CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 of International Application No. PCT/EP2017/062258, filed May 22, 2017, which is incorporated herein by reference in its entirety, and which claims priority to European Application Serial No. 16171720.2 filed May 27, 2016.

The invention relates to a propylene copolymer composition, to the use of the propylene copolymer composition and to articles, preferably pipes, comprising the propylene copolymer composition.

Polypropylene compositions consisting of a propylene homopolymer or a propylene copolymer are known. A propylene homopolymer is obtained by polymerizing propylene under suitable polymerization conditions. A random or block propylene copolymer is 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.

Polypropylene as piping material is mainly used in non-pressure applications (pipe and fitting) and profiles. The advantage of using polypropylene over other polyolefins is the good thermal resistance of polypropylene.

Polypropylene homopolymers, block copolymers and random copolymers are used in pipe. Propylene homopolymers give good pipe rigidity but the impact and creep properties are not very good. Block copolymers give good impact properties but the creep properties are similar to polypropylene homopolymers due to the homopolymer matrix. Random copolymers give better creep resistance compared to propylene homopolymers and block copolymers. Their impact strength is also good. For this reason, random copolymers are used in pressure pipe applications for hot water and industrial pipes.

One of the most important properties of a polymer material used for hot and cold water pressure pipes is its resistance to internal pressure at different temperatures. A standardized method to measure the internal pressure at different temperatures of pipes is described in ISO 1167. ISO 1167-2 specifies the method of preparation of the pipes. The test to determine the time to failure is performed according to ISO 1167-1. The time to failure and the type of failure (brittle, ductile or mixed) at given hoop stresses are determined by this test. The hoop stress applied to the pipe during the test is calculated according to ISO 3213.

An MRS class is a classification of a material for its suitability for use in pressurized pipes and how well the pipes can withstand water pressure for a 50 year period of time. A process for producing pipes with good impact strength, stiffness and an MRS class of 8 by using a random propylene-ethylene copolymer is known.

WO 96/11216 discloses a copolymer composition prepared from copolymers of propene and α-olefin having 2 to 12 carbon atoms, having high molecular weight, a broad molecular weight distribution and an improved comonomer distribution. The use of the composition includes pipes. The composition is made in two or several reactors.

Plumbing Africa, August 2015, Vol 21, Number 6 describes a plastic piping system for internal plumbing and heating, in which limitations in mechanical performance and processability of unimodal PP-R materials were overcome by bimodal PP-R materials such as Borouge's RA130E.

In EP1364986 and EP1312623, a propylene copolymer consisting of polypropylene, C4-C8 a-olefin and/or C2 is disclosed where the propylene copolymer is at least partially crystallized in the β-modification. This gives a better pressure resistance, also at elevated temperatures. In EP1364986 and 1312623, β-nucleating agent and bimodality are used to obtain high MRS class.

WO2006/2778 discloses the use of hexene-1 in combination with a broad molecular weight distribution, wherein the hexene-1 content in the fraction with a higher intrinsic viscosity is higher than in the fraction with a lower intrinsic viscosity.

However, an MRS class of 10 has not been achieved by a random propylene-ethylene copolymer made in one reactor. It is an objective of the present invention to provide a propylene copolymer composition suitable for use in a pipe, which can be obtained by a simple process.

The invention provides a propylene copolymer composition comprising a propylene-ethylene copolymer,

wherein the propylene-ethylene copolymer has a melt flow index in the range of 0.05 to 2.5 dg/min measured according to ISO1133 (2.16 kg/230° C.),

wherein the propylene-ethylene copolymer is a unimodal propylene-ethylene copolymer,

wherein a pipe prepared from the propylene copolymer composition according to ISO 1167-2 has a run time without failure of at least 2500 hours measured according to ISO1167-1 at a temperature of 95° C. and a hoop stress calculated according to ISO3213 of 4.2 MPa.

The inventors have found that a composition from which a pipe can be prepared having a high resistance to internal pressure at different temperatures can be obtained using a one stage polymerization process and using ethylene as the only comonomer.

