WO2025026744A1

WO2025026744A1 - Water blown low density spray foam having good mechanical properties and a high dimensional stability

Info

Publication number: WO2025026744A1
Application number: PCT/EP2024/070304
Authority: WO
Inventors: Josep-Daniel ESLAVA; Adria MALAGON RODRIGUEZ; Roel GUNNINK
Original assignee: Basf Se
Priority date: 2023-07-28
Filing date: 2024-07-17
Publication date: 2025-02-06

Abstract

The present invention relates to a method for the production of a polyurethane spray foam having a density of less than 50 g/dm³ and a closed cell content of at least 85 %, by mixing the following to give a reaction mixture (a) polyisocyanates comprising PMDI, (b) compounds having at least two hydrogen atoms reactive toward isocyanate groups, comprising (b1) at least one polyether polyol obtained by alcoxylation of two or three functional starter molecules having a hydroxyl value of 100 to 200 mg KOH/g, (b2) at least one polyether polyol obtained by alcoxylation of an aliphatic diamine and (b3) at least one polyether polyol obtained by alcoxylation of sugar alcohol, wherein the amount of the polyol (b2) is at least 30 % by weight, based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b), (c) catalyst comprising at least one amine catalyst (c1) and at least one metal based catalyst (c2), (d) blowing agent, comprising 3 to 6 % by weight of water, based on the total weight of components (b) to (e), (e) optionally flame retardant, (f) optionally auxiliaries and additional substances, and spraying the reaction mixture onto a substrate and allowing said reaction mixture to harden to give the polyurethane spray foam. The present invention is further directed to a polyurethane spray foam obtainable according to a method according to the present invention.

Description

Water blown low density spray foam having good mechanical properties and a high dimensional stability

Numerous publications in the patent literature and other literature describe the known production of polyurethane foams, in particular of rigid polyurethane foams, via reaction of polyisocyanates with compounds having at least two hydrogen atoms reactive toward isocyanate groups, in particular with polyether polyols from alkylene oxide polymerization or with polyester polyols from the polycondensation of alcohols with dicarboxylic acids, in the presence of polyurethane catalysts, blowing agents and other auxiliaries and additional substances.

Polyurethane spray foams are polyurethane foams applied directly in situ by spraying. The main applications of polyurethane spray foams are found in the construction industry, acoustic absorbance or thermal insulation, for example in roof insulation.

It is known that, for example by adjusting polarity of the educts for the production of a polyurethane foam, the content of closed cells can be adjusted. Typical additives for adjusting the closed cell content are silicon-based foam stabilizers. In addition, closed cell content can be adjusted by selection of polyols with specific polarities. Especially for insulation purposes a high content of closed cells is advantageous. In addition, a high closed cell content provides an improved water tightness. It is known that the polyurethane foam industry uses chemical and/or physical blowing agents to foam the polymer as it forms. Physical blowing agents have a low boiling point and are therefore converted to the gaseous state by the heat of reaction.

Physical blowing agents mainly used hitherto have comprised chlorofluorocarbons. However, these have now been banned in many parts of the world because of their action in damaging the ozone layer. Physical blowing agents mainly used nowadays comprise fluorinated hydrocarbons, HFCs, fluorinated olefines, HFO’s, and low-boiling-point hydrocarbons, such as pentanes. The shelf life of the respective component is a criterion here and also flammability of the hydrocarbons. In addition, HFC’s and HFO’s are expensive. Therefore, there was a need to replace physical blowing agents at least partly.

Chemical blowing agents are blowing agents that react with the isocyanate function to form a gas, in case of water as chemical blowing agent carbon dioxide is formed. Physical blowing agents are usually larger molecules with low diffusion coefficient and stay in formed closed cells. In contrast, chemical blowing agents have a low diffusion coefficient. Especially carbon dioxide escapes out of closed cells faster than the surrounding air can diffuse into the cells creating a vacuum of up to 0.5 bar. This vacuum creates a pressure on the foam resulting in a shrinkage. Especially if the foam matrix is not strong, for example for low density water blown closed cell foams, shrinkage is a problem.

It was object of the present invention to provide a closed cell polyurethane spray foam having a closed cell content of at least 85% according to ISO 4590 with a density of below 50 g/dm³, which is obtained by the application of water as main blowing agent.

