WO2011025710A1

WO2011025710A1 - Polyurethane spray foams having reduced cold substrate cracking

Info

Publication number: WO2011025710A1
Application number: PCT/US2010/046077
Authority: WO
Inventors: Eric Rexrode; Kelly Flaherty; Steven Crain; Craig Buck
Original assignee: Dow Global Technologies Llc
Priority date: 2009-08-27
Filing date: 2010-08-20
Publication date: 2011-03-03

Abstract

Disclosed is a polyurethane spray foam showing a reduced tendency to cracking when applied against substrates, such as wood or metal construction studs, under relatively low temperature (less than 50°F, or 10°C) conditions. This is achieved by incorporating an effective amount of a bond enhancing agent selected from triethanolamine, 1-methyl-imidazole, an isocyanate component having a functionality greater than 2.7 and containing polymeric methylene diphenyl diisocyanate (PMDI), or a combination thereof into the formulation. The agent serves to increase the pressure and time of pressure within the foam such that a more intimate and longer contact is established and maintained, thereby improving adhesion and/or cohesion to the substrate and reducing the tendency to crack. These foams may also be capable of achieving a desirable flammability rating according to ASTM E84.

Description

POLYURETHANE SPRAY FOAMS HAVING

REDUCED COLD SUBSTRATE CRACKING

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application

No. 61/237,470, filed August 27, 2009, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to the field of polyurethane spray foams. More particularly, the invention relates to the field of polyurethane spray foams for insulation that show a reduced tendency to crack or pull away when prepared against relatively cold substrates, such as along stud lines, and which are also capable of meeting construction flammability requirements.

Background of the Art

Polyurethane spray foams have found widespread use in the building and construction industries, where they are frequently employed as rigid foam insulation. Formulations are widely known in the art that allow efficient preparation of foams for spray application, and many include blowing agents such as fluorohydrocarbons that offer good insulative properties.

It is desirable in the construction industry to be able to work under a wide variety of environmental conditions, including a wide temperature range. Unfortunately, applying spray polyurethane foams to substrates such as oriented strand board (OSB), gypsum, concrete and commercially available insulation for walls and ceilings that may include wooden or metal studs may not be feasible because of problems obtaining adhesion and/or cohesion to the studs under relatively low temperatures, e.g., lower than fifty degrees Fahrenheit (5O⁰F), i.e., ten degrees Celsius (1 O⁰C), At such relatively low temperatures the cured or curing polyurethane foam may tend to crack at or near to the stud, and may further pull away from the stud and wall backing as the spray foam continues to cure and/or shrinks with time. The result may be that air and/or moisture can enter the construction via the crack, and that therefore the insulating performance of the spray foam application in general is compromised.

There is therefore a need in the art to identify means and/or methods to reduce the tendency of polyurethane rigid spray foams to crack or pull away from certain substrates under reduced temperatures. It is also desirable that such foams be capable of meeting construction flammability requirements. SUMMARY OF THE INVENTION

In one aspect the invention is a polyurethane spray foam formulation comprising a bond enhancing agent selected from an effective amount of triethanolamine, 1 -methyl- imidazole, an isocyanate component having a functionality greater than 2.7 and containing polymeric methylene diphenyl diisocyanate (PMDI), and combinations thereof, such that the formulation, if sprayed against a substrate under conditions wherein the temperature of the substrate is less than 1 O⁰C, will cure to form a rigid polyurethane foam that shows a tendency to crack that is reduced when compared with that of an identical formulation absent the effective amount of the bond enhancing agent.

