Low-pressure SMC molding leads news at SPI Composites show.

New product developments and supply arrangements for low-pressure SMC molding compound (LPMC) and a newly developed polyurethane RTM resin system were among several materials developments announced at the SPI Composites Institute's recent Annual Conference and Expo in Cincinnati. In addition, there were numerous entries in fiberglass reinforcements for pultrusion. Also noteworthy was a novel multi-functional additive for thermosets and thermoplastics that appears to be a jack-of-all-trades when it comes to property enhancement. (Next month, Part II of this show report will feature new developments in machinery and equipment.)

LOW-PRESSURE SMC GAINS MOMENTUM

Thermoset polyester "low-pressure molding compound" (LPMC) has been a low-key presence for several years but finally came into the spotlight at this year's meeting. One new factor is the involvement of Owens-Corning Fiberglas Corp., Toledo, which is finalizing a three-way strategic agreement with National Composites Inc., South Bend, Ind., and Scott Bader Co. Ltd. of the U.K.

National Composites has had the exclusive North American license to formulate low-pressure SMC using a unique crystalline polyester resin from Scott Bader, called Crystic Impreg, in blends with conventional polyester or other resins. When molten (above 130 F), Crystic Impreg resin has low viscosity and enhances SMC flow so that it can be molded at pressures down to 150 psi, vs. 1000 psi for normal SMC. When cooled and solidified, the crystalline resin instantly "thickens" the compound to a moldable viscosity, which remains stable indefinitely. Tests show no change in sheet viscosity after 21 days at 80 F.

Under terms of the proposed partnership, Owens-Corning will manufacture Crystic Impreg resin exclusively for National Composites, which will continue to be the compounder and sales agent for LPMC. Another part of the agreement says Owens-Corning will be the prime supplier of glass and resins for National Composites' LPMC. A third provision of the agreement holds that Owens-Corning will assist National Composites in sales and marketing of LPMC. (Superior Fiberglass and Resins in South Bend distributes LPMC for National Composites.)

National Composites has been developing LPMC for several years and has made a number of improvements in its low-pressure moldability and ability to obtain good glass wet-out. Recent achievements include the development of low-density LPMC (1.5 g/cc), flame-retardant grades (UL 94V-0 and V-1), and versions that can be molded at low temperature (200 F)--useful for prototyping in epoxy tools. The company is still working on a phenolic LPMC, and is collaborating with GenCorp Automotive, Akron, Ohio, to develop "Class A" LPMC.

According to John Jenks, Owens-Corning v.p. of Resins & Coatings, LPMC fills a processing niche between SMC and open-mold techniques: It broadens the SMC processing window while allowing open-mold processors to"step up" to a faster, more precise, more automated form of manufacturing with modest capital investment. Not only does LPMC allow use of lower tonnage presses, but low-pressure molds can cost up to 50% less, says Owens-Corning. This helps drive down the part volumes typically required to justify a compression molding operation.

An example of how LPMC is making converts of open-mold processors was on display at the show: Pedden Composites, Inc., Fort Wayne, Ind., exhibited an LPMC sleeper-box roof that was compression molded for a trailer truck. This was the first press-molding job for Pedden, heretofore strictly an open-mold processor. The roof measures up to 60 in. wide x 96 in. long, with an 8-in. vertical wall. It is molded on a 750-ton press, rather than the 3000-ton press that would be required to mold normal SMC.

It looks like Owens-Corning and National Composites won't be alone in exploiting LPMC's opportunities. A second and quite different form of LPMC was announced by Ashland Chemical, Inc., Columbus, Ohio (see PT, Feb. '94, p. 13). Ashland's new Aropreg 3230 LPMC is said to combine the processing advantages of SMC with the lower tooling and equipment costs of RTM. Unlike National Composites' LPMC, Ashland's version is supplied without glass. It's designed for compression molding with a glass preform, which Ashland says provides optimal part strength. The resin charge is placed in a hot mold (195-205 F) between the preform and a layer of surfacing veil. The mold is closed slowly (taking up to a minute) to allow the material to flow. Molding pressures can be below 200 psi, Ashland says. Demold times range from 5 to 10 min. Prior to use, the compound should be stored at or below 77 F.

Aropreg 3230 LPMC is a low-profile compound designed for molding large, complex geometries and reportedly can attain Class A automotive surface finish. One recent commercial application is the hood surround for the Lotus Elan sportscar, made in England.

PUR TOUGHENS RTM

The Polymers Div. of Miles Inc., Pittsburgh, has developed a new polyurethane resin system for RTM that is designed to offer processing and performance benefits over polyesters, vinyl esters, acrylics, and epoxies. Baytec RTM is a two-component RTM resin system specially tailored to provide enhanced flow and glass wet-out, along with shorter demold time and superior toughness. Baytec RTM 532, the initial commercial grade, is a liquid system composed of a modified MDI and a polyether polyol blend designed for a 1:1 mix ratio. A second RTM grade, now undergoing development trials, will be optimized for even better performance and processability.

