CA1162345A - Thermoplastic molding materials and moldings produced from these - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

An ABS molding material comprising a copolymer matrix A in which is dispersed a graft copolymer B. The graft copolymer B is composed of styrene and acrylonitrile as the grafting monomers on polybutadiene as a grafting base and has a mean particle diameter of from 0.2 to 0.45 µm (d50value of the cumulative mass distribution). The gel component, isolated from the molding materials, is required to have a spin-spin relaxation time of from 0.7 to 1.5 µs, so that the molding materials have a high surface gloss coupled with good notched impact strength even at low temperatures. The copolymer A can be a copolymer of styrene and acrylonitrile or a terpolymer additionally containing .alpha.-methylstyrene. The molding material can furthermore contain conventional additives. The molding materials according to the invention can be employed where great toughness coupled with high gloss is required, as in household appliances and in the automotive industry.

Description

~1~i23~;

Thermoplastic molding materials and moldings produced from these The present invention relates to mixtures to styrene/acrylonitrile copolymers made impact-resistant by means of elastomeric polymers, which mixtures give thermoplastic molding materials (of the ABS type) having high impact strength, high surface gloss and good pro-cessing characteristics.

The preparation of thermoplastically processable hlgh-impact molding materials by modifying styrene/acrylo-nitrile copolymers through incorporating elastomers there-in is known. In general, such products are prepared by , a graft copolymerization of styrene and acrylonitrile in the presence of an elastomer, which may or may not be ~ollowed by mixing the grafted product with a separately prepared hard component which in general consists of a styrene/acrylonitrile copolymer. Molding materials with different patterns of properties are obtained according to the nature of the elastomer employ-ed in the process of preparation.
In ABS polymers, polybutadiene is used as the elastomer which makes the mixture impact-resistant. The products thus obtained have good impact strength, in particular at very low temperatures, good chemical resistance and good processability. An example of a process by which such molding materials may be obtained in a technically simple manner is given in German Publish-ed Application DAS 2,427,960.

However, it has been found that conventional molding materials possess either very high impact ~ -- 1 --strength, which can be achieved by employing a high propor-tion of elastomer and/or by employing large elastomer particles, or possess good gloss, which is achieved by employing small elastomer particles. A combination of very high impact strength with very good gloss has hitherto not proved feasible.
It is an object of the present invention to pro~
vide products which possess very high impact strength, even at low temperatures, and from which moldings having high relative gloss can be produced under a great variety of processing conditions.
We have found that this object is achieved, according to the invention, by providing thermoplastic molding materials which contain A) one or more copolymers comprising a hard phase and containing, as copolymerized units, al) from 60 to 80~ by weight of a monomer selected from the group consisting of styrene and a-methylstyrene and mixtures thereof and a2) from 20 to 40% by weight of acrylonitrile, and Bj at least one graft copolymer, in an amount of from 10 to 50% by weight based on A) + B), comprising bl~ from 40 to 80% by weight, based on B), of an elastomeric polymer which contains not less than 93%
by weight of butadiene as polymerized units and b2) from 60 to 20% by weight of grafts, forming a hard phase, formed from the monomers styrene and acrylonitrile in a weight ratio of from 80 : 20 to 65 :
35, the graft copolymer having been obtained by grafting ~234~

t:he mixture of the monomers b2) onto the elastomeric polymer, wherein the graft copolymer B) is composed of particles which have a mean particle diameter of from 0.2 to 0.45 ~m (d50 value of the cumulative mass distribution) and has a spin-spin relaxation time of 0.9 to l.S microseconds and the spin-spin relaxation time of the insoluble constituent isolated from a methyl ethyl ketone extraction of the molding material is from 0.7 to 1.5 microseconds.
The molding material can furthermore contain conventional additives.
The copolymer A contained in the molding materials according to the invention is composed of one or more copolymers of styrene and/or ~-methylstyrene with acrylo-nitrile. The acrylonitrile content in these copolymers of component A should be in each case from 20 to 40% by weight, based on the particular copolymer. As explained in more detail later, the free, non-grafted styrene/
acrylonitrile copolymers produced in the course of the pre-paration of the graft copolymer B are also included underthis copolymer A.
Depending on the conditions chosen for the pre-paration of the graft copolymer B, it is possible that the graft copolymerization in itself will produce a sufficient proportion of copolymer A. In general, however, it is necessary to mix the graft copolymer B with additional, separately produced copolymer A.
The separate~y produced copolymer A may be a styrene/acrylonitrile copolymer, an a-methylstyrene/
acrylonitrile copolymer or an a-methylstyrene/styrene/

