JP2001291503A - Battery separator - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide an alkaline battery separator that is thin, can cope with high capacity, can produce batteries stably with good yield. SOLUTION: This separator is provided with a fiber sheet containing high melting point polypropylene having a melting point of 166 ° C. or more and ultrafine polypropylene fibers having a fiber diameter of 5 μm or less. [Effect] When manufacturing a battery (electrode group configuration), the separator can prevent the burr of the electrode plate from penetrating through the separator and causing a short circuit, or being cut by the electrode plate to prevent a short circuit. Batteries can be manufactured stably with good yield. In addition, since the fiber diameter contains fine polypropylene-based ultrafine fibers of 5 μm or less,
It is possible to use a thin separator, which can contribute to increasing the capacity of the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a battery separator.

[0002]

2. Description of the Related Art Conventionally, a positive electrode and a negative electrode of a battery have been conventionally separated to prevent a short circuit and to maintain an electrolytic solution so that an electromotive reaction can be carried out smoothly. Separators are used.

[0003] In recent years, as electronic devices have become smaller and lighter, the space occupied by the battery has been reduced, but the battery is required to have a performance equal to or higher than that of the conventional one. Is required. For that purpose, it is necessary to increase the amount of the active material of the electrode, so that the volume occupied by the separator is inevitably reduced. That is,
It is necessary to reduce the thickness of the separator. However, if the thickness of the conventional separator is simply reduced, the retention of the electrolytic solution is deteriorated or the fiber is apt to vary. Therefore, the split type composite fiber is used and the fiber web is formed by a wet method ( For example, JP-A-7-29561 and JP-A-8-138645 have improved the retention of the electrolyte and the dispersibility of the fibers. Although such a separator is effective in terms of electrolyte retention and fiber dispersibility, it is cut by an electrode plate at the stage of manufacturing a battery (electrode group configuration), Yield was poor because there was a case where the short circuit could occur. In addition, there are other problems such as low tensile strength and low softness, and the yield is also poor from this point.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a battery which is thin, can cope with a high capacity, has a good yield, and is stable. An object of the present invention is to provide a battery separator that can be manufactured.

[0005]

The battery separator of the present invention (hereinafter sometimes simply referred to as "separator") comprises:
It is provided with a fiber sheet containing ultrafine polypropylene fibers having a fiber diameter of 5 μm or less, including a high melting point polypropylene having a melting point of 166 ° C. or more. This melting point is 166 ° C
The above high melting point polypropylene has high crystallinity or rigidity, and has high fiber strength. Therefore, when manufacturing a battery (electrode group configuration), the burr of the electrode plate shorts through the separator, Can be prevented from being short-circuited. Therefore, good yield,
This is a separator that can stably manufacture a battery. In addition, as described above, high melting point polypropylene has high crystallinity and excellent tensile strength and rigidity. Therefore, from this viewpoint, a battery can be stably manufactured with a high yield. Furthermore, since it contains fine polypropylene-based ultrafine fibers having a fiber diameter of 5 μm or less, a thin separator can be obtained, and as a result, it is possible to contribute to increasing the capacity of the battery.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The ultrafine polypropylene fibers of the present invention contain a high melting point polypropylene having a melting point of 166 ° C. or higher. The melting point of general polypropylene is 160 ° C
Therefore, the high melting point polypropylene constituting the ultrafine polypropylene fiber of the present invention has high crystallinity. The higher the crystallinity of the high melting point polypropylene, the higher the stiffness and the higher the fiber strength. Therefore, the separator containing the polypropylene-based ultrafine fibers can be used to manufacture the battery (electrode group) in the burr of the electrode. Is difficult to penetrate,
It is hard to be cut by the electrode plate. In addition, since the high melting point polypropylene has high crystallinity and excellent tensile strength and rigidity as described above, the use of the separator of the present invention makes it possible to produce a battery with good yield and stability.

