JP3917873B2 - Nonwoven fabric and battery using the same - Google Patents

Description

【０１１８】
（最大孔径の測定）
各不織布の最大孔径を、ポロメータ（コールター社製）を用いてバブルポイント法により測定した。この値は表１に示す通りであった。この表１から明らかなように、最大孔径が小さく地合いが均一であるため、分離性の優れる不織布であることが予測された。
【０１１９】
（比（最大孔径／平均流量孔径）の測定）
各不織布の平均流量孔径を、ポロメータ（Ｐｏｌｏｍｅｔｅｒ、コールター（Ｃｏｕｌｔｅｒ）社製）を用いてミーンフローポイント法により測定した。
【０１２０】
次いで、前述のようにして得られた最大孔径を平均流量孔径で除して、比（最大孔径／平均流量孔径）を算出した。この結果は表１に示す通りであった。表１から明らかなように、本発明の不織布はこの比が小さく、液体を均一に分散した状態で保持できるものであった。
【０１２１】
（空隙率の測定）
まず、各不織布の目付（Ｗ）及び厚さ（Ｔ）を測定した。
【０１２２】
次いで、不織布構成繊維の密度（ｄ）を各構成繊維の密度及び質量比率から算出した。
【０１２３】
次いで、次の式から「空隙率（Ｐ）」を算出した。
空隙率（Ｐ）＝｛１−Ｗ／（Ｔ×ｄ）｝×１００
【０１２４】
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、本発明の不織布は液体の保持量の多いものであることが予測された。
【０１２５】
（長手方向における引張り強さの測定）
幅５ｃｍに裁断した各不織布を、引張り強さ試験機（オリエンテック製、テンシロンＵＴＭ−III−１００）のチャック間（チャック間距離：１０ｃｍ）に固定し、引張り速度３００ｍｍ／ｍｉｎで各不織布を長手方向に引張り、各不織布を破断するために要する力を測定し、この力を長手方向における引張り強さとした。この結果は表１に示す通りであった。この表１から明らかであるように、本発明の不織布は機械的強度の優れるものであった。
【０１２６】
（ニードル式耐貫通力）
円筒状貫通孔（内径：１１ｍｍ）を有する支持台の円筒状貫通孔を覆うように各不織布を１枚載置し、更に各不織布上に、円筒状貫通孔（内径：１１ｍｍ）を有する固定材を、前記支持台の円筒状貫通孔の中心と一致するように載置して各不織布を固定した後、この不織布に対して、ハンディー圧縮試験機（カトーテック製、ＫＥＳ−Ｇ５）に取り付けられたニードル（先端部における曲率半径：０．５ｍｍ、直径：１ｍｍ、治具からの突出長さ：２ｃｍ）を、０．０１ｃｍ／ｓの速度で垂直に突き刺し、ニードルが突き抜けるのに要する力を測定し、この力をニードル式耐貫通力とした。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、本発明の不織布は針状のものが当接しても繊維がより分けられにくい、分離性の高いものであった。
【０１２７】
（単位目付あたりの平均ニードル式耐貫通力）
上記ニードル式耐貫通力の測定を各不織布の３０箇所について行って得た値を平均して平均ニードル式耐貫通力を求めた後、この平均ニードル式耐貫通力を目付（ｇ／ｍ^２）で除して、単位目付あたりの平均ニードル式耐貫通力を算出した。この結果は表１に示す通りであった。この表１からも明らかなように、本発明の不織布は針状のものが当接しても繊維がより分けられにくい、分離性の高いものであった。
【０１２８】
（加圧保液率の測定）
直径３０ｍｍに裁断した各不織布をそれぞれ、温度２０℃、相対湿度６５％の状態下で、水分平衡に至らせた後、質量（Ｍ_０）を測定した。
【０１２９】
次に、不織布中の空気を水酸化カリウム水溶液で置換するように、比重１．３（２０℃）の水酸化カリウム水溶液中に１時間浸漬し、水酸化カリウム水溶液を保持させた。
【０１３０】
次に、この不織布を上下３枚づつのろ紙（直径：３０ｍｍ）で挟み、加圧ポンプにより、５．７ＭＰａの圧力を３０秒間作用させた後、不織布の質量（Ｍ_１）を測定した。
【０１３１】
次いで、次の式により加圧保液率を求めた。なお、この測定は１つの不織布に対して４回行ない、その平均を加圧保液率とした。この結果は表１に示す通りであった。この加圧保液率が１０％以上であると、電解液の保持性に優れていると判断することができる。
加圧保液率（％）＝｛（Ｍ_１−Ｍ_０）／Ｍ_０｝×１００
【０１３２】
この表１から明らかなように、本発明の不織布は液体の保持性に優れるものであった。
【０１３３】
（吸液高さの測定）
各不織布を長手方向に１８０ｍｍ、幅方向に２５ｍｍの長方形状に裁断して試験片を作成した。次いで、各試験片の長手方向における一方の端部から５ｍｍ上方までの領域を水酸化カリウム溶液（１.３ｄ）に浸漬すると共に、各試験片を水酸化カリウム溶液の液面に対して直角方向に配置した。そして、３０分間経過後における水酸化カリウム溶液の上昇した高さを測定した。この測定は温度４０℃、湿度８０％の条件下に１４日間放置する前後において行なった。この結果は表１に示す通りであった。この高さが１００ｍｍ／３０ｍｉｎ．以上であれば、吸液速度が速く、吸液性に優れていると判断することができる。この表１から明らかなように、本発明の不織布は液体の吸液速度が速く、しかもその能力を長期間にわたって維持できるものであることがわかった。
【０１３４】
（電池寿命の測定）
各不織布をセパレータとして用いて、Ｓｕｂ−Ｃサイズのニッケル水素電池（電池容量：２０００Ａｈ）を作成した。各電池を活性化させた後、室温で０．２Ｃで６時間充電し、０.２Ｃで終止電圧０．８Ｖまで放電することを１サイクルとして繰り返し、初期容量の８０％まで容量が低下した時点に至るまでのサイクル数を求めた。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、本発明の不織布は電池用セパレータとして用いると、電池寿命を長くできるものであることがわかった。
【０１３５】
【発明の効果】
本発明の不織布は液体の保持性が長期間にわたって低下しにくいものである。また、液体の吸液速度が速いものである。更には、機械的強度が優れている。
【０１３６】
本発明の電池は電池寿命の長く、効率的に安定して製造できるものである。
【図面の簡単な説明】
【図１】 実施例で用いた放電処理装置の模式的断面図
【符号の説明】
１ａ、１ｂ 平板状電極
２ａ、２ｂ ベルト状誘電体
３ａ、３ｂ 側壁誘電体
４ 高周波電源
５ 融着不織布[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nonwoven fabric and a battery using the same, and more particularly to a nonwoven fabric that can be suitably used as a battery separator or a separator for an electric double layer capacitor, and a battery using the same.
[0002]
[Prior art]
Conventionally, nonwoven fabrics have been applied to various uses. As one of the uses, there are known uses of battery separators or separators for electric double layer capacitors (hereinafter, both are collectively referred to as “separators”) utilizing the separability of nonwoven fabrics. This separator is disposed between the positive electrode and the negative electrode of the battery or capacitor, and has an effect of separating the positive electrode and the negative electrode to prevent a short circuit and holding the electrolytic solution to facilitate an electromotive reaction.
[0003]
Conventionally, an alkaline solution such as potassium hydroxide, an acid solution such as sulfuric acid, or an organic solvent has been used as an electrolytic solution constituting a battery or a capacitor. Therefore, polyolefin fibers are preferably used as the fibers constituting the separator. Although this polyolefin fiber is excellent in electrolytic solution resistance as described above, it has poor affinity with the electrolytic solution and poor retention of the electrolytic solution. Surface treatment is applied. For example, the nonwoven fabric is surface-treated by corona discharge treatment or plasma treatment. Nonwoven fabric that has been surface-treated by these methods has improved affinity with electrolyte to some extent, but it is still insufficient or excellent in initial affinity, but the affinity over time Therefore, a battery or a capacitor using this surface-treated nonwoven fabric as a separator has a short life.
[0004]
In addition, with the recent reduction in size and weight of electronic devices, the space occupied by the battery or capacitor has become narrower. Alternatively, it is required to increase the capacity of the capacitor, and for this purpose, it is necessary to increase the amount of the active material of the electrode. Therefore, the volume occupied by the separator is inevitably reduced, and recently, a separator having a thickness of 0.1 mm or less is required in the market.
[0005]
In order to obtain a separator having such a thickness, if the basis weight is simply reduced, the amount of fibers will be reduced, so that the retention of the electrolytic solution is lowered and the retention of the electrolytic solution, which is the original function of the separator, is reduced. Unfortunately, there is a problem that the life of the battery or the capacitor is shortened as a result. In addition, there has been a problem that the rate of absorption of the electrolyte at the time of manufacturing the battery or capacitor is slow, and the manufacturing efficiency of the battery or capacitor is poor. Furthermore, there is a problem in that the separator may be broken due to the force applied to the separator during manufacturing of the battery or the capacitor, or the active material of the electrode may penetrate the separator and may not function as a separator.
