Fillers hold down rising resin costs.

As resin prices soar through the roof, processors are taking another look at fillers as both cost-saving and value-enhancing additives.

In these days of out-of-sight resin prices and tight supplies, fillers are worth their weight in gold - so to speak. Processors and compounders are increasingly turning to filler additives to keep a lid on material costs and get more mileage out of the material that's available. But resin extension isn't the whole story: Fillers continue to gain recognition for their value as performance additives.

Below, we take a look at some of the new uses to which fillers are being put and at the latest product developments from filler suppliers.

MICROSPHERES ARE ON A ROLL

Suppliers report that hollow and solid glass microspheres have steadily gained acceptance by processors in thermoset applications such as polyester and epoxy laminates and RIM urethanes, as well as in thermoplastics such as PP, nylon, and PVC plastisols.

Murray Richardson, v.p. of sales and marketing at Cataphote Inc., says increased interest in the company's solid glass beads goes beyond resin extension to property enhancement: "Resin producers and compounders are now more knowledgeable about use of glass beads and increasingly consider them as they look for ways to enhance their products." Examples include use of the beads to achieve more durable surfaces in interior automotive components and to reduce warpage in conduit and electrical connector boxes.

Susan Beckerman, market development manager at Potters Industries, says the company's Spheriglass solid glass beads (used primarily in nylon and thermoset polyester) are likewise viewed as more than extenders. They offer processing benefits by increasing flowability, she says, as well as better dimensional stability in the finished part. For example, new data show that shrinkage of untilled or glass-filled nylon 66 can be cut by 70-80% when 30% glass beads are used. And warpage is reduced 95-97% in the same tests.

Suppliers of hollow glass microspheres say the auto industry's push for lighter weight is providing a significant boost in demand for their products. According to Stan Miller, product development manager at PQ Corp., fast-growing markets include PVC plastisols for automotive underbody coatings and seam sealants. "Because of the spheres' lower weight, we see a transition away from calcium carbonate in these applications," he says. "A traditional PVC plastisol filled with calcium carbonate has a density of 1.4 g/cc. With the glass microspheres, we reduce density to 0.75 g/cc."

Potters Industries has seen increased use of its Sphericel hollow glass microspheres in automotive polyester SMC, where the spheres' compressive strength (above 10,000 psi) enables them to withstand molding pressures and their small particle size can provide a Class A finish.

POLYMERICS CHALLENGE GLASS

Microspheres whose shells are copolymers of acrylonitrile or PVDC are offered by Expancel, Pierce & Stevens, and PQ. These products are said to pose a growing challenge to their glass counterparts in reinforced and unreinforced thermoset polyesters, epoxies, urethanes (including RIM), and PVC plastisol underbody coatings and sealants.

One reason is the polymerics' lower density - e.g., 0.02-0.06 g/cc for Expancel spheres and the newest product from PQ (see box), or 0.13 g/cc for Pierce & Stevens' Dualite products, which contain tiny particles of calcium carbonate embedded in the microsphere wall for increased resin compatibility. These ultra-low densities compare with 0.20-0.40 g/cc for typical glass microspheres.

Thus, a very small amount of polymeric spheres can displace a lot of resin and weight with minimal increase in viscosity, suppliers say (see table). "A little goes a long way and can boost a formulation in volume by as much as 50%," says Nicholas Vaylen, market manager at Pierce & Stevens. His firm recommends typical loadings of Dualite spheres of only 1-5% by weight.

Although polymeric spheres cost more per pound than hollow glass types, they can be less costly on a volumetric basis. Likewise, the polymeric spheres typically cost less on a volumetric basis than the resin they displace, according to Expancel marketing manager Mark Cheplen.

That lesson was learned by Leer, Inc. in Elkhart, Ind., which found that 1% by weight of Dualite spheres in a polyester FRP spray-up formulation displaced 6% by weight of resin. The spheres also added some reinforcement, so the level of glass fiber could be cut back as well. As a result, Leer saved $3-4 on each pickup truck cap it was making with the spheres and cut VOC emissions because of the reduction in resin use.

