STORAGE STABLE EPOXY RESIN COMPOSITION

Abstract

The present invention relates to the use of boronic acids to increase the storage stability of epoxy resin compositions and epoxy resin compositions comprising an epoxy resin, a curing agent, a curing accelerator and a boronic acid.

Claims

1. Use of boronic acids of the general formula (I) for increasing the storage stability of epoxy resin compositions comprising an epoxy resin, a curing agent for curing the epoxy resin and a curing accelerator for accelerating the curing of the epoxy resin, wherein formula (I) represents: ##STR00023## wherein radical le means: R.sup.1=alkyl, hydroxyalkyl or a radical of formula (II), wherein formula (II) is: ##STR00024## wherein R.sup.2, R.sup.3, R.sup.4 independently of one another mean and at least one radical R.sup.2, R.sup.3, R.sup.4 is not hydrogen: R.sup.2, R.sup.3, R.sup.4=hydrogen, fluorine, chlorine, bromine, iodine, cyano, C.sub.1 to C.sub.5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH).sub.2, wherein the epoxy resin composition comprises, as a curing accelerator, a curing accelerator according to formula (IV), wherein formula (IV) is: ##STR00025## wherein R.sup.6, R.sup.7, R.sup.8 independently of one another mean: R.sup.6, R.sup.7=independently of one another hydrogen or C.sub.1 to C.sub.5 alkyl, R.sup.8=hydrogen, C.sub.1 to C.sub.15 alkyl, C.sub.3 to C.sub.15 cycloalkyl, aryl, alkylaryl, C.sub.1 to C.sub.15 alkyl substituted with —NHC(O)NR.sup.6R.sup.7, C.sub.3 to C.sub.15 cycloalkyl substituted with —NHC(O)NR.sup.6R.sup.7, aryl substituted with —NHC(O)NR.sup.6R.sup.7 or alkylaryl substituted with —NHC(O)NR.sup.6R.sup.7.

2. Use according to claim 1, wherein radical R.sup.1 in formula (I) means: R.sup.1=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.

3. Use according to claim 1, wherein R.sup.1 in formula (I) is a radical of formula (II), wherein radicals R.sup.2, R.sup.3, R.sup.4 mean: R.sup.2=fluorine, chlorine, bromine, iodine, cyano, C.sub.1 to C.sub.5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH).sub.2, R.sup.3, R.sup.4=hydrogen.

4. Use according to claim 1, wherein R.sup.1 in formula (I) is a radical of formula (II), wherein radicals R.sup.2, R.sup.3, R.sup.4 independently of one another mean: R.sup.2, R.sup.3=independently of one another fluorine, chlorine, bromine, iodine, cyano, C.sub.1 to C.sub.5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH).sub.2, R.sup.4=hydrogen.

5. Use according to claim 1, wherein R.sup.1 in formula (I) is a radical of formula (II), wherein radicals R.sup.2, R.sup.3, R.sup.4 independently of one another mean: R.sup.2, R.sup.3, R.sup.4=fluorine, chlorine, bromine, iodine, cyano, C.sub.1 to C.sub.5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH).sub.2.

6. Use according to claim 1, wherein the epoxy resin composition comprises, as curing agent, cyanamide or a curing agent according to general formula (III), wherein formula (III) is ##STR00026## wherein radicals R.sup.40, R.sup.41, R.sup.42 independently of one another mean: R.sup.40=cyano, nitro, acyl or a radical of the formula —(C═X)—R.sup.43, with X=imino or oxygen, R.sup.43=amino, alkylamino or alkoxy, R.sup.41=hydrogen, C.sub.1 to C.sub.5 alkyl, aryl or acyl, R.sup.42=hydrogen or C.sub.1 to C.sub.5 alkyl.

