JP4410406B2 - Battery separator - Google Patents

Description

【００８１】
（たて方向における引裂き強度）
セパレータの引裂き強度を、ＪＩＳ Ｌ １０９６^-1990（一般織物試験方法、トラベゾイド法）に基づいて測定した。この結果は表１に示す通りであった。この表１から明らかなように、本発明のセパレータは引裂き強度の優れるものであったため、電極を群構成する際に、極板のエッジにより引き裂かれにくいものであることがわかった。
【００８２】
（平均耐貫通力）
セパレータを各々重ねて合計約２ｍｍの厚さとし、その一番上のセパレータに対して、ハンディー圧縮試験機（カトーテック製、ＫＥＳ−Ｇ５）に取り付けられたステンレス製ジグ（厚さ：０．５ｍｍ、先端の刃先角度：６０°）を、０．０１ｃｍ／ｓの速度で垂直に突き刺し、一番上のセパレータを切断するのに要する力を測定し、耐貫通力とした。この耐貫通力の測定を、各々のセパレータの５０箇所について行い、その平均値を算出し、この値を平均耐貫通力とした。この結果は表１に示す通りであった。なお、耐貫通力の最大値と最小値も表１に併記した。この表１から明らかなように、本発明のセパレータは鋭利なステンレス製ジグであっても貫通しにくいものであるため、電極を群構成する際に、極板のバリも貫通しにくいものであることがわかった。また、本発明のセパレータの耐貫通力の最大値と最小値との差が小さいため、極板のバリの貫通しにくい、信頼性の高いものであることもわかった。
【００８３】
（地合指数の測定）
（１）光源から各セパレータに対して光を照射し、照射された光のうち、セパレータの所定領域において反射された反射光を受光素子によって受光して輝度情報を取得した。
（２）セパレータの所定領域を画像サイズ３ｍｍ角、６ｍｍ角、１２ｍｍ角、２４ｍｍ角に等分割して、４つの分割パターンを取得した。
（３）得られた各分割パターン毎に等分割された各区画の輝度値を輝度情報に基づいて算出した。
（４）各区画の輝度値に基づいて、各分割パターン毎の輝度平均（Ｘ）を算出した。
（５）各分割パターン毎の標準偏差（σ）を求めた。
（６）各分割パターン毎の変動係数（ＣＶ）を次の式により算出した。
変動係数（ＣＶ）＝（σ／Ｘ）×１００
ここで、σは各分割パターン毎の標準偏差を示し、Ｘは各分割パターン毎の輝度平均を示す。
（７）各画像サイズの対数をＸ座標、当該画像サイズに対応する変動係数をＹ座標とした結果得られる座標群を、最小二乗法により一次直線に回帰させ、その傾きを算出し、この傾きの絶対値を地合指数とした。
この結果は表１に示す通りであった。この結果から明らかなように、本発明のセパレータは地合が優れているため、長期間使用時に、微小短絡が発生しにくいものであることが予測できた。
【００８４】
（ショート率）
各セパレータを使用して、実際に極板群を形成した際に、電池を製造することができなかった割合をショート率とした。この結果は表１に示す通りであった。この結果から、本発明のセパレータは電極を群構成する際に、電極間の短絡を発生しにくいものであることがわかった。
【００８５】
（電池寿命試験）
電極の集電体として、発泡ニッケル基材を用いたペースト式ニッケル正極（３３ｍｍ幅、１８２ｍｍ長）と、ペースト式水素蔵合金負極（メッシュメタル系合金、３３ｍｍ幅、２４７ｍｍ長）とを作成した。
次いで、各セパレータを３３ｍｍ幅、４１０ｍｍ長に裁断した後、それぞれを正極と負極との間に挟み込み、渦巻き状に巻回して、ＳＣ（ｓｕｂ−Ｃ）型対応の電極群を作成した。この電極群を外装缶に収納し、電解液として５Ｎ水酸化カリウム及び１Ｎ水酸化リチウムを外装缶に注液し、封緘して、円筒型ニッケル−水素電池を作成した。
次いで、それぞれの円筒型ニッケル−水素電池について、（１）０．２Ｃでの１５０％充電と、（２）１Ｃで終止電圧１Ｖまで放電することからなる充放電サイクルを繰り返し、放電容量が初期容量の５０％となった時点で、電池寿命が尽きたと判断し、電池寿命が尽きるまでのサイクル数を測定した。比較例のセパレータを使用した電池のサイクル数を基準（１００）とした時の比率を、表１に示す。この結果から、本発明のセパレータを使用した電池は微小短絡が発生しにくいため、電池寿命が長いことがわかった。
【００８６】
（電池内圧試験）
前記電池寿命試験で用いたものと同様に形成した円筒型ニッケル−水素電池を、０．５Ｃで２０℃にて充電を行い、容量の１５０％での電池内圧を測定した。比較例のセパレータを使用した電池の内圧を基準（１００）とした場合の比率を表１に示す。この結果から、本発明のセパレータを使用した電池は内圧が低く、電池特性に優れていることがわかった。
【００８７】
【発明の効果】
本発明のセパレータは、高強度長繊維と融着長繊維によって強靭な骨格が形成されるため、電極を群構成する際に、セパレータが破断したり、極板のバリがセパレータを突き抜けたり、或いは極板のエッジにより引き裂かれにくく、電極を群構成する際に、電極間における短絡が発生しにくい。また、繊維長の短い極細短繊維は自由度が高く、高強度長繊維及び融着長繊維によって形成された骨格間に、緻密かつ均一に分布することができるため、電池使用時における微小短絡防止性に優れている。
なお、短繊維として、更に引張り強さが４．５ｃＮ／ｄｔｅｘ以上の高強度短繊維を含んでいると、高強度短繊維が緻密かつ均一に分布することによって、前記性能の信頼性が更に向上する。
また、高強度長繊維が、引張り強さが９ｃＮ／ｄｔｅｘ以上で、ヤング率が８００ｋｇ／ｍｍ²以上のポリプロピレン長繊維からなると、電極を群構成する際に加わる圧力や、充放電時における圧力に対して抗して、不織布（セパレータ）の厚さを維持することができるため、電解液の保持性に優れ、電池特性を更に向上させることができる。
更に、前記極細短繊維が中空型分割短繊維に由来していると、より細い極細短繊維であることができるため、より緻密かつ均一な地合のセパレータであることができ、結果として、電池使用時における微小短絡防止性により優れている。
【図面の簡単な説明】
【図１】 本発明で使用できる分割短繊維の模式的横断面図
【図２】 本発明で使用できる別の分割短繊維の模式的横断面図
【図３】 本発明で使用できる更に別の分割短繊維の模式的横断面図
【図４】 本発明で使用できる更に別の分割短繊維の模式的横断面図
【図５】 本発明で使用できる更に別の分割短繊維の模式的横断面図
【図６】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図７】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図８】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図９】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図１０】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図１１】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図１２】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図１３】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【図１４】 本発明で使用できる更に別の中空型分割短繊維の模式的横断面図
【符号の説明】
１ 分割短繊維
１１ 第１成分
１２ 第２成分
Ｓ 中空部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a battery separator.
[0002]
[Prior art]
Conventionally, a separator capable of holding an electrolytic solution is disposed between these electrodes so that a positive electrode and a negative electrode of an alkaline battery are separated to prevent a short circuit and an electromotive reaction can be smoothly performed.
