JP7444920B2 - Separator for liquid lead-acid batteries - 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) that is maintenance-free by making the electrolyte non-fluid, but a so-called liquid battery that has a fluid electrolyte, which is the conventional method. The present invention relates to a separator for liquid lead-acid batteries used in lead-acid batteries (also referred to as vented lead-acid batteries and open-type lead-acid batteries).

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

The microporous film separator is usually made of a raw material composition that is a mixture of the polyolefin resin, the inorganic powder, the plasticizer (blended in a larger amount than the separator composition), the surfactant, and the additives. A base thickness of about 0.1 to 0.3 mm obtained by extruding into a sheet while heating, melting and kneading, roll-rolling to a predetermined thickness, and then extracting and removing all or part of the plasticizer. The sheet has an average pore diameter (mercury intrusion method) of about 0.01 to 0.5 μm and a porosity (mercury intrusion method) 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 the microporous structure (dense and complex pore structure and high porosity) of the microporous film. The microporous film must withstand sheet shrinkage that occurs when the plasticizer is removed during the manufacturing process and maintain dimensional stability.The drying process (moisture removal process) that is performed before the microporous film is used when it is incorporated into a battery. To withstand sheet shrinkage and maintain dimensional stability even during heat treatments such as This includes improving the electrolyte retention of the film.

Therefore, silica fine powder is usually used as the inorganic powder, and is processed by dry method or wet method from the viewpoint of having a large specific surface area, a large oil absorption amount, and having many hydrophilic groups (silanol groups). Synthetic amorphous silica produced by a wet precipitation method is used.

On the other hand, in automotive applications for lead-acid batteries, lead-acid batteries installed in idling-stop vehicles are required to have high charge acceptability because the amount of discharge increases. When trying to improve charge acceptability of lead-acid batteries, it is known that the presence of a large amount of alkali metal (Li, Na, K, Rb, Cs) ions in the electrolyte will hinder the improvement of charge acceptability. (Patent Document 1).

In addition, in lead-acid batteries, if large amounts of halogen (F, Cl, Br, I) impurities are mixed in, it can corrode the lead or lead alloy electrode grids and poles, leading to a decrease in battery life performance. It is also known (Patent Document 2).

Synthetic amorphous silica produced by the precipitation method is a method in which amorphous silica is precipitated by reacting an aqueous alkali silicate (sodium silicate) solution with a mineral acid (sulfuric acid) under neutral or alkaline conditions. The amorphous silica produced contains salts such as sodium sulfate as a by-product, and in the post-process, the salts are removed through filtration and water washing (processing to increase purity). It is being said.

International Publication No. 2014/128803 Japanese Patent Application Publication No. 2005-251394

However, since the salt removal process in the amorphous silica manufacturing process is not complete, 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 trace amount of sodium sulfate, and when used as a separator for lead-acid batteries, the electrolyte will gradually dissolve as the battery is used. If the elution amount is large, it may become a factor that hinders the improvement of charge acceptability.

Further, when the salt removal treatment in the amorphous silica production process is performed by washing with water, the water used for washing may contain Cl, which is a halogen. In other words, when using tap water (which contains residual chlorine) or when using groundwater containing salt (sodium chloride). Therefore, the above-mentioned microporous film produced using fine silica powder that has been washed with water also contains a trace amount of Cl, and when used as a separator for lead-acid batteries. As the battery continues to be used, Cl ions are eluted into the electrolyte, and if the amount eluted is large, corrosion of the electrode plate lattice and pole pillars may be promoted, which may be a factor in reducing the battery life performance.

Therefore, in view of the above-mentioned conventional problems, the present invention provides a separator for liquid lead-acid batteries comprising a microporous membrane manufactured using fine silica powder, which is synthetic amorphous silica manufactured by a precipitation method, as the main raw material. Therefore, even when a battery using this battery is used for a long time, the amount of alkali metal ions and halogen ions eluted from the separator into the electrolyte can be reduced, making it difficult to impede 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 liquid lead-acid batteries of the present invention is produced using a precipitation method in which amorphous silica is synthesized by precipitation by reacting an aqueous alkali silicate solution with mineral acid, and then the purity is adjusted by filtration and water washing. A separator for a liquid lead-acid battery comprising a microporous membrane containing 40% by weight or more of silica fine powder, which is a synthetic amorphous silica manufactured by The concentration of alkali metals (Li, Na, K, Rb, Cs) (ICP emission spectrometry) is 5 mg/100 cm 2 /sheet or less when immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at 50°C for ²⁴ hours and left to stand. (However, the base thickness of the microporous membrane is 0.2 mm) and the concentration of halogen (F, Cl, Br, I) (ICP emission spectrometry) is 0.4 mg/100 cm ² /sheet or less ( However, it is characterized in that the base thickness of the microporous membrane is 0.2 mm (equivalent value).

