Patent Publication Number: US-2022220249-A1

Title: Rigid polyurethane foams suitable for use as panel insulation

Description:
FIELD 
     This specification pertains generally to rigid polyurethane foam-forming compositions, rigid polyurethane foams, and methods for their production, as well as to composite articles comprising such foams sandwiched between facer substrates, including use of such composite elements for side-wall and/or roof insulating elements for refrigerated tractor trailers. The rigid polyurethane foams are produced from an isocyanate-reactive composition comprising: (1) a polyol blend; (2) a hydrochlorofluoroolefin (“HCFO”); and (3) a tertiary amine catalyst composition. 
     BACKGROUND 
     Rigid polyurethane foams are used in numerous industries. They are produced by reacting an appropriate polyisocyanate and an isocyanate-reactive compound, usually a polyol, in the presence of a blowing agent. One use of such foams is as a thermal insulation medium in the construction of refrigerated storage devices. The thermal insulating properties of closed-cell rigid foams are dependent upon a number of factors, including the average cell size and the thermal conductivity of the contents of the cells. Chlorofluorocarbons (“CFCs”) were typically used as blowing agents to produce these foams because of their exceptionally low vapor thermal conductivity. However, CFCs are now known to contribute to the depletion of ozone in the stratosphere and, as a result, mandates have been issued which prohibit their use. 
     Initially, the most promising alternatives to CFCs appeared to be hydrogen-containing chlorofluorocarbons (“HCFCs”). While HCFCs, such as HCFC 141b, have been used as alternatives to CFCs, they have also been found to have some ozone-depletion potential. There is, therefore, a desire to find substitutes for HCFCs as well as CFCs. 
     Alternative blowing agents, such as hydrofluorocarbons (“HFCs”), also replaced CFCs. The compounds are, however, greenhouse gases. Hydrocarbons, such as pentane isomers, have also been used but these are flammable and have lower energy efficiency. Halogenated hydroolefinic compounds, such as HCFOs, are possible candidates as replacements for HFCs, since their chemical instability in the lower atmosphere provides for a low global warming potential and zero or near zero ozone depletion. 
     A drawback to some of HCFOs as blowing agents in the production of satisfactory isocyanate-based foams, however, is shelf-life issues. Blowing agents usually are combined with polyols and other components, such as surfactant(s) and catalyst(s) to form a so-called “B-side” pre-mix that may be stored for up to several months prior to being combined with an “A-side” isocyanate component to form the foam. A drawback of systems that use certain HCFOs is the shelf-life of the B-side composition. If the B-side composition is aged prior to combining with the polyisocyanate, the foam can be of lower quality and may even collapse during formation. The poor foam structure is thought to be attributable to the reaction of certain catalysts with these HCFOs which results in the partial decomposition of the blowing agent and, as a result, undesirable modification of silicone surfactants, resulting in poor foam structure and quality. 
     Foam-forming compositions used in the production of discontinuous panel insulation, such as insulation for refrigerated trailer side-walls and roofs, must exhibit a stringent combination of properties. For example, in addition to good thermal insulation properties, they must exhibit a target gel time conducive to the manufacturing equipment and process that is used, and they must exhibit a long shelf life, which means that this gel time cannot change by a large amount after storage of the foam-forming composition components for a long period of time (several months or more), even when water is used as a blowing agent component in an amount of 2% by weight or more, based on the total weight of the isocyanate-reactive composition. They also must exhibit good dimensional stability (low foam shrinkage) even when the foams have a relatively low core foam density of 1.4 to 1.7 lb/ft 3  (22.4 to 27.2 kg/m 3 ). In addition, it is important that the foam adheres well to facer substrates typically used in refrigerated trailer side-wall and roof applications, such as certain plastic facers. 
     Furthermore, HCFOs are relatively costly. As a result, it would also be desirable to provide a way to either (i) improve the thermal insulation properties of foams produced using HCFO blowing agents, without increasing the amount of HCFO blowing agent required in the formulation, or (ii) maintain the thermal insulation properties of foams produced using HCFO blowing agents, while reducing the amount of HCFO blowing agent used in the formulation. In either case, however, the important combination of properties mentioned above should be maintained. 
     A composition that can fulfill most, if not all, of the foregoing requirements, while utilizing a HCFO blowing agent would, therefore, before highly desirable. 
     SUMMARY 
     In certain respects, the present disclosure is directed to isocyanate-reactive compositions. These isocyanate-reactive compositions comprise: (a) a polyol blend, (b) a blowing agent composition, and (c) a tertiary amine catalyst composition. The polyol blend comprises: (1) 50 to 98% by weight, based on the total weight of the polyol blend, of a saccharide-initiated polyether polyol having an OH number of 200 to 600 mg KOH/g and a functionality of 4 to 6; (2) 1 to 20% by weight, based on the total weight of the polyol blend, of an aliphatic amine-initiated polyether polyol having an OH number of 20 to 120 mg KOH/g and a functionality of 3 to 6; and (3) 1 to 20% by weight, based on the total weight of the polyol blend, of an alkanolamine-initiated polyether polyol having an OH number of at least 500 mg KOH/g and a functionality of 2.5 to 4. The blowing agent composition comprises: (1) a HCFO; and (2) a carbon dioxide generating chemical blowing agent. 
     The present specification is also directed to rigid polyurethane foams produced from such compositions, methods for making such rigid foams, composite articles comprising such rigid foams, refrigerated trailers that include such a composite element as side-wall and/or roof insulation, as well as rigid polyurethane foam-forming compositions. 
    
