An acrylic rubber, including: 50 to 99.9% by weight of a bond unit derived from at least one (meth) acrylic acid ester selected from the group consisting of (meth) acrylic acid alkyl ester and (meth) acrylic acid alkoxyalkyl ester; 0.1 to 20% by weight of a bond unit derived from a monomer containing a reactive group; and 0 to 30% by weight of a bond unit derived from other monomer, wherein the acrylic rubber contains a phenolic anti-aging agent represented by a general formula (1),

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(R1 represents an isopropyl group or a t-butyl group, and R2 represents an alkyl group having 1 to 12 carbon atoms), and the weight average molecular weight (Mw) of the acrylic rubber is in the range of 100,000 to 5,000,000.

A method for producing a fluoropolymer powder including (A1) adding, to a fluoropolymer aqueous dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, and an acid to adjust a pH to 4.0 or less and cause coagulation to thereby obtain a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A), and (B1) heat-treating the wet fluoropolymer powder at a temperature higher than 150° C. and lower than 240° C.: General Formula (1A): H—(CF.sub.2).sub.m—COOH wherein m is 3 to 19.

A method for producing a fluoropolymer powder including (A1) adding, to a fluoropolymer aqueous dispersion obtained by polymerization using a carboxylic acid type hydrocarbon surfactant, and an acid to adjust a pH to 4.0 or less and cause coagulation to thereby obtain a wet fluoropolymer powder containing a fluorine-containing compound represented by the following general formula (1A), and (B1) heat-treating the wet fluoropolymer powder at a temperature higher than 150° C. and lower than 240° C.: General Formula (1A): H—(CF.sub.2).sub.m—COOH wherein m is 3 to 19.

To provide a method capable of producing fluorinated polymer particles in which formation of fine particles or formation of large aggregates is sufficiently suppressed even in the case of a fluorinated polymer having high solubility in a solvent.

The method comprises the following steps (i) and (ii), being a method for producing particles of a fluorinated polymer (A) which has either one or both of structural units (u1) derived from tetrafluoroethylene and structural units (u2) having no sulfonic acid type functional group and having a cyclic structure and fluorine atoms, and which has structural units (u3) having a sulfonic acid type functional group, wherein the proportion of the structural units (u1) is from 0 to 82 mol % in all structural units (100 mol %) in the fluorinated polymer (A): (i) a step of preparing solution or dispersion of the fluorinated polymer (A) having the above fluorinated polymer (A) dissolved or dispersed in a solvent (B), wherein the following conditions (i-1) and (i-2) are satisfied: (i-1) the solvent (B) contains a good solvent (B2) wherein the solubility of the fluorinated polymer (A) is at least 30%, (i-2) even when the above solution or dispersion of the fluorinated polymer (A) is passed through a filter of 200 mesh made of stainless steel, no residue remains on the filter, (ii) a step of mixing the above solution or dispersion of the fluorinated polymer (A) and a solvent (C) to aggregate the fluorinated polymer (A) to form particles of the fluorinated polymer (A), wherein the following conditions (ii-1) to (ii-3) are satisfied: (ii-1) the solvent (C) contains a poor solvent (C1) whereby the degree of swelling of the fluorinated polymer (A) is at most 100%, (ii-2) the degree of swelling of the fluorinated polymer (A) by a mixed solvent (BC) of the solvent (B) and the solvent (C) is from 70 to 250%, (ii-3) the ratio of the mass (W.sub.C) of the solvent (C) to the mass (W.sub.B) of the solvent (B) is from 1 to 5.

To provide a method capable of producing fluorinated polymer particles in which formation of fine particles or formation of large aggregates is sufficiently suppressed even in the case of a fluorinated polymer having high solubility in a solvent.

The method comprises the following steps (i) and (ii), being a method for producing particles of a fluorinated polymer (A) which has either one or both of structural units (u1) derived from tetrafluoroethylene and structural units (u2) having no sulfonic acid type functional group and having a cyclic structure and fluorine atoms, and which has structural units (u3) having a sulfonic acid type functional group, wherein the proportion of the structural units (u1) is from 0 to 82 mol % in all structural units (100 mol %) in the fluorinated polymer (A): (i) a step of preparing solution or dispersion of the fluorinated polymer (A) having the above fluorinated polymer (A) dissolved or dispersed in a solvent (B), wherein the following conditions (i-1) and (i-2) are satisfied: (i-1) the solvent (B) contains a good solvent (B2) wherein the solubility of the fluorinated polymer (A) is at least 30%, (i-2) even when the above solution or dispersion of the fluorinated polymer (A) is passed through a filter of 200 mesh made of stainless steel, no residue remains on the filter, (ii) a step of mixing the above solution or dispersion of the fluorinated polymer (A) and a solvent (C) to aggregate the fluorinated polymer (A) to form particles of the fluorinated polymer (A), wherein the following conditions (ii-1) to (ii-3) are satisfied: (ii-1) the solvent (C) contains a poor solvent (C1) whereby the degree of swelling of the fluorinated polymer (A) is at most 100%, (ii-2) the degree of swelling of the fluorinated polymer (A) by a mixed solvent (BC) of the solvent (B) and the solvent (C) is from 70 to 250%, (ii-3) the ratio of the mass (W.sub.C) of the solvent (C) to the mass (W.sub.B) of the solvent (B) is from 1 to 5.

A composition comprising a mixture of fluoropolyether acids or salts having a number average value of about 800 to about 2500 g/mol. The amount of fluoropolyether acids or salt in the mixture having a molecular weight of not more than 500 g/mol is not more than 50 ppm by weight of the total amount of fluoropolyether acids or salts in the mixture. The amount of fluoropolyether acids or salts in the mixture having a molecular weight of 2500 g/mol or greater is not more than 40% by weight of the total amount of fluoropolyether acids or salts in the mixture. Preferably the fluoropolyether acids or salts comprise an anionic group selected from the group consisting of carboxylate, sulfonate, sulfonamide anion and phosphonate. Also disclosed is an aqueous dispersion polymerization process for fluoropolymer manufacture employing polymerization agent comprising the specified mixture of fluoropolyether acids or salts.

A composition comprising a mixture of fluoropolyether acids or salts having a number average value of about 800 to about 2500 g/mol. The amount of fluoropolyether acids or salt in the mixture having a molecular weight of not more than 500 g/mol is not more than 50 ppm by weight of the total amount of fluoropolyether acids or salts in the mixture. The amount of fluoropolyether acids or salts in the mixture having a molecular weight of 2500 g/mol or greater is not more than 40% by weight of the total amount of fluoropolyether acids or salts in the mixture. Preferably the fluoropolyether acids or salts comprise an anionic group selected from the group consisting of carboxylate, sulfonate, sulfonamide anion and phosphonate. Also disclosed is an aqueous dispersion polymerization process for fluoropolymer manufacture employing polymerization agent comprising the specified mixture of fluoropolyether acids or salts.

A composition comprising a mixture of fluoropolyether acids or salts having a number average value of about 800 to about 2500 g/mol. The amount of fluoropolyether acids or salt in the mixture having a molecular weight of not more than 500 g/mol is not more than 50 ppm by weight of the total amount of fluoropolyether acids or salts in the mixture. The amount of fluoropolyether acids or salts in the mixture having a molecular weight of 2500 g/mol or greater is not more than 40% by weight of the total amount of fluoropolyether acids or salts in the mixture. Preferably the fluoropolyether acids or salts comprise an anionic group selected from the group consisting of carboxylate, sulfonate, sulfonamide anion and phosphonate. Also disclosed is an aqueous dispersion polymerization process for fluoropolymer manufacture employing polymerization agent comprising the specified mixture of fluoropolyether acids or salts.

An acrylic rubber sheet excellent in storage stability and processability, a method for producing the same, an acrylic rubber bale obtained by laminating the sheets, a mixture obtained by mixing the acrylic rubber sheet and the acrylic rubber bale, a method for producing the mixture and a rubber cross-linking product obtained by cross-linking the mixture. The acrylic rubber sheet comprises, an acrylic rubber mainly composed of a (meth) acrylic acid ester and having a weight average molecular weight (Mw) of 100,000 to 5,000,000 and a ratio (Mz/Mw) of a Z-average molecular weight (Mz) and a weight average molecular weight (Mw) is 1.3 or more, and the acrylic rubber sheet contains a phenolic anti-aging agent, and a gel amount is 50 wt % or less. The acrylic rubber sheet is extremely excellent in storage stability and processability and the sheet can be easily produced by the claimed method.

An acrylic rubber sheet excellent in storage stability and processability, a method for producing the same, an acrylic rubber bale obtained by laminating the sheets, a mixture obtained by mixing the acrylic rubber sheet and the acrylic rubber bale, a method for producing the mixture and a rubber cross-linking product obtained by cross-linking the mixture. The acrylic rubber sheet comprises, an acrylic rubber mainly composed of a (meth) acrylic acid ester and having a weight average molecular weight (Mw) of 100,000 to 5,000,000 and a ratio (Mz/Mw) of a Z-average molecular weight (Mz) and a weight average molecular weight (Mw) is 1.3 or more, and the acrylic rubber sheet contains a phenolic anti-aging agent, and a gel amount is 50 wt % or less. The acrylic rubber sheet is extremely excellent in storage stability and processability and the sheet can be easily produced by the claimed method.