Thermosetting epoxy resin composition having low curing temperature and good storage stability

Abstract

The present invention relates to a heat-curable epoxy resin composition containing a dihydrazide selected from the group consisting of glutaric acid dihydrazide, adipic acid dihydrazide, and pimelic acid dihydrazide as a curing agent in combination with a specific urea accelerator, which is characterized by good storage stability and low cure temperatures. This epoxy resin composition is particularly suitable for use as a structural shell (auto body) adhesive.

Description

[Technical field]

[0001] The present invention relates to the field of thermosetting epoxy resin compositions, particularly for use as vehicle body adhesives. [Background technology]

[0002] Heat-curable epoxy resin compositions have been known for some time. Efforts have already been made many times to improve or at least significantly reduce a major disadvantage of epoxy resin compositions, namely their brittleness, the effect of which has been that the cured epoxy resin compositions decompose or break under impact stress. This has already been attempted by the addition of impact modifiers or by chemical modification of the epoxy resins.

[0003] An important field of use of thermosetting epoxy resin compositions is in motor vehicle construction, especially in bonding or foam filling of voids in vehicle bodies. In both cases, after application of the epoxy resin composition, the vehicle body is heated in a cathodic electrocoating oven, so that the thermosetting epoxy resin composition cures and, optionally, foams.

[0004] Accelerators may be used with heat-activated curing agents for epoxy resins to allow for rapid curing. Examples of known types of accelerators include latent imidazole and amine-boron trifluoride complexes.

[0005] However, currently, efforts are underway in the market to reduce the temperature of cathodic electrocoating ovens. Therefore, there is a significant demand in the market for a thermosetting epoxy resin composition that cures even at a relatively low temperature, i.e., 130-140°C, after a short time, typically 10-15 minutes. For example, if aromatic ureas, which are more reactive due to their structure, are used for this purpose, this leads to a major challenge in the storage stability of the thermosetting epoxy resin composition. Therefore, there is a need for a thermosetting epoxy resin composition that cures at a low temperature on the one hand, but has sufficient storage stability. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide a thermosetting epoxy resin composition which on the one hand has good storage stability at room temperature and on the other hand cures rapidly at temperatures between 130°C and 140°C. [Means for solving the problem]

[0007] This object has surprisingly been achieved by a heat-curable epoxy resin composition as claimed in claim 1. This epoxy resin composition has particularly good utility as a one-component heat-curable adhesive, in particular as a heat-curable one-component body adhesive in motor vehicle construction.

[0008] Further aspects of the invention are the subject matter of further independent claims. In particular preferred embodiments of the invention are the subject matter of the dependent claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention relates to a one-component thermosetting epoxy resin composition comprising: (a) at least one epoxy resin A having an average of more than one epoxy group per molecule; (b) at least one hardener B for epoxy resins which is a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide, and pimelic dihydrazide, preferably adipic dihydrazide; and (c) at least one accelerator C of formula (Ia) or (Ib): [ka] (In the formula, R 1 is H or an n-valent aliphatic, alicyclic, or araliphatic group; R 2 and R 3are each independently either an alkyl or aralkyl group; or together are a divalent aliphatic group having 3 to 20 carbon atoms and being part of an optionally substituted heterocycle having 5 to 8, preferably 6, ring atoms; R 1’ is an n′-valent aliphatic, alicyclic, or araliphatic radical; R 2’ is an alkyl group, an aralkyl group, or an alkylene group; R 3’ is independently H or an alkyl or aralkyl group; and n and n' each have a value of 1 to 4, in particular 1 or 2).

[0010] In this specification, the use of the term "independently" in connection with substituents, radicals or groups should be interpreted as meaning that substituents, radicals or groups with the same symbol in the same molecule can occur simultaneously with different meanings.

[0011] The prefix "poly" in the names of substances such as "polyol", "polyisocyanate", "polyether" or "polyamine" herein indicates that the respective substance formally contains more than one of the functional groups occurring in that name per molecule.

[0012] In this specification, "molecular weight" is understood to mean the molar mass (in grams per mole) of one molecule. "Average molecular weight" is the number average molecular weight M of an oligomeric or polymeric mixture of molecules, typically determined by GPC against polystyrene as a standard. n is understood to mean.

[0013] "Primary hydroxyl group" means an OH group bonded to a carbon atom bearing two hydrogens.

[0014] As used herein, the term "primary amino group" refers to an NH group bonded to one organic group, whereas the term "secondary amino group" refers to an NH group bonded to two organic groups which together may also be part of a ring. Thus, amines having one primary amino group are described as "primary amines", those having a secondary amino group are correspondingly described as "secondary amines", and those having a tertiary amino group are correspondingly described as "tertiary amines".

[0015] As used herein, "room temperature" refers to a temperature of 23°C.

[0016] The epoxy resin A having an average of more than one epoxy group per molecule is preferably a liquid epoxy resin or a solid epoxy resin. The term "solid epoxy resin" is very familiar to those skilled in the art of epoxies and is used in contrast to "liquid epoxy resin". The glass transition temperature of solid resins is higher than room temperature, meaning that they are pulverizable at room temperature to give a free-flowing powder.

[0017] A preferred epoxy resin is represented by the formula (II) [ka] has.

[0018] The substituents R' and R'', as used herein, are independently either H or CH3.

[0019] In solid epoxy resins, the index s has a value of >1.5, in particular from 2 to 12.

[0020] Such solid epoxy resins are commercially available, for example, from Dow, or Huntsman, or Hexion.

[0021] Compounds of formula (II) having an index s of 1 to 1.5 are called semi-solid epoxy resins by those skilled in the art. In the context of the present invention, they are also considered to be solid resins. However, preferred solid epoxy resins are epoxy resins in the narrower sense, i.e. when the index s has a value of >1.5.

