GB1600580A

GB1600580A - Thermoplastic elastomeric olefin polymer mixtures

Info

Publication number: GB1600580A
Application number: GB18255/78A
Authority: GB
Original assignee: Stamicarbon BV
Current assignee: Stamicarbon BV
Priority date: 1977-05-16
Filing date: 1978-05-08
Publication date: 1981-10-21
Also published as: AT367084B; ES469774A1; CH641482A5; SE428932B; FI781494A; DE2821342A1; FR2391243B1; BE867043A; IT1103494B; DE2821342C2; FR2391243A1; IT7849399A0; NL7705367A; SE7805609L; ATA335778A

Abstract

A thermoplastic elastomeric polymer mixture contains polypropylene, a copolymer of ethylene, propylene and optionally one or more polyunsaturated monomers, and an ethylene homopolymer or copolymer. The polymer mixture contains a mixture of: A. from 30 to 75 parts by weight of a crystalline, isotactic propylene homopolymer having a melt flow index of between 1 and 25 dg/min, and B. from 25 to 70 parts by weight of a rubber-like copolymer of ethylene, propylene and optionally one or more polyunsaturated monomers, which has a crystallinity of less than 10% by weight, an ethylene content of greater than 58% by weight, a tensile strength of greater than 30 kg/cm<2> and a Mooney viscosity (ML[1+4] 125 DEG C), as a measure of the molecular weight, of from 30 to 90, where C. a maximum of 15 parts by weight of the propylene homopolymer and at least sufficient parts as indicated by half the numerical value of the melt flow index of the propylene homopolymer are replaced by just as many parts by weight of an ethylene homopolymer or copolymer having a density of between 0.91 x 10<3> and 0.98 x 10<3> kg/m<3>. The polymer mixture is used for the production of automobile parts.

Description

(54) THERMOPLASTIC ELASTOMERIC OLEFIN POLYMER MIXTURES (71) We, STAMICARBON B.V., a Netherlands Limited Liability Company of P.O. Box 10, Geleen, the Netherlands, 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 improved thermoplastic elastomeric polymer mixtures of polypropylene, polyethylene and an ethylene-propylene polymer, and to articles wholly or partly formed therefrom.

Such polymer mixtures are described in United States Patent Specification 3,957,919, wherein it is stated that the addition of a small amount of polyethylene to a mixture of polypropylene and ethylene-propylene copolymer inhibits the negative action of cross-linking agents incorporated in the mixture and which decompose at elevated temperature during mixing. The cross-linked mixtures obtained have a low melt index so that they are unsuitable for use in injection moulding techniques.

It is also known from United States Patent Specification 3,919,358 to prepare mixtures of ethylene-propylene copolymers and polyethylene, in which the ethylenepropylene copolymer has a crystallinity of at least 10% and the polyethylene has a density of less than 0.94. Such polymer mixtures can readily be processed, but have less favourable mechanical properties, the high temperature resistance, the impact strength at low temperature, the permanent deformation, stiffness and hardness being unsatisfactory. It is also known to prepare mixtures of ethylene-propylene, copolymer, polyethylene, and an ethylene-vinyl-acetate copolymer, the ethylene-propylene copolymer having a crystallinity of more than 10% bv weight. It is generally considered that ethylene-propylene-copolymers of low crystallinity do not give good properties in admixture with other polyolefins, such as polyethylene.

It has now been found that thermoplastic elastomeric polymer mixtures of polypropylene, polyethylene and an ethylenepropylene polymer can be obtained having good processability and have good mechanical properties. The invention provides a thermoplastic elastomeric polymer mixture of polypropylene, ethylene-propylene polymer and polyethylene, wherein the said mixture is based on a notional composition of A) 30 to 75 parts of a crystalline isotactic propylene homopolymer having a melt index of between 1 and 25 dg/min.

B) 25 to 70 parts of a rubbery ethylene-propylene polymer having a crystallinity of not more than 10% by weight, an ethylene content of more than 58% by weight, a tensile strength of more than 30 kg/cm2, and a Mooney viscosity [ML (1+4) 125 C] of from 30 to 90 as a measure of the molecular weight, and wherein there is incorporated polyethylene having a density of between 0.91 and 0.98 g/cm3, the number of parts of the said polyethylene thus incorporated being such that the actual content of the said polypropylene homopolymer in the said notional composition is reduced by the presence of the said polyethylene by an amount not more than 15 parts and not less than a number of parts corresponding to half the numerical value cf the said melt index of the polypropylene homopolymer.