    
     DETAILED DESCRIPTION 
     Various embodiments are described and illustrated in this specification to provide an overall understanding of the structure, function, properties, and use of the disclosed inventions. It is understood that the various embodiments described and illustrated in this specification are non-limiting and non-exhaustive. Thus, the invention is not limited by the description of the various non-limiting and non-exhaustive embodiments disclosed in this specification. The features and characteristics described in connection with various embodiments may be combined with the features and characteristics of other embodiments. Such modifications and variations are intended to be included within the scope of this specification. As such, the claims may be amended to recite any features or characteristics expressly or inherently described in, or otherwise expressly or inherently supported by, this specification. Further, Applicant reserves the right to amend the claims to affirmatively disclaim features or characteristics that may be present in the prior art. Therefore, any such amendments comply with the requirements of 35 U.S.C. § 112 and 35 U.S.C. § 132(a). The various embodiments disclosed and described in this specification can comprise, consist of, or consist essentially of the features and characteristics as variously described herein. 
     Any patent, publication, or other disclosure material identified herein is incorporated by reference into this specification in its entirety unless otherwise indicated, but only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material expressly set forth in this specification. As such, and to the extent necessary, the express disclosure as set forth in this specification supersedes any conflicting material incorporated by reference herein. Any material, or portion thereof, that is said to be incorporated by reference into this specification, but which conflicts with existing definitions, statements, or other disclosure material set forth herein, is only incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material. Applicant reserves the right to amend this specification to expressly recite any subject matter, or portion thereof, incorporated by reference herein. 
     In this specification, other than where otherwise indicated, all numerical parameters are to be understood as being prefaced and modified in all instances by the term “about”, in which the numerical parameters possess the inherent variability characteristic of the underlying measurement techniques used to determine the numerical value of the parameter. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter described in the present description should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. 
     Also, any numerical range recited in this specification is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all sub-ranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited in this specification is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant(s) reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. All such ranges are intended to be inherently described in this specification such that amending to expressly recite any such sub-ranges would comply with the requirements of 35 U.S.C. § 112 and 35 U.S.C. § 132(a). 
     The grammatical articles “one”, “a”, “an”, and “the”, as used in this specification, are intended to include “at least one” or “one or more”, unless otherwise indicated. Thus, the articles are used in this specification to refer to one or more than one (i.e., to “at least one”) of the grammatical objects of the article. By way of example, “a component” means one or more components, and thus, possibly, more than one component is contemplated and may be employed or used in an implementation of the described embodiments. Further, the use of a singular noun includes the plural, and the use of a plural noun includes the singular, unless the context of the usage requires otherwise. 
     As used herein, the term “functionality” refers to the average number of reactive hydroxyl groups, —OH, present per molecule of the polyol or polyol blend that is being described. In the production of polyurethane foams, the hydroxyl groups react with isocyanate groups, —NCO, that are attached to a polyisocyanate. The term “hydroxyl number” refers to the number of reactive hydroxyl groups available for reaction, and is expressed as the number of milligrams of potassium hydroxide equivalent to the hydroxyl content of one gram of the polyol (ASTM D4274-16). The term “equivalent weight” refers to the weight of a compound divided by its valence. For a polyol, the equivalent weight is the weight of the polyol that will combine with an isocyanate group, and may be calculated by dividing the molecular weight of the polyol by its functionality. The equivalent weight of a polyol may also be calculated by dividing 56,100 by the hydroxyl number of the polyol−Equivalent Weight (g/eq)=(56.1×1000)/OH number. 
     As indicated, certain embodiments of the present specification are directed to rigid foams. A rigid foam is characterized as having a ratio of compressive strength to tensile strength of at least 0.5:1, elongation of less than 10%, as well as a low recovery rate from distortion and a low elastic limit, as described in in “Polyurethanes: Chemistry and Technology, Part II Technology,” J. H. Saunders &amp; K. C. Frisch, Interscience Publishers, 1964, page 239. 
     As earlier mentioned, the isocyanate-reactive composition described in this specification comprises a polyol blend. More particularly, the polyol blend comprises a saccharide-initiated polyether polyol. As used herein, “saccharide-initiated polyether polyol” refers to a polyether polyol prepared by reacting at least one alkylene oxide with one or more suitable initiator compounds in the presence of a suitable catalyst, in which the initiator compounds comprise one or more saccharides. Examples of suitable alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, epichlorohydrin, or a mixture of any two or more thereof. Some examples of suitable saccharide initiators are sucrose, sorbitol, maltitol, or a mixture of any two or more thereof, as well as other mono-saccharides, di-saccharides, tri-saccharides and polysaccharides. Other initiator compounds are often used in combination with the saccharide initiator to prepare the saccharide-initiated polyether polyol. Saccharides can be co-initiated with for example, compounds such as water, propylene glycol, glycerin, ethylene glycol, ethanol amines, diethylene glycol, and mixtures of any two or more thereof, to form a saccharide-initiated polyether polyols. As will be appreciated, it is possible to use a wide variety of individual initiator compounds in combination with one another in which the functionality of the individual initiator compounds does not fall within the functionalities set forth herein, provided that the average functionality of the mixture of initiator compounds satisfies the overall functionality range disclosed herein. 
     Some examples of suitable catalysts which can be used include basic catalysts (such as sodium or potassium hydroxide or tertiary amines such as methyl imidazole), and double metal cyanide (DMC) catalysts. 
     In some embodiments, the saccharide-initiated polyether polyol has an OH number of 200 to 600 mg KOH/g, such as 300 to 550 mg KOH/g, such as 350 to 450 mg KOH/g, or, in some cases, 398 to 422 mg KOH/g, and a functionality of 4 to 6, such as 4 to 5, 4.0 to 4.5, or 4.2 to 4.3. 
     In some embodiments, the saccharide-initiated polyether polyol is utilized in an amount of 50 to 98% by weight, 60 to 98% by weight, 60 to 90% by weight, 70 to 90% by weight, or, in some cases, 70 to 85% by weight, based on the total weight of the polyol blend. 
     As indicated earlier, the polyol blend further comprises an aliphatic amine-initiated polyether polyol having an OH number of 20 to 120 mg KOH/g, such as 40 to 80 mg KOH/g, or, in some cases, 50 to 70 mg KOH/g or 57 to 63 mg KOH/g, and a functionality of 3 to 6, such as 3 to 5, 3.5 to 4.5, or 4.0. 
     As used herein, “aliphatic amine-initiated polyether polyol” refers to a polyether polyol prepared by reacting at least one alkylene oxide with one or more suitable initiator compounds in the presence of a suitable catalyst, in which the initiator compounds comprise one or more aliphatic amines. Suitable alkylene oxides include, for example, ethylene oxide and/or propylene oxide. Suitable aliphatic amine initiators include: ammonia, ethylene diamine, hexamethylene diamine, methyl amine, diaminodiphenyl methane, aniline, and tetrahydroxyl ethyl ethylenediamine, as well as mixtures of any two or more thereof. In some embodiments, the aliphatic amine-initiated polyether polyol is the alkoxylation product of propylene oxide and ethylene diamine. 
     In some embodiments, the aliphatic amine-initiated polyether polyol is utilized in an amount of 1 to 20%, such as 5 to 15% by weight, based upon the total weight of the polyol blend. 
     In certain embodiments, the saccharide-initiated polyether polyol and the aliphatic amine-initiated polyether polyol are present in the polyol blend in a weight ratio of at least 3:1, such as 3:1 to 30:1, 5:1 to 20:1, or, in some cases 5:1 to 15:1, 5:1 to 10:1, or, in some cases, 6:1 to 8:1. 
     As also indicated earlier, the polyol blend further comprises an alkanolamine-initiated polyether polyol. As used herein, “alkanolamine-initiated polyether polyol” refers to a polyether polyol prepared by reacting at least one alkylene oxide with one or more suitable initiator compounds in the presence of a suitable catalyst, in which the initiator compounds comprise one or more alkanolamines. Suitable catalysts including basic catalysts (such as sodium or potassium hydroxide or tertiary amines such as methyl imidazole) and DMC catalysts. In the polyol blends described herein, each of the recited polyether polyols, including the “alkanolamine-initiated polyether polyol” and the “aliphatic amine-initiated polyether polyol”, are different from each other. 
     As used herein, the term “alkanolamine” refers to compounds represented by the formula: 
       NH 2 —Z—OH
 
     in which Z represents a divalent radical which is a straight chain or branched chain alkylene radical having 2 to 6 carbon atoms, a cycloalkylene radical having 4 to 6 carbon atoms or a dialkylene ether radical having 4 to 6 carbon atoms. The dialkylene ether radical may be represented by the formula: 
       R—O—R—
 
     where each R represents a hydrocarbon radical having 2 to 3 carbon atoms. 
     Specific examples of suitable alkanolamines that may be used in the preparation of the alkanolamine-initiated polyether polyol include monoethanolamine, 1-amino-2-propanol, 2-amino-1-propanol, 3-amino-1-propanol, 1-(2-aminoethoxy) ethanol, 1-amino-2-butanol, 2-amino-3-butanol, 2-amino-2-methylpropanol, 5-amino pentanol, 3-amino-2,2-dimethyl propanol, 4-aminocyclohexanol, as well as mixtures of any two or more thereof. 
     To prepare the alkanolamine-initiated polyether polyol, the alkanolamine is reacted with an alkylene oxide. Suitable alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, styrene oxide, and epichlorohydrin, as well as mixtures of any two or more thereof. 
     In some implementations, the alkanolamine-initiated polyether polyol has an OH number of at least 500 mg KOH/g, such as 500 to 900 mg KOH/g, 600 to 800 mg KOH/g, or, in some cases, 680 to 720 mg KOH/g, and a functionality of 2.5 to 4, such as 2.5 to 3.5. 
     In some implementations, the alkanolamine-initiated polyether polyol is utilized in an amount of 1 to 20%, such as 1 to 10% by weight or 4 to 8% by weight, based on the total weight of the polyol blend. 
     In certain implementations, the saccharide-initiated polyether polyol and the alkanolamine-initiated polyether polyol are present in the polyol blend in a weight ratio of at least 5:1, such as 5:1 to 20:1, or, in some cases 5:1 to 15:1 or 10:1 to 15:1. In certain implementations, the aliphatic amine-initiated polyether polyol and the alkanolamine-initiated polyether polyol are present in the polyol blend in a weight ratio of at least 0.8:1, such as 0.8:1 to 4:1, or, in some cases 1:1 to 2:1 or 1:1 to 1.5:1. 
     In some implementations, the polyol blend further comprises an aliphatic triol-initiated polyether polyol having an OH number of 100 to 500 mg KOH/g, such as 200 to 400 mg KOH/g, 200 to 300 mg KOH/g, 200 to 250 mg KOH/g, 230 to 250 mg KOH/g or 233 to 243 mg KOH/g, and a functionality of from greater than 2 to 4, such as 2.5 to 3.5, or, in some cases, 3.0. 
     Such polyether polyols can be prepared by reacting suitable aliphatic divalent, trivalent and/or more valent alcohols, (e.g., ethanediol, propanediol-1,2 and propanediol-1,3, diethylene glycol, dipropylene glycol, butanediol-1,4, hexanediol-1,6, and glycerin), provided that at least one aliphatic trivalent alcohol is used. In some embodiments, the polyvalent alcohol initiator comprises or, in some cases, consists of glycerin and the alkylene oxide comprises, or, in some cases, consists of propylene oxide. 
     In certain embodiments, the aliphatic triol-initiated polyether polyol is utilized in an amount of 1 to 20% by weight, such as 5 to 20% by weight, or 10 to 20% by weight, based on the total weight of the polyol blend. 
     In certain embodiments, the saccharide-initiated polyether polyol and the aliphatic triol-initiated polyether polyol are present in the polyol blend in a weight ratio of at least 3:1, such as 3:1 to 30:1, 3:1 to 20:1, or, in some cases 5:1 to 15:1, 5:1 to 10:1, or, in some cases, 7:1 to 9:1. In certain embodiments, the aliphatic amine-initiated polyether polyol and the aliphatic triol-initiated polyether polyol are present in the polyol blend in a weight ratio of at least 1:1, such as 1:1 to 5:1, or 1:1 to 2:1. In certain implementations, the aliphatic triol-initiated polyether polyol and the alkanolamine-initiated polyether polyol are present in the polyol blend in a weight ratio of at least 0.8:1, such as 0.8:1 to 4:1, or, in some cases 1:1 to 2:1 or 1:1 to 1.5:1. 
     If desired, the polyol blend may include additional compounds that contain isocyanate-reactive groups, such as chain extenders and/or crosslinking agents, and higher molecular weight polyether polyols and polyester polyols not described above. Chain extenders and/or crosslinking agents include, for example, ethylene glycol, propylene glycol, butylene glycol, glycerol, diethylene glycol, dipropylene glycol, dibutylene glycol, trimethylolpropane, pentaerythritol, ethylene diamine, and diethyltoluenediamine. Polyester polyols may be prepared from, for example, an organic dicarboxylic acid having 2 to 12 carbon atoms, such as an aliphatic dicarboxylic acid having 4 to 6 carbon atoms, and a polyvalent alcohol, such as a diol or triol having 2 to 12 carbon atoms. Examples of the dicarboxylic acid are succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid and terephthalic acid. Instead of a free dicarboxylic acid, a corresponding dicarboxylic acid derivative such as a dicarboxylic acid monoester or diester prepared by esterification with an alcohol having 1 to 4 carbon atoms or dicarboxylic anhydride can be used. 
     In certain embodiments, the polyol blend has a weighted average functionality of from 3 to 5, such as 3.5 to 4.5 or 3.8 to 4.2, and/or a weighted average hydroxyl number of 300 to 500 mg KOH/g, such as 350 to 450 mg KOH/g, or 350 to 400 mg KOH/g, and/or a weighted average molecular weight of 800 to 1200 g/mol, such as 850 to 1200 g/mol or 900 to 1000 g/mol. 
     As indicated, the isocyanate-reactive composition of this specification further comprises a blowing agent composition. The blowing agent composition comprises: (1) a physical blowing agent comprising an HCFO; and (2) a carbon dioxide generating chemical blowing agent. Suitable HCFOs include 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd, E and/or Z isomers), 2-chloro-3,3,3-trifluoropropene (HCFO-1233xf), HCF01223, 1,2-dichloro-1,2-difluoroethene (E and/or Z isomers), 3,3-dichloro-3-fluoropropene, 2-chloro-1,1,1,4,4,4-hexafluorobutene-2 (E and/or Z isomers), 2-chloro-1,1,1,3,4,4,4-heptafluorobutene-2 (E and/or Z isomers). In some implementations, the boiling point, at atmospheric pressure, of the HCFO is at least −25° C., at least −20° C., or, in some cases, at least −19° C., and 40° C. or less, such as 35° C. or less, or, in some cases 33° C. or less. The HCFO may have a boiling point, at atmospheric pressure, of, for example, −25° C. to 40° C., or −20° C. to 35° C., or −19° C. to 33° C. 
