WO2005005536A1

WO2005005536A1 - Blends of graft copolymers and styrene/butadiene block copolymers

Info

Publication number: WO2005005536A1
Application number: PCT/EP2004/007202
Authority: WO
Inventors: Norbert Niessner; Rogelio Chavez
Original assignee: Basf Aktiengesellschaft
Priority date: 2003-07-04
Filing date: 2004-07-02
Publication date: 2005-01-20
Also published as: DE10330397A1

Abstract

Molding materials comprise A) from 70 to 99% by weight of a composition comprising al) a graft copolymer comprising a rubber as a grafting base and a graft based on an unsaturated monomer and a2) a matrix polymer and B) from 1 to 30% by weight of a linear or star styrene/butadiene block copolymer comprising 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% by weight, based on the total block copolymer, and the sum of the components A) and B) being 100% by weight. A process for the preparation of molding materials which have a melt stability of 3 cm or less, determined on the basis of the sag of a 1 mm thick film at 2300C, is also described. The block copolymers B) are used for the preparation of such molding materials. Furthermore, the molding materials are used for the production of shaped articles, films or fibers, and refrigerator parts can be obtained using the molding materials.

Description

Blends of graft copolymers and styrene/butadiene block copolymers

The present invention relates to molding materials which comprise

A) from 70 to 99% by weight of a composition comprising a1 ) a graft copolymer comprising a rubber as a grafting base and a graft based on an unsaturated monomer and a2) a matrix polymer and

B) from 1 to 30% by weight of a linear or star styrene/butadiene block copolymer comprising 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% by weight, based on the total block copolymer, and the sum of the components A) and B) being 100% by weight.

The present invention furthermore relates to a process for the preparation of molding materials which have a melt stability of 3 cm or less, determined on the basis of the sag of a 1 mm thick film at 230°C. The present invention furthermore relates to the use of the block copolymers B) for the preparation of such molding materials. The present invention also relates to the use of the molding materials for the production of shaped articles, films or fibers, the shaped articles, films or fibers themselves and refrigerator parts which can be obtained using the molding materials. Further embodiments are evident from the claims and the description.

Molding materials which contain butadiene- or acrylate-based graft copolymers and styrene/butadiene block copolymers are known to a person skilled in the art (e.g. WO 00/36010 and EP-A 767213). These molding materials are suitable, for example, for the production of soft, leather-like films which are used in the interior of automobiles. These films have a good ratio of flowability to thermoforming properties, i.e. they are readily thermoformable. Good thermoformability is to be understood as meaning that, when pressure is exerted on a point of a film at moderately elevated temperatures, said film exhibits substantially uniform flow at all points. The result of this is that the film does not become thin at certain points and form holes or breaks there or at edges.

Furthermore, it was known that styrene/butadiene block copolymers as a blend with styrene polymers, such as general-purpose polystyrene or high-impact polystyrene (HIPS), give molding materials which can be processed to shaped articles which are particularly resistant to impact and stress cracking (e.g. WO 00/58380 and WO 03/11964). These shaped articles are suitable for the production of refrigerators.

It is an object of the present invention to provide molding materials which are based on graft copolymers and block copolymers, have impact resistance and stress cracking resistance and furthermore are resistant to chemical blowing agents. In particular, the molding materials should have a thermoformability of ± 150% or less, determined on the basis of the wall thickness variation of a standard cup at 120°C (cf. under Testing of performance characteristics).

In particular, the molding materials should moreover have good melt stability. Here, 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 (cf. under Testing of performance characteristics).

We have found that these objects are achieved by the molding materials defined at the outset.

According to the invention, the molding materials comprise from 70 to 99, preferably from 70 to 95, in particular from 80 to 90, % by weight of a composition A) and from 1 to 30, preferably from 5 to 30, in particular from 10 to 20, % by weight of block copolymers B), the weight of the components A) and B) summing to 100%. Moreover, the novel molding materials can, if desired, contain additives C). As a rule, the amount thereof is from 0 to 200% by weight, based on the total weight of the components A) and B).

