Note: Descriptions are shown in the official language in which they were submitted.
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RADIATION CURABLE OPTICAL FIBER
COATING COMPOSITION
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation curable
optical fiber coating composition which after curing
results in a coating having enhanced resistance to
moisture and hydrocarbon gel. The invention further
relates to a pigmented radiation curable coating
composition suitable for use as an outer primary coating
for optical fibers.
2. Description of related art
Optical fibers are frequently coated with two
superposed radiation curable coatings, which together form
a primary coating. The coating which contacts the glass is
called the inner primary coating and the overlaying
coating is called the outer primary coating. In older
references, the inner primary coating was called the
primary coating and outer primary coating was called the
secondary coating, but for reasons of clarity, that
terminology was abandoned by the industry in recent years.
The inner primary coating is usually a soft
coating providing resistance to microbending. Microbending
can lead to attenuation of the signal transmission
capability of the coated fiber and is therefore
undesirable. The outer primary coating, which is exposed,
is typically a harder coating providing desired resistance
to handling forces, such as those encountered when the
fiber is cabled.
The coating compositions for the inner and outer
primary coating generally comprise a polyethylenically
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unsaturated oligomer in a liquid ethylenically unsaturated
medium.
Usually the optical fibers are glass fibers.
Optical glass fibers are weakened upon exposure to water.
For example. moisture in air can cause weakening and the
eventual breakage of glass fibers. It is therefore
desirable that the inner and outer primary coating prevent
moisture from attacking the glass substrate. However, many
conventional coating compositions have a peak water
absorption greater than 1.7 ~ and therefore are not
effective in protecting the glass substrate from moisture.
In addition to causing the weakening of glass
substrates, moisture can also cause the coating layers to
delaminate from each other and/or the glass surface. The
delamination of the inner primary coating can result in a
weakened glass substrate, because the inner primary
coating can no longer protect the glass from attack from
moisture.
To avoid moisture damage to the glass surface,
it is desirable to provide a coating composition having
low water absorption, resistance to delamination from
glass, and a low water soak extraction. Moreover a coating
composition for optical glass fibers preferably should
also provide a cured coating having sufficient adhesion to
the glass fiber and yet be strippable for field
applications.
For certain applications, conventional coating
compositions do not provide cured outer primary coatings
having the required combination of sufficient adhesion to
the inner primary coating, strippability, resistance to
water absorption, and a low water soak extraction.
Furthermore, it is frequently desired to color
an outer primary coating to facilitate the selection of
the optical fiber which is desired from among many glass ,
fibers in a cable assembly. Published European Patent
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Application No. 418829 discloses the use of radiation
curable ink or a colored solvent borne lacquer to color or
overcoat an optical fiber which has already been coated
with an inner and outer primary coating. This requires a
third coating operation which is undesirable.
It has been proposed to include sufficient
pigment for desired coloration directly into the outer
primary coating. Such a pigmented outer primary coating is
disclosed in published PCT application WO 90/13579, which
describes an outer primary coating composition containing
pigment particles having a size of less than about 1
micron.
Published Japanese patent application No. 64-
22975 describes an ink composition comprising a UV-curable
resin and an ethoxylated bisphenol-A-diacrylate. This
reference does not disclose using the composition as an
outer primary coating nor how to improve the moisture
resistance of an outer primary coating. Moreover, the
composition disclosed in JP-A-64-22975 is not suitable as
an outer primary coating because, when cured, the coating
does not have the required toughness to protect the
optical glass fiber during handling.
Conventional pigmented outer primary coating
compositions, when cured, have insufficient resistance to
moisture. When the conventional cured pigmented coating is
exposed to water, dimensional changes occur. These
dimensional changes can lead to attenuation of the signal
transmission capability of the glass optical fiber.
Therefore, there is still a need for a coating composition
suitable for use as an outer primary coating, which can be
pigmented, and which provides a cured coating having low
water absorption, a low water soak extraction, and
resistance to attack from hydrocarbon gel cable filling
material.
.
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Summarv of the invention
It is an object of the invention to provide a
coating composition suitable for use as an outer primary
coating which can be pigmented. Another object of the
invention is to provide an outer primary coating
composition that when cured exhibits a low water '
absorption, a low water soak extraction, and resistance to
attack from hydrocarbon gel cable filling material.
The above object and other objects are obtained
by providing a radiation-curable, glass optical fiber
coating composition which when suitably cured exhibits
resistance to attack from hydrocarbon gel cable filing
material. The uncured composition comprises:
A. about 10 to about 90~ by weight of a radiation-
curable oligomer;
C. from 0 to about 40~ by weight of a reactive
diluent;
D. from 0 to about 40~ by weight of a
photoinitiator;
E. from 0 to about 10~ by weight of a pigment; and
about 10 to about 90~ by weight of a second
radiation-curable oligomer according to the
following formula:
g1 - Ll _ Cl _ L2 - Rz ~1~
where:
Rl and R2, independently, each represent a
radiation-curable functional group;
L1 and L2, independently, each represent an
alkyleneoxy chain having from about 2 to
about 40 carbon atoms, wherein L1 and L2 are
linked to C'- through an oxygen atom;
Cl comprises a hydrocarbon having from about 5
to about 40 carbon atoms and containing at
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least one cyclic group.
The weight percentages are relative to the total weight of
components A. through E.
The composition, when cured, results in coatings
having improved water resistance. When exposed to
moisture, the coated glass optical fiber swells less than
conventional fibers, providing enhanced concentricity of
the coated glass optical fibers. Enhanced concentricity of
coated optical fibers results in greater tolerances in the
production process and increased yields. Furthermore,
swelling of the coating can cause undesired microbending
of glass optical fiber.
This invention also relates to an optical glass
fiber coated with an inner primary coating and the above
auter primary coating. The outer primary coatings
according to the invention exhibit good color permanence.
