JP2001214366A - Nonwoven fabric and method for producing the same, separator using the nonwoven fabric and used for secondary battery and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonwoven fabric to which hydrophility is imparted and which can stably be treated in a simple process and is also suitable for high speed continuation, to provide a method for producing the same, to provide a separator which has an excellent electrolyte-retaining property, uses the nonwoven fabric and is used for a secondary battery, and to provide a method for producing the same. SOLUTION: This nonwoven fabric which has >=3 atom % of carboxyl groups measured by X-ray photoelectron spectroscopy in the bond forms of the carbon components on the surface of the substrate of the nonwoven fabric, the nonwoven fabric which has >=1 atom % of fluorine atoms and >=10 atom % of oxygen atoms in the bond forms of the carbon components on the surface of the substrate of the nonwoven fabric, the separator which uses a polyolefin- based nonwoven fabric and is used for a secondary battery, and the method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonwoven fabric and a method for producing the same, and a separator for a secondary battery using the nonwoven fabric and a method for producing the same. More particularly, the present invention is suitably used for a secondary battery using an alkaline electrolyte. The present invention relates to a nonwoven fabric, a separator and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a surface treatment of textile products, improvements in water absorption, water repellency, antistatic properties, antifouling properties, dyeing properties, etc. have been carried out, such as immersion in a chemical, heat treatment in a specific atmosphere. Has been put to practical use. However, for example, a woven cloth having ultra-fine pores has a problem that pores are blocked by a conventional method of dipping in an alkaline solution or the like, and the processing step is complicated, and a function that can be provided is provided. There were also problems such as restrictions.

[0003] For this reason, Japanese Patent Application Laid-Open No. 6-57660 discloses a method of improving cotton dyeing properties by high-frequency plasma treatment at 13.56 MHz in an oxygen atmosphere of 1 Torr. According to this method, the processing can be freely performed in a simple process, and furthermore, since the processing is performed using gas, the problem that the micropores are blocked as described above can be solved. However, low-pressure processing is disadvantageous in terms of continuous processing because it has an exhaust device, and has a problem that processing becomes difficult due to the presence of volatile substances such as water and a plasticizer.

[0004] For this reason, attempts have been made to generate discharge plasma at a pressure close to the atmospheric pressure. For example, Japanese Patent Application Laid-Open No. H7-119021 discloses a method in which a device having a cylindrical electrode covered with ceramic is used. A method for treating textile products under a mixed atmosphere of argon and argon is disclosed.

On the other hand, lightweight and high energy density alkaline secondary batteries have been frequently used in portable electronic devices such as mobile phones and notebook computers. When these batteries are divided into components, most batteries are composed of a positive electrode, a negative electrode, an electrolytic solution, a separator, a container, and the like. Of these, the electrode plays a large role in improving the battery characteristics, and of course, the improvement of the positive electrode and the negative electrode is necessary, but the role of the separator cannot be overlooked. .

[0006] The important role of the separator in the battery is to firstly separate the positive electrode and the negative electrode to prevent an electric short circuit, and secondly to prevent the passage of ions in the electrolyte. is there. In particular, an alkaline battery must be a material having alkali resistance since the electrolyte is a strong alkali.

Conventionally, nonwoven fabrics and woven fabrics made of polyamide having both alkali resistance and hydrophilicity have been often used. Polyamide has alkali resistance at room temperature, but has high alkali resistance at high temperatures or for a long period of time. In particular, alkaline secondary batteries that are repeatedly used for a long period of time after repeated charging and discharging are liable to cause short-circuits due to a decrease in strength, and measures have been required.

[0008] Therefore, utilization of nonwoven fabrics and woven fabrics made of a polyolefin resin having a higher alkali resistance than polyamide, particularly polyethylene or polypropylene resin, has been studied. Separators made of these materials are
The strength does not decrease even when used at a high temperature or when used for a long period of time, and it can be said that it is preferable as a separator for extending the life of the battery.

[0009]

However, the separator made of polyethylene or polypropylene has a problem that the affinity for the alkaline electrolyte is extremely poor and the retention of the alkaline electrolyte is also poor. In order to overcome such a problem and to use it as a separator,
A method of introducing a sulfone group into a polyolefin resin as disclosed in JP-A-101323 or JP-A-63-503074 and JP-A-6-50575.
Various treatment methods such as a method of graft-polymerizing a vinyl monomer by UV irradiation as disclosed in Japanese Patent Publication No. 6 have been proposed, but at present, they are not always sufficient.

Further, in the method described in Japanese Patent Application Laid-Open No. H7-119021, which is a method for treating textile products, the plasma generation region is limited to a narrow range due to insufficient discharge stability. There are problems such as difficulty in increasing the processing speed. Furthermore, in the case of a substrate having a non-smooth surface such as a textile product, the discharge tends to be particularly streamer-like,
It is easy to damage the substrate. For this reason, the treatment atmosphere is limited, and the amount of reactive gas for imparting functions must be reduced to a very small amount, which limits the application range.

In particular, the nonwoven fabric substrate has a drawback that the discharge tends to be unstable due to its structure having irregularities on the surface.

Therefore, the present invention solves the above problems, provides a nonwoven fabric with hydrophilicity, can be stably processed by a simple process, and is suitable for high-speed continuous processing. An object of the present invention is to provide a separator for a secondary battery using the nonwoven fabric, which is excellent in the liquid retaining property of an electrolytic solution, and a method for manufacturing the same.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the hydrophilicity is imparted by performing a specific atmospheric pressure plasma treatment under specific conditions and in the presence of a specific gas. The present inventors have found that a nonwoven fabric suitable for a battery separator can be obtained from the nonwoven fabric thus obtained, and completed the present invention.

That is, the first invention of the present invention (Claim 1)
The present invention provides a nonwoven fabric characterized in that carboxyl groups occupy 3 atom% or more in the bonding form of the carbon component on the surface of the nonwoven fabric substrate measured by X-ray photoelectron spectroscopy.

The second invention of the present invention (the invention according to claim 2) is characterized in that, in the bonding form of the carbon component on the surface of the nonwoven fabric substrate measured by X-ray photoelectron spectroscopy, fluorine atoms are 1 atomic% or more. Further, the present invention provides a nonwoven fabric characterized in that oxygen atoms are 10 atomic% or more.