[0007] The higher the melting point of the high melting point polypropylene, the higher the rigidity, the better the fiber strength, and the above-mentioned effects, so that the melting point is more preferably 167 ° C or more. In addition, even if an olefin component such as ethylene is mixed as a copolymer component in the high-melting polypropylene, the high-melting polypropylene may have a melting point of 166 ° C. or higher. The “melting point” in the present invention refers to a temperature at which a maximum value of a melting endothermic curve obtained by using a differential scanning calorimeter at a heating rate of 10 ° C./min from room temperature is obtained. When there are two or more maximum values, the maximum value at the highest temperature is defined as the melting point.

[0008] The ultrafine polypropylene fiber of the present invention contains the high melting point polypropylene as described above. The state includes, for example, (1) a case where only the high melting point polypropylene as described above is used; In addition to the high-melting polypropylene such as the above, including a polymer having a lower melting point than the high-melting polypropylene, there may be mentioned a case where the low-melting polymer forms at least a part of the surface of the polypropylene-based ultrafine fibers. . The former ultrafine polypropylene fiber (1) has high rigidity and excellent fiber strength, and the latter ultrafine polypropylene fiber (2) has a low melting point polymer in addition to rigidity and fiber strength. Strength can also be imparted to the sheet.

[0009] In the case of the latter ultrafine polypropylene fiber (2), the high melting point polypropylene is 5 mass% in the ultrafine polypropylene fiber so that the rigidity and the fiber strength are excellent.
It is preferably contained at least, more preferably at least 10 mass%, and most preferably at least 30 mass%. On the other hand, the content is preferably 70 mass% or less so as not to impair the fusibility of the low melting point polymer. In the case of the latter (2), the low melting point polymer constituting the ultrafine polypropylene fibers is preferably at least 10 ° C. lower than the melting point of the high melting point polypropylene so that the high melting point polypropylene does not melt during fusion. It is more preferable that the temperature is lower than 20 ° C. Examples of such a low-melting polymer include high-density polyethylene,
Examples include polyethylene such as medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and copolymerized polyethylene, and copolymerized polypropylene.
Such a polymer having a low melting point constitutes at least a part of the surface of the polypropylene-based ultrafine fiber so as to be able to be fused, but constitutes at least 30% of the surface of the polypropylene-based ultrafine fiber so as to have excellent fusibility. Preferably 60
%, More preferably 100%, and most preferably 100%. Examples of the cross-sectional shape of the ultrafine polypropylene fibers containing such a low-melting polymer include, for example, sea-island type, orange type, multiple bimetal type,
A core-in-sheath type (including an eccentric type) and a side-by-side type can be mentioned. Among them, a sea-island type or a core-in-sheath type (an eccentric type) in which a polymer having a low melting point can constitute 100% of the fiber surface. Is preferable).

[0010] The ultrafine polypropylene fiber of the present invention contains the high melting point polypropylene as described above, and has a fiber diameter of 5 µm or less, so that the fiber sheet can be densified and the retention of the electrolyte can be improved. Since the thickness of the fiber sheet can be reduced without lowering it, it is possible to contribute to increasing the capacity of the battery. Furthermore, if the mass is the same, more polypropylene-based ultrafine fibers can be present, so that they can be more uniformly dispersed and a highly reliable separator. A more preferred fiber diameter is 4.5 μm or less. "Fiber diameter" in the present invention
Refers to the diameter when the cross-sectional shape of the fiber is circular, and refers to the diameter when converted to a circular cross-section when the cross-sectional shape of the fiber is non-circular.

[0011] The fiber length of the polypropylene-based ultrafine fiber of the present invention is not particularly limited, but is suitably about 0.5 to 160 mm. Also, in the ultrafine polypropylene fiber,
A functional substance such as an antioxidant, an ultraviolet absorber, a crystal nucleating agent, a moisture absorbent, a stabilizer, an antistatic agent, or a hydrophilizing agent may be mixed.

[0012] Such a polypropylene-based ultrafine fiber can be obtained, for example, by dividing a splittable fiber that can be split by an external force. As this splittable fiber,
For example, there can be mentioned an orange type fiber or a multi-bimetal type fiber made of two or more polymers including high melting point polypropylene. For such splittable fibers, for example, a fluid flow such as a water flow, a needle,
When an external force is applied by a calender or a flat press or the like, the polymer is separated into individual polymers, and ultrafine polypropylene fibers having a fiber diameter of 5 μm or less, including high melting point polypropylene, can be generated.