Further, the filtration and washing are performed using ion-exchanged water or groundwater that does not contain salt (sodium chloride).

Further, the microporous membrane is characterized in that it is a microporous film mainly composed of the silica fine powder and a polyolefin resin.

In addition, the microporous film has a base thickness of 0.1 to 0.3 mm, an average pore diameter (mercury intrusion method) of 0.01 to 0.5 μm, and a porosity (mercury intrusion method) of 50 to 90 vol. % microporous film.

According to the present invention, there is provided a lead-acid battery separator comprising a microporous membrane manufactured using silica fine powder, which is synthetic amorphous silica manufactured by a precipitation method, as the main raw material, and a battery using the separator is provided. Even with advanced use, the amount of alkali metal ions and halogen ions eluted from the separator into the electrolyte can be reduced, making it less likely to impede improvements in charge acceptance and reducing battery life performance. A separator can be provided.

The separator for liquid lead-acid batteries of the present invention synthesizes amorphous silica by precipitation by reacting an aqueous alkali silicate solution with a mineral acid, and then adjusts the purity by filtering and washing with water (removing salts as by-products and amorphous silica). A microporous membrane containing 40% by weight or more of silica fine powder (hereinafter sometimes simply referred to as "the silica fine powder"), which is synthetic amorphous silica produced by a precipitation method that increases the purity of silica. When the microporous membrane (10 cm x 10 cm x 2 sheets) was immersed for 24 hours in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C, the alkali metal content (Li, Na, K, Rb, Cs) concentration (ICP emission spectrometry) is 5 mg/100 cm ² / sheet or less (however, the base thickness of the microporous membrane is 0.2 mm), and the halogen content (F, Cl, Br, I) is The condition is that the concentration (ICP emission spectrometry) is 0.4 mg/100 cm ² /sheet or less (value calculated based on the base thickness of the microporous membrane of 0.2 mm).

The alkali metal content (Li, Na, K, Rb, Cs) when the microporous membrane (10 cm x 10 cm x 2 sheets) was immersed for 24 hours in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C. By adjusting the concentration (ICP emission spectrometry) to be 5 mg/100 cm ² /sheet or less, in a liquid lead-acid battery using the separator for liquid lead-acid batteries of the present invention, alkali eluted from the separator into the electrolyte can be prevented. Since the amount of metal ions can be suppressed, it becomes difficult to impede the improvement of charge acceptability. Therefore, when the microporous membrane (10 cm x 10 cm x 2 sheets) was immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C for 24 hours, the concentration of alkali metal (ICP emission spectrometry) was 4 mg. /100cm ² /sheet or less is more preferable.

The concentration of halogen components (F, Cl, Br, I) (ICP In a liquid lead-acid battery using ^the liquid lead-acid battery separator of the present invention, the halogen ions eluted from the separator into the electrolytic solution are Since the amount can be suppressed, deterioration in battery life performance due to accelerated corrosion of the electrode grid and poles 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 with a specific gravity of 1.26 at a temperature of 50°C for 24 hours and left to stand, the concentration of halogen components (ICP emission spectrometry) was 0. It is more preferably 2 mg/100 cm ² /sheet or less, and even more preferably 0.1 mg/100cm ² /sheet or less.

