High-latency hardeners for epoxy resins

Abstract

The present invention relates to novel high-latency liquid hardeners for hardening of curable polymer resins, especially epoxy resins, and to epoxy resin compositions comprising liquid hardeners for the production of fiber composite materials.

Claims

1. A liquid hardener for curing curable polymer resins, comprising: a) cyanamide; b) at least one urea derivative of the formula (I) or formula (II) ##STR00004## wherein the following applies to the radicals, in each case simultaneously or independently of one another: R.sup.1, R.sup.2=simultaneously or independently of one another hydrogen, C1- to C15-alkyl, C3- to C15-cycloalkyl, or R.sup.1 and R.sup.2 together are C3- to C10-alkylene, thereby forming a ring together with the nitrogen atom to which they are attached; R.sup.3=hydrogen, C1- to C15-alkyl, C3- to C15-cycloalkyl, aryl, arylalkyl, NHC(O)NR.sup.1R.sup.2-substituted C1- to C15-alkyl, NHC(O)NR.sup.1R.sup.2-substituted C3- to C15-cycloalkyl, NHC(O)NR.sup.1R.sup.2-substituted aryl or NHC(O)NR.sup.1R.sup.2-substituted arylalkyl; wherein in formula (I) at least one of R.sup.1, R.sup.2 and R.sup.3 is not hydrogen; R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8=simultaneously or independently of one another hydrogen, C1- to C15-alkyl, C3- to C15-cycloalkyl, aryl, arylalkyl, NHC(O)NR.sup.1R.sup.2, NHC(O)NR.sup.1R.sup.2-substituted C1- to C15-alkyl, NHC(O)NR.sup.1R.sup.2-substituted aryl or NHC(O)NR.sup.1R.sup.2-substituted arylalkyl; and, c) at least one stabiliser comprising inorganic or organic acids, wherein the hardener is liquid at a temperature of 20 C. at normal pressure and has a viscosity less than 1 Pa s.

2. The liquid hardener of claim 1, wherein the hardener includes cyanamide and the at least one urea derivative of the formula (I) or formula (II) in a molar ratio of cyanamide: the at least one urea derivative of 1:1 to 4:1.

3. The liquid hardener of claim 1, wherein the hardener, besides cyanamide, the at least one urea derivative and the stabiliser, includes no solvents or solubilisers or is free of the solvents or the solubilisers.

4. The liquid hardener of claim 1, wherein the hardener includes at least two different urea derivatives of the at least one urea derivative.

5. The liquid hardener of claim 1, wherein the hardener includes a urea derivative of the formula (I), wherein the following applies to the radicals, in each case simultaneously or independently of one another: R.sup.1 and R.sup.2=hydrogen, C1- to C15-alkyl; R.sup.3=C1- to C15-alkyl, C3- to C15-cycloalkyl, NHC(O)NR.sup.1R.sup.2-substituted C1- to C15-alkyl, NHC(O)NR.sup.1R.sup.2-substituted C3- to C15-cycloalkyl, or NHC(O)NR.sup.1R.sup.2-substituted aryl.

6. The liquid hardener of claim 1, wherein the at least one urea derivative is selected from the group consisting of 1,1-dimethylurea, 3-phenyl- 1,1-dimethylurea, 1,1-(methylene-di-p-phenylene)-bis-(3,3-dimethylurea), 1,1-(2-methyl-m-phenylene)-bis-(3,3-dimethylurea) and 1,1-(4-methyl-m-phenylene)-bis-(3,3-dimethylurea), and, wherein the at least one stabiliser is selected from the group consisting of the inorganic and the organic acids.

7. The liquid hardener of claim 1, wherein the inorganic or the organic acid is an acid selected from the group consisting of salicylic acid, phthalic acid, toluene sulfonic acid, sulfuric acid, phosphoric acid, anhydrides thereof and mixtures thereof.

