Note: Descriptions are shown in the official language in which they were submitted.
~2~ 3~
60SI ~96
-- 1 --
NOVEL DUAL CURE SIL][CONE COMPOSITIONS
sackground of the Invention
The present invention generally relates to
compositions which are curable by two different
mechanisms. More particularly, the present invention
relates to compositions which cure by both a free
radical photoinitiated crosslinking reaction and a
platinum catalyzed thermal hydrosilation reaction.
Silicone compositions have become widely
accepted as protective coatings for electronic components
mounted on circuit boards. The misture resistance,
thermal stability and resistivity of silicones make
them ideal for this purpose. Previously developed
silicone conformal coatings have been heat curable
and furnished in organic solvents, however
high energy costs as well as safety and environmental
considerations have led to the development of such
alternate technologies as ultraviolet radiation
curable silicone conformal coatings.
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60SI-896/0043p/GLL:mz
Both heat curable and U~curable silicone conformal coat-
in~s have certain disadvantages. The use of heat curable con-
formal coatings risks damaging many fragile, heat sensitive
electronic components. Consequently, thermal cure cycles can
be extremely long, which in turn reduces production of coated
- circuit boards. On the other hand, while radiation curable
silicone conformal coatings speed processing and avoid damaging
the electronic components, in many instances a eomplete cure of
the conformal coating is not effected due to what is called the
Ushadow effect". Briefly, the shadow eff ect is caused by com-
ponents mounted on circuit boards which, because they project
off the surface of the board, cast shadows and thereby prevent
effectiYe curing. While persons skilled in the art can over-
come much of the shadow effect with mirrors, there can be
crevices and the like where ultraviolet light simply cannot
penetrate and thus where UY-curable compositions cannot be
rured.
In view of the foregoing, the skilled artisan will appre-
ciate that it is highly desirab7e to have available a composi-
tion which is both UY-curable and thermally curable (either at
room temperature or at elevated temperatures) in order to over-
come such shortcomings.
It is also desirable that such compositions can be utili~ed
in other applications, for example, as silicone release coat-
ings.
Platinum catalyzed addition curable silicone compositions
are well known in the art. For example, Grenoble in U.S.
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60SI-896/0043p/GLL:mz
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Patent No. 3,900,617 disclosed that flexible sheet ~aterial can
be rendered non-adherent to surfaces which nonmally adhere
thereto by coating the sheet material with a coating composi-
tion formed from (1) a vinyl chainstopped polysiloxane, (2) a
hydrogen-containing polysiloxane and (33 a platinum catalyst
effective to cause copolymerization of (1) and (2).
Other variations of such technology are disclosed in U.S.
Patent Nos. 4,2~6,870 and 4,340,647 to Eckberg~ both of which
are assigned to the same assignee as the present
1 0 invention .
Ohto et al., U.S. Patent ~o. 3,865,588, discloses photo-
polymerizable compositions which contain at least one organo-
polysiloxane having an unsaturated radical of the formula
Rl R2
I
HC = C - C - O -
Il
o
I5 where pl is a hydrogen atom, a phenyl radical or a halogen
substituted phenyl radical and R2 is a hydrogen atom or a
methyl radical. Exemplary of such radicals are the acryloxy
radical, methacryloxy radical, cinnamoyloxy radical or a halo-
genated cinnamoyloxy radical.
~0 In U.S. Patent No. 3,726,710 to Berger et al. there is dis-
closed a composition comprising a vinyl group containing poly-
organosiloxane having a sensitizer added thereto and which is
curable by exposing it to high intensity ultraviGlet rays.
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60SI~-8~6/0043p/GLL:mz
Hatanaka et al., U.S. Patent No. 4,451,634, discloses sili-
cone elastomeric compositions suitable for ultraviolet ray
curing comprising (A) 100 parts by weight of a polyorganosilox-
ane of the general formula
(CH3)2RlSiO ~~~~~ R2 SiO ~ SiR (CH3j2
wherein Rl represents hydrogen or a monovalent radical
selected from methyl, vinyl and hydroxy, R2 represents
hydrogen or a substituted or unsubstituted monovalent hydrocar-
bon radical, 0.02 - 49.g5% based on the total number of Rl
- 10 and R groups are vinyl radicals, 0.05 - 49.98~ based on the
total number of Rl and R2 groups are hydrogen, and n
represents a number from 10 to 10,000; (B) 0.5 to 10 parts by
~eight of a polyorganosiloxane having the formula
(R )b
(CH2 = CH)a SiO 4-a-b
wherein R3 i5 a substituted or unsubstituted monovalent
hydrocarbon radical other than vinyl, a represents a number of
0.01 c a c 1 on average, b represents a number of 0 c b
3 on average, and a + b is a number from 1 to 3; and (C)
0.1 to 10 parts by weight of a peroxy ester of the formula
R4 - 0 - 0 - C - R5
wherein R4 is a substituted or unsubstituted monovalent ali-
phatic radical and R5 is a substitut.ed or unsubstituted
monovalent aromatic radical.
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60SI-896/D043p/GLL:rnz
Eckberg et al., Cdn. Application Serial No. 469,075
riled Nov. 30, 19~49 and assigned to the same assignee as the
present invention, discloses an ultraviolet radiation curable
composition comprising: (A) a diorganopolysiloxane comprising
units of the formula RR'SiO, wherein R is hydrogen or a Cl 8
alkyl radical and R' is hydrogen, a Cl 8 alkyl radical or a
monovalent mercaptoalkoxyalkyl-functional organic radical of 2
to 20 carbon atoms, ~B) a polysiloxane consisting of from 0.5
to 100 mole percent of vinyl functional siloxane units of the
formula (CH2 = CH)Rn SiO(3 n)/2~ where R is hydrogen or a
Cl 8 alkyl radical and n has a value of O to 2~ inclusive~
and (C) a catalytic amount of photoinitiator~
Nowhere, however, to applicant's knowledge, is there dis-
closed or suggested a silicone composition which cures by both
a free radical catalyzed UY-hydrosilation reaction and
platinum catalyzed hydrosilatton reaction, and thereby avoids
the shortcomings of those compositions which cure by only one
of the recited mechanisms.
Summary of the Invention
It is one object of the present invention to provide compo-
sitions which are curable by both a free radical photoinitiated
crosslinking reaction and a precious metal cataly2ed hydrosila~
tion reaction.
It is another object of the present invention to provide
articles such as circuit boards and the like having such compo-
sitions cured thereon.
