Continuous production method of water-absorbing composite

Abstract

This invention discloses a continuous production method of water-absorbing composite which comprises a complexation step for producing a particle-substrate composite by dropwisely supplying an aqueous solution of polymerizable monomers consisting mainly of an unsaturated carboxylic acid where 20% or more of the carboxyl groups in the unsaturated acid is neutralized, while allowing polymerization to proceed in the droplets, onto a fibrous substrate fed to the drop point to allow the incompletely polymerized polymer particles to adhere thereon, and by completing the polymerization thereafter; and a surface crosslinking step for reacting the composite with a crosslinking agent, having two or more functional groups capable of reacting with carboxyl group and/or carboxylate group, in the presence of 1 to 100 weight parts of water per 100 weight parts of polymer particles derived from the polymerizable monomer contained in the composite. Such continuous production method is successful in producing, in a continuous and efficient manner, a water-absorbing composite excellent in water absorption property and water retention property.

1 . A continuous production method of water-absorbing composite comprising: 
 (A) a complexation step for producing a particle-substrate composite by dropwisely supplying an aqueous solution of polymerizable monomers consisting mainly of an unsaturated carboxylic acid where 20% or more of the carboxyl groups in the unsaturated acid is neutralized, while allowing polymerization to proceed in the droplets, onto a fibrous substrate fed to the drop point to allow the incompletely polymerized polymer particles to adhere thereon, and completing the polymerization thereafter; and    (B) a surface crosslinking step for reacting the composite with a crosslinking agent, having two or more functional groups capable of reacting with carboxyl group and/or carboxylate group, in the presence of 1 to 100 weight parts of water per 100 weight parts of polymer particles derived from the polymerizable monomer contained in the composite.    
     
     
         2 . The continuous production method as claimed in  claim 1 , wherein water content of the polymer particles composing the particle-substrate composite subjected to the surface crosslinking step is within a range from 10 to 40 wt %.  
     
     
         3 . The continuous production method as claimed in  claim 2 , further comprising, prior to the surface crosslinking step, a water content adjustment step for adjusting water content of the polymer particles composing the particle-substrate composite within a range from 10 to 40 wt %.  
     
     
         4 . The continuous production method as claimed in  claim 1 , further comprising, posterior to the complexation step, a residual monomer processing step for processing the polymerizable monomer remaining in the polymer particles composing the particle-substrate composite.  
     
     
         5 . The continuous production method as claimed in  claim 4 , wherein the complexation step, surface crosslinking step and residual monomer processing step are conducted in this order.  
     
     
         6 . The continuous production method as claimed in  claim 4 , wherein the complexation step, residual monomer processing step and surface crosslinking step are conducted in this order.  
     
     
         7 . The continuous production method as claimed in  claim 4 , wherein the complexation step, residual monomer processing step, water content adjustment step and surface crosslinking step are conducted in this order.  
     
     
         8 . The continuous production method as claimed in  claim 4 , wherein the complexation step, water content adjustment step, surface crosslinking step and residual monomer processing step are conducted in this order.  
     
     
         9 . The continuous production method as claimed in  claim 4 , wherein the complexation step, water content adjustment step, residual monomer processing step and surface crosslinking step are conducted in this order.  
     
     
         10 . The continuous production method as claimed in  claim 1 , wherein the unsaturated carboxylic acid is acrylic acid.  
     
     
         11 . The continuous production method as claimed in  claim 10 , wherein 20% or more of carboxyl groups of acrylic acid is neutralized in a form of alkaline metal salt or ammonium salt.  
     
     
         12 . The continuous production method as claimed in  claim 1 , wherein the polymerization of the aqueous solution of polymerizable monomer in the complexation step is initiated by a redox-type polymerization initiator.  
     
     
         13 . The continuous production method as claimed in  claim 12 , wherein the droplets in the complexation step are formed by mixing, in the gas phase, a first solution containing an oxidizing agent as one component of the redox-type polymerization initiator and the aqueous solution of polymerizable monomer, and a second solution containing a reducing agent as another component of the redox-type polymerization initiator and the aqueous solution of polymerizable monomer.  
     
     
         14 . The continuous production method as claimed in  claim 13 , wherein the first solution in a form of liquid column and the second solution in a form of liquid column are mixed by collision.  
     
     
         15 . The continuous production method as claimed in  claim 1 , wherein a polymerization ratio of the polymerizable monomer at the time of the contact with the fibrous substrate is within a range from 20 to 97%.  
     
     
         16 . The continuous production method as claimed in  claim 1 , wherein at least a part of the polymer particles of the particle-substrate composite obtained in the complexation step forms granular aggregates in which the polymer particles are bound with each other, and a part of the polymer particles composing the granular aggregates is not directly bound to the fibrous substrate.  
     
     
         17 . The continuous production method as claimed in  claim 16 , wherein the polymer particles composing the granular aggregates account for 30 wt % or more of the total polymer particles.  
     
