Method for preparing epoxy resin composition for material pre-impregnation

Abstract

The invention relates to a method for producing an epoxy resin composition for pre-impregnation of materials, in which a pre-added epoxy resin is heated to a temperature in the range of 60 DEG C to 100 DEG C and mixed with a curing agent, a curing accelerator, an optional thickening agent and boric acid of general formula (I) as a polymerization inhibitor. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to a method for preparing an epoxy resin composition for pre-impregnating materials under the application of temperature.

[0002] Epoxy resins are widely used due to their good chemical resistance, very good thermal and dynamic mechanical properties and their high electrical insulation capabilities. These epoxy resins can be in liquid or solid form and can be cured with or without the addition of a curing agent and with or without heat input.

[0003] The curing of epoxy resins follows different mechanisms. In addition to curing with phenols or anhydrides, amines are often used for curing. These substances are usually liquids and can usually mix well with epoxy resins. Due to their high reactivity, this type of epoxy resin composition is a two-component. This means that the resin (A component) and the curing agent (B component) are stored separately and mixed in the correct ratio only shortly before use. These two-component resin formulations are also referred to as so-called cold curing resin formulations, wherein the curing agent used for this purpose is usually selected from amines or amidoamines.

[0004] In contrast, one-component heat-curing epoxy resin formulations are ready-to-use, i.e., epoxy resin and hardener are present mixed at the factory. Mixing errors of the individual components during use on site are therefore excluded. A prerequisite for this is a latent hardener system, which does not react with the epoxy resin at room temperature but reacts readily under heating, respectively, depending on the energy input. In this context, "latent" means that the mixture of the individual components is stable under defined storage conditions.

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

[0006] In order to reduce the reaction temperature for curing one-component epoxy resin formulations such as epoxy resin-dicyandiamide mixtures, curing accelerators are usually added to these formulations to reduce the activation energy of curing, making it possible to cure at lower temperatures. However, these curing accelerators reduce the storage stability of epoxy resin compositions. Background Art

[0007] In recognition of such obstacles, proposals to overcome them have been published. For example, international patent specification WO2021 / 023593 describes the use of boric acid for improving the storage stability of an epoxy resin composition comprising an epoxy resin, a curing agent, and a curing accelerator. The epoxy resin composition is storage stable and allows rapid curing by heating.

[0008] In addition, international patent application PCT / EP2022 / 051177 shows that the use of boric acid is also beneficial to improve the storage stability of epoxy resin compositions containing epoxy resin and urea (Uron). In this case, the storage stability of epoxy resin compositions based on N,N-dimethylurea as curing agents is improved by adding boric acid.

[0009] In many cases, in order to introduce other additives into epoxy resin, it is necessary to heat the resin so that the additives can be uniformly mixed or promote the uniform mixing of the additives. The presence of a curing accelerator is disruptive here because the accelerator causes the reactivity of the epoxy resin composition to be enhanced under the application of temperature. Since the viscosity of the epoxy resin composition must be relatively high, it is particularly necessary to apply the temperature to the epoxy resin when producing the epoxy resin composition for prepreg or towpregs. If a low viscosity epoxy resin composition is used at room temperature, a thickener must usually be mixed in. The uniform mixing of epoxy resin and thickener usually requires heating the epoxy resin. If the epoxy resin already has a viscosity suitable for producing prepreg or towpreg, heating the epoxy resin is necessary to mix other necessary additives such as a curing agent, a reaction accelerator or an inhibitor with the resin.

[0010] Viscosity is regulated particularly by adding different resins or powder additives of higher viscosity. If the viscosity of epoxy resin composition increases, the dispersibility of epoxy resin composition decreases. Therefore, the temperature must be increased to reduce viscosity. Here, for the best allocation of all components (such as different epoxy resins of various viscosities, curing agents, curing accelerators and other additives), epoxy resin composition is required to be several hours at the temperature increased. Then they are applied to reinforcing fibers, such as carbon fiber, glass fiber or basalt fiber at the temperature increased. Summary of the invention

[0011] The object of the present invention is therefore to provide a method for producing an epoxy resin composition which is suitable for producing materials pre-impregnated with the resin composition (e.g. prepregs or bundle prepregs). In this case, curing agents, curing accelerators and other additives should be easily incorporated into the epoxy resin composition while the performance characteristics of the composition necessary for the preparation of prepregs or bundle prepregs must be maintained.

[0012] The present invention is solved by a method for preparing an epoxy resin composition for pre-impregnation of materials, the method being characterized in that the pre-added epoxy resin

[0013] a) heating to a temperature in the range of 60°C to 100°C and

[0014] b) mixing boric acid of general formula (I) as a polymerization inhibitor with epoxy resin

[0015]

[0016] The residue R 1 yes:

[0017] R 1 =alkyl, hydroxyalkyl or a residue of formula (II), wherein formula (II) is:

[0018]

[0019] Where R 2 , R 3 , R 4 are represented independently of each other, and at least one residue R 2 , R 3 , R 4 Not Hydrogen:

[0020] R 2 , R 3 , R 4 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH)2,

[0021] c) mixing a curing accelerator with an epoxy resin for accelerated curing of the epoxy resin, wherein the curing accelerator comprises a compound of formula (III)

[0022]

[0023] Where R 6 , R 7 , R 8 Independently of each other are:

[0024] R 6 , R 7 = independently hydrogen or C1- to C 5- alkyl,

[0025] R 8 =Hydrogen, C1- to C 15 -alkyl, C3- to C 15 - cycloalkyl, aryl, alkylaryl,

[0026] NHC(O)NR 6 R 7 Substituted C1- to C 15 -alkyl,

[0027] NHC(O)NR 6 R 7 Substituted C3- to C 15 - cycloalkyl,

[0028] By NHC(O)NR 6 R 7 Substituted aryl or

[0029] NHC(O)NR 6 R 7 Substituted alkylaryl,

[0030] d) optionally mixing a curing agent with the epoxy resin, wherein the curing agent comprises cyanamide and / or a compound of formula (IV),

[0031]

[0032] The residue R 40 , R 41 , R 42 Independently of each other are:

[0033] R 40 =cyano, nitro, acyl or -(C=X)-R 43 wherein X = imino or oxygen,

[0034] R 43 =amino, alkylamino or alkoxy,

[0035] R 41 = hydrogen, C1- to C5-alkyl, aryl or acyl,

[0036] R 42 = hydrogen or C1- to C5-alkyl,

[0037] e) optionally mixing a thickener with the heated epoxy resin from step a),

[0038] wherein the epoxy resin temperature is applied according to step a) for at least 15 minutes and not more than 240 minutes, and

[0039] Two or more of the method steps a) to e) can be carried out simultaneously and / or successively.

[0040] Since epoxy resin compositions which do not contain a curing agent selected from cyanamide and compounds of the formula (IV) have also been found to be sufficiently reactive, a process in which process step d) is omitted is also a subject of the present invention. In a preferred process variant, process step d) is included.