The polymer mixtures according to the present invention have a melt index that is many times higher than the melt index of the mixtures obtained according to the United States Patent Specification 3,957,919, their mechanical properties being at least as good.

The mixtures are particularly suitable for processing by injection moulding techniques. They exhibit favourable combination of properties such as good processability, high impact strength at low temperatures, high temperature resistance and high stiff nest furthermore are comparatively low in cost. Contrary to previous proposals, an ethylene-propylene polymer with a low crystallinity is used in the mixtures according to the invention. Stiffness and resistance to high temperatures is obtained by using a propylene homopolymer. The attendant brittleness at low temperature is mitigated by incorporating polyethylene into the mixture in small amounts dependent on the melt index of the polypropylene.

The ethylene-propylene polymer used in the mixtures according to the invention preferably has an ethylene content of at least 61% by weight. It is known that the tensile strength of ethylene-propylene polymers strongly increases with increasing ethylene content, but the crystallinity will also increase strongly, which is detrimental to a number of properties such as compression set and the toughness at low temperatures.

Consequently, the ethylene content of the copolymer used is preferably below 77% by weight, in particular below 75% by weight. A further advantage of this is the improved elongation at break that is obtained. The best results are obtained if the ethylene content of the copolymer is below 70% by weight. In mixtures with other polyolefins, ethylenepropylene polymers with higher molecular weights generally give better mechanical properties, but the processability will be poorer. Very good properties including processability, are obtained if the ethylene-propylene copolymer has a maximum Mooney viscosity (being a measure of the molecular weight), which depends on the melt index of the propylene homopolymer.This maximum value of the Mooney viscosity is represented by the equation

where m.i. denotes the melt index of the polypropylene in dg/minute, measured at 230"C and 2.16 kg.

The Mooney viscosity (ML (1+4) is measured at 125"C. More preferably the Mooney viscosity is not more than a value expressed by the equation

The preferred and particularly preferred maximum values of the Mooney viscosity for a given melt index of the propylene polymer are set forth in Table I. TABLE 1

Melt index Preferred limit Particularly preferred limit polypropylene 50 100 90 - 90 - m.i. 0.6 m.i. 0.6 dg/min 1 40 2 57 24 3 64 38 4 68 46 5 71 52 6 73 56 7 74 59 8 76 61 9 77 63 10 77 65 15 80 70 20 82 73 25 83 75 The ethylene-propylene polymer used in the mixtures according to the invention furthermore has a crystallinity of not more than 10% by weight, and is preferably made of an amorphous ethylene-propylene copolvmer, i.e. the crvstallinitv not more than 4% by weight, particularly not more than 1% by weight, whereby the permanent deformation after impression and toughness at low temperatures are significantly improved.

Furthermore the rubbery ethylene-propylene polymer preferably has a tensile strength of more than 50 kg/cm2 in the unvulcanized state. The crystallization temperature of the polymer determined by differential scanning calorimetry is preferably higher than OOC, particularly higher than 100C.

The ethylene-propylene polymer may contain a polyunsaturated monomer in an amount of not more than 20% by weight. These polyunsaturated monomers are usually non-conjugated polyenes, especially dienes. They are usually used in amounts of not more than 10% by weight.

Examples of such monomers are dicyclopentadiene, alkylidene norbornene, alkenyl norbornene, alkadienes and cycloalkadiene. Use is preferably made of dicyclopentadiene, ethylidene norbornene, norbornadiene, 1.5-hexadiene, 1.4.-hexadiene, or mixtures of two or more thereof. The ethylene-propylene polymers for use according to the invention may be prepared e.g. by the methods described in the British Patent Specifications 1,014,873; 951,022 and 880,904.

The crystalline, isotactic propylene homopolymer in the mixtures used according to the invention has a melt index of between 1 and 25 dg/min, preferably of between 1.5 and 20, particularly of between 5 and 15 dg/min. In the present invention, this melt index determines the preferred maximum Mooney viscosities of the ethylenepropylene polymer and the amount of polyethylene to be added. The density of the propylene homopolymer used is preferably in the range between 0.900 and 0.910 g/cm'.

