Note: Descriptions are shown in the official language in which they were submitted.
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ADHESIVE FORMULATIONS
This application claims benefit of U.S. Provisional Patent Application No.
60/089,115
filed June 12, 1998.
FIELD OF THE INVENTION
The present invention relates to improved odor of polymerizable or curable
acrylic
adhesives.
BACKGROUND OF THE INVENTION
Acrylic structural adhesives are well known articles of commerce which are
extensively used commercially for bonding metal and plastic materials. Acrylic
structural
adhesives have found growing use in the automotive industry where the adhesive
bonding of
metal parts is replacing welding and mechanical fastening techniques. However,
these
applications give rise to unique requirements not easily met by previously
available
adhesives. These requirements include high bond strength, improved failure
mode and low
odor.
Acrylic adhesives typically comprise a mixture of one or more olefinic
reactive
monomers such as methyl methacrylate or methacrylic acid and curing agents,
with cure or
polymerization being effected through a free radical polymerization mechanism.
The
adhesives preferably contain one or more polymeric materials which may or may
not be
reactive, that is, capable of being polymerized per se or at least capable of
interpolymerizing
with the reactive monomers, such as grafting onto or crosslinking the growing
polymers from
the reactive monomer polymerization. In addition, the adhesives can contain
other additives
for improving adhesion to substrate materials, environmental resistance,
impact strength,
flexibility, heat resistance, and the like.
P.C.T. Publication WO 97/39074 discloses the use of at least one polymeric
material
which can act as a toughening agent in an acrylic adhesive such as
polychloroprene, polymer-
in-monomer syrup, chlorosulphonated polyethylene rubber, copolymers of
butadiene and at
least one monomer copolymerizable therewith, for example, styrene,
acrylonitrile,
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methacrylonitrile (e.g. poly(butadiene-(meth)acrylonitrile or poly(butadiene-
(meth)acrylonitrile-styrene) and mixtures thereof; as well as modified
elastomeric polymeric
materials, such as butadiene homopolymers and copolymers as noted above
modified by
copolymerization therewith of trace amounts of up to about 5 percent by weight
of the
elastomeric material of at least one functional monomer (such as acrylic acid,
methacrylic
acid, malefic anhydride, fumaric acid, styrene, and methyl methacrylate to
give, for example,
methacrylate-terminated polybutadiene homopolymers and/or copolymers).
U.S. Patent No. 4,769,419 ("the '419 patent"), incorporated herein by
reference,
discloses structural adhesive compositions for metal-metal bonding
applications. The
adhesives include as tougheners olefinic terminated liquid rubbers which are
reacted with
monoisocyanate compounds. These tougheners represented by formula I as shown
in column
4 and claim 1 of the '419 patent are referred to herein as "urethane modified
olefinic-
terminated liquid elastomer produced from a carboxylic acid-terminated
alkadiene" or,
alternatively, as "isocyanate-capped methacrylate-terminated polyalkadiene
produced from a
carboxylic acid-terminated polyalkadiene". The '419 patent further describes
acrylic
adhesives with olefinic monomer, olefinic urethane reaction product of an
isocyanate-
functional prepolymer and a hydroxy-functional monomer, phosphorus-containing
compounds, an oxidizing agent and a free radical source.
U.S. Patent No. 5,641,834 ("the '834 patent") and U.S. Patent No. 5,710,235,
both
incorporated herein by reference, disclose adhesives that include as
tougheners an olefinic-
terminated polyalkadiene that includes carboxy ester linking groups and at
least one nascent
secondary hydroxyl group that is capped with a monoisocyanate. These
tougheners
represented by the formulae for polymer A or polymer B in claim 1 are referred
to herein as
"olefinic-terminated liquid elastomer produced from a hydroxyl-terminated
polyalkadiene" or,
alternatively, as "isocyanate-capped methacrylate-terminated polyalkadiene
produced from a
hydroxyl-terminated polyalkadiene". The composition also includes a free
radical-
polymerizable monomer such as an olefinic monomer and, optionally, a second
polymeric
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material. In a preferred embodiment the composition is an adhesive that also
includes a
phosphorus-containing compound and an ambient temperature-active redox
catalyst. The
'834 patent describes polymers A and B with a number average molecular weight
of about
1,500 to 10,000, preferably about 1,500 to 6,000.
