GB1575920A - Process for the manufacture of impact resistant styrene polymers - Google Patents

Description

(54) PROCESS FOR THE MANUFACTURE OF IMPACT RESISTANT STYRENE POLYMERS (71) We, HOECHST AKTIENGESELLSCHAFT, a body corporate organised according to the laws of the Federal Republic of Germany, of 6230 Frankfurt/Main 80, Postfach 80 03 20, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention provides a process for preparing thermoplastic coporymers having a high toughness, a high hardness, good melt flow properties and a high surface gloss.

Graft copolymers of styrene and acrylonitrile on butadiene homo- and copolymers are known as ABS polymers ASS polymers prepared by graft copolymerization of styrene and acryfonitrile on ethylene,7propylenettertiary component rubbers are also known and have an essentially improved weather resistance.

Such graft copolymers may be prepared by bulk or by bulkAuspension polymerization. These processes, in which a solution of the rubber in monomeric styrene or a styrene/acrylonitrile mixture is partly porymerized in bulk and is further polymerized in bulk or in suspension until the polymerization is complete, normally yield impact resistant polystyrene or impact resistant styrene/acrylonitrile copolymers having a good toughness, good flow properties and a good hardness. Injection moulded articles prepared from these products, however, have only a yery poor surface gloss.

For this~reason, ABS polymers intended to have a high surface gloss are most frequently prepared by emulsion polymerization. In this process both the rubber and the graft copolymer of styrene/acrylonitrile on the rubber are prepared in aqueous emulsion. The ABS polymers thus obtained are characterized by an especially high surface gloss of the miection moulded articles prepared therefrom as compared with those prepared by bulk suspension. On the other hand, the emulsion process is more expensive and, consequently, less profitable than the bulk and/or suspension processes, because the waste water obtained must be specially treated to avoid environmental pollution.

Three processes have become known hitherto for partially overcoming the difficulties involved in the bulk/suspension process. The surface gloss may be improved: (1) by using extremely high shearing forces in the prepolymerization (cf. British Patent No. 1,383,017); (2) by adding nonpolar hydrocarbons as solvents (cf. U.S. Published Application No. B 469,468; U.S. Patent No. 3,538,190); and (3) by adding separately prepared graft copolymers of styrene/acrylonitrile on ethylene/ propylene/tertiary component rubber or on polybutadiene to act as oil-in-oil emulsifiers (cf. U.S. Patent No. 3,538,192).

It is further known that polymer melts are subjected to shearing in, for example extruders, which may even cause partial breaking of the polymer molecules. Advantage is taken of this fact especially in the degradation process of melts of high molecular weight polyethylene. It is also known that polymers may be cross-linked in the melt by the addition of appropriate initiators.

The present invention provides a process for preparing impact resistant copoly mers exhibiting high gloss by radical bulk polymerization or bulk/suspension polymerization of (a) from 98 to 70 weight %, preferably from 92 to 75 weight %, of a mixture of (aa) from 90 to 60 weight %, preferably from 90 to 70 weight %, especially from 80 to 70 weight %, of styrene and/or of at least one styrene derivative, and (ab) from 10 to 40 weight %, preferably from 10 to 30 weight %, especially from 20 to 30 weight %, of acrylonitrile and/or of at least one different copolymerizable derivative of acrylic acid, with (b) from 2 to 30 weight %, preferably from 8 to 25 weight %, of an ethylene-pro pylene-tertiary component rubber (EPTR), the quantities of (aa) and (ab) being calculated on the total quantity of (aa) + (ab) and the quantities of (a) and (b) being calculated on the total quantity of (a) + (b); submitting the resulting copolymer to shearing extrusion until the rubber particles have an average size of below 1 ,um; and cross-linking the resulting rubber particles containing from 0.02 to 0.5 weight %, preferably from 0.08 to 0.3 weight %, calculated on the total monomers and rubber, of a cross-linking initiator, under a pressure of from 10 to 700 mm Hg.

Instead of styrene, monomeric component (aa) may be a styrene derivative such as a-methyl-styrene or a styrene methylated in the aromatic nucleus (for example o- or p-vinyl toluene or a vinyl xylene) or a styrene halogenated in the aromatic nucleus (for example o- or p-chloro or bromostyrene) or vinyl cyclohexane or a methylated or halogenated derivative of vinyl cyclohexane, or a mixture of styrene and one or more derivatives of styrene, or a mixture of two or more derivatives of styrene, preferably a mixture of from 95 to 60 weight C/c styrene and from 5 to 40 weight % of a a-methyl-styrene.

Instead of acrylonitrile, monomeric component (ab) may be a different copolymerizable acrylic acid derivative, such as methacrylonitrile or an ester of acrylic acid, of rnethacryLic acid, of itaconic acid (carboxymethylacrylic acid), of inaleic add(carb- oxyacrylic acid) or of fumaric acid with a lower aliphatic alcohol (for example methanol, ethanol, isopropanol, butanol, isobutanol, hexanol, octanol, isooctanol or 2ethylhexanol) alone or in combination or with acrylonitrile.

