MXPA01007005A - Method of producing durable layered coatings - Google Patents

Abstract

The present invention relates to a process for producing a durable multi-layered coating on difficult-to-coat substrates, such as aluminum. The process includes subjecting the surface of the difficult-to-coat substrate to an adhesion promoting step, followed by applying an intermediate layer of flexible primer, which contains a polyester copolymer produced through a two-stage polymerization process. A mar resistant top layer of clear coating composition is then applied over the intermediate layer to produce the multi-layered durable coating on the difficult-to-coat substrate. If desired, the intermediate layer may be pigmented or it may be applied in the form of one or more patterned layers of different colors. Alternatively, one or more patterned layers of different colors may be applied over the intermediate layer before the application of the mar resistant top layer. If desired, the application of the mar resistant top layer and the patterned layers may be delayed by up to 12 weeks to permit the user to mass produce coated components, such as delivery van bodies, with an intermediate layer in a basic color, such as white, which can be then custom coated with various design patterns, followed by the application of the mar resistant top layer.

Description

METHOD OF PRODUCTION OF COATINGS IN DURABLE LAYERS BACKGROUND OF THE INVENTION The present invention relates generally to a method of producing layered coatings and more particularly relates to a simplified process that produces durable coatings on layers on various difficult-to-coat substrates. Protective coatings applied on difficult-to-coat substrates, such as aluminum, tend to be less durable than coatings applied on substrates less difficult to coat, such as steel, wood, or cement substrates. Hard-to-coat substrates generally require extensive surface preparations, such as corona discharge, acid etching, or sandblasting, followed by aqueous cleaning or solvent and priming or first coat of paint before coating of the surface of such substrates. In addition, multi-layer coating systems also generally require surface preparations, such as sand cleaning, before they can be applied REF: 129831 the subsequent coatings. Finally, the durability of such coatings on difficult-to-coat substrates is attenuated when such substrates are exposed to environmental erosion, such as that experienced by car or truck bodies during the normal course of driving conditions. Patent Application EP 0 525 867 A1 (hereinafter '867 application') intended to provide a multi-layer coating system suitable for application to various substrates, particularly aluminum substrates. The application '867 involves the application of a first coating of resins containing melamine or polyacrylate, polyurethane, pilosester, alkyde, epoxy, followed by a coating layer of transparent metallized powder containing mica pigment. However, there is a need for a process with few process steps that result in the production of durable coatings on difficult-to-coat substrates.

DECLARATION OF THE INVENTION The present invention is directed to a process of producing a durable coating on a difficult-to-coat substrate, the process comprising: subjecting the surface of the difficult-to-coat substrate to a treatment that promotes adhesion; applying an intermediate layer of a flexible primer on the surface that promotes the adhesion of the substrate difficult to coat, the flexible primer comprises: a polyester copolymer and a crosslinker, the polyester copolymer is produced through a process of. Two-stage polymerization, the polyester copolymer has a linear segment with terminal hydroxyl groups and a number average molecular weight GPC (Mn) in the range from 500 to 3000, and a branched segment with lateral hydroxyl groups and a number of molecular weight average GPC (Mn) in the range from 750 to 1500; applying a usual wear-resistant top layer of a clear coating composition on the intermediate layer to produce the durable coating on the hard-to-coat substrate, the clear coating composition comprises: a polyisocyanate binder, fluorinated polyisocyanate binder, a binder of acrylic fluorocarbon or a combination thereof. One of the advantages of the present invention is that it allows the user to apply durable coatings on difficult-to-coat substrates with significantly fewer process steps than the steps used in conventional coating processes. Another advantage of the present invention is that it allows the user to delay the application of the usual wear resistant upper layer for significant periods of time without the annoying commitment and time consuming cleaning and sand cleaning steps.