The high melt index that can be obtained by the present invention is of particular importance. For this purpose polypropylene with a sufficiently high melt index must be used, and as a result other mechanical properties will be improved.

The brittleness at low temperatures which is also caused is surprisingly eliminated by replacing the polypropylene by a number of parts of polyethylene that numerically is at least half, preferably at least i, cf the melt index of the polypropylene.

It is particularly surprising that so highly improved properties can be obtained by the use of a polypropylene homopolymer in combination with polyethylene according to the invention.

The polypropylene used according to the invention is basically isotactic and has a high crystalline content, preferably more than 50% by weight measured by X-ray diffraction. It can be prepared by the well-known methods which are mainly based on the use of modified or unmodified titanium chloride that is activated, e.g. by means of an aluminium compound.

The third component that is incorporated in the mixtures according to the invention is a polyethylene having a density of between 0.91 and 0.98 g/cm3 and preferably a melt index of between 0.1 and 35 dg/min., preferably of between 1 and 25 dg/min. The density is preferably more than 0.94 g/cm", particularly higher than 0.96 g/cm3, which means that no or only small amounts of a comonomer may be incorporated in the polyethylene, e.g. less than 0.5% weight A preferred composition for the thermoplastic elastomeric mixture according to the invention Is from 50 to 70 parts of the crystalline, isotactic propylene homopolymer and 30 to 50 parts of the rubbery ethylene-propylene polymer. The special effects obtained by the invention are particularly apparent with a minor proportion of ethylene-propylene polymer.Thus the stiffness and the high-temperature properties are at a high level and the improvement of the impact resistance at low temptsature obtained with the polyethylene component is particularly evident together with excellent processability.

The thermoplastic mixtures can be prepared in conventional manner using equipment commonly used for mixing plastics, such as rollers, extruders, rapid mixers and kneaders, in which the plastics material is subjected to shear forces at elevated temperature, particularly at a temperature of between 1500 and 220"C. For large scale applications preference is given to kneaders and extruders in which the mixing is effected at temperatures of from 1800 and 200"C.

The mixtures according to the invention may incorporate other additives such as pigments, lubricants, fillers, antioxidants, UV-stabilizers, flame-proofing agents, zinc oxide and/or magnesium oxide, carbon black, fibres or combinations of fibrous and powdery substances and oil extenders, without the characteristic properties being lost The polymer mixtures according to the present invention may also be mixed with other polymers, e.g., styrene polymers, polyamides, polyvinyl chloride, polycarbonates, block copolymers of styrene and butadiene, which may be hydrogenated and chlorinated polyolefins eg. chlorinated polyethylene, or mixtures of two or more of such polymers.

The polymer mixtures according to the invention can be used for numerous purposes, as they can be soft and rubbery as well as stiff and impact-resistant. Thus they may be used to render other polymers impact-resistant.

The mixtures are particularly suitable for the manufacture of large articles used in the open air such as bumpers of motor cars, as the mixtures according to the present invention are particularly weather-resistant. This weather-resistance can still be improved further, especially if no carbon black is used, by incorporating in the mixture UV-stabilizers and/or zinc oxide, if so desired in addition to a phenolic antioxidant The UV-stabilizer used by preference is a combination of a so-called UV-quencher e.g.

hindered amine, and a UV-absorber e.g. a benzotriazole and benzophenone compound.

The following Examples of the invention are provided, together with comparative Examples.

Example 1.

A series of mixtures consisting of ethylene-propylene polymer, polypropylene, and in some instances polyethylene with the compositions set forth in Table 2, were prepared in a kneader.

Use was made of an ethylene-propylene-terpolymer rubber, denoted EPDM I, derived from 64% of ethylene, 30% of propylene and 6t' of ethylidene norbornene.

The tensile strength in the unvulcanized state was 65 kg/cm2. The Mooney viscosity (ML (1+4) 1250C) was 52 and the crystallinity was less than 0.25%.

The propylene polymer (not used according to the invention) denoted PP I, is a block copolymer of propylene with 7% of ethylene, having a density of 0.905 and a melt index 2300C/2.16 kg) of 6.0 dg/min.

The propylene homopolymer denoted PP II is a propylene homopolymer with a density of 0.905 g/cm2 and a melt index of 5.2 dg/min. (230"C, 2.16 kg). The polyethvlene denoted PE I has a density of 0.963 g/cm3 and a melt index of 8 dg/min.

