JPH0427672B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a separator for a storage battery, and particularly to a separator for a storage battery made of glass fiber and synthetic fiber. [Background of the Invention] Various types of storage battery separators containing glass fiber have already been proposed and put into practical use, and these can be broadly classified into the following three types. In other words, there are those made mainly of short glass fibers, those made by mixing and molding short glass fibers and synthetic fibers (e.g., JP-A-49-38126), and those in which powder is held in short glass fibers (e.g., JP-A-58). −206046), is. Among these, those mainly composed of short glass fibers have a short fiber length and are hydrophilic, so if they contain a large amount of short glass fibers with a small diameter, they can be used to improve the basic characteristics of storage batteries. Although it has excellent liquid retention and liquid absorption properties, the small diameter short glass fibers are expensive, so the separator made from them is also expensive. Furthermore, a separator formed without using an organic binder has low tensile strength and low rigidity, making it difficult to assemble a storage battery. Furthermore, when molding is performed using an organic binder, when the battery is incorporated into a storage battery and used, the binder may dissolve into the electrolyte and deteriorate the performance of the storage battery. A mixture of short glass fibers and synthetic fibers has high mechanical strength (tensile strength, stiffness, etc.) and has the advantage of being easier to assemble batteries, but synthetic fibers are more hydrophilic than glass fibers. Since the electrolyte retention property is low, the electrolyte retention properties are poor. In the mixture of glass fiber and powder,
Although the liquid absorption property is good, there are problems in that the powder easily peels off and falls off from the separator, and the tensile strength is also low. [Object of the Invention] An object of the present invention is to provide a separator for storage batteries that solves the problems of the above-mentioned prior art, has high tensile strength and rigidity, has excellent electrolyte retention properties, and is inexpensive. It is in. [Structure of the invention] The present invention comprises 60 to 90% by weight of alkali-containing silicate glass fibers with an average diameter of 0.5 to 1.0 μm, and an average diameter of 10 to 1.0 μm.
8-35% by weight of 20 μm alkali-containing silicate glass fiber, 2-7% by weight of 1.0-1.5 denier acrylic fiber and/or polyester fiber, and 0.5-1.0
Denier hot water soluble polyvinyl alcohol fiber
The above object is achieved by a separator for a storage battery which is wet-mixed in a proportion of 0.04 to 0.6% by weight and then heated and dried. That is, the storage battery separator of the present invention has the following a to d
It has excellent characteristics such as. a Contains fine glass fibers with an average diameter of 0.5 to 1.0 μm, and has excellent liquid retention and absorption properties. b This thin glass fiber has an average diameter of 10 to 20μ.
Since glass fibers with a diameter of m are mixed in,
The large-diameter glass fibers serve as a skeleton, and the small-diameter glass fibers are arranged so as to be intertwined between the skeletons, thereby improving tensile strength and porosity. Further, since the price of large diameter glass fibers is significantly lower than that of small diameter glass fibers, the price of the separator is also low. The present inventors have developed a separator in which only small diameter glass fibers with an average diameter of 0.9 μm are wet-mixed, heated and dried, and a separator made of 70% by weight of glass fibers with an average diameter of 0.9 μm and 30% by weight of large diameter glass fibers with an average diameter of 19 μm. When we measured the physical properties of a separator made by wet-mixing, heating and drying the separator, it was found that the tensile strength of the mixture of small-diameter glass fiber and large-diameter glass fiber was higher than that of the thin-diameter glass fiber alone. It was observed that the porosity was high and the maximum pore diameter was small. c Contains a small amount of synthetic fiber to the extent that it does not adversely affect the liquid retention properties, and uses a synthetic fiber that has a large effect of increasing tensile strength and rigidity even in a small amount, and has high mechanical strength and liquid absorption. And there is no decrease in liquid retention. That is, as mentioned above, it has been conventionally