U.S. patent application number 15/708339 was filed with the patent office on 2018-01-11 for laminated porous film, separator for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery.
This patent application is currently assigned to SUMITOMO CHEMICAL COMPANY, LIMITED. The applicant listed for this patent is SUMITOMO CHEMICAL COMPANY, LIMITED. Invention is credited to Takeshi KAWAKAMI, Yasutoshi MINEMOTO, Jian WANG, Satoshi YONEYAMA.
Application Number | 20180013118 15/708339 |
Document ID | / |
Family ID | 52111194 |
Filed Date | 2018-01-11 |
United States Patent
Application |
20180013118 |
Kind Code |
A1 |
KAWAKAMI; Takeshi ; et
al. |
January 11, 2018 |
LAMINATED POROUS FILM, SEPARATOR FOR NON-AQUEOUS ELECTROLYTE
SECONDARY BATTERY AND NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY
Abstract
An object of the present invention is to provide a laminated
porous film excellent in handling ability. A laminated porous film
having a layer containing a polymer other than a polyolefin
laminated on at least one surface of a polyolefin porous film,
wherein the uplift quantity of a side perpendicular to the machine
direction, when allowed to stand still for 1 hour under an
environment of a temperature of 23.degree. C. and a humidity of
50%, is 15 mm or less.
Inventors: |
KAWAKAMI; Takeshi;
(Niihama-shi, JP) ; WANG; Jian; (Niihama-shi,
JP) ; MINEMOTO; Yasutoshi; (Niihama-shi, JP) ;
YONEYAMA; Satoshi; (Niihama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO CHEMICAL COMPANY, LIMITED |
Tokyo |
|
JP |
|
|
Assignee: |
SUMITOMO CHEMICAL COMPANY,
LIMITED
Tokyo
JP
|
Family ID: |
52111194 |
Appl. No.: |
15/708339 |
Filed: |
September 19, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14306891 |
Jun 17, 2014 |
9799867 |
|
|
15708339 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2/166 20130101;
H01M 2/1653 20130101; H01M 10/0525 20130101; H01M 2/1686 20130101;
H01M 2/145 20130101 |
International
Class: |
H01M 2/16 20060101
H01M002/16; H01M 2/14 20060101 H01M002/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 21, 2013 |
JP |
2013-130300 |
Claims
1. A method for producing a laminated porous film having a layer
containing a polymer other than a polyolefin laminated on at least
one surface of a polyolefin porous film, the laminated porous film
being obtained by applying a coating fluid containing a polymer
other than a polyolefin and a medium onto at least one surface of a
polyolefin porous film, and drying the coating fluid at given
drying temperature when imparted to the polyolefin porous film
under the same temperature environment as the drying temperature,
elongation rate thereof is 1% or less.
2. A method for producing a laminated porous film according to
claim 1, wherein the drying temperature is 30 to 80.degree. C.
3. A method for producing a laminated porous film according to
claim 1, wherein 80 wt % or more of the medium is composed of
water.
4. A method for producing a laminated porous film according to
claim 1, wherein drying the coating fluid at given drying
temperature while imparting film tension of 0.05 N or more per 1 mm
of the film width.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
14/306,891, filed Jun. 17, 2014 (allowed), which claims priority to
Japanese Patent Application No. 2013-130300, filed Jun. 21, 2013.
The entire disclosures of the prior applications are considered
part of the disclosure of the accompanying continuation
application, and are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a laminated porous film, a
separator for a non-aqueous electrolyte secondary battery and a
non-aqueous electrolyte secondary battery.
BACKGROUND ART
[0003] Non-aqueous electrolyte secondary batteries such as a
lithium secondary battery are widely used as a battery used for
personal computers, cellular telephones, handheld information
terminals and the like.
[0004] Non-aqueous electrolyte secondary batteries show abnormal
heat generation in some cases due to internal short-circuit or
external short-circuit. For securing safety in abnormal heat
generation, a separator having a shut-down function is used. As the
separator having a shut-down function, a polyolefin porous film is
used.
[0005] Patent document 1 describes a laminated porous film obtained
by laminating a heat-resistant layer containing cellulose ether and
fine particles onto a polyolefin porous film. Patent document 2
describes a laminated porous film obtained by laminating an
adhesion layer containing polyvinylidene fluoride onto a polyolefin
porous film.
PRIOR TECHNOLOGICAL DOCUMENT
Patent Document
[0006] (Patent document 1) JP-A No. 2004-227972
[0007] (Patent document 2) JP-A No. 10-189054
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0008] Conventional laminated porous films have not been
sufficiently satisfactory in handling ability in laminating with an
electrode for use as a separator for a non-aqueous electrolyte
secondary battery.
Means for Solving the Problem
[0009] The present invention includes the following inventions.