[0003]
With recent downsizing and weight reduction of electronic devices, development in the direction of increasing battery capacity has been actively conducted. Under such circumstances, when forming a group of electrodes of a high-capacity battery, it is necessary to use a separator having a small surface density and thickness, and to increase the winding pressure in the group configuration. For this reason, many short circuits occur between the electrodes, which is very problematic in the yield of battery production. Even if the battery can be manufactured without being short-circuited, there has been a problem that a short-circuit is caused while charging and discharging for a long time.
[0004]
In order to solve such problems, the applicant of the present application has determined that the total thickness of the mixed layer in which short fibers having a fiber length of less than 1 to 25 mm and long fibers having a fiber length of 25 mm or more are intertwined is the thickness of the entire nonwoven fabric. It is an alkaline battery separator made of a nonwoven fabric that is 1/3 or more of the length, and it has been proposed that the fibers constituting this nonwoven fabric are preferably composed of ultrafine fibers, high-strength fibers, and fusion fibers ( JP-A-11-31495).
[0005]
[Problems to be solved by the invention]
This separator for alkaline batteries was able to reduce the occurrence of short circuit between the electrodes when grouping the electrodes and was able to suppress the occurrence of micro short circuits during long-term use. However, there has been a long-awaited separator.
The present invention has been made in order to improve the above-mentioned points, and the purpose of this application is to further reduce the occurrence of short-circuiting between the electrodes when the electrodes are grouped. An object of the present invention is to provide a battery separator capable of further suppressing the occurrence of a micro short circuit.
[0006]
[Means for Solving the Problems]
As a result of intensive studies, the present inventors have found that (1) the use of ultrafine fibers having a long fiber length does not significantly affect the prevention of micro short-circuiting during long-term use, and (2) the fiber length. When long high-strength fibers were used, two points were found to be particularly effective in preventing the occurrence of short circuits when the electrodes are grouped. The present invention has been made based on such knowledge, and the battery separator of the present invention (hereinafter simply referred to as “separator”) includes a short fiber having a fiber length of less than 25 mm and a long fiber having a fiber length of 25 mm or more. The total thickness of the mixed layer intertwined is made of a nonwoven fabric occupying one-third or more of the total thickness, and includes the ultrashort fibers having a fiber diameter of 8 μm or less and the fused short fibers as the short fibers, The long fiber is composed of a high strength long fiber having a tensile strength of 4.5 cN / dtex or more and a fusion long fiber. And the mass ratio of the high-strength continuous fiber and the fused continuous fiber is 50 to 90 to 50 to 10 It is characterized by that. As described above, since the long fibers are composed of two types of high-strength long fibers and fusion long fibers, the amount of high-strength long fibers can be increased. As a result, a strong skeleton is formed by the high-strength long fibers and the fusion long fibers, so that when the electrodes are grouped, the separator breaks, the burrs of the electrode plate penetrate the separator, or the electrode plate It is difficult to tear by the edge, and when the electrodes are grouped, a short circuit between the electrodes is difficult to occur. In addition, ultra-fine short fibers with short fiber lengths have a high degree of freedom and can be distributed densely and evenly between the skeletons formed by high-strength long fibers and fusion long fibers, thus preventing micro short-circuits when using batteries. Excellent in properties. In addition, if the high strength short fibers having a tensile strength of 4.5 cN / dtex or more are further included as the short fibers, the high strength short fibers are densely and uniformly distributed, thereby further improving the reliability of the performance. To do. The high-strength long fiber has a tensile strength of 9 cN / dtex or more and a Young's modulus of 800 kg / mm. ² When the above-mentioned polypropylene long fibers are used, the thickness of the nonwoven fabric (separator) can be maintained against the pressure applied when forming the group of electrodes and the pressure during charging and discharging, so the electrolyte can be retained. The battery characteristics can be further improved. Further, when the ultrafine short fiber is derived from the hollow split short fiber, it can be a finer ultrafine short fiber, and thus can be a denser and more uniform separator. As a result, it is more excellent in preventing a short circuit when using a battery.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The separator of the present invention is a nonwoven fabric in which the total thickness of the mixed layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are intertwined accounts for one third or more of the total thickness. Become. This mixed layer has a more uniform electrolyte distribution, a lower battery internal resistance, and a battery with excellent discharge characteristics and high capacity compared to a layer consisting only of short fibers or a layer consisting only of long fibers. The ratio of the mixed layer in the total thickness of the nonwoven fabric is preferably as high as possible. The thickness of the mixed layer preferably occupies two-thirds or more of the total thickness of the nonwoven fabric, and the entire nonwoven fabric (separator) is composed of the mixed layer. Is most preferred. Note that the number of mixed layers is not necessarily one, and two or more may be present. When two or more exist like the latter, the total thickness should just occupy 1/3 or more of the thickness of the whole nonwoven fabric. In addition, the presence / absence of a layer other than the mixed layer contained in the nonwoven fabric (separator) (for example, a layer composed only of short fibers, a layer composed only of long fibers, etc.), the arrangement state of the layers other than the mixed layer and the mixed layer, etc. It is not limited.
[0008]
In the present specification, the “mixed layer” means a layer in which short fibers having a fiber length of less than 25 mm and long fibers having a fiber length of 25 mm or more are intertwined and mixed. Such a mixed layer can be formed by laminating a fiber web made of short fibers and a fiber web made of long fibers and then performing at least one entanglement treatment. In addition, the layer which consists only of a short fiber, the layer which consists only of long fibers, or a mixed layer can be clearly distinguished, for example by observing the cross section of a nonwoven fabric (separator) with a microscope. Moreover, the thickness of this mixed layer means the thickness in a no-load state.
[0009]
In the present invention, short fibers having a fiber length of less than 25 mm are included so that the formation is excellent. If the fiber length is 25 mm or more, the formation tends to be poor or it becomes difficult to form the fiber web itself. Therefore, the preferred fiber length is 5 to 20 mm, and the more preferred fiber length is 5 to 5 mm. 15 mm. The “fiber length” in the present invention refers to the length obtained by JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method).
[0010]
In the present invention, since the short fibers include an ultrafine short fiber having a fiber diameter of 8 μm or less and a fused short fiber, the ultrafine short fiber can be densely and uniformly dispersed, and the fused short fiber Therefore, the state can be maintained, so that it is excellent in preventing a short circuit when the battery is used.
[0011]
The ultrafine short fibers need to have a fiber diameter of 8 μm or less, preferably 5 μm or less, and more preferably 4 μm or less so that they can be densely and uniformly dispersed. The lower limit of the fiber diameter of the ultrafine short fiber is not particularly limited, but about 0.01 μm is appropriate. The “fiber diameter” in the present invention refers to the diameter when the cross-sectional shape of the fiber is circular, and has the same area as the cross-sectional area when the cross-sectional shape of the fiber is non-circular. The diameter of a circle.
[0012]
Such ultra-short fibers can be divided into, for example, split short fibers that can be split by physical action such as fluid flow such as water flow, needles, calenders, etc. It is possible to divide and obtain a split short fiber that can be split by a chemical action such as swelling. As the split short fibers that can be split by the former physical action, for example, as shown in FIGS. 1 to 4, the fiber cross section is an orange-type split short fiber, and as shown in FIG. 5, the fiber cross section is a multiple bimetal. Molded short fibers can be used. It should be noted that the hollow type split short fibers as shown in FIGS. 6 to 14 can generate finer ultrafine short fibers and can be divided by weak physical action, disturbing formation. Therefore, it is possible to obtain a denser and more uniform nonwoven fabric (separator). As the split short fibers that can be split by the latter chemical action, for example, split short fibers with a sea-island type fiber cross section can be used.