In another aspect the invention is a method of preparing a rigid polyurethane foam comprising spraying a polyurethane formulation comprising a polyol component, an isocyanate component, and a blowing agent under foam forming conditions onto a substrate, the substrate having a temperature less than 1 O⁰C, to form a rigid polyurethane foam, wherein the formulation includes an effective amount of a bond enhancing agent selected from triethanolamine, 1 -methyl-imidazole, an isocyanate component having a functionality greater than 2.7 and containing polymeric methylene diphenyl diisocyanate, and combinations thereof, the bond enhancing agent being present in an effective amount such that the rigid polyurethane foam shows a tendency to crack that is reduced when compared with that of an identical formulation absent the effective amount of the bond enhancing agent.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The polyurethane spray foam formulations of the invention provide cured spray foams that exhibit a significant reduction in post-spray cracking, even when spraying is performed under conditions including reduced temperatures. As used herein, the term "reduced temperature" refers to a combination of substrate temperature and surrounding air temperature that is less than 1 O⁰C (5O⁰F). Also as used herein, the term "crack," "cracks," and "cracking" all refer to adhesive and/or cohesive failures occurring very near the stud or other substrate against which the foam is sprayed, i.e., within 5 mm of the surface of the stud or other substrate. Such cracks tend to be relatively small, producing a gap that is up to perhaps 5 mm in width, but that is frequently sufficient to allow significant atmospheric penetration. Cracks may form within minutes of foam application, and for test purposes are considered to be particularly problematic if they occur within 60 minutes of foam application. A significant advantage of the present invention is that the tendency to crack is reduced as compared with formulations that are identical but lack the bond enhancing agent described in greater detail hereinbelow. This means that either cracking does not occur when such formulations are spray-foamed, or that any cracks occurring are, in certain preferred embodiments, less than 3.2 mm (1/8 inch) in width, and more preferably less than 1.6 mm (1/16 inch).

The foam formulations include at least one specified component, termed a bond enhancing agent, which operates to increase the rate of the gelation reaction and therefore the positive pressure exerted by the forming foam. This positive pressure, in turn, increases the contact, both in time and in intimacy, i.e., the actual number of molecules of polymer contacting the substrate, which therefore increases the bond between the formulation as it foams and cures and the selected substrate. The increased time for positive pressure also increases the extent of reaction, which tends to improve the strength of the foam. The better bond is more likely to "hold" even when shrinkage of the foam as it cures exerts a "pull" at or near the substrate. Such tends to be more pronounced when the substrate and the surrounding air temperature are relatively low.

The "bond enhancing agent" employed herein may be any effective amount of (1 ) triethanolamine; (2) 1 -methyl-imidazole; (3) an isocyanate component that has a functionality greater than 2.7 and includes a polymeric methylene diphenyl diisocyanate (PMDI); or (4) a combination thereof. Incorporation of the bond enhancing agent in the formulation is described hereinbelow.

As is well known to those skilled in the art of preparing rigid polyurethane spray foams, a variety of conventional rigid polyurethane foam formulations may be selected, with alterations as needed to accommodate application via conventional spray foam equipment. Such foams are typically prepared from a combination of an isocyanate component, an isocyanate-reactive component, and a blowing agent suitable to foam the isocyanate component and isocyanate-reactive component while they are reacting to form the polyurethane polymer.

Selection of the isocyanate component may be made from a variety of isocyanate-group containing materials. However, in one embodiment of the invention an isocyanate component having an average functionality greater than 2.7 and containing a polymeric methylene diphenyl diisocyanate (PMDI) may be selected as the bond enhancing agent. In certain particular embodiments this isocyanate component has a functionality greater than 3.0, and in still other particular embodiments it has a functionality greater than 3.3. In some non-limiting embodiments the isocyanate component has an equivalent weight from 125 to 300, and in other non-limiting embodiments, from 130 to 175.

In any embodiment of the present invention the isocyanate may comprise PMDI, but in embodiments in which the isocyanate component is selected as a bond enhancing agent, it does comprise PMDI. PMDI is particularly useful in increasing the overall functionality of the isocyanate component, such that the minimum average functionality requirement (greater than 2.7) may be met and the bond enhancing function achieved. In certain particular embodiments the isocyanate component may include an amount of specifically polymeric constituent ranging from at least 60 percent by weight, the remainder being monomeric constituent(s). It will be recognized that many commercially available PMDIs include polymeric-to-monomeric constituent ratios within these ranges. In some embodiments the PMDI included in the present invention may have an even higher polymeric content, from at least 75 percent by weight. In general this PMDI may be present neat, in a mixture, as a part of a prepolymer, or in two or all of these forms.

Where the PMDI is less than 100 percent by weight of the isocyanate component as a whole, additional isocyanate-group containing materials may be included. Such may be selected from a wide variety of polyisocyanates, including but not limited to those that are well known to those skilled in the art. For example, organic polyisocyanates, modified polyisocyanates, isocyanate-based prepolymers, and mixtures thereof may be employed. These can further include aliphatic and cycloaliphatic isocyanates, and in particular aromatic and, more particularly, multifunctional aromatic isocyanates. Some of these may be particularly useful in increasing the overall functionality of the isocyanate component to meet the minimum functionality requirements where the isocyanate component is intended to serve as the bond enhancing agent.

