Ultrahigh molecular weight polyethylene stretched porous film

Patent metadata

Field	Value
Publication number	US-2017125763-A1
Application number	US-201515128772-A
Country	US
Kind code	A1
Filing date	Mar 18, 2015
Priority date	Mar 26, 2014
Publication date	May 4, 2017
Grant date	—

Abstract

To provide an ultrahigh molecular weight polyethylene stretched microporous film having high strength and heat resistance.
An ultrahigh molecular weight polyethylene stretched microporous film, which comprises at least an ultrahigh molecular weight polyethylene having an intrinsic viscosity ([η]) of at least 7 dl/g and at most 60 dl/g, and which has a porosity of at least 10% and at most 70% and a breaking stress of at least 1 MPa when melt-stretched at 150° C., which uses, as the ultrahigh molecular weight polyethylene, preferably ultrahigh molecular weight polyethylene particles which satisfy (1) an intrinsic viscosity ([η]) of at least 7 dl/g and at most 60 dl/g, (2) a bulk density of at least 130 kg/m 3 and at most 700 kg/m 3 , and (3) ΔTm (ΔTm=Tm 1 −Tm 2 ) of at least 9° C. and at most 30° C., which is a difference between the melting point (Tm 1 ) at the 1st scanning and the melting point (Tm 2 ) at the 2nd scanning measured by DSC.

First claim

1 . An ultrahigh molecular weight polyethylene stretched microporous film, which comprises at least an ultrahigh molecular weight polyethylene having an intrinsic viscosity ([η]) of at least 7 dl/g and at most 60 dl/g, and which has a porosity of at least 10% and at most 70% and a breaking stress of at least 1 MPa when melt-stretched at 150° C.

2 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , wherein with respect to endothermic peaks by fusing at the 1st scanning when heated from 0° C. to 230° C. at a temperature-raising rate of 10° C./min (1st scanning) by a differential scanning calorimeter (DSC), the proportion (ΔH >135 /ΔH whole ) of the heat of fusion (ΔH >135 ) at 135° C. or higher based on the total heat of fusion (ΔH whole ) is at least 40%.

3 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which uses, as the ultrahigh molecular weight polyethylene, at least ultrahigh molecular weight polyethylene particles which satisfy all of the following conditions (1) to (3):
(1) an intrinsic viscosity ([η]) of at least 7 dl/g and at most 60 dl/g; (2) a bulk density of at least 130 kg/m 3 and at most 700 kg/m 3 ; and (3) a difference (ΔTm=Tm 1 −Tm 2 ) between Tm 1 and Tm 2 of at least 9° C. and at most 30° C., where Tm 1 is the melting point at the 1st scanning when heated from 0° C. to 230° C. at a temperature-raising rate of 10° C./min (1st scanning) by DSC, and Tm 2 is the melting point at the 2nd scanning when left to stand for 5 minutes after the 1st scanning, cooled to −20° C. at a temperature-decreasing rate of 10° C./min, left to stand for 5 minutes, and then heated from −20° C. to 230° C. at a temperature-raising rate of 10° C./min (2nd scanning).

4 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which uses, as the ultrahigh molecular weight polyethylene, at least ultrahigh molecular weight polyethylene particles which satisfy all of the following conditions (1′) to (3′):
(1′) an intrinsic viscosity ([η]) of at least 15 dl/g and at most 60 dl/g;
(2) a bulk density of at least 130 kg/m 3 and at most 700 kg/m 3 ; and
(3′) a difference (ΔTm=Tm 1 −Tm 2 ) between Tm 1 and Tm 2 of at least 11° C. and at most 30° C., measured in the same manner as the above (3).

5 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which comprises an ultrahigh molecular weight polyethylene composition containing at least an ultrahigh molecular weight polyethylene having an intrinsic viscosity ([η]) of at least 7 dl/g and at most 60 dl/g and a polyethylene having a weight average molecular weight of at most 800,000.