Another object of the present invention is to provide
methods for making the foregoing compositions and articles.
.
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605I-896/0043p/GLL:mz
In accordance with a preferred embodiment of the present
invention there is provided a curable composition comprising:
(A) a polysiloxane having the general formula:
(I) Rl _ Si _ SiO ~ SiO 5 i T ; -
J x R R R
wherein each R is an independently selected substituted or
unsubstituted monovalent hydrocarbon radical haYing from 1 to
20 carbon atoms; Rl is hydrogen, a hydroxyl radical, or a
substituted or unsubstituted, saturated or unsaturated hydro-
carbon or hydrocarbonoxy radical having from 1 to 2Q carbon at-
oms; A is an acrylate radical having the general formula:
R2 R3
(II) HC = C - C - 0 - R4 -
R2 and R3 are, independently, hydrogen or a substituted or
unsubstituted hydrocarbon radical, R4 is a divalent hydro-
carbon radical having from 1 to 10 carbon atoms; x is a number
such that there is from about 0.1 to about 50 mole percent
acrylate-containing siloxy units, y is a number such t~at
there is present from about 0 to about 50 mole percent
hydrogen-containing siloxy units; and x ~ y + z is a number
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60SI-896/0043p/GLL:mz
such that the viscosity of said polysiloxane is from about 25
centipoise to about 2~500,000 centipoise at 25C;
(B) a free radical type photoinitiator;
(C) a precious metal or precious metal containing hydrosi-
lation catalyst;
(D) when y equals ~ero, an organohydrogenpolysiloxane,
(E) optionally, an olefin-containing polysiloxane, and
(F) optionally, a hydrosilation inhibitor.
Most preferably, the polysiloxane of Fonmula I includes up
to about 20 mole percent alkenyl-containing siloxy units~ This
is due to the fact that a precious metal catalyzed SiH addition
to an acrylate radical of Formula II is very slow in comparison
with an SiH addition to an alkenyl radical such as, for
example, vinyl or allyl. Accordingly9 prompt thenmal curing is
insured by including alkenyl radicals in the system, either as
part of the polysiloxane of Formula I or as separate component
(E)n The artisan can therefore appreciate that preferably the
siloxane of Formula I has the general structure
R ~ A ~ ~ H ~ ~ R ~ ~ R5 ~ R
Rl_ SiOJ~SiO ~U~SiO ~SiO~ S i O ~ S j
R \ R J \ R J ~R ~ \2 ~ R
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60SI 896/0043p/GLL:mz
where R, Rl, A, x, y and z are as previously defined, R5 is
an olefinically unsaturated hydrocarbon radical, preferably
vinyl, and w is a number such that there is present up to 20
mole percent alkenyl-containing siloxy units. Those of
ordinary skill in the art will, of course, appreciate that
there are many available variations in which to provide the
silicon-bonded acrylate, hydrogen and alkenyl moieties.
Description of th nvention
In its broadest aspect, the present invention involves
adding both a radical type photoinitiator or photocatalyst and
a precious metal or precious metal-containing hydrosilation
catalyst to a curable composition having silicon-bonded
hydrogen atoms and silicon-bonded acrylate radicals of the
general fonmula:
R2 R3
HC - C - C 0 - R4 _
o
where R2 and R3 are, independently, hydrogen or a substitu-
ted or unsubstituted hydrocarbon radical, preferably methyl,
and R4 is a divalent hydrocarbon radical having from l to lO
carbon at~ms. The si 1 icon-bonded hydrogen atoms and the
silicon-bonded acrylate radicals can be on the same or differ
ent polysiloxane chains. What is essential to the present
invention is that, because of the presence of a photocatalyst,
the silicon-bonded hydrogen atoms and siliconbonded acrylate
radicals will crosslink upon exposure to ultraviolet radiation,
.
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605I-896/0043p/GLL:mz
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and that~ because of the presence of a precious metal or
precious metal-containing catalylst, the silicon-bonded hydrogen
atoms and the silicon-bonded acrylate radicals or silicon-
bonded alkenyl radicals will crosslink at room temperature or
elevated temperatures.
~ n a preferred embodiment of the present invention there is
provided a curable composition comprising:
(A) a polysiloxane having the general formula:
R~ SiO~ jo~ioJ si_Rl
wherein each R is an independently selected sub~tituted or
unsubstituted monovalent hydrocarbon radical having from 1 to
20 carbon atoms; Rl is hydrogen, a hydroxyl radical9 or a
substituted or unsubstituted hydrocarbon or hydrocarb~no~y
radical having from 1 to 20 carbon atoms; A is an acrylate
radical having the general fonmula:
R~ R3 ~:
HC = C - C 0 - R4 -
I
O
where R2 and R3 are~ independently, hydrogen or a substitu-
ted or unsubstituted hydrocarbon radical; R4 is a divalent
hydrocarbon radical having from 1 to 10 carbon atoms; x is a
number such that there is present from about 0.1 to about 50
mole percent acrylate-containing siloxy units; y is a number
such that there is present from about 0 to about 50 mole
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60SI-896/0043p/GLL:mz
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percent hydrogen-containing siloxy units; and x ~ y + z is a
number such that the viscosity of said polysiloxane is from
about 25 centipoise to about 2,~00,000 centipoise at 25DC;
(B) a free radical type photoinitiator;
(C) a precious metal or precious metal containing hydrosi-
lation catalyst;
(D) optionally, an organohydrogenpolysiloxane;
(E) optionally, an olefin-containing polysiloxane; and
(F) optionally, a hydrosilation inhibitor.
In a more preferred embodiment the curable composition of
the present invention includes up ~o about 20 mole percent
alkenyl-containing siloxy units. Such alkenyl-containing
siloxy units, which preferably are vinyl, are preferably
included because a precious metal catalyzed SiH addition to an
acrylate radical of Formula II is slow in comparison with an
SiH addition to an alkenyl radical such as vinyl or allyl.
Hence, the inclusion of alkenyl groups insures more rapid
thermal curing of the composition. The artisan will therefore
appreciate that preferably the siloxane of Formula I has the
structure
Rl 5j ~ 5io ~ 5jO ~ 5jo ~ 5~0 ) Si - R
x R R R
.
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60SI-896/0043p/GLL:mz
where R, Rl, A9 x, y and z are as previously defined, R5 is
an olefinically unsaturated hydrocarbon radical, pr~ferably
vinyl, and w is a number such that there is present up to 20
mole percent alkenyl-containing siloxy units. Of course, it is
still within the intended scolpe of the present invention to
include such alkenyl radicals on a separate polysiloxane.
