MX2008006407A - Method for coating vehicle bodies and parts thereof with rust-preventive ionomeric coatings - Google Patents

Abstract

The present invention is directed to a method for coating car or truck bodies, or part thereof, with a rust-preventive ionomer coating composition as the car or truck body is being conveyed along the assembly line as at the vehicle assembly plant. The method of the present invention is used as a replacement for the electrodeposition priming process used today at vehicle assembly plants.

Description

METHOD FOR COATING BODYWORKS AND PARTS OF THE SAME WITH IONOMERIC COATINGS THAT AVOID THE HERRUMBRE FIELD OF THE INVENTION This invention relates to a method for coating or coating vehicle bodies such as the bodies of a car and truck and parts thereof with ionomeric coatings or coatings that prevent rust to provide bodies protected against corrosion that have a good smooth surface, appearance and resistance to corrosion.

BACKGROUND OF THE INVENTION Electrodeposition of sizes that prevent rust on metal substrates of automobiles is widely used in the automotive industry. In this process a conductive article such as the bodywork of an automobile or a car part is immersed in a bath of an electrodepositable coating composition comprising an aqueous emulsion of a film forming polymer and the article acts as an electrode in the process of electrodeposition. A high-voltage electric current is then passed between the article and the counter-electrode in electrical contact with the coating composition until a coating of the product is deposited.

REF. : 192012 desired thickness on the article. In a typical cathodic electrocoating method, the article to be coated is the cathode and the counter-electrode is the anode. After the electrodeposition process is completed, the resulting coated article is separated from the bath and rinsed with deionized water and then typically cured in an oven at a temperature sufficient to form a crosslinked finish on the article. Once the sizing that prevents rust from electrodeposition on the automotive substrate is applied, the vehicle is then coated on its upper part with a multi-layered automotive exterior finish to provide chipping resistance properties and an attractive aesthetic appearance such as gloss and image distinction. A disadvantage related to conventional electrodeposition processes is that the coating defects tend to form on the surface of the coated article such as pitting and fractures, which can impair the corrosion-protective properties of the electrodeposited film and generate other detrimental effects such like a rough film surface. The high-voltage baths required in electrodeposition coating processes use large amounts of electricity and are also expensive to maintain. In addition, multiple rinses with deionized water are not desirable, since they present significant problems of waste management and water treatment. Accordingly, there is a desire to completely eliminate the electrocoating process and find new coating methods and compositions that are capable of replacing the electrodeposition process and still maintain the desired coating properties for sizing finishes that prevent rust on the coating. automobiles such as a high degree of corrosion resistance and adhesion of paint for pre-treatments that avoid the underlying rust on the surface of the metal and which receive the paint applied thereon during the exterior automobile finishing operations. Various ionomeric coating compositions have been proposed which comprise aqueous dispersions of ionomer resins made of copolymers neutralized in ethylene-acrylic acid or ethylene-methacrylic acid ions for treatment to prevent rust on metal surfaces, for example as described in US Pat. JP 2000-198949 A2 for Akimoto et al., WO 00/50473 Al for Nakata, et al., and the US patent No. 6,458,897 for Tokita et al., Issued on October 1, 2002. Notwithstanding, in none of these has been used to treat complete bodies of vehicles that are transported along a vehicle assembly line, especially using the electrocoating tank emptying the electrocoating composition as the holding / immersion tank for these dispersions of ionomeric resin. Various properties are required for a coating formed of an ionomeric resin dispersion in order to be a suitable commercial substitute for an electrocoating bath. Good edge protection, bath stability and uniformity and corrosion resistance, water impermeability, smooth film condition and ease of use are desired in order to produce a rust preventive coating, high performance automotive quality . The present invention provides a method for coating ionomer resin dispersions in vehicle bodies as they are transported on an automobile assembly line that moves continuously in the vehicle manufacturing plant without impairing the operation of the coating operation at the vehicle level. corrosion protection, when compared to a conventional electronic sizing application procedure. The method of the present invention is capable of forming a sizing finish that prevents rust on vehicle bodies such as car bodies and trucks, or parts thereof that meet the high performance requirements of automotive finishes. Therefore, this method is a suitable commercial substitute for conventional electrodeposition sizing and electronic sizing application procedures used today in automobile assembly plants. The process of the present invention can be applied to typical vehicle body steel such as galvanized steel, but since it is sufficiently robust, it can also be applied to untreated metal to provide corrosion protection by direct contact, which provides substantial savings to automobile manufacturers since most of the vehicle bodies nowadays are constructed of zinc-coated steel (galvanized) which is expensive, in all but the awning area.