Mixtures of from 20 to 30 weight % of acrylonitrile and from 80 to 70 weight % of styrene are especially advantageous to obtain the desired resistance to solvents, tensile strength and crazing and heat resistance, and are therefore preferred.

Suitable ethylene/propylene/tertiary component rubbers are those obtained by polymerization of from 69.5 to 30 weight % of ethylene, from 30 to 69.5 weight % of propylene and from 0.5 to 1S, preferably from 3 to 12, weight % of a non-conjugated diene having at least 5 carbon atoms, such as 3-ethylidene-norbornene-2, di-cyclopentadiene, 2,2,1-bi-cycloheptadiene and 1,4-hexadiene as the tertiary component.

It is preferred first to dissolve the rubber in the non-polar monomer(s) (aa), the addition of conventional nonpolar substances for example white oils (mixtures of aliphatic hydrocarbons having a boiling point of from 100 to 3000 C) being also possible. After heating and addition of the polar monomer(s) (ab), a solution of the EPT rubber in the monomer mixture is present when the polymerization temperature is attained.

The radical polymerization of the monomers is carried out in known manner either thermally or with the use of one or several polymerization initiators soluble in the monomers, for example peroxy compounds such as t-butyl perbenzoate, t-butyl peracetate, dibenzoyl peroxide, t-butyl peroctoate, dilauroyl peroxide or nitrogen compounds yielding radicals upon decomposition such as azodiisobutyronitrile. These polymerization initiators are used in the usual amounts of from about 0.OS to 1 weight %, preferably from 0.1 to 0.4 weight %, calculated on the total monomers and EPT rubber.

Polymerization is carried out by bulk or bulk/suspension processes. Both processes are carried out as bulk polymerization while stirring until a phase inversion can be observed. In the case of the bulk/suspension process polymerization is continued and terminated as a suspension polymerization after suspension in water of the reaction mixture from the bulk polymerization, while in the case of a bulk process the polymerization is continued and terminated as a bulk polymerization.

The bulk/suspension polymerization is usually carried out discontinuously and the bulk polymerization is carried out continuously, although this distinction does not influence the properties of the products formed.

The suspension polymerization is carried out in the presence of from 0.OS to 0.4 weight % of one or more known suspension stabilizers such as water-soluble cellulose ether, gelatine, polyvinyl alcohol, partially saponified polyvinyl acetate or tricalcium phosphate and, optionally, in the presence of one or more complex-forming substances such as sodium ethylenediaminetetraacetate.

The desired degree of polymerization (molecuLar weight) is obtained by means of regulators known for this purpose in styrene polymerization, such as dimeric amethyl-styrenes in a concentration of from about 0.1 to 1 weight % or with mercaptans such as n- or t-dodecyl mercaptan in an amount of from about 0.01 to 0.5 weight %.

The polymerization initiators as well as the molecular weight regulators may be added at the same time or subsequently in measured amounts as the polymerization proceeds in the pre-polymerization (first step/bulk polymerization) and/or in the following second polymerization step (suspension polymerization).

The cross-linking initiator to be used according to the present invention is added most advantageously either prior to or at any time during the course of polymerization.

The essential function of the cross-linking initiator is to initiate the cross-linking of the sheared rubber particles. The initiator may decompose to a minor extent during the course of the polymerization and influence the latter. The initiator is preferably added in an amount of from about 0.06 to 0.6 weight % (calculated on the total monomers and rubber); consideration must be given, however, to the fact that depending on the polymerization temperatures and shearing temperatures, on the moment of addition and on its half life, a more or less significant amount of the cross-linking initiator will be decomposed before the beginning of the cross-linking. The selection of the initiator with respect to its half life, the quantity and the moment of addition and the polymerization and shearing temperature are to be adjusted to each other such that after termination of the shearing the initiator will be present in the polymer in a sufficient amount of from about 0.02 to 0.5 weight %, preferably of from 0.08 to 0.3 weight %, calculated on the total monomers and rubber, so as to guarantee cross-linking of the polymer.

The cross-linking initiator is preferably an organic peroxide having a half life of at least 5 hours at 1200 C.

There may be used, for example, the following cross-linking initiators: dicumyl peroxide, 2,5 - di - (t - butylperoxy) - 2,5 - dimethyl hexane, 1,4 - bis - (2 butylperoxy - isopropyl) - benzene, 3 - t - butylperoxy - 3 - phenyl - phthalide, tbutylhydroperoxide, cumene - hydroperoxide, di - t - butyl peroxide, 3,3,6,6,9,9 -hexamethyl - cyclo - 1,2,4,5 - tetraoxanonane, di - t - amylperoxideS t - butyl - 1,1,3,3 tetramethylbutyl peroxide, bis - (t - butylperoxy) - diphenyl - silane, t - amylhydro- peroxide, bis - (t - butylperoxy) dimethylsilane, t - butylperoxy - trimethyl - silane, tris - (t - butylperoxy) - vinylsilane, 2,4 - pentadione peroxide, 2,5 - dimethyl - 2,5bis - (hydroperoxy) - hexane 2,3 - dimethyl - 2 - t - butylperoxy -3 - hydroperoxy hexane, 2,5 - dimethyr - 2,3 - dtOt - butylperoxy) - heiie - (3) and ,a' - bis - (tbutylperoxy) - diisopropylbenzene.

