Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-09-20
2003-07-22
Gray, J. M. (Department: 2831)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C428S383000, C428S372000, C174S1100PM, C174S1100SR, C174S1200SR, C525S191000, C525S240000
Reexamination Certificate
active
06596392
ABSTRACT:
TECHNICAL FIELD
The present invention relates to sheathed wires and cables, and more particularly to wires and cables with polyethylene resin sheaths having excellent stress crack resistance, abrasion resistance and impact resistance.
BACKGROUND ART
As materials of sheaths for protecting wires (wire sheaths as the outermost layers) and those for protecting power or telegraph cables, synthetic resins such as polyethylene and polyvinyl chloride have heretofore been employed.
Such sheaths need to be excellent in properties such as stress crack resistance (ESCR), abrasion resistance and impact resistance, particularly low-temperature impact resistance, differently from coatings for directly insulating individual wires or cables. As their uses are diversified and the use conditions become severer recently, development of sheathed wires and cables having better properties than before have been more desired.
It is an object of the present invention to provide wires and cables with polyethylene resin sheaths more improved in stress crack resistance, abrasion resistance and impact resistance than the conventional polyethylene sheaths.
DISCLOSURE OF THE INVENTION
The sheathed wire or cable is obtained by coating an outermost layer of a wire or cable with a polyethylene resin (A) produced by polymerization using a single-site catalyst.
In the present-invention, the polyethylene resin (A) is preferably a copolymer of ethylene and an &agr;-olefin of 3 to 20 carbon atoms and has the following properties:
(1) the density (d) is in the range of 0.880 to 0.950 g/cm
3
, and
(2) the melt flow rate (MFR, ASTM D 1238, 190° C., load: 2.16 kg) is in the range of 0.01 to 20 g/10 min.
The polyethylene resin (A) preferably further has the following properties:
the n-decane-soluble component fraction (W (% by weight)) at room temperature and the density (d (g/cm
3
)) satisfy the following relation
in case of MFR≦10 g/10 min:
W
<80×exp(−100(
d
−0.88))+0.1,
in case of MFR>10 g/10 min:
W
<80×(
MFR
−9)
0.35
×exp(−100(
d
−0.88))+0.1.
The polyethylene resin (A) preferably furthermore has the following properties:
the flow index (FI (1/sec)), which is defined as a shear rate at which the shear stress of the polymer 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.
Moreover, it is preferable that when the polyethylene resin (A) is subjected to a temperature rise elution test (TREF), a component that is eluted at a temperature of not lower than 100° C. is present in the resin, and the amount of the component is not more than 10% by weight of the whole elution amount.
In the polyethylene resin (A), high-pressure low-density polyethylene (B) may be contained in an amount of not more than 50% by weight.
In the present invention, the polyethylene resin (A) preferably has the following properties:
(i) the 50% crack occurrence time (F
50
, ASTM D 1698) that becomes an indication of stress crack resistance is not less than 600 hours,
(ii) the abrasion wear as measured by a Taber abrasion test (JIS K 7204, load: 1 kg, truck wheel: CS-17, 60 rpm, 1000 times) is not more than 10 mg, and
(iii) the Izod impact strength (ASTM D 256, notched) as measured at −40° C. is not less than 40 J/m
2
.
BEST MODE FOR CARRYING OUT THE INVENTION
The sheathed wire and cable according to the invention are described in detail hereinafter.
The polyethylene resin for forming sheaths of the sheathed wire and cable according to the invention is a polyethylene resin (A) having specific properties and is prepared by the use of a single-site catalyst such as a hitherto known metallocene catalyst or Brookhart catalyst. In the polyethylene resin (A), high-pressure low-density polyethylene (B) may be contained.
Polyethylene Resin (A)
The polyethylene resin (A) for use in the invention has a density (ASTM D 1505) of usually 0.880 to 0.950 g/cm
3
, preferably 0.885 to 0.940 g/cm
3
, more preferably 0.890 to 0.935 g/cm
3
. When the polyethylene resin (A) having a density in the above range is used, a wire sheath and a cable sheath having excellent abrasion resistance and flexibility can be formed.
