Storage-stable epoxy resin composition and suitable hardener systems

Abstract

The present invention relates to the use of boroxines of formula (I) for increasing the storage stability of epoxy resin compositions and epoxy resin compositions comprising an epoxy resin and a hardener and a boroxine.

Description

[0001] The present invention relates to hardener systems comprising boroxines for providing and curing storage-stable epoxy resin compositions as well as epoxy resin compositions with high storage stability comprising an epoxy resin and the hardener system.

[0002] Epoxy resins are widely used due to their good chemical resistance, excellent thermal and dynamic-mechanical properties, and high electrical insulation properties. These epoxy resins are available in liquid or solid form and can be cured with or without heat by adding hardeners.

[0003] Epoxy resins cure according to various mechanisms. In addition to curing with phenols or anhydrides, curing with amines is often performed. These substances are usually liquid and mix very well with epoxy resins. Due to their high reactivity, such epoxy resin compositions are made as two-component formulations. This means that the resin (component A) and hardener (component B) are stored separately and mixed in the correct ratio shortly before use. These two-component resin formulations are also known as cold-curing resin formulations, with the hardeners used usually being selected from the group of amines or amidoamines.

[0004] One-component, heat-curing epoxy resin formulations, on the other hand, are pre-mixed and ready for use, meaning the epoxy resin and hardener are mixed at the factory. Mixing errors of the individual components during on-site use are therefore eliminated. This requires latent hardener systems that do not react with the epoxy resin at room temperature, but readily react when heated depending on the energy input. "Latent" means that a mixture of the individual components is stable under defined storage conditions.

[0005] For such one-component epoxy resin formulations, dicyandiamide, for example, is a particularly suitable and cost-effective hardener. Under ambient conditions, corresponding epoxy resin-dicyandiamide mixtures can be stored for up to twelve (12) months.

[0006] To reduce the reaction temperature for curing one-component epoxy resin formulations, such as epoxy resin-dicyandiamide mixtures, a curing accelerator is typically added to these formulations. This lowers the activation energy for curing, allowing curing at lower temperatures. However, these curing accelerators often reduce the storage stability of epoxy resin compositions comprising an epoxy resin, a hardener, and a curing accelerator, making storage at room temperature for extended periods impossible. To ensure sufficient storage stability of these one-component epoxy resin formulations, they must be stored at controlled, low temperatures, often at -18°C. Similar storage conditions must be observed when less latent hardeners are used in epoxy resins.This results in considerable additional costs and effort in the storage, transport and processing of these compositions, particularly in the production of prepregs, towpregs or adhesives.

[0007] Aware of such obstacles, proposals for overcoming them have already been published. For example, European patent EP 659793 B1 describes mixtures of boric acid or borates (boric acid esters) and imidazole-epoxy resin adducts as hardeners for epoxy resins. The resulting compositions are storage-stable and allow for rapid curing upon heating.

[0008] Furthermore, European patent EP 2678369 B1 describes liquid hardeners containing cyanamide, at least one urea derivative (uron), and at least one organic or inorganic acid as a stabilizer. These hardeners dissolve excellently in epoxy resins, exhibit high latency in the epoxy resins, and enable long storage stability.

[0009] Furthermore, it is known from European patent EP 2780388 B1 that N,N-dimethylurones can cure epoxy resins as sole hardeners without the addition of a curing accelerator.

[0010] Furthermore, European patent application EP 3257884 A1 describes an epoxy resin mixture consisting of epoxy resin, dicyandiamide, aromatic urea derivative, and boric acid ester. The effectiveness of the boric acid esters listed in the examples, especially the extension of the time to the peak in the heat flow curve at 60 °C, is so low that it is doubtful whether the addition of these esters can eliminate the need for frozen storage and transport.

[0011] In addition, the German patent application DE 10 2019 121 195.6 describes an epoxy resin composition which comprises a hardener, a curing accelerator and a boronic acid for stabilizing the epoxy resin composition.

[0012] To further improve the stability of epoxy resin compositions, patent applications WO 2021 / 023593 A1 and WO 2022 / 161837 A1 propose the use of boronic acids, while ensuring rapid curing through exposure to heat. However, boronic acids have the disadvantage that they can react with the epoxy resin compositions themselves and thus change them, which can adversely affect the further processing of the epoxy resin compositions.

[0013] Despite the progress made so far, there is a need to further improve the stability of epoxy resin compositions in the presence of hardeners without limiting the reactivity of the epoxies during subsequent curing. A low viscosity of the uncured epoxy resin compositions is also of interest, allowing the incorporation of additional additives prior to curing without compromising storage stability.

[0014] The present invention therefore aims to provide novel stabilizers for epoxy resin compositions comprising a hardener that ensure high storage stability while exhibiting the lowest possible reactivity with the epoxy resin composition. Furthermore, the epoxy resin compositions should exhibit a long latency period with an overall low viscosity below the curing temperature and high reactivity at the curing temperature.

[0015] These objects could be achieved by the use of boroxines of the formula (I) in curable epoxy resin compositions, a curing system containing at least one boroxine according to formula (I) and by epoxy resin compositions containing such curing systems.

[0016] The boroxines of formula (I) are characterized by their ability to stabilize epoxy resin compositions in the presence of a hardener, thus increasing the latency (viscosity stability) of the compositions. Despite this good stabilization, the epoxy resin compositions can still be cured well. Furthermore, DSC measurements have shown that the boroxines of formula (I) have only a low tendency to react with the epoxy resin composition itself, so that the monomer compositions are hardly altered by the boroxines during storage.

[0017] Therefore, the use of boroxines of the general formula (I) for increasing the storage stability of epoxy resin compositions, in particular liquid epoxy resin compositions, comprising an epoxy resin, in particular a liquid epoxy resin, and a hardener for hardening the epoxy resin, as well as the hardener systems comprising the hardener and at least one boroxine of the formula (I) is the subject of the present invention, where for formula (I) where for the residues R 1 , R 2 and R 3 independently of each other: R 1 R 2 , R 3 = hydrogen, alkyl, cycloalkyl, hydroxyalkyl, alkoxy or a radical of formula (II), where for formula (II) where the residue of formula (II) can be bonded to the boroxine ring either directly or via an alkylene group having 1 to 5 carbon atoms and where for R 4 , R 5 , R 6independently of each other: R 4 , R 5 , R 6 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1 to C5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl, and wherein the hardener system comprises a hardener according to formula (III), where formula (III) is: where for R 7 , R 8 , R 9 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, R 9 = with -NHC(O)NR 7 R S substituted C1 to C 15 -alkyl, with -NHC(O)NR 7 R S substituted C3 to C 15 -Cycloalkyl, with -NHC(O)NR 7 R S substituted aryl or with -NHC(O)NR 7 R 8 substituted alkylaryl, and wherein the hardener system, in addition to the hardener of the general formula (III), may optionally contain further hardeners, preferably from the group of guanidines, cyanoguanidines, nitroguanidines, acylguanidines and biguanidines, in particular hardeners selected from the group of cyanamide and / or a compound of the formula (IV), wherein for formula (IV) where for the residues R 40 , R 41 , R 42 independently of each other: R 40 = cyano, nitro, acyl or a radical of the formula -(C=X)-R 43 , with X = imino or oxygen, R 43 = amino, alkylamino or alkoxy, R 41 = hydrogen, C1- to C5-alkyl, aryl, benzyl, or acyl, R 42 = hydrogen or C1- to C5-alkyl.

