Polyethylene composition and method for preparing the same
The present disclosure relates to a polyethylene composition capable of producing a molded product having excellent environmental stress crack resistance, and improving total volatile organic compound (TVOC) properties that can be generated by a low molecular weight polymer, and a method for preparing the same.
1 . A polyethylene composition comprising an ethylene homopolymer and a copolymer of ethylene and a C4-12 alpha-olefin monomer in a weight ratio of 99:1 to 99.5:0.5,
wherein the polyethylene composition has:
a melt index, measured according to ASTM D 1238, at 190° C. and 2.16 kg, of 0.20 g/10 min to 0.38 g/10 min,
a molecular weight distribution (Mw/Mn) of 8 to 12,
a density (ASTM D 1505, 23° C.) of 0.953 g/cm 3 to 0.963 g/cm 3 , and
a linear structural fraction (ROL) according to Equation 1 of 5.0% to 10.0%:
R
OL
=
(
A
1
/
A
2
)
×
1
0
0
[
Equation
l
]
in Equation 1,
R OL represents a linear structural fraction (%) contained in the polyethylene composition,
A 1 represents a ratio (A 1 , %) of an integral value in the region where Log MW is less than 3to an integral value in the entire x-axis in a GPC curve graph having an x-axis of log MW and a y-axis of dw/dlogMw, and
A 2 represents a ratio (A 2 , %) of an integral value in the region where Log MW is 3 or more and less than 3.5 to an integral value in the entire x-axis in a GPC curve graph having an x-axis of log MW and a y-axis of dw/dlogMw.
2 . The polyethylene composition of claim 1 , wherein the R OL is 7.5% to 10.0%.
3 . The polyethylene composition of claim 1 , wherein the A 1 is 0.5% or less.
4 . The polyethylene composition of claim 1 , wherein the A 2 is 3.5% to 4.5%.
5 . The polyethylene composition of claim 1 , wherein a difference of A 2 −A 1 is 3.0% to 4.0% in a GPC curve graph having an x-axis of log MW and a y-axis of dw/d log Mw.
6 . The polyethylene composition of claim 1 , wherein a ratio (A 3 ) of an integral value in the region where Log MW is 5.5 or more to an integral value in the entire x-axis in a GPC curve graph having an x-axis of log MW and a y-axis of dw/d log Mw is 11.5% or more.
7 . The polyethylene composition of claim 1 , which has a molecular weight distribution (Mw/Mn) of 10 to 12.
8 . The polyethylene composition of claim 1 , which has a density (ASTM D 1505, 23° C.) of 0.953 g/cm 3 to 0.955 g/cm 3 .
9 . The polyethylene composition of claim 1 , which has a melt index (ASTM D 1238, 190° C., 2.16 kg) of 0.25 g/10 min to 0.35 g/10 min.
10 . A method for preparing the polyethylene composition according to claim 1 , comprising:
preparing the copolymer of ethylene and a C4-12 α-olefin monomer through a copolymerization process of the ethylene and the C4-12 α-olefin monomer in the presence of at least one first metallocene compound represented by Chemical Formula 1; and at least one second metallocene compound selected from the compounds represented by Chemical Formula 2,
mixing the ethylene homopolymer and the copolymer of ethylene and the C4-12 α-olefin in a weight ratio of from 99:1 to 99.5:0.5:
(Cp 1 R a ) n (Cp 2 R b )M 1 Z 1 3-n [Chemical Formula 1]
in Chemical Formula 1,
M 1 is a Group 4 transition metal;
Cp 1 and Cp 2 are the same as or different from each other, and each independently any one selected from the group consisting of cyclopentadienyl, indenyl, 4,5,6,7-tetrahydro-1-indenyl, and fluorenyl radical, each of which is optionally substituted with C 1-20 hydrocarbon;
R a and R b are the same as or different from each other, and each independently hydrogen, C 1-20 alkyl, C 1-10 alkoxy, C 2-20 alkoxyalkyl, C 6-20 aryl, C 6-10 aryloxy, C 2-20 alkenyl, C 7-40 alkylaryl, C 7-40 arylalkyl, C 8-40 arylalkenyl, or C 2-10 alkynyl;
