CURING AGENT FOR EPOXY RESIN ADHESIVES

Abstract

A hardener for epoxy resins, containing at least one amine A1 of formula (I) and at least one amine A2 of formula (II), the weight ratio of amine A1 to amine A2 ranging between 20/1 and 1/2. The hardener allows the manufacture of low-emission epoxy resin adhesives having good workability, a sufficiently long pot-life and open time with rapid curing, high strength, low brittleness, high adhesion, in particular to steel, and a sufficiently high glass transition temperature.

Claims

1. A curing agent for epoxy resins, comprising at least one amine A1 of the formula (I) and at least one amine A2 of the formula (II) ##STR00002## where A is an alkylene radical that optionally contains nitrogen atoms or cyclic or aromatic components and has 2 to 10 carbon atoms, Y is an alkyl, cycloalkyl or aralkyl radical having 1 to 20 carbon atoms, x is 1 or 2, and B represents identical or different alkylene radicals selected from 1,2-ethylene, 1,2-propylene and 1,3-propylene, where the weight ratio between amine A1 and amine A2 is in the range from 20/1 to 1/2.

2. The curing agent as claimed in claim 1, wherein A is a divalent radical selected from the group consisting of 1,2-ethylene, 1,2-propylene, 1,3-propylene, 1,4-butylene, 1,3-butylene, 2-methyl-1,2-propylene, 1,3-pentylene, 1,5-pentylene, 2,2-dimethyl-1,3-propylene, 1,6-hexylene, 2-methyl-1,5-pentylene, 1,7-heptylene, 1,8-octylene, 2,5-dimethyl-1,6-hexylene, 1,9-nonylene, 2,2(4),4-trimethyl-1,6-hexylene, 1,10-decylene, 1,11-undecylene, 2-butyl-2-ethyl-1,5-pentylene, 1,12-dodecylene, 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, (1,5,5-trimethylcyclohexan-1-yl)methane-1,3,4(2)-methyl-1,3-cyclohexylene, 1,3-cyclohexylenebis(methylene), 1,4-cyclohexylenebis(methylene), 1,3-phenylenebis(methylene), 1,4-phenylenebis(methylene), 3-aza-1,5-pentylene, 3,6-diaza-1,8-octylene, 3,6,9-triaza-1,11-undecylene, 3-aza-1,6-hexylene and 3,7-diaza-1,9-nonylene.

3. The curing agent as claimed in claim 1, wherein A is 1,2-ethylene or 1,2-propylene.

4. The curing agent as claimed in claim 1, wherein Y is a radical selected from 2-ethylhexyl, 2-phenylethyl, benzyl, 1-naphthylmethyl and cyclohexylmethyl.

5. The curing agent as claimed in claim 1, wherein the amine A1 of the formula (I) is N-benzylethane-1,2-diamine.

6. The curing agent as claimed in claim 1, wherein the amine A2 of the formula (II) is 3-(3-(dimethylamino)propylamino)propylamine.

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

8. The curing agent as claimed in claim 7, wherein the further amine is an amine A3 of the formula (III).
Y—NH-A-NH—Y  (III)

9. The curing agent as claimed in claim 7, wherein the further amine is an amine A4 which is an aliphatic polyamine having at least two primary amino groups.

10. The curing agent as claimed in claim 9, wherein the amine A4 is a polyalkyleneamine.

11. 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.

12. The epoxy resin composition as claimed in claim 11, wherein it comprises at least one further constituent selected from the group consisting of thinners, accelerators and fillers.

13. A method comprising using the epoxy resin composition as claimed in claim 11 as adhesive, sealant, encapsulating compound, casting resin, coating, primer or as matrix for fiber composite materials.

14. A method of bonding, comprising the steps of (i) mixing the components of the epoxy resin composition as claimed in claim 11, (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 into 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.

15. An article obtained from the method as claimed in claim 14.

Description

EXAMPLES

[0136] 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.