[0022] In liquid epoxy resins, the index s has a value of less than 1. Preferably, s has a value of less than 0.2.

[0023] Thus, diglycidyl ethers of bisphenol A (DGEBA), bisphenol F and bisphenol A / F are preferred. Such liquid resins are available, for example, as Araldite® GY250, Araldite® PY304, Araldite® GY282 (Huntsman), or DER® 331 or DER® 330 (Dow), or Epikote 828 (Hexion).

[0024] Further suitable epoxy resins A are those known as epoxy novolaks. These in particular have the following formula: [ka] (Wherein, R2 is [ka] or CH2, R1 is H or methyl, and z is 0 to 7. has.

[0025] More particularly, these are phenol or cresol epoxy novolacs (R2 = CH2).

[0026] Such epoxy resins are commercially available from Huntsman under the trade names EPN or ECN and Tactix®, or from Dow Chemical in their DEN™ product line.

[0027] Preferably, the epoxy resin A is a liquid epoxy resin of formula (II).

[0028] In a particularly preferred embodiment, the heat-curable epoxy resin composition contains both at least one liquid epoxy resin of formula (II) having s<1, in particular less than 0.2, and at least one solid epoxy resin of formula (II) having s>1.5, in particular from 2 to 12.

[0029] The proportion of the epoxy resin A is preferably 10 to 60% by weight, particularly preferably 30 to 50% by weight, based on the total weight of the epoxy resin composition.

[0030] It is more advantageous if 50 to 100% by weight, particularly 80 to 100% by weight, of the epoxy resin A is the liquid epoxy resin.

[0031] It is further advantageous if 0 to 30% by weight, particularly 0 to 20% by weight, and more preferably 5 to 15% by weight of the epoxy resin A is the above solid epoxy resin.

[0032] The composition of the present invention further comprises, as hardener B, a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide and pimelic dihydrazide. Adipic dihydrazide is preferred.

[0033] The ratio of the proportion in moles of epoxy groups of the epoxy resin A / the proportion in moles of dihydrazides is preferably from 3 to 5, in particular from 3.5 to 4.5, which is advantageous in that high values ​​for the mechanical properties of the cured composition, in particular the modulus and tensile strength, are obtained within this range.

[0034] The dihydrazides preferably have a median particle size D of ≦100 μm, ≦50 μm, 0.5 to 50 μm, 1 to 50 μm, 1 to 40 μm, in particular 1 to 20 μm, preferably 2 to 20 μm, particularly preferably 2 to 15 μm. 50 has.

[0035] Surprisingly, it has been found that this leads to improved adhesion and improved impact peel strength of the compositions of the present invention, as is evident, for example, in Table 2, comparing E1 and E4-E8 for good lap shear strength.

[0036] The term "median particle size" as used herein means the D of the cumulative volume distribution curve where 50% by volume of the particles have a diameter smaller than that value. 50 It means the median particle size or D 50 In the present invention, is determined by a laser diffraction method.

[0037] In this specification, for example, D 10 , D 50 , D 90 and D. 98 means those diameters at which 10%, 50% ("median particle size"), 90% and 98% by volume of the particles have a smaller diameter, respectively, as determined by laser diffraction methods.

[0038] It is further advantageous if the thermosetting epoxy resin composition comprises a minimum amount of dicyandiamide, in which case the weight ratio of dihydrazide to dicyandiamide is ≧0.5, ≧0.75, ≧1, ≧2, ≧5, in particular ≧10, preferably ≧50, more preferably ≧100.

[0039] The amount of dicyandiamide is preferably less than 5% by weight, less than 3% by weight, less than 2% by weight, in particular less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, most preferably less than 0.1% by weight, based on the total weight of the epoxy resin composition. More preferably, the heat-curable epoxy resin composition does not contain any dicyandiamide.

[0040] For example, in Table 2, comparing E1 with E3, it is clear that this leads to improved storage stability, especially when stored at 60° C. for 1 week, and higher lap shear strength and impact peel values ​​are achieved.

[0041] It has also been found that compositions containing dicyandiamide rather than the dihydrazide of the present invention, whether or not combined with urea, do not cure at cure temperatures of 130-140° C. This is evident, for example, in Table 2, comparing E1 and E2 with R4-R8.

[0042] The composition of the present invention comprises (c) further comprising at least one accelerator C of formula (Ia) or (Ib): [ka] (In the formula, R 1 is H or an n-valent aliphatic, alicyclic, or araliphatic group; R 2 and R 3 are each independently either an alkyl or aralkyl group; or together are a divalent aliphatic group having 3 to 20 carbon atoms and being part of an optionally substituted heterocycle having 5 to 8, preferably 6, ring atoms; R 1’ is an n′-valent aliphatic, alicyclic, or araliphatic radical; R 2’ is an alkyl group, an aralkyl group, or an alkylene group; R 3’ is independently H or an alkyl or aralkyl group; and n and n' each have a value of 1 to 4, in particular 1 or 2).

[0043] As used herein, what is meant by "araliphatic group" is an aralkyl group, i.e. an alkyl group substituted by an aryl group (see Roempp, CD Roempp Chemie Lexikon, Version 1, Stuttgart / New York, Georg Thieme Verlag 1995).

[0044] R 1 If is not H, then R 1It is essential to the invention that is an n-valent aliphatic, cycloaliphatic or araliphatic radical and is not an aromatic or heteroaromatic radical. In other words, accelerator C does not in particular have formula (I').

[0045] Similarly, R 3’ If is not H, then R 3’ It is essential that is not an aromatic or heteroaromatic group. This means that the accelerator C in particular does not have the formula (I″). [ka] In the formula, Z 1 and Z 2 is H or any organic group.

[0046] Aromatic R 1 It has been found that the accelerators having the group are not storage stable, meaning that they increase the viscosity of the heat curable epoxy resin composition in a short period of time to an extent that is not negligible with respect to handling of the composition.

[0047] This is evident, for example, in Table 2, comparing E1 and E2 with R2 and R3 for storage stability at 60° C. for 1 week.

[0048] R 1 is in particular the radical of an aliphatic, cycloaliphatic or araliphatic mono-, di-, tri- or tetraisocyanate of formula (III) after removal of the n-isocyanate group. R 1 [NCO] n (III)

[0049] The mono-, di-, tri- or tetraisocyanates of formula (III) are either monomeric mono-, di-, tri- or tetraisocyanates or dimers or oligomers of one or more monomeric di- or triisocyanates, the dimers or oligomers being in particular biurets, isocyanurates and uretdiones.

[0050] Suitable monomeric monoisocyanates are alkyl isocyanates, such as butyl isocyanate, pentyl isocyanate, hexyl isocyanate, octyl isocyanate, decyl isocyanate and dodecyl isocyanate, as well as cyclohexyl isocyanate, methylcyclohexyl isocyanate and benzyl isocyanate.

[0051] Particularly suitable monomeric diisocyanates are butane 1,4-diisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), trimethylhexamethylene diisocyanate (TMDI), 2,5- or 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane, dicyclohexylmethyl diisocyanate (HDI), 12 MDI), m-tetramethylxylylene diisocyanate (TMXDI) and m-xylylene diisocyanate (XDI) and hydrogenated m-xylylene diisocyanate (H8XDI).

[0052] Particularly suitable dimers or oligomers are HDI biuret, HDI isocyanurate, IPDI biuret, IPDI isocyanurate, HDI diuretdione, IPDI isocyanurate.

[0053] Such dimers or oligomers are commercially available, for example, as Desmodur N-100 (Bayer), Luxate HDB 9000 (Lyondell), Desmodur N-3300 (Bayer), Desmodur N-3600 (Bayer), Luxate HT 2000 (Lyondell), Desmodur N-3400 (Bayer), Luxate HD 100 (Lyondell), Desmodur Z 4470 (Bayer), Vestanat T 1890 / 100 (Huels) or Luxate IT 1070 (Lyondell).

[0054] It is also possible to use suitable mixtures of the above di- or triisocyanates.

[0055] R 1 In particular, an alkylene group having 4 to 10 carbon atoms, in particular a hexamethylene group, or [ka] or Biurets or isocyanurates of aliphatic or araliphatic diisocyanates after removal of the isocyanate groups; or Xylylene group, especially m-xylylene group It is.

[0056] R 1 is more preferably HDI, IPDI, HDI biuret and XDI after removal of the NCO groups, more preferably IPDI.

[0057] R 2 and R 3 may together form a butylene, pentamethylene or hexamethylene group, preferably a pentamethylene group.

[0058] More preferably, R 2 and R 3 are each independently an alkyl group having 1 to 5 carbon atoms, particularly each independently an ethyl, methyl or propyl group, and preferably each a methyl group.

[0059] In a particularly preferred embodiment, R 1 is H. This is R 2 and R 3 are each independently a methyl, ethyl or propyl group, preferably a methyl group.

[0060] R 1 is further preferably an n-valent aliphatic, cycloaliphatic or araliphatic radical.

[0061] R 1’are firstly diamines selected from the group consisting of 1,4-diaminobutane, hexamethylenediamine, isophoronediamine, trimethylhexamethylenediamine, 2,5- or 2,6-bis(aminomethyl)bicyclo[2.2.1]heptane, dicyclohexylmethyldiamine, m-tetramethylxylylenediamine and m-xylylenediamine, hydrogenated m-xylylenediamine, ethylenediamine, propane-1,3-diamine and propane-1,2-diamine, in particular after removal of the two amino groups.

[0062] R 2’ First of all, especially C1~C 10 It is an alkyl group or an aralkyl group having 7 to 20 carbon atoms, preferably a methyl, ethyl, propyl, butyl or pentyl group.

[0063] R 1’ is secondly, in particular, an ethylene, propylene, butylene, methylethylene or 1,2-dimethylethylene radical.

[0064] R 2’ is secondly, in particular, an ethylene, propylene, butylene, methylethylene or 1,2-dimethylethylene radical.

[0065] Two alkylene groups R 1’ and R 2’ forms, together with the urea nitrogen atom, a ring, in particular piperazine, or 2,3,5,6-tetramethylpiperazine, or homopiperazine (1,4-diazacycloheptane).

[0066] R 3’ are in particular monomeric monoisocyanates selected from the group consisting of butyl isocyanate, pentyl isocyanate, hexyl isocyanate, octyl isocyanate, decyl isocyanate and dodecyl isocyanate as well as cyclohexyl isocyanate, methylcyclohexyl isocyanate and benzyl isocyanate.

[0067] Accelerators C of formula (Ia) can be readily obtained synthetically from the reaction of an aliphatic, cycloaliphatic or araliphatic mono-, di-, tri- or tetraisocyanate of formula (III) with a secondary amine of formula (IV). [ka]

[0068] In a second synthesis variant, accelerators C of formula (Ia) are prepared from the reaction of a primary aliphatic, cycloaliphatic or araliphatic amine of formula (V) with a compound of formula (VI). [ka]

[0069] The latter variant is advantageous, especially when the polyisocyanates of formula (III) are commercially unavailable or difficult to obtain.

[0070] Accelerators C of formula (Ib) can be readily obtained synthetically from the reaction of an aliphatic, cycloaliphatic or araliphatic monoisocyanate of formula (IIIa) with a secondary amine of formula (IVa) or (IVb). [ka]

[0071] In formula (IVb), x′ and y′ each independently have a value of 1, 2, 3, 4 or 5, and the substituent Q 1’ , Q 2’ , Q 3’ and Q 4’ are each independently H or a C1- to C5-alkyl group. Preferably, x' and y' are 1 or 2, preferably each 1, which means that the secondary amine of formula (IVb) is preferably piperazine or 2,3,5,6-tetramethylpiperazine or homopiperazine (1,4-diazacycloheptane), more preferably piperazine or 2,3,5,6-tetramethylpiperazine.

[0072] The secondary amine of formula (IVa) is therefore in particular of formula R 1’ [NH2] n’ can be readily prepared from the alkylation of primary amines of the formula:

[0073] In particular, preferred amines of formula (IVa) are selected from the group consisting of N,N'-dimethyl-1,2-diaminocyclohexane, N,N'-dimethylethylenediamine, N,N'-dimethylpropane-1,3-diamine, bisisopropylated IPDA (Jefflink-754 (Huntsman)), N,N'-diisobutylethylenediamine and N-ethyl-N'-methylethylenediamine.

[0074] Most preferably, the at least one accelerator C is an accelerator of formula (Ia), in particular - R 1 is H and R 2 and R 3 are each a methyl, ethyl or propyl group, preferably each a methyl group, and n=1; and / or - R 1 teeth, [ka] and R 2 and R 3 are each a methyl, ethyl or propyl group, preferably each a methyl group, and n=2.

[0075] Accelerator C has in particular a molecular weight of less than 1000 g / mol, in particular between 80 and 800 g / mol. At higher molecular weights, the effectiveness of the accelerator is reduced and the required dosage is significantly higher. This can lead to insufficient mechanical properties.

[0076] The amount of accelerator C is advantageously 0.01 to 6.0% by weight, in particular 0.02 to 4.0% by weight, preferably 0.02 to 2.0% by weight, based on the weight of epoxy resin A.

[0077] The ratio of the proportion of accelerator C in grams per mole of epoxy groups of epoxy resin A is preferably 0.01-0.5 g / mol of epoxy groups, in particular 0.05-0.3 g / mol of epoxy groups, more preferably 0.075-0.2 g / mol of epoxy groups, most preferably 0.08-0.15 g / mol of epoxy groups, which is advantageous in that in the case of curing at temperatures of 130-150° C., high storage stability combined with simultaneously good mechanical values ​​and good adhesion properties is obtained within this range.

[0078] The one-component heat-curable epoxy resin composition preferably comprises at least one toughening agent D. The toughening agent D can be a solid or a liquid.

[0079] More particularly, the toughening agent D is selected from the group consisting of endblock polyurethane polymers D1, liquid rubbers D2 and core-shell polymers D3. The toughening agent D is preferably selected from the group consisting of endblock polyurethane polymers D1 and liquid rubbers D2. Endblock polyurethane polymers D1 are particularly preferred.

[0080] The toughening agent D is an endblocked polyurethane prepolymer D1.

[0081] It is preferably an endblocked polyurethane polymer D1 blocked with a blocking agent which is eliminated at temperatures above 100°C.

[0082] Preferred blocking groups are in particular primarily phenols or bisphenols. Preferred examples of such phenols and bisphenols are in particular phenol, cresol, resorcinol, catechol, carbanol (3-pentadecenylphenol (from cashew nut shell oil)), nonylphenol, phenol reacted with styrene or dicyclopentadiene, bisphenol A, bisphenol F and 2,2'-diallylbisphenol A.

[0083] Endblocked polyurethane prepolymers are prepared from linear or branched polyurethane prepolymers terminated with isocyanate groups by one or more isocyanate-reactive compounds. When two or more such isocyanate-reactive compounds are used, the reaction can be carried out sequentially or with a mixture of these compounds.

[0084] The reaction is preferably carried out in such a manner that one or more isocyanate-reactive compounds are used in stoichiometric or stoichiometric excess amounts to ensure that all NCO groups are converted.

[0085] The polyurethane prepolymers having isocyanate end groups are prepared from at least one diisocyanate or triisocyanate and from polymers Q having terminal amino, thiol or hydroxyl groups. PM and / or optionally substituted polyphenol Q PP It can be prepared from

[0086] Suitable diisocyanates are aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, in particular 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 (HDI), ... 12 Commercially available products include HDI, IPDI, MDI, p-phenylene diisocyanate (PPDI), m-toteramethylxylylene diisocyanate (TMXDI), and their dimers. HDI, IPDI, MDI, or TDI are preferred.

[0087] Suitable triisocyanates are trimers or biurets of aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, in particular the isocyanurates and biurets of the diisocyanates described in the previous paragraph. Of course, it is also possible to use suitable mixtures of di- or triisocyanates.

[0088] Particularly suitable polymers Q having terminal amino, thiol or hydroxyl groups PM is a polymer Q having two or three terminal amino, thiol or hydroxyl groups PM It is.

[0089] Polymer Q PM has advantageously 300 to 6000, in particular 600 to 4000, preferably 700 to 2200 g / eq of NCO-reactive groups.

[0090] Preferred Polymer Q PM is a polyol having an average molecular weight of 600 to 6000 Daltons and is selected from the group consisting of polyethylene glycol, polypropylene glycol, polyethylene glycol-polypropylene glycol block polymer, polybutylene glycol, hydroxyl-terminated polybutadiene, hydroxyl-terminated butadiene-acrylonitrile copolymer, and mixtures thereof.

[0091] Particularly preferred polymer Q PM is an α,ω-dihydroxypolyalkylene glycol having C2-C6 alkylene groups or mixed C2-C6 alkylene groups and terminated with amino, thiol or preferably hydroxyl groups. Particularly preferred are polypropylene glycol or polybutylene glycol. Hydroxyl-terminated polyoxybutylene is even more particularly preferred.

[0092] Particularly suitable polyphenol Q PPare bis, tris and tetraphenols. This is understood to mean not only linear phenols, but also optionally substituted phenols. The nature of the substitution can be very varied. More particularly, this is understood to mean substitution directly on the aromatic ring to which the phenolic OH group is attached. Phenol is further understood to mean not only monocyclic aromatics, but also polycyclic or fused aromatics or heteroaromatics with the phenolic OH group directly on the aromatic or heteroaromatic ring.

