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A FOAMING SYSTEM FOR CLOSED-CELL RIGID POLYURETHANE FOAM

This invention relates to a closed-cell rigid polyurethane foam prepared in the presence of a foaming agent comprising a C _5 polyfluorocarbon compound containing no chlorine or bromine atoms.

Rigid closed-cell polyurethane and polyisocyanurate foams are widely used as insulating material. The good insulative properties of such foams are provided for by firstly the fact that they are fine closed-celled foams and secondly that the closed-cell contains within a gas mixture which has a high thermal resistance or alternatively expressed, a low thermal conductivity.

Generally, polyurethane and polyisocyanurate foams are prepared by reacting an organic polyisocyanate with an isocyanate-reactive compound in the presence of an inert liquid that functions as a blowing agent and which as the reaction proceeds provides for concomitant foaming.

Frequently used blowing agents are the fully halogenated chlorofluorocarbons, especially trichlorofluoromethane (Refrigerant, R—11). However, the continued use of such chlorofluorocarbon blowing agents is undesirable in view of the current opinion that their presence in earth's upper atmosphere may be a contributory factor in the observed reduction of the ozone concentrations.

A newly developing trend for the production of such polyurethane foam is to replace the fully halogenated chlorofluorocarbons with hydrogen-containing chlorofluorocarbon compounds. These alternative blowing agents are selected as they have been identified as hav¬ ing significantly lower ozone depletion potentials relative to R-11. Such alternative hydrogen-containing blowing agents include dichlorotrifluoroethane (R-123), dichlorofluoroethane (R-I 1b), chlorodifluoromethane (R-22) and difluorochloroethane (R-I42b), the use of which in the preparation of polyurethane foam has been described; see, for example, U.S. Patents 4,076,644; 4,264,970; and 4,636,529.

A disadvantage of replacing the R-11 gas contained within the cells of the foam by such alternative compounds is a relative loss in the initial and/or aged thermal insulation performance of the foam. Such loss occurs due to the generally higher gas thermal conductivities of the replacement blowing agents.

If insulative foam, especially polyurethane foam is to remain commercially attractive and be able to comply with various national standards relating to energy consumption, it is important that the foam is

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able to retain a good thermal insulation performance with time. This is especially critical where, because of other factors dictating the selection of blowing agent, the initial thermal conductivity of the foam may already be relatively high.

Additionally, the thermal insulation properties of polyurethane and polyisocyanurate foam are known to become inferior with time. The loss of thermal insulation properties of a foam generally results from diffusion into the closed cells of high thermal conductivity gases, particularly nitrogen and oxygen and/or loss of cell gas having a lower thermal conductivity.

One possible means to prevent loss of thermal insulation properties would be to use, for example, a gas impermeable barrier surrounding the foam.

Alternatively, the foam could be modified to minimize or prevent loss of thermal insulating efficiency with time. With respect to this latter approach, the open literature contains relatively few teachings as to how rigid, closed-cell polymer foams might be modified giving products that exhibit an enhanced retention, or minimized loss with time of thermal insulation performance.

U.S. Patent 4,795,763 discloses carbon black- -filled polyurethane foam exhibiting improved aged- -thermal insulation properties. Japanese Patent Appli¬ cation No. 57-147510 discloses the use of carbon black to provide for lower initial thermal conductivities of the foam. The selection of graphite over carbon black for the preparation of foam from a thermoplastic resin

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having increased initial thermal insulation properties is disclosed by Japanese Patent Application No. 63-183941.

However, the use of fillers such as, for example, carbon black and graphite for enhancement of foam thermal insulation properties is not always practical as other physical properties of the resulting foam and processability leading to the foam may suffer. Particularly, a high filler content can lead to highly friable and open-celled foam. Open-celled foams do not provide the desirable thermal insulation performance normally offered by closed-cell foams.

It is therefore desirable to consider the use of alternative blowing agents and processes which provide for closed-cell foam having improved thermal insulation properties whilst additionally maintaining the overall desirable foam physical properties and processability.

In the art, the term "thermal insulation" may be interchanged with the term "K-factor" or "thermal resistance" when discussing thermal physical properties of foams and gases.

It has now been discovered that rigid closed- -cell polyurethane foam having improved aged thermal insulation properties may be prepared in the presence of a foaming system comprising a C2_5 polyfluorocarbon com¬ pound containing no chlorine or bromine atoms.

