One-component epoxy-modified polyurethane and/or polyurea adhesives having high elongation and excellent thermal stability, and assembly processes using same

Abstract

A one-component epoxy-modified polyurethane and/or urea adhesive includes very high levels of reactive urethane group- and/or urea group-containing tougheners, an epoxy resin and epoxy hardener. These adhesives are formulated to cure at high temperatures and surprisingly provide high elongations, excellent thermal stability and good adhesive properties.

Claims

1. A one-component epoxy-modified polyurethane and/or urea adhesive comprising in admixture: components A and B, wherein component A) is one or more non-rubber-modified epoxy resins and component B) is one or more rubber-modified epoxy resins; C) one or more reactive urethane group- and/or urea group-containing tougheners having a number average molecular weight of up to 35,000, at least one polyether or diene rubber segment having a weight of at least 1000 atomic mass units, and capped isocyanate groups of which at least 75% are monophenol- or polyphenol-capped isocyanate groups; D) optionally, one or more core-shell rubbers; E) one or more latent epoxy curing agents; and F) at least one catalyst for the reaction of an epoxide with the curing agent(s); wherein 1) component A constitutes 10 to 25 percent of the combined weight of components A-E; 2) component B constitutes 2 to 30 percent of the combined weight of components A-E; 3) components A and B together constitute 12 to 40 percent of the combined weight of components A-E; 4) component C constitutes 55 to 85 percent of the combined weight of components A-E; 5) components B, C and D together constitute 65 to 85 percent of the combined weight of components A-E; 6) component D constitutes 0 to 15 percent of the combined weight of components A-E; and 7) components A-E together constitute at least 60 weight percent of the one-component epoxy adhesive.

2. The adhesive of claim 1, wherein component C constitutes 60 to 80 percent of the combined weight of components A-E.

3. The adhesive of claim 1, wherein component B includes at least one epoxy-terminated polyether.

4. The adhesive of claim 3 wherein component A includes at least one diglycidyl ether of a bisphenol.

5. The adhesive of claim 1, wherein the catalyst includes at least one imidazoline catalyst having the structure: ##STR00003## where n is 2 or 3.

6. A method for bonding two substrates, comprising forming a layer of the adhesive of claim 1 at a bondline between two substrates to form an assembly, and then curing adhesive layer at the bondline by heating to a temperature of at least 160 C., to form a cured adhesive bonded to the two substrates at the bondline.

7. The method of claim 6, wherein the two substrates have coefficients of linear thermal expansion that are different from each other by at least 510.sup.6 m/m-K.

8. The method of claim 7, wherein one of the substrates is a metal and the other substrate is a thermoplastic organic polymer, a thermoset organic polymer or a fiber composite.

9. A method for forming a bonded and coated assembly, comprising 1) forming a layer of the adhesive of claim 1 at a bondline between a first and a second substrate to form an assembly that includes the first and second substrates each in contact with the adhesive composition at the bondline; then 2) immersing the assembly into a coating bath to form a layer of an uncured coating on at least a portion of the exposed surface of the assembly; and 3) heating the assembly to a temperature of at least 160 C. to cure the adhesive to form a cured adhesive bonded to the substrates at the bondline and simultaneously cure the coating layer.

10. The method of claim 9, wherein the first and second substrates have coefficients of linear thermal expansion that are different from each other by at least 510.sup.6 m/m-K.

11. The method of claim 10, wherein one of the substrates is a metal and the other substrate is a thermoplastic organic polymer, a thermoset organic polymer or a fiber composite.

Description

Examples 1-5 and Comparative Samples A and B

(1) One-component adhesive Examples 1-5 and Comparative Samples A and B are prepared by mixing ingredients as indicated in Table 1:

(2) TABLE-US-00001 TABLE 1 Parts By Weight Comp. Ingredient A* Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. B Ex. 5 NRM Epoxy A 11.8 24.0 14.0 9.0 19.0 14.2 14.2 RM Epoxy A 5.0 0 0 0 0 0 0 RM Epoxy B 18.7 0 0 0 0 0 0 Core-Shell Rubber 9.8 0 0 0 0 0 0 Polyester 3.0 0 0 0 0 0 0 Toughener A 0 40 50 55.2 45 0 0 Toughener B 0 0 0 0 0 0 49.8 Toughener C 13.0 0 0 0 0 49.8 0 Adhesion Promoter 0.1 0.5 0.5 0.5 0.5 0.5 0.5 Colorant 0.7 0.4 0.4 0.4 0.4 0.4 0.4 Catalyst A 1.0 0.8 0.8 0.8 0.8 0.8 0.8 Curing Agent 3.4 2.3 2.3 0.9 1.4 1.4 1.4 Mineral Fillers 33.5 32.0 32.0 33.1 33.0 33.0 33.0 Weight, Components A-E 64.5 66.3 66.3 65.2 65.3 65.3 65.3 % Component A, based on 28.1 36.2 21.1 13.8 29.1 21.7 21.7 Components A-E % Components A and B, 64.9 36.2 21.1 13.8 29.1 21.7 21.7 based on Components A-E % Tougheners, based on 20.1 60.3 75.4 84.5 68.9 76.2 76.2 Components A-E % Tougheners, rubber- 62.4 60.3 75.4 84.5 68.9 76.2 76.2 modified epoxy resins and core-shell rubber particles, based on Components A-E *Not an example of this invention

