Note: Descriptions are shown in the official language in which they were submitted.
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K-17336/-/CGC 1383
WET AD~IESION EPOXY RESIN SYSTE~MS
The present invention relates to epoxy adhesive composi~ions comprising an organosilane
with a terrninal mercapto group for improved wet adhesion, to the products obtained by
curing said compositions and to a process for improving the wet adhesion of an epoxy
adhesive system.
Epoxy resins are extensively utilized as adhesives for the bonding and repair of concrete
surfaces. lt has been determined, however, that epoxy adhesive strength and bond durabili-
ty are poor under moist conditions. Such exposure is frequently encountered under adverse
weather conditions of rain, snow or ice or during application in moist environments. The
unacceptable adhesive characteristics come into play in the bonding of wet or damp
concrete to wet or damp concrete, the bonding of old concrete to new concrete, the bond-
ing of metal to moist concrete, and the like. Since currently utilized epoxy adhesives do
not provide the desired performance, there is a current need for epoxy adhesive systems
which are readily applicable to all surface configurations and which perform under all
environmental conditions.
It has now been surprisingly discovered that by incorporating specified concentrations of
organo silanes containing terminal functional groups into epoxy resin formulations, en-
hanced adhesive perforrmance characteristics are obtained. Thus, the improved systems are
applicable for use under a wide range of conditions. The systems are particularly useful
under moist conditions when the adhesive bonding occurs in a damp environment.
Contrary to prior art systems, excellent adhesive strength and bond durability are obtained.
The instant invention relates to an adhesive composition comprising
a) an epoxy resin having on average more than one epoxy group per molecule
b) an amine hardener therefor; and
c) from about 0.5-10 % by weight of a) and b) of an organo silane containing a terminal
mercapto group.
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The instan~ compositions facilitate the bonding of moist concrete to other concrete compo-
sitions, to metal, and the like.
The epoxy resins used according to the invention may be any polyepoxide so far as it has
on average, more than one epoxy group per molecule. It may be any of saturated and
unsaturated, aliphatic, alicyclic, aromatic and heterocyclic epoxides. If desired, it may
have a non-hindering substituent such as halogen atom, hydroxyl group, ether group, ester
group and the like. Examples of said polyepoxides inciude epoxy novolac resins; poly-
glycidyl ethers of dihydric phenols such as 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-
hydroxyphenyl)ethane, bis(4-hydroxyphenyl)methane, bis(4-hydroxyphenyl)sulfone,
resorcinol and hydroquinone; polyglycidyl ethers of trihydric alcohols such as glycerin;
polyglycidyl esters such as diglycidyl phthalate and diglycidyl isophthalate; cycloaliphatic
epoxy resins; epoxidized esters of polyethylenically unsaturated fatty acids such as epoxi-
dized linseed oil; epoxidized esters of unsaturated alcohols and unsaturated carboxylic
acids such as 3,4-epoxycyclohexylmethyl, 3,4-epoxycyclohexylcarboxylate; and epoxi-
dized polyethylenically unsaturated hydrocarbons.
Diglycidyl ethers of dihydric phenols are preferred. Particularly preferred is the diglycidyl
ether of 2,2-~is(4-hydroxyphenyl)propane.
Applicable resins also include epoxy resins with lowered viscosities resulting from the
presence of reactive diluents such as glycidyl ethers, glycol ethers, aromatic hydrocarbons,
and the like.
As suitable hardeners for use in the systems, there may be mentioned aliphatic or cycloali-
phatic primar~ and secondary amines, including mixnlres. Typical amines include
ethylenediamine, hexamethylenediamine, trimethylhexamethylenediamine, methylpenta-
methylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine,
N,N-dimethylpropylenediamine,1,3, N,N-diethylpropylenediamine-1,3, bis(4-amino-3-
methyl-cyclohexyl)methane, bis(p-aminocyclohexyl)methane, 2,2-bis(4-aminocyclo-
hexyl)-propane, 3,5,5-trimethyl-s-(aminomethyl)-cyclohexylamine, 1,2-diaminocyclo-
hexane, 1,4-diaminocyclohexane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(amino-
methyl)-cyclohexane, N-aminoethylpiperazine, isophorone diamine, p-pllenylenediamine,
m-phenylenediamine, bis(4-aminop'henyl)-methane, bis(4-aminophenyl)ether, bis(4-aminophenyl)ketone, aniline-formaldehyde resins, bis(4-aminophenyl)sulfone, bis(3-
aminophenyl)sulfone and 2,4'-diaminodiphenyl sulfone.
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The preferred hardeners include 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethyl-
hexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, triethylene-
tetramine, tetraethylenepentamine, 1,2-diaminocyclohexane, bis(p-aminocyclohexyl)-
methane, isophorone diamine, 1,4-bis(aminomethyl)-cyclohexane, N-aminoethylpipera-
zine and 1,3-bis(aminomethyl)cyclohexane.
Examples for the organo silanes containing a terminal mercapto group include gamma-
mercapto-propyltrimethoxysilane, beta-mercaptoethyltrimethoxysilane, mercaptomethyl-
trimethoxysilane, beta-mercaptoethyltripropoxysilane, gamma-mercaptopropylphenyldi-
methoxysilalle and beta-mercaptoethylmethyldimethoxysilane.
Particularly preferred is gamma-mercaptopropyltrimethoxysilane.
The silane is present in concentrations varying from 0.5-10 ~o by weight based on the
resin/hardener combination and preferably 0.5-5 % by weight. Concentrations which
noticeably deviate from the prescribed range have an adverse effect on adhesive
properties, particularly on the wet adhesive strength and durability.
The silane may be mixed either with the epoxy resin or with the hardener at room tempe-
rature prior to combination of resin and hardener. In general, it is preferred to mix the
epoxy and vinyl silanes with the epoxy resin and the amino and mercapto silanes with the
amine hardener.
The subsequent curing of the epoxy resin compositions of this invention is within the
knowledge of the art. Curing is generally effected at temperatures of between 5-40C for
the appropriate period of time in the presence of a hardener. The hardener is utilized in
stoichiometric amounts +50 % relative to the modified epoxy resin, with 1:1 stoichiometry
being preferred. Upon curing, a network of high crosslink density occurs. Accordingly, the
expression "cure" as used herein, denotes the conversion of the above epoxide material
into insoluble and infusible crosslinked products. Said products are also an object of the
present invention.
The epoxy resins prepared according to the invention can furthermore be mixed, at any
stage before cure, with usual modifiers such as extenders, fillers and reinforcing agents,
pigments, dyestuffs, organic solvents, plasticizers, tackifiers, rubbers, accelerators,
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diluents, and the like. As extenders, reinforcing agents, fillers and pigments which can be
employed in the curable mixtllres according to the invention there may be mentioned, for
example: coal tar, bitumen, glass fibers, boron fibers, carbon fibers, cellulose, poly-
ethylene powder, polypropylene powder, mica, asbestos, quartz powder, gypsum, anti-
mony trioxide, bentones, lithopone, barite, titanium dioxide, carbon black or g}aphite. It is
also possible to add other usual additives, for example flameproofing agents, agents for
conferring thixotropy, flow conlrol agents such as silicones, cellulose acetate butyr~te,
polyvinyl butyrate, waxes, stearates and the like (which are in part also used as mold
release agents) to the curable mixtures.
Although the curable epoxide resin mixtures are noted as being especially useful in the
fields of adhesion and surface protection and repair, they are also applicable to the
electrical industry, laminating processes and the building industry. They can be used in a
formulation which is in each case suited to the particular end use such as compression
molding compositions, casting resins, tooling resins, laminating resins, sealing and filling
compositions and floor covering compositions.
The following examples will further illustrate the embodiments of the instant invention. In
these examples, all parts are given by weight unless otherwise noted.
Example 1: This example illustrates the preparation of typical epoxy resin adhesive
systems of the instant invention.
Resin: diglycidyl ether of bisphenol A with a functional diluent
(ARALDITE EP-IS from CIBA-GEIGY Corp.).
Hardener: 2,2,4- and/or 2,4,4-trimethylhexamethylene diamine
Wet Bondin~ System Preparation: The epoxy resin or hardener is blended with the
indicated silane (epoxy silane with epoxy resin and amino or mercapto silane with
hardener) at room temperature at the indicated weight ratio.
Evaluation of Bond Stren~th
A. Damp Concrete to Steel - Concrete cubes 5 cm x 5 cm x 5 cm are soaked in water at
room temperature for 24 hours, surface wiped, coated on opposite sides thereof with a
5 mil thick layer of epoxy adhesive and bonded to 5 cm x 5 cm steel adherends. The
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bonded specimens are cured at room temperature for seven days while the concrete block
is maintained in a moist condition. The samples are then placed in an Instron Tensile
Tester whereby the opposing steel adherends are subjected to a tensile pull of
0.127 cm/minute. The pressure load necessary to cause breakage and the type of failure,
i.e. either in the concrete or in ihe adhesive interface, are noted for each system.
B. Damp Concrete to Damp Concrete - Concrete cubes 5 cm x 5 cm x 5 cm are soaked in
water at room temperature for 24 hours, surface wiped and bonded to each other with a
5 mil layer of epoxy adhesive within a bonding area of 13 sq. cm. The bonded cubes are
cured at room temperature for one week and then subjected to impact with a hammer at a
distance of one cm above the bond line until fracture occurs. The failure mode is noted
either as adhesive or concrete, with failure predominantly in the concrete being indicative
of effective adhesive perforrnance.
The results are noted below.
Bond Strength
Conc. Resin/Hardener Test A Test B
Silane (% by wt of R&H) Mix Ratio [N/cm2]
- --- 100:30 110.3 A A
1 0.65 100:35 399.9 C C
1 1.30 100:35 344.7 C C
1 2.60 100:35 320.6 C C
1 5.20 100:35 255.1 C C
A- break in adhesive bond
C- break in concrete
