U.S. patent application number 09/148772 was filed with the patent office on 2001-07-19 for radiation-curable coating compositions, coated optical fiber, radiation-curable matrix forming material and ribbon assembly.
Invention is credited to CHAWLA, CHANDER P..
Application Number | 20010008906 09/148772 |
Document ID | / |
Family ID | 22527308 |
Filed Date | 2001-07-19 |
United States Patent
Application |
20010008906 |
Kind Code |
A1 |
CHAWLA, CHANDER P. |
July 19, 2001 |
RADIATION-CURABLE COATING COMPOSITIONS, COATED OPTICAL FIBER,
RADIATION-CURABLE MATRIX FORMING MATERIAL AND RIBBON ASSEMBLY
Abstract
A radiation-curable, optical fiber coating composition has
enhanced color stabilization and is formulated from a composition
containing at least one radiation-curable oligomer or monomer. A
concentration of urethane and ether linkages in the
radiation-curable composition is such that a cured optical fiber
coating formed from said radiation-curable composition exhibits a
.DELTA.E of about 40 or less after being exposed for 96 hours to
150.degree. C. and then for 144 hours to 180.degree. C. Also
provided is a radiation-curable optical fiber coating composition
which is substantially urethane-free.
Inventors: |
CHAWLA, CHANDER P.;
(BATAVIA, IL) |
Correspondence
Address: |
PILLSBURY MADISON & SUTRO
INTELLECTUAL PROPERTY GROUP
1100 NEW YORK AVENUE NW
NINTH FLOOR EAST TOWER
WASHINGTON
DC
200053918
|
Family ID: |
22527308 |
Appl. No.: |
09/148772 |
Filed: |
September 4, 1998 |
Current U.S.
Class: |
522/90 ; 522/120;
522/182; 526/328 |
Current CPC
Class: |
C09D 155/005 20130101;
C03C 25/106 20130101 |
Class at
Publication: |
522/90 ; 522/120;
522/182; 526/328 |
International
Class: |
C08F 002/48; C08F
020/10 |
Claims
What is claimed is:
1. A radiation-curable, optical fiber coating composition having
enhanced color stabilization when suitably cured, formulated from a
composition comprising: at least one radiation-curable oligomer
containing a backbone made from monomers, wherein said monomers
comprise acrylic acid, (meth)acrylic acid, or a mixture thereof,
and at least one radiation-curable functional group bound to said
backbone, said radiation-functional group selected from the group
consisting of acrylate, methacrylate and N-vinyl functionality,
said oligomer having a number average molecular weight of from
about 500 to about 200,000, and wherein said composition contains
0-5% by weight urethane, based on total weight of the
composition.
2. A radiation-curable, optical fiber coating composition according
to claim 1, wherein said coating composition is formulated to
provide, after cure, a coating selected from the group consisting
of inner primary coatings, outer primary coatings, colored outer
primary coatings, ink coatings, bundling materials, ribbon matrix
materials and colored matrix materials.
3. A radiation-curable, optical fiber coating composition according
to claim 1, wherein said urethane is contained in said
oligomer.
4. A radiation curable, optical fiber coating composition according
to claim 1, wherein at least one said oligomer contains a backbone
comprising at least one member selected from the group consisting
of polyether, polyester, polycarbonate, hydrocarbon, urethane
acrylate and mixtures thereof.
5. A radiation-curable, optical fiber coating composition according
to claim 4, wherein said urethane is contained in said
oligomer.
6. A radiation-curable, optical fiber coating composition according
to claim 1, wherein the concentration of urethane in said
radiation-curable composition is substantially zero.
7. A radiation-curable, optical fiber coating composition according
to claim 1, wherein the composition comprises ether linkages in an
amount of about 15% by weight or less.
8. A radiation-curable, optical fiber coating composition according
to claim 1, wherein said backbone further comprises a polyol.
9. A radiation-curable, optical fiber coating composition according
to claim 1, wherein said radiation-curable functional group is
connected to said backbone via an ester linking group.
10. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said oligomer is present in an amount
of about 5 to about 90% by weight, based on total weight of said
composition.
11. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said composition further comprises a
low viscosity diluent in an amount of from about 1 to about 70% by
weight, based on total weight of said composition.
12. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said composition further comprises a
glass-adhesion promoting agent and is adapted to provide an inner
primary coating when suitably cured.
13. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said composition is adapted to
provide an outer primary coating when suitably cured.
14. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said composition further comprises at
least one pigment in an amount sufficient to provide a visible
color and said composition is adapted to provide an ink coating
when suitably cured.
15. A radiation-curable, optical fiber coating composition
according to claim 1, wherein a concentration of urethane and ether
linkages in said radiation-curable composition is such that a cured
optical fiber coating formed from said radiation-curable
composition has a .DELTA.E of about 40 or less after being exposed
for 96 hours at 150.degree. C. and then 144 hours at 180.degree.
C.
16. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said oligomer is substantially free
of silicon and fluorine.
17. A radiation-curable, optical fiber coating composition
according to claim 1, wherein said composition is substantially
free of fluorine-containing additives and said composition has a
refractive index at least 1.5 after suitable curing.
18. A radiation-curable, optical fiber coating composition
according to claim 1, further comprising a maleimide.
19. A radiation-curable, optical fiber coating composition
according to claim 1, further comprising a photopolymerization
initiator.
20. A radiation-curable, optical fiber coating composition
according to claim 1, where in said composition provides a coating
having a coefficient of friction, film-to-film, of about 0.5 or
less, without use of release agents.
21. A radiation-curable, optical fiber coating composition
according to claim 1, wherein after said coating composition is
suitably cured, coefficient of friction, film-to-film, is less than
coefficient of friction, film-to-steel.
22. A coated optical fiber comprising: an optical fiber; and at
least one coating on said optical fiber comprising at least one
radiation-curable oligomer containing a backbone made from
monomers, wherein said monomers comprise acrylic acid,
(meth)acrylic acid, or a mixture thereof, and at least one
radiation-curable functional group bound to said backbone, said
radiation-functional group selected from the group consisting of
acrylate, methacrylate and N-vinyl functionality, said oligomer
having a number average molecular weight of from about 500 to about
200,000, and wherein said composition contains less than 5% by
weight urethane, based on total weight of the composition.
23. A radiation-curable composition for coating fiber optic
materials comprising the following combination of pre-mixture
ingredients: (A) between about 10 wt. % and about 90 wt. % of a
radiation-curable oligomer comprising an acrylic backbone and at
least one radiation-curable group, wherein said oligomer is
substantially urethane-free; (B) between about 10 wt. % to about 90
wt. % of one or more monomer diluents.
24. A radiation-curable, optical fiber coating composition
according to claim 23, further comprising a maleimide.
25. A radiation-curable, optical fiber coating composition
according to claim 23, further comprising a photopolymerization
initiator.
26. A radiation-curable composition according to claim 23, wherein
said coating composition is formulated to provide, after cure, a
coating selected from the group consisting of inner primary
coatings, outer primary coatings, colored outer primary coatings,
ink coatings, bundling materials, ribbon matrix materials and
colored matrix materials.
27. A radiation-curable composition according to claim 1, wherein
said composition, after radiation-curing to attain at least 90% of
its maximum secant modulus, has a film-to-film coefficient of
friction of less than about 1.0.
28. A radiation-curable composition according to claim 23, wherein
the amount of said oligomer is about 20 wt. % to about 60 wt.
%.
29. A radiation-curable composition according to claim 23, wherein
said composition is substantially urethane-free.
30. A radiation-curable composition according to claim 23, wherein
at least one of said monomer diluents comprises a structure
selected from the group consisting of an aromatic group, a bicyclic
ring, a lactam ring and a lactone ring.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to radiation-curable, optical
fiber coating compositions, which are adaptable for forming
coatings such as inner primary coatings, outer primary coatings,
colored secondary coatings, ink coatings, bundling materials,
ribbon matrix materials and colored matrix materials on optical
fibers. The compositions comprise acrylated acrylic oligomers. The
present invention also relates to a coated optical fiber.
BACKGROUND OF RELATED ART
[0002] Radiation-curable compositions are vital to the optical
fiber industry. Materials used in the manufacture of optical fibers
are typically sensitive to environmental and handling stresses and
can be made of glass, for example. Radiation-curable compositions
have been formulated to provide protective coatings for sensitive
optical fibers. Such compositions include, among others, inner
primary coatings, outer primary coatings, colored outer primary
coatings, single coatings, matrix materials, colored matrix
materials, bundling materials, inks, adhesives, and upjacketting
coatings. Optical fiber cable manufacturers increasingly demand
better performance from these coating compositions in order to
allow the optical fiber to function in a wider array of
environments and have better transmission performance In addition,
compositions are demanded which deliver high performance at reduced
cost.
[0003] Optical fiber assemblies provide a modular design which
simplifies the construction, installation and maintenance of
optical fibers by eliminating the need to handle individual optical
fibers. Examples of optical fiber assemblies include ribbon
assemblies and cables. A typical optical fiber assembly is made of
a plurality of coated optical fibers which are bonded together in a
matrix material. Such optical fiber assemblies containing a
plurality of coated optical fibers have been used for the purpose
of multi-channel transmission. The matrix material can encase the
optical fibers, or the matrix material can edge-bond the optical
fibers together.