Di-t-butyl peroxide is preferably used. This peroxide, owing to its relatively long half life, may be added prior to or during the course of the prepolymerization (when the polymerization is carried out in two steps), without running the risk of excessive decomposition during the polymerization and the following shearing in an extruder. The shorter the half life of the cross-linking initiators the larger must be the quantity added and/or the later must the addition be effected at the given poly- merization and shearing temperatures. These relations may be readily estimated and be determined quantitatively by a few control tests.

The statement that the cross-linking initiator may be added during the course of the polymerization is to be understood to mean that there must be still a sufficiently long period of time for homogeneous distribution of the cross-linking initiator in the polymer prior to the end of the polymerization. It is quite evident that such homogeneous distribution may not be assured if the cross-linking initiator is not added until just before termination of the polymerization. Therefore the cross-linking initiator should be added generally not later than the time at which about 80% conversion has been obtained. This is also the reason why peroxides having a half life of at least 5 hours at 1200 C, permitting early addition are preferably used for the process of the present invention.

According to a preferred feature of the process of the present invention there is added, in addition to the cross-linking initiator, from 0.02 to 0.5, preferably from 0.05 to 0.3 weight %, of a phenolic heat stabilizer, for example 2,6 - di - t - butyl - 4methylphenol, 4 - hydroxy - 3,5 - di - t - butyl - phenyl propionic acid octadecyl ester, tetra - (4 - hydroxy - 3,5 - di - t - butylphenyl propionic acid) - pentraerythrite ester, bis - (4 - hydroxy - 3,3 - di - t - butyiphenyl) - methane, 1,4 - bis - (4'hydroxy - 3' - butyl - 6' - methylphenyl) - butane, bis - 4 - hydroxy - 3 - t - butyl6 - methylphenyl) - sulfide, 1,1,3 - tris - (4 - hydroxy - 3 - t - butyl - 6 - methylphenyl) - butane, 4 - hydroxy - 3,5 - di - t - butyl - anisole or bis - [3,3 - bis(4'hydroxy - 3' - t - butylphenyl)butanic acid] glycol ester.

The resulting polymer substantially~consists of a random copolymer of (aa) and (ab) units, of a graft copolymer of (aa) and (ab) units on (b) and of practically non-cross-linked EPT rubber. The latter is present in the form of relatively coarse particles having an average size of from 5 to 500 m imbedded in the matrix of the random copolymer. The polymer additionally contains from 0.01 to 5% of residual monomer.

The shearing extrusion is advantageously carried out in one or more, preferably in from one to four, shearing sections (where the extruder screw(s) is (are) fitted with shearing elements) of an extruder with one or more screws, in such a way that the material preferably has a temperature of from 150 to 350" C and that the average residence time of the material in the shearing zone(s) preferably varies from 5 seconds to 5 minutes, more preferably from 10 to 60 seconds. The temperature of the material is influenced by external heating, by the geometric shape of the shearing section(s) and by the circuinferential speed of the screw(s), while the average residence time of the material in the shearing zone(s) is determined by the geometric measurements of the shearing zone(s) and by the throughput rate. The essential point is that shearing is continued until the rubber particles have an average size of below 1 ,am, preferably of below 0.6 ssm.

In contrast to known processes, in which relatively large rubber-particles are cross-linked, the process of the present invention produces cross-linked rubber-particles substantially all and preferably more than 98% of which have been comminuted by shearing. Nevertheless, the cross-linking reaction may start during comminution while shearing is taking place, although shearing must not be interrupted by crosslinking. However, the cross-linking which determines the morphology takes place after leaving the last shearing zone of the extruder.

The sheared rubber particles may be cross-linked in the extruder in which shearing is carried out. However, cross-linking may be effected as well in any subsequent container in which the motion of the material is not caused by mechanical devices. It is also possible for cross-linking to begin in the extruder and to continue in a subsequent container. Suitable subsequent containers are especially pipes, static mixers and reaction towers. Especiallv uniform products are obtained when static mixers are used, as compared to those obtained by the use of reaction pipes or reaction towers.

In order to be able to maintain a given cross-linking temperature, the subsequent containers are heated externally. Similarly to the extruder, the product leaves the cross-linking container through a perforated plate or a sieve plate and is then granulated in known manner.

