Composites update - part I: new materials & reinforcements.

Composites Update--Part I: New Materials & Reinforcements

The mood was somewhat subdued at the SPI Composites Institute annual show and conference in Washington, D.C. But despite the atmosphere of economic uncertainty, there was ample news to report in materials and reinforcements, as well as machinery and processing techniques (the latter two will be covered in the second part of our report next month). For additional news, consult our pre-show report (see PT, Feb. '91, p. 15).

REDUCED-EMISSION RESINS

Though still experimental, three new resins and an additive package from Dow Plastics, Midland, Mich., are said to reduce styrene vapor emissions by as much as 75%. Despite containing less than 35% styrene, XU 71928.01 vinyl ester reportedly offers even lower viscosity than standard Derakane 411-45. A modified epoxy backbone also confers higher strength, stiffness and HDT. Corrosion resistance is unchanged.

New XU 71973.00 vinyl ester has 45% vinyl toluene monomer in place of styrene, which reportedly cuts volatile emissions by 50%. It boasts slightly improved chemical resistance, flex strength and modulus over Derakane 411-45, but a bit lower HDT.

Also new is Dow's first isophthalic polyester, which contains 35% styrene and reportedly exceeds the mechanical and thermal properties of a standard isophthalic with 45% monomer.

Dow's fourth new entry is an additive package for vinyl esters that forms a barrier to styrene evaporation during fabricating and curing. Dow says only 1% addition was required in tests where 2% of Byk-S 740 styrene suppressant (from Byk-Chemie U.S.A., Wallingford, Conn.) was needed to reduce emissions to the same level. Dow's additive reportedly has no effect on laminate properties and "minimal" effects on secondary bonding.

These products are expected to be priced about 20-30% higher than competing products. On the other hand, Dow is offering customers a free styrene-exposure monitoring service. Dow will distribute free vapor-monitoring badges (made by 3M Co., St. Paul, Minn.). Dow will pay for analysis of the badges at Midland Molecular Institute, Midland, Mich., and will send reports to the fabricator, along with consultation on how to reduce styrene exposure, if needed.

New polyesters for cultured marble were introduced by Reichhold Chemicals Inc., Triangle Park, N.C. Included among the new products was Polylite 32201, said to be the most thermal-shock resistant polyester ever offered by the company.

Also introduced were two fast-cure resins for fabricators requiring rapid mold turnover. Polylite 32101-00 is a medium-viscosity resin for vanities and other hard-to-mold parts. Polylite 32102-10 is a low-viscosity product for drop-in bowls. Both versions are designed for room-temperature cure using a 40% BPO dispersion.

Another new series of marble resins, named Vibrin, was introduced by Owens-Corning Fiberglas Corp., Toledo. Good color characteristics and thermal-shock resistance are claimed.

Meanwhile, Owens-Corning will gain access to vinyl ester manufacturing technology, as well as new technology for polyesters, through a new three-way licensing exchange with BASF AG of Germany and Takeda Chemical Industries, Ltd. of Japan.

Also new from Reichhold were two RTM resins--Polylite 31515-00 and 31515-50 (prepromoted)--said to give Class A finishes without gel coats.

And for SMC, Reichhold reported that its Atlac ITP urethane-thickened polyesters have overcome previous difficulties in bonding. They reportedly now form high-strength bonds without surface preparation.

Ashland Chemical Co., Columbus, Ohio, introduced three new thickenable vinyl esters for automotive SMC and BMC. When used with about 30% glass, new Arotech 2000, 2001 and 2002 are said to be well suited to under-hood applications such as valve covers and oil pans, structural parts and inner reinforcements for body panels. They provide different balances of low profile, low or zero shrink, heat resistance up to 300 F, elongation up to 1.48%, and flexural strength to 36,200 psi.

Indspec Chemical Corp., Pittsburgh, has expanded its Fire [PRF.sub.2] line of liquid phenolic resins for fire-resistant, low-smoke composites with a variant specifically for pultrusion, and is working on a version for RTM.

SPRAYING & MOLDING COMPOUNDS

Two new sprayable polyester syntactic-foam core materials were introduced at the show. One is a companion product to SprayCore 2000, introduced in 1989 by Omega Chemical, Wildwood, Fla. (see PT, March '89, p. 85). The latter is used largely as a print-through barrier and sandwich core material in marine laminates. Newer SprayCore 9000 No-Roll contains a variety of sizes of silica microspheres, and is said to give lower cost and better surface quality than chopped-glass laminates as a backup for baths, showers, pools, pickup caps, van tops, and architectural facades.

New Alcel GHE-23 syntactic foam yields a density of 43-45 pcf on its own, but can be adjusted down to 23 pcf with addition of Alcel blowing agent as a third component. This system is low in exotherm and shrinkage and non-sagging.

For the first time in many years, Rostone Corp., Lafayette, Ind., is again offering its proprietary SMC/BMC compounds to other molders. The company specializes in electrical grades, of which it currently offers 19, including a conductive version for electrostatic dissipation.

