Alumina slurry, method for producing same, and coating liquid

Abstract

Disclosed is an alumina slurry substantially including alpha-alumina particles and water, wherein the alpha-alumina particles satisfy all particle diameter distribution conditions (a) to (d) mentioned below, the alpha-alumina particles have an alumina purity of 90% by weight or more, the content of alumina in the slurry is 20% by weight or more and 50% by weight or less, and the slurry has a viscosity of 0.5 Pa·s or more and 15 Pa·s or less: condition (a): the average particle diameter is 1 μm or less, condition (b): particles having a particle diameter of less than 0.2 μm account for 7% by weight or less, condition (c): particles having a particle diameter of more than 1.5 μm account for 15% by weight or less, and condition (d): one or more frequency maximums exist in a particle diameter range of 0.1 μm or more and less than 0.5 μm.

1 . An alumina slurry substantially comprising alpha-alumina particles and water, wherein
 the alpha-alumina particles satisfy all particle diameter distribution conditions (a) to (d) mentioned below,   the alpha-alumina particles have an alumina purity of 90% by weight or more,   the content of alumina in the slurry is 20% by weight or more and 50% by weight or less, and   the slurry has a viscosity of 0.5 Pa·s or more and 15 Pa·s or less:   condition (a): the average particle diameter is 1 μm or less,   condition (b): particles having a particle diameter of less than 0.2 μm account for 7% by weight or less,   condition (c): particles having a particle diameter of more than 1.5 μm account for 15% by weight or less, and   condition (d): one or more frequency maximums exist in a particle diameter range of 0.1 μm or more and less than 0.5 μm.   
     
     
         2 . The alumina slurry according to  claim 1 , wherein the alpha-alumina particles further satisfy all particle diameter distribution conditions (e) to (g) mentioned below:
 condition (e): particles having a particle diameter of 0.5 μm or more and less than 1 μm account for 40% by weight or less,   condition (f): one or more frequency maximums exist in a particle diameter range of 1 μm or more, and   condition (g): relations of expressions (1) and (2) below are satisfied:
   2× D 1< D 2<5× D 1  (1)
 
   ( M 1/ M 2)≧0.8  (2)
 
   
       where 
       D1 denotes a maximum particle diameter of a frequency maximum showing the smallest maximum particle diameter among frequency maximums which appear in a particle diameter range of 0.1 μm or more and less than 0.5 μm in the condition (d), and M1 denotes a maximum value; and D2 denotes a maximum particle diameter of a frequency maximum showing the largest maximum particle diameter among frequency maximums which appear in a particle diameter range of 1 μm or more in the condition (f), and M2 denotes a maximum value. 
     
     
         3 . The alumina slurry according to  claim 1 , wherein the amount of coarse particles having a particle diameter of 10 μm or more is 10 ppm or less in the alpha-alumina particles. 
     
     
         4 . The alumina slurry according to  claim 1 , wherein the content of Zr in the alumina solid component is 300 ppm or more calculated on a weight basis. 
     
     
         5 . A method for producing the alumina slurry according to  claim 1 , which comprises:
 adding raw alpha-alumina particles having an alumina purity of 90% by weight or more, a BET specific surface area of 15 m 2 /g or less, and an average particle diameter of 1 μm or more and 30 μm or less to water, which is a solvent, so that the content of alumina becomes 20% by weight or more and 50% by weight or less, thereby allowing the raw alpha-alumina particle to undergo wet grinding.   
     
     
         6 . The method for producing the alumina slurry according to  claim 5 , wherein the wet grinding is performed in the absence of a dispersing agent. 
     
     
         7 . The method for producing the alumina slurry according to  claim 5 , wherein the wet grinding is wet grinding by dispersion media and the dispersion media are ZrO 2  beads having a diameter of 0.65 mm to 1.5 mm. 
     
     
         8 . A coating liquid comprising a binder, alpha-alumina particles, and a solvent, which is used for formation of a heat-resistant layer in a separator for nonaqueous electrolyte secondary battery, including the heat-resistant layer containing alpha-alumina particles and a binder, and polyolefin porous film laminated to each other, wherein
 the coating liquid is prepared by mixing the alumina slurry according to  claim 1  with a binder, and contains the alpha-alumina particles in the amount of 100 to 10,000 parts by weight based on 100 parts by weight of the binder.