Thermoplastic molding composition from ABS-polymers and SBS-polymers

Description

The invention relates to a thermoplastic molding composition comprising an acrylonitril- butadiene-styrene polymer (ABS) and a styrene-butadiene-styrene polymer (SBS) and to a process for the preparation of such molding compositions. The present invention furthermore relates to the use of the SBS-block copolymers for the preparation of such molding materials. The present invention also relates to the use of the molding materi- als for the production of shaped articles, films or fibers. The invention also relates to shaped articles, films or fibers themselves and in particular to refrigerator parts which can be obtained using the molding materials.

Molding compositions which contain butadiene- or acrylate-based graft copolymers and styrene/butadiene block copolymers are known for years, e.g. from WO 2000/36010.

These molding materials are suitable for the production of soft films which are used in the interior of automobiles. These films have a good ratio of flowability to thermoform- ing properties and they are readily thermoformable. A good thermo-formability of a thermoplastic material means that, when pressure is exerted on a point of a film at moderately elevated temperatures, said film exhibits substantially uniform flow at all points. One of the results of a good thermo-formability is that the polymer film does not become thin at certain points and forms holes or breaks.

From WO 2000/58380 and WO 2003/1 1964 it is known that styrene block copolymers as a blend with styrene polymers such as general-purpose polystyrene or high-impact polystyrene (HIPS) can form molding materials which can be processed to shaped articles which are particularly resistant to impact and stress cracking. These shaped articles are suitable for the production of e. g. refrigerators.

DE 44 20 952 discloses a blend of SBS copolymers with a styrene-acrylonitrile-matrix (SAN) mixed in an extruder in order to yield highly tough blends. From EP-A 0 767 213 thermoplastic compositions based on SAN and ASA (acrylonitrile-styrene-acrylonitrile) are known. In EP-A 0 800 554 further compositions containing transparent, elastic copolymers based on styrene and butadiene (e. g. Styroflex of BASF, Ludwigshafen) are disclosed.

It is known from WO 2005/005536 that SBS block copolymers enhance the properties of ABS materials for e. g. the use as refrigerator inliner. Especially the mechanical stability, toughness and Environmental Stress Cracking Resistance (ESCR) are improved.

However, many blends of ABS and SBS block copolymers are less suited, because of so called organo-leptic properties. SBS polymers have the function of enhancing diffusion of residuals and other low volatile organic compounds through their lamellae-type morphology from the inside of a molded or extruded article to the outside.

Especially for high quality refrigerator inliner materials it is important to have a high stress cracking resistance and an excellent impact resistance. Furthermore they should have a neutral or good odor and a neutral smell.

The compositions according to the present invention show this superior property profile. It is one further object of the present invention to provide molding materials which are based on easily available ABS-graft copolymers and SBS block copolymers, which have impact resistance and stress cracking resistance and furthermore are resistant to chemical blowing agents. In particular, the molding materials should have a therrmo- formability of ± 150 % or less, determined on the basis of the wall thickness variation of a standard cup at 120 ⁰ C.

The molding materials according to the invention should moreover have good melt stability. In the context of this invention melt stability is understood as meaning the stress which a melt is capable of withstanding after it has been discharged from a nozzle by means of compressed air and is suspended between nozzle and chill roll. A melt having a high stability exhibits little sag. In particular, it is one of the objects of the present invention that the molding materials should be capable of being processed by means of blow molding to films, in particular large-area films, without the melt sagging during film production.

These objects of the invention are achieved by the molding materials defined below.

According to the invention, the technical problems are solved by a thermoplastic mold- ing compositions comprising the following components:

1.1 75-99 % of a copolymer A consisting of:

1.1 .1 70-76 % of vinylaromatic monomer(s) A1 , e.g. styrene;

1.1.2 24-30 % of vinyl cyanide monomer component(s) A2; e.g. acryloni- trile;

1.1.3 0-50 % of one or more unsaturated copolymerizable monomers A3, e.g. alpha-methyl-styrene or methyl-methacrylate;

1.2 0-60 % of a graft rubber B consisting of: 1.2.1 10-95 % of a graft rubber core B1 containing

1.2.1.1 80-100 % of rubber type monomers, such as or preferably from the group: butadiene, isoprene, butyl acrylate, silicons B1 1 ;

1.2.1.2 0-20 % of double unsaturated monomers, such as or preferably from the group: divinylbenzene, al- lyl(meth)acrylate, multi functional silicons B12; 1.2.2 5-90 % of a graft shell B2 containing

1.2.2.1 75-85 % of vinylaromatic monomer(s) B21 , e.g. styrene;

1.2.2.2 15-25 % of vinyl cyanide monomer component(s) B22, e.g. acrylonitrile;

1.2.2.3 0-50 % of one or more unsaturated copolymerizable monomers B23

1.3 1 -10 % of a thermoplastic SBS block copolymer C, which has at least 2 glass transition temperatures of 70 to 100 ⁰ C and of -60 to 0 ⁰ C, consisting of:

1.3.1 30-70 % vinylaromatic monomer(s) C1 , e.g. styrene;

1.3.2 30-70 % of one or more unsaturated copolymerizable monomers C2, e.g. butadiene or isoprene.

In a preferred embodiment of the invention, the thermoplastic molding composition contains

1.3 1 -10% of a thermoplastic SBS block copolymer C, which has at least 2 glass transition temperatures of 70 to 100 ⁰ C and of -60 to 0 ⁰ C, consisting of:

1.3.1 30-70% vinylaromatic monomer(s) C1 , e.g. styrene;

1.3.2 15-70% of one or more unsaturated copolymerizable monomers C2, e.g. butadiene or isoprene.

A further aspect of the invention deals with a thermoplastic molding composition, in which the components A1 , B21 and C1 are styrene, the components A2 and B22 are acrylonitrile, and the components B11 and C2 are butadiene and/or isoprene.

