In 1906, Dr. Leo Bakeland experimented withthe polymerization of phenolic resins. He foundthat by adding formaldehyde and heat, a chemicalcross linkage took place; thermoset plastics wereborn. Soon after, it was discovered that cottoncloth and paper materials could be impregnatedwith this same mixture, semicured and then madeinto a stack of sheets or wrapped around a man-drel and subsequently put into a hydraulic presswhere heat and pressure could be applied. Fullpolymerization took place rendering hard, dense,reinforced thermoset plastics which today areknown as industrial laminates.

Simply put, thermoset plastics can be com-pared to cement, once cured they’re set, hence thename thermoset. Thermoplastics can be comparedmore to wax in-as-much as they can be remeltedand reshaped upon the reapplication of heat.However, one key resulting difference is that ther-moplastics lack the rigidity of thermoset lami-nates, as the tensile modulus of the followingmaterials indicate:

Graphite Epoxy (thermoset plastic) 40,000,000 psi

Steel (metal) 30,000,000 psi

Aluminum (metal) 10,000,000 psi

Glass Epoxy (thermoset plastic) 5,800,000 psi

Polycarbonate (thermoplastic) 450,000 psi

Thermoset Plastic IndustrialLaminates

Thermoset plastic industrial laminates are uniformly dense and structurally strong materialsthat will not soften appreciably under the reappli-cation of heat. They are extremely durable plasticsthat are lightweight and moisture resistant. Theyare thermoset plastic resin impregnated reinforc-ing substrate materials that are cured under heatand pressure to form solid shapes having high

mechanical and insulating properties. Industriallaminates are available in sheet, rod, tube andangle. Since these laminates are comprised of acombination of materials, they are also referred toas composites.

Thermoset plastic industrial laminates typical-ly have a layered construction with no fewer thantwo components:

The first is a reinforcing substrate such aswoven glass cloth, random glass mat, glass fila-ments, woven canvas cotton fabric, woven linencotton fabric, paper, woven aramid fabric, randommat aramid, woven graphite fabric, random matgraphite and others. The second is a thermosetplastic resin binder that serves to adhere

the layers of reinforcing substrates to each otherto form a solid unit. Resin binders include epox-ies, melamines, phenolics, polyesters, siliconesand others.

Unlike other groups of plastic materials, ther-moset plastic industrial laminates have their ownstandards which are published by NEMA(National Electrical Manufacturers Association).In concert with member manufacturers, NEMAstandards are set and “mininum values” published.The most commonly used NEMA thermoset laminate grades are as follows:

reinforcing substrateresin binder

T

INDUSTRIALLAMINATES

•Epoxy Grades

Melamine GradesSilicone Grades

Polyester GradesPhenolic

Paper GradesPhenolic

Cotton Grades•

Thermoset IndustrialLaminateProperties

•Manufacturing

Process•

Applications

TECHNICALREFERENCE

BL6

Headquarters, Mfg.18 Morris Place, Yonkers, NY 10705

Phone: 914-476-0700Fax: 914 / 476-0533www.acculam.com

Industrial Laminates“The Basics”prepared by Michael Stacey • Accurate Plastics, Inc. • Yonkers, New York

In a comprehensive way, I have attempted to cover the basics of industrial laminates.Thermoset plastic industrial laminates date back over 90 years, and much likeaspirin, industrial laminate is an old friend that continues to present new remediesfor today and tomorrow's toughest engineering headaches. Be sure to prescribeindustrial laminates to your customers...then call me in the morning. (wink!)

Thermoset Laminate Layered Construction

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Epoxy Grades

NEMA grades G10 and FR4 Glass-Cloth Reinforced Epoxy — natural color is

typically a yellowish to lightgreen. The most versatile all-around laminate grades arecontinuous glass woven fabricimpregnated with an epoxyresin binder. (Epoxy resins areamong the most versatile andwidely used plastics in the elec-tronics field, primarily because

water absorption is virtually nil, rendering it an outstanding insulator. Beyondits electrical insulating properties, epoxyresins exhibit superior adhesive propertiesand great dimensional stability — shrinkageis usually less than 1 percent). G10/FR4 hasextremely high mechanical strength, gooddielectric loss properties, and good electricstrength properties, both wet and dry. Themain difference between NEMA Grades G10and FR4 is that FR4 is a fire retardant gradeof G10. Therefore, FR4 can be safely substi-tuted where G10 is called out, while G10 cannever be substituted where FR4 is called for.(G10 certifies to Mil-I-24768/2 GEE; FR4 certifies to Mil-I-24768/27 GEE-F.)