[0018] Thus, in one embodiment, the hardener system comprises no further hardeners, co-hardeners, curing accelerators, or other catalysts for curing epoxy resins besides the hardener of the general formula (III). In an alternative embodiment, the hardener system comprises no further hardeners, co-hardeners, curing accelerators, or other catalysts for curing epoxy resins besides the hardener of the formula (III), with particular preference being given to hardener systems that comprise at least one further hardener of the formula (IV) and / or cyanamide. In a further embodiment, the hardener systems comprise no further hardeners, co-hardeners, curing accelerators, or other catalysts for curing epoxy resins besides the hardeners of the formulas (III) and (IV) and / or cyanamide.

[0019] Thus, according to a further embodiment, the present invention also relates to the use of boroxines of the general formula (I) for increasing the storage stability of epoxy resin compositions, in particular liquid epoxy resin compositions.

[0020] Accordingly, a further subject matter of the present invention are epoxy resin compositions comprising an epoxy resin, in particular a liquid epoxy resin and a hardener system according to the invention, wherein the hardener system contains at least one boroxine of the formula (I) and at least one hardener of the formula (III) for hardening the epoxy resin composition.

[0021] By adding a boroxine according to formula (I) to an epoxy resin composition containing a hardener according to formula (III) in addition to the uncured epoxy resin, a significantly improved latency period can be achieved compared to compositions without the corresponding boroxine. Furthermore, the viscosity of the epoxy resin composition prepared for curing can be maintained at a low level for a very long time, thereby significantly improving storage stability. For example, the latency of an epoxy resin composition containing a urea derivative can be increased by a factor of 6 to 12 by adding boroxines according to the invention (cf. Example 1), so that corresponding epoxy resin compositions can be stored longer at room temperature up to 40°C for a period of at least 2 months and thus kept in stock without curing.Furthermore, it has been shown that the desired storage stability is achieved without significantly changing the reactivity of the composition. The addition of boroxines does not affect the achievable glass transition temperature or the mechanical properties of fiber-reinforced composites. Thus, the curing properties of the hardeners and curing accelerators are essentially retained by the addition of boroxines. A further advantage of boroxines is their relatively inert behavior in epoxy resin compositions, meaning they hardly react with the epoxy resin monomers. This is demonstrated by the relatively high onset and peak temperatures in DSC measurements (see Example 2), which prove that significant reactions between boroxines and the epoxides only occur at relatively high temperatures, which are significantly higher than normal storage temperatures.Overall, an epoxy resin composition can be provided that has a high storage stability at room temperature and a high reactivity at the curing temperature and is ideally suited for use in prepregs, towpregs and one-component adhesives as well as acoustic insulation materials.

[0022] According to the present invention, an epoxy resin composition means a composition whose epoxy resins are thermosetting, i.e., due to their functional groups, namely epoxy groups, they are polymerizable, crosslinkable, and / or crosslinkable by heat. In this case, polymerization, crosslinking, and / or crosslinking occur as a result of a polyaddition reaction induced by the hardener.

[0023] In the context of the present invention, alkyl is understood to mean a saturated, linear or branched, aliphatic radical, in particular an alkyl radical having the general formula C n H2n+1 where n represents the number of carbon atoms in the radical. Alkyl can denote a radical with a larger number of carbon atoms. Alkyl preferably denotes a saturated, linear or branched, aliphatic radical having the general formula C n H 2n+1 where n represents the number of carbon atoms of the radical and n represents a number from 1 to 15. Thus, alkyl preferably means C1 to C 15 -alkyl, more preferably C1- to C 10 -alkyl or C1- to C5-alkyl. It is further preferred that C1- to C 15 -Alkyl in particular methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, 1-Ethylpropyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl or n-pentadecyl means.

[0024] Furthermore, C1- to C5-alkyl means a saturated, linear, or branched alkyl radical having up to five carbon atoms. Preferably, C1- to C5-alkyl means, in particular, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, or 1-ethylpropyl.

[0025] According to the present invention, hydroxyalkyl means an alkyl radical as defined above which is substituted by one, two, or three hydroxy groups. According to the present invention, hydroxyalkyl means, in particular, an alkyl radical having up to 15 carbon atoms and substituted by one hydroxy group. Thus, hydroxyalkyl preferably means C1- to C 15-Hydroxyalkyl. Hydroxyalkyl also preferably represents C1- to C5-hydroxyalkyl. Hydroxyalkyl most preferably represents hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl, or 5-hydroxypentyl.

[0026] In connection with the present invention, C3 to C 15 -Cycloalkyl is understood to mean a saturated, monocyclic or bicyclic aliphatic radical having 3 to 15 carbon atoms, in particular a cycloalkyl radical having the general formula C n H 2n-1 , where n = an integer from 3 to 15. It is preferably provided that C3 to C 15 -Cycloalkyl means in particular cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl, where these cycloalkyl radicals in turn may preferably be mono- or polysubstituted by alkyl of the meaning described above.

[0027] According to the present invention, C3 to C 15-Cycloalkyl particularly preferably cyclopentyl, cyclohexyl, which in turn may be mono- or polysubstituted by alkyl, such as preferably mono-, di-, tri- or tetra-(C1-C5)alkyl-1-cyclopentyl- and mono-, di-, tri- or tetra-(C1-C5)alkyl-1-cyclohexyl-, in particular 3,3,5,5-tetramethyl-1-cyclohexyl.

[0028] Cyano refers to a nitrile group of the general formula CN.

[0029] Nitro refers to a functional group of the general formula NO2.

[0030] Amino refers to a functional group of the general formula NH2.

[0031] Imino refers to a functional group of the general formula NH.

[0032] Alkylamino means a radical of the formula NH n (Alkyl) 2-n , with n = 0 or 1, where alkyl is an alkyl radical as defined above and where the bonding site is located on the nitrogen.

[0033] Carboxyl refers to a functional group with the general formula COOH.

[0034] Alkoxy means a radical of the formula O-alkyl, where alkyl is an alkyl radical as defined above and where the bonding site is located on the oxygen. According to the present invention, alkoxy means, in particular, an alkoxy radical whose alkyl radical has up to 15 carbon atoms, in particular up to 5 carbon atoms. Thus, alkoxy preferably means C1- to C 15 -Alkoxy, and more preferably C1- to C5-alkoxy. Alkoxy particularly preferably means methoxy, ethoxy, n-propoxy, n-butoxy, or n-pentoxy.

[0035] Acyl means a radical of the formula -C(O)-R 5 , where R 5 is bonded to the carbon and can be hydrogen, alkyl, or alkoxy as defined above, and wherein the bonding site of the acyl radical is located on the carbon. Acyl particularly preferably denotes formyl or acetyl.

[0036] Furthermore, alkylsulfonyl means a radical of the formula -SO2-alkyl, where both the bonding site of the alkylsulfonyl radical and the alkyl radical are located on the sulfur, and where alkyl is an alkyl radical as defined above. According to the present invention, alkylsulfonyl means in particular an alkylsulfonyl radical whose alkyl radical has up to 15 carbon atoms. Thus, alkylsulfonyl preferably means C1- to C 15 -Alkylsulfonyl, and more preferably C1- to C5-alkylsulfonyl. Alkylsulfonyl particularly preferably means methylsulfonyl, ethylsulfonyl, n-propylsulfonyl, n-butylsulfonyl, or n-pentylsulfonyl.

[0037] According to the present invention, aryl means an aromatic radical, in particular an aromatic radical having 6 to 15 carbon atoms, which may be monocyclic, bicyclic or polycyclic. Thus, aryl preferably means C6 to C 15-aryl, particularly preferably phenyl, naphthyl, anthryl, phenantryl, pyrenyl or perylenyl, very particularly preferably phenyl. The C6 to C 15 -Aryl radicals can in turn be additionally substituted with aryl and / or arylalkyl groups, in particular with arylmethyl groups, such as phenylmethyl.

