Multilayer coating system for polycarbonate substrates

Abstract

The present invention relates to a multilayer coating system on a polycarbonate substrate, comprising a primer layer applied directly to the substrate, which is obtained from a primer coating composition comprising at least one polyaspartic acid ester and at least one polyisocyanate crosslinking agent, wherein the primer coating composition does not contain epoxy-functional alkoxysilanes and does not contain compounds having reactive OH groups, and at least one organic topcoat layer disposed on the primer layer, which is obtained from a coating composition different from the primer composition.

Description

Technology Field

[0001] The present invention relates to a multilayer coating system for a polycarbonate substrate. Background Technology

[0002] Plastic substrates, particularly polycarbonate substrates, are used in the manufacture of automotive parts such as headlights, bumpers, tailgates, and sunroof panels. Plastic parts must be coated to protect the substrates from wear and weathering. However, coating plastic substrates, especially polycarbonate, is difficult because the adhesion of most binders (e.g., polyurethane) to polycarbonate surfaces is poor.

[0003] It is known that various surface treatments, such as plasma, ion beam, and electron beam processing, can improve adhesion to polycarbonate. Possible disadvantages of these technologies include the high cost of the required equipment and the difficulties in implementing them into line processes. Another method to improve the adhesion of organic coatings to polycarbonate is to use an inorganic hard coat (e.g., silica) as a primer layer. This is often applied via plasma CVD. However, hard coats are expensive and difficult to apply.

[0004] It would be desirable to provide a liquid organic coating system that exhibits excellent adhesion to a polycarbonate substrate without the use of complex surface pretreatment or a hardcoat layer. It is additionally desirable for the coating system to exhibit excellent adhesion in both dry and wet conditions, as well as excellent scratch resistance, particularly wet scratch resistance. Furthermore, it is desirable for the coating system to be easily applied, for example by spraying, and to be integrated into a continuous process.

[0005] To address the aforementioned requirements, the present invention, in a first embodiment, provides a coating system as a multilayer coating system on a polycarbonate substrate comprising the following:

[0006] - A primer layer applied directly to a substrate, obtained from a primer coating composition comprising at least one polyaspartic acid ester and at least one polyisocyanate crosslinking agent, wherein the primer coating composition does not include an epoxy-functional alkoxysilane and does not contain a compound having a reactive OH group, and

[0007] - At least one organic topcoat layer placed on a primer layer, the organic topcoat layer obtained from a coating composition different from the primer composition.

[0008] In another aspect, the present invention provides a method for forming a multilayer coating on a polycarbonate substrate, comprising the following steps:

[0009] a) a step of directly applying a primer coating composition to a substrate,

[0010] b) a step of applying at least one organic topcoat composition different from the primer coating composition to a coated substrate, and

[0011] c) Step of curing the multilayer coating.

[0012] In a further embodiment, the present invention also provides a coated automotive part. Specific details for implementing the invention

[0013] A multilayer coating system on a polycarbonate substrate comprises at least the following coating layers: a primer layer, and at least one topcoat layer placed directly or indirectly on the primer layer.

[0014] Polycarbonate substrate

[0015] The polycarbonate substrate useful for the present invention may be any polycarbonate-containing substrate. Preferably, the polycarbonate substrate contains at least 99 weight percent of polycarbonate. The polycarbonate substrate may comprise bisphenol A polycarbonate and other resin grades (branched, substituted, etc.). It may be copolymerized or blended with other polymers such as PBT, PET, ABS, or polyethylene. Examples of commercially available polycarbonate substrates include Covestro’s Makrolon® AG2677, Makroblend® DP7645, KU2-7609, or Sabic’s Lexan™ LS2.

[0016] According to the present invention, the polycarbonate substrate does not require any surface modification (e.g., using plasma) prior to the application of the primer.

[0017] Primer layer

[0018] The primer layer is located directly on the substrate. The primer layer is obtained from a primer coating composition comprising at least one polyaspartic acid ester and at least one polyisocyanate crosslinking agent.

[0019] Polyaspartic acid esters are amino-functional compounds that can be obtained by reacting a primary polyamine (preferably a diamine) with a maleic acid or fumaric acid ester. Particularly preferred in the present invention is a diaspartic acid ester preferably having the following general formula:

[0020]

[0021] In the above formula, R1 and R2 are independently selected from C1 to C10 alkyl groups, for example, methyl, ethyl, or butyl groups, and X is a divalent group. R1 and R2 may be the same or different and are preferably not reactive with respect to isocyanate groups.

[0022] Polyaspartic acid esters can be obtained by reacting a primary diamine H2N-X-NH2, in which X represents an aliphatic or alicyclic group, with a selectively substituted maleic acid or fumaric acid ester, preferably with the following chemical formula:

[0023]

[0024] The X group is obtained by removing an amino group from a primary diamine and may be, for example, a linear or branched divalent alkyl and / or cycloalkyl group, preferably a cycloalkyl group. Examples of suitable diamines include ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 2,2,4- and / or 2,4,4-trimethyl-1,6-diamino-hexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 4,4'-diaminodicyclohexyl-methane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, and 1,5-diamine-2-methylpentane. Preferably, the X group contains one or more cycloalkyl groups. Preferably, the diamine is selected from 4,4'-diaminodicyclohexylmethane and 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane. The best results were obtained using 4,4'-diaminodicyclo-hexylmethane.

[0025] Examples of suitable maleic or fumaric acid esters include dimethyl maleate, diethyl maleate, dibutyl maleate, and the corresponding fumarates. Substituted maleic or fumaric acid esters are, for example, those substituted with methyl at the 2- and / or 3- positions.

[0026] The reaction between a diamine and a maleic acid or fumaric acid ester can be carried out under conditions known to those skilled in the art for this type of reaction. For example, starting materials can be used at a temperature of 0°C to 150°C in an amount such that about one olefin double bond exists for each primary amino group. After the reaction, excess starting material can be removed by distillation. The reaction can be carried out without a solvent or in the presence of a suitable organic solvent.

[0027] Suitable polyaspartic acid esters are commercially available from Covestro as Desmophen NH 1420, NH 1520, and NH 1220.

[0028] Although not desirable, it is possible to additionally use other binder resins reactive to the polyisocyanate crosslinker, such as OH- or NH-functional binder resins. It is preferable that polyaspartic acid ester be the main binder resin, which means constituting more than 50 weight%, preferably more than 80 weight%, of the total binder resin based on the resin solid content. More preferably, polyaspartic acid ester is the only OH- or NH-functional binder resin in the primer composition.

[0029] In some embodiments, it is preferable that the substrate primer composition does not contain compounds having reactive OH groups, such as polyester polyols, polyacrylate polyols, and polyurethane polyols, because this can reduce the pot-life of the primer composition. Accordingly, it is preferable that the primer layer does not contain polyurethane upon curing (PU-free primer layer).

[0030] Polyisocyanate crosslinkers include polyfunctional isocyanates (polyisocyanates), such as linear, branched, and / or cyclic polyisocyanates. Examples of polyfunctional polyisocyanates include aliphatic diisocyanates, such as hexamethylene diisocyanate and isophorone diisocyanate, and aromatic diisocyanates, such as toluene diisocyanate and 4,4'-diphenylmethane diisocyanate. The isocyanate groups of the polyisocyanate crosslinkers are preferably free, meaning they are reactive at room temperature and not blocked. Other suitable polyisocyanates include isocyanurate trimers, allophanates, and urethdiones of diisocyanates. Suitable polyisocyanates are well known in the art and are widely commercially available. Examples of commercially available isocyanates include Covestro’s DESMODUR® N 3300A, DESMODUR® Z 4470BA, DESMODUR® N 3790 and DESMODUR® N 3900.

[0031] Preferably, the molar ratio of the functional group of the polyaspartic acid ester to the polyisocyanate crosslinker group is stoichiometrically greater, for example, 1:1.1 to 1:5, more preferably 1:1.5 to 1:3.

[0032] The primer composition is preferably clear (transparent). This means that light can pass through it without detectable scattering. This also means that the primer preferably does not contain components that make the composition opaque, such as pigments, fillers, or extenders. Preferably, the primer composition does not contain pigments, fillers, or extenders.

[0033] The primer composition is preferably solvent-based. The solvent-based coating composition comprises an organic solvent or a mixture of organic solvents as the main liquid phase. "Main liquid phase" means that the organic solvent constitutes at least 50 weight percent, preferably at least 80 weight percent, more preferably at least 90 weight percent, and in some embodiments even 100 weight percent of the liquid phase. The primer composition preferably comprises 10 to 70 weight percent, more preferably 20 to 60 weight percent, of organic solvent based on the total weight of the primer composition. More preferably, the primer composition is non-aqueous, which means that it does not contain any water.

