Heat-curing epoxy resin composition with high corrosion resistance

Abstract

The present invention relates to thermosetting one-component epoxy resin compositions comprising a liquid epoxy resin (A), latent curing agent (B), toughness improver (D) and corrosion inhibiting additives (E), wherein the corrosion inhibiting additive (E) is either a combination (E1) of at least one phenol carboxylic acid with at least one flavonoid or at least one hydrolysable tannin (E2). The compositions feature improved corrosion resistance, good storage stability and good usability as a one-component thermosetting adhesive, especially as a thermosetting one-component bodywork adhesive in motor vehicle construction.

Description

[0001] HEAT-CURING EPOXY RESIN COMPOSITION WITH HIGH CORROSION RESISTANCE

[0002] Technical field

[0003] The invention relates to the field of thermosetting one-component epoxy resin compositions, especially for use as bodywork adhesive.

[0004] Prior art

[0005] Thermosetting epoxy resin compositions have long been known. Efforts have already been made for some time to remedy or at least significantly reduce the great disadvantage of epoxy resin compositions, namely their brittleness, the effect of which is that the cured epoxy resin composition cracks or is destroyed under impact stress. Attempts have already been made to do this by the addition of impact modifiers or by chemical modification of epoxy resins.

[0006] An important field of use of thermosetting epoxy resin compositions is in motor vehicle construction, especially in bonding in the bodywork. After the application of the epoxy resin composition, the bodywork is heated in the cathodic electrocoating oven, because of which the thermosetting epoxy resin composition is cured.

[0007] However, efforts are currently under way in the market to increase the corrosion resistance of said thermosetting epoxy resin compositions. Thus, there is a great need on the market for thermosetting epoxy resin compositions containing impact modifiers that display a sufficient resistance to corrosion. There is therefore a need for toughened thermosetting one-component epoxy resin compositions which improved corrosion resistance.

[0008] Known prior art might be: EP3798246A1 disclosing thermosetting epoxy resin compositions comprising epoxy resins, curing agents, and toughness improvers for use in structural applications. WO2022133880A1 describes one-component thermosetting epoxy adhesives containing epoxy resins, epoxy novolacs, glycidyl amine type epoxy resins, latent hardeners, and toughness improvers for improved adhesion at high temperatures. CN112272693A relates to methods for strengthening metal structures using two-component epoxy resin compositions containing epoxy resins, hardeners, impact strength modifiers, and fillers. Summary of the invention

[0009] It is therefore an object of the present invention to provide toughened thermosetting one-component epoxy resin compositions that have improved corrosion resistance.

[0010] This object was surprisingly achieved by a thermosetting one-component epoxy resin composition as claimed in claim 1. This epoxy resin composition has particularly good usability as a one-component thermosetting adhesive, especially as a thermosetting one-component bodywork adhesive in motor vehicle construction.

[0011] Ways of executing the invention

[0012] The present invention relates to thermosetting one-component epoxy resin compositions comprising: a) at least one epoxy resin A having an average of more than one epoxy group per molecule; b) at least one latent curing agent B for epoxy resins, preferably the latent curing agent B is selected from the group consisting of aromatic dicarboxylic dihydrazide B1 , aliphatic dicarboxylic dihydrazide B2 and dicyandiamide B3; c) at least one toughness improver D, preferably selected from the group consisting of terminally blocked polyurethane polymers D1 and liquid rubbers D2, preferably a terminally blocked polyurethane polymer D1 ; and d) at least one corrosion inhibiting additive E.

[0013] The corrosion inhibiting additive E is either: d1 ) a combination E1 of at least one phenol carboxylic acid with at least one flavonoid; or d2) at least one hydrolysable tannin E2.

[0014] In this document, the use of the term "independently" in connection with substituents, radicals or groups should be interpreted such that the substituents, radicals or groups having the same designation in the same molecule may occur simultaneously with different meanings.

[0015] The prefix "poly" in substance names such as "polyol", "polyisocyanate", "polyether" or "polyamine" in the present document indicates that the respective substance, in a formal sense, contains more than one of the functional groups that occur in its name per molecule.

[0016] In the present document, “molecular weight” is understood to mean the molar mass (in grams per mole) of a molecule. “Average molecular weight” is understood to mean the number-average molecular weight Mnof an oligomeric or polymeric mixture of molecules, which is typically determined by means of GPC against polystyrene as standard.

[0017] A “primary hydroxyl group” refers to an OH group bonded to a carbon atom having two hydrogens.

[0018] In the present document, the term "primary amino group" refers to an NH2 group bonded to one organic radical, while the term "secondary amino group" refers to an NH group bonded to two organic radicals which may also together be part of a ring. Accordingly, an amine having one primary amino group is referred to as "primary amine", one having a secondary amino group correspondingly as "secondary amine", and one having a tertiary amino group as "tertiary amine".

[0019] In the present document, "room temperature" refers to a temperature of 23°C.

[0020] All industry standards and norms mentioned in the document refer to the versions valid at the date of first filing, unless stated otherwise.

[0021] However, the prior art compositions described above suffer from several significant limitations. Conventional corrosion inhibitors used in thermosetting epoxy resin compositions typically rely on inorganic compounds such as chromates, phosphates, or zinc-based additives, or synthetic organic compounds. These conventional approaches often present drawbacks including environmental concerns, limited effectiveness under certain conditions, or negative impacts on the mechanical properties or storage stability of the epoxy compositions.

[0022] Furthermore, while some prior art documents disclose epoxy resin compositions with toughness improvers and various additives, none specifically address the combination of corrosion resistance with the particular challenges faced by one- component thermosetting systems. The prior art fails to recognize that achieving effective corrosion inhibition in one-component epoxy systems requires additives that not only provide corrosion protection but also maintain compatibility with the latent curing mechanism and do not adversely affect storage stability over extended periods. A particular gap exists in the prior art regarding the use of naturally-derived compounds as corrosion inhibitors in thermosetting epoxy resin compositions. While natural compounds such as phenolic acids, flavonoids, and tannins are known for their antioxidant properties in other applications, their specific utility as corrosion inhibiting additives in epoxy resin systems has not been recognized or exploited. The prior art does not teach or suggest that combinations of phenol carboxylic acids with flavonoids, or hydrolysable tannins, could provide effective corrosion inhibition while maintaining the required performance characteristics of one-component thermosetting epoxy compositions.

[0023] The present invention addresses these deficiencies by providing corrosion inhibiting additives that are derived from natural sources and offer multiple technical advantages. Unlike conventional synthetic corrosion inhibitors, the phenol carboxylic acid and flavonoid combinations, as well as hydrolysable tannins disclosed herein, provide effective corrosion protection through their inherent chelating and radical scavenging properties. These natural compounds may offer improved environmental compatibility compared to traditional heavy metal-based corrosion inhibitors, while simultaneously providing antioxidant benefits that can enhance the long-term stability of the cured epoxy matrix.

[0024] Moreover, the specific corrosion inhibiting additives of the present invention demonstrate compatibility with the complex chemistry of one-component thermosetting epoxy systems. The phenol carboxylic acids, flavonoids, and hydrolysable tannins do not interfere with the latent curing mechanism, allowing the compositions to maintain their storage stability while providing enhanced corrosion resistance upon curing. This represents a significant technical advancement over prior art approaches that may compromise either storage stability or curing performance when corrosion inhibitors are incorporated.

