Thermoset plastic industrial laminates are uniformly dense and structurally strong materials that will not soften appreciably under the reapplication of heat. They are extremely durable plastics that are lightweight and moisture resistant. They are thermoset plastic resin impregnated reinforcing substrate materials that are cured under heat and pressure to form solid shapes having high mechanical and insulating properties. Industrial laminates are available in sheet, rod, tube and angle. Since these laminates are comprised of a combination of materials, they are also referred to as composites.
Thermoset plastic industrial laminates typically have a layered construction with no fewer than two components: The first is a reinforcing substrate such as woven glass cloth, random glass mat, glass filaments, woven canvas cotton fabric, woven linen cotton fabric, paper, woven aramid fabric, random mat aramid, woven graphite fabric, random mat graphite and others. The second is a thermoset plastic resin binder which serves to adhere the layers of reinforcing substrates to each other to form a solid unit. Resin binders include epoxies, melamines, phenolics, polyesters, silicones and others.
Unlike other groups of plastic materials, thermoset plastic industrial laminates have their own standards which are published by NEMA (National Electrical Manufacturers Association). In concert with member manufacturers, NEMA standards are set and "minimum values" published. The most commonly used NEMA thermoset laminate grades are as follows:
NEMA grades G10 and FR4 Glass-Cloth Reinforced Epoxy - natural color is typically a yellowish to light green. The most versatile all-around laminate grades are continuous glass woven fabric impregnated with an epoxy resin binder. Epoxy resins are among the most versatile and widely used plastics in the electronics field - primarily because water absorption is virtually nil, rendering it an outstanding insulator. Beyond its electrical insulating properties, epoxy resins exhibit great dimensional stability (shrinkage is usually less than 1%) and superior adhesive properties. G10/FR4 has extremely high mechanical strength, good dielectric loss properties, and good electric strength. properties, both wet and dry. The main difference between NEMA Grades G10 and FR4 is that FR4 is a fire retardant grade of G10. Therefore, FR4 can usually* be substituted where G10 is called out, while G10 can never be substituted where FR4 is called for. G10 certifies to Mil-I-24768/2 GEE; FR4 certifies to Mil-1-24768/27 GEE-F.
NEMA grades G11 and FR5 Glass-Cloth Reinforced Epoxy - natural color is typically yellow green to amber. This grade is similar to G10/FR4 with the addition of a higher operating temperature and some improved mechanical strength at elevated temperatures. The main difference between NEMA Grades
G11 and FR5 is that FR5 is a fire retardant grade of G11. Therefore, FR5 can usually* be substituted when G11 is called for while G11 can never be substituted where FR5 is called for. G11 certifies to Mil-I-24768/3 GEB; FIR certifies to Mil-I-24768/28 GEB-F.
*CAUTION: Certain instances i.e., synchronous generator applications (within the Power Generation Industry) and some cryogenic applications which specify G-10 or G-11 may not be suitable for the substitution of FR-4 or FR-5. Circumstances could cause the release of hydrogen bromide gas, which is toxic and reactive with metals. Further research is suggested before substitution is considered.
NEMA grades G5 and G9 Glass-Cloth Reinforced Melamine - natural color is typically a grayish brown. These grades are composed of a continuous glass woven cloth base impregnated with a melamine resin binder. (Melamine resins, once cured, are the hardest, most rigid and abrasion resistant of the standard resins employed in the production of industrial laminates. However, prolonged exposure to high temperature can adversely affect its mechanical and electrical strength properties. Arc resistance, however, may remain unaffected despite excessive thermal exposure.) Melamines are the hardest of laminates, exhibiting good dimensional stability and arc resistance. It is also caustic resistant. A key difference between NEMA Grades G5 and G9 is that G9 is more resistant to the elements of the environment. Thus, G9 can be safely substituted where G5 is called for. G5 certifies to Mil-I-24768/8 GMG; G9 certifies to Mil-I-24768/1 GME.
