Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2003-03-18
2004-07-13
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...
C521S123000, C521S131000, C521S167000
Reexamination Certificate
active
06762214
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of molded rigid foams comprising reacting a polyisocyanate component with an isocyanate-reactive component in the presence of at least one blowing agent, wherein the isocyanate-reactive component comprises a polyether polyol containing alkalinity. The level of alkalinity present in the polyether polyols is equivalent to a hydroxide ion level of from about 0.006% to about 0.21% by weight.
BACKGROUND OF THE INVENTION
Polyether polyols are known to be useful in the production of rigid polyurethane and polyurethane-polyisocyanurate foams. In one of the most common methods for the production of these polyols, a polyhydric alcohol such as sucrose is reacted with an alkylene oxide such as ethylene oxide or propylene oxide in the presence of an alkaline catalyst such as sodium hydroxide. As polyether polyol synthesis is generally practiced, prior to use in the production of foams, any alkaline catalyst present in the polyether polyol is neutralized and/or removed. This is generally accomplished by addition of an acid to neutralize the alkaline catalyst. This neutralization frequently results in the precipitation of a solid salt in the polyether polyol which salt may be removed by filtration. The removed solid is commonly called the filter cake. Traditionally, sulfuric acid has been used to neutralize polyether polyols.
U.S. Pat. No. 4,430,490 discloses a process for producing a polyether polyol from a polyhydric alcohol in which the alkaline catalyst is neutralized with a hydroxy-carboxylic acid, which is soluble in the polyol. The use of this hydroxy-carboxylic acid to neutralize the alkaline catalyst makes it possible to obtain a clear polyol product, which does need to be filtered before use and does not contribute to the generation of a filter cake requiring disposal.
U.S. Pat. No. 5,786,405 discloses a process for the production of a clear amine initiated polyether polyol by epoxidizing an amine in the presence of potassium hydroxide and upon completion of epoxidation, adding lactic acid to the epoxidized mixture in an amount sufficient to neutralize any remaining alkali metal hydroxide. It is beneficial to neutralize polyether polyols with lactic acid because during neutralization, lactic acid produces a lactate salt, such as potassium lactate, which is soluble in the polyether polyol, and therefore, does not require an additional process step to remove. However, the major problems observed with lactic acid neutralized polyether polyols are the increased reactivity and high pressure during the polyurethane foam forming reaction. High reactivity results in insufficient flow and therefore incomplete filling of the cavities of the mold, while increased pressure can lead to deformation of the finished foam.
Amine-initiated polyether polyols and a process for their production are also described in copending U.S. application Ser. No. 10/372,361, filed Feb. 21, 2003. These amine-initiated polyether polyols are short chain polyether polyols, which are prepared by epoxidizing an amine in the presence of an alkaline catalyst, wherein the quantity of alkaline catalyst is reduced and added earlier in the epoxidation process than normal. Once epoxidation is complete, a hydroxy carboxylic acid is added to neutralize any alkaline catalyst remaining. The resultant short chain polyether polyols exhibit foam processing characteristics similar to those of conventional sulfuric acid neutralized polyether polyols.
Surprisingly, it has now been found that non-neutralized polyether polyols, particularly amine-initiated polyether polyols that are not neutralized, can be used to prepare polyurethane foams. The processing of foams prepared with these alkaline polyether polyols proceeds without high pressures and with rapid foam rise rates. Low pressures during foaming are preferred since many rigid foaming processes require filling and/or foaming of the polyurethane-forming reaction mixture behind a thin shell which is not necessarily clamped in a mold during the foaming process. High pressures are preferably avoided as these result in surface imperfections in the foamed part, and in extreme cases, in fracturing of the outer shell. Thus, the present invention provides advantages over the amine-initiated polyether polyols as described in U.S. Pat. Nos. 5,786,405 and 6,339,110. Faster rise rates are advantageous because they allow for reduced cycle times.
SUMMARY OF THE INVENTION
This invention relates to a process for the preparation of a rigid polyurethane foam. This process comprises (1) reacting (A) a polyisocyanate component having an NCO group content of from 20 to 60%, with (B) an isocyanate-reactive component which comprises an alkaline polyether polyol having an OH number of from 200 to 800 and containing from 3 to 8 hydroxyl groups, wherein the level of alkalinity of the polyether polyols is equivalent to a hydroxide ion level of from about 0.006% to about 0.21% by weight; in the presence of (C) at least one blowing agent. In accordance with the present invention, it is preferred that the polyisocyanate components comprise (1) from 50 to 100% by weight of polymethylene poly(phenylisocyanate) having an NCO group content of from 24 to 34%, which comprises from 30 to 80% by weight of monomeric isocyanate and from 20 to 70% by weight of higher ring compounds of the diphenylmethane diisocyanate series, wherein the monomeric isocyanate comprises from 65 to 98% by weight of the 4,4′-isomer of diphenyl-methane diisocyanate, from 2 to 35% by weight of the 2,4′-isomer of diphenylmethane diisocyanate and from 0 to 5% by weight of the 2,2′-isomer of diphenylmethane diisocyanate; and (2) from 0 to 50% by weight of toluene diisocyanate having an NCO group content of 48%.
In accordance with the present invention, it is preferred that (B) the isocyanate-reactive component comprises an amine-initiated polyether polyol, and most preferably an o-toluenediamine initiated polyether polyol. These preferably have an OH number of from 300 to 500 and preferably contain from 3.5 to 4.2 hydroxyl groups. The level of alkalinity of these amine-initiated polyether polyols is preferably equivalent to a hydroxide ion level ranging from about 0.014% to about 0.11% by weight.
DETAILED DESCRIPTION OF THE INVENTION
Suitable polyisocyanate components for the present invention include those having an NCO group content of from 20 to 60%, preferably from 20 to 40% by weight, more preferably from 24 to 34% by weight and most preferably from 28 to 33% by weight. The suitable polyisocyanates which may be used in accordance with the present invention include monomeric diisocyanates, NCO prepolymers, and preferably liquid polyisocyanates and polyisocyanate adducts. Suitable monomeric diisocyanates may be represented by the formula R(NCO)
2
in which R represents an organic group obtained by removing the isocyanate groups from an organic diisocyanate having a molecular weight of about 56 to 1,000, preferably about 84 to 400. Diisocyanates preferred for the process according to the invention are those represented by the above formula in which R represents a divalent aliphatic, hydrocarbon group having 4 to 12 carbon atoms, a divalent cyclo-aliphatic hydrocarbon group having 6 to 13 carbon atoms, a divalent araliphatic hydrocarbon group having 7 to 20 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms. Preferred monomeric diisocyanates are those wherein R represents an aromatic hydrocarbon group.
Examples of the suitable organic diisocyanates include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylenediisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis(4-isocya-natocyclohexyl) methane, 2,4′-dicyclohexylmethane diisocyanate, 1,3- and 1,4-bis(isocyanatomethyl) cyclohexane, bis(4-isoc
Haider Karl W.
Kane Scott A.
Tracy Jerry E.
Yeater Robert P.
Bayer Polymers LLC
Brown N. Denise
Cooney Jr. John M.
Gil Joseph C.
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