Process for preparing an ethylene/α-olefin copolymer

A process for preparing an ethylene/α-olefin copolymer, which comprises:

• (A) copolymerizing ethylene and 1-hexene by continuous vapor phase polymerization;
• (B) copolymerization is conducted in the presence of a prepolymerized catalyst obtained by prepolymerizing ethylene in the presence of
• (a) a transition metal metallocene compound catalyst,
• (b) an organoaluminum oxy-compound,
• (c) a fine particle carrier, and optionally
• (d) an organoaluminum compound;
• (C) copolymerization is conducted under such condition that the partial pressure of the sum of the ethylene and 1-hexene is 10 to 28 kg/cm2;
• and
• (D) the resulting ethylene/1-hexene copolymer has the following properties:
• (i) the density is in the range of 0.880 to 0.960 g/cm3,
• (ii) the melt flow rate of 190° C. under a load of 2.16 kg is in the range of 0.1 to 100 g/10 min,
• (iii) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the relation
• MT≦2.2×MFR−0.84,
• (iv) the quantity fraction (W (% by weight)) of a decane-soluble component of said copolymer at 23° C. and the density (d (g/cm3)) satisfy the relation
• in the case of MFR≦10 g/10 min:
• W<80×exp(−100(d−0.88))+0.1,
• in the case of MFR>10 g/10 min:
• W<80×(MFR−9)0.26×exp(−100(d−0.88))+0.1,
• (v) the temperature (Tm (° C.) at the position of the maximum peak of an endotherm curve of said copolymer measured by a differential scanning calorimeter and the density (d (g/cm3)) satisfy the relation
• Tm<400×d−248,
• (vi) the endotherm curve of said copolymer measured by a differential scanning calorimeter has two or more peaks, and the temperature (Tm1(° C.)) at the position of the peak on the lowest temperature side, the temperature (Tm (° C.)) at the position of the maximum peak and the density (d (g/cm3)) satisfy the relation
• 576−600d>(Tm−Tm1)>558−600d,
• and
• (vii) a component, which is eluted at a temperature of not lower than 100° C. in a temperature rise elution test (TREF), exists in said copolymer, and the amount of the eluted component is 0.5 to 8% of the total amount of the eluate.

An ethylene/α-olefin copolymer which is prepared by copolymerizing ethylene and 1-hexene in a single stage vapor polymerization in the presence of a prepolymerized catalyst obtained by prepolymerizing ethylene in the presence of

• (a) a transition metal compound,
• (b) an aluminoxane compound,
• (c) a fine solid particle carrier, and
• (d) a C1-C4 alkylaluminum compound, or a C1-C4 alkylaluminum halide compound,
• wherein said transition metal compound consists essentially of a single metallocene catalyst of the formula (I):
• MLx (I)
• M is a transition metal atom selected from the group consisting of zirconium, titanium and hafnium,
• x is a valence of the transition metal atom M,
• L is a ligand coordinated to the transition metal atom M, and at least two of the ligands L are each a substituted cyclopentadienyl group having at least one substituent selected from hydrocarbon groups of 3 to 10 carbon atoms, or a
• substituted cyclopentadienyl group having two or more substituents, wherein at least one substituent is a hydrocarbon group of 3 or 4 carbon atoms, and other substituent is methyl or ethyl, and
• the ligand L other than the cyclopentadienyl group is a hydrocarbon group of 1 to 12 carbon atoms, an alkoxy group, a halogen atom, or a hydrogen atom, and
• which consists essentially of a copolymer of ethylene and 4 to 25% by weight of 1-hexene and has the following properties:
• (i) the density is in the range of 0.890 to 0.935 g/cm3,
• (ii) the melt flow rate at 190° C. under a load of 2.16 kg is in the range of 0.5 to 20 g/10 min,
• (iii) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the relation
• MT≦2.2×MFR−0.84,
• (iv) the quantity fraction (W (% by weight)) of a decane-soluble component of said copolymer at 23° C. and the density (d (g/cm3)) satisfy the relation
• in the case of MFR≦10 g/10 min;
• W<80×exp(−100(d−0.88))+0.1,
• in the case of MFR>10 g/10 min:
• W<80×(MFR−9)0.26×exp(−100(d−0.88))+0.1,
• (v) the temperature (Tm (° C.)) at the position of the maximum peak of an endotherm curve of said copolymer measured by a differential scanning calorimeter and the density (d (g/cm3)) satisfy the relation
• Tm<400×d−248,
• (vi) the endotherm curve of said copolymer measured by a differential scanning calorimeter has two or more peaks, and the temperature (Tm1 (° C.)) at the position of the peak on the lowest temperature side, the temperature (Tm (° C.)) at the position of the maximum peak and the density (d (g/cm3) satisfy the relation
• 576−600d>(Tm−Tm1)>558−600d,
• and
• (vii) a component, which is eluted at a temperature of not lower than 100° C. in a temperature rise elution test (TREF), exists in said copolymer, and the amount of the eluted component is 1 to 5% by weight of the total amount of the eluate.