Silica matting agents
A silica matting agent comprises particulate amorphous silica in which the particles of silica have been treated with a hydrophilic polyolefin wax.
1 . A silica matting agent comprising particulate amorphous silica in which the particles of silica have been treated with a hydrophilic polyolefin wax.
2 . A silica matting agent according to claim 1 in which the hydrophilic polyolefin wax has a molecular weight in the range 800 to 30000.
3 . A silica matting agent according to claim 1 in which the hydrophilic polyolefin wax has a melting point in the range 100 to 130° C.
4 . A silica matting agent according to claim 1 in which the hydrophilic polyolefin wax is present in an amount in the range 3 to 20 percent by weight with respect to untreated silica.
5 . A silica matting agent according to claim 1 in which the silica has a weight mean particle size in the range 2 to 20 μm.
6 . A silica matting agent according to claim 1 in which the untreated silica has a BET surface area in the range 100 to 800 m 2 g −1 .
7 . A silica matting agent according to claim 1 in which the untreated silica has a pore volume to nitrogen in the range 1.0 to 2.1 cm 3 g −1 .
8 . A silica matting agent according to claim 1 in which the untreated silica has an oil absorption in the range 100 to 500 cm 3 /100 g.
9 . A method of preparing a silica matting agent comprising passing particulate amorphous silica and a wax through a size reduction apparatus in which the wax is a hydrophilic polyolefin wax.
10 . A method of preparing a silica matting agent according to claim 9 in which the hydrophilic polyolefin wax has a weight mean particle size below 15 μm.
11 . A method of preparing a silica matting agent according to claim 9 in which the silica and wax reach a temperature in the range 100 to 150° C. as they pass through the size reduction apparatus.