U.S. patent application number 09/742015 was filed with the patent office on 2001-09-27 for radiation-curable optical fiber coatings having reduced yellowing and fast cure speed.
This patent application is currently assigned to DSM N.V.. Invention is credited to Bishop, Timothy E., Chawla, Chander P., Szum, David M..
Application Number | 20010025062 09/742015 |
Document ID | / |
Family ID | 21963039 |
Filed Date | 2001-09-27 |
United States Patent
Application |
20010025062 |
Kind Code |
A1 |
Szum, David M. ; et
al. |
September 27, 2001 |
Radiation-curable optical fiber coatings having reduced yellowing
and fast cure speed
Abstract
Radiation-curable inner and outer primary optical fiber coatings
are disclosed having both fast cure speed and reduced rates of
yellowing. The compositions comprise particular photoinitiators and
UV absorbers which are used in amounts to provide the combination
of properties. The UV absorber can have ethylenic unsaturation.
Outer primary coatings can be formulated to screen inner primary
coatings and have fast cure speed.
Inventors: |
Szum, David M.; (Elmhurst,
IL) ; Chawla, Chander P.; (Batavia, IL) ;
Bishop, Timothy E.; (Algonquin, IL) |
Correspondence
Address: |
Pillsbury Madison & Sutro LLP
Intellectual Property Group
Ninth Floor
1100 New York Avenue, NW
Washington
DC
20005-3918
US
|
Assignee: |
DSM N.V.
|
Family ID: |
21963039 |
Appl. No.: |
09/742015 |
Filed: |
December 22, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09742015 |
Dec 22, 2000 |
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09099198 |
Jun 18, 1998 |
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6187835 |
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60050033 |
Jun 18, 1997 |
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Current U.S.
Class: |
522/96 |
Current CPC
Class: |
C03C 25/1065 20130101;
C08F 290/06 20130101; Y10T 428/2938 20150115; C09D 4/06 20130101;
C09D 4/06 20130101; Y10T 428/2933 20150115; Y10T 428/31645
20150401; C03C 25/106 20130101 |
Class at
Publication: |
522/96 |
International
Class: |
C08J 003/28; C08F
002/46 |
Claims
What is claimed is:
1. A radiation-curable composition for an optical fiber coating
comprising the combination of pre-mixture ingredients: about 5 wt.
% to about 95 wt. % of at least one radiation-curable oligomer,
about 5 wt. % to about 95 wt. % of at least one reactive diluent,
about 0.1 wt. % to about 20 wt. % of at least one photoinitiator,
wherein said photoinitiator is selected to provide a fast cure
speed, about 0.1 wt. % to about 20 wt. % of at least one UV
absorbing compound which does not substantially impair said fast
cure speed.
2. A radiation-curable composition according to claim 1, wherein
the amount of said UV absorber is at least 0.1 wt. %.
3. A radiation-curable composition according to claim 2, wherein
the amount of said UV absorber is at least 0.3 wt. %.
4. A radiation-curable composition according to claim 3, wherein
the amount of said UV absorber is at least 0.5 wt. %.
5. A radiation-curable composition according to claim 1, wherein
said oligomer is a urethane acrylate oligomer.
6. A radiation-curable composition according to claim 1, wherein
said composition is cured sufficiently to achieve at least 90% of
its maximum modulus.
7. A radiation-curable composition according to claim 1, wherein
said photoinitiator is a phosphine oxide compound.
8. A radiation-curable composition according to claim 1, wherein
said composition is formulated to be an outer primary optical fiber
coating.
9. A radiation-curable composition according to claim 1, wherein
said composition is formulated to be an inner primary optical fiber
coating.
10. A radiation-curable composition according to claim 1, wherein
said UV absorber comprises a radiation-curable functional
group.
11. A radiation-curable composition according to claim 1, wherein
said composition comprises at least two UV absorbing compounds.
