U.S. patent number RE32,889 [Application Number 06/918,820] was granted by the patent office on 1989-03-14 for thixotropic cyanoacrylate compositions.
This patent grant is currently assigned to Loctite Corporation. Invention is credited to Alan E. Litke.
United States Patent |
RE32,889 |
Litke |
March 14, 1989 |
Thixotropic cyanoacrylate compositions
Abstract
Cyanoacrylate compositions which employ fumed silicas treated
with polydimethylsiloxane or trialkoxyalkylsilane are stable and
exhibit an unexpectedly high thixotropic ratio. Such compositions
are useful in adhesive applications or, when stabilized so as to
prevent polymerizaton in contact with moisture, in latent
fingerprint developing applications.
Inventors: |
Litke; Alan E. (Naugatuck,
CT) |
Assignee: |
Loctite Corporation (Newington,
CT)
|
Family
ID: |
27062672 |
Appl.
No.: |
06/918,820 |
Filed: |
October 14, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
528275 |
Aug 31, 1983 |
04477607 |
Oct 16, 1984 |
|
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Current U.S.
Class: |
523/212; 524/850;
524/533; 525/295 |
Current CPC
Class: |
C09J
4/00 (20130101); C09J 4/06 (20130101); C08F
291/00 (20130101); C09J 4/00 (20130101); C08F
222/00 (20130101); C09J 4/06 (20130101); C08F
283/00 (20130101); C09J 4/06 (20130101); C08F
291/00 (20130101) |
Current International
Class: |
C09J
4/00 (20060101); C09J 4/06 (20060101); C08K
009/04 (); C08K 005/54 () |
Field of
Search: |
;523/212 ;524/850,533
;525/295 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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662626 |
|
May 1963 |
|
CA |
|
107993 |
|
Aug 1979 |
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JP |
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1392763 |
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Sep 1972 |
|
GB |
|
Other References
Chemical Abstracts, vol. 92: 95 114b, p. 31. .
Chemical Abstracts, vol. 91: 40 424c, p. 40. .
Chemical Abstracts, vol. 89: 2164754, p. 51. .
Chemical Abstsracts, vol. 89: 117907c, p. 547. .
"Instant Krazy Glue" Brochure, 2 pp., 1985, Krazy Glue Inc., N.Y.
10010..
|
Primary Examiner: Lilling; Herbert J.
Attorney, Agent or Firm: Vidas & Arrett
Claims
I claim:
1. In a composition comprising an .alpha.-cyanoacrylate ester
monomer and a thixotropic agent, the improvement comprising that
said composition is a non-flowable gel, said thixotropic agent is
present in an amount of 12% or less and is a fumed silica having a
surface treated with a trialkoxyalkylsilane and the said
composition has a 2.5 RPM Brookfield viscosity of about
1.times.10.sup.5 or greater.
2. A composition as in claim 1 wherein the silica surface is
treated with trimethoxyoctysilane.
3. A composition as in claim 1 comprising an organic polymer
dissolved in said monomer.
4. A composition as in claim 3 wherein said polymer is selected
from polyvinyl acetate polymers and copolymers, polyacrylates,
polymethacrylates and polycyanoacrylates.
5. A composition as in claim 1 stabilized so as to be
nonpolymerizable on contact with moisture.
6. A composition as in claim 3 wherein said polymer is present at
levels of between 1 and 15% by weight.
7. A composition as in claim 6 wherein said polymer is present at
levels of between 3 and 10% by weight.
8. A composition as in claim 7 wherein said polymer is
polymethylmethacrylate.
9. A composition as in claim 1 wherein said silica is present in an
amount between about 4 and 8% by weight.
10. A composition as in claim 9 wherein said silica is present in
an amount of about 6% by weight. .Iadd.
