Crash-durable adhesive with enhanced stress durability
View Patent ↗A heat-curable structural adhesive includes a non-rubber-modified epoxy resin, a reaction product of a carboxyl-or amine-terminated butadiene polymer or copolymer and a bisphenol F-based epoxy resin, a elastomeric toughener containing capped isocyanate groups, one or more epoxy curing agents a moisture scavenger and a heat activatable catalyst comprising a mixture of a solid or liquid tertiary amine compound that has a boiling temperature of at least 130° C. and a novolac resin. The structural adhesive develops excellent bonding properties when cured at moderate temperatures, especially from 120 to 170° C., and in addition performs very well in environmental aging stress testing. The adhesive is particularly good for bonding aluminum to another metal, or bonding aluminum to aluminum.
1. A heat-curable structural adhesive comprising:
A) 34.56 to 41 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one diglycidyl ether of bisphenol A having an epoxy equivalent weight of about 186;
B) 23.8 to 26.5 weight percent, based on the total weight of the heat-curable structural adhesive, of a reaction product of 19.6% of a carboxyl-terminated copolymer of butadiene and acrylonitrile, the copolymer of butadiene and acrylonitrile having a number average molecular weight of 2000 to 6000 and 70.2% of a diglycidyl ether of bisphenol F having an epoxy equivalent weight of about 180 which reaction product is further diluted with 10.2% of a diglycidyl ether of bisphenol A having an epoxy equivalent weight of 1600 to 2000;
C) at least one elastomeric toughener containing isocyanate groups capped with phenol;
D) 4 to 5.1 weight percent, based on the total weight of the heat-curable structural adhesive, dicyandiamide;
E) 3 to 4 weight percent of calcium oxide, based on the total weight of the heat-curable structural adhesive;
F) a heat activatable catalyst comprising a mixture of 2,4,6-tris(dimethylaminomethyl)phenol and a novolac resin,
G) 0.1 to 0.2 weight percent, based on the total weight of the heat-curable structural adhesive, of a blocked diethylene triamine catalyst;
H) 0 to 14.8 weight percent, based on the total weight of the heat-curable structural adhesive, of a flame retardant;
I) 4 to 12.7 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one inorganic filler;
J) a surfactant; and
K) a colorant
and further wherein the elastomeric toughener and the rubber portion of component B) together constitute from 16.8 to 17.2% of the total weight of the heat-curable adhesive, and the cured adhesive exhibits a storage modulus of at least 900 MPa at 50° C. as measured by dynamic mechanical analysis according to ASTM E2254-09 and withstands at least 45 cycles of the environmental aging under stress test after curing for 10 minutes at 160° C.
2. A method for bonding an aluminum member to a second metal member, comprising forming a layer of a heat-curable structural adhesive of claim 1 between and in contact with the aluminum member and the second metal member to form an assembly and then heating the assembly including the structural adhesive at a temperature of at least 120° C. up to 170° C. to cure the structural adhesive and form an adhesive bond between the aluminum member and the second metal member.
3. A heat-curable structural adhesive comprising:
A) 41 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one diglycidyl ether of bisphenol A having an epoxy equivalent weight of about 186;
B) 23.8 weight percent, based on the total weight of the heat-curable structural adhesive, of a reaction product of 19.6% of a carboxyl-terminated copolymer of butadiene and acrylonitrile, the copolymer of butadiene and acrylonitrile having a number average molecular weight of 2000 to 6000 and 70.2% of a diglycidyl ether of bisphenol F having an epoxy equivalent weight of about 180 which reaction product is further diluted with 10.2% of a diglycidyl ether of bisphenol A having an epoxy equivalent weight of 1600 to 2000;
C) 12 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one elastomeric toughener containing isocyanate groups capped with phenol;
D) 5.1 weight percent, based on the total weight of the heat-curable structural adhesive, of dicyandiamide;
E) 4 weight percent of calcium oxide, based on the total weight of the heat-curable structural adhesive;
F) 0.6 weight percent, based on the total weight of the heat-curable structural adhesive, of a heat activatable catalyst comprising a mixture of 2,4,6-tris(dimethylaminomethyl)phenol and a novolac resin,
G) 0.2 weight percent, based on the total weight of the heat-curable structural adhesive, of a blocked diethylene triamine catalyst;
H) 12.7 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one inorganic filler;
I) a surfactant; and
J) a colorant
and further wherein the elastomeric toughener and the rubber portion of component B) together constitute 16.8% of the total weight of the heat-curable adhesive, and the cured adhesive exhibits a storage modulus of at least 900 MPa at 50° C. as measured by dynamic mechanical analysis according to ASTM E2254-09 and withstands at least 45 cycles of the environmental aging under stress test after curing for 10 minutes at 160° C.
4. A method for bonding an aluminum member to a second metal member, comprising forming a layer of a heat-curable structural adhesive of claim 3 between and in contact with the aluminum member and the second metal member to form an assembly and then heating the assembly including the structural adhesive at a temperature of at least 120° C. up to 170° C. to cure the structural adhesive and form an adhesive bond between the aluminum member and the second metal member.
5. A heat-curable structural adhesive comprising:
A) 34.56 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one diglycidyl ether of bisphenol A having an epoxy equivalent weight of about 186;
B) 26.5 weight percent, based on the total weight of the heat-curable structural adhesive, of a reaction product of 19.6% of a carboxyl-terminated copolymer of butadiene and acrylonitrile, the copolymer of butadiene and acrylonitrile having a number average molecular weight of 2000 to 6000 and 70.2% of a diglycidyl ether of bisphenol F having an epoxy equivalent weight of about 180 which reaction product is further diluted with 10.2% of a diglycidyl ether of bisphenol A having an epoxy equivalent weight of 1600 to 2000;
C) 12 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one elastomeric toughener containing isocyanate groups capped with phenol;
D) 4 weight percent, based on the total weight of the heat-curable structural adhesive, of dicyandiamide;
E) 3 weight percent of calcium oxide, based on the total weight of the heat-curable structural adhesive;
F) 0.7 weight percent, based on the total weight of the heat-curable structural adhesive, of a heat activatable catalyst comprising a mixture of 2,4,6-tris(dimethylaminomethyl)phenol and a novolac resin,
G) 0.1 weight percent, based on the total weight of the heat-curable structural adhesive, of a blocked diethylene triamine catalyst;
H) 14.8 weight percent, based on the total weight of the heat-curable structural adhesive, of a flame retardant;
I) 4 weight percent, based on the total weight of the heat-curable structural adhesive, of at least one inorganic filler;
J) a surfactant; and
K) a colorant
and further wherein the elastomeric toughener and the rubber portion of component B) together constitute 17.2% of the total weight of the heat-curable adhesive, and the cured adhesive exhibits a storage modulus of at least 900 MPa at 50° C. as measured by dynamic mechanical analysis according to ASTM E2254-09 and withstands at least 45 cycles of the environmental aging under stress test after curing for 10 minutes at 160° C.
6. A method for bonding an aluminum member to a second metal member, comprising forming a layer of a heat-curable structural adhesive of claim 5 between and in contact with the aluminum member and the second metal member to form an assembly and then heating the assembly including the structural adhesive at a temperature of at least 120° C. up to 170° C. to cure the structural adhesive and form an adhesive bond between the aluminum member and the second metal member.