Copolymers and films thereof

Abstract

Novel copolymers having a density (D) in the range 0.895-0.910 g/cm.sup.3, a melt index MI.sub.2 (2.16 kg, 190 C.) in the range of 0.01-6 g/10 min, a Compositional Distribution Branch Index (CDBI) in the range 55-85%, and a sealing initiation temperature (SIT) and density (D) satisfying the relationship SIT(AD)B wherein A is 800 C.cm.sup.3/g and B is 650 C., wherein the SIT ( C.) is determined on a 70 m film at 0.5N/15 mm and D Is in units of g/cm.sup.3 are disclosed. The copolymers may be suitably prepared by use of metallocene catalyst systems and may be used in film applications, in particular as sealing layers for packaging applications.

Claims

1. A copolymer of ethylene and an alpha-olefin, said copolymer having (a) a density (D) in the range 0.895-0.910 g/cm.sup.3, (b) a melt index MI.sub.2 (2.16 kg, 190 C.) in the range of 0.01-6 g/10 min, (c) a Compositional Distribution Branch Index (CDBI) in the range 55-85%, and (d) a sealing initiation temperature (SIT) and density (D) satisfying the relationship
SIT(AD)B wherein A is 1700 C.cm.sup.3/g and B is 1469 C., and wherein the SIT ( C.) is determined on a 70 m film at 0.5N/15 mm and D is in units of g/cm.sup.3, and (e) a Crystallizable Species Fraction below 55 C. (CSF55)12%.

2. A copolymer according to claim 1 having a Compositional Distribution Branch Index (CDBI) in the range 65-85%.

3. A copolymer according to claim 1 having a density in the range 0.901-0.907 g/cm.sup.3.

4. A copolymer according to claim 1 having a melt index MI.sub.2 (2.16 kg, 190 C.) in the range of 0.05-5 g/10 min.

5. A copolymer according to claim 1 having a sealing initiation temperature (SIT)<72 C.

6. A copolymer according to claim 1 having a molecular weight distribution (Mw/Mn) greater than 3.4 and less than 4.5.

7. A copolymer according to claim 1 wherein the alpha-olefin is 1-hexene.

8. A copolymer according to claim 1 prepared in the presence a metallocene catalyst system.

9. A copolymer according to claim 8 wherein the metallocene catalyst system comprises a monocyclopentadienyl metallocene complex.

10. A copolymer according to claim 1 exhibiting a powder compressability (C) as follows:
% C<(AD)+B wherein D is the density in kg/m.sup.3 and A=1 and B=928.

11. A copolymer according to claim 1 exhibiting a powder compressability (C) as follows:
% C<(AD)+B wherein D is the density in kg/m.sup.3 and wherein A=0.5 and B=468.

12. A copolymer according to claim 1 having a Compositional Distribution Branch Index (CDBI) in the range 65-85%.

13. A copolymer according to claim 1 having a sealing initiation temperature (SIT)<65 C.

14. A copolymer according to claim 1 having a Crystallizable Species Fraction below 55 C. (CSF55)15%.

Description

EXAMPLES 1 AND 2

(1) Catalyst Preparation

(2) Treatment of Silica with Triethylaluminium

(3) Under continuous agitation, 2172 L of isohexane and 434.5 kg of silica SY2408 (available from W.R. Grace), were added to a reactor. (The silica was previously calcined under nitrogen to reach a level of hydroxyl groups of 1.5 mol/kg). 21.3 kg of a Statsafe 2500 (supplied by Innospec) solution in iso-hexane (2 g/L) was then added and the mixture was stirred for 15 minutes. 721 kg of a 12 wt % triethylaluminium (TEA) solution in isohexane was then slowly added over 1 hour and the mixture was stirred for 1 hour further at 30 C.

(4) The slurry was filtered and thoroughly washed with isohexane before being transferred to a dryer. 21.3 kg of Statsafe2500 in isohexane (2 g/l) was added and the mixture was finally dried at 60 C. under vacuum.

(5) The aluminium content of the solid was 3.62 wt %.

(6) Preparation of Catalyst Component (1)

(7) To 404.6 kg of a 10.6 wt % solution of [NH)Me(C.sub.18-22H.sub.37-45).sub.2][B(C.sub.6F.sub.5).sub.3(p-OHC.sub.6H.sub.4)] in toluene were added over 15 minutes 35.7 kg of 12 wt % TEA solution in isohexane. The mixture was further stirred for 15 minutes to yield a solution of catalyst component 1.

(8) Preparation of a Mixture of (C.sub.5Me.sub.4SiMe.sub.2N.sup.tBu)Ti(.sup.4-1,3-Pentadiene) with 1-Hexene

(9) 130.2 kg of a 9.87 wt % solution of (C.sub.5Me.sub.4SiMe.sub.2N.sup.tBu)Ti(.sup.4-1,3-pentadiene) in heptane and 83 kg of 1-hexene were mixed together during 15 min.

(10) Preparation of the Supported Catalyst

(11) 483.5 kg of the above prepared silica/TEA was introduced into a reactor. The above prepared solution of catalyst component 1 was fed to the reactor over 60 min and the mixture was then stirred for further 30 minutes.