In one aspect, this invention is a closed-cell rigid polyurethane foam prepared from a foam-forming

composition containing from 0.5 to 20 weight percent based on the total weight of the composition of a physical blowing agent characterized in that the physical blowing agent comprises a C _5 polyfluorocarbon compound containing no chlorine or bromine atoms, and in that the thermal insulation loss of the foam is reduced relative to the thermal insulation loss, with time, of the same foam having the same density and prepared from the same foam-forming composition in the presence of an equivalent molar quantity of a blowing agent in which a C _5 polyfluorocarbon compound containing no chlorine or bromine atoms is absent.

In a second aspect, this invention is a process for producing a closed-cell rigid polyurethane foam 5 containing within its cells a gas mixture comprising a ^2-6 polyfluorocarbon compound containing no chlorine or bromine atoms and characterized in that

_Q (a) an isocyanate-containing compound is mixed and allowed to react with an isocyanate-reactive compound in the presence of from 0.5 to 20 weight percent, based on combined weight of isocyanate-containing 5 compound and isocyanate-reactive compound, of a physical blowing agent comprising the polyfluorocarbon compound, and

(b) wherein the thermal insulation loss of the foam is reduced relative to the 0 thermal insulation loss, with time, of the same foam having the same density and pre¬ pared from the same foam-forming composition in the presence of an equivalent molar quan¬ tity of blowing agent in which a C2_5

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polyfluorocarbon compound, containing no chlorine or bromine atoms, is absent.

In a third aspect, this invention is an isocyanate-reactive composition suitable for reacting with an isocyanate-containing compound in the prepara¬ tion of a closed-cell rigid polyurethane foam characterized in that the composition comprises

(a) an hydrogen-containing compound that has from 2 active hydrogen atoms per molecule and an equivalent weight of from 50 to 700, and

(b) from 1 to 20 weight percent, based on a combined weight of (a) and (b) present, of a physical blowing agent comprising a ^2-6 polyfluorocarbon compound containing no chlorine or bromine atoms,

which provides for a foam wherein the thermal insulation loss of the foam is reduced relative to the thermal insulation loss, with time, of the same foam having the same density and prepared from the same active hydrogen- -containing composition in the presence of an equivalent molar quantity of blowing agent in which a C2_6 polyfluorocarbon compound, containing no chlorine or bromine atoms, is absent.

In a fourth aspect, this invention is a lami¬ nate comprising at least one facing sheet adhered to the polymer foam as described in the first aspect.

In a fifth aspect, this invention is a process for preparing a laminate as described in the fourth aspect.

These findings are surprising in view of the fact that substituting fully halogenated or hydrogen- -containing chlorofluorocarbons with polyfluorocarbons having significantly higher gas thermal conductivities would not be expected to reduce relative thermal insu¬ lation losses and in some instances actually provide foam exhibiting superior insulation properties on aging. The findings are especially significant when considered in combination with the desire to use foaming systems having minimized ozone depletion potentials.

As described hereinabove, in one aspect this invention is a closed-cell rigid polyurethane or polyisocyanurate foam prepared from a foam-forming composition containing a physical blowing agent.

The composition contains the physical blowing agent in a quantity sufficient to provide a foam having an overall density of from 10 to 200, preferably from 10 to 100, more preferably from 15 to 80 and most preferably from 18 to 60 kg/rn*^.

To provide for such foam densities, the physical blowing agent advantageously is present in quantities from 0.5 to 20 weight percent based on the total weight of the foam-forming composition, including physical blowing agent present. Preferably the physical blowing agent is present in from 0.5 to 17, more preferably from 1.0 to 10 and most preferably from 1.5 to 8.0 weight percent based on total weight of the foam-

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-for ing composition and physical blowing agent present. Foams having the higher densities are prepared in the presence of lower quantities of the physical blowing agent. For the purpose of this invention by "foam- forming composition" it is understood a mixture comprising an isocyanate and an isocyanate-reactive substance.

The physical blowing agent used to prepare the foam of this invention is characterized in that it com- prises at least one component which is a C _5 polyfluorocarbon compound containing no chlorine or bromine atoms. The absence of chlorine or bromine atoms is desirable as such compounds generally have effectively a zero or low, typically 0.15 or less, ozone depletion potentials relative to the unity value of trichloro luoromethane (R-11).