In the thermoplastic molding composition according to the invention, the copolymer A is e.g. consisting of:

70-76 % of vinylaromatic monomer(s) A1 24-30 % of vinyl cyanide monomer component(s) A2 and 0-20 % of one or more unsaturated copolymerizable monomers A3.

Preferably, the copolymer A is consisting of:

70-76 % of styrene 24-30 % of acrylonitrile and 0-10 % of alpha-methyl-styrene and/or methyl-methacrylate.

In a particular embodiment of the invention, the thermoplastic molding composition contains a graft rubber B (preferably in an amount from 1 to 30 % by weight) consisting of:

10-95 % of a graft rubber core B1 containing:

80-100 % of the rubber type monomers from the group butadiene, isoprene, butyl acrylate and silicons B11 ;

0-20 % of the double unsaturated monomers from the group divinylbenzene, allyl(meth)acrylate and multi functional silicons B12; and

5-90 % of a graft shell B2 containing:

75-85 % of vinylaromatic monomers from the group styrene and alpha-methyl-styrene B21 ;

15-25 % of acrylonitril B22; 0-20 % of unsaturated copolymerizable monomers B23.

The graft rubber B preferably is consisting of:

10-95 % of a graft rubber core B1 containing:

80-100 % of butadiene, isoprene and/or butyl acrylate; 0-20 % of divinylbenzene and/or allyl(meth)acrylate; 5-90 % of a graft shell B2 containing: 75-85 % of styrene and/or alpha-methyl-styrene;

15-25 % of acrylonitrile;

0-20 % of unsaturated copolymerizable monomers from the group butyl acrylate, ethyl-acrylate and methyl(meth)acryl-amide.

The thermoplastic molding composition according to the invention preferably contains 1 to 5 % by weight of at least one thermoplastic SBS block copolymer C,

wherein the SBS block polymer C has at least two glass transition temperatures from 70 to 100 ⁰ C and from -60 to 0 ⁰ C.

A further aspect are molding compositions comprising 90 to 99 % by weight of copolymer A and 1 to 10 % by weight of a thermoplastic SBS block copolymere, preferably prepared from styrene and butadien.

A further aspect of the invention deals with a process for the preparation of a thermoplastic molding composition as described above in which the copolymer A and the thermoplastic SBS block copolymer C as well as eventually the graft rubber B and other components and additives are mixed.

The invention also relates to the use of a thermoplastic molding composition for the preparation of fibers, folios and moldings, in particular for the preparation of inliners for refrigerators.

The invention also relates to moldings, fibers and folios comprising a thermoplastic molding composition as described above.

The copolymer matrix A is for example prepared from the components acrylonitrile and styrene and/or an α-methylstyrene via bulk polymerization or in the presence of one or more solvents. Preference is given here to copolymers A whose molar masses M _w are from 50 000 to 300 000 g/mol, the molar masses being capable of determination by way of example via light scattering in tetrahydrofuran (GPC with UV detection).

The copolymer matrix A can in particular comprise:

(Aa) polystyrene-acrylonitrile, prepared from styrene and acrylonitrile, or

(Ab) poly-α-methylstyrene-acrylonitrile, prepared from α-methylstyrene and acrylonitrile, or

(Ac) a mixture of copolymer matrix (Aa) and of copolymer matrix (Ab).

The copolymer matrix A can also be obtained via copolymerization of acrylonitrile, styrene, and α-methylstyrene.

The viscosity (Vz) of the copolymeric matrix A amounts by way of example to from 50 to 120 ml/g (measured to DIN 53726 at 25 ⁰ C in a 0.5 % strength by weight solution in DMF). The copolymer matrix A can be prepared e. g. via bulk polymerization or solution polymerization in, for example, toluene or ethylbenzene, by a process as described by way of example in Kunststoff-Handbuch [Plastics Handbook], Vieweg-Daumiller, volume V, (Polystyrol) [Polystyrene], Carl-Hanser-Verlag, Munich 1969, pages 122 et seq., lines 12 et seq.

The graft copolymer component B can be used but must not necessarily be used as a component in the composition. It can have a complex structure and is in essence composed of from 10 to 95 % by weight, based on B, of a graft base (B1 ) and of from 5 to 90 % by weight of a graft shell (B2), the % by weight data always being based on the total weight of component B.

The graft base (B1 ) can by way of example be obtained via reaction of from 0 to 20 % by weight of divinylbenzene and from 80 to 100 % by weight of butadiene, isoprene or butylacrylate and also from 0 to 5 % by weight of ancillary components, the % by weight data being based on the graft base (B 1 ).

The graft shell (B2) can for example be obtained via reaction of from 75 to 85 % by weight of styrene and from 15 to 25 % by weight of acrylonitrile, and also from 0 to 5 % by weight of ancillary components (% by weight, based on the graft shell B2), in the presence of the graft base (B1 ).

The molding composition can also comprise two or more different graft polymers.

For preparation of the graft polymer B it is preferable to use a polymerization initiator, for example a redox initiator system comprising an organic peroxide, and at least one reducing agent.

The organic peroxide used preferably comprises a compound selected from the group of di-tert-butyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and p-menthane hydroperoxide, and mixtures thereof. The reducing agent used generally comprises at least one water-soluble compound with reducing action (e.g. a sugar).

It is preferable that an emulsion polymerization is carried out for the preparation of the graft polymer B.

It is preferable that an emulsion polymerization is carried out for preparation of the graft base (B1 ) and that e.g. potassium peroxodisulfate is used as initiator.

As mentioned above, the copolymer A is preferably composed of the monomers styrene and acrylonitrile, of the monomers α-methylstyrene and acrylonitrile, or of the monomers styrene, α-methylstyrene, and acrylonitrile. However, in principle it is also possible to use polymer matrices which comprise further unsaturated monomer units.