The third invention of the present invention (the invention according to claim 3) provides at least one of a carbon atom, an oxygen atom and a fluorine atom as an element component of a gas used for treating the surface of the nonwoven fabric. A method for producing a nonwoven fabric characterized by performing a normal pressure plasma treatment using a gas containing

The fourth invention (the invention described in claim 4) according to the present invention is characterized in that CO _X (X = 1 or 2),
A method for producing a nonwoven fabric according to the third invention, wherein at least one of O _Y (Y = 2 or 3) and a fluorine-containing gas is used.

The fifth invention of the present invention (the invention according to claim 5) provides a gas used for treating the surface of a nonwoven fabric as a monomer gas having a hydrophilic group and a polymerizable unsaturated bond in a molecule. And a normal pressure plasma treatment using at least one of sulfur and a sulfur-containing gas.

A sixth invention of the present invention (the invention according to claim 6) is characterized in that a rare gas or nitrogen gas is further contained in a gas atmosphere at the time of performing a normal pressure plasma treatment. A method for producing a nonwoven fabric according to any one of the third to fifth aspects of the present invention.

According to a seventh aspect of the present invention (an invention according to claim 7), the normal-pressure plasma processing comprises a pair of electrodes facing each other, and one or both electrodes have a solid dielectric material. The counter electrode coated with the body is disposed under the atmospheric pressure of the processing gas atmosphere, and the polyolefin-based nonwoven fabric substrate is disposed between the counter electrodes. The nonwoven fabric according to any one of claims 3 to 6, wherein a pulse voltage having a pulse duration of 1 to 50 µs, a frequency of 1 to 50 kHz, and an electric field strength of 50 to 100 kV / cm is applied. A manufacturing method is provided.

According to an eighth aspect of the present invention, there is provided a nonwoven fabric used as a separator for a secondary battery, wherein the nonwoven fabric according to the first or second aspect is a polyolefin-based nonwoven fabric. A secondary battery separator is provided.

In a ninth aspect of the present invention, the nonwoven fabric used in the method for producing a nonwoven fabric according to any one of the third to seventh aspects is a polyolefin-based nonwoven fabric. And a method for producing a separator for a secondary battery.

The tenth invention of the present invention (Claim 10)
The present invention is a separator used for an alkaline secondary battery, which is formed using a polyolefin-based nonwoven fabric as a base material, and has a hydrophilic group and a polymerizable unsaturated bond in a molecule vaporized as a surface treatment gas of the polyolefin-based nonwoven fabric. A secondary battery separator characterized in that the separator has been hydrophilized by a discharge plasma treatment performed at about the atmospheric pressure of a gas atmosphere containing a monomer having the following formula:

The eleventh invention of the present invention (claim 11)
The present invention provides the method for producing a separator for an alkaline secondary battery according to the tenth invention, wherein the surface substrate of the polyolefin-based nonwoven fabric is subjected to discharge plasma treatment at about atmospheric pressure.

The twelfth invention of the present invention (Claim 12)
The described invention) comprises a pair of electrodes opposed to each other, one or both of the electrodes facing each other being coated with a solid dielectric, to form a hydrophilic group and a polymerizable unsaturated bond in the molecule. A gas mixture containing at least two of a monomer gas, a carbon-containing gas, and an oxygen-containing gas, which is disposed under atmospheric pressure, and a polyolefin-based nonwoven fabric substrate is disposed between the counter electrodes, and a pulse is applied between the counter electrodes. Rise time 20 μs or less, pulse duration 1
５０50 μs, frequency 1-20 kHz, electric field strength 50
The method for producing a separator for a secondary battery according to the tenth or eleventh aspect, wherein an atmospheric pressure discharge plasma treatment is performed on the polyolefin-based nonwoven fabric substrate by applying a pulse voltage of １００100 kV / cm. I do.

The thirteenth invention of the present invention (Claim 13)
The described invention) comprises a pair of electrodes opposed to each other, one or both electrodes of which are opposed to each other and the opposite surface of which is covered with a solid dielectric, is provided with a hydrophilic group and a polymerizable unsaturated bond in the molecule. Is arranged under the atmospheric pressure of a mixed gas atmosphere containing at least one of a monomer gas having at least one of sulfur-containing gases, and a pulse rising time between the opposed electrodes in a state where the polyolefin nonwoven fabric base material is arranged between the opposed electrodes. 20 μs or less, pulse duration 1-50 μs, frequency 1-20 kHz, electric field strength 50-100 kV / c
The method for producing a separator for a secondary battery according to the tenth or eleventh aspect, wherein an atmospheric pressure discharge plasma treatment is performed on the polyolefin-based nonwoven fabric substrate by applying a pulse voltage of m.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The fibers constituting the nonwoven fabric substrate in the present invention include natural fibers such as plant fibers, animal fibers, and mineral fibers; inorganic fibers,
Examples include artificial fibers such as regenerated artificial fibers, semi-synthetic fibers, and synthetic fibers, and composite materials thereof. Among them, synthetic fibers are preferable.

Examples of the synthetic fibers include polycondensed synthetic fibers such as polyamide, polyester, polyurethane, and polyurea; polyolefin, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyfluoroethylene, and the like. Highly polymerizable synthetic fibers such as polyacrylonitrile, polyvinyl alcohol, and polyvinylidene cyanide can be used. Among them, polyolefin-based synthetic fibers are preferable.

The polyolefin-based synthetic fibers include:
Examples include synthetic fibers such as polyethylene and polypropylene. Further, it may be a porous film obtained by stretching a polyolefin film.

In the present invention, as the nonwoven fabric used for the secondary battery separator, a polyolefin-based nonwoven fabric is preferably used.

The above-mentioned polyolefin-based nonwoven fabric is formed by short-fiber nonwoven fabric by carding method, air lay method, wet method, etc., spun-bonded nonwoven fabric by spun bond method, flash spinning method, melt blow method or the like, or a combination thereof. However, the forming method is not particularly limited, and for example, a method described in Basics and Applications of Nonwoven Fabrics (Japan Textile Machinery Society; issued on August 25, 1993) can be adopted.

For use as a separator in the polyolefin nonwoven fabric formed by the above method, the average fiber diameter is preferably 0.1 to 25 μm. 0.1 μm
If it is less than 25 μm, the strength of the nonwoven fabric is weak, and if it exceeds 25 μm, the number of fibers is reduced, and the variation in quality such as the basis weight tends to increase, which is not preferable.