[0010] <1> A laminated porous film having a layer containing
a polymer other than a polyolefin laminated on at least one surface
of a polyolefin porous film, wherein the uplift quantity of a side
perpendicular to the machine direction, when allowed to standstill
for 1 hour under an environment of a temperature of 23.degree. C.
and a humidity of 50%, is 15 mm or less.
[0011] <2> The laminated porous film according to <1>,
wherein the laminated porous film is a laminated porous film having
a layer containing a polymer other than a polyolefin laminated on
one surface of a polyolefin porous film.
[0012] <3> The laminated porous film according to <1>
or <2>, wherein the layer containing a polymer other than a
polyolefin further contains fine particles.
[0013] <4> The laminated porous film according to <3>,
wherein the fine particles are inorganic fine particles.
[0014] <5> The laminated porous film according to any one of
<1> to <4>, obtained by applying a coating fluid
containing a polymer other than a polyolefin and a medium onto at
least one surface of a polyolefin porous film, and drying at given
drying temperature while imparting film tension with which, when
imparted to the polyolefin porous film under the same temperature
environment as the drying temperature, elongation rate thereof is
1% or less.
[0015] <6> The laminated porous film according to <5>,
wherein the drying temperature is 30 to 80.degree. C.
[0016] <7> The laminated porous film according to <5>
or <6>, wherein 80 wt % or more of the medium is composed of
water.
[0017] <8> The laminated porous film according to any one of
<1> to <7>, wherein the polyolefin porous film shows an
elongation rate of 1% or less when a film tension of 0.05 N/mm per
1 mm of the film width is imparted along the machine direction
under an environment of a temperature of 65.degree. C.
[0018] <9> A separator for a non-aqueous electrolyte
secondary battery, composed of the laminated porous film according
to any one of <1> to <8>.
[0019] <10> A non-aqueous electrolyte secondary battery
containing the separator for a non-aqueous electrolyte secondary
battery according to <9>.
Effect of the Invention
[0020] The laminated porous film of the present invention is
excellent in handling ability in laminating with an electrode for
use as a separator for a non-aqueous electrolyte secondary
battery.
BRIEF EXPLANATION OF DRAWINGS
[0021] FIG. 1 is a schematic explanation view showing a laminated
porous film of the present invention.
MODES FOR CARRYING OUT THE INVENTION
[0022] FIG. 1 is a schematic explanation view showing a laminated
porous film of the present invention (hereinafter, referred to as
"laminated porous film" in some cases). The laminated porous film 1
is obtained by laminating a layer containing a polymer other than a
polyolefin (hereinafter, referred to as "layer B" in some cases)
(not shown) onto at least one surface of a polyolefin porous film
(hereinafter, referred to as "layer A" in some cases), and contains
a side along the machine direction (MD) (hereinafter, described as
MD side in some cases) and a side parallel to the direction (TD)
perpendicular to the machine direction (MD). Also the polyolefin
porous film contains a MD side and a TD side as is the case with
the laminated porous film.
[0023] The layer A contains a polyolefin as the main component, and
is melted and rendered imperforate at higher temperatures. The
layer A is, when the laminated porous film is used as a separator,
melted and rendered imperforate in abnormal heat generation of a
battery, thereby imparting a shut-down function to the laminated
porous film.
[0024] The layer B is laminated onto the layer A. The layer B
imparts a heated shape retaining property at temperatures not lower
than the melting point of the polyolefin when the laminated porous
film is used as a separator, and endows the laminated porous film
with adhesiveness with an electrode, and the like.
<Layer A>
[0025] The layer A has a structure containing communicating pores
in its inside, and a gas and a liquid are capable of penetrating
through from one surface to another surface.
[0026] The proportion of a polyolefin contained in the layer A is
usually over 50 vol %, preferably 70 vol % or more, more preferably
90 vol % or more, further preferably 95 vol % or more based on the
whole layer A.
[0027] The polyolefin contained in the layer A preferably contains
a high molecular weight polyolefin having a weight-average
molecular weight of 5.times.10.sup.5 to 15.times.10.sup.6 since the
layer A and the whole laminated porous film containing the layer A
get enhanced strength.
[0028] The examples of polyolefin include homopolymers or
copolymers having high molecular weight obtained by polymerizing an
olefin such as ethylene, propylene, 1-butene, 4-methyl-1-pentene
and 1-hexene. Of them, preferable are high molecular weight
polyethylenes composed mainly of ethylene and having a
weight-average molecular weight of 1000000 or more.
[0029] In addition to the polyolefin, the layer A may contain other
components in the range not deteriorating the function of the layer
A.
[0030] The diameter of pores in the layer A is preferably 3 .mu.m
or less, further preferably 1 .mu.m or less since when the
laminated porous film is used as a separator of a battery,
excellent ion permeability is attained and entering of particles
into a positive electrode and a negative electrode can be
prevented.
