Method for producing polyurethane foam

Abstract

To provide a method for producing a polyurethane foam which is good in miscibility of a polyol composition and a polyisocyanate composition and is excellent in initial reactivity when forming a polyurethane foam.SOLUTION: The present invention relates to a method in which a polyol composition containing a polyol and a catalyst containing a metal carboxylate is mixed and reacted with a polyisocyanate composition containing a polyisocyanate to perform foaming and curing, thereby producing a polyurethane foam. The production method includes a step of supplying a foaming agent A through a system different from those for the polyol composition and the polyisocyanate composition, the foaming agent A containing a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0°C or lower. The foaming agent A is added to at least one of the polyol composition and the polyisocyanate composition at a ratio of 0.01 to 4 pts.mass based on 100 pts.mass of the polyol in the polyol composition, and the reaction proceeds after the addition.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a polyurethane foam. [Background technology]

[0002] Conventionally, polyurethane foams have been used as heat insulating materials in vehicles such as automobiles, building materials, etc. In general, polyurethane foams are formed by discharging and mixing a polyol composition and a polyisocyanate composition filled in separate containers.

[0003] There are various known methods for producing polyurethane foam, including, for example, a method in which a blowing agent is added to a polyol composition in advance, and the polyol composition and a polyisocyanate composition are mixed at the production site to foam and harden the polyurethane foam. In contrast to this, a method for producing polyurethane foam is known that utilizes a system in which a blowing agent is added to either the polyol composition or the polyisocyanate composition at the production site. For example, Patent Document 1 discloses a method for producing polyurethane foam by adding a certain amount of carbon dioxide (supercritical, subcritical or liquid carbon dioxide) as a blowing agent to at least one of a polyol composition and a polyisocyanate composition at the polyurethane foam production site. Furthermore, in the examples, an embodiment is also disclosed in which a mixture of liquefied carbon dioxide and HFO-1234ze (1,3,3,3-tetrafluoropropene) is added as a blowing agent. It is described that by producing polyurethane foam by such a method, the mixability of both compositions is improved and red phosphorus used as a flame retardant is prevented from being unevenly distributed in the foam. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-70409 A Summary of the Invention [Problem to be solved by the invention]

[0005] When the above-mentioned mixture of carbon dioxide and HFO-1234ze is added as a blowing agent to the polyol composition and / or polyisocyanate composition at the foam production site, the mixability of the two compositions is improved, the foaming ratio is increased, and the heat insulation properties are also improved. However, the above-mentioned method of using a mixture of carbon dioxide and HFO-1234ze as a foaming agent has a problem in that the initial reactivity during foam formation is poor, resulting in low adhesiveness.

[0006] Therefore, an object of the present invention is to provide a production method which has good mixability between a polyol composition and a polyisocyanate composition and is excellent in initial reactivity during formation of a polyurethane foam. [Means for solving the problem]

[0007] The present inventors have discovered that the above-mentioned problems can be solved by adding a metal carboxylate as a catalyst to a polyol composition in a method for producing a polyurethane foam, the method including a step of supplying a blowing agent containing a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0°C or less, via a system separate from that for supplying a polyol composition and a polyisocyanate composition, and have completed the present invention. That is, the present invention relates to the following [1] to [7].

[0008] [1] A method for producing a polyurethane foam by mixing a polyol composition containing a polyol and a catalyst, and a polyisocyanate composition containing a polyisocyanate, reacting them, and foaming and curing them, wherein the catalyst contains a metal carboxylate, and the method includes a step of supplying a blowing agent A in a system separate from the polyol composition and the polyisocyanate composition, the blowing agent A containing a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0°C or less, the blowing agent A being added to at least one of the polyol composition and the polyisocyanate composition in a ratio of 0.01 to 4 parts by mass per 100 parts by mass of polyol in the polyol composition, and the reaction proceeds after the addition. [2] The method for producing a polyurethane foam according to the above [1], wherein the hydrofluoroolefin having a boiling point of 0°C or less is HFO-1234ze. [3] The method for producing a polyurethane foam according to [1] or [2] above, wherein the metal carboxylate is at least one selected from the group consisting of bismuth carboxylates, lead carboxylates, tin carboxylates, and zinc carboxylates. [4] The method for producing a polyurethane foam according to any one of the above [1] to [3], wherein the metal carboxylate is a bismuth carboxylate. [5] The method for producing a polyurethane foam according to any one of the above [1] to [4], wherein the carbon dioxide contained in the blowing agent A is supercritical, subcritical or liquid carbon dioxide. [6] The method for producing a polyurethane foam according to any one of the above [1] to [5], wherein the polyol composition contains a blowing agent B. [7] The method for producing a polyurethane foam according to the above [6], wherein the blowing agent B contains a hydrofluoroolefin. Effect of the Invention

[0009] According to the method for producing a polyurethane foam of the present invention, the mixability of the polyol composition and the polyisocyanate composition is good, and the initial reactivity during the formation of the polyurethane foam is excellent, so that a polyurethane foam having excellent adhesion can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The method for producing a polyurethane foam of the present invention relates to a method for producing a polyurethane foam by mixing a polyol composition containing a polyol and a catalyst with a polyisocyanate composition containing a polyisocyanate, reacting the mixture, and foaming and curing the mixture. In the present invention, there is a step of supplying a blowing agent A in a system separate from the polyol composition and the polyisocyanate composition. The blowing agent A contains a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0°C or less, and the blowing agent A is added to at least one of the polyol composition and the polyisocyanate composition in a ratio of 0.01 to 4 parts by mass per 100 parts by mass of the polyol in the polyol composition, and the reaction proceeds after the addition. In the present invention, the catalyst contains a metal salt of a carboxylate.

