New directions for urethanes.

SPI's annual PUR conference shows where materials, additive, and equipment technologies are headed for rigid and flexible foams, RIM, and elastomers.

Polyurethane foam is headed for zero - that is, zero ozone-depletion potential (ODP). The transition to totally ozone-friendly foaming technologies again occupied center stage at the annual technical conference of SPI's Polyurethane Div. in Las Vegas last month. Deadlines for phasing out the first generation of less ozone-destroying blowing agents are nearly around the corner: 2003 for HCFC-141b and 2010 for both HCFC-22 and HCFC-142b. While European foamers have flocked to hydrocarbon blowing agents for rigid insulation foams, U.S. processors are more interested in alternatives such as liquid HFCs and liquid C[O.sub.2].

This report presents highlights of the new developments in more than 70 technical papers. (Next month we'll cover news from the exhibition.)

* For automotive: High-resilience flexible and low-density all-MDI foams, improved water-based release agents, SRIM advances, new energy-absorbing foams, high-heat polyurea/epoxy RIM, and non-fogging flame retardants.

* For appliances: New open-celled rigid foam for vacuum insulation panels, a new polyol, improvements in low-density HCFC-141b foams.

* For building and tank insulation: Liquid C[O.sub.2] processes expand into semi-rigid and rigid foams.

* For slabstock: Liquid C[O.sub.2] successes, an automated foam recycling process, and lower volatility BHT-replacement antioxidants.

* For footwear and elastomers: Improved water-blown integral-skin foams, new polyols and uv stabilizers.

ROADS TO ZERO ODP

R&D that is paving the way to zero ODP was the number-one topic at this year's conference. A big question is whether some rigid-foam formulators will opt for a two-step conversion - moving first to HCFC-142b or HCFC-22 and then to a zero-ODP option - or will go directly to the latter. The answer will vary according to market segment, says staff chemist John Murphy of Elf Atochem North America, who offers these predictions:

* Construction foams are an especially price-sensitive market segment that is likely to opt for two-step conversion.

* Appliance foams have the highest insulation requirements and are therefore expected to favor liquid HFCs. (These blowing agents are more benign to refrigerator-liner materials than is HCFC-141b.)

* Rigid spray foam is also likely to convert to HFCs, as this segment must avoid flammable blowing agents and requires good shelf stability and viscosity balance.

* Transportation and tank insulation trends will depend on the end use. Reefers require high insulation value and may turn mainly to HFCs or HFC/hydrocarbon blends. Water and the HCFCs could take the rest of that segment.

EFFECT OF BLOWING AGENT ON PUR ENTRY DOOR INSULATION

                                    HCFC-     HFC-
                                    141b      245fa

Density, pcf

Overall                             1.77      1.79
Core                                1.65      1.72

Compressive Str.
 Yield, psi

Parallel                            29.38     30.89
Perpendicular                       8.97      17.43

Volume Change, %

 100 C                 1 day       2.2       3.7
                       14 days      3.5       4.0
 70 C, 100% RH         1 day       0.1       0.5
                       14 days      4.0       2.9
 -30 C                 1 day       1.2       0.7
                       14 days      0.1       0.4

K-Factor (Btu-in./hr [ft.sup.2] [degrees] F)

Initial                             0.130     0.139

Cell Structure

% Closed                            85.7      88.9
% Open                              12.1       8.9

Source: Bayer Corp.

Conference speakers warned that evaluating all the new blowing agents for rigid insulation foams involves more uncertainties than ever before. Owing to the significant differences in boiling points and in vapor pressures, foams made with different blowing agents may appear to have better or worse insulation value depending on the test temperature.

Using new blowing agents also requires you to predict possible plasticizing effects that could compromise long-term dimensional stability of rigid foams. ICI Polyurethanes has devised a new testing methodology to accomplish just that. This "accelerated blowing-agent uptake" conditioning procedure was described in a paper at the conference.

THE LEADING CANDIDATE

The most prominent contenders for replacing HCFC-141b in the U.S. are liquid HFCs, led by AlliedSignal's HFC-245fa. It is reportedly non-flammable, has acceptable environmental characteristics and good toxicological properties, and is stable in the presence of common foam raw materials. From a processing standpoint, Allied has identified certain silicone surfactants (e.g., Goldschmidt B8404 and B8462 and OSi L-6900) that improve the quality of appliance foams blown with HFC-245fa. AlliedSignal expects to find additional surfactants that enhance performance in other foams.

Recent evaluations of unfaced panel core samples show that foams made with HFC-245fa age more slowly than foams made with HCFC-141b and are generally superior in thermal conductivity after several weeks of aging.

In two presentations, Bayer Corp. reported on its initial evaluations of HFC-245fa in insulation for entry doors and water heaters. In doors, the K-factor of the 245fa foams was 7% higher at the same density, but there was no major sacrifice in physical properties (see table). Bayer considers these early results quite promising.

In water heaters, thermal conductivity and physical properties of 245fa foams compared favorably with those of HCFC-141b foams. Results on a number of water heaters using the U.S. Dept. of Energy's 24-hr simulated-use test were quite similar for both foam systems.

