Process for producing granules for being molded into ferrite, granules for being molded into ferrite, green body and sintered body

Abstract

A composition for producing granules for molding ferrite, which includes a ferrite slurry at least having raw ferrite powder; an ethylene-modified polyvinyl alcohol whose ethylene modified amount is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and water mixed therewith, ferrite granules produced from the composition, a ferrite green body produced from the granules and a ferrite sintered body produced from the green body are disclosed.

1 . A composition for producing granules for molding ferrite, which comprises a ferrite slurry at least having 
 raw ferrite powder;    an ethylene-modified polyvinyl alcohol consisting essentially of a polyvinyl alcohol series polymer, wherein the ethylene modified amount of said ethylene-modified polyvinyl alcohol is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and    water mixed therewith.    
     
     
         2 . The composition according to  claim 1 , wherein the average saponification degree of said ethylene-modified polyvinyl alcohol is from 92 to 97 mol %.  
     
     
         3 . The composition according to  claim 1 , wherein the amount of the ethylene-modified polyvinyl alcohol added is from 0.4 to 5 parts by weight based on 100 parts by weight of the raw ferrite powder.  
     
     
         4 . The composition according to  claim 1 , which further comprises 0.1 to 0.5 parts by weight of a polyethylene glycol having a molecular weight of from 1000 to 6000 based on 100 parts by weight of the raw ferrite powder.  
     
     
         5 . The composition according to  claim 1 , which further comprises 0.1 to 1 parts by weight of water-dispersible wax based on 100 parts by weight of the raw ferrite powder.  
     
     
         6 . A process for producing ferrite granules by granulating a composition for producing granules for molding ferrite, which uses a composition comprising a ferrite slurry at least having 
 raw ferrite powder;    an ethylene-modified polyvinyl alcohol consisting essentially of a polyvinyl alcohol series polymer, wherein the ethylene modified amount of said ethylene-modified polyvinyl alcohol is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and    water mixed therewith;    wherein said composition is granulated by a stirring granulation process utilizing a stirring granulator.    
     
     
         7 . Ferrite granules for molding ferrite granulated by a process according  claim 6 .  
     
     
         8 . The ferrite granules according to  claim 7 , wherein at least part of the surface is covered with hexitan higher aliphatic acid ester having a hydrophilicity/oilphilicity ratio of 14 or less.  
     
     
         9 . A ferrite green body produced by dry-pressing ferrite granules of  claim 7 .  
     
     
         10 . A ferrite green body produced by dry-pressing ferrite granules of  claim 8 .  
     
     
         11 . A ferrite sintered body produced by sintering a ferrite green body produced by dry-pressing ferrite granules for molding ferrite granulated by a process for producing ferrite granules by granulating a composition for producing granules for molding ferrite, which uses a composition comprising a ferrite slurry at least having 
 raw ferrite powder;    an ethylene-modified polyvinyl alcohol consisting essentially of a polyvinyl alcohol series polymer, wherein the ethylene modified amount of said ethylene-modified polyvinyl alcohol is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and    water mixed therewith;    wherein said composition is granulated by a spray drying process using a spray dryer.    
     
     
         12 . The ferrite sintered body according to  claim 11 , wherein the average saponification degree of said ethylene-modified polyvinyl alcohol is from 92 to 97 mol %.  
     
     
         13 . The ferrite sintered body according to  claim 11 , wherein the amount of the ethylene-modified polyvinyl alcohol added is from 0.4 to 5 parts by weight based on 100 parts weight of raw ferrite powder.  
     
     
         14 . The ferrite sintered body according to  claim 11 , wherein the composition further comprises 0.1 to 0.5 parts by weight of a polyethylene glycol having a molecular weight of from 1000 to 6000 based on 100 parts by weight of the raw ferrite powder.  
     
     
         15 . The ferrite sintered body according to  claim 11 , wherein the composition further comprises 0.1 to 1 parts by weight of water-dispersible wax based on 100 parts by weight of the raw ferrite powder.  
     
     
         16 . A ferrite sintered body produced by sintering a ferrite green body of  claim 9 .  
     
     
         17 . A ferrite sintered body produced by sintering a ferrite green body produced by dry-pressing ferrite granules for molding ferrite granulated by a process for producing ferrite granules by granulating a composition for producing granules for molding ferrite, which uses a composition comprising a ferrite slurry at least having 
 raw ferrite powder;    an ethylene-modified polyvinyl alcohol consisting essentially of a polyvinyl alcohol series polymer, wherein the ethylene modified amount of said ethylene-modified polyvinyl alcohol is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and    water mixed therewith;    wherein said composition is granulated by a spray drying process using a spray dryer;    wherein the granulation is performed under the conditions that the inlet temperature of the spray dryer is in the range of from 170 to 230° C. and the outlet temperature of the spray dryer is in the range of from 65 to 125° C.    
     
     
         18 . The ferrite sintered body according to  claim 17 , wherein the average saponification degree of said ethylene-modified polyvinyl alcohol is from 92 to 97 mol %.  
     
     
         19 . The ferrite sintered body according to  claim 17 , wherein the amount of the ethylene-modified polyvinyl alcohol added is from 0.4 to 5 parts by weight based on 100 parts weight of raw ferrite powder.  
     
     
         20 . The ferrite sintered body according to  claim 17 , wherein the composition further comprises 0.1 to 0.5 parts by weight of a polyethylene glycol having a molecular weight of from 1000 to 6000 based on 100 parts by weight of the raw ferrite powder.  
     
