Low acid organometallic catalyst for the production of flexible, semi-flexible and rigid polyurethane foams

Polyurethane foams produced by the catalytic reaction of a polyisocyanate with a polyol in the presence of various blowing additives are widely known and used in fabricating parts and equipment for the automotive industry, as well as housing and other industries. One such blowing additive is a chlorofluorocarbon (CFC) blowing agent which vaporizes as a result of the reaction exotherm. The discovery that CFC's may deplete ozone in the stratosphere has resulted in mandates diminishing CFC use. Production of water-blown foams, in which blowing is performed with CO 2 generated by the reaction of water with the polyisocyanate, has therefore become increasingly important.

The production of rigid polyurethane foams is a well-known art, and as such, foams have a wide variety of industrial and commercial applications. Rigid polyurethane foams have been used as packaging materials, flotation materials and various structural components. Rigid polyurethane foam has one of the lowest thermal conductivity ratings of any insulant, which allows efficient retention of heat or, alternatively, maintenance of a refrigerated or frozen environment insulating rigid polyurethane foams may be molded into many useful appliances. The foams may be shaped into sheets of varying thickness and placed between roofs or in floors. They also may be formed into contour shapes useful in insulating pipes and ducts. Rigid polyurethane foam can also be applied to numerous substrates by spray foaming techniques. Spray foam applications are important particularly in such areas as warehouses, schools and offices providing the desired insulation requirements for heating and cooling.

Virtually all commercially manufactured polyurethane foams are made with the aid of at least one catalyst. Catalysts are those compounds that help promote the reaction between an isocyanate and an isocyanate-reactive compound. The types of catalysts that are typically utilized in the formation of rigid polyurethane foams may differ depending on application. The ability to selectively promote either the blowing reaction (reaction of water with isocyanate to generate CO2), the gelling reaction (reaction of polyol with isocyanate) or the trimer reaction (polymerization of isocyanate to form isocyanurate) is an important consideration in selecting the proper catalyst.

If a catalyst promotes the blowing reaction to a high degree, much of the CO2 will be evolved before sufficient reaction of isocyanate and polyol has occurred, and the CO2 will bubble out of the formulation, resulting in a foam of poor quality and physical properties. In contrast, if a catalyst too strongly promotes the gelling reaction, a substantial portion of the CO2 will be evolved after a significant degree of polymerization has occurred. This foam will typically be characterized by high density, broken or poorly defined cells, and/or other undesirable features. Finally, in those applications desiring the production of isocyanurate (trimer), if a catalyst does not generate enough heat (exothermic reaction) early on in the reaction, the amount of trimer that is produced will be low. Again, a poor quality foam, this time characterized by friability, poor dimensional stability and poor fire properties, will be produced.

The following patents and articles are representative of the art in the polyurethane industry:

U.S. Pat. No. 4,200,699 discloses the formation of rigid polyurethane foams using a catalytically effective amount of an antimony carboxylate, a potassium carboxylate, and a zinc carboxylate in combination with tertiary amines or tin compounds.

U.S. Pat. No. 5,342,859 discloses the use of alkali metal catalysts in the presence of excess carboxylic acid, e.g., 2-ethyl-hexoic acid to help improve the flame suppression of polyurethane foam by creating flame resistant amides. It also can help to reduce the water content of in polyurethane formation.

U.S. Pat. No. 6,107,355 discloses the use of alkali and alkaline earth metal salts of mono carboxylic acids to produce polyurethane foams. Cocatalysts consisting of tertiary amines may be used in conjunction with the metal salts.

U.S. Pat. No. 4,256,848 discloses the use of co-catalyst combinations comprised of divalent mono-mercuric salts of organic acids and ionizable mono-organo-mercuric carboxylates as catalysts for the preparation of polyurethanes including solid, non-cellular, and foam urethanes, both rigid and flexible.

U.S. Pat. No. 4,256,847 discloses a method for producing rigid polyurethane foams consisting of an organic polyisocyanate, an organic polyol, a blowing agent, and a catalyst. The catalyst suited for catalyzing the formation of polyurethanes consists of zinc or lithium salts of carboxylic acids.

U.S. Pat. No. 6,242,555 discloses the use of organo bismuth, organo fin and organo lead carboxylates as catalyst types for the production of micro-cellular or noncellular, light stable elastomeric isophorone diisocyanate based polyurethane moldings. Organobismuth carboxylates having less than 60% free acid, preferably less then 25% and most preferably, less than 10% are disclosed.

Arenivar, J. D., Bismuth Carboxylates for Polyurethane Catalysts ., Polyurethanes, 89, Proceedings of the SPI 32 nd Annual Technical/Marketing Conference, Oct. 1-4, 1989, pp 623-627 disclose the use of Bismuth Carboxylates for Polyurethane elastomers and the effect of added acid. Bismuth octoate and bismuth neodecanoate in the presence of 1-4 equivalents acid were disclosed as catalytic materials.