practiced to improve the mechanical strength of the separator by mixing synthetic fibers into the separator for storage batteries, and acrylic fibers and the like with strong acid resistance are widely used as the synthetic fibers. However, synthetic fibers such as acrylic fibers have less hydrophilicity than glass fibers, and if they are mixed in a large amount, they will reduce the liquid retention properties of the separator, whereas if they are mixed in a small amount, they will not have the effect of improving mechanical strength. becomes smaller. Therefore, the inventors investigated synthetic fibers that can significantly improve the mechanical strength of separators by mixing a small amount with glass fibers, and found that a trace amount of hot water-soluble polyvinyl alcohol was added to acrylic fibers and/or polyester fibers. It has been found that a combination of fibers is suitable. d The glass fibers are alkali-containing silicate glass fibers, and the glass fibers can be bonded together without using a water-soluble organic resin binder. That is, the separator of the present invention is formed by wet papermaking, and during this papermaking, an adhesive layer, perhaps a water glass layer, is formed on the surface of the glass fiber due to the reaction between the alkali silicate in the glass fiber and the papermaking water. The glass fibers are bonded to each other by this water glass layer, and sufficient bonding strength is developed. The configuration of the present invention will be explained in more detail below. First, fibers will be explained. The fibers constituting the separator of the present invention are alkali-containing silicate glass fibers and organic fibers. The alkali-containing silicate glass fibers include two types: small diameter ones and large diameter ones. The average diameter of the small diameter glass fibers is 0.5 to 1.0 μm, more preferably
It is 0.6 to 0.9 μm. If the diameter exceeds 1.0 μm, the porosity of the separator becomes small, and conversely, if the diameter becomes smaller than 0.5 μm, the manufacturing cost increases. The content of this small diameter glass fiber is 60 to 90% by weight of the total fiber weight, preferably 65 to 85% by weight. If the content is less than 60%, the liquid absorption and liquid retention properties will be insufficient, and if the content exceeds 90%, the cost of the separator will be high. Further, the average length of this small diameter glass fiber is preferably 7 to 50 mm, more preferably 10 to 40 mm.
If the average length is shorter than 10 mm, the strength of the separator will be reduced, and if it is longer than 50 mm, it will be difficult to uniformly disperse it in water during papermaking. Such alkali-containing silicate glass fibers having an average diameter of 0.5 to 1.0 μm can be produced by the FA method (flame method), centrifugation method, or other short glass fiber manufacturing methods. In the present invention, the average diameter of the glass fibers is calculated by taking photographs of three locations on the sample using an electron microscope, measuring the diameter of each of the 20 fibers in units of 0.1 μm, and taking the average value of these. . The average diameter for large diameter glass fibers is 10 to 20μ.
8 to 35% by weight, preferably 10 to 30% of the total fiber weight. If the average diameter is smaller than 10 μm or the content is 8
If the content is less than 35%, the tensile strength improvement effect will be reduced, and if the average diameter exceeds 20 μm or the content exceeds 35%, the liquid absorption and liquid retention properties of the separator will be reduced. The length of this large diameter glass fiber is preferably 5 to 80 mm, particularly 6 to 40 mm. A suitable range of the composition of the glass fiber will be explained next. The glass fibers constituting the separator of the present invention have an alkali-containing silicate glass composition, and can form water glass on the surface thereof. Furthermore, since it is used in storage batteries, those with good acid resistance are preferably used. The degree of acid resistance is preferably such that the weight loss is 2% or less when measured according to JISC-2202 in the state of glass fibers with an average fiber diameter of 1 μm or less. In addition, the composition of such glass fibers is 60 to 75% SiO ₂ and 8 to 20% SiO 2 by weight.
R ₂ O (any alkali metal oxide such as Na ₂ O, K ₂ O)
(However, SiO ₂ + R ₂ O is 75-90
_% ), and others such as CaO, MgO, _B2O3 ,
Examples include those containing one or more of Al ₂ O ₃ , ZnO, Fe ₂ O ₃ and the like. An example of a preferable alkali-containing silicate glass is shown in Table 1 below.

