JP2003128820A - Method of surface modification of synthetic resin material and method for producing battery separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of surface modification in which a porous synthetic resin sheet including the inside of the voids can be uniformly surface- modified safely and efficiently and a sulfone group and other hydrophilic functional groups are fixed on the material, and which is suitable for providing hydrophilic properties to a nonwoven fabric such as a battery separator. SOLUTION: The porous synthetic resin sheet 3 that is uniformly and efficiently surface-modified including the inside of the voids of the sheet 3 is obtained safely by bringing the porous synthetic resin sheet 3 in a reactor 1 in contact with a gas containing a low concentration of sulfur dioxide, exhausting a part of the gas containing sulfur dioxide outside the reactor 1 to prepare an environment in which the sulfur dioxide gas is remaining under a desired reduced pressure, introducing a gas containing a low concentration of fluorine to bring the sheet 3 in contact with the gas. The method of surface modification is used for a nonwoven fabric mainly comprising a polyolefin fiber to obtain the battery separator excellent in battery properties.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for safely and efficiently surface-modifying a synthetic resin material.
The present invention relates to a surface reforming method suitable for hydrophilizing a nonwoven fabric such as a battery separator in which a sulfo group and other hydrophilic functional groups are fixed to a material, which allows the surface to be uniformly reformed even inside the voids of a porous synthetic resin sheet.

[0002]

2. Description of the Related Art Conventionally, a battery separator made of a polyolefin-based non-woven fabric has been used as an alkaline secondary battery separator because it is excellent in alkali resistance. However, since polyolefin fibers have a poor affinity with the electrolytic solution, various hydrophilic treatment methods for imparting hydrophilicity to polyolefin nonwoven fabrics have been proposed. As a hydrophilic surface modification treatment method, there is a method of fixing sulfurous acid gas or the like as a functional group on the fiber surface by utilizing the oxidizing power of fluorine gas. For example, Japanese Patent Application Laid-Open No. 4-59838 proposes a method of exposing a sheet to a sulfurous acid gas atmosphere of 25 vol% or more and continuously contacting each sheet with each gas in a fluorine gas atmosphere of 25 vol% or more. Further, Japanese Patent Application Laid-Open No. 10-7829 proposes a method of performing surface modification treatment in a state where sulfurous acid gas, oxygen gas, fluorine gas and oxygen are mixed.

[0003]

However, the above surface modification method has the following problems. For example,
In Japanese Patent Application Laid-Open No. 4-59838, a hydrophilic group that improves the affinity with an electrolytic solution can be fixed on the fiber surface, but in the method described above, the surface modification is performed under a gas atmosphere of relatively high concentration of sulfur dioxide and fluorine gas. Since the quality treatment is applied, the temperature of the fiber surface rises due to the exothermic reaction of the two-component gas on the surface of the object to be treated, and when a certain concentration limit value is exceeded, the chemical reaction between the gases is promoted, which is industrially safe. There's a problem. Also,
Since the surface modification treatment is performed under normal pressure, it is difficult for gas to permeate into the inside of non-woven fabrics with high basis weight, high apparent density, or dense non-woven fabrics using ultrafine fibers, and as a result, the inside of the non-woven fabric is hydrophilized. However, there is a drawback that it is difficult to make them uniform. Further, in JP-A-10-7829, since a roll-shaped sample is wound up in a system in which sulfurous acid gas and fluorine gas are mixed at the same time to perform hydrophilic treatment,
The concentration of sulfurous acid gas and fluorine gas in the reaction system changes over time due to the reaction of gases with each other or the reaction of gas with the base cloth, and it is possible to control the uniform hydrophilic treatment in the length direction of the nonwoven fabric. It has the drawback of being difficult. Further, as in the above-mentioned publication, since the surface modification treatment is performed under normal pressure, there is a drawback that it is difficult to make the hydrophilic treatment even inside the nonwoven fabric.

[0004]

Means for Solving the Problems The present invention has been earnestly studied to solve the above-mentioned problems. As a result, a synthetic resin material is passed through a sulfurous acid gas atmosphere in advance, and then a part of the sulfurous acid gas is exhausted to the outside. Keeping the inside of the reactor in a depressurized state, keeping the surface of the synthetic resin material in contact with sufficient residual sulfurous acid gas, and allowing the residual sulfurous acid gas to penetrate into the synthetic resin material and reacting with fluorine gas By letting
While suppressing the temperature rise due to the exothermic reaction between sulfur dioxide gas and fluorine gas in the reactor, the sulfurous acid gas and the fluorine gas are brought into contact with each other uniformly and efficiently even inside the voids of the material, and safely to the synthetic resin material. It was found that it is possible to immobilize a sulfur-containing hydrophilic functional group such as a sulfone group, and other hydrophilic functional groups, and the present invention has been completed. That is, the method for surface modification of a synthetic resin material of the present invention comprises contacting the synthetic resin material in the reactor with a sulfur dioxide-containing gas having a sulfur dioxide gas concentration of 0.5 vol% or more and 10 vol% or less, and then sulfite. A part of the contained gas was exhausted to the outside of the reactor, and the fluorine-containing gas was introduced into the atmosphere in which the sulfurous acid gas remained under a reduced pressure in the range of 1 × 10 ⁴ Pa or more and 8 × 10 ⁴ Pa or less. The material has a fluorine gas concentration of 0.1 vol%
As described above, the gas is brought into contact with the fluorine-containing gas in the range of 10 vol% or less.

