Patent Description:
Syringe barrels of the type commonly used in medical applications require a particular balance of rigidity, impact resistance and optical properties, and the compositions from which they are made must also be suited for the injection moulding process as well as being suitable for sterilisation by radiation. Ionizing radiation, particularly gamma radiation, is known to degrade some polymers.

It is well known to construct containers useful as medical devices, and particularly syringes, out of polypropylene. For example <CIT> discloses injection moulded compositions for syringe barrels made from random propylene ethylene copolymers containing up to 5wt% ethylene and having an MFR in the range <NUM>-<NUM>/<NUM>, more particularly <NUM>-<NUM>/<NUM>.

It is also well known to incorporate into such polypropylene compositions other components in order to improve the properties. <CIT> itself discloses the addition of slip agents such as polyethylene wax to improve operation of the syringe without adversely impacting the optical properties. <CIT> discloses the addition of unsaturated aliphatic compounds such as safflower oil to improve the radiation stability of polypropylene compositions used in medical devices.

It is also known to blend polypropylene with other polymers such as polyethylenes in order to obtain properties suitable for different applications. <CIT> discloses films made from a blend of <NUM>-98wt% of a polypropylene random copolymer with <NUM>-15wt% of an ethylene-based plastomer having a density below <NUM>/m<NUM> and an MI<NUM> of <NUM>-<NUM>/<NUM>.

<CIT> discloses blends of up to 99wt% of a polypropylene homopolymer or copolymer with at least 1wt% of polyethylene produced by single site catalysis and having a narrow molecular weight distribution. The polypropylene is preferably a homopolymer, but random copolymers are also mentioned, although amounts of comonomer are not disclosed, and nor is the MFR of the polypropylene. Examples of the polyethylene have densities in the range <NUM>-<NUM>/m<NUM> and MI<NUM> from <NUM> - <NUM>/<NUM>, and are blended with a polypropylene homopolymer having an MFR of <NUM>/<NUM>. The blends are said to be resistant to degradation by sterilising radiation and to have good optical properties. Applications disclosed include medical devices such as syringe barrels. However, due to the use of propylene homopolymers in the blends, they have relatively high stiffness and haze values. This can be a disadvantage for syringe barrels which need a certain level of flexibility in order to accommodate the plunger and provide a tight seal between the plunger and the barrel. Low haze is also desired to enable the precise determination of the volume to be measured in the syringe.

<CIT> discloses blends of a propylene copolymer or terpolymer and <NUM>-15wt% of an elastomer having a density of <NUM>-<NUM>/m<NUM>, together with an organic peroxide, for use in moulded articles such as containers or syringes. The compositions are said to provide improved impact strength compared with equivalent compositions where the organic peroxide is absent.

Whilst the blending of polypropylene with other components can improve radiation tolerance, it is also important to maintain physical properties such as impact resistance and stiffness as well as optical properties such as clarity and haze. Additionally, processability during the injection moulding process is important. For example, the lower the crystallisation temperature, the longer the cooling step required and hence the longer the cycle time, which obviously reduces productivity.

We have found a polypropylene blend which has an excellent balance of good impact resistance, rigidity and haze as well as a high crystallisation temperature which permits a fast cycle time during injection moulding.

Accordingly in a first aspect the present invention provides a composition as defined in claim <NUM> comprising a blend of.

The blend preferably comprises <NUM> - <NUM> wt%, more preferably <NUM> - 97wt%, based on the blend, of the propylene copolymer and <NUM> - <NUM> wt%, more preferably <NUM> - 7wt%, based on the blend, of the plastomer. Most preferred ranges of propylene copolymer and plastomer are <NUM> - 96wt% and <NUM> - 6wt% respectively.

The blend preferably has an MFR of <NUM> to <NUM>/<NUM>, more preferably <NUM> to <NUM>/<NUM>, and most preferably <NUM> to <NUM>/<NUM>.

The blend has a flexural modulus of <NUM> - <NUM> MPa, preferably <NUM>-<NUM> MPa and more preferably <NUM>-<NUM> MPa.