The object of the present invention has been solved by a polyurethane spray foam having a density of less than 50 g/dm³ and a closed cell content of at least 85 %, which is obtainable by mixing (a) polyisocyanates comprising PMDI, (b) compounds having at least two hydrogen atoms reactive toward isocyanate groups, comprising (b1) at least one polyether polyol obtained by alcoxylation of two or three functional starter molecules having a hydroxyl value of 100 to 200 mg KOH/g, (b2) at least one polyether polyol obtained by alcoxylation of an aliphatic diamine and (b3) at least one polyether polyol obtained by alcoxylation of sugar alcohol, wherein the amount of the polyol (b2) is at least 30 % by weight, based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b), (c) catalyst comprising at least one amine catalyst (c1) and at least one metal based catalyst (c2), (d) blowing agent, comprising 3 to 6 % by weight of water, based on the total weight of components (b) to (e), (e) optionally flame retardant, (f) optionally auxiliaries and additional substances, to give a reaction mixture and spraying the reaction mixture onto a substrate and allowing said reaction mixture to harden to give the polyurethane spray foam. The present invention is further directed to a method for the production of polyurethane spray foam according to the present invention by mixing (a) polyisocyanates comprising PMDI, (b) compounds having at least two hydrogen atoms reactive toward isocyanate groups, comprising (b1) at least one polyether polyol obtained by alcoxylation of two or three functional starter molecules having a hydroxyl value of 100 to 200 mg KOH/g, (b2) at least one polyether polyol obtained by alcoxylation of an aliphatic diamine and (b3) at least one polyether polyol obtained by alcoxylation of sugar alcohol, wherein the amount of the polyol (b2) is at least 30 % by weight, based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b), (c) catalyst comprising at least one amine catalyst (c1) and at least one metal based catalyst (c2), (d) blowing agent, comprising 3 to 6 % by weight of water, based on the total weight of components (b) to (e), (e) optionally flame retardant, (f) optionally auxiliaries and additional substances, to give a reaction mixture and spraying the reaction mixture onto a substrate and allowing said reaction mixture to harden to give the polyurethane spray foam.

The present invention concerns polyurethane spray foams which are applied to the substrate directly in situ by spraying of the reaction mixture onto the substrate, the substrate being by way of example part of a building, for example a wall or a ceiling and especially preferred a roof or parts of a roof of a building.

The polyurethane spray foam according to the invention has a density of 50 g/dm³, preferably 20 to 49 g/dm³, more preferred 30 to 48 g/dm³ and especially preferred 35 to 45 g/dm³. According to the present invention, density of a polyurethane foam is measured according to EN 14315-2-C. In addition, the polyurethane spray foam according to the invention has a closed cell content of at least 85%, preferably 90 to 100 % and more preferred 91 to 95 %, measured according to ISO 4590. Preferably the compression strength of a polyurethane spray foam according to the present invention determined at a compression of 10 % of its thickness and in the perpendicular direction of the insulation faces according to EN 826 is 200 kPa or more, preferably 220 kPa or more and especially preferred 250 kPa and more. The dimensional stability of a polyurethane spray foam according to the invention determined according to EN 14315-1 :2013 fulfils preferably at least the requirements of DS(TH)3, more preferred of DS(TH)4. In addition, the polyurethane spray foam according to the present invention preferably shows a deformation under load of 70 kPa and 70 °C for the duration of 1 week according to EN 14315-1 :2013 of 10 % or less, preferably 5 % or less and especially 3 % or less. Polyisocyanate (a) used comprises polymeric diphenylmethane diisocyanate. Diphenylmethane diisocyanate is also termed “MDI” hereinafter. Polymeric MDI is a mixture of MDI comprising two aromatic rings with MDI homologs comprising a larger number of aromatic rings, for example homologs comprising 3, 4 or 5 aromatic rings, i.e. with 3-, 4- or 5-functional isocyanates. Polymeric MDI can be used together with other diisocyanates conventionally used in polyurethane chemistry, for example toluene diisocyanate (TDI) or naphthalene diisocyanate (NDI). The diisocyanates preferably comprise at least 80% by weight of diphenylmethane diisocyanate, particularly preferably at least 90% by weight of diphenylmethane diisocyanate and in particular exclusively diphenylmethane diisocyanate, based in each case on the total weight of the diisocyanates. The viscosity of the polyisocyanates (a) here at 25°C is preferably 100 mPas to 900 mPas, more preferably 125 mPas to 700 mPas, particularly preferably 150 mPas to 600 mPas and in particular 170 mPas to 300 mPas.

Compounds (b) used having groups reactive toward isocyanates can comprise all known compounds having at least two hydrogen atoms reactive toward isocyanates, for example those with functionality 2 to 8 and with number-average molar mass 62 to 15 000 g/mol: by way of example, it is possible to use polyester polyols and/or polyether polyols, The molar mass of polyetherols and the polyester polyols is preferably 200 to 15 000 g/mol. It is also possible to use low- molecular-weight chain extenders and/or crosslinking agents, alongside polyetherols. For the purposes of the present disclosure, the expressions “polyether polyol” and “polyetherol” as well as polyester polyol and polyesterol are equivalent.

Polyetherols are by way of example produced from epoxides, for example propylene oxide and/or ethylene oxide, or from tetrahydrofuran, by using starter compounds having active hydrogen, for example aliphatic alcohols, phenols, amines, carboxylic acids, water or compounds based on natural materials, for example sucrose, sorbitol or mannitol, with use of a catalyst. Mention may be made here of basic catalysts or double-metal cyanide catalysts, as described by way of example in PCT/EP2005/010124, EP 0090444 or WO 05/090440.

