Abstract:
Foam blowing agent blends containing trans-1,2-dichloroethylene and one or more hydrofluorocarbons are provided, as are foam compositions containing such blends. The resulting foams exhibit dramatic improvement in fire performance.

Description:
This application claims the benefit of copending application Ser. No. 10/336,368, filed Jan. 2, 2003. 
     BACKGROUND OF THE INVENTION 
     This invention relates to foam blowing agent blends containing trans-1,2-dichloroethylene (“Trans 12”) and one or more hydrofluorocarbons (“HFCs”), and to foam compositions containing such blends. Trans 12 is useful to improve the fire performance (that is, to suppress flame spread and smoke generation, as measured by ASTM E 1354 in terms of reduced rate of mass loss and reduced specific extinction area upon ignition) of HFC-blown, closed cell polymer (insulation) foams, such as polystyrene, phenolic and polyurethane foams. 
     Chlorofluorocarbons (“CFCs”) had been used as blowing agents for rigid, closed cell insulation foams for many years because they offer outstanding fire resistance in addition to good thermal insulation, since the CFCs are non-flammable. However, CFCs have been phased out because they are said to be detrimental to the ozone layer. Hydrochlorofluorocarbons (“HCFCs”) such as 1,1 -dichloro-1-fluoroethane (“HCFC-141b”) with low ozone depletion potential (“ODP”) have been alternatives for CFCs. However, HCFCs are also being phased out under the Montreal Protocol. The next generation of foam blowing agents must have zero ODP. For fluorochemical blowing agents, these are generally the HFCs such as 1,1,1,3,3-pentafluorobutane (“HFC-365mfc”). However, HFCs are typically more flammable than the CFCs or HCFCs, so that the new formulations will usually require higher levels of flame retardants in order to achieve the same levels of flammability. This increased level of flame retardant creates a problem because upon burning the flame retardants increase smoke levels. Thus, as disclosed by Albemarle Corporation in its website, Albemarle.com/saytexfr_polyurethane.htm, the addition of a brominated reactive polyol (RB-79) increases the smoke density of foam when subjected to fire tests. It has been reported that the use of 245fa alone will result in foams which generate high smoke density. What is thus needed is a means to achieve satisfactory blowing with HFCs while reducing the amount of fire retardant so as to reduce smoke density and lower overall cost. While Trans 12 has been disclosed as a foam blowing agent, as for example in U.S. Pat. No. 5,126,067, its use to reduce flame spread or smoke density has not been previously disclosed. 
     BRIEF SUMMARY OF THE INVENTION 
     An HFC-based foam blowing agent composition is provided, which composition contains Trans 12 in an amount effective to enhance the fire performance of the blown foam, as well as polyurethane foam compositions comprising a polyol, an isocyanate and the blowing agent composition. Preferred HFCs include HFC-365mfc, 1,1,1,3,3-pentafluoropropane (“EHFC-245fa”) and 1,1,1,2-tetrafluoroethane (“134a”). Typical Trans 12 levels are from about 5 to 40% by weight, based on the total blowing agent weight. 
    
    
     DETAILED DESCRIPTION 
     Trans 12 improves the fire performance (suppresses smoke development and mass loss rate) of HFC blown foams, as well as lowering the global warming potential of the blends compared to HFC alone and lowering the overall cost of the foam formulation by reducing the amount of required flame retardant. As noted above, these blends are particularly useful for making closed cell polymer (insulation) foams having improved fire performance, such as polystyrene, phenolic and polyurethane foams. 
     Trans 12 generally makes up 5–40 weight % of the blends. In the polyurethane foam compositions, the effective concentrations of the blends are typically about 0.1–25 weight % (preferably 0.5–15 weight %), based on the weight of the total polyurethane foam formulation. 
     The blowing agent can be distributed between the “A” and “B” sides of the foam composition. All or a portion of it can also be added at the time of injection. The Trans 12/HFC blends can also contain additional blowing agents such as water or pentane(s). 
     The other components of the premix and foam formulations may be those which are conventionally used, which components and their proportions are well known to those skilled in the art. For example, fire retardants, surfactants and polyol are typical components of the B-side, while the A-side is primarily comprised of polyisocyanate. Water is frequently used as a coblowing agent. The A and B sides are typically mixed together, followed by injection of the catalyst, after which the mixture is poured into a mold or box. 
     The practice of the invention is illustrated in more detail in the following non-limiting examples which compare the performance of HFC-blown foam, using 245fa or 365mfc alone, to the performance of such foams wherein the blowing agent contains 10, 30 or 50 mole % of Trans 12. The formulations used (all having an Iso Index of 275) each contained 156.3 parts D-44V70, a polymeric methane diphenyl diisocyanate (polymeric MDI) available from Bayer Corporation; 100 parts PS2412, a polyester polyol having a hydroxyl number of 230–250 available from the Stepan Company; 0.17 part PC-5, which is pentamethyldiethylenetriamine, a catalyst available from Air Products; 2.71 parts K-15, potassium octoate in dipropylene glycol, a catalyst available from Air Products; 2 parts B-8465, a polysiloxane-polyether copolymer surfactant available from Goldschmidt Chemical Corporation; and about 34–44 parts blowing agent, as more specifically set forth in the table below; all parts are by weight. 
     The A-side (D-44V70) and B-side (a mixture of the polyol, surfactant and blowing agent) were each cooled to 10° C., then mixed, after which the catalyst mixture was injected. After further mixing for about 15–18 seconds, the mixture was poured into a box. The fire behavior of the foams was tested with a cone calorimeter, according to standard test protocols (ISO 5660 or ASTM E 1354). In this test the foam specimens are ignited with a conical radiant heater, the thermal flux applied on the specimen surface being 50 kilowatts per square meter. The specimens tested had a size of 100 mm by 100 mm with a thickness of 50 mm; they were wrapped in aluminum foil in order to have only the upper surface exposed to the radiant heater. Two specimens were used for each measurement and the results were averaged. The total smoke development in 580 seconds (reported according to ASTM E 1354 as the specific extinction area or “SEA”) and the mass loss rate (an indication of the rate of heat release), when calculated between 10 to 90% of weight loss, are reported in the table below: 
                                                                       Mass loss rate   SEA               (in grams per   (in square           Foam ID (with parts of   second per   meters per           blowing agent)   square meter)   kilogram)                                        245 fa only (39.4)   10   852           245 fa (35.46) + Trans 12   8   898           (2.85 or 10 mole %)           245 fa (27.58) + Trans 12   4   507           (8.56 or 30 mole %)           245 fa (19.7) + Trans 12   3   585           (14.26 or 50 mole %)           365 mfc only (43.51)   4   621           365 mfc (39.16) + Trans 12   4   507           (2.85 or 10 mole %)           365 mfc (30.46) + Trans 12   3   556           (8.56 or 30 mole %)           365 mfc (21.76) + Trans 12   3   579           14.26 or 50 mole %)                        
The improvement with the use of Trans 12 is more dramatic when added to 245fa since the 365mfc by itself produces a less flammable foam than 245fa.