Pigment coating techniques

Due to their high near-infrared sensitivity, pigments have been widely used as generation layers. Pigment layers can be prepared by vapor deposition or solvent coating techniques. 

Vapor deposition has been used with some phthalocyanine and peiylene compounds. The basic requirement is that the compound have a high vapor pressure at temperatures sufficiently low to avoid chemical degradation. The principal limitation is that vapor-deposited films are usually amorphous and must be converted to a specific crystal form for optimum sensitometiy. Normally, this is accomplished by a solvent exposure. A further limitation is that vapor-deposition processes are slow and expensive compared with solvent coating techniques. 

Solution coating of dispersions is the most common method for preparing generation layers. The dispersions must be stable to agglomeration during the 

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The investigations comprised zino pigmented coatings with the aim of testing the mechanism of their action and looking for ways of improving protective properties. With the use of impedance technique the meohanism for two periods of activity has been proven with these coatings. 

Another question is the proper technique for the evaluation of protective properties of zinc pigmented coatings. IMtll now, the most popular one is the test in a salt chamber (12.141. This technique does not allow a complete understanding of the complex phenomena oo-ouring in the coating. It seems that the impedance technique selected in this work provides more adequate and useful data. 

The Impedsuice technique permits observation of the effect of modifying dltlves on protective properties of highly zlno pigmented coatings. 

Generation layers have recently been prepared from aqueous dispersions. Hoshino et al. (1991) described the cathodic deposition of various phthalo-cyanines and perylenes from aqueous dispersions containing poly(oxyethylene dodecyl ether) and LiBr. The pigment-polymer aggregate was plated onto an Al cathode. The layer was then coated with a transport layer using conventional solvent coating techniques. Hiruta et al. (1991) described a related technique as thermoinduced deposition. Aqueous phthalocyanine dispersions, as described above, were found to adsorb on an Al substrate at 90 C. 

Coating techniques Pharmaceuticals, food, fertilizers and agricultural chemicals (control of release), microencapsulation of pigments, etc. 

CLSM is a powerful technique for characterising coating microstructure, as shown for 1102 pigments dispersed in an acrylic urethane binder, A1 flake pigments and pearlescent-pigmented coatings [116]. 

The free radicals then initiate curing by attacking residual double bonds in acrylic oligomers and monomers, or in styrene and unsaturated polyester resins. Since most pigments absorb u.v. radiation and can prevent it reaching sufficient photoinitiator molecules, this technique is best suited to transparent coatings or thin pigmented layers (e.g. inks). 

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