JP7248425B2 - Separator for flooded lead-acid battery - Google Patents

Description

The present invention is not a so-called sealed lead-acid battery (also referred to as a valve-controlled lead-acid battery) in which the electrolyte is made non-fluid to make it maintenance-free, but a so-called liquid battery with a fluid electrolyte, which is the conventional method. The present invention relates to a liquid lead-acid battery separator used in a lead-acid battery (also referred to as a vented lead-acid battery or an open lead-acid battery).

Conventionally, as a separator for a liquid lead-acid battery, a polyolefin resin (usually ultra-high molecular weight polyethylene) with a weight average molecular weight of 500,000 or more, which is called a polyethylene separator, is usually used in an amount of 20 to 60% by weight and a specific surface area of 50 m ² /g or more. 40 to 80% by weight of inorganic powder (usually silica fine powder), 0 to 30% by weight of a plasticizer (usually mineral oil) that also serves as a pore opening agent, and 0 to 10% by weight of a surfactant (solid content). There is a microporous film separator containing 0 to 5% by weight of an agent (antioxidant, weathering agent, etc.).

The microporous film separator is usually a raw material composition obtained by mixing the polyolefin resin, the inorganic powder, the plasticizer (mixed in a larger amount than the separator composition), the surfactant, and the additive. A base thickness of about 0.1 to 0.3 mm is obtained by extruding into a sheet while heat-melting and kneading, roll-molding to a predetermined thickness, and then extracting and removing all or part of the plasticizer. The sheet has an average pore size (by mercury porosimetry) of about 0.01 to 0.5 μm and a porosity (by mercury porosimetry) of about 50 to 90% by volume.

The role of the inorganic powder is to adsorb and support the plasticizer when the raw material composition is heated, melted and kneaded, and to create a microporous structure (dense and complex pore structure and high porosity) of the microporous film. To withstand the sheet shrinkage that occurs when the plasticizer is removed during the manufacturing process of the microporous film, and to maintain dimensional stability. To withstand sheet shrinkage and maintain dimensional stability even during heat treatment such as and improving the film's ability to retain electrolyte.

Therefore, silica fine powder is usually used as the inorganic powder, and in particular, from the viewpoints of large specific surface area, large oil absorption, and many hydrophilic groups (silanol groups), dry method or wet method is used. Among the production methods of the method, synthetic amorphous silica produced by a wet precipitation method is used.

On the other hand, in on-vehicle applications of lead-acid batteries, lead-acid batteries mounted in idling stop vehicles are required to have high charge acceptance because the amount of discharge increases. It is known that the presence of a large amount of alkali metal (Li, Na, K, Rb, Cs) ions in the electrolyte interferes with the improvement of the charge acceptance of a lead-acid battery. (Patent Document 1).

In addition, in lead-acid batteries, if a large amount of halogen (F, Cl, Br, I) impurities are mixed in, lead or lead alloy electrode plate grids and electrode poles will corrode, which can be a factor in reducing battery life performance. It is also known (Patent Document 2).

Synthetic amorphous silica produced by the precipitation method is a method of reacting an alkali silicate (sodium silicate) aqueous solution and a mineral acid (sulfuric acid) under neutral or alkaline conditions to precipitate amorphous silica. The amorphous silica produced contains salts such as sodium sulfate as a by-product, and is filtered and washed with water in the post-process to remove salts (treatment to increase purity). It is

WO2014/128803 JP 2005-251394 A

However, since the salt removal treatment in the manufacturing process of the amorphous silica is not perfect, the manufactured amorphous silica usually contains a small amount of by-product sodium sulfate. Therefore, the microporous film produced using such fine silica powder also contains a small amount of sodium sulfate, and when used as a separator for a lead-acid battery, the electrolytic solution If Na ions are eluted inside and the amount of elution is large, it may be a factor that hinders the improvement of charge acceptance.

In addition, when the salt removal treatment in the manufacturing process of the amorphous silica is performed by washing with water, the water used for washing may be mixed with Cl, which is a halogen. That is, when using tap water (which contains residual chlorine), or when using groundwater containing salt (sodium chloride). Therefore, the microporous film produced using silica fine powder that has been washed with water also contains a small amount of Cl, and when used as a lead-acid battery separator, As the use of the battery progresses, Cl ions are eluted into the electrolyte, and if the amount of elution is large, corrosion of the electrode plate lattice and electrode pillars may be accelerated, resulting in a decrease in battery life performance.

Therefore, in view of the above conventional problems, the present invention provides a separator for a liquid lead-acid battery comprising a microporous film produced using silica fine powder, which is synthetic amorphous silica produced by a precipitation method, as a main raw material. Therefore, even if batteries using this material are used more frequently, the amount of alkali metal ions and halogen ions eluted from the separator into the electrolyte can be reduced, making it difficult to prevent the improvement of charge acceptance. An object of the present invention is to provide a separator that is less likely to cause deterioration in battery life performance.

