IMPROVED DUALCURE COATING FABRICS AND THEIR USE

Description

[0001] The invention relates to coating compositions based on dual-cure systems, coatings producible therefrom, and their use for coating components and objects, in particular large machines and vehicles such as ships, aircraft, or rail vehicles. It further relates to coating systems and layer structures, such as basecoat-clearcoat systems, containing the coatings according to the invention.

[0002] Typically, the external surfaces of equipment, machinery, and vehicles are coated. The applied coatings serve to protect the surfaces from environmental influences, while also allowing them to be designed and decorated as desired. Basecoat-clearcoat coating systems are typically used to paint vehicles and machinery. These coating systems comprise at least one coating as a basecoat. At least one further coating as a clearcoat is applied over the basecoat.

[0003] Basecoats generally refer to the color-imparting coating materials. Clearcoats are coating materials that produce a transparent coating after application and curing. Clearcoats generally contain no pigments or fillers to avoid impairing the transparency of the coating. Clearcoats are typically used in coating systems to create the final, finishing layer to protect the underlying layers and enhance gloss.

[0004] Clearcoat layers are primarily intended to provide protection against mechanical damage and weathering. Particularly stable clearcoat layers are achieved through the use of dual-cure systems. The term "dual-cure" or "dual-cure system" refers to coating materials whose binders cure through two different crosslinking reactions.

[0005] Dual-cure coating materials are known that cure through polyurethane formation from polyols and isocyanates and additionally crosslink through UV-induced, radical polymerization of acrylic acid esters. Irradiation with UV light achieves rapid curing in the exposed areas. In the shadow areas, in contrast to exclusively radiation-curing systems, sufficient crosslinking is achieved through the second, radiation-independent reaction.

[0006] Coating compositions are known that contain compounds with OH groups and unsaturated structures such as acryloyl, vinyl, or methacryloyl groups as binders and isocyanates as hardeners. EP 2868681 A1 describes radiation-curable coating materials that, in addition to a urethane acrylate as the main component, also contain an acryloyl-functional amine synergist. However, to achieve the degree of conversion necessary for the required coating resistance, the known systems must be cured at elevated temperatures. Curing is usually achieved via forced drying or oven drying. This means that large parts such as motor vehicles, ships, aircraft, and rail vehicles can only be coated with the known dual-cure clearcoats to a limited extent, depending on the size of the available ovens.

[0007] To cure the coating compositions known to date, conventional medium-pressure mercury lamps are used to generate UV radiation. These lamps are disadvantageous due to their high energy consumption and undesirable waste heat. Furthermore, the broad emission spectrum of these lamps also emits short-wave radiation, necessitating complex protective measures when using this process.

[0008] The use of LEDs as a radiation source for curing coating compositions that crosslink through radiation-induced radical polymerization is known per se. However, to date, dual-cure systems cannot be cured by LED-generated radiation because the energy input from this radiation is too low to effect sufficient crosslinking. Therefore, the object of the present invention is to provide improved dual-cure coating materials that overcome the disadvantages of the known systems.

[0009] The object is achieved by coating compositions according to the main claim. The object is further achieved by coating systems according to the independent claim. Further embodiments are disclosed in the subclaims and the description.

[0010] The coating composition according to the invention comprises at least one component A and one component B, wherein component A contains the binder(s) and component B contains the hardener(s).

[0011] Component A of the coating composition according to the invention contains, in each case based on its total weight, 40 to 70 wt.%, preferably 30 to 60 wt.%, of one or more polyols (a), 2 to 10 wt.%, preferably 2.5 to 6 wt.%, of one or more OH-functional unsaturated aliphatic urethane acrylates (b), 0.2 to 5 wt.%, preferably 0.4 to 2 wt.%, of one or more photoinitiators (c) and a combination of amine synergists (d) comprising 1 to 10 wt.%, preferably 2 to 8 wt.%, particularly preferably 3 to 5 wt.%, of one or more aycryloyl-functional amine synergists (d1) with amine numbers in the range from 130 to 190 mg / g and 1 to 10 wt.%, preferably 2 to 8 wt.%, particularly preferably 3 to 5 wt.%, of one or more aycryloyl-functional amine synergists (d2) with Amine values ​​in the range of 60 to 105 mg / g.

