Process for forming polyisocyantate-based foam and product formed thereby

A blowing agent for use in preparing a polyisocyanate-based foam which comprises a major portion of HCFC-123, a minor portion of HCFC-141b, and hexane and/or octane.

FIELD OF THE INVENTION 
This invention relates generally to foaming systems containing a blowing 
agent, and more particularly to the use of such a blowing agent in forming 
polyisocyanurate foams with a high index, e.g., 250 or more. 
BACKGROUND OF THE INVENTION 
A blowing agent is a composition, usually liquid at room temperature, which 
enters into a chemical reaction, here the reaction of a polyisocyanate and 
an isocyanate-reactive material, to create a rigid foam. The enclosed 
bubbles that comprise the foam contain carbon dioxide and constituents of 
the blowing agent in varying amounts. Yet the blowing agent is unchanged 
in its properties as a result of the chemical reaction; the blowing agent 
goes into solution as a liquid and comes out of solution as a gas during 
the exothermic reaction. In order to constitute a blowing agent, the 
material must be soluble in the constituents of the foam, but not so 
soluble that it destroys the polymeric linkages. It must also have a high 
boiling point for effective bubble formation. 
For many years the blowing agents that became standard as most desirable in 
the preparation of isocyanate-based foams, such as rigid and flexible 
urethane and isocyanurate foams, were what became part of the vernacular 
as CFC's. Most typically, a composition identified as CFC-11 (CCl.sub.3 F) 
became a standard blowing agent. However, the use of this material is now 
banned by international treaty on the grounds that its release into the 
atmosphere damages the ozone layer in the stratosphere. As a consequence, 
this most standard blowing agent for forming isocyanate foams is now no 
longer available for use. 
The result of the ban on CNC's led those of skill in the art to the 
utilization of related compositions. A solution was sought in the area of 
HCFC's, which are hydrogen-containing chlorofluoroalkanes. These HCFC's, 
and most particularly HCFC-123 (CHCl.sub.2 CF.sub.3) and HCFC-141b 
(CH.sub.2 ClCHClF) have relatively short lifetimes in the atmosphere and 
tend to decompose before they reach the earth's stratosphere which 
contains the ozone layer. However, as set forth, for example, in U.S. Pat. 
No. 5,286,759, the art has considered HCFC's to have disadvantages when 
compared with CFC's, and those alleged disadvantages have led persons of 
skill in the art to seek other CFC substitutes. In U.S. Pat. No. 
5,286,759, a blowing agent was disclosed comprising a mixture of a 
hydrocarbon with 4 or more carbon atoms and a polyfluorocarbon component 
with a specific boiling point and molecular weight ratio. Exemplary of 
such components are polyfluorocarbon compounds, for example, 
perfluorocyclohexane, polyfluoroalkanes and polyfluoroethers. Finally, 
this patent proposes a third component, which is stated to be halocarbons, 
ethers, ketones, etc. 
While the art thus searches for more esoteric combinations of ingredients 
in order to meet the need created by the forced nonuse of CFC's, it is the 
purpose of the present invention to provide such a CFC substitute that is 
composed of a specific combination of HCFC's and a hydrocarbon such as 
hexane or octane. The combination of HCFC's that are included in the 
present invention are readily available and environmentally sound. When 
used in the proposed combinations, they have been found to constitute 
satisfactory, indeed more than satisfactory, blowing agents for isocyanate 
resins and create a good foam resistant to decomposition and flammability. 
SUMMARY OF THE INVENTION 
As my invention is more broadly defined, it constitutes a process for 
preparing a polyisocyanate-based foam that has reduced flammability and 
superior cell structure without the use of CFC's by reacting a 
polyisocyanate with an isocyanate-reactive material, all known in the art, 
together with a blowing agent. The blowing agent comprises a mixture 
having a major portion of what is identified by the shorthand designation, 
HCFC-123, a minor portion of HCFC-141b, and about 1 to 30 mole percent of 
a hydrocarbon selected from the group consisting of hexane and octane and 
isomers thereof. Generally, the percent of hydrocarbon used is less than 
30 mole percent, e.g., 20 percent or, even more preferably, 10 percent. 
With respect to the quantities of HCFC-123 used, another broad expression 
of the invention is that this compound is used in approximately 90 to 15 
mole percent, and the HCFC-141b in about 75 to 5 mole percent. More 
specifically, the HCFC-123 is present in about 90 to 65 percent and the 
HCFC-141b in about 25 to 5 mole percent. The percentages of these two 
ingredients can vary. Most preferably, the HCFC-123 is present in about 75 
percent and the HCFC-141b in about 15 mole percent, in which instance the 
hydrocarbon, which preferably is n-hexane, is present in about 10 mole 
percent. 
The invention also takes the form of a polyisocyanate-based foam prepared 
in accordance with the process of my invention. It further takes the form 
of a blend of my blowing agent mixture together with an 
isocyanate-reactive material in water, which blend takes part in a 
reaction with a polyisocyanate. It is the composition of the blowing agent 
that distinguishes these isocyanate-reactive blends from those of the 
prior art.

