WO2023097415A1

WO2023097415A1 - Filled polyolefin composition with improved impact strength and low clte

Info

Publication number: WO2023097415A1
Application number: PCT/CN2021/134217
Authority: WO
Inventors: Emily QIANG; Rock ZHU
Original assignee: Borouge Compounding Shanghai Co., Ltd.
Priority date: 2021-11-30
Filing date: 2021-11-30
Publication date: 2023-06-08

Abstract

A polyolefin composition (PC) comprising: i) from 40.0 to 60.0 wt. -% of a heterophasic propylene-ethylene copolymer (HECO), having an MFR ₂ in the range from 40 to 100 g/10 min; ii) from 3.0 to 25.0 wt. -% of an elastomeric styrene copolymer (SC), having an MFR₅ in the range from 8.0 to 30 g/10 min; iii) optionally from 3.0 to 25.0 wt. -% of an elastomeric ethylene copolymer (EC); iv) from 15.0 to 45.0 wt. -% of a filler (F); and v) from 0.0 to 5.0 wt. -% of additives (A).

Description

FILLED POLYOLEFIN COMPOSITION WITH IMPROVED IMPACT STRENGTH AND LOW CLTE

FIELD

The present invention relates to a polyolefin composition (PC) comprising a heterophasic propylene-ethylene copolymer (HECO) , an elastomeric styrene copolymer (SC) , optionally an elastomeric ethylene copolymer (EC) , a filler (F) and optional additives (A) , as well as articles comprising said polyolefin composition (PC) .

BACKGROUND

Polypropylene is a material used in a wide variety of technical fields, and reinforced polypropylenes have in particular gained relevance in fields previously exclusively relying on non-polymeric materials, in particular metals. One particular field in which polypropylene has had a particularly notable impact is in automotive exteriors, wherein the beneficial balance of stiffness, impact strength and processability of polypropylene is harnessed with great effect. Whilst a number of prior art grades are suitable for use in automotive exteriors, ever increasing demands on the mechanical properties of such articles cannot always be met by such grades, with many for example suffering from relatively inferior impact strength and relatively high thermal expansion upon exposure to high temperatures, resulting in potentially problematic deformation. For thin-walled injection-molded articles in particular, such as bumper and support thereof, body panels, grills, spoilers and tailgates, these features are particularly important, as are the processability properties of the composition, which are relevant for the production of such articles.

At present, despite the significant advances in this field in recent years, there remains a need for new polypropylene grades having improved impact strength, low coefficient of linear thermal expansion (CLTE) , and favourable processing properties. It is these aims that the present invention seeks to resolve.

SUMMARY

The present invention is based on the finding that polyolefin compositions containing a heterophasic propylene-ethylene copolymer (HECO) having a high melt flow rate, an elastomeric styrene copolymer (SC) , an optional elastomeric ethylene copolymer (EC) , a filler (F) and optional additives (A) have improved impact properties and low CLTE at higher melt flow rates (i.e. improved processability) , whilst maintaining reasonable stiffness.

Therefore, in a first aspect, the present invention is directed to a polyolefin composition (PC) comprising:

i) from 40.0 to 60.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of a heterophasic propylene-ethylene copolymer (HECO) , comprising:

a) a crystalline matrix (M) , being either a propylene homopolymer or a propylene copolymer;

b) an elastomeric propylene-ethylene copolymer (E) ;

wherein the heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR ₂) , determined according to ISO 1133 at 230 ℃ at a load of 2.16 kg, in the range from 40 to 100 g/10 min;

ii) from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of an elastomeric styrene copolymer (SC) , having a melt flow rate (MFR ₅) , determined according to ISO 1133 at 230 ℃ at a load of 5.0 kg, in the range from 8.0 to 50 g/10 min;

iii) optionally from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of an elastomeric ethylene copolymer (EC) ;

iv) from 15.0 to 45.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of a filler (F) ; and

v) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) , wherein the total amounts of the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the elastomeric ethylene copolymer (EC) , the filler (F) and the additives (A) add up to at least 90 wt. -%, more preferably at least 95 wt. -%, most preferably at least 98 wt. -%, based on the total weight of the composition.

In another aspect, the present invention is directed to an article comprising more than 75 wt. -%of the polyolefin composition (PC) of the first aspect, preferably a molded article, most preferably an injection molded article.

Definitions

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although, any methods and materials similar or equivalent to those described herein can be used in practice for testing of the present invention, the preferred materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.

Unless clearly indicated otherwise, use of the terms “a, ” “an, ” and the like refers to one or more.

In the following, amounts are given in %by weight (wt. -%) unless it is stated otherwise.

A propylene homopolymer is a polymer that essentially consists of propylene monomer units. Due to impurities especially during commercial polymerization processes, a propylene homopolymer can comprise up to 0.1 mol%comonomer units, preferably up to 0.05 mol%comonomer units and most preferably up to 0.01 mol%comonomer units.

A propylene copolymer is a copolymer of propylene monomer units and comonomer units, preferably selected from ethylene and C ₄-C ₈ alpha-olefins. A propylene random copolymer is a propylene copolymer wherein the comonomer units are randomly distributed along the polymer chain, whilst a propylene block copolymer comprises blocks of propylene monomer units and blocks of comonomer units. Propylene copolymers can comprise comonomer units from one or more comonomers different in their amounts of carbon atoms.