     
         18 . The continuous production method as claimed in  claim 16 , wherein a particle size of the granular aggregates is within a range from 100 to 3,000 μm.  
     
     
         19 . The continuous production method as claimed in  claim 1 , wherein the polymer particles are immobilized on the fibrous substrate in an amount of 50 to 400 g/m 2  in the complexation step.  
     
     
         20 . The continuous production method as claimed in  claim 1 , wherein the crosslinking agent is a compound having glycidyl groups as the groups capable of reacting with carboxyl group and/or carboxylate group.  
     
     
         21 . The continuous production method as claimed in  claim 20 , wherein the compound having glycidyl group is polyglycidyl ether.  
     
     
         22 . The continuous production method as claimed in  claim 1 , wherein the crosslinking agent is sprayed over the particle-substrate composite in a form of aqueous solution or alcoholic solution.  
     
     
         23 . The continuous production method as claimed in  claim 3 , wherein the water content of the polymer particles is reduced in the water content adjustment step by heating the particle-substrate composite.  
     
     
         24 . Canceled.  
     
     
         25 . Canceled.  
     
     
         26 . The continuous production method as claimed in  claim 4 , wherein the residual monomer content of the polymer particles is reduced in the residual monomer processing step by heating the particle-substrate composite at 100 to 250° C.  
     
     
         27 . The continuous production method as claimed in  claim 4 , wherein the residual monomer content of the polymer particles is reduced in the residual monomer processing step by heating the particle-substrate composite after being added with a peroxide and/or azo compound in an amount of 0.01 to 1 weight parts per 100 weight parts of the polymer particles in such particle-substrate composite.  
     
     
         28 . The continuous production method as claimed in  claim 4 , wherein the residual monomer content of the polymer particles is reduced in the residual monomer processing step by irradiating the particle-substrate composite with ultraviolet radiation.  
     
     
         29 . The continuous production method as claimed in  claim 4 , wherein the residual monomer content of the polymer particles is reduced in the residual monomer processing step by irradiating the particle-substrate composite with electromagnetic radioactive ray or particulate ionized radioactive ray.  
     
     
         30 . The continuous production method as claimed in  claim 4 , wherein the residual monomer content of the polymer particles is reduced in the residual monomer processing step by heating the particle-substrate composite after adding a reducing agent in an amount of 0.1 to 20 weight parts per 100 weight parts of the polymer particles in such particle-substrate composite.  
     
     
         31 . Canceled.  
     
     
         32 . Canceled.  
     
     
         33 . The continuous production method as claimed in  claim 4 , wherein the particle-substrate composite is contacted with a superheated steam or steam-containing gas conditioned at a temperature of 80 to 250° C. and at a dew point of 50 to 250° C. in the residual monomer processing step.  
     
     
         34 . The continuous production method as claimed in  claim 1 , wherein the fibrous substrate comprises a non-woven fabric.  
     
     
         35 . The continuous production method as claimed in  claim 34 , wherein the non-woven fabric comprises fibers having a diameter of 10 to 50 μm.  
     
     
         36 . The continuous production method as claimed in  claim 34 , wherein the non-woven fabric has a basis weight of 10 to 100 g/m 2 .  
     
     
         37 . A water-absorbing composite produced by a method as claimed in  claim 1 .  
     
     
         38 - 41 . (Canceled).  
     
     
         42 . A method for the continuous production of a water-absorbing composite, comprising: 
 (A) dropwisely supplying an aqueous solution of polymerizable monomers consisting mainly of an unsaturated carboxylic acid where 20% or more of the carboxyl groups in the unsaturated acid is neutralized, while allowing polymerization to proceed in the droplets, onto a fibrous substrate fed to the drop point to allow the incompletely polymerized polymer particles to adhere thereon, and completing the polymerization thereafter, to produce a particle-substrate composite; and    (B) reacting the composite with a crosslinking agent in the presence of 1 to 100 weight parts of water per 100 weight parts of polymer particles derived from the polymerizable monomer contained in the composite, to surface crosslink the composite, wherein the crosslinking agent has two or more functional groups capable of reacting with a carboxyl group and/or carboxylate group.    
     
     
         43 . The method as claimed in  claim 42 , wherein water content of the polymer particles composed of the particle-substrate composite subjected to (B) is within a range from 10 to 40 wt %.  
     
     
         44 . The method as claimed in  claim 43 , further comprising, prior to (B), (C) adjusting the water content of the polymer particles composed of the particle-substrate composite within a range from 10 to 40 wt %.  
     
     
         45 . The method as claimed in  claim 42 , further comprising, posterior to (A), (D) processing the polymerizable monomer remaining in the polymer particles composed of the particle-substrate composite.  
     
     
         46 . The method as claimed in  claim 45 , wherein (A), (B) and (D) are conducted in that order.  
     
     
         47 . The method as claimed in  claim 45 , wherein A), (D) and (B) are conducted in that order.  
     
