GB1582279A - Thermoplastic rubber compositions - Google Patents

Description

(54) THERMOPLASTIC RUBBER COMPOSITIONS (71) We, BAYER AKTIENGESELLSCHAFT a body corporate organised under the laws of the Federal Republic of Germany of 509 Leverkusen, 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 relates to thermoplastic rubber compositions. More particularly, this invention relates to thermoplastic rubber compositions consisting of mixtures of an isotactic polypropylene and an ethylene-propylene terpolymer.

German Offenlegungsschriften No. 2,202,706 and No. 2,202,738 have previously described mixtures of isotactic polypropylene and ethylene-propylene or ethylenepropylene-diene rubbers which are either partially cross-linked 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"C are still in need of improvement.

Mixtures of polyethylene with EPDM polymers with a crystallinity of from 10 % to 20 % are known from US Patent No. 3,919,358. Although these products show high ultimate tensile strengths, their thermal stability is inadequate on account of the low melting temperature of the polyethylene.

Accordingly, there is a need for products which combine a high tensile strength, elongation at break and flexibility at low temperatures with a high thermal stability.

It has now been found that mixtures of isotactic polypropylene with sequential EPDM satisfy these requirements both in regard to thermal stability and also in regard to the desired mechanical properties.

The mixtures according to German Offenlegungsschrift No. 2,202,706 and German Offenlegungsschrift No. 2,202,738 contain 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 ethylenepropylene terpolymers are normally in the range from 0.5 MPa to 2.0 MPa, whereas the values for sequential polymers are in the range from 8.0 to 20 MPa. The partial crystallinity of the sequential polymers accounts for their high strength (G. Schreier and G. Peitscher, Z.

Anal. Chemie 258 (1972) 199). In contrast to statistical 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 polymers are commercially available, for example, under the name BUNA (Trade Mark) AP 447 (EPDM).

Accordingly, the present invention provides mixtures comprising at least one uncrosslinked tersequential polymer consisting of ethylene, propylene and an unconjugated diene with isotactic polypropylene.

The polypropylene used is in the isotactic form with a high degree of crystallinity; polypropylene with a density of from 0.90 to 0.92 g/cc is particularly preferred.

The terpolymer is a polymer which consists of sequences of ethylene, propylene and a tercomponent which is unconjugated diene for example, 1,4-hexadiene, dicyclopentadine, 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 may be used in accordance with the invention in the mixtures with the polyolefin resins preferably have an ethylene content of from 63 to 90 parts by weight, most preferably from 70 to 80 parts by weight, a propylene content of from 5 to 35 parts by weight, most preferably from 15 to 25 parts by weight, and a tercomponent content of from 1 to 15 parts by weight, most preferably from 5 to 10 parts by weight. They are further preferably characterised by a crude strength of > 3 MPa, preferably > 8 MPa.

The products may be produced in various ways. To this end, the components are mixed in granulate or powder form and then delivered to a mixing unit. In another method, the polypropylene is initially introduced into a mixing unit. After melting, the rubber is then added. The reverse procedure may be adopted, depending upon the type of mixing unit used.

The mixing process may be carried out in conventional machines, including rollers, internal mixers or self-cleaning multiple-shaft screws. In cases where multiple-shaft screws are used, the process may be carried out continuously. With modern screws, it is possible, depending on requirements, to vary the fittings on the screw shaft and hence to adapt the kneading, heating and hence the shearing conditions to the mixing ratio.

This is important because the mechanical properties of the resulting products are dependent upon the temperatures at which the mixtures are produced. It has been found that better mechanical properties can be obtained at higher temperatures than at lower temperatures. The temperature range from 200 to 2900C has proved to be favourable, although it is preferred to work at temperatures in the range from 230 to 2800 C.

In cases where screw machines are used, the product may be further processed in different ways. On the one hand, the strand leaving the screw may be cooled in a water bath and subsequently granulated. On the other hand, an underwater granulation stage may be installed at the end of the screw, in which case a moist granulate is obtained which may subsequently be dried by conventional methods.

The mixtures according to the present invention preferably consist of from 5 to 50 parts by weight of EPDM and of 50 to 95 parts by weight of polypropylene. They represent thermoplastic rubber compositions which can be processed into shaped articles, for example by moulding or extrusion. In cases where these mixtures are used, there is no need for a vulcanisation stage which is required after the shaping or forming operation in the case of the usual rubber polymers. Examples of shaped articles produced from the mixtures of the present invention are fender coverings, seat shells, visors, dashboards.