DETAILED DESCRIPTION OF THE INVENTION As defined herein: "Durable coating" means a coating that substantially does not flake, peel, damage, or delaminate when subjected to the moisture and abrasion typically experienced by the coating, particularly the coatings used on the components of the cars and trucks, such as bodies, door panels, cabins, trailer bodies, airplane components, such as fuselage and wings. The flaking is tested under a modified ASTM D3170-87 Gravelometer Test, described later. "Clean substrate" means a substrate that has been washed with solvent or soap and washed with water but not physically abraded or chemically treated by a chemical attack, such as chromic acid, or by chemical anodization such as with phosphoric acid or chromic acid. Generally, such a cleaning step may be necessary to remove contaminants, if present, on the surface before it can be coated. "Aluminum" means aluminum and aluminum alloys. "Hard-to-coat substrates" means substrates, such as aluminum, chromium plated steel, stainless steel substrates or substrates of certain resins, such as, polyamides, polyetherimides and polyacetals. The process of the present invention is adapted to produce durable protective coatings on difficult-to-coat substrates. The process of the present invention is particularly adapted to aluminum and polyamides and more particularly to aluminum. However, if desired, it could be easily used for the coating of substrates less difficult to coat. In addition, the durable coatings produced by the process of the present invention. besides being protective, they can also be decorative. It has been found that mechanical abrasion of a substrate surface is generally necessary in conventional processes to improve the initial and long-term adhesion of any subsequent coating on the surface of the fundamental substrate. Mechanical abrasion means the use of sandpaper, cleaning with blasting blasting or metal treatment by shot blasting. In contrast, in the process of the present invention, it is generally not necessary to mechanically abrade the surface of the substrate followed by priming the surface to improve the adhesion of the subsequent coatings therein. As a result, the significant number of preparation steps of the surface are eliminated in the process of the present invention and significant cost savings are achieved as a result of this. In addition, when mechanical surface abrasion is not necessary, the structural strength of the fundamental substrate is not fixed, especially when thin substrates are coated. Unless the surface of the substrate is clean, it is desirable to remove any surface contaminants, such as impurities, airborne contaminants, greasy or oily, oily surface substances, prior to the application of durable coatings. by the process of the present invention. In the cleaning step, to ensure that there is no wax, grease, silicone, dust, or other contaminants, a wax and grease remover, solvent, acid or base wash, or soap / water can be used to clean the surface . Durable coatings do not adhere properly to a waxy surface. Depending on the size of the substrate, your surface can be dipped or cleaned by wiping with a clean, dry cloth or paper towel, soaked with a conventional grease remover and wax, such as 3812 S Quick Dryer or 3832 S Reducer, both supplied by DuPont Company, Wilmington, Delaware. A stripping solvent includes 80 to 95 weight percent of an aqueous medium and 5 to 20 weight percent of an organic medium, substantially miscible with the aqueous medium. The organic medium preferably includes: 1. 10 to 50 percent of an alkyl ester; 2. 40 to 85 percent of a glycol ether selected from propoxy alkanol and ethoxy alkanol; and 3. 2.5 to 10 percent of a conventional nonionic surfactant. All weights are based on the total weight of the solvent. After the above cleaning step, the surface of the cleaned substrate is subjected to a treatment that promotes adhesion to improve the adhesion of the surface of the substrate difficult to coat to the subsequent coatings on it. The chemical treatment can be used, such as anodization with chromic acid and anodization with phosphoric acid. however, the preferred treatment that promotes adhesion is described in U.S. Patent No. 5,578,347, which is incorporated herein by reference. Such a preferred method is provided to apply a substantially uniform, thin film of an adhesion promoter described below. By "thin" is meant a layer in the order of a monolayer or an amount not significantly in excess of this, for example, having a dry thickness of less than 2,540 ANGSTROM (Á) (0.1 mil), preferably in the range from 100 Á to 2,500 Á. The necessary thinness of the silane coating is ensured by the removal of the excess of the adhesion promoter. This is typically done by finishing with water or aqueous organic solvent, scrubbing with a wet material with water or blowing with air. The residual water is removed by drying (forced or natural) prior to the application of the primer and / or final coat of paint. The silane adhesion promoter suitable for use in the present invention includes a solution of one or more silanes having the following formula: where x is 1, 2 or 3, R is the same or different alkyl having in the range from 1 to 3 carbon atoms, when it is 0, 1, 2 or 3, b equals 3-a, and R1 is selected of the group consisting of: H2C ACHCH2 _ f H2N, H2N (CH2) 2NH, H2N (CH2) 2NH (CH2) 2NH, and H2N [(CH2) 2NH] 2 where z is 0, 1, 2 or 3, the silane is present in a concentration in the range of 0.001 to 10.0 percent, preferably in the range of 0.5 to 7.0, more preferably in the range of 1.5 to 3.5, all percent by weight are based on the total weight of the solution. Preferred species of silanes include α-glycidoxypropyltrimethoxysilane and α-aminopropyltriethoxy silane. Additional preferred species of silanes are described in US Patent No. 5,578,347, which is incorporated herein by reference. The above silane adhesion promoter is supplied by DuPont Company, Wilmington, Delaware under the trademark METL0K (R) 230S Adhesion System. Until the end of the previous step, an intermediate layer of a flexible primer is conveniently applied on the surface that promotes the adhesion of the substrate difficult to coat. The flexible primer suitable for use in the present invention includes a polyester copolymer and a suitable crosslinker. The polyester copolymer is produced through a two-stage polymerization process and has a linear segment having an average molecular weight number GPC (Mn) in the range from 500 to 3000 with terminal hydroxyl groups, and a branched segment which it has an average molecular weight number GPC (Mn) in the range from 750 to 1500 with lateral hydroxyl groups. In the first stage of the process, a part of the carboxyl groups of a diacid or a diacid anhydride is reacted in approximately stereometric proportions with one of (A) one half of the hydroxyl groups of the linear segment and (B) 10 a 80% of the hydroxyl groups of the branched segment to form a first reaction product, and then, in the second stage of the process, the other half of the hydroxyl groups of the first reaction product is reacted in approximately stoichiometric proportions with the hydroxyl group of the others of (A) and (B). Preferably, after the first stage but before the second polymerization step the branched segment has a number average molecular weight of 750 to 1000, a hydroxyl number of 175 to 300, an acid number of 20 to 60 if the group carboxyl has been reacted first with the branched segment or less than 5 if the carboxyl group has first been reacted with the linear segment, and an average functionality number of 2.5 to 11; and the linear segment has a number average molecular weight of 500 to 3000, a hydroxyl number of 15 to 300, an acid number of less than 5 or 20 to 60, respectively, and an average functionality number of 1.1 to 2. The first reaction stage is preferably conducted at at least 100 ° C, more preferably at least 150 ° C. The second reaction stage is preferably conducted at at least 200 ° C. Linear segments preferably result from the use of one or more of the following monomers: Neopentyl glycol, 1,6-hexanediol, Esterdiol-20 (R), a commercial diol produced by Union Carbide Company, o-phthalic anhydride, acid isophthalic, adipic acid, and azelaic acid. The branched segments preferably result from the use of one or more of the following monomers: Neopentyl glycol, 1,6-hexanediol, trimethylolpropane, o-phthalic anhydride, isophthalic acid, diacid 1,12 dodecanoic, adipic acid, and azelaic acid. .