The nonwoven sheet may be formed into a sheet by a method such as heat fusion with a binder fiber, water entanglement such as water jet, or application of an organic resin binder, but is not particularly limited.

In the present invention, the amounts of carbon atoms, oxygen atoms, fluorine atoms and carboxyl groups present on the surface of the nonwoven fabric can be measured and quantified by X-ray photoelectron spectroscopy.

The nonwoven fabric according to the first invention of the present invention is a nonwoven fabric having a carboxyl group present on the surface of the nonwoven fabric substrate. It accounts for 3 atomic% or more. If the carboxyl content is too small, hydrophilicity cannot be imparted to the nonwoven fabric.
It is limited to at least atomic%, preferably at least 5 atomic%, more preferably at least 15 atomic%.

The nonwoven fabric according to the second aspect of the present invention is a nonwoven fabric having oxygen and fluorine atoms on the surface of the nonwoven fabric substrate, wherein the fluorine atoms are 1 atomic% or more, the oxygen atoms are 10 atomic% or more, On the other hand, if the number of atoms is too large, water repellency may be exhibited. On the other hand, if the number of oxygen atoms is too large, it becomes difficult to introduce oxygen atoms into the substrate surface.
Atomic% and oxygen atoms are preferably 10 to 40 atomic%, more preferably 2 to 10 atomic% of fluorine atoms. When the amount of fluorine atoms and oxygen atoms is too small, the surface of the base material is not sufficiently hydrophilized, and when the amount of oxygen atoms is too small, water repellency due to fluorine atoms may appear.

The nonwoven fabric of the present invention is obtained by treating the surface of the nonwoven fabric in the presence of a gas containing at least one of carbon, oxygen and fluorine atoms.

The compounds containing carbon and oxygen atoms in the present invention include carbon oxides such as carbon monoxide and carbon dioxide, alcohols such as methanol and ethanol,
Organic compounds containing an oxygen element such as ketones such as acetone and methyl ethyl ketone, and aldehydes such as formaldehyde and acetaldehyde are exemplified. These may be used alone or in combination of two or more.

Examples of the gas containing a carbon atom include alkane-based hydrocarbon gases such as ethane, propane, butane, pentane and hexane; ethylene, propylene, butene,
Alkene-based hydrocarbon gases such as butadiene and pentadiene; and alkyne-based hydrocarbon gases such as acetylene and methylacetylene. Further, a compound containing a carbon atom and an oxygen atom described above may be used.

Examples of the gas containing an oxygen atom include oxygen, air, ozone, water, carbon monoxide, carbon dioxide, nitrogen monoxide, nitrogen dioxide, alcohols such as methanol and ethanol, acetone, and methyl ethyl ketone. And organic compounds containing an oxygen element such as aldehydes such as methanal and ethanal.
These may be used alone or in combination of two or more.

As the ozone, for example, those generated from the above-mentioned oxygen gas by discharge using an ozone generator such as an ozonizer can be used.

Examples of the fluorine-containing organic fluorine-based gas include carbon tetrafluoride (CF ₄ ), carbon hexafluoride (C ₂ F ₆ ), and tetrafluoroethylene (CF ₂ CF ₂ ).
Fluorine-carbon compounds such as propylene hexafluoride (CF ₃ CFCF ₂ ) and cyclobutane octafluoride (C ₄ F ₈ ); methane difluoride (CH ₂ CF ₂ ), 1,1,1,4-fluoride Fluorinated hydrocarbon compounds such as ethane (CF ₃ CFH ₂ ) and 1,1,1-3 propylene propylene (CF ₃ CHCH ₂ ); carbon trifluoride (CCIF ₃ ), methane monochloride ( Halogen-carbon compounds such as CHClF ₂ ); fluorine-sulfur compounds such as sulfur hexafluoride (SF ₆ ); and fluorine-substituted products such as alcohols, organic acids and ketones. In particular, from the viewpoint of safety, it is preferable to use carbon tetrafluoride, carbon hexafluoride, propylene hexafluoride and cyclobutane octafluoride, which do not generate hydrogen fluoride which is a harmful gas. These may be used alone or in combination of two or more.

If the amount of the organic fluorine-based gas is too small, the effect of introducing the oxygen-containing functional group is small. If the amount is too large, a water-repellent action by the fluorine-containing functional group or a polymer thereof appears, making it difficult to hydrophilize the nonwoven fabric substrate. Therefore, it is preferable to add 0.1 to 50% by volume to the oxygen gas. Further, the fluorine element-containing compound may be added at 50% by volume or less of the oxygen element-containing compound. By doing so, the hydrophilization may be further promoted.

When the nonwoven fabric of the present invention is used as a separator for an alkaline secondary battery, a monomer having a hydrophilic group and a polymerizable unsaturated bond in a molecule is used as a processing gas.
A nonwoven fabric obtained by depositing a hydrophilic polymer film on the surface of the nonwoven fabric can be used. In particular, in oxidizing the surface of the nonwoven fabric, it is obtained by performing the treatment in an atmosphere of a monomer having a hydrophilic group and a polymerizable unsaturated bond in the molecule.

The hydrophilic group includes a hydrophilic group such as a hydroxyl group, a sulfonic acid group, a sulfonic acid group, a primary or secondary or tertiary amino group, an amide group, a quaternary ammonium base, a carboxylic acid group, and a carboxylic acid group. And the like. Further, even when a monomer having a polyethylene glycol chain is used, a hydrophilic polymer film can be similarly deposited.

The monomers having a hydrophilic group and a polymerizable unsaturated bond in the molecule include acrylic acid, methacrylic acid, acrylamide, methacrylamide, N, N-dimethylacrylamide, sodium acrylate, sodium methacrylate, acrylic acid Potassium, potassium methacrylate, sodium styrenesulfonate, allyl alcohol, allylamine, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate and the like can be mentioned. These monomers are used alone or as a mixture.

When the monomer having a hydrophilic group and a polymerizable unsaturated bond in the molecule is a solid, the monomer dissolved in a solvent is vaporized by means of heating, decompression, gas transport and the like and introduced into plasma. . Examples of the solvent include organic solvents such as methanol, ethanol, and acetone, water, and mixtures thereof. This is not the case when the monomer alone can be vaporized.

