Thermosetting plastic foam

Details Thermosetting plastic foam Thermosetting plastic foam

1999-10-25

2001-10-23

Foelak, Morton (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S155000, C521S174000

Reexamination Certificate

active

06306919

ABSTRACT:

BACKGROUND
Cellular organic rigid thermosetting plastic foams used for thermal insulation are well known in the art. Foams can be made with urethane linkages, or made with a combination of both isocyanurate linkages and urethane linkages, or they can be made via the well known condensation reactions of formaldehyde with phenol, urea, and melamine. All such plastic foams must utilize an expansion agent, often referred to as a “blowing agent”.
The prior art is replete with references to techniques of expanding foam cells. For many years, the dominant blowing agent for all thermosetting foams was trichloromonofluoromethane (CFC-11). Other types of blowing agents have been proposed, such as the use of hydrocarbon mixtures, taught in U.S. Pat. No. 3,558,531. In recent years, various foam expansion methods have been taught in such United States patents as the following (all of which are incorporated herein by reference): U.S. Pat. Nos. 3,993,609, 4,636,529, 4,898,893, 4,927,863, 4,981,876, 4,981,880, 4,986,930, 4,996,242, 5,032,623, 5,070,113, 5,096,933, 5,114,986, 5,130,345, 5,166,182 5,182,309, 5,205,956, 5,213,707, 5,227,088, 5,234,967, 5,236,611, 5,248,433, 5,262,077, 5,277,834, 5,278,196, 5,283,003, 5,290,823, 5,296,516, 5,304,320, 5,314,926, 5,318,996, and 5,336,696.
The relatively recent hydrogenated chlorofluorocarbons (called “HCFCs”) are considered to be environmentally friendly expansion agents, but still contain some chlorine, and therefore have an “Ozone Depletion Potential”(called “ODP”). Because of the ODP, the HCFCs have been mandated for eventual phaseout.
Another known class of blowing agents is the non-chlorinated, partially hydrogenated fluorocarbons (called “HFCs”) which have the general formula: H
z
F
y
C
z
, where x, y, and z are integers. The HFC compounds being proposed for future blowing agents have two serious defects: (1) high intrinsic thermal conductivity properties (i.e., poor thermal insulation); and, (2) expense. In view of the fact that approximately ten percent by weight of rigid foam insulation are the compounds used as blowing agents, high cost combined with the poor insulating value render HFCs less attractive candidates for blowing agents in commercial foam insulation.
Hydrocarbon blowing agents are also known, which class includes halogen-free and CO
2
-free blowing agents. For example, U.S. Pat. No. 5,182,309 to Hutzen teaches the use of iso- and normal-pentane in various emulsion mixtures. Another example of hydrocarbon blowing agents is taught by Volkert in U.S. Pat. No. 5,096,933, pointing out the virtues of commercial cyclopentane distilled and extracted from natural gas wells.
However, the hydrocarbon blowing agents mentioned in connection with such prior art have inadequate miscibility with polyester polyols, commonly used in polyisocyanurate modified polyurethane foam. The use of these alkanes require a chemical surfactant to obtain a suitable mixture. An improvement in the problem of poor miscibility is taught in U.S. Pat. No. 5,166,182 to Blanpied, whereby the use of azeotropes with polar organic solvents enhance the miscibility with polar polyester polyols. However, all of that work was done using cyclopentane extracted from natural gas.
Another problem with some of these alkanes is the poor insulating value. For example, the thermal conductivity of n-butane at 25° C. is 16.3 mW/m*° K, and n-pentane at 25° C. is 14.8 mW/m*° K.
None of the prior art patents known to Applicants discuss how the cyclopentane is obtained for the disclosed foaming process, nor is there any recognition that any certain mode of cyclopentane production may endow the cyclopentane with properties which are beneficial for a foaming operation.
Although some cyclopentane originates from petroleum, most cyclopentane originates from natural gas wells, and is extracted as the bottom layer of distillation in a refinery, allowing the lighter molecules to be transferred through the natural gas pipeline network. Cyclopentane obtained by extraction contains impurities. In fact, cyclopentane sold as “Technical Grade” contains from 22% to 30% impurities.
One route for manufacturing cyclopentane involves recovery by distillation from naphtha streams derived from crude oil or field natural gasoline. Very limited quantities of cyclopentane can be produced via this route due to the low concentrations of naturally occurring cyclopentane. Furthermore, cyclopentane product purity via this route is limited to approximately 75% by the presence of 2,2-dimethyl butane (which has a boiling point less than 1° F. (0.55° C.) different from cyclopentane). Further purification requires more expensive processing such as extractive distillation.
Extracted cyclopentane (“EXTRCP”) has at least five problems which heretofore virtually prohibited it from being considered a serious candidate as a commercial blowing agent for rigid foam insulation. The first problem is that its limited supply is considerably below the amount needed is to meet the quantity demanded of a commercial compound. The second problem is that this inadequate supply contains at least twenty-two percent impurities in the form of hexane isomers and n-pentane, which impurities significantly reduce insulating value of foam made therefrom. The third problem is that extracted cyclopentane is not miscible with the common polyester polyols which are used with HCFCs nor those that were used with CFC-11.
The fourth problem is that extracted cyclopentane does not reduce the viscosity of the polyester polyol foamable blend to a workable level, even when liquid fire retardants are utilized.
The fifth problem is that the foam produced with EXTRCP will not pass the ASTM E-84 maximum 75 Flame Spread Index even with moderate flame retardant.
With respect to the third and fourth above-mentioned problems, the above-dicussed U.S. Pat. No. 5,096,933 to Volkert, while generally alluding to the use of polyester polyols, provides no specific example using polyester polyols. The lack of any specific example is consistent with the present inventors' understanding that mixtures made from polyester polyols and extracted cyclopentane are unstable mixtures. In this regard, extracted cyclopentane is no more suitable as a miscible blowing agent than n-pentane or iso-pentane. All three require chemical surfactants for miscibility.
Perhaps the largest obstacle to the use of hydrocarbon blowing agents in the United States is the fifth problem—flammability of thermoset plastics blown with hydrocarbon blowing agents. U.S. Pat. No. 5,096,933 to Volkert mentions disadvantages caused by the flammability of the cycloalkanes. Volkert alludes to the optional use of flame retardants, but provides no example utilizing a flame retardant. Furthermore, none of the five Polyurethane Rigid Foam examples shown by Volkert would pass the maximum Flame Spread Index (FSI) of 75 (ASTM E-84) required of construction foam in the United States. Likewise, a polyisocyanurate foam, without flame retardant, having an Isocyanate-to-Polyester Polyol INDEX of 2.3 badly failed the ASTM E-84 maximum Flame Spread Index requirement of 75, by achieving a 2174 FSI.
With regard to flammability, it is well known that organic surfactants contribute to the flammability of rigid plastic foam insulation. The three main classes of organic surfactants (anionic, cationic, and nonionic) all add to the flammability problem of plastic foam. However, the use of organic carbonates, such as ethylene carbonate and propylene carbonate, does not increase the flammability of plastic foam.
TABLE I describes experiments attesting to the immiscibility of extracted cyclopentane with the polyester polyol having the most miscible potential with non-polar hydrocarbons, as well as the immiscibility of n-pentane and iso-pentane with this polyester polyol. The first column of TABLE I shows the weight ratio of polyester polyol to hydrocarbon blowing agent, with the proposed blowing agents n-pentane, iso-pentane, and extracted cyclopentane being shown in the second through fourth columns, respectively. In all experiment

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