[0013]
Examples of the resin component constituting the split short fibers that can be split by the physical action or the split short fibers that can be split by the chemical action include, for example, polyamide resins (for example, nylon 6, nylon 66, nylon 12, nylon 6 Nylon copolymer such as copolymer of nylon 12 and the like), ethylene resin (for example, low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, copolymer of ethylene and vinyl alcohol) A copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid, etc.), a propylene resin (eg, a copolymer of polypropylene, propylene and one or more other vinyl compounds), Butene-based resins (for example, polybutene, copolymers of butene and one or more other vinyl compounds) Methylpentene-based resin (polymethyl pentene, and copolymers of methylpentene with other one or more vinyl compounds) include, split short fibers may be comprised of one or more of these resins.
[0014]
Since the short fibers constituting the separator of the present invention include fused short fibers, the fineness and uniformity of the ultrafine short fibers can be maintained. The fusion short fiber is completely melted by the heat of the fusion to completely melt other fibers (for example, ultrafine short fiber, high strength short fiber, high strength long fiber, etc.) (excluding the fusion long fiber) and strength. It is preferable to have a resin component (low melting point component) that does not decrease at least on the fiber surface. That is, when each of the other fibers is composed of one type of resin component, a low melting point component having a lower melting point than any of the resin components (preferably lower by 5 ° C., more preferably lower by 10 ° C.). It is preferable that the short fiber is a fusion-bonded fiber at least on the fiber surface. In addition, when other fibers composed of two or more kinds of resin components are included, the melting point is lower than any of the resin components (preferably lower by 5 ° C., more preferably lower by 10 ° C.). It may be a fused short fiber having at least the component on the fiber surface, or other two or more resin components so that other fibers composed of two or more resin components can be fused simultaneously. It may be a fused short fiber having at least a low melting point component having a melting point similar to that of the resin component constituting the surface of the fiber on the fiber surface.
The “melting point” in the present invention refers to a temperature giving a maximum value of a melting endothermic curve obtained by heating from room temperature at a heating rate of 10 ° C./min using a differential calorimeter.
[0015]
This fused short fiber can be composed of the same resin component as the resin component constituting the above-mentioned split short fiber. That is, polyamide resin (for example, nylon copolymer such as nylon 6, nylon 66, nylon 12, copolymer of nylon 6 and nylon 12), ethylene resin (for example, low density polyethylene, medium density polyethylene, High-density polyethylene, linear low-density polyethylene, a copolymer of ethylene and vinyl alcohol, a copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid, etc.), a propylene-based resin (for example, polypropylene) , Copolymers of propylene and one or more other vinyl compounds), butene resins (for example, polybutene, copolymers of butene and one or more other vinyl compounds), methylpentene resins ( Polymethylpentene, copolymers of methylpentene and one or more other vinyl compounds, etc.) It can consist of one or more resin components.
[0016]
In addition, although the fusion | melting short fiber may be comprised from the single resin component and may be comprised from two or more types of resin components, the latter has more tensile strength of a nonwoven fabric (separator). Since it can improve, it is suitable. When the fusion short fiber is composed of two or more kinds of resin components, the fiber cross-sectional shape can be, for example, a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, a multiple bimetal type, or an orange type.
[0017]
The fiber diameter of the fused short fibers is not particularly limited, but is 1 to 30 μm so as not to impair the uniform formation, the pore diameter of the nonwoven fabric to be too large, and to reduce the strength of the nonwoven fabric. Is preferable, and it is more preferable that it is 3-20 micrometers.
[0018]
If the tensile strength of the fused short fiber is 2.7 cN / dtex or more, the electrode plate group may break due to tension, or the electrode plate burr may penetrate the separator, or the electrode plate It is preferable because the separator is torn by the edge and short circuit is less likely to occur. A more preferable tensile strength is 3.5 cN / dtex or more. Examples of such short fused fibers include fused short fibers containing high-density polyethylene, and more specifically, fused short fibers made of only high-density polyethylene and core components made of polypropylene. And a core-sheath-type fused short fiber whose sheath component is made of high-density polyethylene. The “tensile strength” in the present invention refers to a value measured by JIS L 1015 (chemical fiber staple test method).
[0019]
The short fibers constituting the nonwoven fabric (separator) of the present invention preferably further contain high-strength short fibers having a tensile strength of 4.5 cN / dtex or more. Since the high-strength short fibers are densely and uniformly distributed, when the electrodes are grouped, occurrence of a short circuit between the electrodes can be further suppressed, and a battery can be manufactured with a high yield.
[0020]
The higher the tensile strength of the high-strength short fibers, the better the effect. Therefore, the tensile strength is preferably 6.3 cN / dtex or more, and preferably 9 cN / dtex or more. More preferably, it is 8 cN / dtex or more. In addition, although the upper limit of tensile strength is not specifically limited, about 50 cN / dtex is suitable.
[0021]
The Young's modulus is 800 kg / mm so that the thickness of the high-strength short fiber itself can be maintained against the pressure when forming the electrode plate group or using the battery. ² Preferably, it is 850 kg / mm ² The above is more preferable. The “Young's modulus” in the present invention refers to the value of the apparent Young's modulus calculated from the initial tensile resistance measured according to JIS L 1015.
[0022]
This high-strength short fiber can be composed of one or more resin components similar to the resin component constituting the split short fiber, but from the viewpoint of resistance to electrolyte, the fiber surface is composed of a polyolefin-based resin, polypropylene or average It is preferable to contain ultra high molecular weight polyethylene having a molecular weight of 1,000,000 to 5,000,000. That is, it may be a high-strength short fiber made only of polypropylene or ultrahigh molecular weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000, or a polyolefin resin constitutes the fiber surface, and polypropylene or an average molecular weight of 1,000,000 to 500. Ten thousand ultra-high molecular weight polyethylene may be a high-strength short fiber constituting the inside of the fiber.
[0023]
Among these high-strength short fibers, the tensile strength is 9 cN / dtex or more and the Young's modulus is 800 kg / mm. ² High-strength short fibers made of polypropylene short fibers are preferred. Such high-strength short fibers are, for example, isotactic polypropylene having an isotactic pentad fraction (IPF) of 95 to 100% and a weight average molecular weight / number average molecular weight ratio (Q value) of less than 4. The stretched tank temperature is 120 ° C. or higher by a stretching apparatus using a stretched tank in which a pressurized water tank is arranged in the stretched article introducing part and the stretched product drawing part and filled with high-temperature pressurized steam. It can be obtained by stretching at a stretching ratio of 7 times or more and then cutting to a length of less than 25 mm. The high-strength short fibers obtained by such a method are highly oriented and crystallized in the fiber direction, and when the side surface of the fiber is observed in a crossed Nicol state under polarized light, the refractive index varies intermittently in the fiber direction. It has a unique striped pattern consisting of a linear dark part and a bright part.
[0024]
The fiber diameter of the high-strength short fibers of the present invention is not particularly limited, but it is 1 to 30 μm so as not to impair the uniform formation, the pore diameter of the nonwoven fabric to be too large, and not to reduce the strength of the nonwoven fabric. It is preferable that it is 3 to 20 μm.
[0025]
The short fibers constituting the nonwoven fabric (separator) of the present invention are composed of the ultrafine short fibers and the fused short fibers as described above, and are preferably composed of the ultrafine short fibers, the fused short fibers, and the high-strength short fibers.
As in the former case, when the short fiber is composed of an ultrafine short fiber and a fused short fiber, the mass ratio thereof is (ultrafine short fiber) :( fused short fiber) = 5 to 95:95 to 5. Preferably, (ultrafine short fiber) :( fused short fiber) = 20 to 80:80 to 20 is more preferable.