[0034] Examples of suitable organic solvents include esters (e.g., ethyl acetate, propyl acetate), aromatic solvents (e.g., toluene), ketone solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, diacetone alcohol); aliphatic hydrocarbons; chlorinated hydrocarbons (e.g., CH2Cl2); ethers (e.g., diethyl ether, tetrahydrofuran, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene glycol monobutyl ether) and mixtures thereof. Preferred organic solvents include butyl acetate, methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), propylene glycol monomethyl ether, methoxypropyl acetate (PMA), ethylene glycol monobutyl ether and mixtures thereof.

[0035] The solid content of the primer composition may be in the range of 10 to 90 weight%, preferably 15 to 80 weight%, and more preferably 20 to 70 weight%.

[0036] The primer composition is preferably provided in the form of a 2K coating composition. "2K coating composition" means that the coating composition is provided in the form of separate components, which are mixed immediately before application to the substrate due to their reactivity. "Mixed immediately before application to the substrate" is a term well known to those skilled in the art. In this case, it is preferable that the primer composition be supplied in the form of component A containing a polyaspartic acid ester and component B containing a polyisocyanate crosslinking agent. The mixing ratio of component A and component B can be easily calculated by those skilled in the art based on the desired functional group ratio.

[0037] The primer composition can preferably be cured at ambient temperature, for example, 15°C to 30°C, preferably 20°C.

[0038] The primer composition may additionally include conventional additives such as flow regulators, dispersants, surfactants, plasticizers, thixotropic agents, light stabilizers, etc.

[0039] An important feature of the present invention is that the primer does not contain epoxy-functional alkoxysilanes. Examples of such compounds include glycidyl silanes such as 3-glycidyloxypropyl-trimethoxysilane, 3-glycidyloxypropyltriethoxysilane, and 3-glycidyloxypropyltriisopropoxysilane. Epoxy-functional alkoxysilanes are commercially available, for example, under the trade names Dynasylan® Glymo from Evonik, and Silquest® A187 and A186 from Momentive.

[0040] The use of epoxy-functional alkoxysilanes in combination with polyaspartate esters in coatings is known in WO2014138052. In that publication, epoxy-functional alkoxysilanes were shown to improve the adhesion of a polyaspartate-containing clearcoat to a colored basecoat. However, the present invention reveals that when a polyaspartate-containing coating composition is used directly on a polycarbonate substrate as a primer, the use of epoxy-functional alkoxysilanes is not necessarily required. Excellent adhesion to the polycarbonate substrate was found without the use of epoxysilanes or any alkoxysilanes.

[0041] More generally, it is preferable that the primer coating composition be free of any type of alkoxysilane, its derivatives, or its condensation products. "Derivatives" refers to reaction products of an alkoxysilane and other compounds, e.g., polymers, oligomers, or monomers. In such reactions, the alkoxysilane group is generally preserved.

[0042] In general, the possibility of avoiding the use of epoxy-functional alkoxysilanes offers many advantages. Silanes are known to be reactive and require special handling instructions. The presence of silanes can negatively affect the pot life of coating compositions. Having fewer components in the coating formula means reduced costs, decreased complexity, and easier handling.

[0043] Another floor

[0044] The primer layer is overcoated with at least one topcoat layer. At least one topcoat layer is obtained from a coating composition different from the primer composition. The topcoat layer is placed directly or indirectly (with another layer in between) on the primer layer.

[0045] Preferably, the topcoat layer placed immediately over the primer layer contains one or more organic binder resins. Preferably, it does not include an inorganic hard coating based on a silica binder. Preferably, the topcoat is not a silicon-containing coating, which means there is no silicon-containing binder resin. Such inorganic or hybrid (organically modified inorganic) coatings are generally prepared through the condensation of alkoxysilanes or other sol-gel processes. Preferably, the topcoat layer is not an inorganic or hybrid organic / inorganic coating. Silicon-containing coatings are known, for example, in EP-A 0 947 520.

[0046] Most preferably, the topcoat layer is an organic coating layer, which means that it contains only organic binder resin(s).

[0047] A coating composition for at least one topcoat layer preferably comprises one or more organic binder resins, such as polyurethane, polyester, polyacrylate, or a mixture thereof. Optionally, a crosslinking agent comprising a group reactive to each reactive group of the binder resin(s) may be present. Such systems are known to those skilled in the art. Preferably, the topcoat composition comprises one or more hydroxyl-functional binder resins and a polyisocyanate crosslinking agent.