NEMA grades G11 and FR5 Glass-Cloth Reinforced Epoxy — natural color is

typically yellow green toamber. This grade is similar toG10/FR4 with the addition ofa higher operating temperatureand some improved mechani-cal strength at elevated temper-atures. The main differencebetween NEMA Grades G11and FR5 is that FR5 is a fire

retardant grade of G11. Therefore, FR5 canbe safely substituted where G11 is called out,while G11 can never be substituted whereFR5 is called for. (G11 certifies to Mil-I-24768/3 GEB; FR5 certifies to Mil-I-24768/28 GEB-F.)

Melamine Grades

NEMA grades G5 and G9Glass-Cloth ReinforcedMelamine — natural color istypically a grayish brown.

These grades are composed of a continuousglass woven cloth base impregnated with amelamine resin binder. (Melamine resins,once cured, are the hardest, most rigid andabrasion resistant of the standard resins employed in the pro-duction of industrial laminates. However,

prolonged exposure to high temperature canadversely affect its mechanical and electricalstrength properties. Arc resistance, however,may remain unaffected despite excessive ther-mal exposure). Melamines are the hardest oflaminates, exhibiting good dimensional sta-bility and arc resistance. It’s also caustic resis-tant. A key difference between NEMAGrades G5 and G9 are that G9 is more resis-tant to the elements of the environment.Thus, G9 can be safely substituted where G5is called for. (G5 certifies to Mil-I-24768/8GMG; G9 certifies to Mil-I-24768/1 GME.)

Silicone Grade

NEMA grades G7 Glass-Cloth Rein -forced Silicone — natural color is typicallycream to white. Composed of a continuous

glass woven cloth base impreg-nated with a silicone resinbinder, this grade has excellentheat and arc resistance.

(Silicone thermosetting resins are among thebest of all polymer materials in resistance totemperature. Hence, silicone is broadly usedfor high temperature electronic applicationsrequiring low electrical losses. Silicone isn’t asstrong as epoxies and phenolics upon aging atlower temperatures but is stronger uponaging over 400°F). G7 has extremely gooddielectric loss properties under dry condi-tions and good electrical properties underhumid conditions, although the percentageof change is high. (G7 certifies to Mil-I-24768/17 GSG.)

Polyester Grades

NEMA grade GPO-1 (tan color), GPO-2(red color) and GPO-3 (red color) Glass-Mat Reinforced Polyester — These grades

are composed of random mat(non-woven) fiberglass rein-forcement held together by apolyester resin binder. (Poly -esters are versatile resins whichhandle much like epoxies. Ofcourse, the basic resins arechemically different. It’s theirphysical application forms

which make them similar. Despite lowercosts, the important disadvantages of poly-esters, as compared with epoxies, is loweradhesion to most substrates, higher polymer-ization shrinkage, a greater tendency to crackduring cure or in thermal shock and greaterchange of electrical properties in a humid environment). GPO-2 offers superi-or arc resistance over GPO-1 while GPO-3offers both arc and track resistance. (GPO-1certifies to Mil-I-24768/4 GPO1; GPO-2 certifies to Mil-I-24768/5 GPO2 and GPO-3certifies to Mil-I-24768/6 GPO3).

Phenolic Paper Grades

NEMA grades X, XX and XXX PaperReinforced Phenolic — natural color is

typically light tan to brown.These grades are composed of a paper base impregnatedwith a phenolic resin binder.(Phenolics are the oldest, best-known general purpose ther-moset resins. They are amongthe lowest in cost and easiest toprocess. Phenolics are quite ade-

quate for a fair percentage of electrical applica-tions. Generally speaking, they are not equiva-lent to epoxies in resistance to moisture,humidity, dimensional stability, shrinkage andretention of electrical properties in extremeenvironments). The paper reinforced phenolichas good electric strength properties with fairmechanical strength and are outstanding foruse as template material and/or back-up mate-rial. A good rule of thumb in selecting a papergrade is to remember the more X’s the betterthe electrical properties, while the fewer X’srepresent superior mechanical properties. Papergrades can be modified by adding plasticizersto make them more conducive to part punch-ing resulting in a P suffix added to the X desig-nation, i.e., XP, XXP, XXXP. (Grade X certifiesto Mil-I-24768/12 PBM; grade XX to Mil-I-24768/11 PBG and grade XXX to Mil-I-24768/10 PBE).

Accurate Plastics manufactures Acculam™ industrialthermoset laminate sheet, rod, tube, angle andchannel.

Phenolic Cotton Grades

NEMA grades C and CE CanvasCotton-Cloth Reinforced Phenolic — nat-

ural color is typically light tanto brown. C and CE grades arecomposed of a continuous cot-ton woven cloth impregnatedwith a phenolic resin binder.(Phenolics are the oldest, best-known general purpose ther-moset resins. They are amongthe lowest in cost and easiest to

process. Phenolics are quite adequate for afair percentage of electrical applications.

Generally speaking, they are not equivalentto epoxies in resistance to moisture, humidi-ty, dimensional stability, shrinkage and reten-tion of electrical properties in extreme envi-ronments). These grades contain a mediumweave canvas and are known primarily fortheir mechanical properties. These grades arenot recommended for primary electrical insu-lation. (Grade C certifies to Mil-I-24768/16FBM; grade CE certifies to Mil-I-24768/14FBG).

NEMA grades L and LE Linen Cotton-Cloth Reinforced Phenolic — naturalcolor is typically light tan to brown. This

grade is composed of a continuous cottonwoven cloth impregnated with a phenolicresin binder. This grade contains a fine weavelinen and, like the canvas phenolic; is knownfor its mechanical properties. The finer weaveallows for machining more intricate detailsthan canvas grade, such as gear teeth, etc.These grades are not recommended for pri-mary electrical insulation, but grade LEexhibits superior moisture resistance togrades L, C and CE, and thus is an adequateinsulator for a fair number of applications.(Grade L certifies to Mil-I-24768/15 FBI;grade LE certifies to Mil-I-24768/13 FBE).

THERMOSET INDUSTRIAL LAMINATE PROPERTIESMinimum Values

NEMA grades G10, FR4 G11, FR5 G5, G9 G7 GPO 1 GPO 3 X XX XXX C, CE L, LEProperties reinforcements glass cloth glass cloth glass cloth glass cloth glass mat glass mat paper paper paper canvas linen

resin binders epoxy epoxy HT melamine silicone polyester polyester phenolic phenolic phenolic phenolic phenolic

Tensile Strengthlengthwise, PSI 40,000 40,000 37,000 23,000 12,000 11,000 20,000 16,000 15,000 9,500 12,500crosswise, PSI 35,000 35,000 30,000 18,000 –– –– 16,000 13,000 12,000 7,500 8,750

Compressive Strengthflatwise, PSI 60,000 60,000 70,000 45,000 40,000 30,000 36,000 34,000 32,000 37,000 37,000

edgewise, PSI 35,000 35,000 25,000 14,000 –– –– 19,000 23,000 25,500 23,500 25,000

Flexural Strengthlengthwise, PSI 55,000 55,000 55,000 23,000 23,000 20,000 25,000 15,000 13,500 17,000 15,000crosswise, PSI 45,000 45,000 35,000 20,000 –– –– 22,000 14,000 11,800 15,000 13,750

Modulus of Elasticity in flex x10 -3

lengthwise, PSI 2,700 2,700 2,500 1,400 –– –– 1,800 1,400 1,300 950 1,050crosswise, PSI 2,200 2,200 2,000 1,200 –– –– 1,300 1,100 1,000 850 850

Shear Strength, PSI 19,000 19,000 20,000 17,000 –– –– 12,000 11,000 10,000 11,500 11,750

IZOD Impactflatwise, ft-lb/in of notch 7 7 12 8.5 –– –– 4 1.3 1 3.2, 2.3 2.5, 1.8

edgewise, ft-lb/in of notch 5.5 5.5 8 7.5 –– –– 0.5 0.35 0.35 1.9, 1.4 1.1, 1

Rockwell Hardness M scale 110 110 120 100 –– –– 110 105 110 104 105

Specific Gravity 1.82 1.82 1.9 1.68 1.8 1.85 1.36 1.34 1.32 1.35 1.34

Coefficient of Thermal Expansioncm/cm-°C x 10 -5 .9 .9 1 1 –– –– 6 2 1.4 2 2

Water Absorption.062” thick, % per 24 hrs 0.25 0.25 0.8 0.3 0.35 0.4 6 2 1.4 4.4, 2.2 2.5, 1.95.125” thick, % per 24 hrs 0.15 0.15 0.7 0.2 –– –– 3.3 1.3 0.95 2.5, 1.6 1.6, 1.3.500” thick, % per 24 hrs 0.10 0.10 0.4 0.15 –– –– 1.1 0.55 0.45 1.2, 0.75 0.9, 0.7

Dielectric Strength,volt/milperpendicular to laminations; short

.062” thick 500 500 400 400 370 400 700 700 650 200, 500 200, 500

.125” thick 400 400 350 350 –– –– 500 500 470 150, 360 150, 360

Dissipation Factorcondition A, 1 megacycle 0.025 0.025 0.017 0.003 –– –– 0.06 0.045 0.038 0.1, 0.055 0.1, 0.055

Dielectric Constantcondition A, 1 megacycle 5.2 5.2 7.12 4.2 –– –– 6 5.5 5.3 -, 5.8 -, 5.8