The linear and branched segments are preferably linked together through one or more of the following overlayer agents: o-phthalic anhydride, succinic anhydride, and glutaric anhydride. If desired, the flexible primer may contain conventional pigment, such as a white or colored pigment to improve concealment and also for aesthetic reasons. Suitable crosslinkers include conventional crosslinkers, such as melamine / formaldehyde resins, polyisocyanate resins and urea formaldehyde resins, all typically used in the proportion of 10 percent to 50 percent by weight based on the total weight of the flexible primer. Additional information on the above flexible primer is provided in U.S. Patent No. 4,442,269, which is incorporated herein by reference. Until the completion of the previous step, a usual wear-resistant top layer of a clear coating composition is applied over the intermediate layer to produce a durable coating on the substrate difficult to coat. If desired, the application of the usual wear-resistant upper layer on the intermediate layer can be delayed for up to 1 week to 12 weeks, thus allowing the user to group the articles produced having a standardized base coating, such as a pigmented coating. White color. If the application of the usual wear-resistant upper layer is delayed, the intermediate layer is preferably rinsed with conventional detergents, such as soap, to remove any impurities or grease that may have accumulated thereon, before the application of the layer Superior wear resistant usual in the intermediate layer. In contrast, conventional primers generally require sand cleaning of the coated surface, if additionally coating applications are typically delayed by more than 36 hours. However, in the process of the present invention, the applicants have unexpectedly discovered that, in different conventional primers, the intermediate layer of the present invention does not require any sand cleaning step before it is subjected to the application of the additional coating. , even after a delay of up to 12 weeks. The clear coating composition suitable for use in the present invention includes a polyisocyanate binder, fluorinated polyisocyanate binder, an acrylic fluorocarbon binder or a combination thereof. Any clear conventional polyisocyanate binder is suitable for use in the process of the present invention. Preferred is the fluorinated polyisocyanate binder, an acrylic fluorocarbon binder or a combination thereof, since it is easy to remove unwanted marks, such as graphites, by conventional cleaning means, such as detergents, in the upper layers of these binders Preferably, the clear coating composition includes conventional UV screens, such as Tinuvin 900 UV Absorber (R >; or UV light stabilizers, such as Tinuvin 901 R), supplied by Ciba Specialties of New Milford, Connecticut, to prevent UV degradation of the usual wear-resistant topcoat. The clear coating composition containing the fluorinated polyisocyanate binder includes the fluorinated polyisocyanate, which is a reaction product of an organic polyisocyanate and a fluorinated monofunctional alcohol represented by the formula: where Rf is a group containing fluoroalkyl having at least 4 carbon atoms, X is a divalent radical, R3 is H or an alkyl group having in the range from 1 to 4 carbon atoms, n is 0 or 1 and m is in the range from 0 to 30 provided that when n is 0 then m must be equal to or greater than 1 and when m is 0 then n is 1; wherein in the range from 0.1 to 33 mole percent of the active isocyanate groups are reacted with the fluorinated monofunctional alcohol; and a film-forming polymer, such as an acrylic polymer, a polyester, an alkyd resin, a polyol or a combination thereof. The fluorinated polyisocyanate is an adduct of a fluorinated monofunctional alcohol and a conventional organic polyisocyanate. Any of the conventional aromatic, aliphatic, di-cycloaliphatic and trifunctional polyisocyanates can be used. Typically the useful diisocyanates are 1,6-hexamethylene diisocyanate, isophorone isocyanate, 4,4'-biphenylene diisocyanate, toluene diisocyanate, bis cyclohexyl diisocyanate, tetramethylene xylene diisocyanate, ethyl ethylene diisocyanate, 2,3-dimethyl ethylene diisocyanate, 1-methyltrimethylene diisocyanate. , 1,3-cyclopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,3-phenylene diisocyanate, 1,5-naphthalene diisocyanate, bis- (4-isocyanatocyclohexyl) -methane, and 4,4'-diisocyanatodiphenyl ether. Typically the fluorinated monofunctional alcohols used to form the isocyanate functional adducts are represented by the following formula: í Rf- (X) n- (CH2CH-0) m ~ H where Rf is as defined above, a fluoroalkyl-containing group having at least 4 carbon atoms and preferably a straight chain or branched chain fluoroalkyl group having 4 to 20 carbon atoms which optionally may contain oxygen atoms as groups ether or may contain 1 to 5 chlorine atoms or 1 to 5 hydrogen atoms. Preferably, Rf is a perfluoroalkyl group having 4 to 20 carbon atoms and more preferably, Rf is a perfluoroalkyl group containing 6 to 12 carbon atoms. X is a divalent radical, preferably -CH2CH20-, -S02N (R4) CH2CH20-, -CH2-, -O-, -CH20- where R is an alkyl group preferably having 1-4 carbon atoms. R3 is H or an alkyl group having 1 to 4 carbon atoms, H and methyl are preferred, n is 0 or 1 and m is 0 to 30, provided that if n is 0, then m must be greater than or equal to, if m is 0, then n is 1, if X is -O-, m must be greater than or equal to 1; m is preferably 1 to 20. The fluorinated organic polyisocyanate is prepared by conventional techniques in which the fluorinated monofunctional alcohol and the organic polyisocyanate are charged into a reaction vessel optionally with solvents and a catalyst for about 0.1 to 4 hours and heated at about 50 to 120 ° C preferably, 60 to 85 ° C. The fluorinated polyisocyanate binder described above is described in U.S. Patent No. 5,605,956, which is incorporated herein by reference. The clear coating composition containing the fluorocarbon acrylic binder includes an acrylic polymer and an organic polyisocyanate crosslinking agent. The acrylic polymer is polymerized from a monomer mixture comprising one or more hydroxyl-containing monomers and one or more fluoroalkyl-containing monomers represented by the formula: where R is hydrogen or an alkyl group having 1 or 2 carbon atoms, n is an integer in the range from 1 to 11 and Rf is a fluoroalkyl-containing group having at least 4 carbon atoms, the acrylic polymer has an average molecular weight in the range from 2,000 to 20,000. The additional details of Rf are the same as those described above. The upper layer of the above, in its curing state has a combination of a progressive water contact angle of at least 100 ° and a progressive hexadecane contact angle of at least 40 ° C. The acrylic polymer is polymerized from hydroxyl monomers containing 20 to 45% by weight, based on the weight of the acrylic polymer, of polymerized hydroxyl-containing monomers selected from the following group of hydroxy alkyl acrylate or methacrylates having 1 to 4 carbon atoms in the alkyl group, about 50 to 79.9% by weight, weight basis of the acrylic polymer, polymerized alkyl acrylates and methacrylates having 1 to 18 carbon atoms in the alkyl groups, or styrene or any of the above de-loe mixtures. To the above polymerized acrylic polymer from hydroxyl monomers, 0.1 to 5.0% by weight, based on the weight of the acrylic polymer, of the fluoroalkyl-containing monomer is added. The acrylic fluorocarbon binder described above is described in US Patent No. 5,629,372, which is incorporated herein by reference. The clear coating composition of the present invention and the flexible primer may also contain conventional additives, such as pigments, stabilizers, rheology control agents, flow agents, quenching agents and fillers. The addition of such additives will depend, in course, on the intended use of the coating composition. Thus, the fillers, pigments, and other additives that could adversely effect the clarity of the cured coating will not be included if the composition is intended as a clear coating. Furthermore, if desired, it is contemplated that the intermediate layer may be applied in the form of one or more model layers, each of the model layers containing one or more pigments of different colors. Thus, the design of the model layer or layers can be applied in the form of an advertisement or a commercial message, such as those typically applied to the body of a freight truck or delivery truck. Alternatively, the pattern layer or layers can be applied to the surface of an intermediate layer, preferably of a single solid color. It is further contemplated that the pattern layers may comprise conventional pigmented paints or may be in the form of a self-adhesive decal. The usual wear resistant layer is then applied to the model layers. If desired, the pattern layer or layers can be applied after a delay of 1 week to 12 weeks along with the usual wear resistant layer. As a result, the user is allowed to put together the coated articles produced, such as delivery truck bodies, which have a standardized color intermediate layer, such as white; Supply or chipping coated articles over a period of weeks to customers who can then apply their model designs and wear resistant top coat to the items, without the annoying commitment and cleaning steps. The above process is also suitable for applying durable coatings on difficult-to-coat resin substrates, such as those made from Nylon ppliamides < R > -6 and Nylon < R) -6, 6, Kevlar aromatic amide (R1, all supplied by DuPont Company of Wilmington, Delaware, and Ultem polyetherimide (R > and Delrin polyacetal (R !, both supplied by General Electric Company of Fairfield, Connecticut). above is more suitable for the production of multi-layered, multi-colored coatings resistant to the usual wear on automotive structures or bodies, made of difficult-to-coat substrates, such as aluminum.These structures or aluminum bodies are typically used in commercial vehicles, such as those used in the transportation of beverage bottles.The process is also well suited for the lining of aircraft bodies and aluminum aircraft.

TEST PROCEDURES Durability Hard-coated substrate panels (untreated field aluminum) coated with durable multi-layer coating were tested using ASTM D3170-87 Test Strip Resistance Test (Gravelmeter Test) for durability under harsh environments. The Gravelometer Test was modified to stimulate harsh environments. The coated panels were cycled for significant periods of time by subjecting them to 100% moisture followed by about two hours exposure to freezing temperatures at -28.9 ° C (-20 ° F). The flaking performance was considered on a scale of 0 to 10, representing the initial unproven panel and 0 representing the total removal (100 percent) of the coating of the substrate surface. A reading of 6 and above is considered acceptable.

Adhesion The adhesion of the top layer on the intermediate layer after a noticeable delay was measured under Adhesion Test ASTM D3359-95. The adhesion performance was considered on a scale of 0 to 10, representing the initial unproven panel and 0 representing the total removal (100 percent) of the coated surface coating. A reading of 7 and above is considered acceptable: Moisture The adhesion of the durable layer to the difficult-to-coat substrate was tested under ASTM D2247-94 Moisture Test for significant periods of time. The adhesion of the coatings was then tested under Adhesion Test ASTM D3359-9.5. The following examples illustrate the invention.

EXAMPLES Polyester Primer A polyester primer included in the flexible primer was produced in view of the teachings in Example 1 in US Patent No. 4,442,269, except 22.5 moles of azelaic acid used in the production of the Branched Oligoester 1 of Example 1 was replaced with a mixture of 11.5 moles of adipic acid and 11.5 moles of 1,12 dodecanoic acid.

Flexible Primer The components of Table 1 below were added to the polyester primer described above (all in percent by weight): Table 1 1. Mixture of Barium Sulphate W-12, Calcium Carbonate W-1004 and Aluminum Silicate W-1002, all supplied by Chem Central of Pittsburgh, Pennsylvania. 2. Titanium dioxide TiPure (P> supplied by DuPont of Wilmington, Delaware 3. Baked carbon black powder supplied by Cabot Company of Boston, Massachusetts 4. Benton dispersion 38 in ketone to 8% solids supplied by Rheox, Inc. of Hightstown, New Jersey.

. Acrylic terpolymer ResifloS in 50% aromatic solvent supplied by Chem Central of Pittsburgh, Pennsylvania. 6. Tinuvin UV Light Stabilizer (R > supplied by Ciba Specialties of New Milford, Connecticut.

All coatings, unless otherwise specified, are notable as dry film thickness.

Comparative Example The aluminum control panel used for the application of a conventional multi-layer system (Comparative Example) was cleaned using 3812S quick-drying reducer supplied by DuPont Company, Wilmington, Delaware for the removal of dust, grease, oils or fingerprints fingerprints The clean panel was then cleaned with sand for approximately 10 minutes with 180 grit hardness followed by a second scrubbing with 3812S quick dry reducer. The cleaned and sand cleaned panel was attacked with 615S Variprime (R) self-etching primer supplied by DuPont Company, Wilmington, Delaware. A coating of 12.7 microns (0.5 mil) thick dried instantly under ambient conditions for 30 minutes. The acid etched panel was then coated with 934S Corlar epoxy primer (R1 supplied by DuPont Company, Wilmington, Delaware) The epoxy primer was activated at a 5: 1 volumetric ratio with 936S Corlar (R) modified ketimine activator, supplied by DuPont Company , Wilmington, Del. The activator was diluted to 30 weight percent with acetone.A coating of 30 microns (1.5 mil) thick was dried hot for 30 minutes at 82.2 ° C (180 ° F). Previous priming is necessary to prevent rust damage on aluminum surfaces etched with acid.The primed control panel was then coated to a thickness of 51 microns (2 mil) with white Imron (R) 6000 polyurethane enamel supplied per liter. DuPont Company, Wilmington, Delaware, which was activated at a volumetric ratio of 3: 1 with Imron diisocyanate activator (R >; 193S (@ 75% solids) supplied by DuPont Company, Wilmington, Delaware. The coating was dried immediately under ambient conditions for 15 minutes. The coated control panel was then coated to a thickness of 51 microns (2 mil) with clear top coating of Imron polyurethane enamel (R1 3440S (acrylic-urethane copolymer containing hydroxyl @ 53.4% solids) supplied by DuPont Company, Wilmington, Delaware, which was activated at a volumetric ratio of 3: 1 with Imron diisocyte activator <R! 193S @ 75% solids) mixed with Fast Dry Accelerator 389 S Imron (R) 5000 at 2 volume percent, both supplied by DuPont Company, Wilmington, Delaware. The clear coating was hot dried for 30 minutes at 82.2 ° C (180 ° F). Two sets of control panels were prepared simultaneously for the adhesion test under humidity and subjected to test cycles of flaking performance.

Example 1 The aluminum panel used for the application of a multi-layered system of the present invention was cleaned using 3812S quick-drying reducer supplied by DuPont Company, Wilmington, Delaware for the removal of dust, fats, oils, or fingerprints. The clean panel was then subjected to the step that promotes adhesion. The surface was coated with METALOK (R) 230S supplied by DuPont Company, Wilmington, Delaware. The excess coating dissipated from the surface and then the adhesion promoting surface was dried with air. The adhesion promoting panel was then coated within 15 minutes at about 38 microns (1.5 mil) thick with the flexible primer composition of Table 1 activated at a 4: 1 volumetric ratio with ImrontR diisocyanate activator > 193S @ 75% solids) mixed with Fast Dry Accelerator 389S Imron (R) 5000 at 2 volume percent, both supplied by DuPont Company, Wilmington, Delaware. The coating was dried immediately under ambient conditions for one hour. This was the middle layer. The coated panel was then coated to a thickness of 51 microns (2 mil) with clear top coating of Imron (R) 3440S polyurethane enamel (acrylic-urethane copolymer containing hydroxyl @ 53.4% solids) supplied by DuPont Company, Wilmington, Delaware , which was activated at a volumetric ratio of 3: 1 with Imron (R) 193S diisocyanate activator @ 75% solids) mixed with Fast Dry Accelerator 389 S Imron (R) 5000 at 2 volume percent, both supplied by DuPont Company, Wilmington, Delaware. The clear coating was hot dried for 30 minutes at 82.2 ° C (180 ° F). This was the usual wear resistant upper layer. Two sets of panels coated with multi-layer coating of the present invention were simultaneously prepared for the adhesion test under moisture and subjected to the test cycle of flaking performance. The comparative panel and the panel of Example 1 were each tested for adhesion after exposure for 96 and 240 hours to moisture under ASTM D2247-94 Moisture Test. The results are shown in the following table 2: Table 2 * Loss of adhesion due to flaking of the primer coating. ** Loss of adhesion due to chipping of the primer coating (slight improvement may have occurred initially due to the interaction of the isocyanate with moisture). Low loss of adhesion to discover the substrate.

From Table 2, exposure to moisture is apparent. The second set of panels were exposed to chipping resistance cycles in the following manner. The panels were initially exposed to the Gravelometer Test, then repeatedly exposed to the Gravelometer test after cyclic exposure to 100 percent moisture followed by freezing for 2 hours at -28.9 ° C (-20 ° F). ). The Gravelometer test was conducted after intervals of 96 hours, 240 hours, 500 hours, 750 hours, 1000 hours and 1500 hours of humidity, each interval was spaced for freezing for 2 hours at -28.9 ° C (-20 ° F) . Until the completion of the test, the comparative panel had a reading of 0 (all the coatings were removed from the panel). In contrast, the coated panel of the Example had a reading of 8, thus unexpectedly indicating a high performance. From these results, it is apparently easy that the coated panel of the present invention was not only substantially more durable, but was also produced using significantly fewer process steps, such as sand cleaning and priming, which are typically used in the processes of conventional coating. Another unexpectedly significant advantage of the present invention is that it allows the user to delay the application of the usual wear-resistant upper layer for significant periods of up to 12 weeks, without requiring steps of cleaning and cleaning with sand that consume time. The series of panels were coated with the intermediate layer using the steps described in Example 1, followed after notable delays, by coating with the usual wear resistant upper layer using the steps described in Example 1. The coated panels were tested for adhesion under ASTM D3359-95 hereafter and then exposed to moisture at specified intervals. The results are shown in Table 3 below: Table 3 The adhesion test was carried out in different locations.

From the results shown in Table 3, it is apparent that even a significant delay in the application of recoating (the usual wear resistant upper layer) in the intermediate layer, has an insignificant impact on the adhesion of the top layer resistant to usual wear to the intermediate layer. This result was unexpected, since conventionally clear coatings require a step of cleaning with sand that consumes time followed by the cleaning step, if the application of the upper layer is delayed for more than 36 hours.

It is noted that in relation to this date the best method known to the applicant to carry out the aforementioned invention is that which results from the present description of the invention.

Claims (12)

CLAIMS Having described the invention as above, the contents of the following claims are claimed as property:

1. A process for producing a durable coating on a substrate difficult to coat, characterized in that the process comprises: subjecting the surface of the substrate difficult to coat to a treatment that promotes adhesion; apply an intermediate layer of a flexible primer on the surface that promotes the adhesion of the substrate difficult to coat, the flexible primer comprises: a polyester copolymer and a crosslinker, the polyester copolymer is produced through a two-stage polymerization process , the polyester copolymer has a linear segment with terminal hydroxyl groups and a number average molecular weight GPC (Mn) in the range from 500 to 3000, and a branched segment with lateral hydroxyl groups and an average molecular weight number GPC (Mn) ) in the range from 750 to 1500; applying a usual wear-resistant top layer of a clear coating composition on the intermediate layer to produce the durable coating on the hard-to-coat substrate, the clear coating composition comprises: a polyisocyanate binder, fluorinated polyisocyanate binder, a binder of acrylic fluorocarbon or a combination thereof.

2. The process according to claim 1, characterized in that the flexible primer is pigmented.

3. The coi compliance process. Claim 1 or 2, characterized in that it additionally comprises applying one or more model layers in the intermediate layer, each model layer contains a pigment of a different color.

