WO2003003486A1

WO2003003486A1 - Separator for battery and method for producing the same

Info

Publication number: WO2003003486A1
Application number: PCT/JP2002/002657
Authority: WO
Inventors: Yasunao Shimano; Junsho Kanenori
Original assignee: Komatsu Seiren Co., Ltd.
Priority date: 2001-06-04
Filing date: 2002-03-20
Publication date: 2003-01-09
Also published as: JP2003151523A

Abstract

A separator for battery in which capturing capacity of ammonia can be increased and self discharge of battery can be suppressed when the separator is employed in an alkaline secondary battery. The separator for battery is characterized in that a basic material comprising polyolefin based fibers is subjected to graft copolymerization with a monomer having a sulphonic acid group, i.e. 2-acrylamide 2-methylpropane sulphonic acid, and a monomer having a carboxyl group.

Description

TECHNICAL FIELD The present invention relates to a battery separator and a method of manufacturing the same.

The present invention relates to a battery separator and a method for producing the same, and more particularly to a separator for an alkaline secondary battery using nickel hydroxide as a positive electrode active material. Background art

Conventionally, in a lithium secondary battery using nickel as the positive electrode and cadmium, zinc, hydrogen storage alloy, etc. as the negative electrode, it prevents the positive electrode and the negative electrode from short-circuiting and retains the electrolytic solution such as a hydroxylic power rim. A non-woven fabric or the like made of a polyolefin-based fiber having alkali resistance is used as a separator. For example, Japanese Patent Application Laid-Open No. 52-55054 discloses a method of grafting a vinyl monomer (such as acrylic acid) which reacts with an acid or a base to form a salt on a porous film, polyethylene, or polypropylene nonwoven fabric. A polymerized battery separator is disclosed. Also, Japanese Patent Application Laid-Open No. 57-141,628 discloses a vinyl monomer (acrylic) that reacts with an acid or a base to form a salt on a nonwoven fabric having a polyethylene resin formed on the surface of a polypropylene-based fiber. An acid) is graft-polymerized. In addition, Japanese Patent Application Laid-Open No. 5-234457 discloses that a nonwoven fabric obtained by graft-polymerizing a reactive monomer is used as a separator for a nickel-metal hydride battery.

Thus, hydrophilization of polyolefin-based fibers using graft polymerization is a known technique. The graft polymerization method includes (1) a chemical method in which the polyolefin-based fiber and the vinyl monomer are both heated in the presence of a polymerization initiator, and (2) a UV- or electron-emitting method in which the polyolefin-based fiber is brought into contact with the butyl monomer. There are known methods such as a simultaneous irradiation method of irradiating a ray, and (3) a pre-irradiation method of contacting a monomer after irradiating a polyolefin-based fiber with an ultraviolet ray or an electron beam.

In addition, the grafting polymerization is used as the hydrophilic treatment for the polyolefin-based fiber. In addition, a process of sulfonating polyolefin fibers using fuming sulfuric acid, concentrated sulfuric acid, sulfur trioxide or the like to introduce sulfonic acid groups, and a process of hydrophilizing using fluorine gas have been put to practical use.

By the way, in an alkaline secondary battery using nickel as a positive electrode, self-discharge may occur during the capacity retention period after charging, and the capacity may decrease.

According to Patric Leblanc, et al., J. Electrochem., 145 (3) 844-847 (1998), one of the causes of self-discharge in sealed nickel-metal hydride batteries is ammonia generated in the batteries. It is described that most of the ammonia generated from nickel hydroxide is derived from nickel hydroxide, which is a positive electrode active material. It is also described that a separator obtained by graft polymerization of acrylic acid on polyolefin fibers has a function of trapping ammonia, and can suppress self-discharge of a battery as compared to a polyamide nonwoven fabric or the like having no ammonia trapping function. ing.

The generation of ammonia from nickel hydroxide, which is a positive electrode active material, is caused by the fact that, as disclosed in Japanese Patent Application Laid-Open No. H10-122336, a positive electrode active material comprising nickel hydroxide is used. It is considered that ammonium ions are supplied to the nickel to produce an ammonium complex salt, and nickel hydroxide is grown in this state, so that ammonium ions remain in the positive electrode active material.

However, the conventionally used separators in which acrylic acid is polymerized into acrylic polymer on polyolefin-based fibers and the separators in which polyolefin-based fibers are sulfonated have insufficient ammonia-trapping capacity, and the self-discharge of batteries cannot be ignored. At present, it has not reached the limit.

Thus, the present invention provides a battery that can increase the capacity of capturing ammonia and, when used in an alkaline secondary battery using nickel hydroxide as a positive electrode active material, can further suppress self-discharge of the battery. It is a first object of the present invention to provide a separator and a method for manufacturing the same.

On the other hand, Japanese Patent Application Laid-Open No. H08-241704 discloses that, when comparing the amount of introduction required to make polyolefin-based fibers of the same degree of hydrophilicity, the sulfonic acid group is highly polar. The amount may be about 1/2 to 15 of the carboxy group. By introducing a sulfonic acid group, the hydrophilic treatment can be performed while suppressing an unnecessary increase in the mass of the nonwoven fabric. It is described. In addition, it is described that a sulfonic acid group is more resistant to chemical actions such as oxidation than a carboxy group and has excellent stability.

As described above, it is preferable to introduce a sulfonic acid group for the hydrophilization treatment. However, the olefin-based fiber is sulfonated using fuming sulfuric acid, concentrated sulfuric acid, sulfur trioxide, or the like, and the sulfonic acid group is introduced. In such a case, there is a problem that the polyolefin fiber of the main chain is deteriorated, and the tensile strength and the tear strength are reduced.

Therefore, Japanese Patent Application Laid-Open No. H08-241704 discloses that polyolefin-based fibers include a sulfonic acid derivative such as a metal salt of p_styresinolenoic acid or a metal salt of vinylsulfonic acid and a carboxylic acid derivative. Are graft-copolymerized to introduce both a sulfonic acid group and a carboxy group.

However, even if graft copolymerization is performed as described in Japanese Patent Application Laid-Open No. H08-241704, the fact that both a sulfonic acid group and a carboxy group are actually introduced is based on the following reasons. Extremely difficult.

That is, a carboxylic acid derivative such as acrylic acid has a small molecular weight, swells the polyolefin-based fiber, diffuses into the fiber, and the graft polymerization proceeds. On the other hand, the metal salt of P-styrenesulfonic acid has an extremely large molecular weight as compared with the carboxylic acid derivative, and has an extremely high polarity as compared with the carboxylic acid derivative, so that it does not diffuse into the fiber. It is extremely difficult to graft polymerize a metal salt of p-styrenesulfonic acid because polymerization proceeds only outside the fiber to produce a homopolymer.

In addition, the monomer having a beer group is less polymerizable than the monomer having an acryloyl group, and the polarity of the metal salt of vinyl sulfonic acid is extremely higher than that of the carboxylic acid derivative, so that the monomer is diffused into the fiber. Instead, the polymerization proceeds only outside the fiber to produce a homopolymer, so it is extremely difficult to graft-polymerize a metal salt of vinylsulfonic acid.

When the graft copolymerization is performed as described in JP-A-8-241704, a homopolymer that is difficult to remove is generated outside the fiber, so that after the completion of the polymerization reaction, The cleaning process is complicated. Also, if the separator is attached to the battery with the homopolymer attached, the homopolymer will fall into the electrolyte and the battery performance will decrease. There is also a risk.

It should be noted that whether or not a sulfonic acid group has been introduced can be clarified by performing sulfur analysis based on the Scheniga method. However, Japanese Patent Application Laid-Open No. H08-241704 discloses a method for detecting sulfur. Is not described, and it is not clear whether a sulfonic acid group was actually introduced.

As mentioned above, although the introduction of a sulfonic acid group by graft polymerization has been proposed, no concrete example of introducing a sulfonic acid group by graft polymerization has been reported so far. Therefore, the present invention provides a means for easily introducing a sulfonic acid group without lowering the strength of the polyolefin-based fiber, whereby the weight and the chemical stability can be improved. A second object is to provide a battery separator and a method for manufacturing the same.

In addition, conventionally, when a battery separator obtained by graft polymerization of an acidic group-containing monomer is used for a nickel-free nickel battery, a nickel-hydrogen battery, etc., the oxygen generated during overcharge deteriorates the separator. It is reported that a short circuit may occur, and that the separator may be deteriorated due to oxygen, which may affect the electrode plate and shorten the life of the battery.

For example, P. Alexander, M. Fox; J. polym. Sci., 33, 493 (1958) report that polymethacrylic acid is decomposed by natural oxidation even at a low temperature of 37 ° C. As can be seen from this report, a polymer containing a hydroxyl group, such as polyacrylic acid, introduced by graft polymerization may not be stable against chemical actions such as oxidation. Japanese Patent Application Publication No. 0-0161062 discloses that after a vinyl monomer having a carboxy group is brought into contact with a polyolefin-based fiber and a graft polymerization treatment is performed in the presence of oxygen, the periphery of the polyolefin-based fiber is non-woven. A method for further performing a graft polymerization treatment in a state of being surrounded by a breathable film is disclosed. According to this method, there is no carboxy group on the surface, and when measured by an X-ray photoelectron spectrometer, the structure has a binding energy of 530.5 to 51.5 eV, that is, the surface has A battery separator having a structure in which an oxygen atom or an oxygen molecule is bonded to the battery separator can be obtained. The obtained battery separator has excellent oxidation resistance. It is described that batteries equipped with a radiator have excellent capacity retention and a long cycle life of repeated charge and discharge.

However, the method described in Japanese Patent Application Laid-Open No. 2000-106612 has a problem that the production process is complicated because two-stage graft polymerization is required. I have. Accordingly, the present invention provides a battery separator which can be easily manufactured without going through a complicated manufacturing process, has excellent chemical stability such as oxidation resistance, and has excellent durability, and a method for manufacturing the same. Is the third purpose.

As one of the conventional methods for producing separators obtained by graft-polymerizing acrylic acid onto polyolefin-based fibers, as disclosed in Japanese Patent Application Laid-Open No. 6-509208, etc. A method is known in which a monomer solution containing a monomer having a carboxy group, a polymerization initiator, a surfactant, and the like is prepared, and the prepared monomer solution is impregnated into polyolefin-based fibers, followed by irradiation with ultraviolet rays to perform graft polymerization. ing.

