ONE COMPONENT THERMOSETTING EPOXY RESIN COMPOSITIONS

Abstract

A one-component thermosetting epoxy resin includes compositions that are particularly suitable for the bonding of substrates having different coefficients of thermal expansion, especially in the shell construction of modes of transport or white goods. The one-component thermosetting epoxy resin composition includes a) at least one epoxy resin A having an average of more than one epoxy group per molecule; b) at least one 2,4-diamino-1,3,5-triazine GU containing, in the 6 position, —an alkyl radical having 1 to 20 carbon atoms, in which one hydrogen atom in the α position has been replaced by a 2,4-diamino-1,3,5-triazin-6-yl radical, a cycloalkyl radical having 5 to 12 carbon atoms or -an aryl radical having 6 to 12 carbon atoms; and c) at least one toughness improver D, which is a terminally blocked polyurethane polymer D1.

Claims

1. A one-component 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 2,4-diamino-1,3,5-triazine GU containing, in the 6 position, an alkyl radical having 1 to 20 carbon atoms, in which one hydrogen atom in the α position has been replaced by a 2,4-diamino-1,3,5-triazin-6-yl radical, a cycloalkyl radical having 5 to 12 carbon atoms or an aryl radical having 6 to 12 carbon atoms; c) at least one toughness improver D, which is a terminally blocked polyurethane polymer D1; and wherein the weight ratio of the at least one epoxy resin A having an average of more than one epoxy group per molecule to the at least one toughness improver D is 0.4-3.3.

2. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein the terminally blocked polyurethane polymer D1 is a terminally blocked polyurethane prepolymer of the formula (I) ##STR00012## where R.sup.1 is a p-valent radical of a linear or branched polyurethane prepolymer terminated by isocyanate groups after the removal of the terminal isocyanate groups; p has a value of 2 to 8; and R.sup.2 is a blocking group which is eliminated at a temperature exceeding 100° C.

3. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein b) at least one 2,4-diamino-1,3,5-triazine GU is a 2,4-diamino-1,3,5-triazine (GU) containing, in the 6 position, an alkyl radical having 1 to 20 carbon atoms, in which there is a hydrogen atom in the α position; or an aryl radical having 6 to 12 carbon atoms.

4. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein the b) at least one 2,4-diamino-1,3,5-triazine GU is selected from the list consisting of 6-nonyl-2,4-diamino-1,3,5-triazine (caprinoguanamine), 6-phenyl-2,4-diamino-1,3,5-triazine (benzoguanamine) and 6-methyl-2,4-diamino-1,3,5-triazine (acetoguanamine).

5. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein the molar ratio of the molar amount of 2,4-diamino-1,3,5-triazine GU to the molar amount of epoxy groups in the epoxy resin A is 3.8-4.2.

6. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein b) at least one 2,4-diamino-1,3,5-triazine GU is a 2,4-diamino-1,3,5-triazine (GU) containing, in the 6 position, an aryl radical having 6 to 12 carbon atoms, and the one-component thermosetting epoxy resin composition further comprises dicyandiamide.

7. The one-component thermosetting epoxy resin composition as claimed in claim 6, wherein the molar ratio of 2,4-diamino-1,3,5-triazine GU to dicyandiamide is 9.0-2.0.

8. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein the weight ratio of the at least one epoxy resin A having an average of more than one epoxy group per molecule to the at least one toughness improver D is 0.55-2.4.

9. The one-component thermosetting epoxy resin composition as claimed in claim 8, wherein the weight ratio of the at least one epoxy resin A having an average of more than one epoxy group per molecule to the at least one toughness improver D is 1.0-1.6.

10. The one-component thermosetting epoxy resin composition as claimed in claim 1, wherein the epoxy resin composition includes less than 5% by weight of curing agents for epoxy resins selected from the list consisting of anhydrides of polybasic carboxylic acids and dihydrazides, based on the total weight of the epoxy resin composition.

