Polyester polyols and their use for producing coatings are known per se. For instance, WO 2012/005647 A1 discloses a branched polyester based on a dicarboxylic acid component (A) comprising at least one furandicarboxylic acid or its ester or halide, on a diol component (B), and on a branching component (C) comprising at least one component having at least three or more reactive groups, for esterification and/or transesterification reaction(s). This polyester is used for producing protective and/or decorative coatings, such as in powder coatings or 2-component PU coatings, for example.

WO 2012/005648 A1 describes an unsaturated oligoester or polyester based on at least one carboxylic acid component (A), comprising at least one mono-, di-, tri-, or polybasic carboxylic acid, and on an alcohol component (B), comprising at least one mono-, di-, tri-, or polyhydric alcohol, for one or more esterification and/or transesterification reaction(s), characterized in that the carboxylic acid component (A) comprises at least one furandicarboxylic acid or the ester or halide thereof and in that the carboxylic acid component (A) and/or the alcohol component (B) comprise(s) at least one component having at least one carbon-carbon double or triple bond. The oligoesters or polyesters prepared according to WO 2012/005648 A1 are used for producing decorative and/or protective, solvent-borne or waterborne varnishes, inks, enamels, gelcoats, adhesives, or putties, such as in the production of fiber materials and plastics constructions.

The skilled person is well aware that the disadvantage of the polyesters disclosed in WO 2012/005647 A1 and WO2012/005648 A1 is that the furandicarboxylic acid(s) present significantly lower the solubility of the polyesters in the majority of solvents. Polyesters of low solubility have only limited usefulness in varnishes, since they have to be diluted with substantial amounts of solvents. The use of polyesters based on furandicarboxylic acids in varnishes and inks leads to disadvantages, therefore, because high solubility of the polyester in solvents is an advantage.

It is an object of the present invention, therefore, to provide a polyester polyol whose solubility in solvents is enhanced by comparison with that of the known polyester polyols.

This object is achieved by means of a polyester polyol based on a) a carboxylic acid component (A) which comprises at least one carboxylic acid having at least 2 carboxyl groups, and

b) an alcohol component (B) which comprises at least [5-(hydroxymethyl)tetrahydrofuran-2- yl]methanol.

It has surprisingly been found that the solubility of polyester polyols based on

[5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol in solvents is significantly improved in comparison to polyester polyols containing no [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol. Surprisingly, the solubility of polyester polyols which apart from [5-(hydroxymethyl)- tetrahydrofuran-2-yl]methanol are based on furandicarboxylic acids of low solubility is also significantly improved. At the same time, when polyester polyols based on [5-(hydroxymethyl)- tetrahydrofuran-2-yl]methanol are used in polyurethane (PU) or hexamethoxymethylmelamine (HMMM) varnishes, the properties of these varnishes in respect of hardness, flexibility, elasticity, and also attachment are at least comparable with, and in some cases in fact better than, those of PU or HMMM varnishes that are based on polyester polyols without

[5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol. The reduced use of solvents is also to the benefit of the environment, since smaller amounts of organic solvents escape into the environment on evaporation.

Component A

Used in accordance with the invention as carboxylic acid component (A) are carboxylic acids having at least two carboxyl groups, i.e., di-, tri-, or polycarboxylic acids, preferably di- or tricarboxylic acids, and more preferably dicarboxylic acids.

Suitable dicarboxylic acids are generally aliphatic, cycloaliphatic, aromatic, heteroaromatic, or heterocyclic dicarboxylic acids or their alkyl esters or halides. In general the dicarboxylic acids have 2 to 20 carbon atoms, preferably 4 to 12 carbon atoms, more preferably 6 to 10 carbon atoms. Preference is given to linear or branched aliphatic dicarboxylic acids having 2 to 20 carbon atoms, more preferably having 4 to 12 carbon atoms, and especially preferably having 6 to 10 carbon atoms, to heterocyclic or cycloaliphatic dicarboxylic acids having 5 to 24 carbon atoms, or to heteroaromatic or aromatic dicarboxylic acids having 6 to 24 carbon atoms. Preference is given to using at least one dicarboxylic acid, or the alkyl esters or halides thereof, preferably at least one C6 to C10 dicarboxylic acid, or the alkyl esters or halides thereof.

Preference is given to using alkanedioic acids, alkenedioic acids, cyclohexanedioic acids, cyclopentanedioic acids, benzenedicarboxylic acids, or furandicarboxylic acids, or their esters or halides. Examples of suitable dicarboxylic acids are adipic acid, glutaric acid, succinic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, dodecanedioic acid, octadecanedioic acid, maleic acid, fumaric acid, itaconic acid, 1 ,2-cyclohexanedicarboxylic acid, 1 ,3-cyclohexane- dicarboxylic acid, 1 ,4-cyclohexanedicarboxylic acid, furandicarboxylic acid, isophthalic acid, phthalic acid, or terephthalic acid. Also suitable in general are the alkyl esters and/or dialkyl esters of these carboxylic acids, which may be esterified with alcohols based on 1 to 4 carbon atoms, or the halides thereof, such as chloride, bromide and/or iodide, for example.

In accordance with the invention the stated dicarboxylic acids may be used individually or in a mixture of several dicarboxylic acids.

Preferred dicarboxylic acids of the carboxylic acid component (A) are adipic acid,

octadecanedioic acid, furandicarboxylic acid and/or isophthalic acid; more preferably the carboxylic acid component (A) comprises adipic acid.