When no nucleating agent is present, the blend preferably has a melting temperature Tm of at least <NUM>, more preferably at least <NUM>. It preferably has a crystallisation temperature Tc of at least <NUM>, more preferably at least <NUM>. It preferably has a haze of less than <NUM>%, more preferably less than <NUM>%.

The blend preferably contains less than <NUM> wt% (based on total polymer) of peroxides or peroxide residues, and is preferably free of peroxides or peroxide residues.

The random propylene copolymer comprises units derived from propylene and ethylene and/or another C<NUM> to C<NUM> α-olefin, preferably <NUM>-butene, <NUM>-pentene, <NUM>-hexene, <NUM>-heptene, <NUM>-octene, <NUM>-nonene or <NUM>-decene. Ethylene and/or <NUM>-butene are preferred. Most preferably the copolymer is a propylene-ethylene copolymer.

The MFR (MFR <NUM>/<NUM>) of the random propylene copolymer is determined according to ISO1133, and is preferably from <NUM> to <NUM>/<NUM>, more preferably in the range of <NUM> to <NUM>/<NUM>.

The random propylene copolymer preferably has an XCS content in the range <NUM> - <NUM> wt%, preferably <NUM> - <NUM> wt%.

A first preferred random propylene copolymer has an MFR of <NUM> to <NUM>/<NUM> and an XCS content in the range <NUM> - <NUM> wt%.

A second preferred random propylene copolymer has an MFR of <NUM> to <NUM>/<NUM> and an XCS content in the range <NUM> - <NUM> wt%.

Random propylene copolymers are widely available commercially. They can be produced by polymerization in the presence of any conventional coordination catalyst system including Ziegler-Natta and single site catalysts such as metallocenes, and in any conventional polymerisation process such as gas phase, slurry and propylene bulk processes known in the art.

A preferred polymerisation process is a fluidised bed gas phase process comprising a single reactor or two reactors in series, in which the same copolymer is made in both reactors. Polymerization of propylene and comonomer is conducted in the first reactor. Hydrogen is used to obtain the desired MFR value. The catalyst system components are added at a rate to obtain the desired rate of polymerization.

The polymer powder containing active catalyst residues is intermittently transferred to a depressurization vessel to remove unreacted monomer and other gaseous components. The depressurization vessel is pressurized with nitrogen to convey the polymer powder into the second reactor for further polymerization. Further propylene, comonomer and hydrogen are added in a ratio to obtain the desired composition. The polymer powder is intermittently removed from the second reactor for subsequent removal of all volatile materials followed by compounding to obtain the target composition in the form of pellets.

The random propylene copolymer may optionally be nucleated with at least one α-nucleating agent. Generally any α-nucleating agent can be used. Examples of suitable α-nucleating agents include.

Any nucleating agent is preferably present in the random propylene copolymer in an amount of from <NUM> to 10000ppm, preferably from <NUM> to 5000ppm based on the weight of the copolymer.

The ethylene based plastomer is a copolymer of ethylene and a C<NUM> - C<NUM> alpha-olefin. Suitable C<NUM> - C<NUM> alpha-olefins include <NUM>-propylene, <NUM>-butene, <NUM>-hexene and <NUM>-octene, preferably <NUM>-butene or <NUM>-hexene and most preferably <NUM>-hexene.

The comonomer content of the ethylene based plastomer is typically between <NUM> and <NUM> mol%, preferably between <NUM> and <NUM> mol% and most preferably between <NUM> and <NUM> mol%.

The plastomer preferably has a density in the range of <NUM> - <NUM>/m<NUM>, more preferably in the range of <NUM> - <NUM>/m<NUM> and most preferably in the range <NUM> - <NUM>/m<NUM>.

The plastomer preferably has an MI<NUM> (ISO <NUM>; <NUM>; <NUM>) in the range of <NUM> - <NUM>/<NUM>, preferably in the range of <NUM> - <NUM>/<NUM> and more preferably in the range of <NUM> - <NUM>/min. Particularly preferred ranges are <NUM> - <NUM>/<NUM> and <NUM> to <NUM>/<NUM>.

