Thermoplastic adhesives

Novel thermoplastic adhesive components, prepared from inexpensive and readily available synthetic materials, having melting points between about 20.degree. C. to about 180.degree. C. and broad ranges of hardness, flexibility and compatibility are disclosed. The novel thermoplastic compounds useful in adhesive formulations are comprised of a resinous polyamide reaction product of a polyoxypropylene polyamine having an average molecular weight of from about 190 to about 3,000 and being selected from diamines, triamines, or mixtures thereof, piperazine and an aliphatic or aromatic dicarboxylic acid, ester or anhydride having from about 4 to about 20 carbon atoms per molecule. The resinous polyamide reaction product is prepared by mixing and reacting the polyoxypropylene polyamine, piperazine, and dicarboxylic acid materials in a total amine:acid molar ratio within the range of from about 0.25:1.0 to about 4.0:1.0 at a temperature of from about 175.degree. C. to about 270.degree. C. The inventive thermoplastic polyamides can be formulated with compatible plasticizing agents to prepare a useful adhesive to which can also be added other components, such as a minor amount of a polyepoxide resin having an epoxide equivalent weight of about 150 to about 600, fillers and the like to produce thermoplastic adhesive formulations having desired hardness, flexibility and compatibility that are capable of bonding together a variety of substrates.

A commonly assigned, co-pending application entitled "Thermoplastic 
Adhesives", Ser. No. 622,311, filed Oct. 14, 1975, in the name of Howard 
P. Klein, teaches a novel thermoplastic adhesive compound having a melting 
point of between about 20.degree. C. to about 180.degree. C. which is 
comprised of a resinous polyamide reaction product of a polyoxypropylene 
polyamine having an average molecular weight of about 190 to about 3,000 
selected from diamines, triamines, or mixtures thereof, and an aliphatic 
or aromatic dicarboxylic acid, ester or anhydride having from about 4 to 
about 20 carbon atoms per molecule, prepared by mixing and reacting the 
polyamine and the dicarboxylic acid material in molar ratios of from about 
0.25:1.0 to about 4.0:1.0 polyamine:acid at a temperature of from about 
175.degree. C. to about 270.degree. C. The thermoplastic adhesive 
compounds of our co-pending application are prepared with the addition of 
piperazine to prepare the thermoplastic adhesive compositions of this 
invention. 
BACKGROUND OF THE INVENTION 
This invention relates to thermoplastic adhesives, or hot-melt adhesives, 
and more particularly pertains to novel thermoplastic adhesives which 
include a resinous polyamide reaction product prepared from relatively 
inexpensive and readily available synthetic materials which have broad 
ranges of melting temperatures and exceptional adhesive properties. 
DESCRIPTION OF THE PRIOR ART 
The employment of polyamide reaction products of certain aliphatic 
polyamines and vegetable or animal based long-chain dimer or trimer fatty 
acids and related materials as thermoplastic or hot-melt adhesive 
components for the bonding of a multitude of materials, such as leather, 
textiles, wood, synthetic laminates, and the like, is well-known as shown 
by U.S. Pat. No. 2,969,555. Generally speaking, thermoplastic adhesives 
are prepared by the condensation reaction at elevated temperatures of 
aliphatic polyamines such as ethylenediamine, diethylenetriamine, 
hexamethylene diamine, and other similar aliphatic polyamines having 
primary and/or secondary amine groups, and a vegetable or animal-based 
polymerized polyene fatty acid, ester or anhydride prepared by the thermal 
polymerization of fatty oils containing glycerides of polymerizable fatty 
acids such as soybean oil, linseed oil, cottonseed oil, castor oil, and 
the like. The polyamide reaction products are prepared by heating such 
admixtures at temperatures which readily produce polyaminolysis of the 
fatty esters or dehydration of the polyamine salt of the fatty acids, as 
described in U.S. Pat. No. 2,450,940 to Cowan, et al. 
It is also known that the aforementioned polyamide reaction products can be 
formulated with other components, e.g., polyepoxide resins, to provide 
hot-melt formulations for tailored systems exhibiting certain desired 
physical properties, such as melting points, hardness, flexibility, and 
compatibility. For example, U.S. Pat. No. 2,867,592 to Morris, et al. 
describes an improved thermoplastic adhesive for use in rod form which 
contains an admixture of a polyamide reaction product of an alkylene 
polyamine and a vegetable-based polymerized fatty acid, ester or anhydride 
and a minor amount of a resinous polyepoxide. Patentees teach that the 
addition of the resinous polyepoxide increases the dimensional stability 
and strength of the thermoplastic adhesive during preparation and use. 