NEMA grade G7 Glass-Cloth Reinforced Silicone - natural color is typically cream to white. Composed of a continuous glass woven cloth base impregnated with a silicone resin binder, this grade has excellent heat and arc resistance. (Silicone thermosetting resins are among the best of all polymer materials in resistance to temperature. Hence, silicone is broadly used for high temperature electronic applications requiring low electrical losses. Silicone is not as strong as epoxies and phenolics upon aging at lower temperatures but is stronger upon aging over 400°F.) G7 has extremely good dielectric loss properties under dry conditions and good electrical properties under humid conditions, although the percentage of change is high. G7 certifies to Mil-I-24768/17 GSG.
NEMA grade Glass-Mat Reinforced Polyester - GPO-1 (tan color), GPO-2 (red color) and GPO-3 (red color). These grades are composed of random mat (non-woven) fiberglass reinforcement held together by a polyester resin binder. Polyesters are versatile resins which handle much like epoxies. Of course, the basic resins are chemically different. It is their physical application forms which make them similar. Despite lower costs, the important disadvantages of polyesters, as compared with epoxies, is lower adhesion to most substrates, higher polymerization shrinkage, a greater tendency to crack during cure or in thermal shock and greater change of electrical properties in a humid environment. GPO-2 offers superior arc resistance over GPO-1 while GPO-3 offers both arc and track resistance. GPO-1 certifies to Mil-I-24768/4 GPO1, GPO-2 certifies to Mil-I-24768/5 GPO2 and GPO-3 certifies to Mil-I-24768/6 GPO3.
NEMA grades X, XX and XXX Paper Reinforced Phenolic - natural color is typically light tan to brown. These grades are composed of a paper base impregnated with a phenolic resin binder. (Phenolics are the oldest, best-known general purpose thermoset resins. They are among the lowest cost and easiest to process. Phenolics are quite adequate for a fair percentage of electrical applications. Generally speaking, they are not equivalent to epoxies in resistance to moisture, humidity, dimensional stability, shrinkage and retention of electrical properties in extreme environments.) The paper reinforced phenolic has good electric strength properties with fair mechanical strength and are outstanding for use as template material and/or backup material. A good rule of thumb in selecting a paper grade is to remember the more X's the better the electrical properties while the fewer X's represent superior mechanical properties. Paper grades can be modified by adding plasticizers to make them more conducive to part punching resulting in a P suffix added to the X designation, i.e., XP, XXP, XXXP. Grade X certifies to Mil-I-24768/12 PBM, grade XX to Mil-I-24768/11 PBG, and grade XXX to Mil-I-24768/10 PBE.
NEMA grades C and CE Canvas Cotton-Cloth Reinforced Phenolic - natural color is typically light tan to brown. These grades are composed of a continuous cotton woven cloth impregnated with a phenolic resin binder. (Phenolics are the oldest, best-known general purpose thermoset resins. They are among the lowest cost and easiest to process. Phenolics are quite adequate for a fair percentage of electrical applications. Generally speaking, they are not equivalent to epoxies in resistance to moisture, humidity dimensional stability, shrinkage, and retention of electrical properties in extreme environments.) These grades contain a medium weave canvas and are known primarily for their mechanical properties. These grades are not recommended for primary electrical insulation. Grade C certifies to Mil-I-24768/16 FBM; grade CE certifies to Mil-I-24768/14 FBG.
NEMA grades L and LE Linen Cotton-Cloth Reinforced Phenolic - natural color is typically light tan to brown. This grade is composed of a continuous cotton woven cloth impregnated with a phenolic resin binder. This grade contains a fine weave linen and, like the canvas phenolic, is known for its mechanical properties. The finer weave allows for machining more intricate details than canvas grade, such as gear teeth, etc. These grades are not recommended for primary electrical insulation but grade LE exhibits superior moisture resistance to grades L, C & CE and thus is an adequate insulator for a fair number of applications. Grade L certifies to Mil-I-24768/15 FBI; grade LE certifies to Mil-I-24768/13 FBE.