New resins and reinforcements debut at SPI Composites expo.

Low-pressure SMC, low-VOC resins, resins made from recycled PET, a novel fatigue-resistant epoxy/vinyl ester hybrid, and several new phenolics topped the materials news from the recent annual SPI Composites Institute meeting in Cincinnati. Some unusual reinforcement products that incorporate low-density spheres, uv stabilizer, or electrical conductivity were also introduced.

MORE LOW-PRESSURE SMC

Low-pressure molding compounds (LPMC) continue to draw interest and attract new players to the market. By allowing large parts to be fabricated with low capital investment, these easy-flowing materials reportedly can compete with hand lay-up, spray-up, and RTM. LPMC molding reportedly offers higher productivity, less styrene emissions, and tighter tolerances.

As reported earlier this year, Takeda Chemical Industries Ltd. of Japan unveiled a modified polyester resin series for low-pressure/low-temperature SMC, which Takeda calls "Selecty Mat" (see PT, Jan. '95, p. 31). Company executives interviewed in Cincinnati said Premix Inc., North Kingsville, Ohio, will market SMC based on the resins. Premix may either import the sheet or manufacture it here, depending on market conditions.

The initial offerings of Takeda LPMC will include general-purpose and low-profile grades. The sheet can be compression molded at about 290 psi, and requires water-heated tooling capable of up to 212 F. Inexpensive clamping mechanisms and epoxy or nickel-shell molds can be used. Takeda officials said the sheet will be comparable to traditional SMC materials in terms of price and physical properties.

Takeda officials revealed that the system uses a new type of "hard" glass fiber at levels of 20-35%, as well as a new additive curing system that provides extended gel time for maximum flow. This new reinforcement is said to enhance the material's flow in deep-draw, complex geometries.

Another company developing LMPC is Ashland Chemical Co., Columbus, Ohio. The company is developing "SMC Lite," a Class-A polyester LPMC that reportedly has around 15% lower density than normal SMC and enables processors to reduce molding pressures up to 80%. It can be made on existing compounding equipment and requires no unusual handling or storage, the company says. The material is currently being used to compression mold the massive hood of Chrysler Corp.'s Viper roadster.

LOW-VOC RESINS

New Series 962 low-VOC polyester gel coats from Cook Composites and Polymers Co., Kansas City, are said to provide a 30% reduction in VOC emissions while maintaining superior weatherability and blister resistance.

Also new is Ashland's Hetron 970/35 vinyl ester, which contains less than 35% styrene, so as to satisfy California's Rule 1162. The material is aimed at high-heat applications requiring solvent and acid resistance. It's suitable for hand lay-up, spray-up, and filament winding.

Another resin designed to meet the 35% maximum monomer limit of Rule 1162 is new Polaris MR18201 low-profile laminating polyester from Aristech Chemical Corp. (which is in the process of being acquired by Ashland). It's designed for spray-up and hand lay-up in marine and other applications requiring superior cosmetics. It's based on a new resin chemistry that's said to give better physical properties and surface smoothness than current marine resins, with less print-through as well. But the resin handles the same as others, Aristech says. It comes in winter and summer viscosity grades.

POLYESTERS WITH RECYCLED PET

Polyesters containing depolymerized PET from industrial or post-consumer waste are not new, but they are now for the first time being applied to closed-mold applications. Such resins have been used mainly for open molding (such as boat making) and filament winding. They're said to be less expensive than orthophthalics and yet close to isophthalics in mechanical properties - even exceeding them in toughness.

Envirez Q6215 is a new low-profile SMC polyester from Ashland that contains 25% reclaimed PET. It's said to show good lot-to-lot thickening consistency.

Altek 14-70 RCP is another new polyester for SMC - as well as BMC and pultrusion - that contains 14% recycled PET. It comes from Alpha/Owens Corning LLP, Collierville, Tenn.

A company that wasn't at the show but that recently introduced resins based on reclaimed PET is Plexmar Resins, Inc., Houston. New P-430 resin comes in summer and winter grades. It's said to provide outstanding water resistance and is recommended for large structures, tanks, and boats. It's made with used x-ray film, which contributes a dark blue color that's said to aid in spotting air bubbles.