It should be noted that for purposes of the present inven
tion the term "hydrogen-containing siloxy units" means ~hat
hydrogen is bonded directly to silicon.
Polysiloxane (A) of this invention is represented by the
above Formula I, wherein the R groups can be any substituted or
unsubstituted hydrocarbon radical having from l to 20 carbon
atoms, for example9 alkyl radicals such as methyl~ ethyl,
propyl, butyl, pentyl, hexyl, octyl and decyl, alkenyl
radicals such as vinyl and allyl; cycloalkyl radicals such as
cyclohexyl and cycloheptyl; aryl radicals such as phenyl;
aralkyl radicals such as beta-phenylethyl; and any of such
radicals wherein a part or all of the hydrogen atoms are
replaced, for example, by halogen atoms such as fluorine,
chlorine or bromine; cyanoethyl radicals or 3,3,3 trifluoro-
propyl radicals. From the viewpoint of availability and ease
of synthesis, it is preferable that substantially all of the R
radicals be either methyl or methyl and phenyl.
The Rl radicals can be any of the foregoing R radicals
and, in addition, can also be a hydrogen atom, hydroxyl radical
or a hydrocarbonoxy radical having from l to 20 carbon atoms
such as, for example, methoxy, ethoxy and propoxy.
- . . . . .
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60SI-896/0043p/GLL:mz
-12-
The A moieties have the general formula:
R2 R3
HC = C ; C - 0 - R4
Il
where R2 and R3 are selected, independently, from the group
consisting of hydrogen and substituted or unsubstituted hydro-
carbon radicals; R4 is a divalent hydrocarbon radical having
from 1 to 10 carbon atoms. Examples of organofunctional groups
reprPsented by A include atryloxy, methacryloxy, cinnamoyl, and
crotonate and any other organic groups which crosslink in the
presence of photo or thermal generated free radicals and which
include the G = C structure. Preferably, R4 is a divalent
radical having from 2 to 5 carbon atoms and most preferably has
3 carbon atoms. Preferably R~ and R3 are, independently,
hydrogen or a Cl 3 hydrocarbon radital.
It is not necessary that polysiloxane (A) contain silicon-
bonded hydrogen atoms and silicon-bonded acrylate radicals in
the same molecule. However, when y in Formula I is zero it is
necessary to provide silicon-bonded hydrogen atoms in the form
of a separate organohydrogenpolysiloxane as described more
fully hereinbelow. The number of acrylate-containing siloxy
units is generally from about 0.1 to about 50 mole percent
based on the total number of siloxy units in polysiloxane (A).
The number of hydrogen-containing siloxy units must be suffi-
cient to react with substantially all of the acrylate-contain-
in~ siloxy units and~or substantially all of the siloxane
bonded alkenyl groups. Generally, there is from about 0.1 to
50 mole pert:ent hydrogen-containing siloxy units based on the
total number of siloxy units in polysiloxane (A).
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605I-896/0043p/GLL:mz
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Those skilled in the ~rt will be able to adjust the number of
hydrogen-containing siloxy units and acrylate or alkenyl
containing siloxy units to obtain a cured composition having
predetermined properties.
The artisan will appreciate that the value for x can be
zero in Formula I provided that in such case R will be an
acrylate radical of Formula II. It is also possible to employ
a mixture of polymers, for example, polymers having hydrogen
only on the polymer chain and acrylate radicals in the terminal
positions. Similarly, it is possible to utilize a mixture
wherein hydrogen is present only at the terminal positions and
acrylate radicals only on the polymer chain. Other variations
will be obviDus to those of ordinary skill in the art.
As stat~d earlier, the value of y in For~ula I can be zero
provided that silicon-bonded hydrogen atoms are provided from
another source. When y = 0, a preferred composition has w
greater than zero such that the polymer of Formula I includes
acrylate and alkenyl functionality. However, it should be
understood that in practicing the present invention it is
merely necessary to provide silicon-bonded hydrogen atoms and
silicon-bonded acrylate radicals in combination with a free
radical type photoinitiator and a precious metal or precious
metal-containing hydrosilation catalyst.
When the number of silicon-bonded hydrogen atoms or
acrylate radicals is less than the above-said ranges,
respectively, the adhering ability of the cured composition is
reduced. When the number of ~hese substituents is more than
the above said ranges, respectively, thermal resistance is
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60SI-896/0043p/6LL:mz
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reduced or the curing rate is inadequate. When the number of
silicon-bonded hydrogen atoms and silicon-bonded acrylate
radicals is within the stated ranges, no fo~ming occurs-upon
exposure to ultraviolet radiation due to generation of hydrogen
gas and the composition is sufficiently "set" after brief
exposure to UV radiation to allow the coated article to be
placed elsewhere for thermal curing. Thermal curing, for
purposes of the instant application, includes subjecting the
composition to elevated temperatures or merely allowing the
precious metal ca$alyzed hydrosilation reaction to take place
at room temperature.
The number of diorganosiloxy groups present in polysiloxane
(A3 is not critical and can be anywhere from zero to about 99.8
mole percent. Generally there should be sufficient
dior~anosiloxy units to proYide polysiloxane (A) a viscosity of
from about 25 centipoise to about 2,500,000 centipoise at
25C. It is particularly preferred that some of the R groups
of polysiloxane (A) be alkenyl radicals such as vinyl. It has
been found that optimum results are obtained when the number of
vinyl-containing siloxy units is from about l to about lO mole
percent based on the number of siloxy units in polysiloxane (A).
The artisan will appreciate that in addition to the-
difunctional units illustrated in Formula I, there may also be
present trifunctional siloYy units of the formula R SiOl 5,
where R is as previously detined~ and/or tetrafunctional 5ilo%y
units of the formula SiO~. The number of such units
employed, if any, will depend upon the particular application
under consideration and can readily be detenmined by one of
ordinary skill in the art without undue experimentation.
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60SI 896~0043p/GLL:~z
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In a preferred embodiment of the present invention there is
present from about 2 to about 20 mole percent acrylate-contain-
ing 5iloxy units, from about 2 to about 20 mole percent
hydrogen-containing siloxy units, ~rom about 2 to about 10 mole
percent vinyl-containing siloxy units, and the viscosity of
polysiloxane (A) is from about 100 centipoise to about ~000
centipoise at 25~C.