The plastomer preferably has a molecular weight distribution (Mw/Mn) in the range <NUM> to <NUM>, more preferably <NUM> to <NUM> and most preferably <NUM> to <NUM>.

A first preferred plastomer has a density in the range <NUM> - <NUM>/m<NUM> and an MI<NUM> in the range of <NUM> - <NUM>/min, preferably <NUM> - <NUM>/<NUM> and more preferably <NUM> to <NUM>/<NUM>. It preferably also has a molecular weight distribution (Mw/Mn) in the range <NUM> to <NUM>.

A second preferred plastomer has a density in the range <NUM> - <NUM>/m<NUM> and an MI<NUM> in the range <NUM> - <NUM>/min, preferably <NUM> - <NUM>/<NUM> and more preferably <NUM> to <NUM>/<NUM>. It preferably also has a molecular weight distribution (Mw/Mn) in the range <NUM> to <NUM>.

Furthermore suitable ethylene based plastomers have a glass transition temperature Tg (measured with DMTA according to ISO <NUM>-<NUM>) of below -<NUM>, preferably below -<NUM>, more preferably below -<NUM>.

Suitable plastomers our those disclosed in our copending <CIT>.

The plastomer may suitably be prepared by a process such as that disclosed in <CIT>, using a metallocene catalyst system which is preferably a monocylcopentadienyl metallocene complex having a 'constrained geometry' configuration together with a suitable activator as described in the earlier application.

The plastomer is most suitably prepared in a gas phase process, and most preferably in a gas phase process operating in a fluidised bed. Particularly preferred gas phase processes are those operating in "condensed mode" as described in EP <NUM> and EP <NUM>, the latter being a particularly preferred process. By "condensed mode" is meant the "process of purposefully introducing a recycle stream having a liquid and a gas phase into a reactor such that the weight percent of liquid based on the total weight of the recycle stream is typically greater than about <NUM> weight percent".

One preferred blend comprises the first preferred random propylene copolymer defined above, having an MFR of <NUM> to <NUM>/<NUM> and an XCS content in the range <NUM> - <NUM> wt%, in combination with a plastomer having a density in the range <NUM> - <NUM>/m<NUM> and an MI<NUM> in the range of <NUM> - <NUM>/min, preferably <NUM> - <NUM>/<NUM> and more preferably <NUM> to <NUM>/<NUM>.

Another preferred blend comprises the first preferred random propylene copolymer defined above, having an MFR of <NUM> to <NUM>/<NUM> and an XCS content in the range <NUM> - <NUM> wt%, in combination with a plastomer having a density in the range <NUM> - <NUM>/m<NUM> and an MI<NUM> in the range of <NUM> - <NUM>/min, preferably <NUM> - <NUM>/<NUM> and more preferably <NUM> to <NUM>/<NUM>.

A further preferred blend comprises the second preferred random propylene copolymer defined above, having an MFR of <NUM> to <NUM>/<NUM> and an XCS content in the range <NUM> - <NUM> wt%, in combination with a plastomer having a density in the range <NUM> - <NUM>/m<NUM> and an MI<NUM> in the range of <NUM> - <NUM>/min, preferably <NUM> - <NUM>/<NUM> and more preferably <NUM> to <NUM>/<NUM>.

The blend can be produced by any suitable melt mixing process at temperatures above the melting point of the respective blend. Typical devices for performing said melt mixing process are twin screw extruders, single screw extruders optionally combined with static mixers, chamber kneaders like Farrel kneaders, Banbury type mixers and reciprocating co-kneaders like Buss co-kneaders. Preferably, the melt mixing process is carried out in a twin screw extruder with high intensity mixing segments and preferably at a temperature of <NUM> to <NUM>, more preferably of <NUM> to <NUM>.

It is also possible to produce the blend of the present invention by dry-blending in a suitable mixing equipment, like horizontal and vertical agitated chambers, tumbling vessels, and Turbula mixers, as long as sufficient homogeneity is obtained.

