Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1998-12-23
2001-05-01
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
53, 53, 53, C526S119000, C526S160000, C526S943000, C526S348100, C526S348200
Reexamination Certificate
active
06225410
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ethylene/&agr;-olefin copolymer, and more particularly to an ethylene/&agr;-olefin copolymer having excellent moldability and capable of producing films of excellent transparency and mechanical strength. The invention also relates to an ethylene copolymer composition whose content and usefulness are substantially the same as those of the ethylene/&agr;-olefin copolymer.
The invention further relates to a composition comprising either the ethylene/&agr;-olefin copolymer or the ethylene copolymer composition and another ethylene copolymer.
The invention still further relates to a process for preparing the ethylene/&agr;-olefin copolymer.
BACKGROUND OF THE INVENTION
Ethylene copolymers are molded by various molding methods and used in many fields. The properties required for the ethylene copolymers differ from each other according to the molding methods and the uses of the copolymers. For example, in the production of an inflation film by a high-speed molding method, an ethylene copolymer having high melt tension for its molecular weight must be selected in order to stably perform high-speed molding free from occurrence of bubble swing or bubble break. The similar properties are required to prevent sag or break in a blow molding method or to lower reduction of width to the minimum in a T-die molding method.
In Japanese Patent Laid-Open Publication No. 90810/1981 or No. 106806/1985, a method of increasing melt tension or swell ratio (die swell ratio) of ethylene polymers obtained by the use of Ziegler catalysts, particularly titanium catalysts, to improve moldability of the polymers is reported. In general, the ethylene polymers obtained by the use of the titanium catalysts, particularly low-density ethylene copolymers, however, have wide composition distribution and contain components which cause tackiness when the polymers are used as molded products such as films. Therefore, decrease of the components causing tackiness has been demanded.
Of the ethylene polymers produced by the use of Ziegler catalysts, those obtained by the use of chromium catalysts have relatively high melt tension, but further improvement in the heat stability has been demanded.
A great number of ethylene copolymers obtained by the use of olefin polymerization catalysts containing transition metal metallocene compounds have high melt tension and excellent heat stability, so that they are expected as copolymers filling the above demands. In the ethylene copolymers obtained by the use of the metallocene catalysts, however, the melt tension (MT) is generally proportional to the flow activation energy (Ea).
Polymers having high melt tension show excellent moldability because the bubble stability is good as mentioned above, but they show high flow activation energy (Ea), and this means that the molding conditions thereof have great dependence on the temperature. Therefore, if the molding conditions are not controlled very strictly and uniformly, the resulting molded products suffer unevenness. For example, films may have low transparency.
When the flow activation energy (Ea) is low, occurrence of unevenness in the molded products can be inhibited, but because of low melt tension, unstable bubble is produced and hence moldability is lowered.
OBJECT OF THE INVENTION
The present invention has been made under such circumstances as mentioned above, and it is an object of the invention to provide an ethylene/&agr;-olefin copolymer having excellent moldability and capable of producing films of excellent transparency and mechanical strength. It is another object of the invention to provide an ethylene copolymer composition whose content and usefulness are substantially the same as those of the ethylene/&agr;-olefin copolymer.
SUMMARY OF THE INVENTION
The ethylene/&agr;-olefin copolymer (A) according to the invention is a copolymer of ethylene and an &agr;-olefin of 6 to 8 carbon atoms and has the following properties:
(A-i) the melt tension (MT) at 190° C. and the melt flow rate (MFR) satisfy the following relation
9.0×MFR
−0.65
>MT>2.2×MFR
−0.84
,
(A-ii) the flow activation energy ((E
a
)×10
−4
J/molK) determined from a shift factor of time-temperature superposition of the flow curve, the carbon atom number (C) of the &agr;-olefin in the copolymer and the &agr;-olefin content (x mol %) in the copolymer satisfy the following relation
(0.039Ln(C−2)+0.0096)×x+2.87<(E
a
)×10
−4
≦(0.039Ln(C−2)+0.1660)×x+2.87,
and
(A-iii) the haze of a film having a thickness of 30 &mgr;m produced from the copolymer by inflation molding satisfies the following conditions:
where the flow index (FI) defined as a shear rate which is given when the shear stress reaches 2.4×10
6
dyne/cm
2
at 190° C. and the melt flow rate (MFR) satisfy the relation FI≧100×MFR,
in case of the carbon atom number (C) of the &agr;-olefin being 6,
Haze<0.45/(1−d)×log(3×MT
1.4
)×(C−3)
0.1
in case of the carbon atom number (C) of the &agr;-olefin being 7 or 8,
Haze<0.50/(1−d)×log(3×MT
1.4
),
and
where the flow index (FI) defined as a shear rate which is given when the shear stress reaches 2.4×10
6
dyne/cm
2
at 190° C. and the melt flow rate (MFR) satisfy the relation FI<100×MFR,
in case of the carbon atom number (C) of the &agr;-olefin being 6,
Haze<0.25/(1−d)×log(3×MT
1.4
)×(C−3)
0.1
,
in case of the carbon atom number (C) of the &agr;-olefin being 7 or 8,
Haze<0.50/(1−d)×log(3×MT
1.4
)
wherein d represents density (g/cm
3
) and MT represents melt tension (g).
The ethylene/&agr;-olefin copolymer (A) of the invention can be obtained by copolymerizing ethylene and an &agr;-olefin of 6 to 8 carbon atoms in the presence of an olefin polymerization catalyst comprising:
(a) an organoaluminum oxy-compound;
(b-I) at least one transition metal compound selected from transition metal compounds represented by the following formula (I):
ML
1
x
(I)
wherein M is a transition metal atom selected from Group 4 of the periodic table; L
1
is a ligand coordinated to the transition metal atom M, at least two ligands L
1
are each a substituted cyclopentadienyl group having at least one group selected from hydrocarbon groups of 3 to 10 carbon atoms, and the ligand L
1
other than the substituted cyclopentadienyl group is a hydrocarbon group of 1 to 12 carbon atoms, an alkoxy group, an aryloxy group, a trialkylsilyl group, a halogen atom or a hydrogen atom; and x is a valence of the transition metal atom M;
and
(b-II) at least one transition metal compound selected from transition metal compounds represented by the following formula (II):
ML
2
x
(II)
wherein M is a transition metal atom selected from Group 4 of the periodic table; L
2
is a ligand coordinated to the transition metal atom M, at least two ligands L
2
are each a methylcyclopentadienyl group or an ethylcyclopentadienyl group, and the ligand L
2
other than the methylcyclopentadienyl group or the ethylcyclopentadienyl group is a hydrocarbon group of 1 to 12 carbon atoms, an alkoxy group, an aryloxy group, a trialkylsilyl group, a halogen atom or a hydrogen atom; and x is a valence of the transition metal atom M.
The olefin polymerization catalyst preferably further comprises (c) a carrier on which the organoaluminum oxy-compound (a), the transition metal compound (b-I) and the transition metal compound (b-II) are supported.
The ethylene/&agr;-olefin copolymer (A) has excellent moldability and can produce films of excellent transparency and mechanical strength.
The ethylene copolymer composition (A′) according to the invention has substantially the same content and usefulness as those of the ethylene/&agr;-olefin copolymer, and is a composition comprising:
(B) an ethylene/&agr;-olefin copolymer, and
(C) an ethylene/&agr;-olefin copolymer,
said ethylene/&agr;-olefin copolymer (B) be
Nakagawa Takashi
Sugimura Kenji
Takahashi Mamoru
Yoshitsugu Ken
Choi Ling-Siu
Mitsui Chemicals
Wu David W.
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