-pentadiene, 1 ,3-hexadienes or piperylene or mixtures thereof are preferably used as dienes c-, for the soft block B/S. 1 ,3-Butadiene is particularly preferably used.

A preferred block copolymer is one of the general formulae S-(B/S)-S, X-[-(B/S)-S] ₂ and Y-[-(B/S)-S] ₂ (for the meanings of abbreviations, see above) and a particularly preferred block copolymer is one whose soft phase is divided into blocks (B/S)i -(B/S) ₂ ; (B/S) - (B/S) ₂ -(B/S) _! and (B/S) _! -(B/S) ₂ -(B/S) ₃ ; whose vinylaromatic/diene ratio differs in the individual blocks B/S or changes continuously within a block within the limits (B/S^ (B/S) ₂ , the glass transition temperature T _g of each sub-block being below 25°C.

A block copolymer which has a plurality of blocks B/S and/or S having different molecular weights per molecule is likewise preferred.

A particularly preferred combination of monomers is butadiene and styrene.

Preferably the B/S block is composed of about 75 to 30% by weight of vinylaromatic monomer, preferably styrene, and 25 to 70% by weight of diene, preferably butadiene.

More preferably the B/S block has a diene, in particular butadiene, content of from 35 to 70 wt.-% and a vinylaromatic monomer, in particular styrene, content of from 65 to 30 wt.-%. The amount of the diene, preferably butadiene, in the total block copolymer C is 15 to 65% by weight and that of the vinylaromatic monomer, preferably styrene, is correspondingly 85 to 35% by weight.

Block copolymers C made from a monomer composition consisting of 25 to 60% by weight of diene, preferably butadiene, and 75 to 40% by weight of the vinylaromatic monomer, preferably styrene, are preferred.

More preferred are block copolymers C wherein the amount of diene, in particular butadiene, based on the total block copolymer, is less than 50% by weight. Most preferred are block copolymers C made from a monomer composition consisting of 25 to 45% by weight of diene c-i , in particular butadiene, and 75 to 65% by weight of the vinylaromatic monomer c ₂ , in particular styrene.

The block copolymers C are generally prepared by anionic polymerization in a nonpolar solvent with the addition of a polar cosolvent. The concept here is that the cosolvent acts as a Lewis base toward the metal cation. Preferably used solvents are aliphatic hydrocarbons, such as cyclohexane or methylcyclohexane. Polar aprotic compounds, such as ethers and tertiary amines, are preferred as Lewis bases. Examples of particularly effective ethers are tetrahydrofuran and aliphatic polyethers, such as diethylene glycol dimethyl ether. Examples of tertiary amines are tributylamine and pyridine. The polar cosolvent is added to the nonpolar solvent in a small amount, for example 0.5-5% by volume- Tetrahydrofuran in an amount of 0.1 to 0.3% by volume is particularly pre- ferred. Experience has shown that an amount of about 0.2% by volume is sufficient in most cases.

The copolymerization parameters and the amount of 1 ,2- and 1 ,4-bonds of the diene units are determined by the metering and structure of the Lewis base. The block copol- ymers C contain, for example, 15 to 40% of 1 ,2-bonds and 85 to 60% of 1 ,4-bonds, based on all diene units.

The anionic polymerization is initiated by means of organometallic compounds. Compounds of the alkali metals, particularly lithium, are preferred. Examples of initiators are methyllithium, ethyllithium, propyllithium, n-butyllithium, sec-butyllithium and tert- butyllithium. The organometallic compound is added as a solution in a chemically inert hydrocarbon. In some cases, e.g. when using n-butyl lithium, it is required to add small amounts (up to 5%, preferred 0.01 to 1 %) of an electron donor like ethers, e.g. dimethyl ether, diethyl ether, tetrahydrofurane. The amount metered depends on the desired molecular weight of the polymer but is as a rule from 0.002 to 5 mol %, based on the monomers.

The polymerization temperature may be from 0 to 130°C, preferably from 30 to 100°C. The amount by volume of the soft phase B/S composed of diene and vinylaromatic sequences is 60 to 95, preferably 70 to 90, particularly preferably 80 to 90, % by volume. The blocks S formed from the vinylaromatic monomers constitute the hard phase, which accounts for 5 to 40, preferably 10 to 30, particularly preferably 10 to 20, % by volume.