The poly luorocarbon compound is further char¬ acterized by advantageously having a boiling point at standard atmospheric pressure of less than 65°C, preferably less than 45°C, more preferably less than 25°C and most preferably less than 0°C. Use of polyfluorocarbon compounds having a boiling point above 65°C may not be desirable if resulting foams are to exhibit good low temperature dimensional stability. To allow for convenient handling and foaming of the composition advantageously, the polyfluorocarbon com¬ pound has a boiling point of at least -60°C, preferably at least -40°C and more preferably at least -30°C.

Exemplary of C ₂ polyfluorocarbon compounds suitable for use as physical blowing agents when preparing the foams of this invention are the

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polyfluoroethanes including 1 , 1-difluoroethane (R-152a),

1 ,2-difluoroethane (R-152), 1 , 1 , 1-trifluoroethane

(R-I43a), 1 , 1 ,2-trifluoroethane (R-143),

1,1,1 ,2-tetrafluoroethane (R-134a) ,

1 , 1 ,2,2-tetrafluoroethane (R-134), pentafluoroethane

(R-125)and hexafluoroethane (R-116); and the polyfluoroethylenes including 1,2-difluoroethylene

(R-1132).

Other polyfluorocarbon compounds suitable for use in this present invention also include the C _^ g and preferably the C^.g compounds such as, for example, perfluoropropane, perfluorobutane, perfluoro-n-pentane and isomers thereof, perfluoro-n-hexane, perfluoroacetone, mono- and di- hydrogen containing equivalents of above mentioned perfluorinated compounds and C ₂ _6 polyfluoroether compounds; and mixtures thereof; and cyclic polyfluorocarbon compounds including perfluorocyclopropane (C-216), perfluorocyclobutane (C-318), 1 , 1 ,2,2-tetrafluorocyclobutane (C-354) and 1,2,3,3,4, -hexafluorocyclobut-1 ,2-ene (C-1316) .

The preferred polyfluorocarbon compounds for this present invention are the polyfluoroethanes, especially 1 , 1, 1 ,2-tetrafluoroethane (R-134a); and the perfluorocarbon compounds, especially perfluoro-n-hexane and perfluoro-n-pentane. These compounds are preferred due to their ready availability and currently recognized low ozone depletion potentials.

The above listed polyfluorocarbon compounds may also be used in admixture or in admixture with additional secondary blowing agents providing for the complete blowing requirement to give foams of a desired

density. Suitable secondary blowing agents are listed later.

As already mentioned, the foam of this present invention is characterized in that it exhibits a reduced thermal insulation loss with time in comparison to the same foams having effectively the same overall density and being prepared from the same foam-forming composition but in the absence of a C2_ polyfluorocarbon compound as described above.

To obtain such reduction in thermal insulation loss the initial gas composition within the closed cells of the foam advantageously comprises from 1 and up to 60 mole percent, based on molar quantities of all gases present within the cell, of the C2_5 polyfluorocarbon compound. Preferably, the initial gas composition of the closed cells comprises from 5 to 55, more preferably from 10 to 55 and most preferably from 15 to 50 mole percent of the polyfluorocarbon compound, the remaining part of the cell gas composition being obtained from secondary physical blowing agents and/or blowing agent precursor compounds.

In a preferred embodiment of this invention the polyurethane or polyisocyanurate polymer is prepared additionally in the presence of a blowing agent precursor such as, for example, water providing carbon dioxide gas. In such a preferred embodiment the initial gas composition within the closed cells of the resulting foam comprises

(a) from 1 to 60 mole percent, based on the combined mole quantities of (a) and (b)

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present, of a C _5 polyfluorocarbon compound containing no chlorine or bromine atoms, and (b) from 40 to 99 mole percent, based on the combined quantities of (a) and (b) present, carbon dioxide.

Although foams having initial cell gas compo¬ sitions comprising mole quantities of polyfluorocarbon compound(s) and carbon dioxide outside these given ranges may be prepared, such foams may not exhibit the advantageous thermal insulation aging characteristics as the foams of this present invention. Advantageously, to provide for the optimum physical foam properties including thermal insulation advantageously, the average cell size of the foam is less than 0.5, preferably less than 0.45, and more preferably less than 0.4 mm.

Reference is made to "initial" gas composi¬ tions, as with time the composition of such cell gas mixtures may change due to diffusion in and out of environmental and cell gases respectively.

In the second aspect of this invention, a pro¬ cess for the preparation of a rigid, closed-cell polyurethane or polyisocyanurate foam containing within its cells a gas mixture comprising a C2_6 poly¬ fluorocarbon compound containing no chlorine or bromine atoms is disclosed.