The composition of the invention which comprises the blend may also contain other additives, as is well known in the art. Typical additives used in such compositions are listed below.

Examples of antioxidants are sterically hindered phenols (such as CAS No. <NUM>-<NUM>-<NUM>, also sold as Irganox <NUM> FF™ by BASF), phosphorous based antioxidants (such as CAS No. <NUM>-<NUM>-<NUM>, also sold as Hostanox PAR <NUM> (FF)™ by Clariant, or Irgafos <NUM> (FF)™ by BASF), sulphur based antioxidants (such as CAS No. <NUM>-<NUM>-<NUM>, sold as Irganox PS-<NUM> FL™ by BASF), nitrogen-based antioxidants (such as <NUM>,<NUM>'-bis(<NUM>,<NUM>'-dimethylbenzyl)diphenylamine), or antioxidant blends.

Examples of acid scavengers are calcium stearates, sodium stearates, zinc stearates, magnesium and zinc oxides, synthetic hydrotalcite (e.g. SHT, CAS-no. <NUM>-<NUM>-<NUM>), lactates and lactylates, as well as calcium and zinc stearates.

Examples of antiblocking agents are natural silica such as diatomaceous earth (such as <NPL> (SuperfFloss™), <NPL> (SuperFloss E™), or <NPL> (Celite <NUM>™)), synthetic silica (such as <NPL>, <NPL>, <NPL>, <NPL>, <NPL>, <NPL>, <NPL>, <NPL>, or <NPL>), silicates (such as aluminum silicate (Kaolin) <NPL>, sodium aluminum silicate <NPL>, calcined kaolin <NPL>, aluminum silicate <NPL>, or calcium silicate <NPL>), synthetic zeolites (such as sodium calcium aluminosilicate hydrate <NPL>, <NPL>, or sodium calcium aluminosilicate, hydrate <NPL>).

Examples of UV-stabilisers are, for example, bis-(<NUM>,<NUM>,<NUM>,<NUM>-tetramethyl-<NUM>-piperidyl)-sebacate (<NPL>, Tinuvin <NUM>); <NUM>-hydroxy-<NUM>-n-octoxy-benzophenone (<NPL>, Chimassorb <NUM>).

Examples of nucleating agents are sodium benzoate (<NPL>) and <NUM>,<NUM>:<NUM>,<NUM>-bis(<NUM>,<NUM>-dimethylbenzylidene)sorbitol (<NPL>, Millad <NUM>).

The above additives are typically incorporated in the composition in quantities of <NUM> - 10000ppm for each additive.

When a nucleating agent is present in the composition, the composition preferably has a melting temperature Tm of at least <NUM>, more preferably at least <NUM>, It preferably has a crystallisation temperature Tc of at least <NUM>, more preferably at least <NUM>. It preferably has haze of less than <NUM>%, more preferably less than <NUM>%.

The compositions of the invention are suitable for fabrication into articles, particularly rigid articles such as medical devices, which can also be subject to sterilisation procedures known in the art. A particularly preferred application is syringe barrels.

The meanings of the symbols used in these examples and the units expressing the properties mentioned and the methods for measuring these properties are explained below.

The melt flow rate of the polypropylene (MFR) and the melt index of the polyethylene (MI<NUM>) are determined according to ISO1133 at temperatures of <NUM> (MFR) and <NUM> (MI<NUM>) under a load of <NUM> and are indicated in g/<NUM>.

Density of the polyethylene was measured according to ISO <NUM>-<NUM> (Method A) and the sample plaque was prepared according to ASTM D4703 (Condition C) where it was cooled under pressure at a cooling rate of <NUM>/min from <NUM> to <NUM>.

These were measured by Differential Scanning Calorimetry (DSC) with a cooling rate of <NUM>/min.

Flexural modulus was measured according to ISO <NUM> at <NUM> on ISO 1A plaques of <NUM> width and <NUM> thickness, injection moulded according to ISO <NUM>-<NUM>.

Haze was measured using a "Haze-Guard plus" haze meter from BYK Garder referred to in ASTM-D1003.