This invention also provides a coated glass
optical fiber coated with coating having a room
temperature tensile modulus of at least about 50 MPa, an
elongation at break of at least about 3~, a glass
transition temperature Tg (tan delta max) of at least
about 25°C, and a peak water absorption of no more than
1.7. The coating comprises a suitably radiation-cured,
glass optical fiber coating composition. The coating
composition in uncured form comprises a radiation-curable
coating composition comprising a radiation-curable
aligomer according to the following formula:
Ri Li - C1 - L2 - R2 ( 1 )
where:
R1 and R2, independently, each represent a
radiation-curable functional group;
Ll and L2, independently, each represent an
alkyleneoxy chain having from about 2 to about
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40 carbon atoms, wherein Ll and Lz are linked to
C1 through an oxygen atom;
C1 comprises a hydrocarbon having from about 5
to about 40 carbon atoms and containing at
least one cyclic group.
DETAILED DESCRIPTION OF THE INVENTION
The cured outer primary coating, made bycuring
the above coating composition, has a room temperature
tensile modulus of at least about 50 MPa, an elongation at
break of at least about 3~, a Tg (tan delta max) of at
least about 25°C, and a peak water absorption of no more
than 1.7, as defined herein. Preferably, an outer primary
coating, made by curing the coating composition, has a
room temperature tensile modulus of at least about 400
MPa, an elongation at break of at least about 5~, a Tg of
at least about 40°C, and a peak water absorption of no
more than about 1.5. The outer primary coatings according
to the invention have a good color permanence.
The radiation-curable oligomer A. can be any
radiation-curable oligomer used in radiation-curable,
glass optical fiber coating compositions. One skilled in
the art knows how to select and use radiation-curable
oligomers in order to achieve desired properties. An
example of a suitable radiation-curable oligomer A.
includes an urethane oligomer having a molecular weight of
at least about 500 and containing at least one
ethylenically unsaturated group that can be polymerized
through actinic radiation. Preferably, the oligomer A. has
two terminal radiation-curable functional groups, one at
each end of the oligomer.
Preferably, the molecular weight of the
oligomer A. is at least about 700 and at most about 10,000
Daltons. More preferably the molecular weight is between
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about 1000 and about 5000, and most preferably, between
about 2000 and 4000 Daltons. Molecular weight, as used
throughout this application, is the calculated molecular
- weight of the molecule concerned. In the case of a polymer
structure, it is the calculated average molecular weight
of the expected structure based on the starting materials
and the reaction conditions. The molecular weight can also
be determined using conventional techniques.
Preferably, the oligomer A. is substantially
free of isocyanate functionality.
The radiation-curable oligomer A. is preferably
present in an amount of about 20 to about 40 ~ by weight,
and more preferably about 25 to about 35~ by weight. All
weight percentages used herein are expressed as
percentages relative to the total weight of components A.
through E. present in the composition.
Examples of suitable radiation-curable
functional groups which can be present on the oligomer A.
include ethylenically unsaturated groups having
(meth)acrylate, vinylether, acrylamide, maleate or
fumarate functionality. The language "(meth)acrylate" as
used herein, means methacrylate, acrylate, or mixtures
ther eof .
Preferably, the radiation-curable group in the
oligomer A. is an (meth)acrylate or vinylether group. Most
preferably, the radiation-curable group is an acrylate
group.
Another type of radiation-curable functionality
generally used is provided by, for example, epoxy groups,
or thiol-ene or amine-ene systems. Epoxy groups can be
polymerized through cationic polymerization, whereas the
thiol-ene and amine-ene systems are usually polymerized
through radical polymerization. The epoxy groups can be,
for example, homopolymerized. In the thiol-ene and amine-
ene systems, for example, polymerization can occur between
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g _
a group containing allylic unsaturation and a group
containing a tertiary amine or thiol.
Preferably, the oligomer A. contains at least
two ethylenically unsaturated groups which are bound to an
oligomer backbone. For example, ethylenically unsaturated
groups can be present at each end of the oligomer backbone '
as reactive termini. The oligomer backbone can have a
molecular weight of at least about 200, and can be, for
example, based on a polyether, polyolefin, polyester,
polycarbonate, or copolymers thereof. Preferably, the
oligomer backbone is a polyether. The molecular weight of
the oligomer backbone is preferably at least about 250,
more preferably at least about X00, and most preferably at
least about 600. The molecular weight is preferably not
more than about 10,000, more preferably not more than
about 5,000, and most preferably not more than about 3000.
The oligomer backbone can comprise one or more
polymer blocks coupled with each other via, for example,
urethane linkages.
Preferably, the backbone-oligomer is a
polyether, a polyester, a polycarbonate, a polyolefin, or
a copolymer thereof. If the oligomer backbone is a
polyether, the resulting coatings have a low glass
transition temperature and good mechanical properties. If
the oligomer backbone is a polyolefin, the resulting
coatings have a further improved water resistance.
Oligomer A. can be, for example, prepared by
reaction of (i) an oligomer polyol, (ii) a diisocyanate
and (iii) a hydroxy functional ethylenically unsaturated
monomer, for example hydroxyalkyl(meth)acrylate.
If a oligomer backbone polyol is used,
preferably it has on average at least about 2 hydroxyl
groups. The oligomer backbone polyol may have, on average,
more than 2 hydroxyl groups. Examples of such an oligomer
diol include polyether diols, polyolefin diols, polyester
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diols, polycarbonate diols, and mixtures thereof.
Polyether and polyolefin diols, or combinations thereof,
are preferred.
- If a polyether diol is used, preferably the
polyether is a substantially non-crystalline polyether.
- Preferably, the polyether comprises repeating units of one
or more of the following monomer groups:
-O-CH2-CH2-O-; -O-CH2-CH-O-; -O-CH2-CH2-CH2-O-;
I
CH3
-O-CH2-CHZ-CH2-CH2-O-; -O-CH2-CH-CH2-CH2-O-;
I
CH3
--O-CH-CH2-CH2-CH2-O-; -O-CH-CH2-O-; and
CH3 CHZ-CH3
CH3
I
-O-CH2-C-O-.
