Hardener for epoxy resins

Abstract

A curing agent for epoxy resins has N-benzylethane-1,2-diamine and N,N′-dibenzylethane-1,2-diamine in a weight ratio in the range from 65/35 to 95/5. The curing agent is easy to prepare, thins epoxy resins particularly well, and enables low-emission epoxy resin products that have good workability and a long pot-life, cure reliably and surprisingly fast and can be walked on after a short time, in particular even in cold conditions. Coatings of particularly high mechanical grade, with a high surface quality and a minimal tendency to yellowing, can thus be produced. Epoxy resins of this type are particularly suitable for coating floors.

Claims

1. A curing agent for epoxy resins comprising N-benzylethane-1,2-diamine and N,N′-dibenzylethane-1,2-diamine in a weight ratio in the range from 70/30 to 90/10, wherein the curing agent comprises a reaction mixture obtained from the reductive alkylation of ethane-1,2-diamine with benzaldehyde and hydrogen.

2. The curing agent as claimed in claim 1, wherein the curing agent comprises at least one further amine.

3. The curing agent as claimed in claim 2, wherein the further amine is selected from the group consisting of 2,2(4),4-trimethylhexane-1,6-diamine, 1,2-, 1,3- or 1,4-diaminocyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 2(4)-methyl-1,3-diaminocyclohexane, 1,3-bis(aminomethyl)benzene, polyoxypropylenediamines having an average molecular weight M.sub.n in the range from 200 to 500 g/mol, 3-(3-(dimethylamino)-propylamino)propylamine, bis(6-aminohexyl)amine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, dipropylenetriamine, N-(2-aminoethyl)propane-1,3-diamine, N,N′-bis(3-aminopropyl)ethylenediamine, adducts of these or further polyamines with mono- or diepoxides and Mannich bases.

4. The curing agent as claimed in claim 2, wherein the further amine is 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane.

5. The curing agent as claimed in claim 2, wherein the further amine is 1,3-bis(aminomethyl)benzene.

6. The curing agent as claimed in claim 2, wherein the further amine is triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine or N,N′-bis(3-aminopropyl)ethylenediamine.

7. The curing agent as claimed in claim 2, wherein the further amine is 3-(3-(dimethylamino)propylamino)propylamine.

8. An epoxy resin composition comprising a resin component comprising at least one epoxy resin and a curing agent component comprising the curing agent as claimed in claim 1.

9. The epoxy resin composition as claimed in claim 8, wherein the epoxy resin composition comprises at least one further constituent selected from the group consisting of thinners, accelerators and fillers.

10. A method comprising using the epoxy resin composition as claimed in claim 8 as coating, primer, adhesive, sealant, encapsulating compound, casting resin or as matrix for fiber composite materials.

11. An article obtained from the method as claimed in claim 10.

12. A method of coating, comprising the steps of (i) mixing the components of the epoxy resin composition as claimed in claim 8, (ii) applying the mixed composition to a substrate within the pot life, followed by the curing of the mixed composition.

13. A method of bonding, comprising the steps of (i) mixing the components of the epoxy resin composition as claimed in claim 8, (ii) applying the mixed composition within the pot life, either to at least one of the substrates to be bonded and joining the substrates to form a bond within the open time, or in a cavity or gap between two or more substrates and optionally inserting an anchor into the cavity or gap within the open time, followed by the curing of the mixed composition.

14. The curing agent as claimed in claim 1, wherein the curing agent contains less than 2% by weight of N,N-dibenzylethane-1,2-diamine.

15. A curing agent for epoxy resins comprising N-benzylethane-1,2-diamine and N,N′-dibenzylethane-1,2-diamine in a weight ratio in the range from 80/20 to 90/10.

16. The curing agent as claimed in claim 15, wherein the curing agent comprises at least one further amine.

17. The curing agent as claimed in claim 16, wherein the further amine is selected from the group consisting of 2,2(4),4-trimethylhexane-1,6-diamine, 1,2-, 1,3- or 1,4-diaminocyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, bis(4-aminocyclohexyl)methane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 2(4)-methyl-1,3-diaminocyclohexane, 1,3-bis(aminomethyl)benzene, polyoxypropylenediamines having an average molecular weight M.sub.n in the range from 200 to 500 g/mol, 3-(3-(dimethylamino)-propylamino)propylamine, bis(6-aminohexyl)amine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, dipropylenetriamine, N-(2-aminoethyl)propane-1,3-diamine, N,N′-bis(3-aminopropyl)ethylenediamine, adducts of these or further polyamines with mono- or diepoxides and Mannich bases.

18. An epoxy resin composition comprising a resin component comprising at least one epoxy resin and a curing agent component comprising the curing agent as claimed in claim 15.

19. The epoxy resin composition as claimed in claim 18, wherein the epoxy resin composition comprises at least one further constituent selected from the group consisting of thinners, accelerators and fillers.

20. The curing agent as claimed in claim 15, wherein the curing agent contains less than 2% by weight of N,N-dibenzylethane-1,2-diamine.

Description

EXAMPLES

(1) Working examples are adduced hereinafter, which are intended to elucidate the invention described. The invention is of course not limited to these described working examples.

(2) “AHEW” stands for amine hydrogen equivalent weight.

(3) “EEW” stands for epoxy equivalent weight.

(4) “Standard climatic conditions” refer to a temperature of 23±1° C. and a relative air humidity of 50±5%.

(5) Description of the Measurement Methods:

(6) Viscosity was measured on a thermostated Rheotec RC30 cone-plate viscometer (cone diameter 50 mm, cone angle 1°, cone tip-plate distance 0.05 mm, shear rate 10 s.sup.−1).

(7) Amine value was determined by means of titration (with 0.1 N HClO.sub.4 in acetic acid versus crystal violet).

Substances and Abbreviations Used

(8) TABLE-US-00001 Sikafloor ®-264N (A) Sikafloor ®-264N component A (RAL 5005), filled pigmented resin component of an epoxy resin floor coating, EEW 450 g/eq (from Sika) B-EDA N-benzylethane-1,2-diamine, prepared as described below, AHEW 50 g/eq DB-EDA N,N′-Dibenzylethane-1,2-diamine, prepared as described below, AHEW 120 g/eq B-EDA-mix Reaction mixture comprising N-benzyl- ethane-1,2-diamine and N,N′-dibenzyl- ethane-1,2-diamine in a weight ratio of 85/15, prepared as described below, AHEW 55 g/eq TEPA tetraethylenepentamine, AHEW 30 g/eq (technical grade, from Huntsman) IPDA 3-aminomethyl-3,5,5- trimethylcyclohexylamine, AHEW 42.6 g/eq (Vestamin ® IPD, from Evonik) Adduct-1 adduct of propylene-1,2-diamine and technical grade o-cresyl glycidyl ether, prepared as described below, AHEW 90 g/eq Ca nitrate solution 50% by weight of calcium nitrate tetrahydrate in water Ancamine ® K54 2,4,6-tris(dimethylaminomethyl)phenol (from Air Products)

Reaction Mixture Comprising N-Benzylethane-1,2-diamine (B-EDA Mix)

(9) A round-bottom flask was initially charged with 180.3 g (3 mol) of ethylene-1,2-diamine under a nitrogen atmosphere at room temperature. With good stirring, a solution of 106.0 g (1 mol) of benzaldehyde in 1200 ml of isopropanol was slowly added dropwise, and the mixture was stirred for 2 hours. The reaction mixture was then hydrogenated in a continuous hydrogenation apparatus with a Pd/C fixed bed catalyst at a hydrogen pressure of 80 bar, a temperature of 80° C. and a flow rate of 5 ml/min. To monitor the reaction, IR spectroscopy was used to check whether the imine band at about 1665 cm.sup.−1 had disappeared. Thereafter, the hydrogenated solution was concentrated on a rotary evaporator at 65° C., removing unreacted ethylene-1,2-diamine, water and isopropanol. The reaction mixture thus obtained was a clear, pale yellowish liquid having an amine value of 678 mg KOH/g and a content, determined by means of GC, of N-benzylethane-1,2-diamine of about 81% by weight (retention time 8.47-8.57 min) and N,N′-dibenzylethane-1,2-diamine of about 14% by weight (retention time 14.27 min). This corresponds to a weight ratio between N-benzylethane-1,2-diamine and N,N′-dibenzylethane-1,2-diamine of 85/15.

N-Benzylethane-1,2-diamine (B-EDA)

(10) 50 g of the reaction mixture comprising N-benzylethane-1,2-diamine (B-EDA-mix), prepared as described above, was distilled at 80° C. under reduced pressure, with collection of 31.3 g of distillate at a vapor temperature of 60 to 65° C. and 0.06 mbar. What was obtained was a colorless liquid having a viscosity of 8 mPa.Math.s at 20° C., an amine value of 750 mg KOH/g and a purity, determined by GC, of >97% (retention time 8.47-8.57 min).

N,N′-Dibenzylethane-1,2-diamine (DB-EDA)

(11) A round-bottom flask was initially charged with 30.1 g (0.5 mol) of ethylene-1,2-diamine under a nitrogen atmosphere at room temperature. With good stirring, a solution of 111.5 g (1.1 mol) of benzaldehyde in 1000 ml of isopropanol was slowly added dropwise, and the mixture was stirred for 2 hours. The reaction mixture was then hydrogenated in a continuous hydrogenation apparatus with a Pd/C fixed bed catalyst at a hydrogen pressure of 80 bar, a temperature of 80° C. and a flow rate of 5 ml/min. To monitor the reaction, IR spectroscopy was used to check whether the imine band at about 1665 cm.sup.−1 had disappeared. Thereafter, the hydrogenated solution was concentrated on a rotary evaporator at 65° C., removing unreacted benzaldehyde, water and isopropanol. The reaction mixture thus obtained was a clear, pale yellowish liquid. 100 g of this reaction mixture was distilled at 165° C. under reduced pressure, with collection of 90 g of distillate at a vapor temperature of 135° C. and 0.03 mbar. What was obtained was a colorless liquid having a viscosity of 31 mPa.Math.s at 20° C., an amine value of 460 mg KOH/g and a purity, determined by means of GC, of 96% (retention time 14.27 min).

(12) Adduct-1:

(13) An initial charge of 4.15 kg of propylene-1,2-diamine under a nitrogen atmosphere was heated to 70° C. and then, with good stirring, 2.93 kg of Araldite® DY-K (o-cresyl glycidyl ether, technical grade, from Huntsman) was added gradually, with the temperature of the reaction mixture being from 70 to 80° C. After 1 hour at 80° C., the reaction mixture was cooled down and the volatile constituents were removed by distillation by means of a thin-film evaporator (0.5-1 mbar, jacket temperature 115° C.).

(14) Production of Epoxy Resin Compositions:

EXAMPLES 1 TO 6

(15) For each example, the ingredients of the curing agent component indicated in table 1 were mixed in the indicated amounts (in parts by weight) by means of a centrifugal mixer (SpeedMixer™ DAC 150, FlackTek Inc.) and stored with the exclusion of moisture.

(16) The resin component used was Sikafloor®-264N comp. A (blue) (from Sika) in the amount specified in table 1 (in parts by weight).

(17) The two components of each composition were then processed by means of the centrifugal mixer to give a homogeneous liquid and this was tested immediately as follows:

(18) 10 minutes after mixing, the viscosity was measured at 20° C. (“Viscosity (10′)”). For the determination of Shore D hardness to DIN 53505, two cylindrical test specimens (diameter 20 mm, thickness 5 mm) in each case were produced. One was stored under standard climatic conditions and hardness was measured after 1 day and after 2 days (1 d SCC and 2 d SCC); the other was stored at 8° C. and 80% relative humidity and hardness was measured after 1 day and after 2 days in the cold state (1 d 8°/80% and 2 d 8°/80%).

(19) A first film was applied to a glass plate in a layer thickness of 500 μm, and this was stored/cured under standard climatic conditions. König hardness (König pendulum hardness, measured according to DIN EN ISO 1522) was determined on this film after 1 day (“König hardness (1 d SCC)”), after 2 days (“König hardness (2 d SCC)”), after 4 days (“König hardness (4 d SCC)”), after 7 days (“König hardness (7 d SCC)”) and after 14 days (“König hardness (14 d SCC)”). After 14 days, the appearance of the film was assessed (designated

(20) “Appearance (SCC)” in the table). A film was described as “nice” if it had a glossy and nontacky surface with no structure. “Structure” refers to any kind of marking or pattern on the surface. A film with a nontacky surface without structure and with reduced gloss was described as “matt”.

(21) A second film was applied to a glass plate in a layer thickness of 500 μm and immediately after application this was stored/cured for 7 days at 8° C. and 80% relative humidity and then for 2 weeks under standard climatic conditions. 24 hours after application, a polypropylene bottletop beneath which a damp sponge had been positioned was placed onto the film. After a further 24 hours, the sponge and the bottletop were removed and positioned at a new point on the film, from which it was in turn removed and repositioned after 24 hours, and this was done a total of 4 times. The appearance of this film was then assessed (designated “Appearance (8°/80%)” in the tables) in the same way as described for Appearance (SCC). Also reported in each case here was the number and kind of visible marks that had formed in the film as a result of the damp sponge and/or the bottletop on top. The number of white-colored spots was reported as “blushing”. The intensity of any ring-shaped impression formed by sinking of the first bottletop applied 24 h after application was reported as “ring”. Such a ring-shaped impression indicates that the coating is not ready to be walked upon. The König hardness was again determined on the films thus cured, in each case after 7 days at 8° C. and 80% relative humidity (“König hardness (7 d 8°/80%)”) and then after a further 2 days under SCC (“König hardness (+2 d SCC)”), 7 days under SCC (“König hardness (+7 d SCC)”), and 14 d under SCC (“König hardness (+14 d SCC)”).

(22) As a measure of yellowing, the change in color after stressing in a weathering tester was furthermore determined. For this, a further film was applied to a glass plate in a layer thickness of 500 μm and this was stored/cured under standard climatic conditions for 2 weeks and then stressed for 72 hours (Q-Sun (72 h)) at a temperature of 65° C. in a model Q-Sun Xenon Xe-1 weathering tester having a Q-SUN Daylight-Q optical filter and a xenon lamp having a light intensity of 0.51 W/m.sup.2 at 340 nm. The color difference ΔE of the thus stressed film versus the corresponding unstressed film was then determined using an NH310 colorimeter from Shenzen 3NH Technology Co. LTD equipped with silicon photoelectric diode detector, light source A, color space measurement interface CIE L*a*b*C*H*. ΔE values up to 5 represent slight yellowing.

(23) The results are reported in table 1.

(24) The examples labeled “(Ref.)” are comparative examples.

(25) TABLE-US-00002 TABLE 1 Composition and properties of examples 1 to 6. Example 1 4 5 (Ref.) 2 3 (Ref.) (Ref.) 6 Resin comp.: Sikafloor ® -264N (A) 450.0 450.0 450.0 450.0 450.0 450.0 Curing agent comp.: B-EDA 42.6 — 39.7 33.3 35.1 — DB-EDA — — 7.0 22.2 — — B-EDA-mix — 46.7 — — — 38.5 TEPA 4.5 4.5 4.5 4.5 4.5 4.5 Adduct-1 — — — — 13.5 13.5 Benzyl alcohol 10.0 10.0 10.0 10.0 10.0 10.0 Ca nitrate solution 2.0 2.0 2.0 2.0 2.0 2.0 Ancamine ® K54 2.0 2.0 2.0 2.0 2.0 2.0 Weight ratio .sup.1 100/0 85/15 85/15 60/40 100/0 85/15 Viscosity (10′) [Pa .Math. s] 1.9 1.8 1.8 1.8 2.5 2.3 Shore D  (1 d SCC) 76 72 72 67 66 63  (2 d SCC) 80 76 76 71 71 73 Shore D  (1 d 8°/80%) 42 43 49 17 38 35  (2 d 8°/80%) 72 73 75 55 65 64 König  (1 d SCC) 63 60 62 43 52 45 hardness [s]  (2 d SCC) 84 79 85 72 87 74  (4 d SCC) 102 92 99 88 104 92  (7 d SCC) 112 105 115 98 126 116  (14 d SCC) 119 115 116 101 150 133 Appearance (SCC) nice nice nice nice nice nice Q-Sun (72 h) ΔE 3.7 4.3 4.9 3.4 3.1 3.4 König h.  (7 d 8°/80%) 18 17 18 12 20 18 [s]  (+2 d SCC) 37 33 49 39 55 45  (+7 d SCC) 59 55 60 48 70 64 (+14 d SCC) 80 74 73 59 98 95 Appearance (8°/80%) matt nice nice nice matt nice Blushing 1 0 0 0 1 0 Ring slight none none severe average none .sup.1 weight ratio between N-benzylethane-1,2-diamine and N,N′-dibenzylethane-1,2-diamine