~1623A5 - 4 - O.Z. ooSo,'0339~0 a~rylonitrile terpolymer. The said copolymers may be employed singly or as mixtures with one another, so that component A of the moldirg material according to the in-vention may be, for example, a ~ixture of a styrene/
acrylonitrile copolymer and an ~-methylstyrene/acrylo-nitrile copolymer. l~here component A of the novel molding materials consists of a mixture of a styrene/
acrylonitrile copolymer and an -methylstyrene/acrylo-nitrile copolymer, the acrylonitrile contents of the two copolymers should not differ by more than 10h by weight, preferably by not more than 5% by weight, the percentages in each case being based on the particular copolymer.
However, component A of the novel molding materials can also consist o~ a mixture of styrene/acrylonitrile co-polymers all of the same composition, ~his is the~
case if the same monomer mixture of styrene and acrylo-nitrile is employed both for the graft copolymerization to produce componsnt B and for the preparation of the copolymer A.
The copolymer A may be prepared by conventional methods, for example by copolymeriæing styrene and/or a-methylstyrene with acrylonitrile in the absence of a diluent, or in solution, suspension or aqueous emulsion.
The copolymer A can ha~re an intrinsic ~iscosity of from 40 to 100, especially of from 50 to 85. Copolymer A
accounts for from 90 to 50% by weight of the sum of com-ponents A + B of the molding material.
The emulsion graft copolymer B, the use of ~rhich is preferred according to the invention, is prepared in ~ l~s~? 4 S 0 z. oO50/033940 t~o stages. First, an elastomeric polymer bl is pre-pared, on~o which a mixture of the monomers styrene and acrylonitrile (grafting material b2) is then grafted in a further process s~age, in emulsion.
The elastomeric polymer bl is prepared as follo~s:
The polymerization is carried out at from 0 to 90C, in the presence of emulsifiers, eg. alkali metal alkylsulfonates, alkylarylsulfonates, alkyl-sulfates or fatty alcohol-sulfonates, or alkali metal salts of fatty o acids of 10 to 30 carbon atoms. The use OI the sod-ium al~ylsul~onates and sodium salts of fatty acids o~
12 to 18 carbon atoms ls preferred. The amount of emul~i~ier is ~rom 0.3 to 5% by weight, especially from 0~7 to 2.0% by weight, based on the monomer or monomer mixture. The polymer-ization is carried out n the presence of buffer salts, such as sodium bicarbonate and sodium pyrophosphate, with persulfates or organic peroxides and reducing agents as the initiators. A molecular weight regulator must ~o be used in carrying out this process step. Examples of regulators are mercaptans, terpenes or dimeric a-methylstyrene; they may be added before or during tne emulsion polymerization In general, the polymeriz~-tion reaction is complete after from 5 to 80 hours.
The weight ratio of water to monomer or monomersis in general ~rom 2:1 to 0.7:1. It is economically desirable to continue the polymerization until the mono-mers have very largely polymerized. In other respects, the conditions in this first process stage are sucr, ~hat 1~i23~5 . - 6 -~he specified relaxation time of the elastomeric polymer bl is obtained.
The polymerization conditions should be chosen in such-a way that the elastomeric polymer bl has, after completion of polymerization, a relaxation time of ~
but not more than 2 ms, and preferably from 1.4 to 1.8 ~s. As explained in more detail later, the relaxation time of the elastomeric polymer must be determined in every case before carrying out the grafting. If the elastomeric polymer has a relaxation time of <1 ~s, it is not possible to achieve the relaxation times required in the subsequent stages and in the end product. A
relaxation time of the elastomeric polymer bl of more than I ~s can be achieved, when pol~Jmerizing butadiene or mixtures containing up to 7% by weight of comonomers, by controlling the polymerization temperature and/or ~aryingthenature,amountandrate ofadditionof the regulator and/or stopping the reaction at an appropriate conversion.
A suitable elastomeric polymer bl can be obtain-ed, for instance, by proceeding as described in Example 1.
Alternati~ely, using the polymerization ~ettle described in Example 1, and filled to the same degree as in Example - 1, 100 parts by weight of butadiene may be polymerized in the presence of 0.8 part by weight of sodium stearate, 0.3 part by weight of potassium peroxydisulfate in 150 parts by weight of water at 65C whilst stirring at 70 rpm, 0.5 part by weight of tert.-dodecylmercaptan being added at the beginning of the reaction and a fur-ther 0,5 part by weight after 10 hours' reaction time, . , i16~:34S
- 7 - o.Z. OoSo/0339~0 and the polymerization being taken to a conversion of g6% by weight.
As a further alternative to the above, 1 2 parts by weight of sodium stearate may be used instead of 0.8 part by weight, if 0.3 part by weight o~ tert.-dodecyl-mercaptan is added initially, a further 0.2 part by weight after 7, after ll and after 15 hours, and a fur-ther 0.1 part by weight after l9 hours, and the reaction is stopped at a butadiene conversion of 93% by weight As yet a further example, a suitable elastomeric polymer bl may be obtained by employing a mixture of 0.5 part by weight of tert.-dodecylmercaptan, 0.8 part by weight of sodium stearate, lOO parts by weight of buta-diene and 146 parts by weight of water, starting the re-action at 50C by means of 0.~ part by weight of potassium peroxydisul~ate, raising the temperature to 55C at 23% by weight conversion, raising it urther to 6~C at 37/0 by weight conversion, and continuing the polymerization to a conversion of 98% by weight, all the said conversions being based on butadiene.
Other emulsifiers than those mentioned above may also be used, and the nature, amount and rate of addition of the regulator, the polymerization temperature, and the final conversion can be selected, with the aid of a few exploratory experiments, to give a suitable elastomeric polymer bl.
Suitable comonomers to use in the preparation of the elastomeric polymer bl are styrene and acrylonitrile, in amounts of not more than 7% by weight, but the use o~