[0006]
[Problems to be solved by the invention]
The present invention has been made in order to solve the above-described problems. A nonwoven fabric excellent in liquid retention over a long period of time, having a high liquid absorption rate, and excellent in mechanical strength, and the same are used. An object is to provide a battery.
[0007]
[Means for Solving the Problems]
  The nonwoven fabric of the present invention has a high strength fiber having a tensile strength of 6 cN / dtex or more,It is not in a bundle but in a distributed stateIncluding ultrafine fibers having a fiber diameter of 4 μm or less, The fibers were fixed substantially only by fiber fusionThe nonwoven fabric is characterized in that the amount of fibers exceeding 70 mass% of the nonwoven fabric has a polyethylene resin on the fiber surface, and more oxygen-containing functional groups are present in the nonwoven fabric than on the nonwoven fabric surface. . It has been found that this non-woven fabric contains a large amount of polyethylene fiber having a polyethylene resin on the fiber surface, and the presence of oxygen-containing functional groups makes it difficult for the liquid retainability to deteriorate over a long period of time. Moreover, in addition to the liquid retention, the liquid absorption speed is increased due to the inclusion of ultrafine fibers and uniform texture, and the presence of many oxygen-containing functional groups inside the nonwoven fabric. I found. Furthermore, it has also been found that the mechanical strength is excellent by including a high-strength fiber.
[0008]
  High-strength fibers constituting the nonwoven fabric of the present invention are on the fiber surfaceWith a resin that can be fused, the cross-sectional shape is a core-sheath type, eccentric type or sea-island type fiber, and high-strength fibers are fused,Since the content of high-strength fibers can be increased, the mechanical strength of the nonwoven fabric is further improved.
[0009]
When the ultrafine fiber constituting the nonwoven fabric of the present invention is an ultrafine fiber consisting of island components remaining after removing the sea component of the sea-island type fiber, the texture of the nonwoven fabric is more uniform, so the liquid absorption speed is further increased. In addition, the separation effect can be enhanced.
[0010]
  When 75 mass% or more of the nonwoven fabric of the present invention is provided with a polyethylene resin on the fiber surface, the liquid retainability is unlikely to deteriorate for a longer period of time.Further, the high-strength fiber is made of a polypropylene resin alone, the surface of the ultrafine fiber is a polyethylene resin, further includes a heat-fusible fiber, and the heat-fusible fiber is a non-woven fabric fused. To do. Furthermore, it is characterized by containing 40 mass% or more of fibers provided with high-density polyethylene on the fiber surface.
[0011]
The nonwoven fabric of the present invention is suitable as a battery separator.
[0012]
Since the battery of the present invention uses the above-mentioned nonwoven fabric as a separator, the battery life is long and the productivity is excellent.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The nonwoven fabric of the present invention contains high-strength fibers having a tensile strength of 6 cN / dtex or more so that the nonwoven fabric does not break due to the force applied to the nonwoven fabric. The higher the tensile strength of the high-strength fiber, the easier it is to exhibit the above effects, so that it is preferably 6.5 cn / dtex or more, and more preferably 6.8 cn / dtex or more. The upper limit of the tensile strength of the high-strength fiber is not particularly limited as long as a nonwoven fabric can be formed, but about 50 cn / dtex is appropriate. This “tensile strength” refers to the tensile strength measured by the method defined in JIS L 1015: 1999, Section 8.7.1. The tensile strength is a value measured by a constant speed tension type testing machine.
[0014]
This high-strength fiber may be composed of any resin as long as it has the above-mentioned tensile strength, but a polyolefin-based resin on the fiber surface (excluding both ends of the fiber) so as not to be affected by the liquid. Is preferably present, and the fiber surface (excluding both ends of the fiber) is more preferably composed of only a polyolefin resin. Examples of such polyolefin resins include polyethylene resins (for example, ultrahigh molecular weight polyethylene, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, ethylene copolymer resins (for example, ethylene- Vinyl alcohol copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid, etc.), polypropylene resin (eg, polypropylene, propylene copolymer (eg, ethylene-butene-propylene copolymer, ethylene-butadiene) -Propylene copolymer, ethylene-propylene copolymer, etc.)), polymethylpentene resin (for example, polymethylpentene, methylpentene copolymer) and the like. Among these, as described later, a polyethylene-based resin in which an oxygen-containing functional group is present is preferable because affinity with a liquid is sustained, and high-density polyethylene is particularly preferable because affinity with a liquid is particularly sustained. . Examples of the resin constituting the high-strength fiber other than the polyolefin resin include a polyamide resin and a polyester resin.
[0015]
The high-strength fiber of the present invention may be composed of the above resin alone, or two or more kinds of resins may be mixed or combined. If the fiber surface is a high-strength fiber with a resin that can be fused, the high-strength fiber can also be used as a fused fiber, and the amount of high-strength fiber can be increased. Can be further improved. When the fusible resin is a polyethylene resin, a polyethylene resin in which an oxygen-containing functional group is present is particularly suitable because the affinity with a liquid is sustained. The greater the number of fusible resins (especially polyethylene resins), the better the fusibility, so the cross-sectional shape of the high-strength fiber is, for example, a core-sheath type, an eccentric type, or a sea-island type Is preferred.
[0016]
In order to increase the mechanical strength of the nonwoven fabric, the high-strength fiber preferably has a fiber diameter of 5 to 35 μm, more preferably 7 to 30 μm, and more preferably 8 to 25 μm. preferable. The “fiber diameter” in the present invention refers to the diameter when the cross-sectional shape of the fiber is circular, and the diameter of a circle having the same cross-sectional area when the cross-sectional shape of the fiber is non-circular. Is the fiber diameter.
[0017]
The fiber diameter of the high-strength fiber is 2.5 times or more (preferably 3 times or more, more preferably 3.5 times or more, most preferably 4 times or more) the fiber diameter of the ultrafine fiber as described later. Even if force is applied to the non-woven fabric, the voids of the non-woven fabric can be retained, and the surface area is increased by the ultrafine fibers described later. Therefore, the liquid retainability under pressure is improved.
[0018]
Such a high-strength fiber is easy to exhibit the above-described effect if it is contained in the nonwoven fabric constituting fiber in an amount of 5 mass% or more, and is more preferably contained in an amount of 15 mass% or more. On the other hand, since it is preferable to contain ultrafine fibers as described later, it is preferably 95 mass% or less.
[0019]
The nonwoven fabric of the present invention contains ultrafine fibers having a fiber diameter of 4 μm or less in addition to the high-strength fibers as described above. By including such ultrafine fibers, the texture becomes uniform, and it is possible to contribute to the improvement of the liquid absorption speed and the separability. Moreover, since the fiber surface area in the unit volume of a nonwoven fabric can be enlarged, the retainability of a liquid can further be improved. If the fiber diameter of the ultrafine fiber exceeds 4 μm, the contribution to the above effect tends to decrease, so that a more preferable fiber diameter is 3 μm or less, and a more preferable fiber diameter is 2 μm or less. The lower limit of the fiber diameter of the ultrafine fiber is not particularly limited, but about 0.01 μm is appropriate.
[0020]
The ultrafine fibers preferably have the same fiber diameter between the ultrafine fibers so that the ultrafine fibers form a uniform pore diameter and the liquid distribution is uniform. That is, the value (σ / d) obtained by dividing the standard deviation value (σ) of the fiber diameter distribution of the ultrafine fiber by the average fiber diameter (d) of the ultrafine fiber is 0.2 or less (preferably 0.18 or less). Is preferred. In addition, since the standard deviation value (σ) is 0 when the fiber diameters of all the ultrafine fibers are the same, the lower limit value of the value (σ / d) is 0.
[0021]
The “average fiber diameter (d)” of the present invention is obtained by taking an electron micrograph of a nonwoven fabric, measuring the fiber diameter of 100 or more (n) ultrafine fibers in this electron micrograph, and measuring the measured fiber diameter. The average value. The “standard deviation value (σ)” of the ultrafine fiber is a value calculated from the following equation based on the measured fiber diameter (χ).
Standard deviation = {(nΣχ²-(Σχ)²) / N (n-1)}^1/2
Here, n means the number of measured ultrafine fibers, and χ means the fiber diameter of each ultrafine fiber.
[0022]
In addition, when two or more ultrafine fiber groups exist, it is preferable that the said relationship is materialized about each ultrafine fiber group.
[0023]
Further, it is preferable that the individual ultrafine fibers have substantially the same diameter in the fiber axis direction so that the ultrafine fibers can form a nonwoven fabric having a uniform pore diameter. Such ultrafine fibers having substantially the same fiber diameter between the ultrafine fibers, or individual ultrafine fibers having substantially the same diameter in the fiber axis direction are, for example, regulated in the sea component at the spinneret portion. Then, the island component can be formed by removing the sea component of the sea-island fiber obtained by the composite spinning method in which the island component is extruded and combined. In addition, the method of removing the sea component of the sea-island fiber obtained by the method of spinning after mixing the resin constituting the island component and the resin constituting the sea component, which is generally referred to as a mixed spinning method, or by the melt blow method It is difficult to obtain ultrafine fibers having the same fiber diameter between the ultrafine fibers or individual ultrafine fibers having substantially the same diameter in the fiber axis direction. However, even these ultrafine fibers can be used in the present invention.
