CA2075975A1

CA2075975A1 - Process for producing n=c=o foams and the controlled pre- and post-expansion thereof

Info

Publication number: CA2075975A1
Application number: CA 2075975
Authority: CA
Inventors: Earl N. Doyle
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-02-13
Filing date: 1991-02-12
Publication date: 1991-08-14
Also published as: WO1991012287A1; EP0517858A4; EP0517858A1

Abstract

A method for producing polymeric foams based upon the N=C=O
technology, intended for thermal insulation, floatation, rigidization, and like comprises the use of a liquid gas blowing agent, such as a liquid CO2 in the production of the foam. In addition, the present invention relates to the control of the amount of pre-expansion and post-expansion of the foam. This control can be provided through both the use of a co-blowing agent as well as controlling the pressure at the mixing zone.

Description

091/12287 ~ 2 ~ 7 ~ PCT/US~i/008~
,, I'RO( ESS FOR PROI)UCING N =(- =() F()~M~ NI) TI~E ( O~lTROLLEr) PRE- ,~NI~
I'OST-E.YPANSION THEREOF

Backqround 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=O 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=O 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 l : l to about l.l : ~l for the, N=C=O to the other reactant is emplcyed.

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Modified Isocyanurates typically employ a molar ratio of l.5 : l, up to about 3 : l 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=O. - ` - ~ ~
- Polyureas may be made using a variety of formulations which are also based on the N=C=0 - *echnology.-- The other reactant employed in the reaction is selected from diamines, water, dimethylol urea, and even dimethylol melamine, 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=O 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 phenolicsO
; 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=O backbone, while the remàining reactants are ~- chosen in~order to7:form the'idesirëd 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 3Ø
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.
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~ 091/12287. . 2 0 7 ~ 9 7 5,~3 ~ Pcr/us~l/oo8qs 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 co2 is preferably emplo~ed 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~ c~
~ (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 prepolymer having a functionality greater than about 3.0; (ii) at least 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, -COOH 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 35 subjected in said mixing zone to a pressuré sufficient ,:
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-- 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 is effective in providing a polymer having an N=C=0 backbone.
The process of the present invention also 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 process of the present 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 as a separate stream. Through the use of this type of equipment, formulations may be altered, modified, and changed almost instantaneously.

~ 091/12287 -- 2 o 7 ~ ~ 7 ~ Pcr/us~l~0084~

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--l00F- 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=O, produces gaseous CO2. 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, ll~
'' ''and the ''like. In' some' 'cases, -non-halogenated hydrocarbons such as hexane, heptane, butene-l, 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 comprise a minor amount of the total blowing agent, in an amount sufficient to provide the desirable amount of post-expansion. For example, where water is employed as the co-blowing agent, about l lb. of water provides the same amount of foaming as about 7 lbs. of , ' : ,.~ . .
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6 , 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-expansion is derived from the liquid carbon dioxide. For example, at about lO00 psi to 5000 psi, little to no post-expansion is seen when liquid carbon dioxide is the sole blowing agent. In addition, the degree of post-expansion is ` related to the percentage of CO2 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, occurs almost instantaneous when the mixture emerges from the mixing zone, at pressures above about lO00 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 scope.
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 present invention be limited solely by the scope of the following claim including equivalents thereof.

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Claims

CLAIMS:

1. A process for the production of low density foam having a N=C-O backbone comprising the steps of:
(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 2.9 or a prepolymer having a functionality greater than about 3.0; (ii) at least 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, -COOH 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.

2. The process according to claim 1 wherein the at least one blowing agent comprises a liquid gas having a boiling point below about -100°F.

3. The process according to claim 1 wherein the at least one blowing agent comprises liquid carbon dioxide.

4. The process according to claim 2 or 3 wherein the blowing agent further comprises a co-blowing agent which comprises water, high-boiling point solvents and non-halogenated hydrocarbons.

5. The process according to claim 4 wherein the co-blowing agent comprises a higher-boiling point solvent which comprises methylene chloride, ethyl chloride, chloroform, methyl chloroform, or a hydrochlorofluorocarbon.

6. The method according to claim 4 wherein the co-blowing agent comprises a non-halogenated hydrocarbon which comprises hexane, heptane, butene-1, butane or mixtures thereof.

7. The process according to claim 4 wherein the co-blowing agent comprises water.

8. The process according to claim 1 wherein the foam has a density of about 0.5 to about 6 lbs./cu.ft.

9. The process according to claim 1 wherein the foam comprises a polymer having a N=C=O backbone.

10. The process according to claim 1 wherein the foam comprises a polyurethane, a modified isocyanurate, an isocyanurate, a polyurea, a carbodiimide or a modified phenolic.

11. The process according to claim 2 or 3 wherein a majority of the expansion of the foam occurs when the mixture exits the mixing zone.

12. The process according to claim 4 wherein the expansion of the foam includes both pre-expansion and post-expansion.

13. The method according to claim 12 wherein the amount of co-blowing agent is selected so as to provide a predetermined amount of post-expansion of the foam.

14. The method according to claim 7 wherein the amount of water is selected so as to provide a predetermined amount of post-expansion of the foam.

15. The process according to claim 1 wherein the pressure at the mixing zone is selected so as to provide a predetermined amount of post-expansion of the foam.

16. The process according to claim 1 wherein at least two components are preblended prior to being introduced into the mixing zone.

17. The process according to claim 1 wherein at least one blowing agent is preblended with at lest one other component prior to being introduced into the mixing zone.

18. The process according to claim 4 wherein the co-blowing agent is preblended with at least one other component prior to being introduced into the mixing zone.