WO1999048976A1

WO1999048976A1 - Polymer composition containing a polypropylene polymerized using a high-activity catalyst

Info

Publication number: WO1999048976A1
Application number: PCT/NL1999/000177
Authority: WO
Inventors: Jan Willem Boode; Franciscus Elisabeth Jacobus Essers; Peter Willem Mathias Colbers; Rudy Andre Cornelis Deblieck; Marcus Johannes Henricus Bulters
Original assignee: Dsm N.V.
Priority date: 1998-03-26
Filing date: 1999-03-26
Publication date: 1999-09-30
Also published as: AU3059099A

Abstract

Polymer composition comprising a polypropylene polymerized using a high-activity catalyst, which polymer composition contains an elastomer phase originating from a propylene-ethylene block copolymer, which elastomer phase contains a high-molecular weight ethylene polymer with an intrinsic viscosity (Decalin, 135 °C) of at least 3.0 dl/g. The polypropylene polymerized using a high-activity catalyst has preferably been polymerized using a supported Ziegler-Natta catalyst.

Description

- 1 -

POLYMER COMPOSITION CONTAINING A POLYPROPYLENE POLYMERIZED USING A HIGH-ACTIVITY CATALYST

The invention relates to a polymer composition comprising a polypropylene polymerized using a high-activity catalyst. Such a polymer composition is known, for example, from EP-A-0 , 714 , 948.

An advantage of the use of a high-activity catalyst is that a polypropylene of very high purity is obtained, which contains only a small amount of catalyst residues. Moreover, such catalysts are very effective, so that only small amounts of them need to be used.

A disadvantage of a polypropylene prepared in a polymerization using a high-activity catalyst is, however, that if the polypropylene has a high rigidity, the impact resistance generally is low. Particularly the impact resistance at low temperature is often insufficient. It is possible to increase the impact strength by adding an impact modifier, for example an elastomer, to the polymer, but then a very large amount of impact modifier has to be added, which in turn causes the rigidity to decrease. In addition, it is uneconomic to separately add large amounts of impact modifier to such a polymer composition in this way. The invention aims to provide a polymer composition containing a polypropylene polymerized using a high-activity catalyst, which polymer composition combines high rigidity with a high impact strength, m particular a high impact strength at low temperature . Surprisingly, this aim is achieved m that the polymer composition comprises an elastomer phase originating from a propylene-ethylene block copolymer, which elastomer phase contains a high-molecular weight ethylene polymer having an intrinsic viscosity (measured m Decalin as solvent, at a temperature of 135 °C) of at least 3.0 dl/g.

As a result, the polymer composition has a high impact strength, also when the polymer composition has a high rigidity. At a low temperature, for example at a temperature of 0 °C, the impact strength also has a high value. Furthermore, the polymer composition has good flow properties and a high elongation at break. In a possible embodiment of the polymer composition according to the invention the polymer composition comprises a first polypropylene polymerized using a high-actlvity catalyst, and an elastomer phase, which contains the high-molecular weight ethylene polymer, originating from a second polypropylene, which polypropylene is a propylene-ethylene block copolymer polymerized using a catalyst other than a high-activity catalyst, preferably using a second generation (nonsupported) Ziegler-Natta catalyst . The first polypropylene may for example be a homopolymer, a block copolymer of propylene and ethylene or a random copolymer of propylene with up to 6 mole% of a second α-olefm, preferably ethylene. - 3 -

In another embodiment it is also possible for the polypropylene polymerized using a high-activity catalyst m the polymer composition according to the invention to be an ethylene-propylene block copolymer, and for the elastomer phase containing the high- molecular weight ethylene pol mer to originate from the polypropylene polymerized using the high-activity catalyst .

Polypropylene homopolymers , random copolymers of propylene and ethylene as well as propylene-ethylene block copolymers, the preparation thereof and catalysts for the preparation thereof are described m "Polypropylene and other polyolefins", Studies m Polymer Science 7, Elsevier, Amsterdam (1990), ISBN 0-444-88690-7 (U.S.).

Examples of high-activity catalysts (HAC) for the polymerization to polypropylene are supported Ziegler-Natta catalysts or homogeneous catalysts (single site catalysts) , of which metallocene catalysts are mostly used. Preferably, the polypropylene polymerized using a high-activity catalyst is obtained m a polymerization using a supported Ziegler-Natta catalyst .