(3) Comparative Sample A is a conventional toughened epoxy adhesive. The tougheners constitute about 20% of the weight of the reactive components (A-E). Further flexibilizing is provided by the presence of large amounts of rubber-modified epoxy resins and the core-shell rubber. Examples 1-5 are inventive compositions, in which the only flexibilizer present is the urethane group-containing toughener that has bisphenol-blocked isocyanate groups. In Comparative Sample B, the toughener has amine-blocked isocyanate groups.

(4) Test samples for tensile strength, elongation and elastic modulus measurements are made by curing a portion of each sample for 30 minutes at 180 C. Test specimens are cut from the cured samples and evaluated according to DIN EN ISO 527-1.

(5) Impact peel testing is performed as follows. The test coupons for the impact peel testing are 90 mm20 mm with a bonded area of 3020 mm. The adhesive sample is applied to the bond area of a 1.2 mm-thick HC400 high carbon steel coupon. A 1.2 mm-thick HC 400 steel coupon is placed into contact with the adhesive, and the assembly squeezed under a weight of about 10 kg to prepare each test specimen, with spacers present to maintain an adhesive layer thickness of 0.2 mm. The assembled test specimens are cured at 180 C. for 30 minutes. The impact peel testing is performed in accordance with the ISO 11343 wedge impact method. Testing is performed under a 90 Joule impact load at an operating speed of 2 m/sec with samples at a temperature of 23 C. or at 40 C., as indicated in Table 2.

(6) Lap shear specimens are made using a DX56D low carbon steel coupon and a D100 galvanized steel coupon. The specimens are made by sprinkling glass beads (0.2 mm diameter) onto one of the coupons, applying the adhesive sample, and then positioning the second coupon on top of the adhesive. The bonded area in each case is 2510 mm, and the adhesive layer thickness is controlled by the glass beads to 0.2 mm. The test specimens are cured for 30 minutes at 180 C. and evaluated for lap shear strength in accordance with DIN ISO 1465. Testing is performed at 23 C. and a test speed of 10 mm/minute.

(7) Elastic modulus, tensile strength and elongation at break are evaluated by forming plaques from each adhesive sample, curing the plaques at 180 C. for 30 minutes, and performing the testing on room temperature test samples cut from the cured plaques according to DIN EN ISO 527-1.

(8) Results of the testing are as indicated in Table 2.

(9) TABLE-US-00002 TABLE 2 Result Comp. Comp. Test A* Ex. 1 Ex. 2 Ex. 3 Ex. 4 B* Ex. 5 Impact Peel Str., 35.2 33.2 55.9 29.6 36.3 22.8 33.7 23 C., N/mm Impact Peel Str., 15.5 18.0 29.5 ND ND ND ND 40 C., N/mm Lap Shear Str., ND 16.0 ND 8.9 12.2 8.2 10.6 MPa Elastic Modulus, 251 231 13.6 1 23 ** 12 MPa Tensile Str., MPa 14.7 11.6 7.1 3.8 8.6 ** 8.1 Elongation, % 20 80 146 287 144 ** 216 *Not an example of this invention. ND means not determined. ** - sample could not be tested due to extensive bubble formation during cure.

(10) Comparative Sample A has an elongation of only 20%, despite the presence of more than 62% by weight of various flexibilizing materials (based on the reactive materials). In Example 1, elongation is quadrupled to 80% despite a small decrease in the total amount of flexibilizing materials, by increasing the amount of toughener to about 60% by weight of reactive materials. Examples 2-5 show that even greater elongations are achieved when the amount of phenol-capped toughener is increased further. Very surprisingly, Examples 1-5 exhibit at most a small loss in impact peel strength, compared to Comparative Sample A, and in the case of Example 2 actually shows a significant improvement. The good impact peel strengths indicate that Examples 1-5 are very resistant to thermal degradation, despite the large fraction of material that contains urethane groups.

(11) Comparative Sample B shows the effect of replacing a phenol-capped toughener with an amine-capped one in the high toughener formulations. Bubble formation occurs during plaque formation to the extent that meaningful mechanical properties cannot be measured. Thermal degradation is also evidenced by the impact peel and lap shear resultsthe lower values for Comparative Sample B are indicative of thermal degradation during the curing step.

Examples 6-10

(12) One-component adhesive Examples 6-10 are prepared by mixing ingredients as indicated in Table 3:

(13) TABLE-US-00003 TABLE 3 Parts By Weight Ingredient Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 NRM Epoxy A 0 14.2 12.4 12.2 14.2 RM Epoxy A 0 0 7.0 7.0 0 RM Epoxy B 24.0 0 0 0 0 Toughener A 40.0 49.8 46.0 46.0 49.8 Toughener C 0 0 3.0 3.0 0 Adhesion Promoter 0.5 0.5 0.6 0.6 0.5 Colorant 0.4 0.4 0.4 0.4 0.4 Catalyst A 0.8 0.8 0 0 0 Catalyst B 0 0 0.5 0.7 0.8 Curing Agent 2.3 1.4 1.6 1.6 1.4 Mineral Fillers 32.0 33.0 28.5 28.5 33.0 Weight, Components A-E 66.3 65.3 70.0 70.0 65.3 % Component A, based on 0 21.7 17.7 17.4 21.7 Components A-E % Components A and B, 36.2 21.7 27.7 27.4 21.7 based on Components A-E % Tougheners, based on 60.7 76.3 65.7 65.7 76.3 Components A-E % Tougheners plus 96.5 76.3 75.7 75.7 76.3 rubber-modified epoxy resins, based on Components A-E *Not an example of this invention.

(14) Examples 6-10 are evaluated as in previous examples. In addition, Examples 8, 9 and 10 are also evaluated for lap shear strength after curing the test specimens at 170 C. and 205 C. Results are as in Table 4.

(15) TABLE-US-00004 TABLE 4 Result Test Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Impact Peel Str., 23 C., 57.7 39.2 ND ND 41.3 N/mm Impact Peel Str., 40 31.1 ND ND ND ND C., N/mm Lap Shear Str., 170 C. ND 9.8 11.1 11.0 ND Cure, MPa Lap Shear Str., 180 C. ND 10.9 ND ND 12.9 Cure, MPa Lap Shear Str., 205 C. ND 3.7 8.1 9.8 ND Cure, MPa Elastic Modulus, MPa 13.8 8 ND ND 18 Tensile Str., MPa 6.6 6.5 ND ND 10.1 Elongation, % 146 183 >100% >100 216 *Not an example of this invention. ND means not determined.

(16) All of Examples 6-10 exhibit excellent elongation and good thermal stability up to at least 180 C. curing temperatures. In Examples 8 and 9, this is achieved despite the presence of a small amount of amine-terminated toughener. Examples 8 and 9 further show the benefit of using the imidazoline catalyst when very high curing temperatures are used. With this catalyst, very little thermal degradation is seen even at the 205 C. curing temperature, as shown by comparing the lap shear strengths of the samples cured at 205 C. with those cured at lower temperatures.

Examples 11 and 12

(17) One-component adhesive Examples 11 and 12 are prepared by mixing ingredients as indicated in Table 5:

(18) TABLE-US-00005 TABLE 5 Parts by Weight Ingredient Ex. 11 Ex. 12 RM Epoxy B 12 0 Core-Shell Rubber 12 24 Toughener A 40 40 Adhesion Promoter 0.5 0.5 Colorant 0.4 0.4 Catalyst A 0.8 0.8 Curing Agent 2.3 2.3 Mineral Fillers 32.0 32.0 Weight, Components A-E 66.3 66.3 % Component A, based on 12.1 24.1 Components A-E.sup.1 % Components A and B, 30.2 24.1 based on Components A-E % Tougheners, based on 60.3 60.3 Components A-E % Tougheners plus rubber- 84.5 72.4 modified epoxy resins and core- shell rubber particles, based on Components A-E .sup.1Component A is supplied via the core-shell rubber dispersion, which contains 67% epoxy resin.

(19) Examples 11 and 12 are evaluated as in previous examples. Results are as in Table 6.

(20) TABLE-US-00006 TABLE 6 Results Test Ex. 11 Ex. 12 Impact Peel Str., 23 C., 60.8 65.7 N/mm Impact Peel Str., 40 1.0 66.1 C., N/mm Lap Shear Str., 180 C. 9.5 9.2 Cure, MPa Elastic Modulus, MPa 70 47 Tensile Str., MPa 8.2 9.8 Elongation, % 128 82

(21) Example 12 compared to Example 11 shows that increasing concentration of core-shell rubber does not lead to improvements in elongation, and in fact causes a significant decrease in these tests. Each has excellent impact peel strength at 23 C. and very good lap shear strength, indicating that each resists thermal degradation at the 180 C. cure temperature. Example 11 also shows a higher elastic modulus despite its higher elongation.