Handbook of Plastics, Elastomers and Composites Part 10 pot

360 Chapter Six whose choice of such a coating is based on properties of the generic resin, can be greatly disappointed. Instead, selections must be made on the basis of performance data for spe- cific coatings or finish systems. Performance data are generated by the paint and product manufacturing industries when conducting standard paint evaluation tests. Test methods for coating material evaluation are listed in Table 6.7. 6.4.4 Selection by Electrical Properties Electrical properties of organic coatings and finishes vary by resin (also referred to as polymer) type. When selecting insulating varnishes, insulating enamels, and magnet wire enamels, the electrical properties and physical properties determine the choice. Table 6.8 shows electric strengths, Table 6.9 shows volume resistivities, Table 6.10 shows dielectric constants, and Table 6.11 shows dissipation factors for coatings using most of the available resins. Magnet wire insulation is an important use for organic coat- ings. National Electrical Manufacturer’s Association (NEMA) standards and manufactur- ers’ trade names for various wire enamels are shown in Table 6.12. This information can be used to guide the selection of coatings. However, it is important to remember the afore- mentioned warnings about blends of various resins and the effects on performance proper- ties. 6.5 Coating and Finishing Materials Since it is the resin in the coating’s vehicle that determines its performance properties, coatings and finishes can be classified by their resin types. The most widely used resins for manufacturing modern coatings and finishes are acrylics, alkyds, epoxies, polyesters, polyurethanes, and vinyls. 3 In the following section, the resins used in coatings and fin- ishes are described. 6.5.1 Common Coating Resins 6.5.1.1 Acrylics. Acrylics are noted for color and gloss retention in outdoor exposure. Acrylics are supplied as solvent-containing, high-solids, waterborne, and powder coatings. They are formulated as lacquers, enamels, and emulsions. Lacquers and baking enamels are used as automotive and appliance finishes. Both these industries use acrylics as top- coats for multicoat finish systems. Thermosetting acrylics have replaced alkyds in applica- tions requiring greater mar resistance such as appliance finishes. Acrylic lacquers are brittle and therefore have poor impact resistance, but their outstanding weather resistance allowed them to replace nitrocellulose lacquers in automotive finishes for many years. Acrylic and modified acrylic emulsions have been used as architectural coatings and fin- ishes and also on industrial products. These medium-priced resins can be formulated to have excellent hardness, adhesion, abrasion, chemical, and mar resistance. When acrylic resins are used to modify other resins, their properties are often imparted to the resultant resin system. Uses. Acrylics, both lacquers and enamels, were the topcoats of choice for the auto- motive industry from the early 1960s to the mid 1980s. Thermosetting acrylics are still used by the major appliance industry. Acrylics are used in electrodeposition and have largely replaced alkyds. The chemistry of acrylic-based resins allows them to be used in radiation curing applications alone or as monomeric modifiers for other resins. Acrylic- modified polyurethane coatings and finishes have excellent exterior durability. Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 361 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 362 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plastics in Coatings and Finishes 363 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 364 Chapter Six 6.5.1.2 Alkyds. Alkyd resin-based coatings and finishes were introduced in the 1930s as replacements for nitrocellulose lacquers and oleoresinous coatings. They offer the ad- vantage of good durability at relatively low cost. These low- to medium-priced coatings and finishes are still used for finishing a wide variety of products, either alone or modified with oils or other resins. The degree and type of modification determine their performance properties. They were used extensively by the automotive and appliance industries through the 1960s. Although alkyds are used in outdoor applications, they are not as durable in long-term exposure, and their color and gloss retention is inferior to that of acrylics. Uses. Once the mainstay of organic coatings and finishes, alkyds are still used for fin- ishing metal and wood products. Their durability in interior exposures is generally good, but their exterior durability is only fair. Alkyd resins are used in fillers, sealers, and caulks for wood finishing because of their formulating flexibility. Alkyds have also been used in electrodeposition as replacements for the oleoresinous vehicles. They are still used for fin- ishing by the machine tool and other industries. Alkyds have also been widely used in ar- chitectural and trade sales coatings. Alkyd-modified acrylic latex paints are excellent architectural finishes. 