Note: Descriptions are shown in the official language in which they were submitted.
~ 3 ~ 5 4 ~ ~ 60SI 963
NOVEL SILICONE ADHESIVES AND METHQDS
FOR MAKING AND USING
Background of the Invent~on
The present invention relates to silicone adhesive composi-
tions and methods for making and using such compositions. Moreparticularly, the present invention relates to silicone adhe-
sives comprising an acrylic-functional organopolysiloxàne, a
reactive diluent and a polymerization initiator.
Over the past few years a new class of adhesive or bonding
agent has been developed which offers as its main advantage a
simple no mix application method and rapid bond formation at
ambient temperature. These materials are modi~ied acrylic
systems and are based on new modifying reactive polymers and a
sur~ace-applied activator which catalyzes the polymerization of
the reactive polymers. Application methods are similar to those
used for contact adhesives; the adhesive base (e.g. reactive
polymer and reactive diluent or monomer) is applied to one
substrate surface and the activator is applied to the other
substrate~sur~ace. The two surfaces are then brought together
and held until handling strength is reached.
Generally an elastomeric polymer is colloidally dispersed in
a monomer or a monomer/oligomer/polymer solution. The system is
then polymerized using a ~ree radical mechanism, What occurs is
a rapid, in situ polymerization of a (typically) methyl
methacrylate system, toughened by elastomeric domains that have
been incorporated into the structure by grafting.
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60SI-963
An example of such a reactive adhesive is described in
Bachman, U.S. Patent No. 4,34~,503. Brielly, this composition
comprises 40 to 90 parts per hundred of an acrylic ester
monomer capable of free radical polymerization and 60 to lO
parts per hundred of a monomeric polyacrylate ester prepolymer
having terminal acrylate radicals linked by at least two
divalent polyurethane or polyureide groups, which is catalyzed
with an activator comprising l to lO parts per hundred of an
aromatic perester free radical precursor, 0 5 to lO parts per
hundred of an organic acid capable of cyclic tautomerism and up
to 500 parts per million of a soluble compound of a transition
metal cure accelerator. Bachman also states that it is conven-
tional to include small percentages of silane monomers to
increase moistfure resistance as wel) as to enhance bonding of
the adhesive to glass and similar surfaces.
One shortcoming of prior art reactive adhesives is that
they become brittle at low temperatures and, hence, are not
useful in many applications, such as aernspace, where the
adhesive must remain effective at temperatures as low as -50C
2C or more.
Another disadvantage of prior art reactive adhesives is
that they tend to discolor after extended exposure to ultra-
violet radiation, for example, from the sun.
Summary of the I_vention
It is one object of the present invention to provide
adhesive formulations that are useful over a broader tempera-
ture range than prior art adhesive compositions.
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It is another object of the present invention to
provide adhesive compositions which are substantially
unaffected by ultraviolet radiation.
Another object of the present invention is to
provide adhesive compositions capable oP producing high
levels of bond strength in very brief cure times under
either aerobic or non-aerobic conditions.
Still another object of the pre~ent invention is to
provide method~ for effecting adhesive bonding of two or
more substrates.
These and other objects will be obvious to the
artisan in view of the following description and
appended claims.
In accordance with the pr~sent invention there is
provided as an adhesivP composition, the combination of
an adhesive base and a catalyst, said adhesive base
comprising:
(a) an ePfective amount of acryliccontaining
sllane mono=er,
(b) an e*fective amount of acrylic-containing
polydiorganosiloxane; said acrylic-containing monomer
and said acrylic-containing polydiorganosiloxane
producing upon polymerization thereof an adhesive solid:
and
said catalyst system comprising:
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~3a- 60SI-963
(c) an amount of free radical precursor ef~ective
for cataly~ing the polymerization reaction of said
acrylic containing monomer and said acrylic-containing
polydiorganosiloxane.
