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| United States Patent |
5,744,514
|
|
Shustack
|
April 28, 1998
|
Coated optical fibers having a reduced content of extractable and
volatile material
Abstract
Coated optical fibers with radiation-curable coatings which include
mercaptofunctional oligomers are disclosed. Specifically, the coatings may
comprise the cured reaction products of mercapto-terminated urethane
oligomers of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 3,000 daltons,
particularly in combination with one or more (meth)acrylate-terminated
urethane oligomers; monomer diluents; and optional silane adhesion
promoter, photoinitiator and stabilizers. The coatings, when cured,
exhibit a percent extractables content, as obtained by Soxhlet extraction,
of no more than about 15%, and preferably of no more than about 8%, and a
volatiles content, as obtained by thermogravimetric analysis, of less than
about 7%, and preferably less than about 3%. Processes for preparing such
coated optical fibers and the coatings per se are also disclosed.
| Inventors:
|
Shustack; Paul J. (West Chester, OH)
|
| Assignee:
|
Borden Chemical, Inc. (Columbus, OH)
|
| Appl. No.:
|
740664 |
| Filed:
|
October 31, 1996 |
| Current U.S. Class: |
522/42; 385/123; 385/128; 385/145; 428/378; 428/392; 522/44; 522/79; 522/90; 522/96 |
| Intern'l Class: |
C08J 007/04; G02B 006/02 |
| Field of Search: |
385/122-128,141-145
525/454
522/90,97,96,42,44,79
428/425.6,378,392
427/501,513
|
References Cited [Referenced By]
U.S. Patent Documents
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| 3711451 | Jan., 1973 | Caontos | 260/79.
|
| 3714290 | Jan., 1973 | Kehr et al. | 260/858.
|
| 3729404 | Apr., 1973 | Morgan | 204/159.
|
| 3891327 | Jun., 1975 | Welch | 356/244.
|
| 4003868 | Jan., 1977 | Smith et al. | 260/21.
|
| 4045317 | Aug., 1977 | Larsen | 204/159.
|
| 4120721 | Oct., 1978 | Ketley et al. | 96/36.
|
| 4221646 | Sep., 1980 | Finelli et al. | 204/159.
|
| 4225695 | Sep., 1980 | Schuster et al. | 528/75.
|
| 4629285 | Dec., 1986 | Carter et al. | 350/96.
|
| 4642353 | Feb., 1987 | Berger | 548/431.
|
| 4710523 | Dec., 1987 | Lechtken et al. | 522/14.
|
| 4720529 | Jan., 1988 | Kimura et al. | 525/454.
|
| 4844578 | Jul., 1989 | Pierini et al. | 350/96.
|
| 4854666 | Aug., 1989 | Kohara et al. | 385/128.
|
| 4985472 | Jan., 1991 | Aosai et al. | 522/64.
|
| 5074643 | Dec., 1991 | Petisce | 385/12.
|
| 5082347 | Jan., 1992 | Akasaka et al. | 385/114.
|
| 5100929 | Mar., 1992 | Jochum et al. | 522/64.
|
| 5146529 | Sep., 1992 | Mizutani | 385/10.
|
| 5167882 | Dec., 1992 | Jacobine et al. | 264/22.
|
| 5181268 | Jan., 1993 | Chien | 385/128.
|
| 5208281 | May., 1993 | Glaser | 524/189.
|
| 5236967 | Aug., 1993 | Ohkawa et al. | 522/32.
|
| 5259060 | Nov., 1993 | Edward et al. | 385/128.
|
| 5334421 | Aug., 1994 | McNutt | 427/513.
|
| 5446821 | Aug., 1995 | Nonaka et al. | 385/128.
|
| 5459175 | Oct., 1995 | Woods et al. | 522/180.
|
| 5496870 | Mar., 1996 | Chawla et al. | 522/90.
|
| 5527835 | Jun., 1996 | Shustack | 522/42.
|
| 5538791 | Jul., 1996 | Shustack | 428/392.
|
| 5587403 | Dec., 1996 | Shustack | 522/42.
|
Primary Examiner: Palmer; Phan T. H.
Attorney, Agent or Firm: Roylance, Abrams,Berdo & Goodman, L.L.P.
Claims
What is claimed is:
1. A coated optical fiber having a reduced content of extractable and
volatile material, said coated optical fiber comprising (a) optical fiber;
and (b) a primary coating layer comprising the radiation-cured reaction
product of the following ingredients:
(1) from about 5 to about 40 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 7,000 daltons;
(2) from about 15 to about 70 percent by weight of one or more acrylate- or
methacrylate-terminated urethane oligomers which is the reaction product
of (i) a polyether polyol; (ii) a non-aromatic polyisocyanate; and (iii)
an endcapping monomer capable of providing an acrylate or methacrylate
terminus;
(3) from about 15 to about 70 percent by weight of one or more monomer
diluents selected from the group consisting of
(i) alkyl acrylate and alkyl methacrylate monomers having 6 to 18 carbon
atoms in the alkyl moiety;
(ii) monomers having (i) an aromatic moiety, (2) a moiety containing
acrylic or methacrylic unsaturation, and (3) a hydrocarbon moiety; and
(iii) mixtures thereof;
(4) from about 0 to about 3.0 percent by weight of an acrylate-functional
silane adhesion promoter which binds in with the primary coating
composition during cure; and
(5) from about 0 to about 10.0 percent by weight of a triacylphosphine
oxide photoinitiator,
all of said percentages being percentages by weight based on the weight of
all ingredients.
2. A coated optical fiber having a reduced content of extractable and
volatile material, said coated optical fiber comprising (a) an optical
fiber; and (b) a primary coating layer comprising the radiation-cured
reaction product of a composition comprising a mercapto-terminated
urethane oligomer of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 3,000 daltons.
3. The coated optical fiber of claim 2, wherein said mercapto-terminated
urethane oligomer in (b) is dimercapto-terminated and comprises from about
5 to about 50 percent by weight of the composition.
4. The coated optical fiber of claim 2, wherein, when the radiation-cured
primary coating layer (b) is subjected to Soxhlet extraction, a percent
extractable value of less than about 15% results.
5. The coated optical fiber of claim 2, wherein, when the radiation-cured
primary coating layer (b) is subjected to Soxhlet extraction, a percent
extractable value of less than about 8% results.
6. The coated optical fiber of claim 2, wherein, when the radiation-cured
primary coating layer (b) is subjected to thermogravimetric analysis
(TGA), a percent volatile value of less than about 7% results.
7. The coated optical fiber of claim 2, wherein, when the radiation-cured
primary coating layer (b) is subjected to thermogravimetric analysis
(TGA), a percent volatile value of less than about 3% results.
8. The coated optical fiber of claim 2, wherein said number average
molecular weight of the oligomer in (b) is at least about 6,000 daltons.
9. The coated optical fiber of claim 2, wherein said number average
molecular weight of the oligomer in (b) is at least about 7,000 daltons.
10. The coated optical fiber of claim 2, wherein said primary coating layer
(b) comprises the reaction product of, in addition of said
mercapto-terminated urethane oligomer, from about 10 to about 80 percent
by weight of one or more acrylate- or methacrylate-terminated urethane
oligomers.
11. The coated optical fiber of claim 10, wherein the acrylate- or
methacrylate-terminated urethane oligomer is a reaction product of (i) a
polyether polyol; (ii) a non-aromatic polyisocyanate; and (iii) an
endcapping monomer capable of providing an acrylate or methacrylate
terminus.
12. The coated optical fiber of claim 10 wherein said primary coating layer
(b) comprises the reaction product of, in addition of said
mercapto-terminated urethane oligomer and acrylate or
methacrylate-terminated oligomer, from about 10 to about 75 percent by
weight of one or more monomer diluents selected from the group consisting
of
(i) alkyl acrylate and alkyl methacrylate monomers having 6 to 18 carbon
atoms in the alkyl moiety;
(ii) monomers having (i) an aromatic moiety, (2) a moiety containing
acrylic or methacrylic unsaturation, and
(3) a hydrocarbon moiety; and
(iii) mixtures thereof.
13. The coated optical fiber of claim 12, wherein said monomer diluent is
selected from hexyl acrylate; hexylmethacrylate; ethylhexyl acrylate;
ethylhexylmethacrylate; isooctyl acrylate; isooctyl methacrylate; octyl
acrylate; octyl methacrylate; decyl acrylate; decyl methacrylate; isodecyl
acrylate, isodecyl methacrylate; lauryl acrylate; lauryl methacrylate;
tridecyl acrylate; tridecyl methacrylate; palmitic acrylate; palmitic
methacrylate; stearyl acrylate; stearyl methacrylate; C.sub.14 -C.sub.15
hydrocarbon diol diacrylates; C.sub.14 -C.sub.15 hydrocarbon diol
dimethacrylates; phenoxyalkyl acrylate; phenoxyalkyl methacrylate;
phenoxyalkyl alkoxylate acrylate; phenoxyalkyl alkoxylate methacrylate;
isobornyl acrylate; isobornyl methacrylate, dicyclopentenyl-acrylate;
dicyclopentenylmethacrylate; dicyclopentenyl ethoxylate acrylate;
dicyclopentenyl ethoxylate methacrylate; tetrahydrofurfuryl acrylate;
tetrahydrofurfuryl methacrylate; polyalkylene glycol nonylphenylether
acrylates; polyalkylene glycol nonylphenylether methacrylates; and
mixtures thereof.
14. The coated optical fiber of claim 12, wherein said monomer diluent is a
mixture of
(i) alkyl acrylate and alkyl methacrylate monomers having 6 to 18 carbon
atoms in the alkyl moiety; and
(ii) monomers having (i) an aromatic moiety, (2) a moiety containing
acrylic or methacrylic unsaturation, and (3) a hydrocarbon moiety.
15. The coated optical fiber of claim 10 wherein said primary coating layer
additionally comprises from about 0.1 to about 3.0 percent by weight of an
organofunctional silane adhesion promoter which binds in with the primary
coating during curing.