6.5.1.3 Epoxies. Epoxy resins can be formulated with a wide range of properties. These medium- to high-priced resins are noted for their adhesion, make excellent primers, and are used widely in the appliance and automotive industries. Their heat resistance per- mits them to be used for electrical insulation. When epoxy topcoats are used outdoors, they tend to chalk and discolor because of inherently poor ultraviolet light resistance. Other resins modified with epoxies are used for outdoor exposure as topcoats, and proper- ties of many other resins can be improved by their addition. Two-component epoxy coat- ings and finishes are used in environments with extreme corrosion and chemical conditions. Flexibility in formulating two-component epoxy resin-based coatings and fin- ishes results in a wide range of physical properties. Uses. Owing to their excellent adhesion, they are used extensively as primers for most coatings and finishes over most substrates. Epoxy coatings and finishes provide ex- cellent chemical and corrosion resistance. They are used as electrical insulating coatings and finishes because of their high electric strength at elevated temperatures. Some of the Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Plastics in Coatings and Finishes 365 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 366 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 367 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. 368 Plastics in Coatings and Finishes Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. 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[...]... electrostatic disks and bells Airless electrostatic spray Air-assisted airless electrostatic spray Air electrostatic spray Airless spray High-volume, low-pressure spray Air-assisted airless spray Multicomponent spray Air-atomized spray 95 100 95 100 95 100 95 100 95 100 95 100 95 100 95 100 95 100 95 100 80–90 70–80 70–80 60–70 50–60 40–60 40–60 30–70 30–40 In the selection of a coating method and equipment,... disadvantages of dip coating are film thickness differential from top to bottom, resulting in the so-called wedge effect; fatty edges on lower parts of products; and runs and sags Although this method coats all surface areas, solvent reflux can cause low film build Light products can float off the hanger and hooks and fall into the dip tank Solvent-containing coatings and finishes in dip tanks and drain tunnels... the Terms of Use as given at the website Plastics in Coatings and Finishes Plastics in Coatings and Finishes 391 stalled above the porous plate to charge the finely divided particles Once charged, the particles are repelled by the grid and repel each other, forming a cloud of powder above the grid These electrostatically charged particles are attracted to and coat products that are at ground potential... used for finishing flat sheets of material There are two types of roller coaters, direct and reverse, depending on the direction of the applicator roller relative to the direction of the substrate movement Roller coating can apply multiple coats to the front and back of coil stock with great uniformity The advantages of roller coating are consistent film thickness and elimination of painting operations at... industry, which includes aircraft, automobiles, railroads, trucks, and ships Owing to their chemical resistance and ease of decontamination from chemical, biological, and radiological warfare agents, they are widely used for painting military land vehicles, ships, and aircraft They are used on automobiles as coatings and finishes for plastic parts and as clear topcoats in the basecoat-clearcoat finish systems... surfaces Dry materials are used, saving cost of solvents Deposits coating in selected areas through a mask Provides good pattern deposition and controlled thickness Dip Brush Roller Impregnation Fluidized bed Screen-on Small- and- medium sized parts, castings, moisture and fungus proofing of modules, temporary protection of finished machined parts Motor frames and housings, electronic enclosures, circuit... automobiles, and appliances Typical applications Coils, transformers, field and armature windings, metal castings, and sealing of porous structures Metal decorating of sheet to be used for aluminum siding, gutter and downspouts, and to fabricate cans, boxes Requires flat or smoothly curved surface Preparation of screens is time-consuming Circuit boards, artwork, labels, masking against etching solution, spot... Terms of Use as given at the website Plastics in Coatings and Finishes 392 Chapter Six The advantage of centrifugal coating is that large numbers of small parts can be coated at the same time The disadvantage is that the appearance of the finish is a problem, because the parts touch each other 6.6.5.3 Flow coating In a flow coater (95 100 percent TE), the coating material is pumped through hoses and nozzles... is high Poor thickness control; not for precise applications Coating of individual components, spot repairs, or maintenance High labor cost Viscosity and pot life of dip must be monitored Speed of withdrawal must be regulated for consistent coating thickness Difficult to completely coat complex parts and to obtain uniform thickness and reproducible coverage Limitations Ultrathin, pinhole-free films possible... radius, and corrosion of unpainted cut edges 6.7 Curing No dissertation on organic coatings and finishes is complete without mentioning film formation and cure It is not the intent of this chapter to fully discuss the mechanisms, which are more important to researchers and formulators than to designers and end users, but rather to show that differences exist and to aid the reader in making selections Most of . in long-term exposure, and their color and gloss retention is inferior to that of acrylics. Uses. Once the mainstay of organic coatings and finishes, alkyds are still used for fin- ishing metal and wood products feature of fluorocarbon finishes makes them useful for products such as saws, fan and blower blades, door-lock parts, sliding- and folding-door hardware, skis, and snow shovels. (Courtesy of E. I trucks, and ships. Owing to their chemical resistance and ease of decontamination from chemical, biological, and radiolog- ical warfare agents, they are widely used for painting military land vehicles,