In accordance with a praferred aspect of the
present invention there is provided s an adhesive
composition, the combination of an adhesive base and a
catalyst, said adhesiv~ base comprising:
~a) about lO to about 90 part~ per hundred of
` 10 acrylic-containing monomer, and
(b) about 90 to about 10 parts per hundred of
acrylic-containing polydiorganosiloxane, said
acrylic-containing monomer and said acrylic-containing
; polydiorganosiloxane producing upon polymerization
thereof an adhesive solid; and
: ~ said catalyst comprising:
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60SI-963,
(c) an amount of free radical precursor effective for
catalyzing the polymerization reaction of said acrylic-contain-
ing monomer and said acrylic-containing polydiorganosiloxane.
Preferably, the acrylic-containing monomer is a silane such
as methàcryloxypropyl bis (trimetbylsiloxy) methylsilane, the
acrylic-containing polydiorganosiloxane has from about 0.1 to
about 20 mole percent acrylir groups, and the catalyst is an
amine/aldehyde adduct.
There is also provided a method for the adhesive bonding of
at least two surfaces wherein the adhesive base is applied to
at least one of the surfaces to be bonded and the free radical
precursor is applied to at least one of the surfaces other than `
~ the surface(s) covered with the adhesive base. Contact of the
;~ adhesive base coated surface and the free radical precursor
coated surface generates free radicals so as to cause
- crosslinking of the acrylic-containing components of the
adhesive base.
Description of the Invention
There is provided by a preferred embodiment of the present
invention an adhesive composîtion comprising an adhesive base
~ component and a catalyst system, said adhesive base comprising:
:~ :
~ a) from about 10 to about 90 parts per hundred of
acrylic-containing monomer,
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60SI-963,
(b) from about 90 to about 10 parts per hundred of
acrylic containing polydiorganosiloxane, said acrylic-contain-
ing monomer and said acrylic-containing polydiorganosiloxane
producing upon polymerization thereof an adhesive solid; and
said catalyst system comprising:
(c) an amount of free radical precursor effective for
catalyzing the polymerization reaction of said acrylic-contain-
ing monomer and said acrylic-containing polydiorganosiloxane.
Acrylic-containing monomer ~a),also referred to as reactive
diluent, can ~e present in amounts ranging from about 10 to
about 90 parts per hundred o' the adhesive base. Preferably,
the reactive diluent i5 present in an amount, by weight,
ranging from about 25 to about 90 parts per hundred, and most
preferably is present in an amount of from about 40 to about 90
parts per hundred parts of adhesive base; e.g. components (a)
` and (b).
Suitable acrylate monomers are described in United -
States Patent Number 4j348,503 to Bachman which
patent issued September 7, ~9~82.: Briefly, the
acrylate monomers disclosed by Bachman are the reaction
products of acrylic and/or methacrylic acids with one or more
mono- or polybasic9 substituted or unsubstituted alkyl, aryl or
aralkyl alcohots. Typical of the acrylate monomers disclosed
by Bachman are hydroxyethyl methacrylate, tetraethyleneglycol
dimethacrylate~ hydroxyethyl acrylate and tetraethyleneglycol
diacrylate.
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60SI-963 -- -
Although organic acrylic-containing monomers can be
employed in the practice of the present invention, it has been
found that especially preferable acrylate monomers are silanes
- such as, for ex~mple, methacryloxypropyl bis (trimethylsiloxy)
methylsilane. As in the case of organic monomers, the silane
monomers are also often utilized as a mixture of monomers,
oligimers and cyclics. Other suitable acrylic-containing
silane monomers can, of course, be easily ascertained by the
artisan without undue experimentation. Further9 it should be
understood that mixtures of organic acrylate monomers, mixtures
of silane acrylate monomers, and mixtures of organic and silane
acrylate monomers are within the intended scope of the present
invention.
It is essential that component (b) of the adhesive base be
a polydiorganosiloxane having acrylic-functional groups.
Preferably, there is present from about lO to about 90 parts
acrylic-functional polydiorganosiloxane per lOO parts by weight
of adhesive base; e.s. components (a) and (b). More
preferably, acrylic-functional polydiorganosiloxane is present
in an amount ranging from about lO to about 75 parts by weight
and, most preferably, is present in an amount ranging from
about lO to about 60 parts by weight per lOO parts by weight of
adhesive base.
