One-component thermoset epoxy adhesive with improved adhesion

Abstract

The present invention relates to a one-component thermosetting epoxy resin adhesive comprising at least one epoxy resin A, at least one epoxy-functionalized fatty acid oligomer EFA, at least one latent hardener B for epoxy resins; at least one terminal-blocked polyurethane polymer D1 wherein the weight ratio (D1 / EFA) of the terminal-blocked polyurethane polymer D1 to the epoxy-functionalized fatty acid oligomer EFA, based on the total weight of the one-component thermoset epoxy resin adhesive, is in the range of from 4 to 20, and wherein the weight ratio (D1 / EFA) of the terminal-blocked polyurethane polymer D1 to the epoxy-functionalized fatty acid oligomer EFA is in the range of from 4 to 20. And the sum (D1 + EFA) of the total amount of the terminal-blocked polyurethane polymer D1 and the epoxy-functionalized fatty acid oligomer EFA is from 10 to 17.5% by weight. The epoxy resin adhesive shows a small reduction in overlap shear strength performance in the fully cured state if applied at elevated temperature and humidity, preferably at 40 DEG C and 80% relative humidity for one week, and stored uncured compared to an adhesive that cures immediately after application.

Description

Technical Field

[0001] The present invention relates to the field of one-component thermosetting epoxy resin adhesives and also to their use, in particular in vehicle construction. Prior art

[0002] Thermosetting one-component epoxy resin adhesives have been used as adhesives in vehicle body construction for quite some time. Therefore, an important field of application of one-component thermosetting epoxy resin adhesives is in vehicle construction, where metal substrates such as steel sheets and aluminum are often present, especially in the case of adhesive bonding. After application of the epoxy resin composition, the vehicle body is heated in a CEC (cathodic electrophoretic coating) oven, by which the thermosetting epoxy resin composition is also cured.

[0003] It is common practice in the automotive industry to manufacture parts in one country or region and then export and / or transport them to another location (e.g., country or region) for final assembly. This is called CKD (complete knock-down). In a CKD system, parts can be partially assembled before being transported to the final assembly location. In particular, at a first location (e.g., an automotive parts factory), the parts can be bonded together using an epoxy adhesive and then preferably partially cured, for example, using elevated temperatures. The partially assembled parts are then transported to a second location, such as a final assembly location. Typically, additional assembly is performed at the second location and then the curing process (preferably started at the first location) is completed.

[0004] A common problem is that if components used in automotive bodies are bonded with adhesives at a first location, the adhesive needs to meet specific performance criteria with respect to moisture resistance so that the article assembled at a second location meets product and manufacturing specifications, especially in terms of lap shear strength performance. In particular, if such uncured or partially cured articles are stored or transported at elevated temperatures and humidity, for example at 40°C and 80% relative humidity, the lap shear strength of the final cured article is significantly reduced compared to an article cured immediately after assembly.

[0005] WO 2012158336 A1 describes a thermosetting one-component epoxy resin adhesive having an excess of dicyandiamide hardener relative to the epoxy functional groups for improving lap shear strength after CKD aging. WO 2010098950 A1 describes a thermosetting one-component epoxy resin adhesive containing epoxy-functional fatty acid oligomers and semi-crystalline or crystalline polyester polyols for increasing storage stability.

[0006] WO 2004055092 A1 and WO 2005007720 A1 disclose thermosetting one-component epoxy resin adhesives containing epoxy-functional fatty acid oligomers. The compositions exhibit high impact peel values, especially at low temperatures. SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to provide a one-component thermosetting epoxy resin adhesive which, compared to an adhesive which cures immediately after application, shows little reduction in lap shear strength properties if stored in the uncured state at elevated temperature and humidity, preferably at 40° C. and 80% relative humidity for 1 week.

[0009] Surprisingly, it has been found that this object can be achieved with a one-component, thermosetting epoxy resin adhesive as defined in claim 1 .

[0010] Further aspects of the invention are the subject matter of further independent claims. Particularly preferred embodiments of the invention are the subject matter of the dependent claims.

[0011] Certain embodiments of the invention

[0012] Therefore, the present invention relates to a one-component thermosetting epoxy resin adhesive comprising:

[0013] a) at least one epoxy resin A of formula (II)

[0014]

[0015] The substituents R' and R" are independently H or CH 3 , and the value of subscript s is 0-12, preferably 0-1, and the amount of epoxy resin A is 25-70% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive; and

[0016] b) at least one epoxy-functional fatty acid oligomer EFA; and

[0017] c) at least one latent hardener B for epoxy resin; and

[0018] d) preferably, at least one accelerator C for epoxy resins; and

[0019] e) at least one end-blocked polyurethane polymer D1;

[0020] f) less than 5 wt. % of liquid rubber D2, based on the total weight of the one-component thermosetting epoxy resin adhesive;

[0021] g) less than 1.5 wt. % of a crystalline or semi-crystalline polyester polyol PP, based on the total weight of the one-component thermosetting epoxy resin adhesive, wherein the crystalline or semi-crystalline polyester polyol PP has a hydroxyl equivalent of 500 to 10,000 and preferably has a crystalline melting temperature of 40° C. to 125° C.;

[0022] Wherein, based on the total weight of the one-component thermosetting epoxy resin adhesive, the weight ratio of the end-blocked polyurethane polymer D1 to the epoxy-functionalized fatty acid oligomer EFA (D1 / EFA) is 4-20, and the total amount of the end-blocked polyurethane polymer D1 and the epoxy-functionalized fatty acid oligomer EFA (D1+EFA) is 10-17.5 weight %.