However, the vegetable and animal based long-chain dimer or trimer fatty 
acid materials conventionally employed in the preparation of 
polyamide-based thermoplastic adhesives have become incresingly short in 
supply due to market demands and are continuously increasing in price. 
Moreover, the aliphatic polyamine compounds generally employed for the 
preparation of these thermoplastic adhesives, mentioned hereinabove, are 
also used in great quantities as curing agents for polyepoxide resins, 
synthetic intermediates, and the like, thus making them more obtainable 
and expensive in thermoplastic adhesive manufacture. 
Driven by the need for a satisfactory replacement for these naturally 
derived materials, we have discovered that thermoplastic adhesives having 
broad ranges of hardness, flexibility and compatibility, and which are 
capable of bonding together a variety of substrates can be prepared from 
synthetic materials that are more economical and readily available than 
those heretofore employed and hereinbefore mentioned These novel 
thermoplastic adhesive compounds are comprised of the resinous polyamide 
reaction product of a polyoxypropylene polyamine having an average 
molecular weight of about 190 to about 3,000 and a short chain aliphatic 
or aromatic dicarboxylic acid, ester or anhydride having from about 4 to 
about 20 carbon at-oms per molecule as more particularly described in the 
Klein, commonly assigned co-pending application referred to hereinabove. 
We have now further discovered that the adhesive strength of the 
thermoplastic adhesive compounds described in this co-pending application 
can be greatly improved by the employment of piperazine in their 
preparation. We are unaware of any literature describing the employment of 
piperazine for the improvement of adhesive strength of thermoplastic 
adhesive materials comprised of polyamide reaction products. 
SUMMARY OF THE INVENTION 
The present invention is a compound useful as a thermoplstic adhesive 
component having a broad range of hardness, flexibility, and compatibility 
and is capable of bonding together a variety of substrates with improved 
adhesive strength which is comprised of a resinous polyamide reaction 
product of a polyoxypropylene polyamine selected from diamines, triamines, 
or mixtures thereof having an average molecular weight of from about 190 
to about 3,000, piperazine and an aliphatic or aromatic dicarboxylic acid, 
ester or anhydride having from 4 to about 20 carbon atoms per molecule. 
The themoplastic adhesive compound is prepared by mixing and reacting the 
polyoxypropylene polyamine, piperazine and dicarboxylic acid material in a 
molar ratio of about 0.25:1.0 to about 4.0:1.0 moles total amine:moles 
acid material, wherein the piperazine is present in an amount of up to 
about 80 molar percent, based upon the total molar amount of amine 
present, at a temperature of about 175.degree. C. to about 270.degree. C. 
The reaction time is preferably within the range of about 1 to about 12 
hours. The improved thermoplastic compounds of the invention thus produced 
have broad melting ranges of about 20.degree. C. to about 180.degree. C. 
and can be added to compatible plasticizers to produce adhesives and can 
also be formulated with other components such as a liquid polyepoxide 
resin having an epoxide equivalent weight of from about 150 to about 600, 
filler and the like, to produce thermoplastic adhesive formulations having 
particularly desirable properties for use in tailored systems for bonding 
a variety of substrates. The thermoplastic adhesive compounds of the 
invention exhibit unexpectedly high adhesive strengths.

DETAILED DESCRIPTION OF THE INVENTION 
Polyoxypropylene polyamines, and procedures for their preparation, useful 
in producing the thermoplastic adhesives of the invention are well-known 
and amply described in the literature. See, for example, U.S. Pat. No. 
3,654,370. Polyoxypropylene polyamines are known to be particularly useful 
as curing agents for polyepoxide resins as illustrated in U.S. Pat. No. 
3,462,393. We have found that these polyamine materials, when used in the 
preparation of the polyamide reaction product of the present invention, 
produce new and unexpected hot-melt adhesives. 
