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CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to Ser. No. 101,699, filed Sept. 28, 1987
entitled EPOXIDE AND RUBBER BASED CURABLE COMPOSITIONS.
BACKGROUND OF THE INVENTION
The present invention relates to curable compositions suitable for use as
adhesives and sealants.
In the manufacture and assembly of automobiles, adhesives and sealants are
used for a variety of different purposes. As a consequence, depending upon
the mode of use, each adhesive or sealant has different physical
properties requirements, such as a certain threshold lap shear strength at
a particular temperature, a wide latitude of cure temperatures with the
ability to cure both at very low and at very high temperatures,
resiliency, good elongation and good adhesion to differing substrates.
Heretofore, because of the diversity and disparity in requirements, a
different adhesive or sealant has been necessary for each of the different
applications in automobile manufacture. For example, separate materials
have been used as structural adhesives, as gap filling sealants, or as
anti-flutter adhesives.
There is a need, therefore, for a single curable composition which can be
used for a variety of different purposes and with the capability to meet
all of the physical properties differing requirements.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a one-package,
stable curable composition comprising:
(a) a nonfunctional polydiene;
(b) a polyepoxide;
(c) a sulfur and zinc containing vulcanization system adapted to cure the
polydiene and the polyepoxide; and
(d) an anhydride containing material adapted to promote adhesion of the
curable composition to metal, wherein the anhydride containing material
remains essentially unreacted with the epoxide and is combined in a manner
to obtain dissolution of the anhydride containing material in the epoxide.
Also provided is a method of preparing an adhesive bond between two
surfaces to form a bonded structure.
DETAILED DESCRIPTION OF THE INVENTION
The curable composition of the present invention comprises as one of its
principal constituents a polydiene.
The polydiene polymers include polymers of 1,3-dienes containing from 4 to
12 and preferably from 4 to 6 carbon atoms. Typical dienes include
1,3-butadiene which is preferred, 2,3-dimethyl-1,3-butadiene, isoprene,
chloroprene and piperylene. Also, copolymers of 1,3-butadiene and a
monomer copolymerizable with 1,3-butadiene such as isopropene,
acrylonitrile, and piperylene can be used. Other polymerizable monomers
such as methyl methacrylate, acrylic acid, and styrene can also be used.
Preferably the polydiene polymer is a mixture of 1,4-polybutadiene and a
1,4-polybutadiene acrylonitrile copolymer.
If desired, a variety of vulcanizable or non-vulcanizable synthetic rubbers
can be used as inert fillers in conjunction with the polydiene. Examples
of such synthetic rubbers include butyl rubber, ethylene propolyene
terpolymer, silicone rubbers, polysulfides, polyacrylate rubbers and
chlorinated polyethylene rubbers. Copolymers of many of the aforelisted
synthetic rubbers with styrene can also be utilized.
It should be understood that the polydiene polymer of the present invention
can be either functional or non-functional. In preferred embodiments, the
polydiene polymer is non-functional, that is, it does not contain
functional group such as, for example, hydroxyl, amino, carboxyl or
mercapto.
Another principle constituent of the claimed curable compositions is a
polyepoxide.
The polyepoxides are those materials having a 1,2 epoxide group present in
the molecule. Hydroxyl groups may also be present and often are. A
polyepoxide for the purposes of the present invention contains at least
two 1,2-epoxy groups per molecule. In general, the epoxide equivalent
weight can range from about 289 to about 4,000. These polyepoxides are
saturated or unsaturated, cyclic or acyclic, aliphatic, alicyclic,
aromatic or heterocyclic. They can contain substituents such as halogen,
hydroxyl and ether groups.
One useful class of polyepoxides comprises the epoxy polyethers obtained by
reacting an epihalohydrin (such as epichlorohydrin or epibromohydrin) with
a polyphenol in the presence of an alkali. Suitable polyphenols include
resorcinol, catechol, hydroquinone, bis(4-hydroxyphenyl)-2,2-propane,
i.e., bisphenol A; bis(4-hydroxyphenyl)-1,1-isobutane;
4,4-dihydroxybenzophenone; bis(4-hydroxyphenyl)-1,1-ethane;
bis(2-hydroxynaphenyl)-methane; and 1,5-hydroxynaphthalene. One very
common polyepoxide is a polyglycidyl ether of a polyphenol, such as
bisphenol A. More preferably the polyepoxide is a diglycidyl ether of
bishphenol A.
