JP2003119313A - Method for producing porous film - Google Patents

Abstract

(57) Abstract: A method for producing a porous film having high porosity, high air permeability, good mechanical strength, good shrinkage, and high heat resistance, and a porous film obtained by such a production method. A porous film, a battery separator comprising the porous film, and a battery and a capacitor using the battery separator. A resin composition containing a resin having a crosslinkable unsaturated bond with a polyolefin and a resin composition containing a solvent are melt-kneaded, and the obtained melt-kneaded material is formed into a sheet, and the sheet is formed. In a method for producing a porous film having a step of performing a stretching treatment and a desolvation treatment of a product, a method for producing a porous film having a step of irradiating ultraviolet rays
A porous film obtainable by the method for producing a porous film, a battery separator including the porous film, a battery including the battery separator, and a capacitor including the battery separator.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a porous film, a porous film obtainable by such a production method, a battery separator made of the porous film, and a battery using the battery separator. Regarding capacitors.

[0002]

2. Description of the Related Art Porous films are used for battery separators,
It is used in electrolytic capacitor diaphragms, moisture-permeable waterproof materials, and various filters. Among them, battery separators are gaining attention as an important component of lithium secondary batteries, which are lightweight, have high electromotive force and high energy as batteries, and have little self-discharge. It is also expected as a member.

Up to now, several proposals have been made to improve the heat resistance of separators for lithium secondary batteries, centering on polyolefin-containing porous films. For example,
In Japanese Patent Laid-Open No. 10-12211, a nonwoven fabric made of glass fiber or the like is used by being laminated on a polyolefin-containing porous film. Further, as in JP-A-3-245457 and JP-A-3-193125, there are many cases where a polymer compound crosslinked by a method such as polymerization after film formation is used. Further, not only the compositional aspect but also JP-A-5-7444
As in Japanese Patent Publication No. 4, a proposal has been made in terms of the structure inside the battery, such as bonding the protruding portion of the separator from the electrode plate. Japanese Examined Patent Publication No. 1-18091 and Japanese Unexamined Patent Publication No. 9-16
9867, JP-A-6-153023 and the like disclose porous films containing rubber in addition to polyolefin resins, but these are not intended to improve heat resistance.

The lithium ion secondary battery separator is
The resin that forms the film melts, closing the pores of the film and losing ion permeability during abnormal heating of the battery.
It has a shutdown (SD) function that prevents further heating due to electric current. However, when an abnormality occurs in which a short-circuit current flows in the battery due to an external short circuit of the battery, etc., the temperature rise is extremely rapid, so even if the SD function is fully developed, the temperature is already much higher than the SD temperature of the separator. There is a high risk of reaching extremely high temperatures. In such a case, the separator will be in a completely molten state, and especially in the presence of foreign matter or precipitated lithium dendrites, it easily breaks or breaks, and the positive electrode and negative electrode may come into direct contact with each other, resulting in a short circuit condition. There is a nature. In particular, in an overcharged state or the like, the internal pressure in the battery increases, and the high pressure is applied in the film thickness direction, further increasing the risk of short circuit in the membrane.

[0005]

The object of the present invention is to have high porosity, high air permeability, good mechanical strength and shrinkage, and to be exposed to the high temperature and high pressure state as described above. Even in the case of having a high heat resistance to the extent that it can maintain its shape, particularly a method for producing a porous film suitably used as a separator for a lithium ion secondary battery, a porous film obtained by such a production method, It is intended to provide a battery separator made of a porous film, and a battery and a capacitor using the battery separator.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have constructed a porous film by irradiating it with ultraviolet rays as one step in manufacturing the porous film. It was found that the porosity and the air permeability can be improved at the same time that the crosslinking reaction of the raw material resin can be promoted, and the present invention has been completed.

That is, the gist of the present invention is (1) melt-kneading a resin composition containing a solvent and a resin component containing a polyolefin and a rubber having a crosslinkable unsaturated bond, and the obtained melt-kneaded product into a sheet. (2) The method for producing a porous film, which comprises the step of irradiating with ultraviolet rays in the method for producing a porous film, which comprises the steps of: ) A porous film obtainable by the method for producing a porous film described above, (3) a battery separator comprising the porous film described in (2) above, (4) using the battery separator described in (3) above. And a capacitor using the battery separator according to (3) above.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a porous film of the present invention, for example, a known wet film-forming method can be used, in which a resin composition containing a resin component and a solvent is melted and kneaded by heating, It is preferable that the obtained melt-kneaded product is extruded into a sheet and then cooled, the obtained sheet-shaped molded product is subjected to a stretching treatment, then subjected to a solvent removal treatment, and then irradiated with ultraviolet rays.

