The present invention relates to a polyolefin composition with improved impact and environmental stress crack resistance (ESCR). In particular, the invention relates to a polyolefin blend comprising high density polyethylene (HDPE), impact or hompolymer polypropylene (PP) and polyolefin elastomer (POE).

HDPE exhibits good properties such as high impact resistance especially at low temperatures, high stiffness, low permeability and good chemical resistance. However, for many applications a high environmental stress crack resistance is required.

Typical examples for articles where a high ESCR is need are solar hot water tanks, dangerous goods containers, pipe system parts and fuel tanks. The need for high environmental stress cracking resistance becomes even more evident in application fields where developments are directed towards down gauging for example caps and closures. This allows not only to save raw material but as well to reduce cycle time and energy consumption. Hence, cost and efficiency in the production process can be optimised. Therefore, material with well-balanced properties are needed. The improvement of environmental stress cracking resistance while maintaining impact properties of the material is an essential part of a product development.

The present invention provides a polyolefin composition with surprisingly improved resistance to environmental stress cracking while maintaining good impact.

The polyolefin composition according to the invention comprises high density polyethylene, polyolefin elastomer and polypropylene, wherein the polypropylene is selected from homopolymer PP or impact PP and wherein the amount of high density polyethylene is more than 40% by weight of the total amount of high density polyethylene, polyolefin elastomer and impact or homopolymer polypropylene and wherein the total amount of high density polyethylene, polyolefin elastomer and polypropylene is 100 % by weight and wherein the high density polyethylene has a density in the range from 940 to 960 kg/m ³ .

The polyethylene compositions according to the invention have a high ESCR, combined with a high impact performance. Surprisingly, it was found that a high ESCR and high impact performance can be achieved without the need for a compatiblizer, such as a block copolymer compatibilizer. Further the polyethylene composition according to the invention may be simply applied as a dry-blend for obtaining a product or article. An additional compounding step is not necessary. According to a preferred embodiment of the invention, the polyolefin composition comprises impact or homopolymer polypropylene in a range between > 0.1 % by weight and < 40 % by weight, preferably between > 5 % by weight and < 35 % by weight, more preferably between > 10 %by weight and < 35 % by weight, more preferably between > 15 %by weight and < 30 % by weight, wherein the total amount of high density polyethylene, polyolefin elastomer and impact or homopolymer polypropylene is 100 % by weight.

According to a preferred embodiment of the invention, the polyolefin composition comprises polyolefin elastomer in a range between > 0.1 % by weight and < 40 % by weight, preferably between > 2 % by weight and < 25 % by weight, more preferably between > 5 % by weight and < 21 % by weight, more preferably between > 9 % by weight and < 21 % by weight wherein the total amount of high density polyethylene, polyolefin elastomer and impact or homopolymer polypropylene is 100 % by weight. According to a preferred embodiment of the invention, the polyolefin composition comprises high density polyethylene in a range between > 41 % by weight and < 90 % by weight, preferably between > 45 % by weight and < 80 % by weight, more preferably between > 50 % by weight and < 80 % by weight, more preferably between > 50 % by weight and < 75 % by weight wherein the total amount of high density polyethylene, polyolefin elastomer and impact or homopolymer polypropylene is 100 % by weight.

According to a preferred embodiment of the invention, the polyolefin composition comprises FIDPE in a range between >41 % by weight and <90 % by weight, impact or homopolymer PP in a range between > 0.1 % by weight and < 40 % by weight and POE in a range between > 0.1% by weight and < 40 % by weight.

According to a preferred embodiment of the invention, the polyolefin composition comprises FIDPE in a range between >45 % by weight and <80 % by weight, impact or homopolymer PP in a range between > 5 % by weight and < 35 % by weight and POE in a range between > 2% by weight and < 25 % by weight. According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <80 % by weight, impact or homopolymer PP in a range between > 10 % by weight and < 35 % by weight and POE in a range between > 5% by weight and < 21 % by weight.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <75 % by weight, impact or homopolymer PP in a range between > 15 % by weight and < 35 % by weight and POE in a range between > 9% by weight and < 21 % by weight. According to a preferred embodiment of the invention, the polyolefin composition is characterised in that amount of high density polyethylene is higher than amount of polypropylene and wherein this is based on the wt% of high density polyethylene and the wt% of polypropylene in the composition and/or the amount of polypropylene is higher than the amount of polyolefin elastomer and wherein this is based on the wt% of polypropylene and the wt% of polyolefin elastomer in the composition.