Another class of polyepoxides are the polyglycidyl ethers of polyhydric
alcohols. These compounds may be derived from such polyhydric alcohols as
ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene
glycol, 1,4-butylene glycol, triethylene glycol, 1,2-propylene glycol,
1,4-butylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol,
trimethylolpropane, and bis(4-hydroxycyclohexyl-2,2-propane.
Another class of polyepoxides are the polyglycidyl esters of polycarboxylic
acids. These compounds are produced by the reaction of epichlorohydrin or
a similar epoxy compound with an aliphatic or aromatic polycarboxylic acid
such as oxalic acid, succinic acid, glutaric acid, terephthalic acid,
2,6-naphthalene dicarboxylic acid and dimerized linoleic acid.
Still another class of polyepoxides are derived from the epoxidation of an
olefinicaly unsaturated alicyclic compound. These polyepoxides are
non-phenolic and are obtained by epoxidation of alicyclic olefins, for
example, by oxygen and selected metal catalysts, by perbenzoic acid, by
acid-aldehyde monoperacetate or by peracetic acid. Among such polyepoxides
are the epoxy alicyclic ethers and esters well known in the art.
Useful polyepoxides also include those containing oxyalkylene groups in the
epoxy molecule. Another class of polyepoxides consists of the epoxy
novalac resins. These resins are obtained by reacting an epihalohydrin
with the condensation product of aldehyde and monohydric or
epichlorohydrin with a phenol formaldehyde condensate.
Another group of epoxide containing materials includes acrylic copolymers
containing copolymerized glycidyl acrylate or methacrylate units. These
acrylic copolymers can be prepared by the reaction of alkyl esters of
alpha, beta unsaturated mono- or di-carboxylic acid with either glycidyl
acrylate or methacrylate. Other glycidyl containing copolymerizable
monomers such as diglycidyl itaconate and diglycidyl maleate also can be
used. These monomers can be optionally copolymerized in the presence of
other copolymerizable monomers such as vinyl aromatic compounds, such as
styrenee or vinyl toleuene, and also acrylonitrile or methacrylonitrile.
Preferably the polyepoxide is a diepoxide. Preferably a polyglycidyl ether
of bisphenol A is used, more preferably a diglycidyl ether. Examples of
suitable materials are the EPON epoxy resins which are commercially
availble from Shell Chemical, such as EPON 828.
It should be understood that mixtures of the aforedescribed polyepoxides
can be used herein.
In preferred embodiments of the present invention an epoxy-rubber adduct is
utilized as an additional additive in order to achieve optimum adhesion of
the curable composition to oily metal. A preferred adduct is that which is
prepared from an excess amount of the diglycidyl ether of bisphenol A,
e.g., EPON 828 from Shell Chemical and a carboxyl terminated polybutadiene
acrylonitrile copolymer, e.g., CTBN from B. F. Goodrich. The resultant
epoxy functional adduct is free of carboxyl functionality.
A further principle constituent of the claimed curable composition is a
sulfur and zinc containing vulcanization system which is adapted to cure
the polydiene and the polyepoxide components.
As used in this specification, vulcanization is the physicochemical change
resulting from crosslinking of the polydiene with sulfur, generally with
application of heat. The precise mechanism which produces the network
structure during the cure of the claimed compositions is still not
completely known. However, it is theorized that a physical incorporation
of the epoxide into the polydiene rubber lattice may be in effect. The
vulcanization system comprises a material or mixture of material which is
adapted to effect cure of the polydiene and the polyepoxide. Preferably
the vulcanization system comprises a lower alkyl dithiocarbamate and a
disulfide. A number of lower alkyl dithiocarbamates are useful herein,
particularly those having from 1 to 10, preferably 1 to 5 carbon atoms in
the alkyl portion. Examples of suitable dithiocarbamates include methyl,
ethyl, propyl, butyl and amyl dithiocarbamate. Preferably the dibutyl
dithiocarbamate is utilized herein. These materials are commercially
available in association with zinc in salt form, namely zinc dibutyl
dithiocarbamate, zinc dimethyl dithiocarbamate, zinc diethyl
dithiocarbamate and zinc diamyl dithiocarbamate. These materials can be
commercially obtained from Vanderbilt Chemical Company under the trade
designation ZIMATE.