Suitable polyester polyols can be prepared from organic dicarboxylic acids having 2 to 12 carbon atoms, preferably aromatic, or mixtures of aromatic and aliphatic dicarboxylic acids and polyhydric alcohols, preferably diols, having 2 to 12 carbon atoms, preferably 2 to 6 carbon atoms.

In particular, the following dicarboxylic acids may be considered: succinic acid, glutaric acid, adipic acid, cork acid, azelaic acid, sebacic acid, decandicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid and terephthalic acid. The dicarboxylic acids can be used individually as well as in a mixture. Instead of the free dicarboxylic acids, the corresponding dicarboxylic acid derivatives, such as dicarboxylic acid esters of alcohols with 1 to 4 carbon atoms or dicarboxylic acid anhydrides, can also be used. As aromatic dicarboxylic acids or acid derivatives, phthalic acid, phthalic anhydride, terephthalic acid and/or isophthalic acid are preferably used in a mixture or alone. Particular preference is given to polyester polyols obtained by using exclusively aromatic dicarboxylic acid or its derivatives as acid component. Preferably used as an aromatic dicarboxylic acid, at least a compound selected from the group consisting of terephthalic acid, dimethyl terephthalate (DMT), polyethylene terephthalate (PET), phthalic acid, phthalic anhydride (PSA) and isophthalic acid or mixtures of at least two of these dicarboxylic acids . especially preferred at least one compound from the group consisting of terephthalic acid, dimethyl terephthalate (DMT), polyethylene terephthalate (PET) and phthalic anhydride (PSA) and in particular phthalic acid and/or Phthalic anhydride is used. In a preferred embodiment the aromatic carboxylic acids can be obtained from recycled material or production waste.

Examples of dihydric and polyhydric alcohols, in particular diols, are: monoethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1 ,2- or 1 ,3-propanediol, dipropylene glycol, polypropylene glycol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 1 ,10-decanediol, glycerol, trimethylolpropane and pentaerythritol, as well as alkoxylates of the same starters. Preferably used are monoethylene glycol, diethylene glycol, triethylene glycol, 1 ,2- or 1 ,3- propanediol, dipropylene glycol, as well as ethoxylates of the same starters, for example ethoxylated glycerol, or mixtures of at least one of the mentioned diols. In particular, monoethylene glycol, diethylene glycol, glycerol, as well as ethoxylates of these starters, or mixtures of at least two of the mentioned diols in particular diethylene glycol are used.

Polyester polyols may be produced catalyst-free or preferably in the presence of esterification catalysts, preferably in an atmosphere of inert gas such as nitrogen in the melt at temperatures of 150 to 280 °C, preferably 180 to 260 °C, where appropriate under reduced pressure up to the desired acid number of preferred than 10, more preferred less than 2. For example, iron, cadmium, cobalt, lead, zinc, antimony, magnesium, titanium, and tin catalysts in the form of metals, metal oxides or metal salts can be considered as catalysts.

For the production of polyester polyols the organic polycarboxylic acids and/or derivatives and polyhydric alcohols are advantageously polycondensed in the molar ratio of 1 : 1 to 2.2, preferably 1 : 1.05 to 2.1 and especially preferably 1 : 1.1 to 2.0.

The polyester polyols obtained generally have a number average molecular weight of 200 to

3000, preferably 300 to 1000 and in particular 400 to 800 g/mol and the functionality of the pol- yester polyol preferably is 1.5 to 3, more preferred 2 to 3 and especially preferred 2 to 2.5. Preferably, the amount of the polyesterols is 0 to 50 % by weight, preferably 0 to 5% by weight, based on the total weight of component (b).

Component (b) can moreover comprise chain extenders and/or crosslinking agents, for example in order to modify mechanical properties, e.g. hardness. Chain extenders and/or crosslinking agents used comprise diols and/or triols, and also aminoalcohols having molar masses below 200 g/mol, preferably 60 to 150 g/mol. Examples are two-functional alcohols, as monoethylene glycol, diethylene glycol, 1 ,2-propane diol, 1 ,3 propane diol, 1 ,4 butane diol, 1 ,3 butane diol, 1 ,5 pentane diol, 1 ,6-hexane diol, neopentyl glycol, tetraethylene glycol, dipropylene glycol, cyclohexane diol and aliphatic or aromatic amine based chain extenders as aliphatic or aromatic diamines like ethylene diamine, triethylene diamine and/or diethyl toluene diamine (DETDA). It is equally possible to use aliphatic and cycloaliphatic triols such as glycerol, trimethylolpropane and 1 ,2,4- and 1 ,3,5-trihydroxycyclohexane.