12. A radiation-curable composition for an optical fiber coating
comprising the combination of pre-mixture ingredients: about 5 wt.
% to about 95 wt. % of at least one radiation-curable urethane
acrylate oligomer, about 5 wt. % to about 95 wt. % of at least two
reactive diluents comprising acrylate functionality, about 0.1 wt.
% to about 20 wt. % of at least one phosphine oxide photoinitiator,
about 0.1 wt. % to about 20 wt. % of at least one UV absorbing
compound which comprises an acrylate functionality.
13. A coated optical fiber comprising the combination of: an
optical fiber, a radiation-cured inner primary optical fiber
coating, and a radiation-cured outer primary optical fiber coating,
wherein said outer primary optical fiber coating comprises, before
radiation-cure, the combination of pre-mixture ingredients: about 5
wt. % to about 95 wt. % of at least one radiation-curable oligomer,
about 5 wt. % to about 95 wt. % of at least one reactive diluent,
about 0.1 wt. % to about 20 wt. % of at least one photoinitiator,
wherein said photoinitiator is selected to provide a fast cure
speed, about 0.1 wt. % to about 20 wt. % of at least one UV
absorbing compound which does not substantially impair the fast
cure speed of the inner or outer primary coating.
14. A method for reducing the rate of color degradation in an inner
primary optical fiber coating comprising the combination of steps
of: coating an optical fiber with a radiation-curable inner primary
coating, coating said inner primary coating with a
radiation-curable outer primary coating which comprises a UV
absorber which does not substantially impair the cure speed of the
outer primary coating, radiation-curing said coatings.
15. A radiation-curable composition according to claim 1, wherein
said composition has a cure speed of less than 0.6 J/cm.sup.2
measured wherein cure speed is measured with dose-modulus curves
and is the dose at which 95% of maximum modulus is achieved.
16. A coated optical fiber according to claim 13, wherein said
inner primary coating comprises at least one UV-absorbing
compound.
17. A coated optical fiber according to claim 16, wherein said
inner primary coating comprises at least one urethane acrylate
oligomer, at least two monomer diluents, and at least two
photoinitiators, wherein at least one of said photoinititiators is
a phosphine oxide compound.
18. A coated fiber according to claim 13, wherein said UV-absorber
has ethylenic unsaturation.
19. A coated fiber according to claim 17, wherein said inner
primary coating UV absorber and said outer primary UV absorber each
have ethylenic unsaturation.
20. A coated fiber according to claim 19, wherein the amounts of
said UV absorbers are at least about 5 wt. %.
Description
FIELD OF THE INVENTION
[0001] The invention relates to radiation-curable optical fiber
coating compositions. In particular, the invention relates to
compositions which are both fast-curing and have, upon
radiation-cure, reduced rates of yellowing upon accelerated
aging.
DESCRIPTION OF THE RELATED ART
[0002] Optical fibers have become a medium of choice for
transmitting information in the modern telecommunications era.
Immediately after their manufacture, optical fibers are usually
coated with a radiation-curable inner primary coating (or simply
"primary coating") which directly contacts the underlying optical
fiber. After radiation-cure, this inner primary coating is
relatively soft and susceptible to damage. Therefore, the fiber is
also usually coated with a radiation-curable outer primary coating
(or simply "secondary coating") which overlays the inner primary
coating and is stiffer than the soft inner primary coating. This
dual coating structure maximizes fiber transmission efficiency and
durability and preserves the desirable characteristics of
freshly-prepared, pristine glass fiber. The two coatings must
function together to maximize fiber performance. In many cases,
radiation-curable inks are applied over the outer primary coatings
before the coated fibers are further processed into ribbons and
cables. Besides the two fiber coatings, other radiation-curable
fiber optic materials include matrix and bundling materials which
are used to construct ribbons and cables.
[0003] After their cure, the radiation-curable compositions used in
optical fiber production should not substantially change color over
time, and in particular, should not yellow. Non-yellowing has
become a crucial coating parameter in the optical fiber industry.