[0011] The method for producing a polyurethane foam of the present invention includes a step of supplying a blowing agent A containing a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0° C. or less in a system separate from the polyol composition and the polyisocyanate composition. In other words, this means that at the production site where the polyurethane foam is produced, a flow path for supplying the blowing agent A is provided in addition to a flow path for supplying the polyol composition and a flow path for supplying the polyisocyanate, and the polyurethane foam is produced. In other words, the blowing agent A is not contained in the polyol composition or the polyisocyanate composition during storage, but is added to at least one of the polyol composition and the polyisocyanate composition immediately before the production of the polyurethane foam. In this way, by producing a polyurethane foam by supplying blowing agent A containing a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0°C or less in a system separate from both compositions at the production site, the mixability of the polyol composition and the polyisocyanate composition is improved, and a polyurethane foam with excellent physical properties is formed, with the density and other properties being easily uniform. Furthermore, in the production method of the present invention, since the polyol composition contains a metal carboxylate as a catalyst, the initial reactivity of the polyol and the polyisocyanate is increased, and the adhesiveness of the polyurethane foam formed is improved.

[0012] [Polyol composition] The polyol composition used in the process for producing a polyurethane foam of the present invention contains a polyol and a catalyst.

[0013] (catalyst) The catalyst used in the present invention contains a metal carboxylate. The inclusion of the metal carboxylate increases the initial reactivity of the polyol and the polyisocyanate, improving the adhesiveness of the resulting polyurethane foam. The metal carboxylate is a urethane catalyst used to promote the reaction between the polyol and the polyisocyanate. The carboxylic acid used in the carboxylate metal salt is not particularly limited as long as it is a compound having a carboxylic acid group, and examples thereof include saturated aliphatic carboxylic acids, unsaturated aliphatic carboxylic acids, aromatic carboxylic acids, and dicarboxylic acids. The saturated aliphatic carboxylic acid is a monocarboxylic acid, and examples thereof include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, 2-ethylhexanoic acid, pelargonic acid, capric acid, neodecanoic acid, naphthenic acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated aliphatic carboxylic acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid.

[0014] The metal used in the metal carboxylate is not particularly limited, but is preferably, for example, bismuth, lead, tin, zinc, etc. That is, the metal carboxylate in the present invention is preferably at least one selected from the group consisting of bismuth carboxylate, lead carboxylate, tin carboxylate, and zinc carboxylate.

[0015] Examples of the bismuth carboxylate include bismuth 2-ethylhexanoate, bismuth neodecanoate, and bismuth naphthenate. Examples of the lead carboxylate include lead 2-ethylhexanoate, lead benzoate, and lead naphthenate. Examples of the tin carboxylate include tin acetate, tin 2-ethylhexanoate, tin oleate, tin laurate, dibutyltin diacetate, dimethyltin dilaurate, dibutyltin dilaurate, dibutyltin dineodecanoate, and dioctyltin dilaurate. Examples of the zinc carboxylate include zinc 2-ethylhexanoate and zinc naphthenate.

[0016] Among the above, the metal carboxylate in the present invention is preferably a bismuth carboxylate from the viewpoints of improving initial reactivity and reducing the environmental load, and is particularly preferably bismuth 2-ethylhexanoate.

[0017] The content of the metal carboxylate in the polyol composition is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, and further preferably 1 to 8 parts by mass, based on 100 parts by mass of the polyol. When the content of the metal carboxylate is equal to or more than these lower limits, the initial reactivity is improved, and when it is equal to or less than these upper limits, the reaction is easily controlled.

[0018] In the present invention, a urethanization catalyst other than the metal carboxylate may be used in combination with the metal carboxylate. Examples of the urethanization catalyst other than the metal carboxylate include amine catalysts such as imidazole compounds and piperazine compounds. Examples of the imidazole compound include tertiary amines in which the secondary amine at the 1-position of the imidazole ring is substituted with an alkyl group, an alkenyl group, or the like. Specific examples include N-methylimidazole, 1,2-dimethylimidazole, 1-ethyl-2-methylimidazole, 1-methyl-2-ethylimidazole, 1,2-diethylimidazole, and 1-isobutyl-2-methylimidazole. In addition, examples include imidazole compounds in which the secondary amine in the imidazole ring is substituted with a cyanoethyl group. Furthermore, examples of the piperazine compound include tertiary amines such as N-methyl-N',N'-dimethylaminoethylpiperazine and trimethylaminoethylpiperazine. Examples of the amine catalyst include, in addition to imidazole compounds and piperazine compounds, various tertiary amines such as pentamethyldiethylenetriamine, triethylamine, N-methyldicyclohexylamine, N-methylmorpholinebis(2-dimethylaminoethyl)ether, N,N,N',N",N"-pentamethyldiethylenetriamine, N,N,N'-trimethylaminoethyl-ethanolamine, bis(2-dimethylaminoethyl)ether, N,N-dimethylcyclohexylamine, diazabicycloundecene, triethylenediamine, tetramethylhexamethylenediamine, and tripropylamine.

[0019] The content of the urethanization catalyst is, for example, 0.2 to 20 parts by mass, and preferably 1 to 10 parts by mass, relative to 100 parts by mass of the polyol.

[0020] The catalyst in the present invention preferably contains a trimerization catalyst in addition to the above-mentioned urethanization catalyst. The trimerization catalyst is a catalyst that reacts the isocyanate group contained in the polyisocyanate to trimerize it and promote the formation of an isocyanurate ring. As the trimerization catalyst, nitrogen-containing aromatic compounds such as tris(dimethylaminomethyl)phenol, 2,4-bis(dimethylaminomethyl)phenol, and 2,4,6-tris(dialkylaminoalkyl)hexahydro-S-triazine, carboxylic acid alkali metal salts such as potassium acetate, potassium 2-ethylhexanoate, and potassium octylate, tertiary ammonium salts such as trimethylammonium salt, triethylammonium salt, and triphenylammonium salt, tetramethylammonium salt, tetraethylammonium salt, tetraphenylammonium salt, triethylmonomethylammonium salt, and quaternary ammonium salts such as quaternary ammonium salts of carboxylate, and the like can be used. A preferred specific example of the carboxylic acid in the ammonium carboxylate is at least one selected from the group consisting of 2-ethylhexanoic acid, 2,2-dimethylpropanoic acid, acetic acid, and formic acid. The trimerization catalyst may be used alone or in combination of two or more types, but it is preferable to use two or more types in combination.

[0021] The content of the trimerization catalyst is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, and further preferably 1 to 5 parts by mass, based on 100 parts by mass of the polyol.