[0041] According to the invention, epoxy resin compositions are thermosetting epoxy resins, i.e. compositions which are polymerizable, crosslinkable or crosslinkable due to their functional groups (i.e. epoxide groups) by heating. In this case, polymerization, crosslinking or crosslinking occurs as a result of polyaddition induced by curing agents and curing accelerators.

[0042] In the present description, alkyl is understood to be a saturated, straight-chain or branched aliphatic residue, in particular a alkyl radical having the general formula C n H 2n+1 wherein n represents the number of carbon atoms in the residue. Alkyl may represent residues having more carbon atoms. Preferably, alkyl means a residue having the general formula C n H 2n+1 A saturated, straight-chain or branched aliphatic residue of alkyl, wherein n represents the number of carbon atoms of the residue and n represents a number from 1 to 15. Thus, alkyl preferably represents a C1- to C 15 -alkyl, even more preferably C1-C 10 -alkyl. It is further preferred that C1- to C 15 -Alkyl denotes, 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 or n-dodecyl.

[0043] Furthermore, C1- to C5-alkyl represents a saturated, straight-chain or branched alkyl radical having up to five carbon atoms. Preferably, C1- to C5-alkyl represents, 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.

[0044] According to the invention, hydroxyalkyl is an alkyl radical as defined above which is substituted by one, two or three hydroxy groups. According to the invention, hydroxyalkyl is in particular an alkyl radical having up to 15 carbon atoms and substituted by hydroxy groups. Thus, hydroxyalkyl preferably is a C1- to C 15 -Hydroxyalkyl. Further preferably, hydroxyalkenyl represents C1- to C5-hydroxyalkyl. Particularly preferably, hydroxyalkyl represents hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl or 5-hydroxypentyl.

[0045] In the present specification, C3- to C 15 -Cycloalkyl is also understood to be a saturated monocyclic or bicyclic aliphatic radical having 3 to 15 carbon atoms, in particular a saturated monocyclic or bicyclic aliphatic radical having the general formula C n H 2n-1 wherein n=an integer from 3 to 15. Preferably, C3- to C 15 Cycloalkyl represents in particular cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or cycloheptyl, these cycloalkyl residues in turn being further preferably mono- or polysubstituted by alkyl as defined above.

[0046] According to the present invention, C3- to C 15 Cycloalkyl particularly preferably denotes cyclopentyl, cyclohexyl, which in turn may be mono- or polysubstituted by alkyl, in particular 3,3,5,5-tetramethyl-1-cyclohexyl.

[0047] Cyano represents a nitrile group of the general formula CN.

[0048] Nitro refers to a functional group having the general formula NO2.

[0049] Amino refers to a functional group having the general formula NH2.

[0050] Imino represents a functional group of the general formula NH.

[0051] According to the invention, alkylamino means a radical of the formula NH n (alkyl) 2-n wherein n=0 or 1, wherein alkyl is an alkyl residue as defined above, and wherein the binding site is at the nitrogen.

[0052] The carboxyl group represents a functional group having the general formula COOH.

[0053] According to the invention, alkoxy means a residue of the general formula O-alkyl, where alkyl is an alkyl residue in the above-mentioned sense and where the binding site is at the oxygen. According to the invention, alkoxy means in particular an alkoxy residue whose alkyl residue has up to 15 carbon atoms, in particular up to 5 carbon atoms. Thus, alkoxy preferably means a C1- to C 15 -alkoxy, more preferably C1- to C5-alkoxy. Particularly preferably, alkoxy represents methoxy, ethoxy, n-propoxy, n-butoxy or n-pentoxy.

[0054] According to the present invention, the acyl group is represented by the formula C(O)-R 5 The residues, R 5 is bonded to carbon and may represent hydrogen, alkyl or alkoxy as defined above, and the binding site of the acyl residue is located on carbon. Acyl particularly preferably represents formyl or acetyl.

[0055] Furthermore, alkylsulfonyl is a radical of the formula SO2-alkyl, in which the binding sites of the alkylsulfonyl radical and the alkyl radical are both located on the sulfur and in which the alkyl radical is an alkyl radical in the above-mentioned sense. According to the invention, alkylsulfonyl is an alkylsulfonyl radical, in particular, whose alkyl radical has up to 15 carbon atoms. Thus, alkylsulfonyl preferably means a C1- to C2- 15 - alkylsulfonyl, more preferably C1- to C5-alkylsulfonyl. Particularly preferably, alkylsulfonyl represents methylsulfonyl, ethylsulfonyl, n-propylsulfonyl, n-butylsulfonyl or n-pentylsulfonyl.

[0056] According to the invention, aryl means an aromatic residue, in particular an aromatic residue having 6 to 15 carbon atoms, which may be monocyclic, bicyclic or polycyclic. 15 Aryl. Aryl particularly preferably represents phenyl, naphthyl, anthracenyl, phenanthryl, pyrenyl or perylenyl, very particularly preferably phenyl.

[0057] Furthermore, according to the invention, alkylaryl means an aromatic residue of the above-mentioned type, which in turn is monosubstituted or polysubstituted by an alkyl residue of the above-mentioned type. In particular, alkylaryl means an aromatic residue having 6 to 15 carbon atoms. Thus, aryl preferably means a C6- to C 15 -Alkylaryl. Furthermore, alkylaryl preferably represents methylphenyl, dimethylphenyl or trimethylphenyl.

[0058] Surprisingly, it has been shown that by adding a substituted boric acid of formula (I) according to the present invention to an epoxy resin composition containing an epoxy resin, a curing accelerator and an optional curing agent, the performance and quality loss of the epoxy resin composition under temperature application in the manufacturing method of the epoxy resin composition is minimized. Surprisingly, it has been shown that when the substituted boric acid of the present invention is used, the curing performance and reactivity of the epoxy resin composition are maintained even after heating to a temperature range of 60°C to 100°C. This means that the curing performance quality of the desired prepreg and bundle prepreg is not reduced. In addition, it has been shown that after temperature treatment, the viscosity of the epoxy resin itself is not significantly affected. Therefore, if necessary, the desired viscosity can be adjusted by adding a thickener separately. Therefore, the impregnation performance required for the epoxy resin composition is maintained. The glass transition temperature to be reached is not affected by the addition of the substituted boric acid. Therefore, the overall curing performance of the curing agent and the curing accelerator (the curing performance is obtained without the addition of the substituted boric acid) does not change and is substantially maintained. Therefore, in summary, an epoxy resin composition can be provided which can be subjected to temperature application of 60° C. to 100° C. for several hours without affecting the curing properties and is therefore very suitable for use in prepregs or bundle prepregs.

[0059] According to the present invention, substituted boronic acids of formula (I) can be used, wherein R in formula (I) 1 It may represent an alkyl group, a hydroxyalkyl group or a residue of formula (II). Preferably, R in formula (I) 1 means alkyl or hydroxyalkyl, wherein R 1 Has the following meanings:

[0060] R 1 =methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl or 5-hydroxypentyl.

[0061] According to the present invention, R 1 It may also represent a residue of the formula (II) in which at least one substituent R 2 , R 3 , R 4 is not hydrogen. Therefore, optionally R in formula (I) 1 It may preferably be intended to mean a residue of the formula (II) wherein the residue R 2 , R 3 , R 4 yes:

[0062] R 2 = fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH)2,

[0063] R 3 , R 4 =Hydrogen.

[0064] More preferably, R in formula (I) 1 It can be a residue of formula (II), wherein R 2 , R 3 , R 4 yes:

[0065] R 2 = fluorine, cyano, acyl, alkylsulfonyl or B(OH)2,

[0066] R 3 , R 4 =Hydrogen.

[0067] More preferably, R in formula (I) 1 It can be a residue of formula (II), wherein R 2 , R 3 , R 4 yes:

[0068] R 2 = fluorine, cyano, formyl, acetyl, methylsulfonyl, ethylsulfonyl, n-propylsulfonyl, n-butylsulfonyl, n-pentylsulfonyl or B(OH)2,

[0069] R 3 , R 4 =Hydrogen.

[0070] According to a further alternative, R in formula (I) 1 It may also preferably refer to residues of the formula (II) in which R 2 , R 3 , R 4 yes:

[0071] R 2 , R 3 independently = fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH)2,

[0072] R 4 =Hydrogen.

[0073] More preferably, R in formula (I) 1 It can be a residue of formula (II), wherein R 2 , R 3 , R 4 yes:

[0074] R 2 , R 3 independently = fluoro or alkoxy,

[0075] R 4 =Hydrogen.

[0076] Still further preferably, R in formula (I) 1 It can be a residue of formula (II), wherein R 2 , R 3 , R 4 yes:

[0077] R 2 , R 3 = fluorine, methoxy, ethoxy, n-propoxy, n-butoxy or -n-pentoxy,

[0078] R 4 =Hydrogen.

[0079] According to a further alternative, R in formula (I) 1 Also preferred are residues of the formula (II) in which the residue R 2, R 3 , R 4 Independently of each other are:

[0080] R 2 , R 3 , R 4 =Fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH)2.

[0081] More preferably, R in formula (I) 1 It can be a residue of formula (II), wherein R 2 , R 3 , R 4 Independently of each other are:

[0082] R 2 , R 3 , R 4 = fluorine or C1- to C5-alkyl.

[0083] Still further preferably, R in formula (I) 1 It can be a residue of formula (II), wherein the residue R 2 , R 3 , R 4 Independently of each other are:

[0084] R 2 , R 3 , R 4 = fluorine, methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, n-pentyl.

[0085] Very particularly preferably, formula (I) represents a radical selected from the group consisting of 4-formylphenylboronic acid, 1,4-phenyldiboronic acid, 3-fluorophenylboronic acid, 2,4-difluorophenylboronic acid, 2,5-dimethoxyphenylboronic acid, methylboronic acid, 4-ethylphenylboronic acid, 1-octylboronic acid, 2-carboxyphenylboronic acid, 3-carboxyphenylboronic acid, 4-carboxyphenylboronic acid, (2-hydroxymethyl)phenylboronic acid, 4-cyanophenylboronic acid, 4-(methylsulfonyl)phenylboronic acid, 3,4,5-trifluorophenylboronic acid or mixtures thereof.

[0086] Surprisingly, it has been shown that such epoxy resin compositions are particularly temperature-stable in a temperature range above 60° C., so that homogeneous mixing of epoxy resins with additives or incorporation of thickeners is simplified or made possible for the first time. Thus, it has been shown that epoxy resin compositions containing an inhibitor of formula (I), a curing accelerator of formula (III) and optionally a curing agent of formula (IV) or cyanamide have a low tendency to react at temperatures of more than 60° C. to 100° C., preferably between 65° C. and 90° C., in particular between 70° C. and 85° C., for up to 4 hours.

[0087] The application of the epoxy resin temperature for mixing in the additives should be in the range of 15 minutes to 4 hours, preferably between 30 minutes and 3 hours, in particular between 45 minutes and 2 hours. At higher temperature settings, shorter times are preferred to avoid a significant degree of polymerization in the epoxy resin composition. Therefore, a temperature application of 30 minutes to 90 minutes at a temperature of 70° C. to 90° C., in particular a temperature application of between 30 minutes and 90 minutes at a temperature between 70° C. and 90° C. is particularly preferred.

[0088] Surprisingly, it has been shown that the other curing properties of the epoxy resin composition obtained according to the invention after heating to 60° C. to 100° C., such as reactivity or viscosity, are comparable to the curing and rheological properties of the untempered composition. Furthermore, the rheological properties can be easily adjusted by the method, for example by using thickeners. Therefore, the epoxy resin composition obtained by the method can be used very well for the pre-impregnation of materials, in particular for the production of prepregs or bundle prepregs.

[0089] According to the invention, as a curing agent for curing the epoxy resin in the optional process step d), a curing agent selected from the group consisting of cyanamides or guanidines, in particular cyanoguanidines, nitroguanidines, acylguanidines or biguanides, is applied or used. Preferably, cyanamide or a curing agent according to the general formula (IV) is used as a curing agent, wherein the formula (IV) is as follows

[0090]

[0091] The residue R 40 , R 41 , R 42 Independently of each other are:

[0092] R 40 =cyano, nitro, acyl or -(C=X)-R 43 of residues, among which

[0093] X = imino or oxygen,

[0094] R 43 =amino, alkylamino or alkoxy,

[0095] R 41 = hydrogen, C1- to C5-alkyl, aryl, benzyl or acyl,

[0096] R 42 =Hydrogen or C1- to C5-alkyl.

[0097] Here, such curing agents according to formula (IV) are further preferred, wherein R 41 = hydrogen or C1- to C5-alkyl and / or R 42 = hydrogen or C1- to C5-alkyl, and C1- to C5-alkyl simultaneously or independently of one another represents the radical methyl, ethyl, n-propyl, isopropyl, n-butyl or n-pentyl.

[0098] Particularly preferably, a curing agent of the formula (IV) can be used, for which:

[0099] R 40 = cyano or nitro, especially cyano,

[0100] R 41 = hydrogen, methyl or ethyl, especially hydrogen,

[0101] R 42 = hydrogen, methyl or ethyl, especially hydrogen.

[0102] As curing agents for curing epoxy resins of general formula (IV), cyanoguanidine, 1,1-dimethyl-3-cyanoguanidine, 1-acetyl-3-cyanoguanidine, 1-(p-chlorophenyl)-3-cyanoguanidine, nitroguanidine, 1-methyl-3-nitroguanidine, 1-ethyl-3-nitroguanidine, 1-butyl-3-nitroguanidine, 1-benzyl-3-nitroguanidine, formylguanidine, acetylguanidine, carbamoylguanidine or methoxycarbonylguanidine can be preferably used, and cyanoguanidine is particularly preferred. These cyanoguanidine derivatives or nitroguanidine derivatives are characterized by particularly high latency.

