WO2025073696A1 - New composition and use thereof for metal treatment - Google Patents

Abstract

The instant invention concerns a composition comprising a polymer P obtained by radical copolymerization of a mixture of (i) optionally acrylic acid; (ii) optionally methacrylic acid; and (iii) at least one compound being an ethylenically unsaturated polycarboxylic acid. The present invention also relates to such a composition for metal treatment like before coating, in particular, before adhesive bonding.

Description

NEW COMPOSITION AND USE THEREOF FOR METAL TREATMENT

This application claims priority to the application filed on October 3 2023 in Europe with Nr 23306693.5, the whole content of this application being incorporated herein by reference for all purposes.

The instant invention relates to the field of adhesive bonding of metallic surfaces. The invention is more especially directed to a composition comprising a specific polymer for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer, in particular, in order to impart the resulting bonding with a resistance to the adhesive failure.

TECHNICAL BACKGROUND

In order to provide an enhancement of the adherence of adhesives on metal surfaces, especially on aluminum or steel, several methods have been proposed, including the deposit of inorganic coatings on the surface of the metal, especially the so-called "conversion coating".

The term "conversion coating" is well known in the art and refers to a layer formed on the surface of a metal, that is an advantageous replacement of native oxide on said surface (especially on aluminum), and which is obtained by the controlled chemical formation of a film or layer on the metallic surface by reaction with chemical elements of the metallic surface, so that at least some of the cations dissolved from the metallic material are deposited in the conversion coating.

Typically, coatings such as conversion coatings are obtained by reacting the metal surface with solutions containing metal salts.

Conversion coatings technologies have evolved a lot in the past decades: hexavalent chromium (Cr-VI such as CrO3), widely used in the past especially on aluminum, has seen its uses more and more limited due to its toxicity. Technologies such as Zinc phosphates (Zn-P), which became predominant for mild steel, galvanized steel and multi-metal lines containing less than 30% of aluminum, are more and more challenged these days: in addition to water and energy consumption significantly higher than with other conversion coating technologies, Zn-P conversion generates toxic wastes/sludges which contain toxic metals (Ni, Mn, Co, ... ) and whose disposal is getting more and more expensive. Issues raised by both Cr-VI and Zn-P allowed new technologies to develop: trivalent chromium (Cr-lll such as chromium nitrate Cr(NO₃)₃) and transition metals hexafluorides. While Cr-lll is not classified as of today, it suffers from the bad image of chromium and its usage is becoming increasingly challenged. Hexafluorides are thus Cr-free and Zinc phosphate-free alternative technologies.

However, hexafluorides are known to yield relatively smooth surfaces which can negatively affect paint adhesion while other surface treatment technologies create an entanglement of crystals protruding at the metal surface, thus increasing surface area improving coating adhesion through mechanical interlocking.

For enhancing the adhesion on a coating, such as a conversion coating, it is known to add some additives, especially organic polymers. In this connection, it has been for example described the use of polyacrylic acids. A typical additive is ACUMER™ 1510 available from DOW (and previously from Rohm & Haas) that has been widely described for this kind of application. For more details in this connection, it may be especially be referred to WO97/13588, US 4,191 ,596, or US4921552.

SUMMARY OF THE INVENTION

One aim of the present invention is to provide a new performing solution for improving the bonding between a metallic surface and another surface, preferably metallic as well, through an adhesive layer.

To this end, the instant invention proposes to make use of a specific composition, optionally, but not necessarily, together with, namely before, during, or after, the formation of a conversion coating, to treat a metal surface before bonding it with another surface via an adhesive composition or layer (so-called “adhesive bonding”). It has been discovered that using a composition comprising a specific polymer as coating pretreatment on the metallic surface or as additive in the adhesive composition to be applied between a metallic surface and another surface, provides a particularly good adherence between the two surfaces. The composition comprising the specific polymer according to the invention allows a resistance to the adhesive failure. In the scope of the invention, the inventors have now observed that the strength of the adherence between the adhesive and the metal surface reveals especially high, to such an extent that cohesive failure appears instead of (or at least more preferably than) adhesive failure when a sufficiently high mechanical stress is applied for separating the adhesive-bonded surfaces.

The improvement of the bonding between two surfaces treated by a composition of the invention and then assembled by an adhesive is thus reflected by a resistance to the adhesive failure, which means that a cohesive failure will occur instead, in particular after ageing, compared to other existing treatments.

DEFINITIONS

As used herein, the singular forms "a", "an", and "the" include both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compound" means one compound or more than one compound.

The terms "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes" or "containing", "contains", and are inclusive or open-ended and do not exclude additional, non-recited members, elements or method steps. It will be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein comprise the terms "consisting of", "consists" and "consists of".

Throughout this application, the term "about" is used to indicate that a value includes the standard deviation of error for the device or method being employed to determine the value.

As used herein, the term "average" refers to number average unless indicated otherwise.

