Method for producing polymer

Abstract

[Problem] To provide a method for producing a resist polymer that suppresses elution of a metal from a deep filter and has extremely low amount of metal impurities in a demetallization treatment of a resist polymer containing an acidic group. [Solution] This method for producing a polymer is characterized by comprising: a step for preparing a polymer; and a step for passing a solution obtained by dissolving the polymer in an organic solvent to a deep filter, wherein the deep filter is cleaned with a solution containing an acid having a plurality of carboxyl groups.

Description

Technical Field

[0001] The present invention relates to a method for removing metal impurities contained in a resist polymer. Background Art

[0002] In the photolithography for semiconductor manufacturing, various Novolac polymers, acrylic polymers, oxystyrene polymers represented by hydroxystyrene, etc. are used as photoresist compositions for base polymers. For example, a film of a photoresist, an anti-reflection film, etc. is formed on substrates such as silicon wafers, then, across a mask irradiation excimer laser, etc. depicting a circuit pattern of a semiconductor device, development is performed, and the resulting photoresist pattern is etched to the substrate as a protective film, thus forming a fine pattern corresponding to a semiconductor circuit on the substrate surface. Along with the improvement of integration, it is required to form a finer pattern, and at present, in mass production, the photolithography based on KrF excimer laser (wavelength 248nm), ArF excimer laser (wavelength 193nm) is used. In addition, for the photolithography based on F2 excimer laser (wavelength 157nm) with a shorter wavelength, EUV (extreme ultraviolet light), X-rays, and electron beams with a wavelength shorter than these excimer lasers, research and development are also being promoted.

[0003] As the integration level increases, the miniaturization of semiconductor circuits continues to advance, and the requirements for reducing the amount of impurities contained in polymers used in photolithography have become increasingly stringent. Among them, metal impurities have various adverse effects on the manufacture of semiconductors, so they must be removed as much as possible. For example, if metal impurities are contained in a chemically amplified resist polymer, the metal component will capture the acidic substance produced by the acid generator during exposure, resulting in the polymer as a component of the resist substrate being unable to fully dissolve and unable to form the desired pattern. In addition, not limited to resist polymers, if metal impurities contained in photolithography polymers such as top coating polymers and anti-reflective film polymers eventually remain on the surface of the semiconductor substrate, the electrical properties of the semiconductor will be damaged, reducing the yield of the product.

[0004] As methods for removing metal impurities in polymers, the following methods are known: contacting a solution obtained by dissolving a polymer in an organic solvent with a strongly acidic cation exchange resin (Patent Document 1); treating the polymer with a filter containing a cationic charge regulator that generates a zeta potential, or a filter containing a cation exchanger and / or a chelate former (Patent Documents 2 and 3); extracting the polymer with water and an organic solvent (water washing) (Patent Document 4).

[0005] In particular, the method using a filter is relatively simple, and filters for electronic materials that can remove metals at a high level are currently available on the market.

[0006] These filters have the ability to capture metal ions in liquids at sub-ppb to ppb levels, and through special treatment and manufacturing methods, they can also suppress metal elution from the filter itself. The pretreatment of the filter before use is described in the catalog of each product. Generally speaking, it is carried out by the following method: After passing a specified amount of pure water through the liquid for cleaning, it is replaced with the solvent of the solution passed through the liquid during formal use.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 5-148308

[0010] Patent Document 2: Japanese Patent Application Laid-Open No. 8-165313

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 10-237125

[0012] Patent Document 4: International Publication No. WO2003 / 082933 Summary of the invention

[0013] Problems to be solved by the invention

[0014] However, even if the filter is used for electronic materials as described above and the pretreatment recommended by the manufacturer is performed, metal may be eluted from the filter depending on the type of polymer to be passed through, which becomes a problem in the production of resist polymers where removal of metal impurities is highly required.

[0015] Means for solving problems

[0016] The inventors of the present application have conducted intensive studies to solve the above-mentioned problems and have found that the above-mentioned problems can be solved by using a depth filter washed with a solution containing an acid having multiple carboxyl groups as a depth filter through which a solution of a polymer dissolved in an organic solvent passes, thereby completing the present invention.

