Method of indicating a cure point for ultraviolet radiation curing compositions by color change

Adding a dye with a visible color to an ultraviolet radiation curable composition which contains a photoinitiator which generates free radicals upon exposure to ultraviolet radiation produces a composition which changes visible color upon exposure to ultraviolet radiation. This visible color change indicates that the composition has cured. This cure indication is useful for compositions curable by ultraviolet radiation in the electronics and electrical industry.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method of curing compositions by ultraviolet 
radiation. 
2. Background Information 
The curing of an ultraviolet radiation curable composition upon exposure to 
ultraviolet radiation varies with the kind of ingredients making up the 
composition, the kind of equipment used for generating the ultraviolet 
radiation, the geometry of the device having a film, coating, or 
encapsulant to be cured, and the curing conditions to which the device is 
exposed. These variables make it difficult to determine at what point the 
composition is sufficiently cured. Many times to avoid the chance that a 
composition may be under cured, the dosage of ultraviolet (UV) radiation 
which is given the items to be cured are excessive. Excessive dosages may 
not harm the items, but it could, and furthermore, using excessive dosages 
is expensive and a waste of resource. Therefore, the discovery of the 
present method permits establishing curing conditions which can result in 
sufficient cure without either undercuring or overcuring. 
Materials for the electrical and electronics industry need to meet stricter 
requirements because the electronic devices are becoming smaller and more 
complex. The field of printed circuit boards is no exception. The various 
coatings require that the materials protect the electronic devices and 
components from the environments which they may encounter either during 
processing or in use. Coating printed circuit boards with compositions 
which will cure to a film and which will provide the required protection 
without changing the designed electronic properties or otherwise damage 
the boards components is difficult to achieve because the components are 
very small and often of shapes and design which demands compositions which 
have special uncured properties, special curing properties, and special 
application properties. 
Printed circuit boards often need to be protected from contamination of the 
electrical and electronic components. This protection can be provided by 
coating or encapsulating the device bearing board with a protective film 
to avoid or minimize the reduction in the electrical performance due to 
contamination. Moisture and humidity are considered to be the worst 
contaminant because it must be dealt with in most environments. Moisture 
and humidity can drastically lower insulation resistance between 
conductors, accelerate high voltage breakdown, accelerate dendritic 
growth, and corrode the conductors. Other than moisture, chemical 
contaminants from the environment such as dust, dirt, solvents, acids, 
fungus, oils, and fuels or which are used in the manufacturing process 
such as organic solvents, fluxes, vapors, acids, release agents, and metal 
dust. Handling a printed circuit board can also cause contamination, for 
example, from fingerprints. Conformal coatings are also used to protect 
the electronic components from the harmful aspects of extremes in 
temperature, shock, and abrasion. 
Many conformal coatings and potting compositions are known in the art and 
are available commercially. Each has its advantages and disadvantages. One 
prior art conformal coating material is based on acrylics. Acrylic 
coatings make excellent coating and potting systems because they have 
desirable electrical and physical properties, are resistant to fungus 
growth, have a long life, low or no exotherm during cure, and have little 
or no shrinkage during cure. From some viewpoints, the acrylic coating 
systems have a production advantage because they can be readily applied by 
spraying, dipping, or brushing. However, this is also a disadvantage 
because the films are formed from solvent containing acrylic systems. The 
evaporation of the solvent is a slow and expensive step and the solvent 
vapors need to be controlled for environmental reasons. The solvents 
typically used are the chlorinated solvents, such as trichloroethane and 
methylene chloride. 
The combined impact of high energy costs and more stringent control 
regulations which restrict emissions of volatile solvents into the 
atmosphere has created a need in the coatings industry for high solids or 
solventless systems which do not require a large amount of energy for 
conversion of the system into a high performance coating. Coatings which 
are 100% solids are known and have a rapid cure at a relatively low 
conversion energy demand. Such coatings are acrylated coatings which cure 
by ultraviolet radiation or by electron beam exposure. These are all 
reasons why it is important to have the ability to know when a UV curable 
composition is cured so that extra energy usage is avoided and the cost is 
kept to a minimum. 
SUMMARY OF THE INVENTION 
This invention relates to a method of indicating a cure point of an 
ultraviolet radiation curing composition comprising adding a non-cure 
inhibiting amount of a dye with a visible color to an ultraviolet 
radiation curable composition comprising a photoinitiator which generates 
free radicals upon exposure to ultraviolet radiation and at least one 
material which cures upon exposure to ultraviolet radiation and thereafter 
exposing the resulting composition to a dosage of ultraviolet radiation 
which causes the visible color to either disappear or change to a 
different color indicating that cure has occurred coincidentally, where 
the amount of the dye is less than 30 parts by weight per one million 
parts by weight of the composition and where the dye is selected from the 
group consisting of an anthraquinone dye having a Color Index Solvent Blue 
104, 1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, and an azo 
dye mixture of azo benzene azo naphthyl benzene amine alkyl/alkoxy 
derivatives having a Color Index Solvent Blue 99 and azo benzene azo 
naphthyl benzene amine alkyl derivatives having a Color Index Solvent Red 
166.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The method of the present invention permits a user of ultraviolet radiation 
curable compositions to be assured that the resulting material is fully 
cured. This is accomplished without overcuring by observation of visible 
color change. This color change occurs when a non-inhibiting amount (less 
than 30 parts by weight per one million parts by weight of composition) of 
a dye with a visible color is added to a composition which cures by 
exposure to ultraviolet radiation. The change can be from blue to yellow, 
from red to yellow, from blue to clear, and from yellow to clear. This 
color change usually lasts over long time periods and does not return upon 
standing. If the cure is not sufficiently complete, the original color 
will return upon standing over a period of time, such as from a few 
minutes, to an hour or more, to a couple weeks. For purposes of this 
invention, the use of the term "visible dye" means a dye which will impart 
a color under ordinary visible light. Also, the color changes are those 
which are observable in ordinary visible light. 
The visible dyes useful in the present invention are those which, in the 
presence of free radical generating photoinitiators, changes color upon 
exposure to ultraviolet radiation. This color change occurs and is 
essentially permanent at the point that a UV curable composition is cured 
upon exposure to UV radiation. The visible dyes useful in the present 
invention are selected from an anthraquinone dye having a Color Index 
Solvent Blue 104, 1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, 
and an azo dye mixture of azo benzene azo naphthyl benzene amine 
alkyl/alkoxy derivatives having a Color Index Solvent Blue 99 and azo 
benzene azo naphthyl benzene amine alkyl derivatives having a Color Index 
Solvent Red 166. Examples of these dyes include Sandoz Nitro Fast 2B Blue 
which is a proprietary anthraquinone dye having a C.I. Solvent Blue 104 
sold by Sandoz Chemicals, Charlotte, N.C.; Hytherm Purple KIF which is an 
anthraquinone dye, 1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, 
and having a C.I. Solvent Violet 13, sold by Morton Thiokol, Inc. Morton 
Chemical Division, Chicago, Ill.; and DuPont Oil Purple Liquid which is an 
azo dye mixture of azo benzene azo naphthyl benzene amine alkyl/alkoxy 
derivatives having a C.I. Solvent Blue 99 and azo benzene azo naphthyl 
benzene amine alkyl derivatives having a C.I. Solvent Red 166. 
The amount of visible dye useful in a particular UV curable composition 
should be an amount less than that amount which will inhibit the cure of 
the composition upon exposure to UV radiation. For many compositions, the 
amount will be less than 30 ppm based on the weight of the UV curable 
composition. From experience, the amount is preferably from about 10 ppm 
to 30 ppm of the visible dye based on the weight of the UV curable 
composition. It was found that amounts of the visible dye which became too 
high inhibit the cure of the UV curable composition. The optimum amounts 
of visible dye in a given composition can readily be determined by adding 
a specific amount of visible dye to the composition and observing the 
color change, or lack thereof, upon exposure to UV radiation. If too much 
dye is added, no color change takes place, indicating the composition did 
not cure. At this point, one can increase the dosage of UV to determine 
whether the reason it did not cure was that the dosage was too low. 
Further, evaluation can be used to determine whether the amount of visible 
dye concentration is too high. The dye must be one which changes in color 
at the point of cure by a sufficient degree that the color change is 
readily distinguishable when the composition is being cured in thin films 
or coatings of a few millimeters thickness. 
The UV curable compositions in which this color change can occur are those 
which contain a photoinitiator which produces free radicals upon exposure 
to UV radiation and in which there is at least one material which cures 
upon exposure to UV radiation. Example of photoinitiators which generate 
free radicals include benzophenone, acetonaphthone, acetophenone, benzoin 
methyl ether, benzoin isobutyl ether, 
2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, 
2,2-diethoxyacetophenone, 3-hydroxypropylphenyl ketone, 
3-hydroxypropyl-p-isopropylphenyl ketone, and mixtures there of such as a 
mixture of 50 weight percent of 1-hydroxycyclohexylphenyl ketone and 50 
weight percent benzophenone. 
The amount of photoinitiator is that amount which is conventionally 
required by the particular composition for curing it. 
The UV curable compositions which can be used in the present invention are 
those which are curable by photoinitiators which produce free radicals. 
These compositions can be either silicone compositions, organic 
compositions or compositions which contain both silicone compounds 
(includes polymers) which will cure by exposure to UV radiation in the 
presence of a free radical photoinitiator and organic compounds (includes 
polymers) which cure by exposure to UV radiation in the presence of a free 
radical photoinitiator. These compositions are well known in the art and 
include, that are not limited to, those which are described herein. Some 
of the preferred embodiments of UV curable compositions useful in the 
present method are described below. The compositions containing the 
visible dye and photoinitiator are exposed to UV radiation from 
conventional equipment and under conditions normally used for such 
compositions wherein adjustments are made to reach the cure point by 
observation of the color change. The point at which cure is achieved 
results in a color change. Therefore, the length of time or the dosage of 
UV radiation can be varied to produce the required cure. 
