Use of thermally latent catalysts for improving properties of single-layer polyurethane coatings

Abstract

The invention relates to a method for producing a single-layer polyurethane-coated plastic substrate, comprising or consisting of the following steps: a) providing a plastic substrate; b) applying a polyurethane coating system to the substrate; c) curing the polyurethane coating system to form the single layer polyurethane coated plastic substrate; wherein the polyurethane coating system comprises or consists of the following components: A) at least one polyisocyanate; b) at least one NCO reactive compound; c) at least one thermally latent catalyst; and D) optionally auxiliary agents and / or additives.

Description

[0001] The present invention relates to a process for producing a single-layer polyurethane-coated plastic substrate, to a single-layer polyurethane-coated plastic substrate obtainable or obtained by this process, and to the use of a single-layer polyurethane-coated plastic substrate. Furthermore, the present invention relates to the use of a thermal latent catalyst for improving the adhesion and / or the chemical resistance of the aforementioned single-layer polyurethane-coated plastic substrate. State of the art

[0002] Polyurethane coatings and their products are well known in the art and are used in many different technical fields, for example in the automotive industry. These coatings can be applied in a single layer or in multiple layers.

[0003] In a multi-layer coating system, a primer is first applied to the substrate, which, depending on the substrate, is intended to improve the adhesion between the substrate and the subsequent layers and, if the substrate is susceptible to corrosion, also serves to protect the substrate from corrosion. Typically, one or more pigmented and / or effect layers are applied to the primer surface, which are referred to as basecoats. Finally, a highly cross-linked clearcoat is typically applied to the basecoat, which ensures the desired gloss appearance and protects the paint system (coating system) from environmental effects. Due to these multiple layers, multi-layer coating systems have the disadvantage that the layers must be applied one after the other and are also typically cured, which leads to multiple process steps. Furthermore, the individual layers must match one another in their properties.

[0004] In contrast, a single-layer coating can be applied to the respective surface, which is subsequently cured to directly provide a coated substrate, so that this type of coating is very efficient in terms of time and process economy and costs. Such single-layer polyurethane coatings are for example commonly used in industrial metal coatings.

[0005] However, due to specific challenges when coating plastic surfaces, for example the surface tension / surface energy, the thermal expansion and the flexibility of the plastic substrate, it is typically difficult to achieve adhesion to the plastic substrate (initially and under use conditions). Therefore, a primer is used, which enhances the adhesion of the coating system to the substrate, which is overlaid by a transparent or pigmented topcoat. In contrast, single-layer coatings typically have the disadvantage of low adhesion to the substrate due to the lack of such a primer layer. This is especially true for single-layer coatings which should provide high chemical resistance when coated onto plastic substrates.

[0006] Therefore, there is still a need for a single-layer polyurethane-coated plastic substrate with good chemical resistance, wherein the adhesion between the polyurethane coating system and the plastic substrate is improved in an easy and direct manner.

[0007] Problem It was therefore an object of the present application to provide a simple process for producing a single-layer polyurethane-coated plastic substrate, wherein the single-layer polyurethane-coated plastic substrate has a good or improved chemical resistance, in particular with an improved or at least similar adhesion between the plastic substrate and the polyurethane coating compared to equivalent multi-layer coating systems and / or single-layer coating systems not according to the present application.

[0008] Solution and detailed description This object is achieved by a process for producing a single-layer polyurethane-coated plastic substrate, said process comprising or consisting of the following steps: a) providing a plastic substrate; b) applying a polyurethane coating system to said substrate; c) curing said polyurethane coating system to form said single-layer polyurethane-coated plastic substrate; wherein said polyurethane coating system comprises or consists of A) at least one polyisocyanate; B) at least one NCO-reactive compound; C) at least one thermolatent catalyst; D) optionally auxiliaries and / or additives.

[0009] During the development work leading to the present application, it was surprisingly found that the use of a thermolatent catalyst in a polyurethane coating system (also referred to as paint or lacquer) leads to a single-layer polyurethane-coated plastic substrate having a good or very good chemical resistance as well as an improved adhesion between the polyurethane coating system and the plastic substrate compared to those using ordinary catalysts, such as dibutyltin dilaurate.

[0010] In the present application, chemical resistance is understood as the resistance of the single-layer polyurethane-coated plastic substrate to chemicals. To this end, a cotton swab / stick soaked with a chemical (superior benzine (SB), MPA (methylpropylacetate (MPA), xylene (X), ethanol (EtOH), water (H2O), ethylacetate (EtAc) and / or methyl ethyl ketone (MEK)) as test substance according to DIN 51604-1 is placed on the coated surface and covered with a watch glass to prevent evaporation. After an exposure time of 1 minute or 5 minutes, the cotton stick soaked with the test substance is removed, the exposed area is dried and immediately visually and manually inspected by touching and scratching. Softening or discoloration of the paint surface is evaluated as follows: 0 = no change; 1 = only visible change / traceable change of swelling ring, hard surface, color shade; 2 = slight softening / slight change of color shade of swelling ring; 3 = clear softening (possibly slight blistering) / medium change of color shade / surface can be scratched; 4 = significant softening (possibly severe blistering), can be scratched through to the substrate / significant change of color shade; 5 = complete destruction of the coating without external influence / very significant change of color shade.

[0011] Furthermore, in the present application the adhesion is evaluated and determined by means of a diamond scratch test (crosshatch adhesion test) according to DIN EN ISO 2409:2013 (blade distance 1 mm). Loose pieces / flakes of the paint / coating are removed using a fabric adhesive tape, the tape is pressed with the fingers onto the crosshatch and is suddenly torn off. The damage to the paint / coating is observed with a magnifying glass and evaluated visually, wherein 0 means no damage to the cutting edge and 5 means complete detachment of the paint within the grid. Furthermore, it is also preferred to determine the adhesion after exposure to moisture, wherein the coated substrate (panel / sheet) is stored at 90°C and 90% relative humidity for 5 days, then it is allowed to stand at room temperature for 1 hour to regenerate, and the crosshatch adhesion test as described above is carried out again.

[0012] In the present application, the term plastic in the plastic substrate also includes fiber-reinforced plastics, such as glass or carbon fiber-reinforced plastics, and plastic blends consisting of two or more polymer types. Preferably, the plastic substrate comprises a polymeric material selected from the group consisting of polycarbonates; polycarbonate blends, in particular polycarbonate-polyester blends, polycarbonate-acrylonitrile butadiene styrene blends or mixtures thereof; polyesters, polyester blends; acrylonitrile butadiene styrene; acrylonitrile butadiene styrene blends or mixtures thereof, preferably polycarbonate and / or polycarbonate-acrylonitrile butadiene styrene blends. More preferably, the plastic substrate comprises or consists of a polycarbonate-acrylonitrile butadiene styrene blend.

[0013] The polyisocyanate A) used here can in principle be any polyisocyanate or polyisocyanate mixture known to the person skilled in the art as suitable for the preparation of polyurethanes, in particular aliphatic and / or cycloaliphatic polyisocyanates. In the present application, a polyisocyanate is a compound having at least two isocyanate groups per molecule. The polyisocyanate A) can have biuret, uretdione, isocyanurate, iminooxadiazinedione, allophanate, carbamate and / or carbodiimide / uretonimine structural units. The polyisocyanate A) is preferably a derivative of hexamethylene diisocyanate and / or pentamethylene diisocyanate, more preferably a hexamethylene diisocyanate trimer and / or a pentamethylene diisocyanate trimer.