In order to achieve the above object, the separator for a liquid lead-acid battery of the present invention, as described in claim 1, reacts an alkaline silicate aqueous solution with a mineral acid to precipitate and precipitate amorphous silica, which is then filtered and washed with water. A separator for a liquid lead-acid battery comprising a microporous film containing 40% by weight or more of silica fine powder, which is synthetic amorphous silica manufactured by a precipitation method in which the purity is adjusted by the above microporous film (10 cm × 10 cm × 2 sheets) was immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50 ° C. for 24 hours and left to stand. is 5 mg/100 cm ² /sheet or less (however, the base thickness of the microporous membrane is equivalent to 0.2 mm), and the halogen content (F, Cl, Br, I) concentration (ICP emission spectroscopic analysis) is 0.00. It is characterized by being 4 mg/100 cm ² /sheet or less (however, the base thickness of the microporous membrane is converted to 0.2 mm).

Further, the liquid lead-acid battery separator according to claim 2 is the liquid lead-acid battery separator according to claim 1, wherein the filtering and washing with water does not contain ion-exchanged water or salt (sodium chloride). It is characterized by being carried out using groundwater.

The separator for a liquid lead-acid battery according to claim 3 is the separator for a liquid lead-acid battery according to claim 1 or 2, wherein the microporous film is mainly composed of the fine silica powder and polyolefin resin. It is characterized by being a microporous film.

The separator for a liquid lead-acid battery according to claim 4 is the separator for a liquid lead-acid battery according to claim 3, wherein the microporous film has a base thickness of 0.1 to 0.3 mm, an average It is characterized by being a microporous film having a pore diameter (mercury porosimetry) of 0.01 to 0.5 μm and a porosity (mercury porosimetry) of 50 to 90% by volume.

According to the present invention, there is provided a lead-acid battery separator comprising a microporous film produced using silica fine powder, which is synthetic amorphous silica produced by a precipitation method, as a main raw material, and a battery using this separator. Even when use progresses, the amount of alkali metal ions and halogen ions eluted from the separator into the electrolyte can be reduced, making it less likely to hinder improvement in charge acceptance and reduce battery life performance. A separator can be provided.

The separator for a liquid lead-acid battery of the present invention is prepared by reacting an alkaline silicate aqueous solution and a mineral acid to form amorphous silica by precipitation, and then adjusting the purity by filtration and washing (removing salts as by-products to obtain an amorphous silica). A microporous membrane containing 40% by weight or more of silica fine powder (hereinafter sometimes simply referred to as "silica fine powder") that is synthetic amorphous silica produced by a sedimentation method that increases the purity of silica) There, the alkali metal content (Li, Na, K, Rb, Cs) concentration (ICP emission spectroscopic analysis) is 5 mg/100 cm ² /sheet or less (however, the base thickness of the microporous membrane is converted to 0.2 mm), and the halogen content (F, Cl, Br, I) The condition is that the concentration (ICP emission spectroscopic analysis) is 0.4 mg/100 cm ² /sheet or less (however, the base thickness of the microporous membrane is converted to 0.2 mm).

The alkali metal content (Li, Na, K, Rb, Cs) when the microporous membrane (10 cm × 10 cm × 2 sheets) was immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50 ° C. for 24 hours and left to stand. By setting the concentration (ICP emission spectroscopic analysis) to 5 mg/100 cm ² /sheet or less, in a flooded lead-acid battery using the separator for a flooded lead-acid battery of the present invention, alkalinity eluted from the separator into the electrolyte solution Since the amount of metal ions can be suppressed, the improvement of charge acceptance is less likely to be hindered. Therefore, when the microporous membrane (10 cm × 10 cm × 2 sheets) was immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50 ° C. for 24 hours and left to stand, the alkali metal concentration (ICP emission spectroscopic analysis) was 4 mg. /100 cm ² /sheet or less is more preferable.

Concentration of halogen content (F, Cl, Br, I) (ICP emission spectroscopic analysis) is 0.4 mg/100 cm ² /sheet or less, in a flooded lead-acid battery using the separator for a flooded lead-acid battery of the present invention, halogen ions eluted from the separator into the electrolyte Since the amount can be suppressed, deterioration of battery life performance due to accelerated corrosion of the electrode plate lattice and electrode columns is less likely to occur. Therefore, when the microporous membrane (10 cm x 10 cm x 2 sheets) was immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50°C for 24 hours and allowed to stand, the concentration of halogen (ICP emission spectroscopic analysis) was 0.00. 2 mg/100 cm ² /sheet or less is more preferable, and 0.1 mg/100 cm ² /sheet or less is even more preferable.

The microporous film is preferably a microporous film mainly composed of the fine silica powder and polyolefin resin, and the microporous film has a base thickness of 0.1 to 0.3 mm and an average It is preferably a microporous film having a pore diameter (mercury porosimetry) of 0.01 to 0.5 μm and a porosity (mercury porosimetry) of 50 to 90% by volume. Note that the base thickness is a term used, for example, when the microporous film has rib-like projections, to distinguish it from the total thickness including the rib-like projections, excluding the height of the rib-like projections (rib It refers to the film thickness when no protrusions are provided).