A. UV Curable Compositions Which Cure to Gels 
Compositions curable to gels can be those organosiloxane compositions which 
retain their gel properties at low temperature. These organosiloxane 
compositions cure in the presence of UV radiation and comprise an 
alkenyl-containing polymethylsiloxane with a specified combination of 
mono-, di- and trifunctional siloxane units, an amount of a 
mercaptoalkyl-containing polyorganosiloxane in an amount sufficient to 
cure the composition to a soft, repairable gel and an amount of a 
photoinitiator sufficient to initiate curing of the composition in the 
presence of UV radiation. 
The alkenyl-containing polymethylsiloxane consists essentially of 80 to 97 
mol percent of (CH.sub.3).sub.2 SiO units, 2 to 10 mol percent of CH.sub.3 
SiO.sub.1.5 units, 1 to 6 mol percent of (CH.sub.3).sub.3 SiO.sub.0.5 
units, and 0.2 to 4 mol percent of units represented by the formula 
(CH.sub.3).sub.a R.sup.1 SiO.sub.(3-a)/2, where R.sup.1 represents 
3-cyclohexenyl, cyclohexenylethyl or CH.sub.2 .dbd.CH(CH.sub.2).sub.x --, 
a is 1 or 2, and x represents 0 or an integer from 1 to 6, inclusive. The 
alkenyl-containing polymethylsiloxanes are preferably liquids under 
ambient conditions. 
These alkenyl-containing polymethylsiloxanes in which the alkenyl group is 
vinyl is described in U.S. Pat. No. 4,374,967, which issued to Paul. Brown 
et al. on Feb. 22, 1983. A preferred class of alkenyl-substituted 
polymethylsiloxanes contain from 87 to 95 mol percent of dimethylsiloxane 
units, from 3 to 6 mol percent of monomethylsiloxy units, from 1.5 to 5 
mol percent of trimethylsiloxy units and from 0.5 to 1.5 mol percent of 
dimethylvinylsiloxy units. 
Mercaptoalkyl-containing compounds are combined with the alkenyl-containing 
polymethylsiloxane. The mercaptoalkyl-containing compounds include a 
liquid organic compound containing an average of at least two mercapto 
groups per molecule or a liquid mercaptoalkyl-containing 
polydiorganosiloxane having an average of at least two repeating units per 
molecule corresponding to the formula 
##STR1## 
where R.sup.2 represents a mercaptoalkyl radical, R.sup.3 represents a 
monovalent hydrocarbon or halohydrocarbon radical. The compositions are 
prepared by combining the alkenyl-containing polymethylsiloxane with the 
mercapto-containing compound such that the molar ratio of mercapto groups 
to alkenyl radicals in said composition is 1 or less. 
Preferred embodiments of the mercapto-containing polyorganosiloxane can be 
represented by the general formula 
EQU R.sup.6.sub.2 R.sup.4 SiO(R.sup.7 R.sup.6 SiO) (R.sup.6 R.sup.5 SiO).sub.z 
SiR.sup.4 R.sup.6.sub.2 
where R.sup.7 represents a mercaptoalkyl radical containing from 2 to 6 
carbon atoms, each R.sup.6 represents methyl, phenyl, or 
3,3,3-trifluoropropyl, R.sup.4 represents R.sup.6, R.sup.7 or a hydroxyl 
group, each R.sup.5 is methyl or phenyl, y and z are each 0 or greater, 
with the proviso that R.sup.4 represents a mercaptoalkyl radical when both 
y and z are 0. Most preferably the radicals represented by R.sup.6, 
R.sup.4 and R.sup.5 are methyl, and ingredient B is represented by the 
average formula 
EQU (CH.sub.3).sub.3 SiO{(CH.sub.3).sub.2 SiO}.sub.z (R.sup.7 CH.sub.3 
SiO).sub.y Si(CH.sub.3).sub.3 
where R.sup.7,y and z have the same definitions as above and y is at least 
2. R.sup.7 is preferably 3-mercaptopropyl or mercaptoisobutyl. y is 
preferably from 40 to 45 inclusive and z is preferably from 3 to about 10. 
The organic compounds containing an average of at least 2 mercapto (--SH) 
groups per molecule also contain carbon, hydrogen and, optionally, oxygen. 
These organic compounds preferably contain from 2 to 6 mercapto groups per 
molecule. The organic compound can be, for example, but are not limited 
to, 2,2'-dimercaptodiethylether, 
dipentaerythritolhexa(3-mercaptopropionate), glycol dimercaptoacetate, 
trimethylolpropane trithioglycolate and trimethylolpropane 
trimercaptopropionate. 
The UV curable compositions which cure to gels and which are useful for the 
present invention are those which contain photoinitiators which generate 
free radicals. The photoinitiator is present in an amount sufficient to 
promote curing of the composition upon exposure to UV radiation. 
The photoinitiator should be compatible with the other ingredients of the 
present compositions. Compatibility can readily be determined by blending 
one weight percent of the candidate photoinitiator with the other liquid 
ingredients of the UV curable composition and mixing the resultant 
composition at room temperature or with heating to a temperature of about 
80.degree. C. The resultant composition should be optically clear without 
any dispersed or precipitated material. The photoinitiators are 
exemplified above. 
In addition to the alkenyl-containing polymethylsiloxane, 
mercapto-containing compound, and photoinitiator, the present compositions 
can contain up to about one weight percent of conventional viscosity 
stabilizers to inhibit gelation during storage. Examples of suitable 
viscosity stabilizers include amines such as 2-(diisopropylamino)ethanol 
and trioctylamine, and free radical scavengers such as p-methoxyphenol, 
catechol, hydroquinone, and 2,6-di-t-butyl-p-methylphenol. 
It may be desirable to include an organic peroxide that decomposes at a 
temperature within the range of from about 100.degree. C. to about 
250.degree. C. This is particularly true if the substrate to which the 
composition will be applied is contoured such that a portion of the 
curable composition is shielded from the ultraviolet radiation to which 
the coated substrate is subsequently exposed for the purpose of curing the 
gel composition. 
The UV curable compositions can contain a reinforcing filler or other type 
of reinforcing agent to improve the physical properties of the cured 
material. In those applications where transparency of the cured gel is a 
requirement the reinforcing agent is preferably a finely divided 
hydrophobic silica of the type described in U.S. Pat. No. 4,344,800, 
issued to Michael A. Lutz on Aug. 17, 1982. The disclosure of this patent 
is incorporated into this specification by reference thereto as a teaching 
of silica fillers suitable for use in the optically clear gel compositions 
of this invention. 
The ingredients of the compositions are blended to form a homogeneous 
mixture using any of the known techniques that will not adversely affect 
the storage stability of the composition in the absence of ultraviolet 
light. Unless the composition exhibits borderline storage stability in the 
absence of UV radiation, the order in which the ingredients are added is 
not critical. If the ingredients have a tendency to react, it is 
preferable that the alkenyl-containing polymethylsiloxane be combined 
first with by the viscosity stabilizer and, lastly, the 
mercapto-containing compound and photoinitiator. Curable compositions 
containing a viscosity stabilizer can typically be stored for longer than 
about 6 months under ambient conditions. 
The compositions cure rapidly, typically requiring about one second or less 
of exposure to UV radiation from a medium pressure mercury vapor arc lamp. 
The amount of energy required to cure preferred compositions is from 0.1 
to about 3 joules per square centimeter, depending upon the ingredients 
and the thickness of the layer of curable composition applied to a 
substrate. 
The intensity of the UV radiation used to cure the compositions can be 
measured using any of the available techniques. A preferred method employs 
an integrating photometer which is exposed to a mercury vapor arc lamp or 
other source of UV radiation under the same conditions used to cure the 
coated substrate. A commercially available integrating photometer is the 
"Light Bug" available from International Light. With the method of the 
present invention, the visible dye is added to the composition and upon 
exposure to UV radiation, the color changes when cure is achieved. This 
will eliminate the necessity to constantly cheek with a photometer during 
manufacturing operations. In those instances, where a wet film of the 
composition is exposed to the UV radiation and the color does not change 
or the color returns after a short period of time, it is apparent that the 
dosage is insufficient. 
These organosiloxane gels can include uses as protective coatings and 
encapsulants for electrical and electronic components, particularly solid 
state devices such as integrated circuits, and electrical connectors. The 
gel can prevent penetration of atmospheric moisture and other materials 
that can corrode or otherwise damage the component. 
An example of such UV curable compositions which cure to gels is described 
by Lee et al in U.S. Pat. No. 5,063,102, issued Nov. 5, 1991, and is 
hereby incorporated by reference to show UV radiation curable compositions 
useful in the present invention. 
Other compositions which cure to gels and useful in the present invention 
comprise an acrylamide functional polyorganosiloxane of the general 
formula 
##STR2## 
in which t is an average of at least 44 and has a value such that the mol 
percentage of dimethylsiloxane units in the polydiorganosiloxane is from 
88 to 94.5, s has an average value of at least 2.5 and has a value such 
that the mol percentage of methylphenylsiloxane units is from 5 to 10, r 
is at least 1 and less than 2, R is a divalent alkylene radical having 3 
or 4 carbon atoms, each R' is a hydrogen atom or an acyl radical of the 
formula 
##STR3## 
where at least 15 percent of the R' are 
##STR4## 
and a curing amount of a photoinitiator which generates free radicals when 
exposed to UV radiation. 
