WO2001032321A2

WO2001032321A2 - Liquid coating systems for metal stock, metal stock coated therewith, and processes for preparing such coated metal stock

Info

Publication number: WO2001032321A2
Application number: PCT/US2000/030241
Authority: WO
Inventors: David E. Kubicek; Petra H. L'abbe; William D. Krippes
Original assignee: Ppg Industries Ohio, Inc.
Priority date: 1999-11-02
Filing date: 2000-11-01
Publication date: 2001-05-10
Also published as: AU1455701A; WO2001032321A3

Abstract

The present invention provides novel liquid coating systems for metal stock; metal stock coated therewith; and processes for preparing such coated metal stock. The novel liquid coating systems disclosed herein include, among other things, a base coat portion and a radiation curable topcoat portion. The base coat portion not only is flexible enough to withstand the typical fabrication, forming and bending operations of coil metal stock, but also adheres well to the coil metal stock over which it is applied. Moreover, the radiation curable topcoat portion is also flexible enough to withstand the typical fabrication, forming and bending operations of coil metal stock. This topcoat portion adheres well to the base coat portion over which it is applied.

Description

LIQUID COATING SYSTEMS FOR METAL STOCK, METAL STOCK COATED THEREWITH, AND PROCESSES FOR PREPARING SUCH

COATED METAL STOCK

FIELD OF THE INVENTION

This invention relates to liquid coating systems. More particularly, the present invention relates to multilayer composite coatings, which coatings are particularly useful for coating of coil metal stock.

BACKGROUND OF THE INVENTION

In the production of structural metal building components, there is, among other things, a need to protect the metal surfaces from corrosion. Specifically, prolonged exposure of metal surfaces to corrosive agents and/or environments (e.g., salt and humidity) and corrosive industrial pollutants (e.g., sulfur dioxide, nitrogen dioxide, carbon dioxide and fly ash) tends to degrade the quality and appearance of the metal.

To address this concern, a variety of anticorrosive coating systems have been formulated and applied to sheet metal surfaces. One typical component of such anticorrosive coating systems is a base coat portion which can include a primer layer.

With regard to the primer layer of such a coating system, when employed, it is applied to the metal surface before application of a top coat layer. Such a primer layer typically must have good corrosion resistance, abrasion resistance, and adhesion with the metal substrate over which it is applied and the top coat which is applied thereover. In addition, if used on coil metal stock, such a primer layer must also have good flexibility to facilitate the subsequent forming of the coated metal substrate without film fracture or loss of the adhesion.

Primers of this type are typically applied to sheet metal by a variety of methods, such as by brush, spray and immersion techniques. However, it is generally preferred to coat sheet metal surfaces by coil coating techniques since such techniques are particularly useful for the fast and effective coating of large surface areas. When employed, primers are often applied to continuous coils of metal stock to protect the metal. Typically, the bare coil metal first is cleaned of protective oil and/or pretreated with an inorganic pretreatment composition, and, thereafter, coated with a primer. Then, the primed metal stock is topcoated. Thereafter, the topcoated metal stock is subjected to a wide variety of fabricating and post-forming operations which includes cutting to length, die-forming, roll-forming, or stamping to produce a formed metal object. Due to the wide variety of subsequent fabricating, forming and bending operations, coating systems applied over coil metal stock must possess unusual properties in order to withstand the subsequent cutting, bending, stamping, drawing, and the like whereby the integrity and adhesion to the coiled stock is maintained. Specifically, such systems must have sufficient flexibility and adhesion to withstand subsequent bending operations, as well as sufficient chemical, corrosion, humidity and water resistance. The coating industry continually searches for new and improved systems for coating coil metal stock. Currently, the base coat and top coat portions of conventional coating systems for coil metal stock rely upon a liquid carrier which evaporates after the composition is applied. Since coating processes for coil metal stock typically are run at very fast line speeds, volatile organic solvent-borne liquid carriers are often employed.

Recently, however, there has been a growing trend toward reducing the Volatile Organic Compounds (VOCs) of liquid coating systems. Notwithstanding this trend, the coil metal stock coating industry has continued to employ volatile organic solvent-borne coating systems since most of their lower VOC counterparts did not exhibit the necessary physical properties (e.g., good adherence, flexibility and hardness). Accordingly, in its search for new and improved systems for coating coil metal stock, the coating industry would also welcome such systems which contain lower VOC levels.

One example of an attempt to reduce the VOCs of a liquid coating system for coil metal stock is disclosed in US Patent 4,103,050. Specifically, that Patent discloses a liquid coating system which includes a heat-curable, aqueous primer. The primer disclosed therein includes an aqueous film-forming binder phase and a corrosion-inhibiting pigment phase. The aqueous film-forming binder phase, in turn, includes a water-dispersible polyurethane polymer and a thermosetting or thermoplastic resinous latex.

Another example of a low VOC liquid coating system for coil metal stock is disclosed in "Development of Electron Beam Curable Coating for Prepainted Strip^'" (1995). That publication discloses that, while radiation curable coatings are currently used throughout the plastic, paper and wood coating industries, they have not been used by the metal coating industries. One of the main reasons for this lack of use is their poor adhesion to metals such as steel. According to that publication, radiation curable coatings can be made to adhere directly to metal sheets by adding at least 5 weight percent of an adhesion promoter to the coating. In that publication, the radiation curable coating is applied directly to the metal. Therefore, in addition to any ornamental properties, it must also exhibit all of the properties of a primer layer (e.g., anticorrosion properties). SUMMARY OF THE INVENTION

One object of this invention is to provide multilayered liquid coating systems which have excellent adhesion and anti-corrosion properties to metal substrates over which they are applied.

Another object of this invention is to provide flexible, multilayered liquid coating systems for coil metal stock.

Yet another object of this invention is to provide coil metal stock coated with a flexible, multilayered liquid coating system.

Still another object of this invention is to provide flexible, multilayered liquid coating systems which not only have low VOC ratings, but also can withstand the typical fabrication, forming and bending operations of coil metal stock.

A further object of this invention is to provide a process for coating coil metal stock with flexible, multilayered liquid coating systems which can withstand the typical fabrication, forming and bending operations of such coil metal stock. These and other objects, which will become apparent to those skilled in the art after reading the specification, are achieved through the formulation of novel liquid coating systems. These novel systems include, among other things, a base coat portion and a radiation curable topcoat portion. In particular, the present invention involves a multilayer composite coating which includes a base coat portion deposited from a resinous binder composition which is curable to form a first film adherent to a surface of a metal substrate which has been treated with an inorganic pretreatment composition, and a topcoat portion deposited from a composition which is curable through radiation, such as ionizing radiation through an electron beam, to form a second film adherent to the first film. The resinous binder composition is preferably selected from water-based compositions, solvent-based compositions and compositions in solid particulate form. More preferably, the resinous binder is a film forming polymer selected from acrylics, polyurethanes, epoxies, polyesters, phenolics, polyamides, polyolefins, and mixtures thereof. In preferred embodiments, the resinous binder includes one thermoplastic resin and one thermosetting resin, most preferably in the form of an acrylic polymer emulsion including a first acrylic polymer and a second acrylic polymer different from the first acrylic polymer. The radiation curable composition may be selected from any radiation curable composition, most preferably an acrylated urethane composition. The present invention is also directed to a metal sheet material coated with a multilayer composite coating composition as set forth above, as well as a process for preparing coated sheet metal stock. In the method, a surface of a sheet of metal is treated with an inorganic composition, and a first composition including a resinous binder is applied to the treated surface and cured to form the first film. The second composition of a radiation curable composition is then applied to the first film, and exposed to a source of radiation for curing to form the second film adhered to the first film. Such process may further include a step of cleaning the surface of the metal prior to treating, such as through ultrasonic cleaning.

In an alternative embodiment, the present invention is directed to a multilayer composite coating for coil metal stock which includes a base coat portion deposited from a water-based composition including a resinous binder, which composition is curable to form a first film adherent to metal substrates, and a topcoat portion deposited from a composition which is curable through radiation to form a second film adherent to the first film. By employing such a water-based composition as the base coat portion, excellent adhesion and flexibility are imparted to the coating composition while maintaining corrosion resistance, without the requirement of pretreating the metal surface with an inorganic pretreatment composition. Preferably, the water-based composition is an acrylic emulsion, preferably including one ^' thermoplastic resin and one thermosetting resin, most preferably in the form of an acrylic polymer emulsion including a first acrylic polymer and a second acrylic polymer different from the first acrylic polymer and including an inorganic component. The invention further includes a metal sheet material coated with such a multilayer composite coating, as well as a process for preparing such a material.

In yet a further embodiment, the present invention is directed to a process for coating a continuous moving length of sheet metal. Such process includes cleaning the moving length of sheet metal with a water based solution to remove surface contaminants that may interfere with the coating adhering to the sheet metal. A water based solution or dispersion, such as primer composition, is applied to the moving length of sheet metal, which promotes adhesion of the coating to the surface of the sheet metal. An electron beam curable coating is then applied to the moving length of sheet metal, and exposed to an electron beam to cure the coating. Such process results in low or no emission of pollutants that need to be removed before the emission is released into the atmosphere.