[0022] (Polyol) Examples of the polyol contained in the polyol composition include polylactone polyols, polycarbonate polyols, aromatic polyols, alicyclic polyols, polyester polyols, polymer polyols, and polyether polyols.

[0023] Examples of the polylactone polyol include polypropiolactone glycol, polycaprolactone glycol, and polyvalerolactone glycol. Examples of polycarbonate polyols include polyols obtained by dealcoholization reaction of hydroxyl group-containing compounds such as ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, octanediol, and nonanediol with ethylene carbonate, propylene carbonate, and the like.

[0024] Examples of aromatic polyols include bisphenol A, bisphenol F, phenol novolac, and cresol novolac. Examples of alicyclic polyols include cyclohexanediol, methylcyclohexanediol, isophoronediol, dicyclohexylmethanediol, and dimethyldicyclohexylmethanediol.

[0025] Examples of polyester polyols include polymers obtained by dehydration condensation of polybasic acids and polyhydric alcohols, and condensates of hydroxycarboxylic acids and the above-mentioned polyhydric alcohols. Examples of polybasic acids include adipic acid, azeoic acid, sebacic acid, isophthalic acid (m-phthalic acid), terephthalic acid (p-phthalic acid), and succinic acid. Examples of polyhydric alcohols include bisphenol A, ethylene glycol, 1,2-propylene glycol, 1,4-butanediol, diethylene glycol, 1,6-hexane glycol, and neopentyl glycol. Examples of hydroxycarboxylic acids include castor oil and reaction products of castor oil and ethylene glycol.

[0026] Examples of the polymer polyol include polymers obtained by graft polymerizing an ethylenically unsaturated compound such as acrylonitrile, styrene, methyl acrylate, or methacrylate with an aromatic polyol, an alicyclic polyol, an aliphatic polyol, or a polyester polyol, or polybutadiene polyol, or hydrogenated products thereof.

[0027] Examples of polyether polyols include polymers obtained by ring-opening polymerization of at least one alkylene oxide, such as ethylene oxide, propylene oxide, and tetrahydrofuran, in the presence of at least one low-molecular-weight active hydrogen compound having two or more active hydrogens. Examples of low-molecular-weight active hydrogen compounds having two or more active hydrogens include diols, such as bisphenol A, ethylene glycol, propylene glycol, butylene glycol, and 1,6-hexanediol; triols, such as glycerin and trimethylolpropane; and amines, such as ethylenediamine and butylenediamine.

[0028] The polyol used in the present invention preferably contains at least one selected from polyester polyols and polyether polyols, and more preferably contains at least a polyester polyol. Among them, it is more preferable to contain a polyester polyol obtained by dehydration condensation of a polybasic acid having an aromatic ring, such as isophthalic acid (m-phthalic acid) or terephthalic acid (p-phthalic acid), and a dihydric alcohol, such as bisphenol A, ethylene glycol, or 1,2-propylene glycol. The content of the polyester polyol in 100 parts by mass of the polyol is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, and even more preferably 90 parts by mass or more.

[0029] The hydroxyl value of the polyol is preferably 20 to 300 mgKOH / g, more preferably 30 to 275 mgKOH / g, and even more preferably 50 to 250 mgKOH / g. When the hydroxyl value of the polyol is equal to or less than the upper limit, the viscosity of the polyol liquid does not become excessively high, which is preferable from the viewpoint of handling, etc. On the other hand, when the hydroxyl value of the polyol is equal to or more than the lower limit, the crosslink density of the polyurethane foam increases, thereby increasing the strength. The hydroxyl value of the polyol can be measured in accordance with JIS K 1557-1:2007.

[0030] (Foaming agent B) The polyol composition of the present invention preferably contains a blowing agent B. The blowing agent B can promote the formation of a polyurethane foam by mixing and foaming the polyol composition and the polyisocyanate composition. Unlike the above-mentioned blowing agent A, the blowing agent B is not added immediately before the production of the polyurethane foam, but is blended in the polyol composition before the addition of the blowing agent A. The blowing agent B is not particularly limited, but preferably contains, for example, water, a hydrocarbon compound, a chlorinated aliphatic hydrocarbon compound, a hydrofluorocarbon, a hydrochlorofluorocarbon compound, a hydrofluoroolefin, etc. Among them, from the viewpoint of good foam formation and reducing the environmental load, it is preferable that the blowing agent B contains a hydrofluoroolefin. By containing a hydrofluoroolefin, when a filler described later is used, the dispersibility of the filler in the foam is improved. From the viewpoint of improving foaming properties, blowing agent B preferably contains water, and more preferably contains both water and a hydrofluoroolefin.

[0031] Examples of the hydrofluoroolefin contained in the blowing agent B include fluoroalkenes having 3 to 6 carbon atoms. The hydrofluoroolefin may be a hydrochlorofluoroolefin having a chlorine atom, and therefore may be a chlorofluoroalkene having 3 to 6 carbon atoms. The hydrofluoroolefin is preferably one having 3 or 4 carbon atoms.

[0032] The hydrofluoroolefin used as the blowing agent B is preferably one having a boiling point of more than 0°C at 1 atmospheric pressure, and examples thereof include (E)-1-chloro-3,3,3-trifluoropropene (HFO-1233zd(E)), (Z)-1-chloro-3,3,3-trifluoropropene (HFO-1233zd(Z)), (Z)-1,1,1,4,4,4-hexafluorobut-2-ene (HFO-1336mzz(Z)), (E)-1,1,1,4,4,4-hexafluorobut-2-ene (HFO-1336mzz(E)), (Z)-1-chloro-2,3,3,3-tetrafluoropropene (HFO-1224yd(Z)), and the like.

[0033] From the viewpoint of setting the density of the polyurethane foam in the desired range, the content of the hydrofluoroolefin used as blowing agent B is preferably 5 to 50 parts by mass, more preferably 10 to 40 parts by mass, and even more preferably 15 to 30 parts by mass, per 100 parts by mass of polyol.

[0034] The content of water used as blowing agent B is preferably 0.1 to 15 parts by mass, more preferably 0.2 to 10 parts by mass, and even more preferably 0.5 to 5 parts by mass, per 100 parts by mass of polyol, from the viewpoint of setting the density of the polyurethane foam in the desired range.

[0035] The content of blowing agent B in the polyol composition is preferably 0.1 to 65 parts by mass, more preferably 0.2 to 50 parts by mass, and even more preferably 0.5 to 35 parts by mass, per 100 parts by mass of polyol, from the viewpoint of setting the density of the polyurethane foam in a desired range.

[0036] (Filler) The polyol composition may contain a filler. By containing a filler, it is possible to impart a function according to the type of filler to the polyurethane foam. The filler preferably contains a flame retardant. By using a flame retardant as a filler, it is possible to impart high flame retardant performance to the polyurethane foam. The flame retardant used as the filler is preferably a solid flame retardant. By using a solid flame retardant, the flame retardancy can be more effectively improved. Note that a solid flame retardant is a flame retardant that is solid at room temperature (23°C) and normal pressure (1 atm).

[0037] From the viewpoint of more effectively enhancing flame retardancy, the solid flame retardant is preferably at least one selected from the group consisting of red phosphorus-based flame retardants, boron-containing flame retardants, bromine-containing flame retardants, phosphate-containing flame retardants, chlorine-containing flame retardants, antimony-containing flame retardants, metal hydroxides, and needle-shaped fillers.

[0038] <Red phosphorus flame retardant> The red phosphorus-based flame retardant may be made of red phosphorus alone, may be red phosphorus coated with a resin, a metal hydroxide, a metal oxide, or may be red phosphorus mixed with a resin, a metal hydroxide, a metal oxide, or the like. The resin that coats the red phosphorus or mixes with the red phosphorus is not particularly limited, but examples thereof include thermosetting resins such as phenol resin, epoxy resin, unsaturated polyester resin, melamine resin, urea resin, aniline resin, and silicone resin. From the viewpoint of flame retardancy, metal hydroxide is preferable as the compound to be coated or mixed. The metal hydroxide to be used may be appropriately selected from those described later.

[0039] The amount of the red phosphorus-based flame retardant is preferably 3 to 60 parts by mass, more preferably 10 to 50 parts by mass, and even more preferably 20 to 45 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the red phosphorus-based flame retardant equal to or greater than these lower limits, the effect of containing the red phosphorus-based flame retardant is easily exhibited. On the other hand, by making the amount equal to or less than the upper limits, foaming is not inhibited by the red phosphorus-based flame retardant.

[0040] <Boron-containing flame retardants> Examples of boron-containing flame retardants include borax, boron oxide, boric acid, borates, etc. Examples of boron oxide include diboron trioxide, boron trioxide, diboron dioxide, tetraboron trioxide, and tetraboron pentoxide. Examples of borates include borates of alkali metals, alkaline earth metals, elements of Groups 4, 12, and 13 of the periodic table, and ammonium. Specific examples include alkali metal borates such as lithium borate, sodium borate, potassium borate, and cesium borate, alkaline earth metal borates such as magnesium borate, calcium borate, and barium borate, zirconium borate, zinc borate, aluminum borate, and ammonium borate. The boron-containing flame retardants may be used alone or in combination of two or more kinds. Preferably, the boron-containing flame retardant is a borate, more preferably zinc borate.

[0041] The amount of the boron-containing flame retardant is not particularly limited, but is preferably 3 to 45 parts by mass, more preferably 5 to 40 parts by mass, and even more preferably 10 to 25 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the boron-containing flame retardant equal to or more than these lower limits, the effect of the boron-containing flame retardant is easily exhibited, and flame retardancy is improved. On the other hand, by making the amount equal to or less than the upper limits, foaming is not inhibited by the boron-containing flame retardant.

[0042] <Bromine-containing flame retardants> The bromine-containing flame retardant is not particularly limited as long as it contains bromine in its molecular structure and is a solid at room temperature and pressure. Examples of the bromine-containing flame retardant include brominated aromatic ring-containing aromatic compounds. Examples of the brominated aromatic ring-containing aromatic compound include monomeric organic bromine compounds such as hexabromobenzene, pentabromotoluene, hexabromobiphenyl, decabromobiphenyl, decabromodiphenyl ether, octabromodiphenyl ether, hexabromodiphenyl ether, bis(pentabromophenoxy)ethane, ethylene bis(pentabromophenyl), ethylene bis(tetrabromophthalimide), and tetrabromobisphenol A.

[0043] In addition, the brominated aromatic ring-containing aromatic compound may be a bromine compound polymer.Specific examples include brominated polycarbonates such as polycarbonate oligomers produced from brominated bisphenol A as a raw material, copolymers of this polycarbonate oligomer and bisphenol A, and diepoxy compounds produced by the reaction of brominated bisphenol A and epichlorohydrin.Furthermore, examples include brominated epoxy compounds such as monoepoxy compounds obtained by the reaction of brominated phenols and epichlorohydrin, poly(brominated benzyl acrylate), brominated phenol condensates of brominated polyphenylene ether, brominated bisphenol A, and cyanuric chloride, brominated (polystyrene), poly(brominated styrene), brominated polystyrene such as crosslinked brominated polystyrene, crosslinked or non-crosslinked brominated poly(-methylstyrene), and the like. In addition, compounds other than brominated aromatic ring-containing aromatic compounds such as hexabromocyclododecane may be used. These bromine-containing flame retardants may be used alone or in combination of two or more. Among the above, brominated aromatic ring-containing aromatic compounds are preferred, and among them, monomeric organic bromine compounds such as ethylenebis(pentabromophenyl) are preferred.

[0044] The amount of the bromine-containing flame retardant is preferably 3 to 60 parts by mass, more preferably 10 to 50 parts by mass, and even more preferably 20 to 45 parts by mass, based on 100 parts by mass of the polyol. By making the amount of the bromine-containing flame retardant equal to or greater than these lower limits, the effect of the inclusion of the bromine-containing flame retardant is easily exhibited. On the other hand, by making the amount equal to or less than the upper limits, foaming is not inhibited by the bromine-containing flame retardant.