Further, as the gas for imparting hydrophilicity, a sulfur element-containing gas can be used. For example, sulfur dioxide, sulfur trioxide and the like can be mentioned. Further, sulfuric acid can be used after being vaporized. These may be used alone or in combination of two or more.

Each of the above compounds does not need to be a gas at normal temperature, but may be any gas which is vaporized during the treatment by heating or the like.

In order to use the nonwoven fabric of the present invention as a separator for a secondary battery using an alkaline electrolyte, the polyolefin-based nonwoven fabric needs to be subjected to a hydrophilic treatment. Atmospheric pressure in an atmosphere of a gas containing at least one of atoms, oxygen atoms and fluorine atoms, or an atmosphere of a mixed gas containing at least one of a monomer gas having a hydrophilic group and a polymerizable unsaturated bond and a sulfur-containing gas. In the vicinity, a method is used in which the surface of a polyolefin-based nonwoven fabric substrate is subjected to normal-pressure plasma treatment.

From the viewpoint of economy and safety, it is preferable to carry out the treatment in an atmosphere diluted with a diluent gas as described below, rather than in the atmosphere of the treatment gas alone. Examples of the diluent gas include rare gases such as helium, neon, argon, and xenon, and nitrogen gas. These may be used alone or in combination of two or more.

When a diluting gas is used, it is preferable that the ratio of the processing gas is 1 to 10% by volume. Alternatively, the plasma discharge may be performed in an atmosphere composed of the diluent gas to generate radicals on the surface, and then the radical may be brought into contact with the processing gas.

As an atmosphere gas, a compound having more electrons is more advantageous in increasing the plasma density and performing high-speed processing. Therefore, the most desirable choice in consideration of availability, economy and processing speed is argon and / or
Alternatively, the atmosphere contains nitrogen as a diluent gas.

Conventionally, at a pressure near the atmospheric pressure, the treatment has been carried out in an atmosphere in which helium is present in a large excess, but according to the method of the present invention, argon and nitrogen are less expensive than helium. Stable processing in gas is possible, and by performing processing in the presence of these gases having a large molecular weight and more electrons, a high-density plasma state can be realized and the processing speed can be increased. Therefore, it has great industrial advantages.

In the method for producing a nonwoven fabric according to the present invention, a solid dielectric is provided on at least one of the opposing surfaces of a counter electrode under a pressure close to the atmospheric pressure, and a solid dielectric is provided between the counter electrode and the solid dielectric. Place a nonwoven fabric substrate between each other, in a gas atmosphere containing carbon atoms and oxygen atoms as elemental components,
A pulse electric field is applied between the opposed electrodes.

In the present invention, the term "under pressure near the atmospheric pressure" refers to a pressure of 1.333 × 10 ^{4 to} 10.664 × 10 ⁴ Pa. Above all, the pressure is preferably in the range of 9.331 × 10 ^{4 to} 10.297 × 10 ⁴ Pa, which facilitates pressure adjustment and makes the apparatus simple.

In the present invention, a solid dielectric is provided on at least one counter electrode of the counter electrode. In this case, the portion where the plasma is generated is located between the solid dielectric and the electrode when one of the electrodes is provided with a solid dielectric, and the solid dielectric is provided when both the electrodes are provided with a solid dielectric. It is the space between each other. The treatment is performed by arranging a non-woven fabric which is an object to be processed between the solid dielectric and the electrode or between the solid dielectrics.

Examples of the above-mentioned electrodes include those composed of simple metals such as copper and aluminum, alloys such as stainless steel and brass, and intermetallic compounds. The counter electrode is
In order to avoid occurrence of arc discharge due to electric field concentration, it is preferable that the distance between the opposed electrodes is substantially constant. As the electrode structure satisfying this condition, a parallel plate type,
Examples thereof include a cylindrical opposed flat plate type, a spherical opposed flat plate type, a hyperboloid opposed flat plate type, and a coaxial cylindrical type structure.

In addition, other than a substantially constant structure, a cylindrically opposed cylindrical type having a large cylindrical curvature can be used as a counter electrode because the degree of electric field concentration that causes arc discharge is small. The curvature is preferably at least 20 mm in radius. Although it depends on the dielectric constant of the solid dielectric, at a curvature smaller than that, arc discharge due to electric field concentration tends to concentrate. If the respective curvatures are greater than this, the curvatures of the opposing electrodes may be different. The larger the curvature, the closer to the flat plate, the more stable the discharge can be obtained. Therefore, the radius is more preferably 40 mm or more.

The solid dielectric is provided on one or both of the opposing surfaces of the electrode. At this time, the electrode on the side on which the solid dielectric is placed is in close contact with the electrode, and the opposing surface of the contacting electrode is completely covered. This is because if there is a portion where the electrodes directly face each other without being covered by the solid dielectric, an arc discharge occurs therefrom.

The solid dielectric may be in the form of a sheet or a film, but preferably has a thickness of 0.01 to 4 mm. If the thickness is too large, a high voltage is required to generate discharge plasma. If the thickness is too small, dielectric breakdown occurs when a voltage is applied, and arc discharge occurs.

Examples of the material of the solid dielectric include plastics such as polytetrafluoroethylene and polyethylene terephthalate, glass, metal oxides such as silicon dioxide, aluminum oxide, zirconium dioxide and titanium dioxide, and double oxides such as barium titanate. And the like.

It is preferable that the solid dielectric has a relative dielectric constant of 2 or more (the same applies in a 25 ° C. environment).
Specific examples of the dielectric having a relative dielectric constant of 2 or more include polytetrafluoroethylene, glass, and a metal oxide film. In order to stably generate a high-density discharge plasma, it is preferable to use a fixed dielectric having a relative dielectric constant of 10 or more. The upper limit of the relative permittivity is not particularly limited, but about 18500 is known as an actual material. As a solid dielectric having a relative dielectric constant of 10 or more, a metal oxide film mixed with 5 to 50% by weight of titanium oxide and 50 to 95% by weight of aluminum oxide;
Alternatively, it is preferable to use a metal oxide film containing zirconium oxide and having a thickness of 10 to 1000 μm.