16. The coated optical fiber of claim 15, wherein said adhesion promoter is
selected from acrylate-functional silanes; amino-functional silanes;
mercapto-functional silanes; methacrylate-functional silanes;
acrylamido-functional silanes; alkyl-functional silanes; vinyl-functional
silanes; and mixtures thereof.
17. The coated optical fiber of claim 15, wherein said adhesion promoter is
selected from 3-acryloxypropyltrimethoxy-silane,
3-aminopropyltriethoxysilane, 3-methacryloxypropyl-trimethoxy silane,
3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxy silane, and
mixtures thereof.
18. The coated optical fiber of claim 15, wherein said adhesion promoter is
3-acryloxypropyltrimethoxysilane.
19. The coated optical fiber of claim 10 wherein said primary coating layer
additionally comprises a photoinitiator.
20. The coated optical fiber of claim 19, wherein the photoinitiator
comprises one or more triacyl phosphine oxides.
21. The coated optical fiber of claim 10 wherein said primary coating layer
additionally comprises from about 0.0001 to about 3.0 percent by weight of
a stabilizer selected from the group consisting of organic phosphates;
silanes; hindered phenols; amines and mixtures thereof.
22. The coated optical fiber of claim 21, wherein said stabilizer is
3-aminopropyltrimethoxysilane.
23. The coated optical fiber of claim 21, wherein said stabilizer is
thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate.
24. A coated optical fiber having a reduced content of extractable and
volatile material, said coated optical fiber comprising (a) an optical
fiber; and (b) a primary coating layer comprising the radiation-cured
reaction product of the following ingredients:
(1) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 3,000 daltons;
(2) from about 10 to about 80 percent by weight of one or more acrylate- or
methacrylate-terminated urethane oligomers;
(3) from about 10 to about 75 percent by weight of one or more monomer
diluents;
(4) from about 0 to about 3.0 percent by weight of an organofunctional
silane adhesion promoter which binds in with the primary coating
composition during cure; and
(5) from about 0 to about 10.0 percent by weight of a photoinitiator
all of said percentages being percentages by weight based on the weight of
all ingredients.
25. The coated optical fiber of claim 24, wherein, when the radiation-cured
primary coating layer (b) is subjected to Soxhlet extraction, a percent
extractable value of less than about 15% results.
26. The coated optical fiber of claim 24, wherein, when the radiation-cured
primary coating layer (b) is subjected to Soxhlet extraction, a percent
extractable value of less than about 8% results.
27. The coated optical fiber of claim 24, wherein, when the radiation-cured
primary coating layer (b) is subjected to thermogravimetric analysis
(TGA), a percent volatile value of less than about 78% results.
28. The coated optical fiber of claim 24, wherein, when the radiation-cured
primary coating layer (b) is subjected to thermogravimetric analysis
(TGA), a percent volatile value of less than about 3% results.
29. A primary coating composition for an optical fiber which comprises the
following ingredients:
(1) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 3,000 daltons;
(2) from about 10 to about 80 percent by weight of one or more acrylate- or
methacrylate-terminated urethane oligomers;
(3) from about 20 to about 75 percent by weight of one or more monomer
diluents,
(4) from about 0 to about 3.0 percent by weight of an organofunctional
silane adhesion promoter which binds in with the primary coating
composition during cure, and
(5) from about 0 to about 10.0 percent by weight of a photoinitiator
all of said percentages being percentages by weight based on the weight of
all ingredients.
30. A primary coating composition for an optical fiber which comprises a
mercapto-terminated urethane oligomer of number average molecular weight
as determined by gel permeation chromatography (GPC) of at least about
3,000 daltons.
31. A process for preparing a coated optical fiber comprising
(1) applying to an optical fiber a primary coating composition layer
comprising a mixture of the following ingredients:
(i) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 3,000 daltons;
(ii) from about 10 to about 80 percent by weight of one or more acrylate-
or methacrylate-terminated urethane oligomers;
(iii) from about 10 to about 75 percent by weight of one or more monomer
diluents;
(iv) from about 0 to about 3.0 percent by weight of an organofunctional
silane adhesion promoter which binds in with the primary coating
composition during cure; and
(v) from about 0 to about 10.0 percent by weight of a photoinitiator, all
of said percentages being percentages by weight based on the weight of all
ingredients and
(2) radiation-curing said coating in situ.
Description
BACKGROUND OF THE INVENTION:
The present invention relates to coated optical fibers whose
radiation-curable coatings have a reduced content of extractable and
volatile material.
Until recently, the optical fiber industry was concentrated on so-called
"long haul" applications, wherein optical fibers were used to traverse
long distances such as in transoceanic or transcontinental cables. In such
applications, optical fibers required shielding with voluminous protective
cabling material in sheltered subterranean or submarine environments and
thus were not directly exposed to environmental hazards.
A recent trend in the optical fiber market is in local area networks for
fiber-to-the-home uses. The fibers in such uses are directly exposed to
much harsher conditions than previous applications of glass fibers,
including severe temperature and humidity extremes. Consequently,
previously used coatings did not perform well under such adverse
conditions; hence, a need existed for the development of higher
performance coatings. Such coatings need to be able to withstand the above
conditions, i.e., to possess thermal, oxidative and hydrolytic stability,
and to protect the fiber over the long term, i.e., over twenty-five years'
time.
Optical fibers used for light transmission can be prepared which,
immediately after drawing, are exceptionally strong and have very few
intrinsic defects. However, such pristine fibers are very vulnerable and
easily flawed by exposure to environmental conditions including dust and
moisture. Even a small flaw can reduce the strength of a fiber by an order
of magnitude, rendering it brittle and easily broken by weak external
forces. Therefore, optical glass fibers have, in the prior art, been clad
with at least one resin coat immediately after their preparation, whose
minimum requirement is to protect the underlying pristine fiber from such
external forces.
Typically, at least two coating layers, a primary, or buffer coating layer
and a secondary coating layer, have been used. The inner, or primary,
coating is applied directly to the glass fiber and, when cured, forms a
soft, rubbery, compliant material which serves as a buffer to cushion and
protect the fiber by relieving the stresses created when the fiber is
bent, cabled or spooled. Such stress might otherwise induce microbending
of the fibers and cause attenuation of the light traveling through them,
resulting in inefficient signal transmission. The secondary coating is
applied over the primary coating, and must function as a hard, tough
protective outer layer, preventing damage to the glass fiber during
processing and use.
Certain characteristics are desirable for the primary coating layer. For
example, it must maintain adequate adhesion to the glass fiber during
thermal and hydrolytic aging, yet be strippable therefrom for splicing
purposes. The tensile modulus of the primary coating must be low to
cushion and protect the fiber by readily relieving the stresses on the
fiber which can induce microbending and consequent inefficient signal
transmission. This cushioning effect must be maintained through the
temperature range to which the fiber may be exposed throughout its
lifetime: thus, it is necessary for the primary coating to have a low
glass transition temperature (Tg). This low glass transition temperature
will ensure that the coating remains in its rubbery state throughout the
possible use temperature range.
The primary coating should also have a relatively high refractive index,
i.e., greater than that of the cladding material of the fiber to be
coated. This high refractive index allows for a refractive index
differential between the glass cladding and the primary coating. This
differential allows errant light signals to be refracted away from the
glass core.
Another requisite quality of the primary (buffer) coating is resistance to
moisture. Moisture will rapidly degrade the strength of the coating itself
as well as the underlying glass fiber under stress. The reaction is one of
hydrolysis and stress corrosion. Moisture will also adversely affect the
adhesion of the primary (buffer) coating to the glass, resulting in
possible delamination. It is therefore desirable for the coating to be as
hydrophobic as possible. Preferably, the primary coating should have a
water absorption value of less than 5% by weight, and more preferably less
than 2.5% by weight. Moreover, it should be resistant to solvent swelling,
i.e., it should swell less than about 40%, and, in some embodiments, less
than about 10%, when soaked in gasoline for about 4 hours at room
temperature.
Another important property of optical fiber coatings is that, when cured,
they have a low content of unbound material. While ultraviolet curable
materials are often referred to as 100% solids, they may still contain a
significant amount of chemically unbound material after the ultraviolet
cure. This unbound material can be extractable with solvent or water, or
it can be volatile under certain conditions. The presence of an
extractable or volatile component in optical fiber products can cause
problems which may be detrimental to the fibers; such potential problems
may manifest themselves throughout the lifetime of the optical fiber.
For instance, during production, chemically unbound materials may become
volatized in the presence of the high heat encountered in the ultraviolet
curing chamber of the fiber draw tower. This can create a smoke or fog
inside the center tube of the tower which can decrease the transmission of
ultraviolet light necessary for curing, resulting in incomplete cure of
the optical fiber coating.
If there are chemically uncured and unbound materials present in the cured
optical fiber coating materials, a potential exists for migration of these
materials to other areas of the optical fiber structure during the
lifetime of the fiber. For example, if the cured primary coating layer
contains unbound material, it may migrate or exude over time, either to
the glass coating interface, such that it may affect the coating adhesion
characteristics, or in the direction of the secondary coating, such that
it may enter it and potentially plasticize or soften it. Either event can
affect fiber performance. Likewise, chemically unbound materials present
in the secondary coating may migrate inward, deleteriously affecting the
properties of the primary coating, or outward, affecting the adhesion of
ink to the secondary coating. Similarly, if unbound materials are present
in optical fiber inks or matrix material, they can potentially move about
and cause, for example, harm to ribbon integrity or fiber breakout
properties.
Another potential detriment of chemically unbound material relates to the
physical properties of the remaining coating after the unbound material is
removed. It is very likely that optical fiber products will be exposed to
agents (for example heat, water, solvent or filling compounds) that are
capable of volatilizing or extracting chemically unbound material at some
point during the lifetime of the fibers. The coating may then undergo
shrinkage or embrittlement, both of which may induce stress on the fiber
and result in microbending and signal attenuation. Moreover, if the
unbound materials are volatile, an odor problem during storage can occur.