[0045] <Phosphate-containing flame retardants> Examples of the phosphate-containing flame retardant include phosphates consisting of salts of various phosphoric acids and at least one metal or compound selected from metals in Groups IA to IVB of the periodic table, ammonia, aliphatic amines, aromatic amines, and heterocyclic compounds containing nitrogen in the ring. The phosphoric acid is not particularly limited, but examples thereof include monophosphoric acid, pyrophosphoric acid, and polyphosphoric acid. Examples of metals in Groups IA to IVB of the periodic table include lithium, sodium, calcium, barium, iron (II), iron (III), and aluminum. Examples of the aliphatic amine include methylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, piperazine, etc. Examples of the aromatic amine include aniline, o-triidine, 2,4,6-trimethylaniline, anisidine, 3-(trifluoromethyl)aniline, etc. Examples of the heterocyclic compound containing nitrogen in the ring include pyridine, triazine, melamine, etc.

[0046] Specific examples of phosphate-containing flame retardants include monophosphates such as aluminum triphosphate, pyrophosphates, polyphosphates, etc. Here, the polyphosphates are not particularly limited, but include, for example, ammonium polyphosphate, piperazine polyphosphate, melamine polyphosphate, ammonium amide polyphosphate, aluminum polyphosphate, etc. The phosphate-containing flame retardant may be used alone or in combination of two or more of the above-mentioned compounds.

[0047] The amount of the phosphate-containing flame retardant is not particularly limited, but is 3 to 40 parts by mass, more preferably 5 to 35 parts by mass, and even more preferably 10 to 30 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the phosphate-containing flame retardant equal to or greater than these lower limits, the effect of the inclusion of the phosphate-containing flame retardant is easily exhibited. On the other hand, by making the amount equal to or less than the upper limits, foaming is not inhibited by the phosphate-containing flame retardant.

[0048] <Chlorine-containing flame retardants> Chlorine-containing flame retardants include those commonly used in flame-retardant resin compositions, such as polychlorinated naphthalenes, chlorendic acid, and dodecachlorododecahydrodimethanodibenzocyclooctene sold under the trade name "Dechlorane Plus." The blending amount of the chlorine-containing flame retardant is not particularly limited, but is preferably 3 to 40 parts by mass, more preferably 5 to 35 parts by mass, and even more preferably 10 to 30 parts by mass, relative to 100 parts by mass of the polyol. By making the blending amount of the chlorine-containing flame retardant equal to or more than these lower limit values, the effect of containing the chlorine-containing flame retardant is easily exhibited. On the other hand, by making it equal to or less than the upper limit values, foaming is not inhibited by the chlorine-containing flame retardant.

[0049] <Antimony-containing flame retardants> Examples of antimony-containing flame retardants include antimony oxide, antimony salts, and pyroantimony salts. Examples of antimony oxide include antimony trioxide and antimony pentoxide. Examples of antimony salts include sodium antimonate and potassium antimonate. Examples of pyroantimonate include sodium pyroantimonate and potassium pyroantimonate. The antimony-containing flame retardants may be used alone or in combination of two or more. The preferred antimony-containing flame retardant for use in the present invention is antimony trioxide.

[0050] The amount of the antimony-containing flame retardant is not particularly limited, but is preferably 1 to 40 parts by mass, more preferably 2 to 35 parts by mass, and even more preferably 3 to 30 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the antimony-containing flame retardant equal to or greater than these lower limits, the effect of the inclusion of the antimony-containing flame retardant is easily exhibited, and flame retardancy is improved. On the other hand, by making the amount equal to or less than the upper limits, foaming is not inhibited by the antimony-containing flame retardant.

[0051] <Metal hydroxide> Examples of metal hydroxides used in the present invention include magnesium hydroxide, calcium hydroxide, aluminum hydroxide, iron hydroxide, nickel hydroxide, zirconium hydroxide, titanium hydroxide, zinc hydroxide, copper hydroxide, vanadium hydroxide, tin hydroxide, etc. The metal hydroxides may be used alone or in combination of two or more kinds.

[0052] The amount of the metal hydroxide is, for example, 0.1 to 50 parts by mass, preferably 0.2 to 30 parts by mass, more preferably 0.3 to 20 parts by mass, and even more preferably 0.5 to 15 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the metal hydroxide equal to or more than these lower limits, the effect of the inclusion of the metal hydroxide is easily exhibited, and the flame retardancy is improved. On the other hand, by making the amount equal to or less than the upper limits, foaming is not inhibited by the metal hydroxide.

[0053] <Needle filler> Examples of needle-like fillers include potassium titanate whiskers, aluminum borate whiskers, magnesium-containing whiskers, silicon-containing whiskers, wollastonite, sepiolite, zonolite, elestadite, boehmite, rod-shaped hydroxyapatite, glass fibers, carbon fibers, graphite fibers, metal fibers, slag fibers, gypsum fibers, silica fibers, alumina fibers, silica alumina fibers, zirconia fibers, boron nitride fibers, boron fibers, and stainless steel fibers. These needle-like fillers can be used alone or in combination of two or more.

[0054] The aspect ratio (length / diameter) of the needle-like filler used in the present invention is preferably in the range of 5 to 50, and more preferably in the range of 10 to 40. The aspect ratio can be determined by observing the needle-like filler with a scanning electron microscope and measuring its length and width.

[0055] The amount of the needle-like filler is, for example, 10 to 100 parts by mass, preferably 20 to 90 parts by mass, more preferably 30 to 80 parts by mass, and further preferably 40 to 70 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the needle-like filler equal to or greater than these lower limits, the shape of the polyurethane foam after combustion is easily maintained. On the other hand, by making the amount equal to or less than these upper limits, foaming is less likely to be hindered by the needle-like filler.

[0056] The amount of the solid flame retardant is not particularly limited, but is, for example, 10 to 200 parts by mass, preferably 20 to 150 parts by mass, and more preferably 40 to 120 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the solid flame retardant equal to or greater than these lower limits, it is possible to impart appropriate flame retardancy to the polyurethane foam. By making the amount of the solid flame retardant equal to or less than these upper limits, it is possible to easily obtain a polyurethane foam with a small density difference depending on the location.

