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Firstly, the present invention provides a dispersion comprising 10 to 60% by weight of aluminum oxide powder. The aluminium oxide powder can be easily incorporated into an aqueous medium.
The particle diameter of the aluminium oxide powder is 0.1 mm to 1 mm. The BET surface area of the aluminium oxide powder is 10 to 140 m 2 /g. The gamma*vB/lambda value of the powder is from 55 to 200. The hydroxyl group density is greater than 8 OH/nm2.
The dispersion is prepared by introducing in portions of the powder into deionized water. The pH of the water is kept between 4.0 and 4.1 by addition of propionic acid. The aluminium oxide predispersion is then cooled using a conventional heat exchanger.
The dispersion can be produced by a bead mill, a rotor-stator unit, a dissolver, a planetary kneader/mixer, or an impact mill. A pin mill can also be used for producing aluminium oxide particles. The dispersion is then milled. The fine aluminium oxide particles are the constituents of the ink receiving layer of an ink jet printer.
The tamped density of the aluminium oxide powder is from 30 to 150 g/l. The tamper density can be increased by using methods described in DIN EN ISO 787-11. The aluminium oxide powder can also be heat treated. This can be carried out continuously or batchwise. The heat treatment is preferably carried out at temperatures of 1300 to 1500 deg C.
The average residence time of the aluminium oxide powder is from 1 minute to 24 hours. The residence time depends on the temperature and caloric temperature of the aluminium oxide powder.