Suspension polymerization process using suspending agent-containing slurry

Abstract

A suspending agent-containing slurry is disclosed which comprises a dispersant and a particulate suspending agent having a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is 1 μm or smaller. A method for efficiently producing the suspending agent-containing slurry is also disclosed. A process for suspension polymerization by use of the suspending agent-containing slurry is further disclosed. The slurry not only has such an excellent suspending ability in suspension polymerization that it enables the production of vinyl polymer beads having a narrow bead size distribution, but also is capable of retaining this ability over long and of exhibiting the same ability even when it has a high concentration. The suspension polymerization process enables vinyl polymer beads having a narrow bead size distribution to be produced efficiently due to the use of the slurry.

What is claimed is:  
     
         1 . A suspending agent-containing slurry comprising a particulate inorganic suspending agent, a dispersant and an aqueous medium, said inorganic suspending agent having a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is 1 μm or smaller.  
     
     
         2 . The suspending agent-containing slurry as claimed in  claim 1 , wherein said dispersant is at least one member selected from the group consisting of an inorganic dispersant, a polymeric dispersant and a surfactant.  
     
     
         3 . The suspending agent-containing slurry as claimed in  claim 2 , wherein said inorganic dispersant is an alkali metal salt or ammonium salt of a linear condensed phosphoric acid or of a cyclic condensed phosphoric acid.  
     
     
         4 . The suspending agent-containing slurry as claimed in  claim 2 , wherein said polymeric dispersant contains a hydroxyl group, an amido group, a carboxyl group, a sulfo group or a phosphono group, or an alkali metal or ammonium salt of a carboxyl, sulfo or phosphono group.  
     
     
         5 . The suspending agent-containing slurry as claimed in  claim 2 , wherein said surfactant is either a surfactant containing a hydroxyl group, an amido group, a carboxyl group, a sulfo group or a phosphono group, or an alkali metal or ammonium salt of a carboxyl, sulfo or phosphono group, or an ether-type surfactant.  
     
     
         6 . The suspending agent-containing slurry as claimed in  claim 1 , wherein said dispersant is present in an amount of from 0.01 to 10 parts by weight per 100 parts by weight of said inorganic suspending agent.  
     
     
         7 . The suspending agent-containing slurry as claimed in  claim 1 , wherein said particulate inorganic suspending agent comprises tricalcium phosphate or magnesium pyrophosphate.  
     
     
         8 . The suspending agent-containing slurry as claimed in  claim 1 , wherein said particulate inorganic suspending agent has a weight-average particle diameter of 0.4 μm or smaller.  
     
     
         9 . The suspending agent-containing slurry as claimed in  claim 1 , which has a solid concentration of from 0.05 to 50% by weight.  
     
     
         10 . A method of producing a suspending agent-containing slurry which comprises pulverizing a particulate inorganic suspending agent in an aqueous medium in the presence of a dispersant to such a degree that said inorganic suspending agent comes to have a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is 1 μm or smaller.  
     
     
         11 . The method as claimed in  claim 10 , wherein said dispersant is at least one member selected from the group consisting of an inorganic dispersant, a polymeric dispersant and a surfactant.  
     
     
         12 . The method as claimed in  claim 11 , wherein said inorganic dispersant is an alkali metal salt or ammonium salt of a linear condensed phosphoric acid or of a cyclic condensed phosphoric acid.  
     
     
         13 . The method as claimed in  claim 11 , wherein said polymeric dispersant contains a hydroxyl group, an amido group, a carboxyl group, a sulfo group or a phosphono group, or an alkali metal or ammonium salt of a carboxyl, sulfo or phosphono group.  
     
     
         14 . The method as claimed in  claim 11 , wherein said surfactant is either a surfactant containing a hydroxyl group, an amido group, a carboxyl group, a sulfo group or a phosphono group, or an alkali metal or ammonium salt of a carboxyl, sulfo or phosphono group, or an ether-type surfactant.  
     
     
         15 . The method as claimed in  claim 10 , wherein said dispersant is present in an amount of from 0.01 to 10 parts by weight per 100 parts by weight of said particulate inorganic suspending agent.  
     
     
         16 . The method as claimed in  claim 10 , wherein said particulate inorganic suspending agent comprises tricalcium phosphate or magnesium pyrophosphate.  
     
     
         17 . A process for suspension polymerization which comprises suspension-polymerizing a vinyl monomer in an aqueous medium containing an initiator, a suspending agent and an anionic surfactant, said suspending agent being one supplied by using a suspending agent-containing slurry in an amount of from 0.01 to 10 parts by weight on a solid basis in terms of the amount of the particulate inorganic suspending agent contained therein per 100 parts by weight of said monomer, said suspending agent-containing slurry comprising a particulate inorganic suspending agent, a dispersant and an aqueous medium, said inorganic suspending agent having a particle size distribution in which the particle diameter at weight-cumulative 95%, from the minimum particle size, is  1 μm or smaller.