[0031] The film thickness of the layer A is preferably 4 to 40
.mu.m, more preferably 7 to 30 .mu.m though varying depending on
the film thickness of the layer B.
[0032] The porosity of the layer A is preferably 20 to 80 vol %,
more preferably 30 to 70 vol %. Within the above-described range,
ion permeability is excellent, and when the laminated porous film
is used as a separator for a non-aqueous electrolyte secondary
battery, excellent properties are manifested.
[0033] The unit weight of the layer A is usually 4 to 15 g/m.sup.2,
preferably 5 to 12 g/m.sup.2 since the strength, film thickness,
handling ability and weight of the laminated porous film, further,
the weight energy density and volume energy density of a battery
when the laminated porous film is used as a separator of the
battery, can be increased.
[0034] The method of producing the layer A includes, for example, a
method in which a plasticizer is added to a thermoplastic resin and
the resin is molded into a film, then, the plasticizer is removed
with a suitable solvent (see, JP-A No. 7-29563), a method in which
a film made of a thermoplastic resin produced by a known method is
used, and the structurally weak amorphous portion of the film is
selectively stretched to form fine pores (see, JP-A No. 7-304110)
and a method in which fine particles are added to a thermoplastic
resin and the resin is molded into a film, then, the fine particles
are removed (see, JP-A No. 2002-69221).
[0035] The layer A shows an elongation rate of preferably 1% or
less, more preferably 0.5% or less when a film tension of 0.05 N
per 1 mm of the film width is imparted along the machine direction
under an environment of a temperature of 65.degree. C. Within the
above-described range, uplift of the TD side of the resultant
laminated porous film (hereinafter, described as MD curl in some
cases) tends to be suppressed. Here, the film width is the length
of the TD side. The elongation rate is an increase rate of the
length of the MD side after imparting film tension with respect to
the length before imparting film tension.
<Layer B>
[0036] By selecting the kind of the polymer other than a polyolefin
contained in the layer B, the layer B functions, for example, as an
adhesion layer, a heat-resistant layer or the like, and endows the
laminated porous film with functions such as adhesiveness with an
electrode, a heated shape retaining property at temperatures not
lower than the melting point of a polyolefin, and the like.
Specific examples of the layer B include an adhesion layer and a
heat-resistant layer described below but it is not construed that
the layer B is limited to them.
[0037] When the layer B is an adhesion layer, a separator for a
non-aqueous electrolyte secondary battery composed of a laminated
porous film is used and several layers of a positive electrode and
a negative electrode are laminated via the separator to obtain a
non-aqueous electrolyte secondary battery, and in this battery, the
layer B stands between the layer A and the positive electrode and
between the layer A and the negative electrode, thus, the layer A
and the positive electrode and the layer A and the negative
electrode are connected successfully with the layer B,
respectively.
[0038] When the layer B is a heat-resistant layer, a separator for
a non-aqueous electrolyte secondary battery composed of a laminated
porous film is excellent in shape stability at high temperatures
and excellent in a heated shape retaining property at temperatures
not lower than the melting point of a polyolefin.
[0039] The polymer other than a polyolefin is not particularly
restricted providing it is a polymer other than a polyolefin, and
may advantageously be selected depending on the function of the
layer B.
[0040] When the layer B is an adhesion layer, the polymer other
than a polyolefin is preferably a polymer which manifests excellent
adhesiveness both to a positive electrode and a negative electrode
and to a polyolefin porous film, insoluble in an electrolyte of a
battery and electrically stable in the use range of the battery,
and includes, for example, polyvinylidene fluoride-type resins. The
polyvinylidene fluoride-type resin includes a homopolymer of
vinylidene fluoride (that is, polyvinylidene fluoride), copolymers
of vinylidene fluoride with other copolymerizable monomers, and
mixtures thereof and the like.
[0041] When the layer B is a heat-resistant layer, the polymer
other than a polyolefin is preferably a polymer which is excellent
in heat resistance, and when fine particles are contained in the
layer B as described later, excellent in ability of binding fine
particles mutually or binding the layer A and fine particles,
insoluble in an electrolyte of a battery, and electrically stable
in the use range of the battery, and examples thereof include
fluorine-containing resins such as polytetrafluoroethylene;
fluorine-containing rubbers such as ethylene-tetrafluoroethylene
copolymer; rubbers such as styrene-butadiene copolymer and hydrides
thereof, methacrylate copolymer, acrylonitrile-acrylate copolymer,
styrene-acrylate copolymer, polyvinyl acetate and ethylene-vinyl
acetate-vinyl versatate copolymer; resins having a melting point or
a glass transition temperature of 180.degree. C. or higher such as
polyphenylene ether, polysulfone, polyether sulfone, polyphenylene
sulfide, aramid, polyether imide, polyamideimide, polyether amide
and polyester; binder resins such as polyvinyl alcohol,
polyethylene glycol, cellulose ether, sodium alginate, polyacrylic
acid, polyacrylamide and polymethacrylic acid.