[0057] As the filler, inorganic fillers other than the above-mentioned flame retardants may be blended. As the inorganic filler, alumina, titanium oxide, calcium oxide, magnesium oxide, iron oxide, tin oxide, ferrites, basic magnesium carbonate, calcium carbonate, magnesium carbonate, zinc carbonate, barium carbonate, dawsonite, hydrotalcite, calcium sulfate, barium sulfate, calcium silicate, talc, mica, montmorillonite, bentonite, activated clay, imogolite, sericite, glass beads, aluminum nitride, boron nitride, silicon nitride, various metal powders, magnesium sulfate, lead zirconate titanate, molybdenum sulfide, silicon carbide, various magnetic powders, fly ash, etc. may be appropriately used. The inorganic filler may be used alone or in combination of two or more.

[0058] The content of the filler in the polyol composition is, for example, 10 to 300 parts by mass, preferably 20 to 150 parts by mass, and more preferably 40 to 120 parts by mass, relative to 100 parts by mass of the polyol. By making the amount of the filler blended equal to or greater than these lower limits, it becomes easier to impart a function to the polyurethane foam according to the type of filler. By making the amount of the filler blended equal to or less than these upper limits, it becomes easier to obtain a polyurethane foam with less density difference depending on the location.

[0059] (Liquid flame retardant) The polyol composition may contain a liquid flame retardant. The liquid flame retardant is a flame retardant that is liquid at room temperature (23°C) and normal pressure (1 atm). A specific example of the liquid flame retardant is a phosphoric acid ester. Unlike a solid flame retardant, the liquid flame retardant is less likely to cause precipitation during storage and is easy to handle.

[0060] As the phosphoric acid ester, it is preferable to use a monophosphoric acid ester, a condensed phosphoric acid ester, etc. Examples of the monophosphoric acid ester include trialkyl phosphates such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, and tri(2-ethylhexyl)phosphate, halogen-containing phosphoric acid esters such as tris(β-chloropropyl)phosphate, trialkoxy phosphates such as tributoxyethyl phosphate, aromatic ring-containing phosphoric acid esters such as tricresyl phosphate, trixylenyl phosphate, tris(isopropylphenyl)phosphate, cresyl diphenyl phosphate, and diphenyl(2-ethylhexyl)phosphate, and acidic phosphoric acid esters such as monoisodecyl phosphate and diisodecyl phosphate.

[0061] Examples of the condensed phosphate ester include aromatic condensed phosphate esters such as trialkyl polyphosphate, resorcinol polyphenyl phosphate, bisphenol A polycresyl phosphate, and bisphenol A polyphenyl phosphate. Commercially available condensed phosphate esters include, for example, "CR-733S", "CR-741", and "CR747" manufactured by Daihachi Chemical Industry Co., Ltd., and "ADEKA STAB PFR" and "FP-600" manufactured by ADEKA Corporation.

[0062] The liquid flame retardant may be one of the above-mentioned compounds, or two or more of them may be used in combination. Among them, from the viewpoint of facilitating the production of polyurethane foam and improving the flame retardancy of the polyurethane foam, monophosphate ester is preferred, and tris(β-chloropropyl)phosphate is more preferred.

[0063] When a liquid flame retardant is contained, the blending amount thereof is preferably from 5 to 80 parts by mass, more preferably from 10 to 70 parts by mass, and further preferably from 20 to 60 parts by mass, based on 100 parts by mass of the polyol.

[0064] (Foam stabilizer) The polyol composition preferably contains a foam stabilizer, which improves the foamability of the polyurethane composition obtained by mixing the polyol composition and the polyisocyanate composition. Examples of the foam stabilizer include surfactants such as polyoxyalkylene-based foam stabilizers such as polyoxyalkylene alkyl ethers, and silicone-based foam stabilizers such as organopolysiloxanes. These foam stabilizers may be used alone or in combination of two or more. The amount of the foam stabilizer is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and even more preferably 1 to 5 parts by mass, based on 100 parts by mass of the polyol. When the amount of the foam stabilizer is equal to or greater than these lower limits, the polyurethane composition is easily foamed, and a homogeneous polyurethane foam is easily obtained. When the amount of the foam stabilizer is equal to or less than these upper limits, the balance between the production cost and the obtained effect is good.

[0065] (Other ingredients) The polyol liquid may contain one or more additives selected from additives such as phenol-based, amine-based, and sulfur-based antioxidants, heat stabilizers, metal damage inhibitors, antistatic agents, stabilizers, crosslinking agents, lubricants, softeners, pigments, and tackifying resins, tackifiers such as polybutene and petroleum resins, etc., as necessary, within the scope of the present invention.

[0066] [Polyisocyanate composition] The polyisocyanate composition used in the method for producing a polyurethane foam of the present invention contains a polyisocyanate. As the polyisocyanate, any known polyisocyanate used in the formation of polyurethane foam can be used, such as an aromatic polyisocyanate, an alicyclic polyisocyanate, and an aliphatic polyisocyanate. Examples of aromatic polyisocyanates include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, dimethyldiphenylmethane diisocyanate, triphenylmethane triisocyanate, naphthalene diisocyanate, and polymethylene polyphenyl polyisocyanate.

[0067] Examples of the alicyclic polyisocyanate include cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and dimethyldicyclohexylmethane diisocyanate.

[0068] Examples of the aliphatic polyisocyanate include methylene diisocyanate, ethylene diisocyanate, propylene diisocyanate, tetramethylene diisocyanate, and hexamethylene diisocyanate.

[0069] Among these, from the viewpoints of ease of use and availability, aromatic polyisocyanates are preferred, and diphenylmethane diisocyanate is more preferred. The polyisocyanates may be used alone or in combination of two or more.

[0070] (Isocyanate Index) The isocyanate index of the polyurethane composition obtained by mixing the polyol composition and the polyisocyanate composition of the present invention is not particularly limited, but is preferably 120 to 500, more preferably 150 to 400. If the isocyanate index is equal to or greater than the lower limit, the amount of polyisocyanate relative to the polyol becomes excessive, which makes it easier for isocyanurate bonds to be formed by the trimer of the polyisocyanate, thereby improving the flame retardancy of the polyurethane foam. If the isocyanate index is equal to or less than the upper limit, the balance between the flame retardancy and production cost of the resulting polyurethane foam is good.