UV curable compositions useful in this invention comprise a blend of acryl 
functional polydiorganosiloxanes and a photosensitization system for 
curing the blend when irradiated with UV radiation, wherein the blend is 4 
to 90 mole percent of an acryl functional endblocked polydiorganosiloxane 
of the general formula 
EQU YR.sup.10.sub.2 SiO(R.sup.9.sub.2 SiO).sub.n SiR.sup.10.sub.2 Y, 
9 to 50 mole percent of a mono-acryl functional endblocked 
polydiorganosiloxane of the general formula 
EQU R.sup.10.sub.3 SiO(R.sup.9.sub.2 SiO).sub.n SiR.sup.10.sub.2 Y, 
and 0 to 65 mole percent of a non-functional polydiorganosiloxane of the 
general formula 
EQU R.sup.10.sub.3 SiO(R.sup.9.sub.2 SiO).sub.n SiR.sup.10.sub.3 
where, in the above formulae, R.sup.9 is a monovalent radical selected from 
the group consisting of alkyl, aryl, and fluorinated alkyl; each R.sup.10 
is independently selected from the group consisting of R.sup.9, hydroxyl, 
and a hydrolyzable group, Y is an acryl functional radical bonded to 
silicon atom through silicon-carbon bond where the acryl function has the 
formula 
##STR5## 
or the formula 
##STR6## 
in which R" is a hydrogen atom or methyl, Z is divalent oxygen or 
--N(R.sup.12)--, R.sup.12 is a hydrogen atom or an alkyl of 1-4 carbon 
atoms, R.sup.13 is a divalent hydrocarbon radical having from 1 to 10 
carbon atoms per radical, R.sup.* is a divalent hydrocarbon radical or a 
divalent hydrocarbon radical containing ether linkages and n has a value 
of from 30 to 3,000, the mole percentages being based on the total blend 
as 100 mole percent and where the polydiorganosiloxanes of the blend are 
present in amounts to provide 20 to 95 percent of the endblocking as acryl 
functionality and 5 to 80 percent of the endblocking as non-functional. B. 
UV Curable Silicone Organic Conformal Coating Compositions 
Some preferred conformal coating compositions are those UV radiation 
curable compositions containing aliphatic unsaturated functional silicone 
resin, an organic mercaptan, an acrylate monomer, a photoinitiator, and a 
free radical inhibitor wherein the photoinitiator is a free radical 
generating photoinitiator. In accordance with the present invention 
visible dye is added to them and then they are exposed to UV radiation and 
cure is achieved when the color change occurs. 
The compositions consists essentially of the silicone resin having a 
general average unit formula 
EQU R.sup.i.sub.c SiO.sub.(4-c)/2 
in which each R.sup.i in each unit is independently a monovalent organic 
radical where at least 10 mole percent of the total R.sup.i are phenyl 
radicals and at least two R.sup.i per molecule are aliphatic unsaturated 
radicals which react with mercapto functionality, and c has an average 
value of from 1.2 to 1.8; the organic mercaptan composed of carbon, 
hydrogen, sulfur, and oxygen in which there is at least two mercapto 
groups per molecule; the acrylate monomer having at least one acrylate 
group per molecule in an amount of at least one weight percent based on 
the total weight of the composition; an effective amount of photoinitiator 
to cause the composition to cure upon exposure to UV radiation where the 
photoinitiator generates free radicals upon exposure to the UV radiation; 
and an effective amount of the free radical inhibitor to delay gelation 
during storage, the composition has more than two aliphatic unsaturated 
radicals per molecule in the silicone resin when the organic mercaptan has 
two mercapto groups per molecule, or more than two mercapto groups per 
molecule in the organic mercaptan when the silicone resin has an average 
of two aliphatic unsaturated radicals per molecule, or both more than two 
aliphatic unsaturated radicals per molecule in the silicone resin and more 
than two mercapto groups per molecule in the organic mercaptan, and amount 
of silicone resin and organic mercaptan being such that there is from 0.5 
to 1.5 aliphatic unsaturated radicals in the silicone resin for each 
mercapto group in the organic mercaptan. 
The silicone resins contain aliphatic unsaturated radicals which react with 
mercapto functionality. These silicone resins have an average of 1.2 to 
1.8 organic radical bonded per silicon atom and at least 10 mole percent 
of the organic radicals are phenyl. The silicone resins have per molecule 
at least two aliphatic unsaturated radicals which react with mercapto 
functionality. The silicone resin has a general average unit formula 
EQU R.sup.i.sub.c SiO.sub.(4-c)/2 
in which c has an average value of from 1.2 to 1.8 and R.sup.i is a 
monovalent organic radical where at least 10 mole percent of the R.sup.i 
are phenyl radicals and at least two R.sup.i per molecule are aliphatic 
unsaturated radicals which react with mercapto functionality. The general 
average unit formula is the summation of individual siloxane units which 
are SiO.sub.2 units, R.sup.i SiO.sub.3/2 units, R.sup.i.sub.2 SiO units, 
R.sup.i.sub.3 SiO.sub.178 units and each R.sup.i in each siloxane unit is 
independently selected from the group as defined herein. Each siloxane 
unit does not need to be present in each silicone resin, but the siloxane 
units which are present need to provide an average value for c of from 1.2 
to 1.8. R.sup.i can be independently selected from an alkyl, alkenyl, 
halogenated alkyl, or aryl. The alkyl radicals can be illustrated by 
methyl, ethyl, propyl, isopropyl, butyl, hexyl, and octyl. The alkenyl 
radicals can be illustrated by vinyl, allyl, cyclohexenyl, 1,2-butenyl, 
and 1,2-hexenyl. The halogenated alkyl radicals can be illustrated by 
3,3,3-trifluoropropyl, and other chlorinated, fluorinated, and brominated 
alkyl radicals wherein hydrogen atoms of the alkyl radicals are replace 
with a halogen atom. The preferred alkenyl radicals are vinyl and hexenyl. 
Other preferred radicals are methyl, propyl, 3,3,3-trifluoropropyl, and 
phenyl. Preferred silicone resins are those which are made up of at least 
two siloxane units selected from the group consisting of 
monophenylsilsesquioxane units, monomethylsilsesquioxane units, 
dimethylsiloxane units, diphenylsiloxane units, methylvinylsiloxane units, 
dimethylvinylsiloxy units, and trimethylsiloxy units. The preferred 
silicone resins contain from 20 to 80 mole percent 
monophenylsilsesquioxane units where the remaining siloxane units can be 
those listed above. A more preferred class of silicone resins are those 
made up of from 20 to 40 mole percent monophenylsilsesquioxane units, 10 
to 20 mole percent monomethylsilsesquioxane units, 20 to 35 mole percent 
dimethylsiloxane units, and 10 to 30 mole percent methylvinylsiloxane 
units. The silicone resins can be one resin or a blend of two or more 
resins. The silicone resins can contain residual silicon-bonded groups 
which result from their preparation, such as hydroxyl groups (Si--OH) and 
alkoxy groups (Si--OR**) where R** is an alkyl radical of 1 to 4 carbon 
atoms. 
The crosslinked density, flexibility of cured products, and the modulus of 
cured products are controlled by selecting the amount of aliphatically 
unsaturated radicals in the silicone resin and the average degree of 
substitution of the silicon atoms by silicon-bonded carbon groups. For 
example, increasing the average number of aliphatically unsaturated 
radicals per molecule increases the modulus and decreases the flexibility 
with other composition parameters remaining constant. Increasing the 
average degree of substitution of the silicon atom increases the 
flexibility and decreases the modulus with the other composition 
parameters remaining constant. These are general guidelines and the 
proportional increases and decreases in the modulus and flexibility can be 
varied with the kinds of other R groups, the amount of phenyl, the kind of 
aliphatically unsaturated radicals, and the kinds and amounts of each of 
the siloxane units present in the silicone resin. 
The organic mercaptan contains an average of at least two mercapto 
functional groups per molecule. In these compositions, the number of 
aliphatically unsaturated groups per molecule in the silicone resin is 
more than two, if the number of mercapto functional groups in the organic 
mercaptan is two, or if the number of aliphatically unsaturated groups per 
molecule in the silicone resin is two, then the average number of mercapto 
functional groups per molecule in the organic mercaptan must be more than 
two. These compositions can contain silicone resin having per molecule 
more than two aliphatically unsaturated groups per molecule and organic 
mercaptan having per molecule more than two mercapto functional groups. 
The organic mercaptans can be illustrated by the following: 
trimethylolpropane trithioglycolate, trimethylolpropane 
tri-(3-mercaptopropionate), trimethylolethane trithioglycolate, 
polyethylene glycol dimercaptoacetates, glycol dimercaptoacetate, and 
dipentaerythritol hexa-(3-mercaptopropionate). The preferred organic 
mercaptan is trimethylolpropane tri-(3-mercaptopropionate). Mixtures of 
two or more organic mercaptans can be used. 
These conformal coating compositions can contain, as an ingredient to 
improve the corrosion resistance, improve the adhesion to printed circuit 
board substrates, and improve the thermal resistance, an acrylate monomer. 
These acrylate monomers are illustrated by trimethylolpropane 
trimethylacrylate, pentaerythritol tetraacrylate, ethoxylated 
trimethylolpropane triacrylate, pentraerytritol acrylate (contains three 
acrylate groups), di-(trimethylmethylolpropane tetrataacrylate), 
trimethylolpropane triacrylate, di-(pentraerythritol monohydroxy 
pentaacrylate), hydroxylethyl acrylate, hydroxylpropyl acrylate, 
4-hydroxy-n-butyl acrylate, isobornyl acrylate, proprietary acrylates such 
as functionalized acrylates known as Sartomer 9008 (a triacrylate), 
Sartomer 9012 (an aliphatic triacrylate), and Sartomer 9013 (an aliphatic 
monoacrylate). These are sold by ARCO Chemical Company of Pennsylvania. 
The acrylates are used in amounts of one weight percent or more based on 
the total weight of the composition. 
Ultraviolet radiation capable of causing free radicals to form in the 
composition can be used to cure the composition of this invention. The 
ultraviolet radiation used to generate the free radical crosslinking 
reaction to effect polymerization of the composition and cure requires a 
photosensitization system. Examples of the photosensitization systems are 
known in the art, some specific photoinitiators include 
diethoxyacetophenone, benzophenone, dimethoxyphenylacetophenone, benzoin, 
2-hydroxy-2-methyl-1-phenylpropan-1-one, with optional sensitizors such as 
N-methyldiethanolamine, diisopropylaminoethanol, and 
amyldimethylaminobenzoate. 
