Epoxy adhesive

The invention is an epoxy resin adhesive composition. The composition comprises: PA0 A. An epoxy resin component comprising: PA1 1. 72 to 104 pbw of a vicinal polyepoxide having an average of at least 1.8 reactive 1,2-epoxy groups per molecule, PA1 2. 8 to 16 pbw of trimethylolpropanetriacrylate PA1 3. 10 pbw of a polyoxypropylene diureide of 2000 to 3000 molecular weight; and PA0 B. A curative component comprising: PA1 1. a curing amount of triethyleneglycol diamine or tetraethyleneglycol diamine; and PA1 2. an effective cure acclerating amount of piperazine, N-aminoethylpiperazine or mixture thereof. The fast curing adhesive offers high lap shear strength and relatively high peel strength.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a two part epoxy resin adhesive formulation. 
2. Description of Other Relevant Materials in the Field 
Curing epoxy resins with amino containing compounds to form adhesives is 
known in the art. 
U.S. Pat. No. 4,187,367 to H.G. Waddill teaches an epoxy resin adhesive 
comprising an epoxy resin, a polyether diureide having terminal ureido or 
monosubstituted ureido groups and having a molecular weight of about 2000 
to 3000 and an aminoalkylene derivative of polyoxyalkylenepolyamine. 
U.S. Pat. No. 4,051,195 to W. F. McWhorter teaches curable epoxy resin 
compositions comprising (1) a blend of an epoxide resin and a polyacrylate 
or polymethacrylate ester of a polyol wherein the ester contains more than 
one terminal acrylate or methacrylate and (2) an aliphatic polyamine 
curing agent. The weight ratio of epoxide resin:ester is 100:5 to 100:100. 
The aliphatic polyamine is incorporated into the resin composition in a 
specified amount. The epoxy resin compositions are said to cure rapidly 
even at low temperature and are useful as coatings and adhesives. 
U.S. Pat. No. 4,528,345 to H. G. Waddill teaches a method for making 
weather-resistant epoxy coatings. The method comprises prereacting a 
cycloaliphatic diepoxide resin with aminoethylpiperazine or a mixture of 
aminoethylpiperazine and polyoxyalkylenepolyamine in an amount which is 
balanced to give the maximum level of primary amine reaction without 
yielding an excessively viscous reaction product. The prereacted product 
is reacted with a curing amount of a polyoxyalkylene polyamine and an 
accelerator. 
U.S. Pat. No. 3,875,072 to H. G. Waddill teaches an accelerator for curing 
epoxy resins. The accelerator comprises piperazine and an alkanolamine in 
a weight ratio of 1:8 to 1:1. 
U.S. Pat. No. 4,195,153 to H. G. Waddill teaches a non-crystallizing 
accelerator for curing curing epoxy resins. The accelerator comprises a 
mixture of N-aminoethylpiperazine and triethanolamine. 
U.S. Pat. No. 4,189,564 to H. G. Waddill teaches a non-crystallizing 
accelerator for curing epoxy resins. The accelerator comprises a mixture 
of piperazine, N-aminoethylpiperazine and triethanolamine. The product 
comprising 65 to 80 wt% triethanolamine, 10 to 20 wt% piperazine and 5 to 
10 wt% N-aminoethylpiperazine is sold commercially as Accelerator 399 by 
Texaco Chemical Co. The accelerator is said to be synergistic for 
accelerating the curing of a polyglycidyl ether of a polyhydric phenol 
cured with a polyoxyalkylene polyamine at ambient or elevated 
temperatures. Such amines include polyoxypropylene diamines of the 
formula: 
EQU NH.sub.2 CH(CH.sub.3)CH.sub.2 [OCH.sub.2 CH(CH.sub.3)].sub.x NH.sub.2 
wherein x ranges from 2 to 40. 
These diamines may be synthesized according to U.S. Pat. No. 3,654,370 to 
E. L. Yeakey which teaches a method comprising a nickel, copper and 
chromium catalyst for aminating polyols. These diamines were originally 
taught in U.S. Pat. No. 3,462,393 to Legler. 