[0012] According to the invention, a combination of at least two amine synergists (d1) and (d2) is used. In the following, the term "amine synergists" refers to tertiary amines with α-CH groups that are used as chain transfer auxiliaries in radical polymerizations. The amine synergists (d1) and (d2) have different amine numbers. The amine number is a common indicator for the total content of protonatable or basic nitrogen atoms in a substance. It indicates the amount of potassium hydroxide in mg that can bind as many protons of a very strong acid as 1 g of the substance. The amine number is usually determined by potentiometric titration.According to the invention, amine synergists (d1) have a high amine number in the range from 130 to 190 mg / g, preferably from 140 to 180 mg / g, particularly preferably from 145 to 170 mg / g, very particularly preferably from 150 to 165 mg / g, and amine synergists (d2) have a low amine number in the range from 60 to 105 mg / g, preferably from 65 to 100 mg / g, particularly preferably from 70 to 95 mg / g, very particularly preferably from 75 to 90 mg / g. Suitable amine synergists are acryloyl-functional oligomeric amines. In the following, the term acryloyl-functional is used for substances which have at least one acrylic acid group (C 3 H 3 O-).

[0013] Functionality refers to the number of reactive bonding sites in a molecule that participate in the polymerization reaction. Such bonding sites can be functional groups such as acrylolyl groups (acryloyl functionality) or OH groups (OH functionality). Functionality f is calculated as the product of the number-average molar mass Mz and the concentration of the functional group c in mol / kg (f = c*Mz). The number-average molar mass Mz of a substance is determined by gel permeation chromatography.

[0014] To determine the OH functionality f(OH), the concentration of OH groups in a substance is calculated from the OH number of that substance. The OH number, or hydroxyl number, indicates the amount of potassium hydroxide in milligrams equivalent to the amount of acetic acid bound during the acetylation of 1 gram of substance. The OH number is determined by titration. To determine the acryloyl functionality f(Ac), the concentration of acryloyl groups in a substance is calculated from the iodine number of that substance. The iodine number indicates the amount of iodine in grams that is bound to 100 g of an unsaturated substance. The iodine number is determined by titration.

[0015] According to the invention, the amine synergists (d1) have acryloyl functionalities in the range between 4 and 8, preferably in the range between 4.5 and 7.5, particularly preferably in the range between 5 and 7. The amine synergists (d2) have acryloyl functionalities in the range between 1 and 3.5, preferably in the range between 1.5 and 3.0, particularly preferably in the range between 1.5 and 2.5.

[0016] In addition, the amine synergists (d1) and (d2) have Gardner color numbers of less than 16, preferably less than 12, and particularly preferably less than 8. The Gardener color number is a color number used to characterize the color of clear liquids. It is determined by visually comparing the color of a sample in a glass tube with the color of defined standards. The color of the sample that most closely matches the respective standard is called the Gardener color number. The reference standard of the Gardener color scale consists of 18 glass color standards, each with defined chromaticity coordinates and luminous transmittances.

[0017] Polyols (a) suitable according to the invention are polyacrylate polyols, polyester polyols, polycarbonate polyols, polyacrylate polyester polyols, polyester polyols, and mixtures thereof. Polyacrylate polyols, polyester polyols, polyacrylate polyester polyols, and mixtures thereof are preferred. Polyacrylate polyester polyols are particularly preferred. The polyol or polyol mixture used according to the invention has OH numbers in the range between 220 and 371, preferably in the range between 250 and 350, particularly preferably in the range between 280 and 320. The polyol or polyol mixture used according to the invention further has OH functionalities in the range between 2 and 4, preferably in the range between 2 and 3.5, particularly preferably in the range between 2 and 3. OH-functional unsaturated aliphatic urethane acrylates (b) suitable according to the invention have OH numbers in the range between 0.6 and 45, preferably in the range between 5 and 30, particularly preferably in the range between 15 and 25.Furthermore, the urethane acrylates (b) have OH functionalities in the range between 2 and 6, preferably in the range between 3 and 5, particularly preferably in the range between 3.5 and 4.5.

[0018] Photoinitiators (c) suitable according to the invention are phosphine oxides and / or phosphinates. Preference is given to mixtures thereof, particularly preferably phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and ethylphenyl(2,4,6-trimethylbenzoyl)phosphinate. The photoinitiators used have absorption maxima between 250 nm and 390 nm, preferably between 260 and 375 nm. They particularly preferably each have a maximum in the range between 275 and 365 nm and a maximum in the range between 260 and 375 nm.

[0019] In a further embodiment, component A additionally contains 0.001 to 0.3 wt.%, based on the total weight of component A, preferably 0.005 to 1 wt.%, of one or more catalysts for the OH-NCO reaction. Suitable catalysts are tin complexes with organic ligands. Dibutyltin dilaurate and dibutyltin dineodecanoate are particularly preferred.

[0020] In a further embodiment, component A additionally contains 0.001 to 30 wt.%, based on the total weight of component A, preferably 10 to 30 wt.%, particularly preferably 15 to 30 wt.%, of one or more retarders. A suitable retarder is acetylacetone.

[0021] In a further embodiment, component A additionally contains 0.001 to 5 wt. %, based on the total weight of component A, preferably 1 to 5 wt. %, of one or more reactive diluents. In the following, the term "reactive diluent" refers to acryloyl-functional diluents with a viscosity of less than 50 mPa*s at 25°C, which become part of the binder during curing of the coating material. Reactive diluents suitable according to the invention are mono-, di-, and trifunctional acrylates. Preference is given to mono- and difunctional acrylates. Particular preference is given to cyclic trimethylolpropane formal acrylate CTFA and hexanediol diacrylate HDDA.

[0022] In a further embodiment, component A additionally contains 0.001 to 3 wt.%, based on the total weight of component A, of one or more light stabilizers. Furthermore, component A may contain up to 10 wt.%, based on its total weight, of one or more of the customary additives known to the person skilled in the art, such as, for example, surface-active additives, defoamers, and rheology additives.

[0023] Component B (curing component) of the composition according to the invention contains one or more aliphatic polyisocyanates (e), preferably 40 to 100 wt. %, particularly preferably 60 to 95 wt. %, based in each case on the total weight of component B. Suitable polyisocyanates (e) are all isocyanates commonly used for curing coating materials, such as, for example, polymers and oligomers based on hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanatodicyclohexylmethane (HMDI), and 1,6-diisocyanatotrimethylhexane (TMDI). Mixtures of the isocyanates mentioned can also be used. Polymers and oligomers based on hexamethylene diisocyanate (HDI) and / or isophorone diisocyanate (IPDI) are preferred.

[0024] Component A, which contains the binder, and component B, which contains the hardener, are used in a molar ratio of the OH groups of the binder to the NCO groups of the hardener in the range from 1:0.8 to 1:1.6, preferably from 1:0.9 to 1:1.3, particularly preferably 1:0.9 to 1:1.1.

[0025] In a further embodiment, the composition may comprise a further component C, which contains one or more solvents. Suitable solvents are the conventional solvents familiar to the person skilled in the art, such as ethers, esters, aliphatic and aromatic solvents. Butyl acetate, xylene, 3-methoxy-1-propyl acetate, 3-methoxy-1-butyl acetate, and mixtures thereof are preferred.

[0026] The coating materials of the invention cure through two independent crosslinking reactions. In the shadow areas, crosslinking through polyurethane formation causes complete curing of the coating material to form a durable and stable coating. In the irradiated areas, rapid curing is achieved through free-radical polymerization, which is initiated by the radiation-induced decomposition of the photoinitiators. Although the compositions of the invention, in contrast to the known coating materials, require only small amounts of photoinitiators, they exhibit surprisingly rapid surface drying. In addition, they exhibit reduced oxygen inhibition, so that the coating surfaces are significantly less tacky than those of the known dual-cure coatings, even when cured in air without a protective gas atmosphere.Due to the lower proportion of photoinitiators, the coatings according to the invention also have low yellowing.

[0027] The resulting coatings of the invention exhibit the required surface quality even at low dry film thicknesses. For example, even at a low dry film thickness of 35 µm, the usual standards for the exterior coating of aircraft, rail vehicles, and motor vehicles are achieved, particularly with regard to gloss and leveling. Furthermore, the coatings of the invention exhibit surprising flexibility despite the high degree of crosslinking, which typically results in very hard and brittle coatings. Due to these properties, the coating materials of the invention can be used preferably as clearcoats, particularly preferably as clearcoats in basecoat-clearcoat systems.

[0028] In contrast to the previously known dual-cure coating materials, the coating materials according to the invention can be cured by the use of comparatively low-energy radiation. For curing, it is therefore possible to use light sources such as LEDs which emit radiation in the long-wave UV range with wavelengths between 100 and 380 nm to the short-wave, violet range of visible light with wavelengths between 380 and 420 nm. The use of radiation in the wavelength range between 360 and 420 nm, preferably 380 to 410 nm, particularly preferably 390 to 400 nm is suitable. The irradiation dose used according to the invention is in the range from 1.0 to 2.8 J / cm 2< , preferably 1.2 to 2.5 J / cm 2< , particularly preferably 1.4 to 2.0 J / cm 2< , very particularly preferably 1.5 to 1.8 J / cm 2< . In the following, the radiation dose is understood as a physical quantity that indicates the incident radiation energy of electromagnetic radiation per area.The irradiation intensity used according to the invention is in the range from 0.5 to 8 W / cm 2 , preferably 1 to 7.5 W / cm 2 , particularly preferably 3 to 6.5 W / cm 2 , most particularly preferably 4 to 6.5 W / cm 2 . Irradiation intensity or irradiance is understood below as a physical quantity that indicates the total power of the electromagnetic energy impinging on a surface per unit area.

[0029] Complete curing of the coating materials according to the invention occurs following irradiation at room temperature. Unlike previously known coating materials, no oven drying is required.

[0030] The process according to the invention for producing a coating, preferably a clear coat, therefore comprises the following steps: (i) Providing component A and component B of the coating composition according to the invention (ii) Mixing component A and component B to form a homogeneous mixture, (iii) Applying the mixture to a substrate, (iv) Curing the applied mixture by irradiation with radiation in the wavelength range between 360 to 420 nm generated by LEDs, (v) Further curing at room temperature.

[0031] In a further embodiment, the above-described component C, which contains one or more solvents, can be added in step (ii).

[0032] Curing in step (iv) is carried out with irradiation doses in the range of 1.0 to 2.8 J / cm 2< and with irradiation intensities in the range of 0.5 to 8 W / cm 2< .

[0033] When used as a clearcoat coating material for the production of basecoat-clearcoat coating systems, the mixture obtained from step (ii) is applied to a basecoat layer in step (iii).

[0034] By eliminating oven drying and rapidly curing through irradiation, the coating materials of the invention exhibit short drying times and can be used particularly on large components for which oven drying is generally not feasible. This means that even very large components and entire machines and vehicles, such as aircraft, ships, and rail vehicles, can be readily coated. Examples Clearcoat compositions

[0035] Inventive Example 1, Comparative Examples V2 and V3 Table 1: Compositions of component A Amount in wt.% Example 1 V2 V3 ingredient Aliphatic polyester polyol OHZ = 310 mg / g 55 55 45 Unsaturated aliphatic urethane acrylate f(Ac) = 4; OHZ = 21 mg / g 5,5 5,5 15,5 Acryloyl-functional oligomeric amine Amine number = 84 mg / g as amine synergist 4,5 0 4,5 Acryloyl-functional oligomeric amine Amine number = 152 mg / g as amine synergist 3 7,5 3 Ethylphenyl (2,4,6-trimethylbenzoyl)phosphinate 1 1 1 Dibutyltin dilaurate 0,2 0,2 0,2 Acetylacetone 28 28 28 cyclic trimethylolpropane formal acrylate (CTFA) 1,9 1,9 1, 9 Light stabilizer: 1:1 (mass / mass) mixture of triazine UV absorber and HALS (Hindered Amine Light Stabilizer) 0,9 0,9 0, 9 Table 2: Composition of component B Amount in wt.% Example 1 V2 V3 Component B Aliphatic polyisocyanate based on HDI isocyanurate with an isocyanate concentration of 5.2 mol / kg 90 90 90 Butyl acetate 10 10 10 Production of the test specimens

[0036] To produce the clear coats for Examples 1, V2 and V3, components A and B were mixed, whereby the relative amounts of component A and component B were chosen such that the molar ratio of hydroxyl groups to isocyanate groups was 1:1.

[0037] To produce the test specimens, the clearcoats according to Examples 1, V2, and V3 were applied to 0.5 mm thick aluminum sheets. The aluminum sheets were coated with a commercially available epoxy primer and a commercially available polyurethane basecoat. The clearcoats were sprayed using a cup gun so that the cured clearcoat layers had a dry film thickness of 30 to 35 µm. After flashing off for 15 minutes at 23 °C, the applied clearcoat layer was cured using radiation with a maximum intensity at a wavelength of 395 nm. A Heraeus Semray LED module UVA2 was used. The irradiation dose was 1.6 J / cm² and the irradiation intensity was 6 W / cm². Tests of the specimens

[0038] The degree of dryness of the coatings was determined 15 minutes and 60 minutes after irradiation at 23°C. The degree of dryness describes the degree of drying of a coating material after application. A distinction is made between degrees of dryness 1 to 7. To test for degree of dryness 1, glass beads with a diameter between 125 µm and 250 µm were sprinkled onto the coating and their removability was tested. To test degrees of dryness 2 to 7, a paper disc with a diameter of 26 mm was placed on the coating, followed by a soft rubber disc with a diameter of 22 mm. A weight was then applied to the soft rubber disc for 60 seconds. The sample was then removed from the weight, and the degree of dryness was assessed as follows: Tg 1: Sprinkled glass beads can be easily and completely removed with a hair brush. Tg 2: After a load of 20g, the paper no longer sticks to the coating. Tg 3: After a load of 200g, the paper no longer sticks to the coating. Tg 4: After a load of 2kg, the paper no longer sticks to the coating; immediately after the load is removed, a visible change in the coating surface remains. Tg 5: After a load of 2kg, the paper no longer sticks to the coating; immediately after the load is removed, no visible change in the coating surface remains. Tg 6: After a load of 20kg, the paper no longer sticks to the coating; immediately after the load is removed, a visible change in the coating surface remains. Tg 7: After a load of 20kg, the paper no longer sticks to the coating; immediately after the load is removed, no visible change in the coating surface remains.

[0039] After determining the degree of drying, the specimens were aged for 7 days at room temperature in the absence of light. After aging, the following tests were performed.

[0040] The adhesion of the coatings was tested using cross-cutting. Two cut bands, each with six cuts, were applied to the coating on the test specimen at right angles to each other. The cuts reached down to the substrate surface. After the cuts were applied, the cut area was brushed clean, and then the adhesive tape was abruptly removed under defined conditions. Tesa tape 4657, Beiersdorf, was used as the adhesive tape. The results of the cross-cutting test were visually assessed as follows: Gt 0 smooth cut edges, no chipping Gt 1 up to 5% of the pieces are chipped Gt 2 up to 15% of the pieces are chipped Gt 3 up to 35% of the pieces are chipped Gt 4 over 65% of the pieces are chipped

[0041] The gloss of the coating surface was determined as a reflectometer reading. The reflectometer reading of a sample is defined as the ratio of the luminous flux reflected in the specular direction by the sample surface and a glass surface with a refractive index of 1.567. The measured values ​​were determined using a standard reflectometer at an angle of 60°.

[0042] The ultimate elongation of the coatings was determined in a mandrel bending test. For this purpose, the specimens were bent around a mandrel. The smaller the radius of the mandrel around which the plate can be bent without damaging or breaking the coating, the greater the ultimate elongation of the coating. The diameter of the mandrel is used as the measured value.

[0043] The scratch resistance of the coating surfaces was tested according to the Erichsen method. For this purpose, an Erichsen Type 318 hardness test bar and a carbide test needle with a spherical tip with a diameter of 0.75 mm were drawn across the surface under a defined load. The results are assessed visually, with the maximum force at which no cracking of the coating with material removal is observed.

[0044] The weathering stability of the coatings was also determined. For this purpose, the test specimens were exposed to artificial weathering, which simulated outdoor weathering through the cyclic application of radiation, humidity, and elevated temperature. The test cycle consisting of a drying phase and a condensation phase was repeated for 1500 hours. During the drying phase, the test specimens were irradiated for 4 hours with a QUV-B lamp (emission maximum at 313 nm) at a black panel temperature of 60°C. In the subsequent 4-hour condensation phase, water vapor was condensed on the test specimens at a black panel temperature of 50°C. The gloss and color of the coatings were determined before and after artificial weathering, as well as the color change, which was determined as the color difference between the colors before and after artificial weathering.The change in gloss was calculated as residual gloss, corresponding to the gloss after artificial weathering in percent of the initial gloss before artificial weathering.

[0045] To determine the color tone and calculate the color difference ΔE* ab, the reflection spectrum of the coating surface is determined using a commercially available spectrophotometer and its color location in the CIELab color space is calculated. The CIELab color space represents a spatial coordinate system in which each color tone is uniquely described by three metrics. The value L* is a measure of brightness on the black-white axis, the value a* is a measure of chroma on the red-green axis, and the value b* is a measure of chroma on the yellow-blue axis. The color difference ΔE* ab between two colors is defined as the linear distance between the color locations of the two colors in the CIELab color space.