Further, as in the latter case, when the short fiber is composed of an ultrafine short fiber, a fusion short fiber, and a high strength short fiber, the mass ratio is (ultrafine short fiber): (fusion short fiber): (high strength short fiber) ) = 5 to 90: 5 to 90:90 to 5, preferably (ultrafine short fiber) :( fused short fiber) :( high strength short fiber) = 10 to 80:10 to 80:80 to 10 It is more preferable that (ultrafine short fiber) :( fused short fiber) :( high strength short fiber) = 20-60: 20-60: 60-20.
In addition, as a short fiber of the nonwoven fabric (separator) of this invention, the undivided division | segmentation short fiber, the short fiber over 8 micrometers in a fiber diameter, etc. may be included.
[0026]
In the present invention, in addition to the short fibers as described above, long fibers having a fiber length of 25 mm or more are included in order to improve the tensile strength, tear strength, and bending resistance of the nonwoven fabric (separator). When the fiber length is shorter than 25 mm, the tensile strength, tear strength, and bending resistance may not be sufficiently improved or may not be sufficiently entangled. The preferable fiber length is 30 to 110 mm, and more preferable fiber. The length is 30-60 mm.
[0027]
In the present invention, the long fibers are composed of two types of high-strength long fibers and fusion long fibers having a tensile strength of 4.5 cN / dtex or more, so that the amount of high-strength long fibers can be increased. As a result, a strong skeleton is formed by the high-strength long fibers and the fusion long fibers, so that when the electrodes are grouped, the separator breaks, the burrs of the electrode plate penetrate the separator, or the electrode plate It is difficult to tear by the edge, and short-circuiting between the electrodes hardly occurs when the electrodes are grouped.
[0028]
Such a high-strength long fiber has a higher tensile strength, so that the above effect is excellent. Therefore, the tensile strength is preferably 6.3 cN / dtex or more, and preferably 9 cN / dtex or more. More preferably, it is 10.8 cN / dtex or more. In addition, although the upper limit of tensile strength is not specifically limited, about 50 cN / dtex is suitable.
[0029]
The high-strength long fibers function to form a tough skeleton, and the Young's modulus can be maintained so that the thickness of the nonwoven fabric (separator) can be maintained against the pressure during electrode plate group formation or battery use. Is 800kg / mm ² Preferably, it is 850 kg / mm ² The above is more preferable.
[0030]
This high-strength long fiber can be composed of one or more kinds of resin components similar to the resin component constituting the split short fiber, but from the viewpoint of the resistance to electrolytic solution, the fiber surface is made of polyolefin-based resin, polypropylene or average It is preferable to contain ultra high molecular weight polyethylene having a molecular weight of 1,000,000 to 5,000,000. That is, it may be a high-strength long fiber made of only polypropylene or ultra-high molecular weight polyethylene having an average molecular weight of 1,000,000 to 5,000,000, or a polyolefin-based resin may constitute the fiber surface, and polypropylene or an average molecular weight of 1,000,000 to 500,000. Ten thousand ultra high molecular weight polyethylene may be a high-strength long fiber constituting the inside of the fiber.
[0031]
Among these high-strength long fibers, the tensile strength is 9 cN / dtex or more and the Young's modulus is 800 kg / mm. ² High-strength long fibers made of polypropylene long fibers are preferred. This high-strength long fiber can be produced in the same manner as the high-strength short fiber except that it is cut to 25 mm or more.
[0032]
Note that it is preferable that the high-strength long fibers have crimps because they can further resist pressure and maintain the thickness of the nonwoven fabric (separator). The number of crimps is preferably 3 pieces / inch or more, and more preferably 5 pieces / inch or more. On the other hand, when the number of crimps is too large, the shape stability is deteriorated, and therefore, the number is preferably 30 pieces / inch or less, and more preferably 20 pieces / inch or less.
[0033]
The high-strength long fibers preferably have a large fiber diameter so as to form a skeleton of the nonwoven fabric (separator) and resist pressure. More specifically, it is preferably 1 μm or more, and more preferably 3 μm or more. On the other hand, if the fiber diameter of the high-strength long fibers is too large, the entanglement with the short fibers is deteriorated.
[0034]
Since the nonwoven fabric (separator) of the present invention contains fused long fibers as long fibers, a skeleton formed of high-strength long fibers can be fused and fixed. This fused long fiber completely melts other fibers (for example, ultrafine short fibers, high strength short fibers, high strength long fibers, etc.) (excluding fused short fibers) by heat at the time of fusing. It is preferable to have a resin component (low melting point component) that does not lower the strength on at least the fiber surface. That is, when each of the other fibers is composed of one type of resin component, a low melting point component having a lower melting point than any of the resin components (preferably lower by 5 ° C., more preferably lower by 10 ° C.). It is preferable that it is a fusion spun fiber at least on the fiber surface. In addition, when other fibers composed of two or more kinds of resin components are included, the melting point is lower than any of the resin components (preferably lower by 5 ° C., more preferably lower by 10 ° C.). It may be a fusion long fiber having at least the component on the fiber surface, or other two or more resin components so that other fibers comprising two or more resin components can be fused simultaneously. It is also possible to use a fusion long fiber having at least a low melting point component having the same melting point as the resin component constituting the surface of the fiber on the fiber surface. Note that it is preferable that the low melting point component of the fusion long fiber and the low melting point component of the fusion short fiber have the same melting point because the fusion long fiber and the fusion short fiber can be fused simultaneously. is there.
[0035]
This fusion long fiber can be comprised from the resin component similar to the resin component which comprises the above-mentioned division | segmentation short fiber. That is, polyamide resin (for example, nylon copolymer such as nylon 6, nylon 66, nylon 12, copolymer of nylon 6 and nylon 12), ethylene resin (for example, low density polyethylene, medium density polyethylene, High-density polyethylene, linear low-density polyethylene, a copolymer of ethylene and vinyl alcohol, a copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid, etc.), a propylene-based resin (for example, polypropylene) , Copolymers of propylene and one or more other vinyl compounds), butene resins (for example, polybutene, copolymers of butene and one or more other vinyl compounds), methylpentene resins ( Polymethylpentene, copolymers of methylpentene and one or more other vinyl compounds, etc.) It can consist of one or more resin components.
[0036]
The fused continuous fiber may be composed of a single resin component or may be composed of two or more types of resin components, but the latter has a higher tensile strength of the nonwoven fabric (separator). Since it can improve, it is suitable. When the fusion long fiber is composed of two or more kinds of resin components, the fiber cross-sectional shape can be, for example, a core-sheath type, an eccentric type, a side-by-side type, a sea-island type, a multiple bimetal type, or an orange type.
[0037]
The fiber diameter of this fused continuous fiber is not particularly limited, but it can be firmly fused with the high-strength long fiber to maintain the skeleton formed by the high-strength long fiber and impart elasticity to the nonwoven fabric. Thus, it is preferable that it is 1-30 micrometers, and it is more preferable that it is 3-20 micrometers.
[0038]
In addition, if the tensile strength of the fused continuous fiber is 2.7 cN / dtex or more, it breaks due to the tension when constituting the electrode plate group, the burr of the electrode plate penetrates the separator, or the electrode plate It is preferable because the separator is torn by the edge and short circuit is less likely to occur. A more preferable tensile strength is 3.5 cN / dtex or more. As such a fusion long fiber, for example, a fusion long fiber containing high-density polyethylene can be mentioned. More specifically, a fusion long fiber made of only high-density polyethylene or a core component made of polypropylene. And a core-sheath-type fused continuous fiber whose sheath component is made of high-density polyethylene.
