JPH11300180A - Porous resin membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous resin membrane of which affinity for org. solvent is improved while maintaining the air permeability and which is useful as a separator for a battery, especially for a lithium secondary battery. SOLUTION: This porous resin membrane has 5-200 μm thickness, 20-80% porosity and 10-1,000 sec/100 cc air permeability by a Gurley permeability tester. The contact angle θ1 of the droplet of the liq. mixture of ethylene carbonate and diethyl carbonate in 1:1 volume ration is <=30 deg.C immediately after being dripped, and the contact angle θ1 and the contact angle θ2 of the droplet one minute after being dripped are limited to conform to θ2 /θ1 <=0.85.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a porous resin membrane having gas permeability. More specifically, the present invention provides a porous resin film having improved affinity for an organic solvent and water. Specifically, a porous resin membrane suitable for filtration membranes, battery separators, various packaging materials requiring air permeability, medical materials, clothing materials, and the like can be provided. In particular, separators for lithium secondary batteries can be provided. It is intended to provide a porous resin film suitable for the above.

[0002]

2. Description of the Related Art Porous membranes are used in various industrial fields such as filtration membranes, battery separators, packaging, medical and clothing materials. In particular, when used as a separator for a lithium secondary battery, there is a need for a property of retaining an electrolyte and having ion permeability while insulating the positive and negative electrodes so as not to directly contact them (insulating the electrodes).

At present, porous polyolefin membranes are widely used as separators for lithium secondary batteries.
This polyolefin porous membrane has excellent chemical stability and is unlikely to induce unnecessary chemical reactions inside the battery, and in the event of abnormal overheating, the porous membrane itself melts, closing the pores and causing insulation between the electrodes, causing an abnormal reaction inside the battery. It also has the advantage of playing a role of deterrence.

[0004]

In the above-mentioned lithium secondary battery, a nonaqueous electrolytic solution comprising a combination of an organic solvent such as ethylene carbonate, dimethyl carbonate and diethyl carbonate and an electrolyte is generally used. Is not necessarily good in wettability to these electrolytes, and is not excellent in electrolyte retention. For this reason, when assembling the battery, it takes time to infiltrate the electrolyte into the separator, and also causes the distribution of the electrolyte in the battery. Further, when the electrolyte is not sufficiently retained in the separator, there is a problem that sufficient battery performance such as battery capacity and cycle characteristics cannot be obtained.

[0005] On the other hand, when the porous membrane is used for filtering a liquid, if the wettability to the liquid is poor, there is a problem that the filtration rate is reduced and the efficiency is lowered. Therefore, an object of the present invention is to provide a porous membrane having good wettability to a liquid that has solved the above problems, and particularly has excellent durability and affinity for the electrolyte as a separator of a lithium secondary battery,
Another object of the present invention is to provide a porous membrane having high electrolytic solution retention performance.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies for the above-mentioned objects, and as a result, according to the porous membrane manufactured under specific processing conditions, excellent durability and affinity for the electrolyte, and The present inventors have found that high electrolytic solution retention performance can be exhibited, and have reached the present invention. That is, the gist of the present invention is:
(A) thickness of 5 μm or more and 200 μm or less, (b) porosity of 20% or more and 80% or less, (c) Gurley type air permeability of 10 seconds / 100 cc to 1000 seconds / 100 cc, (d)
The porous resin film is characterized in that the contact angle θ ₁ immediately after dropping of a 1: 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate is 30 ° or less.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The production method of the porous membrane of the present invention is not particularly limited as long as it has the physical properties defined above, but (a) the thickness is 5 μm to 200 μm, preferably 10 μm to 50 μm, ( b) Porosity is 2
0% or more and 80% or less, preferably 40% or more and 60% or less, and (c) Gurley air permeability is 10 seconds / 100 cc or more and 1000 seconds / 100 cc or less, preferably 50 seconds / 1.
It is practical to perform a specific surface treatment or the like on a porous resin base material having a physical property of not less than 00 cc and not more than 900 seconds / 100 cc. As the surface treatment method, a specific plasma treatment method is particularly preferable because it is possible to treat the inside of the pores of the porous resin base material, and it is possible to more efficiently increase the liquid holding property. .

The material of the above-mentioned porous resin substrate which can be used in the present invention is not particularly limited, but polyolefin resin or fluorine resin is preferably used from the viewpoint of durability of the material. Among them, a porous ultrahigh molecular weight polyethylene membrane, a polytetrafluoroethylene porous membrane, a nonwoven fabric made of polyethylene or polypropylene, and the like are used. Most preferably, an ultra-high molecular weight polyethylene porous membrane that exhibits heat blocking properties at a lower temperature is used.

