Epoxy coating compositions containing a dual mixture of a boron trihalide complex and an irradiated charge transfer complex as curing agent

A coated article is made by: (1) admixing an epoxy resin, with a dual curing agent admixture of (a) an irradiated mixture of carboxylic acid anhydride and carbon containing cyclic compound and (b) a boron trihalide complex selected from at least one of boron trihalide:amine and boron trihalide:ether, (2) applying the mixed resin and concentrated dual curing agent to the surface of an article, and (3) curing the applied resin and curing agent.

BACKGROUND OF THE INVENTION 
Carboxylic acid anhydrides, Lewis Acids, and boron trifluoride:amine 
complexes are curing agents that have been found to be useful with epoxy 
resins for insulating applications, as described by Lee and Neville in the 
Handbook of Epoxy Resins, McGraw Hill, 1967, pages 11-1 to 11-8 and 12-1 
to 12-27. Usually, the addition of an accelerator is required to give 
reasonable gel times at elevated temperatures, but at room temperature, 
even with high concentrations of accelerators, very slow gel times are 
experienced. Considerable effort has been devoted in recent years to 
developing improved room temperature curing agents for epoxy-anhydride 
resins. 
Ecke et al., in U.S. Pat. No. 3,114,752, taught the reaction of 
tetrahydrofuran with maleic acid in the presence of a free radical 
initiator to produce monomeric 1:1 adducts. Free radical initiators were 
taught to include ultraviolet light and various persulfates, peroxides and 
nitrides. The compounds formed were bonded adducts rather than 
disassociated species such as free radicals, and were taught as useful 
plasticizers and curing agents for epoxy resins. Smith et al., in U.S. 
Pat. No. 4,273,914, discovered a low temperature, fast curing epoxy 
insulating composition, which consisted of an epoxy resin and a carboxylic 
acid anhydride complex. The anhydride complex was made by the low 
temperature reaction of a selected Lewis Acid catalyst, such as antimony 
pentrachloride, titanium tetrachloride, boron trifluoride, tin 
tetrachloride, or triphenyl tin chloride, with a carboxylic acid 
anhydride. There, the catalyst and anhydride were simply pre-reacted at a 
reacting mass temperature of from 10.degree. C. to about 45.degree. C. The 
complex allowed substantially complete cure of the epoxy resin at 
25.degree. C. in about 48 hours. 
Von Brachel et al., in U.S. Pat. No. 3,499,007, utilized a peroxide 
initiated, non-irradiated, free-radical chain reaction of maleic anhydride 
and straight chain polyalkylene ethers, at from about 80.degree. C. to 
160.degree. C., to provide addition products, noting that the literature 
showed successful reaction of maleic anhydride with tetrahydrofuran, but 
not dioxane, in the presence of radical initiators. These addition 
products were found useful as raw materials for lacquers, and as surface 
active anhydride components in the production of polyesters. These 
addition products were usually reacted at from 100.degree. C. to about 
130.degree. C. with epoxies and the like. 
Charge-transfer systems have recently been shown capable of polymerizing 
monomer and epoxy resins. Williamson et al., J. Polm. Sci., Polm. Chem. 
Ed., Vol. 20, pp. 1875-1984, 1982, "Laser-Initiated Polymerization of 
Charge-Transfer Monomer Systems" described polymer formation after laser 
exposure in three successful systems: 9-vinylanthracene/diethylfumarate; 
2-vinylnaphthalene/fumaronitrile, in methylene chloride solvent; and 
2-vinylnaphthalene/fumaronitrile, in sulfolane solvent. Another article, 
"Laser Initiated Polymerization of Charge Transfer Monomer Systems: 
Copolymerization of Maleic Anhydride with Styrene, Vinyltoluene and 
t-Butylstyrene", by R. K. Sadhir et al., Polym. Prepr. Am. Chem. Soc. Div. 