[0042] Of the above-described polymers, water-insoluble polymers
are preferable. Among water-insoluble polymers, at least one
selected from the group consisting of aramid, polyether imide,
polyamideimide, polyether amide and polyester is preferable, and
aramid is particularly preferable.
[0043] Of the above-described polymers, water-soluble polymers are
preferable from the standpoint of the process and environmental
load. Among water-soluble polymers, at least one selected from the
group consisting of cellulose ether, polyvinyl alcohol and sodium
alginate is preferable, and cellulose ether is particularly
preferable. Cellulose ether includes, specifically,
carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC),
carboxyethylcellulose, methylcellulose, ethylcellulose,
cyanethylcellulose, oxyethylcellulose and the like, and CMC and HEC
excellent in chemical stability are preferable, and CMC is
particularly preferable.
[0044] The proportion of the polymer other than a polyolefin
contained in the layer B is over 50 vol %, preferably 70 vol % or
more, more preferably 90 vol % or more, further preferably 95 vol %
or more, with respect to 100 vol % of the sum of polymers contained
in the layer B.
[0045] In addition to the polymer other than a polyolefin, the
layer B may contain other components in the range not deteriorating
the function of the layer B. Examples of the other components
include fine particles, dispersing agents, plasticizers, pH
adjusters, polymers and the like.
[0046] When the layer B is a heat-resistant layer, if the layer B
further contains fine particles in addition to the polymer other
than a polyolefin, then, the layer B functions as a heat-resistant
layer excellent in a heated shape retaining property, and when
communicating pores are formed inside of the layer B,
communicability of pores can be enhanced.
[0047] The fine particles include inorganic or organic fillers
generally called a filler, and examples thereof include fillers
composed of organic materials such as styrene, vinylketone,
acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl
methacrylate, glycidyl acrylate and methyl acrylate and the like
used singly or copolymers composed of two or more of them;
fluorine-based resins such as polytetrafluoroethylene, ethylene
tetrafluoride-propylene hexafluoride copolymer, ethylene
tetrafluoride-ethylene copolymer and polyvinylidene fluoride;
melamine resins; urea resins; polyethylene; polypropylene;
polymethacrylate and the like, and fillers composed of inorganic
materials such as calcium carbonate, talc, clay, kaolin, silica,
hydrotalcite, diatomaceous earth, magnesium carbonate, barium
carbonate, calcium sulfate, magnesium sulfate, barium sulfate,
aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium
oxide, titanium oxide, alumina, mica, zeolite and glass. As the
filler, inorganic fillers are preferable, inorganic oxides are more
preferable, alumina is particularly preferable, from the standpoint
of heat resistance and chemical stability.
[0048] The fillers can be used singly or two or more of them can be
mixed.
[0049] The alumina includes .alpha.-alumina, .beta.-alumina,
.gamma.-alumina, .theta.-alumina and the like, and .alpha.-alumina
is preferable since thermal and chemical stability thereof is
particularly high.
[0050] The fine particles include fine particles having a shape
such as a spherical shape, an elliptical shape, a rectangle shape
and a gourd shape, and amorphous fine particles having no specific
shape, and can be appropriately selected depending on the method of
producing materials of fine particles and dispersion conditions in
preparing a coating fluid containing components of the layer B.
[0051] The layer B is preferably a porous layer though varying
depending on its function and the degree of swelling of the polymer
other than a polyolefin in an electrolyte of a non-aqueous
electrolyte secondary battery, and its porosity is preferably 30 to
90 vol %, more preferably 40 to 85 vol %. Its pore diameter is
preferably 3 .mu.m or less, further preferably 1 .mu.m or less, in
terms of the diameter of a sphere when a pore is approximated as
the sphere. If the average pore diameter is 3 .mu.m or less, when a
non-aqueous electrolyte secondary battery is produced, then,
short-circuit does not easily occur even if a carbon powder as the
main component of a positive electrode and a negative electrode and
chips thereof drop.
[0052] The thickness of the layer B is usually 0.1 .mu.m or more
and 15 .mu.m or less, preferably 1 .mu.m or more and 10 .mu.m or
less, though varying depending on its function. If the thickness of
the layer B is 10 .mu.m or less, MD curl of the resultant laminated
porous film tends to be suppressed, and when a non-aqueous
electrolyte secondary battery is produced, an excellent load
characteristic tends to be manifested, and if it is 0.1 .mu.m or
more, the function of the layer B is easily manifested.
[0053] When the layer B is formed on both surfaces of a layer A,
the total thickness on the both surfaces is regarded as the
thickness of layer B.
<Method of Laminating Layer B on at Least One Surface of Layer
A>
[0054] The method of laminating the layer B on at least one surface
of the layer A includes a method of separately fabricating a layer
A and a layer B and bonding the layers together, and a method of
preparing a coating fluid containing a component of a layer B and a
medium (hereinafter, referred to as fluid B), applying the coating
fluid on a layer A and removing the medium, and of them, the method
of preparing a fluid B, applying it on a layer A and removing a
medium is simple and preferable.