[0013] The polymer other than the high melting point polypropylene constituting the splittable fiber is preferably a polyolefin type so as to have excellent resistance to an electrolytic solution. Preferably, it is composed of only a polymer. In particular, a splittable fiber obtained by combining high melting point polypropylene and polyethylene (for example, high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, etc.) is preferable because it can be easily spun and produced. It is.

[0014] In such a splittable fiber, the melting point of the high melting point polypropylene constituting the ultrafine polypropylene fiber is 166.
The molecular weight distribution (weight-average molecular weight / number-average molecular weight) of the polypropylene resin to be used is set to be 6 ° C. or higher.
Or less (preferably 5 or less, more preferably 4.5 or less)
Same as the conventional composite spinning method, except that the stretching temperature is 90 ° C. or higher and the temperature is as high as possible so that the polymer does not melt. And can be spun. The weight-average molecular weight and the number-average molecular weight can be measured as polystyrene-equivalent molecular weight by GPC method (gel permeation chromatography) at 1,400 ° C using 1,2,4-trichlorobenzene as a solvent. In addition, as a polymer having excellent stretchability, for example, high-density polyethylene can be given.

[0015] The fiber sheet constituting the separator of the present invention is, in addition to the above-mentioned polypropylene-based ultrafine fibers, ultra-fine fibers having a fiber diameter of 5 µm or less (hereinafter, referred to as "high- Containing ultra-fine fibers). By including such high-melting-point polypropylene-free ultrafine fibers, the thickness of the fiber sheet can be reduced, and the retention of the electrolyte can be improved. be able to. Such high-melting-point polypropylene-free ultrafine fibers, for example, can also be generated simultaneously when the above-mentioned polypropylene-based ultrafine fibers are generated from the splittable fibers, and do not include the high-melting-point polypropylene as described above. Other than the above, it can also be generated from the same splittable fibers as the splittable fibers described above. The polymer constituting the surface of such a high-melting-point polypropylene-free ultrafine fiber is preferably a polyolefin-based polymer so as to have excellent electrolytic solution resistance. In particular, polypropylene having a melting point of less than 166 ° C, high-density polyethylene, It is preferably made of medium density polyethylene, low density polyethylene, linear low density polyethylene, polymethylpentene, or the like.

[0016] The fiber sheet constituting the separator of the present invention comprises:
Fiber diameter exceeds 5 μm, tensile strength is 4.5 cN / d
tex or more high-strength fibers. By including such high-strength fibers, when forming the electrode plate group, it is possible to more efficiently prevent the burr of the electrode plate from penetrating the separator or being cut by the electrode plate to cause a short circuit. Can be. The more preferable high-strength fiber has a tensile strength of 6.2 cN / dtex or more, and the more preferable high-strength fiber has a tensile strength of 8.0 cN / dte.
x or more, and the most preferred high-strength fiber has a tensile strength of 10.7 cN / dtex or more. This “tensile strength” refers to a value measured according to JIS L 1015 (a chemical fiber staple test method). It is preferable that the surface of the high-strength fiber is composed of a polyolefin-based polymer so that the electrolyte solution resistance is also excellent. Particularly, polypropylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene are preferable. , Ultrahigh molecular weight polyethylene, polymethylpentene and the like. The fineness of the high-strength fiber is preferably more than 5 μm and not more than 20 μm so as not to lower the retention of the electrolyte.

[0017] The fiber sheet constituting the separator of the present invention comprises:
It may further include fused fibers. By including such fused fibers, the tensile strength and the softness of the separator can be improved. The fused fiber is a fiber other than the fused fiber (e.g., Melting point (10 ° C.) lower than any of the polymers constituting the surface of polypropylene-based ultrafine fiber, high-melting-point polypropylene-free ultrafine fiber, high-strength fiber, etc.
(Preferably lower than 15 ° C.) (hereinafter referred to as “low melting point polymer component”).
Is preferably used at least on the fiber surface. It is preferable that the low-melting polymer component of the fusion fiber is also composed of a polyolefin-based polymer so that the electrolyte solution resistance is also excellent. The component is preferably composed of a polyethylene-based polymer, and for example, is preferably composed of high-density polyethylene, medium-density polyethylene, low-density polyethylene, or linear low-density polyethylene. This fused fiber may be composed of a single polymer or may be composed of two or more kinds of polymers, but the latter is preferable because the tensile strength of the separator can be further improved. It is. When the fused fibers are composed of two or more polymers, the fiber cross-sectional shape can be, for example, a core-sheath type, an eccentric type, or a side-by-side type. The fiber diameter of the fused fibers is preferably 20 μm or less so as not to deteriorate the retention of the electrolyte.