The high resistance of a pipe prepared from the propylene copolymer composition is indicated by a long run time without failure. For measuring the resistance, a pipe is prepared from the propylene copolymer composition according to ISO 1167-2. According to ISO1167-1, a run time without failure of the pipe is measured while a hoop stress of 4.2 MPa measured according to ISO3213 is applied to the pipe at a temperature of 95° C. The run time without failure of the pipe according to the invention is at least 2500 h (hours).

A propylene-ethylene copolymer may either be a unimodal type or a multimodal type. The propylene-ethylene copolymer according to the invention is a unimodal type.

It is herein understood that the term ‘unimodal propylene-ethylene copolymer’ is a propylene-ethylene copolymer which is unimodal with respect to molecular weight distribution, comonomer content and melt flow index, whereby the copolymer can be polymerised in a single stage batch or preferably a continuous process. The polymerization can be a slurry or gas phase, preferably a slurry, such as loop, polymerization.

The unimodal propylene-ethylene copolymer is preferably produced in one reactor, however, the unimodal propylene-ethylene copolymer may also be produced in a multistage process using, at each stage, process conditions which result in similar polymer properties. The process conditions are substantially the same in these stages, meaning that temperature, pressure, concentrations of the reactants and the catalysts are substantially the same, for example the deviations in each of these conditions is not more than 10%.

The use of a one stage polymerization process is advantageous since it is a simple process using only one reactor.

Comonomer

The propylene copolymer in the composition of the present invention consists of a propylene-ethylene copolymer.

Preferably, the amount of ethylene in the propylene-ethylene copolymer is 2.5 to 4.5 wt %, more preferably 3.1 to 4 wt %, based on the total propylene-ethylene copolymer.

MFI

The propylene-ethylene copolymer in the composition of the present invention has a melt flow index in the range of 0.05 to 2.5 dg/min measured according to ISO1133 (2.16 kg/230° C.). For example, the melt flow index (MFI) is at least 0.10 dg/min or at least 0.13 dg/min, and/or at most 2.0 dg/min, at most 1.0 dg/min, at most 0.8 dg/min, at most 0.5 dg/min, at most 0.4 dg/min or at most 0.35 dg/min.

Preferably, the propylene-ethylene copolymer has a melt flow index in the range of 1 to 10 dg/min measured according to ISO1133 (10.0 kg/230° C.).

Preferably, the propylene-ethylene copolymer has a ratio between the MFI measured according to ISO1133 (2.16 kg/230° C.) and the MFI measured according to ISO1133 (10.0 kg/230° C.) of 0.01 to 0.1. A higher value of this ratio is an indication of a broader MWD.

MWD

Preferably, the propylene-ethylene copolymer in the composition of the present invention has a molecular weight distribution (Mw/Mn) of 5 to 12 wherein Mw stands for the weight average molecular weight and Mn stands for the number average weight, both of which are measured according to ASTM D6474-12 (Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by High Temperature Gel Permeation Chromatography).

XS

Preferably, the propylene-ethylene copolymer in the composition of the present invention has a cold xylene soluble content of less than 10 wt %.

Production of Propylene-Ethylene Copolymer

The propylene-ethylene copolymer in the composition of the present invention is preferably a random propylene-ethylene copolymer.

The term “random propylene-ethylene copolymer,” as used herein, is a copolymer containing monomers of propylene and monomers of ethylene polymerized together to form a polymer wherein the individual repeating units are present in a random or statistical distribution in the polymer chain.

The term “Koenig B-Value” is a measurement of the comonomer distribution across a polymer chain. The “Koenig B-Value” calculates the distribution of the ethylene units of a propylen-ethylene copolymer across the polymer chain. Koenig B-values range from 0 to 2 with 1 designating a perfectly random distribution of comonomer units. The higher the Koening B value, the more alternating the comonomer distribution in the copolymer. The lower the Koenig B value, the more blocky or clustered the comonomer distribution in the copolymer.