It should be pointed out that there is no strict correlation between the abovementioned ratios of vinylaromatic monomer and diene, the abovementioned limits of the phase volumes and the composition which arises from the ranges of the glass transition tem- perature, since the relevant numbers in each case are numerical values rounded up to the nearest tens unit. Any correlation is likely to be merely accidental.

The volume fraction of the two phases can be measured by means of high-contrast electron microscopy or solid-state NMR spectroscopy. The amount of vinylaromatic blocks can be determined by precipitation and weighing following osmium degradation of the polydiene content. The future phase ratio of a polymer can also be calculated from the amounts of monomers used if polymerization is taken to completion every time. In addition, it is to be pointed out (cf. J. Brandrup, E. H. Immergut, Polymer Handbook, John Wiley, N.Y.) that the densities of styrene/butadiene copolymers can be calculated approximately from the mass fractions of the monomers; thus, the density of polybuta- diene (obtained by anionic polymerization) is 0.895 g/ml and the density of polystyrene is about 1.05 g/ml (mean value), whereas the density is stated as 0.933 for a sty- rene/butadiene copolymer (SB rubber) containing 23.5% of styrene. The calculated density would be 0.960.

The block copolymer C is unambiguously defined by the quotient of the volume fraction as a percentage of the soft phase formed from the B/S blocks and the fraction of diene units in the soft phase, which is from 25 to 70% by weight.

The glass transition temperature (T _g ) is influenced by the random incorporation of vinylaromatic monomers in the soft block B/S of the block copolymer and the use of Lew- is bases during the polymerization. A glass transition temperature of from -50 to +25 C, preferably from -50 to +5°C is typical.

The molecular weight of block S is in general from 1000 to 200,000, preferably from 3000 to 80,000, g/mol. Within a molecule, S blocks may have different molecular weights.

The molecular weight of block B/S is usually from 2000 to 250,000, preferably from 5000 to 150,000, g/mol. As in the case of block S, block B/S too may assume different molecular weight values within a molecule.

The coupling center X is formed by the reaction of the living anionic chain ends with a bifunctional or polyfunctional coupling agent. Examples of such compounds are given in U.S. Pat. Nos. 3,985,830, 3,280,084, 3,637,554 and 4,091 ,053. For example, epox- idized glycerides, such as epoxidized linseed oil or soybean oil, are preferably used; divinylbenzene is also suitable. Dichlorodialkylsilanes, dialdehydes, such as tereph- thalaldehyde, and esters, such as ethyl formate or ethyl benzoate, are particularly suitable for the dimerization. Preferred polymer structures are S-B/S-S, X-[-B/S-S]2 and Y-[-B/S-S]2, where the random block B/S itself may in turn be divided into blocks B1/S1-B2/S2-B3/S3-

The random block preferably consists of from 2 to 15, particularly preferably from 3 to 10, random subblocks. The division of the random block B/S into as many subblocks Bn/Sn as possible has the decisive advantage that the B/A block as a whole behaves like a virtually perfect random polymer even in the case of a composition gradient within a subblock Bn/Sn.

Particular preference is given to linear styrene-butadiene block copolymers of the general structure S-(S/B)-S having, situated between the two S blocks, one or more (S/B)- random blocks having random styrene/butadiene distribution. These block copolymers are described by way of example in WO 95/35335 and WO 97/40079. The vinyl content is the relative proportion of 1 ,2-linkages of the diene units, based on the entirety of 1 ,2-, 1 ,4-cis and 1 ,4-trans linkages. The 1 ,2-vinyl content in the styrene- butadiene copolymer block (S/B) is preferably below 20%, in particular in the range from 9 to 15%, particularly preferably in the range from 9 to 12%. Suitable block copol- ymers C having such a 1 ,2-vinyl content in the styrene-butadiene copolymer block (S/B) are described in detail in WO 1997/40079.

Very particular preferred block copolymers A according to the present invention are linear styrene-butadiene block copolymers of the general structure S-(S/B)-S having, situated between the two S blocks, one or more (S/B)-random blocks having random styrene/butadiene distribution, and a 1 ,2-vinyl content in the styrene-butadiene copolymer block (S/B) of below 20%.

Further preferred block copolymers C have a star-shaped molecular architecture, where the star-shaped molecular architecture has at least two different arms of the star, having the structure one of the following general formulae:

Y[(B/S-S) _n ] _m [S],

Y[(S-B/S) _n -S] _m [S], where S B/S n and m have the meaning given above, Y is the moiety of an (m + I)- functional coupling agent, and I is a natural number from 1 to 10. Said star shaped block copolymers C are described in detail in WO 2012/055919.