U.S. Pat. No. 3,496,138 to R. F. Sellers and C. F. Pitt teaches curing 
diepoxides with polyglycol diamines. Suitable glycol precursors to these 
diamines include ethylene glycol, diethylene glycol and polyethylene 
glycol. 
SUMMARY OF THE INVENTION 
The invention is an epoxy resin adhesive composition. The epoxy component 
comprises: a mixture of (1) 72 to 104 parts by weight of a vicinal 
polyepoxide having an average of at least 1.8 reactive 1,2-epoxy groups 
per molecule (2) 8 to 16 parts by weight trimethylolpropane triacrylate, 
and (3) 5 to 15 parts by weight of a polyoxypropylene diureide having a 
molecular weight of 2000 to 3000. The curative component comprises: (1) a 
curing amount of either triethyleneglycol diamine or tetraethyleneglycol 
diamine and (2) an effective cure accelerating amount of piperazine, 
N-aminoethylpiperazine or mixture thereof. 
This system demonstrates a rapid cure, high lap shear strength and 
relatively high peel strength. These qualities are effective for use as 
adhesives. The formulation comprising triethyleneglycol diamine is 
particularly preferred.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Two epoxy adhesive formulations have been discovered which demonstrate 
rapid cure, high lap shear strength and relatively high peel strength. The 
formulation comprises liquid epoxy resin diluted with acrylate ester, an 
adhesion promoting additive, an amine curing agent and a cure accelerating 
composition. 
Generally the vicinal polyepoxide containing compositions which may be 
cured with the products of the invention are organic materials having an 
average of at least 1.8 reactive 1,2-epoxy groups per molecule. These 
polyepoxide materials can be monomeric or polymeric, saturated or 
unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic, and may 
be substituted if desired with other substituents besides the epoxy 
groups, e.g., hydroxyl groups, ether radicals, aromatic halogen atoms and 
the like. These vicinal polyepoxide containing compounds typically are of 
an epoxy equivalent weight of 150 to 250. Preferably the base resin, which 
has an epoxide equivalent weight of from 175 to 195, is derived from 
condensing epichlorohydrin with 2,2-bis(p-hydroxyphenyl)propane to form 
2,2-bis[(p-2,3 epoxy propoxy) phenyl]propane, a derivative of bisphenol A. 
Preferred polyepoxides are those of glycidyl ethers prepared by epoxidizing 
the corresponding allyl ethers or reacting, by known procedures, a molar 
excess of epichlorohydrin and an aromatic polyhydroxy compound, i.e., 
isopropylidene bisphenol, novolac, resorcinol, etc. The epoxy derivatives 
of methylene or isopropylidene bisphenols are especially preferred. 
A widely used class of polyepoxides which are useful according to the 
instant invention includes the resinous epoxy polyethers obtained by 
reacting an epihalohydrin, such as epichlorohydrin, and the like, with 
either a polyhydric phenol or a polyhydric alcohol. Typically the epoxy 
resins have an average of at least 1.8 reactive, 1,2-epoxy groups per 
molecule. An illustrative, but by no means exhaustive, listing of suitable 
dihydric phenols includes 4,4'-isopropylidene bisphenol, 
2,4'-dihydroxydiphenylethyl methane, 3,3'-dihydroxydiphenyldiethylmethane, 
3,4'-dihydroxydiphenylmethylpropylmethane, 
2,3'-dihydroxydiphenylethylphenylmethane, 
4,4'-dihydroxydiphenylpropylphenylmethane, 
4,4'-dihydroxydiphenylbutylphenylmethane, 
2,2'-dihydroxydiphenylditolylmethane, 
4,4'-dihydroxydiphenyltolylmethylmethane and the like. Other polyhydric 
phenols which may also be coreacted with an epihalohydrin to provide these 
epoxy polyethers are such compounds as resorcinol, hydroquinone, 
substituted hydroquinones, e.g., methylhydroquinone, and the like. 
