Nitrile rubber manufacturing method

Abstract

This invention provides a method for producing nitrile rubber with a low ash content. [Solution] The present invention provides a method for producing nitrile rubber, comprising: an emulsion polymerization step of emulsion polymerization of acrylonitrile and 1,3-butadiene to obtain a polymerization solution; an anti-aging agent addition step of adding a phenolic anti-aging agent to the obtained polymerization solution; a coagulation step of contacting the polymerization solution to which the phenolic anti-aging agent has been added with an aqueous solution of a polyvalent metal salt to produce a water-containing crumb in which 60% by mass or more passes through a JIS sieve with an 8 mm mesh size but does not pass through a JIS sieve with an 1.7 mm mesh size; a washing step of washing the produced water-containing crumb with hot water; a dehydration step of dehydrating the washed water-containing crumb at 40°C or higher; and a drying step of drying the washed water-containing crumb to less than 1% by mass.

Description

[Technical Field]

[0001] The present invention relates to a method for producing nitrile rubber, and more particularly to a method for producing nitrile rubber that reduces the ash content of the resulting nitrile rubber. [Background Art]

[0002] Electrochemical devices such as lithium ion secondary batteries, lithium ion capacitors and electric double layer capacitors are compact, lightweight, have high energy density, and further enable repeated charge and discharge, and thus are used in a wide range of applications. Therefore, in recent years, improvements to battery members such as electrodes have been studied for the purpose of achieving higher performance of electrochemical devices.

[0003] Here, an electrode used for an electrochemical device usually includes a current collector and an electrode mixture layer formed on the current collector. The electrode mixture layer is formed, for example, by applying a slurry containing an electrode active material, a conductive material, a binder and the like onto a current collector, and drying the applied slurry.

[0004] Therefore, in recent years, in order to achieve further improvement in the performance of electrochemical devices, attempts have been made to improve binders used for forming electrode mixture layers. For example, hydrogenated nitrile rubber has been studied as a binder.

[0005] For example, Patent Document 1 (WO2023 / 162835) describes a polymerization solution obtained by emulsion polymerization of acrylonitrile and 1,3-butadiene, to which an antioxidant is added. Then, a 25% by mass aqueous calcium chloride solution is added while stirring to coagulate the polymer. After washing with 50 times the volume of ion-exchanged water, the polymer is dried under reduced pressure at 90°C to obtain a precursor nitrile rubber with a weight-average molecular weight of 210,000. Next, the obtained precursor is dissolved in monochlorobenzene and a double decomposition reaction is carried out using a Grubbs catalyst. A Wilkinson catalyst is then added to carry out a hydrogenation reaction. Activated carbon treatment is performed to adjust the concentration of divalent or higher metal ions and remove residual chain transfer agents. The material is then filtered and dried to obtain a hydrogenated nitrile rubber with a weight-average molecular weight of 48,000, an iodine value of 13, and a concentration of divalent or higher metal ions of 200 ppm or less, which is applied to lithium-ion secondary batteries.

[0006] On the other hand, Patent Document 2 (Japanese Patent Publication No. 2018-145434) discloses a low-metal content hydrogenated nitrile rubber containing substituted phenols useful for sealing materials, hose materials, and transmission belts in the automotive field. Acrylonitrile and 1,3-butadiene are emulsion polymerized, then 4-methyl-2,6-tert-butylphenol (BHT) is added, and an aqueous sodium chloride solution or magnesium chloride solution prepared with tap water containing calcium ions is added and solidified. After that, it is washed at 60°C with tap water containing calcium ions and pre-dried with a welding screw to a residual moisture content of 15-25% by weight to obtain NBR with a calcium content of 285-595 ppm, a chlorine content of 190-590 ppm, and a (calcium content / chlorine content) ratio of 0.95-1.87. Next, the obtained NBR is dissolved in chlorobenzene and then hydrogenated with a rhodium-based catalyst. (After diluting the chlorobenzene-polymer solution to remove the rhodium, a 2% calcium chloride aqueous solution and a dilute sodium hydroxide aqueous solution are continuously added by metering to carry out a coagulation reaction and produce hydrogenated nitrile rubber.)

[0007] Furthermore, as an example of low-ash NBR, Patent Document 3 (Japanese Patent Publication No. 2004-156011) discloses a method for producing a high-purity emulsion polymer. Specifically, an aqueous dispersion of NBR latex containing 35% by mass of acrylonitrile, 65% by mass of butadiene, and having a Mooney viscosity of 80 MU (ML1+4 at 100°C) is coagulated with a 50% sulfuric acid solution. The resulting aggregate is then treated with an aqueous NaOH solution at pH 11.5 and a 50% sodium hydroxide solution to adjust the pH to 12. The alkaline suspension is then passed through a vibrating screen, and the wet polymer fragments are continuously conveyed to a dehydration screw equipped with a filter bar to dehydrate them until the residual humidity is 5%, thereby obtaining NBR with ash <0.05%, Na 208 mg / kg, K 149 mg / kg, Ca 4 mg / kg, or ash <0.05%, Na 150 mg / kg, K 62 mg / kg, Ca 2 mg / kg.

[0008] Furthermore, Patent Document 4 (Japanese Patent Publication No. 2010-528142) describes a method in which acrylonitrile and butadiene are emulsion polymerized, an aqueous solution of an antioxidant is added, and then a coagulation reaction is carried out with a 15-26 wt% NaCl aqueous solution at 20-50°C. The resulting aggregates are then washed with Ca-containing water at 20-40°C for 2.5-9 hours. Alternatively, a coagulation reaction is carried out with a 0.3-1.2 wt% CaCl2 aqueous solution at 20°C, the resulting aggregates are washed with deionized water at 20°C for 3.4-3.6 hours. After washing, the rubber aggregates are pre-dehydrated in a welding screw to a residual moisture content of 5-10 wt%, and then vacuum dried to obtain NBR with Ca 325-1290 ppm, Na 6-625 ppm, and K 1-27 ppm.

[0009] However, a suitable method for reducing the ash content of nitrile rubber, which serves as a precursor for low-ash hydrogenated nitrile rubber suitable for electrochemical elements, had not yet been found. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] WO2023 / 162835 publication [Patent Document 2] Japanese Patent Publication No. 2018-145434 [Patent Document 3] Japanese Patent Publication No. 2004-156011 [Patent Document 4] Japanese Patent Publication No. 2010-528142 [Overview of the project] [Problems that the invention aims to solve]

[0011] This invention has been made in view of the above circumstances, and aims to provide a method for producing nitrile rubber with a low ash content. [Means for solving the problem]

[0012] In view of the above problems, the present inventors conducted diligent research and found that adding a polymerization solution obtained by emulsion polymerization of acrylonitrile and 1,3-butadiene to a high-concentration aqueous calcium chloride solution while it is rotating vigorously, and in particular adding the polymerization solution so that it directly hits the central stirring blade that rotates at high speed, improves the washing and dewatering efficiency of the resulting water-containing crumbs. As a result, the amount of ash in the nitrile rubber produced is significantly reduced because the water-containing crumbs generated at that time are concentrated in a specific area with small mesh size.

[0013] The inventors have also found that when alkali metal salts are used as polymerization auxiliary materials, for example, when emulsion polymerization is carried out using an emulsifier such as potassium oleate and the mixture is brought into contact with an aqueous calcium salt solution to produce a hydrated crumb, a large amount of the emulsifier is embedded in the hydrated crumb, reducing the washing efficiency. However, by concentrating the hydrated crumb containing the emulsifier in a specific region, the washing efficiency and dewatering efficiency can be significantly improved.

[0014] The inventors have also found that when sulfates and / or sulfonates are used as polymerization auxiliary materials, the ash obtained by contacting them with an aqueous calcium chloride solution and undergoing a coagulation reaction has a significantly higher calcium and sulfur content. The inventors hypothesize that this is because sulfates and sulfonates remaining in the polymerization solution during the coagulation reaction undergo salt exchange with calcium chloride to produce poorly water-soluble calcium sulfate and calcium sulfonate, which cannot be removed by normal washing operations and remain in the nitrile rubber in the form of poorly water-soluble salts. The inventors have found that even for ash that is difficult to remove in such situations, the ash content in the nitrile rubber produced can be significantly reduced by washing and dewatering a water-containing crumb concentrated in a small, specific area. The inventors have also found that such poorly water-soluble ash can be significantly reduced by washing and dewatering the water-containing crumb concentrated in the above-mentioned specific area within a specific temperature range. Furthermore, we found that by reducing the ash content, which is rich in calcium and sulfur, using this method, alkali metals such as sodium and potassium are almost completely removed from the ash in the nitrile rubber. This significantly improves the dispersibility, battery capacity characteristics, battery resistance characteristics, and high-temperature storage characteristics of hydrogenated nitrile rubber, which is obtained by hydrogenating such nitrile rubber, for use in conductive material dispersions for electrochemical elements.

[0015] Based on these findings, the inventors have completed the present invention.

[0016] Thus, according to the present invention, an emulsion polymerization step is performed to obtain a polymerization solution by emulsion polymerization of acrylonitrile and 1,3-butadiene, The process involves adding a phenolic antioxidant to the resulting polymerization solution, A solidification process in which a polymerization solution containing a phenolic antioxidant is brought into contact with an aqueous solution of a polyvalent metal salt, and more than 60% by mass of the resulting hydrated crumb passes through a JIS sieve with an 8 mm mesh size but does not pass through a JIS sieve with an 1.7 mm mesh size, A washing process in which the generated water-containing crumb is washed with hot water, A dehydration process in which the washed, water-containing crumb is dehydrated at 40°C or higher, A drying process to dry the washed, water-containing crumb to less than 1% by mass, There is provided a method for producing a nitrile rubber comprising.

[0017] In the method for producing a nitrile rubber of the present invention, it is preferable that 30% by mass or more of the hydrous crumbs produced are hydrous crumbs that pass through a JIS sieve with an opening of 4.75 mm and do not pass through a JIS sieve with an opening of 2.36 mm.

[0018] In the method for producing a nitrile rubber of the present invention, it is preferable that the polyvalent metal salt aqueous solution is a calcium chloride aqueous solution.

[0019] In the method for producing a nitrile rubber of the present invention, it is preferable to use at least one salt compound selected from the group consisting of alkali metal salts, sulfates and sulfonates as a polymerization auxiliary material in the polymerization step.

[0020] In the method for producing a nitrile rubber of the present invention, it is preferable that the dehydration of the hydrous crumbs is performed until the water content of the hydrous crumbs becomes 35% by mass or less.

[0021] In the method for producing a nitrile rubber of the present invention, it is preferable that the ash content of the nitrile rubber is 0.7% by mass or less.

[0022] In the method for producing a nitrile rubber of the present invention, it is preferable that the total (Ca+S) proportion of the calcium content (Ca) and the sulfur content (S) in the ash is 40% by mass or more.

[0023] In the method for producing a nitrile rubber of the present invention, it is preferable that the total (Na+K) proportion of the sodium content (Na) and the potassium content (K) in the ash is 30% by mass or less.

[0024] In the method for producing a nitrile rubber of the present invention, it is preferable that the ratio (Ca / S) of the calcium content (Ca) to the sulfur content (S) in the ash is 3 or less.

[0025] In the method for producing nitrile rubber according to the present invention, it is preferable that the ratio of calcium content (Ca) to chlorine content (Cl) in the ash (Ca / Cl) is 2 or more.

[0026] In the method for producing nitrile rubber according to the present invention, it is preferable that the ratio of sulfur content (S) to chlorine content (Cl) in the ash (S / Cl) is 2 or more. [Effects of the Invention]

[0027] The present invention provides a method for producing nitrile rubber that can reduce the ash content. [Brief explanation of the drawing]

[0028] [Figure 1] This figure shows an example of a nitrile rubber manufacturing system according to an embodiment of the present invention. [Modes for carrying out the invention]

[0029] Embodiments of the present invention will be described in detail below.

[0030] (monomer components) There are no particular limitations on the acrylonitrile and 1,3-butadiene used; industrially used materials may be used. If polymerization inhibitors are added to the acrylonitrile and 1,3-butadiene used, they should be removed before use.

[0031] The proportion of acrylonitrile used in the total monomer components is not particularly limited, but is usually in the range of 10 to 60% by mass, preferably 15 to 55% by mass, more preferably 20 to 50% by mass, even more preferably 25 to 45% by mass, and most preferably 30 to 40% by mass. When the proportion of acrylonitrile used is within this range, the hydrogenated nitrile rubber produced by hydrogenating the nitrile rubber enhances the dispersibility of conductive materials in the manufacture of electrochemical elements and improves the cycle characteristics of the electrochemical elements, making it preferable.

[0032] The proportion of 1,3-butadiene used in the total monomer components is not particularly limited, but is usually in the range of 40-90% by mass, preferably 45-85% by mass, more preferably 50-80% by mass, even more preferably 55-75% by mass, and most preferably 60-70% by mass. When the proportion of 1,3-butadiene used is within this range, the hydrogenated nitrile rubber produced by hydrogenating the nitrile rubber is preferable because it enhances the dispersibility of conductive materials in the manufacture of electrochemical elements and improves the cycle characteristics of the electrochemical elements.

[0033] The total proportion of acrylonitrile and 1,3-butadiene used in the total monomer components is not particularly limited, but is usually 70-100% by mass, preferably 80-100% by mass, more preferably 90-100% by mass, even more preferably 95-100% by mass, and most preferably 97-100% by mass.

[0034] In the present invention, in addition to acrylonitrile and 1,3-butadiene, other monomeric components may be used as needed. There are no particular limitations on the other monomers, but polar group-containing monomers are preferably used.

[0035] There are no particular limitations on the polar group of the polar group-containing monomer, but examples include epoxy groups, acetoacetoxyalkyl groups, diester dicarboxylic acid groups, and acidic groups, with acidic groups being preferred.

[0036] Examples of epoxy group-containing monomers include glycidyl methacrylate and glycidyl acrylate, with glycidyl methacrylate being preferred. Examples of acetoacetoxyalkyl group-containing monomers include acetoacetoxyethyl methacrylate. Examples of diester dicarboxylic acid group-containing monomers include dibutyl maleate.

[0037] Examples of monomers containing acidic groups include monomers containing carboxylic acid groups, monomers containing sulfonic acid groups, and monomers containing phosphate groups, with monomers containing carboxylic acid groups being preferred among these.

[0038] Examples of monomers containing a carboxylic acid group include monocarboxylic acids, dicarboxylic acids and their acid anhydrides, with monocarboxylic acids being preferred. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, monobutyl maleate, and monododecyl maleate, with methacrylic acid, acrylic acid, and monobutyl maleate being preferred, and methacrylic acid being more preferred. Examples of dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid.

[0039] Examples of monomers containing sulfonic acid groups include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, styrene sulfonic acid, ethyl 2-(meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-alyloxy-2-hydroxypropanesulfonic acid. Examples of monomers containing phosphate groups include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, and ethyl-(meth)acryloyloxyethyl phosphate.

[0040] These other monomers can be used individually or in combination of two or more. The proportion of the other monomer components in the total monomer components is not particularly limited, but is usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and most preferably 3% by mass or less.

[0041] (Emulsion polymerization process) There are no particular limitations on the emulsifiers used in emulsion polymerization, but examples include salts of fatty acids such as myristic acid, palmitic acid, oleic acid, and linolenic acid; alkylbenzene sulfonates such as dodecylbenzenesulfonic acid; sulfate esters such as sodium lauryl sulfate and phosphate esters such as polyoxyalkylene alkyl ether phosphates; and alkyl sulfosuccinates. Among these, fatty acid salts, alkylbenzene sulfonates, and sulfate esters are preferred, with fatty acid salts and alkylbenzene sulfonates being particularly preferred.

[0042] Examples of salts such as fatty acid salts, alkylbenzene sulfonates, sulfate esters, and phosphate esters mentioned above include alkali metal salts and ammonium salts, with alkali metal salts being preferred, and sodium salts and potassium salts being particularly preferred. Specific examples of emulsifiers include potassium oleate, sodium oleate, potassium palmitate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, ammonium lauryl sulfate, sodium myristyl sulfate, sodium laureth sulfate, sodium polyoxyethylene alkyl sulfate, and sodium polyoxyethylene alkylaryl sulfate, with potassium oleate and sodium dodecylbenzenesulfonate being preferred.

[0043] These emulsifiers can be used individually or in combination of two or more, and the amount used is usually in the range of 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 1 to 3 parts by mass, per 100 parts by mass of monomer component.

[0044] The method for mixing the monomer component, emulsifier, and water can be done according to conventional methods, such as stirring the monomer, emulsifier, and water using a homogenizer or a stirrer such as a disk turbine. The amount of water used is usually in the range of 10 to 750 parts by mass, preferably 50 to 500 parts by mass, and more preferably 100 to 400 parts by mass, per 100 parts by mass of the monomer component.

[0045] In addition to the emulsifiers mentioned above, known polymerization auxiliary materials used in emulsion polymerization can be used by optimizing them as appropriate. Specifically, various polymerization reaction modifiers such as molecular weight modifiers (chain transfer agents), pH modifiers, stabilizers, and reducing and chelating agents for redox catalysts can be used.

[0046] There are no particular limitations on the polymerization initiator used in emulsion polymerization, as long as it is one that is commonly used in emulsion polymerization. For example, radical generators can be used.

[0047] Examples of radical generators include peroxides and azo compounds, with peroxides being preferred. Inorganic or organic peroxides are used as the peroxide.

[0048] Examples of inorganic peroxides include sodium persulfate, potassium persulfate, hydrogen peroxide, and ammonium persulfate. Among these, potassium persulfate, hydrogen peroxide, and ammonium persulfate are preferred, with potassium persulfate being particularly preferred.

[0049] There are no particular limitations on the organic peroxides used, as long as they are known and used in emulsion polymerization. Examples include 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane, 1-di-(t-hexylperoxy)cyclohexane, 1,1-di-(t-butylperoxy)cyclohexane, 4,4-di-(t-butylperoxy)n-butyl valerate, 2,2-di-(t-butylperoxy)butane, t-butyl hydroperoxide, cumene hydroperoxide, and diisopropyl benzyl Examples include 1,1,3,3-tetraethylbutyl peroxide, t-butylcumyl peroxide, di-t-butyl peroxide, di-t-hexyl peroxide, di(2-t-butylperoxyisopropyl)benzene, dicumyl peroxide, diisobutyryl peroxide, di(3,5,5-trimethylhexanoyl) peroxide, and dilauroyl peroxide.

[0050] These polymerization initiators can be used individually or in combination of two or more types, and the amount used is usually in the range of 0.0001 to 5 parts by mass, preferably 0.0005 to 1 part by mass, and more preferably 0.001 to 0.5 parts by mass, per 100 parts by mass of monomer component.

[0051] The amount of water used in the emulsion polymerization reaction may be limited to the amount used during the emulsion formation of the monomer components, but it is usually adjusted to be in the range of 10 to 1000 parts by mass, preferably 50 to 500 parts by mass, more preferably 80 to 400 parts by mass, and most preferably 100 to 300 parts by mass, per 100 parts by mass of the monomer components used for polymerization.

[0052] The emulsion polymerization reaction can be carried out according to a conventional method and may be batch, semi-batch, or continuous. The polymerization temperature and polymerization time are not particularly limited and can be appropriately selected depending on the type of polymerization initiator used. The polymerization temperature is usually in the range of 0 to 100°C, preferably 5 to 80°C, and more preferably 10 to 60°C, and the polymerization time is usually 0.5 to 100 hours, preferably 1 to 10 hours. The polymerization conversion rate of the emulsion polymerization reaction is not particularly limited, but is usually 60% by mass or more, preferably 65% ​​by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more.

[0053] (Addition of anti-aging agent) The present invention's anti-aging agent addition step involves adding a phenolic anti-aging agent to the polymerization solution after emulsion polymerization. Adding the anti-aging agent to the polymerization solution allows for uniform dispersion of the phenolic anti-aging agent in the resulting nitrile rubber or hydrogenated nitrile rubber, which is preferable. Furthermore, adding the phenolic anti-aging agent at this stage is preferable because it prevents deterioration reactions during the drying of the nitrile rubber.

[0054] While there are no particular limitations on the phenolic antioxidant, hindered phenolic antioxidants are preferred. Examples of hindered phenolic antioxidants include 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-pentenyl-4-methylphenol, 2,2-methylenebis(4-methyl-6-t-butylphenol), 2,4-bis(octylthiomethyl)-6-methylphenol, 2,6-di-t-butyl-α-dimethylamino-p-cresol, and 3-(4-hydroxy-3,5 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate butyl, 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate hexyl, 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate octyl, 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate decyl, 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate dodecyl, 3-(4-hydroxy-3,5-di-t-butylphenyl)propionate butyl Examples include octadecyl 3-(4-hydroxy-3,5-diisopropylphenyl)propionate, heptyl 3-(4-hydroxy-3,5-diisopropylphenyl)propionate, octyl 3-(4-hydroxy-3,5-diisopropylphenyl)propionate, dodecyl 3-(4-hydroxy-3,5-diisopropylphenyl)propionate, octadecyl 3-(4-hydroxy-3,5-diisopropylphenyl)propionate, 4,4'-methylenebis(2,6-dibutylphenol), 2,6-di-t-butyl-4-(4,6-bis(octylthio)-1,3,5-triazine-2-ylamino)phenol, and preferably 2,6-di-t-butyl-4-methylphenol (dibutylhydroxytoluene = BHT), 2,2-methylenebis(4-methyl-6-t-butylphenol), and 2,4-bis(octylthiomethyl)-6-methylphenol, with BHT being the most preferred.

[0055] Examples of phenolic antioxidants other than hindered phenolic antioxidants include styrene-phenols such as mono(or di, or tri)(α-methylbenzyl)phenol, butylhydroxyanisole, 2,2'-methylene-bis(4-methyl-6-t-butylphenol), alkylated bisphenols, 2,4-bis[(octylthio)methyl]-6-methylphenol, 2,2'-thiobis-(4-methyl-6-t-butylphenol), and 4,4'-thiobis-(6-t-butyl-o-cresol), with styrene-phenols and 2,4-bis[(octylthio)methyl]-6-methylphenol being preferred.

[0056] These phenolic antioxidants can be used individually or in combination of two or more. The amount of phenolic antioxidant used is not particularly limited, but is usually in the range of 0.001 to 15 parts by mass, preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, particularly preferably 0.3 to 3 parts by mass, and most preferably 0.5 to 2 parts by mass, per 100 parts by mass of monomer component.

[0057] (solidification process) The solidification step of the present invention is characterized by bringing a polymerization solution to which the above-mentioned phenolic antioxidant has been added into contact with an aqueous solution of a polyvalent metal salt to generate a hydrated crumb in a specific region.

[0058] The coagulant used is an aqueous solution of polyvalent metal salt. While there are no particular limitations on the polyvalent metal salts used, Group 2 metal salts of the periodic table are preferred, and calcium chloride is particularly preferred. By using these polyvalent metal salts as coagulants, even if they remain in the manufactured nitrile rubber or the hydrogenated nitrile rubber obtained by hydrogenating the manufactured nitrile rubber, their effect on the electrochemical elements is small.

[0059] Examples of Group 2 metal salts of the periodic table include magnesium chloride, calcium chloride, magnesium nitrate, calcium nitrate, magnesium sulfate, and calcium sulfate, with calcium chloride and magnesium sulfate being preferred, and calcium chloride being particularly preferred.

[0060] Other polyvalent metal salts include, for example, zinc chloride, titanium chloride, manganese chloride, iron chloride, cobalt chloride, nickel chloride, aluminum chloride, tin chloride, zinc nitrate, titanium nitrate, manganese nitrate, iron nitrate, cobalt nitrate, nickel nitrate, aluminum nitrate, tin nitrate, zinc sulfate, titanium sulfate, manganese sulfate, iron sulfate, cobalt sulfate, nickel sulfate, aluminum sulfate, and tin sulfate.

[0061] These coagulants can be used individually or in combination of two or more.

[0062] The solid content concentration of the polymerization solution after emulsion polymerization used in the coagulation reaction is not particularly limited, but is usually adjusted to a range of 5 to 50% by mass, preferably 10 to 45% by mass, and more preferably 20 to 40% by mass.

[0063] The coagulant used is usually an aqueous solution, and when the coagulant concentration of the aqueous solution is in the range of 1 to 60% by mass, preferably 3 to 50% by mass, more preferably 5 to 40% by mass, and particularly preferably 10 to 30% by mass, the particle size of the resulting water-containing crumbs can be uniformly concentrated in a specific region, which is preferable.

[0064] While there are no particular limitations on the temperature during the coagulation reaction, it is generally preferable to have a temperature of 0°C or higher, preferably 10 to 90°C, and more preferably 20 to 80°C, as this is when a uniform hydrated crumb is produced.

[0065] There are no particular limitations on the contact between the polymerization solution and the coagulation solution. For example, either adding the polymerization solution to a stirred coagulation solution or adding the coagulation solution to a stirred polymerization solution is acceptable. However, adding the coagulation solution to a stirred polymerization solution is preferable because it allows for uniformity in the shape and diameter of the resulting water-containing crumbs, and significantly improves the washing and dewatering efficiency of the emulsifier and coagulant.

[0066] There are no particular limitations on the stirring speed (rotation speed) of the coagulation solution, but it is usually 100 rpm or more, preferably 200 rpm or more, more preferably 300 rpm or more, even more preferably 400 rpm or more, and most preferably 500 rpm or more. When the stirring speed (rotation speed) of the coagulation solution is set within this range, it is preferable because the diameter of the water-containing crams that are generated can be made small and concentrated in a specific region. Furthermore, there are no particular limitations on the upper limit of the stirring speed (rotation speed) of the coagulation solution, but it is usually 1000 rpm or less, preferably 900 rpm or less, more preferably 800 rpm or less, even more preferably 750 rpm or less, and most preferably 700 rpm or less.

[0067] The peripheral velocity of the stirred solidifying liquid is expressed as the linear velocity of the outer circumference of the stirring blade of the stirring device. It is preferable that the calcium chloride aqueous solution is stirred vigorously to a certain extent, as this makes it possible to create a smaller and more uniform water cramb diameter. Typically, this velocity is 0.5 m / s or more, preferably 1 m / s or more, more preferably 1.5 m / s or more, even more preferably 2 m / s or more, and most preferably 2.5 m / s or more. There is no particular upper limit to the peripheral velocity of the stirred solidifying liquid, but it is generally easier to control the solidification reaction when it is 50 m / s or less, preferably 30 m / s or less, more preferably 25 m / s or less, and especially preferably 20 m / s or less.

[0068] In this invention, 60% by mass or more of the generated water-containing crumb is water-containing crumb that passes through a JIS sieve with an 8 mm mesh opening but does not pass through a JIS sieve with an 1.7 mm mesh opening. By concentrating the generated water-containing crumb in this region, the amount of ash remaining in the water-containing crumb can be significantly reduced, which is preferable.

[0069] In the present invention, it is also preferable that 30% by mass or more of the generated water-containing crumb is water-containing crumb that passes through a JIS sieve with a mesh size of 4.75 mm but does not pass through a JIS sieve with a mesh size of 2.36 mm. Increasing the amount of water-containing crumb in this range is preferable because it can significantly improve the washing efficiency and dewatering efficiency of the water-containing crumb. In the present invention, the removal efficiency of emulsifiers and coagulants during washing and dewatering can be significantly improved when all of the following conditions (a) to (e) are satisfied.

[0070] (a) The percentage of water-containing crumbs that pass through a JIS sieve with a mesh opening of 9.5 mm is 10% by mass or less, preferably 5% by mass or less, and more preferably 3% by mass or less. (b) The proportion of relatively large water-containing crumbs that pass through a JIS sieve with a mesh size of 9.5 mm but do not pass through a JIS sieve with a mesh size of 6.7 mm is 25% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and most preferably 5% by mass or less. (c) The percentage of water-containing crumbs that pass through a JIS sieve with an 8 mm mesh opening but do not pass through a JIS sieve with an 1.7 mm mesh opening is 60% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. (d) The percentage of water-containing crumbs that pass through a 1.7 mm mesh opening but do not pass through a JIS sieve with a 0.43 mm mesh opening is 25% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and most preferably 5% by mass or less. (e) The percentage of water-containing crumbs that pass through a JIS sieve with a mesh opening of 0.43 mm is 10% by mass or less, preferably 5% by mass or less, and more preferably 3% by mass or less.

[0071] The shape of the resulting hydrated crumbs is not particularly limited, but a perforated shape is preferred. In particular, adding the polymerization solution directly to the central rotating shaft and rotor blades in the vigorously rotating solidifying liquid increases the amount of perforated hydrated crumbs, which is preferable.

[0072] (Washing process) The cleaning process of the present invention preferably uses hot water. While there are no particular limitations on the temperature of the hot water, it is generally preferable to use a temperature of 30°C or higher, preferably 35-100°C, more preferably 40-80°C, even more preferably 40-60°C, and most preferably 40-50°C, as this significantly increases the cleaning efficiency. Calcium sulfate and calcium sulfonate salts, for example, are poorly soluble in water and have low solubility, but their solubility tends to increase at certain temperatures. By setting the temperature of the cleaning water above the aforementioned lower limit, emulsifiers and coagulants are released from the water-containing crumb, further improving the cleaning efficiency.

[0073] While there are no particular limitations on the amount of hot water used for washing, it is effective to wash the hydrated crumb solidified with the above-mentioned high-concentration polyvalent metal salt aqueous solution with a large amount of water. The amount of water used is typically in the range of 10 to 500 times, preferably 25 to 250 times, and more preferably 50 to 100 times, by mass per 100 parts by mass of polymer.

[0074] There are no particular limitations on the washing time, but it is usually in the range of 1 to 120 minutes, preferably 2 to 60 minutes, and more preferably 3 to 30 minutes.

[0075] (Dehydration process) Dehydrating the washed water-containing crumb is preferable because it removes polymerization auxiliary materials such as emulsifiers trapped inside the water-containing crumb.

[0076] In the present invention, it is preferable to carry out the dehydration at a temperature of 40°C or higher, preferably 45°C or higher, and more preferably 50°C or higher. Increasing the dehydration temperature makes the water-containing crumb more flexible, and polymerization auxiliary materials and the like can be more easily removed from the water-containing crumb.

[0077] The water content of the dehydrated crumb is not particularly limited, but is usually 40% by mass or less, preferably 35% by mass or less, more preferably 30% by mass or less, or preferably in the order of 25% by mass or less, 20% by mass or less, 15% by mass or less, 14% by mass or less, 13% by mass or less, 12% by mass or less, 10% by mass or less, and 8% by mass or less.

[0078] There are no particular limitations on the method for dehydrating water-containing crumb, but a method that compresses the crumb using a squeezer or similar device to extract the moisture is preferable. On the other hand, dehydration using a centrifuge or similar device is insufficient as it can only reduce the water content of the crumb to about 50-60% by mass.

[0079] (drying process) The drying method for the dehydrated crumb can follow conventional methods, and can be performed using dryers such as hot air dryers, vacuum dryers, expander dryers, kneader dryers, and screw extruders.

[0080] The shape of the dried rubber (polymer) is not particularly limited and can be, for example, crumb-like, powder-like, rod-like, or sheet-like. The water content of the dried rubber is less than 1% by mass, preferably 0.9% by mass or less, more preferably 8% by mass or less, even more preferably 0.7% by mass or less, and most preferably 0.6% by mass or less.

[0081] <Nitrile rubber> The properties of the nitrile rubber thus obtained are not particularly limited, but those with restricted ash content or ash components, or those that satisfy the following properties, are suitable for hydrogenation to produce hydrogenated nitrile rubber for use in electrochemical elements.

[0082] The ash content of the manufactured nitrile rubber is not particularly limited, but is usually 0.7% by mass or less, preferably 0.65% by mass or less, more preferably 0.6% by mass or less, or preferably in the order of 0.55% by mass or less, 0.5% by mass or less, 0.45% by mass or less, 0.4% by mass or less, 0.35% by mass or less, 0.3% by mass or less, 0.25% by mass or less, and 0.2% by mass or less. When the ash content in the nitrile rubber is within this range, the hydrogenated hydrogenated nitrile rubber can improve the battery capacity characteristics, cycle characteristics, and high-temperature storage properties of the electrochemical element.

[0083] The total ratio of calcium content (Ca) and sulfur content (S) (Ca+S) in the ash of the manufactured nitrile rubber is not particularly limited, but is usually 10% by mass or more, 20% by mass or more, preferably 30% by mass or more, more preferably 40% by mass or more, or preferably 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, and 90% by mass or more, in that order. When the total ratio of calcium content (Ca) and sulfur content (S) (Ca+S) in the ash of the nitrile rubber is within this range, the hydrogenated hydrogenated nitrile rubber can improve the electrode peel strength, battery capacity characteristics, and cycle characteristics of electrochemical elements.

[0084] The ratio of calcium content (Ca) to sulfur content (S) in the ash of the manufactured nitrile rubber (Ca / S) is not particularly limited, but is usually 10 or less, preferably 7 or less, more preferably 5 or less, or preferably in the order of 4.5 or less, 4 or less, 3.5 or less, 3 or less, 2.5 or less, 2 or less, and 1.5 or less, and usually 0.1 or more, preferably 0.3 or more, more preferably 0.5 or more, or preferably in the order of 0.6 or more, 0.8 or more, 1 or more, and 1.2 or more. When the ratio of calcium content (Ca) to sulfur content (S) in the ash of the nitrile rubber (Ca / S) is within this range, the hydrogenated hydrogenated nitrile rubber can improve the electrode peel strength, battery capacity characteristics, cycle characteristics, and high-temperature storage characteristics of electrochemical elements.

[0085] The ratio of calcium content (Ca) to chlorine content (Cl) in the ash of the manufactured nitrile rubber (Ca / Cl) is not particularly limited, but is usually 0.5 or higher, preferably 0.6 or higher, more preferably 0.7 or higher, or preferably 1 or higher, 1.5 or higher, 2 or higher, 2.5 or higher, 3 or higher, 3.5 or higher, and 4 or higher in that order, and is usually 50 or lower, preferably 40 or lower, more preferably 30 or lower, even more preferably 20 or lower, and most preferably 10 or lower. When the ratio of calcium content (Ca) to chlorine content (Cl) in the ash of the nitrile rubber (Ca / Cl) is within this range, hydrogenated hydrogenated nitrile rubber can improve the viscosity characteristics and cycle characteristics of the conductive material dispersion of electrochemical elements.

[0086] The ratio of sulfur content (S) to chlorine content (Cl) in the ash of the manufactured nitrile rubber (S / Cl) is not particularly limited, but is usually 0.5 or higher, preferably 1 or higher, more preferably 1.5 or higher, even more preferably 2 or higher, most preferably 2.5 or higher, and usually 50 or lower, preferably 40 or lower, more preferably 30 or lower, even more preferably 20 or lower, most preferably 10 or lower. When the ratio of sulfur content (S) to chlorine content (Cl) in the ash of the nitrile rubber is within this range, hydrogenated hydrogenated nitrile rubber can improve the electrode peel strength, battery capacity characteristics, cycle characteristics, and high-temperature storage characteristics of electrochemical elements.

[0087] The total ratio of sodium (Na) and potassium (K) content (Na+K) in the ash of the manufactured nitrile rubber is not particularly limited, but is usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, and most preferably 3% by mass or less. When the total ratio of sodium (Na) and potassium (K) content (Na+K) in the ash of the nitrile rubber is within this range, hydrogenated hydrogenated nitrile rubber can improve the battery capacity, cycle characteristics, and high-temperature storage characteristics of electrochemical elements.

[0088] The weight-average molecular weight (Mw) of the manufactured nitrile rubber is not particularly limited, but is usually in the range of 1,000 or more, preferably 10,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, most preferably 150,000 or more, and 5,000,000 or less, preferably 3,500,000 or less, 2,000,000 or less, more preferably 1,000,000 or less, and most preferably 500,000 or less.

[0089] The ratio (Mz / Mw) of the Z-average molecular weight (Mz) to the weight-average molecular weight (Mw) of the nitrile rubber of the present invention is not particularly limited, but is usually 1.5 or higher, preferably 1.6 or higher, more preferably 1.8 or higher, even more preferably 2 or higher, most preferably 2.5 or higher, and usually 4.5 or lower, preferably 4.3 or lower, more preferably 4 or lower, even more preferably 3.8 or lower, most preferably 3.5 or lower. When the Mz / Mw of the nitrile rubber is within this range, the hydrogenated hydrogenated nitrile rubber can improve the dispersibility of conductive material dispersions, electrode peel strength, and battery resistance characteristics of electrochemical elements.

[0090] <Equipment configuration of a nitrile rubber manufacturing system> The following describes the apparatus configuration of the nitrile rubber manufacturing system for producing nitrile rubber according to the present invention. Figure 1 is a diagram showing an example of the nitrile rubber manufacturing system in an embodiment of the present invention.

[0091] Figure 1 schematically illustrates the apparatus configuration of a nitrile rubber manufacturing system according to an embodiment of the present invention, in accordance with the manufacturing process. The nitrile rubber manufacturing system shown in Figure 1 is generally configured to include an emulsion polymerization apparatus 10, a coagulation apparatus 30, a washing apparatus 50, and a squeezer 70.

[0092] (Emulsion polymerization device 10) The emulsion polymerization apparatus 10 is configured to perform the processes related to the emulsion polymerization step. As shown in Figure 1, the emulsion polymerization apparatus 10 has a polymerization tank 11 and a stirring device 12 for copolymerizing monomer components such as acrylonitrile monomer and 1,3-butadiene monomer. The emulsion polymerization apparatus 10 may be batch type, semi-batch type, or chain type, and may be a tank reactor or a tubular reactor.

[0093] The polymerization tank 11 is formed, for example, in a closed cylindrical shape so that it can store the emulsion polymerization liquid. The stirring device 12 is located inside the polymerization tank 11 and includes a stirring blade 13 which is a member that rotates around a predetermined axis, a motor 14 that rotates the stirring blade 13, and a drive control unit (not shown) that controls the rotational number and rotational speed of the stirring blade 13.

[0094] A predetermined amount of acrylonitrile and 1,3-butadiene and water are placed in the polymerization vessel 11, polymerization auxiliary materials such as emulsifiers and molecular weight adjusters are added, and nitrogen purging is performed to remove oxygen from inside the polymerization vessel 11. Then, a polymerization initiator is added while stirring to start the polymerization reaction.

[0095] The stirring device 12 is configured to rotate the stirring blades 13 at a predetermined rotational speed (stirring speed) inside the polymerization vessel 11, thereby enabling proper flow of the emulsion polymerization liquid. The stirring speed of the stirring blades 13, the shape and size of the stirring blades 13, the number of blades installed, etc., are determined as appropriate considering the reaction conditions, etc.

[0096] The temperature of the emulsion polymerization solution inside the polymerization vessel 11 affects the reaction rate, molecular weight distribution, and molecular structure. For example, the proportion of 1,2-bond units in the polymerization units of 1,3-butadiene increases as the temperature of the emulsion polymerization solution increases and decreases as the temperature of the emulsion polymerization solution decreases, so this can be controlled by appropriately controlling the temperature of the emulsion polymerization solution.

[0097] When a predetermined polymerization conversion rate is reached, a polymerization inhibitor is added to the polymerization tank 11 to stop the polymerization reaction. The polymerization inhibitor rate can be used to control the molecular weight, molecular weight distribution, and the proportion of 1,2-bonding units in the 1,3-butadiene polymerization units of the nitrile rubber produced, so it can be appropriately selected according to the required properties. After that, a process related to the addition of an anti-aging agent is carried out, and the anti-aging agent is added to the polymerization tank 11 after the polymerization reaction is completed. Subsequently, the latex in the polymerization tank 11 is transferred to the solidification tank 31 of the solidification device 30.

[0098] (Coagulation device 30) The solidification apparatus 30 is configured to perform processing related to the solidification process. As shown in Figure 1, the solidification apparatus 30 has a solidification tank 31 and a stirring device 32 for solidifying the latex transferred from the emulsion polymerization apparatus 10 and extracting crumb-shaped nitrile rubber (water-containing crumb).

[0099] The solidification tank 31 is formed, for example, in a closed cylindrical shape and is capable of storing a solidified liquid containing a coagulant (for example, calcium chloride). The stirring device 32 is located inside the solidification tank 31 and includes a stirring blade 33 which is a member that rotates around a predetermined axis, a motor 34 that rotates the stirring blade 33, and a drive control unit (not shown) that controls the rotational number and speed of the stirring blade 33.

[0100] In the coagulation apparatus 30, hydrated crumbs are generated by bringing the latex transferred from the emulsion polymerization apparatus 10 into contact with a coagulation solution containing a coagulant (e.g., calcium chloride). The method of contact between the latex and the coagulation solution is not particularly limited; for example, the latex may be added to the agitated coagulation solution, or the coagulation solution may be added to the agitated latex. In this embodiment, the coagulation apparatus 30 employs the method of adding the latex to the agitated coagulation solution. Adding the latex to the agitated coagulation solution concentrates the generated hydrated crumbs so that their shape and diameter are uniform, significantly improving the cleaning efficiency in the subsequent cleaning process.

[0101] The stirring device 32 is configured to rotate the stirring blades 33 at a predetermined rotational speed (stirring speed) within the solidification tank 31, thereby enabling proper flow of the solidified liquid. The stirring speed of the stirring blades 33, the shape and size of the stirring blades 33, and the number of blades installed are determined appropriately considering the reaction conditions, but it is preferable to configure the device to apply a strong shear force in order to generate smaller water-containing crumbs.

[0102] In the method of adding latex to a stirred solidifying solution, the solidifying solution and water (soft water) are filled into the solidifying tank 31 and stirred with the stirring blade 33, and the latex is added to the stirred solidifying solution. The latex that comes into contact with the solidifying solution solidifies and a water-containing crumb is formed.

[0103] The water-containing crumb generated in the solidification tank 31 is removed from the solidification tank 31 by overflowing it along with the solidification liquid and water-containing liquid. The water-containing crumb removed from the solidification tank 31 is transferred to the washing tank 51 of the washing device 50 via the dewatering machine 38.

[0104] As shown in Figure 1, a dewatering machine 38 is positioned between the solidification tank 31 and the washing tank 51. The dewatering machine 38 is configured to separate the water-containing crumb from the liquid (solidified liquid). A screen, wire mesh, electric sieve, etc., can be used for the dewatering machine 38.

[0105] (Cleaning device 50) The washing device 50 is configured to perform the processing related to the washing process. As shown in Figure 1, the washing device 50 has a washing tank 51 for receiving the water-containing crumb and washing water transferred from the solidification device 30, a stirring device 52, and a heating device 55.

[0106] The washing tank 51 is formed, for example, in a closed cylindrical shape and is capable of storing water-containing crumb and washing water. The stirring device 52 is located inside the washing tank 51 and includes a stirring blade 53 which is a member that rotates around a predetermined axis, a motor 54 that rotates the stirring blade 53, and a drive control unit (not shown) that controls the rotational number and speed of the stirring blade 53. The heating device 55 includes a heating unit 56 that heats the inside of the washing tank 51, and a temperature control unit (not shown) that controls the temperature inside the washing tank 51.

[0107] The agitator 52 is configured to rotate the agitator blades 53 at a predetermined rotational speed (agitation speed) within the washing tank 51, thereby washing the water-containing crumbs by appropriately circulating the water-containing crumbs and washing water. The agitation speed of the agitator blades 53, the shape and size of the agitator blades 53, and the number of blades installed are determined appropriately considering the size of the water-containing crumbs and the washing efficiency.

[0108] The heating unit 56 of the heating device 55 sends steam to a jacket provided on the outer circumference of the washing tank 51, for example, and heats the washing liquid through heat exchange with the steam. The temperature of the washing water in the washing tank 51 is controlled to be, for example, 40°C or higher in order to improve the effect of releasing emulsifiers and coagulants from the water-containing crumb.

[0109] The water-containing crumb, washed in the washing tank 51, is removed from the washing tank 51 by overflowing with washing water. The water-containing crumb removed from the washing tank 51 is then transferred to the squeezer 70 via the dewatering machine 58.

[0110] (Squeezer 70) The squeezer 70 is configured to perform the dewatering process. In this embodiment, the squeezer 70 is used as the dewatering machine, but as a dewatering device for dewatering the water-containing crumb, for example, a screw-type extruder dryer that performs dewatering and drying can be used.

[0111] As shown in Figure 1, the squeezer 70 has a two-stage configuration in which an upstream heating mechanism 71 and a downstream pressurizing mechanism 72 are connected by a connecting part 73.

[0112] The heating mechanism 71 includes a chamber 71a and a roller 71b for heating the water-containing cramb, a motor (not shown) that generates rotational power to rotate the roller 71b, and a heating device 71c that supplies steam into the chamber 71a. The roller 71b is housed in the chamber 71a so as to extend in the direction of conveying the water-containing cramb. The shape of the roller 71b is not particularly limited, but for example, it is formed in a screw shape.

[0113] At the upstream end of the chamber 71a, a crumb supply unit 70a is provided for introducing water-containing crumbs transferred from the washing device 50 into the chamber 71a. The downstream end of the chamber 71a is connected to a connecting unit 73. Steam at a predetermined temperature and pressure is supplied into the chamber 71a by a heating device 71c. The steam temperature is set to, for example, 120°C. The steam pressure is set to, for example, 150kPa. By heating the water-containing crumbs with steam in the heating mechanism 71, the dewatering efficiency in the subsequent pressurizing mechanism 72 can be improved.

[0114] The water-containing cramb fed into the cramb supply section 70a is heated while being pushed downstream by the rotation of the roller 71b (roller transport), and then transferred through the connecting section 73 into the chamber 72a of the pressurizing mechanism 72.

[0115] The pressurizing mechanism 72 includes a chamber 72a and a roller 72b for pressurizing the water-containing cramb, and a motor (not shown) that generates rotational power to rotate the roller 72b. The roller 72b is housed in the chamber 72a so as to extend in the direction of conveying the water-containing cramb. The shape of the roller 72b is not particularly limited, but for example, it is formed in a screw shape.

[0116] The upstream end of chamber 72a is connected to a connecting section 73. The downstream end of chamber 72a is provided with a crumb discharge section 70b for discharging the water-containing crumb that has been dewatered in chamber 72a.

[0117] The pressurizing mechanism 72 is configured such that a roller 72b compresses the water-containing crumb within the chamber 72a, squeezing out the moisture from the crumb. The roller 72b may be single or there may be two or more. The water-containing crumb is pushed downstream as moisture is squeezed out by the pressurizing effect of the rotation of the roller 72b, and is discharged from the crumb discharge section 70b. The dewatered water-containing crumb, dewatered by the squeezer 70, is transferred to the crushing device 75. The water content of the dewatered water-containing crumb is usually 35% by mass or less, preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0118] (Crushing device 75) The crushing device 75 is configured to crush and pulverize the water-containing crumb transferred from the squeezer 70. The water-containing crumb discharged by the squeezer 70 after dewatering is uneven in size and shape. By crushing and pulverizing it in the crushing device 75, the drying efficiency in the subsequent drying process can be improved.

[0119] The crushing device 75 can be any device capable of crushing and pulverizing the crumb, such as a hammer-type crusher, a cutter-type crusher, a roller-type crusher, or a pin mill. In particular, considering that it can efficiently and continuously crush water-containing crumb that has elasticity and viscosity, it is preferable to use a hammer-type crusher that crushes and pulverizes the water-containing crumb by the impact of a hammer rotated at high speed.

[0120] The water-containing crumb, which is crushed after dehydration, is dried in a drying process to become dried rubber. [Examples]

[0121] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%", "ppm", and "parts" used to express quantities refer to mass unless otherwise specified.

[0122] Furthermore, in polymers produced by copolymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer is, unless otherwise specified, usually equal to the ratio (starting ratio) of that particular monomer to the total monomers used in the polymerization of the polymer.

[0123] In the examples and comparative examples, various measurements and evaluations were carried out according to the following methods.

[0124] <Moisture content crumb distribution> The water-containing crumbs produced by the coagulation reaction were classified using a JIS classification sieve. Afterward, each classified water-containing crumb was dried in a hot air dryer at 80°C for 3 hours, and the mass was measured to determine the proportions of masses of each crumb diameter (a) to (h). The JIS sieve conformed to the specifications of the Japanese Industrial Standard (JIS Z8801-1). (a) It does not pass through a JIS sieve with a mesh size of 9.5 mm. (b) It passes through a JIS sieve with a mesh size of 9.5 mm but does not pass through a JIS sieve with a mesh size of 8.0 mm. (c) It passes through a JIS sieve with a mesh size of 8.0 mm but does not pass through a JIS sieve with a mesh size of 4.75 mm. (d) It passes through a JIS sieve with a mesh size of 4.75 mm but does not pass through a JIS sieve with a mesh size of 3.35 mm. (e) It passes through a JIS sieve with a mesh size of 3.35 mm but does not pass through a JIS sieve with a mesh size of 2.36 mm. (f) It passes through a JIS sieve with a mesh size of 2.36 mm but does not pass through a JIS sieve with a mesh size of 1.7 mm. (g) It passes through a JIS sieve with a mesh size of 1.7 mm but does not pass through a JIS sieve with a mesh size of 0.43 mm. (h) It passes through a JIS sieve with a mesh size of 0.43 mm.

[0125] <Water content> The water content of the hydrated crumb produced by the coagulation reaction after dehydration was determined according to the "oven method" specified in JIS K6238-1. Specifically, 10 g of hydrated crumb was placed in an oven at 105 ± 5°C and dried until the mass no longer changed substantially. The mass loss before and after drying was determined, and the ratio of the mass loss to the mass of the dried crumb was calculated to determine the water content.

[0126] <Repeat Unit> The acrylonitrile polymerization units and 1,3-butadiene polymerization units (the sum of 1,2-bonding units, 1,4-bonding units, and their hydride units) in the polymer are, 1 The intensity ratio of the peaks originating from each repeating unit was determined using 1H-NMR (nuclear magnetic resonance) spectroscopy, and the content ratio in the polymer was calculated by converting this to a mass ratio.

[0127] <Molecular weight> The weight-average molecular weight (Mw), Z-average molecular weight (Mz), and molecular weight distribution (Mz / Mw) of the polymer were measured by gel permeation chromatography (GPC) using a tetrahydrofuran (THF) solution under the following measurement conditions. • Separation column: TSK-gel SuperHM-H (manufactured by Tosoh Corporation) • Detector: Differential refractometer detector RID-10A (manufactured by Shimadzu Corporation) • Eluent flow rate: 0.6 mL / min Column temperature: 40°C • Standard polymer: TSK standard polystyrene (manufactured by Tosoh Corporation)

[0128] <Anti-aging agent content> The polymer was dissolved in a chlorobenzene solution and analyzed by gas chromatography to determine the percentage of the antioxidant (BHT) content relative to the total mass of the polymer.

[0129] <Ash content> The amount of ash contained in the rubber was measured in accordance with the JIS K6228A method.

[0130] <Ash content> The amounts of each component in the ash were determined by pressing the ash collected during the above ash content measurement onto a Φ20 mm titration filter paper and performing XRF measurement using a ZSXPrimus (manufactured by Rigaku).

[0131] (Example 1) <Nitrile rubber manufacturing> In a reactor with an internal volume of 10 liters, 100 parts of deionized water, 35 parts of acrylonitrile, and 65 parts of 1,3-butadiene were charged. 40 parts of a 10% aqueous solution of sodium dodecylbenzenesulfonate were added as an emulsifier, 0.1 parts of potassium phosphate as a stabilizer, and 0.27 parts of tert-dodecyl mercaptan (TDM) as a molecular weight modifier (chain transfer agent). 0.1 parts of cumene hydroperoxide (QHPO) as a polymerization initiator, along with appropriate amounts of reducing and chelating agents, were added. Emulsification polymerization was carried out at a temperature of 30°C to copolymerize acrylonitrile and 1,3-butadiene. When the polymerization conversion rate reached 80%, polymerization was stopped by adding 0.2 parts of hydroxylamine sulfate per 100 parts of monomer. Subsequently, the mixture was heated and steam distilled under reduced pressure at approximately 90°C to recover the residual monomer. Then, 0.1 parts of dibutylhydroxytoluene (BHT), a phenolic antioxidant, was added to obtain the polymerization solution.

[0132] In a solidification tank equipped with a thermometer and a central stirring blade device, 100 parts of the polymer solids from the obtained polymerization liquid were directly added to a 25% calcium chloride aqueous solution (4 parts as calcium chloride) heated to 45°C and vigorously stirred (600 rpm, peripheral speed 3.1 m / s). The polymer was then solidified by continuously rotating stirring blades (central part) to obtain a water-containing crumb. The obtained water-containing crumb was measured for each component using a JIS classification sieve, and the results are shown in Table 1. Note that Tables 1-1 to 1-3 below are divisions of a single table, and Tables 1-1 to 1-3 together are referred to as Table 1.

[0133] Next, the filtered water-containing crumb was added to a washing tank equipped with a stirring device and filled with deionized water at 45°C. The water-containing crumb was washed by passing 50 times the amount of deionized water (45°C) relative to the polymer while stirring. The washed water-containing crumb was heated to 60°C, dehydrated using a steam-introduced squeezer until the water content was 7%, and then dried under reduced pressure to obtain nitrile rubber A. The repeating unit ratio, molecular weight, molecular weight distribution, antioxidant content, and ash content of the obtained nitrile rubber A were measured and are shown in Table 1. Furthermore, the sodium (Na), potassium (K), calcium (Ca), sulfur (S), and chlorine (Cl) content in the ash was measured, and the ratio of the sum of sodium (Na) and potassium (K) content (Na+K) to the total ash amount, the ratio of the sum of calcium (Ca) and sulfur (S) content (Ca+S) to the total ash amount, the ratio of the sum of sodium (Na) and potassium (K) content (Na+K) to the sum of calcium (Ca) and sulfur (S) content (Ca+S) ((Na+K) / (Ca+S)), the ratio of calcium (Ca) to sulfur (S) content (Ca / S), the ratio of calcium (Ca) to chlorine (Cl) content (Ca / Cl), and the ratio of sulfur (S) to chlorine (Cl) content (S / Cl) were calculated, and these results are shown in Table 1.

[0134] (Example 2) Nitrile rubber B was obtained in the same manner as in Example 1, except that the water content in the dehydration process was changed to 15%. The properties were measured and evaluated, and the results are shown in Table 1.

[0135] (Example 3) Nitrile rubber C was obtained in the same manner as in Example 1, except that the water content in the dehydration process was changed to 25%. The properties were measured and evaluated, and the results are shown in Table 1.

[0136] (Example 4) Nitrile rubber D was obtained in the same manner as in Example 1, except that the water content in the dewatering process was changed to 35%. The properties were measured and evaluated, and the results are shown in Table 1.

[0137] (Example 5) Nitrile rubber E was obtained in the same manner as in Example 1, except that the water content in the dehydration process was changed to less than 1%. The properties were measured and evaluated, and the results are shown in Table 1.

[0138] (Example 6) Nitrile rubber F was obtained in the same manner as in Example 1, except that the polymerization solution was added to the solidification solution at a position at least half the distance from the center to the solidification tank wall (outside the halfway point). The properties were measured and evaluated, and the results are shown in Table 1.

[0139] (Example 7) Nitrile rubber G was obtained in the same manner as in Example 6, except that the stirring rate of the coagulation solution was changed to a rotation speed of 350 rpm (peripheral speed 1.8 m / s). The properties were measured and evaluated, and the results are shown in Table 1.

[0140] (Reference example 1) Nitrile rubber H was obtained in the same manner as in Example 6, except that the stirring rate of the coagulation solution was changed to a rotation speed of 100 rpm (peripheral speed 0.5 m / s) and the water content after dewatering was changed to 25%. The properties were measured and evaluated, and the results are shown in Table 1.

[0141] (Reference example 2) Nitrile rubber I was obtained in the same manner as in Example 6, except that the coagulation method was changed to adding a coagulation solution to the stirred polymerization solution and the water content after dehydration was changed to 25%. The properties were measured and evaluated, and the results are shown in Table 1.

[0142] (Comparative Example 1) Nitrile rubber E was obtained in the same manner as in Reference Example 2, except that the rotation speed of the solidification tank agitator was changed to 100 rpm (peripheral speed 0.5 m / s) and dewatering was not performed. The characteristics of each were measured and evaluated, and the results are shown in Table 1.

[0143] [Table 1-1]

[0144] [Table 1-2]

[0145] [Table 1-3]

[0146] Table 1 shows that nitrile rubbers A to G obtained by the manufacturing method of the present invention all have reduced ash content. In particular, by concentrating 60% or more by mass of the water-containing crumbs produced by the coagulation reaction in the range of 1.7 to 8 mm, the ash content can be reduced significantly (especially in the comparison between Example 3, where the water content after dehydration is the same 25% by mass, and Reference Examples 1 and 2, the ash content was reduced from 1 to 1.1% by mass to 0.35% by mass). Furthermore, the amount of water-containing crumbs concentrated in such a specific range varies greatly depending on the amount of dehydration (the amount of water containing ash squeezed out from the water-containing crumbs), and by reducing the water content after dehydration from 25% by mass to 15% and 7% by mass, the ash content of 0.35% by mass can be further reduced to 0.25% and 0.14% by mass, respectively (comparison of Examples 1 to 3). Although this example does not show a comparison of temperatures during dehydration, the reduction in ash content was less than half without heating, indicating that it is important to keep the water-containing crumb flexible for ash removal. [Explanation of Symbols]

[0147] 10 Emulsion polymerization equipment 11 Polymerization can 12, 32, 52 Stirring device 13, 33, 53 Stirring blade 14, 34, 54 motors 30 Coagulation equipment 31 Solidification Tank 38, 58 Drainer 50 Cleaning device 51 Washing Tank 55, 71c heating device 56 Heating section 70 Squeezer 70a Clam supply section 70b Clam discharge section 71 Heating mechanism 71a, 72a Chamber 71b, 72b Laura 72 Pressurization mechanism 73 Connecting part 75 Crushing device

Claims

1. An emulsion polymerization step to obtain a polymerization solution by emulsion polymerization of acrylonitrile and 1,3-butadiene, The process involves adding a phenolic antioxidant to the resulting polymerization solution, A solidification process in which a polymerization solution containing a phenolic antioxidant is brought into contact with an aqueous solution of a polyvalent metal salt, and more than 60% by mass of the resulting hydrated crumb passes through a JIS sieve with an 8 mm mesh size but does not pass through a JIS sieve with an 1.7 mm mesh size, A washing process in which the generated water-containing crumb is washed with hot water, A dehydration process in which the washed, water-containing crumb is dehydrated at a temperature of 40°C or higher, A drying process to dry the washed, water-containing crumb to less than 1% by mass, A method for producing nitrile rubber containing the following:

2. The method for producing nitrile rubber according to claim 1, wherein 30% by mass or more of the water-containing crumb produced is water-containing crumb that passes through a JIS sieve with a mesh size of 4.75 mm but does not pass through a JIS sieve with a mesh size of 2.36 mm.

3. The method for producing nitrile rubber according to claim 1, wherein the aqueous solution of the polyvalent metal salt is an aqueous solution of calcium chloride.

4. A method for producing nitrile rubber according to claim 1, wherein at least one salt compound selected from the group consisting of alkali metal salts, sulfates, and sulfonates is used as a polymerization auxiliary material in the polymerization process.

5. The method for producing nitrile rubber according to claim 1, wherein the dehydration of the water-containing crumb is carried out until the water content of the water-containing crumb becomes 35% by mass or less.

6. The method for producing nitrile rubber according to claim 1, wherein the ash content of the nitrile rubber is 0.7% by mass or less.

7. A method for producing nitrile rubber according to claim 6, wherein the total ratio of calcium content (Ca) and sulfur content (S) in the ash (Ca + S) is 40% by mass or more.

8. A method for producing nitrile rubber according to claim 6, wherein the total ratio of sodium content (Na) and potassium content (K) in the ash (Na + K) is 30% by mass or less.

9. A method for producing nitrile rubber according to claim 6, wherein the ratio of calcium content (Ca) to sulfur content (S) in the ash (Ca / S) is 3 or less.

10. A method for producing nitrile rubber according to claim 6, wherein the ratio of calcium content (Ca) to chlorine content (Cl) in the ash (Ca / Cl) is 2 or more.

11. A method for producing nitrile rubber according to claim 6, wherein the ratio of sulfur content (S) to chlorine content (Cl) in the ash (S / Cl) is 2 or more.

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