Preferably, we employ polyoxypropylene diamines of the formula: 
EQU NH.sub.2 (HCCH.sub.3)CH.sub.2 --OCH.sub.2 CH(CH.sub.3)].sub.x NH.sub.2 
wherein x is an integer of from about 2 to about 40, and polyoxypropylene 
triamines of the formula 
##STR1## 
where x, y and z represent integers in the range of about 1 to 15, and the 
sum of x, y and z is from about 3 to about 50. The most preferred 
polyoxypropylene diamines of the formula have average molecular weights 
between about 230, where x is an average of 2.6 to about 2,000 where x is 
an average of about 33.1. Preferred polyoxypropylene triamines of the 
above formula have average molecular weights between about 190 to about 
3,000. These polyoxypropylene di- and triamines are readily available 
commercially in a wide variety of molecular weight ranges, such as those 
sold by Jefferson Chemical Company, Inc., Houston, Texas, under the 
trademark JEFFAMINE.RTM.. 
The above-described polyoxypropylene polyamine and piperazine, the 
employment of which is described in more particularity hereafter, can be 
reacted with any known aliphatic or aromatic dicarboxylic acid, ester or 
anhydride compound having from about 4 to about 20 carbon atoms per 
molecule. As well-known in the art, dicarboxylic acids and related 
corresponding esters and anhydrides react with amines in substantially the 
same manner. Therefore, for the purposes of brevity only, these materials 
will hereinafter be referred as dibasic acids. Unexpectedly, we have found 
that the relatively readily available dibasic acids react easily with the 
described polyoxypropylene polyamines and piperazine to provide the 
unexpected hot-melt adhesives of the invention. The preferred aliphatic 
dibasic acids have a divalent, saturated, unsubstituted hydrocarbon group, 
while the preferred aromatic dibasic acids include an unsubstituted 
phenylene group. Examples of preferred dibasic acids and related materials 
include adipic, azelaic, sebacic, isophthalic, and terephthalic acids, 
phthalic and succinic anhydrides, and dimethylterephthalate esters, to 
name a few. The dibasic acids useful in the invention are relatively 
inexpensive and are readily available commercially. However, they have not 
heretofore been employed in the preparation of thermoplastic adhesives 
comprised of polyamide resins inasmuch as polyamide reaction products 
prepared therefrom have excessively high melting points and high rigidity. 
Moreover, such polyamide resins are normally incompatible with other 
components conventionally employed in the preparation of thermoplastic 
adhesive formulations such as polyepoxide resins. In view of these known 
disadvantages, the thermoplastic adhesive composition of the present 
invention was most unexpected. 
The third essential ingredient of the thermoplastic adhesive composition of 
the present invention is piperazine. We have discovered that the 
employment of piperazine in the preparation of the inventive resinous 
polyamide reaction product provides greatly improved adhesive strength, 
yet other physical characteristics such as flexibility, melting points, 
hardness and the like are not adversely affected whatsoever. Heretofore, 
piperazine has not been considered useful in the preparation of 
thermoplastic resins. However, our discovery provides increased 
flexibility in the employment of thermoplastic adhesives prepared from the 
above-described polyoxypropylene polyamines and dibasic acids for the 
production of thermoplastic adhesive formulations which can be tailored 
with particularly desirable physical properties. 
More particularly, the resinous polyamide reaction product of the present 
invention is prepared by mixing the above-described polyoxyproplene 
polyamine and piperazine with the above-described dibasic acid at a 
temperature of between about 175.degree. C. to about 270.degree. C. The 
polyamines and acid compounds are preferably mixed in total polyamine:acid 
molar ratios of from about 0.8:1.0 to about 1.25:1.0 with substantially 
equimolar ratios being especially preferred. The admixture is usually 
heated for several hours, i.e., from about 1 to about 12 hours, at maximum 
temperature to complete the reaction, while by-product water or alcohol, 
depending upon the particular compounds employed, is removed. Preferably, 
the reaction mixture is vacuum stripped by known procedures to develop 
optimum molecular weight. 
The piperazine can be added before, during or after the above-described 
polyoxypropylene polyamine is added to the above-described dibasic acid. 
It is preferred that all three components of the resin are mixed together 
and reacted at once. The piperazine is added in an amount of about 10 to 
about 80 molar percent, preferably about 30 to about 70 molar percent, 
based upon the total molar amount of amine required for the formulation, 
set forth hereinabove. Accordingly, the amount of polyoxypropylene 
polyamine employed is reduced to provide the above-described molar ratios 
of total polyamine:acid which can be readily determined by one having 
ordinary skill in the art without undue experimentation. 