The preferred novel molding materials include those whose melt stability is 2 cm or less, preferably 1.5 cm or less, in particular 1 cm or less, measured as stated below.

According to one of the preferred embodiments, the novel molding materials simultaneously have a thermoformability of ± 150% or less, preferably ± 120% or less, in particular ± 100%, measured on the basis of the wall thickness variation (see below).

According to a particularly preferred embodiment, the novel molding materials are optimized both with regard to their melt stability and thermoformability and with regard to their stress cracking resistance after storage in cyclopentane. Component A)

The composition which is contained according to the invention as component A) in the molding materials comprises a graft copolymer (a1 ). This is to be understood as meaning that either a graft copolymer or a blend of two or more different graft copolymers is to be included.

The graft copolymer contains a rubber as grafting base a11). All rubbers which have a glass transition temperature of 0°C (determined according to DIN 53765) or less are in principle suitable therefor. The rubbers may differ greatly in their nature. For example, silicone rubbers, olefin, such as ethylene, propylene, ethylene/propylene rubbers, EPDM, diene, acrylate, ethylenevinyl acetate or ethylenebutyl acrylate rubbers, Or blends of two or more of these rubbers can be used. These preferably include acrylate and diene rubbers.

The preferred blends include blends of diene and acrylate rubber or of diene and silicone rubber or of diene rubber and rubber based on ethylene copolymers.

However, diene rubbers alone are particularly preferably used as a11). Very particularly preferred are diene rubbers which are composed of

α11) from 50 to 100% by weight of at least one diene having conjugated double bonds and

α12) from 0 to 50% by weight of one or more further monoethylenically unsaturated monomers,

the percentages by weight of α11) and α12) summing to 100.

Particularly suitable dienes having conjugated double bonds, α11), are butadiene, isoprene and their halogen-substituted derivatives, for example chloroprene. Butadiene and isoprene are preferred, in particular butadiene.

The further monoethylenically unsaturated monomers α12) which may be contained in the diene rubber at the expense of the monomers α11) are, for example,

vinylaromatic monomers, preferably styrene or styrene derivatives, such as d- to C₈~ alkyl-substituted styrenes , such as α-methylstyrene, p-methylstyrene, vinyltoluene; unsaturated nitriles, such as acrylonitrile, methacrylonitrile; aliphatic esters, such as Ci- to C -alkyl esters of methacrylic acid or acrylic acid, such as methyl methacrylate, and furthermore the glycidyl esters, glycidyl acrylate and methacrylate;

N-substituted maleimides, such as N-methyl-, N-phenyl- and N-cyclohexylmaleimide; acids, such as acrylic acid, methacrylic acid; furthermore dicarboxylic acids, such as maleic acid, fumaric acid and itaconic acid, and the anhydrides thereof, such as maleic anhydride; nitrogen-functional monomers, such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, vinylimidazole, vinylpyrrolidone, vinylcaprolactam, vinylcarbazole, vinylaniline, acrylamide and methacrylamide;

aromatic and araliphatic esters of (meth)acrylic acid, and such as phenyl acrylate, phenyl methacrylate, benzyl acrylate, benzyl methacrylate, 2-phenylethyl acrylate, 2- phenylethyl methacrylate, 2-phenoxyethyl acrylate and 2-phenoxyethyl methacrylate; unsaturated ethers, such as vinyl methyl ether or vinyl butyl ether.

Of course, mixtures of two or more of these monomers are also suitable.

Preferred monomers α12) are styrene, acrylonitrile, methyl methacrylate, glycidyl acrylate, glycidyl methacrylate and butyl acrylate.

The preparation of the rubbers is known to a person skilled in the art or can be carried out by methods known to a person skilled in the art. For example, the diene rubbers can be prepared in a first step in which they are not obtained in particulate form, for example via solution polymerization or gas-phase polymerization, and then dispersed in the aqueous phase in a second step (secondary emulsification). Heterogeneous, particle-forming polymerization processes are preferred for the preparation of the rubbers. This dispersion polymerization can be carried out, for example, in a manner known per se by the method of emulsion, inverse emulsion, miniemulsion, microemulsion or microsuspension polymerization in the feed process, continuously or in the batch process. The rubbers can also be prepared in the presence of an initially taken finely divided latex (i.e. seed latex polymerization procedure). Suitable seed latices consist, for example, of polybutadiene or polystyrene. In principle, it is possible to use the rubbers as a grafting base after their preparation. However, they can also first be agglomerated to larger particles by agglomeration methods prior to grafting.