These conformal coating compositions can be prepared by mixing the 
ingredients at room temperature with conventional mixing equipment. In 
some cases the blending of the ingredients can be accomplished by some 
heating. Heating these ingredients can create degradation if the 
temperatures become too high or the duration of the heating is for 
prolonged periods of time. The ingredients used to make these compositions 
should be blended to make compatible mixtures. This compatibility is 
desirable to ensure that the cured products will form solid coherent 
coatings, films, sheets, and encapsulants with consistent properties 
throughout. Incompatibility can cause weak spots, fisheyes, and poor 
wetting of substrates on which the composition is deposited. 
A method of making cured films is accomplished by first preparing the 
composition by mixing the silicone resin, the organic mercaptan, the 
acrylate monomer, the photoinitiator, and the free radical inhibitor to 
form a compatible, homogeneous blend, applying the composition to a 
substrate such as an electronics device, and then irradiating the 
composition with ultraviolet radiation in an amount sufficient to cure the 
composition. 
These conformal coating compositions contain an effective amount of a free 
radical inhibitor to delay gelation during storage. These free radical 
inhibitors include p-methoxyphenol (also know as MEHQ), catechol, 
4-t-butylcatechol, phenothiazine, 2,6.-di-t-butyl-p-methylphenol, and 
N-phenyl-2-naphthylamine. The amounts of the free radical inhibitors are 
from zero to one weight percent based on the weight of the composition, 
more preferably from 0.01 to 0.25 weight percent. The most preferred free 
radical inhibitors are p-methoxyphenol, phenothiazine, and mixtures 
thereof. The presence of hydroquinone as a free radical inhibitor appears 
to be undesirable from the standpoint of preparing high modulus and 
tensile strength cured products. 
The conformal coating compositions cure very well, adhere well to 
electronic boards, have a mild odor, and are clear. The presence of the 
acrylate compound in these compositions is vital to protect copper from 
corroding. The compositions of the present invention exhibit improved 
adhesion by preventing salt water from creeping under the coating and 
corroding the metal. However, acrylates without the mercaptan compound 
exhibit insufficient cure and to obtain the excellent properties the 
silicone resin, mercaptan, and acrylate are required. The thermal 
stability of the cured films made from the compositions of this invention 
can be expected to improve further by substituting hexenyl group for the 
vinyl group in the silicone resins. The compositions of this invention 
cure very rapidly compared to other ultraviolet radiation cured conformal 
coating compositions. They also can be cured in very deep sections when 
peroxide is added to them. These conformal coatings can be used as mar 
resistant conformal and protective coatings for printed circuit boards, 
gaskets for automobile engines, coatings for deep cross section pottants, 
optical fiber coatings where the refractive index of these coatings is 
greater than 1.49. 
The preferred composition consist essentially of silicone resin in an 
amount of greater than 35 weight percent, from 5 to 30 weight percent 
mercaptan compound, from 1 to 25 weight percent acrylate compound, from 1 
to 4 weight percent photoinitiator, less than 0.05 weight percent free 
radical inhibitor, and when present organic peroxide in amounts of from 1 
to 5 weight percent. The weight percentages are based on the total weight 
of the composition. 
It is also expected that the mercaptopropylsiloxane and 
mercaptobutylsiloxane containing polymers described in Lee et al ('486) in 
U.S. Pat. No. 4,780,486, issued Oct. 25, 1988, may be useful as 
substitutes for the mercaptans of the present invention, especially those 
in which phenyl-containing siloxane units are also in the polymer. 
Additional modifications which may be useful include acrylate functional 
oligomers, other vinyl functional organic monomers, such as divinyl 
benzene, and thiol functional silicone resins. 
Another example of suitable compositions which can be used in the present 
invention are those described by Lutz et al in U.S. Pat. No. 5,036,114, 
issued Jul. 30, 1991, and is hereby incorporated by reference to show UV 
curable silicone organic compositions. These compositions comprise a 
polydiorganosiloxane having on the average more than about 0.4 acrylamide 
functional groups per molecule and being crosslinkable by exposure to UV 
radiation in the presence of a photosensitization system, an effective 
amount of a heat stability additive selected from the group consisting of 
zinc naphthenate, stannous octoate, and tetraorganotitanate, and an 
effective amount of a photosensitization system. 
Lutz et al also in copending application Ser. No. 07/805,238, filed Dec. 
11, 1991, now abandoned, assigned to the same assignee as the present 
application and is hereby incorporated by reference to show UV curable 
silicone organic compositions. These compositions comprise a compatible 
mixture of an acrylamide functional polyorganosiloxane having an average 
unit formula 
EQU T.sub.d R.sup.14.sub.e SiO.sub.(4-d-e)/2 
in which R.sup.14 is a monovalent organic group where at least 5 to 10 mole 
percent of R.sup.14 are aromatic based on all R.sup.14 equal to 100 mole 
percent, T is an acrylamide functional group bonded to the silicon atom 
through a silicon-carbon bond, d has a value such that there is on the 
average at least 0.4 acrylamide functional group per molecule, e has a 
value such that the polyorganosiloxane can be applied to a substrate and 
cured by exposure to UV radiation, and the sum of d+e is at least 0.7, and 
a photosensitization system. 
C. UV Curable Organic Conformal Coating Compositions 
Organic conformal coating compositions combine the toughness of certain 
resins, low shrinkage of monofunctional nonpolar monomers, low T.sub.g 
resins and monomers, and adhesion promoting monofunctional and 
difunctional monomers. These organic conformal coating compositions have 
low temperature flexibility and good thermal shock resistance and 
electrical properties. The composition can be post cured using a peroxide 
which is stable at normal room temperature processing and has a long shelf 
life, such as six months. The composition can also contain a fire 
retardant. These features are obtained without the use of solvents and can 
be applied to substrates by dip coating, by spray coating, and brushing 
because of the low viscosity. 
These compositions are UV curable compositions consisting essentially of a 
blend of 20 to 45 weight percent of an acrylated urethane oligomer 
containing an average of about 2 acryl groups selected from the group 
consisting of acrylate and methacrylate, said acrylated urethane oligomer 
being based on aliphatic isocyanate, and having a number average molecular 
weight of from 1,000 to 6,000, 5 to 25 weight percent of an acrylate 
selected from the group consisting of an aliphatic monofunctional acrylate 
ester having a molecular weight less than 1,000, a polybutadiene 
diacrylate having a molecular weight less than 4,000, a polyoxyalkylated 
diacrylate having a molecular weight less than 1,000, and a monofunctional 
acrylate of the general formula 
##STR7## 
in which at least one of h or l is at least 1 and the total average value 
of h and l is sufficient to provide a viscosity at 25.degree. C. of 0.01 
to 0.2 Pa.s, and f is 0 or 1, 9.5 to 40 weight percent of an aliphatic 
bicyclic monofunctional acrylate monomer selected from the group 
consisting of isobornyl acrylate, isobornyl methacrylate, 
dicyclopentenyloxyethyl acrylate, and dicyclopentenyloxyethyl 
methacrylate, 0.5 to 6 weight percent of photoinitiator, 0 to 10 weight 
percent of an acrylate ester having at least three acrylate or 
methacrylate groups per molecule and having a molecular weight less than 
600, 0 to 8 weight percent of a peroxide having a 10 hour half life 
temperature of from 85.degree. C. to 105.degree. C. inclusive, 0 to 10 
weight percent of a hydroxy-containing acryl monomer selected from the 
group consisting of hydroxyalkylacrylate and hydroxyalkylmethacrylate, 0 
to 20 weight percent of a fire retardant, 0 to 6 weight percent of an 
adhesion promoter, 1 to 1,000 ppm of polymerization inhibitor in which the 
inhibitor is derived from 0 to 100 ppm of 4-methoxyphenol, 0 to 500 ppm of 
hydroquinone, and 0 to 500 ppm of phenothiazine, 0 to 0.015 weight percent 
of a fluorescent dye, and the composition has a viscosity at 90.degree. F. 
of less than 1 Pa.s. 
These compositions are curable by exposure to UV radiation and also can be 
formulated so that they can be cured by exposure to heat. The compositions 
can be cured by exposure to UV radiation and still be made to possess the 
ability to cure by heating, i.e., post curing or shadow curing. These 
organic conformal coating compositions can be used to coat circuit boards 
which have complex devices or components which have undercuts, i.e. 
regions or locations where the coating composition will be out of sight of 
the UV radiation and thus would remain uncured. Compositions intended to 
be used for coating such circuit boards having devices with undercuts 
should have the ability to cure in the shadowed areas and would be 
formulated to contain peroxide. However, the compositions have the ability 
to cure via heating and thus the regions or locations which are not 
exposed to the UV radiation can be cured by exposure to heat. The amount 
of heat and the duration of the heating necessary with the composition is 
relatively low. The ability to cure the compositions with low amounts of 
heat is important because many of the electronics materials and 
construction can be effected by exposure to high temperatures or to heat 
for long durations. 
These compositions contain from 20 to 45 weight percent of an acrylated 
urethane oligomer having an average of about 2 acrylate or methacrylate 
groups. These urethane oligomers are based on aliphatic isocyanate and 
have a number average molecular weight of from 1,000 to 6,000. The 
aliphatic isocyanates are preferably diisocyanates including 
1,6-hexamethylene diisocyanate, 1,4-hexamethylene diisocyanate, 
2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene 
diisocyanate, 4,4'-methylene-bis(cyclohexyl)-isocyanate, isophorone 
diisocyanate, and 1-methyl-2,4-diisocyanatecyclohexane. The acrylated 
urethane oligomers are known in the art and those which are particularly 
useful in the present invention are those which are described in U.S. Pat. 
No. 4,607,084, issued Aug. 19, 1986, to Morris, which is hereby 
incorporated by reference to show the acrylated urethane oligomers and 
their preparation. 