Discoloration and yellowing is particularly encouraged by
photolytic aging (e.g., aging in the presence of UV or fluorescent
light). Also, discoloration is a general problem with urethane
acrylate-based compositions, now the industry standard, and tends
to be a greater problem with the inner primary rather than outer
primary coatings. Yellowing in either coating, however, is
undesirable.
[0004] Fast cure speed also remains an important coating parameter.
Fiber production is limited by the rate at which the coatings can
be sufficiently cured. Inner primary coatings usually have slower
cure speeds than outer primary coatings.
[0005] Although attempts have been made to solve the aforementioned
yellowing problem, any solution should be arrived at without
impairing other important properties such as fast cure speed. That
combination of properties, however, can be difficult to achieve. In
addition, coating design is complicated by the effects of the outer
primary coating on the cure of the inner primary coating. Systemic
approaches are needed to solve these problems and satisfy stringent
demands made by producers of coated optical fibers, ribbons, and
cables. These producers demand both fast cure speed and
non-yellowing performance from the coating system which prior art
coatings do not provide.
[0006] UV absorbing compounds ("UV absorbers") have been added to
optical fiber coatings, but with mixed results. It is generally
recognized that they slow cure speed. For example, U.S. Pat. Nos.
5,146,531 and 5, 527,835 teach optical fiber coatings which
allegedly are suitably non-yellowing and have suitable cure speed.
However, the use of UV absorbing compounds is not taught in these
patents.
[0007] U.S. Pat. No. 4,482,204 to Blyler et al. discloses that
optical loss in the fiber can be reduced if the radiation-curable
fiber coatings comprise a UV-absorbing additive which functions to
screen UV light (but, unlike a photoinitiator, does not generate
substantial amounts of free radicals upon UV exposure). According
to this patent, however, the UV absorbing material is preferably
located in the inner primary coating, and is not used in the outer
primary coating if a fully-cured outer primary coating is desired.
This patent also does not suggest the preparation of fast cure
speed outer primary coatings which reduce yellowing of the inner
primary coating through use of a UV absorber. Rather, it teaches
away from the use of a UV absorber in the outer primary coating if
fast cure speed is desired.
[0008] Similarly, U.S. Pat. No. 4,935,455 teaches use of UV
absorber in an inner primary coating. However, this patent also
teaches that increasing the amount of UV absorber will slow cure
speed. Hence, it exemplifies use of UV absorber only in low
amounts.
[0009] Therefore, in general, UV absorbers are considered
undesirable when fast cure is essential, and commercial optical
fiber coatings today generally do not include them. Past commercial
optical fiber coatings have employed them, but in very low
concentrations. These coating systems are inadequate to meet
present commercial demands.
[0010] In sum, a long-felt need exists for fast-curing inner and
outer primary coatings which provide both enhanced protection
against light-induced discoloration and fast cure speed.
SUMMARY OF THE INVENTION
[0011] The present invention recognizes that the aforementioned
problems with optical fiber coatings can be resolved by tailoring
the coating's photoinitiator system together with a UV absorbing
system. In addition, inner and outer primary coating compositions
can be designed to function together. As a result, this invention
helps fulfill a long-felt need in the industry to provide optical
fiber coating systems with both fast cure speed and non-yellowing
properties.
[0012] The present invention provides a radiation-curable
composition for an optical fiber coating comprising the combination
of pre-mixture ingredients:
[0013] about 5 wt. % to about 95 wt. % of at least one
radiation-curable oligomer,
[0014] about 5 wt. % to about 95 wt. % of at least one reactive
diluent,
[0015] about 0.1 wt. % to about 20 wt. % of at least one
photoinitiator, wherein the photoinitiator is selected to provide a
fast cure speed,
[0016] about 0.1 wt. % to about 20 wt. % of at least one UV
absorbing compound which does not substantially impair the fast
cure speed.
[0017] The present invention also provides a coated optical fiber
comprising the combination of:
[0018] an optical fiber,
[0019] a radiation-cured inner primary optical fiber coating,
and
[0020] a radiation-cured outer primary optical fiber coating,
wherein
[0021] said outer primary optical fiber coating comprises, before
radiation-cure:
[0022] about 5 wt. % to about 95 wt. % of at least one
radiation-curable oligomer,
[0023] about 5 wt. % to about 95 wt. % of at least one reactive
diluent,
[0024] about 0.1 wt. % to about 20 wt. % of at least one
photoinitiator, wherein the photoinitiator is selected to provide a
fast cure speed,
[0025] about 0.1 wt. % to about 20 wt. % of at least one UV
absorbing compound which does not substantially impair the fast
cure speed of the inner or outer primary coating.
[0026] The present invention also provides a method for reducing
the rate of color degradation in an inner primary optical fiber
coating comprising the combination of steps of:
[0027] coating an optical fiber with a radiation-curable inner
primary coating,
[0028] coating the inner primary coating with an outer primary
coating which comprises a UV absorber which does not substantially
impair the cure speed of the outer primary coating, and
[0029] curing the coatings.
[0030] In particular, the outer primary coating compositions of the
invention advantageously exhibit good cure speed, and after curing,
demonstrate non-yellowing, oxidative stability, good moisture
resistance, and tough film properties.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIGS. 1-2 illustrate the effect of UV absorber on the rate
of yellowing for inner primary coatings.
[0032] FIG. 3 illustrates the effect of UV absorber on cure speed
for an inner primary coating.
[0033] FIGS. 4-7 illustrate the effect of UV absorber in the outer
primary coating on the increased yellowing which occurs upon aging
for combinations of inner and outer primary coatings.
[0034] FIGS. 8-12 illustrate the effect of dose on the modulus of
the coating compositions of Examples 5A-5E as shown in Table
VIII.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] The following definitions apply to the present
invention:
[0036] "(Meth)acrylate" means acrylate and/or methacrylate.
Acrylate is generally preferred over methacrylate to achieve fast
cure speed, but methacrylate can also be used.
[0037] "Pre-mixture ingredient" means the ingredient before it is
mixed with other ingredients. Pre-mixture ingredients may have the
ability to interact or react with each other after mixing.
[0038] "Effective amount" means that a person skilled in the art
can determine the amount based on the particular coating system.
For example, an amount of photoinitiator may depend on the activity
of the photoinitiator or the non-yellowing character of the
photoinitiator. Also important is whether the coating is an inner
or outer primary coating, and whether the fiber production process
for which the coating is designed is a simultaneous or sequential
cure process. Similarly, an effective amount of UV absorber may
depend on the absorption properties of the particular UV
absorber.
[0039] Radiation-curable inner and outer primary coatings can
comprise at least one radiation-curable oligomer, at least one
reactive or monomer diluent, photoinitiator, and additives
including a UV absorbing compound. The UV-absorbing compound can be
in the inner primary coating, the outer primary coating, or both.
In one preferred embodiment, the UV-absorbing compound is present
in the outer primary coating and serves to screen the inner primary
coating from the harmful effects of UV light. The outer primary
coating also comprises at least one photoinitiator which is a fast
cure photoinitator and provides for fast cure speed despite the
presence of the UV absorber.
[0040] A radiation-curable composition is "sufficiently cured" when
cure has proceeded to the extent that modulus has reached at least
about 90% of its maximum value at full cure. In general, such a
cure degree is sufficient to allow for commercial production of
optical fiber. In most cases, however, the degree of cure should be
maximized. It is preferred that the compositions, after sufficient
cure, have a minimal amount of solvent extractable content.