[0048] The top coat layer may be colored (base coat) or uncolored (clear coat) depending on the desired application. Two or more top coat layers may be used in any combination. When using a colored top coat, it is advisable to use an additional clear coat layer to protect the base coat.

[0049] In some embodiments, it may be desirable to have a completely transparent system, which means that all layers are transparent. Such a system is obtained, for example, by using a transparent primer with a transparent top layer (clear coat) that has no colored layer in between. A completely transparent coating system can be used to coat transparent polycarbonate articles, for example, automotive headlights. However, in other embodiments, a colored intermediate coat (i.e., base coat) may exist between the primer layer and the clear coat.

[0050] In the case of a top coat, particularly when it is a clear coat, it is preferable to use a (transparent) coating composition containing a hydroxyl-functional binder resin and a crosslinking agent that reacts with hydroxyl groups. More preferably, the crosslinking agent is a polyisocyanate crosslinking agent.

[0051] The OH-functional binder resin (polyol) in the topcoat composition (particularly, the clearcoat composition) may be any conventional resin such as polyurethane, polyacrylate, polyester, melamine polyol, and mixtures thereof. Preferably, polyacrylate polyol, polyester polyol, melamine polyol, or mixtures thereof are used. Melamine polyol refers to the reaction product of a melamine aldehyde resin and a diol, for example, as described in WO2007028792A1.

[0052] Polyols useful for topcoat compositions (particularly clearcoat compositions) may have a glass transition temperature (Tg) of -20°C to 80°C. Additionally, mixtures of polyols with different Tg values ​​may be used. For example, a mixture of a first polyol having a Tg in the range of -20°C to 0°C and a second polyol having a Tg in the range of 45°C to 80°C may be used. In an alternative embodiment, it may be preferable to use a mixture of two polyols in which both have a Tg in the range of -20°C to 0°C. The glass transition temperature Tg is determined by a modulated differential scanning calorimeter (MDSC) using a TA Instruments Q2000 performed with a modulation option, with an amplitude of 1°C, a period of 40 seconds, and a base heating range of 5°C / min. Helium is used as a purge gas at a flow rate of 50 ml / min. Two standard runs are performed (one at a time using a single method), and the second run is used for Tg reporting.

[0053] Suitable polyols include products marketed by Allnex under the trade names Setalux® and Setal®, in particular Setalux 1152 SS-60, Setalux 1192 SS-60, Setalux 1215 BA-68, Setal 1406, and Setal 1606 BA-80.

[0054] In some embodiments, it may be preferable to use a mixture of polyacrylate and polyester polyol. In other embodiments, it may be preferable to use a mixture of polyacrylate and melamine polyol. Preferably, a mixture of polyacrylate and melamine polyol is used, and more preferably, a mixture in which both polyols have a Tg in the range of -20°C to 0°C is used.

[0055] In some embodiments, the topcoat composition (particularly, the clearcoat composition) may further contain at least one polyaspartic acid ester as a binder resin. In other embodiments, it may be preferable that the topcoat composition (particularly, the clearcoat composition) does not contain a polyaspartic acid ester.

[0056] The number average molecular weight (Mn) of the OH-functional binder resin is preferably 500 to 500,000, and preferably 1,500 to 100,000, when determined by gel permeation chromatography (GPC) on a polystyrene standard using tetrahydrofuran as the mobile phase.

[0057] The polyisocyanate crosslinker is preferably a compound having free reactive isocyanate groups. Suitable compounds are, for example, those mentioned above for the primer composition.

[0058] Although not strictly necessary, a topcoat composition (especially a clearcoat composition) may include an epoxy-functional alkoxysilane as an adhesion promoter.

[0059] The topcoat composition (particularly, the clearcoat composition) is preferably a solvent-based composition. The same solvent mentioned for the primer composition is suitable for the topcoat composition. More preferably, the topcoat composition is non-aqueous. The topcoat composition is preferably supplied in the form of a 2K composition.

[0060] In another embodiment, the system may include the primer discussed above together with a colored base coat and a clear coat.

[0061] For colored basecoats, any existing basecoat composition that may be 1K or 2K, aqueous or solvent-based may be used. The basecoat composition may be physically dried or chemically crosslinked. The selection of a suitable crosslinking agent is made by a person skilled in the art based on the functional groups of the resin binder present in the composition. The basecoat composition preferably contains a pigment. Examples of pigments include color pigments such as titanium dioxide, zinc white, carbon black, iron manganese black, chrome oxide, iron oxide, azo pigments, quinacridone, perinone, phthalocyanine, and aniline black, or effect pigments such as coated or uncoated aluminum, iron, and copper effect pigments.

[0062] The topcoat composition may additionally include conventional additives such as flow regulators, dispersants, surfactants, plasticizers, thixotropic agents, light stabilizers, etc.

[0063] In some embodiments, the system described above may include another coating layer on the back side of the coated polycarbonate substrate. This layer may include a primer, a base coat, and / or a clear coat layer.

[0064] apply

[0065] A method for forming a multilayer coating on a polycarbonate substrate according to the present invention comprises the following steps:

[0066] a) a step of directly applying a primer coating composition as described above to a substrate,

[0067] b) a step of applying at least one organic topcoat composition different from the primer coating composition to a coated substrate, and

[0068] c) Step of curing the multilayer coating.

[0069] In step (a), a primer coating composition is applied onto a polycarbonate substrate. The substrate does not require any pretreatment that would result in surface deformation or pre-coating. In some embodiments, the primer coating composition may be cured before the application of additional layers, but this is not strictly necessary. Curing is generally carried out under ambient conditions (from a few hours to one day) or can be accelerated using a high temperature (e.g., 60°C). A person skilled in the art can determine an appropriate combination of curing temperature and curing time.

[0070] In step (b), at least one topcoat composition is applied. This can be done after the primer layer has been cured or via wet application. The latter means that another layer composition is applied immediately after the primer composition is applied. The flash-off time may generally be in the range of 5 to 20 minutes.

[0071] Preferably, at least one topcoat layer is a clearcoat. In some embodiments, a colored basecoat composition may be applied between steps a) and b) to obtain a basecoat layer.

[0072] The coating composition can be applied by any conventional method, preferably by spray application. The multilayer coating can be cured at room temperature or forced-dried at a high temperature, for example, up to 80°C, preferably 40°C to 60°C.

[0073] use

[0074] The multilayer coating described above is particularly useful for coating polycarbonate parts in the automotive, marine, or aerospace industries. More specifically, the present invention provides a coated automotive part comprising a multilayer coating system on a polycarbonate substrate according to the present invention. The automotive part may be selected from, for example, a headlight, a bumper, a tailgate, or a sunroof panel.

[0075] The present invention will be described in more detail based on the following examples. Unless otherwise specified, all parts and percentages are by weight.

[0076] Examples

[0077] Explanation of the method

[0078] "Dry 1 mm" - This is a dry adhesion test according to ISO 2409:2013. Cross-cuts were made at 1 mm intervals from the coating until the substrate was coated, after which adhesive tape was rapidly applied and removed at a 90-degree angle. The evaluation scale ranged from 0 (best, no coating peeled off) to 5 (worst, significant coating peeled off). "Dry 2 mm" is the same, but the distance between cuts is 2 mm.

[0079] "Wet 1 mm" - This is a wet adhesion test according to ISO 6270-1:1998. The test measured resistance to humidity following continuous condensation conditions. Cross-cuts were made from the coating up to the substrate at intervals of 1 mm. Then, the samples were placed over a reservoir containing water at 40°C for 240 and 480 hours, after which a test using adhesive tape was performed. "Wet 2 mm" is the same, but with a distance of 2 mm between the cuts.

[0080] "Dry HPWJ" - Adhesion test according to ISO 16925:2014 (performed according to BMW AA-0136). An incision was made in the coating, and a high-pressure water jet was applied to the sample for 2 minutes. The evaluation scale ranged from 0 (best, no coating peeled off) to 5 (worst, significant peeling). "Wet HPWJ" was performed in the same manner, but the sample with the incision was conditioned at 100% humidity and 40°C for 240 or 480 hours.

[0081] Wet scratch resistance was evaluated by measuring gloss loss and haze increase after a simulated car wash test according to BMW standard AA-0054. Gloss values ​​at 20° were measured according to ISO 2813:2014. Reflective haze was measured according to ISO 13803:2014.

[0082] A transparent primer composition was prepared using components A and B according to Table 1 (amounts in g). The mixing ratio of A to B varied as 100 g: 55 g (resin excess), 100 g: 63.9 g (stoichiometric), or 100 g: 100 g (isocyanate excess).