4. The process according to claim 1, 2 or 3, characterized in that one or more model layers are applied after a delay of 1 week to 12 weeks.

The process according to claim 1, 2, 3 or 4, characterized in that the usual wear-resistant upper layer is applied after a delay of 1 week to 12 weeks.

6. The process according to claim 1, characterized in that the substrate difficult to coat is aluminum, aluminum alloy, chromium plated steel, stainless steel, polyacetal, polyamide or polyetherimide. The process according to claim 1, characterized in that the treatment that promotes adhesion comprises: cleaning the surface of the substrate difficult to coat; applying a film of a silane adhesion promoter to the clean surface of the aluminum substrate, the film has a dry thickness in the range from 100 Á to 2500 Á, the adhesion promoter comprises: a solution of one or more silanes that has the following formula: where x is an integer between 1 and 3, R is the same or different alkyl having 1 to 3 carbon atoms, when it is 0, or an integer between 1 and 3, b equals 3- a, and R1 is selected from the group consisting of: H2C ACHCH2 Hz Hz Hz N H2N (CH2) 2NH, H2N (CH2) 2NH (CH2) 2NH, and H2N [(CH2) 2NH] where z is 0 or an integer from 1 to 3; the silane is present in a concentration in the range of 0.001 to 10.0 weight percent of the solution; remove any excess amount of the silane adhesion promoter from the surface; and drying the surface having the film of the silane adhesion promoter in it. The process according to claim 7, characterized in that the removal step of the excess amount of the silane adhesion promoter comprises the completion with water or aqueous organic solvent, cleaning by rubbing with wet material with water or blowing with air . The process according to claim 1, characterized in that the fluorinated polyisocyanate binder comprises: a fluorinated polyisocyanate, which is a reaction product of an organic polyisocyanate and a fluorinated monofunctional alcohol represented by the formula: RJ Rf- (X) n- (CH2CH-0) mH where Rf is a fluoroalkyl-containing group having at least 4 carbon atoms, X is a divalent radical, R is H or an alkyl group having in the range from 1 to 4 carbon atoms, n is 0 or 1 and m is in the range from 0 to 30 provided that when n is 0 then m must be equal to or greater than 1 and when m is 0 then n is 1; wherein in the range from 0.1 to 33 mole percent of the active isocyanate groups are reacted with the fluorinated monofunctional alcohol; a polymer that forms film. The process according to claim 9, characterized in that the film forming polymer is selected from the group consisting of an acrylic polymer, a polyester, an alkyd resin, a polyol or a combination thereof. The process according to claim 1, characterized in that the acrylic fluorocarbon binder comprises: an acrylic polymer polymerized from a mixture of monomers comprising one or more hydroxyl-containing monomers and one or more fluoroalkyl-containing monomers represented by the formula: CH2 = CR-C- "0- (CH2) n-Rf where R is hydrogen or an alkyl group having 1 or 2 carbon atoms, n is an integer in the range from 1 to 11 and Rf is a fluoroalkyl-containing group having at least 4 carbon atoms, the acrylic polymer has an average molecular weight in the range from 2,000 to 20,000; and an organic polyisocyanate crosslinking agent, wherein the top layer in its cured state has a combination of a progressive water contact angle of at least 100 ° and a progressive hexadecane contact angle of at least 40 ° C. 12. A substrate difficult to coat characterized in that it is coated with a durable coating according to the process of claim 1. SUMMARY OF THE INVENTION The present invention relates to a process for producing a durable multilayer coating on difficult-to-coat substrates, such as aluminum. The process includes subjecting the surface of the substrate difficult to coat to a step that promotes adhesion, followed by the application of an intermediate layer of a flexible primer, which contains a polyester copolymer produced through a two-stage polymerization process. . A usual wear-resistant top layer of clear coating composition is then applied over the intermediate layer to produce durable multi-layer coating on the substrate difficult to coat. If desired, the intermediate layer can be pigmented or it can be applied in the form of one or more model layers of different colors. Alternatively, one or more pattern layers of different colors can be applied over the intermediate layer before the application of the usual wear resistant upper layer. If desired, the application of the usual wear resistant upper layer and the model layers can be delayed for up to 12 weeks to allow the user to assemble the produced coated components, such as delivery truck bodies, with an intermediate layer in one color basic, such as white, which can then be coated in the same manner with various model designs, followed by the application of the usual wear resistant upper layer.