Bayer also has found ways to improve HCFC-141b foams for appliances. One development is a finer-celled foam, which has been tested commercially on refrigerator cabinets and doors. By tailoring levels of water, catalyst, surfactant, and blowing agent, Bayer achieves 15% smaller cell diameters, which lowers the radiative heat transfer. Bayer also uses less water, thereby producing less C[O.sub.2] and reducing heat transfer by gas-cell conduction. Bayer reports that the end result is a 3.4% lower initial core K-factor and 2.8% less reverse heat leakage than with a standard HCFC-141b foam.

Bayer also reports that a new HCFC-141b foam currently being tested in refrigerator cabinets has 8% lower density than standard commercial appliance foam but shows improvements of at least 3% in both initial and aged K-factors.

BETTER FILLING OF APPLIANCES

Perhaps Bayer's biggest news for appliances is an improved method of filling refrigerator cabinets, developed with its Hennecke machinery subsidiary in Germany. Called TopFlow, the technology reportedly provides better density distribution [ILLUSTRATION FOR FIGURE 1 OMITTED], which results in lower foam usage per cabinet. Material savings greater than 5% have been achieved, Bayer says. The key is simply to inject the foam at a central point (the middle of the cabinet back) rather than at one end (the compressor compartment) as is usually done.

A technology for making vacuum insulation panels has now been scaled up to permit mass production. ICI's technology reportedly produces 100% open-celled rigid foam at the rate of 50 [m.sup.3]/hr. Vacuum panels reportedly can make appliances up to 25% more efficient when substituted for 30% of the usual foam.

Dow Plastics has a novel polyol that can be processed with higher levels of water to yield an open-cell C[O.sub.2]-blown foam with 10-15% lower density but no sacrifice in foam properties compared with foams blown with HCFC-141b. The new foam reportedly shows acceptable compressive strength and little shrinkage at elevated temperatures.

A MORE COMFORTABLE RIDE

Dow Chemical Canada and Johnson Controls Inc. gave a joint paper on production of extra-high-resilience, TDI-based flexible foams. These foams are aimed at newer car-seat designs, referred to as "All Foam in Dead Pan," which rely on PUR foam to make up for the absence of springs. Dow's contribution was a new generation of higher functionality polyether polyols and copolymer polyether polyols. Foams made with these polyols reportedly exhibit superior curing and reduced marking when demolded. The foams also outperform foams made with traditional polyols in a number of durability tests.

These polyols contribute to the important factors of comfort (ball-rebound resilience remains higher than 50% after humid aging) and support (indicated by significantly improved compression set). In a "live" Ride and Drive test, seat cushions made with these products scored higher in the subjective ratings of seat occupants, both in initial comfort and after a 90-min drive evaluation [ILLUSTRATION FOR FIGURE 2 OMITTED].

A new generation of all-MDI systems from ICI is aimed at low-density flexible foams for seat cushions and backs and arm and head rests. The systems reportedly enable large and complex shapes to be processed on conventional equipment with fast cures and reduced levels of catalysts and additives, resulting in lower fogging, ICI says.

Air Products and Chemicals reported on a new water-based release agent for seating foams. It's said to overcome the negative effect of previous water-based products on bonding adhesion of the foam to fabric coverings. The new release reportedly contributes to foam/fabric bond strengths of 6-8 N (1.35-1.8 lb) versus 1-4 N (0.225-0.9 lb) for other water-based releases. Although this is still slightly short of the minimum requirement of 9 N (2.0 lb), Air Products is confident that fine-tuning will reach that goal.

A new polymeric catalyst with low vapor pressure is the key to Bayer's new semi-rigid foam systems for instrument panels. Formed by the reaction of an amine catalyst with a trifunctional polyether, the polymeric catalyst is said to prevent PVC skin staining and degradation because it is reacted into the polymer foam structure. It cannot evaporate inside the cells during foaming. Foams made with these catalysts reportedly have lower viscosity, lower fill weights, and reduced demold times compared with a standard system. Aging tests of foam with vinyl skins show good elongation retention of a thermoformed skin and small color shifts in a slush-molded PVC skin.

NEW APPROACHES TO RIM

For rigid structural parts in automotive and other applications, the newest production technique is the long-fiber injection (LFI) process that was introduced by Krauss-Maffei at the K'95 show in Dusseldorf, Germany, last fall (see PT, Dec. '95, p. 46; Oct. '95, p. 14). In Las Vegas, both Krauss-Maffei and ICI presented papers on this alternative to SRIM that does not use costly glass mat. Instead, the fibers are chopped directly into the foam mix as it is dispensed into an open mold. According to Krauss-Maffei, material costs are thereby lowered by 30-40%. Start-up of the first commercial LFI molding line is due by mid-1997.