(1900C, 2.16 kg).

Before the tests set forth in Table 2 were carried out, the rubbery ethylenepropylene polymer was put in a kneader and after l-minute's kneading, the polypropylene and the polyethylene were added. After 4-minutes' kneading (total time 5 minutes), kneading was continued for about 30 minutes without stamping pressure, after which kneading was continued until a temperature of 1700C was reached.

The mixtures were moulded into sheets that were tested for the properties shown in Table 2. The Table also lists the properties of two commercially-available products.

In Table 2, tests 4 and 5 were according to the invention.

TABLE 2

Commercial Commercial Test no. productA productB 1 2 3 4 5 6 7 EPDMI 40 40 40 40 40 35 35 PPI 60 - - - - 65 55 PPII - 60 57 55 50 - PEI - - 21/1 5 10 - 10 Melt index (dg/min) 9.1 5.2 10.5 8.5 7.8 7.2 5.9 12.5 7.6 Hardness (shore D) 53 48 50 55 54 54 53 53 54 Vicat temperature l kg 97 100 105 127 122 118 107 119 103 ( C) Heat-sag test (mm) 34.5 34.0 28.5 - - 25.5 25.5 - 30 Falling-weight test -40 C on knit-line breaking energy (Nm) 3.16 3.62 3.50 2.70 2.94 3.37 3.74 3.20 3.72 force (N) 1329 1442 1404 1485 1468 1511 1474 1439 1438 type of break tough tough brittle brittle brittle tough tough brittle brittle/ tough tear strength (N/mm) 71 61 69 77 78 76 75 70 73 The various properties were measured by the following standards: Melt index: ASTM D-1238 (230 C - 5 kg) Hardness: ASTM D-2240 (read after 3 sec) Tensile test: NEN 5602, test rod 2, rate of elongation 15 cm/min Vicat temperature: ASTM D-1525, load 1 kg Heat-sag test: 10x1x0.16 cm test specimen, heat load 1 minute at 120 C Falling-weight test: after 48 minutes' conditioning, weight 5 kg, height of fall 1 m, velocity of impact 4.2 m/sec. The falling weight has a flat impact face of 1 cm in diameter. The test specimen of 1.6 mm thickness is supported by a ring of 2 cm in diameter.

Tear strength: DIN 53515 Heat shrinkage: DIN 53497, heat load 24 hours at 90 C.

Table 2 shows that mixtures with polypropylene-homopolymer (Tests 2, 3, 4 and 5) have a considerably better resistance to high temperatures than the polypropylenecopolymer in comparable test 1. The high-temperature resistance is also considerably better than that of the two comparable commercial products. The favourable combination of toughness at low temperatures (high breaking energy, tough break) and a good resistance to high temperatures is basically dependent on the addition of polyethylene.

The Tests 2, 3, 4 and 5 indicate that in order to obtain sufficient toughness at low temperatures, the polyethylene content must be at least as high as half the numerical value of the melt index of the polypropylene-homopolymer, (Tests 4 and 5).

While an excellent resistance to high temperatures can also be achieved with a relatively high content of polypropylene-copolymer (Test 6), but then the toughness at low temperature is insufficient. While the toughness at high temperatures can be raised to an acceptable level by the addition of polyethylene the negative effect on the high-temperature resistance is such that, on balance, the mixtures are not better than the commercial products (Test 7).

Example 2.

The mixtures set forth in Table 3 were made in a laboratory kneader at a kneading temperature of 1800C and a kneading time of 10 minutes. All components of the mixture were put in the kneading chamber simultaneously, and the mixtures were then rolled and moulded into sheets at 2000 C. The components of the mixture have already been described in Example 1, with the exception of PP III, which is a polypropylene homopolymer with a melt index of 1.3 dg/min and a density of 0.905 g/cm'. Table 3 shows that the Tests 1 to 5 are distinguished from Tests 6 and 7 by a greater hardness, a greater stiffness at room temperature, a higher tear strength and a higher tensile strength. From this it may be concluded that mixtures with a polypropylene-homopolymer have better mechanical properties than mixtures with a polypropylene-copoly mer.In Table 3, Tests 2, 3, 4 and 5 were according to the invention.