The process is characterized in that an isocya- nate is mixed and allowed to react with an isocyanate- reactive compound in the presence of from 0.5 to 20 weight percent, based on total combined weights of isocyanate and isocyanate-reactive compound present, of

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a physical blowing agent comprising a C2_5 polyfluorocarbon compound containing no chlorine or bromine atoms, as described hereinabove.

Isocyanates suitable for use in the process of this invention are organic polyisocyanate compounds having an average isocyanate content of from 20 to 50, and preferably from 20 to 33 weight percent.

Polyisocyanates suitable for use in the process of this invention include aromatic, aliphatic and cyclo- aliphatic polyisocyanates and combinations thereof. Representative of these types are diisocyanates such as m- or p-phenylene diisocyanate, toluene-2,4-diisocya- nate, toluene-2,6-diisocyanate, hexamethylene-1 ,6-diiso- cyanate, tetramethylene-1 ,4-diisocyanate, cyclohexane- -1 ,4-diisocyanate, hexahydrotoluene diisocyanate (and isomers), naphthylene-1 ,5-diisocyanate, 1-methylphenyl- -2, -phenyIdiisocyanate, diphenylmethane-4,4'-diisocya¬ nate, diphenylmethane-2,4'-diisocyanate, 4,4'-biphenyl- ene diisocyanate, 3,3 ^r -dimethoxy-4,4'-diphenylenediiso- cyanate and 3,3'-dimethyldiphenylpropane-4,4'-diisocya¬ nate; triisocyanates such as toluene-2,4,6-triisocyanate and polyisocyanates such as 4,4'-dimethyldiphenylmeth- ane-2,2' ,5' ,5'-tetraisocyanate and the diverse poly- methylene polyphenyl polyisocyanates.

A crude polyisocyanate may also be used in the practice of this invention, such as the crude toluene diisocyanate obtained by the phosgenation of a mixture of toluene diamines or the crude diphenylmethane diiso¬ cyanate obtained by the phosgenation of crude methylene diphenylamine. The preferred undistilled or crude poly¬ isocyanates are disclosed in U.S. Patent 3,215,652.

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Especially preferred are methylene-bridged polyphenyl polyisocyanates, due to their ability to cross-link the polyurethane.

_- The isocyanate is used in a quantity sufficient to provide for a well cross-linked rigid, closed-cell foam. Advantageously the isocyanate index, ratio of isocyanate moieties to active hydrogen atoms associated with the isocyanate-reactive compound(s) present in the

10 foam-forming composition, is from 0.9 to 5.0, preferably 0.9 to 3-0, more preferably 1.0 to 2.0 and most preferably from 1.0 to 1.6.

Isocyanate-reactive compounds which are useful

15 in this present invention include those materials having two or more groups which contain an active hydrogen atom that will react with an isocyanate, such as is described in U.S. Patent 4,394,491. Preferred among such

20 compounds are materials having hydro yl, primary or secondary amine, carboxylic acid, or thiol groups. Polyether polyols, i.e., compounds containing a plurality of ether linkages and having at least two hydroxyl groups per molecule, are especially preferred 25 due to their desirable reactivity with polyisocyanates.

Suitable isocyanate-reactive compounds for preparing rigid polyisocyanate-based foams include those having an equivalent weight of 50 to 700, preferably

30 from 70 to 300, more preferably from 90 to 200. Such active hydrogen-containing compounds advantageously have from 2, preferably from 3, and advantageously up to 16 and preferably up to 8 active hydrogen atoms per molecule. The number of active hydrogen atoms may also

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be referred to as "functionality". Active hydrogen- -containing compounds which have functionalities and equivalent weights outside these limits may also be used, but the resulting foam properties may not be desirable for a rigid application.

In addition to polyether polyols other suitable additional isocyanate-reactive materials include polyester polyols, polyhydroxyl-terminated acetal resins, hydroxyl-terminated amines and polyamines. Examples of these and other suitable isocyanate-reactive materials are described more fully in U.S. Patent 4,394,491, particularly in columns 3-5 thereof. Most preferred for preparing rigid foams, on the basis of performance, availability and cost, is a polyether polyol prepared by adding an alkylene oxide to an initiator having from 2 to 8, preferably from 3 to 8 active hydrogen atoms. Exemplary of such polyether polyols include those commercially available under the trademark, V0RANOL and include VORANOL 202, VORANOL 360, V0RAN0L 370, VORANOL 446, VORANOL 490, VORANOL 575, VORANOL 800, all sold by The Dow Chemical Company.

Other most preferred polyols include alkylene oxide derivatives of Mannich condensate as taught in, for example, U.S. Patents 3,297,597; 4,137,265 and -4,383,102; and amino-alkylpiperazine-initiated polyether polyols as described in U.S. Patents 4,704,410 and 4,704,411.

In addition to the foregoing critical components, it is optional but often desirable to employ certain other ingredients in preparing polyisocyanate- -based foams. Among these additional ingredients are

secondary physical blowing agents and blowing agent precursor compounds, catalysts, surfactants, flame retardants, preservatives, colorants, antioxidants, reinforcing agents, fillers and antistatic agents.

Secondary blowing agents suitable for use in admixture with the polyfluorocarbon compound(s) providing for the complete blowing requirement when preparing the foam include physical blowing agents containing chlorine and/or bromine atoms. Preferably, such secondary blowing agents are the hydrogen-

-containing chlorofluorocarbon compounds exemplary of which are Refrigerant 21, Refrigerant 22, Refrigerant 123, Refrigerant 123a, Refrigerant 124, Refrigerant 124a, Refrigerant 133 (all isomers), Refrigerant 141b, Refrigerant 142, Refrigerant 151. Among these, Refrigerant 123 (all isomers), Refrigerant 141b and Refrigerant 142 (all isomers) are most preferred, as these are more readily commercially available in addition to being recognized as having low ozone depletion potentials.

In addition to the above mentioned secondary physical blowing agents, other low boiling substances are also useful herein, including, for example, carbon dioxide, nitrogen and argon.

Blowing agent precursor compounds are compounds which during the preparation of the foam react with one or more components contained within the foam-forming composition, and/or decompose, generating a gas which then functions as a blowing agent. Exemplary of, and a preferred, blowing agent precursor compound is water which reacts with isocyanate leading to the generation

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of carbon dioxide gas. Other carbon dioxide generating blowing agent precursor compounds include amine/carbon dioxide complexes such as disclosed in U.S. Patents 4,735,970 and 4,500,656.

_- When water is contained in the foam-forming o composition advantageously it is present in from 0.5 to 10.0, preferably from 1.0 to 7.0 and more preferably from 2.0 to 6.0, and most preferably from 2.5 to 5.0 weight percent based on total weight of isocyanate- 10 reactive compounds within the composition. When the polyfluorocarbon compound employed is a C-^g polyfluorocarbon compound it is especially advantageous for the benefice of processing and resulting foam properties that water be present in from 2.5 to 5.0, and

15 preferably from 2.8 to 4.5 weight percent.

One or more catalysts for promoting the reaction of the isocyanate-reactive compound with the

20 polyisocyanate is advantageously present. Any suitable urethane catalyst may be used, including tertiary amine compounds and organometallic compounds. Exemplary tertiary amine compounds include triethylenediamine, N-methylmorpholine, pentamethyldiethylenetriamine, 25 tetramethylethylenediamine, 1-methyl-

-4-dimethylaminoethylpiperazine, 3-methoxy-N- -dimethylpropylamine, N-ethylmorpholine, diethylethanolamine, N-cocomorpholine, N,N-dimethyl- -N' ,N'-dimethyl isopropylpropylenediamine, N,N-diethyl-

30 -3-diethylaminopropylamine and dimethylbenzylamine. Exemplary organometallic catalysts include organomercury, organolead, organoferric and organotin catalysts, with organotin catalysts being preferred among these. Suitable tin catalysts include stannous

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chloride, tin salts of carboxylic acids such as dibutyl- tin di-2-ethyl hexanoate, as well as other organometallic compounds such as are disclosed in U.S. Patent 2,846,408. A catalyst for promoting the trimerization of polyisocyanates and formation of polyisocyanurate polymers, such as an alkali metal alkoxide, alkali metal carboxylate, or quaternary amine compound, may also optionally be employed herein.

When employed, the quantity of catalyst used is sufficient to increase the rate of polymerization reaction. Required quantities must be determined experimentally, but generally will range from 0.001 to 3.0 parts by weight per 100 parts isocyanate-reactive compound depending on the type and activity of the catalyst.

It is generally highly preferred to employ a minor amount of a surfactant to stabilize the foaming reaction mixture until it cures. Such surfactants advantageously comprise a liquid or solid organosilicone surfactant. Other, less preferred surfactants, include polyethylene glycol ethers of long chain alcohols, tertiary amine or alkanolamine salts of long chain alkyl acid sulfate esters, alkyl sulfonate esters and alkyl arylsulfonic acids. Such surfactants are employed in amounts sufficient to stabilize the foaming reaction mixture against collapse and the formation of large, uneven cells. Typically, 0.2 to 5 parts of the surfactant per 100 parts by weight polyol are sufficient for this purpose.

In the process of making a polyisocyanate-based foam, the polyol(s), polyisocyanate and other components

are contacted, thoroughly mixed and permitted to expand and cure into a cellular polymer. The particulate mixing apparatus is not critical, and various types of mixing head and spray apparatus are conveniently used. It is often convenient, but not necessary, to preblend certain of the raw materials prior to reacting the polyisocyanate and isocyanate-reactive components. For example, it is often useful to blend the polyol(s), blowing agent, surfactants, catalysts and other components except for polyisocyanates, and then contact this mixture with the polyisocyanate. Alternatively, all components can be introduced individually to the mixing zone where the polyisocyanate and polyol(s) are contacted. It is also possible to pre-react all or a portion of the polyol(s) with the polyisocyanate to form a prepolymer.

In the third aspect of this invention, an isocyanate-reactive composition suitable for reaction with an isocyanate in the preparation of a rigid, closed-cell polyurethane or polyisocyanurate foam is disclosed.

The isocyanate-reactive composition is characterized in that it contains at least one isocyanate-reactive compound as already described and from 0.5 to 20 weight percent, based on total weight of isocyanate-reactive compound and physical blowing agent, of a physical blowing agent comprising a C _ polyfluorocarbon compound containing no chlorine or bromine atoms. Advantageously, the physical blowing agent is present in the composition in from 0.5 to 17, preferably from 1.0 to 10 and more preferably from 1.5 to 8 weight percent.

In the fourth aspect of this invention, a laminate comprising at least one facing sheet contiguous to the above described polyurethane of polyisocyanurate foam is disclosed. Preferably, the facing sheet which may be paper, metal, wood or a thermoplastic or thermoset polymer is contiguous to a polyurethane or polyisocyanurate foam which has been prepared in the presence of a physical blowing agent comprising a C2_5 polyfluorocarbon compound containing no chlorine or bromine atoms.

Suitable processes for preparing such a laminate are disclosed in, for example, U.S. Patents 4,707,401 and 4,795,763.

The rigid closed-cell polymer foams of this invention are of value in a number of applications such as, for example, spray insulation, fσam-in-place appliance foam rigid insulating board stock and laminates.

The following examples are given to illustrate the invention and should not be interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are given by weight.

Foams are prepared using a low pressure foaming machine. Properties of the resulting foams are determined on samples taken from 20 x 20 x 20 box foams having the stated molded density.

Post-demold expansion is measured in milli¬ meters in the parallel-to-rise direction on a molded 20

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x 20 x 20 cm foam. The expansion is observed after a curing time of 10 minutes with an appropriate face of the mold having been opened after 3 or 4 minutes into the curing period. The observed expansion is that of the foam out of the plane of the opened face. Lower value of expansion indicates improved demold performance.

The thermal insulation, K-factor, is measured with an Anacon Model 88 Thermal Conductivity Analyzer having cold and hot plate temperatures of 10.2°C and 37.8°C, respectively. The foam samples used to determine the aged K-factor are stored at ambient temperature, pressure and humidity conditions. Lower values (mW/MK) indicate better thermal insulative properties.

Foam compressive strengths are observed in the parallel-to-rise and perpendicular-to-rise direction using individual 5 x 5 x 5 cm samples taken from the core of a molded 20 x 20 x 20 foam. Compressive strengths are observed at 10 percent compression.

The average foam cell diameter is determined from a thin section of foam using a polarized-light optical microscope together with a Quantimet 520 Image Analysis system to study the cells.

Where reported, the calculated thermal conductivity of the gas mixture within the closed cells of the foam is according to the Lindsay-Bromley procedure, Industrial and Engineering Chemistry, Vol. 42, p. 1508 (1950) using temperature-dependent Sutherland Constant approximations as discussed therein.