[0004] Coated optical fibers for use in optical fiber assemblies
are usually coated with an outer colored layer, called an ink
coating, or alternatively a colorant is added to the outer primary
coating to facilitate identification of the individual coated
optical fibers. Thus, the matrix material which binds the coated
optical fibers together contacts the outer ink coating if present,
or the colored outer primary coating.
[0005] When a single optical fiber of the assembly is to be fusion
connected with another optical fiber or with a connector, an end
part of the matrix layer can be removed to separate each of the
optical fibers.
[0006] Desirably, the primary coatings on the coated optical
fibers, and the ink coating if present, are removed simultaneously
with the matrix material to provide bare portions on the surface of
the optical fibers (hereinafter referred to as "ribbon stripping").
In ribbon stripping, the matrix material, primary coatings, and ink
coating, are desirably removed as a cohesive unit to provide a
clean, bare optical fiber which is substantially free of
residue.
[0007] The production of and useful characteristics for coated
optical fibers are discussed in, for example, U.S. Pat. No.
5,104,433, which is hereby incorporated by reference. Single mode
or multimode fiber can be prepared. Step index and graded index
fibers can be prepared. In the coated fiber, loss due to
absorption, scattering, macrobending and microbending should be
minimized. Avoiding microbending loss is particularly important.
Optical fiber typically is about 125 microns in diameter, and
coating layers of approximately 30 microns are applied thereto.
[0008] Optical fiber ribbons are described in, for example, U.S.
Pat. No. 4,900,126 to Jackson et al.; U.S. Pat. No. 5,373,578 to
Parker et al., U.S. Pat. No. 5,379,363 to Bonicel et al.; the
complete disclosures of which are hereby incorporated by reference.
Ribbon stripping is discussed in, for example: "Testing of 4- and
8-Fiber Ribbon Strippability", G. A. Mills, Int. Wire & Cable
Symp. Proc., 1992, pgs. 472-474; "The Effect of Fiber Ribbon
Component Materials on Mechanical and Environmental Performance",
K. W. Jackson et al., Int. Wire & Cable Symp. Proc., 1993, pgs.
28-34; which are hereby incorporated by reference.
[0009] In addition to ribbon packaging, fiber designs can include
tight buffer, loose tube, filled loose tube, and mini-bundle.
Cables can be packaged by conventional buffering, stranding, and
jacketing steps. Optical fiber fabrication is disclosed in, for
example, the article "Fiber Optics" Encyclopedia of Chemical
Technology, Vol. 10, 4th Ed., pg. 514-538, (John Wiley & Sons,
1993), which is hereby incorporated by reference.
[0010] Inner primary coatings, outer primary coatings and matrix
materials are usually formed from radiation-curable systems. Ink
coatings usually are formed from a pigment dispersed within a
radiation-curable system. The UV curable systems contain a UV
curable oligomer or monomer that is liquid before curing to
facilitate application of the composition, and then a solid after
being exposed to UV radiation.
[0011] Modern high speed optical fiber drawing towers and ribbon
forming towers operate at a very high speed. Thus, the
radiation-curable compositions for forming inner primary, outer
primary and ink coatings must have a very fast cure speed to ensure
complete cure of the coatings and matrix material. In addition, the
compositions should not contain ingredients that can migrate to the
surface of the optical fiber and cause corrosion. Such additives
are "fugitive" or free to migrate from the cured coating. Fugitive
additives are generally undesirable because they might, for
example, migrate and attack the optical fiber or be incompatible
and cause loss of optical clarity. The compositions should also not
contain ingredients which can cause instability in the protective
coatings or matrix material. Ink coatings for optical fibers should
be color fast for decades. The coatings and matrix material should
not cause attenuation of the signal transmission and be impervious
to cabling gels and chemicals.
[0012] Each of the coatings on the optical fiber and matrix
material should be resistant to degradation caused by heat or light
which can result in discoloration or even loss of integrity of the
coatings or matrix material. If coating integrity is lost, the
optical fiber may not be adequately protected from the environment
resulting in signal attenuation. If one of the coating layers
discolors, misidentification of the individual optical fibers may
occur during splicing. Thus, there is a need for a
radiation-curable coating composition suitable for application as a
coating on an optical fiber, such as an inner primary coating,
outer primary coating, colored secondary coating, ink coating,
bundling material, ribbon matrix material and colored matrix
material that exhibits substantial resistance to degradation caused
by heat or light.
[0013] Current optical fiber coatings and matrix materials utilize
acrylate functional monomers and acrylate functional oligomers. The
oligomer backbone is usually derived from one or more polyether,
polycarbonate, polyester or hydrocarbon polyols bound together via
urethane linkages, to which acrylate functional groups are bound
via urethane linkages. Thus, the oligomers used are generally
acrylated polyurethanes. Optical fiber coatings and matrix
materials can degrade when exposed to heat, causing undesirable
yellowing and even loss of integrity of the coating or matrix
material. Thus, there is also a need for radiation-curable
compositions which exhibit enhanced resistance to thermal
degradation.
[0014] Urethane acrylate oligomers are most widely used in the
industry. Organofunctional silane coupling agents (or "adhesion
promoters") are also commonly used in the inner primary coating.
For outer primary coatings, colored outer primary coatings and
matrix materials, important additives include slip additives which
function to lower the coefficient of friction of the cured
material. A low coefficient of friction is important for processing
and handling of coated optical fiber or optical fiber ribbon.
[0015] Typical urethane acrylate containing compositions have, upon
cure, relatively high coefficients of friction. Therefore, despite
problems associated with use of fugitive additives, slip additives
are generally required in many cases to achieve the necessary
performance. Hence, a need exists to lower the coefficient of
friction of cured urethane acrylate compositions without the use of
slip additives, and in particular, without fugitive slip
additives.
[0016] From the above, it is clear that optical fiber technology
places many unique demands on radiation-curable compositions which
more conventional applications, such as printing inks and paints,
do not.
[0017] Formulation and application of radiation-curable
compositions for fiber optic materials in general and optical fiber
coatings in particular can be found in, for example, U.S. Pat. Nos.
4,472,019; 4,572,610; 4,716,209; 5,093,386; 5,384,342; 5,456,984;
5,596,669; and copending U.S. Pat. application 08/701,428, which
are hereby fully incorporated herein by reference. These patents
demonstrate that urethane acrylate oligomers have become well-known
in the optical fiber industry.
SUMMARY OF THE INVENTION
[0018] An objective of the present invention is to provide
radiation-curable compositions that are adaptable for use as inner
primary coatings, outer primary coatings, colored secondary
coatings, ink coatings, bundling materials, ribbon matrix materials
and colored matrix materials on optical fibers, which when suitably
cured exhibit enhanced resistance to thermal degradation, are
non-yellowing and/or have low coefficients of friction, with
compositions directed to secondary coatings, ink coatings, bundling
materials, and matrix materials being preferred.
[0019] The above objectives and other objectives are obtained by
the following. It has now been found that the urethane and
polyether linkages commonly used in inner primary coatings, outer
primary coatings, colored outer primary coatings, ink coatings, and
matrix materials are susceptible to thermal degradation if present
in large amounts. The present invention provides radiation-curable
compositions with low, or substantially no urethane and polyether
linkages to provide optical fiber coatings and matrix materials
having enhanced resistance to thermal degradation. The
radiation-curable compositions according to the present invention
provide coatings and matrix materials having excellent outdoor
durability, resistance to discoloration, and excellent mechanical
properties.
[0020] The present invention provides a novel radiation-curable,
optical fiber coating composition having enhanced color
stabilization when suitably cured. The radiation-curable, optical
fiber coating composition is formulated from a composition
including at least one radiation-curable oligomer containing a
backbone formulated from monomers including acrylic acid,
methacrylic acid, or a mixture thereof, and at least one
radiation-curable functional group bound to the backbone, the
oligomer having a number average molecular weight of from about 500
to about 200,000, wherein the urethane concentration in the
composition is less than 5% by weight, based on the total weight of
the composition.
[0021] The present invention also provides a novel
radiation-curable composition which is formulated from a
composition including at least one radiation-curable oligomer or
monomer, wherein a concentration of urethane and ether linkages in
the radiation-curable composition is such that a cured optical
fiber coating formed from the radiation-curable composition
exhibits a .DELTA.E of about 40 or less after being exposed to 96
hours at 150.degree. C. and then 144 hours at 180.degree. C.
[0022] The present invention further provides a novel
radiation-curable optical fiber coating composition having a low
coefficient of friction without the use of slip additives when
suitably cured including the following combination of pre-mixture
ingredients:
[0023] (A) between about 10 wt. % and about 95 wt. % of at least
one radiation-curable oligomer comprising an acrylic backbone and
at least one radiation-curable acrylate group, wherein the oligomer
is substantially urethane-free;
[0024] (B) between about 5 wt. % to about 95 wt. % of one or more
monomer diluents;
[0025] (C) optionally, an effective amount of at least one
photopolymerization initiator.
[0026] The present invention provides a radiation-curable
composition for fiber optic materials comprising the following
combination of pre-mixture ingredients:
[0027] at least two radiation-curable compounds, wherein at least
one of the compounds is a radiation-curable oligomer comprising at
least one acrylate group and an acrylic oligomeric backbone, the
compounds being substantially urethane-free,
[0028] optionally, at least one photoinitiator,
[0029] wherein the amounts of the pre-mixture ingredients are
effective to provide the radiation-curable composition with a
viscosity of about 1,000 cps to about 10,000 cps.
