Report card on liquid CO2 foaming.

While first-hand information is scarce, reports from processors confirm that this major new technology offers the promise of cost savings - but not until a number of kinks are worked out.

One of the most talked about new technologies for slabstock and molded flexible urethane foams uses liquid C[O.sub.2] as a cost-effective and environmentally benign blowing agent. Liquid-C[O.sub.2]-blown foams require two-thirds less blowing agent than conventional foams, and use a less costly one to boot. Overall formulation cost savings are said to run 6-10%. Equipment suppliers are certainly excited about the technology's future, as are urethane chemicals suppliers. Although foam processors using it are generally reluctant to talk, discussions with a few knowledgeable foamers indicate that there are still problems to be worked out, but liquid C[O.sub.2] is here to stay.

HOW MUCH FIELD EXPERIENCE?

Liquid-C[O.sub.2] blown slabstock foams have been produced commercially for about three years, first in Europe and more recently in the U.S. The driving force has been to eliminate ozone-depleting methylene chloride by using C[O.sub.2] to supplement water in the foaming reaction. Suppliers and processors have been working especially hard to generate lower-density foams with liquid C[O.sub.2] without sacrificing physical properties - an elusive goal with 100% water-blown foams. Another key target of liquid-C[O.sub.2] development is foams with a broader softness-hardness range.

Three equipment suppliers currently offer liquid-C[O.sub.2] systems for making continuous slabstock foam, each with its own patented design. Cannon in Italy pioneered the technology with its CarDio process and appears to have the most extensive production experience and the greatest number of installations. There are currently 23 CarDio units operating commercially worldwide, including eight lines at three major U.S. foam manufacturers. Existing CarDio block foam production units include Cannon Viking Maxfoam plants and retrofit packages on competitors' conventional equipment.

About 10 NovaFlex systems, developed in Germany by Bayer's Hennecke Machinery subsidiary, have been operating commercially for about two years in Europe and for less than a year at one major U.S. foam maker's site. Ten more units are due to be installed here this year. A total of 20 to 24 foam formulations will have been made with NovaFlex technology by early next year, according to Richard Kirschner, Hennecke's slabstock business-team leader. Kirschner says a thorough analysis conducted by one of its NovaFlex customers showed typical raw-material savings approaching 10% are possible.

Hennecke has also licensed Laader Berg of Norway to supply NovaFlex technology for Maxfoam lines. This technology is designed to be readily retrofitted to existing PUR foam production lines using methylene chloride.

A third liquid-C[O.sub.2] system comes from Beamech Group of the U.K. (represented here by LME-Beamech). Its technology has been used in the U.S. for about a year by Foamex International, Orlando, Fla., to produce various slabstock grades. According to Beamech spokesman Derek Greenwood, the company also has two lab units installed in the U.S. and in Europe, another unit about to be installed at a European roamer, and several others currently being commissioned worldwide. About 10 formulations are in full production. The company reports that its liquid-C[O.sub.2] technology is suitable for continuous manufacturing of low-density polyether foams with the Maxfoam/Varimax process, the R.S. Flat Top System, and the Vertifoam Process (both rectangular and round block). A horizontal round block has also been produced.

Much newer than slabstock applications is liquid-C[O.sub.2] technology for molded foams. Most current attention is focused on flexible molded foams for furniture and automotive seating, as well as noise reduction. There also appears to be potential in some semirigid foam applications and possibly in the non-insulation rigid foams arena.

As was the case with slabstock, Cannon also pioneered this technology with the introduction of the CannOxide process at the K'95 show in Dusseldorf. Hennecke was not far behind in introducing its NovaForm system. In Europe, Hennecke has at least one commercial installation that has been operating for less than a year. In the U.S., the only NovaForm systems are used for R&D. Cannon says it currently has 15 installations worldwide. Although there is no production CannOxide application yet in the U.S., domestic R&D installations include ICI Polyurethanes and Lear Seating Corp., Southfield, Mich. Two commercial CannOxide installations are at Recticel in France, which is producing furniture foams, and Mahgreb of Morocco, which makes transportation seating. Cannon says two more production sites will have installed CannOxide capability by the time this article is printed.

Beamech is also working to extend its C[O.sub.2] technology into molded foams. And new liquid-C[O.sub.2] metering units for molding were also recently introduced by two other major PUR equipment sup, pliers, while a third has a system in development.

SUCCESS IN FLEXIBLE SLAB

The new foaming technologies are based on the concept that using C[O.sub.2] as an auxiliary blowing agent in the liquid phase overcomes problems encountered when it is introduced as a gas into the foam mix - namely poor cell structure, voids, and other defects. Liquid C[O.sub.2] is metered into the foam reactants under controlled pressure and temperature. The mix is then carefully released to atmospheric conditions, which produces a froth. The key is maintaining the C[O.sub.2] in the liquid phase until the mix leaves the dispensing system. Otherwise, voids in the foam will again result. Typically the blend activator (water, silicone surfactant, and amine) is mixed into the polyol at low pressure and then blended with the C[O.sub.2] at high pressure. Finally, the polyol side is metered together with the isocyanate and tin stabilizer.