7. An epoxy resin composition comprising at least one epoxy resin and a curing agent for curing the epoxy resin and a curing accelerator for accelerating curing of the epoxy resin, wherein the composition comprises at least one boronic acid of the general formula (I), wherein formula (I) represents: ##STR00027## wherein radical R.sup.1 means: R.sup.1=alkyl, hydroxyalkyl or a radical of formula (II), wherein formula (II) is: ##STR00028## wherein R.sup.2, R.sup.3, R.sup.4 independently of one another mean and at least one radical R.sup.2, R.sup.3, R.sup.4 is not hydrogen: R.sup.2, R.sup.3, R.sup.4=hydrogen, fluorine, chlorine, bromine, iodine, cyano, C.sub.1 to C.sub.5 alkyl, alkoxy, acyl, alkylsulfonyl, aryl, carboxyl or B(OH).sup.2, wherein the epoxy resin composition comprises, as a curing accelerator, a curing accelerator according to formula (IV), wherein formula (IV) is: ##STR00029## wherein R.sup.6, R.sup.7, R.sup.8 independently of one another mean: R.sup.6, R.sup.7=independently of one another hydrogen or C.sub.1 to C5 alkyl, R.sup.8=hydrogen, C.sub.1 to C.sub.15 alkyl, C.sub.3 to C.sub.15 cycloalkyl, aryl, alkylaryl, C.sub.1 to C.sub.15 alkyl substituted with —NHC(O)NR.sup.6R.sup.7, C.sub.3 to C.sub.15 cycloalkyl substituted with —NHC(O)NR.sup.6R.sup.7, aryl substituted with —NHC(O)NR.sup.6R.sup.7 or alkylaryl substituted with —NHC(O)NR.sup.6R.sup.7.

8. Epoxy resin composition according to claim 7, wherein the epoxy resin composition comprises, as a curing agent, cyanamide or a curing agent according to general formula (III), wherein formula (III) is ##STR00030## wherein radicals R.sup.40, R.sup.41, R.sup.42 independently of one another mean: R.sup.40=cyano, nitro, acyl or a radical of the formula —(C═X)—R.sup.43, with X=imino or oxygen, R.sup.43=amino, alkylamino or alkoxy, R.sup.41=hydrogen, C.sub.1 to C.sub.5 alkyl, aryl or acyl, R.sup.42=hydrogen or C.sub.1 to C.sub.5 alkyl.

9. Epoxy resin composition according to claim, wherein the epoxy resin composition based on 100 parts by weight of epoxy resin comprises: a) 1 to 15 parts by weight of curing agent, b) 0.1 to 9 parts by weight of curing accelerator, and c) 0.05 to 3.0 parts by weight of boronic acid according to formula (I).

10. Epoxy resin composition according to claim 7, wherein the weight ratio of curing agent to boronic acid corresponds to a ratio in the range of 1:1 to 240:1, and/or the weight ratio of curing accelerator to boronic acid corresponds to a ratio in the range of 0.05:1 to 160:1.

Description

EXAMPLES

[0228] Materials Used

[0229] Product name: EPIKOTE™ Resin 828 (Hexion Inc.) Unmodified bisphenol A epoxy resin (EEW=184-190 g/eq) (viscosity at 25° C.=12-14Pa*s)

[0230] Product name: Araldite® MY 721 (Huntsman Corp.) Tetrafunctional epoxy resin; N,N,N′,N′-tetraglycidyl-4,4′-methylenebisbenzolamine Clear, brown liquid, (EEW=109-116 g/eq) (viscosity at 50° C.=3000-6000 mPa*s)

[0231] Product name: Epiloxe F17-00 (LEUNA-Harze GmbH) Unmodified bisphenol F epoxy resin (EEW=165-173 g/eq) (viscosity at 25° C.=2500-4500 mPa*s)

[0232] Product name: DYHARD® 100S (AlzChem Trostberg GmbH) Latent curing agent, dicyandiamide, solid material (particle size 98%≤10 μm)

[0233] Urea 1: 1,1′-(4-methyl-m-phenylene)-bis-(3,3-dimethylurea) (AlzChem Trostberg GmbH)

[0234] Latent, bifunctional accelerator according to formula V Solid material (particle size 98%≤10 μm)

[0235] Urea 2: Fenuron (AlzChem Trostberg GmbH) Latent monofunctional accelerator according to formula IV Solid material (particle size 98%≤10 μm)

[0236] Urea 3: N′-[3[[[(dimethylamino)carbonyl]amino]methyl]-3,5,5-trimethylcyclohexyl]-N,N-dimethyl urea (AlzChem Torstberg GmbH) Latent, bifunctional accelerator according to formula VI, solid material

[0237] Urea 4: 1-butyl-3,3-dimethylurea (abcr GmbH) Latent, monofunctional accelerator according to formula IV, (boiling point: 100-110° C.)