[0038] Furthermore, according to the present invention, alkylaryl means an aromatic radical of the type described above, which in turn is mono- or polysubstituted by alkyl of the type described above. In particular, alkylaryl means an aromatic radical having 6 to 15 carbon atoms. Thus, alkylaryl preferably means C6 to C 15 -Alkylaryl. Alkylaryl also preferably means methylphenyl, dimethylphenyl or trimethylphenyl.

[0039] An alkylene group having 1 to 5 carbon atoms denotes a (C1-C5)-alkylene group, which may be linear or branched, preferably a methylene or ethylene group. Thus, the radical of formula (II), which may be bonded to the boroxine ring of formula (I) either directly or via an alkylene group having 1 to 5 carbon atoms, can also be represented by formula (IIa), where the radicals R 4 , R 5 and R 6 have the same meaning as in formula (II), and where the designation C0-alkylene in formula (IIa) means that no alkylene group is present. Preferred radicals of formula (II) are directly bonded to the boroxine ring of formula (I).

[0040] According to the invention, boroxines of formula (I) can be employed or used, where R 1 , R 2 , R 3 in formula (I) can preferably independently of one another be alkyl, hydroxyalkyl or a radical of the formula (II). In particular, R1 , R 2 , R 3 in formula (I) independently of one another are alkyl or hydroxyalkyl or a radical of formula (II), where R 1 , R 2 , R 3 which have the following meaning: R 1 , R 2 , R 3 = hydrogen, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decanyl, hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl or 5-hydroxypentyl or a radical of the formula (II), where for the radicals R 4 , R 5 , R 6 in formula (II) R 4 R 5 , R 6 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1 to C5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl.

[0041] According to the invention, boroxines of the formula (I) can be employed or used, wherein one, two or all three of the radicals R 1 , R 2, R 3 in formula (I) independently of one another are alkyl, hydroxyalkyl, it being preferred that R 1 , R 2 , R 3 which have the following meaning: R 1 , R 2 , R 3 = Methyl, Ethyl, n-Propyl, 1-Methylethyl, n-Butyl, 1-Methylpropyl, 2-Methylpropyl, n-Pentyl, n-Hexyl, n-Heptyl, n-Octyl, n-Nonyl, n-Decanyl, Hydroxymethyl, 2-Hydroxyethyl, 3-Hydroxypropyl, 4-Hydroxybutyl or 5-Hydroxypentyl.

[0042] According to the present invention, preferably one, two or three of the radicals R 1 R 2 , R 3 represent radicals of the formula (II), where the radicals of the formula (II) may be the same or different. In particular, the radicals of the formula (II) may independently of one another be represented by the radicals R 4 , R 5 , R 6 be substituted.

[0043] According to the present invention, preferably one, two or three of the radicals R1 R 2 , R 3 represent radicals of the formula (II), where one, two or all three radicals R 1 R 2 , R 3 in formula (I) is a radical of formula (II) in which the radicals R 4 , R 5 , R 6 in formula (II) are hydrogen.

[0044] According to the present invention, preferably one, two or three of the radicals R 1 R 2 , R 3 represent radicals of the formula (II), where the radical R 4 is not equal to hydrogen. Thus, the radicals R 1 R 2 , R 3 in formula (I) is a radical of formula (II), where the radicals of formula (II) may be the same or different and where R 4 , R 5 , R 6 in formula (II) applies: R 4 = fluorine, chlorine, bromine, iodine, cyano, C1 to C5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl, R 5 , R6 = hydrogen.

[0045] More preferably, one, two or three of the radicals R 1 , R 2 , R 3 in formula (I) independently of one another represent a radical of formula (II), where for the radicals R 4 , R 5 , R 6 in formula (II) applies: R 4 = fluorine, chlorine, C1- to C5-alkyl, acyl or alkoxy, R 5 , R 6 = hydrogen.

[0046] Even more preferably, one, two or three of the radicals R 1 , R 2 , R 3 in formula (I) represent a radical of formula (II), where R 4 , R 5 , R 6 in formula (II) applies: R 4 = fluorine, chlorine, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, formyl, acetyl, methoxy, ethoxy, n-propoxy, n-butoxy or n-pentoxy, R 5 , R 6= hydrogen.

[0047] According to a further alternative, boroxines according to formula (I) can also preferably be employed or used, wherein one, two or three of the radicals R 1 , R 2 , R 3 in formula (I) represent a radical of formula (II), where the radicals of formula (II) may be the same or different and where for the radicals R 4 , R 5 , R 6 in formula (II) applies: R 4 , R 5 = independently of one another fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl, R 6 = hydrogen.

[0048] More preferably, one, two or three of the radicals R 1 , R 2 , R 3 in formula (I) represent a radical of formula (II), where R 4 , R 5 , R 6 in formula (II) applies: R 4 , R 5= independently of one another fluorine, chlorine, C1- to C5-alkyl, acyl or alkoxy, R 6 = hydrogen.

[0049] Even more preferably, one, two or three of the radicals R 1 , R 2 , R 3 in formula (I) represent a radical of formula (II), where R 4 , R 5 , R 6 in formula (II) applies: R 4 , R 5 = independently fluorine, chlorine, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl, formyl, acetyl, methoxy, ethoxy, n-propoxy, n-butoxy or n-pentoxy, R 6 = hydrogen.

[0050] According to a further alternative, boroxines according to formula (I) can preferably be employed or used, wherein one, two or three of the radicals R 1 , R 2 , R 3in formula (I) preferably represent radicals of the formula (II), where the radicals of the formula (II) may be the same or different and where for the radicals R 4 , R 5 , R 6 in formula (II) independently of each other: R 4 , R 5 , R 6 = Fluorine, chlorine, bromine, iodine, cyano, C1 to C5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl.

[0051] More preferably, one, two or all three of the radicals R 1 , R 2 , R 3 in formula (I) represent radicals of formula (II), where R 4 , R 5 , R 6 in formula (II) independently of each other: R 4 , R 5 , R 6 = fluorine, chlorine or C1- to C5-alkyl.

[0052] Even more preferably, one, two or all three of the radicals R 1 , R 2 , R 3 in formula (I) represent radicals of formula (II), where R4 , R 5 , R 6 in formula (II) independently of each other: R 4 , R 5 , R 6 = fluorine, chlorine, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl.

[0053] Particularly preferred are boroxines of the formula (I) in which two or all three of the radicals R 1 , R 2 , R 3 are the same. Particularly preferred are compounds of formula (I) with R 1 = R 2 = R 3 .

[0054] Very particularly preferably, formula (I) represents a substance selected from the group 2-phenylboroxine, 2,4-diphenylboroxine, 2,6-diphenylboroxine, 2,4,6-triphenylboroxine, 2-((C1-C4)-alkylphenyl)boroxine, 2,4-di-((C1-C4)-alkylphenyl)boroxine, 2,6-di-((C1-C4)-alkylphenyl)boroxine, 2,4,6-tri-((C1-C4)-alkylphenyl)boroxine, 2-(fluorophenyl)boroxine, 2,4-di-(fluorophenyl)boroxine, 2,6-di-(fluorophenyl)boroxine, 2,4,6-tri-(fluorophenyl)boroxine, 2-(chlorophenyl)boroxine, 2,4-di-(chlorophenyl)boroxine, 2,6-Di-(chlorophenyl)boroxine, 2,4,6-tri-(chlorophenyl)boroxine, 2-(C1-C4)-alkylboroxine, 2,4-di-(C1-C4)-alkylboroxine, 2,6-di-(C1-C4)-alkylboroxine, 2,4,6-tri-(C1-C4)-alkylboroxine and mixtures thereof, with trisubstituted boroxines, in particular those in which the substituents are the same, being preferred.