However, when graft polymerization is performed by this method, the polymerization of a monomer having a carboxy group proceeds outside the fiber to generate a homopolymer, complicating the washing step and reducing the mass fraction of the graft product. There was something to do.

Therefore, a fourth object of the present invention is to provide a method for producing a battery separator that allows the graft polymerization to proceed stably inside the fiber. DISCLOSURE OF THE INVENTION First, the present inventors have studied to solve the first problem.

Heretofore, there has been no identification of a trapping point of ammonia in a separator in which acrylic acid is graft-polymerized to polyolefin-based fibers or a separator in which polyolefin-based fibers are sulfonated.

The inventor of the present invention has determined the theory based on the force-ream ion exchange capacity IEC (obs) force measured as a characteristic of a battery separator, and the mass fraction of the graft (the mass fraction of the components added by graft polymerization in the entire separator). Ion exchange capacity IEC

It was found that the value was lower than (c a 1).

The IEC (obs) measurement method and the IEC (ca 1) The details of the method of calculating the IEC (obs) will be described in the section of “Examples” .However, in the final product battery separator, the acidic groups at the places that come into contact with the electrolyte are neutralized. ), IEC (ca 1) is the measured value of the potassium ion exchange capacity when the battery separator is immersed in an aqueous solution of potassium hydroxide after the ion exchange group of the battery separator is completely acidified. Each means a theoretical value. Hereinafter, for simplicity of explanation, the term "acidic group" including the acid group that is finally neutralized is simply referred to as "acidic group".

The fact that the measured potassium ion exchange capacity I EC (obs) is lower than the theoretical ion exchange capacity I EC (ca 1) means that all the acidic groups are neutralized when immersed in an aqueous solution of potassium hydroxide. Rather than being converted to a salt, it means that there is an acid and a functional group that remain without being neutralized. The present inventor considered that acidic groups remaining without being neutralized capture ammonia, and as a result, the theoretical ion exchange capacity I EC (ca 1) and the actually measured potassium ion exchange capacity I EC (obs There is a correlation between IEC (ca 1)-IEC (obs) and ammonia trapping capacity, and as IEC (ca 1)-IEC (obs) increases, ammonia trapping capacity increases. The amount was found to increase.

Further, the present inventor has found that among the acidic groups of the polyolefin-based fibers, the groups that are neutralized by the aqueous potassium hydroxide solution and the groups that are not neutralized are related to the distribution of the acidic groups in the polyolefin-based fibers. I thought you were. In other words, the acidic groups present on the surface and near the surface of the fiber are neutralized by contact with the aqueous hydrating solution, while the acidic groups existing inside the surface and near the surface are neutralized by the aqueous hydrating solution. It was not summed up and thought to capture ammonia. We realized that the formation of a large number of acidic groups in the fiber that were not neutralized by aqueous potassium hydroxide solution could increase the capacity of trapping ammonia.As a result, we focused on the above points and conducted a study. Thus, the present inventors have invented a first battery separator of the present invention capable of solving the first problem and simultaneously solving the second problem.

In the first battery separator of the present invention, 2-acrylamide 2-methylpropanesulfonic acid, which is a monomer having a sulfonic acid group, and a monomer having a carboxy group are graft-copolymerized on a substrate made of a polyolefin fiber. Polymerized It is characterized by. Here, acrylic acid or methacrylic acid is preferable as the monomer having a carboxy group. Hereinafter, 2-acrylamide 2-methylpropanesulfonic acid and acrylic acid may be abbreviated as “AXQ” and “AA”, respectively.

The present inventor uses AXQ as a monomer having a sulfonic acid group, and graft copolymerizes AXQ with a monomer having a lipoxy group, thereby reducing the strength of the polyolefin-based fiber without lowering the strength of the polyolefin-based fiber. It has been found that a sulfonate group can be easily introduced into the sample, and that the capacity for trapping phanmoyure can be increased.

Examples of the vinyl monomer having a sulfonic acid group include, in addition to AXQ, sodium p-styrene sulfonate, sodium vinyl sulfonate, sodium arylsulfonate, sodium methallylsulfonate, 3-sulfopropyl acrylate (calidium) Salt), 3-sulfopropylmetharylate (potassium salt), etc., but the present inventor (1) has high polymerizability, and (2) diffuses into polyolefin-based fibers at least near the surface. (3) Stable in strong alkaline electrolyte, (4) AXQ is the best monomer to meet the requirements for stable monomer solution Was found.

(1) When considering the polymerizable Bulle monomers, polymerizable monomers having an Bulle group (CH ₂ = CH ₂₎ Ya Ariru group (CH _₂ = CH- CH _2), the Atariroiru group (CH ₂ = CH- The polymerizability of AXQ having an atariloyl group is higher than that of sodium styrenesulfonate / sodium vinylsulfonate and arylsulfonate because it is lower than that of monomers having CO).

On the other hand, (2) when considering the diffusion intrusion into the inside of the polyolefin fiber, the monomer having a sulfonic acid group is originally difficult to infiltrate because it has higher polarity and higher hydrophilicity than hydrophobic polyolefin. Where the sulfonic acid group

Comparing the (one S0 ₃ H) and sodium sulfonate group (-S0 ₃ "Na ^+), the latter is greater both polar and molecular occupied volume, the diffusion penetration that has become increasingly disadvantageous. Therefore, AXQ having a sulfonic acid group is a monomer having a sulfonic acid sodium group such as sodium p-styrenesulfonic acid and sodium vinylsulfonic acid. (3) Considering stability in a strong alkaline electrolyte in a battery, 3-sulfopropyl atalylate (potassium) (Salt) and 3-sulfopropyl methacrylate (potassium salt) graft polymerized with a monomer having an ester group is not preferable because it is hydrolyzed in a strong alkaline electrolyte and the sulfonic acid group is dropped. .

(4) Considering the stability of the monomer solution, sodium p-styrenesulfonic acid becomes p-styrenesulfonic acid in the presence of acrylic acid, and this p-styrenesulfonic acid has the property of spontaneously polymerizing. As a result, the monomer solution becomes unstable. In addition, sodium vinyl sulfonate shows the same behavior, so it can be used for copolymerization with monomers having acidic groups such as carboxy groups, as shown in Graph 1! / There is a problem with gender.

For the above reasons, when a metal salt of p-styrene sulfonic acid / vinyl sulfonic acid disclosed in JP-A-8-241704 is used, a monomer having a sulfonic acid group is graft-polymerized. However, when AXQ is used, the above requirements must be satisfied, sulfonic acid groups can be easily introduced into the polyolefin fiber, and the sulfur content must be 0.05% or more. I found that I can do it. The method for measuring the sulfur content in the present specification will be described in detail in the section of “Examples”.

As described above, by using AXQ, a sulfonic acid group can be easily introduced into the polyolefin-based fiber.However, AXQ has a larger molecular weight than a monomer having a carboxyl group such as AA. Due to its high polarity, it cannot diffuse into the fiber as much as a monomer having a carboxyl group. Therefore, in the first battery separator of the present invention in which AXQ and a monomer having a carboxy group are graft-copolymerized on a substrate made of a polyolefin-based fiber, the surface and the vicinity of the surface of the polyolefin-based fiber are provided. It seems that AXQ has a structure in which AXQ and a monomer having a carboxy group are graft-copolymerized, and only the monomer having a carboxy group is graft-polymerized from near the surface to the inside. In other words, acidic groups It is considered that both the sulfonic acid group and the sulfonic acid group are introduced on the surface and near the surface of the polyolefin-based fiber, and that only the carboxy group is introduced inside from the vicinity of the surface. .

In the case of contacting the first separator for a battery of the present invention having such a structure with a hydrating aqueous solution, the swelling near the surface is caused by sulfonic acid groups introduced on the surface and near the surface of the fiber. As a result, the diffusion of the potassium ions into the interior is suppressed, and neutralization of the acidic groups by the aqueous solution of potassium hydroxide does not proceed in the region into which only the carboxy group has been introduced. Therefore, according to the first battery separator of the present invention, a large number of acidic groups (carboxy groups) that are not neutralized by the aqueous potassium hydroxide solution can be formed in the fiber, and the capacity for capturing ammonia can be increased. You.

Further, in the first battery separator of the present invention, the mass fraction of the grafted product of AXQ and a monomer having a carboxy group, IEC (ca 1)-IEC (obs), and ammonia trapping capacity It has been found that there is a correlation between the two, and that IEC (ca 1) -IEC (obs) and ammonia capture capacity are maximized when the mass fraction of the graft is about 10%. Therefore, the closer the mass fraction of the graft is to this value, the more dramatically the IEC (c a 1) —IEC (obs) and the capture capacity of the ammonia can be dramatically increased.

Specifically, by setting the mass fraction of the grafted product to 4 to 16%, the IEC (ca 1) —IEC (obs) becomes 0.50 mmo 1 / g or more, and 3 Ommo 1g or more can be found. In addition, it is preferable that the mass fraction of the grafted material is 5 to 15%. By defining as such, IEC (ca 1) —IEC (obs) is 0.6 Ommo 1 Z g As described above, it has been found that the ammonia capturing capacity can be set to 0.5 Ommo 1 / g or more. Further, it is more preferable that the mass fraction of the graft product is 7 to 13%, and by defining as such, the IEC (ca 1)-IEC (obs) is 0.80 mmol / g or more. However, they have found that the ammonia capturing capacity can be 0.6 Ommo 1 / g or more.

In addition, the present inventor added acrylic acid to the conventionally used polyolefin-based fiber. When the ammonia trapping capacity of the graft-polymerized separator and the separator in which the polyolefin-based fiber was sulfonated was measured, the former was about 0.40 mmo 1 / g, the latter was about 0.30 mmol Zg, and only the carboxy group was found. Conventional separator manufacturing technology using only graft polymerization and sulfonation of ammonia cannot achieve an ammonia capture capacity of 0.5 Ommo 1 g or more. For the correlation between the mass fraction of the graft, the IEC (ca 1)-IEC (obs), and the ammonia trapping capacity, and the method of measuring the ammonia trapping capacity in this specification, refer to Examples).