Baytec RTM 532 has a heat-activated catalyst, which provides a 90-sec gel in molds heated to 150 F. Typical demold times are 7-15 min, with no post-cure required. The resin system is solvent free and can be delivered via low-pressure equipment with a static mixer (dynamic mixers are not necessary).

Key physical properties for Baytec RTM 532 at 40% loading of continuous-strand glass mat include a Shore D hardness of 84, tensile strength of 25,000 psi, elongation of 4%, flexural modulus of 1 million psi (740,000 psi at 150 F), notched Izod impact of 10 ft-lb/in., and HDT of 390 F at 264 psi.

Baytec RTM 532 is priced around $1.59/lb, comparable to vinyl esters, and is aimed at construction, transportation, and industrial corrosion applications currently utilizing epoxy and vinyl ester RTM.

SPRAY-UP ACHIEVES 'CLASS A'

Citing initial success in large truck hoods, Reichhold Chemicals Inc., Research Triangle Park, N.C., introduced a Polylite Profile 33545-00 laminating system, which reportedly allows processors to achieve "true Class-A surfaces" using a chopper gun--and without a gel coat. The Polylite Profile resin is a non-promoted, thixotropic polyester containing a low-shrink/low-profile additive system that functions at room temperature. It's a further development of the Polylite Profile technology that was first applied to extremely low-shrink tooling resins (PT, April '92, p. 41).

The resin is filled 20-25% with calcium carbonate and unnamed lightweight fillers, and can be cured at room temperature with Reichhold's Superox 46750 or 46757 peroxide initiators. Reichhold says laminates shrink only 0.00024 in./in., or approx. 1/8 in. over 40 ft. Surface-profile tests of parts laminated with Polylite Profile resin showed Diffracto D-Sight values of 42, vs. 400 with a conventional resin.

MORE NEW MATERIALS

Two new vinyl esters were brought out by Ashland Chemical. Hetron 980/35 is a low-styrene system with 270 F HDT. It's designed for hand lay-up, spray-up, and filament winding. The second is Arotech 9000 vinyl ester for marine applications. It's said to provide better impact and blister resistance than conventional polyesters.

Recent introductions from Georgia-Pacific Resins Inc., Decatur, Ga., include a water-borne phenolic resole resin for pultrusion. GP 442D35 Resi-Set is said to offer strength and stiffness comparable to polyesters, plus flame resistance and low smoke. This one-part liquid has slightly alkaline pH, contains no organic solvents, is styrene-free, and doesn't require adding a catalyst. It's priced at about $1 lb/tl and designed to process on polyester pultrusion equipment.

For "solid-surface" sinks, vanities, and flat stock, Reichhold has introduced Polylite 32169-00, an isophthalic/NPG polyester that cures at room temperature--without post-cure--using only MEKP. This resin is said to overcome past obstacles to taking advantage of the hydrolytic and stain resistance of iso/NPG resins.

Premix Inc., North Kingsville, Ohio, through its affiliation with Takeda Chemical Industries of Japan, is offering in this country materials and processing technology for molding BMC sinks, vanities, and the like with a translucent marble look.

Bulk Molding Compounds Inc., St. Charles, Ill., rolled out its new CoreLyn line of polyester BMC for dinnerware. It contains proprietary fillers, colorants, and other additives that promote deep color, high gloss, and scratch/chip resistance. CoreLyn is designed for compression, injection, or transfer molding. HDT is above 500 F.

Isorca Inc., a technology development firm in Granville, Ohio, recently developed a line of structural core materials for sandwich composites, called Alba-Core. Containing low-density fillers, they are supplied as cured sheets (flat or curved) in various thicknesses. In the future, they may be offered as raw materials so that skin/core composites can be laid up and cured in a single step. Isorca has worked mainly with phenolic resin but says others can be used, including polyester, epoxy, polyurethane, and even thermoplastics such as PPS. With phenolic resin, Isorca has achieved core densities of 7.2-40 lb/cu ft and core compressive strengths of 107 psi to greater than 4000 psi. Cores can contain reinforcements, if needed.

Isorca is applying for a patent on the technology, which permits a wide range of density and engineered properties, together with low cost, according to Steven Katz, business manager and v.p. of operations. Once scaled up to full production, he expects Alba-Core to offer properties competitive with honeycomb cores at a price comparable to balsa or vinyl foam. Projected prices of 1/4-in. sheets of phenolic core run from 80|cents~ to $2.20/sq ft.

REINFORCEMENTS TARGET PULTRUSION

Judging from news at the show, fiberglass producers are focusing particularly on new products for pultrusion, which they view as a high-growth sector of the composite market.

GAF Building Materials Corp., Nashville, Tenn., best known as a supplier of fiberglass for roofing materials, is introducing a new product in its Gaftex 100 Series of single-end rovings for filament winding, pultrusion, and fabrics. Gaftex 105 is aimed especially at phenolic composites. Gary Bolen, sales and marketing manager, says Gaftex 105 provides good wet-out in phenolic, as well as in polyester, vinyl ester and epoxy. The rovings will be produced in Nashville in a plant formerly operated by Reichhold. He says the product will be available in yields of 250, 450, and 675 yd/lb.

