BLOWN FILMS WITH IMPROVED PROPERTY PROFILE

Abstract

Blown films based on a blend of a C.sub.2C.sub.3 random copolymer and a C.sub.2-based plastomer, which combine low scaling initiation temperature (SIT), good optical properties and an improved stiffness/impact balance, and which also show an excellent sterilization behaviour.

Claims

1: A blown film comprising at least 95.0 wt. % of a blend of component (A) and (B), the blend comprising: (A) 60.0 wt. % to 95.0 wt. % of a C.sub.2C.sub.3 random copolymer consisting of: 45.0 to 85.0 wt. % of polymer fraction (A1) having; (i) an ethylene content in the range of from 1.5 to 5.0 wt. % and (ii) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in the range of from 0.8 to 8.0 g/10 min and 15.0 to 55.0 wt. % of polymer fraction (A-2) having; (i) an ethylene content in the range of from 4.0 to 10.0 wt. % and (ii) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in the range of from 0.1 to 3.0 g/10 min, whereby the ethylene content of polymer fraction (A-2) is higher than the ethylene content of polymer fraction (A-1), and the melt flow rate MFR.sub.2 (230° C./2.16 kg) of polymer fraction (A-2) is lower than the MFR.sub.2 (230° C./2.16 kg) of polymer fraction (A-1), and whereby the C.sub.2C.sub.3 random copolymer has (a) a total ethylene content in the range of from 1.0 to 7.0 wt. %; (b) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in the range of from 0.5 to less than 4.0 g/10 min and (c) a melting temperature Tm as determined by DSC according to ISO 11357 of from 110° C. to 140° C., wherein said copolymer is prepared using a single site catalyst, (B) 5.0 wt. % to 40.0 wt. % of an ethylene based plastomer having (i) a density according to ISO 1183 of 860 kg/m.sup.3 to 900 kg/m.sup.3 (ii) an MFR.sub.2 according to ISO 1133 (190° C.; 2.16 kg) in the range of 0.1 to 50.0 g/10 min, and (iii) a comonomer selected from a C.sub.4 to C.sub.8 alpha-olefin, said blown film having a) a dart-drop impact strength (DDI) determined according to ASTM D1709, method A on a 50 μm blown film of at least 60 g up to more than 1700 g and b) an Elmendorf tear strength determined in accordance with ISO 6383/2 measured in machine direction (MD), in the range from at least 5.0 N/mm up to 50.0 N/mm and measured in transverse direction (TD) in the range of from at least 80.0 N/mm up to 300.0 N/mm.

2: The blown film according to claim 1, wherein the C.sub.2C.sub.3 random copolymer (A) has a xylene cold soluble (XCS) fraction measured according to ISO 16152 at 25° C. in the range of from 0.6 to 12.0 wt. %.

3: The blown film according to claim 1, wherein the C.sub.2C.sub.3 random copolymer (A) has: (a) a total ethylene content in the range of from 1.5 to 6.5 wt. %, (b) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in the range of from 0.7 to 3.5 g/10 min, and (c) a melting temperature Tm as determined by DSC according to ISO 11357 of from 115° C. to 135° C.

4: The blown film according to claim 1, wherein the ethylene based plastomer (B) has: (i) a density according to ISO 1183 of 865 kg/m.sup.3 to 895 kg/m.sup.3, (ii) an MFR.sub.2 according to ISO 1133 (190° C.; 2.16 kg) in the range of 0.3 to 20.0 g/10 min, and (iii) a comonomer selected from 1butene or 1octene.

5: The blown film according to claim 1, wherein the film comprises at least 95.0 wt. % of a blend comprising 65.0 to 93.0 wt. % of the C.sub.2C.sub.3 random copolymer (A) and 7.0 to 35.0 wt. % of the ethylene based plastomer (B).

6: The blown film according to claim 1, wherein the film comprises at least 98.0 wt. % of the blend of Component (A) and Component (B).

7: The blown film according to claim 1, wherein the film has a dart-drop impact strength (DDI) determined according to ASTM D1709, method A on a 50 μm blown film in the range of 80 g up to more than 1700 g.

8: The blown film according to claim 1, wherein the film has an Elmendorf tear strength as determined in accordance with ISO 6383/2 as measured in machine direction (MD), in the range of 7.0 up to 45.0 N/mm, and as measured in transverse direction (TD), in the range of 90.0 to 250.0 N/mm.

9: The blown film according to claim 1, wherein the film has a tensile modulus determined according to ISO 527 at 23° C. on blown films with a thickness of 50 μm in machine direction as well as in transverse direction in the range of from 200 to less than 800 MPa.

