Aqueous coating composition, process for producing it and two-pack type curable aqueous coating kit

Abstract

To provide an aqueous coating composition which has a low content of an organic solvent, whereby a burden on an environment is small; in which an increase of the molecular weight, gelation, etc. are suppressed; which performs excellent storage stability and provides a coating film having good water permeability/water resistance. An aqueous coating composition which is a composition obtained by dispersing a fluorocopolymer (A) obtained by a solution polymerization method, in an aqueous medium, and which comprises a repeating unit (1) of fluoroolefin, a repeating unit (2) of a vinyl monomer or an allyl monomer, a repeating unit (3) of a vinyl monomer having a hydroxyl group bonded thereto or of an allyl monomer having a hydroxyl group bonded thereto, and a unit (4) of a vinyl monomer having a carboxylate group bonded thereto or of an allyl monomer, and which comprises a fluorocopolymer (A) wherein a proportion of the repeating unit (4) is from 0.4 mol % to less than 4 mol % based on the total repeating units, and an aqueous medium, wherein an amount of an organic solvent contained in the composition is from 0 to 1 mass %.

1 . An aqueous coating composition which is a composition obtained by dispersing a fluorocopolymer (A) obtained by a solution polymerization method, in an aqueous medium, and which comprises the fluorocopolymer (A) which is a copolymer containing the following units (1) to (4), wherein a proportion of the repeating unit (4) is from 0.4 mol % to less than 4 mol % based on the total repeating units, and an aqueous medium, wherein an amount of an organic solvent contained in the composition is from 0 to 1 mass %:
 Unit (1): a repeating unit of a fluoroolefin   Unit (2): a repeating unit of a vinyl monomer or an allyl monomer, and a hydroxyl group and/or a carboxyl group which may form a salt, is not bonded to the unit   Unit (3): a repeating unit of a vinyl monomer having a hydroxyl group bonded thereto or of an allyl monomer having a hydroxyl group bonded thereto, and a carboxyl group which may form a salt, is not bonded to the unit   Unit (4): a repeating unit of a vinyl monomer or an allyl monomer, which is also a repeating unit to which a carboxylate group in which a part may be a carboxyl group, is bonded.   
   
   
       2 . The aqueous coating composition according to  claim 1 , wherein the unit (1) is a unit represented by the following formula (a1), the unit (2) is a unit represented by the following formula (a2), the unit (3) is a unit represented by the following formula (a3), and the unit (4) is a unit represented by the following formula (a4-1):
   —CFX 1 —CX 2 X 3 —  (a1)   
     (in the formula (a1), each of X 1  and X 2  is independently a hydrogen atom, a chlorine atom or a fluorine atom, X 3  is a chlorine atom, a fluorine atom or —CY 1 Y 2 Y 3  (wherein each of Y 1 , Y 2  and Y 3  is independently a hydrogen atom, a chlorine atom or a fluorine atom); 
     
       
         
         
             
             
         
       
     
     (in the formula (a2), R a  is a hydrogen atom or a methyl group, R 1  is a C 1-12  alkyl group or a C 4-10  monovalent alicyclic hydrocarbon group, j is 0 or 1, and k is 0 or 1); 
     
       
         
         
             
             
         
       
     
     (in the formula (a3), R b  is a hydrogen atom or a methyl group, R 2  is a C 1-10  alkylene group or a C 4-10  divalent alicyclic hydrocarbon group, m is 0 or 1, and n is 0 or 1); 
     
       
         
         
             
             
         
       
     
     (in the formula (a4-1), R c  is a hydrogen atom or a methyl group, R d  is a hydrogen atom or a methyl group, —COOR 3  is a carboxylate group in which a part may be a carboxyl group, R e  is a hydrogen atom or —COOR 3  (—COOR 3  has the same meaning as above), p is 0 or 1, r is 0 or 1, q is 0 or 1, R 4  is a C 1-15  alkylene group or a C 4-10  divalent alicyclic hydrocarbon group, and s is 0 or 1). 
   
   
       3 . The aqueous coating composition according to  claim 1 , wherein the fluorocopolymer (A) contains from 40 to 60 mol % of the unit (1), from 3 to 50 mol % of the unit (2), from 4 to 30 mol % of the unit (3), from 0.4 to less than 4 mol % of the unit (4), and from 0 to 20 mol % of a unit (5) other than the units (1), (2), (3) and (4). 
   
   
       4 . The aqueous coating composition according to  claim 1 , wherein the fluorocopolymer (A) contains from 1.4 to 3.9 mol % of the unit (4). 
   
   
       5 . The aqueous coating composition according to  claim 1 , wherein the proportion of the carboxylate group is at least 60 mol % based on the total amount of the carboxyl group and the carboxylate group which are present in the fluorocopolymer (A). 
   
   
       6 . The aqueous coating composition according to  claim 1 , wherein the carboxylate group is a quaternary ammonium salt group of a carboxyl group. 
   
   
       7 . The aqueous coating composition according to  claim 1 , wherein the aqueous medium comprises only water, or water and an organic solvent, and the amount of the organic solvent is from 0 to 0.5 mass % in the composition. 
   
   
       8 . The aqueous coating composition according to  claim 1  to  7 , wherein a part or whole of the fluorocopolymer (A) is dispersed in the composition. 
   
   
       9 . A process for producing the aqueous coating composition as defined in  claim 1 , which is characterized by carrying out sequentially a step of a copolymerization reaction in an organic solvent to obtain a fluorocopolymer (B) containing the unit (1), the unit (2), the unit (3) and a polymerized unit (4-3) derived from a monomer having a carboxyl group bonded thereto, and a step of neutralizing a part or whole of the carboxyl group in the fluorocopolymer (B) by adding a basic compound; a step of adding water; and a step of removing the organic solvent. 
   
   
       10 . The process for producing the aqueous coating composition according to  claim 9 , wherein the unit (1) is a unit represented by the formula (a1), the unit (2) is a unit represented by the formula (a2), the unit (3) is a unit represented by the formula (a3), and the unit (4-3) is a unit represented by the following formula (a4-3): 
     
       
         
         
             
             
         
       
     
     (in the formula (a4-3), R c  is a hydrogen atom or a methyl group, R d  is a hydrogen atom or a methyl group, R e  is a hydrogen atom or —COOH, p is 0 or 1, r is 0 or 1, q is 0 or 1, R 4  is a C 1-15  alkylene group or a C 4-10  divalent alicyclic hydrocarbon group, and s is 0 or 1). 
   
   
       11 . The process for producing the aqueous coating composition according to  claim 9 , wherein the fluorocopolymer (B) contains from 40 to 60 mol % of the unit (1), from 3 to 50 mol % of the unit (2), from 4 to 30 mol % of the unit (3), from 0.4 to less than 4 mol % of the unit (4-3), and from 0 to 20 mol % of the unit (5) other than the units (1), (2), (3) and (4-3). 
   
   
       12 . The process for producing the aqueous coating composition according to  claim 9 , wherein the step for neutralization with the basic compound and the step of adding water, are carried out as a step of adding the basic compound as an aqueous solution, or a step for neutralization with the basic compound is carried out as a step for neutralization by using an aqueous solution of the basic compound. 
   
   
       13 . A two-pack type curable aqueous coating material kit comprising the aqueous coating composition according to  claim 1 , and a water-soluble or water-dispersible curing agent having a functional group reactive with a hydroxyl group or a carboxyl group, independently.