One-component thermosetting epoxy adhesive with improved adhesion

Abstract

A one-component thermosetting epoxy resin adhesive, including a) at least one epoxy resin A of formula (II) ##STR00001##
wherein substituents R′ and R″ independently of one another are H or CH.sub.3 and index s has value of 0-12, fraction of epoxy resin A being from 20-70 wt.-%, based on total weight of one-component thermosetting epoxy resin adhesive; and b) at least one epoxy novolac EN of formula ##STR00002##
where R2= ##STR00003##
or CH.sub.2, R1=H or methyl and z=0-7, fraction of epoxy novolac EN being from 1-8 wt.-% based on total weight of one-component thermosetting epoxy resin adhesive; and c) at least one latent hardener B for epoxy resins; and d) at least one accelerator C for epoxy resins; and e) at least at least one toughness improver D, fraction of toughness improver D being from 5-40 wt.-%, based on total weight of one-component thermosetting epoxy resin adhesive.

Claims

1. A one-component thermosetting epoxy resin adhesive, comprising; a) at least one epoxy resin A of the formula (II) ##STR00015## wherein: the substituents R′ and R″ independently of one another are either H or CH.sub.3, and the index s has a value of 0-0.2, the fraction of the epoxy resin A being from 20-70 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive; and b) at least one epoxy novolac EN of the formula ##STR00016## wherein: R2= ##STR00017## or CH.sub.2, R1=H or methyl, and z=0-7, the fraction of epoxy novolac EN being from 1-8 wt.-% based on the total weight of the one-component thermosetting epoxy resin adhesive; and c) at least one latent hardener B for epoxy resins; and d) optionally at least one accelerator C for epoxy resins; and e) at least at least one toughness improver D, the fraction of toughness improver D being from 5-40 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive; wherein the epoxy resin adhesive has a viscosity of 500 to 5000 Pas at 25° C., as determined oscillographically by means of a rheometer with a heatable plate when measured with a deformation 0.01 at 5 Hz.

2. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the fraction of epoxy novolac EN is from 2-7 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

3. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein in the epoxy novolac EN, R2=CH.sub.2, R1=H, and z=1-2.

4. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the fraction of the epoxy resin A of the formula (II) is from 25-70 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

5. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein in the epoxy resin A the substituents R′ and R″ are CH.sub.3.

6. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the latent hardener B is selected from the group consisting of dicyandiamide, guanamines, guanidines, aminoguanidines and derivatives thereof, substituted ureas, imidazoles and amine complexes.

7. The one-component thermosetting epoxy resin adhesive according to claim 1, comprising the accelerator C for epoxy resins, which is selected from the group consisting of substituted ureas, imidazoles, imidazolines and blocked amines.

8. The one-component thermosetting epoxy resin adhesive according to claim 1, further comprising: at least one epoxy-bearing reactive diluent G, the fraction of the epoxy-bearing reactive diluent G being from 1-10 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

9. The one-component thermosetting epoxy resin adhesive according to claim 1, further comprising at least one gelling agent.

10. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the toughness improver D is selected from the group consisting of terminally blocked polyurethane polymers D1, liquid rubbers D2 and core-shell polymers D3.

11. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the adhesive withstands ≥20 cycles of lap-shear cycling at a temperature of 23° C. and an applied load of 2400 N after curing for 10 minutes at 160° C.

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

13. A method according to claim 12, wherein in iii) heating the thermosetting epoxy resin adhesive, the thermosetting epoxy resin adhesive is left at the temperature of 100-220° C. for 10 min-6 h.

14. A method comprising: adhesively bonding or strengthening metal structures using the one-component thermosetting epoxy resin adhesive according to claim 1.

15. A method comprising: strengthening filling of cavities in vehicle construction or sandwich panel construction using the one-component thermosetting epoxy resin adhesive according to claim 1.

16. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the fraction of the toughness improver D is from 15-40 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

17. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the toughness improver D is a terminally blocked polyurethane polymer D1.

18. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the fraction of latent hardener B is from 0.5-4 wt.-%, based on the total weight of the one-component thermosetting epoxy resin adhesive.

Description

EXAMPLES

(1) Test methods used for the testing of the respective properties in the examples were as follows:

(2) Stress Durability

(3) The stress durability was determined based on the “Ford Standards Testing” procedure of “BV 101-07 Stress durability test for lap-shear bonds”.

(4) The test samples were determined using the following set-up:

(5) Test temperature: 23° C.

(6) Substrate: 1.6 mm thick alloy 5754 aluminium coupons coated with Alcoa 951 and Quacker DC2-90.

(7) Bond area: 12.7 mm×25.4 mm

(8) Adhesive layer thickness: 0.25 mm

(9) Curing: 10 min at 160° C.

(10) Applied load: 2400N

Testing Examples

(11) The base formulation used for epoxy resin adhesives was a formulation as described below.

(12) TABLE-US-00001 TABLE 1 Ref Ex. 1 Ex. 2 Ex. 3 Raw material wt.-% wt.-% wt.-% wt.-% Liquid epoxy resin of 49.5 46.5 45 43.5 formula (II), DER 331 Reactive diluent G, 2.6 2.6 2.6 2.6 p-t-butyl phenyl glycidyl ether Epoxy novolac EN, 0 3 4.5 6 DEN 439 (EEW 191 to 210 g/eq, functionality 3.8) Terminally blocked 20 20 20 20 polyurethane polymer D1 of formula (I) Latent hardener B, 4 4 4 4 Dicyandiamide Accelerator C for 0.2 0.2 0.2 0.2 epoxy resins, substituted urea Filler mixture of 22.8 22.8 22.8 22.8 calcium carbonate, calcium oxide and fumed silica Gelling agent, 0.9 0.9 0.9 0.9 polyvinyl butryal Total 100 100 100 100 Stress Durability 34 42 65 60 160° C./10′ (Cycles)
The viscosicty of the compositions Ref, and Ex.1-Ex.3 were measured and found to be between 500 to 1300 Pas at 25° C., the viscosity being determined oscillographically by means of a rheometer with heatable plate (MCR 301, AntonPaar) (slot 1000 μm, measuring plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, temperature: 25° C.).