In the present invention, polyolefin is used as one of the resin components. Examples of such polyolefins include homopolymers of olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene, copolymers, and mixtures thereof. From the viewpoint of enhancing the strength of the high quality film, the weight average molecular weight is preferably 5 × 10 ⁵ or more, more preferably 1 × 10 ⁶ or more, and further preferably 1.5.
Ultra high molecular weight polyolefin of 10 ⁶ or more is preferable,
Ultra high molecular weight polyethylene is particularly preferable. The weight average molecular weight can be measured by the method described in Examples below.

The content of the ultrahigh molecular weight polyolefin in the polyolefin is preferably 1% by weight or more, from the viewpoint of sufficient entanglement of the ultrahigh molecular weight polyolefin during melt kneading and sufficient film strength, and 50 to 10
0% by weight is more preferable, and 60 to 90% by weight is further preferable.

The amount of the polyolefin compounded is preferably 50 to 95% by weight, more preferably 60 to 90% by weight, based on the resin component of the resin composition. The blending amount is preferably 50% by weight or more from the viewpoint of improving the film strength, and is preferably 95% by weight or less from the viewpoint that uniform kneading is easy and uneven thickness and characteristic unevenness do not occur.

In the present invention, a rubber having a crosslinkable unsaturated bond is used as another one of the resin components. As such rubbers, from the viewpoint that strength can be exhibited particularly by the ultra-high molecular weight polyolefin, shape retention and mechanical strength can be exhibited even in a high temperature region exceeding the melting point (about 141 ° C.) of the ultra-high molecular weight polyolefin. In the crosslinking treatment step, those capable of forming a crosslinked structure with the ultrahigh molecular weight polyolefin, particularly those having a C = C double bond in the main chain are preferable. Among them, a ring-opening polymer of an unsaturated condensed alicyclic compound or a derivative thereof has an aliphatic ring derived from the monomer unit and a double bond in the main chain, and efficiently forms a crosslinked structure. This is preferable because improvement in heat resistance of the resulting porous film can be expected. Further, in the ring-opening polymer, a part of its double bond may be hydrogenated.

Specific examples of such rubbers are obtained by polymerizing a monomer having a structure in which the terminal hydrogen of a lower hydrocarbon having a double bond at the terminal is substituted with an ethylene group,
Examples of the resin include a resin having a structure in which a methylene group is bonded to the main chain, such as polybutadiene. In addition, examples of the unsaturated condensed alicyclic compound include those of the three series described below.

The first series includes unsaturated compounds having a double bond in one of the rings, which is incorporated into the main chain after ring-opening polymerization, among those classified as condensed alicyclic compounds in a narrow sense. To be In addition, including derivatives in which some of the hydrogen atoms of those unsaturated compounds are replaced by other substituents,
It can be used as an unsaturated condensed alicyclic compound. Specific examples thereof include bicyclo [3.2.0] hept-6-ene, bicyclo [4.2.0] oct-7-ene and their derivatives.

The second series includes unsaturated compounds having a double bond in one of the rings, which is incorporated into the main chain after ring-opening polymerization, among compounds classified as bridged ring compounds. Moreover, the unsaturated condensed alicyclic compound can be used, including a derivative in which some of the hydrogen atoms of these unsaturated compounds are replaced with other substituents. Specific examples of this include bicyclo [2.2.1] hept-5-ene (sometimes referred to as norbornene herein), bicyclo [2.2.1] hept-5-ene-2,3-di Examples thereof include norbornene derivatives such as carboxymethyl ester, bicyclo [2.2.2] oct-2-ene and derivatives thereof.

The third series includes compounds having a bridged ring and a condensed alicyclic ring, and having an aliphatic ring and a double bond in the main chain after ring-opening polymerization. As a concrete example of this,
Tricyclo [5.2.1.0 ^2.6] dec-3,8-diene (dicyclopentadiene), tetracyclododecene, and derivatives thereof.

