Note: Descriptions are shown in the official language in which they were submitted.
~ ir ,t~
MEI'HOD FOR CURING ORGANOPOLYSILOXANE COMPOSITIONS
AND THE COMPOSITIONS
The present invention provides a method for
curing organopolysiloxane compositions. More specifically,
the present invention provides a method for curing
organopolysiloxane compositions which consist of a
photosensitizer and an addition-curable organopoly-
siloxane containing a platinum-type catalyst by heating
and by exposure to ultraviolet radiation or to an electron
beam.
Background Information
It is known in the prior art that organopoly-
siloxane compositions can generally be cured by heating;
refer to Japanese Patents 35-13709 (60-13709), 36-1397
(61-1397) and 46-76798 (71-76798). However, all of these
methods require elevated temperatures and heating for
long periods of time with the resulting drawback of low
productivity. -On the other hand, organopolysiloxane
compositions which can be cured at room temperature or
low temperatures by exposure to ultraviolet radiation or
an electron beam; ~refar to Japanese Kokai [Laid-Open]
Patents 50-61386 !75-61386) ~United Kingdom Patent
Specification No~ 1,433,461, published April 28, 1976~,
50-61486 (75-61486) (U.S. Patent No. 4,064,027, issued
December 20, 1977), and 55-125123 (80-125123) have been
developed due to recent demands for increased productivity
and the increasing diversity of applications. However,
these compositions have certa:Ln drawbacks including one
or more af the ~ollowing: a strong mercaptan odor, quite
poor pot stability at room temperature, slow curing rates
inappropriate for practical applications, and nonuniform
curing in interior sections.
~' .
'
: .
,
'' :', ' ~
~ 7~
Various methods were examined by the present
inventors in order to eliminate the preceding drawbacks
with the resulting development of a method for curing
organopolysiloxane compositions, including uniform curing
in interior sections, by heating and by exposure to
ultraviolet radiation or an electron beam for a short
period of time at low temperatures.
Summary of the Invention
This invention relates to a method for curing
organopolysiloxane compositions consisting essentially of
heating and exposinq to ultraviolet radiation or an
electron beam a photosen~itizer-containing organopoly-
siloxane composition which consists essentially of (A)
100 parts by weight of addition-curable organopol~siloxane
composition which consists essentially o~ (1) an organo-
polysiloxane containing at least two silicon-bonded
alkenyl groups per molecule and other organic groups when
present are selected from the group consisting of alkyl
groups, haiogenated alkyl groups, aryl groups, aralkyl
groups and alkaryl groups, (2) an organohydrogenpoly-
siloxane containing at least tws organohydrogensiloxane
or hydrogensiloxane units per molecule, (3) a platinum-
type catalyst, and (4) an addition-reaction retarder
selected from the group consisting of alkynols, 3-methyl-
3~pentene-1-yne, 3,5-dimethyl-3-hexene-1-yne, methylvinyl-
siloxane cyclics, and mixtures thereof,
and (B) 0.001 to 30 parts by weight of a photosensitizer.
This invention also relate~ to the compositions
, which can be cured by this method
More pa~ticularly, the present invention, in
one aspect, resides in a method for curing organo-
polysiloxane compositions cha~acerized by concurrently
heating and exposing to ultraviolet radiation or an
eleatron beam a photosensitizer-containing organopoly-
siloxane composition which consists of
r~
~ ~ ~r;~
(A) 100 parts by weight of an addition-¢urable
organopolysiloxane aompo~ition which aon~ist~ G~
( 1 ) a polydiorganoB$loxane ConBi~ting of
diorganosiloxane unit~ ~elected from ths group
consisting of dimethylsiloxane units, methyl-
phenylqiloxane unit~ methylvinyl~iloxaneunits, and mixtures thereof, ~aid polydiorgano-
siloxane being endblocked with dimethylvinyl-
5 ~ r i 1~>7 e t ~ 5; I y l
~ ~x~ units, t~ L~ ~y units, or
Rilicon-bonded hydroxyl group~, and having a
vinyl content of ~rom 0.5 to 3 weight peraent;
(2) a ~ ~ ~ ~ ~ ~ endbloaked polysiloxane
containlng methylhydrogen~iloxane units and
optionally dimethylsiloxans units, which has a
visoo~ity o~ from 0.005 to 0.05 Pa.~ a~ 25C,
and which i~ present in an amount of from 2 to
10 parts by weight based on 100 parts by weight
of (1);
(3) a platinum aataly~t ~elected from the group
con~isting of alcohol-modified chloroplatinic
acid, chloroplatinic acid-olefin complexes and
chl oroplatinic acid-vinyl-~iloxane
coordination ¢ompound~, which i~ pre~ent in an
amount of from 50 to 200 parts by weight of
elemental platinum per million parts by wsight
of (1); and (4) an addltion-reaotion r~tarder,
which i~ an alkynol or 3-msthyl-3-pentene-1-yne
and whioh i8 pre~ent in an amount of from o.1
to 1.0 part by weight per 100 part~ by weight
o~ (1); and .