SUMMARY OF THE INVENTION A method is provided for coating a vehicle body such as the body of a car or truck, or a part thereof with an ionomer coating composition that prevents rust, as the vehicle is transported in a line of assembly of vehicles during its original manufacture. The coating method is preferably used as a substitute for the electrocoating of car bodies and trucks. The method comprises: (a) applying to at least one surface of an automotive substrate such as the body of a vehicle or a part thereof, a coating liquid comprising an aqueous dispersion of an ionomeric resin neutralized with ammonium ions and optionally divalent or polyvalent metal ions; (b) instant drying or baking of the coating liquid on the substrate to form an initial sizing layer that prevents rust; (c) applying a metal salt solution or a divalent or polyvalent metal, preferably zinc or aluminum, to the initial size coating that prevents rust; (d) instant drying or baking of the coated substrate to form a hardened sizing coating layer that prevents rust; and (e) optionally applying a sizing filler and / or an automotive topcoat finish such as a basecoat / clearcoat finish onto the hardened rust-preventing scrim layer; wherein the automotive substrate is preferably in continuous motion through the sizing paint application process along the vehicle assembly line. Preferably, the ionomer resin coating liquid is in the existing electrocoating tank which has been emptied of electrocoating composition and which is used as a complete substitute for the conventional automotive electrodeposition coating composition. The old electrocoating tank is preferably used as a coating immersion tank for the new ionomer resin. Preferably, the tank is slotted with electrodes and voltage is applied and preferably operated as a non-electrophoretic coating process. The metal salt solution is preferably housed in an existing water rinsing tank previously placed after the electrocoating tank in the conventional electrodeposition process. Treated articles such as vehicle bodies or parts thereof treated therewith also form a part of this invention. The ionomeric resin dispersion used as the first coating liquid preferably comprises copolymers of ethylene-acrylic acid or methacrylic acid having an acid content of 5-40 weight percent neutralized with ammonium ions and water as the volatile liquid carrier and the solution The metal salt used as the second coating liquid preferably consists of at least one divalent metal cation selected from the group consisting of alkaline earth metals and Zn and water as the volatile liquid carrier.

BRIEF DESCRIPTION OF THE FIGURE The above summary as well as the following detailed description of the preferred embodiments will be better understood when read together with the accompanying figures, in which: Figure 1 is a schematic diagram of an exemplary procedure according to the present invention for applying an ionomer resin coating composition to a car substrate on a mounting line that moves continuously during the manufacture of a vehicle.

DETAILED DESCRIPTION OF THE INVENTION In this description numerous terms and abbreviations are used. The following definitions are provided. The terms "ionomers" or "ionomer resins" are polymers or copolymers of ethylene and acrylic or methacrylic acid that have been optionally neutralized partially or completely with a base, such as a metal hydroxide or an oxide or acetate, ammonium hydroxide or amines. The resulting polymer is capable of forming or behaving as strong crosslinks formed between polymer chains under curing conditions, creating flexible and resistant films. The term "copolymer" means polymers that contain two or more monomers. All "molecular weights" described herein are determined by "GPC" gel permeation chromatography using polystyrene as the standard. Now a method according to the present invention will be described for the application of an ionomeric coating liquid which prevents rusting to an automotive substrate to form a coating layer which prevents rust on it as part of the automobile coating process, with reference to an exemplary continuous automobile coating process described in detail in the following. By means of a "continuous process" it is meant to indicate that the substrate is in continuous movement along the assembly line. However, it should be understood that this exemplary continuous coating process is provided simply as an example of a process in which the invention can be put into practice and the invention should not be considered as limited thereto. It should be understood by a person skilled in the art that the present invention can also be used, for example, in non-continuous, ie, semi-continuous or aligned coating processes, or batch coating processes. Additionally, although the following discussion relates primarily to the coating of automobile bodies, it should be understood that the invention should be practiced on any automotive substrate at any point along the coating line or outside the line. Referring now to Figure 1, there is shown a schematic diagram of a portion of a continuous automobile coating process (indicated generally with the numeral 10) to apply a rust-preventing sizing on one or more surfaces of a car substrate. , for rinsing the coated substrate, if desired, with one or more rinsing compositions and for instant drying or baking of the substrate in a continuous oven. Useful substrates that can be applied as a coating include those formed of metallic materials, for example ferrous metals such as iron, steel and alloys thereof, non-ferrous metals such as aluminum, zinc, magnesium and alloys thereof and combinations thereof. same. Preferably, the substrate is formed from steel sheet, cold rolled, electrogalvanized steel such as electrogalvanized steel by hot dip, aluminum or magnesium. The substrates can be used as components for manufacturing automobile vehicles that include but are not limited to automobiles, trucks and tractors. The substrates can have any shape, for example in the form of automobile body components such as bodies (frames), awnings, doors, fenders, bumpers and / or cutouts for automobile vehicles. A coating system incorporating the concepts of the present invention will be discussed generally in the context of automotive metal body cladding. A person skilled in the art will understand that the coating process embodying the present invention is also useful for coating other automobiles as well as different automotive components. The substrate is typically cleaned first to remove grease, dirt or other foreign materials. This is typically done using conventional cleaning materials and procedures. The materials include light or strong alkaline cleaners such as those commercially available and those conventionally used in metal treatment processes. Examples of alkaline cleaners include Chemkleen 163 and Chemkleen 177, both available from PPG Inries, Pretreatment and Specialty Products. The cleaners are usually followed and / or preceded by one or more rinses with water. Optionally, the metal surface can be rinsed with an aqueous acid solution after cleaning with the alkaline cleaner and before contact with a subsequent coating composition. Examples of rinsing solutions include light or strong acidic cleaners such as dilute solutions of commercially available nitric acid and conventionally used in metal treatment processes. The metal substrate optionally may also be phosphated. Suitable phosphate conversion coating compositions can be any of those known in the art. Examples include zinc phosphate, iron phosphate, manganese phosphate, calcium phosphate, magnesium phosphate, cobalt phosphate, zinc-iron phosphate, zinc-manganese phosphate, zinc-calcium phosphate, and other types of layers. , which may contain one or more multivalent cations. Phosphating compositions are known to those skilled in the art and are described, for example, in the U.S. Patents. Nos. 4,941,930; 5,238,506; and 5,653,790.