The polyoxypropylene-dibasic acid-piperazine polyamide polymers are random 
polymers which have a molecular weight less than about 10,000, and 
normally have a molecular weight ranging from about 2,000 to about 10,000. 
It is important that the molcular weight of the polyamide be within the 
just mentioned range in order that it possess proper utility as an 
adhesive component. Such polyamides of molecular weight lower than 10,000 
have the requisite relatively low melting point whereupon heating a hot 
melt can be achieved which upon rapid cooling forms the desired strong 
adhesive bond. Polyamides having a molecular weight substantially in 
excess of 10,000 do not meet this criteria. Even more importantly, it is 
necessary that the polyamide polymer have such relatively low molecular 
weight in order that it can be properly formulated with other adhesive 
components, and particularly plasticizers. It is necessary that the 
polyamide be soluble or compatible with such plasticizer components. 
Examples of compatible plasticizers which may be used with the polyamides 
here to prepare useful thermoplastic adhesives include toluene 
sulfonamides, dibutyl phthalates, or short chain polyfunctional polyols. 
The amount of compatible plasticizer used to prepare the inventive 
thermoplastic adhesive ranges from about 5 to about 50 weight percent 
based on the weight of the adhesive formulation including the polyamide 
compound, with about 10 to about 40 weight percent being optimum. 
It is also important that the polyamides have a proper molecular weight 
below about 10,000 in order that they exhibit proper flexibility as an 
adhesive component. Again, polyamides of molecular weight substantially 
above 10,000, say about 30,000 or above, molecular weight are too rigid to 
be useful as thermoplastic adhesives. Such polyamides formed from blocks 
of the nylon type while useful as fibers have been found to be completely 
unsuitable as a thermoplastic adhesive component. 
In a preferred embodiment, the above-described inventive resinous polyamide 
reaction product is formulated along with a plasticizer with about 1 to 
about 25 weight percent, based upon the total formulation weight, of a 
polyepoxide resin at a temperature above the melting points of each 
component, e.g., within the range of about 20.degree. C. to about 
180.degree. C. The polyepoxide resin component employed is preferably one 
that is conventionally used in preparing thermoplastic adhesives. Such 
polyepoxides are well-known complex resinous materials and are generally 
prepared by the reaction of polyhydric organic compounds with a 
polyfunctional chlorhydrin. References which describe in detail methods 
for preparing the epoxide resins of the type concerned here include "Epoxy 
Resins", by Lee and Neville, McGraw-Hill Book Company, Inc., (1957), and 
"Epoxy Resins", by Irving Skeist, Reinhold Publishing Company (1958). The 
particularly preferred polyepoxide resins are the polyglycidyl ethers of 
polyhydric phenols, such as the diglycidyl ether of resorcinol, the 
triglycidyl ether of phloroglucinol, the tetraglycidyl ether of 
tetraphenylolethane of the polyglycidyl ether of a phenolformaldehyde 
novolac. Especially preferred is the diglycidyl ether of 
4,4'-isopropylenediphenol, generally known as bisphenol A, containing a 
minor amount of cogeneric materials of higher molecular weight and having 
an epoxide equivalent weight (grams of resin containing 1 equivalent 
epoxide) of approximately 175 to about 190. 
The inventive resinous polyamide reaction compound will normally contain 
several unreacted amine and carboxyl groups. It is believed that these 
unreacted groups react with the epoxy group of the subsequently added 
polyepoxide resin and enhances the tensile strength of the adhesive 
formulation. Thus, preferably, the resinous polyamide reaction product 
component will contain a total amine content of about 0.1 to about 2.0 
meq./g. and will have an acid number of between about 2 to about 20. The 
total amine content and acid number can be readily controlled during the 
preparation of the polyamide reaction product as described hereinabove by 
known procedures and both can be readily determined by well-known 
analytical procedures. 
