THERMOSETTING EPOXY RESIN COMPOSITION HAVING LOW CURING TEMPERATURE AND GOOD STORAGE STABILITY

Abstract

A thermosetting epoxy resin composition including, as curing agent, a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide and pimelic dihydrazide, in combination with a specific urea accelerator, which features good storage stability and a low curing temperature. The epoxy resin composition is especially suitable for use as bodywork adhesive.

Claims

1. A thermosetting epoxy resin composition comprising a) at least one epoxy resin A having an average of more than one epoxy group per molecule; b) at least one curing agent B for epoxy resins, where the curing agent B is a dihydrazide selected from the group consisting of glutaric dihydrazide, adipic dihydrazide and pimelic dihydrazide; and c) at least one accelerator C of the formula (Ia) or (Ib) ##STR00014## where R.sup.1 is H or an n-valent aliphatic, cycloaliphatic or araliphatic radical; R.sup.2 and R.sup.3 are either each independently an alkyl group or aralkyl group; or together are a divalent aliphatic radical which has 3 to 20 carbon atoms and is part of an optionally substituted heterocyclic ring having 5 to 8, preferably 6,8 ring atoms; R.sup.1′ is an n′-valent aliphatic, cycloaliphatic or araliphatic radical; R.sup.2′ is an alkyl group or aralkyl group or alkylene group; R.sup.3′ is independently H or an alkyl group or aralkyl group; and n and n′ each have a value of 1 to 4.

2. The thermosetting epoxy resin composition as claimed in claim 1, wherein R.sup.1 is H, and R.sup.2 and R.sup.3 are each a methyl, ethyl or propyl group, and n=1.

3. The thermosetting epoxy resin composition as claimed in claim 1, wherein R.sup.1 is ##STR00015## and R.sup.2 and R.sup.3 are each a methyl, ethyl or propyl group, and n=2.

4. The thermosetting epoxy resin composition as claimed in claim 1, wherein the ratio of the proportion of epoxy groups of the epoxy resin A in mol/proportion of dihydrazide in mol is 3-5.

5. The thermosetting epoxy resin composition as claimed in claim 1, wherein the dihydrazide has a median particle size D.sub.50 of ≤100 μm.

6. The thermosetting epoxy resin composition as claimed in claim 1, wherein the thermosetting epoxy resin composition includes less than 0.5% by weight, based on the total weight of the epoxy resin composition, of dicyandiamide.

7. The thermosetting epoxy resin composition as claimed in claim 1, wherein the ratio of the proportion of accelerator C in grams per mole of epoxy groups of the epoxy resin A is 0.01-0.5 g/mol of epoxy groups.

8. The thermosetting epoxy resin composition as claimed in claim 1, wherein the thermosetting epoxy resin composition additionally includes at least one toughness improver D selected from the group consisting of terminally blocked polyurethane polymers D1, liquid rubbers D2 and core-shell polymers D3.

9. The thermosetting epoxy resin composition as claimed in claim 1, wherein the proportion of the epoxy resin A is 10-60% by weight, based on the total weight of the epoxy resin composition.

10. The thermosetting epoxy resin composition as claimed in claim 1, wherein the epoxy resin composition has a viscosity at 25° C. of 500-3000 Pa*s.

11. The thermosetting epoxy resin composition as claimed in claim 1, wherein the thermosetting epoxy resin composition is a one-component thermosetting adhesive.

12. A process for the adhesive bonding of heat-stable substrates, comprising the stages of: i) applying a thermosetting epoxy resin composition as claimed in claim 1 to the surface of a heat-stable substrate S1; ii) contacting the thermosetting epoxy resin composition applied with the surface of a further heat-stable substrate S2; iii) heating the composition to a temperature of 100-220° C.; in which the substrate S2 consists of the same material as or a different material from the substrate S1.

13. The process as claimed in claim 12, wherein, in step iii) of heating the composition to a temperature of 100-220° C., the composition is left at the aforementioned temperature for 10 min-6 h.

14. An adhesive-bonded article obtained from a process as claimed in claim 12.

Description

EXAMPLES

[0192] Some examples which further illustrate the invention, but which are not intended to restrict the scope of the invention in any way, are cited below.

[0193] Preparation of a Toughness Improver (“D-1”)

[0194] 150 g of poly-THF 2000 (OH number 57 mg/g KOH) and 150 of Liquiflex H (OH number 46 mg/g KOH) were dried under vacuum at 105° C. for 30 minutes. Once the temperature had been reduced to 90° C., 61.5 g of IPDI and 0.14 g of dibutyltin dilaurate were added. The reaction was carried out under vacuum at 90° C. until the NCO content was constant at 3.10% after 2.0 h (calculated NCO content: 3.15%). Subsequently, 96.1 g of cardanol were added as blocking agent. Stirring was continued at 105° C. under vacuum until it was no longer possible to detect any free NCO. The product was used as such as toughness improver D-1.

TABLE-US-00001 A-Liquid liquid epoxy resin, D.E.R. 331 (bisphenol A diglycidyl resin ether), Dow A-Solid solid epoxy resin (bisphenol A diglycidyl ether-based), resin Dow B1 adipic dihydrazide, Technicure ADH-J (median particle size D.sub.50 of 2.4 μm), A&C Catalysts Inc. B2 adipic dihydrazide, Technicure ADH (median particle size D.sub.50 of 15 μm), A&C Catalysts Inc. B3 adipic dihydrazide, ESIM ADH (median particle size D.sub.50 of 18 μm), ESIM Chemicals B4 adipic dihydrazide, Innochem ADH (median particle size D.sub.50 of 22 μm), Innochem B5 adipic dihydrazide, Harke ADH (median particle size D.sub.50 of 32.5 μm), Harke B6 adipic dihydrazide, Novasol ADH (median particle size D.sub.50 of 42 μm), Novasol Chemie GmbH C1 N,N-dimethylurea (=1,1-dimethylurea), n = 1, R.sup.1 = H, R.sup.2 = R.sup.3 = CH.sub.3, Sigma-Aldrich, Switzerland C2 3-(5-(3,3-dimethylureido)-1,3,3-trimethylcyclohexyl)-N,N- dimethylpropanamide (=Dyhard UR800), n = 2, R.sup.1 = [00012] R.sup.2 = R.sup.3 = CH.sub.3 [00013] C3 diuron, (3-(3,4-dichlorophenyl)-1,1-dimethylurea, Sigma-Aldrich, Switzerland C4 1,1′-(methylenebis(4,1-phenylene))bis(3,3-dimethylurea) Dicy dicyandiamide, Dyhard 100 SF (median particle size D.sub.50 of 2-3 μm), AlzChem Filler Mixture of calcium carbonate, calcium oxide, fumed silica Poly-THF 2000 (difunctional polybutylene glycol) (OH equivalent weight = about 1000 g/OH equivalent), BASF Liquiflex H (hydroxyl-terminated polybutadiene) (OH equivalent weight = about 1230 g/OH equivalent), Krahn Isophorone diisocyanate (=“IPDI”), Evonik Cardolite NC-700 (cardanol, meta-substituted alkenylmonophenol), Cardolite Raw materials used.

[0195] Production of the Compositions

[0196] The reference compositions R1-R8 and the inventive compositions E1 to E8 were produced according to the figures in table 1. The stated amounts in table 1 are in parts by weight.

[0197] The ratio of the proportion of epoxy groups of the epoxy resin A in mol/proportion of dihydrazide in mol is called “B index” in table 1 and reported in [mol of EP groups/mol of dihydrazide].

[0198] The ratio of the proportion of accelerator C in grams per mole of epoxy groups of the epoxy resin A is called “C index” in table 1 and reported in [g of accelerator/mol of EP groups].

[0199] Test Methods:

Modulus of Elasticity (DIN EN ISO 527)

[0200] An adhesive sample was pressed between two Teflon papers to a layer thickness of 2 mm. After curing at 175° C. for 35 min, the Teflon papers were removed and the specimens were die-cut to the DIN standard state. The test specimens were examined under standard climatic conditions at a strain rate of 2 mm/min. 0.05-0.25% modulus of elasticity was determined to DIN EN ISO 527.

Lap Shear Strength (ZSF) (DIN EN 1465)

[0201] Cleaned test specimens of Elo H420 steel (thickness 1.5 mm) that had been reoiled with Anticorit PL 3802-39S were bonded with the adhesive over a bonding area of 25×10 mm with glass beads as spacer in a layer thickness of 0.3 mm, and cured at oven temperature 140° C. for 10 min.

[0202] Lap shear strength was determined on a tensile tester at a strain rate of 10 mm/min in a triple determination to DIN EN 1465.