The cross-linking temperature is preferably from 150 to two400" C, more preferably from 200 to 350 C. The cross-linking time which determines the dimensions of the cross-linking space in the extruder or in the subsequent container, is advantageously from 10 seconds to 60 seconds. The chosen temperature will be relatively high if only a short cross-linking time can be employed for example in an extruder; on the other hand, if the purpose is to cross-link the rubber as gently as possible at a low temperature, a relatively long cross-linking time must be chosen. Moreover, the choice of cross-linking temperature and cross-linking time must also take into consideration the chosen content of cross-linking initiator.

The cross-linking has attained a sufficient degree when the rubber particles no longer exhibit any substantial deformation under shearing stress on processing machines.

This factor, as well as the rubber particle size, can be monitored electron microscopically by examination of thin slices submitted to thorough treatment with osmium tetroxide.

In the process of the present invention, cross-linking is carried out under reduced pressure, for example on a so-called degassing extruder. In the cross-linking section a reduced pressure of from 10 to 700 mm Hg, preferably from 30 to 400 mm Hg, is created via a common degassing socket and the product flsfieed from volatile components. Degassing may also be carried out in the metering zones between two shearing zones.

The shearing extrusion may be effected in the presence of conventional plastics additives, for example heat stabilizers, light stabilizers, anti-static agents, lubricants and colour pigments. The admixture of these materials being usually desirable per se, the shearing extrusion does not mean an additional processing step. In the case of bulk/suspension polymerization it is most useful to blend the granular polymer with the additives after drying in known manner, while in the case of bulk polymerization the feed of a concentrated additive into the extruder is preferably effected by means of a side extruder.

Surprisingly, the presence of lubricants does not impair shearing and the presence of stabilizers does not interfere with cross-linking.

The process has the advantage that the residual monomer content of the polymer decreases during shearing extrusion and the cross-linking operation. This permits either the polymerization time to be reduced and/or the residual monomer content to be maintained lower than can be achieved with known processes.

Surprisingly, when processing in accordance with the present invention, products are obtained which are characterized by an excellent combination of toughness, hardness and gloss which conventional bulk/suspension or bulk polymerization cannot produce.

An important advantage of the process according to the present invention is that the processing steps which had been required in the past by the known processes for preparing similar products described above, such as the separate manufacture of graft copolymers or the application of high shearing forces during prepolymerization, are no longer necessary.

The products manufactured according to the process of the present invention are suitable for the production of all shaped articles which can be made of ABS polymers. The high surface gloss and the excellent weather stability recommend these products for the manufacture of for example, casings for radios, television sets and lawn mowers, garden furniture, plates and dishes for use in camping and boat hulls.

The following Examples illustrate the invention: EXAMPLES.

EXAMPLE 1.

28.4 kg of EPT rubber (composition: about 50 weight % ethylene, about 40 weight % propylene and 10 weight % 5 - ethylidene-norbomene - 2 - units; Mooney viscosity=90) in the form of small pieces were dissolved in 102.8 kg of styrene and 3.29 kg of white oil (boiling point ranging from 100 to 3000 C) over 4 hours at 300 C in a polymerization apparatus comprising a 300 1 pressure vessel for bulk polymerization (prepolymerization) which was equipped with an impeller agitator, a baffle, a reflux cooler with control valve, a bottom valve and with external cooling as well - as heating means. Subsequently, there were added 33.1 kg of acrylonitrile, 329 g of di-t-butyl peroxide as cross-linking initiator and 329 g of dimeric a-methyl styrene. During this latter operation the rubber precipitated in the form of a compact swollen gel. The contents of the vessel were heated to llS" C within 20 minutes, and the EPT rubber gel redissolved. Agitation at this temperature was continued while effecting external and refiux cooling by operating the control valve to the reflux cooler until phase inversion of the reaction mixture occurred, at a solids content of about 35%. The vessel contents were then cooled within 15 minutes to 650 C by means of external cooling cooling by expansion via the reflux cooler. Sub sequen;rly a mixture of 765 g of a 7S6/ water-containing dibenzoyl peroxide, and of 164 g of 2,6-di-t-butyl-4-methylphenol and 164 g of octadecyl 4-hydroxy-3,3-di-t- butyiphenyl-propionate as stabilizers, and of 765 g of styrene was added while stirring the prepolymer mixture thoroughly. The contents of the prepolymerization vessel (pvessel) were then forced through the bottom valve and the feed-in pipe into the 700 1 suspension polymerization pressure vessel (vessel) equipped with an impeller agitator, a baffle, a bottom valve, a feed pipe from the prepolymerization vessel and with external cooling as well as heating means, in which a solution consisting of 255 g of polyvinyl alcohol (having a saponification degree of 88% and a solution viscosity of 40 centpoises, measured on a 4 weight % aqueous solution at 20 C), of 5 g of sodium ethylenediamine-tetraacetate, of 5 g of sodium pyrophosphate and 225 1 of water was stirred - vigorously. The resulting suspension was agitated successively for one hour at 800 C, for one hour at 850 C, for one hour at 900 C and for three hours at 100" C, after which period a conversion rate of 98.9% was obtained. The suspension was then discharged through the bottom valve of the s-vessel onto a filter and after separation of the liquid, the polymer was washed twice with water and dried in an air current at 800 C for three hours. The product still contained about 92% of the initial cross-linking initiator.

