Blow molding companies can turn to coextruded, multilayer fuel tanks to meet new environmental standards, but rotational molders are more limited, so they face a far greater challenge - and they could lose business, roto-advocates warn.
But speakers at the Association of Rotational Molders International fall meeting in Cleveland held out hope, with new resins, coating technologies and other advances.
Major regulations for hydrocarbon emissions are coming from the U.S. Environmental Protection Agency and the California Air Resources Board, said George Kraemer, who heads ARM's permeation committee.
``These rules will affect millions of tanks,'' said Kraemer, president of Kracor Inc., a Milwaukee rotomolder that makes tanks for boats, lawn mowers and other markets.
The rules cover automotive gas tanks, which are made by blow molding, thermoforming or metal fabrication. According to Kraemer, next up are government regulations covering some rotomolding strongholds like agricultural tanks and chemical tanks.
The ARM committee was formed too late to influence initial rulings handed down by CARB, but Kraemer said some new rules are coming in 2006. The committee is working with CARB on testing of rotomolded tanks.
At the Cleveland conference, several speakers pitched their rotomolding materials to the fuel-tank market:
* Greg LeFevre, rotomolding business manager for A. Schulman Inc., made a presentation about a new rotomolding compound, called Polyaxis PR-1000, that resists permeation. The Fairlawn, Ohio, compounder wanted to make a better material for a customer, Scribner Plastics of Rancho Cordova, Calif., which had a project to rotomold 5-gallon gas cans for professional race cars - which are subject to CARB emission standards.
LeFevre said Schulman wanted a standard molding type of material that did not rely on a drop box inside the mold, or any special coatings.
``We decided we were going to try to come up with a single-shot, right out of the box,'' he said.
Polyaxis gas cans have passed CARB testing, although the standards constantly are evolving, LeFevre said in an interview. Schulman has worked with Kracor to test tanks for boats. ``All the testing so far looks good,'' he said.
Polyaxis grades include modified high density polyethylene and low density PE resins. Schulman still is testing applications before it develops a data sheet on Polyaxis PR-1000, he said.
* Cyclics Corp. of Schenectady, N.Y., discussed potential rotomolding applications for its CBT-brand polyesters, a novel form of polybutylene terephthalate that exhibits characteristics of both thermoplastics and thermosets.
Pilot-scale production should begin in January at Cyclics' site in Schwarzheide, Germany, which is at the PBT plant of BASF AG. PBT is the raw material used to make the CBT resin.
Jim Mihalich, Cyclics' sales director for the Americas, said CBT is an ultralow-viscosity material that polymerizes when heated. That means it can be processed ``in a polyethylenelike manner'' by rotomolding.
Designers already understand PBT in injection molding and extrusion. ``So it's not like we're stepping into new ground,'' Mihalich said.
CBT resin does not need to be ground to a powder for rotomolding. It does not sinter in the mold, since it turns into a fluid.
In rotomolding, Mihalic said, the material is heated just enough to polymerize the PBT, then is cooled rapidly. ``Just as with polyethylene, the faster you cool it, the better impact strength you'll get.''
PBT has a very high rating for fuel-tank permeation at room temperature, he said, and at elevated temperatures, the material outperforms PE by a large margin. Other potential rotomolding applications include chemical storage tanks, pressure tanks, small boats and body panels.
Mihalich said that on a start-up scale, Cyclics' CBT-brand material will be very expensive - about $7-$10 a pound. For fuel tanks, CBT might be used as an inside layer in a cross-linked PE fuel tank, he said.
The material requires pre-drying or the parts will be brittle, Mihalich said. ``Water acts as a chain-stopper,'' he said. But he noted that most rotomolders do not have drying equipment. In response, Cyclics is studying shipping dry material to rotomolders.
Cyclics displayed some test balls made by rotomolding, then painted to a high-gloss finish. Mihalich said mechanical properties include very high flexural modulus, tensile strength, scratch resistance and creep resistance. It remains stable, compared with PE. Cyclics is working on an impact grade.
* Houston-based Fluoro-Seal International LP, which has done toll fluorination treatment to boost barrier properties of plastic containers since 1983, introduced its new technology for reducing permeation of fuel through rotomolded tanks.
Fluoro-Seal officials also discovered the process makes fuel tanks more fire-resistant.
The firm runs 11 U.S. plants that do surface modification of bottles, mainly blow molded HDPE bottles. The company is looking to set up regional toll coating operations in areas where rotomolders are heavily concentrated, according to Bernard Bauman, vice president of special projects.
The high-barrier rotomolding surface treatment does not use fluorination. Instead, it starts with a reactive gas treatment on the outside of the tank - a surface treatment that helps the second step, a high-barrier epoxy coating, adhere better to the plastic surface.
To develop the special epoxy coating, Fluoro-Seal worked with Crosslink Technology Inc. of Mississauga, Ontario.
Bauman said the technology also provides high impact resistance and low cost, two traditional problems with coating of plastics.
Surprisingly, he said, many coatings can reduce tanks' impact resistance greatly, because a hard coating makes the plastic much more rigid.
On the flame-retardant front, Fluoro-Seal also discovered that its adhesion-improving surface-modification treatment makes it possible to coat tanks with intumescent coatings. The coatings now are used on steel framework in high-rise buildings, but they almost never are used on plastics.
When fire is applied to the coating, it foams up and forms a noncombustible insulation layer. A rotomolded tank passed the Coast Guard burn test with an endurance time of more than five minutes, the firm said.
``We're ready to start to commercialize this if we find someone interested in it,'' Bauman said.
* Ticona, a unit of Celanese AG of Frankfurt, Germany, promoted its Celcon acetal copolymer to make a permeation barrier for rotomolded fuel tanks.
``It can be used two ways. You can make a single-layer tank, or you can make a liner of acetal for a polyethylene tank,'' said Alan Dubin, market development manager of Florence, Ky.-based Ticona.
Dubin said Celcon acetal costs $1.50-$1.75 pound. ``We feel it represents a good value alternative between polyethylene and the next level up, which would probably be nylon,'' Dubin said.
Acetal copolymer resists chemicals and warpage and does not absorb water or change properties, the firm said. The resin can be rotomolded into complex shapes; it flows around threads and metal inserts. It can be made by traditional grinding.
* Gregory O'Brien, research and development manager for the Technical Polymers Division of Houston-based Atofina Petrochemicals Inc., reported on research showing that permeation levels can be reduced by rotomolding tanks from metallocene polyethylene and a layer of nylon or polyvinylidene fluoride.