Dry film thickness

AppHcation of an adhesion-promoting paint before metal spraying improves the coating. Color-coded paints, which indicate compatibiHty with specific plastics, can be appHed at 20 times the rate of grit blasting, typically at 0.025-mm dry film thickness. The main test and control method is cross-hatch adhesion. Among the most common plastics coated with such paints are polycarbonate, poly(phenylene ether), polystyrene, ABS, poly(vinyl chloride), polyethylene, polyester, and polyetherimide. 

Epoxy and polyester systems filled with flake glass provide a finish that is tough and resistant to abrasion. One commercial system is filled with copper flakes to provide intrinsic antifouling action. These systems are apphed at a total dry film thickness of about 625 p.m and are used on pleasure boats. 

Tanl . Coatings for Hquid cargo tanks ate selected according to the materials that the tanks (qv) ate to contain. Tank coatings protect the cargo from contamination and must be compatible with the material carried. Epoxy systems ate most frequendy selected because they perform well with both aqueous and organic products. A carefully appHed three-coat epoxy system having a dry-film thickness of 225—300 pm can be expected to last for 12 years. 

Blistering is influenced by the total film thickness as well as by the application conditions and the coating material. A minimum dry film thickness of over 250 is required, and this does not take account of the antifouling component [10]. 

Take wet-film thickness for each coat applied and confirm that they are such as to yield the specified dry-film thickness. 

Measure the dry-film thickness of each coat over a representative area and ensure that the specified film thickness has been attained. 

Neither roller nor brush is capable of attaining the same film thickness as airless spray. A paint which consistently gives 100/im dry-film thickness when applied by the latter means is unlikely to produce more than 75 m d.f.t. comfortably by roller or brush the more complex the geometry of a structure the more unlikely it is that consistent results will be obtained. 

Type of paint Method of application Coats Dry film thickness (litn)... 

Theories neglect that catalysts usually have limited turnover numbers due to destructive side reactions. This may not be so obvious in analytical experiments but it has severe consequences for large scale applications. A simple calculation can illustrate this problem if a redox polymer with a monomer molecular weight of 400 Da and a density of 1 g cm " is considered with all redox centers addressable from the electrode and accessible to the substrate with a turnover number of 1000, then, to react 1 nunol of substrate at a 1 cm electrode surface, at least 5 pmol of active catalyst centers corresponding to 2 mg of polymer, or a dry film thickness of 20 pm are required. This is 20 times more than the calculated optimum film thickness for rather favorable conditions... 

Polymer Films. The polymer films were prepared by casting 5% toluene solutions onto glass microscope slides. After air drying in a fume hood, the films were vacuum dried. Film thicknesses were typically 0.05 mm. 

The paints were spray applied to a number of substrates. Two coatings gave a final dry film thickness between 85 to 130 microns. For ac impedance studies the coatings were applied to shot (steel) blasted cold rolled steel plates. For interface metal-loss studies by electrical resistance the coatings were applied to 10 micron Fe foils (99.85 purity), adhesively attached by Araldite 2003 epoxy paste on one side to grit blasted glass plates. 

All paints were electrodeposited on SAE 1010 bare steel paint test panels to yield 20fim dry film thickness, and were baked to yield fully crosslinked, solvent resistant films. 

Polymer films of approximately 1000 microns wet film thickness were laid down with a bar applicator on PTFE coated glass panels and the solvent allowed to evaporate at ambient temperature for a standard period of seven days. A typical plot of solvent weight loss with time is shown in Figure 2. The thickness of the wet film was dictated by the need to have adequate mechanical strength in the dry films in order that they might be suitable for subsequent mechanical test procedures. Dry film thicknesses were approximately 300 microns as measured by micrometer. The dried polymer films were examined by dynamic mechanical thermal analysis (DMTA) (Polymer Laboratories Ltd.). Typical DMTA data for a polymer and paint are... 

Coatings from the resins in Tables III and IV The resin (5.0 g, warmed with steam to just liquify it) and a solution of 0.042 g of p-toluenesulfonic acid in 1.0 g of 2-heptanone were mixed until homogeneous, and then HMMM (3.33 g) was added and mixed. In other experiments the resin/HMMM ratio was varied. The mixtures were cast onto 3"x9"x24 ga "Bonderite 1000" steel panels. A //36 wire drawdown bar was used, leading to dry film thicknesses of 18 to 24 im. The... 

Enamel preparation. Solutions or mixtures of polyol, HMMM and p-TSA in a 75/25/0.25 wt. ratio were cast on steel panels and were baked at 175° for the specified time. Dry film thicknesses were 20 to 25 ym. 

Priming is the process of applying a dilute solution of the adhesive mixed with an organic solvent on the adherend to a dried film thickness between 0.0015 and 0.005 mm (0.00006 to 0.002 in). Priming protects the surface from oxidation, improves wetting, helps prevent adhesive peeling, and serves as a barrier layer to prevent undesirable reactions between the adhesive and the adherent. 

AF polymers can be extruded, compression and injection-molded, solution or spray-coated as well as spin-coated from solution. A representative plot showing the dry-film thickness obtained by spin-casting from two different concentration AF solutions at different spin speeds is shown in Figure 2.8. It is possible to prepare multiple coats of AF using this technique. Although most of the solvent is removed in the spin-coating step the polymer must be heated above its glass transition temperature to ensure removal of the last traces of solvent. 

The ZA was added to the resin at 1.5% on resin solids and thereupon dispersed using a Cowles mixer at high speed for 10 min. All coatings were applied by spraying at 0.051 mm dry film thickness and cured at 77°F, 50% relative humidity for 168 h (alkyd) or 375°F for 12 min (polyester). 

Polyester coating. A high solids polyester baking enamel (Cargill 5776) was prepared and spray-applied to yield a 50 jum dry film thickness (Table 4). 

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