[0023] Epoxy resin adhesives are one-component, which means that the components of epoxy resin adhesives, more particularly epoxy resin and hardener, are present in one component and do not cure at normal ambient or room temperature. Therefore, a one-component epoxy resin adhesive is storage-stable. It can therefore be handled in this form, whereas with a two-component system the components are not mixed until just before use.

[0024] Curing of one-component epoxy resin adhesives is accomplished by heating, typically at temperatures greater than 70°C, such as in the range of 100 to 220°C.

[0025] In expressions such as polyol or polyisocyanate, the prefix "poly" indicates that the compound has two or more of the stated groups. For example, a polyisocyanate is a compound having two or more isocyanate groups.

[0026] The expression "independently of one another" as used below means that in the same molecule, two or more identically represented substituents may have the same or different meanings according to definition.

[0027] The dashed lines in the formulae herein represent in each case the bond between the substituent in question and the relevant remainder of the molecule.

[0028] Unless otherwise stated, room temperature herein refers to a temperature of 23°C.

[0029] The thermosetting one-component epoxy resin adhesive comprises at least one epoxy resin A of formula (II)

[0030]

[0031] The substituents R' and R" are independently H or CH 3 , preferably CH 3 , and the value of the subscript s is 0-12, preferably 0-1, and more preferably 0-0.2.

[0032] Preferably, in epoxy resin A, substituents R' and R" are CH 3 , and the subscript s has a value of 0-1, preferably 0-0.2.

[0033] Based on the total weight of the one-component thermosetting epoxy resin adhesive, the proportion of epoxy resin A is 25-70 wt %, preferably 25-70 wt %, 30-60 wt %, 35-55 wt %, more preferably 40-50 wt %.

[0034] Thus, the resin is preferably diglycidyl ether of bisphenol A (DGEBA), bisphenol F and bisphenol A / F. These types of liquid resins can be used, for example, in the form of GY 250, PY 304, GY 282 (Huntsman) or DER TM 331 or DER TM 330 (Dow) or Epikote 828 (Hexion).

[0035] Preferably, the thermosetting one-component epoxy resin adhesive further comprises at least one reactive diluent G having an epoxy group. Such reactive diluents are known to those skilled in the art. Preferred examples of reactive diluents having an epoxy group are:

[0036] - monofunctional saturated or unsaturated, branched or unbranched, cyclic or open-chain C 4 -C 30 Glycidyl ethers of alcohols, such as butanol glycidyl ether, hexanol glycidyl ether, 2-ethylhexanol glycidyl ether, allyl glycidyl ether, tetrahydrofurfuryl and furfuryl glycidyl ether, trimethoxysilyl glycidyl ether, and the like;

[0037] - bifunctional saturated or unsaturated, branched or unbranched, cyclic or open-chain C 2 -C 30 Glycidyl ethers of alcohols, such as ethylene glycol glycidyl ether, butanediol glycidyl ether, hexanediol glycidyl ether, octanediol glycidyl ether, cyclohexanedimethanol diglycidyl ether, neopentyl glycol diglycidyl ether, etc.;

[0038] - glycidyl ethers of trifunctional or polyfunctional, 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 or trimethylolpropane;

[0039] - 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 cashew nut shell oil), N,N-diglycidyl aniline, etc.;

[0040] - Epoxy amines, such as N,N-diglycidylcyclohexylamine, etc.;

[0041] - epoxidized mono- or dicarboxylic acids, such as glycidyl neodecanoate, glycidyl methacrylate, glycidyl benzoate, diglycidyl phthalate, tetrahydrophthalate and hexahydrophthalate, diglycidyl esters of dimerized fatty acids, etc.;

[0042] - Epoxidized di- or tri-functional, low to high molecular weight polyether polyols, such as polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and the like.

[0043] Particularly preferred are hexanediol diglycidyl ether, cresyl glycidyl ether, p-tert-butylphenyl glycidyl ether, polypropylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether.

[0044] Preferably, based on the total weight of the one-component thermosetting epoxy resin adhesive, the proportion of the epoxy-containing reactive diluent G is 1-10 wt%, 1.5-7.5 wt%, 2-5 wt%, more preferably 2-3 wt%.

[0045] The thermosetting one-component epoxy resin adhesive also contains at least one latent hardener B for epoxy resin. The latent hardener is substantially inert at room temperature and is activated by elevated temperature (usually at 70° C. or higher) to initiate a curing reaction. Conventional latent hardeners for epoxy resins can be used. Nitrogen-containing latent epoxy resin hardeners B are preferred.

[0046] The latent hardener B is preferably selected from dicyandiamide, guanamine, guanidine, aminoguanidine and its derivatives, substituted ureas, imidazoles and amine complexes, preferably dicyandiamide.

[0047] The latent hardener B is preferably used in a stoichiometric amount based on the epoxy groups in the composition. The molar ratio of epoxy groups to active hydrogens of the latent hardener B is preferably 0.8-1.2, in particular 0.9-1.1, preferably 0.95-1.05.

[0048] The proportion of latent hardener B is preferably 0.5 to 12% by weight, more preferably 1 to 8% by weight, and more particularly 2-6% by weight, based on the total weight of the epoxy resin adhesive.

[0049] The thermosetting one-component epoxy resin adhesive further comprises at least one accelerator C for the epoxy resin.

