Gelling agent for alkaline batteries

Abstract

The purpose of the present invention is to provide: a gelling agent for alkaline batteries that maintains long-term discharge characteristics (discharge amount and discharge time) and has excellent impact resistance; and an alkaline battery using the gelling agent. The gelling agent for alkaline batteries contains a crosslinked polymer (A) having an acrylic acid (salt) (a1), an acrylic acid 2-carboxyethyl (salt) (a2), and a crosslinking agent (b) as constituent monomers, wherein the crosslinking agent (b) contains a crosslinking agent (b1) capable of undergoing alkaline hydrolysis and a crosslinking agent (b2) not undergoing alkaline hydrolysis, and the weight ratio [(a1) / (a2) ] of (a1) and (a2) is 99 / 1 to 99.98 / 0.02.

Description

Gelling agent for alkaline batteries

[0001] The present invention relates to a gelling agent for alkaline batteries.

[0002] Conventionally, a mixture of a high-concentration alkaline electrolyte (a high-concentration aqueous potassium hydroxide solution, optionally containing zinc oxide, etc.) and zinc powder and / or zinc alloy powder, etc., has been mainly used for the negative electrode of an alkaline battery. In order to prevent the zinc powder from settling in the alkaline electrolyte, to prevent leakage from the battery, and to suppress spinnability in order to increase the production efficiency of batteries, it has been proposed to use a water-absorbent resin, etc., in which poly(meth)acrylic acid and its salts have been insolubilized with a crosslinking agent as a thickener (Patent Document 1).

[0003] JP 2008-34379 A

[0004] However, in recent years, alkaline batteries have been required to have even higher performance, and alkaline batteries using these water-absorbent resin gelling agents are not sufficient in preventing the precipitation of zinc powder and the like in the alkaline electrolyte, and are not necessarily satisfactory in terms of maintaining the battery's discharge characteristics (discharge amount and discharge time) over a long period of time and impact resistance. Furthermore, when an alkaline battery is subjected to a strong impact or is unintentionally short-circuited, a large current flows inside the battery, generating heat and deteriorating the discharge characteristics, and therefore are not necessarily satisfactory in terms of heat resistance.

[0005] Therefore, an object of the present invention is to provide a gelling agent for alkaline batteries that maintains discharge characteristics (discharge amount and discharge time) over a long period of time and has excellent impact resistance and heat resistance, and an alkaline battery using the same.

[0006] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention. Specifically, the present invention relates to a gelling agent for alkaline batteries containing a crosslinked polymer (A) having, as constituent monomers, acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b), wherein the crosslinking agent (b) contains a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not hydrolyze in an alkaline environment, and the weight ratio of (a1) to (a2) [(a1) / (a2)] is 99 / 1 to 99.98 / 0.02.

[0007] The alkaline battery gelling agent and alkaline battery of the present invention have the following advantages. (1) Because the alkaline battery gelling agent of the present invention is excellent at preventing the settling of zinc powder and other substances in the negative electrode material, when used in alkaline batteries, it is possible to produce batteries with extremely excellent discharge duration and impact resistance over a long period of time, even with a small amount. (2) Because the negative electrode material containing the alkaline battery gelling agent of the present invention exhibits minimal viscosity change upon heat generation, it is possible to produce highly safe batteries with extremely excellent impact resistance and heat resistance. (3) Because the negative electrode material containing the alkaline battery gelling agent of the present invention has an appropriate viscosity range during filling and exhibits good drainage, there is little variation in the amount of negative electrode material filled per battery, allowing for the production of batteries of uniform quality even in mass production. Furthermore, because the negative electrode material can be filled uniformly and quickly even in small-sized batteries, it is possible to produce batteries of uniform quality.

[0008] <Gelling Agent for Alkaline Batteries> The gelling agent for alkaline batteries (G) of the present invention contains a crosslinked polymer (A) having acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b) as constituent monomers, wherein the crosslinking agent (b) contains a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not hydrolyze in an alkaline environment, and the weight ratio of (a1) to (a2) [(a1) / (a2)] is 99 / 1 to 99.98 / 0.02.

[0009] In the present invention, “acrylic acid (salt)” means “acrylic acid” and / or “acrylic acid salt,” and “2-carboxyethyl acrylate (salt)” means “2-carboxyethyl acrylate” and / or “2-carboxyethyl acrylate salt.” Examples of salts include salts of alkali metals such as potassium, sodium, and lithium, and salts of alkaline earth metals such as calcium.

[0010] The constituent monomers derived from acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) may be either unneutralized or neutralized. From the viewpoints of reducing tackiness, improving dispersibility, and ease of production work of the crosslinked polymer (A), it is preferable that the crosslinked polymer (A) is partially or completely neutralized.

[0011] When neutralizing the acrylic acid (a1) and 2-carboxyethyl acrylate (a2) contained in the crosslinked polymer (A), generally, an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, or lithium hydroxide, an alkaline earth metal hydroxide such as calcium hydroxide, or an aqueous solution thereof may be added to the monomer stage before polymerization or to the hydrogel after polymerization. However, since the crosslinking agent (b2), which does not hydrolyze in alkaline conditions as described below, has poor water solubility, if polymerization is carried out with the water-soluble vinyl monomer (a1) at a high degree of neutralization, even if a predetermined amount of crosslinking agent (b2) is added, the crosslinking agent (b2) may separate from the aqueous monomer solution, preventing the desired crosslinking and making it impossible to obtain the crosslinked polymer (A). Therefore, it is more preferable to set the degree of neutralization of the water-soluble vinyl monomer (a1) to 0 to 30 mol %, carry out polymerization by adding the crosslinking agent (b2), and then, if necessary, add an alkali metal hydroxide to the hydrogel to adjust the degree of neutralization.

[0012] The final degree of neutralization of the acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) in the crosslinked polymer (A) (the content (mol %) of the anionic base based on the total number of moles of the anionic groups and anionic bases of the anionic vinyl monomer) is preferably 0 to 90, more preferably 40 to 80, and particularly preferably 60 to 70. Within this range, the discharge characteristics, impact resistance, and heat resistance of the negative electrode material are further improved. Note that the anionic base means a neutralized anionic group.

[0013] From the viewpoint of the absorption capacity of the gelling agent (G), the content of the acrylic acid (salt) (a1) and the 2-carboxyethyl acrylate (salt) (a2) is preferably 98.0 to 99.90% by weight, more preferably 99.0 to 99.85% by weight, and particularly preferably 99.2 to 99.83% by weight, based on the weight of the crosslinked polymer (A).

[0014] The weight ratio [(a1) / (a2)] of the acrylic acid (salt) (a1) to the 2-carboxyethyl acrylate (salt) (a2) in the crosslinked polymer (A) is 99 / 1 to 99.98 / 0.02, preferably 99.5 / 0.5 to 99.95 / 0.05, and particularly preferably 99.7 / 0.3 to 99.9 / 0.1. If this weight ratio [(a1) / (a2)] is less than 99 / 1, the negative electrode material of an alkaline battery to which the gelling agent (G) is added will suffer from poor liquid drainage and variations in the filling amount will occur. If it exceeds 99.98 / 0.02, the viscosity stability of the gelling agent (G) will decrease and zinc powder will settle, tending to deteriorate the discharge characteristics, impact resistance, and heat resistance.