In a further embodiment of the invention, a further copolymerizable, polyfunctional, agglomerating component used for preparation of the graft base (B1 ). For changing the

particle size distribution of the graft base, at least one copolymer composed of C1-C12- alkyl acrylates or of Ci-Ci ₂ -methalkyl acrylates and of polar comonomers from the group of acrylamide, methylacrylamide, ethylacrylamide, n-butylacrylamide, or maleia- mide can be used.

Examples of suitable preparation processes for the graft copolymers B are emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization. In WO-A 2002/10222, DE-A 28 26 925, and in EP-A 022 200 suitable polymerization processes are described.

By way of example, the graft base (B1 ) can be prepared via free-radical-initiated aqueous emulsion polymerization, by using a portion of the monomers in an aqueous reaction medium as initial charge and adding the remaining residual amount of monomers, if appropriate, in the aqueous reaction medium after initiation of the free-radical poly- merization reaction. It is also possible to use at least a portion of the free-radical polymerization initiator and, if appropriate, of further auxiliaries in the aqueous reaction medium as initial charge, to bring the resultant aqueous reaction medium to polymerization temperature, and at this temperature to add the monomers to the aqueous reaction medium. This introduction can also take the form of a mixture, for example the form of an aqueous monomer emulsion.

The reaction is initiated via water-soluble or oil-soluble free-radical polymerization initiators, e.g. inorganic or organic peroxides (for example peroxodisulfate or benzoyl peroxide), or with the aid of redox initiator systems. It is preferable that peroxodisulfate is used as initiator in preparation of the graft base (B1 ). The amount of free-radical initiator used, based on the entire amount of monomer, is generally from 0.01 to 5 % by weight, preferably from 0.1 to 3 % by weight.

The thermoplastic molding composition according to the present invention always com- prises as one component a low amount of at least one SBS-block copolymer (C). As a low amount, for example 1 to 10 %, preferably 1 to 5 % by weight, e.g. 3 %, can be used.

A linear or star block copolymer can be used as component (C). However, as compo- nent (C) two or more different block copolymers may also be suitable. The block copolymers which can be used as component (C) in accordance with the invention preferably comprise at least two hard blocks S1 and S2 of vinylaromatic monomers and at least one, random soft block B/S present in between and comprising vinylaromatic monomers and dienes, the amount of the hard blocks being more than 30, preferably more than 40, % by weight, based on the total block copolymer (C). In preferred block copolymers (C), the 1 ,2-vinyl content in the soft block B/S is less than 20 %.

The vinyl content is understood as meaning the relative proportion of 1 ,2-linkages of the diene units, based on the sum of the 1 ,2-, 1 ,4-cis and 1 ,4-trans linkages. The 1 ,2- vinyl content of the soft blocks is preferably up to 20 %, especially 10 - 20 %, in particu- lar 12 - 16 %.

Styrene, α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene or mixtures thereof can be used as vinylaromatic monomers both for the hard blocks S1 and S2 and for the soft blocks B/S. Styrene is preferably used.

Butadiene, isoprene, 2,3-dimethylbutadiene, 1 ,3-pentadiene, 1 ,3-hexadienes or pipery- lene or mixtures thereof are preferably used as dienes for the soft block B/S. 1 ,3- Butadiene is particularly preferably used.

The block copolymer (C) preferably consists exclusively of hard blocks S1 and S2 and at least one random soft block B/S and contains no homopolydiene blocks B. Preferred block copolymers contain external hard blocks S1 and S2 having different block lengths. The molecular weight of S1 is preferably from 5 000 to 30 000, in particular from 10 000 to 20 000, g/mol. The molecular weight of S2 is preferably more than 35 000 g/mol. Preferred molecular weights of S2 are from 50 000 to 150 000 g/mol.

A plurality of random soft blocks B/S may also be present between the hard blocks S1 and S2. Preferably, at least 2 random soft blocks (B/S)1 and (B/S)2 comprising different amounts of vinylaromatic monomers and therefore having different glass transition temperatures are preferred.

The block copolymers (C) may have a linear or a star structure. A structure S1-(B/S)1 - (B/S)2-S2 is preferably used as the linear block copolymer. The molar ratio of vinylaromatic monomer to diene S/B is preferably less than 0.25 in the block (B/S)1 and preferably from 0.5 to 2 in the block (B/S)2.

Preferred star block copolymers (C) are those having a structure comprising at least one star branch of the block sequence S1 -(B/S) and one star branch of the block sequence S2-(B/S) or those having at least one star branch of the block sequence S1 - (B/S)-S3 and at least one star branch of the block sequence S2-(B/S)-S3. Here, S3 is a further hard block of said vinylaromatic monomers.

Particularly preferred star block copolymers (C) are those having structures which comprise at least one star branch having the block sequence S1 -(B/S)1 -(B/S)2 and at least one star branch having the block sequence S2-(B/S)1-(B/S)2 or which comprise a star branch having the block sequence S1 -(B/S)1-(B/S)2-S3 and at least one star

branch having the block sequence S2-(B/S)1-(B/S)2-S3. The molar ratio of vinylaro- matic monomer to diene S/B is preferably from 0.5 to 2 in the outer block (B/S)1 and preferably less than 0.5 in the inner block (B/S)2. The higher content of vinylaromatic monomers in the outer random block (B/S)1 makes the block copolymer more ductile with unchanged total butadiene content.

The star block copolymers (C) having the additional, inner block S3 have higher rigidity coupled with comparable ductility. The block S3 thus acts as a filler in the soft phase without changing the ratio of hard phase to soft phase. The molecular weight of the blocks S3 is as a rule substantially lower than that of the blocks S1 and S2. The molecular weight of S3 is preferably from 500 to 5 000 g/mol.

According to a particularly preferred embodiment, a linear or star block copolymer (C) comprising external polystyrene blocks S and, in between, styrene/butadiene copoly- mer blocks having a random styrene/butadiene distribution (S/B) _ran dom and

from 15 to 50 % by weight, based on the total weight of C), of butadiene and from 50 to 85 % by weight, based on the total weight of C), of styrene

is used as component (C).