Agglomeration processes are known to a person skilled in the art or the agglomeration can be carried out by methods known per se to a person skilled in the art. Thus, physical processes, such as freezing or pressure agglomeration processes, can be used. However, chemical methods may also be used for agglomerating the primary particles. The latter include the addition of inorganic or organic acids. The agglomeration is preferably carried out by means of an agglomeration polymer in the presence or absence of an electrolyte, such as an inorganic hydroxide. Examples of agglomeration polymers are polyethylene oxide polymers or polyvinyl alcohols. The suitable agglomeration polymers include copolymers of C to C₁₂- alkyl acrylates or C to C₁₂-methalkyl acrylates and polar comonomers, such as acrylamide, methacrylamide, ethacrylamide, n-butylacrylamide or maleamide. The agglomeration is particularly preferably carried out in the presence of copolymers of

from 80 to 99.9, preferably from 90 to 99.9, % by weight of C_r to C₄- alkyl esters of acrylic acid and from 0.1 to 20, preferably from 0.1 to 10, % by weight of acrylamides

(the sum of the abovementioned esters and acrylamides being 100% by weight). Very particularly preferably, the agglomeration is carried out in the presence of these copolymers and in the presence of iOH, NaOH or KOH, in particular KOH.

The rubbers preferably have particle sizes (weight average value d₅₀) of from 100 to 2500 nm. The particle size distribution is preferably virtually or completely monomodal or bimodal.

The graft copolymers a1) contain a graft a12) based on an unsaturated monomer, which is also to be understood as meaning that the graft may be prepared from two or more unsaturated monomers. In principle, the rubbers can be grafted with a very wide range of different unsaturated compounds. Corresponding compounds and methods are known per se to a person skilled in the art. A preferred graft a12) is one comprising

α21) from 50 to 100, preferably from 60 to 90, particularly preferably from 65 to 80, % by weight of a vinylaromatic monomer,

α22) from 0 to 50, preferably from 10 to 40, particularly preferably from 20 to 35, % by weight of acrylonitrile or methacrylonitrile or of a mixture thereof,

α23) from 0 to 40, preferably from 0 to 30, particularly preferably from 0 to 20, % by weight of one or more further monoethylenically unsaturated monomers,

the amounts of the components α21) to α23) summing to 100% by weight. Suitable vinylaromatic monomers are the vinylaromatics stated under α12) or mixtures of two or more thereof, in particular styrene or α-methylstyrene. The further monoethylenically unsaturated monomers include the aliphatic, aromatic and araliphatic esters, acids, nitrogen-functional monomers and unsaturated ethers or mixtures of these monomers mentioned under α12).

The graft a12) can be prepared in one or more process steps. The monomers α21), α22) and α23) can be added individually or as a mixture with one another. The monomer ratio of the mixture may be constant as a function of time or may be a gradient. Combinations of these procedures are also possible.

For example, it is possible to polymerize first styrene alone, and then a mixture of styrene and acrylonitrile, onto the grafting base a11).

Preferred grafts a12) comprise, for example, styrene and/or α-methylstyrene and one or more of the other monomers stated under α22) and α23). Methyl methacrylate, N- phenylmaleimide, maleic anhydride and acrylonitrile are preferred, methyl methacrylate and acrylonitrile being particularly preferred.

Preferred grafts a12) are based on:

a12-1 styrene a12-2 styrene and acrylonitrile a12-3 α-methylstyrene and acrylonitrile a12-4 styrene and methyl methacrylate.

Grafts a12) which comprise from 74 to 80% by weight of styrene and from 20 to 26% by weight of acrylonitrile are particularly preferred.

Graft polymers having a plurality of soft and hard stages, especially in the case of relatively large particles, are furthermore suitable.