11~234S
- S - o.Z~ oo50~033940 butadiene alone is preferred.
The requisite particle diameter of from 0.2 to 0.45 ~m (d50 value of the cumulative mass distribution) is achieved either by ag~lomerating a fine elastomer latex or by maintaining a particular monomer/water ratio during the preparation of the elastomeric polymer bl and at the same time adding the emulsifier ~n a specific manner, as described, for example, in German Published Application DAS 1,269,360 and British Patent 859,080.
If a fine polymer latex is used as the starting material, it may be agglomerated by, for example, adding a dispersion of a polyacrylate (c~. German Published Appl~cation DAS 2,427,960). Preferably, dispersions of copolymers of alkyl acrylates (alkyl being o~ 1 to 4 carbon atoms), more specifically of ethyl acrylate, with from 0.1 to 10% by weight of monomers which ~orm water-soluble polymers, eg- acrylamide ormethacryLamide~are employed. Acopolymer of96% ofethyla~rylatewith 4C~ of methacrylamideis partic~lypreferred. The agglomera-ting dispersion may contain one or more of the acrylate polymers The concentration of the acrylate polymers in the dispersion should in general be ~rom 3 to 40% by weight. To carry out the agglomeration, from 0.2 to 10, pre~erably from 1 to 5, parts by weight of the agglomerating polymer are used per 100 parts of elastomer contained in the latex~ The agglomeration is effected by adding the agglomerzting dispersion to the elastomer latex. me rate of addition is normally not ~16Z34S
9 - O . Z. ooso/0339ao critical; in general, the addition is made over a period of from about 1 to 30 minutes at from 20 to 90C, pre-ferably ~rom 30 to 75C.
The mean diameter (d50 ~alue) of the elastomer particles should be from 0.20 to 0.45 ~m, preferably.
from 0.26 to 0.35 ~m. The agglomerated elastomer latex obtained is relatively stable and can readily be stored and transported without causing coagulation.
To prepare the gra~t copolymer B, a monomer mixture of styrene and acrylonitrile is next polymerized, in a further step, in the presence of the agglomerated or directly prepared latex o~ the elastomeric polymer bl, the weight ratio of styrene to acry~onitrile in the mono-mer mixture being from 80:20 to 65:35, preferably about 70:30. The graft copolymerization of styrene and acrylonitrile onto the elastomeric polymer bl serving as the grafting base is preferably carried out in aqueous emulsion and can advantageously be carried out in the same system in which the elastomeric polymer bl has been 20 . prepared by emulsion polymerization, further emulsifier and initiator being added if necessary.
Preferably, the initiators used are conventional organic or inorganic water-soluble initiators, more especially potassium peroxydisulfate in an amount of from 0.1 to 0.5% by weight, based on the monomer mixture of styrene and acrylonitrile .
The polymerization temperature should be from 50 to 80C.
The grafting mixture of styrene and acrylonitrile can be added to the reaction mixture as a single shot, or -- 10 _ in portions or, preferably, continuously during the poly-merization. The graft copolymerization of the styrene/
acrylonitrile mixture in the presence of the elastomeric polymer bl is conducted so as to obtain a graft copolymer B which contains from 20 to 60% by weight, preferably from 35 to 45% by weight, of styrene/acrylonitrile, ie.
the degree of grafting is from 20 to 6~% by weignt, preferably from 35 to 45~ by weight. Since the grafting yield in such a reaction is not 100,6, a some-what largèr amount of the styrene/acrylonitrile monomermixture has to be employed than corresponds to the desired degree o~ grafting. The means of control of ~he gra~ting yield of a graft copolymerization, and hence the methods of obtaining the desired degree of grafting, are familiar to a skilled worker and include, for example, controlling the rate of addition of the monomers or of the regulator (cf. Chauvel and Daniel, ACS Polymer Preprints 15 (1974), 329 et séq.). In general, from about 5 to 15% by weight, based on the graft copolymer, of free, non-grafted styrene/acrylonitrile copoly~er are produced during the emulsion graft copolymerization;
the amount of this free copoly~er is determined by the method described later~ The preparation of graft copolymers is, inter alia, described in German Published Applicatio~sDAS 2,427,960 and DAS 1,269,360.
The grafting of the styrene and acrylonitrile monomers onto the elastomeric polymer bl, which has a relaxation time of not less than 1 ~s and not more than