The invention is illustrated by the following Examples: EXAMPLE 1 A mixture of polypropylene and sequential EPDM in the ratio indicated was delivered in granulate form to a self-cleaning two-shaft screw by way of a distributing belt weighing machine. The screw had a length of 120 cm (without feed zone). Its volume was 0.4 1. The rotational speed was 300 rpm. The throughput was fixed at 17 kg/h. The screw contained two kneading zones at intervals of 40 cm and 90 cm from the beginning of the screw. The temperature 10 cm behind the feed hopper was 174"C which rose to 2680C in the vicinity of the kneading zones.At the output end of the screw, the temperature was 236"C. The temperature of the external heating was 227"C. After leaving the screw, the stand was cooled in a 4 metre long cooling tank and subsequently chopped to form a granulate. The polypropylene used was highly isotactic. Its melt index (DIN 53 735, method C) was 4.5, its melting range 158 to 1640C and its density 0.906 (red = 3. This product is commercially available for example under the name Vestolen PP 4200. The sequential EPDM has an ethylene content of 67%by weight and a propylene content of 27 %by weight. The number of double bonds per 1000 carbon atoms amounts to 12. The tercomponent was ethylidene norbornene. The Mooney viscosity was 85 and the crude strength amounted to 12.0 MPa. A product such as this is commercially available, for example, under the name Buna AP 447.

Panels were moulded from the granulate at a temperature of 1900C (10 minutes). These panels were tested in accordance with DIN 53 504 (tensile strength, elongation at break, modulus, standard ring I), DIN 53 505 (hardness), DIN 53 512 (shock elasticity) and DIN 53 453 (notched impact strength).

rubber Ratio . 80 60 40 20 0 polypropylene 20 40 60 80 100 Tensile strength MPa 6.5 8.9 16.6 23.6 33 Elongation at break % 620 425 255 85 30 Modulus 100% MPa 2.2 6.8 12.4 300% MPa 4.3 8.4 - - - Hardness 23 Shore A A 71 93 92 93 99 1000 " "A 11 55 88 91 97 " 23 " D 21 43 57 67 73 " 70 " D 0 12 33 44 57 Elasticity 23 % 64 42 40 41 46 " 70 % 46 46 48 47 42 Tear propagation resistance according to Pohle N 80 195 450 740 1045 E-modulus MPa 20 242 727 1210 1790 Notched impact strength 23 + + + 13 3 " 0 + + + 7 1 " -10 + + 38 6 1 " -30 + + 11 3 1 1) + = unbroken EXAMPLE 2 This Examples was carried out in order to demonstrate the superiority of polypropylene to polyethylene. Production was carried out as described in Example 1. The polyethylene used was characterised by the following data: melt index (DIN 53 735) 8, density 0.923, and also by the mechanical values set out in the following Table. This product is commercially available under the name Baylon 19 N 430.

2a 2b 2c 2d 2e rubber 60 60 40 40 0 Ratio 60 60 40 40 0 polyolefin 40PE 40PP 60PE 60PP 100PE Tensile strength 12.8 8.9 13.2 16.6 12.3 Elongation 600 425 720 255 95 Modulus 100% 4.1 6.8 6.0 12.4 - " 300% 5.5 8.4 6.3 - Hardness Shore A 23 85 93 90 92 94 " " 70 59 71 73 94 87 1000 23 55 40 88 41 1200 0 43 0 76 0 ,, 150" 0 17 0 32 0 Shock elasticity 230 46 42 37 40 37 70" 47 46 40 48 33 Tear propagation resistance 125 195 210 450 280 It is clear that, in the range above 50% of polyolefin, the products according to the invention (2d) are superior to the comparative mixtures containing polyethylene (Example 2c) both in their mechanical values (F, M, E) and also in their thermal stability, which is illustrated by the Shore hardness at elevated temperatures.

WHAT WE CLAIM IS: 1. A mixture comprising at least one uncrosslinked tersequential polymer consisting of ethylene, propylene and an unconjugated diene with isotactic polypropylene.

2. A mixture as claimed in claim wherein the unconjugatedieneisdicyclopentadiene or ethylidene norbornene.

3. A mixture as claimed in claim 1 or 2, which comprises isotactic polypropylene with a density of from 0.90 to 0.92 g/cc.