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

As mentioned above, the silica fine powder adsorbs and supports a plasticizer when the raw material composition is heated and melted and kneaded, and the microporous structure of the microporous film (dense and complex pore structure and high porosity). The process of drying the microporous film (moisture removal) before use when incorporating the microporous film into a battery requires the following: To withstand sheet shrinkage and maintain dimensional stability even during heat treatment such as process), to improve the electrolyte absorption property of the microporous film, to improve the electrolyte wettability of the microporous film, to improve the electrolyte wettability of the microporous film, The role of the porous film is to improve the electrolyte retention ability, and therefore, from the viewpoints of having a large specific surface area, large oil absorption, and having many hydrophilic groups (silanol groups), the dry method Alternatively, synthetic amorphous silica manufactured by the wet precipitation method is required, but synthetic amorphous silica produced by the wet precipitation method requires Living organisms contain salts such as sodium sulfate, and although salts are removed through filtration and washing in the post-process, the removal of salts is not complete, and tap water is not used for washing. Because underground water containing residual chlorine (contains residual chlorine) and salt (sodium chloride) can be used, it contains trace amounts of Na and Cl that can adversely affect battery performance. Therefore, in the present invention, synthetic amorphous silica produced by a wet precipitation method is used as fine silica powder, and contains alkali metal components (Li, Na, K, Rb, Cs) and halogen components (F, Cl, The content of Br, I) was determined by the alkali metal content when the final microporous membrane (10 cm x 10 cm x 2 sheets) was immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C for 24 hours. Silica that has been reduced to a level where the concentration of halogen components (ICP emission spectrometry) is 5 mg/100 cm ² /sheet or less, and the halogen concentration (ICP emission spectrometry) is 0.4 mg/100 cm ² /sheet or less. Use fine powder. Further, 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. Note that in this application, groundwater that does not contain salt (sodium chloride) refers to groundwater that has 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 will deteriorate, and if it is less than 0.1 mm, it will have good short circuit resistance. (Short circuits here include penetration short circuits called dendrite shorts, local weak parts of the base material, high pressure, impact, and puncture from convex parts of the electrode plate, oxidative damage due to oxidizing force from the electrode plate, etc.) (refers to both normal short circuits caused by holes or cracks) that become difficult to maintain.

The porosity of the microporous film (mercury intrusion method) is preferably 50% by volume or more, and by having a porosity of 50% by volume or more, it can be used as a separator for liquid lead-acid batteries with low internal resistance (electrical resistance). This contributes to improving the performance of liquid lead-acid batteries. Therefore, the porosity (mercury intrusion method) of the microporous film 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 consisting 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 can be obtained in which numerous communicating pores are formed throughout the membrane, which are uniform, fine, and have intricately intricate paths. An example of a specific manufacturing method is shown below. First, raw materials prepared by adding various additives (surfactants, antioxidants, weathering agents, etc.) as necessary to a predetermined amount of polyolefin resin, the silica fine powder, and a plasticizer are mixed using a Henschel mixer or Loedige mixer. Stir and mix using a mixer 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 heating, melting and kneading, and passed between a pair of forming rolls with predetermined grooves carved on one roll. In this way, a film-like product is obtained in which ribs of a predetermined shape are integrally formed on one side of a flat sheet. Next, this film-like material is immersed in a suitable solvent (for example, n-hexane), a predetermined amount of mineral oil is extracted and removed, and the desired microporous film is obtained. In addition, the raw material composition refers to a composition consisting of all raw materials brought into the melt-kneading process, and is meant to refer to "all raw materials (compositions of)". It does not mean that it refers to a melt-kneaded product.

The microporous film has a total content of polyolefin resin, the silica fine powder, and a plasticizer of 90% by weight or more, a polyolefin resin content of 20 to 60% by weight, and a silica fine powder content of 40 to 80% by weight. 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 content of the polyolefin resin is less than 20% by weight or the content of the silica fine powder is more than 80% by weight, the mechanical strength, oxidation resistance, and sealing properties of the polyolefin resin cannot be secured to the microporous film. If the content of the polyolefin resin exceeds 60% by weight or the content of the silica fine powder is less than 40% by weight, it will be difficult to ensure a large porosity and a fine and complex pore structure in the microporous film. This makes it impossible to maintain good electrical resistance characteristics of the microporous film separator.