The sulfur-containing gas has a concentration of 0.5 vol%.
Above, sulfur dioxide in the range of 10vol% or less, and a concentration of 90v
By containing the nitrogen gas in the range of ol% or more and 99.5 vol% or less, it is possible to suppress a rapid reaction, moderate the temperature rise during the reaction, and perform surface modification safely and efficiently. ,preferable.

When a part of the sulfurous acid-containing gas is exhausted outside the reactor, the residual ratio of the sulfurous acid-containing gas is 10% or more,
The range of 80% or less is preferable because the state in which residual sulfurous acid gas is brought into contact with the surface of the synthetic resin material can be maintained and a suitable amount of sulfone group can be introduced.

After the treatment of the fluorine-containing gas, 50 vol% or more of the fluorine-containing gas is exhausted to the outside of the reactor, then the oxygen-containing gas is introduced, and the pressure is restored to 10 × 10 ⁴ Pa and brought into contact with the synthetic resin material. As a result, hydrofluoric acid (HF), which is a by-product that remains on the surface of the synthetic resin material, can be removed, or residual fluorine gas components can be replaced, and components that may impair hydrophilic performance can be removed. ,preferable.

The synthetic resin material comprises a porous synthetic resin sheet, and the porous synthetic resin sheet wound in a roll shape is installed in a biaxial winding device in the reactor, and is unwound from one shaft. It is preferable that the reaction gas is brought into contact with the other shaft while being wound on the other shaft, since the surface modification is efficiently performed. Furthermore, it is preferable that the number of unwinding and winding processes is two or more because the surface modification efficiency is good.

In the method for producing a battery separator according to the present invention, a non-woven fabric mainly composed of polyolefin fibers in a reactor having a sulfurous acid gas concentration of 0.5 vol% or more and 10 vol% or less is prepared based on the surface modification method. An atmosphere in which sulfurous acid gas remains under reduced pressure in the range of 1 × 10 ⁴ Pa or more and 8 × 10 ⁴ Pa or less by contacting with a sulfurous acid-containing gas having a range, and then exhausting a part of the sulfurous acid-containing gas to the outside of the reactor. By introducing a fluorine-containing gas into the inside and bringing the synthetic resin material into contact with a fluorine-containing gas having a fluorine gas concentration of 0.1 vol% or more and 10 vol% or less, the fiber surface inside the voids of the nonwoven fabric can be sufficiently It is possible to manufacture a battery separator that has been subjected to a hydrophilization treatment and is provided with a hydrophilic functional group such as a sulfone group, a carboxyl group or a hydroxyl group. Hereinafter, the present invention will be described in detail.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the synthetic resin material in the present invention include fibers, threads, films, porous membranes, woven fabrics, knitted fabrics, non-woven fabrics, nets, and molded bodies made of synthetic resin. The complex used above may be used. When the synthetic resin material is a porous sheet, it can be wound in a roll shape, unwound in a reactor and can be repeatedly wound, and the surface reforming method of the present invention causes the most efficient reaction. be able to.

Examples of the material of the synthetic resin material include polyester resins, polyamide resins, polyimide resins, polyolefin resins, polyphenylene sulfide resins, and the like. Particularly, for battery separator applications, alkali resistance is used. From the viewpoint of the above, polyolefin resins such as polypropylene, polyethylene, ethylene-vinyl alcohol copolymer, polymethylpentene and the like are preferable.

[0012] The synthetic resin material is housed in the reactor, and the interior of the reactor is decompressed until it becomes 0.2 × 10 ⁴ Pa (0.02 atm) or less. This is because the reduced pressure may result in insufficient oxidation of the material by the fluorine gas if the inside of the reactor or the synthetic resin material contains water. For example, to explain according to the surface modification method of the synthetic resin material shown in FIG. 1, when the porous synthetic resin sheet (2) wound in a roll shape is used, first, the biaxial shaft in the reactor (1) is used. The winding device (4) is installed, the roll (2) is set on the winding device (4), and the reactor (1) is set.
Seal. The winding device (4) freely unwinds and winds from the A axis (4A) to the B axis (4B) or from the B axis (4B) to the A axis (4A) in each step of gas reaction. It is possible to repeat. Then the exhaust port (6)
The air, water and the like filled in the reactor (1) are discharged from the reactor, and the pressure in the reactor (1) is reduced to 0.2 × 10 ⁴ Pa (0.02 atm) or less. If necessary, after the pressure is reduced, the porous synthetic resin sheet (3) may be unwound and taken up once or more in the reactor to remove the water content in the synthetic resin sheet.

After the depressurization, the gas is prepared so that the synthetic resin material is brought into contact with the sulfurous acid gas in the atmosphere containing the sulfurous acid. The sulfur-containing gas in the reactor has a concentration of 0.5.
It contains sulfur dioxide in the range of vol% or more and 10 vol% or less. The preferable lower limit of the sulfurous acid gas concentration is 1 vol% or more. The preferable upper limit of the sulfurous acid gas concentration is 5 vol% or less. If the sulfur dioxide concentration is less than 0.5 vol%,
If the sulfurous acid gas component cannot be contacted with the synthetic resin material sufficiently and exceeds 10 vol%, when fluorine gas is introduced,
Due to the heat generated by the reaction between the gases, the temperature rise in the reactor becomes significant, which may cause a safety problem.

Further, the sulfurous acid-containing gas has a concentration of 90% in order to suppress a rapid reaction, moderate a temperature rise during the reaction, and safely and efficiently modify the surface.
It is preferable to contain nitrogen gas in the range of vol% or more and 99.5 vol% or less. The more preferable lower limit of the nitrogen gas concentration is 95 vol% or more. A more preferable upper limit of the nitrogen gas concentration is 99 vol% or less.