Many potential sources of chemically unbound species which appear as
extractable or volatile material in a cured ultraviolet curable coating
layer, ink, adhesive or matrix material exist. Since most fiber optic
formulations are urethane acrylate based, they may contain trace levels of
unreacted polyol, nonacrylated urethane, alcohol, residual water, solvent,
or other by-products of the reaction by which the acrylate materials are
manufactured.
Other sources of unbound material include shelf stabilizers,
photoinitiators, antioxidants, surface tension modifiers, release agents,
and coefficient of friction (COF) modifiers. Any material present in the
finished formulation that does not contain a chemically reacted group
could potentially be extractable or volatile.
Other chemically unbound materials may result from incomplete photocure
reaction, including unreacted monomer, oligomer, or other material that
may be extractable or volatile. Also, it is possible for the raw materials
to produce photo by-products or to polymerize only to a low molecular
weight polymer which may be extractable with solvent. Also, a significant
amount of the photoinitiator present in an ultraviolet curable formulation
does not chemically react into the polymer network during cure, and thus
is another source of chemically unbound material.
Moreover, an equilibrium amount of water will be present in all coatings
exposed to the atmosphere. This water will also appear as a volatile
material.
It has now been found that by using, in lieu of at least a portion of the
acrylate-terminated oligomers which typically predominate in optical fiber
coatings, a high molecular weight mercapto-terminated oligomer, the
extractable and volatile material content of cured optical fiber coatings
can be reduced significantly.
SUMMARY OF THE INVENTION
The invention is, thus, in one embodiment, a coated optical fiber including
a primary coating layer which is formulated such that, when it is
subjected to Soxhlet extraction, a percent extractable value of less than
about 8% results and, when it is subjected to thermogravmetric analysis, a
percent volatile value of less than 3% results. Stated differently, the
invention is a coated optical fiber having a reduced content of
extractable and volatile material, said coated optical fiber may comprise
(a) an optical fiber; and (b) a primary coating layer comprising the
radiation-cured reaction product of a composition comprising a
mercapto-terminated urethane oligomer of number average molecular weight,
as determined by GPC (gel permeation chromatography) , as described below,
of at least about 3,000 daltons, preferably at least about 6,000 daltons,
and more preferably at least about 7,000 daltons.
In another embodiment, the invention may be a primary coating layer which
comprises the radiation-cured reaction product of a composition comprising
a high molecular weight mercapto-terminated urethane oligomer, e,g., a
composition comprising the following ingredients
(1) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight (as determined by
GPC) of at least about 3,000 daltons;
(2) from about 10 to about 80 percent by weight of one or more acrylate- or
methacrylate-terminated urethane oligomers;
(3) from about 10 to about 75 percent by weight of one or more monomer
diluents;
(4) from about 0 to about 3 percent by weight of an organofunctional silane
adhesion promoter which binds in with the primary coating composition
during cure; and
(5) from about 0 to about 10 percent by weight of a photoinitiator, all of
said percentages being percentages by weight based on the weight of all
ingredients.
In still another embodiment, the invention is a process for preparing a
coated optical fiber comprising the following ingredients:
(1) applying to an optical glass fiber a primary coating composition layer
comprising
(i) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight (as determined by
GPC) of at least about 3,000 daltons;
(ii) from about 10 to about 80 percent by weight of one or more acrylate-
or methacrylate-terminated urethane oligomers;
(iii) from about 10 to about 75 percent by weight of one or more monomer
diluents;
(iv) from about 0 to about 3 percent by weight of an organofunctional
silane adhesion promoter which binds in with the primary coating
composition during cure; and
(v) from about 0 to about 10 percent by weight of a photoinitiator,
all of said percentages being percentages by weight based on the weight of
all ingredients, and
(2) radiation-curing said coating in situ.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention relates to coated optical fibers which are coated with a
particular radiation-cured primary coating layer composition. The fibers
which are coated may, for example, comprise a glass core and a glass
cladding layer. The core, for example, may comprise silica doped with
oxides of germanium or phosphorus and the cladding, a pure or doped
silicate such as fluorosilicate. Alternately, the fibers may comprise a
polymer-clad silica glass core. Examples of such polymer claddings include
organosiloxanes such as polydimethylsiloxane or a fluorinated acrylic
polymer. The primary coating layer should have, inter alia, the following
properties: moisture resistance; ease of coating and stripping; low
volatiles content; low modulus over the life of the fiber (i.e., less than
about 500 psi, so as to prevent signal attenuation from microbending); low
glass transition temperature; and long shelf life. It should, when cured
and subjected to solvent extraction as defined below, exhibit an
extractable content of less than about 15%, preferably less than about 11%
and more preferably no more than about 8%. Moreover, it should have a
volatiles content, as determined by TGA (thermogravimetric analysis) as
described below, of less than 7%, preferably less than 5%, and more
preferably less than 3%. The secondary coating should form a hard
protective layer; have a relatively high modulus and glass transition
temperature; and also be moisture resistant. Both coatings should be
transparent; nonmalodorous; fast curing; and remain adherent, even upon
aging in high heat and humidity environments.
The following components make up the primary coating layer composition
which, when cured, forms the primary coating layer of the invention.
(1) The Mercapto-Terminated Urethane Oligomer
The primary coating of the present invention includes the cured reaction
product of a composition comprising a urethane oligomer which is
mercapto-terminated, and preferably dimercapto-terminated, and has a
number average molecular weight (Mn) of at least about 3,000 daltons,
preferably at least about 6,000 daltons, and more preferably at least
about 7,000 daltons, as determined by gel permeation chromatography (GPC),
using tetrahydrofuran as solvent at 300.degree. C. at a flow rate of 1.0
ml/min and an injection volume of 100 .mu.l, and using a polystyrene
standard and a GPC PRO 3.13 IBM AT module. This mercapto-terminated
oligomer component comprises from about 5 to about 50 percent by weight of
the composition based on the total weight of all ingredients. Preferably,
this ingredient comprises from about 5 to about 40 percent, and more
preferably from about 10 to about 40 percent by weight of the composition,
based on total weight of the uncured coating composition.
If less than about 5 percent by weight of this component is used, the
extractable content of the cured coating layer may be too high; if more
than 50 percent is used, modulus is too low and a coating which is too
soft may result.
The mercapto-terminated urethane oligomer (1) is typically the reaction
product of (i) a polyol; (ii) a polyisocyanate, and (iii) an endcapping
monomer capable of providing at least one mercapto terminus.
The polyol (i) may be, inter alia, a polyether polyol, a hydrocarbon
polyol, a polycarbonate polyol, a polyisocyanate polyol, and mixtures of
these. The polyether polyol is typically based on a straight chain,
branched or cyclic alkylene oxide of about one to about twelve carbon
atoms. Polyether diols and triols are preferred because they confer good
solvent resistance and are relatively inexpensive. Such polyether polyols
include but are not limited to polytetramethylene polyol, polymethylene
oxide, polyethylene oxide, polypropylene oxide, polybutylene oxide,
isomers thereof, and mixtures thereof. A particularly preferred polyether
polyol comprises at least some units of polytetramethylene oxide and/or
polypropylene oxide. Not suitable are polyester polyols because they are
hydrolytically unstable. The polyol portion of the oligomer should have a
molecular weight sufficiently high as to result in a number average
molecular weight for the oligomer, as determined by GPC (gel permeation
chromatography) , as determined above, of at least about 4,000 daltons,
preferably at least about 6,000 daltons, and more preferably at least
about 7,000 daltons. Such high molecular weight is essential to achieve
the desirably low extractables values of the invention.
The polyol portion (i) is reacted with a polyisocyanate, preferably
aliphatic, containing from about 4 to 20 carbon atoms. Aliphatic
polyisocyanates are preferred because oligomers based on aromatic
polyisocyanates effect yellowing in the cured coating. Suitable saturated
polyisocyanates include isophorone diisocyanate;
dicyclohexylmethane-4,4'-diisocyanate; 1,4-tetramethylene diisocyanate;
1,5-pentamethylene diisocyanate; 1,6-hexamethylene diisocyanate;
1,7-heptamethylene diisocyanate; 1,8-octamethylene diisocyanate;
1,9-nonamethylene diisocyanate; 1,10-decamethylene diisocyanate;
2,2,4-trimethyl-1,5-pentamethylene diisocyanate;
2,2'-dimethyl-1,5-pentamethylene diisocyanate; 3-methoxy-1,6-hexamethylene
diisocyanate; 3-butoxy-1,6-hexamethylene diisocyanate;
omega,omega'-dipropylether diisocyanate; 1,4-cyclohexyl diisocyanate;
1,3-cyclohexyl diisocyanate; trimethylhexamethylene diisocyanate;
1,3-bis(isocyanatomethyl)cyclohexane; 1,4-diisocyanatobutane; biuret of
hexamethylene diisocyanate; norbornane diisocyanatomethyl
2,5(6)-bis(isocyanatomethyl)bicyclo ›2,2,1! heptane; and mixtures thereof.
Isophorone diisocyanate is the preferred aliphatic polyisocyanate.
Suitable (though less preferred) aromatic polyisocyanates include toluene
diisocyanate; diphenylmethylene diisocyanate; tetramethyl xylylene
diisocyanate; 1,3-bis(isocyanatomethyl)benzene; p,m-phenylene
diisocyanate; 4,4'-diphenylmethane diisocyanate; dianisidine diisocyanate
(i.e., 4,4'-diisocyanato-3,3'-dimethoxy-1,1'-biphenyl diisocyanate);
tolidine diisocyanate (i.e.,
4,4'-diisocyanato-3,3'-dimethoxy-1,1'-biphenyl diisocyanate); and mixtures
thereof. Of the aromatic polyisocyanates, toluene diisocyanate is
preferred.
