Fast systems and novel polyols, combined with foaming under reduced pressure, are keys to the new approach. Report by Liz White, editor
Pascal technology is a "breakthrough, it is truly revolutionary fridge technology," claimed Vanni Parenti, Dow's PU global appliance technology leader, based in Coreggio in Italy.
Parenti was making his pitch for Dow's development of the patented Pascal approach to win the Innovations Award, 26 Sept, at the 2011 meeting of the Center for the Polyurethanes Industry, held in Nashville, Tennessee.
Parenti explained that Pascal raises the energy efficiency of refrigerators and freezers by up to 10 percent, and cuts fridge demoulding time by up to 50 percent.
Pascal does this by using fast-reacting PU systems, based on polyols specially developed by Dow, and by filling the appliance cabinets under vacuum to give rapid, efficient flow into every part of complex shapes.
The resulting fine-celled foam gives better insulation with all types of blowing agents.
Dow Polyurethanes, in cooperation with Cannon SpA, who developed the equipment for Vacuum Assisted Injection (VAi) and a Rotojig for fast demoulding, officially launched Pascal 9 Sept, at a Shanghai Summit 2011, held immediately after the UTECH Asia/PU China 2011 event.
The technology was also a highlight at the World Appliance Expo in Shanghai in March 2011. At this event, Qingdao Haier Co. Ltd showed a household refrigerator using the technology, made at its Chongqing plant in western China.
This domestic two-door fridge, the first A**** rated device made in China, consumes 0.19 kwh/24h (average 0.30 - 0.40 kwh/24h for comparable competitor's models).
Dow has sold Haier a license for Pascal/VAi technology and the Chinese group has converted one line, with capacity for a million fridges.
A second license has been signed, with an unnamed appliance maker, who will start production early next year, said Bruno Barbet, Dow's global marketing leader for appliance polyurethanes, based in Horgen, Switzerland.
Fast reacting systems key to fine cells
In a 27 Sept interview in Nashville, Parenti took UTI through how he came up with the new material/process.
"Everybody knows that if you go to very fast reactivity you get finer cell size, and this is the key to the good insulating values of the foam, producing a good K factor (the foam thermal conductivity)," he said.
Foam reactions can be made faster in many ways. "The first thing we did was take a standard cyclopentane system as run in the market, and we lowered the water level, and made it faster," but it didn't flow well and density rose.
"But if you reduce the pressure, you recover the density and flow is better: you get rid of flow issues," he claimed.
The K factor, the ther mal conductivity, is better, but not by much - dropping to 19.4 mW/m.K from 20 mW/m.K, Parenti said.
Parenti said most of the development has been done with cyclopentane (CP) as blowing agent (BA),since this is used in some 80 percent of appliances. CP also performs less well in insulating than BAs such as the hydrofluorocarbon HFC-245fa, so Dow felt it made sense to start there, to maximise the insulation advantages.
Parenti's next step was to take the current insulation system which gave the lowest Lambda-value and make it faster. At the same time "we took a completely new base formulation with new base polyols and reduced the water level to make it react faster."
The 'lowest-Lambda' system gave a conductivity of 19.1 mW/m.K while the new material, christened Pascal, moved down to 18 mW/m.K, because of the combination of the cell-gas composition and new system polyols.
Parenti said the real step-up in performance came when the backbone of the polyol system was drastically changed. With this specific tailored system, consisting of different types of base polyol reactor grades, the experimenters found they could also reduce the catalyst level.
Parenti’s CPI paper says the polyols have higher viscosity, higher aromaticity and higher functionality, and can be used without affecting flow, applied density and demould.
Cannon gets involved
When Parenti had confirmed the value of the new system in the laboratory, the next step was to set up a commercially viable process.
Barbet took up the story: "Dow then needed machinery techno logy to implement with the new polyols, and chose Cannon as its machinery partner to develop the equipment."
Barbet said Cannon was a natural partner, as it has global reach across Europe, the US and the Far East, especially in China. Cannon is also a leader in equipment for the refrigerator market, and "last but not least, Cannon and Dow had worked together previously in Italy on a vacuum-assisted process for making discontinuous insulation panels," Parenti said.
Cannon, Dow felt, would be willing to put the necessary investment into the techno logy to modify the equipment significantly, not only for the vacuum part, but also for demoulding, where the timing is so much improved that you need "some fundamental changes," said Barbet.
Cannon's redesign to allow inject ion under reduced pressure, led to a machine that was efficient and simple in operation, Barbet said.
Limited vacuum
Parenti agreed that the vacuum is a limited one - at 0.75 to 0.95 bar. "You select the right pressure, depending on the wall thickness and geometry. It's not a deep vacuum. It is very easy to achieve and maintain," he added.
"What we needed to optimise was mainly the chemistry. Moving from a la b test to a fridge geometry was very different, and involved a whole new process environment." he said.
Dow is on the third generation of the systems, devised as it gradually refined the details in fridge cabinets, in a pilot plant developed by Cannon.
Dow worked with international appliance group Haier to commercialise the techno logy, but Parenti said it has worked with eight different appliance makers, in two cases on two different models, to make 600 or 700 cabinets and prove the approach works. These are global companies from Europe, North America, China and Japan, Barbet said.
Rapid demould of great value
Parenti regards Pascal/VAi as a breakthrough, because "on top of the increase in energy efficiency and on top of the fact that it works with any BA, you don't need to change plant layout, and you can really exploit the rapid demould."
Fridge makers can either use fewer moulds for the same plant, or produce nearly double the amount of fridges on the same equipment.
Pascal also improves worker health and safety since, for the vacuum to work, seals must be airtight. This means no BA (CP or otherwise) is emitted into the factory atmosphere during production.
All blowing agents possible
Dow has shown it is possible to use its system with any type of BA or blend. "It is just a matter of adjusting for different types of solubility," said Parenti.
Dow has also started to test some of the Generation 4 BAs now coming through, although Parenti indicated tests were restricted by the limited quantities available. He expects Pascal to work here as well. "As soon as they provide the right amount, we can speed up development in the laboratory with any manufacturer," he noted.
Commercial quantities of Honeywell's new liquid BA are not expected before 2013, while Dupont and Arkema's earliest launch for their Generation 4 BAs will not be before 2014, Parenti thinks.
In North America, use of HFC-245fa is common in appliance insulation and using HFC-245fa with Pascal raises energy efficiency further, but fluorinated BAs have high GWP (global warming potential) so there is pressure on users of HFC-245 to phase it out.
And, since users do not want to change their process twice, as it is an industrially massive step, choice of a new BA is critical, Parenti said.