[0015] The crosslinked polymer (A) is crosslinked using a crosslinking agent (b). The crosslinking agent (b) includes a crosslinking agent (b1) that is hydrolyzed in an alkaline condition and a crosslinking agent (b2) that is not hydrolyzed in an alkaline condition.

[0016] In the present invention, (b1) and (b2) are used in combination. The combined use of (b1) and (b2) further improves the viscosity stability of the gelling agent (G) and prevents syneresis of the alkaline electrolyte, allowing the battery to maintain long-term discharge. Furthermore, the electrolyte can be uniformly injected when filling the battery, reducing the deviation in the amount of electrolyte injected per battery. Here, "syneresis" of the alkaline electrolyte means that the gelling agent (G) and the alkaline electrolyte cannot be maintained in a substantially uniform mixed state, resulting in separation of the gelling agent (G) and the alkaline electrolyte.

[0017] In the case of the crosslinking agent (b1) that is hydrolyzed in an alkaline environment, "hydrolyzed in an alkaline environment" means that the constituent monomer derived from (b1) in the crosslinked polymer (A) has a hydrolyzable bond, and the hydrolyzable bond may be a bond that the crosslinking agent (b1) originally has in the molecule (in this case, the crosslinking agent is referred to as a crosslinking agent (b11) that has a hydrolyzable bond in the molecule), or may be a bond that is hydrolyzed by a crosslinking reaction with another monomer {(a1) or (a2)} that constitutes the crosslinked polymer (A) (in this case, the crosslinking agent is referred to as a crosslinking agent (b12) that produces a hydrolyzable bond). Examples of hydrolyzable bonds include ester bonds and amide bonds.

[0018] Examples of the crosslinking agent (b11) having a hydrolyzable bond in the molecule include copolymerizable crosslinking agents having 2 to 10 ethylenically unsaturated bonds in the molecule, such as N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and polyglycerin (degree of polymerization 3 to 13) polyacrylate.

[0019] Examples of the crosslinking agent (b12) that forms a hydrolyzable bond upon crosslinking reaction include reactive crosslinking agents that react with carboxylic acids, such as polyglycidyl compounds (ethylene glycol diglycidyl ether, etc.), polyisocyanate compounds (4,4'-diphenylmethane diisocyanate, etc.), polyamine compounds (ethylenediamine, etc.), and polyalcohol compounds (glycerin, etc.). The reactive crosslinking agent can react with (meth)acrylic acid (salt) to form an ester bond or an amide bond.

[0020] Among the crosslinking agents (b1) that are hydrolyzed under alkaline conditions, from the viewpoint of viscosity stability of the negative electrode material to which the gelling agent (G) has been added, polyacrylamide compounds and polyacrylate compounds are preferred, more preferred are N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate, particularly more preferred are N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethylene glycol diglycidyl ether, and most preferred are N,N'-methylenebisacrylamide and trimethylolpropane tri(meth)acrylate.

[0021] The crosslinking agent (b2) that does not hydrolyze in alkaline conditions is a crosslinking agent that does not have a hydrolyzable bond in the molecule and does not generate a hydrolyzable bond through a crosslinking reaction. Examples of such a crosslinking agent (b2) include a crosslinking agent (b21) having two or more vinyl ether bonds and a crosslinking agent (b22) having two or more allyl ether bonds. From the viewpoint of reactivity, etc., a crosslinking agent having two or more allyl ether bonds is preferable.

[0022] Examples of the crosslinking agent (b21) having two or more vinyl ether bonds include ethylene glycol divinyl ether, 1,4-butanediol divinyl ether, 1,4-cyclohexanedimethanol divinyl ether, 1,6-hexanediol divinyl ether, polyethylene glycol divinyl ether (degree of polymerization 2 to 5), bisphenol A divinyl ether, pentaerythritol trivinyl ether, sorbitol trivinyl ether, and polyglycerin (degree of polymerization 3 to 13) polyvinyl ether.

[0023] Examples of the crosslinking agent (b22) having two or more allyl ether bonds include a crosslinking agent (b221) having two allyl groups and no hydroxyl group in the molecule, a crosslinking agent (b222) having two allyl groups and 1 to 5 hydroxyl groups in the molecule, a crosslinking agent (b223) having 3 to 10 allyl groups and no hydroxyl group in the molecule, and a crosslinking agent (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule. The inclusion of a hydroxyl group in the molecule improves compatibility with the vinyl monomer (a1) and / or (a2) {particularly (meth)acrylic acid (salt)}, increases the uniformity of crosslinking, improves the performance of the gelling agent (G), and further improves the long-term viscosity stability of a negative electrode material containing the gelling agent (G).

[0024] Examples of the crosslinking agent (b221) having two allyl groups and no hydroxyl group in the molecule include 1,4-cyclohexanedimethanol diallyl ether, alkylene (having 2 to 5 carbon atoms) glycol diallyl ether, and polyalkylene (having 2 to 6 carbon atoms) glycol (weight average molecular weight: 100 to 4000) diallyl ether.

[0025] Examples of the crosslinking agent (b222) having two allyl groups and 1 to 5 hydroxyl groups in the molecule include glycerin diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, and polyglycerin (degree of polymerization 2 to 5) diallyl ether.

[0026] Examples of the crosslinking agent (b223) having 3 to 10 allyl groups in the molecule and no hydroxyl group include trimethylolpropane triallyl ether, glycerin triallyl ether, pentaerythritol tetraallyl ether, and tetraallyloxyethane.

[0027] Examples of the crosslinking agent (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule include pentaerythritol triallyl ether, diglycerin triallyl ether, sorbitol triallyl ether, and polyglycerin (degree of polymerization 3 to 13) polyallyl ether.

[0028] Two or more types of crosslinking agents (b2) that do not hydrolyze in alkaline conditions may be used in combination.

[0029] Among the crosslinking agents (b2), crosslinking agents (b22) having two or more allyl ether bonds are preferred, more preferred are crosslinking agents having 1 to 5 hydroxyl groups and 2 to 10 allyl groups {(b222) and (b224)}, particularly preferred are crosslinking agents (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule, and most preferred are pentaerythritol triallyl ether, diglycerin triallyl ether, and sorbitol triallyl ether. Use of these crosslinking agents is preferred because they have good compatibility with the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) that becomes (a1) upon hydrolysis, allowing for efficient crosslinking.

[0030] The content of the alkaline hydrolyzable crosslinking agent (b1) in the crosslinked polymer (A) of the present invention varies depending on the type of crosslinking agent (b1) and the average degree of polymerization, but is preferably 0.05 to 1 wt %, more preferably 0.1 to 0.8 wt %, and particularly preferably 0.1 to 0.5 wt %, based on the weight of the crosslinked polymer (A). Within this range, excessive syneresis of the alkaline electrolyte can be prevented, thereby further improving the long-term discharge characteristics of the battery.

