Thermoplastic Rubber Compositions Comprising Polyolefin and Sequential E/P or EPDM

This invention relates to thermoplastic rubber compositions consisting of mixtures of a polyolefin resin and an ethylene-propylene rubber (EPM) or an ethylene-propylene terpolymer (EPDM), so-called sequential copolymers being used as the EPM-copolymers or EPDM-terpolymers.

German Offenlegungsschriften Nos. 2,202,706 and 2,202,738 previously described mixtures of crystalline polyolefin resins and ethylene-propylene or ethylene-propylene-diene rubbers which are either partially crosslinked by the addition of vulcanising agents after mixing or are produced with EPM or EPDM which has already been partially crosslinked.

Unfortunately, such mixtures do not satisfy all practical requirements because, in particular, their tensile strength values, their elongation at break values, their tear propagation resistance values and also their hardness values, as measured at 100.degree. C., are still in need of improvement.

It was subsequently found that, by using so-called segment copolymers of ethylene and propylene optionally with another tercomponent in mixtures with polyolefin resins, the technical properties could be considerably improved.

The mixtures according to German Offenlegungsschrift Nos. 2,202,706 and 2,202,738 contain ethylene-propylene or ethylene-propylene-diene rubbers which represent an amorphous, arbitrarily oriented elastomeric polymer. In contrast to the statistical and, hence, amorphous polymers, the sequential polymers to be used in the mixtures in accordance with the present invention are characterised by very high crude strengths. Thus, the crude strengths of standard commercial-grade statistical ethylene/propylene terpolymers are normally in the range from 0.5 MPa to 2.0 MPa, whereas the values for segment polymers are in the range from 8.0 to 20 MPa. The reason for the high strength of the sequential polymers is their partial crystallinity (G. Schreier and G. Peitscher, Z. anal. Chemie 258 (1972) 199). In contrast to statistical ethylene-propylene or ethylene-propylene-diene polymers which are substantially amorphous, crystallinity was detected both by X-ray spectroscopy and also by Raman spectroscopy. The degree of crystallinity correlates both with the ethylene content and also with the crude strength. These sequential segment polymers are commercially available, for example, under the names BUNA AP 407, BUNA AP 307 (EPM) and BUNA AP 447 (EPDM).

The improvement in technical properties by using the sequential copolymers instead of the amorphous copolymers according to German Offenlegungsschrift Nos. 2,202,706 and 2,202,738 in the mixtures with polyolefin resins was most unexpected. Indeed, the mixture could have been expected to lose its elastomeric properties through the presence of another partially crystalline component.

Accordingly, the present invention provides mixtures of either partially crosslinked ethylene-propylene or ethylene-propylene-diene sequential polymers with pololefin resins or uncrosslinked ethylene-propylene or ethylene-propylene-diene sequential polymers with polyolefin resins, the partial crosslinking taking place during or after mixing.

Suitable polyolefin resins are polymers obtained in known manner by the polymerisation of olefins for example, ethylene, propylene, 1-butene, 4-methyl pentene, 1-pentene and similar olefinic monomers. It is preferred to use crystalline polyolefins of propylene or ethylene with low or high density. It is particularly preferred to use an isotactic polypropylene with a high degree of crystallinity. Polypropylene having a density of from 0.90 to 0.92 is especially preferred. Mixtures of different polyolefins may also be used.

Suitable ethylene-propylene copolymers or ethylene-propylene-diene sequential terpolymers are polymers which consist of sequences of ethylene, propylene and optionally another tercomponent, the tercomponent generally being an unconjugated diene for example, 1,4-hexadiene, dicyclopentadiene, alkylidene norbornene, such as methylene norbornene or ethylidene norbornene or cyclooctadiene. In most cases, it is preferred to use dicyclopentadiene or ethylidene norbornene. The sequential terpolymers which are used in accordance with the present invention in the mixtures with the polyolefin resins may have an ethylene content of from 63 to 95 parts by weight, preferably from 70 to 85 parts by weight, a propylene content of from 5 to 37 parts by weight, preferably from 15 to 30 parts by weight, and a tercomponent content of from 0 to 15 parts by weight, preferably from 5 to 10 parts by weight. The terpolymers are further characterised by a crude strength of at least 3 MPa, preferably at least 8 MPa.