11. A composition as in claim 1 wherein the composition viscosity
is about 1.times.10.sup.5. .Iaddend. .Iadd.12. A composition
comprising:
an .alpha.-cyanoacrylate ester monomer; between 1 and 15% of a
polymeric thickener; and
an amount less than 12% by weight of the composition of a
trimethoxyoctylsilane treated fumed silica effective to form a
thixotropic gel. .Iaddend. .Iadd.13. A composition comprising:
an .alpha.-cyanoacrylate ester monomer;
between 1 and 15% of a polymeric thickener; and
an amount in the range of about 4%-8% by weight of the composition
of a trimethoxyoctylsilane treated silica, said amount of silica
effective to form a thixotropic gel. .Iaddend. .Iadd.14. A
composition comprising:
an .alpha.-cyanoacrylate ester monomer;
between 1 and 15% of a polymeric thickener; and
a trimethoxyoctylsilane treated silica having a surface area of
about 150 m.sup.2 /gm in an amount, less than 12% by weight of the
composition, effective to form a thixotropic gel. .Iaddend.
.Iadd.15. A composition as in claim 12 wherein the polymeric
thickener is polymethylmethacrylate. .Iaddend. .Iadd.16. A
composition as in claim 13 wherein said polymeric thickener is
polymethylmethacrylate and is present in the range of about
3%-10%. .Iaddend. .Iadd.17. A composition as in claim 16 wherein
the monomer is methyl or ethyl cyanoacrylate. .Iaddend. .Iadd.18. A
composition consisting essentially of:
methyl or ethyl cyanoacrylate;
between 1 and 15% by weight of the composition of
polymethylmethacrylate; and
about 4-8% by weight of the composition of a trimethoxyoctylsilane
treated silica. .Iaddend. .Iadd.19. A composition as in claim 18
which also includes a polymerization stabilizer. .Iaddend.
Description
BACKGROUND OF THE INVENTION
Cyanoacrylate adhesives based on esters of .alpha.-cyanoacrylic
acid have gained wide acceptance in recent years for a broad range
of industrial and consumer uses. The cyanoacrylate esters
themselves, however, are very low viscosity liquids which makes the
use of unfilled compositions difficult. Such compositions often
migrate from the bondline or are absorbed into porous surfaces.
Accordingly, there have been developed a variety of thickened
cyanoacrylate adhesive compositions which incorporate organic
polymers and/or inorganic fillers to reduce adhesive migration.
Examples of such compositions are described in U.S. Pat. Nos.
3,607,542; 3,896,077, 4,105,715, 4,180,913 and in Chemical
Abstracts 89:117907c; 89:216475u; 91:40425c; and 92:95114b.
In the art of thickened cyanoacrylates it is sometimes desirable
that the composition display thixotropic properties. Thus, under
high shear conditions the composition can be processed and easily
applied to the substrate but once applied, will display
significantly reduced migratory tendencies. It is also well known
that the inclusion of fumed silicas in many organic liquid
compositions positions produces thixotropic effects. The use of
such silicas has been reported in cyanoacrylate compositions.
At least certain of the prior art cyanoacrylate compositions
employing fumed silicas have displayed stability problems, however.
Thus U.S. Pat. No. 3,607,542 describes organically filled
cyanoacrylate compositions in which fumed silica is an optional
ingredient. These compositions are reportedly stable for only up to
4 hours. Furthermore, the same patent states that silica by itself
does not readily mix with cyanoacrylate monomer to form a
paste.
Cyanoacrylate formulations also occasionally find non-adhesive
applications. Thus, for instance, the vapors of methyl and ethyl
cyanoacrylates have found use for developing latent fingerprints in
law enforcement applications. For such applications it would be
desirable to develop a nonflowable form of cyanoacrylate monomer so
that small open containers of the monomer can be placed throughout
a room or automobile to release vapors without the danger of
accidental monomer spillage. Desirably the thixotropic additives
will also be kept to a minimum so as not to substantially reduce
the monomer vapor pressure.
In certain applications it has been discovered that hydrophobic
silicas produced by treatment of fumed silica with
dimethyldichlorosilane can be used to give thixotropic
cyanoacrylate compositions with improved stability. However, these
fillers add cure retarding strong acid to the cyanoacrylate
composition. Also, the thixotropic ratio of these silicas in
cyanoacrylate esters (the ratio of apparent viscosity is measured
under specified high and low shear conditions) is quite low.
Therefore, when very high thixotropic effects are desired, such as
when a pasty composition is desired, the amount of acid introduced
by the silica can substantially reduce the cure time of the
composition. Also, for latent fingerprint developing type
applications, higher silica levels may result in lower monomer
vapor pressures.
