Patent Description:
The isotactic polypropylene is endowed with an exceptional combination of excellent properties which render it suitable for a very great number of uses.

In order to improve the properties of the isotactic polypropylene the crystallinity of the propylene homopolymer is decreased by copolymerization of the propylene with small quantities of ethylene and/or α-olefins such as <NUM>-butene, <NUM>-pentene and <NUM>-hexene. In this manner one obtains the so called random crystalline propylene copolymers which, when compared to the homopolymer, are essentially characterized by better flexibility and transparency.

Propylene random copolymers, however, although they have good transparency, do not offer, especially at low temperatures, sufficiently better impact resistance than the homopolymer which can be satisfactory used for the applications listed above.

It has been known for a long time that the impact resistance of polypropylene can be improved by adding an adequate quantity of elastomeric propylene-ethylene copolymer to the homopolymers by mechanical blending or sequential polymerization. However, this improvement is obtained at the expenses of the transparency of the material especially after the sterilization process.

<CIT> relates to a propylene polymer compositions comprising:.

This composition shows a limited increasing of the haze of the film after the sterilization process. However the haze after sterilization can be improved.

<CIT> refers to polypropylene compositions comprising three propylene polymer components suitable for producing films having a low SIT and low haze.

The applicant found a propylene polymer composition that can be used for obtaining sterilized films having a particular balance of properties.

Thus one object of the present disclosure is a propylene polymer composition comprising:.

The term "copolymer" means polymers containing only propylene and ethylene.

The present invention is preferably endowed with one or more of the following features:.

Component A) of the composition of present invention are obtainable by polymerizing propylene and optionally ethylene according to known techniques, for example, slurry polymerization using as a diluent an inert hydrocarbon solvent, or bulk polymerization using the liquid monomer (for example, propylene) as a reaction medium. Moreover, it is possible to carry out the polymerization process in gas-phase operating in one or more fluidized or mechanically agitated bed reactors.

Components B) and C) of the composition of present invention are obtainable by polymerizing propylene and ethylene according to known techniques, for example, slurry polymerization using as a diluent an inert hydrocarbon solvent, or bulk polymerization using the liquid monomer (for example, propylene) as a reaction medium. Moreover, it is possible to carry out the polymerization process in gas-phase operating in one or more fluidized or mechanically agitated bed reactors.

The polymerization to obtain components A), B) and C) is generally carried out at temperatures of from <NUM> to <NUM>, preferably of from <NUM> to <NUM>. When the polymerization is carried out in gas-phase, the operating pressure is generally between <NUM> and <NUM> MPa, preferably between <NUM> and <NUM> MPa. In bulk polymerization, the operating pressure is generally between <NUM> and <NUM> MPa, preferably between <NUM> and <NUM> MPa. Hydrogen is typically used as a molecular weight regulator.

Components A), B) and C) can be prepared and the blended together according to processes well known in the art, otherwise they can be prepared in series. For example component A) can be prepared in a loop reactor in bulk by using propylene as reaction medium, the product prepared in the first loop can be feed in a second loop to polymerize component B) in bulk by using propylene as reaction medium and the reaction product can be feed to a gas phase reactor to obtain component C) and the final composition.

Such polymerisations can be carried out in the presence of Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron-donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminium compound, such as an aluminium alkyl compound.

The catalysts generally used in the process of the invention are capable of producing polypropylene homopolymer with a value of xylene insolubility at ambient temperature greater than <NUM>%, preferably greater than <NUM>%.

Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in <CIT> and <CIT>. Other examples can be found in <CIT>.

The solid catalyst components used in said catalysts comprise, as electron-donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and/or S atoms, and esters of mono- and dicarboxylic acids.

Particularly suitable electron-donor compounds are esters of phtalic acid and <NUM>,<NUM>-diethers of formula:
<CHM>.

wherein RI and RII are the same or different and are C<NUM>-C<NUM> alkyl, C<NUM>-C<NUM> cycloalkyl or C<NUM>-C<NUM> aryl radicals; RIII and RIV are the same or different and are C<NUM>-C<NUM> alkyl radicals; or are the <NUM>,<NUM>-diethers in which the carbon atom in position <NUM> belongs to a cyclic or polycyclic structure made up of <NUM>, <NUM>, or <NUM> carbon atoms, or of <NUM>-n or <NUM>-n' carbon atoms, and respectively n nitrogen atoms and n' heteroatoms selected from the group consisting of N, O, S and Si, where n is <NUM> or <NUM> and n' is <NUM>, <NUM>, or <NUM>, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl, or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatom(s) as substitutes for carbon or hydrogen atoms, or both.