TABLE 3

Test No. 1 2 -- 3 4 5 6 - 7 EPDM I 47 45 40 471H2 45 47 45 PPI I 1 - - - 50 50 PP II 1 50 50 50 - - - - PP III - - - 50 50 - - PE I 2 5 10 %2 5 2l/2 5 Melt index 1.0 1.2 1.3 0.46 0.49 1.3 1.6 (190 OC-10 kg) gamin.

Hardness (shore D) 51 52 53 51 53 46 47 G' x 10-9 (dyne,'cm2) 2.30 2.43 2.69 2.13 2.39 1.39 1.45 Tear strength (N/mm) 73 83 84 83 83 57 61 Tensile strength (MPa) 9.9 10.0 10.6 9.8 10.9 7A 6.1 Elongation at break (io)- 160 150 100 270 290 300 280 The properties were measured by the following standards of methods: Melt index: ASTM D-1228 1900 and 10 kg Hardness: ASTM D-2240, read after 3 sec.

Stiffness (G'): Torsion damping f=0.2 H2, 220C Tear strength: DIN 53515 Tensile strength: NEN 5602, test rod 2, rate of elongation 30 cm/min.

Example 3.

This Example shows that the Mooney viscosity of the ethylene-propylene copolymer has a maximum value dependent on the melt index of the polypropylene-homopolymer, at which a trouble-free processing by injection-moulding techniques is possible.

In the laboratory kneader, 40 parts by weight of ethylene-propylene terpolymer (EPDM), 55 parts by weight of polypropylene-homopolymer, and 5 parts by weight of high-density polyethylene were mixed as described in Example 2. In the 9 mixtures, the Mooney viscosity of the EPDM, as well as the melt index of the polypropylenehomopolymer were varied.

Three ethylene-propylene terpolymers with a Mooney viscosity (MLw (1+4) 125"C) of 39, 52, and 62, respectively, were each mixed with three types of PP-homopolymer having melt indices of 1.3, 5.2, and 9.5 dg/min (2300C - 5 kg), respectively.

The melt indices of the mixtures are listed in Table 5. For the mixture tested, the preferable maximum value of the Mooney viscosity of the EPDM in dependence on the melt index of the polypropylene-homopolymer is set forth in Table 4.

TABLE 4

Melt-index Maximum Mooney Preferable limit maximum polypropylene- viscosity EPDM Mooney viscosity EPDM homopolymer (dg/min) 50 100 (MLMAX = 90 - --- ) (MLMAX = 90 - ---) m.i. 0.6 m.i. 0.6 1.3 47 preferably not to be used 5.2 71 53 9.5 77 64 Table 5 indicates that the Mooney viscosity of the EPDM in samples 6 and 9 is higher than the preferable maximum value. These samples have too low a melt index in order to be well processable. The other samples have a sufficiently low Mooney viscosity and, hence, the melt index of the mixture is such that a good processability is ensured. Optimum processability is found in samples 1, 2, 4 and 7. Samples 3 and 8 will have insufficient processability for critical applications.

TABLE 5

Test No. 1 2 3 4 5 6 7 8 9 Mooney viscosity EPDM ML 39 39 39 52 52 52 62 62 62 (1+4) 125 c Melt index PP-homopolymer 9.5 5.2 1.3 9.5 5.2 1.3 9.5 5.2 1.3 230 C/2.16 kg (dg/min) COMPOSITION OF MIXTURE EPDM II* 40 40 40 - - - - - EPDM I - - - 40 40 40 - - EPDM III* - - - - - - 40 40 40 PP IV* 55 - - 55 - - 55 - PP II - 55 - - 55 - - 55 PP III - - 55 - - 55 - - 55 PE I 5 5 5 5 5 5 5 5 5 Melt index 230 C/5 kg (dg/min) 14,5 9.9 4.52 11.2 7.83 3.51 8.2 5.92 2.71 * EPDM II: 63% by weight ethylene, 5% by weight ethylidene norbornene tensile strength 49 kg/cm2, crystallinity < 0.25%; DSC temperature +7 C.

EPDM III:62% by weight ethylene, 5% by weight ethylidene norbornene tensile strength 55 kg/cm2, crystallinity 0.025%; DSC, temperature +8 C.

PPIV: A polypropylene-homopolymer of melt index (230 /2.16 kg) 9.5 dg/min density 0.905 g/cm3.

1. poor processability for injection-moulding techniques.

2. not suitable for critical applications in which good processability is necessary.