Examples of suitable tricarboxylic acids are linear or branched aliphatic, cycloaliphatic, aromatic, heteroaromatic, or heterocyclic tricarboxylic acids or their alkyl esters or halides. In general tricarboxylic acids have 4 to 20 carbon atoms. Preference is given to using benzenetricarboxylic acids.

For example, trimellitic acid can be used. Preference is given to using trimellitic acid or its alkyl esters, such as methyl or ethyl esters, for example, or halides, such as chlorides, bromides and/or iodides, for example. A particularly preferred embodiment is the use of trimellitic acid.

In accordance with the invention the stated tricarboxylic acids can be used individually or in a mixture of several tricarboxylic acids.

Polycarboxylic acids in the sense of the invention are organic compounds having at least four carboxyl groups. Examples of suitable polycarboxylic acids are linear or branched aliphatic, cycloaliphatic, aromatic, heteroaromatic, or heterocyclic polycarboxylic acids or their alkyl esters or halides. In general the polycarboxylic acids have 5 to 20 carbon atoms.

Preference is given to using benzenepolycarboxylic acids.

Preference is given to using pyromellitic acid or its alkyl esters, such as methyl or ethyl esters, for example, or halides, such as chlorides, bromides and/or iodides, for example. Particularly preferred is the use of pyromellitic acid. In accordance with the invention the stated polycarboxylic acids can be used individually or in a mixture of several polycarboxylic acids. Also suitable in accordance with the invention are mixtures of the stated dicarboxylic, tricarboxylic, or polycarboxylic acids.

The stated dicarboxylic, tricarboxylic, and polycarboxylic acids are available commercially. They may also be obtained from natural raw materials. Natural raw materials is a term used in particular for substances obtained by processing from plants, or from parts of plants (or animals). Furthermore, the stated dicarboxylic, tricarboxylic, and polycarboxylic acids may be produced by microbiological methods. These are common knowledge to the skilled person or, for example, are described by F. Koopman, N. Wierckx, J.H. de Winde, and H.J. Ruijssenaars. Bioresource Technology 2010, volume 101 , No. 16, pages 6291 to 6296.

The carboxylic acid component (A) preferably comprises at least adipic acid, octadecanedioic acid, isophthalic acid and/or furandicarboxylic acid. With particular preference the carboxylic acid component (A) comprises at least adipic acid.

Component B

The alcohol component (B) of the invention comprises at least [5-(hydroxymethyl)tetrahydro- furan-2-yl]methanol. Suitable additional alcohols are generally alcohols having at least two hydroxyl groups, i.e., diols, triols, or polyols. Preference is given to using diols or triols and more preferably diols. Suitable in accordance with the invention are, for example, C2 to C12 alcohols, i.e., alcohols having 2 to 12 carbon atoms, preferably C2 to C10 alcohols, and very preferably C2 to C8 alcohols. Diols suitable in accordance with the invention are generally aliphatic, cycloaliphatic, or aromatic diols, polyester diols or polyether diols, preferably aliphatic diols. Suitable aliphatic diols are common knowledge to the skilled person and comprise, for example, 2,2-dimethyl-1 ,3- propanediol, ethylene glycol, diethylene glycol, 3-oxapentane-1 ,5-diol, 1 ,3-propanediol, 1 ,2- propanediol, dipropylene glycol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 2-methyl-1 ,3- propanediol and 3-methyl-1 ,5-pentanediol, 2-butyl-2-ethyl-1 ,3-propanediol, cyclohexane- dimethanol, or 2-ethyl-1 ,3-hexanediol. Preference is given to using at least 2,2-dimethyl-1 ,3- propanediol, 2-butyl-2-ethyl-1 ,3-propanediol, cyclohexanedimethanol and/or 2-ethyl-1 ,3- hexanediol. Particular preference is given to using at least 2,2-dimethyl-1 ,3-propanediol, and very preferably exclusively 2,2-dimethyl-1 ,3-propanediol.

Suitable triols are generally aliphatic, cycloaliphatic, or aromatic triols, polyester triols or polyether triols, such as glycerol, trimethylolpropane, 1 ,2,3-trihydroxybenzene, 1 ,2,4- trihydroxybenzene, or 1 ,3,5-trihydroxybenzene, for example. Preference is given to using trimethylolpropane and/or glycerol.

Polyols as a constituent of component B are, for the purposes of the invention, organic compounds having at least four hydroxyl groups. Suitable polyols are generally aliphatic, cycloaliphatic, or aromatic polyols, such as pentaerythritol, for example, and also polyester polyols or polyether polyols (polyetherols) having molecular weights of between 200 and 6000 g/mol. Preference is given to using polyetherols with a molecular weight of 200 to

3000 g/mol, and particular preference to using polyetherols having a molecular weight of 200 to 400 g/mol.

Also suitable in accordance with the invention are mixtures of the stated di-, tri-, or polyols.

The stated di-, tri-, or polyols are available commercially. They may also be obtained from natural raw materials. Natural raw materials is a term used in particular for substances obtained by processing from plants, or from parts of plants (or animals). Furthermore, the stated di-, tri-, and polyols may be produced by microbiological methods. These are common knowledge to the skilled person or, for example, are described by F. Koopman, N. Wierckx, J.H. de Winde, and H.J. Ruijssenaars. Bioresource Technology 2010, volume 101 , No. 16, pages 6291 to 6296.

In one preferred embodiment the alcohol component (B) comprises, apart from

[5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol, at least one further C2 to C8 diol, preferably at least 2,2-dimethyl-1 ,3-propanediol, 2-butyl-2-ethyl-1 ,3-propanediol, cyclohexanedimethanol and/or 2-ethyl-1 ,3-hexanediol, more preferably at least 2, 2-dimethyl-1 ,3-propanediol, very preferably 2,2-dimethyl-1 ,3-propanediol.