The base coat portion not only is flexible enough to withstand the typical fabrication, forming and bending operations of coil metal stock, but also adheres well to the coil metal stock over which it is applied. Moreover, the base coat portion also provides corrosion protection for the coil metal stock over which it is applied.

Similarly, the radiation curable topcoat portion is also flexible enough to withstand the typical fabrication, forming and bending operations of coil metal stock. In addition, the radiation curable topcoat portion can also withstand typical "warm forming" metal processes. In such warm forming processes, the coatings employed are typically harder and less flexible at ambient temperatures. Accordingly, when practicing this forming process, the coated metal stock is subjected to elevated temperatures (e.g., at least 50°C, typically at least 70°C). In addition to facilitating forming without cracking or delamination, this process sometimes results in harder, tougher, more stain resistant films than would be possible if the forming was done at ambient temperatures. This technique is often employed in the appliance, automotive, and building products industries.

Moreover, this topcoat portion adheres well to the base coat portion over which it is applied. Since radiation curable coatings traditionally have lower or no VOC ratings, the implementation of coating systems of the present invention result in lower or no levels of VOC escaping into the environment.

DETAILED DESCRIPTION OF THE INVENTION

As stated above, the novel liquid coating system of the present invention is represented by a multilayer composite coating composition including, among other things, a base coat portion and a topcoat portion.

The base coat portion of the novel liquid coating system can be a single coating layer or a multiple coating layer. For example, the base coat portion can include at least one primer layer, at least one pretreatment layer or a combination of a primer layer(s) and a pretreatment layer(s). Regardless of whether the base coat portion is comprised of a single or multiple coating layer, the entire base coat portion must have the following properties: (a) excellent flexibility, and (b) adhesion to metal substrates. Moreover, in certain preferred embodiments as will be discussed in more detail herein, the base coat portion employed when practicing this invention can also, optionally, have a low VOC rating.

Similarly, the topcoat portion of the novel liquid coating system can also be a single coating layer or a multiple coating layer. For example, the topcoat portion can include at least one ornamental pigmented layer, at least one clear coat layer or a combination of an ornamental pigmented layer(s) and a clear coat layer(s). Regardless of whether the topcoat portion is comprised of a single or multiple coating layer, the entire topcoat portion must have the following properties: (a) excellent flexibility, and (b) adhesion to the base coat portion.

As used herein, the term flexibility", as it applies to either the base coat or topcoat portions of the novel coating system disclosed herein, means that these respective portions can withstand the typical fabrication, forming and bending operations to which coated metal stock is subjected without cracking. This property can be quantified a number of different ways. For example, a flexible base coat or topcoat portion employed when practicing this invention will have a certain maximum glass transition temperature (Tg), and a certain T-bend rating as determined in accordance with ASTM D3794.

The preferred minimum flexibility rating of a particular base coat and topcoat portion will depend, in part, upon the desired end use of the coated metal stock, as well as, the particular fabrication, forming and bending operations to which coated metal stock is subjected. Typically, however, the base coat and topcoat portions of the novel coating systems disclosed herein each have a T-bend rating which does not exceed 5T. In certain embodiments where high flexibility is required, the T-bend rating of each portion preferably does not exceed 3T; and more preferably, does not exceed 2T. As used herein, the term "adhesion, as it applies to either the base coat or topcoat portions of the novel coating system disclosed herein, means that particular portion can withstand the typical fabrication, forming and bending operations to which coated metal stock is subjected without delaminating from the substrate over which it is applied. With regard to the base coat portion, the substrate to which it must adhere is either bare metal stock or metal stock which has been cleaned and/or pretreated. On the other hand, with regard to the topcoat portion, the substrate to which it must adhere is that formed by the base coat portion.

As stated herein, in certain embodiments of this invention, the base coat portion also has a low VOC rating. The term "low VOC rating" as used herein means that the base coat portion is less than about 20 weight percent organic solvent on total composition weight. In embodiments where a very low VOC rating is desired, the base coat portion is preferably less than about 10 weight percent organic solvent; more preferably, less than about 5 weight percent organic solvent; and even more preferably, less than about 3 weight percent organic solvent.

The multilayer composite coatings of the present invention are typically used to treat steel, including cold rolled steel, hot rolled steel, electrogalvanized steel, hot- dipped galvanized steel, GAL V ANNEAL steel, and steel plated with zinc alloy. Also, aluminum, aluminum alloys, zinc-aluminum alloys such as GALFAN, GALVALUME, aluminum plated steel and aluminum alloy plated steel substrates may be used.

The multilayer composite coatings adhere particularly well to metal surfaces which have been cleaned and pretreated, for example, with an inorganic composition. Any cleaning processes and materials known in the art may be used to remove contaminants, such as dirt, grease, oil or other residue, from the surface of the metal substrate, which may interfere with the coating adhering to the metal surface. Preferably, cleaning of the metal substrate is accomplished with a water-based solution, thus preventing emission of pollutants into the environment during cleaning. Conventional cleaners may include mild or strong alkaline cleaners such as are commercially available and conventionally used in metal cleaning processes.

Examples of alkaline cleaners include BASE Phase Non-Phos or BASE Phase #6, both of which are available from PPG Industries, Pretreatment and Specialty Products. Such cleaners are generally followed and/or preceded by a water rinse. In particularly preferred embodiments, cleaning of the metal is accomplished by ultrasonic cleaning, as is well known in the art for cleaning coil metal stock.

Pretreatment of the surface of the metal substrate may aid in preventing corrosion of the metal substrate and further promotes adhesion of the multilayer coating thereto. For purposes of the present invention, pretreatment is meant to describe a treatment process that is accomplished prior to application and curing of the multilayer composite coating onto the substrate. Such pretreatment preferably involves treating the surface of the metal with an inorganic composition. Without wishing to be bound by any particular theory, it is believed that pretreatment of the metal surface with such an inorganic composition activates or passivates the surface, and promotes adherence of subsequently applied organic coating compositions. Inorganic pretreatment compositions and procedures are well known in the coating art. Inorganic compositions useful as pretreatment compositions include complex or mixed metal oxides, metal phosphate solutions, organophosphate solutions, organophosphonate solutions, and combinations thereof. Specific examples include those selected from iron phosphate compositions, zinc phosphate compositions, manganese phosphate compositions, calcium phosphate compositions, cobalt phosphate compositions, and mixtures and combinations thereof. In particularly preferred embodiments, the pretreatment composition is an iron phosphate composition, as are known in the art.

The base coat portion of the multilayer coating may be provided in the form of a single curable coating composition, or may be a composite of layers or a mixture of compositions which together form the curable film of the base coat. Preferably, the base coat portion is prepared from a single film-forming composition which is curable to form a first film, such as a first coated film over a sheet of metal, as will be described more fully herein. The base coat portion is formed from a resinous binder composition which forms a film upon curing. The resinous binder composition may be any suitable composition which meets the aforementioned flexibility and adhesion requirements. Preferably, the resinous binder composition comprises one or more polymers, and preferably includes a thermoplastic resin component, a thermosetting resin component, or mixtures of thermoplastic and thermosetting resin components. The resinous binder composition may be selected from water-based compositions, solvent- based compositions, and compositions in solid particulate form, such as powder coating compositions. Examples of useful compositions include film forming polymers selected from acrylics, polyurethanes, epoxies, polyesters, phenolics, polyamides, polyolefins, and mixtures and combinations thereof. Preferably, the base coat portion is formed from a water-based composition. As such, application of the coating composition to the metal substrate will not release as much organic pollutants into the environment, as compared with conventional solvent-based compositions. Examples of useful water-based compositions include those based on acrylic polymers; urethane polymers; polyvinyl acetate; and acrylic polyester, polyurethane and/or polyether polymers, which have been adapted to be water soluble or dispersible.

Preferably, the water-based composition is an acrylic polymer emulsion, more preferably an acrylic polymer emulsion including a first acrylic polymer and a second acrylic polymer which is different from the first acrylic polymer. Particularly preferred compositions are acrylic emulsion compositions including two separate acrylic components, at lease one of which is a water-insoluble, particulate film- forming thermoplastic resin component and at least one of which is a water-insoluble, film forming thermosetting resin component. A preferred thermoplastic resin is 100% acrylic emulsion polymer comprising

45±5% by weight solids having a pH of 7 to 11 and weighing approximately 8.5 to 8.9 pounds per gallon. Such acrylic emulsion polymers are available commercially under the name RHOPLEX^® MV-117 and RHOPLEX^® WL-91, from Rohm and Haas Company. Thermosetting resins contain functional groups that allow for curing to take place, either self-curing or crosslinking with a crosslinking agent. The thermosetting resins may be selected from acrylic polymers, vinyl polymers, polyesters, polyepoxides, and mixtures thereof, and are preferably acrylic polymers, as noted above. A preferred acrylic thermosetting resin for use in the base coat composition is an acrylic emulsion polymer containing 50±1% be weight solids having a pH of 10 to 11 and weighing approximately 8.9 pounds per gallon. Such a resin is available commercially from Rohm and Haas Company under the name EMULSION E-1018.