The substrate can also be contacted with one or more conventional passivating compositions to improve the corrosion resistance. Passivating compositions are typically dispersed or dissolved in a carrier medium, usually an aqueous medium. The passivating composition can be applied to the metal substrate by any known application technique, for example by immersion or by submersion, spraying, intermittent spraying, immersion followed by spraying, spraying followed by dipping, brushing or by coating and rolling. An exemplary passive composition is described in the U.S.A. No. 6,217,674. Referring now to Figure 1, in the first portion 12 of the rust-preventing sizing coating method 10, a liquid in the form of a liquid ionomer resin coating composition 14 is applied to a surface 16 of the body 18 of a car in a first stage 20. The coating composition 14 can be applied, for example, by immersing the car body 18 in a container or bath 22 containing the liquid ionomer resin coating composition 14. Preferably, the container that is used is an existing coating immersion tank that is located along the assembly line in the vehicle assembly plant.

As indicated in the above, the existing electrocoating tank will not be used for electrodeposition in view of the present invention. Instead, it is used as the dip tank 22 for the ionomeric resin coating composition which serves as a replacement or substitute for the electrodeposition coating composition and process. The liquid ionomer resin coating composition 14 has an upper surface 24, the location of the upper surface 24 in the bath 22 may vary between a maximum level and a minimum level, depending on the amount of coating composition 14 in the bath 22 and whether the car body 18 is inside or outside the bath 22. The liquid ionomer resin coating composition 14 can be applied to the surface 16 of the body 18 of an automobile by any suitable well-known dip coating process. those skilled in the art. In the sizing coating process of the present invention, the electrically conductive anode or cathode (not shown) previously used in the electrodeposition process is preferably quenched in the tank and essentially no voltage will be passed between that electrode and its counter-electrode ( the electrically conductive surface 16 of the automobile body 18) for depositing the coating film on the automobile body. From this, in the present invention, the automobile body simply enters the immersion tank 22 and after contact with the liquid ionomer resin composition, an adherent film 26 of the coating composition 14 is deposited on the car body 18. The conditions under which the film deposition is carried out may vary depending on the environmental conditions in the assembly plant, the nature of the liquid coating materials and the desired final film thickness of the adherent coating film, as will be evident to those skilled in the art. It is generally desired to maintain the car body 18 in the immersion tank 22 for about 1 to 300 seconds, more preferably for about 1 to 60 seconds at a bath temperature of 18 to 60 ° C, at atmospheric pressure. Of course, the rust-preventing ionomer treatment can be carried out by any other known mode such as spray, curtain, flow coating, roller coating, brush coating and the like. In automotive applications, the immersion method as described in the above is the one that is generally preferred. Generally, any type of conventional ionomeric resin coating composition can be used in the practice of the present invention. Preferably, the ionomer resin coating composition 14 comprises an aqueous dispersion of ionomer resin in water. The ionomeric resin coating composition may also be dispersed in an aqueous medium which may include a mixture of water with brownish solvents, if desired. The ionomeric resin coating composition is also preferably supplied as a one component system with all the ingredients dispersed and neutralized at least partially in aqueous medium prior to incorporation into an immersion tank. The ionomeric resin coating composition used herein generally comprises an aqueous dispersion of one or more ionomeric film-forming resins such as an ethylene-unsaturated carboxylic acid copolymer and one or more neutralizing agents therefor. The amount of film-forming material in the composition generally ranges from about 5 to 50 weight percent on a solid basis of total weight of the composition. With respect to the components of the aqueous dispersion, the ionomeric resin is typically a polymer comprising a polymer backbone consisting mainly of hydrocarbons and having carboxyl groups in the side chains, wherein at least a portion of the carboxyl groups is neutralized with cationic neutralizing agents. Preferably, the ionomeric resin used in the present invention is a copolymer of unsaturated carboxylic acid with ethylene ("ethylene-acid copolymer") comprising a partially neutralized product which is obtained by neutralizing at least a portion of the carboxyl groups contained therein. the copolymer with either polyvalent metal cations, alkali metal cations, ammonium ions or a mixture of any of the foregoing. The ethylene-unsaturated carboxylic acid copolymer constituting the main structure of the ionomeric resin can be a random copolymer of ethylene and unsaturated carboxylic acid or a graft copolymer in which the unsaturated carboxylic acid is grafted to the main chain comprising polyethylene. In particular, the unsaturated ethylene-carboxylic acid random copolymer is preferable. Furthermore, this ethylene-unsaturated carboxylic acid copolymer may contain one class of unsaturated carboxylic acid only, or two or more classes of unsaturated carboxylic acids. The unsaturated carboxylic acid which is the ethylene-unsaturated carboxylic acid copolymer component includes an unsaturated carboxylic acid having 3 to 8 carbon atoms or the like. Specific examples of the unsaturated carboxylic acid having 3 to 8 carbon atoms include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, isocrotonic acid, citraconic acid, allyl succinic acid, mesaconic acid, glutaconic acid, acid nadic, methylnadic acid, tetrahydrophthalic acid and methylhexahydrophthalic acid. Of these, acrylic acid and methacrylic acid are preferable from the point of view of film-forming properties. In addition, the ethylene-unsaturated carboxylic acid copolymer may contain a third component in the main structure such as a softening monomer in addition to ethylene and unsaturated carboxylic acid. This third component includes carboxylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate and isobutyl (meth) acrylate and vinyl esters such as vinyl acetate. If these monomers are included, it is generally desirable that the content be set in the range of 20% by weight or less, preferably 10% by weight or less, since larger quantities tend to cause the melting point of the coating film to decrease and the heat resistance to be unacceptable. Preferably, the ethylene-acid copolymer is a dipolymer (and not a third comonomer).