The acrylated urethane oligomers can be mixtures of two or more different 
oligomers or prepolymers, preferably a mixture of at least two different 
molecular weight acrylated urethane prepolymers, and a mixture of an 
acrylated urethane prepolymer and a polyester urethane acrylate. The 
acrylated urethane prepolymer provides strength to the cured films and the 
polyester urethane acrylate provides elongation to the cured films. They 
can also be blends, such as those prepared from polyether diols and 
polyether triols. The acrylated urethane oligomers can also contain 
reactive solvents. Such reactive solvents include alkyl acrylates, alkyl 
methacrylates, alkoxyalkyl acrylates, alkoxyalkyl methacrylates, allyl 
acrylate, phenoxyethyl acrylate, cyclohexyl acrylate, 1,6-hexanediol 
diacrylate, trimethylolpropane triacrylate, acrylated fatty alcohols, and 
acrylated aliphatic diglycidyl ethers. A preferred reactive solvent is 
ethoxyethoxyethyl acrylate. The reactive solvent can be present in amounts 
of from 0 to 50 weight percent based on the total weight of the acrylated 
urethane oligomer. Preferably, if the reactive solvent is present, it is 
present in an amount of from about 10 to about 20 weight percent. 
The term "oligomer" and "prepolymer" are interchangeable. Some examples of 
commercially available acrylated urethane oligomer are as follows: Ebecryl 
230 and Ebecryl 4883 sold by Radcure Specialties of Virginia. Ebecryl 230 
is 100 percent solids urethane acrylate prepolymer containing no reactive 
diluents, has a viscosity at 25.degree. C. of 30 to 40 Pa.s, a number 
average molecular weight of about 5,000, and a functionality of two. 
Ebecryl 4883 is 85 weight percent urethane acrylate oligomer or prepolymer 
and 15 weight percent tripropylene glycol diacrylate, the oligomer has a 
number average molecular weight of 1,611 and a viscosity at 60.degree. C. 
in the range of 2.8 to 4.2 Pa.s. Uvithane 782 and Uvithane 783 sold by 
Morton Thiokol Corporation, Morton Chemical Division, Ill. Uvithane 782 is 
a polyester urethane acrylate which has a viscosity at 49.degree. C. of 80 
to 160 Pa.s and Uvithane 783 is similar except that it has a viscosity at 
49.degree. C. of 60 to 200 Pa.s. 
The acrylated urethane oligomer is preferably present in an amount of from 
25 to 40 weight percent. A preferred acrylated urethane oligomer is a 
mixture of 3 to 6 weight percent polyester urethane acrylate, such as 
Uvithane 782, and 19 to 32 weight percent of an acrylated urethane 
prepolymer having a number average molecular weight from 1,000 to 3,000, 
such as Ebecryl 4883, for a total of 25 to 35 weight percent acrylated 
urethane oligomer. Another preferred acrylated urethane oligomer is a 
mixture of 24 to 37 weight percent of an acrylated urethane prepolymer 
having a number average molecular weight of 1,000 to 3,000, such as 
Ebecryl 4883, and 3 to 6 weight percent of an acrylated urethane 
prepolymer having a number average molecular weight of 3,000 to 6,000, 
such as Ebecryl 230, for a total of 30 to 40 weight percent acrylated 
urethane oligomer. 
The acrylate is a unique monomer having a low glass transition temperature, 
T.sub.g which gives the cured films made from these compositions improved 
flexibility at low temperatures and allows the cured films to pass thermal 
cycling shock tests. These acrylate monomers are selected from an 
aliphatic monofunctional acrylate ester having a molecular weight less 
than 1,000, a polybutadiene diacrylate having a molecular weight less than 
4,000, a polyoxyalkylated diacrylate having a molecular weight less than 
1,000, and a monofunctional acrylate of the general formula 
##STR8## 
in which at least one of h or l is at least 1 and the total average value 
of h and l is sufficient to provide a viscosity at 25.degree. C. of 0.01 
to 0.2 Pa.s, and f is 0 or 1. An example of an aliphatic monofunctional 
acrylate ester is C-9013 which is sold by Sartomer Company of 
Pennsylvania, has a boiling point of 121.degree. C. at 10 mmhg, has a 
viscosity at 25.degree. C. of 0.005 to 0.015 Pa.s and contains 160 ppm+ or 
-20 ppm of 4-methoxyphenol. An example of a polybutadiene diacrylate 
having a molecular weight less than 4,000 is C-5000 sold by Sartomer 
Company of Pennsylvania, has a number average molecular weight of 3,000, a 
viscosity at 25.degree. C. of 4.5 to 5 Pa.s, and contains 400 ppm BHT, a 
butylated hydroxy toluene. An example of a polyoxyalkylated diacylate 
having a molecular weight less than 1,000 is C-9000 which has a number 
average molecular weight of 800, a viscosity at 25.degree. C. of 0.12 
Pa.s, and 250 ppm of 4-methoxyphenol. Examples of the acrylates having 
Formula I are shown by the following formulae and are sold by Toagosei 
Chemical Industry Co., Ltd. of Tokyo, Japan: 
M-101, having a viscosity of 25.degree. C. of 0.02 Pa.a, a T.sub.g of 
-25.degree. C., and a formula of 
##STR9## 
M-111, having a viscosity at 25.degree. C. of 0.08 Pa.s, a T.sub.g of 
-8.degree. C., and a formula of 
##STR10## 
M-113, having a viscosity at 25.degree. C. of 0.11 Pa.s, a T.sub.g of 
-43.degree. C., and a formula of 
##STR11## 
and M-117, having a viscosity at 25.degree. C. of 0.13 Pa.s and a T.sub.g 
of -20.degree. C., and a formula of 
##STR12## 
The preferred acrylate monomer is M-113, which is also known as 
alpha-(1-oxo-2-propenyl)-omega-(nonylphenoxy)-poly(oxy-1,2-ethanediyl). 
The acrylate monomer is present in an amount of from 5 to 25 weight 
percent of the composition, preferably 10 to 15 weight percent of the 
composition. 
The aliphatic bicyclic monofunctional acrylate monomer selected from the 
group consisting of isobornyl acrylate, isobornyl methacrylate, 
dicyclopentenyloxyethyl acrylate of the formula 
##STR13## 
dicyclopentenyloxyethyl methacrylate of the formula 
##STR14## 
and mixtures thereof. Isobornyl acrylate has a viscosity at 25.degree. C. 
of about 0.015 Pa.s and usually contains as an inhibitor 100 ppm of 
4-methoxyphenol. Isobornyl methacrylate has a viscosity at 25.degree. C. 
of 0.015 to 0.019 Pa.s. Dicyclopentenyloxy-ethyl acrylate has a viscosity 
at 25.degree. C. of about 0.02 Pa.s. Dicyclopentenyloxyethyl methacrylate 
has a viscosity at 25.degree. c. of 0.015 to 0.019 Pa.s. the aliphatic 
bicyclic monofunctional acrylate is present in an amount of 9.5 to 40 
weight percent of the composition, preferably is present in an amount of 
20 to 35 weight percent. The preferred aliphatic bicyclic monofunctional 
acrylate is dicyclopentenyloxy-ethyl acrylate. 
The photoinitiator to provide the UV radiation curable property can be any 
of those which are known in the art to cure acrylates and methacrylates 
and generate free radicals upon exposure to UV. However, neither the 
photoinitiator nor its by-products should be corrosive to the electronic 
materials which it will come in contact with during its use. Illustrative 
of the photoinitiators are 2,2-diethoxyacetophenone, benzoin methyl ether, 
benzoin ethyl ether, benzoin isopropyl ether, alpha-methylbenzoin, 
alpha-ethyl-benzoin, alpha-methyl benzoin methyl ether, 
alpha-phenylbenzoin, alpha-allylbenzoin, anthraquinone, 
methylanthraquinone, ethyl-anthraquinone, tertiary butylanthraquinone, 
benzil, diacetyl, benzaldehyde, acetophenone, benzophenone, omega-benzoin, 
2,3-pentanedione, hydroxycyclohexylphenyl ketone, hydroxymethyl 
phenylpropanone, and xanthone. The photoinitiator is used in amounts of 
from 0.5 to 6 weight percent of the composition and which are suitable to 
provide cure of the composition when it is exposed to UV radiation. The 
preferred photoinitiator is 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 
the preferred amount is from 2 to 5 weight percent of the composition. 
The acrylate ester is one having at least three acrylate or methacrylate 
groups per molecule and a molecular weight less than 600. These acrylate 
esters can be present in amounts of from 0 to 10 weight percent of the 
composition. Preferably, the acrylate ester is present in an amount of at 
least 0.1 weight percent of the composition with the most preferred 
amounts being from 3 to 8 weight percent of the composition. Some examples 
of the acrylate esters are trimethylolpropane trimethylacrylate (mol. 
wt.=338), pentaerythritol tetraacrylate (mol. wt.=352), ethoxyated 
trimethylolpropane triacrylate (mol. wt.=428), pentaerythritol acrylate 
(contain three acrylate groups, mol. wt.=298), di-trimethylolpropane 
tetraacrylate (mol. wt.=438), tirmethylolpropane triacrylate (mol. 
wt.=296), and di-pentaerythritol monohydroxy pentaacrylate (mol. wt.=524). 
These acrylate esters are available commercially and are usually sold with 
an inhibitor present. Some of these commercially available acrylate esters 
may also contain small amounts of solvent which is a result of their 
preparation. The preferred acrylate ester is di-pentaerythritol 
monohydroxy pentaacrylate. 
