Polyurethane foam and associated process for production

Details Polyurethane foam and associated process for production Polyurethane foam and associated process for production

2000-11-03

2002-02-12

Cooney, Jr., John M. (Department: 1711)

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

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S129000, C521S130000, C521S163000, C521S170000, C521S172000, C521S174000

Reexamination Certificate

active

06346559

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a polyurethane foam and associated production process, in particular flexible to semi-hard block foams or soft molded foams using polyesters or polyethers as polyols.
Polyurethane foams are conventionally produced by mixing a polyisocyanate component of at least one diisocyanate or polyisocyanate with a polyol component of at least one polyether polyol or polyester polyol, in the presence of at least one catalyst and at least one propellant and optionally in the presence of various auxiliaries and additives well known in polyurethane chemistry.
The properties of the polyurethane foams may be adjusted within wide ranges by specific co-use of low molecular diols as chain extenders or of triols and amines as crosslinkers.
Mainly carbon dioxide or halogen alkanes are generally used as propellants for polyurethane foams. Selection of the propellant depends, inter alia, on the reaction mixture to be foamed, the required strength and further properties of the formed polyurethane foam. In addition to water, fluorochlorohydrocarbons (FCHC), hydrogen fluorochlorohydrocarbons (HFCHC), hydrogen fluorohydrocarbons (HFHC) or special carbamates in particular, have been used as propellants for the production of harder polyurethane foams.
Due to the known ecological problems associated with the use of said halogen-containing propellants, their use is continuously minimized in the field of foams.
Use of hydrocarbons, such as isomeric pentanes or of cyclopentanes, as propellants is rare due to the flammability of these substances.
The conventional propellant in the production of flexible block foams or molded foams is water, which is reacted in the reaction with isocyanates to produce carbon dioxide and urea. The sole use of water as a propellant may have the disadvantage of the production of urea that reduces the elasticity of the resulting foams.
Tertiary amines and organic compounds generally serve as catalysts for producing polyurethane foams. Co-catalysis, for example by metal catalysts, is also possible. Catalysts which can be incorporated and are bound into the polymer matrix of a polyurethane foam, via a primary or secondary amine function or via hydroxyl groups, may be used in the production of flexible to semi-hard block foams or molded foams. However, these catalysts have severe disadvantages.
First of all, such catalysts have to be used with a suitable co-catalysis. Inadequate curing results without use of a suitable co-catalysis.
Furthermore, most known catalysts can lead to a phenomenon in block foams which is known as “core discoloration”, that is, the start of oxidative decomposition in the center of the foam block due to the resulting heat of reaction. Catalysis typically cannot be controlled or can be controlled only with difficulty in block foams. It is particularly difficult to adjust the critical ratio of open and closed cells as well as cell opening at the right point in time.
A further difficulty is the deterioration in hydrolysis aging, which results particularly for block foams based on polyester.
When using amine catalysts, there are additional problems with possible persistent amine exhalation, which may lead to odor pollution or even health stresses. Odor pollution is a particular problem in block foams based on polyester.
European granted patent 0 121 850 indeed already describes the use of certain carbamates which carry hydroxyl groups as propellants for polyurethane foams, as can be seen from the exemplary embodiments, preferably in combination with other propellants. However, European granted patent 0 121 850 does not disclose any indication of the surprising finding that the carbamates may also be used as catalysts for the production of polyurethane foams. Due to the special constitution of the carbamates given there, the latter cannot also replace the tertiary amine catalysts.
European granted patent 0 652 250 describes the use of carbamates containing hydroxyl groups as exclusive propellant for integral foams. Here too, it is not a question of the replacement of catalysts. Rather, catalysts are thus used which lead to the above-mentioned undesirable accompanying phenomena, such as odor pollution and PVC discoloration.
The present invention is directed to overcoming one or more of the problems set forth above.
SUMMARY OF THE INVENTION
An aspect of the invention is therefore to provide a process for producing polyurethane foam, in which the co-use of environmentally damaging propellants and largely traditional amine catalysts is unnecessary. The aim is thus to achieve significantly reduced core discoloration and significantly lower odor evaporation than for conventional foams in block foams with similar physical properties.
It has now been found, surprisingly, that certain carbamates of the type described below in more detail are catalysts and at the same time propellants and facilitate the production of polyurethane block foams, especially flexible to semi-hard block foams as well as soft molded foams. The use of additional propellants may thus be completely or partly omitted. Furthermore, traditional amine catalysts are unnecessary. However, co-catalysis, such as metal catalysts, using other catalysts to form polyurethane may be used.
DETAILED DESCRIPTION
The invention provides a process for producing polyurethane foam in the presence of at least one catalyst and at least one propellant, where a carbamate or a mixture of carbamates of the general formula that is hereinafter referenced as “Formula I”:
wherein:
R
1
and R
2
represent the same or different alkyl radicals,
R
3
and R
4
represent the same or different radicals and denote hydrogen or alkyl radicals,
R
5
denotes hydrogen, an alkanol radical, a polyether monool radical or the radical characterized by X,
n represents 2 or 3,
and said carbamate or mixture of carbamates is used as catalyst and at the same time as propellant, essentially excluding amine catalysts.
The process produces polyurethane foams, in particular block foams and soft foams, which have significantly reduced core discoloration and a significantly lower odor than foams produced using conventional catalysts, but with the same strength.
The foams produced according to the invention are characterized by a lower bulk density, compared to foams which have been produced using the same water content, problem-free processing, reduced amine emissions and good stability to hydrolysis. There is no oxidative core discoloration in block foams.
An alkanol radical is understood to mean groups generally known to the chemist under this term, such as for example a methanol radical, ethanol radical, propanol radical, isopropanol radical, butanol radical, isobutanol radical, t-butanol radical, pentanol radical, hexanol radical, or heptanol radical.
“Alkyl radical” is understood to mean all groups falling under the general chemical definition of an alkyl radical, in particular methyl radicals, ethyl radicals, propyl radicals butyl radicals, isopropyl radicals, isobutyl radicals, tertiary butyl radicals, cyclopropyl radicals, cyclopentyl radicals, cyclohexyl radicals, cycloheptyl radicals as well as longer-chain branched or unbranched or cyclic alkyl radicals.
The process is preferably characterized in that the polyurethane foam is produced from a reaction mixture which contains:
a polyisocyanate component having an NCO content of 25 to 48.3 wt. %, consisting of pure or modified toluylene diisocyanate or an optionally modified polyisocyanate or polyisocyanate mixture of the diphenylmethane series and
a polyol component of an average hydroxyl functionality of 2-6 consisting of at least one polyether polyol or polyester polyol having OH numbers<70, optionally with addition of conventional auxiliaries and additives, as are known from polyurethane chemistry.
The reaction mixture may also preferably contain polyester polyols or polyether polyols or mixtures thereof having OH numbers from 70-400.
Suitable isocyanate components are generally aliphatic, cycloaliphatic, araliphatic, aromatic and hete

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