[0238] Product name: 4-carboxyphenylboronic acid; (abcr GmbH) Solid material (purity=97%; melting point=238° C.)

[0239] Product name: 3-carboxyphenylboronic acid; (abcr GmbH) Solid material

[0240] Product name: 2-carboxyphenylboronic acid; (abcr GmbH) Solid material

[0241] Product name: 4-cyanophenylboronic acid; (abcr GmbH) Solid material (purity=97%; melting point >300° C.)

[0242] Product name: 4-(methanesulfonyl)phenylboronic acid; (abcr GmbH) Solid material (melting point=275° C.)

[0243] Product name: 4-formylphenylboronic acid; (Alfa Aesar) Solid material (purity=97%; melting point=260-266° C.)

[0244] Product name: 3-fluorophenylboronic acid; (abcr GmbH) Solid material, (melting point=220° C.)

[0245] Product name: 2,5-dimethoxyphenylboronic acid; (Alfa Aesar) Solid material (purity=98%; melting point=92-94° C.)

[0246] Product name: methylboronic acid; (Alfa Aesar) Solid material (purity=97%; melting point=89-94° C.)

[0247] Product name: 4-ethylphenylboronic acid; (Alfa Aesar) Solid material (purity=97%) (melting point=150-154° C.)

[0248] Product name: 1-octylboronic acid; (Alfa Aesar) Solid material (purity=97%; melting point=81-85° C.)

[0249] Product name: (2-hydroxymethyl)phenylboronic acid (abcr GmbH) Solid material

[0250] Product name: 2,4-difluorophenylboronic acid (Alfa Aesar) Solid material (purity=97%; melting point=247-250° C.)

[0251] Product name: 3,4,5-trifluorophenylboronic acid (Sigma-Aldrich) Solid material (purity≥95%; melting point=290-295° C.)

[0252] Product name: 1,4-benzenediboronic acid (Alfa Aesar) Solid material (purity=96%; melting point>300° C.)

[0253] Product name: VESTAMIN® IPD; (Evonik) Isophorone diamine, amine curing agent, liquid

[0254] Product name: Aradur® 917 (Huntsman Cooperation) Anhydride liquid curing agent consisting of tetrahydro-4-methylphthalic anhydride, 1,2,3,6-tetrahydro-3-methylphthalic anhydride, 1,2,3,6-tetrahydrophthalic anhydride and hexahydro-4-methylphthalic anhydride (viscosity at 25° C.=50-100 mPa.Math.s)

[0255] Product name: Araldite® LY 1556 SP (Huntsman Cooperation) Formulated bisphenol A based epoxy resin (epoxy content=5.30-5.45 eq/kg) (viscosity at 25° C.=10-12 Pa.Math.s)

[0256] Product name: 1-methylmidazole (Carl Roth GmbH & Co KG) Accelerator, liquid (boiling point 195-197° C.)

[0257] Product name: 2-ethyl-4-methylimidazole (Alfa Aesar) Accelerator, solid material (melting point 45° C.)

[0258] Preparation of the Mixtures

[0259] For the investigations of the formulations mentioned in the examples, the individual components of the respective formulation are mixed in a mortar for several minutes until homogeneity is achieved. The formulations listed in Tables 1 to 7 have been converted to 10 g epoxy resin for this purpose.

[0260] Methods Used to Characterize the Compositions

[0261] DSC Investigations

[0262] DSC measurements are performed on a dynamic heat flow difference calorimeter DSC 1 or DSC 3 (Mettler Toledo).

[0263] a) Tg determination:

[0264] For the determination of 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, 10 min holding at 200° C., cooling from 200-50° C. at 20 K/min, 5 min holding at 50° C., heating from 50-200° C. at 20 K/min, 10 min holding at 200° C., cooling from 200-50° C. at 20 K/min, 5 min holding at 50° C., heating from 50-220° C. at 20 K/min. The glass transition temperature is determined from the last two heating cycles in each case by applying a tangent at the inflection point of the largest change in heat capacity (ΔCp) and the average value is given as the final TG.

[0265] b) Isothermal DSC:

[0266] A sample of the formulation is kept constantly at the specified temperature for the specified time (isothermal curing of the formulation). The evaluation is performed by determining the time of the 90% conversion (as a measure for the end of the curing process) of the exothermic reaction peak.

