Solvent coating techniques

There are many coating defects that can degrade the sensitometiy. Film defects have been reviewed by Pierce and Schoff (1986). Drying-related defects can be frequently reduced by the use of surfactants to control the surface tension (Hansen and Pierce, 1974 Jerome, 1990). 

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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. 

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. 

Organic photoreceptors are prepared by solvent coating techniques and can be fabricated in a drum or web configuration. These can be prepared in the single- or dual-layer arrangement. In the dual-layer arrangement, the generation... 

Highly polar solvents such as acetone and the alcohols are poor dispersion media for VMQ type silicones, but ketones are the best choice for fluorosilicone, which is not readily dissolved by aromatic types. Peroxide loss always occurs in solvent coating techniques from reaction with the solvent, volatilisation during the drying stage and deactivation by atmospheric oxygen when cured in thin films. To counteract this effect it is normal practice to double or triple peroxide levels at least compared to those used for moulding or extrusion. 

The coating technique starts by applying a solvent-based adhesive on to a previously pretreated metal substrate. The item is then preheated to 200-250°C, the exact time and temperature depending on the metal thickness. It is then dipped in the plastisol which partly gels owing to the... 

Processes based on fluidized bed coating have been developed (49). In this process, the bioactive agent is dissolved in an organic solvent along with the polymer. This solution is then processed through a Wurster air suspension coater apparatus to form the final microcapsule product. A solvent partition technique based on continuous injection of a polymer-drug solution into flowing mineral oil has been reported (50). 

Latices and pseudolatices are widely used for the coating of solid pharmaceutical dosage forms such as tablets, capsules, and pellets. The major advantage compared to conventional coating techniques is the avoidance of organic solvents. 

Conformance of dry film to the copper surface is a concern, particularly with stiff films. One way to improve conformance is to coat a low viscosity photopolymer liquid direcdy on the substrate. Several coating techniques are available to deposit photoresists directly onto metal substrates. These techniques involve dissolving/dispersing the ingredients in a solvent, coating the solution on the substrate and removing the solvent. Some of the material is lost during the... 

Interconnects are formed into the desired shape using ceramic processing techniques. For example, bipolar plates with gas channels can be formed by tape casting a mixture of the ceramic powder with a solvent, such as trichloroethylene (TCE)-ethanol [90], Coating techniques, such as plasma spray [91] or laser ablation [92] can also be used to apply interconnect materials to the other fuel cell components. 

The solution coating technique involves preparing an excess of solution of known concentration of the stationary phase dissolved in appropriate solvent. A known weight of support is then added slowly to a known volume of solution while the solution is stirred until all of the support is in suspension. This slurry... 

The solution coating technique in most cases is preferred to the evaporative method because there is more uniform deposition of the phase and because there is less chance for damage of support particles. The evaporative procedure is more convenient for preparing high concentration packings (15-20%) of the viscous phases such as Carbowax, and for preparing packings with two or more stationary phases which are not soluble in a common solvent. 

Another alternative technique, solid-phase microextraction (SPME), was used for the determination of fluoxetine [79] and several TCAs [80], SPME is a miniaturized and solvent-free technique, where analytes are extracted from the sample by adsorption on a thin polymer coating fixed to the solid surface of a fiber, located inside an injection needle or a capillary. Its main disadvantage is that special strategies are needed to couple SPME to the LC-MS analysis. 

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