As described above, according to the first battery separator of the present invention, since AXQ and the monomer having a carboxy group are graft-copolymerized, the ammonia capturing capacity can be significantly increased. Therefore, the first battery separator of the present invention is particularly suitable for an alkaline secondary battery using nickel hydroxide as a positive electrode active material. Further, according to the first battery separator of the present invention, self-discharge of the battery can be suppressed more than before, and the capacity retention after charging can be improved.

Further, as described above, according to the first battery separator of the present invention, the sulfonic acid group is easily introduced into the surface of the polyolefin-based fiber and near the surface thereof without lowering the strength of the polyolefin-based fiber. Thus, it has been found that the mass fraction of the graft necessary for hydrophilization can be reduced to the same extent as in the prior art, and the weight can be reduced. In addition, since the sulfonic acid group, which has excellent chemical stability and is hardly oxidized, is introduced on the surface and near the surface of the fiber that comes into contact with the electrolyte, when the battery is attached to a battery, the cycle life of repeated charge and discharge It was found that the battery can be lengthened and the durability of the battery can be improved.

Further, the present inventor has solved the third object by crosslinking an acidic group of at least one monomer graft-polymerized on at least the surface of the polyolefin-based fiber via a polyvalent metal. Having found that it is possible, they have invented the second battery separator of the present invention.

The second battery separator according to the present invention is characterized in that a base material composed of polyolefin fibers is provided with 2-acrylamide 2-methylpropane, a monomer having a sulfonic acid group. It is characterized in that sulfonic acid and a monomer having a carboxy group are graft-copolymerized, and at least the acidic group of at least one type of monomer graft-polymerized on the surface is crosslinked via a polyvalent metal. And Here, it is preferable that the polyvalent metal is at least one selected from calcium, magnesium, barium, aluminum, zinc, titanium, silica, and tin.

Since the second battery separator of the present invention is obtained by graft-copolymerizing AXQ and a monomer having a carboxy group onto a base material composed of polyolefin-based fibers, the second battery separator of the present invention According to this, the same effects as those of the first battery separator of the present invention can be obtained.

Further, according to the second battery separator of the present invention, at least one acidic group graft-polymerized on the surface of the polyolefin-based fiber is crosslinked via a polyvalent metal to form an acidic group. However, further effects can be obtained.

The present inventors can improve the chemical stability such as oxidation resistance and heat resistance by crosslinking the acidic group of at least one kind of monomer graft-polymerized on at least the surface of the polyolefin-based fiber. It has been found that a battery separator having excellent durability can be provided. In addition, it has been found that chemical stability can be significantly improved by crosslinking via an inorganic polyvalent metal, as compared with the case where an acidic group is crosslinked via an organic substance. As described above, since the second battery separator of the present invention is excellent in chemical stability, when the second battery separator of the present invention is mounted on a battery, repeated charging and discharging of the battery is performed. The cycle life can be extended, and the durability of the battery can be improved.

As described above, in the battery separator obtained by using AXQ and a monomer having a carboxy group as the monomer, AXQ and the monomer having a carboxy group are graft-copolymerized on the surface of the polyolefin-based fiber. `` Crosslink the acidic group of at least one monomer polymerized on the surface '' means `` monomer having at least AXQ and hydroxyl group polymerized on the surface. Of these, at least one of the monomers cross-links the acidic group. " In addition, the present inventors immerse the base material after the graft polymerization in a polyvalent metal salt solution (polyvalent metal salt solution) to reduce the acid groups of at least one type of monomer graft-polymerized on at least the surface. It has been found that crosslinking can be carried out via a polyvalent metal, and the second battery separator of the present invention can be easily produced without changing the graft polymerization process.

Therefore, according to the present invention, it is possible to provide a battery separator which can be easily manufactured without going through a complicated manufacturing process, has excellent chemical stability such as oxidation resistance, and has excellent durability. it can.

The above-described first and second battery separators of the present invention can be manufactured by the method for manufacturing a battery separator of the present invention described below. The method for producing a battery separator of the present invention is suitable as a method for producing the first and second battery separators of the present invention, and solves the fourth problem.

The method for producing a battery separator according to the present invention is the first and second method for producing a battery separator according to the present invention described above, wherein 2-acrylamide 2-methylpropanesulfone is provided on a substrate made of polyolefin fiber. A monomer solution impregnating step of impregnating a monomer solution containing an acid and a monomer having a carboxy group; and holding the base material impregnated with the monomer solution between a holding material holding the base material and a polyester film. A high energy beam irradiation step of irradiating the base material with high energy energy from the polyester film side in a state where the polyester film is in a closed state.

Examples of high energy rays include ultraviolet rays, γ rays from Co 60, and electron beams. Of these, ultraviolet rays and electron beams that can be continuously processed are particularly preferable.

In general, when a hydrophilic fiber having an acidic group such as a carboxy group or a sulfonate group is impregnated into a hydrophobic fiber such as a polyolefin fiber, and then grafted with high-energy rays, graft polymerization is performed. It is known that the polarity is too large compared to the polyolefin-based fiber, so that it does not easily diffuse into the fiber, and the polymerization reaction progresses before diffusing into the fiber to generate a homopolymer, which makes it difficult for graft polymerization to occur. ing.

In order to solve this problem, the present inventor has set the temperature of the monomer solution and the base material. As high as possible to promote the diffusion of monomers into the interior of the fiber, and reduce the irradiation energy per unit time of high-energy radiation to reduce the polymerization rate and extend the polymerization time as much as possible. I thought it would be effective.

As a result of studying focusing on the points of strength, in the high energy beam irradiation process, the polyester film was sandwiched between the base material and the holding material such as stainless steel plate / glass plate and the polyester film. By irradiating high-energy rays from the side to advance daraft copolymerization, it was found that part of the high-energy rays could be shielded by the polyester film, and the high-energy ray intensity could be kept low. In addition, as a result, the polymerization rate can be reduced to suppress the formation of homopolymer outside the fiber, the monomer can be uniformly diffused inside the fiber, and the graft copolymerization can proceed stably inside the fiber. Was found.

Furthermore, the following advantages can be obtained by irradiating the base material impregnated with the monomer solution with high-energy rays while holding it between a holding material such as a stainless steel plate or a glass plate and a polyester film. I found it. That is, the base material is heated to a maximum of about 10 ° C. by the heat of polymerization generated upon the initiation of polymerization, but the base material temperature is maintained by promoting the polymerization reaction as described above, and the monomer fiber is heated. It has been found that diffusion into the interior can be promoted and evaporation loss of the monomer solution due to heat can be suppressed.

Further, as described above, in the case where polymerization is started by irradiation with high-energy radiation, graft polymerization does not proceed unless the monomer is diffused into the fiber.

As described in the section of “Prior Art”, a pre-irradiation method or a simultaneous irradiation method is known as a graft polymerization method for irradiating high energy rays. In the pre-irradiation method, high-energy rays are irradiated to form active sites for polymerization on the base material, and then the polymer is brought into contact with the monomer to perform polymerization, so that the diffusion of the monomer into the fiber and the polymerization reaction are reduced. Progress at the same time. Also in the simultaneous irradiation method, the irradiation of the high-energy beam and the contact of the monomer are performed simultaneously, so that the diffusion of the monomer into the fiber and the polymerization reaction proceed simultaneously. As described above, conventionally, it is general that the diffusion of the monomer into the fiber and the polymerization reaction proceed simultaneously. The diffusion of the monomer proceeds as the temperature is higher and the time is longer.However, the present inventor has found that when continuously producing battery separators, the time for irradiating the substrate with high energy rays is 1 to 10 seconds. Because of the extremely short degree, it was thought that if the diffusion of the monomer into the fiber and the polymerization reaction proceeded simultaneously, the polymerization reaction would end without the monomer diffusion sufficiently proceeding. Then, before the high energy beam irradiation (before the start of polymerization), it was considered preferable to diffuse the monomer into the fiber in advance. Heretofore, there has been almost no report on a method of polymerizing a monomer by diffusing the monomer in advance and then irradiating with a high energy beam.

The present inventor focused on the above points, and studied to increase the speed of the graft polymerization reaction. As a result, the base material impregnated with the monomer solution before the high energy ray irradiation step was used. Is preheated at a temperature of 70 to 100 ° C. while holding the base material between the holding material for holding the base material and the polyester film, and a preheating step of diffusing the monomer into the fiber is added. Was found to be preferable.

That is, by pre-heating the base material before the high energy beam irradiation step, the monomer can be diffused inside the polyolefin fiber before the polymerization starts, and the graft polymerization reaction can be accelerated. It has been found that the formation of homopolymer outside the fiber can be suppressed, and the uniformity of the polymerization reaction can be improved.

In the high energy line irradiation step, it is more preferable to irradiate the high energy ray while maintaining the heating temperature in the preheating step. With such a configuration, the monomer in the high energy ray irradiation step is preferably used. It has also been found that the effect of further promoting the diffusion of the metal can be obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a graph showing mass fractions of grafts, IEC (ca 1), IEC (obs), IEC (ca 1)-IEC (obs) and ammo air of the battery separator obtained in the example according to the present invention. FIG. 3 is a diagram showing a relationship between a trapping capacity ATC. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the battery separator of the present invention, 2-acrylamide 2-methylpropanesulfonic acid (AXQ), which is a monomer having a sulfonate group, and a monomer having a carboxy group are graft-copolymerized on a substrate made of polyolefin fiber. It is characterized by being polymerized. ·

Here, a non-woven fabric is suitable as the base material, and the case where the base material is made of a non-woven fabric will be described below as an example.

Examples of the polyolefin fibers constituting the nonwoven fabric as the base material include homopolymers of α-olefin such as ethylene, propylene, butene-11,4-methylpentene_1, and copolymerization of two or more of these α-olefins. In addition to fibers composed of one type of polymer selected from the above copolymers, composite fibers (core-sheath composite fibers, parallel composite fibers, split fibers, etc.) obtained by combining a plurality of the above-mentioned polymers can be used. . Specific examples include a fiber composed of only polypropylene, a fiber composed of only polyethylene, a polypropylene / polyethylene core-sheath composite fiber having polypropylene as a core component, polyethylene as a sheath component, and a split fiber composed of polypropylene and polyethylene. Can be.

