Rigid polyurethane foams

Details Rigid polyurethane foams Rigid polyurethane foams

1997-10-17

2002-06-11

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...

C521S121000, C521S128000, C521S172000, C252S182240

Reexamination Certificate

active

06403665

ABSTRACT:

This invention relates to rigid polyurethane or urethane-modified polyisocyanurate foams, to processes for their preparation and to polyol blends for use in said processes.
Rigid polyurethane and urethane-modified polyisocyanurate foams are in general prepared by reacting a stoichiometric excess of polyisocyanate with isocyanate-reactive compounds in the presence of blowing agents, surfactants and catalysts. One use of such foams is as a thermal insulation medium in, for example, buildings.
Polyesther polyols or polyester polyols are generally used as isocyanate-reactive compounds.
Polyester polyols impart excellent flame retardancy characteristics to the resulting polyurethane foams and are in some cases even less expensive than polyesther polyols.
There is a problem in respect of the stability of polyol blends containing polyester polyols and tertiary amine catalysts. It has been proposed to solve this problem by adding an organic carboxylic acid (such as formic acid, acetic acid, 2-ethylhexanoic acid) to the polyol blend (see U.S. Pat. No. 4,758,605). In order to retain the reactivity over prolonged storage catalyst levels need to be increased. Whereas the instability problem can be solved successfully in this way the processing of these systems is still uncontrollable which is reflected in the rise profile of the rising foam when the polyol blend is reacted with the polyisocyanate composition.
BRIEF SUMMARY OF THE INVENTION
Therefore it is an object of the present invention to provide polyol blends containing polyester polyols and tertiary amine catalysts not showing the disadvantages mentioned above.
DETAILED DESCRIPTION OF THE INVENTION
According to the present-invention polyol blends are provided comprising a polyester polyol, a tertiary amine catalyst and an organic carboxylic acid wherein said carboxylic acid contains at least one OH, SH, NH
2
, or NHR functional group, wherein R is an alkyl, cycloalkyl or aryl group.
The polyol blends of the present invention are stable for several weeks. Improved reaction profiles are obtained when these polyol blends are used to make rigid polyurethane foams; the cream time is decreased while at the same time the expansion of the foam at string time is almost complete. Carboxylic acids to be used in the present invention have the general formula X
n
—R′—(CCOH)
m
wherein X is OH, SH, NH
2
or NHR, R′ is an at least divalent hydrocarbon moiety, typically an at least divalent linear or branched aliphatic hydrocarbon moiety and/or an at least divalent alicyclic or aromatic hydrocarbon moiety, n is an integer having a value of at least 1 and allows for mono and polyfunctional substitution on the hydrocarbon moiety, m is an integer having a value of at least 1 and allows for mono and polycarboxyl substitution on the hydrocarbon moiety.
The “at least divalent hydrocarbon moiety” can be a saturated or unsaturated moiety of 1 to 20 carbon atoms, including a linear aliphatic moiety, a branched aliphatic moiety, an alicyclic moiety or an aromatic moiety. Stated otherwise, R′ can, for example, be a linear or branched alkylene group of 1 to 10 carbon atoms, a cyclic alkylene group of 4 to 10 carbon atoms, or an arylene, an alkylene or an ararylene group of 6 to 20 carbon atoms. Specific non-limiting examples of suitable hydrocarbon moieties are methylidene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, n-amylene, n-decylene, 2-ethylhexylene, o-, m-, p-phenylene, ethyl-p-phenylene 2,5-naphthylene, p,p′-biphenylene, cyclopentylene, cyclopentylene, xylylene, 1,4-dimethylenephenylene and the like. While above-noted radicals have two available substitution sites, at least one for a carboxyl group and one for a OH, SH, NH
2
or NHR group, it is contemplated that additional hydrogen on the hydrocarbon could be replaced with further carboxyl and/or OH, SH, NH
2
or NHR groups.
The carboxylic ac ds useful in the practice of the present invention generally have molecular weights below about 250.
The following carboxylic acids are illustrative of compounds suitable for practicing the present invention: citric acid, dimethylolpropionic acid, bis-(hydroxymethyl)propionic acid, bishydroxypropionic acid, salicylic acid, m-hydroxy benzoic acid, p-hyidroxy benzoic acid, dihydroxybenzoic acid, glycolic acid, &bgr;-hydroxybutyric acid, cresotic acid, 3-hydroxy-2-naphthoic acid, lactic acid, tartaric acid, malic acid, resorcylic acid, hydroferulic acid, glycine, alanine, mercaptoacetic acid and the like.
Preferably X is OH, n is 1, R′ is a linear or branched aliphatic hydrocarbon having 1 to 5 carbon atoms and m is 1, 2 or 3. Polycarboxylic acids are preferred. The hydroxyl group is preferably in a &agr; or &bgr; position with respect to the carboxyl group.
Most preferred carboxylic acids are lactic acid, glycolic acid, malic acid and citric acid.
At least one of said carboxylic acids is used; mixture of two or more of these acids can be used as well.
Particularly preferred carboxylic acids for use in the present invention are malic acid or a combination of malic acid and citric acid, preferably in a weight ratio of between 75:25 and 25:75, most preferably in a weight ratio of about 1:1. Further improvements in reaction profile are observed.
The combination of malic acid and citric acid also leads to improvements in other physical properties of the obtained foam such as compression strength and adhesion; also less variation in density distribution.
The carboxylic acid is generally used in an amount ranging from 0.1 to 5% by weight based on the isocyanate-reactive composition, preferably about 1% to 3%
The term “polyester polyol” as used herein is meant to include any polyester polyol having a hydroxyl functionality of at least two wherein the majority of the recurring units contain ester linkages and the molecular weight is at least 400.
The polyester polyols for use in the present invention advantageously have an average functionality of about 1.8 to 8, preferably about 2 to 6 and more preferably about 2 to 2.5. Their hydroxyl number values generally fall within a range of about 15 to 750, preferably about 30 to 550, more preferably 70 to 5:50 and most preferably about 200 to 550 mg KOH/g. The molecular weight of the polyester polyol generally falls within the range of about 400to about 10000, preferably about 1000 to about 6000. Preferably the polyester polyols have an acid number between 0.1 and 20 mg KOH/g; in general the acid number can be as high as 90 mg KOH/g.
The polyester polyols of the present invention can be prepared by known procedures from a polycarboxylic acid or acid derivative, such as an anhydride or ester of the polycarboxylic acid, and any polyhydric alcohol. The polyacid and/or polyol components may be used as mixtures of two or more compounds in the preparation of the polyester polyols.
The polyols can be aliphatic, cycloaliphatic, aromatic and/or heterocyclic. Low molecular weight, aliphatic polyhydric alcohols, such as aliphatic dihydric alcohols having no more than about 20 carbon atoms are highly satisfactory. The polyols optionally may include substituents which are inert in the reaction, for example, chlorine and bromine substituents, and/or may be unsaturated. Suitable amino alcohols, such as, for example, monoethanolamine, diethanolamine, triethanolamine, or the like may also be used. A preferred polyol component is a glycol. The glycols may contain heteroatoms (e.g., thiodiglycol) or may be composed solely of carbon, hydrogen and oxygen. They are advantageously simple glycols of the general formula C
n
H
m
(OH)
2
or polyglycols distinguished by intervening ether linkages in the hydrocarbon chain, as represented by the general formula C
n
H
2n
O
x
(OH)
2
. Examples of suitable polyhydric alcohols include: ethylene glycol, propylene glycol-(1,2) and -(1,3), butylene glycol-(1,4) and -(2,3), hexanediol-(1,6), octanediol-(1,8), neopentyl glycol, 1,4-bishydroxymethyl cyclohexane, 2-methyl-1,3-propane diol, glycerin, trimethylolethane, hexanetriol-(1,2,6), butanetriol-(1,2,4), quinol, meth

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