As described above, the silica fine powder should adsorb and support a plasticizer when heat-melting and kneading the raw material composition, and the microporous structure of the microporous film (dense and complicated pore structure and high porosity) resistance to sheet shrinkage that occurs when the plasticizer is removed during the manufacturing process of the microporous film and maintains dimensional stability; To withstand sheet shrinkage and maintain dimensional stability even during heat treatment such as step), to improve the electrolyte solution absorption of the microporous film, to improve the electrolyte solution wettability of the microporous film, It has a role of improving the electrolyte retention of the porous film, etc. Therefore, from the viewpoint of a large specific surface area, a large oil absorption, a large number of hydrophilic groups (silanol groups), etc., the dry method Alternatively, of the wet method production methods, it is necessary that the synthetic amorphous silica is produced by the wet precipitation method, but the synthetic amorphous silica produced by the wet precipitation method has Salts such as sodium sulfate are included in organisms, and although the salts are removed by filtration and washing in the post-process, the removal of salts is not complete, and tap water is used for washing. Since groundwater containing residual chlorine (residual chlorine) and salt (sodium chloride) can be used, it contains minute amounts of Na and Cl that can adversely affect battery performance. Therefore, in the present invention, the silica fine powder is a synthetic amorphous silica produced by a wet precipitation method, which contains alkali metal content (Li, Na, K, Rb, Cs) and halogen content (F, Cl, The content of Br, I) was measured by immersing the finally obtained microporous membrane (10 cm × 10 cm × 2 sheets) in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50 ° C. for 24 hours and leaving it to stand. Silica reduced to a level such that the concentration (ICP emission spectroscopic analysis) is 5 mg/100 cm ² /sheet or less and the halogen concentration (ICP emission spectroscopic analysis) is 0.4 mg/100 cm ² /sheet or less Use fine powder. In addition, the water washing treatment (treatment for removing by-product salts) in the manufacturing process of the amorphous silica of the present invention is performed using ion-exchanged water or groundwater that does not contain salt (sodium chloride). is preferred. In the present application, groundwater not containing salt (sodium chloride) refers to groundwater having a salt (sodium chloride) concentration of 300 ppm or less.

The base thickness of the microporous film is preferably 0.1 to 0.3 mm, but if it exceeds 0.3 mm, the electrical resistance deteriorates, and if it is less than 0.1 mm, good short circuit resistance (The term “short circuit” here means permeation short circuit called dendrite short, local weak base material, high pressure, impact or piercing from the convex part of the electrode plate, oxidation loss due to oxidative power from the electrode plate, etc. This refers to both normal short circuits caused by pitting or cracking due to short circuits) become difficult to maintain.

The porosity (mercury intrusion method) of the microporous film is preferably 50% by volume or more. This contributes to improving the performance of liquid lead-acid batteries. Therefore, the porosity of the microporous film (by mercury intrusion method) is preferably 60 to 90% by volume, more preferably 70 to 90% by volume.

The method for obtaining the microporous film is preferably by melt-kneading a raw material composition mainly composed of a polyolefin resin, the silica fine powder, and a plasticizer, and removing part or all of the plasticizer after film formation. . As a result, a membrane is obtained in which a large number of uniform, fine, and intricately intricate channels are formed throughout the membrane. An example of a specific manufacturing method is shown below. First, a raw material obtained by adding various additives (surfactants, antioxidants, weathering agents, etc.) to a predetermined amount of polyolefin resin, the silica fine powder, and a plasticizer as needed is mixed with a Henschel mixer or Loedige mixer, etc. to obtain a raw material mixture. Next, this mixture is put into a twin-screw extruder equipped with a T-die at the tip, extruded into a sheet while being heated, melted and kneaded, and passed between a pair of forming rolls, one of which is provided with a predetermined groove. Then, a film-like material is obtained in which ribs of a predetermined shape are integrally formed on one side of the flat sheet. Next, this film-like product is immersed in a suitable solvent (eg, n-hexane) to extract and remove a predetermined amount of mineral oil, followed by drying to obtain the desired microporous film. In addition, the raw material composition refers to a composition composed of all raw materials brought into the melt-kneading step, and only means "all raw materials (composition of)". Specifically, raw material mixture or a melt-kneaded product.

In the microporous film, the total content of the polyolefin resin, the silica fine powder and the plasticizer is 90% by weight or more, the polyolefin resin content is 20 to 60% by weight, and the silica fine powder content is 40 to 80%. It is preferable that the content of the plasticizer is 0 to 30% by weight and the content of the surfactant is 0 to 8% by weight. If the polyolefin resin content is less than 20% by weight or the silica fine powder content is more than 80% by weight, the polyolefin resin cannot ensure the mechanical strength, oxidation resistance, and sealability of the microporous film. If the polyolefin resin content exceeds 60% by weight or the silica fine powder content is less than 40% by weight, it is difficult to ensure a large porosity and a fine and complicated pore structure of the microporous film. As a result, good electrical resistance characteristics of the microporous film separator cannot be maintained.