The fibers constituting the fiber sheet of the separator of the present invention include fibers other than the above-mentioned fibers (polypropylene-based ultrafine fibers, ultra-fine fibers containing no high-melting-point polypropylene, high-strength fibers, and fused fibers). Can be. For example,
It may contain a splittable fiber (non-split) which is a source of the ultrafine polypropylene-based fiber and / or the ultrafine fiber containing no high-melting-point polypropylene.

The embodiment of the separator of the present invention is not particularly limited as long as the separator is provided with the fiber sheet containing the above-mentioned polypropylene-based ultrafine fibers. It may be a fiber sheet alone, a laminate of such a fiber sheet and a porous film, or the like. Among these, it is preferable to include a nonwoven fabric which is excellent in retention of an electrolytic solution.

The separator of the present invention has an areal density of 20 to 100 g.
/ M ² , more preferably 30 to 80
g / m ² . If the areal density is less than 20 g / m ² , the tensile strength may be insufficient, and if it exceeds 100 g / m ² , the battery tends to be too thick and it is difficult to increase the capacity of the battery.

[0021] The separator of the present invention makes it difficult for the burr of the electrode plate to penetrate when forming the electrode plate group, is hard to be cut by the electrode plate, has excellent tensile strength and rigidity, and can stably produce a battery with good yield. Since it can contribute to increasing the capacity of the battery, the separator of the present invention is, for example, a primary battery such as an alkaline manganese battery, a mercury battery, a silver oxide battery, an air battery, a nickel-cadmium battery, a silver-zinc battery, and a silver battery. -It can be used for secondary batteries such as cadmium batteries, nickel-zinc batteries and nickel-hydrogen batteries.

As the separator of the present invention, a fiber sheet manufactured by a conventional method can be used as a separator, or a separator obtained by integrating a fiber sheet manufactured by a conventional method and a porous film can be used as a separator.

The nonwoven fabric suitable as a fiber sheet constituting the separator of the present invention can be produced, for example, as follows. First, a polypropylene-based ultrafine fiber as described above is prepared. If necessary, ultrafine fibers, high-strength fibers, or fused fibers containing no high-melting-point polypropylene are prepared. In the case where the ultrafine polypropylene fiber or the ultrafine fiber containing no high melting point polypropylene is generated from the above-mentioned splittable fiber, the above-mentioned splittable fiber is prepared.

[0024] Since the polypropylene-based ultrafine fiber of the present invention or the splittable fiber capable of generating the polypropylene-based ultrafine fiber contains high-melting-point polypropylene, it can also be cut without crimping at a cut portion. Play. When the fiber web is formed by a dry method, it is preferable that about 5 to 50 pieces / inch are crimped mechanically or thermally.

Next, a fiber web containing the above-mentioned ultrafine polypropylene fibers or a fiber web containing a splittable fiber capable of generating the ultrafine polypropylene fibers is formed by a dry method or a wet method. In some cases, a fiber web containing ultrafine fibers, high-strength fibers, or fused fibers containing no high-melting-point polypropylene is formed. In addition, when forming a fiber web by a wet method, a fiber having a fiber length of about 0.5 to 25 mm is used. When forming a fiber web by a dry method, a fiber having a fiber length of about 25 to 160 mm is used. Use This fiber web need not be a single layer, and two or more different types of fiber webs may be laminated. In particular, a laminated fiber web in which a fiber web formed by a wet method and a fiber web formed by a dry method are laminated is preferable because a nonwoven fabric having both uniformity and tensile strength can be obtained.