10: The blown film according to claim 1, wherein the film has a sealing initiation temperature (SIT) (determined as described in the experimental part) in the range of from 80° C. to below 115° C.

11: The blown film according to claim 1, wherein the film has: a haze (determined according to ASTM D1003-00 on a blown film with a thickness of 50 μm) in the range of from 0.5 to below 5.0%, and a clarity (determined according to ASTM D1003-00 on a blown film with a thickness of 50 μm) of at least 80.0% up to 100.0%.

12: The blown film according to claim 1, wherein the film has a haze value (determined according to ASTM D 1003-00 on 50 μm blown film) after steam sterilization at 121° C. for 30 min in the range of 1.0 to below 10.0%, and a clarity (determined according to ASTM D1003-00 on blown films with a thickness of 50 μm) after sterilization (steam sterilization at 121° C. for 30 min) of at least 70.0.

13: The blown film according to claim 1, wherein the film has an optomechanical ability (OMA) according the formula: $\mathrm{OMA}=\frac{\mathrm{Tensile}\mathrm{Modulus}\left(\mathrm{MD}\right)\left[\mathrm{MPa}\right]*\mathrm{Tear}\left(\mathrm{MD}\right)\left[N/\mathrm{mm}\right]}{\mathrm{Haze}\left(50\mathrm{\mu m}\right)\left[\%\right]}$ determined on a 50 μm blown film f at least 900 [MPa*N/mm*%] up to 4000 [MPa*N/mm*%].

14: The blown film according to claim 1, wherein the film is a monolayer film.

15. (canceled)

Description

EXPERIMENTAL PART

A. Measuring Methods

[0236] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0237] Melt Flow Rate

[0238] The melt flow rate (MFR) was determined according to ISO 1133—Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics—Part 1: Standard method and is indicated in g/10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR.sub.2 of polyethylene is determined at a temperature of 190° C. and a load of 2.16 kg. The MFR.sub.2 of polypropylene is determined at a temperature of 230° C. and a load of 2.16 kg.

[0239] Calculation of melt flow rate MFR.sub.2 (230° C.) of the polymer fraction (A-2):

[00002]$\mathrm{MFR}\left(A2\right)=10\left[\frac{\log \left(\mathrm{MFR}\left(A\right)\right)-w\left(A1\right)x\log \left(\mathrm{MFR}\left(A1\right)\right)}{w\left(A2\right)}\right]$

[0240] wherein

[0241] w(A1) is the weight fraction [n wt %] of the polymer fraction A-1

[0242] w(A2) is the weight fraction [in wt %] of the polymer fraction A-2,

[0243] MFR(A1) is the melt flow rate MFR.sub.2 (230° C.) [in g/10 min] of the polymer fraction A-1,

[0244] MFR(A) is the melt flow rate MFR.sub.2 (230° C.) [n g/10 min] of the C2C3 random copolymer (A),

[0245] MFR(A2) is the calculated melt flow rate MFR.sub.2 (230° C.) [g/10 min] of the polymer fraction A-2.

[0246] Quantification of Microstructure by NMR Spectroscopy

[0247] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was further used to quantify the comonomer content and comonomer sequence distribution of the polymers. Quantitative .sup.13C{.sup.1H} NMR spectra were recorded in the solution-state using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz for .sup.1H and .sup.13C respectively. All spectra were recorded using a .sup.13C optimised 10 mm extended temperature probehead at 125° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d.sub.2 (TCE-d.sub.2) along with chromium-(Ill)-acetylacetonate (Cr(acac).sub.3) resulting in a 65 mM solution of relaxation agent in solvent (Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatary oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme (Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B., J. Mag. Reson. 187 (2007) 225; Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128). A total of 6144 (6 k) transients were acquired per spectra.

[0248] Quantitative .sup.13C{H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present. Characteristic signals corresponding to the incorporation of ethylene were observed Cheng, H. N., Macromolecules 17 (1984), 1950).

[0249] With characteristic signals corresponding to 2,1 erythro regio defects observed (as described in L. Resconi, L. Cavallo, A. Fait, F. Piemontesi, Chem. Rev. 2000, 100 (4), 1253, in Cheng, H. N., Macromolecules 1984, 17, 1950, and in W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157) the correction for the influence of the regio defects on determined properties was required. Characteristic signals corresponding to other types of regio defects were not observed.