Regarding the unsaturated ethylene-carboxylic acid copolymer, when considering the feasibility of making an aqueous dispersion, the dispersion stability and the physical properties of the coating film obtained with the aqueous dispersion, it is generally desirable that the ethylene-unsaturated carboxylic acid copolymer has an unsaturated carboxylic acid content of 5-40% by weight, preferably 10-35% by weight and most preferably 15-25% by weight. In the case of using a copolymer containing an unsaturated carboxylic acid in an amount that is less than the aforementioned range, it is difficult to obtain a composition having good dispersion stability. In the case of using a copolymer containing an unsaturated carboxylic acid in an amount greater than the aforementioned range, the water resistance (water impermeability) and the mechanical strength of the coated film are reduced. At least a portion of the carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer are neutralized with a base such as a metal hydroxide or oxide, ammonia, ammonium hydroxide or amines or any mixture thereof, to form cross-linkages that they comprise an association of carboxylic acid anions with various metal cations and ammonium ions. To obtain a coating film and especially excellent in its water resistance and film quality, it is more desirable to use a mixture of divalent or polyvalent metal cations and ammonium ions as the neutralizing agent. The metal ions which remain in the film provide the desired corrosion resistance to the coating formed therefrom. Ammonium ions evanesce as ammonia when heated thereby providing the desired impermeability to water, especially compared to alkali metal ions. With respect to the divalent metal cations which may be used herein, alkaline earth metals such as Mg and Ca or Zn are preferred. With respect to the polyvalent metal cations that can be used, Al is generally preferred. Of these, the ionomer resins having Zn are preferable from the point of ease of production. Since the metal cations remain in the final film, it is preferred to expose the neutralization concentrations in terms of metal ion. As will be appreciated by a person skilled in the art, the preferred degree of neutralization by the metal, ie, the preferred ratio of metal ion to carboxylic acid anion will of course depend on the ethylene-acid copolymers and the ions used and of the desired properties. However, the preferred proportion of carboxyl groups neutralized with metal cations for all carboxyl groups having the ethylene-unsaturated carboxylic acid copolymer in the side chain, i.e., the degree of neutralization by the metal, is generally about 10- 100%, and preferably 20-80% and more preferably 25-50% so that a coating having excellent corrosion resistance is obtained. Furthermore, it is to be understood that the compounds containing the above metal cations, if used alone in the bath 22 can cause them to coagulate the aqueous ionomeric resin dispersion, and prevent the formation of a quality film. Therefore, in order to avoid coagulation of the ionomeric dispersion, it is generally preferred in the process of the present invention to use a two-coat or double-dip process, whereby two sequential baths are used, specifically the bath 22 as described above. mentioned in the foregoing and another bath 32 which is described further in what follows. It is preferred that the first bath 22 contains the aqueous ionomeric resin dispersion formed of an ammoniacal dispersion which optionally may contain one or more of the above metal ions, preferably in the range of 10 to 90 moles in proportion, with respect to the carboxylic acid groups. After the substrate is coated with the above ammoniacal dispersion, in the second coating step, it is subsequently coated, preferably by dip coating with a metal salt solution contained in the second bath 32 to form the coating film. hardened finish. The metal used in the second bath can be the same or different from the metal that is optionally used in the first bath. In addition, any monovalent, divalent or polyvalent metal can be used in the second bath to provide a stable metal in the aqueous solution. The production of ionomer resins for use herein in the first bath can be carried out according to various methods well known in the art, for example a method of copolymerization of ethylene, unsaturated carboxylic acid and a third component used in accordance with high-pressure radical polymerization method and neutralize carboxyl groups of the ethylenically unsaturated carboxylic acid copolymer obtained with a cationic compound; or a method of graft polymerization of unsaturated carboxylic acid in polyethylene, and neutralization of carboxyl groups of the obtained graft copolymer with a cationic compound. Furthermore, this production can be carried out by supplying predetermined components in an extruder and melt kneading to carry out the reaction or it can be carried out in water or in an appropriate organic solvent. Instead of preparing the unsaturated ethylene-carboxylic acid copolymer, Nucrel ™, which is a copolymer of poly (ethylene-co-methacrylic acid) sold by DuPont, Wilmington, Delaware, can be used as the starting material. This material is typically sold predispersed in water with ammonia. To produce the ammoniacal dispersion therefrom, which is used as the initial coating in the first bath, a compound having the desired ammonium ions can be used which can be used to neutralize the resin which are ammonia (NH3). or aqueous ammonia (which is also referred to herein as "ammonium hydroxide" or "water with ammonia"). With respect to the components that can be used to produce the first or second bath, compounds having the desired polyvalent metal cations including oxides or hydroxides thereof or water-soluble salts such as zinc acetates, sulfates and nitrates, calcium can be used. , magnesium or aluminum. More specifically, the initial coating composition used in the first bath can be made by introducing ionomeric resin, aqueous ammonia (ammonium hydroxide) and the like and water into a container, after stirring or stirring the mixture of a temperature above of the pressure temperature of the ionomer resin, typically about 100-200 ° C for a time sufficient to uniformly heat, melt and disperse the ionomer resin, preferably for about 10 minutes to 2 hours. The dispersion for the first bath is preferably also carried out with an excess amount of aqueous ammonia (ie, using an amount of ammonia that exceeds the amount that would be needed to neutralize the carboxylic acid groups). The molar ratio of ammonia to carboxylic acid is generally in the range of about 2 to about 6. The metal salt hardening solution of the second bath is worked up by dissolving any of the metal salts described above such as acetate of zinc, calcium acetate and the like, in water. A suitable aqueous dispersion for a rust-preventing coating of car bodies that can be used in the first bath comprises an aqueous dispersion of ethylene-acid copolymer having an acid content of 18-30% by weight and 75-600 moles% ammonia, based on the carboxyl groups of the copolymer. A suitable metal salt hardening solution which can be used in the second bath comprises 25-50 mol% of metal cations, preferably zinc cations, based on the carboxyl groups of the copolymer.