Next, the fibrous webs can be combined to form a nonwoven fabric. As the bonding method, for example, a method of entanglement by applying a fluid flow such as a water flow, a case where a polypropylene-based ultrafine fiber has a polymer having a low melting point on the fiber surface, or a fusion fiber is contained in the fiber web. In this case, a method of fusing the low melting point polymer of the ultrafine polypropylene fiber and / or the low melting point polymer component of the fusion fiber, or a method of using these in combination can be mentioned. When these combining methods are used in combination, the order and the number of times are not particularly limited.

[0027] When the polypropylene-based ultrafine fibers are generated from splittable fibers, it is necessary to split the fiber web before, during or after bonding. Examples of the dividing method include a fluid flow such as a water flow, a needle, a calender, and a flat press. Further, when the fiber web is formed by a wet method, especially when the fiber web contains a divisible fiber composed of only a polyolefin-based polymer capable of generating a polypropylene-based ultrafine fiber, it tends to be difficult to be divided by a fluid flow such as a water flow. After the splittable fibers and / or the fusion fibers are fused to reduce the degree of freedom of the splittable fibers, it is preferable to split the splittable fibers by applying a fluid flow such as a water flow. In this case, in order to impart strength to the nonwoven fabric, it is preferable to fuse the ultrafine polypropylene fibers and / or the fused fibers again.
When a fluid flow such as a water flow is applied after the fusion, the fibers are not entangled so much, and the splittable fibers are mainly split.

The entanglement condition or division condition by the fluid flow applicable in the present invention is, for example, a nozzle diameter of 0.05 to 0.1.
A pressure of 1 MPa to 3 MPa from a nozzle plate in which nozzles are arranged in one row or two or more rows at a pitch of 3 mm and a pitch of 0.2 to 3 mm.
What is necessary is just to eject the fluid flow of 0 MPa. Such a fluid stream is ejected at least once onto one or both sides of the fiber web. If the non-opening portion of the net or the perforated plate on which the fiber web is placed is large when treated with a fluid flow, the resulting nonwoven fabric also has large holes, and a short circuit is likely to occur. It is preferable to use a support having a thickness of 0.25 mm or less.

The fusion treatment in the present invention may be performed under no pressure, may be performed under pressure, or may be performed after melting under no pressure. so,
It is preferable to apply pressure simultaneously or after melting. Apparatuses that can be used for the fusion treatment include, for example, a heat calender, a hot air penetration heat treatment device, a cylinder contact heat treatment device, and the like. When heating and pressing are performed simultaneously, the heating temperature is a temperature within a range from the softening temperature to the melting point of the low melting point polymer component of the polypropylene-based ultrafine fiber and / or the low melting point polymer component of the fusion fiber. When heating is performed alone or when pressure is applied after heating, a temperature higher than the melting point by 20 ° C. or more from the softening temperature of the low melting point polymer component of the polypropylene-based ultrafine fiber and / or the low melting point polymer component of the fused fiber is preferred. It is preferable to carry out in the range up to. The pressurizing condition is linear pressure of 5 to 40 N in each case.
/ Cm is preferable. The “softening point” refers to a temperature at which a differential scanning calorimeter is used to give a starting point of a melting endothermic curve obtained by raising the temperature from room temperature at a rate of 10 ° C./min.

[0030] The fiber sheet thus produced by a conventional method is
It may be used alone as a separator, or may be used as a composite such as being integrated with a porous film.
Examples of the method of forming the composite include a method utilizing the fusibility of the fibers constituting the porous film and / or the fiber sheet, and a method of bonding using a hot melt resin as a medium.

[0031] Since the separator thus manufactured is mainly composed of a polyolefin-based polymer so as to have excellent electrolytic solution resistance, it is preferable to further perform a hydrophilizing treatment so as to have excellent electrolytic solution retention. Examples of the hydrophilic treatment include a sulfonation treatment, a fluorine gas treatment, a graft polymerization of a vinyl monomer, a surfactant treatment, a discharge treatment, and a treatment for imparting a hydrophilic resin.