As the polyolefin resin, homopolymers or copolymers such as polyethylene, polypropylene, polybutene, polymethylpentene, and mixtures thereof can be used. Among these, it is preferable to use polyethylene as the main material in terms of moldability and economical efficiency. Polyethylene has a lower melt molding temperature than polypropylene, has better productivity, and can reduce manufacturing 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 the case of a microporous film containing a large amount of silica fine powder. For this reason, the weight average molecular weight of the polyolefin resin is preferably 1 million or more, more preferably 1.5 million or more. Polyolefin resin has good miscibility with silica fine powder, maintains strength while bonding the skeleton of silica fine powder as an adhesive functional material in a microporous film, and is 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 of various powder properties such as particle size and specific surface area, is relatively inexpensive and easily available, and has 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 becomes finer (densified) and more complex, thereby increasing the short circuit resistance and improving the electrolyte retention of the microporous film. This is preferable because it increases the hydrophilicity of the microporous film by increasing the strength and providing a large number of hydrophilic groups (-OH) on the powder surface. For this reason, 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 silica fine powder is preferably 400 m ² /g or less. If the specific surface area of the silica fine powder exceeds 400 m ² /g, the surface activity of the particles will be high and the cohesive force will be strong, making 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 serve as a plasticizer for polyolefin resins, and 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 made of saturated hydrocarbons (paraffin), higher alcohols such as stearyl alcohol, ester plasticizers such as dioctyl phthalate, etc. can be used. Among these, mineral oil is preferred 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 consisting of polyolefin resin, silica fine powder, and plasticizer.

As mentioned above, the plasticizer is removed after melt-kneading a raw material composition mainly consisting of polyolefin resin, silica fine powder, and plasticizer and forming it into a film-like material of a predetermined shape. The content of plasticizer in the microporous film separator may be zero. However, in a separator for a liquid lead-acid battery, containing an appropriate amount of a plasticizer such as mineral oil can contribute to improving oxidation resistance. In such a case, the content of plasticizer in the separator is preferably 5 to 30% by weight. However, if the plasticizer content is increased, the porosity of the microporous film decreases and the electrical resistance of the microporous film separator worsens, so from this point of view, the plasticizer content should be 20 More preferably, it is less than % by weight.

As the solvent used to extract and remove the plasticizer, saturated hydrocarbon organic solvents such as hexane, heptane, octane, nonane, and decane can be used.

In addition, the raw material composition or the microporous film may contain a surfactant (hydrophilizing agent), an antioxidant, an ultraviolet absorber, a weathering agent, a lubricant, an antibacterial agent, an antifungal agent, and a pigment, as necessary. , dyes, colorants, antifogging agents, matting agents, and other additives may be added (blended) or contained within a range that does not impair the purpose and effects of the present invention.

The microporous film contains a large amount of the silica fine powder, which has a large specific surface area and is highly hydrophilic. The sulfuric acid electrolyte has permeability (infiltration), but when the sulfuric acid electrolyte is injected into a laminate in which electrode plates and separators are tightly assembled in a battery case, it quickly penetrates into the voids of the separator. In order to absorb the electrolyte and quickly replace the voids in the separator with the electrolyte, the microporous film may contain 0.2 to 8% by weight of a surfactant (solid content). preferable.

Methods for incorporating the surfactant into the microporous film include adding it to the raw material composition in advance in a dispersed state before forming the film (internal addition method), and adding the surfactant to the microporous film after the plasticizer has been removed. There is a method (external addition method) of post-processing (adhesion treatment) on the porous film, but this method simplifies the manufacturing process and prevents the surfactant from seeping out from the microporous film of the present invention. , a method of adding it in advance to the raw material composition (internal addition method) is preferable. The content (required amount) of the surfactant (solid content) in the microporous film is 0.2 to 8% by weight. Even if the content of the surfactant (solid content) is increased beyond this range, the effect of improving the hydrophilicity of the microporous film will not increase significantly, and on the contrary, it will reduce the porosity of the microporous film. As a separator for liquid lead-acid batteries, it causes an increase in internal resistance (electrical resistance), and as a separator for liquid lead-acid batteries, it causes an increase in self-discharge. Therefore, the content of the surfactant (solid content) in the microporous film is more preferably 0.2 to 5% by weight.

The surfactant may be any material that can improve the hydrophilicity of the microporous film, and any of nonionic surfactants, cationic surfactants, and anionic surfactants can be used. As the nonionic surfactant, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl allyl ethers, fatty acid monoglycerides, sorbitan fatty acid esters, etc. can be used. As the cationic surfactant, aliphatic amine salts, quaternary ammonium salts, polyoxyethylene alkylamine, alkylamine oxide, etc. can be used. As the anionic surfactant, alkyl sulfonate, alkylbenzene sulfonate, alkylnaphthalene sulfonate, alkyl sulfosuccinate, dodecylbenzene sulfonate, etc. can be used. Among these, it is possible to impart high hydrophilicity to polyolefin resins by adding a small amount, and because it has relatively high heat resistance, it is possible to add surfactants to the raw material composition in advance to form microporous films. Alkylbenzene sulfonate, alkyl sulfosuccinate, and dodecylbenzene sulfonate are preferred because they can be manufactured (manufactured by hot melt molding).

