(Meth) acrylic acid polymer and manufacturing method thereof

A manufacturing method of a (meth)acrylic acid polymer, wherein:

• 60 mol % or more of a hydrophilic monomer containing 50 mol % or more of (meth)acrylic acid is used;
• a pH and a degree of neutralization when conducting a polymerization reaction of said monomer is smaller than 5 and smaller than 40 mol %, respectively;
• and
• a combination of at least one kind of persulfate salts and at least one kind of bisulfite salts is used as an initiator series, the weight ratio of persulfate salts to bisulfate salts being in range of between 0.5:1 and 5:1;
• the total amount of added persulfate salts and bisulfite salts being in the range of 6 grams to 15 grams based on 1 mole of the monomer;
• and
• the (meth)acrylic acid polymer being manufactured to have a clay dispersing ability of 60% or greater in high hard water and a calcium ion trapping ability of 210 mg CaCO3/g or greater.

A method of manufacturing a (meth)acrylic acid polymer, comprising:

• polymerizing, in an aqueous solution, monomers comprising 50-100 mol % of (meth)acrylic acid, and 0-50 mol % of a water-soluble monoethylenic unsaturated monomer copolymerizible with said (meth)acrylic acid;
• initiating polymerization by both one or more persulfate salts and one or more bisulfite salts, the weight ratio of bisulfite salts to persulfate salts being in the range of 1:1 to 4:1, the persulfate salts and bisulfite salts being added together, the total amount of added persulfate salts and bisulfite salts being in the range of 6 grams to 15 grams based on 1 mole of the monomers;
• and
• terminating polymerization with a sulfonic acid group to produce a polymer having an anti-gelling ability Q-value less than 2.0, where said anti-gelling ability Q-value is defined as:
• Q = degree of gelling × 10 5 weight average molecular weigh ⁢ t
• wherein the (meth)acrylic acid polymer is manufactured to have a clay dispersing ability of 60% or greater in high hard water and a calcium ion trapping ability of 210 mg CaCO3/g or greater.