The distance between the electrodes is determined by the thickness of the solid dielectric,
It is appropriately determined in consideration of the magnitude of the applied voltage, the purpose of utilizing the plasma, and the like, and is preferably 1 to 50 mm. If it is less than 1 mm, it may not be sufficient to place the electrodes at intervals. If it exceeds 50 mm, it is difficult to uniformly generate discharge plasma.

In the present invention, first, a nonwoven fabric substrate is disposed between the counter electrode and the solid dielectric or between the solid dielectrics. Next, a pulse electric field is applied between the opposed electrodes in a gas containing at least one of carbon atoms, oxygen atoms and fluorine atoms as an element component or in a monomer gas atmosphere having a hydrophilic group and a polymerizable unsaturated bond in the molecule. I do. The gas may contain a carbon atom, an oxygen atom and a fluorine atom in one compound, or may be a mixed gas of gases containing these.

In the present invention, in the above gas atmosphere,
A pulse electric field is applied between the opposed electrodes. The waveform of the pulsed electric field applied between the electrodes, and the pulse duration, as shown in JP-A-10-154598, impulse type, square wave type, modulation type and the like,
Further, a so-called one-sided waveform in which a voltage is applied to either the positive or negative polarity side may be used.

The shorter the rise time of the pulse voltage, the more efficiently the processing gas is ionized when generating plasma. If the rise time is too long, the discharge state easily transitions to an arc and becomes unstable, so that a high-density plasma state due to a pulsed electric field cannot be expected. Also,
It is better that the rise time is fast, but there is a limitation in a device that has an electric field intensity that is large enough to generate plasma at normal pressure and generates an electric field with a fast rise time.
It is difficult to realize a pulse electric field with an extremely short rise time.

Therefore, the rise time of the pulse electric field is 2
0 μs or less, more preferably 0.1 to 5 μs.
μs. Here, the rise time refers to a time during which the voltage change is continuously positive.

Similarly, the pulse duration is 1 to 50.
μs is preferred. Here, the pulse duration refers to the time during which a pulse is continuous in a pulse electric field composed of repetition of ON and OFF, as shown in JP-A-10-154598.

Further, the frequency of the pulse electric field is 1 to 50
Preferably, it is kHz. If the frequency is less than 1 kHz, the processing takes too much time due to the low plasma density,
If it exceeds Hz, arc discharge is likely to occur. By applying such a high-frequency pulsed electric field, the processing speed can be greatly improved.

Further, the electric field strength is preferably 50 to 100 kV / cm, since if the electric field intensity is too weak, the processing takes too much time, and if the electric field intensity is too strong, an arc discharge easily occurs.

Further, in order to stabilize the discharge, it is preferable to have an OFF time lasting at least 1 μs within 1 ms of the discharge time.

For a target having micropores or a target made of a material having a low melting point, the pulse electric field (basic pulse electric field) is applied at a frequency of 50 to 500 Hz and a duty ratio of 20 to 70%. A waveform modulated by a modulated pulse electric field may be used. With the method of the present invention, stable processing can be performed. However, depending on the object to be processed, generation of a very small streamer may be desired to be suppressed. Such delicate processing is also possible by performing modulation in the above-mentioned frequency and duty ratio ranges.

Further, as long as the dielectric breakdown voltage is not exceeded,
Modulation or bias may be superimposed using pulses having different pulse waveforms, rise times, and frequencies.

The frequency of the pulse electric field is 0.5 to 10
Preferably, it is 0 kHz. If the frequency is less than 0.5 kHz, the plasma density is low, so that it takes too much time for the treatment,
If it exceeds 100 kHz, arc discharge is likely to occur. More preferably, the frequency is 1 kHz or more. By applying such a high-frequency pulsed electric field, the processing speed can be greatly improved.

As a power source for applying the pulse electric field, an apparatus described in Japanese Patent Application Laid-Open No. 10-154598 (for example, a semiconductor device: manufactured by Heiden Laboratories, Inc., manufactured by IXYS, model number "TO-247AD") can be used. .

In the production method of the present invention, the object to be processed may be heated or cooled, but it is sufficiently possible at room temperature. The time required for the above-described processing is appropriately determined in consideration of the applied voltage, the type of the processing gas, the ratio in the mixed gas, and the like.

In the manufacturing method of the present invention, a stable discharge plasma can be continuously generated irrespective of the gas atmosphere by disposing a solid dielectric between the above-mentioned counter electrodes and applying a pulse electric field. It is possible. Therefore, the reactive gas and the shape of the electrode can be freely designed.
Further, by using a high-speed pulse electric field, a high-density plasma state is realized, and high-speed and high-level processing can be performed.

By applying the pulse electric field, it is considered that a cycle in which the discharge is stopped before the discharge state shifts to the arc and the discharge is started again is realized, and the stable discharge state is maintained as a whole. Furthermore, by applying a pulse electric field having a steep rising, gas molecules existing in the space can be efficiently excited,
It is considered that a state is realized in which the absolute number of molecules in the ionized state in the space is large, that is, the plasma density is high.

[0080]

EXAMPLES The present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The processing apparatus and physical property evaluation method used in the examples are as follows. The evaluation was performed immediately after the treatment and after 7 days.

1. Apparatus (1) Processing Apparatus-1 FIG. 1 schematically shows an atmospheric pressure plasma processing apparatus-1 used in Examples and Comparative Examples of the present invention. In FIG. 1, a processing container 2 having a capacity of 10 liters is made of stainless steel, and includes a power supply 1, an upper electrode 4, a lower electrode 5, a solid dielectric 6, a gas inlet tube 7, and a gas outlet 8.
The gas outlet 8 is connected to an oil rotary pump for reducing pressure.

Inside the processing vessel 2, an upper electrode 4 and a lower electrode 5 are provided at a constant interval. The upper electrode 4 is electrically connected to the pulse power supply 1 and the lower electrode 5 is grounded. A normal-pressure plasma 9 can be generated between the upper electrode 4 and the lower electrode 5.