     In some implementations, the HCFO is utilized in an amount of at least 10% by weight, such as 10 to 30% by weight or 10 to 20% by weight, based on the total weight of the isocyanate-reactive composition. 
     In certain implementations, the isocyanate-reactive composition comprises one or more other physical blowing agents, such as other halogenated blowing agents, such as CFCs, HCFCs, and/or HFCs and/or hydrocarbon blowing agents, such as butane, n-pentane, cyclopentane, hexane, and/or isopentane (i.e. 2-methylbutane). In other embodiments, the isocyanate-reactive composition is substantially or, in some cases, completely free, of other physical blowing agents, such as other halogenated blowing agents, such as CFCs, HCFCs, and/or HFCs and/or hydrocarbon blowing agents, such as butane, n-pentane, cyclopentane, hexane, and/or isopentane (i.e. 2-methylbutane). As used herein, the term “substantially free” when used with reference to these blowing agents, means that the blowing agent is present, if at all, in an amount of less than 10% by weight, such as less than 1% by weight, based on the total weight of the blowing agent composition. 
     As indicated above, the isocyanate-reactive composition comprises a carbon dioxide generating chemical blowing agent, such as water and/or a formate-blocked amine. 
     In some of these implementations, the carbon dioxide generating chemical blowing agent, such as water, is utilized in an amount of 0.5 to 5.0% by weight, such as 1 to 4% by weight, or 1.0 to 3.0% by weight, or 2.0 to 3.0% by weight, based on the total weight of the isocyanate-reactive composition. 
     In certain implementations, the blowing agent composition comprises HCFO and a carbon dioxide generating chemical blowing agent, such as water, wherein the HCFO and the carbon dioxide generating chemical blowing agent are present in an amount of at least 90% by weight, such as at least 95% by weight, or, in some cases, at least 99% by weight, based on the total weight of the blowing agent composition. In certain implementations, the HCFO and a carbon dioxide generating chemical blowing agent are present in the blowing agent composition at a weight ratio of at least 2:1, such as at least 4:1, such as 4:1 to 10:1 or 4:1 to 6:1. 
     If desired, the blowing agent composition may include other physical blowing agents, such as (a) other hydrofluoroolefins (HFOs), such as pentafluoropropane, tetrafluoropropene, 2,3,3,3-tetrafluoropropene, 1,2,3,3-tetrafluoropropene, trifluoropropene, tetrafluorobutene, pentafluorobutene, hexafluorobutene, heptafluorobutene, heptafluoropentene, octafluoropentene, and nonafluoropentene; (b) hydrofluorocarbons (c) hydrocarbons, such as any of the pentane isomers and butane isomers; (d) hydrofluoroethers (HFEs); (e) C 1  to C 5  alcohols, C 1  to C 4  aldehydes, C 1  to C 4  ketones, C 1  to C 4  ethers and diethers and carbon dioxide. Specific examples of such blowing agents are described in United States Patent Application Publication No. US 2014/0371338 A1 at [0051] and [0053], the cited portion of which being incorporated herein by reference. 
     In some implementations, the isocyanate-reactive composition also comprises a surfactant. Any suitable surfactant can be used including organosilicon compounds, such as polysiloxane-polyalkyene-block copolymers, such as a polyether-modified polysiloxane. Other useful surfactants include polyethylene glycol ethers of long chain alcohols, tertiary amine or alkanolamine salts of long chain alkyl acid sulfate esters, alkylsulfonic esters, or alkylarylsulfonic acids. Such surfactants are employed in amounts sufficient to stabilize the foaming reaction mixture against collapse and the formation of large and uneven cells. In some embodiments, surfactant is utilized in an amount of 0.2 to 5.0% by weight, such as 1 to 3% by weight, based on the total weight of the isocyanate-reactive composition. 
     The isocyanate-reactive composition further comprises a tertiary amine catalyst composition. In some implementations, the tertiary amine catalyst composition comprises a morpholine and an imidazole, such as where the tertiary amine catalyst composition comprises: (i) 80 to 99% by weight, such as 90 to 99% by weight, or, in some cases, 95 to 98% by weight, based on the total weight of the tertiary amine catalyst composition, of a morpholine; and (ii) 1 to 20% by weight, such as 1 to 10% by weight, or, in some cases, 2 to 5% by weight, based on the total weight of the tertiary amine catalyst composition, of an imidazole. 
     Suitable morpholine catalysts include, for example, dimorpholinodiethylether, dimorpholinodimethylether N-ethylmorpholine, and N-methylmorpholine. Suitable imidazole catalysts include, for example, imidazole, n-methylimidazole, and 1,2-dimethylimidazole. In some embodiments, the morpholine catalyst comprises a mixture of two or more morpholine catalyst, such as a mixture of dimorpholinodiethylether and N-methylmorpholine wherein, for example, the dimorpholinodiethylether is utilized in an amount of 30 to 80% by weight, such as 40 to 80% by weight, and N-methylmorpholine is utilized in an amount of 20 to 70% by weight, such as 20 to 60% by weight, based on the total weight of morpholine catalyst utilized. 
     In certain embodiments, the tertiary amine catalyst composition does not include an acid-blocked amine catalyst. In certain embodiments, the isocyanate-reactive composition does not include a metal catalyst and/or any other catalyst that is not a tertiary amine catalyst. 
     In certain embodiments, the total amount of tertiary amine catalyst utilized in the isocyanate-reactive composition is 1 to 5% by weight, such as 2.5 to 3.5% by weight, based on the total weight of the isocyanate-reactive composition. 