The zinc which is part of the vulcanization system can be introduced in
different ways. One example has been given above in connection with the
vulcanization system; that is, the zinc can be associated with the lower
alkyl dithiocarbamate in salt form. The zinc can also be introduced as
zinc oxide. It should be understood that a variety of grades of zinc oxide
are available and can be utilized for this purpose. The amount of zinc in
the vulcanization system can vary widely, generally from about 0.1 percent
by weight to about 10 percent by weight based on the total weight of the
curable composition. The precise mechanism is not understood; however, it
is believed that the zinc functions as an accelerator for the sulfur
vulcanization.
The disulfide component of the vulcanization system can also be selected
from a variety of materials. Examples of suitable disulfides include
4-morpholinyl-2-benzothiazole disulfide; 4,4'-dithiobismorpholine and
benzothiazyl disulfide. Preferably the disulfide is benzothiazyl
disulfide. It is believed that the dithiocarbamate and the disulfide
components of the vulcanization system function as primary and secondary
accelerators, respectively, for the vulcanization reaction. Moreover, in
preferred embodiments of the present invention it is believed that the
disulfide species functions as a retarder for premature vulcanization. It
is believed that the thiocarbamate operates in conjunction with the sulfur
in order to effect the crosslinked, cured system. It is also believed that
the dithiocarbamate functions not only to assist in vulcanization of the
rubber component of the composition but in addition functions to
incorporate the epoxide component into the crosslinked network. As has
been mentioned above, the precise mechanism for this is not understood.
A further principle constituent of the claimed curable compositions is an
anhydride containing material which is adapted to promote adhesion of the
curable composition to metal. A variety of carboxylic acid anhydrides are
contemplated to be within the scope of the present invention so long as
they are capable of promoting adhesion of the curable composition direct
to metal. The anhydride containing material is preferably a carboxylic
acid anhydride selected from the group consisting of maleic anhydride,
itaconic anhydride and phthalic anhydride. Preferably when a carboxylic
acid anhydride is utilized, maleic anhydride is utilized. If desired,
mixtures of the aforesaid carboxylic anhydrides can be utilized. The
anhydride containing material can also be anhydride adduct. That is, an
adduct comprising the reaction product of a carboxylic acid anhydride
which is adapted to promote adhesion of the curable composition to metal
with an olefinically unsaturated material. Preferably the carboxylic
anhydride which is adducted with the olefinically unsaturated material is
one of the anhydrides listed above. More preferably, it is maleic
anhydride.
Examples of adducts with olefinically unsaturated materials include adducts
formed from an appropriate anhydride as defined above in for example "ene"
type reactions and free radical initiated polymerizations. Examples of
these include adducts formed from the free radical initiated
polymerization of two moles of 1-octene or 1-diene with one mole of maleic
anhydride; and "ene" adducts formed by heating a polydiene such as
polybutadiene with maleic anhydride.
Preferably, the claimed curable compositions are prepared as a moisture
free system. The presence of water is not preferred because it opens the
anhydride ring structure and interferes with the desired cure. Therefore,
dessicant materials are typically added in order to remove water from the
system.
Moreover, preferably the carboxylic acid anhydride is pretreated by heating
it in the presence of a diepoxide for a period of time of at least about
five minutes at a temperature ranging from about 60.degree. C. to about
150.degree. C. It has been observed that when this pretreatment is
conducted the carboxylic acid anhydride remains essentially unreacted. The
pretreatment is an apparent dissolution of anhydride in epoxide. This
result has been confirmed by infrared spectroscopy, acid number
determinations and gel permeation chromatography. It has been observed
that the carboxylic acid anhydride provides optimum stability and also
performance in promoting adhesion to metal when pretreated this way.
In preferred embodiments of the present invention, the claimed curable
composition is essentially free of amino group containing materials. The
presence of amine is not preferred because it detracts from the resiliency
of the resultant cured composition.
The amounts of each of the constituents of the claimed curable composition
can vary widely depending upon the particular properties desired in the
curable composition. For example, by varying the amount of polyepoxide and
dithiocarbamate which is utilized in the curable composition, one can
tailor the hardness of the ultimate cured composition. The more
polyepoxide and dithiocarbamate which is utilized, the harder and stronger
the polydiene polyepoxide cured material becomes. Generally, the amount of
polydiene which is utilized in the claimed curable composition can vary
within the range of from about 2 percent by weight to about 80 percent by
weight. Preferably, the amount of polydiene which is utilized varies from
about 5 percent by weight to about 50 percent by weight, and more
preferably from about 10 percent by weight to about 15 percent by weight.