(B) 0.1 to 5 part~ by weight, per 100 ~arts by weight o~
(A), o~ a photo~en~itizer ~eleated from the group
aon~i~ting o~ 4-allylaaetophenone, benzoph~none,
benzoin ethyl ether, and benzil dimethyl ketal.
- 2a -
l~ .
- , -
.
: ' , .
, .
~ ~ ~r;~7 2
In another aspect, the present invention
resides in a composition consisting of
(A) 100 parts by weight of an addition-aurable
organopolysiloxane composition whiah con~ists of
(1) a polydiorganosiloxane consisting of
diorganosiloxane units selected from the group
aonsisting of dimethylsiloXane units,
methylphenylsiloxane units, methylvinylsiloxane
units, and mixturas thereof, said
polydiorgano~iloxane being endbloaked with
et i ~n skh yl V ;/~ / t r ~ ~e~ l~ Y ~ s i~ l
~me~ v~ C~,~3*~ uIllts, ~ ~e-t~ ~ L o,ty
units, or siliaon-bonded hydroxyl groups, and
having a vinyl content of from 0.5 to-3 weight
percent;
(2) a tri~ot~lail~y-endblocked polysiloxane
containing methylhydrogensiloxane units and
optionally dimethylsiloxane units, which has a
viscosity of .from 0.005 to 0.05 Pa. 8 at 25C,
and which i6 present in an amount of from 2 to
parts by weight based on 100 parts by
weight of tl);
; (3) a platinum catalyst selected from the group
oonsisting of alcohol-modi~ied chloroplatinic
acid, chloroplatinic acid-olefin complexes, and
chloroplatinic acid-vinyl-siloxane coordination
compounds, which is present in an amou~t of
from 50 to 200 parts by weight platinum eleme~t
per million parts by weight of ~1); and
(4) an addition-reaation retarder, wh~ah i~ a~
alkynol or 3-methyl-3-pentene-1-yne an~ which
i~ present in an amount oE rom 0.1 part by
weight per 100 parts by weight o~ (1); and
(B) 0.1 to 5 part~ by weight, per 100 parts by weight by
(A), of a photosensitizer selected from ~he group
consisting of 4-allylaaetophenone, benzophenone,
benzoin ethyl ether, and banzil dimethyl ketal.
- 2b -
.
~ 72
- - Detailed Description of the Invention
The addition-curable organopolysiloxane compo-
sition which contains a platinum-type catalyst and which
comprises component (A) is a composition whose principal
- 2c -
. . ,' . :
~ .
components are organopolysiloxane containing silicon-bonded
alkenyl groups, organohydrogensiloxane, a platinum-type
catalyst, and an addition-reaction retarder and which may
contain organic solvents, extender fillers, thermal
stabilizers, flame retardants, etc., as optional com-
ponents.
The organopolysiloxane containing silicon-bonded
alkenyl groups, (A), preferably contains at least 2
silicon-bonded alkenyl groups in each moLecule from the
standpoint of curability. The molecular structure of
this organopolysiloxane can be straight chain, branched
chain, cyclic, or network and the degree of polymerization
is arbitrary. Examples of the alkenyl group are vinyl,
propenyl, and butenyl. The organic ~roups present in
this organopolysiloxane other than the alkenyl groups are
alkyl groups such as methyl, ethyl, propyl, hutyl, and
octyl; halogenated alkyl groups such as 3-chloropropyl,
and 3,3,3-trifluoropropyl; aryl such as phenyl; aral~yl
groups such as 2-ph0nylethyl and 2-phenylpropyl; and
alkaryl groups such as tolyl.
Examples of the preceding organopolysiloxane
are polydiorganosiloxanes such as dimethylvinylsilyl-
terminated polydimethylsiloxane, dimethylallylsilyl~
terminated polydimethylsiloxane, phenylmethylvinylsilyl-
terminated diphenylsiloxa~e-dimethylsiloxane copolymer,
trimethylsilyl terminated methylvinylsiloxane-dimethyl-
siloxane copolymer, silanol-terminated dimethylsiloxane-
methylvinylsiloxane copolymer, and dimethylvinylsilyl-
terminated polymethyl~3,3,3-trifluoropropyl)siloxane; and
examples of other organopolysiloxanes are polyvinylsil-
sesquioxane and copolymers of dimethylvinylsiloxane units
and SiO2 units.
.
The organohydrogenpolysiloxane (2) must contain
orgarlohydrogensiloxane or hydrogensiloxane units and can
be composed of only organohydrogensiloxane units or
hydrogensiloxane units or can contain other organosiloxane
units. At least 2 organohydrogensiloxane units must be
present in each molecule from the standpoint of curability.
The molecular structure of the organohydrogenpolysiloxane
can be straight chain, branched chain, cyclic, or network
and the degree of poymerization ls arhitrary. The
organohydrogenpolysiloxane (2) has a viscosity
range of ~rom 0.005 to 0.05 Pa's at 25C., and is
present in an amount of from 2 to 10 parts by weight
based on 100 parts by weight of organopolysiloxane ~1).
Examples of the preceding organohydrogenpoly-
siloxane are dimethylhydrogensilyl-terminatea dimethyl-
siloxane-methylhydrogensiloxane copolymer, trimethylsilyl-
terminated dime~hyl~iloxane-methylhydrogensiloxane
copolymer, dimethylphenylsilyl- erminated dimethylsiloxane-
methylhydrogensiloxane copolymer, trimethylsilyl-terminated
methylhydrogenpolysiloxane, and cyclic methylhydrogenpoly-
siloxane.
The mixing ratio of organopolysiloxane which
contains silicon-honded alkenyl to organohydrogenpoly-
siloxane is generally 0.1 to 10 moles silicon-bonded
hydrogen in ~2) per 1 mole silicon-bonded alkenyl group
in (1). Curing will be inadequate when this value is
less than 0.1 mole. When the above value exceeds 10
moles, hydrogen gas bubbles will be generated whlch
adversely affects the stability. However, the above
value may exceed 10 moles when a cured foamed product is
to be produced.
The platinum-type catalysts ~3) include finely
divided platinum particles, finely divided platinum
,
~ n~ 72
par~icles adsoxbed on a carbon powder ~upport, chloro-
platinic acid, alcohoL-modified chloroplatinic acid,
chloroplatinic acid-olefin complexes, chloroplatlnic
acid-vinylsiloxane coordination compounds, platinum
4a
B
, !~ '
,' .' ': . :
.
~2 !35~72
black, palladium, and rhodium catalysts. The quantity of
platinum-type catalys~ used is determined by the require-
ment that it can semi-cure the above organopolysiloxane
composition by heating at 50 to 100C and is generally 1
to 1,000 ppm~as platinum metal relative to the total
weight of the organopolysiloxane (1).
The addition-reaction retarder (4) is an
essential component which has the effect of inhibiting
the reaction at room temperature in order to impart pot
stability to the composition. Examples thereof are
alkynols such as 3-methyl-1-but~ne-3-ol, 3,5-di-
methyl-l-hexyne-3-ol, 3-methyl-1-pentyne-3-ol, and
phenylbutynol; 3-methyl-3-pentene-1-yne; 3,5-dimethyl-3-
hexene-l-yne; methylvinylsiloxane cyclics, and ben-
zotriazole. These compounds can be used as reaction
inhibitors singly or as mixtures of two or more com-
pounds. The quantity of addition-reaction retarder is
determined by the condition that a practical pot life be
imparted to the present composition. Although the
reaction-inhibiting ef~ect will depend on molecular
structure, this quantity is preferably 0.05 to 10 parts
by weight per 100 parts by weight organopolysiloxane (1)
and may be adjusted up or down depending on the purpose.