Component B comprises in general at least 10 wt% of [5-(hydroxymethyl)tetrahydrofuran-2-yl]- methanol, preferably 10 to 100 wt% of [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol, more preferably 50 to 100 wt% of [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol, and especially preferably 75 to 100 wt% of [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol, based on the total weight of component B.

In one especially preferred embodiment the alcohol component (B) consists of [5-(hydroxy- methyl)tetrahydrofuran-2-yl]methanol.

Preparation process

Processes for preparing polyester polyols are common knowledge to the skilled person and are described for example in lonescu, Mihail, Chemistry and Technology of polyols for

polyurethanes. Shropshire, UK, 2005, pages 264 to 279. Examples of processes suitable for preparing polyester polyols are polycondensation reactions, i.e., polycondensation of the functional carboxylic acid groups with the hydroxyl groups, e.g., condensation in the presence of or without addition of solvents, preferably polycondensation without addition of solvents.

Examples of suitable catalysts are iron, cadmium, cobalt, lead, zinc, zirconium, hafnium, aluminum, antimony, magnesium, titanium, or tin catalysts in the form of metals, metal oxides, or metal salts, or acids such as, for example, sulfuric acid, p-toluenesulfonic acid, or bases such as, for example, potassium hydroxide or sodium methoxide. Also suitable are mixtures of these catalysts.

Likewise suitable processes for the preparation of polyester polyols are, for example, high- temperature polycondensation or enzymatically catalyzed polycondensation, or

polycondensation catalyzed by multimetal cyanide catalysts or by zeolite or titanium zeolite catalysts, or ring-opening polymerization of cyclic esters. These processes are common knowledge to the skilled person or are described in EP 2467414 B1 , for example. Preferably the polyester polyol of the invention comprising a carboxylic acid component (A) which comprises at least one carboxylic acid having at least 2 carboxyl groups and an alcohol component (B) which comprises at least [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol is polymerized by polycondensation reaction. More preferably the polyester polyol of the invention comprising a carboxylic acid component (A) which comprises at least one carboxylic acid having at least 2 carboxyl groups and an alcohol component (B) which comprises at least [5-(hydroxymethyl)tetrahydrofuran-2-yl]- methanol is prepared by means of condensation, without addition of solvents, catalyzed by iron, cadmium, cobalt, lead, zinc, zirconium, hafnium, aluminum, antimony, magnesium, titanium, or tin catalysts in the form of metals, metal oxides, or metal salts, or acids such as, for example, sulfuric acid, p-toluenesulfonic acid, or bases such as, for example, potassium hydroxide or sodium methoxide. These processes are common knowledge to the skilled person or are described in EP 2431352 A2, for example. A suitable molar mixing ratio of the carboxylic acid component (A) to the alcohol component (B) is generally 1 :0.5 to 1 :2. Preferably this mixing ratio is 1 :0.67 to 1 :1.5, and more preferably 1 :0.8 to 1 :1.2.

The polyester polyols of the invention generally have a linear or branched molecular structure. Linear means that the polyester polyol molecules each consist only of one polymer chain and possess no branches. A branched polyester polyol is characterized by branches with side chains being attached to the main polymer chain. Branched polyester polyols differ in their degree of branching. Suitable degrees of branching for the polyester polyols of the invention, determined by the method from D. Holter, A. Burgath, H. Frey. Acta Polymer 1997, volume 48, pages 30 to 35, are from 1 to 100, for example, preferably from 1.5 to 10, more preferably from 2 to 5.

The number-average molecular weight of the polyester polyols is determined by means of gel permeation chromatography based on four styrene-divinylbenzene (SDV) columns. Calibration is carried out using polymethyl methacrylate (PMMA) or polyethylene glycol (PEG) standards. The injected sample volume is 100 μΙ having a concentration of 2 mg/ml. Elution is carried out with tetrahydrofuran (THF) at a flow rate of 1 μΙ/min. Suitable molecular weight ranges for the polyester polyols obtained in accordance with the invention are common knowledge to the skilled person. In the embodiment according to the invention, the number-average molecular weight of the polyester polyol is generally in the range from 200 to 8000 g/mol, preferably in the range from 350 to 5000 g/mol, more preferably in the range from 500 to 3000 g/mol.

Polyester polyols of the invention generally have a viscosity of 20 to 6000 mPas, preferably 50 to 4500 mPas, and more preferably 80 to 3000 mPas.

Generally the polyester polyols of the invention have an acid number of 0.1 to 30 mg KOH/g, preferably 0.3 to 25 mg KOH/g, and very preferably 0.5 to 20 mg KOH/g.

Polyester polyols suitable in accordance with the invention generally have a hydroxyl number in the range from 25 to 230 mg KOH/g, preferably in the range from 35 to 140 mg KOH/g, more preferably in the range from 40 to 1 15 mg KOH/g, and very preferably in the range from 70 to 1 10 mg KOH/g.

Suitable solvents for dissolving the polyester polyols of the invention are the solvents known to the skilled person for the dissolution of polyester polyols that are used in order to produce coatings. Encompassed here among others are aprotic-polar or protic solvents or aliphatic hydrocarbon mixtures.

Examples of suitable aprotic-polar solvents are ketones. With preference in accordance with the invention it is possible to make use, for example, of methyl ethyl ketone (MEK), methyl amyl ketone (MAK), or acetone, or mixtures thereof.

Examples of suitable protic solvents are linear or branched carboxylic acids or alcohols.