[0103] As an alternative to or together with the compounds of formula (IV), cyanamides can also be used as curing agents for curing epoxy resins.

[0104] As curing accelerators, in particular urea derivatives, in particular urea derivatives according to formula (III), can be used or employed according to the invention, wherein formula (III) follows:

[0105]

[0106] Where R 6 , R 7 , R 8 Follow independently of each other:

[0107] R 6, R 7 = independently of one another are hydrogen or C1- to C5-alkyl,

[0108] R 8 =Hydrogen, C1- to C 15 -alkyl, C3- to C 15 - cycloalkyl, aryl, alkylaryl,

[0109] NHC(O)NR 6 R 7 Substituted C1- to C 15 -alkyl,

[0110] NHC(O)NR 6 R 7 Substituted C3- to C 15 - cycloalkyl,

[0111] NHC(O)NR 6 R 7 Substituted aryl or

[0112] NHC(O)NR 6 R 7 Substituted alkaryl.

[0113] Among the urea derivatives of the formula (III), preference is given to using aromatic urea derivatives. Further preference is given here to aromatic urea derivatives of the formula (III) in which the residue R 6 , R 7 , R 8 Independently follow:

[0114] R 6 , R 7 independently of one another = C1- to C5-alkyl, in particular methyl or ethyl,

[0115] R 8 = aryl, aralkyl or

[0116] By NHC(O)NR 6 R 7 Substituted aryl or

[0117] NHC(O)NR 6 R 7 Substituted alkaryl.

[0118] Further preferably, the residue R 6 , R 7 , R 8 can be expressed independently of each other:

[0119] R 6 , R 7independently of one another = C1- to C5-alkyl, in particular methyl or ethyl,

[0120] R 8 = -NHC(O)NR 6 R 7 Substituted aryl or

[0121] NHC(O)NR 6 R 7 Substituted alkylaryl, especially

[0122] NHC(O)NR 6 R 7 Substituted alkylaryl.

[0123] Therefore, according to the present invention, urea derivatives are particularly preferred, wherein formula (III) preferably exhibits formula (V), wherein formula (V) follows:

[0124]

[0125] and where the residue R 6 , R 7 , R 9 , R 10 Follow independently of each other:

[0126] R 6 , R 7 = independently of one another = hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl, R 9 , R 10 Independently of one another = hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl.

[0127] Preferably, the residue R associated with formula (V) 6 , R 7 , R 9 Each represents a methyl residue, and R 10 Particularly preferred are 1,1'-(4-methyl-m-phenylene)bis(3,3-dimethylurea) and 1,1'-(2-methyl-m-phenylene)bis(3,3-dimethylurea).

[0128] Among the urea derivatives of the formula (III), aliphatic urea derivatives can also be preferably used. Further preferred here are aliphatic urea derivatives of the formula (III) in which the residue R 6 , R 7 , R 8 Independently follow:

[0129] R 6 , R 7 = independently of one another = hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl, R8 =Hydrogen or C1- to C 15 -alkyl, C3- to C 15 - cycloalkyl,

[0130] NHC(O)NR 5 R 6 Substituted C1- to C 15 -alkyl,

[0131] NHC(O)NR 5 R 6 Substituted C3- to C 15 -cycloalkyl.

[0132] Further preferred are aliphatic urea derivatives according to formula (III), wherein R 6 and R 7 is as defined above, in particular hydrogen, methyl or ethyl, and R 8 represents hydrogen or C1- to C 15 -alkyl, in particular methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl or n-decyl. Particularly preferably, the residue R in formula (III) is 6 , R 7 Respectively represent methyl, R 8 N-(n-butyl-)-N',N'-dimethylurea is particularly preferred.

[0133] Further preferred are aliphatic urea derivatives according to formula (III), wherein R 6 and R 7 is as defined above, in particular hydrogen, methyl or ethyl, and R 3 is -NHC(O)NR 1 R 2 Substituted C1- to C 15 -cycloalkyl.

[0134] Therefore, according to the present invention, urea derivatives are particularly preferred, wherein formula (III) is preferably represented by formula (VI), wherein formula (VI) follows

[0135]

[0136] and where the residues simultaneously or independently follow:

[0137] R 6 , R 7 independently of one another = hydrogen or C1- to C5-alkyl, in particular hydrogen, methyl or ethyl;

[0138] R 11 , R12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 Independently of each other = hydrogen, C1- to C5-alkyl or -NHC(O)NR 6 R 7 Substituted C1- to C5-alkyl.

[0139] Further preferred are curing accelerators comprising aliphatic urea derivatives of formula (VI), wherein R 6 and R 7 are simultaneously or independently hydrogen, methyl or ethyl, and R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 are independently hydrogen, methyl, ethyl, -NHC(O)NR 6 R 7 or -NHC(O)NR 6 R 7 Particularly preferred is 1-(N,N-dimethylurea)-3-(N,N-dimethylurea-methyl)-3,5,5-trimethylcyclohexane, hereinafter also referred to as N'-[3-[[[(dimethylamino)carbonyl]-amino]methyl]-3,5,5-trimethylcyclohexyl]-N,N-dimethylurea (i.e., R 6 =R 7 =R 12 =R 13 =R 16 = methyl and R 17 =-CH2-NHC(O)N(CH3)2 and R 11 =R 14 =R 15 =R 18 =R 19 =R 20 = hydrogen).

[0140] The method described herein preferably produces an epoxy resin composition whose polymerization behavior remains as unchanged as possible after the temperature application. The epoxy resin composition obtained by this method is preferably characterized in that after the temperature application of 80° C. for 1 hour, it has an onset temperature and / or a peak temperature that is at least 5% and at most 20% higher than the corresponding epoxy resin without inhibitor, wherein the onset temperature and the peak temperature are determined by dynamic DSC measurement at a temperature of -30° C. to 250° C. and a heating rate of 10° C. / min.

[0141] Particularly preferably, the epoxy resin composition obtained after the temperature application at 80°C for 1 hour is characterized in that the starting temperature differs from the starting temperature of the corresponding epoxy resin composition without temperature application by at most 3.5%, and / or the peak temperature differs from the peak temperature of the corresponding epoxy resin composition without temperature application by at most 3% after the temperature application at 80°C for 1 hour, wherein the starting temperature and the peak temperature are determined by dynamic DSC measurement at a temperature of -30°C to 250°C at a heating rate of 10°C / min.

[0142] In contrast, in the method described here, the temperature application can be selected such that the just-mentioned onset or peak temperature is reached in the dynamic DSC measurement, wherein the heating duration and the set temperature must be within the range defined for method step a).

[0143] In principle, process steps a), b), c), d) and e) can be carried out in any order. Preferably, process steps a), b), c), d) and e) and in particular the addition of polymerization inhibitor, curing accelerator, optional curing agent and optional thickener are carried out successively or simultaneously.

[0144] In order to obtain the preferred onset temperature and peak temperature in the epoxy resin composition obtained, it is also appropriate to select a specific sequence of process steps. For example, it may be useful to add at least a portion of the polymerization inhibitor to the polymer resin before the curing accelerator, in particular before the curing agent. It is particularly advantageous if at least part of the addition of the polymerization inhibitor occurs after the epoxy resin has been heated. Therefore, in a preferred embodiment of the method described herein, at least 50% by weight of the polymerization inhibitor is added before or together with the curing accelerator, the optional curing agent and the thickener.

[0145] Furthermore, it is advantageous if the entire amount of thickener is not added to the epoxy resin before the further additives are mixed in, so that the viscosity of the mixture remains low before all the additives are incorporated. Thus, in a preferred embodiment of the process described herein, at least 50% by weight of the thickener is added after or together with the inhibitor, cure accelerator and optional curing agent.

[0146] In a further preferred embodiment, at least two, preferably three or all process steps b) to e) are carried out simultaneously, which can reduce the necessary temperature application and process effort. For example, individual additives can be introduced before heating, which are then mixed homogeneously with the epoxy resin during heating (process step a)). Alternatively, the additives, i.e., polymerization inhibitors, curing accelerators, curing agents and thickeners, can also be mixed with the epoxy resin after or during heating.

[0147] According to the present invention, rheology modifiers such as thermoplastic polymers can be introduced into epoxy resin composition as thickener in particular. Thickener has the function of regulating the flow behavior of resin, thereby preventing resin from flowing out of prepreg. In addition, thickener also contributes to the mechanical properties of cured epoxy resin. Usually, thermoplastic additives from the group of phenoxy resin, acrylate, acrylonitrile, polyetherimide, polyether ketone or polysulfone polymer are selected. Because phenoxy resin, polyacrylate or polysulfone have a positive impact on the flow behavior in the processing and the mechanical properties of the cured component, they are preferably used. In addition, powdery inorganic thickeners, such as fumed silica or the like, can also be added. These can be added separately in epoxy resin composition, or mixed by two or more, or mixed with one, two or more thermoplastic polymers.

[0148] By the method, the viscosity of the epoxy resin composition obtained can be adjusted to allow the impregnation of materials (e.g., fibers) during the preparation of prepregs or bundle prepregs. Preferably, the viscosity of the epoxy resin composition is adjusted to a range of 10 Pa*s to 1000 Pa*s, and the temperature for determining the viscosity must be higher than or equal to 50°C and lower than or equal to 80°C. In order to determine the viscosity, a rheometer according to Anton Paar's viscometer MCR302 is used, which has a measuring system D-PP25 (1° measuring cone) and a measuring gap of 0.052 mm. Here, a dynamic run from 50°C to 80°C is performed at a rate of 5°C / min. When the viscosity range just mentioned is reached during the dynamic measurement run, a preferred epoxy resin composition exists.

[0149] In the present description, the term epoxy resin is understood to mean an epoxy monomer composition. Epoxy resins that are liquid at below 100° C., in particular below 90° C., are particularly suitable for preparing epoxy resin compositions. Preferably, the epoxy resin is a polyether having at least one, preferably at least two, epoxy groups, still more preferably at least three epoxy resin groups. These epoxy resins or liquid epoxy resins may have at least one, preferably at least two, epoxy groups, and may be saturated or unsaturated, aliphatic, alicyclic, aromatic or heterocyclic. In addition, these epoxy resins or liquid epoxy resins may have substituents, such as halogen, phosphorus and hydroxyl groups. Bisphenol-based epoxy resins, in particular bisphenol A diglycidyl ether and bromine-substituted derivatives (tetrabromobisphenol A) or bisphenol F diglycidyl ether, novolac epoxy resins, in particular epoxyphenol novolac or aliphatic epoxy resins are preferably used here. Epoxy resins based on glycidyl polyethers of 2,2-bis-(4-hydroxyphenyl)propane (bisphenol A) and bromine-substituted derivatives (tetrabromobisphenol A), glycidyl polyethers of 2,2-bis-(4-hydroxyphenyl)methane (bisphenol F) and glycidyl polyethers of novolacs and those based on aniline or substituted anilines such as p-aminophenol or 4,4'-diaminodiphenylmethane are particularly preferred. Epoxy resins based on glycidyl polyethers of 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) and epoxy resins based on glycidyl polyethers of 2,2-bis(4-hydroxyphenyl)methane (bisphenol F) are particularly preferred.

[0150] According to the invention, other preferred epoxy resins can be used, in particular liquid epoxy resins, whose EEW values ​​(epoxy equivalent weight) are 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, very particularly preferably in the range of EEW = 100 to 300 g / eq.

[0151] For use in prepregs or bundle prepregs, low-cost liquid epoxy resins are particularly preferred, which have a viscosity range of 2Pa*s to 30Pa*s, preferably 8Pa*s to 20Pa*s at 25°C, and which require a thickener to increase the viscosity. Preferred resins with a viscosity of 12-14Pa*s at 25°C are EPIKOTE TM Resin 828 is used as an example. The viscosity of epoxy resin compounds is usually specified by the supplier. Alternatively, the viscosity can also be determined with a rheometer according to Anton Paar's viscometer MCR302 at a measuring gap of 0.052 mm using the measuring system D-PP25 (1° measuring cone). Here, the isothermal viscosity is measured at 25° C. by continuously recording 1 or 0.5 measuring points per minute.

[0152] Particularly preferred are epoxy resins having an onset temperature of between 110° C. and 150° C. and / or a peak temperature of between 120° C. and 160° C. after application of a temperature of 80° C. for 1 hour, the onset temperature and the peak temperature being determined by a dynamic DSC measurement at a temperature of -30 to 250° C. at a heating rate of 10° C. / min, during which the epoxy resin already contains a curing accelerator and optionally a curing agent, but no inhibitor and no thickener.

[0153] The curing profile of the formulations according to the invention can be modified by adding further commercially available additives, such as additives known to those skilled in the art for curing epoxy resins.

[0154] Reactive diluents and thermoplastic additives are commonly used in prepregs, bundle prepregs and adhesive formulations.

[0155] Thus, as part of the claimed method, further additives such as reactive diluents and / or thermoplastic polymers may be added to the epoxy resin. Glycidyl ethers may in particular be used as reactive diluents in the method according to the invention. Monofunctional, difunctional and polyfunctional glycidyl ethers may also be preferably used. In particular, glycidyl ethers, diglycidyl ethers, triglycidyl ethers, polyglycidyl ethers and polyglycidyl ethers and combinations thereof should be mentioned here. Particularly preferred glycidyl ethers may be selected from 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 polyglycidyl ether and combinations thereof.

[0156] Very 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.

[0157] Additives for improving the processability of uncured epoxy resin compositions or for adapting the thermomechanical properties of thermosetting products to the desired properties include, for example, fillers, rheological additives such as thixotropic agents or dispersing additives, defoamers, dyes, pigments, toughening modifiers, impact modifiers, nanofillers, nanofibers or fire retardant additives.

[0158] The amount of substituted boric acid and curing agent and curing accelerator to be used in the epoxy resin composition can be adjusted according to the present invention relative to the amount of epoxy resin to be used. Preferably, based on 100 parts by weight of epoxy resin, in particular 0.05 to 3.0 parts by weight of substituted boric acid according to formula (I) can be used, further preferably 0.1 to 2.0 parts by weight of substituted boric acid according to formula (I), particularly preferably 0.1 to 1.0 parts by weight of substituted boric acid according to formula (I).

[0159] Furthermore, in the method, based on 100 parts by weight of epoxy resin, in particular 1.0 to 15 parts by weight of a curing agent (in particular from the cyanamide group or the curing agent group according to formula (IV)) can be used, further preferably 3.0 to 12.0 parts by weight of a curing agent (in particular from the cyanamide group or the curing agent group according to formula (IV)), and particularly preferably 4.0 to 10.0 parts by weight of a curing agent (in particular from the cyanamide group or the curing agent group according to formula (IV)).

[0160] According to the method, preferably, based on 100 parts by weight of epoxy resin, 0.1 to 9 parts by weight of a curing accelerator (particularly from the curing accelerator group according to formula (III)) can be used, further preferably 0.5 to 5.0 parts by weight of a curing accelerator (particularly from the curing accelerator group according to formula (III)), and particularly preferably 0.5 to 3.0 parts by weight of a curing accelerator (particularly from the curing accelerator group according to formula (III)).

[0161] Preferably, the curing agent and the substituted boric acid are used to prepare the epoxy resin composition in a weight ratio of curing agent to substituted boric acid in the range of 1:1 to 240:1, more preferably 3:1 to 100:1, particularly preferably 6:1 to 40:1.

[0162] Further preferred in the methods described herein are curing accelerators and substituted boric acid in a weight ratio of curing accelerator to substituted boric acid in the range of 0.05:1 to 160:1, more preferably 0.5:1 to 50:1, particularly preferably 0.7:1 to 15:1.

[0163] The epoxy resin composition produced by the method is particularly suitable for producing prepreg materials, especially prepregs and bundle prepregs made of fiber composite materials, which are used to manufacture fiber composite parts used in sports and leisure markets, automotive markets, aerospace industries, and rotor blades for manufacturing wind turbines. All types of fibers known to those skilled in the art can be used for these fiber composite materials. Examples of these materials (but not limited to) are chemical fibers from inorganic material groups, such as carbon fibers, boron fibers, basalt fibers, glass fibers, quartz fibers, slag fibers, metal fibers, nanotube fibers, ceramic fibers, crystal fibers, or chemical fibers from synthetic polymeric material groups, such as polyesters, polyamides, polyimides, aramids, polyamide-imides, polyacrylates (Polyacryl), modified polyacrylonitrile (Modacryl), polytetrafluoroethylene, polyethylene, polyetheretherketone, polypropylene, polychloride, elastic fibers, polybenzimidazoles. The present invention can be a fiber with a homopolymer structure or a copolymer structure, for example, a random copolymer, a gradient copolymer, a block copolymer, an alternating copolymer, a graft copolymer, or a chemical fiber from the group of natural polymer substances, for example, cellulose, cellulose esters, polylactide, alginates, chitin, diene elastic fibers (Elastodien), bio-based polyamides, protein fibers, or a natural fiber from the group of plant fibers, for example, from kapok, cotton Seed fibers such as from flowers, poplar fluff, kudzu, cattail, silk plants, etc., bast fibers such as from bamboo, nettle, hemp, jute, mallow, broom, hops, willow bark, flax, ramie, kenaf, sunns, castor, silver fern (Punga), etc., leaf fibers such as from agave, pineapple, hemp, flax, sugar palm, dwarf palm, yucca, cattail, alfalfa, etc., fruit fibers such as from coconut, etc., in addition to natural fibers from the animal fiber group, such as fibers from the spinning gland, including silk, spider silk, anaphid wild silk, Erise ide, monga, tussah silk, such as fibers from secretions, including sea silk (Byssusseide), such as fibers from hair follicles, including hair and down from sheep, alpacas, llamas, Vikunjas, Guanakos, camels, Angora rabbits, cashmere goats, mohair goats, yaks, goats, cattle, horses, in addition there are mineral fibers, such as glass fibers, quartz fibers, mineral wool, silica fibers, ceramic fibers, in addition there are conversion products of named fibers, for example nitrate silk, copper rayon, and combinations of all named fibers. Preferred fibers are selected from glass fibers, carbon fibers, aramid fibers, basalt fibers, rock wool fibers, polyethylene fibers, flax fibers, hemp fibers and bamboo fibers and combinations thereof.

[0164] These fiber composites can be processed in processing methods such as autoclave, “out-of-autoclave”, vacuum bag and compression molding. Example: Materials used:

[0166] Product Name:EPIKOTE TM Resin 828 (Hexion Inc.)

[0167] Unmodified bisphenol A epoxy resin (EEW ​​= 184-190 g / eq)

[0168] (Viscosity at 25°C = 12-14 Pa*s)

[0169] Product Name: DER TM 337(Blue Cube Germany Assets GmbH&Co.KG)

[0170] Modified semi-solid bisphenol A epoxy resin (EEW ​​= 230-250g / eq)

[0171] (Viscosity at 25°C = 400-800 mPa*s, 70 wt% in diethylene glycol monobutyl ether)

[0172] Product Name: DER TM 671(Blue Cube Germany Assets GmbH&Co.KG)

[0173] Solid epoxy resin (EEW ​​= 475-550g / eq)

[0174] (Melting point = 75-85°C)

[0175] Resin 1: EP EPIKOTE TM Resin 828+DER TM 671 (80 wt% + 20 wt%) was dissolved in EP EPIKOTE at 110°C TM DER in Resin 828 for 2 hours TM 671Product Name: 100S (AlzchemTrostberg GmbH)

[0176] Latent curing agent, dicyandiamide, solid (particle size 98% ≤ 10μm)

[0177] Urea 1: 1,1'-(4-methyl-m-phenylene)-bis-(3,3-dimethylurea) (Alzchem Trostberg GmbH)

[0178] Latent bifunctional accelerator according to formula V

[0179] Solid (particle size 98% ≤ 10 μm)

[0180] Product name: 3-Fluorophenylboronic acid; (abcr GmbH)

[0181] Solid, (melting point = 220°C)

[0182] Product Name: Octylboronic acid; (Alfa Aesar)

[0183] Solid (purity = 97%; melting point = 81-85°C)

[0184] Product Name: 1,4-phenylenediboronic acid (Alfa Aesar)

[0185] Solid (purity = 96%; melting point > 300°C)

[0186] Preparation of the mixture:

[0187] In order to check the formulations mentioned in the examples, the individual components of the respective formulations were mixed in a dissolver for several minutes until homogeneity was achieved. The respective formulations were then divided into three portions. One portion was used for prepreg preparation and subsequent measurement without temperature application. After mixing for 3 hours at 60°C under temperature application, a formulation for prepreg preparation was processed and then prepared for measurement. After mixing for 1 hour at 80°C under temperature application, a formulation for prepreg preparation was processed and then prepared for measurement.

[0188] Methods for characterizing compositions

[0189] DSC inspection:

[0190] DSC measurements were performed on a dynamic heat flow differential calorimeter DSC 1 or DSC 3 (Mettler Toledo).

[0191] a) Dynamic DSC:

[0192] Dynamic DSC measurements were performed on formulation samples at a heating rate of 10°C / min from -30°C to 250°C. The evaluation included the enthalpy of the curing reaction, the onset temperature, and the maximum peak.

[0193] b) Isothermal DSC:

[0194] The formulation samples were kept constant at a defined temperature for a defined period of time (isothermal curing of manufacture). Evaluation was performed by determining the time for 90% conversion of the exothermic reaction peak as a measure of the end of the curing process. In addition, the onset temperature and the peak temperature were evaluated.

[0195] Result list:

[0196] Table 1: Reactivity of comparative epoxy resin compositions

[0197]

[0198] Description and evaluation of the results in Table 1:

[0199] Examples A to F and Reference Example Reference 1 describe epoxy resin compositions consisting of a curing agent and a curing accelerator in a commercially available epoxy resin with or without substituted boric acid. Examples A to F and Reference 1 were subjected to typical temperature applications in the preparation of prepregs and bundle prepregs. Subsequently, analysis was performed by dynamic DSC and isothermal DSC.

[0200] After 3 hours of temperature application at 60°C, the epoxy resin composition was characterized by dynamic DSC. Reference 1 shows that after temperature application, the starting temperature drops by 3% (4°C) and the peak temperature moves to a lower temperature by 2% (3°C). Isothermal DSC analysis performed at 140°C for 1 hour shows that, under Reference 1, after the previous temperature application, the time taken to reach 90% conversion is reduced by 12% (2 minutes). At an isothermal temperature of 120°C for 2 hours, the time is even reduced by 20% (8 minutes). Therefore, DSC measurements show that the resulting epoxy resin composition reacts during temperature application with reference 1, which results in a reduction in starting temperature and peak temperature and a reduction in conversion time.

[0201] By using substituted boric acid in Examples A to F, there is no decrease in the onset temperature or peak temperature in the dynamic DSC analysis after the temperature application. In the isothermal DSC analysis at 140° C. for 1 hour, there is no reduction in the turnover time. At the temperature application at 120° C. for 2 hours, a small reduction in the turnover time can be observed in Examples A and E, which can be attributed to the lower amount of boric acid. In these examples, the values ​​are still significantly lower than the conversion time of the comparative example reference 1. Therefore, the higher proportion of substituted boric acid according to the invention has a lower impact on the epoxy resin formulation due to the previous temperature application.

[0202] In comparative example reference 1, a temperature application at 80°C for 1 hour resulted in a 6% (9°C) decrease in the onset temperature and a 4% (6°C) shift in the peak temperature to a lower temperature. Isothermal DSC analysis at 140°C for 1 hour showed that reference 1 experienced an 18% (3 minutes) decrease in turnover time after the previous temperature application. At a temperature application at 120°C for 2 hours, this value dropped by 24% (10 minutes).

[0203] By using the substituted boric acid according to Examples A to F, there is no drop in the onset temperature or peak temperature in the dynamic DSC analysis after the temperature application. In the isothermal DSC analysis at 140° C. for 1 hour, the turnover time is not significantly reduced. At 120° C. for 2 hours, a smaller reduction in the turnover time is observed in individual cases, which is still lower than the turnover time reduction of Reference 1. By using higher amounts of substituted boric acid, the influence of the previous temperature application on the epoxy resin formulation is reduced.

[0204] In summary, when the substituted boric acid according to Examples A to F of the present invention is used, the polymerization or reaction during the temperature application of the epoxy resin formulation is significantly inhibited. When processed at high temperature for a long time, the epoxy resin formulation does not change. The rheological properties of the resulting composition are not changed. As a result, the quality of the prepreg or bundle prepreg produced with the epoxy resin composition is also not affected.

[0205] Table 2: Comparison of reactivity of epoxy resin compositions

[0206]

[0207] Description and evaluation of the results in Table 2:

[0208] Examples G and H and comparative example reference 2 describe epoxy resin compositions consisting of a curing agent and a curing accelerator in a commercially available epoxy resin with and without substituted boric acid. Examples G and H and reference 2 were subjected to temperature application typically used for prepreg and bundle prepreg preparation. Subsequently, the resulting epoxy resin compositions were analyzed by dynamic DSC and isothermal DSC.

[0209] The examples show that, after temperature application, Examples G and H according to the invention do not have any effect on the properties of the epoxy resin formulation compared to the comparative example reference 2.

[0210] After 1 hour of temperature application at 80° C., Comparative Example Reference 2 showed a 9% (12° C.) decrease in onset temperature and a 6% (8° C.) shift in peak temperature to a lower temperature in dynamic DSC testing. In Examples G to H according to the invention, there was no significant decrease in onset or peak temperature after temperature application.

[0211] By isothermal DSC analysis at 140°C for 1 hour, a 33% (4 minutes) reduction in conversion time was measured in comparative example reference 2 after the previous temperature application, and a 26% (6 minutes) reduction was measured at 120°C for 2 hours. By using substituted boronic acids in examples G and H, a reduction in conversion time was also observed in isothermal DSC analysis. However, they were much shorter than in reference 2. As expected, increasing the proportion of accelerator in the epoxy resin composition enhances its reactivity. Examples G and H show that the addition of substituted boronic acids still significantly reduces the effect of temperature on the epoxy resin composition.

[0212] In summary, the use of substituted boric acid in Examples G and H effectively inhibited polymerization and reaction, respectively, during temperature application in formulated epoxy resin formulations, even at increased accelerator ratios.

[0213] Table 3: Reactivity of comparative epoxy resin compositions

[0214]

[0215] Description and evaluation of the results in Table 3:

[0216] Examples J, K, L, M and comparative examples Reference 3 and Reference 4 describe epoxy resin compositions consisting of a curing agent and a curing accelerator in a modified epoxy resin (each with and without substituted boric acid). These examples were subjected to temperature application commonly used in the preparation of prepregs and bundle prepregs. Subsequently, the epoxy resin compositions were analyzed by dynamic DSC and isothermal DSC.