Ethers of this type are described in published <CIT> and<CIT>.

Representative examples of said diethers are <NUM>-methyl-<NUM>-isopropyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-diisobutyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-isopropyl-<NUM>-cyclopentyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-isopropyl-<NUM>-isoamyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-bis (methoxymethyl) fluorene.

Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Al-triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by way of O or N atoms, or SO<NUM> or SO<NUM> groups.

The Al-alkyl compound is generally used in such a quantity that the Al/Ti ratio be from <NUM> to <NUM>.

The electron-donor compounds that can be used as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si-OR bond, where R is a hydrocarbon radical.

Examples of silicon compounds are (tert-butyl)<NUM>Si(OCH<NUM>)<NUM>, (cyclohexyl)(methyl)Si (OCH<NUM>)<NUM>, (cyclopentyl)<NUM>Si(OCH<NUM>)<NUM> and (phenyl)<NUM>Si(OCH<NUM>)<NUM> and (<NUM>,<NUM>,<NUM>-trimethylpropyl)Si(OCH<NUM>)<NUM>.

<NUM>,<NUM>-diethers having the formulae described above can also be used advantageously. If the internal donor is one of these diethers, the external donors can be omitted.

In particular, even if many other combinations of the previously said catalyst components may allow to obtain propylene polymer compositions according to the present invention, the terpolymers are preferably prepared by using catalysts containing a phthalate as internal donor and (cyclopentyl)<NUM>Si(OCH<NUM>)<NUM> as outside donor, or the said <NUM>,<NUM>-diethers as internal donors.

Preferably said polypropylene composition being obtainable with a polymerization process carried out in the presence of a catalyst system comprising the product obtained by contacting (a) a solid catalyst component having preferably average particle size ranging from <NUM> to <NUM> comprising a magnesium halide, a titanium compound having at least a Ti-halogen bond and at least two electron donor compounds one of which being present in an amount from <NUM> to <NUM>% by mol with respect to the total amount of donors and selected from succinates and the other being selected from <NUM>,<NUM> diethers, (b) an aluminum hydrocarbyl compound and optionally (c) an external electron donor compound.

The regulation of the molecular weight is carried out by using known regulators, hydrogen in particular.

By properly dosing the concentration of the molecular weight regulator in the relevant steps, the previously described MFR and [η] values are obtained.

The catalysts can be pre-contacted with small amounts of olefins (prepolymerization).

The compositions of the present invention can also be obtained by preparing separately the said components A), B) and C) by operating with the same catalysts and substantially under the same polymerization conditions as previously explained (except that a wholly sequential polymerization process will not be carried out, but the said components and fractions will be prepared in separate polymerization steps) and then mechanically blending said components and fractions in the molten or softened state. Conventional mixing apparatuses, like screw extruders, in particular twin screw extruders, can be used.

The compositions of the present invention can also contain additives commonly employed in the art, such as antioxidants, light stabilizers, heat stabilizers, nucleating agents, colorants and fillers.

In particular, the addition of nucleating agents brings about a considerable improvement in important physical-mechanical properties, such as Flexural Modulus, Heat Distortion Temperature (HDT), tensile strength at yield and transparency.

Typical examples of nucleating agents are the p-tert. -butyl benzoate and the <NUM>,<NUM>- and <NUM>,<NUM>-dibenzylidenesorbitols.

The nucleating agents are preferably added to the compositions of the present invention in quantities ranging from <NUM> to <NUM>% by weight, more preferably from <NUM> to <NUM>% by weight with respect to the total weight.

The addition of inorganic fillers, such as talc, calcium carbonate and mineral fibers, also brings about an improvement to some mechanical properties, such as Flexural Modulus and HDT. Talc can also have a nucleating effect.

The melt flow rate of the composition can be adjusted by visbreaking the composition with methods known in the art such as peroxides.

The compositions of the present invention are particularly suited for the production of films such as BOPP films, blow films or cast films mono and multilayer, Cast films are particularly preferred. The film obtained with the composition of the present disclosure can be easy sterilized with a limited worsening of the optical properties such as haze and gloss. The SIT of the film obtained with the composition of the present disclosure is relatively low.

The composition of the present disclosure are especially fit for the production of retortable pouches. Retortable pouches are multi-material laminated packages sterilized to preserve their food content after being sealed. The melting point and the SIT of the composition of the present disclosure allow to prepare mono material packaging completely recyclable while in the art usually the external layer is made with PET.