Nonwoven fabrics made of polyolefin fibers are manufactured by a known method such as a dry (card) method, a spunbond method, a melt blow method, a wet (papermaking) method, and are subjected to secondary processing by a water jet method or the like. good.

The present invention is obtained by graft copolymerizing AXQ and a monomer having a carboxyl group onto a nonwoven fabric made of the above-mentioned polyolefin-based fiber. Here, as the monomer having a carboxy group, acrylic acid (ΑΑ) or methacrylic acid is preferable. Among these, acrylic acid is particularly preferred because of its high solubility in water and excellent operability.

As described above, by using AXQ as a monomer having a sulfonic acid group, a sulfonic acid group can be easily introduced without lowering the strength of the polyolefin-based fiber, and the sulfur content can be reduced to 0.05 to 50%. 0.12%. More specifically, when about 10% of AXQ and ΑΑ are copolymerized in a polypropylene nonwoven fabric, for example, the mass fraction of グラフト graft is 9.65%, and It has been found that the mass fraction of the grafted product of Q can be 0.35% and the sulfur content can be 0.05%. When a nonwoven fabric made of polypropylene Z polyethylene core-sheath composite fiber is used, for example, the mass fraction of the grafted product of AA is 9.20%, the mass fraction of the grafted product of AXQ is 0.80%, and the sulfur content is Was found to be 0.12%.

Further, in the battery separator of the present invention, the mass fraction of the grafted product of AXQ and the monomer having a carboxy group, IEC (ca 1) —IEC (obs), and the ammonia trapping capacity There is a correlation between IEC (ca 1) and IEC (obs), and the ammonia trapping capacity is maximized when the mass fraction of the graft is about 10%. Therefore, the closer the mass fraction of the graft is to this value, the more the IEC (c a1) -one IEC (obs) and the capacity for capturing ammonia can be dramatically increased.

Specifically, by setting the mass fraction of the grafted product to 4 to 16%, the IEC (ca1)-IEC (obs) is 0.50 mmo1 / g or more, and the capacity of capturing the gamma-ray is 0. It can be 3 Ommo 1 / g or more. Further, it is preferable that the mass fraction of the graft is 5 to 15%, and by defining as such, the IEC (ca 1) −IEC (obs) is 0.60 mm o 1 / g or more. The trapping capacity can be set to 0.5 Ommo 1 Zg or more. Further, it is more preferable that the mass fraction of the graft is 7 to 13%, and by defining as such, IEC (ca 1) -IEC (obs) is 0.8 Ommo 1 Zg or more, The ammonia capturing capacity can be 0.6 Ommo 1 / g or more.

As described above, according to the battery separator of the present invention, since AXQ and the monomer having a carboxy group are graft-copolymerized, the ammonia capturing capacity can be increased. Therefore, the battery separator of the present invention is particularly suitable for an alkaline secondary battery using nickel hydroxide as the positive electrode active material. Further, according to the battery separator of the present invention, self-discharge of the battery can be suppressed more than before, and the capacity retention after charging can be improved. '

Further, according to the battery separator of the present invention, a sulfonic acid group is formed on the surface of the polyolefin-based fiber and in the vicinity of the surface without reducing the strength of the polyolefin-based fiber. Since it can be easily introduced, it is possible to reduce the mass of the graft material necessary to make it hydrophilic to the same extent as before, reduce the weight, and at the surface and near the surface of the fiber in contact with the electrolyte. Since the sulfonic acid group with excellent chemical stability is introduced into the battery, when it is installed in a battery, the cycle life of repeated charge / discharge of the battery can be extended, and the durability of the battery can be improved. it can.

The reason why the sulfonic acid group can be easily introduced by using AXQ and the reason that the ammonia trapping capacity can be increased are described in detail in the section "Means to solve the problem". The explanation is omitted.

Further, in the method for producing a battery separator according to the present invention, it is preferable that the acidic group of at least one monomer graft-polymerized on at least the surface of the polyolefin-based fiber is crosslinked via a polyvalent metal. The polyvalent metal is not particularly limited, but calcium, magnesium, barium, aluminum, zinc, titanium, zirconium, tin and the like are preferable.

As described above, the acidic group of at least one monomer graft-polymerized on at least the surface of the polyolefin-based fiber is cross-linked via a polyvalent metal, thereby obtaining the `` means for solving the problems ''. As described above, it is possible to provide a battery separator that can be easily manufactured without going through a complicated manufacturing process, has excellent chemical stability such as oxidation resistance, and has excellent durability. Further, when the battery separator of the present invention is mounted on a battery, the cycle life of repeated charge / discharge of the battery can be extended, and the durability of the battery can be improved.

[Method of manufacturing battery separator]

Next, an example of the method for producing the battery separator of the present invention will be described in detail. The following method for producing a battery separator of the present invention is a method suitable for producing the battery separator of the present invention, but the method for producing the battery separator of the present invention is described below. It is not limited to one. Hereinafter, a case where nonwoven fabric is used as a base material, AX Q and AA are used as monomers, and ultraviolet rays are used as high energy rays will be described as an example.

First, from the polyolefin-based fiber that is the base material of the battery separator of the present invention A non-woven fabric is prepared. Since the structure of the nonwoven fabric suitable for use in the battery separator of the present invention has been described above, the description is omitted.

Next, a monomer solution containing A X Q and AA is prepared. The concentrations of AX Q and A A in the monomer solution are each preferably 5 to 30% by mass. To the monomer solution, it is preferable to add 0.01 to 0.5% by mass of a hydrogen abstraction type polymerization initiator such as benzophenone for extracting hydrogen from the polyolefin-based fiber. The polymerization initiator is added after being dissolved in a solvent such as AA or acetone. In order to prevent the polymerization reaction from proceeding outside the fiber to form a homopolymer, a polymerization inhibitor such as a metal salt (specifically, a salt such as copper or iron) is added to the monomer solution. It is preferable to add 0.1 to 1.0% by mass. Further, in order to improve the wettability of the monomer solution to the polyolefin-based fiber, a nonionic surfactant or an anionic surfactant may be added. If necessary, wettability can be improved by using acetone, isopropyl alcohol, methyl alcohol and the like in combination.

Next, in the monomer solution impregnation step, the nonwoven fabric made of polyolefin-based fibers is impregnated with the monomer solution prepared as described above. In this step, it is preferable that about 200 parts by mass or more of the monomer solution is impregnated into 100 parts by mass of the polyolefin-based fiber.

Next, in the preheating step, the nonwoven fabric impregnated with the monomer solution is placed on a holding material for holding the nonwoven fabric, such as a stainless steel plate or a glass plate, and the opposite side of the nonwoven fabric holding material is coated with a polyester film. Preheat at a temperature of 70 to 100 ° C for 10 seconds to 10 minutes while covering and holding the holding material and the polyester film.

By preheating the non-woven fabric in this way, it is possible to start the diffusion of the monomer before the start of the graft polymerization, to speed up the polymerization reaction and to generate the homopolymer outside the fiber. Thus, the polymerization reaction can be made more uniform. In addition, since AA can be diffused into the fiber before the start of polymerization, the effect of increasing the amount of carboxy groups that trap ammonia can be obtained. In addition, by pre-heating the non-woven fabric sandwiched between the holding material and the polyester film, it is possible to irradiate high energy rays while maintaining the temperature in a subsequent high energy ray irradiation step. Therefore, the evaporation of the monomer solution can be suppressed, and the effect of further promoting the diffusion of the monomer in the high-energy line irradiation process can be obtained.

If the preheating temperature is lower than 70 ° C, the effect of promoting the diffusion of the monomer is small, and if it exceeds 100 ° C, the temperature of the polyester film becomes too high in the subsequent high energy beam irradiation step. Thus, the polyester film may be deformed, and the water and the like contained in the monomer solution evaporate to make the polymerization reaction nonuniform, which is not preferable.

As a method for preheating the nonwoven fabric, a known heating method can be adopted.However, a method using far-infrared rays raises the temperature to a desired temperature of 70 ° C. or more in several 10 seconds to several minutes. It is preferable because it can be used. Further, a method of directly heating the holding material by means such as electric heating is also suitable.

Next, in the high energy beam irradiation step, the nonwoven fabric is irradiated with ultraviolet rays (high energy energy) from the polyester film side while being held between the holding material and the polyester film.

As described above, in the high-energy ray irradiation step, by irradiating ultraviolet rays from the polyester film placed on the nonwoven fabric to promote graft copolymerization, a part of the ultraviolet rays is blocked by the polyester film, and the ultraviolet intensity is reduced. Can be kept as low as 2 O mW / cm ² or less. As a result, the polymerization rate is reduced, the generation of a homopolymer outside the fiber is suppressed, the monomer is uniformly diffused inside the fiber, and the graft copolymerization can proceed stably inside the fiber.

If the UV intensity applied to the nonwoven fabric is higher than ² OmWcm2, the polymerization reaction proceeds before the monomer diffuses inside the fiber, and a homopolymer is likely to be generated outside the fiber. The process becomes complicated, and the mass fraction of the graft may decrease.

In addition, the temperature of the nonwoven fabric rises to a maximum of about 100 ° C due to the heat of polymerization generated at the start of the polymerization and the infrared rays emitted from the ultraviolet lamp. By irradiating ultraviolet rays while sandwiching between the holding material and the polyester film, the temperature of the nonwoven fabric can be maintained, the diffusion of the monomer into the fiber can be promoted, and the loss of evaporation of the monomer solution due to heat Can be suppressed. In addition, in the high energy line irradiation process, the holding material is heated at the same temperature as in the preheating step to maintain the heating temperature in the preheating step. It is more preferable to keep

Examples of the ultraviolet irradiation means include a high-pressure mercury lamp, a metal halide lamp, and a non-electrode type lamp induced at a high frequency. For example, when a lamp of 12 O WZ cm is used, in order to allow the graft copolymerization to proceed stably, a large number of 3 to 10 lamps are required at a transfer speed of 2 to 15 m / "min. In this way, it is preferable to reduce the intensity of the ultraviolet light irradiating the nonwoven fabric and set the irradiation time longer so that the graft copolymerization proceeds efficiently and a homopolymer is generated. Since the ratio can be reduced and the utilization rate of the monomer can be increased, the mass fraction of the graft can be increased, and the uniformity of the reaction can be improved.