[0250] The comonomer fraction was quantified using the method of Wang et. al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157) through integration of multiple signals across the whole spectral region in the .sup.13C{.sup.1H} spectra. This method was chosen for its robust nature and ability to account for the presence of regio-defects when needed. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

[0251] For systems where only isolated ethylene in PPEPP sequences was observed the method of Wang et al. was modified to reduce the influence of non-zero integrals of sites that are known to not be present. This approach reduced the overestimation of ethylene content for such systems and was achieved by reduction of the number of sites used to determine the absolute ethylene content to:

E=0.5(Sββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

[0252] Through the use of this set of sites the corresponding integral equation becomes:

E=0.5(I.sub.H+I.sub.G+0.5(I.sub.C+I.sub.D))

[0253] using the same notation used in the article of Wang et al. (Wang, W-J., Zhu, S., Macromolecules 33 (2000), 1157). Equations used for absolute propylene content were not modified.

[0254] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0255] The weight percent comonomer incorporation was calculated from the mole fraction:

E[wt %]=100*(fE*28.06)/((fE*28.06)+((1−fE)*42.08))

[0256] The comonomer sequence distribution at the triad level was determined using the analysis method of Kakugo et al. (Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150). This method was chosen for its robust nature and integration regions slightly adjusted to increase applicability to a wider range of comonomer contents.

[0257] Calculation of Comonomer Content of the Second Polymer Fraction (A-2):

[00003]$\begin{array}{cc}\frac{C\left(A\right)-w\left(A1\right)xC\left(A1\right)}{w\left(A2\right)}=C\left(A2\right)& \left(I\right)\end{array}$

[0258] Wherein

[0259] w(A-1) is the weight fraction [in wt.-%] of the first polymer fraction (A-1),

[0260] w(A-2) is the weight fraction [in wt.-%] of second polymer fraction (A-2),

[0261] C(A-1) is the comonomer content [in wt-%] of the first polymer fraction (A-1),

[0262] C(A) is the comonomer content [in wt.-%] of the C.sub.2C.sub.3 random copolymer (A),

[0263] C(A-2) is the calculated comonomer content [in wt-%] of the second polymer fraction (A-2).

[0264] Xylene Cold Solubles (XCS)

[0265] The xylene soluble (XS) fraction as defined and described in the present invention is determined in line with ISO 16152 as follows: 2.0 g of the polymer were dissolved in 250 ml p-xylene at 135° C. under agitation. After 30 minutes, the solution was allowed to cool for 15 minutes at ambient temperature and then allowed to settle for 30 minutes at 25+/−0.5° C. The solution was filtered with filter paper into two 100 ml flasks. The solution from the first 100 ml vessel was evaporated in nitrogen flow and the residue dried under vacuum at 90° C. until constant weight is reached. The xylene soluble fraction (percent) can then be determined as follows:

[0266] XS %=(100*m*V.sub.0)/(m.sub.0*v); m.sub.0=initial polymer amount (g); m=weight of residue (g); V.sub.0=initial volume (ml); v=volume of analysed sample (ml).

[0267] Melting Temperature T.sub.m and Crystallization Temperature T.sub.c

[0268] The parameters are determined with a TA Instrument Q2000 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357/part 3/method C2 in a heat/cool/heat cycle with a scan rate of 10° C./min in the temperature range of −30 to +225° C. Crystallization temperature (T.sub.c) is determined from the cooling step, while the melting temperature (T.sub.m) is determined from the second heating step. Melting and crystallization temperatures were taken as the peaks of endotherms and exotherms.

[0269] Sealing Initiation Temperature (SIT); (Sealing End Temperature (SET), Sealing Range)

[0270] The method determines the sealing temperature range (sealing range) of polypropylene films, in particular blown films. The sealing temperature range is the temperature range, in which the films can be sealed according to conditions given below. The lower limit (heat sealing initiation temperature (SIT)) is the sealing temperature at which a sealing strength of 5+/−0.5 N is achieved. The upper limit (sealing end temperature (SET)) is reached, when the films stick to the sealing device.

[0271] The sealing range was determined on a J&B Universal Sealing Machine Type 3000 of the multilayer films as produced indicated below with the following parameters:

[0272] Specimen width: 25.4 mm

[0273] Seal Pressure: 0.1 N/mm.sup.2

[0274] Seal Time: 0.1 sec

[0275] Cool time: 99 sec

[0276] Peel Speed: 10 mm/sec

[0277] Start temperature 80° C.

[0278] End temperature: 150° C.

[0279] Increments: 10° C.

[0280] specimen is sealed A to A at each seal bar temperature and seal strength (force) is determined at each step. The temperature is determined at which the seal strength reaches 5 N.

