GB1003588A - Improvements in control of composition of electrodeposits - Google Patents

Abstract

<PICT:1003588/C6-C7/1> Selected proportions of different materials, particularly pigments, are electrophoretically deposited on to a substrate electrode, e.g. anodized aluminium alloy, from a colloidal suspension of such materials by adjusting the voltage applied between the substrate and a counter-electrode in the suspension to produce the desired composition, particularly of colour, of the deposit. Thus deposits of different colours may be produced from the same suspension or a constant colour may be automatically maintained from a suspension changing in composition, e.g. by depletion. As shown, an anodized strip 40 from supply reel 38 passes around roller 50 in suspension 54 near to counterelectrode 48 to be coated with a dense electrophoretic deposit on one side, then passes over roller 52, through furnace 74 for sealing with steam, and then through washer 68 for washing off loose material to a sensing station 102 where light from source 82 is reflected from the strip and focused upon photosensitive device 90 which controls the potential supply 66 to the conductors 62, 64. For determining colour, a spectroreflectometer 80 may be used. Alternatively a device for measuring magnetic permeability or dielectric losses may be used. The suspension may be maintained ultrasonically. Examples of pigments used in suspension are flavanthrone yellow and phthalocyanine blue, and zinc and cadmium sulphides.