The odor of acrylic adhesives leaves room for improvement.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an adhesive that has
a lower or
less objectionable odor. According to the invention there is provided an
adhesive that
includes a free radical-polymerizable monomer component that includes at least
a reaction
product of a (hydroxy)acrylate with an anhydride but is substantially free of
methyl
methacrylate or methacrylic acid.
DETAILED DESCRIPTION OF THE INVENTION
The free radical-polymerizable monomer component typically is a mixture of
free
radical-polymerizable that at least includes a monomer that is a reaction
product of a
(hydroxy)acrylate with an anhydride. The presence of this reaction product
allows for the
removal from the adhesive formulation of at least one of methyl methacrylate,
methacrylic
acid or other offensive odoriferous monomers. The adhesive compositions are
substantially
free of at least methyl methacrylate or methacrylic acid because the use of
these ingredients in
amounts as little as 2 or 3 weight percent results in offensive odor emissions
in certain
applications. As the term "substantially free of methyl methacrylate or
methacrylic acid" is
used herein, it is intended to mean trace amounts or amounts less than an
offensive odor
generating amount which can be as little as 2 or 3 weight percent of the total
formulation.
The odor of methacrylic acid can be particularly offensive. Thus, according to
one
embodiment of the invention the monomer component can include
methylmethacrylate but is
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substantially free of methacrylic acid.
The (hydroxy) acrylate compound utilized to prepare the reaction product
included in
the monomer component of the invention can be any acrylate compound
characterized by the
presence of a hydroxy group. Examples of suitable hydroxy-functional acrylate
compounds
include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl
acrylate, 2-
hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 2-hydroxybutyl
methacrylate, 3-
hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 3-hydroxypentyl acrylate, 6-
hydroxynonyl
acrylate, 3-hydroxypropyl methacrylate, 2-hydroxypentyl methacrylate, 5-
hydroxypentyl
methacrylate, 7-hydroxyheptyl methacrylate, 5-hydroxydecyl methacrylate, N-
hydroxymethyl
acrylamide, N-hydroxymethyl methacrylamide, diethylene glycol monoacrylate,
diethylene
glycol monomethacrylate, glycerin dimethacrylate, tri-methylol propane
dimethacrylate,
alkoxylated hydroxyethyl acrylate, trimethylolpropane diacrylate, alkoxylated
trimethylolpropane diacrylate, reaction products of polyether glycols of
acrylic or methacrylic
acid and the like.
Other hydroxy-functional acrylate compounds are lactone-modified acrylate or
methacrylate acid esters (hereinafter "lactone-acrylate adducts") prepared by
reacting an
appropriate lactone with a hydroxy-functional acrylate compound defined in the
preceding
paragraph as is known in the art. Lactones employed in the preparation of the
lactone-
acrylate adducts may be the same as the lactones defined above with respect to
the
preparation of the lactone-based polyester polyols. An example of a lactone-
acrylate adduct
is a 2-hydroxyethyl acrylate-caprolactone adduct such as TONE M-100 supplied
by Union
Carbide Corporation.
The anhydride that is reacted with the (hydroxy)acrylate compound can be
malefic
anhydride, succinic anhydride, phathalic anhydride, alkylsuccinic anhydride,
alkenylsuccinic
anhydride and the like. The preferred reaction product is
monomethacryloyloxyethyl
phthalate commercially available from International Specialty Chemicals under
the trade
designation BISOMER EMP.
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The other free radical-polymerizable monomers that can be present in the
monomer
component mixture of the invention are olefinic monomers that are
characterized by the
presence of a -C=C- group, provided they do not give rise to objectionable
odor as
mentioned above. Representative olefinic monomers include esters of
(meth)acrylic acid
such as ethyl methacrylate, butyl methacrylate, butyl acrylate, cyclohexyl
acrylate, hexyl
acrylate, 2-ethylhexyl acrylate, lauryl acrylate, ethyl acrylate, diethylene
glycol
dimethacrylate, dicyclopentadienyloxyethyl methacrylate, cyclohexyl
methacrylate, lauryl
methacrylate, glycidyl methacrylate and tetrahydrofurfuryl methacrylate;
acrylic acid;
substituted (meth)acrylic acids such as itaconic acid, acrylonitrile,
methacrylonitrile,
acrylamide and methacrylamide; styrene; substituted styrenes such as vinyl
styrene,
chlorostyrene, methyl styrene and n-butyl styrene; vinyl acetate; vinylidene
chloride; and
butadienes such as 2,3-dichloro-1,3-butadiene and 2-chloro-1,3-butadiene.
Other olefinic
monomers include maleate esters; fumarate esters; and styrenic compounds such
as styrene,
chlorostyrene, methylstyrene, butylstyrene and vinyl styrene.
A mixture of the (hydroxy)acrylate/anhydride reaction product with at least
one other
of the above-described free radical-polymerizable monomers is preferred. A
combination of
tetrahydrofurfuryl methacrylate (THFMA) and monomethacryloyloxyethyl phthalate
is most
preferred.
The free radical-polymerizable monomer component is present in an amount of 10-
90
°Io by weight of the principal components. For purposes of weight
percent only, the "principal
components" are the free radical-polymerizable monomer component, an adhesion
promoter,
and at least one toughener or toughening agent.. Any amount of the
(hydroxy)acrylate/anhydride reaction product can be present, but about 0.5 to
20 weight
percent, more preferably 1.5 to 10 weight percent, is preferred, based on the
total weight of
the adhesive part that includes the free radical-polymerizable monomer
component.
The adhesive composition also can include 0-20°70 by weight of the
principal
components of an adhesion promoter. An adhesion promoter is any adhesion
promoter known
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to those of ordinary skill in the art as useful in promoting adhesion in
acrylic adhesives.
Preferred adhesion promoters are phosphorus-containing compounds that enhance
metal
adhesion and may be any derivative of phosphinic acid, phosphonic acid or
phosphoric acid
having at least one P-OH group and at least one organic moiety characterized
by the
presence of an olefinic group, which is preferably terminally located. A
listing of such
phosphorus compounds is found in U.S. Pat. No. 4,223,115. A preferred
phosphorus-
containing compound has a structure that may be represented by the formula:
O
O
I I
(CH2 =C -C -O-A~P(OR21 )2-m
R20
OH
wherein Rz~ is selected from the group consisting of hydrogen, an alkyl group
having from
one to 8, preferably one to 4, carbon atoms, and CHZCH-; RZ1 is selected from
the group
consisting of hydrogen, an alkyl group having from one to 8, preferably one to
4 carbon
atoms; A is selected from the group consisting of -RzzO- and R230)", wherein
R'-z is an
aliphatic or cycloaliphatic alkylene group containing from one to 9,
preferably 2 to 6, carbon
atoms; R23 is an alkylene group having from one to 7, preferably 2 to 4,
carbon atoms; n is an
integer from 2 to 10, and m is one or 2, preferably one.
Phosphorus-containing compounds having vinyl unsaturation are preferred over
such
compounds having allylic unsaturation, with monoesters of phosphinic,
phosphonic and
phosphoric acids having one unit of vinyl or allylic, especially vinyl,
unsaturation presently
being preferred. Representative phosphorus-containing compounds include,
without
limitation, phosphoric acid; 2-methacryloyloxyethyl phosphate; bis-(2-
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methacryloxyloxyethyl) phosphate; 2-acryloyloxyethyl phosphate; bis-(2-
acryloyloxyethyl)
phosphate; methyl-(2-methacryloyloxyethyl) phosphate; ethyl
methacryloyloxyethyl
phosphate; methyl acryloyloxyethyl phosphate; ethyl acryloyloxyethyl
phosphate; compounds
of the above formula wherein Rg is hydrogen or methyl and R9 is propyl,
isobutyl, ethylhexyl,
halopropyl, haloisobutyl or haloethylhexyl; vinyl phosphonic acid; cyclohexene-
3-phosphonic
acid; alphahydroxybutene-2 phosphonic acid; 1-hydroxy-1-phenylmethane-l,l-
diphosphonic
acid; 1-hydroxy-1-methyl-1-disphosphonic acid: 1-amino-1 phenyl-1,1-
diphosphonic acid; 3-
amino-1-hydroxypropane-1,1-disphosphonic acid; amino-tris (methylenephosphonic
acid);
gamma-amino-propylphosphonic acid; gamma-glycidoxypropylphosphonic acid;
phosphoric
acid-mono-2-aminoethyl ester; allyl phosphonic acid; allyl phosphinic acid; (3
-
methacryloyloxyethyl phosphinic acid; diallylphosphinic acid; (3 -
methacryloyloxyethyl)
phosphinic acid and allyl methacryloyloxyethyl phosphinic acid. A most
preferred adhesion
promoter is 2-hydroxyethylmethacrylate phosphate.
The adhesive composition also can include about 10-80% by weight of a
toughener or
toughening agent, based on the principal components. The toughening agent
typically is a
polymeric material that provides improved impact and shatter resistance to the
resultant
adhesive and decreases brittleness. The polymeric material may or may not
include an
olefinically unsaturated structure that is capable of being polymerized per se
or
copolymerized with at least one of the free radical polymerizable monomers
described above.
The polymeric material can be for example, various solid and liquid
elastomeric polymeric
materials, and in particular liquid olefinic-terminated elastomers as
described in U.S. Patent
Nos. 4,223,115; 4,452,944; 4,769,419; 5,641,834 and 5,710,235; and olefinic
urethane
reaction products of an isocyanate-functional prepolymer and a hydroxy
functional monomer,
as described in U.S. Patent Nos.4,223,115; 4,452,944; 4,467,071 and 4,769,419,
the entire
disclosure of each which is hereby incorporated by reference.
Representative liquid olefinic-terminated elastomers disclosed in P.C.T.
Publication
WO 97/39074 include homopolymers of butadiene, copolymers of butadiene and at
least one
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monomer copolymerizable therewith, for example, styrene, acrylonitrile,
methacrylonitrile
(e.g. poly(butadiene-(meth)acrylonitrile or poly(butadiene-(meth)acrylonitrile-
styrene) and
mixtures thereof; as well as modified elastomeric polymeric materials, such as
butadiene
homopolymers and copolymers as noted above modified by copolymerization
therewith of
trace amounts of up to about 5 percent by weight of the elastomeric material
of at least one
functional monomer (such as acrylic acid, methacrylic acid, malefic anhydride,
fumaric acid,
styrene, and methyl methacrylate to give, for example, methacrylate-terminated
polybutadiene
homopolymers and/or copolymers).
The present invention may also include an ambient temperature reactive
catalyst
system. The ambient temperature-reactive catalyst systems that may be employed
in the
preferred adhesive systems are well-known redox couple systems and need not be
discussed
herein in detail. Basically, such systems comprise at least one oxidizing
agent and at least
one reducing agent which are co-reactive at room temperature to generate free
radicals
effective to initiate addition polymerization reactions and cure the adhesive.
Substantially
any of the known oxidizing and reducing agents which are so co-reactive can be
employed.
Representative oxidizing agents include, without limitation, organic
peroxides, such as
benzoyl peroxide and other diacyl peroxides, hydroperoxides such as cumene
hydroperoxide,
peresters such as (3-butylperoxybenzoate; ketone hydroperoxides such as methyl
ethyl ketone
hydroperoxide, organic salts of transition metals such as cobalt naphthenate,
and compounds
containing a labile chlorine such as sulfonyl chloride. Representative
reducing agents
include, without limitation, sulfinic acids; azo compounds such as
azoisobutyric acid dinitrile;
alpha-aminosulfones such as bis(tolysulfonmethyl)-benzyl amine; tertiary
amines such as
diisopropanol-p-toluidine (DI>pT), dimethyl aniline, p-halogenated aniline
derivatives and
dimethyl-p-toluidine; and aminealdehyde condensation products, for example,
the
condensation products of aliphatic aldehydes such as butyraldehyde with
primary amines such
as aniline or butylamine. The use of known accelerators and promoters with the
redox couple
catalyst systems can be advantageous. Preferably, the oxidizing agent will be
present in an
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amount in the range from about 0.5 to about 50 percent by weight of bonding
accelerator,
with the amount of reducing agent being in the range from about 0.05 to about
10 preferably
about 0.1 to about 6, percent by weight of polymerizable adhesive composition.
DIIPT is the
most preferred reducing agent. The most preferred oxidizing agent is benzoyl
peroxide.
Although the adhesive of the present invention may take many forms, the most
preferred adhesive systems are provided as multipack or two-part adhesive
systems where one
package or part contains the free radical-polymerizable monomer component and
the reducing
agent and a second part or package contains the oxidizing agent. The two parts
are mixed
together at the time of use in order to initiate the reactive cure. After
mixing the individual
parts, one or both surfaces to be joined are coated with the mixed adhesive
system and the
surfaces are placed in contact with each other.
The second package or part can include a bonding activator that includes the
oxidizing
agent for the redox catalyst system. The bonding activator can include:
(1) from about 0.5 to about 50 percent by weight based on total weight of
bonding
activator of at least one oxidizing agent which can function as an oxidant of
a redox
couple catalyst system; and
(2) from about 30 to about 99.5 percent by weight, based on total weight of
bonding
accelerator, of a carrier vehicle.
The carrier vehicles which are suitable for use in the bonding activators can
be a
simple inert solvent or diluent such as methylene chloride, or butyl benzyl
phthalate,
including mixtures of such solvents or diluents. The Garner vehicle should
contain no more
than 5% by weight of any moiety which is reactive with the oxidizing agent at
room
temperature. The Garner vehicle can be a more complex mixture including at
least one film-
forming binder in addition to inert solvent or diluent. The carrier vehicle
can contain, in
addition to solvent or solvent and film-forming binder, additives such as
external plasticizers,
flexibilizers, suspenders and stabilizers, providing that any such additives
do not
unacceptably adversely affect the stability of the activator composition.
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An exemplary two part system includes:
(I) a first package comprising
(a) 10-90, preferably 20-70, weight percent of the free radical-polymerizable
monomer component of the invention;
(b) 10-80, preferably 20-50, weight percent of at least one toughener;
(c) 0-20, preferably 2-10, weight percent of a phosphorus-containing
compound having one or more olefinic groups
(d) 0.05-10, preferably 0.1-6, weight percent of at least one reducing agent
which is interactive with an oxidizing agent to produce free radicals which
are capable of
initiating and propagating free radical polymerization reactions; and
(II) a second package comprising
a bonding activator containing an oxidizing agent of a room temperature-
active redox couple catalyst system, the oxidizing agent being reactive at
room temperature
with reducing agent (d) when the first and second packages are mixed to
produce free radicals
which are capable of initiating and propagating free radical polymerization,
the amount of the
oxidizing agent being sufficient to interact with agent (d),
wherein the weight percents are based on the total amount of the principal
components.
The adhesive systems of the invention may be used to bond metal surfaces, such
as
steel, aluminum and copper, to a variety of substrates, including metal,
plastics, and other
polymers, reinforced plastics, fibers, glass, ceramics, wood and the like. It
is a feature of the
present invention that the herein-described adhesive compositions can be
employed to bond
metal substrates such as steel, aluminum and copper with little, if any,
pretreatment of the
metal surface prior to application of the adhesive. Thus, bonding can be
effected even to oily
metal surfaces which are otherwise clean without an extensive pretreatment as
is usually
required with the vast majority of currently available primers and adhesives.
Additionally, the
adhesive systems of this invention provide effective bonding at room
temperature, thus heat is
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not required either for applying the adhesive systems to the substrates or for
curing.
Although the adhesives of the present invention are preferred for bonding
metal
surfaces, the present adhesive compositions may be applied as an adhesive,
primer or coating
to any surface or substrate capable of receiving the adhesive. The metals
which are preferred
for bonding with the present adhesives include zinc, copper, cadmium, iron,
tin, aluminum,
silver, chromium, alloys of such metals, and metallic coatings or platings of
such metals such
as galvanized steel including hot dipped, electrogalvanized steel and
galvanealed steel.
The adhesive coatings may be brushed, rolled, sprayed, dotted, knifed or
otherwise
applied to one substrate, but preferably to both substrates to desired
thickness preferably not
to exceed 60 mils. The substrates may be clamped for firmness during cure in
those
installations where relative movement of the two substrates might be expected.
For example,
to adhere metal surfaces, an adherent quantity of the adhesive composition is
applied to one
surface, preferably to both surfaces, and the surfaces are confronted with the
adhesive
composition therebetween. The adhesive should have a thickness less than 60
mils for
optimum results. The smoothness of the surfaces and their clearance (e.g., in
the case of nuts
and bolts) will determine the required film thickness for optimum
bonding. The two metal surfaces and the interposed adhesive composition are
maintained in
engagement until the said adhesive composition has cured sufficiently to bond
the said
surfaces.