[0030] The present invention also provides a novel coated optical
fiber comprising:
[0031] an optical fiber;
[0032] at least one coating on the optical fiber having enhanced
resistance to thermal degradation. The coating has a concentration
of urethane and ether linkages that provides a .DELTA.E of about 40
or less after being exposed for 96 hours to 150.degree. C. and then
for 144 hours to 180.degree. C.
[0033] The present invention also provides a novel
radiation-curable, matrix forming composition having enhanced color
stabilization when suitably cured. The composition is formulated
from a composition comprising at least one radiation-curable
oligomer or monomer. A concentration of urethane and ether linkages
in the radiation-curable composition is such that a cured matrix
material formed from the radiation-curable composition exhibits a
.DELTA.E of about 40 or less after being exposed for 96 hours to
150.degree. C. and then for 144 hours to 180.degree. C.
[0034] The present invention further provides a novel ribbon
assembly comprising:
[0035] a plurality of optical fibers;
[0036] a matrix material binding the plurality of coated optical
fibers together and having enhanced resistance to degradation
caused by heat. The matrix material has a concentration of urethane
and ether linkages that provides a .DELTA.E of about 40 or less
after being exposed for 96 hours to 150.degree. C. and then for 144
hours to 180.degree. C.
BRIEF DESCRIPTION OF THE FIGURE
[0037] The FIGURE illustrates a graph of .DELTA.E versus Time at
elevated temperature for Examples 1-2 and Comparative Example
A.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0038] It has now been found that urethane linkages and ether
linkages present in optical fiber coatings and matrix materials can
substantially degrade over time upon exposure to heat, resulting in
undesirable properties. For example, degradation of the urethane
and/or ether linkages can lead to unwanted yellowing of the optical
fiber coating. Yellowing of the coating on optical fibers used in
ribbon assemblies can lead to misidentification of the individually
color-coded optical fibers. Furthermore, degradation of the
urethane and/or ether linkages in the optical fiber coating can
even lead to a loss of coating integrity, resulting in cracking,
flaking, or peeling of the coating. When such a loss of integrity
occurs, the coating is no longer able to protect the delicate
optical fiber from the environment, which can lead to attenuation
of the signal transmission.
[0039] Radiation-curable optical fiber coating compositions and
radiation-curable matrix compositions are now well known in the
art. Such radiation-curable compositions usually contain at least
one radiation-curable oligomer or monomer, as well as reactive
diluents, photoinitiators, and additives. The term
"radiation-curable composition" hereinafter will be understood to
refer to both radiation-curable, optical fiber coating compositions
(such as, for forming inner primary coatings, outer primary
coatings, colored secondary coatings, ink coatings, bundling
materials, ribbon matrix materials and colored matrix materials on
optical fibers, unless otherwise stated.
[0040] For this invention, "pre-mixture ingredient" means an
ingredient before it is mixed with other ingredients. When
formulating a radiation-curable composition from its ingredients,
some interaction or reaction of the ingredients is possible after
mixing. The present invention is not generally limited by the order
in which the pre-mixture ingredients are mixed. In many cases, for
example, monomer diluent will be present as a solvent during
oligomer preparation and will be further incorporated into the
compositions after oligomer preparation. Also, oligomers can be
purchased as mixtures of oligomer and monomer diluent.
[0041] "(Meth)acrylate" refers to acrylate, methacrylate, or a
mixture thereof. The term "(meth)acrylic" refers to acrylic,
methacrylic, or a mixture thereof. "Urethane-free" means urethane
linkage are not present in the composition.
[0042] It has been found by extensive experimentation that as the
concentration of urethane linkages and ether linkages present in
the radiation-curable composition is decreased, the resistance of
the cured optical fiber coating or matrix material to thermal
degradation is substantially increased. The terms "urethane
concentration" and "ether concentration" represent the weight
percentage of all urethane linkages or ether linkages present in
the radiation-curable composition, relative to the total weight of
the radiation-curable composition. Based on this discovery, the
urethane concentration and/or ether concentration should be
adjusted to a lower level which provides an optical fiber coating
or matrix material having the desired resistance to thermal
degradation. In particular, the urethane concentration and/or ether
concentration can be adjusted to a lower level which provides a
cured optical fiber coating or matrix material having a .DELTA.E
value of 3 or less, preferably a .DELTA.E value of about 2 or less,
and most preferably a .DELTA.E value of about 1 or less when
exposed for 96 hours to 1 50.degree. C. The urethane concentration
and/or ether concentration can also be adjusted to a lower level
which provides a cured optical fiber coating or matrix material
having a .DELTA.E value of about 40 or less, preferably a .DELTA.E
value of about 30 or less, more preferably a .DELTA.E value of
about 20 or less, and most preferably a .DELTA.E value of about 10
or less, when exposed for 96 hours to 150.degree. C. and then 144
hours to 180.degree. C.
[0043] Suitable urethane concentrations have been found to be less
than about 5% by weight, preferably about 3% by weight or less,
more preferably about 1% by weight or less, and most preferably
substantially 0% by weight, based on the total weight of the
radiation-curable coating composition. Suitable ether
concentrations have been found to be about 15% by weight or less,
preferably about 10% by weight or less, and most preferably about
6% by weight or less, based on the total weight of the
radiation-curable coating composition. The urethane concentration
is based on the amount of urethane linkage and the ether
concentration is based on the amount of ether linkage in the
radiation-curable composition.
[0044] The improved radiation-curable compositions according to the
present invention can be based on known radiation-curable
compositions, which contain radiation-curable monomers and
oligomers. The known radiation-curable compositions can only become
the improved radiation-curable compositions according to the
present invention by reducing the urethane and/or ether
concentration, such as by replacing the radiation-curable,
polyurethane and/or polyether, oligomer(s) and monomer(s) used in
known radiation-curable compositions with radiation-curable
oligomer(s) and monomer(s) having reduced quantities of urethane
and/or ether linkages. Examples of suitable radiation-curable
compositions that can be reformulated according to the present
invention include those variously disclosed in U.S. Pat. Nos.
4,624,994; 4,682,851; 4,782,129; 4,794,133; 4,806,574; 4,849,462;
5,219,896; and 5,336,563, all of which are incorporated herein by
reference.
[0045] In a first embodiment of the present invention, the
compositions are urethane-free with a low coefficient of friction
after curing without a slip additive. In a second embodiment of the
present invention also with low coefficient of friction without a
slip additive, the compositions include some urethane linkage, and
preferably, some urethane linkage in the oligomer. In a third
embodiment of the present invention, the compositions are
urethane-free and have improved thermal stability and non-yellowing
characteristics.
[0046] Compositions according to the present invention can be
formulated from (A) an oligomer system, (B) a monomer or reactive
diluent system, (C) an optional photoinitiator system, and (D)
additives.
[0047] (A) Radiation-Curable Oligomer
[0048] Radiation-curable oligomers suitable for use in the present
invention contain one or more radiation-curable functional groups.
The radiation-curable functional groups can be any functional group
capable of polymerization when exposed to actinic radiation.
Usually, the radiation-curable functionality 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, vinyl, vinylether, vinyl ester,
N-substituted acrylamide, N-vinyl amide, maleate esters, and
fumarate esters. Preferably, the ethylenic unsaturation is provided
by a group containing at least one acrylate, methacrylate, or
N-vinyl functionality.
[0049] Another type of 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 a group containing
allylic unsaturation and a group containing a tertiary amine or
thiol.
[0050] Preferably, at least about 80 mole %, more preferably, at
least about 90 mole %, and most preferably substantially all of the
radiation-curable functional groups present in the oligomer are
acrylate, methacrylate or N-vinyl functionalities.
[0051] The radiation-curable oligomers usually comprise a carbon
containing backbone to which the radiation-curable functional
group(s) is bound. Examples of suitable carbon-containing backbones
include polyolefins, polyesters, polyamides, and polycarbonates.
The size of the carbon-containing backbone can be selected to
provide the desired molecular weight. The number average molecular
weight of the oligomer is usually between about 500 g/mol to about
200,000 g/mol, preferably between about 700 g/mol to about 100,000
g/mol, and more preferably between about 1,000 g/mol to about 5,000
g/mol. Number average molecular weight can be determined by gel
permeation chromatography. The average functionality (number of
radiation-curable functional groups) of the oligomer is usually at
least about 1.0, preferably at least about 1.8, and generally lower
than about 20, preferably lower than about 15.
[0052] The invention is not limited by how the oligomer is
prepared. Oligomer synthetic routes can, for example, involve an
esterification of a hydroxyl-functional acrylic oligomer with
(meth)acrylic acid, or the reaction of an epoxy-functional acrylic
oligomer with (meth)acrylic acid.
[0053] The radiation-curable oligomer is preferably formed by
reacting a polymer containing an epoxy group with at least one of
acrylic acid or methacrylic acid. The polymer residue after the
reaction is the carbon-containing backbone to which either an
acrylate or methacrylate is bound. The general reaction of epoxy
groups with acrylic acid and methacrylic acid is well known and
therefore one skilled in the art will easily be able to form the
desired radiation-curable oligomer based on the disclosure provided
herein.
[0054] The radiation-curable oligomer can also be formed by
reacting a polymer containing a hydroxyl group with a compound
containing a carboxylic acid and a radiation-curable functional
group, or a polymer containing a carboxylic acid with a compound
containing a radiation-curable functional group and a hydroxyl
group, to form an ester linkage between the radiation-curable
functional group and the polymer. The residue of the polymer after
the reaction is the carbon-containing backbone. The reaction of
carboxylic acid functional groups with hydroxyl groups to form
ester linkages is well known in the art. Thus, one skilled in the
art will be able to make the desired oligomer according to the
present invention based on the disclosure provided herein. This
method for making the oligomer is not preferred because water is
formed in the reaction, which must be scavenged.
[0055] Acrylic monomers which can be used to prepare the acrylic
oligomer can be represented as the esters represented in formula
(1),
CH.sub.2.dbd.CHCOOR (1)
[0056] In formula (1), the acrylic monomers can be various types of
esters including, for example, n-alkyl esters, secondary and
branched-chain alkyl esters, esters of olefinic alcohols,
aminoalkyl esters, esters of ether alcohols, cycloalkyl esters, and
esters of halogenated alcohols, glycol diacrylates, vinyl acetates
and styrenes. In particular, these monomers may include compounds
with vinyl groups, such as styrene, vinyl acetate and
acrylonitrile.
[0057] Methacrylic monomers, CH.sub.2.dbd.C(CH.sub.3)COOR, which
are analogous to those of the acrylic monomers in formula (1) can
also be used. In general, monomers represented as
CH.sub.2.dbd.CR.sub.1COOR can be used wherein R.sub.1 is a
C.sub.1-C.sub.6 alkyl.
[0058] N-alkyl esters in formula (1) include R being methyl, ethyl,
propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl,
tetradecyl, hexadecyl;
[0059] secondary and branched-chain alkyl esters in formula (1)
include R being isopropyl, isobutyl, sec-butyl, 2-ethylbutyl,
2-ethylhexyl;
[0060] esters of olefinic alcohols in formula (1) include R being
allyl, 2-methylallyl, furfuryl, 2-butenyl;
[0061] aminoalkyl esters in formula (1) include R being
2-(dimethylamino)ethyl, 2-(diethylamino)ethyl,
2-(dibutylamino)ethyl, and 3-(diethylamino)propyl;
[0062] esters of ether alcohols include R being 2-methoxyethyl,
2-ethoxyethyl, tetrahydrofurfuryl, 2-butoxyethyl;
[0063] cycloalkyl esters include R being cyclohexyl,
4-methylcyclohexyl, 3,3,5-trimethylcyclohexyl;
[0064] esters of halogenated alcohols include R being 2-bromoethyl,
2-chloroethyl, 2,3-dibromopropyl;
[0065] esters of glycol diacrylates include R being ethylene glycol
(monoester), ethylene glycol, propylene glycol, 1,3-propanediol,
1,4-butanediol, diethylene glycol, 1,5-pentane diol, triethylene
glycol, dipropylene glycol, 2,5-hexanediol,
2,2-diethyl-1,3-propanediol, 2-ethyl-1,3-hexanediol, and
1,10-decanediol.
[0066] Additional (meth)acrylic acid and ester polymers are
disclosed in, for example, Encyclopedia of Polymer Science &
Engineering, Vol. 1, pgs. 211-305, (John Wiley & Sons, 1985),
the complete disclosure of which is hereby incorporated by
reference.
[0067] Acrylated acrylics can be prepared by conventional synthetic
methods including, for example, (1) partial esterification of
acrylic polymers having pendant carboxylic acid groups with
hydroxyethyl acrylate or glycidyl methacrylate, or in the
alternative, acrylation of glycidyl methacrylate terpolymer with
acrylic acid, or (2) polymerization of monomers which already have
acrylate groups such as, for example, allyl methacrylate or
N,N-dimethylaminoethyl methacrylate.
[0068] The Tg of the oligomer can be lowered by decreasing the
content of methyl methacrylate.
[0069] If desired, the radiation-curable oligomer can also be
easily formed by reacting (1) a polymer containing an amine, (2) a
compound containing a radiation-curable functional group and an
amine, and a (3) polyisocyanate. The general reaction of isocyanate
functional groups with amine groups to form urea linkages is well
known in the art. Thus, one skilled in the art will be able to make
the improved oligomer according to the present invention based on
the disclosure provided herein.
[0070] The carbon-containing backbone can also comprise hydrocarbon
polymeric blocks which are connected via linking groups. Examples
of oligomer containing such a hydrocarbon backbone can be
represented by the following formula (2):
R--L--(P--L).sub.n--R (2)
[0071] where R is a radiation-curable functional group, P1 is a
hydrocarbon, for example, having from about 10 to about 350 carbon
atoms, preferably from about 100 to about 250 carbon atoms;
[0072] L is a linking group, and
[0073] n is a positive integer, such as, from 1 to about 30,
preferably from 1 to about 20.
[0074] Preferably, the oligomer is substantially free of fluorine
and silicon.
[0075] Examples of suitable linking groups include alkoxy or ring
opened epoxy such as ethoxy, propoxy, butoxy, and repeat units
thereof. L can also be an ester, carbonate, amide, imide, or urea
linking group. While not preferred, L can be an ether group or
urethane group in quantities less than 5% by weight of the total
composition. However, the oligomer should not contain a polyether
having more than about 10 ether groups.
[0076] The invention is not limited to the oligomers represented by
formula (2). For example, the oligomer may be branched and may
contain one or more radiation-curable functional groups R.
[0077] Examples of commercially available acrylated acrylic
oligomers include CELRAD 1700 and NOVACURE 1701 (Interez Inc.).
Preferred examples of acrylated acrylic oligomers include those
which can be purchased from Sartomer Co., including PRO 971; PRO
1494, which is a fluoromodified acrylated acrylic; and PRO-1735,
which is a lauryl modified acrylated acrylic.
[0078] The oligomer can include at least one oligomer that contains
a backbone of polyether, polyester, polycarbonate, hydrocarbon,
urethane acrylate or mixtures thereof. The polyether content should
be limited to not more than about 15%.
[0079] The amount of the radiation-curable oligomer (A) can be, for
example, about 5 wt. % to about 95 wt. %, and preferably, about 10
wt. % to about 80 wt. %, and more preferably, about 20 wt. % to
about 60 wt. %. One or more oligomers can be used.
[0080] Preferably, a mixture of ethylenically-unsaturated monomers
is used to provide a copolymer backbone. By using mixtures of
different monomers, the properties of the cured coating formed from
the radiation-curable composition can be easily tailored. For
example, acrylic polymers tend to form soft and tacky coatings,
whereas methacrylic polymers tend to form hard and brittle
coatings. Thus, by using different combinations of acrylic and
methacrylic monomers, copolymers can be formed which provide
coatings having varying hardness and flexibility. In this manner,
the radiation-curable composition can be easily tailored for
forming outer primary coatings, colored secondary coatings, ink
coatings, bundling materials, ribbon matrix materials and colored
matrix materials having the desired hardness and flexibility
properties.
[0081] Examples of suitable ethylenically unsaturated functional
groups for forming the vinyl-addition polymer 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 N-vinyl
functionality.
[0082] Examples of suitable ethylenically-unsaturated monomers
include: methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate,
n-butyl (meth)acrylate, i-butyl (meth)acrylate, ethyl
(meth)acrylate, vinyl acetate, vinyl versatate, N-isobutoxymethyl
acrylamide, N-methylol acrylamide, (meth)acrylic acid, itaconic
acid, and styrene. Acrylic acid and methacrylic acid are
preferred.
[0083] Preferably, the ethylenically-unsaturated monomer also
contains at least one functional group which can be used to attach
a radiation-curable functional group to the formed copolymer
backbone. Examples of suitable functional groups for attaching a
radiation-curable functional group include hydroxyl, amino, and
epoxy. One skilled in the art will be able to attach a
radiation-curable functional group to the vinyl-addition copolymer
using these functional groups. For example, if an
ethylenically-unsaturated monomer containing an amine group is
used, the resulting vinyl-addition polymer will contain the amine
group. A compound containing a radiation-curable functional group
and an isocyanate group can be reacted with the amine group to form
a urea linkage between the radiation-curable functional group and
the vinyl-addition polymer.
[0084] As another example, if an ethylenically-unsaturated monomer
containing a hydroxyl group is used, the resulting vinyl-addition
polymer will contain the hydroxyl group. A compound containing a
radiation-curable functional group and a carboxylic acid group can
be reacted with the hydroxyl group to form an ester linkage between
the radiation-curable functional group and the vinyl-addition
polymer. However, this type of reaction is not preferred because
water is formed which must be scavenged.
[0085] As a further example, if an ethylenically-unsaturated
monomer containing an epoxide group is used, the resulting
vinyl-addition polymer will contain the epoxide group. Acrylic acid
or methacrylic acid can be reacted with the epoxide group to form
an ester linkage between the radiation-curable functional group,
acrylate or methacrylate in this case, and the vinyl-addition
polymer. This type of reaction is the preferred method for forming
the radiation-curable, vinyl-addition copolymer.
[0086] Examples of suitable hydroxy-functional
ethylenically-unsaturated monomers include: hydroxyethyl
(meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl
(meth)acrylate, and hydroxy terminated (meth)acrylate prepolymers
such as "TONE.TM." prepolymers, available from Union Carbide.
[0087] Examples of suitable amine-functional
ethylenically-unsaturated monomers include, for example the adduct
of trimethylolpropane, isophoronediisocyanate and
di(m)ethylethanolamine, the adduct of hexanediol,
isophoronediisocyanate and dipropylethanolamine, and the adduct of
trimethylolpropane, trimethylhexamethylenediisocyanate,
trimethylhexamethylenediisocyanate and di(m)ethylethanolamine.
[0088] Examples of suitable epoxy-functional
ethylenically-unsaturated monomers include, for example glycidyl
(meth)acrylate, epoxy-cyclohexane, phenylepoxyethane,
1,2-epoxy-4-vinylcyclohexane, 1,2-epoxy-4-epoxyethyl-c- yclohexane,
the diglycidylether of polyethylene-glycol, and the diglycidylether
of bisphenol-A, and the like.
[0089] A thermal initiator can be added to enhance the
co-polymerization reaction between the ethylenically-unsaturated
monomer(s). Thermal initiators are well known and one skilled in
the art will easily know how to select and use them, based on the
disclosure herein. Examples of suitable thermal initiators
include:
[0090] t-butylperoxy 2-ethylhexanoate,
[0091] t-butylperoxy benzoate,
[0092] t-butylperoxy pivalate,
[0093] t-amylperoxy 2-ethylhexanoate,
[0094] t-amylperbenzoate,
[0095] t-amylperpivalate, and
[0096] azo compounds such as azobisisobutyronitrile.
[0097] (B) Monomer Diluent
[0098] The compositions according to the invention also comprise a
monomer or reactive diluent system which comprises at least one
monomer diluent. The reactive diluent can be used to adjust the
viscosity of the coating composition. Usually, the viscosity of the
low viscosity diluent monomer is from about 5 to about 500 mPa.s at
25.degree. C. Examples of suitable viscosities for optical fiber
coating compositions range from about 500 to about 50,000 mPa.s at
25.degree. C. Examples of suitable viscosities for optical fiber
coating compositions that are suitable for application on optical
fiber drawing towers range from about 1,000 to about 25,000,
preferably about 2,500 to about 1 1,000 mPa.s at 25.degree. C. The
reactive diluent can be a low viscosity monomer having at least one
functional group capable of polymerization when exposed to actinic
radiation. This functional group may be of the same kind as that
used in the radiation-curable monomer or oligomer. Preferably, the
functional group present in the reactive diluent is capable of
copolymerizing with the radiation-curable functional group present
on the radiation-curable monomer or oligomer.
[0099] Ethylenic unsaturation is preferred. In particular, acrylate
unsaturation is preferred.
[0100] Suitable amounts of the reactive diluent have been found to
be about 1 wt. % to about 80 wt. %, and more preferably about 2 wt.
% to about 60 wt. %, and more preferably, about 3 wt. % to about 50
wt. %.
[0101] For example, the reactive diluent can be a monomer or
mixture of monomers having an acrylate or vinyl ether functionality
and a C.sub.4-C.sub.20 alkyl or polyether moiety. Particular
examples of such reactive diluents include:
[0102] hexyl (meth)acrylate,
[0103] 2-ethylhexyl (meth)acrylate,
[0104] isobornyl (meth)acrylate,
[0105] decyl (meth)acrylate,
[0106] lauryl (meth)acrylate,
[0107] stearyl (meth) acrylate,
[0108] 2-(2-ethoxyethoxy)ethyl (meth)acrylate,
[0109] laurylvinylether,
[0110] 2-ethylhexylvinyl ether,
[0111] N-vinyl formamide,
[0112] isodecyl (meth)acrylate,
[0113] isooctyl (meth)acrylate,
[0114] N-vinyl pyrrolidone,
[0115] N-vinyl caprolactam,
[0116] N-isobutoxymethyl acrylamide
[0117] and the like.
[0118] Another type of reactive diluent that can be used is a
compound having an aromatic group. Particular examples of reactive
diluents having an aromatic group include:
[0119] phenoxyethyl (meth)acrylate
[0120] ethyleneglycolphenylether (meth)acrylate;
[0121] polyethyleneglycolphenylether (meth)acrylate;
[0122] polypropyleneglycolphenylether (meth)acrylate; and
[0123] alkyl-substituted phenyl derivatives of the above monomers,
such as polyethyleneglycolnonylphenylether (meth)acrylate.
[0124] The reactive diluent can also comprise a diluent having two
or more functional groups capable of polymerization. Particular
examples of such monomers include:
[0125] bisphenol A diacrylate
[0126] dicyclohexane dimethanol diacrylate
[0127] C.sub.2-C.sub.8 hydrocarbon-diol di(meth)acrylates,
[0128] C.sub.4-C.sub.18 hydrocarbondivinylethers,
[0129] C.sub.3-C.sub.18 hydrocarbon triol tri(meth)acrylates, and
the polyether analogs thereof, and the like,
[0130] such as
[0131] 1,6-hexanediol di(meth)acrylate,
[0132] trimethylolpropane tri(meth)acrylate,
[0133] hexanedioldivinylether,
[0134] triethylene-glycol di(meth)acrylate,
[0135] pentaerythritol tri(meth)acrylate,
[0136] alkoxylated bisphenol-A di(meth)acrylate, and
[0137] tripropyleneglycol di(meth)acrylate.
[0138] If the radiation-curable functional group of the
radiation-curable monomer or oligomer is an epoxy group, for
example, one or more of the following compounds can be used as the
reactive diluent:
[0139] epoxy-cyclohexane,
[0140] phenylepoxyethane,
[0141] 1,2-epoxy-4-vinylcyclohexane,
[0142] glycidyl (meth)acrylate,
[0143] 1,2-epoxy-4-epoxyethyl-cyclohexane,
[0144] diglycidylether of polyethylene-glycol,
[0145] diglycidylether of bisphenol-A,
[0146] and the like.
[0147] If the radiation-curable functional group of the
radiation-curable monomer or oligomer has an amine-ene or thiol-ene
system, examples of reactive diluents having allylic unsaturation
that can be used include:
[0148] diallylphthalate,
[0149] triallyltri-mellitate,
[0150] triallylcyanurate,
[0151] triallylisocyanurate, and
[0152] diallylisophthalate.
[0153] For amine-ene systems, amine functional diluents that can be
used include, for example: the adduct of trimethylolpropane,
isophoronediisocyanate and di(m)ethylethanolamine; the adduct of
hexanediol, isophoronediisocyanate and dipropylethanolamine; and
the adduct of trimethylol propane,
tri-methylhexamethylenediisocyanate and di(m)ethylethanolamine.
[0154] (C) Optional Photoinitiator
[0155] The composition may optionally further comprise at least one
photoinitiator. A photoinitiator is required for a fast UV cure but
may be omitted for electron beam cure. Conventional photoinitiators
can be used. Examples include benzophenones, acetophenone
derivatives, such as alpha-hydroxyalkylphenylketones, benzoin alkyl
ethers and benzil ketals, monoacylphosphine oxides, and
bisacylphosphine oxides.
[0156] Often mixtures of photoinitiators provide a suitable balance
of properties.
[0157] Preferred photoinitiators include IRGACURE 184 (available
from Ciba Geigy) and LUCIRIN TPO (commercially available from BASF)
and mixtures thereof.
[0158] The amount of photoinitiator system is not particularly
limited but will be effective to provide fast cure speed, ready
processability, reasonable cost, good surface and through cure, and
lack of yellowing upon aging. Typical amounts can be, for example,
about 0.3 wt. % to about 30 wt. % and, preferably, about 1 wt. % to
about 5 wt. %.
[0159] The coating compositions of the invention may comprise a
photoinitiator-free system, such as an acrylate functional resin
and an aliphatic maleimide, which can suitably undergo UV cure
without the aid of a conventional photoinitiator. Such radiation
curable compositions may include one or more reactive unsaturated
species connected to an electron donating group, optionally
combined with an allyl group-containing compound connected to an
electron-donating group. The unsaturated species may include
members of the group consisting of acrylates, methacrylates,
fumarates, maleates, itaconates, citraconates, mesaconates, and
their derivatives, such as fumaric amides, fumaric amide esters and
maleamide esters. Other esters, urethanes, urea, thiourethane and
anhydrides may also be suitable. The reactive unsaturated species
may also be a vinyl ether, a vinyl ester, a vinyl amide, a vinyl
amine, a vinyl thioether, an allyl amine or an allyl amide. Vinyl
ether maleimides and maleimides with acrylates are preferred.
Preferably, acrylates are combined with cyclohexyl maleimides to
form a system capable of radical cure. See Conference Proceedings,
Radtech Europe, (June, 1997), the entire contents of which are
hereby incorporated herein by reference.
[0160] (D) Additives
[0161] A major advantage of one embodiment of the present invention
is that slip additives can be substantially or completely avoided.
If slip additives are present, they are preferably used in amounts
less than about 0.5 wt. %, and more preferably, less than about
0.25 wt. %, and more preferably, less than about 0.1 wt. %.
[0162] Other additives include UV absorbers, particulates,
colorants including dyes and pigments, dispersion aides,
antioxidants, organofunctional silane compounds, light stabilizers
including hindered amine light stabilizers, photopolymerization
synergists, catalysts, and the like. One skilled in the art will
easily be able to make and use such a composition without undue
experimentation based on the disclosure presented herein.
[0163] Preferably, one embodiment of the present invention is
substantially free of additives which are known to cause yellowing.
Examples of such additives include amines.
[0164] The compositions of the present invention may include
acrylate acrylics with urethanes up to the extent that they do not
adversely affect the advantages provided by the compositions of
this invention. Preferably, the total composition will comprise
less than 5 wt. % of urethane linkages which includes the urethane
linkages present in any acrylate acrylics.
[0165] The formulations of the present invention can be adapted to
be inner primary coatings, outer primary coatings, colored outer
primary coatings, inks, matrix materials, colored matrix materials,
bundling materials, adhesives, and upjacketting coatings, and other
fiber optic materials. Outer primary coatings, particularly colored
outer primary coatings, matrix materials and colored matrix
materials are particularly preferred embodiments of the present
invention.
[0166] If the radiation-curable composition of the present
invention is to be used to form an inner primary coating, the
composition preferably contains an effective amount of a glass
adhesion promoting compound. Such amounts have been found to be
from about 0.1 to about 30% by weight, based on the total weight of
the composition. Examples of suitable glass adhesion promoting
agents include .gamma.-mercaptopropyl trimethoxysilane or
(meth)acryloxyalkyltrimethoxysilane.
[0167] A suitable radiation-curable composition includes the
following pre-mixture ingredients:
[0168] from about 10 wt. % to about 90 wt. % of a radiation-curable
oligomer including an acrylic backbone and at least one
radiation-curable group, wherein the oligomer is urethane-free;
[0169] from about 5 wt. % to about 90 wt. % of one or more monomer
diluents; and
[0170] optionally, an effective amount of at least one
photopolymerization initiator.
[0171] Another embodiment of the present invention is a suitable
radiation-curable composition which includes:
[0172] from about 5 to about 90% by weight of at least one
radiation-curable oligomer or monomer;
[0173] from about 0.01 to about 30% by weight of at least one
photoinitiator; and
[0174] optionally from about 1 to about 70% by weight of at least
one low viscosity reactive diluent, wherein the urethane
concentration is about 1% by weight or less and the ether
concentration is about 1% by weight or less, based on the total
weight of the radiation-curable composition.
[0175] A preferred radiation-curable, optical fiber coating
composition includes:
[0176] from about 10 to about 80% by weight of at least one
radiation-curable oligomer including a vinyl-addition polymer to
which at least one acrylate or methacrylate group is bound and
having a number-average molecular weight of about 1,000 to about
200,000;
[0177] from about 0.01 to about 30% by weight of at least one
photoinitiator; and
[0178] optionally from about 1 to about 70% by weight of at least
one low viscosity reactive diluent, wherein the urethane
concentration is about 1% by weight or less and the ether
concentration is about 1% by weight or less, based on the total
weight of the radiation-curable composition.
[0179] A preferred radiation-curable ink coating composition
includes:
[0180] from about 10 to about 80% by weight of at least one
radiation-curable oligomer including a vinyl-addition polymer to
which at least one acrylate or methacrylate group is bound and
having a number average molecular weight of about 1,000 to about
200,000;
[0181] from about 0.01 to about 20% by weight of at least one
photoinitiator;
[0182] from about 1 to about 30% by weight of at least one pigment;
and
[0183] optionally from about 1 to about 70% by weight of at least
one low viscosity reactive diluent, wherein the urethane
concentration is about 1% by weight or less and the ether
concentration is about 1% by weight or less, based on the total
weight of the radiation-curable composition.
[0184] A preferred radiation-curable, matrix forming composition
includes:
[0185] from about 10 to about 80% by weight of at least one
radiation-curable oligomer including a vinyl-addition polymer to
which at least one acrylate or methacrylate group is bound and
having a number average molecular weight of about 1,000 to about
200,000;
[0186] from about 0.01 to about 20% by weight of at least one
photoinitiator; and
[0187] optionally from about 1 to about 70% by weight of at least
one low viscosity reactive diluent, wherein the urethane
concentration is about 1% by weight or less and the ether
concentration is about 1% by weight or less, based on the total
weight of the radiation-curable composition.
[0188] Preferably, the compositions contain from about 10 to about
60% by weight and more preferably from about 10 to about 50% by
weight of the low viscosity diluent(s).
[0189] Preferably, the radiation-curable oligomer(s) is present in
an amount of about 10 to about 60% by weight, more preferably, from
about 10 to about 40% by weight. The radiation-curable oligomer(s)
preferably comprises a vinyl-addition copolymer formed mainly from
acrylic and methacrylic acid which is substantially free of
fluorine and silicon.
[0190] The radiation-curable compositions can be used to form
coatings on optical fibers. The improved coatings formed on the
optical fibers exhibit enhanced resistance to thermal degradation.
The coated optical fibers are useful in telecommunications systems
and cable television systems.
[0191] In producing a coated optical fiber, the liquid
radiation-curable composition can be applied to the optical fiber
and subsequently cured. Typically, the cure is affected using
actinic radiation, such as ultraviolet or visible radiation.
However, other methods are available. For example, the coating can
be cured by electron beam irradiation, where no catalyst is
required. More than one coating according to the present invention
can be applied. In many applications involving optical fibers it is
desirable to have an outermost layer (outer primary coating) that
is tough or hard enough to protect the optical fiber and underlying
coatings, including the inner primary coating. The underlying
coatings and inner primary coating are typically softer in
comparison to the outermost coating. Surprisingly, it was found
that with the compositions according to the present invention, one
can provide both an outer primary coating having good strength
properties and an inner primary coating having the required
properties for preventing microbending in the optical fiber. In
particular, the radiation-curable coating compositions according to
the present invention provide coatings having excellent outdoor
durability, resistance to discoloration, in combination with
excellent mechanical properties.
[0192] In particular, inner primary coatings according to the
present invention possess a modulus and glass transition
temperature suitable for protecting the optical fiber from
microbending. For example, the inner primary coatings possess a
modulus of about 10 MPa or less, preferably about 7 MPa or less,
more preferably between 0.01 to 5 MPa, and glass transition
temperature of about -20.degree. C. or less, preferably about
-30.degree. C. or less.
[0193] Outer primary coatings according to the present invention
possess a modulus and glass transition temperature suitable for
protecting the inner primary coating and optical fiber. For
example, the outer primary coatings possess a modulus of greater
than 10 MPa, preferably greater than 50 MPa to about 2000 MPa and
more preferably about 500 MPa to about 1500 MPa and/or a glass
transition temperature of about 40.degree. C. or greater, more
preferably 50.degree. C. to 140.degree. C.
[0194] Because of the useful properties obtainable with the coating
compositions according to the present invention, in a coated
optical fiber including an inner primary coating, an outer primary
coating, a colored outer primary coating and an ink coating, it is
part of this invention to have either the inner primary coating, or
the outer primary coating, particularly if the outer primary
coating is colored, or the ink coating, or any combination thereof,
being a cured composition according to the present invention.
[0195] Ribbon assemblies are now well known in the art and one
skilled in the art will easily be able to use the disclosure
provided herein to prepare a novel ribbon assembly containing
coated optical fibers for the desired applications. The ribbon
assembly containing the improved matrix material or colored matrix
material according to the present invention exhibits enhanced
resistance to thermal degradation. The ribbon assemblies preferably
contain at least one coated optical fiber having at least one
improved coating according to the present invention. The novel
ribbon assembly made according to this invention are suitable for
use in telecommunication systems. Such telecommunication systems
typically include ribbon assemblies containing optical fibers,
transmitters, receivers, and switches. The ribbon assembly
containing the coated optical fibers are the fundamental connecting
units of telecommunication systems. The ribbon assembly can be
buried under ground or water for long distance connections, such as
between cities. The ribbon assembly can also be used to connect
directly to residential homes.
[0196] The novel ribbon assembly made according to this invention
are also suitable for use in cable television systems. Such cable
television systems typically include ribbon assemblies containing
optical fibers, transmitters, receivers, and switches. The ribbon
assembly containing the coated optical fibers are the fundamental
connecting units of such cable television systems. The ribbon
assembly can be buried under ground or water for long distance
connections, such as between cities. The ribbon assembly can also
be used to connect directly to residential homes.
[0197] Cure speed for these compositions is preferably less than
about 1.0 J/cm.sup.2, and preferably is less than about 0.8
J/cm.sup.2, wherein cure speed is the dose at which a 95%
attainment of the maximum modulus is achieved.
[0198] The compositions preferably will have good clarity before
and after cure. Clarity can be examined with use of an optical
microscope.
[0199] A particularly important property of the present
compositions, after radiation-cure, is the coefficient of friction
(COF). Two types of coefficient of friction which are particularly
important are the film-to-stainless steel COF and the film-to-film
COF. The film-to-stainless steel coefficient of friction is
preferably less than 1.20, and more preferably, is less than 1.10.
The film-to-film COF is preferably less than 1.1, and more
preferably is less than 1.0.
[0200] In a preferred embodiment, the compositions are formulated
to be an outer primary coating having a low coefficient of
friction. An outer primary coating preferably will meet at least
some of the following criteria:
1 Viscosity @ 25.degree. C. (mPa .multidot. s) 3,000-10,000 Elastic
Modulus: E' = 1000 MPa (.degree. C.) >35.degree. C. E' = 100 MPa
(.degree. C.) >48.degree. C. Secant Modulus @ 23.degree. C.
(MPa) 400-1000 Elongation (%) >10 Cure Speed @ 95% modulus
(J/cm.sup.2) <0.3 125.degree. C./30 day color change (.DELTA.E)
<20 Fluorescent/30 day color change (.DELTA.E) <20 Oxidation
Initiation Temp. (.degree. C.) >225 TGA wt. loss, 40 min. @
200.degree. C. (%) <6 Acetone Extractables (%) <4
[0201] Conventional methods in the radiation-cure and optical fiber
arts can be used to cure the compositions including electron-beam
cure and UV cure. Thermal cure is less preferred, although some
thermal cure may possibly occur under a hot UV lamp and with heat
of polymerization. UV cure is preferred. Electron beam cure
provides the advantage that photoinitiators may be omitted.
[0202] In general, exposure to radiation should cause the
composition to attain about 80% and more preferably, about 90% of
the maximum attainable secant modulus.
[0203] Most preferably if fast cure speed is desired, the
radiation-curable group is an acrylate.
[0204] The invention will be further illustrated with use of the
following non-limiting examples.
EXAMPLES 1-6 AND COMPARATIVE EXAMPLE A
[0205] Six radiation-curable compositions according to the present
invention were formed by combining the components shown in Table 1.
A radiation-curable coating composition based on urethane oligomers
was also formed for comparison. 75 micron thick drawdowns of the
radiation-curable compositions were formed and suitably cured by
exposure to UV light to form films.
2TABLE 1 Component (% by weight based on total weight of Comp.
composition) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. A PRO
971.sup.1 35.2 0 0 40 0 0 0 PRO 1494.sup.2 0 35.2 0 0 33 0 0 PRO
1735.sup.3 0 0 35.2 0 0 40.45 0 Oligomer H-T-PTGL1000-T-H 0 0 0 0 0
0 28.92 Monomer H-T-H 0 0 0 0 0 0 3.56 Vinyl Caprolactam 10 10 10
10 12 10.5 0 Bisphenol A Ethoxylate Diacrylate 15 15 15 10.2 0 15
56 Phenol,4,4'-(1-Methyl-Ethylidene)Bis-, 15 15 15 15 15 15 0
Polymer with (Chloromethyl)Oxirane, 2- Propenoate Phenoxy Ethyl
Acrylate 6.75 6.75 6.75 6.75 8.55 0 0 Isobornyl Acrylate 13.8 13.8
13.8 13.8 15.2 14.8 0 Ethoxylated Nonylphenol Acrylate Ester 0 0 0
0 0 0 8 Diphenyl (2,4,6-Trimethylbenzoyl) 1 1 1 1 1 1 1 Phosphine
Oxide and 2-Hydroxy-2-Methyl- 1-Phenyl-1-Propanone
1-Hydroxycyclohexyl Phenyl Ketone 1.5 1.5 1.5 1.5 1.5 1.5 2 Cyagard
UV 416.sup.4 (Cytec) 0.25 0.25 0.25 0.25 0.25 0.25 0 Thiodiethylene
Bis(3,5-di-tertbutyl-4- 0 0 0 0 0 0 0.5 Hydroxy)Hyrocinnamate
Irganox 1076 (Ciba-Geigy) 0.5 0.5 0.5 0.5 0.5 0.5 0 Cyagard AO
711.sup.5 (Cytec) 1 1 1 1 1 1 0 Irgacure 214 (Ciba-Geigy) 0 0 0 0
12 0 0 .sup.1PRO 971 is an urethane-free acrylated acrylic oligomer
obtained from Sartomer having an epoxy value of 0.4 mg KOH/g.
.sup.2PRO 1494 is an urethane-free fluoromodified acrylated acrylic
oligomer obtained from Sartomer having an epoxy value of 1.0 mg
KOH/g. .sup.3PRO 1735 is an urethane-free laurylmodified acrylated
acrylic oligomer obtained from Sartomer having an epoxy value of
2.6 mg KOH/g. .sup.4Cyagard UV 416 is
2-hydroxy-4-acryloxyethoxybenzophenone .sup.5Cyagard AO 711 is
ditridecylthiodiproprionate
[0206] The properties of the films, which were prepared according
to Table 1, were measured and the test results are shown in Table
2.
3TABLE 2 Test Results Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Comp. Ex.
A Viscosity (mPa.s)(25.degree. C.) 3600 21,500 2,000 5,300 10,800
3,900 Gardner Color 11-12 4-5 3-4 Refractive Index 1.507 1.5055
1.506 1.503 1.5025 Clarity Clear Clear Slightly Hazy Tensile
Strength (MPa) 29 19 22 26 18 23 Elongation (%) 9 15 9 8 13 11
Modulus (MPa) 804 423 577 799 502 608 E' = 1000 MPa (.degree. C.)
32 15 20 25 8 15 E' = 100 MPa (.degree. C.) 66 54 73 51 34 56 Tan*
Max (.degree. C.) 68 61 78 55 42 59 E.sub.0 (MPa) 16.4 11.3 19.7
11.4 5.4 14.9 Dose to Achieve 95% of Maximum 0.53 0.42 Attainable
Modulus (J/cm.sup.2) Change in Viscosity, 3 Days at 60.degree. C.
5.4 43.4 (% increase) Coefficient of Friction, film-to-film 0.7 ND
0.4 0.4 0.5 ND Coefficient of Friction, film-to-steel 0.7 0.4 0.8
1.0 0.7 0.4 % Weight Loss, 96 Hours at 150.degree. C. 4.4 11.8 3.9
2.9 % Weight Loss, 96 Hours at 150.degree. C., then 9 15.5 8.8 9.5
144 Hours at 180.degree. C. (%) .DELTA.E 96 Hours at 150 .degree.
C. (%) 1.1 0.67 0.8 3.8 .DELTA.E 96 Hours at 150 .degree. C., and
then 144 hours 11.7 9.4 13.5 55.6 at 180 .degree. C. (%) Urethane
Concentration (wt. %) 0 0 0 0 0 0 5.35 Total Ether Concentration of
Composition 6.4 6.4 6.4 6.4 6.8 5.2 23.2 (wt. %) Ether
Concentration Based on Monomers and 6.4 6.4 6.4 6.4 6.8 5.2 10.4*
Oligomers Having Average Number of Ether Groups 1-2 (wt. %) Ether
Concentration Based on Monomers and 0 0 0 0 0 0 2.8* Oligomers
Having Average Number of Ether Groups >2-10 (wt. %) Ether
Concentration Based on Monomers and 0 0 0 0 0 0 10* Oligomers
Having Average Number of Ether Groups >10 (wt. %) ND = Not
Determinable
[0207] The oligomers and monomers were prepared by reacting the
following components: H=Hydroxyethyl Acrylate; T=Toluene
Diisocyanate; and PTGL1000=1000 molecular weight
polymethyltetrahydrofurfuryl/polytetrahydr- ofurfuryl copolymer
diol, available from Mitsui, N.Y.
[0208] The results shown in Table 2 demonstrate that the present
invention is capable of providing radiation-curable compositions
that are suitable for application to optical fibers and which when
suitably cured exhibit enhanced resistance to thermal degradation.
In particular, the Examples according to the present invention
exhibited a remarkably reduced .DELTA.E compared to the Comparative
Example, which demonstrates that the Examples were substantially
more resistant to thermal degradation. Larger .DELTA.E values, as
well as the degree of associated color change, can negatively
impact thermal degradation.
[0209] The test results also demonstrate that surprisingly the
coefficient of friction (film-to-film) is less than the coefficient
of friction (film-to-steel). Usually, the coefficient of friction
(film-to-steel) is greater than the coefficient of friction
(film-to-film). The coating compositions according to the present
invention are capable of providing a coating on an optical fiber
that inherently has a coefficient of friction suitable for ribbon
stripping, when used in making ribbon assemblies. Thus, when the
coatings according to the present invention are utilized on optical
fibers in ribbon assemblies, the low inherent coefficient of
friction of the coatings allows the matrix material to slide off
the inked or colored secondary optical fiber during ribbon
stripping.
[0210] The test results further demonstrate that the coatings
according to the present invention surprisingly exhibit a high
refractive index without the use of fluorinated additives or
fluorine containing oligomers.
EXAMPLES 7-12
[0211] Formulations were prepared according to the following Table
3. Compositions were cured at 1.0 J/cm.sup.2 under a D lamp with
N.sub.2 (8 cfm) for 3 mil film on glass. Properties of the cured
coatings are provided below.
4TABLE 3 Components Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 PRO 971
(Sartomer) 35.2 40.0 PRO 1494 (Sartomer) 35.2 33 PRO 1735
(Sartomer) 35.2 40.45 vinyl caprolactam 10 10 10 10 12 10.5
ethoxylated bisphenol A 15 15 15 10.2 15 diacrylate PHOTOMER 3016
15 15 15 15 15 15 (Henkel) phenoxyethyl acrylate 6.75 6.75 6.75
6.75 8.55 isobornyl acrylate 13.8 13.8 13.8 13.8 15.2 14.8 LUCIRIN
TPO (BASF) 1 1 1 1.0 1.0 1.0 IRGACURE 184 (Ciba- 1.5 1.5 1.5 1.5
1.5 1.5 Geigy) Cyagard UV 416 0.25 0.25 0.25 0.25 0.25 0.25 (Cytec)
IRGANOX 1076 (Ciba- 0.5 0.5 0.5 0.5 0.5 0.5 Geigy) Cyagard AO 711 1
1 1 1.0 1.0 1.0 (Cytec) IRR 214 (UCB Radcure 12 Specialties)
PROPERTIES viscosity (cps) 3,570 21,500 2,000 5,300 10,800 3,900
tensile strength (MPa) 29.0 19 22 elongation (%) 9 15 9 secant
modulus (MPa) 804 423 577 E' = 1,000 MPa (.degree. C.) 31.9 15.0
20.1 E' = 100 MPa (.degree. C.) 65.6 53.7 72.5 tan delta 68 60.5 78
max (.degree. C.) E.sub.0 (.degree. C.) 16.4 11.3 19.8 Gardner
Color 11-12 4-5 3-4 liquid refractive index 1.507 1.5055 1.506 COF
0.69 0.84 1.04 0.7 Film-to-Film COF Film-to-Stainless 0.74 0.43
0.36 0.42 0.45 Steel
TEST METHODS
[0212] Viscosity Test Method
[0213] The viscosity was measured using a Physica MC10 Viscometer.
The test samples were examined and if an excessive amount of
bubbles was present, steps were taken to remove most of the
bubbles. Not all bubbles need to be removed at this stage, because
the act of sample loading introduces some bubbles.
[0214] The instrument was set up for the conventional Z3 system.
Samples were loaded into a disposable aluminum cup by using a
syringe to measure out 17 cc. The sample in the cup was examined
for bubbles and if an excessive amount of bubbles were present,
they were removed by a direct means such as centrifugation, or by
allowing enough time to lapse to let the bubbles escape from the
bulk of the liquid. Bubbles at the top surface of the liquid are
acceptable.
[0215] The bob was gently lowered into the liquid in the measuring
cup, and the cup and bob were installed in the instrument. The
sample temperature was equilibrated for five minutes with a bath of
circulating liquid. Then, the rotational speed was set to a desired
value to produce the desired shear rate. The desired value of the
shear rate is easily determined by one of ordinary skill in the art
from an expected viscosity range of the sample.
[0216] The instrument panel read out a viscosity value, and if the
viscosity value varied only slightly (less than 2% relative
variation) for 15 seconds, the measurement was complete. If not, it
is possible that the temperature had not yet reached an equilibrium
value, or that the material was changing due to shearing. If the
latter case, further testing at different shear rates will be
needed to define the samples viscous properties. The results
reported are the average viscosity values of three test
samples.
[0217] Tensile Strength, Elongation and Modulus Test Method
[0218] The tensile strength, elongation and modulus of cured
samples was tested using a universal testing instrument, Instron
Model 4201 equipped with a personal computer and software "Series
IX Materials Testing System." The load cells used were 2 and 20
pound capacity. The ASTM D638M was followed, with the following
modifications.
[0219] A drawdown of each material to be tested was made on a glass
plate or MYLAR film and cured using a UV processor. The cured film
was conditioned at 22 to 24.degree. C. and 50.+-.5% relative
humidity for a minimum of sixteen hours prior to testing.
[0220] A minimum of eight test specimens, having a width of
0.5.+-.0.002 inches and a length of 5 inches, were cut from the
cured film. To minimize the effects of minor sample defects, sample
specimens were cut parallel to the direction in which the drawdown
of the cured film was prepared. 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.
[0221] The test specimens were then removed from the substrate.
Caution was exercised so that the test specimens were not stretched
past their elastic limit during the removal from the substrate. If
any noticeable change in sample length had taken place during
removal from the substrate, the test specimen was discarded.
[0222] If the top surface of the film was talc coated to eliminate
tackiness, then a small amount of talc was applied to the bottom
surface of the test specimen after removal from the substrate.
[0223] The average film thickness of the test specimens was
determined. At least five measurements of film thickness were made
in the area to be tested (from top to bottom) and the average value
used for calculations. If any of the measured values of film
thickness deviated from the average by more than 10% relative, the
test specimen was discarded. All specimens came from the same
plate.
[0224] The appropriate load cell was determined by using the
following equation:
[A.times.145].times.0.0015=C
[0225] where: A=sample's maximum expected tensile strength
(MPa);
[0226] 145=conversion factor from MPa to psi;
[0227] 0.00015=approximate cross-sectional area (in.sup.2) of test
specimens; and
[0228] C=load (lbs.). A 2 pound load cell was used for materials
where C=1.8 lbs. and a 20 pound load cell was used for materials
where 1.8<C<18 lbs. If C>19, a higher capacity load cell
was required.
[0229] The crosshead speed was set to 1.00 inch/min, and the
crosshead action was set to "return at break". The crosshead was
adjusted to 2.00 inches jaw separation. The air pressure for the
pneumatic grips was turned on and adjusted as follows: set at
approximately 20 psi(1.5 Kg/cm.sup.2) for primary optical fiber
coatings and other very soft coatings; set at approximately 40 psi
(3 Kg/cm.sup.2) for optical fiber single coats; and set at
approximately 60 psi(4.5 Kg/cm.sup.2) for secondary optical fiber
coatings and other hard coatings. The appropriate Instron computer
method was loaded for the coating to be analyzed.
[0230] After the Instron test instrument had been allowed to
warm-up for fifteen minutes, it was calibrated and balanced
following the manufacturer's operating procedures.
[0231] The temperature and humidity were measured just prior to
measurement of the first test specimen. Specimens were analyzed
only if the temperature was within 23.+-.1.0.degree..degree. C. and
the relative humidity was within 50.+-. 5%. The temperature was
measured for each test specimen. The humidity value was measured
only at the beginning and the end of testing a set of specimens
from one plate.
[0232] Each test specimen was tested by suspending it in the space
between the upper pneumatic grips such that the test specimen was
centered laterally and hanging vertically. Only the upper grip was
locked. The lower end of the test specimen was pulled gently so
that it has no slack or buckling, and it was centered laterally in
the space between the open lower grips. While holding the specimen
in this position, the lower grip was locked.
[0233] The sample number was entered and sample dimensions into the
data system, following the instructions provided by the software
package.
[0234] The temperature and humidity were measured after the last
test specimen from the current drawdown was tested. The calculation
of tensile properties was performed automatically by the software
package.
[0235] The values for tensile strength, % elongation, and (secant
or segment) modulus were checked to determine whether any one of
them deviated from the average enough to be an "outlier." If the
modulus value was an outlier, it was discarded. If there were less
than six data values for the tensile strength, then the entire data
set was discarded and repeated using a new plate.
[0236] Elastic Modulus Test Method The elastic modulus (E'), the
viscous modulus (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
operating system and Rhios.RTM. 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 and approximately 12
mm wide 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.
[0237] 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.
[0238] 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.
[0239] Before conducting the temperature sweep, the test samples
were dried by heating to a temperature of 80.degree. C. in a
nitrogen atmosphere for 5 minutes. The temperature sweep used
included cooling the test samples to about -60.degree. C. or about
-80.degree. C. and increasing the temperature at about 1.degree.
C./minute until the temperature reached about 60.degree. C. to
about 70.degree. C. The test frequency used was 1.0
radian/second.
[0240] .DELTA.E
[0241] A model 7000, Macbeth Color-Eye spectrophotometer
(Kollmorgen Instruments Corp.) was used to measure the color of the
test samples. ASTM D2244-93 was followed to determine the .DELTA.E
from the measured values.
[0242] Weight Loss
[0243] Test samples were made by forming 75 micron thick drawdowns
of each of the different radiation-curable compositions on glass
plates and then suitably curing the drawdowns to form cured films.
The films were separated from the glass plate and cut into
1.5.times.1.5 inch sample squares. The weight of each sample was
measured. The samples were then heated for 96 hours at 150.degree.
C. and then 144 hours at 180.degree. C. The weight of the samples
was measured periodically. The results reported are the average of
three test samples.
[0244] Coefficient of Friction (Film-to-Film) and
(Film-to-Steel)
[0245] Test samples were made by forming drawdowns of each of the
different radiation-curable compositions on glass plates and then
suitably curing the drawdowns to form cured films. The coefficient
of friction between films was determined using an Instron Model No.
4201 as follows. One glass plate was mounted on the support table,
film side up. A portion of the same film was cut to the same size
as the 100 gram sled, and then mounted on the sled. The sled was
placed on the film so that the film on the sled contacted the
surface of the sample film mounted on the support table. A ten
pound load cell was attached to the sled. The cross head speed was
set to 10 inches per minute. The appropriate program for
determining the coefficient of friction was loaded into the
Instron. The weight of the sled, including the film attached to the
sled, and the load cell weight were entered. A path for the sled
was selected which avoided any film defects, such as ripples or
bubbles. The sled travel was selected to be four inches.
[0246] The film-to-steel coefficient of friction was determined in
the same manner as above, except that no sample film was mounted on
the sled. Instead, the sled was placed on the sample film mounted
on the support table with the balls of the sled contacting the
sample film.
[0247] Refractive Index Determination
[0248] The procedure measures the refractive index at visible light
wavelengths for cured fiber optic materials, utilizing Becke'
line/immersion liquid with axial microscopic illumination at a
sharply bounded wavelength. Small sections of the cured coating are
placed on a microscope slide under a cover slip. These sections are
immersed in one of a series of liquids of known refractive index
and the resulting preparation observed through a microscope. The
characteristic optical phenomenon known as the Becke' line is used
to determine the extent and direction of the mismatch between the
liquid and solid. Additional trials are made with other liquids
from the series of known refractive indices until a match is found.
See Mason, 3d Edition, 1958, John Wiley & Sons, New York, Vol.
1, chapter 11, for a detailed treatment of the subject of
refractive index.
[0249] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
those of ordinary skill in the art that various changes and
modifications can be made to the claimed invention without
departing from the spirit and scope thereof.
* * * * *