One-component thermosetting epoxy adhesive with improved adhesion

Abstract

A one-component thermosetting epoxy resin adhesive, including a) at least one epoxy resin A having on average more than one epoxide group per molecule; b) at least one latent hardener for epoxy resins; and c) at least one carboxylic acid selected from substituted or unsubstituted succinic acid and substituted or unsubstituted phthalic acid, wherein the epoxy resin adhesive contains 1.7 to 15 mmol of the at least one carboxylic acid per 100 g of epoxy resin adhesive, and the epoxy resin adhesive has a viscosity of more than 10 000 Pas at 25 C.

Claims

1. A one-component thermosetting epoxy resin adhesive, comprising at least one epoxy resin A having on average more than one epoxide group per molecule; at least one latent hardener for epoxy resins; at least one toughness improver D, a fraction of the at least one toughness improver D being in a range of from 5 to 30 wt %, based on a total weight of the one-component thermosetting epoxy resin adhesive; and at least one carboxylic acid selected from substituted or unsubstituted succinic acid and substituted or unsubstituted phthalic acid, wherein the one-component thermosetting epoxy resin adhesive contains 1.7 to 15 mmol of the at least one carboxylic acid per 100 g of epoxy resin adhesive, and the one-component thermosetting epoxy resin adhesive has a viscosity of more than 10 000 Pas at 25 C., the viscosity being determined oscillographically by means of a rheometer with heatable plate (MCR 301, AntonPaar) (gap 1000 m, measuring plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, temperature: 25 C.).

2. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the at least one carboxylic acid is selected from succinic acid and phthalic anhydride.

3. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the one-component thermosetting epoxy resin adhesive contains 2 to 13 mmol of the at least one carboxylic acid per 100 g of the one-component thermosetting epoxy resin adhesive.

4. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein a fraction of the at least one epoxy resin A having on average more than one epoxide group per molecule is in a range of from 25 to 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 the at least one latent hardener is selected from the group consisting of dicyandiamide, guanamines, guanidines, aminoguanidines and derivatives thereof, substituted ureas, imidazoles, and amine complexes.

6. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the one-component thermosetting epoxy resin adhesive has a viscosity of more than 15 000 Pas at 25 C., the viscosity being determined oscillographically by means of a rheometer with heatable plate (MCR 301, AntonPaar) (gap 1000 m, measuring plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, temperature: 25 C.).

7. The one-component thermosetting epoxy resin adhesive according to claim 1, further comprising at least one physical or chemical blowing agent.

8. A method for adhesively bonding heat-stable substrates, comprising the steps of i) applying the one-component thermosetting epoxy resin adhesive according to claim 1 to a surface of a heat-stable substrate S1; ii) contacting the applied one-component thermosetting epoxy resin adhesive with a surface of a further heat-stable substrate S2; iii) heating the one-component 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.

9. A method comprising applying the one-component thermosetting epoxy resin adhesive according to claim 1 to adhesively bond or strengthen metal structures or to strengthen filling of cavities in vehicle construction or sandwich panel construction.

10. A method comprising mixing a one-component thermosetting epoxy resin adhesive with at least one carboxylic acid selected from substituted or unsubstituted succinic acid and substituted or unsubstituted phthalic acid to improve tensile shear strength of the one-component thermosetting epoxy resin adhesive on curing at 170 C. for 20 min and/or at 205 C. for 40 min, wherein the one-component thermosetting epoxy resin adhesive comprises: at least one epoxy resin A having on average more than one epoxide group per molecule; at least one toughness improver D, a fraction of the at least one toughness improver D being in a range of from 5 to 30 wt %, based on a total weight of the one-component thermosetting epoxy resin adhesive; and at least one latent hardener for epoxy resins; where an amount of the at least one carboxylic acid is in a range of from 1.7 to 15 mmol per 100 g of the one-component thermosetting epoxy resin adhesive, and the one-component thermosetting epoxy resin adhesive has a viscosity of more than 10 000 Pas at 25 C., the viscosity being determined oscillographically by means of a rheometer with heatable plate (MCR 301, AntonPaar) (gap 1000 m, measuring plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, temperature: 25 C.), and the tensile strength is measured according to ASTM D1002-10.

11. A structural foam obtained by heating the one-component thermosetting epoxy resin adhesive according to claim 1.

12. An article comprising a cured adhesively bonded assembly, the adhesively bonded assembly being obtained by the method according to claim 8.

13. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the one-component thermosetting epoxy resin adhesive is a solid at 25 C.

14. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the at least one carboxylic acid is phthalic anhydride.

15. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein the at least one toughness improver D is selected from the group consisting of a terminally blocked polyurethane polymer, a liquid rubber, and a core-shell polymer.