8. A method for curing compositions comprising at least one of curable epoxy resin or curable polyurethane resin, comprising employing the liquid hardener of claim 1.

9. A method for curing impregnated fibre materials or impregnated woven fabrics, knitted fabrics or braiding, comprising employing the liquid hardener of claim 1.

10. The liquid hardener of claim 1, wherein the polymer resins are epoxy resins.

11. The liquid hardener of claim 1, wherein the liquid hardener has a melting point S.sub.m of <20 C. at normal pressure.

12. A liquid hardener for curing curable polymer resins, consisting essentially of: a) cyanamide; b) at least one urea derivative of the formula (I) or formula (II) ##STR00005## wherein the following applies to the radicals, in each case simultaneously or independently of one another: R.sup.1, R.sup.2=simultaneously or independently of one another hydrogen, C1- to C15-alkyl, C3- to C15-cycloalkyl or R.sup.1 and R.sup.2 together are C3- to C10-alkylene, thereby forming a ring together with the nitrogen atom to which they are attached; R.sup.3=C1- to C15-alkyl, C3- to C15-cycloalkyl, aryl, arylalkyl, NHC(O)NR.sup.1R.sup.2-substituted C1- to C15-alkyl, NHC(O)NR.sup.1R.sup.2-substituted C3- to C15-cycloalkyl, NHC(O)NR.sup.1R.sup.2-substituted aryl or NHC(O)NR.sup.1R.sup.2-substituted arylalkyl; R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8=simultaneously or independently of one another hydrogen, C1- to C15-alkyl, C3- to C15-cycloalkyl, aryl, arylalkyl, CF.sub.3, NHC(O)NR.sup.1R.sup.2, NHC(O)NR.sup.1R.sup.2-substituted C1- to C15-alkyl, NHC(O)NR.sup.1R.sup.2-substituted aryl or NHC(O)NR.sup.1R.sup.2-substituted arylalkyl; and, c) at least one stabiliser comprising inorganic or organic acids, wherein the hardener is liquid at a temperature of 20 C. at normal pressure and has a viscosity less than 1 Pa s.

13. The liquid hardener of claim 12, wherein the hardener includes cyanamide and the at least one urea derivative of the formula (I) or formula (II) in a molar ratio of cyanamide: the at least one urea derivative of 1:1 to 4:1.

14. The liquid hardener of claim 12, wherein the hardener, besides cyanamide, the at least one urea derivative and the stabiliser, includes no solvents or solubilisers or is free of the solvents or the solubilisers.

15. The liquid hardener of claim 12, wherein the inorganic or organic acid is an acid selected from the group consisting of salicylic acid, phthalic acid, toluene sulfonic acid, sulfuric acid, phosphoric acid, anhydrides thereof and mixtures thereof.

16. The liquid hardener of claim 12, wherein the polymer resins are epoxy resins.

Description

EXAMPLES

(1) I. Hardeners According to the Invention

(2) 1) Preparation of the Hardeners According to the Invention

(3) Apparatus:

(4) Laboratory agitator (DISPERMAT model AE03-C1), 500 ml metal mixing vessel, agitator plate 60 mm in diameter, metal spatula

(5) Method:

(6) 100 g of the individual components (as in Table 1) were weighed into a 500 ml mixing vessel and mixed together briefly with the aid of a spatula. The mixture was stirred using the agitator at 100-200 rpm until a thin crystal slurry formed. The mixture was then stirred at 500 to 2000 rpm until a temperature of 40 C. was reached. If necessary, 2 g of stabiliser (organic or inorganic acid) was then added per 100 g of hardener to stabilise the liquid. Stirring of the liquid was then continued at 100 rpm until a temperature of 25 C. was reached. The residue produced was filtered off. The liquid phase thus obtained was collected and was stored at room temperature (23 C.).

(7) Yield:

(8) Depending on mixing, the yield was between 75% and 97%.

(9) Adding the stabilisers according to the invention increased the yield from 75-90% to 83-97%.

