JPH113694A - Manufacture of separator material for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a separator for battery, which has excellent charging and discharging characteristic, especially, self-discharging characteristic, with industrial advantage by performing the hydrophilic treatment to a surface of a polyolefin group resin raw material having excellent acid-resistance and alkali-resistance, and thereafter, dipping the raw material with sulfuric acid. SOLUTION: As a polyolefin group resin raw material, non-woven fabric, woven fabric or fine porous film, which is made of fiber mainly composed of polyethylene and polypropylene and to which the hydrophilic treatment is performed on a surface thereof, is used. A method with chemical means and a method with physical means such as plasma discharge is used as a method for hydrophilic treatment. A chemical processing with oxygen gas or sulfurous acid gas, which includes fluorine gas at 0.1-10 capacity %, is desirably used so as to form a radical to be required for efficient modulation. Continuously, the raw material is dipped with sulfuric acid solution having sulfuric acid concentration at 50-98 wt.% at a bathing temperature less than 100 deg.C. After the dipping, the raw material is neutralized by washing, and treated with the surface active agent so as to increase the intruding speed of the alkali solution. Self- discharging characteristic is thereby improved without deteriorating the raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a battery separator material made of a polyolefin resin material. Particularly, the present invention relates to a method for producing a battery separator material having improved self-discharge characteristics, which is suitable for an alkaline storage battery.

[0002]

2. Description of the Related Art Conventionally, nickel-cadmium secondary batteries,
Many nylons have been mainly used as separators for nickel-hydrogen secondary batteries and the like. Nylon has moderate strength, gas permeability, and hydrophilicity, but does not have sufficient chemical resistance such as alkali resistance and oxidation resistance, especially when batteries are charged at high temperatures. Nylon is decomposed into carbon dioxide, water, ammonia, etc. by the oxygen generated in the above, and these adversely affect the battery characteristics, and further decomposition leads to loss of the electrical insulation capacity as a separator. In order to solve this, use of a polyolefin resin has been attempted. Polyolefin-based resins are excellent in alkali resistance and acid resistance, and have the same strength and gas permeability as nylon, but have poor hydrophilicity, and are inferior in affinity for an electrolyte and poor electrolyte retention ability. For this reason, it has been proposed that the surface of the polyolefin resin be subjected to a hydrophilic treatment. For example, JACS, 100: 6, 1948, Ma
r. (1978), Japanese Patent Publication No. 4-7548 (Japanese Unexamined Patent Publication No.
109171) and Japanese Patent Publication No. 5-46056 (Japanese Unexamined Patent Publication No.
No. 109171) have proposed a battery separator made of a polyolefin nonwoven fabric surface-treated with a gas containing fluorine.

[0003] OH groups, C
As a method of introducing a polar group such as an OOH group or an SO ₃ H group and performing a hydrophilic treatment, a plasma discharge method, a corona discharge method, a flame method, an electron beam irradiation method, an ultraviolet irradiation method, or a radiation irradiation may be used in addition to the fluorine gas treatment. Methods, fuming sulfuric acid method, sulfonation method using sulfur trioxide gas and the like have been proposed. Thus, when a polyolefin-based resin is treated by such means, hydroxyl groups, carboxyl groups, and the like are mainly introduced into the resin surface, and although the hydrophilicity and the affinity with the electrolytic solution are improved, the charge / discharge characteristics are sufficient. However, there was still a problem in the performance as a battery separator.

