Polyacrylic acid (salt), polyacrylic acid (salt)-based water-absorbing resin, and process for producing same

Abstract

A polyacrylic acid (salt), or a polyacrylic acid (salt)-based water-absorbing resin, contains a tracer for detecting various troubles in the water-absorbing resin during the period from the production of the water-absorbing resin to the use and discard thereof by a consumer. The polyacrylic acid (salt)-based water-absorbing resin has a stable carbon isotope ratio, as determined by accelerator mass spectrometry, of less than −20% and a radioactive carbon content of 1.0×10 −14 or mole. The polyacrylic acid (salt)-based water-absorbing resin has: a CRC of 10 [g/g] or mole; an AAP of 20 [g/g] or mole; an Ext of 35 wt. % or less; a content of residual monomers of 1,000 ppm or less; a PSD in which the proportion of particles having a particle diameter of 150 μm or larger but less than 850 μm is 90 wt. % or more; and an FSR of 0.15 [g/g/s] or more.

1 - 20 . (canceled) 
     
     
         21 . A polyacrylic acid (salt) having a carbon stable isotope ratio (δ 13 C) measured by accelerator mass spectrometry method of lower than −20‰ and a 14 C/C of 1.0×10 −14  or more. 
     
     
         22 . The polyacrylic acid (salt) according to  claim 21 , wherein the carbon stable isotope ratio (δ 13 C) is −40 to −26‰. 
     
     
         23 . A polyacrylic acid (salt)-type water-absorbing resin obtained from the polyacrylic acid (salt) according to  claim 21 , wherein the polyacrylic acid (salt)-type water-absorbing resin is characterized in satisfying physical properties of the following (1) to (6);
 (1) CRC (ERT441.2-02) is 10 [g/g] or more,   (2) AAP (ERT442.2-02) is 20 [g/g] or more,   (3) Ext (ERT470.2-02) is 35 weight % or less   (4) Residual Monomers (ERT410.2-02) is 1000 ppm or less   (5) Particles with a particle diameter of 150 μm or larger and smaller than 850 μm measured by PSD (ERT 420.2-02) are in an amount of 90 weight % or more; and   (6) FSR is 0.15 [g/g/s] or more.   
     
     
         24 . The polyacrylic acid (salt)-type water-absorbing resin according to  claim 23 , wherein a propionic acid content contained in the polyacrylic acid (salt)-type water-absorbing resin is 2000 ppm or less. 
     
     
         25 . The polyacrylic acid (salt)-type water-absorbing resin according to  claim 23 , wherein the polyacrylic acid (salt)-type water-absorbing resin is surface-crosslinked with an organic surface-crosslinking agent and, if necessary, coated with a surface treatment agent selected from a polyvalent metal salt, a polyamine polymer, and water-insoluble inorganic particles. 
     
     
         26 . The polyacrylic acid (salt)-type water-absorbing resin according to  claim 23 , wherein the polyacrylic acid (salt)-type water-absorbing resin satisfies one or more of the following content:
 the content of 3-hydroxypropionic acid is 1000 ppm or less;   the content of a polymerization inhibitor is 1 to 160 ppm;   the content of Fe is 0 to 2 ppm; and   the content of mono- or di-hydroxyacetone is 0 to 10 ppm or less.   
     
     
         27 . The polyacrylic acid (salt)-type water-absorbing resin according to  claim 23 , wherein further SFC of the polyacrylic acid (salt)-type water-absorbing resin is 10 [×10 −7 ·cm 3 ·s·g −1 ] or more. 
     
     
         28 . The polyacrylic acid (salt)-type water-absorbing resin according to  claim 23 , having a hydrogen isotope ratio (δD‰ vs. SMOW) of −15 to −300‰. 
     
     
         29 . A sanitary material containing the polyacrylic acid (salt)-type water-absorbing resin according to  claim 23 . 
     
     
         30 . A method for producing a polyacrylic acid (salt) selected from a water-soluble polyacrylic acid (salt) or a polyacrylic acid (salt)-type water-absorbing resin comprising a polymerization step for a water-soluble unsaturated monomer and a drying step for the obtained water-containing gel-like crosslinked polymer, wherein the polymerization step is for polymerizing acrylic acid with a carbon stable isotope ratio (δ 13 C) of lower than −20‰ and a radioactive carbon ( 14 C/C) of 1.0×10 −14  or more as the water-soluble unsaturated monomer. 
     
     
         31 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein a raw material main component of the acrylic acid is obtained from biomass derived from a C3 plant. 
     
     
         32 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein the carbon stable isotope ratio (δ 13 C) of acrylic acid in the polymerization step is changed depending on one of a production line, production time, and a product lot number. 
     
     
         33 . The method for producing according to  claim 30 , wherein the water-soluble unsaturated monomer is obtained by mixing acrylic acid having different carbon stable isotope ratios (δ 13 C). 
     
     
         34 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein the dried material obtained in the drying step is surface-crosslinked with an organic surface-crosslinking agent after the drying step and, if necessary, coated with a surface treatment agent selected from a polyvalent metal salt, a polyamine polymer, and water-insoluble inorganic particles after the drying step. 
     
     
         35 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein further the water-soluble unsaturated monomer further satisfies one or more of the following:
 the content of 3-hydroxypropionic acid is 1000 ppm or less;   the content of the polymerization inhibitor is 1 to 160 ppm;   the content of Fe is 0 to 2 ppm; and   the content of mono- or di-hydroxyacetone is 0 to 10 ppm or less.   
     
     
         36 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein a drying temperature at the drying step is 50 to 300° C. (drying is conducted under reduced pressure if the drying temperature is 100° C. or lower) and a drying time at the drying step is 10 to 120 minutes. 
     
     
         37 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein a resin solid content of a dried polymer obtained by the drying step is 85 to 99 weight %. 
     
     
         38 . The method for producing a polyacrylic acid (salt)-type water-absorbing resin according to  claim 30 , wherein a fine powder recycle step is employed besides the above steps. 
     
     
         39 . A method for identifying a polyacrylic acid (salt)-type water absorbing resin after production, wherein  13 C volume and  14 C/C volume of the polyacrylic acid (salt) -type water absorbing resin after production, and  13 C volume and  14 C/C volume of the acrylic acid before polymerization which is used for the production of the polyacrylic acid (salt)-type water-absorbing resin are quantitatively analyzed by accelerator mass spectrometry for  13 C volume and by radioactive carbon dating method for  14 C/C volume. 
     
     
         40 . The method for identifying a polyacrylic acid (salt)-type water-absorbing resin according to  claim 39 , wherein further other trace components and/or a plurality of physical properties are further measured.