SELECTIVELY STRIPPABLE COATINGS FOR METALLIC AND PLASTIC SUBSTRATES

Abstract

The invention relates to a coating material composition comprising at least one hydroxyl-containing polyester (A) having an OH number of 250 to 660 mg KOH/g, at least one polycarbonate diol (B) having an OH number of 35 to 500 mg KOH/g, in an amount of 1 to 20 wt %, based on the overall formula, and at least one polyisocyanate (C) containing biuret groups and having an isocyanate group content of 5.8 to 27 wt %, the hydroxyl-containing polyester (A) being different from the polycarbonate diol (B), and the coating material composition possessing a fraction of organic solvents of less than 420 g/l, and comprising, based on the solids content, 40 to 100 wt % of binders. The invention further relates to a method for producing a multicoat coating using a coating material composition of the invention, to the use of the coating material composition, and to substrates coated therewith.

Claims

1. A coating material composition, comprising: a hydroxyl-containing polyester (A) which has an OH number of 250 to 660 mg KOH/g, a polycarbonate diol (B) which has an OH number of 35 to 500 mg KOH/g, and which is present in an amount of 1 to 20 wt %, based on the total weight of the coating material composition, and a polyisocyanate (C) comprising a biuret group which has an isocyanate group content of 5.8 to 27 wt %, based on the total weight of the polyisocyanate (C), wherein the hydroxyl-containing polyester (A) is different from the polycarbonate diol (B), and wherein the coating material composition comprises less than 420 g/l of organic solvents as a fraction, and comprises 40 to 100 wt % of binders, based on a solids content.

2. The coating material composition according to claim 1, wherein the hydroxyl-containing polyester (A) is aliphatic, branched or both.

3. The coating material composition according to claim 1, wherein the polycarbonate diol (B) is aliphatic, linear or both.

4. The coating material composition according to claim 1, wherein the polycarbonate diol (B) has an OH number of 100 to 250 mg KOH/g.

5. The coating material composition according to claim 1, wherein the polyisocyanate (C) comprising a biuret group is aliphatic.

6. The coating material composition according to claim 1, wherein the polyisocyanate (C) comprising a biuret group is obtained from hexamethylene diisocyanate, isophorone diisocyanate, or both.

7. The coating material composition according to claim 1, wherein the polyisocyanate (C) comprising a biuret group has an isocyanate group content of 15 to 26 wt % based on the total weight of the polyisocyanate (C).

8. The coating material composition according to claim 1, further comprising a component (D) which comprises a pigment, a filler, or both.

9. The coating material composition according to claim 8, wherein the the pigment if present is at least one selected from the group consisting of color-imparting pigments, effect-imparting pigments, color- and effect-imparting pigments, and anticorrosion pigments, and wherein the filler if present is at least one selected from the group consisting of silicates, silicas, and calcium carbonates.

10. The coating material composition according to claim 1, further comprising a component (E) which comprises at least one epoxy resin or a mixture of at least one epoxy resin and at least one hydroxy-functional acrylate resin.

11. The coating material composition according to claim 1, further comprising a binder that is different than the hydroxyl-containing polyester (A), different than the polycarbonate diol (B), and different than the polyisocyanate (C) comprising a biuret group.

12. The coating material composition according to claim 1, wherein the ratio of the hydroxyl groups of the hydroxyl-containing polyester (A) and the polycarbonate diol (B) to the isocyanate groups of the polyisocyanate (C) is from 1:1.1 to 1:1.5.

13. A method for producing a multicoat coating, the method comprising: applying at least one primer composition to a substrate, applying at least one topcoat composition to the substrate coated with a primer composition, optionally applying at least one clear coat composition to the substrate coated with a primer composition and a topcoat composition, and chemically crosslinking at least one selected from the group consisting of the primer composition, the topcoat composition, and the clear coat composition, wherein the at least one primer composition, the at least one topcoat composition, the at least one clearcoat composition, or any combination thereof is the coating material composition according to claim 1, and wherein the substrate is at least one selected from the group consisting of a metal substrate and a plastic substrate.