[0055] Particularly preferred boroxines of the formula (I) are selected from the group 2,4,6-triphenylboroxine, 2,4,6-tri(4-ethylphenyl)boroxine, 2,4,6-tri(4-fluorophenyl)boroxine, 2,4,6-trimethylboroxine.

[0056] By using these boroxines in epoxy resin compositions, the storage stability of epoxy resin compositions prepared for curing can be improved to an exceptionally high degree.

[0057] Surprisingly, it has been shown that such epoxy resin compositions are particularly stable during storage. It has been shown that epoxy resin compositions according to the invention have significantly longer storage lives of several weeks compared to epoxy resin compositions without a corresponding boroxine (see examples). The epoxy resin compositions according to the invention can be stored for at least 5 to 15 times longer, i.e., by at least a factor of 5 to 15, than comparable epoxy resin compositions without boroxine under the same conditions, and are storage-stable for a longer period. Completely surprisingly, it has been shown that the other curing properties, such as the reactivity of the composition, are comparable to the curing properties of known compositions and are not significantly altered.These compositions can be used excellently for the production of prepregs, towpregs and one-component adhesives as well as acoustic insulation materials.

[0058] According to the present invention, urea derivatives according to formula (III) are used or employed as hardeners for curing the epoxy resin, where for formula (III) where for R 7 , R 8 , R 9 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, R 9 = with -NHC(O)NR 7 R S substituted C1 to C 15 -alkyl, with -NHC(O)NR 7 R 8 substituted C3 to C 15 -Cycloalkyl, with -NHC(O)NR 7 R S substituted aryl or with -NHC(O)NR 7 R 8 substituted alkylaryl.

[0059] Due to their properties, these urea derivatives are particularly well-suited for the gentle curing of epoxy resins and epoxy resin compositions.

[0060] Of the urea derivatives described by formula (III), aromatic urea derivatives can preferably be employed or used according to the present invention. Further preference is given to using aromatic urea derivatives of the formula (III), where R 7 , R 8 , R 9 independent applies: R 7 , R 8 = independently of one another C1- to C5-alkyl, in particular methyl or ethyl, R 9 = with -NHC(O)NR 7 R 8 substituted aryl or with -NHC(O)NR 7 R 8 substituted alkylaryl.

[0061] More preferably, the radicals R 7 , R 8 , R 9 independently mean: R 7 , R8 = independently of one another C1- to C5-alkyl, in particular methyl or ethyl, R 9 = with -NHC(O)NR 7 R 8 substituted alkylaryl.

[0062] Thus, according to the present invention, urea derivatives according to formula (III) are particularly preferred, in which a urea derivative according to formula (V) represents a urea derivative according to formula (III). According to the present invention, urea derivatives according to formula (V) are particularly preferred, where the following applies to formula (V): and where the radicals R 7 , R 8 , R 10 , R 11 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl, R 10 , R 11 = independently of one another hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl.

[0063] Preferably, the radicals R7 , R 8 , R 10 in connection with the formula (V) each represents a methyl radical and R 10 means hydrogen. 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) and 1,1'-(2-methyl-m-phenylene)bis(3,3-dimethylurea) are particularly preferred.

[0064] More preferably, the radicals R 7 , R 8 , R 9 independently mean: R 7 , R 8 = independently of one another C1- to C5-alkyl, in particular methyl or ethyl, R 9 = with -NHC(O)NR 7 R 8 substituted aryl, especially with -NHC(O)NR 7 R 8 substituted benzylphenyl.

[0065] Thus, according to the present invention, urea derivatives according to formula (III) are particularly preferred, in which a urea derivative according to formula (VII) represents a urea derivative according to formula (III). According to the present invention, urea derivatives according to formula (VII) are particularly preferred, where the following applies to formula (VII): and where the radicals R 7 , R 8 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl.

[0066] Particularly preferably, the radicals R 7 , R 8 in connection with formula (VII) is methyl. 1,1'-(methylenedi-p-phenylene)bis[3,3-dimethylurea] is particularly preferred.

[0067] Of the urea derivatives described with formula (III), aliphatic urea derivatives can also be used with preference. Aliphatic urea derivatives of the formula (III) are further preferred, where R 7 , R 8 , R 9 independent applies: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl, R 9 = with -NHC(O)NR 7 R S substituted C1 to C 15 -alkyl or with -NHC(O)NR 7 R S substituted C3 to C 15 -Cycloalkyl.

[0068] Also preferred are aliphatic urea derivatives according to formula (III), in which R 7 and R 8 have the meaning given above, in particular methyl or ethyl, and R 9 with -NHC(O)NR 7 R 8 substituted C3 to C 15 -Cycloalkyl means.

[0069] Thus, according to the present invention, urea derivatives according to formula (III) are particularly preferred, in which a urea derivative according to formula (VI) represents a urea derivative according to formula (III). According to the present invention, urea derivatives according to formula (VI) are particularly preferred, where the following applies to formula (VI): where the remainders apply simultaneously or independently: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl; R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 = independently hydrogen, C1- to C5-alkyl or with -NHC(O)NR 7 R 8 substituted C1- to C5-alkyl, where a residue R 12 , R 13 , R 14 , R15 R 16 , R 17 , R 18 , R 19 , R 20 or R 21 with -NHC(O)NR 7 R 8 substituted C1- to C5-alkyl,

[0070] Also preferred are hardeners comprising aliphatic urea derivatives of the formula (VI) in which R 7 and R 8 independently methyl or ethyl and R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 independently hydrogen, methyl, ethyl, -NHC(O)NR 7 R 8 or with - NHC(O)NR 7 R 8 substituted methyl or ethyl. Particularly preferred is 1-(N,N-dimethylurea)-3-(N,N-dimethylurea-methyl)-3,5,5-trimethylcyclohexane, hereinafter also N'-[3-[[[(dimethylamino)carbonyl]-amino]methyl]-3,5,5-trimethylcyclohexyl]-N,N-dimethylurea (i.e. R 7 = R 8 = R13 = R 14 = R 15 = Methyl and R 18 = -CH2-NHC(O)N(CH3)2 and R 12 = R 15 = R 16 = R 17 = R 20 = R 21 = hydrogen).