Polym. Chem., Vol. 23, No. 1, pp. 291-292, March 1982, describes 
vinyl-maleic anhydride systems and a theoretical discussion of 3,600 
Angstrom Unit laser irradiation of such systems to form charge transfer 
systems. 
Later articles, "Laser-initiated Copolymerization of Maleic Anhydride with 
Styrene, Vinyltoluene, and t-Butylstyrene", by R. K. Sadhir et al., J. 
Polym. Sci. Polym. Chem. Ed., Vol. 21, No. 5, pp. 1315-1329, May 1983, and 
"Laser-Initiated Polymerization of Epoxies in the Presence of Maleic 
Anhydride", by R. K. Sadhir et al., J. Polym. Sci. Polym. Chem. Ed., Vol. 
23, pp. 411-427, 1985, give a more detailed description of laser-initiated 
polymerization of styrene, vinyltoluene and t-butystyrene in the presence 
of maleic anhydride, and laser-initiated polymerization of cyclohexene 
oxide in the presence of maleic anhydride, respectively. 
Sadhir et al., in U.S. patent application Ser. No. 739,242, filed on May 
30, 1985, utilized a concentrated, highly reactive, irradiated catalytic 
complex as a low temperature curing agent for organic resins. The complex 
was produced by U.V. or laser irradiating and then cold concentrating a 
mixture of carboxylic acid anhydride and at least one of a cyclic compound 
selected from tetrahydrofuran, dioxane, trioxane, and sulfolane, with no 
use of catalysts or initiators. These concentrated catalytic complexes 
were described as sole room temperature catalysts with epoxy resins and 
vinyl monomers, to provide impregnating, potting, or protective 
encapsulating resins for motor coils, or coil connection insulators for 
high voltage rotating apparatus. Examples showed a quick room temperature 
cure with cycloaliphatic epoxy resins. It has been found, however, that 
these complexes provide a slower room temperature cure with bisphenol A 
epoxy resins than with cycloaliphatic epoxy resins. 
Since the bisphenol A epoxy is the most commonly used and inexpensive type 
of epoxy resin, it is highly desirable to find a fast acting catalyst for 
them which is useful at room temperature, and to provide fast, room 
temperature curable bisphenol A epoxy coating compositions. It would also 
be highly desirable to be able to fast cure cycloaliphatic epoxy resins at 
times below 3 minutes at room temperature, for fast production line, thin 
coating of a variety of articles. 
SUMMARY OF THE INVENTION 
The above problems have been solved and the above needs met by admixing an 
epoxy resin with a dual curing agent consisting essentially of: (1) a 
charge transfer complex produced by mixing and irradiating a combination 
of: (a) a carboxylic acid anhydride, selected from halide or short chain 
alkyl substituted maleic anhydride, and preferably citraconic anhydride or 
maleic anhydride, and their mixtures, and (b) a carbon containing cyclic 
compound containing an electron deficient element, such as sulfur or 
preferably oxygen and their mixtures, selected from the group consisting 
of tetrahydrofuran, dioxane, trioxane, and sulfolane, and their mixtures, 
and (2) a boron trihalide complex, such as a boron trihalide:amine 
complex, a boron trihalide:ether complex or mixtures thereof, where halide 
is preferably fluorine or chlorine. Preferably, the irradiated mixture of 
carboxylic acid anhydride and carbon containing cyclic compound is 
concentrated before or after mixing with the boron trihalide complex. 
The preferred weight ratio of carboxylic acid anhydride:carbon containing 
cyclic compound in the catalytic complex is from about 1:0.8 to 2. In the 
reaction to form the unconcentrated charge transfer complex, no free 
radical initiators are used, and the temperature is preferably kept below 
about 45.degree. C. The weight ratio of charge transfer complex:boron 
trihalide complex can generally be from about 25 to 200:1, but when the 
resin to be cured is a bisphenol A epoxy, the ratio drops to about 25 to 
40:1. 