Preferred graft polymers a1) are those which contain (based on a1)

a11) from 30 to 95, preferably from 40 to 90, in particular from 40 to 85, % by weight of a grafting base (i.e. rubber) and

a12) from 5 to 70, preferably from 10 to 60, in particular from 15 to 60, % by weight of a graft.

Particularly preferred graft polymers a1) are those which contain (based on a1) a11 ) from 40 to 85% by weight of a diene rubber as a grafting base and

a12) from 15 to 60% by weight of a grafting base comprising (based on a12) from 74 to 80% by weight of styrene and from 20 to 26% by weight of acrylonitrile.

In general, the grafting is carried out in emulsion. Suitable process measures are known to a person skilled in the art. If ungrafted polymers are formed from the monomers a12) during the grafting, these amounts, which as a rule are less than 10% by weight of a1 ), are assigned to the mass of the component a2).

The component a2) contains a matrix polymer, which is also understood as meaning blends of two or more different matrix polymers. Suitable matrix polymers a2) are, for example, amorphous polymers. For example, they may be SAN (styrene/acrylonitrile), AMSAN (α-methylstyrene/acrylonitrile), styrene/maleimide/maleic anhydride (SNPMIMA), styrene/maleic acid (anhydride)/acrylonitrile polymers or SMA (styrene/maleic anhydride).

Component a2) is preferably a copolymer of

a21) 60 - 100, preferably 65 - 80, % by weight of units of vinylaromatic monomer, preferably of styrene, of a substituted styrene or of a (meth)acrylic ester or of a mixture thereof, in particular of styrene or α-methylstyrene or of a mixture thereof,

a22) from 0 to 40, preferably 20 - 35, % by weight of units of an ethylenically unsaturated monomer, preferably of acrylonitrile or methacrylonitrile or methyl methacrylate, in particular of acrylonitrile.

According to an embodiment of the invention, a copolymer of styrene and/or α- methylstyrene with acrylonitrile is used as a2). The acrylonitrile content of these copolymers is 0 - 40, preferably 20 - 35, % by weight, based on the total weight of a2).

The molecular weights (weight average value M_w) are as a rule from 50000 to 500000, preferably from 70 000 to 450000, g/mol.

The matrix polymers a2) are known per se or can be prepared by methods known to a person skilled in the art.

The ratio of the components a1) to a2) may vary within wide ranges. In general, the compositions A) contain from 20 to 85, preferably from 25 to 80, % by weight of a1) and from 15 to 80, preferably from 20 to 75, % by weight of a2), the amounts by weight of a1) and a2) summing to 100.

Component B)

A linear or star block copolymer can be used as component B). However, two or more different block copolymers may also be suitable. The block copolymers which can be used as component B) in accordance with the invention and 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, found. In preferred block copolymers, 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 particular 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 piperylene or mixtures thereof are preferably used as dienes for the soft block B/S. 1 ,3- Butadiene is particularly preferably used.

The block copolymer 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 10000 to 20000, g/mol. The molecular weight of S2 is preferably more than 35 000 g /mol. Preferred molecular weights of S2 are from 50000 to 150000 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 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 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 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 vinylaromatic 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 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 5000 g/mol.

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

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

is used as component B).

The block copolymers 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 comonomers 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 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 potassium 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, potassium 2-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-, hexamethyldi-, 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, 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 12. In this way, two living polymer chains Sa-Sb-1 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 12 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 carried 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. Component C)

The molding materials may contain additives. The amount thereof is as a rule from 0 to 200% by weight, based on the total weight of the components A) and B).

Suitable additives are, for example, particulate mineral fillers. Among these, amorphous silica, carbonates, such as magnesium carbonate (chalk), powdered quartz, mica, various silicates, such as clays, muscovite, biotite, suzoite, tin maletite, talc, chlorite, phlogophite, feldspar, calcium silicates, such as wollastonite or kaolin, in particular calcined kaolin, are suitable.