In base coat compositions employing both a thermoplastic resin and a thermosetting resin, the thermoplastic resin, which may be a mixture of resins, is preferably present in the base coat composition of the present invention in an amount of up to 60 percent by weight, preferably from 35 to 45 percent by weight, based on the total weight of the base coat composition, with the thermosetting resin preferably present in an amount ranging from 1 to 20 percent by weight, preferably 5 to 14 percent by weight, based on the total weight of the base coat composition. The weight ratio of thermoplastic to thermosetting resin in the base coat composition is preferably within the range of 6:1 to 3:1, but may be altered as desired.

Additional components may further be provided in the base coat composition of the present invention. For example, the base coat composition based on whole or in part on a thermosetting polymer typically include one or more crosslinking agents, such as polyacids, polyisocyanates and aminoplasts. The coating composition also preferably includes a component which provides a corrosion-inhibiting effect, such as an inorganic component. In such embodiments, the composition preferably includes a heavy metal, which may be provided through a salt of a heavy metal-containing acid. The heavy metal may preferably be selected from chromium, titanium, zirconium, and mixtures thereof. The inorganic component may include chromium, thus providing a chromium-containing composition. Alternatively, the composition may be a chrome- free composition. For example, the inorganic component may be titanium, or zirconium, thus providing, for example, a titanium-containing composition, or a zirconium-containing composition as a film forming composition for the base coat portion. Also, the inorganic component may be provided, for example, through pigment. Such pigments are well known in the coating art.

In one specific embodiment of the present invention, a coating which meets the aforementioned minimum flexibility and adhesion requirements for the base coat portion of the present invention is a thermally curable aqueous primer/pretreatment protective coating composition. More specifically, the coating is a chromium- containing acrylic emulsion coating composition. Examples of such compositions are disclosed in US Patent Nos. 4,088,621; 4,138,276; 4,067,873; 4,069,187; 3,755,018; 4,137,368; and 3,895,969. A particularly useful example of a resinous binder composition useful as the base coat portion is ORGANOKROME^® 2000 available from PPG Industries, Inc.

Moreover, specific water-based compositions as used for the base coat composition have been found to adhere well directly to metal substrate surfaces, irrespective of whether such metal surface has been pretreated with an inorganic composition. Thus, in embodiments involving water-based film forming compositions, the need for an inorganic pretreatment composition may be eliminated, thus eliminating a processing step in the coating of the metal, and thereby reducing coating time and cost. In such embodiments in which water-based coating compositions are used as the base coat composition without any pretreatment of the metal substrate with an inorganic composition, it is preferred that the base coat composition include an inorganic component therein.

Without wishing to be bound by any particular theory, it is believed that the water-based film forming composition of the base coat portion acts as both an adjuvant pretreatment for further preparation of the metal surface, and as a primer composition for the subsequently applied radiation curable topcoat, thus promoting adhesion of the radiation curable topcoat to the metal substrate through the base coat portion and providing corrosion resistance.

The coating layer(s) making up the base coat portion of the present invention can be applied by any suitable means known to those skilled in the art. For example, the coating layer(s) can be applied by brushing, spraying, flow coating, dipping, direct roll coat, and reverse roll coat.

The dry film thickness of the base coat portion depends, in part, on the desired end use of the coated metal stock. Typically, however, the aggregate dry film thickness of the base coat portion ranges from about 0.1 micron to about 100 microns. More typically, the aggregate dry film thickness of the base coat portion ranges from about 1 micron to about 75 microns; and even more typically, from about 5 microns to about 50 microns. The base coat portion is typically at least partially cured prior to the subsequent application of the coating system's topcoat portion thereover. If the base coat portion is made up of multiple coating layers, this can be achieved by: (a) completely curing the individual coating layers prior to the application of any subsequent coating layer, and then at least partially curing the aggregate; (b) partially curing the individual coating layers prior to the application of any subsequent coating layer, and then at least partially curing the aggregate; or (c) applying all coating layers wet-on-wet, and then at least partially curing the aggregate. In most instances, the base coat portion is essentially completely cured prior to the application of the topcoat portion.

Any suitable means can be employed to at least partially cure the base coat portion of the present invention. The preferred means will depend, in part, upon the desired level of cure and the specific coating layer(s) making up the base coat portion of the composite coating composition. The base coat portion is preferably cured by driving off excess water or solvent to form a film, or by crosslinking the chemical constituents of the resinous binder composition. Typically, the base coat portion is cured by drying, preferably through subjecting the base coat portion to elevated temperatures. Under such circumstances, the curing temperature is typically at least about 50°C. However, it has been observed that higher curing temperatures improve certain properties of the coating system. Accordingly, in instances where such improved properties are desired, the base coat portion is typically cured by subjecting it to a curing temperature of at least about 75°C; more typically, at least about 100°C; and even more typically at least about 125°C. These temperatures are peak metal temperatures. As indicated, the multilayer composite coating composition of the present invention also includes a topcoat portion which is formed over the base coat portion. The topcoat portion includes a composition which is curable through radiation to form a second film which adheres to the first film formed as the base coat portion. With regard to the topcoat portion, it can be comprised of any suitable coating(s) which not only meets the aforementioned minimum flexibility and adhesion requirements, but also is radiation curable. The term "radiation curable^'" as used herein refers to a class of coatings which can be cured by being subjected to ionizing radiation (e.g., electron beams) or actinic light (e.g., UV light). Actinic light curing is typically better suited for non-pigmented or slightly pigmented embodiments of coatings making up the topcoat portion of the present invention. However, for higher build pigmented coatings, ionizing radiation curing is preferred.

The radiation curable compositions which meet the aforementioned minimum flexibility and adhesion requirements are not limited to any particular class. After reading this specification, skilled artisans will easily be able to identify particular radiation curable compositions which can be used as the topcoat portion of the present invention.

Preferably, the radiation curable composition is a film forming composition of oligomers or polymers containing functional groups selected from acrylate groups, styrene groups, vinyl groups, allyl groups, and mixtures and combinations thereof. In certain specific embodiments of the present invention, radiation curable compositions which meet the aforementioned minimum flexibility and adhesion requirements are acrylate-based formulations. For example, the radiation curable composition may be an acrylate group-containing oligomer or polymer selected from acrylates, urethane acrylates, epoxy acrylates, polyester acrylates, amino acrylates, and mixtures and combinations thereof. Radiation curable acrylate formulations which can be employed when practicing this invention typically comprise an oligomeric component and a diluent component.

The oligomeric component of such acrylate-based formulations is believed to contribute to the adhesion, toughness and/or flexibility of the resulting film. Examples of oligomers which can be employed include: unsaturated polyesters, epoxy acrylates, urethane acrylates, polyester acrylates, acrylic acrylates/saturated resins, and/or any combination thereof.

The diluent component of such acrylate-based formulations can include a non- reactive sub-component and/or a reactive sub-component. Non-reactive sub- components generally fall into one of two categories ~ volatile organic solvents or plasticizers.

With regard to volatile organic solvents which can be used as at least part of the diluent component of such acrylate-based formulations, although radiation cured coatings typically have a theoretical VOC rating of about 0, small amounts can be incorporated into an oligomeric/diluent mixture to bring the viscosity within the desired range. If employed, the volatile organic solvent concentration is typically less that about 20 weight percent; more typically, less than about 10 weight percent; and even more typically, less than about 5 weight percent. If amounts of greater than 20 weight percent are employed, in addition to the coating being subjected to a radiation curing process, it is also typically subjected to a thermal curing process, the latter of which is designed to drive off the higher levels of volatile organic solvents.

If employed, examples of volatile organic solvents which can be used include: isopropanol, ethanol, glycol ethers, esters of glycol ethers, methyl ethyl ketone, methyl amyl ketone, acetone, tertiary butyl acetate, and/or any combination thereof.

With regard to plasticizers which can be used as at least part of the diluent component of such acrylate-based formulations, they are typically employed in instances where there is a desire for the resulting coating system to have increased flexibility. It has been observed that, in some instances, the use of plasticizers can also reduce the viscosity of such acrylate formulations.

If employed, examples of plasticizers which can be used include: dioctyl phthalate, dipropylene glycol dibenzoate, epoxidized oils, alkyl benzyl phthalate, and/or any combination thereof.

As stated herein, the diluent component of such acrylate-based formulations can also include a reactive sub-component. Specifically, reactive diluents, such as monofunctional or multifunctional monomers, can be added to such acrylate-based formulations as a means of controlling not only the viscosities of the system, but also the degree of crosslinking of the resulting cured films. The terms "monofunctionaF and "multifunctionaF as they relate to monomers which can be employed in such formulations refer to the number of double bonds per molecule.

Examples of reactive diluents which can be employed include: tripropyleneglycol diacrylate, trimethylolpropane triacrylate, hexanediol diacrylate, isobornyl acrylate, isodecyl acrylate, 2-ethyl hexyl acrylate, n vinyl pyrolidone, n vinyl formamide, styrene, and vinyl ether, in addition to their alkoxylated and amine reacted versions.

The acrylate-based formulations which can be employed can further, optionally, include an adhesion promoter component. If employed, examples of adhesion promoters which can be used include methacrylate-based adhesion promoters, epoxy-based adhesion promoters, and/or phosphatized epoxy-based adhesion promoters.

In certain preferred embodiments of the present invention, examples of radiation curable acrylate based formulations which can be employed as at least part of the topcoat portion of the coating system disclosed herein include: urethane acrylates, polyester acrylates, epoxy acrylates, amino acrylates, unsaturated polyesters; and/or any combinations thereof.

In one specific embodiment of the present invention, a coating which meets the aforementioned minimum flexibility and adhesion requirements for the topcoat portion of the present invention is an electron beam curable coating composition comprising a urethane acrylate. Examples of such compositions include DURETHANE^® products and RAYCRON^® products, available from PPG Industries, Inc.

When practicing this preferred embodiment, the urethane acrylate content is at least 20 weight percent. In instances where high levels of flexibility are required, the urethane acrylate content is typically at least about 30 weight percent; more typically, at least about 40 weight percent; and even more typically, at least about 50 weight percent. These weight percentages are based on the total resin solids weight of the electron beam curable coating composition. It should be noted that, as the urethane acrylate content increases, the flexibility of the resulting topcoat also increases.

It has been observed that, as the molecular weight of the urethane acrylate increases, so does the resulting film's flexibility. Moreover, it has also been observed that, as the linearity of the urethane acrylate increases, so does the resulting film's toughness.

The preferred urethane acrylate and its concentration depends, in part, on many parameters, such as the desired flexibility and toughness. Depending upon the specific end use, after reading this specification, those skilled in the art will be able to determine, without undue hardship, the preferred concentration, molecular weight and linearity of a single urethane acrylate to employ, or the preferred blend of urethane acrylates to employ.

The coating layer(s) making up the topcoat portion of the present invention can be applied by any suitable means. For example, the coating layer(s) can be applied by brushing, spraying, flow coating, dipping, direct roll coat, and reverse roll coat.

The dry film thickness of the topcoat portion depends, in part, on the desired end use. Typically, however, the aggregate dry film thickness of the topcoat portion ranges from about 0.1 micron to about 100 microns. More typically, the aggregate dry film thickness of the topcoat portion ranges from about 1 micron to about 75 microns; and even more typically, from about 5 microns to about 50 microns.

In one particular embodiment of this invention, the radiation curable topcoat portion is at least partially cured by exposure to ionizing radiation. Under such circumstances, the coating is typically exposed to ionizing radiation in an amount in the range of from about 0.01 megarad to about 30 megarads, although doses greater than 20 megarads may be used satisfactorily. The dose, however, should not be so great that the chemical or physical properties of the coating are seriously impaired. Typically, the dose is in the range of from about 0.1 megarad to about 20 megarads. The preferred dose is in the range of from about 1 megarad to about 10 megarads. In another particular embodiment of this invention, the radiation curable topcoat portion is at least partially cured by exposure to actinic light. Under such circumstances, a photoinitiator, photosensitizer or mixtures of photoinitiator and photosensitizer are typically present in the coating formulation to absorb photons and produce the free radicals necessary for crosslinking.

In still other particular embodiments of this invention, the radiation curable topcoat portion is cured by exposure to: ionizing radiation and actinic light; elevated temperatures and ionizing radiation; elevated temperatures and actinic light, or elevated temperatures, ionizing radiation and actinic light. The multilayer composite coating of the present invention can be applied over any suitable substrate. However, due to its inherent properties, this composite coating is especially useful for application over coil metal stock such as steel or aluminum.

Thus, in addition to encompassing the aforementioned composite coating and the processes for applying and curing the same over coil metal stock, the present invention also encompasses the resultant coated metal substrate. In this embodiment of the invention, a metal substrate is coated with a multilayered film. A first coating layer of this multilayered film is in direct contact with the metal substrate. This first coating layer results from curing the base coat portion of the composite coating disclosed herein. A second coating layer of this multilayered film is in direct contact with the first coating layer. This second coating layer results from curing the topcoat portion of the composite coating disclosed herein.

The multilayered film, as an aggregate, adheres exceptionally well to the metal substrate. Moreover, this multilayered film, as an aggregate, is extremely flexible.

In addition to the adhesion and flexibility characteristics of the multilayer composite coating, the coating also prevents the metal substrate from visibly showing through the coating, thus imparting excellent hiding characteristics to the coating. More particularly, radiation cured coating compositions including pigmentation typically may not provide sufficient hiding power to prevent the metal substrate from showing through the coating. If the amount of pigment is increased in order to overcome this problem, the coating composition does not cure sufficiently, resulting in a poor coating film. It has been found through the present invention that the base coat composition can further aid in hiding power of the overall coating composition, thus reducing the need to incorporate additional pigmentation into the radiation curable top coat portion, and eliminating the poor curing resulting therefrom. In preferred embodiments, the base coat portion includes a composition which includes pigmentation or filler components capable of assisting in the hiding power of the coating composition. For example, compositions as described above with respect to the base coat portion of the composite coating composition and which include titanium dioxide are particularly useful in connection with the present invention.

Application of the multilayer composite coating composition to a metal substrate will now be described in further detail, in terms of coating both sides of a coil of sheet metal stock material in a continuous coil coating process. In such continuous coil coating processes, sheet metal is typically wound from one coil, known as a pay off roll, and passed through a welder joiner, which joins the end of one exhausted coil with the beginning of a new coil. The sheet metal is then forwarded through a cleaning apparatus, such as an ultrasonic cleaning apparatus, for cleaning one, and preferably both surfaces of the sheet metal to remove contaminants therefrom. Such a cleaning step may typically involve cleaning with a detergent, preferably a water-based detergent as discussed above, rinsing the metal surfaces, and drying the surfaces.

The thus cleaned sheet metal can then be treated with an inorganic composition as a pretreatment prior to application of the composite coating, as discussed above. As noted, such a pretreatment step may be eliminated when specific base coating compositions are used in accordance with the present invention. During the pretreatment step, the inorganic pretreatment composition is applied to the cleaned surfaces of the sheet metal, in accordance with procedures well known in the art.

After the metal substrate has been cleaned and, if necessary, pretreated, the metal substrate is then ready for coating with the multilayer composite coating composition. A first composition including a resinous binder as detailed above is applied to one or both surfaces of the metal substrate, for example by roll coating opposite sides of the metal sheet as it is passed along a series of rollers. After the first composition is applied, it is cured, for example by drying the composition in an oven including infrared heating elements. Such curing forms a first film adhered directly to the surfaces of the sheet metal.

After both surfaces of the metal substrate have been coated with the first coating composition to form the first film, a radiation curable second composition as described above is applied to one or both surfaces of the metal substrate, for example in a similar roll coating procedure as described above, directly over the first film as formed thereon. The sheet metal with the second composition applied thereto is then passed through a source of radiation, such as an electron beam for producing ionizing radiation, as is known in the art. Such radiation treatment cures the second composition, resulting in a second film adhered to the first film.

EXAMPLES The examples which follow are intended to assist in a further understanding of this invention. Particular materials, species and conditions employed are intended to be illustrative of certain embodiments of the invention and do not, in any way, limit the reasonable scope thereof.

EXAMPLE 1 In this example, a liquid coating system was prepared for application over coil metal stock. This liquid coating system was made in accordance with the present invention.

An aqueous primer/pretreatment protective coating made in accordance with the examples in US Patent No. 4,088,621, was applied as the base coat portion of the liquid coating system over a steel panel. After being applied, this base coat portion was thermally cured.

An electron beam curable coating was then applied as the topcoat portion of the liquid coating system over the cured base coat portion. This electron beam curable coating was a urethane acrylate-based coating wherein the urethane acrylate content was over 50 weight percent, based on the total weight of the electron beam curable coating's resin solids.

The multilayered film was then tested for adhesion using ASTM D3359 Tape Adhesion procedure and for flexibility using ASTM D D3794 T-Bend procedure. The adhesion property of the resulting multilayered film was "no pick off; and the flexibility property was below 5T.

In view of the above, the liquid coating system set out in this example can be used to coat coil metal stock which will be subjected to downstream cutting, bending and forming processes. In addition to the above, the VOC rating of the liquid coating system set out in this example is not greater than 20 weight percent.

