Mesoporous Zinc Oxide Powder and Method for Production Thereof

Abstract

A zinc oxide powder is described, which, when used in a dispersion at a concentration of at least 50 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of; at least 70%, at least 75%, at least 80% or at least 85%. The powder has a number average zinc oxide aggregate size of at least 0.8 microns, at least 1 micron, at least 2 microns or at least 3 microns. Use of the zinc oxide powder reduces the risk of transdermal penetration.

1 . A zinc oxide powder which, when used in a dispersion at a concentration of at least 50 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 70%, at least 75%, at least 80% and at least 85%, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         2 . The zinc oxide powder of  claim 1  which, when used in a dispersion at a concentration of at least 40 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 70%, at least 75%, at least 80% and at least 85%, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         3 . The zinc oxide powder of  claim 1  which, when used in a dispersion at a concentration of at least 30 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 70%, at least 75%, at least 80% and at least 85%, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         4 . The zinc oxide powder of  claim 1  which, when used in a dispersion at a concentration of at least 20 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 70%, at least 75%, at least 80% and at least 88%, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         5 . The zinc oxide powder of  claim 1  which, when used in a dispersion at a concentration of at least 10 wt % of zinc oxide produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 75%, at least 80%, at least 85% and at least 93%, the powder having a number average zinc oxide aggregate size of at least 0.8 microns or at least 1 micron. 
     
     
         6 . A zinc oxide powder which, when used in a dispersion at a concentration of at least 50 wt % zinc oxide produces a CIE whiteness index less than 30, or less than 40, or less than 50, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         7 . The zinc oxide powder of  claim 6  which, when used in a dispersion at a concentration of at least 30 wt % produces a CIE whiteness index less than 25, or less than 35, or less than 45, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         8 . The zinc oxide powder of  claim 6  which, when used in a dispersion at a concentration of at least 20 wt % produces a CIE whiteness index less than 25, or less than 35, or less than 45, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         9 . The zinc oxide powder of  claim 6  which, when used in a dispersion at a concentration of at least 10 wt % produces a CIE whiteness index less than 10, or less than 20, or less than 30, the aggregates having a number average aggregate size of at least 0.8 micron or at least 1 micron. 
     
     
         10 . The zinc oxide powder of  claim 1  characterized in that the aggregates are mesoporous and have a total mesopore volume of at least 0.25 cm 3 /g or at least 0.35 cm 3 /g or at least 0.5 cm 3 /g. 
     
     
         11 . The zinc oxide powder of  claim 6  characterized in that the aggregates are mesoporous and have a total mesopore volume of at least 0.25 cm 3 /g or at least 0.35 cm 3 /g or at least 0.5 cm 3 /g. 
     
     
         12 . The zinc oxide powder of  claim 1  wherein the aggregates have sizes in the range of 0.1 micron to 100 microns. 
     
     
         13 . The zinc oxide powder of  claim 6  wherein the aggregates have sizes in the range of 0.1 micron to 100 microns. 
     
     
         14 . The zinc oxide powder of  claim 1  wherein the number average zinc oxide aggregate size is compared with a target aggregate size and reduced using milling if the number average zinc oxide aggregate size is larger than the target aggregate size. 
     
     
         15 . The zinc oxide powder of  claim 6  wherein the number average zinc oxide aggregate size is compared with a target aggregate size and reduced using milling if the number average zinc oxide aggregate size is larger than the target aggregate size. 
     
     
         16 . The zinc oxide powder of  claim 1  when used in a dispersion to provide a transparent composition, wherein, for a given weight percentage of zinc oxide added to the composition, the SPF of the composition is greater than the SPF achieved for an equivalent composition comprising non-porous zinc oxide particles having a particle size equivalent to the number average zinc oxide aggregate size. 
     
     
         17 . The zinc oxide powder of  claim 6  when used in a dispersion to provide a transparent composition, wherein, for a given weight percentage of zinc oxide added to the composition, the SPF of the composition is greater than the SPF achieved for an equivalent composition comprising non-porous zinc oxide particles having a particle size equivalent to the number average zinc oxide aggregate size. 
     
     
         18 . The zinc oxide powder of  claim 1  wherein the refractive index of the powder is adjustable by filling the open mesopores of the aggregates with a substance other than air. 
     