The block copolymers (C) can be formed, for example, by sequential anionic polymerization, at least the polymerization of the soft blocks (B/S) being effected in the presence of a randomizer. The presence of randomizers results in the random distribution of the dienes and vinylaromatic units in the soft block (B/S). Suitable randomizers are donor solvents, such as ethers, for example tetrahydrofuran, or tertiary amines or soluble potassium salts. For an ideal random distribution, amounts of, as a rule, more than 0.25 percent by volume, based on the solvent, are used in the case of tetrahydrofuran. At low concentrations, tapered blocks having a gradient in the composition of the co- monomers are obtained.

In the case of stated relatively large amounts of tetrahydrofuran, the relative proportion of the 1 , 2-linkages of the diene units simultaneously increases to about 30 to 35 %.

On the other hand, when potassium salts are used, the 1 ,2-vinyl content in the soft block increases only insignificantly. The block copolymers (C) obtained are therefore less suitable to crosslinking and, with the same butadiene content, have a lower glass transition temperature.

The potassium salt is generally used in less than the molar amount, based on the anionic polymerization initiator. A molar ratio of anionic polymerization initiator to potas-

sium salt of, preferably, from 10:1 to 100:1 , particularly preferably from 30:1 to 70:1 , is chosen. The potassium salt used should in general be soluble in the reaction medium. Suitable potassium salts are, for example, potassium alcoholates, in particular a potassium alcoholate of a tertiary alcohol of at least 5 carbon atoms.

Potassium 2,2-dimethyl-1 -propanolate, potassium 2-methylbutanolate (potassium tert- amylate), potassium 2,3-dimethyl-3-pentanolate, potassium2-methylhexanolate, potassium 3,7-dimethyl-3-octanolate (potassium tetrahydrolinaloolate) and potassium 3- ethyl-3-pentanolate are particularly preferably used. The potassium alcoholates are obtainable, for example, by reacting elemental potassium, potassium/sodium alloy or potassium alkylates and the corresponding alcohols in an inert solvent.

Expediently, the potassium salt is added to the reaction mixture only after the addition of the anionic polymerization initiator. In this way, hydrolysis of the potassium salt by traces of protic impurities can be avoided. The potassium salt is particularly preferably added shortly before the polymerization of the random soft block B/S.

The conventional mono-, bi- or polyfunctional alkali metal alkyls, aryls or aralkyls can be used as an ionic polymerization initiator. Organolithium compounds, such as ethyl-, propyl-, isopropyl-, n-butyl-, sec-butyl-, tert-butyl-, phenyl-, diphenylhexyl-, hexame- thyldi-, butadienyl-, isoprenyl- and polystyryllithium, 1 ,4-dilithiobutane, 1 ,4-dilithio-2- butene or 1 ,4-dilithiobenzene, are expediently used. The required amount of polymerization initiator depends on the desired molecular weight. As a rule, it is from 0.001 to 5 mol%, based on the total amount of monomers.

In the preparation of the asymmetric star block copolymers (C), a polymerization initiator is added at least twice. Preferably, the vinylaromatic monomer Sa and the initiator 11 are simultaneously added to the reactor and completely polymerized, followed, once again simultaneously, by vinylaromatic monomer Sb and initiator I2. In this way, two living polymer chains Sa-Sb-H and Sb-I2 are obtained side by side, onto which subsequently the block (B/S)1 is polymerized by joint addition of vinylaromatic monomer and dienes and, if required, the block (B/S)2 is polymerized by further joint addition of vinylaromatic monomer and dienes and also, if required, block S3 is polymerized by further addition of vinylaromatic monomer Sc. The ratio of initiator 11 to initiator I2 determines the relative proportion of the respective star branches which are present randomly distributed in the individual star block copolymers after the coupling. Here, the block S1 is formed from the meterings of the vinylaromatic monomers Sa and Sb, and the blocks S2 and S3 by the metering of Sb or Sc alone. The molar initiator ratio 12/11 is preferably from 4/1 to 1/1 , particularly preferably from 3.5/1 to 1.5/1.

The polymerization can be carried out in the presence of a solvent. Suitable solvents are the aliphatic, cycloaliphatic or aromatic hydrocarbons of 4 to 12 carbon atoms which are customary for anionic polymerization, such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, isooctane, benzene, alkylbenzenes, such as toluene, xylene, ethylbenzene or decalin, or suitable mixtures. Cyclohexane and methylcyclohexane are preferably used.

In the presence of metal organyls, such as magnesium, aluminum or zinc alkyls, which have a retardant effect on the polymerization rate, the polymerization can also be car- ried out in the absence of a solvent.

After the end of the polymerization, the living polymer chain can be blocked by means of a chain terminator. Suitable chain terminators are protic substances or Lewis acids, for example water, alcohols, aliphatic or aromatic carboxylic acids and inorganic acids, such as carbonic acid or boric acid.

Instead of the addition of a chain terminator after the end of the polymerization, the living polymer chains can also be linked in a star-like manner by polyfunctional coupling agents, such as polyfunctional aldehydes, ketones, esters, anhydrides or epoxides. Here, symmetrical and asymmetrical star block copolymers whose arms may have the abovementioned block structures can be obtained by coupling identical or different blocks. Asymmetrical star block copolymers are obtainable, for example, by separate preparation of the individual star branches or by multiple initiation, for example double initiation with division of the initiator in the ratio 2/1 to 10/1.

The further components of the composition:

The invention also provides a thermoplastic molding composition which comprises, as further components (K), one or more components selected from the group of the dis- persing agents (DA), buffer substances (BS), molecular weight regulators (MR), fillers (F), and additives (D).

The molecular weight regulator (MR) used can by way of example comprise tert- dodecyl mercaptan (TDM), which can be added continuously or else at various junc- tures during the process of preparation of the rubber latex. The manner of addition of the regulator can have an effect on the properties of the final product.