[0025] The invention further distinguishes itself from the prior art by addressing the specific needs of bodywork adhesive applications in motor vehicle construction, where compositions must withstand both mechanical stresses and corrosive environments over extended service life. The natural corrosion inhibiting additives disclosed herein provide a sustainable approach to achieving the required corrosion resistance without relying on environmentally problematic compounds, thereby meeting evolving regulatory and environmental requirements in the automotive industry.

[0026] The thermosetting one-component epoxy resin composition comprises a) at least one epoxy resin A having an average of more than one epoxy group per molecule. Preferred epoxy resins A have the formula (I)

[0027] In this formula, the substituents R’” and R”” are each independently H or CH3, preferably H. In addition, the index r has a value of 0 to 1 . Preferably, r has a value of less than 0.2.

[0028] These are thus preferably diglycidyl ethers of bisphenol A (DGEBA), of bisphenol F and of bisphenol A / F (here, the designation "A / F" refers to a mixture of acetone with formaldehyde which is used as the reactant in the preparation thereof).

[0029] Most preferably, the at least one epoxy resins A are diglycidyl ethers of bisphenol F. Such liquid resins are available, for example, as Araldite® GY 250, Araldite® PY 304, Araldite® GY 282 (Huntsman), or D.E.R. ™ 331 , or D.E.R. ™ 330 (Olin), or Epikote 828 (Hexion).

[0030] Moreover, so-called novolacs are suitable epoxy resins A. These have in particular the following formula: or CH2, R1

[0031] = H or methyl and z = 0 to 7.

[0032] In particular, they are phenol or cresol novolacs (R2 = CH2).

[0033] Such epoxy resins are commercially available under the trade names EPN or ECN as well as Tactix® 556 from Huntsman or under the product line D.E.N. ™ from Dow Chemical. Most preferably, the epoxy resin A is a liquid epoxy resin of the formula (I), wherein the substituents R’” and R”” are each H and the index r has a value of less than 0.2.

[0034] Preferably, the proportion of the at least one epoxy resin A1 is 35 - 65 % by weight, more preferably 40 - 60 % by weight, most preferably 45 - 55 % by weight, based on the total weight of the thermosetting one-component epoxy resin composition. This concentration range provides sufficient crosslinking density for mechanical performance while allowing adequate space for the corrosion inhibiting additives and toughness improvers to function effectively. The preferred range of 45-55 wt.% ensures optimal balance between structural integrity and functional additive performance.

[0035] The composition of the invention also contains b) at least one latent curing agent B for epoxy resins. Latent curing agents are substantially inert at room temperature and are activated by elevated temperature, typically at temperatures of 70°C or more, thereby initiating the curing reaction. The customary latent curing agents for epoxy resins can be used. Preference is given to a latent curing agents B containing nitrogen.

[0036] Preferably, the latent curing agent B is selected from dicyandiamide, dihydrazides, guanamines, guanidines, anhydrides of polybasic carboxylic acids and aminoguanidines, more preferably, the latent curing agent B is selected from dicyandiamide and dihydrazides.

[0037] It can be especially preferred, if the latent curing agent B is selected from the group consisting of aromatic dicarboxylic dihydrazide B1 and aliphatic dicarboxylic dihydrazide B2, preferably aliphatic dicarboxylic dihydrazide B2. This selection provides enhanced compatibility with hydrolysable tannin corrosion inhibitors, as demonstrated by superior corrosion resistance performance in the ADH (aliphatic dicarboxylic dihydrazide) curing system compared to dicyandiamide systems. In case of the forgoing selections, it can be especially preferred, if the at least one corrosion inhibiting additive E is at least one hydrolysable tannin E2, preferably tannic acid. This is advantageous with respect to storage stability and reduction in LSS values after corrosion treatment. This can be seen, for example, in the comparison of E9 with E25.

[0038] It can also be especially preferred, if the latent curing agent B is dicyandiamide B3.

[0039] In case the latent curing agent B is selected from the group consisting of aromatic dicarboxylic dihydrazide B1 and aliphatic dicarboxylic dihydrazide B2, the amount of the latent curing agent B for epoxy resins is preferably 2 to 15 wt%, more preferably 6 to 14 wt%, more particularly 8-12 wt%, based on the total weight of the thermosetting one-component epoxy resin composition.

[0040] In case the latent curing agent B is dicyandiamide B3, the amount of the latent curing agent B for epoxy resins is preferably 0.5 to 12 wt%, more preferably 1 to 8 wt%, more particularly 2-6 wt%, based on the total weight of the thermosetting one- component epoxy resin composition.

[0041] Preferably, the thermosetting epoxy resin composition additionally contains at least one accelerator C for epoxy resins. Preferably, the accelerator C for epoxy resins is selected from the list consisting of substituted ureas, imidazoles, imidazolines and blocked amines, preferably substituted ureas, more preferably aliphatic substituted ureas.

[0042] This preferably comprises substituted ureas of the formula (III) in which R1and R2are independently hydrogen atoms or monovalent alkyl radicals which have 1 to 10 carbon atoms and optionally also comprise oxygen atoms, nitrogen atoms and / or aromatic units or together form a divalent alkyl radical having 1 to 10 carbon atoms, and which may additionally comprise oxygen atoms, nitrogen atoms or aromatic units; R3and R4are independently hydrogen atoms or monovalent alkyl radicals which have 1 to 10 carbon atoms and optionally also comprise oxygen atoms or nitrogen atoms; and the index n has a value of 1 or 2.

[0043] The substituted urea of the formula (III) is preferably selected from the group consisting of p-chlorophenyl-N,N-dimethylurea (monuron), 3-phenyl-1 ,1- dimethylurea (fenuron), 3,4-dichlorophenyl-N,N-dimethylurea (diuron), N- methylurea, N,N-dimethylurea, N,N'-dimethylurea, N,N,N'-trimethylurea, N,N,N',N'- tetramethylurea and derivatives thereof, where some or all methyl groups are instead ethyl groups.

[0044] Preferably, R1and R2are independently hydrogen atoms or monovalent linear or branched alkyl radicals which have 1 to 10, preferably 1 to 5, more preferably 1 to 4, carbon atoms and optionally together constitute a divalent alkyl radical that forms a ring structure with the adjacent nitrogen atom, and / or R3and R4independently represent hydrogen atoms or monovalent linear or branched alkyl radicals which have 1 to 10, preferably 1 to 5, more preferably 1 to 4, carbon atoms and optionally together constitute a divalent alkyl radical that forms a ring structure with the adjacent nitrogen atom.

[0045] Very particularly preferred substituted ureas of the formula (III) are those in which R1and R2in formula (III) are both hydrogen atoms and / or in which R3and R4are both ethyl or methyl groups, preferably methyl groups.

[0046] Further preferred urea derivatives of the formula (III) include those in which R1, R2, R3and R4in formula (III) all represent ethyl or methyl, preferably methyl groups, or in which R1, R2and R3represent ethyl or methyl, preferably methyl, and R4is a hydrogen atom, or where R1and R4both represent hydrogen atoms, and R2and R3both represent ethyl or methyl groups, preferably methyl groups.

[0047] Suitable urea derivatives are commercially available, for example, under the Dyhard ® trade name (from AlzChem Group AG), under the Omicure® trade name (from CVC Thermoset Specialties), under the Amicure® trade name (from Evonik) and from Sigma Aldrich. In case the latent curing agent B is selected from the group consisting of aromatic dicarboxylic dihydrazide B1 and aliphatic dicarboxylic dihydrazide B2, the fraction of the accelerator C for epoxy resins is preferably from 0.005 - 0.5 wt.-%, more preferably 0.01 - 0.2 wt.-%, most preferably 0.02 - 0.1 wt.-%, based on the total weight of the thermosetting epoxy resin composition.

[0048] In case the latent curing agent B is dicyandiamide B3, the fraction of the accelerator C for epoxy resins is preferably from 0.05 - 2 wt.-%, more preferably 0.1 - 1.5 wt.- %, most preferably 0.5 - 1 .2 wt.-%, based on the total weight of the thermosetting epoxy resin composition.

[0049] Preferably, the one-component thermosetting epoxy resin composition comprises at least one toughness improver D. The toughness improvers D may be solid or liquid, preferably liquid.

[0050] The toughness improver D is preferably selected from the group consisting of terminally blocked polyurethane polymers D1 , liquid rubbers D2 and and core-shell polymers D3. Particular preference is given to a terminally blocked polyurethane polymer D1. This selection provides optimal balance between impact resistance and compatibility with the corrosion inhibiting additives. Terminally blocked polyurethane polymers offer controlled reactivity that does not interfere with the chelating and radical scavenging mechanisms of the natural corrosion inhibitors, while providing effective toughening through their elastic segments.

[0051] It is preferably a terminally blocked polyurethane polymer D1 blocked with a blocking group that is eliminated at a temperature above 100°C.

[0052] Preferred blocking groups are especially firstly phenols or bisphenols. Preferred examples of such phenols and bisphenols are especially phenol, cresol, resorcinol, catechol, 4-Hydroxyanisole (HQMME), cardanol (3-pentadecenylphenol (from cashewnutshell oil)), nonylphenol, phenols that have been reacted with styrene or dicyclopentadiene, bisphenol A, bisphenol F and 2,2'-diallylbisphenol A. The terminally blocked polyurethane prepolymer is prepared from a linear or branched polyurethane prepolymer terminated by isocyanate groups with one or more isocyanate-reactive compounds. If two or more such isocyanate-reactive compounds are used, the reaction can be effected sequentially or with a mixture of these compounds.

[0053] The reaction is preferably effected in such a way that the one or more isocyanatereactive compounds are used stoichiometrically or in a stoichiometric excess in order to ensure that all NCO groups have been converted.

[0054] The polyurethane prepolymer with isocyanate end groups can be prepared from at least one diisocyanate or triisocyanate and from a polymer QPM having terminal amino, thiol or hydroxyl groups and / or from an optionally substituted polyphenol Qpp, preferably polymer QPM having terminal amino, thiol or hydroxyl groups.

[0055] Suitable diisocyanates are aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, especially commercial products such as methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), toluidine diisocyanate (TODI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (TMDI), 2,5- or 2,6- bis(isocyanatomethyl)bicyclo[2.2.1 ]heptane, naphthalene 1 ,5-diisocyanate (NDI), dicyclohexylmethyl diisocyanate (H12MDI), p-phenylene diisocyanate (PPDI), m- tetramethylxylylene diisocyanate (TMXDI), etc. and dimers thereof. Preference is given to HDI, IPDI, MDI or TDI.

[0056] Suitable triisocyanates are trimers or biurets of aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, especially the isocyanurates and biurets of the diisocyanates described in the previous paragraph. It is of course also possible to use suitable mixtures of di- or triisocyanates.

[0057] Especially suitable polymers QPM having terminal amino, thiol or hydroxyl groups are polymers QPM having two or three terminal amino, thiol or hydroxyl groups. The polymers QPM advantageously have an equivalent weight of 300-6000, especially of 600-4000, preferably of 700-2200, g / equivalent of NCO-reactive groups.

[0058] Preferred polymers QPM are polyols having average molecular weights between 600 and 6000 daltons, selected from the group consisting of polyethylene glycols, polypropylene glycols, polyethylene glycol-polypropylene glycol block polymers, polybutylene glycols, hydroxyl-term inated polybutadienes, hydroxyl-term inated butadiene-acrylonitrile copolymers and mixtures thereof.

[0059] Especially preferred polymers QPM are a-co-di hydroxy polyalkylene glycols having C2-Ce-alkylene groups or having mixed C2-Ce-alkylene groups, terminated by amino, thiol or, preferably, hydroxyl groups. Particular preference is given to polypropylene glycols or polybutylene glycols. Particular preference is further given to hydroxyl group-terminated polyoxybutylenes.

[0060] Especially suitable polyphenols Qpp are bis-, tris- and tetraphenols. This is understood to mean not just straight phenols but optionally also substituted phenols. The nature of the substitution may be very varied. More particularly, this is understood to mean substitution directly on the aromatic ring to which the phenolic OH group is bonded. Phenols are additionally understood to mean not just monocyclic aromatics but also polycyclic or fused aromatics or heteroaromatics that have the phenolic OH group directly on the aromatic or heteroaromatic system.

[0061] In a preferred embodiment, the polyurethane prepolymer is prepared from at least one diisocyanate or triisocyanate and from a polymer QPM having terminal amino, thiol or hydroxyl groups. The polyurethane prepolymer is prepared in a manner known to the person skilled in the art of polyurethane, especially by using the diisocyanate or triisocyanate in a stoichiometric excess in relation to the amino, thiol or hydroxyl groups of the polymer QPM.

[0062] The polyurethane prepolymer having isocyanate end groups preferably has elastic character. It preferably exhibits a glass transition temperature Tg of less than 0°C. The toughness improver D may be a liquid rubber D2. This may be, for example, a carboxy- or epoxy-term inated polymer.

[0063] In a first embodiment, this liquid rubber may be a carboxy- or epoxy-term inated acrylonitrile / butadiene copolymer or derivative thereof. Such liquid rubbers are commercially available, for example, under the Hypro I Hypox® CTBN and CTBNX and ETBN name from Emerald Performance Materials. Suitable derivatives are especially elastomer-modified prepolymers having epoxy groups, as sold commercially under the Polydis® product line, especially from the Polydis® 36.. product line, by Struktol® (Schill+Seilacher Gruppe, Germany) or under the Albipox product line (Evonik, Germany).

[0064] In a second embodiment, this liquid rubber may be a polyacrylate liquid rubber which is fully miscible with liquid epoxy resins and separates to form microdroplets only in the course of curing of the epoxy resin matrix. Such polyacrylate liquid rubbers are available, for example, under the 20208-XPA name from Dow.

[0065] It is of course also possible to use mixtures of liquid rubbers, especially mixtures of carboxy- or epoxy-term inated acrylonitrile / butadiene copolymers or derivatives thereof.

[0066] The toughness improver D, in a third embodiment, may be a core-shell polymer D3. Core-shell polymers consist of an elastic core polymer and a rigid shell polymer. Particularly suitable core-shell polymers consist of a core of elastic acrylate or butadiene polymer encased by a rigid shell of a rigid thermoplastic polymer. This core-shell structure either forms spontaneously as a result of separation of a block copolymer or is defined by the conduct of the polymerization as a latex or suspension polymerization with subsequent grafting. Preferred core-shell polymers are what are called MBS polymers, which are commercially available under the Clearstrength™ trade name from Arkema, Paraloid™ from Dow or F-351 ™ from Zeon.

[0067] Preferably, the proportion of toughness improver D, especially of terminally blocked polyurethane polymer D1. Preferably, the amount of the toughness improver D is 5 - 22.5 % by weight, especially 10 - 20 % by weight, preferably 12.5 - 17.5 % by weight, based on the total weight of the thermosetting one-component epoxy resin composition. This concentration range ensures adequate impact resistance while maintaining the effectiveness of the corrosion inhibiting additives. Higher concentrations may dilute the corrosion inhibitor effectiveness, while lower concentrations may not provide sufficient toughening for demanding applications such as automotive bodywork.

[0068] The composition of the invention also contains d) at least one corrosion inhibiting additive E, wherein the corrosion inhibiting additive E is either: d1 ) a combination E1 of at least one phenol carboxylic acid with at least one flavonoid; or d2) at least one hydrolysable tannin E2.

[0069] Preferably, the at least one phenol carboxylic acid is selected from the list consisting of chlorogenic acid, neochlorogenic acid, isochlorogenic acid, cryptochlorogenic acid, ferulic acid, p-coumaric acid, caffeic acid, sinapinic acid, cinnamic acid, quinic acid, salicylic acid, 4-hydroxybenzoic acid, gentisic acid, gallic acid, ellagic acid, protocatechuic acid and vanillic acid, more preferably selected from chlorogenic acid and gallic acid. Most preferably, the phenol carboxylic acid is gallic acid. These phenol carboxylic acids provide effective metal ion chelation through their multiple hydroxyl groups, contributing to corrosion inhibition by forming stable complexes with metal ions that would otherwise participate in corrosion processes. Gallic acid is particularly effective due to its three adjacent hydroxyl groups providing optimal chelating geometry.

[0070] It can be further preferable if the phenol carboxylic acid is added in the form of avocado seed powder, coffee powder, grape seed powder and green tea powder, preferably in the form of avocado seed powder. Preferably, the beforementioned powder have a mean particle size D (0.5) between 25 - 250 pm, preferably between 50 - 200 pm. The term “mean particle size” here preferably relates to the D (0.5) value of the cumulative volume distribution curve, in which 50% by volume of the particles have a particle size that is smaller than the value. The mean particle size or the D (0.5) value is preferably determined by laser diffractometry. Preferably, the amount of said powder is 0.5 - 10 wt.-%, preferably 1 - 6 wt.-%, more preferably 1.5 - 4.5 wt.-%, most preferably 2 - 4 wt.-%, based on the total weight of the thermosetting one-component epoxy resin composition. This concentration range provides optimal release of active phenol carboxylic acids and flavonoids from the natural powder matrix while maintaining good dispersion and avoiding potential interference with the epoxy curing process. The preferred range of 2-4 wt.% ensures sufficient active compound concentration for effective corrosion inhibition. This is advantageous with respect to storage stability and reduction in LSS values after corrosion treatment.

[0071] Preferably, the phenol carboxylic acid is present in the thermosetting one- component epoxy resin composition in a concentration of 0.01 - 100 mM, preferably 0.1 - 10 mM, 0.5 - 5 mM, more preferably 1 - 2.5 mM. This molar concentration range ensures sufficient availability of chelating sites for metal ion complexation while avoiding potential interference with the epoxy curing chemistry. The preferred range of 1 -2.5 mM provides optimal balance between corrosion inhibition effectiveness and system compatibility.

[0072] Flavonoids have the general structure of a 15-carbon skeleton, which consists of two phenyl rings (A and B) and a heterocyclic ring (C, the ring containing the embedded oxygen).

[0073] Flavonoids are divided according to the structure of the skeleton into chaicones, flavan derivatives, aurones and isoflavones. The flavan derivatives are further subdivided according to the degree of oxidation of the central 2-pyran ring (ring C) into: flavanones, flavones, flavonols, leucoanthocyanidins, catechins and anthocyanidins.

[0074] Flavonoids can also differ in the number of hydroxy and methoxy substituents. Prenylated flavonoids are usually substituted with a C5 group on the A ring.

[0075] Flavonoids can also occur as mono- or oligoglycosides. Flavonoids are also sometimes esterified with aliphatic or aromatic acids, e.g. with malonic acid or caffeic acid.

[0076] In embodiments, the flavonoid is a flavan derivative, preferably the flavonoid is selected from the group consisting of flavanones, flavones, flavonols, leucoanthocyanidins, catechins and anthocyanidins, more preferably flavonols and catechins, most preferably catechins.

[0077] A preferred flavonol is quercetin.

[0078] More preferably, the flavonoid is a catechin, preferably selected from the group consisting of (2R,3S)-Catechin (+), (2R,3R)-Epicatechin (-), (2R,3S)-Gallocatechin (+), (2R,3R)-Epigallocatechin (-), (2R,3S)-Afzelechin, (2S,3S)-Epiafzelechin, (2R,3S)-Robinetinidol and (2R,3S)-Fisteinidol, preferably (2R,3S)-Catechin (+), (2R,3R)-Epicatechin (-), most preferably (2R,3S)-Catechin (+). Catechins provide dual functionality through their phenolic hydroxyl groups, acting as both radical scavengers and metal chelators. The specific stereochemistry of (2R,3S)-Catechin (+) provides optimal molecular conformation for interaction with metal surfaces and reactive species, enhancing the overall corrosion inhibition effectiveness when combined with phenol carboxylic acids.

[0079] Preferably, the flavonoid is present in the thermosetting one-component epoxy resin composition in a concentration of 0.01 - 100 mM, preferably 0.1 - 10 mM, 0.25 - 3 mM, more preferably 0.5 - 1.5 mM. This concentration range provides effective radical scavenging activity and synergistic enhancement of the phenol carboxylic acid chelating effect. The preferred range of 0.5-1 .5 mM ensures optimal antioxidant protection while maintaining compatibility with the one-component system storage requirements.

[0080] It can be further preferable if the flavonoid is added in the form of avocado seed powder, coffee powder, grape seed powder and green tea powder, preferably in the form of avocado seed powder. Preferably, the beforementioned powder have a mean particle size D (0.5) between 25 - 250 pm, preferably between 50 - 200 pm. The term “mean particle size” here preferably relates to the D (0.5) value of the cumulative volume distribution curve, in which 50% by volume of the particles have a particle size that is smaller than the value. The mean particle size or the D (0.5) value is preferably determined by laser diffractometry.

[0081] Preferably, the amount of said powder is 0.5 - 10 wt.-%, preferably 1 - 6 wt.-%, more preferably 1.5 - 4.5 wt.-%, most preferably 2 - 4 wt.-%, based on the total weight of the thermosetting one-component epoxy resin composition. This is advantageous with respect to storage stability and reduction in LSS values after corrosion treatment.

[0082] A hydrolysable tannin is a type of tannin that, on heating with hydrochloric or sulfuric acids, yields gallic or ellagic acids. Preferably, the hydrolysable tannin is a hydrolysable tannin as described in the online Rdmpp Chemie Lexikon (Thome Verlag), accessed on 18.09.2024, under “tannins” and “tanning agents”.

[0083] Hydrolysable tannins can be extracted from different vegetable plants, such as chestnut wood, oak wood, tara pods, gallnuts, myrobalan, sumac and Aleppo gallnuts.

[0084] The hydrolysable tannin is preferably selected from the group consisting of tannic acid, ellagitannins and gallotannins, preferably tannic acid and ellagitannins, more preferably tannic acid. This selection provides enhanced corrosion resistance performance, with tannic acid demonstrating superior effectiveness in reducing lap shear strength degradation after corrosive exposure, particularly achieving LSSA values of -34% compared to reference compositions showing -49% degradation.

