PROPYLENE BASED POLYMER COMPOSITION

FIELD OF THE INVENTION

[0001] The present disclosure relates to a composition comprising a copolymer of propylene with 1 -hexene and a copolymer of propylene and ethylene particularly suited for preparing films, in particular biaxially oriented polypropylene films (BOPP) and cast films having a low seal initiation temperature (SIT) and high crystallization temperature.

BACKGROUND OF THE INVENTION

[0002] Copolymer of propylene and 1 -hexene are already known in the art, for example WO 2006/002778 relates to a copolymer of propylene and 1 -hexene having from 0.2 to 5 wt% of 1- hexene derived units. This copolymer has a molecular weight distribution of monomodal type and are used for pipes systems.

[0003] WO2017/097579 relates to a composition comprising a copolymers of propylene with 1 -hexene and a copolymer of propylene and ethylene particularly suited for preparing films, in particular biaxially oriented polypropylene films (BOPP) and cast films having a low seal initiation temperature (SIT) and high transparency. The seal initiation temperature obtained is still not satisfactory and can be lowered.

[0004] WO 2018/202396 relates to a propylene polymer composition comprising: from 35 wt% to 65 wt% of a propylene 1 -hexene copolymer containing from 10.2 to 13% by weight, of 1 -hexene derived units and from 35 wt% to 65 wt% of a propylene ethylene copolymer containing from 1.5 wt% to 6.5 wt% of ethylene derived units. Even if the composition exemplified shows a very low SIT the xylene soluble content is very high and as show in the comparative example the number of gels can be reduced.

[0005] The applicant found that it is possible to produce BOPP and cast films having a low seal initiation temperature (SIT), high crystallization temperature and good optical properties by using a composition comprising a propylene 1 -hexene copolymer, propylene, 1 -hexene, ethylene terpolymer and a propylene ethylene copolymer. SUMMARY OF THE INVENTION

[0006] Thus, the present disclosure provides a propylene polymer composition comprising: a) from 20 wt% to 44 wt% of a propylene 1 -hexene copolymer containing from 5.0 to 8.3 % by weight, of 1 -hexene derived units having a Melt Flow Rate (MFR, measured according to ISO 1133, 230°C/2.16 kg, i.e. at 230°C, with a load of 2.16 kg) from 3.5 to 8.5 g/10 min; b) from 25 wt% to 45 wt% of a propylene 1 -hexene ethylene terpolymer containing from 7.2 to 12.0 % by weight, of 1-hexene derived units and from 0.5 to 2.5 wt% of ethylene derived units wherein the a Melt Flow Rate (MFR, measured according to ISO 1133, 230°C/2.16 kg, i.e. at 230°C, with a load of 2.16 kg) of components a) + b) is from 3.5 to 8.5 g/10 min; c) from 25 wt% to 50 wt% of a propylene ethylene copolymer containing from 3.5 wt% to 8.7 wt% of ethylene derived units,

[0007] wherein the Melt Flow Rate (MFR, measured according to ISO 1133, 230°C/2.16 kg, i.e. at 230°C, with a load of 2.16 kg) of components a)+b)+c) is from 3.5 to 12.0 g/10 min;

[0008] the sum of the amount of a), b) and c) being 100;

[0009] wherein: i) the xylene soluble content at 25°C of the composition ranges from 16.4 wt% to 35.3 wt%; ii) the melting point of the composition ranges from 122°C to 132°C.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The present disclosure provides a propylene polymer composition comprising: a) from 20 wt% to 44 wt% preferably from 27 wt% to 40; more preferably from 29 wt% to 35 wt% of a propylene 1-hexene copolymer containing from 5.0 wt% to 8.3 wt% preferably from 6.3wt% to 7.8 wt% ; more preferably from 6.5 wt% to 7.4 wt%, of 1 -hexene derived units having a Melt Flow Rate (MFR, measured according to ISO 1133, 230°C/2.16 kg, i.e. at 230°C, with a load of 2.16 kg) from 3.5 to 8.5 g/10 min, preferably ranging from 4.4 to 8.0 g/10 min; more preferably ranging from 5.0 to 7.0 g/10 min; b) from 25 wt% to 45 wt% preferably from 35 wt% to 40 wt%; more preferably from 36 wt% to 39 wt% of a propylene 1 -hexene ethylene terpolymer containing from 7.2 wt% to 12.0 wt%; preferably from 7.5 wt% to 9.5 wt%; more preferably from 8.2 wt% to 9.1 wt% , of 1 -hexene derived units and from 0.5 wt% to 2.5 wt%, preferably from 0.7 wt% to 2.2 wt%, more preferably 0.8wt% to 2.0 wt% of ethylene derived units; wherein the Melt Flow Rate (MFR, measured according to ISO 1133, 230°C/2.16 kg, i.e. at 230°C, with a load of 2.16 kg) of components a) + b) 3.5 to 8.5 g/10 min, preferably ranging from 4.4 to 8.0 g/10 min; more prelOferably ranging from 5.0 to 7.0 g/10 min c) from 25 wt% to 50 wt% preferably from 27 wt% to 40 wt%; more preferably from 29 wt% to 35 wt% of a propylene ethylene copolymer containing from 3.5 wt% to 8.7 wt%; preferably from 4.5 wt% to 8.4 wt% ; more preferably from 4.8 wt% to 8.1 wt% of ethylene derived units, wherein the Melt Flow Rate (MFR, measured according to ISO 1133, 230°C/2.16 kg, i.e. at 230°C, with a load of 2.16 kg) of components a)+b)+c) is from 3.5 to 12.0 g/10 min; preferably ranging from 4.4 to 8.0 g/10 min; more preferably ranging from 5.0 to 8.5 g/10 min;