[0014] According to the present application, the polyurethane coating system comprises at least one NCO-reactive compound B) (isocyanate-reactive). NCO-reactive compounds are understood to mean compounds which can react with polyisocyanates to give polyisocyanate polyaddition compounds, in particular polyurethanes. The NCO-reactive compounds used can be any compounds known to the person skilled in the art having an average OH or NH functionality of at least 1.5. The NCO-reactive compounds B) are preferably selected from polymeric polyols, such as polyether polyols, polyester polyols, polyurethane polyols, polysiloxane polyols, polycarbonate polyols, polyether polyamines, polybutadiene polyols, polyacrylate polyols, polymethacrylate polyols, copolymers thereof or mixtures thereof, preferably polyester polyols, polycarbonate polyols, polycarbonate-polyester polyols, polyacrylate polyols or mixtures thereof. Low-molecular-weight OH-containing substances, such as ethane-1,2-diol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, glycerol, trimethylolpropane, pentaerythritol, can optionally be used as blend partners for the polymeric polyols mentioned above.

[0015] The polymeric polyhydroxyl compounds preferably have a mass average molecular weight Mw of > 500 Dalton, more preferably between 800 and 100 000 Dalton, in particular between 1000 and 50 000 Dalton, measured by means of gel permeation chromatography (GPC) against polystyrene standards.

[0016] The polymeric polyhydroxyl compounds preferably have an OH number of 30 to 400 mg KOH / g, in particular between 100 and 300 KOH / g. The hydroxyl number (OH number) indicates the number of milligrams of potassium hydroxide equivalent to the amount of acetic acid bound in acetylation per gram of substance. In this determination, the sample is boiled with acetic anhydride / pyridine and the acid formed is titrated with potassium hydroxide solution (DIN 53240-2).

[0017] The glass transition temperature of the polymeric polyhydroxyl compounds, measured by means of DSC measurement according to DIN EN ISO 11357-2, is preferably between -150 and 100°C, more preferably between -120°C and 80°C.

[0018] The polyether polyols can be obtained by alkoxylation of suitable starter molecules under base catalysis or using double metal cyanide compounds (DMC compounds) in a manner known per se. Suitable starter molecules for the preparation of polyether polyols are, for example, simple low-molecular-weight polyols, water, organic polyamines having at least two N-H bonds or any desired mixtures of such starter molecules.

[0019] Preferred starter molecules for the preparation of polyether polyols by alkoxylation, especially by the DMC process, are especially simple polyols, such as ethylene glycol, 1,3-propanediol and butane-1,4-diol, hexane-1,6-diol, neopentyl glycol, 2-ethylhexane-1,3-diol, glycerol, trimethylolpropane, pentaerythritol and also any desired mixtures of such polyols with low-molecular-weight hydroxyl-containing esters of dicarboxylic acids of the type specified by way of example below, or low-molecular-weight ethoxylated or propoxylated products of such simple polyols, or such modified or unmodified alcohols. Suitable alkylene oxides for the alkoxylation are especially ethylene oxide and / or propylene oxide, which can be used in any order or in mixtures for the alkoxylation.

[0020] It is also possible to use tetrahydrofuran-based polyether polyols known in the art, such as polyTHF diols.

[0021] Suitable polyester polyols are described, for example, in EP-A-0 994 117 and EP-A-1 273 640. Polyester polyols can be prepared in known manner by polycondensation of low-molecular-weight polycarboxylic acid derivatives, such as succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimeric fatty acids, trimeric fatty acids, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, citric acid or trimellitic acid, with low-molecular-weight polyols, such as ethylene glycol, diethylene glycol, neopentyl glycol, hexanediol, butanediol, propanediol, glycerol, trimethylolpropane, 1,4-hydroxymethylcyclohexane, 2-methylpropane-1,3-diol, butane-1,2,4-triol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycol, or by ring-opening polymerization of cyclic carboxylic acid esters, such as ε-caprolactone. Furthermore, it is also possible to polycondense hydroxycarboxylic acid derivatives, such as lactic acid, cinnamic acid or omega-hydroxycaproic acid, to give polyester polyols. However, it is also possible to use polyester polyols of oleochemical origin. Such polyester polyols can be prepared, for example, by complete ring opening of epoxidized triglycerides containing at least partially olefinically unsaturated fatty acids with one or more alcohols having 1 to 12 carbon atoms and by subsequent partial transesterification of the triglyceride derivative onto alkyl ester polyols having 1 to 12 carbon atoms in the alkyl group.

[0022] Suitable polycarbonate polyols are linear or slightly branched and have a molecular weight Mn of 400 to 6000, preferably 600 to 3000. They are usually produced by the reaction of carbonic acid derivatives, such as diphenyl carbonate, dimethyl carbonate or phosgene, with polyols, preferably diols. Suitable diols are, for example, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, 1,4-bis(hydroxymethyl)cyclohexane, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentane-1,3-diol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, bisphenol A, tetrabromobisphenol A and lactone-modified diols. Polyether-polycarbonate diols as described, for example, in DE-A-37 17 060 can also be used.

[0023] Preferably, the polycarbonate polyols are linear. Slightly branched polycarbonate polyols produced by (partial) use of polyfunctional OH compounds, such as glycerol, trimethylolpropane (TMP), hexanetriol-1,2,6, butanetriol-1,2,4, trimethyloloxyethane, pentaerythritol, sugar-based alcohols, such as mannitol, sorbitol, methyl glycoside or 1,3,4,6-bisanhydrohexitol, can also be used.

[0024] The polyurethane polyols are preferably produced by reaction of a polyester or polycarbonate prepolymer with a suitable di- or polyisocyanate and are described, for example, in EP-A-1 273 640. Suitable polysiloxane polyols are described, for example, in WO-A-01 / 09260 and the polysiloxane polyols listed therein can preferably be used in combination with other polyhydroxy compounds, especially those having a higher glass transition temperature.

[0025] The very particularly preferred polyacrylate polyols according to the application are generally copolymers and preferably have a mass average molar mass Mw of between 1000 and 20 000 Dalton, especially between 5000 and 10 000 Dalton, measured by means of gel permeation chromatography (GPC) against a polystyrene standard. The glass transition temperature of the copolymers is generally between -100 and 100°C, especially between -50 and 80°C (measured by means of DSC measurement according to DIN EN ISO 1 1357-2).

[0026] The polyacrylate polyols preferably have an OH number of 60 to 250 mg KOH / g, especially between 70 and 200 mg KOH / g, and an acid number of between 0 and 30 mg KOH / g. The acid number here is the number of milligrams of potassium hydroxide used to neutralize 1 gram of the respective compound (DIN EN ISO 21 14).

[0027] The preparation of suitable polyacrylate polyols is known per se to the person skilled in the art. They are obtained by free-radical polymerization of olefinically unsaturated monomers having hydroxyl groups or by free-radical copolymerization of olefinically unsaturated monomers having hydroxyl groups with optional further olefinically unsaturated monomers, such as, for example, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, 3,3,5-trimethylhexyl acrylate, 3,3,5-trimethylhexyl methacrylate, stearyl acrylate, stearyl methacrylate, lauryl acrylate or lauryl methacrylate, cycloalkyl acrylate and / or cycloalkyl methacrylate, such as, for example, cyclopentyl acrylate, cyclopentyl methacrylate, isobornyl acrylate, isobornyl methacrylate or, in particular, cyclohexyl acrylate and / or cyclohexyl methacrylate. Suitable olefinically unsaturated monomers having hydroxyl groups are, in particular, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, in particular 4-hydroxybutyl acrylate and / or 4-hydroxybutyl methacrylate.