Among these unsaturated condensed alicyclic compounds, norbornene and norbornene derivatives are preferable from the viewpoint of supplying raw materials. Moreover, these unsaturated condensed alicyclic compounds can be ring-opening-polymerized individually or in a mixture of two or more kinds.

As the ring-opening polymer of the unsaturated condensed alicyclic compound, polynorbornene or the like is preferably used, and particularly polynorbornene having a high weight average molecular weight is preferably used from the viewpoint of dispersibility.

By using these rubbers, preferably together with the above-mentioned ultra-high molecular weight polyolefin, especially ultra-high molecular weight polyethylene, the shape and mechanical strength of the porous film can be maintained even in a high temperature region, and the present invention is further provided. The heat resistance can be improved by cross-linking treatment by ultraviolet irradiation, which is one of the features of the manufacturing method of, for example, when the separator is exposed to high temperature and high pressure in a battery using the porous film as a battery separator. Since the positive electrode and the negative electrode can be kept separated from each other, the safety of such a battery is improved.

The amount of the rubber compounded is preferably 1 to 50% by weight in the resin component of the resin composition, and 1 to 20% by weight.
Weight percent is more preferred. The blending amount is preferably 1% by weight or more from the viewpoint of improving the crosslink density contributing to heat resistance, and is preferably 50% by weight or less from the viewpoint of maintaining / improving the strength and air permeability of the resulting porous film.

Further, other resins which can be crosslinked with the above rubbers may be optionally used as a resin component. Examples of such resins include ethylene-acrylic monomer copolymers, modified polyolefins such as ethylene-vinyl acetate copolymers, polystyrene-based, polyolefin-based, polydiene-based, vinyl chloride-based, thermoplastic elastomers such as polyester-based, For example, high / medium / low density polyethylene, polypropylene, copolymers thereof and the like can be mentioned.

These resins can be used alone or in admixture of two or more. The blending amount thereof is preferably 5 to 50% by weight in the resin component of the resin composition, and is 10 to 4%.
0% by weight is more preferred.

As the solvent, those having excellent solubility of the above-mentioned polyolefin and rubber having a crosslinkable unsaturated bond and thermoplastic elastomer are preferable, and examples thereof include nonane, decane, undecane, dodecane, decalin and liquid paraffin. Aliphatic or cyclic hydrocarbons such as, mineral oil fractions having a boiling point corresponding to these,
A non-volatile solvent containing a large amount of alicyclic hydrocarbon such as liquid paraffin is preferable. Further, as the compounding amount of the solvent, kneading torque, rolling, stretching stress is appropriate and excellent in productivity, and neck-in at the die exit when forming into a sheet can be favorably molded without causing a problem, and is appropriate. From the viewpoint that a porous film in which micropores having a uniform pore size are formed can be obtained, the resin composition in the resin composition is preferably 5 to
30 parts by weight and 70 to 95 parts by weight of solvent, more preferably 10 to 30 parts by weight of resin component and 70 to 90 parts by weight of solvent, still more preferably 10 to 25 parts by weight of resin component and 75 to 9 parts of solvent.
0 parts by weight.

Further, if desired, additives such as an antioxidant, an ultraviolet absorber, a dye, a nucleating agent, a pigment, an antistatic agent, etc. are added to the resin composition within a range not impairing the object of the present invention. be able to.

The resin composition composed of the resin component and the solvent is prepared, for example, by mixing in a uniform slurry form. Subsequently, the resin composition is melt-kneaded and molded into a sheet, and such a step may be performed according to a known method, using a Banbury mixer, a kneader or the like, under an appropriate temperature condition, preferably 100. It may be kneaded in batch at ~ 200 ° C, then sandwiched in a cooled metal plate or roll and rapidly cooled to form a sheet-like molded product by rapid crystallization. An extruder equipped with a T-die or the like may be used. You may obtain a sheet-shaped molded article. The thickness of the sheet-shaped molded product thus obtained is not particularly limited, but is preferably 3 to 20 mm.

