New polymer and uses thereof for metal treatment

Abstract

New carboxylic acid based polymer and its use in metal treatment, in particular for bonding a metallic surface to a film forming composition such as a paint, a varnish or an adhesive composition.

Description

[0001] NEW POLYMER AND USES THEREOF FOR METAL TREATMENT

[0002] This application claims priority to PCT applications EP2024 / 077660 filed on October 2, 2024 and EP2024 / 077605 filed on October 1 , 2024, the whole content of these applications being incorporated herein by reference for all purposes.

[0003] The instant invention relates to the field of metal treatment, in particular to the bonding of metallic surfaces. The invention is more specifically directed to a polymer and its use in a composition for improving the bonding between a metallic surface (S1 ) and another surface or a film forming composition such as a paint, a varnish or an adhesive composition.

[0004] TECHNICAL BACKGROUND

[0005] In order to provide an enhancement of the adherence of adhesives or paints on metal surfaces, especially on aluminum, zinc or steel, several methods have been proposed, including the deposition of inorganic coatings on the surface of the metal, especially the so-called "conversion coating".

[0006] 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 zinc), 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.

[0007] 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.

[0008] 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.

[0009] For enhancing the adhesion on a coating, such as a conversion coating, it is known to include additives, especially organic polymers. In this connection, it has been for example described the use of copolymers made from acrylic acid and vinyl phosphonic acid. For more details in this connection, it may especially be referred to GB 2331942 and US 6,020,030. A typical additive is Addibond™ 021 available from SYENSQO that has been widely described for this kind of application.

[0010] However, P-based ingredients are more and more under scrutinity.

[0011] In the last decades, several cities in China and western countries passed bills limiting the concentration in phosphorous of aqueous effluents released into the environment.

[0012] In that context, there’s a need for a P-free polymer showing performances similar to P-based polymers.

[0013] SUMMARY OF THE INVENTION

[0014] One aim of the present invention is to provide a new solution for bonding a metallic surface to a film forming composition such as a paint, a varnish or an adhesive composition, such that this new solution does not contain phosphorous but provides performances similar to well established P-based solutions.

[0015] To this end, the instant invention proposes a specific polymer (namely a carboxylic acid based polymer) and its use, 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 eventually via an adhesive composition or layer (so-called “adhesive bonding”). It has been discovered that using a composition comprising the 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.

[0016] The improvement of the bonding between two surfaces treated by a composition comprising the polymer 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.

[0017] DEFINITIONS

[0018] Before the issues of the invention are described in detail, the following should be considered:

[0019] 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.

[0020] 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".

[0021] 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.

[0022] 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.

[0023] As used herein, the terms “radical polymerization” and “radical copolymerization” are interchangeable, and encompass conventional radical polymerization as well as reversible-deactivation radical polymerization (i.e. controlled radical copolymerization), according to methods known to people familiar with the art.

[0024] 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.

[0025] “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.

[0026] “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.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] More precisely, the instant invention is directed to a polymer comprising the following monomers:

[0029] (i) acrylic acid or a salt thereof, e.g. a sodium salt thereof;

[0030] (ii) methacrylic acid or a salt thereof, e.g. a sodium salt thereof; and

[0031] (iii) hex-5-ene-1 ,3,5-tricarboxylic acid (HTA) or a salt thereof, e.g. a sodium salt thereof.

[0032] Preferably, this polymer is obtained by radical polymerization of a mixture comprising monomers (i), (ii) and (iii) as defined above. In a preferred embodiment, the present invention concerns a polymer consisting essentially of the following monomers:

[0033] (i) acrylic acid;

[0034] (ii) methacrylic acid; and

[0035] (iii) HTA or a salt thereof.

[0036] By “consisting essentially of”, it is understood to mean that the polymer comprises the three components above (i), (ii) and (iii) as sole monomers.

[0037] Preferably, this polymer is obtained by radical polymerization of a mixture comprising monomers (i), (ii) and (iii) as sole monomers.

[0038] Preferably, the polymer has the following molar ratio, based on the total quantity of acrylic acid, methacrylic acid and HTA: acrylic acid: from 5 to 95%, notably from 10 to 90%, preferably from 30 to 85% methacrylic acid: from 1 to 50%, preferably from 5 to 40%, more preferably from 10 to 20%

[0039] HTA: from 1 to 90%, for example from 5 to 50%, notably from 5 to 45%.

[0040] The above molar ratios of each monomer in the polymer are showing particularly good results in terms of resistance to the adhesive failure to the bonding when compared to polymers that are out of the above ranges.

[0041] The presence of methacrylic acid confers a higher hydrophobicity to the polymer and thus to the bonding, improving the resistance to wet atmospheres.

[0042] The polymer according to the invention preferably has a molecular weight, typically a weight average molecular weight, of at least 5.5 kDa, e.g. 6 kDa to 1 ,500 kDa, for example 7 kDa to 500 kDa, notably between 8 and 150 kDa.

[0043] 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(acrylic acid) equal to 0.1875 mL / g.

[0044] The present invention also concerns the use of a composition C comprising at least one polymer as described above, for improving the 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.

[0045] In a preferred embodiment, composition C is used for improving the bonding between a metallic surface (S1 ) and another surface (S2) through an adhesive layer.

[0046] In a particular embodiment of the invention, the composition C used to impart resistance to the bonding is further comprising from 30 to 90% by weight, preferably from 60 to 80% by weight, based on the total weight of the composition, of compound (I). Advantageously, the polymer is mixed with unreacted compound (I) and this mixture (which does not further react) is applied on 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.

[0047] In a preferred embodiment, the composition C used according to the present invention, consists essentially of the polymer and optionally compound (I). It may be useful according to another preferred embodiment to add to the composition comprising the polymer and optionally the compound (I), solutions containing fluorides or so-called complex fluorides like H2TiFe, H2ZrFe, FhHfFe, H2AIF6, FhSiFe, FhGeFe, H2SNF4, or HBF4 and other transition metal derivatives such as Zr(OH)2CO3-ZrO2.

[0048] One specific object of the instant invention is the use of a composition C comprising at least one polymer 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, both surfaces preferably being part of the surfaces of two solid parts (especially metallic ones) to be bonded together through adhesive bonding.

[0049] An additional advantage of the use of a composition C comprising the polymer 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, composition C comprising the polymer 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).

[0050] In other words, the use of a composition C comprising at least one polymer 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.

[0051] 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.

[0052] In shear tests, the adhesive is applied to the joint between two solid parts so that one continuous length is formed. The two ends of the resulting assemblies are then placed into their respective grips in the shear tester. The tensile shear tester is then used to apply a load to the joint until it is ruptured. 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 two or more solid parts is accomplished by the solidification or hardening of a non-metallic adhesive material, placed between the surfaces of the parts. It is widely used in industry, notably in the automotive industry.

[0053] The composition C comprising at least one polymer 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.

[0054] Preferably, metallic surface (S1 ) is part of the surface of a solid metallic part (1 ) to be bonded to another solid part (2), preferably also metallic, 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).

[0055] 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.

[0056] The invention is especially suitable for treating metal surfaces of:

[0057] - Aluminum or an aluminum-based alloy ; or

[0058] - Steel, for example galvanized steel (electrogalvanized, EG, hot dip galvanized, HDG, containing up to about 0.2% of aluminum, and steel coated with both Zinc and Al containing about 55% of aluminum such as Galvalume™ or Steel coated with both Zinc, 3.5% of aluminum and 3% of Magnesium such as Magnelis™ ; or cold rolled steel (CRS) ; or stainless steel

[0059] - Magnesium or magnesium-based alloys ; or

[0060] - Zinc or zinc-based alloys ; or

[0061] - Titanium or titanium-based alloys ; or

[0062] - Copper and Copper-based alloys such as Co-Ni alloys.

[0063] The invention is especially interesting for metal surfaces 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, 5005, 5182, 6111 , 6113, 6014, 6016, 6022, 6060, 6063, 6182, 7075.

[0064] 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 adherents. It is widely used in industry, notably in the automotive industry.

[0065] According to an advantageous embodiment, the second surface (S2) is a metallic surface also treated with a composition C comprising a polymer as described above, generally but not necessarily identical to the composition comprising a polymer used on the first surface (S1 ).

[0066] According to an interesting variant, both surfaces (S1 ) and (S2) are metallic surfaces of aluminum or aluminum alloys.

[0067] More generally, the composition C comprising the polymer of the invention is preferably used for treating at least part of 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 C can be used as additive incorporated to an adhesive composition used to form the adhesive layer between the two surfaces.

[0068] 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 C as defined previously ; and optionally treating all or parts of said second surface (S2) with the composition C as defined previously ; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

[0069] The surface (S1 ) and / or (S2) are preferably cleaned and / or activated before the treatment with the composition C.

[0070] In this process according to the invention, the composition C 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.

[0071] 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:

[0072] - the conversion composition includes all or part of the composition C comprising the polymer as an additive ; and / or

[0073] - the conversion coating is applied on the surface (S1 ) and then all or part of the composition C comprising the polymer is applied on the conversion coating.

[0074] 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).

[0075] 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 C comprising the polymer as defined above.

[0076] According to this possible embodiment, the composition C comprising the polymer of the invention may typically be introduced in the adhesive composition for example as a solid powder, said powder comprising the composition C alone or the composition C comprising the polymer at the surface of a filler (said powder may typically be obtained by spray drying a solution or suspension of the composition C comprising the polymer, typically in presence of a filler).

[0077] 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 C 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 C comprising the polymer of the invention may typically be:

[0078] - a conversion composition or a part of it ; and / or

[0079] - 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

[0080] - an adhesive composition or a part of it.

[0081] Typically, the composition C may be present in the conversion composition and / or in a solution or dispersion applied on a conversion coating. In that case, the adhesive is applied on a surface previously treated by the composition C.

[0082] According to some specific embodiments, an additional layer is applied between the treated surface (S1 ) (and / or (S2)) and the adhesive. This is for example 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, ... ).

[0083] When a conversion coating is applied on at least part of 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 may 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.

[0084] The conversion composition used according to the invention may typically contain fluorides or so-called complex fluorides like H2TiFe, H2ZrFe, FhHfFe, H2AIF6, FhSiFe, FhGeFe, H2SNF4, or HBF4 and other transition metal derivatives such as Zr(OH)2CO3*ZrO2,. The conversion composition may also include other compounds, such as silane precursors for example, and / or cerium salts, and / or terbium molybdate.

[0085] The invention also concerns coating and adhesive compositions comprising the polymers described above, including but not limited to inks and paints, such as water-borne and powder paints, as well as the use of the above described polymers as adhesion promoters in coatings, inks and paints (e.g., water-borne paints and powder paints) or as adhesion promoters imparting corrosion resistance in (post-)conversion coatings i.e. in any step performed prior to painting, with paints such as water-borne paints, solvent-borne paints or powder paints or prior to varnishing. This means that these polymers can be incorporated into inks and paints, including for example water-borne paints and powder paints as additives that promote the adhesion of the ink / paint to a substrate and / or the adhesion of another coating on the ink / paint. Or they can be incorporated as additives in conversion coatings as defined above in order to promote adhesion of a painting thereon.

[0086] 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.

[0087] Powder paints / coatings are typically applied electrostatically as a free- flowing, dry powder and then cured under heat or with ultraviolet light.

[0088] In a preferred embodiment, the present invention concerns a process for bonding a paint or varnish to a metallic surface (S1 ), including: treating all or parts of said metallic surface (S1 ) with a composition C comprising at least one polymer as described above ; and applying a paint or varnish to the surface (S1 ).

[0089] In the embodiments set forth above, during the treatment step with composition C, the concentration of the polymer in the treatment medium is preferably from 1 to 10,000ppm, more preferably from 10 to 8,000ppm, typically from 20 to 5,000ppm.

[0090] Finally, the present invention also concerns a metallic surface (S1 ) comprising a polymer as described above, on at least part of it. Such a metallic surface can be obtained according to the process described above and which consists in treating at least part of the surface (S1 ) with a composition C as defined above.

[0091] 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.

[0092] The following examples illustrate some preferred embodiments of the invention.

[0093] EXPERIMENTAL PART

[0094] 1. HTA monomer synthesis:

[0095] The HTA monomer was synthesized through a 2-step process as described below:

[0096] Hex-5-ene-1 ,3,5-tricarboxylic acid (HTA)

[0097] Step 1 : Phosphine catalyzed coupling of methyl acrylate and wiped film evaporation

[0098] The triester was obtained following the process described for the preparation of alkyl acrylate dimer (Ref. WO 2023 / 066829). After this catalytic first step, a distillation under vaccum has been performed to obtain in good purity the dimer product. The remaining distillation residue was mainly composed of methyl acrylate oligomers.

[0099] In order to obtain the desired triester, two successive distillations were performed using a wiped film evaporator apparatus.

[0100] First, 900g of distillate residue was introduced at 5g / min rate, 190°C and under 2mbar pressure. This first feeding allowed to remove all the heavy oligomers and salts residue, thus obtaining a mixture (605g) of remaining dimer, trimer and quadrimer. This fraction was then disti Hated at 5g / min rate, 150°C and under 25mbar pressure, allowing us to obtain 285g of a purified fraction in trimer (>90% by1H NMR).

[0101] Step 2: Triester hydrolysis to afford diacid+triacid mixture.

[0102] H+cat.

[0103] In a 1 L double-jacketed reactor equipped with a mechanical stirrer, a short path distillation bridge connected to a 500m L round bottom flask and a temperature probe were added:

[0104] • 275g of the mixture obtained in step 1 above.

[0105] • 259m L of water

[0106] • 0.138g of hydroquinone.

[0107] The mixture was then allowed to stir at 450 rpm and 5.8mL of H2SO4 (98%, 10.7g, 10mol% with respect to the reactants) was progressively added into the mixture while monitoring for the exotherm.

[0108] The reaction mixture was then allowed to stir at 130°C in order to carry out the hydrolysis and to distillate out the formed methanol by-product (which distillates along with H2O). Over the course of the distillation, an additional amount of water was progressively added into the reactor in order to compensate water loss through the distillation. After 16h00 stirring at 130°C,1H NMR analysis showed complete conversion of the ester to the acid. In total 304g of water has been added into the reactor and 573g of distillate has been collected. The temperature of the reaction mixture was then cooled down at 80°C and 28.4g of NaOHaq (35 wt%) (2 eq. wrt. H2SO4) were added into the mixture for catalyst neutralization (pH~2.5).

[0109] The solution was then allowed to cool down at room temperature. Diisopropylether (200m L) was then added allowing recrystallization of the triacid product to occur. The solid was then filtered out and washed with diisopropyl ether (3*100mL). The solid was then dried at 50°C to obtain a white solid, Hex-5-ene-1 ,3,5-tricarboxylic acid (HTA).

[0110] 2. Synthesis of polymers:

[0111] Polymers were synthesized in water, at 77°C, with all the monomers added entirely in the initial charge, or with part of the monomers added in the initial charge and part of them fed over 2h, with 2 more hours for curing, according to the Table 1 below.

[0112] Monomer conversions were assessed using1H NMR spectroscopy, indicating complete conversion for acrylic acid (AA), methacrylic acid (MAA), and HTA.

[0113] The final molecular weights were determined by size exclusion chromatography (SEC) coupled with multi-angle light scattering (MALS), results are collected in Table 1 below.

[0114] DIW: deionized water ; V501 : 4,4'-Azobis(4-cyanovaleric acid)

[0115] 3. Performance testing

[0116] The use of polymers to treat metal substrates prior to bonding them with adhesives is described below. 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 standard ASTM D1002-10.

[0117] Step 1- 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) go through each of the following steps:

[0118] • degreasing by immersion for 3mn in a 4L stainless steel bath containing NP Kleen 160 from Quaker (1wt%) heated to 50°C under light stirring,

[0119] • rinsing with tap water (at about 50°C),

[0120] • etching by immersion for 1 mn in a 4L stainless steel containing NP Kleen 190 (1wt%) and Additivo 200 (0.075wt%) heated to 50°C under light stirring,

[0121] • rinsing with tap water (at about 50°C),

[0122] • rinsing with deionized water.

[0123] Step 2- the coupons are then treated by dipping for 2mn in a 4L stainless steel treatment bath, containing the polymer at 50°C and at several concentrations indicated in Table 2 below. They are then rinsed altogether with a flow of deionized water for 1mn and dried for 30mn at 60°C.

[0124] Step 3- the coupons are then bonded with Betamate™ 1496, from DuPont as described in Step 3 of the Examples of patent application WO 2022 / 073879.

[0125] Step 4- tensile strength tests are performed on the assemblies obtained in step 3, as described in Step 4 of the Examples of patent application WO 2022 / 073879. Tensile tests are also done on such assemblies that have been aged using a cyclic test described in Step 5 of the Examples of patent application WO 2022 / 073879.

[0126] The conditions used in step 2 are summarized in Table 2 below.

[0127] Table 2: Conditions used for step 2

[0128] Below are the performances before ageing, after ageing, and the ratio between values after ageing and values before ageing, called “retention” (Tables 3-6):

[0129]

[0130] Table 3: STRAIN measured at maximum load

[0131] Table 4: Maximum LOAD able 5: ENERGY measured at the maximum load

[0132] Table 6: FACIES after tensile test

[0133] (c): cohesive fracture, (~c): rather cohesive fracture, (a): adhesive fracture

[0134] Conclusion All new terpolymers according to the invention provide performances similar to the performances of Addibond™ 021 , a P-based polymeric additive well established on the market.

Claims

CLAIMS1. A polymer comprising the following monomers:(iv) acrylic acid or a salt thereof;(v) methacrylic acid or a salt thereof; and(vi) hex-5-ene-1 ,3,5-tricarboxylic acid (HTA) or a salt thereof.

2. The polymer according to claim 1 , consisting essentially of monomers (i), (ii) and (iii).

3. The polymer according to claim 1 or 2, having the following molar ratio, based on the total quantity of acrylic acid, methacrylic acid and HTA: acrylic acid: from 5 to 95%, notably from 10 to 90%, preferably from 30 to 85% methacrylic acid: from 1 to 50%, preferably from 5 to 40%, more preferably from 10 to 20%HTA: from 1 to 90%, for example from 5 to 50%, notably from 5 to 45%.

4. The use of a composition C comprising at least one polymer according to any of claims 1 to 3, for improving the 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.

5. The use of a composition C comprising at least one polymer according to any of claims 1 to 3, 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.

6. The use according to claim 5, wherein metallic surface (S1 ) is part of the surface of a solid metallic part (1 ) to be bonded to another solid part (2), preferably alsometallic, of which (S2) is part of the surface and wherein surfaces (S1 ) and (S2) are bonded together.

7. The use according to any of claims 4 to 6, wherein metallic surface (S1 ) is 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.

8. A process for bonding a metallic surface (S1 ) with another surface (S2), including: treating all or parts of said metallic surface (S1 ) with a composition C according to claim 4 or 5; and optionally treating all or parts of said second surface (S2) with the composition C; and bonding the surfaces (S1 ) and (S2) via an adhesive layer applied between the two surfaces.

9. A process for bonding a paint or varnish to a metallic surface (S1 ), including:- treating all or part(s) of said metallic surface (S1 ) with a composition according to claim 4 or 5; and- applying a paint or varnish to the surface (S1 ).

10. A metallic surface (S1 ) comprising a polymer according to any of claims 1 to 3 on at least part of it.

Images