The photosensitizer comprising component (B)
accelerates the curing reaction of the present com-
position upon exposure to ultra~iolet radiation or an
electron beam and is a known compound usually used ~or
ultraviolet-curable resins. Examples are axomatic
ketones such as acatophenone, benzophenone, trimethyl-
silylated benzophenone, propiophenone, 3~methylacetophenone,
4-methylacetophenone, benzoin ethyl ether, dimethylpoly-
siloxane in which both ends are bonded through ether
linkages with benzoin,
' B
(4-isopropyl)phenyl-1-hydroxyisopropyl ketone, 4-allyl~
acetophenone, 3-benzylacetophenone, and ~-methoxyben-
zophenone; amine compounds such as triphenylamine; and
azo compounds such as azobisisobutyroni~rile.
The preceding photosensitizer must be used at
0.001 to 30 parts by weight and preferably 0.05 to 20
parts by weight per 100 parts by weight of the platinum
catalyst-containing, addition-curable organopolysiloxane
composition, component (A).
In the method of the present invention, the
photosensitizer-containing organopolysiloxane composition
consisting of the preceding components (A) and (B) is
converted into a rubbery elastomer or cured resin by
heating and by exposure to ultraviolet radiation or an
electron beam.
The heating conditions depend on the type of
preceding organopolysiloxane, the quantity of addition of
platinum-type catalyst and the thickness of the coated
film; however, the heating conditions are determined by
the requirement that the present composition be semi-cured
by the heat treatment alone. For example, the heating
temperature is 50 to 100C and the heating time is
several tens of seconds or less.
The ultraviolet-generating source is any such
source known in the prior art and examples thereof are
hydrogen discharge tubes, xenon discharge tubes, and low-
pressure, medium-pressure, and high-pressure mercury
lamps.
The electron beam source is any such source
known in the prior art and examples thereof are scanning
electron beam generators and curtain electron beam
generators.
:
'
' '
r~
The conditions of exposure to the ultraviolet
radiation or electron beam are arbitrary as long as
exposure alone can semi-cure the present composition.
With regard to the order of treatment, ultra-
violet or electron beam exposure can be executed after
the heat treatment, the heat treatment can be executed
after ultraviolet or electron beam exposure, or the heat
treatment and ultraviolet or electron beam exposure can
be executed simultaneously. However, when the composition
o~ the present invention is dissolved or dispersed in
organic solvent, it is preerably exposed to ultraviolet
radiation or an electron beam after the heat treatment.
According to the method of the present invention,
the composition is completely cured by a combination of
heating at low temperatures for a brief period with
ultraviolet or electron beam exposure for a brief period.
The composition is cured at temperatures much lower than
in a prior-art heat treatment alone and is cured in times
much shorter than in prior-art ultraviolet or electron
beam exposure alone. Process productivity is thus
increased and the mild heating conditions are appropriate
for applications such as in the electronic materials
industry, in coating synthetic resins and in the use of
release agents.
The present invention will be explained using
demonstrational examples. Parts in the examples are
parts by weight, % denotes wt~, and the viscosity was
measured at 25~C.
~ e 1
100 parts dimethylvinylsilyl-terminated dimethyl-
siloxane methylvinylsiloxane copolymer with a 1.0 Pa s
viscosity and a 2.0% vinyl group content were mixed with
~ 7~
8 parts trimethylsilyl-terminated methylhydrogenpoly-
siloxane with a 0.006 Pa-s viscosity, 0.3 part 3-methyl-
1-butyne-3-ol as the addition-reaction retarder, and 2
parts benzophenone as photosensitizer and this was then
combined with a vinylsiloxane-chloroplatinic acid complex
~100 ppm as platinum based on the total weight) and mixed
to homogeneity. The resulting composition, denoted as
Sample 1, had a viscosity of 0.81 Pa s.
To provide Comparison Example 1, a composition
was produced by the same method as for Sample 1 with the
exception that the benzophenone was omitted. ~he
resulting composition had a viscosity of 0.816 Pa s. In
addition, compositions for Comparison Examples 2 and 3
were prepared by the same method as for the preceding
Sample 1 by omitting the 3-methyl-1-butyne-3-ol or the
platinum catalyst, respectively. The composition of
Comparison Example 3 had a viscosity of 0.808 Pa s while
the composition of Comparison Example 2 gels in mixing
and its viscosity could not be measured.