Supported Ziegler-Natta catalysts usually contain a carrier that has been prepared by allowing the carrier material to precipitate from a solution to obtain carrier particles having a fine morphology and applying the catalyst proper to the surface of the carrier particles, usually m the form of a relatively thin layer of a titanium compound, preferably titanium tetrachloride . As carrier material use is often made of a magnesium compound, for example magnesium chloride.

Second-generation (non-supported) Ziegler- Natta catalysts for the polymerization to polypropylene contain the titanium compound, itself formed into catalyst particles having a fine morphology, usually by combining a titanium compound from solution, preferably titanium tetrachloride, with a suitable reagent, so that the catalyst precipitates to yield titanium trichloride m the form of particles. Propylene-ethylene block copolymers are generally prepared by polymerizing, m a first polymerization phase, a first block built up of propylene monomer units or of propylene monomer units and up to about 6 wt . % monomer units of a second α-olefm, and m a subsequent polymerization phase polymerizing a second block, built up of ethylene and propylene monomer units, m which the content of ethylene monomer units relative to the first block is relatively high. The second block is present m the form of an elastomer phase, which contains an ethylene- propylene elastomer, besides the semi-crystallme phase formed by the first block.

The high-molecular weight ethylene polymer may be a pure homopolymer, but it is also possible for the ethylene polymer to contain for example up to 50 wt . % monomer units of one or more other α-olefins, for example propylene or butene.

It is important that the high-molecular weight ethylene polymer has such a content of ethylene monomer units that the ethylene polymer is semi- crystallme. Preferably, the high-molecular weight ethylene polymer contains 0-30 wt . % of a second α- olefm, even more preferably the high-molecular weight ethylene polymer contains 0-15 wt . % of a second α- olefm. Preferably, the high-molecular weight ethylene polymer has an intrinsic viscosity (m Decalin, 135 °C) of at least 3.7 dl/g.

An added advantage is created if the high- molecular weight ethylene polymer has an intrinsic viscosity (Decalin, 135 °C ) of at least 4.2 dl/g. This yields a polymer composition which besides the above- mentioned advantages also has the advantage that articles manufactured from the composition have a very good surface quality and m particular exhibit few surface defects.

The high-molecular weight ethylene polymer is preferably formed during the polymerization of the propylene-ethylene block copolymer. This can for example be effected by reducing the hydrogen gas content of the feed during the preparation of the second block of the block copolymer, or by leaving the hydrogen gas out of the feed altogether, by choosing a high ethylene/propylene ratio m the reactor feed and/or by choosing a sufficiently low polymerization temperature during the polymerization of the elastomer phase, preferably lower than 70 °C, even more preferably lower than 63 °C .

It is also possible to prepare the high- molecular weight ethylene polymer after the polymerization of the second block, m a subsequent polymerization phase, for example by using a feed that is very rich m ethylene or that consists entirely of ethylene m this phase. It is also possible to add the high-molecular weight ethylene polymer to the ethylene- propylene block copolymer.

The high-molecular weight ethylene polymer can be present m various states m the elastomer phase. The ethylene polymer may for example be dissolved m the elastomer phase or be present in the form of particles whose dimensions are smaller than those of the particles of the elastomer phase itself. The elastomer phase originating from the propylene-ethylene block copolymer contains, for example, 10-98 wt . % ethylene propylene elastomer and 2-90 wt . % high-molecular weight ethylene polymer.

Preferably, the elastomer phase contains 30-80 wt . % ethylene-propylene elastomer and 70-20 w . % high molecular weight ethylene polymer.

