Method for producing cationic surface sizing agent, and sizing agent obtained by method

Abstract

The present invention relates to a method for producing a cationic surface sizing agent, and contains a first step of obtaining a copolymer (A) by solution-polymerizing a monomer mixture containing a monomer having a tertiary amino group (a), a specific (meth)acrylic acid ester (b) and styrenes (c) in the specific proportion in the presence of a chain transfer agent; a second step of obtaining a copolymer (B) by polymerizing the copolymer (A) and a hydrophobic monomer (d), in order to have a specific proportion of the copolymer (A), in an oxidation-reduction system using a water-soluble free-radical initiator and a heavy metal salt in the absence of a surfactant; and a third step of obtaining a quaternary ammonium salt of the copolymer (B) by quaternizing a tertiary amino group present in the copolymer (B).

1 . A method for producing a cationic surface sizing agent comprising a first step of obtaining a copolymer (A) by solution-polymerizing a monomer mixture which comprises a monomer having a tertiary amino group (a) in the amount of 15 to 45% by weight, a (meth)acrylic acid ester (b) in the amount of 15 to 85% by weight, and styrenes (c) in the amount of 0 to 70% by weight in the presence of a chain transfer agent, wherein an ester moiety of the (meth)acrylic acid ester (b) is a chainlike alkyl having 4 to 18 carbon atoms, a cyclic alkyl having 4 to 18 carbon atoms, or aryl having 6 to 18 carbon atoms;
 a second step of obtaining a copolymer (B) by polymerizing the copolymer (A) and a hydrophobic monomer (d) in an oxidation-reduction system using a water-soluble free-radical initiator and a heavy metal salt in the absence of a surfactant, wherein the copolymer (A) is used at the proportion of 30 to 70% by weight with respect to the entire components including the copolymer (B), and the monomer having a tertiary amino group (a) is used so as to be 8 to 20% by weight with respect to the entire components including the copolymer (B); and   a third step of obtaining a quaternary ammonium salt of the copolymer (B) by quaternizing a tertiary amino group present in the copolymer (B).   
     
     
         2 . The method according to  claim 1 , wherein the water-soluble free-radical initiator is hydrogen peroxide, and the heavy metal salt is ferrous sulfate. 
     
     
         3 . The method according to  claim 1 , wherein the tertiary amino group moiety present in the copolymer (A) is completely neutralized by using acid to be brought into the form of an aqueous solution in the first step. 
     
     
         4 . The method according to  claim 1 , wherein the copolymer (A) has an average particle diameter of 50 nm or less. 
     
     
         5 . The method according to  claim 1 , wherein the quaternary ammonium salt of the copolymer (B) has an average particle diameter of 100 nm or more. 
     
     
         6 . The method according to  claim 1 , wherein 50 mol % or more of the tertiary amino group present in the copolymer (B) is quaternized. 
     
     
         7 . The method according to  claim 1 , wherein the quaternization is performed by using epichlorohydrin. 
     
     
         8 . The method according to  claim 1 , wherein the monomer having a tertiary amino group (a) is at least one selected from the group consisting of dialkylaminoalkyl (meth)acrylate and dialkylaminoalkyl (meth)acrylamide. 
     
     
         9 . A cationic surface sizing agent produced by the method according to  claim 1 . 
     
     
         10 . A method for surface treating paper or a paper board, comprising a step of coating the surface of the paper or paper board with the cationic surface sizing agent according to  claim 9  or a mixture of this sizing agent and a water-soluble high-molecular compound. 
     
     
         11 . Paper or a paper board prepared by the method according to  claim 10 . 
     
     
         12 . The paper or paper board according to  claim 11 , wherein the paper or paper board before coated with a cationic surface sizing agent is paper or a paper board not containing an internal sizing agent, a neutralized paper having a Stockigt sizing degree of 2 second or less and a pH of paper surface of 6.5 to 8.5, or a neutralized paper board having water absorbency by a two minutes Cobb test of 100 g/m 2  or more, and a pH of paper surface of 6.5 to 8.5.