Insofar as chain extenders, crosslinking agents or mixtures thereof are used for the production of the rigid polyurethane foams, quantities advantageously used of these are 0 to 15% by weight, preferably 0 to 5% by weight, based on the total weight of component (b). In a preferred embodiment no chain extenders and/or crosslinking agents are used.

According to the invention the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b) comprise (b1) at least one polyether polyol obtained by alcoxylation of two or three functional starter molecules having a hydroxyl value of 100 to 200 mg KOH/g, (b2) at least one polyether polyol obtained by alcoxylation of an aliphatic diamine and (b3) at least one polyether polyol obtained by alcoxylation of sugar alcohol, wherein the amount of the polyol (b2) is at least 30 % by weight, based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b).

In a preferred embodiment the compounds (b) may further comprise at least one polyether polyol (b4) obtained by alcoxylation of two functional starter molecules having a hydroxyl value of 200 to 500, preferably 210 to 400 and especially preferred 220 to 300 mg KOH/g.

In a preferred embodiment polyetherpolyol (b1) is obtainable by alkoxylation of a three functional starter molecule such as glycerol, having a hydroxy value of preferably 120 to 180 mg KOH/g. In a further preferred embodiment polyol (b2) is obtainable by propoxylation of ethylenediamine having an OH-number of preferably 350 to 550 mg KOH/g and more preferably 420 to 520 mg KOH/g.

In a further preferred embodiment polyol (b3) is obtainable by propoxylation and ethoxylation of a five to eight-functional starter molecule. In a preferred embodiment a mixture of starter molecules are used such as sugar alcohols as sucrose, saccharose, sorbitol, mannite and glucose, and lower alcohols such as treefunctional and twofunctional alcohols such as glycerol or trimethylolpropane. Polyols (b3) preferably have an average functionality of 4 to 8, more preferred 4.5 to 6.5 and an OH-number of preferably 300 to 600 mg KOH/g and more preferred 400 to 500 mg KOH/g.

If mixtures of starter molecules with different functionalities are used, fractional functionalities can be obtained. Influences on the functionality, for example through side reactions, are not considered in the nominal functionality.

It is especially preferred when the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b) comprise polyols (b1), (b2), (b3) and (b4). In a particular preferred embodiment the content of polyol (b1) is 10 to 40 % by weight, preferably 20 to 30 % by weight, of polyol (b2) is 30 to 50 % by weight, preferably 35 to 45 % by weight, of polyol b3) is 5 to 20 % by weight, preferably 8 to 15 % by weight, of polyol (b4) is 5 to 30 % by weight, preferably 10 to 25 % by weight, each based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b). In an even more preferred embodiment, the content of polyols (b1) to (b4) is at least 80% by weight more preferred at least 90 % by weight, particularly preferred at least 95 % by weight and in particular 100 % by weight, based on the total weight of compound (b).

Catalysts (c) greatly accelerate the reaction of the compounds (b) having at least two hydrogen atoms reactive toward isocyanate groups and chemical blowing agents (d) with the polyisocyanates (a). Catalysts (c) comprise at least one amine catalyst (c1) and at least one metal-based catalyst (c2).

Typical amine catalysts (c1) include for example amidines, such as 2,3-dimethyl-3,4,5,6- tetrahydropyrimidine, tertiary amines, such as triethylamine, tributylamine, dimethylbenzylamine, N-methyl-, N-ethyl- and N-cyclohexylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylbutanediamine, N,N-Bis[3-(dimethylamino)propyl]-N',N'-dimethylpropane- 1 ,3-diamine, N,N,N',N'-tetramethylhexanediamine, pentamethyldiethylenetriamine, tetramethyl- diaminoethyl ether, bis(dimethylaminopropyl)urea, dimethylpiperazine, 1 ,2-dimethylimidazole, 1- azabicyclo[3.3.0]octane and preferably 1,4-diazabicyclo[2.2.2]octane, and alkanolamine compounds such as triethanolamine, triisopropanolamine, N-methyl- and N-ethyldiethanolamine and dimethylethanolamine.

In a preferred embodiment the amine catalysts (c1) comprise at least one incorporable amine catalyst. Incorporable amine catalysts have at least one, preferably 1 to 8 and particularly preferably 1 to 2 groups reactive toward isocyanates, such as primary amine groups, secondary amine groups, hydroxyl groups, amides or urea groups, preferably primary amine groups, secondary amine groups, hydroxyl groups. Incorporable amine catalysts are mostly used for production of low-emission polyurethanes especially employed in automobile interiors. Such catalysts are known and described for example in EP1888664. These comprise compounds which, in addition to the isocyanate-reactive group(s), preferably comprise one or more tertiary amino groups. At least one of the tertiary amino groups in the incorporable catalysts preferably bears at least two aliphatic hydrocarbon radicals, preferably having 1 to 10 carbon atoms per radical, particularly preferably having 1 to 6 carbon atoms per radical. It is particularly preferable when the tertiary amino groups bear two radicals independently selected from methyl and ethyl radical plus a further organic radical. Examples of incorporable catalysts that may be used are bis(dimethylaminopropyl)urea, bis(N,N-dimethylaminoethoxyethyl) carbamate, dimethylaminopropylurea, N,N,N-trimethyl-N-hydroxyethylbis(aminopropylether), N,N,N-trimethyl-N- hydroxyethylbis(aminoethylether), diethylethanolamine, bis(N,N-dimethyl-3-aminopropyl)amine, dimethylaminopropylamine, 3-dimethylaminopropyl-N,N-dimethylpropane-1,3-diamine, dimethyl- 2-(2-aminoethoxyethanol), (1,3-bis(dimethylamino)propan-2-ol), N,N-bis(3- dimethylaminopropyl)-N-isopropanolamine, bis(dimethylaminopropyl)-2-hydroxyethylamine, N,N,N-trimethyl-N-(3-aminopropyl)-bis(aminoethylether), 1,4-diazabicyclo[2.2.2]octane-2- methanol and 3-dimethylaminoisopropyl diisopropanolamine or mixtures thereof.

Preferred metal catalysts (c2) include for example preferably organic tin compounds, such as tin(ll) salts of organic carboxylic acids, for example tin(ll) acetate, tin(ll) octoate, tin(ll) ethylhexoate and tin(ll) laurate, and the dialkyltin(IV) salts of organic carboxylic acids, for example dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate and dioctyltin diacetate, and also bismuth carboxylates, such as bismuth(lll) neodecanoate, bismuth 2-ethylhexanoate and bismuth octanoate, or mixtures thereof.

At least one blowing agent (d) comprising 3 to 6 % by weight of water, based on the total weight of components (b) to (e), is used in the invention. Blowing agents may further comprise additional chemical blowing agents and/or physical blowing agents. These blowing agents are de- scribed by way of example in "Polyurethane Handbook”, Carl Hanser Verlag, 2^nd edition 1994, chapter 3.4.5. The term chemical blowing agent here means compounds which form gaseous products through reaction with isocyanate. Examples of these blowing agents are water and carboxylic acids. The term physical blowing agents means compounds which have been dissolved or emulsified in the starting materials for the polyurethane production reaction and evaporate under the conditions of formation of polyurethane. These are by way of example hydrocarbons, halogenated hydrocarbons, halogenated hydroolefines and other compounds, examples being perfluorinated alkanes such as perfluorohexane, chlorofluorocarbons, and ethers, esters, ketones, acetals, and/or liquid carbon dioxide.

In a preferred embodiment as blowing agents according to the present invention less than 10 % by weight of physical blowing agents, based on the total weight of the blowing agents (d) are employed and especially preferred exclusively water is used as blowing agent (d). The amount of blowing agent is chosen to obtain a density of the spray foam of preferably 20 to 49 g/dm³, more preferred 30 to 48 g/dm³ and especially preferred 35 to 45 g/dm³. To obtain these densities 3 to 6 % by weight, more preferred 3.1 to 5 % by weight of water agent (d), based on the total the total weight of compounds (b) to (f), is employed.

According to the invention flame retardant (e) may be added. Examples of suitable flame retardants (e) are brominated esters, brominated ethers (Ixol) and brominated alcohols such as dibromoneopentyl alcohol, tribromoneopentyl alcohol and PHT-4-diol, and also chlorinated phosphates such as tris(2-chloroethyl) phosphate, tris(2-chloropropyl) phosphate (TCPP), tris(1 ,3-dichloropropyl) phosphate, tricresyl phosphate, tris(2,3-dibromopropyl) phosphate, tetrakis(2-chloroethyl) ethylenediphosphate, dimethyl methanephosphonate, diethyl diethano- laminomethylphosphonate, and also commercially available halogenated flame-retardant polyols. Other phosphates or phosphonates used can comprise diethyl ethanephosphonate (DEEP), triethyl phosphate (TEP), dimethyl propylphosphonate (DMPP), and diphenyl cresyl phosphate (DPC) as liquid flame retardants.

Materials that can also be used other than the abovementioned flame retardants to provide flame retardancy to the rigid polyurethane foams are inorganic or organic flame retardants such as red phosphorus, preparations comprising red phosphorus, aluminum oxide hydrate, antimony trioxide, arsenic oxide, ammonium polyphosphate and calcium sulfate, expandable graphite and cyanuric acid derivatives, e.g. melamine, and mixtures of at least two flame retardants, e.g. ammonium polyphosphates and melamine, and also optionally maize starch or ammonium polyphosphate, melamine and expandable graphite; aromatic polyesters can optionally also be used for this purpose. Preferred flame retardants do not include any bromine. Particularly preferred flame retardants consist of atoms selected from the group consisting of carbon, hydrogen, phosphorus, nitrogen, oxygen and chlorine, more especially from the group consisting of carbon, hydrogen, phosphorus and chlorine.