[0024]
As long as this ultrafine fiber has the fiber diameter as described above, it may be composed of any resin. For example, the same resin as that constituting the above-mentioned high-strength fiber, that is, a polyolefin-based resin, a polyamide-based resin A resin or a polyester resin can be used. Among these, since the polyethylene resin having an oxygen-containing functional group maintains affinity with the liquid, it is preferable that the polyethylene resin is present on the surface of the ultrafine fiber. It is more preferable that it is made of a polyethylene resin.
[0025]
If the ultrafine fiber contains a resin component that can participate in fusion (hereinafter sometimes referred to as “fusion component”), the fusion can be fused by this fusion component, and the ultrafine fiber is securely fixed. This is a preferred embodiment because the ultrafine fibers do not fall off or become fuzzy.
[0026]
When this ultrafine fiber is fused, the ultrafine fiber may be composed of only the fusion component, or a component having a melting point higher than the fusion component and the fusion component (hereinafter referred to as “non-fusion component”). May be comprised of two or more types of components. When the ultrafine fiber is composed of two or more components including a fusion component and a non-fusion component as in the latter case, it is more preferable because the fiber form can be maintained even if the fusion component is fused.
[0027]
When the ultrafine fibers are composed of two or more kinds of components, the fusion component preferably occupies part or all of the surface of the ultrafine fibers and can be fused. When this ultrafine fiber is comprised from two or more types of components, it is preferable that the cross-sectional shape is, for example, a core-sheath type, an eccentric type, or a sea-island type. The non-fusion component preferably has a melting point that is 10 ° C. or more higher than the melting point of the fusion component so that the fiber shape can be maintained, and more preferably 20 ° C. or more.
[0028]
As described above, the ultrafine fiber composed of two or more kinds of resin components including the fusion component and the non-fusion component is used as a base for extruding the island component when the sea-island fiber is spun by a conventional composite spinning method. Two or more types of resin components can be used when spinning a sea-island type fiber by a conventional compound spinning method, such as a core-sheath type, an eccentric type, or a sea-island type. It can be obtained by supplying the mixed resin to a die for extruding the island component, spinning sea-island type fibers, and removing the sea component.
[0029]
The “melting point” in the present invention refers to a temperature that gives a maximum value of a melting endothermic curve obtained by using a differential scanning calorimeter at a temperature rising temperature of 10 ° C./min and raising the temperature from room temperature. When there are two or more maximum values, the highest temperature maximum value is taken as the melting point.
[0030]
The cross-sectional shape of the ultrafine fiber of the present invention is preferably circular so that the texture of the nonwoven fabric can be improved. Further, it is preferable that the ultrafine fibers are not in a bundle but in a dispersed state so that the texture of the nonwoven fabric is excellent.
[0031]
The ultrafine fibers are preferably short fibers having a high degree of freedom (fiber length is 30 mm or less) so that they can be uniformly dispersed. However, when ultrafine fibers or sea-island fibers are cut, the ultrafine fibers or island components are separated from each other. Will be in a state like a fibrillated fiber, and the dispersibility will decrease, so it is necessary to use ultrafine fibers or sea-island type fibers that are difficult to crimp between ultrafine fibers or island components when cutting. preferable. Examples of such ultrafine fibers or sea-island fibers that are difficult to press-bond include ultrafine fibers with high crystallinity (island components in the case of sea-island fibers). More specifically, when the ultrafine fiber (island component in the case of sea-island type fibers) contains polymethylpentene or polypropylene, the polypropylene has a melting point of 166 ° C. or higher (preferably 168 ° C. The above is preferable.
[0032]
Such an ultrafine fiber is likely to exhibit the above-described effect if it is contained in the nonwoven fabric constituting fiber by 5 mass% or more, more preferably 10 mass% or more, and more preferably 12 mass% or more. Is more preferable. On the other hand, since it is necessary to contain high-strength fibers so that the nonwoven fabric has excellent mechanical strength, it is preferably 95 mass% or less.
[0033]
In addition to the high-strength fiber and the ultrafine fiber, the fiber constituting the nonwoven fabric of the present invention preferably contains a heat-fusible fiber. By including the heat-fusible fiber, the mechanical strength of the nonwoven fabric can be further improved.
[0034]
The fusion component of the heat-fusible fiber preferably has a melting point that does not adversely affect fibers other than the heat-fusible fiber (for example, high-strength fibers, ultrafine fibers, etc.). For example, fibers having a polyethylene-based resin on the fiber surface (for example, high-strength fibers, ultrafine fibers, etc.) are preferable as fibers other than heat-fusible fibers so that the liquid retainability is excellent. The fusion component of the adhesive fiber is preferably made of a polyethylene resin. In this case, since the amount of the polyethylene-based resin is increased, there is an effect that the liquid retainability is improved.
[0035]
This heat-fusible fiber may be composed only of the fusion component, or may contain a non-fusion component having a melting point higher than that of the fusion component in addition to the fusion component. If the latter is composed of a fusion component and a non-fusion component, the mechanical strength of the nonwoven fabric can be further improved. The cross-sectional shape of the heat-fusible fiber in this case can be, for example, a core-sheath type, an eccentric type, or a sea-island type. The non-fusion component is preferably made of a resin that is higher by 10 ° C. or more than the melting point of the fusion component, and is preferably made of a resin that is higher by 20 ° C. or more.
[0036]
Such heat-fusible fibers are preferably contained in the nonwoven fabric constituting fiber in an amount of 10 mass% or more, more preferably 15 mass% or more, so that the mechanical strength of the nonwoven fabric can be improved. . On the other hand, it is preferable that it is 90 mass% or less from the balance with the above high-strength fibers and ultrafine fibers.
[0037]
The non-woven fabric of the present invention basically includes the above-described high-strength fibers and ultrafine fibers, and preferably includes heat-fusible fibers, but other than these fibers within the range not impairing the function of the non-woven fabric of the present invention. Of fiber may be included. In addition, there are (1) ultrafine fiber and high-strength fiber, and (2) ultrafine fiber, high-strength fiber and heat-fusible fiber as suitable fiber blends of the nonwoven fabric of the present invention. In the case of (1) above, (fine fiber) :( high strength fiber) is in the order of 5 to 95:95 to 5, 10 to 85:90 to 15, and 12 to 80:20 to 88. Preferably, in the case of the combination of (2), (ultrafine fiber) :( high strength fiber) :( heat-fusible fiber) is 5 to 80: 5 to 80:10 to 90, 10 to 70:15 to 75:15. The blending mass ratios of -75 and 12-60: 20-68: 20-68 are preferred in order.
[0038]
If the mass ratio of the high-strength fibers is 1 or more times the mass ratio of the ultrafine fibers, the high-strength fibers form a skeleton, and the ultrafine fibers are filled between the skeletons. This is preferable because of improved properties.
[0039]
The nonwoven fabric of the present invention is composed of the above-described fibers (for example, high-strength fibers, ultrafine fibers, heat-fusible fibers, etc.), but the amount of fibers exceeding 70 mass% of the nonwoven fabric is a polyethylene resin on the fiber surface. It has. It has been found that when there are many fibers having a polyethylene-based resin on the fiber surface, the deterioration with time of liquid retention is small when oxygen-containing groups are present. That is, even if fibers of 70 mass% or less of the nonwoven fabric are provided with a polyethylene resin on the fiber surface, the liquid retainability deteriorates with time. Preferably, fibers of 75 mass% or more of the nonwoven fabric are polyethylene on the fiber surface. More preferably, 80 mass% or more of the nonwoven fabric has a polyethylene resin on the fiber surface. In addition, although the polyethylene-type resin of the fiber provided with the polyethylene-type resin on the fiber surface does not need to be the same, it is preferable that the fiber provided with the high-density polyethylene on the fiber surface contains 40 mass% or more. It is more preferable to contain 50 mass% or more of fibers having polyethylene on the fiber surface.
[0040]
The nonwoven fabric constituting fibers of the present invention (for example, high-strength fibers, ultrafine fibers, heat-fusible fibers, etc.) may be in an unstretched state, but in a stretched state so as to have excellent mechanical strength. preferable.
[0041]
In addition, the fiber length of the nonwoven fabric constituting fibers (for example, high-strength fibers, ultrafine fibers, heat-fusible fibers, etc.) is not particularly limited, but the shorter the fiber length, the higher the degree of freedom of the fibers and the uniform dispersion Therefore, the fiber length is preferably 0.5 to 30 mm, and more preferably 1 to 20 mm. Moreover, it is preferable that it is the cut | disconnected fiber. “Fiber length” refers to the length obtained by JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method).