On the other hand, JP-A-56-3973 and JP-A-57
-191956, JP-B-07-32008 (JP-A-58-1983)
175256), JP-A-62-115657, JP-A-01-130242 and JP-A-1-132244, etc. disclose a method of sulfonating a polyolefin resin with a fuming sulfuric acid solution, sulfur trioxide (SO ₃ ) gas or a hot sulfuric acid aqueous solution. Is disclosed. It is said that the sulfone group provided by these methods has excellent lyophilicity as a battery separator, and is excellent in charge / discharge characteristics, particularly self-discharge characteristics. However, in these methods, the inside of the polyolefin is sulfonated due to the strong acid treatment, and the strength of the polyolefin resin is lost, so that sufficient strength cannot be obtained as a separator. There is a drawback that they are desorbed or oxidized during the manufacturing process and do not exhibit the required good battery characteristics. In order to solve these problems, the fuming sulfuric acid method employs a mild post-treatment method of gradually immersing in a dilute sulfuric acid aqueous solution after the treatment, but the process is not simplified and is not necessarily industrial. It is not excellent.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and uses a polyolefin resin material excellent in acid resistance and alkali resistance to improve charge and discharge characteristics, particularly self-discharge characteristics. It is an object of the present invention to provide a method for producing an excellent battery separator material in an industrially advantageous manner.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above object, and as a result, have found that the surface of a polyolefin resin material has --OH, --COOH, SO ₃ H or --COF, SO ₂ Fx groups. After performing the treatment of imparting at least one functional group, by further immersing in a sulfuric acid solution, particularly a sulfuric acid aqueous solution, it is possible to obtain a highly durable alkaline storage battery separator material having excellent charge / discharge characteristics such as self-discharge. Heading, the present invention has been achieved. That is, the gist of the present invention resides in a method for producing a battery separator material, characterized in that a surface of a polyolefin-based resin material is subjected to a hydrophilic treatment and then immersed in sulfuric acid.

According to the study of the present inventors, when a polyolefin film such as polypropylene or polyethylene is treated with fluorine gas, at least one functional group of a carbonyl group, a carboxyl group, a hydroxyl group or a sulfofluorine group (SO ₂ Fx) is obtained. It is confirmed by the absorption by the FT-IR method and the ESCA analysis by the chemical modification method, and it is considered that the same functional group is provided to the polyolefin-based nonwoven fabric.

It is clear from the above-mentioned known literatures that the generation of these hydrophilic groups significantly improves the water absorption (liquid absorption speed, liquid absorption height) and the like. However, when the hydrophilic nonwoven fabric sample is supplied to a nickel-metal hydride storage battery separator, the capacity retention rate at 45 ° C. × 7 days is about 50%, and sufficient self-discharge characteristics cannot be obtained. Further, the sample that produces sulfofluorine groups (SO ₂ Fx) is immersed in hot alkali and converted into a sulfonic acid salt (such as SO ₃ K) to reduce ion exchange capacity (neutral salt resolution) to zero. Even if it is used as a separator for a nickel-metal hydride storage battery at 0.01 to 0.06 meq / g, sufficient self-discharge characteristics cannot be obtained.

Accordingly, the present inventors have paid attention to the dehydrating ability and etching ability of sulfuric acid. Sulfuric acid does not wet the water-repellent polyolefin, and the treatment effect cannot be expected as it is. In order to treat polyolefin, the fuming sulfuric acid method is usually considered. However, the handling of the vapor pressure of sulfuric anhydride is a problem, and the deterioration of the base material is a serious problem as described above. As a result of intensive studies to effectively express these functions, the present inventors have reached the present invention in which a polyolefin material is subjected to hydrophilization and then treated with sulfuric acid.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the polyolefin resin used in the present invention include those mainly composed of polypropylene or polyethylene. The material made of such a resin is not particularly limited in its shape, and examples thereof include a sheet, a film, a woven fabric, a nonwoven fabric, a microporous film, and a laminate sheet in which these are laminated in multiple layers.

Specifically, a sheet or film of polypropylene, polyethylene, their copolymer or polymer blend, or polypropylene, polyethylene, ethylene-vinyl alcohol copolymer, ethylene-
Fiber consisting of a single component such as a vinyl acetate copolymer, polyethylene mainly composed of polypropylene, polyethylene-
Vinyl alcohol copolymer, polyethylene-vinyl acetate copolymer or the like, or a blend of polypropylene and polyethylene alone or a composite fiber composed of these, for example, a composite fiber material having a core component of polypropylene and a sheath component of polyethylene, or And woven and non-woven fabrics made of a mixture of these fibers. Examples of the microporous film include a microporous film of ultra-high molecular weight polypropylene.

As the material used for the separator, a non-woven fabric, a woven fabric, a porous membrane and the like are suitable, and a non-woven fabric is particularly preferable. The manufacturing method and standard of the nonwoven fabric are not particularly limited, and the manufacturing method and standard used for the battery separator are applied. However, the basis weight is preferably 100 g / m ² or less, and the thickness is 0.01 to 0.01 g / m ^2. 5 mm, preferably 0.1 to 1 m
m. Various known techniques can be used for producing these polyolefin materials.