The procedure for preparing the sulfurous acid-containing gas is as follows:
It is not particularly limited as long as it is a means for adjusting to a desired gas concentration, for example, a method using a mixed gas in which sulfur dioxide gas and nitrogen gas are mixed in advance, or after introducing a predetermined amount of nitrogen gas into the reactor, finally There is a method of introducing a sulfurous acid-containing gas, and the latter is convenient because it is easy to finely adjust the sulfurous acid gas concentration and control the reaction time. Specifically, first, nitrogen gas is introduced into the reactor in a range of 50 vol% or more and 90 vol% or less. Then, sulfur dioxide gas diluted with nitrogen gas is introduced into the reactor to adjust the gas. The sulfur dioxide gas concentration at the time of introduction is preferably in the range of 10 vol% or more and 20 vol% or less. Sulfurous acid gas concentration at the time of introduction is 1
If it is less than 0 vol%, it takes more time than necessary to adjust the gas concentration when the inside of the reactor is adjusted to the desired sulfurous acid gas concentration, resulting in poor processability. Sulfurous acid gas concentration at the time of introduction is 20 vo
This is because if it exceeds 1%, the diffusion of sulfurous acid gas in the reactor becomes poor and it becomes difficult to prepare a uniform sulfurous acid gas atmosphere.

After preparing the atmosphere of the sulfurous acid-containing gas in the reactor, the synthetic resin material housed in the reactor is reacted. The reaction conditions are preferably such that the reaction temperature is 0 ° C. or higher and 40 ° C. or lower. If the reaction temperature is lower than 0 ° C, there is a risk of liquefaction of sulfurous acid gas, and if it exceeds 40 ° C, an excessive reaction may occur. Further, the reaction time is preferably 30 seconds or more. Specifically, when the roll-shaped porous synthetic resin sheet (2) shown in FIG. 1 is used, a sulfur dioxide-containing gas is ejected from the ejection nozzle (5) into the depressurized reactor (1). Then, the inside of the reactor (1) is adjusted to a gas atmosphere containing sulfurous acid. Then roll (2)
Start unrolling and react. The winding speed (gas contact speed) is not particularly limited, but it is preferable to wind at 30 m / min or less in order to contact the sulfurous acid gas sufficiently and uniformly. Further, the number of times of unwinding and winding may be appropriately set according to the reaction efficiency, and may be performed once or more.

Next, the sulfurous acid-containing gas in the reactor (1) is introduced into the reactor by a suction device such as a vacuum pump (7) at a pressure of 1 × 10 ⁴ Pa (0.1 atm) or more, 8 × 10 ⁴ or more. Pa
A part of the gas is exhausted from the exhaust port (6) to the outside of the reactor while reducing the pressure to a range of (0.8 atm) or less. A part of the sulfurous acid-containing gas is exhausted, and a part of the gas is left in the reactor (1) under reduced pressure within the above range, so that the residual sulfurous acid gas is always in contact with the surface of the synthetic resin material, Since the fluorine gas reaction in the next step can be performed, the sulfurous acid gas component can be efficiently added to the synthetic resin material.
In particular, in the case of the porous synthetic resin sheet (3), after the sulfurous acid-containing gas is contacted, the inside of the reactor is depressurized, so that when the pressure is restored in the next step, the sulfurous acid gas becomes voids of the porous synthetic resin sheet (3). It is convenient because it easily penetrates into the interior. Residual rate of sulfur-containing gas by exhaust is 10% or more, 80%
The following is preferable. A more preferable lower limit of the remaining rate is 20%. The more preferable upper limit of the remaining rate is 50.
% Or less. When the residual rate of sulfurous acid gas is less than 10%, the concentration of sulfurous acid gas existing on the surface of the material is low, and sulfur components such as sulfone groups cannot be sufficiently added.
When the residual rate exceeds 80%, the sulfur dioxide gas concentration in the atmosphere inside the reactor is high, and when the fluorine gas is introduced, the introduced fluorine gas reacts with the residual sulfur dioxide gas in the reactor, resulting in uniform treatment. Hard to do.

After exhausting a part of the sulfurous acid-containing gas,
A fluorine-containing gas is prepared so that the fluorine gas treatment is performed. The fluorine-containing gas in the reactor has a concentration of 0.1 vol%
The fluorine gas is contained in the range of 10 vol% or less.
The preferable lower limit of the fluorine gas concentration is 0.5 vol% or more. The preferable upper limit of the fluorine gas concentration is 5 vol% or less. When the fluorine gas concentration is 0.1 vol% or less,
Sufficient hydrophilization treatment is difficult and fluorine gas concentration is 10
If it exceeds vol%, the exothermic reaction with residual sulfurous acid gas is promoted and safety may become a problem.

The fluorine-containing gas preferably contains nitrogen gas in order to suppress a rapid reaction, moderate a temperature rise during the reaction, and safely and efficiently modify the surface. . The nitrogen gas concentration is determined by setting the residual sulfurous acid gas concentration and the fluorine gas concentration within desired ranges.