Z 1 are each independently a halogen atom, C 1-20 alkyl, C 2-10 alkenyl, C 7-40 alkylaryl, C 7-40 arylalkyl, C 6-20 aryl, substituted or unsubstituted C 1-20 alkylidene, substituted or unsubstituted amino, C 2-20 alkylalkoxy, or C 7-40 arylalkoxy; and
n is 1 or 0:
in Chemical Formula 2,
B is boron,
M is a group 4 transition metal,
R 1 to R 4 are the same as or different from each other, and are each independently hydrogen, C 1-20 alkyl, C 3-20 cycloalkyl, or C 6-20 aryl, or at least one pair of R 1 and R 2 or R 3 and R 4 is bonded to each other to independently form a substituted or unsubstituted C 6-60 aromatic ring,
R 5 and R 6 are the same as or different from each other, and are each independently C 1-20 alkyl, C 3-20 cycloalkyl, or C 6-20 aryl, or R 5 and R 6 are bonded to each other to form a C 3-60 aliphatic ring or a C 6-60 aromatic ring,
X 1 and X 2 are the same as or different from each other, and are each independently C 1-20 alkyl or —O(CO)R′, wherein R′ is C 1-20 alkyl,
Q is a substituted or unsubstituted C 2 - 60 heterocyclic ring containing at least one selected from the group consisting of N, O and S,
Y and Y′ are elements constituting Q,
Y is N, O, or S,
Y′is an element of Q and adjacent to Y, and Y′ is N or C.
11 . The method for preparing the polyethylene composition of claim 10 , wherein in Chemical Formula 1, M 1 is zirconium or hafnium; each of R a and R b is independently hydrogen, C 1-6 alkyl, C 7-12 arylalkyl, C 2-12 alkoxyalkyl, C 6-12 aryl, or C 2-6 alkenyl; and each Z 1 is independently a halogen atom.
12 . The method for preparing the polyethylene composition of claim 10 , wherein the first metallocene compound is a compound represented by any one of the following structural formulae:
13 . The method for preparing the polyethylene composition of claim 10 , wherein in Chemical Formula 2, M is zirconium; and R 1 to R 4 are the same as or different from each other, and are each independently hydrogen or methyl, or at least one pair of R 1 and R 2 or R 3 and R 4 is bonded to each other to independently form a benzene ring or a 1,2,3,4-tetrahydronaphthalene ring, which is unsubstituted or substituted with one to four substituents selected from the group consisting of methyl, tertbutyl and 4-tertbutyl phenyl.
14 . The method for preparing the polyethylene composition of claim 10 , wherein in Chemical Formula 2, R 5 and R 6 are the same as or different from each other, and are each independently methyl or phenyl, or R 5 and R 6 are bonded to each other to form a cyclooctane ring.
15 . The method for preparing the polyethylene composition of claim 10 , wherein in Chemical Formula 2, X 1 and X 2 are the same as or different from each other, and are each independently methyl or acetate.
16 . The method for preparing the polyethylene composition of claim 10 , wherein in Chemical Formula 2, Q is a pyridine ring, a 4,5-dihydrooxazole ring, a pyrazole ring, or a benzoxazole ring, each of which is unsubstituted or substituted with one to four substituents selected from the group consisting of methyl, isopropyl and diphenylamino.
17 . The method for preparing the polyethylene composition of claim 10 , wherein the second metallocene compound is a compound represented by any one of the following structural formulae:
18 . The method for preparing the polyethylene composition of claim 10 , wherein the first metallocene compound and the second metallocene compound are included in a molar ratio of 1:2 to 1:5.
19 . The method for preparing the polyethylene composition of claim 10 , wherein the polymerization step is performed while introducing hydrogen gas in an amount of 35 ppm to 250 ppm based on a molar amount of the ethylene.
20 . An injection-molded product comprising the polyethylene composition according to claim 1 .