(12) The contents of the reactor was then cooled to 15 C. and the above prepared solution of (C.sub.5Me.sub.4SiMe.sub.2N.sup.tBu)Ti(.sup.4-1,3-pentadiene) and 1-hexene was fed over a period of 30 minutes, and then the mixture was further stirred for 40 minutes.

(13) 12.8 kg of a Statsafe2500 solution in isohexane (200 g/l) was then added and the mixture was dried at 60 C. during 13 hours until the residual solvent content in the catalyst was <1 wt %. Analysis of the resulting free flowing powder showed the titanium content to be 56 mol/g, the boron content to be 59 mol/g and the aluminium content to be 2.9 wt %.

EXAMPLE 3 (COMPARATIVE)

(14) Example 3 is an ethylene-octene copolymer commercialized by Borealis under the reference QUEO 0201 produced using a metallocene catalyst in a solution polymerisation process.

EXAMPLE 4 (COMPARATIVE)

(15) Example 4 is an ethylene-octene copolymer commercialized by Borealis under the reference QUEO 1001 produced using a metallocene catalyst in a solution polymerisation process.

EXAMPLE 5 (COMPARATIVE)

(16) Example 5 is an ethylene-hexene copolymer of density 0.918 g/cm.sup.3 manufactured according to the teaching parameters in the aforementioned WO 2008/074689.

(17) Polymerization

(18) Polymerizations using the catalysts prepared in examples 1 and 2 were carried out continuously using a fluidized bed gas phase reactor of 74 cm diameter, with a vertical cylindrical section of 7 m. Polymerization conditions used are shown in Table 1 as follows

(19) TABLE-US-00001 TABLE 1 Example 1 2 Production Rate Kg/h 187 188 Reaction temp ( C.) 70 72 Reaction pressure (barg) 20 20 C2 partial pressure (bar) 11.6 12.3 H2 to C2 pressure ratio (mol/mol) 0.0038 0.0036 C6 partial pressure (bar) 0.069 0.067 C5 partial pressure (bar) 1.6 1.7 Residence time (hrs) 3.3 4 Condensation rate (wt %) 0 0
Product Characteristics

(20) The product characteristics are shown below in Table 2.

(21) TABLE-US-00002 TABLE 2 Example 1 Example 2 CE3 CE4 CE5 Density (g/cm.sup.3) 0.9013 0.9063 0.9007 0.9097 0.918 MI.sub.2 (2.16 kg/190 C.) 1.13 1.15 1.26 1.1 1.3 CDBI (%) 69.8 83.3 88.5 94.0 68.2 (A D) B* 71.04 75.04 70.56 77.76 84.4 SIT at 0.5N ( C.) 60 71 72 79 92 Mn (kDa) 32.2 30.4 30.5 27.2 29.0 Mw (kDa) 117.3 115.2 92.6 89.6 117 Mz (kDa) 265.3 261.2 188.3 199.0 276 Mw/Mn 3.6 3.8 3.0 3.3 3.8 Mz/Mn 2.3 2.3 2.0 2.2 2.4 Peak melting temp C. 86.5/114.7 91.9/114.9 95.4 104.8 102/117.7/121.4 CSF55 (%) 17.4 11.4 11.1 3.9 0.8 Maximum Hot tack 10.9 11.8 10.0 9.8 11.3 strength (N) Temperature with 87 89 99 107 124 Hot tack strength of 3N ( C.) Powder compressability (%) 14.8 10.2 *A = 800 and B = 650.
Melt index (190/2.16) was measured according to ISO 1133.
Density was measured using a density column according to ISO 1872/1 method except that the melt index extrudates were not annealed but left to cool on a sheet of polymeric material for 30 minutes.
Gel Permeation Chromatography Analysis for Molecular Weight Distribution Determination
Apparent molecular weight distribution and associated averages, uncorrected for long chain branching, were determined by Gel Permeation Chromatography using a GPC IR device from Polymer ChAR (, with 3 TSK GMHh r-H (S) columns from TOSOH CORPORATION and a IR5 detector a infra-red detector supplied by Polymer ChAR. The solvent used was 1,2,4 Trichlorobenzene at 160 C., which is stabilised with BHT, of 0.1 g/litre concentrationer. Polymer solutions of 1.0 g/litre concentration were prepared at 160 C. for one hour with stirring only at the last 30 minutes. The nominal injection volume was set at 200 l and the nominal flow rate was 1 ml/min.

(22) A relative calibration was constructed using 13 narrow molecular weight linear polystyrene standards:

(23) TABLE-US-00003 PS Standard Molecular Weight 1 3900 000 2 1 950 000 3 1 160 000 4 9952 600 5 488 400 6 195 900 7 70 950 8 49 170 9 30 230 10 19 760 11 10 680 12 1 930

(24) The elution volume, V, was recorded for each PS standards. The PS molecular weight was then converted to PE equivalent using the following Mark Houwink parameters k.sub.ps=1.7510.sup.4, .sub.ps=0.67, k.sub.pe=5.110.sup.4, .sub.pe=0.706. The calibration curve Mw.sub.PE=f(V) was then fitted with a first order linear equation. Number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz) are computed using the formula given the text book Properties of Polymers correlation with chemical structure by D. W. Van Krevelen, Elsevier Publishing Company, Amsterdam, 1972. All the calculations are done with GPC one software from Polymer Char.