The composition of the gas mixture considered for the calculation is that which can be anticipated if there is a full retention of all blowing agents and gases within the initial foam based on components of the reacting mixture.

The physical properties of the various blowing agents used in the following examples are summarized:

* comparative blowing agent for the purpose of this invention ^® potentials are relative to Refrigerant R-11

Example 1

This example illustrates the aged thermal insu¬ lation performance of a polyurethane foam containing a cell gas mixture of 50 mole percent carbon dioxide and 50 mole percent physical blowing agent (based on components present in the foam-forming composition).

Sample 1 indicates the advantageous use of Refrigerant 13***a. Comparative samples A and B illustrate foams prepared with comparative blowing agents, Refrigerant 11 and Refrigerant 142b.

Foam properties are presented in Table I and thermal insulation properties in Table II.

The data presented in Table I indicates foams prepared with Refrigerant 134a exhibit equivalent or better mechanical physical properties than foams pre¬ pared with comparative blowing agents.

In Table II, the thermal insulation properties show that the thermal insulation loss on aging is reduced for foam comprising Refrigerant 134a in the cell gas mixture.

The higher initial foam thermal conductivity values of the example is not unexpected when considering the relative thermal conductivities of the gases. How¬ ever, what is very surprising is the significantly reduced thermal insulation loss relative to the calculated cell gas conductivity of the initial gas mixture contained within the cells of the foam.

The cells of the foams initially contain 50 mole percent carbon dioxide which is able to diffuse out relatively quickly, leaving the cells with a gas mixture containing highly enriched levels of the physical blow¬ ing agent. It would therefore normally be anticipated that foams containing within their cells enriched con¬ centrations of higher thermal conductivity gas would show significantly greater thermal insulation losses with time, but this is not observed.

Considering the difference between the calcu¬ lated thermal conductivity of the initial cell gas mixture and that initially observed for the foam is

indicative of heat transfer by radiation and solid conduction mechanisms as opposed to gas conduction. Once the foam structure is established, the quantity of heat transfer through the foam by solid conduction and radiation mechanisms does not change on aging and therefore any change in thermal insulation properties of a foam with time can be related specifically to the cell gas composition.

It is interesting to note that the foam pre- pared in the presence of Refrigerant 13*a exhibits significantly lower heat transfer by the solid conduction and radiation mechanisms than the comparative foams.

TABLE I

Physical blowing agent (B.A.)

1 A* B* (R-13 a) (R-11) (R-I42b)

Polyol ©

Isocyanate .© Isocyanate Index

BA wt% on polyol BA wt% composition

Molded foam density ( g/m ) 32.5 30 30

Post expansion (mm)

3 min. (10 min. cure) 5.1 7.2 8.1

4 min. (10 min. cure) 2.0 6.4 6.3

Compressive strengths 10% compression (KPa) 164/193 125/72 119/82 II/l to rise

Average foam cell diameter (mm) 0.44 0.58 0.60

* Comparative example, not an example of this invention

® A fully formulated polyol system comprising a sucrose- -glycerine initiated polyether polyol and about 3 weight percent water

© A crude polymeric methylene diphenylisocyanate, average functionality 2.7, NCO wt percentage 31

TABLE II

1 A* B*

(R-134a) (R-11) (R-I42b)

Calculated cell gas 15.91 11.44 14.54 conductivity (mW/MK)

Observed Foam ( W/MK) conductivity: initial 21 ,5 19.0 21 ,0 aged (47 days) 263 23.9 25 ,6

Observed loss (mW MK) 4.8 4.9 4.6

; observed loss/cell 30.1 42.8 31.6 gas conductivity

* Comparative example, not an example of this invention

Example 2

A similar series of foams as prepared in Example 1 is prepared, however the foams differ in that the initial cell gas mixture contains 78 mole percent carbon dioxide and 18 mole percent physical blowing agent. The physical properties of the resulting foams and their thermal insulation properties are given in Tables III and IV respectively.

The percentage observed thermal insulation loss relative to initial thermal conductivity of the cell gas mixture is shown to be significantly reduced when using Refrigerant 134a.

In this example, the observed thermal conduc¬ tivity of foam comprising Refrigerant 134a within the gas mixture of the closed cells is lower after 40 days aging than foams prepared with the comparative physical blowing agent.