[0042]
The fiber length of the high-strength fiber is preferably 2.5 times or more (preferably 3 times or more, more preferably 4 times or more, still more preferably 5 times or more) the fiber length of the ultrafine fibers. In this case, the high-strength fibers form a skeleton, and the ultrafine fibers are easily filled between the skeletons, thereby improving the liquid retention.
[0043]
The nonwoven fabric of the present invention is preferably composed only of fibers that are not substantially fibrillated. This is because, when it is composed only of fibers that are not substantially fibrillated, the texture is uniform, and the liquid can be maintained in a well-balanced state throughout the nonwoven fabric. In addition, it is preferable not to use in the present invention, because fibers obtained by beating mechanically splittable fibers with a beater or the like, pulp, fibers obtained by flash spinning, etc. are fibrillated fibers.
[0044]
Although the nonwoven fabric of this invention is substantially comprised from the above fibers, it is preferable that a nonwoven fabric consists of a substantially single layer structure so that the uneven distribution of a liquid may not arise. This “substantially one-layer structure” means that the average fiber diameter of the different portions of the nonwoven fabric in terms of fiber composition and fiber composition is the average fiber diameter of the entire nonwoven fabric in the thickness direction of the nonwoven fabric. It means that it is included within the range of ± 20%. Therefore, as long as the average fiber diameter is within the above range, a plurality of fiber webs can be laminated. The simplest forming method is a method of forming one fiber web from the same fiber blend. The “thickness direction” refers to a direction perpendicular to a non-woven fabric plane (a non-woven fabric surface is flat and a flat non-woven fabric side surface when a flat plate is placed on the non-woven fabric surface).
[0045]
The nonwoven fabric of the present invention has an apparent total surface area of 20 m per unit weight.²The above is preferable. With such an apparent total surface area, the fiber surface is wide, and the liquid retainability is excellent. Therefore, even if the nonwoven fabric is as thin as 0.1 mm or less, the liquid can be held for a long period of time. More preferable total apparent surface area is 22m²That's it, 25m²The above is more preferable. In order to obtain such an apparent total surface area, for example, the amount of the ultrafine fiber as described above is increased, or the high-strength fiber and / or the heat-sealable fiber as described above having a small fiber diameter is used. It can be achieved by using them or combining them.
[0046]
The “weight per unit area” means the basis weight obtained based on the method specified in JIS P 8124 (paper and paperboard—basis weight measurement method), and “the apparent total surface area of fibers per unit area” The sum of the surface areas of the fibers (excluding the cross-sectional area of the fibers) in a state before the fibers of the fibers existing in the basis weight are fixed. For example, the basis weight is 40 g / m²In the case of 20 mass% of ultrafine fibers and 80 mass% of high strength fibers, the surface area (excluding the cross-sectional area of the fibers) of 8 g (= 40 × 0.2) of ultrafine fibers and 32 g of high strength fibers (= 40 × 0) .8) Total surface area (excluding fiber cross-sectional area). In addition, when the nonwoven fabric constituting fiber is fused, the apparent total surface area is calculated based on the surface area of the heat-fusible fiber before the fusion (excluding the cross-sectional area of the fiber). Further, the surface area of the fiber can be calculated from the fiber diameter, basis weight, composition ratio, and fineness, and the surface area of the heat-fusible fiber before fusing is the fiber diameter at the position where heat fusion is not performed. It can be calculated using the diameter.
[0047]
In the nonwoven fabric of the present invention, it is preferable that the fibers are substantially fixed only by fusion of the fibers. This is because the texture is excellent by being fixed only by fiber fusion. For example, when fibers are fixed by entanglement other than fusion, penetration from the front surface to the back surface of the nonwoven fabric is caused by an action (for example, fluid flow such as water flow, needle, etc.) to entangle the fibers. Holes tend to be formed and the texture tends to deteriorate. However, if the fibers are fixed only by fusion, the fiber arrangement is not disturbed, and the texture is excellent.
[0048]
In addition, when manufacturing a nonwoven fabric, fibers may get entangled. For example, when a fiber web is formed by a carding machine or a fiber web is formed by a wet method, the form of the fiber web can be maintained to some extent, so that the fibers are more or less intertwined. However, since this entanglement does not disturb the texture of the nonwoven fabric, it can be considered that it is not substantially entangled. Thus, “substantially only fiber fusion” means that the fibers are fixed only by fusion after the fiber web is formed. From another viewpoint, this state is a state in which the fibers constituting the nonwoven fabric are substantially two-dimensionally arranged.
[0049]
The nonwoven fabric of the present invention is composed of the fibers as described above, and more oxygen-containing functional groups are present inside the nonwoven fabric than the surface of the nonwoven fabric, so that the liquid absorption speed is high and the liquid retainability is high. Also excellent. Further, the present inventors have found that the amount of fibers provided with a polyethylene resin on the fiber surface is large, and that the retention of liquid can be sustained for a long time when oxygen-containing functional groups are present in these polyethylene resins.
[0050]
Examples of the oxygen-containing functional group include a carboxyl group, a carbonyl group, and a hydroxyl group. The amount of such oxygen-containing functional groups is greater in the nonwoven fabric than in the nonwoven fabric surface, but the oxygen-containing functional group content in the nonwoven fabric is preferably at least twice the amount of oxygen-containing functional groups in the nonwoven fabric surface. The above is more preferable.
[0051]
It should be noted that the oxygen-containing functional group has an oxygen-containing functional group (carboxyl group, carbonyl group, and hydroxyl group) (Oi) measured by an X-ray photoelectron spectrometer inside the nonwoven fabric so that the liquid retention and the liquid absorption speed are high. The ratio (Oi / C) to the number of carbon atoms (C) is preferably 0.1 or more, more preferably 0.14 or more, and further preferably 0.2 or more. In addition, the ratio (Oo / C) of the oxygen-containing functional groups (carboxyl group, carbonyl group, and hydroxyl group) (Oo) to the number of carbon atoms (C) measured by an X-ray photoelectron spectrometer on the nonwoven fabric surface was 0.01. The above is preferable, 0.02 or more is more preferable, and 0.03 or more is further preferable.
[0052]
This ratio (Oi / C) is measured by measuring the nonwoven fabric using L1076-1992 (Peeling test method for woven and knitted fabrics) C method (bottom area of sample holder: about 20 cm).²After removing the fibers on the nonwoven fabric surface by pressing load: about 3.90 N, rotation speed: 100 rotations), measurement can be performed under the following conditions using an X-ray photoelectron spectrometer. In other words, using an accelerating voltage of 10 kV and an emission current of 10 mA as an X-ray source, after performing a narrow scan of carbon elements with an analysis area of 6 mm (diameter), waveform separation is performed, and waveform separation of carboxyl groups, carbonyl groups, and hydroxyl groups is performed. Do. Next, the X-ray intensity of each functional group is calculated, and the ratio (Oi / C) of the total number of carboxyl groups, the number of carbonyl groups, and the total number of hydroxyl groups (Oi) to the number of carbon atoms (C) is calculated.
[0053]
The ratio (Oo / C) is measured as follows. First, a nonwoven fabric ratio (Ot / C) is measured under the following conditions using an X-ray photoelectron spectrometer. In other words, using an accelerating voltage of 10 kV and an emission current of 10 mA as an X-ray source, after performing a narrow scan of carbon elements with an analysis area of 6 mm (diameter), waveform separation is performed, and waveform separation of carboxyl groups, carbonyl groups, and hydroxyl groups is performed. Do. Next, the X-ray intensity of each functional group is calculated, and the ratio (Ot / C) of the number of carboxyl groups, the number of carbonyl groups, and the total number of hydroxyl groups (Ot) to the number of carbon atoms (C) is calculated. Next, the ratio (Oo / C) can be calculated by subtracting the ratio (Oi / C) measured in the same manner as described above from this ratio (Ot / C). That is, the value obtained by the following equation.
Ratio (Oo / C) = {ratio (Ot / C)}-{ratio (Oi / C)}
[0054]
The texture of the nonwoven fabric of the present invention is excellent, but “texture index” can be cited as an index of the texture of the nonwoven fabric. When the formation index value is within 0.15, the formation is excellent, the separation property is excellent, and the liquid can be held uniformly. A more preferable formation index is 0.10 or less.
[0055]
The “geometric index” is a value obtained by the method disclosed in Japanese Patent Laid-Open No. 2001-50902. That is, the value obtained as follows.
(1) Light is applied to the nonwoven fabric from the light source, and the reflected light reflected in a predetermined region of the nonwoven fabric is received by the light receiving element, and the luminance information is acquired.
(2) A predetermined region of the nonwoven fabric is 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 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.
[0056]
The maximum pore size of the nonwoven fabric of the present invention is preferably 40 μm or less, more preferably 35 μm or less, and further preferably 30 μm or less. With such a maximum pore size, the texture is excellent and the separability is excellent. The “maximum pore diameter” refers to a value measured by a bubble point method using a porometer (manufactured by Coulter).