     
         48 . The method as claimed in  claim 45 , wherein (A), (D), (C) and (B) are conducted in that order.  
     
     
         49 . The method as claimed in  claim 45 , wherein (A), (C), (B) and (D) are conducted in that order.  
     
     
         50 . The method as claimed in  claim 45 , wherein (A), (C), (D) and (B) are conducted in that order.  
     
     
         51 . The method as claimed in  claim 42 , wherein the unsaturated carboxylic acid is acrylic acid.  
     
     
         52 . The method as claimed in  claim 51 , wherein 20% or more of the carboxyl groups of the acrylic acid is neutralized in a form of an alkaline metal salt or ammonium salt.  
     
     
         53 . The method as claimed in  claim 42 , wherein the polymerization of the aqueous solution of polymerizable monomer in (A) is initiated by a redox-type polymerization initiator.  
     
     
         54 . The method as claimed in  claim 53 , wherein the droplets (A) are formed by mixing, in the gas phase, a first solution containing an oxidizing agent as one component of the redox-type polymerization initiator and the aqueous solution of polymerizable monomer, and a second solution containing a reducing agent as another component of the redox-type polymerization initiator and the aqueous solution of polymerizable monomer.  
     
     
         55 . The method as claimed in  claim 54 , wherein the first solution in a form of liquid column and the second solution in a form of liquid column are mixed by collision.  
     
     
         56 . The method as claimed in  claim 42 , wherein a polymerization ratio of the polymerizable monomer at the time of the contact with the fibrous substrate is within a range from 20 to 97%.  
     
     
         57 . The method as claimed in  claim 42 , wherein at least a part of the polymer particles of the particle-substrate composite obtained in (A) forms granular aggregates in which the polymer particles are bound with each other, and a part of the polymer particles composed of the granular aggregates is not directly bound to the fibrous substrate.  
     
     
         58 . The method as claimed in  claim 57 , wherein the polymer particles composed of the granular aggregates account for 30 wt % or more of the total polymer particles.  
     
     
         59 . The method as claimed in  claim 57 , wherein a particle size of the granular aggregates is within a range from 100 to 3,000 μm.  
     
     
         60 . The method as claimed in  claim 42 , wherein the polymer particles are immobilized on the fibrous substrate in an amount of 50 to 400 g/m 2  in (A).  
     
     
         61 . The method as claimed in  claim 42 , wherein the crosslinking agent is a compound having glycidyl groups as the groups capable of reacting with carboxyl group and/or carboxylate group.  
     
     
         62 . The continuous production method as claimed in  claim 61 , wherein the compound having glycidyl groups is a polyglycidyl ether.  
     
     
         63 . The continuous production method as claimed in  claim 42 , wherein the crosslinking agent is sprayed over the particle-substrate composite in a form of aqueous solution or alcoholic solution.  
     
     
         64 . The method as claimed in  claim 44 , wherein the water content of the polymer particles is reduced in (C) by heating the particle-substrate composite.  
     
     
         65 . The method as claimed in  claim 45 , wherein the residual monomer content of the polymer particles is reduced in (D) by heating the particle-substrate composite at 100 to 250° C.  
     
     
         66 . The method as claimed in  claim 45 , wherein the residual monomer content of the polymer particles is reduced in (D) by heating the particle-substrate composite after being added with a peroxide and/or azo compound in an amount of 0.01 to 1 weight parts per 100 weight parts of the polymer particles in such particle-substrate composite.  
     
     
         67 . The method as claimed in  claim 45 , wherein the residual monomer content of the polymer particles is reduced in (D) by irradiating the particle-substrate composite with ultraviolet radiation.  
     
     
         68 . The method as claimed in  claim 45 , wherein the residual monomer content of the polymer particles is reduced in (D) by irradiating the particle-substrate composite with electromagnetic radioactive ray or particulate ionized radioactive ray.  
     
     
         69 . The method as claimed in  claim 45 , wherein the residual monomer content of the polymer particles is reduced in (D) by heating the particle-substrate composite after adding a reducing agent in an amount of 0.1 to 20 weight parts per 100 weight parts of the polymer particles in such particle-substrate composite.  
     
     
         70 . The method as claimed in  claim 45 , wherein the particle-substrate composite is contacted with a superheated steam or steam-containing gas conditioned at a temperature of 80 to 250° C. and at a dew point of 50 to 250° C. in (D).  
     
     
         71 . The method as claimed in  claim 42 , wherein the fibrous substrate comprises a non-woven fabric.  
     
     
         72 . The method as claimed in  claim 71 , wherein the non-woven fabric comprises fibers having a diameter of 10 to 50 μm.  
     
     
         73 . The method as claimed in  claim 71 , wherein the non-woven fabric has a basis weight of 10 to 100 g/m 2 .  
     
     
         74 . A water-absorbing composite produced by a method as claimed in  claim 42.