Although organometallic catalysts have found acceptance in many commercial coatings, adhesives, sealants, and elastomers (C.A.S.E.) applications, their use in urethane-based flexible and semi-flexible foams has been limited. Tertiary amines are currently the industry standard polyurethane foam catalyst, yet their distinct odor and volatility has had the industry searching for catalytic alternatives.

The present invention relates to an improvement in flexible, semi-flexible and rigid foams formed by the catalytic reaction of a reaction mixture comprised of an aromatic polyisocyanate, an organometallic catalyst, a polyol and a blowing agent. The improvement resides in a bismuth carboxylate or bismuth sulfonate having less than 34% free acid as the organometallic catalyst.

Several advantages can be achieved by the use of a bismuth carboxylate or bismuth sulfonate as the catalyst and these include:

an ability to produce flexible, semi-flexible and rigid foams of excellent quality;

an ability to produce a foam having an excellent low value of thermal conductivity;

an ability to produce a foam having essentially no odor; and,

an ability to reduce cell size and improve insulating properties (k-factor value).

Low-density flexible, semi-flexible and rigid foams having a density of 1-5 pounds per cubic foot (pcf) are highly cross-linked polymers with a closed cell structure. Each cell within this polymeric matrix maintains a high percentage of unbroken cell walls so that gas diffusion, in and out of these cells, is very difficult. CFCs (chlorofluorocarbons), HCFCs (hydrochlorofluorocarbon), HFCs (hydrofluorocarbon), hydrocarbons or other auxiliary blowing agents are usually contained within these cells. Because these blowing agents tend to have much lower thermal conductivity than air, these rigid closed-cell foams have a significantly lower thermal conductivity than most other competitive insulative materials.

In attempts to further optimize this technology, a family of bismuth based catalysts have been identified that can, solely or in conjunction with tertiary amine catalysts, substantially reduce cell size and the k-factor (measure of thermodynamic properties—lower the better) in a rigid polyurethane foam formulated with water, CFCs, HCFCs, HFCs, or hydrocarbons as conventional blowing agents. This family of organometallic compounds has the general structure:

[M] + [N] −

where [M] + corresponds to the tri-valent metal cation bismuth (Bi) and [N] − corresponds to the anions of any carboxylic or sulfonic acids. These catalysts can be used to promote the reaction, solely or in conjunction with a tertiary amine or other organometallic compound, between an aromatic isocyanate functional compound, i.e., MDI, TDI and an active hydrogen-containing compound e.g., a polyol, and amine or water especially the urethane (gelling) reaction of polyol hydroxyls with the isocyanate and the blowing reaction of water with isocyanate and/or the trimerization of the isocyanate functionality to form polyisocyanurates.

Examples of bismuth carboxylates and sulfonates include the carboxylates of C 515 aliphatic acids. Specifically the 2-ethyhexanoic acid (octoate) and neodecanoic acid. Examples of sulfonates include aromatic sulfonates such as p-toluenesulfonate and aliphatic sulfonates such as methanesulfonate and trifluoromethanesulfonate.

Examples of tertiary amines which can be utilized with the bismuth carboxylates and sulfonates include diazabicyclooctane (triethylenediamine), quinuclidine and substituted quinuclidines; substituted pyrrolizidines and substituted pyrrolidines; bisdimethylaminoethyl ether, pentamethyldiethylenetriamine, higher permethylated polyamines, branched polyamines, 2-[N-(dimethylaminoethoxyethyl)-N-methylamino]ethanol, alkoxylated polyamines, imidazole-boron compositions, and aminopropylbis(aminoethyl)ether compositions to produce flexible and rigid foams with enhanced foam physical properties without negatively impacting the existing foam processing properties (e.g. reactivity profile, line speed, mold temperature) of existing rigid polyurethane foam formulations.

Other tertiary amines suited for use with the bismuth carboxylates and sulfonates include mono-ureas and bis-ureas such as 2-dimethylaminoethyl urea; N,N′-bis(2-dimethylaminoethyl) urea; N,N-bis(2-dimethylaminoethyl) urea; 3-dimethyl-aminopropyl urea; N,N′-bis(3-dimethylaminopropyl) urea; N,N-bis(3-dimethylamino-propyl) urea; 1-(N-methyl-3-pyrrolidino)methyl urea; 1,3-bis(N-methyl-3-pyrrolidino)methyl urea; 3-piperidinopropyl urea; N,N′-bis(3-piperidinopropyl) urea; 3-morpholino-propyl urea; N,N′-bis(3-morpholinopropyl) urea; 2-piperidinoethyl urea; N,N′-bis(2-piperidinoethyl) urea; 2-morpholinoethyl urea; and N,N′-bis(2-morpholinoethyl) urea.