[0085] The hydrolysable tannin E2 selected from tannic acid, ellagitannins and gallotannins provides significant technical advantages in thermosetting one-component epoxy resin compositions, particularly in terms of corrosion resistance and system compatibility.

[0086] The experimental data demonstrates that hydrolysable tannins substantially improve corrosion resistance compared to reference compositions without corrosion inhibiting additives. The corrosion resistance is measured by the percentage reduction in lap shear strength (LSSA) after exposure to corrosive conditions according to VDA 233-102 testing protocol.

[0087] Compositions containing tannic acid show marked improvement in corrosion resistance across different curing systems. In the adipic dihydrazide (ADH) curing system, composition E9 containing 3.3 wt.% tannic acid exhibits a LSSA of -34%, representing a significant improvement over the reference composition R1 which shows -49% reduction. This corresponds to a 30% improvement in corrosion resistance performance. Similarly, in the dicyandiamide curing system, composition E25 with 3.3 wt.% tannic acid demonstrates a LSSA of -42% compared to reference R8 at -53%, indicating a 21% improvement in corrosion resistance. Compositions incorporating walnut shell powder, which contains ellagitannins, also demonstrate enhanced corrosion resistance. Composition E8 with 3.3 wt.% walnut shell powder shows a LSSA of -45% in the ADH system, while composition E19 exhibits -43% in the dicyandiamide system, both representing improvements over their respective reference compositions.

[0088] The hydrolysable tannins exhibit optimal performance within specific concentration ranges. The experimental data reveals that tannic acid concentrations around 1.5-2.5 mM provide the most effective corrosion inhibition. This is evidenced by composition E9 (3.3 wt.% tannic acid) showing superior performance with LSSA of -34% compared to compositions E10 (1.7 wt.%, LSSA = -44%) and E11 (5 wt.%, LSSA = -40%). This concentration-dependent behavior indicates that the hydrolysable tannins function through a specific mechanism that requires optimal loading levels for maximum effectiveness.

[0089] The hydrolysable tannin in particular selected from the group consisting of tannic acid, ellagitannins and gallotannins, preferably tannic acid and ellagitannins, more preferably tannic acid provide advantageous storage stability characteristics when used within the preferred concentration ranges. The compositions maintain their performance properties during extended storage periods, which is critical for one-component thermosetting systems that must remain stable until activation by heat. This storage stability is particularly important for industrial applications where long shelf life is required.

[0090] The hydrolysable tannins in particular selected from the group consisting of tannic acid, ellagitannins and gallotannins, preferably tannic acid and ellagitannins, more preferably tannic acid demonstrate broad compatibility with different latent curing systems used in one- component epoxy compositions. The experimental results show effective performance with both aliphatic dicarboxylic dihydrazide (ADH) and dicyandiamide curing agents. Notably, the hydrolysable tannins show enhanced performance in the ADH curing system, with composition E9 achieving better corrosion resistance (-34% LSSA) compared to the corresponding dicyandiamide system composition E25 (-42% LSSA).

[0091] The technical effect of hydrolysable tannins in particular selected from the group consisting of tannic acid, ellagitannins and gallotannins, preferably tannic acid and ellagitannins, more preferably tannic acid may be attributed to their inherent chelating properties and radical scavenging capabilities. These natural compounds can interact with metal ions and reactive species that contribute to corrosion processes, thereby providing protection to the substrate-adhesive interface during exposure to corrosive environments. The phenolic hydroxyl groups present in the tannin structure enable multiple coordination sites for metal ion chelation, while the aromatic systems provide antioxidant activity that may contribute to long-term stability of the cured epoxy matrix. The demonstrated technical effects establish that hydrolysable tannins, particularly tannic acid, provide a viable and effective approach to achieving enhanced corrosion resistance in one-component thermosetting epoxy resin compositions while maintaining compatibility with existing curing systems and storage requirements.

[0092] Preferred ellagitannins are selected from the group of primary ellagitannins, dehydroellagitannins, modified dehydroellagitannins, C-glycosidic ellagitannins and oligomeric ellagitannins, preferably primary ellagitannins, most preferably punicalagin.

[0093] Even more preferably, the hydrolysable tannin is selected from the group consisting of tannic acid and ellagitannins, more preferably tannic acid and punicalagin.

[0094] Most preferably, the hydrolysable tannin is tannic acid.

[0095] Preferably, the hydrolysable tannin is present in the thermosetting one-component epoxy resin composition in a concentration of 0.01 - 100 mM, preferably 0.1 - 10 mM, 0.5 - 5 mM, more preferably 1 .5 - 2.5 mM. This concentration range provides optimal corrosion inhibition effectiveness while maintaining storage stability. Concentrations within the preferred range of 1.5-2.5 mM demonstrate superior performance, as evidenced by composition E9 (3.3 wt.% tannic acid) achieving better corrosion resistance (LSSA = -34%) compared to lower concentrations E10 (1.7 wt.%, LSSA = -44%) and higher concentrations E11 (5 wt.%, LSSA = -40%). This is advantageous with respect to storage stability. This can be seen, for example, in the comparison of E9 with E10 and E11 and in the comparison of E25 with E26 and E27. It is further advantageous, especially if an aliphatic dicarboxylic dihydrazide B2 is used as a curing agent, with respect to reduction in LSS values after corrosion treatment. This can be seen, for example, in the comparison of E9 with E10 and E11.

[0096] It can be further preferable if the hydrolysable tannin is added in the form of walnut shell powder. Preferably, the walnut shell powder has a mean particle size D (0.5) between 25 - 250 pm, preferably between 50 - 100 pm. The term “mean particle size” here preferably relates to the D (0.5) value of the cumulative volume distribution curve, in which 50% by volume of the particles have a particle size that is smaller than the value. The mean particle size or the D (0.5) value is preferably determined by laser diffractometry.

[0097] Preferably, the amount of walnut shell powder is 0.5 - 10 wt.-%, preferably 1 - 6 wt.-%, more preferably 1 .5 - 4.5 wt.-%, most preferably 2 - 4 wt.-%, based on the total weight of the thermosetting one-component epoxy resin composition. This is advantageous with respect to storage stability and reduction in LSS values after corrosion treatment.

[0098] In a further preferred if the thermosetting one-component epoxy resin composition additionally comprises at least one filler F. Preference is given here to mica, talc, kaolin, wollastonite, feldspar, titanium oxide, syenite, chlorite, bentonite, montmorillonite, calcium carbonate (precipitated or ground), dolomite, quartz, silicas (fused or precipitated), cristobalite, calcium oxide, aluminum hydroxide, magnesium oxide, hollow ceramic beads, hollow glass beads, hollow organic beads, glass beads, color pigments. Particular preference is given to fillers selected from the group consisting of calcium carbonate, calcium oxide, wollastonite, titanium oxide, and fumed silicas.

[0099] Advantageously, the total proportion of the overall filler F is 5 - 35 % by weight preferably 10 - 25 % by weight, more preferably 15 - 20 % by weight, based on the total weight of the thermosetting one-component epoxy resin composition.