The density is determined as follows. Strands obtained in the measurement of melt flow rate (MFR) at 190° C. under a load of 2.16 kg is heat treated at 120° C. for 1 hour and slowly cooled to room temperature over a period of 1 hour. Then, the density is measured by a density gradient tube.
The polyethylene resin (A) has a melt flow rate (MFR, ASTM D 1238, 190° C., load: 2.16 kg) of usually 0.01 to 20 g/10 min, preferably 0.03 to 15 g/10 min, more preferably 0.05 to 10 g/10 min.
The n-decane-soluble component fraction (W (% by weight)) in the polyethylene resin (A) for use in the invention at room temperature and the density (d (g/cm
3
)) of the resin satisfy the following relation
in case of MFR <10 g/10 min:
W
<80×exp(−100(
d
−0.88))+0.1,
preferably
W
<60×exp(−100(
d
−0.88))+0.1,
more preferably
W
<40×exp(−100(
d
−0.88))+0.1,
in case of MFR>10 g/10 min:
W
<80×(MFR−9)
0.35
×exp(−100(
d
−0.88))+0.1.
It can be said that such an ethylene copolymer has a narrow composition distribution.
The n-decane-soluble component fraction (W) in the polyethylene resin (A) at room temperature is desired to be not more than 3% by weight, preferably not more than 2% by weight. When the n-decane-soluble component fraction (W) is not more than 3% by weight, a sheath that is free from surface tackiness when exposed to high temperatures can be obtained.
The n-decane-soluble component fraction (W) at room temperature is determined by completely dissolving 0.5 g of a polyethylene resin in 500 ml of n-decane under reflux at a boiling point of n-decane, then cooling the resulting solution to room temperature (25° C.), filtering the solution, evaporating n-decane from the filtrate, and calculating a weight ratio of the residue to the initial polyethylene resin.
The flow index (FI (1/sec)) of the polyethylene resin (A) for use in the invention, which is defined as a shear rate at which the stress of the polymer in a molten state at 190° C. reaches 2.4×10
6
dyne/cm
2
, and the melt flow rate (MFR (g/10 min)) of the resin satisfy the following relation
FI>75×MFR,
preferably FI>80×MFR,
more preferably FI>85×MFR.
The flow index (FI) is determined by extruding a resin from a capillary with changing a shear rate and measuring a shear rate corresponding to the given stress. That is, this measurement was carried out using the same sample as in the MT measurement and using a capillary type flow property tester manufactured by Toyo Seiki Seisakusho K. K. under the conditions of a resin temperature of 190° C. and a shear stress range of about 5×10
4
to 3×10
6
dyne/cm
2
. In this measurement, the diameter of a nozzle is changed as follows according to the MFR (g/10 min) of the resin to be measured.
MFR>20: 0.5 mm
20≧MFR>3: 1.0 mm
3≧MFR>0.8: 2.0 mm
0.8≧MFR: 3.0 mm
When a polyethylene resin having a narrow composition distribution is prepared by the prior art technique, also the molecular weight distribution is usually narrowed, resulting in bad flowability (moldability) and small FI. When the polyethylene resin (A) for use in the invention has the above relation between. FI and MFR, a low stress can be retained even in the high shear rate region and the moldability becomes better.
When the polyethylene resin (A) for use in the invention is subjected to a temperature rise elution test (TREF), a component that is eluted at a temperature of not lower than 100° C. is desired to be present and the amount of the component is preferably not more than 10% of the whole elution amount. The component that is eluted at a temperature of not lower than 100° C. is a highly crystalline high-density component. If the amount of this high-density componen
Kimura Tomohiko
Nagano Shinichi
Tanaka Mutsuhiro
Birch & Stewart Kolasch & Birch, LLP
Mitsui Chemicals Inc.
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