The method for stretching the sheet-shaped molded product is not particularly limited, and may be an ordinary tenter method, roll method, inflation method or a combination of these methods, and uniaxial stretching. Any method such as biaxial stretching can be applied. In the case of biaxial stretching, either longitudinal / transverse simultaneous stretching or sequential stretching may be used, but longitudinal / transverse simultaneous stretching is preferred. The temperature of the stretching treatment is preferably 100 to 150 ° C, more preferably 11
It is 5 to 130 ° C.

The thickness of the sheet before stretching is preferably 0.
2 to 1.2 mm, more preferably 0.2 to 0.8 mm, and the thickness after stretching is preferably 50 to 150 μm,
More preferably, it is 60 to 100 μm. The stretching speed is preferably 5 mm / sec or less, more preferably 3 mm / sec or less.
It is not more than mm / sec, and it is preferable if it is within such a range, because breakage of stretching does not occur during stretching.

The desolvation treatment is a step of removing the solvent from the sheet-shaped molded product to form a microporous structure.
It can be carried out by washing the sheet-shaped molded product with a solvent to remove the residual solvent. Examples of the solvent include hydrocarbons such as pentane, hexane, heptane and decane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoroethane, ethers such as diethyl ether and dioxane. Volatile solvents,
These may be used alone or in combination of two or more. The cleaning method using such a solvent is not particularly limited, and examples thereof include a method of immersing the sheet-shaped molded product in the solvent to extract the solvent, and a method of showering the solvent on the sheet-shaped molded product. The solvent removal treatment may be performed before stretching. For example, the sheet composition may be subjected to desolvation treatment and then subjected to a stretching treatment, or may be subjected to desolvation treatment before the stretching treatment and then subjected to the desolvation treatment again after the stretching treatment.

In the present invention, rolling treatment may be further performed before and after the stretching and desolvation treatment. For example, the sheet-shaped molded product is directly subjected to rolling treatment, followed by stretching treatment and desolvation treatment (either stretching or desolvation may be performed first).
You may go. Alternatively, the rolling treatment may be performed between the stretching treatment and the desolvation treatment, for example, the desolvation treatment is performed before the rolling treatment, and the stretching treatment and the desolvation treatment are performed again after the rolling treatment (the order of stretching and desolvation is May be performed first) to remove the residual solvent.

Such rolling treatment is carried out by heat pressing or the like, preferably 100 ° C. or higher, more preferably 100 to
While heating at 140 ° C., the sheet-shaped molded product before rolling is molded to a thickness of 1/5 to 1/20 of the thickness.

After the above resin component is formed into a film by these known methods, the obtained film is preferably irradiated with ultraviolet rays. The ultraviolet irradiation is preferably ultraviolet light having substantially no wavelength distribution of 200 nm or less, and more preferably 250 n from the viewpoint of maintaining sufficient film strength.
0.5 μm of ultraviolet light having substantially no wavelength distribution below m
It is performed by irradiating the film obtained after the film formation for about 20 minutes. By such ultraviolet irradiation, all or part of the double bond derived from the resin having crosslinkability disappears,
Crosslinking occurs between the resins or between the resin and the polyolefin in the obtained porous film, and the heat resistance (film rupture resistance under high temperature and high pressure) of the porous film is maintained and improved. Further, in the present invention, irradiation with ultraviolet rays improves porosity and air permeability at the same time as improving heat resistance. Conventionally, the improvement of the porosity and air permeability of the porous film has been performed by appropriately adjusting the raw material resin, etc., and when high porosity and air permeability are desired, the usable raw material resin is limited. As a result, the strength of the porous film may have to be sacrificed.
However, in the present invention, a film having sufficient strength is first obtained, and then ultraviolet rays are irradiated to obtain a porosity.
Since the air permeability is improved, an excellent porous film having sufficient strength and further improved porosity and air permeability can be obtained.

The cross-linking treatment may be carried out, for example, on the film after film formation as it is or by impregnating it with a methanol solution containing a polymerization initiator and drying methanol as a solvent.
Irradiate with ultraviolet rays using a low pressure mercury lamp or a high pressure mercury lamp. From the viewpoint of maintaining sufficient film strength, it is preferable to use the above-mentioned mercury lamp that emits ultraviolet rays having substantially no wavelength distribution of 250 nm or less for the irradiation of ultraviolet rays.

