GB1597060A - Rigid polyurethane foams - Google Patents

Description

(54) RIGID POLYURETHANE FOAMS (71) We, TEXACO DEVELOPMENT CORPORATION, a Corporation organized and existing under the laws of the State of Delaware, United States of America, of 135 East 42nd Street, New York, New York 10017, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention pertains to the field of polyurethane foams. More particularly, this invention relates to the use of a certain combination of polyols useful in preparing rigid polyurethane foams of excellent dimensional stability and heat distortion properties.

It is known to prepare foam from polyurethanes by the reaction of a polyisocyanate, a polyol and a blowing agent such as a halogenated hydrocarbon, water or both, in the presence of a catalyst. One particular area of polyurethane technology is based upon rigid polyurethane foams.

The art is replete with a wide variety of polyols useful as one of the main components in preparing polyurethanes such as polyurethane foams. As an example, U.S. Patent No. 2,965,615 suggests use of copolymers of alkenylsubstituted aromatic compounds such as styrene, and ethylenically unsaturated monohydric alcohols such as allyl alcohol as a useful resinous polyol in urethane production. Also disclosed as useful polyol sources are alkoxylated reaction products of the above copolymers.

It has now been found that in the rigid polyurethane foam field, a special combination of polyols involving the just-mentioned allyl alcohol-styrene copolymer constituent yields a final polyurethane rigid foam of excellent dimensional stability and heat distortion properties. It has been found that use of a styrene-allyl alcohol copolymer in preparing rigid polyurethane foams leads to serious handling problems of the copolymer in that it is itself a solid. Likewise, the alkoxylated copolymer, while it can be handled in an acceptable manner, has a hydroxyl number too low to prepare suitable rigid foams.

The present invention relates to the use of a polyol useful in the rigid polyurethane field based on an allyl alcohol-styrene copolymer which can be conveniently handled, and yet yields a final rigid polyurethane foam of suitable physical properties, and particularly acceptable dimensional stability and heat distortion temperature properties.

It has now been found that a polyol combiflation utilizing as one component an allyl alcohol-styrene copolymer may be prepared which is particularly useful in making rigid polyurethane foams of excellent properties. The rigid polyurethane foam is obtained by reacting in the presence of a blowing agent and a catalyst of polyurethane formation, an aromatic polyisocyanate and a polyol combination comprising 5-85 percent by weight of a copolymer of allyl alcohol and styrene and 15-95 percent by weight of a polyether polyol having a hydroxyl number ranging from about 200 to about 800, said weight percentages being based on the total weight of said polyol combination.

The polyol combination used in this invention comprises two components. The first component making up 5-85 percent by weight of the total polyol weight comprises a copolymer of allyl alcohol and styrene. Such copolymers are known materials and may be prepared conventionally as set out in the art exemplified by the aforementioned U.S. Patent No. 2,965,615. Preferred allyl alcohol-styrene copolymers are those copolymers comprising 1-90 weight percent each of allyl alcohol and styrene moieties based on the total weight of the copolymer. More often the - copolymer comprises 4080 percent of allyl alcohol groups and 2060 percent by weight of styrene groups. As set out in U.S. Patent No. 2,965,615 due to the difference in relative polymerization reactivities of the two constituents it is necessary in all cases to use large excesses of allyl alcohol to prepare a copolymer of desired allyl alcohol to styrene ratio in the final copolymer product.

The second constituent of the overall polyol combination used in preparing rigid polyurethane foams is a polyether polyol having a hydroxyl number of 200800. The polyether polyol comprises 15-95 percent by weight of the total polyol combination weight. Preferred polyether polyols of this type are the reaction products of a polyfunctional active hydrogen initiator and propylene oxide, ethylene oxide or mixed propylene oxide and ethylene oxide. The polyfunctional active hydrogen initiator most preferably has a functionality of 2-6.

A wide variety of initiators may be alkoxylated to form useful polyether polyols. Thus, for example, polyfunctional amines and alcohols of the following type may be alkoxylated: monoethanolamine, diethanolamine, triethanolamine, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerine, sorbitol, and trimethylolpropane.

Such above amines or alcohols may be reacted with an alkylene oxide such as ethylene oxide, propylene oxide, or mixed ethylene oxide and propylene oxide using techniques known to those skilled in the art. Thus, for example, the reaction of alkylene oxides with initiators of this type is set forth in U.S. Patent Nos.

2,948,757 and 3,000,963. Essentially such alkoxylations are carried out in the presence of a basic catalyst at a temperature sufficient to sustain the reaction. The hydroxyl number which is desired for the finished polyol would determine the amount of alkylene oxide used to react with the initiator. As noted above, the polyether polyols used here have a hydroxyl number ranging from about 200 to about 800. The reaction mixture is then neutralized and water and excess reactants are stripped from the polyol. The polyether polyol may be prepared by reacting the initiator with propylene oxide or ethylene oxide, or by reacting the initiator first with propylene oxide followed by ethylene oxide or vice versa in one or more sequences to give a so-called block polymer chain or by reacting the initiator at once with propylene oxide and ethylene oxide mixture to achieve a random distribution of such alkylene oxides.

The final polyol combination more preferably comprises 4080 percent by weight of said polyether polyol and 2060 percent by weight of said copolymer.

The polyol combination in many instances has a total hydroxyl number of 300-700 and most often has a hydroxyl number ranging from about 400 to about 600.

As noted above, in order to achieve a rigid polyurethane foam of excellent dimensional stability and high heat distortion temperature, it is important that the herein defined polyol combination be used as set out. As discussed above, use of the copolymer alone in preparing rigid polyurethane foams is unacceptable due to severe handling problems of the solid material. Likewise, the alkoxylated copolymer has a hydroxyl number below about 200 which is too low to prepare an acceptable rigid foam. Likewise, when one attempts to utilize a polyether polyol defined here alone without further resort to the here defined allyl alcohol-styrene copolymer, the final rigid polyurethane foam has been found to have a dimensional stability and heat distortion temperature both too low to be acceptable for commercial applications. Thus, the total polyol combination as herein discussed is necessary to give one a rigid polyurethane foam of acceptable properties.

Any aromatic polyisocyanate may be used in the practice of the present invention. Typical aromatic polyisocyanates include m-phenylene diisocyanate, pphenylene diisocyanate, polymethylene polyphenylisocyanate, 2,4-toluene diisocyanate, 2,6-tolylene diisocyanate, dianisidine diisocyanate, bitolylene diisocyanate, naphthalene- 1 ,4-diisocyanate, diphenylene-4,4'-diisocyanate, aliphatic-aromatic diisocyanates, such as xylylene- 1 ,4-diisocyanate, xylylene- 1,2- diisocyanate, xylylene- 1 ,3-diisocyanate, bis(4-isocyanatophenyl) methane, bis(3 methyl.4-isocyanatophenyl) methane, and 4,4'-diphenylpropane diisocyanate.

Greatly preferred aromatic polyisocyanates used in the practice of the invention are methylene-bridged polyphenyl polyisocyanate mixtures which have a functionality of from about 2 to about 4. These latter isocyanate compounds are generally produced by the phosgenation of corresponding methylene bridged polyphenyl polyamines, which are conventionally produced by the reaction of formaldehyde and primary aromatic amines, such as aniline, in the presence of hydrochloric acid and/or other acidic catalysts. Known processes for preparing the methylene-bridged polyphenyl polyamines and corresponding methylene-bridged polyphenyl polysiocyanates therefrom are described in the literature and in many patents, for example, U.S. Patent Nos. 2,683,730; 2,950,263; 3,012,008, 3,344,162; and 3,362,979.

Most preferred methylene-bridged polyphenyl polyisocyanate mixtures used here contain from about 20 to about 100 weight percent methylene diphenyl diisocyanate isomers with the remainder being polymethylene polyphenyl polyisocyanates having higher functionalities and higher molecular weights. Typical of these are polyphenyl polyisocyanate mixtures containing about 20 to 100 weight percent methylene diphenyl diisocyanate isomers, of which 20 to about 95 weight percent thereof is the 4,4'-isomer, with the remainder being polymethylene polyphenyl polyisocyanates of higher molecular weight and functionality that have an average functionality of from about 2.1 to about 3.5. The isocyanate mixtures are known commercially available materials and can be prepared by the process described in U.S. Patent No. 3,362,979, issued January 9, 1968 to Floyd E. Bentley.

It is the production of rigid polyurethane foams in the practice of the invention, other known additives are necessary. One such constituent is the blowing agent. Some examples of such material are trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, 1,1 -dichloro- I - fluoromethane, 1,1 -difluoro- 1 ,2,2-trichloroethane and chloropentafluoroethane.

Other useful blowing agents include low-boiling hydrocarbons such as butane, pentane, hexane and cyclohexane. See U.S. Patent No. 3,072,582, for example.

Surfactant agents, better known as silicone oils, may be added to serve as a cell stabilizer. Some representative materials are sold under the names of SF-1109, L520, L-521 and DC-193 which are, generally, polysiloxane polyoxyalkylene blocked copolymers, such as those disclosed in U.S. Patents 2,834,748; 2,917,480; and 2,846,458, for example.

Should fire retardancy be required for the polyurethane foam, two types of fire retardants are available; those that are incorporated by mere mechanical mixing and those that become chemically bound in the polymer chain. Representative of the first type are tris(chloroethyl) phosphate, tris(2,3-dibromopropyl) phosphate, diammonium phosphate, various halogenated compounds and antimony oxide.

Representative of the chemically bound type are chlorendic acid derivatives, and various phosphorus-containing polyols.

The catalysts which may be used to make the foams of our invention are well known. There are two general types of catalyst, tertiary amines and organometallic compounds. Examples of suitable tertiary amines, used either individually or in mixture, are the N-alkylmorpholines, N-alkylalkanolamines, N,Ndialkylcyclohexylamines and alkylamines where the alkyl groups are methyl, ethyl propyl and butyl. In some circumstances the polyether polyol which is part of the polyol combination may act as the catalyst. Examples of specific tertiary amine catalysts useful in our invention are triethylenediamine, tetramethylethylenediamine, triethylamine, tripropylamine, tributylamine, triamylamine, pyridine, quinoline, dimethylpiperazine, dimethylhexahydroaniline, N-ethylmorpholine, dimethylaniline, nicotine, dimethyl-aminoethanol, tetramethylpropanediamine, and methyltriethylenediamine. Piperazine and 2methylpiperazine may also be used. Useful organo-metallic compounds as catalysts include those of bismuth, lead, tin, titanium, iron, antimony, uranium, cadmum, cobalt, thorium, aluminum, mercury, zinc, nickel, cerium, molybdenum, vanadium, copper, manganese and zirconium. Some examples of these metal catalysts include lead 2-ethylhexoate, lead benzoate, lead oleate, dibutyltin dilaurate, tributyltin, butyltin trichloride, stannous octoate, stannous oleate, dibutyltin di(2-ethylhexoate), antimony glycolate and tin glycolates. Metallic compounds such as bismuth nitrate, stannic chloride, ferric chloride and antimony trichloride may also be used. Selection of the individual catalysts and proportions to use in the polyurethane reaction are well within the knowledge of those skilled in the art, and an amine and organo-metallic compound are often used together in the polyurethane reaction.

The rigid polyurethane foams prepared here can be maded in one step by reacting all the ingredients together at once (one-shot process) or the rigid foams can be made by the so-called "quasi-prepolymer method". In accordance with this method, a portion of the polyol component is reacted in the absence of a catalyst with the polyisocyanate component in proportion so as to provide from about 20 percent to about 40 percent of free isocyanato groups in the reaction product, based on the polyol. To prepare foam, the remaining portion of the polyol is added and the two components are allowed to react in the presence of a catalyst and other appropriate additives such as blowing agents, foam stabilizing agents and fire retardants. The blowing agent, the foam stabilizing agent and the fire retardant, may be added to either the prepolymer or remaining polyol, or both, prior to the mixing of the component, whereby at the end of the reaction a rigid polyurethane foam is provided.

In a preferred embodiment the amount of polyol combination is used such that the isocyanato groups are present in the foam in at least an equivalent amount, and preferably in slight excess, compared with the free hydroxyl groups. Preferably, the ingredients will be proportional so as to provide for about 1.05 to about 1.5 mol equivalents of isocyanato groups per mole equivalent of hydroxyl groups.

The invention will be illustrated further with respect to the following specific examples, which are given by way of illustration and not given as limitations on the scope of this invention. In these Examples, the propoxylated triethanolamine component of the polyol combination acts as the catalyst. The tertiary amine function is sufficient to promote the reaction.

EXAMPLE I Here a typical polyol combination for use in the invention was prepared.