In the atmospheric pressure plasma processing apparatus having the above structure, the gas in the processing vessel 2 is discharged from the gas discharge port 8 and the processing gas whose flow rate has been adjusted is introduced into the processing stainless steel vessel 2 from the gas introduction pipe 7. Then, the inside of the stainless steel container 2 is set to a processing gas atmosphere under a pressure near the atmospheric pressure, and in this state, a pulse voltage is applied between the upper electrode 4 and the lower electrode 5 from the pulse power supply 1 so that the glow discharge plasma is generated. And the surface treatment (hydrophilization treatment) of the polyolefin-based nonwoven fabric substrate is continuously performed by disposing the polyolefin-based nonwoven fabric substrate 10 between the upper electrode 4 and the lower electrode 5, and the separator 11 Can be obtained. In addition, the material of the processing container 2 is not particularly limited, and examples thereof include resin, glass, and metal.

(2) Apparatus-2 FIG. 2 schematically shows a normal-pressure plasma processing apparatus-2 used in an embodiment of the present invention. In FIG. 2, a processing vessel 2 having a capacity of 10 liters is made of stainless steel, and includes a power supply 1, an upper cylindrical electrode 4, a lower cylindrical electrode 5, a solid dielectric 6, a gas inlet tube 7, and a gas outlet 8.
The gas outlet 8 is connected to an oil rotary pump for reducing pressure.

Inside the processing vessel 2, an upper cylindrical electrode 4 and a lower cylindrical electrode 5 are provided as a pair and are arranged at regular intervals. The upper cylindrical electrode 4 is electrically connected to the pulse power supply 1, and the lower cylindrical electrode 5 is grounded. A normal-pressure plasma 9 is generated between the paired upper cylindrical electrode 4 and lower cylindrical electrode 5. Can be done.

In the atmospheric pressure plasma processing apparatus having the above structure, the gas in the processing vessel 2 is discharged from the gas discharge port 8, and the processing gas whose flow rate has been adjusted is introduced into the processing stainless steel vessel 2 from the gas introduction pipe 7. Then, the inside of the stainless steel container 2 is set to a processing gas atmosphere under a pressure near the atmospheric pressure, and in this state, a pulse voltage is applied between the upper electrode 4 and the lower electrode 5 from the pulse power supply 1 so that the glow discharge plasma is generated. And the surface treatment (hydrophilization treatment) of the polyolefin-based nonwoven fabric substrate is continuously performed by disposing the polyolefin-based nonwoven fabric substrate 10 between the upper electrode 4 and the lower electrode 5, and the separator 11 Can be obtained. In addition, the material of the processing container 2 is not particularly limited, and examples thereof include resin, glass, and metal.

2. Physical property evaluation method (1) Surface element amount The element ratio of the surface of the nonwoven fabric was measured using an X-ray photoelectron spectrometer (XPS). XPS is monochromatic (monochrome use)
The measurement was performed using an AlKα ray at an applied X-ray voltage of 15 kV and an emission current of 5 mA. The ratio of the detected oxygen, carbon, nitrogen, and fluorine, and the ratio of oxygen, carbon, and sulfur were determined.

(2) Amount of carboxyl group The surface of the nonwoven fabric was measured under the same conditions using the XPS, and the detected carbon peak was separated into peaks to quantify the amount of the carboxyl group in the bonding form of the carbon component.

(3) Liquid Absorption Rate The surface-treated nonwoven fabric was cut into strips of 25 mm × 200 mm, and the opposite short side was suspended while immersing the leading end 5 mm in a 30% by weight KOH aqueous solution for 30 minutes. Later, the length of the KOH aqueous solution that penetrates upward is measured.

(4) Liquid Retention Ratio The surface-treated nonwoven fabric was cut into 10 cm × 10 cm, weighed to four decimal places (weighing value: W1), and then 30% K
The sample was immersed in an OH aqueous solution. After 60 minutes, the sample was pulled up, cut off the liquid for 10 minutes, and weighed again (weight value: W2). Using the measured values W1 and W2, the liquid retention was calculated based on the following equation. Liquid retention rate (%) = (W2−W1) / W1 × 100 This is measured ten times, and the average value is taken as the measured value.

Example 1 In the processing apparatus shown in FIG. 1, an upper electrode 4 (SU) coated with a sprayed film of Al ₂ O ₃ (solid dielectric) of 1.5 mm was used.
S304, size 120 mm x 50 mm) and lower electrode 5 (SUS304, size 120 mm x 50 mm)
The distance between the electrodes is 2 mm, and in the space between the upper and lower electrodes, a polypropylene non-woven fabric substrate (manufactured by Tonen Tapils,
(Average fiber diameter: 3 μm, width: 100 mm, thickness: 150 μm).

Next, the processing container 2 was evacuated by an oil rotary pump until the internal pressure of the processing container 2 reached 1.333 × 10 ² Pa, and oxygen gas was introduced from the gas inlet 7 until the pressure in the container reached atmospheric pressure. In this state, a pulse voltage having an impulse waveform (rise time 10 μs, duration 20 μs, frequency 10 kHz) is applied between the upper electrode 4 and the lower electrode 5.
z, electric field strength of 80 kV / cm) to generate normal-pressure plasma and
It was run at a speed of m / min to perform a surface treatment (hydrophilic treatment). The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Example 2 A gas mixture of carbon dioxide / nitrogen gas (20/80% by volume) was used as the gas used for the surface treatment.
Processing was performed in the same manner as in Example 1. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Example 3 A treatment was carried out in the same manner as in Example 1 except that only carbon dioxide was used as the gas used for the surface treatment. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Example 4 Processing was performed in the same manner as in Example 1 except that a mixed gas of ethyl alcohol / nitrogen gas (10/90% by volume) was used as a gas used for the surface treatment. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Example 5 Processing was performed in the same manner as in Example 1, except that a mixed gas of acetylene gas / oxygen gas (20/80% by volume) was used as a gas used for the surface treatment. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Example 6 As a gas used for the surface treatment, a mixture gas of ozone and oxygen / argon gas (20/80 volume) generated by passing oxygen through an ozone generator (OZDS-3000A manufactured by Ebara Corporation) was generated. %), Except that (%) was used. The ratio of ozone in the mixed gas (20% by volume) of ozone and oxygen generated by the above device is 5%.
% By volume. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Embodiment 7 In the processing apparatus-2 shown in FIG. 2, an electrode having a cylinder radius of 50 mm and a cylinder length of 120 mm (both upper and lower electrodes)
Electrode having a cylindrical opposed cylindrical electrode structure in which a sprayed film of Al ₂ O ₃ (solid dielectric) is coated at a thickness of 1.5 mm.
The pair was installed on a traveling processor. The distance between the electrodes was 1.5 mm at the nearest part. In the space between the upper and lower electrodes,
A polypropylene nonwoven fabric substrate (manufactured by Tonen Tapils, average fiber diameter 3 μm, width 100 mm, thickness 150 μm) was arranged. The surface treatment (hydrophilic treatment) was performed in the same manner as in Example 1 except that the treatment gas was a mixed gas of 30% oxygen / 70% argon. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

Example 8 A surface treatment (hydrophilic treatment) was performed using the processing apparatus used in Example 7 in the same manner as in Example 2 except for gas conditions, discharge conditions, and processing conditions. The carboxyl group content, liquid retention speed, and liquid retention ratio on the surface of the obtained surface-treated nonwoven fabric were measured. Table 1 shows the results.