The heterophasic propylene copolymers typically comprise:

a) a crystalline propylene homopolymer or copolymer matrix (M) ; and

b) an elastomeric rubber, preferably a propylene-ethylene copolymer (EC) .

The present invention will now be described in more detail.

DETAILED DESCRIPTION

Heterophasic propylene-ethylene copolymer (HECO)

The main component of the polyolefin composition (PC) is the heterophasic propylene-ethylene copolymer (HECO) .

The heterophasic propylene-ethylene copolymer (HECO) comprises:

a) a crystalline matrix (M) , being either a propylene homopolymer or a propylene copolymer; and

b) an elastomeric propylene-ethylene copolymer (E) .

The heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR ₂) , measured according to ISO 1133 at 230 ℃ and 2.16 kg, in the range from 40 to 100 g/10 min, more preferably in the range from 50 to 90 g/10 min, most preferably in the range from 60 to 80 g/10 min.

It is preferred that the heterophasic propylene-ethylene copolymer (HECO) has a xylene cold solubles (XCS) content in the range from 15.0 to 30.0 wt. -%, preferably in the range from 16.0 to 25.0 wt. -%, most preferably in the range from 17.0 to 22.0 wt. -%.

It is preferred that the heterophasic propylene-ethylene copolymer (HECO) has a total comonomer content, more preferably a total ethylene (C2) content, in the range from 5.0 to 15.0 wt. -%, preferably in the range from 6.0 to 12.0 wt. -%, most preferably in the range from 7.0 to 9.0 wt. -%.

It is preferred that the heterophasic propylene-ethylene copolymer (HECO) has a comonomer content of the xylene cold soluble fraction, more preferably an ethylene content of the xylene cold soluble fraction (C2(XCS) ) , in the range from 25.0 to 45.0 wt. -%, preferably in the range from 30.0 to 40.0 wt. -%, most preferably in the range from 34.0 to 38.0 wt. -%.

It is preferred that the heterophasic propylene-ethylene copolymer (HECO) has an intrinsic viscosity of the xylene cold soluble fraction (IV (XCS) ) in the range from 1.0 to 4.0 dl/g, preferably in the range from 1.5 to 3.5 dl/g, most preferably in the range from 1.8 to 3.0 dl/g.

Whilst the crystalline matrix (M) may be either a propylene homopolymer or a propylene copolymer, it is preferred that the crystalline matrix (M) is a crystalline propylene homopolymer matrix.

It is further preferred that the crystalline propylene homopolymer matrix (M) of the heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR ₂) , measured according to ISO 1133 at 230℃ and 2.16 kg, in the range from 80 to 300 g/10 min, more preferably in the range from 100 to 250 g/10 min, most preferably in the range from 120 to 200 g/10 min.

The heterophasic propylene-ethylene copolymer (HECO) preferably comprises a polymeric nucleating agent.

A preferred example of such a polymeric nucleating agent is a vinyl polymer, such as a vinyl polymer derived from monomers of the formula

H ₂C = CH-CHR ¹R ²

wherein R ¹ and R ², together with the carbon atom they are attached to, form an optionally substituted saturated or unsaturated or aromatic ring or a fused ring system, wherein the ring or fused ring moiety contains four to 20 carbon atoms, preferably 5 to 12 membered saturated or unsaturated or aromatic ring or a fused ring system, or independently represent a linear or branched C4-C30 alkane, C4-C20 cycloalkane or C4-C20 aromatic ring. Preferably R ¹ and R ², together with the C-atom wherein they are attached to, form a five-or six-membered saturated or unsaturated or aromatic ring, or independently represent a lower alkyl group comprising from 1 to 4 carbon atoms.

Preferred vinyl compounds for the preparation of a polymeric nucleating agent to be used in accordance with the present invention are in particular vinyl cycloalkanes, in particular vinyl cyclohexane (VCH) , vinyl cyclopentane, and vinyl-2-methyl cyclohexane, 3-methyl-1-butene, 3-ethyl-1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene or mixtures thereof. It is particularly preferred that the vinyl polymer is a vinyl cycloalkane polymer, preferably selected from vinyl cyclohexane (VCH) , vinyl cyclopentane and vinyl-2-methyl cyclohexane, with vinyl cyclohexane polymer being a particularly preferred embodiment.

It is further preferred that the vinyl polymer of the polymeric nucleating agent is a homopolymer or a copolymer, more preferably a homopolymer, yet more preferably a vinyl cycloalkane homopolymer, most preferably a vinyl cyclohexane homopolymer.

The heterophasic propylene-ethylene copolymer (HECO) of the present invention may either be synthesized or selected from commercially available polypropylenes.

The heterophasic propylene-ethylene copolymer (HECO) of the present invention is preferably produced in a sequential multistage polymerization process in the presence of a Ziegler-Natta catalyst.

A preferred multistage process is a “loop-gas phase” -process, such as developed by Borealis A/S, Denmark (known as

technology) described e.g. in patent literature, such as in EP 0 887 379, WO 92/12182, WO 2004/000899, WO 2004/111095, WO 99/24478, WO 99/24479 or in WO 00/68315.

A further suitable slurry-gas phase process is the

process of Basell described e.g. in figure 20 of the paper by Galli and Vecello, Prog. Polym. Sci. 26 (2001) 1287-1336.

Elastomeric styrene copolymer (SC)

Another essential component of the polyolefin composition (PC) is the elastomeric styrene copolymer (SC) .