Component D

Graft rubber copolymer D as described above is preferably built up from

(d-,) from 12 to 20% by weight, based on (D), of a graft base (d^, and (d ₂ ) from 80 to 88% by weight, based on (D), of a graft (d ₂ ), grafted onto the graft base.

Preferred is a graft rubber copolymer D as described above wherein component d ₂ 3 is not present.

Furthermore preferred is a graft rubber copolymer D as described above wherein component dn is 1 ,3-butadiene. Furthermore preferred is a graft rubber copolymer D as described above wherein component di ₂ is styrene.

Furthermore preferred is a graft rubber copolymer D as described above wherein component d ₂₁ is styrene.

Furthermore preferred is a graft rubber copolymer D as described above wherein component d ₂ 2 is acrylonitrile.

More preferred is graft rubber copolymer D as described above built up from:

(d-,) 10 to 25%, preferably 12 to 20%, by weight, based on (D), of a graft base (d _n ) made from

(dn) 75 to 100% by weight, based on (d,), 1 ,3-butadiene, and (d ₁₂ ) 0 to 25% by weight, based on (d^, styrene; and

(d ₂ ) 75 to 90%, preferably 80 to 88% by weight, based on (D), of a graft (d ₂ ), grafted onto the graft base and built up from (d ₂₁ ) 68 to 82%, preferably 70 to 80%, by weight, based on (d ₂ ), styrene,

(d ₂₂ ) 18 to 32%, preferably 20 to 30%, by weight, based on (d ₂ ), acrylonitrile. The graft base d _! can be a linear polymer, a long-chain branched polymer or a star- branched polymer. Graft base di generally is a soluble polymer with no or negligible amount of insoluble parts. Comonomers d-π and d ₁₂ can be polymerized statistically, in block form or in tapered form (gradient composition of d^ and d ₁₂ ). Preferably graft base d-ι is obtained by anionic polymerization.

The mass polymerization is preferably conducted in a monomer medium rather than in water, usually employing a series of two or more continuous reactors. The graft base (d-ι ) used in this process is most commonly a solution polymerized diene homo- or co- polymer. Often a solution of the graft base (d^ in the monomers (d ₂₁ ) and (d ₂₂ ) is prepared for feeding to the reactor system. It is also possible to use only a part of the monomers (d ₂₁ ) and (d ₂₂ ) (fresh and unreacted monomers from the devolatilization) and to feed the remaining part to the reactors. In the mass process, the graft base (d-i ) initially dissolved in the monomer mixture will phase separate, forming discrete rubber particles as polymerization of monomers (d ₂ i ) and (d ₂ 2) proceeds. This process is referred to as phase inversion since the continuous phase shifts from rubber to graft rubber copolymers D during the course of polymeriza- tion. Special reactor designs are used to control the phase inversion portion of the reaction. By controlling the shear rate in the reactor, the rubber particle size can be modified to optimize properties. Grafting of some of the copolymerized monomers (d ₂ i ) and (d ₂ 2) onto the rubber particles occurs. The reaction recipe can include polymerization initiators, chain-transfer agents, and other additives. Diluents are sometimes used to reduce the viscosity of the monomer and polymer mixture to facilitate processing at high conversion. The reaction is preferably carried out as a free radical-solution polymerization. The product from the reactor system is usually devolatilized to remove the unreacted monomers and is then pelletized. Equipment used for devolatilization includes single- and twin-screw extruders and flash and thin film/strand evaporators. Unreacted monomers can be recovered and recycled back to the reactors to improve the process yield.

The suspension polymerization process utilizes a mass reaction to produce a partially converted mixture of polymer and monomer and then employs a batch suspension pro- cess to complete the polymerization. When the conversion of the monomers is approximately 15 to 30% complete, the mixture of polymer and unreacted monomers is suspended in water with the introduction of a suspending agent. The reaction is continued until a high degree of monomer conversion is attained and then unreacted monomers are usually stripped from the product before the slurry is centrifuged and dried, produc- ing product in the form of small beads. The morphology and properties of the mass suspension product are similar to those of the mass-polymerized product. The suspension process retains some of the process advantages of the water-based emulsion process, such as lower viscosity in the reactor and good heat removal capability. In case that the graft rubber copolymer D is obtained by free-radical solution polymerization at least one solvent is used such as methylethyl ketone, acetone, toluene and/or ethyl benzene. Preferably the particles of the graft rubber copolymer D have a weight average particle size D _w in the range of 0.55 to 1.50 μιτι, preferably 0.60 to 1 .00 pm.

