POLYPROPYLENE COATING COMPOSITION

Abstract

The present invention relates to use of a polypropylene composition comprising a polypropylene having—a melt flow rate MFR2 (230° C./2.16 kg) measured according to ISO 1133 of 10 to 40 g/10 min, —a melting temperature T.sub.m as determined by DSC according to ISO 11357 of 149 to 160° C., and—a molecular weight distribution MWD of 2.4 to 4.5 as determined by GPC, for extrusion coating of an article, to a process for extrusion coating of an article and to an extrusion coated article.

Claims

1. A process for coating an article, comprising extrusion coating the article with a polypropylene composition comprising a polypropylene having a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 of 10 to 40 g/10 min, a melting temperature T.sub.m as determined by DSC according to ISO 11357 of 149 to 160° C., and a molecular weight distribution MWD of 2.4 to 4.5 as determined by GPC.

2. The process according to claim 1 wherein the polypropylene is a propylene homopolymer.

3. The process according to claim 1 wherein the polypropylene has a number of 2,1 and 3,1 regio defects of from 0.01 to 1.2 mol %.

4. The process according to claim 1 wherein the polypropylene has been produced in the presence of a single-site catalyst.

5. The process according to claim 1 wherein the polypropylene has a melt flow rate MFR.sub.2 of 15 to 37 g/10 min and/or a melting temperature T.sub.m as determined by DSC according to ISO 11357 of 150 to 158° C.

6. The process according to claim 1 wherein the polypropylene has a melt flow rate MFR.sub.2 of 20 to 35 g/10 min and/or a melting temperature T.sub.m as determined by DSC according to ISO 11357 of 153 to 157° C.

7. The process according to claim 1 wherein the polypropylene has a MWD of 2.5 to 4.5 as determined by GPC and/or a xylene cold soluble (XCS) fraction as determined according to ISO 16152 of from 0.05 to below 5 wt. %.

8. The process according to claim 1 wherein the polypropylene has a MWD of 2.7 to 4.0 as determined by GPC and/or a xylene cold soluble (XCS) fraction as determined according to ISO 16152 of from 0.1 to 4 wt. %.

9. The process according to claim 1 wherein the polypropylene has a crystallization temperature T.sub.c as determined by DSC according to ISO 11357 in the range of 100 to 130° C. and/or a flexural modulus as determined according to ISO 178 on injection moulded specimens of 1200 to 1800 MPa.

10. The process according to claim 1 wherein the polypropylene has a crystallization temperature T.sub.c as determined by DSC according to ISO 11357 in the range of 105 to 125° C. and/or a flexural modulus as determined according to ISO 178 on injection moulded specimens of 1250 to 1650 MPa.

11. The process according to claim 1 wherein the polypropylene has a crystallization temperature T.sub.c as determined by DSC according to ISO 11357 in the range of 110 to 120° C. and/or a flexural modulus as determined according to ISO 178 on injection moulded specimens of 1300 to 1600 MPa.

12. The process according to claim 1 wherein the polypropylene comprises two polymer fractions (PPH-1) and (PPH-2) wherein the split between fractions (PPH-1) and (PPH-2) is from 30:70 to 70:30, preferably is from 45:55 to 65:35, and more preferably is from 55:45 to 60:40.

13. A process for extrusion coating of an article in which a polypropylene composition comprising a polypropylene having a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 of 10 to 40 g/10 min, a melting temperature T.sub.m as determined by DSC according to ISO 11357 of 149 to 160° C., and a molecular weight distribution MWD of 2.4 to 4.5 as determined by GP, is coated onto an article by extrusion.

14. The process according to claim 1 wherein the article is paper, paperboard, a fibrous substrate, and/or a metal foil.

15. A coated article having a coating layer of a polypropylene composition comprising polypropylene having a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 of 10 to 40 g/10 min, a melting temperature T.sub.m as determined by DSC according to ISO 11357 of 149 to 160° C., and a molecular weight distribution MWD of 2.4 to 4.5 as determined by GPC.

Description

[0083] In the following, the measurement and determination methods for the parameters as used herein are given and the present invention is further illustrated by way of example and comparative example by reference to the figures, which show:

[0084] FIG. 1: Sealing curve of Inventive Example 1 (IE1)

[0085] FIG. 2: Sealing curve of Comparative Example 2 (CE2).

[0086] Measurement and Determination Methods

[0087] a) Measurement of Melt Flow Rate MFR.sub.2

[0088] MFR.sub.2 (230° C.) is measured according to ISO 1133 (230° C., 2.16 kg load).