EXAMPLES 2-25

Unless otherwise indicated, all of the examples discussed herein involve coating compositions applied to unpolished ACT cold roll steel panels having dimensions of 4 inches wide, 12 inches long and 0.32 inches thick. All steel panels were cleaned prior to application of the coating compositions with an aqueous cleaning solution containing approximately 24% potassium hydroxide, commercially available as BASE Phase #6LF, from PPG Pretreatment and Specialty Products of Troy MI. The cleaning solution was diluted to a ratio of 500 ml cleaning solution to 16 liters of tap water. Cleaning was conducted through pressure spraying both sides of the panel at a pressure of about 20 pounds per square inch at 140-150° C for a period of 10-12 seconds. The panels were then rinsed with deionized water, and were air dried.

When pretreatment was conducted, the above-described cleaning process was eliminated. In such instances, the steel panels were received as pretreated with an aqueous-based iron-phosphate pretreatment solution of BONDERITE^® 1000, a product of Henkel Corporation.

Application of both the base coat film-forming coating composition and the top coat film-forming coating composition was accomplished by draw down with wire wound draw down bars available from R.D. Specialties of Webster, NY, with specific bar sizes set forth in the individual examples.

Curing of the base coat film forming composition was accomplished in a Transco gas fired conveyor oven, at conditions set forth in the individual examples. Curing of the top coat film forming composition was accomplished by subjected it to a scanning electron beam, available from High Voltage Engineering, Inc. of Burlington, MA. The electron beam had a voltage of 210 kilovolts and an amperage of 5.0 ma. The electron beam curing was conducted in a nitrogen atmosphere with 47-48 ppm oxygen, at conditions set forth in the individual examples.

EXAMPLE 2

This Example represents a comparative example, involving a radiation curable coating composition applied to a metal substrate with no pretreatment of the metal substrate and no primer composition as a base coat portion. An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above.

A radiation curable coating composition comprised of a pigmented urethane acrylate polymer available as RAYCRON^® R1211 W66 from PPG Industries, Inc. was applied to the cleaned steel panel. The composition was applied by draw down with a 018 wire wound draw down bar. After application, the coating composition was cured by scanning electron beam, at a dosage of 8.3 megarads. The resulting film coating had a dry film thickness of 0.8-1.5 mils (20-37.5 microns), to produce a coated panel represented as Panel 2.

EXAMPLE 3 This example represents a comparative example, demonstrating a radiation curable coating composition as applied to a metal substrate with pretreatment, and without any primer composition as a base coat portion. In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided.

A radiation cured coating composition was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 2, to produce a coated panel represented as Panel 3.

EXAMPLE 4

This example involves a radiation curable coating composition applied to a metal substrate without pretreatment, and with a solvent-based epoxy primer composition as a base coat portion. An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above.

A base coat was prepared from a phosphatized thermosetting epoxy resin composition dissolved in an aromatic solvent and including pigmentation, available as APPY 1989 Epoxy Primer from PPG Industries, Inc., and commonly used as an appliance coating in conventional coil metal stock coating applications. The solvent- based epoxy coating composition was applied by draw down with a 014 wire wound draw down bar. The solvent-based coating as applied was thermally cured as discussed above, at a peak metal temperature of 480° F (249°C) with a dwell time within the oven of 22 seconds, resulting in a base coat film having a film thickness of 0.2-0.25 mils (5-6.25 microns).

The radiation curable coating composition of Example 2 was applied over the base coat film in a similar manner as set forth in Example 2. The resulting film coating had a dry film thickness of 0.8-1.5 mils (20-37.5 microns), to produce a coated panel represented as Panel 4. EXAMPLE 5

This example involves a radiation curable coating composition applied to a metal substrate with pretreatment of the metal substrate, and with the solvent-based epoxy primer composition of Example 4 as a base coat portion. An unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided.

A multilayer composite coating composition including a base coat portion and a topcoat portion was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 4, to produce a coated panel represented as Panel 5.

EXAMPLE 6

This example involves a radiation curable coating composition applied to a metal substrate without any pretreatment of the metal substrate, and with a solvent- based acrylic primer composition typically used over oleoresinous and solvent- sensitive finishes as a base coat portion.

An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above.

A base coat was prepared from a thermoplastic butyl methacrylate copolymer composition dissolved in aromatic solvent, available as Paraloid^® F-10 Thermoplastic Solution Resin from Rohm and Haas Company. The composition was applied by draw down with a 007 wire wound draw down bar, and thermally cured as discussed above at a peak metal temperature of 350° F (176°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film having a film thickness of approximately 0.1 mils (2.5 microns).

The radiation curable coating composition of Example 2 was applied over the base coat film in a similar manner as set forth in Example 2. The resulting film coating had a dry film thickness of 0.8-1.5 mils (20-37.5 microns), to produce a coated panel represented as Panel 6. EXAMPLE 7

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a solvent-based thermosetting acrylic polymer as a base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 6, to produce a coated panel represented as Panel 7.

EXAMPLE 8 This example involves a radiation curable coating composition applied to a metal substrate without any pretreatment of the metal substrate, and with a solvent- based acrylic primer composition as a base coat portion.

An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above. A base coat was prepared from a thermoplastic methyl methacrylate/butyl acrylate copolymer composition dissolved in toluene, available as Paraloid^® B-48S Thermoplastic Solution Resin from Rohm and Haas Company. The composition was applied by draw down with a 007 wire wound draw down bar, and thermally cured as described above at a peak metal temperature of 350° F (176°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film having a film thickness of approximately 0.11 mils (2.75 microns).

The radiation curable coating composition of Example 2 was applied over the base coat film in a similar manner as set forth in Example 2. The resulting film coating had a dry film thickness of 0.8-1.5 mils (20-37.5 microns), to produce a coated panel represented as Panel 8.

EXAMPLE 9

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a solvent-based thermoplastic acrylic polymer base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 8, to produce a coated panel represented as Panel 9. EXAMPLE 10

This example involves a radiation curable coating composition applied to a metal substrate without any pretreatment of the metal substrate, and with a water- based acrylic primer composition as a base coat portion. An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above.

A base coat was prepared from a thermosetting acrylic emulsion polymer having a glass transition temperature of approximately 38° C, available as Rhoplex^® E-1018 Acrylic Emulsion Polymer from Rohm and Haas Company. The composition was applied by draw down with a 004 wire wound draw down bar, and thermally cured at a peak metal temperature of 350° F (176°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film having a film thickness of approximately 0.12-0.17 mils (3-4.25 microns).

The radiation curable coating composition of Example 2 was applied over the base coat film thus formed in a similar manner as set forth in Example 2, to produce a coated panel represented as Panel 10.

EXAMPLE 11

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a water-based thermosetting acrylic polymer base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 10, to produce a coated panel represented as Panel 11.

EXAMPLE 12 This example also involves a water-based acrylic primer composition as a base coat portion in conjunction with a radiation curable coating composition.

An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above. A base coat was prepared from an aqueous-based all-acrylic thermoplastic emulsion polymer having a glass transition temperature of approximately 17° C, available as Rhoplex^® MV-117 Acrylic Emulsion Polymer from Rohm and Haas Company. The composition was applied by draw down with a 004 wire wound draw down bar, and thermally cured at a peak metal temperature of 350° F (176°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film having a film thickness of approximately 0.12-0.17 mils (3-4.25 microns).

The radiation curable coating composition of Example 2 was applied over the base coat film in a similar manner as set forth in Example 2, to produce a coated panel represented as Panel 12.

EXAMPLE 13

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a water-based thermoplastic acrylic polymer as a base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 12, to produce a coated panel represented as Panel 13.

EXAMPLE 14

This example involves a radiation curable coating composition applied to a metal substrate without any pretreatment of the metal substrate, and with a base coat portion including a chrome-containing water-based primer composition incorporating two separate acrylic polymer emulsions and including pigmentation.

An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above. A base coat was prepared from an acrylic emulsion polymer incorporating a thermoplastic acrylic polymer and a thermosetting acrylic polymer having distinct glass transition temperatures, available as ORGANOKROME^® 2000 from the Coatings & Resins division of PPG Industries, Inc. The composition was applied by draw down with a 003 wire wound draw down bar, and thermally cured at a peak metal temperature of 350° F (176°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film having a film thickness of approximately 0.06-0.1 mils (1.5-2.5 microns). The radiation curable coating composition of Example 2 was applied over the base coat film in a similar manner as set forth in Example 2, to produce a coated panel represented as Panel 14.

EXAMPLE 15

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a chrome-containing water-based acrylic emulsion base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 14, to produce a coated panel represented as Panel 15. EXAMPLE 16

This example involves a radiation curable coating composition applied to a metal substrate without any pretreatment of the metal substrate, and with a base coat portion including a chrome-free water-based primer composition incorporating two separate acrylic polymer emulsions, and without any pigmentation. An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above.

A base coat was prepared from an acrylic emulsion polymer incorporating a thermoplastic acrylic polymer and a thermosetting acrylic polymer capable of curing with a curing agent. In particular, the composition included a mix of two resins, namely 24.66 grams of thermosetting resin EMULSION E-1018 and 80.61 grams of thermoplastic resin RHOPLEX MV-117, both available from Rohm and Haas Company, as well as 5.69 grams of a dispersing agent (ACRYSOL 1-62, available from Rohm and Haas Company), 7.5 grams of an aminoplast (DYNOMIN UM-15, available from CYTEC Industries, Inc.) and 1.02 grams of ammonia. These components were added together and shaken. The composition was applied by draw down with a 003 wire wound draw down bar, and thermally cured at a peak metal temperature of 350° F (176°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film having a film thickness of approximately 0.07-0.09 mils (1.75-2.25 microns).

The radiation curable coating composition of Example 2 was applied over the base coat film as formed herein in a similar manner as set forth in Example 2, to produce a coated panel represented as Panel 16. EXAMPLE 17

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a chrome-free water-based primer including two separate acrylics without pigmentation as a base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 16, to produce a coated panel represented as Panel 17.

EXAMPLE 18

This example involves a radiation curable coating composition applied to a metal substrate without any pretreatment of the metal substrate, and with a base coat portion including a chrome-free water-based primer composition incorporating two separate acrylic polymer emulsions.

An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above. A base coat was prepared from an acrylic emulsion polymer incorporating a thermoplastic acrylic polymer and a thermosetting acrylic polymer. In particular, 7.5 grams of a dispersing agent (ACRYSOL 1-62), five grams of deionized water, five grams of a flow control agent (propylene glycol), 1.25 grams of a coalescing agent (butyl carbitol), 0.5 grams of ammonium hydroxide, 3.75 grams of an aminoplast (DYNOMIN UM-15), 11.25 grams of an aqueous calcium fluoride slurry, a defoaming agent (DREWPLUS L-475), and 10.75 grams total of two silicon dioxide pigments (7.5 grams SHIELDEX AC-3 and 3.25 grams SYLOID C-809) were ground together into a paste. This paste was blended together with two resins (125.5 grams of thermoplastic resin RHOPLEX MV-1C and 32.5 grams of thermosetting resin EMULSION E-1018), 2.75 grams of a thickening agent (ENVIRON THICKENER), 18.25 grams of deionized water, and 2.5 grams of ammonium carbonate. A composition containing a mixture of 25 grams, 15 grams and 0.1 grams, respectively, of potassium hexafluorotitanate, water, and ammonium hydroxide was prepared (having a pH of about 11) and added to the composition described above. The mixture was added at a ratio of five parts of the total composition described above to one part of the potassium hexafluorotitanate mixture. The final composition had a pH of about 6.7. The composition was applied by draw down with a 003 wire wound draw down bar, and thermally cured at a peak metal temperature of 350°F ( 177°C) with a dwell time within the oven of 30 seconds, resulting in a base coat film on the steel panel.

The radiation curable coating composition of Example 2 was applied over the base coat film as formed herein in a similar manner as set forth in Example 2 and cured at a dosage of 8.65 megarads, to produce a coated panel represented as Panel 18.

EXAMPLE 19

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a chrome-free water-based primer including two separate acrylics as a base coat portion and a radiation curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 18, to produce a coated panel represented as Panel 19. EXAMPLE 20

This example involves a coating composition curable by actinic light applied to a metal substrate without any pretreatment of the metal substrate, and with a base coat portion including a chrome-containing water-based primer composition incorporating two separate acrylic polymer emulsions, and pigmentation.

The base coat primer composition of Example 14 was prepared and applied according to the composition and procedure as set forth in Example 14. Thereover, a coating composition curable by actinic light was applied over the base coat film as formed. In particular, a clear urethane acrylate composition including a photoinitiator was applied over the base coat film by draw down with a 032 wire wound draw down bar. The coating composition was then cured by UV curing in an air atmosphere with four, 200 W/inch medium pressure mercury lamps, at a dosage of 614 mJ/cm², resulting in a film thickness of approximately 1.7 mils (42.5 microns), represented as Panel 20.

EXAMPLE 21

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a chrome-containing water-based primer including two separate acrylics with pigmentation as a base coat portion and a UV curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 20, to produce a coated panel represented as Panel 21. EXAMPLE 22

This example involves a coating composition curable by actinic light applied to a metal substrate without any pretreatment of the metal substrate, and with a base coat portion including a chrome-free water-based primer composition incorporating two separate acrylic polymer emulsions, and without any pigmentation.

An unpolished ACT cold roll steel panel was cleaned, rinsed and dried with an aqueous cleaning solution as described above. The base coat primer composition of Example 16 was prepared and applied according to the composition and procedure as set forth in Example 16.

Thereover, a UV curable coating composition as described in Example 20 was applied cured over the base coat film as formed according to the composition and procedures set forth in Example 20, to produce a coated panel represented by Panel 22.

EXAMPLE 23

In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a chrome-free water-based primer including two separate acrylics without pigmentation as a base coat portion and a UV curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 22, to produce a coated panel represented as Panel 23.

EXAMPLE 24 This example involves a coating composition curable by actinic light applied to a metal substrate without any pretreatment of the metal substrate, and with a base coat portion including a chrome-free water-based primer composition incorporating two separate acrylic polymer emulsions.

The base coat primer composition of Example 18 was prepared and applied according to the composition and procedure as set forth in Example 18. Thereover, a UV curable coating composition as set forth in Example 20 was applied and cured over the base coat film as formed, to produce a coated panel represented as Panel 24.

EXAMPLE 25 In this example, an unpolished ACT cold roll steel panel pretreated with an iron phosphate pretreatment solution was provided. A multilayer composite coating composition, including a chrome-free water-based primer including two separate acrylics as a base coat portion and a UV curable urethane acrylate topcoat portion, was formed on the pretreated steel panel in accordance with the compositions and procedures as set forth in Example 24, to produce a coated panel represented as Panel 25.

Each of the steel panels as prepared in Examples 2-25 were subjected to various testing procedures for adhesion and flexibility, as follows.

Crosshatch adhesion was measured using a variation of ASTM D3359. In particular, a 10 by 10 Crosshatch, including 11 substantially perpendicular cuts, was cut into each panel as coated with the respective coating composition, using a razor blade and a "cross-cut guide for adhesion testing", available from KTA-TATOR Inc. of Pittsburgh, PA. The distance between the cuts was approximately 1/16 inch (0.16 cm), and the cuts were made substantially parallel and perpendicular to the long axis of the panels. After crosshatching, Scotch brand 610 Transparent Cellophane Tape was applied to the Crosshatch with the long axis of the tape parallel to the long axis of the panel and one of the axes of the Crosshatch. The tape was rubbed onto the panel with the cap end of a fine point marker. The tape was then immediately pulled off at an approximately 45° to 90° upward angle. The number of intact squares are set forth in Table I. The approximate total adhesion in the Crosshatch is also set forth in Table I, based on the number of squares removed and the amount of the squares remaining on the panel.

Reverse impact testing was also conducted. Each panel was placed face down in a Gardner Impact Tester with a 4 pound weight. The weight was raised and then dropped from two separate heights to give both a 96 in-lb impact and a 48 in-lb impact. The bumps were then examined visually for cracking, and were tested for tapeoff using Scotch brand 610 Transparent Cellophane Tape, which was rubbed onto the bump and immediately pulled off at an upward angle of 45° to 90°. The results are set forth in Table I.

T-bend testing was further conducted on each of the panels, according to a variation of ASTM D4145-83. In particular, a 1 inch (2.54 cm) by approximately 10 inch (25.4 cm) long strip was cut from each coated panel. Bends of approximately 3/8 to Vi inch (0.95-1.27 cm) were made across the long axis of the strip using a Diacro Finger Brake No. 12, with the paint on the outside of the bends. A bend was made in each panel at 180° loosely, then each panel was placed in a vise and tightened until there was no space between the two layers of metal. The bends were immediately examined for cracking using an 8x magnifier, with the crack test results set forth in Table I. Then each bend was tested for tape with Scotch brand 610 Transparent Cellophane Tape, which was rubbed onto the bump and immediately pulled off at an upward angle of 45° to 90°. If no tapeoff and no cracking were found, the test was discontinued. Any panel in which tapeoff and/or cracking were found was provided with an additional bend as set forth above, which bending and testing process was continued until no tapeoff and no cracking were found. The T-bend numbers as recorded are discussed in ASTM D4145-83, with a lower number representing good flexibility and a high number representing poor flexibility.

The results of all of these testing procedures are set forth in Table I.

TABLE I

"100-" and "100—" ratings indicate that the squares well all intact, but that small corners were removed, including a few of the corners or most of the corners, respectively.