[0011] the sum of the amount of a), b) and c) being 100;

[0012] wherein: i) the xylene soluble content at 25°C of the composition ranges from 16.4 wt% to 35.3 wt%; preferably from 18.3 wt% to 30.1 wt%; more preferably from 22.1 wt% to 28.3 wt%; ii) the melting point of the composition ranges from 122°C to 132°C; preferably from 125°C to 131°C; mor preferably from 126°C to 130°C

[0013] The propylene 1 -hexene copolymer of the present disclosure contains only propylene and 1 -hexene derived units. The propylene ethylene copolymer of the present disclosure contains only propylene and ethylene derived units. The propylene 1 -hexene ethylene terpolymer of the present disclosure contains only propylene, 1 -hexene and ethylene derived units [0014] The composition of the present disclosure is endowed with a very low seal initiating temperature (SIT) so that this material can be advantageously used for the production of film in particular cast or BOPP films.

[0015] In particular the difference between the melting point of the composition and the SIT is particularly large for the composition of the present disclosure. A relatively high melting point allow a better processability of the polymer when used in particular for obtaining film and at the same time a low SIT value improve the use of the film in sealing applications.

[0016] Preferably the SIT value is comprised between 70°C and 85°C; preferably between 75°C and 82°C. The difference between the melting point and the SIT (Tm-SIT) preferably ranges from 45°C to 60°C; preferably ranges from 46°C to 58°C.

[0017] Furthermore the composition of the present disclosure is endowed with a particularly good optical properties such as haze value measured on BOPP film lower than 0.90% preferably lower than 0.80% mor preferably lower than 0.78. Preferably haze is higher than 0.20 %

[0018] The process for preparing the propylene ethylene copolymer of the present disclosure is carried out in presence of a highly stereospecific heterogeneous Ziegler-Natta catalyst. The Ziegler-Natta catalysts suitable for producing the propylene ethylene copolymer of the disclosure comprise a solid catalyst component comprising at least one titanium compound having at least one titanium-halogen bond and at least an electron-donor compound (internal donor), both supported on magnesium chloride. The Ziegler-Natta catalysts systems further comprise an organo-aluminum compound as essential co-catalyst and optionally an external electron-donor compound.

[0019] Suitable catalysts systems are described in the European patents EP45977, EP361494, EP728769, EP 1272533 and in the international patent application W000163261.

[0020] The organo-aluminum compound is preferably an alkyl-Al selected from the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n- butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum's with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesqui chlorides such as AlEt2Cl and AhEtsCh.

[0021] Preferred external electron-donor compounds include silicon compounds, ethers, esters such as ethyl 4-ethoxybenzoate, amines, heterocyclic compounds and particularly 2, 2,6,6- tetramethyl piperidine, ketones and the 1,3 -di ethers. Another class of preferred external donor compounds is that of silicon compounds of formula Ra ⁵ Rb ⁶ Si(OR ⁷ ) _c where a and b are integer from 0 to 2, c is an integer from 1 to 3 and the sum (a+b+c) is 4; R ⁵ , R ⁶ , and R ⁷ , are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containing heteroatoms. Particularly preferred are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, di cyclopentyldimethoxysilane, 2-ethylpiperidinyl-2-t-butyldimethoxysilane and 1,1,1 ,trifluoropropyl-2-ethylpiperidinyl-dimethoxysilane and 1,1,1 ,trifluoropropyl-metil- dimethoxysilane. The external electron donor compound is used in such an amount to give a molar ratio between the organo-aluminum compound and said electron donor compound of from 0.1 to 500; preferably from 1 to 100; more preferably from 2 to 50.