As the sulfonation treatment, for example, fuming sulfuric acid,
A method of immersing the separator in a sulfuric acid, chlorosulfuric acid, or sulfuryl chloride solution, a method of bringing the separator into contact with sulfur trioxide gas, and causing a discharge in the presence of sulfur monoxide or sulfur dioxide to introduce a sulfonic acid group into the separator. There are methods.

As the fluorine gas treatment, for example, fluorine gas diluted with an inert gas (eg, nitrogen gas, argon gas, etc.) and at least one gas selected from oxygen gas, carbon dioxide gas, sulfur dioxide gas, etc. The treatment can be performed by exposing the separator to a gas obtained by mixing different types of gases. The method of bringing sulfur dioxide gas into the separator in advance and then contacting it with fluorine gas is as follows:
It is a more efficient and permanent method of hydrophilic treatment.

[0034] The graft polymerization method of the vinyl monomer includes:
For example, (1) a method in which a separator is immersed in a solution containing a vinyl monomer and a polymerization initiator and heated, (2) a method in which a vinyl monomer is applied to a separator and then radiation is applied, and (3) a separator is irradiated with radiation. And (4) impregnating the separator with a vinyl monomer solution containing a sensitizer and then irradiating the separator with ultraviolet light. Before the contact between the vinyl monomer solution and the separator, if the separator surface is treated by ultraviolet irradiation, corona discharge, plasma discharge, etc.,
Graft polymerization can be performed efficiently because of high affinity with the vinyl monomer solution. As the vinyl monomer, for example, acrylic acid, methacrylic acid, acrylic acid ester,
Methacrylic acid ester, vinylpyridine, vinylpyrrolidone, styrene, or the like can be used. In addition, when styrene is graft-polymerized, it is preferable to sulfonate in order to have an affinity with the electrolytic solution. Among these, acrylic acid can be suitably used because of its excellent affinity with the electrolytic solution.

The surfactant treatment includes, for example, an anionic surfactant (for example, an alkali metal salt, an alkyl sulfonate, or a sulfosuccinate salt of a higher fatty acid) or a nonionic surfactant (for example, polyoxy The separator can be immersed in a solution of ethylene alkyl ether or polyoxyethylene alkyl phenol ether, or the solution can be applied or sprayed to adhere the separator.

As the discharge treatment, for example, corona discharge treatment,
Examples include plasma treatment, glow discharge treatment, surface discharge treatment, and electron beam treatment. Among these discharge treatments, a separator is arranged between a pair of electrodes each carrying a dielectric under atmospheric pressure in the air so as to contact both dielectrics, and an AC voltage is applied between these two electrodes. When the method is applied and a discharge is generated inside the separator, not only the outside of the separator but also the fiber surface inside the fiber sheet constituting the separator can be treated. Therefore,
Since the electrolyte retains excellently in the inside of the separator, it is possible to manufacture a battery having excellent oxygen absorption during overcharge and excellent internal pressure characteristics.

As the hydrophilic resin application treatment, for example, a hydrophilic resin such as carboxymethyl cellulose, polyvinyl alcohol, crosslinkable polyvinyl alcohol, or polyacrylic acid can be attached. After dissolving or dispersing these hydrophilic resins in an appropriate solvent, the separator can be immersed in the solvent, or the solvent can be applied or sprayed, and then dried and adhered. In addition, it is preferable that the adhesion amount of the hydrophilic resin is 0.3 to 2 mass% of the whole separator so as not to impair the air permeability.

As the crosslinkable polyvinyl alcohol, for example, there is a polyvinyl alcohol in which a part of a hydroxyl group is substituted by a photosensitive group, and more specifically, a styrylpyridinium-based, styrylquinolinium-based,
There is polyvinyl alcohol substituted with styrylbenzothiazolium. This crosslinkable polyvinyl alcohol can be crosslinked by irradiating light after it is attached to the separator in the same manner as other hydrophilic resins. Polyvinyl alcohol in which a part of such hydroxyl groups is substituted with a photosensitive group has excellent alkali resistance, and has many hydroxyl groups capable of forming chelates with ions.
It is preferable because, during discharging and / or charging, a chelate is formed with the ions before the dendritic metal is deposited on the electrode plate, and a short circuit between the electrodes hardly occurs.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments. The melt index of polypropylene is JIS K6758.
The melt index of polyethylene is a value measured according to ASTM D1238.