Commercially available fumed silicas are also known which have been
treated with hexamethyldisilazane. It has discovered that
thixotropy ratios are also very low for these materials and that at
least some of these materials tend to destabilize cyanoacryalte
compositions. The destabilization effect is thought to result from
residual ammonia or amine in the filler.
Accordingly there exists a need for a cyanoacrylate thixotrope,
stable to the cyanoacrylate monomer, which has a significantly
improved thixotropy ratio over dimethyldichlorosilane or
hexamethyldisilazane treated silicas, and which does not adversely
affect the fixture time of adhesive formulations.
SUMMARY OF THE INVENTION
The present application relates to cyanoacrylate compositions which
employ fumed silicas treated with a polydimethylsiloxane or a
trialkoxyalkylsilane as a thixotropic additive. It has been
unexpectedly found that such silicas when incorporated into
cyanoacrylate compositions do not adversely effect the stability of
the composition, display a significantly higher thixotropy ratio
than the previously mentioned treated silicas and, in adhesive
compositions, do not adversely effect fixture time even at levels
of about 10-12% where the compositions become pasty and very
difficult to stir or apply uniformly.
The inventive compositions may consist primarily of an
appropriately stabilized cyanoacrylate ester monomer and the
specified silica. However, it is preferred that a small amount of
an organic polymer such as polymethylmethacrylate be dissolved in
the monomer.
The inventive compositions are also useful in nonadhesive
applications such as nonflowable latent fingerprint developing
formulations.
DETAILED DESCRIPTION OF THE INVENTION
Fumed silicas which have been found to impart desired thixotropic
properties to the inventive compositions fall into two categories.
The first, and most preferred, are polydimethylsiloxane treated
silicas such as Cab-O-Sil N70-TS.[..TM..]..Iadd..sup..TM.
.Iaddend., sold by the Cabot Corporation. The silica has a carbon
content of 5 weight percent and a surface area of .[.70M.sup.2
/gm.]. .Iadd.70m.sup.2 /gm .Iaddend.according to the
manufacturer.
The second category of silicas usable in the inventive compositions
are trialkoxyalkylsilanes. An example is Aerosil
R805.[..TM..]..Iadd..sup..TM. .Iaddend., an experimental product
available from Degussa Corporation. Aerosil R805.[..TM..].
.Iadd..sup..TM. .Iaddend.is a trimethoxyoctylsilane treated silica
having a surface area of 150 m.sup.2 /gm.
The superior thixotropic performance of the inventive cyanoacrylate
compositions is best obtained at silica levels of about 4-8%. These
properties were demonstrated by comparative testing of an ethyl
cyanoacrylate formulation containing 6% of a 0.4-0.5 million mw
polymethylmethacrylate and 6% hydrophobic silica. The composition
was stabilized with 5 ppm methanesulfonic acid (MSA) approximately
2500 ppm hydroquinone and 5 ppm SO.sub.2. The formulations were
prepared with the aforementioned Cab-O-Sil N70-TS.[..TM..].
.Iadd..sup..TM. .Iaddend.and Aerosil R805.[..TM..]. .Iadd..sup..TM.
.Iaddend.as well as two hexamethyldisilazane treated silicas
(Tellenox 500.[..TM..]. .Iadd..sup..TM. .Iaddend.solb by Tulco,
Inc. and Wacker HDK 2000.[..TM..]. .Iadd..sup..TM. .Iaddend.sold by
Wacker-Chemie) and three-dimethyldichlorosilane treated silicas
(Aerosils R972.[..TM..]..Iadd..sup..TM. .Iaddend., R974.[..TM..].
.Iadd..sup..TM. .Iaddend.and R976.[..TM..]..Iadd..sup..TM.
.Iaddend., all sold by Degussa). Table I gives the results of
comparative Brookfield viscosity and acid level (calculated as ppm
MSA) determinations.
TABLE I
__________________________________________________________________________
Brookfield Viscosity 2.5 RPM 20 RPM helipath helipath Ratio Total
Comp. Silica (spindle) (spindle) 2.5/20 Acid
__________________________________________________________________________
A Cab-O-Sil N70-TS .[..TM..]..Iadd..sup..TM..Iaddend. 2.9 .times.
10.sup.5 (TE) 4.2 .times. 10.sup.4 (TE) 6.9 27 B Aerosil R805
.[..TM..]..Iadd..sup..TM..Iaddend. 1.4 .times. 10.sup.5 (TE) 2.8
.times. 10.sup.4 (TE) 5.0 32 C Tellenox 500
.[..TM..]..Iadd..sup..TM..Iaddend. 4.4 .times. 10.sup.4 (TE) 2.1
.times. 10.sup.4 (TE) 2.1 26 D Wacker HDK2000
.[..TM..]..Iadd..sup..TM..Iaddend. 3.3 .times. 10.sup.2 (TA) 3.0
.times. 10.sup.2 (TA) 1.1 29 E Aerosil R972
.[..TM..]..Iadd..sup..TM..Iaddend. 1.2 .times. 10.sup.4 (TC) 3.8
.times. 10.sup.3 (TC) 3.2 38 F Aerosil R974
.[..TM..]..Iadd..sup..TM..Iaddend. 2.1 .times. 10.sup.4 (TC) 5.2
.times. 10.sup.3 (TC) 4.0 40 G Aerosil R976
.[..TM..]..Iadd..sup..TM..Iaddend. 2.6 .times. 10.sup.4 (TC) 8.1
.times. 10.sup.3 (TC) 3.2 39
__________________________________________________________________________
As can be seen from the table, compositions A and B, which are
within the invention, show much higher low shear viscosity and
substantially higher thixotropic ratios than compositions C-G which
are not within the invention. It was also observed that, when
unagitated, compositions A and B were nonflowable gels whereas
compositions C-G were all ungelled and pourable.
Compositions similar to formulation E but compounded with
sufficient Aerosil R972.[..TM..]..Iadd..sup..TM. .Iaddend.to
produce non-flowable gels comparable to those of compositions A and
B in Table I have been prepared and have been observed to require
longer fixture times than those of compositions A and B. This is
believed to result from increased strong acid imparted by the
dimethyldichlorosilane treated silica. The significantly higher
acid numbers of compositions E-G is evidence that the
dichlorosilane treated silicas do contribute strong acid to the
cyanoacrylate formulations.
Both hexamethyldisilazine treated silicas had impractically low
thixotropic ratios as shown by Table I. Furthermore, at least one
of the hexamethyldisilazane treated silicas .[.appars.].
.Iadd.appears .Iaddend.to destabilize cyanoacrylate monomers.
Formulation C, which utilizes the Tellenox 500.[..TM..].
.Iadd..sup..TM. .Iaddend.silica polymerized in less than one day in
a sealed tube at 82.degree. C. while compositions A, B and D-G all
lasted at least 15 days under the same conditions.
It is preferred that the cyanoacrylate compositions of the
invention include a minor amount of dissolved organic polymer.
Suitable polymers include polyacrylates and polymethacrylates,
polycyanoacrylates such as poly(ethyl cyanoacrylate), and
poly(vinyl acetate) polymers and copolymers. The organic polymers
are preferably included witin the range of approximately 1-15% of
the composition by weight. Preferably, the organic polymers are
included in the range of 3-10%. The inclusion of the organic
polymer is recommended in order to prevent or significantly
diminish the settling out of the silica from the inventive
compositions. The compositions containing dissolved polymer are
also observed to produce higher viscosities at equivalent silica
concentrations and to recover thixotropic behavior faster after
agitation than without dissolved polymers.
Other additives, conventional within the cyanoacrylate formulation
art, may be included within the compositions of the invention
without departing from the teaching hereof. Examples of such
additives need not be specified since they are within the skill of
those working in the art.
As mentioned above, it would be desirable for latent fingerprint
developing applications to have a nonflowable form of cyanoacrylate
with high vapor pressure. Gel compositions of the invention which
have been stabilized to the point where they will not polymerize on
contact with moisture are especially useful for such applications.
The gel form pevents spillage and the over-stabilization guards
against bonding of fingers ("finger-stick") are other articles. A
typical such formulation includes 88% methylcyanoacrylate
stabilized with 0.2% methane sulfonic acid and 2500 hydroquinone,
6% polymethylmethacrylate and 6% polydimethylsiloxane treated
silica.
From the foregoing it can be seen that the invention is not limited
by the specific examples set forth above, the invention being
limited only as set forth in the following claims.
* * * * *