The shearing extrusion and the cross-linking in the presence of the crass-linking initiator were carried out on a commercially available double screw extruder having the trade name of ZSK 53/v (a product of Messrs. Werner & Pfleiderer, W. Germany). The two mating screws, each having two shearing zones, separated by a metering zone, had a diameter of 53 mm and a length of 36.5 D, were driven by a 32 kW-motor at 270 rpm. The casing was divided in seven segments, which could be independently heated electrically or cooled with water under the control of a regulator. The extruder was additionally equipped with a degassing socket located about 60 cm upstream of the extruder outlet and in which a vacuum pump produced a pressure of 0.OS bar. The 10 strands leaving the extrsion head were cut to chips in a strand granulator after having been cooled in water. The average residence times of the material in the shearing zones was about 8 seconds and in the cross-linking zone (downstream of the second shearing zone) was about 15 seconds. The shearing temperature (temperature of the material during shearing) was 2700 C measured 7 cm downstream of the first shearing zone and the cross-linking temperature (temperature of the material during cross-linking) was 2900 C, measured at the extrusion head. The average residence times in the shearing and cross-linking zones respectively of the extruder were determined approximately on the basis of the average residence time of the copolymer in the extruder as a whole and of the length of the shearing and cross-linking zones respectively. The product characteristics are set out in Table 1.

EXAMPLE 2.

Example 1 was repeated with the following modifications: Prior to prepolymerization 165 g of di-t-butyl-peroxide were added to the EPT rubber solution instead of 329 g, prepolymerization was carried out at a temperature of 1200 C instead of llSo C until a solids content of about 35% was achieved and after having cooled the product to 650 C an additional quantity of 820 g of tris-(t-butylperoxy)-inylsilane (50% moisture) was added as a second cross-linking initiator. The shearing extrusion and the cross-linking were carried out in the manner described in Example 1. The properties of the product are set out in Table 1.

EXAMPLES 3 to 6.

Example 1 was repeated with the modifications to the prepolymerization as stated in Table 2. The n-dodecyl-mercaptan and a-methyl-styrene mentioned therein were added to the rubber solution prior to the prepolymerization. The properties of the products are set out in Table 1.

TABLE 2 Modifications of Examples 3 to 6 as compared to Example 1

Example 3 4 5 6 Dimeric a-Methylstyrene kg 0.658 0.329 0.670 0 n-Dodecylmercaptan kg 0.033 0 0.034 0 White Oil kg 3.29 0 3.29 3.29 EPT Rubber kg 28.4 28.4 22.0 22.0 aMethylstyrene kg 0 0 0 38.4 Styrene kg 102.8 102.8 109.5 71.1 TABLE 1 Properties of the products of Examples 1 to 6

Example 1 2 Average size of EPT rubber particles (CLm) 0.4 0.2 Impact strength % no breakage 60 40 (DIN 53 453) at 230C (kg cm/cm2) 72 63 at -400C (kg cm/cm2) 60 57 Notched impact strength (DIN 53 453) at 230C (kg cm/cm2) 20.9 9.0 Gloss (ASTM D-523-67) + (So) 72 95 Gloss (according to Lange) ++ (SO) 89 > 100 Ball indentation hardness (DIN 5 TABLE 1 (Continued)

Example 3 4 Average size of EPT rubber particles (d 0.2 0.1 Impact strength % no breakage 30 100 (DIN 53 453) at 230C (kg cm/cm2) 63 at -400C (kg cm/cm2) 53 70 Notched impact strength (DIN 53 453) at 230C (kg em/em2) 13.6 9.5 Gloss (ASTM D-523-67) + (SO) 80 90 Gloss (according to Lange) ++ (%) 100 > 100 Ball indentation hardness (DIN 53 456) (kg /cm) 988 1000 Melt index MFI 220/10 (g/lO') (DIN 53 735) 13.4 13.4 Shear stability of EPT rubber particles upon re-granulation yes yes + at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) TABLE 1 (Continued)

Example 5 6 Average size of EPT rubber particles (d 0.3 0.1 Impact strength % no breakage 20 0 (DIN 53 453) at 230C (kg cm/cm2) 61 67 at -400C (kg cm/cm2) 63 42 Notched impact strength (DIN 53 435) at 230C (kg cm/cm2) 10.1 14.1 Gloss (ASTM D-523-67)+ ( ) 83 80 Gloss (according to Lange) ++ (NO) 91 > 100 Ball indentation hardness (DIN 53 456) (kg cm/cm2) 1022 1013 Melt index MFI 220/10 (g/10') (DIN 53 735) 23.8 22.7 Shear stability of EPT rubber particles upon re-granulation yes yes + at an angle of incidence of 600 referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) EXAMPLES 7 to 13.