Thus a further object of the present disclosure are films prepared with the propylene polymer composition above described. Preferably cast film are prepared with the propylene polymer composition above described. More preferably multilayer films comprising the propylene polymer composition above described. Even more preferably propylene polymer composition above described is fit for the preparation of a multilayer sterilizable film.

The sterilization can be carried out with the processes commonly known in the art such as heat the polymer at temperatures higher than <NUM> but lower than the melting point of the polymer.

The particulars are given in the following examples, which are given to illustrate, without limiting, the present invention.

Determined according to ISO <NUM> (<NUM>° C, <NUM>).

<NUM>C NMR spectra were acquired on a Bruker AV-<NUM> spectrometer equipped with cryoprobe, operating at <NUM> in the Fourier transform mode at <NUM>.

The peak of the Sββ carbon (nomenclature according to "<NPL>) was used as internal reference at <NUM> ppm. The samples were dissolved in <NUM>,<NUM>,<NUM>,<NUM>-tetrachloroethane-d2 at <NUM> with a <NUM> % wt/v concentration. Each spectrum was acquired with a <NUM>° pulse, <NUM> seconds of delay between pulses and CPD to remove <NUM>-13C coupling. <NUM> transients were stored in <NUM> data points using a spectral window of <NUM>.

The assignments of the spectra, the evaluation of triad distribution and the composition were made according to Kakugo ("<NPL>) using the following equations: <MAT> <MAT> <MAT>.

The molar percentage of ethylene content was evaluated using the following equation:
E% mol = <NUM> * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation: <MAT>
where P% mol is the molar percentage of propylene content, while MWE and MWP are the molecular weights of ethylene and propylene, respectively.

The product of reactivity ratio r<NUM>r<NUM> was calculated according to Carman (<NPL>) as: <MAT>.

The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTββ (<NUM>-<NUM> ppm) and the whole Tββ (<NUM>-<NUM> ppm).

The amount of ethylene derived units of components B) and C) have bene calculated by using the following formula <MAT>.

To be used at various stages of the polymerization process. Wherein C2tot is the amount of ethylene derived units in the composition; C2A is the amount of ethylene derived units in component A); C2B is the amount of ethylene derived units in component B); C2c is the amount of ethylene derived units in component C) and A, B and C are the amounts of components A), B) and C) wherein A+B+C=<NUM>.

Cast films have been prepared by extruding each test composition in a single screw Dr. Collin cast film extruder equipped with a three layers co-extrusion cast film line (main extruder screw diameter <NUM>, L/D <NUM>; two side extruders screw diameter <NUM>, L/D <NUM>) at a melt temperature of <NUM>-<NUM>.

The cast film has been produced with a nominal thickness of <NUM>, which is the final specimen thickness. Some films were produced in the same way also with a nominal thickness of <NUM>.

Some films with a thickness of <NUM> are prepared by extruding each test composition in a single screw Collin extruder (length/diameter ratio of screw <NUM>:<NUM>) at a film drawing speed of <NUM>/min and a melt temperature do <NUM>-<NUM>. Each resulting film is superimposed on a <NUM> thick film of a propylene homopolymer having a xylene insoluble fraction of <NUM> wt% and a MFR L of <NUM>/<NUM>. The superimposed films are bonded to each other in a Carver press at <NUM> under a <NUM> load, which is maintained for <NUM> minutes. The resulting laminates are stretched longitudinally and transversally, i.e. biaxially, by a factor <NUM> with a TOM Long film stretcher at <NUM>, thus obtaining a <NUM> thick film (<NUM> homopolymer+<NUM> test). 2x5 cm specimens are cut from the films.

Seal strength has been measured according to ASTM F2029-<NUM> and ASTM F88-<NUM>. By plotting the seal strength versus the sealing temperature, a sealing curve is produced. Then, SIT on cast film is determined as the temperature at the sealing force that corresponds to the half-height of the plateau of the sealing curve (plateau defined as D F ≤ 3N).

A film with a given thickness is prepared by extruding the polymer in a single screw Collin extruder (length/diameter ratio of screw: <NUM>) at a film drawing speed of <NUM>/min. and a melt temperature of <NUM>-<NUM>.

Determined on cast films of the test composition. The measurement was carried out on a 50x50 mm portion cut from the central zone of the film.