Among the polyhydric alcohols which can be coreacted with an epihalohydrin 
to provide these resinous epoxy polyethers are such compounds as ethylene 
glycol, propylene glycols, butylene glycols, pentane diols, 
bis(4-hydroxycyclohexyl)dimethylmethane, 1,4-dimethylolbenzene, glycerol, 
1,2,6-hexanetriol, trimethylolpropane, mannitol, sorbitol, erythritol, 
pentaerythritol, their dimers, trimers and higher polymers, e.g., 
polyethylene glycols, polypropylene glycols, triglycerol, 
dipentaerythritol and the like, polyallyl alcohol, polyhydric thioethers, 
such as 2,2'-, 3,3'-tetrahydroxydipropylsulfide and the like, mercapto 
alcohols such as monothioglycerol, dithioglycerol and the like, polyhydric 
alcohol partial esters, such as monostearin, pentaerythritol monoacetate 
and the like, and halogenated polyhydric alcohols such as the 
monochlorohydrins of glycerol, sorbitol, pentaerythritol and the like. 
Another class of polymeric polyepoxides which can be cured by the products 
of the invention in accordance with the present invention includes the 
epoxy novolac resins obtained by reacting, preferably in the presence of a 
basic catalyst, e.g., sodium or potassium hydroxide, an epihalohydrin, 
such as epichlorohydrin, with the resinous condensate of an aldehyde, 
e.g., formaldehyde, and either a monohydric phenol, e.g., phenol itself, 
or a polyhydric phenol. Further details concerning the nature and 
preparation of these epoxy novolac resins can be obtained in Lee, H. and 
Neville, K., Handbook of Epoxy Resins, McGraw Hill Book Co., New York, 
1967. 
The polyoxypropylene diureide having a molecular weight of 2000-3000 may be 
described by the formula: 
##STR1## 
This diureide is produced by reacting a diamine of the formula: 
EQU H.sub.2 NCH(CH.sub.3)CH.sub.2 --[OCH.sub.2 CH(CH.sub.3)].sub.x NH.sub.2 
wherein x is about 33.1, with two moles of urea. The diamine is available 
commercially as JEFFAMINE.RTM. D-2000. The diureide is available 
commercially as JEFFAMINE.RTM. BuD-2000. 
The amine cured resins having superior adhesion in accordance with the 
instant invention are prepared in a conventional manner. The amine curing 
agent combination is admixed with the polyepoxide composition in amounts 
according to the amine equivalent weight of the curing agent combination 
employed. Generally the number of equivalents of amine groups is from 
about 0.8 to about 1.2 times the number of epoxide equivalents present in 
the curable epoxy resin composition, with a stoichiometric amount being 
preferred. In the instant invention about 21 to 23 parts by weight 
triethyleneglycol diamine or about 30 to 33 parts by weight 
tetraethyleneglycol diamine has been determined to be an effective curing 
amount. When an accelerator is used, amounts from 1 to about 15 parts by 
weight based on 100 parts by weight of the resin are generally 
satisfactory. The exact amount of constituents in accordance with the 
above general requirements will depend primarily on the application for 
which the cured resin is intended. 
The diureide and triacrylate are incorporated into the uncured resin by 
admixing. The curing agent and accelerator are admixed separately. The 
constituents forming the curable material are then intimately admixed by 
standard methods. 
Although all of the epoxy resins disclosed herein are generally useful in 
accordance with the instant invention concept, those based on aliphatic 
compounds are preferably not used exclusively. The presence of resins 
containing polyglycidyl ethers of polyhydric phenols in amounts greater 
than 50% by weight of the resin constituent, and more preferably 80% by 
weight has been shown to greatly enhance the desirable properties of the 
cured material, especially the adhesive strength. 
Generally, the mixture of epoxy resin, the polyether diureide, the 
triacrylate, the polyethyleneglycol diamine and the accelerator 
combination is allowed to self-cure at ambient temperatures of between 
0.degree. C. to about 45.degree. C. The data shows that excellent adhesive 
properties are developed at room temperature of about 25.degree. C. 