A suitable aqueous dispersion for a rust-preventing coating preferably also has its average particle diameter dispersed in the range of about 0.1 μm or less, and preferably 0.05 μm or less and its concentration of solids content in the range of 10- 45% by weight and preferably 15-35% by weight and more preferably 15-30% by weight. A suitable aqueous dispersion typically also has a pH of 7 or more and a viscosity of about 30-2,000 mPa • s and particularly about 50-1,500 mPa-s, at the time of application for good susceptibility to operation. Various other additives may be combined in the initial dispersion to provide additional attributes to the coating depending on the needs, provided that the objective of the present invention is not impaired. For example, various additional and / or crosslinked film-forming resins such as water-soluble polyester polyols, acrylics and water-soluble covalent curing agents such as aminoresins and the like. The water-soluble aminoresin is used in particular to improve the strength of the coating and examples thereof include water-soluble melamine resin, hexametoxymelamine, methylolated benzoguanamine resins and methylolated urea resins. Examples of the other components include organic and inorganic thickeners to adjust viscosity, surfactants to improve stability, water-soluble polyvalent or monovalent metal salts and other rust-preventing aids, vapor-phase corrosion inhibitors, mildew-proof agents , fungicides, biocides, substances that absorb ultraviolet radiation, heat stabilizers, fuming agents, rheology control agents, pigments, fillers and thinners. In addition to the above materials, in order to obtain a coating film with sufficient water resistance for automotive applications (ie, impervious to agents that can cause metal corrosion), it is generally desired to include at least one corrosion inhibitor. in the non-water-soluble vapor phase such as dicyclohexylamine in the dispersion. The thickness of the final coating applied to the substrate can vary based on factors such as the type of substrate and the proposed use of the substrate, i.e. the environment in which the substrate is to be placed and the nature of the contact materials. Generally, the coating is applied so that the final thickness of the coating formed on the substrate varies between approximately 0.1-20 μm and more preferably for coating in a thickness of 0.3-10 μm. Referring again to Figure 1, the initial coating composition 14 in the bath 22 can be recycled in a conventional manner, for example by the recycling system 28 having a Pl pump which prevents the solids in the coating composition from settling in the bottom of the bath 22. In addition, the temperature of the coating composition 14 can be controlled by the use of a heat exchanger (not shown) in flow communication with the bath 22 in any conventional manner, for example through pipes or conduits. The initial coating composition of the bath 22 may also be in flow communication with a conventional ultrafiltration system (not shown) to remove soluble impurities and the filtrate is recycled to the ionomer bath 22. In the ultrafiltration system, the coating composition 14 flows on a water permeable membrane and small particles, eg, less than about 1,000 Mw such as salts. The ultrafiltrate or "permeate", i.e., the portion of the coating composition which passes through the membrane can be used in subsequent rinsing operations (if used) and a portion of the permeate can be discarded., for example about 20 weight percent. The "non-permeate" portion of the coating composition is directed back to the bath 22, for example, through one or more ducts or tubes. After transport from the ionomeric coating bath 22, the coated car body 18 is preferably exposed to the air to allow excess deposited coating composition to drain from the interior cavities and surfaces of the car body 18 back to the bath 22 After coating with the rust-preventing ionomer coating composition on a substrate, the agent can dry spontaneously (eg, flash drying under ambient conditions or at slightly elevated temperature, preferably at an air temperature ranging from about 10 ° C. to about 40 ° C) but it is preferable to carry out baking in a conventional continuous oven 30 which is typically located after the ionomer resin dip tank along the automobile assembly line. The baking temperature in the oven is approximately 60-250 ° C. The coated car body 18 is preferably transported to the continuous furnace 30 and heated in the above temperature range for about 1 second to 30 minutes to remove the volatile components so that a rust preventing layer formed of a coating can be formed. It has good resistance to corrosion. After step 30 of sufficient baking and cooling, preferably to room temperature, the coated car body 18 is preferably transported to a second container or bath 32 containing the metal salt solution 34 to further harden the ionomeric coating that it is applied in the first stage 20. Preferably, the container that is used as the coating immersion tank in this stage is the existing electrodeposition coating rinsing tank which is located along the assembly line in a cement plant. assembly of vehicles which has become an immersion tank. As discussed previously, various solutions of ionic salts may be used at this stage, although those containing Zn, Ca or Al are generally preferred. These may be simple salts such as acetate, sulfate or nitrate. The metal salt solution 34 has an upper surface 36, the location of which on the upper surface 36 in the bath 32 may vary between a maximum level and a minimum level depending on the amount of salt solution 34 in the bath 32 and whether the car body 18 is inside or outside the bath 32. The metal salt solution is preferably applied by dipping the car body 18 into the second container or bath 32 containing the liquid metal solution to form a film. of hardened ionomeric coating that prevents rust on the surface of the vehicle. With respect to the application of the ionomeric dispersion any dip coating process well known to those skilled in the art can be used. Of course, the metal salt solution treatment can also be carried out by any other known manner such as spray, curtain, flow coater, sheet coater, and brush and brush coating or the like. In automotive applications, the immersion method is generally preferred, as described above. Thus, when the body of the coated car is transported to a second tank 32 which contains the metal salt solution, the second bath 32 is maintained at a temperature that allows the metal to diffuse the film and crosslink with the remaining acid functionality in the polymer film. Generally, the second bath temperature is preferably maintained at about 70 to 90 ° C at an atmospheric pressure. It is generally desired to maintain the car body 18 in the second immersion tank 32 for approximately 1 to 40 minutes. This produces an extremely tough hardened coating that results in a significant increase in corrosion resistance and chipping resistance of the coating, compared to the one-dip method described above, and the ionomeric coatings are not subjected to a second immersion. The metal salt solution in the bath 32 can also be recycled in a conventional manner, for example, by the recycling system 38 having a pump P2 which prevents the solids of the coating composition from settling on the bottom of the bath 32. In addition, the temperature of the salt solution 34 can be controlled by the use of a heat exchanger (not shown) in flow communication with the bath 32 in any conventional manner, for example by pipes or conduits. The metal salt solution 34 in the second bath 32 may also be in flow communication with a conventional ultrafiltration system (not shown) to remove soluble impurities and the recycled filtrate to the salt bath 32. In the ultrafiltration system, salt solution 34 flows over a water permeable membrane and small particles, for example those less than about 1,000 Mw, such as salts. The ultrafiltrate or "permeate", that is, the portion of the saline solution passing through the membrane, can be used in further subsequent rinsing operations (if used) and a portion of the permeate, for example approximately 20% by weight, can be discarded. The "non-permeate" portion of the salt solution is directed back to the bath 32, for example through one or more ducts or tubes. After transport from the metal salt solution bath 32, the coated car body 18 is preferably exposed to the air to allow the excess coating composition deposited from the interior cavities and surfaces of