Impact Peel Strength (IP RT) (to ISO 11343)

[0203] The specimens were produced with the adhesive and DC04+ZE steel with dimensions of 90×20 x 0.8 mm. The bonding area here was 20×30 mm at a layer thickness of 0.3 mm with glass beads as spacer. The samples were cured for 10 minutes at oven temperature 140° C. Impact peel strength was measured at 23° C. as a triple determination on a Zwick 450 impact pendulum. The impact peel strength reported is the average force in N/mm under the measurement curve from 25% to 90% to ISO11343.

Viscosity/Storage Stability of Adhesives

[0204] Viscosity measurements of the adhesives were effected 1 d after production on an Anton Paar MCR 101 rheometer by oscillation using a plate-plate geometry at a temperature of 25° C. with the following parameters: 5 Hz, 1 mm gap, plate diameter 25 mm, 1% deformation. The measurement is displayed in table 2 under “Visco initial 25° C.”.

[0205] For assessment of the storage stability of the adhesives, the viscosity measurement was repeated after storage at the specified temperature for a specified time in weeks, and the percentage rise in viscosity that results after the storage was ascertained. The measured viscosity in Pa*s measured at a temperature of 25° C. after storage for 1 week at 50° C. and 60° C. is displayed in table 2 under “Visco 1W 50 25° C.” and “Visco 1W 60 25° C.” respectively. The value between parentheses shows the percentage rise in viscosity.

TABLE-US-00002 TABLE 1 R1 E1 E2 R2 R3 R4 R5 R6 R7 A- 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 Liq- uid resin A- 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 Sol- id resin D1 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 Dicy 2.87 2.87 2.87 2.87 C1 0.02 0.02 C2 0.01 0.01 C3 0.02 0.02 C4 0.01 B1 8.19 8.19 8.19 8.19 8.19 B2 B3 B4 B5 B6 Fill- 44.54 44.54 44.54 44.54 44.54 44.54 44.54 44.54 44.54 ers Sum: 101.73 101.75 101.74 101.75 101.74 96.41 96.43 96.42 96.43 B 4 4 4 4 4 in- dex C 0.1 0.05 0.1 0.05 0.1 0.05 0.1 in- dex R8 E3 E1 E4 E5 E6 E7 E8 A- 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 Liquid resin A- 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 Solid resin D1 12.00 12.00 12.00 12.00 12.00 12.00 12.00 12.00 Dicy 2.87 1.44 C1 0.02 0.02 0.02 0.02 0.02 0.02 0.02 C2 C3 C4 0.01 B1 8.19 B2 4.10 8.19 B3 8.19 B4 8.19 B5 8.19 B6 8.19 Fillers 44.54 44.54 44.54 44.54 44.54 44.54 44.54 44.54 Sum: 96.42 99.10 101.75 101.75 101.75 101.75 101.75 101.75 B 2 4 4 4 4 4 4 index C 0.05 0.1 0.1 0.1 0.1 0.1 0.1 0.1 index

TABLE-US-00003 TABLE 2 R1 E1 E2 R2 R3 R4 R5 R6 R7 R8 E3 E1 E4 E5 E6 E7 E8 Modulus of 3470 3430 3450 3570 3640 n.d. n.d. n.d. n.d. n.d. 3720 elasticity (35′ 175° C.) LSS (10′ 13.7 ± 21.4 ± 17.3 ± 24.2 ± 20.2 ± n.c. n.c. n.c. n.c. n.c. 19.0 ± 21.4 ± 19.5 ± 18.1 ± 19.2 ± 17.5 ± 12.7 ± 140° C.) 1.3 0.5 0.6 0.5 0.9 1.2 0.5 0.7 0.5 0.4 0.8 1.7 IP RT (10′ 1.4 ± 8.7 ± 4.3 ± 9.5 ± 9.8 ± n.c. n.c. n.c. n.c. n.c. 5.2 ± 140° C.) 1.8 1.2 1.3 0.1 0.2 0.4 Visco 1890 2790 1900 1940 2110 n.d. n.d. n.d. n.d. n.d. 2370 2790 2110 2110 2120 2250 2430 initial 25° C. Visco 1W 2160 2610 2240 2710 2840 n.d. n.d. n.d. n.d. n.d. 2590 2610 2500 2600 2700 2500 2650 50 25° C. (+14) (-6) (+18) (+40) (+35) (+9) (-6) (+18) (+23) (+27) (+11) (+9) Visco 4450 4070 3520 c. c. n.d. n.d. n.d. n.d. n.d. 5340 4070 7470 4610 10700 8990 5310 1W60 (+135) (+46) (+85) (+125) (+46) (+254) (+118) (+405) (+300) (+119) 25° C. n.c. = not cured c. = cured n.d. = not determined