Suitable crosslinking agents are peroxidic crosslinking agents, such as aromatic diacyl peroxides and aliphatic diacyl peroxides, peroxides of dibasic acids, ketone peroxides, alkyl peroxide esters, alkyl hydroperoxides, such as diacetyl peroxide, dibenzoyl peroxide, bis-2,4-dichlorobenzoyl peroxide, di-tert.-butyl peroxide, dicumyl peroxide, tert.-butyl perbenzoate, tert.-butyl cumyl peroxide, 2,5-bis-(tert.-butyl-peroxy)-2,5-dimethyl hexane, 2,5-bis-(tert.-butyl-peroxy)-2,5-dimethyl-3-hexine, 4,4,4',4'-tetra-(tert.-butyl-peroxy)-2,2-dicyclohexyl propane, 1,4-bis-(tert.-butyl-peroxyisopropyl)-benzene, 1,1-bis-(tert.-butyl-peroxy)-3,3,5-trimethyl cyclohexane, lauryl peroxide, succinic acid peroxide, cyclohexanone peroxide, tert.-butyl peracetate and butyl hydroperoxide.

In a first alternative embodiment of the invention, partially crosslinked ethylene-propylene or ethylene-propylene-diene sequential terpolymer may be mixed with the polyolefin resin. In order to obtain partial crosslinking, the sequential terpolymer is reacted in a suitable unit with from 0.05 to 10% by weight, based on the sequential terpolymer, and preferably with 0.1 to 2% by weight, of a crosslinking agent, as a result of which partial crosslinking occurs.

In order to obtain partial crosslinking, the EPDM-rubber is mixed with a small quantity of a crosslinking agent and exposed to vulcanisation conditions in suitable units. Vulcanisation should only take place partially, so that the polymer must still be partially soluble. Completely crosslinked polymers, i.e. polymers insoluble in hydrocarbons, are unsuitable for further processing. Vulcanisation may be carried out in standard apparatus, for example in kneaders, roll stands or screw machines. Mixing with the polypropylene after the partial crosslinking step is carried out in the same apparatus as described above.

The reaction temperature is governed by the decomposition temperature of the crosslinking agent used, so that it cannot be exactly defined. In general, the reaction is carried out at temperatures in the range from 150.degree. to 250.degree. C. and preferably at a temperature in the range from 170.degree. to 220.degree. C.

The proportion of polyolefin resin in the mixture amounts to between 10 and 95% by weight, preferably to between 20 and 70% by weight and, with particular preference, to between 30 and 60% by weight.

In the other alternative embodiment of the invention, the sequential copolymer is initially mixed with the polyolefin resin and then partially crosslinked with the crosslinking agent.

To produce the products according to this alternative embodiment, it is possible for example initially to mix the EP-component with the polyolefin. This step may be carried out in kneaders, on mixing rolls or in self-cleaning multiple-shaft screws. The two components may also be mixed in the form of powders or granulates in high-speed mixers or other stirring units.

This mixture is then partially vulcanised in a kneader with addition of the required quantity of crosslinking agent. Internal mixers, mixing rolls and multiple-shaft screws may be used for this purpose. Crosslinking may also be carried out in conventional vulcanisation presses or in salt baths, UHF-installations or superheated steam ducts. These process steps may be carried out continuously or in batches, depending upon the particular type of unit used. The two components may also be simultaneously mixed with the crosslinker. Another variant is to add the crosslinker in partial batches. In this case, an initial batch of, for example, 20 to 30% of the crosslinking agent is immediately added and the rest is added in 2 to 4 partial batches. This process may be carried out both in batches (internal mixer) and also continuously (screw).

The quantity of crosslinker used and the temperatures applied are the same as in the first alternative.

The mixtures according to the invention are thermoplastic rubber compositions which may be processed into shaped article, for example by moulding or extrusion. In cases where these mixtures are used, there is no need for the vulcanisation step which has to be carried out after the shaping or forming step in the case of conventional rubber polymers. Examples of shaped articles are fender covers, manometer housings, seat shells, visors and dashboards.

The physical properties determined are set out in Table 2:

Examples 4 and 5 are Comparison Examples. The improvement in the tensile strength and elongation at break values in Examples 1 to 3 (sequential EPDM) over the EPDM-types with statistical distribution (Examples 4 and 5) is clearly apparent.

the physical properties quoted in the Tables were determined in accordance with the following Specifications: