Process for producing rigid polyurethane foams

Details Process for producing rigid polyurethane foams Process for producing rigid polyurethane foams

1995-01-27

1996-11-26

Foelak, Morton

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

Synthetic resins

Cellular products or processes of preparing a cellular...

521130, 521131, C08G 1800

Patent

active

055786510

DESCRIPTION:

BRIEF SUMMARY
Owing to their outstanding heat insulation properties, closed-cell rigid polyurethane foams have been employed for many years for the insulation of appliances for cooling and refrigeration, industrial installations, petrol stations, pipelines, in shipbuilding and for numerous insulating functions in the construction industry.
The thermal conductivity of rigid polyurethane foam, which has to a large extent closed cells, is largely dependent on the type of foaming agent or cell gas used. The perhalogenated chlorofluorocarbons (FCKW) have proved to be particularly suitable for this purpose, especially trichlorofluoromethane (R11), which has a particularly low thermal conductivity. The said materials are chemically inert and consequently non-toxic and non-combustible. Owing to their high stability, however, the perhalogenated chlorofluorocarbons enter the stratosphere, where they are thought to contribute to the breakdown of the ozone present there by reason of their chlorine content (for example, Molina, Rowland Mature 249 (1974) 810; First interim report of the Bundestags-Enquete-Kommission "Vorsorge zum Schutz der Erdatmosphare" [Bundestag Commission of Enquiry, "Provisions for Protection of the Earth's Atmosphere"] dated Feb. 11, 1988, Deutscher Bundestag, Referat Offentlichkeitsarbeit, Bonn).
The use of partly fluorinated hydrocarbons (hydrofluoroalkanes) such as 1,1,1,4,4,4-hexafluorobutane instead of the perhalogenated chlorofluorocarbons as foaming agents for plastic foams, including polyurethane foams, has therefore been proposed (cf. EP-PS 344 537, U.S. Pat. No. 4,931,482).
The hydrofluoroalkanes, which retain at least one carbon-hydrogen bond, contain no chlorine atoms and consequently have an ODP value (Ozone Depletion Potential) of zero. (In comparison:R11:ODP=1)
A typical representative of this class of substances apart from 1,1,1,4,4,4-hexafluorobutane (R356) is 1,1,1,2-tetrafluoroethane (R134a).
Owing to their chemical structure, partly fluorinated hydrocarbons are highly non-polar and so do not mix well with the polyols conventionally used for producing rigid foam. However, this is an important prerequisite for the conventional technique of production, wherein the polyol and isocyanate components are mechanically mixed with one another.
In addition to the reactive polyether polyol or polyester polyol, the polyol components also contain the foaming agent and the auxiliary substances such as activators, emulsifiers and stabilisers in dissolved form. The polyol component is thus a one-phase mixture.
In equimolar substitution of conventional foaming agents such as, for example, R11, by the new, environmentally friendly compounds in commercially available formulations, the low solubility of the partly fluorinated hydrocarbons leads to the formation of two phases which cannot be processed further by conventional methods.
The object of the present invention was therefore to increase the solubility in polyols of partly fluorinated hydrocarbons, so that in the equimolar substitution of R11 by the said substances a one-phase polyol component is obtained.
Surprisingly, it has been found that the solubility of partly fluorinated alkanes in the polyol is significantly increased by adding specific solubilisers.
The invention provides a process for producing rigid polyurethane foams by the reaction of
1) polyisocyanates with
2) compounds of a molecular weight of from 92 to 10,000 having at least two hydrogen atoms active towards isocyanates in the presence of
3) hydrofluoroalkanes as foaming agents and of
4) solubilisers as well as optionally in the presence of
5) other auxiliary substances and additives known per se, solubilisers (4) ##STR5## wherein R.sup.1 and R.sup.2 signify C.sub.1 -C.sub.12 -alkyl or together C.sub.2 -C.sub.6 -alkylene and n signifies an integer from 0 to 6, ##STR6## wherein R.sup.1 to R.sup.3 signify C.sub.1 -C.sub.12 -alkyl which is optionally substituted by halogens, C.sub.5 -C.sub.10 -cycloalkyl or optionally substituted aryl, ##STR7## wherein R.sup.1 and R.sup.2 signify C.sub.1 -C

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