Other polyisocyanates that may be useful in the present invention include 2,4- and 2,6-toluenediisocyanate and the corresponding isomeric mixtures; 4,4'-, 2,4'- and 2,2'- diphenyl-methanediisocyanate and the corresponding isomeric mixtures; and toluene diisocyanates. Also useful for preparing the rigid polyurethanes of the present invention are aliphatic and cycloaliphatic isocyanate compounds such as 1 ,6-hexa-methylene diisocyanate; 1 -isocyanato-3,5,5-trimethyl-1 ,3-isocyanatomethylcyclohexane; and 2,4- and 2,6-hexahydrotoluene diisocyanate, as well as the corresponding isomeric mixtures; and 4,4'-, 2,2'- and 2,4'-dicyclohexylmethanediisocyanate and the corresponding isomeric mixtures. Also useful is 1 ,3-tetramethylene xylene diisocyanate.

Also advantageously used for the isocyanate are the so-called modified multifunctional isocyanates, that is, products which are obtained through chemical reactions of the above diisocyanates and/or polyisocyanates. Exemplary are polyisocyanates containing esters, ureas, biurets, allophanates and preferably carbodiimides and/or uretonomines; isocyanurate and/or urethane group containing diisocyanates or polyisocyanates. Liquid polyisocyanates containing carbodiimide groups, uretonomine groups and/or isocyanurate rings, having isocyanate groups (NCO) contents of from 20 to 40 weight percent, more preferably from 20 to 35 weight percent, may also be used. These include, for example, polyisocyanates based on 4,4'-, 2,4'- and/or 2,2'-diphenylmethane diisocyanate and the corresponding isomeric mixtures; 2,4- and/or 2,6-toluenediisocyanate and the corresponding isomeric mixtures; mixtures of diphenylmethane diisocyanates; and mixtures of toluenediisocyanates and/or diphenylmethane diisocyanates. As already noted hereinabove, PMDI may be included with any of the above, but since the invention may instead include one or more of the alternative bond enhancing agents, PMDI may be omitted completely from the isocyanate component and the benefits of the invention obtained via such alternative route(s), i.e., the triethanolamine and/or 1 -methyl-imidazole.

Suitable prepolymers for use as the polyisocyanate component of the formulations of the present invention are prepolymers having NCO contents of from 2 to 40 weight percent, more preferably from 4 to 30 weight percent. These prepolymers may be prepared by reaction of the di- and/or poly-isocyanates with materials including lower molecular weight diols and triols, but may alternatively be prepared with multivalent active hydrogen compounds such as di- and tri-amines and di- and tri-thiols. Individual examples are aromatic polyisocyanates containing urethane groups, preferably having NCO contents of from 5 to 40 weight percent, more preferably 20 to 35 weight percent, obtained by reaction of diisocyanates and/or polyisocyanates with, for example, lower molecular weight diols, triols, oxyalkylene glycols, dioxyalkylene glycols, or polyoxyalkylene glycols having molecular weights up to about 800. These polyols may be employed individually or in mixtures as di- and/or polyoxyalkylene glycols. For example, diethylene glycols, dipropylene glycols, polyoxyethylene glycols, ethylene glycols, propylene glycols, butylene glycols, polyoxypropylene glycols and polyoxypropylene polyoxyethylene glycols may be used. Polyester polyols can also be used, as well as alkyl diols such as butane diol. Other diols that are also useful include bishydroxyethyl- and bishydroxypropyl-bisphenol A, cyclohexane dimethanol, and bishydroxyethyl hydroquinone.

Useful as the polyisocyanate component of prepolymer formulations are: (i) polyisocyanates having an NCO content of from 8 to 40 weight percent containing carbodiimide groups and/or urethane groups, from 4,4'-diphenylmethane diisocyanate or a mixture of 4,4'- and 2,4'-diphenylmethane diisocyanates; (ii) prepolymers containing NCO groups, having an NCO content of from 2 to 35 weight percent, based on the weight of the prepolymer, prepared by the reaction of polyols, having a functionality of preferably from 1.75 to 4 and a molecular weight of from 800 to 15,000, with 4,4'-diphenylmethane diisocyanate or with a mixture of 4,4'- and 2,4'-diphenylmethane diisocyanate; mixtures of (i) and (ii); and (iii) 2,4' and 2,6-toluene-diisocyanate and the corresponding isomeric mixtures. The viscosity of the isocyanate component is, in some embodiments, from 25 to 5,000 centipoise (cP) at 25⁰C (0.025 to about 5 Pascal^*seconds (Pa^*s)), but values from 100 to 1 ,000 cP at 25⁰C (0.1 to 1 Pa^*s) may be preferred for ease of processing.

The isocyanate-reactive component may be alternatively referred to as the polyol component. This component includes primarily polymers containing groups that react with the isocyanate component to form a rigid polyurethane foam. Frequently these groups are hydroxyl groups, but other isocyanate-reactive groups, including but not limited to amine, ether and ester groups, may optionally be selected. They are generally formed by base-catalyzed addition of propylene oxide (PO) and/or ethylene oxide (EO) onto a hydroxyl- or amine-terminated initiator, or by polyesterification of a diacid, such as adipic acid, with glycols, such as ethylene glycol or dipropylene glycol. Polyols extended with PO or EO are polyether polyols. Polyols formed by polyesterification are polyester polyols. The choice of initiator, extender, and molecular weight of the polyol greatly affect the physical state and the physical properties of the polyurethane polymer. In general, spray foam formulations are very fast-reacting formulations, and rigid foams are conventionally formed by favoring PMDI as the isocyanate component and polyols having high functionality initiators as the polyol component or constituents thereof. Such high functionality initiators may include, for example, sucrose (f=8), sorbitol (f=6), toluenediamine (f=4), Mannich bases (f=4), and Novolac-initiated polyols. Polyester polyols, which include low molecular weight aromatic types that are manufactured by, for example, transesterification (glycolysis) of recycled polyethyleneterephthalate (PET) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol, may also be useful in preparing polyurethane spray foams.

The polyol or polyols that make up the polyol component may desirably have a viscosity ranging from 100 centipoise (cP) to 100,000 cP, and in certain more desirable but non-limiting embodiments, from 200 cP to 100,000 cP.

The third major component of the formulation is the blowing agent. While it is frequently included in the polyol component, prior to combination with the isocyanate component, it may also alternatively be a separate component in itself, combining simultaneously with the isocyanate component and polyol component in, for example, conventional spray equipment capable of feeding three streams at once. Blowing agent selections may include water, hydrocarbons, chlorinated hydrocarbons, fluorinated hydrocarbons, chlorofluorocarbons, and combinations thereof. Of particular use may be HFC-245fa. Other examples may include HCFC-141 b, HCFC-22, HFC-134a, n-pentane, isopentane, cyclopentane, HCFC-124, HFC-365mfc, and combinations thereof. Some halocarbon blowing agents, in particular, may be effective in reducing viscosity to a desirable level to optimize sprayability.

In addition to the isocyanate component, polyol component, and blowing agent, as described hereinabove, the formulation of the present invention may, in certain embodiments, contain a bond enhancing agent selected from triethanolamine, 1 -methyl- imidazole, and combinations thereof. One or both of these bond enhancing agents may be employed in any amount effective to improve the bond between the rigid polyurethane spray foam and the substrate (hereinafter "effective amount"), particularly where such spray is applied under conditions where the substrate and/or air temperature surrounding the substrate is less than ten degrees Celsius (1 O⁰C), which is fifty degrees Fahrenheit (5O⁰F), and in certain embodiments, less than minus one degree Celsius (-1⁰C), which is thirty degrees Fahrenheit (3O⁰F). In the present invention such effective amount may be met by any one bond enhancing agent, by two bond enhancing agents together, or by all three bond enhancing agents together. In certain particular embodiments the triethanolamine or 1 -methyl-imidazole is used in an amount from 0.5 to 15 parts by weight, based on the weight of the polyol component as a whole, including with the weight of the polyol(s) itself/themselves the weight of the bond enhancing agent(s) and the weight of any additional additives. In particular embodiments the effective amount of either the triethanolamine or the 1 -methyl-imidazole, or of both combined, may be from 1.5 to 6.5 parts by weight, on the same basis, and in other particular embodiments the amount may be from 1.5 to 3.5 parts by weight, on the same basis.

As noted hereinabove, and without wishing to be bound by any theory, the authors suggest that the bond enhancing agent affects the timing of the gel versus the blow (and, where applicable, trimerization) reactions, sequencing the gel reaction such that it occurs predominantly prior to the end of rise. This generates the pressure necessary for more intimate contact of the foam with the substrate and provides for a stronger foam prior to the pull on the substrate that results from foam shrinkage. Those skilled in the art will recognize that the non-isocyanate bond enhancing agents disclosed herein are acting essentially as strong gel catalysts, and that their use, based on either their character or their relative effective amount, adjusts the overall catalysis to favor the gel reaction. Additional catalysts may, however, in certain particular embodiments be included in the formulation to further adjust the catalyst balance and/or to serve as primarily blow and/or trimerization catalysts.