(25) The very low molecular weight fractions (below 600 Daltons) were routinely excluded in the calculation of number average molecular weight, Mn, and hence the polymer polydispersity, Mw/Mn, in order to improve integration at the low end of the molecular weight curve, leading to a better reproducibility and repeatability in the extraction and calculation these parameters.

(26) Peak Melting temperature was determined by differential scanning calorimetry using a Perkin Elmer Diamond model following the methodology outlined in ASTM D3417 except that the first heating was carried out at 20 C./mn. The peak temperature is taken as the temperature correspond to a maximum heat flow observed during the second heating of the polymer at 10 C./mn. In case of several peaks during melting are observed, for each maximum a peak melting temperature is recorded.
Composition distribution breadth index (CDBI) is defined as the weight percent of the copolymer molecules having a comonomer content within 50% of the median total molar comonomer content. The CDBI is determined by Temperature Rising Elution Fraction (TREF). TREF experiments analysis was conducted in a commercial CRYSTAF model 200 instrument from Polymer Char. Approximately 60 mg of polymer is dissolved at 150 C. for 60 minutes in 25 mL of 1,2,4 Trichlorobenzene stabilised with BHT, of 0.1 g/litre. 1.8 ml of the solution is then transferred into the column and allowed to equilibrate for approximately 45 minutes at 95 C. The polymer solution is then cooled to 35 C. using a cooling rate of 0.5 C./min. After 20 mn stabilization, TCB is eluted through the column at 0.5 ml/mn at 35 C. The polymer concentration is measured at the column outlet by an Infra Red detector. After the soluble species is fully eluted, the column temperature is increased at 1 C./mn until 120 C. After completion of the elution, CDBI is calculated from the elution profile.
Crystallizable Species Fraction below 55 C. (CSF55) is defined as the weight percentage of copolymers eluted between 35 and 55 C. over the eluted amount between 35 to 120 C. CSF55 is determined by TREF under the same conditions used for CDBI determination.
Powder Compressability

(27) The compressibility factor C (%) was determined on a Flow Rate Indicizer supplied by Johanson Innovations Inc, 102 Cross Street Suite #110 San Luis Obispo, Calif. 93401. The Flow Rate Indicizer equipment enables to assess qualitatively the powder flowability due to the compressibility factor being defined as:

(28) $C\left(\%\right)=\frac{\mathrm{BDI}-\mathrm{FDI}}{\mathrm{BDI}}*100$
where: FDI: Feed Density Index, which is the powder bulk density at silo feed, i.e. close to Settled Bulk Density.

(29) BDI: Bin Density Index, which the bulk density of the powder submitted to 500 standard impacts according to NFT 51-042.

(30) Both Density Indexes were determined at 60 C.

(31) Film Characteristics

(32) The films were extruded on a blown film line under the following conditions

(33) TABLE-US-00004 Supplier Dr Collin Model Extruder M type 180/600 Screw diameter 45 mm Screw L/D Ratio 25D Die diameter 100 mm Die gap 1.2 mm Temperature Profile 190/200/205/210/215/215/220/220 C. Output 15 kg/h Blow-up ratio 2:1 Frostline height 330 mm Film thickness 70 m

(34) The sealing initiation temperature (SIT) was calculated from the sealing strengthsealing temperature curve for a sealing strength of 0.5 N/15 mm. Seal strength is determined by cutting two superimposed film specimen of 130 mm150 mm70 m in transversal direction (TD) using the film cutting template. To avoid the film sticking to the hot plate, the test specimen are placed between two layers of Mylar film (25 m) then put between the hot jaws of the sealing machine from OTTO BRUGGER with the transversal direction of the film along the length of the jaws. The films are sealing at the set temperatures corresponding to 10 C. step between 50 and 140 C. The pressure is 2 bars and sealing time is 0.5 s. Three 15 mm width strips are cut in the Machine Direction and conditioned for 24 h at 23 C. at 50% relative humidity. The specimens are peeled in a tensile machine at 200 mm/mn with a initial distance between the two jaws of 50 mm. The sealing strength is recorded at specimen breakage and average across the three specimens.

(35) The temperature with a hottack strength of 3N and maximum hottack strength were calculated from the hottack strengthsealing temperature curve and corresponds to the lowest sealing temperature for which the hottack strength is superior or equal to 3 N and highest strength recorded between 50 to 140 C. respectively.

(36) The hottack strength is determined with a Topwave Hot Tack Tester on 25 mm-width film specimens in the TD direction. The film specimens are back-taped with a thermo-resistant adhesive tape (reference 51588 from VAN ROLL ISOLA). The Hot Tack Tester settings were: Seal Pressure: 0.14 N/mm2 Seal Time: 0.4 sec Cool Time: 0.3 sec Peel Speed: 150 mm/sec Force Range: 100N Seal temperature: 80-90-95-100-105-120-125-130-140-150-160-170-180