Polymerizations were carried out according to Example 1, and the shearing extrusion and the cross-linking of the polymer were effected on the double-screw extruder described in Example 1. The screws employed here differed by the number of shearing zones, and further modifications related to temperatures and residence times for the shearing and cross-linking. The details of these modifications are set out in Table 3. The properties of the products obtained are set out in Table 4.

TABLE 3 Shearing and cross-linking conditions of Examples 7 to 13

Example 7 8 9 10 11 12 13 Number of shearing zones 1 1 1 1 4 1 1 Shearing temperature C (after 1st shearing. zone) 160 210 240 160 260 200 320 Average residence time (seconds) in shearing zones 8 12 6 10 20 10 15 Cross-linking temperature OC 285 285 345 285 275 240 300 Average residence time (seconds) in cross linking zone 60 55 25 50 15 20 20 TABLE 4 Properties of products of Examples 7 to 13

Example 7 8 Average size of EPT-rubber particles ({ 0.2 0.2 Impact strength % no breakage 60 100 (DIN 53 453) at 230C (kg cm/cm2) 63 at -400C (kg cm/cm2) 81 67 Notched impact strength (DIN 54 453) at 23 C (kg cm/cm) 24.9 16 Gloss (ASTM D-523-67)+ (%) 86 94 Gloss (according to Lange) ++ ( 10) 100 95 Ball indentation hardness (DIN 53 456) (kg cm/cm2) 1020 1025 Melt index MFI 220/10 (g/lO') 9.9 11.3 (DIN 53 735) Shear stability of EPT-rubber particles upon re-granulation yes yes + at an angle of.incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450).

TABLE 4 (Continued)

Example 9 10 Average size of EPT-rubber particles ( m) 0.3 0.1 Impact strength % no breakage 60 100 (DIN 53 453) at 230C (kg cm/cm2) 74 ?-406C (kg cm/cm2) 53 71 Notched impact strength (DIN 53 453) at 230C (kg cm/cm2) 18.1 17 Gloss (ASTM D-52367) + (%) 93 96 Gloss (according to Lange) ++ 96 > 100 Ball indentation hardness (DIN 53 436) (kg cm/cm) 1020 1005 Melt index MFI 220/10 (g/10') (DIN 53 735) 13.9 10.7 Shear stability of EPT-rubber particles upon re-granulation yes yes + at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) TABLE 4 (Continued)

Example 11 12 13 Average size of EPT-rubber particles (un) 0.2 0.3 0.2 Impact strength % no breakage 80 100 70 (DIN 53 453) at 230C (kg cm/cm2) 84 - 68 at -400C (kg cm/cm2) 58 77 66 Notched impact strength (DIN 53 453) at 230C (kg cm/cm2) 10.8 20.2 19 Gloss (ASTM D-523-67) + (gO) 92 79 88 Gloss (according to Lange) ++ (%) > 100 87 98 Ball indentation hardness (DIN 53 456) (kg /cm2) 959 1010 990 Melt index MFI 220/10 (g /10' (DIN 53 7351 10.7 4.2 8.8 Shear stability of EPT-rubber particles upon re-granulation yes yes yes + at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) EXAMPLES 14 to 16.

The polymerizations were carried out according to Example 1. The polymers obtained were blended in a common Henschel-mixing device for pulverulent sub stances, with the following additives: Example 14: 2.0% of a commercial titanium dioxide, dispersable in plastics and made water-repellent Example 15: 0.3% of 2,6-di-t-butyl-4-methylphenol as heat stabilizer Example 16: 0.3% of 2.6-di-t-butyl-4-methylphenol as heat stabilizer and 0.15% of N-2-(2'-hydroxy-5'-t-butyl-phenyl)-benzotriazole as light stabilizer.

The shearing extrusion and the cross-linking of the mixtures were carried out as described in Example 9. The properties of the products are set out in Table 5.

EXAMPLE 17.

The polymerization was carried out in accordance with Example 1. Shearing extrusion and cross-linking were carried out in a double-screw extruder (20 D manufactured by Paul Leistritz, Niirnberg, W. Germany) with a subsequent static mixing tube, under a vacuum-pump pressure of 0.05 bar. The screws had a 34 mm diameter and were driven by a 4 kW motor at 70 rpm. The shearing zone was located next to the head of the screw, so that the cross-linking operation took place substantially in the mixing tube. The static mixing tube had an inside diameter of 37.5 mm and a length of 1800 mm and could be heated electrically from the outside in the same way as the extruder. The shearing temperature (temperature of the material) was 1800 C, measured 5 cm downstream of the shearing zone of the screw, and the crosslinking temperature (temperature of the material) was 2300 C, measured at the outlet nozzle. The average residance times were 14 seconds in the shearing zone and about 20 minutes in the static mixing tube. The properties of the product are set out in Table 5.