[0267] c) Latency

[0268] To determine the latency (storage stability), approx. 10 g of the respective formulation are freshly prepared and then stored at a temperature of 40° C. or 60° C. in a heating cabinet. By regularly measuring the dynamic viscosity, the progressive cross-linking (hardening) of the formulation under these storage conditions is recorded. The dynamic viscosity is determined using a Haake viscometer [cone (1°)-plate method, measurement at 25° C., shear rate 5.0 s.sup.−1]. A formulation is classified as storage stable (still suitable for processing) until the viscosity doubles.

LISTING OF RESULTS

[0269]

TABLE-US-00001 TABLE 1 Latency of epoxy resin compositions in comparison Formulations Ref. 1 A B C D E F G EPIKOTE ™ Resin 828 100 100 100 100 100 100 100 100 DYHARD ® 100S 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 Urea 1 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 4-formylphenylboronic acid 0.4 1,4-benzendiboronic acid 0.4 3-fluorophenylboronic acid 0.4 2,5-dimethoxyphenylboronic acid 0.4 methylboronic acid 0.4 4-ethylphenylboronic acid 0.4 1-octylboronic acid 0.4 Dynamic DSC Final Tg [° C.] 135 138 137 138 135 138 135 137 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 11 14 12 11 13 13 12 10 Latency at 40° C. [days] 3 28 33 23 14 10 10 10

[0270] Description and Evaluation of the Results from Table 1

[0271] Comparison of Examples A to G according to the invention with Ref. 1, comprising a technically common curing agent and curing accelerator in a commercially available epoxy resin, shows that comparable characteristic values for the curing process can be determined when using the boronic acids according to the invention. This can be determined from the values obtained from the DSC analysis, including the determination of the final Tg and the recording of an isothermal DSC at 140° C. to determine the 90% conversion of the cure. In addition, it can be shown via the latency measurement that by adding the boronic acids of the invention (Examples A to G), the latency at 40° C. can be extended by a factor of 3 to 10 compared to Ref. 1.

[0272] Thus, the comparison of formulations Ref. 1 and formulations A to G shows that, by means of the boronic acids according to the invention, epoxy resin-based prepregs, towpregs and adhesives can have an extended latency of up to more than four weeks at 40° C. with unchanged curing properties. For the skilled person, manufacturer and user of prepregs, towpregs and adhesives, this means easier handling of these products, and that they can be stored, transported and processed without cooling. Likewise, the storage stability of prepregs, towpregs and adhesives is increased, so that products with the above-mentioned formulations A to H, according to the boronic acids of the invention, have stabilities that are up to a factor of 10 longer. Thus, in addition to easier and safer application, costs can also be reduced. A longer stability also means fewer rejects and thus less waste. This should reduce the consumption of expensive raw materials such as carbon fiber and thereby also protect the environment.

TABLE-US-00002 TABLE 2a Latency of epoxy resin compositions in comparison Formulations Ref. 2 H I J EPIKOTE ™ Resin 828 100 100 100 100 DYHARD ® 100S 6.5 6.5 6.5 6.5 Urea 1 5.0 5.0 5.0 5.0 1-octylboronic acid 0.1 0.4 1 Dynamic DSC Final Tg [° C.] 130 130 131 130 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 7 6 8 10 Latency @ 40° C. [days] 2 6 10 17

[0273] Description and Evaluation of the Results from Table 2a

[0274] Based on the formulations H, I, and J according to the invention in Table 2a, it is shown in comparison to Ref. 2 that by varying the amount of the boronic acid according to the invention, the storage stability of the 1-component epoxy resin formulation can be adjusted. Thus, the values from the DSC analysis show that the curing time (90% conversion at 140° C.) and the final properties (final Tg) of the cured formulation show no significant interference. The latency is still higher by at least a factor of 3 for formulations H, I, and J compared to Ref. 2. Thus, depending on the desired property profile, first of all the latency and thus storage stability, a precisely epoxy resin formulation can be produced. The advantages such as storage stability, reduction of rejects due to overstocking, environmentally friendly action and safer and easier application are still retained.

