Grinding method and grinding medium

Abstract

A method for manufacturing microfibrillated cellulose, a particulate grinding medium suitable for use in said method, a material which wears rough, and a method for making said particulate grinding medium.

1 .- 44 . (canceled) 
     
     
         45 . A method for manufacturing microfibrillated cellulose, the method comprising a step of microfibrillating a fibrous substrate comprising cellulose by grinding in the presence of a particulate grinding medium which is to be removed after the completion of grinding, wherein the particulate grinding medium has a specific gravity of at least about 3.5, and wherein at the beginning of grinding the particulate grinding medium has a surface roughness of at least about 0.5 μm. 
     
     
         46 . A method for manufacturing microfibrillated cellulose, the method comprising a step of microfibrillating a fibrous substrate comprising cellulose by grinding in the presence of a particulate grinding medium which is to be removed after the completion of grinding, wherein the particulate grinding medium has a specific gravity of at least about 3.5, and wherein at the beginning of grinding the particulate grinding medium has a mean coefficient of friction of at least about 0.10. 
     
     
         47 . The method according to  claim 45 , wherein at the beginning of grinding the particulate grinding medium also has a mean coefficient of friction of at least about 0.10. 
     
     
         48 . The method according to  claim 47 , wherein after the completion of grinding, the surface roughness is at least about 90% of the surface roughness at the beginning of grinding. 
     
     
         49 . The method according to  claim 47 , wherein after the completion of grinding the mean coefficient of friction is at least about 90% of the mean coefficient of friction at the beginning of grinding. 
     
     
         50 . The method according to  claim 47 , wherein after the completion of grinding, the surface roughness is at least the same as the surface roughness at the beginning of grinding. 
     
     
         51 . The method according to  claim 47 , wherein after the completion of grinding the mean coefficient of friction is at least the same as the mean coefficient of friction at the beginning of grinding. 
     
     
         52 . The method according to  claim 47 , wherein the particulate grinding medium wears rough during grinding, further wherein after the completion of grinding, the surface roughness is greater than the surface roughness at the beginning of grinding. 
     
     
         53 . The method according to  47 , wherein the particulate grinding medium wears rough during grinding, and further wherein, after the completion of grinding, the mean coefficient of friction is greater than the mean coefficient of friction at the beginning of grinding. 
     
     
         54 . The method according to  claim 52 , wherein the surface roughness increases by at least 5% during grinding and/or the mean coefficient of friction increases by at least 5% during grinding. 
     
     
         55 . The method according to  claim 53 , wherein the mean coefficient of friction increases by at least 5% during grinding. 
     
     
         56 . The method according to  claim 47 , wherein the particulate grinding medium is a ceramic grinding medium. 
     
     
         57 . The method according to  claim 56 , wherein the ceramic grinding medium is formed of a material comprising alumina, zirconia, zirconium silicate, yttria, ceria, or yttria and/or ceria stabilized zirconia, and mixtures thereof. 
     
     
         58 . The method according to  47 , wherein at the beginning of grinding the particulate grinding medium has a surface roughness of from about 1.0 μm to about 5.0 μm. 
     
     
         59 . The method according to  claim 47 , wherein at the beginning of the grinding the particulate grinding medium has a mean coefficient of friction of from about 0.15 to about 0.50. 
     
     
         60 . The method according to  claim 47 , wherein the particulate grinding medium comprises rod-shaped particles having an aspect ratio of equal to or greater about than 1.5:1, for example, equal to or greater than about 2:1. 
     
     
         61 . The method according to  claim 45 , wherein the grinding is performed in the presence of an inorganic particulate material which is not to be removed after completion of grinding, producing a microfibrillated cellulose comprising said inorganic particulate material. 
     
     
         62 . The method according to  claim 46 , wherein the grinding is performed in the presence of an inorganic particulate material which is not to be removed after completion of grinding, producing a microfibrillated cellulose comprising said inorganic particulate material. 
     
     
         63 . The method according to  claim 47 , wherein the grinding is performed in the presence of an inorganic particulate material which is not to be removed after completion of grinding, producing a microfibrillated cellulose comprising said inorganic particulate material. 
     
     
         64 . The method according to  claim 63 , wherein the microfibrillating step is conducted in an aqueous environment. 
     
     
         65 . The method according to  claim 63 , wherein the grinding is performed in one or more grinding vessels. 
     
     
         66 . The method according to  claim 65 , wherein the grinding is performed in one or more grinding vessels, wherein the grinding vessel is a stirred media detritor. 
     
     
         67 . The method according to  claim 66 , wherein the total amount of energy used in the method is less than that used in a comparable method in which the particulate grinding medium has at the beginning of grinding: (i) a surface roughness which is less rough; or (ii) a lesser mean coefficient of friction; or both (i) and (ii). 
     
     
         68 . A particulate ceramic grinding medium having (i) a surface roughness of at least about 0.5 μm, or (ii) a mean coefficient of friction of at least about 0.10, or both (i) and (ii), wherein the grinding medium is formed by sintering a composition comprising at least one of zirconia (ZrO 2 ) and alumina (Al 2 O 3 ). 
     
     
         69 . The particulate ceramic grinding medium according to  claim 68 , wherein the composition further comprises ceria (Ce 2 O 3 ). 
     