For example, other amine catalysts may be employed, provided that they, due to either character or amount, do not negate the benefits of the bond enhancing agent(s) as disclosed herein. Such typically include the N-alkylmorpholines, N-alkylalkanolamines, N,N-dialkylcyclohexylamines, alkylamines where the alkyl groups are methyl, ethyl, propyl, butyl and isomeric forms thereof, and heterocyclic amines. Typical but non-limiting specific examples thereof are triethylenediamine, tetramethylethylenediamine, bis(2- dimethylaminoethyl)ether, triethylamine, tripropylamine, tributylamine, triamylamine, pyridine, quinoline, dimethylpiperazine, piperazine, N,N-dimethylcyclohexylamine, N- ethylmorpholine, 2-methylpropanediamine, methyltriethylenediamine, 2,4,6-tri- dimethylaminomethyl)phenol, N,N',N"-tris(dimethylaminopropyl)-sym-hexahydrotriazine, and combinations thereof. A preferred group of tertiary amines comprises bis(2-dimethyl- aminoethyl)ether, dimethylcyclohexylamine, N,N-dimethyl-ethanolamine, triethylenediamine, triethylamine, 2,4,6-tri(dimethylaminomethyl)phenol, N, N', N- ethylmorpholine, and combinations thereof.

Non-amine catalyst may also be used in the present invention. Typical of such catalysts are organometallic compounds of bismuth, lead, tin, titanium, iron, antimony, uranium, cadmium, cobalt, thorium, aluminum, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper, manganese, zirconium, and combinations thereof. Included as illustrative examples only are bismuth nitrate, lead 2-ethylhexoate, lead benzoate, lead naphthenate, ferric chloride, antimony trichloride, and antimony glycolate. A preferred group of organo-tin catalysts is the stannous salts of carboxylic acids, such as stannous acetate, stannous octoate, stannous 2-ethylhexoate, and stannous laurate, as well as the dialkyl tin salts of carboxylic acids, such as dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin dimaleate, dioctyl tin diacetate, and combinations thereof.

One or more trimerization catalysts may be used with the present invention. The trimerization catalyst employed may be any known to those skilled in the art which will catalyze the trimerization of an organic isocyanate compound to form the isocyanurate moiety. For typical isocyanate trimerization catalysts, see The Journal of Cellular Plastics, November/December 1975, page 329: and U.S. Patents 3,745,133; 3,896,052; 3,899,443; 3,903,018; 3,954,684; and 4,101 ,465; the disclosures of which are incorporated herein in their entireties by reference. Typical trimerization catalysts include the glycine salts and tertiary amine trimerization catalysts, as well as the alkali metal carboxylic acid salts and combinations thereof. Preferred species within the classes are sodium N-2-hydroxy-5- nonylphenyl) methyl-N-methylglycinate, N,N-dimethylcyclohexylamine, and mixtures thereof. Also included in this list are the epoxides disclosed in U.S. Patent 3,745,133, the disclosure of which is incorporated herein in its entirety by reference.

In addition to the general components and additives disclosed above, further additives or modifiers such as are well-known in the art may optionally be included in the rigid polyurethane spray foam formulation. Since rigid spray foams are often used in construction and structure applications, flame retardants may be particularly desirable. Such materials suitable for modifying the combustion performance of the foams may be neat additives, such as certain halogen-containing and phosphorus-containing compounds including but not limited to tris(2,3-dibromopropyl) phosphate (TRIS), bis(2,3- dibromopropyl) phosphate, triethylphosphate (TEP), tris(2-chloroethyl) phosphate, tris(2- chloropropyl)phosphate, tris(1 ,3-dichloropropyl)phosphate, diammonium phosphate, halogenated aromatic compounds, antimony oxide, alumina trihydrate, polyvinyl chloride, and combinations thereof. Bromine and/or phosphorus may also be incorporated in a formulation as modified polyols. Examples may include decabromodiphenyl ether (decaBDE) and other polybrominated diphenyl ethers (PBDEs), including, for example, pentabromodiphenyl ether (pentaBDE), octabromodiphenyl ether (octaBDE), tetrabromobisphenol A (TBBPA or TBBP-A), hexabromocyclododecane (HBCD), and combinations thereof. Other examples may include brominated aromatic ester polyols such as PHT4-Diol, available from Chematura, and RB79, available from Albemarle Corporation.

Dispersing agents, cell stabilizers, surfactants, colorants, fillers, and materials serving two or more of these functions may also be incorporated into the formulations. Surfactants may including organic and silicone-based additives. Exemplary materials may be commercially available under the designations SF-1 109, L-520, L-521 and DC-193, which are, generally, polysiloxane polyoxyalkylene block copolymers. Further information may be found in U.S. Patents 2,834,748; 2,917,480; and 2,846,458; the disclosures of which are incorporated herein in their entireties by reference. Also included are organic surfactants containing polyoxyethylene-polyoxybutylene block copolymers as described in, for example, U.S. Patent 5,600,019, the disclosure of which is incorporated herein in its entirety by reference. Fillers may include both natural and synthetic minerals, clays, and similar particulates.

In proportions it is generally desirable that the isocyanate component and the polyol component be admixed at any suitable volume or weight ratio as desired for the particular foam composition, formulation method or equipment. In certain non-limiting embodiments, any bromine or phosphorus-containing flame retardant additives may be included in amounts ranging from 0 to 20 parts by weight, based on the total weight of the polyol component. Surfactants, such as TEGOSTAB^* B-8404, may be included in any amount ranging from 0 to 6 parts by weight, on the same basis. (TEGOSTAB^* B-8404 is available from Evonik.) Catalysts, such as NIAX^* A-1 , POLYCAT^* 9 and/or POLYCAT^* 77, may be included in amounts from 1 to 15 parts by weight, on the same basis. (NIAX^* A-1 is available from General Electric. POLYCAT^* 9 and POLYCAT^* 77 are available from Air Products.) Additional catalysts, such as TOYOCAT^* DM 70 or other gelling catalysts, may be included in amounts ranging from O to 5 parts by weight, on the same basis. (TOYOCAT^* DM 70 is available from Tosoh Corporation.)

In the polyurethane foam formulations including water as the blowing agent, the water is desirably present in an amount of from 0.5 to 40 parts by weight, based on 100 parts of polyol component. In more particular and non-limiting embodiments, water may be used in an amount of from 1 to 35 parts by weight, on the same basis, and in still more preferred but non-limiting embodiments, water may be employed in an amount of from 2 to 30 parts by weight, again, on the same basis.

In preparing the formulations and final foam products of the present invention any methods and means known or contemplated by those skilled in the art as useful for preparing rigid polyurethane spray foams may be employed. It is typical to include any additives or modifiers with the polyol component, and then enable the isocyanate component and the polyol component to contact one another and appropriately mix within a dual-action spray gun, whereby the polymerization reaction proceeds to completion on the substrate to which the spray foam is applied, e.g., a ceiling, wall, or other substrate. While the invention is concerned particularly with adhesive and/or cohesive failures between the spray foam and studs, it is also important that adhesion and/or cohesion to sheathing materials is acceptable or better. Such sheathing materials may include, for example, oriented strand board (OSB), plywood, gypsum sheetrock, foam board, THERMAX^* insulation boards (available from The Dow Chemical Company) and other structural insulated panels, fiberboard, cellulosic sheathing, and flexible foam-faced polyisocyanurate insulation boards. The equipment frequently used for spraying may include "double acting" positive displacement pumps which have the advantage of supplying an accurate component ratio of isocyanate component to polyol component in a continuous stream. Such systems tend to function more reliably, i.e., experience less cavitation, when each component has a viscosity of less than 1 ,000 cP at 25⁰C. Another parameter that is considered by those skilled in the art is that the commercially adopted standard design for such equipment usually requires a 1 :1 volume ratio of isocyanate component to polyol component, though there are instances where different ratios may be effectively employed.

Final foam density may, in certain non-limiting embodiments, range from about 0.4 to about 10 pounds per cubic foot (pcf); in other non-limiting embodiments, from about 0.8 to about 5 pcf; and in still other non-limiting embodiments, from about 1 .5 to about 4 pcf. Such density ranges may be particularly desirable in preparing a construction providing both a desirable level of insulation and good flammability performance. The spray foams of the invention may achieve excellent and desirable flammability ratings when tested according to the American Society of Testing Materials (ASTM) E84 Test. This means that in certain embodiments they exhibit a Flame Spread Index that is less than or equal to 75, preferably less than or equal to 50, and more preferably less than or equal to 25.