The first component was the styrene-allyl alcohol copolymer. This particular copolymer was prepared according to the directions of U.S. Patent 2,965,615 and had a Mn (number average molecular weight) of 1,000, 5.3 moles hydroxyl per mole and 6.6 moles styrene per mole. The weight average molecular weight of the polyol was 1,450 and its hydroxyl number was 280. The second polyol constituent was prepared in the usual manner by propoxylating triethanolamine for sufficient time to produce the polyol here having an hydroxyl number of 642.

The polyol combination was prepared by adding 260 grams (60.5 weight percent) of the above polyether polyol to a 500 ml flask. The polyether polyol was then heated up to about 100"C. under nitrogen, at which time 170 grams (39.5 weight percent) of the above described styrene-allyl alcohol resin was added. The mixture was stirred well until a homogenous, clear solution developed. Upon cooling the blended product was a viscous liquid having a viscosity at 250 C. of 30,000 cps (Brookfield) and a hydroxyl number of 506.

EXAMPLE II A rigid polyurethane foam was prepared using the polyol blend of Example I.

The formulation and foam physical properties are shown below. It should be noted that the dimensional stability and heat distortion properties of the rigid foam were excellent in both instances.

Formulation, pbw Polyol blend (Example I) 38.5 Silicone oil 0.5 Trichloromonofluoromethane blowing agent 13.0 Methylene-bridged polyphenyl polyisocyanate mixture (functionality of 2.7%) 48.0 Reaction Times (sec.) Cream 12.0 Tack Free 55.0 Rise 75.0 Physical Properties Density (Ib/ft) 1.63 K-Factor 0.120 Compressive Strength, psi with (x)-rise 40.96 Compressive Strength, psi cross-rise 10.92 Heat Distortion ("C.) 154.0 Percent Closed Cells 94.54 Dimensional Stability V W L 158"F., 100% Rel. Humidity for one week +2.7 -0.9 +2.0 EXAMPLE III An additional polyol combination for use in the invention was prepared as follows.

Here the styrene-allyl alcohol copolymer had a Mn of 1150, 5.3 moles hydroxyl per mole and 8.3 moles styrene per mole. The weight average molecular weight of the polyol was 1,700 and its hydroxyl number was 249. The second polyol constituent was a 2 mol propylene oxide adduct of triethanolamine.

To a 500 ml., round bottom flask, fitted with a stirrer and thermometer was added 500 grams of a propoxylated triethanolamine which was heated up to 90- 100"C. under nitrogen. Then 270 grams (35 weight percent) of the styrene allyl alcohol copolymer was added slowly so as to prepare a homogeneous solution. The solution was vacuum stripped at 100"C. to yield a polyol combination product having a hydroxyl number of 496. The blended product had a viscosity (250 C.) of 18,000 cps (Brookfield).

EXAMPLE IV A polyol combination was prepared as in Example III with the exception that 270 grams of the styrene-allyl alcohol copolymer of Example I was utilized. The final polyol combination had a hydroxyl number of 500, and a viscosity (250C.) of 16,000 cps (Brookfield).

EXAMPLES V-VIII Here further rigid polyurethane foams were prepared using the polyol blends of Examples III and IV. Results with respect to formulation details and foam physical properties are shown below.

5 6 7 8 Formulation, pbw Polyol blend (Example III) 38.6 28.72 - Polyol blend (Example IV) - - 38.5 28.64 Fyrol 6(1) (OH=460) - 7.18 - 7.16 Firemaster (R.T.M.) T-23-P(2) - 6.0 - 6.0 Silicone Oil 0.5 0.5 0.5 0.5 Trichloromono fluoromethane (blowing agent) 13.0 12.0 13.0 12.0 Methylene-bridged polyphenyl polyisocyanate mixture (functionality of 2.7) 47.9 45.6 48.0 45.7 Isocyanate Index 1.05 1.10 1.05 1.10 Mixing Time (sec.) 12 12 12 12 Cream Time (sec.) 20 16 17 16 Tack Free Time (sec.) 60 60 58 58 Rise Time (sec.) 130 130 110 105 Initial Surface Friability None None None None Foam Appearance Good Good Good Good Density (lb.ft. ) 1.91 1.66 1.90 1.89 K-Factor 0.121 0.126 1.117 0.124 Compressive Strength psi, with rise 47.59 40.69 44.89 41.91 psi, cross rise 15.19 13.12 14.44 13.22 Heat Distortion ( C.) 141 162 144 162 Percent Closed Cells 94.26 94.05 94.67 94.19 Friability (% wt. loss) 1.09 0.8 1.4 3.4 Butler Chimney Test Flame height (in.) - 8.8 - 10 Seconds to Extinguish - 13.7 - 14.7 % Closed Cells - 80.4 - 84.8 Dimentional Stability #V #W #L #V #W #L #V #W #L #V #W #L 158 F., 100% RH, 1 week +4.7 0 +2.5 +10.2 -1.4 +8.5 +5.3 0 +3.0 +25.5 -1.6 +19.0 200 F., Dry, 1 week +3.7 0 +2.0 +2.5 0 +1.7 +3.5 +0.1 +2.0 +2.7 -0.2 + 1.7 -20 F., Dry, 1 week -2.2 +0.4 -1.4 -7.7 +0.5 -7.0 -2.7 +0.7 -1.5 -3.7 +0.2 - 3.0 (1) Fire retardant difunctional phosphorous ester from Stauffer Chemical Co.