Two new glass reinforcements for pultrusion were introduced by Vetrotex CertainTeed Corp., Valley Forge, Pa. Unifilo 5228 is a continuous-strand mat compatible with polyester and vinyl ester resins, providing superior dry and wet tensile strength for complex-shape composites. Available in weights from 0.75 to 3 oz, Unifilo 5228 will be imported from Vetrotex in Italy.

The second product, R099 67B, is a replacement for the firm's 670 line of pultrusion rovings. Compared with 670, 67B offers improved wet-out and tensile strength, and has reduced fuzz and snarling characteristics for easier handling, the company says.

In addition, CertainTeed is planning to roll out a new phenolic-compatible roving for pultrusion later this year.

OCMat 4500 is a new lightweight pultrusion mat from Owens-Corning. This nonwoven mat is composed of uniform, randomly dispersed, chopped fibers with a polyester-compatible binder. Available in 54-in. rolls, OCMat 4500 reportedly offers high bulk and improved die fillage, which translate into cost advantages. It weighs only 1 oz/sq ft, while offering the same wet and dry tensile strength as mats that weigh twice as much, the company says. Compared with continuous-strand mat, the new product is said to be whiter, more uniform, and easier to slit to narrow widths. While it's not intended to completely replace continuous-strand mat, the new product gives similar laminate mechanical properties, according to initial tests.

Owens-Corning also is unveiling a new roving for pultrusion. Designated 102A, it's compatible with polyester, vinyl ester and epoxy and is said to permit high speeds and smooth product finish. The product is manufactured in three yield sizes (57, 62, and 115) and targets applications in transportation and electronics.

PPG Industries, Pittsburgh, has a new multi-end pultrusion roving that's said to provide improved shear strength in the final product, owing to good wet-out and wet-through. Type 784 roving employs a new sizing compatible with polyester, vinyl ester, and epoxy.

And for other applications, Vetrotex CertainTeed came out with a new 27L panel roving that's said to give low visual fiber prominence for a "water-clear" product appearance. The roving is compatible with acrylic-modified polyesters and reportedly generates low static charge when chopped.

Novel & Highly Versatile Additive

The most unusual news in additives at the SPI conference was the public debut of GeoPlas, an additive that apparently offers multiple benefits in a wide range of thermosets and thermoplastics (see also Technology Newsfocus section). A product of GeoPlas Inc. in Granville, Ohio, the additive is a naturally occurring complex hydrocarbon of the class known as asphaltites. This black/brown, coal-like solid (1.04 specific gravity) is mined in Utah. It is supplied as a free-flowing powder with a nominal particle size of 10 microns (finer grinds are also available). Numerous effects have been observed at use levels of 2-6%.

* Surface finish: "Virtually all work conducted on thermosets and thermoplastics indicates a general improvement in surface smoothness and gloss," the company claims. Improved fidelity of mold-surface reproduction is also cited. When combined with low-shrink additives, GeoPlas reportedly can approach low-profile results at lower cost than with conventional low-profile agents. In one of its first commercial applications, GeoPlas will be used to improve the surface appearance of an engine valve cover for a 1994 European car. This part will be injection molded of low-shrink vinyl ester BMC.

* Paintability and bonding adhesion: Benefits result partly from increased surface smoothness and partly because GeoPlas increases surface energy of SMC (and even polypropylene) so as to enhance paint adhesion. Improved adhesive bonding of SMC is another effect of higher surface energy.

* Mechanical properties: GeoPlas is believed to improve fiber wet-out and resin/fiber bonding, owing to increased resin surface energy. This is believed responsible for the 250-400% increases in cycles-to-weep observed in tests of filament-wound vinyl ester pipe.

* Moisture resistance: GeoPlas is hydrophobic, and as little as 3% reduces water absorption of orthophthalic and isophthalic polyesters, vinyl esters, and phenolics by 10-25% in water-boil tests.

* Electrical properties: GeoPlas reportedly enhances dielectric strength, surface and volume resistivity, and arc and track resistance.

* Weathering: Polyesters, phenolics and PVC containing GeoPlas perform better in accelerated-weathering tests.

* Fire resistance: At higher loadings, the product functions as an intumescent upon exposure to direct flame.

* Pigmentation: Although not as highly tinting as carbon black, around 5% loadings of GeoPlas are said to pigment virtually all resin systems to an opaque black.

Because GeoPlas contains nine different functional groups and free radicals, it can affect SMC thickening and curing reactions. The company recommends reducing normal thickener levels by 50% and cautions that GeoPlas may reduce shelf life of SMC. GeoPlas will also react with BPO and MEKP initiators, but works well with perbenzoate or other heat-activated catalysts, accompanied by suitable inhibitors to prevent pregel. With perbenzoate, GeoPlas actually promotes initiation of curing above 200 F.

The company says animal feeding studies and other tests show that GeoPlas "has a very low order of toxicity and is not carcinogenic." Nor is it expected to be irritating to eyes or skin. The company also states that "GeoPlas is chemically inert and environmentally safe," presenting no disposal problems.

Pricing ranges from 28|cents~ to $1.10/lb f.o.b. Salt Lake City, depending on grade, volume, packaging, and destination.