16. The one-component thermosetting epoxy resin adhesive according to claim 1, wherein a fraction of the at least one epoxy resin A having on average more than one epoxide group per molecule is in a range of from 30 to 55 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) Viscosity

(3) The viscosity was measured oscillographically by means of a rheometer with heatable plate (MCR 301, AntonPaar) (gap 1000 m, measuring plate diameter: 25 mm (plate/plate), deformation 0.01 at 5 Hz, temperature: 20 C.-70 C., heating rate 10 C./min).

(4) Tensile Shear Strength (LSS)

(5) The determination follows the general lines of ASTM D1002-10. The tensile shear strength was determined using the following set-up (dimensions in mm):

(6) Test temperature: 23 C.

(7) Bond area: 12.7 mm25.4 mm

(8) Adhesive layer thickness: 0.8 mm

(9) Curing: 20 min at 170 C., or 40 min at 205 C.

(10) Test velocity: 13 mm/min

(11) Cohesive Facture/Adhesive Fracture (Fracture Mode)

(12) Visual assessment of the fracture mode obtained from the tensile shear strength, divided into CF and AF. CF=cohesive fracture, AF=adhesive fracture.

(13) Testing Examples

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

(15) Base Formulation:

(16) TABLE-US-00001 Raw material wt % Liquid epoxy resin of formula (II) with an index s 20 smaller than 0.2 Solid epoxy resin of formula (II) with an index s 15 from 2 to 12 Dicyandiamide 3 Terminally blocked polyurethane polymer D1 of formula (I) 10 Liquid rubber D2 10 Blowing agent 0.1 Drying agent 3 Filler mixture of calcium carbonate, calcium oxide 38.9 and fumed silica

(17) Added to the base formulation in each case was a carboxylic acid in a defined fraction as recited in Table 1 below (amounts in mmol acid/100 g epoxy resin adhesive). As a reference, the base formulation was tested without addition of carboxylic acid (Ref1 and Ref2). Moreover, as a non-inventive carboxylic acid, 1-[2-(isopropenylcarbonyloxy)ethyl] succinate was used (Ref3 and Ref4). The substrate used for the adhesion testing was oiled steel sheet and, respectively, aluminium.

(18) TABLE-US-00002 Steel (HDG) Electrolytically galvanized steel oiled DC06 + ZE 75/75 APO sheet, oiled Aluminium Aluminium alloy 6061 Aluminium alloy

(19) The results of the measurements of the tensile shear strength (LSS) and also of the fracture mode are likewise recited in Table 1. From these results it is apparent that the compositions without carboxylic acid exhibit significantly lower levels of tensile shear strength. Also in evidence is an adhesive fracture mode on the aluminium substrate at both curing temperatures.

(20) Moreover, 1-[2-(isopropenylcarbonyloxy)ethyl] succinate, as a monoester of (2-hydroxyethyl) methacrylate (HEMA) and succinic acid, proves to be a negative example of a non-inventive carboxylic acid (Ref3 and Ref4). These compositions as well exhibit significantly lower levels of tensile shear strength.

(21) All the compositions Ref1-Ref4 and also Ex1-Ex6 were solid at 25 C. and therefore had a viscosity at 25 C. of more than 25 000 Pas. The viscosity at 60 C. was 10 000 Pas.

(22) TABLE-US-00003 TABLE 1 LSS LSS Fracture Brown Experiment Substrate Carboxylic acid mmol* (20@170 C.) (40@205 C.) mode discolorations** Ref 1 Steel oiled No acid 7.2 MPa 4.2 MPa CF/AF none (HDG) Ex 1 Steel oiled Succinic acid 4.2 10.6 MPa 9.0 MPa CF/CF very few (HDG) Ex 2 Steel oiled Phthalic anhydride 3.4 9.6 MPa 8.1 MPa CF/CF none (HDG) Ex 3 Steel oiled Succinic acid 8.4 10.0 MPa *8.0 MPa CF/CF few (HDG) Ex 4 Steel oiled Succinic acid 12.6 8.9 MPa **7.5 MPa CF/AF many (HDG) Ref 2 Aluminium No acid 4.4 MPa 3.1 MPa AF/AF none Ex 5 Aluminium Succinic acid 4.2 9.1 MPa 9.1 MPa CF/CF very few Ref 3 Aluminium 1-[2- 2.2 6.4 MPa 6.5 MPa CF/AF none (Isopropenylcarbonyloxy)ethyl] succinate Ref 4 Aluminium 1-[2- 4.4 6.6 MPa 5.2 MPa CF/AF none (Isopropenylcarbonyloxy)ethyl] succinate Ex 6 Aluminium Phthalic anhydride 3.4 8.4 MPa 7.4 MPa CF/CF none *mmol carboxylic acid per 100 g epoxy resin adhesive, **brown dot-like discolorations on the cured adhesive.