Gel for alkaline battery

Abstract

Provided are: a gel for alkaline batteries, which has excellent impact resistance and can maintain long-term discharge characteristics (discharge amount and discharge time); and an alkaline battery using the same. A gel for alkaline batteries, which contains a cross-linked polymer (A) that comprises, as constituent monomers, acrylic acid (salt) (a1), acrylic acid-2-carboxyethyl ester (salt) (a2), and a cross-linking agent (b), the cross-linking agent (b) comprising a cross-linking agent (b1) that is hydrolyzable under alkaline conditions and a cross-linking agent (b2) that is not hydrolyzable under alkaline conditions, the weight ratio of (a1) to (a2) [(a1) / (a2)] being 99 / 1 to 99.98 / 0.02.

Description

Technical Field

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

[0002] Conventionally, the negative electrode of an alkaline battery mainly uses a mixture of a high-concentration alkaline electrolyte (an aqueous solution of high-concentration potassium hydroxide, a solution containing zinc oxide or the like as needed), zinc powder, and / or zinc alloy powder. From the viewpoints of preventing the sedimentation of zinc powder in the alkaline electrolyte, preventing liquid leakage from the battery, and improving the production efficiency of the battery, for the purpose of suppressing drawability, a scheme has been proposed to use a water-absorbing resin obtained by insolubilizing poly(meth)acrylic acid and its salts with a crosslinking agent as a thickening agent (Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-34379 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention

[0007] However, in recent years, alkaline batteries have been required to have further high performance. The alkaline batteries using these gelling agents containing water-absorbing resins cannot be said to have sufficient anti-sedimentation properties of zinc powder and the like in the alkaline electrolyte, and may not be able to satisfy the requirements in terms of maintaining the long-term discharge characteristics (discharge capacity and discharge time) and impact resistance of the battery. In addition, when a strong impact is applied to the alkaline battery or in the case of accidental short-circuit, a large current flows through the battery and generates heat, resulting in a decrease in discharge characteristics. Therefore, it may not be able to satisfy the requirements from the viewpoint of heat resistance.

[0008] Therefore, an object of the present invention is to provide a gelling agent for alkaline batteries and an alkaline battery using the same, which are excellent in maintaining long-term discharge characteristics (discharge capacity and discharge time), impact resistance, and heat resistance.

[0009] Technical Solution for Solving the Technical Problem

[0010] The inventors of the present invention have conducted in-depth research to solve the above technical problems and as a result, completed the present invention. That is, the present invention is a gelling agent for alkaline batteries, which contains a crosslinked polymer (A) having acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b) as constituent monomers, the crosslinking agent (b) includes a crosslinking agent (b1) that can be hydrolyzed under alkaline conditions and a crosslinking agent (b2) that cannot be hydrolyzed under alkaline conditions, and the weight ratio [(a1) / (a2)] of (a1) to (a2) is 99 / 1 to 99.98 / 0.02.

[0011] Advantages of the Invention

[0012] The gelling agent for alkaline batteries and the alkaline battery of the present invention exhibit the following effects.

[0013] (1) Since the gelling agent for alkaline batteries of the present invention has excellent anti-settling properties for zinc powder and the like in the negative electrode material, when used in alkaline batteries, it is possible to manufacture batteries with a small amount and a long discharge duration and extremely excellent impact resistance.

[0014] (2) The negative electrode material added with the gelling agent for alkaline batteries of the present invention has a small viscosity change during heating, so it is possible to manufacture batteries with extremely excellent impact resistance, heat resistance and high safety.

[0015] (3) The viscosity of the negative electrode material added with the gelling agent for alkaline batteries of the present invention is in an appropriate range during filling, and the liquid breakage of the negative electrode material is good. As a result, the deviation of the filling amount of the negative electrode material per battery is small. Therefore, even in mass production, it is possible to produce batteries with uniform quality. In addition, even in small-sized batteries, the negative electrode material can be filled uniformly and at high speed, so it is possible to manufacture batteries with uniform quality. Detailed implementation mode

[0016] <Gelling agent for alkaline batteries>

[0017] The gelling agent (G) for alkaline batteries of the present invention contains a crosslinked polymer (A) composed of acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2) and a crosslinking agent (b). The crosslinking agent (b) includes a crosslinking agent (b1) that can be hydrolyzed by an alkali and a crosslinking agent (b2) that cannot be hydrolyzed by an alkali. The weight ratio [(a1) / (a2)] of (a1) to (a2) is 99 / 1 to 99.98 / 0.02.

[0018] In the present invention, "acrylic acid (salt)" means "acrylic acid" and / or "acrylate", and "2-carboxyethyl acrylate (salt)" means "2-carboxyethyl acrylate" and / or "salt of 2-carboxyethyl acrylate". As the salt, it includes alkali metal salts such as potassium, sodium, and lithium, and alkaline earth metal salts such as calcium.

[0019] The constituent monomers derived from acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) may be unneutralized bodies or neutralized bodies. In addition, from the viewpoints of reducing adhesiveness, improving dispersibility, and the operability in the manufacture of the crosslinked polymer (A), it is preferable that part or all of the crosslinked polymer (A) is neutralized.

[0020] In the case of neutralizing acrylic acid (a1) and 2-carboxyethyl acrylate (a2) contained in the crosslinked polymer (A), usually an alkali metal hydroxide such as potassium hydroxide, sodium hydroxide, 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, the crosslinking agent (b2) that does not hydrolyze under alkaline conditions lacks water solubility. Therefore, if polymerization is carried out in a state where the neutralization degree of the water-soluble vinyl monomer (a1) is high, sometimes even if a specified amount of the crosslinking agent (b2) is added, the crosslinking agent (b2) will separate from the monomer aqueous solution and the specified crosslinking cannot be carried out, and the crosslinked polymer (A) cannot be obtained. More preferably, the neutralization degree of the water-soluble vinyl monomer (a1) is set to 0 to 30 mol%, and after polymerizing while also containing the crosslinking agent (b2), an alkali metal hydroxide is added to the hydrogel as needed to adjust the neutralization degree.

[0021] The final neutralization degree {content (mol%) of the anionic base based on the total number of moles of the anionic groups and the anionic base of the anionic vinyl monomer} of the acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) in the crosslinked polymer (A) is preferably 0 to 90, more preferably 40 to 80, and particularly preferably 60 to 70. If it is in this range, the discharge characteristics, impact resistance, and heat resistance of the negative electrode material become better. It should be noted that the anionic base refers to the neutralized anionic group.

[0022] From the viewpoint of the absorption capacity of the gelling agent (G), based on the weight of the crosslinked polymer (A), the content of the acrylic acid (salt) (a1) and 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.

[0023] The weight ratio [(a1) / (a2)] of the acrylic acid (salt) (a1) to 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. When this weight ratio [(a1) / (a2)] is less than 99 / 1, the liquid breakage of the negative electrode material of the alkaline battery to which the gelling agent (G) is added deteriorates, and there is a deviation in the filling amount. When it exceeds 99.98 / 0.02, the viscosity stability of the gelling agent (G) decreases, and sedimentation of zinc powder occurs, so there is a tendency for the discharge characteristics, impact resistance, and heat resistance to deteriorate.

[0024] The crosslinked polymer (A) is crosslinked using a crosslinking agent (b). The crosslinking agent (b) includes a crosslinking agent (b1) that hydrolyzes under alkaline conditions and a crosslinking agent (b2) that does not hydrolyze under alkaline conditions.

[0025] In the present invention, (b1) and (b2) are used in combination. By using (b1) and (b2) in combination, the viscosity stability of the gelling agent (G) is further improved, the liquid separation of the alkaline electrolyte can be prevented, and thus the long-term discharge of the battery can be maintained. Furthermore, when filling the battery, it can be uniformly injected, and the deviation of the injection amount of the electrolyte for each battery also becomes smaller. It should be noted that here, the "liquid separation" of the alkaline electrolyte means that the substantially uniform mixing state of the gelling agent (G) and the alkaline electrolyte cannot be maintained, and the gelling agent (G) and the alkaline electrolyte are separated.

[0026] In the crosslinking agent (b1) that hydrolyzes in an alkaline medium, "hydrolyzes in an alkaline medium" means that in the crosslinked polymer (A), the constituent monomer derived from (b1) has a hydrolyzable bond. The hydrolyzable bond can be a bond originally possessed by the crosslinking agent (b1) in the molecule {the crosslinking agent at this time is the crosslinking agent (b11) having a hydrolyzable bond in the molecule}, or a hydrolyzable bond obtained by hydrolyzing a bond formed by a crosslinking reaction with other monomers {(a1) or (a2)} constituting the crosslinked polymer (A) {the bond formed by the crosslinking reaction of the crosslinking agent at this time is used as the hydrolyzable crosslinking agent (b12)}. Examples of the hydrolyzable bond include an ester bond and an amide bond.

[0027] 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 polyglycerol (degree of polymerization 3 to 13) polyacrylate.

[0028] Examples of the crosslinking agent (b12) in which the bond formed by the crosslinking reaction is hydrolyzable 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 polyol compounds (glycerol, etc.). The reactive crosslinking agent can react with (meth)acrylic acid (salt) to form an ester bond or an amide bond.

[0029] Among the crosslinking agents (b1) that hydrolyze under alkaline conditions, from the perspective of the viscosity stability of the negative electrode material to which the gelling agent (G) is added, polyacrylamide compounds and polyacrylate compounds are preferred, N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate are further preferred, N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethylene glycol diglycidyl ether are particularly further preferred, and N,N'-methylenebisacrylamide and trimethylolpropane tri(meth)acrylate are most preferred.

[0030] The crosslinking agent (b2) that does not hydrolyze under alkaline conditions is a crosslinking agent that does not have a hydrolyzable bond in the molecule and does not generate a hydrolyzable bond due to the crosslinking reaction. As such a crosslinking agent (b2), crosslinking agents (b21) having two or more vinyl ether bonds and crosslinking agents (b22) having two or more allyl ether bonds can be cited. From the perspective of reactivity and the like, a crosslinking agent having two or more allyl ether bonds is preferred.

[0031] As the crosslinking agent (b21) having two or more vinyl ether bonds, the following can be cited: 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 polyglycerol (degree of polymerization 3 to 13) polyvinyl ether, etc.

[0032] As the crosslinking agent (b22) having two or more allyl ether bonds, the following can be cited: a crosslinking agent (b221) having two allyls in the molecule and no hydroxyl group, a crosslinking agent (b222) having two allyls in the molecule and 1 to 5 hydroxyl groups, a crosslinking agent (b223) having 3 to 10 allyls in the molecule and no hydroxyl group, a crosslinking agent (b224) having 3 to 10 allyls in the molecule and 1 to 3 hydroxyl groups, etc. When the molecule contains a hydroxyl group, the compatibility with the vinyl monomer (a1) and / or (a2) {especially (meth)acrylic acid (salt)} is good, the uniformity of crosslinking increases, the performance of the gelling agent (G) improves, and the long-term stability of the viscosity of the negative electrode material containing the gelling agent (G) is further excellent.

[0033] As the crosslinking agent (b221) having two allyls in the molecule and no hydroxyl group, the following can be cited: 1,4-cyclohexanedimethanol diallyl ether, alkylene (2 to 5 carbon atoms) glycol diallyl ether, and polyalkylene (2 to 6 carbon atoms) glycol (weight average molecular weight: 100 to 4000) diallyl ether, etc.

[0034] As the crosslinking agent (b222) having two allyl groups and 1 to 5 hydroxyl groups in the molecule, examples thereof include glycerol diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, polyglycerol (degree of polymerization 2 to 5) diallyl ether, and the like.

[0035] As the crosslinking agent (b223) having 3 to 10 allyl groups and no hydroxyl groups in the molecule, examples thereof include trimethylolpropane triallyl ether, glycerol triallyl ether, pentaerythritol tetraallyl ether, tetraallyloxyethane, and the like.

[0036] As the crosslinking agent (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule, examples thereof include pentaerythritol triallyl ether, diglycerol triallyl ether, sorbitol triallyl ether, polyglycerol (degree of polymerization 3 to 13) polyallyl ether, and the like.

[0037] Two or more kinds of crosslinking agents (b2) that are not hydrolyzed under alkaline conditions can be used in combination.

[0038] Among the crosslinking agents (b2), crosslinking agents (b22) having two or more allyl ether bonds are preferred, crosslinking agents {(b222) and (b224)} having 1 to 5 hydroxyl groups and 2 to 10 allyl groups are more preferred, crosslinking agents (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule are particularly preferred, and pentaerythritol triallyl ether, diglycerol triallyl ether, and sorbitol triallyl ether are most preferred. When these crosslinking agents are used, the compatibility with the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) that becomes (a1) by hydrolysis is good, and efficient crosslinking can be carried out, so they are preferred.

[0039] The content of the crosslinking agent (b1) that is hydrolyzed under alkaline conditions in the crosslinked polymer (A) of the present invention also depends on the type and average degree of polymerization of the crosslinking agent (b1). Based on the weight of the crosslinked polymer (A), it is preferably 0.05 to 1% by weight, more preferably 0.1 to 0.8% by weight, and particularly preferably 0.1 to 0.5% by weight. If it is within this range, excessive liquid removal of the alkaline electrolyte can be prevented, and thus the long-term discharge characteristics of the battery are further excellent.

[0040] The content of the crosslinking agent (b2) that is not hydrolyzed under alkaline conditions in the crosslinked polymer (A) also depends on the type of the crosslinking agent (b2). Based on the weight of the crosslinked polymer (A), it is preferably 0.05 to 1% by weight, more preferably 0.05 to 0.5% by weight, and particularly preferably 0.1 to 0.3% by weight. If it is within this range, the long-term discharge characteristics of the battery are further excellent.

[0041] The weight ratio [(b1) / (b2)] of the crosslinking agent (b1) to the crosslinking agent (b2) in the crosslinked polymer (A) is preferably 1.5 to 5, more preferably 1.7 to 4, and particularly preferably 1.9 to 3. If it is within this range, excessive liquid separation of the alkaline electrolyte can be prevented, and thus the long-term discharge characteristics of the battery are further excellent.

[0042] The total content of the crosslinking agent (b1) and the crosslinking agent (b2) is preferably 0.10 to 2.0% by weight, more preferably 0.30 to 1.0% by weight, and particularly preferably 0.40 to 0.8% by weight based on the weight of the crosslinked polymer (A). If it is within this range, excessive liquid separation of the alkaline electrolyte can be prevented, and thus the long-term discharge characteristics of the battery are further excellent. In addition, the stability of the gelling agent (G) is improved, and the long-term stability and temperature stability of the viscosity of the alkaline electrolyte containing the gelling agent (G) are further excellent.

[0043] 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 indicating the balance between hydrophilicity and lipophilicity, and can be calculated, 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], from the ratio of the organic value to the inorganic value of the organic compound.

[0044] HLB = 10 × inorganicity / organicity

[0045] Regarding the organic value and inorganic value used for deriving the HLB, the values in the table described on page 213 of the above-mentioned "Introduction to Surfactants" can be used for calculation.

[0046] As the surfactant (D), it includes an ionic surfactant and a non-ionic surfactant.

[0047] As the ionic surfactant, it includes known anionic surfactants, amphoteric surfactants, and cationic surfactants. Specifically, examples include the ionic surfactants described in WO99 / 03577 pamphlet, WO2002 / 005949 pamphlet, and USP4331447 specification.

[0048] As the surfactant (D), from the viewpoints of the viscosity of the gel and the high-speed injectability of the negative electrode material, a non-ionic surfactant is preferred.

[0049] Nonionic surfactants do not exhibit ionic properties even when dissolved in water, but show surface activity. In the present invention, the nonionic surfactant is not particularly limited, and from the viewpoints of the viscosity of the gel and the high-speed injectability of the negative electrode material, at least one selected from sucrose fatty acid esters, sorbitan fatty acid esters, glycerol fatty acid esters, and fatty acid amides is preferred.

[0050] As the sucrose fatty acid ester, it includes sucrose fatty acid esters in which fatty acids having 8 to 22 carbon atoms are ester-bonded to sucrose. Specifically, sucrose stearate can be cited [for example, sucrose stearate manufactured by Daiichi Kogyo Seiyaku Co., Ltd. {DKESTER F-50 (HLB = 6), F-70 (HLB = 8), and F-110 (HLB = 11), etc.}, sucrose stearate manufactured by Mitsubishi Chemical Foods Co., Ltd. {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), etc.}, etc.].

[0051] As the sorbitan fatty acid ester, it includes sorbitan fatty acid esters in which fatty acids having 8 to 22 carbon atoms are ester-bonded to sorbitol. Specifically, sorbitan palmitate can be cited [sorbitan palmitate manufactured by Kao Corporation {RHEODOL SP-P10 (HLB = 6.7), etc.} and sorbitan palmitate manufactured by Riken Vitamin Co., Ltd. {RIKEMAL P-300 (HLB = 5.6), etc.}, etc.].

[0052] As the glycerol fatty acid ester, it includes glycerol fatty acid esters in which fatty acids having 8 to 22 carbon atoms are ester-bonded to glycerol and / or polymers of glycerol (degree of polymerization 2 to 20). Specifically, diglycerol monolaurate can be cited [diglycerol monolaurate manufactured by Riken Vitamin Co., Ltd. {POEM DL-100 (HLB = 9.4), etc.}, etc.], diglycerol monomyristate [diglycerol monomyristate manufactured by Riken Vitamin Co., Ltd. {POEM DM-100 (HLB = 8.7), etc.}, etc.], diglycerol monostearate [diglycerol monostearate manufactured by Riken Vitamin Co., Ltd. {POEM DS-100A (HLB = 7.7), etc.}, etc.], diglycerol monooleate [diglycerol monooleate manufactured by Riken Vitamin Co., Ltd. {POEM DO-100V (HLB = 7.3), RIKEMALDO-100 (HLB = 7.4), etc.}, etc.], decaglycerol stearate [decaglycerol stearate manufactured by Riken Vitamin Co., Ltd. {POEMJ-0081HV (HLB = 12), POEM J-0381V (HLB = 12), etc.}, etc.].

[0053] As the fatty acid amide, it includes a fatty acid amide formed by amide-bonding a fatty acid having 8 to 22 carbon atoms with ethanolamine. Specifically, examples include coconut oil fatty acid monoethanolamide [coconut oil fatty acid monoethanolamide manufactured by Sanyo Chemical Industries, Ltd. {PROFAN AB-20 (HLB = 11), etc.}], stearic acid monoethanolamide [stearic acid monoethanolamide manufactured by Sanyo Chemical Industries, Ltd. {PROFAN SME (HLB = 10), etc.}], and the like.

[0054] From the viewpoints of the high-speed injectability of the negative electrode material and the dehydration shrinkage of the negative electrode material, the HLB of the surfactant (D) is preferably 1 to 12, more preferably 3 to 11, and particularly preferably 5 to 9.

[0055] In addition, as the surfactant (D), from the viewpoints of the high-speed injectability of the negative electrode material and the dehydration shrinkage of the negative electrode material, a nonionic surfactant is preferred, and more preferably at least one selected from sucrose fatty acid esters, sorbitan fatty acid esters, glycerol fatty acid esters, and fatty acid amides.

[0056] In the gelling agent (G) of the present invention, based on the weight of the crosslinked polymer (A), from the viewpoints of the high-speed injectability of the negative electrode material and the dehydration shrinkage of the negative electrode material, 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.

[0057] When the shape of the surfactant (D) is powdery, the particle size of the surfactant is not particularly limited. From the viewpoint of dry blending property in the crosslinked polymer (A), 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.

[0058] Next, a method for manufacturing the gelling agent (G) for an alkaline battery of the present invention will be described.

[0059] As the polymerization method for obtaining the crosslinked polymer (A), known polymerization methods can be applied. For example, it can be any one of aqueous solution polymerization, suspension polymerization, bulk polymerization, inverse suspension polymerization, or emulsion polymerization.

[0060] Among these polymerization methods, aqueous solution polymerization, suspension polymerization, inverse suspension polymerization, and emulsion polymerization are preferred. Further preferred are aqueous solution polymerization, inverse suspension polymerization, and emulsion polymerization. Particularly preferred are aqueous solution polymerization and inverse suspension polymerization, and most preferred is aqueous solution polymerization. These polymerizations can use well-known polymerization initiators, chain transfer agents, and / or solvents, etc. Most preferably, it is an aqueous solution polymerization method in which a crosslinking agent (b) is added to and dissolved in a monomer aqueous solution mainly composed of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) for polymerization, and a so-called inverse suspension polymerization method in which the same monomer aqueous solution is dispersed and suspended in a hydrophobic organic solvent (such as hexane, toluene, xylene, etc.) in the presence of a dispersant for polymerization. If these polymerization methods are used, a gelling agent with excellent discharge characteristics, impact resistance, and heat resistance can be obtained.

[0061] The method of polymerizing acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) by the aqueous solution polymerization method or the inverse suspension polymerization method can be a well-known method. For example, a method of polymerization using a radical polymerization initiator, a method of irradiating radiation, ultraviolet rays, electron beams, etc. can be cited.

[0062] In the case of using a radical polymerization initiator, examples of such initiators 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-tert-butyl peroxide, cumene hydroperoxide, etc.], redox initiators [combinations of reducing agents such as sulfites or bisulfites of alkali metal salts, ammonium sulfite, ammonium bisulfite, L-ascorbic acid, etc. and peroxides such as persulfates of alkali metal salts, ammonium persulfate, hydrogen peroxide water, etc.]. Two or more of them can be used in combination.

[0063] The polymerization temperature varies depending on the type of initiator used, etc. From the viewpoint of increasing the degree of polymerization of the polymer, it is preferably -10°C to 100°C, more preferably -10°C to 80°C.

[0064] Regarding the amount of the initiator, there is no particular limitation either. From the viewpoint of increasing the degree of polymerization of the polymer, it is preferably 0.000001 to 3.0% by weight, more preferably 0.000001 to 0.5% by weight, relative to the total weight of the vinyl monomers (a1) and (a2).

[0065] In the case of aqueous solution polymerization, the polymerization concentration (wt%) of the monomer varies depending on other polymerization conditions. In the case of acrylic acid (a1), if the polymerization concentration is increased, pseudo-crosslinking (self-crosslinking) of the monomer itself is likely to occur in parallel with the polymerization reaction, resulting in a decrease in the absorption amount and a decrease in the average degree of polymerization of the polymer. In addition, it is difficult to control the temperature during polymerization, which is likely to lead to a decrease in the average degree of polymerization of the polymer and an increase in the oligomer component. Therefore, the polymerization concentration is preferably 10 to 40 wt%, more preferably 10 to 30 wt%. In addition, regarding the polymerization temperature, it is preferably -10 to 100 °C, more preferably -10 to 80 °C. Regarding the dissolved oxygen amount during polymerization, although it also depends on the addition amount of the radical initiator, etc., it is preferably 0 to 2 ppm (2×10 -4 wt% or less), more preferably 0 to 0.5 ppm (0.5×10 -4 wt% or less). If it is within these ranges, a crosslinked polymer (A) with a high degree of polymerization can be produced.

[0066] Regarding the neutralization degree of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) during polymerization, there is no particular limitation as long as a specified amount of crosslinking agent (b) can be completely dissolved in the monomer aqueous solution. However, compared with the crosslinking agent (b1) that can be hydrolyzed under alkaline conditions, the crosslinking agent (b2) that is not hydrolyzed under alkaline conditions has poor water solubility. In addition, especially for the solubility of the aqueous solution of acrylic acid (salt), it is extremely low. Even if a specified amount of (b2) is added, (b2) sometimes separates from the monomer aqueous solution and the specified crosslinking cannot be carried out. Therefore, the neutralization degree of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) during polymerization is preferably polymerized at 0 to 30 mol%, and if necessary, further neutralized after polymerization. More preferably, it is polymerized in an unneutralized state and then neutralized as needed after polymerization.

[0067] In addition, in the case of polymerizing acrylic acid under the same conditions, the degree of polymerization is likely to increase when the neutralization degree is low. Therefore, in order to increase the degree of polymerization of the polymer, it is also preferably polymerized in a state of low neutralization degree.

[0068] Regarding the inverse suspension polymerization method, it is a polymerization method in which an aqueous solution of acrylic acid (salt) is suspended and dispersed in the presence of a dispersant in a hydrophobic organic solvent represented by hexane, toluene, xylene, etc. In this polymerization method, as in the above, the monomer concentration in the monomer aqueous solution is preferably 10 to 40 wt%, more preferably 10 to 30 wt%. If it is within this range, a crosslinked polymer (A) with a high degree of polymerization can be produced.

[0069] It should be noted that regarding this inverse suspension polymerization method, a dispersant can be used during polymerization. Examples of the dispersant include sorbitan fatty acid esters such as sorbitan monostearate with an HLB value of 3 to 8, glycerol fatty acid esters such as glycerol monostearate, and sucrose fatty acid esters such as sucrose distearate; maleated ethylene / acrylic acid copolymers, maleated ethylene / vinyl acetate copolymers, styrene sulfonic acid (salt) / styrene copolymers, etc., which are polymer dispersants having a hydrophilic group in the molecule and soluble in a solvent capable of dispersing the aqueous monomer solution (hydrophilic group: 0.1 to 20% by weight, weight average molecular weight: 1000 to 1000000). When using a polymer dispersant as the dispersant, it is easy to adjust the size of the suspended particles of the aqueous monomer solution in the solvent, and a hydrogel of the crosslinked polymer (A) with a desired particle size can be prepared, so it is preferred.

[0070] From the viewpoint of the discharge characteristics of the alkaline battery, the addition amount of the dispersant 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.

[0071] The weight ratio (W / O ratio) of the aqueous monomer solution to the hydrophobic organic solvent in the inverse suspension polymerization is preferably 0.1 to 2.0, more preferably 0.3 to 1.0. If it is within these ranges, the particle size of the crosslinked polymer (A) is further easily adjusted.

[0072] In the production of the crosslinked polymer (A), except for not using a crosslinking agent, it is further preferred to carry out the polymerization under the condition that the average degree of polymerization of the polymer when producing the polymer under exactly the same conditions is preferably 5000 to 1000000, more preferably 10000 to 1000000.

[0073] If the polymerization is carried out under the condition that the average degree of polymerization is 5000 or more, by using an appropriate amount of crosslinking agent, it is possible to prevent the decrease in viscosity and / or the increase in drawability of the highly concentrated alkaline aqueous solution added with the gelling agent. The above-mentioned average degree of polymerization is measured by gel permeation chromatography (GPC method).

[0074] In the present invention, the crosslinked polymer (A) obtained by aqueous solution polymerization or inverse suspension polymerization or the like is obtained in the form of a gel containing water (hydrogel). The hydrogel is used as a gelling agent after drying.

[0075] Regarding the drying method of the hydrogel, in the case of aqueous solution polymerization, the following methods can be exemplified: The hydrogel is finely divided to a certain extent (the level of fine division is about 0.5 to 20 mm square) or strip-shaped using a meat grinder or a cutting type coarse crusher. After neutralizing the hydrogel by adding alkali metal hydroxide as needed, air-permeable drying (stacking the hydrogel on a perforated metal or a sieve and drying by forcibly passing hot air at 50 to 150 °C, etc.) or air-circulation drying (placing the hydrogel in a container, drying by passing and circulating hot air, and further finely dividing the gel with a machine such as a rotary kiln while drying) and other methods are carried out. Among them, air-permeable drying can be carried out efficiently in a short time, so it is preferred.

[0076] On the other hand, for the drying method of the hydrogel during inverse suspension polymerization, generally, after solid-liquid separation of the polymerized hydrogel and the organic solvent by methods such as decantation, vacuum drying (degree of vacuum: about 100 to 50000 Pa) or air-circulation drying is carried out.

[0077] As another drying method for the hydrogel in aqueous solution polymerization, there is a contact drying method in which the hydrogel is compressed and stretched on a drum dryer and then dried. However, since the heat conductivity of the hydrogel is poor, a thin film of the hydrogel needs to be formed on the drum in order to dry it. However, the material of the commercially available drum dryer is usually formed of metals with a lower ionization tendency than zinc, such as iron, chromium, and nickel, so the frequency of each hydrogel contacting the metal surface of the drum is extremely high. In addition, the hydrogel is a hydrogel of poly (meth) acrylic acid (salt), so the content of metal elements with a lower ionization tendency than zinc dissolved in the gel increases. Furthermore, the contact frequency of the hydrogel with the drum is extremely high, and the hydrogel has high adhesion, so it is necessary to bring a knife or the like into contact with the drum dryer to peel the dried product from the drum dryer. Due to mechanical wear of the drum and the knife, the metal surface of the drum or the knife wears, and metal is mixed into the dried product. As described above, when a contact drying method such as a drum dryer is used, metal ions and metal powders are easily mixed into the gel, and a considerable amount of metal ions and metal powders having an ionization tendency lower than these zinc (metals represented by atomic symbols such as Cr, Fe, Ni, Sn, Pb, Cu, Hg, and Ag because they are metals having a lower standard electrode potential than zinc) are contained. When these gels are used as gels for alkaline batteries, zinc powder in the battery forms a cell with the metal ions or metal powders having an ionization tendency lower than zinc, so hydrogen gas is generated by electrolysis, thereby increasing the pressure inside the battery, which may cause the alkaline electrolyte to flow out, and in severe cases, cause the battery to be damaged. Furthermore, in the case of a film-like dried product obtained by compressing and stretching the hydrogel on a drum dryer or the like, even if the particle size of the dried product is adjusted to a desired particle size by pulverizing the dried product, the particles are flaky, and therefore, the strength is very weak compared to the pulverized product of a block-like dried product obtained by the air-permeable drying method or the ventilation drying method. If the hydrated gel is swollen in a high-concentration alkaline aqueous solution and mechanically stirred and mixed with zinc powder, the swollen gel is destroyed and the gel becomes smaller. Therefore, it is preferable not to use a contact drying method such as a drum dryer.

[0078] In the present invention, the drying temperature when drying the hydrogel varies depending on the dryer used, the drying time, etc., and is preferably 50 to 150°C, and more preferably 80 to 130°C. If the drying temperature is 150°C or less, the polymer is not easily crosslinked by the heat during drying, the degree of crosslinking does not increase excessively due to thermal crosslinking, the absorption amount does not decrease, and the viscosity in the alkaline electrolyte does not decrease. If it is 50°C or more, drying does not require a long time, which is effective. The drying time also varies depending on the type of dryer used and the drying temperature, and is preferably 5 to 300 minutes, and more preferably 5 to 120 minutes.

[0079] The dried crosslinked polymer (A) thus obtained is pulverized into powder as needed. The pulverization method can be a known method, for example, it can be carried out using an impact mill (pin mill, cutter mill, Skirel mill, ACM mill, etc.), an air mill (jet mill, etc.).

[0080] The pulverized crosslinked polymer (A) can be sieved using a sieve machine (vibrating sieve machine, centrifugal sieve machine, etc.) equipped with a required sieve as needed to collect dry powder of a required particle size.

[0081] In the present invention, the volume average particle diameter of the gelling agent (G) is preferably 20 to 500 μm, more preferably 30 to 170 μm, and particularly preferably 30 to 100 μm. If the volume average particle diameter is within this range, the viscosity of the alkaline electrolyte added with the gelling agent (G) becomes an appropriate range, the liquid breaking of the negative electrode material becomes good, so that a battery with stable quality can be manufactured, and the sedimentation of zinc powder in the negative electrode material can be prevented, so that a battery with excellent discharge characteristics over time can be produced.

[0082] It should be noted that the above volume average particle diameter is measured by the following method.

[0083] <Measurement method of volume average particle diameter of gelling agent (G)>

[0084] The gelling agent (G) of the present invention is dispersed in methanol and measured using a laser diffraction particle size distribution measuring device [Microtrac (manufactured by Nikkiso Co., Ltd.)]. It should be noted that the volume average particle diameter of the gelling agent (G) in the following examples is measured according to the above method.

[0085] The crosslinked polymer (A) can be reacted with a surface crosslinking agent as needed to perform surface crosslinking treatment.

[0086] As the surface crosslinking agent, known surface crosslinking agents can be used, for example, the surface crosslinking agents described in Japanese Patent Laid-Open No. 2003-225565. Among these surface crosslinking agents, from the viewpoint of the discharge characteristics of alkaline batteries, a crosslinking agent having at least two or more functional groups capable of reacting with the carboxyl groups of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) is preferred, a polyglycidyl group is more preferred, ethylene glycol diglycidyl ether and glycerol diglycidyl ether are particularly preferred, and ethylene glycol diglycidyl ether is most preferred.

[0087] From the viewpoint of the discharge characteristics of alkaline batteries, the content (mol%) of the surface crosslinking 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 monomers.

[0088] The method of surface crosslinking reaction can be applied by using publicly known methods (for example, Japanese Patent Publication No. 3648553, Japanese Unexamined Patent Application Publication No. 2003-165883, Japanese Unexamined Patent Application Publication No. 2005-75982, Japanese Unexamined Patent Application Publication No. 2005-95759).

[0089] 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 substances having a surfactant (D) near the surface of the crosslinked polymer (A) include substances obtained by the following methods.

[0090] (1) A method of directly mixing the solid surfactant (D) into the crosslinked polymer (A) by, for example, a dry mixing method;

[0091] (2) A method of dispersing the surfactant (D) in a slurry form in water or a hydrophilic organic solvent and mixing it with the crosslinked polymer (A);

[0092] (3) A method of dissolving the surfactant (D) in a hydrophobic organic solvent, impregnating the crosslinked polymer (A), and drying it.

[0093] Among these mixing methods, (1) is preferred from the viewpoints of ease of drying and less residual solvent.

[0094] In the gelling agent (G) of the present invention, additives can be added as needed at any stage (such as in the polymerization process, chopping process, drying process, pulverization process, surface crosslinking process in the manufacturing process of the crosslinked polymer (A), and / or before and after these processes, and after the process of mixing (A) and (D), etc.).

[0095] It should be noted that in the present invention, it is preferred to use a magnetic iron remover to remove mixed metal powders such as iron at any stage after drying. However, even if the iron removal is carried out quite precisely using an iron remover, it is difficult to remove non-magnetic metals using the iron remover. In addition, for magnetic metals, it is also impossible to remove the magnetic metals contained inside the dried polymer particles and the magnetic metals attached to the dried particles. Therefore, in order not to mix in these metals from the beginning, it is also desirable to fully consider the production equipment.

[0096] The amount of soluble components of the crosslinked polymer (A) in a 40 wt% aqueous potassium hydroxide 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). If the amount of soluble components is within this range, the viscosity of the alkaline electrolyte added with the gelling agent (G) is within an appropriate range, the liquid cutoff of the negative electrode material becomes good, so that a battery with stable quality can be manufactured, and the sedimentation of zinc powder in the negative electrode material can be prevented, so that a battery with excellent discharge characteristics over time can be produced. If the amount of soluble components exceeds 30 wt%, the alkaline electrolyte added with the gelling agent (G) shows drawability, the liquid cutoff of the negative electrode material deteriorates significantly, and there are deviations in the filling amount, so the quality of the battery is unstable. When the amount of soluble components is less than 10 wt%, the viscosity of the alkaline electrolyte added with the gelling agent (G) becomes low, and zinc powder settles, so the shock resistance and discharge characteristics deteriorate.

[0097] 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.

[0098] <Method for Measuring the Amount of Soluble Components of (A) in a 40 wt% Aqueous Potassium Hydroxide Solution>

[0099] Precisely weigh 1 g of the gelling agent (G) (let the precisely weighed value be S0), add it to 250 ml of a 40 wt% aqueous potassium hydroxide solution, stir for 3 hours, and then remove the swollen gel with a filter paper (Qualitative Filter Paper No. 1 manufactured by ADVANTEC). The filtrate obtained after removing the gel is used as the extract of the soluble components. Put about 25 ml of the extract of the soluble components obtained by the above method into an eggplant-shaped flask with a volume of 50 ml, and use an evaporator to distill off water under reduced pressure. Add about 25 ml of the extract to the eggplant-shaped flask, and repeat the operation of distilling off water under reduced pressure to distill off water from the total amount of the extract. Then, leave the eggplant-shaped flask containing the residue in an air-circulating dryer at 130 °C for 90 minutes, and then leave it in the dryer for 15 minutes to cool the eggplant-shaped flask to room temperature. Measure the weight (S1) of the residue in the eggplant-shaped flask after cooling. Perform the same operation on physiological saline equal in amount to the extract used in the previous operation, and measure the weight (S2) of the residue after cooling. It should be noted that the weight of the residue after cooling is obtained by subtracting the weight of the eggplant-shaped flask previously measured from the weight of the eggplant-shaped flask containing the residue after cooling. Using (S0), (S1), and (S2) obtained above, calculate the amount of soluble components by the following formula.

[0100] Amount of soluble components (%) = (S1 - S2) ÷ S0 × 100

[0101] It should be noted that the soluble component amount of the crosslinked polymer (A) in the following-described examples in a 40 wt% aqueous potassium hydroxide solution was measured according to the above method.

[0102] 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. If it is within this range, the long-term discharge characteristics are further excellent. Here, the gel (GA) 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 (G) until uniform, and is the gel after standing at 40°C for 24 hours. The viscosity (N1(40)) of this gel (GA) is measured by the following method.

[0103] <Method for Measuring the Viscosity (N1(40)) of Gel (GA)>

[0104] Using a digital B-type viscometer (manufactured by TOKIMEC), the viscosity of the gel (GA) at a measurement temperature of 40°C was measured in accordance with JIS 7117-1:1999 as the viscosity of the gel (GA). It should be noted that rotor No. 4 was used and the measurement was performed at a rotational speed of 3 rpm. It should be noted that the viscosity of the gel (GA) in the following-described examples was measured according to the above method.

[0105] In addition, the ratio (N1(40) / N60(40)) of the viscosity (N1(40)) of the gel (GA) of the gelling agent (G) of the present invention to the viscosity (N60(40)) after further 59 days at 40°C is preferably 0.85 to 1.15, more preferably 0.90 to 1.10. If it is within this range, the zinc powder in the electrolyte is further less likely to settle, and thus the discharge characteristics and shock resistance are further excellent. The viscosity ratio (N1(40) / N60(40)) of the gel (GA) is measured by the following method. It should be noted that the viscosity ratio (N1(40) / N60(40)) of the gel (GA) in the following-described examples was measured according to the following method.

[0106] <Method for Measuring the Viscosity Ratio (N1(40) / N60(40)) of Gel (GA)>

[0107] The sample after the measurement of the viscosity (N1(40)) of the gel (GA) was sealed and further placed in a thermostat at 40°C for 59 days. The viscosity of the gel (GA) measured under the same conditions as the viscosity (N1(40)) was taken as the viscosity (N60(40)) of the gel (GA) after standing for 60 days. The viscosity ratio (N1(40) / N60(40)) of the gel (GA) was calculated by the following formula.

[0108] The ratio of the viscosity of the gel (GA) (N1(40)) to the viscosity after 59 days at 40°C (N60(40)) (N1(40) / N60(40)) = {viscosity (N1(40))} / {viscosity (N60(40))}

[0109] Furthermore, the ratio of the viscosity of the gel (GA) of the gelling agent (G) of the present invention (N1(40)) to the viscosity of the gel (GA) after temperature adjustment at 150°C (N1(150)) (N1(40) / N1(150)) is preferably 0.85 to 1.15, more preferably 0.90 to 1.10. If it is within this range, the zinc powder in the electrolyte under high temperature conditions is further less likely to settle, so the impact resistance and heat resistance are further excellent. The viscosity ratio of the gel (GA) (N1(40) / N1(150)) is measured by the following method. It should be noted that the viscosity ratio (N1(40) / N1(150)) during the temperature change of the gel (GA) in the examples described later is measured according to the following method.

[0110] <Method for Measuring the Viscosity Ratio (N1(40) / N1(150)) of the Gel (GA)>

[0111] After the measurement of (N1(40)) of the gel (GA) is completed, the sample is sealed and temperature-adjusted in a constant temperature machine at 150°C for 10 minutes. After temperature adjustment at 150°C for 10 minutes, it is temperature-adjusted at 40°C for 1 hour. The viscosity of the gel (GA) is measured under the same conditions as the viscosity (N1(40)) as the viscosity of the gel (GA) after temperature adjustment at 150°C (N1(150)). The viscosity ratio of the gel (GA) (N1(40) / N1(150)) is obtained by the following formula.

[0112] The viscosity ratio of the gel (GA) (N1(40) / N1(150)) = {viscosity (N1(40))} / {viscosity (N1(150))}

[0113] <Alkaline Battery>

[0114] The alkaline battery of the present invention has a gel-like negative electrode containing the gelling agent (G) and zinc powder. As the alkaline battery having a gel-like negative electrode containing the gelling agent (G) and zinc powder, there is no particular limitation, and it can be applied not only to general alkaline batteries, such as LR-20 (single 1-type alkaline battery) and LR-6 type (single 3-type alkaline battery), but also to various other alkaline batteries. An alkaline battery generally has a structure in which a positive electrode agent, a current collector rod, and a gel negative electrode are sealed in an outer can, and the positive electrode agent and the gel negative electrode are separated by a separator or the like.

[0115] As a method of filling a gel-like negative electrode containing the gelling agent (G) and zinc powder into an alkaline battery, the following methods can be exemplified:

[0116] (1) A method of pre-mixing the gelling agent (G), an alkaline electrolyte (e.g., a high-concentration aqueous potassium hydroxide solution, containing zinc oxide, etc. as required), zinc powder (and / or zinc alloy powder), and other additives as required to prepare a mixture of negative electrode materials, and filling it into the negative electrode container of the battery to form a gel-like negative electrode;

[0117] (2) A method of filling the gelling agent (G), zinc powder (and / or zinc alloy powder), and other additives as required into the negative electrode container of the battery, and then filling an alkaline electrolyte to generate a gel-like negative electrode in the container, etc.

[0118] Among them, the method of (1) in which the zinc powder can be uniformly dispersed in the negative electrode container of the battery is preferred. The addition amount of the gelling agent (G) varies depending on the structure of the negative electrode container, the particle size of the zinc powder, and the concentration of the alkaline electrolyte. Based on the weight of the alkaline electrolyte, it is preferably 0.5 to 10% by weight, and more preferably 1.0 to 5.0% by weight. If the addition amount is 0.5 to 10% by weight, the viscosity of the alkaline electrolyte containing the gelling agent becomes appropriate, the sedimentation of the zinc powder can be prevented, and the operability is also easy.

[0119] The sedimentation property of the zinc powder of the gelling agent (G) is preferably less than 10 mm, and more preferably less than 5 mm. It should be noted that the sedimentation property of the zinc powder of the gelling agent (G) is measured by the method described in the examples.

[0120] Examples

[0121] Hereinafter, the present invention will be further described by way of examples and comparative examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified, ultrapure water means water having a conductivity of 0.06 μS / cm or less, and ion-exchanged water means water having a conductivity of 1.0 μS / cm or less.

[0122] <Example 1>

[0123] In a 3-L adiabatic polymerization tank, 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 wt% relative to acrylic acid), 0.45 g of trimethylolpropane triacrylate (0.18 wt% relative to acrylic acid), and 750 g of ion-exchanged water were added, stirred and mixed. After preparing an aqueous acrylic acid solution, the aqueous acrylic acid solution was cooled to 3°C. After cooling, nitrogen was introduced into the aqueous acrylic acid solution at a flow rate of 5 L / min to make the dissolved oxygen concentration in the aqueous acrylic acid solution 0.10 ppm or less. The dissolved oxygen concentration was measured using an oxygen concentration meter (ORBISPHERE 510, manufactured by HACH ULTRA Co., Ltd.) based on the diaphragm electrode method. After confirming that the aqueous acrylic acid solution was 3°C, while continuously introducing nitrogen, 5.0 g of an aqueous solution of 2,2'-azobis(2-amidinopropane) hydrochloride (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-50) with a concentration of 10 wt% as a polymerization initiator, 5.0 g of an aqueous hydrogen peroxide solution with a concentration of 1.0 wt%, 5.0 g of an aqueous L-ascorbic acid solution with a concentration of 1.0 wt%, and 5.0 g of an aqueous iron(III) sulfate solution with a concentration of 0.1 wt% were added to the adiabatic polymerization tank. After adding the polymerization initiator, nitrogen was continuously introduced for 25 minutes, and then the introduction of nitrogen was stopped, and the mixture was allowed to stand for 16 hours for the polymerization reaction. After standing for 16 hours, the hydrogel obtained by the polymerization reaction was taken out from the polymerization reaction tank. The taken-out hydrogel was shredded into strips with a thickness of 3 to 10 mm using a small meat grinder (manufactured by ROYAL Co., Ltd.). After adding 250 g of a 49 wt% aqueous sodium hydroxide (special grade reagent) solution to the shredded hydrogel, the above small meat grinder was used to uniformly knead and mix in the hydrogel for neutralization. The neutralized hydrogel was stacked in layers with a thickness of 5 cm on a screen made of SUS with a mesh 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 Metal Co., Ltd.) to evaporate the water in the hydrogel and obtain a dried gel. After crushing the dried gel using a cooking blender, the gel with a particle size of 75 μm (200 mesh) was collected using a sieve to obtain the gelling agent (G-1) of the present invention. In addition, the volume average particle size of (G-1) was 50 μm.

[0124] <Example 2>

[0125] In Example 1, 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). Except for this, the same operations as in Example 1 were carried out to obtain the gelling agent (G-2) of the present invention.

[0126] <Example 3>

[0127] In Example 1, the addition amount of acrylic acid was 249 g, and the addition amount of 2 - carboxyethyl acrylate was 1 g ([(a1) / (a2)] = 99.6 / 0.4). Except for this, the same operations as in Example 1 were carried out to obtain the gelling agent (G - 3) of the present invention.

[0128] <Example 4>

[0129] In Example 1, the addition amount of acrylic acid was 247.5 g, and the addition amount of 2 - carboxyethyl acrylate was 2.5 g ([(a1) / (a2)] = 99 / 1). Except for this, the same operations as in Example 1 were carried out to obtain the gelling agent (G - 4) of the present invention.

[0130] <Example 5>

[0131] In Example 2, after adding 250 g of a 49 wt% aqueous sodium hydroxide (super special grade reagent) solution and uniformly kneading and neutralizing in the hydrogel using the above - mentioned small meat grinder, 0.5 g of sucrose stearate (HLB: 7) was further added and uniformly kneaded in the hydrogel using the above - mentioned small meat grinder. Except for this, the same operations as in Example 1 were carried out to obtain the gelling agent (G - 5) of the present invention.

[0132] <Example 6>

[0133] In Example 2, the gel with a particle size passing through 30 μm (500 mesh) was collected using a sieve. Except for this, the same operations as in Example 2 were carried out to obtain the gelling agent (G - 6) of the present invention. It should be noted that the volume - average particle size of (G - 6) is 10 μm.

[0134] <Comparative Example 1>

[0135] In Example 1, 2 - carboxyethyl acrylate was not added, and the addition amount of acrylic acid was 250 g. Except for this, the same operations as in Example 1 were carried out to obtain the comparative gelling agent (H - 1).

[0136] <Comparative Example 2>

[0137] In Example 1, the addition amount of acrylic acid was 245 g, and the addition amount of 2 - carboxyethyl acrylate was 5 g ([(a1) / (a2)] = 98 / 2). Except for this, the same operations as in Example 1 were carried out to obtain the comparative gelling agent (H - 2).

[0138] For 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, the results of measuring the volume-average particle diameter, the amount of soluble components, and the viscosity of the gel (GA) by the said method, together with the weight ratio [(a1) / (a2)] of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2), are shown in Table 1.

[0139] [Table 1]

[0140]

[0141] Furthermore, using the gelling agents (G-1) to (G-6) of the present invention and the comparative gelling agents (H-1) and (H-2), the results of measuring the sedimentation property of zinc powder and the deviation of the injection amount by the following method are shown in Table 2.

[0142] (1) Sedimentation property of zinc powder

[0143] In a 1-liter biaxial kneader (manufactured by Irie Shokai Co., Ltd., trade name: PNV-1), 150 g of a 40 wt% potassium hydroxide aqueous solution, 300 g of zinc powder with a volume-average particle diameter of 200 μm (manufactured by UNION MINIERES.A.), and 3.0 g of a gelling agent were added, and they were mixed at a rotation speed of 50 rpm for 60 minutes to produce a negative electrode material. 50 g of the produced negative electrode material was put into a closable 50-ml sample bottle (diameter 34 mm, height 77 mm, made of polypropylene), and the bubbles generated during mixing were degassed under reduced pressure. The sample bottle was closed and placed in a constant-temperature bath at 40°C for 60 days. Then, using the device attached to a powder tester (manufactured by Hosokawa Micron Corporation), the sample bottle was tapped 300 times at a rate of 30 times per minute from a height of 3 cm to promote the sedimentation of the zinc powder. After the tapping was completed, the distance (mm) from the initial position of the zinc powder (the position of the upper end of the negative electrode material in the sample bottle) to the most sedimented position of the zinc powder was measured, and this was taken as the sedimentation property (mm) of the zinc powder. The sedimentation property of the zinc powder was evaluated according to the following evaluation criteria.

[0144] <Evaluation criteria>

[0145] ◎: Less than 5.0 mm

[0146] ○: 5.0 mm or more and less than 10.0 mm

[0147] ×: 10.0 mm or more

[0148] (2) Deviation of injection amount

[0149] In a twin-screw kneader with a capacity of 1 liter, 150 g of a 40 wt% aqueous potassium hydroxide solution, 300 g of zinc powder (manufactured by UNION MINIERES.A.) with a volume-average particle diameter of 200 μm, and 3.0 g of a gelling agent were added, and the mixture was mixed at a rotational speed of 50 rpm for 60 minutes to produce a negative electrode material. The produced negative electrode material was transferred to a beaker, and the bubbles generated during mixing were degassed under reduced pressure. The degassed negative electrode material was suctioned into a 10-ml syringe having an inner diameter of 2 mm at the injection port and graduated in 0.1-ml units. From the height of the mouth of a 5-ml sample bottle (inner diameter 18 mm, height 40 mm), the syringe was pressed in by 5.0 ml, and the negative electrode material was injected into the sample bottle, and the weight of the negative electrode gel injected into the sample bottle was measured. The same operation was repeated 20 times in total, and the standard deviation (σ) of the injection volume was calculated as the deviation of the injection volume. The deviation of the injection volume was evaluated according to the following evaluation criteria.

[0150] <Evaluation Criteria>

[0151] ◎: 0.02 or less

[0152] ○: 0.03 or more and -0.10 or less

[0153] ×: 0.11 or more

[0154] [Table 2]

[0155]

[0156] Industrial Applicability

[0157] The gelling agent (G) of the present invention is useful not only as a cylindrical alkaline battery but also as a gelling agent for primary and secondary alkaline batteries such as alkaline button batteries, silver oxide batteries, nickel-cadmium storage batteries, and nickel-metal hydride storage batteries. In addition, the alkaline battery using the gelling agent of the present invention has excellent shock resistance and heat resistance, excellent maintenance of discharge characteristics, and excellent viscosity stability of the negative electrode material, and thus is useful as an alkaline battery for improving production efficiency and safety.

Claims

1. A gelling agent for alkaline batteries, characterized in that: A cross-linked polymer (A) containing acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2) and a cross-linking agent (b) as constituent monomers, The crosslinking agent (b) comprises a crosslinking agent (b1) that can be hydrolyzed under alkali conditions and a crosslinking agent (b2) that is not hydrolyzed under alkali conditions, The weight ratio of (a1) to (a2), i.e., (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) soluble in a 40 wt % potassium hydroxide aqueous solution is 10 wt % to 30 wt % based on the weight of (A).

3. The gelling agent for alkaline batteries according to claim 1 or 2, wherein 97 parts by weight of a 40% by weight potassium hydroxide aqueous solution and 3 parts by weight of the alkaline battery gelling agent are stirred and mixed until uniform, and the viscosity N1(40) of the gel (GA) after being left at 40° C. for 24 hours is 70 Pa·s to 120 Pa·s.

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

15.

5. The gelling agent for alkaline batteries according to any one of claims 1 to 4, wherein The preparation is prepared by stirring and mixing 97 parts by weight of a 40% by weight potassium hydroxide aqueous solution and 3 parts by weight of the gelling agent for alkaline batteries until they are uniformly mixed, and the ratio N1(40) / N1(150) of the viscosity of the gel (GA) after being left at 40°C for 24 hours to the viscosity 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, wherein The gelling agent for alkaline batteries further contains 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, glycerol fatty acid esters and fatty acid amides.

8. An alkaline battery, characterized in that: A gelled negative electrode comprising a gelling agent for alkaline batteries and zinc powder, wherein the gelling agent for alkaline batteries comprises a crosslinked polymer (A) having acrylic acid (salt) (a1), 2-carboxyethyl acrylic acid (salt) (a2) and a crosslinking agent (b) as constituent monomers, The crosslinking agent (b) comprises a crosslinking agent (b1) that can be hydrolyzed under alkali conditions and a crosslinking agent (b2) that is not hydrolyzed under alkali conditions, The weight ratio of (a1) to (a2), i.e., (a1) / (a2), is 99 / 1 to 99.98 / 0.

02.

9. The alkaline battery according to claim 8, wherein The sedimentation of zinc powder in the gel for alkaline batteries is less than 10.0 mm.

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