Dual reactor polyethylene resins for medical packaging - films, bags and pouches

A medical packaging film, bag or pouch made from a linear low density polyethylene having a density from 0.914 to 0.945 g/cm3 and a melt flow ratio (MFR (I21/I2) determined according to ASTM D 1238) from 23 to 32 prepared by A) polymerizing ethylene optionally with one or more C3-12 alpha olefins, in solvent in a first stirred polymerization reactor at a temperature of from 80 to 200° C. and a pressure of from 10,500 to 35,000 KPa, (1,500 to 5,000 psi) in the presence of (a) a catalyst which is an organometallic complex of a group 3, 4 or 5 metal, characterized by having at least one phosphinimine ligand;

• and (b) co-catalyst selected from the group consisting of:
• (i) an aluminoxane compound of the formula R122AlO(R12AlO)mAlR122 wherein each R12 is independently selected from the group consisting of C1-20 hydrocarbyl radicals and m is from 3 to 50, and optionally a hindered phenol to provide a molar ratio of Al:hindered phenol from 2:1 to 5:1 if the hindered phenol is present;
• (ii) an ionic activator that may be selected from the group consisting of:
• (A) compounds of the formula [R13]+ [B(R14)4]− wherein B is a boron atom, R13 is a cyclic C5-7 aromatic cation or a triphenyl methyl cation and each R14 is independently selected from the group consisting of phenyl radicals which are unsubstituted or substituted with 3 to 5 substituents selected from the group consisting of a fluorine atom, a C1-4 alkyl or alkoxy radical which is unsubstituted or substituted by a fluorine atom;
• and a silyl radical of the formula —Si—(R15)3;
• wherein each R15 is independently selected from the group consisting of a hydrogen atom and a C1-4 alkyl radical;
• and
• (B) compounds of the formula [(R18)tZH]+[B(R14)4]− wherein B is a boron atom, H is a hydrogen atom, Z is a nitrogen atom or phosphorus atom, t is 2 or 3 and R18 is selected from the group consisting of C1-8 alkyl radicals, a phenyl radical which is unsubstituted or substituted by up to three C1-4 alkyl radicals, or one R18 taken together with the nitrogen atom may form an anilinium radical and R14 is as defined above;
• and
• (C) compounds of the formula B(R14)3 wherein R14 is as defined above;
• and
• (iii) mixtures thereof;
• and
• B) passing said first polymer solution into a second stirred polymerization reactor at a pressure from 10,500 to 35,000 KPa (1,500 to 5,000 psi) and a temperature at least 20° C. higher than the first reactor and polymerizing further ethylene, optionally with one or more C3-12 alpha olefins, in said second stirred polymerization reactor in the presence of (a) a catalyst which is an organometallic complex of a group 3, 4 or 5 metal, characterized by having at least one phosphinimine ligand;
• and (b) a co-catalyst as described above;
• said polyethylene, having a melt index less than 2 as measured by ASTM D 1238, when formed into a monolayer or a co-extruded multi-layer film at a blowup ratio from 2 to 4 and a thickness from 0.5 to 6 mils using a blown film line at a production rate that is greater than 6 lbs/hr/inch (1 kg/hr/cm) of die circumference, has haze values 59 to 65% lower, gloss 45° values 49 to 55% higher, hexane extractables 58 to 79% lower, a plateau seal temperature of about 110° C., hot tack strength (at 115° C.) 25 to 70% higher, dart impact strengths 97 to 142% higher, machine direction (MD) tear strengths 26 to 95% higher, and puncture energy values 74 to 124% higher than films made from resin produced by conventional Ziegler-Natta catalysis, wherein the conventional Ziegler-Natta resin has a melt index of up to 0.15 g/10 min lower than the melt index of the linear low density polyethylene prepared according to said steps A) and B.