Further, the porous film obtained may be heat-set (heat-fixed) from the viewpoint of preventing heat shrinkage subsequent to the crosslinking treatment step. The temperature for heat setting is, for example, 110 to 140 ° C., and the temperature may be set for about 0.5 to 2 hours.

The thickness of the porous film obtained as described above is preferably 10 to 50 μm, more preferably 15 to 40 μm. Within this range,
A battery using a battery separator made of the porous film has good performance and is preferable. The air permeability thereof is preferably 800 seconds / 100 cc or less, more preferably 750 seconds / 100 cc or less. Also, preferably 100 seconds / 100 cc or more, more preferably 1
50 seconds / 100 cc or more. When the air permeability is within the above range, the permeability of the electrolytic solution and the liquid retaining property are good, and the electric resistance is appropriate, and a good battery can be assembled by using such a porous film as a separator. The porosity is preferably 30 to 70% and 3
5 to 50% is more preferable. When the porosity is within the above range, the micropore distribution is appropriate, and further, the short circuit of the battery can be suppressed even in the overcharged state. Puncture strength is 3N /
It is preferably 25 μm or more, more preferably 4 N / 25 μm or more. When the puncture strength is within the above range, the film has sufficient strength without rupturing. Further, the gel fraction is preferably 5 from the viewpoint of obtaining sufficient mechanical strength.
0 to 90%. Various properties of these porous films can be measured by the methods described in Examples below.

The porous film of the present invention has high film properties and high heat resistance to the extent that its shape can be maintained even under high temperature and high pressure conditions, and is particularly suitable as a separator for lithium ion secondary batteries. Can also be used for capacitor separator, oil absorption sheet,
It can also be applied as a filter.

The battery of the present invention may be any one using the above-mentioned porous film as a separator, and its structure, constituent materials, manufacturing method and the like may be the same as those of known batteries and are not particularly limited. The battery is excellent in safety because it uses the porous film of the present invention as a separator. Also, a capacitor can be obtained by using the porous film as a separator. This capacitor can be manufactured in the same manner as a known capacitor and is excellent in safety.

[0037]

EXAMPLES The present invention will be described in more detail based on examples, but the present invention is not limited to such examples. The various characteristics of the porous films obtained in each of the examples and comparative examples were measured according to the following procedures.

(1) Weight average molecular weight Gel permeation chromatograph "GPC-" manufactured by Waters
150C ", o-dichlorobenzene was used as a solvent, and a column" SHODEX- "manufactured by Showa Denko KK was used as a column.
80M "at 135 ° C. Data processing is
The data processing system manufactured by TRC was used. Also,
The molecular weight was calculated based on polystyrene.

(2) Film thickness 1/10000 The film thickness (μ
m) was measured.

(3) Porosity The porous film to be measured was cut out into a circular shape having a diameter of 6 cm, the volume and weight thereof were determined, and the volume and weight were calculated using the following formula. Porosity (vol%) = 100 × [volume (cm ³⁾ - Weight (g) / porous average density of the resin component of the film (g / cm ^3)] / volume (cm ³⁾

(4) Air permeability (Gurley value) In accordance with JIS P8117, air permeability (second / 100c)
c) was measured.

(5) Puncture test A puncture test was performed using a compression tester "KES-G5" manufactured by Kato Tech Co., Ltd. The maximum load was read from the obtained load change curve and defined as the puncture strength (N). A needle having a diameter of 0.75 mm and a tip radius of curvature of 0.5 mm was used, and the speed was 2 cm / sec. All values are thickness 2
It was converted to 5 μm.

(6) Shrinkage rate The film cut into a circle with a diameter of 6 cm was read at 144 dpi with an image scanner, and the area was converted into the number of pixels to obtain a blank value. Next, the film was kept in a thermostatic dryer at 105 ° C. for 1 hour, taken out and read by an image scanner at 144 dpi, and the area was converted into the number of pixels to obtain a value after heat treatment. From the number of area pixels after blanking and heat treatment, R ₁ (shrinkage rate) (%) was calculated by the following formula. R ₁ = 100 × (P ₀ −P ₁ ) / P ₀ (P ₀ : number of pixels before heat shrink, P ₁ : number of pixels after heat shrink)