I
2 5 CH3
Hence, the polyether can be made from epoxy-
ethane, epoxy-propane, tetrahydrofuran, methyl-substituted
tetrahydrofuran, epoxybutane, and the like.
An example of a polyether polyol that can be
used is the polymerization product of 20 percent by weight
of 3-methyltetrahydrofuran and 80 percent by weight of
tetrahydrofuran, both of which have undergone a ring
opening polymerization. This polyether copolymer contains
both branched and non-branched oxyalkylene repeating units
and is marketed as PTG-L 1000 (Hodogaya Chemical Company
of Japan). Another example of a polyether that can be used
is PTG-L 2000 (Hodogaya Chemical Company).
If a polyolefin diol is used, the polyolefin is
preferably a linear or branched hydrocarbon containing a
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plurality of hydroxyl end groups. Preferably, the
hydrocarbon is a non-aromatic compound containing a
majority of methylene groups (-CH2-) and which can contain
internal unsaturation and/or pendent unsaturation. Fully -
saturated, for example, hydrogenated hydrocarbons, are
preferred because the long term stability of the cured '
optical fiber coating increases as the degree of
unsaturation decreases. Examples of hydrocarbon diols
include, for example, hydroxyl-terminated, fully or
partially hydrogenated 1,2-polybutadiene; 1,4- 1,2-
polybutadiene copolymers, 1,2-polybutadiene-ethylene or -
propylene copolymers, polyisobutylene polyol; mixtures
thereof, and the like. Preferably, the hydrocarbon diol is
a substantially, fully hydrogenated 1,2-polybutadiene or
1,2-polybutadiene-ethene copolymer.
Examples of polycarbonate diols are those
conventionally produced by the alcoholysis of diethylene
carbonate with a diol. The diol can be, for example, an
alkylene diol having about 2 to about 12 carbon atoms,
such as, 1,4-butane diol, 1,6-hexane diol, 1,12-dodecane
diol, and the like. Mixtures of these diols can also be
utilized. The polycarbonate diol can contain ether
linkages in the backbone in addition to carbonate groups.
Thus, for example, polycarbonate copolymers of alkylene
oxide monomers and the previously described alkylene diols
can be used. Alkylene oxide monomers include, for example,
ethylene oxide, tetrahydrofuran, and the like. These
copolymers produce cured coatings that exhibit a lower
modulus and also inhibit crystallinity of the liquid
coating composition compared to polycarbonate diol
homopolymers. Admixtures of the polycarbonate diols and
polycarbonate copolymers can also be utilized.
Polycarbonate diols include, for example,
Duracarb 122 (PPG Industries) and Permanol KM10-1733
(Permuthane, Inc., Ma.). Duracarb 122 is produced by the
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alcoholysis of diethylcarbonate with hexane diol.
Examples of polyester diols include the reaction
products of saturated polycarboxylic acids, or their
- anhydrides, and diols. Saturated polycarboxylic acids and
anhydrides include, for example, phthalic acid,
isophthalic acid, terephthalic acid, trimellitic acid,
tetrahydrophthalic acid, hexahydrophthalic acid,
tetrachlorophthalic acid, adipic acid, azelaic acid,
sebacic acid, succinic acid, glutaric acid, malonic acid,
pimelic acid, suberic acid, 2,2-dimethylsuccinic acid,
3,3-dimethylglutaric acid, 2,2-dimethylglutaric acid, the
like, anhydrides thereof and mixtures thereof. Diols
include, for example, 1,4-butanediol, 1,8-octane diol,
diethylene glycol, 1,6-hexane diol, dimethylol
cyclohexane, and the like. Included in this classification
are the polycaprolactones, commercially available from
Union Carbide under the trade designation Tone Polylol
series of products, for example, Tone 0200, 0221, 0301,
0310, 2201, and 2221. Tone Polyol 0301 and 0310 are
trifunctional.
Any organic polyisocyanate (ii), alone or in
admixture, can be used as the polyisocyanate. Thereby, a
product is obtained which is end-capped with the reaction
product from the isocyanate/ethylenically unsaturated
monomer reactionon at least one end of the molecule.
"End-capped" means that a functional group caps one of the
two ends of the oligomer diol.
The isocyanate/hydroxy functional monomer
reaction product attaches to the oligomer backbone (i)
diol via a urethane linkage. The urethane reactions can
take place in the presence of a catalyst. Catalysts for
the urethane reaction include, for example,
diazabicyclooctane crystals and the like.
Preferably the polyisocyanate (ii) is a
diisocyanate. Examples of diisocyanates (ii) include
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isophorone diisocyanate (IPDI), toluene diisocyanate
(TD/), diphenylmethylene diisocyanate, hexamethylene
diisocyanate, cyclohexylene diisocyanate, methylene
dicyclohexane diisocyanate, 2,2,4-trimethyl hexamethylene '
diisocyanate, m-phenylene diisocyanate, 4-chloro-1,3-
phenylene diisocyanate, 4,4'-biphenylene diisocyanate, '
1,5-naphthylene diisocyanate, 1,4-tetramethylene
diisocyanate, 1,6-hexamethylene diisocyanate, 1,10-
decamethylene diisocyanate, 1,4-cyclohexylene
diisocyanate, and polyalkyloxide and polyester glycol
diisocyanates such as polytetramethylene ether glycol
terminated with TDI and polyethylene adipate terminated
with TDI, respectively. Preferably, the isocyanates are
TDI and IPDI.
Generally the compound providing a reactive
terminus (iii) contains a functional group which can
polymerize under the influence of actinic radiation, and
the compound contains a functional group which can react
with the diisocyanate. Hydroxy functional ethylenically
unsaturated monomers are preferred. More preferably, the
hydroxy functional ethylenically unsaturated monomer _
contains acrylate, (meth)acrylate, vinyl ether, maleate or
fumarate functionality.
