Polymers for metal surface treatment

Abstract

The present invention relates to the use of polymers obtained by free radical copolymerization of a mixture of: (1) acrylic acid; (2) methacrylic acid; and (3) at least one allylcatechol selected from 4-allylbenzene-1,2-diol, 3-allylbenzene-1,2-diol; methylated forms thereof (eugenol); and mixtures thereof, for treating metal surfaces intended for adhesive bonding to another surface in order to render the resulting bond resistant to adhesive failure.

Description

[0001] This application claims priority from application No. 20305515.7 filed in Europe on May 19, 2020, the entire contents of which are incorporated herein by reference for all purposes.

[0002] The present invention relates to the field of treatment of metal-based surfaces, and more particularly metal surfaces intended to be coated with adhesive compositions. The invention more particularly relates to the treatment of said metal surfaces intended to provide enhanced adhesion of film-forming organics.

[0003] In order to provide an enhanced adhesion of film-forming organic compositions such as paints, varnishes or adhesives on metal surfaces, in particular on aluminum or steel, several methods have been proposed, including in particular the deposition of inorganic coatings, in particular so-called "conversion coatings", on the metal surfaces.

[0004] The term "conversion coating" is well known in the art and refers to a layer formed on a metal surface which is a favourable alternative to the native oxide on said surface, in particular on aluminium, and which is obtained by controlled chemical formation of a film on the metal surface by reaction with chemical elements of the metal surface, so that at least some of the cations dissolved from the metal material are deposited in the conversion coating.

[0005] Typically, coatings such as conversion coatings are obtained by reacting a metal surface with a solution containing metal cations and fluoride ions. In the past, chromium-containing coatings have been proposed (typically obtained by reacting the surface with a solution containing H2CrF6), and more recently, less toxic coatings based on, for example, zirconium, titanium, or other metals have been proposed (e.g., obtained by reacting the surface with a solution containing H2TiF6, H2ZrF6, H2HfF6, H2AlF6, H2SiF6, H2GeF6, H2SNF4, or HBF4). Conversion coatings may include other compounds, such as, for example, silane precursors.

[0006] In order to enhance the adhesion of coatings such as conversion coatings, it is known to add additives, in particular organic polymers. In this regard, the use of polyacrylic acid has been described, for example. A typical additive is ACUMER available from DOW (and previously from Rohm & Haas). TM 1510, which has been extensively described for this application. For more details on this point, reference may be made to, inter alia, WO 97 / 13588, US 4,191,596 or US 4,921,552.

[0007] An object of the present invention is to provide a new method for treating metal surfaces which imparts good adhesion of a film-forming organic composition or adhesive composition applied to the metal surface.

[0008] To this end, the present invention proposes the use of a specific polymer, optionally (but not necessarily) in conjunction with the formation of a conversion coating (i.e., before, during, or after), resulting in a treated metal surface that exhibits the following: when coated with a film-forming composition (such as a paint, varnish, or adhesive composition), good adhesion is achieved between the surface and the coated composition. In addition, the surface is well protected, especially against corrosion. When a metal surface is coated with an adhesive layer, the coated surface can typically be used to ensure a so-called "adhesive bond" between the coated metal surface and another surface (typically a similar metal surface treated with the same polymer) placed in contact with all or part of the adhesive coating. In this application, the specific polymer used according to the invention allows for resistance to adhesive failure. Within the scope of the present invention, the inventors have now observed that the strength of the adhesion between the adhesive and the metal surface is particularly high, to the extent that, when a sufficiently high mechanical stress is applied to separate the adhesive-bonded surfaces, cohesive failure occurs instead of (or at least more preferably than) adhesive failure.

[0009] Adhesion failure is understood to mean that failure between two surfaces bonded by an adhesive occurs on the surfaces, the adhesive being retained on one surface.

[0010] Cohesive failure is understood to mean that the failure between two surfaces bonded with an adhesive occurs within the adhesive, so that the adhesive is retained on both surfaces.

[0011] Thus, the improvement in the bond between two surfaces treated with the polymers of the present invention and then assembled with an adhesive is reflected by resistance to adhesive failure, meaning that cohesive failure would occur instead, particularly after aging, compared to other existing treatments.

[0012] More precisely, the present invention uses at least one polymer P which is

[0013] Polymers obtained by free radical copolymerization of a mixture of:

[0014] - acrylic acid (AA);

[0015] - methacrylic acid (MAA); and

[0016] - at least one methylated or unmethylated allylcatechol selected from 4-allylbenzene-1,2-diol; 3-allylbenzene-1,2-diol, and mixtures thereof; and the corresponding eugenols.

[0017] The compounds 4-allylbenzene-1,2-diol and 3-allylbenzene-1,2-diol have the following formulae, respectively:

[0018]

[0019] The compounds referred to herein as the "corresponding eugenols" of the 4-allylbenzene-1,2-diol and 3-allylbenzene-1,2-diol are compounds having the formula:

[0020]

[0021] According to a specific embodiment, the polymer P typically contains a mixture of the two isomers 4-allylbenzene-1,2-diol and 3-allylbenzene-1,2-diol as allylcatechol, the mixture typically having a molar ratio of 4-allylbenzene-1,2-diol to 3-allylbenzene-1,2-diol of between 30 / 70 and 70 / 30, for example between 50 / 50 and 70 / 30.

[0022] The polymer P preferably contains acrylic acid (AA) in an amount of 10 to 90 mol%, methacrylic acid (MAA) in an amount of 1 to 90 mol%, for example, 1 to 85 mol%, and allylcatechol in an amount of 1 to 20 mol%, each molar ratio being calculated based on the total amount of AA, MAA, and allylcatechol. The ratio MAA / AA is generally preferably greater than 1 / 1, for example, greater than 2 / 1, and even greater than 3 / 1 or even 4 / 1. Furthermore, the methacrylic acid (MAA) content is advantageously greater than 50%, for example, between 55 and 85 mol%, for example, between 60 and 80 mol%.

[0023] The molecular weight, typically the weight average molecular weight, of the polymer P is typically between 10 and 150 kDa, for example between 15 and 100 kDa.

[0024] According to a specific embodiment, the polymer P contains allylcatechol in an amount of 1 to 5 mol %. In that case, the polymer P generally contains MAA in an amount of up to 90 mol % and has a molecular weight M of 80 kDa or less. w (weight average molecular weight).

[0025] According to another particular embodiment, the polymer P contains allylcatechol in an amount of 5 to 10 mol%. In that case, the polymer P generally contains MAA in an amount of at most 40 mol% and has a molecular weight M of 40 kDa or less. w (weight average molecular weight).

[0026] According to another particular embodiment, the polymer P contains allylcatechol in an amount of 10 to 15 mol%. In that case, the polymer P generally contains MAA in an amount of at most 20 mol% and has a molecular weight M of 30 kDa or less. w (weight average molecular weight).

[0027] According to another particular embodiment, the polymer P contains allylcatechol in an amount of 15 to 20 mol%. In that case, the polymer P generally contains MAA in an amount of at most 10 mol% and has a molecular weight M of 20 kDa or less. w (weight average molecular weight).

[0028] The molecular weight average (typically weight average) is measured by size exclusion chromatography (SEC). Notably, SEC is equipped with a multi-angle laser light scattering (MALLS) Mini Dawn TREOS detector and a concentration detector (RI detector) from Agilent Technologies. The SEC-MALLS system is operated at a flow rate of 1 mL / min on a three-column Varian Aquagel OH mixed H, 8 μm, 3*30 cm, and has the following mobile phase: 85% water, 100 mM NaCl, 25 mM NaH2PO4, 25 mM Na2HPO4-15% methanol. The polymer sample is diluted to 0.5 active wt% in the mobile phase and maintained for at least 4 hours, then filtered in a 0.45 μm microporous filter, and 100 microlitres are injected into the mobile phase stream. Absolute molar mass is obtained, where the dn / dC of poly (acrylic acid) is equal to 0.1875 mL / g.

[0029] A specific object of the present invention is to use at least one polymer P as defined above for treating a first metal surface (S1) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting to the bonding an anti-adhesion failure property. Another advantage of the adhesive bonding obtained according to the present invention is its high corrosion resistance and moisture resistance, which results in a durable adhesive bond. In most cases, the polymer is also used to obtain this additional effect (i.e., further imparting corrosion resistance and moisture resistance to the bonding, in other words, for obtaining very effective and durable adhesion). In other words, the use of at least one polymer P as defined above for treating a first metal surface (S1) intended to be bonded to a second surface (S2) by adhesive bonding and for imparting to the bonding an anti-adhesion failure property also provides very good adhesive bond aging resistance. This characteristic can be measured according to a tensile test on a so-called "single lap shear" (SLS) assembly, as defined in ASTM D-1002 10, performed on a newly bonded SLS assembly, and performed on the SLS assembly after aging in a corrosive atmosphere, a moisture atmosphere, or repeated cycles of a corrosive atmosphere followed by a moisture atmosphere (e.g., ASTM G85 A3). Other tests combine corrosion stress and mechanical stress (e.g., compressive loading), such as Bv 101-07, the Ford durability stress test known as Adhesive Lap Shear Bond or Arizona Proven Ground Exposure (APGE). Notably, adhesive bonding between two surfaces S1 and S2 using the polymer P according to the present invention has been shown to provide a failure phase that maintains greater cohesion after aging.

[0030] Typically (but not necessarily), the second surface (S2) is also a metal surface, which may or may not have the same properties as the first surface (S1). According to an advantageous embodiment, the second surface (S2) is a metal surface also treated with a polymer P having formula (a), usually but not necessarily the same as the polymer P of the first surface (S1).

[0031] More generally, the polymer P used according to the invention is preferably used for treating both surfaces (S1) and (S2) prior to adhesive bonding of the two surfaces, especially when (S2) is a metal surface.

[0032] According to a preferred embodiment, the surface treated according to the invention is rinsed after the treatment with the polymer P. The sought improvement is shown to be even better with a rinsing step after the treatment of the surface (S1) and, if present, the surface (S2) with the polymer P.

[0033] The first metal surface (S1) to be treated is preferably a surface comprising a metal selected from the group consisting of aluminum, steel, zinc, magnesium, titanium, copper and alloys thereof, or a cobalt-nickel alloy. The present invention is particularly interesting for metal surfaces of aluminum or aluminum alloys.

[0034] The second surface (S2) may be a metal or non-metal surface.

[0035] According to an interesting embodiment, the second surface (S2) is a surface comprising a metal advantageously chosen from aluminum, steel, zinc, magnesium, titanium, copper and alloys thereof, or a cobalt-nickel alloy. According to one embodiment, the properties of surfaces (S1) and (S2) are identical, but according to other possible embodiments of the invention, they may also be different. According to an interesting variant, both surfaces (S1) and (S2) are metal surfaces of aluminum or an aluminum alloy.

[0036] According to another possible embodiment, the second surface (S2) is a non-metallic surface, such as a plastic surface (eg based on polyamide, PEEK or ABS); or a composite surface (eg based on CFRP or glass fiber reinforced plastic).

[0037] Regardless of the exact nature of the surfaces (S1) and (S2), according to a possible embodiment, a conversion coating can be applied to the metal surface (S1) by reacting said surface with a conversion composition (in other words, the conversion composition is applied to the metal surface for forming a conversion coating thereon). However, according to the present invention, the use of a conversion coating is not mandatory, and according to a specific embodiment, no conversion coating is applied to the surface (S1). When a conversion composition is used, typically:

[0038] - the conversion composition comprises all or part of the polymer P as an additive; and / or

[0039] - applying a conversion coating to the surface (S1) and then applying all or part of the polymer P to the conversion coating.

[0040] Under the same conditions, the second surface (S2) may also receive a similar conversion coating, especially when the second surface (S2) is a metal surface. However, according to the present invention, the use of a conversion coating is not mandatory, and depending on the specific embodiment, a conversion coating may not be applied to the surface (S2).

[0041] According to another possible embodiment compatible with the previous one, all or part of the polymer P is contained in the adhesive composition applied to the surfaces (S1) and (S2). According to this embodiment, the polymer can typically be introduced into the adhesive composition as a solid powder, said powder comprising the polymer alone or on the surface of a mineral filler (said powder can typically be obtained by spray drying a solution or suspension of the polymer, typically in the presence of a mineral filler).

[0042] According to another aspect, another particular object of the present invention is a method for bonding a first metal surface (S1) to a second surface (S2) (the surfaces preferably being as defined above), the method comprising:

[0043] - treating said first surface (S1) with at least one composition comprising at least one polymer P as defined above (preferably said surface (S1) is cleaned and / or activated before treatment with polymer P); and

[0044] - optionally treating the second surface (S2) with at least one composition comprising at least one polymer P as defined above (preferably said surface (S2) is then cleaned and / or activated before the treatment with the polymer P); and

[0045] - Bonding of these two surfaces (S1) and (S2) by means of an adhesive composition applied between these two surfaces.

[0046] Within that range, the composition comprising polymer P may typically be:

[0047] - a conversion composition comprising a polymer P; and / or

[0048] - a solution or dispersion of the polymer P, which is preferably applied to the surface to be treated after the conversion coating has been applied to the surface; and / or

[0049] - an adhesive composition, which may comprise the polymer P in whole or in part.

[0050] Typically, the polymer P is present in a conversion composition and / or in a solution or dispersion which is applied to the conversion coating. In that case, the adhesive is applied to the surface previously treated with the polymer.

[0051] According to some embodiments, an additional layer is applied between the treated surface (S1) and the adhesive (this is the case, for example, of a metal coil or part being treated in a first location, which then has to be bonded in a second location: in that case, a lubricant can be applied to the treated coil or part in order to protect it during transport and storage, and to facilitate downstream operations (coil cutting into sheets, blanking, stamping, forming, ...).

[0052] According to yet another aspect, a particular object of the present invention is a material comprising two adhesively bonded surfaces comprising a first metal surface comprising a metal surface (S1) which is wholly or partially (i) treated with a polymer P as defined above and (ii) preferably adhesively bonded to a second surface (S2) as defined above.

[0053] These materials include, in particular, materials having a metal surface (S1) which is fully or partially covered by:

[0054] at least one coating (typically a conversion coating and / or a paint, varnish or adhesive layer) comprising at least one polymer P; and / or

[0055] - a layer (typically a conversion coating) comprising a reaction product of a polymer P as defined above with the metal of the treated surface or another compound present in said layer, or a polymer P firmly linked to said other compound (e.g. by complexation, ionic bonds or hydrogen bonds).

[0056] Specific features and possible embodiments will now be described in more detail.

[0057] Metal surface (S1)

[0058] Any metal surface can be treated with the polymer P of the present invention, but the present invention is particularly suitable for treating the metal surfaces of:

[0059] - aluminium or an aluminium-based alloy; or

[0060] - steel, such as galvanized steel (hot-dip galvanized HDG or electrogalvanized EG); or cold rolled steel (CRS); or

[0061] - magnesium or a magnesium-based alloy; or

[0062] - zinc or zinc-based alloys; or

[0063] - Titanium or titanium-based alloys.

