Formulations for surface preparations and processes using same

Abstract

The present disclosure concerns liquid formulations for treating metallic surfaces prior to coating, more particularly formulations for preparing a metallic surface for ensuing coating processes, the formulations comprise at least one mild organic acid, or a salt, a complex or a derivative thereof, dissolved in at least one carrier liquid.

Description

[0001] Formulations for surface preparations and processes using same

[0002] TECHNOLOGICAL FIELD

[0003] The present disclosure concerns formulations for treating metallic surfaces prior to coating, more particularly formulations for preparing a metallic surface for ensuing coating processes.

[0004] BACKGROUND ART

[0005] References considered to be relevant as background to the presently disclosed subject matter are listed below:

[0006] - US patent publication no. 5,868,820

[0007] - PCT patent application publication no. WO 2010077901

[0008] Acknowledgement of the above references herein is not to be inferred as meaning that these are in any way relevant to the patentability of the presently disclosed subject matter.

[0009] BACKGROUND

[0010] Several techniques for coating metallic surfaces by durable coating layers are in commercial use today. For many applications, such as industrial components in machinery, vehicles, wires or construction parts, e-coating and powder coating techniques are used to coat metallic surfaces that are exposed to corrosive conditions during their use. Water- or solvent-based paint coatings are also commonly used for a wide variety of metallic objects.

[0011] In order to enable good adhesion of the coating to the metal’s surface, and for the coating to be durable and have continuous covering, treatment of the surface prior to the coating is often required. Such treatment may involve, but is not limited to, the removal of various contaminants from the surface (for example, by degreasing, washing, pickling, sand blasting, etc.), conditioning (such as depositing species intended to serve as crystallization seeds for the next treatment layer), and the formation of a bonding layer (such as phosphatizing, for example with zinc phosphate), which provides suitable surface structures to increase the adhesion to the coating material and permit mechanical capturing of the coating onto the surface. Other materials intended for adhesion of subsequent layers, including topcoats, can be applied onto the surface as well. To date, surface treatments for preparing a surface for coatings, especially powder coating and / or e-coats, involve complex multi-step processes, typically utilizing highly toxic and non- environmentally friendly materials, such as aggressive and highly toxic acids. Furthermore, some stages of the treatment require high-energy investments (for example heating of the surface and / or the liquids for treatment).

[0012] Therefore, there is a need to provide a more cost-effective and environmentally friendly process for preparing metallic surfaces for coatings.

[0013] GENERAL DESCRIPTION

[0014] The present disclosure provides formulations for preparing metallic surfaces for coating, particularly e-coating and / or powder coating, that are environmentally friendly, applicable on a variety of metallic surfaces and enable significant reduction in complexity and energy / cost investment of surface preparation processes prior to coating.

[0015] The formulations of this disclosure are designed to alter the surface chemistry of the metal, and / or increase surface roughness and / or surface area, while concomitantly removing (at least partially) various metal oxides and / or other contaminants residing on the metal surface that may hinder adhesion of the coating, at relatively short treatment times (e.g. within a few minutes). This renders the treated metal surface with a suitable surface for effective adhesion of the coating formulation that is subsequently applied in various techniques, such as spraying, brushing, dipping, powder coating, e-coating, etc. Compared to standard techniques for surface preparation used to date, the formulations of this disclosure permit significant simplification and reduction in the number of process steps and their energy investment, while substantially avoiding utilization of toxic and / or hazardous formulation components.

[0016] According to one of its aspects, this disclosure provides a liquid formulation for treating a metal surface prior to coating, the formulation comprising at least one mild organic acid, or a salt, a complex or a derivative thereof, dissolved in at least one carrier liquid. Within the context of the present disclosure, the term coating (or coating layer) means to denote one or more layers of materials or formulations that are applied onto the treated surface of the metal, i.e. after being treated with a formulation of this disclosure, to endow it with a desired property. Coating includes, inter alia, paint layer(s), binder layer(s) (e.g. applied before application of paint layers), adhesives, sealers, topcoats, etc. The coating layer can be applied on portions of the surface or onto the entire surface of the treated metal part.

[0017] In the formulations of this disclosure, at least one mild organic acid, with or without additional active components, is used for obtaining a plurality of effects once applied onto the surface of the metal. Once in contact with the surface of the metal, the organic acid reacts with the metal oxides (and at times with other, typically organic contaminants) residing on the metal surface, to obtain at least partial decomposition or detachment of such metal oxides, thereby at least partially cleaning the metal surface from pre-existing contaminants that are detrimental for the subsequent coating. Further, once the surface metal oxides (and other contaminants) are removed, the mild organic acid and / or its reaction products with the removed oxides (optionally with additional components in the formulation) mildly etch the surface of the metal, thereby potentially causing an increase in surface area of the metal and increase in its roughness. Such changes in the surface area and roughness render the surface with appropriate topology to allow for effective mechanical interlocking of a coating material or formulation to be subsequently applied onto the surface. Complexation or conversion products that remain bound to the surface may also contribute anchoring sites and / or contribute suitable topography to the later-stage coating material applied on the treated surface. Anchoring sites may be achieved by surface adsorption of the active component(s) of the formulation. Anchoring sites may also be achieved by the alteration of the treated surface’s chemistry, so that it now includes chemical groups which are suitable for chemical bonding (e.g. hydrogen bonding) with the materials of the later-applied topcoat.