Anew approach to formulating high-heat-stable RIM polyureas for auto body panels was presented by Dow Plastics. Addition of an aromatic epoxy resin to the isocyanate side during processing, followed by postcuring, reportedly eliminates the blisters that occur in conventional RIM polyureas when they are exposed to high temperatures shortly after humid aging. Another novelty of this approach is that it uses no catalyst.

WIDER SCOPE FOR LIQUID C[O.sub.2]

Several papers at the conference testified to the growing range of applications for new liquid-C[O.sub.2] blowing technologies. At K'95, the Cannon Group of Italy introduced its CannOxide process for foam molding with liquid C[O.sub.2] (PT, Dec. '95, p. 46). In Las Vegas, Cannon reported on one recent European application in which furniture parts with complex inserts were molded with 17% lower average density but no loss in physical properties or curing speed relative to water-blown flame-retardant formulations.

Cannon also says recent R&D has generated promising results on the use of CannOxide for discontinuous molding of rigid foam insulation panels. In this application, liquid C[O.sub.2] reportedly offers numerous potential advantages over water-blown foams, such as improved adhesion to facings, better mechanical properties, reduced exotherm, and faster demolding.

Meanwhile, Beamech Group of the U.K. (represented here by LME-Beamech) reports that its own liquid-C[O.sub.2] process has been shown to be suitable for continuous manufacturing of low-density polyether foams on the Maxfoam/Varimax process. Liquid C[O.sub.2] works with the R.S. Flat Top System, the Inclined Conveyor process with Rising Side Film or Planiblock Flat Top System, and the Vertifoam Process (both rectangular and round block).

Beamech says foams made with Arco's Softcell polyethers show density reduction from 2.2 pcf down to 1.7 pcf using 2 php of C[O.sub.2]. Beamech has also used Dow copolymer polyols to achieve densities in the range of 1.0 pcf with good hardness properties.

INNOVATIVE FOAM RECYCLING

A new process that produces molded parts directly from shredded slabstock trimmings and production scrap was described by Bayer. The ReMoTec process (Rebond Molded Technology), first introduced at K'95 (PT, Dec. '95, p. 47), was jointly developed in Germany by Bayer's Hennecke subsidiary and foam processor Greiner Schaumstofftechnik. It's an automated process for grinding the foam scrap, mixing it with virgin PUR binder, and dispensing the mix into molds on a rotary table. This process is already commercial in Europe for making automotive headrests, armrests, door liners, and noise/vibration insulation. Typical parts weigh up to 3 lb and have densities of 3.5-25 pcf. Maximum part size is 45 x 45 in.

FOOTWEAR AND ELASTOMERS

Recent progress in making water-blown polyether integral-skin foams for footwear was reported at the conference by Bayer. A heat-activated catalyst is one component of a new generation of systems Bayer is designing specifically for water blowing. Researchers say these systems more closely mimic the surface densification of physically blown foams. In fact, Bayer claims to have exceeded the density gradient provided by HFC-134a in integral-skin foams. The new systems reportedly exhibit improved abrasion resistance and flexural properties.

New polyols for elastomers were discussed by three suppliers. Shell Chemical reported on a new saturated hydrocarbon diol, KLP L-2203. It's said to make soft TPUs and cast elastomers that exhibit very broad service-temperature ranges due to the low glass-transition temperature of their soft segment (-50 C) and high softening temperature of the hard segment. Shell also claims improved resistance to hot, humid environments as compared with using standard PPG polyols. Shell foresees uses in elastomers for polymer modification, blend compatibilization, and coextrusion tie layers.

Two new families of high-performance polyether polyols that bridge the cost and performance gap between premium PTMEG and conventional PPG polyols were introduced recently by Arco Chemical and BASF (PT, Oct. '96, p. 30; Feb. '96, p. 12). The low monol content of these new products reportedly yields elastomers with much higher molecular weight and improved properties, as well as shorter demold times and excellent green strength.

NEWS IN ADDITIVES

To reduce windshield fogging and staining of foam covering materials, BHT can be replaced with combinations of less volatile liquid antioxidants, according to research by Ciba Additives. For best storage stability and scorch resistance in polyether foams, Ciba recommends a combination of phenolic antioxidant Irganox 1135 and the aromatic amine Irganox 5057. In polyesters, Ciba recommends a phenolic like Irganox 1135 plus a phosphite like Irgafos DDPP for optimal scorch resistance.

Ciba also is working on uv stabilizers for weatherable MDI-based PUR elastomers, which usually discolor rapidly. Accelerated weathering tests of a RIM-type PUR, a polyester elastomer, and a TPU show that a combination of a benzotriazole uv absorber with a HALS is the most effective system, Ciba reports. In some cases, even better results were obtained with a developmental uv absorber based on new chemistry.

Halogenated flame retardants can be replaced in flexible polyester foams, according to research by Hoechst AG in Germany (parent of Hoechst Celanese Corp.). Hostaflam TP OP 550, a new reactive phosphorus-containing polyol, is said to show excellent migration stability and aging resistance with no sacrifice in physical properties. Low fogging is said to result. As little as 3 php may be used, and flame-retardant properties of foams actually improve with heat aging, Hoechst says.