According to a greatly preferred embodiment, resins of the polyglycidyl 
ether of polyhydric phenol type incorporating therein 8 to 16 parts by 
weight trimethylolpropane triacrylate and 5 to 15 parts by weight of the 
urea terminated polyoxyalkylenepolyamine having a molecular weight of 
about 2000; are cured with a stoichiometric amount of tri- or 
tetraethyleneglycol diamine and from 1 to 10 parts by weight percent based 
on 100 parts by weight of the resin of an accelerator comprising an 
admixture of piperazine, N-aminoethylpiperazine and triethanolamine. The 
composition is cured at room temperature to produce products having 
superior adhesive strength in accordance with the instant invention. 
It will further be realized that various conveniently employed additives 
can be admixed with the adhesive composition prior to final cure. For 
example, pigments, dyes, fillers, flame retarding agents and the like may 
be added to produce a custom formulation for a particular end use. 
Furthermore, although not preferred, known solvents for polyepoxide, 
materials such as toluene, benzene, xylene, dioxane, ethylene glycol 
monomethylether and the like can be used. Polyepoxide resins containing 
the additives can be used in any of the applications for which 
polyepoxides are customarily used. The compositions of the instant 
invention can be used most importantly, as adhesives. 
The formulations effective in bringing about the increased adhesion and 
peel strength properties were discovered empirically as demonstrated in 
the example. Particularly, trimethylolpropanetriacrylate was found to 
speed cure rate and impart flexibility to the cured adhesive. 
The following examples illustrate the nature of the instant invention but 
are not intended to be limitative thereof. 
EXAMPLE 1 
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Adhesive Properties of Systems Containing Epoxy Resins and an 
Aliphatic Amine 
-33 -33 -33 -33 -33 
A B C D E 
______________________________________ 
Formulation, pbw (6170) 
Liquid epoxy resin (EEW 188) 
90 70 50 30 10 
EPI-REZ .RTM. 50727 
10 30 50 70 90 
Triethyleneglycol diamine 
20.9 22.3 23.7 25.1 26.4 
Adhesion Properties 
after 24 hrs 25.degree. C. 
Tensile shear strength, psi 
-- -- -- -- 790 
T-peel strength, pli 
-- -- -- -- 11.5 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
1300 1600 2200 3000 3400 
T-peel strength, pli 
* 3.5 3.5 4.4 5.6 
______________________________________ 
*Test Samples broke apart before testing 
Although properties of Formulation 6170-33E are good after a 7-day cure, 
strength properties are very low after a 24-hr. cure. 
EXAMPLE 2 
______________________________________ 
Adhesion Properties of Formulated Systems 
-42A -42B -42C -42D 
______________________________________ 
Formulation, pbw (6170) 
Liquid epoxy resin (EEW 188) 
80 60 40 20 
EPI-REZ .RTM. 50727 
20 40 60 80 
2000AMINE BuD .RTM. 
10 10 10 10 
Triethyleneglycol diamine 
21 23 24 26 
Accelerator 399 5 5 5 5 
Adhesion Properties 
after 6 hrs. 25.degree. C. 
Tensile shear strength, psi 
1300 400 -- -- 
T-peel strength, pli 
12.2 25.8 -- -- 
after 16 hrs. 25.degree. C. 
Tensile shear strength, psi 
3700 3300 -- -- 
T-peel strength, pli 
8.3 9.9 -- -- 
after 24 hrs. 25.degree. C. 
Tensile shear strength, psi 
3700 3200 2800 2500 
T-peel strength, pli 
6.9 6.9 8.8 10.8 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
4000 3500 -- -- 
T-peel strength, pli 
10.0 4.8 -- -- 
______________________________________ 
These systems develop excellent adhesive properties in less than 16 hours 
at normal room temperature (25.degree. C.). 