[0018] Typically, the liquid formulation is suitable for treating surfaces of ferrous metals and alloys (including pure iron, crude iron, wrought iron, cast steel, carbon steel, ironbased alloy which is non-stainless steel or stainless steel), aluminum and aluminum alloys (e.g. 5083, 6061, 5XXX series, 6XXX series, etc.), or other metals or metal alloys. The metal surface can be galvanized or non-galvanized. The term mild organic acid refers to an organic molecule having typical pKa (in water or aqueous solvent) of above 0.5, and more commonly above 2.5. In the case of polyprotic acids, the above value refers to the first (lowest) pKa.

[0019] According to some embodiments, the mild organic acid is selected from carboxylic acids bearing one or more carboxylic groups (such as acetic lactic, citric, oxalic, folic and tartaric acids); enediols and their tautomers, optionally conjugated to a carbonyl group (for example, ascorbic acid); optionally conjugated carboxylic acids; acidic polymers (“polyacids”), such as organic polymers having pendant groups of sulfonic, boronic or phosphonic acid; organic compounds with sulfonic, boronic or phosphonic acid functional groups; acidic polysaccharides, such as alginate or hyaluronic acid conjugated to a carbonyl group, carboxymethyl cellulose, chitosan; phenolic acids, with or without electron withdrawing groups; thiols, with or without electron withdrawing groups; and mixtures thereof.

[0020] By some embodiments, the mild organic acid is an enediol conjugated to a carbonyl group.

[0021] By some preferred embodiments, the mild organic acid is ascorbic acid or a derivative thereof (such as methyl-13-(2-(3,4-dihydroxy-5-oxo-2,5-dihydrofuran-2-yl)- 2-hydroxyethoxy)propanoate).

[0022] According to other embodiments, the formulation comprises at least one organic antioxidant (i.e. the formulation can comprise both a mild organic acid and an organic antioxidant, provided that the mild organic acid is different from the organic antioxidant).

[0023] The term organic antioxidant means to denote an organic molecule or species that interferes with or slows redox reactions between at least two other materials (for example, between a reactive oxygen species and its substrate undergoing oxidation) and / or is a radical reaction inhibitor. In the formulations of this disclosure, the organic antioxidant is selected to have a significantly higher standard reduction potential than that of the mild organic acid, e.g. at least about 20 mV higher. According to some embodiments, the difference between the standard reduction potential of the organic antioxidant and that of the mild organic acid is at least about 50 mV, at least about 100 mV, at least about 150 mV, at least about 200 mV, at least about 250 mV, at least about 300 mV, or even higher.

[0024] By some embodiments, the at least one organic antioxidant is selected from polyphenols (including quercetins, catechins, flavonoids), tocopherols (including water soluble derivatives, such as 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox™)), carotenoids e.g. beta carotene, lutein, astaxanthin), terpenes, curcuminoids e.g. curcumin), saponins, steroids (such as estradiol and estriol), bio-molecules (such as bilirubin, uric acid, glutathione), chemical species with pi -conjugation along an aromatic and / or poly-ene molecular structure, and / or chemical species which enable high stabilization of radicals formed at sites prone to homolytic cleavage of chemical bonds.

[0025] When applied onto the surface of the metal, the mild organic acid assists in breaking metal oxides on the surface. The metal ions are then available for complexation, which can be performed by the antioxidant (in original or oxidized form), the neutral or anionic form of the acid (in formulations where the acid and antioxidant are distinct components), or with a complexating agent (if present in the formulation, as described further below). With the breaking of the previously existing metal oxides on the surface, the surface can be accessed by the organic antioxidant and / or the mild acid, which can now react with the metal surface. Such a reaction can include mildly etching the surface of the metal into the desired degree of roughness and / or altering the identity of the surface species. This alteration includes the formation of reaction products (e.g. new metal oxide species, species with hydroxyl groups, complexated organic species), to which the components of the topcoat can adhere better than they would have compared to the untreated surface.

[0026] The liquid formulation is acidic with a pH of below 7. According to some embodiments, the formulation has a pH of between about 0.5 and about 6 at room temperature (i.e. at about 25°C), typically between about 2 and 6.

[0027] By some embodiments, the liquid formulation comprises at least one auxiliary acid, such as carboxylic acids (for example, acetic acid, propionic acid), phenolic acids (such as polyphenolic acids, hydroxybenzoic acids), hydroxycinnamic acids (such as ferulic acid) and others, the auxiliary acid being different from said mild organic acid.

[0028] In some embodiments, the liquid formulation comprises at least about 0.1 wt% of said at least one mild organic acid.

[0029] In other embodiments, the liquid formulation comprises between about 0.3 wt% and 30 wt% of said at least one mild organic acid.

[0030] In some embodiments, the liquid formulation comprises at least about 0.1 wt% of said at least one organic antioxidant.

[0031] In other embodiments, the liquid formulation comprises between about 0.3 wt% and 30 wt% of said at least one organic antioxidant. The carrier liquid is typically a polar and / or protic solvent to permit dissolution of the at least one mild organic acid and / or organic antioxidant therein. By some embodiments, the at least one carrier liquid is selected from water, alcohols, amines, polymers having sufficient fluidity at ambient temperatures such as poly ethers (optionally with further functionalization), liquid ions, and mixtures thereof.

[0032] According to some embodiments, the at least one carrier liquid is an aqueous liquid. According to other embodiments, the at least one carrier liquid is water.

[0033] The liquid formulation can, by some embodiments, further comprise at least one auxiliary antioxidant. Without wishing to be bound by theory, the auxiliary antioxidant can function to modify the rate and / or yield of the organic antioxidant reaction, as well as adapt the formulation to various substrate types and / or to final surface reaction products. It can also function to prolong the shelf-life of the formulation during storage.

[0034] According to some embodiments, the at least one auxiliary antioxidant is selected from tocopherols (including water soluble derivatives such as 6-hydroxy-2, 5,7,8- tetramethylchroman-2-carboxylic acid), carotenoids (e.g. beta carotene, lutein, astaxanthin), terpenes, curcuminoids (e.g. curcumin), saponins and steroids (such as estradiol and estriol), other bio-molecules (such as bilirubin, uric acid, glutathione), chemical species with pi-conjugation along an aromatic and / or poly-ene molecular structure, and / or chemical species which enable high stabilization of radicals formed at sites prone to homolytic cleavage of chemical bonds, and combinations thereof, provided that the auxiliary antioxidant is different from the organic antioxidant and from the mild organic acid.

[0035] According to some embodiments, the formulation comprises at least about 0.01 wt% of said at least one auxiliary antioxidant. According to other embodiments, the liquid formulation comprises between about 0.1 wt% and about 30 wt% of said at least one auxiliary antioxidant.

[0036] By some embodiments, the weight ratio (w / w) of the mild organic acid to said auxiliary antioxidant ranges between about 1 : 100 and about 100: 1.

[0037] By some embodiments, the weight ratio (w / w) of the organic antioxidant to said auxiliary antioxidant ranges between about 1 : 100 and about 100: 1.

[0038] The liquid formulation can, by some embodiments, further comprise at least one complexating agent. The complexating agent reacts and / or binds with one or more of the metal ions or metal oxides to contribute to changes in surface topography and / or assist in the decomposition of metal-ion containing species on the untreated surface and / or to form anchoring sites on the surface. Anchoring sites may also be achieved by surface adsorption of the complexating agent. Anchoring sites are sites on the surface to which materials in the topcoat can bind, thus enabling the required adhesion between the topcoat and the metal surface. While the complexating agent may have some antioxidant activity, it is noted that within the scope of the present disclosure, the complexating agent has significantly lower antioxidant activity as compared to the mild organic acid and / or the organic antioxidant, while having increased complexating capabilities to ionic metal species or neutral metal surfaces.

[0039] According to some embodiments, the at least one complexating agent is selected from polyphenols (including quercetins, catechins, flavonoids, tannins), tocopherols (including water soluble derivatives such as 6-hydroxy-2,5,7,8-tetramethylchroman-2- carboxylic acid), carotenoids (e.g. beta carotene, lutein, astaxanthin), terpenes, curcuminoids (e.g. curcumin), saponins, steroids (such as estradiol and estriol), other biomolecules (such as bilirubin, uric acid, glutathione), other chemical species with pi- conjugation along an aromatic and / or poly-ene molecular structure, and / or chemical species which enable high stabilization of radicals formed at sites prone to homolytic cleavage of chemical bonds, polyethers (including crown ethers) and polyvinyl alcohols, polysaccharides, polyamines, polyureas, polyvinyl alcohols, acrylates, polyepoxides, polysulfones, polystyrenes, polyesters, polyamides, polyphenols, and / or small chelating molecules such as: aminopolycarboxylates (most notably EDTA), iminodisuccinic acid (IDS), S,S-ethylenediamine-N,N'-disuccinic acid (EDDS), L-Glutamic acid N,N-diacetic acids (GLDA), methylglycinediacetic acid (MGDA), aminopolycarboxylates, nitrilotriacetic acids (NTA), polyaspartic acids, combinations thereof or derivatives thereof, provided that the complexating agent is different from said mild organic acid and / or said organic antioxidant.

[0040] According to some embodiments, the formulation comprises at least about 0.01 wt% of said at least one complexating agent. According to other embodiments, the liquid formulation comprises between about 0.1 wt% and about 30 wt% of said at least one complexating agent.

[0041] Depending on the desired application method, the viscosity of the liquid formulation can be modified by adding one or more viscosity modifying agents. The viscosity modifying agent functions to increase or decrease the viscosity of the liquid formulation.

[0042] By some embodiments, the formulation comprises at least one gelling agent. The gelling agent is an agent that is capable of altering the viscosity of the liquid formulation to a desired viscosity. Typically, the gelling agent forms thin films when applied onto the metal surface, thereby increasing the residence time of the formulation onto the metal surface and / or assisting in obtaining the required surface modification. The gelling agents are capable of forming a 3 -dimensional network of macromolecules, for example a viscoelastic network of polymeric chains, capturing the mild organic acid and other components, if present, within the structure of the network. Such physical capturing prolongs the contact time of the mild organic acid with the metal surface and, as a consequence, increases the efficiency of the formulation. Further, the gelling agent can function to increase the stability of the formulation (e.g. prevent sedimentation of the antioxidants during storage), thereby increasing the shelf-life of the formulations. Further, the 3D network or film formed with the assistance of the gelling agent may serve as a substrate for the binding of the desired coating.

[0043] The gelling agent may be selected from water-soluble or colloidal water-soluble polymers (hydro-colloids), such as modified cellulose (e.g. hydroxyethyl cellulose, methyl cellulose, hydroxypropylmethyl cellulose) and other polysaccharides, polyvinyl alcohol, polyquaternium-10, guar gum, hydroxypropyl guar gum, xanthan gums, gellans, Aloe vera gel, amia, carrageenan, oat flour, starch and modified starch, gelatin, ghatty gum, gum Arabic, inulin, Konjac gum, locust bean gum, fenugreek, marshmallow root, pectin and modified pectins, solagum, tragacanth gum (TG), etc.

[0044] The gelling agent can be selected from one or more polymers, such as acrylic acid / ethyl acrylate copolymers, carboxyvinyl polymers (e.g. Carbopol resins), polyvinyls, polyalkenyl polyether cross-linked acrylic acid polymer, hydrophobically modified crosslinked acrylic acid polymers, and others.

[0045] According to some embodiments, the gelling agent may be selected from xanthan, gellan, sodium alginate, pectin, low or high methoxy pectins, chitosan, polyvinyl alcohols, and mixtures thereof.

[0046] According to some embodiments, the formulation comprises said at least one gelling agent in a concentration ranging between about 0.001 wt% and about 10 wt%. According to some embodiments, the formulation has a viscosity of between about 0.5 and 1500 mPa-sec.

[0047] According to some embodiments, the formulation further comprises at least one functional additive selected from surfactants, emulsifiers, dispersants, defoamers, surface binding agents, antimicrobial agents, biocides, binders, colorants, odorants, odormasking agents, UV-stabilizers, flame retardants, and others.

[0048] By another aspect, this disclosure provides a process for treating a metal surface prior to coating, the process comprising applying the liquid formulation disclosed herein onto said metal surface for a period of time sufficient to achieve the required surface properties.

[0049] According to some embodiments, the period of time is sufficient to at least partially remove metal oxides from the metal surface.

[0050] According to other embodiments, the period of time is sufficient to increase the roughness of said metal surface and / or to form the minimal amount of chemical species required for sufficient adhesion of the topcoat to the surface.

[0051] According to other embodiments, the period of time is sufficient to enable the chemical reaction between the components in the formulation with the metal surface such that the beneficial reaction products (such as certain metal oxides or other chemical species, whether inorganic or organic, or complexes thereof) are formed to an extent sufficient for the adhesion of the desired topcoat.

[0052] By some embodiments, the period of time is between about 5 seconds and about 600 seconds. Hence, compared to known processes, processes of this disclosure permit obtaining one or more of increase the surface area of the metal surface, at least partially remove metal oxides from the metal surface, and increase the roughness of said metal surface, formation of beneficial surface species, in a relatively short contact time of the formulation with the metal surface.

[0053] According to some embodiments, the liquid formulation is maintained at a temperature of between about 1°C and about 80°C during said applying. By some embodiments, the liquid formulation is applied onto the metal surface by dipping, brushing, or spraying.

[0054] By some embodiments, the process is a continuous process. By some embodiments, the process is an industrial process. Such processes can be stand-alone processes, or can be incorporated as process steps in mass-production lines for production of treated metal parts.

[0055] By some embodiments, the process is customized to provide consecutive precoating treatment for multiple metal objects in a consecutive manner.

[0056] According to some embodiments, the formulation is removed from said metal surface after said period of time, typically by letting the formula drip off and / or having it blown off (such as with an air-blade) with or without assistive heating, and / or washing it off with water or an aqueous liquid. This washing can be performed by dipping into a liquid bath, one or multiple consecutive baths.

[0057] According to some embodiments, after the formula has been applied to the metal, the treated metal is heated to the temperatures suitable for e-coating and / or powder coating processes. Typical temperature ranges are between about 60°C and about 280°C.

[0058] As the metal parts or elements to be treated are often machined or molded prior to surface treating, it may be desirable to remove any lubricants or other processing residues, particularly oily or fatty residues, from the surface of the metal prior to surface treating. Thus, by some embodiments, the process further comprises degreasing the metal surface prior to application of the liquid formulation.

[0059] According to some embodiments the liquid formulation is suitable for use onto various metal components of a structural element with different finishings or surface traits, such as mill scale, galvanized steels, aluminum parts, weld regions, soldered regions, etc.

[0060] According to some embodiments, the liquid formulation is applied once onto the surface of the metal prior to coating with a coating formulation or coating material.

[0061] According to other embodiments, the formulation can be applied two or more times, with optional washing-off or removal of excess formulation or by-products in between applications. In each such cycle of application, the liquid formulation is permitted to come into contact with the metal surface or the previously applied layer for said period of time. When such cycled application is carried out, the liquid formulation applied in each cycle can be the same (i.e. having the same composition) or different (i.e. in each cycle a different liquid formulation of this disclosure being applied, for example differing in the mild organic acid and / or organic antioxidant, concentration, presence of the auxiliary antioxidant(s), efc.).

[0062] According to another aspect, there is provided a process for treating a metal surface prior to coating, the process comprising:

[0063] (a) degreasing the metal surface by applying one or more degreasing compositions;

[0064] (b) washing the metal surface to remove the one or more degreasing compositions;

[0065] (c) applying a liquid formulation as disclosed herein onto said metal surface for a period of time sufficient to create a large enough concentration of required surface species as products of the chemical reaction between the formula and the surface and / or modify the topology of the metal surface; and

[0066] (d) removing said liquid formulation after said period of time, thereby obtaining a metal surface ready for coating.

[0067] According to another aspect, there is provided a process for obtaining a coated metal surface, the process comprising:

[0068] (A) degreasing the metal surface by applying one or more degreasing compositions;

[0069] (B) washing the metal surface to remove the one or more degreasing compositions;

[0070] (C) applying a liquid formulation as disclosed herein onto said metal surface for a period of time sufficient to create a large enough concentration of required surface species as products of the chemical reaction between the formula and the surface and / or modify the topology of the metal surface;

[0071] (D) removing said liquid formulation after said period of time, thereby obtaining a metal surface ready for coating; and

[0072] (E) applying one or more coating layers onto the metal surface of step (D).

[0073] By another aspect, there is provided a process for obtaining a coated metal surface, the process comprising:

[0074] (A’) degreasing the metal surface by applying one or more degreasing compositions; (B’) washing the metal surface to remove the one or more degreasing compositions;

[0075] (C’) applying a liquid formulation as disclosed herein onto said metal surface for a period of time sufficient to modify the topology of the metal surface; and

[0076] (D’) applying one or more coating layers onto the metal surface of step (C’).

[0077] As used herein, the singular form "a" , "an" and "the" include plural references unless the context clearly dictates otherwise.

[0078] As used herein, the term about is meant to encompass deviation of ±10% from the specifically mentioned value of a parameter, such as concentration, temperature, pH, etc.

[0079] Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging / ranges between" a first indicate number and a second indicate number and "ranging / ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween. It should be noted that where various embodiments are described by using a given range, the range is given as such merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range.

[0080] Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as "comprises" and "comprising ' , will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any integer or step or group of integers and steps.

[0081] Generally it is noted that the term “ ...at least one... ” as applied to any component of the formulations, processes and / or methods of this disclosure should be read to encompass one, two, three, four, or even more different occurrences of said component in the formulations, processes and / or methods of this disclosure.

[0082] It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

[0083] The processes of the present disclosure involve numerous process steps which may or may not be associated with other common physical-chemical processes so as to achieve the desired result. Unless otherwise indicated, such process steps, if present, may be set in different sequences without affecting the workability of the process and its efficacy in achieving the desired end result.

[0084] BRIEF DESCRIPTION OF THE DRAWINGS

[0085] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0086] Figs. 1A-1B are heat maps for degree of rusting for e-coated tested samples of steel (Fig. 1A) and Aluminum (Fig. IB) treated with formulations of this disclosure, compared to reference e-coat samples. The scale ranges from 5 (rusted) to 10 (no rust observed). Results are shown for 60 CCT cycles.

[0087] Figs. 2A-2C are heat maps for degree of rusting for powder-coated tested samples of steel (Fig. 2A), galvanized steel (Fig. 2B) and Aluminum (Fig. 2C) treated with formulations of this disclosure. The scale ranges from 5 (rusted) to 10 (no rust observed). Results are shown for 60 CCT cycles.

[0088] Figs. 3A-3D are images of powder-coated steel samples, treated with formulations of this disclosure, after immersion tests: 96 hours at room temperature, front and back images (Figs. 3A-3B), and 120 hours at 49°C, front and back images (Figs. 3C-3D).

[0089] Figs. 4A-4D are SEM images of carbon steel: non-treated surface (Fig. 4A), treated with an organic antioxidant in an acidic solution (Fig. 4B) shows both newly formed submicronic structure and etching, treated with two organic antioxidants in an acidic solution (Fig. 4C), and treated with a solution containing antioxidants and a dispersant in an acidic solution (Fig. 4D). Figs. 5A-5B are electrochemical impedance test results for pickled steel surfaces treated with formulations of this disclosure: Fig. 5A shows the effect of drying time (0, 30, 90 and 120 seconds), Fig. 5B shows the effect of different test formulations.

[0090] Figs. 6A-6B are XPS results for oxygen atoms (Fig. 6A) and iron atoms (Fig. 6B) carried out on carbon steel samples, untreated and treated by a formulation according to this disclosure.

[0091] DETAILED DESCRIPTION OF EMBODIMENTS

[0092] Formulations of this disclosure were prepared by mixing an acidic organic antioxidant, in an aqueous carrier liquid, with one or more auxiliary antioxidants, and optionally with one or more additives.

[0093] Table 1: Exemplary formulations

[0094] In order to show the efficacy of surface treatment utilizing formulations of this disclosure, comparative studies were carried out vis-a-vis the standard zinc phosphate and / or sand blasting standard treatments.

[0095] Samples preparation:

[0096] 75mmx 150mm sheet samples of steel, galvanized steel, and aluminum alloy were used for testing. The samples were degreased by immersion in a degreasing solution, and then washed with water and allowed to dry, before either:

[0097] (1) dipping in a formulation according to this disclosure for 90 seconds,

[0098] (2) treated by standard zinc phosphate treatment, or

[0099] (3) sand blasting. Samples treated with formulations of this disclosure were either e-coated or powder-coated. Reference e-coat samples were zinc-phosphate treated, while reference powder coat steel and aluminum samples were sand blasted prior to coating E-coating and powder coated were carried out according to industry-standard coating proceedings.

[0100] Environmental tests

[0101] The coated samples were subjected to cyclic corrosion testing (CCT) in an Ascott CC1000IP test chamber. The CCT procedure was based on SAE J2334, method C, that simulates accelerated corrosion conditions. Each cycle included the following steps sequence:

[0102] - Humid stage: 50°C, 100% humidity, 6 hours

[0103] Salt fog application stage: 15 minutes

[0104] - Dry stage: 60°C, 50% RH, 17 hours and 45 minutes.

[0105] Samples were analyzed after 500, 1000,1500, 2000 hours. The samples were imaged prior to environmental testing, as well as in each testing time point. All imaging was carried out in a designated imaging booth, equipped with 20MP industrial computer vision camera (Triton by LUCID vision labs).

[0106] The following assessments (Table 2) were made for each coated sample:

[0107] Table 2: Sample assessment metrics

[0108] Results

[0109] E-coating samples

[0110] Figs. 1A-1B are maps of the tested steel and aluminum samples, respectively, treated with formulation of this disclosure compared to reference samples (zinc phosphate treatment), showing a rusting index. As can be seen no significant rusting was observed after 60 CCT cycles (SAE J 2334), indicating that the formulations of this disclosure provide at least as good as surface treatment to the standard treatment of zinc phosphate.

[0111] Crosscut test, blistering and rusting test results are shown in Table 3.

[0112] Table 3: Crosscut test blistering and rusting for e-coated samples, for 60 CCT cycles

[0113] As can be seen, the samples treated with formulations of this disclosure show the same results as those of reference samples surface-treated by the standard zinc phosphate treatment, showing that the formulations of this disclosure can substitute the industry standard zinc phosphate treatment to significantly simplify the surface treatment process prior to e-coating, as well as potentially eliminating the use such toxic components in the process. The formulation provided prevention of surface area corrosion, the formation of blisters, cracking flaking, and other defects while maintaining good adhesion of the topcoat to the surface of steel, aluminum and galvanized steel.

[0114] Powder -coating samples

[0115] Figs. 2A-2C are maps of the tested steel, galvanized steel and Aluminum samples, respectively, treated with formulation of this disclosure compared to reference samples (sand blasting treatment), showing a rusting index. As can be seen, there is no significant difference in rusting were observed for 60 CCT cycles (SAE J 2334), indicating that the formulations of this disclosure provide good surface treatment with and without sand blasting.

[0116] Crosscut test, blistering and rusting test results for 60 CCT cycles are shown in Table 4

[0117] Table 4: Crosscut blistering and rusting for powder coated samples, 60 CCT cycles

[0118] As can be seen from Table 4, the samples treated with formulations of this disclosure show the same results as those of reference samples surface-treated by the standard sandblasting, showing that the formulations of this disclosure can substitute the industry standard sandblasting, to significantly simplify the surface treatment process prior to e-coating, as well as potentially eliminating the use such toxic components in the process. The formulation provided prevention of surface area corrosion, the formation of blisters, cracking flaking, and other defects while maintaining good adhesion of the topcoat to the surface of steel, aluminum and galvanized steel.

[0119] As can be seen from Figs. 2A-2C, the coating remained intact, without evidence of blistering, rusting or impact on adhesion. Hence, for formulations of this disclosure provide at least comparable surface treatment as industry standard pre-treatments prior to coating. However, unlike the aggressive treatments currently carried out for surface preparation towards coating, formulations of this disclosure are safer for the applying personnel and more environmentally friendly, while also requiring less energy investment for application and fewer steps in the pretreatment process compared to standard surface preparation processes such as sand blasting or zinc phosphate treatments.

[0120] Characterization of treated samples

[0121] The effect on the surface topology obtained by the formulations of this disclosure in metal surface was assessed, as can be seen in Figs. 4A-4D, which show scanningelectron microscopy (SEM) images of metal surfaces.

[0122] Steel samples were thoroughly washed with water and organic solvents and vacuum dried. Each of the samples was then dipped for 100 seconds in a different formulation of Table 1.

