Pigments

Claim 2

A pigment according to claim 1 in which the refractive index of the layers of titanium dioxide is 1.85 to 1.95 or of zirconium dioxide or alkaline earth metal titanate is 1.69 to 1.75 and the refractive index of the layers of interleaving agent is 1.45 to 1.50.

Claim 3

A pigment according to claim 1 comprising three to eight thin, clear layers of titanium or zirconium dioxide or an alkaline earth metal titanate.

Claim 4

A pigment according to claim 1 in which the thickness of the layers of titanium or zirconium dioxide or alkaline earth metal tiTanate and of the interleaving layers is 0.03 to 0.1 micron, the layers vary in thickness within the range and the pigment is white.

Claim 5

A pigment according to claim 1 in which the thickness of the layers of titanium or zirconium dioxide or alkaline earth metal titanate and of the interleaving layers is 0.05 to 0.3 microns, the layers are of controlled thickness within this range, and the pigment is coloured.

Claim 6

A pigment according to claim 1 in which each pigment particle is 5 to 50 microns across.

Claim 7

Process for the preparation of a pigment which comprises applying to a support a release layer and then alternately layers, each of which is uniform and each of which is from 0.03 to 0.3 microns thick, of (I) a hydrolysable titanic or zirconic ester or alkaline earth metal titanic ester and (II), as interleaving agent former, an organic film-forming substance containing hydroxyl, carboxylic anhydride or carboxylic ester groups or a sulphonamide-formaldehyde resin, hydrolysing each hydrolysable layer immediately after application to a clear layer by contact with water vapour such that after hydrolysis of each hydrolysable layer the refractive index of (I) exceeds that of layer (II) by at least 0.05; and when at least two layers of the titanic or zirconic ester or alkaline earth metal titanic ester have been applied and hydrolysed releasing the multilayer product from the support by dissolving away the release layer.

Claim 8

Process according to claim 8 in which the interleaving agent former used is cellulose diacetate, ethyl-hydroxyethyl-cellulose, polyvinyl acetel, polyvinyl butyral, partially hydrolysed polyvinyl acetate, nitrocellulose, a sulphonamide-formaldehyde resin, a silicone-glycol copolymer, a methyl vinyl ether-maleic anhydride copolymer, a methyl vinyl ether-ethyl hydrogen maleate copolymer a p-t-butyl-phenol-formaldehyde novolak resin, a phenol-formaldehyde novolak resin or ethyl-cellulose.

Claim 9

Process according to claim 8 in which the hydrolysable titanic or zirconic ester or alkaline earth metal titanic ester used is an alkyl titanate, zirconate, or alkaline earth metal titanate, in which each alkyl contains 1 to 8 carbon atoms.

Claim 10

Process according to claim 10 in which tetra-isopropyl titanate, tetra-n-butyl titanate, tetra-n-propyl zirconate, or calcium titanium isopropoxide is used.

Claim 11

Process according to claim 8 in which the support is of glass, polished metal, or polyethylene terephthalate film.

Claim 12

Process according to claim 8 in which the support is first provided with a water-soluble release layer.

Claim 13

Process according to claim 13 in which the release layer is polyethylene glycol of molecular weight 6,000 to 100,000, or polyvinyl pyrrolidone.

Claim 14

Process according to claim 8 in which the hydrolysable titanic or zirconic ester or alkaline earth metal titanic ester is applied as a solution in an inert volatile solvent, and the said solvent is evaporated before the said ester is hydrolysed.

Claim 15

Process according to claim 15 in which the said solvent is a volatile hydrocarbon.

Claim 16

Process according to claim 8 in which three to eight layers of hydrolysable titanic or zirconic ester or alkaline earth meal titanic ester are applied to the support and hydrolysed.

Claim 17

Process according to claim 8 in which, after removal from the support, the pigment is comminuted to a particle size of from 1 to 70 microns.

Claim 18

Process according to claim 18 in which, after removal from the support, the pigment is comminuted to a particle size of 5 to 50 microns.

Claim 19

Process according to claim 8 in which the layers are applied to the support by a reverse roller kiss-coating technique.