According to a particularly preferred embodiment, particulate fillers are used, at least 95, preferably at least 98, % by weight of the particles of which have a diameter (largest dimension), determined on the finished product, of less than 45 μm, preferably less than 40 μm, and whose aspect ratio is preferably from 1 to 25, especially from 2 to 20, determined on the finished product, i.e. as a rule an injection-molded particle. The particle diameters can be determined, for example, by recording electron micrographs of thin sections of the polymer blend and using at least 25, preferably at least 50, filler particles for the evaluation. The determination of the particle diameter can also be effected by means of sedimentation analysis, according to Transactions of ASAE, page 491 (1983). The amount by weight of the fillers, which are less than 40 mm in size, can also be measured by means of sieve analysis. The aspect ratio is the ratio of particle diameter to thickness (largest dimension to smallest dimension).

Talc, kaolin, such as calcined kaoϋn, or wollastonite or mixtures of two or all of these fillers are particularly preferred as particulate fillers. Among these, talc having a proportion of at least 95% by weight of particles with a diameter of less than 40 mm and an aspect ratio of from 1.5 to 25, determined in each case on the finished product, is particularly preferred. Kaolin preferably has a proportion of at least 95% by weight of particles with a diameter of less than 20 μm and an aspect ratio of from 1.2 to 20, determined in each case on the finished product. These fillers may be used in amounts of from 0 to 20% by weight, based on the total weight of the components A) and B). If present, the amount thereof is preferably from 1 to 10% by weight, based on the total weight of the components A) and B).

Fibrous fillers, such as carbon fibers, potassium titanate whiskers, aramid fibers and preferably glass fibers can also be used as component C), at least 50% by weight of the fibrous fillers (glass fibers) having a length of more than 50 mm. The (glass) fibers used can preferably have a diameter of up to 25 μm, particularly preferably from 5 to 13 μm. Preferably, at least 70% by weight of glass fibers have a length of more than 60 μm. Particularly preferably, the mean length of the glass fibers is from 0.08 to 0.5 μm in the finished shaped article. The length of the glass fibers is based on a finished shaped article which is obtained, for example, by injection molding. The glass fibers can be added to the molding materials in the appropriately long form or in the form of rovings. In general, these fibers are used in amounts of from 0 to 50, preferably from 0 to 30, % by weight, based on the total weight of the components A) and B).

Phosphorus-containing flameproofing agents can be used as component C). Examples are tri-(2,6-dimethylphenyl) phosphate, triphenyi phosphate, tricresyl phosphate, diphenyl 2-ethyl-cresyl phosphate, diphenyl cresyl phosphate, tri(isopropylphenyl) phosphate and bisphenyl 4-phenyl phosphate, phenyl bis(4-phenylphenyl) phosphate, tris(4-phenylphenyl) phosphate, bisphenyl benzylphenyl phosphate, phenyl bis(benzylphenyl) phosphate, tris(benzylphenyl) phosphate, phenyl bis[1- phenylethylphenyl] phosphate, phenyl bis[1-methyl-1-phenylethylphenyl] phosphate and phenyl bis[4-(1-phenethyl)-2,6-dimethylphenyl] phosphate. They may also be used as a mixture with triphenylphosphine oxide or tri(2,6-dimethylphenyl)phosphine oxide.

In addition, resorcinol diphosphate and appropriately higher oligomers, hydroquinone diphosphate and appropriate higher oligomers are preferred as flameproofing agents.

The flameproofing agents are used as a rule in amounts of from 0 to 30% by weight. When they are present, they are preferably used in amounts of from 3 to 15% by weight. The stated amounts are based in each case on the total weight of the components A) and B).

Examples of further additives are processing assistants, stabilizers and antioxidants, heat stabilizers and UV stabilizers, lubricants and mold release agents, dyes and pigments and plasticizers. The amount thereof is in general from 0 to 15% by weight and, where present, from 0.1 to 5% by weight, based on the total weight of the components A) and B).

Pigments and dyes are generally contained in amounts of from 0 to 10% by weight, and, where present, from 0.001 to 7% by weight, based on the total weight of the components A) and B).

The pigments for coloring thermoplastic are generally known. A first preferred group of pigments which may be mentioned comprises white pigments, such as zinc oxide, zinc sulfide, lead white (2PbCO₃-Pb(OH)₂), lithopone, antimony white and titanium dioxide. Of the two most commonly used crystal modifications (rutile and anatase type) of titanium dioxide, in particular the rutile form is used for whitening the novel molding materials.

