Process for bonding a metallic surface with another surface

Abstract

The instant invention concerns a process for bonding a metallic surface (S1) with another surface (S2), said process including the treatment of all or parts of said metallic surface (S1) with a composition C comprising at least one polymer P obtained by radical polymerization of a compound of formula I below.

Description

[0001] PROCESS FOR BONDING A METALLIC SURFACE WITH ANOTHER SURFACE

[0002] This application claims priority to the application filed on October 3, 2023 in Europe with Nr 23306694.3, the whole content of this application being incorporated herein by reference for all purposes.

[0003] The instant invention relates to the field of adhesive bonding of metallic surfaces / parts. The invention is more especially directed to a process for bonding a metallic surface (S1 ) with another surface (S2), said process including the treatment of all or parts of said metallic surface (S1 ) with a composition comprising a specific polymer, in particular, in order to impart the resulting bonding with a resistance to the adhesive failure.

[0004] TECHNICAL BACKGROUND

[0005] 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".

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

[0008] 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.

[0009] 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.

[0010] For enhancing the adhesion on a coating, such as a conversion coating, it is known to add some additives, especially organic polymers.

[0011] According to the article “Failure modes of polyurethane / alumimium oxide joints primed with hydrophilic macromolecules”, INT. J. ADHESION AND ADHESIVES VOL.8 NO.2 APRIL 1988, the use of a near-monolayer thickness of poly(itaconic acid) macromolecule primer significantly improves the durability of bonds in polyurethane-aluminium oxide joint systems exposed to hot alkaline solutions. In the experiments presented in this article, the substrates were dipped into the macromolecule aqueous solutions and then dried in an oven to transform the macromolecule from solution to a solid film.

[0012] The Applicant has now found that the adhesion promotion activity of homopolymers of the monomer of formula (I), like those of the itaconic acid type, in primers can be significantly improved if the aqueous solutions have an acidic pH.

[0013] SUMMARY OF THE INVENTION

[0014] One aim of the present invention is to provide a new performing process for improving the bonding between a metallic surface and another surface, preferably metallic as well, through an adhesive layer, both surfaces preferably being part of the surfaces of two solid parts (especially metallic ones) to be bonded together through adhesive bonding.

[0015] It has been discovered that using a composition comprising a specific polymer as coating pretreatment on the metallic surface and at an acidic pH, provides a particularly good adherence between the two surfaces. The process according to the invention allows a resistance to the adhesive failure. 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 the process 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] Although compositions based on polymers P as described below have been proposed in prior art for treating metallic surfaces, their use in adhesive bonding of solid parts, especially metallic ones, has never been disclosed.

[0018] DEFINITIONS

[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.

[0022] As used herein, the term "average" refers to number average unless indicated otherwise.

[0023] 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.

[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. “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.

[0025] “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.

[0026] DETAILED DESCRIPTION OF THE INVENTION

[0027] More precisely, the instant invention is 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 a composition C comprising at least one polymer P obtained by radical polymerization of a compound of formula I below: wherein:

[0028] - 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;

[0029] - R1and R2are, independently from one another, H or the compound of formula (I) is in the form of a salt, with R1and / or R2being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium+NR34, wherein R3are independently from one another H or methyl or ethyl;

[0030] - n is an integer ranging from 1 to 4;

[0031] - m is an integer ranging from 0 to 4;

[0032] - Ra, Rb and Rc are, independently from one another, selected from H, a - COOR4group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, with R4having the same definition as the one of R1and 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. optionally treating all or parts of said second surface (S2) with the composition C ; and bonding the surfaces (S1 ) and (S2) optionally via an adhesive layer applied between the two surfaces, wherein the treatment step with composition C is made at a pH within the range 1 .5- 4.5, preferably in the range 1.5-3.5, even more preferably in the range 2.0-2.8.

[0033] During the treatment step with composition C, the pH is preferably set at the desired value by adding either an organic or a mineral acid, preferably a mineral acid, more preferably sulfuric acid; or by adding a base, preferably a base deriving from Groups 1 and 2 of the periodic table such as sodium hydroxide, potassium hydroxide, sodium carbonate or a an organic base such as ammonia or an amine.

[0034] During the treatment step with composition C, 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.

[0035] One specific object of the instant invention is to provide adhesive bonding and to impart to the bonding a resistance to adhesive failure.

[0036] Preferably, metallic surface (S1 ) is part of the surface of a solid part (1 ) to be bonded to another solid part (2) (preferably metallic as well) 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).

[0037] An additional advantage 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 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).

[0038] In other words, the process of the invention is imparting a resistance to the adhesive failure to the bonding and is also providing a very good resistance to ageing to the adhesive bonding.