Despite these common principles, each machine supplier claims that its system confers particular benefits. Cannon maintains that its CarDio equipment is producing the greatest range of liquid-C[O.sub.2] foam formulations - around 50 different products - and attributes this to its proprietary laydown concept, whose versatility accommodates a broad range of foam density and hardness without the need to change the laydown device. Cannon also claims that its process is more "forgiving" and allows use of pigments and fillers such as melamine and calcium carbonate.

Meanwhile, Hennecke maintains that its NovaFlex system produces a more homogeneous cell structure than other processes and can generate foams with finer cells and unusual elasticity. Says Kirschner, "We are able to produce foam that's as good as, if not better than, foam produced with CFC or methylene chloride." One key aspect of this system's design is an expanding device attached to the modified mixhead. The device is said to carefully control the out-gassing of the liquid C[O.sub.2]. In addition, NovaFlex reportedly delivers uniform density throughout the foam. A slab measuring 83 in. wide and 43 in. high was tested in nine locations and exhibited a density of 0.95 [+ or -] 0.002 pcf and IFD at 25% of 23.3 [+ or -] 0.25, Kirschner reports.

Beamech's Greenwood says his firm's liquid-C[O.sub.2] system has its own advantages. "The key difficulty with these processes has been in ensuring that the C[O.sub.2] does not blow off too soon. In early models it would release itself quickly and explosively. We have proprietary mixing and process technology that overcome these problems." The company's patented foam laydown unit is said to offer controlled pressure reduction and enhanced mixing. These features are said to ensure excellent cell structure and avoid pinholes and "chimneys." This system has running times longer than 4 hr and has run HR and polymer polyol foams successfully, Greenwood says.

CONTINUOUS EVOLUTION

Continuous modifications and enhancements of these systems appear to have closed some gaps between different systems' capabilities. For example, all three equipment suppliers now claim they can vary both output rate and formulation on the fly. All maintain that their systems can now make very low-density to very high-density foams by varying the C[O.sub.2] level from 1.0 to 6.0 pph. More recently, Cannon has produced a low-density, super-soft foam with 10 pph of C[O.sub.2].

Meanwhile, Hennecke aims to modify the NovaFlex process to produce higher-density foams that are even more resilient and softer than those made to date. Cannon is working on extending CarDio technology into very soft foams and densities lower than 0.87 pcf, as well as high-resilience, filled, and all-MDI foams. The company also continues its R&D effort to adapt CarDio to continuous rigid-foam panel production. Cannon reports that using C[O.sub.2] instead of water lowers urea content of rigid foams, thereby improving compressive strength and adhesion to facings. The company also sees liquid C[O.sub.2] as a promising way to blow polyisocyanurate panels to meet increasingly strict flammability standards.

WHAT USERS SAY

Obtaining testimony from processors on how liquid-C[O.sub.2] technology is performing is rather tough at this stage. Few foamers are willing to share information publicly. Still, two CarDio users did discuss their experience with PLASTICS TECHNOLOGY. The MPI branch of Leggett & Platt in Coldwater, Miss., has been running two CarDio lines for nearly two years in production of foam densities from 0.85 to 1.8 pcf, though mainly in the range of 1.2 pcf or less, according to technical director Jerry Pool. He says the cell structure is somewhat irregular or "random," but the result is much higher resilience, which is excellent for furniture products. On the other hand, the cell structures achieved so far have not been ideal for foams as thin as 0.25 in. or less for specialty applications like packaging.

Says Pool, "We are looking to achieve smaller and more uniform cell structure that results in the smooth surface desired in specialty foams." He has heard that the Hennecke and Beamech systems don't have a problem achieving a fine, uniform cell structure. On the other hand, he has also heard that the other systems - unlike CarDio - have problems with solid particles such as fillers or pigments.

Besides ongoing R&D in equipment and process modifications, Pool sees improvements in liquid-C[O.sub.2] performance coming also from the chemical side, such as new silicones designed to provide smaller cells. He also notes, "Major silicone surfactant suppliers have been working to develop universal silicone products that will work well with fire-retardant formulations." The most commonly used products today are said to be Goldschmidt's BF2370, B8220, and B8010.

Witco's OrganoSilicones Group (formerly OSi Specialties) now offers two "universal" surfactants (L5770, L603) which reportedly work in all liquid-C[O.sub.2] flexible slabstock processes. Senior marketing manager C.V. Rose says Witco is now developing silicone surfactants and total additive packages tailored to the peculiarities of each process. A series of products is now available for all three types of liquid-CO2 equipment.