For the purposes of the polymerization process described, dispersing agents (DA) are also used, which keep not only the monomer droplets but also the polymer particles formed in the aqueous medium in dispersion and thus ensure that the aqueous polymer dispersion produced is stable. Dispersing agents (DA) that can be used are not

only the protective colloids usually used for conduct of free-radical aqueous emulsion polymerizations but also commercially available emulsifiers.

Examples of suitable protective colloids are polyvinyl alcohols, polyalkylene glycols, alkali metal salts of polyacrylic acids and polymethacrylic acids, and gelatin derivatives. Examples of suitable protective colloids are copolymers, and their alkali metal salts, comprising acrylic acid, methacrylic acid, maleic anhydride, 2-acrylamido-2- methylpropanesulfonic acid, and/or 4-styrenesulfonic acid.

Other suitable protective colloids are homo- and copolymers comprising N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylcarbazole, 1 -vinylimidazole, 2-vinylimidazole, 2-vinylpyridine, 4-vinylpyridine, acrylamide, methacrylamide, amino- group-bearing acrylates, methacrylates, acrylamides, and/or methacrylamides. Houben-Weyl, Methoden der organischen Chemie, [Methods of organic chemistry], volume XIV/1 , Makromolekulare Stoffe, [Macromolecular substances], Georg-Thieme- Verlag, Stuttgart, 1961 , pages 41 1 -420 gives a detailed description of other suitable protective colloids.

It is, of course, also possible to use a mixture composed of protective colloids and/or of emulsifiers. The dispersing agents used often comprise exclusively emulsifiers whose macromolecular weights, unlike those of the protective colloids, are usually below 1000. They can be either anionic, cationic, or non-ionic. If mixtures of surfactants are used, the individual components must, of course, be compatible with one another. Anionic emulsifiers are generally compatible with one another and with non-ionic emulsifi- ers.

The same applies to cationic emulsifiers, while anionic and cationic emulsifiers are mostly not compatible with one another. Houben-Weyl, Methoden der organischen Chemie, [Methods of organic chemistry], volume XIV/1 , Makromolekulare Stoffe, [Mac- romolecular substances], Georg-Thieme-Verlag, Stuttgart, 1961 , pages 192-208 gives an overview of suitable emulsifiers. According to the invention, emulsifiers are in particular used as dispersing agents, examples being anionic, cationic, or non-ionic surfactants. Examples of familiar non-ionic emulsifiers are ethoxylated mono-, di- and trialkyl- phenols and also ethoxylated fatty alcohols. Examples of usual anionic emulsifiers are the alkali metal and ammonium salts of alkyl sulfates (with alkyl radicals of: C8-C12), of sulfuric half-esters of ethoxylated alkanols (alkyl radical: Ci ₂ -Ci ₈ ) and of ethoxylated alkylphenols (alkyl radicals: C ₄ -Ci ₂ ) and of alkylsulfonic acids (alkyl radical: Ci ₂ -Ci ₈ ).

Suitable cationic emulsifiers are generally C ₆ -Ci ₈ -alkyl-bearing or alkylaryl-bearing or heterocyclic-radical-bearing primary, secondary, tertiary or quaternary ammonium salts, pyridinium salts, imidazolinium salts, ozazolinium salts, morpholinium salts, tro-

pylium salts, sulfonium salts and phosphonium salts.

By way of example, mention may be made of dodecylammonium acetate or the corresponding sulfate, disulfates or acetates of the various 2-(N, N, N- trimethylammonium)ethyl paraffinates, N-cetylpyridinium sulfate and N-laurylpyridinium sulfate. The emulsifiers and protective colloids can also be used in the form of mixtures.

The total amount used of the emulsifiers preferably used as dispersing agents is ad- vantageously from 0.005 to 5 % by weight, preferably from 0.01 to 5 % by weight, in particular from 0.1 to 3 % by weight, always based on the total monomer concentration. The total amount used of the protective colloids used as dispersing agents, instead of the emulsifiers or in addition thereto is often from 0.1 to 10 % by weight and frequently from 0.2 to 7 % by weight, always based on the total concentration of monomers. How- ever, the dispersing agents used preferably comprise anionic and/or non-ionic emulsifiers and particularly preferably anionic emulsifiers.

Further polymerization auxiliaries that can be used in the polymerization are the conventional buffer substances (BS) which can establish pH values which are preferably from 6 to 1 1 , examples being sodium bicarbonate and sodium pyrophosphate, and also from 0 to 3 % by weight of a molecular weight regulator (MR), such as mercaptans, terpinols or dimeric α-methylstyrene. The buffer substances can also have complexing action.

The polymerization reaction for the components can be carried out in the range from 0 to 170 ⁰ C. The temperatures used are generally from 40 to 120 ⁰ C, often from 50 to 110 ⁰ C and frequently from 60 to 100 ⁰ C.

Ancillary and processing additives that can be added to the inventive molding composi- tions comprise amounts of from 0 to 10 % by weight, preferably from 0 to 5 % by weight, in particular from 0 to 4 % by weight, of various additives (D).

Additives (D) that can be used are any of these substances which are usually used for the processing or modification of the polymers. Examples that may be mentioned are dyes, pigments, colorants, antistatic agents, antioxidants, stabilizers for improving thermal stability, stabilizers for increasing lightfastness, stabilizers for raising resistance to hydrolysis and to chemicals, agents to counteract thermal decomposition, and in particular lubricants, these being advantageous for the production of moldings. These further additives can be metered into the material at any stage of the preparation or production process, but preferably at an early juncture, in order to utilize the stabilizing effect (or other specific effects) of the additives at an early stage. With respect to fur-

ther conventional auxiliaries and additives, reference is made by way of example to "Plastics Additives Handbook", Ed. Gachter and Mϋller, 4th edition, Hanser Publ., Munich, 1996.

