TWO-COMPONENT ROOM TEMPERATURE CURABLE TOUGHENED EPOXY ADHESIVES

Abstract

Room temperature curing, two-component epoxy adhesives useful in bonding oily substrates include a resin side A and a curative side B. The resin side A includes an epoxy resin, a toughening component, a plasticizer and filler, and the curative side B includes a polyetheramine, amine-terminated butadiene rubber and a curing catalyst.

Claims

1. A two-component epoxy adhesive comprising a resin side A and a curative side B, wherein: a) the resin side A comprises A-1) a liquid epoxy resin or a liquid mixture of non-rubber-modified epoxy resins; A-2) at least one of i) core-shell rubber particles, ii) an elastomeric toughener having capped isocyanate groups and iii) a rubber-modified epoxy resin, in an amount sufficient to provide resin side A with a rubber content of 5 to 50 weight percent, based on the total weight of the resin side A; A-3) 1 to 20 weight percent, based on the total weight of the resin side A, of at least one plasticizer; and A-4) 5 to 40 weight percent, based on the total weight of the resin side A, of at least one particulate filler; and b) the curative side B comprises B-1) at least one liquid polyether amine having at least two primary and/or secondary amino groups and a number average molecular weight of 200 to 6000; B-2) at least one liquid amine-terminated polymer of butadiene having an amine hydrogen equivalent weight of 200 to 3000; and B-3) at least one epoxy curing catalyst.

2. The two-component epoxy adhesive of claim 1, wherein the plasticizer is one or more of an alkyl phthalate in which the alkyl groups each have 7 to 21 carbon atoms, an alkyl benzyl phthalate, wherein the alkyl group has 7 to 21 carbon atoms, a phenyl esters of an alkylsulfonic acid in which the alkyl group has 10 to 21 carbon atoms and an alkyl ester of 1,2-cyclohexanedicarboxylic acid in which the alkyl groups have 7 to 21 carbon atoms.

3. The two-component epoxy adhesive of claim 1 wherein the resin side A contains 6 to 12 weight percent of the plasticizer.

4. The two-component epoxy adhesive of claim 1 wherein the curative side B further comprises B-4) at least one polyethyleneimine curing agent that has a number average molecular weight of at least 25,000 by gel permeation chromatography.

5. The two-component epoxy adhesive of claim 1 wherein A-2 is present in an amount sufficient to provide resin side A with a rubber content of 10 to 30 weight percent, based on the total weight of the resin side A.

6. The two-component epoxy adhesive of claim 1 wherein A-2 is a mixture of the core-shell rubber particles and the elastomeric toughener having capped isocyanate groups.

7. The two-component epoxy adhesive of claim 1 wherein the resin side A contains 3 to 15 weight percent of the core-shell rubber particles and 5 to 15 weight percent of the elastomeric toughener having capped isocyanate groups.

8. The two-component epoxy adhesive of claim 1 wherein the curative side B further comprises B-5) up to 10 weight percent of a latent hardener.

9. The two-component epoxy adhesive of claim 1 wherein the curative side B further comprises 1 to 4 weight percent, based on the weight of curative side B, of at least one of an acryl-modified silane compound and an acryl-modified phosphate compound.

10. The two-component epoxy adhesive of claim 9 wherein the acryl-modified silane compound is present and has the structure ##STR00004## wherein R.sup.4 is alkyl, preferably methyl or ethyl; each R.sup.2 is independently alkylene, R.sup.3 is hydrogen or alkyl, and x is 1 or 2.

11. The two-component epoxy adhesive of claim 9 wherein the acryl-modified phosphate compound and has the structure: ##STR00005## wherein R.sup.2 is independently alkylene, R.sup.3 is hydrogen or alkyl, and x is 1 or 2.

12. The two-component epoxy adhesive of claim 10 wherein the acryl-modified silane compound is 2-methacryloyloxyethyl-trimethoxysilane.

13. The two-component epoxy adhesive of claim 11 wherein the acryl-modified phosphate compound is selected from bis (2-methacryloyloxyethyl) phosphate and 2-methacryloyloxyethyl phosphate.

14. The two-component epoxy adhesive of claim 1 wherein the epoxy curing catalyst includes at least one tertiary amine compound.

15. The two-component epoxy adhesive of claim 1 wherein component A-1) constitutes 30 to 70% of the total weight of resin side A.

16. A method for bonding two substrates, comprising combining the resin side A and the resin side B of the adhesive of any of the preceding claims to form a curable adhesive mixture, forming a layer of the curable adhesive mixture at a bondline between two substrates, and then curing adhesive layer at the bondline to form a cured adhesive bonded to the two substrates at the bondline.

17. The method of claim 16 wherein at least one of the substrates is an oily metal.

18. The method of claim 16 wherein the curing is performed at a temperature of 10 to 50 C.

19. The method of claim 16 wherein the curing is partially performed at a temperature of 10 to 50 C., followed by an elevated temperature cure.

20. The method of claim 16 wherein the cured adhesive exhibits an elongation of 4 to 25%, a tensile strength of at least 10 MPa, and an elastic modulus of at least 400 MPa, when measured according to DIN EN ISO 527-1.

Description

[0089] The following examples are provided to illustrate the invention but are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated. All molecular weights are number averages unless otherwise indicated.

[0090] In the following examples:

[0091] The Epoxy Resin is a diglycidyl ether of bisphenol A having an epoxy equivalent weight of about 186.

[0092] The CSR (core-shell rubber) is a dispersion of 25% by weight core-shell rubber particles in 75% by weight of a diglycidyl ether of bisphenol A.

[0093] The Toughener is a 2000 molecular weight tetrahydrofuran that is reacted with a diisocyanate to form an isocyanate-terminated prepolymer, followed by capping the isocyanate groups with bisphenol A.

[0094] The RME (rubber-modified epoxy resin) is a reaction product of a carboxyl-terminated butadiene/acrylonitrile copolymer and the Epoxy Resin, at a weight ratio of about 30:1.

[0095] Plasticizer A is a commercially available diisononylphthalate product.

[0096] Plasticizer B is a commercially available C.sub.7-9 alkyl benzyl phthalate.

[0097] Plasticizer C is a commercially available C.sub.8-10 dialkyl phthalate.

[0098] Plasticizer D is a commercially available C.sub.10-21 alkyl sulfonic acid phenyl ester.

[0099] Plasticizer E is a commercially available diisononyl ester of 1,2-cyclohexanedicarboxylic acid.

[0100] Filler A is a mixture of chlorite, wollastonite, talc and fumed silica, except when noted otherwise.

[0101] Filler B is a mixture of talc and fumed silica.

[0102] The Adhesion Promoter is a commercially available silane.

[0103] The Polyethyleneimine is a commercially available material having a molecular weight of about 750,000, as reported by its manufacturer.

[0104] Polyetheramine A is a branched amine-terminated polypropylene oxide having about 3 primary amino groups per molecule and a molecular weight of about 440.

[0105] Polyetheramine B is a linear 2000 molecular weight, primary amine-terminated polypropylene oxide).

[0106] Polyetheramine C is 4,7,10-trioxa-1,13-tridecanediamine.

[0107] The Accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

[0108] The ATBN is a commercially available amine-terminated butadiene-acrylonitrile copolymer having an amine hydrogen equivalent weight of 900-1200.

Examples 1-7 and Comparative Sample A

[0109] Resin side compositions 1 through 8 are prepared by blending the ingredients listed in Table 1:

TABLE-US-00001 TABLE 1 Parts by Weight Ingredient A* 1 2 3 4 5 6 7 Epoxy Resin 34.5 31.5 29.5 27.5 25.5 23.5 29.5 28.5 CSR 34.0 31.0 29.0 27.0 25.0 23.0 29.0 28.0 Toughener 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 Plasticizer A 0 4 8 12 16 20 12 12 Filler A 21.0 23.0 23.0 23.0 23.0 23.0 19.0 21.0 Colorant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Adhesion Promoter 3.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Rubber Content 16.5% 15.75% 15.25% 14.75% 14.25% 13.75% 15.25% 15.0% *Not an example of the invention.

[0110] Curative side B-1 is prepared separately by blending the ingredients listed in Table 2:

TABLE-US-00002 TABLE 2 Ingredient Parts by Weight Polyethyleneimine 4.0 Polyetheramine A 24.5 Polyetheramine C 9.0 Accelerator 12.0 ATBN 36.2 Filler B 10.0 Dicyandiamide 4.0 Adhesion Promoter 0.3

[0111] Comparative Sample A and Adhesive Examples 1-7 are made by mixing Curative side B-1 with Resin sides C and A-1 through A-7, respectively. In each case the Curative and Resin side are mixed at a 1:2 weight ratio and then formed into an adhesive layer between two test coupons for lap shear strength measurement according to DIN EN 1465. One of the test coupons is Thyssen-Krupp DC04+ZE 75/57 electrogalvanized steel and the other is Thyssen-Krupp DX56D+Z100 hot-dipped galvanized steel. The coupons are degreased and then regreased with Anticorit PL 3802-39S anticorrosion lubricant prior to applying the adhesive. The adhesive layer thickness is 0.2-0.3 mm The applied adhesive is cured under air for 7 days at 23 C. Lap shear testing is performed at 23 C. Results are as indicated in Table 3.

TABLE-US-00003 TABLE 3 Designation Lap Shear strength, MPa % Cohesive Failure A* 7.7 0 1 11.9 0 2 13.2 20 3 14.3 100 4 13.5 100 5 12.8 100 6 12.9 20 7 13.5 50 *Not an example of this invention.

[0112] Examples 1 through 5 show the effect of replacing a portion of the epoxy resin and core-shell rubber particles with the plasticizer. Lap shear strength increases dramatically. Failure mode changes from 100% adhesive failure to 100% cohesive failure with the inclusion of 12-20% plasticizer by weight of the resin side A.

[0113] In Examples 6 and 7, the amount of epoxy resin and core shell rubber particles is higher than in Example 3, which contains the same amount of plasticizer. The amount of filler is also higher than in Examples 1-5. Lap shear strength remains high, although there is more adhesive failure.

[0114] Example 3 and Comparative Sample A are taken for lap shear testing on several different oily and degreased substrates, in some cases using an accelerated curing protocol in which the samples are cured for 1 day at 23 C. followed by 30 minutes at 180 C. The substrates and applied oils are as reported in Table 4, together with lap shear testing results.

TABLE-US-00004 TABLE 4 Lap Shear % Curing Ad- Strength, Cohesive Substrate Lubricant Protocol hesive MPa Failure DC05B + ZE None 7 day RT A* 23.9 80 75/75 EG steel (Degreased) Ex. 3 20.5 100 Palatinol 7 day RT A 6.5 0 B804/3 Ex. 3 14.1 100 COW1 DX56D + Anticorit 7 day RT A 9.9 0 Z100MB 3802-39S Ex. 3 12.6 30 EG steel Quaker Accelerated A N.D. 0 Ferrocat Ex. 3 13.0 100 N6130 Anticorit Accelerated A N.D. 100 RP 41705S Ex. 3 13.0 100 DX56D + Palatinol 7 day RT A 13.9 30 Z100MB/ B804/3 Ex. 3 14.5 100 DC05B + COW1 ZE 75/75 Anticorit 7 day RT A 7.7 0 3802-39S Ex. 3 12.6 80 DX56D + Anticorit 7 day RT A 4 0 Z100/ 3802-39S Ex. 3 14.3 100 DC04A + ZE 75/75P AC 120 None 7 day RT A 15.9 100 Aluminum (Degreased) Ex. 3 14.5 100 Quaker Accelerated A N.D. 0 Ferrocat Ex. 3 12.0 100 N6130 Anticorit Accelerated A N.D. 0 RP 41705S Ex. 3 12.0 100 *Not an example of the invention.

[0115] As can be seen in the data in Table 4, the comparative adhesive bonds well to degreased surfaces but not oily ones. Example 3 bonds well to a variety of metals having a variety of applied oils. Lap shear strength is uniformly increased relative to Comparative Adhesive A, as is the incidence of the desired cohesive failure. Good results are seen with ambient and accelerated cure.

Examples 8-10

[0116] Examples 8-10 are made and tested in the same general manner described in the previous examples, using the same substrates and curing conditions as indicated with regard to Examples 1-7. The curative side is Curative Side B-1 as described in the previous examples. Examples 8-10 are made using Resin Sides 8-10, respectively, which have the same composition as Resin Side 3 above, except the plasticizer is replaced with an equal weight of a different plasticizer as follows:

[0117] Resin Side 8: Plasticizer C

[0118] Resin Side 9: Plasticizer D

[0119] Resin Side 10: Plasticizer E

[0120] Results of lap shear testing are as indicated in Table 5. The results of Comparative Sample A are repeated for comparison.

TABLE-US-00005 TABLE 5 Lap Shear % Cohesive Designation strength, MPa Failure A* 7.7 0 8 12.6 20 9 13.1 30 10 13.0 10 *Not an example of the invention.

[0121] The presence of Plasticizers C, D and E all result in a very large increase in lap shear strength. They increase the incidence of cohesive failure mode, but not as effectively as does Plasticizer A at the same loading.

Examples 11-13

[0122] Examples 11-13 are made and tested in the same general manner described in the previous examples, using the same substrates and curing conditions as indicated with regard to Examples 1-7. The curative side is Curative Side B-1 as described in the previous examples. The resin sides are made by mixing the ingredients indicated in Table 6. Lap shear strength and % cohesive failure are as indicated in Table 6.