Preferred flame retardants comprise no groups reactive toward isocyanate groups. It is preferable that the flame retardants are liquid at room temperature. Particular preference is given to TCPP, DEEP, TEP, DMPP and DPC, especially to TCPP.

In a preferred embodiment the flame retardants (e) comprises 1 to 15 % by weight, more preferred 2 to 10 % by weight and especially preferred 3 to 8 % by weight, each based on the total weight of compounds (b) to (e), of liquid phosphorous flame retardant.

It is also optionally possible to add further auxiliaries and/or additional substances (f) to the reaction mixture for the production of the polyurethane spray foams of the invention. Mention may be made by way of example of surface-active substances, foam stabilizers, cell regulators, fillers, light stabilizers, dyes, pigments, hydrolysis stabilizers, and substances having fungistatic and bacteriostatic action and antioxidants. Such substances are known and described for example in "Polyurethane Handbook”, Hanser Publishers Munich, 2nd edition 1993, chapter chapters 3.4.4 and 3.4.6 to 3.4.11.

Examples of surface-active substances that can be used are compounds which serve to support homogenization of the starting materials and which optionally are also suitable for regulating the cell structure of the plastics. Mention may be made by way of example of emulsifiers, for example the sodium salts of castor oil sulfates and of fatty acids and salts of fatty acids with amines, for example diethylamine oleate, diethanolamine stearate, diethanolamine ricinoleate, salts of sulfonic acids, for example alkali metal or ammonium salts of dodecylbenzene- or dinaphthylmethanedisulfonic acid and ricinoleic acid; foam stabilizers, for example siloxane-oxyalkylene copolymers and other organopolysiloxanes, ethoxylated alkylphenols, ethoxylated fatty alcohols, paraffin oils, castor oil esters or ricinoleic esters, turkey red oil and peanut oil, and cell regulators, for example paraffins, fatty alcohols and dimethylpolysiloxanes. Other materials suitable for improving emulsifying action and cell structure and/or foam stabilization are the oligomeric acrylates described above having, as pendant groups, polyoxyalkylene moieties and fluoroalkane moieties. Quantities usually used of the surface-active substances are 0.01 to 10 parts by weight, based on 100 parts by weight of component (b). Foam stabilizers used can comprise conventional foam stabilizers, for example those based on silicone, examples being siloxane-oxyalkylene copolymers and other organopolysiloxanes and/or ethoxylated alkylphenols and/or ethoxylated fatty alcohols.

Light stabilizers used can comprise light stabilizers known in polyurethane chemistry. These comprise phenolic stabilizers, for example 3,5-di-tert-butyl-4-hydroxytoluenes and/or Irganox products from BASF, phosphites, for example triphenylphosphites and/or tris(nonylphenyl) phosphites, UV absorbers, for example 2-(2-hydroxy-5-methylphenyl)benzotriazoles, 2-(5- chloro-2H-benzotriazol-2-yl)-6-(1,1-dimethylethyl)-4-methylphenol, 2-(2H-benzotriazol-2-yl)-6- dodecyl-4-methylphenol, branched and linear, and 2,2'-(2,5-thiophenediyl)bis[5-tert- butylbenzoxazoles], and also those known as HALS stabilizers (hindered amine light stabilizers), for example bis(1-octyloxy-2,2,6,6-tetramethyl-4-piperidinyl) sebacate, n-butyl-(3,5-di- tert-butyl-4-hydroxybenzyl)bis(1,2,2,6-pentamethyl-4-piperidinyl) malonate and diethyl succinate polymer with 4-hydroxy-2, 2, 6, 6-tetram ethyl- 1 -piperidineethanol.

Examples of antioxidants are phenolic substances, such as 2,6-di-tert-butyl-4-methylphenol, benzenepropanolic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-C7-C9 branched alkyl esters, aminic antioxidants such as N,N'-di-isopropyl-p-phenylenediamine, thiosynergists, such as dilauryl 5-thiodipropionate, phosphites and phosphonites, such as triphenylphosphites, diphenylalkylphosphites, benzofuranones and indolinones, other antioxidants such as O-, N- and S- benzyl compounds, triazine compounds, amides of |3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionic acid, esters of substituted and unsubstituted benzoic acids, nickel compounds and esters of p-10-thiodipropionic acid or a mixture of two or more of these antioxidants. Such antioxidants are described, for example, in WO2017125291 and are commercially available for example under the trade names Irganox 1076, Irganox 245, Irganox 2000, Irganox E201 (vitamin E), Irganox 5057 or Irgafos 38.