[0281] Flexural Modulus

[0282] The flexural modulus was determined in 3-point-bending according to ISO 178 on 80×10×4 mm3 test bars injection moulded at 23° C. in line with EN ISO 1873-2.

[0283] Tear resistance (determined as Elmendorf tear (N)): Applies both for the measurement in machine direction (MD) and transverse direction (TD). The tear strength is measured using the ISO 6383/2 method. The force required to propagate tearing across a film sample is measured using a pendulum device. The pendulum swings under gravity through an arc, tearing the specimen from pre-cut slit. The film sample is fixed on one side by the pendulum and on the other side by a stationary clamp. The tear resistance is the force required to tear the specimen. The relative tear resistance (N/mm) is then calculated by dividing the tear resistance by the thickness of the film.

[0284] Tensile Modulus

[0285] Tensile modulus in machine and transverse direction were determined according to ISO 527-3 at 23° C. on the films as produced indicated below. Testing was performed at a cross head speed of 1 mm/min.

[0286] Dart Drop Strength (DDI)

[0287] Dart-drop was measured using ASTM D1709, method A (Alternative Testing Technique) from the films as produced indicated below. A dart with a 38 mm diameter hemispherical head is dropped from a height of 0.66 m onto a film clamped over a hole. Successive sets of twenty specimens are tested. One weight is used for each set and the weight is increased (or decreased) from set to set by uniform increments. The weight resulting in failure of 50% of the specimens is calculated and reported.

[0288] Haze and Clarity

[0289] Haze and clarity were determined according to ASTM D 1003-00 on films as produced indicated below.

[0290] Steam sterilization was performed in a Systec D series machine (Systec Inc., USA). The samples were heated up at a heating rate of 5° C./min starting from 23° C. After having been kept for 30 min at 121° C., they were removed immediately from the steam sterilizer and stored at room temperature until being processed further.

B. Examples

[0291] C.sub.2C.sub.3 Random Copolymer (Component A)

[0292] The catalyst used in the polymerization processes for the C.sub.2C.sub.3 random copolymer of the inventive examples (IE1, IE2) and (CE1) was prepared as follows:

[0293] The metallocene (MC1) (rac-anti-dimethylsilandiyl(2-methyl-4-phenyl-5-methoxy-6-tert-butyl-indenyl)(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconium dichloride)

##STR00007##

[0294] has been synthesized according to the procedure as described in VO2013007650, E2.

[0295] Preparation of MAO-Silica Support

[0296] A steel reactor equipped with a mechanical stirrer and a filter net was flushed with nitrogen and the reactor temperature was set to 20° C. Next silica grade DM-L-303 from AGC Si-Tech Co, pre-calcined at 600° C. (7.4 kg) was added from a feeding drum followed by careful pressuring and depressurising with nitrogen using manual valves. Then toluene (32 kg) was added. The mixture was stirred for 15 min. Next 30 wt.-% solution of MAO in toluene (17.5 kg) from Lanxess was added via feed line on the top of the reactor within 70 min. The reaction mixture was then heated up to 90° C. and stirred at 90° C. for additional two hours. The slurry was allowed to settle and the mother liquor was filtered off. The MAO treated support was washed twice with toluene (32 kg) at 90° C., following by settling and filtration. The reactor was cooled off to 60° C. and the solid was washed with heptane (32.2 kg). Finally MAO treated SiO.sub.2 was dried at 60° C. under nitrogen flow for 2 hours and then for 5 hours under vacuum (−0.5 barg) with stirring. MAO treated support was collected as a free-flowing white powder found to contain 12.6% Al by weight.

[0297] Catalyst System Preparation

[0298] 30 wt.-% MAO in toluene (2.2 kg) was added into a steel nitrogen blanked reactor via a burette at 20° C. Toluene (7 kg) was then added under stirring. Metallocene MC1 (286 g) was added from a metal cylinder followed by flushing with 1 kg toluene. The mixture was stirred for 60 minutes at 20° C. Trityl tetrakis(pentafluorophenyl) borate (336 g) was then added from a metal cylinder followed by a flush with 1 kg of toluene. The mixture was stirred for 1 h at room temperature. The resulting solution was added to a stirred cake of MAO-silica support prepared as described above over 1 hour. The cake was allowed to stay for 12 hours, followed by drying under N2 flow at 60° C. for 2 h and additionally for 5 h under vacuum (-0.5 barg) under stirring. Dried catalyst was sampled in the form of pink free flowing powder containing 13.9 wt-% Al and 0.26 wt.-% Zr

[0299] The polymerization for preparing the inventive C.sub.2C.sub.3 random copolymer (PRC) was performed in a Borstar pilot plant with a 2-reactor set-up (loop—gas phase reactor (GPR 1)). In Table 1 the polymerization conditions are given.