[0089] b) Calculation of Melt Flow Rate MFR.sub.2 of the Polymer Fraction PPH-2:

[00001]$\mathrm{MFR}\left(A2\right)={10}^{\left[\frac{\log \left(\mathrm{MFR}\left(A\right)\right)-w\left(A1\right)\times \log \left(\mathrm{MFR}\left(A1\right)\right)}{w\left(A2\right)}\right]}\left(\mathrm{II}\right)$

wherein
w(A1) is the weight fraction [in wt. %] of the polymer fraction PPH-1
w(A2) is the weight fraction [in wt. %] of the polymer fraction PPH-2,
MFR(A1) is the melt flow rate MFR.sub.2 (230° C.) [g/10 min] of the polymer fraction PPH-1,
MFR(A) is the melt flow rate MFR.sub.2 (230° C.) [g/10 min] of the entire polypropylene (PPH),
MFR(A2) is the calculated melt flow rate MFR.sub.2 (230° C.) [g/10 min] of the polymer fraction PPH-2.

[0090] c) Quantification of Microstructure by NMR Spectroscopy

[0091] 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 optimized 10 mm extended temperature probe head at 125° C. using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d2 (TCE-d2) along with chromium-(III)-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 optimized 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.

[0092] Quantitative .sup.13C{.sup.1H} 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).

[0093] 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.

[0094] 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.

[0095] 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))

[0096] 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))

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.

[0097] The mole percent comonomer incorporation was calculated from the mole fraction:

E[mol %]=100*fE

[0098] The weight percent comonomer incorporation was calculated from the mole fraction:

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

[0099] 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.

[0100] d) Xylene Solubles (XCS, Wt. %)

[0101] The xylene soluble (XS) fraction as defined and described in the present invention was 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:

XS %=(100*m*V0)/(m0*v);

m0=initial polymer amount (g);
m=weight of residue (g);
V0=initial volume (ml);
v=volume of analysed sample (ml).

[0102] e) DSC Analysis, Melting (Tm) and Crystallization Temperature (Tc)

[0103] Data were measured 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.

[0104] Crystallization temperature (Tc) and crystallization enthalpy (Hc) are determined from the cooling step, while melting temperature (Tm) and melting enthalpy (Hm) are determined from the second heating step.

[0105] f) Flexural Modulus

[0106] Flexural modulus is determined according to ISO 178 on 80×10×4 mm.sup.3 test bars injection moulded in line with EN ISO 1873-2.

[0107] g) Hexane Extractables

[0108] The hexane extractable fraction is determined according to FDA method (federal registration, title 21, Chapter 1, part 177, section 1520, s. Annex B) on cast films of 100 μm thickness produced on a monolayer cast film line with a melt temperature of 220° C. and a chill roll temperature of 20° C. The extraction was performed at a temperature of 50° C. and an extraction time of 30 min.

[0109] h) Molecular Weight Properties

[0110] Number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity (Mw/Mn) were determined by Gel Permeation Chromatography (GPC) according to the following method:

[0111] The weight average molecular weight Mw and the polydispersity (Mw/Mn), wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) is measured by a method based on ISO 16014-1:2003 and ISO 16014-4:2003. A Waters Alliance GPCV 2000 instrument, equipped with refractive index detector and online viscosimeter was used with 3×TSK-gel columns (GMHXL-HT) from TosoHaas and 1,2,4-trichlorobenzene (TCB, stabilized with 200 mg/L 2,6-Di tert butyl-4-methyl-phenol) as solvent at 145° C. and at a constant flow rate of 1 mL/min. 216.5 μl of sample solution were injected per analysis. The column set was calibrated using relative calibration with 19 narrow MWD polystyrene (PS) standards in the range of 0.5 kg/mol to 11 500 kg/mol and a set of well characterized broad polypropylene standards. All samples were prepared by dissolving 5-10 mg of polymer in 10 mL (at 160° C.) of stabilized TCB (same as mobile phase) and keeping for 3 hours with continuous shaking prior sampling in into the GPC instrument.

[0112] h) Sealing Behavior

[0113] The sealing behavior of the coatings was determined by measuring the hot tack force as follows:

[0114] The maximum hot-tack force, i.e. the maximum of a force/temperature diagram was determined and reported. Hot tack measurements were made with J&B hot tack tester following the method ASTM F 1921. The standard requires that the samples have to be cut into 15 mm slices in width. The samples are placed into the hot tack testing machine in vertical direction both ends attached to a mechanical lock. Then the tester seals and pulls out the hot seal and the resisting force is measured.