[0031] The content of the crosslinking agent (b2) that does not hydrolyze in alkaline conditions in the crosslinked polymer (A) varies depending on the type of crosslinking agent (b2), but is preferably 0.05 to 1 wt %, more preferably 0.05 to 0.5 wt %, and particularly preferably 0.1 to 0.3 wt %, based on the weight of the crosslinked polymer (A).Within this range, the long-term discharge characteristics of the battery are further improved.

[0032] The weight ratio of the crosslinking agent (b1) to the crosslinking agent (b2) in the crosslinked polymer (A), [(b1) / (b2)], is preferably 1.5 to 5, more preferably 1.7 to 4, and particularly preferably 1.9 to 3. Within this range, excessive syneresis of the alkaline electrolyte can be prevented, and the long-term discharge characteristics of the battery are further improved.

[0033] The total content of the crosslinking agent (b1) and the crosslinking agent (b2) is preferably 0.10 to 2.0 wt %, more preferably 0.30 to 1.0 wt %, and particularly preferably 0.40 to 0.8 wt %, based on the weight of the crosslinked polymer (A). This range prevents excessive syneresis of the alkaline electrolyte, further improving the long-term discharge characteristics of the battery. Furthermore, the stability of the gelling agent (G) is improved, and the long-term viscosity stability and temperature stability of the alkaline electrolyte containing the gelling agent (G) are further improved.

[0034] The gelling agent (G) of the present invention may contain a surfactant (D) having an HLB of 1 to 12. Here, "HLB" is an index showing the balance between hydrophilicity and lipophilicity, and can be calculated from the ratio of the organicity value to the inorganicity value of an organic compound, for example, by the Oda method described on page 212 of "Introduction to Surfactants" (published by Sanyo Chemical Industries, Ltd. in 2007, written by Takehiko Fujimoto). HLB = 10 × inorganicity / organicity The organicity value and inorganicity value used to derive the HLB can be calculated using the values ​​in the table on page 213 of "Introduction to Surfactants."

[0035] The surfactant (D) includes ionic surfactants and nonionic surfactants.

[0036] Examples of ionic surfactants include known anionic surfactants, amphoteric surfactants, and cationic surfactants, and specific examples include those described in International Publication Nos. 99 / 03577, 2002 / 005949, and U.S. Pat. No. 4,331,447. As the surfactant (D), nonionic surfactants are preferred from the viewpoints of gel viscosity and high-speed injection of the negative electrode material.

[0037] A nonionic surfactant does not exhibit ionicity even when dissolved in water, but exhibits surface activity. In the present invention, the nonionic surfactant is not particularly limited, but from the viewpoints of gel viscosity and high-speed injection of the negative electrode material, at least one selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, and fatty acid amides is preferred.

[0038] Examples of sucrose fatty acid esters include those in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to sucrose, and specific examples include sucrose stearates [for example, those manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. {DK Ester F-50 (HLB=6), F-70 (HLB=8), and F-110 (HLB=11)}, and those manufactured by Mitsubishi-Kagaku Foods Corporation {Ryoto Sugar Ester S-370 (HLB=about 3), S-770 (HLB=about 7), S-970 (HLB=about 9), S-1170 (HLB=about 11), and S-1170F (HLB=about 11)}].

[0039] Sorbitan fatty acid esters include those in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to sorbitan, and specific examples thereof include sorbitan palmitate [manufactured by Kao Corporation (Rheodol SP-P10 (HLB=6.7) and the like) and manufactured by Riken Vitamin Co., Ltd. (Rikemal P-300 (HLB=5.6) and the like].

[0040] The glycerin fatty acid esters include those in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to glycerin and / or a glycerin polymer (degree of polymerization 2 to 20). Specific examples thereof include diglycerol monolaurate (manufactured by Riken Vitamin Co., Ltd. {Poem DL-100 (HLB=9.4)}, etc.), diglycerol monomyristate (manufactured by Riken Vitamin Co., Ltd. {Poem DM-100 (HLB=8.7)}, etc.), diglycerol monostearate (manufactured by Riken Vitamin Co., Ltd. {Poem DS-100A (HLB=7.7)}, etc.), diglycerol monooleate (manufactured by Riken Vitamin Co., Ltd. {Poem DO-100V (HLB=7.3), Rikemal DO-100 (HLB=7.4)}, etc.), and decaglycerol stearate (manufactured by Riken Vitamin Co., Ltd. {Poem J-0081HV (HLB=12), Poem J-0381V (HLB=12)}, etc.).

[0041] The fatty acid amide includes an amide bond between a fatty acid having 8 to 22 carbon atoms and ethanolamine. Specific examples include coconut oil fatty acid monoethanolamide [manufactured by Sanyo Chemical Industries, Ltd. {Prophane AB-20 (HLB=11)}, etc.] and stearic acid monoethanolamide [manufactured by Sanyo Chemical Industries, Ltd. {Prophane SME (HLB=10)}, etc.].

[0042] The HLB of the surfactant (D) is preferably 1 to 12, more preferably 3 to 11, and particularly preferably 5 to 9, from the viewpoints of high-speed injection of the negative electrode material and syneresis of the negative electrode material.

[0043] Moreover, as the surfactant (D), from the viewpoints of high-speed injectability of the negative electrode material and syneresis of the negative electrode material, a nonionic surfactant is preferable, and more preferably at least one surfactant selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, and fatty acid amides.

[0044] In the gelling agent (G) of the present invention, the content of the surfactant (D) is preferably 0.001 to 2.0% by weight, more preferably 0.005 to 1.0% by weight, particularly preferably 0.01 to 0.8% by weight, and most preferably 0.01 to 0.5% by weight, based on the weight of the crosslinked polymer (A), from the viewpoints of high-speed injectability of the negative electrode material and syneresis of the negative electrode material.

[0045] When the surfactant (D) is in the form of a powder, the particle size of the surfactant is not particularly limited, but the volume average particle size is preferably 0.1 to 2000 μm, more preferably 0.5 to 1500 μm, and particularly preferably 1 to 1000 μm, from the viewpoint of dry blendability with the crosslinked polymer (A).

[0046] Next, a method for producing the gelling agent (G) for alkaline batteries of the present invention will be described.

[0047] As the polymerization method for obtaining the crosslinked polymer (A), a known polymerization method can be applied, and for example, any of aqueous solution polymerization, suspension polymerization, bulk polymerization, reversed phase suspension polymerization, and emulsion polymerization may be used.

[0048] Of these polymerization methods, aqueous solution polymerization, suspension polymerization, reversed-phase suspension polymerization, and emulsion polymerization are preferred, aqueous solution polymerization, reversed-phase suspension polymerization, and emulsion polymerization are more preferred, aqueous solution polymerization and reversed-phase suspension polymerization are particularly preferred, and aqueous solution polymerization is most preferred. For these polymerizations, known polymerization initiators, chain transfer agents, and / or solvents can be used. Most preferred are aqueous solution polymerization, in which a crosslinking agent (b) is added to and dissolved in an aqueous monomer solution primarily composed of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2), followed by polymerization, and reversed-phase suspension polymerization, in which a similar aqueous monomer solution is dispersed and suspended in a hydrophobic organic solvent (e.g., hexane, toluene, xylene, etc.) in the presence of a dispersant, followed by polymerization. These polymerization methods make it possible to obtain gelling agents with excellent discharge characteristics, impact resistance, and heat resistance.