In the present invention, the surface of the polyolefin resin material is first subjected to a hydrophilic treatment. In the case of a nonwoven fabric, for example, the surface treatment of the raw fibers or the surface treatment of the nonwoven fabric itself is possible, but the surface treatment of the nonwoven fabric itself is preferred from the viewpoint of simplicity of the treatment process. Examples of the method for hydrophilization include physical methods such as a plasma discharge method, a corona discharge method, a flame method, an electron beam irradiation method, an ultraviolet irradiation method, and a radiation irradiation method, and chemistry such as a fluorine treatment method using a mixed gas containing a fluorine gas. Although any of the methods by a suitable means can be applied, treatment by a fluorine gas-containing gas is preferable.

The concentration of the fluorine mixed gas used for the hydrophilization treatment is not particularly limited, but usually, the fluorine gas is contained in the range of 0.01 to 30% by volume, more preferably 0.1 to 30% by volume.
It is used in the range of 1 to 10% by volume. Fluorine gas is 0.
When the concentration is less than 1% by volume, it is difficult to efficiently form radicals required for the modification on the surface of the polyolefin to be contacted, and it becomes difficult to introduce a hydrophilic group. When the fluorine gas concentration becomes high, the exothermic reaction with the polyolefin cannot be ignored and causes deterioration of the base material. In addition, there is a fear that a combustion reaction may occur, and it is desirable to use 10% or less.

Fluorine gas can be used alone for the hydrophilization treatment by mixing it with an inert gas such as nitrogen or helium, but preferably, it is further used by mixing oxygen gas and / or sulfurous acid gas. Is preferred. Sulfurous acid gas in the mixed gas is 0 to 30% by volume, preferably 0.1 to 30% by volume.
%, More preferably a concentration in the range of 0.5 to 20% by volume. High-concentration sulfurous acid gas generates explosive mixed heat with fluorine, so it is within 30%, preferably 20%
Within. Oxygen gas effectively acts on hydrophilicity,
It has the function of suppressing the radical reaction caused by fluorine gas,
Regulation is difficult. Generally 0 to 95% by volume, preferably 0
It is selected from a concentration range of ~ 85% by volume. Therefore, air can be used as a diluting gas for fluorine gas.

The contact temperature between the fluorine-containing gas and the polyolefin is selected from conditions that do not cause direct fluorination reaction or resin deterioration, but the range is usually from -70 to 100.
° C, preferably from 0 to 80 ° C. That is, if the temperature is lower than 0 ° C., the reactivity of fluorine is extremely reduced. If the temperature exceeds 80 ° C., the polyolefin is liable to be deteriorated. If the temperature is higher than 90 ° C., the fluorination reaction is liable to occur. The contact time with the fluorine mixed gas is appropriately selected and is usually selected from the range of 1 second to 10 days, preferably 1 second to 10 hours.

The reaction between the fluorine mixed gas and the polyolefin material is performed by introducing the polyolefin material into a closed reaction vessel, degassing the inside of the vessel, and then introducing the mixed gas.
Alternatively, after the inside of the reaction vessel is replaced with a mixed gas in advance, a polyolefin material to be treated is introduced and brought into contact with the mixed gas, or a mixed gas is filled in a processing chamber having a good gas seal, and the material to be treated is introduced into the chamber from outside. And the like. In this case, in order to increase the contact efficiency of the mixed gas, the materials to be treated can be fixed so as not to come into contact with each other, or the roll-shaped sheet can be unwound and wound in a container.

The method of introducing the fluorine mixed gas may be such that fluorine gas and an inert gas, or fluorine gas and at least one of a sulfurous acid gas and an oxygen gas are mixed at a predetermined concentration and used. At least one gas of oxygen gas may be brought into contact with the polyolefin material, and a fluorine gas may be introduced therein, or at least one of a sulfurous acid gas and an oxygen gas may be introduced together with the fluorine gas. After the reaction between the fluorine gas-containing gas and the nonwoven fabric is completed, unreacted mixed gas and by-product exhaust gas such as hydrogen fluoride are removed. Known techniques can be used for the method of detoxifying exhaust gas. For example, a method in which unreacted fluorine is passed through a tube in which alumina particles are sealed and immobilized as aluminum fluoride, or a method in which gas is passed through an alkaline aqueous solution is used. In addition, there is a method in which a small amount of hydrogen fluoride is adsorbed on sodium fluoride particles.