[0071] Thus, an epoxy resin composition is also preferred, in particular a liquid epoxy resin composition, which comprises an epoxy resin, in particular a liquid epoxy resin, and a hardener for hardening the epoxy resin selected from the group of hardeners according to formula (V), formula (VI) or formula (VII), and at least one boroxine of the general formula (I), where the following applies to formula (I): where the residue of formula (II) can be bonded to the boroxine ring either directly or via an alkylene group having 1 to 5 carbon atoms and where for the residues R 1 , R 2 and R 3 independently of each other: R 1 R 2 , R 3= Alkyl or a radical of formula (II), where for formula (II) where for R 4 , R 5 , R 6 independently of each other: R 4 , R 5 , R 6 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, or carboxyl, where formula (V) is: and where the radicals R 7 , R 8 , R 10 , R 11 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl, R 10 , R 11 = independently of one another hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl, where formula (VI) is: where the remainders apply simultaneously or independently: R 7 , R 8= independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl; R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 = independently hydrogen, C1- to C5-alkyl, especially methyl or ethyl, or with -NHC(O)NR 7 R 8 substituted C1- to C5-alkyl, in particular with -NHC(O)NR 7 R 8 substituted methyl or ethyl, where a residue R 12 , R 13 , R 14 , R 15 R 16 , R 17 , R 18 , R 19 , R 20 or R 21 with -NHC(O)NR 6 R 7 substituted C1- to C5-alkyl, where formula (VII) is: and where the radicals R 7 , R 8 independently of each other: R 7 , R8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl, wherein the epoxy resin composition, in addition to the hardener of the general formula (V), formula (VI) or formula (VII), may optionally comprise further hardeners from the group of cyanamide and the guanidines, cyanoguanidines, nitroguanidines, acylguanidines, biguanidines, in particular according to the general formula (IV), wherein the following applies to formula (IV): where for the residues R 40 , R 41 , R 42 independently of each other: R 40 = cyano, nitro, acyl or a radical of the formula -(C=X)-R 43 , with X = imino or oxygen, R 43 = amino, alkylamino or alkoxy, R 41 = hydrogen, C1- to C5-alkyl, aryl, benzyl, or acyl, R 42 = hydrogen or C1- to C5-alkyl.

[0072] In a preferred embodiment, the epoxy resin composition comprises, in addition to the hardener of the general formula (V), formula (VI) or formula (VII), no further hardeners, co-hardeners, curing accelerators or other catalysts for curing epoxy resins.

[0073] In an alternative preferred embodiment, the epoxy resin composition comprises, in addition to the hardener of the general formula (V), formula (VI) or formula (VII), and at least one hardener from the group of compounds of the formula (IV) and cyanamide.

[0074] Thus, an epoxy resin composition is also preferred, in particular a liquid epoxy resin composition, which comprises an epoxy resin, in particular a liquid epoxy resin, and a hardener for hardening the epoxy resin selected from the group of hardeners according to formula (V), formula (VI) or formula (VII), and at least one boroxine of the general formula (I), where the following applies to formula (I): where for the residues R 1 , R 2 and R 3 independently of each other: R 1 R 2 , R 3 = Alkyl or a radical of formula (II), where for formula (II) where the residue of formula (II) can be bonded to the boroxine ring either directly or via an alkylene group having 1 to 5 carbon atoms and where for R 4 , R 5 , R 6 independently means: R 2 , R 3 , R 4 = hydrogen, fluorine, chlorine, C1- to C4-alkyl or alkoxy, where formula (V) is: and where the radicals R 7 , R 8 , R 10 , R 11 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl, R 10 , R 11= independently of one another hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl, where for formula (VI) where the remainders apply simultaneously or independently: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl; R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 = independently hydrogen, C1- to C5-alkyl, especially methyl or ethyl, or with -NHC(O)NR 7 R 8 substituted C1- to C5-alkyl, in particular with -NHC(O)NR 7 R 8 substituted methyl or ethyl, where a residue R 12 , R 13 , R 14 , R 15 R 16 , R 17 , R 18 , R 19 , R 20 or R21 with -NHC(O)NR 7 R 8 substituted C1- to C5-alkyl, where formula (VII) is: and where the radicals R 6 , R 7 independently of each other: R 6 , R 7 = independently of one another hydrogen or C1- to C5-alkyl, in particular methyl or ethyl, and wherein the epoxy resin composition, in addition to the hardener of the general formula (V), formula (VI) or formula (VII), may optionally comprise further hardeners from the group consisting of cyanamide and the guanidines, cyanoguanidines, nitroguanidines, acylguanidines, biguanidines, in particular according to the general formula (IV), wherein the following applies to formula (IV): where for the residues R 40 , R 41 , R 42 independently of each other: R 40 = cyano, nitro, acyl or a radical of the formula -(C=X)-R 43 , with X = imino or oxygen, R 43= amino, alkylamino or alkoxy, R 41 = hydrogen, C1- to C5-alkyl, aryl, benzyl, or acyl, R 42 = hydrogen or C1- to C5-alkyl. or in an alternative embodiment, does not comprise any further hardener from the group cyanamide and a hardener of the formula (IV) and optionally also does not comprise any further hardener, co-hardener, curing accelerator or other catalysts for curing epoxy resins, in particular no other hardeners from the group of guanidines, cyanoguanidines, nitroguanidines, acylguanidines and biguanidines.

[0075] According to a further idea, the present invention therefore also relates to an epoxy resin composition, in particular a liquid epoxy resin composition, which consists of at least one epoxy resin, in particular at least one liquid epoxy resin, and a hardener for hardening the epoxy resin and at least one boroxine of the general formula (I), wherein the hardener consists of at least one urea derivative according to formula (V) or formula (VI) or formula (VII) or contains such a urea derivative.

[0076] According to the invention, the epoxy resin composition comprises at least one epoxy resin, in particular a liquid epoxy resin. The epoxy resin or liquid epoxy resin is preferably a polyether with at least one, preferably at least two, epoxy groups, and even more preferably with at least three epoxy resin groups. These epoxy resins or liquid epoxy resins can have at least one, preferably at least two, epoxy groups and can be saturated or unsaturated, aliphatic, cycloaliphatic, aromatic, or heterocyclic. Furthermore, these epoxy resins or liquid epoxy resins can have substituents such as halogens, phosphorus, and hydroxyl groups. Bisphenol-based epoxy resins, in particular bisphenol A diglycidyl ether and the bromine-substituted derivative (tetrabromobisphenol A) or bisphenol F diglycidyl ether, novolak epoxy resins, in particular epoxyphenol novolak, or aliphatic epoxy resins, are preferred.Epoxy resins based on glycidyl polyether of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and the bromine-substituted derivative (tetrabromobisphenol A), glycidyl polyether of 2,2-bis(4-hydroxyphenyl)methane (bisphenol F), and glycidyl polyether of novolaks, as well as those based on aniline or substituted anilines such as p-aminophenol or 4,4'-diaminodiphenylmethane, are particularly preferred. Epoxy resins based on glycidyl polyether of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and epoxy resins based on glycidyl polyether of 2,2-bis(4-hydroxyphenyl)methane (bisphenol F) are especially preferred.

[0077] Further preferably, according to the present invention, epoxy resins, in particular liquid epoxy resins, can be used which have an EEW value in the range of EEW = 100 to 1500 g / eq, in particular in the range of EEW = 100 to 1000 g / eq, in particular in the range of EEW = 100 to 600 g / eq, further preferably in the range of EEW = 100 to 400 g / eq and very particularly preferably in the range of EEW = 100 to 300 g / eq.

[0078] The curing profile of the formulations according to the invention can be varied by adding further commercially available additives, as are known to the person skilled in the art for curing epoxy resins.

[0079] Reactive diluents and thermoplastic additives are commonly used in prepreg, towpreg, and adhesive formulations. Thus, the epoxy resin composition according to the invention can contain a reactive diluent and / or a thermoplastic additive in addition to the epoxy resin, hardener, and boroxines.

[0080] Glycidyl ethers, in particular, can be used as reactive diluents in the process according to the invention or in the epoxy resin matrix. Monofunctional, difunctional, and polyfunctional glycidyl ethers can also be used. In particular, glycidyl ethers, diglycidyl ethers, triglycidyl ethers, polyglycidyl ethers, and multiglycidyl ethers, and combinations thereof, are to be mentioned here. Glycidyl ethers from the group comprising 1,4-butanediol diglycidyl ether, trimethylolpropane triglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, C8-C 10 -alcohol glycidyl ether, C 12 -C 14-Alcohol glycidyl ether, cresol glycidyl ether, poly(tetramethylene oxide) diglycidyl ether, 2-ethylhexyl glycidyl ether, polyoxypropylene glycol diglycidyl ether, polyoxypropylene glycol triglycidyl ether, neopentyl glycol diglycidyl ether, p-tert-butylphenol glycidyl ether, polyglycerol multiglycidyl ether, and combinations thereof.