Next, examples of the present invention will be described in detail together with comparative examples.
(Example 1)
1000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point approximately 135°C) with a weight average molecular weight of 1.5 million as a polyolefin resin, and synthetic amorphous silica manufactured by a precipitation method with 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 produced as by-products in the manufacturing process was reduced by increasing the flow rate of the washing water than before, and the Cl content was lower than before. By using less washing water, the contamination of Cl content is reduced, and the final microporous membrane (10 cm x 10 cm x 2 sheets) is immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C for 24 hours. The concentration of alkali metals (Li, Na, K, Rb, Cs) (ICP emission spectroscopic analysis) is 5 mg/100cm ² /sheet or less, and the halogen content (F, Cl, Br, I) when left as is. 2,590 parts by weight of ^5,380 parts by weight of paraffinic mineral oil as a plasticizer, and an alkyl sulfosuccinate as a surfactant. (solid content) in a Loedige mixer, and extruded this raw material composition into a sheet while heating and melting and kneading it using a twin-screw extruder equipped with a T-die at the tip. A film that is passed between a pair of forming rolls with predetermined grooves for the main ribs for contacting the electrode plate, and integrally formed with the main ribs for contacting the electrode plate in a predetermined shape on one side of a flat sheet. I got something like that. Next, this film-like material is immersed in n-hexane, a predetermined amount of paraffinic mineral oil is extracted and removed, and dried. Composed of 16.0% by weight of mineral oil and 1.8% by weight of surfactant (solid content), base thickness is 0.20mm, porosity is 62% by volume by mercury intrusion method, by mercury intrusion method. A ribbed microporous film with an average pore diameter of 0.09 μm and a maximum pore diameter of 0.65 μm determined by mercury intrusion method was obtained. This was used as the separator for liquid lead-acid batteries of Example 1.

(Example 2)
1000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point approximately 135°C) with a weight average molecular weight of 1.5 million as a polyolefin resin, and synthetic amorphous silica manufactured by a precipitation method with 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 produced as by-products in the manufacturing process was further reduced by increasing the flow rate of the washing water than in Example 1, and By using washed water with a low Cl content, the contamination of Cl content is reduced, and the final microporous membrane (10 cm x 10 cm x 2 sheets) is soaked 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 spectrometry) is 4 mg/100cm ² /sheet or less, and the halogen content (F, Cl, Br , 2,590 parts by weight of I) (in which the concentration (ICP emission spectrometry) is 0.4 mg/100 cm ² / sheet or less), 5,380 parts by weight of paraffin mineral oil as a plasticizer, and alkyl as a surfactant. 109 parts by weight of 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. A main rib of a predetermined shape for contacting the electrode plate is integrally formed on one side of the flat sheet by passing it between a pair of forming rolls in which a predetermined groove for the main rib for contacting the electrode plate is cut into the roll. A processed film-like product was obtained. Next, this film-like material is immersed in n-hexane, a predetermined amount of paraffinic mineral oil is extracted and removed, and dried. Composed of 16.0% by weight of mineral oil and 1.8% by weight of surfactant (solid content), base thickness is 0.20mm, porosity is 62% by volume by mercury intrusion method, by mercury intrusion method. A ribbed microporous film having an average pore diameter of 0.09 μm and a maximum pore diameter of 0.65 μm determined by mercury intrusion method was obtained. This was used as a separator for a liquid lead-acid battery in Example 2.