[0057]
The nonwoven fabric of the present invention preferably has a maximum pore size of 2 times or less (more preferably 1.9 times or less) of the average flow pore size. Within such a range, the pore size distribution is narrow and the liquid can be kept uniform. Ideally, the maximum pore size is one time the average flow pore size, that is, the total pore size is the same. The “average flow pore size” in the present invention refers to a value obtained by a method defined in ASTM-F316, for example, a value measured by a mean flow point method using a porometer (Polometer, manufactured by Coulter). It is.
[0058]
The porosity of the nonwoven fabric of the present invention is preferably 45 to 65%, more preferably 50 to 60% so that the amount of liquid retained is increased. This “porosity (P)” is a value obtained by the following equation.
Porosity (P) = {1−W / (T × d)} × 100
Here, W is a basis weight (g / m²), T means the thickness (μm) of the nonwoven fabric, and d means the density (g / cm) of the resin (for example, fiber) constituting the nonwoven fabric.³). In addition, when two or more types of nonwoven fabric constituent resin exist, the density of nonwoven fabric constituent resin says the mass average of each constituent resin. For example, density d₁Resin A is a (mass%) and density d₂When the resin B is present in b (mass%), the density of the resin constituting the nonwoven fabric is a value obtained by the following formula.
d = d₁× a / 100 + d₂× b / 100
[0059]
The nonwoven fabric of the present invention preferably has a tensile strength in at least one direction of 20 N / 5 cm width or more, more preferably 30 N / 5 cm width or more, and 40 N / 5 cm width so that the mechanical strength is excellent. The above is more preferable. This “tensile strength” is determined by fixing a nonwoven fabric cut to a width of 5 cm between chucks (distance between chucks: 10 cm) of a tensile strength tester (Orientec, Tensilon UTM-III-100), and a tensile speed of 300 mm / It refers to the force required to pull the nonwoven fabric in min and break the nonwoven fabric.
[0060]
The nonwoven fabric of the present invention preferably has a needle penetration resistance of 500 gf or more, more preferably 600 gf or more, and even more preferably 700 gf or more so that the non-woven fabric of the present invention is excellent in separability.
[0061]
This needle type penetration resistance means the value obtained as follows.
One non-woven fabric is placed so as to cover the cylindrical through-hole of the support base having a cylindrical through-hole (inner diameter: 11 mm), and a fixing material having a cylindrical through-hole (inner diameter: 11 mm) is further formed on the non-woven fabric. After placing the nonwoven fabric so as to coincide with the center of the cylindrical through hole of the support base and fixing the nonwoven fabric, a needle attached to a handy compression tester (KES-G5, manufactured by Kato Tech) The radius of curvature at the tip: 0.5 mm, diameter: 1 mm, protruding length from the jig: 2 cm) was stabbed vertically at a speed of 0.01 cm / s, and the force required for the needle to penetrate was measured. The force is the needle penetration resistance.
[0062]
The nonwoven fabric of the present invention preferably has an average needle penetration resistance per unit weight of 14 gf or more, more preferably 15 gf or more, still more preferably 16 gf or more, and most preferably 18 gf or more. . This high value means that there are no through holes, fibers are uniformly dispersed, and the texture is excellent. “Average needle type penetration resistance” means a value obtained by averaging the values obtained by measuring the above needle type penetration resistance at 30 locations of the nonwoven fabric, and “average needle type penetration resistance per unit weight” Is the average needle type penetration resistance (g / m²) Means the value divided by.
[0063]
The basis weight of the nonwoven fabric of the present invention is 5 to 75 g / m.²Is preferable, and more preferably 10 to 60 g / m.²It is. The thickness of the nonwoven fabric of the present invention is preferably 0.15 mm or less, more preferably 0.12 mm or less, and even more preferably 0.10 mm or less. The “thickness” in the present invention refers to a thickness measured by an outer micrometer (0 to 25 mm) defined in JIS B 7502: 1994.
[0064]
The nonwoven fabric of this invention can be manufactured as follows, for example.
[0065]
First, the above-described high-strength fibers and ultrafine fibers, preferably heat-fusible fibers are prepared. At this time, it is prepared so that the amount of fibers exceeding 70 mass% of the nonwoven fabric is provided with a polyethylene resin on the fiber surface.
[0066]
Next, a fiber web is formed from the prepared fibers. The method for forming the fiber web is not particularly limited, but can be formed by a dry method (for example, a card method, an air lay method, a spun bond method, a melt blow method, etc.) or a wet method. Among these, it is preferable to form by a wet method which can take a dense structure and can produce a nonwoven fabric having excellent liquid retention and liquid absorption speed. This wet method can be formed by a conventionally known method, for example, a horizontal long net method, an inclined wire type short net method, a circular net method, or a long net / circular net combination method.
[0067]
Subsequently, the fiber which comprises this fiber web is fixed, and a nonwoven fabric is manufactured. This fixing of the fiber is preferably carried out only by thermal fusion. This is because fixing by heat fusion alone does not disturb the arrangement of the fibers, so that it is easy to produce a nonwoven fabric that is excellent in texture, excellent in separability, and capable of evenly distributing the liquid. Therefore, it is preferable that the fibers (for example, high-strength fibers, ultrafine fibers, and heat-fusible fibers) constituting the fiber web have a fusing component.
[0068]
The fiber web may be heat-sealed under no pressure, under pressure, or after the fusion component has been melted under no pressure (preferably immediately pressurized). You may do it. In any case, the heating temperature is preferably within the range from the softening temperature of the fusion component to a temperature 30 ° C. higher than the melting point, and the pressure when pressing forms a nonwoven fabric having the required mechanical strength. There is no particular limitation as long as it is a pressure that can be generated. This pressure can be appropriately set by repeating the experiment. The “softening temperature” in the present invention refers to a temperature that gives a starting point of a melting endothermic curve obtained by using a differential calorimeter and raising the temperature from room temperature at a temperature rising rate of 10 ° C./min.
[0069]
Next, oxygen-containing functional groups are introduced into the nonwoven fabric so that more oxygen-containing functional groups exist inside the nonwoven fabric than on the nonwoven fabric surface. As a method for introducing the oxygen-containing functional group, for example, a pair of electrodes each supporting a dielectric is sandwiched between the nonwoven fabrics as described above, and the oxygen-containing functional group is interposed between the electrodes in the presence of an oxygen-containing gas at atmospheric pressure. The method of introduce | transducing by applying an alternating voltage and generating discharge by the internal space of a nonwoven fabric can be mentioned. When this discharge is applied, for example, by appropriately adjusting the applied voltage, the type of dielectric, the discharge treatment time, the atmospheric humidity, and the type of oxygen-containing gas, the abundance of oxygen-containing functional groups on the nonwoven fabric surface and inside the nonwoven fabric Can be adjusted.
[0070]
As the dielectric, for example, glass, ceramic (for example, alumina), rubber (for example, synthetic rubber, for example, silicone rubber, chloroprene rubber, or butadiene rubber, or natural so as to increase the amount of oxygen-containing functional groups Rubber or the like), or a thermoplastic resin (for example, polytetrafluoroethylene or polyester) or the like can be used. The thickness of the dielectric is not particularly limited, but is preferably about 0.05 to 5 mm.
[0071]
The oxygen-containing gas is not particularly limited as long as it contains oxygen, and examples thereof include air, oxygen gas, carbon dioxide gas, and carbon monoxide gas. Among these, air is particularly suitable because it is easy to handle.
[0072]
The AC voltage applied to generate the discharge is not particularly limited, but is 0.25 KVp or more, preferably 0.5 KVp or more so that the amount of the oxygen-containing functional group can be increased (KVp is Indicates the voltage difference from the maximum AC voltage peak value to 0). In addition, the upper limit of an alternating voltage should just be a voltage which does not damage a nonwoven fabric, and is not specifically limited.
[0073]
The frequency of the alternating voltage is preferably 0.1 KHz or more, more preferably 0.5 KHz or more, and further preferably 1 KHz or more so that the oxygen-containing functional group amount can be increased. On the other hand, the upper limit of the frequency is not particularly limited as long as it is a frequency that does not damage the nonwoven fabric, but is preferably 100 KHz or less, and more preferably 50 KHz or less.
[0074]
The output of the alternating current is 0.1 W / cm so that the amount of the oxygen-containing functional group can be increased.²Preferably, it is 0.5 W / cm²The above is more preferable. The upper limit is not particularly limited as long as the output does not damage the nonwoven fabric.
[0075]
Furthermore, the waveform of the applied voltage is not particularly limited, and examples thereof include a sine wave, a triangular wave, a rectangular wave, and a pulse wave.
[0076]
The discharge treatment time is preferably 2 seconds or longer, and more preferably 3 seconds or longer so that the amount of the oxygen-containing functional group can be increased. Further, the atmospheric humidity is preferably 80 RH% or less, and more preferably 70 RH% or less so that the amount of oxygen-containing functional groups can be increased.