Such a porous resin substrate can be manufactured by a known method. For example, in the case of an ultra-high molecular weight polyethylene porous membrane, a swelling agent which is solid or liquid at ordinary temperature, and which is liquid under melt molding conditions, is melt-kneaded with ultra-high molecular weight polyethylene, and the composition is extruded and formed by a molding method such as extrusion molding. To extract a swelling agent, and if necessary, stretching before or after the extraction.

The above-mentioned plasma treatment, which is preferable as a method for obtaining the porous film of the present invention from the porous resin substrate as described above, is performed on one or both surfaces of the substrate. It is necessary to carry out without closing the holes. Examples of a plasma source used when performing plasma processing on a substrate include a radio-frequency power source, a microwave power source, and a DC power source. Of these, a radio frequency power supply is preferred. The plasma treatment is usually performed in an appropriate chamber, and the internal pressure is generally 0.1 Pa (about 1 mmTorr) to atmospheric pressure, preferably 2 Pa (about 20 mmTorr) to 400 Pa (about 3 T).
orr), particularly preferably 3 Pa (about 30 mmTorr).
r) Discharge is performed under a pressure in the range of 100 Pa (about 750 mmTorr) to generate plasma, and the substrate is processed under the plasma atmosphere. The chamber contains a gas selected from rare gases (helium, neon, argon, xenon), nitrogen, oxygen, carbon dioxide, hydrogen, or vapors of organic compounds such as hydrocarbons, oxygen-containing organic compounds, and nitrogen-containing organic compounds. , Preferably a rare gas or a mixture of a rare gas and an organic compound vapor is introduced, and if necessary, the pressure is reduced by a vacuum pump to adjust the pressure to an appropriate pressure.

[0011] By controlling the processing conditions such as the amount and type of gas introduced during discharge and plasma processing in the chamber, characteristics of organic compounds, chamber pressure, plasma output, etc., the generation of functional groups on the substrate surface and The surface energy of the material surface and / or the inside of the hole can be controlled. Preferred conditions for the plasma treatment include a plasma output W (J / sec).
c) divided by the electrode plate area S (cm ² ) is 0.01 to ² J / sec · cm ² , particularly 0.02 to 0.
It is 6 J / sec · cm ² .

As described above, the porous resin film of the present invention obtained by performing a specific plasma treatment or the like has a thickness of 5 μm to 200 μm, preferably 10 μm to 50 μm, and a porosity of 20%. Not less than 80%, preferably not less than 40% and not more than 60%. The Gurley air permeability of the membrane is 10 seconds / 100 cc or more and 1500 seconds / 100
cc or less, preferably 50 seconds / 100 cc or more and 900 seconds / 100 cc or less. The film thickness, porosity and Gurley type air permeability of the above membrane are preferably in the same range as in the case of the raw material porous resin substrate, and if it is outside of this range, it is difficult to use as a battery separator. Is not preferred.

In addition, the porous resin film of the present invention differs greatly in physical properties from the raw material porous substrate immediately after the dropping of the droplet in the 1: 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate. Is 30 degrees or less, and preferably 25 degrees or less from the viewpoint of affinity with the electrolyte. Further, from the viewpoint of the permeability of the electrolyte, the contact angle θ ₁ immediately after dropping and the contact angle θ 1 minute after dropping with respect to a 1: 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate are considered. more preferably ₂ relationship is θ ₂ / θ ₁ ≦ 0.85, and most preferably a further absolute value of theta ₂ is less than 20 degrees. The above-mentioned contact angles θ ₁ and θ ₂ are defined as follows: a droplet of a 1: 1 (volume ratio) mixture of ethylene carbonate and diethyl carbonate is formed on the surface of the sample film, and the surface of the droplet and the surface of the sample film are A tangent to the droplet passing through the intersection is drawn, and the angle formed by the tangent and the surface of the sample film, and the angle that includes the droplet is the contact angle of the sample film with the mixture, and immediately after the droplet is dropped. Value (θ ₁ ) and the value one minute after dropping (θ ₂ )
It shows.

In a lithium secondary battery using the porous membrane of the present invention as a separator, for example, as a negative electrode, a lithium metal, an alloy of lithium and aluminum, or a carbon electrode capable of absorbing and releasing lithium ions is used. And a known electrode such as manganese dioxide is used as the positive electrode. As the shape of the battery, for example, a case in which the composite porous membrane of the present invention is wound between the positive electrode and the negative electrode, or a case in which each electrode is wrapped in a bag-shaped composite porous membrane together with an electrolytic solution, And a sealed battery. As the electrolyte, for example, a non-aqueous solution in which an electrolyte such as LiPF ₆ is dissolved in an aprotic polar solvent such as ethylene carbonate (EC) or dimethyl carbonate (DMC) is used.