The following examples are provided for illustration purposes only and are not
intended to limit the scope of the invention in any manner.
FXAMPT.R~
The following masterbatch was prepared:
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Material Parts by Weight
Tetrahydrofurfurylmethacrylate (THFMA) 16.88
Monomethacryloyloxyethyl phthalate 2.21
2-hydroxyethylmethacrylate phosphate 3.11
isocyanate-capped methacrylate-terminated
butadiene oligomer
produced from a hydroxyl-terminated polybutadiene
as described in the '834 patent (in 20% THFMA)44.65
Wollastonite 8.00
Silica 4.50
Titanic 2.65
DIIPT 1.00
Chloroanilic acid 0.002
Inhibitor (ETHANOX 330 from Albemarle Corp.)0.003
0.2 mm glass beads 7.60
Total 90.6
EUROPRENETM was added to the masterbatch as set forth in the table below. The
EUROPRENETM polymer, EUROPRENETM SOL T 193A, used was a commercial product of
EniChem Elastomers Americas, Inc. EUROPRENETM SOL T 193A is a terblock polymer
of
styrene and isoprene with polystyrene blocks (25 parts by weight) at the ends
and
polyisoprene block at the center (75 parts by weight). It is a rubbery solid
polymer and has a
pellet form. EUROPRENETM SOL T 193A has a reasonable solubility in THFMA. A 20
part
by weight solution of EUROPRENETM SOL T 193A in THFMA has been used for
formulation convenience.
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TABLE I: EUROPRENETM Ladder vs. T-Peel Property
Formulation A B C D
Ratio of primary toughener to auxiliary100/0 99/1 97/3 95/5
toughener EUROPRENETM
master batch 90.60 90.60 90.60 90.60
20% EUROPRENETM 0 1.88 5.64 9.40
isocyanate-capped methacrylate-terminated2.35 1.88 0.94 -
butadiene oligomer produced from
a hydroxyl-
terminated polybutadiene as described
in the
'834 patent
THFMA 7.05 5.64 2.82 -
Total 100.00 100.00 100.00 100.00
The above four formulations were prepared in 4 oz. polyethylene jars and
allowed to age
overnight. The formulations were loaded into two-part dispensing equipment
(4:1 side Aside
B mix ratio by volume). The curative (side B) used here was a benzoyl peroxide
containing
curing agent.
The substrate (1" x 4" x 0.032") tested was galvanealed steel. The coupons
were bent
one inch from the end to give a 90 degree angle. The coupons were treated with
an aqueous
lubricant (Chempet 4465 available from ADCHEM) with acid brush according to
the
following preparation for blank wash:
1. Add material with brush until even wetting of surface is maintained when
brushing
(horizontal).
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2. Every five minutes, re-brush until all water has evaporated.
3. After water has evaporated, tilt coupons on about a 45 degree angle and let
dry
overnight (4 hour minimum).
4. Bond the upper part of the coupon away from drainage.
T-peel samples were assembled and allowed to cure at room temperature
overnight, then
postbaked at 325°F for 20 min., cooled at room temperature for 60 min.,
postbaked again at
250°F for 30 min. After 4 hours of cooling at room temperature, T-peel
test was performed
on the Instron (Model 4204) at a 2.0 in/min at room temperature. The T-peel
test results are
shown below:
TABLE II: EUROPRENETM Ladder vs. T-Peel Strength (pli)
Formulation Versilok~ 262 A B C D
Toughener ratio - 100/0 99/1 97/3 95/5
Peel Strength 35.3 29.2 35.6 35.0 32.8
Std. Dev. of Peel Strength2.55 0.75 0.44 1.95 0.47
Failure Mode COH/TCOH ADH ADH COH COH
Versilok~ 262 is a structural adhesive commercially available from Lord
Corporation that
does not include two distinct tougheners of different MW or EUROPRENE. "COH"
designates cohesive (substrate) failure, "TCOH" designates a thin layer of
cohesive (substrate)
failure and "ADH" designates adhesive failure.
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