After the completion of the polymerization reaction, the nonwoven fabric is washed with hot water or hot water containing an alkali agent such as sodium hydroxide or sodium hydroxide to remove the homopolymer on the surface, and, if necessary, to dilute it with hydrochloric acid or acetic acid. Neutralize with solution.

Next, when the acidic groups of at least one monomer graft-polymerized on at least the surface are crosslinked via a polyvalent metal, a dilute solution of a polyvalent metal salt such as calcium chloride, zinc acetate, or aluminum chloride is used. (Polyvalent metal salt solution)

The acidic group of at least one monomer graft-polymerized on at least the surface is reacted with a polyvalent metal, and the acidic group of at least one monomer graft-polymerized on at least the surface is cross-linked via the polyvalent metal. I do.

Finally, the battery separator of the present invention can be manufactured by drying using a heating means such as a cylinder roll filled with hot air, infrared rays, or steam.

According to the method for producing a battery separator of the present invention described above, the graft polymerization can proceed stably inside the fiber, and the battery separator of the present invention can be produced stably. Also, at least one surface graft-polymerized on at least In the case of crosslinking the acidic groups of various kinds of monomers via a polyvalent metal, it is only necessary to add a step of immersing the nonwoven fabric after graft polymerization in a solution of a polyvalent metal salt (polyvalent metal salt solution). Therefore, it can be easily manufactured without changing the graft polymerization process.

Although only the case where ultraviolet rays are used as high energy rays has been described above, the present invention is not limited to this. Hereinafter, as another example of the method for producing a battery separator of the present invention, a case where an electron beam is used as a high energy beam will be described.

First, a nonwoven fabric is prepared and a monomer solution is prepared in the same manner as in the case where ultraviolet rays are used as high energy rays. In addition, it is preferable to remove dissolved oxygen by bubbling an inert gas such as nitrogen into the prepared monomer solution. Next, as in the case of using ultraviolet light as a line of high energy, the nonwoven fabric is impregnated with a monomer solution, and the nonwoven fabric is sandwiched between a holding material and a polyester film, and preheating is performed. In the process, an electron beam is irradiated from the polyester film side using an electron beam accelerator or the like. In this step, the holding material is preferably heated by electric heating or the like in order to hold the nonwoven fabric at 70 ° C. or more. In this step, the irradiation amount of the electron beam is adjusted so that the irradiation amount of the electron beam irradiated on the nonwoven fabric is 5 to 25 kGy per pass, and the number of passes is set to 2 to 10 times. It is preferable to perform the electron beam irradiation so that the total irradiation amount becomes 10 to 250 kGy. As described above, it is preferable that the irradiation amount of the electron beam irradiating the nonwoven fabric is kept low and the total irradiation time is set long.

Thereafter, the mixture may be further heated at 70 to 100 ° C. for 1 to 10 minutes using a far-infrared heating device or the like, so that the diffusion and polymerization of the monomer may proceed. The operation after the completion of the graft polymerization is the same as the case where ultraviolet rays are used as the high-energy rays, and the description is omitted.

Thus, even when an electron beam is used as the high energy beam, the same effect as when ultraviolet light is used as the high energy line can be obtained, and the graft polymerization can proceed stably inside the fiber. Stable battery separator of the present invention Can be manufactured. 【Example】

Next, examples and comparative examples according to the present invention will be described.

In Examples 1 to 7, Examples 9 to 14, and Comparative Examples 1 to 7, battery separators were manufactured, and the obtained battery separators were evaluated. In each of Examples and Comparative Examples, an Ecker hydrogen battery was manufactured using the obtained battery separator, and the obtained batteries were evaluated. In Example 8, 16 kinds of battery separators of the present invention including the battery separators of Examples 1 to 3 were produced in the same manner as Examples 1 to 3, and the obtained battery separators were evaluated. Was done.

In Examples 1 to 8 and Comparative Examples 1 to 5, the surface was not crosslinked with the acidic group of the monomer subjected to daraft polymerization, whereas Examples 9 to 14 and Comparative Examples 6 and 7 were grafted on the surface. The acidic group of the polymerized monomer was crosslinked to prepare a battery separator. In Examples 1 to 12 and Comparative Examples 1 to 6, ultraviolet rays were used as high energy rays, and in Examples 13, 14, and Comparative Example 7, a battery separator was formed using an electron beam as high energy rays. Produced.

(Evaluation items and evaluation methods for battery separators)

The evaluation items and evaluation methods for the battery separator obtained in each example are as follows. In each comparative example, the evaluation of the separator was performed in the same manner. Mass fraction of product>

The mass fraction of the graft was measured as follows.

The mass W o of the nonwoven fabric before the graft polymerization was measured, and after the polymerization reaction was completed, the mass W s after drying at 120 ° C. for 3 minutes was measured. Based on the following formula (1), the graft product was obtained. Was calculated for the mass fraction G (%). When cross-linking the acid group of the monomer graft-polymerized on the surface, after the polymerization reaction is completed, the nonwoven fabric is washed with hot water and treated with a polyvalent metal salt solution (before cross-linking the acid group). After drying at 0 ° C for 3 minutes, the mass was defined as Ws. G (%) = (Ws-Wo) / W s X 100 (1)

In the examples, since AXQ and AA were graft-copolymerized, as shown in the following formula (2), the mass fraction G of the graft product was the mass fraction G of the AXQ graft product, the sum of the mass fraction G _M of the graft material. Where AX

Mass fraction G _{M (1} of Q graft of the as possible out be calculated from the sulfur content to be described later. Further, the mass fraction G _M of the graft of the AA, the mass fraction of the graft of AXQ. From steel, it can be calculated based on the following equation (3).

G = G job + G _M

G _M = GG _Mg ... (3)

Sulfur content>

The sulfur content was measured based on the Shiniga method.

After weighing the mass Mo (mg) of the separator sample of about 2 Omg, the sample was wrapped with a filter paper with little ash during combustion, and stored in a platinum basket with electrodes. Next, the platinum basket containing the sample was inserted into a combustion flask containing the hydrogen peroxide solution without touching the hydrogen peroxide solution, and sealed. Then, after sufficiently replacing the inside of the flask with oxygen gas, a high current is applied to the platinum portion to completely burn the sample and the filter paper, and the resulting sulfur oxides are dissolved in hydrogen peroxide solution, and sulfuric acid is dissolved therein. Ion. Then, after cooling the flask with ice water, transfer 50 ml of hydrogen peroxide solution containing ionic sulfate to a volumetric flask and make the volume constant, and determine the sulfate ion concentration C (mg / 1) by high-performance liquid chromatography using a calibration curve method. The sulfur content S (%) in the sample was calculated based on the following equation (4). π _/ ή.CX0.05X32,1,

S I =

96.1XMO In the formula (4), 32.1 is atomic weight of sulfur, 96.1 represents the molecular weight of the sulfate ion (S0 ₄₎ ² ". Theoretical ion exchange capacity IEC (ca1)>

The theoretical ion exchange capacity I E C (c a 1) was calculated as follows.

AXQ mo 1 number in 1 g of nonwoven fabric sample after graft copolymerization

1) was calculated based on the following equation (5) from the sulfur content S (%) force measured as described above. Further, the mo 1 number C _M of AA in the nonwoven sample 1 g after graft copolymerization (mmo 1), from the mass fraction G of the graft of AA calculated as described above, according to the following equation (6) Calculated

G AA

CAA mniol) = X 1000 / 72.1 (6)

100 In the formula (5), 3 2. indicates the atomic weight of sulfur. In equation (6), 7 2

.1 indicates the molecular weight of AA.

Then, the theoretical ion exchange capacity IEC (ca 1) was calculated based on the following equation (7) using C _{A] (i} (mm o 1), C _M (mm o 1), and force data.

IEC (ca 1) = C ™ (mm o 1) + C _M (mm o 1) (7)

The potassium ion exchange capacity I E C (obs) was measured as follows. Approximately 0.5 g of the separator sample was immersed in an aqueous solution of 0.1 mol Zl of hydrochloric acid to completely convert the ion-exchange groups into an acid form, rinsed with distilled water, and dried at 100 ° C. After weighing the dried mass W, put the dried sample in a 100 ml polyethylene bottle, and then add 10 ml of a 0.1 m 01/1 aqueous hydroxide water solution with a whole pipette. Was. In addition, a known amount of distilled water was added to completely immerse the sample. Let Am 1 be the sum of the aqueous potassium hydroxide solution and distilled water. On the other hand, a polyethylene bottle containing no sample was prepared by the same procedure for a blank test.

The polyethylene bottle containing the sample and the polyethylene bottle for the blank test After storing at 60 ° C for 2 hours, cool naturally to room temperature, take out the remaining aqueous solution of hydroxylated lime in each polyethylene bottle with an appropriate amount (Bm 1) hole pipe, and transfer each to a conical beaker for titration. The amount of remaining potassium hydroxide was determined by neutralization titration with 0.1 mol / l hydrochloric acid aqueous solution using phenolphthalein as an indicator. The potassium ion exchange capacity I EC (obs) was calculated by the following equation (8). Calculated based on

I EC (obs) = (A / B) X 0.1 X f X (tb— ts) / W ·. (8) In formula (8), 0.1 is the hydrochloric acid used for the neutralization titration. The concentration of the aqueous solution, f is the factor of the hydrochloric acid aqueous solution used for the neutralization titration, tb is the titration value of the hydrochloric acid aqueous solution required in the blank test (ml), and ts is the titration value of the hydrochloric acid aqueous solution required when processing the sample ( ml). Your capture capacity>

The ammonia trapping capacity was measured as follows.

A 25 Om1 stoppered Erlenmeyer flask was charged with 125 ml of an aqueous 8 mo1 / 1 aqueous solution of ammonia containing 1.5 mmo1 of ammonia and about 2 g of a precisely weighed separator sample, and then stoppered. And sealed with parafilm. On the other hand, a blank tester with no separator was prepared.

After stirring the contents in the flask containing the separator sample and the flask for the blank test, the contents were stored at 40 ° C. for 2 hours, and then the contents were cooled with ice water so that ammonia did not volatilize. Next, 10 Om 1 of the solution in the flask was sampled, and the amount of untrapped ammonia was quantified by the Kjeldahl method. That is, ammonia was distilled and recovered in 2 Oml of 0.1 lmo 1/1 hydrochloric acid aqueous solution, and the remaining hydrochloric acid aqueous solution that had not been neutralized was used as a 0.1 w / v% methyl red alcohol solution indicator. Titration was performed using a 0.05 mol 1/1 sodium hydroxide aqueous solution, and the ammonia capture capacity ATC was calculated from the titration value based on the following equation (9).