6 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 5 , which comprises an ultrahigh molecular weight polyethylene composition having [η] of at most 0.75 time [η] of the ultrahigh molecular weight polyethylene component, and wherein with respect to endothermic peaks by fusing when heated from 0° C. to 230° C. at a temperature-raising rate of 10° C./min by DSC, the proportion (ΔH >135 /ΔH whole ) of the heat of fusion (ΔH >135 ) at 135° C. or higher based on the total heat of fusion (ΔH whole ) is at least 40% and at most 80%, and the ΔH whole is at least 190 J/g.

7 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 5 , wherein, when heated from 0° C. to 230° C. at a temperature-raising rate of 10° C./min by DSC, within ranges of at most 134° C. and at least 140° C., there is a temperature at which the endothermic heat flux (W/g) is at least 60% of the maximum heat flux (W/g).

8 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which has a tensile break strength measured at 23° C. of at least 150 MPa and a heat shrinkage of at most 2%.

9 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which has a film thickness of at most 15 μm, and which constitutes, when employed as a separator for a lithium ion secondary battery, a lithium ion secondary battery having a direct current resistance of at most 10 Ω·cm 2 and having a charge and discharge efficiency (=discharge capacity/charge capacity×100) of at least 95% when charged and discharged at a constant current (0.5 C) at which the fully charged lithium ion secondary battery is discharged in 2 hours.

10 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 3 , which uses, as the ultrahigh molecular weight polyethylene, ultrahigh molecular weight polyethylene particles which also satisfy such a condition that (4) a sheet formed by heat-rolling the particles at a pressing temperature of 190° C. under a pressing pressure of 20 MPa, followed by cooling at a mold temperature lower by 10° C. to 30° C. than the melting point (Tm 2 ) at the 2nd scanning measured by the above (3), has a tensile break strength (TS (MPa)) satisfying the following formula (a):
TS≧ 1.35× Tm 2 −130  (a)

11 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 3 , which uses, as the ultrahigh molecular weight polyethylene, ultrahigh molecular weight polyethylene particles which also satisfy such a condition that (5) a sheet formed by heat-rolling has a breaking stress (MTS (MPa)) of at least 1.5 MPa when melt-stretched at 150° C.

12 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 3 , which uses, as the ultrahigh molecular weight polyethylene, ultrahigh molecular weight polyethylene particles which also satisfy such a condition that (6) the breaking stress (MTS (MPa)) when melt-stretched measured by the above (5) and the intrinsic viscosity ([η]) satisfy the following formula (b):
MTS≧ 0.11×[η]  (b)

13 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which is obtained by mixing the ultrahigh molecular weight polyethylene particles or the ultrahigh molecular weight polyethylene composition and an organic solvent at a temperature of at least 50° C. and at most 300° C. to form a sheet-shaped product, subjecting the sheet-shaped product to biaxial stretching at a draw ratio of at least 2 times×2 times, and removing the organic solvent.

14 . The ultrahigh molecular weight polyethylene stretched microporous film according to claim 1 , which is at least one member selected from the group consisting of a gas separation membrane, a semipermeable membrane, a tape, a tube and a battery separator.

15 . A separator for a lithium ion secondary battery made of an ultrahigh molecular weight polyethylene, which constitutes, when applied to a lithium ion secondary battery using cobalt/manganese/nickel composite oxide-lithium as a cathode, graphite as an anode and LiPF6/ethyl carbonate/diethyl carbonate as an electrolyte, a lithium ion secondary battery having a direct current resistance of at most 10 Ω·cm 2 and having a charge and discharge efficiency (=discharge capacity/charge capacity×100) of at least 95% when charged and discharged at a constant current corresponding to 0.5 C, and which has a porosity of from 10 to 70%, a breaking stress of at least 1 MPa when melt-stretched at 150° C. and a film thickness of at most 15 μm.

Assignees

• Tosoh Corp

Inventors

• Inatomi Kei
• Wakabayashi Yasutake
• Abe Shigehiko

Classifications

• H01M10/0525 Primary

  Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries · CPC title

• H01M4/525

  of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy · CPC title

• B01D53/228

  characterised by specific membranes · CPC title

• H01M4/505

  of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy · CPC title

• H01M4/133

  Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx · CPC title