The elastomeric styrene copolymer (SC) has a melt flow rate (MFR ₅) , determined according to ISO 1133 at 230 ℃ at a load of 5.0 kg, in the range from 8.0 to 50.0 g/10 min, more preferably in the range from 10.0 to 40.0 g/10 min, most preferably in the range from 15.0 to 30.0 g/10 min.

It is preferred that the elastomeric styrene copolymer (SC) is a triblock copolymer of styrene and butadiene, which has chain ends of styrene units along backbone chain, and middle chain segments of butadiene. The styrene segments are hard, and butadiene segments are soft, which impart the copolymer with elasticity.

More preferably, it is a hydrogenated triblock copolymer of styrene and butadiene, which has chain ends of styrene units along backbone chain, and middle chain segments of hydrogenated butadiene (i.e. ethylene and butylene units) . It is also called as SEBS copolymer. The segments of ethylene/butylene units are soft relative to styrene segments.

The triblock copolymer of styrene and butadiene, or the hydrogenated copolymer thereof, may comprises some diblock oligomer of styrene and butadiene/or hydrogenated butadiene with a relatively shorter chain than backbone chain, i.e. half triblock oligomer. The presence of diblock oligomer increase cross-linking between long macro-molecular chains of the copolymer.

The elastomeric styrene copolymer (SC) , preferably triblock copolymer of styrene and butadiene, more preferably hydrogenated triblock copolymer of styrene and butadiene, preferably has a styrene content in the range from 5.0 to 25.0 wt. -%, more preferably in the range from 8.0 to 20.0 wt. -%, most preferably in the range from 10.0 to 18.0 wt. -%.

The elastomeric styrene copolymer (SC) , preferably triblock copolymer of styrene and butadiene, more preferably hydrogenated triblock copolymer of styrene and butadiene, preferably has a content of diblock oligomer with chain ends of styrene units and chain segments of hydrogenated butadiene units in the range from 10.0 to 50.0 wt. -%, more preferably in the range from 20.0 to 40.0 wt. -%, most preferably in the range from 25.0 to 35.0 wt. -%.

The elastomeric styrene copolymer (SC) , preferably triblock copolymer of styrene and butadiene, more preferably hydrogenated triblock copolymer of styrene and butadiene, preferably has a density, determined according to ASTM D4025, in the range from 0.870 to 0.930 g/cm ³, more preferably in the range from 0.880 to 0.920 g/cm ³, most preferably in the range from 0.890 to 0.910 g/cm ³.

The elastomeric styrene copolymer (SC) , or triblock copolymer of styrene and butadiene, or hydrogenated triblock copolymer of styrene and butadiene, are known in the art, can be commercially available, or prepared by known process of living anionic polymerization.

Elastomeric ethylene copolymer (EC)

The polyolefin composition (PC) may additionally comprise an optional elastomeric ethylene copolymer (EC) .

The optional elastomeric ethylene copolymer (EC) of the present invention, if present, is used to replace some of the elastomeric styrene copolymer (SC) , reducing the cost of the polyolefin composition (PC) . Furthermore, by increasing the amount of elastomeric ethylene copolymer (EC) and simultaneously decreasing the amount of the elastomeric styrene copolymer (SC) , the stiffness and compatibility of components within the polyolefin composition can be improved. When the amount of elastomeric ethylene copolymer (EC) is decreased and the amount of the elastomeric styrene copolymer (SC) is increased, improved impact can be achieved. The desired balance of stiffness and impact strength influences the choice of how much elastomeric ethylene copolymer (EC) and elastomeric styrene copolymer (SC) are present in the polyolefin composition (PC) .

It is preferred that the elastomeric ethylene copolymer (EC) is a copolymer of ethylene and one or more comonomers selected from C4 to C12 alpha olefins, more preferably selected from C4 to C8 alpha olefins, most preferably the elastomeric ethylene copolymer (EC) is an ethylene-octene copolymer or an ethylene-hexene copolymer or an ethylene-butylene copolymer.

It is preferred that comonomer content of the elastomeric ethylene copolymer, as determined by FT-IR spectroscopy, calibrated using ¹³C-NMR spectroscopy, is in the range from 15.0 to 60.0 wt. -%, more preferably in the range from 20.0 to 50.0 wt. -%, most preferably in the range from 25.0 to 45.0 wt. -%, based on the weight of the elastomeric ethylene copolymer (EC) .

It is preferred that the elastomeric ethylene copolymer (EC) has a melt flow rate (MFR ₂) , determined according to ISO 1133 at 190 ℃ and 2.16 kg, in the range from 0.1 to 30.0 g/10 min, more preferably in the range from 0.3 to 15.0 g/10 min in the range from 0.5 to 10.0 g/10 min.

It is preferred that the elastomeric ethylene copolymer (EC) has a density, determined according to ISO 1183-187, in the range from 0.845 to 0.890 g/cm ³, more preferably in the range from 0.850 to 0.880 g/cm ³, most preferably in the range from 0.855 to 0.870 g/cm ³.

It is preferred that the elastomeric ethylene copolymer (EC) has a melting temperature, melting temperature, determined according to ISO 11357, in the range from 20 to 100 ℃, more preferably in the range from 25 to 70 ℃, most preferably in the range from 30 to 45 ℃.

Filler (F)

Another essential component of the polyolefin composition (PC) is the filler (F) .