As the polyolefin resin, homopolymers or copolymers such as polyethylene, polypropylene, polybutene, polymethylpentene, and mixtures thereof can be used. Among them, it is preferable to use polyethylene as a main component in terms of moldability and economy. Polyethylene has a melt-molding temperature lower than that of polypropylene, and has good productivity and low production costs. By setting the weight average molecular weight of the polyolefin resin to 500,000 or more, the mechanical strength of the film can be ensured even in a microporous film containing a large amount of fine silica powder. For this reason, the polyolefin resin preferably has a weight average molecular weight of 1,000,000 or more, more preferably 1,500,000 or more. Polyolefin-based resins have good mixability with fine silica powder, and maintain strength while binding the skeleton of fine silica powder in the microporous film as an adhesive functional material, and are chemically stable and highly safe. .

As the silica fine powder, one having a fine particle size and having a pore structure inside or on the surface can be used. Among inorganic powders, silica has a wide selection range for various powder characteristics such as particle diameter and specific surface area, is relatively inexpensive and readily available, and contains few impurities. When the silica fine powder has a specific surface area of 100 m ² /g or more, the pore structure of the microporous film is made finer (densified) and more complicated to improve the short circuit resistance, and the electrolyte solution retention of the microporous film. It is preferable because it enhances the hydrophilicity of the microporous film by increasing the strength and providing a large number of hydrophilic groups (--OH) on the powder surface. Therefore, it is more preferable that the specific surface area of the silica fine powder is 150 m ² /g or more. Further, the specific surface area of the fine silica powder is preferably 400 m ² /g or less. When the specific surface area of the silica fine powder exceeds 400 m ² /g, the surface activity of the particles is high and the cohesive force is strong, which makes it difficult to uniformly disperse the silica fine powder in the microporous film, which is not preferable.

As the plasticizer, it is preferable to select a material that can be used as a plasticizer for polyolefin resins. Various organic liquids that are compatible with polyolefin resins and can be easily extracted with various solvents can be used. Mineral oils such as industrial lubricating oils composed of saturated hydrocarbons (paraffin), higher alcohols such as stearyl alcohol, and ester plasticizers such as dioctyl phthalate can be used. Among them, mineral oil is preferable because it is easy to reuse. The plasticizer is preferably blended in an amount of 30 to 70% by weight in the raw material composition mainly composed of polyolefin resin, fine silica powder and plasticizer.

As described above, the plasticizer is melt-kneaded with a raw material composition mainly composed of a polyolefin resin, silica fine powder, and a plasticizer to form a film-like material having a predetermined shape, and then removed to form a porous film. The content of the plasticizer in the microporous film separator may be zero. However, in a separator for a liquid lead-acid battery, by containing an appropriate amount of a plasticizer such as mineral oil, it is possible to contribute to improvement in oxidation resistance. In such a case, the content of the plasticizer in the separator is preferably 5 to 30% by weight. However, if the content of the plasticizer is increased, the porosity of the microporous film decreases and the electrical resistance of the microporous film separator deteriorates. % by weight or less is more preferable.

As a solvent used for extracting and removing the plasticizer, a saturated hydrocarbon-based organic solvent such as hexane, heptane, octane, nonane, and decane can be used.

In addition, if necessary, the raw material composition or the microporous film may contain a surfactant (hydrophilic agent), an antioxidant, an ultraviolet absorber, a weathering agent, a lubricant, an antibacterial agent, an antifungal agent, and a pigment. , dyes, coloring agents, anti-fogging agents, matting agents, etc., may be added (compounded) or contained within a range that does not impair the object and effect of the present invention.

The microporous film contains a large amount of the silica fine powder having a large specific surface area and high hydrophilicity. Sulfuric acid electrolyte has permeability (penetrability), but when sulfuric acid electrolyte is poured into a laminate in which electrode plates and separators are densely assembled in a battery case, it quickly penetrates into the gaps of the separator. 0.2 to 8% by weight of a surfactant (solid content) may be contained in the microporous film in order to absorb the electrolytic solution and quickly replace the voids in the separator with the electrolytic solution. preferable.

As a method for incorporating the surfactant into the microporous film, there is a method in which the surfactant is added in advance in a dispersed state to the raw material composition before film formation (internal addition method), There is a method (external addition method) of post-processing (adhesion treatment) to the porous film, but it is possible to simplify the manufacturing process and to prevent the surfactant from oozing out from the microporous film of the present invention. A method of preliminarily adding to the raw material composition (internal addition method) is preferred. The content (required amount) of the surfactant (solid content) is 0.2 to 8% by weight in the microporous film. Even if the content of the surfactant (solid content) is increased beyond this range, the effect of improving the hydrophilicity of the microporous film does not increase significantly, and conversely, the porosity of the microporous film decreases. As a separator for a liquid lead-acid battery, it causes an increase in internal resistance (electrical resistance), and as a separator for a liquid lead-acid battery, it causes an increase in self-discharge. Therefore, the content of the surfactant (solid content) is more preferably 0.2 to 5% by weight in the microporous film.