If the elastomer phase originating from the propylene-ethylene block copolymer contains 50-90 w . % high-molecular weight ethylene polymer, the polymer composition according to the invention has a very high scratch resistance and a very high heat distortion temperature . If the elastomer phase originating from the propylene-ethylene block copolymer contains 20-70 wt . % high-molecular weight ethylene polymer, the polymer composition according to the invention has a very high impact strength. Very good results are achieved if the polymer composition contains 50-100 parts by weight of a first polypropylene polymerized using a high-activity catalyst, 0-50 parts by weight of a second polypropylene, which is an ethylene-propylene block copolymer, polymerized using a catalyst other than a high-activity catalyst, the total polypropylene content amounting to 100 parts by weight, of which the elastomer phase which contains the high-molecular weight ethylene polymer accounts for up to 40 parts by weight . Per 100 parts by weight m total of polypropylene the polymer composition according to the invention may contain 0-30 parts by weight of a separately added impact modifier, for example a plastomer, preferably an elastomer. Preferably, the content of the separately added impact modifier, which the composition according to the invention contains, is as low as possible. Preferably this content is 0-20 parts by weight, even more preferably 0-10 parts by weight, and most preferably the polymer composition according to the invention contains no separately added impact modifier at all . Examples of suitable elastomers for separate addition are copolymers of ethylene and a second olefin with 3-10 C atoms, preferably propylene. As elastomer use can also be made of a copolymer of ethylene, propylene and or more dienes, for example EPDM. Examples of suitable plastomers are LLDPΞ and vLDPE .

In a preferred embodiment the polymer composition according to the invention contains :

95-50 parts by weight of a polypropylene block copolymer polymerized using a high-activity catalyst, with a melt index > 2 dg/mm (230 °C,

2.16 kg, ISO 1133), containing Al . 85-50 wt . % of a block which contains 0-6 wt . % ethylene monomer units and 94-100 wt . % propylene monomer units, A2. 15-50 wt . % of a block which contains 30-80 wt . % ethylene monomer units and 70-20 wt . % propylene monomer units, B. 50-5 parts by weight of a polypropylene block copolymer polymerized using a second-generation

(non-supported) Ziegler-Natta catalyst, w th a melt index of

0.1-100 dg/mm (230 °C, 2.16 kg, ISO 1133), containing

Bl. 95-50 wt . % of a block containing 0-6 wt . % of ethylene monomer units and 94-100 wt . % of propylene monomer units, B2. 50-5 wt . % of a block containing 30-80 wt . % of ethylene monomer units and 70-20 w . % of propylene monomer units, which block forms the elastomer phase which contains the high-molecular weight ethylene polymer, on condition that components A and B together account for 100 parts by weight,

C. 0-30 parts by weight of impact modifier,

D. 0-100 parts by weight of filler.

Thanks to its highly favourable combination of properties, m particular rigidity, impact strength and flow, such a polymer composition is suitable for use in automotive parts, for example bumpers, dashboards, stone guards, etc.

Component A can in principle be prepared according to any method known for the purpose to one skilled in the art using a high activity catalyst. Component A is preferably prepared in a gas-phase reactor for the preparation of polypropylene. Component A can for example be prepared using a supported Ziegler-Natta catalyst and the method described in 096/32427.

Preferably, the polymer composition according to the invention contains 70-95 parts by weight of component A. The melt index of component A preferably amounts to 4-100, more preferably 5-50 dg/min (230 °C, 2.16 kg, according to ISO 1133).

Component B can in principle be prepared according to any method known for the purpose to one skilled in the art using a second-generation Ziegler- Natta catalyst. Preferably, component B is prepared in a slurry reactor for the preparation of polypropylene. Component B can for example be prepared using the method described in US-4 , 210 , 738 , on condition that the polymerization has been carried out so that the high- molecular weight ethylene polymer is present in the elastomer phase of component B, for example as a result of one or more of the above-mentioned measures for the formation of the high-molecular weight ethylene polymer .

Preferably, the polymer composition according to the invention contains 5-30 parts by weight of component B. The melt index of component B preferably amounts to 1-50 dg/min (230 °C, 2.16 kg, according to ISO 1133) .

As component C, the impact modifier, use is preferably made of the above-mentioned impact modifier that is to be added separately

As component D, the filler, use can for example be made of chalk, clay, glass fibres having a length up to 12 mm, hammered glass, wollastonite, etc. Preferably, talc is used. The invention also relates to moulded articles containing the composition according to the invention, preferably injection moulded articles, more preferably injection moulded articles having a wall thickness of less than 4 mm, even more preferably less than 3 mm.

Examples

The invention will be elucidated on the basis of the following Examples, without being limited thereto.

Component A

Component A was prepared in a gas phase reactor in a two-step polymerization process using a supported Ziegler-Natta catalyst. The catalyst was a MgCl₂- supported TiCl₄ catalyst. As cocatalyst use was made of triethyl aluminium; and as external donor use was made of a dialkyldialkoxy silane.