As used herein, the terms "% by weight", "wt%", "weight percentage", or "percentage by weight", and the terms "% by volume", "vol%", "volume percentage", or "percentage by volume", are used interchangeably.

The recitation of numerical ranges by end points includes all integer numbers and, where appropriate, fractions subsumed within that range (e.g. 1 to 5 can include 1 , 2, 3, 4 when referring to, for example, a number of elements, and can also include 1.5, 2, 2.75 and 3.80, when referring to, for example, measurements). The recitation of end points also includes the end point values themselves (e.g. from 1 .0 to 5.0 includes both 1 .0 and 5.0). Any numerical range recited herein is intended to include all sub-ranges subsumed therein.

“Adhesive failure” is understood to mean that failure between two surfaces bonded by an adhesive layer occurs at the surface, the adhesive being retained on one surface.

“Cohesive failure” is understood to mean that failure between two surfaces bonded by an adhesive layer occurs within the adhesive, which is thus retained on both surfaces. DETAILED DESCRIPTION OF THE INVENTION

More precisely, the instant invention is directed to the use of a composition comprising a. at least one polymer P obtained by radical copolymerization of a mixture comprising:

(i) optionally acrylic acid;

(ii) optionally methacrylic acid; and

(iii) at least one compound of formula I below:

wherein:

- R and R' are selected from H or a methyl group, provided at least one of R or R' is H, preferably both are H;

- R¹ and R² are, independently from one another, H or the compound of formula I is in the form of a salt, with R¹ and/or R² being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium ⁺NR³4, wherein R³ are independently from one another H or methyl or ethyl;

- n is an integer ranging from 1 to 4;

- m is an integer ranging from 0 to 4;

- Ra, Rb and Rc are, independently from one another, selected from H, a - COOR⁴ group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR⁴ group, with R⁴ having the same definition as the one of R¹ and R², preferably H; provided when Ra, Rb and/or Rc is an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR⁴ group, then at least one of Ra, Rb or Rc is H, preferably at least two of Ra, Rb or Rc are H. b. at least one compound (iii) having the formula I as defined above, and/or at least one ethylenically unsaturated compound P1 containing at least one phosphorous atom. One specific object of the instant invention is the use of the composition as defined above for treating a first metallic surface (S1 ) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting to the bonding a resistance to adhesive failure.

An additional advantage of the use of a composition according to the invention is that the bonding obtained according to the invention is highly resistant to corrosive atmospheres and to wet atmospheres, which leads to a long lasting adhesive bonding. In most cases, the composition of the invention is also used for obtaining this additional effect (namely for further imparting to the bonding a resistance to corrosive atmospheres and to wet atmospheres, in other words for obtaining both a very effective, but also long lasting adhesion).

In other words, the use of a composition as defined above for treating a first metallic surface (S1 ) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting a resistance to the adhesive failure to the bonding is also providing a very good resistance to ageing of the adhesive bonding.

Such a property can be measured according to tensile tests on so-called “Single Lap Shear” (SLS) assemblies, such as defined in ASTM D-1002 10, performed on freshly bonded SLS assemblies and performed on SLS assemblies after ageing in corrosive atmospheres, wet atmospheres, or repeated cycles of corrosive atmospheres followed by wet atmospheres, such as ASTM G85 A3. Other tests simultaneously combine a corrosion stress and a mechanical stress (e.g. compression load), such as the Bv 101 -07, known as Ford Durability Stress Test or Arizona Proven Ground Exposure (APGE). Notably an adhesive bonding with the composition according to the invention between two surfaces S1 and S2 has been demonstrated to provide failure facies, after ageing, which remain more cohesive.

The composition of the invention can be used as surface treatment of all or parts of the metallic surface (S1 ) and optionally all or parts of the surface (S2) and/or as additive in the adhesive layer.

In a preferred embodiment, the polymer P is obtained by radical copolymerization of a mixture consisting essentially of:

(i) optionally acrylic acid;

(ii) optionally methacrylic acid; and

(iii) at least one compound of formula I.

By “consisting essentially of”, it is understood to mean that the polymer P is produced by using one, two or three components (i), (ii) and (iii) as sole monomers. Preferably, the polymer P is obtained by radical copolymerization of a mixture having the following molar ratio of the compound of formula I, based on the total quantity of acrylic acid, methacrylic acid and compound of formula I: at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably 100%.

Besides, the polymer P used according to the invention preferably has a molecular weight, typically a weight average molecular weight, of at least 2,500 Da, e.g. 2.5 kDa to 1 ,500 kDa, for example 2.5 kDa to 150 kDa, notably between 5 and 100 kDa. Typically, the polymer P used according to the invention has a molecular weight of from 5.5 to 75 kDa, e.g., 10 to 50 kDa.

A polymer P especially suitable for the invention is a polymer having a weight average molecular weight of about 10 to 20 kDa.