The hydrophilization treatment by various physical means can be performed by a method known per se, for example, JP-A-05-6760, JP-A-07-134979, JP-A-07-142047, JP-B-04-1774, JP-A-07-134980. And the like. The polyolefin material whose surface has been hydrophilized is then immersed in sulfuric acid. The effect of sulfuric acid immersion is more pronounced at higher concentrations and higher temperatures,
On the other hand, there arises a problem that the material is deteriorated and the working and equipment durability environment is deteriorated. Therefore, the sulfuric acid used in the present invention is
The bath temperature should be less than 100 ° C and the sulfuric acid concentration should be 50% or more and 98%.
% Is preferable. When the sulfuric acid concentration exceeds 98%, evaporation of sulfuric anhydride cannot be ignored,
Quality control and equipment / work management become complicated. 100 ° C
At the above-mentioned bath temperature, sulfuric anhydride is generated due to evaporation of water, which complicates work management. The bath temperature is usually about room temperature to achieve the intended purpose.

The immersion time is selected from 1 second to 1 day, preferably from 10 seconds to 5 hours. Thereafter, the material is neutralized by washing with water or the like, and dried at a temperature of 50 ° C to 100 ° C to obtain a material suitable for a battery separator. The separator material obtained according to the present invention is a polyolefin resin having excellent chemical resistance, heat resistance, without impairing properties such as mechanical strength, etc., performance suitable for battery materials, that is, an increase in alkali aqueous solution affinity, Shows good self-discharge characteristics.

The material treated with sulfuric acid according to the method of the present invention has a slower penetration rate of the alkaline aqueous solution, which is a measure of the affinity for the alkaline aqueous solution, as compared with a material simply subjected to a hydrophilic treatment, but has an improved self-discharge characteristic. Therefore, it is considered that it is difficult to permeate, but hard to come off, and therefore, the liquid retaining property is high. On the other hand, in the case of only the hydrophilization treatment, it is considered that it easily permeates but easily comes off.

According to the present invention, the polyolefin material subjected to the surface hydrophilization treatment and the sulfuric acid immersion treatment can be treated with a surfactant, if necessary, to greatly increase the penetration rate of the aqueous alkali solution. The surfactant treatment is performed, for example, by subjecting a surfactant such as polyoxyethylene nonyl phenyl ether, sodium dodecylbenzene sulfonate or the like to an aqueous solution having a concentration of about 0.7 to 1.0% by weight, surface-hydrophilizing treatment and sulfuric acid immersion. The treated polyolefin material may be dipped or applied to the surface.

Although the mechanism by which the self-discharge characteristic of the polyolefin resin material is improved by the method of the present invention is not clear,
It is estimated as follows. The sulfuric acid treatment of the present invention is considered to be effective for removing and fixing impurities and trace additives contained in polyolefin by concentrated sulfuric acid or for etching, and it is considered that the formation of sulfone groups is not an essential condition. As shown in the Examples below, the sulfone groups on the surface of the material obtained by the method of the present invention are extremely small at 0.01 meq / g or less, which is considered to be a structure different from that of the material obtained by the conventional fuming sulfuric acid treatment. The present invention, by hydrophilizing the polyolefin resin material, enables sulfuric acid treatment under mild conditions, suppresses deterioration of the material, and further improves self-discharge performance, as in the case of using fuming sulfuric acid. It is considered successful in obtaining the effect.

[0024]

Next, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the following examples,
Each measurement was performed by the following method.

(1) XRF Measurement Using a fluorescent X-ray analyzer RIX3001 manufactured by Rigaku Denki Co., Ltd. and using a Rh tube as a primary X-ray source, 40 kV-70 m
In vacuum under the conditions of A, the intensity (kcps) was measured by using the company's spectral crystal RX40 for the F-Kα line and the O-Kα line, and using the company's Ge for the S-Kα line. In addition, the value of the intensity used the value output by the software attached to the apparatus.