Preferably, the polyepoxide resin component is added to the resinous 
polyamide reaction product and plasticizer composition in an amount of 
from about 5 to about 25 weight percent, based upon the total weight of 
the formulation. The specific amount employed is dependent upon the 
epoxide equivalent weight of the polyepoxide resin and the total amine 
content and acid number of the polyamide reaction product and should be an 
amount which will not produce gelation. The specific amount for given 
components can be readily determined by one having ordinary skill in the 
art with only minor experimentation using known procedures, such as that 
described in U.S. Pat. No. 2,867,592, which is incorporated herein by 
reference. The experimentation described therein includes heating a series 
of resinous polyamide components containing varying amounts of polyepoxide 
resin to 150.degree. C. in 1-inch glass tubes and dropping a 3/16-inch 
steel ball therein. Gelation is defined therein as the state whereby the 
steel ball will not fall or will not fall regularly through the resinous 
component. 
In an espcially preferred embodiment of the invention, a diglycidyl ether 
of bis-phenol A having an epoxide equivalent weight of about 175 to 190 is 
added to the above-described polyamide reaction product in an amount of 
about 5 to about 25 weight percent, based upon total formulation weight, 
while the resinous polyamide component is heated at about 100.degree. C. 
to about 130.degree. C. Upon cooling, the resulting compound does not 
exhibit gelation and has a melting point between about 100.degree. C. to 
about 180.degree. C., depending upon the compounds employed in the 
preparation of the resinous polyamide reaction product component. 
Moreover, compatible fillers can be employed if desired in amounts from 0 
percent up to about 30 weight percent without reducing the adhesive 
properties or other physical characteristics of the inventive compound. In 
fact, compatible fillers have been found to increase the adhesion bond 
when the adhesive compounds are applied to certain substrates by reducing 
thermal expansion, thus reducing strain during curing of the system. 
Examples of compatible fillers include fumed silica, calcium carbonate, 
kaolin clays, alumina or titanium oxides, and the like. 
The following examples illustrate the invention in more detail, but are not 
to be construed as limitative. JEFFAMINE.RTM. is the registered trademark 
for polyoxypropylenedi- and triamines sold by Jefferson Chemical Company, 
Inc., Houston, Texas. 
EXAMPLES I-III 
Three thermoplastic adhesive formulations were prepared employing the 
compounds set forth in the following Table 1. The resinous polyamide 
reaction product compounds employed in the Examples of Table 1 were 
prepared by admixing the described polyamine components with isophthalic 
acid in the described molar ratios and heating the admixtures at a 
temperature of 200.degree.-240.degree. C. for 6-8 hours with continuous 
removal of water. The reaction product mixtures were vacuum stripped 
during the last stages of reaction to develop the optimum molecular 
weight. The resinous polyamide reaction product components were then mixed 
at a temperature of about 120.degree.-140.degree. C. with the designated 
amounts of polyepoxide resin (diglycidyl ether of bis-phenol A, epoxide 
equivalent weight of 182-189), plasticizer and fillers. Glass beads were 
added to each formulation to insure even coat-ing between substrates. Each 
formulation was then coated between the designated substrates in a liquid 
state and allowed to solidify. The adhesion values are set forth in Table 
1. 
Table 1 
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Example No. I II III 
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Polyamide .sup.(1) 100 -- -- 
Polyamide.sup.(2) -- 100 -- 
Polyamide.sup.(3) -- -- 100 
Liquid DGEBA epoxy resin (EEW 182-189) 
15 15 15 
Plasticizer.sup.(4) 45 45 15 
Fumed silica.sup.(5) 1.5 1.5 1.5 
Glass beads, 0.0035" dia. 
0.3 0.3 0.3 
Tensile shear strength, psi (ASTM D1002) 
Aluminum-to-aluminum 2150 .+-. 190 
1520 .+-.50 
2590 .+-. 420 
Steel-to-steel 2530 .+-. 80 
2360 .+-. 340 
1895 .+-. 60 
Laminate-to-laminate.sup.(6) 
880 .+-. 60 
780 .+-. 60 
920 .+-. 60 
Wood-to-wood 360 .+-. 40 
300 .+-.40 
-- 
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.sup.(1) Prepared from JEFFAMINE .sup.R D-400, a polyoxypropylene diamine 
having an average molecular weight of 400 (Jefferson Chemical Company, 
Inc.): piperazine:isophthalic acid; molar ratio 0.3:0.7:0.9. 
.sup.(2) Prepared from JEFFAMINE .sup.R D-230, a polyoxypropylene diamine 
having an average molecular weight of 230 (supra): isophthalic acid; mola 
ratio 1.01 to 1.0. 