Component E

Component E is at least one - preferably one - inorganic additive E selected from phyl- losilicates (E1 ) and nano calcium carbonate (E2).

If component E1 is present, it is preferably used in an amount of from 0.01 to 5 pbw, more preferred 0.05 to 3 pbw, based on 100 parts by weight of the molding composi- tion consisting of components A to D.

If component E2 is present, it is preferably used in an amount of from 0.01 to 5 pbw, more preferred 0.05 to 5 pbw, based on 100 parts by weight of the molding composition consisting of components A to D.

Component E1 is a phyllosilicate. Suitable phyllosilicates are described, by way of example, in Hollemann Wiberg, Lehrbuch der anorganischen Chemie, Walter de Gruyter, Berlin, N.Y. 1985, pp. 771 -776.

Use is preferably made of serpentine types, such as chrytosile or antigorite, kaolinite types, such as dickite, nacrite, or halloysite, pyrophyllite, micaceous silicates from the vermiculite group, illite group, or montmorillonite/beidellite group, such as montmorillo- nite, or else mica, or an aluminosilicate, such as muskovite, phlogopite, or biotite. Very particular preference is given to mica. For the purposes of the present invention, kaolinite types include kaolin, the main mineral of which is kaolinite, and mica-like silicates include bentonite, the main mineral of which is montmorillonite.

According to the invention nano calcium carbonate (E2) means nano-particles of calcium carbonate (NPCC) with a mean size of less than 100 nm, in particular a mean size of 15 to 60 nm, most preferred a mean particle size of about 40 nm. The morphology of the nano-particle can be of different shape such as cubic, spindle, rod or flake, a cubic shape being preferred.

Suitable nano calcium carbonates can be obtained by High Gravity Controlled Precipitation (HGCP) technology and are commercially available from NanoMaterials Technology ^® . Component F

Use may be made of other additives (different from component E) and/or processing aids as component F.

Examples of substances of this type are lubricants, mold-release agents, waxes, pig- ments, dyes, flame retardants, antioxidants, stabilizers to counter the effect of light, fibrous or pulverulent fillers, fibrous or pulverulent reinforcing agents, and antistatic agents, and also other additives, and mixtures of these.

Examples of suitable lubricants and mold-release agents are stearic acids, stearyl al- cohol, stearic esters, stearamides, and also silicone oils, montan waxes, and those based on polyethylene or polypropylene. Said lubricants and mold release agents are generally used in amounts up to 3 parts by weight, preferably up to 2 parts by weight, based on 100 parts by weight of the molding composition consisting of components A to D.

Examples of pigments are titanium dioxide, phthalocyanines, ultramarine blue, iron oxides, and carbon black, and the entire class of organic and inorganic pigments. For the purposes of the present invention, dyes are any of the dyes which can be used for the transparent, semitransparent, or non-transparent coloring of polymers, in partic- ular those dyes which are suitable for coloring styrene copolymers. Dyes of this type are known to the skilled worker. Said pigments and dyes are generally used in amounts up to 20 pbw, preferably up to 10 pbw, based on 100 parts by weight of the molding composition consisting of components A) to D). Examples of suitable flame retardants are antimony oxides, such as Sb ₂ 0 ₃ , and/or hal- ogenated organic compounds.

Particularly suitable antioxidants are sterically hindered mononuclear or polynuclear phenolic antioxidants, which may have various substituents and may also have bridg- ing by substituents. These include both monomeric and oligomeric compounds, which may have been built up from two or more phenolic building blocks. It is also possible to use hydroquinones or hydroquinone analogs, or substituted compounds, or else antioxidants based on tocopherols or on derivatives of these. It is also possible to use mixtures of various antioxidants. Usually said antioxidants are used in amounts up to 1 pbw, based on 00 parts by weight of the molding composition consisting of components A to D. In principle, use may be made of any compounds which are commercially available or are suitable for styrene copolymers.

Together with the phenolic antioxidants mentioned above by way of example, concomi- tant use may be made of what are known as costabilizers, in particular phosphorus- or sulfur-containing costabilizers. These P- or S-containing costabilizers are known to the skilled worker and are available commercially.

