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Demanding electronics spark resin development.

New engineering resin families and improvements in existing ones are staying a step ahead of the need for better processing and performance.

Plastics parts for electrical/electronics applications are growing more complex and pushing the limits of today's material properties. New families of engineering polymers are rising to the challenge with higher performance, easier and faster processing, and lower cost for applications from connectors and switches to circuit breakers and electrical enclosures. This trend is especially evident in connectors, where new product generations require longer flow, finer pitches, and thinner walls. According to one LCP supplier, typical pitch tolerances will decrease from the present 50 mils to 25 mils by the end of the decade, and wall thicknesses may drop below 10 mils.

Thinner walls and tighter tolerances increase demands on resin performance as well as processability. For example, increasing circuit density of semiconductor devices leads to higher heat loads.

Developments in engineering thermoplastics are keeping pace with escalating product requirements. Several brand-new polymers are currently being commercialized or will hit the market in the next 12-18 months. They're expected to bring improved processing and performance at costs competitive with those of existing resins. The same dynamics of cost and performance hold true for established engineering polymers from PPS to nylons and polyesters, all of which are jockeying for competitive position behind LCPs.

There's also news in conductive formulations for semiconductor manufacturing and other electronic uses. Greater emphasis is being placed on inherently and permanently conductive polymers, especially for clean-room uses.

BRAND-NEW RESIN FAMILIES

Several new engineering-resin families offer intriguing combinations of properties for E/E applications, including high heat resistance, dimensional stability, and processability.

Aliphatic polyketones are one brand-new semicrystalline resin category (see PT, March '95, p. 11). Shell Chemical announced commercialization of its Carilon polymers late last year, and a second family of aliphatic polyketones is under development in the U.K. by BP Chemicals and GE Plastics (PT, May '96, p. 69). Shell says Carilon is distinguished from other resins by its combination of good toughness, moisture resistance, and outstanding resistance to a broad range of chemicals and solvents. It also can be flame retarded with low levels of additives that don't contain halogens or red phosphorus. It's available in neat, high-flow, and reinforced grades (Table 1). Although Carilon's developmental price is $3.50/lb, commercial pricing will be more competitive [TABULAR DATA FOR TABLE 1 OMITTED] with polyesters and nylons, Shell says. Initial applications will include connectors and electromechanical devices such as bobbins and switch gears, plus components of business machines and household batteries.

Because Carilon polymers have good hydrolysis resistance, they need less drying before processing. They also reportedly have excellent flowability for thin-wall parts and can be processed with short cycles. The standard injection molding grade has a melt flow index of 6 g/10 min at 464 F. A high-flow grade has an MFI 10 times higher. Low moisture absorption and isotropic shrinkage give the material good dimensional stability. Future developments will include grades with improved balance of stiffness and toughness, higher heat resistance, and improved barrier properties.

Two developmental resin families from Dow Plastics are also targeting E/E markets. One is a new type of amorphous polycarbonate copolymer to be sold under the name Inspire when it is commercialized next year (PT, Jan. '96, p. 13). New-business development manager Scott Moore says Inspire will find a niche in E/E applications requiring a combination of high heat resistance, ignition resistance, and good transparency. Dimensional stability is another benefit. Typical applications will include lighting reflectors, fuses, transparent connectors, and chip carriers. Inspire's three grades are expected to be rated UL94 V-0 and 5V for flammability. The line includes two grades comparable in heat resistance to polyetherimide (GE's Ultem) and polysulfone, while offering easier flow and better transparency. The Inspire grades are expected to sell for 25-30% less than those competing resins. The third Inspire grade, with lower heat resistance than the other two, will be priced slightly above standard PC (Table 2).

Complementing the amorphous polymer is Dow's new semicrystalline syndiotactic polystyrene (SPS). It offers a potential fit in E/E uses and will compete against a range of resins from LCP to PCT polyester, says E/E market-development manager Mike Szabo. Key properties of SPS include low moisture absorption and good chemical resistance, dimensional stability, and electrical properties, he says. It also has a melt viscosity comparable to commonly used grades of LCP. SPS will offer potential processing advantages such as lower fill pressures than PCT and PBT. It is hot-water moldable and produces less flash than PPS. Dow plans to offer SPS in general-purpose, flame-retardant, and 30-40% filled grades. Preliminary properties for filled grades include an HDT of 480 F (making it suitable for infrared reflow soldering conditions) and water absorption of 0.01%. Specific gravity is relatively low, ranging from 1.42 to 1.47 for flame-retardant grades. Mold shrinkage of the 30% filled grade is comparable to PCT and PBT; that of the 40% grade is comparable to PPS. SPS is expected to be priced competitively with comparable materials.