.sup.(3) Prepared from JEFFAMINE .sup.R D-400 (supra): 
piperazine:isophthalic acid; molar ratio 0.5:0.5:0.9. 
.sup.(4) N-ethyl, o-, p-toluenesulfonamides. 
.sup.(5) Cab-o-sil .sup.R fumed silica (Cabot Corp.). 
.sup.(6) Formica .sup.R phenolic laminate (American Cyanamid Co.). 
As illustrated in Table 1, thermoplastic adhesives of the present invention 
employing piperazine in combination with the polyoxypropylene polyamine 
(Examples I and III) exhibit greatly improved adhesive strength in bonding 
metals, wood and laminates. 
EXAMPLES IV-VII 
Four thermoplastic adhesive formulations were prepared employing the 
compounds in the amounts set forth in the following Table 2. The resinous 
polyamide reaction product compounds and adhesive formulations of Table 2 
were prepared in accordance with the procedures described in Examples 
I-III. The polyoxypropylene diamine employed in Examples IV-VII was the 
same as that in Example I. 
Table 2 
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Example No IV V VI VII 
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Resinous Polyamide 
Composition, moles: 
JEFFAMINE .RTM. D-400.sup.(1) 
1.0 0.75 0.50 0.30 
Piperazine -- 0.30 0.50 0.70 
Isophthalic acid 0.9 1.0 0.90 0.90 
Polyamide Resin Properties 
Ball and ring softening point, .degree. C. 
(ASTM E28-67) 46 -- 98 124 
Adhesive Formulation, grams 
Polyamide 100 100 100 100 
Epoxy resin.sup.(2) 15 25 15 15 
N-Ethyl-o,p-toluene sulfonamide 
10 10 15 60 
Fumed silica 1 1 1 1 
Adhesive Properties 
Tensile shear strength 
(ASTM D1002-64T), lbs/in..sup.2 
Aluminum-to-aluminum 
510 1200 2590 2150 
Laminate-to-laminate.sup.(3) 
90 86 920 710 
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.sup.(1) A polyoxypropylene diamine having a molecular weight of 400, 
Jefferson Chemical Company, Inc. 
.sup.(2) Liquid diglycidyl ether of bis-phenol A, epoxide equivalent 
weight 190. 
.sup.(3) Formica .RTM. phenolic laminate, American Cyanamide Co. 
The results of Table 2 confirm the results set forth in Table 1 in regard 
to the improved adhesive strength of the inventive thermoplastic adhesive 
compositions. Compare Examples II and IV to Examples I and V-VII. In 
addition, a comparison of the results of Examples V, VI and VII show that 
piperazine can be employed in amounts over a wide range with improved 
adhesive strengths being observed. 
EXAMPLES VIII-X 
Three additional thermoplastic adhesive formulations were prepared in 
accordance with the procedures described in Examples I-III utilizing the 
compounds in the amounts set forth in the following Table 3. The 
polyoxypropylene polyamine employed in Example II. The results of the 
following Table 3 further confirm the results set forth in Table 1. 
Table 3 
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Example No. VIII IX X 
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Resinous Polyamide Composition, moles: 
JEFFAMINE.RTM. D-230.sup.(1) 
1.01 0.71 0.52 
Piperazine -- 0.30 0.50 
Isophthalic acid 1.00 1.00 1.00 
polyamide Resin Properties 
Ball and ring softening point, .degree. C. 
(ASTM E28-67) 118 133 159 
Adhesive Formulation, gms. 
Polyamide 100 100 100 
Epoxy resin.sup.(2) 15 15 15 
N-Ethyl-o,p-toluene sulfonamide 
45 45 75 
Fumed silica 1 1 1 
Adhesive Properties 
Tensile shear strength 
(ASTM D1002-64T), lbs/in.sup.2 
Aluminum-to-aluminum 1520 2450 2440 
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.sup.(1) A polyoxypropylene diamine having a molecular weight of 230, 
Jefferson Chemical Company, Inc. 
.sup.(2) Liquid diglycidyl ether of bis-phenol A, epoxide equivalent 
weight 190. 
Obviously, many modifications and variations of the invention as 
hereinbefore set forth may be made without departing from the spirit and 
scope thereof and, therefore, only such limitations should be imposed as 
are indicated in the claims.