11. A method of adhesive bonding of heat-stable substrates, comprising the steps of: a) applying a thermosetting epoxy resin composition as claimed in claim 1 to the surface of a heat-stable substrate S1; b) contacting the thermosetting epoxy resin composition applied with the surface of a further heat-stable substrate S2; c) heating the epoxy resin composition to a temperature of 100 to 220° C.; d) cooling the epoxy resin composition to a temperature of less than 50° C.; e) reheating the epoxy resin composition to a temperature of 100 to 220° C.; f) recooling the epoxy resin composition to a temperature of less than 50° C.; g) reheating the epoxy resin composition to a temperature of 100 to 220° C.

12. The method as claimed in claim 11, wherein, in step c) and in step e), heating the epoxy resin composition, the epoxy resin composition is left at the temperature specified.

13. The method as claimed in claim 11, wherein a local transport step takes place between steps c) and e) and with the composite of the epoxy resin composition with the heat-stable substrates S1 and S2.

14. An adhesive-bonded article obtained from the method as claimed in claim 11.

15. A method of using a thermosetting epoxy resin composition as claimed in claim 1, the method comprising applying the thermosetting epoxy resin composition as a one-component thermosetting adhesive in vehicle construction or sandwich panel construction.

Description

EXAMPLES

[0217] 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.

Determination of Isocyanate Content

[0218] The isocyanate content was determined in % by weight by means of a back-titration with di-n-butylamine used in excess and 0.1 M hydrochloric acid. All determinations were conducted in a semi-manual manner on a Mettler-Toledo DL50 Graphix titrator with automatic potentiometric endpoint determination. For this purpose, 600-800 mg in each case of the sample to be determined was dissolved while heating in a mixture of 10 ml of isopropanol and 40 ml of xylene, and then reacted with a solution of dibutylamine in xylene. Excess di-n-butylamine was titrated with 0.1 M hydrochloric acid, and the isocyanate content was calculated therefrom.

Level of Force

[0219] The level of force was determined as described above under “Description of test method for the level of force”. A triple determination was conducted for each epoxy resin composition. The level of force is the force measured at the end of the cooling phase at 25° C., i.e. on attainment of a longitudinal expansion of 2.145 mm for the 1st cure or 1.820 mm for the 3rd cure.

Tensile Strength (ZF), Elonqation at Break (BD) and Modulus of Elasticity (DIN EN ISO 527)

[0220] 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. Tensile strength, elongation at break and the 0.05-0.25% modulus of elasticity were measured to DIN EN ISO 527.

Tensile Shear Strength (ZSF) (DIN EN 1465)

[0221] Cleaned test specimens of H420+Z steel (thickness 1.2 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 1.5 mm, and cured under the curing conditions specified.

[0222] Curing conditions: a) 35 min at oven temperature 175° C.

[0223] 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.

T-Peel Strength (DIN 53281)

[0224] 130×25 mm test sheets of DC-04+ZE steel (thickness 0.8 mm) were prepared. Test sheets were processed at a height of 30 mm with a suitable die-cutting machine (90°). The cleaned 100×25 mm surfaces that had been reoiled with Anticorit PL 3802-39S were bonded with the adhesive with glass beads as spacer in a layer thickness of 0.3 mm, and cured for a dwell time of 35 min from attainment of oven temperature 175° C. T-peel strength was determined on a tensile testing machine at a strain rate of 100 mm/min in a duplicate determination as peel force in N/mm in the traversed distance range from ⅙ to ⅚ of the distance covered.

Impact Peel Strength (IP) (to ISO 11343)

[0225] The specimens were produced with the adhesive and DC04+ZE steel with dimensions of 90×20×0.8 mm. The bonding area here was 20×30 mm at a layer thickness of 0.3 mm with glass beads as spacer. Impact peel strength was measured in each case at the temperatures specified (23° C., −30° C.) as a triple determination on a Zwick 450 impact pendulum at 2 m/s. The impact peel strength reported is the average force in N/mm under the measurement curve from 25% to 90% to ISO11343.

[0226] The adhesives were cured at oven temperature 175° C. for 35 min.