[0022] The polymerization process, which can be continuous or batch, is carried out following known techniques and operating in gas phase, or in liquid phase in the presence or not of inert diluent, or by mixed liquid-gas techniques. It is preferable to carry out the polymerization in gas phase in three reactors one for each component of the composition.

Preferably in the first two reactors components a) and b) respectively are obtained while component c) is obtained in the third and last reactor.

[0023] Polymerization reaction time, pressure and temperature are not critical, however it is best if the temperature is from 20 to 100°C. The pressure can be atmospheric or higher.

[0024] As previously mentioned, the regulation of the molecular weight is carried out by using known regulators, hydrogen in particular.

[0025] The composition of the present disclosure can also contain additives commonly used for olefin polymers like, for example, nucleating and clarifying agents and processing aids.

[0026] The composition of the present disclosure are preferably characterized by a number of gels No(>0.1 mm) of less than 250; preferably less than 150. The number of gels is indicative of the homogeneity of the product: the lower the number of gels, the greater the homogeneity of the polymer.

[0027] The propylene polymer composition of the present disclosure can be advantageously used for the production of films. Preferably cast or BOPP film mono or multilayer wherein at least one layer comprises the composition of the present disclosure. EXAMPLES

[0028] The following examples are given to illustrate the present invention without limiting purpose.

[0029] The data relating to the polymeric materials and the films of the examples are determined by way of the methods reported below.

Melting and crystallization temperature (ISO 11357-2013)

[0030] Determined by differential scanning calorimetry (DSC). according to ISO 11357- 20133, at scanning rate of 20°C/min both in cooling and heating, on a sample of weight between 5 and 7 mg., under inert N2 flow. Instrument calibration made with Indium.

Melt Flow Rate (MFR)

[0031] Determined according to ISO 1133, 230°C, 2.16kg.

Solubility in xylene at 25°C

[0032] Solubility in xylene at 25°C: 2.5 g of polymer sample and 250 ml of xylene are introduced in a glass flask equipped with a refrigerator and a magnetic stirrer. The temperature is raised in 30 minutes up to 135°C. The obtained clear solution is kept under reflux and stirring for further 30 minutes. The solution is cooled in two stages. In the first stage, the temperature is lowered to 100°C in air for 10 to 15 minute under stirring. In the second stage, the flask is transferred to a thermostatically controlled water bath at 25°C for 30 minutes. The temperature is lowered to 25°C without stirring during the first 20 minutes and maintained at 25°C with stirring for the last 10 minutes. The formed solid is filtered on quick filtering paper (eg. Whatman filtering paper grade 4 or 541). 100 ml of the filtered solution (SI) is poured in a previously weighed aluminum container, which is heated to 140°C on a heating plate under nitrogen flow, to remove the solvent by evaporation. The container is then kept on an oven at 80°C under vacuum until constant weight is reached. The amount of polymer soluble in xylene at 25 °C is then calculated. XS(tot) and XSA values are experimentally determined. The fraction of component (B) soluble in xylene at 25 °C (XSB) can be calculated from the formula:

XS = W(A)X(XSA) + W(B)X(XSB)

[0033] wherein W(A) and W(B) are the relative amounts of components (A) and (B), respectively, and W(A)+ W(B)=1. Determination of 1-hexene content by NMR

[0034] ¹³ C NMR spectra are acquired on an AV-600 spectrometer operating at 150.91 MHz in the Fourier transform mode at 120 °C. The peak of the propylene CH was used as internal reference at 28.83. The ¹³ C NMR spectrum is acquired using the following parameters:

[0035] The total amount of 1 -hexene as molar percent is calculated from diad using the following relations:

[P] = PP + 0.5PH

[H] = HH + 0.5PH

[0036] Assignments of the ¹³ C NMR spectrum of propylene/1 -hexene copolymers have been calculated according to the following table: Ethylene (C2) content

¹³ C NMR of propylene/ethylene copolymers

[0037] ¹³ C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cry oprobe, operating at 160.91 MHz in the Fourier transform mode at 120°C.