Preference is given for example to using butyl acetate, dimethyl carbonate, or isopropanol, or mixtures thereof, as solvent. Examples of aliphatic hydrocarbon mixtures suitable as solvents are alkanes or isoalkanes or mixtures thereof. Preference is given to using C9 to C12 isoparaffinic hydrocarbon mixtures, such as Shellsol ^® T, for example.

Preference is given to using butyl acetate, isopropanol, dimethyl carbonate, methyl amyl ketone (MAK), methyl ethyl ketone (MEK), acetone, or C9 to C12 isoparaffinic hydrocarbon mixtures as solvents. One particularly preferred embodiment uses methyl ethyl ketone or butyl acetate as solvent. With very particular preference, methyl ethyl ketone is the solvent used.

Mixtures of the stated solvents are suitable in accordance with the invention as well.

The concentrations of the polyester polyol of the invention that are used in the solvent are likewise common knowledge to the skilled person. In general the polyester polyol of the invention is soluble in concentrations of at least 55 wt% in a solvent for polyester polyols, with preference being given to the use of 55 to 85 wt% of polyester polyol, more preferably 60 to 85 wt% of polyester polyol, and very preferably 70 to 85 wt% of polyester polyol, based on the solvent and on the polyester polyol.

Use

The polyester polyols of the invention can be used for producing coatings, such as varnishes, for example. Preference is given to using the polyester polyols of the invention for producing polyurethane (PU) varnish or hexamethoxymethylmelamine (HMMM) varnish.

Processes for producing polyurethane (PU) varnish are common knowledge to the skilled person or are described in WO 2014/191503 A9, for example. For the production of PU varnish in accordance with the invention, the polyester polyol is generally dissolved in solvent. Examples of such solvents have already been described above and are already common knowledge to the skilled person. The concentrations used are also common knowledge to the skilled person. Suitably in accordance with the invention, the polyester polyol is soluble in general in concentrations of at least 55 wt% in a solvent for polyester polyols, preferably 55 to 85 wt% of polyester polyol, more preferably 60 to 85 wt% of polyester polyol, and very preferably 70 to 85 wt% of polyester polyol are used, based on the solvent and on the polyester polyol.

Added to the dissolved polyester polyol is an isocyanate component (C) which comprises at least one isocyanate having at least one isocyanate group. Suitable as isocyanate component (C) are in general compounds having at least one isocyanate group, i.e., monoisocyanates, or polyisocyanates, or isocyanurate, biuret, or allophanate compounds. Polyisocyanates in the sense of the invention are organic compounds having at least two isocyanate groups. Polyisocyanates are used with preference. With particular preference, diisocyanates are used.

Suitable diisocyanates are generally linear or branched aliphatic, araliphatic, cycloaliphatic and/or aromatid diisocyanates, examples being 2,2'-, 2,4'-, and/or 4,4'-diphenylmethane diisocyanate (MDI), 1 ,5-naphthylene diisocyanate (NDI), 2,4- and/or 2, 6-tolylene diisocyanate (TDI), diphenylmethane diisocyanate, 3,3'-dimethylbiphenyl diisocyanate, 1 ,2-diphenylethane diisocyanate and/or phenylene diisocyanate, tri-, tetra-, penta-, hexa-, hepta- and/or octa- methylene diisocyanate, 2-methylpentamethylene 1 ,5-diisocyanate, 2-ethylbutylene 1 ,4- diisocyanate, pentamethylene 1 ,5-diisocyanate, butylene 1 ,4-diisocyanate, 1 -isocyanato-3,3,5- trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 1 -isocyanato-4-[(4- isocyanatocyclohexyl)methyl]cyclohexane (H12MDI), 1 -methyl-2,4- and/or -2, 6-cyclohexane diisocyanate and/or 4,4'-, 2,4'-, and 2,2'-dicyclohexylmethane diisocyanate (H12MDI), 2,6-diisocyanatohexanecarboxylic esters, 1 ,4- and/or 1 ,3-bis(isocyanatomethyl)cyclohexane (HXDI), 1 ,4-cyclohexane diisocyanate, 1 -methyl-2,4- and/or -2, 6-cyclohexane diisocyanate and/or 4,4'-, 2,4'-, and 2,2'-dicyclohexylmethane diisocyanate, preferably 2,2'-, 2,4'- and/or 4,4'- diphenylmethane diisocyanate (MDI), 1 ,5-naphthylene diisocyanate (NDI), 2,4- and/or 2,6- tolylene diisocyanate (TDI), hexamethylene diisocyanate, 4,4'-, 2,4'-, and/or 2, 2'-dicyclo- hexylmethane diisocyanate (H12MDI), and/or IPDI, more preferably 4,4'-diphenylmethane diisocyanate (MDI) and/or hexamethylene diisocyanate and/or H12MDI.

Mixtures of the stated diisocyanates are also suitable in accordance with the invention. In one preferred embodiment the isocyanate component (C) comprises at least hexamethylene diisocyanate. With particular preference the isocyanate component (C) consists of

hexamethylene diisocyanate.

Preference is given to using polyisocyanurates of aliphatic polyisocyanates, more preferably polyisocyanurates of aliphatic diisocyanates, and very preferably polyisocyanurates of hexamethylene diisocyanate, such as Basonat H1100 ^® , for example.

Other mono- and polyisocyanates which can be used are common knowledge to the skilled person.

Mixtures of the stated isocyanates and/or polyisocyanates are also suitable in accordance with the invention.

The stated isocyanates and polyisocyanates are available commercially or can be obtained from natural raw materials. Natural raw materials are more particularly substances obtained by processing from plants, or parts of plants (or animals).

Suitable catalysts are the catalysts that are common knowledge to the skilled person for the synthesis of polyurethanes, and are described in, for example, WO 2014/191053 A9 or WO 201 1/083000 A1 , such as tertiary amines or organic metal compounds, for example.

Examples of suitable tertiary amines are triethylamine, dimethylcyclohexylamine, N-methyl- morpholine, Ν,Ν'-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, and

diazabicyclo[2.2.2]octane.

Suitable organic metal compounds are, for example, Lewis-acidic organic metal compounds. Lewis acids are understood to be compounds with the ability to form a covalent bond by acceptance of an electron pair (electron pair acceptors). Examples of suitable Lewis-acidic organic metal compounds are tin compounds or zinc salts, or tin-free and zinc-free catalysts, such as titanic esters or iron compounds, for example. Suitable tin-free and zinc-free catalysts include organic metal salts of bismuth, zirconium, titanium, aluminum, iron, manganese, nickel, and cobalt, and also cerium salts and cesium salts. Suitable iron compounds are, for example, iron(lll) acetylacetonate or the like. Suitable titanic esters are, for example, titanium tetrabutoxide or titanium tetraisopropoxide. Examples of suitable zirconium compounds are zirconium acetylacetonate and zirconium 2,2,6,6-tetramethyl- 3,5-heptanedionate.

Other suitable Lewis-acidic organic metal compounds are tin compounds, such as tin dialkyl salts of aliphatic carboxylic acids, or zinc salts, such as tin diacetate, tin dioctoate, tin dilaurate, dimethyltin diacetate, dibutyltin dibutyrate, dibutyltin bis(2-ethylhexanoate), dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, zinc(ll) diacetate or zinc(ll) dioctoate, for example.

Preferred Lewis-acidic organic metal compounds are tin compounds or the tin dialkyl salts of aliphatic carboxylic acids, such as, for example, tin diacetate, tin dioctoate, tin dilaurate, dimethyltin diacetate, dibutyltin dibutyrate, dibutyltin bis(2-ethylhexanoate), dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate, or zinc salts, such as zinc(ll) diacetate, zinc(ll) dioctoate, or zirconium compounds, such as, for example, zirconium acetylacetonate or zirconium 2,2,6,6- tetramethyl-3,5-heptanedionate, or bismuth compounds, or titanic esters. One particularly preferred embodiment in accordance with the invention is the use of dibutyltin dilaurate as catalyst.

Mixtures of the stated catalysts are also suitable in accordance with the invention. Examples of suitable catalyst amounts are from 0.00001 to 0.1 part by weight per 100 parts by weight of polyhydroxyl compound.

In a further embodiment in accordance with the invention, further, typical varnish components and/or additives may be added to the varnish. These are common knowledge to the skilled person. Suitable in accordance with the invention are, for example, antioxidants, UV stabilizers such as UV absorbers and suitable radical scavengers (especially HALS compounds, hindered amine light stabilizers), activators (accelerators), dryers, fillers, pigments, dyes, antistatic agents, flame retardants, thickeners, thixotropic agents, surface-active agents, viscosity modifiers, plasticizers, or chelating agents. Mixtures of the stated typical varnish components and/or additives are also suitable in accordance with the invention. Further details regarding suitable typical varnish components and/or additives and also concerning the amounts used are common knowledge to the skilled person or are described in WO 2014/191503 A9, for example.

A suitable mixing ratio of the isocyanate component (C) to the polyester polyol composed of the carboxylic acid component (A) and the alcohol component (B) is, for example, a molar ratio of isocyanate groups to isocyanate-reactive hydroxyl groups of in general 0.2:1 to 5:1 , preferably 0.75:1 to 2.5:1 , more preferably 0.8:1 to 2:1 , and very preferably 0.8:1 to 1.5:1 . Methods for applying the coating composition to substrates, for the curing of the coating composition, and for the optional removal of solvents are known in general to the skilled person or are described in WO 2014/191503 A9, for example.

Methods for the coating of substrates encompass, for example, the application of the coating composition to a substrate to be coated, in the desired thickness, and also the removal of volatile constituents optionally present in the coating composition, by means of heating, for example. For this purpose, for example, the isocyanate component (C) is first mixed with the polyester polyol of the invention and optionally with further components and then applied to a substrate. Application may take place, for example, by spraying, troweling, coating with a doctor knife, brushing, rolling, roller coating, pouring, laminating, injection backmolding, or coextruding. Further method constituents and methods are known to the skilled person or are described in WO 2014/191503 A9, for example.

Suitable substrates for the varnish formulations of the invention are likewise common knowledge to the skilled person or are described in WO 2014/191503 A9, for example.

The coating mixture can be subsequently be cured at an ambient temperature of 20 to 150°C, preferably of 25 to 80°C, and more preferably of 30 to 60°C (e.g., for refinish applications or large objects which are difficult to place in an oven). In another preferred embodiment, for OEM applications, for example, the varnish mixture is cured generally at 1 10 to 150°C, preferably at 120 to 140°C. The thickness of a layer of this kind for curing may be from 0.1 μηη up to several mm, preferably from 1 to 2000 μηη, more preferably 5 to 200 μηη, very preferably from 5 to 60 μηη (based on the varnish in the state in which the solvent is removed from the varnish).

The coating compositions and varnish formulations of the invention are suitable for interior and exterior coatings and also for daylight exposure. They can be used as clearcoat, basecoat, and topcoat materials and also as primers and fillers, and they are also suitable for the coating of plastic and/or rubber articles. Further and more detailed possibilities for use are known to the skilled person or are described in WO 2014/191503 A9, for example. Processes for the preparation of hexamethoxymethylmelamine (HMMM) varnish are common knowledge to the skilled person or are described in WO 201 1/101301 A1 , for example.