[0071] The isocyanate index can be calculated by the following method. Isocyanate Index = equivalents of polyisocyanate ÷ (equivalents of polyol + equivalents of water) × 100 Here, each equivalent number can be calculated as follows: Equivalent number of polyisocyanate = Amount of polyisocyanate used (g) × NCO content (mass%) / Molecular weight of NCO (mol) × 100 Equivalent weight of polyol = OHV × amount of polyol used (g) ÷ molecular weight of KOH (mmol) OHV is the hydroxyl value of the polyol (mg KOH / g). Equivalents of water = amount of water used (g) / molecular weight of water (mol) × number of OH groups in water In the above formulas, the molecular weight of NCO is 42 (mol), the molecular weight of KOH is 56100 (mmol), the molecular weight of water is 18 (mol), and the number of OH groups in water is 2.

[0072] [Step of supplying foaming agent A] The method for producing a polyurethane foam of the present invention includes a step of supplying a blowing agent A in a system separate from the polyol composition and the polyisocyanate composition. In other words, at a production site where a polyurethane foam is produced, a flow path for supplying a blowing agent A is provided separately from a flow path for supplying a polyol composition and a flow path for supplying a polyisocyanate, and a polyurethane foam is produced. By producing a polyurethane foam at the production site by supplying a blowing agent A in a system separate from both compositions in this way, the mixability of the polyol composition and the polyisocyanate composition is improved, and the density and the like are easily uniform, and a polyurethane foam having excellent physical properties is formed.

[0073] In the present invention, a polyurethane foam is produced by mixing a polyol composition and a polyisocyanate composition, reacting them, and foaming and curing them. The foaming agent A may be supplied to either the polyol composition or the polyisocyanate composition before mixing the polyol composition and the polyisocyanate composition, but it is preferable to supply the foaming agent A to the polyol composition in consideration of ease of foam formation. The foaming agent A may be mixed at the same time as the polyol composition and the polyisocyanate composition are mixed (i.e., the foaming agent A may be supplied to the position where both compositions are mixed).

[0074] The blowing agent A includes a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0°C or less. The carbon dioxide is supercritical, subcritical, or liquid carbon dioxide. Supercritical, subcritical, or liquid carbon dioxide is carbon dioxide gas that is pressurized at a predetermined temperature to be in a supercritical state, subcritical state, or liquid state. Specifically, carbon dioxide in a supercritical state is carbon dioxide in a fluid state where both the pressure and temperature exceed the critical points of the critical pressure and critical temperature or higher. Carbon dioxide in a subcritical state is carbon dioxide in a liquid state where the pressure is equal to or higher than the critical pressure and the temperature is lower than the critical pressure and the temperature is higher than the critical temperature, or carbon dioxide in a state where the temperature and pressure are lower than the critical points but close to them. Furthermore, liquid carbon dioxide is carbon dioxide that has been liquefied under temperature and pressure conditions of the triple point or higher. The mass ratio of carbon dioxide to hydrofluoroolefin having a boiling point of 0°C or less in the mixture (carbon dioxide / hydrofluoroolefin having a boiling point of 0°C or less) is not particularly limited, but from the viewpoint of improving the mixability of the composition, it is, for example, 0.05 to 5, preferably 0.1 to 2, and more preferably 0.2 to 1.

[0075] Examples of hydrofluoroolefins having a boiling point of 0°C or less include 1,3,3,3-tetrafluoropropene (HFO-1234ze), 1,2,3,3,3-pentafluoropropene (HFO-1225ye), 1,1,1,3,3-pentafluoropropene (HFO-1225zc), and 2,3,3,3-tetrafluoropropene (HFO-1234yf). Hydrofluoroolefins having a boiling point of 0°C or less may be used alone or in combination of two or more. Among these, HFO-1234ze is preferred as a hydrofluoroolefin having a boiling point of 0°C or less. That is, the blowing agent A preferably contains a mixture of carbon dioxide and HFO-1234ze, and more preferably consists of only carbon dioxide and HFO-1234ze. In this specification, the boiling point means the boiling point at 1 atmospheric pressure.

[0076] The foaming agent A may be added to at least one of the polyol composition and the polyisocyanate composition before mixing the polyol composition and the polyisocyanate composition, but is preferably supplied to the polyol composition in consideration of ease of foam formation, etc. The foaming agent A may be added simultaneously with mixing the polyol composition and the polyisocyanate composition (i.e., the foaming agent A may be supplied to the position where both compositions are mixed). The foaming agent A is added to at least one of the polyol composition and the polyisocyanate composition in a ratio of 0.01 to 4 parts by mass relative to 100 parts by mass of the polyol in the polyol composition. If the amount of foaming agent A added is less than 0.01 parts by mass, the mixability of the polyol composition and the polyisocyanate composition decreases. If the amount of foaming agent A added is more than 4 parts by mass, it is likely to adversely affect the foaming characteristics. From this viewpoint, the amount of foaming agent A added is preferably 0.1 to 3 parts by mass, more preferably 0.2 to 2 parts by mass, relative to 100 parts by mass of the polyol. After the addition of the blowing agent A, the polyol in the polyol composition and the polyisocyanate in the polyisocyanate composition react with each other, foaming and curing to form a polyurethane foam.

[0077] In the present invention, when the polyol composition and the polyisocyanate composition are mixed and foamed and cured, various known methods for producing polyurethane foams can be used. For example, various methods such as coating, injection, and spraying can be applied. Specifically, there are a method of applying a polyurethane composition obtained by mixing a polyol composition and a polyisocyanate composition to an adherend, foaming and curing, a method of injecting a polyurethane composition into a structure having a cavity, foaming and curing, and a method of spraying the polyurethane composition onto an adherend. A spraying device equipped with a carbon dioxide supplying device can be used for spraying. Specifically, the temperature of a polyol composition and a polyisocyanate composition in separate containers is adjusted in the spraying device, a blowing agent A is supplied to either of the compositions by the carbon dioxide supplying device, and then the two compositions are mixed by collision at the tip of a spray gun, and the mixed liquid is misted by air pressure. EXAMPLES

[0078] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. The components used in the examples and comparative examples are shown below.