[0081] Particularly preferred glycidyl ethers are 1,4-butanediol diglycidyl ether, trimethylolpropane triglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether and combinations thereof.

[0082] Typically, thermoplastic additives are selected from the groups of phenoxy resins, acrylate, acrylic, acrylonitrile, polyetherimide, polyetherketone, or polysulfone polymers. Due to their positive influence on flow behavior during processing and the mechanical properties of the cured component, phenoxy resins, polyacrylates, or polysulfones are preferred.

[0083] Additives to improve the processability of uncured epoxy resin compositions or to adapt the thermal-mechanical properties of the thermosetting products to the requirements profile include, for example, fillers, rheology additives such as thixotropic agents or dispersing additives, defoamers, dyes, pigments, toughness modifiers, impact modifiers, nano-fillers, nano-fibers, or fire protection additives.

[0084] The amounts of boroxines according to the invention and the hardeners to be used in the epoxy resin compositions can be adjusted according to the present invention with respect to the amount of epoxy resin to be used. Preferably, based on 100 parts by weight of epoxy resin, 0.05 to 10.0 parts by weight of boroxines according to formula (I) can be used, more preferably 0.1 to 5.0 parts by weight of boroxines according to formula (I), and particularly preferably 0.2 to 2.0 parts by weight of boroxines according to formula (I) can be used.

[0085] Furthermore, based on 100 parts by weight of the epoxy resin, in particular 0.1 to 10 parts by weight of hardener from the group of hardeners according to formula (III), more preferably 0.5 to 8 parts by weight, particularly preferably between 0.8 and 4 parts by weight of hardener according to formula (III), can be used, wherein in some embodiments, parts by weight of hardener according to formula (III) of 4 to 6 can also be advantageous.

[0086] Furthermore, based on 100 parts by weight of epoxy resin, in particular 0 to 15 parts by weight of additional hardeners, in particular from the group of hardeners according to formula (IV) or cyanamide, may be present. Further preferred are 2 to 12 parts by weight, particularly preferably 4 to 10 parts by weight of additional hardeners, in particular from the group of hardeners according to formula (IV) and cyanamide.

[0087] The epoxy resin composition can preferably comprise the hardener according to formula (III) and the boroxines in a weight ratio of hardener to boroxine which corresponds to a ratio in the range 0.1:1 to 200:1, more preferably from 0.2:1 to 100:1, even more preferably from 0.5:1 to 50:1 and particularly preferably from 1:1 to 20:1.

[0088] More preferably, the epoxy resin composition can comprise the optional hardener, in particular from the group of hardeners of formula (IV) and cyanamide, and the boroxines in a weight ratio of optional hardener to boroxine which corresponds to a ratio in the range 1:1 to 300:1, more preferably from 2:1 to 120:1 and particularly preferably from 6:1 to 100:1 and in particular from 10:1 to 40:1.

[0089] As already mentioned, the epoxy resin compositions described herein can be stored for extended periods without any curing being observed. Furthermore, these epoxy resin compositions exhibit a curing profile that allows for a wide range of applications. However, epoxy resins according to the invention are particularly suitable for use in fiber composites.

[0090] Thus, the use of an epoxy resin composition of the type described herein for producing a fiber composite material, prepreg and towpreg is also the subject of the present invention.

[0091] Fiber composites such as prepregs or towpregs are characterized by the fact that they are pre-impregnated and partially cured fiber composites made of an epoxy resin and fibers. These partially cured materials are in a so-called B-stage, a partially cured state. Since the corresponding epoxy resin composition is only partially cured in this state, the epoxy resin can continue to cure. In epoxy resin formulations based on epoxy resin-uron mixtures, corresponding fiber composites such as prepregs and towpregs can continue to react at room temperature, thus negatively affecting the desired properties and quality of the fiber composites. Therefore, storage at room temperature for extended periods is not possible.To ensure sufficient storage stability of fiber composite materials such as prepregs or towpregs, they must be stored at controlled, low temperatures, often at -18 °C. This results in considerable additional costs and considerable effort in the storage, transport, and processing of prepregs and towpregs. Therefore, it is advantageous if the epoxy resin composition used guarantees a high latency in order to extend the storage conditions of fiber composite materials such as prepregs and towpregs to the benefit of their properties and quality. Epoxy resin compositions according to the invention exhibit a particularly high latency. Thus, epoxy resin compositions according to the invention of the type described herein are particularly suitable for solving this problem.

[0092] The present invention also relates to the fiber composite material itself, which comprises: a) a carrier material, in particular reinforcing fibres, and b) an epoxy resin composition according to the invention.

[0093] Fiber composites, especially prepregs and towpregs, are used for the production of fiber composite components in a wide variety of industries. For example, fiber composites are used in the automotive industry for the production of interior trim or fenders, and in the aerospace industry for a wide variety of components. Fiber composites are also used to manufacture sports and leisure equipment, such as tennis rackets or bicycle frames, as well as to manufacture rotor blades for wind turbines. All fiber types known to those skilled in the art can be used for these fiber composites. For example, glass, carbon, aramid, plastic, basalt, and natural fibers, or rock wool, are used. These fiber composites can be processed using processes such as autoclaves, out-of-autoclave, vacuum bag, and compression molding.

[0094] With regard to the selection of the carrier materials to be used, according to the present invention, in particular reinforcing fibers, more preferably reinforcing fibers selected from the group of carbon fibers, glass fibers, aramid fibers and basalt fibers, can be used.

[0095] These reinforcing fibers can further preferably be provided or used in the form of filaments, threads, yarns, woven fabrics, braids or knitted fabrics.

[0096] Reinforcing fibers made from silicon carbide, aluminum oxide, graphite, tungsten carbide, and boron can also be used. Furthermore, reinforcing fibers can be selected from the group of natural fibers such as seed fibers (e.g., kapok, cotton), bast fibers (e.g., bamboo, hemp, kenaf, flax), and leaf fibers (such as henequen and abac). Combinations of these reinforcing fibers can also be used as carrier materials.

[0097] As already mentioned, the epoxy resin compositions described herein can be stored for a relatively long period of time without any curing being observed. Furthermore, these epoxy resin compositions exhibit a curing profile that allows for a wide range of applications. Epoxy resins according to the invention are therefore also particularly suitable for use in 1-component adhesives and acoustic insulation materials. These adhesives and insulation materials are used, for example, in automotive and aircraft construction.

[0098] Thus, the use of an epoxy resin composition of the type described herein for producing a 1-component adhesive or an acoustic insulation material is also the subject of the present invention.

[0099] A large number of adhesives or acoustic insulation materials based on 1-component epoxy resin compositions are available in a liquid, medium- to high-viscosity state for use. On an industrial scale, these must be brought to an appropriate processing temperature before use. Since fully continuous mass production is preferably carried out with drum products, the adhesive or acoustic insulation contained therein must be processed with the aid of drum heating mats, but often with the aid of a melting plate in a drum melting system. The use of a melting plate, which is attached to the plunger of the drum melting system, places particular thermal stress on the epoxy resin composition.Because the plunger must be pressed against the epoxy resin to convey the molten, epoxy-based adhesive or acoustic insulation material, the pressure of the plunger on the drum contents creates additional shear forces, which further heat the epoxy resin locally. The molten resin must be conveyed through a small hose connection attached to the plunger, which usually leads to an application head, assembly gun, or melting device. This pressure and temperature-intensive stress negatively impacts the pot life and leads to a reduction in the latency of the epoxy resin composition. This can impair the properties of the adhesive or acoustic insulation material.Therefore, it is advantageous if the epoxy resin composition used for adhesives and acoustic insulation materials guarantees a high latency in order to ensure a significant latency extension under stress, but also during storage, of the material, which benefits the adhesive and insulating properties and thus the quality. Thus, epoxy resin compositions according to the invention of the type described herein are particularly suitable for solving this problem. Examples of implementation:

[0100] Materials used: Product name: EPIKOTE ® 828 LVEL (Westlake Corp.) Unmodified bisphenol A epoxy resin (EEW = 182 - 187 g / eq) (Viscosity at 25°C = 10 - 12 Pa*s) Hardener: DYHARD ® 100S (AlzChem Trostberg GmbH) Latent hardener, dicyandiamide (DCD), solid (particle size 98% ≤ 10 µm) Urea derivative: 1,1'-(4-methyl-m-phenylene)-bis-(3,3-dimethylurea) (Alzchem Trostberg GmbH) bifunctional hardener according to formula III, solid (particle size 98% ≤ 10 µm) Boroxin (Formulation 2): 2,4,6-Trimethylboroxine (Manufacturer ABCR GmbH, Karlsruhe) Liquid (Purity = >99%) Boroxine (Formulation 3): 2,4,6-Tri(4-ethylphenyl)boroxine; (Manufacturer ABCR GmbH, Karlsruhe) Solid, (Purity = >98%) Boroxine (Formulation 4): 2,4,6-tri(4-fluorophenyl)boroxine; (Manufacturer: ABCR GmbH, Karlsruhe) Solid (purity = >97%) Boroxin (Formulation 6): 2,4,6-Triphenylboroxine; (Manufacturer ABCR GmbH, Karlsruhe) Solid (purity = >98%) 3-Fluorophenylboronic acid (manufacturer ABCR GmbH, Karlsruhe) Solid (purity = na) Benzeneboronic acid (manufacturer ABCR GmbH, Karlsruhe) Solid (purity = >98%) Example 1: Preparation of the mixtures

[0101] For the tests of the formulations mentioned in the examples, the individual components of the respective formulation are mixed in a mortar for several minutes until homogeneous. The formulations listed in Table 1 have been converted to 10 g of epoxy resin. Methods used to characterize the compositionsDSC studies

[0102] DSC measurements are carried out on a dynamic heat flow differential calorimeter DSC 3+ (Mettler Toledo). a) Onset Temperature, Peak Temperature, and Enthalpy Determination To determine the onset, peak temperature, and enthalpy, a sample of the formulation is subjected to the following DSC temperature program: heating from 30 to 250 °C at 10 K / min, cooling from 250 to 30 °C at 20 K / min. The onset and peak temperatures are determined from the heating cycle. The reaction enthalpy in J / g is calculated from the sample weight and the area between the measurement curve and the baseline. b) Tg determination: To determine the maximum glass transition temperature (final Tg), a sample of the cured formulation is subjected to the following DSC temperature program: heating from 30 - 200 °C at 20 K / min, holding at 200 °C for 10 min, cooling from 200 - 50 °C at 20 K / min, holding at 50 °C for 5 min, heating from 50 - 200 °C at 20 K / min, holding at 200 °C for 10 min, cooling from 200 - 50 °C at 20 K / min, holding at 50 °C for 5 min, heating from 50 - 220 °C at 20 K / min. The glass transition temperature is determined from the last two heating cycles by drawing a tangent at the inflection point of the largest change in heat capacity (ΔCp) and the mean value is given as the final TG. c) Isothermal DSC: A sample of the formulation is kept constant at the specified temperature for the specified time (isothermal curing of the formulation). The evaluation is performed by determining the time of 90% conversion (as a measure of the end of the curing process) of the exothermic reaction peak. d) Latency: To determine latency (storage stability), approximately 10 g of the respective formulation are freshly prepared and then stored in an oven at 40 °C. Regularly measuring the dynamic viscosity records the progressive crosslinking (curing) of the formulation under these storage conditions. Dynamic viscosity is determined using a Haake viscometer [cone (1 °)-plate method, measurement at 25 °C, shear rate 5.0 s-1]. A formulation is considered storage-stable (still suitable for processing) until its viscosity doubles. Table 1: Latency of epoxy resin compositions in comparison Recipes* 1 2 3 4 5 6 EPIC HOME TM Resin 828 100 100 100 100 100 100 DCD (hardener) 6,5 6,5 6,5 6,5 6,5 6,5 Urea derivative 1 1 1 1 5 5 2,4,6-Trimethylboroxine 0,3 2,4,6-Tri(4-ethylphenyl)boroxine 0,3 2,4,6-tri(4-fluorophenyl)boroxine 0,3 2,4,6-Triphenylboroxine 0,4 Dynamic DSC (30 - 250°C) Onset temperature [°C] 143 153 149 148 133 138 Peak temperature [°C] 151 161 157 158 140 145 Enthalpy [J / g] 350 375 385 368 450 435 Final Tg [°C] 143 143 143 142 132 135 Isothermal DSC; 1 hour at 140°C Time to 90% turnover [min] 15 22 13 21 7 9 Latency at 40 °C Viscosity doubling [days] 3 25 21 40 2 19 *Components of the recipes in weight proportions

[0103] A comparison of the inventive examples according to formulations 2, 3, and 4 with the comparative example according to formulation 1 and the inventive example according to formulation 6 with the comparative example according to formulation 5, each consisting of DCD (hardener), a uron-based hardener in a commercially available epoxy resin, shows that comparable, characteristic values for the curing process can be determined when using the inventive boroxines. This is demonstrated by the values from the DSC analysis, the determined final Tg values, and the values from the isothermal DSC determination at 140°C to determine the 90% cure conversion. The latency measurements confirm that by adding the inventive boroxines to the inventive examples (formulations 2, 3, 4, and 6), the latency at 40°C can be significantly extended, at least sevenfold.For Examples 2-4, the viscosity doubling time is increased by a factor of approximately 7 to 14 compared to Comparative Example 1. The latency in Example 6 according to the invention increases by a factor of approximately 10 compared to the corresponding Comparative Example 5.

[0104] Thus, the results in Table 1 show that, using the boroxines according to the invention, epoxy resin-based compositions can be provided for the production of prepregs, towpregs, and adhesives that have a significantly extended latency at 40 °C, while the curing properties remain virtually unchanged. This means that prepregs, towpregs, adhesives, and acoustic insulation materials can be handled more easily, e.g., they can be stored, transported, and further processed without refrigeration.