DETAILED DESCRIPTION OF THE INVENTION 
Since they form an important part of the present invention, the two HCFC's 
that are blended together with a hydrocarbon to form a blowing agent 
according to my invention will be defined more specifically. HCFC-123 is 
dichlorotrifluoroethane, i.e., C.sub.2 HF.sub.3 Cl.sub.2. HCFC-141b is 
dichlorofluoroethane, (C.sub.2 H.sub.3 FCl.sub.2). Of course, hexane is a 
saturated alkane with 6 carbon atoms, while octane is a saturated alkane 
with 8 carbon atoms. These two HCFC's, when used in proper proportions, 
together with hexane or octane or mixtures thereof, do not require any 
additional component to be used as a blowing agent mixture that is a 
satisfactory replacement for the banned CFC's. The mixture is satisfactory 
in and of itself, and the compounds for use in the mixture are readily and 
economically available. 
As presently advised, the most preferred embodiment of my invention for a 
blowing agent is 75 mole percent of HCFC-123, 15 mole percent of 
HCFC-141b, and 10 mole percent of n-hexane. However, this mixture of 
compounds can vary, more particularly when considering the amount of 
flammability that is desired to be incorporated into the final product. 
Thus, it will be apparent that the flammability of the HCFC's is 
determined by the number of hydrogen atoms in the molecules. HCFC-123 
contains one hydrogen atom, being doubly chlorinated and triply 
fluorinated. It is essentially non-flammable. On the contrary, HCFC-141b, 
being doubly chlorinated and only singly fluorinated, will have 3 hydrogen 
atoms, and thus be far more flammable than HCFC-123. 
While both HCFC-123 and HCFC-141b are polar molecules and thus capable of 
serving as a solvent, the flammability of the mixture will vary in 
accordance with the percentages of the compounds used. Since it is desired 
that the resulting foam be substantially nonflammable, my preferred 
composition contains a major portion of HCFC-123 and a minor portion of 
HCFC-141b. Thus, while in one example a blowing agent can comprise 90 to 
15 percent HCFC-123 and 75 to 5 percent HCFC-141b, all percentages being 
mole percents, it is preferred that the quantity of HCFC-123 predominates, 
e.g., that the HCFC-123 be 90 to 65 percent, or more preferably, 70 to 30 
mole percent. Where flammability is not an issue, the HCFC-123 can be 
present in about 55 to 15 mole percent and the HCFC-141b present in about 
75 to 35 mole percent. 
With respect to the hydrocarbon that is used, I have found hexane and 
octane to be satisfactory, although hexane is preferred. While because of 
its availability, n-hexane is most preferred, isomers of hexane and octane 
are also satisfactory. Regarding the quantity of the hydrocarbon, i.e., 
hexane or octane, that is utilized, in its broadest range the hydrocarbon 
is present in from 1-30 percent. However, it is preferred that the 
quantity of hydrocarbon be a lesser percent, no greater than 20 mole 
percent, and in my most preferred embodiment of the present invention, the 
amount of n-hexane utilized is 10 mole percent. 
As those of skill in this art are aware, a blowing agent such as that 
disclosed here is ordinarily mixed with the isocyanate-reactive compound, 
and the mixture reacted with a polyisocyanate to create the foam. 
Preferred reactive materials have an isocyanate-reactive hydrogen atom. 
Thus polyols, which have at least two hydroxyl groups per molecule are 
particularly preferred due to their reactivity. It is with this reactive 
material that the blowing agent of my invention is blended prior to the 
blend being reacted with the polyisocyanate. This preblend may also 
include water, surfactants and catalysts, the presence of which does not 
constitute part of the present invention and which are generally known to 
the art. 
While a prime advantage of my blowing agent is the lack of ozone depletion 
that exemplifies CFC's, there are other advantages. For example, the 
present composition has the following advantages over the prior art 
characterized by HCFC-141b: it goes into solution much more easily; there 
is a smaller loss of blowing agent during the reaction; the blowing agent 
stays in solution at lower temperatures (40F); it is much more flame 
resistant; it has about 20% more yield for the same amount of blowing 
agent; it can use less catalyst and flame retardant; it can tolerate more 
water; it has much less shrinkage and better adhesion to the substrate; 
the cell structure is finer and more uniform; it has higher compressive 
strength and a lower K factor at equivalent densities; it has a tougher 
and smoother skin. Also, no surfactant is needed to avoid separation in 
solution. Further, it is non-flammable as a liquid and is EPA approved: 
ozone depletion potential 0.03 compared to 0.1 for HCFC-141b, and there is 
no delamination between passes of spray-applied foam. 
It will be apparent to these of skill in this art that certain 
modifications and alterations can be made in this disclosure without 
departing from the spirit of the invention. For example, 
tolylenediisocyanate foams are also improved by use of the blowing agent 
of my invention, and where the blowing agent is used with polystyrene 
foams, HCFC-142b (1-chloro-1,1-difluoroethane) can be used as a substitute 
for HCFC-141b. As to all such changes, it is desired that they be included 
within the purview of the invention which is to be limited only by the 
scope, including equivalents, of the following, appended claims.