[0038] The peak of the Spp carbon (nomenclature according to “Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Mode ” C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) was used as internal reference at 29.9 ppm. The samples were dissolved in 1, 1,2,2- tetrachloroethane-d2 at 120°C with a 8 % wt/v concentration. Each spectrum was acquired with a 90° pulse, 15 seconds of delay between pulses and CPD to remove 1H-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0039] The assignments of the spectra, the evaluation of triad distribution and the composition were made according to Kakugo (“Carbon- 13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with 8-titanium trichloridediethylaluminum chloride” M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equations:

PPP = 100 Tpp/S PPE = 100 Tps/S EPE = 100 T ₅₅ /S

PEP = 100 Spp/S PEE= 100 Sps/S EEE = 100 (0.25 Syg+0.5 S ₅₅ )/S

S = Tpp + Tps + Tss + Spp + Sps + 0.25 Syg + 0.5 Sss

[0040] The molar percentage of ethylene content was evaluated using the following equation: E% mol = 100 * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation:

100 * E% mol * MWE

E% wt. = >

E% mol * MWE + P% mol * MWp

[0041] where P% mol is the molar percentage of propylene content, while MWE and MWp are the molecular weights of ethylene and propylene, respectively. [0042] The product of reactivity ratio n was calculated according to Carman (C. J. Carman,

R.A. Harrington and C.E. Wilkes, Macromolecules, 1977; 10, 536) as:

[0043] The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTpp (28.90-29.65 ppm) and the whole Tpp (29.80-28.37 ppm).

¹³ C NMR of propyl ene/ethylene copolymers:

[0044] ¹³ C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cry oprobe, operating at 160.91 MHz in the Fourier transform mode at 120°C.

[0045] The peak of the Spp carbon (nomenclature according to “Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Mode ” C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) was used as internal reference at 29.9 ppm. The samples were dissolved in 1, 1,2,2- tetrachloroethane-d2 at 120°C with a 8 % wt/v concentration. Each spectrum was acquired with a 90° pulse, 15 seconds of delay between pulses and CPD to remove 1H-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0046] The assignments of the spectra, the evaluation of triad distribution and the composition were made according to Kakugo (“Carbon- 13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with 8-titanium trichloridediethylaluminum chloride” M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equations:

PPP = 100 Tpp/S PPE = 100 Tps/S EPE = 100 Tss/S

PEP = 100 Spp/S PEE= 100 Sps/S EEE = 100 (0.25 Syg+0.5 S ₅₅ )/S

S = Tpp + Tps + Tss + Spp + Sps + 0.25 Syg + 0.5 Sss

[0047] The molar percentage of ethylene content was evaluated using the following equation: [0048] E% mol = 100 * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation: * E% mol * MWE

E% wt. =

E% mol * MWE + P% mol * MWp

[0049] where P% mol is the molar percentage of propylene content, while MWE and MWp are the molecular weights of ethylene and propylene, respectively.

[0050] The product of reactivity ratio nr? was calculated according to Carman (C. J. Carman,

R.A. Harrington and C.E. Wilkes, Macromolecules, 1977; 10, 536) as:

[0051] The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTpp (28.90-29.65 ppm) and the whole Tpp (29.80-28.37 ppm)

1-hexene and ethylene content:

[0052] Determined by ¹³ C-NMR spectroscopy in terpolymers:

[0053] NMR analysis. ¹³ C NMR spectra are acquired on an AV-600 spectrometer operating at 150.91 MHz in the Fourier transform mode at 120 °C. The peak of the propylene CH was used as internal reference at 28.83. The ¹³ C NMR spectrum is acquired using the following parameters:

Spectral width (SW) 60 ppm Spectrum centre (01) 30 ppm Decoupling sequence WALTZ 65_64pl Pulse program ⁽¹⁾ ZGPG Pulse Length (Pl) ⁽²⁾ for 90°

Total number of points (TD) 32K

Relaxation Delay ⁽²⁾ 15 s

Number of transients ⁽³⁾ 1500

[0054] The total amount of 1 -hexene and ethylene as molar percent is calculated from diad using the following relations:

[P] = PP + 0.5PH + 0.5PE

[H] = HH + 0.5PH

[E] = EE+ 0.5PE

[0055] Assignments of the ¹³ C NMR spectrum of propylene/l-hexene/ethylene copolymers have been calculated according to the following table:

[0056] The 1 -hexene contents of component b have been calculated from the 1 -hexene total content of the composition by using the formula C6tot=C6 _a xWa + C6bxWb, Wheerin C6 is the 1- hexene content and Wa and Wb are the amount of components a and b.