Average molecular weights (typically weight average molecular weight) are measured by Size Exclusion Chromatography (SEC). Notably the SEC is equipped with a MultiAngle Laser Light Scattering (MALLS) Mini Dawn TREOS detector and an Agilent concentration detector (Rl detector). The SEC-MALLS system is running on three columns Varian Aquagel OH mixed H, 8pm, 3*30cm at a flow rate of 1 mL/min and with the following mobile phase: 100% water, 100mM NaCI, 25mM NaH2PO4, 25Mm Na2HPO4. Polymer samples were diluted down to 0.5 active wt% in the mobile phase for at least 4h then filtrated in a Millipore filter 0.45pm and 10OpL were injected in the mobile phase flow. Absolute molar masses were obtained with the dn/dC of the poly(itaconic acid) equal to 0.155mL/g.

In a particular embodiment of the invention, the composition comprises from 30 to 90% by weight, preferably from 60 to 80% by weight, based on the total weight of the composition, of compound (iii) as ingredient b. Advantageously, the polymer P is mixed with unreacted compound (iii) as ingredient b and this mixture is applied on all or parts of the metallic surface (S1 ) and optionally all or parts of surface (S2) and/or as additive in the adhesive layer.

In a preferred embodiment, the composition according to the present invention, consists essentially of the polymer P and the compound (iii) as ingredient b. It may be useful according to another preferred embodiment to add to the composition comprising the polymer P and the compound (iii) as ingredient b, solutions containing fluorides or so-called complex fluorides like H2TiFe, H2ZrFe, H2HfFe, H2AIF6, H2SiFe, H2GeFe, H2SNF4, or HBF4 and other transition metal derivatives such as Zr(OH)2CO3*ZrO2. In the compound of formula I, R and R' are selected from H or a methyl group, provided at least one of R or R' is H, preferably both are H.

Also, R¹ and R² are, independently from one another, H or the compound of formula I is in the form of a salt, with R¹ and/or R² being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium ⁺NR³4, wherein R³ are independently from one another H or Me or Ethyl. Preferably R¹ and R² are H or the compound of formula I is a salt, with R¹ and R² being sodium.

In the compound of formula I, n is an integer ranging from 1 to 4, preferably 1 or 2 and m is an integer ranging from 0 to 4, preferably 0 or 1 .

Regarding Ra, Rb and Rc, they are, independently from one another, selected from H, a -COOR⁴ group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR⁴ group, with R⁴ having the same definition as the one of R¹ and R², preferably H; provided when Ra, Rb and/or Rc is an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR⁴ group, then at least one of Ra, Rb or Rc is H, preferably at least two of Ra, Rb or Rc are H. In particularly preferred embodiment Rb and Rc are H and Ra is either H or CH2- COOH, and this to ensure solubility in water

A particularly preferred embodiment corresponds to the composition wherein the compound of formula I in polymer P is selected from the group consisting of itaconic acid, alpha-methylene glutaric acid, but-3-ene-1 ,2,3-tricarboxylic acid, their salts and mixtures thereof.

According to a first preferred embodiment, the compound of formula I in polymer P is itaconic acid or salt thereof, for instance a sodium salt thereof.

According to a second preferred embodiment, the compound of formula I in polymer P is alpha-methylene glutaric acid (MGA) or salt thereof, for instance a sodium salt thereof.

According to a third preferred embodiment, the compound of formula I in polymer P is but-3-ene-1 ,2,3-tricarboxylic acid (BTA) or salt thereof, for instance a sodium salt thereof.

According to a fourth preferred embodiment, the compound of Formula I is hex-5-ene-1 ,3,5-tricarboxylic acid (HTA) or sodium salt thereof.

In a particularly preferred embodiment of the invention, the compound of formula I in polymer P is itaconic acid or sodium salt thereof.

The ethylenically unsaturated compound P1 containing at least one phosphorous atom of the invention is preferably selected from the group consisting of: phosphonic acid monomers, phosphoric acid monomers, dioxaphospholane monomers, phosphonic acid (meth)acrylate and (meth)acrylamido monomers, phosphoric acid (meth)acrylate and (meth)acrylamido monomers, and monomers comprising 2 phosphorous atoms like 2-[2,2- bis(diisopropoxyphosphoryl)ethoxy]methyl methacrylate and propyl /V,/V- tetramethylbis(phosphonate)-2-hydroxybismethylamine methyl methacrylate.

Phosphonic acid monomers P1 of the polymer P may be for instance compounds of formula I

where

R¹ = H, a C1-C4 alkyl or a

group where R = H or C1-C4 alkyl, preferably ethyl, (t)butyl

R² = H or a C1-C4 alkyl, preferably methyl, ethyl or (i)propyl

X = a single bond or a spacer chosen from a C1-C4 alkyl, ether or ketone, preferably from -CH2-, -CH2-CH2-, -CH2-O-CH2-CH2, -CH2-O-CO-CH2-, -CH2-O- (CH2)n-, -O-(CH2)n - wherein n = 1 or 2.