[0123] As seen, a non-treated surface (Fig. 4A) showed a relatively smooth surface, bearing the usual expected defects and machining traces. A surface treated with an organic antioxidant in an acidic solution (Fig. 4B) showed both newly formed submicronic structure and etching. A surface treated with two organic antioxidants in an acidic solution (Fig. 4C) showed significantly less etching but much more distinct micronic and sub-micronic surface structures. A surface treated with a solution containing several antioxidants in an acidic solution, to which a dispersant was added, showed significant surface coverage by sub-micronic structures (Fig. 4D). Hence, formulations of this disclosure were shown to effectively modify the surface structure of metal surfaces, rendering these suitable for ensuing coating processes.

[0124] Electrochemical impedance tests were carried out on pickled steel samples treated with a formulation according to Table 1, and dried in different drying conditions (Fig. 5A) as well as different formulation of this disclosure (Fig. 5B). The measurements were performed between Ihz to 0.8MHz. As can be seen from Figs. 5A-5B the treatment in exemplary formulations reduces the resistivity of the metal surface, which in turn enables shorter electrifying durations for electrostatic coating procedures and supports the finding that the surface properties have been altered by this treatment.

[0125] XPS analysis

[0126] In order to assess the effect of the formulations on metal surfaces once applied thereon, X-Ray Photoelectron Spectroscopy (XPS) was carried out for treated and untreated metal samples, as follows.

[0127] Carbon-steel samples, bare of millscale or rust, but with a protective grease layer (as received from manufacture), were dipped for 1 minute in a standard, commercial degreasing solution and then washed twice with distilled water.

[0128] Some of the samples were then dipped for 3 minutes in a formulation according to Table 1 above ("Sample"), while the other samples were not treated with the formulation ("Ref'). Then, both types of samples were cleaned by dipping into a first distilled water container (30 sec.), dipping into a second distilled water container (30 sec.) and then washing with a stream of ethanol, isopropanol, and drying under pressurized airflow for 2 minutes. Both types of samples were then transferred to a high vac (<10‘5Torr) for 16 hours for evaporation of remnants of solvents or loosely bound species from the surfaces.

[0129] The samples were then analyzed by XPS, in an analysis chamber (UHV - 21 O'10Torr during analysis) using a Versaprobe III - PHI Instrument (PHI, USA). The sample was irradiated with a Focused X-Ray AlKa monochromated X-rays source (1486.6eV) using an X-Ray beam (size lOOmicron, 25 W, 15kV). The outcoming photoelectrons are directed to a Spherical Capacitor Analyzer (SCA). The sample charging was compensated by a Dual Beam charge neutralization based on a combination of a traditional electron flood gun and a low energy argon ion beam.

[0130] Surface survey of the samples is detailed in Table 5.

[0131] Table 5: Percentage of elements by type on the surface of the samples

[0132] As can be seen, treating the metal with the formulation has led to increased presence of oxygen atoms on the surface, as well as decreases thickness of organic layer on the metal surface - as evidenced by a higher percentage of exposed iron atoms at the surface of the samples.

[0133] Fig. 6A provides an analysis of oxygen atoms on the surface of the samples. As can be seen, the samples treated with the formulation show both a higher presence of iron oxides and a higher presence of hydroxides on the surface. Such species may serve as potential sites for chemical bonding with the materials in the topcoats.

[0134] Fig. 6B provides an analysis of iron atoms on the surface of the samples. As can be seen, the treated samples demonstrate a higher presence of iron oxides formed on the surface of the samples, as compared to non-treated samples. Such species may serve as potential sites for chemical bonding with the materials in the topcoats.

[0135] From the results, it is evident that the surface of the treated samples was significantly altered, as compared to non-treated samples. This alteration is significant enough to withstand multiple washing and exposure to high vacuum, indicating that the surface has undergone chemical conversion.

[0136] The layer formed by treatment with the disclosed solution is apparently thin, likely in the order of several nanometers, as indicated by the observed signals of non-oxidized iron, attesting to the potential capability of the formulation to assist in the removal of the greasing cover from the metal surface. Furthermore, as it is known that leftovers of greasing materials hinder topcoat coverage and adhesion to the metal surface, replacing these with other organic components originating from the formulation, can potentially promote adhesion of the treated topcoat rather than hinder it.

[0137] The treatment with the formulation has shown to promote the formation of a layer enriched with iron oxides, indicating that the formulation promotes oxidation of the metal. The layer formed by treatment was found to be enriched with oxygen atoms and hydroxide groups. Such a layer provides surface binding sites which promote the strong binding of topcoats to the surface, for example by hydrogen bonding between these sites and the functional groups in the topcoat molecules / polymers. In addition, due to the formation of surface oxides, and / or due to the binding of organic species from the formulation onto the metal surface, such a layer can potentially provide protection against surface corrosion.

Claims

CLAIMS:

1. A liquid formulation for treating a metal surface prior to coating, the formulation comprising at least one mild organic acid, or a salt, a complex or a derivative thereof, dissolved in at least one carrier liquid.

2. The liquid formulation of claim 1, wherein said at least one mild organic acid is selected from carboxylic acids bearing one or more carboxylic groups; enediols and their tautomers, optionally conjugated to a carbonyl group; optionally conjugated carboxylic acids; saccharides; acidic polymers; organic compounds with sulfonic, boronic or phosphonic acid functional groups; acidic polysaccharides; phenolic acids, with or without electron withdrawing groups; and thiols with or without electron withdrawing groups.