SPS is being produced in limited quantities at Dow's pilot plant in Midland, Mich. Idemitsu Petrochemicals, Dow's development partner, will open a market-development plant in Japan later this year.

A new PET moldable composite sheet (MCS) for compression molding has been developed by DuPont Engineering Polymers (Table 3). MCS contains long strands of randomly oriented glass fibers. MCS is available in both insulating and conductive grades, and the type of reinforcing fibers and orientation and loading can be tailored for specific applications. Conductivity is achieved with proprietary nonmetallic additives. DuPont says it is feasible to produce parts with both conductive and insulating MCS layers in a one-step process.

One potentially major application for MCS is encapsulating large transformers (1 to 100 kVA or more). Thermoplastic encapsulation offers advantages over thermoset epoxies, eliminating VOC emissions and long cure times. DuPont says the large encapsulating job (e.g., 4.4 lb of MCS for a 3-kVA transformer) would involve prohibitive expense for molds and machinery if injection molding were used. Also, experiments reportedly show that injection-molded thermoplastic encapsulation is unlikely to survive the heat cycles of up to 392 F that are typical of large transformers. Compression-moldable MCS has been successfully used by DuPont to insulate a 3-kVA transformer with SC125 and SC140 grades to encapsulate the metal core and windings. In a concept still under development, the core and windings are then overmolded with a thermally and electrically conductive SC500 layer, which includes carbon additives. The result is said to be an environmentally protected transformer that is stable when heat cycled.

A new family of metallocene-catalyzed cyclic-olefin copolymers (COCs) is being developed jointly by Hoechst AG in Germany and Mitsui Petrochemicals in Japan (PT, July '95, p. 13). Hoechst Technical Polymers in the U.S. is evaluating these materials, trade-named Topas, for the North American E/E market. The COC family is composed of at least four grades that are distinguished [TABULAR DATA FOR TABLE 3 OMITTED] primarily by their heat resistance (Table 4). Commercial pricing is expected to be competitive with polycarbonate. Hoechst identifies optical-storage media, capacitor films, and lighting lenses and diffusers as potential applications.
TABLE 2 - ADVANCED COPOLYCARBONATE RESINS


 Resin Resin Resin
Properties 170 190 220


Glasss Transition Temp., F 336 374 428


Heat-Deflection Temp.
 66 psi, F (unannealed) 311 347 401


Specific Gravity 1.2 1.2 1.2


Relative Temp. Index,
Mechanical, F 275 293 338


UL 94 Class., 0.125 in. V-2/V-0 V-0/5V V-0/5V


Notched Izod Impact,
ft-lb/in. 12 2 2
Yellowness Index, % 3 6 12


DEVELOPMENTS IN LCPS

Reducing the cost of liquid-crystal polymers (LCPs) is a continuing goal of resin suppliers. As a step in that direction, Hoechst Technical Polymers recently obtained UL approval for use of 50% regrind with the principal grades of Vectra A-, K-, and E-Series LCPs. The company also plans to introduce a slightly less expensive LCP grade this fall, priced about 5% below its Vectra A-130 while maintaining very similar properties. Last summer, the company brought out two Vectra K-Series grades priced about 15% below Vectra A-130 but with moderately reduced toughness (PT, Aug. '95, p. 46). However, the more highly glass-filled K-140 version offered faster cycle times, further [TABULAR DATA FOR TABLE 4 OMITTED] reducing part costs, according to Charles McChesney, Hoechst's E/E market manager for LCP resins. He says Hoechst is working on a third generation of LCPs based on new chemistry. The goal is to maintain high performance while cutting resin cost by 10-20%.

Amoco is testing a developmental LCP grade that will be priced 10-20% lower than current high-end LCPs, according to Peggy Plucinsky, E/E industry manager. The grade will sacrifice some heat resistance, but should be suitable for a wide range of surface mount-applications, she says. Look for it in the third quarter of this year.

In other LCP developments, Hoechst recently introduced an improved Vectra E-130I grade with better flow at lower melt temperatures while maintaining an HDT of 536 F. Hoechst also recently signed a distribution agreement that allows it to make and sell compounds based on Amoco's Xydar LCP. Next year, Hoechst plans to begin compounding the Xydar G930 grade and is investigating new Xydar formulations with improved processability and higher heat resistance (e.g., an HDT over 570 F). For the longer term, McChesney foresees a bigger role for very fine mineral-fiber reinforcements as the connector industry pushes toward finer pitches and wall thicknesses below 5-10 mils.

New lubricated Zenite 6130L LCP from DuPont is said to fill parts better and reduce sticking problems in tools. Zenite business manager Paul Carfagna notes that the resin's high stiffness at elevated temperature allows it to set up faster in the mold for a cycle-time advantage over competing LCPs. DuPont is working on LCPs with higher temperature performance and improved oxygen barrier. Also in R&D are LCP alloys with higher heat resistance, lower viscosity, and lower cost.