[0055] The medium is a solvent or a dispersing medium, and it may
advantageously be a medium with which a component of a layer B can
be dissolved or dispersed uniformly and stably. The medium include
water, alcohols such as methanol, ethanol and isopropanol, acetone,
toluene, xylene, hexane, N-methylpyrrolidone,
N,N-dimethylacetamide, N,N-dimethylformamide and the like. The
medium may be used singly or the several media may be mixed
providing they are compatible.
[0056] It is preferable that 80 wt % or more of the medium is
composed of water and it is more preferable that the medium is
composedly only of water, from the standpoint of the process and
environmental load.
[0057] The method of applying a fluid B on a layer A is not
particularly restricted providing uniform wet coating is possible,
and conventionally known methods can be adopted. The applying
method includes, for example, a capillary coat method, a spin coat
method, a slit die coat method, a spray coat method, a roll coat
method, a screen printing method, a flexo printing method, a bar
coater method, a gravure coater method, a die coater method and the
like. The thickness of a layer B can be adjusted by controlling the
application amount of a fluid B, the concentration of a polymer in
a fluid B, and, when the fluid B contains fine particles, the ratio
of fine particles to the polymer. Usually, application of a fluid B
on a layer A and removal of a medium from the fluid B applied on
the layer A are continuously conducted while conveying the layer A.
By this procedure, a layer A and a layer B can be laminated
continuously even if the layer A has long size. The direction of
conveying a layer A is the machine direction.
[0058] The method of obtaining a fluid B is not particularly
restricted providing a uniform fluid B can be obtained. When a
fluid B contains, in addition to the polymer other than a
polyolefin, other components, particularly, fine particles,
preferable are a mechanical stirring method, an ultrasound
dispersing method, a high pressure dispersing method, a media
dispersing method and the like, and a high pressure dispersing
method is more preferable since more uniform dispersion is easy.
The mixing order in this case is not restricted, and a polymer and
other components such as fine particles may be added in one step to
a medium and mixed, or these may be added in any order to a medium
and mixed, or these may be dissolved or dispersed separately in a
medium before mixing the solutions or dispersions, providing
special problems such as generation of a precipitat dot not
occur.
[0059] When a medium of a fluid B contains water, it is preferable
to previously perform a hydrophilization treatment on a layer A,
before applying a fluid B on a layer A. By the hydrophilization
treatment of a layer A, applicability is improved more, and a more
uniform layer B can be obtained. This hydrophilization treatment is
effective particularly when the concentration of water in a medium
is high.
[0060] The hydrophilization treatment of a layer A includes a
treatment with a chemical such as acids and alkalis, a corona
treatment, a plasma treatment and the like.
[0061] A corona treatment is preferable since a layer A can be
hydrophilizated in relatively short time, and additionally,
modification of a polyolefin owing to corona discharge is limited
only to portions near the surface of a layer A, and high
applicability can be ensured without changing the nature of the
inside of a layer A.
[0062] For removal of a medium from a fluid B applied on a layer A,
drying is simple and preferable. The drying method includes, for
example, natural drying, blast drying, heat drying,
reduced-pressure drying and the like, and preferable is heat
drying. Though varying depending on the medium to be used, the
drying temperature is preferably 30 to 80.degree. C., more
preferably 50 to 80.degree. C. When 30.degree. C. or higher,
sufficient drying speed is obtained, and when 80.degree. C. or
lower, a laminated porous film having excellent appearance is
obtained.
[0063] It is preferable that drying is conducted at given drying
temperature while imparting film tension with which, when imparted
to a layer A carrying no applied fluid B under the same temperature
environment as the drying temperature, the elongation rate the
layer A is 1% or less, from the standpoint of suppression of MD
curl of the resulting laminated porous film. This MD curl
suppression effect is obtained more remarkably when a layer B is
laminated on only one surface of a layer A, than in the case of
lamination of a layer B on both surface of a layer A.
[0064] Film tension with which the elongation rate of a layer A
carrying no applied fluid B is 1% or less under given temperature
environment can be measured by a heat tensile test.
[0065] Film tension is over 0 N, preferably 0.02 N or more, more
preferably 0.05 N or more per 1 mm of the film width, from the
standpoint of suppression of generation of wrinkles on a layer
A.
[0066] It may be permissible that film tension is applied for a
certain time during drying, and it is preferable that film tension
is applied constantly during drying. Initiation of application of
film tension is preferably carried out after application of a fluid
B and before drying, and more preferably carried out before
application of a fluid B, though it may be initiated from midstream
of drying. Further, it may also be permissible that application of
a fluid B is conducted under the same temperature environment as
the drying temperature, and drying is conducted as it is at the
same temperature.