[0093] In a preferred embodiment, the polyurethane prepolymer is prepared from at least one diisocyanate or triisocyanate and a polymer Q having terminal amino, thiol or hydroxyl groups. PM The polyurethane prepolymer is especially prepared from polymer Q. PM The polyurethanes are prepared in a manner known to those skilled in the art by using a diisocyanate or triisocyanate in a stoichiometric excess relative to the amino, thiol or hydroxyl groups of the polyurethane.

[0094] The polyurethane prepolymer having isocyanate end groups preferably has elastic characteristics. It preferably exhibits a glass transition temperature Tg of less than 0°C.

[0095] The toughening agent D can also be a liquid rubber D2. It can be, for example, a carboxy or epoxy terminated polymer.

[0096] In a first embodiment, the liquid rubber may be a carboxy or epoxy terminated acrylonitrile / butadiene copolymer or a derivative thereof. Such liquid rubbers are commercially available, for example, under the names Hypro / Hypox® CTBN and CTBNX and ETBN from Emerald Performance Materials. Suitable derivatives are in particular elastomer-modified prepolymers with epoxy groups, which are commercially sold by Struktol® (Schill+Seilacher Gruppe, Germany) in the Polydis® product line, in particular the Polydis® 36.. product line or the Albipox product line (Evonik, Germany).

[0097] In a second embodiment, the liquid rubber can be a polyacrylate liquid rubber that is fully miscible with the liquid epoxy resin and that separates to form only microdroplets during the curing of the epoxy resin matrix. Such a polyacrylate liquid rubber is available, for example, from Dow under the name 20208-XPA.

[0098] It is also possible to use mixtures of liquid rubbers, in particular mixtures of carboxy- or epoxy-terminated acrylonitrile / butadiene copolymers or derivatives thereof.

[0099] The toughening agent D can be a core-shell polymer D3 in a third embodiment. The core-shell polymer consists of an elastic core polymer and a rigid shell polymer. Particularly suitable core-shell polymers consist of a core of an elastic acrylate or butadiene polymer encapsulated by a rigid shell of a rigid thermoplastic polymer. This core-shell structure forms spontaneously as a result of the separation of a block copolymer or is defined by carrying out the polymerization as a latex or suspension polymerization with subsequent grafting. A preferred core-shell polymer is one called MBS polymer, which is commercially available under the trade name Clearstrength™ from Arkema, Paraloid™ from Dow or F-351™ from Zeon.

[0100] The following proportions are preferred: Based on the total weight of the epoxy resin composition, 10-60% by weight, in particular 20-30% by weight, of toughening agent D1; 10-30% by weight, in particular 20-30% by weight, of toughening agent D2; 10-30% by weight, especially 20-30% by weight, of toughening agent D3.

[0101] In a further preferred embodiment, the composition comprises at least one filler F. Here, preference is given to mica, talc, kaolin, wollastonite, selenium, syenite, chlorite, bentonite, montmorillonite, (precipitated or ground) calcium carbonate, dolomite, quartz, (fumed or precipitated) silica, cristobalite, calcium oxide, aluminum hydroxide, magnesium oxide, hollow ceramic beads, hollow glass beads, hollow organic beads, glass beads, colorant pigments. Particular preference is given to fillers selected from the group consisting of calcium carbonate, calcium oxide and fumed silica.

[0102] Advantageously, the total proportion of all fillers F is between 5 and 40% by weight, preferably between 10 and 30% by weight, based on the total weight of the epoxy resin composition.

[0103] In a further preferred embodiment, the composition may comprise a physical or chemical blowing agent, such as, for example, those available under the trade name Expancel™ from Akzo Nobel, or Celogen™ from Chemtura, or Luvopor® from Lehmann & Voss. The proportion of blowing agent is advantageously between 0.1 and 3% by weight, based on the total weight of the epoxy resin composition.

[0104] In a further preferred embodiment, the composition may further additionally comprise at least one epoxy-containing reactive diluent G. Such reactive diluents are known to those skilled in the art. Preferred examples of epoxy-containing reactive diluents are: - Monofunctional saturated or unsaturated, branched or unbranched, cyclic or open-chain C4-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, etc.; - Difunctional, saturated or unsaturated, branched or unbranched, cyclic or open-chain C2-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.; - glycidyl ethers of tri- or polyfunctional saturated or unsaturated, branched or unbranched, cyclic or open-chain alcohols, such as, for example, epoxide castor oil, epoxide trimethylolpropane, epoxide pentaerythritol or polyglycidyl ethers of aliphatic polyols, such as sorbitol, glycerol, trimethylolpropane; - glycidyl ethers of phenolic and aniline compounds, such as phenyl glycidyl ether, cresyl glycidyl ether, p-tert-butylphenyl glycidyl ether, nonylphenol glycidyl ether, 3-n-pentadecenyl glycidyl ether (derived from cashew nut oil), N,N-diglycidylaniline, etc.; - epoxide amines, such as N,N-diglycidylcyclohexylamine; epoxide mono- or dicarboxylic acids, such as glycidyl neodecanoate, glycidyl methacrylate, glycidyl benzoate, glycidyl phthalate, tetrahydrophthalate and hexahydrophthalate, diglycidyl esters of dimeric fatty acids, etc.; Epoxide di- or trifunctional low to high molecular weight polyether polyols, such as polyethylene glycol glycidyl ether, polypropylene glycol diglycidyl ether, etc.

[0105] Particularly preferred are hexanediol diglycidyl ether, cresyl glycidyl ether, p-tert-butylphenyl glycidyl ether, polypropylene glycol diglycidyl ether and polyethylene glycol diglycidyl ether.

[0106] Advantageously, the total proportion of epoxy-containing reactive diluent G is between 0.1 and 15% by weight, preferably between 0.1 and 5% by weight, particularly preferably between 0.1 and 2% by weight and more preferably between 0.2 and 1% by weight, based on the total weight of the epoxy resin composition.

[0107] The composition may comprise further components, in particular catalysts, stabilizers, in particular heat and / or light stabilizers, thixotropic agents, plasticizers, solvents, mineral or organic fillers, foaming agents, dyes and pigments, corrosion inhibitors, surfactants, defoamers and adhesion promoters.

[0108] Suitable plasticizers are in particular phenol alkylsulfonates or N-butylbenzamides, commercially available from Bayer as Mesamoll® or Dellatol BBS.

[0109] 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).

[0110] Particularly preferred one-component epoxy resin compositions include: - 10 to 60% by weight, in particular 30 to 50% by weight, of epoxy resin A having an average of more than one epoxy group per molecule, based on the total weight of the epoxy resin composition; preferably 50 to 100% by weight, in particular 80 to 100% by weight, of epoxy resin A are liquid epoxy resins and 0 to 30% by weight, in particular 0 to 20% by weight, more preferably 5 to 15% by weight, of epoxy resin A are solid epoxy resins; - hardener B, preferably adipic dihydrazide; at least one accelerator C of formula (Ia) or (Ib), in particular of formula (Ia), in particular - R 1 is H and R 2 and R 3 are each a methyl, ethyl or propyl group, preferably each a methyl group, and n=1; and / or - R 1 teeth, [ka] and R 2 and R 3 are each a methyl, ethyl or propyl group, preferably each a methyl group, and n=2; at least one toughening agent D preferably chosen from the group consisting of an endblock polyurethane polymer D1, a liquid rubber D2 and a core-shell polymer D3, in a proportion, based on the total weight of the epoxy resin composition, of the following: toughening agent D1 10-60% by weight, in particular 20-30% by weight; toughening agent D2 10-30% by weight, in particular 20-30% by weight; Toughness enhancer D3 10-30% by weight, particularly 20-30% by weight at least one toughening agent D, - preferably 5 to 50% by weight, preferably 10 to 30% by weight, of a filler F selected from the group consisting of calcium carbonate, calcium oxide and fumed silica, based on the total weight of the epoxy resin composition; - preferably 0.1 to 15% by weight, preferably 0.1 to 5% by weight, particularly preferably 0.1 to 2% by weight, more preferably 0.2 to 1% by weight of an epoxy-containing reactive diluent G, based on the total weight of the epoxy resin composition.

[0111] The ratio of the proportion of accelerator C in grams per mole of epoxy groups of epoxy resin A is preferably 0.01-0.5 g / mol epoxy groups, in particular 0.05-0.3 g / mol epoxy groups, more preferably 0.075-0.2 g / mol epoxy groups and most preferably 0.08-0.15 g / mol epoxy groups.

[0112] The ratio of the molar proportion of epoxy groups of the epoxy resin A / the molar proportion of dihydrazides is preferably 3 to 5, in particular 3.5 to 4.5.

[0113] It can be further advantageous if the preferred one-component epoxy resin composition consists of the above-mentioned components in an amount of more than 80% by weight, preferably more than 90% by weight, in particular 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 composition.

[0114] An example of a particularly preferred composition is E1 in Table 1.

[0115] It is advantageous if the epoxy resin composition of the present invention has a viscosity of 500 to 3000 Pa·s, in particular 1000 to 2500 Pa·s, preferably 1000 to 2000 Pa·s at 25° C. This is advantageous in that good applicability is ensured.

[0116] It is also advantageous if the epoxy resin composition of the present invention has an increase in viscosity, measured at a measurement temperature of 25° C., of less than 500%, less than 300%, less than 200%, less than 150%, less than 120%, less than 100%, less than 50% after storage for one week at 60° C. one day after preparation.

[0117] The described thermosetting epoxy resin compositions have been found to be particularly suitable for use as one-component thermosetting adhesives, in particular as one-component thermosetting body adhesives in motor vehicle construction. Such one-component adhesives have a wide range of possible uses. Such adhesives are required for adhesively bonding thermostable materials. Thermostable 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, polyamides, polyphenylene ethers, composite materials, such as SMC, unsaturated polyester GFP, epoxy or acrylate composite materials. Uses in which at least one material is metal are preferred. A particularly preferred use is considered to be the bonding of identical or different metals, in particular in body construction in the automotive industry. Preferred metals are in particular steel, in particular electrolytically galvanized, hot-dip galvanized or oiled steel, Bonazinc coated steel, post-phosphated steel and aluminum, in particular in the variants which typically occur in automotive construction.

[0118] Adhesives based on the thermosetting compositions of the present invention make it possible to achieve a desirable combination of high crash strength and low cure temperatures.

[0119] Such adhesives are in particular contacted with the materials which are first bonded at a temperature of from 10°C to 80°C, in particular from 10 to 60°C, and then typically cured at a temperature of from 130 to 220°C, preferably from 130 to 180°C, more preferably from 130 to 150°C.

[0120] A further aspect of the present invention relates to a method for bonding thermally stable substrates comprising the steps of: (i) applying the heat-curable epoxy resin composition as described in detail above to the surface of a heat-stable substrate S1, in particular a metallic surface; (ii) contacting the applied thermosetting epoxy resin composition with a surface of a further heat-stable substrate S2, in particular a metallic surface; (iii) Heating the composition to a temperature of 100 to 220°C, particularly 120 to 200°C, preferably 130 to 150°C, and more preferably 130 to 140°C.

[0121] Substrate S2 herein consists of the same material as substrate S1 or of a different material than substrate S1.

[0122] The substrates S1 and / or S2 are in particular the abovementioned metals and plastics.

[0123] In step (iii) of heating the composition to a temperature of preferably 100 to 220°C, particularly 120 to 200°C, preferably 130 to 150°C, more preferably 130 to 140°C, the composition is maintained 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.

[0124] Such bonding methods of thermally stable materials result in adhesively bonded articles, which are preferably vehicles or parts of vehicles.

[0125] Thus, a further aspect of the present invention relates to adhesively bonded articles obtained from the above-mentioned method.It is of course possible to use the composition of the present invention to realize not only thermosetting adhesives but also sealing compounds.Furthermore, the composition according to the present invention is suitable for use not only in automobile construction, but also in other fields.Particularly mentioned are related applications in the construction of means of transport, such as ships, trucks, buses or rail vehicles, or in the construction of consumer products, such as washing machines.

[0126] Materials adhesively bonded with the compositions according to the invention are typically used at temperatures of from 120°C to -40°C, preferably from 100°C to -40°C, in particular from 80°C to -40°C.

[0127] A particularly preferred use of the thermosetting epoxy resin composition of the present invention is its use as a thermosetting one-component body adhesive in motor vehicle construction, or as a stiffening compound, or as a foamable thermosetting composition for the reinforcement of voids and reinforcing elements in structural parts.

[0128] A further aspect of the present invention relates to a cured epoxy resin composition obtained by heating the thermosetting epoxy resin composition as described in detail above. Heating is typically carried out in an oven at a temperature of 100-220° C., preferably 130-150° C., more preferably 130-140° C., preferably at said temperature for a period of 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.

[0129] The accelerator C of the invention, already described in detail above as a component of the heat-curable epoxy resin composition, has been found to be suitable in combination with the curing agent B of the invention as an accelerator for heat-curable epoxy resin compositions, in particular at curing temperatures of 130-150° C.

[0130] Surprisingly, it has been found that other accelerators for heat-curable epoxy resin compositions do not meet the requirements for acceleration at low temperatures while maintaining storage stability. For example, in Table 2, it is clear that when diuron or 1,1'-(methylenebis(4,1-phenylene))bis(3,3-dimethylurea) is used, the storage stability of the corresponding epoxy resin composition deteriorates to such an extent that the composition cures after one week at 60°C. This is evident, for example, in the comparison of E1 and E2 with R2 and R3.

[0131] It was particularly surprising that comparative composition R1, which did not contain accelerator, had a greater increase in viscosity after one week at 60° C. than compositions E1 and E2, which contained accelerator C.

[0132] Furthermore, from a comparison of compositions E1 and E2 with compositions R4-R8 in Table 2, it is apparent that the comparative compositions containing only dicyandiamide as the curing agent do not cure under the cure conditions for the measurement of lap strength at 140° C. for 10 minutes, and are therefore not suitable for use with or without an accelerator. EXAMPLES

[0133] Some examples are described below to further illustrate the invention but are not intended to limit the scope of the invention in any way.

[0134] Preparation of toughness enhancer ("D-1") 150g poly-THF2000 (OH value 57mg / g KOH) and 150g Liquiflex H (OH value 46mg / g KOH) were dried under vacuum at 105°C for 30 minutes. When the temperature was reduced to 90°C, 61.5g IPDI and 0.14g dibutyltin dilaurate were added. After 2.0 hours, the reaction was carried out under vacuum at 90°C until the NCO content was constant at 3.10% (calculated NCO content: 3.15%). Then, 96.1g cardanol was added as a blocking agent. Stirring was continued under vacuum at 105°C until no free NCO was detectable. This product was used as toughening agent D-1.

[0135] [Table 1-1]

[0136] [Table 1-2]

[0137] Preparation of the composition Reference compositions R1 to R8 and compositions E1 to E8 according to the invention were prepared according to the numbers in Table 1. The amounts specified in Table 1 are in parts by weight.

[0138] The ratio of the percentage of epoxy groups in epoxy resin A in moles to the percentage of dihydrazide in moles is referred to as "B Index" in Table 1 and is reported as [moles of EP groups / moles of dihydrazide].

[0139] The ratio of the proportion of accelerator C in grams per mole of epoxy groups in epoxy resin A is referred to as "C Index" in Table 1 and is reported in [g of accelerator / mole of EP groups].

[0140] Test Method: Elastic modulus (DIN EN ISO 527) The adhesive samples were pressed between two Teflon papers to a layer thickness of 2 mm. After curing for 35 minutes at 175°C, the Teflon papers were removed and test specimens were punched out to the DIN standard condition. The test specimens were tested in standard weather conditions at a loading rate of 2 mm / min. The elastic modulus was determined according to DIN EN ISO 527 from 0.05 to 0.25%.

[0141] Lap shear strength (ZSF) (DIN EN 1465) Cleaned specimens of Elo H420 steel (thickness 1.5 mm) re-oiled with Anticorit PL 3802-39S were adhesively bonded over a bonding area of ​​25 x 10 mm using glass beads as spacers with a layer thickness of 0.3 mm and cured for 10 minutes at an oven temperature of 140°C.

[0142] The lap shear strength was determined according to DIN EN 1465 on a tensile tester at a loading rate of 10 mm / min in triplicate measurements.

[0143] Impact Peel Strength (IP RT) (ISO 11343) Test specimens were produced using adhesive and DC04+ZE steel with dimensions 90x20x0.8mm, where the bonded area was 20x30mm with a layer thickness of 0.3mm using glass beads as spacers. The samples were cured for 10 minutes at an oven temperature of 140°C. Impact peel strength was measured on a Zwick 450 impact pendulum at 23°C as triplicate determinations. The reported impact peel strength is the average force in N / mm under the measurement curve from 25% to 90% to ISO 11343.

[0144] Adhesive Viscosity / Storage Stability Viscosity measurements of the adhesives were carried out 1 day after preparation on an Anton Paar MCR 101 rheometer by oscillation using a plate-plate arrangement at a temperature of 25° C., using the following parameters: 5 Hz, 1 mm spacing, plate diameter 25 mm, 1% deformation. The measurements are indicated in Table 2 as “Visco initial 25° C.”

[0145] For evaluation of the storage stability of the adhesives, the viscosity measurements were repeated after storage at the specified temperatures for the specified periods of time in several weeks, and the rate of increase in viscosity occurring after storage was ascertained. The measured viscosities in Pa·s measured at a temperature of 25°C after one week of storage at 50°C and 60°C are respectively indicated in Table 2 as "Visco 1W 50 25°C" and "Visco 1W 60 25°C". The values ​​in brackets indicate the rate of increase in viscosity.

[0146] [Table 1-3]

[0147] [Table 2] The present disclosure also includes the following: [1] A thermosetting epoxy resin composition comprising: (a) at least one epoxy resin A having an average of more than one epoxy group per molecule; (b) at least one hardener B for epoxy resins which is a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide, and pimelic dihydrazide, preferably adipic dihydrazide; and (c) at least one accelerator C of formula (Ia) or (Ib):

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[10] A thermosetting epoxy resin composition according to any one of Aspects 1 to 9, characterized in that the composition has a viscosity at 25°C of 500 to 3000 Pa·s, particularly 1000 to 2500 Pa·s, and preferably 1000 to 2000 Pa·s.

[11] 11. Use of the thermosetting epoxy resin composition according to any of the embodiments 1 to 10 as a one-component thermosetting adhesive, in particular as a thermosetting one-component body adhesive in motor vehicle construction.

[12] A method for adhesively bonding thermally stable substrates, comprising: (i) applying a thermosetting epoxy resin composition according to any one of the first to tenth aspects to a surface of a thermally stable substrate S1, in particular to a metallic surface; (ii) contacting the applied thermosetting epoxy resin composition with a surface of a further heat-stable substrate S2, in particular a metallic surface; (iii) heating the composition to a temperature of 100 to 220° C., particularly 120 to 200° C., preferably 130 to 150° C., more preferably 130 to 140° C.; Here, the substrate S2 is made of the same material as the substrate S1 or a material different from that of the substrate S1.

[13] The method according to aspect 12, wherein in step (iii) of heating the composition to a temperature of 100 to 220° C., particularly 120 to 200° C., preferably 130 to 150° C., more preferably 130 to 140° C., the composition is held at said 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] 14. An adhesively bonded article obtainable from the method according to claim 12 or 13.

Claims

1. A thermosetting epoxy resin composition comprising: (a) at least one epoxy resin A having an average of more than one epoxy group per molecule, which is a bisphenol diglycidyl ether or an epoxy novolac; (b) at least one hardener B for epoxy resins which is a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide, and pimelic dihydrazide; and (c) at least one accelerator C of formula (Ia) or (Ib): [Formula 1] (In the formula, R １ is H or an n-valent aliphatic, alicyclic, or araliphatic group; R ２ and R ３ are each independently either an alkyl or aralkyl group; or together are a divalent aliphatic group having 3 to 20 carbon atoms and being part of an optionally substituted heterocycle having 5 to 8 ring atoms; R １’ is an n′-valent aliphatic, alicyclic or araliphatic group; R ２’ is an alkyl group, an aralkyl group, or an alkylene group; R ３’ is independently H or an alkyl or aralkyl group; and n and n' each have a value of 1 to 4. the ratio of the proportion of epoxy groups of the epoxy resin A in moles to the proportion of dihydrazides in moles is 3 to 5; The dihydrazide has a median particle size D of 0.5 to 50 μm. ５０ The thermosetting epoxy resin composition has the following structure:

2. R １ is H and R ２ and R ３2. The thermosetting epoxy resin composition according to claim 1, wherein each of n is a methyl, ethyl, or propyl group, and n=1.

3. R １ teeth, [chemical 2] and R ２ and R ３ 2. The thermosetting epoxy resin composition according to claim 1, wherein n is a methyl, ethyl, or propyl group, respectively, and n=2.

4. The heat-curable epoxy resin composition according to any one of claims 1 to 3, comprising less than 0.5 wt% of dicyandiamide, based on the total weight of the heat-curable epoxy resin composition.

5. 5. The thermosetting epoxy resin composition according to claim 1, wherein the ratio of the proportion of accelerator C in grams per mole of epoxy groups of the epoxy resin A is 0.01 to 0.5 g / mole of epoxy groups.

6. The thermosetting epoxy resin composition according to any one of claims 1 to 5, further comprising at least one toughening agent D selected from the group consisting of an endblock polyurethane polymer D1, a liquid rubber D2, and a core-shell polymer D3.

7. The thermosetting epoxy resin composition according to any one of claims 1 to 6, wherein the ratio of the epoxy resin A is 10 to 60% by weight based on the total weight of the thermosetting epoxy resin composition.

8. The thermosetting epoxy resin composition according to any one of claims 1 to 7, characterized in that it has a viscosity of 500 to 3000 Pa·s at 25°C.

9. Use of the heat-curable epoxy resin composition according to any one of claims 1 to 8 as a one-component heat-curable adhesive.

10. A method for adhesively bonding thermally stable substrates comprising: (i) applying the heat-curable epoxy resin composition according to any one of claims 1 to 8 to the surface of a heat-stable substrate S1; (ii) contacting the applied heat-curable epoxy resin composition with a surface of a further heat-stable substrate S2; (iii) heating the thermosetting epoxy resin composition to a temperature of 100 to 220°C; Here, the substrate S2 is made of the same material as the substrate S1 or a material different from that of the substrate S1.

11. 11. The method of claim 10, wherein in step (iii) of heating the heat-curable epoxy resin composition to a temperature of 100 to 220° C., the heat-curable epoxy resin composition is held at said temperature for a period of from 10 minutes to 6 hours.

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