Ratings: Slight = only a few specks off; Moderate = a lot removed with tape but good areas still present; Severe = Virtually all of the center circle of impact taped off; Very severe = all of impact areas and parts of other areas taped off.

Ratings: Fine = a fine network of cracks; Slight = a couple of cracks; Moderate = cracks with some pop out; Severe = cracks and some bits missing; Star Crack = cracks radiating out from impact center rather than a network.

Comparative Example

Retested at higher T-bend and failed

As can be seen from the results shown in Table I, Panel No. 2 which included a radiation curable topcoat without any pretreatment provided acceptable adhesion to the metal substrate as demonstrated through Crosshatch adhesion, but provided very poor reverse impact strength and T-bend flexibility results. Panel 3, on the other hand, which included an inorganic pretreatment prior to application of the radiation curable composition, provided just as good or better adhesion, with improved reverse impact strength and T-bend flexibility.

As shown in Examples 4 and 5, the use of an inorganic pretreatment composition in conjunction with a conventional solvent-based thermosetting epoxy primer composition provides slightly improved flexibility as compared with no pretreatment, but still provides poor reverse impact results. Further, a comparison of Examples 2-3 with Examples 4-5 demonstrates that the use of a conventional solvent- based primer composition with radiation cured topcoats improves flexibility of the composite coating as compared with coatings having no primer composition.

Examples 6-7 provide no adhesion and poor flexibility. Such results, however, are expected, as the solvent-based acrylic primer composition used in these examples is typically used for oleoresinous substrates, and is not well suited for metal substrates. Examples 8 and 9, on the other hand, including a different solvent-based acrylic primer composition, provide excellent adhesion results and acceptable T-bend ratings for flexibility. Moreover, in comparing Examples 8 and 9, it can be seen that the inorganic pretreatment composition improves the adhesion and flexibility as demonstrated through the improved results of the reverse impact tests.

A review of Examples 10 and 11 demonstrates that the inorganic pretreatment improves adhesion and flexibility when water-based thermosetting acrylic primer compositions are used as a base coat composition for radiation curable coating compositions. Little change was seen with the use of an inorganic pretreatment composition with water-based thermoplastic acrylic primer compositions, as shown in Examples 12 and 13. A comparison of Examples 4-9 with Examples 10-13 demonstrates that multilayer composite coating compositions including base coats formed from water-based primer compositions with radiation curable topcoats provide at least as good if not improved adhesion and flexibility as compared with solvent- based primer compositions. Thus, water-based compositions can be used as primer base coats with similar adhesion and flexibility of the composite coating and without the deleterious environmental effects of solvent-based coating systems.

Moreover, a comparison of Examples 14-17 with Examples 10-13 demonstrates that improved adhesion and flexibility are seen through the use of water- based primer compositions which include both a thermoplastic resin component and a thermosetting resin component. For example, excellent adhesion and good T-bend results are seen in all of Examples 14-17, with no tapeoff and no or only fine cracking seen in the reverse impact testing. In Examples 10-13, on the other hand, at least slight to severe tapeoff and at least fine cracking to star cracking are seen for reverse impact testing.

Further, a comparison of Example 14 and Example 15, unexpectedly demonstrates that no pretreatment is necessary when using a primer composition including both a thermoplastic resin component and a thermosetting resin component. For example, as noted above, a comparison of Example 2 and Example 3 demonstrates that improved reverse impact strength and T-bend flexibility are seen through the use of an inorganic pretreatment composition with radiation curable coating compositions. To the contrary, Example 14 demonstrates that excellent adhesion and T-bend flexibility with no tapeoff and only fine cracking in reverse impact testing are achieved through a primer composition including both a thermoplastic resin component and a thermosetting resin component which is applied to a cleaned untreated steel panel. When the steel panel is pretreated with an inorganic pretreatment composition, good results are still obtained, but the T-bend flexibility is reduced, and fine cracking appears through reverse impact testing.

Still further, a comparison of Examples 14-15 with Examples 16-19 demonstrates that excellent composite coatings having excellent adhesion and flexibility can be achieved using either chrome-containing or chrome-free base coat compositions.

Also, Examples 20-25 demonstrate that UV curable coatings can also be used on metal stock. A comparison of Examples 20 and 21, 22 and 23, and 24 and 25, respectively, demonstrates that the use of an inorganic pretreatment assists in adhesion of the composite coating. Further, a comparison of Examples 23 and 25, with Example 21, demonstrates that improved results are achieved for UN curable topcoats when a base coat primer of an acrylic emulsion without chrome is used as compared with one with a chrome-containing formulation, regardless of whether an inorganic pretreatment composition has been used.

It is evident from the foregoing that various modifications, which are apparent to those skilled in the art, can be made to the embodiments of this invention without departing from the spirit or scope thereof. Having thus described the invention, it is claimed as follows.

Claims

WHAT IS CLAIMED IS:

1. In a coating for metal substrates, said coating including a radiation curable composition, the improvement comprising a multilayer composite coating including a base coat portion comprising a resinous binder composition which is curable to form a first film which adheres to a surface of said metal substrate treated with an inorganic pretreatment composition, said radiation curable composition provided as a topcoat portion which is curable through radiation to form a second film which adheres to said first film.

2. A coating as in claim 1, wherein said resinous binder composition is selected from the group consisting of water-based compositions, solvent-based compositions and compositions in solid particulate form.

3. A coating as in claim 1, wherein said resinous binder composition comprises a film forming polymer selected from the group consisting of acrylics, polyurethanes, epoxies, polyesters, phenolics, polyamides, polyolefins, and mixtures thereof.

4. A coating as in claim 3, wherein said resinous binder composition is an acrylic polymer emulsion comprising a first acrylic polymer and a second acrylic polymer different from said first acrylic polymer.

5. A coating as in claim 1, wherein said resinous binder composition comprises a film forming polymer including a thermoplastic resin component and a thermosetting resin component.

6. A coating as in claim 1, wherein said radiation curable composition comprises a composition which is curable through ionizing radiation or actinic light.

7. A coating as in claim 1, wherein said radiation curable composition comprises a film forming composition selected from the group consisting of acrylate group- containing oligomers and polymers, styrene group-containing oligomers and polymers, vinyl group-containing oligomers and polymers, allyl group-containing oligomers and polymers, and mixtures and combinations thereof.

8. A coating as in claim 7, wherein said radiation curable composition comprises an acrylate group-containing oligomer or polymer selected from the group consisting of acrylates, urethane acrylates, epoxy acrylates, polyester acrylates, amino acrylates, and mixtures and combinations thereof.

9. A coating as in claim 8, wherein said radiation curable composition comprises a urethane acrylate composition.

10. A coating as in claim 1, wherein said inorganic pretreatment composition is selected from the group consisting of iron phosphate compositions, zinc phosphate compositions, manganese phosphate compositions, calcium phosphate compositions, cobalt phosphate compositions, metal oxides, and mixtures thereof.

11. In a metal sheet material coated with a coating including a radiation curable composition, the improvement comprising said metal sheet including a surface treated with an inorganic pretreatment composition, said metal sheet further including a base coat portion comprising a resinous binder composition which is curable to form a first film which adheres to said treated surface of said metal sheet, said radiation curable composition provided as a topcoat portion comprising a composition which is curable through radiation to form a second film which adheres to said first film.

12. A metal sheet material as in claim 11, wherein said resinous binder composition is selected from the group consisting of water-based compositions, solvent-based compositions and compositions in solid particulate form.

13. A metal sheet material as in claim 11 , wherein said resinous binder composition comprises a film forming polymer selected from the group consisting of acrylics, polyurethanes, epoxies, polyesters, phenolics, polyamides, polyolefins, and mixtures thereof.

14. A metal sheet material as in claim 13, wherein said resinous binder composition is an acrylic polymer emulsion comprising a first acrylic polymer and a second acrylic polymer different from said first acrylic polymer.

15. A metal sheet material as in claim 11 , wherein said resinous binder composition comprises a film forming polymer including a thermoplastic resin component and a thermosetting resin component.

16. A metal sheet material as in claim 11 , wherein said radiation curable composition comprises a composition which is curable through ionizing radiation or actinic light.

17. A metal sheet material as in claim 11 , wherein said radiation curable composition comprises a film forming composition selected from the group consisting of acrylate group-containing oligomers and polymers, styrene group-containing oligomers and polymers, vinyl group-containing oligomers and polymers, allyl group- containing oligomers and polymers, and mixtures and combinations thereof.

18. A metal sheet material as in claim 17, wherein said radiation curable composition comprises an acrylate group-containing oligomer or polymer selected from the group consisting of acrylates, urethane acrylates, epoxy acrylates, polyester acrylates, amino acrylates, and mixtures and combinations thereof.

19. A metal sheet material as in claim 17, wherein said radiation curable composition comprises a urethane acrylate composition.