MORE HIGH-HEAT RESINS

The evolution of finer pitches and higher pin counts in connectors requires improvements in both properties and processability from PPS resins, according to John Dole, market-development manager for Fortron PPS at Hoechst Technical Polymers. As pitch decreases to 20-25 mils with the next generation of connectors, molders will have to be more selective in their material choice because not every grade will be able to fill the resultant 8-15 mil wall thicknesses, he says.

To meet the needs of next-generation connectors, Hoechst's goal is to improve flow, cycle time, and cost by a minimum of 20% each. Dole expects Hoechst to introduce a new Fortron PPS grade that meets those criteria by early next year. The new product is also expected to require reduced mold maintenance and cleaning. In the nearer term, the company plans to introduce a PPS grade with improved flow, though cost and cycle time will be comparable to those of present grades.

A new BR-4-230 grade of Ryton PPS has been developed specifically for the electronics market by Phillips Chemical Co. It reportedly offers low flashing, "exceptional" thin-wall filling capability, high HDT ([greater than]500 F), and superior dimensional stability. Targeted applications include edge-card connectors, chip carriers, and sockets. Phillips is also developing a compound that will offer zero-flash injection molding and ability to fill thin-wall parts over long flow lengths. More expensive LCP was once the only material considered for such applications, Phillips says. The new Ryton will be available in commercial quantities in the fourth quarter.

An FR grade of Amodel polyphthalamide (PPA) meeting UL 94V-0 was introduced last year by Amoco. AF-4133X V0 can be processed with hot-water tooling at temperatures as low as 150 F.

The latest addition to GE Plastics' Noryl GTX line of PPE/nylon alloys is GTX918W, which has improved flow. GE Plastics plans to introduce new blends this year with even better flow and lower cost, according to Les Goff, industry manager for electronics.

New from Bayer is an impact-modified general-purpose PC, Makrolon DP1-1456, which is said to be very tough and have good flow and resistance to heat degradation during molding. It's suitable for thin-wall (40-mil) electrical housings.

NEW POLYESTERS AND BLENDS

An enhanced PCT polyester (Thermex CG907L) from Eastman Chemical Co. is said to offer improved processability, less plate-out, and faster cycles. Also new from Eastman is Thermex CG932, which has low volatility, better flow, and faster cycling in thin-wall parts. According to Eastman, Thermex PCT competes with PPS and other high-temperature thermoplastics in edge-card connectors, owing to PCTs white color, fast cycles, and low flashing.

New unfilled Celanex 2004-2 PBT from Hoechst Technical Polymers is a very high-flow material for thin-wall connectors. The company also introduced Celanex 4306 with better dimensional stability and processability for air-bag sensors and connectors. Also new: Celanex 4016, which enables customers to use up to 50% regrind and reportedly offers good elongation and UL 94V-0 rating; Celanex 6500R with 25% post-consumer recyclate; and Celanex 3226 with 20% glass and V-0 rating for thin-wall connectors.

New high-flow versions of Valox PBT from GE Plastics have appeared over the last several months as drop-in replacements for its standard Valox line. Three grades - EF4530 (30% glass), EF4517 (17% glass), and EF3500 (unfilled) - have lower viscosity than standard grades and can incorporate up to 50% regrind, the company says.

Two new high-flow Crastin PBTs are the latest in a line that DuPont introduced from Europe to the U.S. just last year (PT, May '95, p. 43). New CE2501 (30% glass) and 2505 (15% glass) are said to have 50% greater flow than previous 30% glass-filled FR grades. Unlike competing high-flow PBTs, which tend to brittleness, DuPont's new products achieve both higher flow and improved elongation, says Crastin business manager David Trerotola. These products achieve both higher flow and improved elongation.

Also in development are a "super-tough" CE2400 unfilled PBT, rated UL 94V-0. In addition, a relatively new low-warp FR grade, Crastin XMB7919, has good elongation despite its 30% glass/mica reinforcement. It's aimed at housings and terminal boxes, as well as multi-pin connectors.

Low-warp PBT/ASA alloys with 20% and 30% glass were recently introduced by DuPont (Crastin LW9020 and LW9030) and BASF (Ultradur S) to compete with PC/PBT and glass-filled PBT in electrical housings and automotive connectors. PBT/ASA is said to excel in surface finish, flow, and dimensional stability, while also giving lower moisture absorption than glass-filled PBT (PT, Jan. '96, p. 13).

Also targeted for electrical housings is new Makroblend DP4-1389 PC/PET from Bayer Corp. This FR grade meets UL746C requirements for uv exposure and water submersion and is available in all colors. It reportedly has better impact strength than straight polycarbonate, plus high flow.