The level of bismuth catalyst employed for forming the polyurethane will range from 0.05 to 5 parts per hundred weight parts polyol (pphp), preferably 0.2 to 3 pphp (weight basis).

The level of amine will range from 0.055 pphp when the two are use in combination, the ratio of bismuth catalysts to the tertiary amine will range from approximately 1:10 to 10:1 (weight basis).

These flexible, semi-flexible and rigid polyurethane foam formulations are prepared using any suitable aromatic polyisocyanates well know in the art including, for example, phenyl diisocyanate, toluene diisocyanate (TDI) and 44′-diphenylmethane diisocyanates (MDI) with % NCO content typically ranging between 20 and 50. Suitable mixtures include 2,4- and 2,6-TDI's individually or together as their commercially available mixtures. Other suitable isocyanates are mixtures of diisocyanates known commonly as “crude MDI”, which contain 4,4′-diphenylmethane diisocyanates along with other isomeric and analogous higher polyisocyanates. Also suitable are “prepolymers” of these polyisocyanate comprising a partially pre-reacted mixture of a polyisocyanate and a polyether or polyester polyol.

Illustrative of suitable polyols as a component of the polyurethane formulation are the polyalkylene ether and polyester polyols. The polyalkylene ether polyols include the poly(alkylene oxide) polymers such as poly(ethylene oxide) and poly(propylene oxide) polymers and copolymers with terminal hydroxyl groups derived from polyhydric compounds, including diols and triols; for example, among others, ethylene glycol, propylene glycol, 1,3-butane diol, 1,4-butane diol, 1,6-hexane diol, neopentyl glycol, diethylene glycol, dipropylene glycol, pentaerythritol, glycerol, diglycerol, trimethylol propane, and like low molecular weight polyols. These polyether polyol derivations may be initiated with sucrose, glycerol, glycerine, aliphatic and aromatic amines, propylene glycol, Mannich bases, and/or sorbitol, individually or in combinations. Typical OH# values for these materials may range from 23-800.

In the practice of this invention, a single high molecular weight polyether polyol may be used. Also, mixtures of high molecular weight polyether polyols such as mixtures of di- and tri-functional materials and/or different molecular weight or different chemical composition materials may be used.

Useful polyester polyols include those produced by reacting a dicarboxylic acid with an excess of a diol, for example, adipic acid with ethylene glycol or butanediol, or reacting an anhydride with an excess of a diol, such as, phthalic anhydride with diethylene glycol or reacting a lactone with an excess of a diol such as caprolactone with propylene glycol. Typical hydroxyl number (OH#) values for these materials range from 160-490.

In addition to the polyether and polyester polyols and their combinations, the masterbatches, or premix compositions, frequently contain a polymer polyol. Polymer polyols are used in polyurethane foam to increase the foam's resistance to deformation, i.e., to increase the load-bearing properties of the foam. Currently, two different types of polymer polyols are used to achieve load-bearing improvement. The first type, described as a graft polyol, consists of a triol in which vinyl monomers are graft copolymerized. Styrene and acrylonitrile are the usual monomers of choice. The second type, a polyurea modified polyol, is a polyol containing a polyurea dispersion formed by the reaction of a diamine and TDI. Since TDI is used in excess, some of the TDI may react with both the polyol and polyurea. This second type of polymer polyol has a variant called PIPA polyol which is formed by the in-situ polymerization of TDI and alkanolamine in the polyol. Depending on the load-bearing requirements, polymer polyols may comprise 20-80% of the polyol portion of the masterbatch.

Blowing agents such as water, methylene chloride, hydrochlorofluorocarbons, such as, trichlorofluoromethane and pentafluoropropane; hydrocarbons, liquid carbon dioxide and the like can be used in preparing the foam formulations.

Optionally, cell stabilizers such as silicones; chain extenders such as ethylene glycol and butanediol; and crosslinkers such as diethanolamine, diisopropanolamine, triethanolamine and tripropanolamine are employed in foam formulations.;

A general polyurethane rigid foam formulation having a 0.5-5.0 lb/ft 3 (8.0-80.2 kg/m 3 ) density containing a organometallic catalyst, composition according to the invention, would comprise the following components in parts by weight (pbw):

A general polyurethane flexible foam formulation having a density of 1-3 lb/ft 3 (16-48 kg/m 3 ) (e.g., automotive seating) containing catalysts such as the bismuth carboxylate catalyst compositions according to the invention would comprise the following components in parts by weight (pbw):

The term conventional polyol and polymer polyol is intended to refer to a polyol that is used as the base polyol for formulation of flexible molded foam. It is void of grafts using Styrene Acrylonitrile (SAN). A co-polymer is one that has SAN grated onto the conventional or base polyol. This helps to build load in the system.

The following examples are given to illustrate various embodiments of the invention and should not be interpreted as limiting in any way.