A NEW HYBRID

A new vinyl ester/epoxy hybrid resin from Interplastic Corp.'s Commercial Resins Div. in St. Paul, Minn., is said to cost less than vinyl ester while surpassing it in high-stress flexural fatigue resistance. (Vinyl ester still won out in high-stress tensile-fatigue tests, however.) Heat resistance is comparable to a bisphenol-A vinyl ester. (Tg is around 230 F.) And overall mechanical performance exceeds that of a flexible, high-strength isophthalic, the company says. It can be used in virtually all processes, though it has not yet been made thickenable for SMC/BMC. The resin is commercially available but still has the experimental designation VEX 186-024.

In other resin news, three new two-component, low-profile polyesters for RTM are available from Cook Composites. Stypol 40-8051, 40-8052 and 40-8054 are aimed at truck sleeper cabs. The three have similar properties but different viscosities - from 150 to 800 cp. The 8054 version also has a longer gel time at room temperature (23 min vs. 18 min for 8051). Cook is also developing spray-up versions, designated Stypol 40-4370 and 40-0152.

Dow Plastics, Midland, Mich., recently began offering a new grade of divinylbenzene (DVB) monomer with 63% activity that can be used to formulate fast-curing Class-A automotive SMC and BMC. Dow received an exclusive license by Union Carbide Corp., Danbury, Conn., which developed the formulation technology. Carbide's research shows that DVB can improve interlaminar shear strength, thereby reducing or eliminating blistering and paint popping and improving part gloss. The result is that mold cycles can be shortened by around 10% while maintaining Class-A finish.

Dow can now license compounders and molders on how to use its new DVB-CP grade to achieve such results. DVB-CP makes up less than 10% of the resin formulation and can replace part of the styrene monomer. Union Carbide will also supply DVB as part of its Neulon low-profile additive mixtures for fast-cure formulations.

Georgia-Pacific Resins Inc., Decatur, Ga., rolled out several new phenolics for various types of processing. GP 442D35 Resi-Set is a phenolic resole for pultrusion. It's waterborne and styrene-free, contains no organic solvents, and requires no external catalyst.

GP 413D40 Resi-Set is a hot-melt phenolic for aerospace prepregs. It offers stability and viscosity required for the hot-melt prepreg process without the need for a solvent, and it cures after 60 min at 275 F. Also for impregnating applications is new GP 413D97, a low-VOC, waterborne phenol-formaldehyde resin.

The company also has a new line of flaked phenolic novolac resins intended as curing agents for epoxy molding systems.

NEW REINFORCEMENTS

Aside from several pultrusion reinforcements reported last month (PT, March '95, p. 38), there were a smattering of other glass-fiber news for other composite processes:

* Lo-D Mat from Isorca, Inc., Granville, Ohio, is a continuous-strand mat combined with hollow glass micro-spheres for reducing density in RTM and SRIM. It reportedly does not sacrifice mat thermoformability or resin flowability.

* Two firms showed off new conductive or semiconductive nonwoven surfacing veils. Freudenberg Nonwovens, Chelmsford, Mass., offers aluminum-coated Viledon nonwovens to protect against static discharge in environments where flammable solvents are used.

And Precision Fabrics Group, Greensboro, N.C., offers highly conductive black Nexus polyester veil. It can be used for static elimination, grounding, heating, or EMI/RFI shielding. Another potential use is placement behind the corrosion barrier in large tanks. By means of an electrode suspended in the tank's liquid contents and a second electrode placed on the exterior wall, periodic checks could be made on the integrity of the corrosion barrier. A failure would be signaled by increased conductivity.

The company also offers new Nexus UV veil, which is impregnated with a uv stabilizer that will diffuse into the resin at the surface of the part - where it is most useful.

* A new factor in knitted fabrics is Fiber Glass Industries, Inc., Amsterdam, N.Y. It offers 0/90 [degrees] fabrics in 18-32 oz weights. By midyear, the firm plans to introduce [+ or -]45 [degrees] knits.

* CollinsCraft Composites Group, Inc., Walhalla, S.C., has new patent-pending capability for chemical/thermal bonding of different fabrics. Now it can bond its multi-axial Cofab knits and/or mats, veils, and rovings together in any customized combination and any weight from 10 to 96 oz.

* A new chopped strand for automotive BMC contains a polyester-compatible silane sizing. Star Stran 706C from Schuller International, Inc., Toledo, Ohio, is said to be an especially economical product.