[0227] The following commercial products were used for the production of the impact modifier SM:

TABLE-US-00001 TABLE 1 Compound Description Manufacturer BHT (Ionol ® CP) Butylhydroxytoluene Evonik stabilizer PolyTHF ® 2000 Difunctional BASF polytetramethylene ether glycol having a molar mass of 2000 g/mol Poly bd ® R45V Hydroxyl-terminated Cray Valley polybutadiene having a molar mass of 2800 g/mol, OH functionality about 2.4-2.6 Vestanat IPDI Isophorone diisocyanate Evonik Dibutyltin dilaurate Catalyst Thorson 4-Methoxyphenol Blocking agent Solvay

[0228] 200 g of PolyTHF 2000, 200 g of Poly bd R45V and 2.00 g BHT as stabilizer were dewatered at 90° C. under reduced pressure with minimal stirring for 1 h. Subsequently, 80.64 g of isophorone diisocyanate (IPDI) and 0.053 g of dibutyltin dilaurate (DBTDL) were added. The reaction was conducted under moderate stirring at 90° C. under reduced pressure for 2 h in order to obtain an isocyanate-terminated polymer: Measured free NCO content: 2.81%.

[0229] To the resultant NCO-terminated polymer were added 0.106 g of dibutyltin dilaurate (DBTDL) and 47.93 g of 4-methoxyphenol (HQMME), and the isocyanate groups were depleted by reaction at 110° C. under reduced pressure for 5 h. Measured free NCO content: (directly after preparation) 2.82%, (1 day after preparation) 0.09%.

Adhesive Compositions Z1 to Z11, Z2a/Z6a and Z2b/Z6b/Z7b

[0230] The impact modifier SM was used in each case for production of epoxy resin compositions according to table 2. The proportions of the compounds present in the epoxy resin compositions are displayed in parts by weight in table 2.

TABLE-US-00002 TABLE 2 Z1-Z11 Z2a, Z6a Z2b, Z6b, Z7b Parts by Parts by Parts by weight weight weight Chemical composition Function 38 53 33 Epoxy resin based on Epoxy resin matrix bisphenol A, liquid 12 12 12 Epoxy resin based on Epoxy resin matrix bisphenol A, solid 0.5 0.5 0.5 p-tert-Butylphenyl Reactive diluent glycidyl ether 35 20 40 Blocked polyurethane, SM-X Impact modifier * * * Dicyandiamide Curing agent * * * Benzoguanamine Curing agent * * * Acetoguanamine Curing agent * * * Caprinoguanamine Curing agent ** — — Substituted urea Accelerator 5.0 5.0 5.0 CaCO.sub.3 Filler 6.0 6.0 6.0 Calcium oxide Moisture scavenger 8.0 8.0 8.0 Fumed silica Thixotropic agent 0.3 0.3 0.3 Carbon black Coloring * according to table 3, ** only Z1 additionally includes 0.8 part by weight of a substituted urea

[0231] The respective epoxy resin compositions were mixed in a planetary mixer in a batch size of 350 g. For this purpose, the mixing vessel was filled with the liquid components, followed by the solid components, and they were mixed at 70° C. under reduced pressure. During the mixing operation (about 45 min), the vacuum was broken several times and the mixing tool wiped clean. After a homogeneous mixture had been obtained, the epoxy resin composition was dispensed into cartridges and stored at room temperature.

[0232] Table 3 shows the amount of 2,4-diamino-1,3,5-triazine GU, or dicyandiamide (Dicy), additionally added to the epoxy resin compositions in table 2, in parts by weight.

[0233] “Curing agent/EP” describes the ratio of the total amount of 2,4-diamino-1,3,5-triazine GU plus, if appropriate, the total amount of dicyandiamide to the total amount of epoxy groups in the epoxy resin A for a stoichiometric curing necessary ratio, in %. 100% corresponds to stoichiometric curing. For this purpose, a curing agent functionality of 4 is assumed for 2,4-diamino-1,3,5-triazine GU, and a curing agent functionality of 5.5 for dicyandiamide.

[0234] “GU/Dicy” denotes the molar ratio of 2,4-diamino-1,3,5-triazine GU to dicyandiamide.

[0235] “A/D” describes the weight ratio of the at least one epoxy resin A having an average of more than one epoxy group per molecule to the at least one toughness improver D.

[0236] Table 4 shows the results of the evaluation of the epoxy resin compositions obtained.

[0237] The measurements under “Adhesive properties after 1st cure 35 min/175° C.” were obtained by means of test specimens that were produced by means of the step of “Simulation of the cure state after cathodic electrocoating oven” 4A.) (1st cure), as described above under “Test specimens used and preparation thereof” in “Preparation”.

[0238] The measurements under “Adhesive properties after 1st cure 35 min/175° C.+2nd cure 35 min/160° C.+3rd cure 35 min/165° C.” were obtained by means of test specimens that were produced by means of the step of “Simulation of the cure state after passing through all process ovens” 4B.) (3rd cure), as described above under “Test specimens used and preparation thereof” in “Preparation”.

[0239] “Blisters” refers to the isolated occurrence of blisters owing to evolution of gas during curing in the fracture profile of the cured test specimens. These are disadvantageous in that their resultant defects (cavities) can have an adverse effect on mechanical properties.

[0240] FIGS. 1 to 4 show the evolution of the level of force during step 5.) Cooling of the samples after the simulation of the cure state 4A.) (1st cure), or 4B.) (3rd cure), as described above under “Test specimens used and preparation thereof” in “Preparation”.

TABLE-US-00003 TABLE 3 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10 Z11 Z2a Z6a Z2b Z6b Z7b Dicy 3.57 3.57 — — — 0.71 1.07 0.71 1.07 0.71 1.07 4.81 0.96 3.16 0.63 0.95 Benzo- — — 10.94 — — 8.75 7.66 — — — — — 11.79 — 7.74 6.77 guanamine Aceto- — — — 7.31 — — — 5.85 5.12 — — — — — — — guanamine Caprino- — — — — 13.87 — — — — 11.10  9.71 — — — — — guanamine Curing 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% agent/EP GU/Dicy — — — — — 12.3  7.2  — — — — — 12.3 — 12.3  7.1  A/D 1.43 1.43  1.43 1.43  1.43 1.43 1.43 1.43 1.43 1.43 1.43 3.25 3.25 1.13 1.13 1.13

TABLE-US-00004 TABLE 4 Z1 Z2 Z3 Z4 Z5 Z6 Z7 Z8 Z9 Z10 Z11 Z2a Z6a Z2b Z6b Z7b Adhesive properties after 1st cure 35 min/175° C. Modulus of 1070 1030 60 970 568 606 1000 1170 1110 929 943 1730 1680 842 384 619 elasticity [MPa] ZF [MPa] 25 27 1.3 18 10 12 22 23 23 19 20 38.1 3 22.5 10 13 BD [%] 20 21 240 6 40 40 25 7 11 16 21 8.3 0.2 40.9 100 83 ZSF [MPa] 25.7 26.8 6.0 17.4 12.9 18.5 23.3 25.4 25.7 23.8 24.8 29.1 19.6 24.6 18 19.8 IP 23° C. 49.6 45.3 1.6 33.7 6.2 41 47 40.6 45.4 39 40.2 43.8 7 52.7 45.2 49.2 IP −30° C. 51.2 46.8 0.2 17.7 0.2 0 8.3 33.6 39.4 0 0 29.5 0.4 55.2 0 14.5 T-peel 11.1 12.2 2.0 5.7 3 11.1 11.9 10.7 10 6.2 6.1 7.3 3.3 12.8 11.6 12.3 Blisters − − + + + − − + − + − − − − − − Adhesive properties after 1st cure 35 min/175° C. + 2nd cure 35 min/160° C. + 3rd cure 35 min/165° C. Modulus of 1060 1000 1060 1080 998 1070 1200 1150 1080 1030 1050 1750 2090 830 848 871 elasticity [MPa] ZF [MPa] 26 27 22 22 21 22.7 26 23 23 22.4 23 39.3 42.2 23.2 19 20 BD [%] 25 21 7 6 13 15.5 19 9 9 9.1 15 7.6 6.5 47.7 28 31 ZSF [MPa] 24.8 27.6 19.6 24.4 19.7 26.4 25.7 26.3 26.3 24.9 23.8 30 29.7 26.6 23.5 23 IP 23° C. 52 46 36.4 37.5 31.6 47.6 49.4 43.7 45.5 39.7 47.3 46.6 33.3 54.3 47.4 50 IP −30° C. 53 48 13.4 30.6 2.9 41.1 43.4 37.9 42.8 10.8 38.5 31.7 3.8 59.2 45 45.3 T-peel 12.2 12.8 8.9 10 6.2 12.4 12.3 11.5 12 10.1 8.9 7.5 7.7 12.9 12.6 12.4