C2C3 random copolymer

Abstract

New C.sub.2C.sub.3 random copolymers, which combine low sealing initiation temperature (SIT), high hot-tack, low C6-solubles, good optical properties and an improved stiffness/impact balance, which are particularly suited for preparing blown films. The present invention is furthermore related to the manufacture of said copolymers and to their use, as well as to the blown films comprising such C.sub.2C.sub.3 random copolymers.

Claims

1. A C.sub.2C.sub.3 random copolymer (A) consisting of 50.0 to 85.0 wt % of polymer fraction (A-1) having (i) an ethylene content in a range of from 2.0 to 5.2 wt % and (ii) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in a range of from 0.5 to 5.0 g/10 min and 15.0 to 50.0 wt % of polymer fraction (A-2) having (i) an ethylene content in a range of from 5.5 to 10.0 wt % and (ii) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in a range of from 0.1 to 3.0 g/10 min, wherein the melt flow rate MFR.sub.2 (230° C./2.16 kg) of polymer fraction (A-2) is lower than the melt flow rate MFR.sub.2 (230° C./2.16 kg) of polymer fraction (A-1), and wherein the C.sub.2C.sub.3 random copolymer has (a) a total ethylene content in a range of from 3.0 to 7.5 wt %; (b) a melt flow rate MFR.sub.2 (230° C./2.16 kg) measured according to ISO 1133 in a range of from 0.5 to 5.0 g/10 min and (c) a melting temperature Tm as determined by DSC according to ISO 11357 of from 110° C. to 135° C.

2. The C.sub.2C.sub.3 random copolymer according to claim 1, wherein the C.sub.2C.sub.3 random copolymer (A) has an amount of hexane solubles (C6 solubles, FDA) measured on a 100 μm thick blown film according to FDA 177.1520 in a range of from 0.1 to 2.0 wt %.

3. The C.sub.2C.sub.3 random copolymer composition according to claim 1, wherein the C.sub.2C.sub.3 random copolymer (A) is obtained in the presence of a metallocene catalyst.

4. A process for producing the C.sub.2C.sub.3 random copolymer according to claim 1, comprising the following steps a) polymerizing in a first reactor (R1) propylene and ethylene, to obtain polymer fraction (A-1) of the C.sub.2C.sub.3 random copolymer (A), b) transferring said polymer fraction (A-1) and unreacted comonomers of the first reactor (R1) into a second reactor (R2), c) feeding to said second reactor (R2) propylene and ethylene, d) polymerizing in said second reactor (R2) and in the presence of said polymer fraction (A-1) propylene and ethylene, to obtain polymer fraction (A-2), wherein said polymer fraction (A-1) and said polymer fraction (A-2) form the C.sub.2C.sub.3 random copolymer (A), wherein the polymerizing takes place in the presence of a metallocene catalyst comprising (i) a complex of formula (I): ##STR00020## wherein M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from —R′.sub.2C—, —R′.sub.2C—CR′.sub.2—, —R′.sub.2Si—, —R′.sub.2Si—SiR′.sub.2—, or —R′.sub.2Ge—, wherein each R′ is independently a hydrogen atom, C.sub.1—C.sub.20-hydrocarbyl, tri(C.sub.1-C.sub.20-alkyl)silyl, C.sub.6-C.sub.20-aryl, C.sub.7-C.sub.20-arylalkyl or C.sub.7-C.sub.20-alkylaryl; R.sup.2 and R.sup.2′ are each independently a C.sub.1-C.sub.20-hydrocarbyl radical optionally containing one or more heteroatoms from groups 14-16; R.sup.5, is a C.sub.1-C.sub.20-hydrocarbyl group containing one or more heteroatoms from groups 14-16 optionally substituted by one or more halogen atoms; R.sup.6 and R.sup.6′ are each independently hydrogen or a C.sub.1-20-hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16; R.sup.7 is hydrogen or C.sub.1-20-hydrocarbyl group optionally containing one or more heteroatoms from groups 14-14, and R.sup.7′ is hydrogen; Ar and Ar′ each are independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R.sup.1; each R.sup.1 is a C.sub.1-20-hydrocarbyl group or two R.sup.1 groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered non aromatic ring with the Ar or Ar′ group, said ring being itself optionally substituted with one or more groups R.sup.4; wherein each R.sup.4 is a C.sub.1-20-hydrocarbyl group; and (ii) a cocatalyst comprising at least one or two compounds of a group 13 metal.

5. The process according to claim 4, wherein as cocatalyst (ii) a cocatalyst system comprising a boron containing cocatalyst and an aluminoxane cocatalyst is used and the catalyst is supported on a silica support.

6. An article, comprising the C.sub.2C.sub.3 random copolymer (A) according to claim 1.

7. The article according to claim 6, wherein the article is a blown film.

8. The article according to claim 7, wherein the blown film comprises (i) a sealing initiation temperature (SIT) (determined as described in the experimental part) in a range of from 80° C. to below 112° C., (ii) a hot-tack force determined as described in the experimental part on 50 μm blown film) of 1.8 N up to 5.0 N, (iii) a haze (determined according to ASTM D1003-00 on blown film with a thickness of 50 μm) in a range of from 0.1 to 8.0%, and (iv) a clarity (determined according to ASTM D1003-00 on blown film with a thickness of 50 μm) of at least 80.0% up to 100.0%.