In the reaction between hydroxy group of (i) and
isocyanate groups of (ii), it is preferred to employ a
stoichiometric balance between hydroxy and isocyanate
functionality and to maintain the reaction temperature of
at least 25°C. The hydroxy functionality should be
substantially consumed. The mole ratio of the isocyanate
to the hydroxy functional ethylenically unsaturated
monomer is about 3:1 to 1.2:1, preferably about 2:1 to
1.5:1. The hydroxy functional ethylenically unsaturated
monomer attaches to the isocyanate via an urethane
linkage. Monomers having (meth)acrylate functional groups .
include, for example, hydroxy functional acrylates such as
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2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the
like. Monomers having vinyl ether functional groups
include, for example. 4-hydroxybutyl vinyl ether, and
triethylene glycol monovinyl ether. Monomers having
maleate functional groups include, for example, malefic
' acid and hydroxy functional maleates.
Component B. is a radiation-curable oligomer
according to the following formula:
R1 - L1 - C1 - LZ - R2 C1)
where:
R1 and RZ, independently, each represent a
radiation-curable functional group;
L1 and LZ, independently, each represent an
alkyleneoxy chain having from about 2 to
about 40 carbon atoms, wherein Ll and LZ are
linked to C1 through an oxygen atom;
C1 comprises a hydrocarbon having from about 5
to about 40 carbon atoms and containing at
least one cyclic group.
Radiation-curable functional groups are well
known and within the skill of the art. Based on the
disclosure provided herein, one skilled in the art will
know what radiation-curable functional groups to use as R1
and R2, to provide the desired curing properties.
Commonly, the radiation-curable functionality
used is ethylenic unsaturation, which can be polymerized
through radical polymerization or cationic polymerization.
Specific examples of suitable ethylenic unsaturation are
groups containing acrylate, methacrylate, styrene,
vinylether, vinyl ester, N-substituted acrylamide, N-
vinyl amide, maleate esters, and fumarate esters.
Preferably, the ethylenic unsaturation is provided by a
group containing acrylate, methacrylate, or styrene
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functionality.
Another type of functionality generally used is
provided by, for example, epoxy groups, or thiol-ene or
amine-ene systems. Epoxy groups in can be polymerized -
through cationic polymerization, whereas the thiol-ene and
amine-ene systems are usually polymerized through radical '
polymerization. The epoxy groups can be, for example,
homoplymerized. In the thiol-ene and amine-ene systems,
for example, polymerization can occur between a group
containing allylic unsaturation and a group containing a
tertiary amine or thiol.
The groups L1 and L2 are each alkyleneoxy chains
having from about 2 to about 40 carbon atoms, preferably
about 2 to about 20 carbon atoms, and most preferably
about 2 to about 10 carbon atoms. The groups L1 and L2
each comprise about 1 to about 12 alkylether groups, and
preferably, from about 1 to about 6 alkylether groups.
Examples of suitable alkylether groups include ethylether,
propylether and butylether. The alkylether groups can also
comprise cyclic groups. Preferably, the alkylether group
is made from an epoxy containing alkane, such a
epoxyether, epoxypropane, and epoxybutane.
The groups L1 and LZ connect to C1 through an
oxygen atom. The oxygen connecting the group L1 to the
group Cl is considered part of the group L'- and the oxygen
connecting the group L2 to the group C1 is considered part
of the group L2.
The group C'- comprises about 5 to about 40
carbon atoms and contains at least one cyclic group.
Preferably, the group Cl comprises about 5 to about 20
carbon atoms.
The cyclic groups can be saturated or fully or
partially unsaturated cyclic alkylene groups. Examples of
suitable saturated cyclic alkylene groups include, but are
not limited to, cyclopentane, cyclohexane, cycloheptane,
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and cyclooctane. Cylcopentane and cyclohexane are
preferred. The cyclic alkylene groups can also be
partially unsaturated such as cyclobutene, cyclopentene,
cyclohexene, cycloheptene, and cyclooctene. Cyclopentene
and cyclohexene are preferred. Further examples of
- suitable cyclic alkylene groups include arylenes, such as
benzene and naphthalene. Preferably, the cyclic group is
benzene.
The cyclic groups can be substituted with
hydrocarbon groups, such as methyl, ethyl, propyl, and
butyl groups.
Preferably, the group C1 comprises at least two
cyclic groups which are either directly connected or
connected via one or more hydrocarbon groups. Examples of
such preferred groups Cl are represented by the following
formulae (2) or (3):
Xi _ X2 (2 )
X1 - Y1 - XZ (3)
Where:
X1 and XZ are each cyclic alkylene groups as
described herein; and
Yl is a hydrocarbon having from about 1 to about
15 carbon atoms, preferably about 1 to
about 10 carbon atoms.
Preferably X1 and X2 are arylenes.
The Y'- group can be saturated or unsaturated,
and branched or linear. Examples of suitable saturated Yl
groups include, methyl, ethyl, propyl, and butyl.
- Specific examples of suitable groups C1 are
derived from bisphenol A, saturated bisphenol A, bisphenol
- F, saturated bisphenol F, tricyclodecane dimethanol or
cyclohexane dimethanol.
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An example of a suitable Component B. is an
alkoxylated bisphenol di(meth)acrylate. The alkoxylated
bisphenol di(meth)acrylate can be any alkoxylated
bisphenol di(meth)acrylate and can be prepared in any
known manner. Preferably, Component B. is an alkoxylated
bisphenol-A-diacrylate. Preferably the alkoxylated
bisphenol-A-di(meth)acrylate is an ethoxylated or
propoxylated bisphenol-A-diacrylate. An example of a
particularly suitable alkoxylated bisphenol-A-diacrylate
is ethoxylated bisphenol-A-diacrylate, commercially
available as SR 349A Monomer, supplied by Sartomer.