2 ~s, must be carried out in such a way that the rela~a-~16Z345 ~ - 11 - o.Z. 0050/033~c tion time of the resulting graft copolymer is from 0.9 to 1.5 ms. The relaxation time is measured by the method described later. The required relaxation time can be achieved by, for example, carrying out the graft copolymerization at from 65 to 75C in the presence o~
from 0.3 to 0.4% by weight of potassium peroxydisullate.
The novel molding materials may be obtained by various methods. E a sufficient proportion of copolymer A is formed during the graft copolymerization, the molding material can be obtained by precipitation from the dispersion (where appropriate after having intro-duced the additives C into the dispersion~, followed by gentle drying. In all other cases, the no~el molding material must be produced by mixing the components A
and B, with or wlthout C. The mixing of components A and B to give the novel molding materials may be carried out by conventional methods. If, for example, the components have been prepared by emulsion polymer-ization, it is possible to mix the resulting polymer dispersions with one another, after which the polymers are coprecipitated and the polymer mixture is wor~ed up under gentle conditions. Preferably, however, com-ponents A and B (with or without C) are mixed by co-extrusion, or by kneading or milling the components with one another at below 270C. The graft copolymers B, which are preferably produced in a~ueous dispersion, are pre~erably partially dried and then mixed, as moist crumb, with the copolymer A and with additive C, i~ any, during which mixing the final drying occurs. Such a " ~L162345 process is described in German Published Application DAS 2,037,784; it is,however,absolutely essential that in such a process the temperature of the mixture should not exceed 270C, and preferably not exceed 250C.
In addition to components A and B, the novel molding materials may contain, as a further component C, conventional additives employed in ABS polymers.
Examples of such additives are fillers, additional and compatible plastics, dyes, pigments, antistatic agents, lo antioxidants, flameproofing agents and lubricants.
These additives are employed in the conventional effective amour.ts, which are in general from 0.1 to 30/0 by weight, based on the molding material comprising components A
and B. Examples of suitable antistatic agents are polyethylene glycols, polypropylene glycols and ethylene oxide/propylene oxide copolymers. Salts of alkyl-sulfonic acids and of alkylarylsulfonic acids, and oxy-ethylated long-chain alkylamines, may also be used as antistatic agents.
The novel molding materials have a relaxation time of from 1 to 2 ~s, preferably from 1 to 1.4 ~5, if the conditions stated in connection with the preparation of the elastomeric poly~er bl are observed. It is furthermore important that the graft copolymer should ha~e a relaxation time within the range stated earlier, and that the preparation of the molding material should be carried out under gentle conditions. If all these requirements are met, the "insoluble component" isolated from the molding material has a relaxation time of from ,~