TABLE-US-00006 TABLE 6 Resin side Parts by Weight Ingredient 11 12 13 Epoxy Resin 30.5 31.5 27.5 CSR 30.0 31.0 27.0 Toughener 8.0 0 8.0 Plasticizer B 6.0 12.0 12.0 Filler A 22.0 23.0 23.0 Colorant 0.5 0.5 0.5 Adhesion Promoter 3.0 2.0 2.0 Rubber Content 15.5% 7.75% 14.75% Lap Shear Strength, 13.2 14.5 11.2 MPa % Cohesive Failure 60 50 0

[0123] In these formulations, the presence of Plasticizer B greatly improves lap shear strength. In Examples 11 and 12, it increases the incidence of the desired cohesive failure mode as well.

Examples 14-20

[0124] Examples 14-20 are made from resin side compositions as set forth in Table 7 and curative side compositions as set forth in Table 8.

TABLE-US-00007 TABLE 7 Resin Side Compositions Parts by Weight Ingredient Ex. 14 Ex. 15-17 Ex. 18 Ex. 19 Ex. 20 Epoxy Resin 27.5 24.5 25.5 25.5 22.5 CSR 27.0 24.0 25.0 25.0 22.0 Toughener 8.0 8.0 0 0 4.0 Plasticizer A 12.0 12.0 12.0 10.0 10.0 Filler A.sup.1 23.0 29.0 35.0 37.0 39.0 Colorant 0.5 0.5 0.5 0.5 0.5 Adhesion 2.0 2.0 2.0 2.0 2.0 Promoter Rubber 14.75% 14.0% 6.25% 6.25% 9.5% Content .sup.1No fumed silica in Example 19.

TABLE-US-00008 TABLE 8 Curative Side Compositions Parts by Weight Ex. 14, Ingredient 15, 18 Ex. 16 Ex. 17 Ex. 19 Ex. 20 Polyethyleneimine 4.0 4.0 4.0 4.0 4.0 Polyetheramine A 24.5 0 12.5 24.5 24.5 Polyetheramine B 0 24.50 12.5 0 0 Polyetheramine C 9.0 9.0 9.0 9.0 9.0 Accelerator 12.0 12.0 12.0 12.0 12.0 ATBN 33.2 33.2 33.2 33.2 33.2 Filler B 10.0 10.0 10 10 10 Dicyandiamide 4.0 4.0 4.0 4.0 4.0 Adhesion Promoter 0.3 0.3 0.3 0.3 0.3 Bis(2- 3.0 0 0 0 0 methacryloyloxy- ethyl) phosphate 2- 0 3.0 3.0 3.0 0 methacryloyloxyethyl- trimethoxysilane 1-meethacryloyloxy- 0 0 0 0 3.0 ethyl phosphate

[0125] Lap shear testing is performed as described in the previous examples, using the same substrates and curing conditions as indicated with regard to Examples 1-7 except testing is performed after only 3 days curing at room temperature. Results are as indicated in Table 9. The results for Comparative Sample A are included for purposes of comparison.

TABLE-US-00009 TABLE 9 Lap Shear % Cohesive Designation strength, MPa Failure A* 4.0 0 14 12.6 50 15 14.2 100 16 9.7 100 17 13.7 100 18 14.8 100 19 13.6 100 20 14.1 100 *Not an example of the invention.

[0126] All of Examples 14-20 exhibit vastly improved lap shear strength and very high incidence of desirable cohesive failure.

[0127] The tensile properties of Comparative Adhesive A and Examples 3, 11, and 14-17 are measured according to DIN EN ISO 527-1. Tensile properties of Examples 16 and 17 are additionally measured after the accelerated curing protocol described before. Results are as indicated in Table 10.

TABLE-US-00010 TABLE 10 Tensile Str., Elongation at Elastic Designation Curing Protocol MPa Break, % Modulus, MPa A* 7 day RT 31 5 2050 3 7 Day RT 19 12 1050 11 7 Day RT 25 8 1500 14 7 Day RT 19 12 1050 15 7 Day RT 17 18 900 16 7 day RT 13 17 464 Accelerated 10 24 145 17 7 Day RT 17 17 720 Accelerated 11 18 323 *Not an example of the invention.

[0128] Impact peel resistance is measured at 23 C. for Comparative Sample A and Example 15, according to ISO 11343. The substrates are DC06A+ZE 75/75 and DX56D+Z100 galvanized steels, coated with Anticorit PL 3802-39S anticorrosive lubricant. The impact peel resistance for Comparative Sample A is zero, with 100% adhesive failure. The impact peel resistance for Example 15 is 12 N/mm, with 100% cohesive failure.