The organic peroxide can be present in an amount sufficient to provide cure 
when the composition is exposed to heat after the composition is cured by 
exposure to UV radiation. The amount of organic peroxide can be from 0 to 
8 weight percent of the composition. The organic peroxide is one which has 
a 10 hour half life temperature of from 85.degree. C. to 105.degree. C. 
inclusive. Peroxides which have this 10 hour half life temperature 
provides compositions which can be packaged in one container for shipment, 
i.e. they have an acceptable shelf life for commercial shipping. These 
peroxides also can be cured at an acceptable temperature when the 
application is for conformal coatings on printed circuit boards. When the 
compositions of this invention are used for printed circuit boards which 
have devices with undercuts, it is preferred to have the organic peroxide 
present in amounts of from 0.1 to 6 weight percent of the composition, so 
that the compositions can be cured in the shadowed areas by heating. The 
preferred amount of organic peroxide is at least 0.5 weight percent of the 
composition, with the most preferred amounts being from 0.5 to 4 weight 
percent. Thus, the organic peroxide is one which will provide a storage 
stable uncured composition, which will cure upon heating, and which will 
not produce acidic by-products that can cause corrosion to electronic 
materials. Suitable organic peroxides include the following where the 10 
hour half life temperature is in parentheses following the peroxide name, 
1,1- bis(t-butylperoxy) cyclohexane (93.degree. C.), 
o,o-tertiary-butyl-o-isopropyl monoperoxy carbonate (99.degree. C.), 
2,5-dimethyl-2,5-di-(2-ethylhexanoylperoxy) hexane (87.degree. C.), 
1,1-di(t-butylperoxy)-3,3,5-trimethylcylcohexane (92.degree. C.), 
2,2-di(t-butylperoxy) butane (104.degree. C.), and 1-cyano-1-(t-butylazo) 
cyclohexane (96.degree. C.). The preferred organic peroxide is 
1,1-bis(tertiary-butylperoxy) cyclohexane and the preferred amounts of 
this peroxide are 0.5 to 4 weight percent. It might be possible to use 
organic peroxides which have 10 hour half life temperatures between 
105.degree. C. and 130.degree. C. if the compositions are to be used on 
substrates which are very heat stable, such as on certain ceramic printed 
circuit boards. The preferred organic peroxide is 1,1-bis(t-butylperoxy) 
cyclohexane. 
The hydroxy-containing acryl monomer in amounts of from 0 to 10 weight 
percent of the composition. The hydroxy-containing acryl monomer can be a 
hydroxyalkylacrylate or a hydroxyalkylmethacrylate. The hydroxy-containing 
acryl monomer can be illustrated by hydroxyethyl acrylate, hydroxypropyl 
acrylate, 4-hydroxy-n-butyl acrylate, hydroxyethyl methacrylate, 
hydroxypropyl methacrylate, and 4-hydroxy-n-butyl methacrylate. The 
preferred hydroxy-containing acryl monomer is hydroxyethyl methacrylate. 
The hydroxy-containing acryl monomer is preferably present in amounts of 
0.5 weight percent of the composition and the more preferred compositions 
contain from 3 to 9 weight percent. The hydroxy-containing acryl monomer 
reduces the viscosity of the composition and also increases the adhesion 
of the cured films to substrates. 
The fire retardant can be trixylenol phosphate. The amount of fire 
retardant can be from 0 to 20 weight percent of the composition, 
preferably in amounts of at least 1 weight percent of the composition. A 
preferred composition contain fire retardant in an amount of from 3 to 10 
weight percent and it is preferably trixylenyl phosphate. Because many of 
the fire retardants can be corrosive to the electronic materials and 
components, the selection of a fire retardant should be considered 
carefully and preferably tested before it is used, to determine whether it 
will be corrosive. The preferred fire retardants are the triorganic 
phosphates, such as the trixylenyl phosphate. The halogenated fire 
retardants are known to be too corrosive to be useful in the compositions 
of this invention because they corrode the electronic components which 
come into contact with the cured composition. 
The adhesion promoter can be present in amounts of from 0 to 6 weight 
percent of the composition. The adhesion promoter is preferably a 
phosphorus material of the formula 
##STR15## 
and a mixture of compounds of the formulae 
##STR16## 
These phosphorus materials increase the adhesion of the cured films to 
various substrates, specifically to copper, tin, G-10 boards, and 
electronic components. The amount of adhesion promoter is preferably at 
least 0.1 weight percent of the composition and is preferably the mixture 
of phosphorus materials defined above in amounts of from 2 to 4 weight 
percent. 
These organic conformal coating compositions need to have from 1 to 1,000 
ppm by weight of a polymerization inhibitor percent based on the total 
weight of the composition wherein the inhibitor is derived from 0 to 100 
ppm of 4-methoxy-phenol, 0 to 500 ppm of hydroquinone, and 0 to 500 ppm of 
phenothiazine. These inhibitors can be present from the other ingredients 
or can be added to give the proper shelf stability. The inhibitor is 
preferably present in an amount of at least 100 ppm by weight based on the 
total weight of the composition. The most preferred compositions have from 
200 to 500 ppm by weight of polymerization inhibitor where a mixture of 
hydroquinone and phenothiazine are each present in amounts of from 100 to 
300 ppm by weight. 
These compositions can also contain a fluorescent dye in amounts of from 0 
to 0.015 weight percent of the composition. These fluorescent dyes are 
used to determine the degree of coverage of the films on the printed 
circuit boards so that one can be sure that the film covers all of the 
areas necessary and to the film thickness desired or required for a 
particular printed circuit board. The preferred compositions contain at 
least 0.005 weight percent of a fluorescent dye and the most preferred 
compositions contain from 0.005 to 0.01 weight percent of fluorescent dye. 
An example of a fluorescent dye is Uvitex OB. 
The organic conformal coating compositions may contain other ingredients 
such as fungicides, as long as these materials do not add to the corrosive 
nature of the composition or deleteriously effect the electrical 
properties of the uncured composition or the cured product. 
These compositions are ones in which the composition will not corrode the 
electronic components which it contacts either in the uncured or cured 
state. The composition is essentially neutral and must not contain 
ingredients which may change this neutrality. A change in neutrality 
results in a composition which causes corrosion to materials used in 
electronic components. For example, the composition of the present 
invention should not contain amines, such as the tertiary organic amines 
which are often used as photosensitizers, because these amines cause 
corrosion to metal substrates found in the electronic components. Also 
acidic materials should not be used in the compositions of the present 
invention because these materials also cause corrosion. 
These compositions are particularly useful in coating and encapsulating 
electronic components because the viscosity of the composition is less 
than 1 Pa.s at 90.degree. F. Circuit boards can be dipped into this 
coating composition, allowed to drip to an even coat, then exposed to 
ultraviolet radiation for a few seconds for curing, and in those 
situations where post curing is required, the coated boards are heated to 
complete the curing cycle. These compositions can also be sprayed or 
brushed onto the circuit boards. Under certain coating circumstances or 
with certain combinations of composition and substrate, dewetting of the 
coating on the substrate might be experienced. If such a problem is 
encountered, such as might result from contamination of the substrate 
surface, a surfactant can be added to the composition. However, 
surfactants can cause foaming during preparative steps, as well as, during 
the coating steps and therefore is not recommended. If the use of a 
surfactant cannot be avoided, a recommended surfactant is one of the 
glycol siloxane type, such as Dow Corning.RTM. 57 paint additive. Amounts 
of surfactant up to about 2 weight percent have been found to be 
effective. Surfactants may also cause the composition to be hazy. After 
the curing step or steps are completed, the boards can be tested, used, or 
shipped immediately. For the purposes of this application the terms 
printed wire boards and printed circuit boards refer to the same type of 
article of manufacture. 
These compositions have a long pot life, a long shelf life, low temperature 
flexibility which is sufficient to provide stress relieving properties on 
coated printed circuit boards, pass thermal shock test, cure fast, are 
easy to use in production, are essentially solvent free, are a one package 
(one part or one component) system, have good electrical properties and 
can be made flame retardant without substantially changing the other 
characteristics of the present invention. The shelf life of the 
compositions of this invention which contain organic peroxide can be 
extended by keeping the composition from contacting temperature above 
25.degree. C., and if one has concern about the stability of the 
composition on storage, the compositions can be stored under 
refrigeration. 
These compositions can be prepared by mixing the ingredients. The method of 
mixing is not particularly critical except that the ingredients should be 
mixed to homogeneity. Because some of the ingredients may be more viscous 
than others, the mixing procedure maybe more difficult and slight heating 
may help readily disperse the ingredients. However, if heat is used, it 
would be preferred to leave the peroxide out of the mixture until it is 
cooled to room temperature. The peroxide is sensitive to heat and may 
cause some unwanted reaction if present during any heating during the 
preparation procedure. It may also be an advantage if the polymerization 
inhibitors are present during the early stages of the mixing procedure. 
After the composition is prepared, it is stored in containers which 
protect it from ultraviolet radiation until cure is desired. When peroxide 
is present, care should be taken to avoid high temperatures, especially 
for prolonged periods of time. 
These compositions can be cured by exposure to ultraviolet radiation, and 
if peroxide is present thereafter heated to cure any portion of the 
coating or encapsulant which did not receive ultraviolet radiation. Such 
heating will cause the composition to cure in the dark regions (regions 
not receiving ultraviolet radiation exposure) and thus the compositions of 
this invention have the ability to shadow cure. If these compositions are 
heat cured before they are exposed to ultraviolet radiation, the surface 
of the resulting film will be tacky. Surfaces which are tacky are 
unacceptable on printed circuit boards. 
A preferred composition consists essentially of a blend of from 25 to 35 
weight percent of an acrylated urethane oligomer mixture made up of 19 to 
32 weight percent acrylated urethane prepolymer and from 3 to 6 weight 
percent of polyester urethane acrylate, from 10 to 15 weight percent 
alpha-(1-oxo-2 -propenyl)-omega-(nonylphenoxy)-poly(oxy-1,2-ethanediyl) 
having a viscosity at 25.degree. C. of from 0.1 to 0.12 Pa.s, from 20 to 
35 weight percent isobornyl acrylate, from 2 to 3 weight percent 
2-hydroxy-2-methyl-l-phenyl-propan-l-one, from 4 to 8 weight percent 
dipentaerythritol monohydroxy pentaacrylate, from 1.5 to 4 weight percent 
1,1-bis-(tertiary-butylperoxy) cyclohexane, from 3 to 6 weight percent 
2-hydroxyethylmethacrylate, from 5 to 10 weight percent trixylenyl 
phosphate, from 2 to 3 weight percent of a mixture of compounds of the 
formulae 
##STR17## 
from 200 to 500 ppm of a mixture of hydroquinone and phenothiazine each 
being present in an amount of from 100 to 300 ppm, and from 0.005 to 0.01 
weight percent of a fluorescent dye. This preferred composition exhibits 
the advantageous properties as described herein for conformal coatings, 
but it was observed for some formulations the cured films developed a 
tackiness on the surface over a short period of time, such as a within one 
month after being cured. This surface tackiness was more pronounced with 
formulations containing the higher concentrations of isobornyl acrylate. 