[0028] Further monomer units for the polyacrylate polyols can be vinylaromatics, such as, for example, vinyltoluene, alpha-methylstyrene or, in particular, styrene, amides or nitriles of acrylic acid or methacrylic acid, vinyl esters or vinyl ethers, and, in a subordinate amount, in particular, acrylic acid and / or methacrylic acid.

[0029] It is preferred that the NCO-reactive compounds B) are polyhydric compounds. Preferably, the polyhydric compounds are selected from the group consisting of polyester polyols, polyurethane polyols, polysiloxane polyols, polycarbonate polyols, polyacrylate polyols and mixtures thereof.

[0030] It is furthermore preferred that the ratio of the polyisocyanate A) to the NCO-reactive compounds B) is from 0.8:1.0 to 2.0:1.0, preferably from 1.0:1.0 to 1.5:1.0, more preferably from 1.05:1.0 to 1.25:1.0, based on the molar amount of the polyisocyanate groups relative to the NCO-reactive groups.

[0031] The polyurethane coating system according to the present application contains at least one thermal latent catalyst C). According to the present application, a thermal latent catalyst is any catalyst which does not accelerate or does not significantly accelerate the crosslinking reaction of the at least one polyisocyanate with the at least one NCO-reactive compound to form urethane bonds at temperatures below its activation temperature, preferably between 50°C and 70°C. Thus, the thermal latent catalyst does not significantly accelerate the crosslinking reaction at temperatures below 25°C, especially below 30°C, preferably below 40°C, but it significantly accelerates the crosslinking reaction at temperatures above 60°C, especially above 70°C. By "does not significantly accelerate" is meant here that the presence of the thermal latent catalyst in the polyurethane coating system has no any significant influence on the reaction rate of the reaction which is carried out in any case at temperatures below 25°C, especially below 30°C, preferably below 40°C. By significantly accelerate is understood that the presence of the thermal latent catalyst in the coating has a clear influence on the reaction rate of the reaction which is carried out in any case at temperatures above 60°C, especially above 70°C. Preferred thermal latent catalysts C) are inorganic tin-containing compounds which do not have a direct tin-carbon bond. It is further preferred that the thermal latent catalyst C) comprises or consists of a cyclic tin compound of formula I, II or III or mixtures thereof: wherein: D is -O-, -S- or -N(R1)-; wherein R1is a saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical which has up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or is hydrogen or a radical or R1and L3together are -Z-L5-; D*is -O- or -S-; X, Y and Z are identical or different radicals selected from the group consisting of alkylene of formula -C(R2)(R3)-, -C(R2)(R3)-C(R4)(R5)- or -C(R2)(R3)-C(R4)(R5)-C(R6)(R7)- or ortho-arylene of formula wherein R2to R11are independently saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals which have up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or are hydrogen; L1, L2and L5are independently -O-, -S-, -OC(=O)-, -OC(=S), -SC(=O)-, -SC(=S)-, -OS(=O)2O-, -OS(=O)2- or -N(R12)-, wherein R12 is a saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical having up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or hydrogen; L3 and L4 are independently -OH, -SH, -OR13, -Hal, -OC(=0)R14, -SR15, -OC(=S)R16, -OS(=0)2OR17, -OS(=0)2R18, or -NR19R20, or L3 and L4 together are -L1-X-D-Y-L2-, wherein R13 to R20 are independently a saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radical having up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or hydrogen.

[0032] Preferably, D is -N(R1)-.

[0033] Preferably, R1 is hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 20 carbon atoms or a radical More preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 12 carbon atoms or a radical Most preferably hydrogen or methyl, ethyl, propyl, butyl, hexyl or octyl, wherein propyl, butyl, hexyl and octyl are all isomeric propyl, butyl, hexyl and octyl, or Ph-, CH3Ph- or a radical .

[0034] Preferably, D* is -0-.

[0035] Preferably, X, Y and Z are alkylene-C(R2)(R3), -C(R2)(R3)-C(R4)(R5)- or ortho-arylene .

[0036] Preferably, R2 to R7 are hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 20 carbon atoms, more preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl radical having up to 8 carbon atoms, more preferably hydrogen or an alkyl radical having up to 8 carbon atoms, more preferably hydrogen or methyl.

[0037] Preferably, R8 to R11 are hydrogen or an aryl radical having up to 8 carbon atoms, more preferably hydrogen or methyl.

[0038] Preferably, L1, L2and L5are -NR12-, -S-, -SC(=S)-, -SC(=0)-, -OC(=S)-, -O- or -OC(=0)-, more preferably -O- or -OC(=0)-.

[0039] Preferably, R12is hydrogen or an alkyl, aralkyl, alkaryl or aryl group having up to 20 carbon atoms, more preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl group having up to 12 carbon atoms, more preferably hydrogen or a methyl, ethyl, propyl, butyl, hexyl or octyl group, wherein propyl, butyl, hexyl and octyl are all isomeric propyl, butyl, hexyl and octyl groups.

[0040] Preferably, L3and L4are -Hal, -OH, -SH, -OR13, -OC(=0)R14, wherein the R13and R14groups have up to 20 carbon atoms, more preferably up to 12 carbon atoms.

[0041] More preferably, L3and L4are Cl-, MeO-, EtO-, PrO-, BuO-, HexO-, OctO-, PhO-, formate, acetate, propionate, butyrate, valerate, hexanoate, octanoate, laurate or benzoate, wherein Pr, Bu, Hex and Oct are all isomeric propyl, butyl, hexyl and octyl groups, more preferably Cl-, MeO-, EtO-, PrO-, BuO-, HexO-, OctO-, PhO-, hexanoate, laurate or benzoate, wherein Pr, Bu, Hex and Oct are all isomeric propyl, butyl, hexyl and octyl groups.

[0042] Preferably, R15to R20are hydrogen or an alkyl, aralkyl, alkaryl or aryl group having up to 20 carbon atoms, more preferably hydrogen or an alkyl, aralkyl, alkaryl or aryl group having up to 12 carbon atoms, more preferably hydrogen or a methyl, ethyl, propyl, butyl, hexyl or octyl group, wherein propyl, butyl, hexyl and octyl are all isomeric propyl, butyl, hexyl and octyl groups.

[0043] The L1-X, L2-Y and L5-Z units are preferably -CH2CH2O-, -CH2CH(Me)O-, -CH(Me)CH2O-, -CH2C(Me)2O-, -C(Me)2CH2O- or -CH2C(=0)0-.

[0044] HN[CH2CH2O-]2, HN[CH2CH(Me)O-]2, HN[CH2CH(Me)O-][CH(Me)CH2O-], HN[CH2C(Me)20-]2, HN[CH2C(Me)20-][C(Me)2CH2O-], HN[CH2C(=0)0-]2, MeN[CH2CH2O-]2, MeN[CH2CH(Me)O-]2, MeN[CH2CH(Me)O-][CH(Me)CH2O-], MeN[CH2C(Me)20-]2, MeN[CH2C(Me)20-][C(Me)2CH2O-], MeN[CH2C(=0)0-]2, EtN[CH2CH2O-]2, EtN[CH2CH(Me)O-]2, EtN[CH2CH(Me)O-][CH(Me)CH2O-], EtN[CH2C(Me)20-]2, EtN[CH2C(Me)20-][C(Me)2CH2O-], EtN[CH2C(=0)0-]2, PrN[CH2CH2O-]2, PrN[CH2CH(Me)O-]2, PrN[CH2CH(Me)O-][CH(Me)CH2O-], PrN[CH2C(Me)20-]2, PrN[CH2C(Me)20-][C(Me)2CH2O-], PrN[CH2C(=0)0-]2, BuN[CH2CH2O-]2, BuN[CH2CH(Me)O-]2, BuN[CH2CH(Me)O-][CH(Me)CH2O-], BuN[CH2C(Me)20-]2, BuN[CH2C(Me)20-][C(Me)2CH2O-], BuN[CH2C(=0)0-]2, HexN[CH2CH2O-]2, HexN[CH2CH(Me)O-]2, HexN[CH2CH(Me)O-][CH(Me)CH2O-], HexN[CH2C(Me)20-] 2、 HexN[CH2C(Me)20-][C(Me)2CH2O-], HexN[CH2C(=0)0-]2, OctN[CH2CH2O-]2, OctN[CH2CH(Me)O-]2, OctN[CH2CH(Me)O-][CH(Me)CH2O-], OctN[CH2C(Me)20-] 2、OctN[CH2C(Me)2O -] [C(Me)2CH2O -], OctN[CH2C(=0)0 -]2, wherein Pr, Bu, Hex and Oct can be all isomeric propyl, butyl and octyl groups, PhN[CH2CH2O -]2, PhN[CH2CH(Me)O -]2, PhN[CH2CH(Me)O -] [CH(Me)CH2O -], PhN[CH2C(Me)2O -]2, PhN[CH2C(Me)2O -] [C(Me)2CH2O -], PhN[CH2C(=0)0 -]2, .

[0045] Methods for preparing suitable thermal latent catalysts according to the present application are described, for example, in EP 2 900 716 A1, EP 2 900 717 A1, EP 2 772 496 A1, EP 14182806, J. Organomet. Chem. 2009 694 3184-3189, Chem. Heterocycl. Comp. 2007 43 813-834, Indian J. Chem. 1967 5 643-645 and the documents cited therein, the entire disclosures of which are hereby incorporated by reference.

[0046] As known to the person skilled in the art, tin compounds have an oligomerization tendency, so that usually either polynuclear tin compounds or mixtures of mononuclear and polynuclear tin compounds are present. In polynuclear tin compounds, the tin atoms are preferably connected to each other via oxygen atoms ("oxygen bridges"). Typical oligomeric complexes (polynuclear tin compounds) are formed, for example, by condensation of tin atoms via oxygen or sulfur, for example with n > 1 (see formula II). In the case of low oligomerization, cyclic oligomers are often encountered, and in the case of high oligomerization, linear oligomers with OH or SH end groups are often encountered (see formula III).

[0047] In one embodiment of the present application, the thermal latent catalyst is selected from the following types of mononuclear and polynuclear tin compounds: 1,1 -Di- "R" -5- "organyl" -5-aza-2,8-dioxa-1 -stannocin, 1,1 -Di- "R" -5- (N- "organyl" )aza-3,7-di- "organyl" -2,8-dioxa-1 -stannocin, 1,1 -Di- "R" -5- (N- "organyl" )aza-3,3,7,7-tetra- "organyl" -2,8-dioxa-1 -stannocin, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, wherein "R" is D*, L3 or L4 as defined above and "organyl" is R1 as defined above.

[0048] In a preferred embodiment of the application, the heat latent catalyst is selected from the group consisting of: 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 2, 4, 6, 10, 12, 14-hexamethyl- 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 4, 12-di- "organyl" - 1, 7, 9, 15-tetraoxa-4, 12-diaza-8-stannaspiro[7.7] pentadecane, 1, 1-dichloro-5-methyl-5-aza-2, 8-dioxa-1-stannacyclooctane or mixtures thereof.

[0049] It is further preferred that the heat-latent catalyst C) comprises or consists of a cyclic tin compound selected from the group consisting of 4,12-di-n-butyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,6,10,14-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10,10-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10-trimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,10-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2-methyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 2,2,4,10,10,12-hexamethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane or mixtures thereof.

[0050] The concentration of tin derived from the heat-latent catalyst C) is preferably 50 to 2000 ppm, preferably 100 to 1500 ppm, more preferably 500 to 1000 ppm, based on the solids content of the polyisocyanate A).

[0051] The heat-latent catalyst can be combined with other catalysts / activators known in the art; for example, titanium, zirconium, bismuth, tin(II) and / or iron catalysts as described, for example, in WO 2005 / 058996. Amines or amidines can also be added as cocatalysts. Furthermore, in the polyisocyanate polyaddition reaction, acidic compounds, such as 2-ethylhexanoic acid or alcohols, can also be added to control the reaction.

[0052] The polyurethane coating system can additionally comprise an effective amount of typical additives and other auxiliaries, such as solvents. The effective amount of solvent is preferably at most 150% by weight, more preferably at most 100% by weight, in particular at most 70% by weight, in each case based on the non-volatile constituents of the respective coating composition (polyurethane coating system). The effective amount of further additives is preferably at most 25% by weight, more preferably at most 10% by weight, in particular at most 5% by weight, in each case based on the non-volatile constituents of the respective coating composition (polyurethane coating system).

[0053] Examples of suitable additives and auxiliaries are, inter alia, light stabilizers, such as UV absorbers and sterically hindered amines (HALS), and stabilizers, fillers and anti-settling agents, antifoams, anti-cratering and / or wetting agents, flow agents, film-forming auxiliaries, matting agents, reactive diluents, solvents, rheology control substances, slip additives and / or components which prevent soiling of the cured paint and / or improve the cleanability of the cured paint.

[0054] Light stabilizers, in particular UV absorbers, such as substituted benzotriazoles, S-phenyltriazines or oxalanilides, and sterically hindered amines, in particular having a 2,2,6,6-tetramethylpiperidyl structure, which are referred to as HALS, are described, for example, in A. Valet, Lichtschutzmittel für Lacke [Light Stabilizers for Coatings], Vincentz Verlag, Hanover, 1996.

[0055] Stabilizers, such as free-radical scavengers and other polymerization inhibitors, such as sterically hindered phenols, stabilize the paint components during storage and are intended to prevent discoloration during curing. Acidic stabilizers can also be used in isocyanate-containing components, such as alkyl-substituted metaphosphates and water scavengers, such as triethyl orthoformate.

[0056] Preferred fillers are those compounds which have no adverse effect on the appearance of the varnish or topcoat layer. Examples are nanoparticles based on silicon dioxide, aluminum oxide or zirconium oxide; reference is also made additionally to Römpp Lexicon »Lacke und Druckfarben« [Coatings and Printing Inks] Georg Thieme Verlag, Stuttgart, 1998, pages 250 to 252.

[0057] If fillers, matting agents or pigments are present in the varnish or topcoat, it can be advisable to add an anti-settling agent to prevent separation of the constituents during storage.