The alkoxylated bisphenol-A-di(meth)acrylate B.
is preferably present in an amount of about 10 to about
80~ by weight, more preferably about 40 to about 80 ~ by
weight, and most preferably about 50 to about 70~ by
weight.
The composition according to the invention may
comprise a reactive diluent as Component C. The reactive
diluent can be used to adjust the viscosity of the coating
composition. Thus, the reactive diluent can be a low
viscosity monomer containing at least one functional group
capable of polymerization when exposed to actinic
radiation.
The reactive diluent is preferably added in such
an amount that the viscosity of the coating composition is
in the range of about 1,000 to about 10,000 mPas. Suitable
amounts of the reactive diluent have been found to be
about 1 to about 20 ~ by weight, and more preferably about
5 to about 15~ by weight.
The reactive diluent preferably has a molecular
weight of not more than about 550 or a viscosity at room
temperature of not more than about 300 mPa.s (measured as _
100 diluent).
The radiation-curable functional group present _
on the reactive diluent may be of the same nature as that
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used in the radiation-curable oligomer A. or Component B.
Preferably, the radiation-curable functional group present
in the reactive diluent is capable of -copolymerizing with
- the radiation-curable functional group present on the
radiation-curable oligomer A or Component B.
' Preferably, reactive diluent C. comprises a
monomer or monomers having an acrylate or vinyl ether
functionality and an C4-C2o alkyl or polyether moiety.
Examples of such reactive diluents are hexylacrylate,
2-ethylhexylacrylate,
isobornylacrylate,
decylacrylate,
laurylacrylate,
stearylacrylate,
ethoxyethoxy-ethylacrylate,
laurylvinylether,
2-ethylhexylvinyl ether,
N-vinyl formamide,
isodecyl acrylate,
isooctyl acrylate,
vinyl-caprolactam,
N-vinylpyrrolidone and the like.
This type of reactive diluent preferably is present in an
amount between about 1 and about 35 wt.~.
Another preferred type of reactive diluent is a
compound comprising an aromatic group. Examples of
diluents having an aromatic group include:
ethyleneglycolphenyletheracrylate,
polyethyleneglycolphenyletheracrylate,
polypropyleneglycolphenyletheracrylate, and
alkyl-substituted phenyl derivatives of the above
monomers, such as
polyethyleneglycolnonylphenyletheracrylate.
This type of reactive diluent preferably is present in an
amount between about 1 and about 35 wt.~.
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Furthermore, reactive diluent C. preferably
contains two groups capable of polymerization using
actinic radiation. A diluent having three or more of such
reactive groups can be present as well. Examples of such
monomers include:
C2-Cle hydrocarbondioldiacrylates, '
C4-C18 hydrocarbondivinylethers,
C3-C18 hydrocarbontrioltriacrylates,
the polyether analogues thereof, and
the like, such as
1,6-hexanedioldiacrylate, trimethylolpropanetriacrylate,
hexanedioldivinylether,
triethyleneglycoldiacrylate,
pentaeritritoltriacrylate, and
tripropyleneglycol diacrylate.
Preferably the reactive diluent is an alkoxylated alkyl
phenol (meth)acrylate, most preferably an ethoxylated
nonyl phenol (meth)acrylate.
If the radiation-curable functional group of the
radiation-curable oligomer A. or Component B. is an epoxy
group, for example, one or more of the following compounds
can be used as the reactive diluent:
epoxy-cyclohexane,
phenylepoxyethane,
1,2-epoxy-4-vinylcyclohexane,
glycidylacrylate,
1,2-epoxy-4-epoxyethyl-cyclohexane,
the diglycidylether of polyethylene-glycol,
the diglycidylether of bisphenol-A, and the like.
If the radiation-curable functional group of the
radiation-curable oligomer A. or Component B. has an
amine-ene or thiol-ene system, examples of reactive _
diluents having allylic unsaturation that can be used
include:
diallylphthalate,
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triallyltri-mellitate,
triallylcyanurate.
triallylisocyanurate, and
- diallylisophthalate.
For amine-ene systems, amine functional diluents that can
be used include, for example:
the adduct of trimethylolpropane, isophorondiisocyanate
and di(m)ethylethanolamine,
the adduct of hexanediol, isophorondiisocyanate and
dipropylethanolamine, and
the adduct of trimethylol propane,
trimethylhexamethylenediisocyanate and
di(m)ethylethanolamine.
Preferably, the oligomer A., the oligomer B. and
the reactive diluent C. (if present) each contain an
acrylate group as a radiation-curable group. More
preferably, Rl and R2 are both acrylate groups, the
ethylenic unsaturation on said oligomer A. is provided by
acrylate groups and the reactive diluent C. (if present)
contains an acrylate group.
The photoinitiator, Component D., is useful when
conducting an ultraviolet radiation-cure. In other
embodiments, for example, when using an electron beam cure
of a free radical system, the photoinitiator D. can be
omitted. In cationally cured systems, however, a
photoinitiator D. is useful even when performing an
electron beam cure.
The photoinitiator D., when used in an effective
amount to promote radiation cure, preferably provides
reasonable cure speed without causing premature gelling of
the composition. The cure speed desired will depend on the
application of the coating and a skilled artisan will
easily be able to adjust the amount and type of
photoinitiator to obtain the desired cure speed. The type
of photoinitiator which is used will be dependent on
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whether a free radical-type system or a cationic cure
type-system is used.
Examples of free radical-type photoinitiators
include, but are not limited to, the following:
hydroxycyclohexylphenylketone;
hydroxymethylphenylpropanone; dimethoxyphenylacetophenone;
2-methyl-1-[4-(methyl thio)-phenyl] -2-morpholino-
propanone-1;
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one; 1-
(4-dodecyl-phenyl)-2-hydroxy- 2-methylpropan-1-one;
4-(2-hydroxyethoxy)phenyl-2(2-hydroxy-2-propyl)-ketone;
diethoxyphenyl acetophenone;
2,4,6 trimethylbenzoyl diphenylphosphone;
a mixture of (2,6-dimethoxy benzoyl)-2,4,4
trimethylpentylphosphineoxide and 2-hydroxy-2-methyl-1-
phenyl-propan-1-one; and
mixtures of these.