     
         70 . The particulate ceramic grinding medium according to  claim 69 , wherein the composition comprises from about 5 to about 25 wt. % ceria, based on the total weight of the composition. 
     
     
         71 . The particulate ceramic grinding medium according to  claim 70 , wherein the composition comprises from about 10 to about 20 wt. %. 
     
     
         72 . The particulate ceramic grinding medium according to  claim 69 , wherein the composition comprises up to about 90 wt. % ceria stabilized zirconia. 
     
     
         73 . The particulate ceramic grinding medium according to  claim 72 , further comprising at least about 10 wt. % alumina. 
     
     
         74 . The particulate ceramic grinding medium according to  claim 68 , wherein the composition comprises at least 90 wt. % alumina. 
     
     
         75 . The particulate ceramic grinding medium according to  claim 68 , wherein the composition comprises at least 95 wt. % alumina. 
     
     
         76 . The particulate ceramic grinding medium according to  claim 68 , wherein the composition comprises at least 99.5 wt. % alumina. 
     
     
         77 . A particulate grinding medium, wherein the grinding medium wears rough during grinding, in a method comprising a step of microfibrillating a fibrous substrate comprising cellulose by grinding in the presence of said particulate grinding medium which is to be removed after the completion of grinding. 
     
     
         78 . The particulate grinding medium according to claim  25 , wherein the particulate grinding medium has: (i) a surface roughness of at least about 0.5 μm; or (ii) a mean coefficient of friction of at least about 0.1 O; or both (i) and (ii). 
     
     
         79 . The particulate ceramic grinding medium according to  claim 68 , wherein the grinding medium wears rough during grinding, in a method comprising a step of microfibrillating a fibrous substrate comprising cellulose by grinding in the presence of said particulate grinding medium which is to be removed after the completion of grinding. 
     
     
         80 . The particulate ceramic grinding medium according to  claim 68 , wherein the particulate ceramic grinding medium has a specific gravity of at least 3.5 to about 6.5. 
     
     
         81 . A particulate grinding medium having a (i) a surface roughness of at least about 1.6 um, or (ii) a mean coefficient of friction of at least about 0.25, or both (i) and (ii). 
     
     
         82 . A method for making a particulate ceramic grinding medium according to  claim 68 , the method comprising:
 a) obtaining, providing or making a composition comprising raw materials suitable for making the ceramic grinding medium;   b) mixing the composition comprising raw materials, forming a mixture;   c) combining the mixture with binder, forming a bound mixture;   d) granulating the bound mixture by mixing the bound mixture composition over a period of time during which the mixing speed is reduced; and   e) sintering the granulated composition.   
     
     
         83 . The method according to  claim 82 , further comprising the step of drying the granulated composition. 
     
     
         84 . The method according to  claim 83 , further comprising the step of shaping the granulated composition. 
     
     
         85 . The method according to  claim 84 , further comprising the step of sizing the granulated composition. 
     
     
         86 . The method according to  claim 68 , wherein steps b) to d) are performed in a mixer equipped with an impeller, wherein the impeller speed during step b) is greater than the impellor speed during steps c) and d), and wherein the impeller speed during step c) is equal to or greater than the impellor speed during step d). 
     
     
         87 . The method according to  claim 82 , wherein an initial mixing speed in step b) is at least about 150% greater than a final mixing speed in step d). 
     
     
         88 . The method according to  claim 87 , wherein the initial mixing speed is between about 2750 and 3250 rpm, and the final mixing speed is between about 600 and 1200 rpm. 
     
     
         89 . A method of manufacturing microfibrillated cellulose by microfibrillating a fibrous substrate comprising cellulose by grinding in the presence of a particulate grinding medium without replenishing the method with fresh grinding media, wherein at the beginning of the grinding the particulate grinding medium has: (i) a surface roughness of at least about 0.5 um; or (ii) a mean coefficient of friction of at least about 0.1 O; or both (i) and (ii). 
     
     
         90 . A method of simultaneously manufacturing (a) microfibrillated cellulose and (b) a roughened particulate grinding medium, comprising grinding a fibrous substrate comprising cellulose by grinding in the presence of a particulate grinding medium which has at the beginning of grinding: (i) a surface roughness of at least about 0.5 um; or (ii) a mean coefficient of friction of at least about 0.1; or both (i) and (ii). 
     
     
         91 . The particulate ceramic grinding medium according to  claim 68 , wherein the grinding medium is obtainable by a method comprising:
 a) obtaining, providing or making a composition comprising raw materials suitable for making the ceramic grinding medium;   b) mixing the composition comprising raw materials, forming a mixture;   c) combining the mixture with binder, forming a bound mixture;   d) granulating the bound mixture by mixing the bound mixture over a period of time during which the mixing speed is reduced; and   e) sintering the granulated composition.   
     
     
         92 . The particulate ceramic grinding medium according to  claim 91 , further comprising the step of drying the granulated composition. 
     
     
         93 . The particulate ceramic grinding medium according to  claim 92 , further comprising the step of shaping the granulated composition. 
     
     
         94 . The particulate ceramic grinding medium according to  claim 93 , further comprising the step of sizing the granulated composition.