Examples of suitable pigments are titanium dioxide, phthalocyanines, ultramarine blue, iron oxides, or carbon black, and also the entire class of organic pigments.

Examples of suitable colorants are any of the dyes that can be used for the transparent, semitransparent, or nontransparent coloring of polymers, in particular those which are suitable for the coloring of styrene copolymers.

Examples of suitable flame retardants that can be used are the compounds known to the person skilled in the art and which comprise halogen or comprise phosphorus, other examples being magnesium hydroxide, and also other familiar compounds, or a mixture of these.

Examples of suitable antioxidants are sterically hindered mononuclear or polynuclear phenolic antioxidants, which can have various types of substitution and can also have bridging by way of substituents. Among these are not only monomeric but also oligomeric compounds which can be composed of a plurality of phenolic parent systems. Hydroquinones and hydroquinone-analogous, substituted compounds can also be used, as also can antioxidants based on tocopherols and on derivatives of these. It is also possible to use a mixture of various antioxidants. In principle, it is possible to use any of the commercially available compounds or compounds suitable for styrene copolymers, e.g. Irganox. The substances known as co-stabilizers, in particular co-stabilizers comprising phosphorus or comprising sulfur, can be used concomitantly together with the phenolic antioxidants mentioned by way of example above. The person skilled in the art is aware of these co-stabilizers comprising P or comprising S.

Examples of suitable light stabilizers are various substituted resorcinols, salicylates, benzotriazoles, and benzophenones. Matting agents that can be used are not only inorganic substances, such as talc, glass beads, or metal carbonates (e.g. MgCC>3, CaCO ₃ ), but also polymer particles - in particular spherical particles whose diameters d ₅ o (weight-average) are above 1 mm - based on, for example, methyl methacrylate, styrene compounds, acrylonitrile, or a mixture of these. It is also possible to use polymers which comprise copolymerized acidic and/or basic monomers.

Examples of suitable antidrip agents are polytetrafluoroethylene (Teflon) polymers and ultrahigh-molecular-weight polystyrene (molecular weight M _w above 2 000 000).

Examples that may be mentioned of fibrous or pulverulent fillers are carbon fibers or glass fibers in the form of glass wovens, glass mats, or glass silk rovings, chopped glass, or glass beads, or else wollastonite, particularly preferably glass fibers. If glass fibers are used, these may have been equipped with a size and with a coupling agent to improve compatibility with the components of the blend.

The glass fibers incorporated can take the form either of short glass fibers or else of continuous-filament strands (rovings).

Examples of suitable particulate fillers are carbon black, amorphous silica, magnesium carbonate (chalk), powdered quartz, mica, bentonites, talc, feldspath, or in particular calcium silicates, such as wollastonite, and kaolin.

Examples of suitable antistatic agents are amine derivatives, such as N,N-bis(hydroxyalkyl)alkylamines or -alkyleneamines, polyethylene glycol esters, copolymers composed of ethylene oxide glycol and of propylene oxide (in particular two-block or three-block copolymers in each case composed of ethylene oxide blocks and of propylene oxide blocks) glycol, and glycerol mono- and distearates, and also mixtures of these.

Examples of suitable stabilizers are hindered phenols, but also vitamin E and compounds whose structure is analogous thereto, and also butylated condensates of p-cresol and dicyclopentadiene. HALS stabilizers (Hindered Amine Light Stabilizers), benzophenones, resorcinols, salicylates, and benzotriazoles are also suitable. Exam- pies of other suitable compounds are thiocarboxylic esters. It is also possible to use C ₅ - C20 fatty acid esters of thiopropionic acid, particularly the stearyl esters and lauryl esters. It is also possible to use dilauryl thiodipropionate, distearyl thiodipropionate, or a mixture of these. Examples of further additives are HALS absorbers, such as bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, or UV absorbers, such as 2H- benzotriazol-2-yl(4-methyphenol). The amounts usually used of these additives are from 0.01 to 2 % by weight (based on the entire mixture).

Suitable lubricants and mold-release agents are stearic acids, stearyl alcohol, stearic esters, amide waxes (bisstearylamide), polyolefin waxes, and generally higher fatty acids, derivatives of these, and corresponding fatty acid mixtures having from 12 to 30 carbon atoms. Another particularly suitable substance is ethylenebisstearamide (e.g. Irgawax, producer: Ciba, Switzerland). The amounts of these additives are in the range from 0.05 to 5 % by weight.

Silicone oils, oligomeric isobutylene, or similar substances can be used as additives. The usual amounts, if they are used, are from 0.001 to 3 % by weight. It is also possi-

ble to use pigments, dyes, and optical brighteners, such as ultramarine blue, phthalo- cyanines, titanium dioxide, cadmium sulfides, derivatives of perylenetetracarboxylic acid. The amounts usually used of processing aids and stabilizers, such as UV stabilizers, heat stabilizers (e.g. butylated reaction products of p-cresol and dicyclopentadiene; Wingstay L; producer: Goodyear; or else dilauryl thiodipropionate, Irganox, producer: Ciba), lubricants, and antistatic agents (e.g. ethylene oxide-propylene oxide copolymers, such as Pluronic (producer: BASF), if they are used, are usually from 0.01 to 5 % by weight, based on the entire molding composition.

The amounts used of the individual additives are generally the respective conventional amounts. The graft polymers can be mixed in any desired manner with the other constituents, by any of the known methods, to give the molding compositions. However, it is preferable that the components are blended by extruding, kneading, or rolling of the components together, e.g. at temperatures in the range from 180 to 400 ⁰ C, the compo- nents having been isolated, if required, in advance from the aqueous dispersion or solution obtained during polymerization. The graft copolymerization products obtained in aqueous dispersion can, for example, be precipitated with magnesium sulfate. They can preferably be only partially dewatered and mixed in the form of moist crumb (for example with a residual moisture level of from 1 to 40 %, in particular from 20 to 40 %), whereupon then the complete drying of the graft copolymers takes place during the mixing process. The particles can also be dried according to DE-A 19907136.