ATC (mm o 1 / g)

= (1 25/100) X 0.05 X f X (V s -Vb) / W (9) where, in equation (9), f _{Na () H} is the hydroxyl used in the titration. The factor of sodium aqueous solution, V s, is the amount of sodium hydroxide aqueous solution required when processing the sample. The titration value (ml) and Vb indicate the titration value (ml) of the aqueous sodium hydroxide solution in the blank test.

(Production of nickel-metal hydride battery)

In Examples 1 to 7, Examples 9 to 14, and Comparative Examples 1 to 7, a method for producing a nickel-metal hydride battery using the obtained battery separator will be described.

As a current collector of the electrode, a paste-type nickel positive electrode using a foamed nickel base material and a hydrogen storage alloy (mish metal alloy) negative electrode using a nickel-plated stainless steel punching metal base material were prepared. Then, the separator obtained was sandwiched and wound in a spiral to produce an AA-sized electrode. This electrode was housed in an outer can, and a 7 N aqueous hydroxide solution and a 1 N aqueous lithium hydroxide solution were injected into the can as an electrolytic solution, and then sealed to produce a cylindrical nickel-metal hydride battery.

(Evaluation items and evaluation methods for nickel hydrogen batteries)

The evaluation items and evaluation methods of the nickel-metal hydride batteries obtained in Examples 1 to 7, Examples 9 to 14, and Comparative Examples 1 to 7 are as follows.

<Self-discharge characteristics (capacity retention)>

The obtained nickel-metal hydride battery was charged at 20 ° C. and 0.1 C at 150% (capacity ratio), and the initial capacity (A) at a discharge of 0.1 C and a cut-off voltage of 1.0 V was measured. Then, charge at 150 ° C (capacity ratio) at 20 ° C and 0.1 C, leave at 60 ° C for 3 days, discharge at 0.1 ° C at 20 ° C, and end voltage of 1.0V (B) was measured. The capacity retention was calculated from the obtained data based on the following equation (10).

Capacity retention (%) = (A / B) X 100 · · · (10)

The obtained nickel-metal hydride battery is repeatedly charged and discharged at 20 ° C, 1 C, and 120%, discharged at 1 C, and discharged at a final voltage of 1.0 V. The number of charge / discharge cycles up to 50% was measured. (Example 1)

As the base material, a spunbond nonwoven fabric made of 100% polypropylene (PP) fiber having a fiber diameter of about 10 μm and having a basis weight of 50 g / m ² was used.

The monomer solution having the composition shown in Table 1 were prepared, after the solution is impregnated in pairs 1 0 0 part by weight nonwoven 2 0 0 parts by weight, placed on the stainless steel plate, further a thickness of the nonwoven fabric of ⁵ 0 polyester film. As the nonionic surfactant added to the monomer solution, Emulgen 910 manufactured by Kao Corporation was used (the same applies to the following Examples and Comparative Examples).

Next, after preheating to 80 ° C. using a far-infrared heating device, the mixture was passed through an ultraviolet irradiation device in which five 160 W / cm mercury lamps were arranged to perform graft copolymerization. The graft copolymerization was performed by irradiating ultraviolet rays from the polyester film side.

After the completion of the polymerization reaction, the nonwoven fabric was washed with a 1% aqueous sodium hydroxide solution at 80 ° C. for 3 minutes. Further, after washing with water for 1 minute, it was passed through a 0.1% hydrochloric acid aqueous solution for 1 minute, and then dried to obtain a battery separator of the present invention.

(Example 2)

A battery separator of the present invention was obtained in the same manner as in Example 1, except that a monomer solution having the composition shown in Table 1 was prepared.

(Example 3)

Instead of passing through a UV irradiator with five 6 OW / cm mercury lamps and performing graph copolymerization, instead of an ultraviolet irradiator with five 80 W / cm mercury lamps And the graft copolymerization was carried out in the same manner as in Example 1 to obtain a battery separator of the present invention.

(Comparative Example 1) Using only AA as a monomer, a monomer solution shown in Table 1 was prepared, and a battery separator was obtained in the same manner as in Example 1 except that preheating was not performed before ultraviolet irradiation.

(Comparative Example 2)

A separator used in a commercially available nickel-metal hydride battery was taken out and evaluated in the same manner as in Examples 1 to 3 and Comparative Example 1. When this separator was analyzed, it was found that a polypropylene nonwoven fabric with a basis weight of about 50 g / m ² was graft-polymerized with only AA by 10.7%. It was also confirmed that the acid groups of the grafted AA were not crosslinked.

(Comparative Example 3)

A battery separator was obtained in the same manner as in Example 1 except that sodium p-styrenesulfonate was used instead of AXQ, and a monomer solution shown in Table 1 was prepared.

(Comparative Example 4)

A battery separator was obtained in the same manner as in Example 1, except that sodium vinyl sulfonate was used instead of AXQ, and a monomer solution shown in Table 1 was prepared.

Example Example Comparative example Comparative example Comparative example

1 3 2 1 3 4 Non-woven fabric Ρ Ρ p p p p p p p p p

AXQ 1 d 9Π

n Ρ — styrene dinosolen acetic acid K 1 lb

Lithium

Sodium bininoles norephonate 15

ΑΑ 15 20 40 15 15 Benzophenone 0.1 0.1 0.1 0.1 0.1 Nonionic surfactant 0.3 0.3 0.3 0.3 0.3 Ferrous chloride 0.2 0.2 0.2 0.2 0.2 Water 69.4 59.4 59.4 69.4 69.4

(Example 4)

Using a core-sheath composite fiber with a fiber diameter of 10 μπι and a core component consisting of 50% by mass of polypropylene (PP) and a sheath component of 50% by mass of polyethylene (PE), the basis weight is 50 gZm ² by the wet (papermaking) method. Was obtained.

Then, a monomer solution having the composition shown in Table 2 were prepared, placed on the after solution was 200 parts by impregnation with respect to the nonwoven fabric 100 parts by mass of resulting, on the stainless steel plate having a thickness of 0. 6 _M m Then, the nonwoven fabric is covered with a polyester film having a thickness of 50 μm, and then preheated to 80 ° C using a far-infrared ray drying device, and then passed under five 160 W / cm metal halide lamps to form a graft. Polymerization was performed. The graft copolymerization was performed by irradiating ultraviolet rays from the side of the polyester film having a thickness of 50 μm.

The nonwoven fabric after the completion of the polymerization reaction was washed and dried in the same manner as in Example 1 to obtain a battery separator of the present invention.

(Example 5)

Using the same nonwoven fabric as used in Example 4, a monomer solution having the composition shown in Table 2 was prepared. A battery separator of the present invention was obtained in the same manner as in Example 1 except for producing the battery separator. (Comparative Example 5).

A battery separator was obtained in the same manner as in Example 4, except that only AA was used as the monomer and the monomer solutions shown in Table 2 were prepared. Table 2

(Example 6)

As the base material, used as the basis weight 50 g / m ² spunbond nonwoven fiber diameter of 100% polyethylene (PE) fibers about 12 mu m, except that to prepare a monomer solution having the composition shown in Table 3 is performed In the same manner as in Example 1, a battery separator of the present invention was obtained.

(Example 7)

As the base material, used as the basis weight 40 gZm ² in meltblown nonwoven fiber diameter of about 2 Myupaiiota polypropylene (PP) 100% fiber, except that to prepare a monomer solution having the composition shown in Table 3 as in Example 1 Thus, a battery separator of the present invention was obtained. Table 3

(Example 8)

In the same manner as in Examples 1 to 3, 16 types of battery separators of the present invention including the battery separators of Examples 1 to 3 were produced. In addition, by changing the monomer concentration, the mass fraction of the Qitk zaraft product was changed within the range of 3 to 16% to produce the battery separator of the present invention.

(Example 9)

As a substrate, a spunbond nonwoven fabric made of 100% polypropylene (PP) fiber having a fiber diameter of about 10 μm and having a basis weight of 50 gZm ² was used.

Prepare a monomer solution having the composition shown in Table 4, impregnate this solution with 200 parts by mass of 100 parts by mass of the nonwoven fabric, place it on a stainless steel plate, and further place the nonwoven fabric on a polyester film with a thickness of 50 μπι. Coated. As shown in Table 4, a monomer solution having the same composition as in Example 1 was used.

Next, after preheating to 80 ° C. using a far-infrared heating device, the mixture was passed through an ultraviolet irradiation device in which six 16 OWZcm mercury lamps were arranged to perform graft copolymerization. The graft copolymerization was performed by irradiating ultraviolet rays from the polyester film side. '

After the polymerization reaction, the nonwoven fabric is washed in hot water of 90 ° C for 3 minutes, and then the polyvalent metal It was immersed in an aqueous solution of calcium chloride (0.5% by mass) at 80 ° C. as a salt solution for 3 minutes to crosslink the acidic groups of the monomers graft-polymerized on the surface via calcium. Furthermore, after washing with water for 1 minute, it was dried with a steam cylinder at 120 ° C. to obtain a battery separator of the present invention.

(Example 10)

A monomer solution having the composition shown in Table 4 was used, and a zinc acetate aqueous solution (0.5% by mass) was used as the polyvalent metal salt solution. The acidic groups of the monomers graft-polymerized on the surface were crosslinked via zinc. In the same manner as in Example 9, a battery separator of the present invention was obtained. As shown in Table 4, a monomer solution having the same composition as in Example 2 was used.

(Comparative Example 6)

A battery separator was obtained in the same manner as in Example 9 except that only AA was used as the monomer and the monomer solutions shown in Table 4 were prepared. Table 4

(Example 11) The core component is polypropylene (PP) 50 Weight ^_0/0, the sheath component is polyethylene (PE) 50 wt. /. Using a core-sheath composite fiber having a fiber diameter of 10 / zm, a nonwoven fabric having a basis weight of 50 g / m ² was obtained by a wet (papermaking) method.

