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
2000-09-19
2002-02-12
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000
Reexamination Certificate
active
06346576
ABSTRACT:
TECHNICAL FIELD
The present invention relates to packaging films made of polyethylene.
BACKGROUND ART
A great number of films have been hitherto produced, and films having properties appropriate for the purpose have been selected and employed. Above all, films produced from linear low-density polyethylene are extensively employed, but they differ from one another in the properties depending upon the type of the monomer units constituting the polyethylene or the type of the process for preparing the polyethylene.
For example, films produced from a linear low-density ethylene/1-butene copolymer have excellent transparency and surface smoothness, but they easily suffer tearing in the molding process because their mechanical strength properties indicated by dart impact strength and Elmendorf tear strength are low, and hence there is a limit of increasing a molding speed.
On the other hand, films produced from linear low-density polyethylene prepared by the use of a metallocene catalyst which has been recently highlighted are known as films hardly suffering blocking because the linear low-density polyethylene has a narrow composition distribution. Especially when a linear low-density ethylene/1-hexene copolymer prepared by the use of a metallocene catalyst is used to produce films, the resulting films exhibit excellent mechanical strength, transparency and heat sealing properties. However, if the melt flow rate (MFR) of the linear low-density ethylene/1-hexene copolymer is low, e.g., not more than 1 g/10 min, melt fracture easily takes place, and as a result, the films have poor surface smoothness.
Accordingly, there is desired development of high-strength packaging films capable of being produced at a high speed with retaining properties inherent in films of linear low-density polyethylene, such as transparency and surface smoothness.
It is an object of the present invention to provide packaging films which exhibit excellent mechanical strength properties such as high dart impact strength with retaining properties inherent in films of linear low-density polyethylene, such as transparency and surface smoothness.
It is another object of the invention to provide films having such excellent low-temperature properties (e.g., low-temperature drop-bag strength properties) that they can be satisfactorily used for heavy-duty packaging bags even in the cold districts having below-zero temperatures.
DISCLOSURE OF THE INVENTION
The first ethylene resin packaging film according to the invention is an ethylene resin packaging film comprising an ethylene/&agr;-olefin copolymer (A) which is a copolymer obtained by copolymerizing ethylene and an &agr;-olefin of 6 to 20 carbon atoms in the presence of an olefin polymerization catalyst comprising (a) a compound of a transition metal of Group IV of the periodic table, said compound (a) containing a ligand having cyclopentadienyl skeleton, and (b) an organoaluminum oxy-compound, and which has the following properties:
(i) the density is in the range of 0.918 to 0.935 g/cm
3
,
(ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.05 to 2.0 g/10 min,
(iii) the decane-soluble component fraction (W (% by weight) at room temperature and the density (d (g/cm
3
)) satisfy the following relation
W<80×exp(−100(d−0.88))+0.1,
(iv) the flow index (FI (l/sec)), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10
6
dyne/cm
2
, and the melt flow rate (MFR (g/10 min)) satisfy the following relation
FI>75×MFR, and
(v) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the following relation
MT>2.2×MFR
−0.84
,
preferably 5.5×MFR
0.65
>MT>2.2×MFR
−0.84
.
It is preferable that the ethylene/&agr;-olefin copolymer (A) further has the following property:
the mean value (B1) of the numbers of branches on the higher molecular weight side, as determined by GPC-IR, and the mean value (B2) of the numbers of branches on the lower molecular weight side, as determined by GPC-IR, satisfy the following relation
B1≧B2.
The second ethylene resin packaging film according to the invention is an ethylene resin packaging film comprising an ethylene/&agr;-olefin copolymer composition (B) which comprises:
(I) 50 to 99 parts by weight of an ethylene/&agr;-olefin copolymer (a-1), and
(II) 1 to 50 parts by weight of high-density polyethylene (b-1),
wherein the ethylene/&agr;-olefin copolymer (a-1) is a copolymer obtained by copolymerizing ethylene and an &agr;-olefin of 6 to 20 carbon atoms in the presence of an olefin polymerization catalyst comprising (a) a compound of a transition metal of Group IV of the periodic table, said compound (a) containing a ligand having cyclopentadienyl skeleton, and (b) an organoaluminum oxy-compound, and has the following properties:
(i) the density is in the range of 0.900 to 0.935 g/cm
3
,
(ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.01 to 1.0 g/10 min,
(iii) the decane-soluble component fraction (W (% by weight)) at room temperature and the density (d (g/cm
3
)) satisfy the following relation
W<80×exp(−100(d−0.88))+0.1,
(iv) the flow index (FI (l/sec)), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10
6
dyne/cm
2
, and the melt flow rate (MFR (g/10 min)) satisfy the following relation
FI>75×MFR,
(v) the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 min)) satisfy the following relation
MT>2.2×MFR
−0.84
,
preferably 5.5×MFR
−0.65
>MT>2.2×MFR
−0.84
, and
(vi) the temperature (Tm (° C.)) at the maximum peak position in an endothermic curve of said copolymer (a-1), as measured by a differential scanning calorimeter (DSC), and the density (d) satisfy the following relation
Tm<400d−250; and
the high-density polyethylene (b-1) is ethylene monopolymer or ethylene/&agr;-olefin copolymer obtained by copolymerizing ethylene and an &agr;-olefin of 3 to 20 carbon atoms, which has the following properties:
(i) the density is in the range of 0.935 to 0.975 g/cm
3
, and
(ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.1 to 100 g/10 min.
The ethylene resin packaging films mentioned above preferably have (A) a Young's modulus of not less than 4,000 kg/cm
2
and (B) a dart impact strength of not less than 55 kg/cm.
The third ethylene resin packaging film according to the invention is an ethylene resin packaging film comprising an ethylene/&agr;-olefin copolymer composition (C) which comprises:
(I) 1 to 50 parts by weight of an ethylene/&agr;-olefin copolymer (a-2), and
(II) 50 to 99 parts by weight of an ethylene copolymer (b-2),
wherein the ethylene/&agr;-olefin copolymer (a-2) is a copolymer obtained by copolymerizing ethylene and an &agr;-olefin of 4 to 12 carbon atoms in the presence of an olefin polymerization catalyst comprising (a) a compound of a transition metal of Group IV of the periodic table, said compound (a) containing a ligand having cyclopentadienyl skeleton, and (b) an organoaluminum oxy-compound, and has the following properties:
(i) the density is in the range of 0.880 to 0.925 g/cm
3
,
(ii) the melt flow rate (MFR (g/10 min)) at 190° C. under a load of 2.16 kg is in the range of 0.01 to 5.0 g/10 min,
(iii) the decane-soluble component fraction (W (% by weight)) at room temperature and the density (d (g/cm
3
)) satisfy the following relation
W<80×exp(−100(d−0.88))+0.1,
(iv) the flow index (FI (l/sec)), which is defined as a shear rate at which the shear stress of said copolymer in a molten state at 190° C. reaches 2.4×10
6
dyne/cm
2
, and the melt flow rate (MFR (g/10 min)) satisfy the following relation
FI>75×MFR, and
(v) the melt tension (MT
Mitsui Chemicals Inc
Nutter Nathan M.
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