Examples for suitable antioxidants are:

Esters of 3,5-di-tert.-butyl-4-hydroxyphenylacetic acid with monohydric or polyhydric alcohols, such as for example and preferably decanol, undecanol, dodecanol, tride- canol, tetradecanol, pentadecanol, hexadecanol, octadecanol, 1 ,6-hexanediol, neopen- tyl glycol, 1 ,9-nonanediol, ethylene glycol, diethylene glycol, triethylene glycol, pentae- rythritol, 3-thiaundecanol, 3-thiapentadecanol, trimethylol propane;

Esters of -(3,5-di-tert.-butyl-4-hydroxyphenyl)-propionic acid with the afore-mentioned monohydric or polyhydric alcohols; and

Esters of p-(5-tert.-butyl-4-hydroxy-3-methylphenyl)-propionic acid with monohydric or polyhydric alcohols, with the afore-mentioned monohydric or polyhydric alcohols;

Esters of -(3,5-dicyclohexyl-4-hydroxyphenyl)-propionic acid with the afore-mentioned monohydric or polyhydric alcohols.

Preferred antioxidants are 3,3'-thiodipropionic acid dioctadecylester (CAS-No. 693-36- 7), octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate (CAS-No. 2082-79-3) and the butylated reaction product of p-cresol and dicyclopentadiene (CAS-No. 68610-51- 5).

Examples of suitable stabilizers to counter the effect of light are various substituted resorcinols, salicylates, benzotriazoles, benzophenones, and HALS (hindered amine light stabilizers), for example those commercially available as Tinuvin.

Preferred are Tinuvin 770 DF 1 , bis(2,2,6,6,-tetramethyl-4-piperidyl)sebaceate (CAS- No. 52829-07-9), Tinuvin P, 2-(2H-benzotriazol-2-yl)-p-cresol (CAS-No. 2440-22-4), Cyasorb UV 3853, 2,2,6,6-tetramethyl-4-piperidinyl stearate (CAS-No. 167078-06-0), Hostavin N 845 (CAS-No. 86403-32-9) and mixtures thereof.

Said stabilizers are generally used in amounts up to 2 pbw, based on 100 parts by weight of the molding composition consisting of components A to D. Examples of fibrous or pulverulent fillers are carbon fibers and glass fibers in the form of glass wovens, glass mats, or glass silk rovings, chopped glass, glass beads, and also wollastonite, particularly preferably glass fibers. When glass fibers are used, these may have been provided with a size and with a coupling agent to improve compatibility with the components of the blend. The glass fibers incorporated may either be in the form of short glass fibers or else in the form of continuous strands (rovings). Said filler materials usually are used in amounts up to 20 pbw, preferably up to 10 pbw, based on 100 parts by weight of the molding composition consisting of components A) to D). If not in particular mentioned, the amounts used of each of the additives are those which are usual, and it is therefore unnecessary to give further details in this connection.

Preparation of the Molding Compositions

The preparation of the thermoplastic molding compositions follows conventional proce- dures which are well known in the art.

Preferably, the components A to D and optional components E and F are extrusion blended or compounded in conventional mixing apparatuses (preferably in multi- cylinder mills, mixing extruders or internal kneaders). Preferably components A, B,C, D and, optionally, components E and F are mixed and compounded and extruded at ele- vated temperature, generally at temperatures of from 150°C to 300°C. During the production, working up, further processing and final shaping, the optional additives E and/or F can be added to the thermoplastic molding composition. The final shaping can be carried out on commercially available processing machines, and comprises, for example, injection-molding processing, sheet extrusion with optionally subsequent hot forming, cold forming, extrusion of tubes and profiles and calender processing.

A further aspect of the invention is a shaped article made from the thermoplastic molding composition. The thermoplastic molding composition can be formed into shaped articles by a variety of means such as injection molding, extrusion, compression form- ing, vacuum forming, blow molding etc. well established in the art. Preferred shaped articles are sheets formed by extrusion or layered sheets formed by sheet layer extrusion (co-extrusion). Said sheets can be used for thermoforming and can consist solely of the thermoplastic molding composition as described above or can have a layer structure where at least one cap-layer consists of said molding composition. A further aspect of the invention is the use of shaped articles, in particular ther- moformed sheets, made from the thermoplastic molding compositions as described above for equipment liners (inliners) of cooling -apparatuses, e.g. refrigerators.