Next, a monomer solution having the composition shown in Table 5 was prepared, and this solution was impregnated with 200 parts by mass with respect to 100 parts by mass of the obtained nonwoven fabric, and then placed on a stainless steel plate having a thickness of 0.6 μπι. Further, the nonwoven fabric was covered with a 50 / zm-thick polyester film. As shown in Table 5, a monomer solution having the same composition as in Example 4 was used.

Next, after preheating to 80 ° C. using a far-infrared ray drying device, the mixture was passed under six 8 OW / cm metal halide lamps to perform graft copolymerization. The graft copolymerization was performed by irradiating ultraviolet rays from the polyester film side.

Finally, as in Example 9, after washing the nonwoven fabric after the polymerization reaction, the acid groups of the monomers graft-polymerized on the surface are crosslinked via calcium and dried to obtain the battery for the battery of the present invention. A separator was obtained.

(Example 1 2)

Graft polymerization was carried out in the same manner as in Example 9, except that the same nonwoven fabric as used in Example 11 was used, and a monomer solution having the composition shown in Table 5 was used. Finally, as in Example 10, after washing the nonwoven fabric after the completion of the polymerization reaction, the acid 'I' live groups of the monomer graft-polymerized on the surface are crosslinked via zinc and dried to form The battery separator of the present invention was obtained.

Table 5

(Examples 13 and 14)

As the substrate, the same polypropylene nonwoven fabric as used in Example 9 was used. Also, a monomer solution having the composition shown in Table 6 was prepared, and this solution was impregnated with 200 parts by mass with respect to 100 parts by mass of the nonwoven fabric, and then placed on a stainless steel plate. The sample was covered with a polyester film, and in this state, preheating was performed by using a far-infrared heating device while maintaining the temperature at 80 ° C. or higher for 5 minutes.

Next, the nonwoven fabric was irradiated with an electron beam from the polyester film side using an electron beam irradiation device (EC250-15-18OL, manufactured by Iwasaki Electric Co., Ltd.). In this process, the stainless steel plate was heated electrically to keep the temperature of the nonwoven fabric at 80 ° C or higher. The non-woven fabric was irradiated with an electron beam at an irradiation amount of 1 OkGy per pass, 5 passes, and a total irradiation amount of 50 kGy.

After the electron beam irradiation was completed, the temperature was kept at 80 ° C for 5 minutes using a far-infrared heating device to complete the graph polymerization. After the completion of the polymerization reaction, the nonwoven fabric was washed with hot water at 95 ° C for 5 minutes, immersed in a magnesium chloride solution (0.5% by mass), which is a polyvalent metal salt solution, for 3 minutes, and further washed with water for 3 minutes. After drying at 100 ° C for 2 minutes, a battery separator of the present invention was obtained.

(Comparative Example 7)

Except for using only AA as the monomer and preparing the monomer solution shown in Table 6, In the same manner as施例1 3, 14, _c table to obtain a battery separator 6

(Results of Examples 1 to 3 and Comparative Examples 1 to 4)

Evaluation results of the battery separators and batteries obtained in Examples 1 to 3 and Comparative Examples 1, 3, and 4 using a spunbond nonwoven fabric made of 100% polypropylene (PP) fiber as the nonwoven fabric, and a commercially available nickel Table 7 shows the results obtained in Comparative Example 2 in which the separator taken out of the hydrogen battery was evaluated.

In Examples 1 to 3 in which AXQ and AA were graft-copolymerized, no homopolymer was formed on the fiber surface after completion of the polymerization reaction, and the appearance was not different from that before polymerization. As shown in Table 7, the sulfur content of the obtained separator was 0.05% or more, and it was confirmed that sulfonic acid groups had been introduced. The obtained separator has an IEC (ca 1)-IEC (obs) of at least 0.55 mmol / g and an ammonia trapping capacity of at least 0.3 lmmo 1 / g. Was found to have. In particular, the separators obtained in Examples 1 and 2 had an IEC (ca 1)-IEC (obs) of 0.93 mmo 1 Zg or more, and an ammonia capture capacity of 0.6 Ommo 1 Zg or more. It was found to have a high ammonia trapping capacity.

Further, the capacity retention of the battery equipped with the separator obtained in Examples 1 to 3 Is as high as 61% or more, the repetition cycle life of charge and discharge is as long as 100 cycles or more, self-discharge can be suppressed, a high capacity retention rate, and a battery with excellent durability can be obtained. Was completed. In particular, the batteries equipped with the separators obtained in Examples 1 and 2 have a very high capacity retention of 69% or more, and a repetitive charge / discharge cycle life of at least 125 cycles. Self-discharge was further suppressed, and a higher capacity retention ratio and a more durable battery were obtained.On the other hand, only AA was used as the monomer, and preheating was performed before UV irradiation. In Comparative Example 1 where the polymerization was not performed, a large amount of a homopolymer was generated in the form of a paste on the fiber surface after the completion of the polymerization reaction, and the homopolymer could not be removed, so that the separator and the battery could be evaluated. Never As described above, it was found that when preheating was not performed before UV irradiation, even when only AA having a small molecular weight was graft-polymerized, a homopolymer was generated by the progress of the polymerization reaction outside the fiber. In Comparative Example 2 in which a commercial nickel-metal hydride battery was evaluated for a separator (a nonwoven polypropylene nonwoven fabric obtained by grafting only 10.7% of AA), Comparative Example 2 was compared with Examples 1 and 2. The IEC (ca 1) -IEC (obs) of the separator and the ammonia trapping capacity were all small, and the capacity retention rate of the obtained battery was low, and the cycle life of charge and discharge was short.

Further, as compared with Example 3, it was found that although the ammonia trapping capacity was excellent, the cycle life of repeated charge / discharge was inferior. In Comparative Example 2, only AA was graft-polymerized, the chemical stability to the electrolyte was excellent, and the sulfonate group that was not easily oxidized was not introduced, resulting in poor battery durability. It seems to be.

In Comparative Examples 3 and 4 in which sodium p-styrenesulfonate or sodium butylsulfonate was used instead of AXQ, a large amount of a homopolymer was present on the fiber surface after the completion of the polymerization reaction. It could not be completely removed. The sulfur content of the obtained separator was 0%. Thus, even when sodium p-styrenesulfonate or sodium vinylsulfonate is used as the monomer having a sulfonic acid group, the polymerization reaction proceeds only outside the fiber. It was found that sulfonic acid groups could not be introduced.

Further, as compared with Examples 1 and 2, both the IEC (ca 1)-IEC (obs) and the ammonia trapping capacity of the separator were small, and the capacity retention rate of the obtained battery was low. The cycle life was found to be short. Further, as compared with Example 3, it was found that although the ammonia trapping capacity was excellent, the cycle life of repeated charge and discharge was inferior. In Comparative Examples 3 and 4, it is considered that the durability of the battery was inferior because the electrolyte was excellent in chemical stability and a sulfonic acid group that was not easily oxidized was introduced. Table 7

(Results of Examples 4, 5 and Comparative Example 5)

In Examples 4 and 5 and Comparative Example 5 in which a nonwoven fabric composed of a core-sheath composite fiber having a core component of polypropylene (PP) and a sheath component of polyethylene (PE) was used as the nonwoven fabric, the obtained battery separator and battery were evaluated. Table 8 shows the results.

In Examples 4 and 5 in which AXQ and AA were graft-copolymerized, no homopolymer was formed on the fiber surface after completion of the polymerization reaction, and the appearance was not different from that before polymerization. As shown in Table 8, the sulfur content of the obtained separator was 0.08% or more, and it was confirmed that sulfonic acid groups had been introduced. In addition, the obtained separator has an EC (ca 1)-IEC (obs) of 0.88 mm o lZg or more, and an ammonia trapping capacity of 0.55 mniol Zg or more. Was found to have.

In addition, the capacity retention of the batteries equipped with the separators obtained in Examples 4 and 5 was as high as 70% or more, and the cycle life of charge and discharge was as long as 1150 cycles or more, and self-discharge was suppressed. As a result, a battery with high capacity retention and excellent durability was obtained.

In contrast, in Comparative Example 5, in which only AA was used as the monomer, a large amount of homopolymer was present on the fiber surface after the completion of the polymerization reaction, and it took a long time to wash and remove. Further, as compared with Examples 4 and 5, the separator has a small IEC (ca 1) -one IEC (obs) and a small ammonia trapping capacity, has a low capacity retention rate of the obtained battery, and has a repetitive charge / discharge cycle. It was found that the cycle life was short. Table 8

(Results of Examples 6 and 7)

Evaluation of battery separator and battery obtained in Example 6 using spunbonded nonwoven fabric consisting of 100% polyethylene (PE) fiber as nonwoven fabric and Example 7 using meltblown nonwoven fabric consisting of 100% polypropylene (PP) fiber Table 9 shows the results.

In Examples 6 and 7 in which AXQ and AA were graft-copolymerized, no homopolymer was formed on the fiber surface after the completion of the polymerization reaction, and the appearance was not different from that before polymerization. As shown in Table 9, the obtained separator had a sulfur content of 0.09% or more, and it was confirmed that sulfonic acid groups had been introduced. In addition, the obtained separator has an IEC (ca 1) -IEC (obs) of 0.84 mmo 1 / g or more, and a van Moyua capture capacity of 0.52 mmo 1 Zg or more. Capacity Was found to have.

In addition, the batteries equipped with the separators obtained in Examples 6 and 7 have a high capacity retention of 68% or more, and have a long charge-discharge cycle life of at least 1190 cycles, and thus suppress self-discharge. A battery with high capacity retention and excellent durability was obtained.

Table 9

(Results of Example 8)

Graft fraction, IEC (ca 1), IEC (obs), IEC (ca 1) — IEC (obs), ammonia capture of the 16 types of battery separators obtained in Example 8 The capacity ATC is summarized in Figure 1.

As shown in Fig. 1, there is a correlation between the mass fraction of the graft and IEC (ca 1), IEC (obs), IEC (ca 1) — IEC (obs), and ammonia trapping capacity ATC. It turned out that there is.

That is, it was found that IEC (c a1) and IEC (obs) increased as the mass fraction of the graft increased. In contrast, IEC (ca 1) — IEC (obs) and ammonia trapping capacity ATC increase with increasing graft mass fraction up to about 10% graft mass fraction However, it was found that when the mass fraction of the graft product exceeded about 10%, it decreased with an increase in the mass fraction of the graft product, and both showed exactly the same behavior.