[0017] That is, according to the present invention, the following inventions are provided.

[0018] [1] A method for producing a polymer, comprising:

[0019] a process for preparing a polymer; and

[0020] A step of passing a solution prepared by dissolving the above-mentioned polymer in an organic solvent through a depth filter

[0021] The depth filter is a depth filter washed with a solution containing an acid having a plurality of carboxyl groups.

[0022] [2] The method for producing a polymer according to [1], wherein the polymer is a polymer containing a structural unit having an acidic group.

[0023] [3] The method for producing a polymer according to [2], wherein the acidic group is one or more groups selected from the group consisting of a phenolic hydroxyl group, a carboxyl group, and a sulfonic group.

[0024] [4] The method for producing a polymer according to any one of [1] to [3], wherein the acid having a plurality of carboxyl groups is a divalent to tetravalent carboxylic acid.

[0025] [5] The method for producing a polymer according to any one of [1] to [3], wherein the acid having a plurality of carboxyl groups is at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, citric acid, 1,2,3,4-butanetetracarboxylic acid and ethylenediaminetetraacetic acid.

[0026] [6] The method for producing a polymer according to any one of [1] to [5], wherein the depth filter is a filter comprising one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

[0027] [7] A method for producing a polymer as described in any one of [1] to [5], wherein the depth filter is a filter comprising: one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose; and a cationic charge regulator and / or ion exchanger (excluding Na-type ion exchangers) that generates a zeta potential.

[0028] [8] The method for producing a polymer according to any one of [1] to [3], wherein the acid having a plurality of carboxyl groups is a divalent to tetravalent carboxylic acid,

[0029] The depth filter is a filter including at least one selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

[0030] [9] The method for producing a polymer according to any one of [1] to [3], wherein the acid having a plurality of carboxyl groups is a divalent to tetravalent carboxylic acid,

[0031] The aforementioned deep filter is a filter comprising: one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose; and a cationic charge regulator and / or ion exchanger (excluding Na-type ion exchangers) that generates Zeta potential.

[0032]

[10] A method for producing a polymer, comprising:

[0033] Process for preparing polymers;

[0034] After placing the depth filter in a filter filtration device, the depth filter is washed with a solution containing an acid having a plurality of carboxyl groups, and then washed with water and / or an organic solvent; and

[0035] A step of passing a solution prepared by dissolving the polymer in an organic solvent through the cleaned depth filter.

[0036]

[11] The method for producing a polymer according to

[10] , wherein the polymer is a polymer containing a structural unit having an acidic group.

[0037]

[12] The method for producing a polymer according to

[11] , wherein the acidic group is one or more groups selected from the group consisting of a phenolic hydroxyl group, a carboxyl group, and a sulfonic group.

[0038]

[13] The method for producing a polymer according to any one of

[10] to

[12] , wherein the acid having a plurality of carboxyl groups is a divalent to tetravalent carboxylic acid.

[0039]

[14] The method for producing a polymer according to any one of

[10] to

[12] , wherein the acid having a plurality of carboxyl groups is a divalent to tetravalent carboxylic acid,

[0040] The depth filter is a filter including at least one selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

[0041]

[15] The method for producing a polymer according to any one of

[10] to

[12] , wherein the acid having a plurality of carboxyl groups is a divalent to tetravalent carboxylic acid,

[0042] The aforementioned deep filter is a filter comprising: one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose; and a cationic charge regulator and / or ion exchanger (excluding Na-type ion exchangers) that generates Zeta potential.

[0043] Effects of the Invention

[0044] According to the present invention, a resist polymer can be produced which suppresses metal elution from a depth filter in demetallization treatment of a resist polymer having an acidic group, is suitable for the most advanced lithography such as EUV lithography, and has extremely low metal impurities. DETAILED DESCRIPTION

[0045] [Method for producing polymer]

[0046] The method for producing a polymer of the present invention comprises: a step of preparing a polymer; and a step of passing a solution obtained by dissolving the polymer in an organic solvent (hereinafter sometimes referred to as a "polymer solution") through a depth filter. In addition, the method for producing a polymer of the present invention may further comprise a step of washing the depth filter before the passing step.