[0039] 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.

[0040] In single lap shear tests, the adhesive is applied on a first solid part, and a second solid part is placed on top to form, after the adhesive is cured, an adhesive joint between the two solid parts. The two ends of the resulting assembly 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 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.

[0041] Other tests simultaneously combine a corrosion stress and a mechanical stress. 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.

[0042] The polymer P used according to the invention is a homopolymer, preferably having 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., from 10 to 50 kDa.

[0043] A polymer P especially suitable for the invention is a homopolymer having a weight average molecular weight from 10 to 20 kDa.

[0044] 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, 8 pm, 3*30 cm at a flow rate of 1 mL I 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 4 hours then filtrated in a Millipore filter 0.45 pm and 100 microliters were injected in the mobile phase flow. Absolute molar masses were obtained with the dn / dC of the poly(itaconic acid) equal to 0.155 mL / g. In a preferred embodiment, the composition C according to the present invention, consists essentially of the polymer P. It may be useful according to another preferred embodiment to add to the composition comprising the polymer P, 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,.

[0045] 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.

[0046] Also, R1and R2are, independently from one another, H or the compound of formula (I) is in the form of a salt, with R1and / or R2being selected from the group consisting of alkali metals, alkaline earth metals, and quaternary ammonium+NR34, wherein R3are independently from one another H or Me or Ethyl. Preferably R1and R2are H or the compound of formula I is a salt, with R1and R2being sodium.

[0047] 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 .

[0048] Regarding Ra, Rb and Rc, they are, independently from one another, selected from H, a -COOR4group, an aryl group that may be bearing a sulfonic or sulfonate group or a C1-C4 linear alkyl group that may be bearing a -COOR4group, with R4having the same definition as the one of R1and 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 -COOR4group, 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

[0049] A particularly preferred embodiment corresponds to the composition wherein the compound of formula I in polymer P is itaconic acid or salt thereof, for instance a sodium salt thereof. Hence, in this embodiment, polymer P is a homopolymer of itaconic acid i.e. poly(itaconic acid).

[0050] In other preferred embodiments of the invention, the compound of formula I in polymer P is alpha-methylene glutaric acid (MGA) or a sodium salt thereof, or hex-5-ene-1 ,3,5-tricarboxylic acid (HTA) or sodium salt thereof.

[0051] Besides, the Applicants believe that homopolymers of HTA have never been described or synthesized. Hence in another aspect, the present invention relates to homopolymers of hex-5-ene-1 ,3,5-tricarboxylic acid (HTA), and their synthesis and uses as described therein. The Applicants found out that, even if the monomer is more hindered compared to other monomers such as MGA, it can be successfully homopolymerized in certain conditions, especially with a partial neutralization of the carboxylic acid groups and an adequate introduction of initiators during the polymerization, reaching conversions above 80% at high solid contents.

[0052] 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.

[0053] The invention is especially suitable for treating metal surfaces of:

[0054] - Aluminum or an aluminum-based alloy ; or

[0055] - Steel, for example galvanized steel (electrogalvanized, EG, hot dip galvanized, HDG, containing up to about 0.2wt% 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 ; or

[0056] - Magnesium or magnesium-based alloys ; or

[0057] - Zinc or zinc-based alloys ; or

[0058] - Titanium or titanium-based alloys.

[0059] 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.

[0060] As for the other surface (S2) it may be a metallic surface as well, identical or different from the metallic surface (S1 ), preferably identical.

[0061] 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.

[0062] According to an advantageous embodiment, the second surface (S2) is a metallic surface also treated with a composition C as described above, generally but not necessarily identical to the composition C used on the first surface (S1 ).

[0063] According to an interesting variant, both surfaces (S1 ) and (S2) are metallic surfaces of aluminum or aluminum alloys.

[0064] More generally, the composition C 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.

[0065] The surface (S1 ) and / or (S2) are preferably cleaned and / or activated before the treatment with the composition C. Most typical processes include an alkaline degreasing step followed by an acidic etching step. It is namely so that especially in case of metal surfaces, an oil may be present thereon. The type of oil present on the substrate and the metal top surface morphology and composition depend on the substrates and its manufacturing process. For example, the presence of a mechanically damaged layer with rolling oil inclusions is well known for aluminum sheets. In this case, the degreasing step aims at removing most of the oil and removing surface oxides as well, while the acidic step mostly aims at removing intermetallic particles.

[0066] 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.

[0067] 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:

[0068] - the conversion composition includes all or part of the composition C of the invention as an additive ; and / or

[0069] - 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.

[0070] 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).

[0071] 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 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, ...