(2) Brominated phosphorus ester from Michigan Chemical Co.

EXAMPLE IX Here, a neutral polyol blend was prepared as follows. To a 1 liter, round bottom. 3-necked flask, fitted with a mechanical stirrer, thermometer and nitrogen flow system was added 500 grams of a polypropylene glycol having a molecular weight of about 400 (hydroxyl numer=272). The water white polyol was heated under nitrogen to 1000C. Thereafter, 270 grams of the styrene-allyl alcohol copolymer described in Example III was slowly added to the glycol. The resultant homogeneous solution was stripped under high vacuum to about 1--2 mm.

Hg/l 100C. The product was a slightly viscous liquid of low color having a viscosity (25"C) of 4,000 cps (Brookfield), and a hydroxyl number of 272.

Claims (12)

WHAT WE CLAIM IS:

1. A rigid polyurethane foam obtained by reacting in the presence of a blowing agent and a catalyst of polyurethane formation, an aromatic polyisocyanate and a polyol combination comprising 5-85 percent by weight of a copolymer of allyl alcohol and styrene and 15-95 percent by weight of a polyether polyol having a hydroxyl number ranging from 200 to 800, said weight percentages being based on the total weight of said polyol combination.

2. A rigid polyurethane foam as claimed in Claim 1, wherein said polyol combination has a hydroxyl number ranging from 300 to 700.

3. A rigid polyurethane foam as claimed in Claim 1 or 2, wherein said polyol combination comprises 4080 weight percent of said polyether polyol and 2060 weight percent of said copolymer.

4. A rigid polyurethane foam as claimed in Claim 1, wherein said copolymer comprises IO--90 weight percent each of allyl alcohol and styrene based on the weight of said copolymer.

5. A rigid polyurethane foam as claimed in any preceding claim, wherein said polyether polyol is the reaction product of a polyfunctional active hydrogen initiator and propylene oxide, ethylene oxide or mixed propylene oxide and ethylene oxide.

6. A rigid polyurethane foam as claimed in Claim 5, wherein said polyfunctional active hydrogen initiator is selected from monoethanolamine, diethanolamine, triethanolamine, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerine, sorbitol, and trimethylolpropane.

7. A rigid polyurethane foam as claimed in Claim 5, wherein said polyether polyol is the reaction product of propylene oxide and triethanolamine.

8. A rigid polyurethane foam as claimed in any preceding claim, wherein the catalyst of polyurethane formation is a polyether polyol having a tertiary amine function.

9. A rigid polyurethane foam as claimed in claim 5, wherein said initiator has a functionality of 2-6.

10. A rigid polyurethane foam as claimed in any preceding claim, wherein said organic polyisocyanate is employed in an amount sufficient to provide 1.05 to 1.5 mol equivalents of isocyanato groups per mol equivalent of hydroxyl groups present in said polyol combination.

11. A method for producing a rigid polyurethane foam which comprises reacting in the presence of a blowing agent and a catalyst of polyurethane formation, an aromatic polyisocyanate and a polyol combination comprising 5-85 percent by weight of a copolymer of allyl alcohol and styrene and 15-95 percent by weight of a polyether polyol having a hydroxyl number ranging from about 200 to about 800, said weight percentages being based on the total weight of said polyol combination.

12. A rigid polyurethane foam as claimed in claim 1 and substantially as hereinbefore described with reference to any of the Examples.