     Additional materials which may optionally be included in the foam-forming compositions of the present invention include: pigments, colorants, fillers, antioxidants, flame retardants, and stabilizers. Exemplary flame retardants useful in the foam-forming composition of the present invention include, but are not limited to, reactive bromine based compounds and chlorinated phosphate esters, including but not limited to, tri(2-chloroethyl)phosphate (TECP), tri(1,3-dichloro-2-propyl)phosphate, tri(1-chloro-2-propyl)phosphate (TCPP) and dimethyl propyl phosphate (DMPP). 
     Some implementations of the present specification relate to rigid polyurethane foam-forming compositions. These foam-forming compositions comprise: (a) a diisocyanate and/or polyisocyanate (collectively “polyisocyanate”); and (b) an isocyanate-reactive composition as described above. 
     Any of the known organic isocyanates, modified isocyanates or isocyanate-terminated prepolymers made from any of the known organic polyisocyanates may be used. Suitable organic polyisocyanates include aromatic, aliphatic, and cycloaliphatic polyisocyanates and combinations thereof. Useful polyisocyanates include: diisocyanates, such as m-phenylene diisocyanate, p-phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 1,6-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclo-hexane diisocyanate, isomers of hexahydro-toluene diisocyanate, isophorone diisocyanate, dicyclo-hexylmethane diisocyanates, 1,5-naphthylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-biphenylene diisocyanate, 3,3′-dimethoxy-4,4′-biphenylene diisocyanate and 3,3′-dimethyl-diphenyl-propane-4,4′-diisocyanate; triisocyanates such as 2,4,6-toluene triisocyanate; and polyisocyanates such as 4,4′-dimethyl-diphenylmethane-2,2′,5,5′-tetraisocyanate and the polymethylene polyphenyl-polyisocyanates. 
     Undistilled or crude polyisocyanates may also be used. The crude toluene diisocyanate obtained by phosgenating a mixture of toluene diamines and the crude diphenylmethane diisocyanate obtained by phosgenating crude diphenylmethanediamine (polymeric MDI) are examples of suitable crude polyisocyanates. Suitable undistilled or crude polyisocyanates are disclosed in U.S. Pat. No. 3,215,652. 
     Modified polyisocyanates are obtained by chemical reaction of polyisocyanates. Useful modified polyisocyanates include, but are not limited to, those containing ester groups, urea groups, biuret groups, allophanate groups, carbodiimide groups, isocyanurate groups, uretdione groups and/or urethane groups. Examples of modified polyisocyanates include prepolymers containing NCO groups and having an NCO content of from 25 to 35 weight percent, such as from 29 to 34 weight percent, such as those based on polyether polyols or polyester polyols and diphenylmethane diisocyanate. 
     In certain embodiments, the polyisocyanate comprises a methylene-bridged polyphenyl polyisocyanate and/or a prepolymer of methylene-bridged polyphenyl polyisocyanates having an average functionality of from 1.8 to 3.5, such as from 2.0 to 3.1, isocyanate moieties per molecule and an NCO content of from 25 to 32 weight percent, due to their ability to cross-link the polyurethane. 
     The present specification is also directed to processes for producing rigid polyurethane foams. In such processes, a polyisocyanate is reacted with an isocyanate-reactive composition of the type described above. In some embodiments, the polyisocyanate and the isocyanate-reactive compositions are mixed at an isocyanate index of from 90 to 140, such as 100 to 110. 
     In certain embodiments, the polyol blend of the isocyanate-reactive composition is reacted with an organic polyisocyanate in the presence of a blowing agent, water, a tertiary amine catalyst composition, a surfactant and any other optional ingredients. The rigid foams may be prepared by blending all of the components of the isocyanate-reactive composition together in a phase stable mixture, and then mixing this in the proper ratio with the organic polyisocyanate. Alternatively, one or more of the components, such as the surfactant, may be combined with the organic polyisocyanate prior to mixing it with the isocyanate-reactive composition. Other possible embodiments of the invention would include adding one or more of the components as a separate stream, together with the isocyanate-reactive composition and organic polyisocyanate. 
     Many foam machines are designed to condition and mix only two components in the proper ratio. For use of these machines, a premix of all the components except the polyisocyanate can be advantageously employed. According to the two-component method (component A: polyisocyanate; and component B: isocyanate-reactive composition which typically includes the polyol blend, blowing agent, water, catalyst and surfactant), the components may be mixed in the proper ratio at a temperature of 5 to 50° C., such as 15 to 35° C., injected or poured into a mold having the temperature controlled to within a range of 20 to 70° C., such as 35 to 60° C. The mixture then expands to fill the cavity with the rigid polyurethane foam. This simplifies the metering and mixing of the reacting components which form the polyurethane foam-forming mixture, but requires that the isocyanate-reactive composition be phase stable. 
     Furthermore, the rigid polyurethane foam can be prepared in a batch or continuous process by the one-shot or quasi-prepolymer methods using any well-known foaming apparatus. The rigid polyurethane foam may be produced in the form of slab stock, moldings, cavity fillings, sprayed foam, frothed foam or laminates with other materials such as hardboard, plasterboard, plastics, paper or metal as facer substrates. 
     For closed-cell insulating foams, the object is to retain the blowing agent in the cells to maintain a low thermal conductivity of the insulating material, i.e., the rigid polyurethane foam. Thus, a high closed-cell content in the foam is desirable. Foams produced according to embodiments of the present specification have more than 80 percent, typically more than 85 percent, or more than 88 percent closed-cell content as measured according to ASTM D6226-15. Furthermore, the thermal conductivity of foams produced according to various embodiments of the present specification, measured at 35° F. (2° C.), is less than 0.160 BTU-in/h-ft 2 -° F. for foam from the core of 3-inch thick panels, as measured according to ASTM C518-17. 