Seal Initiation Temperature (SIT)

Preparation of the film specimens

[0057] Some films with a thickness of 50 pm are prepared by extruding each test composition in a a single screw Collin extruder (length/diameter ratio of screw 1 :25) at a film drawing speed of 7 m/min and a melt temperature do 210-250 °C. Each resulting film is superimposed on a 1000 pm thick film of a propylene homopolymer having a xylene insoluble fraction of 97 wt% and a MFR L of 2 g/10 min. The superimposed films are bonded to each other in a Carver press at 200°C under a 9000 kg load, which is maintained for 5 minutes. The resulting laminates are stretched longitudinally and transversally, i.e. biaxially, by a factor 7 with a Karo 4 Brueckener film stretcher at 160°C, thus obtaining a 20 pm thick film (18 pm homopolymer+2 pm test).

Determination of the SIT.

[0058] Film Strips, 6 cm wide and 35 cm length are cut from the center of the BOPP film he film was superimposed with a BOPP film made of PP homopolymer. The superimposed specimens are sealed along one of the 2 cm sides with a Brugger Feinmechanik Sealer, model HSG-ETK 745. Sealing time is 5 seconds at a pressure of 0.14 MPa (20 psi). The starting sealing temperature is from about 10 °C less than the melting temperature of the test composition. The sealed strip is cut in 6 specimens 15 mm wide long enough to be claimed in the tensile tester grips. The seal strength is tested and load cell capacity 100 N, cross speed 100 mm/min and grip distance 50 mm. The results is expressed as the average of macimum seal strength (N). from are left to cool and then their unsealed ends are attached to an Instron machine where they are tested at a traction speed of 50 mm/min.

[0059] The test is than repeated by changing the temperature as follows:

[0060] If seal strength <1.5 N then increase the temperature

[0061] If seal strength >1.5 N then decrease the temperature

[0062] Temperature variation must be adjusted stepwise, if seal strength is close to target select steps of 1°C if the strength is far from target select steps of 2°C.

[0063] The target seal strength (SIT ) is defined as the lowest temperature at which a seal strength higher or equal to 1.5 N is achieved

PREPARATION OF THE COPOLYMER

Catalyst system

Procedure for the preparation of the spherical adduct

[0064] Microspheroidal MgCh pCvHsOH adduct was prepared according to the method described in Comparative Example 5 of W098/44009, with the difference that BiCh in a powder form and in an amount of 3 mol% with respect to the magnesium is added before the feeding of the oil.

Procedure for the preparation of the solid catalyst component

[0065] Solid catalyst component has bene prepared according to Example 1 of EP 728769 with the following differences:

[0066] The second and third titanations have been carried out at 110°C instrado of 120°C;

[0067] MgC12.3 C2H50H in the form of spherical solid particles with a maximum diameter less than or equal to 65 micron instead of 50 micron is used. CATALYST SYSTEM AND PREPOLYMERIZATION TREATMENT

[0068] Before introducing it into the polymerization reactor, the solid catalyst component described above is contacted at 15 °C for about 6 minutes with aluminum tri ethyl (TEAL) and dicyclopentyl dimethoxy silane (DCPMS) as external donor.

[0069] The catalyst system is then subjected to prepolymerization by maintaining it in suspension in liquid propylene at 20 °C for about 20 minutes before introducing it into the polymerization reactor.

[0070] Polymerization

[0071] Into a first gas phase polymerization reactor a propylene 1 -hexene copolymer (component (a)) is produced by feeding in a continuous and constant flow the prepolymerized catalyst system, hydrogen (used as molecular weight regulator), propylene and 1 -hexene in the gas state. The polypropylene copolymer produced in the first reactor is discharged in a continuous flow and is introduced, in a continuous flow, into a second gas phase polymerization reactor, together with quantitatively constant flows of hydrogen, 1 -hexene and propylene in the gas state.

[0072] The polypropylene copolymer produced in the second reactor is discharged in a continuous flow and, after having been purged of unreacted monomers, is introduced, in a continuous flow, into a third gas phase polymerization reactor, together with quantitatively constant flows of hydrogen, 1 -hexene and propylene in the gas state.

[0073] The polymerization conditions are reported in table 1

Table 1

C3 = propylene; C6 = 1 -hexene ; C2 ethylene; H2 = hydrogen

[0074] The polymer obtained according to table 1 have been additivated with 0.05% Irg.1010; 0.1% Irg.168 and 0.05% CaSt then pelletized. The features of the compositions are reported in table 2 Table 2

C3 = propylene; C6 = 1 -hexene ; C2 ethylene;

* calculated by using the general formula Ytot=XaYa+XbYb wherein Y is the comonomer content and Xa and Xb are the splits (Xa+Xb=l).

[0075] From table 2 results that the lower SIT with good haze is obtained with the composition according to the invention