Acrylic-functional polydiorganosiloxanes are known in the
art and are readily available from many commercial sources.
Suitable acrylic-functional polydiorganosiloxanes are described
in U.S. Pat. Nos. 2,793,223 to Merker; 2,922,8D6 to Merker;
3,782,940 to Ohto et al.; 3,878,263 to Martin; -
.
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60S I -9 63
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and 4,035,355 to Baney et al. The prPferred poly-
siloxanes for practicing the present invention have acrylate~
functional siloxy units of the formula
(I) ~ CH~ - C - C - D - (CH ~ (Rl)n SiO3 n
R ~ 2
where R is hydrogen or methyl, Rl is a monovalent hydrocarbon
radical, x is an integer equal to 1 to ~ inclusive, and n has a
value of 1 or 2.
Acrylic-functional siloxy units of formula I are typically
copolymerized with siloxy units having the formula
Rl
(II) -- SiO
R1
,
where R' is as previously defined.
Preferably there is from about 0.1 to a~out 20 mole percent
of acrylic^functional siloxy units. More preferably there is
from about 0.5 to about lO mole percent of acrylic-functional
siloxy units and, most preferably there is from about 1 to
about S mole percent acrylic-functional siloxy units.
60SI 963. - -
--8--
The viscosity of acryllc-functional polydiorganosiloxane
(b) is not crît~cal bu~ preferably is ~rorn about 10 centipoise
at 25C to about 100,000 eentipoise at 25C. In more
preferable embodiments of the present invention the viscosity
ranges from about 100 cen~ipoise to abou~ 50,000 centipoise at
25C. Most preferably the viscosity of polydiorganbsil~xane
- (b) is from about lO00 centipoise to about 15,000 centipoise at
2~C.
: It is also intended for purposes of the present invention
that the term polydiorganosiloxane includes an amount of
organic units or blocks effective for imparting the
advantageous properties of organic polymers to the compositions
of the present invention. Such organic units can also have
acrylic functionality~ although this is not essential.
Furthermore, such polydiorganosiloxane-organic copolymers ean
be either random copDlymers or block copol~ners. Examples of
suitable organic units can be found in U.S. Pat. No. 4,34B,503
to Bachman and includes vinyl polymers, acrylic polymers,
polyester polymers and glycGl polymers. specially preferable
organic units are polyurethane units. It is also contemplated
that mixtures of polydiorganosiloxanes, mixtures of
polydioryanosilo%ane-organic copolymers, or mixtures of
polydiorganosiloxanes and polydiorganosiloxane-organic
copolymers can be utilized in the practice of the present
invention.
The catalyst system is based essentially upon an aromatic
perester free radical prec~rsor that will generally be capable
of activation by neating or, for example~ an amine/aldehyde
adduct. The aromatic perester catalyst is typified by t-butyl
; perbenzoate, although other aromatic peresters having catalytic
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60SI-953
properties and suitabl~ for use herein are known and will be
evident to those skilled in the art. For example, other
benzoic acid perester derivatives9 as well as peresters derived
from phthalic acid, chlorobenzoic acid and the like may be
suitable for practiFing the present invention.
In general the amount of catalyst used will be from about 1
to about 10 parts by weight and, preferably, from about 2 to
about 6 parts by weight, per hundred `parts by weight of
adhesive base.
If curing i5 to be effected at room temperature rather than
by heating it will be necessary to further include an activator
; in the catalyst system. The preferred activator is any
co~mercially available amine/aldehyde adduct which reacts with
the catalyst to produce the free radicals necessary to initiate
polymerization. Typical of such adducts are the rubber
vulcanization accelerators sold by R.T. ~anderbilt Company
under the trademarks VANAX 808 and VANAX 833. The artisan
will, of course, be able to determine other suitable activators
without undue experimentation.