     
         21 . The ferrite sintered body according to  claim 17 , wherein the composition further comprises 0.1 to 1 parts by weight of water-dispersible wax based on 100 parts by weight of the raw ferrite powder.  
     
     
         22 . A ferrite sintered body produced by sintering a ferrite green body produced by dry-pressing ferrite granules for molding ferrite granulated by a process for producing ferrite granules by granulating a composition for producing granules for molding ferrite, which uses a composition comprising a ferrite slurry at least having 
 raw ferrite powder;    an ethylene-modified polyvinyl alcohol consisting essentially of a polyvinyl alcohol series polymer, wherein the ethylene modified amount of said ethylene-modified polyvinyl alcohol is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and    water mixed therewith;    wherein said composition is granulated by a spray drying process using a spray dryer;    wherein at least part of the surface of the granules is covered with hexitan higher aliphatic acid ester having a hydrophilicity/oilphilicity ratio of 14 or less.    
     
     
         23 . The ferrite sintered body according to  claim 22 , wherein the average saponification degree of said ethylene-modified polyvinyl alcohol is from 92 to 97 mol %.  
     
     
         24 . The ferrite sintered body according to  claim 22 , wherein the amount of the ethylene-modified polyvinyl alcohol added is from 0.4 to 5 parts by weight based on 100 parts weight of raw ferrite powder.  
     
     
         25 . The ferrite sintered body according to  claim 22 , wherein the composition further comprises 0.1 to 0.5 parts by weight of a polyethylene glycol having a molecular weight of from 1000 to 6000 based on 100 parts by weight of the raw ferrite powder.  
     
     
         26 . The ferrite sintered body according to  claim 22 , wherein the composition further comprises 0.1 to 1 parts by weight of water-dispersible wax based on 100 parts by weight of the raw ferrite powder.  
     
     
         27 . A ferrite sintered body produced by sintering a ferrite green body of  claim 10 .  
     
     
         28 . A ferrite sintered body produced by sintering a ferrite green body produced by dry-pressing ferrite granules for molding ferrite granulated by a process for producing ferrite granules by granulating a composition for producing granules for molding ferrite, which uses a composition comprising a ferrite slurry at least having 
 raw ferrite powder;    an ethylene-modified polyvinyl alcohol consisting essentially of a polyvinyl alcohol series polymer, wherein the ethylene modified amount of said ethylene-modified polyvinyl alcohol is from 4 to 10 mol %, average polymerization degree is from 500 to 1700, and average saponification degree is from 90.0 to 99.5 mol %; and    water mixed therewith;    wherein said composition is granulated by a spray drying process using a spray dryer;    wherein the granulation is performed under the conditions that the inlet temperature of the spray dryer is in the range of from 170 to 230° C. and the outlet temperature of the spray dryer is in the range of from 65 to 125° C.;    wherein at least part of the surface of the granules is covered with hexitan higher aliphatic acid ester having a hydrophilicity/oilphilicity ratio of 14 or less.    
     
     
         29 . The ferrite sintered body according to  claim 28 , wherein the average saponification degree of said ethylene-modified polyvinyl alcohol is from 92 to 97 mol %.  
     
     
         30 . The ferrite sintered body according to  claim 28 , wherein the amount of the ethylene-modified polyvinyl alcohol added is from 0.4 to 5 parts by weight based on 100 parts weight of raw ferrite powder.  
     
     
         31 . The ferrite sintered body according to  claim 28 , wherein the composition further comprises 0.1 to 0.5 parts by weight of a polyethylene glycol having a molecular weight of from 1000 to 6000 based on 100 parts by weight of the raw ferrite powder.  
     
     
         32 . The ferrite sintered body according to  claim 28 , wherein the composition further comprises 0.1 to 1 parts by weight of water-dispersible wax based on 100 parts by weight of the raw ferrite powder.  
     
     
         33 . A process for producing ferrite granules by granulating a composition for producing granules for molding ferrite, which uses the composition according to  claim 2 .  
     
     
         34 . The process according to  claim 33 , wherein said composition is granulated by a stirring granulation process utilizing a stirring granulator.  
     
     
         35 . Ferrite granules for molding ferrite granulated by a process according to  claim 33 .  
     
     
         36 . Ferrite granules for molding ferrite granulated by a process according to  claim 34 .  
     
     
         37 . The ferrite granules according to  claim 35 , wherein at least part of the surface of the granules is covered with hexitan higher aliphatic acid ester having a hydrophilicity/oilphilicity ratio of 14 or less.  
     
     
         38 . The ferrite granules according to  claim 36 , wherein at least part of the surface of the granules is covered with hexitan higher aliphatic acid ester having a hydrophilicity/oilphilicity ratio of 14 or less.  
     
     
         39 . A ferrite green body produced by dry-pressing ferrite granules of  claim 35 .  
     
     
         40 . A ferrite green body produced by dry-pressing ferrite granules of  claim 36 .  
     
     
         41 . A ferrite sintered body produced by sintering a ferrite green body of  claim 39 .  
     
     
         42 . A ferrite sintered body produced by sintering a ferrite green body of  claim 40 .  
     
     
         43 . The ferrite sintered body according to  claim 41 , which has a water absorbency of not less than 0.2% by weight.  
     
     
         44 . The ferrite sintered body according to  claim 42 , which has a water absorbency of not less than 0.2% by weight.