Phosphonic acid monomers which can be used in the frame of the invention are those of the following formula:

Still other phosphonic acid monomers which can be used in the frame of the invention are diallyl aminophosphonic acids and esters/salts thereof, preferably diallyl aminomethylphosphonic acids and esters/salts thereof, preferably those having the following formula:

where R² is as defined above.

Phosphoric acid monomers P1 of the polymer P may be for instance compounds of formula II

where R¹ and R² are as defined above and where X is a single bond or a spacer chosen from a C1-C4 alkyl or ether eventually bearing hydroxyl and/or phosphate group(s) (PO4H2), preferably from -CH2-, -CH2-CH2-, -O-(CH₂)₄-, -O-CH2-CHOH- CH2-, -CH2-O-CH2-CHOH-CH2-, -O-CH2-C(PO₄H2)-CH2-, -CH2-O-CH2-C(PO₄H2)- CH2-.

Dioxaphospholane monomers P1 of the polymer P may be for instance compounds of formula III:

where X is a spacer chosen from C1-C4 ethers, preferably from -O-CH2 or -CH2-O- CH2.

Phosphonic acid (meth)acrylate and (meth)acrylamido monomers P1 of the polymer P may be for instance compounds of formula IV

where Ri = H or CH3, X = -O-, -NH- or -N(CH3)-, R² is as defined above and Y is a spacer chosen from C1-C10 alkyl or ether or thioether eventually bearing hydroxyl and or phenyl group (Ph), preferably -CH2-CH2-, -C(CH3)2-CH2-CH2-CH2-, -(CH2- CH₂)3-O-CH2-CH2- -CH2-CHOH-CH2-O-CO-CH2-, -CH2-Ph-CH₂-, CH2-CHOH- CH₂-S-Ph-, CH₂-CHOH-CH₂-O-Ph-.

Phosphoric acid (meth)acrylate and (meth)acrylamido monomers P1 of the polymer P may be for instance compounds of formula V

where R¹ = H or CH3, X = -O-, -NH- or -N(CH3)-, R² is as defined above and Y is a spacer chosen from C1-C10 alkyl or alkylene oxide units, preferably ethylene oxide and/or propylene oxide units, -CH2-CH2-.

Phosphoric acid (meth)acrylate and (meth)acrylamido monomers which have been tested in the frame of the invention are those of the following formula:

wherein p is from 1 to 2

wherein n is from 3 to 9.

We can also consider PO/EO monomers containing P like the ones of the following formula:

wherein m+n is at most equal to 15, preferably 10; and when n = 0: m = 1 5, preferably 1 -3; and when n > 0: n > m+2.

Good results are obtained when the ethylenically unsaturated compound P1 containing at least one phosphorous atom of the invention is VPA.

In a preferred embodiment of the invention, the compound of formula I in polymer P is itaconic acid and compound (iii) as ingredient b is chosen from itaconic acid and/or VPA.

According to a first preferred embodiment, the compound of formula I in polymer P is itaconic acid and compound (iii) as ingredient b is itaconic acid.

According to a second preferred embodiment, the compound of formula I in polymer P is itaconic acid and compound (iii) as ingredient b is VPA.

According to a most preferred embodiment of the invention, polymer P is a homopolymer of itaconic acid and compound (iii) as ingredient b is chosen from itaconic acid and/or VPA.

The present invention also concerns the use of a composition as described above for improving the adhesive bonding between a metallic surface (S1 ) and a film forming composition, such as a paint, a varnish or an adhesive composition, the latter being preferred. In particular, the composition of the invention can be used for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer. More precisely, it can be used for imparting to the bonding a resistance to adhesive failure and eventually for further imparting to the bonding a resistance to corrosive atmospheres and to wet atmospheres.

Regarding the nature of the metallic surface (S1 ) it can be a surface comprising a metal selected from aluminum, steel, zinc, magnesium, titanium, copper and their alloys, or cobalt-nickel alloys, preferably a surface of aluminum or aluminum alloy.

The invention is especially suitable for treating metal surfaces of:

- aluminum or an aluminum-based alloy; or

- steel, for example galvanized steel (electrogalvanized EG steel; hot dip galvanized HDG steel for instance containing up to about 0.2wt% of aluminum; steel coated with both Zn and Al and for instance containing about 55% of aluminium such as Galvalume™; or steel coated with both Zn, 3.5% of aluminum and 3% of Mg such as Magnelis™; cold rolled steel (CRS); or stainless steel; or

- magnesium or magnesium-based alloys; or

- zinc or zinc-based alloys; or - titanium or titanium-based alloys.

The invention is especially interesting for metal surface of aluminum and aluminum alloys, such as Aluminum Alloy AA 5754 tested in the appended examples, or other alloys such as those of series 1xxx, 2xxx, 3xxx, 4xxx, 5xxxx, 6xxx, 7xxx, such as AA1050, 2024, 3003, 5182, 5005, 6111 , 6113, 6014, 6016, 6022, 6060, 6063, 6182, 7075.