While users agree that liquid C[O.sub.2] does reduce formulation costs, there are some trade-offs. Says Pool, "There is the cost of engineering technology and of higher-pressure equipment - you are going from a 20-60 psi machine to 200-1000 psi. Also, the maintenance and cleaning required is more demanding than with conventional slabstock foam machinery."

A concurring opinion comes from Glenn Cavanaugh, v.p. and technical director at Trinity Foam in High Point, N.C., another CarDio user. He notes, "Payback for the capital investment theoretically can be arrived at rather quickly - under two years. But the R&D formulation work with a one- to two-year learning curve and scrap generation sets that back quite some time."

Trinity retrofitted two continuous flexible foam lines with CarDio systems over a year ago. One is a round-block line originally built by Uretech and the other is a Maxfoam square-block line. Cavanaugh says Trinity is still debugging the retrofitted round-block line, which produces a 50-in. cylinder to make bed quilting. On the square-block line, Trinity is making foams from 0.8 to 2.0 pcf. Cavanaugh says there is no question that liquid C[O.sub.2] should provide an economic advantage. However, he notes that process inconsistencies and the long learning curve indicate that there are a lot more improvements yet to be made.

MOLDED FOAMS ARE NEXT

Cannon's CannOxide and Hennecke's NovaForm liquid-C[O.sub.2] systems for molded PUR foams are currently seen as having the most potential in flexible foams for furniture, car seats, and noise-reduction applications. Equipment suppliers also see a future in very low-density semi-rigid foams and integral-skin foams for auto instrument panels at very low C[O.sub.2] levels. There may also be some potential for rigid molded foams in panels where insulation value is not critical.

The low cost and high blowing capacity of liquid C[O.sub.2] is also the key advantage in these systems. Both CannOxide and NovaForm allow for blowing cold-curing flexible foam with the addition of very small amounts of C[O.sub.2] - typically 0.5 to 1%. Hennecke says molded-foam furniture upholstery can be made with up to 20% lower density than with conventional foam processes. Cannon reports density reductions of 1230% versus conventional foams, as well as up to 50% better density distribution and up to 30% shorter demold times. Despite the frothing action in this process, both suppliers claim good flowability and mold-filling ability. Suppliers also say that formulation adjustments are necessary to optimize use of these.

Both CannOxide and NovaForm allow either direct injection of liquid C[O.sub.2] into the mixhead or preblending the C[O.sub.2] in the day tank. The difference is that C[O.sub.2] injection at the mixhead permits continuously varying the density in different parts of the molded foam, as in the case of dual-density auto seating. Both suppliers say liquid-C[O.sub.2] capability can be retrofitted to existing foam molding equipment.

Herman Miller Co., Zeeland, Mich., which manufactures all-water-blown MDI foams for high-end office seating, recently used the ICI Polyurethanes' CannOxide lab unit to run a two-day trial. "We shot one type of cushion and were able to achieve upwards of 25% weight reduction while maintaining the physical properties," reports staff engineer Will Delie. He also says the liquid-C[O.sub.2] process improved moldability and eliminated knit lines.

Herman Miller is still deciding whether to purchase a liquid-C[O.sub.2] system and whether to replace or retrofit its existing lines. Delie also notes reluctance to be the first to try liquid-C[O.sub.2] molding commercially in the U.S. "We are all a little uneasy to be the first, and we also want to wait and see what additional modifications are made by the equipment suppliers." He estimates that payback could take 12-18 months, but that could depend on the length of the learning curve and amount of foam scrap likely to be generated during the break-in period.

RELATED ARTICLE: New Liquid-C[O.sub.2] Metering Systems

Besides Cannon's CannOxide and Hennecke's NovaForm systems, at least two other equipment suppliers have introduced liquid-C[O.sub.2] metering units for molded foams, although none are yet in commercial use in North America.

* Linden Industries recently sold its first Froth-Ex C[O.sub.2]-metering unit. The unit allows for metering liquid C[O.sub.2] at the mixhead as well as into the polyol component of flexible and rigid PUR and PIR foams. Linden sees the most potential for this system in automotive seating and furniture, where Linden claims to achieve the same physical properties at 80% of the density of water-blown foams. Up to 10% savings in isocyanate usage reportedly results because of lower water levels.

* Gusmer-Admiral is continuing to refine its new liquid-C[O.sub.2] metering and dispensing module. Technical director Andrew Lehnert says the system is designed to introduce the C[O.sub.2] through the mixhead. Extensive trials have been conducted with TDI or TDI/MDI foams for sound absorption, seating, and head-rests. "Density reduction of 10% is our current aim," Lehnert says.

* Meanwhile IFTA Canada Inc. in Montreal, the North American representative of Impianti OMS of Italy, says OMS is in the process of developing a liquid-C[O.sub.2] system for molding flexible foams.