3. The liquid formulation of claim 1 or 2, wherein the mild organic acid is an enediol conjugated to a carbonyl group4. The liquid formulation of any one of claims 1 to 3, wherein the mild organic acid is ascorbic acid or a derivative thereof.

5. The liquid formulation of any one of claims 1 to 4, comprising at least about 0.1 wt% of said at least one mild organic acid.

6. The liquid formulation of claim 5, comprising between about 0.3 wt% and 30 wt% of said at least one mild organic acid.

7. The liquid formulation of any one of claims 1 to 6, wherein the formulation further comprises at least one organic antioxidant.

8. The liquid formulation of claim 7, wherein the organic antioxidant is selected from polyphenols, tocopherols, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, carotenoids, terpenes, curcuminoids, saponins, steroids, bilirubin, uric acid, glutathione, chemical species with pi-conjugation along an aromatic and / or poly-ene molecular structure, chemical species which enable high stabilization of radicals formed at sites prone to homolytic cleavage of chemical bonds, and combinations thereof, provided that the organic antioxidant is different from the mild organic acid.

9. The liquid formulation of 7 or 8, comprising at least about 0.1 wt% of said at least one organic antioxidant.

10. The liquid formulation of claim 9, comprising between about 0.3 wt% and 30 wt% of said at least one organic antioxidant.

11. The liquid formulation of any one of claims 1 to 10, wherein said at least one carrier liquid is a polar and / or protic liquid.

12. The liquid formulation of claim 11, wherein said at least one carrier liquid is selected from water, alcohols, amines, polymers having sufficient fluidity at ambient temperatures, liquid ions, and mixtures thereof.

13. The liquid formulation of 12, wherein said at least one carrier liquid is an aqueous liquid.

14. The liquid formulation of claim 13, wherein said at least one carrier liquid is water.

15. The liquid formulation of any one of claims 1 to 14, further comprising at least one auxiliary antioxidant.

16. The liquid formulation of claim 15, wherein said at least one auxiliary antioxidant is selected from tocopherols, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid, carotenoids, terpenes, curcuminoids, saponins, steroids, bilirubin, uric acid, glutathione, and chemical species with pi-conjugation along an aromatic and / or poly-ene molecular structure, chemical species which enable high stabilization of radicals formed at sites prone to homolytic cleavage of chemical bonds, and combinations thereof, provided that the auxiliary antioxidant is different from the organic antioxidant and from the mild organic acid.

17. The liquid formulation of claim 15 or 16, wherein the formulation comprises at least about 0.01 wt% of said at least one auxiliary antioxidant.

18. The liquid formulation of claim 17, comprising between about 0.1 wt% and 30 wt% of said at least one auxiliary antioxidant.

19. The liquid formulation of any one of claims 1 to 18, having a pH of between about 0.5 and about 6.

20. A process for treating a metal surface prior to coating, the process comprising applying a liquid formulation according to any one of claims 1 to 19 onto said metal surface for a period of time sufficient to modify the topology of the metal surface.

21. The process of claim 20, wherein said period of time is sufficient to at least partially remove metal oxides from the metal surface.

22. The process of claim 20 or 21, wherein said period of time is sufficient to increase the roughness of said metal surface and / or to form the minimal amount of chemical species required for sufficient adhesion of the topcoat to the surface.

23. The process of any one of claims 20 to 22, wherein said period of time is between about 5 seconds and about 600 seconds.

24. The process of any one of claims 20 to 23, wherein the liquid formulation is maintained at a temperature of between about 1 °C and about 80 °C during said applying.

25. The process of any one of claims 20 to 24, wherein said applying is carried out by dipping, brushing, or spraying.

26. The process of any one of claims 20 to 25, wherein, prior to said applying, the metal surface is degreased.

27. The process of any one of claims 20 to 26, wherein, the formulation is removed from said metal surface after said period of time.

28. A process for treating a metal surface prior to coating, the process comprising:(a) degreasing the metal surface by applying one or more degreasing compositions;(b) washing the metal surface to remove the one or more degreasing compositions;(c) applying a liquid formulation according to any one of claims 1 to 19 onto said metal surface for a period of time sufficient to modify the topology of the metal surface; and(d) removing said liquid formulation after said period of time, thereby obtaining a metal surface ready for coating.

29. A process for obtaining a coated metal surface, the process comprising:(A) degreasing the metal surface by applying one or more degreasing compositions;(B) washing the metal surface to remove the one or more degreasing compositions;(C) applying a liquid formulation according to any one of claims 1 to 19 onto said metal surface for a period of time sufficient to modify the topology of the metal surface;(D) removing said liquid formulation after said period of time, thereby obtaining a metal surface ready for coating; and(E) applying one or more coating layers onto the metal surface of step (D).

30. A process for obtaining a coated metal surface, the process comprising:(A’) degreasing the metal surface by applying one or more degreasing compositions;(B’) washing the metal surface to remove the one or more degreasing compositions;(C’) applying a liquid formulation according to any one of claims 1 to 19 onto said metal surface for a period of time sufficient to modify the topology of the metal surface; and(D’) applying one or more coating layers onto the metal surface of step (C’).

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