The amount of amine/aldehyde activator employed is not
critical and generally will be that which is provided by
coating therewith one of the surfaces to be bonded. Of course,
the concentration should be sufficient to react with
substantially all of the catalyst present in the adhesive
Z5 composition and to insure migration throughout the adhesive
composition in a relatively short period of time. Typically,
the activator will be employed in a volumetric ratio of about
1:4 to the adhesive formulation.
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6ûS I -953
-10-
When a dramatically increased rate of cure is required
there may be further added to the adhesive compos~tion of the
present ln~ention certain dibasic acids as a cure accelerator.
Further, an increased cure rate is provided by both acrylic
S acid and methacrylic acid~
Another optional component is a transition metal cure
accelerator. These transition metal cure accelerators are
compounds of iron, copper, cobalt, manganese, tin, ti~anium,
chromium and antimony Preferably the compound will pro~ide
the metal in an oxidized valence state. Examples of suitable
transition metal cure accelerators are cobalt naphthalate,
cupric octoate, ferric sulfate, manganic sulfate and the like.
Other suitable compounds will be obvious to those skilled in
the art~
When used, the transition metal cure accelerator is
normally incorporated in small quantities, for example~ about 2
parts per hundred or less. Even amounts as low as 50 to 500
parts per million will have a significant effect on the rate of
cure. Of course, if the monomers employed in a particular
formulation are especially slow to polymerize, even larger
quant-ties of ~ransition metal cure acceterator can be used.
Because the metal accelerator can be included in the
adhesiYe base without causing premature curing, it can be
dispersed homogeneously throughout and, upon initiation of`the
reaction (by chemical or th~rmal means) the metal will be
immediately accessible to all reacti~e portions of the
co~position, thereby promoting uniform and complete curing.
This feature is especially valuable in applications in which
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60SI-963/
the surfaces to be bonded are spaced more than a minimum
distance from one another, for example, more than l5 or 20 mils
apart.
In addition to the foregoing principal components, other
materials may also be incorporated int~ the present
compositions. For example, it is conventional to include inert
fillers to improve impact resistance or to modify viscosity.
Other substances, such as dyes9 fire retardants, stabilizers,
plasticizers, antioxidants, and the like may also be included.
The adhesive compositions of the present invention are used
to bond two or more surfaces together by applying to at least
one of the surfaces the adhesive base as previously described.
Contact of the coated surface with a second surface to be
bonded thereto is effected; the perester catalyst is activated
to generate free radicals, and contact between the ~surfaces is
maintained for a period of time and under such conditions as to
effect curing of the adhesive composition. The method
preferably is one in which an amine/aldehyde adduct activator
is entployed; in which case the adduct is applied to the second
surface to be bonded.
In order to better enable those skilled in the art to
practice the present invention, the following examples are
provided by way of illustration and not by way of limitation.
All parts are by w~ight unless otherwise noted.
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605 I -963
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EXAMPL ES
- Example 1
In these examples an adhesive base was prepared with
varying amounts of methacryloxypropyl bis (trimethylsiloxy)
methylsilane reactive diluent (monomer/oligimer/cyclics) and
polydimethylsiloxane polymer having 2X methacrylic groups on
the polymer chain. To 100 parts by weight of the adhesive base
was added 4 parts by weight t-butylperbenzoate initiator, 0 or
3 parts by weight methacrylic acid accelerator and 0 or 1 part
by weight cobalt naphthalate. To this mixture was then added
; ~ - 25 parts by weight Vanox ~08 activator. The time required for
: gelation to occur was measured in order to determine preferred
ratios of the various ingredients. The results are set forth
in Table I.
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60S I -963, -
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Table I
- Expmt. ~1) ReactiYe (2) Methacrylic Naphth- Cure(3
No. Polymer Diluent Acid alate Time
la lO0 pts ~ ---- l week
lb " ---- 3 pts ~ l4 hrs
lc " ~ 3 pts . l pt 3 hrs
2a 75 pts 25 pts. ---- ---- l wk
2b " " 3 pts ---- 4.5 hrs
2c " " 3 pts l pt ~ 3.5 hrs
3a 50 pts 50 pts -~~~ ~~~~ l wk
3b " " 3 pts ---- :3.5 ~rs
3c " " 3 pts l pt 4.5 hrs
4a 25 pts 75 pts ~ l wk
; ~ 4b " " ~ 3 pts ---- : 2.5 h~rs
: 15 4c " ~ 3 pts l pt 9 hrs
: 5a ---- lO0 pts ---- ---- l wk :
., .
5b ~ " 3 pts ---- 1.3 hrs
, .
: 5c ---- " ; 3 pts; l pt 20 hrs~
~l) polydimethylsiloxane having 2X methacrylic groups
(2) methacryloxypropyl bis(trimethylsiloxy)methylsilane
: ~ (monomer/oligimer/cyclics)
(3) ~ime from iddition of activitor to gelation
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60SI-963
-14-
The properties of each of the foregoing adhesive materials
were studied and a polymer to reactive diluent ratio of 1:1 was
found to provide the most acceptable formulation for further
,
study.-
Example 2
In this example there was employed 50 parts by weight of
the polymer of example 1, 50 parts by weight of the reactive
diluent of example 1, 4 parts by weight t-butylperbenzoate, 25
parts by weight Vanox 808 accelerator, and the amount of
: ~ 10 methacrylic acid was varied to determine the effect on cure
: time. The results are set forth-in Table II.
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605 I -963
~15-
Table 11
Metyhacrylic Acld Cure Time
1 part 3.5 hours
3 parts 3.3 hours
. 6 parts 3.0 hours
9 parts 2 8 hours
~ .
12 parts ; 2.5 hours
: ~ 15 parts . 2.4 hours
18 parts : 2.2 hours
: 21 parts ~- 2.2 hours
24 parts 2.0 hours
:: :
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60SI-963 .
-16-
Although the gelation time continued to decrease, the
physical properties of the adhesive material began to
Jeteriorate when more than about 15 parts methacrylic acid were
included in the composition. Thus, 9 parts by weight
methacrylic acid were utilized-in the following examples, :
Example 3
In this example there was employed 50 parts by weight of
the polymer of example 1, 50 parts by weight of the reactive
diluent of example 1, 4 parts by weight t-butylperbenzoate, 9
parts by weight methacrylic acid, and the amount of activator
(Vanox 808) was varied to determine the effect on cure time.
The results are set forth in Table III.
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60S I -963
Table III
,
Activator Cure Time
. 25 parts : 1.5 hours
' ,, '' :
20 parts 1.3 hours
,
15 parts 1.1 hours
~: ~ lO parts : 0.8 hour
5 parts ~ 0.6 hour
4 parts : ~ : ~ 0.4 hour ~ :
.: :
:`~ : :3 parts: ~: 0.4 hour
,
~, . .
i : . 1:0 ~ 2 parts 0.17 hour
; ~ ~ l part ~ 0.17 hour
O.S part~ 0.25 hour
;~ : 0.25 part 0.25 hour ~ :
` These results illustrate that optimum cure time for this
formulation was obtained ~when 1 to 2 parts of activator are
:
; employed.
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60SI-953
-18-
Example 4
In this example there was employed 50 parts by weight of
the polymer of~ example 1, 50 parts by weight of the reactive
diluent of example 1, 9 parts by weight methacrylic acid, 2
parts by weight activator (Yanox 808) and the amount of
t-butylperbenzoate catalyst was varied to determine the eFfect
on cure time. The results are set forth in Table I~.
.
Table IV
t-bu_~lperbenzoateCure Time
- . _
l part lZ min~
2 parts 10.5 min.
3 parts , 10.5 min.
4 parts 10.5 min.
~ 5 parts 10.5 min.
10 parts 10 min.
15 parts 10 min.
These results show that it is merely necessary to provide
an effective amount of t-butylperbenzoate initiator as the cure
time is not significantly affected by including an excess of
2G catalyst.