Examples of cationic cure-type photoinitiators
include, but are not limited to, onium salts such as
iodonium, sulfonium, arsonium, azonium, bromonium, or
selenonium. The onium salts are preferably chemically
modified to render them more hydrophobic, for example, by
incorporating saturated hydrocarbon moieties such as alkyl
or alkoxy substituents of from about 4 to about 18 carbon
atoms. Preferred cationic cure initiators include:
(4-octyloxyphenyl) phenyl iodonium hexafluoro antimonate;
(4-octyloxyphenyl) diphenyl sulfonium hexafluoro
antimonate;
(4-decyloxyphenyl) phenyl~iodonium hexafluoro antimonate;
and
(4-octadecyloxyphenyl) phenyl iodonium hexafluoro
antimonate.
When a pigment E. is present in the composition
according to the invention, it is preferred to use as
component D. an acyl phosphine oxide photoinitiator, more
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specifically a benzoyl diaryl phosphine oxide
photoinitiator. Such a photoinitiator provides a high cure
speed even in the presence of relatively high amounts of
pigment. Published PCT application WO 90/13579 discloses
coating compositions containing pigments, and is
incorporated herein by reference. Examples of suitable
benzoyl diaryl phosphine oxide photoinitiators include:
2,4,6-trimethylbenzoyldiphenyl-phosphine oxide (Lucirin
TPO by BASF), and bis(2,6-dimethoxybenzoyl)-2,4,4-
trimethylpentyl-phosphine oxide (Irgacine 1700 by Ciba
Geigy).
For an optimum cure speed in the presence of pigment, it
is advantageous to combine an acyl phosphine oxide
photoinitiator with one or more other photoinitiators,
such as hydroxy-cyclohexylphenylketone.
The photoinitiator is preferably present in an
amount of about 1 to about 20 ~ by weight, more preferably
in an amount of about 1 to about 10~ by weight, and most
preferably, about 1 to about 5~ by weight.
The pigment E. can be any pigment suitable for
use in pigmented colored optical fiber coatings.
Preferably, the pigment E. is in the form of small
particles and is capable of withstanding UV-radiation.
Examples of suitable pigments include:
titanium dioxide white (Dupont R-960),
carbon black (Degussa Special 4A or Columbian Raven 420),
lamp black (General carbon LB#6),
phtalo blue G (Sun 249-1282),
phtalo blue R (Cookson BT698D),
phtalo green B (Sun 264-0238),
phtalo green Y (Mobay 65420),
light chrome yellow (Cookson Y934D),
diarylide yellow (Sun 274-3954),
organic yellow (Hoechst H4G),
medium chrome yellow (Cookson Y969D),
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yellow oxide (Pfizer YL02288D),
lead free-yellow (BASF Paliotol 1770),
raw umber (Hoover 195),
burnt umber (Lansco 3240X),
lead free orange (Hoechst RL70),
red oxide (Pfizer R2998D),
moly orange (Cookson YL988D),
arylide red (Hoechst FSRKA),
quinacridone red (Ciba RT759D), and
quinacridone violet (Ciba RT887D).
Preferably, the pigment has a mean particle size of not
more than about 1 Nm. The particle size of the commercial
pigments can be lowered by milling if necessary. The
pigment is preferably present in an amount of about 1 to
about 10 ~ by weight, and more preferably in an amount of
about 3 to about 8~ by weight.
Other components that can be present in the
composition include, but are not limited to, light
sensitive and light absorbing components, catalysts,
initiators, lubricants, wetting agents, organofunctional
silanes, antioxidants, and stabilizers, which do not
interfere with the desired resistance to moisture. These
additives may be added to the compositions according to
the invention in an amount that is usual for the additive
when used in optical fiber coatings.
The examples of polymeric coating compositions
set forth above are intended only to be illustrative of
the coating compositions that may be employed in the
present invention. The compositions according to the
invention can be applied on an optical fiber using
conventional coating technology. -
In producing a coated optical fiber, a liquid
coating composition is applied to a substrate and
subsequently cured. Typically, the cure is affected using
ultraviolet or visible radiation. However, other methods
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of curing can be used. For example, thermal curing,
usually in the presence of an initiator, can be used.
Alternatively, the coating can be cured by electron beam
' irradiation where no catalyst is required. More than one
coating can be applied. Typically, a first coating is
applied and cured followed by a second coating and so on
until the desired number of coatings have been applied.
Alternatively, the layers can be applied on top of each
ather as liquids, typically referred to as a wet-on-wet
process, with one final curing step at the end.
For example, on a bare glass fiber having a
diameter of about 125 pm, a UV-curable inner primary
coating can be provided, such that the fiber with inner
primary coating has a diameter of about 180 Nm. Then, the
Coating composition according to the invention can be
applied in a thickness of between about 10 and about 150
Vim, and preferably between about 20 and about 60 pm, and
then cured.
Although the coating composition is suitable as
an outer primary coating, it is also possible to use the
compositions described herein as a single coating on the
glass optical fiber. Single coatings can be made which
have a sufficiently low modulus that it they minimize the
microbending problems at low temperatures and which are
hard and tough enough to protect the optical glass fiber.
The invention will be further explained by the
following non-limiting examples.
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Example I
A coating composition was prepared by mixing the
following components:
Component: Percent
Polyether urethane acrylate 28.7
Ethoxylated bisphenol-A-diacrylate 56.0
Ethoxylated nonylphenolacrylate 7.2
[Photomer 4003 by Henkel)
2,4,6-trimethylbenzoyldiphen~l-
phosphine oxide 0.9
[Lucirin TPO by BASF)
Hydroxycyclohexylphenylketone 1.8
[Irgacure 184 by Ciba Geigy)
Thiodiethylene-bis-
(3,5-di-tert-butyl-4-hydroxy)
hydrocinnamate 0.4
[Irganox 1035 by Ciba Geigy)
Bis(1,2,2,6,6,-pentamethyl-4-piperidinal)
sebacate 0.4
[Tinuvin 292 by Ciba Geigy)
Titanium dioxide, rutile 5.0
The polyether urethane acrylate was p repared as
follows:
Toluene diisocyanate (119.158; 1.3664 equivalents),
commercially obtained as Mondur TD-80 Grad e A from Mobay,
Inc. of Pittsburgh, Pa. was combined with BHT, a
preservative (0.538). The mixture was char ged into a one
liter, 4-necked round bottom flask.
The flask was equipped with a stirrer , a dry air
sparge, a reflux condenser, a thermometer and a heating
mantle on an automatic jack controlled by a thermostat.
The mixture was held at 26C (78.8F) and 2-hydroxyethyl
_
acrylate (HEA) 84.94 grams; 0.7315 equival ents) was added
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to the flask containing the mixture over a two (2) hour
and twenty (20) minute period.
The mixture was maintained at 26.6°C (78.8°F for
about three (3) hours after which it was heated to 50°C
122°F). PTGL 1000 (277.72 g; 0.6073 g equivalents, made by
- Hodogaya Chemical, Japan, was added all at once to the
mixture. PTGL 1000 is a copolymer of 3-
methyltetrahydrofuran and tetrahydrofuran, both of which
have undergone a ring opening polymerization. The PTGL
1000 is the polymerization product of about 20 percent by
weight 3-methyltetrahydrofuran and about 80 percent by
weight of tetrahydrofuran.
The resulting mixture was allowed to mix for five
minutes. Diazabicyclooctane crystals (0.25g), (DABCO
crystals), from Air Products in Allentown, Pennsylvania,
were then added to the mixture. The exothermic reaction
was permitted to heat the mixture to 83°C (181.4°F). The
contents of the flask were then held at 70°C (158°F) until
the percent of free isocyanate in the oligomer was
negligible (< 0.1 percent).
The structure of the resulting oligomer is
represented schematically as HEA-(-TDI-PTGL 1000-)o.e-
TDI-HEA.
Example II
A coating composition was prepared in the same manner
as Example 1. The same polyether urethane acrylate as in
Example I was used in the following composition:
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Component: Percent
Polyether urethane acrylate 32.5
Ethoxylated bisphenol-A-diacrylate 56.0
Ethoxylated nonylphenolacrylate 8.0
[Photomer 4003 by Henkel]
2,4,6-trimethylbenzoyldiphenyl- '
phosphine oxide 1.0
[Lucirin TPO by BASF]
Hydroxycyclohexylphenylketone 2.0
[Irgacure 184 by Ciba Geigy]
Thiodiethylene-bis-
(3,5-di-tert-butyl-4-hydroxy)
hydrocinnamate 0.5
[Irganox 1035 by Ciba Geigy]
Comparative example A
A coating composition was prepared by mixing the
following components:
Component: Percent
Polyether urethane acrylate 49.1
Epoxy acrylate g.6
Trimethylol propane triacrylate '7,1
N-vinyl pyrrolidone 3.9
N-vinyl caprolactam
Phenothiazine (stabilizer) 0.01
2,4,6-trimethylbenzoyldiphenyl phosphine 2.4
oxide
Silicone oil [DC 193 from DOW Corning] 0.2
2-hydroxyethylacrylate O,g
Titanium dioxide, rutile 20.0
The polyether urethane acrylate was the reaction
product of a stoichiometric proportion of 2-hydroxyethyl
acrylate with an isocyanate-terminated oligomer, which is
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the urethane reaction product of polyoxytetramethylene
glycol of a molecular weight 650 with toluene
diisocyanate. The product had a NCO-content of 7.5~ by
weight. The isocyanate-terminated product used had a
viscosity at 30°C of 8000 centipoises.
The epoxy acrylate was the diacrylate of Epon
828 (Shell) which is a diglycidyl ether of bisphenol A
having a molecular weight of 390.
The above mixture was sandmilled to a particle
size finer than represented by a 7.5 North Standard grind
gauge rating and checked by light microscopy to make sure
that no particles having a size greater than 1 micron (1
micrometer) were present.
Comparative example B
A coating composition was prepared using the
following:
Component: Percent
Polycaprolactone urethane acrylate 41.4
Phenoxyethyl acrylate 45.1
Trimethylol propane triacrylate 5.0
2,4,6-trimethylbenzoyldiphenyl phosphine 3.0
oxide
Silicone oil [DC 203 from DOW Corning] 0.01
Titanium dioxide, rutile 5.0
Triethanol amine 0.5
The above mixture was sandmilled to a particle
size finer than represented by a North Standard grind
gauge rating and checked by light microscopy to make sure
that no particles having a size greater than 1 micron was
present.
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Comparative example C
The white colored secondary coating composition
from Neorad F480 (ICI) was used.
The coating compositions prepared in Examples I
and II, and Comparative examples A, B and C, were applied '
as a 3 mil film on a glass plate and cured by passing
beneath a single fusion ~~D~~ lamp at 1.0 J/cm2 in a
nitrogen atmosphere. The properties of the cured films
were measured according to the test procedures provided
below. The results are shown in Table 1.
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Table 1: Properties of coating compositions
Exp. I Exp. II Comp. Comp. Comp.