High density polyethylene (HDPE)

According to a preferred embodiment of the invention, the polyolefin composition is characterized in that the MFI of high density polyethylene ranges between >0.1 and <30 g/10min.

According to another preferred embodiment of the invention, the polyolefin composition is characterized in that the MFI ranges between >0.6 and <15 g/10min, more preferably between >0.6 and <4 g/10min.

The MFI is measured according to ISO 1 133 at 190 degrees Celsius and 2.16 kg. According to a preferred embodiment of the invention, the polyolefin composition is characterized in that the density of high density polyethylene ranges between >940 and <958 kg/m ³ , more preferably ranges between >945 and <955 kg/m ³ .

The density is measured according to measured according to ISO 1 183. The HDPE may be unimodal HDPE or multimodal HDPE for example bimodal HDPE or trimodal HDPE. Preferably, the HDPE is bimodal HDPE.

The production processes of the HDPE and is summarised in “Handbook of Polyethylene” by Andrew Peacock (2000; Dekker; ISBN 0824795466) at pages 43-66. Suitable catalysts for the production of polyethylene include Ziegler Natta catalysts, chromium based catalysts and single site metallocene catalysts. The unimodal polyethylene may be obtained for example by polymerizing ethylene and optionally at least one olefin comonomer in slurry in the presence of a silica-supported chromium-containing catalyst and/or an alkyl boron compound. Suitable comonomers include for example propylene, 1 -butene, 1 -pentene, 4-methyl-1 -pentene, 1 -hexene and/or 1 -octene.

The unimodal polyethylene may be obtained for example by polymerizing ethylene and optionally at least one olefin comonomer in a gas phase polymerisation or in slurry polymerisation process.

The production processes for bimodal high density polyethylene (HDPE) are summarised at pages 16-20 of “PE 100 Pipe systems” (edited by Bromstrup; second edition, ISBN 3-8027-2728-2). The production of bimodal high density polyethylene (HDPE) via a low pressure slurry process is described by Alt et al. in “Bimodal polyethylene-interplay of catalyst and process” (Macromol.Symp. 2001 , 163, 135-143). The characteristics of the polyethylene are determined amongst others by the catalyst system and by the concentrations of catalyst, comonomer and hydrogen. The production of bimodal high density polyethylene (HDPE) via a low pressure slurry process may also be performed via a three stage process. The concept of the two stage cascade process is elucidated at pages 137-138 by Alt et al. “Bimodal polyethylene-interplay of catalyst and process” (Macromol. Symp. 2001 , 163).

Polyolefin elastomer (POE)

According to the invention, the polyolefin elastomer is a copolymer. Copolymer needs to be understood as a polymer that is derived from more than one species of monomer. The characteristic sequence arrangements of the monomeric units within the copolymer may for example be statistical or random. Preferably the copolymer is derived from two different monomer species.

Preferably, the copolymerisation is always done in the presence of at least a second monomer in the reaction mixture. Preferably, the monomers are not added in sequence to the reaction mixture.

The polyolefin elastomer according to the invention is a copolymer that does not include block sequence arrangements of the monomeric units within the copolymer (block copolymers).

Block copolymers or copolymers with block sequence arrangement need to be understood as copolymers which are composed of at least two blocks. Block means that adjacent segments are essentially or completely derived from different species of monomer, meaning that the blocks differ in chemical or physical properties. Essentially in this respect should be understood in the sense that more than 70 mol% of the monomeric species based on the total amount of monomeric species of that block are derived from different species of monomer compared to the adjacent block. Suitable examples of polyolefin elastomers may be ethylene-alpha olefin copolymers and include for example ethylene-1 -octene copolymers and ethylene-1 -butene copolymers as described for example by L.T.Kale et al in “Structure property relationship of ethylene -1 -octene copolymer and ethylene-1 -butene copolymer made using insite technology” (1995 Polymers, Lamination and coatings Conference, pages 423-433).

Suitable ethylene- alpha olefin copolymers are also disclosed in US8729200B2, US6559230B2, EP2076551 B, EP2326654B, EP2077269B, EP2365990B, EP2010576 and EP218561 1 B. According to a preferred embodiment of the invention, the polyolefin composition is characterized in that the polyolefin elastomer is an ethylene-alpha olefin copolymer, preferably an ethylene-octene copolymer.