[0079] <Polyol> (A-1) Polyester polyol (manufactured by Kawasaki Chemical Industries, Ltd., product name: Maximol RLK-087, hydroxyl value 200 mg KOH / g) (A-2) Polyester polyol (manufactured by Kawasaki Chemical Industries, Ltd., product name: Maximol RFK-505, hydroxyl value = 250 mg KOH / g) (A-3) Polyester polyol (manufactured by Kawasaki Chemical Industries, Ltd., product name: Maximol RFK-509, hydroxyl value = 200 mg KOH / g)

[0080] <Urethane catalyst> (B-1) Bismuth carboxylate: Bismuth 2-ethylhexanoate (manufactured by Nitto Kasei Co., Ltd., product name: Bi28), concentration 81 to 90% by mass (B-2) Tin carboxylate Tin 2-ethylhexanoate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (B-3) Amine catalyst: N-methyldicyclohexylamine (manufactured by Evonik Japan, product name: Polycat 12)

[0081] <Trimerization catalyst> - Quaternary ammonium carboxylate (DABCO TMR-7, manufactured by Evonik Japan Co., Ltd.), concentration 45 to 55% by mass

[0082] <Foam stabilizer> (C-1) Polyoxyalkylene foam stabilizer (SH-193, manufactured by Toray Dow Corning Co., Ltd.)

[0083] <Foaming agent B> (D-1) HFO-1233zd(E) (Solstice LBA manufactured by Central Glass Co., Ltd.) (D-2) HFO-1336mzz(Z) (Opteon 1100 manufactured by Chemours) water

[0084] <Foaming agent A> A mixture of liquid carbon dioxide and HFO-1234ze. Manufactured by Tokyo Koatsu Yamazaki Co., Ltd. Liquid CO2:HFO-1234ze = 3:7 (weight ratio)

[0085] <Polyisocyanate> Polyisocyanate (MDI, manufactured by Sumitomo Chemical Co., Ltd., product name: Sumidur 44V20)

[0086] The evaluation method is as follows. <Mixability> In each of the Examples and Comparative Examples, the polyol composition and the polyisocyanate composition were sprayed onto a slate board, and then the two compositions were visually observed to see whether they were mixed. 〇: The mixture was uniform and had good mixability. △ Some unmixed areas were observed. ×: There were many unmixed areas and mixing was poor. <Cream Time> In each of the Examples and Comparative Examples, the polyol composition and the polyisocyanate composition were sprayed onto a slate board, and the time until the color changed to white (cream time) was measured and used as an index of initial reactivity. The shorter the cream time, the higher the initial reactivity.

[0087] [Examples 1 to 8] On-site foaming spraying equipment equipped with a liquefied carbon dioxide supply device (manufactured by Asahi Yukizai Co., Ltd., product name: A polyurethane foam was formed using a polyurethane foaming agent (AYK-1000 series) as follows. A polyol composition was prepared by mixing the polyol, urethane catalyst, trimerization catalyst, foam stabilizer, and blowing agent B shown in Table 1. In the flow path of the polyol composition, the blowing agent A (liquid CO2 / HFO-1234ze) in the amount shown in Table 1 was supplied to the polyol composition and mixed, and then the polyol composition mixed with the blowing agent A and a polyisocyanate composition consisting of polyisocyanate (MDI) were contact-mixed at a volume ratio of 1:1 to obtain a mixture (polyurethane composition). After contact-mixing, the mixture (polyurethane composition) was continuously sprayed onto the surface of a slate board (size 900 mm x 900 mm) to foam and harden, thereby producing a polyurethane foam.

[0088] [Comparative Example 1] A polyurethane foam was produced in the same manner as in the example, except that blowing agent A (liquid CO2 / HFO-1234ze) was not used.

[0089] [Comparative Example 2] A polyurethane foam was prepared in the same manner as in the Example, except that an amine catalyst was used instead of a metal carboxylate as the urethanization catalyst.

[0090] [Table 1]

[0091] From the results of each example, it was found that in the manufacturing method of the present invention, the polyol composition and the polyisocyanate composition have good mixability, and the cream time is short, resulting in high initial reactivity. In contrast, in Comparative Example 1, in which the blowing agent A (liquid CO2 / HFO-1234ze) was not used, the mixability of the polyol composition and the polyisocyanate composition was poor. In addition, in Comparative Example 2, in which the carboxylate metal salt was not used, the cream time was long and the initial reactivity was low.

Claims

1. A method for producing a polyurethane foam by mixing a polyol composition containing a polyol and a catalyst with a polyisocyanate composition containing a polyisocyanate, reacting the mixture, and foaming and curing the mixture, comprising the steps of: the catalyst comprises a metal carboxylate; A step of supplying a foaming agent A in a system separate from the polyol composition and the polyisocyanate composition, The blowing agent A contains a mixture of carbon dioxide and a hydrofluoroolefin having a boiling point of 0° C. or less, The foaming agent A is added to at least one of a polyol composition and a polyisocyanate composition in an amount of 0.01 to 4 parts by mass per 100 parts by mass of the polyol in the polyol composition, and the reaction proceeds after the addition.

2. The method for producing a polyurethane foam according to claim 1, wherein the hydrofluoroolefin having a boiling point of 0° C. or less is HFO-1234ze.

3. The method for producing a polyurethane foam according to claim 1 or 2, wherein the metal carboxylate is at least one selected from the group consisting of bismuth carboxylates, lead carboxylates, tin carboxylates, and zinc carboxylates.

4. The method for producing a polyurethane foam according to any one of claims 1 to 3, wherein the metal carboxylate is a bismuth carboxylate.

5. The method for producing a polyurethane foam according to any one of claims 1 to 4, wherein the carbon dioxide contained in the blowing agent A is supercritical, subcritical or liquid carbon dioxide.

6. The method for producing a polyurethane foam according to any one of claims 1 to 5, wherein the polyol composition contains a blowing agent B.

7. The method for producing a polyurethane foam according to claim 6, wherein the blowing agent B contains a hydrofluoroolefin.

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