(10) TABLE-US-00001 TABLE 1 Compositions of the liquid hardeners according to the invention Cyanamide Urea B1 Urea B2 Urea B3 Urea B4 Stabiliser Liquid Molar Molar Molar Molar Molar Molar hardeners fraction fraction fraction fraction fraction fraction H1 3 1 0.16 H2.S2 3 0.72 0.24 0.06 H1.S3 3 0.72 0.24 0.04 H1.S4 3 1.25 0.30 0.11 H1.S5 3 0.97 0.16 0.06 H1.S6 3 1.01 0.21 0.07 H1.S7 3 1.43 0.32 0.07 H1.S8 3 0.97 0.16 0.09 H2 2 1.0 H2.S8 2 1.0 0.05 H3 2 1 H3.S3 2 1 0.04 H4 2 0.07 1 H4.S3 2 0.07 1 0.04 H5 3 0.40 H5.S2 3 0.40 0.09

(11) Raw Materials Used Cyanamide: AlzChem AG Urea B1: 1,1-dimethylureaAlzChem AG Urea B2: Technical isomer mixture 1,1-(4-methyl-m-phenylene)-bis(3,3-dimethylurea) and 1,1-(2-methyl-m-phenylene)-bis-(3,3-dimethylurea)AlzChem AG Urea B3: UreaMerck KGaA Urea B4: 1-(N,N-dimethylurea)-3-(N,N-dimethylureamethyl)-3,5,5-trimethylcyclohexaneCAS: 39992-90-0AlzChem AG E 828: Epikote 828Momentive Specialty Chemicals E 828LVEL: Epikote 828 LVELMomentive Specialty Chemicals Stabiliser S2: [Phosphoric acid (liquid) 85% according to analysis by Merck] Stabiliser S3: [Salicylic acid (solid) & phosphoric acid (liquid) (H.sub.3PO.sub.4 85% according to analysis by Merck)] in ratio of 1:1 Stabiliser S4: [Salicylic acid (solid) extremely high purity from Merck] Stabiliser S5: [Phthalic acid (solid) min. 99.5% from Merck] Stabiliser S6: [Phthalic acid anhydride (solid) >98% from Merck] Stabiliser S7: [Toluene-4-sulfonic acid monohydrate (solid) >97% from Merck] Stabiliser S8: [Sulfuric acid (liquid) >97% from J T Baker] RIMR 135: Epoxy resin Momentive Specialty Chemicals RIMH 137: Liquid amine curing agentMomentive Specialty Chemicals Vestamin IPDA: Liquid amine curing agentEvonik Degussa GmbH

(12) 2) Viscosities of the Liquid Hardeners According to the Invention

(13) Determining Viscosity:

(14) Measurement on a HAAKE Rheostress 1 carried out at 25 C. in mPa.Math.s, 35 mm diameter and 1 with shear rate of 5.0/s (per second)

(15) TABLE-US-00002 TABLE 2 Viscosity in mPa .Math. s at given temperatures Hardener at 10 C. at 15 C. at 20 C. at 25 C. at 30 C. H1 12-14 11-13 10-12 10-11 10-11 H1.S2 12-14 11-13 10-12 10-11 10-11 H1.S3 12-14 11-13 10-12 10-11 10-11 H1.S4 12-14 11-13 10-12 10-11 10-11 H1.S5 12-14 11-13 10-12 10-11 10-11 H1.S6 12-14 11-13 10-12 10-11 10-11 H1.S7 12-14 11-13 10-12 10-11 10-11 H1.S8 12-14 11-13 10-12 10-11 10-11 H2 9-11 7-9 7-9 6-8 5-7 H2.S8 9-11 7-9 7-9 6-8 5-7 H3 5-7 5-7 5-6 4-5 H3.S3 7-10 5-7 5-7 5-6 4-5 H4 8-10 8-10 7-9 6-8 5-7 H4.S3 8-10 8-10 7-9 6-8 5-7 H5 13-15 12-14 11-13 10-12 10-11 H5.S2 13-15 12-14 11-13 10-12 10-11

(16) Table 2 shows that the viscosities of the mixtures according to the invention are not affected by the acid stabilisation.

(17) 3) Melting Points of the Hardeners According to the Invention

(18) Melting points determined by DSC.

(19) Measurement on Mettler Toledo DSC 822

(20) Dyn DSC 40 C.-60 C. at a heating rate of 10K/min

(21) TABLE-US-00003 TABLE 3 Melting point Hardener First peak Second peak H1 12-16 C. H1.S2 11-16 C. H1.S3 12-17 C. H1.S4 12-16 C. H1.S5 12-16 C. H1.S6 12-16 C. H1.S7 12-16 C. H1.S8 11-16 C. H2 24-22 C. 10-17 C. H2.S8 12-19 C. H3 30-8 C. 13-15 C. H3.S3 13-16 C. H4 30-28 C. 8-9 C. H4.S3 10-15 C. H5 13-17 C. H5.2 12-16 C.

(22) The melting points of hardeners H2, H3 and H4 are raised by 30 to 40 C. by the acid stabilisation, in which case the second peaks are absent.

(23) II. Epoxy Resin Composition According to the Invention

(24) 1) Preparation of Epoxy Resin Compositions

(25) 100 parts by weight of epoxy resin and 7 parts by weight of the hardeners according to the invention were weighed into a 250 ml mixing vessel and mixed using the agitator at 500 rpm for 2 minutes. The mixture was then degassed under vacuum for 10 minutes.

(26) 2) Measuring Methods Dyn. DSC: standard 30-250 C. at a heating rate of 10K/min Cold Tg: standard 30-250 C., at a heating rate 10K/min Final Tg: standard Tg Heat from 30 C. to 200 C. at 20 C./min Hold for 10.0 min at 200 C. Cool from 200 C. to 50 C. at 20 C./min Hold for 5.0 min at 50 C. Heat from 50 C. to 200 C. at 20 C./min Hold for 10.0 min at 200 C. Cool from 200 C. to 50 C. at 20 C./min Hold for 5.0 min at 50 C. Heat from 50 C. to 220 C. at 20 C./min Viscosity at 25 C. in Pa.Math.s (1 cone) Gelling time at 140 C. Infusion tests on the heating plate at 80 C.

(27) TABLE-US-00004 TABLE 4 Use Tests - Epoxy resin composition with liquid hardener according to the invention (or without stabiliser, not according to the invention) - in each case 100 parts by weight of epoxy resin, 7 parts by weight of liquid hardeners or powder mixture unless otherwise specified Dyn Dyn Gelling Glass DSC DSC Integral time at transition Viscosity at peak onset heat 140 C. temperature 25 C. in No. Epoxy resin composition [ C.] [ C.] [J/g] [min:sec] Tg [ C.] Pa .Math. s E1 E828:(powder mixture:cyanamide + 153.3 142.0 143 03:30 119 5.7 B1 + B2) (no stabiliser) E2 E828:H1 (no stabiliser) 147 136 287 03:40 123 4.0 E2.S2 E828LVEL:H1.S2 153 143 288 04:30 123 4.8 E2.S3 E828LVEL:H1.S3 153 143 249 04:30 124 4.1 E2.S4 E828LVEL:H1.S4 150 139 235 04:10 126 4.5 E2.S5 E828LVEL:H1.S5 150 140 247 04:15 123 4.7 E2.S6 E828LVEL:H1.S6 150 140 287 04:15 124 4.6 E2.S7 E828LVEL:H1.S7 150 142 282 04:30 126 4.2 E2.S8 E828LVEL:H1.S8 149 140 366 04:00 124 4.1 E3 E828:(powder mixture:cyanamide + 144.7 130.0 339 04:10 122 5.5 B1) (no stabiliser) E4 E828:H2 (no stabiliser) 143 128 380 03:15 126 3.4 E4.S8 E828LVEL:H2.S8 148 138 422 03:45 125 4.3 E5 E828:(powder mixture:cyanamide + 171.4 158.1 150 53:00 138 nd B3) (no stabiliser) E6 E828:H3 (no stabiliser) 172 156 65 32:00 144 3.9 E6.S3 E828LVEL:H3.S3 173 163 30 44:00 137 4.4 E7 E828:(powder mixture:cyanamide + 162.7 140.9 169 10:00 130 nd B3 + B2) (no stabiliser) E8 E828:H4 (no stabiliser) 154 135 310 05:30 137 4.8 E8.S3 E828LVEL:H4.S3 160 142 283 10:00 139 5.1 E9 E828:VESTAMIN IPDA 100:23 115.5 79.7 453 13:30 at 99 5.3 (no stabiliser) 80 C. E10 RIMR135:RIMH137 100:30 125.9 87.9 436.0 40:00 at 98 4.1 (no stabiliser) 80 C. E11 E828:H5 139.0 147.3 296 04:50 131 5.5 E11.S2 E828:H5.S2 145.9 152.8 380 05:30 130 5.8 nd = not determinable, since when the powders are added individually agglomerations are formed which prevent a precise measurement of the viscosity within the epoxy resin