The reaction rate between the polyol and the polyisocyanate may be
increased, e.g., by use of a catalyst in an amount of 100 to 200 ppm.
Suitable catalysts include dibutyl tin dilaurate, dibutyl tin oxide,
dibutyl tin di-2-hexoate, stannous oleate, stannous octoate, lead octane,
ferrous acetoacetate, and amines such as triethylamine,
diethylmethylamine, triethylenediamine, dimethylethylamine, morpholine,
N-ethyl morpholine, piperazine, N,N-dimethyl benzylamine, N,N-dimethyl
laurylamine, and mixtures thereof. A preferred catalyst is dibutyl tin
dilaurate.
The endcapping monomer (iii) is a hydroxyl-terminated aliphatic
monomercaptan or an aliphatic dimercaptan. Suitable such monomercaptan
monomers include hydroxyethyl mercaptan and hydroxypropylmercaptan.
Suitable dimercaptans include dimercaptoethane or dimercaptopropane. The
molar ratio of polyol, polyisocyanate and endcapping monomer is preferably
approximately 1:2:2, in the case of diol, or approximately 1:3:3, in the
case of triol, yielding an oligomer having at each of its termini a
mercaptan (thiol) group. Again, the entire oligomer has a number average
molecular weight (Mn) as determined by gel permeation chromatography
(GPC), per the method described above, of at least about 3,000 daltons,
preferably at least about 6,000 daltons, and more preferably at least
about 7,000 daltons.
Suitable commercially available mercapto-terminated oligomers include
PERMAPOL.RTM. P2-805, PERMAPOL.RTM. P2-850, PERMAPOL.RTM. P2-935, and
PERMAPOL.RTM. P2-985 all from Courtaulds Aerospace (formerly PRC),
Burbank, Calif. PERMAPOL.RTM. P2-935 is the most preferred of this group.
These oligomers are the reaction products of a polyether polyol, toluene
diisocyanate and alkylene dithiol. Properties of these monomers are
summarized below:
______________________________________
PERMAPOL .RTM. P2 OLIGOMER/
POLYMER
PROPERTY P2-805 P2-850 P2-935
P2-985
______________________________________
Appearance Light straw color, viscous liquid
Sulfur content, %
2.5-3.0 2.5-3.0 1.0-2.0
2.0-2.5
Number Average
8000 8000 9000 7400
Molecular weight (GPC)
Equivalent Weight
2100 2100 3700 3200
Viscosity, poise 25.degree. C.
2000 1400 1000 2800
Acidity, pH (H20 ext.)
6.5 6.5 6.5 6.5
Non-volatile content, %
99 96 99 99
Flash Point, PMCC, .degree.F.
309 124 309 309
Moisture content, %
0.1
Specific gravity, 25.degree. C.
1.04
Functionality 3.81 3.81 2.43 2.31
______________________________________
(2) The (Meth)acrvlate-Terminated Urethane Oligomer
The mercapto-terminated urethane oligomer is used in combination with one
or more acrylate- or methacrylate-terminated oligomers. These acrylate- or
methacrylate-terminated oligomers are capable of homopolymerization, but
in this invention, are at least partially coreacted with the
mercapto-terminated oligomers, above, to form the primary coating layer of
the invention.
More specifically, this acrylate- or methacrylate-terminated ingredient is
a wholly aliphatic urethane acrylate or methacrylate oligomer. Preferably,
it is based on an aliphatic polyether polyol, which is reacted with an
aliphatic polyisocyanate and either acrylated or methacrylated.
Alternatively, it may be based on any backbone which does not adversely
affect the cured coating. Other suitable examples of backbones include
hydrocarbon polyols, polycarbonate polyols, polyisocyanate polyols, and
mixtures of these. However, polyether polyol backbones are preferred,
because, in general, they have good solvent resistance and are relatively
inexpensive.
This component is chosen to confer good thermal and hydrolytic properties
on the cured coating, and to be somewhat non-yellowing.
The urethane acrylate or methacrylate oligomer comprises from about 10
percent to about 80 percent by weight of the uncured primary coating
material (composition), based on the total weight of the composition (all
ingredients present, required and optional). Preferably, this component
comprises from about 15 percent to about 70 percent, and more preferably
about 20 percent to about 60 percent by weight of the composition based
upon the total weight of all ingredients. If less than about 10 percent by
weight of this component is used, flexibility, elongation to break and
overall toughness will suffer. If more than about 80 percent by weight is
used, the viscosity of the composition may be undesirably high and thus
make application of the liquid composition difficult unless special
provisions, such as heating the application die, are made.
The acrylate- or methacrylate-terminated urethane oligomer utilized in the
present invention is the reaction product of (i) an aliphatic polyol; (ii)
an aliphatic polyisocyanate; and (iii) an endcapping monomer capable of
supplying a reactive terminus, either acrylate or methacrylate.
The polyol (i) may be an aliphatic polyol which does not adversely affect
the properties of the composition when cured. Examples again include
polyether polyols; hydrocarbon polyols; polycarbonate polyols;
polyisocyanate polyols; and mixtures thereof. Polyols which should be
limited or preferably excluded include polyester or epoxy backbones.
The oligomeric component may contain very small amounts of urethane
acrylates based on polyesters, but preferably contains only the above
kinds of oligomers, for optimal long term stability.
A representative polyether polyol is based on a straight chain, cyclic, or
branched alkylene oxide of from one to about twelve carbon atoms. The
polyether polyol may be prepared by any method known in the art.
Preferably, it has a number average molecular weight (M.sub.n), as
determined in this case by vapor pressure osmometry (VPO), per ASTM
D-3592, sufficient to give the entire oligomer based on it a molecular
weight of not more than about 6,000 daltons, preferably not more than
about 5,000 daltons, and more preferably not more than about 4,000
daltons. Such polyether polyols include but are not limited to
polytetramethylene polyol, polymethylene oxide, polyethylene oxide,
polypropylene oxide, polybutylene oxide, isomers thereof, and mixtures
thereof.
Representative hydrocarbon polyols which may be used include but are not
limited to those based on a linear or branched hydrocarbon polymer of from
600 to 4,000 molecular weight such as fully or partially hydrogenated
1,2-polybutadiene; 1,2-polybutadiene hydrogenated to an iodine number of
from 9 to 21; and fully or partially hydrogenated polyisobutylene.
Unsaturated hydrocarbon polyols are not desirable because the oligomers
made from them, when cured, are susceptible to oxidation.
Representative polycarbonate polyols include but are not limited to the
reaction products of dialkyl carbonate with an alkylene diol, optionally
copolymerized with alkylene ether diols.
The polyisocyanate component (ii) is non-aromatic. oligomers based on
aromatic polyisocyanates effect yellowing in the cured coating.
Non-aromatic polyisocyanates of from 4 to 20 carbon atoms may be employed.
Suitable saturated aliphatic polyisocyanates include but are not limited
to isophorone diisocyanate; dicyclohexylmethane-4, 4'-diisocyanate;
1,4-tetramethylene diisocyanate; 1,5-pentamethylene diisocyanate;
1,6-hexamethylene diisocyanate; 1,7-heptamethylene diisocyanate;
1,8-octamethylene diisocyanate; 1,9-nonamethylene diisocyanate;
1,10-decamethylene dissocyanate; 2,2,4-trimethyl-1,5-pentamethylene
diisocyanate; 2,2'-dimethyl-1,5-pentamethylene diisocyanate;
3-methoxy-1,6-hexamethylene diisocyanate; 3-butoxy-1,6-hexamethylene
diisocyanate; omega, omega'-dipropylether diisocyanate; 1,4-cyclohexyl
diisocyanate; 1,3-cyclohexyl diisocyanate; trimethylhexamethylene
diisocyanate; and mixtures thereof. Very small amounts of aromatic
polyisocyanates may be used; however, long term stability on aging may
suffer somewhat.
The reaction rate between the hydroxyl-terminated polyol and the
diisocyanate may be increased by use of a catalyst in the amount of 100 to
200 ppm. Suitable catalysts include but are not limited to dibutyl tin
dilaurate, dibutyl tin oxide, dibutyl tin di-2-hexoate, stannous oleate,
stannous octoate, lead octoate, ferrous acetoacetate, and amines such as
triethylamine, diethylmethylamine,triethylenediamine,dimethylethylamine,
morpholine, N-ethyl morpholine, piperazine, N,N-dimethyl benzylamine,
N,N-dimethyl laurylamine, and mixtures thereof.
The endcapping monomer (iii) may be one which is capable of providing at
least one reactive terminus and which preferably provides acrylate or
methacrylate termini. Suitable hydroxyl-terminated compounds which may be
used as the endcapping monomers include but are not limited to
hydroxyalkyl acrylates or methacrylates such as hydroxyethyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl
methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and so
forth.
A particularly preferred endcapping monomer is hydroxyethyl acrylate or
hydroxyethyl methacrylate.
The molar ratio of the polyol, diisocyanate and endcapping monomer is
preferably approximately 1:2:2.
Some commercially available oligomers which are suitable for the
(meth)acrylated oligomer component of this invention include but are not
limited to the following:
1. Echo Resins ALU-350 series resins, i.e., 350, 351, 352, 353 and 354,
from Echo Resins and Laboratory, Versailles, Mo., all polytetramethylene
polyol-based acrylated aliphatic urethane oligomers of increasing
molecular weight and viscosity and decreasing modulus with increasing
number in the series. Certain physical properties for this series of
resins are summarized below:
__________________________________________________________________________
ALU-350
ALU-351
ALU-352
ALU-353
ALU-354
__________________________________________________________________________
Density @ 20.degree. C. (g/cm.sup.3)
1.052 1.048 1.027
1.019 1.019
(lbs/gal)
8.76 8.73 8.55 8.49 8.49
Refractive Index
1.496 1.492 1.478
1.468 1.460
Viscosity @ 78.degree. F. (cps)
320,000
120,000
wax wax wax
@ 140.degree. F. (cps)
7,300 5,400 8,900
21,750
30,000-40,000
Color, Gardner
<1 <1 <1 <1 <2
Functionality
2 2 2 2 2
Percent Shrinkage,
3.6 2.8 1.7 1.3 1.1
Cured
Number Average
1,390 1,410 2,300
3,550 4,880
Molecular Weight (VPO)
__________________________________________________________________________
For these oligomers, number average molecular weight was determined by
vapor pressure osmometry (VPO) using a Knauer VPO, calibrated with benzil,
tetracosane and polystyrene standards, using toluene as solvent, for 3
minutes at 40.degree. C., zero balance of 9 and range of 8, using a
Universal probe.