More specifically, it is preferable that the mass fraction of the graft is 4 to 16%, and by defining as such, IEC (ca 1) -IEC (obs) is 0.50 mmol / g or more, and the ammonia capture capacity ATC was found to be 0.30 mmol / g or more. Further, it is more preferable that the mass fraction of the graft product is 5 to 15%. By defining as such, IEC (ca 1) —I It was found that EC (obs) can be set to 0.60 mmo 1 / g or more, and ammonia capture capacity ATC can be set to 0.5 Ommo lZg or more. Further, it is particularly preferable that the mass fraction of the graft is 7 to 13%, and thus, the IEC (ca 1)-IEC (obs) is 0.8 Ommo 1 g or more. It was found that the ammonia trapping capacity ATC can be 0.6 Ommo 1 / g or more.

(Results of Examples 9, 10 and Comparative Example 6)

The spunbond nonwoven fabric consisting of 100% polypropylene (PP) fiber was used as the nonwoven fabric, and the acidic groups of the monomers graft-polymerized on the surface were crosslinked via calcium or zinc in Examples 9, 10 and Comparative Example 6. Table 10 shows the evaluation results of the battery separators and batteries that were used.

In Examples 9 and 10, where AXQ and AA were graft-copolymerized and the acid groups of the monomers graft-polymerized on the surface were crosslinked via calcium or zinc, a homopolymer was formed on the fiber surface after the polymerization reaction. There was no change and the appearance was the same as before polymerization. As shown in Table 10, the sulfur content of the obtained separator was 0.05% or more, and it was confirmed that sulfonic acid groups had been introduced. In addition, the obtained separator has an IEC (ca 1) -IEC (obs) of 0.93 mmo 1 / g or more, and an ammonia capture capacity of 0.6 Ommo 1 / g or more, and has a high ammonia capture capacity. Was found to have.

The capacity retention of the batteries equipped with the separators obtained in Examples 9 and 10 is as high as 71% or more, and the cycle life of charge and discharge is as long as 1320 cycles or more, and self-discharge is suppressed. As a result, a battery with high capacity retention and excellent durability was obtained.

On the other hand, in the separator obtained in Comparative Example 6 using only AA as the monomer, the IEC (ca 1) —IEC (obs), and the ammonia capturing capacity of the separator were all smaller than those of Examples 9 and 10. It was found that the battery obtained had a low capacity retention rate and a short cycle life of repeated charge and discharge.

In Examples 9 and 10, the same monomer solutions were prepared as in Examples 1 and 2, respectively. The graft copolymerization was carried out in the same manner as in Examples 1 and 2, and differs from Examples 1 and 2 in that the acidic group of the monomer graft-polymerized on the surface was crosslinked via calcium or zinc. However, based on the results of Examples 9 and 10 and Examples 1 and 2, the acidic groups of the monomer polymerized in the surface on the surface were cross-linked through calcium or zinc, thereby improving the capacity retention and charge / discharge of the battery. It was found that the cycle life could be improved (see Tables 7 and 10). Table 10

(Results of Examples 11 and 12)

Example in which a nonwoven fabric made of a core-sheath composite fiber with a core component of polypropylene (PP) and a sheath component of polyethylene (PE) was used as the nonwoven fabric, and the acidic group of the monomer graft-polymerized on the surface was crosslinked via calcium or zinc. Tables 11 and 12 show the evaluation results of the obtained battery separators and batteries.

In Examples 11 and 12 in which AXQ and AA were graft-copolymerized, and the acid groups of the monomers graft-polymerized on the surface were cross-linked via calcium or zinc, the homopolymer was formed on the fiber surface after the polymerization reaction. There was almost no formation, and the appearance was no different from that before polymerization. As shown in Table 11, the obtained separator had a sulfur content of 0.08% or more, and it was confirmed that sulfonic acid groups had been introduced. In addition, the obtained separator has an IEC (ca 1)-IEC (obs) of 0.88 mmo lZg or more, and an ammonia trapping capacity of 0.55 mmo 1 Zg or more, indicating a high ammonia trapping capacity. did.

In addition, the capacity retention of the battery equipped with the separator obtained in Examples 11 and 12 was as high as 72% or more, and the cycle life of repeated charge and discharge was 1250 sa. As a result, a battery having a high capacity retention rate and excellent durability was obtained.

In Example 11, the same monomer solution as in Example 4 was prepared, and graft copolymerization was performed in the same manner as in Example 4.The acid group of the monomer graft-polymerized on the surface was replaced with calcium. Example 4 is different from Example 4 in that cross-linking was performed through the intermediary process. Example 11 1 From the results of Example 4, it was found that the acid capacity of the monomer graft-polymerized on the surface was cross-linked through calcium to increase the battery capacity. It was found that the retention rate and the cycle life of charge / discharge cycles could be improved (see Table 8 and Table 11). Table 11

(Results of Examples 13 and 14)

The battery separator obtained in Examples 13 and 14 and Comparative Example 7 in which graft copolymerization was performed using an electron beam as a high energy beam, and the acidic group of the monomer graft-polymerized on the surface was crosslinked via magnesium. Table 12 shows the evaluation results of the batteries and batteries.

Even when an electron group is used as a high-energy beam and the acidic group of the monomer graft-polymerized on the surface is cross-linked via magnesium, the acidic group of the monomer graft-polymerized on the surface using an ultraviolet ray as the high-energy ray The same results as in Examples 9 to 12 in which crosslinking was carried out via calcium or zinc were obtained. No homopolymer was formed on the fiber surface after the completion of the polymerization reaction, and the appearance was not different from that before polymerization. Further, as shown in Table 12, the sulfur content of the obtained separator was 0.05% or more, and it was confirmed that sulfonic acid groups had been introduced. In addition, the obtained separator has an IEC (ca 1)-IEC (obs) of 0.73 mmo 1 / g or more, and a ammonia capture capacity of 0.54 mmo 1 / g or more, and a high ammonia capture capacity. Was found to have.

In addition, the batteries equipped with the separators obtained in Examples 13 and 14 have a high capacity retention of 70% or more, and a long cycle life of charge and discharge of 1280 or more, which suppresses self-discharge. As a result, a battery having a high capacity retention rate and excellent durability was obtained.

On the other hand, the IEC (ca 1)-IEC (obs) and the capacity to capture ammonia in the separator obtained in Comparative Example 7 using only AA as the monomer were all compared to those in Examples 13 and 14. It was found that the capacity retention of the obtained battery was low, and the cycle life of charge and discharge was short. Table 12

From the above results, according to the present invention, irrespective of the type of nonwoven fabric or high-energy ray used, a sulfone group can be introduced by graft copolymerization of AXQ and AA, and a high trapping capacity for ammonia can be obtained. It has been found that a battery separator having the following characteristics can be provided. In addition, it was found that by attaching the obtained separator, a battery having a high capacity retention rate, a long cycle life of repeated charge and discharge, and excellent performance can be provided.

Further, it is preferable that AXQ and AA are graft-copolymerized, and the acidic group of the monomer graft-polymerized on the surface is cross-linked via a polyvalent metal, and by mounting the battery separator of the present invention having such a configuration. It was found that the capacity retention rate and the cycle life of repeated charge / discharge could be further improved.

Claims

The scope of the claims

1. Graft copolymerization of 2-acrylamide 2-methylpropanesulfonic acid, a monomer having a sulfonic acid group, and a monomer having a carboxy group, on a substrate made of polyolefin fiber. Battery separator.

2. On a substrate made of polyolefin fiber, 2-acrylamide 2-methylpropanesulfonic acid, a monomer having a sulfonic acid group, and a monomer having a carboxy group are graft-copolymerized, and

A battery separator, wherein an acidic group of at least one kind of monomer graft-polymerized on at least the surface is crosslinked via a polyvalent metal.

3. The battery separator according to claim 2, wherein the polyvalent metal is at least one selected from calcium, magnesium, barium, aluminum, zinc, titanium, zirconium, and tin.

4. The battery separator according to claim 1, wherein the monomer having a carboxy group is acrylic acid or methacrylic acid.

5. The battery separator according to claim 1, wherein the sulfur content is 0.05% or more.

6. The difference between the theoretical ion exchange capacity I EC (ca 1) obtained from the mass fraction of the graft and the measured potassium ion exchange capacity I EC (obs) is 0.50 mmolZg or more. The battery separator according to claim 1, wherein

7. The battery separator according to claim 1, wherein the ammonia capturing capacity is 0.3 Ommo 1 / g or more.

8. The battery separator according to claim 1, wherein the graft has a mass fraction of 4 to 16%.

9. Confirm that the difference between the theoretical ion exchange capacity I EC (ca 1) obtained from the mass fraction of the graft and the measured potassium ion exchange capacity I EC (obs) is 0.6 Ommo 1 / g or more. The battery separator according to claim 1, wherein the battery separator is a battery separator.

10. The battery separator according to claim 1, wherein the ammonia trapping capacity is 0.5 Ommo1 / g or more.

1 1. The battery separator according to claim 1, wherein the mass fraction of the graft product is 5 to 15%.

1 2. The battery separator according to claim 1, wherein the separator is for an alkaline secondary battery using nickel hydroxide as a positive electrode active material.

1 3. A method for producing a battery separator according to claim 1, wherein

A monomer solution impregnating step of impregnating a substrate made of polyolefin fiber with a monomer solution containing 2-acrylamide 2-methylpropanesulfonic acid and a monomer having a carboxy group;

A high-energy ray that irradiates the substrate with a high-energy ray from the polyester film side in a state in which the base material impregnated with the monomer solution is sandwiched between a holding material holding the base material and a polyester film. A method for producing a battery separator, comprising an irradiation step.

14. Before the high energy ray irradiation step, in a state where the base material impregnated with the monomer solution is sandwiched between a holding material holding the base material and a polyester film,

14. The battery separator according to claim 13, further comprising a preheating step of preheating at a temperature of 70 to 100 ° C. and diffusing the monomer into the fiber. Construction method.

15. The method for producing a battery separator according to claim 14, wherein in the high energy ray irradiation step, high energy rays are irradiated while maintaining a heating temperature in the preheating step.