[0050] Such accelerating curing agents are preferably substituted ureas, such as 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea (chlorotoluron) or phenyldimethylurea, especially p-chlorophenyl-N,N-dimethylurea (monuron), 3-phenyl-1,1-dimethylurea (fenuron) or 3,4-dichlorophenyl-N,N-dimethylurea (diuron). In addition, imidazole compounds, such as 2-isopropylimidazole or 2-hydroxy-N-(2-(2-(2-hydroxyphenyl)-4,5-dihydroimidazol-1-yl)ethyl)benzamide, imidazoline, trihalide complexes, preferably BF 3 Complexes, blocked amines and encapsulated amines.

[0051] Preferably, the accelerator C for epoxy resins is selected from substituted ureas, imidazoles, imidazolines and blocked amines, preferably substituted ureas.

[0052] More preferably, the accelerator C for epoxy resins is selected from the list consisting of substituted ureas and blocked amines, especially when the latent hardener B is a guanidine, especially dicyandiamide.

[0053] Most preferably, the latent hardener B is a guanidine, especially dicyandiamide, and the one-component thermosetting epoxy resin composition additionally comprises an accelerator C for the epoxy resin selected from substituted ureas and blocked amines, especially substituted ureas.

[0054] Preferably, the proportion of the accelerator C for the epoxy resin is 0.05-2 wt %, preferably 0.1-1 wt %, more preferably 0.15-0.5 wt %, based on the total weight of the one-component thermosetting epoxy resin adhesive.

[0055] The one-component thermosetting epoxy resin adhesive comprises b) at least one epoxy-functional fatty acid oligomer EFA.

[0056] Epoxy-functional fatty acid oligomers are oligomeric unsaturated fatty acids in which the carboxylic acid groups have been capped or otherwise converted to introduce terminal epoxy groups.

[0057] The oligomeric fatty acid preferably has a degree of polymerization of about 2 to about 4. The starting fatty acid preferably has 14 to 24 carbon atoms, more preferably 16 to 18 carbon atoms.

[0058] The oligomers are preferably hydrogenated to remove any residual carbon-carbon double bonds that may be present after the oligomerization reaction.

[0059] Preferred oligomeric fatty acids are the so-called "dimerized fatty acid" products, which are readily commercially available. These dimerized fatty acid products have an average degree of polymerization of 1.9-2.5, about 1.9-2.5 carboxylic acid groups per molecule and 32-45 carbon atoms.

[0060] The epoxy-functional fatty acid oligomers may be prepared by capping the carboxylic acid groups with a polyepoxide, preferably any of the epoxy resin materials described above as epoxy resin A of formula (II).

[0061] Preferably, the epoxy-functional fatty acid oligomer EFA is a dimerized fatty acid having 32 to 45 carbon atoms and 1.9 to 2.5 carboxyl groups per molecule, wherein the carboxyl groups have been capped with a polyepoxide, preferably an epoxy resin A of formula (II).

[0062] Preferably, the end-capping reaction is carried out with at least 1 mole of polyepoxide per equivalent of carboxylic acid groups in the oligomeric fatty acid to end-cap the carboxylic acid groups without significant chain extension. More excess polyepoxide is more preferred because this results in a product comprising epoxy-functionalized fatty acid oligomers and a certain amount of excess unreacted polyepoxide.

[0063] The epoxy-functional fatty acid oligomer EFA preferably accounts for 3-8% by weight of the total weight of the one-component thermosetting epoxy resin adhesive. The preferred amount is 5-7% by weight of the total weight of the one-component thermosetting epoxy resin adhesive.

[0064] For purposes of the present invention, the weight of the epoxy-functionalized fatty acid oligomer EFA does not include any excess unreacted polyepoxide that may be present. Any such excess polyepoxide, if it falls under the definition of epoxy resin A of formula (II), is included as part of the epoxy resin A portion of formula (II) of the structural adhesive. In the case where the epoxy-functionalized fatty acid oligomer EFA is formed by capping a fatty acid oligomer with a polyepoxide, the weight of the epoxy-functionalized fatty acid oligomer EFA can be calculated as the weight of the starting fatty acid oligomer plus the weight of one mole of polyepoxide per equivalent of fatty acid oligomer used in the capping reaction.

[0065] The one-component thermosetting epoxy resin adhesive contains g) less than 1.5 wt% of a crystalline or semi-crystalline polyester polyol PP, based on the total weight of the one-component thermosetting epoxy resin adhesive, wherein the crystalline or semi-crystalline polyester polyol PP has a hydroxyl equivalent of 500 to 10,000, preferably 1,000 to 4,000, and preferably has a crystalline melting temperature of 40 to 125°C. The crystalline melting temperature is preferably determined by differential scanning calorimetry (DSC). This crystalline or semi-crystalline polyester polyol PP preferably contains an average of 1.8 to 4, preferably 1.8 to 2.5 hydroxyl groups per molecule. Suitable polyester polyols include those available under the trade name Dynacoll TM Those commercially available from Evonik Industries. Specific polyester polyol products include Dynacoll TM 7300、Dynacoll TM 7380 and DynacollTM 7381.

[0066] Preferably, based on the total weight of the one-component thermosetting epoxy resin adhesive, the amount is less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%.Most preferably, the one-component thermosetting epoxy resin adhesive does not contain such crystalline or semi-crystalline polyester polyol PP.

[0067] The one-component thermosetting epoxy resin adhesive comprises e) at least one end-blocked polyurethane polymer D1.

[0068] It is preferably a terminally blocked polyurethane prepolymer of formula (I).

[0069]

[0070] In this formula, R 1 is the p-valent group of the linear or branched polyurethane prepolymer terminated by an isocyanate group after removal of the terminal isocyanate group, and p has a value of 2 to 8.

