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Many metal objects are treated with a coating to establish an aesthetic effect, to maintai n the original quality over a long period of time, to improve the performance a nd so on. Adhesion is a crucial factor for the success of the coating. Due to the complexity of the adhesion, especially on metai alloys, it appeared difficult to obtain robust adhesion promoting systems, VVe!l known successful products are siianes, carboxylic acids, sulphonates and phosphates, in particula r epoxy phosphate esters of bisphenol A (BP A) resins,

Those skiiled-in-the-art are familiar with the high regulatory pressure on BPA as it is considered as an endocrinic disrupter, Consequently, BPA-containing compounds are about to be expelled from coatings coming into direct contact with food or beverages, for example in two- and three piece cans, starting from internal, but it is likely that the external coatings, including inks, will be dema nded to be BPA-free as well.

New adhesion promoters for coatings to be applied for direct food contact have to meet the criteria for FDA and the European Food Safety Authority (EFSA). In addition, they have to comply with REACH and other regional registrations for chemical substances, Polymers, several naturally occurring products etc, have been exempted from REACH,

Apart from the regulatory aspects, adhesion of coatings on stee! appears to be very difficult. Whereas commercially many adhesion promoters for aluminum are available, proven adhesion promoters for steel are very hard to find. Small variations in the steel composition can lead to substantially different bonding strengths, possibly resulting in loss of adhesion.

Invention Surprisingly, Applicant found that excellent adhesion of coating compositions can be achieved upon adding a compound comprising the following structure:

X and Y can be independently selected from hydrogen, alkyl, ary!, substituted aikyls, substituted aryls, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic acids and sulphinic acids. One of the substituents X or Y must be a carboxyfic acid, phosphonic acid, phosphinic acid, sulphonic add, sulphinic acid and heterocycle or its

corresponding sonic form (either metal salts or neutralized with an alkaline, such as an amino compound}. The substitution on the aromatic ring can be ort o, meta or para. Higher substituted benzene molecules are also available and can meet also the criteria for adhesion promotion,

W and 7. can be independently selected from hydrogen, a!kyl, aryl, substituted aikyls, substituted aryls, polycyiic aromatics, substituted polycyclic aromatics, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic acids and su!phinic acids.

Next to benzene, the aromatic moiety can also be selected from naphthalene, anthracene, phenanthrene and structure homologues as well as Huckel rule aromatic compounds, possibly containing higher degree of substitution.

The present invention further pertains to a coating composition comprising a resin and an adhesion promoter of the formula:

wherei n is a number from 0 to 1000, Xi and Yi are independently selected from hydroxy! and polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic adds, phosphinic acids, su!phonic acids, suiphinic acids and heterocycies.

W3, are independently selected from hydrogen, alkyl, aryl, substituted aikyis, substituted aryis, polycyilc aromatics, substituted polycydic aromatics, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic acids, suiphinic acids and heterocylces;

wherein at least one of Xj and Yi is hydroxy! and the other group is a polar functional group. Substituent Yj can be in the meta, ortho or para position in relation to the Xj substituent. In a preferred

embodiment, the adhesion promoter comprises an X^ and Y ₂ selected from hydroxy! and an acid group selected from carboxylic acid, sulphonic acid, phosphonic acid. Preferably, X _T and Y, are selected from hydroxy! and carboxylic acid. Even more preferably, j is hydroxy! and Yj is an acid group, preferably carboxylic acid. In one embodiment, the molar amount of the benzylic moiety having X _a is hydroxy! and Y\ is an acid group is at least 50% of the total of benzy!ic moieties in the adhesion promoter, preferably at least 80%, more preferably at least 70%, even more preferably at least 80% and most preferably at least 90% of the total of benzylic moieties in the adhesion promoter. Preferably, the adhesion promoter comprises a condensate of salicylic acid and formaldehyde and optionally of other compounds, such as phenol and phenol-containing compounds, in one embodiment, the molar amount of salicylic acid is at least 50% of the total of benzylic moieties in the adhesion promoter, preferably at least 60%, more preferably at least 70%, even more preferably at least 80% and most preferably at least 90% of the total of benzylic moseties in the adhesion promoter. Preferably, the adhesion promoter does not comprise a benzylic compound, in particular a phenol, comprising an alkyl substituent like e.g. methyl and tert-butyl. Also adhesion promoters prepared with oligomerized or polymerized aldehyde such as paraformaldehyde having more than 8 monomeric aldehyde units are not preferred.

The adhesion promoter of the invention has a value n of from 0 to 1000. Preferably, n is at least 1, more preferably at least 2, even more preferably at least 3, even more preferably at least 4 and most preferably at least 5, and preferably at most 75, more preferably at most 50., even more preferably at most 30 and most preferably at most 20,

The adhesion promoter of the invention is generally prepared under acidic conditions and/or with a stoichiometric or below-stoichiometric amount of the formaldehyde or corresponding reactants. in this way, the adhesion promoter will generally comprise the methylene groups on the ortho position of the X or Xt substituent rendering a promoter of the rsovolac type. Alternatively, the adhesion promoter can be prepared under alkaline conditions and/or with an excess of the formaldehyde or corresponding reacta nts. In this way, the adhesion promoter will generally comprise the methylene groups on the ortho and/or the para position of the X or Xj substituent rendering a promoter of the resol type. Although the invention comprises both the novolac and the resot ty pe adhesion promoter. Of these promoters the novolac type adhesion promoter is preferred.

The condensates of the novolac type that are in accordance with the invention are prepared using a benzylic compound and an aldehyde such as formaldehyde. The molar ratio of the benzylic compound to the aldehyde In this process is generally at least 1, preferably at least 1.1, more preferably at least 1.2 and most preferably at least 1.5, and generally at most 1000, preferably at most 500, more preferably at most 100, even more preferably at most 50, even more preferably at most 20 and most preferably at most 10. The same ratios apply when the benzylic compound is a combination of at least two benzylic com pounds.

Typical candidates meeting these criteria are hydroxyl benzoic acids, such as salicylic acid, condensated with an aldehyde, preferably formaldehyde. These products combine the properties of both forming a n ionic bonding with a meta! surface, an aromatic structure for stabilization/complexation and a hydroxy! functionality to react with a cross linker, such as aminoplasts. As the molecules have a high density of active bonding sites, they show superior adhesion.

As the products accordi ng to the invention are polymers, they have been exempted from REACH regulations. Both salicylic acid and formaldehyde comply with the FDA {21CFR175.300} and EFSA (EU directive, No 10/2011) lists for direct food contact, It must be noted that formaldehyde is under suspicion, but no free formaldehyde will be present in the final cured coatings.

The adhesion promoter of the invention is generally present in the composition in an amount of at most 10 weight percent {wt }, based on the total weight of the resin. Preferably, the composition comprises at most 10 wt of the adhesion promoter, more preferab!y at most 5 wt%, even more preferably at most 2 wt%, and most preferably at most 1 wt%, and preferably at least 0.01 wt%, more preferably at least 0.1 wt%, even more preferably at least 0.5 wt% and most preferably at least 1 wt% of the adhesion promoter, based on the total weight of resin.

The resin suitable for the composition of the invention can be any resin known in the art. Such resins inc!ude polyols, polyacrylates, polyesters, aminoplasts, phenoplasts, polyurethanes and aikyd resins. Other suitable resins include polyoiefins such as polyethylene and polypropylene. U nsaturated polyo!efins such as natural rubber are less preferred resins.

The poiyol of the invention may be a monomer, an oligomer or polymer. Examples of polyols are poiyols prepared from the monomeric polyols comprising hydroxy! functional groups include 1,4- butanedioi, 1,3-butanediol, 1,5-penta nediol, 1,6-hexanediol, 2,5-hexanediol, 2-methyl-l,3-pentanediol, 2 -ethyl- 1,3-hexanediol, 2,2-diniethyhl,3-pentanediol, 1,4-cyclohexanediol, trimethylolethane, trimethyiolpropane, pentaerythritoi, dipentaerythritol, 1,4-cyclohexanedimethanol, 1,2- bisihydroxymethyijcyciohexane, l,2-bi$(hydroxyethyl)cyclohexane, trimethyiolpropane, 2,2- dimethyl-3- hydroxypropyl-2,2~dimethyl-hydroxyproprionate, diethylene glycol, triethylene glycol, dipropylene glycol, tetraethylene glycol, trimethylolethane, glycerol, and sorbitol;

Although Bispheno! containing compounds are not meeting the objective bisphenol-free, adhesion promoter compositions can be prepared based on polyols comprising oxirane functional groups bisphenol A, bisphenol F, bisphersol S, alkoxylated bispheno! A such as etnoxylated bisphenol A and propoxylated bispheno! A and alkoxylated bisphenol F such as etnoxylated bisphenol F and propoxylated bisphenol F; polyols comprising oxirane functional groups bisphenol A diglycidy! ether, 2,2'~bis{4- hydroxyphenyl)propane bis(2,3-epoxypropylether, bisphenol F digiycidyl ether, novolac glycldyl ether, ethoxylated bisphenol A and propoxylated bisphenol

Examples of suitable polyesters include Uradii SZ255 {TMP-based polyester}, polyglycoltde (PGA), polycapro!actone {PCI.}, polyhydroxyalkanoate (PHA), polyhydroxybutyrate {PHB), polyethylene adipate (PEA), polybutylene succinate (PBS), poly(3-hyd roxybutyrate-co-3- hydroxyvalerate (PH8V), polyethylene terephthalate (PET), polybutyiene terephthalate {PBT}, polytrimethylene terephthalate (PTT), polyethylene naphthaiate (PEN) and Vectran.

Examples of alkyd resins include polyesters which are modified by fatty acids or corresponding triglycerides like for example the commercially available under tradenames Uralac AN621 S- 2 60 and Uralac AN637 S-2 60 (both ex DS Resins). The aikyd resins may further be modified using phenolic resin, styrene, vinyl toluene, acrylic monomers and/or po!yurethanes.

More details of suitable aikyd resins and possible modifications can be found in US

2014/0360408.

Examples of polyacrylate resins include polymers derived from one or more of acrylate, methacry!ate, ethyl acrylate, 2-ch!oroethy! vinyl ether, 2-ethy!hexyi acrylate, 2-hydroxyethyl methacryiate, butyl acrylate, butyl rnetbacrysate, 2-hyd oxy propyl methacryiate, 3-hydrox propyl methacryiate, 2-hydroxypropyl methacry!ate, 3-hydroxypropyl methacrylate, hydroxystearyl acrylate and hydroxystearyl methacryiate. Copolymers of two or more of the aforementioned resins are also contemplated as long as the resulting resin contains reactive groups as is required by the invention. The aminoplast of the invention may be a monomer, an oligomer or polymer. Polymeric aminoplasts may include melamine resin, dicysnimide resin, glycoluril resins, urea resins and copolymers thereof. Of these polymeric aminoplasts melamine resins are preferred. Oligomeric aminoplasts include dimers, trimers and tetramers of monorneric aminoplasts. Examples of suitable monorneric aminoplasts include condensation products of an aldehyde and methylurea, glycoluril, benzourea, dicyandiamide, formaguanamine, acetoguanamine, ammeline, 2-chloro-4 _J 6-diamino-l,3,5-triazine, 6-methyl-2,4- diaminO"l,3,5-triazine, 3,5-diaminotriazole, triamirtopyrimidine, 2-mercapto-4,6-diaminopyrimidine, 2,4,6-triethyl-triamino-l,3,5-tria2ine _J 1,3,5-triaminobenzene and melamine. Of these aminoplasts aldehyde condensation products with melamine are preferred. Suitable aldehydes Include

formaldehyde, acetaldehyde, crotonaldehyde, acrolein, benzaldehyde, glyoxal and furfural.

Formaldehyde is the preferred aldehyde. Further modification of the aminoplasts can also be considered, including etherification with a monoalcohol, such as methanol,, ethanoi, propano!, butanol, pentanol, hexanol and heptanol. Examples of such aminoplasts Include hexamethoxymethyl melamine (Cymel 300 and Cyme! 303), butylated melamine formaldehyde resin (Cymel 1156 and Cymel 1158 and Cymel MB- 14), and partially butylated, methylated melamine formaldehyde resin (Cymel 1130) and butoxylated glycoluril formaldehyde resin, such as Cymel 1170, Of these hexamethoxymethyl melamine is usually preferred owing to price and availability. Further examples of aminoplasts include derivatives of methylurea, giycoluril, benzourea, dicyandiamide, formaguanamme, acetogua namine, ammeline, 2- chloro-4,6-dia rnino-l,3,5-triazine, 6-methyl-2,4-dtamino-l,3,5-triazine, 3,5-diaminotriazole,

triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine, 2,4,6-triethyl-triamino-l,3,5-triazine, 1,3,5- triaminobenzene and meiamlne, wherein the derivative comprises functional groups selected from the group consisting of vinyl, oxetane, carboxylic acid, hydroxy! and thiol- Examples of such derivatives include derivative of glycoluril such as TA-G, TG-G, TC-G, TH-G and TS-6. The invention also contemplates using two or more of such aminoplasts. When two or more aminoplasts are present in the coating composition, the total number of first functional groups in the two or more aminoplasts is used in the calculation of the molar ratio of first and second functional groups, Polyolefins are polymers or copolymers obtained by polymerization of at least one ethylenically unsaturated monomer. Such polymers include polyolefins and modified polyolefins, which are known to the man skiiied-in-the-art The polyolefin or modified polyolefin can be a homopolymer or a copolymer, terpolymer of grafted polymer. Unsaturated polyolefins such as natural rubber are not preferred.

Examples of (modified) polyolefins include polyethylene, polypropylene, po!ybutyiene, polystyrene, polyvinyl chloride, polyvinyisdene chloride and ethyiene-propylene rubber, propylene-butene copolymer, etbyiene-vinyi chloride copolymer, ethylene-vinyl acetate copolymer, acrylonitrile-butadiene-styrene copolymer (ABS), acryionitrile-acrylate-styrene copolymer (AAS), methyl methacrylate-butadiene-styrene copolymer {MBS}, chlorinated polyethylene, chlorinated polypropylene, ethylene-acrylate copolymer, vinyl chloride-propy!ene copolymer, rnafeic anhydride-grafted polyoiefin, maleic acid-grafted polyolefin, a nd mixtures thereof. Preferred polyolefins are polyethylene, polypropylene, polystyrene and polyvinyl chloride.

Suitable examples of polyethylene are high-density polyethylene (HDPE), low-density polyethylene (LDPE), straight chain low-density polyethylene, ultra-low density polyethylene and ultrahigh molecular weight polyethylene. Further examples of ethyiene-based copolymers include ethylene- vinyl acetate copolymer (EVA), ethylene-ethyt acetate copolymer (EEA), ethylene-methy! acrylate copolymer (E A) and ethylene-acry!ic acid copolymer (EAA).

Preferred polyolefins are polyethylene and polypropylene, which include emulsions and dispersions thereof. Such emulsions and dispersions can be water-based or solvent-based, The inhibitor of the invention can be used in both water-based and solvent-based emulsions and dispersions.

Exa mples of such polyoiefin dispersions or emulsions include Mitsui Unisol R1G0 G, Mitsui XP04A, Mitsui 5300, Mitsui Chemipearl W900 and Dow Canvera 1110. In one embodiment of the invention, the coating composition comprises the resin in an amount of at Ieast 10 % by weight (wt%), based on the total weight of the coating composition. Preferably, the resin is present in an amount of at Ieast 25 wt%, more preferably at least 40 wt%, even more preferably at Ieast 65 wt% and most preferably at Ieast 70 wt%, and preferably at most 99 wt , more preferably at most 95 wt , even more preferably at most 90 wt% and most preferably at most 75 wt , based on the total weight of the coating composition.