14. A composition for the coating of a metallic substrate, a plastic substrate or both, the composition comprising the coating material composition according to claim 1 wherein the composition is at least one selected from the group consisting of a primer composition, a topcoat composition, and a clearcoat composition.

15. The composition according to claim 14, wherein the substrate is at least one selected from the group consisting of an airplane body or part of an airplane body, rotor blades of a wind energy system, a ship's hull or a part of a ship's hull, and a machine.

16. A substrate coated with a chemically crosslinked coating material obtained by curing the coating material composition according to claim 1, wherein the substrate comprises at least one selected from the group consisting of a metal and a plastic.

17. The coating composition according to claim 8, further comprising a binder that is different than the hydroxyl-containing polyester (A), different than the polycarbonate diol (B), different than the polyisocyanate (C) comprising biuret groups, and different than the component (D) which comprises a pigment, a filler, or both.

18. The coating composition according to claim 10, further comprising a binder that is different than the hydroxyl-containing polyester (A), different than the polycarbonate diol (B), different than the polyisocyanate (C) comprising biuret groups, and different than the component (E) which comprises at least one epoxy resin or a mixture of at least one epoxy resin and at least one hydroxyl-functional acrylate resin.

19. The coating composition according to claim 10, wherein the ratio of the hydroxyl groups of the hydroxyl-containing polyester (A), polycarbonate diol (B), and the component (E) which comprises at least one epoxy resin or a mixture of at least one epoxy resin and at least one hydroxyl-functional acrylate resin to the isocyanate groups of the polyisocyanate (C) is from 1:1.1 to 1:1.5.

20. The method according to claim 13, comprising applying at least one clear coat composition to the substrate coated with a primer composition and a topcoat composition.

Description

EXAMPLES

[0091] Paint constituents used were as follows:

TABLE-US-00001 Materials used Component Abbreviation and chemical designation (A) A1: aliphatic, branched OH-functional polyester with an OH number of 425 mg KOH/g (76% in butyl acetate) A2: OH-functional polyester with an OH number of 266 mg KOH/g (77% in butyl acetate) (B) B1: linear, aliphatic polycarbonate diol with an OH number of 171 mg KOH/g (C) C1: polyisocyanate containing biuret groups with an NCO content of 23 wt % in the solids content (70 wt % strength solution in xylene) C2: polyisocyanate containing biuret groups with an NCO content of 23 wt % in the solids content (70 wt % strength solution in methoxypropyl acetate) C3: polyisocyanate containing biuret groups with an NCO content of 23 wt % in the solids content (90 wt % strength solution in methyl isobutyl ketone) C4: polyisocyanate containing biuret groups with an NCO content of 23 wt % in the solids content (76 wt % strength solution in butyl acetate) C1-V: polyisocyanate containing isocyanurate groups with an NCO content of 23 wt % in the solids content (70 wt % strength solution in xylene) C2-V: polyisocyanate containing isocyanurate groups with an NCO content of 23 wt % in the solids content (70 wt % strength solution in methoxypropyl acetate) CX-V: polyisocyanate containing isocyanurate groups with an NCO content of 23 wt % in the solids content (76 wt % strength solution in cyclohexanone/methoxypropyl acetate, 1/1) (D) D1: dimethyldichlorosilane-modified hydrophobic silica (filler) D2: white pigment based on rutile D3: anticorrosion pigment comprising zinc orthophosphate hydrate D4: very fine talc (filler) D5: pigmentary carbon black (black pigment) D6: talc D7: red iron oxide pigment (E) E1: isocyanate-crosslinking epoxy-functional acrylic resin (72 wt % strength in xylene/Shellsol A/Butoxyl, 2/2/1) E2: epoxy resin based on bisphenol A and epichlorohydrin (75 wt % strength in xylene) E1-V: styrene-free adhesion resin based on polyester (60 wt % strength in butyl acetate) (F) F1: block copolymer with amine groups (30 wt % strength in methoxypropyl acetate/butyl acetate, 6/1) (wetting and dispersing agent) F2: polyether-modified polymethylalkylsiloxane (52 wt % strength in alkylbenzene/butyrolactone, 1/1), surface additive F3: polysiloxane-based defoamer (52 wt % strength in alkylbenzene) F4: polyacrylate solution (51 wt % strength), flow control and deaerating agent F5: modified urea (52 wt % strength in dimethyl sulfoxide), rheological additive F6: polyacrylate-based flow control agent (75 wt % strength in dibasic ester) F7: silicone-free defoamer F8: 3-glycidyloxypropyltrimethoxysilane F9: dimethyltin dineodecanoate (catalyst) F10: bismuth(III) neodecanoate F11: mixture of bis(1,2,2,6,6-pentamethyl-4- piperidyl) sebacate and methyl 1,2,2,6,6- pentamethyl-4-piperidyl sebacate (light stabilizer additive) F12: UV absorber based on a hydroxyphenyltriazine (85 wt % strength)

[0092] Also employed, in addition to the solvents already present in certain commercial products, were the following organic solvents: L1: acetylacetone, L2: butyl acetate, L3: cyclohexanone, L4: methoxypropyl acetate, and L5: methyl isobutyl ketone.

[0093] OH numbers and NCO contents and the like in the table above are always based on the active ingredient or solid without solvents.

[0094] The materials listed above were used to produce a variety of inventive and noninventive coating material compositions as per tables 1 to 4 below. Noninventive materials and noninventive coating material compositions are denoted by the addition of V, as comparative materials and compositions.

[0095] The numerical data in the tables of the formulas of the coating material compositions correspond to the parts by weight of the materials that were used. Al=10, for example, thus means that 10 parts by weight of a 76 wt % strength solution of the aliphatic, branched, OH-functional polyester with an OH number of 425 mg KOH/g in butyl acetate were used. All parts by weight in the formulas below add up in each case to 100 parts by weight. In the case of Al=10 (76 wt % strength in butyl acetate), this means that 7.6 wt % of a hydroxy-functional polyester (A) having an OH number of 425 mg KOH/g are present in the coating material composition.

TABLE-US-00002 TABLE 1 Clearcoats Components KL1 KL1-V KL2 KL2-V KL3 KL4 A1 24.65 24.65 A2 29.44 29.44 26.67 26.67 B1 9.30 9.30 11.11 11.11 13.89 13.89 C1 53.50 44.44 44.44 C1-V 53.50 44.44 C2 44.44 F1 0.47 0.47 0.56 0.56 0.56 0.56 F2 0.05 0.05 0.06 0.06 0.06 0.06 F9 0.28 0.28 0.33 0.33 0.33 0.33 F10 0.19 0.19 0.22 0.22 0.22 0.22 F11 0.70 0.70 0.83 0.83 0.83 0.83 F12 0.70 0.70 0.83 0.83 0.83 0.83 L1 0.47 0.47 0.56 0.56 0.56 0.56 L2 9.69 9.69 11.62 11.62 11.61 11.61 Total 100.00 100.00 100.00 100.00 100.00 100.00

[0096] The inventive clearcoats KL1 and KL2 differ from the noninventive clearcoats KL1-V and KL2-V in that in the noninventive examples a polyisocyanate containing isocyanurate groups was used rather than a polyisocyanate containing biuret groups. The inventive clearcoats KL1 and KL2 differ from one another in the choice of different inventively employable components (A), while the inventive clearcoats KL3 and KL4 differ in the choice of different inventively employable polyisocyanates (C) containing biuret groups.

TABLE-US-00003 TABLE 2 Basecoats Components BL1 BL1-V BL2 BL2-V BL3 BL3-V BL4 BL4-V A1 17.96 17.96 A2 20.41 20.41 20.41 20.41 22.45 22.45 B1 7.78 7.78 8.84 8.84 8.84 8.84 6.80 6.80 C1 40.11 31.97 C1-V 40.11 31.97 C2 31.97 31.97 C2-V 31.97 31.97 D1 0.30 0.30 0.34 0.34 0.34 0.34 0.34 0.34 D2 21.86 21.86 24.83 24.83 24.83 24.83 24.83 24.83 F1 1.20 1.20 1.36 1.36 1.36 1.36 1.36 1.36 F2 0.06 0.06 0.07 0.07 0.07 0.07 0.07 0.07 F9 0.24 0.24 0.27 0.27 0.27 0.27 0.27 0.27 F10 0.18 0.18 0.20 0.20 0.20 0.20 0.20 0.20 F11 0.90 0.90 1.02 1.02 1.02 1.02 1.02 1.02 F12 0.90 0.90 1.02 1.02 1.02 1.02 1.02 1.02 L1 0.60 0.60 0.68 0.68 0.68 0.68 0.68 0.68 L2 2.99 2.99 3.40 3.40 3.40 3.40 3.40 3.40 L4 3.12 3.12 3.55 3.55 3.55 3.55 3.55 3.55 L5 1.80 1.80 2.04 2.04 2.04 2.04 2.04 2.04 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00

[0097] The inventive basecoats BL1, BL2, BL3, and BL4 differ from the noninventive basecoats BL1-V, BL2-V, BL3-V, and BL4-V in that in the noninventive examples polyisocyanates containing isocyanurate groups were used rather than polyisocyanates containing biuret groups. The inventive basecoat BL1 differs from the inventive basecoat BL2 in the choice of a different inventively employable component (A), while the inventive basecoat BL2 differs from the inventive basecoats BL3 and BL4 in the choice of a different inventively employable polyisocyanate (C) containing biuret groups.

TABLE-US-00004 TABLE 3 Use as adhesion-promoting coating for refinishing Components HL1 HL2 HL3 HL4 A1 12.84 12.84 12.75 12.75 B1 8.57 8.57 8.50 8.50 C3 28.33 28.33 28.33 28.33 D1 0.27 0.27 0.27 0.27 D2 13.93 13.93 13.82 13.82 D3 5.09 5.09 5.05 5.05 D4 3.21 3.21 3.19 3.19 D5 0.11 0.11 0.11 0.11 E1 5.95 5.95 E1-V 5.95 5.95 F1 0.54 0.54 0.53 0.53 F2 0.11 0.11 0.11 0.11 F3 0.03 0.03 0.03 0.03 F6 0.38 0.38 0.37 0.37 F8 0.16 0.16 0.59 0.59 F9 0.05 0.05 0.05 0.05 L1 3.46 3.46 3.46 3.46 L2 7.51 7.51 7.47 7.47 L4 8.31 8.31 8.27 8.27 L5 1.15 1.15 1.15 1.15 Total 100.00 100.00 100.00 100.00

[0098] The adhesion promoter coatings HL1 to HL4 are all inventive. HL1 and HL2 differ from one another by HL2 comprising the inventively advantageous component (E), whereas HL1 uses a polyester-based adhesion promoter instead. The same applies in respect of coatings HL3 and HL4, with coating material HL4 comprising the inventively advantageously employable component (E). In comparison to HL1 and HL2, HL3 and HL4 also contain larger amounts of the adhesion-boosting silane F8.

TABLE-US-00005 TABLE 4 Surfacer compositions Components F1 F2 F2-V A1 12.67 18.24 18.24 B1 9.33 2.52 2.52 C4 33.33 37.11 CX-V 37.11 D1 0.67 0.63 0.63 D2 13.00 12.26 12.26 D3 4.87 4.59 4.59 D6 8.00 7.55 7.55 D7 0.67 0.63 0.63 E2 3.33 3.14 3.14 F1 0.67 0.63 0.63 F2 0.20 0.19 0.19 F4 0.53 0.50 0.50 F5 0.20 0.19 0.19 F7 0.07 0.06 0.06 F8 0.20 0.19 0.19 F9 0.40 0.38 0.38 F10 0.20 0.19 0.19 L1 1.00 0.94 0.94 L3 2.00 1.89 1.89 L4 8.66 8.17 8.17 Total 100.00 100.00 100.00

[0099] The inventive surfacer compositions F1 and F2 differ significantly in the ratio of components (A) and (B) to one another and also, in particular, in the absolute amount of (B) used. The inventive surfacer composition F2 differs from the noninventive composition F2-V in that the former contains a polyisocyanate containing biuret groups, while the latter comprises a polyisocyanate containing isocyanurate groups.

[0100] Application of the Coating Materials

[0101] Substrate Preparation

[0102] The substrates selected were as follows: aluminum (pure aluminum pickled for 4 minutes at room temperature with 16 wt % strength aqueous sodium hydroxide solution and then for 2 minutes with nitric acid, subsequently washed with water and cleaned); aluminum alloy 2024 (plated or unplated and pickled, washed, and cleaned according to the above method); aluminum alloy 2024 (plated or unplated; chromic acid anodized or tartaric-sulfuric acid anodized); pure titanium (abraded with 180 grade); stainless steel (V2A and V4A abraded with 180 grade and acid-pickled); epoxy resin plates (glass fiber-reinforced and carbon fiber-reinforced, abraded with 180 grade); polyurethane and polyurea substrates (cleaned with isopropanol or abraded).

[0103] Application as Primer

[0104] The substrates were coated with the compositions of the specified examples, using a gravity feed gun, by spray application (dry film thickness on aluminum: about 20-25 m, dry film thickness on steel: about 50 m; dry film thickness on nickel: about 50 m) and after drying were coated with a topcoat (Glasurit 68 Line, High Solids 2K-CV topcoat, RAL 9016; dry film thickness 70 m).

[0105] Application as Intermediate Coat

[0106] As a primer, a polyurethane primer (Glasurit CV Universal primer-surfacer; 60 m dry film thickness) was spray-applied to the substrate, after which the compositions of the examples were spray-applied, and then a topcoat (Glasurit 68 Line, High Solids 2K-CV topcoat, RAL 9016; dry film thickness 70 m) was applied.

[0107] Application as Topcoat

[0108] The procedure was the same as for the application as intermediate coat, but without the application of the topcoat described therein other words, the inventive coating materials themselves form the topcoat.

[0109] Application as Clearcoat

[0110] The procedure used was the same as for the application as topcoat, except that rather than an inventive pigmented paint an inventive clearcoat was used as topcoat.

[0111] Performance Tests

[0112] Strippability (with a Stripper/Restripper Suitable for the Airplane Industry)

[0113] Two samples are dried at room temperature for 7 days. One of the samples is aged additionally for 96 hours at 70 C., after which the samples are each removed using a stripper suitable for the aircraft industry (Turco 1270-5 stripper, based on benzyl alcohol; available from Henkel Technologies). This is done by wetting each sample with the stripper. There follows a maximum seven-hour exposure time. The swollen material can subsequently be removed from the substrate using commercial cloths, sponges, spatulas, or the like. Effectiveness varies according to system, paint construction, and film thicknesses, and so removability much earlier than after 7 hours is also possible. Evaluation is in accordance with the +/principle: +=material removable after no later than seven hours, =material not removable after 7 hours, o=material only partly removable within the exposure period of seven hours.

[0114] Clemens Scratch Hardness Testing before and after Skydrol Exposure

[0115] After the coatings have dried at room temperature for 7 days, the scratch hardness is determined by means of a scratch stylus which runs automatically over the coating while constantly increasing its load. A triplicate determination should be carried out here.

[0116] The instrument used is from Erichsen (Sikkens model 601 scratch hardness tester). The samples are subsequently stored in Skydrol for 42 days at room temperature. A scratch hardness test is then carried out again as described above.

[0117] Determination of Tensile Adhesion

[0118] After drying of the coatings at room temperature for 7 days, a test die is adhered to the coating. After 24 hours of through-drying, or 24 hours of through-drying followed by 4 days of storage at 70 C. and 100% humidity, a tensile testing machine is used to pull the sample slowly and uniformly, perpendicularly to the substrate, until fracture takes place. Critical here is not only the measurement value, which is reported in N/mm.sup.2, but also the description of the fracture mode: adhesive fracture (between two coats) or cohesive fracture (within one coat).

[0119] UV Weathering

[0120] Prior to UV weathering, the parameters specified above (see description) are measured. A QUV-Lab instrument (model: QUV/SE) is used. The effect of sunlight, and also dew and rain, is simulated. Irradiation with UV light is at 60 C., and weathering with condensed water at 40 C. Each cycle here lasts 4 hours. Depending on requirement, the samples remain in the test apparatus for 1000 h, 2000 h, or 3000 h. After that, the measurements specified above are repeated.