Free radical type photoinitiators or photocatalysts are
well known in the art. Photoinitiator (B) of the present
lû invention can be any known silicone compatible free radical
type photoinitiator effective fDr promoting crosslinking
between unsaturated silicon-bonded groups sueh as acrylate and
vinyl and silicon-bonded hydrogen atoms.
Especially preferred photoinitiators for promoting cross-
linking between unsaturated groups and SiH groups are disclosed
by Eckberg et al,-in Canadian Patent Application Serial
Number 469,075 which application was filed on -
November 30,-1984-and which application is
assigned to the same assignee as the present
invention. Briefly, Eckberg et al. disclose that
combinations of certain perbenzoate esters having the general
formula:
o
(III) R5 - - - IC ~ Z
where R5 is a monovalent alkyl or aryl group and Z is
hydrogen, alkyl, halogen, nitro, amino, or amido and
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60SI-896/0043p/GLL:mz
-16-
pho~osensitizers such as benzophenone photocatalyze the
additinn reaction of SiH group!i and unsaturated groups bonded
to siloxy units. The nature oF the Z substituent will affect
the stability of the peroxy bond; an electron-poor substituent
stabilizing the peroxy bond and an electron rich substituent
making the peroxy bond more reactive. These perbenzoate esters
may be synthesized in known ways, such as by reacting benzoyl
halides with hydroperoxides (see, e.g. the descriptions in
Blomquist and Berstein, J. Amer. Chem. Soc., 73, ~546 (1951)).
Preferred perben20ate esters include t-butylperbenzoate and its
para-substitu~ed derivatives, t-butylper-p-nitrobenzoate,
t-butylper-p-methoxybenzoate, t~butylper-p-methylben20ate and
t-butylper-p-chlorobenzoate.
The amDunt of photoinitiator employed is not critical, so
long as proper crosslinking is achieved. As with any catalyst,
it is preferable to use the smallest effective amount
possible. 6enerally ~ he amount of photoinitiator can be
anywhere from about to about 10 parts by weight based on
100 parts by weight of polysiloxane (A~. More preferably~ the
photocatalyst level is from about 1 to about 5 parts by weight
per 100 parts by weight polysiloxane (A).
Other photoinitiators, whose suitability for use in a
particular situation can easily be ascertained by the artisan,
are described in U.S~ Patent Nos. 3,759,807, 3,968i305,
3,966,573, 4,113,592, 4,131,529, 4,310,600, and 4,348,462.
Diethoxyacetophenone is an examplP of a silicone soluble photo-
initiator particularly useful in photocatalyzing crosslinking
of acryloxy-containing silicones.
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60SI-896/0043p/GLL:mz
Component (C) can be any precious metal or pr~cious metal-
containing catalyst effective for initiating a thenmal
hydrosilation cure reaction. Especially included are all of
the well known platinum and rhodium catalysts which are
effective for catalyzing tne addition reaction between
silicon-bonded hydrogen atoms and silicon-bonded olefinic
groups. Examples of platinum or platinum-containing complexes,
which are the most preferred of the precious metal catalysts,
include platinum metal on charcoal, the platinum hydrocarbon
complexes described in U.S. Patent Nos. 3,159,601 and 3,159,662
to Ashby, the platinum alcoholate catalysts described in U.S.
Patent No. 3,220,970 to Lamoreaux, the platinum complexes
described in U.S. Patent No. 3,814,730 to Karstedt, and the
platinum chloride-olefin complexes described in United
States-Patent Number 3,814,730 to Karstedtr
and the platinum chloride-olefin complexes
described in-~nited States Patent No. 3,516,946 to M~dic
The most preferred catalyst for facilitating the thermal
hydrosilation reaction are the Ashby catalysts described in
U.S. Patent Nos. 3,159,501 and 3,159,662. Other platinum metal
and platinum-containing catalysts which can be employed in the
present invention are well known to those skilled in the art.
~ydrosilation catalysts other than those based on platinum
may also be used to effect thenmal curing. For example,
complexes of the metals rhodium, ruthenium1 palladium, osmium
and irridium can be utilized. Of the non-platinum based
catalysts, those based on rhodium are most preferred. The
preparation and description of preferred rhodium catalysts are
set forth in U.S. Patent No. 4,347,346 to Eckberg.
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60SI-896/0043p/GLL:mz
As with photoinitiator (B), the amount of precious metal or
precious-metal containing catalyst (C) is not critical so long
as proper crosslinking is achieved. Typically, the amount of
precious metal or precious metal-containing catalyst is from
about 10 to about 500 ppm as metal atoms based on polysiloxane
(A) If the optional organohydrogenpolysiloxane (D) and vinyl
containing polysiloxane (E) are included it may be desirable to
utilize a greater amount of catalyst (C). Of course, the
skilled artisan can determine the appropriate amount of
catalysts (8) and (C) without undue experimentation. The
artisan will also appreciate that it is within the scope of the
present invention to employ mixtures of the various photo-
catalysts and precious metal or precious metal-containing
catalysts.
Organohydrogensiloxane (D)-can be either a fluid, resin or
mixture thereof which those skilled in the art utilize as a
crosslinking agent in addition curable silicone systems.
Particularly useful organohydrogenpolysiloxanes for practieing
the present invention are trimethyl chainstopped polymethylhy-
drogensiloxane fluids having from approximately lOX to 100~ SiH
groups, any remaining groups being dimethylsiloxy units, and
having a viscosity in the range from about 10 to about 1000
centipoise at 25~C. However, any organohydrogenpolysiloxane
having the general fonmula
(IV) RaHb SiO 4 a b
is within the srope of the present invention. Such organohy-
drogenpolysiloxanes are well known in the art, fcr example, as
, described in U.S. Patent Nos. 3,344,111 an~ 3,436,366.
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60SI-896/0043p/GLL:mz
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Among the radicals included within R of Forrnula III are
alkyl such as methyl, ethyl and propyl; cycloalkyl such as
cyclopentyl, cyclohexyl and cycloheptyl, aryl such as phenyl,
naphthyl, tolyl and xylyl, aral kyl such as phenylethyl and
phenylpropyl; and substituted radicals of any of the fore-
going, for example, halogen substituted and cyanoalkyl
substituted.
Other organohydrogenpolysiloxane fluids are well known in
the art and are described in greater detail in United
States Patent Number which issued to Grenoble and --
Eckberg.
.
It is possible to utilize an organohydrogenpolysiloxane
resin in place of, or in addition to, the organohydrogenpoly-
siloxane fluid. Such organohydrogenpolysiloxane resins are
aiso well known in the art, for example, as described in
Unlted States Patent Number 4,041,010 to
Jeram. Briefly-, organohydrogenpolysiloxane resins
comprise either . ._-
R
H _ li0.5 units and SiO2 units, where the
R
ratio of R ~ H units to SiO2 units ranges from 1.0 to 2.7 and
where R is as previously defined, or
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60SI-896/0043p/GLL:mz
-20-
R
H - 5iO0 5units, R2SiO units, and SiO~ units,
R
where the ratio of R + H units to SiQ2 units ranges from 1.2
to 2.0 and where R is as previously defined.
If an organohydrogenpolysilloxane is employed, it can be
employed in any amount to obtain specific properties in the
cured product. Generally, it should be utilized in a range of
from about 1.0 parts by weight to about 10 parts by weight per
100 parts by weight of polysiloxane (A). In a preferred
embodiment there is utilized a mixture of organohydrogenpoly-
siloxane fluid and organohydrogenpolysiloxane resin. While no
particular ratio o~ fluid to resin is requireJ, a~ratio of from
a~out 0.1 parts fluid per part resin on a weight basis to about
10 parts fluid per part resin on a weight basis has been found
to provi~e compositions suitable for use as a coating
composition.
Another optional component for practicing the instant
invention is olefin~containing polydiorganosiloxane (E). As
with organohydrogenpolysiloxane (D), olefin-containing poly-
diorganosiluxane (E) can be either a fluid or a resin and
preferably is a mixture thereof. Most preferably component (E)
is a vinyl-containing polydiorganosiloxane. A typical vinyl-
containing polydiorganosiloxane fluid has the formula:
~ R ~ ~R5 ~
(V) H2C = CH ~ SiO t 51 ~ sIi ~ 1 CH ~ CH2
. . ' , . , .- .
.
-
:
~:~S~i~3~
60SI-896/~043p/GLL:mz
wherein R is as previously defined; R5 is a radical having
alkenyl unsaturation, preferably vinyl; and a and b are
positive integers such that the Yinyl chainstopped polysiloxane
has up to about 20% by weight RS groups. The viscosity of
such a polysiloxane ranges from about 50 to about 100,000
centipoise at 2~C. Such polysiloxane fluids are also
described in U.S. Patent No. 4,448,813 to Grenoble and Eckberg.
Vinyl-containing silicone resins are also known in the art,
for example, as described in U.S. Patent No. 4,041,010 to
Jeram. 6enerally these resins are selected from the class
consisting of resins having YiR2SiOo 5 units and SiO2
units where the ratio of hydrocarbon substituents to Si varies
from 0.8 to 2.7 and resins having ViR2SiOo 5 units, R2SiO
units and SiQ2 units where the ratio of hydrocarbon
substituents to Si varies from 0.8 to 2.4. For more specific
details relating to such resins and their preparation the
reader is referred to the cited Jeram patent No. 4,041,010.
If a vinyl-containing polysiloxane is employed in the
present invention it can be utilized in any amount. As the
artisan will appreciate, including precious metal or precious
metal-containing catalyst (C) in the same package as polysilox-
ane (A) will result in product gelation or curing before it
reaches the consumer provided polysiloxane (A) includes
silicon-bonded hydrogen atoms. Accordingly, in a commercial
environment, olefin-containing polysiloxane (E) serves
primarily as a carrier of precious metal catalyst (C). Thus,
in one embodiment of the present invention, the curable
composition is provided in two or more packages; one package
including therein the alkenyl-containing polysiloxane, precious
.
3L 2~ 2 3~i
60SI-896/0043p/GLL:mz
metal catalyst and optional inhibitor, and the other package
containing the remaining in~redients. Such two package systems
are well known in the art. A particularly preferred multi-
component packaging system can be adapted from the teachings of
6renoble and Eckberg in U.S. Patent No. 4,448,815.
It is also contemplated that: a hydrosilation inhibitor (F)
can be included in the curable composition of the present
invention in order to extend the work life of the composition.
One example of a suitable inhibitor is disclosed in U.S. Patent
IO No. 4,256,870 wherein Eckberg teaches the use of organic esters
of maleic acid to selectively retard the thermal addition cure
reaction.
Eckberg discloses in U.S. Patent No. 4,262,107 that other
suitable inhibitor compounds are certain acetylenic compounds,
olefinic carboxylic acid esters of aliphatic alcohols such as
vinyl acetate, alkenyl isocyanurates and mixtures thereof.
In United States Patent~No. 4,476rl66 which issue
October 9, 19-84 ., and assigned to the same assignee as the
present invention, Eckberg discloses that a blend of a ~icar-
boxylic acid ester having carbon to carbon unsaturation and an
ole,inic carboxylic acid ester of an aliphatic alcohol is
particularly effective as an inhibitor.
. . . , -- .
In another aspect of -the present invention there are
provided methods for making the curable compositions of
the present invention and methods for making articles
having the compositions cured thereon.
.
, -
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.~ .
' ' ' ' '
3~
60SI 896/0043p/GLL:mz
-23-
The curable compositions are prepared merely by combining
the various ingredients or by mixing the pac~ages in which the
various ingredients were provided. The articles of ~he present
invention are prepared by apl~lying such composition to a
substrate such as a circuit board if it is to be used as a
confonmal coating, or to a fllexible sheet material such as
Mylar ~ or paper if it is to be used as a release coating,
thereafter exposing the coated substrate to ultraviolet radia-
tion sufficient to set the composition, and finally allowing
curing to be completed by exposing the article to either room
temperature or elevated temperature. Of course, the higher the
temperature, the more rapidly complete cure will take place.
In order that those skilled in the art might be better able
to practice the present invention, the following examples are
given by way of illustration and not by way of limitation. All
parts are by weight unless otherwise indicated.
Example 1
To a one liter flask there was added 15~ grams dimethyldi-
ch10rosilane (1.2 moles) and 42 grams methylvinyldichlorosilane
(0.3 mole). These monomers were then hydrolyzed with 24 grams
water (1.33 moles) dispersed in 33 grams acetone oYer a 75
minute period at 18 - 24~C. The reaction mixture was main-
tained at 20C for 40 minutes and at 40C for 40 minutes before
beiny stripped under 33 mm vacuum at 105C for 15 minutes to
provide 107 grams of a Cl-stopped linear copolymer. The linear
chloro-stopped species was then treated with 114 grams
methylmethacryloxypropyldichlorosilane (0.47 moles), ~3 grams
,- ~
.~ ' . ' ' ` ' .