Compositions which did not develop this surface tackiness of the cured 
films were discovered. These compositions consist essentially of a blend 
of from 30 to 40 weight percent of a mixture made up of 24 to 37 weight 
percent of an acrylated urethane prepolymer having a number average 
molecular weight of from 1,000 to 3,000 and of 3 to 6 weight percent of an 
acrylated urethane prepolymer having a number average molecular weight of 
from 3,000 to 6,000, from 10 to 15 weight percent 
alpha-(1-oxo-2-propenyl)-omega-(nonylphenoxy)-poly(oxy-1,2-ethanediyl) 
having a viscosity at 25.degree. C. of from 0.1 to 0.12 Pa.s, from 25 to 
35 weight percent of dicyclopentenyloxyethyl acrylate, from 3 to 5 weight 
percent 2-hydroxy-2-methyl-1-phenyl-propan-1-one, from 3 to 7 weight 
percent dipentaerythritol monohydroxy pentaacrylate, from 0.5 to 2 weight 
percent 1,1-bis-(tertiary-butylperoxy) cyclohexane, from 4 to 9 weight 
percent 2-hydroxyethyl-methacrylate, from 3 to 8 weight percent trixylenyl 
phosphate, from 2 to 4 weight percent of a mixture of compounds of the 
formulae 
##STR18## 
from 200 to 500 ppm of a mixture of hydroquinone and phenothiazine each 
being present in an amount of from 100 to 300 ppm, and from 0.005 to 0.01 
weight percent of a fluorescent dye. These preferred compositions do not 
develop surface tackiness on the cured film. However, the tensile strength 
is observed to be a lower value, but still acceptable for conformal 
coatings. In addition to overcoming cured surface tackiness, those 
compositions which are used as conformal coatings for printed wire boards 
desirably contain the 2 to 4 weight percent of the phosphorus containing 
adhesion promoter to ensure adhesion of the cured film to the board to 
prevent board failure due to atmospheric contamination such as moisture 
(corrosion). 
These compositions have solvent resistance to such solvents as xylene, 
acetone, isopropanol, methyl ethyl ketone, freons, and urethane thinners. 
Adhesion of the cured compositions to metal and plastic substrates, such 
as metal leads and plastic connector materials, is obtained. The 
compositions are non-corrosive before, during, and after cure, where cure 
includes both the ultraviolet cure and the post heat cure. The 
compositions have the ability to withstand thermal shock from -65.degree. 
C. to 150.degree. C. The compositions of this invention exhibit a low 
weight loss upon cure. The compositions exhibit acceptable electrical 
properties for use as insulative coatings and encapsulants for electronic 
components, such as volume resistivity and dielectric withstanding 
voltage. The composition of the present invention exhibits sufficient 
fungus resistance without the addition of additional fungicides, but in 
certain applications it may be advantageous to add to this fungus 
resistance. If additional fungicide is needed, careful evaluation of the 
fungicide should be conducted to determine its effect on other properties, 
such as corrosion. The compositions also exhibit humidity resistance and 
resistance to soldering heat. If fire retardant properties more than 
provided by the composition are needed, the fire retardant as describe 
above should be used. 
Other kinds of UV curable compositions which can be used in this invention 
can be found in U.S. Pat. No. 4,780,486, issued Oct. 25, 1988, issued to 
Chi-long Lee and Michael A. Lutz. 
The method of the present invention can be used for UV curable compositions 
which make films, coatings, encapsulants in the electrical and electronics 
industries such as for printed circuit boards, electrical connectors and 
electrical splices. 
The following examples are presented for illustrative purposes and should 
not be construed as limiting the invention which is properly delineated in 
the claims. In the following examples, "part" or "parts" represents "part 
by weight" or "parts by weight", "%" are percent by weight unless 
otherwise stated. 
EXAMPLE 1 
A curable composition of this invention was prepared by blending 0.002 part 
of an anthraquinone dye purchased from Sandoz Chemical, Charlotte, N.C. as 
Nitro-Fast Blue 2B, (which is also known as C.I. Solvent Blue 104) with 
the following ingredients to homogeneity: 
97.5 parts of an organosiloxane copolymer containing the following units, 
expressed in mol percent: 94% dimethylsiloxane units, 1% 
dimethylvinylsiloxy units, 2% trimethylsiloxy units, and 3% 
monomethylsiloxy units. The viscosity of the copolymer was 10.sup.-5 
m.sup.2 /s at 25.degree. C.; 
1.25 parts of a trimethylsiloxy-terminated polydiorgano-siloxane copolymer 
containing an average of 43 dimethylsiloxane units and 4 
methyl(3-mercaptopropyl)siloxane units per molecule; and 
1.25 parts of 2-hydroxy-2-methyl-1-phenylpropan-1-one as the 
photoinitiator. 
The blended composition was blue. A 10 g sample of the blue composition was 
passed through a UV-6 Single Lamp Conveyorized UV Curing Unit manufactured 
by Colight, Minneapolis, Minn. The conveyor was set at about 3 ft/min and 
the lamp was at 200 watts. The composition changed to light yellow and was 
fully cured. The cured sample remained yellow for at least six months. 
EXAMPLE 2 
An ultraviolet radiation curable siloxane composition was prepared by 
adding 0.002 part of Nitro-Fast Blue 2B to a mixture of 65.5 parts of a 
silicone resin having the average siloxane unit formula 
EQU (MeSiO.sub.3/2).sub.7.5 (PhSiO.sub.3/2).sub.37.6 (Me.sub.2 SiO).sub.30.1 
(MeViSiO).sub.20.0 - 
EQU (Me.sub.3 SiO.sub.1/2).sub.4.8 (OH).sub.h 
which had a vinyl content of 5.2 weight percent, a value for h to provide 
an OH content of 1.49 weight percent, a non-volatile content of 97.4 
weight percent, and a viscosity of 14.5 Pa.s, 17.5 parts of an organic 
mercaptofunctional compound having the formula 
##STR19## 
{trimethylolpropane tri-(3-mercaptopropionate)]}[TMPTMP], 10 parts of 
tripropylene glycol diacrylate [TRPGDA], 5 parts of isobornyl acrylate 
[IBA], 3.08 parts of photoinitiator of the formula 
##STR20## 
and 0.005 part of a UV dye fluorescent indicator, Uvitex OB. A sample of 
this mixture was blue and after exposing it to UV radiation as described 
in Example 1, it turned yellow and remained yellow. 
EXAMPLE 3 
A UV curable organic composition in accordance with this invention was 
prepared by adding 0.002 part of Nitro-Fast Blue 2B to a mixture prepared 
by blending at room temperature in a container which protects the 
composition from exposure to ultraviolet radiation, until the mixture was 
homogeneous Ebecryl 4883, Ebecryl 230, QM-672, 2-hydroxyethyl 
methacrylate, alpha-(1-oxo-2propenyl)-omega-(nonylphenoxy)-poly(oxy-1,2-et 
hanediyl) (M-113), trixylenyl phosphate, 
2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur 1173), adhesion promoter 
(PM-2), dipentaerythritol monohydroxy pentaacrylate, fluorescent dye, 
inhibitors, and 1,1-bis-(tertiary-butylperoxy) cyclohexane. The resulting 
composition was a conformal coating composition which cured both by 
exposure to ultraviolet radiation and by heating. The ingredients and 
their amounts were as shown as follows: 
______________________________________ 
Percent Ingredient 
______________________________________ 
4.36 Acrylated urethane prepolymer. Ebecryl 230 
sold by Radcure Specialties, Virginia 
28.8 Dicyclopentenyloxyethyl acrylate, QM-672 
sold by Rohm and Haas Company of 
Pennsylvania 
7.6 2-Hydroxyethyl methacrylate, sold as Rocryl 
400 by Rohm and Haas Company of 
Pennsylvania 
13.1 M-113 sold by Toagosei Chemical Industry 
Co., Ltd, of Tokyo, Japan 
4.36 Trixylenyl phosphate, Kronitex(R) TXP sold 
by FMC Corporation, Industrial Chemical 
Group Pennsylvania 
4.18 Darocur(R) 1173, sold by EM Chemicals, EM 
Industries Company, Hawthorne, New York 
1.74 Kayamer PM-2, sold by Nippon Kayaku Co., 
Ltd., Plastic Division, Tokyo, Japan, 
this is the mixture of phosphorus 
material having the formulae described 
herein for the adhesion promoter 
30.5 Acrylated urethane oligomer, Ebecryl 4883 
sold by Radcure Specialties, Virginia, 
this material is 85% acrylated urethane 
oligomer and 15% tripropylene glycol 
diacrylate 
4.36 Dipentaerythritol monohydroxy 
pentaacrylate, SR-399, sold by Sartomer 
Company, Division of Sartomer Industries, 
Inc., Pennsylvania 
1.0 1,1-bis-(t-butylperoxy)cyclohexane, 
SP-400P sold by Witco Chemical, U.S. 
Peroxygen Division, California 
0.009 Uvitex OB, fluorescent dye 
200 ppm Hydroquinone 
200 ppm Phenothiazine 
______________________________________ 
This mixture was blue and had a viscosity of 0.42 Pa.s at 25.degree. C., 
HAV, spindle number 3, 50 rpm, at 2 minutes. When this mixture was exposed 
to ultraviolet radiation as described in Example 1, it changed to yellow 
and was fully cured. 
EXAMPLE 4 
UV curable compositions were prepared as described in Example 1, except the 
2-hydroxy-2-methyl-1-phenylpropan-1-one were left out and another 
photoinitiator was used in its place as indicated below. The mixtures were 
prepared by mixing 0.79 part of the photoinitiators listed below with 49.5 
parts of the UV curable composition as described in Example 1 but without 
the 2-hydroxy-2-methyl-1-phenylpropan-1-one. The Colight system used to 
expose the samples to UV radiation was the same as described in Example 1. 