XCS was determined at <NUM> according to ISO <NUM> by putting <NUM> of polymer in a solution in <NUM> of metaxylene at boiling temperature, cooling the solution to <NUM> by immersion in a water bath and maintaining the solution at that temperature for <NUM> hour, and filtering the soluble fraction at <NUM> on filter paper.

Resilience was measured according to ISO <NUM> at room temperature using an instrumented drop tower. A striker with a diameter of <NUM> and a total weight of <NUM> was dropped from a height of <NUM> metre, giving an impact speed of <NUM>/s and an impact energy of <NUM> J.

Copolymers having ethylene contents ranging from <NUM> to <NUM>. 0wt% were made in a single reactor continuous fluidised bed gas phase polymerisation reactor system having a vertical cylindrical section of <NUM> height and <NUM> diameter.

Polymerisation was initiated by the introduction of a high activity supported titanium containing Ziegler-Natta catalyst component commercially available from Grace under the trade name C602 through a liquid propylene-flushed catalyst addition nozzle. A mixture of selectivity control agent (SCA), commercially available from Grace under the trade name D-<NUM>, plus trialkylaluminum (TEA) co-catalyst in hexane was fed separately to the first reactor through a different liquid propylene-flushed addition nozzle to obtain a Al/SCA ratio of about <NUM> and a Al/Ti ratio of about <NUM>. Hydrogen, ethylene and propylene were fed to the reactor through separate mass-flow meters in order to achieve the desired powder melt flow rate (MFR) and ethylene content. The reactor temperature was maintained at <NUM>.

Polymer was continuously with drawn from the reactor and subjected to a reduction in pressure to remove all volatile materials, followed by a final degassing step. The polymer powder was then homogenised in an Ancheschi F6950 cylinder-conical discontinuous homogeniser. The properties of the random propylene copolymer powders are given in Tables <NUM> and <NUM>.

The plastomer was made as described in the Examples of <CIT> in a fluidized bed gas phase reactor of <NUM> diameter, with a vertical cylindrical section of <NUM>. The resulting polymer powder was pelletized in an extruder together with 800ppm Irgafos <NUM> and 275ppm Irganox <NUM>. The properties of the ethylene plastomer pellets are given in Tables <NUM> and <NUM>.

The random propylene copolymer powder and plastomer pellets were blended in a Papenmeier mixer (volume <NUM> dm<NUM>, rotation speed <NUM> tr/min for <NUM> mins), together with additives in the amounts given in Table <NUM> and <NUM>. The additives used were the following:.

The homogenized mixture was then pelletized in an APV 19TC25 extruder. The barrel temperature used was <NUM>, the screw speed was <NUM> rpm and the throughput was <NUM>/h. The barrel diameter D was <NUM> and the barrel length to diameter (L/D) ratio was <NUM>.

Examples labelled "CE" below are comparative examples.

A comparison of comparative Example CE1 (which contains no plastomer) with Examples <NUM> and <NUM> shows that the pure copolymer has relatively poor resilience. Resilience is typically improved by increasing the comonomer content, but that reduces the crystallisation temperature and rigidity. However it can be seen that inventive Examples <NUM> and <NUM> have much better resilience, but still have essentially the same crystallisation temperature and similar flexural modulus.

However in Examples CE4-CE6 no such improvement in resilience is observed upon addition of the plastomer, indicating that there is an optimum level of comonomer in the random copolymer.

Claim 1:
Composition comprising a blend of
<NUM> - 99wt%, based on the blend, of a random propylene copolymer having a melt flow rate (MFR <NUM>/<NUM>) of <NUM> - <NUM>/<NUM> and containing <NUM> - <NUM>.5wt% ethylene, and
<NUM> - <NUM> wt%, based on the blend, of an ethylene based plastomer having a density of <NUM> - <NUM>/m<NUM> and an MI<NUM> (<NUM>/<NUM>) of <NUM> to <NUM>/<NUM>,
wherein the composition has a flexural modulus of <NUM> - <NUM> MPa, determined as disclosed in the description.