[0121] Shade Measurement

[0122] The shade is measured using a shade measuring instrument from Largo with the program Largo Match 2000.

[0123] Test Results

TABLE-US-00006 TABLE 5 Test results for the clearcoats from table 1 Tests KL1 KL1-V KL2 KL2-V KL-3 KL-4 Strippability + + + + Clemens scratch hardness (in kg) on aluminum substrate before/after Skydrol exposure Film thickness in 49.8 57.6 45.9 47.4 39.9 38.4 m before exposure 4.5 3.5 3.2 1.9 4.8 4.6 after exposure 2.7 2.3 1.9 2.2 2.1 (35 d)

[0124] Table 5 shows that the inventive clearcoats are fully strippable, whereas full strippability is not ensured for the noninventive clearcoats, which comprise an unsuitable polyisocyanate. Furthermore, from direct comparisons of KL1 with KL1-V and of KL2 with KL2-V, it is clearly apparent that even with a lower film thickness, the inventive coatings KL1 and KL2 possess higher scratch hardnesses before and after Skydrol exposure.

TABLE-US-00007 TABLE 6 Test results for the basecoats from table 2 Tests BL1 BL1-V BL2 BL2-V BL3 BL3-V BL4 BL4-V Strippability + + + + Clemens scratch hardness (in kg) on aluminum substrate before/after Skydrol exposure Film 30.2 33.7 30.7 27.9 30.1 28.4 36.0 38.8 thickness in m before 8.6 7.8 >8.9 8.5 8.7 8.1 >8.9 7.3 exposure after 4.6 2.3 5.0 2.5 4.3 1.6 4.3 2.0 exposure Shade after UV weathering dL 0.39 0.45 0.30 0.35 0.44 0.51 0.36 0.42 da 0.26 0.33 0.24 0.28 0.37 0.46 0.28 0.34 db 0.79 0.84 0.80 0.87 0.86 0.96 0.83 1.02 dE 0.84 0.96 0.83 0.85 0.92 1.01 0.94 1.07

[0125] Table 6 shows that the basecoats comprising fillers and pigments likewise possess effective strippability only when a polyisocyanate containing biuret groups has been used. The comparison of basecoats BL1 and BL2 shows that even when different components (A) are employed, outstanding results are achieved. Furthermore, from direct comparisons of BL1 with BL1-V, of BL2 with BL2-V, of BL3 with BL3-V, and of BL4 with BL4-V, it is clearly apparent that the inventive paints BL1, BL2, BL3, and BL4 possess higher scratch hardnesses before and after Skydrol exposure. Moreover, the deviations in shade in the inventive paints after UV weathering are much lower than for the noninventive basecoats.

TABLE-US-00008 TABLE 7 Test results for the paints from table 3 Test Substrate HL1 HL2 HL3 HL4 Strippability + + + + Tensile adhesion in N/mm.sup.2 after Nickel 2.06 3.46 3.52 5.32 1 day RT V2A steel 1.78 3.69 3.36 4.66 aluminum, pickled 4.38 5.21 5.89 7.36 after Nickel 2.89 5.16 3.59 12.78 1 day RT and V2A steel 2.80 4.89 3.73 10.93 4 days 70 C., aluminum, pickled 3.65 9.63 5.52 14.93 100% humidity

[0126] All of the samples tested in table 7 are inventive and exhibit outstanding stripping behavior. For all of the samples, in the case of the stated exposure, there was a 100% adhesive fracture between primer and substrate. Formulations HL2 and HL4, however, comprise an epoxy-functional acrylic resin in accordance with inventively employable component (E), while formulations HL1 and HL3 comprise a polyester-based adhesion resin. The paints additized with epoxy-functional acrylate resins exhibit a significantly better tensile adhesion behavior in the coatings obtained from the inventive coating materials. The tensile adhesive strength can be increased further, moreover, by adding larger amounts of a silane, as is clearly apparent from a comparison of HL1 with HL3 and of HL2 with HL4.

TABLE-US-00009 TABLE 8 Test results for the surfacers from table 4 Test F1 F2 F2-V Strippability + +

[0127] The inventive surfacers exhibit a significantly better stripping behavior than the noninventive surfacer F2-V.