The amount of polyepoxide generally can vary within the range of from
about 1 percent by weight to about 75 percent by weight, preferably from
about 5 percent by weight to about 40 percent by weight, and more
preferably from about 10 percent by weight to about 20 percent by weight,
the percentages based on the total weight of the curable composition. The
sulfur containing vulcanization system is utilized in amounts varying from
about 0.5 to about 25 percent by weight based on the total weight of the
curable composition.
In preferred embodiments the dithiocarbamate primary accelerator can be
present in an amount ranging from about 0.1 percent by weight to about 7
percent by weight, preferably from about 0.5 percent by weight to about 3
percent by weight and more preferably from about 1 percent by weight to
about 2 percent by weight. The disulfide secondary accelerator can be
present in an amount ranging from about 0.2 percent by weight to about 14
percent by weight, preferably from about 1 percent by weight to about 6
percent by weight and more preferably from about 2 percent by weight to
about 4 percent by weight. All the percentages are based on the total
weight of the curable composition.
The amount of sulfur which is part of the vulcanization system can also
vary widely. Generally the amount of sulfur varies from about 0.1 percent
by weight to about 15 percent by weight, preferably from about 0.2 percent
by weight to about 5 percent by weight and more preferably from about 0.5
percent by weight to 1.5 percent by weight, the percentages based on the
total weight of the curable composition. The sulfur can be utilized in a
variety of forms but typically it is elemental sulfur and it is used as a
solid oil-treated powder. For example, suitable sources of sulfur for the
vulcanization system are the CRYSTEX brand sulfurs which are commercially
available from the Stauffer Chemical Company.
It should be understood that the accelerator materials discussed above can
contribute a minor amount of the required sulfur in the vulcanization
system.
The amount of anhydride containing material can also vary widely depending
upon the particular choice of material.
When the anhydride containing material is an unreacted carboxylic acid
anhydride the amount can vary generally from about 0.1 percent by weight
to about 10 percent by weight, preferably from about 0.2 percent by weight
to about 5 percent by weight and more preferably from about 0.3 percent by
weight to about 1.5 percent by weight. When the anhydride containing
material is an adduct of an appropriate anhydride and anolefinically
unsaturated material, the amount of the adduct can vary from about 0.1
percent by weight to about 20 percent by weight, preferably from about 0.5
percent by weight to about 10 percent by weight and more preferably from
about 4 percent by weight to about 8 percent by weight. All of the
percentages enumerated above are based on the total weight of the curable
composition.
The claimed curable compositions can comprise a variety of other optional
additives in addition to the principle constituents which have been
detailed above. Examples of additives include fillers such as calcium
carbonate, stearic acid treated calcium carbonate, polybutadiene treated
calcium carbonate, barium sulfate, calcium and magnesium oxide, carbon
blacks, hydrocarbon tackifiers and various phthalate and adipate
plasticizers and antioxidants. Examples of suitable antioxidants are
butylated hydroxytoluene, butylated and styrenated phenols and cresols,
alkylated quinones and hydroquinones and butylated hydroxy benzyl
isocyanates.
The claimed one package, stable curable compositions have a very wide
latitude of cure temperatures. The claimed curable compositions can be
cured by baking at a temperature within the range of from about
220.degree. F. to about 550.degree. F. (104.degree. C. to 288.degree. C.)
for a period of time ranging from about 10 minutes to about 60 minutes.
Preferably, the claimed curable compositions are cured by baking within a
temperature of from about 325.degree. F. to about 400.degree. F.
(163.degree. C. to 204.degree. C.) in a period of time ranging from about
15 minutes to about 30 minutes. One very unexpected advantage of the
claimed curable compositions is their ability to cure both at very high
temperatures and at very low temperatures while achieving comparable
physical properties at both extremes. This capability reduces problems
associated with underbaking and overbaking and permits the tailoring of
compositions to suit a variety of application conditions.
In addition, the claimed curable compositions have outstanding adhesion
direct to metal, particularly to oily metal. Moreover, the claimed curable
compositions are capable of adhering to a wide variety of other substrates
such as aluminum, primed metal, plastic, wood, and other substrates. It is
believed that the anhydride containing material is very important in
achieving the adhesion of the claimed curable compositions direct to
metal.