TABLE-US-00003 TABLE 2b Latency of epoxy resin compositions in comparison Formulations Ref. 2 K L M N O P Q R EPIKOTE ™ Resin 828 100 100 100 100 100 100 100 100 100 DYHARD ® 100S 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 Urea 1 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 2-carboxyphenylboronic acid 0.4 3-carboxyphenylboronic acid 0.4 4-carboxyphenylboronic acid 0.4 (2-hydroxymethyl)phenylboronic acid 0.4 4-cyanophenylboronic acid 0.4 4-(methanesulfonyl)phenylboronic acid 0.4 3,4,5-trifluorophenylboronic acid 0.4 2,4-difluorophenylboronic acid 0.4 Dynamic DSC Final Tg [° C.] 130 133 132 135 134 133 132 133 132 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 7 8 11 10 11 9 8 9 8 Latency at 40° C. [days] 2 6 18 14 16 22 21 15 24

[0275] Description and Evaluation of the Results from Table 2b

[0276] Table 2b shows that even with an increased amount of urone accelerator, the boronic acids of the invention from formulations K to R also show their advantages in comparison to Ref. 2. For faster curing systems, faster curing times can be realized, as can be seen from the isothermal DSC analysis to determine the conversion at 90% at 140° C. In this case, the curing time remains in approximately the same range, while the latency increases again by at least a factor of 3 to over a factor of 10. The final properties adapt to the formulation and always remain in the same desired range compared to Ref. 2.

[0277] Thus, it is shown that the increase in latency maintains its effect even when the amount of accelerator is varied and continues to support advantages such as storage stability, reduction of rejects due to overstocking, environmentally friendly action and safer and easier application.

TABLE-US-00004 TABLE 3 Latency of epoxy resin compositions in comparison Formulations Ref. 1 A Ref. 3 S Ref. 4 T Ref. 5 U EPIKOTE ™ Resin 828 100 100 100 100 100 100 100 100 DYHARD ® 100S 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 Urea 1 3.0 3.0 Urea 2 3.0 3.0 Urea 3 3.0 3.0 Urea 4 3.0 3.0 methylboronic acid 0.4 0.4 0.4 0.4 Dynamic DSC Final Tg [° C.] 135 138 132 131 136 135 121 121 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 11 13 17 19 23 28 27 29 Latency at 40° C. [days] 3 10 3 16 — — — — Latency at 60° C. [days] — — — — 3 11 2 9

[0278] Description and Evaluation of the Results from Table 3

[0279] Moreover, it is shown in Table 3 that the effect of the boronic acids of the invention is independent of the urone accelerators used. In direct comparison of Ref. 1 with formulation A, and Ref. 3 with formulation S, Ref. 4 with formulation T and Ref. 5 with formulation U, it is shown that the storage stability at 40° C. and 60° C. is significantly extended, again by more than a factor of 3 with the respective boronic acid. Reactivity (time to 90% conversion at 140° C.) and final Tg are insignificantly affected. Thus, formulations with different accelerator types, mono- as well as multifunctional, aliphatic, cycloaliphatic as well as aromatic accelerator types based on urones can be used in combination with the boronic acids according to the invention. Users also benefit from the advantages already described, such as storage stability, reduction of rejects due to overstocking, environmentally friendly action and safe and easier application.

TABLE-US-00005 TABLE 4 Latency of epoxy resin compositions in comparison Formulations Ref. 6 V Ref. 7 W Araldite ® MY 721 100 100 Epilox ® F17-00 100 100 DYHARD ® 100S 9.5 9.5 7.1 7.1 Urea 1 5.0 5.0 5.0 5.0 Methylboronic acid 0.4 0.4 Dynamic DSC Final Tg [° C.] 181 178 115 116 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 5 6 6 7 Latency at 40 C [days] 4 13 2 9

[0280] Description and Evaluation of the Results from Table 4

[0281] Further, it is shown in Table 4 that the effect of the boronic acids according to the invention is independent of the resins used. In direct comparison of Ref. 6 with formulation V, as well as Ref. 7 to formulation W, it is shown that the storage stability at 40° C. is significantly extended, again by more than a factor of 3 with the respective boronic acid. Reactivity (time to 90% conversion at 140° C.) and final Tg are insignificantly affected. Thus, formulations with different resin types, bi- as well as multifunctional epoxy-based resins can be used in combination with the boronic acids according to the invention. Furthermore, users also benefit from the advantages already described, such as storage stability, reduction of rejects due to overstocking, environmentally friendly action and safer and easier application.

TABLE-US-00006 TABLE 5 Latency of epoxy resin compositions in comparison Formulations Ref. 2 K I X Y Z EPIKOTE ™ Resin 828 100 100 100 100 100 100 DYHARD ® 100S 6.5 6.5 6.5 Urea 1 5.0 5.0 5.0 VESTAMIN ® IPD 23 23 23 2-carboxyphenylboronic acid 0.4 0.4 1-octylboronic acid 0.4 0.4 Dynamic DSC Final Tg [° C.] 130 133 131 158 153 163 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 7 8 8 9 9 8 Latency at 23° C. [days] — — — 0.05 0.04 0.05 Latency at 40° C. [days] 2 6 10 — — —

[0282] Description and Evaluation of the Results from Table 5

[0283] Table 5 compares formulations with amine-based curing agents with formulations K and I according to the invention. The table shows that amine-based curing agents such as VESTAMIN®IPD, chemical isophorone diamine, do not achieve any latency increase in combination with boronic acids. The corresponding formulations X, Y and Z each show no increase in latency at 23° C. Only the formulations Ref.2, K and I, taken for comparison, show the already discussed effect of latency increase by using boronic acids with ureas. Thus, it is concluded that the boronic acids of the invention have no inherent effect on the amine function. No latency increases are detected and the latencies of the formulations remain identical.

TABLE-US-00007 TABLE 6 Latency of epoxy resin compositions in comparison Formulations Ref. 2 K I AD AE AF AG AH AI EPIKOTE ™ Resin 828 100 100 100 100 100 100 100 100 100 DYHARD ® 100S 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 6.5 Urea 1 5.0 5.0 5.0 1-methylimidazole 3.0 3.0 3.0 2-ethyl-4-methylimidazole 3.0 3.0 3.0 2-carboxyphenylboronic acid 0.4 0.4 0.4 1-octylboronic acid 0.4 0.4 0.4 Dynamic DSC Final Tg [° C.] 130 133 131 134 135 131 135 140 137 Isothermal DSC; 1 hour at 140° C. Time to 90% conversion [min] 7 8 8 2 2 2 2 3 2 Latency at 23° C. [days] — — — 0.4 0.4 0.4 — — — Latency at 40° C. [days] 2 6 10 — — — 0.13 0.14 0.14

[0284] Description and Evaluation of the Results from Table 6

[0285] Table 6 shows the comparison of urea-accelerated to imidazole-accelerated formulations, in particular the effect of the boronic acids on each formulation. Therein, the accelerators 1-methylimidazole, formulations AD-AF, and 2-ethyl-4-methylimidaol, formulations AG-AI, are compared to the urea-based ones. For all imidazole-based formulations, no latency increases are detected by addition of the boronic acids of the invention. The latencies of formulations AD-AF and AG-AI are in an identical time range, so that not the same latency effects as in formulations K and I occur.

[0286] Only the formulations Ref.2, K and I, taken for comparison, show the already discussed effect of latency increase by using boronic acids with ureas. Thus, it is concluded that the boronic acids according to the invention have no effect on imidazoles. No latency increases are detected, and the latencies of the formulations again remain identical.

TABLE-US-00008 TABLE 7 Latency of epoxy resin compositions in comparison Formulations Ref. 2 I AE AF EPIKOTE ™ Resin 828 100 100 DYHARD ® 100S 6.5 6.5 Araldite ® LY 1556 SP 100 100 Aradur ® 917 90 90 Urea 1 5.0 5.0 1-methylmidazole 3.0 3.0 octylboronic acid 0.4 0.4 Latency at 23° C. [days] — — 0.7 0.7 Latency at 40° C. [days] 2 10 — —

[0287] Description and Evaluation of the Results from Table 7

[0288] Table 7 shows the attempt to increase the latency of an anhydride-curing agent-based formulation. Therein, 1-methylimidazole is selected as accelerator. As can be seen from Table 7, formulation AF to which boronic acid was added shows no increase in latency over AE. The boronic acid does not achieve any effect in an anhydride-based formulation. The boronic acid according to the invention increases the latency only in the urea-accelerated formulation I, the latency increases by a factor of 5.

[0289] Thus, the boronic acids of the invention provide a latency increase in urea-based formulations, thereby providing significant advantages such as increased storage stability of corresponding formulations.