(2) 30% KOH soak rate In an environment of a temperature of 24 ° C. and a humidity of 65%, when 10 μl of an electrolytic solution (30% by weight aqueous solution of potassium hydroxide) is dropped on a nonwoven fabric which is left horizontally, the electrolytic solution Was measured until it completely soaked into the sample. (3) Self-discharge characteristics The sample was incorporated into a nickel-hydrogen secondary battery as a separator, and after 10 cycles of charge and discharge, the capacity retention rate after standing at 45 ° C for 7 days was measured.

Example 1 A nonwoven fabric of a mixture of polyethylene and polypropylene (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Of SUS316, which is resistant to fluorine,
The vessel was evacuated at 25 ° C., and 2.0% by volume of fluorine gas and 98.0% by volume of nitrogen gas were introduced and reacted for 5 minutes. After completion of the reaction and evacuation, the pressure was restored with nitrogen, and a sample was taken out. This sample was placed at 25 ° C, 95
% Sulfuric acid for 1 hour, washed with water and dried at 50 ° C. for 7 hours. Using this sample A as a separator, nickel-
A self-discharge characteristic was measured using a hydrogen secondary battery. The results are shown in Table 1.

Table 2 shows the results of 30% KOH aqueous solution penetration rate and XRF analysis. Further, the surface functional groups were observed by the FT-IR method. As shown in FIG. 1, the result was a sulfone group (1040 cm ⁻¹ , 1200 c
m ^-1 ) and absorption of a carbonyl group (1720 cm ^-1 ) were not observed. The ion exchange capacity of a strong acid (≒ sulfone group) was measured by the neutral salt decomposition method.
eq / g or less. The same nonwoven fabric as used in Example 1 was immersed in fuming sulfuric acid at room temperature for 20 minutes without washing, washed with water, and then dried in the same manner as in Example 1,
Observation of the surface functional group by the FT-IR method (FIG. 2) clearly shows that the sulfone group (1034 cm ⁻¹ , 1165 cm)
^-1 ) was observed.

Example 2 A nonwoven fabric of a mixture of polyethylene and polypropylene (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Of SUS316, which is resistant to fluorine,
After the vessel was evacuated at 25 ° C., 2.0% by volume of fluorine gas, 80% by volume of oxygen gas and 18.0% by volume of nitrogen gas were introduced and reacted for 5 minutes. After completion of the reaction and evacuation, the sample was taken out by restoring the pressure with nitrogen, and the sample was immersed in 25% conc.
Dry at 7 ° C. for 7 hours. Using this sample B as a separator, a nickel-hydrogen secondary battery was assembled, and the self-discharge characteristics were measured. The results are shown in Table 1. In addition, 30% KOH
Table shows the results of the solution penetration rate and XRF analysis.
2 is shown. The ion exchange capacity was measured in the same manner as in Example 1, but the amount was 0.01 meq / g or less.

Comparative Example 1 A nonwoven fabric of a mixture of polyethylene and polypropylene (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Of SUS316, which is resistant to fluorine,
The vessel was evacuated at 25 ° C., and 3.0% by volume of fluorine gas, 10.0% by volume of sulfurous acid gas, and 87.0% by volume of nitrogen gas were introduced and reacted for 5 minutes. After ending the reaction and evacuating, re-pressurize with nitrogen to take out the sample,
The sample was placed in a 30% aqueous solution of potassium hydroxide at 60 ° C for 1 hour.
It was immersed for a period of time, washed with water, and dried at 50 ° C. for 7 hours. Neutral salt resolution was 0.027 meq / g. Using this sample C as a separator, a nickel-hydrogen secondary battery was assembled,
The self-discharge characteristics were measured. The results are shown in Table 1. Table 2 shows the results of a 30% KOH aqueous solution penetration rate and XRF analysis.