The charge transfer complex can be concentrated without the use of heat, 
in, for example, a vacuum chamber or other vacuum means, to from about 55% 
to about 90% of its original weight, to remove any plasticizing compounds. 
This concentration is preferably done after mixing the unconcentrated 
charge transfer complex and the boron trihalide complex. If the charge 
transfer complex is concentrated before mixing with the boron trihalide 
complex, solubility problems with the boron trihalide complex in the 
concentrated charge transfer complex are possible. The highly reactive 
dual mixture of charge transfer complex and boron trihalide complex, is 
herein defined as the "dual curing agent" of this invention. When it is 
cold concentrated and added in a weight ratio of epoxy resin:dual curing 
agent of from about 1:0.2 to 1.5, it will effect substantially complete 
cure at 25.degree. C. to 2 mil thick coatings of bisphenol A epoxy resins 
in about 10 minutes. No additional curing agents are needed. 
The irradiation to form the unconcentrated charge transfer complex can be, 
for example, from a laser or a U.V. lamp, and contains radiation within 
the wavelength range of from about 130 Angstrom units to about 7,000 
Angstrom units. The irradiation is effective only when both the selected 
carboxylic acid anhydride and the selected carbon containing cyclic 
compound are mixed together, the irradiation of the mixed product solution 
producing an active species which is responsible for helping to initiate 
resin polymerization at room temperature. The resins incorporating these 
dual curing agents can be used to encapsulate electrical articles, to act 
as an insulating adhesive, and particularly, to act as fast, room 
temperature curable, surface coating paints of 0.02 inch thickness or 
less, for steel, other metals, wood, and plastics.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
It has been found that selected carbon containing cyclic compounds, 
containing an electron deficient element, can effectively interact and 
complex with selected carboxylic acid anhydrides, through irradiation 
containing radiation within the radiation wavelength range of from about 
130 Angstrom units to about 7,000 Angstrom units, preferably in the range, 
of from about 2,000 Angstrom units to about 7,000 Angstrom units, and most 
preferably from about 2,000 Angstrom units to about 3,900 Angstrom units. 
The irradiation need not be wide band, but can be any portion within the 
band. Laser irradiation, for example with an Argon laser at about 3,600 
Angstrom units, is a very concentrated and energy efficient substitute for 
common ultraviolet (U.V.) lamp sources, and allows the reaction to proceed 
at about 25.degree. C. without the need for cooling. 
When a laser is used, 5 minutes to 60 minutes irradiation will provide an 
effective amount of reactive species, which when mixed with a boron 
trihalide complex can be used to cure epoxy resins, and particularly 
bisphenol A epoxy organic resins. When a 250 watt to 500 watt U.V. lamp is 
used, 15 minutes to 90 minutes will provide an effective amount of 
reactive species, which when mixed with a boron trihalide complex can be 
used to quick cure epoxy resins, and in particular, bisphenol A epoxy 
resins. Preferably, especially if bisphenol A epoxies are to be used, the 
charge transfer complex will be further concentrated. In the case of the 
U.V. lamp, the reacting mixture is preferably surrounded by a 
refrigeration means, so that the heat of the U.V. lamp does not cause 
undue evaporation of the reactants before the reaction is completed. In 
all cases, the temperature should be kept below about 45.degree. C., to 
prevent evaporation of reactants, for example, maleic anhydride has a 
sublimation temperature of about 52.degree. C. and tetrahydrofuran has a 
boiling point of about 66.degree. C. 
The useful carbon containing cyclic compounds for the cyclic charge 
transfer complex component of the dual curing agent of this invention 
contain one or more sulfur and/or oxygen, preferably oxygen, electron 
deficient elements or components, where the electron deficient element or 
component need not be present in the ring structure. Particularly useful 
compounds of this type include sulfolane, trioxane, and preferably dioxane 
(1,4-dioxane) and tetrahydrofuran, whose respective chemical structures 
are shown below: 
##STR1## 
Useful carboxylic acid anhydrides for these complexes include a class of 
carboxylic acid anhydrides having the chemical formula: 
##STR2## 
where R and R'=H, CH.sub.3, C.sub.2 H.sub.5, Cl, Br or I, for example, R' 
can =Cl and R can =CH.sub.3. 