Any of nonionic surfactants, cationic surfactants, and anionic surfactants can be used as the surfactant as long as it can improve the hydrophilicity of the microporous film. As nonionic surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl allyl ethers, fatty acid monoglycerides, sorbitan fatty acid esters and the like can be used. As cationic surfactants, aliphatic amine salts, quaternary ammonium salts, polyoxyethylene alkylamines, alkylamine oxides and the like can be used. As the anionic surfactant, alkylsulfonate, alkylbenzenesulfonate, alkylnaphthalenesulfonate, alkylsulfosuccinate, dodecylbenzenesulfonate and the like can be used. Among them, it is possible to impart high hydrophilicity to polyolefin resins by adding a small amount, and has relatively high heat resistance, so that surfactants can be added in advance to the raw material composition to form a microporous film. Alkylbenzenesulfonates, alkylsulfosuccinates, and dodecylbenzenesulfonates are preferred because they can be manufactured (manufacture by heat-melting molding).

Next, examples of the present invention will be described in detail together with comparative examples.
(Example 1)
1,000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point: about 135°C) with a weight average molecular weight of 1,500,000 as a polyolefin resin, and synthetic amorphous silica produced by a sedimentation method, which has a specific surface area of 200 m ² by the BET method. / g of silica fine powder (However, the content of salts such as sodium sulfate generated as a by-product in the manufacturing process is reduced by increasing the flow rate of the washing water than before, and the Cl content is higher than before. By using a small amount of water for washing, the contamination of Cl is reduced, and the finally obtained microporous membrane (10 cm x 10 cm x 2 sheets) is immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50 ° C for 24 hours. Alkaline metal content (Li, Na, K, Rb, Cs) concentration (ICP emission spectroscopic analysis) is 5 mg/100 cm ² /sheet or less, and halogen content (F, Cl, Br, I) when left to stand. concentration (ICP emission spectroscopic analysis) of 0.4 mg/100 cm ² /sheet or less) 2590 parts by weight, 5380 parts by weight of paraffinic mineral oil as a plasticizer, and alkyl sulfosuccinate as a surfactant (Solid content) 109 parts by weight are mixed in a Lödige mixer, and this raw material composition is extruded into a sheet while being heated and melted and kneaded using a twin-screw extruder equipped with a T-die at the tip, and transferred to one roll. A film obtained by passing between a pair of forming rolls having predetermined grooves for electrode plate contact main ribs and integrally forming the electrode plate contact main ribs of a predetermined shape on one surface of a flat sheet. I got something. Next, this film-like material is immersed in n-hexane to extract and remove a predetermined amount of paraffinic mineral oil, and dried to obtain 22.9% by weight of polyethylene resin, 59.3% by weight of silica fine powder, and paraffin. Base mineral oil 16.0% by weight, surfactant (solid content) 1.8% by weight, base thickness 0.20 mm, porosity by mercury intrusion method 62% by volume, by mercury intrusion method A ribbed microporous film having an average pore size of 0.09 μm and a maximum pore size of 0.65 μm by mercury porosimetry was obtained. This was used as a separator for a liquid lead-acid battery of Example 1.

(Example 2)
1,000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point: about 135°C) with a weight average molecular weight of 1,500,000 as a polyolefin resin, and synthetic amorphous silica produced by a sedimentation method, which has a specific surface area of 200 m ² by the BET method. / g of silica fine powder (however, the content of salts such as sodium sulfate generated as a by-product in the manufacturing process is further reduced by increasing the flow rate of the water for washing treatment than in Example 1, and By using washed water with a low Cl content, the contamination of Cl content is reduced, and the finally obtained microporous membrane (10 cm × 10 cm × 2 sheets) is placed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50 ° C. The concentration of alkali metals (Li, Na, K, Rb, Cs) (ICP emission spectroscopic analysis) is 4 mg/100 cm ² or less when immersed in water for 24 hours and left to stand, and the halogen content (F, Cl, Br , I) so that the concentration (ICP emission spectroscopic analysis) is 0.4 mg/100 cm ² /sheet or less) 2590 parts by weight, 5380 parts by weight of paraffinic mineral oil as a plasticizer, and alkyl as a surfactant 109 parts by weight of a sulfosuccinate (solid content) was mixed in a Loedige mixer, and this raw material composition was extruded into a sheet while being heated and melted and kneaded using a twin-screw extruder equipped with a T-die at the tip. The rolls are passed between a pair of forming rolls in which predetermined grooves for the electrode plate contacting main ribs are engraved, and the electrode plate contacting main ribs of a predetermined shape are integrally formed on one surface of the flat sheet. A processed film was obtained. Next, this film-like material is immersed in n-hexane to extract and remove a predetermined amount of paraffinic mineral oil, and dried to obtain 22.9% by weight of polyethylene resin, 59.3% by weight of silica fine powder, and paraffin. Base mineral oil 16.0% by weight, surfactant (solid content) 1.8% by weight, base thickness 0.20 mm, porosity by mercury intrusion method 62% by volume, by mercury intrusion method A ribbed microporous film having an average pore size of 0.09 μm and a maximum pore size of 0.65 μm by mercury porosimetry was obtained. This was used as a separator for a liquid lead-acid battery of Example 2.