Example 3 Nonwoven fabric of polyethylene and polypropylene mixture (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Of SUS316, which is resistant to fluorine,
After the vessel was evacuated and evacuated, 3.0% by volume of fluorine gas, 10.0% by volume of sulfurous acid gas and 87.0% by volume of nitrogen gas were introduced and reacted for 5 minutes. After completion of the reaction and evacuation, the sample was taken out by restoring the pressure with nitrogen, and the sample was immersed in 95% concentrated sulfuric acid for 1 hour at 25 ° C.
For 7 hours. The neutral salt resolution of this sample was less than 0.01 meq / g. Using this sample D as a separator, a nickel-hydrogen secondary battery was assembled, and the self-discharge characteristics were measured. The results are shown in Table 1. Also, 30
Table 2 shows the results of the permeation rate of the aqueous KOH solution and XRF analysis.

Example 4 A nonwoven fabric of a mixture of polyethylene and polypropylene (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Is placed in a container made of SUS316 which is resistant to fluorine, and after evacuation, 3.0% by volume of fluorine gas, 10.0% by volume of sulfurous acid gas and 87.0% by volume of nitrogen gas are introduced and reacted for 5 minutes. Was. After the reaction was completed and the system was evacuated, the pressure was restored with nitrogen, and the sample was taken out. The sample was immersed in 95% concentrated sulfuric acid for 1 hour at 25 ° C., washed with water, and washed with 0.3% nonionic surfactant (polyoxyethylene nonyl). Phenyl ether)
After immersion in the aqueous solution, it was dried at 50 ° C. for 7 hours. The neutral salt resolution of this sample was less than 0.01 meq / g. Using this sample E as a separator, a nickel-hydrogen secondary battery was assembled, and the self-discharge characteristics were measured. Table-Results
1 is shown. Table 2 shows the results of a 30% KOH aqueous solution penetration rate and XRF analysis.

Comparative Example 2 Nonwoven fabric of polyethylene and polypropylene mixture (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Is placed in a container made of SUS316 which is resistant to fluorine, and after evacuation, 2.0% by volume of fluorine gas, 80.0% by volume of oxygen gas and 17.0% by volume of nitrogen gas are introduced and reacted for 5 minutes. Was. After the reaction was completed and the system was evacuated, the pressure was restored with nitrogen, and the sample was taken out. The neutral salt resolution of this sample is 0.01 meq /
g. Using this sample F as a separator, a nickel-hydrogen secondary battery was assembled, and the self-discharge characteristics were measured. The results are shown in Table 1. Table 2 shows the results of a 30% KOH aqueous solution penetration rate and XRF analysis.

Comparative Example 3 Nonwoven fabric of polyethylene and polypropylene mixed (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Is placed in a container made of SUS316 which is resistant to fluorine, and after evacuation, 3.0% by volume of fluorine gas, 10.0% by volume of sulfurous acid gas and 87.0% by volume of nitrogen gas are introduced and reacted for 5 minutes. Was. After the reaction was completed and evacuated, the pressure was restored with nitrogen, and the sample was taken out, washed with water and dried at 50 ° C. for 7 hours. The neutral salt resolution of this sample is 0.01 meq
/ G. Using this sample G as a separator, a nickel-hydrogen secondary battery was assembled, and the self-discharge characteristics were measured. The results are shown in Table 1. Table 2 shows the results of a 30% KOH aqueous solution penetration rate and XRF analysis.

Comparative Example 4 Polyamide nonwoven fabric (basis weight 65 g / m ² , thickness 0.18
A self-discharge characteristic was measured by assembling a nickel-hydrogen secondary battery using a separator sample H having a size of 18 mm × 18 cm). The results are shown in Table 1. In addition, 30% K
Table 2 shows the results of the OH aqueous solution penetration rate and XRF analysis.

Example 5 A nonwoven fabric of a mixture of polyethylene and polypropylene (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Is placed in a container made of SUS316 which is resistant to fluorine, and after evacuation, 3.0% by volume of fluorine gas, 10.0% by volume of sulfurous acid gas and 87.0% by volume of nitrogen gas are introduced and reacted for 5 minutes. Was. After the reaction was completed and the system was evacuated, the pressure was restored with nitrogen, and the sample was taken out. Thereafter, the sample was immersed in a 30% aqueous potassium hydroxide solution at 60 ° C. for 1 hour, and the neutral salt resolution was 0.027 meq / g. This sample is 25
The sample was immersed in concentrated sulfuric acid at 95 ° C. for 1 hour, washed with water and dried at 50 ° C. for 7 hours. Using this sample H, a nickel-hydrogen secondary battery was assembled, and the self-discharge characteristics were measured. The results are shown in Table 1. Table 2 shows the results of a 30% KOH aqueous solution penetration rate and XRF analysis. A nickel-hydrogen secondary battery was assembled using the separator I, and after 10 cycles of charge / discharge, the capacity retention rate after standing at 45 ° C. for 7 days was measured. The results are shown in Table 1. Table 2 shows the results of a 30% KOH aqueous solution penetration rate and XRF analysis.

