Gel for alkaline battery

Abstract

Provided are: a gel for alkaline batteries, which has excellent impact resistance and heat resistance, while maintaining 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), and wherein the weight ratio of (a1) to (a2) [(a1) / (a2)] is 98.5 / 1.5-99.95 / 0.05, and the volume average particle diameter is 20-500 [mu] m.

Description

Technical Field

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

[0002] Conventionally, the negative electrode of alkaline batteries primarily utilizes 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. To prevent sedimentation of zinc powder in the alkaline electrolyte, prevent leakage of liquid from the battery, and improve battery production efficiency, a proposal has been made to use a water-absorbing resin, such as one obtained by insolubilizing poly(meth)acrylic acid and its salts using a crosslinking agent, as a thickener to suppress stringiness (Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[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, alkaline batteries have been required to perform even better in recent years. However, alkaline batteries using gelling agents made from these water-absorbing resins cannot adequately prevent zinc powder and other substances from settling in alkaline electrolytes, and may not necessarily meet the requirements for maintaining the battery's long-term discharge characteristics (discharge capacity and discharge time) and impact resistance. Furthermore, when a strong impact or an accidental short circuit is applied to the alkaline battery, a large current flows within the battery, generating heat and degrading the discharge characteristics. Consequently, heat resistance may not be satisfactory.

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

[0009] Technical solutions to technical problems

[0010] The present inventors have conducted intensive research to solve the above-mentioned technical problems and have completed the present invention. Specifically, the present invention is a gelling agent for alkaline batteries comprising a crosslinked polymer (A) composed of acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b) as constituent monomers, wherein the weight ratio of (a1) to (a2) [(a1) / (a2)] is 98.5 / 1.5 to 99.95 / 0.05, and the volume average particle size is 20 to 500 μm.

[0011] Effects of the Invention

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

[0013] (1) 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. Therefore, when used in alkaline batteries, it is possible to produce batteries having excellent duration and impact resistance in terms of long-term discharge with a small amount of discharge.

[0014] (2) The negative electrode material to which the gelling agent for alkaline batteries of the present invention is added has a small change in viscosity when heated, and thus a highly safe battery with excellent impact resistance and heat resistance can be produced.

[0015] (3) The viscosity of the negative electrode material to which the gelling agent for alkaline batteries of the present invention is added is within an appropriate range during filling, and the liquid shedding ("liquid cutting" in Japanese) of the negative electrode material is good, thereby reducing the deviation in the amount of negative electrode material filled in each battery. Therefore, batteries with uniform quality can be produced even in mass production. In addition, the negative electrode material can be filled uniformly and quickly even in small-sized batteries, thereby enabling the manufacture of batteries with uniform quality. DETAILED DESCRIPTION

[0016] <Gel 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) as constituent monomers, wherein the weight ratio of (a1) to (a2) [(a1) / (a2)] is 98.5 / 1.5 to 99.95 / 0.05, and the volume average particle size is 20 to 500 μm.

[0018] In the present invention, "acrylic acid (salt)" refers to "acrylic acid" and / or "acrylic acid salt," and "2-carboxyethyl acrylate (salt)" refers to "2-carboxyethyl acrylate" and / or "salt of 2-carboxyethyl acrylate." Salts include 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 or neutralized. Furthermore, from the viewpoints of reduced adhesion, improved dispersibility, and operability in the production of the cross-linked polymer (A), the cross-linked polymer (A) is preferably partially or completely neutralized.

[0020] When neutralizing acrylic acid (a1) and 2-carboxyethyl acrylate (a2) contained in the cross-linked polymer (A), 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 is generally added to the monomer stage before polymerization or to the hydrogel after polymerization. However, the cross-linking agent (b2) described below, which does not hydrolyze under alkaline conditions, has low water solubility. Therefore, if polymerization is carried out in a state where the degree of neutralization of the water-soluble vinyl monomer (a1) is high, even if a predetermined amount of cross-linking agent (b2) is added, the cross-linking agent (b2) may separate from the aqueous monomer solution, preventing the predetermined cross-linking and thus failing to obtain the cross-linked polymer (A). It is more preferable to adjust the degree of neutralization of the water-soluble vinyl monomer (a1) to 0 to 30 mol %, so that the cross-linking agent (b2) is also contained, and then, after polymerization, add an alkali metal hydroxide to the hydrogel as needed to adjust the degree of neutralization.

[0021] The final neutralization degree of acrylic acid (salt) (a1) and 2-carboxyethyl acrylic acid (salt) (a2) in the crosslinked polymer (A) {the content of the anionic base (mol %) based on the total number of moles of the anionic groups of the anionic vinyl monomer and the anionic base} 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. It should be noted that the anionic base refers to the neutralized anionic group.

[0022] From the viewpoint of the absorptive capacity of the gelling agent (G), the content of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) is preferably 98.0 to 99.90 wt %, more preferably 99.0 to 99.85 wt %, and particularly preferably 99.2 to 99.83 wt %, based on the weight of the cross-linked polymer (A).

[0023] The weight ratio [(a1) / (a2)] of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2), which are monomers constituting the cross-linked polymer (A), is 98.5 / 1.5 to 99.95 / 0.05, preferably 99.5 / 0.5 to 99.9 / 0.1, and particularly preferably 99.7 / 0.3 to 99.85 / 0.15. If this weight ratio [(a1) / (a2)] is less than 98.5 / 1.5, the negative electrode material of the alkaline battery to which the gelling agent (G) is added deteriorates in liquid separation and causes variations in the filling amount. If it exceeds 99.95 / 0.05, the viscosity stability of the gelling agent (G) decreases, causing sedimentation of the zinc powder, which tends to deteriorate in discharge characteristics, impact resistance, and heat resistance.

[0024] The cross-linked polymer (A) is cross-linked using a cross-linking agent (b). Examples of the cross-linking agent (b) include a cross-linking agent (b1) that hydrolyzes under alkali conditions and a cross-linking agent (b2) that does not hydrolyze under alkali conditions.

[0025] In the present invention, it is preferred to use (b1) and (b2) in combination. By using (b1) and (b2) in combination, the viscosity stability of the gelling agent (G) is further improved, and the dehydration of the alkaline electrolyte can be prevented, thereby maintaining the long-term discharge of the battery. Furthermore, when filling the battery, the electrolyte can be injected evenly, and the deviation of the injection amount of the electrolyte per battery is also reduced, so it is preferred. It should be noted that, herein, "dehydration" of the alkaline electrolyte means that the gelling agent (G) and the alkaline electrolyte cannot be maintained in a roughly uniform mixed state, and the gelling agent (G) is separated from the alkaline electrolyte.

[0026] In the crosslinking agent (b1) that hydrolyzes under alkali, "hydrolyzes under alkali" means that the constituent monomers derived from (b1) in the crosslinked polymer (A) have a hydrolyzable bond. The hydrolyzable bond may be a bond originally present in the crosslinking agent (b1) molecule {in this case, the crosslinking agent is referred to as a crosslinking agent (b11) having a hydrolyzable bond in the molecule}, or a hydrolyzable bond formed by hydrolysis of a bond formed by a crosslinking reaction with another monomer {(a1) or (a2)} constituting the crosslinked polymer (A) {in this case, the crosslinking agent is referred to as a hydrolyzable crosslinking agent (b12)}. Examples of the hydrolyzable bond include ester bonds and amide bonds.

[0027] Examples of the cross-linking agent (b11) having a hydrolyzable bond in the molecule include copolymerizable cross-linking 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 (polymerization degree 3 to 13) polyacrylate.

[0028] Examples of crosslinking agents (b12) in which the bonds formed by the crosslinking reaction are hydrolyzable include reactive crosslinking agents that react with carboxylic acids, such as polyglycidyl compounds (such as ethylene glycol diglycidyl ether), polyisocyanate compounds (such as 4,4'-diphenylmethane diisocyanate), polyamine compounds (such as ethylenediamine), and polyol compounds (such as glycerol). Reactive crosslinking agents can react with (meth)acrylic acid (salt) to form ester bonds or amide bonds.

[0029] Among the cross-linking agents (b1) that hydrolyze under alkali conditions, from the viewpoint of 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 preferred, and N,N′-methylenebisacrylamide and trimethylolpropane tri(meth)acrylate are most preferred.

[0030] The cross-linking agent (b2) that does not hydrolyze under alkaline conditions is a cross-linking agent that does not have a hydrolyzable bond in the molecule and does not generate a hydrolyzable bond due to a cross-linking reaction. Examples of such a cross-linking agent (b2) include a cross-linking agent (b21) having two or more vinyl ether bonds and a cross-linking agent (b22) having two or more allyl ether bonds. From the perspective of reactivity, a cross-linking agent having two or more allyl ether bonds is preferred.

[0031] Examples of the cross-linking 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 (polymerization degree 2 to 5), bisphenol A divinyl ether, pentaerythritol trivinyl ether, sorbitol trivinyl ether, and polyglycerol (polymerization degree 3 to 13) polyvinyl ether.

[0032] Examples of the cross-linking agent (b22) having two or more allyl ether bonds include a cross-linking agent (b221) having two allyl groups and no hydroxyl groups in the molecule, a cross-linking agent (b222) having two allyl groups and 1 to 5 hydroxyl groups in the molecule, a cross-linking agent (b223) having 3 to 10 allyl groups and no hydroxyl groups in the molecule, and a cross-linking agent (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule. When a hydroxyl group is contained in the molecule, compatibility with the vinyl monomer (a1) and / or (a2) {particularly (meth)acrylic acid (salt)} is good, the uniformity of cross-linking is increased, the performance of the gelling agent (G) is improved, and the long-term stability of the viscosity of the negative electrode material containing the gelling agent (G) is further excellent.

[0033] Examples of the crosslinking agent (b221) having two allyl groups in the molecule and no hydroxyl group include 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.

[0034] Examples of the cross-linking agent (b222) having two allyl groups and 1 to 5 hydroxyl groups in the molecule include glycerol diallyl ether, trimethylolpropane diallyl ether, pentaerythritol diallyl ether, and polyglycerol (polymerization degree 2 to 5) diallyl ether.

[0035] Examples of the cross-linking agent (b223) having 3 to 10 allyl groups and no hydroxyl group in the molecule include trimethylolpropane triallyl ether, glycerol triallyl ether, pentaerythritol tetraallyl ether, and tetraallyloxyethane.

[0036] 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, diglycerol triallyl ether, sorbitol triallyl ether, and polyglycerol (polymerization degree 3 to 13) polyallyl ether.

[0037] Two or more cross-linking agents (b2) that are not hydrolyzed under alkaline conditions may be used in combination.

[0038] Among the crosslinking agents (b2), preferred are crosslinking agents (b22) having two or more allyl ether bonds, more preferred are crosslinking agents {(b222) and (b224)} having 1 to 5 hydroxyl groups and 2 to 10 allyl groups, 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, diglycerol triallyl ether, and sorbitol triallyl ether. These crosslinking agents are preferred because they have good compatibility with the water-soluble vinyl monomer (a1) and the vinyl monomer (a2) that is hydrolyzed to form (a1), enabling efficient crosslinking.

[0039] The content of the crosslinking agent (b1) hydrolyzed under alkaline conditions 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% by weight, more preferably 0.1 to 0.8% by weight, and particularly preferably 0.1 to 0.5% by weight, based on the weight of the crosslinked polymer (A). Within this range, excessive desalination of the alkaline electrolyte can be prevented, thereby further improving the long-term discharge characteristics of the battery.

[0040] The content of the alkaline-insensitive crosslinking agent (b2) in the crosslinked polymer (A) also depends on the type of crosslinking agent (b2), but 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, based on the weight of the crosslinked polymer (A). Within this range, the long-term discharge characteristics of the battery are further improved.

[0041] 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 desalting of the alkaline electrolyte can be prevented, thereby further improving the long-term discharge characteristics of the battery.

[0042] The total content of the crosslinking agent (b1) and the crosslinking agent (b2) is preferably 0.10 to 2.0 weight %, more preferably 0.30 to 1.0 weight %, and particularly preferably 0.40 to 0.8 weight %, based on the weight of the crosslinked polymer (A). Within this range, excessive dehydration of the alkaline electrolyte can be prevented, thereby further improving the long-term discharge characteristics of the battery. In addition, 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.

[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 in "Surfactant Primer" (published by Sanyo Chemical Industries, Ltd. in 2007, author Takehiko Fujimoto), page 212, from the ratio of the organic property value to the inorganic property value of an organic compound.

[0044] HLB = 10 × inorganic / organic

[0045] The organic and inorganic values ​​for deriving the HLB can be calculated using the values ​​in the table described on page 213 of the aforementioned "Introduction to Surfactants."

[0046] The surfactant (D) includes ionic surfactants and nonionic surfactants.

[0047] Examples of the ionic surfactant include known anionic surfactants, amphoteric surfactants, and cationic surfactants. Specific examples include ionic surfactants described in International Publication No. 99 / 03577, International Publication No. 2002 / 005949, and USP 4,331,447.

[0048] As the surfactant (D), a nonionic surfactant is preferred from the viewpoint of the viscosity of the gel and the high-speed injection property of the negative electrode material.

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

[0050] Examples of the sucrose fatty acid esters include those in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to sucrose. Specific examples include sucrose stearates [e.g., sucrose stearates manufactured by Daiichi Kogyo Seiyaku Co., Ltd. {DKESTER F-50 (HLB = 6), F-70 (HLB = 8), and F-110 (HLB = 11), etc.}, and sucrose stearates 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.}].

[0051] Examples of the sorbitan fatty acid esters include those in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to sorbitan. Specific examples include sorbitan palmitate [such as sorbitan palmitate {RHEODOL SP-P10 (HLB = 6.7) manufactured by Kao Corporation} and sorbitan palmitate {RIKEMAL P-300 (HLB = 5.6) manufactured by Riken Vitamin Co., Ltd.}].

[0052] Examples of the glycerol fatty acid esters include glycerol fatty acid esters in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to glycerol and / or a polymer of glycerol (polymerization degree 2 to 20). Specific examples include diglyceryl monolaurate [diglyceryl monolaurate manufactured by Riken Vitamin Co., Ltd. {POEM DL-100 (HLB = 9.4) etc.}], diglyceryl monomyristate [diglyceryl monomyristate manufactured by Riken Vitamin Co., Ltd. {POEM DM-100 (HLB = 8.7) etc.}], diglyceryl monostearate [diglyceryl monostearate manufactured by Riken Vitamin Co., Ltd. {POEM DS-100A (HLB = 7.7) etc.}], diglyceryl monooleate [diglyceryl monooleate manufactured by Riken Vitamin Co., Ltd. {POEM DO-100V (HLB = 7.3), RIKEMAL DO-100 (HLB = 7.4) etc.}], decaglyceryl stearate [decaglyceryl stearate manufactured by Riken Vitamin Co., Ltd. {POEM J-0081HV (HLB = 12), POEM J-0381V (HLB=12) etc.

[0053] Examples of fatty acid amides include those formed by amide bonding between a fatty acid having 8 to 22 carbon atoms and an ethanolamine. Specific examples include coconut oil fatty acid monoethanolamide [such as coconut oil fatty acid monoethanolamide {PROFAN AB-20 (HLB = 11) manufactured by Sanyo Chemical Industries, Ltd.}] and stearic acid monoethanolamide [such as stearic acid monoethanolamide {PROFAN SME (HLB = 10) manufactured by Sanyo Chemical Industries, Ltd.}].

[0054] The HLB of the surfactant (D) is preferably 1-12, more preferably 3-11, and particularly preferably 5-9 from the viewpoint of high-speed injection of the negative electrode material and syneresis of the negative electrode material.

[0055] In addition, as a surfactant (D), from the perspective of high-speed injection of the negative electrode material and 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 cross-linked polymer (A), from the viewpoint of high-speed injection of the negative electrode material and dehydration shrinkage of the negative electrode material, the content of the surfactant (D) is preferably 0.001 to 2.0 weight %, more preferably 0.005 to 1.0 weight %, particularly preferably 0.01 to 0.8 weight %, and most preferably 0.01 to 0.5 weight %.

[0057] When the surfactant (D) is in powder form, the particle size of the surfactant is not particularly limited. From the perspective of dry mixing properties in the cross-linked 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, the method for producing the gelling agent (G) for alkaline batteries of the present invention will be described.

[0059] As the polymerization method for obtaining the cross-linked 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.

[0060] Among these polymerization methods, aqueous solution polymerization, suspension polymerization, reversed suspension polymerization and emulsion polymerization are preferred, aqueous solution polymerization, reversed suspension polymerization and emulsion polymerization are further preferred, aqueous solution polymerization and reversed suspension polymerization are particularly preferred, and aqueous solution polymerization is most preferred. These polymerizations can use known polymerization initiators, chain transfer agents and / or solvents. Most preferably, aqueous solution polymerization is a method of adding a crosslinking agent (b) and dissolving polymerization in a monomer aqueous solution containing acrylic acid (salt) (a1) and acrylic acid-2-carboxyethyl ester (salt) (a2), and a method of dissolving polymerization, and a method of dispersing and suspending the same monomer aqueous solution in a hydrophobic organic solvent (e.g., hexane, toluene, xylene, etc.) in the presence of a dispersant and polymerizing the so-called reversed suspension polymerization method. If these polymerization methods are used, a gelling agent having 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 aqueous solution polymerization or reversed-phase suspension polymerization may be a known method, for example, a method of polymerization using a radical polymerization initiator, a method of irradiating with radiation, ultraviolet rays, electron beams, etc.

[0062] 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-tert-butyl peroxide, cumene hydroperoxide, etc.], and redox initiators [combinations of reducing agents such as alkali metal salts of sulfites or bisulfites, ammonium sulfite, ammonium bisulfite, and L-ascorbic acid with peroxides such as alkali metal salts of persulfates, ammonium persulfate, and aqueous hydrogen peroxide]. Two or more of these may be used in combination.

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

[0064] The amount of the initiator is not particularly limited, but is preferably 0.000001 to 3.0 wt %, more preferably 0.000001 to 0.5 wt %, based on the total weight of the vinyl monomers (a1) and (a2), from the viewpoint of increasing the degree of polymerization of the polymer.

[0065] In the case of aqueous solution polymerization, the polymerization concentration (wt%) of the monomers varies depending on other polymerization conditions. If the polymerization concentration of acrylic acid (a1) is increased, pseudo crosslinking (self-crosslinking) of the monomers themselves is likely to occur in parallel with the polymerization reaction, resulting in a decrease in the amount of absorption 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 result in 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, the polymerization temperature is preferably -10 to 100°C, more preferably -10 to 80°C. The amount of dissolved oxygen during polymerization is preferably 0 to 2 ppm (2×10 -4 wt% or less), more preferably 0 to 0.5 ppm (0.5×10 -4 Within these ranges, a cross-linked polymer (A) having a high degree of polymerization can be produced.

[0066] The degree of neutralization of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) during polymerization is not particularly limited as long as a predetermined amount of the crosslinking agent (b) can be completely dissolved in the aqueous monomer solution. However, compared with the crosslinking agent (b1) that can be hydrolyzed under alkaline conditions, the crosslinking agent (b2) that does not hydrolyze under alkaline conditions has poor water solubility. Furthermore, the solubility of the crosslinking agent (b2) in aqueous acrylic acid (salt) solutions is extremely low. Therefore, even if a predetermined amount of (b2) is added, (b2) may separate from the aqueous monomer solution, preventing the predetermined crosslinking. Therefore, the degree of neutralization of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) during polymerization is preferably 0 to 30 mol %, and further neutralized after polymerization as needed. More preferably, the polymerization is carried out in an unneutralized state and then neutralized after polymerization as needed.

[0067] Furthermore, when acrylic acid is polymerized under the same conditions, the polymerization degree tends to increase when the neutralization degree is low. Therefore, in order to increase the polymerization degree of the polymer, it is also preferable to polymerize with a low neutralization degree.

[0068] The reversed-phase suspension polymerization method 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, or xylene in the presence of a dispersant to carry out polymerization. In this polymerization method, as described above, the monomer concentration in the aqueous monomer solution is preferably 10 to 40% by weight, more preferably 10 to 30% by weight. Within this range, a cross-linked polymer (A) having a high degree of polymerization can be produced.

[0069] It should be noted that a dispersant may be used during the polymerization of the reversed-phase suspension polymerization method. Examples of dispersants include surfactants such as 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; and polymeric dispersants (hydrophilic group content: 0.1 to 20% by weight, weight-average molecular weight: 1,000 to 1,000,000) having a hydrophilic group in the molecule and soluble in the solvent for dispersing the monomer aqueous solution, such as maleated ethylene / acrylic acid copolymers, maleated ethylene / vinyl acetate copolymers, and styrenesulfonic acid (salt) / styrene copolymers. The use of polymeric dispersants is preferred because the size of the suspended particles of the monomer aqueous solution in the solvent can be easily adjusted, allowing the formation of a crosslinked polymer (A) having a desired particle size.

[0070] From the viewpoint of 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, relative to the weight of the hydrophobic organic solvent.

[0071] The weight ratio (W / O ratio) of the monomer aqueous 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.

[0072] In the production of the crosslinked polymer (A), it is preferred that the average degree of polymerization of the polymer produced under completely 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.

[0073] If polymerization is performed under conditions where the average degree of polymerization is 5000 or higher, the use of an appropriate amount of a crosslinking agent can prevent a decrease in viscosity and / or an increase in stringiness in a high-concentration alkaline aqueous solution containing a gelling agent. The above-mentioned average degree of polymerization is measured by gel permeation chromatography (GPC).

[0074] 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 (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 (about 0.5 to 20 mm square) or cut into strips using a meat grinder or a chopping machine, and after neutralizing the hydrogel by adding an alkali metal hydroxide or the like as needed, the hydrogel is subjected to air drying (eg, stacking the hydrogel on a perforated metal or mesh and forcibly passing hot air at 50 to 150°C to dry it) or ventilation drying (placing the hydrogel in a container and drying it by circulating hot air, and drying it while further dividing the gel into smaller pieces using a machine such as a rotary kiln). Of these, ventilation drying is preferred because it allows for efficient drying in a short time.

[0076] On the other hand, the method for drying the hydrogel during reverse phase suspension polymerization is generally to separate the polymerized hydrogel and the organic solvent into solid and liquid by decantation or the like, followed by vacuum drying (pressure reduction degree: about 100 to 50,000 Pa) or ventilation drying.

[0077] Other drying methods for hydrogels during aqueous solution polymerization include contact drying, where the hydrogel is compressed, stretched, and dried in a drum dryer. However, due to the poor thermal conductivity of hydrogels, a thin film of the hydrogel must be formed on the drum for drying. However, commercially available drum dryers are typically made of metals with lower ionization tendencies than zinc, such as iron, chromium, and nickel. Consequently, each hydrogel frequently contacts the metal surface of the drum. Furthermore, since the hydrogel is a poly(meth)acrylic acid (salt) hydrogel, the amount of metal elements with lower ionization tendencies than zinc that dissolve in the gel increases. Furthermore, the high frequency of contact between the hydrogel and the drum and the high adhesiveness of the hydrogel necessitates contact with a blade or similar material to remove the dried product from the drum dryer. Mechanical wear between the drum and the blade can wear away the metal surfaces of the drum or blade, leading to metal contamination of the dried product. As described above, when contact drying methods such as those used in drum dryers are used, metal ions and metal powders are easily incorporated into the gel, resulting in the gel containing a considerable amount of metal ions and metal powders with a lower ionization tendency than zinc (metals represented by atomic symbols such as Cr, Fe, Ni, Sn, Pb, Cu, Hg, and Ag, since these metals have lower standard electrode potentials than zinc). When these gels are used as gels for alkaline batteries, the zinc powder in the battery forms a cell with the metal ions or metal powders with a lower ionization tendency than zinc. This generates hydrogen gas through electrolysis, which increases the pressure inside the battery, potentially causing leakage of the alkaline electrolyte and, in severe cases, battery damage. Furthermore, even if the film-like dried product obtained by compressing and stretching the hydrogel in a drum dryer or the like is subsequently pulverized to adjust the particle size of the dried product to the desired size, the particles remain flaky. Therefore, the strength of the pulverized product is significantly weaker than that of the block-like dried product obtained by air-through drying or through-air drying. Furthermore, if the hydrogel is swollen in a high-concentration alkaline aqueous solution and mechanically stirred and mixed with zinc powder, the swollen gel is destroyed, resulting in a smaller gel. Therefore, contact drying methods that do not utilize a drum dryer or the like are preferred.

[0078] In the present invention, the drying temperature for drying the hydrogel varies depending on the dryer used, the drying time, and other factors, but is preferably 50-150°C, more preferably 80-130°C. A drying temperature of 150°C or lower prevents crosslinking of the polymer due to the heat of drying, preventing excessive increase in the degree of crosslinking caused by thermal crosslinking, and thus preventing a decrease in absorption and viscosity in alkaline electrolytes. A temperature of 50°C or higher reduces the need for prolonged drying, resulting in efficient drying. The drying time also varies depending on the type of dryer used, the drying temperature, and other factors, but is preferably 5-300 minutes, more preferably 5-120 minutes.

[0079] The dried product of the cross-linked polymer (A) thus obtained is pulverized as needed to form a powder. The pulverization method may be a known method, for example, an impact mill (pin mill, cutter mill, Skirel mill, ACM mill, etc.) or an air mill (jet mill, etc.).

[0080] The powdered cross-linked polymer (A) can be collected into a dry powder having a desired particle size using a sieving machine (vibrating sieving machine, centrifugal sieving machine, etc.) equipped with a desired mesh, as needed.

[0081] The volume average particle size of the gelling agent (G) in the present invention is 20 to 500 μm, preferably 30 to 400 μm, more preferably 30 to 170 μm, and particularly preferably 30 to 100 μm. When the volume average particle size is within this range, the viscosity of the alkaline electrolyte to which the gelling agent (G) is added is within an appropriate range, and the negative electrode material exhibits excellent liquid separation, thereby enabling the production of batteries with stable quality. Furthermore, the sedimentation of zinc powder in the negative electrode material can be prevented, thereby enabling the production of batteries with excellent discharge characteristics over time.

[0082] In addition, the said volume average particle diameter is measured by the following method.

[0083] <Method for measuring volume average particle size of gelling agent (G)>

[0084] The gelling agent (G) of the present invention was dispersed in methanol and measured using a laser diffraction particle size distribution analyzer [Microtrac (manufactured by Nikkiso Co., Ltd.)]. The volume average particle size of the gelling agent (G) in the examples described below was measured according to the above method.

[0085] The cross-linked polymer (A) may react with a surface cross-linking agent as needed to perform a surface cross-linking treatment.

[0086] As the surface crosslinking agent, a known surface crosslinking agent can be used, for example, a surface crosslinking agent described in Japanese Patent Application Laid-Open No. 2003-225565.

[0087] 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 reactive with the carboxyl groups of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) is preferred, a polyvalent glycidyl group is more preferred, ethylene glycol diglycidyl ether and glycerol diglycidyl ether are particularly preferred, and ethylene glycol diglycidyl ether is most preferred.

[0088] From the viewpoint of 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.

[0089] As the method of the surface cross-linking reaction, known methods (for example, Japanese Patent No. 3648553, Japanese Patent Application Laid-Open No. 2003-165883, Japanese Patent Application Laid-Open No. 2005-75982, and Japanese Patent Application Laid-Open No. 2005-95759) can be applied.

[0090] 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 cross-linked polymer (A).

[0091] As a material having a surfactant (D) near the surface of the cross-linked polymer (A), a material obtained by the following method can be mentioned.

[0092] (1) A method in which a solid surfactant (D) is directly mixed with the crosslinked polymer (A), for example, by dry mixing;

[0093] (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 cross-linked polymer (A);

[0094] (3) A method in which a surfactant (D) is dissolved in a hydrophobic organic solvent, the cross-linked polymer (A) is impregnated with the solvent, and the mixture is dried.

[0095] Among these mixing methods, (1) is preferred from the viewpoint of easy drying and small amount of residual solvent.

[0096] Additives can be added to the gelling agent (G) of the present invention as needed at any stage {the polymerization step, the chopping step, the drying step, the pulverization step, the surface cross-linking step, and / or before and after these steps in the production process of the cross-linked polymer (A), and after the step of mixing (A) and (D), etc.}.

[0097] In the present invention, it is preferred to use a magnetic iron remover at any stage after drying to remove contaminated metal powders such as iron. However, even with very precise iron removal, it is difficult to remove non-magnetic metals using the iron remover. Furthermore, magnetic metals cannot be removed, and magnetic metals contained within the dried polymer particles or adhered to the dried particles. Therefore, in order to prevent these metals from being mixed in from the outset, it is necessary to take full account of the production equipment.

[0098] The amount of the crosslinked polymer (A) soluble in a 40% by weight aqueous potassium hydroxide solution of the present invention is preferably 10 to 30% by weight, more preferably 10 to 20%, and particularly preferably 10 to 15%, based on the weight of (A). When the soluble content is within this range, the viscosity of the alkaline electrolyte to which the gelling agent (G) is added is within an appropriate range, the negative electrode material is well-discharged, and thus a battery with stable quality can be manufactured. Sedimentation of the zinc powder in the negative electrode material can be prevented, thereby producing a battery with excellent discharge characteristics over time. If the soluble content exceeds 30% by weight, the alkaline electrolyte to which the gelling agent (G) is added exhibits stringiness, significantly deteriorating the negative electrode material discharge, causing variations in the filling amount and resulting in unstable battery quality. If the soluble content is less than 10% by weight, the viscosity of the alkaline electrolyte to which the gelling agent (G) is added decreases, causing sedimentation of the zinc powder, thereby deteriorating impact resistance and discharge characteristics.

[0099] The amount of the cross-linked polymer (A) soluble in a 40% by weight potassium hydroxide aqueous solution can be measured by the following method.

[0100] <Method for measuring the amount of soluble components in a 40 wt% potassium hydroxide aqueous solution of (A)>

[0101] Accurately weigh 1 g of the gelling agent (G) (the accurate weighing value is set to S0), add it to 250 ml of a 40 wt% potassium hydroxide aqueous solution and stir for 3 hours, then remove the swollen gel with filter paper (Filter Paper No. 1 qualitative filter paper manufactured by ADVANTEC). The filtrate obtained after removing the gel is used as the extract of the soluble component. About 25 ml of the extract of the soluble component obtained by the above method is placed in a 50 ml eggplant flask, and water is distilled off under reduced pressure using an evaporator. About 25 ml of the extract is added to the eggplant flask, and the operation of distilling off water under reduced pressure is repeated to distill off water for the total amount of the extract. Then, the eggplant flask containing the residue is allowed to stand in an air circulation dryer at 130°C for 90 minutes, and then allowed to stand in the dryer for 15 minutes to cool the eggplant flask to room temperature. Measure the weight of the residue in the eggplant flask after cooling (S1). Perform the same operation on an amount of physiological saline equal to the extract used in the previous operation, and measure the weight of the residue after cooling (S2). The weight of the residue after cooling was determined by subtracting the weight of the eggplant-shaped flask measured in advance from the weight of the eggplant-shaped flask containing the residue after cooling. Using (S0), (S1), and (S2) obtained above, the soluble content was calculated using the following formula.

[0102] Soluble content (%) = (S1-S2)÷S0×100

[0103] In addition, the amount of the cross-linked polymer (A) soluble in a 40 wt % potassium hydroxide aqueous solution in the examples described below was measured by the above-mentioned method.

[0104] 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. Within this range, long-term discharge characteristics are further improved. Here, the 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 gelling agent (G) until uniform, and then leaving the mixture at 40°C for 24 hours. The viscosity (N1(40)) of the gel (GA) is measured by the following method.

[0105] <Method for measuring viscosity (N1(40)) of gel (GA)>

[0106] The viscosity of the gel (GA) was measured at a temperature of 40°C using a digital Brookfield viscometer (manufactured by TOKIMEC Co., Ltd.) in accordance with JIS 7117-1:1999. This viscosity was determined using a rotor No. 4 at a rotation speed of 3 rpm. The viscosity of the gel (GA) in the examples described below was measured using the aforementioned method.

[0107] 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 59 days at 40°C is preferably 0.85 to 1.15, and more preferably 0.90 to 1.10. If it is within this range, the zinc powder in the electrolyte is less likely to settle, so the discharge characteristics and impact 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 examples described below is measured according to the following method.

[0108] <Method for measuring the viscosity ratio (N1(40) / N60(40)) of gel (GA)>

[0109] The sample after the viscosity (N1(40)) of the gel (GA) was measured was sealed and 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 used as the viscosity of the gel (GA) after 60 days of storage (N60(40)). The viscosity ratio of the gel (GA) (N1(40) / N60(40)) was calculated using the following formula.

[0110] 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))}

[0111] Furthermore, the ratio (N1(40) / N1(150)) of the viscosity (N1(40)) of the gel (GA) of the gelling agent (G) of the present invention to the viscosity (N1(150)) of the gel (GA) after temperature adjustment at 150°C is preferably 0.85 to 1.15, and more preferably 0.90 to 1.10. Within this range, the zinc powder in the electrolyte under high temperature conditions is less likely to settle, so the impact resistance and heat resistance are further improved. The viscosity ratio (N1(40) / N1(150)) of the gel (GA) is measured by the following method. It should be noted that the viscosity ratio (N1(40) / N1(150)) of the gel (GA) during temperature change in the examples described later is measured by the following method.

[0112] <Method for measuring the viscosity ratio (N1(40) / N1(150)) of gel (GA)>

[0113] After the measurement of the gel (GA) (N1(40)) is completed, the sample is sealed and temperature-controlled in a thermostat at 150°C for 10 minutes. After temperature-controlled at 150°C for 10 minutes, the temperature is controlled at 40°C for 1 hour. The viscosity of the gel (GA) is measured under the same conditions as the viscosity (N1(40)) and is taken as the viscosity of the gel (GA) after temperature-controlled at 150°C (N1(150)). The viscosity ratio of the gel (GA) (N1(40) / N1(150)) is calculated by the following formula.

[0114] The viscosity ratio of gel (GA) (N1(40) / N1(150)) = {viscosity (N1(40))} / {viscosity (N1(150))}

[0115] <Alkaline batteries>

[0116] The alkaline battery of the present invention comprises a gelled negative electrode containing the gelling agent (G) and zinc powder. The alkaline battery comprising the gelled negative electrode containing the gelling agent (G) and zinc powder is not particularly limited and can be applied to not only conventional alkaline batteries such as LR-20 (single 1-type alkaline battery) and LR-6 (single 3-type alkaline battery), but also various other alkaline batteries. Alkaline batteries typically have a structure in which a positive electrode material, a current collector rod, and a gelled negative electrode are enclosed in an outer can, with the positive electrode material and the gelled negative electrode separated by a separator or the like.

[0117] As a method for filling an alkaline battery with the gelled negative electrode containing the gelling agent (G) and zinc powder, the following method can be exemplified:

[0118] (1) A method of preparing a gelled negative electrode by pre-mixing the gelling agent (G), an alkaline electrolyte (e.g., a high-concentration potassium hydroxide aqueous solution containing zinc oxide, etc., as needed), zinc powder (and / or zinc alloy powder), and other additives as needed to prepare a negative electrode material mixture, and then filling the mixture into a negative electrode container of a battery;

[0119] (2) A method in which the gelling agent (G) and zinc powder (and / or zinc alloy powder) and other additives as needed are filled into a negative electrode container of a battery, and then an alkaline electrolyte is filled to form a gelled negative electrode in the container.

[0120] Among them, the method (1) described above is preferred, as it allows the zinc powder to be uniformly dispersed in the negative electrode container of the battery. The amount of the 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. It is preferably 0.5 to 10% by weight, and more preferably 1.0 to 5.0% by weight, 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 moderate, which can prevent the zinc powder from settling and facilitates handling.

[0121] The sedimentation of the zinc powder in the gelling agent (G) is preferably less than 10 mm, more preferably less than 5 mm. The sedimentation of the zinc powder in the gelling agent (G) is measured by the method described in the Examples.

[0122] Example

[0123] The present invention is further described below by way of examples and comparative examples, but the present invention is not limited thereto. Hereinafter, unless otherwise specified, ultrapure water refers to water having an electrical conductivity of 0.06 μS / cm or less, and ion-exchanged water refers to water having an electrical conductivity of 1.0 μS / cm or less.

[0124] <Example 1>

[0125] In a 3-liter adiabatic polymerization tank, 249.875 g of acrylic acid, 0.125 g of 2-carboxyethyl acrylate ([(a1) / (a2)]=99.95 / 0.05), 0.80 g of pentaerythritol triallyl ether (0.32% by weight relative to the acrylic acid), and 750 g of ion-exchanged water were added and stirred to prepare an acrylic acid aqueous solution. The acrylic acid aqueous solution was then cooled to 3°C. After cooling, nitrogen gas was passed through the acrylic acid aqueous solution at a flow rate of 5 L / min to adjust the dissolved oxygen concentration in the acrylic acid aqueous solution to 0.10 ppm or less. The dissolved oxygen concentration was measured using an oxygen concentration meter (ORBISPHERE 510, manufactured by Hach Ultra) using the diaphragm electrode method. After confirming that the acrylic acid aqueous solution was at 3°C, 5.0 g of a 10% by weight aqueous solution of 2,2′-azobis(2-amidinopropane) hydrochloride (Wako Pure Chemical Industries, Ltd., trade name: V-50) was added to the insulated polymerization tank while continuing to flow nitrogen gas. A 10% by weight aqueous solution of 2,2′-azobis(2-amidinopropane) hydrochloride (Wako Pure Chemical Industries, Ltd., trade name: V-50) was added as a polymerization initiator, along with 5.0 g of a 1.0% by weight aqueous hydrogen peroxide solution, 5.0 g of a 1.0% by weight aqueous solution of L-ascorbic acid, and 5.0 g of a 0.1% by weight aqueous solution of iron(III) sulfate. Following the addition of the polymerization initiator, nitrogen gas flow was continued for 25 minutes, then stopped, and the mixture was allowed to stand for 16 hours to allow the polymerization reaction to proceed. After 16 hours of standing, the resulting hydrogel was removed from the polymerization tank. The removed hydrogel was finely divided into strips 3 to 10 mm thick using a small meat grinder (manufactured by ROYAL). 250 g of a 49% by weight aqueous sodium hydroxide solution (special grade reagent) was added to the finely divided hydrogel and then uniformly kneaded in the hydrogel using the aforementioned small meat grinder for neutralization. The neutralized hydrogel was layered onto a 5 cm thick SUS screen with an 850 μm mesh. A small air permeation dryer (manufactured by Inoue Metal Co., Ltd.) was used to pass 150°C hot air through the hydrogel for 1 hour to evaporate the water in the hydrogel, yielding a dried gel. The dried gel was pulverized using a cooking blender and then sieved to obtain a gel with a particle size of 75 μm (200 mesh). This yielded the gel (G-1) of the present invention. The volume average particle size of (G-1) was 50 μm.

[0126] <Example 2>

[0127] The same operation as in Example 1 was carried out except that the added amount of acrylic acid was 247.0 g and the added amount of 2-carboxyethyl acrylate was 3.0 g ([(a1) / (a2)]=98.8 / 1.2) to obtain the gelling agent (G-2) of the present invention.

[0128] <Example 3>

[0129] The gelling agent (G-3) of the present invention was obtained by the same operation as in Example 1, except that the amount of pentaerythritol triallyl ether added was changed to 0.50 g (0.20 wt % relative to acrylic acid) and 0.50 g of ethylene glycol diglycidyl ether (0.20 wt % relative to acrylic acid) was additionally added as a crosslinking agent.

[0130] <Example 4>

[0131] In Example 3, the same procedures as in Example 3 were carried out except that the added amount of acrylic acid was changed to 249.5 g, the added amount of 2-carboxyethyl acrylate was changed to 0.5 g ([(a1) / (a2)]=99.8 / 0.2), and trimethylolpropane triacrylate was used instead of ethylene glycol diglycidyl ether, to obtain a gelling agent (G-4) of the present invention.

[0132] <Example 5>

[0133] The same operation as in Example 4 was carried out except that the added amount of acrylic acid was 249.0 g and the added amount of 2-carboxyethyl acrylate was 1.0 g ([(a1) / (a2)]=99.6 / 0.4) to obtain the gelling agent (G-5) of the present invention.

[0134] <Example 6>

[0135] The same procedures as in Example 4 were followed, except that a sieve was used to collect the gel having a particle size of 250 μm (60 mesh), to obtain the gelling agent (G-6) of the present invention. The volume average particle size of (G-6) was 150 μm.

[0136] <Example 7>

[0137] The same procedures as in Example 4 were followed, except that a sieve was used to collect the gel having a particle size of 600 μm (26 mesh), to obtain the gelling agent (G-7) of the present invention. The volume average particle size of (G-7) was 380 μm.

[0138] <Example 8>

[0139] In Example 4, the same procedures as in Example 2 were performed except that 250 g of a 49 wt% aqueous solution of sodium hydroxide (special grade reagent) was added and then uniformly kneaded in the aqueous gel using the above-mentioned small meat grinder for neutralization, and then 0.5 g of sucrose stearate (HLB: 7) was further added and uniformly kneaded in the aqueous gel using the above-mentioned small meat grinder to obtain the gelling agent (G-8) of the present invention.

[0140] <Comparative Example 1>

[0141] A comparative gelling agent (H-1) was obtained by the same operation as in Example 1 except that the added amount of acrylic acid was 249.95 g and the added amount of 2-carboxyethyl acrylate was 0.05 g ([(a1) / (a2)]=99.98 / 0.02).

[0142] Comparative Example 2

[0143] A comparative gelling agent (H-2) was obtained by the same operation as in Example 4 except that the added amount of acrylic acid was 245 g and the added amount of 2-carboxyethyl acrylate was 5 g ([(a1) / (a2)]=98 / 2).

[0144] Comparative Example 3

[0145] A comparative gel (H-3) was obtained by the same procedure as in Example 1, except that the gel having a particle size of 30 μm (500 mesh) was collected using a sieve. The volume average particle size of (H-3) was 10 μm.

[0146] Comparative Example 4

[0147] The same procedures as in Example 1 were followed, except that the gel that passed through a particle size of 600 μm (26 mesh) was removed using a sieve and the gel remaining on the sieve was collected, to obtain a comparative gel (H-4). The volume average particle size of (H-4) was 750 μm.

[0148] For the gelling agents (G-1) to (G-8) produced in Examples 1 to 8 and the comparative gelling agents (H-1) to (H-4) produced in Comparative Examples 1 to 4, the results of measuring the volume average particle size, the amount of soluble components, and the viscosity of the gel (GA) using the above-mentioned method are shown in Table 1, together with the weight ratio [(a1) / (a2)] of acrylic acid (salt) (a1) to 2-carboxyethyl acrylic acid (salt) (a2).

[0149] [Table 1]

[0150]

[0151] Furthermore, using the gelling agents (G-1) to (G-8) of the present invention and comparative gelling agents (H-1) to (H-4), the sedimentation properties of zinc powder and the variation in injection amount were measured by the following method. The results are shown in Table 2.

[0152] (1) Sedimentation of zinc powder

[0153] A negative electrode material was prepared by adding 150 g of a 40% by weight aqueous potassium hydroxide solution, 300 g of zinc powder with a volume average particle size of 200 μm (from Union Minieres A.), and 3.0 g of a gelling agent to a 1-liter biaxial kneader (manufactured by Irie Shokai Co., Ltd., trade name: PNV-1). The mixture was mixed at 50 rpm for 60 minutes to prepare the negative electrode material. 50 g of the prepared negative electrode material was placed in a sealable 50 ml sample bottle (34 mm diameter, 77 mm height, made of polypropylene). Air bubbles introduced during mixing were removed under reduced pressure. The sample bottle was sealed and placed in a thermostatic bath at 40°C for 60 days. The sample bottle was then tapped 300 times at a rate of 30 taps / minute from a height of 3 cm using a device attached to a powder tester (manufactured by Hosokawa Micron Co., Ltd.) to promote the sedimentation of the zinc powder. After tapping, 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 point where the zinc powder settles most is measured and used as the sedimentation of the zinc powder (mm). The sedimentation of the zinc powder is evaluated according to the following evaluation criteria.

[0154] <Evaluation Criteria>

[0155] ◎: less than 5.0mm

[0156] ○: 5.0 mm or more and less than 10.0 mm

[0157] ×: 10.0mm or more

[0158] (2) Deviation of injection volume

[0159] In a 1-liter biaxial kneader, add 150 g of a 40 wt% potassium hydroxide aqueous solution, 300 g of zinc powder with a volume average particle size of 200 μm (manufactured by UNION MINIERES.A.), and 3.0 g of a gelling agent, and mix at a speed of 50 rpm for 60 minutes to prepare a negative electrode material. The prepared negative electrode material is transferred to a beaker, and the bubbles generated during mixing are degassed under reduced pressure. The degassed negative electrode material is drawn into a 10 ml syringe with an injection port having an inner diameter of 2 mm and a scale of 0.1 ml units. From the height of the mouth of a 5 ml sample bottle (inner diameter 18 mm, height 40 mm), press the syringe into 5.0 ml, inject the negative electrode material into the sample bottle, and measure the weight of the negative electrode gel injected into the sample bottle. Repeat the same operation a total of 20 times, and calculate the standard deviation (σ) of the injection amount as the deviation of the injection amount. Evaluate the deviation of the injection amount according to the following evaluation criteria.

[0160] <Evaluation Criteria>

[0161] ◎: 0.02 or less

[0162] ○: 0.03 or more and -0.10 or less

[0163] ×: 0.11 or more

[0164] The evaluation results are shown in Table 2.

[0165] [Table 2]

[0166]

[0167] Industrial Applicability

[0168] The gelling agent (G) of the present invention is useful not only as a gelling agent 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, and nickel-metal hydride storage batteries. Furthermore, alkaline batteries using the gelling agent of the present invention exhibit excellent impact resistance and heat resistance, excellent retention of discharge characteristics, and excellent viscosity stability of the negative electrode material, thereby being useful as alkaline batteries with improved production efficiency and safety.

Claims

1. A gelling agent for alkaline batteries, characterized in that: The gelling agent for alkaline batteries contains a cross-linked polymer (A) composed of acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2) and a cross-linking agent (b) as constituent monomers, wherein the weight ratio of (a1) to (a2), i.e., (a1) / (a2), is 98.5 / 1.5 to 99.95 / 0.05, and the volume average particle size of the gelling agent for alkaline batteries is 20 to 500 μm.

2. The gelling agent for alkaline batteries according to claim 1, wherein The crosslinking agent (b) includes a crosslinking agent (b1) that can be hydrolyzed under alkali conditions and a crosslinking agent (b2) that is not hydrolyzed under alkali conditions.

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

4. The gelling agent for alkaline batteries according to any one of claims 1 to 3, wherein 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 are stirred and mixed until uniform, and the viscosity N1(40) of the gel (GA) after being placed at 40° C. for 24 hours is 70 Pa·s to 120 Pa·s.

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

15.

6. The gelling agent for alkaline batteries according to any one of claims 1 to 5, wherein The preparation is carried out 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 uniform, and the ratio N1(40) / N1(150) of the viscosity N1(40) of the gel (GA) after being left 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.

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

8. The gelling agent for alkaline batteries according to claim 7, 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.

9. 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 cross-linked polymer (A) composed of acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a cross-linking agent (b) as constituent monomers, wherein the weight ratio of (a1) to (a2), i.e., (a1) / (a2), is 98.5 / 1.5 to 99.95 / 0.05, and the volume average particle size of the gelling agent for alkaline batteries is 20 to 500 μm.

10. 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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