It is preferred that the filler is an inorganic filler, more preferably is selected from the group containing talc, calcium carbonate, barium sulfate, mica, and mixtures thereof.

Most preferably, the filler (F) is talc.

It is preferred that the filler (F) has a median diameter (d ₅₀) in the range from 0.1 to 15.0 μm, more preferably in the range from 0.5 to 10.0 μm, most preferably in the range from 1.0 to 5.0 μm.

It is preferred that the filler (F) has a top cut diameter (d ₉₅) in the range from 1.0 to 30.0 μm, more preferably in the range from 2.0 to 20.0 μm, most preferably in the range from 3.0 to 10.0 μm.

Additives

The polyolefin composition (PC) of the present invention may contain additives (A) in an amount of from 0.0 to 5.0 wt. -%. The skilled practitioner would be able to select suitable additives that are well known in the art.

The additives (A) are preferably selected from antioxidants, UV-stabilisers, anti-scratch agents, mold release agents, acid scavengers, lubricants, anti-static agents, colorant or pigment, and mixtures thereof.

It is understood that the content of additives (A) , given with respect to the total weight of the polyolefin composition (PC) , includes any carrier polymers used to introduce the additives to said polyolefin composition (PC) , i.e. masterbatch carrier polymers. An example of such a carrier polymer would be a polypropylene homopolymer in the form of powder.

Polyolefin composition (PC)

The polyolefin composition (PC) of the present invention comprises several essential components, including the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , and the filler (F) , as well as an optional elastomeric ethylene copolymer (EC) and optional additives (A) .

Accordingly, the polyolefin composition (PC) comprises, more preferably consists of:

i) from 40.0 to 60.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the heterophasic propylene-ethylene copolymer (HECO) ;

ii) from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) optionally from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric ethylene copolymer (EC) ;

iv) from 15.0 to 45.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

v) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) , wherein the total amounts of the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the optional elastomeric ethylene copolymer (EC) , the filler (F) and the additives (A) add up to at least 90 wt. -%, more preferably at least 95 wt. -%, yet more preferably at least 98 wt. -%, most preferably 100 wt. -%, based on the total weight of the composition.

In some embodiments, the polyolefin composition contains the elastomeric ethylene copolymer (EC) , whilst in other embodiments the polyolefin composition does not contain the elastomeric ethylene copolymer (EC) .

In the first embodiment, the polyolefin composition (PC) comprises more preferably consists of:

iii) from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric ethylene copolymer (EC) ;

v) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) .

In this first embodiment, it is preferred that the polyolefin composition (PC) comprises more preferably consists of:

i) from 40.0 to 55.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the heterophasic propylene-ethylene copolymer (HECO) ;

ii) from 4.0 to 20.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 4.0 to 20.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric ethylene copolymer (EC) ;

iv) from 20.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

In this first embodiment, it is especially preferred that the polyolefin composition (PC) comprises more preferably consists of:

i) from 40.0 to 50.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the heterophasic propylene-ethylene copolymer (HECO) ;

ii) from 5.0 to 18.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 5.0 to 15.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric ethylene copolymer (EC) ;

iv) from 30.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

In the first embodiment, it is preferred that the combined contents of the elastomeric styrene copolymer (SC) and the elastomeric ethylene copolymer (EC) (i.e. [SC] + [EC] ) are in the range from 5.0 to 30.0 wt. -%, more preferably in the range from 10.0 to 25.0 wt. -%, most preferably in the range from 15.0 to 20.0 wt. -%, relative to the total weight of the polyolefin composition (PC) .

In the second embodiment (i.e. wherein the polyolefin composition (PC) does not comprise the elastomeric ethylene copolymer (EC) ) , the polyolefin composition (PC) comprises, more preferably consists of:

ii) from 5.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 15.0 to 45.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

iv) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) .

In this second embodiment, it is preferred that the polyolefin composition (PC) comprises more preferably consists of:

ii) from 10.0 to 22.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 20.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

In this second embodiment, it is especially preferred that the polyolefin composition (PC) comprises more preferably consists of:

ii) from 15.0 to 20.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 30.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

In each of these embodiments, the individual contents of the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the optional elastomeric ethylene copolymer (EC) , the filler (F) , and the optional additives (A) preferably add up to at least 90 wt. -%, more preferably at least 95 wt. -%, yet more preferably at least 98 wt. -%, most preferably 100 wt. -%, relative to the total weight of the polyolefin composition (PC) .

The polyolefin composition (PC) preferably has a melt flow rate (MFR ₂) , determined according to ISO 1133 at 230 ℃ at a load of 2.16 kg, in the range from 10 to 100 g/10 min, more preferably in the range from 15 to 70 g/10 min, most preferably in the range from 20 to 40 g/10 min.

The polyolefin composition (PC) preferably has an ash content, determined according to ISO 3451-1 (1997) , in the range from 20.0 to 40.0 wt. -%, more preferably 25.0 to 40.0 wt. -%, most preferably 30.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) .

The polyolefin composition (PC) preferably has a Charpy Notched impact strength at 23 ℃, determined according to ISO 179 using 80x10x4 mm ³ test bars injection-molded in line with ISO 19069-2, in the range from 30.0 to 100.0 kJ/m ², more preferably in the range from 35.0 to 90.0 kJ/m ², most preferably in the range from 40.0 to 80.0 kJ/m ².