EXAMPLES

The following materials are used in the Examples:

Polyol component:

"Polyol Blends 1 , 2 and 3" are each a blend of polyether and polyester polyols, chain extender and proprietary catalyst package.

"Additives" include surfactants, flame suppressants, additional blowing and gelling catalysts, and curative agents.

"Water" and "HFC-245fa" as a blowing agent.

"1 -methyl-imidazole" as a bond enhancing agent.

"Triethanolamine (TEOA)" as a bond enhancing agent. lsocyanate component:

"lsocyanate 1 " is a PMDI-containing isocyanate product, functionality of 2.7.

"lsocyanate 2" is a PMDI-containing isocyanate product, functionality of 3.0, a bond enhancing agent.

Walls built for test purposes include:

1 . THERMAX^* Wall:

A 4 foot by 8 foot wall assembly with three cavities constructed at 8, 16 and 24 inches on center and using 1 inch thick THERMAX® HD and 16 gauge Dietrich CSJ 3-5/8 inch steel studs with an extra C-channel on top.

2. Oriented Strand Board (OSB) Wall:

A 4 foot by 8 foot wall assembly with three cavities constructed at 8, 16 and 24 inches on center using 7/16" thick oriented strand board (OSB) and 2 inch by 4 inch wood studs.

3. ASTM E84 Wall:

The wall sample is prepared to a nominal thickness of 2 inches, and is sprayed in one pass.

Test Procedures:

Each wall is first sprayed with formulation in a picture-framing protocol, around the perimeter of each stud cavity. Each cavity is then filled to the desired foam depth. The test results designated in Table 1 under "THERMAX^* wall (3O⁰F)" refer to a non-standard test which is herein defined as the Foam Deflection Force test. This is carried out using Type T thermocouples to monitor and record the temperature of the foam during the spray application. The thermocouple is inserted in the middle of a 24- inch cavity between wall studs to a height of 0.5 inch. The temperature is recorded at 1 Hertz (Hz). The Type T thermocouples are made from Thermo Electric NN24T copper constantan (55 percent copper, 45 percent nickel alloy) wire. The junction is made by twisting the bared wire ends and soldering. The thermocouple wire is accurate to 0.1⁰F. The test also requires an Omega LCFA-5 miniature compression load cell with a load capacity of 5 pound (Ib), for both compression and tension. This is used to evaluate the compressive (foaming) and tensile (shrinking) behavior of the foam when applied to a 24- inch cavity. A hole approximately 1 .2 inches in diameter is cut into the middle of the wall header on center. The LCFA is attached to a bracket that is bolted on either side of the hole such that the bottom edge of the LCFA is flush with the inner wall of the cavity. Aluminum tape is placed over the entire hole such that the LCFA is attached to the tape and the tape is extended 0.5 inch around the hole. The load cell pressure is recorded at 1 Hz. The load cell has an accuracy of 0.2 percent.

Examples 1 -6

Three spray foam formulations are prepared using the materials and amounts shown in Table 1 , by first combining all of the polyol component constituents, including the blowing agent. Each formulation is then fed through a proportioning machine and a spray gun, to contact the polyol component, isocyanate component, and blowing agent (HFC-245fa and water) and apply it to the substrate wall, including studs. One (volume) part of isocyanate component is matched with one (volume) part of polyol component. Foam is sprayed at an air and substrate temperature of -1⁰C (3O⁰F) for those tests that evaluate cracking, while the temperature of the environment and walls used for preparing samples for ASTM E84 testing is 3O⁰C (5O⁰F). For interpretation purposes, Examples 1 and 2 are considered to be comparative to one another, as are Examples 3 and 4, and Examples 5 and 6, respectively. As noted in Table 1 , Example 1 , which does not contain a bond enhancing agent, is not an example of the invention. TABLE 1

^** not an example of the invention, included hereinabove for comparative purposes

-- not present in formulation In the test designated as "THERMAX^* wall (3O⁰F)" "pass" means either that the foam did not delaminate from the installed pressure transducer measuring the pull force, or there was no crack for at least 60 minutes. In the same test "Fail" means that the foam pulled away from the pressure transducer or cracked along at least part of the stud/foam interface in less than 60 minutes. The results for the "OSB Wall (3O⁰F)" refer to minutes from completion of spraying until a crack visible to the unenhanced human eye appears. After 60 minutes the widest crack width is measured using a feeler gauge. Thus, while these foams may, in some cases, still "crack," meaning that they crack in less than 60 minutes, delays in initiation time and/or extent of cracking (for example, width of crack in mm, as shown in Table 1 ) are still considered to be representative of improved performance in a given test, i.e., they exhibit a tendency to crack that is reduced when compared with formulations that are identical except that they lack at least one of the bond enhancing agents identified herein. The final foams are also tested for combustion performance using the ASTM E84 wall, according to ASTM E84. They are evaluated as achieving a desirable flammability rating, based on Flame Spread Index measurements of 25 or less.