As for the other surface (S2) it may be a metallic surface as well, identical or different from the metallic surface (S1 ), preferably identical. In this embodiment, preferably, metallic surface (S1 ) is part of the surface of a solid part (1 ) to be bonded to another solid part (2) of which (S2) is part of the surface. In this case, generally, it is intended to bond surfaces (S1 ) and (S2) together in order to make an adhesive bonding between both said solid parts (1 ) and (2) generally with the aim of making a structure extending beyond surfaces (S1 ) and (S2). The composition of the invention is particularly suitable for providing a cohesive nature to ruptures in shear testing of solid parts/pieces (especially metallic ones) bonded through adhesive bonding. Adhesive bonding is a process in which joining between two or more solid parts is accomplished by the solidification or hardening of a non-metallic adhesive material, placed between the faying surfaces of the parts. It is widely used in industry, notably in the automotive industry.

According to another embodiment, the other surface (S2) is a non-metallic surface, for example a plastic surface e.g. based on polyamide, PEEK or ABS, or a composite surface based e.g. on CFRP or Glass Fiber Reinforced Plastics.

According to an advantageous embodiment, the second surface (S2) is a metallic surface also treated with a composition as described above, generally but not necessarily identical to the composition used on the first surface (S1 ).

According to an interesting variant, both surfaces (S1 ) and (S2) are metallic surfaces of aluminum or aluminum alloys.

More generally, the composition according to the invention is preferably used for treating both surfaces (S1 ) and (S2) before the adhesive bonding of the two surfaces through an adhesive layer, especially when (S2) is a metallic surface.

Alternatively or additionally, the composition according to the invention can be used as additive incorporated to an adhesive composition used to form the adhesive layer between the two surfaces. The present invention is also directed to a process for bonding a metallic surface (S1 ) with another surface (S2), including: treating all or parts of said metallic surface (S1 ) with the composition as defined previously; and optionally treating all or parts of said second surface (S2) with the composition as defined previously; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

The surface (S1 ) and/or (S2) are preferably cleaned and/or activated before the treatment with the composition C.

In this process, the composition according to the invention may be: a conversion composition; and/or a solution or a dispersion applied on the surface after having applied a conversion coating on the surface to be treated.

According to a possible embodiment, a conversion coating may be applied on the metallic surface (S1 ), by reaction of said surface with a conversion composition (in other words, a conversion composition is applied on the metallic surface for forming a conversion coating thereon). The use of a conversion coating is however not compulsory according to the invention, and, according to a specific embodiment, no conversion coating is applied on the surface (S1 ). When a conversion composition is used, typically:

- the conversion composition includes all or part of the composition of the invention as an additive; and/or

- the conversion coating is applied on the surface (S1 ) and then all or part of the composition of the invention is applied on the conversion coating.

The second surface (S2) may also receive a similar conversion coating, in the same conditions, especially when this second surface (S2) is a metallic surface. But again, the use of a conversion coating is not compulsory according to the invention, and, according to a specific embodiment, no conversion coating may be applied on the surface (S2).

The present invention is also directed to a process for bonding a metallic surface (S1 ) with another surface (S2), including: bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces, said adhesive layer comprising the composition as defined above.

According to this possible embodiment, the composition as described above may typically be introduced in the adhesive composition for example as a solid powder, said powder comprising the composition alone or said composition at the surface of a filler (said powder may typically be obtained by spray drying a solution or suspension of the composition, typically in presence of a filler).

According to a preferred embodiment, said process further includes, before the step of bonding the surfaces (S1 ) and (S2), a step consisting in: treating all or parts of said metallic surface (S1 ) with the composition as defined previously; and optionally treating all or parts of said second surface (S2) with the composition C as defined previously.

In other words, the composition of the invention may typically be:

- a conversion composition or a part of it; and/or

- a solution or a dispersion or a part of it, applied on the surface(s) after having applied a conversion coating on the surface to be treated; and/or

- an adhesive composition or a part of it.

Typically, the composition of the invention can be present in the conversion composition and/or in a solution or dispersion applied on a conversion coating. In that case, the adhesive can be applied on a surface previously treated by the composition of the invention.

According to some specific embodiments, an additional layer is applied between the treated surface (S1 ) (and/or (S2)) and the adhesive. This can for example be the case for the treatment of a metal coil or part on a first site that has then to be bonded on a second site. In that case, a lubricant and/or an oil may be applied on the treated coil or part, in order to protect it during transportation and storage and to facilitate downstream operations (coil cutting into sheets, blanking, stamping, forming, ....