When the preceding compositions was allowed to
stand at 25C, Sample 1 and the compositions of Comparison
Examples 1 and 3 did not exhibit an increase in viscosity
over 1 day and thus were quite stable.
Sample 1 and the compositions of Comparison
Examples 1 and 3 were each coated at 1.0 g/m2 on poly-
propylene film, heated in a hot air-circulation oven at
70C for 5 minutes, and then immediately irradiated with
a 160 W/cm high-pressure mercury lamp at a distance of 5
cm for 0~1 second. Sample 1 was completely cured while
the compositions of Comparison Examples 1 and 3 were not
cured. Sample 1 was not cured only by heating at 70C
for 120 seconds or only by exposure to ultraviolet
radiation under the same conditions as above.
.
` ~ '
'' , ` "` " '
' ~ ' , , ~
~ .
Example 2
100 parts dimethylvinylsilyl-terminated dimethyl-
siloxane-methylphenylsiloxane-methylvinylsiloxane copolymer
with a 3.0 Pa-s viscosity`(containing 1.8% vinyl groups
and 3.0% phenyl groups) were mixed with 8 parts trimethyl-
silyl-terminated dimethylsiloxane-methylhydrogensiloxane
copolymer with a viscosity of 0.02 Pa s (Si-bonded
H:methyl molar ratio=1:3~, 0.6 part 3-methyl-3-pentene-
1-yne addition-reaction retarder and 1.5 parts benzil
dimethyl ketal as photosensitizer, and this was then
combined with a vinylsiloxane-chloroplatinic acid complex
(180 ppm as platinum based on the total weigh-t) followed
by mixing to homogeneity. The resulting composition,
denoted as Sample 2, had a viscosity of 2.36 Pa~s.
- Compositions for Comparison Examples 4, 5, and
6 werP prepared by the same method as for the preceding
Sample 2 with the respective omission of the preceding
dimethylsiloxane-methylhydrogensiloxane copolymer, the
benzil dimethyl ketal photosensitizer, or the vinyl-
siloxane-chloroplatinic acid complex. The viscosities of
the samples were 2.92 Pa s for Comparison Example 4, 2.48
Pa s for Comparison Example 5, and 2.39 Pa-s for Comparison
Example 6.
When the preceding compositions were allowed to
stand at 25C for 1 day, they did not present an increase
in viscosity and were thus stable. Sample 2 and the
compositions of Comparison Examples 4, 5, ànd 6 were each
coated at 1.5 g/m2 on a polyethylene-laminated kraft
paper, irradiated with a 160 W/cm high-pressure mercury
lamp from a distance of 5 cm for 0.1 second and then
immediately heated in a hot air-circulation oven at 80C
for S seconds. Sample 2 was completely cured while the
compositions for Comparison Examples 4, 5, and 6 were not
,
, ~ .
jt,;~4;~
cured. Sample 2 was not cured only by heating at 80C
for 120 seconds or only by ultraviolet exposure under the
above-mentioned conditions.
Example 3
100 parts hydroxyl-terminated dimethylsiloxane-
methylvinylsiloxane copolymer gum with a 1.0~ vinyl group
content were dissolved in 1,000 parts toluene and this
was combined with 4 parts trimethylsilyl~terminated
methylhydrogenpolysiloxane with a 0.02 Pa-s viscosity,
0.2 part phenylbutynol as addition-reaction retarder, and
4 parts benzoin ethyl ether as photosensitizer ancl this
was then stirred to give a homogeneous solution.
An alcohol solution of chloroplatinic acid (60
ppm based on the total polysiloxane weight) was homo-
geneously dissolved in the preceding polysiloxane solution.
The resulting composition, denoted as Sample 3, had a
viscosity of 0.48 Pa s.
Compositions for Comparison Examples 7, 8, and
9 were prepared by the same method as for the preceding
Sample 3 with the respective omission of benzoin ethyl
ether, the alcohol solution of chloroplatinic acid, or -
phenylbutynol. The preceding compositions were allowed
to stand at 25C for 1 day. Sample 3 and the com-
positions of Comparison Examples 7 and 8 did not present
an increase in viscosity. The composition of Comparison
Example 9 underwent an increase in viscosity and com-
pletely gelled in 2 minutes after combination with the
alcoholic chloroplatinic acid and the attempt to stir to
homogeneity.
Sample 3 and the compositions of Comparison
Examples 7 and 8 were each coated at 1.2 g/m2 as solids
on aluminum plates. The toluene was evaporated at room
. .
,
rd~a~
temperature and the compositions were then heated in a
hot air-circulation oven at 70C for 5 seconds and then
immediately irradiated with a 160 W/cm high-pressure
mercury lamp from a distance of 5 cm for 0.07 seconds.
Sample 3 was completely cured while the compositi~ns of
Comparison Examples 7 and 8 were not cured. The com-
positions of Comparison Examples 7 and 8 were not cured
by irradiation with the mercury lamp for 5 seconds under
the above conditions.
Sample 3 was not cured only by heating at 70C
for 120 seconds or only by irradiation with ultraviolet
radiation under the above conditions.
Example 4
100 parts trimethylsilyl-terminated dimethyl~
siloxane-methylvinylsiloxane copolymer 10 Pa s viscosity,
1.7~ vinyl group content) were combined with 10 parts
fumed silica and heated at 160C for 2 hours. This
mixture was then dissolved in 200 parts toluene and then
combined and mixed with 5 parts trimethylsilyl-terminated
methylhydrogenpolysiloxane with a 0.04 Pa-s viscosity,
0.4 part 3-methyl-1-butyne-3-ol, and 4 parts ~enzophenone
as photosensitizer to give a homogeneous solution. The
resulting mixture was then combined with vinylsiloxane-
chloroplatinic acid complex (180 ppm as platinum based on
the entire quantity of polysiloxane~ and ~ixed to homo-
geneity. The resulting composition, denoted as Sample 4,
had a viscosity of 0.29 Pa s.
For Comparison Example 10l a composition was
prepared by the same method as above with the use of a
trimethylsilyl-terminated polydimethylsiloxane with a lO
Pa s viscosity instead of the dimethylsiloxane-methyl-
vinylsiloxane copolymer used for Sample 4.
,
Sample 4 and the composition of Comparison
Example 10 were allowed to stand at 25C for 2 days;
however, they did not present an increase in viscosity.
These compositions were each coated at 1.1 g/m2
as solids on polyester film, heated in a hot air-
circulation oven at 70C for 5 seconds and then immediately
irradiated with a 160 W/cm high-pressure mercury lamp
from a distance of 5 cm for 0.1 second. Sample 4 was
completely cured while the composition of Comparison
Example 10 was not cured. In addition, Sample 4 was not
cured only by heating at 70C for 120 seconds or only by
ultraviolet irradiation under the above conditions.
Example 5
100 parts dimethylvinylsilyl-terminated climethyl-
siloxane-methylvinylsiloxane copolymer with a viscosity
of 1.5 Pa s and containing 2.0% vinyl groups were combined
with 5 parts trimethylsilyl-terminated methylhydrogenpoly-
siloxane with a viscosity of 0.01 Pa s, 0.3 part,
3,5-dimethyl-1-hexyne-3-ol, and 0.5 part 4-allylaceto-
phenone as photosensitizer and mixed to give a solution.
The resulting solution was combined with vinyl-
siloxane-chloroplatinic acid complex (120 ppm as platinum
based on the total weight) and this was mixed to homogen-
eity. The resulting composition, denoted as Sample 5,
had a viscosity of 1.31 Pa s. For Comparison Example 11,
a composition was prepared by the same method as used for
Sample 5 with the exception that the vinylsiloxane-chloro-
platinic acid complex was omitted. ~ample 5 and the
composition of Comparison Example 11 were both allowed to
stand at 25C for 2 days; however/ they did not exhibit
an increase in viscosity. These compositions were each
coated at 0.8 g/m on polyester film, ~eated in a hot
12
. . .. .. .
'. ~ '. ' ', ' ' :
-
. - ~
,, . ~'. , '. :
, : : '
.
. .
.
air-circulation oven at 70C for 4 seconds and then
immediately irradiated with a 1 Mrad electron beam does
from a curtain eleetron beam generator. Sample 5 was
completely cured while the eomposition of Comparison
Example 11 was not completely eured. In addition, the
cured product o~ Sample 5 did not have an undesirable
odor.