(Example 3)
1000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point approximately 135°C) with a weight average molecular weight of 1.5 million as a polyolefin resin, and synthetic amorphous silica manufactured by a precipitation method with 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 produced as by-products in the manufacturing process was reduced by increasing the flow rate of the washing water than before, and the Cl content was lower than in Example 1. By using washed water with a low content, the contamination of Cl content is further reduced, and the final microporous membrane (10 cm x 10 cm x 2 pieces) 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 spectrometry) is 5 mg/100cm ² /sheet or less, and the halogen content (F, Cl, Br , 2,590 parts by weight of I) (in which the concentration (ICP emission spectrometry) is 0.1 mg/100 cm ² / sheet or less), 5,380 parts by weight of paraffinic mineral oil as a plasticizer, and alkyl as a surfactant. 109 parts by weight of 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. A main rib of a predetermined shape for contacting the electrode plate is integrally formed on one side of the flat sheet by passing it between a pair of forming rolls in which a predetermined groove for the main rib for contacting the electrode plate is cut into the roll. A processed film-like product was obtained. Next, this film-like material is immersed in n-hexane, a predetermined amount of paraffinic mineral oil is extracted and removed, and dried. Composed of 16.0% by weight of mineral oil and 1.8% by weight of surfactant (solid content), base thickness is 0.20mm, porosity is 62% by volume by mercury intrusion method, by mercury intrusion method. A ribbed microporous film having an average pore diameter of 0.09 μm and a maximum pore diameter of 0.65 μm determined by mercury intrusion method was obtained. This was used as a separator for a liquid lead-acid battery in Example 3.

(Comparative example 1)
1000 parts by weight of ultra-high molecular weight polyethylene resin powder (melting point approximately 135°C) with a weight average molecular weight of 1.5 million as a polyolefin resin, and synthetic amorphous silica manufactured by a precipitation method with 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 produced as by-products 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 content is reduced. The final microporous membrane (10 cm x 10 cm x 2 sheets) was immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C for 24 hours. spectroscopic analysis) exceeds 5 mg/100 cm ² /sheet, and the concentration of halogen content (ICP emission spectroscopic analysis) exceeds 0.4 mg/100 cm ² /sheet) 2590 parts by weight, and paraffin mineral as a plasticizer. 5,380 parts by weight of oil and 109 parts by weight of alkyl sulfosuccinate (solid content) as a surfactant were mixed in a Loedige mixer, and this raw material composition was passed through a twin-screw extruder equipped with a T-die at the tip. It is extruded into a sheet while being heated, melted and kneaded, and passed between a pair of forming rolls, one of which has a predetermined groove carved into it for the main rib for contacting the electrode plate, to form a predetermined shape on one side of the flat sheet. A film-like product was obtained in which the main rib for contacting the electrode plate was integrally molded. Next, this film-like material is immersed in n-hexane, a predetermined amount of paraffinic mineral oil is extracted and removed, and dried. Composed of 16.0% by weight of mineral oil and 1.8% by weight of surfactant (solid content), base thickness is 0.20mm, porosity is 62% by volume by mercury intrusion method, by mercury intrusion method. A ribbed microporous film having an average pore diameter of 0.09 μm and a maximum pore diameter of 0.65 μm determined by mercury intrusion method was obtained. This was used as a separator for a liquid lead acid battery in Comparative Example 1.

(Comparative example 2)
The fine silica powder is synthetic amorphous silica manufactured by the precipitation method and has a specific surface area of 200 m ² /g by the BET method (however, it contains salts such as sodium sulfate that are produced as by-products in the manufacturing process). The amount is the same as before, but by using washing water with a lower Cl content than before, the contamination of Cl content is reduced, and the final microporous membrane (10 cm x 10 cm x 2 pieces) is heated to When immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at 50°C for 24 hours and left for 24 hours, the concentration of alkali metals (ICP emission spectrometry) exceeds 5 mg/100cm ² /sheet, and the concentration of halogens (ICP emission spectrometry) Polyethylene resin ^22.9 % by weight, silica fine powder 59.3% by weight, Composed of 16.0% by weight of paraffinic mineral oil and 1.8% by weight of surfactant (solid content), base thickness is 0.20mm, porosity is 62% by volume by mercury intrusion method, mercury intrusion method A ribbed microporous film with an average pore diameter of 0.09 μm by mercury intrusion method and a maximum pore diameter of 0.65 μm by mercury intrusion method was obtained. This was used as a separator for a liquid lead-acid battery in Comparative Example 2.