``. ~16234S

0.7 to 1.5 ~s, preferably from 0.9 to 1.3 ~s- This insoluble component of the novel molding material is isolated by a ~ethod described later.
We have found, surprisingly, tha~ the novel molding materials not only have excellent surface gloss but also a very high notched impact strength, especially at low temperatures. Thus, moldings having good sur-face gloss can be produced from the novel molding materials even under unfavorable processing conditions.
lo The novel molding materials may be processed by the conventional methods for thermoplastics, for example extrusion and injection molding, to give a great diYer-sity of moldings, eg. housings for household appliances, telephones, sheets, pipes and toys. The novel molding materials are also suitable for the production of colored moldings of the stated type, such colored articles being used particularly for housings of elec-trical appliances, for toys and in furniture.
- The parameters referred to in the description and in the Examples are determined as follows:
The mean particle diameter (d50 of the cumulative mass distribution) follows from measurements carried out with an analytical ultracentrifuge, using the method of W. Scholtan and H. Lange, Kolloid-Z.Polymere 250 (1972), 732 - 796. The grafting yield and hence the propor-tion of the graft copolymer B in the product obtained from the graft copolymerization reaction can be deter-mined by extracting the polymer with methyl ethyl ketone at 25C. The intrinsic viscosity is measured in an ~L16234.~
- 1~ - o.Z. Qo5~033940 0.5% strength solution in dimethylformamide, at 25C
(DIN 53,726).
The notched impact strength of the novel molding materials is determined, in accordance with DIN 53,45~, on injection-molded standard small bars at 23C and at _40C- The bars are injection-molded at 250C.
To test the gloss characteristics of the novel molding materials, sheets of size 50 x 40 x 2 mm are produced on an Arburg-Allrounder Type 200 injection molding machine at 230, 255 and 280C, with mold tem-peratures of 30 and 60C and injection times of 0.4 and 2 seconds. The gloss of these test specimens is deter~ined by reflectance measurements, using a Lange photometer. The standard used is a white blotting pa-per (~ 0 scale divisions) and a black glass mirror (~ 100 scale divisions).
The-relaxation time is determined by NMR measure-ments, using a Minispec P 20 NMR-spectrometer from Bruker Analytische Me~technik GmbH, Karlsruhe, at 2~C
- and 20 MHz. The drop in nuclear magnetization, ie.
the free induction decay, after applying a 90 pulse was observed. At room temperature, the measurements on the novel molding materials give a curve consisting o~ 2 components o~ high and low time constant respec-tively (spin-spin relaxation time T2) ~cf. R.A. Asink and G.L. Wilkies, Polymer Engineering and Science, 17 (lg77), 606 and T. Nishi, Rubber Chemical Technology 51 (1978), 1075]- The component with the io~ time c~n-11~i234~
_ 15 -stant corresponds to the molecularly immobile copolymer A and the component with the large time constant corres-ponds to the molecularly mobile elastomeric graft polymer bl. Since the signal of the styrene/acrylo-nitrile component has fallen completely to 0 after a time of 100 ~s, measured from the start of the 90 pulse, the time constant of the signal of the elastomeric poly-mer bl can be determined from the subsequent variation of the signal. For this purpose, the signal level S
lo is measured at times o~ 100 and 320 ~s, using an auxiliary analog computation unit. For the present purpose, the circuitry of this unit was modified so that the two 1ntegrators which were used for a determina-tion of S were identical with one anot'ner. T2 is calculated from the equation T2 = 220/ln (k.S(100)/S (320) assuming an exponential variation of the signal. k is a correction factor to allow for the influence of mag-netic inhomogeneity. In the present case, k was 0.9843. The NMR signal was measured in the diode position, in order to exclude interference due to mag-netic field fluctuations.
To measure the relaxation times of the elasto-meric polymer b~ and o~ the graft copolymer B, the stated polymers were each precipitated from the dis-persion by means of magnesium sulfate solution in the absence of oxygen, and were then filtered and dried for 16 hours at 60C under a pressure of 1 mm Hg.
To determine the relaxation times of the il~234~
- 16 - o.~. ooso/033s~0 insoluble component, the molding material (A + B, ~ith or without C) is extracted with methyl ethyl ketone at 23C. For this purpose, ~ g of the molding material are stirred for 8 hours in 135 ml of methyl ethyl ketone at 23C after which the mixture is left to stand for 12 hours at the same temperature, centrifuged for half an hour at 14,000 rpm, and decanted.
This procedure is repeated twice more. The resulting insoluble constituent is then dried for 16 lo hours at 60C under 1 mm Hg. Thereafter, the relaxa-tion time is determined.
The determination of the relaxation time of the molding material is carried out by drying a sample of the material for 7 hours at 70C und~r 1 mm Hg and then e~fecting the measurement.
The Examples which follow illustr~te the inven-tion. In the Examples, parts and percentages are by weight, unless stated otherwise.
Preparation of copolymer A
A copolymer containing 65 parts by weight of styrene and 35 partsby weight of acrylonitrile as co-polymerized units is prepared by continuous solution polymerization using a method as described, for example, in ~unststoff-Handbuch, Vieweg-Daumiller, Volume IV (polystyrene), Carl-Hanser Verlag, Munich 1969, page 124, lines 12 et seq. The copolymer has an intrinsic viscosity of 80.