20. A metal sheet material as in claim 11, wherein said inorganic pretreatment composition is selected from the group consisting of iron phosphate compositions, zinc phosphate compositions, manganese phosphate compositions, calcium phosphate compositions, cobalt phosphate compositions, metal oxides, and mixtures thereof.

21. In a process for coating sheet metal stock with a radiation curable composition, the improvement comprising: a) treating a surface of a sheet of metal with an inorganic composition; b) applying a first composition to said treated surface of said sheet of metal, said first composition comprising a resinous binder; and c) curing said first composition to form a first film adhered to said sheet of metal; said radiation curable composition being provided as a second composition over said first film and being exposed to a source of radiation to cure said second composition, thereby forming a second film adhered to said first film.

22. A process as in claim 21, further comprising a step of cleaning said surface of said sheet of metal prior to said treated step (a).

23. A process as in claim 22 wherein said cleaning step comprises ultrasonically cleaning said surface of said sheet of metal.

24. A process as in claim 21, wherein said source of radiation comprises an electron beam.

25. A process as in claim 21, wherein said resinous binder composition is selected from the group consisting of water-based compositions, solvent-based compositions and compositions in solid particulate form.

26. A process as in claim 21, wherein said resinous binder composition comprises a film forming polymer selected from the group consisting of acrylics, polyurethanes, epoxies, polyesters, phenolics, polyamides, polyolefins, and mixtures thereof.

27. A process as in claim 21 , wherein said resinous binder composition is an acrylic polymer emulsion comprising a first acrylic polymer and a second acrylic polymer different from said first acrylic polymer.

28. A process as in claim 21 , wherein said resinous binder composition comprises a film forming polymer including a thermoplastic resin component and a thermosetting resin component.

29. A process as in claim 21 , wherein said radiation curable composition comprises a composition which is curable through electron beam irradiation or actinic light.

30. A process as in claim 21, wherein said radiation curable composition comprises a film forming composition selected from the group consisting of acrylate group-containing oligomers and polymers, styrene group-containing oligomers and polymers, vinyl group-containing oligomers and polymers, allyl group-containing oligomers and polymers, and mixtures and combinations thereof.

31. A process as in claim 30, wherein said radiation curable composition comprises an acrylate group-containing oligomer or polymer selected from the group consisting of acrylates, urethane acrylates, epoxy acrylates, polyester acrylates, amino acrylates, and mixtures and combinations thereof.

32. A process as in claim 31 , wherein said radiation curable composition comprises a urethane acrylate composition.

33. A process as in claim 21, wherein said inorganic pretreatment composition is selected from the group consisting of iron phosphate compositions, zinc phosphate compositions, manganese phosphate compositions, calcium phosphate compositions, cobalt phosphate compositions, metal oxides, and mixtures thereof.

34. In a coating for coil metal stock, said coating including a radiation curable composition, the improvement comprising a multilayer composite coating including a base coat portion comprising a water-based composition including a resinous binder, said water-based composition being curable to form a first film which adheres to said metal substrate, said radiation curable composition provided as a topcoat portion which is curable through radiation to form a second film which adheres to said first film.

35. A coating as in claim 34, wherein said water-based composition is selected from the group consisting of acrylic polymers, urethane polymers, polyvinyl acetate, and polyurethane, polyester and polyether polymers which have been adapted to be water soluble.

36. A coating as in claim 34, wherein said water-based composition comprises an acrylic emulsion.

37. A coating as in claim 36, wherein said water-based composition is an acrylic emulsion comprising a thermoplastic resin component and a thermosetting resin component.

38. A coating as in claim 37, wherein said water-based composition is an acrylic emulsion comprising a first acrylic polymer and a second acrylic polymer different from said first acrylic polymer.

39. A coating as in claim 34, wherein said water-based composition includes an inorganic component.

40. A coating as in claim 39, wherein said water-based composition is a chromium-containing composition.

41. A coating as in claim 39, wherein said water-based composition is a chromium-free composition.

42. A coating as in claim 41, wherein said water-based composition is a titanium- containing composition.

43. A coating as in claim 34, wherein said radiation curable composition comprises a composition which is curable through ionizing radiation or actinic light.

44. A coating as in claim 34, wherein said radiation curable composition is selected from the group consisting of acrylate group containing oligomers and polymers, styrene group containing oligomers and polymers, vinyl group containing oligomers and polymers, allyl group containing oligomers and polymers, and mixtures and combinations thereof.

45. A coating as in claim 34, wherein said radiation curable composition comprises a urethane acrylate composition.

46. In a metal sheet material coated with a coating including a radiation curable composition, the improvement comprising a multilayer composite coating including a base coat portion comprising a water-based composition including a resinous binder, said water-based composition being curable to form a first film which adheres to metal substrates, said radiation curable composition provided as a topcoat portion which is curable through radiation to form a second film which adheres to said first film.

47. A metal sheet material as in claim 46, wherein said water-based composition is selected from the group consisting of acrylic polymers, urethane polymers, polyvinyl acetate, and polyurethane, polyester and polyether polymers which have been adapted to be water soluble.

48. A metal sheet material as in claim 46, wherein said water-based composition comprises an acrylic emulsion.

49. A metal sheet material as in claim 46, wherein said water-based composition is an acrylic emulsion comprising a thermoplastic resin component and a thermosetting resin component.

50. A metal sheet material as in claim 47, wherein said water-based composition is an acrylic emulsion comprising a first acrylic polymer and a second acrylic polymer different from said first acrylic polymer.

51. A metal sheet material as in claim 46, wherein said water-based composition includes an inorganic component.

52. A metal sheet material as in claim 51 , wherein said water-based composition is a chromium-containing composition.

53. A metal sheet material as in claim 51, wherein said water-based composition is a chromium-free composition.

54. A metal sheet material as in claim 53, wherein said water-based composition is a titanium-containing composition.

55. A metal sheet material as in claim 46, wherein said radiation curable composition comprises a composition which is curable through ionizing radiation or actinic light.

56. A metal sheet material as in claim 46, wherein said radiation curable composition is selected from the group consisting of acrylate group-containing oligomers and polymers, styrene group-containing oligomers and polymers, vinyl group-containing oligomers and polymers, allyl group-containing oligomers and polymers, and mixtures and combinations thereof.

57. A metal sheet material as in claim 46, wherein said radiation curable composition comprises a urethane acrylate composition.

58. In a process for coating sheet metal stock with a radiation curable composition, the improvement comprising: a) applying a first composition to a surface of a sheet of metal, said first composition comprising a water-based composition including a resinous binder; and b) curing said first composition to form a first film adhered to said sheet of metal; wherein said radiation curable composition is applied as a second composition to said first film and exposed to a source of radiation, thereby forming a second film adhered to said first film.

59. A process as in claim 58, further comprising a step of cleaning said surface of said sheet of metal prior to said applying step (a).

60. A process as in claim 59, wherein said cleaning step comprises ultrasonically cleaning said surface of said sheet of metal.

61. A process as in claim 58, further comprising a step of treating a surface of a sheet of metal with an inorganic composition prior to said applying step (a).

62. A process as in claim 58, wherein said curing of said first composition comprises drying said water-based composition.

63. A process as in claim 58, wherein said source of radiation comprises an electron beam.

64. A process as in claim 58, wherein said water-based composition is selected from the group consisting of acrylic polymers, urethane polymers, polyvinyl acetate, and polyurethane, polyester and polyether polymers which have been adapted to be water soluble.

65. A process as in claim 64, wherein said water-based composition comprises an acrylic emulsion.

66. A process as in claim 65, wherein said water-based composition comprises an acrylic emulsion comprising a first acrylic polymer and a second acrylic polymer different from said first acrylic polymer.

67. A process as in claim 58, wherein said water-based composition is a chromium-containing composition.

68. A process as in claim 58, wherein said water-based composition is a chromium-free composition.

69. A process as in claim 68, wherein said radiation curable composition comprises a composition which is curable through ionizing radiation.

70. A process as in claim 58, wherein said radiation curable composition is selected from the group consisting of acrylate group-containing oligomers and polymers, styrene group-containing oligomers and polymers, vinyl group-containing oligomers and polymers, allyl group-containing oligomers and polymers, and mixtures and combinations thereof.

71. A process as in claim 58, wherein said radiation curable composition comprises a urethane acrylate composition.

72. In a coating for coil metal stock, said coating including a radiation curable composition, the improvement comprising a multilayer composite coating including a base coat portion comprising a water-based acrylic emulsion composition including a thermoplastic acrylic polymer and a thermosetting acrylic polymer and including an inorganic component, said water-based composition being curable to form a first film which adheres to metal substrates, said radiation curable composition provided as a topcoat portion which is curable through ionizing radiation to form a second film which adheres to said first film.

73. A coating as in claim 72, wherein said inorganic component is selected from chromium, titanium, zirconium, and mixtures thereof.

74. A coating as in claim 73, herein said inorganic component is selected from, titanium, zirconium, and mixtures thereof, and said water-based composition is chrome-free.