Handbook of Materials for Product Design Part 9 pdf

Elastomeric Materials and Processes 6.83 6.16 Natural Rubber (NR) Natural rubber, the original elastomer, still plays an important role among elastomers. Worldwide consumption of NR in 2000 is expected to be about 7 million metric tons/y, based on earlier reporting by the International Rubber Study Group. Chemically, natural rubber is cis1,4-polyisoprene and occurs in Hevea rubber trees. NR tapped from other rubber trees (gutta-percha and balata) is the trans isomer of polyisoprene. 23 NR’s principal uses are automotive tires, tire tread, and mechanical goods. Automotive applications are always com- pounded with carbon black to impart UV resistance and to increase mechanical properties. 10d Latex concentrate is used for dipped goods, adhesives, and latex thread. 23 Latex concentrate is produced by cen- trifuge-concentrating field latex tapped from rubber trees. The dry rubber content is subsequently increased from 30 to 40 to 60% mini- mum. 23 Vulcanization is the most important NR chemical reaction. 23 Most applications require cross-linking via vulcanization to increase resil- iency and strength. Exceptions are crepe rubber shoe soles and rubber cements. 23 There are a number of methods for sulfur vulcanization, with certain methods producing polysulfidic cross-linking and other methods producing more monosulfidic cross-links. 10d NR is imported from areas such as Southeast Asia to the world’s most industrial regions, North America, Europe, and Japan, since it is not indigenous to these regions. The huge rubber trees require about 80 to 100 in/y (200 to 250 cm/y) rainfall, and they flourish at an alti- tude of about 1000 ft (300 m). 23 As long as NH is needed for tires, in- dustrial regions will be import dependent. NR has good resilience; high tensile strength; low compression set; resistance to wear and tear, cut-through and cold flow; and good elec- tricalproperties. 10a Resilience is the principal property advantage compared with synthetic rubbers. 10a For this reason, NH is usually used for engine mounts, because NR isolates vibrations caused when an engine is running. NH is an effective decoupler, isolating vibrations such as engine vibration from being transmitted to another location such as the passenger compartment. 10d With decoupling, vibration is returned to its source instead of being transmitted through the rub- ber. 10d Polychloroprene is used for higher under-hood temperatures above NR service limits; butyl rubber is used for body mounts and for road vibration frequencies, which occur less frequently than engine vi- brations or have low energy; EPDM is often used for molded rubber bumpers and fillers throughout the vehicle, such as deck-lid over-slam bumpers. 06bMargolis Page 83 Wednesday, May 23, 2001 10:13 AM 6.84 Chapter 6, Part 2 Degree of crystallinity (DC) can affect NH properties, and milling reduces MW. MW is reduced by mastication, typically with a Banbury mill, adding a peptizing agent during milling to further reduce MW, which improves NR solubility after milling. 23 NR latex grades are pro- vided to customers in low (0.20 wt %) and high (0.75 wt %), with am- monia added as a preservative. 23 Low NH 4 has reduced odor and eliminates the need for deammoniation. 23 Properties of polymers are improved by compounding with enhanc- ing agents (additives), and NR is not an exception. Compounding NR with property enhancers improves resistance to UV oxygen, and ozone, but formulated TPEs and synthetic rubbers overall have better resistance than compounded NR to UV, oxygen, and ozone. 10a NR does not have satisfactory resistance to fuels, vegetable, and animal oils, while TPEs and synthetic rubbers can possess good resistance to them. 10a NR has good resistance to acids and alkalis. 10a It is soluble in aliphatic, aromatic, and chlorinated solvents, but it does not dissolve easily because of its high MW. Synthetic rubbers have better aging properties; they harden over time, while NR softens over time (see Ta- ble 6.28). 10a There are several visually graded latex NRs, including ribbed smoked sheets (RSS) and crepes such as white and pale, thin and thick brown latex, etc. 23 Two types of raw NR are field latex and raw coagu- lum, and these two types comprise all NR (“downstream”) grades. 23 TABLE 6.28 Typical Thermal and Electrical Property Profile of NR 23 Property Value Specific gravity @ 32°F (0°C) @ 68°F (20°C) T g , °F (°C) Specific heat Heat of combustion, cal/g (J/g) Thermal conductivity, (BTU-in) (h-ft 2 -°F) W/(m ⋅ K) Coefficient of cubical expansion, in 3 /°C Dielectric strength, V/mm Dielectric constant Power factor @ 1000 cycles Volume resistivity, Ω ⋅ cm Cohesive energy density, cal/cm 3 (J/cm 3 ) Refractive index 68°F (20°C) RSS * 68°F (20°C) pale crepe * RSS = ribbed smoked sheet. 0.950 0.934 –98 (–72) 0.502 10,547 (44,129) 0.90 0.13 0.00062 3.937 2.37 0.15–0.20 1015 64 (266.5) 1.5192 1.5218 06bMargolis Page 84 Wednesday, May 23, 2001 10:13 AM Elastomeric Materials and Processes 6.85 Depolymerized NR is used as a base for asphalt modifiers, potting compound, and cold-molding compounds for arts and crafts. 10b 6.17 Conclusion Producers can engineer polymers and copolymers, and compounders can formulate recipes for a range of products that challenges the de- signers’ imaginations. Computer variable-controlled machinery, tools, and dies can meet the designers’ demands. Processing elastomeric ma- terials is not as established as the more traditional thermoplastic and thermosetting polymers. Melt rheology, more than just viscosity, is the central differentiating characteristic for processing elastomeric mate- rials. Processing temperature and pressure settings are not fixed ranges; they are dynamic, changing values from the hopper to the demolded product. Operators and management of future elastomeric materials processing plants will be educated to the finesse of melt pro- cessing these materials. Elastomeric materials industries, welcome to the twenty-first century. References 1. James M. Margolis, “Elastomeric Polymers 2000 to 2010: Properties, Processes and Products” Report, 2000. 2. K RATON Polymers and Compounds, Typical Properties Guide, Shell Chemical Com- pany, Houston, Texas, 1997. 3. Products, Properties and Processing for PELLETHANE Thermoplastic Polyure- thane Elastomers, Dow Plastics, The Dow Chemical Company Midland, Michigan, ca. 1997. 4. Modern Plastics Encyclopedia ’99, McGraw-Hill, New York, 1999, pp. B-51, B-52. 5. Engage, A Product of DuPont Dow Elastomers, Wilmington, Delaware, December 1998. 6. Product Guide, Goodyear Chemical, Goodyear Tire & Rubber Company, Akron, Ohio, October 1996. 7. Injection Molding Guide for Thermoplastic Rubber–Processing, Mold Design, Equipment, Advanced Elastomer Systems LP, Akron, Ohio, 1997. 8. Santoprene Rubber Physical Properties Guide, Advanced Elastomer Systems LP, Akron, Ohio, ca. 1998. 9. Hifax MXL 55A01 (1998), FXL 75A01 (1997) and MXL 42D01 Developmental Data Sheets secured during product development and subject to change before final com- mercialization. Montell Polyolefins Montell North America Inc., Wilmington, Dela- ware. 10. Charles B. Rader, “Thermoplastic Elastomers,” in Handbook of Plastics, Elas- tomers, and Composites, 3d ed., Charles A. Harper, ed., McGraw-Hill, New York, 1996. 10a. Joseph F. Meier, “Fundamentals of Plastics and Elastomers,” in Handbook of Plas- tics, Elastomers, and Composites, 3d ed., Charles A. Harper, ed., McGraw-Hill, New York, 1996. 10b. Leonard S. Buchoff, “Liquid and Low-Pressure Resin Systems,” in Handbook of Plastics, Elastomers, and Composites, 3d ed., Charles A. Harper, ed., McGraw-Hill, New York, 1996. 06bMargolis Page 85 Wednesday, May 23, 2001 10:13 AM 6.86 Chapter 6, Part 2 10c. Edward M. Petrie. “Joining of Plastics, Elastomers, and Composites,” in Handbook of Plastics, Elastomers, and Composites, 3d ed., Charles A. Harper, ed., McGraw- Hill, New York, 1996. 10d. Ronald Toth, “Elastomers and Engineering Thermoplastics for Automotive Appli- cations,” in Handbook of Plastics, Elastomers, and Composites, 3d ed., Charles Harper, ed., McGraw-Hill, New York, 1996. 11. Aflas TFE Elastomers Technical Information and Performance Profile Data Sheets, Dyneon LLC, A 3M-Hoechst Enterprise, Oakdale, Minnesota, 1997. 12. Vistalon User’s Guide, Properties of Ethylene-Propylene Rubber, Exxon Chemical Company, Houston, Texas, Division of Exxon Corporation, ca. 1996. 13. K RATON Liquid L-2203 Polymer, Shell Chemical Company, Houston, Texas, 1997. 14. Affinity Polyolefin Plastomers, Dow Plastics, The Dow Chemical Company, Mid- land, Michigan, 1997. 14a. Affinity HF-1030 Data Sheet, Dow Plastics, The Dow Chemical Company Midland, Michigan, 1997. 14b. Affinity PF 1140 Data Sheet, Dow Plastics, The Dow Chemical Company Midland, Michigan, 1997. 15. Bayer Engineering Polymers Properties Guide, Thermoplastics and Polyure- thanes, Bayer Corporation, Pittsburgh, Pennsylvania, 1998. 16. Rubber World Magazine, monthly, 1999. 17. Jim Ahnemiller, “PU Rubber Outsoles for Athletic Footwear,” Rubber World, De- cember 1998. 18. Charles D. Shedd, “Thermoplastic Polyolefin Elastomers,” in Handbook of Thermo- plastic Elastomers, 2d ed., Benjamin M. Walker and Charles P. Rader, eds., Van Nostrand Reinhold, New York, 1988. 18a. Thomas W. Sheridan, “Copolyester Thermoplastic Elastomers,” Handbook of Ther- moplastic Elastomers, 2d ed., Benjamin M. Walker and Charles P. Rader, eds., Van Nostrand Reinhold, New York, 1988. 18b. William J. Farrisey “Polyamide Thermoplastic Elastomers,” in Handbook of Ther- moplastic Elastomers, 2d ed., Benjamin M. Walker and Charles P. Rader, eds., Van Nostrand Reinhold, New York, 1988. 18c. Eric C. Ma, “Thermoplastic Polyurethane Elastomers, in Handbook of Thermoplas- tic Elastomers, 2d ed., Benjamin M. Walker and Charles P. Rader, eds., Van Nos- trand Reinhold, New York, 1988. 19. N. R. Legge, G. Holden, and H. E. Schroeder, eds., Thermoplastic Elastomers, A Comprehensive Review, Hanser Publishers, Munich, Germany, 1987. 20. P S. Ravisbanker, “Advanced EPDM for W & C Applications,” Rubber World, De- cember 1998. 21. Junling Zbao, G. N. Chebremeskel, and J. Peasley “SBR/PVC Blends With NBR As Compatibilizer,” Rubber World, December 1998. 22. John E. Rogers and Walter H. Waddell, “A Review of Isobutylene-Based Elas- tomers Used in Automotive Applications,” Rubber World, February 1999. 23. Kirk-Othmer Concise Encyclopedia of Chemical Technology, John Wiley & Sons, New York, 1999. 24. PetroChemical News (PCN), weekly, William F. Bland Company Chapel Hill, North Carolina, September 14,1998. 25. PeroChemical News (PCN), weekly, William F. Bland Company, Chapel Hill, North Carolina, 1998 and 1999. 26. PetroChemical News (PCN), weekly William F. Bland Company, Chapel Hill, North Carolina, February 22, 1999. 27. C. P. J. van der Aar, et al., “Adhesion of EPDMs and Fluorocarbons to Metals by Using Water-Soluble Polymers,” Rubber World, November 1998. 28. Larry R. Evans and William C. Fultz, “Tread Compounds with Highly Dispersible Silica,” Rubber World, December 1998. 29. Vector Styrene Block Copolymers, Dexco Polymers, A Dow/Exxon Partnership, Houston, Texas, 1997. 30. Fluoroelastomers Product Information Manual (1997), Product Comparison Guide (1999), Dyneon LLC, A 3M-Hoechst Enterprise, Oakdale, Minnesota, 1997. 06bMargolis Page 86 Wednesday, May 23, 2001 10:13 AM Elastomeric Materials and Processes 6.87 31. Engel data sheets and brochures, Guelph, Ontario, 1998. 32. Catalloy Process Resins, Montell Polyolefins, Wilmington, Delaware. 32a. Catalloy Process Resins, Montell Polyolefins, Wilmington, Delaware, p.7. 33. EniChem Europrene SOL T Thermoplastic Rubber, styrene butadiene types, sty- rene isoprene types, EniChem Elastomers Americas Inc., Technical Assistance Laboratory, Baytown, Texas. 34. “Arnitel Guidelines for the Injection Molding of Thermoplastic Elastomer TPE-E,” DSM Engineering Plastics, Evansville, Ind., ca, 1998. 35. Correspondence from DuPont Engineering Polymers, July 1999. 36. Correspondence from DuPont Dow Elastomers, Wilmington, Delaware, August 1999. 06bMargolis Page 87 Wednesday, May 23, 2001 10:13 AM 7.1 7 Ceramics and Ceramic Composites Dr. Jerry E. Sergent TCA, Inc. Corbin, Kentucky 7.1 Introduction Ceramics are crystalline in nature, with a dearth of free electrons. They have a high electrical resistivity, are very stable (chemically and thermally), and have a high melting point. They are formed by the bonding of a metal and a nonmetal and may exist as oxides, nitrides, carbides, or silicides. An exception is diamond, which consists of pure carbon subjected to high temperature and pressure. Diamond sub- strates meet the criteria for ceramics and may be considered as such in this context. The primary bonding mechanism in ceramics is ionic bonding. An ionic bond is formed by the electrostatic attraction between positive and negative ions. Atoms are most stable when they have eight elec- trons in the outer shell. Metals have a surplus of electrons in the outer shell, which are loosely bound to the nucleus and readily become free, creating positive ions. Similarly, nonmetals have a deficit of electrons in the outer shell and readily accept free electrons, creating negative ions. Figure 7.1 illustrates an ionic bond between a magnesium ion with a charge of +2 and an oxygen ion with a charge of –2, forming magnesium oxide (MgO). Ionically bonded materials are crystalline in nature and have both a high electrical resistance and a high relative dielectric constant. Due to the strong nature of the bond, they have a high melting point and do not readily break down at elevated temper- atures. By the same token, they are very stable chemically and are not attacked by ordinary solvents and most acids. 07Sergent Page 1 Wednesday, May 23, 2001 10:14 AM 7.2 Chapter 7 A degree of covalent bonding may also be present, particularly in some of the silicon and carbon-based ceramics. The sharing of elec- trons in the outer shell forms a covalent bond. A covalent bond is de- picted in Fig. 7.2, illustrating the bond between oxygen and hydrogen to form water. A covalent bond is also a very strong bond and may be present in liquids, solids, or gases. Figure 7.1 Magnesium oxide ionic bond. Figure 7.2 Covalent bond between oxygen and hydrogen to form water. 07Sergent Page 2 Wednesday, May 23, 2001 10:14 AM Ceramics and Ceramic Composites 7.3 A composite is a mixture of two or more materials that retain their original properties but, in concert, offer parameters that are superior to either. Composites in various forms have been used for centuries. Ancient peoples, for example, used straw and rocks in bricks to in- crease their strength. Modern day structures use steel rods to rein- force concrete. The resulting composite structure combines the strength of steel with the lower cost and weight of concrete. Ceramics are commonly used in conjunction with metals to form composites for electronic applications, especially thermal manage- ment. Ceramic-metal (cermet) composites typically have a lower TCE than metals, possess a higher thermal conductivity than ceramics, and are more ductile and more resistant to stress than ceramics. These properties combine to make cermet composites ideal for use in high-power applications. This chapter considers the properties of ceramics used in microelec- tronic applications, including aluminum oxide (alumina, Al 2 O 3 ), beryl- lium oxide (beryllia, BeO), aluminum nitride (AlN), boron nitride (BN), diamond (C), and silicon carbide (SiC). Several composite mate- rials, aluminum silicon carbide (AlSiC) and Dymalloy, a diamond/cop- per structure, are also described. Although the conductive nature of these materials prevents them from being used as a conventional sub- strate, they have a high thermal conductivity and may be used in ap- plications where the relatively low electrical resistance is not a consideration. 7.2 Ceramic Fabrication It is difficult to manufacture ceramic substrates in the pure form. The melting point of most ceramics is very high, as shown in Table 7.1, and most are also very hard, limiting the ability to machine the ceramics. For these reasons, ceramic substrates are typically mixed with fluxing and binding glasses, which melt at a lower temperature and make the finished product easier to machine. The manufacturing process for Al 2 O 3 , BeO, and AlN substrates is very similar. The base material is ground into a fine powder, several microns in diameter, and mixed with various fluxing and binding glasses, including magnesia and calcia, also in the form of powders. An organic binder, along with various plasticizers, is added to the mix- ture, and the resultant slurry is ball-milled to remove agglomerates and to make the composition uniform. The slurry is formed into a sheet, the so-called green state, by one of several processes as shown in Fig. 7.3 1 and sintered at an elevated temperature to remove the organics and to form a solid structure. 07Sergent Page 3 Wednesday, May 23, 2001 10:14 AM 7.4 Chapter 7 Roll compaction. The slurry is sprayed onto a flat surface and par- tially dried to form a sheet with the consistency of putty. The sheet is fed through a pair of large parallel rollers to form a sheet of uniform thickness. Tape casting. The slurry is dispensed onto a moving belt that flows under a knife-edge to form the sheet. This is a relatively low-pressure process compared to the others. Powder pressing. The powder is forced into a hard die cavity and subjected to very high pressure (up to 20,000 psi) throughout the sin- TABLE 7.1 Melting Points of Selected Ceramics Material Melting point, °C SiC 2700 BN 2732 AlN 2232 BeO 2570 Al 2 O 3 2000 Figure 7.3 Flow chart for ceramic substrate processing. 07Sergent Page 4 Wednesday, May 23, 2001 10:14 AM Ceramics and Ceramic Composites 7.5 tering process. This produces a very dense part with tighter as-fired tolerances than other methods, although pressure variations may pro- duce excessive warpage. Isostatic powder pressing. This process utilizes a flexible die sur- rounded with water or glycerin and compressed with up to 10,000 psi. The pressure is more uniform and produces a part with less warpage. Extrusion. The slurry, less viscous than for other processes, is forced through a die. Tight tolerances are hard to obtain, but the pro- cess is very economical and produces a thinner part than is attainable by other methods. In the green state, the substrate is approximately the consistency of putty and may be punched to the desired size. Holes and other geome- tries may also be punched at this time. Once the part is formed and punched, it is sintered at a temperature above the glass melting point to produce a continuous structure. The temperature profile is very critical, and the process may actually be performed in two stages: one stage to remove the volatile organic ma- terials and a second stage to remove the remaining organics and to sinter the glass/ceramic structure. The peak temperature may be as high as several thousand degrees celsius and may be held for several hours, depending on the material and the type and amount of binding glasses. For example, pure alumina substrates formed by powder pro- cessing with no glasses are sintered at 1930°C. It is essential that all the organic material be removed prior to sin- tering. Otherwise, the gases formed by the organic decomposition may leave serious voids in the ceramic structure and cause serious weaken- ing. The oxide ceramics may be sintered in air. In fact, it is desirable to have an oxidizing atmosphere to aid in removing the organic materi- als by allowing them to react with the oxygen to form CO 2 . The nitride ceramics must be sintered in the presence of nitrogen to prevent ox- ides of the metal from being formed. In this case, no reaction of the or- ganics takes place; they are evaporated and carried away by the nitrogen flow. During sintering, a degree of shrinkage takes place as the organic is removed and the fluxing glasses activate. Shrinkage may range from as low as 10% for powder processing to as high as 22% for sheet cast- ing. The degree of shrinkage is highly predictable and may be consid- ered during design. Powder pressing generally forms boron nitride substrates. Various silica and/or calcium compounds may be added to lower the processing temperature and improve machinability. Diamond substrates are typi- cally formed by chemical vapor deposition (CVD). Composite sub- strates, such as AlSiC, are fabricated by creating a spongy structure of SiC and forcing molten aluminum into the crevices. 07Sergent Page 5 Wednesday, May 23, 2001 10:14 AM [...]... Conductivity of Alumina Substrates with Different Concentrations of Alumina Volume percentage of alumina Thermal conductivity, W/m-°C 85 16.0 90 16.7 94 22.4 96 24.7 99 .5 28.1 100 31.0 kT = P1 k1 + P2 k2 (7.5) where kT = net thermal conductivity P1 = volume percentage of material one in decimal form k1 = thermal conductivity of material one P2 = volume percentage of material two in decimal form k2 = thermal... Density, GPa MPa MPa MPa MPa g/cm3 Alumina (99 %) 370 500 2600 386 352 3 .98 Alumina (96 %) 344 172 2260 341 331 3 .92 Beryllia (99 .5%) 345 138 1550 233 235 2.87 43 2410 6525 800 Aluminum nitride 300 310 2000 300 2 69 3.27 Silicon carbide 407 197 4400 470 518 3.10 1000 1200 11000 94 0 1000 3.52 Boron nitride (normal) Diamond (type IIA) 7.5.2 53.1 1 .92 Modulus of Rupture Ordinary stress-strain testing is... modulus of rupture in n/m2 Fr = force at rupture The modulus of rupture for selected ceramics is shown in Table 7.5 7.5.3 Tensile and Compressive Strength A force applied to a ceramic substrate in a tangential direction may product tensile or compressive forces If the force is tensile, in a direction such that the material is pulled apart, the stress produces plastic deformation as defined in Equation (7 .9) ... where (7. 19) F = coefficient of thermal endurance P = tensile strength in MPa α = thermal coefficient of expansion in 1/K Y = modulus of elasticity in MPa k = thermal conductivity in W/m-K ρ = density in kg/m3 c = specific heat in W-s/kg-K The coefficient of thermal endurance for selected materials is shown in Table 7 .9 The phenomenally high coefficient of thermal endurance for BN is primarily a result of the... increases, the number of collisions increases, and the thermal conductivity of most materials decreases A plot of the thermal conductivity vs temperature for several materials is shown in Fig 7 .9. 3 One material not plotted in this graph is diamond The thermal conductivity of diamond varies widely with composition and the method of preparation, and it is much higher than those materials listed Diamond... which lists the thermal conductivity of alumina as a function of the percentage of glass Although the thermal conductivity of the glass binder is lower than that of the alumina, the drop in thermal conductivity is greater than expected from the addition of the glass alone If the thermal conductivity is a function of the ratio of the materials alone, it follows the rule of mixtures 07Sergent Page 11 Wednesday,... result of the high tensile strength to modulus of elasticity ratio as compared to other materials Diamond is also high, primarily due to the high tensile strength, the high thermal conductivity, and the low TCE TABLE 7 .9 Thermal Endurance Factor for Selected Materials at 25°C Material Thermal endurance factor Alumina (99 %) 0.640 Alumina (96 %) 0.234 Beryllia (99 .5%) 0.225 Boron nitride (“a” axis) 648 Aluminum... result of an increase in the vibrational energy of the atoms when heated, and the specific heat of most materials increases with temperature up to a temperature called the Debye temperature, at which point it becomes essentially independent of temperature The specific heat of several common ceramic materials as a function of temperature is shown in Fig 7.10 The heat capacity, C, is similar in form, except... similar in form, except that it is defined in terms of the amount of heat required to raise the temperature of a mole of material by one degree and has the units of watt-s/mol-°C 7.4.3 Temperature Coefficient of Expansion The temperature coefficient of expansion (TCE) arises from the asymmetrical increase in the interatomic spacing of atoms as a result of increased heat Most metals and ceramics exhibit... (@ 1 MHz) 9. 0 10.8 0.0002 Alumina (96 %) 25°C 500°C 1000°C >1014 4 × 1 09 1 × 106 8.3 Alumina (99 .5%) 25°C 500°C 1000°C >1014 2 × 1010 2 × 106 8.7 9. 4 10.1 0.0001 Beryllia 25°C 500°C >1014 2 × 1010 6.6 6.4 6 .9 0.0001 0.0004 Boron nitride Silicon carbide * Diamond (Type II) >1013 14 8 .9 0.0004 >10 Aluminum nitride 14 61 4.1 0.0003 >10 13 >10 14 0.7 40 1000 5.7 0.05 0.0006 * Depends on method of preparation; . 199 8. 29. Vector Styrene Block Copolymers, Dexco Polymers, A Dow/Exxon Partnership, Houston, Texas, 199 7. 30. Fluoroelastomers Product Information Manual ( 199 7), Product Comparison Guide ( 199 9),. Michigan, ca. 199 7. 4. Modern Plastics Encyclopedia 99 , McGraw-Hill, New York, 199 9, pp. B-51, B-52. 5. Engage, A Product of DuPont Dow Elastomers, Wilmington, Delaware, December 199 8. 6. Product Guide,. LP, Akron, Ohio, ca. 199 8. 9. Hifax MXL 55A01 ( 199 8), FXL 75A01 ( 199 7) and MXL 42D01 Developmental Data Sheets secured during product development and subject to change before final com- mercialization.