[0071] In addition, R 2 is independently at each occurrence a substituent selected from the group consisting of:

[0072]

[0073] In these formulas, R 5 , R 6 , R 7 and R 8 Each independently of one another is an alkyl group or a cycloalkyl group or an aralkyl group or an arylalkyl group, or R 5 With R 6 Together, or R 7 With R 8 Together they form part of an optionally substituted 4 to 7 membered ring.

[0074] In addition, R 9’ and R 10 are each independently alkyl or aralkyl or aralkyl, or alkoxy or aryloxy or aralkyloxy, and R 11 It is an alkyl group.

[0075] R 12 , R 13 and R 14 Each is independently of one another an alkylene group having 2 to 5 carbon atoms, which optionally has a double bond or is substituted, or a phenylene group or a hydrogenated phenylene group.

[0076] R 15 , R 16 and R 17are each independently H or alkyl or aryl or aralkyl, and R 18 is an aralkyl group or a monocyclic or polycyclic, substituted or unsubstituted aromatic group, which optionally has an aromatic hydroxyl group.

[0077] Finally, R 4 is an aliphatic, cycloaliphatic, aromatic or araliphatic epoxide radical containing a primary or secondary hydroxyl group after removal of the hydroxyl and epoxide groups, and m has a value of 1, 2 or 3.

[0078] On the one hand, R 18 It should be considered to include in particular phenols or polyphenols after removal of the hydroxyl groups, more particularly bisphenols. Preferred examples of such phenols and bisphenols are in particular phenol, cresol, resorcinol, catechol, cardanol (3-pentadecenylphenol (from cashew nut shell oil)), nonylphenol, phenol reacted with styrene or with dicyclopentadiene, bisphenol A, bisphenol F and 2,2'-diallylbisphenol A. On the other hand R 18 It should be understood to comprise in particular hydroxybenzyl alcohol and benzyl alcohol after removal of the hydroxyl group.

[0079] If R 5 , R 6 , R 7 , R 8 , R 9 , R 9 '、R 10 , R 11 , R 15 , R 16 or R 17 is an alkyl radical, the radical is more particularly a straight-chain or branched C 1 -C 20 alkyl.

[0080] If R 5 , R 6 , R 7 , R 8 , R 9 , R 9 '、R 10 , R 15 , R 16 , R 17 or R 18 is aralkyl, then this moiety is more particularly an aromatic group bonded via a methylene group, more particularly a benzyl group.

[0081] If R 5 , R 6 , R 7 , R 8 , R 9 , R 9’ or R 10is an alkylaryl radical, the radical is more particularly a C 1 -C 20 Alkyl, for example tolyl or xylyl.

[0082] Group R 2 Preferred substituents are:

[0083]

[0084] The following formula The preferred substituent is ε-caprolactam after removal of the NH proton.

[0085] The following formula ---OR 18 Preferred substituents are monophenols or polyphenols after removal of the phenolic hydrogen atoms, more particularly bisphenols. 2 Particularly preferred examples are groups selected from the following:

[0086]

[0087] The radical Y in these formulae is a saturated, aromatic or ethylenically unsaturated hydrocarbon radical having 1 to 20 carbon atoms, more particularly 1 to 15 carbon atoms. Preferred Y is in particular allyl, methyl, nonyl, dodecyl, phenyl, alkyl ether, carboxylic ester or an unsaturated C 2-11-13 double bond. 15 alkyl.

[0088] The best choice is R 2 Yes ---OR 18 .

[0089] The terminal-capped polyurethane prepolymer of formula (I) is prepared by reacting a linear or branched polyurethane prepolymer terminated with an isocyanate group with one or more isocyanate-reactive compounds R 2 H Preparation. If two or more such isocyanate-reactive compounds are used, the reaction can be carried out sequentially or with a mixture of these compounds.

[0090] The reaction preferably takes place such that the one or more isocyanate-reactive compounds R 2 H is used in stoichiometric amount or in stoichiometric excess to ensure that all NCO groups have undergone reaction.

[0091] With R 1 The isocyanate-terminated polyurethane prepolymer based on the invention can be composed of at least one diisocyanate or triisocyanate and also of a polymer Q having terminal amino groups, thiol groups or hydroxyl groups. PM and / or an optionally substituted polyphenol Q PP preparation.

[0092] Suitable diisocyanates are aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, in particular commercial products such as methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), tolidine 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 (HDI), diisocyanate (D ... 12 The preferred diisocyanates are MDI, p-phenylene diisocyanate (PPDI), m-tetramethylxylylene diisocyanate (TMXDI), and dimers thereof. HDI, IPDI, MDI or TDI is preferred.

[0093] Suitable triisocyanates are trimers or biurets of aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, more particularly isocyanurates and biurets of the diisocyanates described in the preceding paragraph. Of course, mixtures of suitable diisocyanates or triisocyanates can also be used.

[0094] Particularly suitable as polymer Q having terminal amino groups, thiol groups or hydroxyl groups PM The polymer Q has two or three terminal amino groups, thiol groups or hydroxyl groups. PM .

[0095] Polymer Q PM Advantageously, it has an equivalent weight of 300 to 6000, more particularly 600 to 4000, preferably 700 to 2200 g per equivalent of NCO-reactive groups.

[0096] Preferred polymers Q PM The polyol is a polyol having an average molecular weight of 600-6000 Daltons selected from polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol block polymer, polybutylene glycol, hydroxyl-terminated polybutadiene, hydroxyl-terminated butadiene-acrylonitrile copolymer and mixtures thereof.