[0039]
The long fibers of the present invention are composed of the above-mentioned high-strength long fibers and fused long fibers, but the mass ratio can form a tough skeleton with the high-strength long fibers and firmly fix the high-strength long fibers. Thus, it is preferable that (high-strength long fiber) :( fusion long fiber) = 10-90: 90-10, (high-strength long fiber) :( fusion long fiber) = It is more preferable that it is 20-80: 80-20.
[0040]
In the nonwoven fabric constituting the separator of the present invention, the ratio of short fibers to long fibers is excellent in the density and uniformity due to the short fibers and the tensile strength, tear strength or bending resistance due to the long fibers. (Short fiber) :( long fiber) = 10 to 90:90 to 10 is preferable, and (short fiber) :( long fiber) = 20 to 80:80 to 20 is more preferable.
[0041]
The surface density of the nonwoven fabric (separator) of the present invention is 30 to 100 g / m. ² Is preferably 40 to 80 g / m. ² It is more preferable that Areal density is 30 g / m ² If it is less than 100 g / m, the tensile strength may be insufficient. ² This is because the nonwoven fabric becomes too thick and it is difficult to increase the capacity of the battery. The thickness is preferably 0.08 to 0.3 mm.
[0042]
The nonwoven fabric (separator) of the present invention has an oxygen and / or sulfur-containing functional group (for example, sulfonic acid group, sulfonic acid group, sulfofluoride group, carboxyl group, It is preferable that a carbonyl group or the like is present, a hydrophilic monomer is graft-polymerized, a surfactant is attached, or a hydrophilic resin is attached.
[0043]
The tensile strength in the longitudinal direction (length direction) of the nonwoven fabric (separator) of the present invention is preferably 100 N / 50 mm or more, and 140 N / 50 mm so as not to break by the tension at the stage of producing the electrode plate group. The above is more preferable. This tensile strength is a value measured at a tensile speed of 300 mm / min with a separator having a width of 50 mm fixed to a tensile strength tester (Orientec, Tensilon UTM-III-100) (distance between chucks: 100 mm). .
[0044]
The tear strength in the vertical direction (length direction) of the nonwoven fabric (separator) of the present invention is 50 N / 50 mm width or more so as not to be torn by the edge of the electrode plate at the stage of manufacturing the electrode plate group. Is preferable, and it is more preferable that it is 55 N / 50 mm width or more. This tear strength is JIS L 1096 ^-1990 The value measured by (general textile test method, trabezoid method).
[0045]
When the formation index of the nonwoven fabric (separator) of the present invention is 0.18 or less, the short fibers are in a dense and uniformly dispersed state, and it is preferable because minute short-circuits are unlikely to occur. A more preferable formation index is 0.16 or less.
This “geographic index” refers to a value obtained by the method described in Japanese Patent Application No. 11-152139. That is, the value obtained as follows.
(1) Light is irradiated from the light source to the object to be measured (separator), and the reflected light reflected by the predetermined region of the object to be measured is received by the light receiving element, and the luminance information is acquired. .
(2) A predetermined region of the object to be measured is equally divided into an image size of 3 mm square, 6 mm square, 12 mm square, and 24 mm square to obtain four divided patterns.
(3) The luminance value of each section equally divided for each obtained division pattern is calculated based on the luminance information.
(4) Based on the luminance value of each section, the average luminance (X) for each division pattern is calculated.
(5) A standard deviation (σ) for each division pattern is obtained.
(6) The coefficient of variation (CV) for each division pattern is calculated by the following equation.
Coefficient of variation (CV) = (σ / X) × 100
Here, σ indicates a standard deviation for each divided pattern, and X indicates a luminance average for each divided pattern.
(7) A coordinate group obtained as a result of taking the logarithm of each image size as the X coordinate and the coefficient of variation corresponding to the image size as the Y coordinate is regressed to a linear line by the least square method, and the inclination is calculated. The absolute value of is the formation index.
[0046]
The separator of this invention can be manufactured as follows, for example.
[0047]
When the ultra-short fiber is obtained from a split fiber that can be physically divided, a short fiber web (preferably including a high-strength short fiber) including a split fiber that can be physically split and a fusion staple fiber is used. One or more sheets are formed by a wet method. On the other hand, one or more long fiber webs composed of high-strength long fibers and fusion long fibers are formed by, for example, a dry method (for example, a card method, an air array method, a spun bond method, etc.).
[0048]
Next, one or more short fiber webs and one or more long fiber webs are laminated to form a laminated fiber web. In addition, when laminating at least one of the short fiber web and the long fiber web, the short fiber web and the long fiber web are formed so as to easily form a mixed layer in which the short fibers and the long fibers are entangled. It is preferable to laminate alternately.
[0049]
Next, a fluid flow such as a water flow is ejected from the laminated fiber web to carry out the entanglement process. In this entanglement process, a fluid flow with higher energy than before is applied so that the long fibers and the short fibers are entangled. The split short fibers are intertwined by the action of the fluid flow and simultaneously split to generate ultrafine short fibers. In addition, before making a fluid flow etc. act, you may divide | segment a division | segmentation short fiber by a calendar process, a needle punch process, etc.
[0050]
More specifically, when the fluid flow having higher energy than the conventional one is applied, when the nozzle diameter is R (unit: mm) and the internal pressure of the nozzle is P (unit: MPa), (formula) E = R × P ² That is, a fluid flow having an E value of 10 or more, preferably 15 or more, more preferably 18 or more, and most preferably 20 or more is caused to act at least once. In this formula, kinetic energy is proportional to the square of mass and velocity, so that the larger the nozzle diameter, the larger the mass of the fluid that is ejected and the greater the acting pressure, and the higher the internal pressure of the nozzle, the more ejected. This is a pseudo representation of the kinetic energy of the fluid flow because the fluid velocity is high.
[0051]
As conditions for the fluid flow ejection, for example, a nozzle plate having a nozzle diameter of 0.05 to 0.3 mm, a pitch of 0.2 to 3 mm, and a nozzle plate arranged in one or more rows and having an internal pressure of about 10 MPa to 30 MPa is used. Can be entangled. Also, the fluid flow can be ejected on one side or both sides of the laminated fiber web. In addition, it is preferable that the fluid flow is ejected twice or more, and is ejected so that the total of the above E values is 30 or more, more preferably 40 or more, and 60 or more. More preferably, it is ejected so that it becomes 80 or more. Furthermore, if a coarse support is used as the support for supporting the laminated fiber web when the fluid flow is ejected, a non-woven fabric having apertures is formed, which increases the possibility of short-circuiting. It is preferred to use a finer support.
[0052]
Next, the nonwoven fabric (separator) of the present invention can be obtained by fusing at least the fusion short fibers and the fusion long fibers constituting the entangled nonwoven fabric. This fusion treatment may be performed under no pressure, may be pressurized simultaneously with the heating, or may be performed immediately after being heated under no pressure. In addition, the heating temperature in the fusion treatment is, when heated under no pressure, the softening point of the low melting point component having a higher softening point among the low melting point component of the fusion short fiber and the low melting point component of the fusion long fiber. To about 20 ° C. higher than the melting point of the low melting point component having a higher melting point. The heating temperature in the case of pressurizing at the same time as the heating is the low melting point with the higher melting point from the softening point of the low melting point component of the fusion short fiber and the low melting point component of the fusion long fiber, which has a higher softening point. The range up to the melting point of the components is preferred. Moreover, as for pressurization conditions, it is preferable that linear pressure is 5-30 N / cm in any case. The “softening point” in the present invention refers to a temperature that gives a starting point of a melting endothermic curve obtained by using a differential scanning calorimeter and raising the temperature from room temperature at a heating rate of 10 ° C./min.