The polyolefin composition (PC) preferably has a Flexural Modulus, determined according to ISO 178 using 80x10x4 mm ³ test bars injection-molded in line with ISO 19069-2, in the range from 1600 to 4000 MPa, more preferably in the range from 1800 to 3000 MPa, most preferably in the range from 2000 to 2500 MPa.

The polyolefin composition (PC) preferably has a coefficient of linear thermal expansion (CLTE) in the flow direction, determined according to ASTM E 831, of less than 4.7 ×10 ^-6 (K ^-1) , preferably in the range from 3.8 to 4.6 ×10 ^-6 (K ^-1) .

The polyolefin composition (PC) preferably has a coefficient of linear thermal expansion (CLTE) in the cross-flow direction, determined according to ASTM E 831, less than 6.0 ×10 ^-6 (K ^-1) , preferably in the range from 4.5 to 5.9 ×10 ^-6 (K ^-1) , most preferably in the range from 5.0 to 5.8 ×10 ^-6 (K ^-1) .

Process

A process for producing a polyolefin composition (PC) according to the first aspect comprises the steps of:

a) providing the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the optional elastomeric ethylene copolymer (EC) , the filler (F) , and optional additives (A) ;

b) blending and extruding the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the optional elastomeric ethylene copolymer (EC) , the filler (F) , and ptional additives (A) at a temperature in the range from 120 to 250 ℃ in an extruder, preferably a twin-screw extruder, thereby generating the polyolefin composition (PC) , preferably in pellet form.

In particular, it is preferred to use a conventional compounding or blending apparatus, e.g. a Banbury mixer, a 2-roll rubber mill, Buss-co-kneader or a twin-screw extruder. More preferably, mixing is accomplished in a co-rotating twin-screw extruder. The polymer materials recovered from the extruder are usually in the form of pellets.

It is particularly preferred that the polyolefin composition (PC) of the present invention is used for the production of injection-molded articles. It is thus preferred that the process further comprises, after step b) , the step of:

c) injection molding the polyolefin composition (PC) produced in step b) to form an injection-molded article.

Article

In another aspect, the present invention is directed to an article comprising more than 75 wt. -%, preferably more than 80 wt. -%, more preferably more than 90 wt. -%, yet more preferably more than 95 wt. -%, of the polyolefin composition (PC) of the first aspect, most preferably the article consists of the polyolefin composition (PC) .

It is preferred that the article is a molded article, such as a blow-molded or injection-molded article, more preferably, the article is an injection-molded article.

Preferably, the article is a part of automotive articles, especially of car exteriors, for example bumpers, grills, tailgates, body panels, and spoilers.

EXAMPLES

1. Definitions/Measuring Methods

The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

Density is measured according to ISO 1183-187 (elastomeric ethylene copolymer) or ASTM D4025 (elastomeric styrene copolymer) . Sample preparation is done by compression molding in accordance with ISO 1872-2: 2007.

MFR: The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR ₂ of polypropylene is determined at a temperature of 230 ℃ and a load of 2.16 kg. The MFR ₂ of elastomeric ethylene copolymers is determined at a temperature of 190℃ and a load of 2.16 kg. The MFR ₅ of a polymer is measured analogously to the MFR ₂, with the exception that a load of 5.0 kg is used.

Melting temperature Tm: The melting temperature is measured according to ISO 11357-3.

Quantification of propylene copolymer microstructure by NMR spectroscopy

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the propylene polymers.

Quantitative ¹³C { ¹H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for ¹H and ¹³C respectively. All spectra were recorded using a ¹³C optimised 10 mm extended temperature probehead at 125 ℃ using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1, 2-tetrachloroethane-d ₂ (TCE-d ₂) along with chromium- (III) -acetylacetonate (Cr (acac) ₃) resulting in a 65 mM solution of relaxation agent in solvent as described in G. Singh, A. Kothari, V. Gupta, Polymer Testing 2009, 28 (5) , 475.

To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme as described in Z. Zhou, R. Kuemmerle, X. Qiu, D. Redwine, R. Cong, A. Taha, D. Baugh, B. Winniford, J. Mag. Reson. 187 (2007) 225 and V. Busico, P. Carbonniere, R. Cipullo, C. Pellecchia, J. Severn, G. Talarico, Macromol. Rapid Commun. 2007, 28, 1128. A total of 6144 (6k) transients were acquired per spectra. Quantitative ¹³C { ¹H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present.

With characteristic signals corresponding to 2, 1 erythro regio-defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4) , 1253, in Cheng, H.N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) the correction for the influence of the regio-defects on determined properties was required. Characteristic signals corresponding to other types of regio-defects were not observed.

Characteristic signals corresponding to the incorporation of ethylene were observed (as described in Cheng, H.N., Macromolecules 1984, 17, 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer.

The comonomer fraction was quantified using the method of W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157, through integration of multiple signals across the whole spectral region in the ¹³C { ¹H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

The mole percent comonomer incorporation was calculated from the mole fraction.

The weight percent comonomer incorporation was calculated from the weight fraction.

Styrene content

The styrene content is measured by Fourier transform infrared spectroscopy (FTIR) . A thin film of 300 μm thickness is prepared from pelletized material by hot-pressing (190 ℃, 100 bar, 1 minute) . Per sample, two films are prepared. The so prepared film-samples are measured by a Perkin Elmer IR-Spectrophotometer System 2000FTIR. The peak at 1602 cm-1 (Phenyl-Absorption) is integrated and evaluated by using an internally established calibration curve. The arithmetic mean of two measurements is given as result.