[0058] Wetting and levelling agents improve the surface wetting and / or levelling of the coating. Examples are fluorine-containing surfactants, silicone surfactants and certain polyacrylates. Rheology control additives are important to control the properties of the liquid coating during application and in the levelling phase on the substrate and are additives known, for example, from patent specification WO 94 / 22968, EP-A-0 276 501, EP-A-0 249 201 or WO 97 / 12945; crosslinked polymer microparticles as disclosed, for example, in EP-A-0 008 127; inorganic phyllosilicates such as aluminium-magnesium silicates, sodium-magnesium and sodium-magnesium-fluorine-lithium phyllosilicates; silicas such as Aerosil®; or synthetic polymers having ionic and / or associative groups such as polyvinyl alcohol, poly(meth)acrylamide, poly(meth)acrylic acid, polyvinylpyrrolidone, styrene-maleic anhydride or ethylene-maleic anhydride copolymers and derivatives thereof, or hydrophobically modified ethoxylated urethanes or polyacrylates.

[0059] Suitable solvents should be used in a manner known to the person skilled in the art, which is matched to the binder used and the application method. The solvents are intended to dissolve the components used and to facilitate their mixing and to avoid incompatibilities. Furthermore, during application and curing, they should facilitate film formation and crosslinking reactions in order to ultimately produce a dried paint layer ("coating") which has a very good appearance and is free from defects such as popping or pinholes.

[0060] The polyurethane coating system can also contain pigments, dyes and / or fillers. Pigments, dyes and / or fillers for this purpose are known to the person skilled in the art.

[0061] According to step a) of the method according to the application, a plastic substrate is provided. According to step b), a polyurethane coating system is applied to this substrate. The plastic substrate provided in step a) is an uncoated plastic substrate, i.e. it is not coated with any coating system. This means that after the polyurethane coating system is applied to the plastic substrate provided in step a) in step b), there is no further coating between the plastic substrate itself and the polyurethane coating system.

[0062] To facilitate the application of the polyurethane coating system in step b), the NCO- reactive compounds B) and / or the polyisocyanates A) can be present in a suitable solvent. Suitable solvents are those which have sufficient solubility for the NCO-reactive compounds and / or the polyisocyanates and which do not contain isocyanate-reactive groups. Examples of such solvents are ketones, such as acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, methyl isoamyl ketone, diisobutyl ketone, esters, such as ethyl acetate, n-butyl acetate, 2-methoxypropyl acetate (MPA), ethylene glycol diacetate, butyrolactone, diethyl carbonate, propylene carbonate, ethylene carbonate or other solvents, such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, N-ethylpyrrolidone, methylal, ethylal, butylal, 1,3-dioxolane, glycerol formal, benzene, toluene, n-hexane, cyclohexane or solvent naphtha.

[0063] The polyurethane coating system can be applied in step b) of the process of the present application from a solution, a dispersion in a liquid dispersant such as water or from a melt, and in the case of a powder coating in solid form onto the substrate. Application from an organic solution is preferred. Suitable application methods are, for example, printing, painting, roll coating, casting, dipping, fluidized bed processes and / or preferably spraying, for example compressed air spraying, airless spraying, high-speed rotation, electrostatic spray application (ESTA), optionally in combination with thermal spray application, for example hot air spraying.

[0064] Preferably, a flash-off and film-forming step is carried out between steps b) and c), wherein the film-forming step is carried out for a duration of at least 30 seconds. During the film-forming step, the polyurethane coating system applied to the plastic substrate coagulates and forms a film. The solvent and / or water present gradually leaves the film by evaporation. This operation can be accelerated by the supply of heat or an air flow at the surface of the coating. This causes the film to shrink. Generally, simultaneously with the evaporation of the solvent, the crosslinking reaction of the at least one polyisocyanate A) with the at least one NCO-reactive compound B) in the polyurethane coating system starts. The supply of heat or catalytically active coating / paint components can accelerate the crosslinking reaction in particular. It is essential in the present application that this crosslinking reaction does not take place during the film-forming phase, or only to such a slow extent that the polyisocyanate does not crosslink significantly. Depending on the conditions such as air temperature, air flow, relative humidity, it takes a few seconds to a few minutes in the process of the present application to form a film in step d) and to substantially leave the film of any solvent and / or water present. By "substantially" is meant that more than 60%, preferably more than 85%, more preferably more than 95% of the amount of solvent and / or water used has left the film. Preferably, the flash-off and film-forming step of the process of the present application is completed after 1 to 5 minutes, more preferably after 2 to 3 minutes, before the start of the curing step c) by heating.

[0065] The curing in step c) is preferably carried out at a plastic substrate temperature of less than 120°C, more preferably less than 110°C, still more preferably less than 100°C, and especially less than 90°C, wherein the curing in step c) is preferably completed in less than 45 minutes, more preferably in less than 40 minutes, still more preferably in less than 35 minutes, and most preferably in less than 30 minutes. "Substantially completed" as used herein means that the residual isocyanate content after the curing in step d) is less than 20%, preferably less than 15%, especially preferably less than 10%, more preferably less than 5%, and still more preferably less than 3%, based on the isocyanate content of the polyisocyanate in step b). The percentage of isocyanate groups still present can be determined by comparison of the isocyanate group content in weight-% in step b) with the isocyanate group content in weight-% after the curing in step c), for example by comparison of the intensity of the isocyanate band at about 2270 cm -1 -1, by means of infrared spectroscopy.

[0066] The present application further relates to a monolayer polyurethane-coated plastic substrate obtainable or obtained by the process according to the present application.

[0067] Furthermore, the present application also relates to the use of a monolayer polyurethane-coated plastic substrate according to the present application as an automotive part or other industrial plastic article, especially for household appliances or electronic devices.

[0068] Since the addition of the thermolatent catalyst especially leads to an improvement in adhesion and / or chemical resistance, the present application also relates to the use of a thermolatent catalyst, especially as described above, for improving the adhesion and / or chemical resistance of a monolayer polyurethane-coated plastic substrate according to the present application.

[0069] Embodiments The present application especially relates to the following embodiments: According to a first embodiment, the present application relates to a process for the production of a monolayer polyurethane-coated plastic substrate, comprising or consisting of the following steps: a) providing a plastic substrate; b) applying a polyurethane coating system to the substrate; c) curing the polyurethane coating system to form the monolayer polyurethane-coated plastic substrate; wherein the polyurethane coating system comprises or consists of A) at least one polyisocyanate; B) at least one NCO-reactive compound; C) at least one thermolatent catalyst; D) optionally auxiliaries and / or additives.

[0070] According to a second embodiment, the present application relates to the method according to the first embodiment, characterized in that the plastic substrate comprises a polymeric material selected from the group consisting of polycarbonates; polycarbonate blends, in particular polycarbonate-polyester blends, polycarbonate-acrylonitrile butadiene styrene blends or mixtures thereof; polyesters, polyester blends; acrylonitrile butadiene styrene; acrylonitrile butadiene styrene blends or mixtures thereof, preferably polycarbonates and / or polycarbonate-acrylonitrile butadiene styrene blends.

[0071] According to a third embodiment, the present application relates to the method according to the first or second embodiment, characterized in that the polyisocyanate A) is an aliphatic and / or cycloaliphatic polyisocyanate.

[0072] According to a fourth embodiment, the present application relates to the method according to any of the preceding embodiments, characterized in that the polyisocyanate A) is a derivative of hexamethylene diisocyanate and / or pentamethylene diisocyanate.

[0073] According to a fifth embodiment, the present application relates to the method according to any of the preceding embodiments, characterized in that the polyisocyanate A) is a hexamethylene diisocyanate trimer and / or pentamethylene diisocyanate trimer.

[0074] According to a sixth embodiment, the present application relates to the method according to any of the preceding embodiments, characterized in that the NCO-reactive compound B) is selected from the group consisting of ethane-1,2-diol, propane-1,3-diol, propane-1,2-diol, butane-1,4-diol, glycerol, trimethylolpropane, pentaerythritol, polyether polyols, polyester polyols, polyurethane polyols, polysiloxane polyols, polycarbonate polyols, polyether polyamines, polybutadiene polyols, polyacrylate polyols, polymethacrylate polyols, copolymers thereof or mixtures thereof, preferably polyester polyols, polycarbonate polyols, polycarbonate-polyester polyols, polyacrylate polyols or mixtures thereof. According to a seventh embodiment, the present application relates to the method according to any of the preceding embodiments, characterized in that the thermal latent catalyst C) comprises or consists of a cyclic tin compound of formula I, II or III or mixtures thereof: wherein: D is -0-, -S- or -N(R1)- wherein R1is a saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical having up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or is hydrogen or a radical or R1 and L3 together are -Z-L5-; D* is -O- or -S-; X, Y and Z are identical or different radicals selected from the group consisting of alkylene of the formula -C(R2)(R3)-, -C(R2)(R3)-C(R4)(R5)- or -C(R2)(R3)-C(R4)(R5)-C(R6)(R7)- or ortho-arylene of the formula wherein R2 to R11 are independently saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals having up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or are hydrogen; L1, L2 and L5 are independently -O-, -S-, -OC(=O)-, -OC(=S), -SC(=O)-, -SC(=S)-, -OS(=O)2O-, -OS(=O)2- or -N(R12)-, wherein R12 is a saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic radical or an optionally substituted aromatic or araliphatic radical having up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or is hydrogen; L3 and L4 are independently -OH, -SH, -OR13, -Hal, -OC(=O)R14, -SR15, -OC(=S)R16, -OS(=O)2OR17, -OS(=O)2R18 or -NR19R20, or L3 and L4 together are -L1-X-D-Y-L2-, wherein R13 to R20 are independently saturated or unsaturated, straight-chain or branched, aliphatic or cycloaliphatic or optionally substituted aromatic or araliphatic radicals having up to 20 carbon atoms and can optionally contain heteroatoms selected from oxygen, sulfur, nitrogen, or are hydrogen.

[0075] According to an eighth embodiment, the present application relates to the process according to any of the preceding embodiments, characterized in that the thermolatent catalyst C) comprises or consists of a cyclic tin compound selected from the group consisting of 4,12-di-n-butyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,6,10,14-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10,10-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10-trimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,10-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 4,12-di-n-butyl-2-methyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane, 2,2,4,10,10,12-hexamethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stannaspiro[7.7]pentadecane or mixtures thereof.

[0076] According to a ninth embodiment, the present application relates to the process according to embodiment 7 or 8, characterized in that the concentration of tin derived from the thermolatent catalyst C) is in the range of 50 to 2000 ppm, preferably 100 to 1500 ppm, more preferably 500 to 1000 ppm, based on the solids content of the polyisocyanate A).

[0077] According to a tenth embodiment, the present application relates to the process according to any of the preceding embodiments, characterized in that the ratio of the polyisocyanate A) to the NCO-reactive compound B) is in the range of 0.8:1.0 to 2.0:1.0, preferably 1.0:1.0 to 1.5:1.0, more preferably 1.05:1.0 to 1.25:1.0, based on the molar amount of the polyisocyanate groups relative to the NCO-reactive groups.

[0078] According to an eleventh embodiment, the present application relates to the process according to any of the preceding embodiments, characterized in that a film forming step is carried out between steps b) and c), wherein the film forming step is carried out for a duration of at least 30 seconds.

[0079] According to a twelfth embodiment, the present application relates to the process according to any of the preceding embodiments, characterized in that the curing in step c) is carried out at a plastic substrate temperature below 120 °C.

[0080] According to a thirteenth embodiment, the present application relates to the process according to any of the preceding embodiments, characterized in that the curing in step c) is completed within less than 45 minutes.

[0081] According to a fourteenth embodiment, the present application relates to a single layer polyurethane coated plastic substrate obtainable or obtained by the process according to any of embodiments 1 to 13.

[0082] According to a fifteenth embodiment, the present application relates to the use of a single layer polyurethane coated plastic substrate according to embodiment 14 for or as an automotive part or other industrial plastic article, in particular a household appliance or electronic device.

[0083] According to a sixteenth embodiment, the present application relates to the use of a thermal latent catalyst, in particular according to any of embodiments 7 to 9, for improving the adhesion and / or chemical resistance of a single layer polyurethane coated plastic substrate according to claim 14. Example

[0084] The present application is discussed below with reference to examples, but is not limited thereto.

[0085] All percentages are based on weight, unless otherwise stated.

[0086] To produce a solvent borne clearcoat as used in automotive OEM finishing in a three layer system on metal, the polyol (Setalux 1774 SS-65) is mixed with a commercial flow additive (Byk-331), a solvent mixture of butyl acetate and solvent naphtha (1 : 1, in order to adjust the theoretical solid content to the same value) and optionally a catalyst at room temperature. Also optionally the catalyst is added to the polyisocyanate of component II and mixed by stirring. The formulation is calculated to have a 10% excess of polyisocyanate.

[0087] To produce a solvent borne clearcoat for a single layer polymeric paint / coating system, the polyol Desmophen VP LS 2249 / 1 is mixed homogenously with a commercial flow additive (BorchiGel OL 17) and in case of comparative experiment 1, a commercial catalyst Addocat 201, by vigorous mixing at room temperature. Thereafter, component I is diluted with BA, in order to have a solid content of 34.3% for this clearcoat formulation.

[0088] The amount of catalyst is calculated as "tin ppm based on solid polyisocyanate resin" in both paints.

[0089] Table 1 shows the composition of the respective formulations.

[0090] The polycarbonate sheets were heat treated at 120 °C for 1 hour and then cleaned with isopropanol. All other substrates were only cleaned with isopropanol and then used. For the production of the clearcoat layers, the above mixtures were each applied to the sheets with a gravity flow cup gun (nozzle: SATA / 1.2 mm).

[0091] After the drawdown of the films, all paints were flashed for 10 minutes at room temperature. Then, the OEM clearcoat finishes, which are usually used in a three-layer system on metal, were dried for 30 minutes at 80 °C, while the single-layer clearcoats were dried for 7 minutes at 100 °C (experiments 4+5) or for 20 minutes at 100 °C (experiments 6-9). All paints were aged for 16 hours at 60 °C and the paint tests were carried out not earlier than 1 hour after room temperature.

[0092] The König pendulum hardness was determined according to DIN EN ISO 1522:2007. The pendulum hardness was measured at different times. In all cases, the sheets were flashed for 10 minutes at room temperature after application and dried for 7 minutes at 100 °C in an oven. The pendulum hardness was then measured either 1 hour or 24 hours after drying or after the sheets had been aged for 16 hours at 60 °C, i.e. at least two sheets were produced for these measurements.

[0093] The gloss of the resulting coatings was measured by reflection measurement according to DIN EN ISO 2813:2105 at an angle of 20°. The gloss is reported in gloss units (GU).