Insulation ResistanceCondition: 96 hours at 90% relative

humidity (in megaohms) 200,000 200,000 10,000 200,000 –– –– –– –– –– –– ––

Bond Strength, in lbs 2,000 1,600 1,700 650 –– –– 700 800 950 1,800 1,600

Max Operating Temperatureapproximate ° F continuous 285 300 285 465 265 265 285 285 285 265 265

sheet mil spec: Mil-I-24768 / _ _, 2, GEE 3, GEB 8, GMG 17 4 6 12 11 10 16, FBM 15, FBItype 27, GEE-F 28, GEB-F 1, GME GSG GPO1 GPO3 PBM PBG PBE 14, FBG 13, FBE

APPLICATIONSFOR THERMOSET

INDUSTRIALLAMINATES

Industrial laminates are used in the

following industries:

• Electronics

• Electrical

• Machinery

• Automotive and Trucking

• Metal Finishing

• Aviation

• Chemical

• Home Appliance

• Textile

Of these, the largest markets areelectrical and electronics, wherethermoset industrial laminates provide strong reliable insulatorsfor applications in :

• Relays • Switches

• Bus Bars • Standoffs

• Washers • Arc Shields

• Vanes • Test Board

• Panels • Sockets

• Coils • Fuses

• Motors • Generators

• Gaskets • Transformers

• Circuit • Condensers

Boards • Terminal Strips

These laminates, as a group, arethe hidden work horses in manyindustrial applications.

MANUFACTURING FLOW CHART

Resin

OvenDip Pan

Shear Sheet

Press

B Stage�Pallet

Tube

Tube Roller

Base�Mat’l

Manufacturing Process

Thermoset plastic industrial laminates areidentified in process by three stages A, B andC stages:

A-stage refers to the key raw materialsdescribed earlier – reinforcing substrates andresin binders.

B-stage refers to the product producedwhen reinforcing substrates and resin bindersare brought together but not cured. The rein-forcing substrate is unwound from a largemaster roll and dipped into a bath of lique-fied resin binder. The reinforcing substratebecomes either saturated, as is the case withabsorbent papers and cotton cloths, or coat-ed, as is the case with glass and graphitecloths. Once the wet resin binder is joinedwith the reinforcer substrate in this method,it is slowly drawn through a long convey-orized oven where the liquefied resin binder isdried. The result leaves dry semicured resinbinder in and/or on the reinforcing substrate.Once joined and dried in this fashion, theproduct is referred to as B-stage or prepreg,and the process described is called B-staging,prepreging or treating.

C-stage refers to sheet, rod, tube, angle orother in their “cured stage.”

• Sheets — B-stage is sheeted into plysthen laid on top of each other into predeter-mined stacks that will render a given thick-ness. These stacks are placed into thehydraulic laminating press between two flatsurfaces and pressure is applied. While underpressure, heat is introduced to begin the bakecycle. The resin in the B-stage product is re-activated by the heat to a sticky state which

moves slowly, filling and bonding the layerstogether until it eventually hardens and cures.Once plys bond to each other and cure theyare referred to as C-stage laminate sheet andthe process described is called laminating orpressing.

• Rods — the B-stage is convolutelywrapped under tension onto itself, much likea roll of paper towels is wound. Once the B-stage is rolled to form a rod, it is placed intoa laminating press which has upper and lowerhalf round mold cavities. When the two halfround molds close and meet each other a fullround is formed. The size of the mold cavitydetermines the diameter of the finished rod.Once pressure is applied, the layers arepressed together filling all voids. Similar pres-sures and heat cycles employed for makingsheet are used. When the layers bond to eachother and cure, they are referred to as C-stagelaminate rod or rolled and molded rod.

• Tubes — rolling tubes are nearly identi-cal to rolling rods with the exception that asteel rod called a mandrel is employed to sizeand form the inside diameter of the tube. B-stage rolled tubes are usually placed into anoven chamber as opposed to a press. Tubebake cycles compare to those of sheet and rod.Once cured, the center mandrel is extracted.The final cured product is referred to as C-stage laminate tube or rolled tube.

• Angles — this process is nearly identicalto that of sheets except the mold cavities are“V” shaped rather than flat surfaces. The finalcured product is referred to as C-stage lami-nate angle or molded angle.

• Other shapes — once cured, the endproduct is referred to as C-stage.

West VirginiaPO Box 2287, Weirton, WV 26062

Phone: 914-476-0700 • Fax 304-723-1625

New York18 Morris Place, Yonkers, NY 10705

Phone: 914-476-0700 • Fax 914-476-0533

Massachusetts33 Tech Park Drive, Falmouth, MA 02536Phone: 914-476-0700 • Fax 508-457-9275

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