[0067] In the laminated porous film, the uplift quantity of the TD
side (hereinafter, described as MD curl quantity in some cases),
when allowed to stand still under an environment of a temperature
of 23.degree. C. and a humidity of 50% for 1 hour, is 15 mm or
less. The MD curl quantity is preferably 10 mm or less, more
preferably 5 mm or less. Since the MD curl quantity is 15 mm or
less, when the laminated porous film is used as a separator for a
non-aqueous electrolyte secondary battery, it is easily laminated
with an electrode and handling ability thereof is excellent.
Further, even if a separator is cut and work is stopped in
fabricating a battery, the position of the end of the separator
scarcely changes, thus, it is possible to re-start the work
promptly. For obtaining a laminated porous film showing the MD curl
quantity within the above-described range, there is, for example, a
method of drying while applying given film tension in forming a
layer B as described above, and further, it is effective that the
above-prescribed films are used as the polyolefin porous film, and
the thickness of a layer B is adjusted in the above-described
range. When the MD curl quantity is large, the TD side is uplifted
and thus the MD side is curved significantly, thus, it becomes
difficult for the laminated porous film to be laminated with an
electrode, leading to lowering of handling ability.
[0068] The value of the MD curl quantity is obtained as follows:
that is, a laminated porous film cut into a rectangle having a MD
side length of 300 mm and a TD side length of 200 mm is allowed to
stand still on a flat plane under an environment of a temperature
of 23.degree. C. and a humidity of 50% for 1 hour, then, the
distance from the flat plane to the TD side is measured at a
position wherein uplift of the TD side from the flat plane is
maximum.
[0069] The thickness of the whole laminated porous film (layer
A+layer B) is usually 5 to 50 .mu.m, preferably 8 to 40 .mu.m,
particularly preferably 9 to 30 .mu.m. When the thickness of the
whole laminated porous film is 5 .mu.m or less, if a non-aqueous
electrolyte secondary battery is produced using a laminated porous
film as a separator, then, initial failure due to internal
short-circuit easily occur, and when 50 .mu.m or more, the capacity
of the battery tends to be small.
[0070] The laminated porous film may have a porous film such as a
heat-resistant film, an adhesive film and a protective film, other
than the layer A and the layer B, in the range no t deteriorating
the object of the present invention.
[0071] The laminated porous film can be suitably used as a
separator for batteries, particularly, non-aqueous electrolyte
secondary batteries such as a lithium secondary battery.
[0072] When a non-aqueous electrolyte secondary battery is produced
using a separator for a non-aqueous electrolyte secondary battery,
a high load property is obtained, the separator exerts an excellent
shut-down function, and an excellent non-aqueous electrolyte
secondary battery is obtained.
[0073] The present invention will illustrated further in detail by
examples below, but the present invention is not limited to these
examples.
EXAMPLES
[0074] In examples and comparative examples, the physical
properties and the like of a layer A and a laminated porous film
were measured by the following methods.
(1) Elongation Behavior of Layer A:
[0075] A tensile test was conducted at a strain rate of 250%/min at
each measuring temperature using a tensile tester (manufactured by
A&D Co., Ltd, tensilon universal tester RTG-1310) according to
JISK7127. Based on the resultant strass-strain curve at 30.degree.
C. or 55.degree. C., film tension with which the elongation rate of
a layer A was 1% or less and the elongation rate when a tension of
0.05 N/mm was applied to a layer A at 65.degree. C. were
measured.
(2) Thickness Measurement (Unit: .mu.m):
[0076] The thickness of a laminated porous film was measured by a
high-precision digital length measuring machine manufactured by
Mitutoyo Corporation.
(3) Unit Weight (Unit: g/m.sup.2):
[0077] A laminated porous film was cut into a square having a side
having a length of 10 cm, and its weight W (g) was measured. The
unit weight was calculated according to the equation: unit weight
(g/m.sup.2)=W/(0.1.times.0.1). The unit weight of a layer B was
calculated by subtracting the unit weight of a layer A from the
unit weight of a laminated porous film.
(4) MD Curl Quantity (Unit: Mm):
[0078] A laminated porous film was cut into a rectangle having a MD
side length of 300 mm and a TD side length of 200 mm as a sample,
the resultant sample was allowed to stand still on a flat plane
under an environment of a temperature of 23.degree. C. and a
humidity of 50% for 1 hour, then, the distance from the flat plane
to the TD side at a position wherein uplift of the TD side from the
flat plane was maximum was measured using a ruler, and the measured
value was adopted as the MD curl quantity. When the MD side of the
sample wound in the form of roll, the MD curl quantity was
unmeasurable.