(28) The advantages of the liquid hardeners according to the invention when hardening epoxy resins by comparison with the individual addition of the comparable hardeners and accelerators as powder components can be seen from Table 4.

(29) With the liquid mixtures according to the invention, by comparison with the powder mixtures of the same compositions hardening consistently begins at lower temperatures and the times before polymerisation begins (gelling time at 140 C.) are shorter. The mixtures according to the invention lower the viscosity of the epoxy resins significantly, by up to approximately 50%, which makes them suitable for use as hardeners for infusion resin systems, and increases their glass transition temperatures. The integral heat values (J/g), which are consistently higher, indicate a more spontaneous reaction of the mixtures according to the invention by comparison with the individual powder components used as hardeners and accelerators. Moreover, only half or a third of the quantity of hardener is required (by comparison with known liquid amine hardeners). This enables a considerable cost advantage to be realised.

(30) By comparison with this, although the known and usual liquid amine hardeners such as RIMH 137 (from Momentive) or IPDA (from Evonik) display lower curing temperatures, the mixtures according to the invention begin polymerisation at comparable times and achieve much higher glass transition temperatures.

(31) Furthermore, the summary table shows that the reactivity values of the hardeners according to the invention are changed only slightly by being stabilised with acids, by comparison with the underlying mixtures. The reactivity values are somewhat smaller as a result of the acid stabilisation. The glass transition temperatures and viscosities also remain in the same order of magnitude.

(32) TABLE-US-00005 TABLE 5 Latencies of the epoxy resin compositions according to Table 4 in days (d) - at 23 C. in an environmental chamber (viscosity measured at 25 C.) No. Start 1 d 4 d 5 d 6 d 7 d 8 d 10 d 12 d 16 d 18 d 20 d 25 d 30 d 35 d 40 d Result E1 5.7 4.8 7.2 10 21 102 >500 solid E2 4.0 4.2 10.1 17.9 40.1 4 days E2.S2 4.8 4.8 4.9 4.9 4.9 5.0 5.1 5.2 5.3 6.9 12.7 25.1 16-17 days E2.S3 4.1 4.1 4.1 4.2 4.3 4.6 4.8 5.5 6.7 11.9 62.8 14-15 days E2.S4 4.5 4.5 4.6 4.8 4.9 7.9 13.9 55.3 7-8 days E2.S5 4.7 4.7 4.8 4.9 5.7 6.6 11.0 32.3 7-8 days E2.S6 4.6 4.6 4.7 4.9 5.3 6.5 11.5 42.3 7-8 days E2.S7 4.2 4.3 4.5 5.0 6.0 7.0 11.0 38.1 7-8 days E2.S8 4.1 4.3 4.6 5.2 5.4 5.7 9.7 21.3 7-8 days E3 5.5 5.6 14 14 14 21 solid 2 days E4 3.4 3.9 9.5 53.0 3 days E4.S8 4.3 4.3 4.3 4.3 4.3 4.5 4.7 4.9 11.9 133 10-11 days E5 nd nd nd nd nd nd nd nd nd solid E6 3.9 3.9 4.2 4.4 5.6 8.1 13.0 13.0 7 days E6.S3 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.5 4.5 4.6 6.8 38.4 35 days E7 nd nd nd nd nd nd nd nd nd solid nd E8 4.8 4.8 5.2 6.7 13.9 47.6 5 days E8.S3 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.1 5.2 5.3 5.5 5.7 5.9 13.1 33.0 30 days E9 5.3 solid >1 day E10 4.1 solid >1 day E11 5.5 5.5 5.5 5.5 5.5 5.5 5.6 5.7 6.7 8.0 12.9 37.6 17 days E11.S2 5.8 5.8 5.8 5.8 5.8 5.8 5.8 5.8 5.8 5.8 5.9 6.0 6.1 6.4 7.8 10.1 40 days nd = not determinable, since when the powders are added individually agglomerations are formed which prevent a precise measurement of the viscosity within the epoxy resin

(33) The storage capacities=latencies of hardener/accelerator systems in the epoxy resin are affected to a considerable extent by the solubility of these systems in the resin. The fact that powder hardener/accelerator systems are relatively insoluble in epoxy resin at temperatures <60 C. enables long storage times of these mixtures with no reaction between the components.

(34) It can be anticipated that mixtures of liquid hardener/accelerator in epoxy resin will result in rapid reaction between the components, giving drastically restricted storage capacities=latencies. This is shown by the amine hardeners listed in Table 5 (RIMH 137 from Momentive and Vestamin IPDA from Evonik).

(35) Surprisingly, however, the liquid hardeners according to the invention do not show fast reaction with epoxy resins at room temperature, so their storage capacities=latencies in epoxy resins is significantly longer than those of conventional liquid amine hardener systems.

(36) In Table 5, the full effect of the hardeners according to the invention with acid stabilisation is seen by comparison with their underlying mixtures. The latencies of the stabilised mixtures are drastically lengthened, which substantially increases the safety in use of epoxy resin formulations when they are used as one-component infusion or injection resin formulations.

(37) Petri Dish Test:

(38) 30 g of a mixture of E828LVEL and a liquid hardener in a ratio of 100:7.0 were weighed into a Petri dish with a diameter of 10 cm (pre-treated with XTEND Release 19CMS as a release agent), which was closed with a lid. The Petri dish was put into a drying cabinet at 80 C. and taken out again once the mixture had solidified. After cooling, the resulting plate was removed and part of the plate was used for a cold Tg and final Tg test.

(39) TABLE-US-00006 TABLE 6 Cold Tg and final Tg test of epoxy resin compositions according to the invention as in Table 4 Epoxy resin Cold Residual heat Final Tg No. composition Tg [ C.] [J/g] [ C.] E2 E828LVEL:H1 82.0 54 132 E2.S8 E828LVEL:H1.S3 71.5 103 131 E2.S3 E828LVEL:H1.S3 69.1 131 129 E4.S1 E828LVEL:H4 89.9 82 132 E4.S8 E828LVEL:H4.S8 63.0 158 126 E11.S2 E828LVEL:H5.S1 97.2 72 139

(40) During curing of the composition, the mixtures according to the invention behave like their unstabilised starting mixtures

(41) Method of Trial Infusion:

(42) Epoxy resin compositions according to Table 4 were mixed and preheated in a heatable storage vessel. The inlet line was introduced into the storage vessel and fixed, the outlet line (see structure of an infusion test, Table 7) was connected to the vacuum pump by way of a safety valve, and the pump was switched on. The heating plate (which simulates the heatable mould) was brought to the infusion temperature. On application of the vacuum, the epoxy resin composition was drawn through the fibre composite. Once impregnation was complete, the inlet and outlet lines were clamped off and capped and the entire structure was then cured on the heating plate, forming a laminate. After curing and cooling were complete, the laminate was removed from the structure.

(43) TABLE-US-00007 TABLE 7 Fibre composite - structure for infusion tests Component part Material Base layer R&G vacuum film No. 390160 Seal Tacky Tape SM5126- X Separating film (bottom) Nylon Peel ply (plain weave 64 g/m.sup.3) shifted Laminate (glass fibre) 3-layer Atlas FK 144 (296 g/m.sup.3) Separating film (top) Nylon Peel ply (plain weave 64 g/m.sup.3) shifted Release film R&G release film No. 390190 Aerating film R&G non-woven No. 390180 Vacuum mesh Degassing mesh 150 g/m.sup.3 (running direction - black) Vacuum film R&G vacuum film No. 390160 Lines (inlet and outlet) PVC, clear (3.0 mm internal dia, 5.0 mm external dia) Support Glass plate

(44) Mould: heating plate

(45) Storage container: glass beaker

(46) Vacuum: Vacuum pump, standard (<20 mbar)

(47) TABLE-US-00008 TABLE 8 Infusion test with epoxy resin compositions as in Table 4 - resin:hardener ratio of 100:7.0 (comparisons) Curing time Injection in h Epoxy resin time in Temperature Cold Final composition minutes in C. Tg Tg Remarks E2 5 1 h 59-63 C. 72 128 Fibre composite readily 5 h 69-74 C. removable from core Fibre composite looks good, is even and has no voids E2.S3 4 4.25 h 80 C. 107 134 Fibre composite readily removable from core Fibre composite looks good, is even and has no voids E4 12 20 h 70 C. 79 137 Fibre composite readily removable from core Fibre composite looks good, is even and has no voids E6 45 6 h 80 C. 56 134 Fibre composite readily removable from core Fibre composite looks good, is even and has no voids E8 45 5.5 h 75-78 C. 97 140 Fibre composite readily removable from core Fibre composite looks good, is even and has no voids E9 20 6 h 70 C. 93 99 Fibre composite readily removable from core Fibre composite looks good, is even and has no voids E10 18 6.5 h 40 C. 68 93 Fibre composite readily and then removable from core 16 h 80 C. Fibre composite looks good, is even and has no voids

(48) The powder hardener/accelerator systems of the individual components are unsuitable for polymerising the epoxy resins by the infusion method. When mixed with epoxy resin, the mixtures thereof are filtered out (separated) by the fine-mesh fabrics at the suction inlet points, and are no longer available for hardening the epoxy resins. Thus, the epoxy resin compositions E1, E3, E5 and E7 are not suitable for preparing composites by means of the infusion method.

(49) However, Table 8 shows that, like the known two-component amine systems (RIMH 137 from Momentive, IPDA from Evonik), the epoxy resin compositions according to the invention E2, E4, E6 and E8, which contain the liquid hardeners H1, H2, H3 and H4 according to the invention, enable impregnation of the fabric fibres by the infusion method and in comparable time periods. In this connection, however, they typically need shorter curing periods at 80 C. and achieve significantly higher glass transition temperatures.

(50) Furthermore, by comparison with the two-component amine systems (RIMH 137 from Momentive, IPDA from Evonik), a significantly smaller quantity of hardener is needed.

(51) The superiority of the novel liquid hardeners is also shown by the fact that a higher glass transition temperature (final Tg) is achieved in the composite.

(52) In the infusion method, too, all the hardeners according to the invention can be used like their unstabilised starting mixtures.