In HMMM varnishes, the polyester polyol of the invention may be used, for example, as binder. For the preparation of HMMM varnishes, the polyester polyol of the invention is generally dissolved in solvent. The concentrations and solvents employed here correspond to those already described above, to those used, as already described, for the preparation of PU varnishes, or else are common knowledge to the skilled person. Examples of solvents are also found in WO 201 1/101301 A1. Preferred solvents for the preparation of HMMM varnishes are methyl ethyl ketones, ethyl acetates, cyclohexanone, methyl isobutyl ketone, isopropanol, n-butanol, methoxypropyl acetate, or xylene, and also mixtures of these solvents. Particular preference is given to using methyl ethyl ketone.

Concentrations suitable in accordance with the invention are generally at least 55 wt% of polyester polyol, with preference being given to use of 55 to 85 wt% of polyester polyol, more preferably 60 to 85 wt% of polyester polyol, and very preferably 70 to 85 wt% of polyester polyol, based on the solvent and on the polyester polyol.

Amino resins which can be used are all of the compounds known to the skilled person, as described in WO 201 1/101301 A1 , for example, examples being melamine-formaldehyde resins, benzoguanamine/formaldehyde resins, or urea/formaldehyde resins, preferably melamine-formaldehyde resins. Mixtures of the stated amino resins are also suitable in accordance with the invention. These resins may optionally have been at least partly etherified, and preferably are at least partly etherified, via an ether bond, for example, with alcohols such as methanol, ethanol, isobutanol, and n-butanol, and mixtures thereof, for example. A preferred embodiment is the use of at least partially etherified melamine-formaldehyde resins. Particularly preferred is the use of methanol ethers of melamine-formaldehyde resins such as, for example, Luwipal 066 LF ^® . Methods and compositions, such as molar incorporation ratios, for example, for the preparation of the amino resins of the invention are known to the skilled person or are described in WO 201 1/101301 A1 , for example. The processes for reacting the amino resin used with the polyester polyol are common knowledge to the skilled person or are described in WO 201 1/101301 A1 , for example. The reaction of the polyester polyol with the amino resin may take place by transetherification, in which, in the case of hydroxyl groups already etherified in the amino resin, the ether group is eliminated and is replaced by a free hydroxyl group of the polyester polyol; or by etherification, in which a free hydroxyl group of the amino resin is converted into an ether by a free hydroxyl group of the polyester polyol. The two reactions may take place simultaneously, insofar as free hydroxyl groups are present.

The reaction may take place both with and without catalysis, and with or without addition of an entrainer, such as toluene, for example.

Catalysts contemplated for the crosslinking of the coating compositions are the catalysts which are common knowledge to the skilled person for the synthesis of HMMM varnishes, such as weak and strong acids, for example. Examples are known, moreover, from WO 201 1/101301 A1 . Weak acids for the purposes of the present invention are mono- or polybasic, organic or inorganic, acids, preferably organic acids, having a pK _a value of between 1 .6 and 5.2, preferably between 1 .6 and 3.8. Examples thereof are carbonic acid, phosphoric acid, formic acid, acetic acid, maleic acid, glyoxylic acid, bromoacetic acid, chloroacetic acid, thioglycolic acid, glycine, cyanoacetic acid, acrylic acid, malonic acid, hydroxypropanedioic acid, propionic acid, lactic acid, 3-hydroxypropionic acid, glyceric acid, alanine, sarcosine, fumaric acid, acetoacetic acid, succinic acid, isobutyric acid, valeric acid, ascorbic acid, citric acid, nitrilotriacetic acid, cyclopentanecarboxylic acid, 3-methylglutaric acid, adipic acid, hexanoic acid, benzoic acid, cyclohexanecarboxylic acid, heptanedioic acid, heptanoic acid, phthalic acid, isophthalic acid, terephthalic acid, toluic acid, phenylacetic acid, phenoxyacetic acid, mandelic acid, or sebacic acid. Preference is given to organic acids, preferably mono- or polybasic carboxylic acids. Particularly preferred are formic acid, acetic acid, maleic acid, or fumaric acid.

Strong acids for the purposes of the present invention are mono- or polybasic, organic or inorganic, acids, preferably organic acids, having a pK _a value of less than 1 .6, preferably less than 1 . Examples thereof are sulfuric acid, pyrophosphoric acid, sulfurous acid, tetrafluoroboric acid, trichloroacetic acid, dichloroacetic acid, oxalic acid, or nitroacetic acid. Preference is given to organic acids, preferably organic sulfonic acids. Particularly preferred are methanesulfonic acid, para-toluenesulfonic acid, benzenesulfonic acid, dodecylbenzenesulfonic acid, cyclododecanesulfonic acid, or camphorsulfonic acid. One particularly preferred embodiment in accordance with the invention is the use as catalyst of p-toluenesulfonic acid neutralized with amines, such as in Nacure® 2500, for example.

Acids can be used as free acids or in blocked form. "Blocking" of the acid means that an acid is present in the form, for example, of a salt of the acid with primary, secondary, and tertiary amines.

Mixtures of the above acids are likewise suitable. The acids are used generally in amounts of up to 10 wt%, preferably of 0.1 to 8 wt%, more preferably of 0.3 to 6 wt%, very preferably of 0.5 to 5 wt%, and especially preferably of 1 to 3 wt%, based on the amino resin used.