4. A mixture as claimed in any of claims 1 to 3, which comprises 5 to 50 parts by weight of the tersequential polymer and 50 to 95 parts by weight of isotactic polypropylene.

5. A mixture as claimed in any of claims 1 to 4, wherein the tersequential polymer has the following composition: 63 to 90 parts by weight of ethylene, 5 to 35 parts by weight of propylene and 1 to 15 parts by weight of an unconjugated diene.

6. A mixture as claimed in claim 5, wherein the tersequential polymer has the composition: 70 to 80 parts by weight of ethylene, 15 to 25 parts by weight of propylene and 5 to 10 parts by weight of an unconjugated diene.

7. A mixture as claimed in claim 1, substantially as herein described with reference to either of the specific Examples.

8. A process for producing a mixture as claimed in any of claims 1 to 7, wherein an uncrosslinked tersequential polymer consisting of ethylene, propylene and an unconjugated diene is mixed with isotactic polypropylene at a temperature of from 200 to 290"C.

9. A process as claimed in claim 8, wherein mixing is carried out at a temperature of from 230"C to 2800C.

10. A process as claimed in claim 8 substantially as herein described with reference to either of the specific Examples.

11. A mixture when produced by a process as claimed in any of claims 8 to 10.

12. A thermoplastic rubber comprising a mixture as claimed in any of claims 1 to 7 and 11.

13. A shaped article comprising a mixture as claimed in any of claims 1 to 7 and 11.

14. A shaped article as claimed in claim 13 which is a fender covering, seat shell, visor or dashboard.

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

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. 2a 2b 2c 2d 2e rubber 60 60 40 40 0 Ratio 60 60 40 40 0 polyolefin 40PE 40PP 60PE 60PP 100PE Tensile strength 12.8 8.9 13.2 16.6 12.3 Elongation 600 425 720 255 95 Modulus 100% 4.1 6.8 6.0 12.4 - " 300% 5.5 8.4 6.3 - Hardness Shore A 23 85 93 90 92 94 " " 70 59 71 73 94 87 1000 23 55 40 88 41 1200 0 43 0 76 0 ,, 150" 0 17 0 32 0 Shock elasticity 230 46 42 37 40 37 70" 47 46 40 48 33 Tear propagation resistance 125 195 210 450 280 It is clear that, in the range above 50% of polyolefin, the products according to the invention (2d) are superior to the comparative mixtures containing polyethylene (Example 2c) both in their mechanical values (F, M, E) and also in their thermal stability, which is illustrated by the Shore hardness at elevated temperatures. WHAT WE CLAIM IS:

1. A mixture comprising at least one uncrosslinked tersequential polymer consisting of ethylene, propylene and an unconjugated diene with isotactic polypropylene.

2. A mixture as claimed in claim wherein the unconjugatedieneisdicyclopentadiene or ethylidene norbornene.

3. A mixture as claimed in claim 1 or 2, which comprises isotactic polypropylene with a density of from 0.90 to 0.92 g/cc.

4. A mixture as claimed in any of claims 1 to 3, which comprises 5 to 50 parts by weight of the tersequential polymer and 50 to 95 parts by weight of isotactic polypropylene.

5. A mixture as claimed in any of claims 1 to 4, wherein the tersequential polymer has the following composition: 63 to 90 parts by weight of ethylene, 5 to 35 parts by weight of propylene and 1 to 15 parts by weight of an unconjugated diene.

6. A mixture as claimed in claim 5, wherein the tersequential polymer has the composition: 70 to 80 parts by weight of ethylene, 15 to 25 parts by weight of propylene and 5 to 10 parts by weight of an unconjugated diene.

7. A mixture as claimed in claim 1, substantially as herein described with reference to either of the specific Examples.

8. A process for producing a mixture as claimed in any of claims 1 to 7, wherein an uncrosslinked tersequential polymer consisting of ethylene, propylene and an unconjugated diene is mixed with isotactic polypropylene at a temperature of from 200 to 290"C.

9. A process as claimed in claim 8, wherein mixing is carried out at a temperature of from 230"C to 2800C.

10. A process as claimed in claim 8 substantially as herein described with reference to either of the specific Examples.

11. A mixture when produced by a process as claimed in any of claims 8 to 10.

12. A thermoplastic rubber comprising a mixture as claimed in any of claims 1 to 7 and 11.

13. A shaped article comprising a mixture as claimed in any of claims 1 to 7 and 11.

14. A shaped article as claimed in claim 13 which is a fender covering, seat shell, visor or dashboard.