Rigid polyurethane foams

Details Rigid polyurethane foams Rigid polyurethane foams

1997-10-17

2001-03-27

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, C521S130000, C252S182240

Reexamination Certificate

active

06207725

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.
Polyether polyols or polyester polyols are generally used as isocyanate-reactive compounds. Polyester polyols impart excellent flame retardancy characteristics to the resulting polyurethane foams and can in some cases even be less expensive than polyether polyols.
Tertiary amines are generally used as catalyst in rigid polyurethane foam systems based on polyester polyols. A problem encountered when using tertiary amine catalysts in these polyester rigid foam systems is that a cross-linked mass is obtained at a time when the foam has not fully filled the cavity yet (for example, of a laminated building panel). This leads to dimensional stability problems due to density distribution problems and cell stretching of the obtained foam.
Therefore it is an object of the present invention to provide a process for making rigid polyurethane foams based on polyester polyols not showing the disadvantages mentioned above.
According to the present invention a process for making rigid polyurethane or urethane-modified polyisocyanurate foams is provided by reacting an organic polyisocyanate composition with an isocyanate-reactive composition comprising a polyester polyol in the presence of an amine catalyst (B) characterised in that the pK
a
of the conjugated ammoniumsalt of the amine (BH
+
) is less than 12, preferably less than 10, more preferably less than 8.
pK
a
=−log K
a
=−log [B][H
+
]/[BH
+]
An acceptable rise profile is obtained having a fast initial foam rise leading to a smooth processability resulting in a better density distribution, lower minimum stable density and fill weights and higher compression strength of the foam.
Preferred catalysts to be used in the process of the present invention include aliphatic or aromatic tertiary amines preferably containing a supplemental heteroatom in the ring or functional groups having a positive inductive and/or positive mesomeric effect (for example, alkyl groups or amino groups). Examples include 2,2′-dimorpholinodiethylether, Texacat DP-914 (available from Texaco Chemical), N,N-dimethylpiperazine, 1-methylimidazole, 2-methyl-1-vinylimidazole, 1-allylimidazole, 1-phenylimidazole, 1,2,4,5-tetramethylimidazole, 1(3-aminopropyl)imidazole, pyrimidazole, 4-dimethylaminopyridine, 4-pyrrolidinopyridine, 4-morpholinopyridine, 4-methylpyridine, N-dodecyl-2-methylimidazole and triazines such as tris(dimethylaminopropyl)hexahydrotriazine. Especially preferred catalysts are 2,2′-dimorpholinodiethylether, Texacat DP-914, 1-methylimidazole and 4-dimethylaminopyridine. One or more of the above described catalysts can be used in the process of the present invention.
Some of the above described catalysts are known in polyurethane foam production primarily for flexible foam production (see, for example, U.S. Pat. No. 5,430,071, U.S. Pat. No. 3,645,925, U.S. Pat. No. 3,661,808, U.S. Pat. No. 4,228,248, EP 672696, EP 401787). Their use in rigid polyurethane foam systems based on polyester polyols has not been described heretobefore.
In general, the catalysts described above are used according to the invention in an amount of between 0.05 and 5%, preferably between 0.1 and 4% by weight based on the isocyanate-reactive composition.
In addition to the above described catalyst other catalysts known in rigid polyurethane foam production can be used. These include aliphatic tertiary amines having pK
a
values above 12. Examples of additional amine catalysts include dimethylbenzylamine, bis-dimethylaminoethylether (Niax A1 available from Osi) and pentamethyl diethylenetriamine (Desmorapid PV available from BASF). Especially addition of Desmorapid PV is preferred; the reaction profile is further smoothen. Said additional catalysts are generally used in amounts varying between 0.01 and 5%, preferably between 0.05 and 2% by weight based on the isocyanate-reactive composition.
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 and more preferably about 200 to 550 mg KOH/g. The molecular weight of the polyester polyol generally falls within the range of about 400 to 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
2n
(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, methyl glucoside, triethyleneglycol, tetraethylene glycol and higher polyethylene glycols, dipropylene glycol and higher polypropylene glycols, diethylene glycol, glycerol, pentaerythritol, trimethylolpropane, sorbitol, mannitol, dibutylene glycol and higher polybutylene glycols. Especially suitable polyols are alkylene glycols and oxyalkylene glycols, such as ethylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, tetraethylene glycol, tetrapropylene glycol, trimethylene glycol, tetramethylene glycol and 1,4-cyclohexanedimethanol (1,4-bis-hydroxymethylcyclohexane).
The polycarboxylic acid component may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and may optionally be substituted, for example, by halogen atoms and/or may be unsaturated. Examples of suitable carboxylic acids and derivatives thereof for the preparation of the polyester polyols include: oxalic acid, malonic acid, adipic acid, glutaric acid, succinic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, phthalic acid anhydride, terephthalic anhydride, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic acid anhydride, pyromellitic dianhydride, hexahydrophthalic acid anhydride

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