The order of preparing the fluorine-containing gas is as follows:
It is not particularly limited as long as it is a means for adjusting to a desired gas concentration, and for example, a method using a mixed gas in which fluorine gas and nitrogen gas are mixed in advance, or after introducing a predetermined amount of nitrogen gas into the reactor, finally There is a method of introducing a fluorine-containing gas, and the latter is convenient because the exothermic reaction is suppressed because the fluorine-containing mixed gas is introduced into an atmosphere in which nitrogen gas is present in advance. Specifically, 50 vol% of the nitrogen gas shown in FIG. 1 was blown into the reactor (1) from the nozzle (5).
As described above, the gas is introduced in the range of 90 vol% or less, and the pressure in the reactor (1) is restored to about 9 × 10 ⁴ Pa (0.9 atm). Next, fluorine gas diluted with nitrogen gas is introduced into the reactor (1) from the blowout nozzle (5) to adjust the gas, and finally the pressure is restored to about 10 × 10 ⁴ Pa (1 atm). . The fluorine gas concentration at the time of introduction is preferably in the range of 5 vol% or more and 40 vol% or less. If the fluorine gas concentration at the time of introduction is less than 5 vol%, it takes more time than is necessary to adjust the inside of the reactor to a desired fluorine gas concentration, which is not convenient. Fluorine gas concentration at the time of introduction is 40
If it exceeds vol%, the concentration of fluorine that is in direct contact with the synthetic resin material at the time of gas preparation is high, which may accelerate rapid heat generation.

After the inside of the reactor is adjusted to a fluorine-containing gas atmosphere, the synthetic resin material contained in the reactor is reacted. The reaction conditions are preferably such that the reaction temperature is 0 ° C. or higher and 40 ° C. or lower. If the reaction temperature is lower than 0 ° C, there is a risk of liquefaction of sulfurous acid gas, and if it exceeds 40 ° C, an excessive reaction may occur. Further, the reaction time is preferably 30 seconds or more. Specifically, when the porous synthetic resin sheet (2) wound in a roll shape shown in FIG. 1 is used, a fluorine-containing gas is introduced from a blow-out nozzle (5), and the inside of the reactor (1) is fed with fluorine. After the atmosphere of the contained gas is adjusted, the unwinding of the roll (2) is started to react. The winding speed (gas contact speed) is not particularly limited, but in order to bring the fluorine gas into contact with the fluorine gas sufficiently and uniformly, it is preferably wound at 30 m / min or less. Further, the number of times of unwinding and winding may be appropriately set in accordance with the reaction efficiency, and the reaction efficiency is good when they are contacted once or more, preferably twice or more.

Further, during the reaction of the fluorine-containing gas, the fluorine gas consumed by the reaction between the fluorine gas and the synthetic resin material or the reaction between the fluorine gas and the sulfurous acid gas is supplied into the reactor so that the fluorine concentration in the reactor is increased. Is preferably uniform. As the additional fluorine gas amount, it is preferable to supply a fluorine-containing gas diluted with nitrogen gas in a concentration range of 5 vol% or more and 40 vol% or less at 1 to 10 l / min via a mass flow controller (not shown). . When the supply amount is less than 1 l / min, it is difficult to stably supply the fluorine gas into the reactor because the pressure inside the reactor is normal pressure. If the supply rate exceeds 10 l / min, the pressure rise in the reactor becomes large, which may cause a safety problem. Further, if the additional fluorine gas is supplied in the above range, the inside of the reactor may be pressurized, but it is preferable to discharge the unnecessary amount of gas to the outside of the reactor to keep the internal pressure of the reactor constant.

After the above-mentioned fluorine gas treatment is completed, the residual gas in the reactor is exhausted from the exhaust port, and nitrogen gas or the like for about 1
The pressure is restored to about 0 × 10 ⁴ Pa (1 atm), and the surface-modified synthetic resin material is taken out. At this time, if necessary, the residual fluorine gas in the reactor may be adjusted to 5 × 10 ⁴ Pa (0.5 at).
m) using the vacuum pump suction device, while reducing the pressure inside the reactor, exhaust from the exhaust port to the outside of the reactor,
Further, the decompression system is decompressed with an oxygen-containing gas to about 10
After the pressure is restored to about 10 ⁴ Pa (1 atm), the synthetic resin material can be treated in the oxygen-containing gas. By performing the above-mentioned treatment, there is an effect of removing hydrofluoric acid (HF), which is a by-product remaining on the surface of the synthetic resin material, and replacing the residual fluorine gas component. The oxygen-containing gas may be only oxygen gas or may contain nitrogen gas. The mixing ratio of the nitrogen gas and the oxygen gas is not particularly limited as long as the oxygen gas is contained in such an amount that the above effects can be expected.

The synthetic resin material surface-modified as described above is taken out of the reactor. The surface-modified synthetic resin material may have residual hydrofluoric acid or a small amount of low-molecular-weight components decomposed by fluorine gas remaining on the surface.Therefore, alkali cleaning treatment, warm water cleaning treatment, and drying treatment are required. Is given. In the alkaline cleaning treatment, the type of the alkaline cleaning liquid is not particularly limited, but in the case of using a synthetic resin material for the alkaline battery separator, a cleaning liquid of the same quality as the alkaline electrolyte, for example, potassium hydroxide, It is preferable to use sodium hydroxide, lithium hydroxide, or the like. Alkali concentration is 1 mass% or more, 30
It is preferably in the range of mass% or less. The more preferable lower limit of the alkali concentration is 3 mass%. The more preferable upper limit of the alkali concentration is 10 mass% or less. If the alkali concentration is less than 1 mass%, the cleaning ability will be poor, and if the alkali concentration exceeds 30 mass%, it will be difficult to remove the alkali component in the water washing step after the alkali cleaning. The temperature of the alkaline cleaning liquid is preferably 10 ° C or higher and 90 ° C or lower. The more preferable lower limit of the temperature of the alkaline cleaning liquid is 30 ° C. The more preferable upper limit of the temperature of the alkaline cleaning liquid is 70 ° C. Alkaline cleaning solution temperature is 1
When the temperature is lower than 0 ° C, the cleaning ability is poor, and when the temperature is higher than 90 ° C, the alkaline component is easily vaporized, and it becomes difficult to control the concentration. The contact time between the synthetic resin material and the alkali cleaning solution is not particularly limited, but if it is usually 10 seconds or more, a sufficient cleaning effect can be expected. Further, in the case of the porous synthetic resin sheet, a surfactant may be mixed in the alkaline solution in order to enhance the permeability of the alkaline cleaning solution into the voids and the cleaning efficiency. The type of surfactant is not particularly limited, and a known surfactant may be used.