The results observed were as described below along with the photoinitiator 
used in each case. 
Sample 1: Benzophenone: passed through the Colight system once did not cure 
or change color, a second pass through the Colight system changed the 
color a little to a paler blue and the film was slightly cured, after four 
passes through the Colight system the blue was almost gone. 
##STR21## 
passed through the Colight system once produced a good cure and the color 
changed to yellow. 
Sample 3: Diethoxyacetophenone passed through the Colight system once 
produced a good cure and the color changed to dark yellow. 
Sample 4: A mixture of 50 weight percent 
##STR22## 
and 50 weight percent benzophenone passed through the Colight system once 
produced a good cure and the color changed to dark yellow. This yellow was 
the same as observed for Sample 3. 
These samples showed that the color change occurred with different kinds of 
free radical producing photoinitiators. 
EXAMPLE 5 
A masterbatch of a ultraviolet radiation curable composition was prepared 
and used by blending with various dyes at various dye concentrations as 
described below. This masterbatch was prepared by mixing 1.25 parts by 
weight of a trimethylsiloxy-terminated polydiorganosiloxane copolymer 
containing an average of 43 dimethylsiloxane units and 4 
methyl(3-mercaptopropyl)siloxane units per molecule with 25 parts by 
weight methyl hydroquinone (added in the form of a 10 weight percent 
solution in toluene) per million parts by weight of the composition. The 
resulting mixture was then added to and mixed in a metal can with 97.5 
parts by weight of an organosiloxane copolymer containing the following 
units, expressed in mole percent: 94% dimethylsiloxane units, 1% 
dimethylvinylsiloxy units, 2% trimethylsiloxy units, and 3% 
monomethylsilsesquioxane units. After the resulting mixture was thoroughly 
mixed, 1.25 parts by weight of 2-hydroxy-2-methyl-1-phenylpropan-1-one as 
the photoinitiator was added and the total mixture was mixed by rolling 
for 30 minutes on a can roller. Each of the dyes described below were 
added to a quantity of masterbatch ultraviolet radiation curable material 
by mixing and then shaking the resulting mixture until a uniform 
dispersion of the dye in the masterbatch was obtained. The dye containing 
mixture was allowed to de-air at ambient conditions. For each dye 
containing masterbatch, 15 grams of the masterbatch was placed in a 4 
ounce round-bottle and cured by exposure for 22 seconds to ultraviolet 
irradiation (UV) from a medium pressure mercury bulb with a power of 200 
watts per inch where the dye containing masterbatch was placed about 65 mm 
from the bulb. The bulb was in a UVEXS Modular Cure Unit (MCU), from 
UVEXS, Inc., Sunnyvale, Cal. Another 15 grams of dye containing 
masterbatch was poured into the bottle over the dye containing masterbatch 
which had been exposed to the UV, and then the second 15 grams of 
masterbatch was exposed to UV from the MCU unit for 22 seconds. A third 15 
grams of dye containing masterbatch was poured into the bottle over the 
second 15 grams of dye containing masterbatch which had been exposed to UV 
from the MCU unit for 22 seconds. The three 15 grams quantities of dye 
containing masterbatch were required to obtain sufficient depth for 
measuring the penetration of the UV exposed materials. The penetration was 
determined by a blunt head shaft penetrometer with a weight bead of 19.5 
+/-0.05 g. The head was positioned at the surfce of the gel and the head 
was then released with gravity pulling the head into the gel. The distance 
the head drops from the surface into the gel in five seconds was the 
penetration value. The penetration results were reported in tenths of a 
millimeter. 
The results obtained from each dye are described below. 
Dye A: 1 part by weight of Sandoz Nitro Fast 2B Blue (an anthraquinone dye 
having a C.I. Solvent Blue 104, sold by Sandoz Chemicals, Charlotte, N.C.) 
was dispersed in 99 parts by weight of toluene. Uncured dye containing 
masterbatch at 25 ppm of dye was blue and became light yellow when exposed 
to curing UV radiation. The cured film had a penetration value of 128 
initially and after aging at ambient conditions for 35 days and the color 
remained yellow, which indicated a good cure. Uncured dye containing 
masterbatch at 58 ppm dye was deep blue and became a deep yellow when 
exposed to curing UV radiation and became dark green-yellow after aging at 
ambient conditions for 35 days which indicated that the film was not 
completely cured. The initial cured film had a penetration of 135 which 
showed that the film was softer and after aging at ambient conditions the 
film had a penetration of 152 which showed instability of the film and a 
softening indicating an incomplete cure. Uncured dye containing 
masterbatch at 100 ppm dye was dark blue and became muddy blue-brown 
after exposure to curing UV radiation and became dark muddy blue-green 
after aging 35 days at ambient condition. The initial penetration value 
was 149 which showed that the film had not cured thoroughly and the 
penetration value increase to 161 after aging at ambient conditions for 35 
days. This softening showed that the film was not stable and that the cure 
was incomplete. 
Dye B: 1 part by weight of Hytherm Purple KIF (an anthraquinone dye, 
1-hydroxy-4-[(methylphenyl)amino]-9,10-anthracenedione, sold by Morton 
Thiokol, Inc., Morton Chemical Division, Chicago, Ill.) was dispersed in 
99 parts by weight of toluene. Uncured dye containing masterbatch at 25 
ppm dye was purple and became light yellow after exposure to curing UV 
radiation and after 35 days aging at ambient conditions the film was still 
yellow. The initial penetration value was 130 and the value after aging 
for 35 days was 143 which showed some softening but the color remained 
yellow indicating that the film was cured. 
Dye C: 1 part by weight of DuPont Oil Purple Liquid [an azo dye mixture, 
azo benzene azo naphthyl benzene amine alkyl/alkoxy derivatives (C.I. 
Solvent Blue 99) and azo benzene azo naphthyl benzene amine alkyl 
derivatives (C.I. Solvent Red 166), sold by DuPont Chemicals, Wilmington, 
Del.] dispersed in 99 parts by weight of toluene. Uncured dye containing 
masterbatch at 25 ppm dye was pale blue-violet and became very light 
yellow after exposure to curing UV radiation and the color remained yellow 
after aging for 35 days at ambient conditions. The film had a penetration 
of 127 initially and 151 after 35 days aging at ambient conditions. 
Although the film softened, the color did not change over the aging period 
which indicated that the film was cured. 
Dye D: 1 part by weight of Sandoz Sando Plast Red 2B powder (an 
anthraquinone dye, 1-amino-2-bromo-4-hydroxyanthraquinone, sold by Sandoz 
Chemicals, Charlotte, N.C.) was dispersed in 99 parts by weight of 
toluene. Uncured dye containing masterbatch at 25 ppm dye was light pink 
and became salmon pink after being exposed to curing UV radiation. This 
color change would be insufficient in thinner films to make a distinction 
between cured and uncured. (Comparison experiment). 
Dye E: 1 part by weight of methylene blue was dispersed in 99 parts by 
weight of isopropyl alcohol. Uncured dye containing masterbatch at 25 ppm 
dye was pale violet and became very light blue after exposure to curing UV 
radiation. This color change would be insufficient in thinner films to 
make a distinction between cured and uncured. (Comparison experiment). 
Dye F: 3 parts by weight of Sandoz Nitro Fast Yellow B powder (a disazo 
dye, also known as C.I. Solvent Yellow 30, C.I. 21240, having a formula 
C.sub.37 H.sub.36 N.sub.4 O.sub.2 and a CAS number 3321-10-6) sold by 
Sandoz Chemicals, Charlotte, N.C.) was dispersed in 97 parts by weight of 
methylphenylvinylsiloxy terminated polydimethylsiloxane having a viscosity 
of about 0.4 Pa.s. Uncured dye containing masterbatch at 9 ppm dye was 
deep yellow and became light yellow after exposure to curing UV radiation. 
This color change is insufficient to distinguish between cured and uncured 
film when the film is in thin thicknesses. (Comparison experiment). 
Dye G: I part by weight of Uvitex OB, [a fluorescent dye having no visible 
color, 2,2'-(2,5-thiophenediyl)bis(5-tertbutylbenzoxazole) CAS Reg No. 
7128-64-5, sold by Ciba-Geigy Corporation, Plastics & Additives Division, 
Hawthorne, N.Y.] was dispersed in 99 parts by weight of toluene. Uncured 
dye containing masterbatch was water white and after being exposed to 
curing UV radiation the composition did not cure and remained water white. 
(Comparison experiment). 
Dye H: I part by weight of Calco Oil Red (a disazo dye sold by BASF 
Corporation Chemicals Division, Parsippany, N.J.) dispersed in 99 parts by 
weight of toluene. Uncured dye containing masterbatch was pale red and 
became light yellow after being exposed to curing UV radiation. This film 
became too soft on aging and it was difficult to see it on a device. 
(Comparison experiment). 
Dye I: 1 part by weight of Calcozine Blue 2R-EG Liquid (also known as Blue 
G Liquid, a triphenylmethane dye, sold by BASF Corporation Chemicals 
Division, Parsippany, N.J.) dispersed in 99 parts by weight of toluene. 
Uncured dye containing masterbatch was light blue and became very light 
yellow after being exposed to curing UV radiation. This film became too 
soft on aging and it was difficult to see it on a device. (Comparison 
experiment). 
Dye J: 1 part by weight of DuPont Oil Blue B Liquid Dye [an anthraquinone 
dye, 1-4-bis[(2-ethylhexyl/methyl/phenyl)-amino] anthraquinone, sold by 
DuPont Chemicals, Wilmington, Del.] dispersed in 99 parts by weight of 
toluene. Uncured dye containing masterbatch was pale blue and became very 
light yellow after being exposed to curing UV radiation. This film became 
too soft on aging and it was difficult to see it on a device. (Comparison 
experiment). 
No Dye: Uncured masterbatch without any dye was water white and became 
light yellow after being exposed to curing UV radiation.