The term fillers, in particular reinforcing fillers, means the conventional organic and inorganic fillers, reinforcing agents, weighting agents, and agents for improving abrasion behavior in paints, coating compositions, etc., these being known per se. Individual examples that may be mentioned are: inorganic fillers such as silicatic minerals, for example phyllosilicates such as antigorite, serpentine, hornblends, amphiboles, chrysotile and talc, metal oxides, for example kaolin, aluminum oxides, titanium oxides and iron oxides, metal salts, for example chalk, barite, and inorganic pigments, for example cadmium sulfide and zinc sulfide, and also glass, etc. It is preferable to use kaolin (china clay), aluminum silicate and coprecipitates of barium sulfate and aluminum silicate, and also natural and synthetic fibrous minerals, for example wollastonite, and fibers of various lengths made of metal and in particular of glass; these can optionally have been sized. Examples of organic fillers that can be used are: carbon, melamine, colophony, cyclopentadienyl resins and graft polymers, and also cellulose fibers, polyamide fibers, polyacrylonitrile fibers, polyurethane fibers and polyester fibers derived from aromatic and/or aliphatic dicarboxylic esters, and in particular carbon fibers.

The inorganic and organic fillers can be used individually or in the form of mixtures, quantities of these added to the reaction mixture advantageously being 0 to 50% by weight, preferably 1 to 40% by weight, based on the weight of components (a) to (f), where however the content of mats, nonwovens and wovens made of natural and synthetic fibers can reach up to 80% by weight, based on the weight of components (a) to (f). In a preferred embodiment no fillers are added.

Production of the polyurethane according to the invention generally comprises mixing (a) polyisocyanate, (b) polymeric compounds having isocyanate-reactive groups, (c) catalysts and optionally (d) blowing agents and optionally (e) flame retardants and (f) auxiliaries and/or additives to afford a reaction mixture and reacting the reaction mixture to afford the polyurethane. The expression reaction mixture here means for the purposes of the present invention the mixture of the isocyanates (a) with the compounds (b) reactive toward isocyanate when the action conversions are below 90%, based on the isocyanate groups.

It is preferable here to use the two-component process where all of the starting materials (a) to (f) are present either in the isocyanate component (A) or in the polyol component (B). It is preferable here that all of the substances that can react with isocyanate are added to the polyol component (B), while starting materials not reactive toward isocyanates can be added either to the isocyanate component (A) or to the polyol component (B). It is particularly preferable that additives added to isocyanate component (A) are only those bearing no functional groups that react with the NCO function of the isocyanate, i.e. the only additives used in the isocyanate component (A) are those that are inert in relation to the isocyanate. Isocyanate component (A) and polyol component (B) are mixed to form the reaction mixture. In a preferred embodiment isocyanate component (A) comprising polyisocyanates (a), and a polyol component (B) comprising compounds (b) having at least two hydrogen atoms reactive toward isocyanate groups, catalyst (c) and blowing agent (d) are produced, and then isocyanate component (A) and polyol component (B), are mixed to give the reaction mixture. Polyol component (B) and isocyanate component (A) are preferably reacted in a weight ratio of 90 to 150 parts by volume of isocyanate component (A) to 100 parts by volume of the polyol component (B) more preferred 100 to 130 parts by volume of isocyanate component (A) to 100 parts by volume of the polyol compo- nent (B) and especially preferred 110 to 135 parts by volume of isocyanate component (A) to 100 parts by volume of the polyol component (B).

The components (a) to (c) and optionally (d) to (f) are reacted in amounts such that the equivalence ratio of NCO groups of the polyisocyanates (a) to the sum of the reactive hydrogen atoms of the components (b), (c), (d) and, if present (e) and (f), is preferably 1 to 1.5:1 , more preferred 1.05 to 1.40 to 1 and especially preferred 1.08 to 1.20 :1. A ratio of 1 :1 here corresponds to an isocyanate index of 100.

An isocyanate component (A) and a polyol component (B) are storage stable and usually can be stored at room temperature for several months. After storage, it might be necessary to homogenize the components (A) and/or (B). In a preferred embodiment the polyol component (B) has a viscosity at 25 °C of 50 to 800 mPas, more preferred 150 to 600 mPas and especially preferred 210 to 550 mPas.

The polyurethane spray foam obtained by a method according to the present invention shows a high mechanical stability and no shrinkage after production. In addition, it is it has a high water tightness and low thermal conductivity and can be used as insulation material especially for roof insulation.

Examples are used below to explain the invention.

The following parameters were determined:

The following substances were used to produce the examples:

Polyol 1 : polyetherol starting from glycerol as starter molecule and ethylene oxide and propylene oxide having a hydroxy number of 160 mg KOH/g

Polyol 2: polyetherol starting from ethylenediamine as starter molecule and propylene oxide with hydroxy number 470 mg KOH/g

Polyol 3: a mixture of sucrose and glycerol as starter molecules and propylene oxide with an average functionality of 6 and a hydroxy number 425 mg KOH/g

Polyol 4: polyetherol starting from propylene glycol as starter molecule and propylene oxide with hydroxy number 250 mg KOH/g Cat 1 : Triethanolamine

Cat 2: Tris-(dimethylaminopropyl)amine

Cat 3: Diemethylethanolamine (DMEA)