[0115] The sealing parameters were:

TABLE-US-00001 Seal Pressure: 1.5 N/mm.sup.2 Seal Time: 0.5 sec Cool time: 0.20 sec Peel Speed: 200 mm/sec Width: 15.0 mm

EXAMPLES

[0116] A polypropylene in accordance with the invention (Inventive Example 1, IE1), using a single-site metallocene catalyst was prepared as follows:

[0117] Catalyst System IE1:

[0118] Metallocene (MC1) (rac-anti-dimethylsilandiyl(2-methyl-4-phenyl-5-methoxy tert-butyl-indenyl)(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconium dichloride)

##STR00001##

was synthesized according to the procedure as described in WO 2013/007650, E2.

[0119] A MAO-silica support was prepared as follows: 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 SiO2 was dried at 60° 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.

[0120] The final catalyst system was prepared as follows: 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.

[0121] The polymerization for preparing the inventive polymer of IE1 was performed in a Borstar pilot plant with a 2-reactor set-up (loop—gas phase reactor (GPR 1)) and a pre-polymerizer, using the catalyst system as described above.

[0122] In Table 1, the polymerization conditions for IE1 and the final properties of the resins of IE1 and CE2 are given.

TABLE-US-00002 TABLE 1 IE1 CE2 Prepolymerizer Temperature ° C. 25 Pressure kPa 5153 Loop Temperature ° C. 75 Pressure kPa 5400 Feed H2/C3 mol/kmol 0.48 Split wt % 62 MFR g/10 min 26.2 GPR1 Temperature ° C. 80 H2/C3 mol/kmol 3 Split wt % 38 MFR (final PP) g/10 min 27 Final polymer MFR g/10 min 27 27 XCS wt % 0.9 4.5 Tm ° C. 153 158 Tc ° C. 115 111 2, 1e mol % 0.7 0 2, 1t mol-% 0 0 3, 1 mol-% 0 0 FM MPa 1450 1403 MWD 3.4 4.7 g′ 1.0 n.d.

[0123] The resin of CE2 corresponds to the propylene homopolymer as prepared with a Ziegler-Natta catalyst and used in the inventive examples of WO2017/118612, to which it is referred.

[0124] The polymer powders were compounded in a co-rotating twin-screw extruder Coperion ZSK 57 at 220° C.0.1 wt % antioxidant (Irgafos 168FF); 0.1 wt % of a sterically hindered phenol (Irganox 1010FF); 0.05 wt % of Ca-stearat).

[0125] Using the compounded resins of IE1 and CE2 as described above, coating layer on paper was prepared by extrusion coating of the resins as follows:

[0126] Extrusion coating runs were made on Beloit co-extrusion coating line. It had Peter Cloeren's EBR die and a five layer feed block. The die width is 1000 mm and optimal working width is 600-800 mm. Designed top speed of the line is 1000 m/min, during production of test samples line speed was maintained at 150 m/min.

[0127] In the coating line above a UG kraft paper 70 g/m.sup.2 was coated with a co-extruded structure, which was composed of the resin of IE1 or CE2 (Layer 1, 9 g/m.sup.2), as disclosed above, and a Layer 2 (9 g/m.sup.2) of polypropylene resin WG341C (commercially available from Borealis, density: 910 kg/m.sup.3, melt Flow Rate (230° C./2.16 kg): 25 g/10 min, melting temperature (DSC) 161° C., Vicat softening temperature A, (10 N) 132° C.) attached to the paper substrate.

[0128] Layer 1 of the coating composed of the resin of IE1 accordingly had a branching index g′ of 1.0.

[0129] The temperature of the polymer melt was set to 290° C. and the extruders' temperature profile was 200-240-290-290° C. The chill roll was matt and temperature of its surface was 15° C. Used die opening was 0.65 mm and nip distance was 180 mm. Melt film touched the substrate for the first time+10 mm from nip to substrate side. Pressure of the pressure roll was 3.0 kp/cm.sup.2. The line speed was 150 m/min.

[0130] Hot tack of each sample was established by testing hot tack forces with temperatures ranging from 90° C. to temperature where the measured hot tack force was below 1 N. The standard requires at least 3 parallel measurements to be done. The temperature was increased in steps of 10 or 5° C.

[0131] The results of the hot tack force measurements of the coatings of IE1 and CE 2 are given in FIGS. 1 and 2, respectively.

[0132] SIT and SET values are obtained from hot tack measurement. In the present invention the lowest sealing temperature (SIT) is defined to be the temperature (° C.), where hot-tack strength is reaching 2 N, and highest sealing temperature (SET) is the temperature (° C.), where hot-tack strength is still at 2 N.

[0133] Maximum hot-tack strength is defined to be the highest strength (N) level over 20° C. interval of sealing range.

[0134] As can be seen from the data in FIGS. 1 and 2, the coating prepared in 1E1 provides lower sealing temperature and higher sealing force.