[0064] The present invention is of particular interest to metal surfaces of aluminum and aluminum alloys such as the aluminum alloy AA5005 tested in the accompanying examples or other alloys such as those of series 1xxx, 2xxx, 3xxx, 4xxx, 5xxxx, 6xxx, 7xxx (such as AA1050, 2024, 3003, 5182, 5754, 6111, 6016, 6060, 6063, 6182, 7075).

[0065] Optional conversion coating

[0066] When a conversion coating is applied to one or both of the surfaces (S1) and / or (S2), the conversion coating may be obtained by contacting the surfaces with any conversion composition known from the prior art.

[0067] Bringing the metal surface into contact with the conversion composition can be carried out by any means known per se, such as dipping in a conversion bath, or spraying, as illustrative examples.

[0068] The conversion composition used according to the present invention may typically contain fluoride anions and cationic metals, for example compounds such as H2CrF6, or more preferably chromium-free compounds such as H2TiF6, H2ZrF6, H2HfF6, H2AlF6, H2SiF6, H2GeF6, H2SNF4 or HBF4.

[0069] The conversion composition may also contain other compounds, such as, for example, silane precursors, and / or cerium salts, and / or terbium molybdate.

[0070] Furthermore, according to a specific embodiment, the conversion composition may comprise all or part of the polymer P used according to the invention for treating the surface. In that case, the application of the conversion layer itself results in the surface treatment according to the invention.

[0071] In other aspects, the treatment is typically obtained after the conversion layer has been formed by contacting the metal surface carrying the conversion layer with a polymer P (which can typically be applied to the conversion layer in the form of a solution or suspension of the polymer P, or in a paint, varnish or adhesive composition applied to the conversion layer).

[0072] Depending on the specific embodiment, it is conceivable to use the polymer P both in the conversion composition and in the adhesive composition applied to the conversion layer.

[0073] Should the disclosure of any patents, patent applications, and publications incorporated by reference into this application conflict with the description of this application to the extent that a term is unclear, this description shall take precedence.

[0074] The following examples illustrate the invention.

[0075] Example 1

[0076] Synthesis of polymers useful according to the invention

[0077] Poly(AA-stat-MAA-stat-allylcatechol)

[0078] Example 1.1

[0079] Polymer P1 (AA / MAA / allylcatechol=26 / 70 / 04 mol / mol / mol) was prepared as follows:

[0080] To a 500 mL three-necked round-bottom flask were added 4-allylcatechol (5.50 g, 36.6 mmol) with a 60 / 40 molar ratio of 4-allylbenzene-1,2-diol to 3-allylbenzene-1,2-diol, 58.4% acrylic acid (AA) in water (1.47 g, 11.9 mmol), and 5% 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50) in water (74.49 g, 13.7 mmol). After stirring under nitrogen for 20 minutes, the round-bottom flask was placed in a 66°C oil bath. Ten minutes later, two aqueous solutions containing 58.4% AA (13.96 g, 113.1 mmol) and 58.4% methacrylic acid (MAA) (37.79 g, 256.4 mmol) were added dropwise over 2 hours. After completion, two more aqueous solutions with 58.4% AA (13.96 g, 113.1 mmol) and 58.4% MAA (56.68 g, 384.5 mmol) were added dropwise over 4 and 6 hours, respectively. After the final 2 hours of cooking, the round-bottom flask was removed from the oil bath.

[0081] The reaction mixture was analyzed by 1H NMR spectroscopy and size exclusion chromatography.

[0082] Proton nuclear magnetic resonance (1H NMR) spectra were recorded using a Bruker 300 MHz spectrometer. To measure the conversion of AA, MAA, and 4-allylcatechol, four drops of the reaction mixture were diluted in approximately 1 g of deuterated water (D2O). Conversion of AA = 99%; Conversion of MAA = 97%; Conversion of 4-allylcatechol = 91%

[0083] The molar mass was measured by size exclusion chromatography (SEC) equipped with a multi-angle laser light scattering (MALLS) Mini Dawn TREOS detector and an Agilent concentration detector (RI detector). The SEC system was run at a flow rate of 1 mL / min on a three-column Agilent Aquagel OH mixed H, 8 μm, 3*30 cm, with the following mobile phase: H2O 100% vol., 0.1 M NaCl, 25 mM NaH2PO4, 25 mM Na2HPO4 buffer solution (pH 7). The polymer sample was dissolved in the mobile phase at 0.5 wt% for at least 4 hours and then filtered in a microporous filter (0.45 μm). The absolute molar mass was obtained, where dn / dC for poly(acrylic acid) was equal to 0.1875 mL / g. Mw = 33 kg / mol; Mn = 16.5 kg / mol;

[0084] Example 1.2

[0085] Polymer P2 (AA / MAA / allylcatechol = 80 / 12 / 08 mol / mol / mol) was prepared using the same protocol as in Example 1.1, with the differences indicated in Table 1 below. The results were as follows: AA conversion = 96%; MAA conversion = 99.9%; 4-allylcatechol conversion = 81% - Mw = 29 kg / mol; Mn = 14 kg / mol;

[0086]

[0087] *Both feeds started 10 minutes after heating **Both feeds started at the end of feed #1

[0088] Table 1 : Preparation of polymers P1 and P2

[0089] Example 2

[0090] Use of the polymer of Example 1

[0091] The performance of polymers P1 and P2 was evaluated by single lap shear (SLS) testing before and after aging under corrosive conditions. The test specimens were prepared according to the following protocol and assembled to form single lap assemblies as described in D 1002-10.

[0092] Step 1 - 20 specimens (aluminum alloy specimens: AA5754, from FBCG; 100 mm long, 25 mm wide, 3 mm thick) were cleaned and etched together in a single step at 50° C. in a 4 L bath contained in a stainless steel tank. The cleaning and etching were combined. The bath was typically prepared by diluting the commercially available formulation DBT ALU 200 (available from Chemtec Aertec) (5 g of DBT ALU 200 diluted in 995 g of water) under gentle stirring for 3 minutes. The specimens were then rinsed twice with deionized water over a period of 1 minute.

[0093] Step 2 - The specimens were then pretreated by immersing for 2 minutes in a treatment bath containing the polymers at 50°C and at several concentrations indicated in Table 1 below. They were then rinsed together (except for one test indicated in Table 2) with a stream of deionized water for 1 minute and dried at 60°C for 30 minutes.

[0094] Step 3 - The specimens were then assembled in pairs, with each pair forming a so-called single lap shear "assembly": the two specimens were placed horizontally and parallel, one on top of the other, forming an overlap of 12.5 mm long and 25 mm wide (the "overlap area" includes a terminal area of ​​each of the two specimens that is 25 mm wide, i.e., the last 12.5 mm of the 100 mm long specimen). A bead of structural high T curing epoxy adhesive (Betamate 1496, from The Dow Chemical Company) was applied to the overlap area of ​​the lower specimen using a spray gun at 7 bar. The upper specimen was then pressed to form a bonding area of ​​12.5 mm long and 25 mm wide. A paper clip was used to maintain the integrity of the assembly before and during curing. The adhesive was then cured according to the adhesive manufacturer's guidelines, typically at 180°C for 40 minutes. Finally, the paper clip was removed.

[0095] Step 4 - Tensile strength test of the assembly obtained in step 3

[0096] Materials used : Zwick / Roell-Z50, where the jaws grip the assembly tips over 50 mm and the pulling speed is 10 mm / min (each jaw grips one of a pair of bonded specimens over a 50 mm gripping area of ​​each specimen at the end of the specimen opposite the overlap area. The jaws are then moved to pull each specimen horizontally starting from the bond area towards the gripping area).

[0097] Step 5- After aging Tensile strength test II on the component obtained in step 3

[0098] 5.1. Aging cycle test

[0099] Cyclic aging tests were performed in a corrosion chamber Q-FOG CRH 600L (from Q-FOG) according to ASTM G85 Annex 3 (SWAAT, 2011).

[0100] Under the following conditions:

[0101] 30 minutes of acidified salt spray, followed by

[0102] Soak for 90 minutes at relative humidity >98%

[0103] Under the following conditions:

[0104] Room temperature - constant 49°C

[0105] Air saturator temperature - constant 57°C

[0106] Relative humidity -> 98%

[0107] pH of the fall out solution - 2.8-3.0

[0108] Volume of falling solution - 1.0-2.0 ml / 80 cm² / hour

[0109] Exposure period - 1000 hours

[0110] After the exposure period is complete, rinse the components with lukewarm water to remove and neutralize excess acid and any remaining salt residue.

[0111] All components were then air-dried using forced ambient temperature before being subjected to lap shear tensile testing.

[0112] 5.2. Tensile strength test

[0113] Under the conditions of the tensile strength test I in step 4

[0114] The results obtained are reported in Tables 2-4 below (values ​​are averages: 3-4 modules tested before aging, 5 modules tested after aging), with the following changes in step 2:

[0115] Test Number polymer Concentration of polymer in the treatment bath pH Post-treatment rinse steps 1 None (control) - - - 2 P1 1000ppm 2.47 yes 3 P2 1000ppm 2.54 yes 4 P2 1000ppm 2.54 no

[0116] Table 2: Conditions for Step 2

[0117]

[0118] Table 3: Maximum strain

[0119]

[0120] Table 4: Maximum load

[0121]

[0122]

[0123] Table 5: Maximum energy

[0124]

[0125] Table 6: Phase after failure

[0126] (c): Cohesive fracture (~c): Slightly (rather) cohesive fracture

[0127] (a): Adhesion breakage (~a): Slight adhesion breakage

[0128] (a / c): 50% adhesion 50% cohesion

[0129] Example 3

[0130] Comparison of polymers C2 and C3:

[0131] Two comparative polymers were prepared using benzotriazole ethyl methacrylate instead of allyl catechol. The details are given below:

[0132] general formula:

[0133]

[0134] Comparative polymer C2: 4 mol% benzotriazole ethyl methacrylate (BztMA)

[0135] MAA / AA / BztMA=76 / 20 / 4 mol%

[0136] Mw=30 000 g / mol, Mn=15 000 g / mol (same measurement method as described previously).

[0137] Comparative polymer C3: 10 mol% benzotriazole ethyl methacrylate (BztMA)

[0138] MAA / AA / BztMA=67 / 23 / 10mol%

[0139] Mw=30 000 g / mol, Mn=15 000 g / mol (same measurement method as described previously).

[0140] Example 4

[0141] Comparison of the uses of polymers C2 and C3

[0142] The properties were evaluated by single lap shear (SLS) testing before and after aging under corrosive conditions. Test specimens were prepared according to the protocol described in Example 2 and assembled to form SLS assemblies as described in D 1002-10.

[0143] condition

[0144] Step 1: A bath was prepared with Chemtec DBT ALU 200 (5%) and heated to 50° C. The specimen was immersed therein for 3 min and then rinsed in hot water for 1 min and then in deionized water.

[0145] Step 2: Heat the bath to 50°C; adjust the pH with sulfuric acid; immerse the specimen for 2 min, and then rinse with deionized water for 1 min.

[0146]

[0147] Table 7: Conditions for Step 2

[0148]

[0149] Table 8: Strain at maximum load

[0150]

[0151] Table 9: Maximum loads

[0152]

[0153] Table 10: Energy at maximum load

[0154]

[0155] Table 11: Phase after bond failure

[0156] c: cohesive fracture; ~c: slight cohesive fracture; c / a: both cohesive and adhesive fracture; ~a: slight adhesive fracture; a: adhesive fracture.