Calibration: Various polypropylene-compounds consisting of PP and a styrene-containing elastomer (of known styrene-content) are prepared and measured according to the method described above.

Comonomer content of elastomeric ethylene copolymer

The comonomer content was measured in a known manner based on Fourier transform infrared spectroscopy (FTIR) calibrated with ¹³C-NMR, using Nicolet Magna 550 IR spectrometer together with Nicolet Omnic FTIR software. Films having a thickness of about 250 μm were compression moulded from the samples. Similar films were made from calibration samples having a known content of the comonomer. The comonomer content was determined from the spectrum from the wave number range of from 1430 to 1100 cm ^-1. The absorbance is measured as the height of the peak by selecting the so-called short or long base line or both. The short base line is drawn in about 1410 -1320 cm ^-1 through the minimum points and the long base line about between 1410 and 1220 cm ^-1. Calibrations need to be done specifically for each base line type. Also, the comonomer content of the unknown sample needs to be within the range of the comonomer contents of the calibration samples.

The xylene soluble fraction (XCS) at room temperature (XCS, wt. -%) : The amount of the polymer soluble in xylene is determined at 25 ℃ according to ISO 16152; first edition; 2005-07-01. The remaining part is the xylene cold insoluble (XCU) fraction.

The intrinsic viscosity (IV) is measured according to ISO 1628-1 (at 135 ℃ in decalin) .

Charpy impact test: The Charpy notched impact strength (NIS) was measured according to ISO 179-1 eA at +23 ℃ and -20 ℃, using injection-molded bar test specimens of 80x10x4 mm ³ prepared in accordance with ISO 19069-2.

Flexural Modulus: The flexural modulus was determined in 3-point-bending at 23℃ according to ISO 178 on 80x10x4 mm ³ test bars injection-molded in line with ISO 19069-2.

Average particle size (diameter) d ₅₀ and top cut d ₉₅ were calculated from the particle size distribution [mass percent] as determined by laser diffraction method, using Laser Mastersizer, according to ISO 13320-1. The d ₅₀ is defined as the median diameter, whilst d ₉₅ is the diameter at the 95 ^th percentile, as observed from the particle size distribution.

Coefficient of linear thermal expansion (CLTE) : The coefficient of linear thermal expansion (CLTE) was determined in accordance with ASTM E 831.

The test is conducted on a TMA (Thermal Mechanical Analysis) equipment, commercially available from Perkin Elmer Inc, MA, USA, with the model of ＂Pyrus Diamond TMA STD＂, S/N –10100575000008. In the test, temperature range for test is from -30 ℃ to 80 ℃, and temperature increases at a rate of 5 ℃/min.

Ash content: The ash content was measured according to ISO 3451-1 (1997) .

2. Examples

2.1. Synthesis of the heterophasic propylene-ethylene copolymer (HECO)

The catalyst used in each of the polymerization was a Ziegler-Natta catalyst from Borealis having Ti-content of 1.9 wt. -% (as described in EP 591 224) . Before the polymerization, the catalyst was prepolymerized with vinyl-cyclohexane (VCH) as described in EP 1 028 984 and EP 1 183 307. The ratio of VCH to catalyst of 1: 1 was used in the preparation, thus the final poly-VCH content was less than 100 ppm.

In the first stage the catalyst described above was fed into prepolymerization reactor together with propylene and small amount of hydrogen (2.5 g/h) and ethylene (330 g/h) . Triethylaluminium as a cocatalyst and dicyclopentyldimethoxysilane as a donor was used. The aluminium to donor ratio was 7.5 mol/mol and aluminium to titanium ratio was 300 mol/mol. Reactor was operated at a temperature of 30 ℃ and a pressure of 55 barg.

The subsequent polymerization has been effected under the following conditions.

Table 1: Polymerization conditions for the HECO

In addition, the following commercially available components were used in the inventive compositions:

EO an elastomeric ethylene-octene copolymer with a trade name of Fortify C1055D, commercially available from Sabic (Shanghai) Trading Co. Ltd (China) , having an MFR ₂ (190 ℃) of 1.0 g/10 min, a density of 0.857 g/cm ³, and a melting temperature of 37 ℃.

SEBS a hydrogenated copolymer of styrene and butadiene, i.e. a so-called styrene-ethylene-butylene-styrene copolymer with a trade name of Kraton G1657, commercially available from Kraton Polymers Corp (USA) , having an MFR ₅ (230 ℃) of 22.0 g/10 min, a styrene content of 13 wt. -%, a content of diblock oligomer of styrene-ethylene-butylene with chain ends of styrene units and middle chain segments of hydrogenated butadiene units of 30 wt. -%, and a density of 0.900 g/cm ³.

F talc with a trade name of Jetfine 3CA, commercially available from Imerys (France) , with median diameter d50 of 3.9 μm and top cut diameter d95 of 7.8 μm.

Additives an additive masterbatch, consisting of, 0.20 wt. -%of an antioxidant with a trade name of Irganox 1010 (CAS-no. 6683-19-8) , available from BASF SE (Germany) , 0.20 wt. -%of an antioxidant with a trade name of Irgafos 168 (CAS-no. 31570-04-4) , available from BASF SE (Germany) , 0.20 wt. -%of calcium stearate (CAS-no. 1592-23-0) , available from FACI Chemicals (Zhangjiagang) Co., Ltd (China) , 0.40 wt. -%of a UV stabiliser with a trade name of Cyasorb 3808PP5, available from Solvay (China) , and 1.00 wt. -%of a carbon black-containing masterbatch with a trade name of 1073-BK-50, available from Polyone (USA) , based on 100%of total weight of the polyolefin composition.