The thermoplastic molding compositions as described above exhibit an improved envi- ronmental stress crack resistance (ESCR) in presence of aggressive olefinic unsaturated blowing agents, in particular in presence of hydrofluoro olefins (HFO) and are suitable to manufacture thermoformed equipment liners of cooling apparatuses containing insulation foamed with "Fourth Generation" blowing agents or mixtures containing them.

The examples and claims below give further illustration of the invention. Examples

Graft Rubber Copolymer A Preparation of the Graft Base ayi

The particulate cross-linked fine-particle rubber base used for the preparation of component A (emulsion graft rubber copolymer) was prepared by radical emulsion polymerization of butadiene and styrene (monomer weight ratio 90/10) in the presence of distilled tallow fatty acid (CAS-No. 67701 -06-8, C14-C 8-saturated and C15-C18- unsaturated straight chain aliphatic monocarboxylic acid), tert-dodecylmercaptan as chain transfer agent, potassium persulfate as initiator at temperatures from 60° to 85°C. As salt tetrasodium pyrophosphate is used.

The addition of initiator marked the beginning of the polymerization. Finally the fine- particle butadiene rubber latexes are 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. The starting styrene/butadiene-rubber (SBR) rubber base so obtained has solid content of 41 wt.-%, a rubber gel content of 93 % (wire cage method in toluene), a rubber composition comprising units derived from styrene and butadiene in a weight ratio of 10/90 and a weight-average particle size of 0.08 μητι (determined via Differential Centrifuga- tion using a disc centrifuge from CPS Instruments). The starting SBR was subjected to particle size enlargement with acetic anhydride in two batches to a weight-average particle size D _w of 0.25 Mm and 0.55 pm, respectively.

In order to achieve agglomerated butadiene rubber latices with D _w of 0.25 pm, the fine- particle butadiene rubber latexes are being provided first at 25°C and are adjusted if necessary with deionized water to a concentration of 36 wt.-% and stirred. The temperature was raised to 40°C. To this dispersion, 1.3 weight parts of acetic anhydride based on 100 parts of the solids from the fine-particle butadiene rubber latex as aqueous mixture is added and mixed with the latex. After this the agglomeration is carried out for 10 minutes without stirring. Anionic dispersant of sulfonic polyelectrolyte type (Sodium naphthalene sulfonate formaldehyde condensates, CAS 9084-06-04) are added as aqueous solution to the agglomerated latex and mixed by stirring. Subsequently KOH are added as aqueous solution to the agglomerated latex and mixed by stirring. The solid content of the agglomerated butadiene rubber latex with D _w of 0.25 pm is 28.5 wt.-%.

In order to achieve agglomerated butadiene rubber latices with D _w of 0.55 pm, the fine- particle butadiene rubber latices are being provided first at 25°C and are adjusted if necessary with deionized water to a concentration of 33 wt.% and stirred.

To this dispersion, 2 weight parts of acetic anhydride based on 100 parts of the solids from the fine-particle butadiene rubber latex as aqueous mixture is added and mixed with the latex. After this the agglomeration is carried out for 30 minutes without stirring. Anionic dispersant of sulfonic polyelectrolyte type (Sodium naphthalene sulfonate for- maldehyde condensates, CAS 9084-06-04) are added as aqueous solution to the agglomerated latex and mixed by stirring. Subsequently KOH are added as aqueous solution to the agglomerated latex and mixed by stirring. The solid content of the agglomerated butadiene rubber latex with D _w of 0.55 pm is 24.7 wt.-%. The two latexes with 0.25 pm (80 pts.) and 0.55 pm (20 pts.) were combined to rubber base a1 which is used in the further reaction step in the form of polymer latexes which have a solids content of 26 wt.-%.

Preparation of the Graft Rubber Copolymer A: The graft copolymer A is prepared (as parts by weight) from 52 styrene/butadiene- rubber (SBR), 34 styrene, 14 acrylonitrile, together with cumene hydroperoxide, dextrose, ferrous sulfate, t-dodecylmercaptane, disproportionated potassium rosinate soap, and emulsion graft polymerization was conducted.