Cat 4: Pentamethyldiethylene triamine (PMDETA)

Cat 5: Dibutyltin dilaurate

Surfactant: silicone surfactant, Vorasurf® DC 193 from Dow

Flame retardant 1 (FR1): tris(2-chloropropyl) phosphate (TCPP)

Isocyanate: Lupranat® M20 S from BASF (polymeric methylenediphenyl diisocyanate (PMDI) with viscosity about 210 mPa*s at 25°C)

Production process

Polyol components (B) and isocyanate components (A) were produced as disclosed in Table 1. All amounts are given in parts by weight, based on the polyol component or the isocyanate component, respectively. The components are thoroughly mixed and then foamed by the process described below. The components were foamed via intensive mixing of the polyol component.

The following properties were determined:

Density: density of a polyurethane foam is measured according to EN 14315-2-C.

Closed Cell content: closed cell content was measured according to ISO 4590

Compression strength: compression strength was determined at a compression of 10 % according to EN 826

Dimensional stability: dimensional stability was determined according to EN 14315-1 :2013 Deformation under load and temperature (DTL): Deformation under load and temperature was determined according to EN 14315-1 :2013 (EN 1605) at 70 kPa and 70 °C for the duration of 1 week

Table 1

Examples 1 to 5 are comparative examples, examples 6 and 7 are according to the invention. A simple reduction of the density by addition of more water is not possible since mechanical stability is not met. Only the combination of water content, polyols (b1), (b2) and (b3), preferably reacted at an index of more than 108 results in a low-density foam with high mechanical stability.

Claims

1. A method for the production of a polyurethane spray foam having a density of less than 50 g/dm³ and a closed cell content of at least 85 %, by mixing the following to give a reaction mixture:

(a) polyisocyanates comprising PM DI

(b) compounds having at least two hydrogen atoms reactive toward isocyanate groups, comprising (b1) at least one polyether polyol obtained by alcoxylation of two or three functional starter molecules having a hydroxyl value of 100 to 200 mg KOH/g, (b2) at least one polyether polyol obtained by alcoxylation of an aliphatic diamine and (b3) at least one polyether polyol obtained by alcoxylation of sugar alcohol, wherein the amount of the polyol (b2) is at least 30 % by weight, based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b),

(c) catalyst comprising at least one amine catalyst (c1) and at least one metal based catalyst (c2)

(d) blowing agent, comprising 3 to 6 % by weight of water, based on the total weight of components (b) to (e)

(e) optionally flame retardant

(f) optionally auxiliaries and additional substances, spraying the reaction mixture onto a substrate and allowing said reaction mixture to harden to give the polyurethane spray foam.

2. Method according to claim 1 wherein the polyether polyol obtained by alcoxylation of an aliphatic diamine and (b3) has a hydroxyl value of 300 to 600 mg KOH/g.

3. Method according to claim 1 or claim 2, wherein the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b) comprise at least one polyether polyol (b4) obtained by alcoxylation of two functional starter molecules having a hydroxyl value of 200 to 500 mg KOH/g.

4. Method according to any of claims 1 to 3, the flame retardant (e) comprises 1 to 15 % by weight, based on the total weight of compounds (b) to (e), of liquid phosphorous flame retardant.

5. Method according to any of claims 1 to 4, wherein compounds having at least two hydrogen atoms reactive toward isocyanate groups (b) comprise 10 to 30 % by weight of polyol (b1), 30 to 50% by weight of polyol (b2), 5 to 20 % by weight of polyol (b3) and 5 to 30 % by weight of polyol (b4), each based on the total weight of the compounds having at least two hydrogen atoms reactive toward isocyanate groups (b).

6. Method according to any of claims 1 to 5, wherein the content of polyols (b1) to (b4) is at least 80% by weight, based on the total weight of compound (b).

7. Method according to any of claims 1 to 6, wherein the amine catalysts (c1) comprise at least one incorporable amine catalyst.

8. Method according to any of claims 1 to 7, wherein the compounds (a) to (f) are mixed at an isocyanate index of 105 to 140.

9. Method according to any of claims 1 to 8, wherein an isocyanate component (A) comprising polyisocyanates (a), and a polyol component (B) comprising compounds (b) having at least two hydrogen atoms reactive toward isocyanate groups, catalyst (c) and blowing agent (d) are produced, and then isocyanate component (A) and polyol component (B), are mixed to give the reaction mixture.

10. Method according to any of claims 1 to 9, wherein the substrate is a part of a building.

11 . Polyurethane spray foam obtainable according to a method according to any of the claims 1 to 10.

12. Polyurethane spray foam according to claim 11 having a closed cell content of 90 % or more, a compression strength at 10 % deformation of 200 kPa or more, a dimensional stability according to EN 1604 of at least 3 and a deformation under 70 kPa load at 70 °C for one week according to EN 1605 of 5 % or less.