The remaining part of the coating composition may comprise other components commonly used in coating compositions. With the resin and the adhesion promoter the other components add up to 100 wt% of the total weight of the coating composition. The coating composition of the invention may further comprise a solvent. The solvent may be any suitable solvent known in the art. Preferred solvents are reactive solvents that comprise third functional groups capable of reacting with the aminoplast and/or the first resin, preferably the poiyol. The third functional groups may be hydroxy I, amine or thiol Preferably, the third functional group is a hydroxyl or an amine. Examples of reactive solvents include alcohols, such as methanol, ethano!, diethanol, amino ethanoi, glycol, n-propartol, iso-propanol and ethanethiol, ethylene glycol, propylene glycol and neopentyi glycol; and amines, such as methyl amine, ethanoi amine, dimethyl amine, methyl ethanoi amine, dsphenyl amine, trirnethyl amine, triphenyl amine and piperidine; and acryiates such as acrylate, methacrylate, ethyl acrylate, 2-chioroethy! vinyl ether, 2-ethy!hexyl acrylate, 2-bydroxyethyi methacrylate, butyl acrylate, butyl methacrylate, 2-hydroxypropyi methacrylate, 3-hydroxypropyt methacrylate, 2-hydroxypropyl methacrylate, and 3-hydroxypropyl methacrylate; and water. In one embodiment of the invention, the coating composition further comprises water as solvent, possibly as the reactive solvent.

Examples of non-reactive solvents include Solvent Naphtha ^® , heavy benzene, various Solvesso* grades, various Sheilsol ^® grades and DeasoP, various white spirits, mineral turpentine oil, tetralin, decal ^' m, methyl ethyl ketone, acetone and methyl n-propyl ketone. Non-reactive solvents that are incorporated at Ieast partially and preferably completely, into the cured resin are preferred. Preferably, the non-reactive solvent has a boiling point above the curing temperature, preferably above 250 ^* C The coating composition of the invention may comprise a reactive solvent and a non-reactive solvent, a combination of two or more solvents, or a combination of two or more reactive solvents. Coating compositions comprising a reactive solvent are preferred. The coating composition of the invention may comprise the non-reactive solvent and/or the reactive solvent in an amount of at most 30 % by weight (wt%), based on the total weight of the coating composition. Preferably, the non-reactive solvent and/or the reactive solvent is present in an amount of at most 25 wt%, more preferably at most 20 wt%, even more preferably at most 15 wt% and most preferably at most 30 wt%, and preferably at least 1 wt%, more preferably at least 2 wt%, even more preferably at least 5 wt% and most preferably at ieast 10 wt%, based on the total weight of the coating composition.

The coating composition may further comprise additives commorsfy used in coating compositions including pigments and dyes, surfactants, flow controlling agents, thixotropic agents, anti-gassing agents, ultraviolet light stabilizers, adhesion enhancing promoters, waxes, filling agents, matting agents, defoamers and curing catalysts. The additives can be any additive known in the art. Examples of pigments and dyes include metal oxides like titanium dioxide, iron oxide, zinc oxide and chromium oxide; metal hydroxides; metal sulfides, metal sulfates, metal carbonates such as calcium carbonate; carbon black, china clay, phtha!o blues and greens, organo reds and other organic dyes. The coating compositions of the invention may increase the color intensity of the pigments and dyes. This may lead to a reduction in the total amount of pigment and/or dye used. Examples of ultraviolet light stabilizers include benzophenone, such as hydroxydodecyi benzophenone, 2,4-dihydroxy-3',5'-d ^' s-t- buty!benzophenone, 2-hydroxy-4-acryloxyethoxybenzophenone and 2-hydroxy-4-methoxy-2'- carboxybenzophenone. The coating composition of the invention may comprise the additives in an amount of at most 30

% by weight (wt%), based on the total weight of the coating composition. Preferably, the additive is present in an amount of at most 25 wt , more preferably at most 20 wt%, even more preferably at most 15 wt% and most preferably at most SO wt , and preferably at least 1 wt%, more preferably at Ieast 2 wt%, even more preferably at Ieast 5 wt% and most preferably at Ieast 10 t , based on the total weight of the coating com osition.

The invention also pertains to a coated substrate comprising a substrate and a cured coating composition applied to at Ieast part of the substrate., the coating composition being in accordance with the invention, in an embodiment of the invention the coated substrate is a food or beverage container.

The substrate of the invention can be any substrate known in the art. The substrate may be porous or non porous. Examples of suitable substrates include metals, such as aluminum, aluminum alloys, steel, steel alloys, tin, tin allows, zinc, zinc alloys, chrome and chrome alloys; glass, such as fused silica glass,, aluminositicate glass, soda-lime-si!ica glass, borosilicate glass and lead-oxide glass; ceramics, such as porcelain, bone china, alumina, ceria, zirconia, carbides, borides, nitrides and silicides; plastic such as functionalized polyetfiylene (PE), functionalized polypropylene {PP}, poSyethylerie terephtha!ate (PET), polyvinyl chloride (PVC) and nylons; and wood. Preferably, the substrate is metal, In particular aluminum and steel, which as such can be pretreated or partly pretreated with ink. The adhesion promoter of the invention causes a considerably improved adhesion and a dearly improved scratch resistance when used in coatings coated on a wide variety of substrate surfaces; in particular surfaces of "difficult" substrates such as stee! can be coated with good adhesion and scratch resista nce properties.

In the context of the present application the term "cure" or "cured" refers to the process of hardening of the coating composition by polymerization and/or crossli ki g. This curing process can be initiated by exposure to ultraviolet radiation, heat, such as by infrared radiation, by microwave radiation or by heating, e.g. in an oven, electron beams and chemical additives. The coating com ositions of the invention preferably cure through exposure to ultraviolet radiation and heat, preferably through heat.

Coatings comprising an adhesion promoter according to the invention showed excellent adhesion in several IK stoving coating systems, such as polyester/aminoplast, aikyd resin/aminoplast and po!yol/aminoplast. The adhesion on steel was found to be surprisingly well.

Apa rt from the adhesion promotion, the compounds showed catalytic in hibition of the oxidative radical-induced degradation of polymers susceptible to oxy radical-induced attack/decom position, e.g. polyethylene, polypropylene, homo-, co- and terpolymers as well as functionalized polymers. This is in line with another invention recently filed by the Applica nt, showing an inhibitor to prevent oxidative radical degradation via a benzylic hydrogen abstraction mechanism, effective in an amount of less than 1% (w/w) based on the solid weight of the total polymer resin. The inhibitor comprises a conjugated benzyl moiety, capable of forming a sta ble benzylic radical, which in turn can be regenerated to the original benzyl moiety. The aromatic moiety can be selected from benzene, naphthalene, anthracene or phena nthrene.

Next to adhesion promotion a nd catalytic inhibition of radical induced degradation, several coating compositions showed high chemical and physical resistance especially towards wet adhesion.

The invention further pertains to an adhesion promoter of formula (1):

wherein n is a num ber from 0 to 1000, X _a and ¥]. are independently selected from hydroxy! and polar functional groups, such as alcohol, mercapto, nitro, amines, primary a mides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic adds, suiphinic acids and heterocycles; and

Wj are independently seiected fram hydrogen, alkyl, ary!, substituted alkyis, substituted aryls, polycylic aromatics, substituted polycyciic aromatics, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxylic acids, phosphonic acids, phosphinic acids, sulphonic acids, suiphinic acids and heterocycles; wherein at least one of X _3. and Y _; is hydroxyl and the other group is a polar functional group, for use as an adhesion promoter in coating compositions comprising at most 10 wt% of the adhesion promoter, based on the total weight of resin.

The invention further pertains to the use of an adhesion promoter of formula (1):

wherein n is a number from 0 to 1000, X _a and \ are independently selected from hydroxyl and r functional grou ps, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxy!ic acids, phosphorsic acids, phosphinic acids, sutphonic acids and sulphinic acids; and

Wi are independently selected from hydrogen, alkyl, aryl, substituted alkyis, substituted aryls, poiycylic arornatics, substituted polycyc!ic aromatics, polar functional groups, such as alcohol, mercapto, nitro, amines, primary amides, secondary amides, ketones, aldehydes, epoxy phosphate esters, sulphates, carboxytic acids, phosphonic acids, phosphinic acids, suiphonic acids and sulphinic acids;

wherein at least one of X-, and Y-, is hydroxy! and the other group is a polar functional group, in coating compositions comprising at most 10 wt% of the adhesion promoter, based on the total weight of resin.