     This specification also relates to the use of the rigid polyurethane foams described herein for thermal insulation. These rigid foams can be used, for example, as an intermediate layer in composite elements or for filling hollow spaces of refrigerators and freezers, or refrigerated trailers. These foams may also find use in the construction industry or for thermal insulation of long-distance heating pipes and containers. 
     As such, the present invention also provides a composite article comprising rigid polyurethane foam as disclosed herein sandwiched between one or more facer substrates. In certain embodiments, the facer substrate may be plastic (such a polypropylene resin reinforced with continuous bi-directional glass fibers or a fiberglass reinforced polyester copolymer), paper, wood, or metal. For example, in certain embodiments, the composite article may be a refrigeration apparatus such as a refrigerator, freezer, or cooler with an exterior metal shell and interior plastic liner. In certain embodiments, the refrigeration apparatus may be a trailer, and the composite article may include the polyurethane foams produced according to the present invention in sandwich composites for trailer side-walls and roofs. 
     It is currently believed that the particular isocyanate-reactive compositions described herein are capable of producing rigid foams that have a particular combination of properties that make them suitable for use in sandwich composites for trailer side-walls and roofs. 
     First, the rigid foams can have a thermal conductivity measured at 75° F. (23.9° C.) of less than 0.160 BTU-in/h-ft 2 -° F., for foam from the core of 3 inch thick panels, as measured according to ASTM C518-17 at a core foam density of 1.4 to 1.7 lb/ft 3  even when the amount of HCFO blowing agent used in the isocyanate-reactive composition is less than 11% by weight, based on the total weight of the isocyanate-reactive composition. Second, the isocyanate-reactive composition has a long shelf life. Here, when it is stated that the isocyanate-reactive composition has a “long” shelf life of it means that after storing the isocyanate-reactive composition for 6 days at 60° C., when the isocyanate-reactive composition is combined with the polyisocyanate, the gel time of the foam produced thereby remains within 10% of the initial gel time (the gel time of such a foam if produced immediately and not after storing the isocyanate-reactive composition for 6 days at 60°) even when the isocyanate-reactive composition comprises 2% by weight or more of water. In some cases, this initial gel time is 105 seconds, ±15 seconds, which can be ideally suited for trailer side-wall and roof applications. Third, the rigid foams exhibit low shrinkage, which means that the volume change of a free-rise density foam produced from the foam-forming compositions described herein is less than 14% after aging the foam for 4 weeks at ambient conditions of temperature and pressure (25° C. and 1 atm pressure). Fourth, the foams exhibit excellent adhesion to facer substrates typically used in the manufacture of composite elements for refrigerated trailer side-wall and roof insulation, particularly plastic facers, specifically polypropylene resin reinforced with continuous bi-directional glass fibers and fiberglass reinforced polyester copolymer. As used herein, “excellent adhesion” means that the rigid foam has an average peel strength of greater than 30 lb-f/in when measured according to ASTM D 1781-98 (2012) using a crosshead speed of 1.0 inch/minute when adhered to such plastic facer substrates. 
     In addition, it is currently believed possible, utilizing an isocyanate-reactive composition that comprises the polyol blends described herein, to either (i) improve the thermal insulation properties of foams produced using HCFO blowing agents, without increasing the amount of HCFO blowing agent used in the formulation, or (ii) maintain the thermal insulation properties of foams produced using HCFO blowing agents, while reducing the amount of HCFO blowing agent used in the formulation. In either case, however, it is also currently believed possible to maintain the important combination of properties mentioned above. 
     The non-limiting and non-exhaustive examples that follow are intended to further describe various non-limiting and non-exhaustive embodiments without restricting the scope of the embodiments described in this specification. 
     EXAMPLES 
     Foam-forming compositions were prepared using the ingredients and amounts (in parts by weight) set forth in Table 1. The following materials were used: 
     POLYOL 1: a sucrose, glycerin, propylene glycol, and water-initiated polyether polyol having an OH number of 398-422 mg KOH/g and an average functionality of 4.3; 
     POLYOL 2: a glycerin-initiated propylene oxide-based triol having an OH number of 233-243 mg KOH/g; 
     POLYOL 3: an ethylenediamine-initiated propylene oxide-based tetrol having an OH number of 57-63 mg KOH/g; 
     POLYOL 4: a glycerin-initiated propylene oxide-based triol having an OH number of 106-118 mg KOH/g; 
     POLYOL 5: a monoethanolamine-initiated polyether polyol having an OH number of 685 to 715, a functionality of 3, and a nitrogen content of 5.8% by weight, prepared by propoxylating monoethanolamine; 
     SURF: TEGOSTAB® B-8499; 
     CAT 1: 2,2′-dimorpholinodiethylether (JEFFCAT® DMDEE from Huntsman); 
     CAT 2: N-methylmorpholine catalyst (JEFFCAT® NMM from Huntsman); 
     CAT 3: 1,2-dimethylimidazole (DABCO® 2040 or 2041 from Evonik); 
     HCFO: trans-1-Chloro-3,3,3-trifluoropropene (Solstice® LBA from Honeywell); and 
     ISO: polymeric diphenylmethane diisocyanate (pMDI); NCO weight 31.5%; viscosity 200 mPa·s @ 25° C.; equivalent weight 133; functionality 2.8 (MONDUR® MR from Covestro LLC). 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 2 
                   
