Curing agent for low-emission epoxy resin compositions

Abstract

A curing agent for epoxy resins, containing at least one amine adduct of formula (I) which can be obtained as an addition product of a mixture of a primary diamine, a monoalkylated other diamine and a polyepoxide. The curing agent makes it possible to produce low-odor, low-emission epoxy resin products, in particular coatings, which have a surprisingly low viscosity, a high curing rate, a high final hardness, and a surprisingly appealing surface.

Claims

1. A curing agent for epoxy resins comprising at least one adduct amine of the formula (I) ##STR00005## where A.sup.1 is an alkylene radical which has 6 to 15 carbon atoms and optionally has cyclic components and optionally secondary or tertiary amino groups, A.sup.2 is an alkylene radical different than A.sup.1 and that has 2 to 10 carbon atoms, Y is an alkyl or cycloalkyl or aralkyl radical having 1 to 20 carbon atoms, Z is a (p+q)-valent hydrocarbyl radical optionally containing ether oxygen and having a molecular weight in the range from 56 to 1,500 g/mol, and p and q are independently 1 or 2 or 3 and (p+q) is 2 or 3 or 4.

2. The curing agent as claimed in claim 1, wherein A.sup.1 is selected from the group consisting of 2-methyl-1,5-pentylene, 1,6-hexylene, 2,2(4),4-trimethyl-1,6-hexamethylene, 1,3-cyclohexylenebis(methylene), 1,4-cyclohexylenebis(methylene), 1,3-phenylenebis(methylene), 1,4-phenylenebis(methylene), 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, (1,5,5-trimethylcyclohexan-1-yl)methane-1,3, 4(2)-methyl-1,3-cyclohexylene, 3-aza-1,5-pentylene, 3,6-diaza-1,8-octylene, 3,6,9-triaza-1,11-undecylene, 3,6,9,12-tetraaza-1,14-tetradecylene, 3,6,9,12,15-pentaaza-1,17-heptadecylene, 4-aza-2,6-heptylene, 4-aza-1,7-heptylene, 4,7-diaza-1,10-decylene and 7-aza-1,13-tridecylene.

3. The curing agent as claimed in claim 1, wherein A.sup.2 is an alkylene radical having 2 to 6 carbon atoms.

4. The curing agent as claimed in claim 1, wherein A.sup.2 is 1,2-propylene and A.sup.1 is selected from the group consisting of 2-methyl-1,5-pentylene, 1,6-hexylene, 2,2(4),4-trimethyl-1,6-hexamethylene, 1,3-cyclohexylenebis(methylene), 1,4-cyclohexylenebis(methylene), 1,3-phenylenebis(methylene), 1,4-phenylenebis(methylene), 1,2-cyclohexylene, 1,3-cyclohexylene, 1,4-cyclohexylene, (1,5,5-trimethylcyclohexan-1-yl)methane-1,3, 4(2)-methyl-1,3-cyclohexylene, 3-aza-1,5-pentylene, 3,6-diaza-1,8-octylene, 3,6,9-triaza-1,11-undecylene, 3,6,9,12-tetraaza-1,14-tetradecylene, 3,6,9,12,15-pentaaza-1,17-heptadecylene, 4-aza-2,6-heptylene, 4-aza-1,7-heptylene, 4,7-diaza-1,10-decylene and 7-aza-1,13-tridecylene.

5. The curing agent as claimed in claim 1, wherein Y is a radical of the formula ##STR00006## where R.sup.1 is a hydrogen radical or is methyl or phenyl, and R.sup.2 is a five- or six- or seven-membered cycloalkyl or aryl radical which has 4 to 7 carbon atoms and is optionally alkyl-substituted.

6. The curing agent as claimed in claim 1, wherein Y is selected from the group consisting of 2-ethylhexyl, 2-phenylethyl, cyclohexylmethyl, benzyl, 1-phenylethyl and 1-naphthylmethyl.

7. The curing agent as claimed in claim 1, wherein Z is the residue of a di-, tri- or tetravalent aryl glycidyl ether after removal of the glycidoxy groups.

8. A process for producing the curing agent as claimed in claim 1, wherein an amine mixture comprising at least one amine of the formula (II) and at least one monoalkylated amine of the formula (III) is reacted with at least one glycidyl ether of the formula (IV). ##STR00007##

9. The process as claimed in claim 8, wherein the molar ratio of the sum total of amine of the formula (II) and amine of the formula (III) relative to the epoxy groups is in the range from 1.5/1 to 15/1.