[0049] The method for polymerizing the acrylic acid (salt) (a1) and the 2-carboxyethyl acrylate (salt) (a2) by aqueous solution polymerization or reversed-phase suspension polymerization may be a known method, and examples thereof include a method of polymerization using a radical polymerization initiator and a method of irradiating with radiation, ultraviolet light, an electron beam, or the like.

[0050] When a radical polymerization initiator is used, examples of the initiator include azo compounds [azobisisovaleronitrile, azobisisobutyronitrile, 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis [2-methyl-N-(2-hydroxyethyl)propionamide, 2,2'-azobis(2-amidinopropane) hydrochloride, etc.], inorganic peroxides [hydrogen peroxide, potassium persulfate, ammonium persulfate, sodium persulfate, etc.], organic peroxides [di-t-butyl peroxide, cumene hydroperoxide, etc.], redox initiators [combinations of reducing agents such as alkali metal salts of sulfite or bisulfite, ammonium sulfite, ammonium bisulfite, L-ascorbic acid, etc., and peroxides such as alkali metal salts of persulfate, ammonium persulfate, and aqueous hydrogen peroxide], etc. Two or more of these may be used in combination.

[0051] The polymerization temperature varies depending on the type of initiator used, but is preferably from -10°C to 100°C, more preferably from -10°C to 80°C, from the viewpoint of increasing the degree of polymerization of the polymer.

[0052] The amount of the initiator is not particularly limited, but is preferably 0.000001 to 3.0% by weight, more preferably 0.000001 to 0.5% by weight, based on the total weight of the vinyl monomers (a1) and (a2), from the viewpoint of increasing the degree of polymerization of the polymer.

[0053] In the case of aqueous solution polymerization, the polymerization concentration (wt%) of the monomer varies depending on other polymerization conditions. However, when the polymerization concentration of acrylic acid (a1) is increased, pseudo-crosslinking (self-crosslinking) of the monomer itself tends to occur in parallel with the polymerization reaction, resulting in a decrease in the absorption amount and a decrease in the average polymerization degree of the polymer. In addition, it is difficult to control the temperature during polymerization, which tends to result in a decrease in the average polymerization degree of the polymer and an increase in oligomer components. Therefore, the polymerization concentration is preferably 10 to 40 wt%, more preferably 10 to 30 wt%. The polymerization temperature is preferably -10 to 100°C, more preferably -10 to 80°C. The amount of dissolved oxygen during polymerization depends on the amount of radical initiator added, etc., but is preferably 0 to 2 ppm (2 x 10 －４ % by weight or less), and more preferably 0 to 0.5 ppm (0.5 × 10 －４ Within these ranges, a crosslinked polymer (A) with a high degree of polymerization can be produced.

[0054] The degree of neutralization of the acrylic acid (a1) and 2-carboxyethyl acrylate (a2) during polymerization is not particularly limited as long as a predetermined amount of crosslinking agent (b) can be completely dissolved in the aqueous monomer solution. However, the crosslinking agent (b2) that does not hydrolyze in an alkaline environment is poorer in water solubility than the crosslinking agent (b1) that can be hydrolyzed in an alkaline environment, and in particular has extremely low solubility in an aqueous acrylic acid (salt) solution, so that even if a predetermined amount of (b2) is added, (b2) may separate from the aqueous monomer solution and fail to achieve the desired crosslinking. Therefore, it is preferable to carry out the polymerization with a degree of neutralization of 0 to 30 mol % for the acrylic acid (a1) and 2-carboxyethyl acrylate (a2) during polymerization, and if necessary, further neutralize after polymerization. It is more preferable to polymerize in an unneutralized state and then, if necessary, neutralize after polymerization.

[0055] Furthermore, when acrylic acid is polymerized under the same conditions, the degree of polymerization is more likely to increase when the degree of neutralization is low. Therefore, in order to increase the degree of polymerization of the polymer, it is preferable to carry out the polymerization in a state where the degree of neutralization is low.

[0056] Inverse phase suspension polymerization is a polymerization method in which an aqueous solution of acrylic acid (salt) is suspended and dispersed in a hydrophobic organic solvent such as hexane, toluene, xylene, etc. in the presence of a dispersant, and polymerized. In this polymerization method, the monomer concentration in the aqueous monomer solution is preferably 10 to 40% by weight, more preferably 10 to 30% by weight, as described above. Within this range, a crosslinked polymer (A) with a high degree of polymerization can be produced.

[0057] In this reversed-phase suspension polymerization method, a dispersant may be used during polymerization. Examples of dispersants include surfactants such as sorbitan fatty acid esters (e.g., sorbitan monostearate) having an HLB value of 3 to 8, glycerin fatty acid esters (e.g., glycerin monostearate), and sucrose fatty acid esters (e.g., sucrose distearate); and polymer dispersants (hydrophilic group: 0.1 to 20% by weight, weight-average molecular weight: 1,000 to 1,000,000) that have a hydrophilic group in the molecule and are soluble in a solvent for dispersing the aqueous monomer solution, such as maleated ethylene / acrylic acid copolymer, maleated ethylene / vinyl acetate copolymer, and styrene sulfonic acid (salt) / styrene copolymer. However, it is preferable to use a polymer dispersant as the dispersant, since it is easier to adjust the size of suspended particles of the aqueous monomer solution in the solvent, and it is possible to prepare a hydrogel of the crosslinked polymer (A) having the required particle size.

[0058] From the viewpoint of the discharge characteristics of alkaline batteries, the amount of the dispersant added is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, based on the weight of the hydrophobic organic solvent.

[0059] The weight ratio (W / O ratio) of the aqueous monomer solution to the hydrophobic organic solvent in the reversed-phase suspension polymerization is preferably 0.1 to 2.0, more preferably 0.3 to 1.0. Within these ranges, the particle size of the crosslinked polymer (A) can be more easily adjusted.

[0060] In producing the crosslinked polymer (A), it is further preferred to carry out polymerization under conditions such that the average degree of polymerization of the polymer produced under the same conditions except that no crosslinking agent is used is preferably 5,000 to 1,000,000, more preferably 10,000 to 1,000,000.

[0061] When polymerization is carried out under conditions that result in an average degree of polymerization of 5,000 or more, the use of an appropriate amount of crosslinking agent can prevent a decrease in viscosity and / or an increase in spinnability of a high-concentration alkaline aqueous solution to which a gelling agent has been added. The average degree of polymerization was measured by gel permeation chromatography (GPC).

[0062] In the present invention, the crosslinked polymer (A) obtained by aqueous solution polymerization or reversed-phase suspension polymerization is obtained as a gel containing water (aqueous gel). The aqueous gel is used as a gelling agent after drying.