~j6;23~
60SI-8g6/0043p/GLL :mz
~24-
methyltrichlorosilane (0,36 molles), and 54 grams of a 70D
centipoise silanol endstopped linear d~methylpolysiloxane
fluid, and hydrolyzed with 130 grams water in a reaction medium
of l:l toluene:aretone at 54-6~C. This resulted in 264 ~rams
of a clear 392 centipoise fluid designated polysiloxane
(Al). End group analysis revealed 2.0X hydroxyl
functionality as OH. 150 grams of this fluid (approximately
0.18 mo1es OH) were then hydrolyzed with ~8.3 grams
trimethylchlorosilane (0.35 mole) in excess water at 60C.
IO Solvent and byproduct (Me3 SiOo 5)2 were removed in vacuo
to furnish a final product designated polysiloxane (A2)
having a viscosity of about l75 centipoise at ~5C and a
hydroxyl content of about 0.l2%.
These polysiloxanes (e.g. Al and A2) were evaluated for
UV cure performance. Comparative properties of interest are
set forth in Table I.
Tabl e
Visc., l~a~i~u~ Co~pat{billty~
Co~ tion ,~ ~t~ ~ ~'~
2 A12 392 2.0 1.5 ~/8 Incompatlble
A 175 0.12 1.0 ~/s Preely ~i~cible in
propor~ion~
* 2 ~il c~ating on supercalendared kraft (SCK) stock,
400- watts per square inch UV power, nitrogen
atmosphere, 4X diethoxyacetophenone (DEAP)
photoinitiator. nCure~ is defined as smear-free
coating.
** MDHM = methylhydrogenpolysiloxane having a
viscosity of about 25 cps. at 25C; x 'Z'20.
-, - , , '
:.
,
Ei 23~
60SI-~96/0043ptGLL:mz
-25-
Thermal cure studies were then conducted on the following
blends:
a.) 100 parts polysiloxane (A2) + 4 parts MDHM +
100 ppm Pt-containing catalyst as Pt.
b.) 90 parts polysiloxane (A2) ~ 10 parts MDHM +
100 ppm Pt-containing catalyst at Pt.
c.) 90 parts polysiloxane (A2) + 10 parts MDXHM + 50
ppm Pt-containing catalyst at Pt.
The results of such thermal cure studies are set forth in
Table II.
Table II
.
~ini~ual 15D ~C
Blend A~ e
a SO ~ec. 3.5 ~our~
b lS ~ec. 20 ~inutes
c 15 ~cO 35 ninutes
1 ~ 3at~ng~ ~n ~C~ stoc~. Cure defined as above.
, ,. ., . : .
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60SI-896/0043p/GLL:mz
-26-
Addition of 4X DEAP to blend (c) enabled UV cure comparable
to polysiloxane (A2) despite the presence of 10 percent
methylhydrogenpolysiloxane crosslinking agent. Blend (c) was
then applied in a layer 5 mil thick to a stainless steel Q
panel and passed through a UV processor at 50 feet per minute
under a nitrogen atmosphere and 400 watts per square inch lamp
power. Areas kept in shadow were obserYed to cure to a non-
tacky surface after being left undisturbed at 25C in the dark
for 20 hours. Exposed areas were fully UV-cured immediately on
exposure. This example illustrates the most preferred embodi-
ment of the present invention.
The preferred~packaging of such a dual cure composition
would be to place in package A the UV curable polymer9 photo;
initiaLor and precious metal or precious metal-containing
catalyst, and to place in package B the organohydrogenpoly~
siloxane crosslinking agent. A small amount of inhibitor such
as butylallylmaleate or vinylacetate may also be included in
package A.
:
Example 2
In this example 25 grams of a 20 cps methylhydrogenpoly-
siloxane fluid, 30 grams sym-tetramethyltetravinylcyclotetra-
siloxane and 445 grams octamethylcyclotetrasiloxane were equil-
ibrated under nitrogen at 83C for 18.5 hours with 5 grams
Filtrol 20 acid clay catalyst to furnish a 2000 centipoise
fluid having the general fonmula
MDH Dyi DzM
.
: . . ' ' . .
:,
.' ~ ~ -,
~L2~;6:239
60SI-B96/~043p/GLL:mz
-27-
where D is a dimethylsiloxy unit, DH is 3 methylhydrogen-
siloxy unit and DVi is a methylvinyl silsxy unit. 100 grams
of a methacrylate ~unctional silane having the fonmula
Cl O
3 Sl (CH2)3 C l CH2
Cl CH3
were added to the equilibrate as well as 0.05 gram di-t-butyl-
hydroquinone. The mixture was agitated for one hour at 83C
and then filtered to remove the heterogeneGus equilibration
catalyst. The fluid so obtained was a 70 centipoise fluid
having 3.22 weight percent hydrolyzable chloride as chain-
stopper. 100 grams of such 70 cps. chloro-stopped fluid were
then added to a 500 ml flask (0.0882 mole Cl) along with 50
~rams toluene. The solution was agitated at 39C as 1.56 grams
water (0.0867 mole) dissolved in 20 grams acetone were slowly
added over a ten minute period. The temperature was maintained
a~ 30-35C for thirty minutes following the water addition.
Twenty five grams water were then added to consume any remain-
ing hydroly~able chloride. The product mixture was transferred
to a separatory funnel, the aqueous layer discarded, and the
organic layer washed with 100 ml of 5X aqueous sodium bicarbon-
ate. 85 grams of a 700 centipoise fluid designated polysilox-
ane (A3) were obtained a~ter 120C, 15 mm vacuum stripping,
and having the fonmula
-- . . . .
- , ~ . .
: . :. . ., . -
60SI-896/0043p/GLL:mz
-?8-
HOtSiOt SiO--~ SiO ~ SiO 1 SiO
\ (CH2)3 ~ CH3 / ~ CH3 Jb \CH3 ~ c(CH2)3 J
O O
C = O C = O
CH C
3 . CH3 - C
~H2 CH2
where the molecular weight is about 11,000, and where b is
approximately equal to c which is approximately equal to 1/8 a.
Ultraviolet cure characteristics were determined by
preparing 2 coating bath oonsisting of 10 parts polymer, 2.5
parts benzophenone and 4 parts diethoxyacetophenone. Cure
studies were conducted under 400 watts per square inch focused
total UV power in a PPG model 1202 QC Processor. The results
are set ~orth in Table III.
.. . . .
. .. - . ~ ' . : .
.
~ ' - ' .
. , - ~ .
.
3L 2~;S 2 3~
60SI-896/0043p/GLL:mz
-29-
Ta~le III
Coat~n~ Cure
Substr~te Th7ckness Atmos~here Line 5peed
coating; smears with
press~re.
SC~ Thin fi7m Air 20 fp~ ~ n
SCK ! mil N2 loo fpm Exee~lent cure to
. sme~r- ree coating; oood
anchorage :
SCK I mi7 N2 2DQ fpm Cured to mi~rat~on-free
coating; smears with ~ .
pressure
PEK 4 mil N2 lO0 fpm Excellent cure t~
smear-free;~~ossy,
tough ~oatin~, ~ood
anchorage.
NOrES: SCK ~ 40~ream supercalendered kraft paper
PEK ~ polyethylenelaminated kraft paper
'Thin film' i5 ~ 1.5 grams/meterZ
'' ' ' '
-,
- ,
..
~25 6~
60SI 896/0043p/GLL:mz
-30-
The observation that the cured coatings do not migrate tc
Scotch ~ ~610 cellophane tape suggested that the compositions
of the present invention will function as release coatings.
Accordingly~ a coating ~ath was prepared ~s follows: 10 grams
of the abo~e-described polysiloxane (A3), 0.25 grams benzo-
phenone, and 0.4 grams diethaxyacetophenone dispersed in 50
grams acetone and ~ grams hexane. This mixture was coated onto
SCK using a ~8 wire-wound rod and then cured under exposure to
400 watts/inch2 UV radiation at 100 feet per minute line
speed under nitrogen. 5even miles of an aggressive SBR
adhesive (Fasson SS-l) were coated and cured onto the silicone
layer, then top~coated with another layer of S~K. Two inch
wide tapes were prepared and the silicone layer delaminated
from the adhesive layer at a 180 angle and 400 ~eet per minute
pull speed. 70 to ~0 grams force was required to separate the
lamina which represents good release perfonmance.
The thenmal cure perfor~ance of polysiloxane (A3) was
then tested. Nine grams of polysiloxane (A3) was combined
with one gram of a 400 centipoise vinyl endstopped di~ethyl-
polysiloxane and 300 ppm of a platinum~containing hydrosilation
catalyst (as platinum metal). The result was a clear fluid
containing 30 ppm catalyst at Pt metal, Cure performance was
assessed on SCK substrate at 150C. The results are provided ~ -
in Table IV.
Table IY
Thickness Oven Dwell Ti~e Re~arks
1 mil 50U cured to ~ on-free,
smear-free csating
I mil 30~ , with slight migration,
Thin fil~ 30~ cured to ~igration-free release
(As defined ~bove)
. .
. - , , ~
~", ,
:- .:
. .
,
2 3~
60SI-896/0043p/GLL:mz
The foregoinQ illustrates that polysiloxane (A3) can
combine both UY curing and thermial curing so as to overcome the
"shadow effect" suffered by prior art compositions which
utilize only UY curing. this example also illustrates that the
rate of UY curing release coatings can be increased since
complete cure will be effected afterwards by thermal curing.
Example 3
In this example 850 ~rams of dimethyldichlorosilane (6.6
moles), 92 grams methylhydrogendichloros~lane ~0.8 moles), and
86 grams methylvinyldichlorosilane (0.6 mole) were treated with
a dispersion of 130 grams water (7.22 moles) in 180 grams
- acetone by slow addition of the aqueous phase over a 150 minute
period. The temperature was maintained at 16-26~C during the
addition. The hydrilyzate was stripped to 100C, 40 mm vacuum
to furnish 504 grams of a 120 oentipoise ~luid haYing 6.04
weight percent DH units and 0.4 weight percent ~ydrolyzable
chloride (as HCl). 200 grams of this chloride-stopped fluid
was cambined wi~h 2DD gr~ms of methylmethacryloxypropyldi-
chlorosilane and 200 grams of a ~00 cps. silanol stopped
dimethylpolysiloxane fluid in a blend of 400 ml acetone and 400
ml toluene. The mixture was then treated with 300 ml water by
dropwise addition over a 7~ minute period at 4~-60C. Follow-
ing hydrolysis, the product mixture ~as transferred to a
separatory funnel, the aqueous layer dis~arded and the organio
phase washed with 300 ml of a 5X NaHC03 solution. Stripping
the organic phase of solvent and light ends at 100C, 25 mm
vacuum, afforded 4~4 grams of polysiloxane (A4~. To poly~
siloxane ~A4) there was added 9.1 grams benzophenone and 18.2
grams diethoxyacetopheRone. The final produot was a 160
.
-
- ;
;6Z3~
60SI~896/0043p/GLL:mz
-32-
centipoise fluid having 3.0 we~ght percent DH units. It is
convenient to prepare the Cl-DH DVi-D-Cl precursor fluid ;n
situ, then carry out the cohydrolysis with the acrylic
functional silane in the same pDt. This eliminates the need to
isolatP the hydrolytically unstable chloride-stopped
polydimethyl-methylhydrogen-methyl- vinylsiloxane intermediate.
In situ preparation of the chloride stopped precursor was
employed to prepare polysiloxane (A5) as follows: 136 grams
dimethyldichlorosilane (1.054 moles), 3S grams methylhydrogen-
~` 10 dichlorosilane (0.304 mole) and 21 grams methylvinyldichloroO
silane (0.149 mole) were hydrolyzed via a one hour addition of
23.3 grams water (1.29 moles) dispersed in 32.3 grams acetone
at 18-25~C. Stripping this material afforded 90 grams of a
fluid containing 0.15X hydrolyzable chloride. This chloride-
stopped polymer was then trPated with 150 ml toluene and 150 ml
acetone, 90 grams methylmethacryloxypropyldichlorosilane, 45
grams of a silanol endstopped dimethylpolysiloxane having a
viscosity of about 700 cps., and 45 grams methyltrichloro-
silane. The silane solution was then hydrolyzed with 12~ ml
water via addition over a period of 45 minutes at 45-58C. The
resultant polysiloxane (A5) had a viscosity of about 4~0 cps.
and included 4.05% DH units (217 grams yield). To polysilox-
ane (A ) there was added 4.9 grams benzophenone and 8.6 grams
diethoxyacetophenone.