(7) Gel fraction Porous film was cut into 4 cm × 4 cm squares and cut into 5 cm
The sample was sandwiched between metal meshes of 5 cm x 5 cm to form a 5 cm x 5 cm square sample. Measure the initial weight of this sample,
The gel fraction R ₂ (%) was measured from the weight change by immersing in 100 ml of m-xylene (boiling point 139 ° C.), raising the temperature, boiling the xylene for 3 hours, taking out, washing and drying. R ₂ (%) = 100 × P1 / P0 [P0: initial weight (g), P1: weight after boiling xylene treatment (g)]

(8) Heat resistance A strip-shaped porous film having a width of 3 mm is provided between chucks 10 times.
mm, and set in a thermal stress strain analyzer TMA / SS100 manufactured by Seiko Denshi, and a heating rate of 2 ° C / m
The temperature was raised in. The temperature at which the strip-shaped porous film broke was defined as the heat-resistant rupture temperature (° C) as an index of heat resistance.

Example 1 85 parts by weight of liquid paraffin and ultrahigh molecular weight polyethylene (trade name: Hizex Milli, manufactured by Mitsui Chemicals, Inc.)
on 240S, melting point 136 ° C, weight average molecular weight 2 × 1
0 ⁶ ) 70% by weight, polynorbornene rubber (norbornene ring-opening polymer powder, manufactured by Nippon Zeon Co., Ltd., trade name: Nosolex NB, weight average molecular weight 2 × 10 ⁶ or more) 8% by weight, polyolefin thermoplastic elastomer TPE8
21 (Sumitomo Chemical Co., Ltd., trade name: TPE821, polyethylene / polypropylene copolymer) 15 parts by weight of a mixture of 22% by weight, and a twin-screw extruder (Toshiba Machinery, TE
M-35B) at 160 ° C., extruded with a fish tail die, then passed through a sizing die and rapidly cooled to dry ice temperature (−30 ° C.) to a thickness of about 8 m.
A gel-like molded product of m was produced. 1 with a heating press
After preheating at 15 ° C. for 5 minutes, the spacer was pressed with a spacer thickness of 9 mm, held for 3 minutes, and then inserted into a press machine cooled to a water temperature and rapidly cooled to obtain a gel sheet having a thickness of about 110 mm. This sheet is batch type simultaneous biaxial stretching machine (Iwamoto Seisakusho, BI
X-712-S) was preheated at 127 ° C. and then stretched by about 3.2 × 3.2 times to obtain a gel film having a thickness of about 90 μm. The stretching speed was set to 4 mm / sec. The obtained gel film was fixed to a square SUS frame,
The solvent was extracted with n-heptane in the bath, and the heptane was dried at room temperature to obtain a porous film. Then, while being fixed to the SUS frame, a conveyor-type high-pressure mercury lamp irradiation device capable of generating ultraviolet rays having substantially no wavelength distribution of 200 nm or less (manufactured by Eye Graphics Co., UE021-2
UV irradiation for 15 minutes at 03C, output 2 kW, conveyor speed 3 m / min), and then put into the dryer as it is, and heat set treatment is performed sequentially at 85 ° C. for 12 hours and 117 ° C. for 2 hours. A porous film having a thickness of 24 μm, a porosity of 40%, an air permeability of 470 seconds / 100 cc, a puncture strength of 6 N / 25 μm, a shrinkage rate of 13%, a gel fraction of 72%, and a heat-resistant rupture temperature of 200 ° C. or higher was obtained.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the ultraviolet irradiation was not carried out, and the thickness was 24 μm, the porosity was 35%, the air permeability was 670 seconds / 100 cc, the puncture strength was 6.5 N / 25 μm, and the shrinkage rate was 12. %, A gel fraction of 75%, and a heat-resistant breaking temperature of 200 ° C. or higher were obtained.

Example 2 In Example 1, a mixture of 88% by weight of ultrahigh molecular weight polyethylene and 12% by weight of polynorbornene rubber was used, the temperature during stretching was 125 ° C., the stretching speed was 2 mm /
Seconds, UV irradiation time 10 minutes, heat set treatment 8
Same procedure as above, except that the procedure was performed at 5 ° C. for 12 hours and at 130 ° C. for 2 hours, the thickness was 23 μm, the porosity was 33%, and the air permeability was 650.
A porous film having a second / 100 cc, a puncture strength of 7 N / 25 μm, a shrinkage rate of 3%, a gel fraction of 80% and a heat-resistant rupture temperature of 240 ° C. or higher was obtained.