Firstly, the afore-mentioned SBR latex was charged, and the temperature was raised to 70°C. Styrene, acrylonitrile, t-dodecylmercaptane, disproportionated potassium rosinate soap and deionized water were added. At 70°C, the catalyst solution (sodium pyrophosphate, dextrose, cumene hydroperoxide and ferrous sulfate dissolved in water) was added. After completion of the addition, the stirring was continued for further 30 minutes, and then the mixture was cooled. To the graft copolymer latex thus obtained, an aging-preventive agent (e.g. Antioxidant PL / Wingstay L, Phenol, 4- methyl-, reaction products with dicyclopentadiene and isobutene, CAS-No. 68610-51 -5) was added, and the mixture was added under stirring to an aqueous magnesium sul- fate solution heated to 95°C, for coagulation. The coagulated product was washed with water and dried to obtain a high rubber content resin composition in the form of a white powder.

Matrix Copolymer B Statistical SAN-copolymer B1 was produced by suspension polymerization from 72 wt.- % styrene and 28 wt.-% acrylonitrile with a weight average molar mass of 230,000 kg/mol (determined by gel permeation chromatography and using polystyrene for calibration) and MVR of 3.5 cm ³ /1 Omin (220°C/10 kg load (ISO 1133-1 :201 1 )).

Statistical SAN-copolymer B2 was produced by suspension polymerization from 66 wt.- % styrene and 34 wt.-% acrylonitrile with a weight average molar mass of 89,000 kg/mol (determined by gel permeation chromatography and using polystyrene for calibration) and MVR of 75 cm ³ /10min (220X/10 kg load (ISO 1 133-1 :201 1 )).

Statistical SAN-copolymer B3 was produced by suspension polymerization from 66 wt- % styrene and 34 wt.-% acrylonitrile with a weight average molar mass of 180,000 kg/mol (determined by gel permeation chromatography and using polystyrene for calibration) and MVR of 3 cm ³ /10min (220°C/10 kg load (ISO 1 133-1 :201 1 )). Statistical SAN-copolymer B4 was produced by mass polymerization from 69 wt.-% styrene and 31 wt.-% acrylonitrile with a weight average molar mass of 140,000 kg/mol (determined by gel permeation chromatography and using polystyrene for calibration) and MVR of 19 cm ³ /10min (220°C/10 kg load (ISO 1 133-1 :201 1 )). Statistical SAN- copolymer B5 was produced by suspension polymerization from 69 wt.-% styrene and 31 wt.-% acrylonitrile with a weight average molar mass of 200,000 kg/mol (determined by gel permeation chromatography and using polystyrene for calibration) and MVR of 4 cm ³ /10min (220°C/10 kg load (ISO 1 133-1 :201 1 )).

Component C (SBC)

a linear styrene-butadiene triblock copolymer of the structure S-(S/B)-S with a weight average molecular weight (M _w ) of 130 kDalton (GPC, calibrated with monodisperse polystyrene standards) comprising 20 TDalton polystyrene blocks on the outside and statistical S/B block (90 TDalton) on the inside, the amount of the monomers in the total block copolymer is 33% by weight of butadiene and 67% by weight of styrene; the weight ratio of the blocks is 16/68/16; MVR: 13 (200°C/5 kg) cm ³ /10 min. Component C was produced by anionic polymerization in cyclohexane initiated by s-buthyl lithium. The statistical S/B block is obtained by simultaneously addition of both monomers in the presence of K/Li = 1/37 (molar ratio).

Graft Rubber Copolymer D (mABS):

Continuous mass ABS copolymer D was produced by free-radical solution polymerization from 17% butadiene, 63% styrene, 20% acrylonitrile by weight in the presence of methylethyl ketone with a gel content of 30% (acetone method), a weight average par- tide size of the grafted rubber of 0.6 to 1 pm (determined via Differential Centrifugation using a disc centrifuge from CPS Instruments) and a MVR of 5.5 cm ³ /10 min (ISO 1 133-1 :201 1 ).

The gel content was determined in acetone or toluene as dispersant. Approximately, 0.25 g of the polymer composition were dispersed in 20 g of dispersant for 12-24 h and separated with an ultracentrifuge at 20,000 rpm at 25°C into the gel and sol phase. The separated phases were dried and the gel content is calculated by the following formula: gel = mass(gel phase) / (mass(gel phase) + mass(sol phase))*100 [%]

Preparation of the Thermoplastic Molding Compositions:

In the following examples and comparative examples, the afore-mentioned copolymers A, B, C and D and the following components F were used in the amounts as given in Table 1. The additives and processing aids (component F) were added to 100 parts by weight (pbw.) of the polymer components as listed in Table 1 (left column).