[0217] After 3 hours of temperature application at 60°C, the resulting epoxy resin composition was characterized by dynamic DSC. Comparative Examples Reference 3 and Reference 4 show that after temperature application, the starting temperature decreases by 3% (4°C) and 1% (2°C), respectively, and the peak temperature shifts to lower temperatures by 2% (3°C) and below 1% (1°C), respectively. The epoxy resin formulations of Examples J and K or L and M according to the present invention do not show a decrease in the starting temperature or peak temperature after measurement.

[0218] At isothermal temperature of 120°C for 2 h, the turnover time was reduced by 20% (8 minutes) in reference 3 and by 9% (3 minutes) in reference 4. By using substituted boronic acids, no significant changes in the turnover time were observed in isothermal DSC measurements in Examples J, K (compared to reference 3) and M (compared to reference 4). Example L showed a slightly smaller reduction in the turnover time compared to reference 4.

[0219] After 1 hour of temperature application at 80°C, dynamic DSC measurements showed that reference 3 and reference 4 experienced a 6% (9°C) and 9% (13°C) decrease in onset temperature and a 4% (6°C) and 5% (7°C) shift in peak temperature to lower temperatures, respectively. No significant decrease in onset or peak temperature was detected in the examples according to the invention. At an isothermal temperature of 120°C for 2 hours, the turnover time was reduced by 22% (8 minutes) in reference 3 and by 18% (7 minutes) in reference 4. By using substituted boric acids, no significant changes in turnover time were detected in isothermal DSC measurements of examples J and K and L and M, respectively.

[0220] Also in the case of modified resins, the substituted boric acids of Examples J, K, L and M provide sufficient inhibition of polymerization or reaction during temperature application in the preparation of the corresponding epoxy resin formulations. The quality of such resin formulations is maintained, and thus the quality of prepreg materials such as prepregs and bundle prepregs is maintained.

Claims

1. A method for preparing an epoxy resin composition for material pre-impregnation, characterized in that The epoxy resin added in advance a) heating to a temperature in the range of 60°C to 100°C and b) mixing the boric acid of general formula (I) as a polymerization inhibitor with the epoxy resin The residue R 1 yes: R 1 =alkyl, hydroxyalkyl or a residue of formula (II), wherein formula (II) is: Where R 2 , R 3 , R 4 are represented independently of each other, and at least one residue R 2 , R 3 , R 4 Not Hydrogen: R 2 , R 3 , R 4 = hydrogen, fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH)2, c) mixing a curing accelerator with an epoxy resin for accelerated curing of the epoxy resin, wherein the curing accelerator comprises a compound of formula (III) Where R 6 , R 7 , R 8 Independently of each other are: R 6 , R 7 independently of one another = hydrogen or C1- to C5-alkyl, R 8 =Hydrogen, C1- to C 15 -alkyl, C3- to C 15 - cycloalkyl, aryl, Alkyl aryl, NHC(O)NR 6 R 7 Substituted C1- to C 15 -alkyl, NHC(O)NR 6 R 7 Substituted C3- to C 15 - cycloalkyl, By NHC(O)NR 6 R 7 Substituted aryl or NHC(O)NR 6 R 7 Substituted alkylaryl, d) optionally mixing a curing agent with the epoxy resin, wherein the curing agent comprises cyanamide and / or a compound of formula (IV), The residue R 40 , R 41 , R 42 Independently of each other are: R 40 =cyano, nitro, acyl or -(C=X)-R 43 of residues, among which X = imino or oxygen, R 43 =amino, alkylamino or alkoxy, R 41 = hydrogen, C1- to C5-alkyl, aryl or acyl, R 42 =Hydrogen or C1- to C5-alkyl e) optionally mixing a thickener with the heated epoxy resin from step a), The temperature of the epoxy resin according to step a) is applied for at least 15 minutes and not more than 240 minutes, and two or more of the method steps a) to e) can be carried out simultaneously and / or sequentially.

2. The method according to claim 1, characterized in that The epoxy resin is heated in process step a) to a temperature in the range of 70° C. to 90° C.

3. The method according to any one of claims 1 or 2, characterized in that The epoxy resin comprising the curing accelerator and the optional curing agent but not comprising an inhibitor and a thickener has an onset temperature between 110°C and 150°C and / or a peak temperature between 120°C and 160°C after a temperature application of 80°C for 1 hour, wherein the onset temperature and the peak temperature are determined by a dynamic DSC measurement performed at a heating rate of 10°C / min at a temperature of -30°C to 250°C.

4. The method according to any one of claims 1 to 3, characterized in that The epoxy resin composition has an onset temperature and / or a peak temperature that is at least 5% to at most 20% higher than that of a corresponding epoxy resin without an inhibitor after a temperature of 80°C is applied for 1 hour, wherein the onset temperature and the peak temperature are determined by a dynamic DSC measurement performed at a heating rate of 10°C / min at a temperature of -30°C to 250°C.

5. The method according to any one of claims 1 to 4, characterized in that The epoxy resin composition has a starting temperature that differs by at most 3.5% from the starting temperature of the corresponding epoxy resin composition without temperature application after temperature application of 80°C for 1 hour, and / or a peak temperature that differs by at most 3% from the peak temperature of the corresponding epoxy resin composition without temperature application after temperature application of 80°C for 1 hour, wherein the starting temperature and the peak temperature are determined by dynamic DSC measurement performed at a heating rate of 10°C / min at a temperature of -30°C to 250°C.

6. The method according to any one of claims 1 to 5, characterized in that According to process step e), a thickener is used which is selected from the class of thermoplastic polymers such as phenoxy resins, acrylate polymers, acrylic polymers, acrylonitrile polymers, polyetherimide polymers, polyetherketone polymers, polysulfone polymers and / or powdered inorganic thickeners.

7. The method according to any one of claims 1 to 6, characterized in that The residue R in formula (I) 1 is selected from the group consisting of methyl, ethyl, n-propyl, 1-methylethyl, n-butyl, 1-methylpropyl, 2-methylpropyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, hydroxymethyl, 2-hydroxyethyl, 3-hydroxypropyl, 4-hydroxybutyl or 5-hydroxypentyl.

8. The method according to any one of claims 1 to 7, characterized in that R in formula (I) 1 represents a residue of formula (II) wherein the residue R 2 , R 3 and R 4 At least one of them is a residue selected from the group consisting of fluorine, chlorine, bromine, iodine, cyano, C1- to C5-alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl and B(OH)2.

9. The method according to any one of claims 1 to 8, characterized in that The epoxy resin composition prepared based on 100 parts by weight of the epoxy resin comprises a) 0.05 to 3.0 parts by weight of boric acid according to formula (I), b) 0.1 to 9 parts by weight of a curing accelerator according to formula (III) and c) 1 to 15 parts by weight of a curing agent according to formula (IV).

10. The method according to any one of claims 1 to 9, characterized in that A weight ratio of curing agent to boric acid in the range of 1:1 to 240:1, and / or a weight ratio of curing accelerator to boric acid in the range of 0.05:1 to 160:1 is used.

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