Vaylen adds that polymeric microspheres are elastic enough to compress under pressure during processing and then bounce back, unlike glass spheres. "Low-density glass spheres are friable and do not stand up as well to spraying pressure," he says. "Consequently, breakage tends to occur. There is also a certain amount lost during the shearing process as they are mixed into the system." Resilient polymeric spheres reportedly can be mixed at high speeds and sprayed at high pressure without breakage. (See box for new microsphere products.)

CaC[O.sub.3] SUPPLY STILL TIGHT

Demand for calcium carbonate continues to outpace supply (see PT, Nov. '93, p. 61), driven especially by growth in construction-related applications. Although suppliers are working to expand capacity, tightness persists, especially in ultra-fine, and fine wet-ground grades and to some degree in medium-to-fine dry-ground product. Suppliers note that customers have responded to higher resin prices by raising filler loadings - e.g., a move from 20% to 30% loadings in PVC pipe. One consequence has been rising prices - several major producers raised them again by 7-10% last month.

MICROSPHERES IN POLYESTER RESIN

WEIGHT % HOLLOW MICROSPHERES

Mix Density,    Expancel     Glass       Phenolic    Silica
g/cc            0.04 g/cc    0.2 g/cc    0.2 g/cc    0.7 g/cc

1.2             0            0           0           0
0.8             1.5          11          11          80
0.6             3.5          25          25           -
0.4             7.5          60          60           -

Source: Expancel Inc.

Key trends in calcium carbonate include new surface modifications and manufacturing technology and a move to smaller particle sizes. For example, ECC International is developing new forms and surface modifications for introduction within the next two years. "Instead of traditional granular products, you may see some beads or even popcorn shapes," predicts director of sales Tony Thompson. They will be targeted for use in film and injection molding of HDPE and PP, as well as PVC pipe and conduit.

Whereas typical surface modifications have been based on stearic acid or calcium stearate, Thompson hints that ECC is considering novel materials such as high-melting-point polymers and various latex coatings. Other technologies being explored include coatings that expand upon heating and addition of surface treatments during the grinding stage, which imparts different characteristics.

Smaller particle sizes are another market trend. Bob Freas, sr. v.p. of Franklin Industrial Minerals, says there is increased interest in 2-micron rather than 3-micron products due to a trend in PVC water pipe toward smaller pipe diameters and thinner walls.

Smaller particle sizes offer improved impact resistance, says Bob North, general manager of sales and marketing at Genstar Stone Products. Genstar's Camel Fine ST, a 2-micron, surface-treated grade is being used more in applications such as vinyl siding and profiles, as well as injection molded and extruded polyolefins.

Super-Pflex precipitated calcium carbonate from Specialty Minerals has been gaining wide application in rigid PVC siding because its very narrow particle-size distribution allows higher loadings, according to Mike Tapper, manager of minerals business development. Average particle size is 0.8 microns, but the top size is only 2-3 microns. By contrast, other products with 0.8-1.0 micron average size have a 5-6 micron top size.

As for other mineral fillers, surface treatment (primarily with silanes) is also a big trend in silica and mica, as is lower particle size for certain applications. New high-aspect-ratio, fine-particle talcs and wollastonite are said to provide improved performance properties in PP copolymers, rigid PVC, and RIM. (See box for new product developments.)

Anhydrous gypsum is also said to be gaining interest in plastics. One reason is its ability to function as an extender for titanium dioxide pigment, which has escalated sharply in price of late (PT, Dec. '93, p. 66; June '94, p. 107; Feb. '95, p. 82). Anhydrous gypsum (which can be processed at high temperatures, unlike hydrated grades that release water at around 300 F) sell for 10-12[cents]/lb, vs. current prices of 94[cents]/lb for Ti[O.sub.2].

Growing demand is prompting additional suppliers to introduce anhydrous gypsum products (see box). And the leading supplier, U.S. Gypsum, says its CAS-20-4 white anhydrous gypsum has been drawing increased interest for use in rigid and flexible PVC and as a Ti[O.sub.2] extender in color concentrates. At typical loadings of 10% in PVC siding and auto-interior moldings, it reportedly maintains the impact properties obtained with higher-priced calcium carbonate. The company estimates that the product has a cost-saving potential of 15-20% in these applications. In intricate extruded profiles, lower melt viscosity also has been reported.