3. processability just sufficient for injection-moulding complicated articles.

Example 4.

The series of mixtures with a polypropylene homopolymer with a melt index of 9.5 dg/min (PP IV) mentioned in Table 5 were prepared as described in Example 1.

However the samples were moulded into sheets under different conditions i.e. at a higher temperature and a lower pressure. Hence the results of the tests are not altogether comparable to those of the previous tests.

Table 6 shows that a propylene homopolymer with a melt index of 9.5 dg/min (PP IV) can also be used to prepare mixtures that have a high toughness at low temperatures. It is necessary, however, that the amount of polyethylene used be greater than about 5% by weight i.e. greater than half the numerical value of the melt index of the polypropylene homopolymer.

TABLE 6

Test No. 1 2 3 4 Composition EPDM I 40 40 40 40 PP IV 60 57M2 55 50 PE I - 21/2 5 10 Properties Melt index 2300C - 5 kg(dg/min) 14.3 12.4 10.0 7.8 Hardness (Shore D) 56 56 56 54 Tear strength (DIN 53515 (N/mm)) 83 82 80 80 Falling-weight test (-40 OC) on knit-line - breaking energy (Nm) 3.2 3.7 3.9 4.1 maximum force (N) 1622 1616 1616 1609 - type of break brittle brittle brittle tough tough yield stress (N/mm2) 18.1 19.1 17.1 17.1 stretching stress (N/mm2) 15.6 16.6 15.7 15.2 tensile strength (N/mm2) 20.2 19.6 19.6 19.6 elongation at break (So) 470 450 470 440 Example 5.

This example shows that the advantage of adding polyethylene as described in the invention are cancelled by too high an amount of polyethylene. The mixtures listed in Table 7 were made in the kneader in the way described in Example 1. In tests 1 and 2, all have a good processability; Mixture 3 with 20% by weight of PE has a high polyethylene content and has too low a melt index. Also the tensile strength is unsatisfactory.

TABLE 7

Test No. 1 2 3 EPDM I 35 35 35 PP II 60 55 45 PE 1 5 10 20 Melt index (dg/min) 9.0 7.2 2.5 Hardness (Shore D) 57 56 56 Tensile strength (N/mm2) 12.5 11.4 9.8 Elongation at break (No) 255 250 250 Vicat temperature 123 119 110 Example 6.

This Example shows that the density of the polyethylene may also be of influence to the effectivity of the polyethylene in improving the mechanical properties. 40 parts of EPDM 1, 55 parts of PP 1 and 5 parts of polyethylene were mixed mechanically in a kneader, as described in Example 1.

The types of polyethylene used in the 5 mixtures are set forth in Table 8.

TABLE 8

Melt index (190 , 216 kg Density (dg/min) PE I 0.963 g/cm3 8 PE II 0.953 24 PE III 0.948 0.3 PE IV 0.953 1.4 PE V (LDPE) 0.918 7.5 To determine the properties, the samples were moulded into sheets, as described in Example 4. The properties are set forth in Table 9. TABLE 9

Test No. 1 2 3 4 5 Composition EPDM I 40 40 40 40 40 PP II 55 55 55 55 55 PEI 5 - - - PEII - 5 - - - PE III - - 5 - - PEIV - - - 5 - PE V (LDPE) - - - - 5 Properties Melt index 2300C-5 kg (dg/min) 5.2 5.9 5.5 5.3 5.7 Hardness (Shore D) 54 53 54 54 53 Tear strength DIN 53515 (N/mm) 75 73 75 74 74 Falling-weight test (-400C) on knit line -breaking energy (Nm) 4.0 4.2 4.0 4.2 3.9 - maximum force (N) 1649 1623 1639 1631 1586 - type of break tough tough tough tough tough Yield stress (N/mm2) 18.4 17.8 18.5 18.3 17.6 Stretching stress (N/mm2) 17.0 16.0 17.0 16.6 16.5 Tensile strength (N/mm2) 21.3 21.6 21.1 20.9 21.0 Elongation at break (6XG) 430 420 430 420 420 Table 9 shows that better results are obtained with polyethylene with a density of over 0.94 g/cm3.

Example 7.

As described in Example 2, 40 parts by weight of ethylene-propylene terpolymer, 55 parts by weight of propylene homopolymer and 5 parts by weight of polyethylene were compounded into mixtures in the laboratory kneader. Next the mixtures were rolled and moulded into sheets at 200 C. 4 mixtures were made. In 3 of them 'greenstrength' EPDM types were used. The properties of the mixtures are set forth in Table 10.