The polymerization was carried out under the customary conditions. Component A contained 68 wt . % of block al , which was built up of propylene monomer units, and 32 wt . % of block a2 , which contained 55 wt . % ethylene monomer units and 45 wt . % propylene monomer units. The melt index was 22 dg/mm. (230°C, 2.16 kg)

Components B (Bl and B2 )

Component Bl was used m the polymer compositions according to Examples 1-3 and 7.

Component Bl was prepared m a slurry reactor in a two-step polymerization process using a catalyst prepared as described m US-4 , 210 , 738. The catalyst was a precipitated TιCl₃ catalyst . As cocatalyst diethyl aluminium chloride was used.

In a first polymerization phase block bl was formed, which was built up of propylene monomer units. In a subsequent polymerization phase block b2 was formed, the polymerization temperature was 60°C; the reactor feed used contained no hydrogen gas whatsoever, and ethylene and propylene m a weight ratio of 40/60. The melt index of component Bl was 50 dg/mm (230°C, 2.16 kg)

Component Bl contained 90 wt . % of block bl and 10 wt . % of b2. The ethylene-propylene elastomer content (b21), and the high molecular weight ethylene polymer content (b22) block b2 of component Bl were determined as follows:

Component Bl was dissolved a concentration of 5 gram per liter m boiling p-xylene. The solution was cooled to 95 °C . This caused polypropylene homopolymer to precipitate, the precipitate was separated from the solution.

Subsequently, the solution was cooled to 25°C. This caused the high-molecular weight ethylene polymer (b22) formed during the polymerization of block b2 to precipitate, while the ethylene-propylene elastomer (b21) remained m solution. The high-molecular weight ethylene polymer was then separated from the solution.

Subsequently, the high-molecular weight ethylene polymer was redissolved m Decalin and the intrinsic viscosity was determined at a temperature of 135 °C . The intrinsic viscosity was 4.0 dl/g. From the fractions the high-molecular weight ethylene polymer content (b22) m block b2 was calculated to be 60 wt . % of block b2 and the ethylene-propylene elastomer content (b21) to be 40 wt . % .

Component B2 was used m the polymer compositions according to the Examples 4-6. Component

B2 was produced m a comparable manner to component Bl . The melt index was 1 dg/mm (230 °C, 2.16 kg) . Component B2 contained 79 wt . % of block bl, which itself was built up entirely of propylene monomer units. Component B2 further contained 21 wt . % of block b2. Block b2 contained 66 wt . % of high-molecular weight ethylene polymer (b22) having an intrinsic viscosity of 4.2 dg/mm and 34 wt . % of ethylene-propylene elastomer (b21) .

Component C

As component C Vistalon^® 785 was used, an ethylene-propylene elastomer (EPM) .

Component D

As component D a fine talc was used, 99 wt . % of which has a particle size <10 micron.

Preparation of the polymer composition

Components A-D were mixed, together with usual additives, m the ratios given m Table 1 to produce dry blends. In a twin-screw kneader (ZSK (TM) , supplied by Werner and Pfleiderer m Germany) the dry blends were compounded at a temperature of 230 °C . The blends were then granulated and injection moulded using an Arburg (TM) injection moulding machine at a temperature of 250°C to produce specimens from which test bars were cut for the determination of the mechanical properties.

The melt index

Of the mixtures the melt index was determined at 230 °C, with a weight of 2.16 kg (I₂) and a weight of 5 kg (I₅) according to ISO 1133.

Mechanical properties

The following mechanical properties were determined on the above-mentioned test bars:

Izod according to ISO 180, at -20 °C, perpendicular to the direction of injection moulding. 3 -point bending test according to ASTM D

790 for the determination of the E-modulus, perpendicular (E_mod 7 and parallel to (E_mod | | ) the direction of injection moulding.

Examples 1-7, comparative experiment A

The polymer compositions according to the 14

Examples and the polymer composition used in comparative experiment A are presented in Table I. The polymer compositions are composed so that the total elastomer phase content in the composition, that is the sum of the concentrations of block a2 , block b2 and component C, is almost constant.

Table I

Example/ wt.% A wt.% Bl wt.% B2 wt . % C wt . % D Comp . Exp .