TRENDS IN FR FILLERS

In fillers that also provide flame resistance, one trend is toward surface-treated alumina trihydrate (ATH) grades that provide improved physical properties. Another is toward calcium sulfate (gypsum) grades that can compete with ATH in certain applications.

R.J. Marshall Co. is developing surface-treated ATH grades for customers that cannot meet performance requirements with unmodified ATH. Silanes, for example, provide increased tensile and compressive strengths, while stearates increase impact resistance, according to v.p. of technology and operations Larry Musselman.

Precipitated grades of ATH are available for the first time in a new size range for polyester SMC, pultrusion, and hand lay-up, according to sources at Alcan Chemicals (PT, Jan. '95, p. 32). Precipitated FRF grades come in four versions with median particle sizes of 7.7 to 20 microns. These are said to have unusually low surface areas (1.1 to 0.5 [m.sup.2]/g, respectively) and smoother, rounded particle surfaces, instead of the platy or cracked and split particles that result from mechanically ground grades. Although the new precipitated grades cost more - $540-1140/ton, vs. $440-680/ton for comparable ground grades - they are said to give lower viscosity in SMC, allowing higher loadings for lower compound cost and greater flame resistance. Lower surface moisture also is said to give better control of thickening, and lower surface area absorbs less catalyst, permitting faster cures, Alcan says.

Meanwhile, dihydrate forms of gypsum are said to be replacing ATH in some FRP applications. "At under 5[cents]/lb, they have pretty much replaced ATH [costing 12-25[cents]/lb] in room-temperature polyester tub/shower spray-up applications," says Sue Dichter, product marketing manager at U.S Gypsum.

U.S. Gypsum recently introduced XLP Filler, a byproduct gypsum (obtained from flue-gas scrubbers) that contains about 20% water. Price is comparable to that of natural gypsum, but XLP is said to be more widely available and therefore freight costs can be lower.

Also relatively new is the Charmax LS series of proprietary blends of flame-retardant synergists with various fillers, supplied by R.J. Marshall. For example, blends with ATH are aimed at PVC plenums. Blends with glass or polymeric microspheres are targeted for use in polyolefins. And Charmax blends with calcium carbonate are aimed at engineering resins. By combining several additives in a one-pack product, these blends are designed for formulating convenience. Although they weren't considered economically attractive in the past, Musselman says these products are now proving very successful in highly-loaded thermoplastic systems such as PVC and crosslinked-PE cable. Other potential applications include extruded sheet and injection molded nylon or PP parts such as fan shrouds.

RELATED ARTICLE: What's New in Microspheres

Emerson & Cuming Composite Materials Inc. (recently spun off by W.R. Grace & Co.), has added a new SDT series with very small particle sizes to its line of Eccosphere hollow glass microballoons. SDT-60, SDT-40, and SDT-28 have median particle sizes of 6, 12, and 16 microns, respectively. The smaller spheres reportedly offer much better compressive strength, reducing breakage during mixing. About 93% of the balloons survive 4000 psi. SDT products have potential in injection molded epoxies and silicones for aerospace, as well as in highly filled PP.

Expancel Inc. is now marketing grade 091 DU 80 hollow polymeric sphere for use in PP and HDPE extrusion as an alternative to chemical blowing agents for density reduction. Its density is 0.03 g/cc.

Expancel 091 is gaining uses in automotive LD-RIM bumper systems because the microspheres help reduce part shrinkage while also reducing density.

Pierce & Stevens is offering a series of higher-performance Dualite polymeric microspheres distinguished by increased heat, pressure, and solvent resistance. They can be processed at temperatures above 350 F (vs. 250 F for other Dualite spheres).

PQ Corp. has two developmental hollow glass products based on a new composition that reportedly offers improved crush resistance. PM 7220 (0.20 g/cc) and PM 7228 (0.28 g/cc) are intended for high-quality epoxy syntactic foams in aerospace applications.