[0053]
On the other hand, when the ultrafine short fibers are obtained from chemically splittable short fibers, first, the resin components of the divided short fibers are dissolved and removed, or the resin components are swollen and divided to produce ultrafine short fibers. To do. Subsequently, one or more short fiber webs (preferably including high-strength short fibers) including ultrafine short fibers and fusion short fibers are formed by, for example, a wet method. Further, one or more long fiber webs composed of high strength long fibers and fusion long fibers are formed by, for example, a dry method (for example, a card method, an air array method, a spun bond method, etc.). Thereafter, the nonwoven fabric (separator) of the present invention is obtained by performing formation of a laminated fiber web, entanglement treatment by fluid flow, fusion treatment of fusion short fibers and fusion long fibers in exactly the same manner as described above. be able to.
[0054]
In addition, the nonwoven fabric (separator) having a tensile strength in the vertical direction (length direction) of 100 N / 50 mm or more uses high-strength long fibers with high tensile strength or increases the amount of high-strength long fibers. Further, it can be obtained by satisfying various conditions such as strong fusion with the short fusion fibers and long fusion fibers, strong entanglement, and an increase in the amount of fusion long fibers.
[0055]
Moreover, the nonwoven fabric (separator) whose tear strength in the vertical direction (length direction) is 50 N / 50 mm width or more uses high-strength long fibers with high tensile strength or increases the amount of high-strength long fibers. Further, it can be obtained by satisfying various conditions such as strong fusion with the short fusion fibers and long fusion fibers, strong entanglement, and an increase in the amount of fusion long fibers.
[0056]
Furthermore, the nonwoven fabric (separator) having a formation index of 0.18 or less uses hollow fine divided short fibers when ultra fine fibers having a smaller fiber diameter are used or when the ultra short fibers are generated from the divided short fibers. Or a fine support (especially a non-porous support) is used as a support when a fluid flow is applied.
[0057]
In order to improve the electrolyte retention of the nonwoven fabric (separator) of the present invention, for example, sulfonation treatment, fluorine gas treatment, graft treatment, surfactant treatment, discharge treatment, hydrophilic resin adhesion treatment, etc. At least one hydrophilization treatment is performed to introduce oxygen and / or sulfur-containing functional groups (for example, sulfonic acid group, sulfonic acid group, sulfofluoride group, carboxyl group, carbonyl group, etc.) on the fiber surface. It is preferable to graft polymerize a hydrophilic monomer, attach a surfactant, or attach a hydrophilic resin. Such hydrophilic treatment may be performed at the fiber stage (that is, before the nonwoven fabric is formed), but the hydrophilic treatment after the nonwoven fabric is formed is more excellent in workability. Hereinafter, although the method to hydrophilize after forming a nonwoven fabric is demonstrated, it can implement similarly when carrying out the hydrophilization of a fiber.
[0058]
Examples of the sulfonation treatment include a method of introducing a sulfonic acid group by immersing a nonwoven fabric as described above in a solution composed of fuming sulfuric acid, sulfuric acid, chlorosulfuric acid, sulfuryl chloride, or the like, as described above for sulfur trioxide gas. There are a method of introducing a sulfonic acid group by contacting a non-woven fabric, a method of introducing a sulfonic acid group by applying a discharge in the presence of sulfur monoxide gas or sulfur dioxide gas, and the like.
[0059]
As the fluorine gas treatment, for example, fluorine gas diluted with an inert gas (for example, nitrogen gas, argon gas, etc.) and at least one kind of gas selected from oxygen gas, carbon dioxide gas, sulfur dioxide gas, etc. The nonwoven fabric can be hydrophilized by exposing the nonwoven fabric to the mixed gas.
[0060]
Examples of the graft polymerization treatment of the vinyl monomer include, for example, a method in which the nonwoven fabric is immersed in a solution containing the vinyl monomer and a polymerization initiator, a method in which the nonwoven fabric is irradiated with radiation after the vinyl monomer is applied to the nonwoven fabric, and a radiation in the nonwoven fabric. There are a method of contacting with a vinyl monomer after applying, a method of irradiating ultraviolet rays after applying a vinyl monomer solution containing a sensitizer to a nonwoven fabric, and the like. As this vinyl monomer, for example, acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, vinyl pyridine, vinyl pyrrolidone, or styrene can be used. When styrene is graft-polymerized, it is preferably sulfonated so as to have excellent affinity with the electrolytic solution. If the nonwoven fabric is modified by ultraviolet irradiation, corona discharge, plasma discharge or the like before the vinyl monomer solution and the nonwoven fabric are brought into contact with each other, the affinity with the vinyl monomer solution is increased, so that graft polymerization can be efficiently performed.
[0061]
Examples of the surfactant treatment include an anionic surfactant (for example, an alkali metal salt of a higher fatty acid, an alkyl sulfonate, or a sulfosuccinate ester salt), or a nonionic surfactant (for example, a polyoxyethylene alkyl). The nonwoven fabric can be immersed in a solution of ether or polyoxyethylene alkylphenol ether), or this solution can be applied to or dispersed on the nonwoven fabric.
[0062]
Examples of the discharge treatment include corona discharge treatment, plasma treatment, glow discharge treatment, and electron beam treatment. In addition, under atmospheric pressure in the air, between the pair of electrodes each carrying a dielectric, a non-woven fabric is disposed so as to contact both of these dielectrics, and an alternating voltage is applied between these both electrodes, In the method of generating discharge in the internal voids of the nonwoven fabric, the fiber surface can be hydrophilized inside the nonwoven fabric, so that a separator having excellent internal pressure characteristics can be manufactured.
[0063]
As hydrophilic resin provision processing, hydrophilic resins, such as carboxymethylcellulose, polyvinyl alcohol, crosslinkable polyvinyl alcohol, or polyacrylic acid, can be made to adhere, for example. These hydrophilic resins can be dissolved or dispersed in a suitable solvent, and then the nonwoven fabric can be immersed in the solvent, or this solvent can be applied or dispersed on the nonwoven fabric and dried to be adhered.
[0064]
Examples of the crosslinkable polyvinyl alcohol include polyvinyl alcohol in which a part of the hydroxyl group is substituted with a photosensitive group. More specifically, the photosensitive group is a styrylpyridinium type or styrylquinolinium type. There is a polyvinyl alcohol in which a part of the hydroxyl group is substituted with a styrylbenzothiazolium type. This crosslinkable polyvinyl alcohol can also be crosslinked by being irradiated with light after being adhered to the nonwoven fabric in the same manner as other hydrophilic resins. Polyvinyl alcohol in which a part of such hydroxyl groups is substituted with a photosensitive group is excellent in alkali resistance and contains many hydroxyl groups that can form chelates with ions, and is dendritic on the electrode plate during discharge and / or charge. It can be preferably used because it can form a chelate with an ion before the metal is deposited to prevent a short circuit between the electrodes.
[0065]
Thus, the separator of the present invention can further reduce the occurrence of a short circuit between the electrodes when the electrodes are grouped, and can further suppress the occurrence of a micro short circuit during long-term use. Suitable for primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, air batteries, secondary batteries such as nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries Can be used for
[0066]
Although the Example of the separator of this invention is described below, this invention is not limited to these Examples.