[0063] Examples of methods for drying the hydrogel include, in the case of aqueous solution polymerization, using a meat chopper or cutter-type coarse crusher to break down the hydrogel to a certain degree (the level of break down is about 0.5 to 20 mm square) or to form noodles, and then neutralizing the hydrogel by adding an alkali metal hydroxide or the like, followed by air drying (layering the hydrogel on a punched metal or screen and forcibly passing hot air at 50 to 150°C through it to dry it, etc.) and air drying (placing the hydrogel in a container and drying it by passing and circulating hot air through it, and then drying the gel while further breaking it down into smaller pieces using a machine such as a rotary kiln). Of these, air drying is preferred because it allows for efficient drying in a short time.

[0064] On the other hand, in the case of reversed-phase suspension polymerization, the method for drying the hydrogel is generally to separate the polymerized hydrogel and the organic solvent into a solid and a liquid by a method such as decantation, followed by drying under reduced pressure (degree of vacuum: about 100 to 50,000 Pa) or drying by ventilation.

[0065] Other methods for drying hydrogels in aqueous solution polymerization include contact drying, in which the hydrogel is compressed and stretched on a drum dryer and dried. However, because hydrogels have poor thermal conductivity, it is necessary to form a thin film of hydrogel on a drum or other surface for drying. However, commercially available drum dryers are generally made of metals with lower ionization tendency than zinc, such as iron, chromium, and nickel, resulting in extremely high contact frequency with the metal drum surface per hydrogel. Furthermore, because the hydrogel is a hydrogel of poly(meth)acrylic acid (salt), the content of metal elements with lower ionization tendency than zinc that dissolves in the gel is high. Furthermore, because the hydrogel comes into contact with the drum very frequently and is highly adhesive, it is necessary to use a knife or similar tool to contact the drum dryer to remove the dried product from the drum dryer. However, mechanical wear of the drum and knife causes wear on the metal surfaces of the drum or knife, resulting in metal contamination in the dried product. As described above, when a contact drying method such as a drum dryer is used, metal ions or metal powders are likely to be mixed into the gelling agent, resulting in the gelling agent containing a significant amount of ions or metal powders of metals with a lower ionization tendency than zinc (metals with a lower standard electrode potential than zinc, which can be represented by atomic symbols such as Cr, Fe, Ni, Sn, Pb, Cu, Hg, and Ag). When these gelling agents are used as gelling agents for alkaline batteries, the zinc powder in the battery forms a battery with the metal ions or metal powder with a lower ionization tendency than zinc, generating hydrogen gas through electrolysis, which increases the pressure inside the battery and may even cause the alkaline electrolyte to leak or, in severe cases, damage to the battery. Furthermore, when a hydrogel is compressed, stretched, or dried on a drum dryer or the like, the dried thin film-like material remains scaly even after subsequent pulverization to adjust the particle size of the dried material to the desired particle size, and is therefore much weaker in strength than pulverized block-shaped dried material obtained by the air drying method or through-air drying method.When the swollen gel is swelled in a high-concentration alkaline aqueous solution and mechanically stirred and mixed with zinc powder, the swollen gel is destroyed and becomes smaller. Therefore, it is preferable not to use a contact drying method such as a drum dryer.

[0066] In the present invention, the drying temperature when drying the hydrogel varies depending on the dryer used, drying time, etc., but is preferably 50 to 150°C, more preferably 80 to 130°C. If the drying temperature is 150°C or lower, the polymer is less likely to crosslink due to heat during drying, the degree of crosslinking does not increase too much due to thermal crosslinking, the absorption amount does not decrease, and the viscosity in the alkaline electrolyte does not decrease. If the drying temperature is 50°C or higher, drying does not take a long time and is efficient. The drying time also varies depending on the model of dryer used, drying temperature, etc., but is preferably 5 to 300 minutes, more preferably 5 to 120 minutes.

[0067] The dried crosslinked polymer (A) thus obtained is optionally pulverized into powder by a known method, for example, an impact pulverizer (e.g., a pin mill, a cutter mill, a skillel mill, an ACM pulverizer) or an air pulverizer (e.g., a jet pulverizer).

[0068] The powdered crosslinked polymer (A) can be collected into a dry powder having a desired particle size using a sieving machine (such as a vibrating sieving machine or a centrifugal sieving machine) equipped with a desired screen, if necessary.

[0069] The volume average particle diameter of the gelling agent (G) in the present invention is preferably 20 to 500 μm, more preferably 30 to 170 μm, and particularly preferably 30 to 100 μm. When the volume average particle diameter is within this range, the viscosity of the alkaline electrolyte to which the gelling agent (G) has been added falls within a suitable range, improving drainage of the negative electrode material, enabling the production of batteries with stable quality, and preventing sedimentation of zinc powder in the negative electrode material, enabling the production of batteries with excellent discharge characteristics over time.

[0070] The volume average particle diameter is measured by the following method. <Method for measuring volume average particle diameter of gelling agent (G)> The gelling agent (G) of the present invention is dispersed in methanol, and the volume average particle diameter is measured using a laser diffraction particle size distribution measuring device [Microtrac (manufactured by Nikkiso Co., Ltd.)]. The volume average particle diameter of the gelling agent (G) in the examples described later was measured according to the above method.

[0071] If necessary, the crosslinked polymer (A) may be subjected to a surface crosslinking treatment by reacting it with a surface crosslinking agent.

[0072] As the surface cross-linking agent, known surface cross-linking agents, for example, the surface cross-linking agents described in JP-A No. 2003-225565, can be used. Among these surface cross-linking agents, from the viewpoint of the discharge characteristics of alkaline batteries, cross-linking agents having at least two functional groups capable of reacting with the carboxy groups of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) are preferred, polyglycidyls are more preferred, ethylene glycol diglycidyl ether and glycerin diglycidyl ether are particularly preferred, and ethylene glycol diglycidyl ether is most preferred.

[0073] The content (mol %) of the surface cross-linking agent is preferably 0.001 to 0.30, more preferably 0.005 to 0.25, and particularly preferably 0.010 to 0.20, based on the number of moles of the constituent monomer, from the viewpoint of the discharge characteristics of the alkaline battery.

[0074] As the method for the surface crosslinking reaction, known methods (for example, methods described in Japanese Patent No. 3648553, JP-A No. 2003-165883, JP-A No. 2005-75982, and JP-A No. 2005-95759) can be applied.

[0075] From the viewpoint of high-speed injection of the negative electrode material, the gelling agent (G) of the present invention preferably has a surfactant (D) near the surface of the crosslinked polymer (A). Examples of the gelling agent (G) having a surfactant (D) near the surface of the crosslinked polymer (A) include those obtained by the following methods: (1) A method in which the solid surfactant (D) is directly mixed with the crosslinked polymer (A) as is, for example, by dry blending; (2) A method in which the surfactant (D) is dispersed in water or a hydrophilic organic solvent in a slurry form and mixed with the crosslinked polymer (A); (3) A method in which the surfactant (D) is dissolved in a hydrophobic organic solvent, the crosslinked polymer (A) is impregnated with the surfactant, and the mixture is dried. Of these mixing methods, (1) is preferred from the viewpoints of ease of drying and little residual solvent.