[Table] In addition to such alkali-containing silicate glass fibers, the separator of the present invention contains thermoplastic acrylic fibers and/or polyester fibers as organic fibers. The mixing ratio of acrylic fibers and/or polyester fibers is 2 to 7% by weight, particularly preferably 3 to 6%, based on the weight of the separator. If the mixing ratio of these fibers exceeds 7% by weight, depending on the material of the fibers, it may have an adverse effect on the performance of the storage battery, and if it falls below 2%, the strength modification effect will be reduced. The acrylic fibers and/or polyester fibers used have a denier of 1.0 to 1.5, and preferably have a length of about 2 to 10 mm. The separator of the present invention further includes hot water-soluble polyvinyl alcohol fibers as the organic fibers. As mentioned above, acrylic fibers and polyester fibers are more hydrophobic than glass fibers, so if the amount of these fibers is increased, the liquid retention and absorption properties of the separator will decrease, but hot water-soluble polyvinyl alcohol The tensile strength and buckling strength of the separator can be greatly improved by mixing only a small amount of fiber. Therefore, only a small amount of acrylic fiber and/or polyester fiber is required, and the strength of the separator is increased, and a decrease in liquid retention and absorption properties can be prevented. The amount of polyvinyl alcohol fiber mixed is 0.04~0.6% by weight of the separator weight, especially 0.05~0.6% by weight of the separator weight.
Preferably, it is 0.2% by weight. Moreover, the length is preferably about 2 to 10 mm. The separator for storage batteries of the present invention is prepared by placing small diameter and large diameter alkali-containing silicate glass fibers, acrylic fibers and/or polyester fibers, and hot water-soluble polyvinyl alcohol fibers in water with a pH value of 2.5 to 3.5, for example. Disperse the fibers for a certain period of time, e.g. 5 to 20 minutes, using a water jet dispersion machine, etc. without cutting them as much as possible, and then perform wet papermaking to form an adhesive layer, perhaps a water glass layer, on the surface of the glass fibers. It can be obtained by bonding the glass fibers to each other by the water glass on their surfaces by heating the glass fibers to a predetermined temperature, for example, 80 to 180°C. That is, since the glass fibers constituting the separator of the present invention have an alkali-containing silicate glass composition as described above, the alkali components and silica components in the glass react with water for dispersion, resulting in a water glass layer. This water glass layer is formed on the surface of the glass fibers and acts as an adhesive to bond the glass fibers together. Note that the acrylic fibers, polyester fibers, and polyvinyl alcohol fibers mixed as part of the fibers also exert a shaping or adhesion effect in the subsequent heat treatment step (for example, the drying step), thereby increasing the strength of the separator. The thickness of the separator itself of the present invention varies depending on the storage battery used, but is preferably 0.3 to 3 mm. Note that a dispersant may be used when dispersing the fibers in water. In addition, by spraying dialkyl sulfosuccinate onto a wet-processed fiber paper product, for example, a fiber paper product on a paper-making conveyor, so that the dialkyl sulfosuccinate adheres to the glass fibers in an amount of 0.005 to 10% by weight. The hydrophilicity of succinate can improve the liquid retention of the separator. Instead of spraying the dialkyl sulfosuccinate as described above, it may be mixed into the dispersion water in the papermaking tank. Note that if paper is made by mixing powder such as silica powder or glass powder with short glass fibers, a separator with a small maximum pore diameter can be obtained. However, this separator has a high density and a low porosity. As a separator for storage batteries, it has the advantages of a small maximum pore diameter, high porosity, and excellent liquid retention and absorption properties, and the material price is low, and the separator price is also low. This is important for industrial production. By combining glass fibers with a large diameter (for example, an average diameter of 19 μm) and glass powder into a separator having the basic structure of the separator of the present invention, it is possible to obtain a separator for storage batteries that is inexpensive and has excellent performance. Become. [Embodiments of the Invention] Examples will be described below. The composition is A in Table 1, 75 parts by weight of thin glass fibers with an average diameter of 0.8 μm and an average length of 10 mm, and the composition is A in Table 1, with an average diameter of 19 μm and an average length of 25