[0047] [Polymer preparation process]

[0048] The polymer prepared in the present invention can be used without particular limitation as long as it is a conventionally known polymer for resists, and is particularly preferably a polymer having a structure containing an acidic group. When a polymer containing an acidic group is filtered using a depth filter, undesirable metal components may be eluted from the depth filter, causing the polymer to be contaminated. The present invention can prevent such contamination.

[0049] Examples of the acidic group include a phenolic hydroxyl group, a carboxyl group, a sulfonic group, etc. Among these, a polymer having a structure including a phenolic hydroxyl group can be preferably used for resist applications.

[0050] The polymerization method and purification method of the polymer are not particularly limited, and can be carried out by the same methods as those for polymerization and purification of conventionally known resist polymers.

[0051] [Polymer solution passing step]

[0052] The present invention includes a step of filtering the polymer solution using a depth filter in order to remove metal impurities in the polymer.

[0053] In the present invention, the filter material of the deep filter used includes: fiber components such as kapok, pulp, cellulose fiber, cellulose acetate fiber, polyacrylonitrile fiber, nylon fiber, rayon fiber, polyester fiber, polyvinyl chloride fiber, and the like; and particle components such as diatomaceous earth, perlite, magnesium oxide (magnesia), talc, activated carbon, zeolite, and colloidal silica. Among these, cellulose fiber, cellulose acetate fiber, polyacrylonitrile fiber, nylon fiber, rayon fiber, polyester fiber, polyvinyl chloride fiber, diatomaceous earth, perlite, zeolite, and colloidal silica are preferably used for processing electronic materials such as resists.

[0054] In addition, the deep filter can include cation exchange resin, anion exchange resin, chelate resin or their mixture. When the included ion exchange resin and chelate resin are in the state of alkali metal counterions such as sodium ion type, it is appropriate to process with acid in advance and be converted into proton type. This acid treatment is an operation different from the cleaning performed by the solution of the acid with a plurality of carboxyl groups with utilization of the present invention, and the acid used now preferably uses hydrochloric acid, sulfuric acid etc. It should be noted that if the included ion exchange resin or chelate resin are proton type at first, then this operation is not needed. After the acid cleaning, the filter can be dehydrated by further cleaning with an aqueous miscible organic solvent such as ethyl lactate, acetone or / and other organic solvents.

[0055] In addition, the depth filter may contain a cationic charge regulator such as polyamide polyamine epichlorohydrin cationic resin, melamine-formaldehyde cationic resin, etc. The cationic charge regulator imparts cationic charge to the filter, and generates a zeta potential between the filter and the impurities in the liquid passing through, which are charged substances during the filtration process, and is effective in removing fine foreign matter and metal impurities.

[0056] The nominal pore size of the depth filter is preferably 1.0 μm or less, more preferably 0.9 μm or less, further preferably 0.7 μm or less, and further preferably 0.5 μm or less. In addition, it can be 0.01 μm or more, 0.02 μm or more, or 0.05 μm or more. The nominal pore size mentioned here refers to the nominal pore size indicating the separation performance of the filter, for example, the pore size determined by the test method determined by the filter manufacturer such as the bubble point test, mercury intrusion test, and standard particle capture test. When a commercial product is used, it is the value recorded in the manufacturer's catalog data.

[0057] Examples of commercially available depth filters particularly for electronic material applications include 3M's ZetaPlus 40Q series, Zeta Plus GN series, and Zeta Plus EC series.

[0058] [Depth filter cleaning process]

[0059] In the present invention, a depth filter washed with a solution containing an acid having a plurality of carboxyl groups (hereinafter, sometimes referred to as a "washing solution") is used.

[0060] In addition, before the step of passing the polymer solution through the filter, a step of washing the depth filter with a washing solution may be included. Specifically, it is preferred that after the depth filter is placed in the filter filtration device, the depth filter is washed with a washing solution and then washed with water and / or an organic solvent.

[0061] In the present invention, even if a deep filter containing a filter material that can contain transition metals is used, the metal can be prevented from eluting from the deep filter by washing it in advance. Examples of the filter material that can contain transition metals include diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

[0062] There is no limitation as long as the number of carboxyl groups of the acid contained in the cleaning solution is 2 or more, but it is preferably 2 to 4. In addition, these may be hydroxycarboxylic acids also having a hydroxyl group.

[0063] Specific examples of the carboxylic acid having two carboxyl groups include oxalic acid, malonic acid, succinic acid, glutaric acid, malic acid, tartaric acid, maleic acid, citraconic acid, itaconic acid, etc. Among these, oxalic acid, malonic acid, and succinic acid are preferred, and oxalic acid is particularly preferred.

[0064] Specific examples of the carboxylic acid having three carboxyl groups include citric acid, isocitric acid, tricarballylic acid, etc. Among these, citric acid is preferred.

[0065] Specific examples of the carboxylic acid having four carboxyl groups include 1,2,3,4-butanetetracarboxylic acid, ethylenediaminetetraacetic acid, etc. Among these, 1,2,3,4-butanetetracarboxylic acid is preferred.

[0066] In addition, it is also preferred to clean the depth filter with pure water or other solvents before and after cleaning with the above-mentioned cleaning solution. It is particularly preferred to allow pure water or other solvents to flow sufficiently after acid cleaning to remove the acid in the depth filter. Immediately before passing the polymer solution, it is preferred to replace the filter with a solvent that is the same as or compatible with the solvent of the polymer solution.

[0067] In order to remove the insoluble components and metals in the polymer, in addition to the above-mentioned deep filter, it is also possible to further utilize a membrane filter, a hollow fiber membrane filter, a pleated filter, etc. for filtration. Examples of these filters include polyethylene filters such as MicroGard and Optimizer-D made by Entegris Japan, nylon filters such as Ultipleat P-nylon 66 and Ultipor N66 made by Pall Japan, PhotoShield and ElectroPore IIEF made by 3M, and fluorinated polyethylene filters such as Penflon (Japanese: ペンフロン) made by Pall Japan. These filters are also preferably further cleaned with a method recommended by the manufacturer before use, usually after washing with pure water, and then with an aqueous mixed organic solvent or / and other organic solvents (preferably the same solvent as the solution to be treated).

[0068] Example

[0069] Hereinafter, the embodiment of the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples. It should be noted that, in the following Examples, parts are based on mass unless otherwise specified.

[0070] [Metal Analysis in Polymers]

[0071] The metal contents of the polymers synthesized below were determined using ICP mass spectrometry.

[0072] ICP mass spectrometer: Agilent 8900cs manufactured by Agilent Technologies

[0073] [Depth filter]

[0074] The depth filters used in the examples were all clean filters sold for metal removal from electronic materials such as photoresists. However, due to differences between lots, filters from a plurality of different lots were prepared and designated as lots A to D.

[0075] ·3M Zeta Plus TM 020GN (nominal pore size 0.2μm, )Batch A

[0076] ·3M Zeta Plus TM 020GN (nominal pore size 0.2μm, )Batch B

[0077] ·3M Zeta Plus TM 40QSH (nominal pore size 0.2~0.5μm, )Batch C

[0078] ·3M Zeta Plus TM 40QSH (nominal pore size 0.2~0.5μm, )Batch D

[0079] [Example 1]

[0080] (Manufacture of polymers)

[0081] A p-hydroxystyrene composition obtained by dehydrogenating p-ethylphenol (25% by mass of p-hydroxystyrene, 41% by mass of p-ethylphenol, 23% by mass of methanol, and 11% of water) and tert-butyl acrylate were dissolved in methanol so that the molar ratio of the monomers became 66:34, and AIBN was added as a polymerization initiator to prepare a monomer solution.

[0082] A quarter of the monomer solution was placed in a reaction vessel equipped with a stirrer, a cooler, and a thermometer, and after forming a nitrogen atmosphere, the temperature was raised to 80° C. while stirring. The remaining three quarters of the monomer solution was added dropwise at a constant rate over 3 hours, and the polymerization reaction was further continued for 1 hour, and then cooled to room temperature.

[0083] As for the polymer solution, toluene as a poor solvent and acetone as a good solvent were used to precipitate and purify the polymer by a known method to remove impurities such as the polymerization solvent and unreacted monomers contained in the polymer. The properties of the obtained polymer were PHS:TBA=66:34, weight average molecular weight (Mw)=20,000, and molecular weight distribution (Mw / Mn)=2.5. Then, the polymer was dissolved in acetone again, and the concentration of the polymer solution was prepared to be 20% by mass.

[0084] (Depth filter cleaning process)

[0085] 3M depth filter, Zeta Plus 020GN Batch A was installed in the filter housing, pure water was pumped by a pump to fill the housing, and the housing was left standing for 30 minutes. Then, 85 g of 3 mass % oxalic acid aqueous solution and then 150 g of acetone were passed to clean the filter.

[0086] In addition, 3M depth filter, Zeta Plus 40QSH Batch C was also cleaned by the same procedure as 020GN.

[0087] (Polymer solution passing through depth filter)

[0088] 200 g of the polymer solution having a concentration of 20% by mass was circulated and filtered five times through a cleaned 020GN filter, and then filtered once through a cleaned 40QSH filter.

[0089] The metal content in the polymer was analyzed at each stage before the filter treatment, after the 020GN filter treatment, and after the 40QSH filter treatment. The results are shown in Table 1.

[0090] [Comparative Example 1]

[0091] In the cleaning of the 020 filter and the 40QSH filter, the filter pre-cleaning was performed in the same manner as in Example 1, except that the 3 mass % oxalic acid aqueous solution was changed to pure water. 200 g of the same 20 mass % polymer solution as in Example 1 was circulated and filtered 5 times through the cleaned 020GN filter, and then filtered once through the cleaned 40QSH filter.

[0092] The metal content in the polymer was analyzed at each stage after the 020GN filter treatment and after the 40QSH filter treatment. The results are shown in Table 1.

[0093] [Table 1]

[0094]

[0095] When the filter was cleaned with pure water, vanadium eluted from the filter and mixed into the polymer solution due to the flow of the polymer solution. However, when the filter was cleaned with an aqueous oxalic acid solution, almost no vanadium eluted from the filter and the amount of other metals was also reduced.

[0096] [Example 2]

[0097] (Manufacture of polymers)

[0098] The polymerization and purification of p-hydroxystyrene and tert-butyl acrylate were carried out in the same procedure as in Example 1, and finally the polymer concentration was adjusted to 30% by mass using acetone.

[0099] (Depth filter cleaning process)

[0100] 3M depth filter, Zeta Plus 40QSH Batch D was installed in the filter housing, pure water was pumped by a pump to fill the housing, and the housing was left standing for 30 minutes. Then, 85 g of 3 mass % oxalic acid aqueous solution and then 150 g of acetone were passed to clean the filter.

[0101] (Polymer solution passing through depth filter)

[0102] 200 g of the polymer solution having a concentration of 30% by mass was filtered once using the washed 40QSH batch D.

[0103] The metal content in the polymer was analyzed at each stage before and after the filter treatment. The results are shown in Table 2.

[0104] [Comparative Example 2]

[0105] The filter was cleaned in the same manner as in Example 2 except that the oxalic acid aqueous solution was changed to pure water in the cleaning of the 40QSH filter.

[0106] 200 g of the same 30 mass % polymer solution as in Example 2 was filtered once using the washed 40QSH batch D.

[0107] The metal content in the polymer after the filter treatment was analyzed, and the results are shown in Table 2.

[0108] [Table 2]

[0109]

[0110] [Example 3]

[0111] (Manufacture of polymers)

[0112] 4-Hydroxyphenyl methacrylate and tert-butyl acrylate were dissolved in equimolar amounts in a mixed solvent of PGME and methanol (mass ratio 70:30), and dimethyl 2,2-azobisisobutyrate was added thereto to prepare a monomer solution.

[0113] A mixed solvent of PGME and methanol (mass ratio 70:30) was placed in a reaction vessel equipped with a stirrer, a cooler, and a thermometer, and after forming a nitrogen atmosphere, the temperature was raised to 80°C while stirring. The above-mentioned monomer solution was added dropwise at a constant rate for 4 hours, and then the polymerization reaction was continued for another 3 hours, and then cooled to room temperature. The polymer solution was analyzed by GC, and the result was that the conversion rate of the monomer was more than 99%.

[0114] The properties of the obtained polymer were 4-hydroxyphenyl methacrylate: tert-butyl acrylate = 50:50, weight average molecular weight (Mw) = 23,000, molecular weight distribution (Mw / Mn) = 2.4. The concentration of the resin solution was 27.4%.

[0115] (Depth filter cleaning process)

[0116] A 3M deep filter, Zeta Plus 020GN Batch B, was installed in the filter housing, pure water was pumped in and filled up the housing, and the housing was left standing for 30 minutes. Then, 85 g of a 3 mass % oxalic acid aqueous solution was passed through, followed by 150 g of acetone to clean the filter.

[0117] (Polymer solution passing through depth filter)

[0118] 200 g of the unpurified polymer solution (polymer concentration: 27.4 mass %) was filtered once using the washed 020GN batch B.

[0119] Focusing on the elution of vanadium from the filter, the vanadium content in the polymer was analyzed before and after the filter treatment. The results are shown in Table 3.

[0120] [Comparative Example 3]

[0121] The 020GN filter was cleaned in the same manner as in Example 3 except that the oxalic acid aqueous solution was changed to pure water.

[0122] 200 g of the same polymer solution as in Example 3 was filtered once using the washed 020GN batch B.

[0123] The vanadium content in the polymer after the filter treatment was analyzed. The results are shown in Table 3.

[0124] [Table 3]

[0125]

[0126] When a filter washed with oxalic acid was used, the incorporation of vanadium was suppressed to a low level even when a p-hydroxyphenyl methacrylate / t-butyl acrylate copolymer solution was passed through the filter. However, when a filter washed with pure water was used, a large amount of vanadium was eluted during the passing of the polymer liquid and was mixed into the polymer.

[0127] [Example 4]

[0128] (Manufacture of polymers)

[0129] The polymerization and purification of p-hydroxystyrene and tert-butyl acrylate were carried out in the same procedure as in Example 1, and finally the polymer concentration was adjusted to 20% by mass using acetone.

[0130] (Depth filter cleaning process)

[0131] A 3M deep filter, Zeta Plus 020GN Batch B, was installed in the filter housing, and pure water was pumped to fill the housing, and the housing was left standing for 30 minutes. Then, 85 g of a 3 mass % oxalic acid aqueous solution was passed through, followed by 150 g of acetone to clean the filter.

[0132] (Polymer solution passing through depth filter)

[0133] 200 g of a polymer solution having a concentration of 20% by mass was filtered once using the washed 020GN batch B.

[0134] Focusing on the elution of vanadium from the filter, the vanadium content in the polymer was analyzed before and after the filter treatment. The results are shown in Table 4.

[0135] [Examples 5-6]

[0136] The 020GN filter was cleaned in the same manner as in Example 4 except that the 3 mass % oxalic acid aqueous solution was changed to a 3 mass % citric acid aqueous solution and a 3 mass % 1,2,3,4-butanetetracarboxylic acid aqueous solution, respectively.

[0137] 200 g of the same 20 mass % polymer solution as in Example 4 was filtered once using the washed 020GN batch B.

[0138] The vanadium content in the polymer after the filter treatment was analyzed. The results are shown in Table 4.

[0139] [Comparative Examples 4 to 7]

[0140] The filter was cleaned in the same manner as in Example 4 except that the 3 mass % oxalic acid aqueous solution was replaced with pure water, 3 mass % hydrochloric acid, 3 mass % methanesulfonic acid aqueous solution, 3 mass % acetic acid aqueous solution, and 3 mass % citric acid aqueous solution, respectively.

[0141] 200 g of the same 20 mass % polymer solution as in Example 4 was filtered once using the washed 020GN batch B.

[0142] The vanadium content in the polymer after the filter treatment was analyzed. The results are shown in Table 4.

[0143] [Table 4]

[0144]

[0145] When a filter cleaned with oxalic acid, citric acid, or 1,2,3,4-butanetetracarboxylic acid was used, the incorporation of vanadium was suppressed to a low level even when a p-hydroxystyrene / tert-butyl acrylate copolymer solution was passed through the filter. However, when a filter cleaned with pure water, hydrochloric acid, methanesulfonic acid, or acetic acid was used, a large amount of vanadium was dissolved during the passage of the polymer liquid and was mixed into the polymer.

Claims

1. A method for producing a polymer, characterized in that: include: a process for preparing a polymer; and A step of passing a solution prepared by dissolving the polymer in an organic solvent through a depth filter, The depth filter is a depth filter washed with a solution containing an acid having a plurality of carboxyl groups.

2. The method for producing a polymer according to claim 1, wherein The polymer is a polymer including a structural unit having an acidic group.

3. The method for producing a polymer according to claim 2, wherein: The acidic group is any one or more groups selected from the group consisting of a phenolic hydroxyl group, a carboxyl group, and a sulfonic group.

4. The method for producing a polymer according to any one of claims 1 to 3, wherein The acid having multiple carboxyl groups is a divalent to tetravalent carboxylic acid.

5. The method for producing a polymer according to any one of claims 1 to 3, wherein The acid having a plurality of carboxyl groups is at least one selected from the group consisting of oxalic acid, malonic acid, succinic acid, citric acid, 1,2,3,4-butanetetracarboxylic acid, and ethylenediaminetetraacetic acid.

6. The method for producing a polymer according to any one of claims 1 to 3, wherein The depth filter is a filter comprising at least one selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

7. The method for producing a polymer according to any one of claims 1 to 3, wherein The deep filter is a filter comprising: one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose; and a cationic charge regulator and / or ion exchanger (excluding Na-type ion exchangers) that generates a zeta potential.

8. The method for producing a polymer according to any one of claims 1 to 3, wherein The acid having multiple carboxyl groups is a divalent to tetravalent carboxylic acid, The depth filter is a filter comprising at least one selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

9. The method for producing a polymer according to any one of claims 1 to 3, wherein The acid having multiple carboxyl groups is a divalent to tetravalent carboxylic acid, The deep filter is a filter comprising: one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose; and a cationic charge regulator and / or ion exchanger (excluding Na-type ion exchangers) that generates a zeta potential.

10. A method for producing a polymer, comprising: Process for preparing polymers; After placing the depth filter in a filter filtration device, the depth filter is washed with a solution containing an acid having a plurality of carboxyl groups, and then washed with water and / or an organic solvent; and A step of passing a solution prepared by dissolving the polymer in an organic solvent through the washed depth filter.

11. The method for producing a polymer according to claim 10, wherein: The polymer is a polymer including a structural unit having an acidic group.

12. The method for producing a polymer according to claim 11, wherein The acidic group is any one or more groups selected from the group consisting of a phenolic hydroxyl group, a carboxyl group, and a sulfonic group.

13. The method for producing a polymer according to any one of claims 10 to 12, wherein The acid having multiple carboxyl groups is a divalent to tetravalent carboxylic acid.

14. The method for producing a polymer according to any one of claims 10 to 12, wherein The acid having multiple carboxyl groups is a divalent to tetravalent carboxylic acid, The depth filter is a filter comprising at least one selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose.

15. The method for producing a polymer according to any one of claims 10 to 12, wherein The acid having multiple carboxyl groups is a divalent to tetravalent carboxylic acid, The deep filter is a filter comprising: one or more selected from the group consisting of diatomaceous earth, magnesium oxide, perlite, talc, colloidal silica, activated carbon, zeolite, clay, and cellulose; and a cationic charge regulator and / or ion exchanger (excluding Na-type ion exchangers) that generates a zeta potential.

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