the car body 18 to drain back into the air. bath 32. After applying the metal salt on the automotive substrate, the agent can dry spontaneously (eg flash drying under ambient conditions or slightly elevated temperature, preferably at air temperature ranging from about 10 ° C to about 40 ° C), but preferably baking is carried out in a typical conventional continuous furnace 40 located downstream of the ionomer resin dip tank along the automobile assembly line. The baking temperature of the oven is approximately 60-250 ° C. Preferably, the body 18 of the coated car is transported a continuous furnace 40 and heated in the above temperature range for about 1 second to 30 minutes to remove the volatile components so that a rust preventing layer comprising a coating that has good resistance to corrosion. The thickness of the coating layer that prevents rust forming on the substrate is appropriately selected according to the purpose of use of the treated metal products to prevent rust, rust preventing agents used, class, thickness and the like of a top coating paint and the like, and is not particularly limited in the present. Generally, in order to present sufficient rust impeding ability without causing breakage in the rust preventing layer when it is dried after coating with the agent to treat and prevent rust, it is preferably coated to a thickness of about 7 to 60. μm (0.3-2.5 mils), preferably 2 to 36 μm (0.5-1.5 mils). The coated car body can then be transported to a rinsing process 42 to remove unbound metals and other impurities and any excess coating from the surface. The wiping procedure 42 may include one or more spraying and / or immersion rinsing operations, as desired. Preferably, the coated car is transported over a spray rinse tank 44 where a rinse composition 46, preferably deionized water or tap water is applied by spray to the coated surfaces of the car body 18. The excess spray composition is allowed to drain to the lower rinse tank for recirculation, for example, by means of a recirculation system 48 having a recirculation pump P3 for subsequent spraying operation. The body of the coated car is then transported out of the spray rinse area and the excess rinse composition is allowed to drain back into the tank for reuse. The rinsing tank used may be one of the other existing rinsing tanks that are located along the vehicle assembly line in a vehicle assembly plant which has previously been used in a conventional electrodeposition process. The method of the invention also includes a subsequent cooling step (not shown) to cool the finish to room temperature before the vehicle is further worked or manufactured. The rust-preventing coating layer formed in this way on the automobile body has excellent corrosion resistance and also good adhesion to an upper coating paint such as a car sizing., filling material or base coating paint. The rust-preventing coating method of the present invention is also useful especially on uncoated metal, which is particularly desirable in the automotive industry when the metal is used to build vehicle bodies such as car bodies and trucks. In the rust-preventing treatment method of the present invention, after the rust-preventing sizing coating layer is dried, it is traditionally coated on top or coated on its top with a sizing tackle to provide a Smooth film free of imperfections on the surface on which an automotive topcoat finish such as a basecoat / clearcoat finish can be applied. The upper coating paint that is applied as a coating on the coating layer that prevents rust from forming on it can be any car sizing equipment, filler or basecoat paint with color or a basecoat paint / transparent coating. The nature of the size dressing, the filler material or the basecoat or the basecoat / clearcoat composition used in the method of the present invention is by no means critical. Any of a wide variety of sizing, filler, base coatings, transparent coatings, commercially available, may be used in the present invention. Typically, the sizing-tack is then applied (not shown) to smooth the surface and provide a coating thick enough to allow grinding to a smooth, flat finish and then heated in an oven. A topcoating system (not shown) is then applied, sometimes as a one-color coating, most often now as a pigmented basecoat with a continuous color or flake pigments followed by a clear clear protective coating, to protect and preserve the attractive aesthetic qualities of the finish on the vehicle even in the event of prolonged exposure to the environment or the treatment of the environment. It has become customary, particularly in the automotive industry, to apply a clear topcoat over the basecoat by "wet moistened" application, i.e., the clearcoat is applied to the basecoat without completely coating or drying the coating. base. The coated substrate is then heated for a predetermined period of time to allow the simultaneous curing of the base and clear coatings. Conventional coating methods such as spraying, electrostatic spraying, rotational high electrostatic hoods and the like can be used to apply any of these top coatings. Preferred techniques for applying these three coatings are atomized air spray with and without electrostatic enhancement and high speed rotating atomizing electrostatic bells since these techniques are typically used in modern automobile and truck assembly plants. When the rigging and sizing coating material is applied to automotive bodies according to the present invention, any of the above techniques can be used. The sizing-tack coating material preferably forms a dry coated layer having a thickness of about 7 to 60 μm (0.3-2.5 mils), preferably 12 to 36 μm (0.5-1.5 mils), but may vary with the proposed use. Sizing after the application typically dries instantaneously at room temperature and then baked in an oven at 100-150 ° C for about 15-30 minutes to form a cured dressing and sizing layer on the substrate. After the sizing and rigging layer is formed on the car body, the layer can be cooled and ground as desired. Then, the colored base coating material which can contain a continuous color, metallic flakes, opalescent pigments and / or other effect and a clear and transparent coating material are typically applied in the wet wet manner to form the Base coating and a clear coating layer. The basecoating material can be applied as a coating and sizing material with the use of an electrostatic spray coating on an electrostatic spray hood rotating so as to have a dry thickness of 3 to 40 μm) ( 0.1 to 1.6 thousandths of an inch). The base coat typically dries instantaneously for a short period at room temperature or a slightly elevated temperature before the car body is subjected to transparent coating. The material applied as a transparent coating is then applied to the basecoat for the purpose of smoothing the roughness or providing gloss, which occurs due to the presence of a lustrous-colored pigment and to protect the surface of the coating layer. base. The clear coated material can be applied as the base coating material using the rotating atomizing electrostatic hoods. The clear coated layer is preferably formed such that it has a dry thickness of about 25-75 μm (1.0-3.0 mils). The base coat and the clear coat obtained as described above are then cured simultaneously in an oven at 100-150 ° C for about 15-30 minutes to form a desired multi-layered finish on the car body. The process of the invention may also include a subsequent cooling step (not shown) to cool the finish to ambient temperatures before the vehicle is further worked during its manufacture. The total thickness of the multi-layered composite in drying and curing is generally about 40-150 μm (1.5-6 mils) and is preferably 60-100 μm (2.5-4 mils). The car body treated to avoid the rust that is obtained by the rust-preventing coating method of the present invention, contains a rust-preventing layer which has excellent water resistance and rust-preventing properties and therefore It can be used properly as parts for automobiles. The coatings formed from the method of this invention have excellent properties that prevent rust and provide a high level of addition to treated or untreated metals and are resistant, flexible, resistant to flaking by stones and are relatively impervious to moisture and others. corrosive agents and can provide rust-preventing coatings having desirable properties for automotive finishes. The following examples illustrate the invention. All parts and percentages are on a weight basis, unless otherwise indicated.

EXAMPLE Preparation of a metal plate treated to prevent rust Washing of cold rolled steel panels (7.6 cm) (3") x 12.7 cm (5") x 032", alloy APR10288 C, available from ACT Laboratories, Inc., Hillsdale MI), with acetone and deionized water and then air dried.A ionomeric resin dispersion is prepared Nucrel ™ when diluting 1500 ml of Nucrel Michem Prime ™ 4983R, 25% w / w (21% acrylic acid / ethylene copolymer at 25% solids in water with ammonia available from Michelman Inc., Cincinnati, OH) at 12.5% w / w with 1500 ml of deionized water to obtain a 12.5% dispersion The diluted dispersion is allowed to stand at room temperature for 1 hour to remove air bubbles, then 21 cleaned steel panels are immersed in the diluted dispersion and then baked in a oven at 90 ° C for 10 minutes The panels are divided into 3 groups of 7. One group is immersed in a 5% aqueous solution, w / w of zinc acetate at 90 ° C for 10 minutes. in a 5% w / w aqueous solution of calcium acetate at 90 ° C for 10 minutes. or group is not treated with subsequent immersion.

Test results The corrosion resistance is determined according to the ASTM B117 test method. The panels are subjected to 330 hours in a salt spray chamber in accordance with ASTM B117. The 7 panels that were not submerged subsequently show extensive rust. The panels that were subjected to subsequent immersion show few small rust spots, which is a significant improvement in terms of corrosion resistance. Various modifications, alterations, additions or additional substitutions to the components or methods and compositions of this invention will be apparent to those skilled in the art without thereby deviating from the spirit and scope of this invention. This invention is not limited to the illustrative embodiments set forth herein, rather, it is defined by the following claims. 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 is clear from the present description of the invention.

Claims (15)

1. CLAIMS Having described the invention as above, the content of the following claims is claimed as property: 1. A coating method for applying an anti-rust coating to a car substrate, characterized in that it comprises: (a) applying to at least one surface of an automotive substrate such as the body of a vehicle or a portion thereof a coating liquid comprising an aqueous dispersion of an ionomeric resin neutralized with ammonium ions and optionally divalent or polyvalent metal ions; (b) instantaneous drying or baking of the coating liquid on the substrate to form an initial sizing layer that prevents rust; (c) applying a polyvalent divalent metal metal salt solution onto the initial rust-preventing primer layer; (d) instant drying or baking of the coated substrate to form an additional hardened sizing coating layer which prevents rust at temperatures between about 60 ° C and 250 ° C; and (e) optionally applying an automotive topcoat finish and / or an automotive topcoat finish such as a basecoat / clearcoat finish onto the rust-preventing hardened sizing layer. The method according to claim 1, characterized in that the substrate is a car or truck body or a part thereof, 3. The method according to claim 1, characterized in that the automobile substrate is in continuous movement. through the process steps of application of size paint (a) - (d) as it travels along an automobile assembly line. The method according to claim 1, characterized in that the metal coating liquid in step (a) is an aqueous dispersion of an ionomer resin that is free of metal cation ions. '5. The method according to claim 4, characterized in that the metal salt solution comprises a salt solution of a divalent metal which is selected from the group consisting of Zn and Ca. The method according to claim 5, characterized in that the ionomer resin is an ethylene-unsaturated carboxylic acid copolymer having an acid content of 10-35% by weight. 7. The method according to claim 5, characterized in that the ionomer resin is an ethylene-acrylic or methacrylic acid copolymer having an acid content of 10-35% by weight. 8. The method according to claim 6, characterized in that the divalent metal ion is selected from Zn. 9. The method according to claim 8, characterized in that the dispersion has a solids content of 10 to 45% by weight. The method according to claim 5, characterized in that the dispersion also contains a water-insoluble vapor phase corrosion inhibitor. The method according to claim 1, characterized in that the metal coating liquid in step (a) is an aqueous dispersion of an ionomer resin partially neutralized by a mixture of ammonia and one or more divalent metal ions. 12. The method according to claim 5, characterized in that the solution temperature is between 70 ° C and 90 ° C. The method according to claim 5, characterized in that the surface is rinsed with water after the final baking. 14. A substrate for automobile, characterized in that it is treated to prevent rust applied as a coating by the method according to claim 1. 15. The car or truck body substrate, characterized in that it is treated to prevent rust, coated by the method according to claim 1.