[0094] For the measurement of the layer thickness, a digital surface profilometer (Elcometer 223) from Elcometer, UK, was used according to DIN EN ISO 2808:2019 (Method 1C).

[0095] As a measure of the resistance to chemicals (Superior Benzine (SB), MPA (Methoxypropyl Acetate (MPA), Xylene (X), Ethanol (EtOH), Water (H2O), Ethyl Acetate (EtAc) and / or Methyl Ethyl Ketone (MEK)), a cotton swab soaked with the chemical as test substance according to DIN 51604-1 was placed on the paint surface and covered with a watch glass to prevent evaporation. After the exposure period of 1 minute or 5 minutes, the cotton swab soaked with the test substance was removed, the exposed area was dried and immediately visually and manually inspected by touching and scratching. The softening and discoloration of the coating surface were evaluated as follows: 0 = no change; 1 = only visible change / traces of change in swelling ring, hard surface, color shade; 2 = slight softening / slight change in color shade of swelling ring; 3 = clear softening (possibly slight blistering) / moderate change in color shade / surface can be scratched; 4 = significant softening (possibly severe blistering), scratchable through to substrate / significant change in color shade; 5 = complete destruction of coating without external influence / very significant change in color shade.

[0096] The adhesion strength ("adhesion") was determined in accordance with DIN EN ISO 2409:2013 (blade distance 1 mm) by means of crosshatching (crosshatch adhesion test / diamond scratch test). Loose flakes of paint / coating were removed by means of a fabric adhesive tape from 3M Deutschland (Scotch 389, 19 mm x 50 m, 0.26 mm, black), the tape was pressed onto the crosshatch with the fingers and pulled off suddenly. The damage to the paint was observed with a magnifying glass and assessed visually, where 0 indicates no damage to the cut edge and 5 indicates complete detachment of the paint / coating within the grid.

[0097] To determine the adhesion after exposure to moisture, the coated sheet was stored at 90°C and 90% relative humidity for 5 days, then left to stand at room temperature for 1 hour to regenerate, and a further crosshatch test was carried out.

[0098] Tables 2 and 4 show the results of the performance tests by comparison.

[0099] Starting compounds used The materials were used without further pretreatment or cleaning, unless stated otherwise.

[0100] Desmophen VPLS 2249 / 1 Solvent-free branched short-chain polyester polyol with an OH content of 15.5% and a viscosity of 1900 mPas at 23°C. Produced by Covestro Deutschland AG, Leverkusen, DE.

[0101] Desmophen C 1200 Linear aliphatic polycarbonate polyester with a hydroxyl value of approximately 56.1 mg KOH / g. Produced by Covestro Deutschland AG, Leverkusen, Germany.

[0102] Desmodur ultra N 3900 Aliphatic polyisocyanate resin based on hexamethylene diisocyanate with an NCO content of 23.5% and a viscosity of 730 mPas at 23 °C. Produced by Covestro Deutschland AG, Leverkusen, DE.

[0103] Desmodur N 3200 Aliphatic polyisocyanate resin based on hexamethylene diisocyanate (low viscosity HDI biuret) with an NCO content of 23% and a viscosity of 2500 mPas at 23 °C. Produced by Covestro Deutschland AG, Leverkusen, Germany.

[0104] Desmodur ultra N3300 Aliphatic polyisocyanate resin based on hexamethylene diisocyanate (HDI trimer) with an NCO content of 21.8% and a viscosity of 2500 mPas at 25 °C. Produced by Covestro Deutschland AG, Leverkusen, Germany.

[0105] Desmodur ultra N 3390 BA Aliphatic polyisocyanate (HDI trimer), 90% solution in butyl acetate with an NCO content of 19.6% and a viscosity of approximately 450 mPas at 25 °C. Produced by Covestro Deutschland AG, Leverkusen, Germany.

[0106] BorchiGel OL 17 Additive for improving the levelling of paint formulations, used as a 10% solution in butyl acetate. Produced by OMG AG+ Co. KG, Langenfeld, Germany.

[0107] Addocat 201 Dibutyltin dilaurate, used as a 10% solution in butyl acetate. Available from Lanxess AG, Cologne, Germany.

[0108] Setalux 1774 SS-65 Solvent-borne polyacrylic resin with an OH content of 5% based on solids, 64-66% in the solvent naphtha:butyl acetate:tert-butanol (57:40:3). Available from Allnex GmbH, Frankfurt, Germany.

[0109] Byk 331 Polyether-modified polydimethylsiloxane, used as a leveling agent. Manufactured by BYK-Chemie GmbH, Wesel, Germany.

[0110] Butyl acetate Butyl acetate, CAS 123-86-4, solvent, manufactured by BASF SE, Ludwigshafen, Germany.

[0111] MPA 1-Methoxy-2-propyl acetate, CAS 108-65-6, solvent, produced by BASF SE, Ludwigshafen, Germany.

[0112] solvent naphtha CAS 64742-94-6, Solvent, manufactured by Azelis Deutschland GmbH, Sankt Augustin, Germany.

[0113] Cat 1 – Thermally latent catalyst – 4,12-di-n-butyl-2,6,10,14-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, used as a 10% solution in butyl acetate.

[0114] Methods for preparing suitable thermally latent catalysts according to the present invention are described in, for example, EP 2 900 716 A1, EP2 900 717 A1, EP 2 772 496 A1, EP 14182806, J. Organomet. Chem. 2009 694 3184-3189, Chem. Heterocycl. Comp. 2007 43 813-834, Indian J. Chem. 1967 5 643-645 and other references therein, the entire disclosure of which is hereby incorporated herein by reference.

[0115] Substrates used The substrates used for solvent-based clear coats in applications such as OEM automotive finishing are the following materials used for testing adhesion strength: - Makrofol DE 1-1 (polycarbonate), produced by Covestro Deutschland AG, Leverkusen, Germany.

[0116] - Makroblend UT 235M colour 901510 (polycarbonate / polyester), produced by Covestro Deutschland AG, Leverkusen, Germany.

[0117] - Makroblend UT 235M colour 901510 (polycarbonate / polyester), produced by Covestro Deutschland AG, Leverkusen, Germany.

[0118] - Durethan BKV 30 H2.0 black (polyamide), produced by Lanxess, Cologne, Germany.

[0119] - Bayblend T 65 SF (PC / ABS), produced by Covestro Deutschland AG, Leverkusen, Germany.

[0120] The substrates for the single-layer polymer lacquers were polycarbonate films under the trade name Bayfol DF 1-2 (PC / ABS, produced by Covestro Deutschland AG, Leverkusen, Germany) and Makrofol DE 1-1 (see above). Prior to lacquering / coating, the sheets were heat-treated at 120 °C for 1 hour and then cleaned with isopropanol.

[0121] Table 1 OEM clearcoat formulations. All numbers in g, unless otherwise stated. comp. = comparative example.

[0122] Table 2: Summary of the test results for the OEM clearcoats applied to various substrates comp. = comparative example.

[0123] As can be seen in Table 2, none of the clearcoats as commonly used in three-layer system OEM automotive coatings on metal provided sufficient adhesion on standard polymer substrates, especially after moisture exposure.

[0124] Therefore, clearcoats as commonly used in plastic coatings and applied as single-layer coatings were developed (see Table 3).

[0125] Table 3 Plastic clearcoat formulations. All numbers in g, unless otherwise stated. comp. = comparative example.