[0083] Table 1 Primer composition

[0084] Ingredient A Ingredient B Desmophen NH1420 - Polyaspartic acid ester 60 Desmodur N 3390 BA / SN - Polyisocyanate HDI-trimeric isocyanurate 68.3 Antifoamer* 0.4 n-butyl acetate 31.7 Flow Additive Mix** 2.5 n-butyl acetate 35.1 2-Butoxyethyl acetate 2 Total (g) 100 Total (g) 100

[0085] * BASF's Efka PB 2010, 50% solids; ** Mixture of Byk-300 and Byk-310 in methoxypropyl acetate

[0086] For a comparative example, a primer composition containing an epoxysilane was prepared. This composition was identical to that in Table 1, except that 1.5 wt% or 3.5 wt% of Evonik’s Dynasylan® Glymo was added to component B based on the total weight of component B. Dynasylan GLYMO is a difunctional 3-glycidyloxypropyltrimethoxysilane. For the composition containing the epoxysilane, the mixing ratio of A to B was 100 g:100 g.

[0087] A primer composition was sprayed onto a polycarbonate panel (Sabic's Lexan LS2, dimensions 60 cm x 20 cm x 3 mm). Before application, the panel was degreased with isopropanol and dried with a soft cloth. After flashing off for 10 minutes, some panels were recoated with a clear coat (CC1 or CC2).

[0088] CC1 - A clearcoat composition containing components A and B. Component A contains 68 wt% acrylic polyol (OH value 150 mg KOH / g, Tg 69°C, solid content 55 wt%), 10 wt% polyester polyol (OH value 170 mg KOH / g, Tg -7°C, solid content 85 wt%), DBTDL, benzoic acid, a UV absorber, a flow additive, and a solvent. Component B contains 45 wt% HDI trimer isocyanate and a solvent. The mixing ratio of A to B was 100:100.

[0089] CC2 - A clearcoat composition comprising components A, B, and C. Component A comprises 60 wt% acrylic polyol (OH value 140 mg KOH / g, Tg -6°C, solid content 74 wt%), 13.7 wt% melamine polyol (OH value 312 mg KOH / g, Tg -14°C, solid content 83 wt%), DBTDL, benzoic acid, a UV absorber, a flow additive, and a solvent. Component B contains 81 wt% polyisocyanate HDI-trimer isocyanurate and a solvent. Component C contains a solvent. The mixing ratio of A:B:C was 100:60:20.

[0090] After curing the coated panels under ambient conditions for one week, adhesion and scratch resistance tests were performed. Additionally, the same polycarbonate panels were coated with the Kwasny SprayMax system from Peter Kwasny GmbH, a conventional commercial polycarbonate primer (epoxy-based, not containing polyaspartic acid esters).

[0091] The coated panels underwent adhesion and wet scratch resistance tests.

[0092] First, adhesion tests were performed on epoxysilane-free systems with different A:B ratios in the primer composition. The results are shown in Table 2.

[0093] Table 2 Adhesion test for different A:B ratios

[0094] # Primer A:B, g:g Clear coat Dry 1 mm Dry 2 mm Dry HPWJ Wet 1 mm Wet 2 mm Wet HPWJ 1 100:55 - 0 0 0 0 0 0 2 100:63.9 - 0 0 0 0 0 0 3 100:100 - 0 0 0 0 0 0 4 100:55 CC1 0 0 0 0 0 0 5 100:63.9 CC1 0 0 0 0 0 0 6 100:100 CC1 0 0 0 0 0 0 7 100:100 CC2 0 0 0 0 0 0

[0095] As can be seen in Table 2, the A:B mixing ratio did not affect the adhesion test results. For all mixing ratios, the adhesion of the coating system (primer or primer overcoated with clear coat) was excellent in all cases. For additional testing, the A:B mixing ratio was selected as 100:100.

[0096] Tables 3 and 4 show the results of adhesion and wet scratch resistance tests for the system according to the present invention and the comparison system.