- Exp. A Exp. B Exp. C
Film 150 75 75 150 150
thickness (N)
clarity opaque clear opaque opaque opaque
color white clear white white white
viscosity 5390 6200 24,250 2550 12,850
(mPa.s)
95~ cure 1.4 0.2 "6 0.3 0.7
(J/cm2 )
tensile (MPa) 18 24 - 20 36
elongation 7 18 - 27 22
modulus (MPa) 500 560 - 670 1100
T (C) 17 20 24 31 46
T . - (C) 47 52 77 43 76
tan delta max 49 53 78 45 >8
(oC)
E (MPa) 22 26 33 11 13
after aging:
T E~ ~ loo0 22 22 19 38 61
(oC)
T ~~ = loo 51 53 75 49 89
(C)
tan delta max 52 56 74 51 94
(oC)
Eo (MPa) , 23 ' 24 25 7 9
(increase ,) (+5~) (-8~) (-24~) (-36~) (-31~)
Color white clear yellowed white yellowed
Peak water 1.1 1.2 3.2 2.1 6.6
absorption
Water soak 1.4 0.8 1.7 0.6 3.8
Extraction
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Exp. I Exp. II Comp. Comp. Comp.
Exp. A Exp. B Exp. C
Total water 2.5 2.0 4.9 2.7 10.4
sensitivity
From Table 1, it is clear that the coating
compositions of Examples I and II, according to the
invention, produced cured coatings having a better peak
water absorption than the coatings produced from the
coating compositions of Comparative Examples A, B and C.
The coatings produced using the coating compositions
according to the invention also exhibited an enhanced
stability in the aging test. In particular, the modulus
increased only 5~ in Example I and decreased only 8~ in
Example II. In contrast, the comparative coatings
decreased from 24~ to 36~. .Moreover, the color of the
coatings of Examples I and II is unchanged after aging.
Furthermore, the coatings of Examples I and II exhibited a
good resistance against attack from hydrocarbon gel.
Test Procedures
The water soak extraction and absorption were
measured using the following procedure. A drawdown of each
material to be tested was made at a film thickness as
indicated in Table 1 on a glass plate and cured. The cured
film was cut to form three sample specimens, approximately
3 cm x 3 cm on the glass plate. The glass plate containing
the three sample specimens was heated at 80°C for one hour
and then placed in a desiccator for 15 minutes. The
relative humidity and temperature of the desiccator were
measured.
125 ml (4 oz.) of deionized or distilled water
was poured into three 125 ml (4 oz.) glass jars, '
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maintained at a temperature of 23 _+ 2°C. Each of the
sample specimens were removed from the glass plate and
weighed on an analytical balance using corrugated Teflon
' paper to prevent sticking. Each sample specimen was then
placed into one the jars of water.
The sample specimens were soaked in the water
for 30 minutes and then removed from the glass jars. The
water remaining on the surface of the sample specimens was
removed by blotting them with lint free wiping tissue.
The samples were reweighed as above and placed
back into their respective jars.
The above procedure was repeated at 1, 2, 3, and
24 hours, and at 7 and 14 days.
At 21 days, the sample specimens were removed
from the glass jars and reweighed as above. The sample
specimens were placed onto a glass plate and heated at
80°C for one hour, and then placed in a desiccator for 15
minutes. The relative humidity and temperature of the
desiccator were measured. The sample specimens were
reweighed as before.
The percent weight change at each time interval
f or each sample specimen was determined. The values for
the three sample specimens at each time interval were
averaged. The water absorption reported is the largest,
positive average percent weight change.
The water extraction for each sample specimen
was determined by dividing the difference of the initial
and 21-day dried weights by the initial dried weight and
multiplying by 100. The reported value is the average of
the three sample specimen values.
The total water sensitivity is the sum of the
absolute values of the water absorption and the water
extraction.
The elastic modulus (E'), the viscous 'module
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(E'), and the tan delta max (E"/E') of the examples were
measured using a Rheometrics Solids Analyzer (RSA-11),
equipped with: 1) A personal computer having MS-DOS 5.0 or
later operating system and having Rhiosm software (Version
4.2.2 or later) loaded; 2) A liquid nitrogen controller
system for low-temperature operation.
The test samples were prepared by casting a film
of the material, having a thickness in the range of 0.02
~mm to 0.4 mm, on a glass plate. The sample film was cured
using a UV processor. A specimen approximately 35 mm (1.4
inches) long was cut from a defect-free region of the
cured film. For soft films, which tend to have sticky
surfaces, a cotton-tipped applicator was used to coat the
cut specimen with talc powder.
The film thickness of the specimen was measured
at five or more locations along the length. The average
film thickness was calculated to ~0.001 mm. The thickness
cannot vary by more than 0.01 mm over this length. Another
specimen was taken if this condition was not met. The
width of the specimen was measured at two or more
locations and the average value calculated to + 0.1 mm.
The geometry of the sample was entered into the
instrument. The length field was set at a value of 23.2 mm
and the measured values of width and thickness of the
sample specimen were entered into the appropriate fields.
Before conducting the temperature sweep,
moisture was removed from the test samples by subjecting
the test samples to a temperature of 80°C in a nitrogen
atmosphere for 5 minutes. The temperature sweep used
included cooling the test samples to about -60°C to about
-70°C and increasing the temperature at about 1°/minute
until the temperature reached about 60°C to about 70°C. .
The test frequency used was 1.0 radian/second.
The tensile strength of cured samples was tested
using a universal testing instrument, Instron Model 4201
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equipped with a personal computer and software "Series IX
Materials Testing System." The cells were loaded at a 2
and 20 pound capacity. The ASTM D638M was followed, with
the following modifications.
A drawdown of each material to be tested was
made on a glass plate and cured using a UV processor. The
cured film was conditioned at 23 + 2°C and 50 + 5~
relative humidity for a minimum of sixteen hours prior to
testing.
A minimum of eight test specimens, having a
width of .5+ 0.002 inches and a length of 5 inches, were
cut from the cured film. If the cured film was tacky to
the touch, a small amount of talc was applied to the film
surface using a cotton tipped applicator.
While the invention has been described in detail
and with reference to specific embodiments thereof, it
will be apparent to one of ordinary skill in the art that
various changes and modifications can be made therein
without departing from the spirit and scope thereof.