As the hot water washing treatment, for example, when a synthetic resin material is used for a separator for an alkaline battery, it is preferable to use ion-exchanged water in order to reduce mixing of ionic impurities. The temperature for washing with warm water is 10 ℃
As described above, it is preferably in the range of 90 ° C. or lower. The more preferable lower limit of the warm water washing temperature is 30 ° C or higher. The more preferable upper limit of the warm water washing temperature is 70 ° C. If the washing temperature with warm water is less than 10 ° C, the washing efficiency of the residual alkali components may be reduced, and if it exceeds 90 ° C, the form of the hydrophilic functional group introduced by the hydrophilic treatment may be changed. Is. The contact time between the synthetic resin material and the hot water is not particularly limited, but a sufficient cleaning effect can be expected if it is usually 1 min or more.

As the drying step, hot air penetration type,
It is not particularly limited as long as it can be dried, such as a heating roll contact type. The porous synthetic resin sheet is preferable because the hot air penetrating type can efficiently dry the inside of the voids. The drying temperature is preferably 40 ° C. or higher and 90 ° C. or lower. The more preferable lower limit of the drying temperature is 50 ° C. More preferable upper limit of the drying temperature is
It is 70 ° C or lower. If the impression temperature is less than 40 ° C., a great amount of time is spent for sufficient drying, which is not efficient. This is because if the temperature exceeds 90 ° C, the form of the hydrophilic functional group may change. As the passing time of the drying process,
Although not particularly limited, for example, if the synthetic resin material is a polyolefin-based nonwoven fabric, a sufficient drying effect can be expected in 2 minutes or more. The synthetic resin material surface-modified in this manner can have various functions such as hydrophilicity and ion exchange performance by imparting sulfone groups and other polar groups to the surface of the material.

Next, a method for manufacturing the battery separator of the present invention will be described. First, as the fibers used in the present invention, fibers mainly made of one or more kinds of polyolefin resins such as polypropylene, polyethylene, ethylene-vinyl alcohol copolymer and polymethylpentene are mainly used. For example, a single fiber of the above polyolefin resin, ethylene-propylene copolymer / polypropylene, high density polyethylene / polypropylene, low density polyethylene /
Sheath-core type composite fiber made of a combination of polypropylene or the like, or poly-4-methylpentene-1 / polypropylene, poly-4-methylpentene-1 / high density polyethylene, polypropylene / high density polyethylene, polypropylene / ethylene-vinyl alcohol copolymer Examples of the composite fiber include a split type conjugate fiber, a sea-island type conjugate fiber, and the like, and the cross-sectional shape of the fiber may be circular, irregular, hollow, or the like.

A fiber web mainly composed of the above-mentioned polyolefin fiber is prepared. Examples of the fibrous web form include a card web, an air laid web, a wet papermaking web,
Spunbond web, melt blown web, etc.
Alternatively, they are used by stacking. Above all, it is preferably used because of the uniformity and denseness of the nonwoven fabric from which the wet papermaking web is obtained. Further, since the strength of the web may be lowered by the fluorine treatment, it is preferable to bond the fibers to each other by a bonding means such as heat treatment with hot air or a hot roll, or hydroentangling treatment. The nonwoven fabric thus obtained is once wound into a roll.

Next, the non-woven fabric roll is treated by the surface modification method of the synthetic resin material. First, the non-woven fabric roll is set on a biaxial winding device in the reactor, the reactor is sealed, and the pressure is once reduced to remove excess water. Then, a sulfurous acid-containing gas is introduced from the blowing nozzle,
Sulfurous acid gas concentration in the reactor is 0.5 vol% or more, 10 vol
% Of the sulfurous acid-containing gas atmosphere, unrolling of the roll is started, unrolling and winding are repeated 1 to 5 times, and sulfurous acid gas is contacted. Then
Sulfurous acid-containing gas in the reactor was sucked by a vacuum pump, and the inside of the reactor was 1 × 10 ⁴ Pa (0.1 atm) or more, 8 × 10 ⁴ Pa
While reducing the pressure to (0.8 atm) or less, a part of the gas is exhausted outside the reactor. After discharging, the fluorine-containing gas was introduced from the blow-out nozzle, and the fluorine gas concentration in the reactor was 0.5 vo.
After preparing a fluorine-containing gas atmosphere in the range of 1% or more and 10 vol% or less, unrolling of the roll is started, and unrolling and winding are repeated once or twice to bring the fluorine gas into contact. After completion of the fluorine gas treatment, residual by-products are removed with nitrogen gas and oxygen gas as necessary, and the product is taken out of the reactor to obtain a roll-shaped hydrophilic polyolefin-based nonwoven fabric.