The table shows that the mixture with non green-strength EPDM (test 1) differs from the other mixtures with 'green-strength' EPDM (tests 2 ,3, and 4) by a lower hardness, tear strength and tensile strength. Hence, to utilize the advantages described in the invention fully, the use of a 'green-strength' EPDM in the mixtures is required.

High ethylene contents will cause a low elongation at break (test 3).

TABLE 10

Test No. 1 2 3 4 Composition EPDM IV 1) 40 - - - EPDM I 40 - - EPDM V 2) - - 40 - EPDMVl') - - - 40 PP II 55 55 55 55 PE 1 5 5 5 5 Properties 2) Melt index 2300C-5 kg (dg/min) 7.3 7.8 6.5 6.5 Hardness (Shore D) 49 55 55 55 Tear strength DIN 53515 (N/mm) 75 89 99 95 Tensile strength (N/mm2) 10.4 11.9 12.6 12.4 Elongation at break (%) 110 130 80 130 t) EPDM IV: ethylene content 55% by weight, ethylidene norbornene 5% by weight tensile strength 2.4 kg/cm , crystailinity < 0.25%, Mooney ML (1 + 4) 125 OC: 54, DSC temperature -17 OC.

2) EPDM V: ethylene content 75% by weight, hexadiene -1,4 3% by weight, tensile strength 124 kg/cm2, crystallinity 8%, Mooney ML (1 + 4) 1250C: 64, DSC temperature +38 OC.

3) EPDM VI: ethylene content 70% by weight, ethylidene norbornene 4.5% by weight, tensile strength 120 kg/cm2, crystallinity 3% Mooney ML (1 + 4) 125 OC: 61. DSC temperature +240C.

WHAT WE CLAIM IS: 1. A thermoplastic elastomeric polymer mixture of polypropylene, ethylenepropylene polymer and polyethylene, wherein the said mixture is based on a notional composition of: A) 30 to 75 parts of a crystalline isotactic propylene homopolymer having a melt index of between 1 and 25 dg/min.

B) 25 to 70 parts of a rubbery ethylene-propylene polymer having a crystallinity of not more than 10% by weight, an ethylene content of more than 58% by weight, a tensile strength of more than 30 kg/cm2, and a Mooney viscosity [ML (1+4) 125 C.] of from 30 to 90 as a measure of the molecular weight, and wherein there is incorporated polyethylene having a density of between 0.91 and 0.98 g/cm3, the number of parts of said polyethylene thus incorporated being such that in the actual content of the said polypropylene homopolymer in the said notional composition is reduced by the presence of the said polyethylene, by an amount not more than 15 parts and not less than a number of parts corresponding to half the numerical value of the said melt index of the polypropylene homopolymer.

2. A mixture according to Claim 1, wherein the maximum Mooney viscosity of the rubbery ethylene-propylene polymer is given by the equation

where m.i. denotes the melt index of the said polypropylene homopolymer.

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

Claims

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

TABLE 10

Test No. 1 2 3 4 Composition EPDM IV 1) 40 - - - EPDM I 40 - - EPDM V 2) - - 40 - EPDMVl') - - - 40 PP II 55 55 55 55 PE 1 5 5 5 5 Properties 2) Melt index 2300C-5 kg (dg/min) 7.3 7.8 6.5 6.5 Hardness (Shore D) 49 55 55 55 Tear strength DIN 53515 (N/mm) 75 89 99 95 Tensile strength (N/mm2) 10.4 11.9 12.6 12.4 Elongation at break (%) 110 130 80 130 t) EPDM IV: ethylene content 55% by weight, ethylidene norbornene 5% by weight tensile strength 2.4 kg/cm , crystailinity < 0.25%, Mooney ML (1 + 4) 125 OC: 54, DSC temperature -17 OC.

2) EPDM V: ethylene content 75% by weight, hexadiene -1,4 3% by weight, tensile strength 124 kg/cm2, crystallinity 8%, Mooney ML (1 + 4) 1250C: 64, DSC temperature +38 OC.

3) EPDM VI: ethylene content 70% by weight, ethylidene norbornene 4.5% by weight, tensile strength 120 kg/cm2, crystallinity 3% Mooney ML (1 + 4) 125 OC: 61. DSC temperature +240C.