In the next two years, PQ also hopes to commercialize new hollow glass spheres for use as flow aids in thermoplastics such as PVC and polyesters. These microspheres are intended to improve flow and reduce warpage in injection molded and extruded products at very low use levels (2-4 phr).

PQ has two polymeric microsphere products under development. The first likely to be launched is PM 6545. It has a very low density (0.02 g/cc) and will be aimed at epoxies, urethanes, and polyesters in syntactic foams and medical cushioning.

3M Co.'s Industrial Specialty Chemicals Div. offers new S-38 hollow glass bubbles with a density of 0.38 g/cc and compressive strength of 4000 psi. S-38 is aimed at PVC automotive sealants, low-density RIM fascias, pultrusion of thermoset polyester consumer items (i.e., lawn tools), and thermoset syntactic foams for underwater oil-pipe applications.

RELATED ARTICLE: What's New in Mineral Fillers

Allied Custom Gypsum will launch an anhydrous calcium sulfate filler later this year. It can be used in plastics processed at over 300 F without releasing water, unlike hydrated gypsum used for flame retardance.

Aspect Minerals is a three-year-old producer of wet-ground, high-aspect-ratio muscovite mica for plastics applications such as RIM auto fascias. It has two major product lines: AlbaShield is a general-purpose series (20-30[cents]/lb) of highly delaminated products in a range of particle sizes. AlbaFlex is an ultra-high-aspect-ratio line - also in a range of sizes - that offers higher purity and narrower particle-size distribution (30-60[cents]/lb). Surface-treated grades are available.

Burns & Russell has a new surface-modified, -20 mesh natural granite for decorative cast products. Compared with unmodified grades, it's said to offer a 30% increase in compressive strength, reduced shrinkage, and increased abrasion and stain resistance.

The company also recently improved its surface-modified fine-particle silicas (Series F-1200, F-1500, and F-2100) so as to provide better surface properties and improved particle uniformity.

Georgia Marble Co. plans to introduce a new calcium carbonate for thermoset polyester SMC/BMC applications. New technology will be used to give this product greater uniformity so that it will impart better viscosity control in SMC/BMC.

J.M. Huber Corp.'s Engineered Minerals Div. (recently formed by consolidating Huber's Calcium Carbonate, Solem, and Clay Divs.) has two new calcium carbonate products. Optifil and Optifil T have an 8-micron top cut and low tendency toward particle agglomeration. These characteristics reportedly provide improved physical properties such as high impact strength in PVC siding and window profiles. The company also has a new, very white calcium carbonate for cultured marble. (Last year, Huber's Solem div. introduced the Granite Elite ATH line for cast marble.)

KMG Minerals (now a division of Franklin Industrial Minerals) is developing high-purity micas of less than 15 microns vs. traditional micas of 35-200 microns. Finer grades are designed to replace specialty tales as TPO reinforcements and are said to increase stiffness without degrading impact properties. Three such products will be introduced in 1996.

KMG will also launch a pelletized mica sometime next year for use in injection molded thermoplastics and RIM.

Nyco Minerals has a new high-aspect-ratio, fine-particle wollastonite for polyurethane low-density RIM. New RRIMCLOS I 10013 has a specially engineered aspect ratio and a surface treatment that's said to form a reactive bond with the PUR matrix. Improved flexural modulus and impact strength are said to result, along with lower CLTE and uniform shrinkage parallel and perpendicular to flow.

Also new is a high-aspect-ratio wollastonite intended as an alternative to talc in automotive PP copolymers. Nyad G Special reportedly provides improved mar and scratch resistance, improved impact strength, and reduced knit lines.

Polar Minerals will introduce new products once it completes a 150-million-lb/yr expansion of ultrafine calcium carbonate capacity at Mount Vernon, Ind., next month. The company will bring out a new 2-micron, high-brightness grade to supplement its 3- and 5- micron products.

Specialty Minerals has new Ultratalc 609 with a very fine particle size (0.9-6.0 microns). This high-aspect-ratio product reportedly provides increased stiffness without degrading impact strength. Besides uses in rigid PVC, it is gaining interest for PP and automotive TPOs.

R.T. Vanderbilt has new 3-micron Vantalc 2003 for PP copolymers used in automotive under-hood applications.