In general, the lower molecular weight members of the series are preferred
because they are less waxy and easier to work with, and because the
compositions including them swell less when contacted with solvents which
they may encounter.
The methacrylate equivalents of these oligomers are equally suitable.
2. PURELAST.RTM. aliphatic urethane acrylate oligomers based on polyether
backbones, available from Polymer Systems Corporation, Orlando, Fla.
Suitable PURELAST.RTM. oligomers include 566, 566A, 569, 569A, 586, 586A,
590, 590A, 595 and 595A. This series of oligomers increases in modulus
with increasing number in the series. These oligomers are either
difunctional (no suffix) or monofunctional ("A" suffix). All of these
oligomers are sold neat.
Methacrylate analogs of these oligomers are suitable as well.
3. SARTOMER CN 980 and 981, both polyether-backboned aliphatic urethane
acrylates, also from Sartomer Company, Exton, Pa.
4. BR-372, BR-543, BR-571, BR-582, all polyether-backboned aliphatic
urethane acrylates, from Bomar Specialties, Winsted, Conn.
5. EBECRYL.RTM. 8800, EBECRYLO 270, and EBECRYL.RTM. 4826 oligomers, all
from UCB Chemicals Corporation, Smyrna, Ga., all aliphatic urethane
diacrylate oligomers based on polyethers.
EBECRYL.RTM. 8800 oligomer is diluted 10% with ethoxyethoxyethyl acrylate;
has a viscosity at 65.degree. C. of 8,000-18,000 cps and a Gardner Color
Index of 2 max. Its density is 8.75 pounds per gallon; its theoretical
molecular weight is 1,700. When cured it has a tensile strength of 3,150
psi; a tensile elongation of 83%, and a glass transition temperature of
48.degree. C.
EBECRYL.RTM. 270 oligomer, previously sold as EBECRYL.RTM. 4826 oligomer,
contains no diluent monomer; has a viscosity of 2,500-3,500 cps at
60.degree. C. and a Gardner Color Index of 2 max. Its density is 8.91
pounds per gallon; its theoretical functionality is 2 and its theoretical
molecular weight is 1,500. When cured it has a tensile strength of 1,200
psi, a tensile elongation of 87% and a glass transition temperature of
-27.degree. C.
Methacrylate equivalents of these oligomers may also be used.
6. UVITHANE.RTM. ZL-1178 oligomer from Morton Thiokol, Inc., Morton
Chemical Division, Princeton, N.J., polyether based aliphatic urethane
acrylate. This oligomer has a viscosity of 55-75 poises at 120.degree. F.
and 700-800 poises at 78.degree. F. and, when cured neat, has a tensile
strength of 325 psi and an ultimate elongation of 45%.
The methacrylate analog of this monomer may be used as well.
7. EBECRYL.RTM. 4842, which is a silicone-modified polyether-based
aliphatic urethane acrylate, sold neat, and EBECRYL.RTM. 19-6264, which is
not silicone-modified, but which is a polyether-based aliphatic urethane
acrylate and which contains about 15% by weight of 1,6-hexanediol
diacrylate as a reactive solvent, both from UCB Chemicals Corporation,
Smyrna, Ga.
8. Hydrocarbon polyol-based aliphatic urethane acrylate oligomers such as
are disclosed in U.S. Pat. No. 5,146,531, issued to Applicant. The content
of that patent is expressly incorporated herein by reference. These
oligomers are based on a linear or branched hydrocarbon polymer of from
600 to 4,000 molecular weight such as fully or partially hydrogenated
1,2-polybutadiene; 1,2-polybutadiene hydrogenated to an iodine number of
from 9 to 21; and fully or partially hydrogenated polyisobutylene.
9. Furthermore, any aliphatic urethane acrylate or methacrylate oligomer of
the type exemplified above is believed to be suitable so long as the
desirable properties of the claimed composition are not adversely
effected.
The cured primary coating of this invention has a water absorption value of
less than about 5% by weight, and preferably less than about 3%.
Furthermore, the cured material should swell less than 40% in length, and,
in some embodiments, less than about 30% in length, when soaked in
gasoline for about 4 hours at room temperature.
(3) The Monomer Diluent
The monomer diluent component which is reacted with the above-described
oligomer in preparing the primary coating layer of the invention is
selected to be one that is compatible with the oligomers above. It should
be reactive with both of the above-described oligomers, and preferably has
one or more acrylate or methacrylate moieties per monomer. The monomer
diluent is capable of lowering the Tg (glass transition temperature) of
the cured composition including it, and of lowering the viscosity of the
uncured (liquid) composition to within the range of about 1,000 to about
10,000 cps (centipoises) at 250.degree. C., preferably about 4,000 to
about 8,000 cps, as measured by a Brookfield viscometer, Model LVT,
spindle speed #34, at 25.degree. C. If a viscosity higher than about
10,000 cps results, the liquid (uncured) composition including it may
still be useful if certain processing modifications are effected (e.g.,
heating the dies through which the liquid coating composition is applied).
The monomer diluent comprises about 10 to about 75 percent, preferably
about 15 to about 70 percent, and more preferably about 20 to about 65
percent by weight of the uncured (liquid) composition, based on the total
weight of the composition (all ingredients) . If less than about 10
percent of the monomer is present, viscosity may, again, be too high;
conversely, if more than 75 percent is present, viscosity would be too
low.
Suitable examples of monomer diluents include, but are not limited to,
aromatic-containing monomers such as phenoxyalkyl acrylates or
methacrylates (e.g., phenoxyethyl(meth)acrylate); phenoxyalkyl alkoxylate
acrylates or methacrylates (e.g., phenoxyethyl ethoxylate (meth)acrylate
or phenoxyethyl propoxylate(meth)acrylate); or one of any other such
monomer diluents known to adjust the refractive index of a composition
including it. Combinations including one or more of these are suitable as
well. Such monomer diluents belonging to the later category are disclosed
and described in U.S. Pat. No. 5,146,531 of Applicant herein incorporated
by reference and may, for example, contain (1) an aromatic moiety; (2) a
moiety providing a reactive (e.g., acrylic or methacrylic) group; and (3)
a hydrocarbon moiety.
Samples of aromatic monomer diluents additionally containing hydrocarbon
character and a vinyl group include but are not limited to polyalkylene
glycol nonylphenylether acrylates such as polyethylene glycol
nonylphenylether acrylate or polypropylene glycol nonylphenylether
acrylate; polyalkylene glycol nonylphenylether methacrylates such as
polyethylene glycol nonylphenylether methacrylate or polypropylene glycol
nonylphenylether methacrylate; and mixtures of these.
Such monomers are, for example, available from Toagasei Chemical Industry
Company, Ltd., Tokyo, Japan under the trade names ARONIX.RTM. M111, M113,
M114 and M117, and from Henkel Corporation, Ambler, Pa., under the trade
name PHOTOMER.RTM. 4003.
Other suitable monomer diluents additionally include hydrocarbon alkyl
acrylates or methacrylates which are either straight chain or branched,
and may contain 8 to 18 carbon atoms in the alkyl moiety such as hexyl
acrylate; hexyl methacrylate; ethylhexyl acrylate; ethylhexyl
methacrylate; isooctyl methacrylate; octyl acrylate; octyl methacrylate;
decyl acrylate; decyl methacrylate; isodecyl acrylate; isodecyl
methacrylate; lauryl acrylate; lauryl methacrylate; tridecyl acrylate;
tridecyl methacrylate; palmitic acrylate; palmitic methacrylate; stearyl
acrylate; stearyl methacrylate; cetyl acrylate; cetyl methacrylate;
C.sub.14 -C.sub.15, hydrocarbon diol diacrylates; C.sub.14 -C.sub.15
hydrocarbon diol dimethacrylates; and mixtures of the above. Of these,
cetyl, lauryl and stearyl acrylates or methacrylates are most desired.
Also suitable are cyclic monomers such as isobornyl acrylate; isobornyl
methacrylate; dicyclopentenyl acrylate; dicyclopentenyl methacrylate;
dicyclopentenyl ethoxylate acrylate; dicyclopentenyl ethoxylate
methacrylate; tetrahydrofurfuryl acrylate; tetrahydrofurfuryl
methacrylate; and mixtures thereof.
Monomers which are unsuitable include hydrophilic ones such as n-vinyl
pyrrolidone and n-vinyl formamide. N-vinyl pyrrolidone, which has in the
past been widely used in optical fiber coating applications, is
particularly undesirable because it is hydrophilic and, on long term water
soaking, confers very poor water resistance. Moreover, it has been found
recently to be carcinogenic. Thus, the composition should be substantially
free of these monomers.
Preferred monomers include the refractive-index modifying type monomers as
disclosed herein, alone or in combination with an alkyl (meth)acrylate
such as lauryl acrylate.
Other Ingredients
(4) Adhesion Promoter
Also included in the composition which makes up the primary coating layer
may be, in some embodiments, an adhesion promoter. Adhesion becomes a
particularly pertinent problem in high humidity and high temperature
environments, where delamination is more of a risk. For uses protected
from such environments, an adhesion promoter may be required.
It is known in the art to use either acid-functional materials or
organofunctional silanes to promote adhesion of resins to glass. While
acid-functional materials are operative herein, organofunctional silanes
are preferred. Acid-functional materials are less preferred, however,
because of their possible corrosivity towards the materials, and their
tendency to lose their adhesion properties on exposure to moisture. (In
general, acid-functional materials should be avoided in the compositions
of the invention.) Silanes tend to be much more suitable in terms of these
factors and, therefore, are the adhesion promoters of choice.
Additionally, it is useful to have an adhesion promoter having a
functionality which binds in with the system during cure, again to
minimize the quantities of unbound volatiles. Various suitable
organofunctional silanes include but are not limited to
acrylate-functional silanes; amino-functional silanes; mercapto-functional
silanes; methacrylate-functional silanes; acrylamido-functional silanes;
allyl-functional silanes; and vinyl-functional silanes. The adhesion
promoters preferably are methoxy- or ethoxy-substituted as well. Preferred
organofunctional silanes include but are not limited to mercaptoalkyl
trialkoxy silane, (meth)acryloxyalkyl trialkoxy silane, aminoalkyl
trialkoxy silane, mixtures thereof, and the like. Methacrylated silanes
are desirable, inasmuch as they bind in well with the cured system, but
tend to slow the cure speed of the system down. The mercapto-functional
adhesion promoters also chemically bind in during cure, but do not
appreciably slow down the cure speed of the system.
Some preferred organofunctional silanes that enhance adhesion in humid
conditions include 3-acryloxypropyltrimethoxy silane,
vinyl-tris(2-methoxyethoxysilane), 3-methacryloxypropyltrimethoxy silane,
3-aminopropyltriethoxy silane, 3-mercaptopropyl trimethoxy silane and
3-mercaptopropyl(gamma-mercaptopropyl)triethoxy silane, and mixtures
thereof. A particularly preferred adhesion promoter is
3-acryloxypropyltrimethoxy silane.
The silane component should be incorporated into the composition which is
to be cured to form primary coating layer in a small but effective amount
to enhance the adhesion of the composition to the surface of the
substrate. The silane component comprises from about 0.1 percent to about
3.0 percent by weight of the composition, based on total weight of all
ingredients. Preferably, the silane comprises from about 0.2 percent to
about 2.0 percent, and more preferably from about 0.3 percent to about 1.0
percent, based on the total weight of the composition.
(5) The Photoinitiator
Another component of the composition which makes up the primary coating
layer may be a photoinitiator. The necessity for this component depends on
the envisioned mode of cure of the composition: if it is to be ultraviolet
cured, a photoinitiator is needed; if it is to be cured by an electron
beam, the material may comprise substantially no photoinitiator.
In the ultraviolet cure embodiment, the photoinitiator, when used in a
small but effective amount to promote radiation cure, must provide
reasonable cure speed without causing premature gelation of the
composition. Further, it must not interfere with the optical clarity of
the cured coating. Still further, the photoinitiator must itself be
thermally stable, non-yellowing, and efficient.
Suitable photoinitiators include, but are not limited to, the following:
hydroxycyclohexylphenyl ketone;
hydroxymethyl-phenylpropanone;dimethoxyphenylacetophenone;
2-methyl-1-›4-methyl
(thio)phenyl!-2-morpholino-propanone-1;1-(4-isopropylphenyl)-2-hydroxy-2-m
ethylpropan-1-one;1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one;
4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone;
diethyoxyacetophenone; 2,2-di-sec-butoxyacetophenone; diethoxy-phenyl
acetophenone; and mixtures of these.
A preferred class of photoinitiators are the triacylphospine oxides, such
as trimethylbenzoyldiphenylphosphine oxide (available from BASF Corp.,
Chemicals Division, Charlotte, N.C. as LUCIRIN TPO)
trimethylbenzoylethoxyphenylphosphine oxide (available from BASF as
LUCIRIN 8893); bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine
oxide (available from Ciba-Geigy Corp., Ardseley, N.Y.); and mixtures
thereof. The BASF phosphine oxides marketed as LUCIRIN TPO and LUCIRIN
8893, alone or, particularly, in combination, are preferred.
The photoinitiator, when used, preferably comprises from about 0.5 percent
to about 10.00 percent by weight of the uncured composition, based upon
the weight of the total composition. Preferably, the amount of
photoinitiator is from about 1.0 percent to about 6.0 percent. The
photoinitiator should be used at a level such that a cure speed, as
measured in a dose versus modulus curve, of less than 0.7 J/cm.sup.2, and
preferably less than 0.5 J/cm.sup.2, is obtained.
(6) Stabilizer
To improve shelf life (storage stability) of the uncured primary coating
composition, as well as to increase thermal and oxidative stability of the
cured primary coating layer, one or more stabilizers may be included in
the composition. Examples of suitable stabilizers include tertiary amines
such as diethylethanolamine and trihexylamine, hindered amines, organic
phosphites, hindered phenols, mixture thereof, and the like. Some
particular examples of antioxidants which can be used include
octadecyl-3-(3',5,'-di-tert-butyl-4'-hydroxyphenyl)propionate,
thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate, and
tetrakis ›methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)! methane.
Additionally, certain silanes in small quantities, e.g., as low as 0.0001
percent to 0.1 percent by weight, may be used as stabilizers. An example
of suitable such silane is 3-aminopropyl trimethoxy silane.
When a stabilizer is used, it may be incorporated in an amount from about
0.0001 percent to about 3.0 percent, based on the weight of the
composition. Preferably, it is included in the range from about 0.25
percent to about 2.0 percent by weight, and more preferably in the range
from about 0.5 percent to about 1.5 percent by weight, based on the total
weight of all of the ingredients. Desirable properties of a stabilizer
include (1) non-migration (probably enhanced by low polarity) and (2)
basicity (to allow it to help in neutralizing residual acid which might
prematurely initiate polymerization). Preferred stabilizers are
thiodiethylene bis(3,5-di-tert-butyl-4-hydroxy)hydrocinnamate and
3-aminopropyl trimethoxysilane.
The primary coating composition which makes up the primary coating layer of
this invention may either be topcoated with a secondary coating as known
in the art, or may, in some cases, if tailored to be suitable therefor, be
a monocoat wherein only this primary coating is required. A suitable
secondary optical fiber coating, when used, optimally possess good
thermal, oxidative and hydrolytic stability; hardness; high modulus; high
glass transition temperature; and high refractive index.
An optional secondary coating may be applied atop the primary coatings of
the invention. Suitable secondary coatings are those which are known in
the art, including but not limited to those disclosed in Applicant's U.S.
Pat. No. 5,352,712, issued Oct. 4, 1994 (expressly incorporated herein by
reference).
Such secondary coating may, for example, comprise the reaction product of
from about 10 percent to about 90 percent by weight of an aliphatic
urethane oligomer based on a polyester and/or polyether and containing a
reactive terminus; from about 20 percent to about 60 percent by weight of
a hydrocarbonaceous viscosity-adjusting component capable of reacting with
the reactive terminus of the oligomer; and optionally, from about 0.05
percent to about 10.0 percent by weight of a photoinitiator.
One preferred secondary coating may comprise the reaction product of from
about 40 percent to about 80 percent by weight of a mixture of aliphatic
urethane acrylate oligomers based on polyether backbones; from about 25
percent to about 50 percent by weight of a mixture of isobornyl acrylate
and hexanediol diacrylate; and from about 2.0 percent to about 7.0 percent
by weight of hydroxycyclohexylphenyl ketone photoinitiator.
Preparation of a Coated Optical Fiber
The invention also relates to a process for preparing a coated optical
fiber having a reduced content of extractable and volatile material. The
process comprises
(1) applying to an optical glass fiber a primary coating composition layer
comprising a mercapto-terminated urethane oligomer of number average
molecular weight of at least 3,000 daltons, e.g., a composition comprising
the following ingredients:
(1) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight (by GPC) of at least
about 3,000 daltons;
(2) from about 10 to about 80 percent by weight of one or more acrylate- or
methacrylate-terminated urethane oligomers;
(3) from about 10 to about 75 percent by weight of one or more monomer
diluents;
(4) from about 0 to about 3 percent by weight of an organofunctional silane
adhesion promoter which binds in with the primary coating composition
during cure; and
(5) from about 0 to about 10 percent by weight of a photoinitiator
all of said percentages being percentages by weight based on the weight of
all ingredients, and
(2) radiation-curing said coating in situ.
In one embodiment, the process comprises applying only the primary coating
composition of the invention to the optical fiber and radiation-curing the
coating in situ.
In an alternative embodiment, a secondary coating composition may be
applied atop the primary coating composition of this invention, and the
two coatings sequentially or simultaneously radiation cured.
The primary and/or secondary coatings may be applied and cured by any
method known in the art. A preferred method, whereby two coatings are
applied wet-on-wet, is disclosed in U.S. Pat. No. 4,474,830 to C. Taylor
of AT&T Bell Laboratories. The coating or coatings may then be cured in
situ, preferably by ultraviolet irradiation, to obtain a cured polymeric
coating. Alternatively, the primary coating may be applied and cured,
after which the secondary coating may be applied and cured.
The Primary Coating Composition of the Invention
In a preferred embodiment, the invention relates to a primary coating
composition for an optical fiber which comprises the cured reaction
product of the following ingredients:
(1) from about 5 to about 50 percent by weight of a mercapto-terminated
urethane oligomer of number average molecular weight as determined by gel
permeation chromatography (GPC) of at least about 3,000 daltons;
(2) from about 10 to about 80 percent by weight of one or more acrylate- or
methacrylate-terminated urethane oligomers;
(3) from about 10 to about 75 percent by weight of one or more monomer
diluents;
(4) from about 0 to about 3.0 percent by weight of an organofunctional
silane adhesion promoter which binds in with the primary coating
composition during cure; and
(5) from about 0 to about 10.0 percent by weight of a photoinitiator
all of said percentages being percentages by weight based on the weight of
all ingredients.