Polyurethane foams can be prepared where the initial cell gas mixture consists essentially of carbon dioxide (gas conductivity 16 mW/MK). Such foams at an equivalent density, typically exhibit initial foam thermal conductivities of 23 to 24 mW/MK and which on aging for the same period of time decay to values of typically 32 to 33 mW/MK. Further, such foams generally display relatively poor dimensional stability character¬ istics in contrast to acceptable dimensional stability properties accorded by the foams of this present invention.

It is clearly seen that foams prepared in the presence of a polyfluorocarbon compound containing no chlorine or bromine atoms exhibit reduced thermal insulation losses on aging, relative to foams prepared with the comparative, alternative blowing agents currently under consideration for commercial use in "environmentally safer" processes.

TABLE II I

Physical blowing agent (B.A.)

Polyol © Water

Isocyanate © Isocyanate Index

BA wt% on polyol BA wt% composition

Reactivity (sec.) CT/GT/TFT -/37/60 8/35/60 -/36/60

Free-rise density 23-9 23.9 24.1

Molded foam density (kg/m ) 30 30 30

Post expansion (mm)

3 min. (10 min. cure) 6.6 6.8 6.3

4 min. (10 min. cure) 4.6 4.6 5.0

Compressive strengths 10% compression (KPa) 145/97 133/75 135/86 II/l to rise

Average foam cell diameter (mm) 0.40 0.48 0.44

* Comparative example, not an example of this invention

© A fully formulated polyol system comprising a sucrose-glycerine initiated polyether polyol and about 3 weight percent water

© A crude polymeric methylene diphenylisocyanate, average functionality 2.7, NCO wt percentage 31

TABLE IV

C* D*

(R-134a) (R-11) (R-I42b)

Calculated cell gas 16.7 14.5 15.9 conductivity (mW/MK)

Observed Foam (mW/MK)

Observed loss (mW/MK) 5.9 7.3 6.8

%; observed loss/cell 35.3 44.1 42.7 gas conductivity

* Comparative example, not an example of this invention

Example 3

In this example a combination of tetrafluoroethane (R-134a) and perfluorohexane (FC-72) is used as physical blowing agent. The initial cell gas composition contains 52 mole percent carbon dioxide, 30 mole percent tetrafluoroethane and 18 mole percent perfluorohexane. The physical properties of the resulting foam is given below. The comparative example presented uses dichlorotrifluoroethane (R-123) as the physical blowing agent.

TABLE v

Polyol ^® Isocyanate ,®^ Isocyanate Index BA wt% on polyol BA wt% composition

Reactivity (sec.) CT/GT/TFT -/45/90 4/38 /60

Free-rise density

Molded foam density (kg/πr)

Compressive strengths 10% compression ( Pa) II/l to rise

Average foam cell diameter (mm)

Observed Foam (mW/MK) conductivity: initial

: aged (20 days)

Observed loss (mW/MK) 2.8 7.2

* Comparative example, not an example of this invention

® A fully formulated polyol system comprising a sucrose- -glycerine initiated polyether polyol and about 3 weight percent water

© A crude polymeric methylene diphenylisocyanate,

Example 4

In this example a combination of perfluorohexane (FC-72) and dichlorotrifluoroethane (R- 123) is used as physical blowing agent. The initial cell gas composition contains 52 mole percent carbon dioxide, 10 mole percent perfluorohexane and 38 mole percent dichlorotrifluoroethane. The physical properties of the resulting foam is given below. The comparative example presented uses dichlorotrifluoroethane (R-123) as the physical blowing agent. From the data presented in Table VI it can be seen that use of a foaming system containing the combination of a polyfluorocarbon compound containing no chlorine or bromine atoms and a secondary blowing agent containing chlorine atoms also provides for the desirable thermal aging performance.

TABLE VI

Polyol ®

Isocyanate ,® Isocyanate Index BA wt% on polyol BA wt% composition

Reactivity (sec.) CT/GT/TFT

Free-rise density

Molded foam density (kg/m ³ )

Compressive strengths 10% compression (KPa) II/l to rise

Average foam cell diameter (mm)

Observed Foam (mW/MK) conductivity: initial

: aged( 20 days) : aged(125 days)

Observed loss (mW/MK) 5.7 7.2

* Comparative example, not an example of this invention

A fully formulated polyol system comprising a sucrose-glycerine initiated polyether polyol and about 3 weight percent water

A crude polymeric methylene diphenylisocyanate, average NCO functionality 2.7 average functionality 2.7, NCO weight percentage 31 functionality 2.7, NCO wt percentage 31

10

15

20

25

30