TABLE-US-00001 TABLE 1 Component (A) Prepoly reactor Temperature [° C.] 25 Pressure [Pa] 5149 Catalyst feed [g/h] 2.0 C.sub.3 feed [kg/h] 52 H.sub.2 feed [g/h] 0.3 Residence time [h] 0.4 loop reactor Temperature [° C.] 68 Pressure [Pa] 5385 Feed H.sub.2/C.sub.3 ratio [mol/kmol] 0.24 Feed C.sub.2/C.sub.3 ratio [mol/kmol] 48.3 Polymer Split [wt.-%] 67 MFR.sub.2 [g/10 min] (MFR of A-1) 2.0 Total C.sub.2 loop [wt.-%] (C2 of A-1) 3.7 XCS loop [wt.-%] 3.5 Residence time (h) 0.4 GPR1 Temperature [° C.] 75 Pressure [Pa] 2500 H.sub.2/C.sub.3 ratio [mol/kmol] 2.0 C.sub.2/C.sub.3 ratio [mol/kmol] 224 Polymer residence time (h) 1.8 Polymer Split [wt.-%] 33 Total MFR.sub.2 [g/10 min] 1.1 MFR.sub.2 [g/10 min] in GPR1 (MFR of A-2) 0.3 Total C.sub.2 [wt.-%] (loop + GPR1) 4.1 C.sub.2 in GPR1 [wt.-%] (C.sub.2 of A-2) 4.9 XCS [wt.-%] 4.7

[0300] The polymer powder was compounded in a co-rotating twin-screw extruder Copenion ZSK 57 at 220° C. with 0.2 wt-% antiblock agent (synthetic silica; CAS-no. 7631-86-9); 0.1 wt.-% antioxidant (Irgafos 168FF); 0.1 wt.-% of a sterical hindered phenol (Irganox 1010FF); 0.02 wt.-% of Ca-stearat) and 0.02 wt-% of a non-lubricating stearate (Synthetic hydrotalcite; CAS-no. 11097-59-9).

TABLE-US-00002 TABLE 2 polymer properties Pellet Component (A) XCS [wt.-%] 4.7 Total C.sub.2 [wt.-%] 4.1 MFR.sub.2 [g/10 min] 1.1 Tm [° C.] 125 Tc [° C.] 85

[0301] For Inventive Examples IE1 and IE2 the C.sub.2C.sub.3 random copolymer (A) produced as described above was mixed with an ethylene based plastomer (B).

[0302] The following commercially available plastomer (B) has been used:

[0303] Queo™ 8201, ethylene-octene plastomer, density 882 kg/n.sup.3, MFR.sub.2 (190° C., 2.16 kg) 1.1 g/10 min and melting point 76° C., commercially available from Borealis AG

[0304] Mixing was done in a co-rotating twin-screw extruder Coperion ZSK 57.

[0305] Film Production

[0306] All film properties were determined on monolayer blown films of 50 μm thickness produced on a Collin blown film line. This line has a screw diameter of 30 millimeters (mm), L/D of 30, a die diameter of 60 mm, a die gap of 1.5 mm and a duo-lip cooling ring. The film samples were produced at 190° C. with an average thickness of 50 μm, with a 2.5 blow-up ratio and an output rate of about 8 kilograms per hour (kg/h). Properties of the films can be seen in Table 3.

TABLE-US-00003 TABLE 3 CE1 IE1 IE2 C.sub.2C.sub.3 copolymer wt.-% 100 90 75 Queo 8201 wt.-% 10 25 50 μm BF Tensile Modulus MD MPa 638 527 341 Tensile Modulus TD MPa 664 540 319 DDI g 43 116 >1700 Haze/b.s. % 4.9 3.9 2.6 Clarity/b.s. % 91.8 91.8 90.7 Haze/a.s. % 4.9 4.6 5.2 Clarity/a.s. % 91.1 89.9 85.0 Tear/MD N/mm 6.6 7.6 19.7 Tear/TD N/mm 21.2 119.4 168.0 SIT ° C. 109 105 90 OMA 859 1027 2584 b.s. before steam sterilization a.s. after steam sterilization

[0307] From the above table it can be clearly seen that the inventive blown films base on the specific blend, show an advantageous combination of low sealing initiation temperature (SIT), high tear resistance as wells as impact strength, and good optical properties, like low haze. Furthermore, such films have an improved overall performance, i.e. high OMA.