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Method of molding rigid polyurethane foams
Updated: 2013-10-22 14:40 Source: PUWORLD share:

While it is known that some catalysts may promote both blowing and curing (so-called "balanced" catalysts), such are conventionally differentiated by their tendency to favour blow reaction (urea or water and isocyanate reaction), in the case of the blowing catalyst, or the curing reaction (urethane or polyol and isocyanate reaction), in the case of the curing catalyst. In some non-limiting embodiments, a catalyst that technically may catalyze both blowing and curing may be selected for its less-favoured tendency, e.g., curing, and combined with another catalyst directed more toward the other purpose, e.g., blowing, and vice versa.

Examples of suitable blowing catalysts that may tend to favour the urea reaction are short chain tertiary amines or tertiary amines containing at least an oxygen and may include bis-(2-dimethylaminoethyl)ether; pentamethyldiethylenetriamine, triethylamine, tributyl amine, N,N-dimethylaminopropylamine, dimethylethanolamine, N,N,N',N'-tetra-methylethylenediamine, or urea. In one embodiment, a combination of bis(dimethylaminoethyl)ether and dipropylene glycol may be an effective blowing catalyst, for example, in a 70/30 weight percent ratio. Combinations of any of the above may also be selected.

Examples of suitable curing catalysts that may tend to favour the urethane reaction include, generally, amidines, tertiary amines, organometallic compounds, and combinations thereof. These may include, but are not limited to, amidines such as 1,8-diazabicyclo[5.4.0]undec-7-ene and 2,3-dimethyl-3,4,5,6-tetrahydropyrimidine, and their salts.

Organometallic compounds may include organotin compounds, such as tin(II) salts of organic carboxylic acids, e.g., tin(II) diacetate, tin(II) dioctanoate, tin(II) diethylhexanoate, and tin(II) dilaurate, and dialkyltin(IV) salts of organic carboxylic acids, e.g., dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate. Bismuth salts of organic carboxylic acids may also be selected, such as, for example, bismuth octanoate. The organometallic compounds may be selected for use alone or in combinations, or, in some embodiments, in combination with one or more of the highly basic amines listed hereinabove.

Example of catalysts able to promote both blowing and curing reactions are cyclic tertiary amines or long chain amines containing several nitrogens such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl-, and N-cyclohexylmorpholine, N,N,N',N'-tetra-methylethylenediamine, N,N,N',N'-tetramethylbutanediamine and -hexanediamine, pentamethyldiethylenetriamine, tetramethyldiaminoethyl ether, bis(dimethylamino-propyl)urea, dimethylpiperazine, dimethylcyclohexylamine, 1,2-dimethyl-imidazole, 1-aza-bicyclo[3.3.0]octane, triethylenediamine (TEDA).

Another class of catalysts for both blowing and curing reactions are alkanolamine compounds, such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine, and dimethylethanolamine may also be selected. Combinations of any of the above may also be effectively employed.

Examples of commercially available blowing, curing or blowing/curing catalyst include NIAX A-4, NIAX A6, POLYCAT 6, POLYCAT 5, POLYCAT 8, Niax A1; POLYCAT 58, DABCO T, DABCO NE 300, TOYOCAT RX 20, DABCO DMDEE, JEFFCAT ZR 70, DABCO™ 33 LV, NIAX A-33, DABCO R-8020, NIAX TMBDA, POLYCAT 77, POLYCAT 6, POLYCAT 9, POLYCAT 15, JEFFCAT ZR 50, TOYOCAT NP, TOYOCAT F94, DABCO NEM, etc. POLYCAT and DABCO catalysts are available from Air Products; TOYOCAT catalysts are available from Tosho Corporation; NIAX Catalysts are available from Momentive Performance Material; and JEFFCAT catalysts are available from Huntsman.

Some of these catalysts being solids or crystals are dissolved in the proper solvent which can be polyol, water, blowing agent, DPG or any carrier compatible with the polyurethane foaming

A third class of catalysts is the trimerization catalyst, able to promote reaction of isocyanate on itself. tris(dialkylaminoalkyl)-s-hexahydrotriazines such as 1,3,5-tris(N,N-dimethylaminopropyl)-s-hexahydrotriazine; DABCO TMR. 30; DABCO K 2097 (potassium acetate), DABCO K15 (potassium octoate); POLYCAT 41, POLYCAT 43, POLYCAT 46, DABCO TMR, CURITHANE 52; tetraalkylammonium hydroxides such as tetramethylammonium hydroxide; alkali metal hydroxides such as sodium hydroxide; alkali metal alkoxides such as sodium methoxide and potassium isopropoxide; and alkali metal salts of long-chain fatty acids having 10 to 20 carbon atoms and, in some embodiments, pendant hydroxyl groups.

Some of these catalysts are solids or crystals and can be dissolved in the proper solvent which can be the polyol, water, dipropylene glycol or any other carrier with the polyurethane foaming composition.

In one particular embodiment, the combined amount of catalysts, not considering the solvents, is greater than about 1.7 percent, based on the weight of the polyol formulation. In some embodiments, the combined amount of blowing and curing catalysts is 2 percent or greater of the polyol formulation. Generally the level of blowing and curing catalyst is less than 5 percent of the polyol formulation. The amount of catalyst can vary based on the temperatures of the materials.

If desired, various additives can be incorporated into the reaction mixture for producing the rigid foams of the present invention. Examples are chain extenders, crosslinking agents, surface- active substances, foam stabilizers, cell regulators, flame retardants, fillers, dyes, pigments, hydrolysis inhibitors, fungistatic and bacteriostatic substances.


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