[0077]
In addition to the discharge treatment as described above, sulfonation treatment, fluorine gas treatment, and surfactant addition within the range in which the amount of oxygen-containing functional groups on the surface of the nonwoven fabric does not exceed the amount of oxygen-containing functional groups inside the nonwoven fabric. Application of hydrophilic resin, corona discharge treatment, plasma treatment, glow discharge treatment, creeping discharge treatment, or electron beam irradiation treatment can be performed.
[0078]
The nonwoven fabric of the present invention can be produced, for example, as described above, but a nonwoven fabric having a formation index of 0.15 or less, a nonwoven fabric having a maximum pore size of 40 μm or less, or a maximum pore size of twice or less than the average flow pore size. The non-woven fabric is a non-fibrillated fiber as a fiber constituting the non-woven fabric, a short fiber having a fiber length of about 1 to 20 mm, a fiber web formed by a wet method, or only by fusing. It can manufacture by using these together, such as fixing fibers (not performing an entanglement process).
[0079]
The non-woven fabric having a porosity of 45 to 65% of the present invention reduces the amount of ultrafine fibers, reduces the amount of fibers used, adjusts the thickness by adjusting the pressure when fusing, etc. It can manufacture by using these together.
[0080]
The nonwoven fabric having a tensile strength in at least one direction of the present invention of 20 N / 5 cm width or more is a state in which the orientation of the fiber is close to one direction by adjusting the moving speed of the net for making up the fiber and the slurry flow rate, It can be produced by using these in combination, such as increasing the degree of fusion or increasing the fiber length.
[0081]
The nonwoven fabric with needle penetration resistance of 500 gf or more according to the present invention or the nonwoven fabric with average needle penetration resistance per unit weight of 14 gf or more uses high-strength fibers with high tensile strength, Adjust various conditions such as increasing the number of fibers, uniformly dispersing high-strength fibers, firmly fusing them with heat-fusible fibers, or fusing heat-fusible fibers and then immediately applying pressure. Can be manufactured.
[0082]
Nonwoven fabric in which the amount of oxygen-containing functional groups in the nonwoven fabric of the present invention is at least twice the amount of oxygen-containing functional groups in the nonwoven fabric surface, the nonwoven fabric in which the ratio (Oi / C) in the nonwoven fabric is 0.1 or more, and the ratio in the nonwoven fabric surface The non-woven fabric having (Oo / C) of 0.01 or more is, for example, the above-mentioned at atmospheric pressure in the presence of an oxygen-containing gas in a state where the non-woven fabric is sandwiched between a pair of electrodes each supporting a dielectric. When introducing an AC voltage between both electrodes and generating a discharge in the inner space of the nonwoven fabric, the applied voltage, dielectric type, discharge treatment time, atmospheric humidity, and oxygen-containing gas type are adjusted accordingly. Alternatively, it can be produced by using a discharge treatment or a fluorine gas treatment different from the discharge treatment.
[0083]
As described above, the nonwoven fabric of the present invention is excellent in liquid retention over a long period of time, has a high liquid absorption speed, and is excellent in mechanical strength. Therefore, it is suitably used for applications requiring these physical properties. be able to. For example, it can be suitably used for applications such as battery separators, electric double layer capacitor separators, wiping materials, and printing substrates.
[0084]
Among these, when the nonwoven fabric of the present invention is used as a battery separator, a remarkable effect is obtained. In other words, since the electrolyte retainability is excellent for a long period of time, the battery life can be extended. Moreover, since the liquid absorption speed of the electrolytic solution is high, the battery can be manufactured efficiently. Furthermore, the non-woven fabric (separator) is not easily broken by the force applied to the non-woven fabric (battery separator) at the time of battery production, and the active material of the electrode is difficult to penetrate the non-woven fabric (separator). it can. Moreover, even if the thickness of the non-woven fabric is thin, the above-described effect can be achieved, so that the battery can be increased in capacity. The nonwoven fabric of the present invention can be used as a separator for any battery, for example, primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, air batteries, nickel-cadmium batteries, silver-zinc batteries, silver -It can use as a separator of secondary batteries, such as a cadmium battery, a nickel- zinc battery, a nickel-hydrogen battery, and can be used especially suitably as a separator of a nickel-cadmium battery or a nickel-hydrogen battery.
[0085]
Since the battery of the present invention uses a nonwoven fabric as described above as a separator, the battery life is long and can be manufactured efficiently and stably. The battery of the present invention can have the same structure as that of a conventional battery except that the nonwoven fabric as described above is used as a separator.
[0086]
For example, a cylindrical nickel-hydrogen battery has a structure in which an electrode group in which a nickel positive electrode plate and a hydrogen storage alloy negative electrode plate are spirally wound through a nonwoven fabric (separator) as described above is inserted into a metal case. Have As the nickel positive electrode plate, for example, a sponge-like porous porous material filled with an active material made of nickel hydroxide solid solution powder can be used. As the hydrogen storage alloy negative electrode plate, for example, a nickel plated perforated steel plate, For foamed nickel or nickel net, AB₅-Based (rare earth) alloy, AB / A₂B-based (Ti / Zr-based) alloy or AB₂Those filled with a (Laves phase) -based alloy can be used. As the electrolytic solution, for example, a potassium hydroxide / lithium hydroxide two-component system or a potassium hydroxide / sodium hydroxide / lithium hydroxide three-component system can be used. The case is sealed with an insulating gasket by a sealing plate provided with a safety valve. Furthermore, a positive electrode current collector and an insulating plate are provided, and if necessary, a negative electrode current collector is provided.
[0087]
Examples of the battery of the present invention include primary batteries such as alkaline manganese batteries, mercury batteries, silver oxide batteries, air batteries, nickel-cadmium batteries, silver-zinc batteries, silver-cadmium batteries, nickel-zinc batteries, nickel-hydrogen batteries. A secondary battery such as a battery can be mentioned, and a nickel-cadmium battery or a nickel-hydrogen battery is preferable, and a sealed nickel-cadmium battery or a nickel-hydrogen battery is particularly preferable. Note that the battery need not be cylindrical, and may be rectangular, button-shaped, or the like. In the case of a square type or a button type, it has a laminated structure in which a nonwoven fabric (separator) is disposed between a positive electrode plate and a negative electrode plate.
[0088]
Although the Example of the separator of this invention is described below, this invention is not limited to these Examples. The amount of the oxygen-containing functional group was measured by the method described above.
[0089]
【Example】
Example 1
Prepared as a sea-island-type fiber by a composite spinning method in which 25 island components made of polypropylene are present in a sea component made of poly-L-lactic acid (fineness: 1.65 dtex, cut fiber length: 2 mm) did. Next, this sea-island type fiber was immersed in a bath composed of a 10 mass% sodium hydroxide aqueous solution at a temperature of 80 ° C. for 30 minutes to remove poly-L-lactic acid, which is a sea component of the sea-island type fiber, to obtain a polypropylene extra fine fiber ( Fiber diameter: 2 μm, ρ / d: 0.083, melting point: 172 ° C., cut fiber length 2 mm, density: 0.91 g / cm³Non-fibrillated, stretched, cross-sectional shape: circular, having substantially the same diameter in the fiber axis direction).
[0090]
As high-strength fibers, polypropylene is coated with high-density polyethylene (fusion component, melting point: 135 ° C.), and the cross-sectional shape is a core-sheath type composite fiber (tensile strength: 6.8 cN / dtex, fiber diameter: 11.0 μm, fiber length: 5 mm, density: 0.94 g / cm³, Not fibrillated, stretched).
[0091]
Subsequently, 20 mass% of the above-mentioned polypropylene ultrafine fibers and 80 mass% of the core-sheath type composite fiber (high strength fiber) were mixed, and a fiber web was formed from the dispersed slurry by a wet method (horizontal long net method). In this fiber web, the polypropylene microfibers were not in a bundle but in a dispersed state.
[0092]
Next, the fiber web is left in a hot air circulation dryer set at a temperature of 135 ° C. for 3 minutes to dry the fiber web and use the sheath component (high-density polyethylene) of the core-sheath composite fiber (high-strength fiber). Thermal fusion was performed to form a fusion nonwoven fabric having a substantially single layer structure.
[0093]
Next, the fused nonwoven fabric 5 was placed at 6 m / min. Between the belt-like dielectrics 2a and 2b of the discharge treatment apparatus as shown in FIG. (Discharging treatment time: 5 seconds), and in the state where the fused nonwoven fabric 5 is sandwiched between the belt-like dielectrics 2a, 2b, both in the presence of air (humidity: 60RH%) under atmospheric pressure. An AC voltage is applied between the electrodes 1a and 1b (voltage: 24 kVp, output: 2.8 kW (1.83 W / cm²), Frequency: 25 KHz, waveform: sine wave), and discharge was generated inside the fused nonwoven fabric.
[0094]
In addition, the specific structure of the discharge processing apparatus was as follows.
(1) Flat electrode 1a, 1b: A stainless steel plate sprayed with alumina having a thickness of 100 μm on the opposing surface is placed facing each other in a flow direction length of 500 mm, a width of 1020 mm, a thickness of 35 mm.