[0126] Table 4: Summary of test results for polymeric clear coating formulations comp. = comparative example; - = not determined.

[0127] As can be seen in Table 4, the clear coating formulations according to the application are superior to the comparative examples in many respects. The residual gloss after reverse flow is much higher in experiment 5 according to the application than in comparative experiment 4; the adhesion on Bayfol DF 1-2 as well as the chemical resistance are significantly better. Unusually, the pendulum hardness of comparative experiment 4 is much higher after 24 hours than in experiment 5, but the final hardness is much higher after 16 hours of aging at 60°C.

[0128] In experiments where component I consists of a polyester polyol and a polycarbonate polyol (experiments 6-9), the advantages are also apparent when using the thermolatent catalyst according to the application. Thus, in particular, in many cases the adhesion after moisture exposure is much better in examples 6 and 8 (according to the application) than in comparative experiments 5 and 7, where a conventional catalyst is used added to component A.

[0129] Table 5 : Test results for plastic clear coating formulations and properties comp. = comparative example.

[0130] The results shown in Table 5 demonstrate that the coating properties of the clear coating formulations according to the application (examples 11, 13) with 2 different hardeners are superior to the corresponding comparative examples (10, 12) in terms of chemical resistance as well as adhesion on several plastic substrates.

Claims

1. A method for producing a single-layer polyurethane-coated plastic substrate, comprising or consisting of the following steps: a) Provide plastic substrates; b) Apply the polyurethane coating system to the substrate; c) Curing the polyurethane coating system to form the single-layer polyurethane-coated plastic substrate; The polyurethane coating system described herein contains or is composed of the following components. A) At least one polyisocyanate; B) At least one NCO reactive compound; C) At least one thermally latent catalyst; D) Optional adjuvants and / or additives.

2. The method according to claim 1, characterized in that... The plastic substrate comprises a polymer material selected from polycarbonate; polycarbonate blends, especially polycarbonate-polyester blends, polycarbonate-acrylonitrile butadiene styrene blends or mixtures thereof; polyester, polyester blends; acrylonitrile butadiene styrene; acrylonitrile butadiene styrene blends or mixtures thereof, preferably polycarbonate and / or polycarbonate-acrylonitrile butadiene styrene blends.

3. The method according to claim 1 or 2, characterized in that... The polyisocyanate A) is an aliphatic and / or alicyclic polyisocyanate.

4. The method according to any one of the preceding claims, characterized in that... The polyisocyanate A is a derivative of hexamethylene diisocyanate and / or pentamethylene diisocyanate.

5. The method according to any one of the preceding claims, characterized in that... The polyisocyanate A is a hexamethylene diisocyanate trimer and / or a pentamethylene diisocyanate trimer.

6. The method according to any one of the preceding claims, characterized in that... The NCO reactive compound B) is selected from ethylene-1,2-diol, propylene-1,3-diol, propylene-1,2-diol, butane-1,4-diol, glycerol, trimethylolpropane, pentaerythritol, polyether polyol, polyester polyol, polyurethane polyol, polysiloxane polyol, polycarbonate polyol, polyether polyamine, polybutadiene polyol, polyacrylate polyol, polymethyl methacrylate polyol, copolymers thereof, or mixtures thereof, preferably polyester polyol, polycarbonate polyol, polycarbonate-polyester polyol, polyacrylate polyol, or mixtures thereof.

7. The method according to any one of the preceding claims, characterized in that... The thermally latent catalyst C) comprises a cyclic tin compound of formula I, II, or III, or a mixture thereof, or is composed of a cyclic tin compound of formula I, II, or III, or a mixture thereof: in: D is -O-, -S-, or -N(R1)- R1 is a saturated or unsaturated, straight or branched, aliphatic or alicyclic group or optionally substituted aromatic or aryliphatic group, having up to 20 carbon atoms and optionally containing heteroatoms selected from oxygen, sulfur, nitrogen, or hydrogen or other groups. Or R1 and L3 together are -Z-L5-; D* is either -O- or -S-; X, Y, and Z are the same or different groups of alkylene or ortho-aryl groups selected from -C(R2)(R3)-, -C(R2)(R3)-C(R4)(R5)-, or -C(R2)(R3)-C(R4)(R5)-C(R6)(R7)-. R2 to R11 are independently saturated or unsaturated, straight or branched, aliphatic or alicyclic or optionally substituted aromatic or aryliphatic groups, having up to 20 carbon atoms and optionally containing heteroatoms selected from oxygen, sulfur, nitrogen, or hydrogen. L1, L2, and L5 are independently -O-, -S-, -OC(=O)-, -OC(=S), -SC(=O)-, -SC(=S)-, -OS(=O)2O-, -OS(=O)2-, or -N(R12)-. R12 is a saturated or unsaturated, straight or branched, aliphatic or alicyclic group or optionally substituted aromatic or aryliphatic group, having up to 20 carbon atoms and optionally containing heteroatoms selected from oxygen, sulfur, nitrogen, or hydrogen. L3 and L4 independently are -OH, -SH, -OR13, -Hal, -OC(=O)R14, -SR15, -OC(=S)R16, -OS(=O)2OR17, -OS(=O)2R18 or –NR19R20, or L3 and L4 together are -L1-XDY-L2-. R13 to R20 are independently saturated or unsaturated, straight or branched, aliphatic or alicyclic or optionally substituted aromatic or aryliphatic groups having up to 20 carbon atoms and optionally containing heteroatoms selected from oxygen, sulfur, nitrogen, or hydrogen.

8. The method according to any one of the preceding claims, characterized in that... The thermally latent catalyst C) comprises or is composed of cyclic tin compounds selected from 4,12-di-n-butyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,6,10,14-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10,10-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10,10-tetramethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2,10-trimethyl-1,7,9,15-tetraoxa-4 ,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,10-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2,2-dimethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 4,12-di-n-butyl-2-methyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane, 2,2,4,10,10,12-hexamethyl-1,7,9,15-tetraoxa-4,12-diaza-8-stanzaspiro[7.7]pentadecane or a mixture thereof.

9. The method according to claim 7 or 8, characterized in that... Based on the solid content of polyisocyanate A), the concentration of tin derived from the thermally latent catalyst C) is 50 to 2000 ppm, preferably 100 to 1500 ppm, and more preferably 500 to 1000 ppm.

10. The method according to any one of the preceding claims, characterized in that... Based on the molar amount of the polyisocyanate group relative to the NCO reactive group, the ratio of polyisocyanate A) to NCO reactive compound B) is 0.8:1.0 to 2.0:1.0, preferably 1.0:1.0 to 1.5:1.0, and more preferably 1.05:1.0 to 1.25:1.

0.

11. The method according to any one of the preceding claims, characterized in that... A film-forming step is performed between steps b) and c), wherein the film-forming step lasts for at least 30 seconds.

12. The method according to any one of the preceding claims, characterized in that... The curing in step c) is carried out at a temperature below 120°C on the plastic substrate.

13. A single-layer polyurethane-coated plastic substrate that can be obtained or acquired by the method according to any one of claims 1 to 12.

14. The single-layer polyurethane-coated plastic substrate of claim 14 is used for or as automotive parts or other industrial plastic articles, especially for household appliances or electronic devices.

15. The use of a thermally latent catalyst, particularly the thermally latent catalyst according to any one of claims 7 to 9, for improving the adhesion and / or chemical resistance of a single-layer polyurethane-coated plastic substrate according to claim 13.

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