WHAT WE CLAIM IS: 1. A thermoplastic elastomeric polymer mixture of polypropylene, ethylenepropylene polymer and polyethylene, wherein the said mixture is based on a notional composition of: A) 30 to 75 parts of a crystalline isotactic propylene homopolymer having a melt index of between 1 and 25 dg/min.

B) 25 to 70 parts of a rubbery ethylene-propylene polymer having a crystallinity of not more than 10% by weight, an ethylene content of more than 58% by weight, a tensile strength of more than 30 kg/cm2, and a Mooney viscosity [ML (1+4) 125 C.] of from 30 to 90 as a measure of the molecular weight, and wherein there is incorporated polyethylene having a density of between 0.91 and 0.98 g/cm3, the number of parts of said polyethylene thus incorporated being such that in the actual content of the said polypropylene homopolymer in the said notional composition is reduced by the presence of the said polyethylene, by an amount not more than 15 parts and not less than a number of parts corresponding to half the numerical value of the said melt index of the polypropylene homopolymer.
2. A mixture according to Claim 1, wherein the maximum Mooney viscosity of the rubbery ethylene-propylene polymer is given by the equation

where m.i. denotes the melt index of the said polypropylene homopolymer.
3. A mixture according to Claim 2, wherein the maximum Mooney viscosity is

iven bv the equation
4. A mixture according to any of Claims 1 to 3, wherein the said mixture is based on a notional starting composition of A) 50 to 70 parts of propylene homopolymer, and B) 30 to 50 parts of ethylene-propylene polymer.
5. A mixture according to any of Claims 1 to 4, wherein the said actual content of the said propylene homopolymer is reduced by a number of parts corresponding to not less than three-quarters of the numerical value of the melt index of the said homopolymer.
6. A mixture according to any of Claims 1 to 5, wherein the said rubbery ethylene-propylene polymer has an ethylene content of at least 61% by weight.
7. A mixture according to Claim 6, wherein the said rubbery ethylene-propylene polymer contains not more than 77% by weight of ethylene.
8. A mixture according to Claim 6, wherein the said rubbery ethylene-propylene polymer contains not more than 70% by weight of ethylene.
9. A mixture according to Claims 1 to 7, wherein the said rubbery ethylenepropylene copolymer has a crystallinity of not more than 4% by weight.
10. A mixture according to Claim 10, wherein the said rubbery ethylene-propylene polymer has a crystallinity of not more than 1% by weight.
11. A mixture according to any of Claims 1 to 10, wherein the said rubbery ethylene-propylene polymer has a tensile strength of more than 50 kg/cm2.
12. A mixture according to any of Claims 1 to 11, wherein the said ethylenepropylene polymer contains a poly-unsaturated monomer in an amount of not more than 20% by weight.
13. A mixture according to Claim 12, wherein the said ethylene-propylene polymer contains not more than 10% by weight of poly-unsaturated polymer.
14. A mixture according to Claim 12 or Claim 13, wherein the said polyunsaturated monomer is dicyclopentadiene, ethylidene norbornene, 1,4-hexadiene, 1,5hexadiene or norbornadiene.
15. A mixture according to any of Claims 1 to 14, wherein the said crystalline propylene homopolymer has a melt index of between 1.5 and 20 dg/min.
16. A mixture according to Claim 15, wherein the said melt index is between 5 and 15 dg/min.
17. A mixture according to any of Claim 1 to 10, wherein the said propylene homopolymer has a density of between 0.900 and 0.910 g/cm3.
18. A mixture according to any of Claims 1 to 17, wherein the said polyethylene has a density of more than 0.94 g/cm3.
19. A mixture according to Claim 18, wherein the said polyethylene has a density of more than 0.96 g/cm3.
20. A mixture according to any of Claims 1 to 19, wherein the said polyethylene has a melt index of between 0.1 and 35 dg/min.
21. A mixture according to Claim 20, wherein the said melt index is between 1 and 25 dg/min.
22. A mixture according to any of Claims 1 to 21, wherein the said polyethylene contains not more than 0.5% by weight of comonomers.
23. A mixture according to Claim 1, substantially as hereinbefore described, with particular reference to the Examples.
24. Articles wholly or partly formed from a mixture according to any of Claims 1 to 23.