[0076] If necessary, an additive can be added to the gelling agent (G) of the present invention at any stage (such as the polymerization step, chopping step, drying step, pulverization step, and surface crosslinking step in the process for producing the crosslinked polymer (A), and / or before or after these steps, and after the step of mixing (A) and (D)).

[0077] In the present invention, it is preferable to remove metal powder such as iron that has been mixed in using a magnetic iron remover at any stage after drying. However, even if iron is removed quite precisely using an iron remover, it is difficult to remove non-magnetic metals with the iron remover, and even with regard to magnetic metals, those contained inside the dried polymer particles or attached to the dried particles cannot be removed. Therefore, it is desirable to take sufficient care with regard to production equipment so that these metals do not get mixed in from the beginning.

[0078] In the present invention, the amount of soluble components of the crosslinked polymer (A) in a 40 wt % potassium hydroxide aqueous solution is preferably 10 to 30 wt %, more preferably 10 to 20 wt %, and particularly preferably 10 to 15 wt %, based on the weight of (A). When the amount of soluble components is within this range, the viscosity of the alkaline electrolyte to which the gelling agent (G) has been added falls within a suitable range, improving drainage of the negative electrode material, enabling the manufacture of batteries with stable quality. Furthermore, this prevents the settling of zinc powder in the negative electrode material, resulting in the production of batteries with excellent discharge characteristics over time. If the amount of soluble components exceeds 30 wt %, the alkaline electrolyte to which the gelling agent (G) has been added becomes spinnable, significantly worsening drainage of the negative electrode material and causing variations in the filling amount, resulting in unstable battery quality. If the amount of soluble components is less than 10 wt %, the viscosity of the alkaline electrolyte to which the gelling agent (G) has been added decreases, resulting in the settling of zinc powder, resulting in poor impact resistance and discharge characteristics.

[0079] The amount of soluble components of the crosslinked polymer (A) in a 40 wt% aqueous potassium hydroxide solution can be measured by the following method. <Method for measuring the amount of soluble components of (A) in a 40 wt% aqueous potassium hydroxide solution> 1 g of gelling agent (G) is precisely weighed (the weight is designated as S0), added to 250 ml of a 40 wt% aqueous potassium hydroxide solution, and stirred for 3 hours. The swollen gel is then removed using filter paper (Advantec Filter Paper No. 1 qualitative filter paper). The filtrate obtained after removing the gel is used as the soluble component extract. Approximately 25 ml of the soluble component extract obtained by the above method is placed in a 50 ml eggplant-shaped flask, and water is distilled off under reduced pressure using an evaporator. Approximately 25 ml of the extract is added to the eggplant-shaped flask, and the process of distilling off water under reduced pressure is repeated until the entire extract is distilled off. Next, the eggplant-shaped flask containing the residue is placed in a circulating air dryer at 130°C for 90 minutes, and then placed in a desiccator for 15 minutes to cool the eggplant-shaped flask to room temperature. After cooling, the weight (S1) of the residue in the eggplant-shaped flask is measured. The same procedure is performed on an equal amount of physiological saline to the extract used in the previous procedure, and the weight (S2) of the residue after cooling is measured. The weight of the residue after cooling is determined by subtracting the weight of the eggplant-shaped flask, which was measured in advance, from the weight of the eggplant-shaped flask containing the residue after cooling. Using the (S0), (S1), and (S2) obtained above, the amount of soluble component is calculated using the following formula: Amount of soluble component (%) = (S1 - S2) ÷ S0 × 100. In the examples described below, the amount of soluble component of the crosslinked polymer (A) in a 40 wt% potassium hydroxide aqueous solution was measured according to the above method.

[0080] The viscosity (N1(40)) of the gel (GA) of the gelling agent (G) of the present invention is preferably 70 to 120 Pa·s, more preferably 80 to 110 Pa·s, and particularly preferably 90 to 100 Pa·s. This range provides even better long-term discharge characteristics. Here, the gel (GA) is a gel prepared by stirring and mixing 97 parts by weight of a 40 wt % aqueous potassium hydroxide solution and 3 parts by weight of the gelling agent (G) until homogeneous, and then allowed to stand at 40°C for 24 hours. The viscosity (N1(40)) of this gel (GA) is measured by the following method. <Method for measuring the viscosity (N1(40)) of the gel (GA)> The viscosity of the gel (GA) at a measurement temperature of 40°C is measured in accordance with JIS 7117-1:1999 using a digital B-type viscometer (manufactured by TOKIMEC Corporation), and this is taken as the viscosity of the gel (GA). Rotor No. The viscosity of the gel (GA) in the examples described later was measured according to the above method.

[0081] Furthermore, the gelling agent (G) of the present invention preferably has a ratio (N1(40) / N60(40)) of the viscosity of the gel (GA) (N1(40)) to the viscosity after 59 days at 40°C (N60(40)) of 0.85 to 1.15, more preferably 0.90 to 1.10. Within this range, the zinc powder in the electrolyte is less likely to settle, resulting in even better discharge characteristics and impact resistance. The viscosity ratio (N1(40) / N60(40)) of the gel (GA) is measured by the following method. The viscosity ratio (N1(40) / N60(40)) of the gel (GA) in the examples described below was measured according to the following method. <Method for measuring the viscosity ratio (N1(40) / N60(40)) of the gel (GA)> After measuring the viscosity (N1(40)) of the gel (GA), the sample was sealed and left for a further 59 days in a thermostatic chamber at 40°C. The viscosity of the gel (GA) obtained by measuring under the same conditions as the viscosity (N1(40)) was taken as the viscosity (N60(40)) of the gel (GA) after being left for 60 days. The viscosity ratio (N1(40) / N60(40)) of the gel (GA) was calculated using the following formula: The ratio (N1(40) / N60(40)) of the viscosity (N1(40)) of the gel (GA) to the viscosity (N60(40)) after a further 59 days at 40°C: (N1(40) / N60(40)) = {viscosity(N1(40))} / {viscosity(N60(40))}

[0082] Furthermore, in the gelling agent (G) of the present invention, the ratio (N1(40) / N1(150)) of the viscosity of the gel (GA) (N1(40)) to the viscosity of the gel (GA) after temperature control at 150°C (N1(150)) is preferably 0.85 to 1.15, more preferably 0.90 to 1.10. Within this range, the zinc powder in the electrolyte solution is even less likely to settle under high temperature conditions, resulting in even better impact resistance and heat resistance. The viscosity ratio (N1(40) / N1(150)) of the gel (GA) is measured by the following method. Note that the viscosity ratio (N1(40) / N1(150)) of the gel (GA) with temperature change in the examples described below was measured according to the following method. <Method for measuring the viscosity ratio (N1(40) / N1(150)) of gel (GA)> After measuring the viscosity ratio (N1(40)) of gel (GA), the sample is sealed and regulated in a thermostatic chamber at 150°C for 10 minutes. After regulating the temperature at 150°C for 10 minutes, the temperature is regulated at 40°C for 1 hour. The viscosity of gel (GA) is measured under the same conditions as for viscosity (N1(40)), and this is taken as the viscosity (N1(150)) of gel (GA) after regulating the temperature at 150°C. The viscosity ratio (N1(40) / N1(150)) of gel (GA) is calculated using the following formula: Viscosity ratio of gel (GA) (N1(40) / N1(150)) = {viscosity(N1(40))} / {viscosity(N1(150))}