[0015]

EXAMPLES The present invention will be described specifically with reference to Examples.
The present invention is not limited to the following examples unless it exceeds the gist. In addition, in the following examples, each measurement was based on the following method. (1) Air permeability Measured according to JIS P8117. As a measuring device, a B-type Gurley type densometer (trade name) manufactured by Toyo Seiki Co., Ltd. was used. (2) Porosity From the volume and weight of the film and the density of the material, the volume of the void portion (space without material) occupying the inside of the film was expressed in percentage. (3) Contact angle 1: 1 of ethylene carbonate and diethyl carbonate on the sample resin film
(Volume ratio) A droplet of the mixed liquid is formed, a tangent to the droplet passing through the point where the droplet surface and the sample film intersect is drawn, and the angle formed by the tangent and the film surface and the angle containing the droplet is defined as the angle. The contact angle of the sample with the above-mentioned mixed solution was defined as the contact angle. The value immediately after dropping (θ ₁ ) and the value one minute after dropping (θ ₂ ) were measured. Comparative Example 1 After 20% by weight of polyethylene having a viscosity average molecular weight of 2.3 million was blended with 80% by weight of stearyl alcohol, the mixture was left in an oven at 170 ° C. for 30 minutes to wet the polyethylene with alcohol. At this time, 0.5 part by weight of a phenolic stabilizer was added to 100 parts by weight of the mixture. This mixture was kneaded for 10 minutes at a temperature of 170 ° C. and a rotation speed of 100 rpm. Resin temperature is 1
The mixture was constant at 85 ° C., the torque was constant, and the mixture was transparent and homogeneous in the molten state.

170 ° C. before the homogeneous mixture cools and solidifies
At a temperature of 0.5 mm to obtain a 0.5 mm pressed sheet. The sheet is subjected to a biaxial stretching at a temperature of 120 ° C. for 2 hours.
Stretching 4 × 4 times was performed at the same time at 00% / sec. The stretched sheet is placed in isopropanol at 60 ° C. for 5 minutes.
It was immersed for a minute to extract stearyl alcohol. This sheet was white due to porosity. Table 1 shows the physical properties of the finally obtained porous resin film. Comparative Example 2 82 parts by weight of stearyl alcohol and 0.5 part by weight of a phenolic additive were powder-blended to 18% by weight of ultrahigh molecular weight polyethylene having a viscosity average molecular weight of 2.3 million, and the supply unit was cooled with a water cooling jacket. 50mmφ
The mixture was supplied to an extruder, and a 40 mmφ extruder was further attached to the end of the extruder. The extruder was melted and mixed at 210 ° C. to obtain a uniform melt.

The homogenous mixture was extruded from a T-die having a width of 550 mm and a die clearance of 0.3 mm, and was drawn at a draft rate of 1.8 to obtain a sheet having a thickness of 0.15 mm. 60% stearyl alcohol from this sheet
Extraction and removal with isopropanol at ℃ resulted in a porous sheet. The sheet is stretched 3.0 times in the machine direction at 100 ° C. using a roll stretching machine, and then stretched 130 times using a tenter stretching machine.
The film was stretched 5.5 times in the transverse direction at ℃. Table 1 shows the properties of the obtained film. Example 1 The ultrahigh molecular weight polyethylene porous membrane obtained by the method of Comparative Example 1 described above was placed in a chamber having a circular parallel plate electrode having a diameter of 15 cm inside, and the chamber was sufficiently evacuated. And the chamber was maintained at about 20 Pa while introducing argon gas. Discharge was started by a 13.56 MHz radio wave power supply, and processing was performed for 1 minute at an output of 40 W. The W / S value at this time is 0.22 (J / sec.
Cm ² ). Table 1 shows the physical properties of the obtained porous resin film. Example 2 A porous resin film was obtained in the same manner as in Example 1 except that helium was used instead of argon. Table 1 shows the physical properties of the obtained porous resin film. Example 3 A porous resin film was obtained in the same manner as in Example 1 except that nitrogen was used instead of argon. Table 1 shows the physical properties of the obtained porous resin film. Example 4 The ultrahigh molecular weight polyethylene porous membrane obtained by the method of Comparative Example 1 described above was placed in a chamber having a circular parallel plate type electrode having a diameter of 15 cm inside, and the chamber was sufficiently evacuated. , Dimethyl carbonate vapor at 5
While introducing cc, the chamber pressure was maintained at about 20 Pa.
The discharge is started by the radio frequency power of 13.56 MHz,
Processing was performed for 1 minute at an output of 40 W. Table 1 shows the physical properties of the obtained porous resin film. Example 5 The ultrahigh molecular weight polyethylene porous membrane obtained by the above-described method was placed in a chamber having a parallel plate type electrode inside, and after sufficiently exhausting the chamber, argon gas was introduced to maintain the chamber pressure at about 20 Pa. Discharge was started by a 13.56 MHz radio wave power supply, and processing was performed at an output of 80 W for 1 minute. The W / S value at this time is 0.45 (J / sec).
Cm ² ). Table 1 shows the physical properties of the obtained porous resin film. Example 6 The porous film obtained in Comparative Example 2 was 30 cm wide and 25 cm long.
After placing the inside of a chamber having a parallel plate electrode having a diameter of 10 cm and exhausting the chamber sufficiently, the inside of the chamber was maintained at about 40 Pa while introducing argon gas and oxygen gas at a rate of 10 cc and 30 cc per minute, respectively. 13.56
Discharge was started at an output of 10 W with a radio frequency power supply of MHz, and the porous film was continuously passed between parallel plate electrodes to perform processing. The time required for the film to pass between the electrodes was 30 seconds, and the W / S value was 0.013 (J
/ Sec · cm ² ). Table 1 shows the physical properties of the obtained porous membrane.

As described above, the porous films of Examples 1 to 6 which were subjected to the specific plasma treatment were different from the porous resin films of Comparative Examples 1 and 2 which were not subjected to the plasma treatment, in that ethylene carbonate and carbonate were used. The contact angle with respect to a 1: 1 (volume ratio) mixed solution of diethyl was reduced, and the porous resin membranes of Examples 1 to 6 were smaller than the porous membrane of the comparative example by 1 to 1 times of ethylene carbonate and diethyl carbonate. It can be seen that a 1: 1 (volume ratio) mixed solution easily permeates.

[0019]

[Table 1] θ1: contact angle immediately after dropping.

Θ2: contact angle one minute after dropping. Ar: argon,

[0021]

According to the present invention, there is provided a porous resin membrane having improved affinity for an organic solvent while maintaining air permeability, and which is useful as a battery parator, particularly as a separator for a lithium secondary battery. .

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08J 9/00 CEW C08J 9/00 CEWZ H01M 2/16 H01M 2/16 P // H01M 10/40 10/40 Z

Claims (11)

[Claims] (1) a thickness of 5 μm or more and 200 μm or less,
(B) Porosity of 20% or more and 80% or less, (c) Gurley type air permeability of 10 seconds / 100cc or more and 1000 seconds / 100c
c or less, (d) 1: 1 of ethylene carbonate and diethyl carbonate
(Volume ratio) The contact angle θ ₁ immediately after the drop of the mixed liquid is 30
A porous resin film, wherein the temperature is not more than a degree. 2. A 1: 1 mixture of ethylene carbonate and diethyl carbonate.
(Volume ratio) The relationship between the contact angle θ ₁ immediately after dropping of the mixed liquid droplet and the contact angle θ ₂ one minute after dropping of the liquid droplet is θ ₂ / θ ₁ ≦ 0.85. 1 porous resin membrane. 3. The porous resin film according to claim 1, wherein the porous resin is subjected to a plasma treatment. 4. (a) a thickness of 5 μm or more and 200 μm or less,
(B) Porosity of 20% or more and 80% or less, (c) Gurley type air permeability of 10 seconds / 100cc or more and 1000 seconds / 100c
4. The porous resin film according to claim 3, wherein the porous resin having a value of c or less is subjected to plasma treatment. 5. A plasma processing apparatus comprising:
A discharge process in which one or two or more gases selected from rare gases, halogen gases, nitrogen, oxygen, hydrogen, and carbon dioxide are introduced, and the atmosphere is subjected to a discharge treatment under a pressure of 0.1 Pa or more. Item 4. The porous resin film according to item 3 or 4. 6. The plasma treatment is a discharge treatment in which a mixture of a rare gas and an organic compound vapor is introduced into a plasma treatment tank, and the plasma treatment is performed under a pressure of 0.1 Pa or more in the atmosphere. 4 is a porous resin film. 7. A plasma processing method, wherein a value (W / S value) obtained by dividing a plasma output (W) by an electrode plate area (S) is 0.01 to
The porous resin film according to any one of claims 3 to 6, which is performed at ² J / sec · cm ² . 8. The porous resin film according to claim 1, wherein the porous resin is a polyolefin resin. 9. The porous resin film according to claim 1, wherein the porous resin is a fluorine-containing resin. 10. A battery separator comprising the porous resin film according to any one of claims 1 to 9. 11. A lithium secondary battery comprising the battery separator according to claim 10.