[0105] Example 2: Production of the mixtures

[0106] For the tests of the formulations mentioned in the examples, the individual components of the respective formulation are mixed in a mortar for several minutes until homogeneous. The formulations listed in Table 2 have been converted to 10 g of epoxy resin. Methods used to characterize the compositionsDSC studies

[0107] DSC measurements are performed on a DSC 3+ dynamic heat flow differential calorimeter (Mettler Toledo). To determine the onset, peak, and enthalpy temperatures, a sample of the formulation is subjected to the following DSC temperature program: heating from 30 to 300 °C at 10 K / min, cooling from 300 to 30 °C at 20 K / min. The onset and peak temperatures are determined from the heating cycle. Table 2: Reactivity of boroxines and boronic acids in comparison Recipes* 7 8 9 10 EPIKOTE™ 828LVEL 100 100 100 100 3-Fluorophenylboronic acid 3 2,4,6-tri(4-fluorophenyl)boroxine 3 Benzeneboronic acid 3 2,4,6-Triphenylboroxine 3 Dynamic DSC (30-300°C) Onset temperature [°C] 69 103 90 156 Peak temperature [°C] 114 148 155 190 Components of the recipes in weight proportions

[0108] The results in Table 2 show that the boroxines in epoxy resins (formulations 8 and 10) exhibit significantly higher onset and peak temperatures than analogous boronic acids (formulations 7 and 9). The higher onset and peak temperatures indicate that the reactivity of the boroxines with the epoxy resin is significantly lower than that of the corresponding boronic acids. Due to the lower reactivity of the boroxines with the resin, they are better suited than boronic acids for increasing the latency of epoxy resin compositions without impairing subsequent curing of the resin. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 659793 B1

[0007] EP 2678369 B1

[0008] EP 2780388 B1

[0009] EP 3257884 A1

[0010] DE 10 2019 121 195.6

[0011] WO 2021 / 023593 A1

[0012] WO 2022 / 161837 A1

[0012]

Claims

[1] Use of boroxines of the general formula (I) for improving the storage stability of epoxy resin compositions comprising an epoxy resin and a hardener for hardening the epoxy resin, wherein the formula (I) applies: where the residue of formula (II) can be bonded to the boroxine ring either directly or via an alkylene group having 1 to 5 carbon atoms and where for the residues R 1 , R 2 and R 3 independently of each other: R 1 R 2 , R 3 = hydrogen, alkyl, cycloalkyl, hydroxyalkyl, alkoxy or a radical of the Formula (II), where for formula (II) where for R 4 , R 5 , R 6 independently of each other: R 4 , R 5 , R 6 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl, and the hardener is selected from compounds according to formula (III), where formula (III) is: where for R 7 , R 8 , R 9 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, R 9 = with -NHC(O)NR 7 R S substituted C1 to C 15 -alkyl, with -NHC(O)NR 7 R S substituted C3 to C 15 -Cycloalkyl, with -NHC(O)NR 7 R S substituted aryl or with -NHC(O)NR 7 R 8 substituted alkylaryl. [2] Use according to claim 1, characterized by that in addition to the hardener of the general formula (III), further hardeners, preferably from the group of guanidines, cyanoguanidines, nitroguanidines, acylguanidines and biguanidines, are contained in the epoxy resin composition. [3] Use according to one of claims 1 and 2, characterized in that in addition to the hardener of the general formula (III), further hardeners are contained in the epoxy resin composition, which are selected from the group consisting of cyanamide and / or a compound of the formula (IV), where for formula (IV) where for the residues R 40 , R 41 , R 42 independently of each other: R 40 = cyano, nitro, acyl or a radical of the formula -(C=X)-R 43 , with X = imino or oxygen, R 43 = amino, alkylamino or alkoxy, R 41 = hydrogen, C1- to C5-alkyl, aryl, benzyl, or acyl, R 42 = hydrogen or C1- to C5-alkyl. [4] Use according to any one of the preceding claims, characterized by that the boroxine is selected from compounds of formula (I) where for the residues R 1 , R 2 and R 3independently of each other: R 1 R 2 , R 3 = C1- to C5-alkyl or a radical of the formula (II), where for formula (II) where R 4 , R 5 , R 6 independently of one another represent a radical selected from the group hydrogen, fluorine, chlorine, C1- to C4-alkyl and alkoxy. [5] Use according to any one of the preceding claims, characterized bythat the boroxines of the formula (I) are selected from compounds of the group 2-phenylboroxine, 2,4-diphenylboroxine, 2,6-diphenylboroxine, 2,4,6-triphenylboroxine, 2-((C1-C4)-alkylphenyl)boroxine, 2,4-di-((C1-C4)-alkylphenyl)boroxine, 2,6-Di-((C1-C4)-alkylphenyl)boroxine, 2,4,6-tri-((C1-C4)-alkylphenyl)boroxine, 2-(fluorophenyl)boroxine, 2,4-di-(fluorophenyl)boroxine, 2,6-di-(fluorophenyl)boroxine, 2,4,6-tri-(fluorophenyl)boroxine, 2-(chlorophenyl)boroxine, 2,4-di-(chlorophenyl)boroxine, 2,6-di-(chlorophenyl)boroxine, 2,4,6-tri-(chlorophenyl)boroxine, 2-(C1-C4)-alkylboroxine, 2,4-di-(C1-C4)-alkylboroxine, 2,6-di-(C1-C4)-alkylboroxine, 2,4,6-Tri-(C1-C4)-alkylboroxine. [6] Use according to one of the preceding claims, characterized by that the hardener of formula (III) consists of compounds of formula (III) with the radicals R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, R 9 = with -NHC(O)NR 7 R 8substituted C1 to C 15 -alkyl, with -NHC(O)NR 7 R 8 substituted C3 to C 15 -Cycloalkyl, with -NHC(O)NR 7 R 8 substituted aryl or with -NHC(O)NR 7 R 8 substituted alkylaryl or mixtures thereof. [7] Use according to one of the preceding claims, characterized by that the epoxy resin composition comprises bisphenol-based epoxy resins. [8] Hardener system containing a) at least one boroxine of the general formula (I), where formula (I) applies: where the residue of formula (II) can be bonded to the boroxine ring either directly or via an alkylene group having 1 to 5 carbon atoms and where for the residues R 1 , R 2 and R 3 independently of each other: R 1 R 2 , R 3= hydrogen, alkyl, cycloalkyl, hydroxyalkyl, alkoxy or a radical of formula (II), where for formula (II) where for R 4 , R 5 , R 6 independently of each other: R 4 , R 5 , R 6 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl or carboxyl, b) a hardener selected from compounds according to formula (III), where formula (III) applies: where for R 7 , R 8 , R 9 independently of each other: R 7 , R 8 = independently of one another hydrogen or C1- to C5-alkyl, R 9 = with -NHC(O)NR 6 R 7 substituted C1 to C 15 -alkyl, with -NHC(O)NR 6 R 7 substituted C3 to C 15 -Cycloalkyl, with -NHC(O)NR 6 R 7substituted aryl or with -NHC(O)NR 6 R 7 substituted alkylaryl, and if necessary c) further hardeners, preferably from the group of guanidines, cyanoguanidines, nitroguanidines, acylguanidines and biguanidines, in particular selected from the group of cyanamide and / or a compound of formula (IV), where formula (IV) applies where for the residues R 40 , R 41 , R 42 independently of each other: R 40 = cyano, nitro, acyl or a radical of the formula -(C=X)-R 43 , with X = imino or oxygen, R 43 = amino, alkylamino or alkoxy, R 41 = hydrogen, C1- to C5-alkyl, aryl, benzyl, or acyl, R 42 = hydrogen or C1- to C5-alkyl. [9] Epoxy resin composition, characterized by that the composition comprises a hardener system according to claim 8. [10] Epoxy resin composition according to claim 9, characterized by that the epoxy resin composition based on 100 parts by weight of epoxy resin a) 0.05 to 5.0 parts by weight of boroxine according to formula (I), b) 0.1 to 10 parts by weight of hardener according to formula (III) and optionally c) up to 15 parts by weight of additional hardeners. [11] Use of an epoxy resin composition according to one of claims 9 and 10, characterized by that the composition is used for the production of prepregs, towpregs or adhesives.