[0097] Particularly preferred as polymer Q PM The one with C 2 -C 6 Alkylene or mixed C 2 -C 6 Alkylene α,ω-dihydroxypolyalkylene glycols, which are terminated with amino groups, thiol groups or preferably hydroxyl groups. Particularly preferred are polypropylene glycol or polybutylene glycol. Further particularly preferred are hydroxyl-terminated polyoxybutylenes.

[0098] Especially suitable as polyphenol Q PPThe term refers not only to pure phenols but also, where appropriate, to substituted phenols. The nature of the substitution can be very different. This is understood more specifically to mean substitutions directly on the aromatic ring system to which the phenolic OH group is bonded. Furthermore, phenols are not only monocyclic aromatic compounds but also polycyclic or condensed aromatic or heteroaromatic compounds which have a phenolic OH group directly on the aromatic or heteroaromatic part.

[0099] In a preferred embodiment, the polyurethane prepolymer is composed of at least one diisocyanate or triisocyanate and a polymer Q having terminal amino groups, thiol groups or hydroxyl groups. PM Preparation. The polyurethane prepolymer is prepared in a manner known to those skilled in the art of polyurethanes, more particularly by using a prepolymer having a relative molecular weight of 100 μm. PM A stoichiometric excess of diisocyanate or triisocyanate is added to the amino, thiol or hydroxyl groups.

[0100] The polyurethane prepolymer having isocyanate end groups is preferably elastomeric in nature and has a glass transition temperature Tg preferably below 0°C.

[0101] Surprisingly, it was found that the combination of the mentioned weight ratios (D1 / EFA) and the sum of the total amounts of (D1+EFA) leads to a reduced decrease in the lap shear strength values ​​after application of the adhesive composition and storage (open time) at 40°C / 80% relative humidity (rH) for one week before curing, compared to application of the adhesive composition and immediate curing.

[0102] The weight ratio of the end-capped polyurethane polymer D1 to the epoxy-functional fatty acid oligomer EFA (D1 / EFA) is between 4 and 20. A weight ratio (D1 / EFA) below 4 or above 20 does not surprisingly lead to a reduced (LSS difference (%)) lap shear strength value after an open time of 1 week at 40°C / 80%RH compared to the initial value.

[0103] Preferably, the weight ratio of the end-capped polyurethane polymer D1 to the epoxy-functional fatty acid oligomer EFA (D1 / EFA) is 4.5-15, preferably 4.5-10, more preferably 4.5-7.5. Such a weight ratio is advantageous for high lap shear strength values ​​both initially and after an open time of 1 week at 40°C / 80% rH. Further advantageous is the reduction in the lap shear strength values ​​after an open time of 1 week at 40°C / 80% rH compared to the initial values ​​(LSS difference (%)). This is shown, for example, in Tables 1 and 2 in the comparison of E1 with E2 and with Ref.4-Ref.6 and E3 with E4 and with Ref.7-Ref.11.

[0104] The sum of the total amount of the end-capped polyurethane polymer D1 and the epoxy-functional fatty acid oligomer EFA (D1+EFA) is 10-17.5 wt. % based on the total weight of the one-component thermosetting epoxy resin adhesive. It was found that a total amount (D1+EFA) of less than 10 wt. % or greater than 17.5 wt. % does not lead to a surprising reduction in the lap shear strength value (difference LSS (%)) after an open time of 1 week at 40° C. / 80% rH compared to the initial value.

[0105] Preferably, the sum of the total amount of the end-blocked polyurethane polymer D1 and the epoxy-functional fatty acid oligomer EFA (D1+EFA) is 10.5-15 wt. %, preferably 10.5-13 wt. %, more preferably 10-12 wt. %, based on the total weight of the one-component thermosetting epoxy resin adhesive. Such a weight ratio is advantageous for high shear strength values ​​at 40°C / 80% relative humidity (rH) both initially and after an open time of 1 week. It is further advantageous that the lap shear strength values ​​after an open time of 1 week at 40°C / 80% RH are reduced compared to the initial values ​​(LSS difference (%)). This is shown, for example, in Tables 1 and 2 in the comparison of E1 and E2 with E3 and E4 and E1-E4 with Ref.2-Ref.3, Ref.14-Ref.15, respectively.

[0106] The one-component thermosetting epoxy resin adhesive contains f) less than 5 wt% of liquid rubber D2, based on the total weight of the one-component thermosetting epoxy resin adhesive. Preferably, the amount is less than 2.5 wt%, preferably less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt%, based on the total weight of the one-component thermosetting epoxy resin adhesive. Most preferably, the one-component thermosetting epoxy resin adhesive does not contain liquid rubber D2.

[0107] In a first embodiment, the liquid rubber D2 may be a carboxyl or epoxide terminated acrylonitrile / butadiene copolymer or a derivative thereof. This type of liquid rubber may be known, for example, under the name CTBN and CTBNX and ETBN are commercially available from Emerald Performance Materials. Suitable derivatives are in particular elastomer-modified prepolymers containing epoxy groups, which are available under the product line Especially by Product line of the company (Germany Schill+Seilacher Group) 36.., or the type commercially available under the product line Albipox (Evonik, Germany).

[0108] In a second embodiment, the liquid rubber may be a polyacrylate liquid rubber which is completely miscible with the liquid epoxy resin and separates to form droplets only when the epoxy resin matrix cures. This type of liquid polyacrylate rubber may be obtained, for example, from Dow under the name 20208XPA.

[0109] It is of course also possible to use mixtures of liquid rubbers, more particularly mixtures of carboxyl- or epoxide-terminated acrylonitrile / butadiene copolymers or derivatives thereof.

[0110] Preferably, the liquid rubber D2 is a carboxyl- or epoxide-terminated acrylonitrile / butadiene copolymer or a derivative thereof.

[0111] In a preferred embodiment, the one-component thermosetting epoxy resin adhesive further comprises at least one filler F. Preference is given to mica, talc, kaolin, wollastonite, feldspar, syenite, chlorite, bentonite, montmorillonite, calcium carbonate (precipitated or ground), dolomite, quartz, silicon dioxide (pyrogenic 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 calcium carbonate, calcium oxide and fumed silica.

[0112] The total fraction of total fillers F is advantageously 10-55% by weight, preferably 20-50% by weight, most preferably 25-45% by weight, based on the total weight of the epoxy resin adhesive.

[0113] One-component, heat-curing epoxy resin adhesives may comprise further ingredients, in particular stabilizers, in particular heat and / or light stabilizers, plasticizers, solvents, dyes and pigments, corrosion inhibitors, surfactants, defoamers and adhesion promoters.

[0114] The one-component thermosetting epoxy resin adhesive has a viscosity of 500-5000 Pas at 25° C. Preferably, the viscosity at 25° C. is 500-2000 Pas, 500-1500 Pas, preferably 500-1300 Pas. The viscosity is determined oscillometrically by a rheometer (MCR 301, Anton Paar) with heatable plates (slit 1000 μm, measuring plate diameter: 25 mm (plate / plate), deformation 0.01 at 5 Hz, temperature: 25° C.).

[0115] Particularly preferred thermosetting one-component epoxy resin adhesives include:

[0116] - 25-70 wt. %, 30-60 wt. %, 35-55 wt. %, more preferably 40-50 wt. % of at least one epoxy resin A, based on the total weight of the one-component thermosetting epoxy resin adhesive,

[0117] - preferably 1.5-7.5 wt. %, more particularly 2-5 wt. %, 2-3 wt. %, based on the total weight of the one-component thermosetting epoxy resin adhesive, of at least one reactive diluent G carrying epoxy groups;

[0118] 1 to 8% by weight, more particularly 2 to 6% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive, of at least one latent hardener B for epoxy resins, more particularly dicyandiamide;

[0119] - preferably, 0.05-2% by weight, more particularly 0.1-1% by weight, more preferably 0.15-0.5% by weight, of at least one accelerator C for epoxy resins, based on the total weight of the one-component thermosetting epoxy resin adhesive;

[0120] at least one epoxy-functional fatty acid oligomer EFA, preferably a dimer fatty acid having 32 to 45 carbon atoms and 1.9 to 2.5 carboxyl groups per molecule, wherein the carboxylic acid groups have been terminated with a polyepoxide;

[0121] - at least one terminally blocked polyurethane polymer D1, preferably a terminally blocked polyurethane prepolymer of formula (I);

[0122] - based on the total weight of the one-component thermosetting epoxy resin adhesive, less than 1.0 wt%, preferably less than 0.5 wt%, more preferably less than 0.1 wt% of crystalline or semi-crystalline polyester polyol PP, the crystalline or semi-crystalline polyester polyol PP having a hydroxyl equivalent of 500 to 10000, preferably 1000 to 4000, and preferably having a crystalline melting temperature of 40°C to 125°C;

[0123] - less than 2.5 wt. %, preferably less than 1.0 wt. %, preferably less than 0.5 wt. %, more preferably less than 0.1 wt. %, of liquid rubber D2, preferably carboxyl- or epoxide-terminated acrylonitrile / butadiene copolymers or derivatives thereof, based on the total weight of the one-component thermosetting epoxy resin adhesive;

[0124] - Preferably, based on the total weight of the one-component thermosetting epoxy resin adhesive, 10-55 wt%, preferably 20-50 wt%, most preferably 25-45 wt% of filler F, the filler F being selected from the group consisting of calcium carbonate, calcium oxide and fumed silica.

[0125] The weight ratio of the terminal blocked polyurethane polymer D1 to the epoxy functionalized fatty acid oligomer EFA (D1 / EFA) is 4.5-15, preferably 4.5-10, more preferably 4.5-7.5, and the total sum of the terminal blocked polyurethane polymer D1 and the epoxy functionalized fatty acid oligomer EFA (D1+EFA) is 10.5-15 weight%, preferably 10.5-13 weight%, more preferably 10-12 weight%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

[0126] Preferably, the viscosity of the thermosetting one-component epoxy resin adhesive at 25° C. is 500 to 2000 Pas, 500 to 1500 Pas, preferably 500 to 1300 Pas.

[0127] It may further be advantageous if the preferred one-component thermosetting epoxy resin adhesive consists of the abovementioned components to an extent of more than 80% by weight, preferably more than 90% by weight, more particularly more than 95% by weight, particularly preferably more than 98% by weight and most preferably more than 99% by weight, based on the total weight of the epoxy resin adhesive.

[0128] Advantageously, after application of the adhesive to a test specimen and storage at 40°C / 80% humidity for 1 week, the cured (30 minutes at 180°C) one-component thermosetting epoxy resin adhesive of the present invention exhibits the following lap shear strength, preferably measured according to the LSS protocol from the experimental part: ≥20 MPa, preferably ≥23 MPa, ≥25 MPa, ≥27 MPa, most preferably ≥28 MPa.

[0129] It is further advantageous that after an open time of 1 week at 40°C / 80% rH, the lap shear strength value of the cured (30 minutes at 180°C) one-component thermosetting epoxy resin adhesive decreases (LSS difference (%)) by less than 18%, preferably less than 16%, more preferably less than 12%, most preferably less than 5% compared to the initial value. The lap shear strength is measured as mentioned before.

[0130] Adhesives of this type are needed for bonding heat-stable materials. Heat-stable materials are materials that are dimensionally stable at a curing temperature of 100-220° C., preferably 120-200° C., at least during the curing time. More specifically, they are metals and plastics, such as ABS, polyamide, polyphenylene oxide, composite materials such as SMC, unsaturated polyester GRP and complex epoxide or acrylate materials. Furthermore, in particular, the heat-stable plastic is polysulfone or polyethersulfone.

[0131] A preferred application is when at least one material is a metal.

[0132] Particularly preferred applications are adhesive bonding of identical or dissimilar metals, in particular in body construction in the automotive industry. Preferred metals are in particular steel, in particular electrolytically galvanized, hot-dip galvanized, oiled steel, Bonazinc-coated steel and subsequently phosphated steel, and aluminum, in particular the aluminum varieties typically encountered in automobile construction.

[0133] This adhesive is especially first brought into contact with the material to be bonded at a temperature between 10° C. and 80° C., especially between 10° C. and 60° C., and then cured at a temperature of typically 130-220° C., preferably 140-180° C., more preferably 150-170° C. Preferably, the time between contacting the adhesive with the material to be bonded and curing at a temperature of typically 130-220° C. is 1 week or more, preferably 1 week to 8 weeks.

[0134] Another aspect of the present invention relates to a method for bonding thermally stable substrates, comprising the steps of:

[0135] i) applying a thermosetting epoxy resin adhesive as described in detail above to a surface of a thermally stable substrate S1, in particular a metal surface;

[0136] ii) contacting the applied thermosetting epoxy resin adhesive with a surface of another thermally stable substrate S2, in particular a metal surface;

[0137] iii) heating the thermosetting epoxy resin adhesive to a temperature of 100-220°C, especially 120-210°C, preferably 130 to 190°C, 140 to 180°C, more preferably 150 to 170°C.

[0138] Here, the substrate S2 is composed of the same material as or a different material from that of the substrate S1.

[0139] The substrates S1 and / or S2 are in particular the above-mentioned metals and plastics.

[0140] Preferably, in step iii), the thermosetting epoxy resin adhesive is heated to a temperature of 100-220°C, especially 120-210°C, preferably 130 to 190°C, 140 to 180°C, more preferably 150 to 170°C, and the composition is placed at the above temperature for 10 minutes to 6 hours, 10 minutes to 2 hours, 10 minutes to 60 minutes, 10 minutes to 30 minutes, 10 minutes to 20 minutes, more preferably 10 minutes to 15 minutes.

[0141] Preferably, the time between steps ii) and iii) is 1 week or more, preferably 1 week to 8 weeks. More preferably, the thermosetting epoxy resin adhesive is stored at 23° C. or more, more preferably 40° C. or more, at a relative humidity of 50% or more, preferably 80% or more for this time.

[0142] This method of bonding heat-stable materials results in a bonded article. Such an article is preferably a motor vehicle or a part of a motor vehicle.

[0143] Therefore, another aspect of the present invention is an article bonded by the adhesive obtained by the above method. In addition, the composition of the present invention is not only suitable for automotive construction, but also for other fields of application. Particular mention should be made of relevant applications in the field of transportation, such as ships, trucks, buses or rail vehicles, or in the construction of consumer products such as washing machines.

[0144] The materials bonded by the composition adhesive of the present invention are used at a temperature of generally 120°C to -40°C, preferably 100°C to -40°C, particularly 80°C to -40°C.

[0145] A particularly preferred use of the thermosetting epoxy resin adhesive of the invention is its use as a thermosetting body structural adhesive in vehicle construction.

[0146] Another particularly preferred use of the thermosetting epoxy resin adhesive of the invention is its use for bonding metal structures.

[0147] Therefore, another aspect of the present invention relates to a cured epoxy resin adhesive obtained by heating the thermosetting epoxy resin adhesive described in detail above to a temperature of 100-220°C, preferably 120-210°C.

[0148] After passing through the CEC bath, the car body enters a CEC oven where the CEC coating is baked at a temperature of typically 160 to 190° C. The thermosetting composition reacts chemically here by cross-linking, causing the adhesive to cure.

[0149] The present invention is further illustrated below by examples, however, these examples are not intended to limit the present invention in any way. Example

[0150] The test methods used to test the corresponding properties in the examples are as follows:

[0151] Lap shear strength

[0152] The test specimens for the lap shear test were prepared based on the method "CSQP 580-1". The test specimens were measured using the following setup:

[0153] Aging (if not initial): 1 week at 40°C and 80% rH

[0154] Base material: HDG (DX51, 1.5mm), 100×25mm

[0155] Degreasing: Heptane

[0156] Lubrication: Anticorit PL 3802-39S

[0157] Overlap: 10mm

[0158] Adhesive layer thickness: 0.2mm (glass beads)

[0159] Curing: 30 minutes at 180°C

[0160] Test speed and climate: 10mm / min, 25℃, 50% relative humidity

[0161] Test Example

[0162] The base formulation used for the epoxy resin adhesive was the formulation described below.

