N,N'-DIALKYL METHYLCYCLOHEXANEDIAMINE AS REACTIVE DILUENT WITHIN EPOXY RESIN SYSTEMS

Abstract

Secondary diamine N,N′-dialkyl methylcyclohexanediamine acts as a reactive diluent for curable epoxy resin compositions. The addition of this compounds significantly reduces the initial viscosity of the epoxy resin composition while the resulting cured epoxy resin exhibits comparable favorable mechanical, chemical resistance and thermal properties such as low water uptake and high glass transition temperatures. Such compositions are particular suitable for manufacturing of composites with high mechanical and heat resistance properties by the means of resin transfer molding (RTM), vacuum aided resin transfer molding (VARTM) or infusion technology.

Claims

1. A hardener component, comprising: N,N′-dialkyl methylcyclohexanediamine; and at least one curing agent, wherein the at least one curing agents are amino hardeners having at least one primary aliphatic amine group and an NH-functionality of at least 3.

2. The hardener component according to claim 1, wherein a content of the N,N′-dialkyl methylcyclohexanediamine is up to 70% by weight, based on the total amount of N,N′-dialkyl methylcyclohexanediamine and the at least one curing agent of the hardener component.

3. The hardener component according to claim 1, wherein a content of the N,N′-dialkyl methylcyclohexanediamine is from 15 to 60% by weight, based on the total amount of N,N′-dialkyl methylcyclohexanediamine and the at least one curing agent of the hardener component.

4. The hardener component according to claim 1, wherein the at least one curing agents are amino hardeners having two primary aliphatic amino groups.

5. The hardener component according to claim 1, wherein the at least one curing agents are amino hardeners selected from the group of consisting of 2,2-dimethyl-1,3-propanediamine, 1,3-pentanediamine, 1,5-pentanediamine, 1,5-diamino-2-methylpentane, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, 2,5-dimethyl-1,6-hexanediamine, 2,2,4- and 2,4,4-trimethylhexamethylenediamine, dimethyl dicykan, isophoronediamine, diethylenetriamine, triethylenetetramine, aminoethylpiperazine, meta-xylylene diamine, styrene modified meta-xylylene diamine, 1,3-bis(aminomethyl cyclohexane), bis(p-aminocyclohexyl)methane, methylenedianiline, polyetheramines, diaminodiphenylmethane, diaminodiphenylsulfone, 2,4-toluenediamine, 2,6-toluenediamine, methylcyclohexane-1,3-diamine, diethyltoluenediamine, 1,3-diaminobenzene, 1,4-diaminobenzene, diaminocyclohexane, 1,8-menthanediamine, diaminodiphenyl oxide, 3,3′,5,5′-tetramethyl-4,4′-diaminobiphenyl and 3,3′-dimethyl-4,4′-diaminodiphenyl.

6. The hardener component according to claim 1, wherein the N,N′-dialkyl methylcyclohexanediamine is N,N′-dialkyl 4-methylcyclohexane-1,3-diamine of formula I: ##STR00003## or N,N′-dialkyl 2-methylcyclohexane-1,3-diamine of formula II: ##STR00004## or a mixture thereof, wherein each R1 is independently of each other an alkyl group having from 1 to 4 carbon atoms.

7. The hardener component according to claim 1, wherein the N,N′-dialkyl methylcyclohexanediamine is N,N′-diisopropyl 4-methylcyclohexane-1,3-diamine, N,N′-diisopropyl 2-methylcyclohexane-1,3-diamine, or a mixture thereof.

8. The hardener component according to claim 1, which further comprises an accelerator for the curing.

9. An epoxy resin composition comprising: the hardener component according to claim 1; and a resin component, which comprises at least one epoxy resin.

10. The epoxy resin composition according to claim 9, wherein the at least one epoxy resin is selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of hydrogenated bisphenol A, and diglycidyl ether of hydrogenated bisphenol F.

11. The epoxy resin composition according to claim 9, which further comprises additives.

12. A process for the production of cured epoxy resins, the process comprising: curing an epoxy resin composition according to claim 9.

13. A cured epoxy resin which is obtained by the process according to claim 12.

14. A cured epoxy resin which is obtained by curing of an epoxy resin composition according to claim 9.

15. A process, comprising employing N,N′-dialkyl methylcyclohexanediamine as reactive diluent for epoxy resin compositions.

Description

EXAMPLES

Example 1: Preparation of N,N′-diisopropyl methylcyclohexanediamine (DIP-MCDA)

[0046] 730 g (5.7 mol) of a mixture of the isomers 4-methylcyclohexane-1,3-diamine (approx. 80% by weight) and 2-methylcyclohexane-1,3-diamine (approx. 20% by weight) were provided in an autoclave (volume of 3.5 L) with stirring device together with an excess of acetone (1093 g, 18.8 mol). 75 g TiO.sub.2 catalyst and 75 g of a Pd/Ag catalyst supported on Alox have been added within a catalyst cage. The autoclave has been closed and flushed with nitrogen. The reaction mixture was stirred for 4 h at 154° C. Subsequently hydrogen has been added at a pressure of 100 bar and the mixture has been stirred for additional 6 h at 154° C. Reaction water and low boilers has been distilled off in a rotary evaporator at a temperature of 60° C. and a pressure of 30 mbar. The resulting product was a mixture of N,N′-diisopropyl methylcyclohexanediamine (83% by weight) and N-isopropyl methylcyclohexanediamine (17% by weight). To increase the yield of the diisopropyl modified diamine, this reaction product has been mixed again with 1093 g of acetone and the above described procedure has been repeated with fresh catalyst. Now the ratio of N,N′-diisopropyl methylcyclohexanediamine to N-isopropyl methylcyclohexanediamine was >98: 2. DIP-MCDA has been prepared with a selectivity of >95% and a conversion of >99%. The row product has been finally purified by distillation.

Example 1a: Preparation of N,N′-diisobutyl methylcyclohexanediamine (DIB-MCDA)

[0047] DIB-MCDA was prepared is the same way as DIP-MCDA (Example 1), but using an excess of 2-butanone instead of acetone.

Example 1 b: Viscosity of Mixtures of Epoxy Resin and Modified MCDA

[0048] Epoxy resin (bisphenol A diglycidyl ether, BADGE, Epilox A19-03, EEW of 184 g/mol, Leuna Harze) was mixed with DIP-MCDA (Example 1), with DIB-MCDA (Example 1a) and for comparison with N,N′-di(2-ethylhexyl) meta-xylylenediamine (DEH-MXDA; prepared according to US 20150344406, “Amine 1”), each in a weight ratio of 83 parts to 17 parts. Viscosity of the mixtures (mixing viscosity) at a temperature of 23° C. was determined using a conventional shear stress controlled cone-plate rheometer (MCR 301, Anton Paar) with a plate and cone diameter of 50 mm, a cone angle of 1° and a gap distance of 0.1 mm (mixing viscosity). The results are summarized in table 1.

TABLE-US-00001 TABLE 1 Viscosity of mixtures of epoxy resin and modified MCDA and modified MXDA Mixture (each with ratio of 83:17 b.w.) Viscosity (mPas) BADGE + DIP-MCDA 1769 BADGE + DIB-MCDA 1753 BADGE + DEH-MXDA 2456

Example 2: Preparation of Epoxy Resin Compositions

[0049] Compositions of epoxy resin (bisphenol A diglycidyl ether, BADGE, Epilox A19-03, EEW of 184 g/mol, Leuna Harze), amine hardener (methylcyclohexyldiamin (MCDA, Baxxodur EC210, BASF)) or diethyltoluenediamine (DETDA, Lonzacure 80, Lonza)) and reactive diluent (N,N′-diisopropyl methylcyclohexanediamine (DIP-MCDA, according to Example 1)), 1,4-butanediol diglycidyl ether (BDGE, Epilox 13-21, EEW of 135 g/mol, Leuna Harze), 1,6-hexanediol diglycidylether (HDGE, Epilox 13-20, EEW of 150 g/mol, Leuna Harze), monoglycidyl ether of C12-C14 aliphatic alcohols (MGE, Epilox 13-18, EEW of 288 g/mol, Leuna Harze), or as a control without reactive diluent)) were prepared using a 1:1 stoichiometric ratio of epoxy groups to NH-functionalities whereas the epoxy groups or the NH-functions of the used reactive diluents were also considered. The epoxy-hardener mixtures were stirred in a propeller mixture at 2000 rpm for 1 min. Detailed amounts of the prepared compositions are summarized in table 2.

TABLE-US-00002 TABLE 2 Epoxy resin compositions of the invention (Exp. 1 to 4) and for comparison (Cmp. 1 to 10) BADGE MCDA DETDA DIP-MCDA BDGE HDGE MGE (g) (g) (g) (g) (g) (g) (g) Exp. 1 100 14.7 14.7 Exp. 2 100 18.2 4.5 Exp. 3 100 15.6 20.5 Exp. 4 100 21.8 5.9 Cmp. 1 100 23.7 14.7 Cmp. 2 100 21.0 4.5 Cmp. 3 100 21.2 14.7 Cmp. 4 100 20.7 4.5 Cmp. 5 100 19.8 Cmp. 6 100 31.2 20.5 Cmp. 7 100 25.9 5.9 Cmp. 8 100 31.2 20.5 Cmp. 9 100 30.1 20.5 Cmp. 10 100 24.0

Example 3: Rheological and Exothermic Profile and Glass Transition Temperature of the Epoxy Resin Compositions

[0050] Differential scanning calorimetry (DSC) and rheological experiments were conducted for the epoxy resin compositions of Example 2 immediately following the preparation of the reactive mixtures. DSC was used to determine the reaction and thermal profile (onset temperature (To), peak temperature (Tp), glass transition temperature (Tg)) according to ASTM D 3418 using a heating rate of 20° C./min starting with ambient temperature (23° C.). The results are summarized in table 3.

TABLE-US-00003 TABLE 3 Exothermic profile of the epoxy resin compositions To (° C.) Tp (° C.) Tg (° C.) MCDA curing Exp. 1 86 119 134 Exp. 2 82 112 152 Cmp. 1 75 106 144 Cmp. 2 76 106 158 Cmp. 3 85 119 135 Cmp. 4 81 111 148 Cmp. 5 79 108 169 DETDA curing Exp. 3 121 165 118 Exp. 4 120 159 158 Cmp. 6 120 158 142 Cmp. 7 121 158 164 Cmp. 8 125 164 136 Cmp. 9 129 166 115 Cmp. 10 122 158 178

[0051] The initial viscosity (mixing viscosity) at a temperature of 23° C. (for MCDA and DETDA curing) and of 75° C. (for MCDA curing) or 50° C. (for DETDA curing) was determined using a conventional shear stress controlled cone-plate rheometer (MCR 301, Anton Paar) with a plate and cone diameter of 50 mm, a cone angle of 1° and a gap distance of 0.1 mm (mixing viscosity). The rheological profiles (pot life and gel time) at a temperature of 23° C. (for MCDA curing) or 45° C. (for DETDA curing) and of 75° C. (for MCDA and DETDA curing) were determined using a conventional shear stress controlled plate-plate rheometer (MCR 301, Anton Paar) with a plate diameter of 15 mm and a gap distance of 0.25 mm, using rotational mode (pot life) or under oscillatory forces (gel time). The pot life is the time at a given temperature need to attain a viscosity of 6000 mPas. The gel point was defined as the crossover point of the storage and loss moduli and the gel time was defined as the time taken, from addition of the hardener to the reaction mixture, to reach the gel point. The results are summarized in tables 4 and 5.

TABLE-US-00004 TABLE 4 Mixing viscosity of the epoxy resin compositions at 75° C. (for MCDA curing) or 50° C. at 23° C. (for DETDA curing) mixing mixing viscosity (mPas) viscosity (mPas) MCDA curing Exp. 1 597 67 Exp. 2 895 96 Cmp. 1 377 62 Cmp. 2 709 91 Cmp. 3 305 52 Cmp. 4 609 83 Cmp. 5 1052 111 DETDA curing Exp. 3 1610 140 Exp. 4 4350 230 Cmp. 6 1280 234 Cmp. 7 3720 403 Cmp. 8 1200 257 Cmp. 9 831 176 Cmp. 10 7550 803

TABLE-US-00005 TABLE 5 Rheological profile of the epoxy resin compositions at 23° C. (for MCDA curing) or 45° C. (for DETDA curing) at 75° C. pot life gelpoint pot life gelpoint (min) (min) (min) (min) MCDA Exp. 1 288 1738 44 120 curing Exp. 2 158 923 24 50 Cmp. 1 206 830 20 52 Cmp. 2 140 716 18 43 Cmp. 3 186 880 28 75 Cmp. 4 113 568 22 50 Cmp. 5 160 727 20 41 DETDA Exp. 3 1695 546 curing Exp. 4 1440 434 Cmp. 6 1826 457 Cmp. 7 1550 420 Cmp. 8 1815 484 Cmp. 9 2724 672 Cmp. 10 1370 401

Example 4: Mechanical Testing of the Cured Epoxy Resin Compositions

[0052] Immediately following the preparation of the reactive mixtures, they were degassed at 1 mbar. Subsequently the epoxy resin compositions were cured for 2 h at 80° C. and subsequently 3 h at 125° C. After curing the mechanical tests (tensile modulus (E_t), tensile strength (σ_M), flexural modulus (E_f), flexural strength (σ_fM) were carried out according to ISO 527-2:1993 and ISO 178:2006. The results are summarized in table 6.

TABLE-US-00006 TABLE 6 Mechanical properties of the cured epoxy resin compositions tensile test flexural test E_t σ_M E_f σ_fM (MPa) (MPa) (MPa) (MPa) MCDA Exp. 1 2968 82 3058 123 curing Exp. 2 2883 85 2955 126 Cmp. 1 2833 80 2934 120 Cmp. 2 2835 83 2927 120 Cmp. 3 2921 78 3026 121 Cmp. 4 2848 82 2940 125 Cmp. 5 2894 86 2889 125 DETDA Exp. 3 3030 119 curing Exp. 4 2760 110 Cmp. 6 2590 104 Cmp. 7 2470 107 Cmp. 8 2883 116 Cmp. 9 2849 112 Cmp. 10 2760 110

Example 4: Determination of the Water Uptake of the Cured Epoxy Resin Compositions

[0053] Immediately following the preparation of the reactive mixtures, they were degassed at 1 mbar. Subsequently the epoxy resin compositions were cured for 2 h at 80° C. and subsequently 3 h at 125° C. After curing the water-uptake measurements were carried out according to ISO 62:2008. The water uptake is measured as percent of the mass increase after storing the cured epoxy resins in water for 7 days at 23° C. The results are summarized in table 7.

TABLE-US-00007 TABLE 7 Water uptake of the cured epoxy resin compositions MCDA curing DETDA curing mass increase (%) mass increase (%) Exp. 1 0.31 Exp. 3 0.23 Exp. 2 0.33 Exp. 4 0.30 Cmp. 1 0.42 Cmp. 6 0.36 Cmp. 2 0.39 Cmp. 7 0.33 Cmp. 3 0.33 Cmp. 8 0.40 Cmp. 4 0.35 Cmp. 9 0.28 Cmp. 5 0.30 Cmp. 10 0.33