EXAMPLE 3 
______________________________________ 
Effect of Other Additives on Adhesive Properties 
A B C D 
______________________________________ 
Formulation, pbw 
Liquid epoxy resin (EEW 188) 
80 60 40 20 
EPI-REZ .RTM. 50727 20 40 60 80 
Additive 10 10 10 10 
Triethyleneglycol diamine 
.rarw.a curing amount.fwdarw. 
Accelerator 399 5 5 5 5 
Adhesive Properties 
after 24 hrs. 25.degree. C. 
Additive = JEFFAMINE .RTM. BuD-2000 
(6170-42) 
Tensile shear strength, psi 
3700 3200 2800 2500 
T-Peel strength, pli 6.9 6.9 8.8 10.8 
Additive = JEFFAMINE .RTM. T-5000 
(6170-55) 
Tensile shear strength, psi 
2800 3100 3000 2400 
T-Peel strength, pli 10.1 5.4 7.5 8.8 
Additive = JEFFAMINE .RTM. D-2000 
(6170-53) 
Tensile shear strength, psi 
3700 3100 2300 430 
T-Peel strength, pli 4.6 7.0 4.3 7.3 
Additive = JEFFAMINE .RTM. DU-700 
(6170-58); 20 pbw instead of 10 pbw 
Tensile shear strength, psi 
2900 2200 1600 1000 
T-Peel strength, pli 3.7 9.0 13.0 14.0 
______________________________________ 
JEFFAMINE .RTM. BuD2000 gives the best combination of sheer strength and 
peel strength. 
EXAMPLE 4 
______________________________________ 
Adhesive Properties and Curing Characteristics of Systems 
Containing Epoxy Resins and an Aliphatic Amine 
-82A -82B -82C -82D 
______________________________________ 
Formulation, pbw (6170) 
Liquid epoxy resin (EEW 188) 
80 60 40 20 
EPI-REZ .RTM. 50727 
20 40 60 80 
Tetraethyleneglycol diamine 
30.2 32.1 34.0 35. 
Adhesion Properties 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
4000 4100 4000 3000 
T-Peel strength, pli 
6.3 5.4 4.4 9.1 
Drying time, hrs 
set to touch 3.6 3.9 0.7 0.2 
surface dry 5.7 4.6 2.1 0.5 
thru dry 10.8 9.6 9.5 4.2 
______________________________________ 
EXAMPLE 5 
______________________________________ 
Adhesion Properties and Curing 
Characteristics of Adhesive Systems 
-73A -73B -73C -73D 
______________________________________ 
Formulation, pbw (6170) 
Liquid epoxy resin (EEW 188) 
80 60 40 20 
EPI-REZ .RTM. 50727 
20 40 60 80 
JEFFAMINE .RTM. BuD-2000 
10 10 10 10 
Tetraethyleneglycol diamine 
30.2 32.1 34.0 35.9 
Accelerator 399 5 5 5 5 
Adhesion Properties 
after 8 hrs 25.degree. C. 
Tensile shear strength, psi 
360 160 -- -- 
T-Peel strength, pli 
17.2 10.6 -- -- 
after 16 hrs 25.degree. C. 
Tensile shear strength, psi 
2300 1700 -- -- 
T-Peel strength, pli 
16.7 26.7 -- -- 
after 24 hrs 25.degree. C. 
Tensile shear strength, psi 
3500 2700 2100 1200 
T-Peel strength, pli 
11.3 15.8 23.5 27.1 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
3500 3500 3100 2000 
T-Peel strength, pli 
10.3 10.7 11.6 9.6 
Drying time, hrs 
set to touch 2.5 2.1 1.5 -- 
surface dry 3.6 3.3 2.6 0.5 
thru dry 6.3 4.4 3.7 2.5 
______________________________________ 
EXAMPLE 6 
______________________________________ 
Effects of Other Curing Agents on Adhesion Properties 
A B C D 
______________________________________ 
Resin Blends, pbw 
Liquid epoxy resin (EEW 188) 
80 60 40 20 
EPI-REZ 50727 20 40 60 80 
JEFFAMINE BuD-2000 10 10 10 10 
Adhesive Properties 
Curative = Triethylenetetramine 
(6170-69) 
Curative Conc., pbw 13.8 14.7 15.6 16.5 
after 24 hrs 25.degree. C. 
Tensile shear strength, psi 
2300 3000 3200 2200 
T-Peel strength, pli 4.7 3.9 3.2 3.7 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
3400 3200 1900 3100 
T-Peel strength, pli 5.0 4.1 * 4.0 
Curative = Polyamide (Amine value 
370-400) (6170-70) 
Curative Conc., pbw 56 59 63 66 
after 24 hrs 25.degree. C. 
Tensile shear strength, psi 
1200 460 440 330 
T-Peel strength, pli 23.4 17.2 15.2 9.8 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
3200 2800 2900 2600 
T-Peel strength, pli 9.9 10.2 10.6 10.3 
Curative = JEFFAMINE .RTM. D-230 
(6170-71), with 5 pbw Accelerator 399 
Curative Conc., pbw 34 36 39 41 
after 24 hrs 25.degree. C. 
Tensile shear strength, psi 
1500 630 270 170 
T-Peel strength, pli 10.2 10.9 8.4 2.6 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
3000 2200 1900 2100 
T-Peel strength, pli 6.8 6.2 3.1 2.6 
Curative = JEFFAMINE .RTM. D-400 
(6170-72), with 5 pbw Accelerator 399 
Curative Conc., pbw 57 61 64 68 
after 48 hrs 25.degree. C. 
Tensile shear strength, psi 
440 120 90 80 
T-Peel strength, pli 13.8 7.2 5.2 3.5 
after 7 days 25.degree. C. 
Tensile shear strength, psi 
1900 1100 770 270 
T-Peel strength, pli 10.0 13.0 10.1 7.2 
______________________________________ 
*Test sample broke before testing 
Although most of these other curing agents offered adequate adhesive 
properties after a 7 day ambient cure, they did not cure rapidly. 
______________________________________ 
TABLE OF TEST METHODS 
______________________________________ 
T-peel strength (pli) 
ASTM D-1876 
Tensil shear strength (psi) 
ASTM D-1002 
______________________________________ 
TABLE OF COMPOUNDS 
EPI-REZ.RTM. 50727 is a blend of 40% trimethylolpropanetriacrylate and 60% 
of a bisphenol A epoxy resin. 
JEFFAMINE.RTM. BuD-2000 is the polyoxypropylene diureide having a molecular 
weight of 2000-3000 described by the formula: 
##STR2## 
JEFFAMINE.RTM. D-230, D-400 and D-2000 are represented by the structure: 
EQU H.sub.2 NCH(CH.sub.3 CH.sub.2 --[OCH.sub.2 CH(CH.sub.3)].sub.x NH.sub.2 
wherein: 
______________________________________ 
JEFFAMINE .RTM. x(approx.) 
______________________________________ 
D-2000 33.1 
D-400 5.6 
D-230 2.6 
______________________________________ 
JEFFAMINE.RTM. T-403 is represented by the structure: 
##STR3## 
wherein x+y+z averages 5.3. 
The use of these products as epoxy resin curing agents is described in U.S. 
Pat. No. 4,189,564. 
Accelerator 399 is a blend of 10-20% piperazine, 5-10% 
N-aminoethylpiperazine and 65-80% triethanolamine. 
JEFFAMINE.RTM. DU-700 is an amine represented by the formula: 
EQU [H.sub.2 NCH(CH.sub.3)CH.sub.2 --[OCH.sub.2 CH(CH.sub.3)].sub.x NH].sub.2 
--C.dbd.O 
wherein: x averages 5.6 
JEFFAMINE.RTM. EDR-148 is triethyleneglycol diamine. 
JEFFAMINE.RTM. EDR-192 is tetraethyleneglycol diamine. 
While particular embodiments of the invention have been described, it is 
well understood that the invention is not limited thereto since 
modifications may be made. It is therefore contemplated to cover by the 
appended claims any such modifications that fall within the spirit and 
scope of the claims.