Use of a higher alkyl than C.sub.2 H.sub.5 as R or R' will slow the 
irradiation reaction with the carbon containing cyclic compound. The most 
preferred carboxylic acid anhydrides are those where R=H and R'=CH.sub.3, 
and where R and R'=H, i.e., citraconic anhydride, and preferably maleic 
anhydride, respectively: 
##STR3## 
Other carboxylic acid anhydrides, such as hexahydrophthalic anhydride, 
succinic anhydride, and dodecenyl succinic anhydride, are not effective to 
provide catalytic reactive species. The double bond opposite the central, 
single bonded oxygen, appears to be of critical importance in providing 
catalytic reactive species with the abovedescribed carbon containing 
cyclic compounds during irradiation. The carbon containing cyclic 
compounds act as a solvent for the selected acid anhydrides which are 
usually in solid form. The preferred weight range of (selected carboxylic 
acid anhydride):(selected carbon containing cyclic compound) is from about 
(1):(0.8 to 2). Less than 0.8 part/1 part acid anhydride, a solution will 
not result. Over 2 parts/1 part acid anhydride, the complex may not form. 
Usually, the selected acid anhydride is added to the selected liquid carbon 
containing cyclic compound, acting as solvent, and mixed, at about 
25.degree. C. to 30.degree. C., until a solution results. At this point 
there is no interaction between the two ingredients other than solution 
formation, i.e., the product of the mixture contains no complexes or 
reactive species. Then a source of irradiation, such as a bank of U.V. 
lamps or, for example, an Argon ion laser beam, which provides 
concentrated radiation and fast interaction, is directed into the 
solution. FIG. 1 of the Drawings, shows the use of a coherent CR-18 Argon 
ion laser to produce useful complexes for curing resins. In FIG. 1, 
mirrors 1 reflect laser beam 2, from laser source 3, through convex lens 4 
into monomer solution 5, attached to magnetic stirrer means 6, and having 
optional nitrogen bubbler means 7. 
Upon irradiation of the solution, preferably with radiation containing the 
wavelength range of from about 2,000 Angstrom units to about 5,200 
Angstrom units, and most preferably within the range of from about 2,000 
Angstrom units to about 3,900 Angstrom units, a charge transfer complex 
forms. Although applicants are not to be held to any particular theory, 
using the interaction between maleic anhydride and dioxane as an example, 
the possible reactions that, it is thought, might occur include: 
##STR4## 
As shown in the previously described reactions, it is believed that argon 
ion laser action on the product solution and mixture of maleic anhydride 
and dioxane in step (A) produces a singlet excited species which goes to 
triplet excited state via step (B). The triplet excimer thus produced 
reacts with another maleic anhydride unit in the ground state (step C) and 
produces the reactive charge transfer complex (after step C). This charge 
transfer complex then abstracts a hydrogen atom from dioxane. This results 
in a color change between step (C) and step (D) to provide catalytic 
complexes consisting essentially of reactive species such as cation (I), 
radical anion (II) and a free radical (III) containing only an electron as 
a reactive component; which are capable of initiating cationic 
polymerization in epoxies. In addition to the reactive species shown, it 
has now been found that a substantial amount, i.e., from about 20% to 
about 50% of carbon containing cyclic compound added, i.e., such as 
dioxane, remains unreacted. No deliberate heating is used, care being 
taken to react only up to about 45.degree. C., with no catalysts, or 
initiators being present, the reaction proceeding solely due to 
irradiation effects. 