Claims

1. Use of at least one polymer P for treating a first metal surface (S1) intended to be bonded to a second surface (S2) by adhesive bonding and for rendering the bond resistant to adhesive failure, wherein the second surface (S2) is a metal surface, The treatment of the surface (S1) and, if present, the surface (S2) is followed by a washing step, the polymer P containing acrylic acid (AA) in an amount of 10 to 90 mol %; methacrylic acid (MAA) in an amount of 1 to 90 mol % and allylcatechol in an amount of 1 to 20 mol %, each molar ratio being calculated based on the total amount of AA, MAA and allylcatechol; the at least one polymer P being obtained by free-radical copolymerization of a mixture of -acrylic acid; - methacrylic acid; as well as - at least one methylated or unmethylated allylcatechol selected from 4-allylbenzene-1,2-diol; 3-allylbenzene-1,2-diol; the corresponding eugenol; and mixtures thereof.

2. The use according to claim 1, for further imparting to the bond resistance to corrosive atmospheres and humid atmospheres.

3. The use according to claim 1 or 2, wherein The polymer P contains a mixture of two isomers of allylcatechol, 4-allylbenzene-1,2-diol and 3-allylbenzene-1,2-diol.

4. The use according to claim 1 or 2, wherein The polymer P contains a mixture of the two isomers of allylcatechol, 4-allylbenzene-1,2-diol and 3-allylbenzene-1,2-diol, with a molar ratio of 4-allylbenzene-1,2-diol to 3-allylbenzene-1,2-diol between 30 / 70 and 70 / 30.

5. The use according to claim 1 or 2, wherein The polymer P has a molecular weight between 10 and 150 kDa.

6. The use according to claim 1, wherein The methacrylic acid (MAA) content is greater than 50% by mol.

7. The use according to claim 1, wherein The polymer P has a ratio MAA / MA greater than 1 / 1.

8. The use according to claim 1 or 2, wherein The metal surface is a surface comprising a metal selected from the group consisting of aluminum, steel, zinc, magnesium and alloys thereof.

9. The use according to claim 8, wherein The metal surface is the surface of aluminum or an aluminum alloy.

10. The use according to claim 1 or 2, wherein This polymer P is used to treat both surfaces (S1) and (S2) prior to adhesive bonding of these two surfaces.

11. A method for bonding a first metal surface (S1) to a second surface (S2), the method comprising: - treating said first surface (S1) with at least one composition comprising at least one polymer P as defined in any one of claims 1 to 5; and - optionally treating the second surface (S2) with at least one composition comprising at least one polymer P as claimed in any one of claims 1 to 5; as well as - bonding of the two surfaces (S1) and (S2) by means of an adhesive composition applied between the two surfaces, wherein the second surface (S2) is a metal surface, wherein the treatment of the surface (S1) and, if present, the surface (S2) is followed by a rinsing step, the polymer P containing acrylic acid (AA) in an amount of 10 to 90 mol %; methacrylic acid (MAA) in an amount of 1 to 90 mol % and allylcatechol in an amount of 1 to 20 mol %, each molar ratio being calculated based on the total amount of AA, MAA and allylcatechol.

12. The method according to claim 11, wherein The composition comprising the polymer P is: - a conversion composition comprising a polymer P; and / or - a solution or dispersion of the polymer P; and / or The adhesive composition comprises a polymer P.

13. The method according to claim 12, wherein: The solution or dispersion of the polymer P is applied to the surface to be treated after the conversion coating has been applied to the surface.

14. A material comprising two adhesively bonded surfaces comprising a first metal surface comprising a metal surface (S1) which is wholly or partially (i) treated with a polymer P as defined in any one of claims 1 to 5 and (ii) adhesively bonded to a second surface (S2), and the second surface (S2) being a metal surface, the material being a material having a metal surface which is wholly or partially covered by: - at least one coating comprising at least one polymer P as defined in any one of claims 1 to 5; and / or - a layer comprising a reaction product of a polymer P as defined in any one of claims 1 to 5 with the metal of the treated surface or another compound present in the layer, or a polymer P firmly bonded to said other compound.

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