(Example 1) As a first component, a melt index (MI) is 10 and a molecular weight distribution (Mw / Mn) is 3
Is a high density polyethylene having a melt index (MI) of 9 (melting point: 127).
° C), and extruded at a gear pump ratio of 1: 1 using a spinning nozzle capable of spinning an orange type splittable fiber to obtain an undrawn yarn. Next, this undrawn yarn was drawn 5.3 times at a temperature of 120 ° C. to obtain a drawn yarn having a fineness of 1.9 dtex (tensile strength: 6.0 cN / dtex). Next, the drawn yarn is cut using a shear cutter and has a fineness of 1.9 dt.
ex, a high melting point polypropylene-high density polyethylene splittable fiber having a fiber length of 5 mm was obtained. The high-melting-point polypropylene-high-density-polyethylene splittable fiber is made up of eight ultrafine polypropylene-based fibers (melting point: 167 ° C) having a fiber diameter of 4.1 µm made of only high-melting-point polypropylene and a fiber diameter of four made of only high-density polyethylene. It could be divided into eight high-density polyethylene ultrafine fibers of 0.1 μm (melting point: 131 ° C.).

On the other hand, as a fusion fiber, the core component is made of polypropylene (melting point: 165 ° C.), and the sheath component is made of low-density polyethylene (melting point: 106 ° C.).
x (fiber diameter: 18 μm), a core-sheath type fused fiber having a fiber length of 10 mm was prepared.

Then, the high melting point polypropylene-high density polyethylene splittable fiber and the core-sheath type fused fiber were mixed at a mass ratio of 1: 1 with an acrylamide-sodium acrylate copolymer (thickener) and polyoxyethylene. It was dispersed in a dispersion bath composed of water containing nonylphenyl ether (surfactant), and was made into a paper by a square hand-made paper machine to form a fiber web.

Next, the fiber web was heat-treated at a temperature of 125 ° C. to fuse only the low-density polyethylene component of the core-sheath type fused fiber. Next, the fiber web to which only the low-density polyethylene component was fused was applied with a wire diameter of 0.15.
mm on a net with a pressure of 12.7MP from a nozzle plate with a nozzle diameter of 0.13mm and a pitch of 0.6mm.
The water stream a was jetted twice alternately on both sides alternately to split the high-melting-point polypropylene-high-density polyethylene splittable fiber to generate a polypropylene-based ultrafine fiber and a high-density polyethylene fiber. Thereafter, the fiber web treated with the water stream is heated to a temperature of 1 ° C.
Heat treatment was performed at 25 ° C., and only the low-density polyethylene component, which is the sheath component of the fused fibers, was fused again to form a nonwoven fabric. Further, the nonwoven fabric was calendered at a linear pressure of 9.8 N / cm, and then immersed in fuming sulfuric acid at a temperature of 60 ° C. and a concentration of 15% for 2 minutes to perform a sulfonation treatment to obtain a surface density of 58 g / cm 2.
A separator having a thickness of m ² and a thickness of 0.16 mm was formed.

Example 2 A separator having an areal density of 56 g / m ² and a thickness of 0.15 mm was obtained in exactly the same manner as in Example 1 except that the fiber length of the high-melting-point polypropylene-high-density polyethylene splitting fiber was 10 mm. Was formed.

(Comparative Example 1) As splittable fibers, eight ultrafine polypropylene fibers (melting point: 163 ° C) having a fiber diameter of 4.4 µm consisting of only polypropylene and a fiber diameter consisting of only high-density polyethylene were used. 2.2 d fineness having an orange cross section, divisible into eight 4 μm high-density polyethylene ultrafine fibers (melting point: 133 ° C.)
tex, a fiber density of 54 g / m ² and a thickness of 0.1 in the same manner as in Example 1 except that a fiber having a fiber length of 5 mm was used.
A 5 mm separator was formed.