The unreacted, carbon containing cyclic compound remaining after charge 
transfer complex production, be it dioxane, sulfolane or tetrahydrofuran, 
has been found to provide a plasticizing effect on epoxy resins, slowing 
resin cure at 25.degree. C. Continued irradiation has not been found to 
reduce substantially the plasticizing effect of the unconcentrated charge 
transfer complex. Heating the charge transfer complex in an attempt to 
reduce the amount of unreacted, carbon containing cyclic compound causes 
decomposition of the already formed complex. A means to cold concentrate 
the charge transfer complex, such as passing a stream of nitrogen gas over 
the catalytic complex at 25.degree. C., or preferably using a vacuum 
chamber at 25.degree. C., has been found useful to remove substantially 
all of the unreacted, carbon containing cyclic compound and reduce 
substantially the plasticizing effect of the complex. It is also 
speculated that the concentration may open up some rings of the carbon 
containing cyclic compounds, providing additional reactive species. 
At this point the boron trihalide complex is added to the charge transfer 
complex. The boron trihalide complex is selected from the group of 
boron:trihalide amine complex and boron:trihalide ether complex having the 
respective chemical structures: 
##STR5## 
and their mixtures, where halide X is selected from the group consisting 
of F, Cl, Br and I, with F and Cl preferred. R.sub.1 is selected from H, 
alkyl having from 1 to 6 carbon atoms, aryl, saturated carboxcyclic, and 
their combinations; and R.sub.2 is selected from alkyl having from 1 to 6 
carbon atoms, aryl, saturated carbocyclic, and their combinations. Boron 
trihalide:amine complexes are the preferred of the two additives. 
Preferred boron trihalide amines would include: boron 
trifluoride:aliphatic amine complex, boron trifluoride:aromatic amine 
complex, boron trifluoride amine complex where the amine contains both 
aliphatic and aromatic groups, boron trichloride:aliphatic amine complex, 
boron trichloride:aromatic amine complex, and boron trichloride amine 
complex where the amine contains both aliphatic and aromatic groups. 
Applicants are not at this point sure why the combination effect of charge 
transfer complex plus boron trihalide complex produces dramatic 
differences in cure times. 
It is speculated that there may be some interactivity between the two. It 
is also speculated that in the presence of an epoxy group 
##STR6## 
hydrogen will split off the amine or ether to form radical anions, for 
example R.sub.1 R.sub.2 N:BF.sub.3.sup.- +H.sup.+ or R.sub.1 R.sub.2 
O:BF.sub.3.sup.- +H.sup.+. The boron trihalide complex is slowly added to 
the charge transfer complex, in the weight ratio of charge transfer 
complex:boron trihalide complex of from about 25 to 200:1 when 
cycloaliphatic epoxy resins are present in the resin system to be cured, 
and from about 25 to 40:1 when the resin to be cured is solely a bisphenol 
A epoxy, at a temperature of up to about 45.degree. C. 
Preferably, the combination, charge transfer complex-boron trihalide 
complex is cold concentrated to provide the dual curing agent of this 
invention. The charge transfer complex can also be concentrated first and 
then the boron trihalide complex added. In this latter instance, unless 
concentration is on the range of only about 80% to 90% there may be a 
problem of getting the boron trihalide complex to dissolve in the 
concentrated charge transfer complex. 
In all instances, the unreacted carbon containing cyclic compound is 
evaporated during concentration. Since a minor amount of boron trihalide 
complex is used, one can talk of concentrating either the charge transfer 
complex or the mixture of charge transfer complex and boron trihalide 
complex. Concentration of the charge transfer complex or of the charge 
transfer complex-boron trihalide complex mixture can be from about 55% to 
90%, preferably from about 65% to 80% of its original weight. 
Concentration below about 60% is very difficult, and not concentrating 
below about 90% does not yield much benefit in terms of gel and cure times 
to justify the expense of utilizing a cold concentrating means. 