(2) Opposing belt-like dielectrics 2a and 2b: silicone belts having a width of 1200 mm and a thickness of 3 mm
(3) Side wall dielectrics 3a and 3b: Each side wall of each flat electrode 1a and 1b is completely covered with 5 mm thick epoxy resin.
(4) Application means: The flat electrode 1a is connected to the high frequency power source 4 and the flat electrode 1b is grounded.
[0095]
Next, the discharge-treated fused nonwoven fabric was calendered to form a single-layered nonwoven fabric (weight per unit: 40 g / m², Thickness: 0.10 mm, apparent total surface area: 39 m²The fibers are arranged substantially two-dimensionally, and 80% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.20, and the ratio (Oo / C) on the nonwoven fabric surface was 0.03.
[0096]
(Example 2)
As a sea-island fiber, a fiber obtained by a composite spinning method in which 25 island components made of high-density polyethylene are present in a sea component made of poly-L-lactic acid (fineness: 1.68 dtex, cut fiber length: 2 mm) Prepared. Next, this sea-island type fiber was immersed in a bath composed of a 10 mass% sodium hydroxide aqueous solution at a temperature of 80 ° C. for 30 minutes to remove poly-L-lactic acid, which is a sea component of the sea-island type fiber, to obtain ultrafine high-density polyethylene Fiber (fiber diameter: 2 μm, ρ / d: 0.084, melting point: 135 ° C., cut fiber length 2 mm, density: 0.95 g / cm³Non-fibrillated, stretched, cross-sectional shape: circular, having substantially the same diameter in the fiber axis direction).
[0097]
Moreover, the same core-sheath type composite fiber as Example 1 was prepared as a high strength fiber.
[0098]
Further, as the heat-fusible fiber, the core component (non-fusion component) is polypropylene (melting point: 168 ° C., density: 0.91 g / cm).³The sheath component (fusion component) is low density polyethylene (melting point: 124 ° C., density: 0.92 g / cm³) Core-sheath composite heat-fusible fiber (fineness: 1.2 dtex, fiber length: 5 mm, mass ratio of core component to sheath component is 1: 1, not fibrillated, stretched) did.
[0099]
Next, 20 mass% of the above-mentioned high-density polyethylene ultrafine fiber, 30 mass% of the core-sheath type composite fiber (high strength fiber), and 50 mass% of the core-sheath type composite heat-fusible fiber are mixed and dispersed from the slurry. A fiber web was formed by (horizontal long net system). In this fiber web, the high-density polyethylene microfibers were not in a bundle but in a dispersed state.
[0100]
Next, the fiber web is left in a hot-air circulating dryer set at a temperature of 124 ° C. for 3 minutes to dry the fiber web and heat the sheath component (low-density polyethylene) of the core-sheath type composite heat-fusible fiber. Fusion was performed to form a fusion nonwoven fabric having a substantially single layer structure.
[0101]
Subsequently, the discharge treatment and the calendar treatment were carried out in the same manner as in Example 1, and a single-layered nonwoven fabric (weight per unit: 40 g / m)², Thickness: 0.10 mm, apparent total surface area: 35 m²The fibers are arranged substantially two-dimensionally, and 100% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.23, and the ratio (Oo / C) on the nonwoven fabric surface was 0.05.
[0102]
(Example 3)
As a sea-island type fiber, 25 island components composed of high-density polyethylene and polypropylene are present in a sea component composed of poly-L-lactic acid, and a fiber obtained by a composite spinning method (fineness: 1.66 dtex, cut fiber length) : 2 mm). Next, this sea-island type fiber was immersed in a bath composed of a 10 mass% sodium hydroxide aqueous solution at a temperature of 80 ° C. for 30 minutes to remove poly-L-lactic acid, which is a sea component of the sea-island type fiber, to obtain a high-density polyethylene- Polypropylene composite ultrafine fiber (fiber diameter: 2 μm, cross-sectional shape: sea island shape, ρ / d: 0.083, melting point of high density polyethylene: 135 ° C., cut fiber length: 2 mm, density: 0.94 g / cm³Non-fibrillated, stretched, cross-sectional shape: circular, having substantially the same diameter in the fiber axis direction).
[0103]
Further, as a high-strength fiber, a fiber made of polypropylene (tensile strength: 10.7 cN / dtex, fiber diameter: 13.7 μm, fiber length: 10 mm, density: 0.91 g / cm³, Not fibrillated, stretched).
[0104]
Further, as the heat-fusible fiber, the core component (non-fusion component) is polypropylene (melting point: 168 ° C., density: 0.91 g / cm).³The sheath component (fusion component) is high density polyethylene (melting point: 135 ° C., density: 0.95 g / cm³) Core-sheath composite heat-fusible fiber (fineness: 1.2 dtex, fiber length: 5 mm, mass ratio of core component to sheath component is 1: 1, not fibrillated, stretched) did.
[0105]
Next, 20 mass% of the high-density polyethylene-polypropylene composite ultrafine fiber, 20 mass% of polypropylene fiber (high-strength fiber), and 60 mass% of the core-sheath type composite heat-fusible fiber are mixed and dispersed from the slurry. A fiber web was formed by (horizontal long net system). In this fiber web, the high-density polyethylene-polypropylene composite ultrafine fibers were not in a bundled state but in a dispersed state.
[0106]
Next, the fiber web is left in a hot air circulation dryer set at a temperature of 135 ° C. for 3 minutes to dry the fiber web and to form the high density polyethylene-polypropylene composite ultrafine fiber and the core-sheath composite heat-fusible fiber. High density polyethylene was thermally fused to form a fused nonwoven fabric having a substantially single layer structure.
[0107]
Subsequently, the discharge treatment and the calendar treatment were carried out in the same manner as in Example 1, and a single-layered nonwoven fabric (weight per unit: 40 g / m)², Thickness: 0.10 mm, apparent total surface area: 36 m²The fibers are arranged substantially two-dimensionally, and 80% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.22, and the ratio (Oo / C) on the nonwoven fabric surface was 0.04.
[0108]
(Comparative Example 1)
A non-woven fabric having a single-layer structure (weight per unit: 40 g / m) in exactly the same manner as in Example 3 except that 20 mass% of the same polypropylene ultrafine fiber as in Example 1 was used as the ultrafine fiber.², Thickness: 0.10 mm, apparent total surface area: 37 m²The fibers are arranged substantially two-dimensionally, and 60% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.14, and the ratio (Oo / C) on the nonwoven fabric surface was 0.01.
[0109]
(Comparative Example 2)
As the ultrafine fiber, the same polypropylene extrafine fiber as in Example 1 was prepared, and as the heat fusible fiber, the same core-sheath type composite heat fusible fiber as in Example 3 was prepared.
[0110]
Subsequently, 20 mass% of the above-mentioned polypropylene ultrafine fibers and 80 mass% of the core-sheath type composite heat-fusible fiber were mixed, and a fiber web was formed from the dispersed slurry by a wet method (horizontal long net method). In this fiber web, the polypropylene microfibers were not in a bundle but in a dispersed state.
[0111]
Next, a fusion nonwoven fabric was formed in the same manner as in Example 3, and after performing a discharge treatment, a calendar treatment was carried out to form a single-layer nonwoven fabric (weight per unit: 40 g / m).², Thickness: 0.10 mm, apparent total surface area: 37 m²The fibers are arranged substantially two-dimensionally, and 80% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.17, and the ratio (Oo / C) on the nonwoven fabric surface was 0.02.
[0112]
(Comparative Example 3)
The same core-sheath type composite fiber as in Example 1 was prepared as the high-strength fiber, and the same core-sheath type composite heat-sealable fiber as in Example 3 was prepared as the heat-sealable fiber.
[0113]
Next, after the core-sheath type composite fiber 40 mass% and the core-sheath type composite heat-fusible fiber 60 mass% are mixed and dispersed, a fiber web is formed by a wet method (horizontal long net method). A fused nonwoven fabric is formed in the same manner as in Example 3, and after performing a discharge treatment, a calendar treatment is performed to form a single-layer nonwoven fabric (weight per unit: 40 g / m).², Thickness: 0.10 mm, apparent total surface area: 25 m²The fibers are arranged substantially two-dimensionally, and 100% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.19, and the ratio (Oo / C) on the nonwoven fabric surface was 0.03.
[0114]
(Comparative Example 4)
After the discharge treatment was performed on the fusion nonwoven fabric having substantially a single layer structure manufactured in the same manner as in Example 1, the calendar treatment was performed to form a single layer nonwoven fabric (weight per unit: 40 g / m).², Thickness: 0.10 mm, apparent total surface area: 39 m²The fibers are arranged substantially two-dimensionally, and 80% by mass of the nonwoven fabric is provided with a polyethylene resin on the fiber surface). The ratio (Oi / C) inside the nonwoven fabric was 0.01, and the ratio (Oo / C) on the nonwoven fabric surface was 0.16. The discharge treatment was performed under the following conditions.