[0163]

[0164]

[0165]

Claims

1. One-component thermosetting epoxy resin adhesive, comprising: a) at least one epoxy resin A of formula (II) wherein the substituents R' and R" are independently H or CH3, and the value of the subscript s is 0-12, preferably 0-1, and the proportion of the epoxy resin A is 25-70% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive; as well as b) at least one epoxy-functional fatty acid oligomer EFA; c) at least one latent hardener B for epoxy resin; and d) preferably, at least one accelerator C for epoxy resins; and e) at least one end-blocked polyurethane polymer D1; f) less than 5 wt. % of liquid rubber D2, based on the total weight of the one-component thermosetting epoxy resin adhesive; as well as g) less than 1.5 wt. % of a crystalline or semi-crystalline polyester polyol PP, based on the total weight of the one-component thermosetting epoxy resin adhesive, the crystalline or semi-crystalline polyester polyol PP having a hydroxyl equivalent of 500 to 10,000 and preferably having a crystalline melting temperature of 40° C. to 125° C.; Wherein, based on the total weight of the one-component thermosetting epoxy resin adhesive, the weight ratio of the end-blocked polyurethane polymer D1 to the epoxy-functionalized fatty acid oligomer EFA (D1 / EFA) is 4-20, and the total amount of the end-blocked polyurethane polymer D1 and the epoxy-functionalized fatty acid oligomer EFA (D1+EFA) is 10-17.5 weight %.

2. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the weight ratio of the end-blocked polyurethane polymer D1 to the epoxy-functionalized fatty acid oligomer EFA (D1 / EFA) is 4.5-15, preferably 4.5-10, and more preferably 4.5-7.

5.

3. The one-component thermosetting epoxy resin adhesive according to claim 1 or 2, wherein based on the total weight of the one-component thermosetting epoxy resin adhesive acid oligomer EFA, the sum of the total amount of the terminal blocked polyurethane polymer D1 and the epoxy functionalized fat a (D1+EFA) is 10.5-15% by weight, preferably 10.5-13% by weight, more preferably 10-12% by weight, based on the total weight of the one-component thermosetting epoxy resin adhesive.

4. The one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the proportion of the epoxy resin A of formula (II) is 25-70 wt%, 30-60 wt%, 35-55 wt%, more preferably 40-50 wt%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

5. A one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein in the epoxy resin A, the substituents R' and R" are CH3, and the value of the subscript s is 0-1, preferably 0-0.

2.

6. A one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the latent hardener is selected from dicyandiamide, guanamine, guanidine, aminoguanidine and its derivatives, substituted ureas, imidazoles and amine complexes, preferably dicyandiamide.

7. A one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the accelerator C for the epoxy resin is selected from substituted ureas, imidazoles, imidazolines and blocked amines, preferably substituted ureas.

8. A one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the epoxy-functional fatty acid oligomer EFA is a dimerized fatty acid having 32 to 45 carbon atoms and 1.9 to 2.5 carboxyl groups per molecule, wherein the carboxylic acid groups have been terminated with a polyepoxide, preferably an epoxy resin A of formula (II).

9. The one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the amount of liquid rubber D2 is less than 2.5 wt %, preferably less than 1.0 wt %, preferably less than 0.5 wt %, more preferably less than 0.1 wt %, based on the total weight of the one-component thermosetting epoxy resin adhesive.

10. The one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the one-component thermosetting epoxy resin adhesive contains 10-55 wt. %, preferably 20-50 wt. %, most preferably 25-45 wt. % of at least one filler F, based on the total weight of the epoxy resin adhesive, the filler F is preferably selected from calcium carbonate, calcium oxide and fumed silica.

11. The one-component thermosetting epoxy resin adhesive according to any one of the preceding claims, wherein the one-component thermosetting epoxy resin adhesive has a viscosity of 500 to 5000 Pas at 25° C., wherein the viscosity is determined oscillometrically by means of a rheometer (MCR 301, Anton Paar) with heatable plates (slit 1000 μm, measuring plate diameter: 25 mm (plate / plate), deformation 0.01 at 5 Hz, temperature: 25° C.).

12. A method for bonding thermally stable substrates, comprising the steps of: i) applying a thermosetting epoxy resin adhesive according to any one of claims 1 to 11 to the surface of a thermally stable substrate S1, more particularly a metal; ii) contacting the applied thermosetting epoxy resin adhesive with a surface of a further thermally stable substrate S2, more particularly a metal surface; iii) heating the thermosetting epoxy resin adhesive to a temperature of 100-220°C, more particularly 120-210°C, preferably 130 to 190°C, 140 to 180°C, more preferably 150 to 170°C; The substrate S2 is made of the same material as or a different material from the substrate S1.

13. The method according to claim 12, wherein in step iii) the thermosetting epoxy resin adhesive is heated to a temperature of 100-220°C, especially 120-210°C, preferably 130 to 190°C, 140 to 180°C, more preferably 150 to 170°C, and the thermosetting epoxy resin adhesive is placed at the above temperature for 10 minutes to 6 hours, 10 minutes to 2 hours, 10 minutes to 60 minutes, 10 minutes to 30 minutes, 10 minutes to 20 minutes, more preferably 10 minutes to 15 minutes.

14. The method according to claim 12 or 13, wherein the time between steps ii) and iii) is 1 week or more, preferably 1 week to 8 weeks, and preferably, the thermosetting epoxy resin adhesive is stored at 23°C or higher, more preferably 40°C or higher, at a relative humidity of 50% or higher, preferably 80% or higher for this period of time.

15. Method for using the thermosetting epoxy resin adhesive according to any one of claims 1 to 11 for adhesively bonding or reinforcing metal structures or for reinforcing vehicle construction or for filling of cavities in sandwich panel construction.

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