When a conversion coating is applied on one or both of the surfaces (S1 ) and/or (S2), it may be obtained by contacting the surface with any conversion composition known from the prior art. Contacting the metal surface with the conversion composition can be made by any means known per se, such as roll coating, immersion (coil coating, parts coating) or spray (coil coating, parts coating), as illustrative examples. The bath, when polluted by multi-valent cations leaching from the substrate, such as Al³⁺ in the case of aluminum strips or parts, may be rejuvenated by off-line or preferable on-line methods such as those known by people familiar with the art (ion exchange resin). When the conversion step is followed by a rinse step, this rinse water may contain some polymer; the polymer may be recovered from the rinse water by reverse osmosis membrane and returned to the conversion bath.

The conversion composition used according to this embodiment of the invention may typically contain fluorides or so-called complex fluorides, e.g. compounds such as H₂CrFe, or more preferably chromium free compounds such as H₂TiF₆ , H₂ZrF₆ , Zr(OH)₂CO3«ZrO2„ H₂HfF₆ , H₂AIF₆ , H₂SiF₆ , H₂GeF₆ , H₂SNF₄ , or HBF4. The conversion composition may also include other compounds, such as silane precursors for example, and/or cerium salts, and/or terbium molybdate.

The invention also concerns the use of the above described composition as adhesion promoters in adhesives, coatings, inks and paints (e.g., water-borne paints and powder paints). This means that the above described composition can be incorporated into adhesives, coatings, inks and paints, including for example waterborne paints and powder paints as additives that promote their adhesion to a substrate and/or the adhesion of another coating on the ink/paint.

Water-borne paints are aqueous compositions that typically provide coatings through the action of a voltage, or physical and/or chemical phenomena e.g. water evaporation, UV crosslinking etc.

Powder paints/coatings are typically applied electrostatically as a free- flowing, dry powder and then cured under heat or with ultraviolet light.

Preferably, the water-borne or powder paint is cured at high temperature i.e. at a temperature sufficient for the compound (iii) as ingredient b to react in a reasonable time frame in order to obtain a coating that is substantially free of unreacted monomer.

In the embodiments set forth above, during the treatment step with composition:

- the concentration of polymer P in the treatment medium is preferably from 1 to 10,000 ppm, more preferably from 10 to 8,000 ppm, typically from 20 to 5,000 ppm; and

- the concentration of compound (iii) as ingredient b is preferably from 100 to 100,000 ppm, more preferably from 200 to 10,000 ppm, typically from 500 to 8,000 ppm. Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

The following examples illustrate some preferred embodiments of the invention.

EXPERIMENTAL PART:

1. Polymer synthesis and characterization:

Polymers 1 and 2: homopolymers of itaconic acid

Polymer 1 : Itaconic acid was homopolymerized according to state-of the art methods. It was neutralized with caustic soda and polymerized in water at a temperature approaching 100°C in the presence of f-BHP (0.008mol for 0.769mol of IA) over 24h. The product was then recovered at 70°C in order to manage its high viscosity. A sample was taken and analyzed by ¹ H NMR in D2O. The final conversion in IA was around 91 %. The molecular weight was determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector.

Polymer 2 was prepared using a similar process.

Analytical results are gathered in Table 1 below.

Table 1: lA-homopolymer used for the test

2. Performance tests: Single Lap Shear (SLS): Performances were assessed through Single Lap Shear (SLS) tests, before and after ageing in corrosive conditions. Coupons were prepared according to the protocol below and assembled to form SLS assemblies as described in D1002-10.

Step 1 is performed according to Step 1a or Step Ibis or Step 1 ter:

Step 1a - 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) go through each of the following steps:

- degreasing by immersion for 1min in a 4L stainless steel bath containing NP Kleen 160 from Quaker (1wt%) heated to 50°C under light stirring,

- rinsing with tap water (at about 50°C),

- etching by immersion for 30s in a 4L stainless steel containing sulfuric acid (10%) heated to 50°C under light stirring,

- rinsing with tap water (at about 50°C),

- rinsing with deionized water.

Step Ibis - 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) go through each of the following steps:

- degreasing by immersion for 3min in a 4L stainless steel bath containing NP kleen 160 from Quaker (1wt%) heated to 50°C under light stirring,

- rinsing with tap water (at about 50°C),

- etching by immersion for 3min in a 4L stainless steel containing NP Kleen 190 (1wt%) and Additivo 200 (0.075wt%) heated to 50°C under light stirring,

- rinsing with tap water (at about 50°C),

- rinsing with deionized water.

Step 2- the coupons are then treated by dipping for 2min in a 4L stainless steel treatment bath, containing the polymer at 50°C and at several concentrations indicated in the Table 1 below. They are then rinsed altogether with a flow of deionized water for lmin and dried for 30min at 60°C. Step 3- the coupons are then assembled in pairs, each pair forming a so-called single lap shear "assembly": two coupons are placed horizontally, parallel, one above the other forming an overlap of 12.5mm length and 25mm width ("overlap zone", including one of terminal zone of each of the two coupons, namely the last 12.5mm of the 100mm length of the coupon). A structural high T curing epoxy adhesive bead (Betamate 1496, from DuPont) is applied with a 7bar compressed air gun on the overlap zone of the lower coupon and glass beads are sprinkled over the adhesive bead to guarantee a 0.2-0.25pm bond line. The upper coupon is then positioned on the overlap zone, thus forming a bonding zone of 12.5mm length, and 25mm width. Paper clips are used to maintain the assembly integrity before and during curing. The adhesive is then cured according to adhesive producer guidelines, typically for 40min at 180°C. Finally, paper clips are removed.