20 parts by weight of glass fiber (manufactured by Kuraray Co., Ltd., 4.9 parts by weight of 1.2-denier thick acrylic fiber (manufactured by Kanebo Co., Ltd., trade name: Kanekalon S) cut into lengths of 3 mm), polyvinyl alcohol fiber (manufactured by Kuraray Co., Ltd., product name) given name
Pour 0.1 part by weight of VPB105) cut into 3 mm lengths into water, stir and disperse using a water jet disperser, and then add sulfuric acid to bring the pH of the water to 2.7, about 10
Hold for minutes. Next, papermaking was performed and heated to 150°C to produce a pine-shaped storage battery separator. It was observed that each glass fiber and powder constituting this separator were bonded to each other by water glass formed on the surface of the glass fiber. Table 2 shows the results of measuring the tensile strength, porosity, maximum pore diameter, and buckling strength of the separator according to this example. For comparison, the same characteristics were measured using the same fiber materials as in the examples but with different formulations as shown in Table 2. The results are also shown in Table 2.

[Table] The method for measuring these characteristic values is as follows. (1) Thickness (mm) 20Kg/d in the thickness direction of the sample
Measured under pressure with a load of ^m2 . (JISC-
2202) (2) Density (g/cm ³ ) When T is the thickness of the sample when a 20 kg load (W) is applied to the sample area (S) of 10 cm x 10 cm, the formula: W/(S x T)
It is expressed as a value given in (g/cm ³ ). (3) Fabric weight (g/cm ² ) This is the value obtained by dividing the sample weight by the sample area. (4) Tensile strength (g) Display the external force (g) when pulling both ends of a 10 mm wide sample and causing it to break. (5) Porosity (%) When the density of the separator is b and the density of the glass constituting the glass fiber is a, it is expressed as {(a-b)/a}×100(%). (6) Maximum pore diameter (μm) After fully immersing the pine-shaped sample in methanol, place it in a holder with an opening of 15 mm in diameter, and gradually blow air through the opening. Detects the differential pressure ΔP before and after the airflow passes through the sample when air bubbles are first generated from the sample,
Calculated using the following formula. Maximum pore diameter (μm) = k/ΔP (k: constant) (7) Buckling strength (g) Width 10 mm between a pair of parallel plates,
Hold a sample with a flow width of 50 mm in the width direction, gradually increase the holding pressure of the parallel plates, and calculate the load (g) when it buckles. From Table 2, it can be seen that the storage battery separators according to Examples have extremely high tensile strength and buckling strength, as well as large porosity and small maximum pores. In particular, when comparing Example and Comparative Example 3, in which the only substantial difference was the presence or absence of polyvinyl alcohol fibers, it was found that the tensile strength and buckling strength were significantly improved by mixing the polyvinyl alcohol fibers. It will be done. When similar tests were conducted on glass fibers B and C in Table 1, similar results were obtained. [Effects of the Invention] As detailed above, the storage battery separator of the present invention has high tensile strength and rigidity, and thus facilitates the assembly work of the storage battery. In addition, it has a large porosity and can retain a large amount of electrolyte, and has a small maximum pore diameter and excellent liquid absorption. Furthermore, since large-diameter glass fibers are cheaper than small-diameter ones, they are inexpensive.

Claims (1)

[Scope of Claims] First-order fibers: 60-90% by weight of alkali-containing silicate glass fibers with an average diameter of 0.5-1.0 μm, 8-35% by weight of alkali-containing silicate glass fibers with an average diameter of 10-20 μm, 1.0~1.5
2 to 7% by weight of denier acrylic fibers and/or polyester fibers and 0.04 to 0.6% by weight of 0.5 to 1.0 denier hot water-soluble polyvinyl alcohol fibers are wet-mixed and heat-dried. Separator for storage batteries.