[0067]
【Example】
Example 1
As a split short fiber, as shown in FIG. 6, a polypropylene component (symbol 12 in the figure, a polypropylene microfiber having a fiber diameter of 3.6 μm (melting point: 160 ° C.) can be generated eight) and a high-density polyethylene component (FIG. It is composed of medium symbol 11 and eight high-density polyethylene ultra-short fibers (melting point: 135 ° C.) having a fiber diameter of 3.5 μm, and has one hollow section S with a circular section having a center coincident with the fiber axis. Split short fiber with a straight line extending from the fiber axis at a certain angle (about 22.5 °) as a boundary between the polypropylene component and the high-density polyethylene component (fineness: 1.43 dtex, fiber length: 5 mm, 16 splittable) ) Was prepared.
[0068]
Further, as a short fused fiber, low density polyethylene (melting point: 115 ° C.) as a sheath component and polypropylene as a core component (melting point: 160 ° C.), fineness 1.21 dtex (fiber diameter: 13.1 μm), fiber length A core-sheath type composite fused short fiber having a tensile strength of 10 mm and a tensile strength of 2.7 cN / dtex was prepared.
Furthermore, as a high-strength short fiber, the tensile strength is 10.8 cN / dtex and the Young's modulus is 850 kg / mm. ² A polypropylene high-strength short fiber (melting point: 174 ° C.) having a fineness of 1.32 dtex (fiber diameter: 13.7 μm) and a fiber length of 10 mm was prepared.
[0069]
Next, a short fiber web (surface) is prepared from a slurry obtained by mixing and dispersing the above-described split short fibers, core-sheath type composite fusion short fibers, and polypropylene high-strength short fibers at a mass ratio of 60:20:20 by a wet papermaking method. Density 30g / m ² ) Was formed.
[0070]
On the other hand, as a fusion long fiber, low density polyethylene (melting point: 115 ° C.) is a sheath component, polypropylene is a core component (melting point: 160 ° C.), fineness 1.65 dtex (fiber diameter: 15.3 μm), fiber length A core-sheath type composite fused continuous fiber having a thickness of 51 mm, a number of crimps of 8 per inch, and a tensile strength of 2.7 cN / dtex was prepared.
Also, as high-strength long fibers, tensile strength 10.8 cN / dtex, Young's modulus 850 kg / mm ² A polypropylene high-strength long fiber (melting point: 174 ° C.) having a fineness of 1.32 dtex (fiber diameter: 13.7 μm), a fiber length of 38 mm, and a number of crimps of 9.2 pieces / inch was prepared.
[0071]
Subsequently, the core-sheath type composite fusion long fiber and the polypropylene high-strength long fiber were mixed with a mass ratio of 50:50, and then opened by a card machine to obtain a unidirectional long fiber web (surface density 20 g / m). ² ) Was formed.
[0072]
Next, after laminating the unidirectional long fiber web and the short fiber web, the laminated fiber web was placed on a plain woven net having an opening of 0.175 mm, and the nozzle diameter was 0.15 mm and the pitch was 0.8 mm. From a nozzle plate having an internal pressure of 12 MPa arranged in a row, a water stream was ejected in the order of a unidirectional long fiber web, a short fiber web, a unidirectional long fiber web, and a short fiber web (one E value: 21.6, E value total: 86.4), and entangled nonwoven fabric was formed by generating ultrafine short fibers at the same time.
[0073]
Next, the entangled nonwoven fabric was heated at 115 ° C. for 10 seconds, and then immediately pressed by a calender roll having a linear pressure of 9.8 N / cm to melt the core-sheath type composite fusion short fiber and the core-sheath type composite fusion long fiber. To form a fusion-entangled nonwoven fabric.
[0074]
Thereafter, this fusion-entangled nonwoven fabric was treated with fluorine gas with a mixed gas of fluorine gas, oxygen gas and sulfur dioxide gas diluted with nitrogen gas, and a sulfofluoride group was introduced on the fiber surface, and the surface density was 50 g / m. ² A separator having a thickness of 0.12 mm was formed. In addition, when the entanglement state was observed by photographing an electron micrograph in the cross section of the separator, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.
[0075]
(Example 2)
As the split short fiber, an ethylene-vinyl alcohol copolymer component (symbol 12 in the figure, fiber diameter: 4.4 μm ethylene-vinyl alcohol copolymer ultrafine short fiber (melting point: 155 ° C.) as shown in FIG. 1 is used. 8) and a polypropylene component (symbol 11 in the figure, fiber diameter: 8 polypropylene fine fibers having a fiber diameter of 4.6 μm (melting point: 160 ° C.) can be generated), and a certain angle (about 22 from the fiber axis). .5 °) using 60 mass% of split short fibers (fineness: 3.3 dtex, fiber length: 6 mm, 16 splittable) with a straight line extending every 5 °) as the boundary between the ethylene-vinyl alcohol copolymer component and the polypropylene component. Except for the above, the surface density of 50 g / m was introduced in the same manner as in Example 1 by introducing a sulfofluoride group on the fiber surface. ² A separator having a thickness of 0.12 mm was formed. In addition, when the entanglement state was observed by photographing an electron micrograph in the cross section of the separator, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.
[0076]
(Comparative example)
A short fiber web was produced in the same manner as in Example 1 except that the split short fibers, the core-sheath type composite fused short fibers, and the polypropylene high strength short fibers were mixed and dispersed at a mass ratio of 50:25:25. (Area density: 30 g / m ² ) Was formed.
[0077]
On the other hand, as the divided long fibers, as shown in FIG. 3, a polypropylene component (symbol 12 in the drawing, the polypropylene cross-section having a substantially triangular fiber cross section and a fiber diameter of 3.5 .mu.m, melting point: 160.degree. C.) A polypropylene ultrafine fiber (melting point: 160 ° C.) having a circular fiber cross section and a fiber diameter of 1.8 μm), a high-density polyethylene component (symbol 11 in the figure, the fiber cross-sectional shape is A straight line that consists of high-density polyethylene ultra-thin fibers (melting point: 132 ° C) with a fiber diameter of 3.5 µm and can be generated at regular angles (about 22.5 °) from the fiber axis. Was prepared as a split long fiber (fineness: 1.43 dtex, fiber length: 25 mm, 17 splittable).
Further, the same core-sheath type composite fused continuous fiber and polypropylene high-strength continuous fiber as in Example 1 were prepared.
Next, after splitting long fibers, core-sheath type composite fusion long fibers, and polypropylene high-strength long fibers at a mass ratio of 40:25:35, they are opened by a carding machine, and the unidirectional long fiber web is opened. (Area density 20 g / m ² ) Was formed.
[0078]
Next, in exactly the same way as in the examples, lamination of unidirectional long fiber webs and short fiber webs, hydroentanglement treatment, fusion treatment, and fluorine gas treatment were carried out to introduce sulfofluoride groups on the fiber surface. A surface density of 50 g / m ² A separator having a thickness of 0.12 mm was formed. In addition, when the entanglement state was observed by photographing an electron micrograph in the cross section of the separator, a mixed layer in which short fibers and long fibers were entangled was present over the entire thickness of the separator.
[0079]
(Tensile strength in the vertical direction)
The separator cut to a width of 50 mm is fixed to a tensile strength tester (Orientec, Tensilon UTM-III-100) (distance between chucks: 100 mm), pulled at a tensile speed of 300 mm / min, and tensile strength in the vertical direction. Was measured. The results are shown in Table 1. As can be seen from Table 1, the separator of the present invention was excellent in tensile strength, and thus it was found that the separator was difficult to break when the electrodes were grouped.
