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
2001-01-19
2002-07-30
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
06426384
ABSTRACT:
This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/JP99/02659 which has an International filing date of May 20, 1999, which designated the United States of America.
TECHNICAL FIELD
The present invention relates to a polyethylene film for packaging. More particularly, the present invention relates to a polyethylene film for packaging which possesses excellent tear resistance, impact resistance and transparency and suitable for use mainly in wrapping a boxed tissue pile, a cleaning bag, etc.
TECHNICAL BACKGROUND
Polyethylene has a wide variety of applications as a film material because of its excellent waterproof, chemical resistance, transparency and hygienic properties. Therefore, polyethylene has been widely used as a packaging material.
A polyethylene film made from, e.g., a composition of a high-density polyethylene and a low-density polyethylene prepared by high-pressure polymerization process has been hitherto used as a packaging material for wrapping a boxed tissue pile, a cleaning bag, etc., utilizing its transparency. On the other hand, however, it is pointed out that strength of the polyethylene film is yet insufficient and film moldability is poor since surface roughening occurs unless a molding temperature is elevated. Furthermore, the polyethylene film tears in the longitudinal direction (machine direction: MD) of a film or occasionally generates holes depending upon application. Therefore, it has been desired to improve tear resistance in the longitudinal direction and impact resistance.
An object of the present invention is to provide a polyethylene film for packaging which is excellent not only in transparency but also in moldability, a smooth surface and tear resistance in the longitudinal direction (MD) and impact resistance, as compared to a conventional polyethylene film formed from a composition of a high-density polyethylene and a low-density polyethylene prepared by high-pressure polymerization process.
DISCLOSURE OF THE INVENTION
The polyethylene film for packaging in accordance with the present invention is prepared from a polyethylene resin composition comprising (A) a low-density polyethylene prepared using a metallocene-based catalyst and (B) a high-density polyethylene.
More specifically, the polyethylene film for packaging of the present invention is formed from a polyethylene resin composition comprising (A) a low-density polyethylene prepared using a metallocene-based catalyst and (B) a high-density polyethylene, in a weight ratio of 30/70 to 70/30 [(A)/(B)], characterized in that the low-density polyethylene (A) has the following properties:
(i) the density is in the range of 0.900 to 0.920 g/cm
3
;
(ii) the melt flow rate is in the range of 0.05 to 1.0 g/10 mins.; and,
(iii) the molecular weight distribution (Mw/Mn) is in the range of 1.5 to 3.5;
the high-density polyethylene has the following properties:
(i) the density is in the range of 0.954 to 0.970 g/cm
3
; and,
(ii) the melt flow rate is in the range of 0.1 to 10.0 g/10 mins.; and,
the polyethylene film has the following properties:
(i) the thickness is in the range of 10 to 30 &mgr;m;
(ii) the Elmendorf tear strength is at least 20 kg/cm in the longitudinal direction;
(iii) the dart impact strength is at least 50 g; and,
(iv) the HAZE value is not greater than 8%.
Low-Density Polyethylene (A)
The low-density polyethylene (A) used in the present invention is an ethylene/&agr;-olefin copolymer comprising ethylene and an &agr;-olefin, preferably an &agr;-olefin having 3 to 12 carbon atoms, which is prepared using a metallocene-based catalyst.
As the &agr;-olefin an &agr;-olefin having 3 to 12 carbon atoms is preferred. Specific examples of preferred &agr;-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, etc. When the &agr;-olefin is used as a comonomer, one or more kinds may also be used.
Typical examples of the low-density polyethylene (A) which can be preferably employed in the present invention are ethylene/1-butene copolymer, ethylene/1-pentene copolymer, ethylene/1-hexene copolymer, ethylene/4-methyl-1-pentene copolymer and ethylene/1-octene copolymer.
The low-density polyethylene (A) used in the present invention has an ethylene content of generally 95 to 99 mol %, preferably 96 to 98 mol %, in which the &agr;-olefin content as the comonomer is generally from 1 to 5 mol %, preferably 2 to 4 mol %.
The low-density polyethylene (A) used in the present invention has the density ranging from 0.900 to 0.920 g/cm
3
, preferably 0.905 to 0.915 g/cm
3
.
The low-density polyethylene (A) has the melt flow rate in the range of 0.05 to 1.0 g/10 mins., preferably 0.1 to 0.8 g/10 mins.
The molecular weight distribution of the low-density polyethylene (A) used in the present invention is in the range of 1.5 to 3.5 , preferably 2.0 to 2.5, indicating the low-density polyethylene has a narrow molecular weight distribution. The molecular weight distribution referred to in the invention is distribution of a molecular weight (Mw/Mn, Mw: weight-average molecular weight, Mn: number-average molecular weight) measured by GPC, which will be later described.
The linear polyethylene (A) of the present invention preferably has the property that the melt tension (MT (g)) at 190° C. and the melt flow rate (MFR (g/10 mins.)) satisfy the following relation.
MT
>2.2
×MFR
−0.84
(i)
The linear polyethylene (A) of the present invention preferably has the property that the content (W (% by weight)) of a decane-soluble component at room temperature and the density (d (g/cm
3
)) satisfy the following relation.
W
<80×exp(−100(
d
−0.88))+0.1 (ii)
The linear polyethylene (A) of the present invention preferably has the property that the temperature (Tm (° C.)) at which the endothermic curve measured by a differential scanning calorimeter (DSC) shows the maximum peak and the density (d) satisfy the following relation.
Tm
<400
×d
−248 (ii)
More preferably, the linear polyethylene (A) of the present invention satisfies the relations (i), (ii) and (iii) at the same time.
Most preferably, the linear polyethylene (A) of the present invention further satisfies the following relation between the flow index (FI (1/sec)) defined by a shear rate which is given when a shear stress of molten polymer at 190° C. reaches 2.4×10
6
dyne/cm
2
and the melt flow rate (MFR (g/10 mins)).
FI
>75
×MFR
(iv)
The low-density polyethylene (A) employed in the invention can be prepared by copolymerizing ethylene and an &agr;-olefin, preferably an &agr;-olefin having 3 to 12 carbon atoms, in the presence of a so-called metallocene-based catalyst for olefin polymerization, including metallocene catalyst components (a) described in, for example, Japanese Laid-Open Patent Application No. HEI 6-9724, 6-136195, 6-136196 and 6-207057.
Such a metallocene-based catalyst conventionally comprises (a) a metallocene catalyst component comprising a compound of a transition metal of Group IVB in the periodic table containing at least one ligand having cyclopentadienyl skeleton and (b) an organoaluminum oxy-compound catalyst component, and if necessary and desired, further comprises (c) a particulate carrier, (d) an organoaluminum compound catalyst component, or (e) an ionizing ionic compound catalyst component.
The metallocene catalyst component (a) which is preferably employed in the present invention is, for example, a compound of the transition metal of Group IVB in the periodic table containing at least one ligand having cyclopentadienyl skeleton. Such a transition metal compound includes a compound represented, for example, by general formula [I] below:
ML
1
x
[I]
wherein:
x is a valence of transition metal atom M;
M is a transition metal atom selected from the Group IVB in the periodic table, among which metals zirconium is preferred; and,
L
1
is ligands that coor
Inoue Hiroshi
Nishimura Toshihiro
Takeuchi Michio
Mitsui Chemicals Inc.
Nutter Nathan M.
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