According to a preferred embodiment of the invention, the polyolefin composition is characterized in that MFI of the ethylene-alpha olefin copolymer ranges between >0.5 and <30 g/10min, preferably between >0.6 and <10 g/10min, more preferably between >0.6 and <4 g/10min. The melt flow index (MFI) is measured according to ASTM D1238 at 190 degrees Celcius and 2.16 kg.

According to a preferred embodiment of the invention, the polyolefin composition is characterized in that density of the ethylene-alpha olefin copolymer ranges between >857 and <880 kg/m ³ , preferably between >865 and <870 kg/m ³ . The density is measured according to ASTM D1505.

Polypropylene (PP)

According to the invention, the PP is characterized in that it is either impact PP or homopolymer PP.

According to a preferred embodiment of the invention, the polyolefin composition is characterized in that the MFI of the PP ranges between >0.3 and <100 g/10min, preferably ranges between >0.3 and <10 g/10min, more preferably ranges between >0.3 and <4 g/10min. The MFI is measured according to IS01 133 at 230 degrees Celsius and 2.16 kg.

According to a preferred embodiment of the invention, the polyolefin composition is characterized in that the density of the PP ranges ranges between >900 and <920 kg/m ³ , preferably ranges between > 904 and < 906 kg/m ³ . The density is measured according to ISO 1 183.

Homopolvmer PP

Polypropylene compositions consisting of a propylene homopolymer are known. Propylene homopolymer may be obtained by polymerizing propylene under suitable polymerization conditions.

In contrast to that a propylene copolymer may be obtained by copolymerizing propylene and one or more other olefins, preferably ethylene, under suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is, for example, described in Moore, E. P. (1996) Polypropylene Handbook. Polymerization, Characterization, Properties, Processing, Applications, Hanser Publishers: New York.

Homopolymer polypropylene can be made by any known polymerization technique as well as with any known polymerization catalyst system. Regarding the techniques, reference can be given to slurry, solution or gas phase polymerizations; regarding the catalyst system reference can be given to Ziegler-Natta, metallocene or single-site catalyst systems.

Impact PP

The impact PP according to the invention is a heterophasic propylene copolymer wherein the heterophasic propylene copolymer consists of

(a) a propylene-based matrix,

wherein the propylene-based matrix consists of a propylene homopolymer and/or a propylene copolymer consisting of at least 70 wt% of propylene and at most 30 wt% of ethylene and/or an a-olefin having 4-10 carbon atoms, based on the total weight of the propylene-based matrix and

wherein the propylene-based matrix is present in an amount of 60 to 95 wt% based on the total heterophasic propylene copolymer and

wherein the propylene-based matrix has a melt flow index of at least 0.1 dg/min and at most 45 dg/min, measured according to IS01 133 (2.16 kg/230°C) and (b) a dispersed ethylene-oolefin copolymer, wherein the dispersed ethylene-oolefin copolymer is an ethylene-propylene copolymer, wherein the ethylene-a olefin copolymer is present in an amount of 40 to 5 wt% based on the total heterophasic propylene copolymer and

wherein the sum of the total amount of propylene-based matrix and total amount of dispersed ethylene-a-olefin copolymer is 100wt%.

Heterophasic propylene copolymers are generally prepared in one or more reactors, by polymerization of propylene in the presence of a catalyst and subsequent polymerization of a propylene-a-olefin mixture. The resulting polymeric materials are heterophasic, but the specific morphology usually depends on the preparation method and monomer ratio.

Properties of the polyolefin composition Polyolefin composition according to a preferred embodiment characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is > 50 kJ/m ² , preferably > 60 kJ/m ² , more preferably >69 kJ/m ² . Polyolefin composition according to a preferred embodiment characterised in that the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 500 hours, preferably > 600 hours, more preferably > 650 hours.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >41 % by weight and <90 % by weight, impact or homopolymer PP in a range between > 0.1 % by weight and < 40 % by weight and

POE in a range between > 0.1 % by weight and < 40 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and

wherein the MFI of HDPE ranges between >0.1 and <30 g/10min, the MFI of the PP ranges between >0.3 and <100 g/10min, the MFI of the POE ranges between >0.5 and <30 g/10min and the density of the POE ranges between >857 and <880 kg/m ³ .