The claimed curable compositions can be applied by conventional means
although typically they are applied by extrusion.
The claimed one package, stable curable compositions also demonstrate a
wide variety of other advantageous properties such as solvent resistance,
heat resistance, good elongation, resiliency, good lap shear strength at
high temperatures and in addition they demonstrate good overall strength
at ambient temperature. The claimed curable compositions also exhibit good
cohesive failure. Also, they have excellent package stability for
prolonged periods of up to three months.
The following examples are intended to be illustrative of the invention and
are not intended to be limiting.
EXAMPLE I
This Example illustrates the preparation of a curable composition according
to the claimed invention.
______________________________________
Parts by Weight
Ingredients (grams)
______________________________________
HYCAR 1312 LV.sup.1
12.85
EPON 828.sup.2 13.22
MULTIFLEX SC.sup.3 23.10
butylated hydroxytoluene
1.92
butyl zimate.sup.4 0.86
ALTAX.sup.5 1.72
POLIOL 130.sup.6 11.26
calcium carbonate 17.75
calcium oxide 5.17
sulfur.sup.7 1.72
carbon black 1.25
plasticizer.sup.8 0.96
EPOXY-CTBN adduct.sup.9
5.75
IDMA/STEREON 840 A.sup.10
1.00
maleic anhydride.sup.11
0.50
______________________________________
.sup.1 This unsaturated resin is a butadieneacrylonitrile copolymer which
is commercially available from B. F. Goodrich.
.sup.2 This epoxy resin is the diglycidyl ether of bisphenol A which is
commerically available from Shell Chemical Company. It has an epoxy
equivalent weight of 185 to 192.
.sup.3 This is a stearic acid treated calcium carbonate which is
commerically available from Pfizer.
.sup.4 This is a zinc dibutyldithiocarbamate which is commerically
available from R. T. Vanderbilt Chemical Co. R. T. Vanderbilt Chemical Co
.sup.5 This is benzothiazyl disulfide which is commercially available fro
R. T. Vanderbilt Chemical Co.
.sup.6 This unsaturated resin is the polymerization product of
1,3butadiene which is commerically available from Huls. The molecular
weight is approximately 3,000.
.sup.7 This is CRYSTEX OT90 from Stauffer Chemical which is an oil
treated powder having a 90 percent sulfur content.
.sup.8 Diisododecyl phthalate plastizer.
.sup.9 This epoxy resin is the reaction product of a carboxy terminated
acrylonitrilebutadiene copolymer (commercially available from B. F.
Goodrich) and EPON 828 in excess EPON 828.
.sup.10 This is a dissolution product of 30 percent by weight STEREON
840A, a styrenebutadiene copolymer available from Firestone, in 70 percen
isodecylmethacrylate. It was used as a flow additive.
.sup.11 The maleic anhydride was heated for approximately one hour at
120.degree. C. with EPON 828. It is demonstrated by IR, GPC and acid
numbers, that the maleic anhydride in this solution is essentially
unreacted.
The adhesive composition was prepared by combining the ingredients together
with mild agitation. The compositions was tested for physical properties
as follows.
Lap Shear Strength
Lap shear bonds for testing were prepared using two strips of cold rolled
steel 1 inch.times.4 inches.times.0.062 inch (2.54 cm.times.10.16
cm.times.0.158 cm). A 118 mil (2.95 millimeters) thick film of a
composition was applied onto one of the metal strips and then a second
strip was placed over top of the first strip so that only a one-half
square inch (3.16 square centimeter) strip overlapped. The composition was
cured at 160.degree. C. for 30 minutes, 190.degree. C. for 30 minutes and
at 205.degree. C. for 120 minutes (three different bonds were prepared,
one for each temperature). The lap shear strength of the bond in pounds
per square inch (psi) (newtons per square millimeter) was determined
according to ASTM D-1002-65. The data presented for each temperature was
an average of three separate determinations. (The ends of the strips were
pulled with an INSTROM TESTER device and the lap shear strength of the
bond measured.)
Tensile Strength
A 0.100 inch (0.254 cm) thick layer of a composition was applied onto a
TEFLON treated glass panel measuring 12 inches.times.12 inches.times.0.100
inch (30 cm.times.30 cm.times.0.254 cm). The composition was cured by
baking at 190.degree. C. for 30 minutes and then the panel was cooled to
room temperature. The free films were prepared and evaluated for tensile
strength according to ASTM D 638. Each value in psi (newtons per square
millimeter) is an average of three separate determinations. The percent
elongation was also determined according to this ASTM test.