FR NYLONS WITHOUT HALOGEN

Among several nylon developments for electrical parts are new halogen-free flame-retardant grades of Ultramid nylon 6 from BASF. Available in light colors, they use mineral-based FR additives that release bound water when burned. These products reportedly achieve UL 94V-0 and V-2 ratings with low levels of FR filler and so retain superior mechanical properties. One new grade is KR4450 (10% glass, 35% mineral), which is rated V-2 and said to have high flow for a filled compound. KR4455 (10% glass, 50% mineral) has very low warpage and V-0 rating. And KR4460 (20% glass) offers low density, improved flow, and V-2 rating. These products will compete with nylon 66 and thermosets in circuit breakers, auxiliary switches, and arc-suppressor housings.

Available for three years in Europe, a high-heat grade of nylon 6/6T (Ultra-mid T KR4365-G5) has now been introduced to the U.S. by BASF Corp. It reportedly can withstand reflow soldering for surface-mount applications.

FLAME-RETARDANT TPEs, TOO

Two new flame-retardant grades of Arnitel polyether-ester TP elastomer have been introduced by DSM Engineering Plastics. Arnitel PL720-S (72 Shore D) is an injection molding grade suitable for hot-runner processing and rated V-0 in all colors. Because of its high crystallization rate, this grade can provide 30% faster cycles than competitive TPEs, DSM claims. It handles service temperatures from -40 F to 260 F.

The second new Arnitel product is PL460-S (46 D), which is rated V-0 only in black. DSM says it has excellent impact strength and no odor.

For cable jacketing, two relatively new olefinic TPEs for GTO (gas, tube, and oil burner) applications are available from DSM Thermoplastic Elastomers. Sarlink 4380 is an 80 A grade rated V-0. Sarlink 4370 with 70 A durometer is the softest olefinic TPE for the GTO market that meets V-0, says general sales manager Malcolm Thompson. Although GTO applications now require service temperatures up to 221 F, DSM plans to introduce this year grades capable of higher temperatures - perhaps up to 257 F.

The company also has commercialized new "wet electrical" grades of Sarlink (both FR and non-FR) that can withstand water immersion. DSM also plans to introduce dioxin-free FR materials this year.

PERMANENT CONDUCTIVITY

Several new compounds based on inherently conductive polymers are said to have advantages over carbon-filled materials for clean-room manufacturing of semiconductors.

Six new electrostatic-dissipative (ESD) Stat-Rite compounds were introduced earlier this year by BFGoodrich's new ESD materials business unit. Based on polyether and polyester TPUs, ABS, PETG, and glass-filled PBT, the compounds are designed for clean-room applications such as chip rails, board trays, and fixturing devices, as well as thermoformed packaging, hose and tubing, and floor or table mats. The grades are all alloys based on BFG's inherently conductive Stat-Rite urethane-based resin, which is not humidity dependent and will not migrate, leach out, or change its antistatic properties over time, the company says. The alloys' big advantage for clean-room use is that there is no off-gassing and no coating or particles to flake and scratch off. Because they need no carbon filler, light colors are possible. The alloys reportedly comply with MIL 81705-C and provide surface and volume resistivities of [10.sup.9] to [10.sup.12] ohm/sq and ohm-cm, respectively.

New extrudable Stat-Kon and Stat-Loy compounds for ESD have been introduced by LNP Engineering Plastics, which already offers injection molding versions. Stat-Loy extrudable materials are available in 13 different base resins (including a clear ABS) and have surface resistivities of [10.sup.9] to [10.sup.11] ohm/sq. These products are alloys with an unidentified inherently conductive polymer that is non-migratory and not humidity dependent. The latter properties are said be gaining interest for semiconductor manufacturing applications, according to product manager Don Cianelli. Stat-Kon extrusion grades are based on a variety of resins, such as PC, ABS, and PP, and can be filled with carbon powder or reinforced with stainless steel to achieve surface resistivity anywhere from 100 to [10.sup.11] ohm/sq.

RTP Co. has expanded its PermaStat line of permanently antistatic compounds to include transparent acrylic grades and a translucent ABS. RTP is also working on a transparent PC grade. The PermaStat line uses an inherently dissipative polymer (not the BFG material) providing surface resistivity in the [10.sup.10] to [1.sup.011] ohm/sq range. Also new from RTP is a conductive styrenic TPE with a volume resistivity of less than 1 ohm-cm and surface resistivity of less than 10 ohm/sq. It reportedly meets MIL B-81705C ESD requirements and is aimed at gaskets and seals for electronic and business equipment.
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Author:De Gaspari, John
Publication:Plastics Technology
Date:Jun 1, 1996
Words:3227
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