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >45 % by weight and <80 % by weight, impact or homopolymer PP in a range between > 5 % by weight and < 35 % by weight and POE in a range between > 2% by weight and < 25 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and

wherein the MFI ranges of the HDPE ranges between >0.6 and <15 g/10min, the density of the HDPE ranges between >940 and <958 kg/m ³ , the MFI of the PP ranges between >0.3 and <100 g/10min, the MFI of the POE between >0.6 and <10 g/10min and the density of POE ranges between >857 and <880 kg/m ³ .

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <80 % by weight, impact or homopolymer PP in a range between > 10 % by weight and < 35 % by weight and POE in a range between > 5% by weight and < 21 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the

MFI of the HDPE ranges between >0.6 and <15 g/10min, the density of the HDPE ranges between >940 and <958 kg/m ³ , the MFI of the PP ranges between >0.3 and <100 g/10min, the MFI of POE ranges between >0.6 and <10 g/10min and the density of POE ranges between >865 and <870 kg/m ³ .

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <75 % by weight, impact or homopolymer PP in a range between > 15 % by weight and < 35 % by weight and POE in a range between > 9% by weight and < 21 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the

MFI of the HDPE ranges between >0.6 and <4 g/10min, the density of the HDPE ranges between >945 and <955 kg/m ³ , the MFI of the PP ranges between >0.3 and <4 g/10min, thePOE is an ethylene-octene copolymer, the MFI of POE ranges between >0.6 and <4 g/10min and the density of POE ranges between >865 and <870 kg/m ³ .

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >41 % by weight and <90 % by weight, impact or homopolymer PP in a range between > 0.1 % by weight and < 40 % by weight and POE in a range between > 0.1 % by weight and < 40 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the polyolefin composition is characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is > 50 kJ/m ² , and the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 500 hours.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >45 % by weight and <80 % by weight, impact or homopolymer PP in a range between > 5 % by weight and < 35 % by weight and POE in a range between > 2% by weight and < 25 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the

the polyolefin composition is characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is > 60 kJ/m ² , and the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 600 hours.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <80 % by weight, impact or homopolymer PP in a range between > 10 % by weight and < 35 % by weight and POE in a range between > 5% by weight and < 21 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the and wherein the polyolefin composition is characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is >69 kJ/m ² and the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 650 hours.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <75 % by weight, impact or homopolymer PP in a range between > 15 % by weight and < 35 % by weight and POE in a range between > 9% by weight and < 21 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the

the polyolefin composition is characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is >69 kJ/m ² and the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 650 hours.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >41 % by weight and <90 % by weight, impact or homopolymer PP in a range between > 0.1 % by weight and < 40 % by weight and POE in a range between > 0.1 % by weight and < 40 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and

wherein the MFI of HDPE ranges between >0.1 and <30 g/10min, the MFI of the PP ranges between >0.3 and <100 g/10min, the MFI of the POE ranges between >0.5 and <30 g/10min and the density of the POE ranges between >857 and <880 kg/m ³ and wherein

the polyolefin composition is characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is > 50 kJ/m ² , and the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 500 hours.

According to a preferred embodiment of the invention, the polyolefin composition comprises HDPE in a range between >50 % by weight and <75 % by weight, impact or homopolymer PP in a range between > 15 % by weight and < 35 % by weight and POE in a range between > 9% by weight and < 21 % by weight, wherein the total amount of HDPE, POE and polypropylene is 100 % by weight and wherein the

MFI of the HDPE ranges between >0.6 and <4 g/10min, the density of the HDPE ranges between >945 and <955 kg/m ³ , the MFI of the PP ranges between >0.3 and <4 g/10min, thePOE is an ethylene-octene copolymer, the MFI of POE ranges between >0.6 and <4 g/10min and the density of POE ranges between >865 and <870 kg/m ³ and wherein

the polyolefin composition is characterised in that the impact performance measured by Izod according to ISO180 using testbar 4A at 23 °C in machine direction is > 50 kJ/m ² , and the ESCR performance measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C) in machine direction 50% failure is > 500 hours.

The polymer composition comprising high density polyethylene, a polyolefin elastomer and impact or homopolymer polypropylene may be applied as dry blend and as a compound.

All components may be added directly on the injection molding machine using a gravimetric dosing system.

All components can be added together as a dry blend. Mixing of the materials can be done by industrial mixing devices, such as Nauta mixer and Henschel mixers. All components may be added together as a compound by melt blending. The compounding is usually carried out in a mixer (also known as a compounder), a single screw extruder or a twin screw extruder, wherein the polymer and the additives are melt-blended. Compounding techniques are well-known in the art.