[0097] Table 3 Adhesion Test

[0098] # Epoxysilane in primer, weight% Clear coat Dry 1 mm Dry 2 mm Dry HPWJ Wet 1 mm Wet 2 mm Wet HPWJ 3* - - 0 0 0 0 0 0 6 - CC1 0 0 0 0 0 0 7 - CC2 0 0 0 0 0 0 8* 1.5 - 0 0 0 0 0 0 9* 3.5 - 0 0 0 0 0 0 10* 1.5 CC1 0 0 0 0 0 0 11* 1.5 CC2 0 0 0 0 0 0 12* Kwasny** Kwasny 0 3 - 0 (240h)5 (480h) 0 (240h)5 (480h) 0 (240h)5 (480h)

[0099] * Comparative example; **The Kwasny SprayMax system consists of a cleaner, primer, and clear coat.

[0100] Table 4 Wet Scratch Resistance Test

[0101] Epoxysilane in primer, weight% Clear coat Gloss 20° Hayes beginning After the test Gloss loss (%) beginning After the test Increase in haze 3* - - 88.4 46.9 47 12.2 68.9 6 6 - CC1 85.9 49.8 42 48.3 83.7 1 7 - CC2 87.3 72.7 17 15.5 38.1 2 8* 1.5 - 88.8 49.5 44 14.3 66.5 5 9* 3.5 - 88.5 53.7 39 11.7 58.5 5 10* 1.5 CC1 81.2 46.0 43 108 102 1 11* 1.5 CC2 87.4 65.2 25 14.2 49.5 3

[0102] As can be seen from these tables, Comparative System 3 (no clear coat) had excellent adhesion but low wet scratch resistance (loss of gloss and, in particular, increased haze). This did not change significantly when the primer contained epoxysilane (Comparative Systems 8, 9).

[0103] The coating systems (6, 7) according to the present invention exhibited excellent drying and wet adhesion results similar to the comparative systems (10, 11) using epoxysilane, despite the fact that the primers did not contain epoxysilane. The wet scratch resistance of the coating systems (6, 7) of the present invention, which do not contain epoxysilane, was as good as or much better than that of the comparative systems (10 to 11) containing epoxysilane. The content of epoxysilane appears to play no role. The results surprisingly demonstrated that excellent adhesion and scratch resistance results can be obtained on polycarbonate substrates without the need to use epoxysilane in the primers.

[0104] Commercial benchmark product 12 (polyaspartic acid ester-free) showed slight delamination in the "dry 2 mm" test and complete delamination in the wet adhesion test after 480 hours.

Claims

Claim 1 A multilayer coating system on a polycarbonate substrate, comprising: a primer layer applied directly to the substrate, which is obtained from a primer coating composition comprising at least one polyaspartic acid ester and at least one polyisocyanate crosslinking agent, wherein the primer coating composition does not contain an epoxy-functional alkoxysilane and does not contain a compound having a reactive OH group; and at least one organic topcoat layer disposed on the primer layer, wherein the organic topcoat layer is obtained from a coating composition different from the primer composition and the organic topcoat layer is a clearcoat. Claim 2 A coating system according to claim 1, wherein the polyaspartic acid ester is prepared from maleic acid of a diamine and a fumaric acid ester, and the diamine is selected from 4,4'-diaminodicyclohexylmethane and 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane. Claim 3 A coating system according to claim 1, wherein the primer coating composition is a solvent-based composition. Claim 4 In claim 1, the primer coating composition is a transparent coating system. Claim 5 A coating system according to claim 1, further comprising a colored basecoat layer between the primer and the clearcoat. Claim 6 A coating system according to claim 1, wherein the clear coat layer is obtained from a coating composition comprising at least one hydroxyl-functional binder resin and a crosslinking agent reacting with a hydroxyl group. Claim 7 In claim 6, the coating system in which the crosslinking agent in the clear coat composition is a polyisocyanate crosslinking agent. Claim 8 In claim 6, the hydroxyl-functional binder resin is a coating system selected from polyurethane, polyacrylate, polyester, melamine polyol, or a mixture thereof. Claim 9 A method for forming a multilayer coating on a polycarbonate substrate according to any one of claims 1 to 8, comprising: a) applying a primer coating composition directly to the substrate; b) applying at least one organic topcoat composition different from the primer coating composition to the coated substrate; and c) curing the multilayer coating, wherein at least one topcoat composition is a clearcoat composition. Claim 10 A method according to claim 9, further comprising the step of curing a primer coating composition after step a). Claim 11 A method according to claim 9, further comprising the step of applying a colored base coat between step a) and step b). Claim 12 A coated automotive part comprising a multilayer coating system on a polycarbonate substrate according to any one of claims 1 to 8. Claim 13 delete Claim 14 delete

Images