The Koenig B-Value is determined according to the method of J. L. Koenig (Spectroscopy of Polymers, 2nd Edition, Elsevier, 1999). B is defined for a propylene/ethylene copolymer as:
B=f(EP+PE)/(2·FE·Fp)
where f(EP+PE)=the sum of the EP and PE diad fractions; FEand Fp=the mole fraction of ethylene and propylene in the copolymer, respectively. The diad fraction can be derived from triad data according to:
f(EP+PE)=[EPE]+[EPP+PPE]/2+[PEP]+[EEP+PEE]/2.

The propylene-ethylene copolymer of the composition according to the invention is preferably a random propylene-ethylene copolymer, for example the propylene-ethylene copolymer has a Koenig B value of 0.5 to 1.5, for example from 0.8 to 1.2.

The propylene-ethylene copolymer of the composition according to the invention can be produced using any conventional technique known to the skilled person, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization. Preferably the propylene-ethylene copolymer is produced using a gas phase polymerization, for example in a horizontal stirred bed reactor or in a fluidized bed reactor, which may for example be operated in condensed mode.

As mentioned in US2012095171, gas-phase or vapor-phase olefin polymerization processes are disclosed generally in “Polypropylene Handbook” pp. 293-298, Hanser Publications, NY (1996), and more fully described in “Simplified Gas-Phase Polypropylene Process Technology” presented in Petrochemical Review, March, 1993. These publications are hereby incorporated herein by reference.

The invention further relates to a process for the preparation of the propylene copolymer composition according to the invention, comprising the step of contacting propylene and ethylene in a gas phase reactor, preferably in one reactor. According to the invention, the propylene-ethylene copolymer is preferably prepared in the presence of a catalyst disclosed in WO03/068828. WO03/068828 describes suitable catalysts for the present invention as a solid catalyst component for polymerization of olefins, comprising magnesium, titanium, a halogen and an electron donor, wherein said electron donor comprises at least one polyol ester compounds of the formula (I):
R1CO—O—CR3R4-A-CR5R6—O—CO—R2(1)
wherein, R1and R2groups, which may be identical or different, can be substituted or unsubstituted hydrocarbyl having 1 to 20 carbon atoms, R3-R6groups, which may be identical or different, can be selected from the group consisting of hydrogen, halogen or substituted or unsubstituted hydrocarbyl having 1 to 20 carbon atoms, R1-R6groups optionally contain one or more hetero-atoms replacing carbon, hydrogen atom or the both, said hetero-atom is selected from the group consisting of nitrogen, oxygen, sulfur, silicon, phosphorus and halogen atom, two or more of R3-R6groups can be linked to form saturated or unsaturated monocyclic or polycyclic ring;

A is a single bond or bivalent linking group with chain length between two free radicals being 1-10 atoms, wherein said bivalent linking group is selected from the group consisting of aliphatic, alicyclic and aromatic bivalent radicals, and can carry C1-C20linear or branched substituents; one or more of carbon atom and/or hydrogen atom on the above-mentioned bivalent linking group and the substituents can be replaced by a hetero-atom selected from the group consisting of nitrogen, oxygen, sulfur, silicon, phosphorus, and halogen atom, and two or more said substituents on the linking group as well as above-mentioned R3-R6groups can be linked to form saturated or unsaturated monocyclic or polycyclic ring.

All examples of the solid catalyst components mentioned in WO03/068828 are incorporated herein by reference as catalysts suitable for the preparation for the random propylene copolymer according to the invention.

Preferably, the electron donor in the catalyst used for preparing the propylene-ethylene copolymer in the composition according to the invention is


wherein R1═R2=phenyl, R3═R5=methyl, R1═R2=R4═R6=hydrogen. This is 2,4-pentanediol dibenzoate as described in synthetic example 5 of WO03/068828.
Additives

The propylene copolymer composition according to the invention may contain additives. Additives suitable for use in pipes include but are not limited to nucleating agents, stabilizers, anti-oxidants pigments and/or colorants, impact modifiers, flame retardants, acid scavengers, anti-microbials and the like. Such 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.

