Note: Descriptions are shown in the official language in which they were submitted.
~ 92/~8760 PC~r/US91/08267
2072~
ACRYLIC-MODIFIED EPOXY RESIN ADHESIVE COMPOSITIONS
WITH IMPROVED RHEOLOGICAL CONTROL
This invention pertains to the use of epoxy
resins in adheQive compositions with improved
properties. The invention also provides for a
physically stable dispersion which may be used in such
adhesive compo3itions.
Epoxy resins have a spectrum of properties that
are well adapted for use in coatings, adhesives,
fiber-reinforced laminates, composites, engineering
plastics and specialty applications, such as potting
resins and mortars. Such properties include excellent
strength, toughness, corrosion and solvent resistance,
good adhesion and electrical propertieQ, good
dimensional stability, hardness, and low shrinkage on
cure.
Adhesives are a particularly important
application for epoxy resins. Epoxy-based adhesives
o~fer many advantages to end-users such as high strength
and moisture resistance while providing protective sealA
as well as load-bearing properties.
Generally, epoxy resins are formulated into
either one- or two-component, ambient or heat-cured
paste or film adhesives. Typical ingredients, in
- -
. ~ -
- ;- . ~
W092/08760 PCT/US9~/08267~
207~0~0 2 ~ ~
addition to the epoxy resin, include curing agents,
catalysts and accelerators, fillers, pigments, reactive
diluents, nonreactive diluents, solvents, flexibilizers,
toughening agents, extenders and rheological control
agents.
Good rheological control is important to an
epoxy adhesive. It must thin under shear to allow for
easy application and wetting of surfaces; however, once
it has been applied slumping or sagging of the adhesive
bead can be a problem. At the same time, separation of
the formulation ingredients mu~t be avoided.
Heretofore, adhesive formulations based upon
epoxy resins, toughened with insoluble dispersions of
acrylic elaQtomers, show poor rheological control.
Epoxy resins toughened with reactive liquid polymers,
such as carboxyl-terminated butadiene-acrylonitrile
liquid polymers, also pose certain difficulties in
formulating and handling.
First, resins in the prior art toughened with
reactive liquid polymers need a fair amount of fumed
slllca to achieve good rheological control. High
loading o~ fumed sillca, usually more than 5 weight
percent, is necessary to achieve good rheological
control. High concentrations Or fumed silica or other
rillers may cause abrasion problems, alter polymer
properties and lower the adhesive strength. Second,
since these resins are highly viscous (500,000 to
900,000 centipoise (Cp3) (500,000 to 900,000 mPa.s) at
25C), it i9 dirricult to incorporate large amounts of
fumed silica into them. Thererore, additional diluents
and procesqing Qteps, such as a let-down procedure, are
., ~
- -. . .
, . . . . . . . . . .. . .... .
- ; : ~ .. ;-
- . : ' . ~ . : . ' . . !
~ 092/08760 PCT/~S91/08267
:.
-3- 2~72~
required for the formulation of such epoxy resins
toughened with reactive liquid polymers.
Rheological control in paste-type adhesive
system~ is especially important in robotic diYpensing
applications. In automotive assembly lines the adhesive
is dispensed with a robot and the part with uncured
adhesive is tran~ferred to other work stations for
curing and further processing. Under these conditions
it is imperative that the assembly line is not
contaminated with drippings from uncured adhesive.
In a one-part epoxy adhesive, satisfactory
rheological control for the uncured system requires ease
of pumplng and no stringing once the adhesive is
dispensed and the robot is removed. Then, regardless of
the type of surface (cold-rolled steel, hot-dipped
galvanized, electrogalvanized, aluminum, etc.) and
regardless of the cleanliness of t~e surface (solvent-
-wiped, oily, laser-treated, etc.) the adhesive needs to
stay on the surface without sagging, drooping or
dripping. Most commonly, one-part epoxy adhesives are
cured at elevated temperatures. As the temperature of
the adhe-qive ls increased, resin viscosity will decrease
and the wettability of the adhesive will increase. It
ls al~o important, however, that the adhesive does not
sag or drip at elevated temperatures before cure takes
place.
In a two-part paste adhesive system, ~ag
control can be partially or completely achieved by room
temperature cure. In this caqe, rheological control is
achieved by rapid build-up of microstructure. If
rheological control is primarily achieved by
microQtructure build-up at ambient conditions, a balance
, ~
t
:. ~ ' ' `
WO 92/08760 PCI/US91/08267~
2~720~o -4- '
between cure rate and dispensing rate must be
maintained.
In 91OW gelling two-part adhesives, until the
right amount of microstructure build-up occurs,
requirements for rheological control are similar to one-
-part adhesives. Again, handling, abrasiveness and loss
of properties are valid concern~. In addition, long
molecular chains, formed because of the ambient cure,
will be a likely cause of stringing. In this case,
depending on the viscosity of the system, some
mechanical solutions can be offered. If the mechanical
approach is not adequate or cannot be used, this
lnvention offers solutions for two-part as well as for
one-part adhesives.
Four U.S. patents describe the preparation of
stable acrylic elastomer dispersions in epoxy resins for
toughened epoxy resins: U.S. Patent 4,521,490; U.S.
Patent 4,524,181; U.S. Patent 4,708,996; and U.S.
Patent 4,789,712. While these patents describe a wide
range of preferred vinyl monomers and comonomerq, in
particular the esters of acrylic or methacrylic acid
with alkanols having 1 to 18 carbon atoms, the inclu~ion
f hydroxy-functional comonomers for rheological control
i9 not considered.
The formulation of acrylic dispersions into
pa~te adheqives iq deqcribed in U.S. Patent 4,521,490.
However, the question of rheological control i-~ not
addreqsed in this patent. In particular, the
formulation of the diQpersion with fumed silica and its
rheology iQ not described.
The preQent invention solves some of those
problems described above by disclosing a thixotropic
.
~ 92/08760 PCT/US~1/08267
2 ~ ~ 2 ~ ~ ~
adhesive composition which has improved rheological
control and sag resistance over known adhesives.
This invention is a thixotropic adhesive
compoYition exhibiting good sag resistance comprising a
mixture of a polymer-modified epoxy resin and a
rheological control agent. More precisely, the
invention comprises a mixture of a dispersion which
comprises an uncured epoxy resin as a continuous phase
having dispersed therein an in situ polymerized -
insoluble acrylic elastomer which has a plurality of
hydroxyl functionality and an effective amount of a
rheological control agent which haQ a plurality of
pendent hydroxyl groups. Acrylic epoxy resin
diQpersions containing added hydroxyl functionality have
been discovered to unexpectedly give improved
rheological control.
The invention is also a method of preparing an
adhesive composition with superior rheological control
and toughne-~s at lower viscosities compared to existing
one- or two-part toughened epoxy resin adhesives. In
addition, the invention shows a method of adhering
surfaces together using an epoxy resin based adhesive.
The method of preparing the adhesive
oomposition comprises (a) preparing a dispersion which
comprises an uncured epoxy resin as a continuous pha~e
having dispersed therein an in situ polymerized
insoluble acrylic elastomer which has a plurality of
hydroxyl functionality, and (b) mixing together the
dispersion and an effective amount of a rheological
control agent which has a plurality of pendent hydroxyl
groups. Such a rheological control agent should be
capable of rheological control without sag or stringing
,- ;.
. - . -
.: . : ~ ;
.:
. .
- - . - ,. ~ : .:
W092/08760 PCT/US91/08267
.",
~ 2~90 -6-
at relatively low, easy to pump viscosity levels.
Optionally, an epoxy resin curing agent may be added to
the composition during the mixing together of the
dispersion and the rheological control agent.
~ ,....
The method of uQing the adhesive composition
comprises first applying the adhesive composition to a
first surface; contacting the first surface having the
adhe~ive composition applied thereto to a second surface
in a bonding relationship with the adhesive composition
disposed between the surfaces; and curing the adhesive
composition. An epoxy resin cure accelerator can aliso
be optionally used for rapid cure.
The invention requires a novel polymer-modified
epoxy resin in which acrylic elaisitomer particles have
added hydroxyl functionality. The main function of the
acrylic elastomer iiQ to improve toughness. Toughness of
the epoxy resin is accomplished by selecting an optimum
dispersed polymer phase and by balancing that with
rheological control agents, thixotropes, fillers, curing
agents, and other additives. Rheological control is
achieved specifically by matching the hydroxyl groups of
the rheological control agent with the hydroxyl
~unctionality of the dispersed polymer phase of the
epoxy resin. Hydroxyl functionality groups can be
applled in different concentration levels, can be
seleoted from a number of different chemical structures,
preferably of acrylic or polyurethane composltion, and
3 can be grafted onto different moieties in the dlspersed
polymer phase.
The adhesive of the present invention has
improved rheological control and adhesive performance
while maintaining polymer properties such as low
~ ., ......... - . . ,; . . ..
,, , ., ~ ~ -
.. ....
92/08760 PCT/US91/08267
-7-
2~'~20~
viscositieq, high glaQs transition temperature~,
toughness, and moisture resiqtance. The invention
reduces the amount of thixotrope needed, extending the
shelr life Or common thixotropeq giving reliable
rheological propertieQ, and reduce~ raw material costs.
At ambient and elevated temperatures adhesive
sy~temq engineered according to the invention show
better rheological and sag control characteristic3
compared to adhesives prepared heretofore with liquid
reactive resins, such as carboxyl-terminated butadiene-
-acrylonitrile liquid polymers, liquid epoxy resins and
unmodified insoluble polymer dispersions in liquid epoxy
resin~.
AdhesiveQ engineered according to the invention
exhibit excellent sag control characteri~tics over at
least several months at temperatures ranging from
ambient temperature up to 450F (232C). The invention
ellminates the uqe Or additional diluents to incorporate
large quantities of fumed silica for the purpose of sag
control. Ba-qed on resin compositions without diluents,
lower vi~cosities for ease of handling are posQible.
Glass transltion temperatures are higher and moisture
re~istance is improved over known epoxy resin adhesives.
Adhesives prepared according to the invention are also
more economical since cheaper grade-q of hydrophilic
fumed silica can be used instead of the more expensive
grades. The preqent invention has also ~olved
3 rheological control problems in paste-type toughened
epoxy adheqives.
The invention has immediate use in adhesive and
sealant applications, especially in structural
adhesi~es. Other epoxy resin application~ where
"
,. , : :-. ;, . -:
WO92/08760 PCT/US91/08267~
~ 7~o -8-
rheological control is important include coatings, civil
engineering applications, laminates, composites,
reinforced plastics, and electrical encapsulations.
The present invention is alqo a stable
dispersion of an organic polymer in an epoxy resin as a
continuous phase, characterized in that the dispersion
remainq insoluble in the epoxy resin at a temperature of
at lea-qt 60C. The dispersed phase can be prepared by
the polymerization of one or more monomers in a step
reaction, in an addition reaction such as a cationic,
anionic, or coordination polymerization, or ~ree radical
chain addition. Preferably, the dispersed phase is the
polymerizate of an in situ polymerized ethylenically
unsaturated functional monomer. It is also preferred
that the di3persion contains a dispersion stabilizer.
Preferably, the diqpersion compriqes an uncured epoxy -
resin as a continuous phase having dispersed therein an
in situ polymerized inqoluble acrylic elastomer which
has a hydroxyl functionality and a dispersion stabilizer
which has a moiety compatible with the epoxy resin and a
moiety compatible with the in situ polymerized insoluble
acrylic elastomer.
In the present specification and claims, the
term "epoxy res1n" is employed to designate a compound
or mixture containing, on an average, greater than one
1,2-epoxy group per molecule, which can be croqslinked
into flnal form by means of a chemical reaction with a
3 variety of curing agents uqed with or without heat.
Typlcally the 1,2-epoxy group is a glycidyl residue:
(-CH2C\H/CH2)
,
.. . . , . .:
.. - : ., :,, ... ... , .. ,:,... . . .
~ 92/08760 P~r/US91/08267
9 2~72~0
such as is found in glycidyl ethers, glycidyl esters or
glycidyl amines. Examples of epoxy resins include
diglycidyl ether of bisphenol A and tetraglycidyl-
methylenedianiline. In general, lower viscosity epoxy
resins are used for paqte adhesives. However, the
materials can be diluted with reactive diluents,
typically mono-functional, low viscosity epoxides.
Preferably, the epoxy resin is a liquid epoxy resin at
ambient temperature.
In the present invention, a polymer-modified
epoxy resin is used. Preferably, a dispersion which
comprises an uncured epoxy resin as a continuous phase
having dispersed therein as a discontinuous phase an
in situ polymerized insoluble acrylic elastomer which
has a plurality of hydroxyl functionality is used.
In the present specification and claims, the
term "in situ polymerized insoluble acrylic elastomer"
is employed to designate a discontinuous particulate
pha~e which is made by polymerizing or copolymerizing
vinyl monomers in a continuous epoxy resin phase. The
particulate phase can be prepared by the polymerization
Or one or more monomers in a step reaction
(oondensation), in an additlon reaction such as a
cationic, anionic, or coordination polymerization, or
free radical chain addition.
The particulate pha3e i9 normally elastomeric
i~ the glass transition temperature (Tg) is below room
temperature. Typically, low glass transition
temperatures, below room temperature, are obtained by
in¢luding alkyl esters of acrylic or methacrylic acid as
monomers. Generally, acrylic acid is used. Preferably,
the alkyl group of such alkyl esters of acrylic or
. . . . . . .... .. . . .. . . .
~ , - . . . -
. - . : : ~ . .; . . . .
- . . .
., . - .. -. . . - ,~ : -.
. :~ ,. .: : : . .. ., . - .
.
W092J08760 PCT/US91/08267~ ~
~7~9Q~ -'- :
methacrylic acid~ contains at least 4 carbon atoms and
more preferably 4 to 8 carbon atoms. Thus, butyl
acrylate and 2-ethylhexyl acrylate are preferred.
The disper3ed phase can be in an amount of from
5 to 70 weight percent, preferably 5 to 50 weight
percent, most preferably 5 to 20 weight percent, of the
total dispersion as long as the epoxy resin is the
continuous phase. The optimum concentration of the
polymeric dispersed phase can and will be varied
depending upon the materials employed and the end-use
that is envisaged. The dispersionq are usually made at
a solids level at which the dispersions are to be used.
However, it i9 possible to prepare dispersions of higher
solids level and dilute to the final solids level.
The disperqions are more easily prepared and
have superior stability and other properties when a
disperqion stabilizer is included in the composition.
Esqentially, the dispersion stabilizer can be any
compound which contains at least two different moieties
in it~ molecule, with at least one moiety compatible
with the epoxy resin and at least one other moiety
compatible with the in situ polymerized insoluble
acrylic elastomer. The term "compatible" in reference
to the moieties is meant to designate that a moiety is
misclble or soluble in a phase of the diqperqion. A
preferred disperQion stabilizer is the polymerizate of
at lea~t one vinyl monomer and a vinylized epoxy resin
3 adduct.
A process for preparing the dispersion
described above iQ characterized by the stepq of
(1) providing a vinylized epoxy resin adduct by reacting
a minor amount of functional monomer with a polyepoxide
:
. , . . . . . . .. ~ -
- , . .. . .
~092~08760 PCT/US91/08t67
" 2~7~
continuous phase, (2) providing a dispersion stabilizer
by reacting the adduct with at least one vinyl monomer
and (3) polymerizing said vinyl monomers in the
polyepoxide continuous phase and in the presence of said
disper~ion stabilizer. Alternatively, steps (2) and (3)
are performed at the same time. Also alternatively, the
dispersion stabilizer is prepared separately and added
to the polyepoxide before or during the addition and
polymerization of the vinyl monomer.
The vinylized epoxy re~in adduct is the
reaction product of a functional monomer with an epoxy
resin. Such a functional monomer has a reactive group
in addition to a polymerizable double bond. Preferably,
the vinylized adduct is made by reaction of a functional
monomer which is reactive with an oxirane group of an
epoxy resin. The reactive group may be, for example,
the acti~e hydrogen in a carboxylic acid, phenol,
thiophenol, isocyanate, or an amine group. Such
reactivity and methods for reacting the functional
monomers wlth oxirane groups and the useful reaction
parameters are known and judicious selection can be made
by reference to the literature and simple preliminary
experiment. Preferably, the functional monomer is an
ethylenically unsaturated functional monomer. A
preferred functional monomer is a substituted carboxylic
acid. Preferably, the reaction product is an acrylic or
methacrylic acid ester of the diglycidyl ether of
bisphenol A.
In the present specification and claims, the
term "adhesive" is employed to designate a formulation
which iQ capable of bonding other substances together by
sur~ace attachment.
:. : , ~ , .. . . .
W092/08760 PCT/US91/08267~
2072a~ -12- `
. .
In the present specification and claims, the
term "rheological control agent" is employed to
designate a material which affects the deformation and
flow of an adhesive in terms of stress, strain and time.
Any acceptable level of rheological control agent may be
used in the dispersion, but typically the rheological ~ -
control agent is used in a level of up to 10 percent by
weight of the total adhesive composition. An effective
amount of a rheological control agent will be an amount
necessary to achieve a desired level of deformation and
flow of an adhesive and will generally be predetermined
by the formulators of the adhesive. Such deformation
and flow properties of an adhesive will generally be
dictated by specific consumer or industrial need
requirements and, as such, will vary from product to
product.
Typical rheological control agents have
included fumed silica, asbestos, carbon black, clays and
chopped Kevlar fibers. Because of the carcinogenicity
of asbesto~, ineffectiveness of clays and the expense of
Kevlar fibers, the most typical rheological control
agents are fumed silicas such as those made by Cabot
Corporation and sold under the trade name of
CAB-0-SIL'~. In the present invention, hydrophilic
~umed ~lllca ls preferred.
The special properties of hydrophilic fumed
s1lica result from its unusual surface which is
3 populated by hydrogen-bonded hydroxyl groups, pendant
hydroxyl groups, and siloxane groups. The pendant
hydroxyl groups contribute greatly to the unique
behavior of fumed silica because they can bond to
pendant hydroxyl groups on other hydrophilic fumed
silica particles forming a temporary three-dimensional
., ,. , . -,
- - - - , .
. - ' ' '' ' . ': ' ~' ' . .
- . - . - . . :
'' .. ~: . . . .
.
~92~08760 PCT/US91tO8267
;, .. ,i .
_13_ ; ~72~
network oP particles that will pervade a liquid system.
The hydrogen bonding is easily broken under shear stress
during mixing and the viscosity decreases. But these
bonds reform and the visco~ity increases again
("thixotropy"). See, for example, the Cabot
Corporation's "CAB-O-SIL'~ Fumed Silica Properties and
Functions" (1990) booklet.
In contrast, hydrophobic fumed silica is fumed
silica which has been reacted with a compound to form a
10 treated fumed silica. Typical compounds used to form
treated fumed silicas include dimethyldichlorosilane and
hexamethyldisilazane. Treatment with such compounds
replaces many of the surface hydroxyl groups on the t
15 fumed silica with other groups, such as methyl groups.
Any remaining surface hydroxyl groups typically become
effectively shielded from interactions with other
hydroxyl groups due to the added groups. See, for
example, the Cabot Corporation's booklet
"CAB-O-SIL~ TS-720 Treated Fumed Silica" (1990).
While the theory for how fumed silica works as
a rheological control agent is simple, in practice the
results are much more complicated because many of the
formulation addltlves can interact with the hydrophilic
fumed silica to reduce its effectiveness. Polyamide
hardeners or monofunctional alcohols can reduce
effectiveness severely. Other additives, such as
diethylene glycol or glycerine, will increase the
3 erfectiveness.
In the present specification and claims, the
term "hydroxyl functionality" is employed to designate
the presence of the hydroxyl chemical group (-OH). This
functionality can be introduced in the in situ
- . . , . .................... . . - . ,
.
: : :''. , -' ' , " .:'' " .. '- :." , ' . '. .' :
W092/08760 PCT/US91/08267~
~ ~.
2 ~ 2 ~a -14-
polymerized insoluble acrylic elastomer by adding a
hydroxyl functional vinyl comonomer such as hydroxyethyl
acrylate, hydroxypropyl acrylate and methacrylate and
hydroxybutyl acrylate and methacrylate. Almost any
level of hydroxyl functional vinyl comonomer may be used
so as to achieve a desired level of rheology control.
Typically, however, low levels of hydroxyl functional
vinyl comonomer should be used so as to achieve good
rheology control but so as not to adversely affect other
properties of the epoxy resin. As such, the hydroxyl
functional vinyl comonomer can be in an amount of from 1
to 10 weight percent, most preferably 2 to 5 weight
percent, of total monomer added to the epoxy resin.
In the present ~pecification and claims, the
term "thixotropes" is employed to designate materials
which impart the ability of certain colloidal gels to
liquify under stress. Examples include clays.
In the present specification and claims, the
term "fillers" is employed to designate inert materials
which are used to provide a certain degree of stiffness
and hardness and to decreaAe the cost of the product.
Examples include calcium carbonatel s~licates, and soft
olay~. Any acceptable level of filler may be used in
tho adhos1ve composition, but typically the filler is
u~od ln a leYel of up to 50 percent by weight of the
total adhesive composition.
. ,
In the pre~ent spec1rication and claims, the
term "curing" i9 employed to designate the conversion of
a raw re~ln product to a finished and useful condition,
usually by application o~ heat and/or chemicals which
induce phy~ico-chemical changes. The term "curing
.. ' ,' . ~ . -, : ,: . , ', ' : '
-
.
. . . .
'' ' ' ::,: '' :'
. - . , . ;.
. : -, . - : , -:
~ 92/08760 PCT/US91/08267
~ 5~ 2~2~9~ ~
agent" is employed to designate active
hydrogen-containing compounds such as amines, amides,
mercaptans, acids, phenolics, alcohols, anhydrides,
Lewis acids, and bases which are added to a formulation
to ald in curing of the formulation. Dicyandiamide is a
5 preferred curing agent. Any acceptable level of curing
agent may be used in the adhesive composition, but
typically the curing agent is used in a catalytic level
up to a stoichiometric level based on the active t
10 hydrogen content of the adhesive composition, although a
31ight excess of curing agent may be used.
In the present specification and claims, the
term "other additives" is employed to designate
15 materials such as surfactants, antioxidants,
stabilizers, colorants, inhibitors, and plasticizers
which are added to a for~ulation as dictated by need
requirements. Any acceptable level of other additives
may be used in the adhesive composition, but typically
20 the other additives are used in a level of up to
5 percent by weight of the total adhesive composition.
"Sagging" is defined a.s run or flow-off of
adhesive from an adherent surface due to application of
25 exoess or low-viscosity material. A typical example of
a sag test oan be found in General Motors En~ineerin~
Standards Bulletin, "Sag Test For Structural Adhesives,
GM9749P", available from General Motors Corporation.
The oonoept of the invention is illustrated in
the following examples, which should not be construed as
llmltatlons upon the overall scope of the invention. In
the examples, all parts and percentage9 are by weight
unless otherwi-~e ~pecified.
W092/08760 PCT/US91/08267~
~07~ 16-
Example 1 - Preparation of an Acrylic Elastomer-
-Modified Dispersion With Additional Hydroxy
Functionality for Rheolo~ical Control
A diglycidyl ether of bisphenol A having an
epoxide equivalent weight of from 176 to 186 and a
vlscosity at 25C of between 9,000 and 11,500 cps (9,000
and 11,500 mPa.s) and sold commercially by The Dow
Chemical Company as D.E.R.TM 383 LER liquid epoxy resin
(1,200 grams (g)), methacrylic acid (15 g), and catalyst
(0.5 g, ethyltriphenyl phosphonium acetate-acetic acid
complex, 70 percent solution in methanol), and
hydroxyethyl methacrylate (HEMA) (15 g) are charged into
a 3-liter, 3-necked, round-bottom flask which is
equipped with a stirrer, addition funnel, condenqer,
thermocouple and nitrogen sparge. The resin is heated
with stirring under an air atmosphere to 120C. After
an additional 60 minutes, analysis of the mixture by
titration with standard base demonstrates that greater
than 97 percent of the methacrylic acid has reacted with
the epoxy resin to form a vinyl ester.
A mixture (monomer/initiator solution) of
2-ethylhexyl acrylate (291 g), glycidyl methacrylate
(9 g), tert-butyl peroctoate (3 g), and tert-butyl
perbenzoate (1.5 g) is added to the modified epoxy resin
at 120C over approximately a 60 minute period. After
addition of the monomer/initiator solution, the
temperature is held at 120C for an additional three
hours. Additional tert-butyl perbenzoate (o.6 g) is
then added. The reactor temperature is raised to 140C
and held for an additional two hours. The product is
cooled and bottled.
The final product is a stable dispersion of
acrylic elastomer in a liquid epoxy resin. The product
". .'
.. ' ~ '' :
. - ....................... .......: ,
. ~
~ 92~08760 PCT/US91/08267
- 2~72~9~
has a hydroxyl functionality due to the hydroxyl groups
bound to the inqoluble acrylic rubber particles in the
curable epoxy base re~in. The product has a Brookfield
vi~cosity of 84,000 cpq (84,000 mPa.s) at 25C and an
epoxlde equivalent weight of 240.
Comparative Example A - Preparation of an Acrylic
Elastomer-Modified Dispersion Without
Additional HYdroxY~ Functionalitv
By way of comparison, an additional stable
disper~ion of vinyl polymer in an epoxy resin is
prepared using techniqueq and materials similar to those
described hereinbefore in Example 1, except that no
hydroxyethyl methacrylate is added to the epoxy resin.
mD-arative-Example B
As a further comparative, an unmodified sample ~ -
of a diglycidyl ether of bisphenol A having an epoxide
equivalent weight of from 176 to 186 and a viscosity at
25C of between 9,000 and 11,500 cps (9,000 and
11,500 mPa.s) is u~ed.
Comparative ExamDle C
As a further comparative, a diglycidyl ether of
bisphenol A having an epoxide equivalent weight of from
172 to 176 and a vlqcosity at 25C of between 4,000 and
6,000 cps (4,000 and 6,000 mPa.s) and sold commercially
by The Dow Chemical Company as TACTI~ 123 epoxy resin
is used.
Unmodifled and elastomer-modified epoxy resins
are blended with 4 parts fumed silica per 100 part~
epoxy resin. The results for the formulations are shown
in Table I.
;
.. ~ ' , , ' . . . . .
. ~ . . . ~ . . .
.: ~ .. . .
W092/08760 PCT/US91/08267~
2 ~ 18-
TABLE I
.
Vi3cosity
Resin Description of Blended Blending Resin
(~ a~ With Fumed Silica
Example 1 84,ooo thick and not
_ _ runny
Comparative Example A 64,000 thicker than
unblended resin,
but still runny
Comparative Example B 10,000 thicker than
unblended resin,
but slightly runny
Comparative Example C 5,000 thicker than
unblended resin,
_ but very runny
The data in Table I illustrate the differences
in viscosities and rheological control of modified and
unmodified disper~ions of epoxy resins. As can be seen,
the lowest viscosities are obtained with the samples
with unmodified liauid epoxy resins but rheological
control is poor. Comparative Example A, modified
without hydroxyethyl methacrylate, has a higher
vlscosity arter being blended with hydrophilic fumed
s1110a but still has poor rheological control. In
oontrast, Example 1, modiried with hydroxyethyl
methacrylate, has both a high viscosity and good
rheological control.
Example 2 - Preparation Or Adhesive Based on
HEMA-Modified Liauid EDOXY Resin
The compoqition of Example 1 (375 g,
HEMA-modified poly(2-ethylhexyl acrylate) elastomer in
D.E.R.~ 383), calcium carbonate (100 g), and
hydrophilic fumed ~ilica (25 g) are mixed together in a
.
.
-
- . . . : . :
~ 92/08760 PCT/US91/08t67
~9 2~ ~J~
mixer. Dicyandiamide, CG-1200 grade (available from Air
Products and Chemicals Company), is used as a curing
agent at 95 percent of stoichiometric ratio and a
p,p'-methylene bis(phenyldimethylurea) catalyst at
6 parts per hundred of catalyst to resin (phr) level is
used to accelerate cure characteristics.
Comparative Example D - Preparation of an Adhesive
Based on Unmodified Liauid Epoxy Resin
D.E.R.TU 383 liquid epoxy resin (375 g), calcium
carbonate (100 g), and hydrophilic fumed silica (25 g)
are blended together. Dicyandiamide CG-1200 grade is
used as a curing agent at 95 percent of stoichiometric
ratio and a p,p'-methylene bis(phenyldimethylurea)
catalyst at 6 phr level is used to accelerate cure
characteristics.
A dynamic strain sweep measurement experiment
is conducted at a constant rate of 1 radian per second -
on the adhesive compositions of Example 2 and
Comparative Example D after respectively different
storage times. Yield values are measured at ambient
temperature using the Fluids Rheometer RF 7800 by
Reometrics, Inc., Piscataway, New Jersey.
. ~ , ' . . .
, ' ' ' . ' :;
.. , . . . -, . . . ..
WO92/08760 PCT/US91/08267~
. ;. .,
-20-
2~72~9V
TABLE II
5 _ Modulu3, G' ¦ G" (Vi cous
Example Measurement Component) Component
1 0 L I Taken~ ¦ ~
2 1 1.202 x 104 3.346 x 103 ,
2 1.193 x 104 3.421 x 103
Comparative 1 2.767 x 102 1.504 x 103
_ _ 2 1.909 x 102 1. 333 x 103
*1: Measurement made 7 weeks after formulation of
adhesive
2: Measurement made 10 weeks after formulation of
adhesive
The data in Table II show that the adhesive of
Example 2 behaves more like a solid than a liquid
(i.e., G' is significantly greater than G"). The
adhesive Or Example 2 has a high yield value (yield
25 value is greater than 4.55 x 103 dyne
(4.55x10-2 N)/square oentimeter) and has an easily
pumpable viscosity (complex viscosity is
1.250 x 104 poise (1.250x103 Pa.s) at 20C). In a
horizontal sag test (where the adhesive beads are laid
3 parallel to table-top and are placed vertically), at
room temperature, thickest adhesive bead te~ted
(0.30 inch (0.8x10-2 m) depth) did not sag for at least
4.5 months. At 155C convection oven temperatures,
: ' .
,, ,,¢~,.. ~ . , .
,
.` ' . ~ :
92/08760 PCT/US91/08267
-21-
2~2~90
0.20 inch (0.5x10-2 m) thick adhesive bead does not sag,
and in less than 30 minutes cures maintaining its shape.
In comparison, the adhesive of Comparative
Example D behaves more like a liquid than a _olid ~ -
(i.e., G' is significantly less than G"). The adhesive
Or Comparative Example D does not have a yield value and
fails the sag test before the test is started both at
room temperature and at 155C.
Comparative Example E - Preparation of Adhesive Based
on Modified Liquid EDOXY Resin
The composition of Comparative Example A
(375 g, poly(2-ethylhexyl acrylate) elastomer in
D.E.R.TM 383), calcium carbonate (100 g), and
hydrophilic rumed sllica (25 g) are mixed together.
Dicyandiamide, CG-1200 grade, is used as a curing agent
at 95 percent of stoichiometric ratio and a
p,p'-methylene bis(phenyldimethylurea) catalyst at 6 phr
level i~ used to accelerate cure characteristics.
Sag test results for the Example 2 adhesive
show excellent sag control at ambient and at 155C
convection oven temperatures. Thickest adhesive bead
tested (0.30 inch (0.8xlo-2 m) depth) does not qag at
ambient temperature for at least 4.5 months and
0,20 inoh (0.5x10-2 m)adhesive bead does not sag at
155C. In comparlQon, the adhesive of Comparative
Example E after 30 minutes at ambient temperature, the
thickest bead that did not sag wa~ 0.15 inch
(0.4x10-2 m). After 24 hours at ambient temperature,
the thickest bead remaining for the Comparative
Example E adhesive is 0.05 inch (O.lx10-2 m) and the
adhe~ive completely ~ail~ the 155C convection oven
te~t.
- - : : , - -
. - . . . .. , .: :.: . . .,--:
, ' '; , . . '
: ., '- , ' . '' . : -,
W092/08760 PCT/US91/08267~
~ ~ 7 2 ~ 22-
ComParative Example F
A one part adheQive, available from
PPG Indu~tries, Inc. as HC6227 Structural Epoxy
Adhesive, is used as a further comparative.
Com~arative ExamPIe G
A one-part adhesive, available from American
Cyanamid Company as CY80NDTN 4551G Adhesive, is used as
a further comparative. (CYBOND is a trademark of the
American Cyanamid Company.)
The adhesive~ of Example 2 and Comparative
Examples D, E, F and G are subjected to tests to
determine the lap shear strength, side impact strength,
~5 ~ide impact qtrength failure mode, T-peel strength, and
T-peel strength failure mode.
The results of several tests performed on the
adhesives of Example 2 and Comparative Examples D, E, F
and G are ~hown in Tables III-VIII. Unle3s otherwi~e
noted, these test~ were performed according to standard
ASTM Test Methods.
.. ~ .
. ~
'
'
'
92/08760 PCT/US91/08267
-23- '~
TABLE III
_ Yield Value~ Comple-
Adhe~ives Sag Control (tyne~ Viscosities*
(~ample No.) Character stics (~10-5N)/ at 22;C
centimeter) (mPa.S))
Example 2Excellent>4.55 x 103 1,240,000
Comparative D Did not pass No yield 135,000 :-
_ sag test value
Comparative E Dit not pass value N/A
Comparative F E~cellent 1.38 ~ 103 1,470,000
Comparative G E~cellent <2.40 x 103 1,500,000
*Ssmples that are runny and that do not have a yield value
have complex vi~cosities that are very close to steady
viscosities.
Yield values were measured at ambient
temperature, at a rate of 1 radian/second using the
Fluids Rheometer RF 7800 by Reometrics, Inc.,
Piscataway, New Jersey. The exact yield value of the
Example 2 adhesive cannot be measured because it exceeds
the upper limit of the measuring capabilities of the
in~trument at 1 radian/second. Comparative Example G
adheslve yleld value measurement made at
0.5 radian/second gives 1.04 x 103 dynes
(1.04x10-2 N)/square centimeter, and at
5.0 radian/second gave 2.40 x 103 dynes
(2.40x10-2 N)/square centimeter. Since the yield value
increases with increasing rate, at 1 radlan/second it
will be less than 2.40 x 103 dynes (2.40x10-2 N)/square
.. . . . .
, '
.. . ', . ' ; . ~ I '' , ' , ' . .
W092/08760 PCT/US91~08267~.
~ ~ 7 2 ~ D~ ~ 24--
centimeter but greater than 1.04 x 103 dynes
(1.04x10-2 N)/~quare centimeter.
TABLE IV
Lap Shear Strength Data for
Sample Adhesive Compositions
Cure Condition~ Lap Shear
Adhe3ive __ Strength
10 Compo~ition Temperature Time ~q. in.
(C) (minute~) (kPa))
Example 2 155 20 4800
Example 2 155 60 5300
(36500)
Comparative D 155 30 3500
(24100)
Comparative F 155 30 2500
(17200) ~.
20 Comparative F 155 60 4700
(32400)
Comparative F 177 60 5400
(37200)
Comparative G 177 30 3600
25 Comparative G 177 60 3900
(26900)
_
Test Conditions: 63 mil (1.6x10-3 m) cold-rolled
steel (CRS) substrate, ground-to-ground, 0.5 weight
peroent 4 mil (1x10-4 m) glass beads, 0.1 in
(2.5x10-3 m)/min cros~head ~peed; ASTM Test Method
D-1002
.. ..
- .:, i .
. ~ -
.
..
. . .
~ 92/08760 P~r/US91/08267
-25- ~ 0 72 0
TABLE V
Side Impact Data Strength for
I __Sam ple Adhesive Compositio ~s
Cure Condition~ Side : ~ .
Adhesive _ Impact
Compo~ition Temperature Time Strength .
_ (C) (minute~) (m Kg)) ~:
l Example 2 155 20 31 (0.36)
10Example 2 155 60 39 (0.45)
._
Comparative D 155 30 19 (0.22)
Comparative F 155 60 18 (0.21)
Comparat~ve G 177 30 12 (0.14)
15Comparative G 177 60 13 (0.15)
Te~t Conditions: Charpy Side Impact Strength on 63
mil (1.6x10-3 m) CRS ~ubstrate, ground-to-ground,
0.5 weight percent 4 mil (1x10-4 m) glass beads.
. ..
- , ,., . ; , ~
W092/08760 PCT/US91/08267~
2Q72~9 ~ -26-
TABLE VI
Side Impact Strength Failure Mode Data
for Sample Adhesive Compositions
Cure Condition~ Mode Or
Adhesive ~ Failure
Compo~ition Temperature Length o~ (Percent
l (C) Time Cohe~ive)~ : .
Example 2 155 20 ~ 100
Example 2 155 60 100
Comparative D 155 30 17
Comparative F 155 60 100 .-
Comparative G 177 30 100
Comparative G _ 177 60 100
All failures were at the adhe~ive-substrate
interface (thin-film cohesive), with the exception
Or Example 2.
Te9t Conditions: Charpy Side Impact Strength on
63 mil (1.6x10-3 m) CRS sub~trate,
ground-to-ground, 0.5 weight percent 4 mil
(1x10-4 m) glass beads.
~ ..
~ '' ' ,',~ ', ` ;
~ " - ' .. '
~092/08760 PcT/ussl/o8267
-27-
2~2~
~ .
TABLE VII
T~Peel Strength Data for
Sa] nple Adhesive Compositions
Cure Conditions T-Peel Strength
(pounds/linear
Adheqive Temperature LenTgithef (pli) Ich
~ ( C) (minutes) vPaelauk Pvaaltueeu
Example 2 155 30 45 25
(800) (450)
Example 2 155 60 42 24
. (750) (430)
Comparative D 155 30 15 2
(270) (35)
Comparative F 155 60 33 14
(590) (250)
Comparative G 177 3 23 7
(410) (125)
Comparative G 177 60 29 12
(520) (215)
Test Conditions; 32 mil (8x10-4 m) one-fourth
hardness CRS ground-to-ground, 0.5 weight percent
4 mil (1x10-4 m) glaqs beads, 10.0 in (0.25 m)/min
25 cros9head speed; ASTM Test Method D-1876
. - - : . : , . ................... : . . ... . .
.: ........ ..: - ......... - ~ .... .. : . . , - .
- : . . ~ . . ~ . . .: . . . - -........... .
W092/08760 PCT/US91/08267
-28-
2~72~
TABLE VIII
T Peel Strength Failure Mode for
Sample Adhesive Compositions
_ Cure Conditions
Mode Or
Adhe~lve Failure
Compo~ition Temperature Length of (Percent
I - (C) Time Cohe~ive)
Example 2 _ 55 3 _ 100
Example 2 155 60 100
Comparative D155 30 11
Comparative F155 60 100*
15 Comparative G177 30 100
Comparative G177 60 100
*Failure at the adhesive--qubstrate interface.
Test Conditions: 32 mil (8x10-4 m) one-fourth
hardneq.q CRS ground-to-ground, 0.5 weight percent
4 mil (1x10-~ m) glass bead~, 10.0 in (0.25 m)/min
cro~head qpeed~
..
, . .
,. . . , - - :,
, ~:
.
'
: . ... :
~, ~