1~i2~45 - 17 - 0.2. 0050/0339~0 Preparation of a graft copolvmer B
a) Preparation of the elastomeric polymer bl 48.0 kg of distilled water, 5.3 kg of butadiene, 0.256 kg of sodium stearate, 0.096 kg of potassium peroxydisulfate, 0.109 kg of sodium bicarbonate and 0.64 kg of terpinolenes are stirred for 0.17 hour at - 65C, and at a stirrer speed of 70 rpm, in a stirred ~ettle made from ~2A, equipped with a paddle stirrer, and having the following technical data External diameter of vessel x wall thickness ~mm] 600 x 12 Height of ~essel 705 Total height 1000 Stirrer diameter 300 Stirrer height 270 Distance of stirrer from bottom 60 Thickness of stirrer paddles lO
Baffle diameter 35 Distance of baffle from bottom 162 Distance of baffle from wall 98 Bottom curvature,~according to DIN 28011 Lid curvature, according to DIN 28012 26.7 kg of butadiene are then run in continuously over 5 hours. When the conversion reaches 80% by weight, based on butadiene, the polymerization is stopped by releasing the pressure. A polybutadiene latex in which the mean particle diameter (d50 of the cumulative mass distribution) is 0.06 ~m, is obtained. The elastomer has a relaxation time of 1.56 ms.

~i~3~
- 18 - o.Z. 0050/033940 b) Agglomeration and grafting 25.0 kg of the above polybutadiene latex are stirred for 1 hour, at 65C, with 2.0 k~ of distilled water and ~.4 kg of an emulsion, of 10% by weight solids content, cf a copolymer of 96 parts by weight of ethyl acrylate and 4 parts by weight of methacrylamide; this results in a polybutadiene latex having a mean particle diameter of 0.35 ~m (d50 value of the cumulative mass distribution). After having added 0.065 kg of sodium stearate, 0.017 kg of potassium peroxydisulfate and 2 kg of distilled water, 5.6 kg of a mixture of styrene and acrylonitrile in the weight ratio of 70:30 are introduced continuously in the course of 4 hours, at 75C. Polymerization is then continued for a further hour. The con~ersion, based on styrene/acrylonitrile, is ~irtually quantitative. The graft elastomer dispersion obtained is precipitated with magnesium sul-fate solution. A sample of the material is dried ~nd used to determine the relaxation time. The graft copolymer is separated off and washed with distilled water.
A granular mixture containing 42 parts by weight of graft copolymer B, 58 parts by weight of copolymer A
and 0.2 part by weight of a phenolic antioxidant (com-ponent C) is prepared on a compoundin~ extruder at 220 - 250C.
The characteristics of the elastomeric polymer bl, of the graft elastomer B and of the mold1ng material, as well as those of the insoluble constituent isolated -- 19 -- 0.2;. 0050/033~GO

from the molding material, are shown in Table 1, whilst Table 2 shows the gloss and supplementary data.