(Example 3)
1,000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point: about 135°C) with a weight average molecular weight of 1,500,000 as a polyolefin resin, and synthetic amorphous silica produced by a sedimentation method, which has a specific surface area of 200 m ² by the BET method. / g of silica fine powder (However, the content of salts such as sodium sulfate generated as a by-product in the manufacturing process is reduced by increasing the flow rate of the water for washing treatment than before, and Cl By using washed water with a small content, the contamination of Cl content is further reduced, and the finally obtained microporous membrane (10 cm × 10 cm × 2 sheets) is placed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50 ° Alkali metal content (Li, Na, K, Rb, Cs) concentration (ICP emission spectroscopic analysis) is 5 mg/100 cm ² /sheet or less, and halogen content (F, Cl, Br , I) having a concentration (ICP emission spectroscopic analysis) of 0.1 mg/100 cm ² /sheet or less) 2590 parts by weight, 5380 parts by weight of paraffinic mineral oil as a plasticizer, and an alkyl as a surfactant 109 parts by weight of a sulfosuccinate (solid content) was mixed in a Loedige mixer, and this raw material composition was extruded into a sheet while being heated and melted and kneaded using a twin-screw extruder equipped with a T-die at the tip. The rolls are passed between a pair of forming rolls in which predetermined grooves for the electrode plate contacting main ribs are engraved, and the electrode plate contacting main ribs of a predetermined shape are integrally formed on one surface of the flat sheet. A processed film was obtained. Next, this film-like material is immersed in n-hexane to extract and remove a predetermined amount of paraffinic mineral oil, and dried to obtain 22.9% by weight of polyethylene resin, 59.3% by weight of silica fine powder, and paraffin. Base mineral oil 16.0% by weight, surfactant (solid content) 1.8% by weight, base thickness 0.20 mm, porosity by mercury intrusion method 62% by volume, by mercury intrusion method A ribbed microporous film having an average pore size of 0.09 μm and a maximum pore size of 0.65 μm by mercury porosimetry was obtained. This was used as a separator for a liquid lead-acid battery of Example 3.

(Comparative example 1)
1,000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point: about 135°C) with a weight average molecular weight of 1,500,000 as a polyolefin resin, and synthetic amorphous silica produced by a sedimentation method, which has a specific surface area of 200 m ² by the BET method. / g of silica fine powder (However, the content of salts such as sodium sulfate generated as a by-product in the manufacturing process is the same as before, and when using washing water with the same Cl content as before, the contamination of Cl is reduced. The concentration of alkali metals (ICP emission spectroscopic analysis) exceeds 5 mg/100 cm ² /sheet, and the halogen concentration (ICP emission spectroscopic analysis) exceeds 0.4 mg/100 cm ² /sheet) 2590 parts by weight, and a paraffinic mineral as a plasticizer 5380 parts by weight of oil and 109 parts by weight of alkyl sulfosuccinate (solid content) as a surfactant are mixed in a Lödige mixer, and this raw material composition is extruded using a twin-screw extruder equipped with a T-die at the tip. The sheet is extruded while being heated, melted and kneaded, passed between a pair of forming rolls, one of which is provided with a predetermined groove for the electrode plate contacting main rib, and a predetermined shape is formed on one surface of the flat sheet. A film-like material was obtained in which the main ribs for contacting the electrode plate were integrally formed. Next, this film-like material is immersed in n-hexane to extract and remove a predetermined amount of paraffinic mineral oil, and dried to obtain 22.9% by weight of polyethylene resin, 59.3% by weight of silica fine powder, and paraffin. Base mineral oil 16.0% by weight, surfactant (solid content) 1.8% by weight, base thickness 0.20 mm, porosity by mercury intrusion method 62% by volume, by mercury intrusion method A ribbed microporous film having an average pore size of 0.09 μm and a maximum pore size of 0.65 μm by mercury porosimetry was obtained. This was used as a liquid lead-acid battery separator of Comparative Example 1.

(Comparative example 2)
As the silica fine powder, silica fine powder having a specific surface area of 200 m ² /g by the BET method, which is synthetic amorphous silica produced by a sedimentation method (however, it contains salts such as sodium sulfate produced as a by-product in the production process The amount is the same as before, but by using washing water with less Cl content than before, the contamination of Cl content is reduced, and the finally obtained microporous membrane (10 cm × 10 cm × 2 sheets) is heated. When immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at 50° C. for 24 hours and allowed to stand, the alkali metal concentration (ICP emission spectroscopic analysis) exceeds 5 mg/100 cm ² /sheet and the halogen concentration (ICP emission spectroscopic analysis). is 0.4 mg/100 cm ² /sheet or less) in the same manner as in Comparative Example 1, 22.9% by weight of polyethylene resin, 59.3% by weight of silica fine powder, Composed of 16.0% by weight of paraffinic mineral oil and 1.8% by weight of surfactant (solid content), base thickness is 0.20 mm, porosity by mercury porosimetry is 62% by volume, mercury porosimetry A microporous film with ribs having an average pore size of 0.09 μm and a maximum pore size of 0.65 μm by mercury porosimetry was obtained. This was used as a liquid lead-acid battery separator of Comparative Example 2.

(Comparative Example 3)
As the silica fine powder, silica fine powder having a specific surface area of 200 m ² /g by the BET method, which is synthetic amorphous silica produced by a sedimentation method (however, it contains salts such as sodium sulfate produced as a by-product in the production process Although the amount was reduced by increasing the flow rate of the washing water compared to the conventional one, when using the washing water with the same Cl content as before, the contamination of the Cl content was not reduced, and the finally obtained microporous The alkali metal concentration (ICP emission spectroscopic analysis) of the film (10 cm x 10 cm x 2 sheets) is 5 mg/100 cm ² /sheet or less when immersed in 126 g of sulfuric acid having a specific gravity of 1.26 at a temperature of 50°C for 24 hours and left to stand. , in the same manner as in Comparative Example 1, except that the concentration of halogen content (ICP emission spectroscopic analysis) exceeded 0.4 mg/100 cm ² /sheet), 22.9 weight of polyethylene resin %, silica fine powder 59.3% by weight, paraffinic mineral oil 16.0% by weight, surfactant (solid content) 1.8% by weight, base thickness 0.20 mm, mercury porosimetry A microporous film with ribs having a porosity of 62% by volume, an average pore size of 0.09 µm by mercury porosimetry, and a maximum pore size of 0.65 µm by mercury porosimetry was obtained. This was used as a liquid lead-acid battery separator of Comparative Example 3.

Next, the separators of Examples 1 to 3 and Comparative Examples 1 to 3 obtained above were subjected to various property evaluations by the following methods. Table 1 shows the results. It should be noted that MD (MD direction) refers to the manufacturing direction of a sheet to be manufactured, and CD (CD direction) refers to a direction perpendicular to the MD direction. <Base thickness>
Using a dial gauge (Peacock G-6 manufactured by Ozaki Seisakusho Co., Ltd.), arbitrary points and several points of the microporous film (where rib-like projections are not included when having rib-like projections) were measured. <Tensile strength, elongation>
A test piece is obtained by cutting a microporous film into a rectangular size of 10 mm×70 mm in the MD and CD directions. Using a Shopper type or similar tensile tester with a capacity of 294 N or less, the interval (a) between the grips of the tester is about 50 mm, the test piece is attached, and the tensile test is performed at a tensile speed of 200 mm per minute. Read the tensile load (b) and distance (c) when the is cut. Tensile strength is calculated by dividing the tensile load (b) by the cross-sectional area of the test piece. Elongation is calculated by dividing the distance (c) by the grip spacing (a) of the tester.
<Porosity>
It was calculated by the following formula from the pore volume (mercury intrusion method) and the true density (immersion method) of the microporous film.
Porosity = Vp / ((1/ρ) + Vp)
where Vp: pore volume (cm ³ /g), ρ: true density (g/cm ³ )
<Average pore size>
The pore size distribution was calculated from the pressure and the volume of mercury at the time of mercury intrusion. The average pore diameter (median diameter) was defined as the pore diameter when 50% of the total pore volume of mercury was injected.
<Maximum hole diameter>
From the pore size distribution curve in the average pore size test, the pore size at which mercury injection started was taken as the maximum pore size.
<Permeability>
A test piece obtained by cutting a microporous film into a square size of 70 mm × 70 mm is floated on the surface of sulfuric acid having a specific gravity of 1.20 at a temperature of 20 ° C., and then sulfuric acid permeates the surface of the test piece. The time until the part changed color was measured and defined as permeability (seconds).
<Electrical resistance>
Cut the microporous film into a square size of 70 mm × 70 mm to make a test piece, SBA
Measured with a testing apparatus conforming to S 0402.
<Oxidation resistance life>
A 50 mm × 50 mm square positive electrode and negative electrode made of a lead plate are sandwiched between a microporous film separator cut into a 70 mm × 70 mm square, and laminated concentrically and in the square direction. After applying a pressure of 19.6 kPa to an electrode group consisting of a positive electrode (one sheet), a separator (one sheet), and a negative electrode (one sheet) and incorporating it into a battery case, a diluted 1,000 ml of sulfuric acid electrolyte was injected, a DC constant current of 5.0 A was applied at a liquid temperature of 50 ± 2 ° C, and the energization time was measured when the terminal voltage became 2.6 V or less or the voltage difference became 0.2 V or more. , oxidation resistance time (h). Table 1 shows relative values when the value of Comparative Example 1 is set to 100.
<Dendrite short characteristic>
A microporous film cut into a 70 mm × 70 mm square is sandwiched between two 50 mm × 50 mm square lead electrode plates (made of pure lead, thickness 3 mm), and the microporous film and the two lead electrode plates are sandwiched. The center of the three squares is aligned and the sides of the three squares are parallel to each other, and placed horizontally in the battery case, and a 5 kg weight is placed on it (at the center of the square) After that, a saturated lead sulfate aqueous solution is injected. Thereafter, a current of 3.2 mA is applied to the lead electrode plate, and changes in voltage are continuously recorded. The voltage rises slightly after the start of energization, and then gently drops. Time is measured until the voltage drops to 70% of the maximum voltage at this time. Table 1 shows relative values when the value of Comparative Example 1 is set to 100.
<ICP emission spectroscopic analysis>
Two microporous films cut into squares of 100 mm×100 mm are placed in a beaker containing 126 g of sulfuric acid having a specific gravity of 1.26. This is placed in a constant temperature water bath maintained at 50° C. and allowed to stand for 24 hours. After standing still for 24 hours, the microporous film is taken out from the sulfuric acid (extract). Sulfuric acid (extract) is diluted to 1/10, and the alkali metal content (Li, Na, K, Rb, Cs) and halogen content (F, Cl, Br, I) in the diluted solution are measured by ICP emission spectroscopy. Quantitatively analyze with an analyzer. The obtained value is converted from ppm to mg/100 cm ² /sheet (weight per sheet of microporous film having an area of 100 cm ² ) (however, the term "per sheet of microporous film" refers to the base thickness of 0.5 cm). 2 mm, and if the base thickness differs from this, the value is converted and corrected so that it corresponds to a base thickness of 0.2 mm).
<Battery test (charge acceptance, battery life)>
Charge acceptability is determined by measuring the charge current after the start of charging when the battery is discharged for 2.5 hours at a 5-hour rate current based on JIS D 5301 (2006). The battery life is determined by performing a charge/discharge cycle test by a light load life test method based on JIS D 5301 (2006), and measuring the number of cycles when the voltage becomes 7.2 V or less at 30 seconds. The charge acceptance and battery life in Table 1 are relative values (relative results) when the value of Comparative Example 1 is set to 100.