2.3. Compounding preparation of inventive examples

The inventive examples were prepared according to the recipes indicated in Table 2 by compounding in a co-rotating twin-screw extruder “STS35” from Coperion under the conditions described in Table 3, wherein the additives were fed into one main feeder and HECO, EO and SEBS are fed into a different main feeder, whilst the talc is added into a side feeder of the extruder.

Table 2: Recipes for inventive examples

Table 3: Compounding conditions for inventive examples in twin-screw extruder

2.3. Properties of inventive and comparative examples

The properties of the resultant compositions (IE1 to IE5) are given in Table 4, alongside the properties of the comparative example, which is the prior grade Daplen EF341AEC, commercially available from Borouge Compounding Pte. Ltd, representing a state of the art composition for preparing injection-molded automotive exterior articles with low CLTE.

Table 4: Properties of the comparative example and inventive examples

As can be seen from Table 4, the inventive examples have considerably improved impact strength and melt flow rate, relative to the comparative example, as well as low CLTE (in the flow direction) , comparable to the prior grade, and an even lower CLTE (specifically in the cross flow direction) , whilst maintaining acceptable levels of stiffness (Flexural Modulus) . The higher MFR ₂ of the inventive examples facilitates the preparation of thin-wall injection-molded articles.

It can be seen from comparing IE2, IE4 and IE5 that by increasing the SEBS content at the expense of the EO content, the impact properties can be improved greatly, whilst it can also be seen from comparing IE1, IE2 and IE3 that increasing the talc content at the expense of HECO content, the stiffness improves, whilst the CLTE notably decreases.

The properties of IE2 represent a particularly beneficial balance of the key properties.

Claims

A polyolefin composition (PC) comprising:

i) from 40.0 to 60.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of a heterophasic propylene-ethylene copolymer (HECO) , comprising:

a) a crystalline matrix (M) , being either a propylene homopolymer or a propylene copolymer;

b) an elastomeric propylene-ethylene copolymer (E) ;

wherein the heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR ₂) , determined according to ISO 1133 at 230 ℃ at a load of 2.16 kg, in the range from 40 to 100 g/10 min;

ii) from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of an elastomeric styrene copolymer (SC) , having a melt flow rate (MFR ₅) , determined according to ISO 1133 at 230 ℃ at a load of 5.0 kg, in the range from 8.0 to 50 g/10 min;

iii) optionally from 3.0 to 25.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of an elastomeric ethylene copolymer (EC) ;

iv) from 15.0 to 45.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of a filler (F) ; and

v) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) ,

wherein the total amounts of the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the elastomeric ethylene copolymer (EC) , the filler (F) and the additives (A) add up to at least 90 wt. -%, more preferably at least 95 wt. -%, most preferably at least 98 wt. -%, based on the total weight of the composition.
The polyolefin composition (PC) according to any one of the preceding claims, wherein the heterophasic propylene-ethylene copolymer (HECO) has one or more, preferably all, of the following properties:

i) a melt flow rate (MFR ₂) , determined according to ISO 1133 at 230 ℃ at a load of 2.16 kg, in the range from 50 to 90 g/10 min, more preferably in the range from 60 to 80 g/10 min.

ii) a total ethylene (C2) content in the range from 5.0 to 15.0 wt. -%, preferably in the range from 6.0 to 12.0 wt. -%, most preferably in the range from 7.0 to 9.0 wt. -%;

iii) a xylene cold solubles (XCS) content in the range from 15.0 to 30.0 wt. -%, more preferably in the range from 16.0 to 25.0 wt. -%, most preferably in the range from 17.0 to 22.0 wt. -%;

iv) an ethylene content of the xylene cold soluble fraction (C2 (XCS) ) in the range from 25.0 to 45.0 wt. -%, more preferably in the range from 30.0 to 40.0 wt. -%, most preferably in the range from 34.0 to 38.0 wt. -%; and

v) an intrinsic viscosity of the xylene cold soluble fraction (IV (XCS) ) in the range from 1.0 to 4.0 dl/g, preferably in the range from 1.5 to 3.5 dl/g, most preferably in the range from 1.8 to 3.0 dl/g.
The polyolefin composition (PC) according to any one of the preceding claims, wherein the crystalline matrix (M) of the heterophasic propylene-ethylene copolymer (HECO) is a propylene homopolymer, preferably having a melt flow rate (MFR ₂) , determined according to ISO 1133 at 230 ℃ and 2.16 kg, in the range from 80 to 300 g/10 min, more preferably in the range from 100 to 250 g/10 min, most preferably in the range from 120 to 200 g/10 min.
The polyolefin composition (PC) according to any one of the preceding claims, wherein the heterophasic propylene-ethylene copolymer (HECO) comprises a polymeric nucleating agent, preferably a vinyl cycloalkane polymer, more preferably a vinyl cyclohexane polymer, most preferably a vinyl cyclohexane homopolymer.
The polyolefin composition (PC) according to any one of the preceding claims, wherein the elastomeric styrene copolymer (SC) is a hydrogenated block copolymer of styrene and butadiene with chain ends of styrene units along backbone chain, preferably having one or more, more preferably all, of the following features:

a) a melt flow rate (MFR ₅) , determined according to ISO 1133 at 230 ℃ and 5.0 kg, in the range from 10.0 to 40.0 g/10 min, most preferably in the range from 15.0 to 30.0 g/10 min; and

b) a styrene content in the range from 5.0 to 25.0 wt. -%, more preferably in the range from 8.0 to 20.0 wt. -%, most preferably in the range from 10.0 to 18.0 wt. -%.
The polyolefin composition (PC) according to any one of the preceding claims, wherein the elastomeric ethylene copolymer (EC) is a copolymer of ethylene and one or more comonomers selected from C4 to C12 alpha olefins, preferably wherein the elastomeric ethylene copolymer (EC) , has one or more, preferably all, of the following properties:

a) a melt flow rate (MFR ₂) , determined according to ISO 1133 at 190 ℃ and 2.16 kg, in the range from 0.1 to 30.0 g/10 min, more preferably in the range from 0.3 to 15.0 g/10 min in the range from 0.5 to 10.0 g/10 min; and

b) a density, determined according to ISO 1183-187, in the range from 0.845 to 0.890 g/cm ³, more preferably in the range from 0.850 to 0.880 g/cm ³, most preferably in the range from 0.855 to 0.870 g/cm ³.
The polyolefin composition (PC) according to any one of the preceding claims, wherein the filler (F) is an inorganic filler, more preferably selected from the group containing talc, calcium carbonate, barium sulfate, mica, and mixtures thereof, most preferably the inorganic filler (F) is talc.
The polyolefin composition (PC) according to any one of the preceding claims, which comprises, more preferably consists of:

i) from 40.0 to 60.0 wt. -%, more preferably 40.0 to 55.0 wt. -%, most preferably 40.0 to 50.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the heterophasic propylene-ethylene copolymer (HECO) ;

ii) from 3.0 to 25.0 wt. -%, more preferably 4.0 to 20.0 wt. -%, most preferably 5.0 to 18.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 3.0 to 25.0 wt. -%, more preferably 4.0 to 20.0 wt. -%, most preferably 5.0 to 15.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric ethylene copolymer (EC) ;

iv) from 15.0 to 45.0 wt. -%, more preferably 20.0 to 40.0 wt. -%, most preferably 30.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

v) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) ,

wherein the total amounts of the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the elastomeric ethylene copolymer (EC) , the filler (F) and the additives (A) add up to at least 90 wt. -%, more preferably at least 95 wt. -%, most preferably at least 98 wt. -%, based on the total weight of the composition.
The polyolefin composition (PC) according to any one of claims 1 to 7, which comprises, more preferably consists of:

i) from 40.0 to 60.0 wt. -%, more preferably 40.0 to 55.0 wt. -%, most preferably 40.0 to 50.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the heterophasic propylene-ethylene copolymer (HECO) ;

ii) from 5.0 to 25.0 wt. -%, more preferably 10.0 to 22.0 wt. -%, most preferably 15.0 to 20.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the elastomeric styrene copolymer (SC) ;

iii) from 15.0 to 45.0 wt. -%, more preferably 20.0 to 40.0 wt. -%, most preferably 30.0 to 40.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of the filler (F) ; and

iv) from 0.0 to 5.0 wt. -%, relative to the total weight of the polyolefin composition (PC) , of additives (A) ,

wherein the total amounts of the heterophasic propylene-ethylene copolymer (HECO) , the elastomeric styrene copolymer (SC) , the filler (F) and the additives (A) add up to at least 90 wt. -%, more preferably at least 95 wt. -%, most preferably at least 98 wt. -%, based on the total weight of the composition.
The polyolefin composition (PC) according to any one of the preceding claims, having a melt flow rate (MFR ₂) , determined according to ISO 1133 at 230 ℃ at a load of 2.16 kg, in the range from 10 to 100 g/10 min, more preferably in the range from 15 to 70 g/10 min, most preferably in the range from 20 to 40 g/10 min.
The polyolefin composition (PC) according to any one of the preceding claims, having a Charpy Notched impact strength at 23 ℃, determined according to ISO 179 using 80x10x4 mm ³ test bars injection-molded in line with ISO 19069-2, in the range from 30.0 to 100.0 kJ/m ², more preferably in the range from 35.0 to 90.0 kJ/m ², most preferably in the range from 40.0 to 80.0 kJ/m ².
The polyolefin composition (PC) according to any one of the preceding claims, having a coefficient of linear thermal expansion (CLTE) in the cross-flow direction, determined according to ASTM E 831, less than 6.0 ×10 ^-6 (K ^-1) , more preferably in the range from 4.5 to 5.9 ×10 ^-6 (K ^-1) , most preferably in the range from 5.0 to 5.8 ×10 ^-6 (K ^-1) .
The polyolefin composition (PC) according to any one of the preceding claims, having a coefficient of linear thermal expansion (CLTE) in the flow direction, determined according to ASTM E 831, less than 4.7 ×10 ^-6 (K ^-1) , more preferably in the range from 3.8 to 4.6 × 10 ^-6 (K ^-1) .
An article comprising more than 75 wt. -%of the polyolefin composition (PC) according to any one of the preceding claims, preferably a molded article, most preferably an injection molded article.