     
         19 . The zinc oxide powder of  claim 6  wherein the refractive index of the powder is adjustable by filling the open mesopores of the aggregates with a substance other than air. 
     
     
         20 . A method of manufacturing a zinc oxide powder which, when used in a dispersion at a concentration of at least 50 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 70%, at least 75%, at least 80% and at least 85%, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron, the method characterized in that a mesoporous zinc precursor material is heat treated to form the mesoporous zinc oxide powder at a temperature sufficiently low temperature to retain and increase the mesoporosity of the precursor material. 
     
     
         21 . The method of  claim 20  further comprising the step of synthesizing the mesoporous zinc oxide precursor powder by reacting an aqueous solution of zinc chloride with an aqueous solution of sodium carbonate while agitating to cause precipitation of a mesoporous zinc carbonate powder. 
     
     
         22 . The method of  claim 20  wherein the molar ratio of zinc chloride to sodium carbonate present when the aqueous solution of zinc chloride and the aqueous solution of sodium carbonate are reacted is one of at least 1:2 and at least 1:3. 
     
     
         23 . A method of manufacturing a zinc oxide powder which, when used in a dispersion at a concentration of at least 50 wt % zinc oxide produces a CIE whiteness index less than 30, or less than 40, or less than 50, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron, the method characterized in that a mesoporous zinc precursor material is heat treated to form the mesoporous zinc oxide powder at a temperature sufficiently low temperature to retain and increase the mesoporosity of the precursor material. 
     
     
         24 . The method of  claim 23  further comprising the step of synthesizing the mesoporous zinc oxide precursor powder by reacting an aqueous solution of zinc chloride with an aqueous solution of sodium carbonate whilst agitating to cause precipitation of a mesoporous zinc carbonate powder. 
     
     
         25 . The method of  claim 23  wherein the molar ratio of zinc chloride to sodium carbonate present when the aqueous solution of zinc chloride and the aqueous solution of sodium carbonate are reacted is one of at least 1:2 and at least 1:3. 
     
     
         26 . A method of manufacturing a zinc oxide powder which, when used in a dispersion at a concentration of at least 50 wt % of zinc oxide, produces a transparent composition having a total visible transmittance through a path length of 20 microns at 550 nm of at least one of at least 70%, at least 75%, at least 80% and at least 85%, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron, the method characterized in that a mesoporous zinc precursor material is heat treated to form the mesoporous zinc oxide powder at a heat treatment temperature in at least one of the range of 250-575° C., the range of 300-525° C., the range of 350-475° C., and the range of 400-450° C. 
     
     
         27 . The method of  claim 26  further comprising the step of synthesizing the mesoporous zinc oxide precursor powder by reacting an aqueous solution of zinc chloride with an aqueous solution of sodium carbonate whilst agitating to cause precipitation of a mesoporous zinc carbonate powder. 
     
     
         28 . The method of  claim 26  wherein the molar ratio of zinc chloride to sodium carbonate present when the aqueous solution of zinc chloride and the aqueous solution of sodium carbonate are reacted is one of at least 1:2 and at least 1:3. 
     
     
         29 . A method of manufacturing a zinc oxide powder which, when used in a dispersion at a concentration of at least 50 wt % zinc oxide produces a CIE whiteness index less than 30, or less than 40, or less than 50, the powder having a number average zinc oxide aggregate size of at least 0.8 micron or at least 1 micron, the method characterized in that a mesoporous zinc precursor material is heat treated to form the mesoporous zinc oxide powder at a heat treatment temperature in at least one of the range of 250-575° C., the range of 300-525° C., the range of 350-475° C., and the range of 400-450° C. 
     
     
         30 . The method of  claim 29  further comprising the step of synthesizing the mesoporous zinc oxide precursor powder by reacting an aqueous solution of zinc chloride with an aqueous solution of sodium carbonate whilst agitating to cause precipitation of a mesoporous zinc carbonate powder. 
     
     
         31 . The method of  claim 29  wherein the molar ratio of zinc chloride to sodium carbonate present when the aqueous solution of zinc chloride and the aqueous solution of sodium carbonate are reacted is one of at least 1:2 and at least 1:3.