Next, the non-woven fabric roll is unwound, subjected to an alkali washing treatment, a warm water washing treatment and a drying treatment to remove residual low molecular weight components, and once the roll is wound up,
Alternatively, after the drying treatment, a calender roll is used to adjust to a desired thickness to obtain a battery separator. Also,
In the present invention, a hydrophilic treatment method other than fluorine treatment, such as sulfonation, corona discharge, plasma discharge, graft polymerization, ozone treatment, and surfactant treatment may be used together.
The battery separator thus obtained is provided with a hydrophilic functional group containing a sulfur component such as a sulfone group or a hydrophilic functional group such as a hydroxyl group, so that internal resistance inside the battery and suppression of internal pressure are suppressed. And has an excellent charge / discharge cycle life, and is useful as a separator for alkaline secondary batteries, lithium ion secondary batteries, electric double layer capacitors, capacitors and the like. It is also useful as an ion exchange separator (ion catcher).

[0031]

EXAMPLES Specific examples of the present invention will be described below with reference to examples. Various performances were measured by the following methods.

[Thickness] 175 kPa load (JIS-B-7
By the measurement with the micrometer according to 502),
Measure the thickness at 10 different points on each of the 3 samples,
The average value of 30 locations was calculated.

[Liquid retention rate] Mass W of test piece in water equilibrium state
(Mg) is measured to the nearest 1 mg. Next, K with a specific gravity of 1.30
The test piece was immersed in an OH solution, the KOH solution was absorbed for 1 hour, then pulled out of the solution and allowed to stand for 10 minutes, and then the mass W ₁ (mg) of the test piece was measured. It was calculated. Hoekiritsu _{(%) = ((W 1} -W) / W) × 100

[Liquid absorption height] The sample was cut into a strip shape having a width of 25 mm and a height of 200 mm, and the portion from the sample end to 5 mm was immersed in a 30 mass% potassium hydroxide aqueous solution, and the temperature was 25 ° C and the room temperature was 65 ° C. When it was stood vertically in an atmosphere whose humidity was adjusted to%, the rising height (mm) of the aqueous solution of potassium hydroxide after 30 minutes was measured.

[Production of Cylindrical Sealed Nickel-Hydrogen Battery] The negative electrode was prepared by adding water to a hydrogen storage alloy, carbonyl nickel, carboxymethyl cellulose (CMC) and polytetrafluoroethylene (PTFE) and kneading to prepare a slurry. This slurry was dip-coated on a nickel-plated punching metal, dried at 80 ° C., and pressure-molded to produce a hydrogen storage alloy negative electrode. A known sintered nickel electrode was used as the positive electrode. Each separator was sandwiched between the negative electrode and the positive electrode, inserted into a battery case, and the electrolytic solution was injected to prepare a cylindrical sealed nickel-hydrogen battery.

[Internal resistance] A 3225 milliohm meter (manufactured by Hioki Electric Co., Ltd.) was used to measure the resistance value of the cylindrical sealed nickel-hydrogen battery with an impedance resistance of frequency 1 KHz.

[Cycle Life] The cylindrical sealed nickel-hydrogen battery was charged at a rate of 0.1 C for 12 hours, stopped for 0.5 hours, and discharged at a rate of 0.1 C at a final voltage of 1.0 V, and repeatedly charged and discharged for 10 cycles. The initial battery activity was performed. Then
A cylindrical sealed nickel-metal hydride battery with a charge rate of 1.0C
The number of cycles was calculated when the utilization rate to the theoretical capacity was 80% or less at 1.1 hours, 1.0 hour of rest, and 1.0 C discharge rate (final voltage 1.0 V). Charging / discharging was performed at 25 degreeC.

[Example 1] As a synthetic resin material, a combination of ethylene-vinyl alcohol copolymer / polypropylene was used, and the fineness was 3.3 dt which was radially divided into 16 parts.
ex, split type composite fiber with fiber length 6 mm (manufactured by Daiwa Spinning Co., Ltd.,
DF-2) 50 mass%, sheath component is high-density polyethylene, core component is polypropylene fineness 1.7 dtex,
30 mass% of sheath-core type heat-bondable composite fiber (manufactured by Daiwa Boshoku Co., Ltd., NBF (H)) having a fiber length of 10 mm and a fineness of 0.7 dt
ex, polypropylene single fiber of 10 mm fiber length (PZ, manufactured by Daiwa Boshoku Co., Ltd.) was mixed at 20 mass% and heat-bonded by the sheath component of the sheath-core type heat-bondable composite fiber with a cylinder dryer at 135 ° C. A wet non-woven fabric of 55 g / m ² and a thickness of 220 μm was wound around a paper tube to prepare a non-woven fabric roll of 500 mm width × 200 m length.

As shown in FIG. 1, the non-woven fabric roll is set on the A-axis in the reactor (capacity 2300 l), and is unwound from the A-axis to the B-axis or the B-axis to the A-axis, and is guided so that it can be wound up. The reactor was completely sealed. Then, the air in the reactor was exhausted to the outside from the exhaust port with a vacuum pump, and the inside of the reactor was depressurized to 0.13 × 10 ⁴ Pa (0.013 atm). Next, nitrogen gas was ejected from the ejection nozzle to give 2070 l.
(90 vol%) was introduced into the reactor. Next, 230 l (10 v) of sulfurous acid gas diluted to 10 vol% with nitrogen gas
Gas was prepared so that the inside of the reactor was filled with 1 vol% sulfurous acid gas and 99 vol% nitrogen gas. Next, the non-woven fabric roll was unwound twice at a winding speed of 16 m / min in the order of A->B-> A axis to perform a winding process.