Those skilled-irvthe-art understand that the poiyacidic (carboxylic, suiphonic, sulphinic, phosphonic or phosphinic) products in accordance with the invention also may be applied in many other areas, such as stabilization of hardness in water treatment systems, corrosion inhibition of metals, concrete superplasticizer, chelating agent, wetting agent etc.

In a further embodiment of the invention, the coating composition of the invention can be used in appiication where corrosion protection and/or cured coating flexibility and formability are required. Examples of such applications include coii coating applications, car refinish, and automotive a pplications.

Background

Good adhesion is difficult to achieve. Adhesion is a surface phenomenon and is related to physical forces and chemical reactions/interactions at the interface. The highest molecular bonding strengths a re primary bonds, viz. ionic (150-250 kcai/mole), covalent (15-170 kcai/mole) and metallic (27-83 kcai/mole). Secondary bonds, such as hydrogen bonds (<12 kcai/mole) and Van der Waals bonds (<10 kcal/mote) are much weaker.

Metal surfaces are usually alkaline in nature, especially In relation to active bonding sites, due to oxidation. Consequently, acidic products (low pK _a ) will show a higher reactivity on these surfaces.

One of the most powerful coating adhesion promoters to date for aluminum is a n epoxy phosphate ester of bisphenot A, commercialized by DSM under the brand name Uradii DD79. its excellent performance is assigned to the formation of strong ionic bonds (phosphate-metal), the aromatic character (stability and complexing properties) as well as the polymeric structure (introducing high moiecuiar mass, flexibility etc.}, A new adhesion promoter has to contain all these properties.

It is evident that the mechanism of adhesion under wet conditions differs from dry adhesion. It must be noted that adhesion is more critical under wet conditions: Adhesion loss is very eminent under steam condition, even more under pasteurization condition, mostly ursder retort sterilization condition. During retort sterilization., high pressure and high temperature steam migrates through the coating, breaking the weakest bonds at the metal-polymer surface. Epoxy phosphate ester adhesion promoters show excellent adhesion up to pasteurization conditions, yet tend to ioose adhesion under retort- sterilization conditions. It is obvious that a new adhesion promoter preferably remains its function under retort-sterilization.

Recently, Applicant has reported excellent performance of coating compositions, comprising alkylated poiyamine a nd a substituted phenol, preferably salicylic acid {WO2012/177121 and

WO2012/177122). The special characteristics in terms of stability and performance are attributed by the chemical structure of salicylic acid, wherein intramolecular exchange of protons can take place in a six membered ring structure. The dry adhesion properties of these compositions were found to be excellent. However, adhesion failure has been observed under wet conditions.

Salicylic acid can be condensated with formaldehyde in different rrsofar ratios to form polymers in a very straightforward process (US 4,245,083}. The resulting products have been claimed to be suitable as fixing agent for dye stuffs in paper printing. These compounds as well as many similar products have been extensively studied, but have never been recognized nor reported as adhesion promoters.

Condensation products of formaldehyde and phenol sulphonic acids have been reported as well, e.g. US 4,457,874. These compounds ca n be appiied as dispersing agent in hydraulic cement, mortar, concrete or the like. Formaldehyde condensates of naphthalene sulphonic acids are widely applied as wetting and dispersi ng agent. Phenol condensates with aidehydes have been extensively described in the literature e.g. US 4,026,867. The resulting products are generally known as phenopiasts. !n principle, each phenolic compound can be polymerized in the presence of a proper aldehyde.

Typical starting molecules which meet the criteria for adhesion promotion are salicylic acid, 3- hydroxybenzoic acid, 4-hydroxybenzoic acid, resorcylic acids (dihydroxy benzoic acids), gailic acid

(trihydroxy benzoic add}, hydroxy! phthalic acids, dihydroxy! dicarboxylic benzenes, cashew nut shell liquid, amtnobenzoic acid, !igi osu!phonaies, phenol suiphonic acid, 4-hydroxyl sulphonic acid, 4- hydroxybenzyl phosphonic acid, or mixtures thereof.

Apart from formaldehyde, also other aldehydes can be applied to obtain condensation products according to the invention, e.g. glyoxal (US 6,379.800), propionaldehyde (4,154,769), hutyra dehyde (US 2,178,951) or furfural (US 2,745,816), Sometimes mixtures of aldehydes have been applied as well.

It is obvious for those skil!ed-in-the-art that upon varying the aromatic compounds and/or the aldehydes a wide range of moiecuies can be prepared, capable of promoting adhesion. The molecular weight and the amou nt, of active bonding sites present can be also tuned by adjusting the reaction conditions, monomers or monomer mixtures selection, and molar ratios.

Examples

Examples 1 and 2 and Compa rative Examples A and B Formaldehyde salicylic acid condensation products have been synthesized according to the procedure described in US 4,245,083, example 1. After reaction, the poiymer has been dissolved in butylglycol and neutralized with dimethylaminoethanol and diluted with water to obtain a yellow liquid, which ca n be handled easily

The formaldehyde salicylic acid condensate has been admixed (5% as solid on total amount of resin) with standard thermal curable coating system and tested on both aluminum and steel panels. The standard coating system contains: 10.0 g Cyme! 3745, 1.0 g 1,6-hexanediol, 3.0 g butylglycol, 0.14 1- bittanoS and 0.03 g Cycat 500. After thermal curing (200 °C, 3 minutes), cross cuts have been made in the panels and pasteurized for one hour at 90 *C. Adhesion has been tested with Scotch 3M tape {ASTM D33S9).

The experiments show that the components according the invention showed excellent adhesion in various concentrations on both aluminum and steel.

5

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1100 aacciidd ccaattaallyysstt aanndd 1100 gg ddeemmiinneerraaiiiizzeedd wwaatteerr.. TToo tthhee vvaarrnniisshheess ooff tthhee iinnvveennttiioonn aa ccoommppoouunndd ooff tthhee

iinnvveennttiioonn iiss aaddddeedd iinn aann aammoouunntt ooff 55wwtt%%;; tthhee ccoomm ppoouunnddss aarree ttaabbuullaatteedd iinn tthhee TTaabbllee bbeellooww.. TThhee ccoommppoouunnddss oorr ccoonnddeennssaatteess wweerree pprreeppaa rreedd bbyy tthhoorroouugghhllyy mmiixxiinngg tthhee ssttaartrtiinngg mmaatteerriiaallss ((iinn ccoommppoossiittiioonn ccoolluummnn)) iinn aa 225500 mmii ggllaassss ffllaasskk.. SSuubbsseeqquueennttllyy,, 00..55gg ssuullpphhoonniicc aacciidd ccaattaallyysstt ((NNaaCCuurree 115555 bbyy KKiinngg iinndduussttrriieess)) wwaass aaddmmiixxeedd.. TThhee mmiixxttuurree wwaass ssttiirrrreedd aanndd aalllloowweedd ttoo bbooiill ffoorr 22 hhoouurrss.. TToo ssoommee ooff tthhee

1155 rreeaaccttiioonn mmiixxttuurreess -- iinn ccaasseess tthhaatt rreeqquuiirree wwaatteerr ssoolluubbiilliittyy -- aaqquueeoouuss ddiimmeetthhyyllaammiinnoo eetthhaannooll iiss aaddddeedd ttoo ssoolluubbiilliizzee tthhee ccoonnddeennssaattee..

(10g/llg/21g)

The treated aluminium pieces are cured at 19Q°C in a box oven. Ail sampSes showed over SO double ME rubs, which means that the varnishes are fully cured. Cured aluminum pieces are subjected to pasteurization at 95 °C for 10 and 30 minutes, respectively, and evaluated on adhesion and scratch resistance. The results are shown in the Table below.

Ali varriishes in accordance with the invention show a considerable improvement in adhesion properties and appearance compared to the varnishes of Comparative Example C, The best results are obtained with salicylic acid-containing condensates.