[0100] In a further preferred embodiment, the composition additionally comprises at least one epoxy-bearing reactive diluent G. Such reactive diluents are known to the person skilled in the art. Preferred examples of epoxy-bearing reactive diluents are:

[0101] - glycidyl ethers of monofunctional, saturated or unsaturated, branched or unbranched, cyclic or open-chain, C4-C30 alcohols, e.g. butanol glycidyl ether, hexanol glycidyl ether, 2-ethylhexanol glycidyl ether, allyl glycidyl ether, tetrahydrofurfuryl and furfuryl glycidyl ether, trimethoxysilyl glycidyl ether, and the like;

[0102] - glycidyl ethers of tri- or more than trifunctional, saturated or unsaturated, branched or unbranched, cyclic or open-chain, alcohols, such as epoxidized castor oil, epoxidized trimethylolpropane, epoxidized pentaerythritol or polyglycidyl ethers of aliphatic polyols, such as sorbitol, glycerol, trimethylolpropane, and the like;

[0103] - glycidyl ethers of phenol compounds and aniline compounds, such as phenyl glycidyl ether, cresyl glycidyl ether, p-tert-butylphenyl glycidyl ether, nonylphenol glycidyl ether, 3-n-pentadecenyl glycidyl ether (from cashewnutshell oil), N, N-diglycidylaniline, and the like;

[0104] - epoxidized amines, such as N,N-diglycidylcyclohexylamine, and the like;

[0105] - epoxidized mono- or dicarboxylic acids, such as glycidyl neodecanoate, glycidyl methacrylate, glycidyl benzoate, diglycidyl phthalate, tetrahydrophthalate and hexahydrophthalate, diglycidyl esters of dimeric fatty acids, and the like;

[0106] - epoxidized di- or trifunctional, low to high molecular weight polyether polyols, such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and the like.

[0107] Particular preference is given to p-fe / t-butylphenyl glycidyl ether.

[0108] Advantageously, the total proportion of the epoxy-bearing reactive diluent G is 0.1 - 5% by weight, preferably 0.2-3% by weight, especially preferably 0.5 - 2 % by weight, based on the total weight of the thermosetting one-component epoxy resin composition.

[0109] The composition may include further constituents, especially catalysts, stabilizers, especially heat and / or light stabilizers, thixotropic agents, plasticizers, solvents, mineral or organic fillers, blowing agents, dyes and pigments, anticorrosives, surfactants, defoamers and adhesion promoters.

[0110] Suitable plasticizers are especially phenol alkylsulfonates or N-butylbenzamide, as commercially available as Mesamoll® or Del latol BBS from Bayer.

[0111] Suitable stabilizers are especially optionally substituted phenols such as BHT or Wingstay® T (Elkem), sterically hindered amines or N-oxyl compounds such as TEMPO (Evonik). It is advantageous when the epoxy resin composition of the invention has a viscosity at 25°C of 750 - 4500 Pa*s, especially 1000 - 3500 Pa*s, preferably 1200 - 3000 Pa*s, more preferably 1500 - 2700 Pa*s, especially measured with a rheometer in oscillation using a plate-plate geometry with the following parameters: 5 Hz, measurement gap 1 mm, plate-plate diameter 25 mm, 1 % deformation. This viscosity range ensures good applicability for industrial coating and bonding processes while maintaining proper wetting of substrates. The preferred range of 1500-2700 Pa*s provides optimal balance between processability and the ability to maintain the corrosion inhibiting additives in proper dispersion during application. This is advantageous in that this assures good applicability.

[0112] It has been found that the thermosetting one-component epoxy resin compositions described are particularly suitable for use as one-component thermosetting adhesives, especially as a thermosetting one-component bodywork adhesive in motor vehicle construction. Such a one-component adhesive has a range of possible uses. Such adhesives are required for the bonding of heat -stable materials. Heat-stable materials are understood to mean materials which are dimensionally stable at a curing temperature of 100 - 220°C, preferably 120 - 200°C, at least during the curing time. In particular, these are metals and plastics, such as ABS, polyamide, polyphenylene ether, composite materials, such as SMC, unsaturated polyesters GFP, epoxy or acrylate composite materials. Preference is given to the use in which at least one material is a metal. A particularly preferred use is considered to be the bonding of identical or different metals, especially in bodywork construction in the automobile industry. The preferred metals are in particular steel, especially electrolytically galvanized, hot-dip-galvanized or oiled steel, Bonazinc- coated steel, and post-phosphated steel, and also aluminum, especially in the variants which typically occur in automobile construction.

[0113] A further aspect of the present invention relates to a process for the bonding of heatstable substrates, which comprises the stages: i) applying a thermosetting one-component epoxy resin composition as described in detail above to the surface of a heat-stable substrate S1 , especially of a metal; ii) contacting the thermosetting one-component epoxy resin composition applied with the surface of a further heat-stable substrate S2, especially of a metal; iii) heating the composition to a temperature of 100-220°C, especially of 120-200°C, preferably between 130 and 190°C, more preferably between 130 and 180°C.

[0114] The substrate S2 consists here of the same material as or a different material from the substrate S1. The substrates S1 and / or S2 are in particular the aforementioned metals and plastics.

[0115] Preferably, in step iii), the composition is heated to a temperature of 100-220°C, especially of 120-200°C, preferably between 130 and 190°C, more preferably between 130 and 180°C, and the composition is left at the aforementioned temperature for 10 min - 6 h, 10 min - 2 h, 10 min - 60 min, 10 min - 30 min, 10 min - 20 min, more preferably 10 min - 15 min.

[0116] Such a method of bonding heat-stable materials results in an adhesive-bonded article. Such an article is preferably a vehicle or part of a vehicle.

[0117] A further aspect of the present invention accordingly relates to an adhesive-bonded article obtained from the abovementioned process. Furthermore, the compositions according to the invention are suitable not only for automobile construction but also for other fields of use. Particular mention should be made of related applications in the construction of transportation means, such as ships, trucks, buses or rail vehicles, or in the construction of consumer goods, such as, for example, washing machines.

[0118] The materials adhesive-bonded by means of a composition according to the invention are used at temperatures between typically 120°C and -40°C, preferably between 100°C and -40°C, in particular between 80°C and -40°C.

[0119] A particularly preferred use of the thermosetting one-component epoxy resin composition of the invention is the use thereof as a thermosetting one-component bodywork adhesive in motor vehicle construction or as a stiffening compound or as a foamable, thermosetting composition for the reinforcement of voids in structural components and reinforcing elements. A further aspect of the present invention relates to a cured epoxy resin composition as obtained by heating a thermosetting one-component epoxy resin composition as described in detail above.

[0120] More preferably, the compositions of the invention have the following properties:

[0121] -LSS1 , measured as described in the experimental section, of > 25 MPa, especially

[0122] > 30 MPa, more preferably > 32 MPa;

[0123] - LSS2, measured as described in the experimental section, of > 18 MPa, especially

[0124] > 20 MPa, more preferably > 22 MPa;

[0125] - LSSA, measured as described in the experimental section, of < 50%, especially < 45%, more preferably < 40%;

[0126] - Vise. A, measured as described in the experimental section, of < 150%, especially < 100%, more preferably < 50%.

[0127] The invention further encompasses the use of a corrosion inhibiting additive E, wherein the corrosion inhibiting additive E is either: a combination E1 of at least one phenol carboxylic acid with at least one flavonoid; or at least one hydrolysable tannin E2, as described above, for increasing the corrosion resistance of a one-component thermosetting epoxy resin composition, especially a thermosetting epoxy adhesive, preferably in motor vehicle construction and sandwich panel construction. Preference is given to a thermosetting epoxy resin composition as described above.

[0128] The increase in the corrosion resistance is based on the comparison with one- component thermosetting epoxy resin compositions that do not contain any of the aforementioned corrosion inhibiting additive E.

[0129] Corrosion resistance is preferably determined by measuring the lap shear strength after oven curing for 40 min at 180°C and followed by 12 cycles VDA 233-102 (DIN EN 1465) of the one-component thermosetting epoxy resin composition, especially on the basis of the determination of the percentage decrease between the value of the lap shear strength after oven curing for 40 min at 180°C and the value of the lap shear strength after oven curing for 40 min at 180°C followed by 12 cycles VDA 233- 102. Most preferably, the corrosion resistance is determined as described in the experimental section as show as “LSSA” (percentage drop).

[0130] Preferably, the type and amount used of the corrosion inhibiting additive E correspond to the type and amount described above; more particularly, the types and amounts designated as preferred above are also used with preference.

[0131] Examples

[0132] Some examples which further illustrate the invention, but which are not intended to restrict the scope of the invention in any way, are cited below.

[0133] Raw materials used for preparing the impact modifier D1 and the reference compositions R1 -R13 and the inventive compositions E1 -E28 were as follows:

[0134]

[0135] Table 1 Preparation of the toughness improver (D1)

[0136] 150 g of poly-THF 2000 (OH number 57 mg / g KOH) and 150 of Liquiflex H (OH number 46 mg / g KOH) were dried under vacuum at 105°C for 30 minutes. Once the temperature had been reduced to 90°C, 61.5 g of IPDI and 0.14 g of dibutyltin dilaurate were added. The reaction was carried out under vacuum at 90°C until the NCO content was constant at 3.10% after 2.0 h (calculated NCO content: 3.15%). Subsequently, 96.1 g of cardanol were added as blocking agent. Stirring was continued at 105°C under vacuum until it was no longer possible to detect any free NCO. The product was used as such as toughness improver D1.

[0137] Preparation of the base composition 1 (BC-1 ) with ADH (B2) as curing agent

[0138] Table 2

[0139] The composition as indicated in table 2 was used as base formulation and the amount of additives as indicated in table 4 was added. The amount indicated in table 4 is the amount (*) of additive in wt.-% in the final compositions E1 -E11 , respectively R1 -7. The same amount of additive in wt.-% that was added to a specific composition was removed from the amount of filler F1 shown in table 2 in this composition. For example, in the composition E1 , 3.3 wt.-% of additive E1-1 (avocado seed powder) was added to the base composition 1 whereby the amount of filler F1 was reduced to 3.03 wt.-% to obtain the composition E1 . Preparation of the base composition 2 (BC-2) with Dicy (B3) as curing agent

[0140] Table 3

[0141] The composition as indicated in table 3 was used as base formulation and the amount of additives as indicated in table 5 was added. The amount indicated in table 5 is the amount (*) of additive in wt.-% in the final compositions E12-28, respectively R8-R13. The same amount of additive in wt.-% that was added to a specific composition was removed from the amount of filler F1 shown in table 3 in this composition. For example, in the composition E12, 3.3 wt.-% of additive E1-1 (avocado seed powder) was added to the base composition 2 whereby the amount of filler F1 was reduced to 3.7 wt.-% to obtain the composition E12.

[0142] Viscosity / storage stability of compositions

[0143] Viscosity measurements of the compositions were effected 1 d after production on an Anton Paar MCR 101 rheometer by oscillation using a plate-plate geometry at a temperature of 25°C with the following parameters: 5 Hz, measurement gap 1 mm, plate-plate diameter 25 mm, 1 % deformation. The measurement in Pa*s is displayed in table 4 and 5 under "Visc.1".

[0144] For assessment of the storage stability of the adhesives, the viscosity measurement was repeated after storage for 1 week at 50°C and the percentage rise in viscosity that results after the storage was ascertained. The measured viscosity in Pa*s measured at a temperature of 25°C after storage for 1 week at 50°C is displayed as "Visc.2". The value of the percentage rise in viscosity is displayed as “Visc.A”. shear strenqth oven curinq for 40 min / 180°C (“LSS1”) (DIN EN

[0145] Cleaned test specimens of HDG H420 steel (thickness 1.2 mm) that had been reoiled with Anticorit PL 3802-39S were bonded with the adhesive over a bonding area of 25 x 10 mm with glass beads as spacer in a layer thickness of 0.2 mm, and cured at oven temperature 180°C for 40 min.

[0146] Lap shear strength in MPa was determined on a tensile tester at a strain rate of 10 mm / min in a triple determination to DIN EN 1465 at a temperature of 23°C ("LSS1"). n curinq for 40 min / 180°C and 12 cycles VDA 233-102

[0147] Cleaned test specimens of HDG H420 steel (thickness 1.2 mm) that had been reoiled with Anticorit PL 3802-39S were bonded with the adhesive over a bonding area of 25 x 10 mm with glass beads as spacer in a layer thickness of 0.2 mm, and cured at oven temperature 180°C for 40 min. Said specimens were then exposed to 12 cycles VDA 233-102 before determining the lap shear strength. A test cycle lasts 1 week which consists of:

[0148] A. 24h cycle: 3h neutral salt spray atmosphere (35°C / 1 % NaCI solution / pH 6.5 to 7.2) and 21 h humid climate (30-50°C / 50-95% relative humidity) B. 24h humid climate (25-50°C / 70-98% relative humidity) C. 24h cycle: 5h freezing phase (- 15°C / 70% relative humidity) and 19h humid climate (35-50°C / 70-95% relative humidity). The test cylcle has the following sequence over the 7 days: BACABBA.

[0149] Lap shear strength in MPa was then determined on a tensile tester at a strain rate of 10 mm / min in a triple determination to DIN EN 1465 at a temperature of 23°C ("LSS2").

[0150] The reduction from the lap shear strength values of "LSS1" and "LSS2" in percentage is show as “LSSA” (percentage drop).

[0151] The fracture patterns of the lap shear measurements were assessed by eye in the following order (the earlier mentioned position in the sequence corresponds to better adhesion behavior (best to worst) and indicated in percentage):

[0152] Cohesion failure (“CF”) Surface-close cohesion failure (“SCF”)

[0153] White failure (“WF”)

[0154] Adhesion failure (“AF”)

[0155] The visual assessment of the measurements from “LSS1 ” are shown as “Fracl ”, the visual assessment of the measurements from “LSS2” are shown as “Frac2” respectively.

[0156] In addition, the composition E1 was used in an open circuit potential measurement and compared to the reference composition R1 . The Open circuit potential (OOP) is the potential difference between a working electrode (WKG), which is the sample with the adhesive and a reference electrode (REF). These electrodes are immersed in an electrolyte and relate to a voltmeter. Open circuit means that the potential is present when the electrodes are detaches and there is no external potential. The result of the measurement is illustrated in a diagram that shows the OOP vs. the immersion time. A higher value and therefore a higher potential difference indicates that more metal ions were set free from the surface. This means that the system is weaker and the corrosion performance is worse. In the case of the adhesives, a lower and constant OOP indicates that a corrosion inhibiting additive act as a corrosion inhibitor. The reference electrode was an Ag / AgCI electrode with constant potential. Each adhesive sample (working electrode) were immersed together with the reference electrode in an electrolyte for over 100 hours. This electrolyte was a 0.1 M sodium chloride solution.

[0157] Three independent measurements showed that the first 72 hours of the investigation the behaviour of the reference composition R1 and the sample with the composition E1 was near the same. After this time the OCP of the reference composition R1 increased. This indicates a higher zinc content in the solution and therefore a faster corrosion process. The OCP of the adhesive compositions E1 remained constant after 72 hours. This indicates that the corrosion process was inhibited by the corrosion inhibiting additive.

[0158] A contact angle measurement showed no difference between the composition E1 and the reference composition R1 indicating that the corrosion inhibiting additive E1 -1 in E1 does not have an influence on the adhesion. The results of the measurements of the adhesive E1 and the reference R1 are near the same. The free surface energy was determined based on the contact angle measurements with water and diiodomethane. The contact angle is a degree for the wettability. It is the angle at the intersection point of a drop and a solid surface. Free surface energy is defined as the work that needs to be done to increase the surface of a phase (liquid / solid). The unit is J / m2It determines the wettability of a solid phase. A high surface energy of a solid phase leads to a good wettability. The tested substrate was HDG H420 (1.2mm). The samples were cleaned with heptane and oiled with the standard oil Anticorit PL 3802 -39S. Five drops of each solution were placed on one sample.

[0159] The above-mentioned results of the comparison of E1 with R1 indicate that the corrosion inhibiting additives E of the present invention work by inhibition of the corrosion during the 12 cycles VDA 233-102 and not by generally increasing the adhesion to the substrate. This is also consistent with the findings of the fracture patterns.

[0160] Table 4

[0161] Table 5

Claims

1. Claims1 . A thermosetting one-component epoxy resin composition comprising: a) at least one epoxy resin A having an average of more than one epoxy group molecule; molecule; b) at least one latent curing agent B for epoxy resins, preferably the latent curing agent B is selected from the group consisting of aromatic dicarboxylic dihydrazide B1, aliphatic dicarboxylic dihydrazide B2 and dicyandiamideB3; c) at least one toughness improver D, preferably selected from the group consisting of terminally blocked polyurethane polymers D1 and liquid rubbers D2, preferably a terminally blocked polyurethane polymer D1 ; and d) at least one corrosion inhibiting additive E, wherein the corrosion inhibiting additive E is either: d1 ) a combination E1 of at least one phenol carboxylic acid with at least one flavonoid; or d2) at least one hydrolysable tannin E2.

2. The thermosetting one-component epoxy resin composition as claimed in claim 1 , characterized in that the hydrolysable tannin E2 is selected from the group consisting of tannic acid, ellagitannins and gallotannins, preferably tannic acid and ellagitannins, more preferably tannic acid.

3. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that phenol carboxylic acid is selected from the list consisting of chlorogenic acid, neochlorogenic acid, isochlorogenic acid, cryptochlorogenic acid, ferulic acid, p-coumaric acid, caffeic acid, sinapinic acid, cinnamic acid, quinic acid, salicylic acid, 4-hydroxybenzoic acid, gentisic acid, gallic acid, ellagic acid, protocatechuic acid and vanillic acid, more preferably selected from chlorogenic acid and gallic acid, most preferably, the phenol carboxylic acid is gallic acid.

4. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the flavonoid is a flavan derivative, preferably selected from the group consisting of flavanones, flavones, flavonols,leucoanthocyanidins, catechins and anthocyanidins, more preferably catechins, most preferably the flavonoid is a catechin.

5. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the hydrolysable tannin E2 is present in the thermosetting one-component epoxy resin composition in a concentration of 0.01 - 100 mM, preferably 0.1 - 10 mM, 0.5 - 5 mM, more preferably 1.5 - 2.5 mM.

6. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the flavonoid is present in the thermosetting one-component epoxy resin composition in a concentration of 0.01 - 100 mM, preferably 0.1 - 10 mM, 0.25 - 3 mM, more preferably 0.5 - 1 .5 mM.

7. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the phenol carboxylic acid is present in the thermosetting one-component epoxy resin composition in a concentration of 0.01 - 100 mM, preferably 0.1 - 10 mM, 0.5 - 5 mM, more preferably 1 - 2.5 mM.

8. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the at least one epoxy resin A has the formula (I)wherein the substituents R’” and R”” are each independently H or CH3, preferably H, the index r has a value of 0 to 1 , preferably, r has a value of less than 0.2.

9. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the latent curing agent B is selected from the group consisting of aromatic dicarboxylic dihydrazide B1 and aliphaticdicarboxylic dihydrazide B2, preferably aliphatic dicarboxylic dihydrazide B2, and the at least one corrosion inhibiting additive E is at least one hydrolysable tannin E2, preferably tannic acid.

10. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the thermosetting one-component epoxy resin composition additionally includes at least one accelerator C selected from the list consisting of substituted ureas, imidazoles, imidazolines and blocked amines, preferably imidazoles and substituted ureas, most preferred substituted ureas.11 . The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the thermosetting one-component epoxy resin composition additionally includes at least one filler F, preferably selected from the group consisting of calcium carbonate, calcium oxide, wollastonite, titanium oxide, and fumed silicas; preferably the total proportion of the filler F is 5 - 35 % by weight preferably 10 - 25 % by weight, more preferably 15 -20 % by weight, based on the total weight of the thermosetting one- component epoxy resin composition.

12. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the proportion of the epoxy resin A is 35 - 65 % by weight, more preferably 40 - 60 % by weight, most preferably 45 - 55 % by weight, based on the total weight of the one-component epoxy resin composition.

13. The thermosetting one-component epoxy resin composition as claimed in any of the preceding claims, characterized in that the one-component epoxy resin composition has a viscosity at 25°C of 750 - 4500 Pa*s, especially 1000 - 3500 Pa*s, preferably 1200 - 3000 Pa*s, more preferably 1500 - 2700 Pa*s, wherein the viscosity is measured with a rheometer in oscillation using a plate-plate geometry with the following parameters: 5 Hz, measurement gap 1 mm, plateplate diameter 25 mm, 1 % deformation .

14. The use of a thermosetting one-component epoxy resin composition as claimed in any of claims 1 to 13 as one-component thermosetting adhesive, especially as thermosetting one-component bodywork adhesive in motor vehicle construction.

15. A process for the adhesive bonding of heat-stable substrates, comprising the stages of: i) applying a thermosetting one-component epoxy resin composition as claimed in any of claims 1 to 13 to the surface of a heat-stable substrate S1 , especially of a metal; ii) contacting the thermosetting one-component epoxy resin composition applied with the surface of a further heat-stable substrate S2, especially of a metal; iii) heating the composition to a temperature of 100-220°C, especially of 120- 200°C, preferably between 130 and 190°C, more preferably between 130 and 180°C; in which the substrate S2 consists of the same material as or a different material from the substrate S1.

16. The use of a corrosion inhibiting additive E, wherein the corrosion inhibiting additive E is either: a combination E1 of at least one phenol carboxylic acid with at least one flavonoid; or at least one hydrolysable tannin E2; preferably as described as the corrosion inhibiting additive E in claims 1 to 13, for increasing the corrosion resistance of a one-component thermosetting epoxy resin composition, especially a thermosetting epoxy adhesive, preferably in motor vehicle construction and sandwich panel construction, more preferably it is a one-component thermosetting epoxy resin composition as claimed in any of claims 1 to 13, preferably the corrosion resistance is determined as described in the description.

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