Step 4- tensile strength test on assemblies as obtained in step 3 eventually after ageing in a cyclic test as described below.

Tensile strength test

Used material: Zwick/Roell - Z50, with jaws grasping assembly tips over 2.50cm. The upper jaw is then moved upwards at 10mm/min till the joint breaks.

Ageing cyclic test

A cyclic ageing test is performed according to ASTM G85 - Annex 3 (SWAAT, 2011) in a corrosion chamber Q-FOG CRH 600L, from Q-FOG in the following conditions:

• a 30min acidified salt fog spray followed by

• a 90min soak at >98% relative humidity under the following conditions:

• Chamber temperature - constant 49°C

• Air saturator temperature - constant 57°C

• Relative humidity - >98%

• pH of fall out solution - 2.8-3.0 Volume of fall out solution - 1.0-2.0 ml/80cm²/h

Exposure period - l,000h

After the exposure period is completed, the assemblies are washed down with luke-warm water to remove and neutralize excess acid and any remaining salt residues.

All assemblies are then air dried using forced ambient temperature before being for submitted to lap-shear tensile testing.

Performances are reported in Tables 3-6. The values are average values: the tests were performed on 3 assemblies before ageing and on 5 assemblies after ageing, with the variations in steps 1 and 2 given in Table 2.

Table 2: conditions used for Step 1 and Step 2

Table 3: STRAIN measured at maximum load

Table 4: Maximum LOAD

Table 5: ENERGY measured at the maximum load

Table 6: FACIES after tensile test ***■

(c): cohesive fracture

(~c): rather cohesive fracture

(c/a): significantly adhesive fracture (a): adhesive fracture

The results above show that the addition of IA monomer to an IA homopolymer does not affect its adhesive properties according to the SLS - SWAAT test. Similarly, the addition of VPA monomer to an IA homopolymer does not affect its adhesive properties according to the SLS - SWAAT test.

On the other hand, the addition of IA monomer to an IA homopolymer has a very positive effect on the results of a much more severe test that will be described below, namely the APGE test. Similarly, the addition of VPA monomer to an IA homopolymer has a very positive effect on the results of APGE.

3. Performance tests: Ford Bond Durability Stress test (APGE test)

The Ford Bond Durability Stress test aims at evaluating the relative performance of adhesively bonded joints exposed to simultaneous tensile load (2400N in the examples provided below) and corrosive environment. In addition, it is performed with a lubricant applied on the surface treatment prior to the adhesive. This test is thus recognized as the most difficult ageing test in the field of adhesive bonding. It is carried out according to BV 101-07 standard. a) Surface treatment

A4 sheets of 2mm-thick A5754, supplied by FBCG, were cut in half to obtain two A5 sheets per A4 sheet. They were cleaned and treated in 4L stainless steel baths according to the protocol below

Step 1- alkaline degreasing:

Immersion for 3min in a bath made with lwt% of NP Kleen 160 (Quaker) at 50°C

Step 2- Rinsing with hot tap water close to 50°C Step 3- Acidic etching: immersion for 3min in a bath made with lwt% of NP Kleen 190 (Quaker) combined with 0.075wt% of Additivo 200 (Quaker) at 50°C, pH: ~1.5

Step 4- Rinsing with tap water (close to 50°C) and then RT DIW

Step 5- Surface treatment: immersion in the conversion bath for 2min at 50°C

Step 6- Rinsing with then RT DIW

Step 7- Drying first with compressed air and then in an oven (30min @ 60°C or 5min at 80°C)

The sheets for test 5 were only treated with steps 1-4 and 6, 7 (step 5 having been omitted). The sheets for the other tests were treated with steps 1-7, the composition of the bath of step 5 being indicated in Table 7 below.

Table 7: Conditions for the preparation of the tests sheets b) Production of coupons, assemblies and tubes:

These A5 sheets are then cut into 56mmx25mm coupons, the length of the coupons being parallel to the lamination direction. A lubricant is applied on each coupon (lg/m², DC 290 from Quaker). The oiled coupons are then assembled by pairs with Betamate 4601 from DuPont (12.5mm overlap) which is cured 30min at 178°C. Six assemblies are bolted in a row, forming a straight line and eventually bolted to end links to form the test tube as described in the BV 101-07 standard. A tensile load of 2,400N is applied on each tube. c) Performance data: Each tube is exposed to a corrosive environment for at least 45 cycles, corresponding to 9 weeks:

One cycle corresponds to:

- 15min immersion in a salt solution - 105min vertical drip drying in ambient air

- 22h exposure to humidity/temperature (cabinet)

Each Friday night, the tubes are inserted into a climate chamber, at 90%RH, 50°C. Each tube is carefully inspected after each cycle; the load is readjusted to 2,400N if needed; the number of intact adhesive joints is counted; any adhesive joint which failed is replaced by a new assembly whose coupons are bolted together, not adhesively bonded.