[0083] <Alkaline Battery> The alkaline battery of the present invention has a gelled negative electrode containing the gelling agent (G) and zinc powder. The alkaline battery having the gelled negative electrode containing the gelling agent (G) and zinc powder is not particularly limited, and can be applied to general alkaline batteries such as LR-20 (D alkaline battery) and LR-6 (AA alkaline battery), as well as various other alkaline batteries. Alkaline batteries generally have a structure in which a positive electrode material, a current collector, and a gelled negative electrode are sealed in an outer can, and the positive electrode material and the gelled negative electrode are separated by a separator or the like.

[0084] Examples of methods for filling an alkaline battery with a gelled negative electrode containing the gelling agent (G) and zinc powder include: (1) a method in which the gelling agent (G), an alkaline electrolyte (e.g., a high-concentration aqueous potassium hydroxide solution, optionally containing zinc oxide, etc.), zinc powder (and / or zinc alloy powder), and other additives are premixed to prepare a mixture of negative electrode materials, which is then filled into the battery's negative electrode container to form a gelled negative electrode; and (2) a method in which the gelling agent (G), zinc powder (and / or zinc alloy powder), and other additives are filled into the battery's negative electrode container, and then the container is filled with alkaline electrolyte to form a gelled negative electrode. Of the above methods, method (1) is preferred, as it allows the zinc powder to be uniformly dispersed within the battery's negative electrode container. The amount of gelling agent (G) added varies depending on the structure of the negative electrode container, the particle size of the zinc powder, and the concentration of the alkaline electrolyte, but is preferably 0.5 to 10 wt %, and more preferably 1.0 to 5.0 wt %, based on the weight of the alkaline electrolyte. When the amount added is 0.5 to 10% by weight, the viscosity of the alkaline electrolyte containing the gelling agent becomes appropriate, which prevents the zinc powder from settling and makes the handling easy.

[0085] The settling property of the zinc powder in the gelling agent (G) is preferably less than 10 mm, more preferably less than 5 mm. The settling property of the zinc powder in the gelling agent (G) is measured by the method described in the Examples.

[0086] The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereto. Unless otherwise specified, ultrapure water refers to water with an electrical conductivity of 0.06 μS / cm or less, and ion-exchanged water refers to water with an electrical conductivity of 1.0 μS / cm or less.

[0087] Example 1 249.95 g of acrylic acid, 0.05 g of 2-carboxyethyl acrylate ([(a1) / (a2)]=99.98 / 0.02), 0.55 g of pentaerythritol triallyl ether (0.22% by weight relative to the acrylic acid), 0.45 g of trimethylolpropane triacrylate (0.18% by weight relative to the acrylic acid), and 750 g of ion-exchanged water were placed in a 3-liter adiabatic polymerization vessel and mixed with stirring to prepare an aqueous acrylic acid solution, which was then cooled to 3° C. After cooling, nitrogen was passed through the aqueous acrylic acid solution at a flow rate of 5 L / min to adjust the dissolved oxygen concentration in the aqueous acrylic acid solution to 0.10 ppm or less. The dissolved oxygen concentration was measured using an oxygen concentration meter (ORBISPHERE 510, manufactured by HACH ULTRA) based on the diaphragm electrode method. After confirming that the acrylic acid aqueous solution was at 3°C, 5.0 g of a 10 wt% aqueous solution of 2,2'-azobis(2-amidinopropane) hydrochloride (manufactured by Wako Pure Chemical Industries, Ltd., product name: V-50), 5.0 g of a 1.0 wt% aqueous solution of hydrogen peroxide, 5.0 g of a 1.0 wt% aqueous solution of L-ascorbic acid, and 5.0 g of a 0.1 wt% aqueous solution of iron(III) sulfate were added as polymerization initiators to the insulated polymerization vessel while continuing to pass nitrogen through. After the addition of the polymerization initiator, nitrogen pass was continued for 25 minutes, after which the nitrogen pass was stopped and the vessel was allowed to stand for 16 hours to carry out the polymerization reaction. After the vessel was allowed to stand for 16 hours, the hydrogel obtained by the polymerization reaction was removed from the polymerization reaction vessel. The extracted hydrogel was broken down into noodle-like pieces with a thickness of 3 to 10 mm using a small meat chopper (manufactured by Royal Co., Ltd.). 250 g of 49 wt % aqueous sodium hydroxide (special grade reagent) was added to the broken down hydrogel, and the mixture was then uniformly kneaded into the hydrogel using the small meat chopper to neutralize it. The neutralized hydrogel was layered to a thickness of 5 cm on a SUS screen with a mesh size of 850 μm, and hot air at 150°C was passed through the hydrogel for 1 hour using a small air-permeable dryer (manufactured by Inoue Metals Co., Ltd.) to evaporate the water in the hydrogel, thereby obtaining a dried gel. The dried gel was pulverized using a cooking mixer, and then particles with a particle size of 75 μm (200 mesh) were collected using a sieve to obtain the gelling agent (G-1) of the present invention. The volume average particle diameter of (G-1) was 50 μm.

[0088] Example 2 A gelling agent (G-2) of the present invention was obtained by performing the same operation as in Example 1, except that the amount of acrylic acid added was 249.5 g and the amount of 2-carboxyethyl acrylate added was 0.5 g ([(a1) / (a2)]=99.8 / 0.2).

[0089] Example 3 A gelling agent (G-3) of the present invention was obtained by performing the same operation as in Example 1, except that the amount of acrylic acid added was 249 g and the amount of 2-carboxyethyl acrylate added was 1 g ([(a1) / (a2)]=99.6 / 0.4).

[0090] Example 4 A gelling agent (G-4) of the present invention was obtained by performing the same operation as in Example 1, except that the amount of acrylic acid added was 247.5 g and the amount of 2-carboxyethyl acrylate added was 2.5 g ([(a1) / (a2)]=99 / 1).

[0091] Example 5 A gelling agent (G-5) of the present invention was obtained by carrying out the same operations as in Example 1, except that in Example 2, 250 g of a 49 wt % aqueous solution of sodium hydroxide (special reagent grade) was added, and the resulting solution was uniformly kneaded into the hydrogel using the small meat chopper to neutralize it, and then 0.5 g of sucrose stearate (HLB: 7) was further added, and the resulting solution was uniformly kneaded into the hydrogel using the small meat chopper.

[0092] Example 6 The same procedure as in Example 2 was carried out, except that particles having a particle size passing through a sieve of 30 μm (500 mesh) were collected, to obtain a gelling agent (G-6) of the present invention. The volume average particle size of (G-6) was 10 μm.