F1 : Ethylene bis stearamide, CAS-No.110-30-5

F2: Silicone oil, 60,000 cSt, polydimethylsiloxane, CAS-No. 63148-62-9

F3: Thiosynergic heat stabilizer, 3,3'-thiodipropionic acid dioctadecylester, CAS-No. 693-36-7

F4: Phenolic primary antioxidant, octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)- propionate, CAS-No. 2082-79-3

F5: Titanium dioxide, CAS-No. 13463-67-7

The components A, B, C and D according to Table 1 and the afore-mentioned additives and processing aids F were compounded under the following conditions: Extruder Machine L/D: 30, diameter: 40mm, co-rotating twin screw, manufacture: KraussMaffei Berstorff, Germany, die head and melt temp: 250°C, throughput: 50-60 kg/h. The thermoplastic compositions were tested using the following methods:

Notched Charpy impact strength [kJ/m ² ]:

The notched Charpy impact strength is measured on test specimen (80 x 10 x 4 mm, injection molded at a mass temperature of 240°C and a mold temperature of 70°C), at 23°C according to ISO 179-1 A.

Notched Izod impact strength [kJ/m ² ]:

The notched Izod impact strength [kJ/m ² ] is measured on test specimen (80 x 10 x 4 mm, injection molded at a mass temperature of 240°C and a mold temperature of 70°C), at 23°C according to ISO 180-1 A. Melt volume index (MVR [ml/10 min]):

The melt volume rate MVR is measured on a polymer melt at 220°C and 10 kg load according to ISO 1 133.

Tensile strain at break [%]:

The tensile strain at break [%] is measured on Dumbbell test specimen 170 x 10 x 4 mm (injection molded at a mass temperature of 240°C and a mold temperature of 70°C) at 23°C according to DIN EN ISO 527.

Gloss measurement: The surface gloss is measured on injection molded plaques (60 mm x 40 mm x 2 mm, injection molded at a mass temperature of 240°C and a mold temperature of 70°C) according to DIN 67530 at a reflection angle of 60°.

ESCR method: After compounding, the obtained thermoplastic compositions were injection molded into test bars with the dimension 80x10x4mm ³ under following conditions: Clamping force: 120 MT, manufacturer: Dongshing, Korea, injection temperature: 240°C, Injection speed: 60%, cycle time: 45 sec, mold temp: 60°C. The molded bars were tested in regard to their chemical resistance according to the following environmental stress crack resistance (ESCR) test:

Injection molded test bars (80x10x4mm ³ ) are mounted on a jig which maintains constant curvature at 2.5 % outer fiber strain. The jig with the test pieces is placed into a jar filled with the chemical agent in a way that the test bars are completely covered.

During the experiment, the proceeding degradation is monitored and reviewed in de- pendence of time. After allowing the test pieces to stand in the prescribed environmental conditions for a specific period of time (in normal case 300 min or till complete crack) and removing them from the jig, the condition of physical degradation is checked.

The determination of chemical resistance was done optically in dependence of the fol- lowing criteria: complete crack, partial crack, surface crack, edge crack, and surface quality after aging. A summary (see Table 2) is then given by the following symbols:

X: degraded A : highly affected ▲ ▲: affected ▲ ▲ A : a little affected

▲ A A : not affected (A ): 0.5 A

To better compare different materials also a ranking (see Table 2) is given (1 = material with highest chemical resistance of all tested materials, 2 = material with second highest chemical resistance of all tested materials, etc.).

Common chemicals for testing like cyclopentane were applied at room temperature. In case of trans-1-chloro-3,3,3-trifluoropropene (b.p. 19°C) the tests were done at 0°C to prevent evaporation of the agent while maintaining constant test conditions.

In the tables "Cp." means "comparative example" 1 , 2 etc. Table 1 shows the components of the Thermoplastic compositions.

Table 2 shows that the best ESCR test results are obtained with the thermoplastic molding compositions according to inventive example 1. The chemical resistance of the inventive thermoplastic composition against both against trans-1-chloro-3,3,3- trifluoropropene and cyclopentante according to example 1 is extremely good. This is important since manufacturers use mixtures of blowing agents for their applications in most cases.

Additionally, inventive example 1 shows the favorable properties known for ABS mate- rials; good processability (MVR, elongation at break), toughness (impact strength) and appearance (gloss).

Table 1 : Thermoplastic compositions

Table 2: ESCR results and mechanical data