[0100]

[Table 1]

Example 9 Fluorine gas (CF ₄ ) was used as a gas for surface treatment.
The processing was performed in the same manner as in Example 1 except that a mixed gas of / oxygen gas (3/97% by volume) was used. Elemental analysis, liquid retention speed, and liquid retention ratio of the surface of the obtained surface-treated nonwoven fabric were measured. Table 2 shows the results.

Example 10 As a gas used for the surface treatment, an organic fluorine gas (C ₃
Processing was performed in the same manner as in Example 1 except that a mixed gas of F ₆ ) / dry air (3/97% by volume) was used. Elemental analysis, liquid retention speed, and liquid retention ratio of the surface of the obtained surface-treated nonwoven fabric were measured. Table 2 shows the results.

Example 11 The same as Example 1 except that a mixed gas of carbon dioxide / fluorine gas (CF ₄ ) / oxygen gas (20/10/70% by volume) was used as the gas used for the surface treatment. Was processed. Elemental analysis, liquid retention speed, and liquid retention ratio of the surface of the obtained surface-treated nonwoven fabric were measured. Table 2 shows the results.

Comparative Example 1 A treatment was carried out in the same manner as in Example 1, except that only nitrogen was used as a gas for the surface treatment. Elemental analysis, liquid retention speed, and liquid retention ratio of the surface of the obtained surface-treated nonwoven fabric were measured. Table 2 shows the results.

[0105]

[Table 2]

Example 12 Using the same processing apparatus as in Example 1, 150
Acrylic acid monomer gas vaporized at ℃ (vaporization speed 40m
1 / min) and 10 SLM of argon as a transport gas
A normal pressure plasma was generated under the same conditions as in Example 1 except that the non-woven fabric was introduced into the processing container, and a polypropylene nonwoven fabric (manufactured by Tonen Tapils, average fiber diameter 3 μm, width 100 mm, thickness 1) was used.
(50 μm). Elemental analysis, liquid retention speed, and liquid retention ratio of the surface of the obtained surface-treated nonwoven fabric were measured. Table 3 shows the results. The weight of the obtained nonwoven fabric increased by 2% by weight, and the ratio of carboxyl groups (carboxylic acid ratio) in carbon bonds on the surface was 13%.

Example 13 A nonwoven fabric surface treatment was performed in the same manner as in Example 12 except that a mixed gas of 3% SO ₂ /97% argon was added to the mixed gas of 5 SLM and Example 12 as an introduced gas. .
Elemental analysis of the surface of the obtained surface-treated nonwoven fabric, liquid retention rate,
The liquid retention was measured. Table 3 shows the results. The weight of the obtained nonwoven fabric was increased by 2.1% by weight, and the ratio of carboxyl groups (carboxylic acid ratio) in carbon bonds on the surface was 12%.

Example 14 The surface treatment of the nonwoven fabric was performed in the same manner as in Example 12 except that a mixed gas of 20% O ₂ /80% argon was added to the mixed gas of 5 SLM and Example 12 as an introduced gas. .
Elemental analysis of the surface of the obtained surface-treated nonwoven fabric, liquid retention rate,
The liquid retention was measured. Table 3 shows the results. The weight of the obtained nonwoven fabric increased by 2.5% by weight, and the ratio of carboxyl groups (carboxylic acid ratio) in carbon bonds on the surface was 15%.

[0109]

[Table 3]

Comparative Example 2 Instead of a pulsed electric field, a discharge was attempted using an AC voltage having a sin waveform having a frequency of 2.4 kHz. 10 before discharge occurs
A voltage of kV was required, and streamer-like light emission was observed simultaneously with the occurrence of discharge. Immediately after the application was stopped and the object to be processed was confirmed, the polypropylene nonwoven fabric was melted. Since the melted base material had a reduced strength as a structure and caused a short circuit, it was unsuitable as a separator and could not be evaluated.

From these results, according to the discharge plasma treatment of the present invention performed near the atmospheric pressure, the surface-treated nonwoven fabric stably generates a large amount of surface carboxyl groups and has excellent characteristics as a secondary battery separator. (Examples 1 to 8). Further, it can be seen that a state in which the water absorption rate and the liquid retention rate are excellent is maintained due to the presence of an appropriate fluorine atom (Examples 9 to 11). In addition, the surface of the nonwoven fabric can be easily treated with a monomer having a hydrophilic group and a polymerizable unsaturated double bond (Examples 12 and 14), and a sulfone group can be easily present on the surface simultaneously with a carboxyl group. (Example 13), it is known that these hydrophilic groups are effective as hydrophilic groups for an alkaline secondary battery separator.

[0112]

Since the nonwoven fabric of the present invention has the above-mentioned constitution, it is possible to impart hydrophilicity to the nonwoven fabric. For this reason, it imparts hydrophilicity, water absorption, dyeability, affinity with specific substances, adhesion, etc., so that air filters, air cleaners, nonwoven fabric for civil engineering, battery separators, diapers, sanitary products, artificial leather , Medical gauze, house wrapping, tape core material, clothing core material and the like.

In the method for producing a nonwoven fabric according to the present invention, the surface of the nonwoven fabric is subjected to discharge plasma treatment using the above-mentioned gas.
It can be manufactured stably with a simple process. It is also suitable for high-speed continuation, and can perform various treatments without damaging the fibers. Furthermore, in the production method of the present invention, the effect of introducing a functional group is large, and the surface of the substrate can be made hydrophilic.