[0046] In addition, moisture resistance was determined. For this purpose, the specimens were stored in distilled water at 23°C for 14 days, then wiped dry with a cloth and then stored for one hour at 23°C and 50% relative humidity. The adhesion and scratch resistance of the coating were then tested using a cross-cut test and the Erichsen test as described above. Table 3: Results Example 1 V2 V3 Degree of dryness Day 1 Sticky, Tg 1 not reached Sticky, Tg 1 not reached 15 minutes after irradiation Degree of dryness Day 6 Day 4 Day 3 60 minutes after irradiation Adhesion, cross-cut Gt0 GT1 GT2 Elongation at break, mandrel diameter in mm 6 6 10 Scratch resistance in Newton 20 12 15 Gloss in percent before artificial weathering 95 89 88 Colour change due to artificial weathering Colour difference ΔE* from 1,31 1, 98 2,13 Gloss in percent after artificial weathering 86 71 73 Residual gloss after artificial weathering in percent of the initial gloss 90 80 82 Adhesion after water storage, cross-cut Gt0 GT2 GT4 Scratch resistance after water immersion in Newton 20 10 12

[0047] In comparison to the non-inventive examples V2 and V3, the inventive example 1 shows reduced oxygen inhibition of curing, which results in lower tack after radiation curing, faster curing, stronger adhesion to polyurethane basecoats, higher flexibility with simultaneous improved scratch resistance, better flow and resulting increased gloss even at low dry film thicknesses, improved weathering resistance, gloss retention and color fastness as well as higher moisture resistance.

Claims

1. Coating material composition comprising at least one component A and one component B, with the component A having 40 to 70 wt.-% of one or more polyols (a), 2 to 10 wt.-% of one or more OH-functional unsaturated aliphatic urethane acrylates (b), 0.2 to 5 wt.-% of one or more photoinitiators (c) as well as a combination of tertiary amines with CH groups in alpha position as amine synergists having 1 to 10 wt.-% of one or more acryloyl-functional amine synergists (d1) with amine numbers in the range of 130 to 190 mg / g and 1 to 10 wt.-% of one or more acryloyl-functional amine synergists (d2) with amine numbers in the range of 60 to 105 mg / g, each based on the total weight of component A, and with component B having one or more aliphatic polyisocyanates (e).

2. Composition according to claim 1, characterised in that the amine synergists (d1) have acryloyl functionalities in the range of 4 to 8.

3. Composition according to one of the preceding claims, characterised in that the amine synergists (d2) have acryloyl functionalities in the range of 1.5 to 3.

4. Composition according to one of the preceding claims, characterised in that the polyols (a) are selected from polyacrylate polyols, polyester polyols, polycarbonate polyols and mixtures thereof.

5. Composition according to claim 4, characterised in that the polyols (a) have OH numbers between 220 and 371.

6. Composition according to claim 4 or 5, characterised in that the polyols (a) have OH functionalities between 2 and 4.

7. Composition according to one of the preceding claims, characterised in that the unsaturated aliphatic urethane acrylates (b) have OH functionalities in the range of 2 to 6.

8. Composition according to claim 7, characterised in that the unsaturated aliphatic urethane acrylates (b) have OH numbers in the range of 0.6 to 45.

9. Composition according to one of the preceding claims, characterised in that the photoinitiators (c) have absorption maxima between 250 nm and 390 nm.

10. Composition according to claim 9, characterised in that the photoinitiators (c) are selected from phosphine oxides and phosphinates.

11. Composition according to one of the preceding claims, characterised in that the aliphatic polyisocyanates (e) are polymers based on hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diisocyanato dicyclohexylmethane (HMDI), 1,6-diisocyanato trimethylhexane (TMDI) and mixtures thereof.

12. Composition according to one of the preceding claims, characterised in that the component A and the component B are used in a molar ratio of the OH groups of component A to the NCO groups of component B of 1 : 0.8 to 1 : 1.6.

13. Composition according to one of the preceding claims, characterised in that the composition further has a component C which comprises one or more solvents.

14. Composition according to one of the preceding claims, characterised in that the composition further contains one or more catalysts for OH-NCO reactions.

15. Composition according to one of the preceding claims, characterised in that the composition further contains one or more reactive diluents.

16. Composition according to one of the preceding claims, characterised in that the composition further contains one or more retarders.

17. Use of the composition according to any one of claims 1 to 16 as clear coat coating material in base coat - clear coat systems.

18. Method for the production of a clear coat layer comprising the steps (i) providing the coating material composition according to any one of claims 1 to 16, (ii) mixing component A and component B in order to obtain a mixture, (iii) applying the mixture, (iv) curing the applied mixture by exposure to rays having a wavelength range between 360 to 420 nm, (v) further curing at room temperature.

19. Method according to claim 18, characterised in that in step (ii), additionally, component C is mixed with components A and B.

20. Method according to claim 18 or 19, characterised in that in step (iii) the mixture is applied to a base coat layer.