[0080]
[Table 1]

[0081]
(Tear strength in the vertical direction)
The tear strength of the separator is measured according to JIS L 1096. ^-1990 Measured based on (General Textile Test Method, Trabezoid Method). The results are shown in Table 1. As is apparent from Table 1, since the separator of the present invention was excellent in tear strength, it was found that when the electrodes were grouped, they were not easily torn by the edge of the electrode plate.
[0082]
(Average penetration resistance)
Each separator is stacked to a total thickness of about 2 mm, and a stainless steel jig (thickness: 0.5 mm, attached to a handy compression tester (Kato Tech, KES-G5) is attached to the uppermost separator. The tip edge angle: 60 °) was stabbed vertically at a speed of 0.01 cm / s, and the force required to cut the uppermost separator was measured to determine penetration resistance. The penetration resistance was measured at 50 locations of each separator, the average value was calculated, and this value was taken as the average penetration resistance. The results are shown in Table 1. The maximum and minimum penetration resistance values are also shown in Table 1. As is apparent from Table 1, the separator of the present invention is difficult to penetrate even with a sharp stainless steel jig, and therefore, when the electrodes are grouped, the burr of the electrode plate is also difficult to penetrate. I understood it. Moreover, since the difference between the maximum value and the minimum value of the penetration resistance of the separator of the present invention is small, it has been found that the separator is difficult to penetrate the burr of the electrode plate and has high reliability.
[0083]
(Measurement of formation index)
(1) Light was applied to each separator from a light source, and the reflected light reflected in a predetermined region of the separator was received by the light receiving element among the irradiated light to obtain luminance information.
(2) A predetermined area of the separator was equally divided into image sizes of 3 mm square, 6 mm square, 12 mm square, and 24 mm square to obtain four divided patterns.
(3) The luminance value of each section equally divided for each obtained division pattern was calculated based on the luminance information.
(4) Based on the luminance value of each section, the luminance average (X) for each division pattern was calculated.
(5) The standard deviation (σ) for each divided pattern was obtained.
(6) The coefficient of variation (CV) for each divided pattern was calculated by the following equation.
Coefficient of variation (CV) = (σ / X) × 100
Here, σ indicates a standard deviation for each divided pattern, and X indicates a luminance average for each divided pattern.
(7) A coordinate group obtained as a result of taking the logarithm of each image size as the X coordinate and the coefficient of variation corresponding to the image size as the Y coordinate is regressed to a linear line by the least square method, and the inclination is calculated. The absolute value of was used as the formation index.
The results are shown in Table 1. As is clear from this result, since the separator of the present invention is excellent in formation, it can be predicted that minute short-circuits are unlikely to occur during long-term use.
[0084]
(Short rate)
When each electrode plate was actually formed using each separator, the ratio at which the battery could not be manufactured was defined as the short circuit rate. The results are shown in Table 1. From this result, it was found that the separator of the present invention hardly causes a short circuit between the electrodes when the electrodes are grouped.
[0085]
(Battery life test)
As the electrode current collector, a paste type nickel positive electrode (33 mm width, 182 mm length) using a foamed nickel base material and a paste type hydrogen storage alloy negative electrode (mesh metal alloy, 33 mm width, 247 mm length) were prepared.
Next, each separator was cut into a width of 33 mm and a length of 410 mm, and then sandwiched between a positive electrode and a negative electrode and wound in a spiral shape to create an electrode group corresponding to SC (sub-C) type. This electrode group was housed in an outer can, and 5N potassium hydroxide and 1N lithium hydroxide were poured into the outer can as an electrolytic solution and sealed to prepare a cylindrical nickel-hydrogen battery.
Next, for each cylindrical nickel-hydrogen battery, a charge / discharge cycle consisting of (1) 150% charge at 0.2 C and (2) discharge to 1 V at 1 C was repeated, and the discharge capacity was the initial capacity. When the battery life reached 50%, it was determined that the battery life was exhausted, and the number of cycles until the battery life was exhausted was measured. Table 1 shows the ratio when the cycle number of the battery using the separator of the comparative example is defined as the reference (100). From this result, it was found that a battery using the separator of the present invention has a long battery life because a micro short-circuit hardly occurs.
[0086]
(Battery pressure test)
A cylindrical nickel-hydrogen battery formed in the same manner as that used in the battery life test was charged at 20 ° C. at 0.5 C, and the battery internal pressure at 150% of the capacity was measured. Table 1 shows the ratio when the internal pressure of the battery using the separator of the comparative example is defined as a reference (100). From this result, it was found that the battery using the separator of the present invention had a low internal pressure and excellent battery characteristics.
[0087]
【The invention's effect】
In the separator of the present invention, a tough skeleton is formed by the high-strength long fibers and the fusion long fibers. Therefore, when the electrodes are grouped, the separator breaks, the burrs of the electrode plates penetrate the separator, or It is hard to be torn by the edge of an electrode plate, and when forming an electrode group, a short circuit between electrodes is hard to generate | occur | produce. In addition, ultra-fine short fibers with short fiber lengths have a high degree of freedom and can be distributed densely and evenly between the skeletons formed by high-strength long fibers and fusion long fibers, thus preventing micro short-circuits when using batteries. Excellent in properties.
In addition, if the high strength short fibers having a tensile strength of 4.5 cN / dtex or more are further included as the short fibers, the high strength short fibers are densely and uniformly distributed, thereby further improving the reliability of the performance. To do.
The high-strength long fiber has a tensile strength of 9 cN / dtex or more and a Young's modulus of 800 kg / mm. ² When the above-mentioned polypropylene long fibers are used, the thickness of the nonwoven fabric (separator) can be maintained against the pressure applied when forming the group of electrodes and the pressure during charging and discharging, so the electrolyte can be retained. The battery characteristics can be further improved.
Furthermore, since the ultrafine short fiber is derived from the hollow split short fiber, it can be a finer ultrafine short fiber, so that it can be a denser and uniform separator, resulting in a battery. Excellent in preventing short circuit during use.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a segmented short fiber that can be used in the present invention.
FIG. 2 is a schematic cross-sectional view of another segmented short fiber that can be used in the present invention.
FIG. 3 is a schematic cross-sectional view of still another divided short fiber that can be used in the present invention.
FIG. 4 is a schematic cross-sectional view of still another divided short fiber that can be used in the present invention
FIG. 5 is a schematic cross-sectional view of still another divided short fiber that can be used in the present invention.
FIG. 6 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 7 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 8 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 9 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 10 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 11 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 12 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 13 is a schematic cross-sectional view of still another hollow split fiber that can be used in the present invention.
FIG. 14 is a schematic cross-sectional view of yet another hollow split short fiber that can be used in the present invention.
[Explanation of symbols]
1 Split short fiber
11 First component
12 Second component
S Hollow part

Claims (4)

The total thickness of the mixed layer in which the short fibers having a fiber length of less than 25 mm and the long fibers having a fiber length of 25 mm or more are intertwined is made of a nonwoven fabric that occupies one third or more of the total thickness, and the short fibers As a high-strength long fiber comprising a high-strength long fiber having a tensile strength of 4.5 cN / dtex or more and a fusing long fiber. The battery separator is characterized in that the mass ratio of the fusion-bonded long fibers is 50 to 90 to 50 to 10 .   The battery separator according to claim 1, further comprising high-strength short fibers having a tensile strength of 4.5 cN / dtex or more as the short fibers. The battery separator according to claim 1 or 2, wherein the high-strength long fibers are made of polypropylene long fibers having a tensile strength of 9 cN / dtex or more and a Young's modulus of 800 kg / mm ² or more.   The battery separator according to any one of claims 1 to 3, wherein the ultrafine short fibers are derived from hollow split short fibers.

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