“ANEW” stands for amine hydrogen equivalent weight.
“EEW” stands for epoxy equivalent weight.
“Standard climatic conditions” (“SCC”) refer to a temperature of 23±1° C. and a relative air humidity of 50±5%.

Description of the Measurement Methods:

[0137] 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).

[0138] Amine value was determined by means of titration (with 0.1N HClO.sub.4 in acetic acid versus crystal violet).

Substances and Abbreviations Used:

[0139] Sikadur®-30 (A) Sikadur®-30 component A, quartz-filled resin component of a structural epoxy resin adhesive, containing bisphenol A diglycidyl ether and butane-1,4-diol diglycidyl ether, EEW about 700 g/eq (from Sika) [0140] B-EDA N-benzylethane-1,2-diamine, prepared as described below, AHEW 50 g/eq [0141] DMAPAPA 3-(3-(dimethylamino)propylamino)propylamine, AHEW 53 g/eq (DMAPAPA, from Arkema). [0142] TEPA tetraethylenepentamine, AHEW about 30 g/eq (technical grade, from Huntsman) [0143] BHMT technical grade quality of bis(6-aminohexyl)amine with a purity in the range from 50% to 78% by weight, AHEW about 48 g/eq (Dytek® BHMT Amine (50-78%), from Invista) [0144] Quartz flour grain size 0 to 75 μm [0145] Quartz sand grain size 0.1 to 0.3 mm [0146] Precipitated chalk stearate-coated precipitated chalk (Socal® U1S2, from Solvay)

[0147] B-EDA is an amine A1 of the formula (I). DMAPAPA is an amine A2 of the formula (II).

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

[0148] 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. 50 g of this were 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 8.3 mPa.Math.s at 20° C., an amine value of 750 mg KOH/g and a purity, determined by GC, of >97%.

Production of Epoxy Resin Adhesives:

Examples 1 to 11

[0149] For each example, the ingredients of the curing agent component indicated in tables 1 to 2 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.

[0150] The resin component used was Sikadur®-30 component A (from Sika) in the amount specified in tables 1 and 2 (in parts by weight).

[0151] For each example, the resin and the curing agent component were then processed by means of the centrifugal mixer to give a homogeneous paste and this was immediately tested as follows:

[0152] Pot life was determined under standard climatic conditions by moving the mixed adhesive by means of a spatula every 5 min until the adhesive had thickened to such an extent that it was no longer processible.

[0153] Mechanical properties were tested by applying and curing the mixed adhesive under standard climatic conditions to a silicone mold to give dumbbell-shaped specimens having a thickness of 10 mm and a length of 150 mm with a gage length of 80 mm and a gage width of 10 mm. The tensile specimens were removed from the mold after a curing time of 7 days, and these were used to determine tensile strength and elongation at break to EN ISO 527 at a strain rate of 1 mm/min.

[0154] The characteristics of the surface were assessed on the dumbbell-shaped specimens to determine the mechanical properties on the side exposed to the air in the course of curing. A non-tacky surface was referred to as “smooth”, and a tacky surface as “sticky”. A tacky surface is a sign of blushing.

[0155] Lap shear strength on steel (LSS steel) was measured by producing multiple adhesive bonds, wherein the mixed adhesive was applied between two heptane-degreased steel sheets in a layer thickness of 0.5 mm with an overlapping bonding area of 10×25 mm. After a storage time of 7 days under standard climatic conditions, lap shear strength was determined to DIN EN 1465 at a strain rate of 10 mm/min.

[0156] Lap shear strength on carbon fiber composite (CFRP) (LSS CFRP) was measured by producing multiple adhesive bonds, wherein the mixed adhesive was applied between two heptane-degreased Sika® CarboDur® S512 lamellas in a layer thickness of 0.5 mm with an overlapping bonding area of 10×50 mm. After a storage time of 7 days under standard climatic conditions, lap shear strength was determined as described.

[0157] Compressive strength was determined by applying the mixed adhesive under standard climatic conditions in a silicone mold to give cuboids of dimensions 12.7×12.7×25.4 mm and curing them under standard climatic conditions. After 7 days, several such cuboids were removed from the mold and compressed to destruction as per ASTM D695 at a testing speed of 1.3 mm/min, reading off the compressive strength value at the maximum force in each case.

[0158] Tg (glass transition temperature) was determined by means of DSC on cured adhesive samples that had been stored under standard climatic conditions for 14 days with a Mettler Toledo DSC 3+700 instrument and the following measurement program: (1) −10° C. for 2 min, (2) −10 to 200° C. at a heating rate of 10 K/min (=1st run), (3) 200 to −10° C. at a cooling rate of −50 K/m in, (4) −10° C. for 2 min, (5) −10 to 180° C. at a heating rate of 10 K/min (=2nd run).

[0159] The results are reported in tables 1 to 2.

[0160] The examples labeled “(Ref.)” are comparative examples.

TABLE-US-00001 TABLE 1 Composition and properties of examples 1 to 6. 1 5 6 Example (Ref.) 2 3 4 (Ref.) (Ref.) Resin comp.: 300.0 300.0 300.0 300.0 300.0 300.0 Sikadur ®-30 (A) Curing agent comp.: 21.5 18.7 15.8 11.1 6.4 — B-EDA DMAPAPA — 3.0 6.0 11.0 16.0 22.7 Quartz flour 35.3 35.3 35.2 34.9 34.8 34.5 Quartz sand 28.2 28.0 28.0 28.0 27.8 27.8 Precipitated chalk 15.0 15.0 15.0 15.0 15.0 15.0 A1/A2 ratio.sup.1 — 6.2/1 2.6/1 1/1 1/2.5 — Pot life [h:min] 2:00 1:45 1:30 1:15 1:05 0:45 Tensile strength: 34 37 35 33 32 31 [MPa] Elongation at break: 0.3 0.3 0.3 0.2 0.2 0.2 [%] Surface smooth smooth smooth smooth sticky sticky LSS steel [MPa] 6.2 9.1 11.2 13.7 14.9 16.6 LSS CFRP [MPa] 8.3 8.4 8.5 8.2 8.1 9.5 Compressive 90 96 109 110 115 115 strength: [MPa] Tg 1st/2nd run [° C.] 48/57 52/58 58/60 60/59 55/38 45/32 .sup.1Weight ratio between amine A1 and amine A2

TABLE-US-00002 TABLE 2 Composition and properties of examples 7 to 11. Example 7 8 9 10 11 Resin comp.: 300.0 300.0 300.0 300.0 300.0 Sikadur ®-30 (A) Curing agent comp.: 13.6 10.8 10.8 7.1 5.6 B-EDA DMAPAPA 6.0 6.0 6.0 6.0 6.0 TEPA 1.5 3.0 — 3.0 3.0 BHMT — — 4.8 3.5 5.0 Quartz flour 35.2 36.5 34.7 36.6 36.6 Quartz sand 28.7 28.7 28.7 28.8 28.8 Precipitated chalk 15.0 15.0 15.0 15.0 15.0 A1/A2 ratio.sup.1 2.3/1   1.8/1   1.8/1   1.2/1     1/1.1 Pot life [h:min] 1:20 1:15 1:30 1:30 1:30 Tensile strength: [MPa] 36 33 40 37 35 Elongation at break: [%] 0.3 0.2 0.3 0.3 0.3 Surface smooth smooth smooth smooth smooth LSS steel [MPa] 10.6 9.9 12.5 13.7 15.2 LSS CFRP [MPa] 9.0 10.0 12.1 10.2 10.0 Compressive 111 107 111 109 110 strength: [MPa] Tg 1st/2nd run [° C.] 58/68 59/68 57/63 61/64 61/69 .sup.1Weight ratio between amine A1 and amine A2