EXAMPLE 18.

Example 17 was repeated under modified cross-linking conditions but under the same pressure. Screws were employed the shearing zone of which was located in the middle of the screw. The extruder segments which followed the shearing zone, as well as the heating segments of the static mixer, were adjusted to 300 C, so that a cross-linking temperature of 305" C was attained, measured at the head nozzle of the mixing tube. The average residence time in the total cross-linking zone of the extruder and of the mixing tube was 12 minutes. The properties of the product are set out in Table .5.

EXAMPLE 19.

Example 17 was repeated but with the static mixing tube replaced by a heated tube without mixing elements. This tube had a length of 1200 mm and an inside diameter of 30 mm. The polymer was processed in the same manner as in Example 3 prior to extrusion. The cross-linking temperature was 2800 C and the average residence time in the tube was about 5 minutes. The properties of the product are set out in Table 5.

TABLE 5

Example 14 15 16 Colour white yellowish yellowish Improved heat stability no yes yes Improved light stability no yes yes Impact strength (DIN 53 453) at 230C (kg cm/cm2) 75- 83 63 at -400C (kg cm/cm2) 71 76 86 Notched impact strength (DIN 53 453) at 230C (kg cm/cm2) 8.8 23.7 22.3 Gloss (ASTM D523-67)+ (%) 90 92 88 Gloss (according to Lange) ++ (%) 94 90 93 Ball indentation hardness (DIN 53 456) (kg/cm2) 1030 1020 1010 Melt index MFI 220/10 (g/10') 9.5 9.6 9.7 (DIN 53 735) Shear stability of EPT-rubber particles upon re-granulation yes yes yes + at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) TABLE 5 (Continued)

Example 17 18 19 Impact strength (DIN 53 453) at 230C (kg cm/cm2) 73 81 65 at 400C (kg cm/cm2) 68 70 62 Notched impact strength (DIN 53 453) at 230C (kg cm/cm2) 16 11.4 9.0 Gloss (ASTM D-52367) + ( tO) 89 81 85 Gloss (according to Lange) ++ (No) 85 91 88 Ball indentation hardness (DIN 53 456) (kg /cm2) 1020 1030 990 Melt index MFI 220/10 (g/10') (DIN 53 735) 7.2 5.9 16.5 Shear stability of PT-rubber particles upon re-granulation yes yes yes + at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450C) COMPARATIVE EXAMPLES.

COMPARATIVE EXAMPLE 1.

Polymerization was carried out as described in Example 1, but was not followed by any shearing extrusion or cross-linking operations. The properties of the product are set out in Table 6.

COMPARATIVE EXAMPLE 2.

Polymerization was carried out as described in Example 1. However, prior to discharging the suspension onto the filter, the EPT rubber was cross-linked by stirring the suspension for five hours at 140 C. Subsequently, filtering and drying were carried out as described in Example 1. The shearing extrusion step was omitted. The pro perties of the product are set out in Table 6.

COMPARATIVE EXAMPLE 3.

Polymerization was carried out as described in Example 1. The polymer was submitted to shear extrusion and cross-linking on a laboratory scale extruder (manu factured by Maschinenfabrik Alpine, Augsburg, W. Germany, and available under the denomination HS 35) equipped with a shearing zone located next to the screw head, the extruder having been connected to the static mixing device described in Example 17. The shearing temperature was 1900 C, measured immediately downstream of the shearing zone at the static mixer inlet, the average residence time in the shearing zone being from 1 to 2 seconds. The cross-linking temperature was 2300 C measured at the outlet nozzle of the mixing tube, and the average residence time during the cross-linking operation was about 20 minutes. The properties of the pro' duct are set out in Table 6 COMPARATIVE EXAMPLE 4.

The procedure described in Example 7 was repeated except that the screws in the shearing zones shortened by 2/3 of their length. The average residence time in thd shearing zone was 2.5 seconds, the shearing temperature was 2000 C, the cross-linking temperature 245 C and the average residence time in the cross-linking zone was 3q seconds. The properties of the product are set out in Table 6.