(Comparative example 3)
The fine silica powder is synthetic amorphous silica manufactured by the precipitation method and has a specific surface area of 200 m ² /g by the BET method (however, it contains salts such as sodium sulfate that are produced as by-products in the manufacturing process). The amount of Cl content was reduced by increasing the flow rate of the washing water compared to the conventional method, but if washing water with the same Cl content as before was used, the contamination of Cl content would not be reduced and the final microporous material When a membrane (10 cm x 10 cm x 2 pieces) is immersed in 126 g of sulfuric acid with a specific gravity of 1.26 at a temperature of 50°C for 24 hours and left to stand, the concentration of alkali metal (ICP emission spectrometry) is 5 mg/100 cm ² /sheet or less. Polyethylene resin ^22.9 weight %, silica fine powder 59.3% by weight, paraffinic mineral oil 16.0% by weight, surfactant (solid content) 1.8% by weight, base thickness 0.20mm, mercury intrusion method. A ribbed microporous film was obtained with a porosity of 62% by volume, an average pore diameter of 0.09 μm as determined by mercury intrusion, and a maximum pore diameter of 0.65 μm as determined by mercury intrusion. This was used as a separator for a liquid lead-acid battery in Comparative Example 3.

Next, various characteristic evaluations were performed on each of the separators of Examples 1 to 3 and Comparative Examples 1 to 3 obtained above using the following methods. The results are shown in Table 1. Note 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.), measurements were taken at arbitrary points and several locations on the microporous film (in cases where the film had rib-like protrusions, the portions did not contain the rib-like protrusions).
<Tensile strength, elongation>
A test piece is cut from the microporous film into a rectangular size of 10 mm x 70 mm in the MD and CD directions. Using a Schopper type tensile testing machine with a capacity of 294N or less or a similar tensile testing machine, the interval (a) between the grips of the testing machine was set to about 50mm, a test piece was attached, and a tensile test was performed at a tensile speed of 200mm/min. Read the tensile load (b) and distance (c) when it is cut. The 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 testing machine.
<Porosity>
It was calculated using the following formula from the pore volume (mercury intrusion method) and true density (immersion method) of the microporous film.
Porosity = Vp/((1/ρ)+Vp)
However, Vp: pore volume (cm ³ /g), ρ: true density (g/cm ³ )
<Average pore diameter>
The pore size distribution was calculated from the pressure and mercury volume during mercury intrusion. The pore diameter at the time when 50% of the total pore volume of mercury was injected was defined as the average pore diameter (median diameter).
<Maximum hole diameter>
From the pore size distribution curve in the average pore size test, the pore size at which mercury injection started was determined as the maximum pore size.
<Permeability>
A test piece made by cutting a microporous film into a square size of 70 mm x 70 mm was floated on the surface of sulfuric acid with a specific gravity of 1.20 at a temperature of 20°C. The time until the area changes color was measured and defined as permeability (seconds).
<Electrical resistance>
The microporous film was cut into a square size of 70 mm x 70 mm to prepare a test piece, and the test piece was measured using a test device compliant with SBA S 0402.
<Oxidation resistance life>
A positive electrode and a negative electrode made of square lead plates measuring 50 mm x 50 mm are laminated concentrically and squarely aligned with a microporous film separator cut into a square shape of 70 mm x 70 mm in between. After applying a pressure of 19.6 kPa to the electrode group consisting of a positive electrode (1 piece), a separator (1 piece), and a negative electrode (1 piece) and assembling it in a battery case, Inject 1000ml of sulfuric acid electrolyte, apply a constant DC current of 5.0A at a liquid temperature of 50±2°C, and measure the energization time when the terminal voltage becomes 2.6V or less or the voltage difference becomes 0.2V or more. , oxidation resistance time (h). Note that Table 1 shows relative values when the value of Comparative Example 1 is set to 100.
<Dendrite short characteristics>
A microporous film cut into a 70 mm x 70 mm square is sandwiched between two 50 mm x 50 mm square lead electrode plates (made of pure lead, thickness 3 mm), and the microporous film and two lead electrode plates are assembled. Place it horizontally in the battery case so that the centers of the three squares match and the sides of the three squares are parallel to each other, and place a 5 kg weight on top of it (at the center of the square). After that, inject a saturated lead sulfate aqueous solution. Thereafter, a current of 3.2 mA is applied to the lead electrode plate, and changes in voltage are continuously recorded. The voltage increases slightly after the start of energization, and then gradually decreases. The time is measured until the voltage drops to 70% of the maximum voltage at this time. Note that Table 1 shows relative values when the value of Comparative Example 1 is set to 100.
<ICP emission spectrometry analysis>
Two microporous films cut into squares of 100 mm x 100 mm are placed in a beaker containing 126 g of sulfuric acid with a specific gravity of 1.26. This was placed in a constant temperature water bath maintained at 50°C and left standing for 24 hours. After standing still for 24 hours, the microporous film is taken out from the sulfuric acid (extract liquid). The sulfuric acid (extract) was 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 were analyzed by ICP emission spectroscopy. Perform quantitative analysis using an analyzer. The obtained value is converted from ppm to mg/100cm ² /sheet (weight per microporous film with an area of 100cm ² ) (however, "per microporous film" means base thickness 0. If the base thickness is different from this, the value is converted and corrected to be per 0.2 mm of the base thickness).
<Battery test (charge acceptance, battery life)>
Charge acceptability is determined based on JIS D 5301 (2006) by measuring the charging current after the start of charging when discharging at a 5 hour rate current for 2.5 hours. The battery life is determined by performing a charge/discharge cycle test using the 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. Note that the charging acceptability and battery life in Table 1 are relative values (relative results) when the value of Comparative Example 1 is set as 100.