Zero or one adhesive joint failure per tube within 45 cycles is a "PASS". More than one failure per tube within 45 cycles is a "FAIL". The test can be extended to 50 cyles or 60 cycles (optional). The test is always interrupted as soon as 4 joints break per tube.

Number of adhesive joints that remain intact :

Claims

1. Composition comprising a. at least one polymer P obtained by radical copolymerization of a mixture comprising

(i) optionally acrylic acid;

(ii) optionally methacrylic acid; and

(iii) at least one compound having the formula I below:

wherein:

R and R' are selected from H or a methyl group, provided at least one of R or R' is H, preferably both are H;

R¹ and R² are, independently from one another, H or the compound of formula I is in the form of a salt, with R¹ and/or R² being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium ⁺NR³4, wherein R³ are independently from one another H or Me or Ethyl; n is an integer ranging from 1 to 4; m is an integer ranging from 0 to 4;

Ra, Rb and Rc are, independently from one another, selected from H, a -COOR⁴ group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a - COOR⁴ group, with R⁴ having the same definition as the one of R¹ and R², preferably H; provided when Ra, Rb and/or Rc is an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR⁴ group, then at least one of Ra, Rb or Rc is H, preferably at least two of Ra, Rb or Rc are H; and b. at least one compound having the formula I as defined above and/or at least one ethylenically unsaturated compound P1 containing at least one phosphorous atom.

2. The composition according to claim 1 , wherein the polymer P is obtained by radical copolymerization of a mixture consisting essentially of:

(i) optionally acrylic acid;

(ii) optionally methacrylic acid; and

(iii) at least one compound of formula I.

3. The composition according to claim 1 or 2, wherein the polymer P is obtained by radical copolymerization of a mixture having the following molar ratio of the compound of formula I, based on the total quantity of acrylic acid, methacrylic acid and compound of formula I: at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably 100%.

4. The composition according to any one of claims 1 to 3, wherein the compound (iii) as ingredient b represents from 25 to 75% by weight, preferably from 50 to 75% by weight, based on the total weight of the composition.

5. The composition according to any one of claims 1 to 4, wherein the compound of formula I in polymer P is selected from the group consisting of itaconic acid, alpha-methylene glutaric acid, but-3- ene-1 ,2,3-tricarboxylic acid or salts thereof, and hex-5-ene-1 ,3,5- tricarboxylic acid or salts thereof, preferably itaconic acid or sodium salt thereof.

6. The composition according to any one of claims 1 to 5, wherein the ethylenically unsaturated compound P1 containing at least one phosphorous atom of the invention is VPA (Vinyl Phosphonic Acid).

7. The composition according to any one of claims 1 to 6, wherein the compound of formula I in polymer P is itaconic acid and compound (iii) as ingredient b is chosen from itaconic acid and/or VPA.

8. Use of the composition as defined in any of claims 1 to 7, for improving the bonding between a metallic surface (S1 ) and a film forming composition, such as a paint, a varnish or an adhesive composition, preferably an adhesive composition, or as adhesion promoter (additive) in adhesives, coatings, inks and paints (e.g., water-borne paints and powder paints).

9. Use of the composition as defined in any of claims 1 to 7, for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer.

10. The use according to claim 9, for imparting to the bonding a resistance to adhesive failure.

11 . The use according to claim 9 or 10, for further imparting to the bonding a resistance to corrosive atmospheres and to wet atmospheres.

12. The use according to any one of claims 9 to 11 , wherein the composition is used as surface treatment of all or parts of a metallic surface (S1 ), preferably a surface comprising a metal selected from aluminum, steel, zinc, magnesium, titanium, copper and their alloys, or cobalt-nickel alloys, preferably a surface of aluminum or aluminum alloy, and optionally all or parts of surface (S2) and/or as additive in the adhesive layer.

13. A process for bonding a metallic surface (S1 ) with another surface (S2), including : treating all or parts of said metallic surface (S1 ) with the composition as defined in any of claims 1 to 7; and optionally treating all or parts of said second surface (S2) with the composition as defined in any of claims 1 to 7; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

14. A process for bonding a metallic surface (S1 ) with another surface (S2), including : bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces, said adhesive layer comprising the composition as defined in any of claims 1 to 7.

15. A process according to claim 19, further including, before the step of bonding the surfaces (S1 ) and (S2), a step consisting in : treating all or parts of said metallic surface (S1 ) with the composition as defined in any of claims 1 to 7; and optionally treating all or parts of said second surface (S2) with the composition as defined in any of claims 1 to 7.