After the treatment with the sulfurous acid-containing gas, the sulfurous acid-containing gas was exhausted to the outside of the reactor by a vacuum pump so that the sulfurous acid-containing gas remained in the reactor at 1725 l (75 vol%). pressure was reduced to 10 ⁴ Pa (0.75atm). The residual rate of the sulfur-containing gas at this time is 75%
Met. And nitrogen gas 460l from the blowing nozzle
(20vol%) is introduced, and further 10vol% with nitrogen gas
115 l (5 vol%) of the diluted fluorine gas was introduced to prepare a mixed gas of nitrogen / sulfurous acid / fluorine containing 0.5 vol% fluorine gas in the reactor. Then, take up the non-woven fabric roll at 16m / min
Then, the film was unwound once on the A → B axis and wound up.
At this time, 10 vol% of diluted fluorine gas was introduced into the reactor 2.
It was supplied at a flow rate of 8 l / min to keep the fluorine gas concentration constant.

After the fluorine gas treatment, the fluorine-containing gas was exhausted from the exhaust port to the outside of the reactor by a vacuum pump so that 1150 l (50 vol%) of the mixed gas in the reactor remained, and the inside of the reactor was 5 × 10 ^4. The pressure was reduced to Pa (0.5 atm). Next, 1150 l (50 vol%) of oxygen gas having an oxygen gas concentration of 100 vol% was introduced into the reactor through a blowing nozzle to prepare a mixed gas containing 50 vol% of oxygen gas. Next, roll the non-woven fabric at a winding speed of 16 m / min and move from B to A axis 1
It was unwound and wound up. After winding is complete,
The mixed gas in the reactor was evacuated to 0.13 × 10 ⁴ Pa
The pressure was reduced to (0.013 atm), 2300 l of nitrogen gas was introduced into the reactor to restore the pressure to 10 × 10 ⁴ Pa (1 atm), and then the reactor was opened to obtain a hydrophilic non-woven fabric. Obtained.

Next, the obtained hydrophilic treated non-woven fabric roll is set in a post-treatment machine having an alkali washing step, a hot water washing step and a drying step shown in FIG. 2, unrolled at a line speed of 5 m / min, and wound up. Processed. For alkaline cleaning, the nonwoven fabric is immersed in an alkaline cleaning tank filled with an aqueous potassium hydroxide solution at a temperature of 60 ° C and a concentration of 5 mass%, and for hot water cleaning, the nonwoven fabric is placed in a warm water cleaning tank filled with ion-exchanged water at a temperature of 60 ° C. Was dipped. Drying was performed with a hot air circulation dryer having a temperature of 70 ° C. The obtained non-woven fabric was adjusted to a thickness of 150 μm using a thermal calendar roll to obtain a battery separator.

[Example 2] 575 l after treatment with sulfurous acid gas
(25 vol%) The sulfurous acid-containing gas was exhausted to the outside of the reactor and the pressure was reduced to 2.5 × 10 ⁴ Pa so that the residual rate of the sulfurous acid-containing gas was 25%.
of the nitrogen gas / sulfuric acid / fluorine containing 0.5 vol% of fluorine gas in the reactor by introducing 115 l (5 vol%) of fluorine gas diluted to 10 vol% with nitrogen. A battery separator was obtained in the same manner as in Example 1 except that the mixed gas was used.

[Comparative Example 1] 2255 after treatment with sulfurous acid gas
l (98vol%) of gas is exhausted to the outside, 0.2 ×
A battery separator was obtained in the same manner as in Example 1 except that the pressure was reduced to 10 ⁴ Pa and the residual rate of the sulfurous acid-containing gas was set to 2%.

[Comparative Example 2] The nonwoven fabric roll of Example 1 was set on the A axis in the reactor, and the A axis → B axis or the B axis → A.
The reactor was completely unsealed by unwinding it on a shaft and guiding it so that it could be wound up. Then, the air inside the reactor was exhausted to the outside from the exhaust port with a vacuum pump, and the inside of the reactor was changed to 0.13 ×.
The pressure was reduced to 10 ⁴ Pa (0.013 atm). Then
Fluorine gas 3vol%, Sulfurous acid gas 5vol%, Nitrogen gas 92
After introducing 2300 liters of mixed gas of vol% into the reactor from the blowing nozzle, the non-woven fabric roll is wound up at a speed of 16 m / min.
Then, the film was unwound once on the A → B axis and wound up.

Then, in the same manner as in Example 1, alkali washing, warm water washing and drying were performed, and the thickness was adjusted to 150 μm using a hot calender roll to obtain a battery separator. The liquid retention of the nonwoven fabrics of Examples 1-2 and Comparative Examples 1-2, the liquid absorption height, and the initial internal resistance and cycle life when the nonwoven fabrics were used as a battery separator and incorporated in a sealed cylindrical nickel-hydrogen battery The measured results are shown in Table 1.

[0047]

[Table 1]

The battery separators of Examples 1 and 2 were highly hydrophilized and were excellent in liquid retention and liquid absorption. Also in terms of battery performance, a hydrophilic functional group containing a sulfur component such as a sulfone group was highly provided, and the battery had a low internal resistance and a long cycle life. On the other hand, in Comparative Example 1, since most of the sulfurous acid gas is exhausted to the outside in the process and the hydrophilic functional group is added with the fluorine gas, the hydrophilic functional groups such as sulfo group, carboxyl group, and hydroxyl group formed on the surface. The amount of groups was small, and the hydrophilicity and battery characteristics were inferior. In Comparative Example 2, since the fluorine gas and the sulfurous acid gas are simultaneously mixed and subjected to the hydrophilic treatment, the fluorine gas chemically reacts with the sulfurous acid gas over time, and both the fluorine gas and the sulfurous acid gas are consumed. Similarly, the amount of hydrophilic functional groups introduced was small and the hydrophilicity and battery characteristics were poor.