The results in Table 1 reveal the following.
(1) The separator of Example 1 of the present invention has an alkali metal concentration (ICP emission spectroscopic analysis) of 5 mg/100 cm ² /sheet or less, so that the charge acceptance is improved and the halogen concentration is By setting (ICP emission spectroscopic analysis) to 0.4 mg/100 cm ² /sheet or less, corrosion of the electrode plate lattice and electrode columns was prevented, and the battery life was improved.
(2) Compared to the separator of Example 1, the separator of Example 2 of the present invention has a concentration of alkali metals (ICP emission spectroscopic analysis) of 4 mg/100 cm ² /sheet or less. has improved further.
(3) Compared to the separator of Example 1, the separator of Example 3 of the present invention has a halogen content concentration (ICP emission spectroscopic analysis) of 0.1 mg/100 cm ² /sheet or less, thereby improving the battery life. has improved further.
(4) Therefore, if the separators of Examples 1 to 3 of the present invention are applied to lead-acid batteries for automobiles, it is considered that they contribute to improvement of charge acceptance and battery life required for idling stop vehicles.
(5) The separator of Comparative Example 1 has an alkali metal concentration (ICP emission spectroscopic analysis) of more than 5 mg/100 cm ² /sheet, so the charge acceptance is 100%, which shows no improvement. The minute concentration (ICP emission spectroscopic analysis) exceeded 0.4 mg/100 cm ² /sheet, which accelerated the corrosion of the electrode grid and the electrode columns, and the battery life was 100%, showing no improvement.
(6) The separator of Comparative Example 2 has a halogen concentration (ICP emission spectroscopic analysis) of 0.4 mg/100 cm ² /sheet or less, which prevents corrosion of the electrode grid and electrode columns and extends the battery life. Although it was improved, the concentration of alkali metal (ICP emission spectroscopic analysis) exceeded 5 mg/100 cm ² /sheet, so the charge acceptability was 100% and no improvement was observed.
(7) The separator of Comparative Example 3 had an alkali metal concentration (ICP emission spectroscopic analysis) of 5 mg/100 cm ² /sheet or less, thereby improving charge acceptance, but the halogen concentration (ICP emission spectroscopic analysis) exceeded 0.4 mg/100 cm ² /sheet, corrosion of the electrode grid and electrode columns was accelerated, and the battery life was 100% with no improvement.

Claims (4)

40% by weight or more of fine silica powder, which is synthetic amorphous silica produced by a sedimentation method in which amorphous silica is synthesized by reacting an aqueous alkali silicate solution with a mineral acid to precipitate, and then the purity is adjusted by filtering and washing with water. A method for producing a separator for a flooded lead-acid battery comprising a microporous film comprising a microporous film having a base thickness of 0.2 to 0.3 mm, Alkaline metal content (Li, Na, K, Rb, Cs) concentration (ICP Emission spectroscopic analysis) is 5 mg / 100 cm ² /sheet or less (however, the base thickness of the microporous membrane is converted to 0.2 mm), and the concentration of halogen content (F, Cl, Br, I) (ICP emission spectroscopic analysis ) is 0.4 mg/100 cm ² /sheet or less (however, the base thickness of the microporous membrane is equivalent to 0.2 mm). 2. The method of producing a separator for a flooded lead-acid battery according to claim 1, wherein said filtration and washing are performed using ion-exchanged water or groundwater containing no salt (sodium chloride). 3. The method of producing a separator for a liquid lead-acid battery according to claim 1, wherein said microporous film is a microporous film mainly composed of said fine silica powder and polyolefin resin. The microporous film is a microporous film having an average pore diameter (mercury porosimetry) of 0.01 to 0.5 μm and a porosity (mercury porosimetry) of 50 to 90% by volume. 4. A method of producing a separator for a flooded lead-acid battery according to claim 3.