[0093] Comparative Example 1 A comparative gelling agent (H-1) was obtained by carrying out the same procedure as in Example 1, except that 2-carboxyethyl acrylate was not added and the amount of acrylic acid added was 250 g.

[0094] Comparative Example 2 A comparative gelling agent (H-2) was obtained by performing the same operation as in Example 1, except that the amount of acrylic acid added was 245 g and the amount of 2-carboxyethyl acrylate added was 5 g ([(a1) / (a2)]=98 / 2).

[0095] The volume average particle size, the amount of soluble components, and the viscosity of the gel (GA) of the gelling agents (G-1) to (G-6) produced in Examples 1 to 6 and the comparative gelling agents (H-1) and (H-2) produced in Comparative Examples 1 and 2 were measured by the above-mentioned methods. The results are shown in Table 1 together with the weight ratio [(a1) / (a2)] of acrylic acid (salt) (a1) to 2-carboxyethyl acrylate (salt) (a2).

[0096]

[0097] Furthermore, the settling properties of zinc powder and the variation in the injection amount were measured using the gelling agents (G-1) to (G-6) of the present invention and the comparative gelling agents (H-1) and (H-2) by the following methods. The results are shown in Table 2.

[0098] (1) Sedimentation of Zinc Powder In a 1-liter twin-screw kneader (manufactured by Irie Shokai, product name: PNV-1), 150 g of 40 wt% potassium hydroxide aqueous solution, 300 g of zinc powder (manufactured by UNION MINIERES.A.) with a volume average particle size of 200 μm, and 3.0 g of gelling agent were added and mixed at a rotation speed of 50 rpm for 60 minutes to prepare a negative electrode material. 50 g of the prepared negative electrode material was placed in a sealable 50 ml sample bottle (diameter 34 mm, height 77 mm, made of polypropylene), and air bubbles that had entered during mixing were degassed under reduced pressure. The sample bottle was sealed and left in a thermostatic bath at 40 ° C. for 60 days. After that, the sample bottle was tapped 300 times at a rate of 30 times / min from a height of 3 cm using a device attached to a powder tester (manufactured by Hosokawa Micron Corporation) to promote the sedimentation of the zinc powder. After tapping was completed, the maximum settling distance (mm) of the zinc powder from the initial position of the zinc powder (the position of the top end of the negative electrode material in the sample bottle) was measured and defined as the settling property (mm) of the zinc powder. The settling property of the zinc powder was evaluated according to the following evaluation criteria. <Evaluation criteria> ⊚: Less than 5.0 mm ◯: 5.0 mm or more and less than 10.0 mm ×: 10.0 mm or more

[0099] (2) Variation in Injection Amount 150 g of 40 wt% potassium hydroxide aqueous solution, 300 g of zinc powder (manufactured by UNION MINIERES.A.) with a volume average particle size of 200 μm, and 3.0 g of gelling agent were added to a 1-liter twin-screw kneader and mixed at a rotation speed of 50 rpm for 60 minutes to prepare a negative electrode material. The prepared negative electrode material was transferred to a beaker, and air bubbles that had entered during mixing were degassed under reduced pressure. The degassed negative electrode material was sucked into a 10 ml syringe with an injection port having an inner diameter of 2 mm and graduated in 0.1 ml increments. The syringe was pushed down 5.0 ml from the height of the mouth of a 5 ml sample bottle (inner diameter 18 mm, height 40 mm) to inject the negative electrode material into the sample bottle, and the weight of the negative electrode gel injected into the sample bottle was measured. The same procedure was repeated 20 times to calculate the standard deviation (σ) of the injection amount, which was taken as the variation in the injection amount. The variation in the injection amount was evaluated according to the following evaluation criteria. <Evaluation criteria> ◎: 0.02 or less ○: 0.03 or more and -0.10 or less ×: 0.11 or more

[0100]

[0101] The gelling agent (G) of the present invention is useful not only for cylindrical alkaline batteries but also as a gelling agent for primary and secondary alkaline batteries such as alkaline button batteries, silver oxide batteries, nickel-cadmium storage batteries, nickel-metal hydride storage batteries, etc. Furthermore, alkaline batteries using the gelling agent of the present invention are useful as alkaline batteries with improved production efficiency and safety because they have excellent impact resistance and heat resistance, excellent retention of discharge characteristics, and excellent viscosity stability of the negative electrode material.

Claims

1. A gelling agent for alkaline batteries containing a crosslinked polymer (A) whose constituent monomers are acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b), wherein the crosslinking agent (b) contains a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not hydrolyze in an alkaline environment, and the weight ratio of (a1) to (a2) [(a1) / (a2)] is 99 / 1 to 99.98 / 0.

02.

2. The gelling agent for alkaline batteries according to claim 1, wherein the amount of the crosslinked polymer (A) that is soluble in a 40% by weight aqueous potassium hydroxide solution is 10 to 30% by weight based on the weight of (A).

3. The gelling agent for alkaline batteries according to claim 1 or 2, which is prepared by stirring and mixing 97 parts by weight of a 40 wt % aqueous potassium hydroxide solution and 3 parts by weight of the gelling agent for alkaline batteries until homogeneous, and after leaving it at 40°C for 24 hours, the viscosity (N1(40)) of the gel (GA) is 70 to 120 Pa s.

4. The gelling agent for alkaline batteries according to any one of claims 1 to 3, which is prepared by stirring and mixing 97 parts by weight of a 40% by weight aqueous potassium hydroxide solution and 3 parts by weight of the gelling agent for alkaline batteries until homogeneous, and in which the ratio (N1(40)) of the viscosity of the gel (GA) after standing at 40°C for 24 hours to the viscosity (N60(40)) after 59 days at 40°C is 0.85 to 1.15 (N1(40) / N60(40)).

5. The gelling agent for alkaline batteries according to any one of claims 1 to 4, which is prepared by stirring and mixing 97 parts by weight of a 40 wt% aqueous potassium hydroxide solution and 3 parts by weight of the gelling agent for alkaline batteries until homogeneous, and in which the ratio (N1(40) / N1(150)) of the viscosity of the gel (GA) after standing at 40°C for 24 hours to the viscosity (N1(150)) of the gel (GA) after temperature adjustment at 150°C is 0.85 to 1.

15.

6. The gelling agent for alkaline batteries according to any one of claims 1 to 5, further comprising a surfactant (D) having an HLB of 1 to 12.

7. The gelling agent for alkaline batteries according to claim 6, wherein the surfactant (D) is at least one selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters and fatty acid amides.

8. An alkaline battery having a gelled negative electrode containing zinc powder and a gelling agent for alkaline batteries, the gelling agent comprising a crosslinked polymer (A) having constituent monomers of acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b), the crosslinking agent (b) comprising a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not hydrolyze in an alkaline environment, the weight ratio of (a1) to (a2) [(a1) / (a2)] being 99 / 1 to 99.98 / 0.

02.

9. The alkaline battery according to claim 8, wherein the zinc powder in the gelling agent for alkaline batteries has a sedimentation property of less than 10.0 mm.

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