Comparative Example 2 The same procedure as in Example 2 was carried out except that the ultraviolet ray irradiation was not performed, and the thickness was 23 μm, the porosity was 30%, the air permeability was 880 seconds / 100 cc, the puncture strength was 7.5 N / 25 μm, and the shrinkage rate was 3. %, A gel fraction of 78% and a heat-resistant breaking temperature of 240 ° C. or higher were obtained.

Example 3 85 parts by weight of liquid paraffin and ultrahigh molecular weight polyethylene (manufactured by Mitsui Chemicals, Inc., trade name: Hizex Milli)
on 240S, melting point 136 ° C, weight average molecular weight 2 × 1
0 ⁶ ) 70% by weight, polynorbornene rubber (norbornene ring-opening polymer powder, manufactured by Nippon Zeon Co., Ltd., trade name: Nosolex NB, weight average molecular weight 2 × 10 ⁶ or more) 8% by weight, polyolefin-based thermoplastic elastomer TPE8
21 (Sumitomo Chemical Co., Ltd., trade name: TPE821, polyethylene / polypropylene copolymer) 15 parts by weight of a mixture of 22% by weight, and a twin-screw extruder (Toshiba Machinery, TE
M-35B) was kneaded at 160 ° C., extruded with a fish tail die, and then rapidly cooled to a dry ice temperature through a sizing die to prepare a gel-like molded product having a thickness of about 8 mm. This is heated at 115 ° C for 5 minutes with a heating press
After preheating for a minute, it was pressed with a spacer thickness of 9 mm, held for 3 minutes, and then inserted into a press machine cooled to a water temperature and rapidly cooled to obtain a gel sheet having a thickness of about 110 mm. This sheet is batch-type simultaneous biaxial stretching machine (manufactured by Iwamoto Seisakusho, BIX-712-
S) after preheating at 127 ° C., approximately 3.2 × 3.
The film was stretched 2 times to obtain a gel film having a thickness of about 90 μm. The stretching speed was set to 4 mm / sec. The obtained gel film was fixed on a square SUS frame, the solvent was extracted with n-heptane in 3 baths, and the heptane was dried at room temperature to obtain a porous film. Next, while being fixed to the SUS frame, a conveyor type high-pressure mercury lamp irradiation device capable of generating ultraviolet rays having substantially no wavelength distribution of 250 nm or less (manufactured by Eye Graphics Co., UE021-203C, output 2 kW, conveyor UV irradiation for 15 minutes at a speed of 3 m / min), then put it into the dryer as it is,
Heat setting treatment was sequentially performed at 85 ° C. for 12 hours and 117 ° C. for 2 hours to finally obtain a thickness of 24 μm and a porosity of 39%.
Air permeability 480 seconds / 100cc, puncture strength 6.5N /
A porous film having a thickness of 25 μm, a shrinkage rate of 12%, a gel fraction of 74% and a heat-resistant rupture temperature of 200 ° C. or higher was obtained.

Example 4 The same as Example 3 except that the ultraviolet irradiation was carried out for 15 minutes with a conveyor type high pressure mercury lamp irradiation device capable of generating ultraviolet having substantially no wavelength distribution of 200 nm or less. , Thickness 24μm, porosity 40%, air permeability 47
A porous film having 0 second / 100 cc, a puncture strength of 6 N / 25 μm, a shrinkage rate of 13%, a gel fraction of 72%, and a heat-resistant rupture temperature of 200 ° C. or higher was obtained.

Comparative Example 3 The procedure of Example 3 was repeated except that the ultraviolet irradiation was not performed, and the thickness was 24 μm, the porosity was 35%, the air permeability was 670 seconds / 100 cc, the puncture strength was 6.5 N / 25 μm, and the shrinkage rate was 12. %, A gel fraction of 75%, and a heat-resistant breaking temperature of 200 ° C. or higher were obtained.