a) A polybutadien~ latex is prepared as described in Example 1, except that in place of terpinolenes 0.256 kg of tert.-dodecylmercaptan is added at the start of the reaction and 0.064 kg of tert.~dodecyl-mercaptan after a reaction time of 10 hours, and that the polymerization is stopped at a conversion of 96% by weight, based on butadiene employed.
b) 21.0 kg of the polybutadiene latex are stirred, after addition of 3.4 kg of an emulsion, of 10% by weight solids content, of a copolymer of 96 parts by weight of ethyl acry~at~ ~ and ~- parts by weight of methacrylamide, for 1 hour at 65C, giving a polybutadiene latex having a mean particle size of 0.35 ~m (d50 value of the cumulative mass distribution).
After adding 0.065 kg of sodium stearate, 0.017 kg of - potassium peroxydisulfate and 8.0 kg of distilled water, the grafting, sampling and working up are carried out as described in Example 1.
EXAMPLE ~
The procedure followed is as described in Example 2, except that 0.40 kg of tert.-dodecylmercaptan is added at the beginning of the reaction.

The procedure followed is as described in Example 1, except that instead of terpinolenes 0.064 kg ~lG2à4S
- 20 - o.z. Oo50/033940 of tert.-dodecylmercaptan is added at the beginning of the reaction.
COMPARATIVE EXPERI~ENTS
Comparative Exper~ment A
This corresponds to Example 4, except that the polymerization is terminated at a conversion of 96% by weight, instead of 80% by weight, based on butadiene, and that the agglomeration and grafting are carried out as described in Example 2.
Comparative Experiment B
This corresponds to Example 2, except that 28.8 kg of butadiene and ~.2 kg of styrene are employed to prepare the polybutadiene latex.
Comparative Experiment C
A polybutadiene latex having a mean particle size of 0.5 ~m is prepared as described in British Patent 859,080 and is then processed further as described in Example 2.
As may be seen from the data in Tables 1 and 2, the novel molding materials have good mechanical pro-perties coupled with a degree of gloss which is rela-tively independent of the processing conditions. In contrast, the molding materials prepared according to Comparative Experiments A, B and C at best show a good gloss, but coupled with a poor notched impact strength, in particular at -40C, or good impact strength, but then coupled with extremely poor gloss.

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermoplastic molding material comprising A) at least one copolymer comprising a hard phase and containing, as copolymerized units, a1) from 60 to 80% by weight of a monomer selected from the group consisting of styrene and .alpha.-methyl-styrene and mixtures thereof and a2) from 20 to 40% by weight of acrylonitrile, and B) at least one graft copolymer, in an amount of from 10 to 50% by weight based on A) +B), comprising b1) from 40 to 80% by weight, based on B), of an elastomeric polymer which contains not less than 93% by weight of butadiene as polymerized units and b2) from 60 to 20% by weight of grafts, forming a hard phase, formed from the monomers styrene and acryloni-trile in a weight ratio of from 80:20 to 65:35, the graft copolymer having been obtained by grafting the mixture of the monomers b2) onto the elastomeric polymer, wherein the graft copolymer B) is composed of particles which have a mean particle diameter of from 0.2 to 0.45 µm (d50 value of the cumulative mass distribution) and has a spin-spin relaxation time of 0.9 to 1.5 microseconds and the spin-spin relaxation time of the insoluble constituent isolated from a methyl ethyl ketone extraction of the molding material is from 0.7 to 1.5 microseconds.

2. A molding material as claimed in claim 1, wherein an emulsion graft copolymer is used as component B).

3. A molding material as claimed in claim 1, wherein a graft copolymer having a relaxation time of from 0.9 to 1.5 µs is used.

4. A molding material as claimed in claim 1,which further comprises effective amounts of conventional additives.

5. A molding produced from a molding material as claimed in claim 1.