The inventive molding compositions can be prepared from the components A and C (and, if desired, from B and further polymers, fillers and from conventional additives D), by any of the known methods.

However, it is preferable that the components are blended via mixing in the melt, for example by extruding, kneading, or rolling the components together. This is carried out at temperatures in the range from 160 to 400 ⁰ C, preferably from 180 to 280 ⁰ C.

In one preferred embodiment, component (B) is isolated to some extent or completely in advance from the aqueous dispersion obtained during the respective steps of preparation. By way of example, the graft copolymers B can take the form of moist or dry crumb/powder when mixed with pellets of the thermoplastic copolymer matrix A and the SBS-polymer (C) in an extruder.

The invention also provides the use of the molding compositions described for production of moldings, such as sheets or semifinished products, foils, fibers, or else foams, and also the corresponding moldings, such as sheets, semifinished products, foils, fi- bers, or foams. These moldings can be used for the preparation of inliners for refrigerators.

Processing can be carried out by means of the known methods of thermoplastics processing, and in particular production processes that can be used are thermoforming, extrusion, injection molding, calendering, blow molding, compression molding, pressure sintering or other types of sintering, preference being given to injection molding.

The molding compositions have particular melt stability, good colorability, little intrinsic color, and also excellent mechanical properties, such as toughness, stiffness and ESCR. Surprisingly, furthermore, the inventive molding compositions were found to have improved low-temperature toughness, and improved flowability.

The polymers have a high extent of crosslinking of the polymer particles, and this can be discerned from the relaxation times (12).

A method of characterization of the extent of crosslinking of crosslinked polymer particles is measurement of the swelling index (Sl), which is a measure of the swellability, by a solvent, of a polymer with some degree of crosslinking. Examples of conventional swelling agents are methyl ethyl ketone or toluene. The swelling index of the inventive molding compositions is usually in the range (Sl) = from 10 to 60, preferably from 15 to 55, and particularly preferably from 20 to 50. Another measure for characterization of the graft base used in the ABS molding compositions and its extent of crosslinking is gel content, i.e. the proportion of product which has been crosslinked and is therefore insoluble in a certain solvent.

The solvent used for determination of gel content is preferably the same as that used for determination of swelling index. Usual gel contents of the graft bases used are in the range from 50 to 90 %, preferably from 55 to 90 %, and particularly preferably from 60 to 85 %.

An example of a method for determination of swelling index uses an amount of, for example, 50 g of toluene to swell about 0.2 g of the solids of a graft base dispersion filmed via evaporation of the water. After, for example, 24 hours, the toluene is removed by suction and the specimen is weighed. The specimen is again weighed after drying in vacuo. The swelling index is consequently the ratio of the final weight after the swelling procedure to the final dry weight after the renewed drying process.

Gel content is correspondingly calculated from the ratio of the dry weight after the swelling step to the initial weight prior to the swelling step (x 100 %).

The test methods used for characterization of the polymers are briefly collated below:

a) Charpy notched impact resistance (ak) [kJ/m ² ]:

Notched impact resistance is determined at 23 ⁰ C or -40 ⁰ C to ISO 179-2/1 eA (F) on test specimens (80 x 10 x 4 mm, produced to ISO 294 in a family mold at a melt temperature of 250 ⁰ C and at a mold temperature of 60 ⁰ C).

b) Penetration (multiaxial toughness) [Nm]:

Penetration is determined to ISO 6603-2 on plaques (60 x 60 x 2 mm, produced to ISO 294 in a family mold at a melt temperature of 240 ⁰ C and at a mold temperature of 50 ⁰ C).

c) Flowability (MVR[ml/10']):

Flowability is determined to ISO 1 133 B on a polymer melt at 220 °C with a load of 10 kg.

d) Elasticity (modulus of elasticity [MPa]):

Elasticity is tested to ISO 527-2/1 A/50 on test specimens (produced to ISO 294 at a melt temperature of 250 ⁰ C and at a mold temperature of 60 ⁰ C).

e) Amount of coagulate:

The amount of coagulate, dried for 17 hours at 80 ⁰ C under nitrogen (200 mbar) is determined, based on the graft rubber after filtration by way of a sieve whose mesh width is about 1 mm.

f) Particle size:

The data for average particle size (d) are the weight-average particle size, which can be determined by means of an analytical ultracentrifuge by the method of

W. Machtle, S. Harding (eds.), Analytische Ultrazentrifuge [Analytical ultracentrifuge] (AUC) in Biochemistry and Polymer Science, Royal Society of Chemistry Cambridge, UK 1992, pp. 1447-1475. The ultracentrifuge measurement provides the cumulative weight distribution of the particle diameter of a specimen. From this, it is possible to deduce the percentage by weight of the particles whose diameter is equal to or smaller than a certain size.

Particle size can also be determined by hydrodynamic fractionation (HDF). HDF measurement uses flow of a liquid carrier material through a column packed with a polymeric carrier material. Whereas small particles which can penetrate even relatively small interstices pass through the column at a low rate of flow, particles with relatively large diameter are transported more rapidly. Particles size is determined by means of a UV detector (at wave length 254 nm) at the end of the column. The specimens to be tested are preferably diluted to a concentration of 0.5 g/l of the liquid carrier material, and then subjected to a filtration process, and then charged to the column. Commercially available HDF equipment is supplied by Polymer Laboratories, for example. The HDF values stated are based on volume distribution. The weight-average particle size diameter d ₅₀ is that particle diameter which is smaller than that of 50 % by weight of all of the particles and larger than that of 50 % by weight of all of the particles.

g) Swelling index and gel content [%]:

A film was produced from the aqueous dispersion of the graft base via evaporation of the water, and 50 g of toluene was admixed with 0.2 g of this film. After 24 hours, the toluene was removed by suction from the swollen specimen, and the final weight of the specimen was measured. After 16 hours of drying of the specimen in vacuo at 110 ⁰ C, the final weight of the specimen was again determined.