Example 5 In Example 3, a mixture of 88% by weight of ultra high molecular weight polyethylene and 12% by weight of polynorbornene rubber was used, the temperature during stretching was 125 ° C., the stretching speed was 2 mm /
Second, UV irradiation time by a conveyor type high pressure mercury lamp irradiation device capable of generating UV light having substantially no wavelength distribution of 250 nm or less is 10 minutes, heat setting treatment is 85 ° C. for 12 hours, 130 ° C. for 2 hours. The procedure is the same as above, except that the thickness is 23 μm, the porosity is 33%, and the air permeability is 68.
0 seconds / 100 cc, puncture strength 7.5 N / 25 μm,
A porous film having a shrinkage ratio of 3%, a gel fraction of 81% and a heat-resistant breaking temperature of 240 ° C. or higher was obtained.

Example 6 The same procedure as in Example 3 was carried out except that ultraviolet irradiation was carried out for 10 minutes with a conveyor type high pressure mercury lamp irradiation device capable of generating ultraviolet rays having substantially no wavelength distribution of 200 nm or less. , Thickness 23μm, porosity 33%, air permeability 65
A porous film having 0 second / 100 cc, a puncture strength of 7 N / 25 μm, a shrinkage rate of 3%, a gel fraction of 80%, and a heat-resistant rupture temperature of 240 ° C. or higher was obtained.

Comparative Example 4 The same procedure as in Example 5 was carried out except that the ultraviolet ray irradiation was not performed, and the thickness was 23 μm, the porosity was 30%, the air permeability was 880 seconds / 100 cc, the puncture strength was 7.5 N / 25 μm, and the shrinkage rate was 3. %, A gel fraction of 78% and a heat-resistant breaking temperature of 240 ° C. or higher were obtained.

[0056]

[Table 1]

From the results shown in Table 1, the porous films of Examples 1 to 6 obtained by irradiating with ultraviolet rays were manufactured without irradiating with ultraviolet rays, and Comparative Examples 1 to 4 corresponding to the respective examples.
The heat resistance and strength are maintained, while the porosity and air permeability are improved as compared with the porous film of No. Also,
From the comparison between Examples 3 and 4 and Examples 5 and 6, it can be seen that the porous film obtained by irradiating with ultraviolet rays having no wavelength distribution of 250 nm or less does not cause reduction in strength.

[0058]

EFFECTS OF THE INVENTION According to the present invention, it is possible and possible to produce a porous film made of a crosslinked polymer, which has improved porosity, air permeability, and good mechanical strength and shrinkage. It is possible to produce a battery or capacitor having good desired characteristics by using the porous film as a battery separator, under abnormal conditions,
The shape and mechanical strength of the separator can be maintained even when exposed to high temperature in the battery, and the state in which the positive electrode and the negative electrode are separated can be maintained, so that the safety of the battery or the capacitor can be improved.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazunari Yamamoto             1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko             Within the corporation (72) Inventor Shunsuke Nomi             1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko             Within the corporation (72) Inventor Mutsuko Yamaguchi             1-1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko             Within the corporation F-term (reference) 4F074 AA16 AA17 AA54 AA98 AD01                       AG20 AH01 BB25 CB03 CB16                       CB28 CC02 CC45 CC50 DA49                 5H021 BB01 BB04 BB05 BB13 BB15                       CC00 EE02 EE04 HH03

Claims (8)

[Claims] 1. A melt-kneaded resin composition containing a resin component containing a polyolefin and a rubber having a crosslinkable unsaturated bond and a solvent, and molding the obtained melt-kneaded product into a sheet, A method for producing a porous film, which comprises a step of irradiating ultraviolet rays in a method of producing a porous film, which comprises the steps of stretching and desolvating a molded product. 2. The method for producing a porous film according to claim 1, wherein the ultraviolet rays have substantially no wavelength distribution below 250 nm. 3. The method for producing a porous film according to claim 1, wherein the polyolefin is ultra-high molecular weight polyethylene. 4. The method for producing a porous film according to claim 1, wherein the rubber having a crosslinkable unsaturated bond is polynorbornene. 5. A porous film obtainable by the method for producing a porous film according to claim 1. 6. A battery separator comprising the porous film according to claim 5. 7. A battery using the battery separator according to claim 6. 8. A capacitor comprising the battery separator according to claim 6.