The results in Table 1 revealed the following.
(1) The separator of Example 1 of the present invention has an alkali metal concentration (ICP emission spectrometry) of 5 mg/100 cm ² /sheet or less, which improves charge acceptance and improves halogen concentration. (ICP emission spectroscopy) was set to 0.4 mg/100 cm ² /sheet or less, which prevented corrosion of the electrode plate grid and pole pillars and improved battery life.
(2) Compared to the separator of Example 1, the separator of Example 2 of the present invention has an alkali metal concentration (ICP emission spectrometry) of 4 mg/100 cm ² /piece or less, which improves charge acceptance. has further improved.
(3) Compared to the separator of Example 1, the separator of Example 3 of the present invention has a halogen concentration (ICP emission spectrometry) of 0.1 mg/100 cm ² /sheet or less, which improves battery life. has further improved.
(4) Therefore, if the separators of Examples 1 to 3 of the present invention are applied to automotive lead-acid batteries, it is thought that it will contribute to improving the charging acceptability and battery life required for idling stop vehicles.
(5) Since the separator of Comparative Example 1 has an alkali metal concentration (ICP emission spectrometry) of more than 5 mg/100 cm ² /sheet, the charge acceptance is 100%, which shows no improvement. Since the concentration (ICP emission spectrometry) of 0.4 mg/100 cm ² /plate was more than 0.4 mg/100 cm 2 /sheet, corrosion of the electrode plate grid and pole pillars was accelerated, and the battery life was 100%, with no improvement observed.
(6) The separator of Comparative Example 2 has a halogen concentration (ICP emission spectrometry) of 0.4 mg/100 cm ² /sheet or less, which prevents corrosion of the electrode grid and pole pillars and shortens battery life. Although it was improved, since the concentration of alkali metal content (ICP emission spectrometry) exceeded 5 mg/100 cm ² /sheet, the charge acceptability was 100% and no improvement was observed.
(7) In the separator of Comparative Example 3, the concentration of alkali metal components (ICP emission spectrometry) was set to 5 mg/100 cm ² /sheet or less, which improved charge acceptance. Spectroscopic analysis) exceeded 0.4 mg/100 cm ² /sheet, so corrosion of the electrode plate grid and pole pillars was accelerated, and the battery life was 100%, with no improvement observed.

Claims (3)

A separator for a liquid lead-acid battery comprising a microporous membrane containing 40% by weight or more of silica fine powder, which is synthetic amorphous silica, the microporous membrane having a base thickness of 0.18 to 0.3 mm. It is a microporous film, and the alkali metal content (Li, Na, K, Rb, Cs) concentration (ICP emission spectrometry) is 5 mg/100 cm ² /sheet or less (however, the base thickness of the microporous membrane is 0.2 mm), and the halogen content (F, Cl, Br , I) for a liquid lead-acid battery, characterized in that the concentration (ICP emission spectrometry) is 0.4 mg/100 cm ² /sheet or less (value calculated based on the base thickness of the microporous membrane of 0.2 mm). Separator. 2. The separator for a liquid lead-acid battery according to claim 1 , wherein the microporous membrane is a microporous film mainly composed of the silica fine powder and a polyolefin resin. The microporous film is a microporous film having an average pore diameter (mercury intrusion method) of 0.01 to 0.5 μm and a porosity (mercury intrusion method) of 50 to 90% by volume. Item 2 : A separator for a liquid lead-acid battery according to item 2.