<Polyolefin Porous Film A1 (Layer A)>
[0079] An ultra-high molecular weight polyethylene powder (GUR4032,
manufactured by Ticona Corporation)(70 parts by weight) and a
polyethylene wax having a weight-average molecular weight of 1000
(FNP-0115, manufactured by Nippon Seiro Co., Ltd.) (30 parts by
weight), and, 0.4 parts by weight of an antioxidant (Irg1010,
manufactured by Ciba Specialty Chemicals), 0.1 part by weight of an
antioxidant (P168, manufactured by Ciba Specialty Chemicals) and
1.3 parts by weight of sodium stearate, based on 100 parts by
weight of the sum of the ultra-high molecular weight polyethylene
and the polyethylene wax, were added, further, calcium carbonate
having an average particle size of 0.1 .mu.m (manufactured by Maruo
Calcium Co., Ltd.) was added so that its amount was 37 vol % with
respect to the whole volume, and these were mixed as they were in
the form of powder in a Henschel mixer, then, melt-kneaded by a
twin screw kneader to give a polyolefin resin composition. The
polyolefin resin composition was rolled by a pair of rolls having a
surface temperature of 150.degree. C. to fabricate a sheet. This
sheet was immersed in a hydrochloric acid aqueous solution
(hydrochloric acid 4 mol/L, nonionic surfactant 0.5 wt %) to remove
calcium carbonate, and subsequently, stretched 6 times at
105.degree. C., to obtain a polyolefin porous film A1.
[0080] The film tension with which the elongation rate of the
resultant polyolefin porous film A1 (film thickness: 18 .mu.m, unit
weight: 7 g/m.sup.2) was 1% or less was 0.17 N/mm or less at
55.degree. C. per 1 mm of the film width. The elongation rate of
the film when a tension of 0.05 N/mm was applied at 65.degree. C.
was 0.3%.
<Polyolefin Porous Film A2 (Layer A)>
[0081] A commercially available polyethylene porous film (film
thickness: 12 .mu.m, unit weight: 7.0 g/m.sup.2) was used as a
polyolefin porous film A2.
[0082] The film tension with which the elongation rate of the
polyolefin porous film A2 was 1% or less was 0.10 N/mm or less at
30.degree. C. and 0.07 N/mm or less at 55.degree. C., per 1 mm of
the film width. The elongation rate of the film when a tension of
0.05 N/mm was applied at 65.degree. C. was 1.2%.
Example 1
(1) Preparation of Fluid B1
[0083] A fluid B1 was prepared by the following procedure.
[0084] To a medium composed of pure water and isopropyl alcohol at
a weight ratio of 95:5 were added carboxymethylcellulose (CMC,
manufactured by Daicel FineChem Ltd.: 1110) and alumina
(manufactured by Sumitomo Chemical Co., Ltd.: AKP3000) at a weight
ratio of 3:100 so that the solid content was 28 wt %, and these
were mixed and treated three times under high pressure dispersion
conditions, to prepare a fluid B1.
(2) Production of Laminated Porous Film
[0085] The fluid B1 was applied directly on one surface of the
polyolefin porous film A1 using a gravure coater and dried at
55.degree. C. while applying a film tension of 0.04 N/mm per 1 mm
of the film width, to obtain a laminated porous film having a whole
thickness of 22 .mu.m. The physical properties of the resultant
laminated porous film are shown in Table 1.
Example 2
[0086] A laminated porous film having a whole thickness of 15 .mu.m
was obtained in the same manner excepting that the layer A was the
polyolefin porous film A2, in (2) production of laminated porous
film of Example 1. The physical properties of the resultant
laminated porous film are shown in Table 1.
Example 3
[0087] A laminated porous film having a whole thickness of 15 .mu.m
was obtained in the same manner excepting that the drying
temperature of 30.degree. C. in Example 2. The physical properties
of the resultant laminated porous film are shown in Table 1.
Example 4
(1) Preparation of Fluid B2
[0088] A fluid B2 was prepared by the following procedure.
[0089] To a medium composed of pure water and isopropyl alcohol at
a weight ratio of 90:10 were added polyvinyl alcohol (manufactured
by Wako Pure Chemical Industries, Ltd: Polyvinyl alcohol 3500,
partial saponification type) and alumina (manufactured by Sumitomo
Chemical Co., Ltd.: AKP3000) at a weight ratio of 3:100 so that the
solid content was 20 wt %, and these were mixed and treated under
high pressure dispersion conditions, to prepare a fluid B2.
(2) Production of Laminated Porous Film
[0090] The fluid B2 was applied directly on one surface of the
polyolefin porous film A2 using a gravure coater and dried at
60.degree. C. while applying a film tension of 0.07 N/mm per 1 mm
of the film width, to obtain a laminated porous film having a whole
thickness of 16 .mu.m. The physical properties of the resultant
laminated porous film are shown in Table 1.
Example 5
(1) Preparation of Fluid B3
[0091] A fluid B3 is prepared by the following procedure.