Claims

CLAIMS:

1 . A polyurethane spray foam formulation comprising a bond enhancing agent selected from triethanolamine, 1 -methyl-imidazole, an isocyanate component having a functionality greater than 2.7 and containing polymeric methylene diphenyl diisocyanate, and combinations thereof, the bond enhancing agent being present in an effective amount such that the formulation, which further includes a polyol component and a blowing agent, if sprayed against a substrate under conditions such that the temperature of the substrate is less than ten degrees Celsius (1 O⁰C), will cure to form a rigid polyurethane foam that exhibits a tendency to crack that is reduced when compared with that of an identical formulation absent the effective amount of the bond enhancing agent.

2. The polyurethane spray foam formulation of claim 1 wherein the effective amount of the bond enhancing agent is, for triethanolamine or 1 -methyl-imidazole, from 0.5 to 15 parts by weight, based on the weight of the polyol component.

3. The polyurethane spray foam formulation of claim 2 wherein the effective amount of the bond enhancing agent is, for triethanolamine or 1 -methyl-imidazole, from 1.5 to 6.5 parts by weight, based on the weight of the polyol component.

4. The polyurethane spray foam formulation of claim 1 wherein the isocyanate component has a functionality greater than 3.0.

5. The polyurethane spray foam formulation of claim 4 wherein the isocyanate component has a functionality greater than 3.3.

6. The polyurethane spray formulation of claim 1 wherein the isocyanate component has a polymeric content of at least 60 percent.

7. The polyurethane spray formulation of claim 6 wherein the isocyanate component has a polymeric content of at least 75 percent.

8. The polyurethane spray formulation of claim 1 wherein the temperature of the substrate is less than minus one degree Celsius (-1⁰C).

9. The polyurethane spray foam formulation of claim 1 wherein the rigid polyurethane foam achieves a Flame Spread Index that is less than or equal to 75 when tested according to ASTM E84.

10. The polyurethane spray foam formulation of claim 9 wherein the rigid polyurethane foam achieves a Flame Spread Index that is less than or equal to 25 when tested according to ASTM E84.

1 1 . A method of preparing a rigid polyurethane foam comprising spraying a polyurethane formulation comprising a polyol component, an isocyanate component, and a blowing agent under foam forming conditions onto a substrate, the substrate having a temperature less than ten degrees Celsius (1 O⁰C), to form a rigid polyurethane foam, wherein the formulation includes an effective amount of a bond enhancing agent selected from triethanolamine, 1 -methyl-imidazole, an isocyanate component having a functionality greater than 2.7 and containing polymeric methylene diphenyl diisocyanate, and combinations thereof, the bond enhancing agent being present in an effective amount such that the rigid polyurethane foam shows a tendency to crack that is reduced when compared with that of an identical formulation absent the effective amount of the bond enhancing agent.

12. The method of claim 1 1 wherein the effective amount of the bond enhancing agent is, for triethanolamine or 1 -methyl-imidazole, from 0.5 to 15 parts by weight, based on the weight of the polyol component.

13. The method of claim 12 wherein the effective amount of the bond enhancing agent is, for triethanolamine or 1 -methyl-imidazole, from 1.5 to 6.5 parts by weight, based on the weight of the polyol component.

14. The method of claim 1 1 wherein the isocyanate component has a functionality greater than 3.0.

15. The method of claim 14 wherein the isocyanate component has a functionality greater than 3.3.

16. The method of claim 1 1 wherein the isocyanate component has a polymeric content of at least 60 percent.

17. The method of claim 16 wherein the isocyanate component has a polymeric content of at least 75 percent.

18. The method of claim 1 1 wherein the temperature of the substrate is less than minus one degree Celsius (-1⁰C).

19. The method of claim 1 1 wherein the rigid polyurethane foam achieves a Flame Spread Index that is less than or equal to 75 when tested according to ASTM E84.

20. The method of claim 19 wherein the rigid polyurethane foam achieves a Flame Spread Index that is less than or equal to 25 when tested according to ASTM E84.