Bulk Molding Compounds (BMC) Inc., St. Charles, Ill., has a new BMC 800 series of high-performance compounds. Six grades include corrosion-resistant polyesters and vinyl esters, and tough hybrid resin systems with notched Izod impact strength up to 30 ft-lb/in. HDTs exceed 500 F. Injection and compression grades are available for 80 [cents]-$1.20/lb tl.

The first in a series of low-cost BMCs was introduced by Glastic Corp., Cleveland. SLC-1000 is aimed at case circuit breakers and other electrical parts, and reportedly costs 15-25 [cents]/lb less than other medium-strength, UL 94V-0 compounds. Shrinkage is adjustable.

A new nylon film has been developed by Allied-Signal Corp., Morristown, N.J., as a carrier web for SMC. Due to go into full-scale commercial production next month, ER-15 HR is a blown, rather than cast, film and has higher tensile and dart-drop impact strengths. It also reportedly has better roll conformity, gauge distribution and processability. It's expected to cost about 10% more.

NEW REINFORCEMENTS

A large number of fiber products were introduced, itemized here by application:

* BMC injection molding: Owens-Corning Fiberglas plans to introduce during this quarter a new chopped-strand fiber, labeled 101C, offering better properties in injection molded BMC than any other fiber, according to the company. Used in conjunction with new processing technology, 101C reportedly can increase impact strength by 25-50% and tensile/flexural strengths by 10-15% Spokesmen for Rostone and BMC Inc. speak favorably of 101C.

* SMC: Type 5528 medium-hard roving is new from PPG Industries, Pittsburgh. From Owens-Corning, new 973 roving is for high-glass-content, structural automotive SMC. It was developed for The Budd Co. to use in sheet containing 55-65% glass. It reportedly minimizes "squeeze-out" at the sheet edges, improves wet-through, and has lower fuzz and fly than OCF's 433 roving.

* Pultrusion: PPG also brought out Type 798 bulked or texturized roving that incorporates transverse filaments to impart biaxial strength. (Owens-Corning introduced a similar product in 1988.) Also new from PPG is Hybon 2011 single-end roving, a "soft strand that is easily opened with minimal working," according to a company spokesman, resulting in "maximum wetout" and high strength.

Also, Manville has a developmental XR100A single-end roving.

* Filament winding: From Owens-Corning, 158 type 30 roving is a replacement for its 346 type 30. Initial tests in epoxy pipe show stronger glass-to-resin adhesion and 15% higher burst strength than pipes made with either Owens-Corning's 346 or similar reinforcements.

* Spray-up: OCF's 357B Gun Roving boasts improved choppability and dispersion to eliminate clumping CertainTeed Corp., Valley Forge, Pa., has new Roving 255, designed for isophthalic and vinyl ester resins. It has a silane sizing for good clarity.

* Panels: OCF's new 992BB Roving for translucent panels reportedly provides 16% better weatherability than other panel rovings.

PPG's new Type 7812W has a refractive index that nearly matches that of acrylic-modified polyester, thus providing high clarity. It also reportedly does not cause pigment flocculation and wets out very fast.

* Phenolics: Manville Corp., Toledo, brought out what is believed to be the first American-made 1/16-in. chopped strand, called Star Stran 754. It's manufactured under a technology licensing agreement with Nippon Electric Glass (NEG) of Japan and is designed for phenolic molding compounds, where it reportedly gives improved flow and surface appearance. Star Stran 754 chopped strand is said to be cost-competitive with milled fibers.

* Nylon: Another new product based on NEG technology is Manville's Star Stran 702 chopped strand for nylon compounds, in 1/8-in. and 3/16-in. lengths.

* Preforming: PPG introduced three rovings for directed-fiber preforms. Type 5555 is for smooth cosmetic surfaces; Type 5553 is coarser and provides higher impact strength and easier resin flow in noncosmetic parts.

Spray Veil, the third roving provides a surface veil layer that hides print-through of underlying reinforcements. This product eliminates hand labor and waste in cutting and fitting veil mat. To apply Spray Veil, PPG developed a special "Air Impingement" process (available for licensing), which injects high-pressure air into the stream of chopped roving before it leaves the preform directing tube. This, together with a special sizing, ensures separation and dispersion of the veil filaments.

Owens-Corning's new M8650 Preformable Continuous Strand Mat is a modification of its experimental M8650 formable mat for RTM and SRIM. This one reportedly needs lower preforming heat and pressure and lower resin pumping pressure; it also improves heat stability in finished preforms and part fill-out with filled resin.

MORE ON MATS, FABRICS

Owens-Corning recently expanded its mat production capacity by 25% and installed new computer controls, which reportedly have reduced mat weight variation by 35%, improved roll density, and reduced "telescoping" of roll ends.

Brunswick Technologies, Inc., Brunswick, Maine, unveiled a new binderless Cofil mat that is said to give unusually good wetout and conformability.

Another unusual fabric is new phosphorescent Nexus polyester veil from Precision Fabrics Group Inc. (formerly Burlington Industries), Greensboro, N.C. This glow-in-the-dark treated veil could be used for safety purposes in hard hats, gratings, handrails, and the like.

PHOTO : Bayliner Marine Corp. of Arlington, Wash., is using Reichhold's new Polylite 31515-50 resins to make bow platforms by RTM without requiring a gel coat to achieve a Class-A finish.