Output: 1000W
Electrode: Two electrodes having a width of 110 cm × 2 cm are arranged above and below the fusion nonwoven fabric so that the gap between the electrodes is 2 mm.
Discharge processing tempo: 4 m / min.
Humidity: 60RH%
[0115]
(Measurement of formation index)
The formation index of each nonwoven fabric was measured as follows.
(1) Light was irradiated to the nonwoven fabric from the light source, and the reflected light reflected in the predetermined area | region of the nonwoven fabric was received by the light receiving element among the irradiated lights, and the luminance information was acquired.
(2) A predetermined region of the nonwoven fabric 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. In addition, a formation index means that the fiber is disperse | distributed uniformly, so that a number is small.
[0116]
The results are shown in Table 1. As is apparent from Table 1, the nonwoven fabric of the present invention was very excellent in formation.
[0117]
[Table 1]

[0118]
(Maximum pore size measurement)
The maximum pore diameter of each nonwoven fabric was measured by a bubble point method using a porometer (manufactured by Coulter). This value was as shown in Table 1. As apparent from Table 1, since the maximum pore diameter is small and the texture is uniform, it is predicted that the nonwoven fabric has excellent separability.
[0119]
(Measurement of ratio (maximum pore size / average flow pore size))
The average flow pore size of each nonwoven fabric was measured by a mean flow point method using a porometer (Polometer, manufactured by Coulter).
[0120]
Next, the ratio (maximum pore diameter / average flow pore diameter) was calculated by dividing the maximum pore diameter obtained as described above by the average flow pore diameter. The results are shown in Table 1. As is apparent from Table 1, the nonwoven fabric of the present invention has a small ratio, and can hold the liquid in a uniformly dispersed state.
[0121]
(Measurement of porosity)
First, the basis weight (W) and thickness (T) of each nonwoven fabric were measured.
[0122]
Next, the density (d) of the nonwoven fabric constituent fibers was calculated from the density and mass ratio of each constituent fiber.
[0123]
Next, “porosity (P)” was calculated from the following equation.
Porosity (P) = {1−W / (T × d)} × 100
[0124]
The results are shown in Table 1. As is apparent from Table 1, the nonwoven fabric of the present invention was predicted to have a large amount of liquid retention.
[0125]
(Measurement of tensile strength in the longitudinal direction)
Each non-woven fabric cut into a width of 5 cm is fixed between chucks (distance between chucks: 10 cm) of a tensile strength tester (Orientec, Tensilon UTM-III-100), and each non-woven fabric is elongated at a pulling speed of 300 mm / min. The force required to break each nonwoven fabric was measured, and this force was defined as the tensile strength in the longitudinal direction. The results are shown in Table 1. As is clear from Table 1, the nonwoven fabric of the present invention was excellent in mechanical strength.
[0126]
(Needle-type penetration resistance)
One non-woven fabric is placed so as to cover the cylindrical through-hole of the support base having a cylindrical through-hole (inner diameter: 11 mm), and a fixing material having a cylindrical through-hole (inner diameter: 11 mm) on each non-woven fabric. Are fixed so that they coincide with the center of the cylindrical through-hole of the support base, and each nonwoven fabric is fixed. Then, the nonwoven fabric is attached to a handy compression testing machine (KES-G5, manufactured by Kato Tech). A needle (curvature radius at the tip: 0.5 mm, diameter: 1 mm, protrusion length from the jig: 2 cm) was pierced vertically at a speed of 0.01 cm / s, and the force required to penetrate the needle was measured. This force was defined as needle-type penetration resistance. The results are shown in Table 1. As is apparent from Table 1, the nonwoven fabric of the present invention was highly separable because it was more difficult to separate the fibers even when the needle-shaped material contacted.
[0127]
(Average needle-type penetration resistance per unit weight)
The average needle type penetration resistance is obtained by averaging the values obtained by measuring the needle type penetration resistance for 30 locations of each nonwoven fabric, and then obtaining the average needle type penetration resistance (g / m²The average needle type penetration resistance per unit weight was calculated. The results are shown in Table 1. As is clear from Table 1, the nonwoven fabric of the present invention was highly separable because it was more difficult to separate the fibers even when the needle-shaped material contacted.
[0128]
(Measurement of pressure retention rate)
Each nonwoven fabric cut to a diameter of 30 mm was brought to water equilibrium under the conditions of a temperature of 20 ° C. and a relative humidity of 65%.₀) Was measured.
[0129]
Next, the air in the non-woven fabric was immersed in an aqueous potassium hydroxide solution having a specific gravity of 1.3 (20 ° C.) for 1 hour so that the aqueous potassium hydroxide solution was replaced, and the aqueous potassium hydroxide solution was retained.
[0130]
Next, the nonwoven fabric was sandwiched between three upper and lower filter papers (diameter: 30 mm), and a pressure of 5.7 MPa was applied for 30 seconds with a pressure pump.₁) Was measured.
[0131]
Subsequently, the pressurization liquid retention was calculated | required by the following formula. In addition, this measurement was performed 4 times with respect to one nonwoven fabric, and the average was made into the pressurization liquid retention. The results are shown in Table 1. It can be judged that the holding | maintenance of electrolyte solution is excellent in this pressurization liquid retention being 10% or more.
Pressure retention ratio (%) = {(M₁-M₀) / M₀} × 100
[0132]
As is apparent from Table 1, the nonwoven fabric of the present invention was excellent in liquid retention.
[0133]
(Measurement of liquid absorption height)
Each nonwoven fabric was cut into a rectangular shape of 180 mm in the longitudinal direction and 25 mm in the width direction to prepare a test piece. Next, an area from one end in the longitudinal direction of each test piece to 5 mm above is immersed in a potassium hydroxide solution (1.3d), and each test piece is perpendicular to the liquid level of the potassium hydroxide solution. Arranged. And the height which the potassium hydroxide solution rose after 30 minutes passed was measured. This measurement was performed before and after leaving for 14 days under conditions of a temperature of 40 ° C. and a humidity of 80%. The results are shown in Table 1. This height is 100 mm / 30 min. If it is above, it can be judged that the liquid absorption speed is high and the liquid absorption is excellent. As apparent from Table 1, it was found that the nonwoven fabric of the present invention has a high liquid absorption rate and can maintain its ability over a long period of time.
[0134]
(Measurement of battery life)
Sub-C size nickel metal hydride batteries (battery capacity: 2000 Ah) were prepared using each nonwoven fabric as a separator. Each battery was activated, charged at room temperature for 6 hours at 0.2C, and discharged at 0.2C to a final voltage of 0.8V as one cycle, and when the capacity decreased to 80% of the initial capacity. The number of cycles to reach was determined. The results are shown in Table 1. As is apparent from Table 1, it was found that the nonwoven fabric of the present invention can extend the battery life when used as a battery separator.
[0135]
【The invention's effect】
In the nonwoven fabric of the present invention, the liquid retainability is hardly lowered over a long period of time. Moreover, the liquid absorption speed is high. Furthermore, the mechanical strength is excellent.
[0136]
The battery of the present invention has a long battery life and can be produced efficiently and stably.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an electric discharge treatment apparatus used in Examples.
[Explanation of symbols]
1a, 1b Flat electrode
2a, 2b Belt-shaped dielectric
3a, 3b Side wall dielectric
4 High frequency power supply
5 Fusion nonwoven fabric

Claims (8)

The high-strength fiber having a tensile strength of 6 cN / dtex or more and the ultrafine fiber having a fiber diameter of 4 μm or less in a dispersed state that is not in a bundle state , the fibers are substantially only by fusion of the fibers. It is a fixed nonwoven fabric, and the amount of fibers exceeding 70 mass% of this nonwoven fabric has a polyethylene resin on the fiber surface, and more oxygen-containing functional groups are present in the nonwoven fabric than on the nonwoven fabric surface. Characteristic nonwoven fabric. The high-strength fiber is provided with a resin that can be fused to the fiber surface, the cross-sectional shape is a core-sheath type, eccentric type or sea-island type fiber, and the high-strength fiber is fused, The nonwoven fabric according to claim 1.   The nonwoven fabric according to claim 1 or 2, wherein the nonwoven fabric is an ultrafine fiber composed of island components remaining after removing sea components of sea-island fibers.   The nonwoven fabric according to any one of claims 1 to 3, wherein 75 mass% or more of the nonwoven fabric has a polyethylene resin on the fiber surface. The high-strength fiber is made of polypropylene resin alone, the surface of the ultrafine fiber is a polyethylene-based resin, further includes a heat-fusible fiber, and the heat-fusible fiber is a non-woven fabric fused, The nonwoven fabric according to claim 1, claim 3, or claim 4. The non-woven fabric according to any one of claims 1 to 5, comprising 40 mass% or more of fibers having high-density polyethylene on the fiber surface. Characterized by using as a separator for a battery, the nonwoven fabric according to any one of claims 1-6. A battery using the nonwoven fabric according to any one of claims 1 to 7 as a separator.

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