The amount of the additive in the polypropylene composition is chosen from 0 and 5 wt % based on the total weight of the polypropylene composition, preferably the amount of additive is from 0.01 and 3 wt %, for example from 0.1 to 2 wt %, based on the total weight of the polypropylene composition.

Process

The composition of the invention may be obtained by a process comprising melt-mixing the propylene-ethylene copolymer with applicable additives. Preferably, the composition of the invention is made in a form that allows easy processing into a shaped article in a subsequent step, like in pellet or granular form. The composition can be a mixture of different particles or pellets; like a blend of the propylene-ethylene copolymer and a masterbatch of additives. Preferably, the composition of the invention is in pellet or granular form as obtained by mixing all components in an apparatus like an extruder; the advantage being a composition with homogeneous and well-defined concentrations of the additives.

With melt-mixing is meant that the components are mixed at a temperature that exceeds the melting point of the propylene-ethylene copolymer. Melt-mixing may be done using techniques known to the skilled person, for example in an extruder. Generally, in the process of the invention, melt-mixing is performed at a temperature in the range from 20-300° C.

Suitable conditions for melt-mixing, such as temperature, pressure, amount of shear, screw speed and screw design when an extruder is used are known to the skilled person.

When using an extruder, a conventional extruder such as a twin-screw extruder may be used. The temperature can vary through the different zones of the extruder as required. For example, the temperature may vary from 100° C. in the feed zone to 300° C. at the die. Preferably, the temperature in the extruder varies from 200 to 290° C.; lower temperatures may impede reactions between the peroxide and an optional co-agent, for example polyfunctional monomers such as BDDMA and, as a consequence, compositions with the desired melt flow index may not be obtained; too high temperatures may induce undesired degradation processes, which may for example result in compositions having poor mechanical properties. Likewise, the screw speed of the extruder may be varied as needed. Typical screw speed are in the range from about 100 rpm to about 400 rpm.

The residence time in the extruder for the propylene-ethylene copolymer may be lower than 1 minute, for example between 10 and 40 seconds.

The composition according to the invention is preferably processed using extrusion. The invention further relates to an article comprising the composition according to the invention. In particular, the invention relates to an article comprising the composition according to the invention, wherein the article is made by extrusion. Extrusion is for example widely used to produce articles, such as rods, sheets, films and pipes.

Preferably, the article according to the invention is a pipe, a sheet or a film. Particularly preferred, the article according to the invention is a pipe.

The invention further relates to a process for the production of a pipe from the propylene copolymer composition according to the invention.

The invention further relates to use of the propylene copolymer composition according to the invention for the production of a pipe.

The pipe is prepared preferably from at least 95 wt %, for example at least 96 wt %, for example at least 97 wt %, for example at least 98 wt % of the propylene-ethylene copolymer based on the pipe as described above.

In another embodiment therefore, the invention also relates to a pipe containing at least 95 wt % for example at least 96 wt %, for example at least 97 wt %, for example at least 98 wt % of the propylene-ethylene copolymer of the invention.

Pipe Properties

A pipe prepared from the propylene copolymer composition according to ISO 1167-2 has a run time without failure of at least 2500 h measured according to ISO1167-1 at a temperature of 95° C. and a hoop stress calculated according to ISO3213 of 4.2 MPa.

Preferably, a pipe prepared from the propylene copolymer composition according to ISO 1167-2 has a run time without failure of at least 750 h measured according to ISO1167-1 at a temperature of 95° C. and a hoop stress calculated according to ISO3213 of 4.4 MPa.

Preferably, a pipe prepared from the propylene copolymer composition according to ISO 1167-2 has a run time without failure of at least 100 h measured according to ISO1167-1 at a temperature of 95° C. and a hoop stress calculated according to ISO3213 of 4.9 MPa.

Preferably, a pipe prepared from the propylene copolymer composition according to ISO 1167-2 has a run time without ductile failure of at least 100 h measured according to ISO1167-1 at a temperature of 20° C. and a hoop stress calculated according to ISO3213 of 15.5 MPa.

It is noted that the invention relates to all possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product/composition comprising certain components also discloses a product/composition consisting of these components. The product/composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product/composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