The instrument used for the test was a Gardner photometer with Haze-meter UX-<NUM> equipped with a G. <NUM> lamp and filter C. The instrument calibration was made by carrying out a measurement in the absence of the sample (<NUM>% Haze) and a measurement with intercepted light beam (<NUM>% Haze).

Determined by differential scanning calorimetry (DSC). A sample weighting <NUM> ±<NUM>, is heated to <NUM> ±<NUM>° C at a rate of <NUM>/min and kept at <NUM> ±<NUM>° C for <NUM> minutes in nitrogen stream and it is thereafter cooled at a rate of <NUM>° C/min to <NUM> ±<NUM>° C, thereby kept at this temperature for <NUM> to crystallise the sample. Then, the sample is again fused at a temperature rise rate of <NUM>° C/min up to <NUM> ±<NUM>° C. The melting scan is recorded, a thermogram is obtained, and, from this, melting temperatures is read.

Xylene Solubles has been measured according to ISO <NUM><NUM>-<NUM>; with solution volume of <NUM>, precipitation at <NUM> for <NUM> minutes, <NUM> of which with the solution in agitation (magnetic stirrer), and drying at <NUM>°.

Determined according to FDA <NUM>, <NUM> by suspending in an excess of hexane a specimen of the composition. The film is prepared by extrusion. The suspension is put in an autoclave at <NUM> for <NUM> hours then the hexane is remove by evaporation and the dried residue is weighted.

The catalyst system has been prepared according to example <NUM> of <CIT>. Dicyclopentyldimethoxysilane (Donor-D) has been used as external donor.

The polymerization run is carried out in continuous mode in a series of three reactors equipped with devices to transfer the product from one reactor to the one immediately next to it. The first and the second reactors are liquid phase loop reactors, the third reactor is a fluidized bed gas-phase reactor. Components A) and B) are prepared in the loop reactors while component C) is prepared in the gas-phase reactor. Hydrogen is used as molecular weight regulator. The gas phase (propylene, ethylene and hydrogen) is continuously analyzed via gas-chromatography. At the end of the run the powder is discharged and dried under a nitrogen flow.

The main polymerization conditions and the analytical data relating to the polymers produced in the three reactors are reported in Table <NUM>. Properties of the polymer are reported on Table <NUM>.

The polymer of example <NUM> has been added with the additives reported on table <NUM> and visbrooken.

Properties of the polymer obtained after visbreaking are reported on table <NUM>.

The product of table <NUM> has been used for producing cast films having thickness of <NUM> and <NUM> the properties of the film have been reported on table <NUM>.

The haze of the films of example <NUM> are compared in table <NUM> with the haze reported for a <NUM> film of the polymer of example <NUM> of <CIT> (comparative example <NUM>).

the haze of <NUM> film of example <NUM> is considerably lower with respect to the have of the <NUM> of comparative example <NUM>. Furthermore the haze of <NUM> film of example <NUM> is lower than the <NUM> of comparative example <NUM>. The difference between the haze before and after the sterilization is considerably lower in the <NUM> of example <NUM> with respect to the <NUM> of comparative example <NUM> (<NUM> vs. <NUM>).

Claim 1:
Propylene polymer compositions comprising:
A) from <NUM> wt% to <NUM> wt% of a propylene homopolymer or a copolymer of propylene with ethylene, containing up to <NUM> wt%, of ethylene derived units, measured by NMR; having a melting point, measured by DSC, comprised between <NUM> and <NUM>;
B) from <NUM> wt% to <NUM> wt%, of a copolymer of propylene with ethylene, containing from <NUM> wt% to <NUM> wt%, of ethylene derived units, measured by NMR;
C) from <NUM> wt% to <NUM> wt%, of a copolymer of propylene with ethylene, containing from <NUM> wt% to <NUM> wt %, of ethylene derived units;
the sum of the amount of A,B and C being <NUM> wt%;
wherein in the propylene polymer composition:
- the melt flow rate, (ISO <NUM> (<NUM>° C, <NUM>).) ranges from <NUM>/<NUM> to <NUM>/<NUM>;
- the xylene soluble fraction measured at <NUM> ranges from <NUM> wt % to <NUM> wt%;
- the total content of ethylene derived units, measured by NMR; ranges from <NUM> wt% to <NUM> wt%;
- the content of ethylene derived units, measured by NMR; in the fraction soluble in xylene at <NUM> ranges from <NUM> wt% to <NUM> wt%;
- the melting point measured by DSC ranges from <NUM> to <NUM>;