Self-crosslinking resin for coating a metallic substrate

Abstract

The present invention relates to a metal coil coated with a coating obtained by crosslinking a coating composition based on a self-crosslinking resin formed by copolymerization of specific acrylic monomers. It also relates to a self-crosslinking resin formed by copolymerization of specific acrylic monomers, as well as a coating composition comprising this resin and a solvent.

Description

Title of the invention: Self-crosslinking resin for coating a metallic substrate. OBJECT OF THE INVENTION

[0001] The present invention relates to a metal coil coated with a coating obtained by crosslinking a coating composition based on a self-crosslinking resin formed by copolymerization of specific acrylic monomers. It also relates to a self-crosslinking resin formed by copolymerization of specific acrylic monomers, as well as a coating composition comprising this resin and one or more solvents. BACKGROUND OF THE INVENTION

[0002] Coil coating, also called pre-coating of metal coils or "coil coating," is an industrial technique that allows for the uniform and controlled application of one or more coating layers (pre-coating and / or topcoats) onto a metal substrate (particularly steel or aluminum) unwound from a coil. This process is carried out at high speeds on continuous production lines, reaching speeds of several hundred meters per minute. Coils of a metal substrate, after being rolled, are first unwound and stretched at a constant speed to form strips. These strips are then coated, baked, and rewound. This technique offers productivity gains compared to spraying or immersion processes, which are slower and often less precise.The resulting products offer enhanced performance in various fields, such as construction (facade panels, roofing, cladding), automotive (bodywork components or protected internal parts), household appliances, and packaging.

[0003] Coatings for metal coils must meet stringent performance and durability requirements. They must therefore be able to accommodate the deformation of the metal during bending without cracking or peeling, which translates, for example, into the lowest possible "T-bend" value (T-bend flexibility test), as measured according to ISO 17132:2007. They must also exhibit good resistance to interlocking, i.e., the adhesion of the wound layers to one another. Furthermore, like any coating, they must exhibit good adhesion to the metal substrate, as well as good resistance to solvents and UV radiation, and optical properties (gloss, color fastness) that meet customer specifications.

[0004] Coating formulations intended for application on metallic substrates, particularly on metal coils, typically contain a binder dispersed in water or a solvent, as well as pigments and various additives. This binder may, in particular, be a two-component binder composed of a polyester, such as the Synolac® 9605 S65 resin marketed by the Applicant, and a crosslinking agent such as hexamethoxymethylmelamine (HMMM), a blocked isocyanate, or an epoxy resin. Alternatively, it may be an acrylic copolymer, used in a mixture with a fluorinated polymer and / or a functionalized polyester (DE2260377; CN101177515), or in the form of an interpenetrating polymer network formed from this acrylic copolymer and a functionalized polyester (US-3,607,802).

[0005] Although these binders are generally satisfactory, it would be desirable to have self-crosslinking binders, i.e. available in the form of a single-component system (i.e. a binder based on a single resin, said binder not including an external crosslinking agent capable of reacting with the resin), in order to facilitate their implementation on an industrial scale.

[0006] In this context, it has already been suggested to use a self-crosslinking binder based on acrylic copolymer in the coating of metal surfaces (US-5,618,586; EP0488605), in particular metal coils (DE2208255).

[0007] There remains, however, the need to have a coating composition for a metallic substrate, in particular a metallic coil, which includes a self-crosslinking binder and gives the coating improved mechanical and / or optical properties compared to prior art compositions.

[0008] After intense research, the Applicant has developed a coating composition that meets the above requirement. Summary of the invention

[0009] The invention relates to a metal coil coated with a coating obtained by crosslinking a coating composition based on a self-crosslinking resin formed by copolymerization of monomers comprising or consisting of: a. at least one compound selected from an N-(Ci-C4-hydroxyalkyl) (meth)acrylamide and its ethers with a Ci-C8-alkanol, b. at least one Ci-Ci2-alkyl (meth)acrylate, c. optionally, at least one (meth)acrylic acid, d. 0 to 1% by weight of at least one C2-C4-hydroxyalkyl (meth)acrylate, relative to the total weight of the resin monomers, e. optionally, at least one styrenic monomer, and f. possibly, at least one (meth)acrylamide,

[0010] said coating composition being devoid of functionalized polymer other than the self-crosslinking resin.

[0011] It also relates to a self-crosslinking resin formed by copolymerization of monomers comprising or consisting of: a. at least one compound selected from an N-(CrC4-hydroxyalkyl) (meth)acrylamide and its ethers with a Ci-C8-alkanol, b. at least one Ci-Ci2-alkyl (meth)acrylate, c. possibly, at least one (meth)acrylic acid, d. 0 to 1% by weight of at least one C2-C4-hydroxyalkyl (meth)acrylate, e. 0 to 5% by weight of styrenic monomer, f. possibly, at least one (meth)acrylamide,

[0012] said percentages being expressed in relation to the total weight of the monomers of the resin.

[0013] Another object of the invention relates to the use of a self-crosslinking resin as defined above in the manufacture of a metallic substrate coating, in particular by coating metallic coils.

[0014] The invention further relates to a coating composition comprising the aforementioned resin and at least one solvent selected from: water, organic solvents and their mixtures.

[0015] The invention also relates to a method of coating a metallic substrate, comprising the application on said substrate, possibly coated with a primer layer, of this coating composition, in particular by coating metallic coils. DETAILED DESCRIPTION

[0016] In the remainder of this description, the expression "between" is understood to mean a range of values ​​including the bounds mentioned.

[0017] The invention relates to a metal coil coated with a coating obtained by crosslinking a coating composition based on a particular self-crosslinking resin.

[0018] By "metal coil" is meant a metal strip wound on itself such as those used in "coil coating" processes and which generally has a width of at least one meter.

[0019] By “self-crosslinking resin” is meant a polymer capable of forming intramolecular bonds when subjected to a heating step, in the presence or absence of a catalyst but in the absence of any external crosslinking agent.

[0020] By “external crosslinking agent” is meant a compound other than the self-crosslinking resin capable of reacting with the functional groups present on the self- crosslinking. Examples of external crosslinking agents are polyisocyanates, blocked polyisocyanates, melamines or aminoplast resins such as 1' hexamethoxy methylimelamine (HMMM).

[0021] The self-crosslinking resin can in particular be functionalized by N-(C i-C4-hydroxyalkyl) (meth)acrylamide groups, allowing the formation of ether bridges between the polymer chains according to the following reaction:

[0022] [Chem.l] O 0 OO ^-0. - II II R' R! R' R'

[0023] in which

[0024] each R and R' is independently chosen from H and an alkyl in CrC8;

[0025] each Alk is independently chosen from a Ci-C4 alkylene. Self-crosslinking resin

[0026] The self-crosslinking resin used according to the invention is formed by copolymerization of monomers comprising or consisting of: a. at least one compound selected from an N-(Ci-C4-hydroxyalkyl) (meth)acrylamide and its ethers with a Ci-C8-alkanol, b. at least one Ci-Ci2-alkyl (meth)acrylate, c. possibly, at least one (meth)acrylic acid, d. 0 to 1% by weight of at least one C2-C4-hydroxyalkyl (meth)acrylate, relative to the total weight of monomers in the resin, e. possibly at least one styrenic monomer, and f. possibly, at least one (meth)acrylamide.

[0027] The self-crosslinking resin is formed by copolymerization of components (a) to (f). Thus, the self-crosslinking resin can be formed from a polymerizable composition comprising components (a) to (f). In other words, the self-crosslinking resin comprises polymerized units from components (a) to (f).

[0028] Component (a) advantageously represents from 2 to 20% by weight, preferably from 3 to 15% by weight, more preferably from 5 to 12% by weight, relative to the total weight of the monomers of the resin. In some embodiments, component (a) represents from 4 to 20% by weight, preferably from 4 to 15% by weight, relative to the total weight of the monomers of the resin. It comprises or is composed of at least one compound selected from an N-(Ci-C4-hydroxyalkyl) (meth)acrylamide and its ethers with a CrC8-alkanol and may thus be selected in particular from N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-(2-hydroxypropyl) (meth)acrylamide and their mixtures. It is preferred that component (a) comprise at least one compound selected from N-methylol acrylamide (NMA), N-butoxymethyl acrylamide (NBMA) and their mixtures.

[0029] Constituent (b) comprises or is composed of at least one Ci-Ci2-alkyl (meth)acrylate. The alkyl group may be selected from linear Ci-C12 alkyls, branched C3-Ci2 alkyls, and cyclic C4-Ci2 alkyls. Examples of such compounds include: methyl (meth)acrylate; ethyl (meth)acrylate; n-propyl (meth)acrylate; n-butyl (meth)acrylate; isobutyl (meth)acrylate; t-butyl (meth)acrylate; amyl (meth)acrylate; isoamyl (meth)acrylate; n-hexyl (meth)acrylate; 2-ethylhexyl (meth)acrylate; n-octyl (meth)acrylate; isooctyl (meth)acrylate; 2-octyl (meth)acrylate; n-nonyl (meth)acrylate; Isononyl (meth)acrylate; n-Decyl (meth)acrylate; Isodecyl (meth)acrylate; 2-Propylheptyl (meth)acrylate; n-Dodecyl (meth)acrylate; Isobomyl (meth)acrylate; Cyclohexyl (meth)acrylate; 3,3,5-Trimethylcyclohexyl (meth)acrylate;tert-butylcyclohexyl (meth)acrylate; cyclic trimethylolpropane (meth)acrylate; dicyclopentadienyl (meth)acrylate; tetrahydrofurfuryl (meth)acrylate; (2,2-dimethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate; (2-ethyl-2-methyl-1,3-dioxolan-4-yl)methyl (meth)acrylate; and mixtures thereof.

[0030] Constituent (b) advantageously represents 60 to 95% by weight, preferably 65 to 92% by weight, relative to the total weight of the monomers of the resin.

[0031] The monomers constituting the resin may further comprise a constituent (c) selected from acrylic acid, methacrylic acid and mixtures thereof. Constituent (c) advantageously represents from 0.5 to 4% by weight, preferably from 0.7 to 2%, and more preferably from 0.8 to 1.5% by weight, relative to the total weight of the monomers in the resin.

[0032] Alternatively or in addition, the monomers constituting the resin may include a component (d) comprising or consisting of at least one C2-C4-hydroxyalkyl (meth)acrylate, representing at most 1% by weight, relative to the total weight of the monomers of the resin. Hydroxyalkyl (meth)acrylates include, in particular: 2-hydroxyethyl (meth)acrylate; 2-hydroxypropyl (meth)acrylate; 3-hydroxypropyl (meth)acrylate; 4-hydroxybutyl (meth)acrylate; and mixtures thereof.

[0033] Component (d) advantageously represents 0 to 1.5% by weight, preferably 0 to 1%, and more preferably 0 to 0.5% by weight, relative to the total weight of the monomers in the resin. In a preferred embodiment of the invention, component (d) is absent.

[0034] Alternatively or in addition, the monomers constituting the resin may include a constituent (e) comprising or consisting of at least one styrenic monomer. As used herein, the term "styrenic monomer" refers to a monomer that contains a carbon-carbon double bond in the alpha position relative to an aromatic ring. The styrene monomer may be selected from styrene, alpha-methylstyrene, tert-butylstyrene, ortho-, meta- or para-methylstyrene, ortho-, meta- or para-ethylstyrene, ro-methyl-p-isopropylstyrene, p-chlorostyrene, p-bromostyrene, o,p-dichlorostyrene, o,p-dibromostyrene, ortho-, meta- or para-methoxystyrenes, indenes possibly substituted, vinylnaphthalenes possibly substituted (for example, by at least one group selected from halogen, hydroxyl, alkyl and alkoxy), acenaphthylene, diphenylethylene, vinylanthracene and mixtures thereof. Styrene is preferred.

[0035] The constituent (e) advantageously represents from 0 to 30% by weight, for example from 0 to 5% by weight or from 20 to 30% by weight, relative to the total weight of the monomers in the resin. In a preferred embodiment of the invention, the constituent (e) is absent.

[0036] Alternatively or in addition, the monomers constituting the resin may include a component (f) comprising or consisting of acrylamide, methacrylamide, and mixtures thereof. Component (f) may, in particular, represent from 0 to 5% by weight, and preferably from 0.5 to 2% by weight, relative to the total weight of the monomers in the resin.

[0037] Alternatively or in addition, the monomers constituting the resin may include a component (g) comprising or consisting of a monomer other than monomers (a), (b), (c), (d), (e) and (f). Component (g) may, in particular, represent from 0 to 10% by weight, and preferably from 0 to 5% by weight, relative to the total weight of the monomers in the resin.

[0038] The total weight of the monomers(a), (b), (c), (d), (e), (f) and (g) may in particular represent 100% of the total weight of the monomers constituting the resin.

[0039] The self-crosslinking resin can be prepared by radical polymerization of the monomers described above, according to a solution, suspension, emulsion, or microemulsion polymerization process. Preferably, the self-crosslinking resin is prepared by solution polymerization. The copolymerization reaction is generally carried out in the presence of a radical initiator.

[0040] The radical initiator may, in particular, be a peroxide. For example, it may be hydrogen peroxide; a t-alkyl peroxyester, such as tert-butyl peroxypivalate (or TBPPI), tert-amyl peroxypivalate, tert-amyl peroxyacetate, or tert-butyl peroctoate; a peroxydicarbonate, such as bis(4-tert-butyl cyclohexyl) peroxydicarbonate; an alkali metal persulfate, percarbonate, or perborate, such as sodium or potassium persulfate; ammonium persulfate; benzoyl peroxide and its derivatives; a diacyl peroxide, such as dilauroyl peroxide and disuccinoyl peroxide; a tert-alkyl hydroperoxide such as tert-butyl hydroxyperoxide; an alkyl peroxide such as dimethyl peroxide, diethyl peroxide, dioctadecyl peroxide, a tert-alkyl peroxide such as tert-butyl peroxide; a tert-alkyl peroxyalkane such as 2,5-bis(tert-butylperoxy)-2,5-dimethylhexane; and mixtures thereof.

[0041] The radical initiator may, in particular, be a redox system comprising a peroxide as described above and a reducing agent such as a ferrous compound, a carboxylic acid, and / or sodium metabisulfite. The use of a reducing agent notably accelerates the decomposition of the peroxide.

[0042] Alternatively, the radical initiator may be an azo compound such as 2,2'-azobisisobutyronitrile, 4,4'-azobis (4-cyanovaleric acid) or 2,2'-azobis (2-methylbutyronitrile).

[0043] Preferably, the radical initiator is a peroxide, more preferably tert-butyl peroxide.

[0044] The radical initiator may in particular represent from 0 to 5%, in particular from 0.1 to 2%, more particularly from 0.2 to 1% by weight, relative to the weight of the monomers.

[0045] To form the self-crosslinking resin used according to the invention, the monomers are generally introduced over a period of one to five hours into one or more solvents, heated under reflux, for example at 80-125°C, optionally under an inert atmosphere, either separately or in a mixture with at least a fraction of any radical initiator and any additives. The polymerization reaction can be continued for two to eight hours to obtain the self-crosslinking resin according to the invention.

[0046] The solvent may be chosen from water, organic solvents, and mixtures thereof. Examples of organic solvents include ketones such as methyl ethyl ketone (MEK); esters of alcohols or polyols, such as butyl acetate, propylene glycol acetate, and hexyl acetate; alcohols such as ethanol and n-butanol; ethers, such as glycol ethers, particularly propylene glycol monopropyl ether; aromatic hydrocarbons, particularly in the form of Cl0-Ci2; and mixtures thereof. Preferably, a mixture of alcohols and / or glycol ethers with at least one aromatic hydrocarbon is used.

[0047] In particular, the following may be used as additives: chain limiting agents, in particular alkyl mercaptans such as dodecyl mercaptan, tert-dodecyl mercaptan, iso-octyl 3-mercaptopropionate, iso-octyl mercaptoacetate and 2-ethylhexyl thioglycolate; anionic or non-ionic surfactants; colloids (stabilizers); and mixtures thereof. Coating composition

[0048] The self-crosslinking resin described above is used as a binder to form a coating composition, in particular for coating metal coils.

[0049] The coating composition comprises the self-crosslinking resin described above. It is free of any functionalized polymer other than the self-crosslinking resin according to the invention, in particular free of any polymer functionalized by an OH, COOH, amino, and / or F group, such as a fluorinated polymer (e.g., PVF or PVDF), a functionalized acrylic polymer, or a functionalized polyester. Preferably, the coating composition is free of any polymer other than the self-crosslinking resin according to the invention. A polymer may, in particular, have a number-average molecular weight greater than 500 g / mol, preferably greater than 750 g / mol, and preferably greater than 1000 g / mol, as measured by size-exclusion chromatography in THF in polystyrene equivalents.

[0050] In addition, the coating composition is preferably also free of external crosslinking agent, such as a polyisocyanate, a blocked polyisocyanate, a melamine or an aminoplast resin, or more generally monomeric compounds functionalized by a COOH, OH, SH, F, NCO, amino, epoxy and / or acrylamide group, provided that their sole function is not to solubilize the self-crosslinking resin.

[0051] For the purposes of the present invention, "a composition devoid of X" means a composition comprising less than 0.5%, preferably less than 0.2%, more preferably less than 0.1%, more preferably still less than 0.01%, by weight of X relative to the weight of the composition.

[0052] The coating composition may in particular be a paint composition.

[0053] The coating composition may in particular include at least one solvent chosen from: water, organic solvents and their mixtures. Examples of suitable organic solvents are as described above.

[0054] The coating composition may include one or more additives.

[0055] These additives can for example be chosen from the following compounds: antioxidants, photostabilizers, light absorbers, polymerization inhibitors, antifoaming agents, antistatic agents, leveling agents, dispersants (wetting agents, surfactants), sliding agents, adhesion promoters, lubricants, pigments, dyes, fillers, rheological agents (thixotropic, thickening), mattifying agents, opacifying agents, impact resistance agents, waxes, and mixtures thereof.

[0056] It is preferred that the coating composition comprise one or more pigments, which may represent from 5 to 30% by weight, more preferably from 10 to 25% by weight, relative to the total weight of the composition. The pigments may in particular be chosen from inorganic pigments, especially metal oxides. such as titanium dioxide; organic pigments, such as azo pigments, phthalocyanines and quinacridones; and mixtures thereof. Method for coating a metallic substrate

[0057] The coating composition described above can be applied to a metallic substrate, in particular to a metallic coil, in order to give it different properties.

[0058] The metallic substrate may comprise or be made of stainless steel, aluminum, or copper. In particular, it may be steel coated with a layer of metal on one or both of its faces, notably galvanized steel or steel coated with a zinc alloy containing aluminum, magnesium, and / or silicon, or an aluminum alloy containing silicon and iron.

[0059] The application to the substrate can be carried out by any means known to those skilled in the art. In a preferred embodiment of the invention, a coil coating process is used. Such a process comprises the steps of: - unwind a metal substrate plate wound in coil form, - subject said plate to one or more chemical pretreatment processes, including degreasing said plate, washing, rinsing, subjecting it to a passivation process with chromium or with titanium and / or zirconium fluoride, and drying it, - apply a coat of primer to the pre-treated plate, - crosslink and then cool said primer layer, - Apply a topcoat over the primer coat, - cross-link and then cool the topcoat. - roll up the coated plate thus obtained into a coil.

[0060] This process is typically carried out continuously on a production line fed by a single reel comprising a metal strip wound upon itself, or by several reels whose strips are connected to one another. The reels generally have a width of between 1 m and 1.8 m, preferably from 1 m to 1.5 m, and the strip typically has a thickness of 0.17 to 3 mm, preferably from 0.3 to 1.5 mm.

[0061] In this process, the coating composition according to the invention can constitute the primer coat and / or the topcoat. It is preferred that it constitute the topcoat. In this case, the primer coat generally contains a binder based on epoxy, polyester, acrylic, or polyurethane resin. In all cases, the primer coat can have a thickness of 1 to 20 µm, preferably 1 to 10 µm, more preferably 1 to 5 µm. The topcoat, for its part, can have a thickness of 20 to 300 µm, preferably 100 to 200 µm. The process can furthermore understanding the application of one or more adhesive layers, directly onto the metallic substrate and / or onto the primer layer.

[0062] The application of the primer coat and the topcoat can be carried out by any means and in particular by means of a roller, curtain or knife applicator, by means of a spiral filmograph or by spraying.

[0063] The self-crosslinking resin present in the coating composition can in particular be crosslinked by application of heat.

[0064] At the end of the process, a coated coil is obtained which can be transported to its site of use, where it can be slit into thinner coils or cut into strips, before being shaped, for example by cold bending.

[0065] The coated coil according to the invention can be used in the manufacture of construction panels (facade, roof or wall elements), furniture, household appliances, beverage cans, parts for the automotive industry (fuel tanks, bodywork), etc. EXAMPLES

[0066] The invention will be better understood in the light of the following examples, which are given purely for illustrative purposes and are not intended to limit the scope of the invention, as defined by the attached claims.

[0067] Example 1: Preparation of acrylic resins

[0068] Different acrylic resins RI to R7 were prepared in the following manner, from the constituents described in Table 1 below.

[0069] A mixture of organic solvents, consisting of a C10-C12 aromatic hydrocarbon marketed by EXXONMOBIL CHEMICAL under the name Solvesso 150ND and n-butanol, was loaded into a Dean Stark flask and heated under nitrogen reflux (120-125°C). A mixture of monomers (b), (c), and (e) and a portion of the radical initiator, as well as component (a) solubilized in n-butanol, were added over 5 hours. The mixture was kept under reflux so as not to exceed 108°C. An additional fraction of the radical initiator in n-butanol was then added, and the mixture was stirred for 1 hour. Reflux was prolonged until the Gardner viscosity at 61% dry extract reached Z4 / Z6. The temperature then increased and care was taken to ensure that it did not exceed 135°C.Additional quantities of radical initiator in the aromatic solvent were added to Ih, then the mixture was cooled to 100°C and the dry extract was adjusted if necessary by adding more aromatic solvent.

[0070] [Tables 1] RI R2 R3 R4 R5 R6 R7 (a) NBMA NBMA NBMA NBMA NBMA NBMA %(1) 11 11 11 11 10 11 NMA 7.1 (b) %(1) AE 64 AE 64 AE 64 AE 51 AE 46 AE 51 AE 55 MAM 24 MAM 37 MAM 34 MAM 37 MAM 36.9 MAIBO 9.1 (c) %(1) AMA AMA AMA AMA AMA AMA AA 1 1 1 1 0.9 1 1 (d) %(1) — — — — — — — 0 0 0 0 0 0 0 (e) %(1) STY STY — — — — — 24 24 — — — — — Radical initiator %® TBPO TBPO TBPO TBPO TBPO TBPO TBPO 0.5 1.23 0.54 0.3 0.3 0.47 0.83 Organic solvents (%) 40.52 30.88 34.97 34.70 34.70 41.68 39.74 Water (%) 0 0 0 0 0 0 4.27 1. relative to the total percentage of monomers 2. relative to the total weight of the composition

[0071] where the following acronyms are used:

[0072] NBMA: N-butoxymethyl acrylamide (as a mixture containing 68-90% N-butoxymethyl acrylamide and in particular 1 to 5.3% acrylamide) - Aerotex® NBMA 801 Monomer from ALLNEX

[0073] NMA: N-methylol acrylamide in the form of an aqueous composition containing 28% N-methylol acrylamide and 20% acrylamide.

[0074] AE: ethyl acrylate

[0075] MAM: methyl methacrylate

[0076] MAIBO: isobornyl methacrylate

[0077] AMA: methacrylic acid

[0078] AA: acrylic acid

[0079] STY: styrene

[0080] TBPO: tert-butyl peroxide Example 2#: Paint Formulation

[0081] Formulations Fl to F7 described in Table 2 below were prepared respectively from resins RI to R7 prepared as described in Example 1.

[0082] [Tables2] Fl F2 F3 F4 F5 F6 F7 Resin 43.81 43.70 50.18 45.50 48.20 43.64 45.68 Butyldiglycol 12.75 12.44 8.29 12.17 9.84 13.39 12.16 Aromatic hydrocarbons 12.75 12.56 8.48 12.33 9.68 13.31 11.48 Dispersing agent 0.73 0.65 0.69 0.63 0.67 0.61 0.63 Pyrogenated silica 0.31 0.26 0.27 0.25 0.27 0.24 0.25 Amorphous silica 2.17 2.27 2.40 2.18 2.35 2.13 2.21 Titanium dioxide 24.51 25.25 26.67 24.19 26.04 23.61 24.53 Catalyst (at 10% in n-butanol) 0.81 0.90 0.95 0.86 0.92 0.88 0.86 Leveling agent 0.25 0.18 0.18 0.17 0.18 0.16 0.17 UV absorber 1.91 1.79 1.89 1.72 1.85 2.03 2.03 Total 100.00 100.00 100.00 100.00 100.00 100.00 100.00

[0083] The procedure for preparing these formulations was as follows.

[0084] One third of the resin was introduced into a double-walled tank thermostatically controlled at 25°C, a quarter of the planned solvents, as well as the dispersing agent.

[0085] After 5 minutes of slow stirring, the feedstocks were added in descending order of oil absorption, while increasing the dispersion speed to maintain a continuous vortex. Depending on the feedstocks, a ball milling method was used.

[0086] Once all the fillers had been added, they were dispersed for 20 minutes under vigorous stirring to create a good vortex. The remaining resin was then added, and stirring was maintained for 5 minutes before the catalyst, other additives, and solvent were introduced to obtain the desired application viscosity.

[0087] A comparative formulation was also prepared, which had the composition shown in Table 3 below:

[0088] [Tables3] Polyester resin* 41.57 HMMM** Butyldiglycol 9.6 Aromatic hydrocarbons 9.74 Dispersing agent 0.71 Fumed silica 0.28 Amorphous silica 2.48 Titanium dioxide 27.51 Catalyst (at 10% in n-butano 1) 0.97 Leveling agent 0.19 UV absorber 2.07 Total 100.00

[0089] * Synolac® 9605 S 65 from ARKEMA

[0090] ** Hexamethoxymethylmelamine (crosslinking agent)

[0091] The characteristics of these formulations were evaluated as follows.

[0092] Dynamic viscosity:

[0093] The dynamic viscosity is measured at 25°C as described in DIN ISO 2884-1, using a plane cone viscometer and with a shear of 10,000 s1.

[0094] Dry extract:

[0095] In an aluminum dish, 1 g (±0.05 g) of a sample with a mass of ml is poured. The dish is then placed in an oven at 150°C for 1h. The resulting residue of mass m2 is then weighed.

[0096] The dry extract (SE) is defined as follows: SE(%) = 100 x (m2 / ml)

[0097] Pigment charge:

[0098] Pigment load (PVC) is defined as the weight quantity of pigments (including additives) per volume of formulation.

[0099] The following results were obtained:

[0100] [Tables4] Comp. Fl F2 F3 Dynamic viscosity (mPa.s) 539 400 350 490 ES (%) 67.30% 53.40% 59.40% 62.70% PVC (%) 23.72 21.6 21.3 21.6 F4 F5 F6 F7 Dynamic viscosity (mPa.s) 380 540 414 467 ES (%) 56.10% 60.80% 55.80% 62.70% PVC (%) 21.6 21.6 21.6 21.6

[0101] It is thus observed that the formulations according to the invention have properties similar to those of the comparative formulation, suitable for application as a paint. Example 3#: Coating of metal plates

[0102] Using a spiral filmograph, a primer based on ARKEMA's Synolac® 9640 SD 65 and HMMM was applied to galvanized steel substrates to obtain a film 5 µm thick after 25 to 30 seconds of curing in a preheated oven (peak-metal temperature: 232°C). Each of the paint formulations prepared in Example 2 was then applied to this primer to obtain a film 18 µm thick after 20 to 30 seconds of curing in a preheated oven (peak-metal temperature: 232°C).

[0103] At the end of the cooking process, the painted substrate was immersed in a tank of demineralized water to cool it.

[0104] It was then subjected to various mechanical, chemical and optical tests to evaluate the performance of the coating.

[0105] MEKDER:

[0106] The MEK DR is a resistance test to the MEK (methyl ethyl ketone) solvent used to measure the degree of crosslinking of a cured film. It consists of rubbing the surface of a film with cotton soaked in MEK, using a Taber abrasive tester equipped with a module carrying a 1 kg load, which moves laterally over the film. The number of cycles (round trips) required to damage the coating indicates its resistance to solvent. The minimum acceptable value is considered to be 100.

[0107] Folding test:

[0108] The T-bend test consists of bending a pre-painted metal panel, wound around a mandrel, back on itself (by 180°) using a press applying a pressure of 30 bar. The test is performed on coated metal panels, conditioned for 24 hours in a climate-controlled room at 23°C and 50% relative humidity. The coating is examined under a magnifying glass after bending to observe any signs of cracking or delamination. If the coating is cracked or split, a new bend is made until an undamaged surface is obtained. The result is expressed in terms of "T" (for example, 0T, 0.5T, 1T...) where 0T corresponds to the metal being bent completely back on itself without any gaps. The maximum acceptable value is considered to be 2T.

[0109] UV durability:

[0110] Gloss (specular reflection) is measured using a micro-TRLgloss (BYK) glossmeter according to ISO 2813:2014. For this purpose, a beam of light is projected onto the surface to be measured at an angle of 60°. The amount of light reflected at an equal but opposite angle is measured. The unit of measurement for gloss is the GU (Gloss Units). Gloss is measured initially (Bo), and then the measurement is repeated after exposure to UVA at 80°C for 2,000 h (Buv). Gloss retention is defined as: (Bo - Buv) / Bo x 100.

[0111] Delta E corresponds to the difference between the original color of the film and its color after exposure of the film to UVA under the conditions described above, measured in the CIELAB color space (or Lab CIE 1976*).

[0112] The results of these tests are summarized in Table 5 below:

[0113] [Tables 5] Comp Fl F2 F3 F4 F5 F6 F7 MEK DR (Taber) >100 >100 >100 >100 >100 >100 >100 >100 T-Bend 2.5 T 1 T 1.5 T 1.5 T 1.5 T 1.5 T 1.5 T 1.5 T UVA Durability (80°C - 2000 h) Gloss Retention 60° 51.8 66.1 63.2 51 58.4 64.3 59.7 61.7 AE 1.84 0.64 0.83 1.21 1.1 1.7 1.67 1.39

[0114] As these tests show, the paints according to the invention exhibit greater flexibility than the comparative paint, making them more suitable for use in coil coating. They also exhibit solvent resistance comparable to that of the comparative paint. Paints F1-F2 and F4-F7 Paints F1-F4 and F7 exhibit better gloss retention after UV exposure than the comparison paint.

Claims

Demands

1. Metal coil coated with a coating obtained by crosslinking a coating composition based on a self-crosslinking resin formed by copolymerization of monomers comprising or consisting of: a. at least one compound selected from an N-(CrC4-hydroxyalkyl) (meth)acrylamide and its ethers with a CrC 8-alkanol, b. at least one Ci-Ci2-alkyl (meth)acrylate, c. optionally, at least one (meth)acrylic acid, d. 0 to 1% by weight of at least one C2-C4-hydroxyalkyl (meth)acrylate, relative to the total weight of the monomers of the resin, e. optionally, at least one styrenic monomer, and f. optionally, at least one (meth)acrylamide, said coating composition being devoid of any functionalized polymer other than the self-crosslinking resin.

2. Coil according to claim 1, characterized in that constituent (a) represents from 2 to 20% by weight, preferably from 3 to 15% by weight, more preferably from 5 to 12% by weight, relative to the total weight of the monomers of the resin.

3. Coil according to claim 1 or 2, characterized in that component (a) comprises at least one compound selected from N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide, N-butoxymethyl (meth)acrylamide, N-hydroxyethyl (meth)acrylamide, N-(2-hydroxypropyl) (meth)acrylamide and mixtures thereof, preferably component (a) comprises at least one compound selected from N-methylol acrylamide, N-butoxymethyl acrylamide and mixtures thereof.

4. Coil according to any one of claims 1 to 3, characterized in that constituent (e) comprises at least one compound selected from styrene, alpha-methylstyrene, tert-butylstyrene, ortho-, meta- or para-methylstyrene, ortho-, meta- or para-ethylstyrene, ro-methyl-p-isopropylstyrene, p-chlorostyrene, p-bromostyrene, o,p-dichlorostyrene, o,p-dibromostyrene, ortho-, meta- or para-methoxystyrenes, indenes optionally substituted, vinylnaphthalenes possibly substituted, acenaphthylene, diphenylethylene, vinylanthracene and mixtures thereof, preferably styrene.

5. Coil according to any one of claims 1 to 4, characterized in that constituent (d) is absent.

6. Coil according to any one of claims 1 to 5, characterized in that constituent (e) is absent.

7. Self-crosslinking resin formed by copolymerization of monomers comprising or consisting of: a. at least one compound selected from an N-(CrC4-hydroxyalkyl) (meth)acrylamide and its ethers with a CrC8-alkanol, b. at least one Ci-Ci2-alkyl (meth)acrylate, c. optionally, at least one (meth)acrylic acid, d. 0 to 1% by weight of at least one C2-C4-hydroxyalkyl (meth)acrylate, e. 0 to 5% by weight of styrenic monomer, f. optionally, at least one (meth)acrylamide. Said percentages being expressed as a percentage of the total weight of the monomers in the resin.

8. Coating composition, in particular paint, comprising the resin according to claim 7 and at least one solvent selected from: water, organic solvents and mixtures thereof.

9. Use of a self-crosslinking resin according to claim 7 in the manufacture of a metallic substrate coating, in particular by coating metallic coils.

10. Method of coating a metallic substrate, comprising applying to said substrate, optionally coated with a primer layer, a coating composition according to claim 8, in particular by coating metallic coils.