9. The article according to claim 8 having a tensile modulus determined according to ISO 527-3 at 23° C. on blown films with a thickness of 50 μm in machine direction and in transverse direction in a range of 300 to 700 MPa.

10. The article according to claim 8, having a dart-drop impact (DDI) strength determined according to ASTM D1709, method A on a 50 μm blown film of 10 g to 200g.

11. The article according to claim 8 having an optomechanical ability (OMA) determined according to the formula given below: $OMA=\frac{\mathrm{Tensile}\mathrm{Modulus}\left(\mathrm{MD}\right)\left[MPa\right]*DDI\left(g\right)}{\mathrm{Haze}\left(50\mathrm{\mu m}\right)\left[\%\right]}$ of 3000 MPa*g/% to 15000 MPa*g/%.

12. The article according to claim 8 having an Elmendorf tear strength determined in accordance with ISO 6383/2 measured in machine direction (MD) in a range from 4.0 N/mm to 15.0 N/mm, and measured in transverse direction (TD) in a range of from 15.0 N/mm to 40.0 N/mm.

13. A flexible packaging system, selected from bags or pouches for food or pharmaceutical packaging comprising an article according to claim 9.

Description

2. EXAMPLES

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

(2) 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)

(3) ##STR00019##
has been synthesized according to the procedure as described in WO2013007650, E2.

(4) Preparation of MAO-Silica Support

(5) 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 depressurizing 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.

Catalyst System Preparation for Inventive Example IE1

(6) 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

(7) The polymerization for preparing the inventive C.sub.2C.sub.3 random copolymer (A) IE1 and IE2 was performed in a Borstar pilot plant with a 2-reactor set-up (loop—gas phase reactor (GPR 1)).

(8) In Table 1 the polymerization conditions for IE1 and IE2 are given.

(9) TABLE-US-00003 TABLE 1 IE1 IE2 Prepoly reactor Temperature [° C.] 25 25 Pressure [Pa] 5163 5157 Residence time [h] 0.4 0.4 loop reactor Temperature [° C.] 68 68 Pressure [Pa] 5391 5397 Feed H2/C3 ratio [mol/kmol] 0.29 0.30 Feed C2/C3 ratio [mol/kmol] 48.3 48.3 Polymer Split [wt %] 67 74 MFR2 [g/10 min] (MFR of A-1) 1.7 1.5 Total C2 loop [wt %] (C2 of A-1) 4.0 4.8 Residence time 0.4 0.4 GPR1 Temperature [° C.] 75 75 Pressure [Pa] 2500 2500 H2/C3 ratio [mol/kmol] 2.8 3.0 C2/C3 ratio [mol/kmol] 222 215 Polymer residence time (h) 1.8 1.7 Polymer Split [wt %] 33 26 Total MFR2 [g/10 min] 1.2 1.2 MFR2 [g/10 min] in GPR1 0.6 0.7 (MFR of A-2) Total C2 [wt %] (loop + GPR1) 4.7 4.6 C2 in GPR1 [wt %] (C2 of A-2) 6.1 5.7 XCS [wt %] 2.4 7.9 Total productivity (kg PP/g cat) 22 20

(10) Both polymer powders were compounded in a co-rotating twin-screw extruder Coperion 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).

(11) TABLE-US-00004 TABLE 2 polymer properties Pellet IE1 IE2 XCS [wt %] 2.4 7.9 Total C2 [wt %] 4.7 4.6 MFR2 [g/10 min] 1.1 1.2 Tm [° C.] 119 118 Tc [° C.] 80 79 Tm-Tc [° C.] 39 39 For CE1 the commercial grade RB801CF-01 available from Borealis AG, Austria has been used. RB801CF-01 is an unnucleated propylene-ethylene random copolymer having a melting temperature Tm of 140° C., a crystallization temperature Tc of 91° C., a difference (Tm−Tc) of 49° C., an MFR.sub.2 (230° C.) of 1.9 g/10 min, a total C2 content of 4.5 wt % and an XCS content of 8.1 wt %.

(12) In Table 3 film parameters as determined on a 50 μm monolayer blown film produced on a Collin lab-scale blown film line are shown.

(13) TABLE-US-00005 TABLE 3 film parameters IE1 IE2 CE1 Tensile [MPa] 584 629 738 modulus (MD) Tensile [MPa] 622 654 709 modulus (TD) SIT [° C.] 105 104 122 Tm-SIT [° C.] 14 14 18 Hot-tack force [N] 2.12 2.40 2.16 Haze [%] 4.7 4.9 18 Clarity [%] 88 98 89 C6 solubles, [wt %] 1.16 1.23 2.6 FDA* Relative tear [N/mm] 6.4 8.5 5.7 resistance/MD Relative tear [N/mm] 23.3 20.3 12.9 resistance/TD DDI [g] 42 56 55 OMA 5219 7263 2255 *Measured on 100 μm monolayer blown film

(14) From the above table it can be clearly seen that the inventive C.sub.2C.sub.3 random copolymers (A) provide blown films, which show an advantageous combination of low sealing initiation temperature (SIT), high hot-tack and good optical properties, like low haze and high clarity. Furthermore such films have low C6 solubles and an improved overall performance, i.e. high OMA.