Black pigments which can be used according to the invention are iron oxide black (Fe₃O ), spinel black (Cu(Cr,Fe)₂O₄), manganese black (mixture of manganese dioxide, silica and iron oxide), cobalt black and antimony black and particularly preferably carbon black, which is generally used in the form of furnace black or gas black.

Of course, inorganic colored pigments can be used according to the invention for establishing specific hues. Furthermore, it may be advantageous to use said pigments or dyes as a mixture, for example carbon black with copper phthalocyanines, since the color dispersion in the thermoplastic is generally facilitated.

Antioxidants and heat stabilizers which can be added to the thermoplastic materials according to the invention are, for example, halides of metals of group I of the Periodic Table of the Elements, for example sodium and lithium halides, if required in combination with copper(l) halides, e.g. chlorides, bromides and iodides. The halides, in particular of copper, may also contain electron-rich p-ligands. Copper halide complexes with, for example, triphenylphosphine may be mentioned as an example of such copper complexes. Furthermore, zinc fluoride and zinc chloride may be used. Sterically hindered phenols, hydroquinones, substituted members of this group, secondary aromatic amines, HALS, if required in combination with phosphorus- containing acids or salts thereof, and mixtures of these compounds may also be used, preferably in concentrations of from 0 to 2% by weight, based on the total weight of the components A) and B).

Examples of UV stabilizers are various substituted resorcinols, salicylates, benzotriazoles and benzophenones, which are used in general in amounts of from 0 to 2% by weight, based on the total weight of the components A) and B).

Lubricants and mold release agents, which are added as a rule in amounts of from 0 to 2% by weight, based on the total weight of A) and B), are stearic acid, stearyl alcohol, alkyl stearates and stearamides and esters of pentaerythritol with long-chain fatty acids. Salts of calcium, of zinc or of aluminum with stearic acid and dialkyl ketones, e.g. distearyl ketone, may also be used. Furthermore, ethylene oxide/propylene oxide copolymers may also be used as lubricants and mold release agents.

The preparation of the novel thermoplastic molding materials is carried out by processes known per se, by mixing the components A) to C). It may be advantageous to premix individual components. Mixing of the components in solution with removal of the solvents is also possible, but is less preferable.

Examples

Testing of performance characteristics

The thermoformability was determined on the basis of the wall thickness variation of a standard cup at 145°C. The standard cup had the following dimensions: approx. 11 x 10 cm² length x width, wall height: 8 cm. The standard cup was thermoformed from a 1 mm thick film by pressing in a punch with the dimensions 10 x 9 cm² (length x width), wall height 8 cm. The wall thickness was measured at 3 points distributed over the wall of the standard cup by means of a micrometer.

The melt stability is determined on the basis of the sag of the melt. The distance in cm between the ideal horizontal line of the melt and the point of inflection of the curve which describes the melt when it sags is determined. The determination is carried out using a 1 mm thick melt at 230°C.

The stress cracking resistance is measured after storage for 24 hours in cyclopentane at 23°C using tensile test bars according to ISO 527-2. The evaluation of the cracks was effected visually on a scale from 0 to 5, where 0 = no cracks observed, 3 = many cracks and 5 = very many cracks.

The flowability was determined on the basis of the melt volume rate (MVR) according to ISO 1133 at 220°C and 10 kg load.

The notched impact strength (Charpy) of the products was determined on ISO bars according to ISO 179 1eA at 23°C and -40°C.

The multiaxial impact strength (IPT) was determined according to ISO 6603/2.

The heat distortion resistance of the sample was determined by means of the Vicat softening temperature. The Vicat softening temperature was determined according to ISO 306, VST/B/50.

The ultimate tensile strength was measured according to ASTM D638 at a rate of 5 mm/min.

The elongation at break was determined according to ASTM D638. The tensile strength was measured according to ASTM D638 at a rate of 5 mm/min.

The tensile stress was measured according to ISO 527-2.