Shore A Hardness
A 0.100 inch (0.254 cm) thick layer of a composition was applied onto a
metal panel. The composition was cured by baking at 190.degree. C. for 30
minutes and then cooled to room temperature. The Shore A hardness was
determined using a Shore Durometer Hardness Type A-2 instrument according
to ASTM D676.
T-peel Strength
The composition was evaluated for T-peel strength according to ASTM D1876.
T-peel bonds for evaluation were prepared as follows. Two strips of cold
rolled steel measuring 1 inch.times.6 inches.times.0.031 inch (2.54
centimeters.times.15.24 centimeters.times.0.079 centimeters) were used. A
118 mil (2.95 millimeters) thick film of adhesive composition was applied
onto one of the metal strips and then a second metal strip was placed
overtop the first strip so that a 4 square inch (25.81 square centimeter)
section was bonded. Then the two ends of the panels which were not bonded
were bent to form a T-shape. The load for the T-peel strength
determination was applied at 5.0 inch (12.7 centimeters) per minute. The
T-peel strength is measured in pounds per linear inch (lbs/in)
(killinewtons per meter). The results are set out below:
______________________________________
Lap Shear Strength at 190.degree. C./30 min:
410 psi (2.8 newtons/mm.sup.2)
Lap Shear Strength at 110.degree. C./30 min:
280 psi (1.9 newtons/mm.sup.2)
Lap Shear Strength at 205.degree. C./120 min:
360 psi (2.5 newtons/mm.sup.2)
T-peel Strength: 38 psi (2.6 killinewtons/
meter)
Tensile Strength: 508 psi (3.5 newtons/mm.sup.2)
Elongation: 180 percent
Shore A Hardness: 68
______________________________________
______________________________________
EXAMPLES II to VI
(Parts by Weight in Grams)
Ingredients II III IV* V VI
______________________________________
HYCAR 1312 LV 16.60 12.85 12.85 12.85
12.85
EPON 828 15.22 13.22 13.22 13.22
13.22
MULTIFLEX SC 23.10 23.10 23.10 23.10
23.10
butylated hydroxytoluene
1.92 1.92 1.92 1.92 1.92
butyl zimate 0.86 0.86 0.86 0.86 0.86
ALTAX 1.72 1.72 1.72 1.72 1.72
POLIOL 130 11.26 11.26 11.26 11.26
11.26
calcium carbonate
17.25 17.25 17.25 17.25
17.25
calcium oxide 5.17 5.17 5.17 5.17 5.17
sulfur of footnote.sup.7
1.72 1.72 1.72 1.72 1.72
carbon black 1.25 1.25 1.25 1.25 1.25
plasticizer of
footnote.sup.8 0.96 0.96 0.96 0.96 0.96
epoxy-CTBN adduct
of footnote.sup.9
0.00 5.75 5.75 0.00 5.75
IPDA/STEREON 840 A
1.00 1.00 1.00 1.00 1.00
maleic anhydride
0.50 0.00 0.00 0.50 0.00
phthalic anhydride
0.00 0.00 4.00 0.00 0.00
itaconic anhydride
0.00 1.50 0.00 0.00 0.00
dimer acid- 0.00 0.00 0.00 5.75 0.00
epoxy adduct.sup.12
rosin-maleic an-
0.00 0.00 0.00 0.00 2.00
hydride adduct.sup.13
______________________________________
.sup.12 This epoxy resin is the reaction product of the dimer acid of
rosin and EPON 828 in excess EPON 828.
.sup.13 This DielsAlder adduct was prepared by reacting 0.9 mole of malei
anhydride with 1 mole of rosin at 180.degree. C. for 4 hours.
*Had less than two weeks package stability at room temperature.
Each of the adhesive compositions were prepared and evaluated as has been
described above in Example I. Evaluations were done for lap shear
strength, elongation and Shore A Hardness. The results appear below. The
cure temperature was 190.degree. C. for 30 minutes in Examples II to V.
______________________________________
Lap Shear Strength
Elongation
Shore A
Example (psi) (newtons/mm.sup.2)
(percent)
Hardness
______________________________________
II 366 2.54 60 64
III 210 1.46 180 65
IV 140 0.97 120 90
V 180 1.25 90 38
VI 215 1.49 100 70
______________________________________
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