The polymers in the resin composition and also the resin composition according to the invention may contain additives, for instance nucleating agents and clarifiers, stabilizers, release agents, fillers, plasticizers, anti-oxidants, lubricants, antistatics, scratch resistance agents, high performance fillers, pigments and/or colorants, impact modifiers, blowing agents, acid scavengers, recycling additives, coupling agents, anti microbial, anti-fogging additives, slip additives, anti-blocking additives, flame retardants and polymer processing aids. These additives are well known in the art. The skilled person will choose the type and amount of additives such that they do not detrimentally influence the aimed properties of the composition.

According to a preferred embodiment of the invention, the polyolefin composition are used for the production of injection molded articles and blow molded articles.

According to another preferred embodiment of the invention, the polyolefin composition are used for the production of pipe system parts, solar hot water tanks, dangerous goods containers, industrial containers, fuel tanks, caps or closures.

Further, the invention is directed to a blow molded article or an injection molded article comprising the polyolefin composition according to the invention.

Further, the invention is directed to pipe system parts, solar hot water tanks, dangerous goods containers, industrial containers, fuel tanks, caps or closures comprising the polyolefin composition according to the invention.

According to another preferred embodiment of the invention, the polyolefin composition is used for the production of parts in automotive applications. This may for example be airducts and windscreenwasher tanks.

According to another preferred embodiment of the invention, the polyolefin composition is used for the production of fuel tanks for lawnmower, boats, chainsaws, tractors, garden equipment.

The invention will now be illustrated by the following non-limiting examples. Examples

Materials

The materials mentioned in Table 1 were used.

Table 1 : Used Materials.

Sample preparation

All components were added together as a dry blend and directly used for injection molding. The dry blends were injection molded on a Arburg Allrounder machine using a standard mold. Injection molding techniques are well-known in the art.

Measurement methods

-Bell test

The ESCR was measured according to ASTM D1693 Bent Strip ESCR test (Bell test) (10% Igepal CO-630, 50°C).

-Izod

Impact was measured by Izod according to ISO180 using testbar 4A at 23 °C. Results

Table 2 and Table 3 give an overview of the prepared samples and their ESCR and Impact performance. The inventive examples of Table 2 comprise impact PP, the inventive examples of Table 3 comprise PP homopolymer. Measurements were performed on the injection molded samples in machine direction.

Table 2: Overview of Comparative and Inventive examples and measurement results. The inventive examples comprise HDPE, impact PP and POE.

The inventive examples lnv.1 and lnv.2 show in comparison to pure HDPE, example C1 , an enormous improvement in impact, measured by Izod, and in ESCR, measured by the Bell test.

Blends of HDPE and POE show a higher impact and ESCR performance in comparison to pure HDPE, which is demonstrated here by C2 in comparison to C1 . However, the ESCR of HDPE and POE blends is not as good as in comparison to the inventive examples, which is shown here for C2 comparison to Inv. 1 .

This is also the case for blends of HDPE and impact PP, as shown for example C3. The inventive samples have a comparable impact performance, but much better ESCR.

Blends of HDPE, POE and random PP do not lead to such high ESCR performance either. This is shown for example C4 in comparison to Inv. 2.

Best impact and ESCR performance are achieved for the inventive examples Inv.1 and lnv.2. Table 3: Overview of Comparative examples and Inventive examples and measurement results. The inventive examples comprise HDPE, PP homopolymer and POE.

The inventive examples lnv.3, lnv.4 and lnv.5 show in comparison to pure HDPE, example C1 , an enormous improvement in impact, measured by Izod, and in ESCR, measured by the Bell test.

Blends of HDPE and POE show a higher impact and ESCR performance in comparison to pure HDPE, which is demonstrated here by C2 in comparison to C1 . However, the ESCR of HDPE and POE blends is not as good as in comparison to the inventive examples, which is shown here for C2 comparison to Inv. 3 and lnv.4.

Blends of HDPE and PP homopolymer show the same impact and an only slightly improved ESCR performance in comparison to pure HDPE, which is demonstrated here by C5 in comparison to C1. However, the ESCR of HDPE and PP homopolymer blends is not as good as in comparison to the inventive examples, which is shown here for C5 comparison to Inv. 3.

Best impact and ESCR performance are achieved for the inventive examples lnv.3, lnv.4 and lnv.5.