The viscosity number was determined in ml/min of a 0.5% strength by weight solution in toluene at 23°C.

The particle size of the graft rubbers is the weight median d₅₀, determined in accordance with W. Scholtau and H. Lange, Kolloid-Z. und Z Polymere 250 (1972), pages 782-796, by means of analytical ultracentrifuge.

Components A1

A composition which contained 40% by weight of a graft copolymer based on 62% by weight of a polybutadiene rubber agglomerated prior to grafting and 38% by weight of a graft comprising 80% by weight of styrene and 20% by weight of acrylonitrile and which contained 60% by weight of a copolymer having a viscosity number of 64, which contained 76% by weight of styrene and 26% by weight of acrylonitrile was used as component A . The particle size was 350 nm.

Component B1

A star styrene/butadiene block copolymer was obtained as component B1 by sequential anionic polymerization of styrene and butadiene in cyclohexane as a solvent at from 60 to 90°C and subsequent coupling with epoxidized linseed oil (Edenol B 316 from Henkel).

The component B1 had the following structure:

[S2-(B/S) (B/S)₂-S3] x [S3-(B/S)₂-(B/S) S1].

The star styrene/butadiene block copolymer contained the branch shown above left once on average and the branch shown above right 3.5 times on average.

Table 1 shows the amounts and order of metering: Table 1:

Molding materials F1 to F4

For the preparation of the molding materials F1 to F4, the components A1 and B1 were reacted in the ratio stated in table 2 in a twin-screw extruder at a melt temperature of from 220 to 250°C. The melt was passed through a water bath and granulated. The granules were then injection molded to give test specimens at an injection temperature of 250°C.

Table 2

for comparison not suitable, i.e. thermoforming with identical cycle times only possible at a film temperature approx. 5°C above experiments F1 to F4 Values which are measured after storage for 24 hours at 23°C in cyclopentane

Claims

We claim:-

1. A molding material comprising A) from 70 to 99% by weight of a composition comprising a1) a graft copolymer comprising a rubber as a grafting base and a graft based on an unsaturated monomer and a2) a matrix polymer and

2. A molding material as claimed in claim 1 , wherein the graft copolymer a1) has an acrylate or diene rubber as the grafting base.

3. A molding material as claimed in either of claims 1 and 2, wherein the graft of the graft copolymer has a1 ) an acrylonitrile content of not more than 26% by weight.

4. A molding material as claimed in any of claims 1 to 3, which has a melt stability of 3 cm or less, determined on the basis of the sag of a 1 mm thick film at 230°C.

5. A process for the preparation of molding materials having a melt stability of 3 cm or less, determined on the basis of the sag of a 1 mm thick film at 230°C, comprising a composition A) comprising a1 ) a graft copolymer comprising a rubber as a grafting base and a graft based on an unsaturated monomer and a2) a matrix polymer, wherein from 70 to 99% by weight of the composition A) are mixed with from 1 to 30% by weight of a linear or star styrene/butadiene block copolymer B) comprising 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% by weight, based on the total block copolymer.

6. The use of linear or star styrene/butadiene block copolymers B) comprising 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 block being more than 30% by weight, based on the total block copolymer, for the preparation of molding materials having a melt stability of 3 cm or less, determined on the basis of the sag of a 1 mm thick film at 230°C, the molding materials comprising from 70 to 99.9% by weight of a composition A) comprising a1 ) a graft copolymer comprising a rubber as a grafting base and a graft based on an unsaturated monomer and a2) a matrix polymer and from 0.1 to 30% by weight of the linear or star styrene/butadiene block copolymers B) and the sum of the components A) and B) being 100% by weight.

7. The use of a molding material as claimed in any of claims 1 to 4 or obtained as claimed in claim 5 for the production of shaped articles, films or fibers.

8. A shaped article, film or fiber obtainable using a molding material as claimed in any of claims 1 to 4 or obtained as claimed in claim 5.

9. The use of a molding material as claimed in claim 8 for the production of refrigerator parts.

10. A refrigerator part obtainable using a molding material as claimed in any of claims 1 to 4 or obtained as claimed in claim 5.