EXAMPLES
The following Examples serve to further illustrate the invention. In these
Examples and elsewhere throughout this application, all parts and
percentages are by weight, on a dry solids basis, and all temperatures are
in degrees centigrade unless expressly stated to be otherwise. In all of
the Examples, cure doses were measured with an International Light IL 390
radiometer. Unless otherwise noted, throughout the Examples and the
remainder of this application, "modulus" refers to 2.5% tensile modulus,
at 25.degree. C., measured using an Instron Model 1122 tensile tester, per
ASTM-D882.
All percent extractables values reported herein were obtained by Soxhlet
extraction as described below. A flask containing EM Science Omnisolv
grade methyl ethyl ketone (MEK) which is equipped with a side tube is
fitted with a preweighed 33 mm.times.30 mm Whatman single thickness
cellulose extraction thimble containing a sample of cured film. Each
thimble was filled with approximately five 31/2'.times.5'.times.6 mil
drawdowns. 180ml of methyl ethyl ketone (MEK), the extracting solvent, is
gently boiled (i.e., at about 80.degree. C.), such that the solvent vapor
passes up the side tube and its condensate drops onto the film sample and
slowly leaches out extractable material. The process is carried out for
approximately 16 hours, after which time the sample is dried in air to a
constant weight at 23.+-.2 C. and 50.+-.5% RH. The percent extractables
value is determined as the difference in weight of the sample before and
after the extraction and drying .times.100.
All TGA (thermogravemetric analysis) volatiles values reported herein were
obtained according to the following method. A sample of cured composition
was conditioned at 23.+-.2.degree. C. and 50.+-.5% relative humidity for
at least 16 hours. TGA analysis was conducted using a Perkin Elmer TGS-2
thermogravemetric analyzer. The analysis was done under nitrogen at a flow
rate of 50 cc/minute. The thermogravemetric analysis program was isothermal
at 25.degree. C. for a minute, heated at 35.degree. C./minute to
200.degree. C., then held isothermal at 200.degree. C. for 40 minutes.
Number average molecular weights were determined either by gel permeation
chromatography (GPC) or by vapor pressure osmometry (VPO), as indicated
below, unless otherwise indicated. When determined by GPC, the measurement
was made in THF solvent; at a flow rate of 1.0 ml/min and an injection
volume of 100 .mu.l, using a GPC PRO 3.13 IBM AT module. When determined
by VPO it was performed using a Knauer VPO, calibrated with benzil,
tetracosane and polystyrene standards, using toluene as solvent, for 3
minutes at 40.degree. C., zero balance of 9 and range of 8, using a
Universal probe.
As in the remainder of the application, parts by weight in the Examples
refers to the total composition described in that Example, including all
ingredients, whether required or optional. The optional ingredients are
identified by an asterisk (*) in the Examples. It should be noted that,
although the specification teaches that the photoinitiator is optional, it
is required in the Examples, all of which employ ultraviolet cure. The
other components may be essential for use, if the exemplified coating is
to meet the rigorous requirements for a commercially acceptable coating
for optical glass fiber.
EXAMPLE 1
A Composition Which, When Cured, Comprises About 7.43 Percent Extractables
and Low Volatiles
The following composition was made up:
______________________________________
Ingredient Percent by Weight
______________________________________
PERMAPOL .RTM. P2-935 mercapto-terminated
27.00
urethane oligomer, average mercapto functionality of
2.43, number average molecular weight (GPC) of
about 9000 daltons, from Courtaulds Aerospace,
Burbank, CA
ALU-351 polytetramethylene polyol-based acrylated
20.00
aliphatic urethane oligomer of number average
molecular weight (VPO) of about 1,410 daltons,
from Echo Resins and Laboratories, Versailles, MO
PURELAST .RTM. 590 aliphatic urethane diacrylate
6.00
oligomer based on polyether backbone, from
Polymer Systems Corporation, Orlando, FL
ARONIX .RTM. M-111 polyethylene glycol
43.04
nonylphenylether acrylate, from Toagasei Chemical
Industry Company, Ltd., Tokyo, Japan
LUCIRIN 8893 trimethylbenzoyl-ethoxyphenyl-
1.05
phosphine oxide photoinitiator from BASF, Corp.,
Charlote, NC
LUCIRIN TPO trimethylbenzoyldi-phenylphosphine
0.95
oxide photoinitiator, also from BASF, Corp.
IRGANOX .RTM. 1035 thiodiethylene bis (3,5-di-tert-
1.00
butyl-4-hydroxy) hydrocinnamate stabilizer, from
Ciba-Geigy, Ardsley, NY*
AO 397 3-acryloxypropyl trimethoxysilane adhesion
0.95
promoter, from United Chemical Technology,
Bristol, PA*
A1110 3-aminopropyltrimethoxysilane stabilizer,
0.01
from OSi Specialties, Inc., Danbury, CT*
______________________________________
The above uncured composition had a viscosity of 8750 cps.
A 6 mil coating of this composition was applied to a flat glass sheet using
a Conrad Hanovia Bird applicator and cured in air at 0.7 J/cm.sup.2 using a
200 watts per inch medium pressure mercury vapor lamp. A tensile modulus
for this coating of 214.5 psi was measured according to ASTM-D882. When
subjected to Soxhlet extraction in the manner described above, a percent
extractable value of 7.43 for the primary coating layer (average of two
samples) was noted, as well as a TGA volatiles value of 1.75%, both of
which are well within the parameters the invention.
EXAMPLE 2
Another Composition Yielding a Coating Exhibiting Low Extractables and
Volatiles
A composition similar to the one described in Example 1 but including more
mercapto-functional oligomer and also including 10% by weight of lauryl
acrylate was prepared as follows:
______________________________________
Ingredient Percent by weight
______________________________________
PERMAPOL .RTM. P2-935 mercapto-terminated
35.49
urethane oligomer, as above
ALU-351 polytetramethylene polyol-based acrylated
22.55
aliphatic urethane oligomer, of number average
molecular weight (VPO) of about 1,410 daltons,
from Echo Resins
PURELAST .RTM. 590 aliphatic urethane diacrylate
6.00
oligomer based on polyether backbone, from
Polymer Systems
ARONIX .RTM. M-111 polyethylene glycol
22.00
nonylphenylether acrylate, from Toagasei
AGEFLEX .RTM. lauryl acrylate from CPS Chemical,
10.00
Old Bridge, NJ
AO 397 3-acryloxypropyl trimeth-oxysilane
0.95
adhesion promoter, from United Chemical
Technology
LUCIRIN 8893 trimethylbenzoyl-ethoxyphenyl-
1.05
phosphine oxide photoinitiator, from BASF Corp.
LUCIRIN TPO trimethylbenzoyldi-phenylphosphine
0.95
oxide photoinitiator, from BASF Corp.
IRGANOX .RTM. 1035 thiodiethylene bis (3,5-di-tert-
1.00
butyl-4-hydroxy) hydrocinnamate stabilizer, from
Ciba Geigy Corp.*
A1110 3-aminopropyltrimethoxy-silane stabilizer
0.01
from OSi Specialties, Inc.*
______________________________________
The uncured composition had a viscosity, as measured using a Brookfield
viscometer at the above-noted parameters, of about 9,000 cps.
When cured in the manner of Example 1, a tensile modulus, per ASTM-D882, of
207.4 psi was recorded, and a refractive index of 1.4797 was noted. When a
sample was soaked in gasoline for four hours at room temperature it
swelled 37.3% in length, which is considered acceptable solvent
resistance.
When subjected to Soxhlet extraction, an average percent extractables
value, based on two samples, of 7.74 was measured, as well as a TGA
volatiles value of 1.80%, also well within the parameters of this
invention.
COMPARATIVE EXAMPLE I
A Coating Having Acceptable Extractable and Volatile Contents, But Having
Unacceptable Modulus
Another coating, lacking a mercapto-functional urethane oligomer, and
having acceptable extractables and volatiles content but a very
unacceptable modulus value was made up as follows:
______________________________________
Ingredient Percent by weight
______________________________________
ALU-351 acrylated oligomer, from Echo Resins
51.85
PURELAST .RTM. 590 oligomer, from Polymer
6.35
Systems
ARONIX .RTM. M-111, polyethylene glycol
33.43
nonylphenylether acrylate, from Toagasei
IRGACURE .RTM. 184 cyclohexylphenyl ketone
6.35
photoinitiator, from Ciba Geigy
IRGANOX .RTM. 1035 thiodiethylene bis (3,5-di-tert-
1.06
butyl-4-hydroxy) hydrocinnamate, from Ciba
Geigy*
Y-11167 mercaptopropyltrimeth-oxysilane, from
0.42
OSi Specialties, Inc.*
A-174 methacryloxypropyl trimethoxy silane, also
0.53
from OSi*
A1110 3-aminopropyltrimethoxy-silane stabilizer,
0.01
also from OSi*
______________________________________
The composition, when cured, had an average MEK (Soxhlet) extractable
value, based on two samples, of 9.85%. However, the cured composition's
tensile modulus was 736.6 psi, and thus would be expected to result in an
unacceptable coating susceptible to microbending.
EXAMPLE 3
A composition identical to that of Comparative Example 1 but additionally
including the mercapto-functional urethane oligomer PERMAPOL.RTM. P2-935
of number average molecular weight (GPC) 9000 daltons in a 65:35 ratio
(i.e., in a ratio of 65.00% of the Comparative Example 1 composition to
35.00% of P2-935) was made up. When cured, it has a tensile modulus of
337.5 psi, TGA volatiles of 4.43%, and average percent extractables value
of 9.51.
COMPARATIVE EXAMPLE 2
A composition identical to Comparative Example 1 but additionally
containing the mercapto-functional urethane oligomer PERMAPOL.RTM. P2-795,
average mercapto functionality of 2, number average molecular weight (GPC)
of 2300 daltons (also from Courtaulds Aerospace) in a 65:35 ratio (i.e.,
in a ratio of 65.00% of the composition of Comparative Example 1 to 35.00%
of PERMAPOL.RTM. P2-795) was made up. When cured, it had a tensile modulus
of 220.0 psi, percent extractables (average) of 18.4, and TGA volatiles of
5.1%. It is believed that the unacceptable extractables value results from
using an oligomer of such low molecular weight.