Concentrating between 65% and about 80% yields a very workable thick 
slurry material. Concentration between about 55% and 65% yields a still 
useful material of increasing solidity as 55% is approached. The term 
"cold concentration" as used herein is defined as concentration in the 
temperature range of from about 18.degree. C. to about 30.degree. C. The 
term " X% concentrated" as used herein is defined as concentrated to X% of 
its original weight, i.e., 60% concentrated means that 40% of the original 
weight has been evaporated. 
Bisphenol based epoxy resins are useful, especially with the preferred, 
highly concentrated dual curing agents previously described. These resins 
may be used as the base resin in the invention, or used in combination 
with, for example, a cycloaliphatic epoxy. A bisphenol type resin is 
obtainable by reacting epichlorohydrin with a dihydric phenol in an 
alkaline medium at about 50.degree. C., using 1 to 2 or more moles of 
epichlorohydrin per mole of dihydric phenol. The heating is continued for 
several hours to effect the reaction and the product is then washed free 
of salt and base. The product, instead of being a single simple compound, 
is generally a complex mixture of glycidyl polyethers, but the principal 
product may be represented by the chemical structural formula: 
##STR7## 
where n is an integer of the series, 0, 1, 2, 3 . . . , and R represents 
the divalent hydrocarbon radical of the dihydric phenol. Typically R is: 
##STR8## 
to provide a diglycidyl ether of bisphenol A type epoxy resin or 
##STR9## 
to provide a diglycidyl ether of bisphenol F type epoxy resin. 
The bisphenol epoxy resins used in the invention have a 1, 2 epoxy 
equivalency greater than one. They will generally be diepoxides. By the 
epoxy equivalency, reference is made to the average number of 1, 2 epoxy 
groups, 
##STR10## 
contained in the average molecule of the dlycidylether. 
Other epoxy resins that are particularly useful alone or in admixture with 
bisphenol epoxy resins are epoxy novolacs and cycloalphatic epoxides. The 
polyglycidylethers of a novolac suitable for use in accordance with this 
invention are prepared by reacting an epihalohydrin with phenol 
formaldehyde condensates. While the bisphenol-based resins contain a 
maximum of two epoxy groups per molecule, the epoxy novolacs may contain 
as many as seven or more epoxy groups per molecule. In addition to phenol, 
alkyl-substituted phenols such as o-cresol may be used as a starting point 
for the production of epoxy novolac resins. 
Other epoxy resins useful alone or in mixture with bisphenol types include 
glycidyl esters, hydantoin epoxy resins, cycloaliphatic epoxy resins and 
diglycidyl ethers of aliphatic diols. Of these latter four varieties of 
epoxies, cycloaliphatic epoxies are most useful. The cycloaliphatic type 
epoxy resins that can be employed as the resin ingredient in the invention 
are selected from nonglycidyl ether epoxy resins containing more than one 
1,2 epoxy group per molecule. These are generally prepared by epoxidizing 
unsaturated hydrocarbon compounds, such as cyclo-olefins, using hydrogen 
peroxide or peracids such as peracetic acid and perbenzoic acid. The 
organic peracids are generally prepared by reacting hydrogen peroxide with 
either carboxylic acids, acid chlorides ketones to give the compound 
R--COOOH. 
Examples of cycloaliphatic epoxy resins would include: 
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (containing two 
epoxide groups which are part of ring structures, and an ester linkage); 
vinyl cyclohexene dioxide (containing two epoxide groups, one of which is 
part of a ring structure); and 3,4-epoxy-6-methylcyclohexyl 
methyl-3,4-epoxy-6-methylcyclohexane caboxylate. All of these types of 
epoxy resins described previously are well known in the art, and reference 
can be made to U.S. Pat. No. 4,273,914 for additional details in their 
production. Cycloaliphatic epoxy resins used alone do not require cold 
concentrating of the dual curing agent admixture of this invention. 
Other useful organic resins that can be used in minor amounts with the 
epoxies and the dual curing agents previously described include vinyl 
monomers, such as, styrene, 4-methoxy styrene, vinyl toluene, methyl 
methacrylate, methyl vinyl ketone, or 1,1 diphenyl ethylene and the like, 
and their mixtures. These resins are well known in the art. 
The preferred weight ratio range of epoxy resin: dual curing agent is from 
about 1:0.2 to 1.5, preferably from about 1:0.4 to 0.60. Use of less than 
about 0.2 part dual curing agent/1 part organic resin will provide little 
gel or cure time improvement. Use of over 1.5 parts dual curing agent/1 
part organic resin will result in minimal pot life or working time. The 
range between about 1:0.60 to 1.5 can be especially useful when a filler 
is used, since filler inclusion often seems to substantially delay gel 
time. 
Natural oil extenders, such as epoxidized linseed or soy bean oils, may 
also be used in small amounts. Thixotropic agents, such as fumed alumina 
or fumed silica, having particle sizes of from about 0.005 micron to 0.025 
micron, and coloring pigments, such as titanium dioxide, zinc chromate, 
zinc oxide, zinc sulfide, zirconium oxide, iron oxide, and the like may be 
used in minor amounts as aids in enhancing the color tones of the cured 
resins and making paint like compositions. 
Similarly, various inorganic particulate fillers, such as alumina 
trihydrate, silica, quartz, mica, chopped glass fibers, beryllium aluminum 
silicate, magnesium silicate, lithium aluminum silicate, mixtures thereof, 
and the like, in average particle sizes of from about 5 microns to about 
150 microns, may be employed in amounts up to about 50 parts per 100 parts 
of resin, to improve electrical properties of the resin formulation, and 
to lower costs. Photoinitiators are neither required nor desired, since 
they can provide an impurity element in the composition. 
Referring now to FIG. 2 of the Drawings, a metal substrate 20 is coated 
with a thin coating 21 of the resinous composition of this invention. 
Substrates can include aluminum, copper and other metals, wood, plastic, 
and the like. These compositions can be coated in thickness of 0.02 inch 
or less. Thin films, from about 0.0005 inch to 0.005 inch thick, can be 
cured in air at from about 25.degree. C. to about 30.degree. C. in about 1 
minute to 15 minutes, to provide coatings which are quite flexible and 
have excellent adhesion and electrical insulating properties. When a 
cycloaliphatic epoxy resin is used alone, or is a major component with a 
bisphenol A epoxy resin, a dual mixing spray applicator, having a tank 
filled with resin and a tank filled with dual curing agent, both of which 
feed into a mixing nozzle, can be used to coat electrical articles, such 
as transformers, on an assembly line, where the coating will room 
temperature cure within about 5 minutes. 
EXAMPLE 1 
A batch of charge transfer complex solution was first made, containing 50 
grams (0.51 mole) of maleic anhydride (MAH) dissolved in 50 milliliters 
(44.5 grams) of tetrahydrofuran (THF). The MAH and THF were well mixed in 
a stainless steel beaker with a magnetic stirrer. The beaker was wrapped 
with copper tubing and the beaker was kept in a bath of ethylene 
glycol-water mixture. Refrigerated ethylene glycol-water coolant, kept at 
-20.degree. C. using an Endocol, Neslab refrigeration unit, was circulated 
through the copper coil wrapped around the beaker and also dipped in the 
ethylene glycol-water bath. The bath temperature was about 2.degree. C. 
During stirring, the mixture was subjected to U.V. irradiation from a 300 
watt U.V.-D bulb having a wavelength band between 2,000 Angstrom units and 
4,000 Angstrom units, with primary wavelengths between about 3,600 
Angstrom units and 3,900 Angstrom units. The cooling arrangement was 
necessary to dissipate the heat energy generated by the D bulb, so that 
the mixture components would not evaporate before reaction. In all cases 
the temperature must be maintained below about 40.degree. C. 
After 30 seconds of irradiation, the mixture temperature increased from 
18.degree. C. to 35.degree. C., after which the D bulb was shut off and 
the mixture was allowed to cool down to 18.degree. C. over a 2 minute 
period. Then the solution was irradiated until a 35.degree. C. temperature 
was reached, after which it was again cooled to 18.degree. C. This 
irradiation and cooling cycle was repeated until a total U.V. exposure 
time of 15 minutes was obtained. During the 15 minutes irradiation, the 
colorless MAH-THF solution had turned to red, indicating some interaction 
between the MAH and the THF. The development of color was followed 
spectrophotometrically. In the MAH-THF mixture, charge transfer complexes, 
having an absorption maxima at about 4,480 Angstrom units were formed. The 
irradiated, highly fluid solution of MAH-THF, the charge transfer complex, 
was found to contain a substantial amount of unreacted tetrahydrofuran, 
the carbon containing cyclic compound, from about 20% to about 50% of the 
THF added. 
To 5 grams of this unconcentrated charge transfer complex, 0.15 gram of 
boron trifluoride:amine complex was added, providing a weight ratio of 
charge transfer complex:boron trifluoride complex of 33:1. The boron 
trifluoride:amine complex easily dissolved in the charge transfer 
solution. The mixture was then placed in a small vacuum chamber apparatus, 
i.e., a vacuum dessicator attached to a vacuum line drawing 0.5 Torr to 
1.0 Torr., until its weight was reduced to 85% of its original weight. 
This concentration was carried out at 25.degree. C., and produced a 
concentrated, dual curing agent solution having substantially all of the 
unreacted THF removed without decomposing the already formed charge 
transfer complex or affecting the boron trifluoride. The concentrated 
charge transfer complex was still in liquid form. 
This concentrated mixture of charge transfer complex and boron 
trifluoride:amine was then used to cure thin coatings of an all bisphenol 
A epoxy resin system on 3".times.6".times.0.1" steel strips, as shown 
below in Table 1: 
TABLE 1 
__________________________________________________________________________ 
Complete 
Wt. Ratio 
Pot Life 
Coating 
Cure Time 
Bend X-Hatch 
Resin:Dual 
25.degree. C. 
Thickness 
25.degree. C. 
1/4" Adhesion 
Resin 
Curing Agent 
Minutes 
Inch Minutes 
Mandrel 
Test 
__________________________________________________________________________ 
bisphenol 
2:1 5 0.001 10 Pass Pass 
A epoxy* 
bisphenol 
2:1 5 0.002 10 Pass 90% 
A epoxy* 
__________________________________________________________________________ 
*liquid diglycidyl ether of bisphenol A having an epoxy equivalent weight 
of 180-188 and a viscosity at 25.degree. C. of 6500-9000 cps (sold 
commercially by Shell Chemical Company under the tradename Epon 826). 
As can be seen, flexible, thin coatings having good adherence resulted, 
with very fast cure times at 25.degree. C. for an all bisphenol A system. 
A similar, 0.0015 inch thick coating of Epon 826 bisphenol A epoxy, with a 
wt. ratio of resin:concentrated MAH-THF charge transfer complex of 2:1, 
but without any boron trifluoride amine, took 7 days to completely cure at 
25.degree. C. 
Cure times as low as 1 to 4 minutes at 25.degree. C. for 0.0015 inch 
thickness were achieved when a cycloaliphatic epoxy resin was used alone 
with the boron trifluoride containing dual curing agent described in this 
Example, where a resin:dual curing agent ratio of 2:1 was used; compared 
to about 24 hours at 25.degree. C. when the boron trihalide was omitted 
from the curing agent. As can be seen, the combination of boron trihalide 
and MAH-THF charge transfer complex provides a dramatic difference in 
curing epoxy resins, especially bisphenol A types.