                 4 
               
               
                 Ingredient 
                 1 
                 (Comparative) 
                 3 
                 (Comparative) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 POLYOL 1 
                 62.05 
                 66.35 
                 64.56 
                 68.32 
               
               
                 POLYOL 2 
                 6.19 
                 6.63 
                 — 
                 — 
               
               
                 POLYOL 3 
                 8.11 
                 8.67 
                 4.30 
                 4.92 
               
               
                 POLYOL 4 
                 — 
                 — 
                 4.00 
                 4.00 
               
               
                 POLYOL 5 
                 5.00 
                 — 
                 5.00 
                 — 
               
               
                 SURF 
                 2.10 
                 2.10 
                 2.00 
                 2.00 
               
               
                 CAT 1 
                 2.00 
                 2.00 
                 1.90 
                 2.00 
               
               
                 CAT 3 
                 0.15 
                 0.15 
                 0.25 
                 0.33 
               
               
                 CAT 2 
                 1.00 
                 1.00 
                 0.70 
                 0.82 
               
               
                 Water 
                 3.07 
                 3.00 
                 1.90 
                 1.86 
               
               
                 HCFO 
                 10.33 
                 10.10 
                 15.39 
                 15.75 
               
               
                 Total 
                 100.00 
                 100.00 
                 100.00 
                 100.00 
               
               
                 ISO 
                 129.00 
                 124.00 
                 110.00 
                 106.00 
               
               
                   
               
            
           
         
       
     
     For each of the Examples, the polyols, catalysts, surfactant, water, and HCFO were combined in the amounts indicated in Table 1. All foams were prepared in a laboratory using a small scale laboratory press. Successful laboratory results were prepared using a scale and an air motor mixer set at 3000 rpm. The liquids were maintained at a constant 21° C. and the polyol and isocyanate components were each weighed out to the desired ratio, poured together and mixed with the air mixer for 8 seconds and poured for a set time into a mold before closing the mold. The minimum fill density was determined from foaming a panel poured into a temperature controlled mold (43.3° C.) having dimensions—13 inches by 26 inches by 3 inches (33.0 cm×66.0 cm×7.6 cm) that didn&#39;t fill the mold entirely, then a calculated minimum panel mass value was determined. After the minimum fill density was determined, then foam was packed to obtain desired density of approximately 2.20 lb/ft 3 . The foam was sandwiched between one aluminum facer and one fiber reinforced plastic facer. Foamed parts were held in the mold at 43.3° C. for 15 to 25 minutes before de-molding. Overall density for each of the foams was between 2.15 and 2.25 lb/ft 3  (34.4 to 36.0 kg/m 3 ), measured according to ASTM D1622-14. 
     The foams were tested for various properties and the results are set forth in Table 2. K-factor was measured at a mean temperature of 75° F. (23.9° C.)−(cold plate 55° F. (12.8° C.), hot plate 95° F.)(35° C.) for foam from the core of 3-inch thick panels, according to ASTM C518-17. For shelf life, the foam was considered a “Pass” if the gel time and free-rise density of the foam after storing the isocyanate-reactive composition for 6 days at 60° C. or longer was within 10% of the initial gel time and 5% of the initial foam free-rise density (the gel time and free-rise density of such a foam if produced immediately and not after storing the isocyanate-reactive composition for 6 days at 60° C.). Dimensional stability was assessed by measuring the volume change of a free-rise density foam after aging the foam for 4 weeks at ambient conditions of temperature and pressure (25° C. and 1 atm pressure) with a change of less than 12% volume. Peel strength was measured according to ASTM D 1781-98 (2012) using a crosshead speed of 1.0 inch/minute. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 2 
                   
                 4 
               
               
                   
                   
                   
                 (Compar- 
                   
                 (Compar- 
               
               
                 Test 
                 Units 
                 1 
                 ative) 
                 3 
                 ative) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Peel 
                 lbf 
                 35.3 
                 27.7 
                 24.0 
                 22.7 
               
               
                 Strength 1   
               
               
                 Shelf-life 
                 — 
                 Pass 
                 Pass 
                 Pass 
                 Pass 
               
               
                 K-factor @ 
                 BTU-in/ 
                 0.159 
                 0.159 
                 0.154 
                 0.154 
               
               
                 75° F. 
                 h-ft 2 -° F. 
               
               
                 Dimensional 
                 % volume 
                 5.20% 
                 5.20% 
                 5.60% 
                 5.60% 
               
               
                 Stability 
                 Change 
               
               
                   
               
               
                   1 Reported results are an average of three sample measurements 
               
            
           
         
       
     
     As is apparent, the inventive examples exhibited improved peel strength, as measured according to ASTM D 1781-98 (2012) relative to their respective comparative examples, while not negatively impacted shell-life, thermal insulation performance, or dimensional stability. 
     Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.