The following were calculated:

weight of swollen specimen after removal of solvent by suction swelling index SI = weight of specimen dried in vacuo

. , , weight of specimen dried in vacuo _{λ n} ^ _n/ gel content = . ... , ^a . / _{: :} — — • 100% initial weight of specimen prior to swelling

h) Viscosity

Viscosity number (V _z ) is determined to DIN 53726 on a 0.5 % strength solution of the polymer in DMF.

i) Gloss (gloss sensitivity)

To determine gloss, an injection-molding machine was used to produce rectangular plaques of dimensions 40 mm x 60 mm x 2 mm from the polymer melt. Temperatures used here were 230, 255, and 280 ⁰ C. The mold temperature was 30

⁰ C, and the injection times were from 0.1 to 0.5 seconds. Gloss is determined via measurement of reflection to the standard ISO 2813 at an angle of 45°, in each case on ten test plaques, using equipment from BYK Mikroglas.

j) Extent of crosslinking

A method of characterizing the extent of crosslinking of polymers is measurement of NMR relaxation times of the labile protons, these being known as T ₂ times. The greater the extent of crosslinking of a particular polymer, the lower its T ₂ times.

Usual T ₂ times for the inventive graft bases are T ₂ times in the range from 1 to 50 ms, preferably from 2.5 to 40 ms, and particularly preferably from 2.5 to 30 ms, in each case measured on filmed specimens at 80 ⁰ C. The T ₂ time is measured via measurement of NMR relaxation of a dewatered and filmed specimen of the graft base dispersion. For this, by way of example, the specimen is dried overnight in vacuo after drying in air and is then tested with suitable test equipment. Comparison can only be made between specimens which have been tested by the same method, since relaxation is highly temperature-dependent. The effective transverse relaxation time of the materials is in the range from 1 to

50 ms when measured at proton resonance frequency of 20 MHz and a temperature of 140 ⁰ C. A magnetization decay curve is utilized to determine the relaxation times and is composed of a solid echo and from a plurality of spin-echo measurements. The effective relaxation time is defined as the time after which the magnetization decay curve has decayed to a factor of 1/e in comparison with the initial amplitude determined by means of the solid echo.

The examples below are used for further illustration of the invention:

Example 1 : General preparation of copolymer matrix A

Various embodiments of copolymer matrix A can be prepared via solution polymerization, e.g. in an organic solvent, such as toluene or ethylbenzene. A process as de- scribed in general terms by way of example in Kunststoff-Handbuch [Plastics Handbook], Vieweg-Daumiller, volume V, (Polystyrol) [Polystyrene], Carl-Hanser-Verlag, Munich 1969, pages 122 et seq., lines 12 et seq. can be used as the basis for operations here. It is also possible to prepare a matrix in the form of a mixture of two (or more) matrices.

1 a) In a specific example, the copolymer matrix (A-1 ) can be prepared with viscosity V _z of 65 ml/g, starting from 76 % by weight of styrene and 24 % by weight of acryloni-

trile at a temperature of from 150 to 180 ⁰ C with a proportion of from 10.5 to 20.5 % by weight of solvent, without use of an initiator.

Example 2: General preparation of the graft rubber B

General description of a possible preparation process:

The rubber latex (B1 ) can generally be prepared starting from 0 to 10 % by weight of styrene (B1 1 ) and from 90 to 100 % by weight of butadiene (B12).

The aqueous emulsion is polymerized at about 67 ⁰ C, and the temperature here can be raised up to 80 ⁰ C. The reaction proceeds up to monomer conversion of as least 90 %. By way of example, tert-dodecyl mercaptan (TDM) is used as molecular weight regula- tor and is preferably added in from three to five portions. This generally gives rubber particles with the following properties:

Particle size distribution:

d ₅ o (weight-average, ultracentrifuge) 90 +/- 25 nm, d ₅ o (number-average, ultracentrifuge) 80 +/- 25 nm;

swelling index: (Sl) of from 25 to 75 (measured in toluene); gel content: 65 ± 20%.

This rubber then can be reacted in a emulsion polymerization with styrene and acry- lonitrile to form the graft copolymer (B).

Example 3 Preparation of the thermoplastic molding composition

In the following example, the following commercially available components were used:

Component A: Terluran (a graft ABS copolymer from BASF);

Component C1 : Styrolux (a SBS copolymer ("stiff") with a butadiene-content of 26 % by weight, produced by BASF);

Component C2: Styroflex (a SBS copolymer ("elastomere" with a butadiene content of 33 % by weight, produced by BASF).

The thermoplastic compositions according to the invention were tested by using the following methods:

Description of the "LG Method":

The Environmental Stress Cracking Resistance (ESCR) was measured.

1. Specimen preparation

- Cut from extrusion sheet machine direction and transverse direction - Specimen size: 200 mm x 20 mm

2. Fix the specimens on the strain jig.

3. Immerse the jig in the cyclopentane for 30 seconds, full out the jig and leave it for 2 minutes.

4. After 2 minutes, take out the specimen and bend it at 180 degrees. 5. Check the crack of the specimen, repeat the test according to the strain.

Description of "smell" detection:

1. Cut 2 grams of the molded material into 1-3 mm small pieces and put it in a 100 ml beaker with cover.

2. Place boiling water (10 ml) into the beaker and put the cover on top.

3. Wait 5 seconds.

4. Open the lid and evaluate the smell: 0 = no detectable smell, 1 = slight smell, 2 = clear smell, 3 = strong smell, 4 = disgusting smell.

Table 1 (Thermoplastic Compositions with components in weight-%)

It can be seen that toughness and Environmental Stress Cracking Resistance (ESCR) are improved for the compositions of Example C and Example D according to the invention. Example D having only 3 % by weight of Styroflex and 97 % by weight of Ter- luran as preferred properties.