Also, When used for separators such as high-capacity, miniaturized batteries, the fiber surface is hydrophilic,
It is preferable because the time for immersion in the electrolytic solution can be shortened and the speed of the process can be increased. Furthermore, by using a polyolefin-based nonwoven fabric as the nonwoven fabric, a separator for a secondary battery having a high liquid absorption rate and excellent electrolyte retention performance can be obtained.

Since the separator for a secondary battery of the present invention uses the above-described production method, the effect of introducing a functional group onto the surface of the polyolefin-based nonwoven fabric substrate is large, and therefore, the surface of the substrate is made hydrophilic and the liquid absorption rate is reduced. It is a separator for a secondary battery that is fast and has excellent electrolyte retention performance.

Further, according to the method for manufacturing a separator for a secondary battery of the present invention, the discharge plasma treatment is performed under a pressure near the atmospheric pressure, so that the polyolefin-based nonwoven fabric is not damaged and is inexpensive. Hydrophilic treatment is possible,
A secondary battery separator excellent in battery performance can be provided.

[Brief description of the drawings]

FIG. 1 is an atmospheric pressure discharge plasma processing apparatus used in an embodiment.
1 is a diagram schematically showing a configuration of FIG.

FIG. 2 is an atmospheric pressure discharge plasma processing apparatus used in Examples.
FIG. 2 is a diagram schematically showing a configuration of No. 2;

[Explanation of symbols]

 Reference Signs List 1 pulse power supply 2 processing container 4 upper electrode 5 lower electrode 6 solid dielectric 7 gas inlet 8 gas outlet 9 discharge plasma 10 nonwoven fabric 11 separator

 ──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 11-336490 (32) Priority date November 26, 1999 (November 26, 1999) (33) Priority claim country Japan (JP)

Claims (13)

[Claims] The carboxyl group in the bonding form of the carbon component on the surface of the nonwoven fabric substrate measured by X-ray photoelectron spectroscopy is
A nonwoven fabric characterized by at least 3 atomic%. 2. A nonwoven fabric characterized in that in the bonding form of the carbon component on the surface of the nonwoven fabric substrate measured by X-ray photoelectron spectroscopy, fluorine atoms are 1 atomic% or more and oxygen atoms are 10 atomic% or more. 3. The method according to claim 1, wherein a gas containing at least one of carbon atoms, oxygen atoms and fluorine atoms is used as an elemental component of the gas used when treating the surface of the nonwoven fabric, and is subjected to normal pressure plasma treatment. Nonwoven fabric manufacturing method. 4. A gas comprising CO _x (X = 1 or 2),
4. The method for producing a nonwoven fabric according to claim 3, wherein at least one of O _Y (Y = 2 or 3) and a fluorine-containing gas is used. 5. A normal pressure plasma treatment using at least one of a monomer gas having a hydrophilic group and a polymerizable unsaturated bond in a molecule and a sulfur-containing gas as a gas used in treating the surface of the nonwoven fabric. A method for producing a nonwoven fabric, characterized in that the nonwoven fabric is applied. 6. The production of a nonwoven fabric according to claim 3, wherein a rare gas or a nitrogen gas is further contained in a gas atmosphere when the atmospheric pressure plasma treatment is performed. Method. 7. The normal-pressure plasma processing comprises a pair of electrodes opposed to each other, and one or both of the electrodes are coated with a solid dielectric to form an opposite electrode near the atmospheric pressure of the processing gas atmosphere. In the state where the polyolefin-based nonwoven fabric base material is arranged between the opposed electrodes, the pulse rising time is 20 μs or less, the pulse duration is 1 to 50 μs, the frequency is 1 to 50 kHz, and the electric field strength is between the opposed electrodes. The method for producing a nonwoven fabric according to any one of claims 3 to 6, wherein a pulse voltage of 50 to 100 kV / cm is applied. 8. A non-woven fabric used as a separator for a secondary battery, wherein the non-woven fabric according to claim 1 is a polyolefin-based non-woven fabric. 9. A method for manufacturing a separator for a secondary battery, wherein the nonwoven fabric used in the method for manufacturing a nonwoven fabric according to any one of claims 3 to 7 is a polyolefin-based nonwoven fabric. 10. A separator used in an alkaline secondary battery, wherein the separator is formed using a polyolefin-based nonwoven fabric as a base material, and has a hydrophilic group and a polymerizable unsaturated bond in a molecule vaporized as a surface treatment gas of the polyolefin-based nonwoven fabric. A separator for a secondary battery, wherein the separator has been hydrophilized by a discharge plasma treatment performed at about atmospheric pressure in a gas atmosphere containing a monomer. 11. The method for producing a separator for an alkaline secondary battery according to claim 10, wherein the substrate surface of the polyolefin-based nonwoven fabric is subjected to a discharge plasma treatment at about atmospheric pressure. 12. A counter electrode composed of a pair of electrodes facing each other, one or both electrodes of which are opposed to each other and covered with a solid dielectric, having a hydrophilic group and a polymerizable unsaturated bond in the molecule. With a polyolefin-based nonwoven fabric substrate placed between the counter electrodes, a pulse rises between the counter electrodes in a mixed gas atmosphere containing at least two of a monomer gas, a carbon-containing gas, and an oxygen-containing gas. Time is 20μs or less, pulse duration is 1
５０50 μs, frequency 1-20 kHz, electric field strength 50
The method for producing a separator for a secondary battery according to claim 11, wherein the polyolefin-based nonwoven fabric substrate is subjected to an atmospheric pressure discharge plasma treatment by applying a pulse voltage of -100 kV / cm. 13. A counter electrode comprising a pair of electrodes facing each other, one or both electrodes of which are opposed to each other and covered with a solid dielectric, comprising a hydrophilic group and a polymerizable unsaturated bond in the molecule. With the polyolefin-based nonwoven fabric substrate disposed between the opposed electrodes, the pulse rise time was set to 20 μs in a mixed gas atmosphere containing at least one of a monomer gas and a sulfur-containing gas. Hereinafter, the pulse duration is 1 to 50 μs, the frequency is 1 to 20 kHz, and the electric field strength is 50 to 100 kV / c.
The method for producing a separator for a secondary battery according to claim 11, wherein the polyolefin-based nonwoven fabric substrate is subjected to an atmospheric pressure discharge plasma treatment by applying a pulse voltage of m.