The coating compositions may be admixed additionally, as described in WO 201 1/101301 A1 , with cocrosslinkers, examples being trisalkylcarbamoyltriazines (TACT), preferably

trismethylcarbamoyltriazines, tris-n-butylcarbamoyltriazines and/or mixed methylated/ n-butylated trisalkylcarbamoyltriazines.

The varnish mixtures may further be admixed with typical varnish components and/or additives. These are common knowledge to the skilled person, such as, for example, antioxidants, stabilizers, activators (accelerators), fillers, pigments, dyes, antistatic agents, flame retardants, thickeners, thixotropic agents, surface-active agents, viscosity modifiers, plasticizers, or chelating agents. Examples can be found in WO 201 1/101301 A1 . Mixtures of the stated typical varnish components and/or additives as well are suitable in accordance with the invention.

Methods for the coating of the substrates with the coating compositions of the invention, and the curing of the varnishes, are known to the skilled person or described in WO 201 1/101301 A1 , for example.

For coating, generally, at least one varnish formulation of the invention is applied in the desired thickness to the substrate that is to be coated, and the volatile constituents of the coating composition are removed (drying), optionally with heating. Coating may take place by spraying, troweling, coating with a doctor knife, brushing, rolling, roller coating, or pouring, under the conditions specified in WO 201 1/101301 A1 , for example. The coating thickness may be in a range from 3 to 1000 g/m ² and preferably 10 to 200 g/m ² . In drying, generally, solvent substantially present is removed; furthermore, there may also already be a reaction with the binder, whereas the curing encompasses essentially the reaction with the binder. Varnish curing takes place by the methods known to the skilled person, as are described in WO 201 1/101301 A1 , for example, generally depending on the amount of coating material applied and on the crosslinking energy introduced by way of high-energy radiation, by transfer of heat from heated surfaces, or via convection of gaseous media, for example. In addition to or instead of the thermal curing, curing may also take place by means of IR and NIR radiation. Suitable substrates for the varnish formulations of the invention are general knowledge to the skilled person and are described in WO 201 1/101301 A1 , for example, examples being thermoplastic polymers, metals or alloys, wood, paper, textile, leather, nonwoven, surfaces of plastic, glass, ceramic, or mineral building materials.

Uses of the coating composition or varnish formulation of the invention are common knowledge to the skilled person and are described in WO 201 1/101301 A1 , for example. The coating composition of the invention or the HMMM varnish of the invention is suitable, for example, for the coating of the above-described substrates and is in general suitable, moreover, for use as an exterior coating. Other fields of use may be the coating of containers (can coating) and metal strips (coil coatings), and also use as primer, filler, topcoat, or clearcoat. Further details of this are described in WO 201 1/101301 A1 , for example. The present specification further provides a PU varnish comprising at least one polyester polyol based on a carboxylic acid component (A) which comprises at least one carboxylic acid having at least 2 carboxyl groups, and on an alcohol component (B) which comprises at least [5- (hydroxymethyl)tetrahydrofuran-2-yl]methanol.

The present specification further provides an HMMM varnish comprising at least one polyester polyol based on a carboxylic acid component (A) which comprises at least one carboxylic acid having at least 2 carboxyl groups, and on an alcohol component (B) which comprises at least [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol.

The invention is illustrated by the examples below.

Examples

Measurement methods Viscosity determination:

The viscosity of the polyols is determined unless otherwise specified at 25°C according to DIN EN ISO 3219 (October 1 , 1994 edition) with a Rheotec RC 20 rotational viscometer using spindle CC 25 DIN (spindle diameter: 12.5 mm; measuring cylinder internal diameter:

13.56 mm) at a shear rate of 50 1/s.

Measurement of hydroxyl number:

The hydroxyl numbers are determined by the phthalic anhydride method of DIN 53240

(December 1 , 1971 edition) and reported in mg KOH/g. Measurement of acid number:

The acid number is determined according to DIN EN 1241 (May 1 , 1998 edition) and is reported in mg KOH/g.

Comparative example 1

A 3000 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged initially with 413.7 g of isophthalic acid, 496.8 g of 2,2-dimethyl-1 ,3- propanediol, 121 .3 g of adipic acid, and 1 17.7 g of trimellitic acid. The temperature is raised to 160°C, with distillation of water beginning from 154°C. The temperature is raised further and, when the reaction temperature reaches 175°C, the batch becomes clear. The temperature is raised further to 220°C and held at this temperature for 4.5 hours. The resulting polymer is cooled and discharged when it has reached an acid number of less than 25 mg KOH/g.

The resulting polymer has the following properties:

Acid number: 20.7 mg KOH/g

Hydroxyl number: 68 mg KOH/g

Comparative example 2

A 500 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged with 189.6 g of adipic acid, 71 .8 g of isophthalic acid, and 300.9 g of 1 ,4-cyclo- hexanedimethanol. The mixture is heated to 170°C, with distillation beginning when a temperature of 154°C is reached. The temperature is raised further to 220°C and held for 4 hours. After reaching an acid number of less than 2 mg KOH/g, the product is cooled and discharged.

The resulting polymer has the following properties:

Acid number: 0.6 mg KOH/g

Hydroxyl number: 72.4 mg KOH/g

Viscosity at 75°C: 6120 mPas

Comparative example 3 A 500 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged with 189.6 g of adipic acid and 297.5 g of cyclohexanedimethanol. The mixture is heated to 180°C, with distillation of water beginning at 164°C. The mixture is heated further at 180°C until 42 g of the distillate have been removed. Then the batch is cooled to 100°C and 67.5 g of furandicarboxylic acid are added. The mixture is in turn heated to a temperature of 200°C, which is maintained for 6 hours. After reaching an acid number of less than 2 mg KOH/g, the product is cooled and discharged.