10. The process as claimed in claim 8, wherein the amine mixture used in the process additionally comprises at least one dialkylated amine of the formula (IIIa)
Y-NH-A.sup.2-NH-Y(IIIa)

11. The process as claimed in claim 8, wherein the amine of the formula (III) used in the process and any amine of the formula (IIIa) additionally present are part of a reaction mixture from the partial alkylation of at least one amine of the formula A.sup.2(NH.sub.2).sub.2 with at least one alkylating agent.

12. A reaction product from the process as claimed in claim 8.

13. 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.

14. A method comprising applying the epoxy resin composition as claimed in claim 13 as a coating onto a substrate.

15. A cured composition obtained from the curing of an epoxy resin composition as claimed in claim 13.

Description

EXAMPLES

(1) Working examples are adduced hereinafter, which are intended to give detailed elucidation of the invention described. It will be appreciated that the invention is not restricted to these described working examples.

(2) AHEW stands for amine hydrogen equivalent weight.

(3) EEW stands for epoxy equivalent weight.

(4) Standard conditions refer to a temperature of 231 C. and a relative air humidity of 505%. SCC stands for standard climatic conditions.

(5) Description of Measuring 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 0.1N HClO.sub.4 in acetic acid versus crystal violet).

(8) Substances Used: Araldite GY 250: bisphenol A diglycidyl ether, EEW about 187.5 g/eq (from Huntsman) Araldite DY-E: monoglycidyl ether of C.sub.12 to C.sub.14 alcohols, EEW around 290 g/eq (from Huntsman) IPDA 3-aminomethyl-3,5,5-trimethylcyclohexylamine, AHEW 42.6 g/eq (Vestamin IPD from Evonik) 1,3-BAC: 1,3-bis(aminomethyl)cyclohexane, AHEW 35.5 g/eq (from Mitsubishi Gas Chemical) MXDA: 1,3-bis(aminomethyl)benzene, AHEW 34 g/eq (from Mitsubishi Gas Chemical) Cardanol: from cashewnutshell oil, comprising 3-(8,11,14-pentadecatrienyl)phenol as its main constituent, Cardolite NX-2026 (from Cardolite Corp.)

N-Benzylpropane-1,2-diamine

(9) A round-bottom flask was initially charged with 444.8 g (6 mol) of propane-1,2-diamine under a nitrogen atmosphere at room temperature. With good stirring, a solution of 212.2 g (2 mol) of benzaldehyde in 1500 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 90 bar, a temperature of 85 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 propane-1,2-diamine and isopropanol. A clear, pale yellowish liquid was obtained. 300 g of this were distilled at 80 C. under reduced pressure, with collection of 237.5 g of distillate at a vapor temperature of 60 to 63 C. and 0.08 to 0.09 bar. A colorless liquid having an amine value of 682 mg KOH/g was obtained, which, by .sup.1H NMR, was a mixture of N.sup.1-benzylpropane-1,2-diamine and N.sup.2-benzylpropane-1,2-diamine in a ratio of about 2/1 and had a GC purity of >97%.

(10) Production of Curing Agents Comprising Adduct Amines of the Formula (I):

(11) Adduct A1:

(12) An initial charge of 17.0 g (0.1 mol) of IPDA and 16.4 g (0.1 mol) of N-benzylpropane-1,2-diamine under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 C. After 1 hour at 80 0, the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 494 mg KOH/g, a viscosity of 2.03 Pa's at 20 C. and an AHEW of about 68.7 g/eq.

(13) Adduct A2:

(14) An initial charge of 25.6 g (0.15 mol) of IPDA and 8.2 g (0.05 mol) of N-benzylpropane-1,2-diamine under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 C. After 1 hour at 80 C., the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 497 mg KOH/g, a viscosity of 4.90 Pa.Math.s at 20 C. and an AHEW of about 64.2 g/eq.

(15) Adduct A3:

(16) An initial charge of 8.5 g (0.05 mol) of IPDA and 24.7 g (0.15 mol) of N-benzylpropane-1,2-diamine under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 C. After 1 hour at 80 C., the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 501 mg KOH/g, a viscosity of 1.04 Pa's at 20 C. and an AHEW of about 74.0 g/eq.

Preparation of Adducts without Adduct Amine of the Formula (I) Comparison

(17) Adduct R1:

(18) An initial charge of 34.1 g (0.2 mol) of IPDA under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 0. After 1 hour at 80 C., the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 497 mg KOH/g, a viscosity of 13.70 Pa-s at 20 C. and an AHEW of about 60.2 g/eq.

(19) Adduct R2:

(20) An initial charge of 32.9 g (0.2 mol) of N-benzylpropane-1,2-diamine under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 C. After 1 hour at 80 C., the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 503 mg KOH/g, a viscosity of 0.53 Pa-s at 20 C. and an AHEW of about 80.2 g/eq.

(21) Adduct R3:

(22) An initial charge of 17.0 g (0.1 mol) of IPDA and 13.6 g (0.1 mol) of MXDA under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 C. After 1 hour at 80 C., the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 534 mg KOH/g, a viscosity of 2.80 Pa.Math.s at 20 C. and an AHEW of about 55.7 g/eq.

(23) Adduct R4:

(24) An initial charge of 17.0 g (0.1 mol) of IPDA and 14.2 g (0.1 mol) of 1,3-BAC under a nitrogen atmosphere was heated to 70 C. and then, with good stirring, 10.7 g (0.057 mol of epoxy groups) of Araldite GY 250 was added gradually, with the temperature of the reaction mixture from 70 to 80 C. After 1 hour at 80 C., the reaction mixture was cooled down. What was obtained was a clear, pale yellowish liquid having an amine value of 529 mg KOH/g, a viscosity of 3.79 Pa.Math.s at 20 C. and an AHEW of about 56.5 g/eq.

Production of Epoxy Resin Compositions

Examples 1 to 16

(25) For each example, the ingredients specified in tables 1 and 2 were mixed in the specified amounts (in parts by weight) of the curing agent component by means of a centrifugal mixer (SpeedMixer DAC 150, FlackTek Inc.) and stored with exclusion of moisture.

(26) The ingredients of the resin component specified in tables 1 and 2 were likewise processed and stored.

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

(28) 10 minutes after mixing, the viscosity was determined at 20 C. (Viscosity (10)).

(29) A first film was coated onto a glass plate in a layer thickness of 500 m, and this was stored/cured standard climatic conditions. Knig hardness (Knig pendulum hardness, measured according to DIN EN ISO 1522) was determined on this film after 1 day (Knig hardness (1d SCC)), after 2 days (Knig hardness (2d SCC)), after 4 days (Knig hardness (4d SCC)), after 7 days (Knig hardness (7d SCC)) and after 14 days (Knig hardness (14d SCC)). After 14 days, the appearance of the film was assessed (designated Appearance (SCC) in the table). A nice film referred to one which was clear and had a shiny and nontacky surface with no structure. Structure refers to any kind of marking or pattern on the surface.

(30) A second film was coated onto a glass plate in a layer thickness of 500 m and, immediately after application, this was stored/cured at 8 C. and 80% relative humidity for 7 days and then under standard climatic conditions for 3 weeks. 24 hours after application, a polypropylene bottletop beneath which a small moist sponge had been positioned was placed onto the film. After a further 24 hours, the sponge and the lid were removed and positioned at a new point on the film, where it was removed again and repositioned after 24 hours, a total of 4 times. Subsequently, the appearance of this film was assessed (designated as Appearance (8/80%) in the tables), in the same way as described for Appearance (SCC). Also reported in each case here was the number of white marks that were visible in the film as a result of the moist sponge. Again, the K nig hardness was determined on the films thus cured, in each case after 7 days at 8 C. and 80% relative humidity (Knig hardness (7d 8/80%)), then after a further 2 days under SCC (Knig hardness (+2d SCC)), 7 days under SCC (Knig hardness (+7d SCC)) and 14 d under SCC (Knig hardness (+14d SCC)).

(31) A further measure of yellowing that was determined was the change in color after weathering stress in a weathering tester. For this purpose, a further film in a layer thickness of 500 m was coated onto a glass plate and stored/cured under standard climatic conditions for 2 weeks and then subjected to weathering stress in a weathering tester of the Q-Sun Xenon Xe-1 type with a Q-SUN Daylight-Q optical filter and a xenon lamp with a light intensity of 0.51 W/m.sup.2 at 340 nm at a temperature of 65 C. for 72 hours (Q-Sun (72 h)).

(32) Subsequently, the color difference E of the film thus subjected to weathering stress as compared with the corresponding unstressed film was determined by means of 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*. E values of 0.5 to 1.5 represent a minor difference in color, 1.5 to 3 a slight difference in color, 3 to 6 a distinct difference in color, and more than 6 a major difference in color.

(33) The results are reported in tables 1 to 2.

(34) The examples labeled (Ref.) are comparative examples.

(35) TABLE-US-00001 TABLE 1 Composition and properties of examples 1 to 8. Example 2 4 6 8 1 (Ref.) 3 (Ref.) 5 (Ref.) 7 (Ref.) Resin comp.: Araldite GY 250 167.2 167.2 167.2 167.2 167.2 167.2 167.2 167.2 Araldite DY-E 31.8 31.8 31.8 31.8 31.8 31.8 31.8 31.8 Curing agent comp.: Adduct A1 68.7 68.7 Adduct A2 64.2 Adduct A3 74.0 Adduct R1 30.1 30.1 45.2 15.1 Adduct R2 40.1 40.1 20.1 60.2 Benzyl alcohol 29.7 29.7 27.7 27.7 Cardanol 29.7 29.7 31.7 31.7 Viscosity (10) [Pa .Math. s] 1.15 1.27 2.02 2.17 1.50 1.81 1.57 1.70 Knig hardness [s] (1 d SCC) 27 29 63 78 45 36 49 43 (2 d SCC) 94 104 122 144 122 127 102 109 (4 d SCC) 164 161 162 158 174 168 150 140 (7 d SCC) 181 179 176 183 188 174 167 162 (14 d SCC) 190 185 189 192 206 196 162 179 Appearance nice nice nice nice nice nice nice nice (SCC) Q-Sun (72 h) E 2.1 2.8 2.3 2.2 2.3 2.1 2.1 3.1 Knig hardness [s] (7 d 8/80%) 38 32 59 60 46 36 45 38 (+2 d SCC) 123 136 127 118 130 134 119 127 (+7 d SCC) 164 176 155 168 168 167 154 155 (+14 d SCC) 179 193 167 179 178 179 155 162 Appearance nice nice nice sl. mk..sup.1 sl. mk..sup.1 matt/ nice nice (8/80%) sl. mk..sup.1 Number of marks 1 1 1 1 1 1 1 1 .sup.1slight marking on the surface

(36) TABLE-US-00002 TABLE 2 Composition and properties of examples 9 to 16 Example 9 10 11 12 13 14 15 16 (Ref.) (Ref.) (Ref.) (Ref.) (Ref.) (Ref.) (Ref.) (Ref.) Resin comp.: Araldite GY 250 167.2 167.2 167.2 167.2 167.2 167.2 167.2 167.2 Araldite DY-E 31.8 31.8 31.8 31.8 31.8 31.8 31.8 31.8 Curing agent comp.: Adduct R1 60.2 60.2 Adduct R2 80.2 80.2 Adduct R3 55.7 55.7 Adduct R4 56.5 56.5 Benzyl alcohol 25.8 34.4 23.9 24.2 Cardanol 25.8 34.4 23.9 24.2 Viscosity (10) [Pa .Math. s] 3.20 0.90 2.24 3.17 6.24 1.86 4.58 5.90 Knig hardness [s] (1 d SCC) 63 6 67 80 97 31 123 127 (2 d SCC) 140 25 111 108 148 71 148 153 (4 d SCC) 185 66 164 160 179 125 176 174 (7 d SCC) 195 94 179 178 198 145 179 180 (14 d SCC) 200 111 174 179 195 160 176 176 Appearance nice nice nice sl. mk..sup.1 nice nice sl. mk..sup.1 sl. mk..sup.1 (SCC) Q-Sun (72 h) E 1.8 3.8 5.2 3.4 2.3 3.1 3.8 2.1 Knig hardness [s] (7 d 8/80%) 57 11 49 60 70 34 70 83 (+2 d SCC) 126 55 92 97 109 95 105 109 (+7 d SCC) 154 123 140 150 132 119 139 91 (+14 d SCC) 175 122 154 154 136 120 154 126 Appearance matt nice matt/ matt matt nice mk..sup.2 matt (8/80%) mk..sup.2 Number of marks 4 none 4 4 4 1 4 4 .sup.1slight marking on the surface .sup.2hazy marking on the surface