Background of the Invention

The present invention relates to a process for utilizing liquid gases such as carbon dioxide as a sole, or co-blowing agent for polyurethanes, modified isocyanurates, isocyanurates, polyureas, carbodiimides, and modified phenolics, and all types of polymeric foams based on N=C=0 technology.

Polyurethanes and other associated polymers based on diisocyanate chemistry are foamed for use in thermal insulation, floatation, and rigidizing applications. For example, these foam products can be employed in refrigeration systems, building materials, storage tanks, truck and railway tankers and cars which form the bulk of the thermal insulation industry. Moreover, these foams, can be used in a flotation environment which encompasses, the filling of cavities in boats, barges, drilling platforms, etc., with low- density foams to prevent sinking of the vessel when accidents occur. These foams have also been used to rigidize aircraft, helicopter blades, automobiles, and the like.

Each of these polymers is based in principal on the N=C=0 backbone. The reactants which are reacted with diisocyanates vary greatly depending on the desired end product. For example, in making a polyurethane, the most widely used reactants are those compounds which terminate with an -OH group, -NH group or a -SH group. In making typical polyurethanes, a molar ratio of about 1 : 1 to about l.l : 1 for the, N=C=0 to the other reactant is employed.

Modified Isocyanurates typically employ a molar ratio of 1.5 : 1, up to about 3 : 1 for the, N=C=0 to reactant while pure Isocyanurates employ molar ratios above about 3:1. Special catalysts which are known in the art, are utilized to trimerize the excesses of N=C=0.

Polyureas may be made using a variety of formulations which are also based on the N=C=0 technology. The other reactant employed in the reaction is selected from diamines, water, dimethylol urea, and even dimethylol elamine, with the diamine being more preferred. Carbodiimides may also be produced using a variety of formulations, with the most preferred being the reaction of the N=C=0 with polycarboxylic acids, again utilizing special catalysts for the reaction. The "modified" phenolics are so called, since the reaction is not an acid cure, as in production of pure phenolics. The modified phenolics are made by reacting the N=C=0 with hydroxyl-bearing phenols, nonyl phenols and diphenols such as resorcinol.

All these above-described polymers have the common N=C=0 backbone, while the remaining reactants are chosen in order to form the desired polymer having more or less the above nomenclatures. The isocyanates employed in such reactions range in functionality from about 2.0 to about 2.9. In addition, the polymers can be prepared using prepolymers which have a functionality well above 3.0.

In order to foam these polymers into low- density materials, blowing agents are used. In the past, the chlorofluorocarbons were the preferred blowing agents. However, due to the world-wide limitations on, and upcoming elimination of these products, alternative blowing agents must be found.

U.S. Patent 4,337,318 to Doyle is an example illustrating alternate blowing agents which have been used to replace the chlorofluorocarbons. In this patent, liquid carbon dioxide is used to achieve complete and immediate foaming of the polyurethane as it emerges from a mixing zone. This technique is known as "pre-expansion" of the foam. The process occurs in the absence of "post-expansion", i.e., the expansion of the foam which occurs over time after the foam leaves the mixing zone.

Summary of the Invention

By the process of the present invention, any desired percentage of pre-expansion and post-expansion may be obtained, where liquid C0 ₂ is preferably employed as the principal blowing agent, with the further use of co-blowing agents and other techniques such as altering the pressure to the mixing zone that allow for the controlled pre- and post-expansion of the foamed polymer.

In particular, the process of the present invention comprises:

(a) mixing together in a mixing zone at ambient temperature (i) a first component comprising a diisocyanate having a functionality within the range of about 2.0 to about 2.9 or a prepoly er having a functionality greater than about 3.0; (ii) at leaεt one surfactant capable of producing a closed cell foam, (iii) at least one catalyst, (iv) a blend of one or more compounds within the group consisting of -OH terminated compounds, -C00H terminated compounds, -NH terminated compounds, -SH terminated compounds, hydroxyl-containing phenols, ureas, melamines and water? and (v) at least one blowing agent, said mixture being subjected in said mixing zone to a pressure sufficient

to maintain said at least one blowing agent in the liquid state at ambient temperature, said pressure being from about 300 to about 5000 psi;

(b) ejecting said mixture from said mixing zone to atmospheric pressure, thereby completely and instantaneously vaporizing said blowing agent: and

(c) curing the resulting foam.

Description of the Invention The present invention relates to a process for making a polymer foam which comprises the reaction between an isocyanate with one or more compound which iε effective in providing a polymer having an N=C=0 backbone. The procesε of the preεent invention alεo relates to the use of at least one blowing agent such as liquid carbon dioxide in the production of polymers having an N=C=0 backbone.

The equipment employed in preforming the above process is essentially the same as the standard equipment employed with conventional processes. For example, either positive-displacement piston-type pumps, or variable-speed gear or vane type pumps may be employed. The only requirement is that the equipment must be capable of producing pressures to the mixing zone on the order of about 300 to about 5000 psi.

In the procesε of the preεent invention, ten separate pumps or more may be employed, with each pump pumping a separate component to the mixing zone. In many cases, two or more of the components may be pre- blended and then pumped to the mixing zone aε a separate stream. Through the use of thiε type of equipment, formulationε may be altered, modified, and changed almost instantaneously.

The blowing agent(s) may be introduced at any point prior to the mixing zone, e.g., into one or more of the reactant streams, or it may be introduced directly into the mixing zone. The preferred principal blowing agent is liquid carbon dioxide _/ because of low cost, high gas production, and good stability associated with its use. However, any liquid gas having a boiling point below approximately -100"F may be used, such as nitrogen, helium, argon, tetrafluoromethane, fluoroform, hexafluoroethane, chlorotrifluoromethane, or mixtures thereof.

One technique for controlling the amount of pre- and post-expansion of the foam involves the use of co- blowing agents.

Co-blowing agents which produce the desired degree of post-expansion include water, which when reacted stoichiometrically with the N=C=0, produces gaseous C0 ₂ • Other co-blowing agents include higher- boiling solvents, such as methylene chloride, ethyl chloride, chloroform, methyl chloroform, and hydrochlorofluorocarbons, such as Freon 21, 22, 113, 114 and the like. In some cases, non-halogenated hydrocarbons such as hexane, heptane, butene-1, butane, and the like may be used.

The co-blowing agents may be introduced as a separate stream(s) to the mixing zone, or may be pre- blended into one or more of the other components prior to the mixing zone. In a majority of applications, the co-blowing agent would compriεe a minor amount of the total blowing agent, in an amount εufficient to provide the desirable amount of post-expansion. For example, where water is employed as the co-blowing agent, about 1 lb. of water provides the same amount of foaming as about 7 lbs. of

the liquid carbon dioxide. As another example, approximately 3 lbs. of Freon 22 would provide the same amount of foaming as about 2 lbs. of the liquid carbon dioxide. In another aspect of the present invention, controlled amounts of post expansion of the foam can be obtained by lowering the pressure at which the ingredients are subjected to at the mixing zone. For example, where liquid carbon dioxide is the sole blowing agent, the use of pressures at the mixing zone of about 300-500 psi provides for considerable amounts of post- expansion. Furthermore, the higher the pressure at the mixing zone, the lesser the amount of post-expanεion iε derived from the liquid carbon dioxide. For example, at about 1000 psi to 5000 psi, little to no post-expanεion iε εeen when liquid carbon dioxide iε the εole blowing agent. In addition, the degree of poεt-expansion is related to the percentage of C0 ₂ in the mixture. In particular, the higher the percentage of carbon dioxide in the total mix, the lesser the amount of post- expansion that may be obtained.

The pre-expansion, on the other hand, occurε almost instantaneous when the mixture emerges from the mixing zone, at pressures above about 1000 psi. The principals, preferred embodiments, and modes of operation of the present invention have been described in the foregoing. The invention however, is not to be limited to the particular embodiments disclosed, since they are illustrative only in εcope. Variations and modifications may be made by those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the scope of the preεent invention be limited εolely by the εcope of the following claim including equivalents thereof.