The resulting polymer has the following properties: Acid number: 0.1 mg KOH/g

Hydroxyl number: 68.4 mg KOH/g

Viscosity at 75°C: 37100 mPas

Comparative example 4

A 1000 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged with 163.6 g of adipic acid, 349.0 g of 2,2-dimethyl-1 ,3-propanediol, and 58.4 g of trimellitic acid. The mixture is heated to 180°C, with distillation of water beginning at 164°C. The mixture is heated further at 180°C until 40 g of the distillate have been removed. Then the batch is cooled to 100°C and 174.7 g of furandicarboxylic acid are added. The mixture is in turn heated to a temperature of 200°C, which is maintained for 14 hours. After reaching an acid number of less than 10 mg KOH/g, the product is cooled and discharged.

The resulting polymer has the following properties:

Acid number: 5.3 mg KOH/g

Hydroxyl number: 106 mg KOH/g Viscosity at 75°C: 41400 mPas

Inventive example 5 A 3000 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged initially with 1309.9 g of adipic acid and 1513.2 g of [5-(hydroxymethyl)- tetrahydrofuran-2-yl]methanol. The mixture is heated to 180°C, during which, at 167°C, the distillation of water begins. The temperature is raised further to 220°C and held for 8 hours. After reaching an acid number of less than 2 mg KOH/g, the product is discharged.

The resulting polymer has the following properties:

Acid number: 0.7 mg KOH/g

Hydroxyl number: 109.7 mg KOH/g

Viscosity at 75°C: 527 mPas

Inventive example 6

A 500 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged with 202.9 g of adipic acid and 291 .6 g of [5-(hydroxymethyl)tetrahydrofuran-2-yl]- methanol and this initial charge is heated to 180°C. When the quantity of distillate has reached 41 g, the mixture is cooled to 100°C and 72.2 g of furandicarboxylic acid are added. This is followed by reheating to 200°C. After a further reaction time of 6 hours, the batch becomes clear. After an acid number of less than 10 mg KOH/g has been reached, the product is discharged.

The resulting polymer has the following properties:

Acid number: 5.0 mg KOH/g

Hydroxyl number: 79.1 mg KOH/g

Viscosity at 75°C: 2749 mPas

Inventive example 7 A 1000 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged with 413.7 g of isophthalic acid, 247.9 g of 2,2-dimethyl-1 ,3-propanediol, 314.2 g of [5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol, 121 .3 g of adipic acid, and 1 17.7 g of trimellitic acid. The mixture is heated to 200°C and the temperature is maintained for 12 hours. When an acid number of less than 20 mg KOH/g has been reached, the product is discharged.

The resulting polymer has the following properties: Acid number: 17.5 mg KOH/g

Hydroxyl number: 83.7 mg KOH/g Inventive example 8

A 500 ml round-neck flask equipped with thermometer, nitrogen inlet, stirrer, and heating jacket is charged with 200.8 g of adipic acid, 76.1 g of isophthalic acid, and 289.1 g of

[5-(hydroxymethyl)tetrahydrofuran-2-yl]methanol. The mixture is heated to 200°C and the temperature is maintained for 12 hours, during which the water of reaction formed is removed. When an acid number of less than 10 mg KOH/g has been reached, the product is cooled and discharged.

The resulting polymer has the following properties:

Acid number: 2.5 mg KOH/g

Hydroxyl number: 79.2 mg KOH/g

Viscosity at 75°C: 2387 mg KOH/g

Solubility of the polyester polyols of the above examples

The polymers obtained are investigated for their solubility in butyl acetate and methyl ethyl ketone. This is done by dissolving the samples at 55%, 70%, and 85% in the two solvents.

The results can be summarized as follows.

Table 1 : Solubility of the polymers from the comparative examples and the inventive examples in butyl acetate

Table 2: Solubility of the polymers from the comparative examples and the inventive exam in methyl ethyl ketone

Varnish properties

The pendulum damping PD is determined in analogy to DIN EN ISO 1522:2006. The pendulum damping is a measure of the hardness of the coating. High values in this case denote high hardness.

The Erichsen cupping EC is determined in analogy to DIN EN ISO 1520:2006. The Erichsen cupping is a measure of the flexibility and elasticity. It is reported in millimeters (mm). High values denote high flexibility. The adhesion is determined via the cross-cut test (DIN EN ISO 2409:2013) on Bonder® panel. G in the table denotes the score for cut, T denotes the score for adhesive tape. Application example 10, varnish 1a (PU varnish)

A formulation of 60 wt% polyol in methyl ethyl ketone, Basonat HI 100®, and 1 drop of DBTL (dibutyltin dilaurate) are mixed with one another. Subsequently a wet film 200-300 μηη thick is applied to the Bonder® panel and glass substrates.

After flashing off the solvent (15 minutes, room temperature), the film is cured at 120°C for 30 minutes.

Application example 11 , varnish 1 b (HMMM varnish)

A formulation of 60 wt% polyol in methyl ethyl ketone, Luwipal 066 LF®, and Nacure 2500 (Kings Industries) are mixed with one another. Subsequently a wet film 200-300 μηη thick is applied to the Bonder® panel and glass substrates. After flashing off the solvent (15 minutes, room temperature), the film is cured at 140°C for 30 minutes.

Table 3: Hardness, flexibility, and elasticity and also adhesion of inventive PU and HMMM varnishes in comparison to noninventive PU and HMMM varnishes.