[0092] To a medium composed of N-methylpyrrolidone are added an
aramid resin, alumina 1 (manufactured by Evonik Industries AG:
Alumina C) and alumina 2 (manufactured by Sumitomo Chemical Co.,
Ltd.: AA03) at a weight ratio of 1:1:1 so that the solid content is
4.4 wt %, and these are mixed and treated under high pressure
dispersion conditions, to prepare a fluid B3.
(2) Production of Laminated Porous Film
[0093] A laminated porous film is obtained in the same manner as
Example 1. The MD curl quantity of the resultant laminated porous
film is 15 mm or less.
Example 6
(1) Preparation of Fluid B4
[0094] A fluid B4 is prepared by the following procedure.
[0095] To a medium composed of pure water and isopropyl alcohol at
a weight ratio of 95:5 are added a styrene-butadiene rubber,
carboxymethylcellulose (manufactured by Daicel FineChem Ltd.: 1110)
and alumina (manufactured by Sumitomo Chemical Co., Ltd.: AKP3000)
at a weight ratio of 3:1:100 so that the solid content is 28 wt %,
and these are mixed and treated under high pressure dispersion
conditions, to prepare a fluid B4.
(2) Production of Laminated Porous Film
[0096] A laminated porous film is obtained in the same manner as
Example 1. The MD curl quantity of the resultant laminated porous
film is 15 mm or less.
Example 7
(1) Preparation of Fluid B5
[0097] A fluid B5 is prepared by the following procedure.
[0098] To a medium composed of pure water and isopropyl alcohol at
a weight ratio of 95:5 are added an ethylene-vinyl acetate-vinyl
versatate copolymer (manufactured by Sumika Chemtex Co., Ltd.:
Sumikaflex.RTM. 950HQ), carboxymethylcellulose (manufactured by
Daicel FineChem Ltd.: 1110) and alumina (manufactured by Sumitomo
Chemical Co., Ltd.: AKP3000) at a weight ratio of 3:1:100 so that
the solid content is 28 wt %, and these are mixed and treated under
high pressure dispersion conditions, to prepare a fluid B5.
(2) Production of Laminated Porous Film
[0099] A laminated porous film is obtained in the same manner as
Example 1. The MD curl quantity of the resultant laminated porous
film is 15 mm or less.
Example 8
(1) Preparation of Fluid B6
[0100] A fluid B6 is prepared by the following procedure.
[0101] To a medium composed of pure water and isopropyl alcohol at
a weight ratio of 95:5 are added a styrene-acrylic copolymer
(manufactured by Showa Denko K.K.: Polysol.RTM. AP-1900),
carboxymethylcellulose (manufactured by Daicel FineChem Ltd.: 1110)
and alumina (manufactured by Sumitomo Chemical Co., Ltd.: AKP3000)
at a weight ratio of 5:2:100 so that the solid content is 28 wt %,
and these are mixed and treated under high pressure dispersion
conditions, to prepare a fluid B6.
(2) Production of Laminated Porous Film
[0102] A laminated porous film is obtained in the same manner as
Example 1. The MD curl quantity of the resultant laminated porous
film is 15 mm or less.
Comparative Example 1
[0103] A laminated porous film having a whole thickness of 15 .mu.m
was obtained in the same manner excepting that the film tension was
0.13 N/mm per 1 mm of the film width in Example 2. The physical
properties of the resultant laminated porous film are shown in
Table 1. In the resultant laminated porous film, the MD side wound
in the form of roll, thus, the MD curl quantity was
unmeasurable.
TABLE-US-00001 TABLE 1 Drying Film Thick- Unit temperature tension
ness weight MD curl (.degree. C.) (N/mm) (.mu.m) (g/m.sup.2)
quantity (mm) Example 1 55 0.04 22 6.8 7 Example 2 55 0.04 15 3.8
11 Example 3 30 0.04 15 3.8 8 Example 4 55 0.07 16 4.1 15
Comparative 55 0.13 15 3.8 unmeasurable Example 1
[0104] Each laminated porous film obtained in Examples 1 to 4 was,
when used as a separator for a non-aqueous electrolyte secondary
battery, easily laminated with an electrode, and its handling
ability was excellent. Each laminated porous film obtained in
Examples 5 to 8 is, when used as a separator for a non-aqueous
electrolyte secondary battery, easily laminated with an electrode,
and its handling ability is excellent. The laminated porous film
obtained in Comparative Example 1 wound in the form of roll and
was, when used as a separator for a non-aqueous electrolyte
secondary battery, hardly laminated with an electrode, and its
handling ability was poor.
INDUSTRIAL APPLICABILITY
[0105] The laminated porous film of the present invention is
excellent in handling ability in laminating with an electrode for
use as a separator for a non-aqueous electrolyte secondary
battery.
EXPLANATION OF REFERENCES
[0106] 1 laminated porous film [0107] 2 MD side [0108] 3 TD
side
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