1 62.15 15 12.5 10

2 68.65 10 11 10

3 75.65 5 9 10

4 63.65 15 11 10

5 69.65 10 10 10

6 75.65 5 9 10

7 33.65 34 20 12

A 84.65 5 10

The melt index and the mechanical properties of the polymer compositions of Table I are presented in Table I I . 15

Tabl e I I

Example/ ι₂ Is Izod ^Emod ^ ^Emod 1 Comp . Exp . (dg/min) (dg/min) -20°C (N/mm²) (N/mm²)

(kJ/m²)

1 15 61 10.6 980 1050

2 15 63 12.5 975 1018

3 16 63 N.D. N.D. N.D.

4 9.5 39 66.2 956 1043

5 12 47 59.5 952 1023

6 16 63 43.5 943 1003

7 15 63 9.8 1080 1229

A 14.3 57 8.6 909 978

N.D. = not determined.

The Examples clearly show an improved combination of mechanical properties for the composition according to the invention, by the beneficial effect of the presence of the high-molecular weight ethylene polymer.

Claims

- 16 -C A I M S

1. Polymer composition comprising a polypropylene polymerized using a high-activity catalyst, characterized m that the polymer composition contains an elastomer phase originating from a propylene-ethylene block copolymer, which elastomer phase contains a high-molecular weight ethylene polymer having an intrinsic viscosity (Decalin, 135┬░C) of at least 3.0 dl/g.

2. Polymer composition according to claim 1, characterized that the polypropylene polymerized using a high-activity catalyst has been polymerized using a supported Ziegler-Natta catalyst .

3. Polymer composition according to claim 1 or claim 2, characterized m that the high-molecular weight ethylene polymer contains 0-30 wt.% of a second ╬▒-olefm.

4. Polymer composition according to any one of claims 1-3, characterized m that the high- molecular weight ethylene polymer has an intrinsic viscosity of at least 3.7 dl/g.

5. Polymer composition according to any one of claims 1-4, characterized m that the elastomer phase containing the high-molecular weight ethylene polymer contains 30-80 wt.% ethylene- propylene elastomer and 70-20 wt.% high-molecular weight ethylene polymer.

6. Polymer composition according to any one of claims 1-5, characterized m that the polymer composition contains 50-100 parts by weight of a first polypropylene, polymerized using a high- activity catalyst, 0-50 parts by weight of a second polypropylene, which is an ethylene- propylene block copolymer, polymerized using a catalyst other than a high-activity catalyst, with the total polypropylene content amounting to 100 parts by weight, the elastomer phase containing the high-molecular ethylene polymer accounting for up to 40 parts by weight.

7. Polymer composition according to any one of claims 1-6, characterized m that per 100 parts by weight of total polypropylene the polymer composition contains 0-20 parts by weight of a separately added impact modifier.

8. Polymer composition according to claim 7, characterized m that per 100 parts by weight of total polypropylene the polymer composition contains 0-10 parts by weignt of a separately added impact modifier.

9. Polymer composition according to any one of claims 1-8, characterized m that the polymer composition contains:

A. 95-50 parts by weight of a polypropylene block copolymer polymerized using a high- activity catalyst, with a melt index > 2 dg/mm (230 ┬░C, 2.16 kg, ISO 1133), containing

Al . 85-50 wt.% of a block containing 0-6 wt.% of ethylene monomer units and 94-100 wt.% of propylene monomer units, A2. 15-50 wt.% of a block containing 30-80 wt.% of ethylene monomer units and 70-20 wt.% of propylene monomer units,

B. 50-5 parts by weight of a polypropylene block copolymer polymerized using a second- generation (non-supported) Ziegler-Natta catalyst, with a melt index of 0.1-100 dg/min (230 ┬░C, 2.16 kg, ISO 1133), containing Bl. 95-50 wt.% of a block containing 0-6 wt.% of ethylene monomer units and 94-100 wt.% of propylene monomer units, B2. 50-5 wt.% of a block containing 30-80 wt.% of ethylene monomer units and 70-20 wt.% of propylene monomer units, which block forms the elastomer phase that contains the high- molecular weight ethylene polymer, on condition that components A and B together account for 100 parts by weight,

C. 0-30 parts by weight of impact modifier,

D. 0-100 parts by weight of filler.

10. Polymer composition according to claim 9, characterized in that the melt index of component A is 4-100 dg/min.

11. Polymer composition according to claim 9 or 10, characterized in that the melt index of component B is 1-50 dg/min.

12. Molded article containing a polymer composition according to anyone of claims 1-11.