TABLE 6 Description of the products of comparative Examples 1 to 4

Comparative Example 1 2 Average size of EPT-rubber particles ( 15 5 Impact strength (DIN 53 453) at 230C (kg cm/cm2) 51 42 at -400C (kg cm/cm2) 25 22 Notched impact strength (DIN 53 453) at 23 C (kg cm/cm) 7.7 7.4 Gloss (ASTM D-523-67) + (%) 49 Gloss (according to Lange) ++ (No) 46 35 Ball indentation hardness (DIN 53 456) (kg/cm2) 742 850 Melt index MFI 220/10 (g/10') (DIN 53 735) 2.0 3.2 Shear stability of EPT-rubber particles upon re-granulation no yes -+ at an angle of incidence of 60 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) TABLE 6 (Continued)

Comparative Example 3 4 Average size of EPT-rubber particles (pm) 4 2.5 Impact strength (DIN 53 453) at 230C (kg cm/cm2) 75 68 at -400C (kg cm/cm2) 51 65 Notched impact strength (DIN -53 453) at 230C (kg cm/cm2) 8.0 12.3 Gloss (ASTM D-523-67) F (%) 48 52 Gloss (according to Lange) ++ (NO) 53 58 Ball indentation hardness (DIN 53 456) (kg/cm2) 980 1020 Melt index MFI 220/10 (g/10') - 8.1 (DIN 53 735) Shear stability of EPT-rubber particles upon re-granulation yes yes

+ at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) WHAT WE CLAIM IS: 1. A process for the manufacture of an impact resistant copolymer which com prises submitting to radical bulk polymerization or bulk/suspension polymerization (a) from 98 to 70 weight % of a mixture of (aa) from 90 to 60 weight % of styrene and/or at least one styrene derivative and (ab) from 10 to 40 weight % of acrylonitrile and/or at least one other copolymeri- zable derivative of acrylic acid, with (b) from 2 to 30 weight % of an ethylene-propylene-tertiary component rubber (EPTR), the quantities of (aa) and (ab) being calculated on the total quantity of (aa) + (ab) and the quantities of (a) and (b) being calculated on the total quantity of (a) + (b); submitting the resulting copolymer to shearing extrusion until the rubber particles have an average size of below 1 ,um; and cross-linking the resulting rubber particles containing from 0.02 to 0.5 weight %, calculated on the total monomers and rubber, of a cross-linking initiator, under a pressure of from 10 to 7000 mm Hg.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   TABLE 6 (Continued)

   Comparative Example 3 4 Average size of EPT-rubber particles (pm) 4 2.5 Impact strength (DIN 53 453) at 230C (kg cm/cm2) 75 68 at -400C (kg cm/cm2) 51 65 Notched impact strength (DIN -53 453) at 230C (kg cm/cm2) 8.0 12.3 Gloss (ASTM D-523-67) F (%) 48 52 Gloss (according to Lange) ++ (NO) 53 58 Ball indentation hardness (DIN 53 456) (kg/cm2) 980 1020 Melt index MFI 220/10 (g/10') - 8.1 (DIN 53 735) Shear stability of EPT-rubber particles upon re-granulation yes yes

   + at an angle of incidence of 600 ++ referring to a black glass standard according to Bruno Lange; the measurements were carried out on a Lange-gloss measuring apparatus (450) WHAT WE CLAIM IS: 1. A process for the manufacture of an impact resistant copolymer which com prises submitting to radical bulk polymerization or bulk/suspension polymerization (a) from 98 to 70 weight % of a mixture of (aa) from 90 to 60 weight % of styrene and/or at least one styrene derivative and (ab) from 10 to 40 weight % of acrylonitrile and/or at least one other copolymeri- zable derivative of acrylic acid, with (b) from 2 to 30 weight % of an ethylene-propylene-tertiary component rubber (EPTR), the quantities of (aa) and (ab) being calculated on the total quantity of (aa) + (ab) and the quantities of (a) and (b) being calculated on the total quantity of (a) + (b); submitting the resulting copolymer to shearing extrusion until the rubber particles have an average size of below 1 ,um; and cross-linking the resulting rubber particles containing from 0.02 to 0.5 weight %, calculated on the total monomers and rubber, of a cross-linking initiator, under a pressure of from 10 to 7000 mm Hg.
2. 2. A process according to claim 1, wherein the cross-linking initiator is an organic peroxide having a half life of at least 5 hours at 1200 C.
3. 3. A process according to claim 1 or claim 2, wherein the copolymer to be sheared contains from 0.02 to 0.5 weight % of a phenolic lieat stabilizer.
4. 4. A process according to any one of claims 1 to 3, wherein shearing is carried out at a temperature of from 1500 to 3500 C.
5. 5. A process according to any one of claims 1 to 4, wherein the residence time of the copolymer in the shearing zone is from 5 seconds to 5 minutes.
6. 6. A process according to any one of claims 1 to 5, wherein cross-linking of the rubber particles is carried out at a temperature of from 150 to 4000 C.
7. 7. A process according to any one of claims 1 to 6, wherein the average residence time of the copolymer during cross-linking is from 10 seconds to 60 minutes.
8. 8. A process according to any one of claims 1 to 7, wherein volatile components are eliminated from the copolymer during the cross-linking step.
9. 9. A process according to any one of claims 1 to 8, wherein cross-linking is carried out without imparting any motion to the polymer by mechanical means.
10. 10. A process according to claim 1 carried out substantially as described in any one of Examples 1 to 19 herein.
11. 11. An impact-resistant styrene copolymer whenever obtained by a process according to any one of Claims 1 to 10.