A third polymer, designated polysiloxane (A6), was
prepared as was polysiloxane (A ) except that the reactants
(85 grams Cl-DDHDVi-Cl fluid, 85 grams methylmethacrylic-
dichlorosilane, 64 grams 470 cps. silanol endstopped
polydimethylsiloxane and 21 grams methyltrichlorosilane3 were
.~ . , .
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-
, : ,. ;. .
~25~23~3
60SI-895/0043p/GLL:mz
33-
such so as to provide 209 grams of 130 cps. product having 5.8X
DH units. To polysiloxane (A6) there was added 2 weight
percent benzophenone and 4 weight percent diethoxyacetophen-
one. All three of the compositions based on polysiloxane
5(A4)~ (A5) and (A6) were c~mplete one-part products for
UY-cure applications. Qualitative UY cure perf~rmance was
assessed as in Example 2. The results are set forth in Table V.
Table V
Th~cknes~ Atmo~Phere ~ a~
A' 2 mil N2100 fpm Cured to ~mear-free glo sy
coating
200 fpm _ndercured smear~ badly
Air5 fpm Cured to smear-free glossy
co~tinq.
A5 2 mil N22no fpm Cured to smear-free glossy~
hard coatingO
~300 ipm Cured; slight ~e~r
AiE30 fpm ~ -
AS 2 mil ~100 fpm ~red to ~mear-free glo~y
co~ting
Il 9200 fpm ~ - some
s~ear.
Air10 fpm Cured; slight ~ear
.
~2~ 3 ~
~Q5I-896/0043p/GLL:mz
-34-
Next a catalyst mixture was prepared as follows: 490 grams
of a 400 Cp5 blend of 95 parts dimethylvinyl_stopped dimethyl
fluid and 5 parts soft (M~ 3007000) dimethylvinyl endstopped
dimethyl silicone gum were combined with a platinum~containing
catalyst su~ficient to furnish 300 ppm Pt metal. To this
mixture was added 11.8 grl~ms (2 weight percent) benzophenone.
This fluid proved to be compatible with methacrylated polysi-
loxanes (A4), (A5) and (A ) to yield clear mixtures.
Thermal cure was ascertained by blending one part o~ the
I0 catalyst blend with 9 parts of each of polysilaxanes (A4),
(A5) and (A6). There was 30 ppm catalyst as Pt metal in
e~ch blend. A 2 ml thick coating of each experimental eompo~i-
tion was applied on SCK substrate and placed in a forced air
ov~n maintained at 150C. The thermal cure results are set
forth in Table VI.
Table VI
Oven Dwell I ~e~.
A4 30 nder~ured; smear~
- 60 Cured~ mear
2 ~ " 90 ~!~; no s~ear
A5 20 Under~:ured; smearls
~ no ~raear
A6 20 ~o cure observed
~ 30 lJnder~:ur~d; 13lDear~
Co~Plete ~ure DO ss~le~r
. , , ~
' ' ' . ' ' ','. ' - ' . '' ' '': ' ' ' ' ' ', ':
-,
~25623g
60SI-B96/0043p/GLL:mz
-35-
A ~shadow effect~ experiment was then carried out using a
9:1 blend of polysiloxane (A5) and the above-described catal-
yst mixture. Four ml thick coatings were applied to stainless
steel panels, and a one inch L-shaped metal piece was then
placed across the coated panel so as to effectively block
ultraviolet radiation from reaching the composition across a
one inch wide strip. The coatings were exposed to 400 watts
focused UV radiation in a nitrDgen atmosphere. Exposed areas
cured to smear-free, glossy surfaces at 100 feet per minute
line speed. Unexposed areas were wet a~ter removal from the VY
processor, but oured to tack-free surfaces after )6 hours at
25C in the dark.
Example 4
These dual curable (meth)acrylated silicone polymers can be
prepared in many ways besides the high-acid reverse hydrolyses
illustrated in some o~ the previous examples. A dual-cure com-
position designated A7 was synthesized in this fashion:
48g of methylmethacryloxyprQpyldichlorasilane (0.2 moles) +
79 methylvinyldichlorosilane (0.05 moles) ~ 2089 dimethyldi-
chlorosilane (1.75 moles) were dispersed in 300 cc of toluene,
then the silane solution slowly added to 10009 of water over a
2.5 hour period at a temperature of 25-40C. The organic phase
obtained from the ~ow-acid hydrolysis was stripped to 150C, 28
mm to yield g59 of low molecular weight silanol-stopped poly-
2~ siloxanes represented as HO ~ DDViDMA ~ OH. Silanol
content was about 5 weight percent as OH. This hydrolyzate was
in turn dispersed in 3009 toluene, heated to reflux (113~C)~
when 0.89 stannous octoate was added. After 10 minutes at
- - ~ - :
, - .
.
' ' ''- ~" ~
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60SI-896/0043p/GLL:m~
113C about 0.6 ml H20 had formed and was tr~pped out in a
Claisen apparatus. The reaction mixture was cooled to 70C,
209 (.17 mole) of dimethylvinylchlorosilane added follcwed by
dropwise addition of 50 cc H2~ at 70~C to convert silanol
chainstopper to MYi chainstopper. The product was worked up
by washing with 5X NaHC03 solution ~aqueous), isolated by a
90C strip at 15 ~m ~acuum. 989 of MVi ~ DDViDMA) MVi
were finally treated with 3.99 diethoxyacetophenone photo-
initiator and sufficient soluble platinum catalyst to
1 0 furnish ~, 25 ppm Pt. The complete blended pr~duct ~as a ele~r
57 cps. fluid. (Persons skilled in the art will see that the
viscosity of th;s product can be controlled by monitoring the
amount of water ccndensed during the tin octoate-bodying step.)
2 mil coatings of the product A cured to a smear-free,
1~ glossy surface on SCK substrate when exposed to 400
watts/square inch focused ultraviolet power at 1~0 ft/min. line
s~eed in nitrogen. 100 parts of A blended with 4 parts of
25 cps. trimethylsiloxy-stopped polymethylhydrogen fluid cured
tG a smear and migration-free coating when applied at 2 mil
.hickness on SCK paper upon 30 seconds dwell time at lSO~C;
the UV-cure performance of the 100:4 blend proved indistin-
guishable from $hat of the unblended A7 product. The blended
mixture was a clear fluid which set up to a soft gel in 2 hours
at 25~C.
The example A7 demonstrated that this invention is not
limited by its mode of processing~ and that compositions of
which these examples are representative fall within the scope
of this application however they might be prepared.
.
: ~, - . -
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.. . . :.' .
