Note: Descriptions are shown in the official language in which they were submitted.
I
BACKGROUND OF THE Invention
1. Field of the Invention
This invention relates to one-component epoxy
formulations. These epoxy heat curable formulations
contain an aside in combination with aphosphine compound
which affords faster cures and also lowers the curing
temperature. The composition can be used as an adhesive,
sealant or coating.
2. Description of the Prior Art
The heat curing of epoxy resins with asides is well
known in the art. Asides such as dicyandiamide and
mailmen are employed commercially to cure epoxy resins.
The use of these materials, per so, however, require
temperatures of 200 or 300C or more in order to obtain a
fully cured product.
OBJECTS OF THE INVENTION
One object of the instant invention is to produce a
one-component epoxy formulation. Another object of the
instant invention is to produce a one-component epoxy
formulation which is heat curable at a lower temperature
than present commercial formulations. Still another
object is to produce a one-component epoxy formulation
which is heat curable at a defined temperature in a
shorter time period. Other objects will become apparent
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from a reading hereinafter.
DESCRIPTION OF THE INVENTION
The present invention relates to a one-component, heat
curable epoxy formulation containing an aside in
combination with a phosphine compound. Such a formulation
affords faster cures than epoxy-amide formulations and
also allows curing at lower temperatures than said
epoxy-amide formulations.
The invention further provides a process for adhering
two substrates which comprises contacting the substrates with
a heat curable composition comprising if) an epoxy resin,
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(2) 1 to 10 weight percent of (1) of an aside and (3) 1
to 15 weight percent of I of a phosphine compound of the
group consisting of (a) RIP wherein R is alkyd, cycloalkyl,
aureole and alkaryl wherein said alkyd groups contain 1 to 10
carbon atoms (b) carboxylic acid salts of (a) and (c)
mixtures of (a) and by and applying heat thereto comprising
an epoxy resin, an aside and a phosphine compound.
The phosphine compounds operable herein to accelerate
the curing reaction are of the formula:
. .
- pa-
Z7~¢~`~
RIP or carboxylic acid salts thereof wherein R is
alkyd, cycloalkyl, aureole or alkaryl wherein said alkyd
groups contain l to 10 carbon atoms. Specific examples of
said phosphine compounds include, but are not limited to,
triphenyl phosphine, tricyclohexyl phosphine~
tris(orthotolyl) phosphine and tri-n-octyl phosphine
2,2-dimethylol prop ionic acid salt.
The carboxylic acid salts of the RIP compounds are
synthesized by methods well known in the art. One method
consists of reacting equimolar amounts of the RIP
compound and a carboxylic acid in solvent with stirring at
room temperature, removing the solvent under reduced
pressure and recovering the salvo
The phosphine compound is added to the composition in
an amount ranging from 1 to 15% by weight of the epoxy
resin
- There are various known aside compounds used to cure
epoxy resin. Said aside compounds include amino-
polyamides. Such materials include, but are not limited
to, mailmen, N,N-diallymelamine, dicyandiamide,
alkoxyalkyl melamines, such as hexamethoxymethyl mailmen,
melamine-formaldehyde resins, ursea-formaldehyde resins
such as monomethylol urea and dimethylol urea, triallyl
sonority, guanamines, imidazoles such as 2-ethyl-4-methyl-
imidazole, hydrazides exemplified by carbohydrazide,
adipic acid deodorized, guanidines, polyalkylene mines
such as ethyleneimine, sulfonamides and the like. These
materials are all well known amide-containing curing
agents for epoxy resins.
The asides are added to the composition in amounts
ranging prom 1 to 10 weight percent based on the weight of
the epoxy resin.
The epoxy resin oboe used in the composition of the
invention comprises those materials possessing more than
one epoxy , i . e .,
I I
group. These compounds may be saturated or unsaturated,
aliphatic, cycloaliphatic, aromatic or heterocyclic and
may be substituted with substituents, such as chlorine,
hydroxyl groups, ether radicals and the like.
The term epoxy resin" when used herein and in the
appended claims contemplates any of the conventional
monomeric, dim Eric, oligomeric or polymeric epoxy
materials containing a plurality, more than one, e. g.,
1.1,, epoxy functional groups. Preferably, they will be
members of classes described chemically as (a) an epoxidic
ester having two epoxycycloalkyl groups; (b) an epoxy
resin prepolymer consisting predominately of the monomeric
diglycidyl ether of bisphenol-A; (c) a polyepoxidized
phenol novolak or crossly novolak; (d) a polyglycidyl ether
of a polyhydric alcohol; (e) diepoxide of a cycloalkyl or
alkylcycloalkyl hydrocarbon or ether; or (f) a mixture of
- any of the foregoing. To save unnecessarily detailed
description, reference is made Jo the Encyclopedia of
Polymer Science and Technology Vol. 6, 1967, Intrusions
; Publishers, New York, pages 209-~71, incorporated herein
; 25 by reference.
Suitable commercially available epoxidic esters are
preferably, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclo-
hexanecarboxylate (Union Carbide ERR 4221, Cuba Geigy
SUE); as well as bis(3,4-epoxy-6-methylcyclohexyl-
methyl)adipate (Union Carbide ERR 4289); and Boyce-
epoxycyclohexylmethyl)adipate (Union Carbide ERR 4299).
Suitable commercially available diglycidyl ethers of
bisphenol-A are Cuba Geigy Araldite 6010, Dow Chemical DYER
331, and Shell Chemical Eon 828 and 826.
* Trademark
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A polyepoxidized phenol formaldehyde novo]dk
prepolymer is available from Dow Chemical DEN 431 and 438,
and a polyepoxidized crossly formaldehyde novolak
prepolymer is available from Ciba-Geigy Araldite 538.
A polyglycidyl ether of a polyhydric alcohol is
available from Cuba Geigy, based on butane-ld4-diol,
Araldite RD-2; and from Shell Chemical Corp., based on
glycerine, Eon 812.
A suitable diepoxide of an alkylcycloalkyl hydrocarbon
is vinyl ~yclohexene dioxide, Union Carbide ERR 4206, and
a suitable diepoxide of a cycloalkyl ether is Boyce-
epoxycyclopentyl)-ether, Union Carbide ERR 0400.
Other examples include the epoxidized esters of the
polyethylenically unsaturated monocarboxylic acids, such
as epoxidized linseed, soybean, purl, oiticica, lung,
walnut and dehydrated castor oil, methyl linoleate, bottle
linoleate, ethyl 9,12-octadecadienoate, bottle 9,12,15-
octadecatrienoate, bottle eleostearate, monoglycerides of
lung oil fatty acids, monoglycerides of soybean oil,
sunflower, rhapsody, hemp seed, sardine, cottonseed oil and
the like.
In practicing the instant invention it is also
possible, although optional, to add a thermoplastic
material to the composition. These thermoplastic
materials are composed of 100% non-volatile materials
i. e., containing no water, solvent or other volatile
carriers. They are solid or liquid at room temperature
but become more fluid at elevated temperatures, thereby
allowing for easy application. The thermoplastic
i 30 materials operable herein include, but are not limited trod
polyamides, polyvinyl chloride, polyvinyl acetals and
polyester resins ethylene-vinyl acetate (EVA) copolymers,
ethylene-ethyl acrylate EYE) copolymers, butadiene-
acrylonitrile copolymers and styrene-ethylene-butylene
* Trademark
.,
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:ll2~27~
copolymersO Some of the newer materials of the more
conventional "rubber" variety are the block copolymers,
styrene-butadiene or styrene-isoprene sold under the
trademark "WriteNow"
One thermoplastic material useful in the compositions
of the present invention includes those thermoplastic
segmented copolyesters disclosed in US. Patent
No. 4,059,715, incorporated herein by reference. These
are solid, non-tacky, strongly cohesive, solvent-free
thermoplastic polymers which are themselves not subject to
cold flow and are non-blocking below their melting
temperatures but which become aggressively tacky and
bondable upon being melted. They consist essentially of
from about 5 to 75 percent by weight of amorphous ester
units and 95 to 25 percent by weight of crystallizable
ester units joined through the ester linkages
Other thermoplastic materials which are useful in the
compositions of the present invention include other
thermoplastic polyesters (e g., that available under the
trade designation "5096" from Cooper Polymers, Into),
thermoplastic polyurethane (e.g., that available under
the trade designation "Q-thane PI 56" from K.J. Quinn
Co., Inc. ?, thermoplastic polyamides (e.g., that
available under the trade designation "Caromed 2430" from
Cooper Polymers, Inc.?, "Elvamides" available from Dupont
and "Macro melt" available from Heckle; thermoplastic
rubbers (e.g., those available under the trade
designation "Keaton 1101" and "Keaton 1107" from Shell
Chemical Co.) and ethylene vinyl acetate (e.g., that
available under the trade designation "Elvax 40" from
ELI. Dupont de Numerous Co., Inc. and "Ultrathin"
available from US). Still other thermoplastic materials
operable as a component in the composition include, but
are not limited to, butydiene-acrylonitrile copolymers
* Trademark
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i,;,
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available under the trade designation "Hycar'l from
I Goodrich, urethane-acrylates, urethane-epoxides and
urethane-polyenes. In addition, other thermoplastic
materials are polyvinyl acetals such as polyvinyl formal
and polyvinyl betrayals. The thermoplastic material, when
present, is present in the composition in amounts ranging
from 1~95~ by weight with the balance being the epoxy
resin.
The components of the composition can be admixed in
any order, preferably at room temperature up to 100C.
After admixture to a homogeneous mass, curing can be
accomplished by elevating the temperature. The curing
reaction is carried out at temperatures ranging from about
115 to 285C depending upon the combination of aside and
phosphine compound employed.
The heating can be carried out by conventional means,
e.g., an air oven, as well as by radio frequency (RF)
techniques. RF heating can be utilized as a faster and
more efficient means of curing than conventional air oven
heating. In addition to the formation of high strength
bonds, RF bonding techniques aid in (a) fast bond setting
time sand (b) automated part handling and assembly.
In the instant invention, when the composition is used
as an adhesive, RF heating can be employed with the
adhesive composition herein to adhere (1) plastic to
plastic, (2) plastic to metal and (3) metal to metal.
For example, dielectric heating can be used to bond (1)
and (2) swooper if one member of the adhesive composition,
i.e., resin, aside or phosphine compound contains
sufficient polar groups to heat the composition rapidly
and allow it to bond the adherents. Inductive heating can
also be used to bond (1), (2) and (3). That is, when at
least one of the adherents is an electrically conductive
or ferrom~gr~et c metal, the heat generated therein is
* Trademark
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of.
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conveyed by conductance to the adhesive composition
thereby initiating the cure to form a thermoses adhesive.
In the instance where both adherents are plastic, it is
necessary to add an energy absorbing material, i.e., an
electrically conductive or ferromagnetic material,
preferably in fiber or particle form (10-400 mesh), either
per so or encapsulated to the adhesive composition. The
energy absorbing material is usually added in amounts
ranging from 0.1 to 2 parts by weight, per 1 part by
weight of the composition.
The particulate RF energy absorbing material used in
the composition when induction heating is employed can be
one of the magnetizable metals including iron, cobalt and
nickel or magnetizable alloys or oxides of nickel and iron
and nickel and chromium and iron oxide. These metals and
alloys have high Curie points (730-2,0~0~F).
Electrically conductive materials operable herein when
inductive heating is employed include, but are not limited
to, the noble metals, copper, aluminum, nickel, zinc as
well as carbon black, graphite and inorganic oxides.
There are two forms of radio frequency heating
operable herein, the choice of which is determined by the
material to be adhered. The major distinction is whether
or not the material is a conductor or non-conductor of
electrical current If the material is a conductor, such
as iron or steel, then the inductive method is used If
the material is an insulator, such as wood, paper,
textiles, synthetic resins, rubber, eta,, then dielectric
- heating can also be employed.
Most naturally occurring and synthetic polymers are
non-conductors and, therefore, are suitable for dielectric
heating. These polymers may contain a variety of dipoles
and ions which orient ion an electric field and rotate to
maintain their alignment with the field when the field
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oscillates. The polar groups may be incorporated into the
polymer backbone or can be pendant side groups, additives,
extenders, pigments, etc. For example, as additives,
lousy fillers such as carbon black at a one percent level
can be used to increase the dielectric response of the
adhesive. When the polarity of the electric field is
reversed millions of times per second, the resulting high
frequency of the polar units generates heat within the
material.
The uniqueness of dielectric heating is in its
uniformity, rapidity, specificity and efficiency. Most
plastic heating processes such as conductive, convective
or infrared heating are surface-heating processes which in
order to establish a temperature within the plastic must
subsequently transfer the heat to the bulk of the plastic
by conduction. Hence, heating of plastics by these
methods is a relatively slow process with a non-uniform
temperature resulting in overheating of the surfaces. By
contrast, dielectric heating generates the heat within the
material and is therefore uniform and rapid, eliminating
the need for conductive heat transfer. In the dielectric
heating system herein the electrical frequency of the
electromagnetic field is in the range 1-3,000 megahertz
said field being generated from a power source of
OWE kilowatts.
Induction heating is similar, but not identical, to
dielectric heating The following differences exist:
(a) magnetic properties are substituted for dielectric
properties; (b) a coil is employed to couple the load
rather than electrodes or plates; and (c) induction
heaters couple maximum current to the load. The
generation of heat by induction operates through the
rising and falling of a magnetic field around a conductor
with each reversal of an alternating current source The
I
practical deployment of such field is generally
accomplished by proper placement of a conductive coil.
When another electrically conductive material is exposed
to the field, induced current can be created. These
induced currents can be in the form of random or "eddy"
currents which result in the generation of heat.
Materials which are both magnetizable and conductive
generate heat more readily than materials which are only
conductive. The heat generated as a result of the
magnetic component is the result of hysteresis or work
done in rotating magnetizable molecules and as a result of
eddy current flow. Polyolefins and other plastics are
neither magnetic nor conductive in their natural states.
Therefore, they do not, in themselves, create heat as a
result of induction
The use of the RF induction heating method for
adhesive bonding of plastic structures has proved feasible
by interposing selected RF energy absorbing materials in
an independent adhesive composition layer or gasket
conforming to the surfaces to be bonded, RF energy passing
through the adjacent plastic structures (free of such
energy absorbing materials) is readily concentrated and
absorbed in the adhesive composition by such energy
absorbing material thereby rapidly initiating cure of the
adhesive composition to a thermoses adhesive
RF energy absorbing materials of various types have
been used in the RF induction heating technique for some
time. For instance, inorganic oxides and powdered metals
have been incorporated in bond layers and subjected to RF
radiation. In each instance, the type of energy source
influences the selection of energy absorbing material.
Where the energy absorbing material is comprised of finely
divided particles having ferromagnetic properties and
such particles are effectively insulated from each other
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by particle containing nonconducting matrix material, the
heating effect is substantially confined to that resulting
from the effects of hysteresis. Consequently, heating is
limited to the "Curie" temperature of the ferromagnetic
material or the temperature at which the magnetic
properties of such material cease to exist.
The RF adhesive composition of this invention may take
the form of an extruded ribbon or tape, a molded gasket or
cast sheet or film. In liquid form it may be applied by
brush to surfaces to be bonded or may be sprayed on,
pumped or used as a dip coating for such surfaces.
The foregoing adhesive composition, when properly
utilized as described hereinafter, results in a solvent
free bonding system which permits the joining of metal of
plastic items without costly surface pretreatment. The RF
induced bonding reaction occurs rapidly and is adaptable
to automated fabrication techniques and equipment.
To accomplish the establishment of a concentrated and
specifically located heat zone by induction heating in the
context of bonding in accordance with the invention, it
has been found that the RF adhesive compositions described
above can be activated and a bond created by an induction
heating system operating with an electrical frequency of
the RF field of from about 0.1 to about 30 megacycles and
preferably from about 0.3 to 30 megacycles, said field
being generated from a power source of from about 1 to
about 30 kilowatts, and preferably from about 2 to about
5 kilowatts. The RF field is applied to the articles to
be bonded for a period of time of less than about
2 minutes.
As heretofore mentioned, the RF induction bonding
system and improved RF adhesive compositions of the
present invention are applicable to the bonding of metals,
thermoplastic and thermoses material, including fiber
reinforced thermoses material
I V
The composition of the present invention may, if
desired, include such conventional additives as
antioxidant, inhibitors, fillers, antistatic agents,
flame-retardant agents, thickeners, thixotropic agents,
surface-active agents, viscosity modifiers, plasticizers,
tackifiers and the like within the scope of this
invention. Such additives are usually preblended with the
epoxy resin prior to or during the compounding step.
Operable fillers which can be added to the system to
reduce cost include natural and synthetic resins, glass
fibers, wood flour, clay, silica, alumina, carbonates,
oxides, hydroxides, silicates, glass flakes, borate,
phosphates, diatomaceous earth, talc, kaolin, barium
sulfate, calcium sulfate, calcium carbonate, wollastonite,
carbon fibers and the like. The aforesaid additives may
be present in quantities up to 500 parts or more per
100 parts of the epoxy resin by weight and preferably
about 0.005 to about 300 parts on the same basis.
The following examples are set out to explain, but
expressly not limit, the instant invention. Unless
otherwise noted, all parts and percentages are by weight.
The onset curing temperature of the formulations was
obtained by Differential Scanning Calorimetry.
Example 1
Varying amounts of triphenyl phosphine were added to
100 g of diglycidyl ether of bisphenol-A, commercially
available from Shell Chemical Co. under the trade name
EPON-828, at 100C to obtain a homogeneous solution.
After cooling to room temperature, 6 g of dicyandiamide
were added to the epoxy resin mixture. Samples of the
epoxy resin dicyandiamide mixture containing various
amounts of triphenyl phosphine were placed in a
Perkin-Elmer Differential Scanning Calorimeter The onset
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curing temperatures of the various samples are shown in
TABLE I:
TUBULE
Triphenyl Phosphine (g) 0 2 4 6 8
Onset Curing Temperature (C) 191 161 155 147 131
Example 2
A formulation was made up as in Example 1 with varying
amounts of triphenyl phosphiner Samples of the various
formulations were charged to a Perkin-Elmer Differential
Scanning Calorimeter The calorimeter was heated to 170C
and time measurements were made to ascertain how long it
required for the epoxy resin to cure (90% cure) at this
temperature. The results are shown in TABLE II:
- TABLE II
Triphenyl Phosphine (g) 0 2 4 6 8
Time (min.) to reach 90~
cure at 170C 24 13 13 13 13
Example 3
120 g of an epoxy resin, commercially available from
Shell Chemical Co. under the trade name EPON-828, were
admixed with 80 g of a thermoplastic material, i.e., an
acrylonitrile-butadiene copolymer with carboxylate end
groups, commercially available from BY Goodrich under
the trade name HIKER, and 0.5 g of triphenyl
phosphine. The admixture was reacted at 110-120C for
3 hours to form an epoxy-terminated prepolymer,
hereinafter referred to as prepolymer A.
issue
Example 4
100 parts of prepolymer A from Example 3 were admixed
with 2 parts of mailmen. A sample of the admixture was
charged to a Differential Scanning Calorimeter. The onset
curing temperature was 344C.
Example 5
100 parts of prepolymer A from Example 3 were admixed
with 6 parts of mailmen and 5 parts of triphenyl
phosphine. A sample of the admixture was charged to a
Differential Scanning Calorimeter. The onset curing
temperature was 250C. A completely cured solid material
was obtained in 20 minutes at 285C.
Example 6
100 parts of prepolymer A from Example 3 were admixed
with 6 parts of mailmen and 5 parts of tricyclohexyl
phosphine. A sample of the admixture was charged to a
Differential Scanning Calorimeter. The onset curing
temperature was 236C.
Example 7
Varying amounts of tricyclohexyl phosphine were added
to 100 g of diglycidyl ether of bisphenol-A containing 6 g
of dicyandiamide at 60C to obtain an orange color
mixture. Samples of the mixture containing various
amounts of tricyclohexyl phosphine were placed in a
Perkin-Elmer Differential Scanning Calorimeter. The onset
curing temperatures of the various samples are shown in
TABLE III:
TABLE III
30 Tricyclohexyl phosine (g) 0 1 3 5 7
Onset Curing
Temperature (C) 193164 158 132 132
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Example 8
.. .
To 0.01 mole of tricyclohexyl phosphine dissolved in
20 ml of ethylene chloride was charged 0.01 mole of
2,2-dimethylolpropionic acid (DMPA) in 20 ml of methanol.
After stirring for 30 minutes, the solvent in the reaction
mixture was removed under a reduced pressure. Tricycle-
hexylphosphinium 2,2-dimethylolpropionate in white
crystalline form was obtained.
Example 9
Varying amounts of the salt from Example 8 were added
to 100 g of diglycidyl ether of bisphenol-A containing 6 g
of dicyandiamide at room temperature. Samples containing
various amounts of this salt were placed in a Perkin-Elmer
Differential Scanning Calorimeter. The onset curing
temperatures of the various samples are shown in TABLE IV:
TABLE IV
-
Tricyclohexyl
I: phosphine (DMPA) 0 2 4 6 8
20 Onset curing
temperature (C) 193 181 174 172 146
Example 10
5 g of an epoxy resin, commercially available from
Shell Chemical Co. under the trade name "EPoN-828", were
admixed with 0.3 g of dicyandiamide and 0.3 g of trio-
toll phosphine. A sample of the admixture was charged to
a Differential Scanning Calorimeter. The onset curing
temperature was 188C. A completely cured solid material
was obtained in 20 minutes at 170C.
Example 11
.
7.5 g of EPON-828 and 2.5 g of a polyvinyl bitterly
having a weight average molecular weight in the range
180,000 to 270,000 and commercially available from
Monsanto Co. under the trade name Butvar B-72 were admixed
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lo
with 0.5 g of dicyandiamide and 0.4 g of triphenyl
phosphine~ The admixture was dissolved in a mixture of
90 ml of methanol and 90 ml of ethylene chloride after
which the solvents were vacuumed off in a 50C vacuum
oven. A sample of the dissolved material was charged to a
Differential Scanning Calorimeter. The onset curing
temperature was 143C. A completely cured, solid material
was obtained in 20 minutes at 170C.
Example 12
0.1 mole of tri-n-octyl phosphine was added to
0.1 mole of 2,2-dimethylolpropionic acid in 300 ml of
methanol. The solution was stirred over night and became
clear. The solvent was removed under a reduced pressure
and tri-n-octyl phosphinium 2,2-dimethylolpropionate in
crystalline form was obtained.
Example 13
5.0 g of EPON-828, 0.3 g of dicyandiamide and 0.3 g of
the crystalline salt material from Example 12 were admixed
together. A sample of the admixture was charged to a
Differential Scanning Calorimeter. The onset curing
temperature was 164C A completely solid material was
obtained in 20 minutes at 170C.
Example 14
6 g of triphenyl phosphine were added to 100 g of
diglycidyl ether of bisphenol-A, commercially available
from Shell Chemical Co. under the trade name "EPoN-828", at
100C to obtain a homogeneous solution. After cooling to
room temperature 6 g of dicyandiamide were added to the
epoxy resin mixture. The admixture was applied between
carbon steel shims at a thickness of about 2 miss and the
shims were lapped. The shim sample was placed in an
induction heating apparatus and at a frequency of
350 kilocycles was heated for 4 seconds at 250C. A solid
adhesive bond resulted.
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