Comparative Example 5 A nonwoven fabric of a mixture of polyethylene and polypropylene (polyethylene / polypropylene = 35/65 (weight ratio), basis weight 5
(5 g / m ² , thickness 0.15 mm, 18 cm × 18 cm)
Was immersed in a 95% concentrated sulfuric acid solution at 25 ° C., but the nonwoven fabric did not wet with the concentrated sulfuric acid solution. Therefore, sulfuric acid treatment could not be performed.

[0038]

Table 1: Separator treatment method and self-discharge characteristics (capacity retention ratio) Separator type Capacity retention ratio (%) A (Example 1) 70% B (Example 2) 67% C (Comparative Example 1) 52% D (Example 3) 70% E (Example 4) 68% F (Comparative Example 2) 50% G (Comparative Example 3) 52% H (Comparative Example 4) 45% I (Example 5) 69%

[0039]

[Table 2] Table 2: Separator processing method and penetration rate, XRF data XRF (kcps) Separator type Penetration rate O / CS / CA (Example 1) 41 minutes 0.0031 0.33 B (Example) 2) 38 minutes 0.0036 0.34 C (Comparative Example 1) 32 minutes 0.0065 0.65 D (Example 3) 51 minutes 0.0076 1.04 E (Example 4) 20 seconds 0.0101 0 .42 F (Comparative Example 2) 30 seconds 0.0082-G (Comparative Example 3) 38 minutes 0.0042-H (Comparative Example 4) 30 seconds-I (Example 5) 63 minutes 0.0074 1.123

[0040]

According to the present invention, a material mainly composed of polyolefin is hydrophilized by a simple process without requiring a special operation such as gas replacement, and the material is deteriorated by a sulfuric acid treatment. Without increasing the self-discharge characteristics, and succeeded in imparting characteristics suitable for a battery separator.

[Brief description of the drawings]

FIG. 1 shows FT-I on the surface of sample A obtained in Example 1.
R measurement diagram

FIG. 2 is an FT-IR measurement diagram of the surface of a sample obtained by immersing the nonwoven fabric of Example 1 in fuming sulfuric acid.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Minoru Kashino, 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory (72) Inventor Masayuki Watanabe 1000, Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation Yokohama Research Laboratory

Claims (9)

[Claims] 1. A method for producing a battery separator material, wherein a surface of a polyolefin resin material is subjected to a hydrophilic treatment and then immersed in sulfuric acid. 2. The method for producing a battery separator material according to claim 1, wherein the polyolefin resin material is a porous body mainly composed of polyethylene and / or polypropylene. 3. The polyolefin resin material is made of a non-woven fabric or a woven fabric made of fibers mainly composed of polyethylene and / or polypropylene.
A method for producing the battery separator material described above. 4. The method according to claim 1, wherein the method of the hydrophilic treatment is selected from flame treatment, plasma discharge treatment, corona discharge treatment, ultraviolet irradiation treatment and electron beam irradiation treatment. A method for producing a battery separator material. 5. The method according to claim 1, wherein the hydrophilization treatment is a treatment using a fluorine gas-containing gas.
The method for producing a battery separator material according to any one of the above. 6. The method for producing a battery separator material according to claim 5, wherein the fluorine gas-containing gas contains a fluorine gas, an oxygen gas, and / or a sulfurous acid gas. 7. The method for producing a battery separator material according to claim 1, wherein the material is immersed in a sulfuric acid aqueous solution having a sulfuric acid concentration of 50 to 98% by weight at a bath temperature of less than 100 ° C. 8. The method for producing a battery separator material according to claim 1, wherein a treatment with a surfactant is performed after immersion in sulfuric acid. 9. A separator material for an alkaline storage battery obtained by the method according to claim 1. Description: