Most relevant foam selection criteria k-Values and densities of different blowing agents:
The 2 most important criteria of selecting foam material are the thermal conductivity (k-value) and the density: The lower the thermal conductivity is the less energy will be lost,
the less density is reached, the less material is needed to fill a cavity, the less it costs.
The following table contain compared test data under production conditions as made by foaming material producers (BASF-Elastogran, Huntman-I.C.I, Bayer and Dow), by some refrigerant producers, for HFC-365mfc (Solvay, licence of Bayer) and HFC-245a (Honeywell) by blowing agent producers. The overall density have a range: the lower range values can be reached in simpler cabinet geometry foamed in bath position and if the filling hole is centralised on the bottom point (so called top flow technology) while the upper overall density value is reached by longer foam rising ways filled from compressor compartment side or top plate side. Only in few single case their were deviations with worse values outside the given range as a result of not optimal production or material conditions. We did not take into consideration special controlled “laboratory” conditions which often could reach 1-2 mW/m*K better k-values as to be realised in running production even with strict quality control on material, machines and process. We estimate that the HCF-365mfc and HCF-245fa values could be improved in the future by 1-1.5mW/m*K similar to the values reached by other blowing agents after 2-3 years of research when the systems will be optimised.
² At –20°C the k-values are often higher than at +20°C for low boiling materials. Lowest values are often reached in the range of 15-20°C. To receive a more realistic k-value we selected the comparison value on 10°C as average value because freezers are inside <-20°C, representing normally 33% of refrigeration volume, refrigerator inside 3-8°C and environment temperature for both are 18-38°C for subtropical class, up to 18-43°C
for tropical class. Because of a condensation effect for lower temperatures underneath 0°C Cyclopentane foam have significant lower K-values than CFC-11.
³ see remarks to changes of standardisation of GWP 4 Old IPCC 1996 value, which probably have to be creased by 20% to make in comparable with WMO 1999
values 5 The value of CO2 can also be 0 id CO2 is taken from air and not by burning of fossil Hydrocarbon.
The data base of HFC-245fa is incomplete and on HFC-365mfa still very small. We did not mentioned anymore HCFC-123 which did not pass the health test (PAFT) as well as HFC-152a, because relevant research data were not yet presented or not known yet by us.
A Handicap for the replacement of HCFC-141b by HFC-245 or HFC-365mfa is the high prices of these 2 blowing agents. US$ 9,00 per kg HFC-245fa and US$ 5,50 for HFC-365mfa is much more expensive than Cyclopentane.
Besides environmental aspects and density, which means cost of foam per refrigerator (the lower density can be reached the cheaper is the foam), an effective production is a decisive criterion for the economic efficiency of PU foams. The production efficiency are influenced by - foam material characteristics , specially the demoulding behaviour and flow behaviour, and also by - the used technology: foaming machines, the supporting jigs, opening and closing speed, heating, mixing heads,
cabinet carriage and their movement speed, which we will analyse separately. First we will concentrate of the foam material itself and after reanalysing many articles and research reports in this field we decided to cite an article of Udo Rotermund, Gottfried Knorr, Holger Seifert, Werner Wiegmann: Technical Comparison of Various Blowing Agents with Different PU-Systems set for the Appliances Industry, Elastogran (BASF), 2000.
FIELD OF THE INVENTION
The present invention pertains to rigid insulating foams prepared from the reaction of pentane blown methylene diphenylene diisocyanates and its higher ring content oligomers and polyols which exhibit low flammability while at the same time possessing low thermal conductivities. More particularly, the present invention pertains to polyurethane and polyisocyanurate foam systems employing a brominated halocarbon in addition to an aliphatic hydrocarbon as a blowing agent.
BACKGROUND OF THE INVENTION
Since the widespread adoption of the Montreal Protocol, the urethane industry has concentrated efforts directed to eliminating the use of chlorofluorocarbons, such as the widely used CFC-11, from polyurethane foam formulations of all types. The use of HCFC's such as HCFC-22, monochlorodifluoromethane, which have lower ozone depletion potentials (ODP's) has been promoted as an interim solution. However, HCFC-22, an HCFC of choice, is a gas at room temperature with poor system solubility, and thus extraordinary processing equipment must be used, including in some cases, pressurized day tanks.
Water has been utilized for many years in polyurethane and polyisocyanurate foam systems. However, the carbon dioxide generated by the water/isocyanate reaction is markedly inferior to the CFCs and HCFCs with respect to preparing rigid foams having low K-factors. To overcome this deficiency, it has been suggested to include perfluorocarbons (PFAs) in a water blown formulations. However PFAs are quite expensive despite being used in modest amounts; have exceptionally poor system solubility, often requiring emulsification rather than solution; and moreover offer only a modest advantage over all-water-blown systems.
Low-boiling aliphatic hydrocarbons have been suggested as blowing agents for polymeric foams, and are widely used in the expandable and expanded polystyrene industry. However, they have been eschewed by the polyurethane industry due to the flammability of the foams produced through their use, as well as the high K-factors obtained in rigid foams, making them undesirable for use in many applications.
Ageing of foam.
But we also should not look only on initial values after manufacturing, as it is part of the
refrigerator standards, but on values over the full lifetime of a refrigerator. For example CFC-11 and HCFC-141b used as blowing agent in foam produce foam with excellent initial k-values in the range of 17 mW/m*K (CFC-11) respective 17.5 mW/m*K (HCFC-141b); but after 310 days (CFC-11) respective 280 days (HCFC-141b) because of faster diffusion of this small molecules out of the cellular foam matrix, their k-values of foam became higher, that means lower insulating, as if larger blowing agent molecules, like Cyclopentane (18 mW/m*K) or HFC-365mfc (18 mW/m*K; not yet optimised). The speed of ageing depends from
- the temperatures the foam is exposed during life,
- the skin of foam (in the refrigerator one side in direction of cold storage are plastic like Polystyrene or ABS and the other side is quite good sealing steel),
-the size of molecule,
-the partial vapour pressure, which in case of Cyclopentane is slightly reduced because of partial solubility
inside the foam matrix.
After 6-9 years the k-values of foam produced with different blowing agents will become similar to each other in the range of 27-28 kW/m*K, that is the value after complete diffusion of the blowing agent, so that the foam matrix is only filled by air. Therefore the discussion which blowing agent are the best should not to be taken too serious if the k-values are deviating only by 1kW/m*K - except under ODP, health aspect and bid differences of GWP values.
Values like:
- the cabinet constant (= reverse heat leakage), that represents the energy needed to maintain the temperature difference of a cold storage to its environment,
- the pull down energy (this is a question of the efficiency of the cooling circuit and has nothing to do with the insulation), and last not least
- energy consumption of the refrigerator, depending on insulation, design and cooling circuit construction) are the most important factor of global warming to be considered in the refrigeration sector.
At moment refrigerator companies in USA and Japan are using HCFC-141b, in Europe nearly only Cyclopentane and Cyclopentane mixtures and in the rest of the world mainly Cyclopentane.
Modern (crap) fridges often contain insulating foam that is blown with hydrocarbon (HC)
blowing agents, usually cyclopentane but may also include n-pentane and i-pentane,
collectively referred to in this report as “pentane”. These hydrocarbon blowing agents
have replaced the use of chlorofluorocarbon (CFC) and Hydrochlorofluorocarbon
(HCFC)blowing agents (ozone depleting substances (ODS)) and Hydrofluorocarbons (HFC) blowing agents (gases with high global warming potential (GWP)). HC blowing agents are not ODS and do not have a high GWP but pose greater fire risk due to their high flammability.
Permitted fridge treatment facilities accept fridges (those containing CFC/HCFC/HFC/HC refrigerants and blowing agents) and process them to remove the oil and capture the refrigerant from the cooling circuit. Once this is done, in accordance with the WEEE Directive and associated Defra BATRRT guidance4, the degassed CFC, HCFC and HFC fridge carcasses must be treated in dedicated plant, which will ensure that the blowing agent is collected and sent for destruction (e.g.incineration).
Pentane blowing agents that are used in the insulating foam of fridges have the R11
(highly flammable) risk phrase (note: term not to be confused with “R11” CFC
refrigerant). The pentane is entrained within the foam and therefore the material
should be assessed for flammability as a solid in accordance with Test Method A.10
Flammability (Solids). If the foam is assessed as being hazardous (i.e. under the
R11 risk phrase) then it would be assigned the H3A (highly flammable) hazardous
property and appliances that contain it as a component would be classified
hazardous waste under European Waste Code 16 02 13* (discarded equipment
containing hazardous components other than those mentioned in 16 02 09 to 16 02
12) or 20 01 35* (discarded electrical and electronic equipment other than those
mentioned in 20 01 21 and 20 01 23 containing hazardous components).
The GC MS analysis of the blowing agent(s) contained in the foam panels confirmed
that each panel contained a hydrocarbon blowing agent, as had been marked on the
exterior of the appliances (see Appendix 1). The results also confirmed that
cyclopentane was the principal hydrocarbon blowing agent used in the foam panels.
However, 9 foam panels also contained iso-pentane as a minor constituent (with
cyclopentane identified as the main constituent), and 2 panels contained iso-pentane
as the main constituent.
Burning rates:
All foam samples burned the required distance (100mm) in a time under 20 seconds.
The slowest burn rate recorded was 19.3 seconds (test sample 3, fridge 1) and the
fastest recorded was 2.8 seconds (test sample 1, fridge 8). The average burning rate
time across all 60 samples was 9.4 seconds.
The fastest and slowest burning samples both contained cyclopentane blowing
agent. The type of hydrocarbon blowing agent did not appear to have a significant
effect on the burning rate of the foam samples, with the average burning rate
between the 3 types (i.e. those containing a) cyclopentane, b) cyclopentane and iso-
pentane (as minor constituent) and c) iso-pentane (as main constituent)) being 9.7,
9.3 and 9.2 seconds respectively. Therefore, variability in burning rate between
samples was possibly due to variability in hydrocarbon blowing agent content
(quantity), rather than type.
When assessing waste electrical equipment, such as fridges, it is the presence or
absence of hazardous components that determines if they are classed as hazardous
waste or not. Insulation foam that has been blown with a hydrocarbon blowing agent
(pentane) has been demonstrated to posses the hazardous property H3A (highly
flammable). This means it is a hazardous component and would, amongst other
components, make a fridge a hazardous waste.
IT was concluded that all fridge panels tested should be considered as highly
flammable solid materials. As a result of this, we believe that all fridge insulation
foam produced using a hydrocarbon blowing agent should be considered highly
flammable, unless tested and demonstrated otherwise.
APPENDIX-1:
I'VE ALWAYS SAID.............FREON12 (R12) FOREVER (AT LEAST NOT FLAMMABLE).................
