Method for producing gelling agent for alkaline battery

Abstract

The present invention is a method for producing a gelling agent (X) for an alkaline battery containing a crosslinked polymer (A), which contains an acrylic acid (salt) (a1), an acrylic acid 2-carboxyethyl (salt) (a2), and a crosslinking agent (b) as constituent monomers, the crosslinking agent (b) including an alkaline and hydrolyzable crosslinking agent (b1) and an alkaline and non-hydrolyzable crosslinking agent (b2), and the weight ratio of the acrylic acid (salt) (a1) and the acrylic acid 2-carboxyethyl (salt) (a2) being 99 / 1 to 99.99 / 0.01. The method includes: a polymerization step for obtaining a water-containing gel containing the crosslinked polymer (A); a drying step for drying the water-containing gel; and a classification step. The apparent density of the gelling agent is 0.45-0.90 g / ml, and the angle of repose thereof is 30-50°. According to the present invention, it is possible to provide a method for producing a gelling agent for alkaline batteries having excellent ability to prevent precipitation of zinc powder and the like in an alkaline electrolyte solution.

Description

Method for producing a gelling agent for an alkaline battery

[0001] The present invention relates to a method for producing a gelling agent for an alkaline battery.

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

[0003] Japanese Patent Application Laid-Open No. 2008-34379

[0004] However, in recent years, alkaline batteries have been required to have further improved performance. Alkaline batteries using these gelling agents for water-absorbing resins cannot be said to have sufficient sedimentation prevention performance for zinc powder and the like in the alkaline electrolyte, and there has been a demand for a gelling agent for an alkaline battery that maintains long-term discharge characteristics (discharge capacity and discharge time) and has excellent impact resistance.

[0005] An object of the present invention is to provide a method for producing a gelling agent for an alkaline battery that has excellent sedimentation prevention performance for zinc powder and the like in an alkaline electrolyte.

[0006] The present inventors, after diligent study to solve the above problems, arrived at the present invention. That is, the present invention is a method for producing a gelling agent (X) for alkaline batteries containing a crosslinked polymer (A) comprising acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b) as constituent monomers, wherein the crosslinking agent (b) comprises a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not undergo hydrolysis in an alkaline environment, and the weight ratio of acrylic acid (salt) (a1) to 2-carboxyethyl acrylate (salt) (a2) [(a1) / (a2)] is 99 / 1 to 99.99 / 0.01, wherein the crosslinked polymer (A) contains a water-containing A method for producing an alkaline battery gelling agent (X), comprising: a polymerization step to obtain a gel; a drying step in which the water-containing gel is supplied onto a continuously moving support and dried by bringing hot air at a supply temperature of 90 to 230°C into contact with the water-containing gel while the water-containing gel is continuously moved on the support; a grinding step in which the dried water-containing gel is ground in a grinder to obtain a pulverized product of the water-containing gel; and a classification step in which the pulverized product is classified using a sieve with a mesh opening of 200 to 500 μm, wherein the apparent density of the alkaline battery gelling agent (X) is 0.45 to 0.90 g / ml and the angle of repose is 30 to 50°.

[0007] According to the method for producing the gelling agent (X) for alkaline batteries of the present invention, it is possible to provide a gelling agent for batteries that has excellent properties in preventing the sedimentation of zinc powder and the like in the negative electrode material.

[0008] <Method for producing a gelling agent (X) for alkaline batteries> The present invention provides a method for producing a gelling agent (X) for alkaline batteries, comprising a crosslinked polymer (A) containing acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b) as constituent monomers, wherein the crosslinking agent (b) comprises a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not undergo hydrolysis in an alkaline environment, and the weight ratio of acrylic acid (salt) (a1) to 2-carboxyethyl acrylate (salt) (a2) [(a1) / (a2)] is 99 / 1 to 99.99 / 0.01. The process comprises a polymerization step to obtain a water-containing gel containing the crosslinked polymer (A), a drying step in which the water-containing gel is supplied onto a continuously moving support and dried by bringing hot air at a supply temperature of 90 to 230°C into contact with the water-containing gel while the water-containing gel is continuously moved on the support, a grinding step in which the dried water-containing gel is ground in a grinder to obtain a pulverized product of the water-containing gel, and a classification step in which the pulverized product is classified using a sieve with a mesh opening of 200 to 500 μm, wherein the apparent density of the gelling agent (X) for alkaline batteries is 0.45 to 0.90 g / ml and the angle of repose is 30 to 50°.

[0009] In this invention, "acrylic acid (salt)" means "acrylic acid" and / or "acrylic acid salt," and "2-carboxyethyl acrylate (salt)" means "2-carboxyethyl acrylate" and / or "2-carboxyethyl acrylate salt." Salts include alkali metal salts such as potassium, sodium, and lithium, and alkaline earth metal salts such as calcium.

[0010] The constituent monomers derived from acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) may be unneutralized or neutralized. Furthermore, it is preferable that the crosslinked polymer (A) is partially or completely neutralized from the viewpoint of reducing tackiness, improving dispersibility, and improving the workability of the crosslinked polymer (A) during manufacturing.

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

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

[0013] The content of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) is 98.0 to 99.85% by weight, particularly preferably 99.2 to 99.83% by weight, based on the weight of the crosslinked polymer (A), from the viewpoint of the absorption capacity of the gelling agent (X) for alkaline batteries.

[0014] The weight ratio [(a1) / (a2)] of acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) in the crosslinked polymer (A) is 99 / 1 to 99.99 / 0.01, preferably 99.5 / 0.5 to 99.95 / 0.05, and particularly preferably 99.7 / 0.3 to 99.9 / 0.1. If this weight ratio [(a1) / (a2)] is less than 99 / 1, the liquid drainage of the negative electrode material of the alkaline battery to which the gelling agent for alkaline batteries (X) has been added deteriorates, causing variations in the filling amount. If it exceeds 99.99 / 0.01, the viscosity stability of the gelling agent for alkaline batteries (X) decreases, causing sedimentation of zinc powder, which tends to worsen impact resistance and discharge characteristics.

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

[0016] In this invention, (b1) and (b2) are used in combination. By using (b1) and (b2) in combination, the viscosity stability of the gelling agent (X) for alkaline batteries is further improved, and the separation of the alkaline electrolyte can be prevented, thereby maintaining the battery's discharge over a long period of time. Furthermore, it is possible to inject the electrolyte uniformly when filling the battery, and the unevenness in the amount of electrolyte injected per battery is also reduced. Here, "separation" of the alkaline electrolyte means that a nearly uniform mixing state between the gelling agent (X) for alkaline batteries and the alkaline electrolyte cannot be maintained, and the gelling agent (X) for alkaline batteries and the alkaline electrolyte separate.

[0017] In the case of a crosslinking agent (b1) that undergoes hydrolysis in an alkaline environment, "hydrolyzed in an alkaline environment" means that the constituent monomers derived from (b1) in the crosslinked polymer (A) have hydrolyzable bonds. These hydrolyzable bonds may be bonds that the crosslinking agent (b1) originally has within its molecule {in this case, the crosslinking agent is a crosslinking agent (b11) having hydrolyzable bonds within its molecule}, or the bonds formed by a crosslinking reaction with other monomers {(a1) or (a2)} constituting the crosslinked polymer (A) may be hydrolyzable {in this case, the bonds formed by the crosslinking reaction of the crosslinking agent are hydrolyzable crosslinking agent (b12)}. Hydrolyzable bonds include ester bonds and amide bonds, etc.

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

[0019] Examples of crosslinking agents (b12) whose bonds formed by crosslinking reactions are hydrolyzable include reactive crosslinking agents that react with carboxylic acids, such as polyvalent glycidyl compounds (ethylene glycol diglycidyl ether, etc.), polyvalent isocyanate compounds (4,4'-diphenylmethane diisocyanate, etc.), polyvalent amine compounds (ethylenediamine, etc.), and polyvalent alcohol compounds (glycerin, etc.). Reactive crosslinking agents can react with (meth)acrylic acid (salt) to form ester bonds or amide bonds.

[0020] Among the crosslinking agents (b1) that hydrolyze in an alkaline environment, polyvalent acrylamide compounds and polyvalent acrylate compounds are preferred from the viewpoint of viscosity stability of the negative electrode material to which the gelling agent (X) for alkaline batteries is added. More preferably, N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and pentaerythritol tri(meth)acrylate are preferred. Particularly more preferably, N,N'-methylenebisacrylamide, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and ethylene glycol diglycidyl ether are preferred. Most preferably, N,N'-methylenebisacrylamide and trimethylolpropane tri(meth)acrylate are preferred.

[0021] A crosslinking agent (b2) that does not hydrolyze in an alkaline environment is a crosslinking agent that does not have hydrolyzable bonds within its molecule and does not generate hydrolyzable bonds through the crosslinking reaction. Examples of such crosslinking agents (b2) include a crosslinking agent (b21) having two or more vinyl ether bonds and a crosslinking agent (b22) having two or more allyl ether bonds. Preferably, from the viewpoint of reactivity, a crosslinking agent having two or more allyl ether bonds is preferred.

[0022] Examples of crosslinking agents (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 (degrees of polymerization 2 to 5), bisphenol A divinyl ether, pentaerythritol trivinyl ether, sorbitol trivinyl ether, and polyglycerin (degrees of polymerization 3 to 13) polyvinyl ether.

[0023] Examples of crosslinking agents (b22) having two or more allyl ether bonds include crosslinking agents (b221) having two allyl groups in the molecule and no hydroxyl groups, crosslinking agents (b222) having two allyl groups and 1 to 5 hydroxyl groups in the molecule, crosslinking agents (b223) having 3 to 10 allyl groups and no hydroxyl groups in the molecule, and crosslinking agents (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule. When hydroxyl groups are included in the molecule, the compatibility with vinyl monomers (a1) and / or (a2) {especially (meth)acrylic acid (salt)} is good, improving the copolymerizability between crosslinking agent (b) and vinyl monomers (a1) and / or (a2), increasing the uniformity of crosslinking, improving the performance of the gelling agent (X) for alkaline batteries, and further improving the long-term stability of the viscosity of the negative electrode material containing the gelling agent (X) for alkaline batteries.

[0024] Examples of crosslinking agents (b221) having two allyl groups in the molecule and not containing hydroxyl groups include 1,4-cyclohexanedimethanol diallyl ether, alkylene (2-5 carbon atoms) glycol diallyl ether, and polyalkylene (2-6 carbon atoms) glycol (weight-average molecular weight: 100-4000) diallyl ether.

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

[0026] Crosslinking agents (b223) having 3 to 10 allyl groups in the molecule and no hydroxyl groups include trimethylolpropane trialyl ether, glycerin trialyl ether, pentaerythritol tetraallyl ether, and tetraallyloxyethane.

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

[0028] Two or more alkaline, non-hydrolyzable crosslinking agents (b2) may be used in combination.

[0029] Among the crosslinking agents (b2), a crosslinking agent (b22) having two or more allyl ether bonds is preferred, more preferably a crosslinking agent (b222 and (b224)) having 1 to 5 hydroxyl groups and 2 to 10 allyl groups, particularly preferably a crosslinking agent (b224) having 3 to 10 allyl groups and 1 to 3 hydroxyl groups in the molecule, and most preferably pentaerythritol trialyl ether, diglycerin trialyl ether, and sorbitol trialyl ether. The use of these crosslinking agents is preferred because they have good compatibility with water-soluble vinyl monomer (a1) and vinyl monomer (a2) that becomes (a1) by hydrolysis, and efficient crosslinking can be performed.

[0030] The content of the alkaline hydrolyzable crosslinking agent (b1) in the crosslinked polymer (A) depends 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, the settling of zinc powder is good, and excessive separation of the alkaline electrolyte can be prevented, thus further improving the long-term discharge characteristics of the battery.

[0031] The content of the crosslinking agent (b2) that does not hydrolyze in alkaline conditions in the crosslinked polymer (A) 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 settling properties of the zinc powder are good, and the long-term discharge characteristics of the battery are further improved.

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

[0033] The total content of crosslinking agents (b1) and (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). Within this range, excessive separation of the alkaline electrolyte can be prevented, resulting in even better long-term discharge characteristics of the battery. In addition, the stability of the gelling agent (X) for alkaline batteries is improved, and the long-term stability of the viscosity of the alkaline electrolyte containing the gelling agent (X) for alkaline batteries is further improved.

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

[0035] Surfactants (D) include ionic surfactants and nonionic surfactants.

[0036] Ionic surfactants include known anionic surfactants, amphoteric surfactants, and cationic surfactants, specifically those described in International Publication No. 99 / 03577, International Publication No. 2002 / 005949, and USP 4331447.

[0037] As the surfactant (D), a nonionic surfactant is preferred from the viewpoint of the viscosity of the alkaline electrolyte and the ability to rapidly inject the alkaline electrolyte.

[0038] Nonionic surfactants do not exhibit ionic properties when dissolved in water, but they do exhibit surface activity. In the present invention, there are no particular limitations on the nonionic surfactant, but from the viewpoint of the viscosity of the alkaline electrolyte and the ability to rapidly inject the alkaline electrolyte, at least one selected from the group consisting of sucrose fatty acid esters, sorbitan fatty acid esters, glycerin fatty acid esters, and fatty acid amides is preferred.

[0039] Sucrose fatty acid esters include those in which a fatty acid with 8 to 22 carbon atoms is esterified to sucrose. Specifically, examples include sucrose stearate esters [for example, those manufactured by Daiichi Kogyo Seiyaku Co., Ltd. {DK ester F-50 (HLB=6), F-70 (HLB=8), and F-110 (HLB=11), etc.}, and those manufactured by Mitsubishi Chemical Corporation {Ryoto sugar ester S-370 (HLB=approx. 3), S-770 (HLB=approx. 7), S-970 (HLB=approx. 9), S-1170 (HLB=approx. 11), and S-1170F (HLB=approx. 11), etc.}].

[0040] Sorbitan fatty acid esters include those in which sorbitan is esterified with a fatty acid having 8 to 22 carbon atoms. Specifically, examples include sorbitan palmitate [such as those manufactured by Kao Corporation (e.g., Leodol SP-P10 (HLB = 6.7)) and those manufactured by Riken Vitamin Co., Ltd. (e.g., Rikemar P-300 (HLB = 5.6))].

[0041] As the glycerin fatty acid ester, those in which a fatty acid having 8 to 22 carbon atoms is ester-bonded to glycerin and / or a polymer of glycerin (degree of polymerization: 2 to 20) are included. Specifically, diglycerin monolaurate [manufactured by Riken Vitamin Co., Ltd. {Poem DL-100 (HLB = 9.4), etc.}], diglycerin monomyristate [manufactured by Riken Vitamin Co., Ltd. {Poem DM-100 (HLB = 8.7), etc.}], diglycerin monostearate [manufactured by Riken Vitamin Co., Ltd. {Poem DS-100A (HLB = 7.7), etc.}], diglycerin monooleate [manufactured by Riken Vitamin Co., Ltd. {Poem DO-100V (HLB = 7.3), Rikemal DO-100 (HLB = 7.4), etc.}], decaglycerin stearate [manufactured by Riken Vitamin Co., Ltd. {Poem J-0081HV (HLB = 12), Poem J-0381V (HLB = 12), etc.}] and the like can be mentioned.

[0042] As the fatty acid amide, those in which a fatty acid having 8 to 22 carbon atoms and ethanolamine are amide-bonded are included. Specifically, coconut oil fatty acid monoethanolamide [manufactured by Sanyo Chemical Industries, Ltd. {Profan AB-20 (HLB = 11), etc.}], stearic acid monoethanolamide [manufactured by Sanyo Chemical Industries, Ltd. {Profan SME (HLB = 10), etc.}] and the like can be mentioned.

[0043] The HLB of the surfactant (D) is preferably 1 to 12, more preferably 3 to 11, and particularly preferably 5 to 9 from the viewpoints of the high-speed injectability of the alkaline electrolytic solution and the salting-out of the alkaline electrolytic solution.

[0044] Further, as the surfactant (D), from the viewpoints of the high-speed injectability of the alkaline electrolytic solution and the salting-out of the alkaline electrolytic solution, a nonionic surfactant is preferable, and more preferably at least one selected from the group consisting of sucrose fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester and fatty acid amide.

[0045] In the gelling agent (X) for alkaline batteries, 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, from the viewpoints of the high-speed injection property of the alkaline electrolyte and the salting-out of the alkaline electrolyte, based on the weight of the crosslinked polymer (A).

[0046] When the shape of the surfactant (D) is powdery, the particle size of the surfactant is not particularly limited, but the volume-average particle size is preferably 0.1 to 2000 μm, more preferably 0.5 to 1500 μm, and particularly preferably 1 to 1000 μm, from the viewpoint of the dry blending property to the crosslinked polymer (A).

[0047] Next, the manufacturing method of the gelling agent (X) for alkaline batteries will be described.

[0048] 〔Polymerization step〕The polymerization step is a step of obtaining a water-containing gel containing the crosslinked polymer (A). As the method for obtaining the crosslinked polymer (A), known polymerization methods can be applied. For example, any of aqueous solution polymerization, suspension polymerization, bulk polymerization, inverse phase suspension polymerization, or emulsion polymerization may be used.

[0049] Among these polymerization methods, aqueous solution polymerization, suspension polymerization, inverse phase suspension polymerization, and emulsion polymerization are preferable, more preferably aqueous solution polymerization, inverse phase suspension polymerization, and emulsion polymerization, particularly preferably aqueous solution polymerization and inverse phase suspension polymerization, and most preferably aqueous solution polymerization. For these polymerizations, known polymerization initiators, chain transfer agents, and / or solvents, etc. can be used. Most preferably, an aqueous solution polymerization method in which a crosslinking agent (b) is added 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 phase suspension polymerization method in which a similar monomer aqueous solution is dispersed and suspended in a hydrophobic organic solvent (e.g., hexane, toluene, xylene, etc.) for polymerization in the presence of a dispersant. With these polymerization methods, a gelling agent excellent in discharge characteristics and impact resistance can be obtained.

[0050] The polymerization methods for acrylic acid (salt) (a1) and 2-carboxyethyl acrylate (salt) (a2) by aqueous solution polymerization or reverse-phase suspension polymerization may be known methods, such as polymerization using a radical polymerization initiator or irradiation with radiation, ultraviolet light, electron beams, etc.

[0051] When using radical polymerization initiators, 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-t-butyl peroxide, cumene hydroperoxide, etc.], and redox initiators [combinations of reducing agents such as alkali metal salts (sulfite or bisulfite), ammonium sulfite, ammonium bisulfite, L-ascorbic acid, etc.) and peroxides such as alkali metal salts (sulfite or bisulfite), ammonium persulfite, ammonium persulfite, hydrogen peroxide solution, etc.]. Two or more of these may be used in combination.

[0052] The polymerization temperature varies depending on the type of initiator used, but from the viewpoint of increasing the degree of polymerization of the polymer, it is preferably -10°C to 100°C, and more preferably -10°C to 80°C.

[0053] There are no particular limitations on the amount of initiator, but from the viewpoint of increasing the degree of polymerization of the polymer, it is preferably 0.000001 to 3.0% by weight, and more preferably 0.000001 to 0.5% by weight, relative to the total weight of vinyl monomers (a1) and (a2).

[0054] In aqueous polymerization, the polymerization concentration (wt%) of the monomer varies depending on other polymerization conditions. However, with acrylic acid (a1), increasing the polymerization concentration makes it easy for pseudo-crosslinking (self-crosslinking) of the monomer itself to occur in parallel with the polymerization reaction, leading to a decrease in absorption and a decrease in the average degree of polymerization of the polymer. Furthermore, temperature control during polymerization is difficult, which tends to lead to a decrease in the average degree of polymerization of the polymer and an increase in oligomer components. Therefore, the polymerization concentration is preferably 10 to 40 wt%, and more preferably 10 to 30 wt%. The polymerization temperature is preferably -10 to 100°C, and more preferably -10 to 80°C. The amount of dissolved oxygen during polymerization depends on the amount of radical initiator added, but is 0 to 2 ppm (2 × 10⁻⁶). －４ Preferably less than 10% by weight, and more preferably 0 to 0.5 ppm (0.5 × 10⁻¹⁶). －４ (Weight percent or less). Within these ranges, a high degree of polymerization crosslinked polymer (A) can be produced.

[0055] 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 crosslinking agent (b) can be completely dissolved in the monomer aqueous solution. However, crosslinking agent (b2), which does not hydrolyze in an alkaline environment, has poor water solubility compared to crosslinking agent (b1), which can be hydrolyzed in an alkaline environment. In particular, its solubility in aqueous acrylic acid (salt) solutions is extremely low, and even if a predetermined amount of (b2) is added, (b2) may separate from the monomer aqueous solution, preventing the desired crosslinking from occurring. Therefore, it is preferable to carry out polymerization with a degree of neutralization of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) of 0 to 30 mol%, and to further neutralize after polymerization if necessary. It is even more preferable to polymerize in an unneutralized state and then neutralize after polymerization if necessary.

[0056] Furthermore, when acrylic acid is polymerized under the same conditions, a lower degree of neutralization tends to result in a higher degree of polymerization. Therefore, in order to increase the degree of polymerization of the polymer, it is preferable to perform polymerization at a low degree of neutralization.

[0057] In the production of the crosslinked polymer (A), when the polymer is produced under exactly the same conditions except that no crosslinking agent is used, the average degree of polymerization of the polymer is preferably 5,000 to 1,000,000, and more preferably 10,000 to 1,000,000.

[0058] When polymerization is carried out under conditions where the average degree of polymerization is 5,000 or higher, the viscosity of the high-concentration alkaline aqueous solution to which the gelling agent has been added can be prevented from decreasing and / or increasing its stringiness by using an appropriate amount of crosslinking agent. The above average degree of polymerization was measured by gel permeation chromatography (GPC).

[0059] In the present invention, the crosslinked polymer (A) obtained by aqueous polymerization or the like is obtained as a water-containing gel (hydrated gel). The hydrated gel is used as a gelling agent (X) for alkaline batteries after drying.

[0060] The water content of the water-containing gel after the polymerization step varies depending on the manufacturing process and application, but is generally preferred to be in the range of 60% to 90%. If it exceeds 90%, the drying efficiency in the drying step described later will be poor, and if it is less than 60%, the polymerization temperature of the crosslinked polymer (A) cannot be controlled, making it difficult to obtain a polymer with a high degree of polymerization.

[0061] The hydrated gel obtained in the polymerization step described above can be shredded as needed. The size (longest diameter) of the shredded gel is preferably 50 μm to 10 cm, more preferably 100 μm to 2 cm, and particularly preferably 1 mm to 1 cm. Within this range, drying performance in the drying step is further improved.

[0062] The aforementioned water-containing gel can be shredded by known methods, and known shredding devices can be used. Examples of shredding devices include dual-arm kneaders, internal mixers (Banbury mixers), self-cleaning mixers, gear compounders, screw extruders, screw kneaders, and mincing machines.

[0063] A neutralizing agent may be mixed to neutralize the acidic groups contained in the water-swellable polymer in the hydrated gel, allowing for simultaneous shredding and neutralization of the hydrated gel. Alternatively, a crosslinking agent having two or more functional groups that react with the crosslinked polymer (A) in the gel may be mixed to induce a crosslinking reaction. If necessary, additives or bulking agents such as residual vinyl monomer reducing agents (sodium sulfite, hydrogen peroxide, etc.), preservatives, fragrances, deodorizers, colorants, fibrous materials, antioxidants, silica, zeolites, etc., may be added.

[0064] Furthermore, by adding surfactant (D) to the water-containing gel, the shredding properties of the gel are improved and the fusion of gels can be suppressed. The amount of surfactant (D) added to the water-containing gel is preferably 0.005 to 1% by weight, and more preferably 0.05 to 0.5% by weight, relative to the solid content of the cross-linked polymer (A). If the amount added is less than 0.005% by weight, the shredding properties of the gel and the fusion effect between gels are poor, and if it exceeds 1% by weight, it adversely affects the powder flowability after drying and worsens the handling properties in the grinding process described later.

[0065] The method of adding surfactant (D) to the aqueous gel is not particularly limited, but surfactant (D) may be added as is, or as an aqueous solution or dispersion of surfactant (D). Alternatively, it may be sprinkled on before, during, or after the aqueous gel passes through the shredder. Any of these methods can be used, but it is preferable to sprinkle it on after passing through so that the surfactant (D) is dispersed as uniformly as possible on the surface of the aqueous gel during gel transfer to the dryer. If a large shear force is applied to shred the gel after surfactant (D) has been added, the surfactant (D) may penetrate into the interior of the aqueous gel and its effect will be diminished, so it is preferable not to apply a large shear force after uniform addition. Furthermore, surfactant (D) may be added both before and after passing through the shredder, or surfactant (D) may be added during polymerization.

[0066] [Drying Process] The drying process involves supplying the water-containing gel, which has been shredded as necessary, onto a continuously moving support, and drying the water-containing gel by bringing it into contact with hot air at a supply temperature of 90 to 230°C while the water-containing gel is continuously moved on the support.

[0067] The support is for carrying and moving the water-containing gel, and the support is typically in the form of perforated metal, a screen, a conveyor belt, or a conveyor roller, and is not particularly limited as long as it can carry and move the water-containing gel stably and withstand the drying temperature. The material and structure of the support can be selected according to the properties of the water-containing gel and the drying conditions, and the movement speed of the support can be adjusted in accordance with the progress of drying, thereby optimizing the drying time.

[0068] As for the material of the support, stainless steel is preferred from the viewpoint of durability, abrasion prevention, and corrosion prevention, since the water-containing gel comes into direct contact with it.

[0069] Stainless steel typically contains 16-20% by weight of chromium. Chromium forms a chromium dioxide oxide film on the surface of the stainless steel, improving corrosion resistance. Adding 8-12% by weight of nickel further enhances corrosion resistance and toughness. Furthermore, suitable stainless steel contains at least 0.08% by weight of carbon. The inclusion of carbon improves the strength of the stainless steel and increases the productivity of the drying process.

[0070] The support may have a number of openings. From the viewpoint of drying efficiency of the water-containing gel and prevention of sedimentation of zinc powder, the opening ratio is preferably 30 to 70%, more preferably 35 to 60%, and particularly preferably 35 to 50%. Here, the opening ratio represents the proportion of the area of ​​the support that is occupied by the openings.

[0071] The height of the water-containing gel placed on the support is preferably 1 to 8 cm, and more preferably 2 to 7 cm, from the viewpoint of drying efficiency and productivity of the water-containing gel.

[0072] The method for supplying the water-containing gel onto a continuously moving support is not particularly limited and can be carried out by known methods. The means for continuously moving the support is not particularly limited and, for example, a conveyor equipped with the support can be exemplified.

[0073] In the drying process described above, the temperature of the hot air brought into contact with the water-containing gel is 90 to 230°C, preferably 100 to 220°C. If the temperature of the hot air brought into contact with the water-containing gel is 230°C or lower, the polymer is less likely to crosslink due to the heat during drying, the degree of crosslinking does not increase too much due to thermal crosslinking, the absorption amount does not decrease, and the viscosity in the alkaline electrolyte does not decrease. If the temperature is 90°C or higher, drying does not require a long time and is efficient.

[0074] In the drying process described above, the wind speed of the hot air brought into contact with the water-containing gel is preferably 0.5 to 3.0 m / s, and more preferably 0.7 to 2.5 m / s, from the viewpoint of productivity of the drying process and the 3% by weight solution viscosity of the gelling agent (X) for alkaline batteries in the 40% by weight potassium hydroxide aqueous solution described later.

[0075] In the drying process described above, the time for which hot air is brought into contact with the water-containing gel varies depending on the wind speed and temperature of the hot air, but is generally 5 to 300 minutes, preferably 5 to 120 minutes.

[0076] The drying process may include multiple drying conditions that differ with respect to the direction of movement of the support. This allows the water-containing gel to be dried in stages, resulting in a uniformly dried state. Furthermore, by setting a lower supply temperature towards the end of the drying process, the dried gel can be returned to an appropriate temperature, thus maintaining its quality.

[0077] If the drying step includes a plurality of drying conditions that differ with respect to the direction of movement of the support, the drying step preferably involves continuously moving the water-containing gel on the support while bringing hot air with a supply temperature of 210 to 230°C into contact with the water-containing gel, and then drying the water-containing gel by bringing hot air with a supply temperature of 90 to 130°C into contact with the water-containing gel.

[0078] The drying process is preferably a continuous process for efficiently drying the water-containing gel, from the viewpoint of improving drying efficiency, reducing uneven drying, and improving product quality. This improves productivity in the production of the gelling agent (X) for alkaline batteries.

[0079] Examples of dryers used in the drying process include parallel flow band dryers (tunnel dryers), vented band dryers, jet flow (nozzle jet) dryers, vented vertical dryers, and box-type hot air dryers. Multiple dryers can also be used in combination.

[0080] The water content of the water-containing gel after drying is preferably 0.5 to 8% by weight, and more preferably 1 to 5% by weight, from the viewpoint of productivity of the drying process and the handling of the gelling agent (X) for alkaline batteries.

[0081] Other drying methods for hydrated gels include contact drying, where the hydrated gel is compressed and stretched on a drum dryer. However, because hydrated gels have poor thermal conductivity, it is necessary to create a thin film of the hydrated gel on the drum or elsewhere for drying. However, commercially available drum dryers are generally made of metals with a lower ionization tendency than zinc, such as iron, chromium, and nickel. As a result, the frequency of contact between the hydrated gel and the drum metal surface becomes extremely high. Furthermore, since the hydrated gel is an acrylic acid (salt) copolymer, it contains a large amount of metal elements with a lower ionization tendency than zinc that dissolve into the gel. Moreover, because the frequency of contact between the hydrated gel and the drum is extremely high and the hydrated gel is highly adhesive, it is necessary to use something like a knife to detach the dried material from the drum dryer. This mechanical wear between the drum and the knife causes the metal surface of the drum or knife to wear down, resulting in metal particles being mixed into the dried material. As described above, when using contact drying methods such as drum dryers, metal ions and metal powders tend to be mixed into the gelling agent, resulting in a considerable amount of metal ions and metal powders with a lower ionization tendency than zinc (metals whose standard electrode potential is lower than zinc, and which can be represented by atomic symbols such as Cr, Fe, Ni, Sn, Pb, Cu, Hg, Ag, etc.). When these gelling agents are used as gelling agents for alkaline batteries, the zinc powder in the battery forms a battery with metal ions or metal powders with a lower ionization tendency than zinc, which generates hydrogen gas through electrolysis. This increases the pressure inside the battery, and can even lead to leakage of the alkaline electrolyte or, in severe cases, damage to the battery. Furthermore, when a water-containing gel is compressed and stretched and dried on a drum dryer or the like, the resulting thin film-like material, even after subsequent pulverization to adjust the particle size to the desired level, retains its flaky particle structure. Compared to pulverized block-shaped material dried using air permeability or aeration drying methods, its strength is significantly weaker. Moreover, when swollen in a high-concentration alkaline aqueous solution and mechanically mixed with zinc powder, the swollen gel is destroyed, resulting in smaller gel particles. Therefore, it is preferable not to use contact drying methods such as drum dryers.

[0082] [Grinding Process] The grinding process involves grinding the dried water-containing gel obtained in the drying process using a grinder to obtain a pulverized product of the water-containing gel. The grinding method can be any known method, for example, an impact grinder (hammer mill, pin mill, ball mill, disc mill, etc.) or an air grinder (jet mill, etc.) can be used. A hammer mill is a device that grinds materials with a hammer that rotates at high speed, and is capable of relatively coarse grinding. A pin mill is a device that grinds materials between a fixed pin and a rotating pin, and is capable of obtaining a uniform particle size distribution. A ball mill is a device in which balls in a rotating drum grind materials, and is capable of fine grinding. A disc mill is a device that grinds materials between a fixed disc and a rotating disc, and is capable of fine grinding using shear force and compressive force. A disc mill is suitable when a uniform powder is required, as it can obtain a uniform particle size distribution. The degree of grinding can be finely controlled by adjusting the shape and spacing of the discs, the rotation speed, etc. Furthermore, disc mills can operate at relatively low speeds and suppress heat generation during grinding, making them suitable for grinding heat-sensitive materials. Jet mills are devices that grind materials using high-speed airflow, enabling very fine grinding. From the viewpoint of productivity of the gelling agent (X) for alkaline batteries, an impact grinder is preferably used, and a disc mill is even more preferably used.

[0083] The grinding conditions are adjusted as appropriate to control the particle size distribution of the ground product. Specifically, these include the grinder's rotation speed, grinding time, input amount, and cooling conditions. Since these conditions affect the particle size distribution, shape, and surface properties of the ground product, they are optimized with consideration for the performance of the final product. In particular, it is desirable that the particle size of the ground product be set within an appropriate range to enable efficient classification in the classification process described later.

[0084] In the grinding process, a cooling system can be used to prevent deterioration of the pulverized product due to the heat generated during grinding. Cooling systems such as jackets that circulate cooling water or systems that blow in cooling gas can be used to suppress the temperature rise during grinding and maintain the quality of the pulverized product.

[0085] [Classification Process] The classification process is a process of classifying the pulverized product obtained in the pulverization process into a predetermined particle size range. The classification method may be a known method, and for example, a classifying device such as a vibrating screen or an air classifier can be used. From the viewpoint of the apparent density and angle of repose of the gelling agent (X) for alkaline batteries, a vibrating screen is preferred, characterized in that a screen with a mesh opening of 200 to 500 μm is used, and it is preferable to use a screen with a mesh opening of 300 to 400 μm from the viewpoint of the apparent density and angle of repose of the gelling agent (X) for alkaline batteries.

[0086] In this invention, it is preferable to remove any mixed-in metal powder, such as iron, using a magnetic iron removal machine at any stage after drying. However, even if iron removal is performed fairly precisely using an iron removal machine, it is difficult to remove non-magnetic metals with the machine. Furthermore, even with magnetic metals, those contained inside the dried polymer particles or attached to the dried particles cannot be removed. Therefore, it is desirable to take sufficient care in the production equipment to prevent these metals from being mixed in from the beginning.

[0087] The iron content of the gelling agent (X) for alkaline batteries is preferably less than 50 ppm, from the viewpoint of suppressing the reaction with zinc contained in the negative electrode of the alkaline battery. The lower limit of the iron content of the gelling agent (X) for alkaline batteries is not particularly limited, but from the viewpoint of economy, it is, for example, 1 ppm or more.

[0088] The apparent density of the alkaline battery gelling agent (X) produced by the manufacturing method of the present invention is 0.45 to 0.90 g / ml, preferably 0.50 to 0.85 g / ml, more preferably 0.55 to 0.80 g / ml, and particularly preferably 0.60 to 0.75 g / ml. When the apparent density is within this range, the dispersibility of the alkaline electrolyte to which the alkaline battery gelling agent (X) is added is improved, enabling uniform gelation and thus stabilizing the battery's performance. In particular, an appropriate apparent density prevents the sedimentation of zinc powder in the electrolyte and improves the long-term discharge characteristics of the battery.

[0089] Furthermore, the angle of repose of the alkaline battery gelling agent (X) is 30 to 50°, preferably 32 to 48°, more preferably 34 to 46°, and particularly preferably 36 to 44°. When the angle of repose is within this range, the fluidity of the alkaline battery gelling agent (X) is good, making it easy to handle in the alkaline battery manufacturing process. In particular, an appropriate angle of repose improves the packing properties of the alkaline battery gelling agent (X), allowing for uniform mixing during the battery manufacturing process. As a result, batteries with stable performance and excellent discharge characteristics can be produced.

[0090] The apparent density and angle of repose mentioned above are measured by the following method. <Method for measuring the apparent density of the gelling agent for alkaline batteries (X)> First, 50 g of the gelling agent for alkaline batteries (X) is prepared and measured using a tap densimeter (Autotap, Quantachrome, Instruments). The measurement is performed by placing the sample in a cylinder, recording the volume after 1000 taps, and calculating the apparent density. The apparent density is obtained by dividing the mass of the sample by the volume after tapping. The apparent density of the gelling agent for alkaline batteries (X) in the examples described later was determined according to the above method.

[0091] <Method for measuring the angle of repose of the gelling agent (X) for alkaline batteries> First, 100g of the gelling agent (X) for alkaline batteries was prepared and piled up in a cone shape. Next, the angle between the inclined surface of the piled powder and the horizontal line was measured and defined as the angle of repose.

[0092] The crosslinked polymer (A) may be crosslinked on its surface by reacting it with a surface crosslinking agent if necessary.

[0093] As the surface crosslinking agent, known surface crosslinking agents, such as the surface crosslinking agent described in Japanese Patent Publication No. 2003-225565, can be used.

[0094] Of these surface crosslinking agents, from the viewpoint of the discharge characteristics of alkaline batteries, crosslinking agents having at least two functional groups that can react with the carboxyl groups of acrylic acid (a1) and 2-carboxyethyl acrylate (a2) are preferred, more preferably polyvalent glycidyl, particularly preferably ethylene glycol diglycidyl ether and glycerin diglycidyl ether, and most preferably ethylene glycol diglycidyl ether.

[0095] 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 per unit.

[0096] Methods for the surface crosslinking reaction can be those described in the publicly available publications {for example, Japanese Patent No. 3648553, Japanese Unexamined Patent Publication No. 2003-165883, Japanese Unexamined Patent Publication No. 2005-75982, and Japanese Unexamined Patent Publication No. 2005-95759}.

[0097] The amount of the crosslinked polymer (A) soluble in a 40% by weight potassium hydroxide aqueous solution is preferably 10 to 30% by weight, more preferably 10 to 20% by weight, and particularly preferably 10 to 15% by weight, based on the weight of (A). When the amount of the crosslinked polymer (A) soluble in a 40% by weight potassium hydroxide aqueous solution is within this range, the viscosity of the alkaline electrolyte to which the gelling agent for alkaline batteries (X) has been added becomes suitable, the liquid drainage of the negative electrode material improves, and a battery with stable quality can be manufactured. Furthermore, the sedimentation of zinc powder in the negative electrode material can be prevented, thus enabling the production of a battery with excellent discharge characteristics over time. If the amount of the crosslinked polymer (A) soluble in a 40% by weight potassium hydroxide aqueous solution exceeds 30% by weight, stringiness appears in the alkaline electrolyte to which the gelling agent for alkaline batteries (X) has been added, the liquid drainage of the negative electrode material deteriorates significantly, and variations in the filling amount occur, resulting in unstable battery quality. If the amount of the crosslinked polymer (A) soluble in a 40% potassium hydroxide aqueous solution is less than 10% by weight, the viscosity of the alkaline electrolyte to which the gelling agent for alkaline batteries (X) has been added will decrease, causing the zinc powder to settle, which will worsen the impact resistance and discharge characteristics.

[0098] The viscosity of a 3% solution of the gelling agent (X) for alkaline batteries in a 40% potassium hydroxide aqueous solution 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 3% solution of the gelling agent (X) for alkaline batteries in a 40% potassium hydroxide aqueous solution is the solution (S) prepared by stirring and mixing 97 parts by weight of a 40% potassium hydroxide aqueous solution and 3 parts by weight of the gelling agent (X) for alkaline batteries until homogeneous, and then leaving it at 40°C for 24 hours. The viscosity of this solution is measured by the following method. <Method for measuring the viscosity of solution (S)> Using a digital B-type viscometer (manufactured by TOKIMEC), the viscosity of solution (S) at a measurement temperature of 40°C is measured in accordance with JIS 7117-1:1999 and is defined as the viscosity of solution (S). Note that rotor No. Using 4, the measurement was performed at a rotation speed of 3 rpm. The viscosity of solution (S) in the examples described later was measured according to the method described above.

[0099] Examples of methods for filling an alkaline battery with the aforementioned gelling agent (X) include: (1) a method of pre-mixing the gelling agent (X), alkaline electrolyte (for example, a highly concentrated aqueous potassium hydroxide solution, optionally containing zinc oxide, etc.), zinc powder (and / or zinc alloy powder), and optionally other additives to prepare a mixture of negative electrode material, and filling this mixture into the negative electrode container of the battery to form a gel-like negative electrode; and (2) a method of filling the negative electrode container of the battery with the gelling agent (X), zinc powder (and / or zinc alloy powder), and optionally other additives, and then filling with alkaline electrolyte to generate a gel-like negative electrode within the container. Of the above, method (1) is preferred as it allows the zinc powder to be uniformly dispersed within the negative electrode container of the battery. The amount of gelling agent (X) to be added varies depending on the structure of the negative electrode container, the particle size of the zinc powder, and the concentration of the alkaline electrolyte, but is preferably 0.5 to 10% 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 (X) for alkaline batteries becomes appropriate, preventing the sedimentation of zinc powder and making it easy to handle.

[0100] The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. In the following, parts refer to parts by weight. Unless otherwise specified, ultrapure water refers to water with an electrical conductivity of 0.06 μS / cm or less, and ion-exchanged water refers to water with an electrical conductivity of 1.0 μS / cm or less.

[0101] <Example 1> In an insulated polymerization tank, 249.5 parts acrylic acid, 0.5 parts 2-carboxyethyl acrylate ([(a1) / (a2)] = 99.8 / 0.2), 0.50 parts pentaerythritol trialyl ether (0.20 wt%) relative to acrylic acid, 0.40 parts trimethylolpropane triacrylate (0.16 wt%) relative to acrylic acid, and 750 parts 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 was passed through the acrylic acid aqueous solution at a flow rate of 5 L / min to reduce 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 based on the diaphragm electrode method (ORBISPHERE 510, manufactured by HACH ULTRA). After confirming that the acrylic acid aqueous solution was at 3°C, 5.0 parts of a 10% by weight aqueous solution of 2,2'-azobis(2-amidinopropane) hydrochloride (manufactured by Wako Pure Chemical Industries, Ltd., trade name: V-50), 5.0 parts of a 1.0% by weight hydrogen peroxide solution, 5.0 parts of a 1.0% by weight L-ascorbic acid aqueous solution, and 5.0 parts of a 0.1% by weight iron(III) sulfate aqueous solution were added to the insulated polymerization tank as polymerization initiators while continuing nitrogen aeration. After continuing nitrogen aeration for 25 minutes following the addition of the polymerization initiators, the nitrogen aeration was stopped and the mixture was allowed to stand for 16 hours to carry out the polymerization reaction. After standing for 16 hours, the water-containing gel obtained by the polymerization reaction was removed from the polymerization reactor. The extracted water-containing gel was mixed and shredded in a mincing machine (ROYAL 12VR-400K) while 250 parts of a 49 wt% sodium hydroxide (reagent grade) aqueous solution were added and mixed. After shredding in the mincing machine (ROYAL 12VR-400K), shredded gel was obtained. The shredded gel was stacked to a thickness of 5 cm on a SUS belt conveyor with an opening ratio of 50%, and a small air permeable dryer (Inoue Metal Co., Ltd.) was used to dry the shredded gel under the conditions of hot air at a wind speed of 1.5 m / s, by passing 220°C hot air through the shredded gel for 25 minutes, then 200°C hot air through the shredded gel for 20 minutes, and then 100°C hot air through the shredded gel for 15 minutes to evaporate the water in the shredded gel and obtain a dry powder containing a cross-linked polymer. The weight percentage of particles with a particle size of 2.8 mm or larger relative to the total weight of the dry powder was 48 wt%.Next, the dried powder was crushed in a roll mill (RM-10 type roll-type pulverizer, Asano Iron Works Co., Ltd.) with a clearance of 0.35 mm. Then, a sieve with a mesh size of 312 μm (55 mesh) was used to collect the material that passed through the sieve. Iron-derived foreign matter was removed using an iron removal machine to obtain the gelling agent for alkaline batteries (X-1). The apparent density was 0.71 g / ml.

[0102] <Example 2> The same procedure as in Example 1 was followed, except that the amount of pentaerythritol trialyl ether added was changed to 0.90 parts (0.36% by weight of acrylic acid) and trimethylolpropane triacrylate (0.70 parts by weight of acrylic acid) instead of 0.50 parts (0.20% by weight of acrylic acid) and 0.40 parts (0.16% by weight of acrylic acid) respectively, to obtain a gelling agent for alkaline batteries (X-2).

[0103] <Example 3> The same procedure as in Example 1 was followed, except that instead of 249.5 parts acrylic acid and 0.5 g of 2-carboxyethyl acrylate ([(a1) / (a2)] = 99.8 / 0.2), the amount of acrylic acid added was 249.975 parts and the amount of 2-carboxyethyl acrylate added was 0.025 parts ([(a1) / (a2)] = 99.99 / 0.01), to obtain a gelling agent for alkaline batteries (X-3).

[0104] <Example 4> The same procedure as in Example 1 was followed, except that instead of adding 249.5 parts acrylic acid and 0.5 g of 2-carboxyethyl acrylate ([(a1) / (a2)] = 99.8 / 0.2), the amount of acrylic acid added was 247.5 parts and the amount of 2-carboxyethyl acrylate added was 2.5 parts ([(a1) / (a2)] = 99 / 1), to obtain a gelling agent for alkaline batteries (X-4).

[0105] <Example 5> In Example 5, the procedure was the same as in Example 1, except that instead of using a sieve with a mesh size of 312 μm (55 mesh) and collecting the material that passed through the sieve, a sieve with a mesh size of 496 μm (35 mesh) was used and the material that passed through the sieve was collected. A gelling agent for alkaline batteries (X-6) was obtained. The apparent density of (X-5) was 0.60 g / ml.

[0106] <Example 6> In Example 6, the procedure was the same as in Example 1, except that instead of using a sieve with a mesh size of 312 μm (55 mesh) and collecting the particles that passed through the sieve, a sieve with a mesh size of 213 μm (70 mesh) was used and the particles that passed through the sieve were collected. The gelling agent for alkaline batteries (X-6) was obtained. The apparent density was 0.77 g / ml.

[0107] <Example 7> The same procedure as in Example 1 was performed, except that the opening was 35% and a SUS belt conveyor was used, to obtain a gelling agent for alkaline batteries (X-7).

[0108] <Example 8> The same procedure as in Example 1 was performed, except that the opening was 65% and a SUS belt conveyor was used, to obtain a gelling agent for alkaline batteries (X-8).

[0109] <Example 9> The same procedure as in Example 1 was followed, except that the wind speed condition of the hot air of the small air permeable dryer was set to 0.8 m / s, to obtain a gelling agent for alkaline batteries (X-9).

[0110] <Example 10> The same procedure as in Example 1 was followed, except that the wind speed condition of the hot air in the small air permeable dryer was set to 2.8 m / s, to obtain a gelling agent for alkaline batteries (X-10).

[0111] <Comparative Example 1> The same procedure as in Example 1 was followed, except that 2-carboxyethyl acrylate was not added, to obtain a gelling agent for alkaline batteries (ratio X-1).

[0112] <Comparative Example 2> In Example 1, the amount of acrylic acid added was 245 parts and the amount of 2-carboxyethyl acrylate added was 5 parts ([(a1) / (a2)] = 98 / 2), except that the procedure was the same as in Example 1, except that instead of 249.5 parts acrylic acid and 0.5 g of 2-carboxyethyl acrylate ([(a1) / (a2)] = 99.8 / 0.2), the amount of acrylic acid added was 245 parts and the amount of 2-carboxyethyl acrylate added was 5 parts ([(a1) / (a2)] = 98 / 2), and a gelling agent for alkaline batteries (ratio X-2) was obtained.

[0113] <Comparative Example 3> In the same procedure as in Example 1, a sieve with a mesh size of 312 μm (55 mesh) was used to collect particles of a certain particle size that could pass through the sieve, while in this case, a sieve with a mesh size of 30 μm (500 mesh) was used to collect particles of a certain particle size that could pass through the sieve. The gelling agent for alkaline batteries (Ratio X-3) was obtained by performing the same procedure as in Example 1. The apparent density of (Ratio X-3) was 0.94 g / ml.

[0114] <Comparative Example 4> In the same procedure as in Example 1, a sieve with a mesh size of 600 μm (26 mesh) was used instead of a sieve with a mesh size of 312 μm (55 mesh) used to collect the material that passed through the sieve. The gelling agent for alkaline batteries (Ratio X-4) was obtained. The apparent density of (Ratio X-4) was 0.41 g / ml.

[0115] <Comparative Example 5> In Example 1, instead of using a small air permeable dryer (manufactured by Inoue Metal Co., Ltd.) to permeate the shredded gel with 220°C hot air for 25 minutes, 200°C hot air for 20 minutes, and 100°C hot air for 15 minutes, a small air permeable dryer (manufactured by Inoue Metal Co., Ltd.) was used to permeate the shredded gel with 280°C hot air for 25 minutes, 250°C hot air for 20 minutes, and 100°C hot air for 15 minutes. The same procedure as in Example 1 was followed to obtain a gelling agent for alkaline batteries (ratio X-5).

[0116] <Comparative Example 6> In Example 1, instead of using a small air permeable dryer (manufactured by Inoue Metal Co., Ltd.) to permeate the shredded gel with 220°C hot air for 25 minutes, 200°C hot air for 20 minutes, and 100°C hot air for 15 minutes, a small air permeable dryer (manufactured by Inoue Metal Co., Ltd.) was used to permeate the shredded gel with 80°C hot air for 60 minutes. The same procedure as in Example 1 was followed to obtain a gelling agent for alkaline batteries (Ratio X-6). However, (Ratio X-6) was insufficiently dried and became lumpy, making classification by sieving impossible, and therefore could not be evaluated.

[0117] Table 1 or 2 shows the results of measuring the apparent density, angle of repose, and 3% viscosity of (X) in a 40% wt% potassium hydroxide aqueous solution for the alkaline battery gelling agents (X-1) to (X-10) and (ratio X-1) to (ratio X-6) produced in Examples 1 to 10 and Comparative Examples 1 to 6, as well as the results of evaluating the sedimentation properties of zinc powder using the following method.

[0118]

[0119]

[0120] <Evaluation Method> [Evaluation Method for the Settling Properties of Zinc Powder] 150 g of 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 gelling agent were added to a 1-liter twin-screw kneader (manufactured by Irie Shoji Co., Ltd., product name: PNV-1), and the mixture was mixed at a rotation speed of 50 rpm for 60 minutes to prepare a negative electrode material. 50 g of the prepared negative electrode material was placed in a sealable 50 ml sample bottle (diameter 34 mm, height 77 mm, made of polypropylene), and air bubbles that entered during mixing were removed under reduced pressure. The sample bottle was sealed and left 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 from a height of 3 cm at a rate of 30 times / min to promote the settling of the zinc powder. After tapping was completed, the distance (mm) at which the zinc powder settled from its initial position (the position of the upper end of the negative electrode material in the sample bottle) was measured and defined as the sedimentation property (mm) of the zinc powder. The sedimentation property of the zinc powder was evaluated according to the following criteria: [Evaluation Criteria] ◎: The distance at which the zinc powder settled was less than 5.0 mm ○: The distance at which the zinc powder settled was 5.0 mm or more and less than 10.0 mm ×: The distance at which the zinc powder settled was 10.0 mm or more

[0121] [Method for Evaluating Iron Content (unit: ppm)] 0.5 g of alkaline battery gelling agent (X) was placed in a Teflon decomposition container, and 10 ml of commercially available concentrated nitric acid (70 wt% aqueous solution) was added. The container was sealed and heated at 180°C for 30 minutes using a microwave decomposition device to completely decompose the sample. If necessary, 3 ml of commercially available hydrogen peroxide (30 wt% aqueous solution) was added to accelerate decomposition. After decomposition, the solution was cooled to room temperature, filtered through filter paper, and insoluble matter was removed. The filtrate was transferred to a 100 ml volumetric flask and diluted to 100 ml with ultrapure water. Using the prepared solution, the iron content was measured using an inductively coupled plasma atomic emission spectrometer (Agilent, ICP-OES5900) after calibration with iron standard solutions (1, 5, 10, and 100 ppm). The plasma conditions were as follows. RF power 1.2 kW, plasma gas flow rate 15 L / min, auxiliary gas flow rate 1.5 L / min, nebulizer gas flow rate 0.7 L / min.

Claims

1. A method for producing a gelling agent (X) for alkaline batteries, comprising a crosslinked polymer (A) containing acrylic acid (salt) (a1), 2-carboxyethyl acrylate (salt) (a2), and a crosslinking agent (b) as constituent monomers, wherein the crosslinking agent (b) comprises a crosslinking agent (b1) that can be hydrolyzed in an alkaline environment and a crosslinking agent (b2) that does not hydrolyze in an alkaline environment, and the weight ratio of acrylic acid (salt) (a1) to 2-carboxyethyl acrylate (salt) (a2) [(a1) / (a2)] is 99 / 1 to 99.99 / 0.01, the method comprising: a polymerization step of obtaining a hydrated gel containing the crosslinked polymer (A); a drying step of supplying the hydrated gel onto a continuously moving support, and drying the hydrated gel by bringing hot air at a supply temperature of 90 to 230°C into contact with the hydrated gel while the hydrated gel is continuously moved on the support; A method for producing an alkaline battery gelling agent (X), comprising a grinding step of grinding the dried water-containing gel with a pulverizer to obtain a pulverized product of the water-containing gel, and a classification step of classifying the pulverized product using a sieve with a mesh opening of 200 to 500 μm, wherein the apparent density of the alkaline battery gelling agent (X) is 0.45 to 0.90 g / ml and the angle of repose is 30 to 50°.

2. The method for producing a gelling agent (X) for alkaline batteries according to claim 1, wherein the support is a conveyor belt having an open area ratio of 30 to 70%.

3. The method for producing a gelling agent (X) for alkaline batteries according to claim 1, wherein the drying step is a step of supplying a water-containing gel onto a support that moves continuously, bringing hot air with a supply temperature of 210 to 230°C into contact with the water-containing gel while the water-containing gel moves continuously on the support, and then drying the water-containing gel by bringing hot air with a supply temperature of 90 to 130°C into contact with it.

4. A method for producing an alkaline battery gelling agent (X) according to any one of claims 1 to 3, wherein the iron content of the alkaline battery gelling agent (X) is 1 to less than 50 ppm.

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