EXAMPLE 4
A Lower Modulus Coating of High Viscosity
Another composition identical to that of Comparative Example 1 was made,
but in this case, additionally including the PERMAPOL.RTM. P2-935
mercapto-functional urethane oligomer in a 50:50 weight ratio with the
Comparative Example 1 composition (i.e., 50% weight percent of the
Comparative Example I composition and 50% weight percent of P2-935).
Though the viscosity of this composition was very high (it could not be
measured with the Brookfield viscometer) , when cured, the coating had a
modulus of 219.4 psi, TGA volatiles of 3.65, and average percent
extractables value of 9.82, all of which were acceptable values.
EXAMPLE 5
A Coating Based on a Very High Molecular Weight Mercapto Oligomer
A dimercapto-terminated oligomer "X" was prepared as follows. A one liter
reaction kettle with a four-necked lid was fitted with a mechanical
stirrer, a stopper for additions and sampling, a thermocouple, an adapter
for gas sparging, and an Allihn condenser was used. 50.82 grams of
isophorone diisocyanate (eq. weight 111.0) and 435.12 grams of
polytetramethylene oxide polymer (eq. weight 1425.67) were charged to the
reactor. A nitrogen purge was begun and mixing started while applying heat
to bring the reaction mass to 580.degree. C. When the contents of the
kettle reached 58.degree. C., five drops of tin catalyst were added. The
reaction temperature was controlled to 60.degree. C. and allowed to
proceed until the isocyanate content reached 1.32%. Approximately 14 grams
of 3-mercapto-1-propanol(eq. weight 92.16) and five more drops of catalyst
were added. The reaction was allowed to proceed until the isocyanate
content, as determined by infrared spectroscopy, was essentially zero. The
resultant oligomer was later determined by GPC (in THF solvent at
30.degree. C., flow rate 1.0 ml/min; injection volume 100 .mu.l; using a
GPC PRO 3.13 IBM AT module) to have a number average molecular weight (Mn)
of 27,500 daltons.
A low extractables coating composition was made up by mixing this oligomer
with the following ingredients:
______________________________________
Ingredient Percent by weight
______________________________________
Dimercapto-terminated oligomer "X", number
14.00
average molecular weight (by GPC) of 27,500, as
described above
ALU-351 oligomer, from Echo Resins
15.00
PURELAST .RTM. 590 oligomer, from Polymer
8.00
Systems
ARONIX .RTM. M-111 polyethylene glycol
44.04
nonylphenylether acrylate, from Toagaesei
AGEFLEX .RTM. lauryl acrylate, from CPS
15.00
LUCIRIN 8893 photoinitiator, from BASF Inc.
2.00
A0397 3-acryloxypropyltrimeth-oxysilane, from OSi
0.95
Specialties Inc.*
IRGANOX .RTM. 1035 thiodiethylene bis (3,5-di-tert-
1.00
butyl-4-hydroxy hydrocinnamate stabilizer, from
Ciba Geigy*
A1110 3-aminopropyltrimethoxy-silane stabilizer,
0.01
from OSi Specialties Inc.*
______________________________________
The resulting composition had an viscosity of 5290 cps, and, when cured,
had a tensile modulus of 210.6 psi and 10.4% extractables when subjected
to Soxhlet extraction.
EXAMPLE 6
A Coating with Higher, Though Still Acceptable, Extractables and Volatiles
Content
The following composition was made up, which employs a different
mercapto-functional oligomer:
______________________________________
Ingredient Percent by weight
______________________________________
PERMAPOL .RTM. P2-850 mercapto-terminated
17.70
urethane oligomer, average mercapto functionality
of 3.81, number average molecular weight (GPC)
about 8000 daltons, from Courtaulds Aerospace
ALU-351 acrylated oligomer, from Echo Resins
23.30
PURELAST .RTM. 590 oligomer, from Polymer
6.00
Systems
ARONIX .RTM. M-111, polyethylene glycol
45.09
nonylphenylether acrylate monomer, from Toagasei
IRGACURE .RTM. 184 cyclohexylphenyl ketone
6.00
photoinitiator, from Ciba Geigy
IRGANOX .RTM. 1035 thiodiethylene bis (3,5-di-tert-
1.00
butyl-4-hydroxy) hydrocinnamate, from Ciba
Geigy*
Y-11167 mercaptopropyltrimethoxy-silane, from
0.40
OSi Specialties, Inc.*
A-174 methacryloxypropyl trimethoxy silane, also
0.50
from OSi*
A1110 3-aminopropyltrimethoxy-silane stabilizer,
0.01
also from OSi*
______________________________________
The uncured composition had a viscosity of 6900 cps. When cured, the
coating's modulus was 214.0 psi; its average extractables (based on two
samples) content was 14.52%; and its TGA volatiles content was 6.52%.
EXAMPLE 7
Another Coating Having a Higher, Though Still Acceptable, Extractable
Content
Another dimercapto-terminated oligomer, "Y", was prepared as follows. A
reaction kettle (fitted with a four-necked lid, a mechanical stirrer, a
stopper, a thermocouple, an adapter and a condenser) was charged with 63.8
grams of isophorone diisocyanate and 410 grams of polytetramethylene polyol
(number average molecular weight, as determined by the acetic anhydride
method, of 2900 daltons) at 28.degree. C. A nitrogen purge was begun and
mixing was commenced. When the reaction mixture reached 33.degree. C.,
three drops of a tin catalyst were added. The reaction was continued at
about 50.degree. C. until the free isocyanate content reached about 2.54%.
At that temperature, about 26.5 grams of 3-mercapto-1-propanol were added,
and the reaction allowed to proceed with periodic addition of further tin
catalyst. When the free isocyanate content reached about 0.0, the reaction
was complete. Subsequent analysis by GPC (in THF solvent at 30.degree. C.,
flow rate 1.0 ml/min; injection volume of 100 .mu.l; using a GPC PRO 3.13
IBM AT module) revealed a molecular weight (Mn) of about 8100 daltons.
This oligomer "Y" was combined with the following ingredients:
______________________________________
Ingredient Percent by weight
______________________________________
Oligomer "Y" described above, number average
17.50
molecular weight (Mn) by GPC of about 8100
daltons
ALU-351 oligomer, from Echo Resins
25.54
PURELAST .RTM. 590 oligomer, from Polymer
8.00
System
ARONIX .RTM. M-111 polyethylene glycol
30.00
nonylphenylether acrylate monomer, from Toagasei
AGEFLEX .RTM. lauryl acrylate, from CPS Chemical
15.00
LUCIRIN 8893 photoinitiator, from BASF
2.00
AO 397 3-acryloxypropyltri-methoxysilane
0.95
adhesion promoter, from OSi*
A 1110 3-aminopropyltrimethoxy-silane stabilizer,
0.01
from OSi*
IRGANOX 1035 stabilizer, from Ciba Geigy*
1.00
______________________________________
The uncured composition had a viscosity of about 5640 cps and cured to form
a coating of 261.4 psi tensile modulus. When subjected to Soxhlet
extraction, an average extractable value of 13.35% was measured.
EXAMPLE 8
A Coating Based on a Lower Molecular Weight Mercapto Oligomer
Another mercapto-terminated oligomer "Z" was prepared as follows. A
reaction vessel as described in the previous synthetic examples was used.
To it were added 304.8 grams of DuPont PTMO 1000 polytetramethyl oxide
polyether polyol and 138 grams of isophorone diisocyanate. A nitrogen
purge was begun and mixing effected while heating the reaction mixture to
63.degree. C., at which time 2 drops of tin catalyst were added. The
reaction was allowed to proceed until the isocyanate content reached
5.89%. 57.3 grams of 3-mercapto-1-propanol and 2 drops of catalyst were
subsequently added. The temperature was raised to 65.degree.-72 C. and the
reaction was allowed to continue for another approximately 1.5 hours, after
which time the isocyanate content was measured to be 0.25%, and another 5
drops of catalyst were added. After another two hours of reaction,
isocyanate content was measured, by IR scan, to be 0.0%. The oligomer
which resulted was later determined by GPC to have a number average
molecular weight (Mn) of 3,300 daltons.
A suitable low extractables composition was made up using the above
oligomer as follows:
______________________________________
Ingredient Percent by weight
______________________________________
Oligomer "Z", number average molecular weight
15.00
by GPC of 3,300 daltons
PURELAST .RTM. 590 oligomer, from Polymer
8.00
System
ALU-351 oligomer, from Echo Resins
28.04
ARONIX .RTM. M-111 polyethylene glycol
30.00
nonphenylether acrylate, from Toagasei
AGEFLEX .RTM. lauryl acrylate, from CPS
15.00
LUCIRIN 8893 photoinitiator, from BASF
2.00
IRGANOX 1035 thiodiethylene bis(3,5-di-tert-
1.00
butyl-4-hydroxy) hydrocinnamate stabilizer, from
Ciba Geigy*
AO 397 3-acryloxypropyltri-methoxysilane, from
0.95
OSi*
A 1110 3-aminopropyltrimethoxy-silane stabilizer,
0.01
from OSi
______________________________________
The resulting composition had a viscosity of 3150 cps, and, when cured, had
a tensile modulus of 230.6 psi and 12.4% extractables (average of two
values) when subjected to Soxhlet extraction.
Although the present invention has been described with reference to
preferred embodiments, it will be understood that the invention is not
limited to the details thereof. Various substitutions and modifications
have been described in the course of the foregoing description, and others
will be apparent to those of ordinary skill in the art. All such
substitutions and modifications are intended to fall within the scope of
the invention as described in the appended claims.
* * * * *
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