[0072] 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.

[0073] 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 AI3+ 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.

[0074] The conversion composition used according to this embodiment of 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.

[0075] The invention also concerns the use of the above described process for promoting the adhesion of coatings, inks and paints (e.g., water-borne paints and powder paints). This means that the surface (S2) in the process of the invention may be a coating, ink or paint, including for example water-borne paints and powder paints. In this case, no adhesive is required between both surfaces (S1 ) and (S2).

[0076] 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.

[0077] Powder paints / coatings are typically applied electrostatically as a free- flowing, dry powder and then cured under heat or with ultraviolet light.

[0078] 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.

[0079] The following examples illustrate some preferred embodiments of the invention. EXPERIMENTAL PART:

[0080] FIRST EXPERIMENTAL CAMPAIGN

[0081] 1. Polymer synthesis and characterization:

[0082] Polymer 1 : homopolymer of itaconic acid

[0083] 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 t-BHP (0.008 moles for 0.769 moles 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 by1H 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.

[0084] Table 1: lA-homopolymer used for the test

[0085] 2. Performance tests: Bond Durability Stress test

[0086] The Bond Durability Stress test aims at evaluating the relative performance of adhesively bonded joints exposed to simultaneous tensile load (2,400N 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. 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

[0087] Step 1- alkaline degreasing:

[0088] Immersion for 3 min 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

[0089] Step 3- Acidic etching:

[0090] Immersion for 3 min in a bath made with l%w 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

[0091] Step 5- surface treatment: Immersion in the conversion bath for 2 min at 50°C

[0092] Step 6- Rinsing with then RT DIW

[0093] Step 7- Drying first with compressed air and then in an oven (30' @ 60°C or 5' at 80°C)

[0094] The sheets for test A 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 2 below.

[0095] Table 2: Conditions for the preparation of the tests sheets b) Production of coupons, assemblies and tubes:

[0096] 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 30' 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:

[0097] Each tube is exposed to a corrosive environment for several cycles.

[0098] One cycle corresponds to:

[0099] - 15 min-immersion in a salt solution

[0100] - 105 min vertical drip drying in ambient air

[0101] - 22h exposure to humidity / temperature (cabinet) at 90%RH, 50°C.

[0102] Each tube is carefully inspected after each cycle:

[0103] - the number of intact adhesive joints is counted ;

[0104] - any adhesive joint which failed is replaced by a new assembly whose coupons are bolted together, not adhesively bonded

[0105] - the load is readjusted to 2,400N if needed.

[0106] The more cycles are passed with the less failures, the better the surface treatment.

[0107] Number of adhesive joints that remain intact:

[0108] Table 3: adhesive bonding test results

[0109] SECOND EXPERIMENTAL CAMPAIGN

[0110] Polymers synthesis and characterization: Polymer 2: homopolymer of MGA

[0111] The polymer was prepared by polymerization in water solution, initiated with hydroperoxide at 100°C. In a reactor, 101.90 grams of methylene glutaric acid (MGA, 86% purity) and 50.90 grams of water are added. 50% of the MGA was then deprotonated with sodium hydroxide while maintaining a temperature below 40°C. The temperature of the thermostatic bath was set to 100°C. 0.85 grams of a 70% tBHP solution are added. The polymerization was carried out at 100°C for 6 hours. A conversion of 99% of MGA was determined at the end of the polymerization by 1 H NMR. The molecular weight was determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector. Results are reported Table 4.

[0112] Polymer 3: homopolymer of HTA

[0113] The polymer was prepared by polymerization in water solution, initiated with hydroperoxide at 100°C. In a reactor, 25 grams of HTA monomer were added. The monomer was then neutralized with 30.84 grams of a 30% sodium hydroxide solution. In parallel, 5.73 grams of an 8% aqueous solution of tBHP were prepared. The polymerization was carried out at 100°C for 8 hours with an initial addition of 1.43 grams of the tBHP solution. Then, 3 additional additions of the tBHP solution were made every 2 hours, followed by a 2h-curing. A conversion of 81 % of HTA was determined by 1 H NMR. The molecular weight was determined by size exclusion chromatography (SEC) coupled with a Rl and a multi-angle light scattering diffusion (MALLS) detector. Results are reported Table 4. Table 4: MGA and HTA homopolymers used for the test

[0114] 2. Performance tests:

[0115] 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 D1002-10.

[0116] Step 1 -

[0117] 20 coupons (aluminum alloy coupons: AA5754, from FBCG; 100mm long, 25mm wide, 3mm thick) went 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 were 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 the Table 1 below. They were then rinsed altogether with a flow of deionized water for 1 mn and dried for 30mn at 60°C.

[0124] Step 3- the coupons were 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 7-bar 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 40mn at 180°C. Finally, paper clips are removed.

[0125] Step 4- tensile strength test on assemblies as obtained in step 3 eventually after ageing in a cyclic test as described below.

[0126] Tensile strength test

[0127] Used material: Zwick / Roell - Z50, with jaws grasping assembly tips over 2.50cm. The upper jaw is then moved upwards at 10mm / mn till the joint breaks.

[0128] Ageing cyclic test

[0129] 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:

[0130] • a 30-m inute acidified salt fog spray followed by

[0131] • a 90-m inute soak at >98% relative humidity under the following conditions:

[0132] • Chamber temperature - constant 49°C

[0133] • Air saturator temperature - constant 57°C

[0134] • Relative humidity - >98%

[0135] • pH of fall out solution - 2.8 - 3.0

[0136] • Volume of fall out solution - 1 .0 - 2.0 ml / 80cm2 / hour

[0137] • Exposure period - 1000 hours

[0138] After the exposure period is completed, the assemblies are washed down with lukewarm 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. The conditions used in step 2 are summarized Table 5 below.

[0139] Table 5: Conditions used for step 2

[0140] Below are performances before ageing, after ageing, and the ratio between values after ageing and values before ageing, called “retention” (Tables 6-9):

[0141] Table 6: STRAIN measured at maximum load

[0142] Table 7: Maximum LOAD

[0143] Table 8: ENERGY measured at the maximum load

[0144] Table 9: FACIES after tensile test

[0145] (c): cohesive fracture

[0146] (~c): rather cohesive fracture

[0147] (a): adhesive fracture

[0148] Compared to the controls, the polymers according to the invention make the adhesive bond resist better to ageing and improve the cohesivity fractures, approaching or equaling performances of Addibond™ 021 , a polymer well known for the adhesive bonding of aluminum substrates, but containing phosphorous.

Claims

CLAIMS1. 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 comprising at least one polymer P obtained by radical polymerization of a 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 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 -COOR4group, 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;- optionally treating all or parts of said second surface (S2) with the composition C ; and- bonding the surfaces (S1 ) and (S2) optionally via an adhesive layer applied between the two surfaces, wherein the treatment step with composition C is made at a pH in the range 1 .5 - 4.5, preferably in the range 1 .5 - 3.5, more preferably in the range 2.0 - 2.8.

2. The process according to claim 1 , wherein during the treatment step with composition C, the pH is set at the desired value by adding either an organic or a mineral acid, preferably a mineral acid, more preferably sulfuric acid; or by adding a base, preferably a base deriving from Groups 1 and 2 of the periodic table such as sodium hydroxide, potassium hydroxide, sodium carbonate or a an organic base such as ammonia or an amine.

3. The process according to claim 1 or 2, for imparting to the bonding a resistance to adhesive failure.

4. The process according to any one of claims 1 to 3, for imparting to the bonding a resistance to corrosive atmospheres and to wet atmospheres.

5. The process according to any one of claims 1 to 4, wherein the polymer P is a homopolymer preferably having a molecular weight of from 5.5 to 75 kDa, more preferably from 10 to 50 kDa, even more preferably from about 10 to 20 kDa.

6. The process according to any one of claims 1 to 5, wherein the composition C consists essentially of the polymer P.

7. The process according to any one of claims 1 to 6, wherein polymer P is a homopolymer of itaconic acid i.e. poly(itaconic acid), or a homopolymer of alpha-methylene glutaric acid (MGA) or a sodium salt thereof, or a homopolymer of hex-5-ene-1 ,3,5-tricarboxylic acid (HTA) or sodium salt thereof..

8. The process according to any one of claims 1 to 7, wherein the metallic surface (S1 ) is a surface comprising a metal selected from aluminum, steel, zinc, magnesium, titanium, copper and their alloys, or cobaltnickel alloys, preferably a surface of aluminum or aluminum alloy.

9. The process according to any one of claims 1 to 8, wherein surface (S2) it a metallic surface as well, identical or different from the metallic surface (S1 ), preferably identical.

10. The process according to any one of claims 1 to 9, wherein composition C is used for treating both surfaces (S1 ) and (S2) before bonding the two surfaces through an adhesive layer.

11. The process according to any one of claims 1 to 10, wherein the surface (S1 ) and / or (S2) are cleaned and / or activated before the treatment with the composition C.

12. The process according to any one of claims 1 to 8, wherein surface (S2) is a coating, ink or paint, including for example water-borne paints and powder paints, and wherein no adhesive is used between both surfaces (S1 ) and (S2).

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