[0049]

Industrial Applicability According to the surface reforming method for a synthetic resin material of the present invention, the synthetic resin material in the reactor is brought into contact with a low-concentration sulfur-containing gas, and then a part of the sulfur-containing gas is exhausted outside the reactor. However, after the atmosphere containing the sulfurous acid-containing gas remained under reduced pressure in the range of 1 × 10 ⁴ Pa or more and 8 × 10 ⁴ Pa or less, a low-concentration fluorine-containing gas was introduced and brought into contact with the inside of the reactor. While suppressing the temperature rise due to the exothermic reaction between sulfur dioxide gas and fluorine gas, the sulfurous acid gas component is brought into contact with the inside of the voids of the material evenly and efficiently by the depressurizing action, and the surface of the synthetic resin material such as sulfone group The sulfur component-containing hydrophilic functional group or other hydrophilic functional group can be fixed. The synthetic resin material is used as a porous synthetic resin sheet, and the porous synthetic resin sheet wound in a roll shape is installed in a biaxial winding device in the reactor, unrolled from one shaft, and the other shaft. The surface modification is more efficiently performed by bringing the reaction gas into contact with the film while winding it up.

By using the above-mentioned surface modification method on a non-woven fabric mainly composed of polyolefin fibers, hydrophilic functional groups containing a sulfur component such as a sulfone group or hydrophilic functional groups such as a hydroxyl group are imparted to the interior of the battery. Internal resistance at
It is possible to obtain a battery separator that enables suppression of internal pressure and has an excellent charge / discharge cycle life.

[Brief description of drawings]

FIG. 1 shows an example of a method for modifying the surface of a synthetic resin material of the present invention.

FIG. 2 shows an example of post-treatment after the surface modification of the present invention.

[Explanation of symbols]

1. Reactor 2. Rolled porous synthetic resin sheet 3. Porous synthetic resin sheet 4. Unwinding and winding device 4A. A axis 4B. B axis 5. Blowout nozzle 6. exhaust port 7. Vacuum pump

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 2/16 D06M 7/02 C // C08L 101: 00 11/00 Z D06M 101: 20 (72) Invention Nobuo Aoki 877, Komiya, Harima-cho, Kako-gun, Hyogo Prefecture Daiwa Bow Polytech Co., Ltd., Harima Research Center (72) Inventor Shuji Hori, 877, Komiya, Harima-cho, Kako-gun, Hyogo Daiwa Bow Polytech Co., Ltd., Harima Research Center (72) Inventor Kida Tatsuno, 877, Komiya, Harima-cho, Kako-gun, Hyogo Daiwa Bow Polytech Co., Ltd., Harima Research Center (72) Inventor Toshio Kamisasa, 877, Komiya, Harima-cho, Kako-gun, Hyogo Prefecture F-Term (Reference) 4F073, Harima Research Center, Daiwa Bow Polytec Co., Ltd. AA01 BA07 BA08 BB01 DA04 EA32 4L031 AA14 AB34 BA07 BA08 BA17 CA11 DA08 5H021 BB09 CC02 EE04 HH01 HH06

Claims (7)

[Claims] 1. The synthetic resin material in the reactor is brought into contact with a sulfur dioxide-containing gas having a sulfur dioxide gas concentration of 0.5 vol% or more and 10 vol% or less, and then a part of the sulfur dioxide-containing gas is taken out of the reactor. Exhaust, 1 × 10 ⁴ Pa or more, 8 × 10 ⁴ Pa
Fluorine-containing gas is introduced into the atmosphere in which the sulfurous acid-containing gas remains under reduced pressure in the following range, and the synthetic resin material is contacted with the fluorine-containing gas having a fluorine gas concentration of 0.1 vol% or more and 10 vol% or less. A surface modification method. 2. Sulfurous acid-containing gas having a concentration of 0.5 vol% or more and 10 vol% or less, and a concentration of 90 vol%
2. The surface modification method according to claim 1, wherein the nitrogen gas is contained in the range of not less than 9% and not more than 99.5 vol%. 3. The residual ratio of the sulfurous acid-containing gas when a part of the sulfurous acid-containing gas is exhausted outside the reactor is 10% or more, 80
The surface modification method according to claim 1 or 2, which is in the range of not more than%. 4. After treatment with a fluorine-containing gas, 50 vol% or more of the fluorine-containing gas is exhausted outside the reactor, then an oxygen-containing gas is introduced, and the pressure is restored to 10 × 10 ⁴ Pa and brought into contact with a synthetic resin material. The surface modification method according to claim 1. 5. The synthetic resin material comprises a porous synthetic resin sheet, and the porous synthetic resin sheet wound into a roll is installed in a biaxial winding device in the reactor, and unrolled from one shaft. The surface modification method according to claim 1, wherein the reaction gas is brought into contact with the other shaft while being wound on the other shaft. 6. The surface modification method according to claim 5, wherein the number of unwinding and winding processes is two or more. 7. A non-woven fabric composed mainly of polyolefin fibers in a reactor, the sulfur dioxide gas concentration of which is 0.5 vol% or more,
Contacting with a sulfurous acid-containing gas having a range of 10 vol% or less, and then exhausting a part of the sulfurous acid-containing gas to the outside of the reactor,
Fluorine-containing gas was introduced into the atmosphere in which the sulfurous acid-containing gas remained under a reduced pressure in the range of 1 × 10 ⁴ Pa or more and 8 × 10 ⁴ Pa or less, and the synthetic resin material had a fluorine gas concentration of 0.1 vol%.
As described above, the method for producing a battery separator, in which the nonwoven fabric is hydrophilized by contacting it with a fluorine-containing gas in the range of 10 vol% or less.