(Comparative Example 2) The same splittable fiber as Comparative Example 1, a tensile strength of 8 cN / dtex and a fineness of 2.2 dte
x (fiber diameter: 18 µm), polypropylene high-strength fiber with a fiber length of 10 mm (melting point: 170 ° C) and a core component made of polypropylene (melting point: 165 ° C), and a sheath component made of low-density polyethylene (melting point: 106 ° C) Fineness 2.2
A core-sheath type fused fiber having a dtex (fiber diameter: 18 μm) and a fiber length of 10 mm was prepared. Then, exactly the same as in Example 1, except that the splittable fiber, the polypropylene high-strength fiber, and the core-sheath type fused fiber were mixed at a ratio of 40 mass%, 35 mass%, and 25 mass%, respectively.
A separator having an area density of 55 g / m ² and a thickness of 0.15 mm was formed.

(Tensile strength in vertical direction) The tensile strength in the vertical direction of the separator was fixed between chucks of a tensile strength tester (Tensilon UTM-III-100 manufactured by Orientec) (between chucks). The distance was measured at 100 mm) and the tensile speed was 300 mm / min. The measurement was performed at a separator width of 50 mm. The results were as shown in Table 1.

(Penetration resistance index) Examples 1-2 and Comparative Examples 1-2
, Each having a total thickness of about 2 mm,
A stainless steel jig (thickness: 0.5 mm, tip angle: 60 °) attached to a handy compression tester (KES-G5, manufactured by Kato Tech) was placed on the top separator, using a 0. The piercing was performed vertically at a speed of 01 cm / s, and the force required to pierce the top separator was measured. At this time, when the force required to pierce the separator of Comparative Example 1 was set as a reference (100), the percentage of the force required to pierce each separator was defined as the penetration resistance index (%) of the separator. The results were as shown in Table 1.

(Pressure Retention Ratio) After the separators of Examples 1 and 2 and Comparative Examples 1 and 2 cut to a diameter of 30 mm were brought into water equilibrium at a temperature of 20 ° C. and a relative humidity of 65%, respectively. , And mass (M ₀ ) were measured. Next, a specific gravity of 1.3 was set so that the air in the separator was replaced with a potassium hydroxide solution.
(20 ° C.) for 1 hour in a potassium hydroxide solution to hold the potassium hydroxide solution. Next, the separator was sandwiched between filter papers (diameter: 30 mm) of three upper and lower sheets, a pressure of 5.7 MPa was applied by a pressure pump for 30 seconds, and then the mass (M ₁ ) of the separator was measured. Then, the pressurized liquid holding ratio was determined by the following equation. In addition, this measurement is 1
The measurement was performed four times for each of the separators, and the average was defined as the pressurized liquid holding ratio. The results were as shown in Table 1. It is known that there is no practical problem if the pressurized liquid holding ratio is 5% or more. Pressure retention rate (%) = [(M ₁ −M ₀ ) / M ₀ ] × 100

[0050]

【table 1】

As is clear from Table 1, since the separator of the present invention has a high penetration resistance, the burr of the electrode plate does not penetrate the separator and short-circuits, or the electrode plate is cut by the electrode plate to cause short-circuit. It was found that the battery could be manufactured stably. In addition, it was also found that since the electrolyte solution was excellent in retaining property, the thickness could be reduced to cope with an increase in battery capacity.

[0052]

The battery separator of the present invention prevents the burr of an electrode plate from shorting through a separator or being cut by an electrode plate to cause a short circuit when a battery (electrode group configuration) is manufactured. Therefore, the separator can be manufactured stably with a high yield. Further, since the battery separator of the present invention contains fine polypropylene-based ultrafine fibers having a fiber diameter of 5 μm or less, the separator can be made thinner, which can contribute to increasing the capacity of the battery. is there.

Claims (3)

[Claims] 1. A battery separator comprising a fiber sheet containing polypropylene-based ultrafine fibers having a fiber diameter of 5 μm or less, including high melting point polypropylene having a melting point of 166 ° C. or more. 2. The battery separator according to claim 1, wherein the polypropylene-based ultrafine fibers are made of only the high-melting-point polypropylene. 3. The ultrafine polypropylene fiber contains the high-melting polypropylene and a polymer having a lower melting point than the high-melting polypropylene, and the low-melting polymer forms at least a part of the surface of the ultrafine polypropylene fiber. The battery separator according to claim 1, wherein: