Method for producing methacrylic-based polymer

1. A method for producing a methacrylic-based polymer, comprising the following Steps (1) and (2):

Step (1): using a complete mixing reactor (A) to thereby obtain a first syrup with the step comprising the following steps (1)-1, (1)-2 and (1)-3:

(1)-1: continuously feeding a monomer mixture containing 80 to 99.9 mass % of methyl methacrylate and 0.1 to 20 mass % of an alkyl acrylate, 0.01 to 1.0 parts by mol of a mercaptan based on 100 parts by mol of the monomer mixture, and a first radical polymerization initiator (a) in an amount satisfying the following formula (1), to the complete mixing reactor (A):

5.0×10 −5 <α≦1.75×β×10 −6 +6.0×10 −5   (1)

wherein in the formula (1), α is a number of moles of the first radical polymerization initiator (a) based on 1 mol of the monomer mixture; and β is a proportion (mass %) of an alkyl acrylate unit in the methacrylic-based polymer to be produced;

(1)-2: carrying out stirring and mixing at a temperature of the complete mixing reactor (A) interior of 110 to 160° C., and carrying out polymerization so that a content of a polymer of the monomer mixture becomes 40 to 60 mass %; and

(1)-3: continuously obtaining the first syrup from the complete mixing reactor (A);

Step (2): using a reaction apparatus (D) comprising a plug flow mixer (B) and a plug flow reactor (C) to thereby obtain a second syrup, wherein a second radical polymerization initiator (c) is added to the first syrup with the plug flow mixer (B) having an inner wall temperature set at the temperature of the complete mixing reactor (A) interior or higher and 230° C. or lower to thereby make a syrup mixture, and then polymerization is carried out by the plug flow reactor (C) to obtain the second syrup.

2. A method for producing a methacrylic-based polymer, comprising the following Steps (1) to (3):

Step (1): using a complete mixing reactor (A) to thereby obtain a first syrup with the step comprising the following steps (1)-1, (1)-2 and (1)-3:

(1)-1: continuously feeding a monomer mixture containing 80 to 99.9 mass % of methyl methacrylate and 0.1 to 20 mass % of an alkyl acrylate, 0.01 to 1.0 parts by mol of a mercaptan based on 100 parts by mol of the monomer mixture, and a first radical polymerization initiator (a) in an amount satisfying the following formula (1), to the complete mixing reactor (A):

5.0×10 −5 <α≦1.75×β×10 −6 +6.0×10 −5   (1)

wherein in the formula (1), α is a number of moles of the first radical polymerization initiator (a) based on 1 mol of the monomer mixture; and β is a proportion (mass %) of an alkyl acrylate unit in the methacrylic-based polymer to be produced;

(1)-2: carrying out stirring and mixing at a temperature of the complete mixing reactor (A) interior of 110 to 160° C., and carrying out polymerization so that a content of a polymer of the monomer mixture becomes 40 to 60 mass %; and

(1)-3: continuously obtaining the first syrup from the complete mixing reactor (A);

Step (2): using a reaction apparatus (D) comprising a plug flow mixer (B) and a plug flow reactor (C) to thereby obtain a second syrup with the step comprising the following steps of (2)-1, (2)-2 and (2)-3:

(2)-1: adding a second radical polymerization initiator (c) satisfying the following conditions (i) to (iii) to the first syrup, and carrying out mixing with the plug flow mixer (B) having an inner wall temperature set at the temperature of the complete mixing reactor (A) interior or higher and 230° C. or lower to thereby make a syrup mixture:

Condition (i): a half-life period of the second radical polymerization initiator (c) at an inner wall temperature of the plug flow mixer (B) is 1,000 sec or shorter;

Condition (ii): a half-life period of the second radical polymerization initiator (c) at an inner wall temperature of the reactor (C) is 1,000 sec or shorter; and

Condition (iii): an amount of the second radical polymerization initiator (c) added satisfies the following formula (2):

1.0×10 −6 <γ≦0.25×β×10 −6 +5.0×10 −5   (2)

wherein in the formula (2), γ is a number of moles of the second radical polymerization initiator (c) based on 1 mol of the monomer mixture; and β is a proportion (mass %) of an alkyl acrylate unit in the methacrylic-based polymer to be produced;

(2)-2: polymerizing the syrup mixture in the plug flow reactor (C) having an inner wall temperature set at the temperature of the complete mixing reactor (A) interior or higher and 230° C. or lower to thereby make a polymerized mixture; and

(2)-3: obtaining the second syrup having a content of a polymer in the polymerized mixture of 50 to 90 mass %; and

Step (3): feeding the second syrup to a volatile-removing apparatus (E), and continuously separating and removing volatile.

3. The method for producing a methacrylic-based polymer according to claim 1 , comprising using a reaction apparatus (D) wherein n sets of a plug flow mixer (Bn) and a plug flow reactor (Cn) (n is an integer of 1 or more) are arranged in the order of a plug flow mixer (Bn) and a plug flow reactor (Cn), and adding the second radical polymerization initiator (cn) (n is an integer of 1 or more) in an inlet port of each of the mixers (Bn) and successively carrying out polymerization in each of the reactors (Cn) to thereby obtain the second syrup.

4. The method for producing a methacrylic-based polymer according to claim 1 , wherein an amount of the first radical polymerization initiator (a) fed in Step (1) satisfies the following formula (3):

5.0×10 −5 <α≦1.75×β×10 −6 +5.0×10 −5   (3)

wherein in the formula (3), α is a number of moles of the first radical polymerization initiator (a) based on 1 mol of the monomer mixture; and β is a proportion (mass %) of an alkyl acrylate unit in the methacrylic-based polymer to be produced.

5. The method for producing a methacrylic-based polymer according to claim 1 ,

wherein a residence time of the syrup in the mixer (B) in Step (2) is 1 to 30 sec;

wherein the following formula (4) is satisfied:

y<x+ 5  (4)

wherein x is a syrup temperature (° C.) at an inlet port of the mixer (B), and y is a syrup temperature (° C.) at an outlet port of the mixer (B); and

wherein a residual ratio of the second radical polymerization initiator (c) contained in the syrup at the outlet port of the mixer (B) is 95% or higher.