[0041] As used herein, a "ultraviolet absorbing compound" or "UV
absorber" is differentiated from a "photoinitiator" on the basis of
the cure rate of the radiation-curable compositions which comprise
these ingredients. A UV absorber does not substantially increase
the cure rate of the composition, whereas a photoinitiator does
increase cure rate by, for example, generating free radicals. UV
absorbers in general can convert the absorbed ultraviolet light
energy into heat. Alternatively, absorbed energy in a UV absorber
can be dissipated through fluorescence or phosphorescence. However,
UV absorbers which dissipate energy by heat are preferred. The
distinction between a photoinitiator, which accelerates
photopolymerization, and a UV absorber additive, which serves to
prevent degradation, is well-recognized in the art.
[0042] UV absorbers are preferably selected which screen or absorb
UV light so as to maximize the cure speed of the coating system and
yet minimize the yellowing of the coating system. A balancing of
these effects can be achieved for a particular application
depending on, for example, the UV absorption bands of the inner and
outer primary coating, the UV absorption bands of the inner and
outer primary coating photoinitiators, the amount of photoinitiator
in the inner and outer primary coating, and the relative strength
of the UV absorber and photoinitiator absorption bands.
[0043] For example, the UV absorption spectrum of the outer primary
UV absorber preferably has absorption bands which do not
substantially compete with (overlap) the absorption bands of the
photoinitiator in the inner and outer primary coating, and in
particular, the outer primary coating. When some competition
between photoinitiator and UV absorber cannot be avoided, the
amount of photoinitiator can be increased as necessary to overcome
the absorption effect of the UV absorber and maintain cure
speed.
[0044] Also, the UV absorber can be selected to absorb light which
induces yellowing, particularly in the inner primary coating. Light
which induces yellowing can be associated with the absorption bands
of, for example, the inner primary coating. Hence, the UV absorber
can be selected to substantially match these absorption bands to
minimize yellowing.
[0045] By using these principles, the optimum balance of cure speed
and non-yellowing can be achieved for a particular application by
selecting the identity and amount of UV absorber together with
selecting the identity and amount of photoinitiator in the coating
system, including both inner and outer primary coatings. In some
cases, non-yellowing of the inner primary coating may be more
important, whereas in other cases, a fast cure speed in the outer
primary coating may be more important. The UV absorber and
photoinitiators can be adjusted according to the need.
[0046] Suitable types of UV absorbers include
o-hydroxybenzophenone, o-hydroxyphenyl salicylate, cyanoacrylate,
or 2-(o-hydroxyphenyl)benzotri- azole types, or mixtures thereof.
Other UV absorbers include those discussed in the publication,
"Light Stabilization of UV Cured Coatings: A Progress Report" by A.
Valet et al. in November/December 1996 Radtech Report, pgs. 18-22,
which is hereby incorporated by reference. According to this
publication, UV absorber types of compounds include
hydroxyphenyl-benzotriazoles, hydroxyphenyl-s-triazines,
hydroxybenzophenones, and oxalic anilides.
[0047] A radiation-polymerizable UV absorber is preferred.
Preferably, the UV absorber comprises a (meth)acrylate
functionality, and preferably, an acrylate. These UV absorbers
allow the extractable content of the coating to be minimized.
[0048] Examples of UV absorbers include:
[0049] 2,6-dihydroxybenzophenone,
[0050] 2,2'-dihydroxybenzophenone,
[0051] 2,2'-dihydroxv-4,4-dimethoxybenzophenone,
[0052] 2,4-dihydroxybenzophenone,
[0053] 2-drhydroxy-4-methoxybenzophenone,
[0054] 2-hydroxy-4-octoxybenzophenone,
[0055] 2-hydroxy-4,4'-dimethoxybenzophenone,
[0056] 3-benzoyl-2,4-dihydroxybenzophenone,
[0057] 2-hydroxy-4-dodecyloxybenzophenone,
[0058] 2,2'-dihydroxy-4-n-octyloxybenzophenone,
[0059] phenyl salicylate,
[0060] p-octylphenyl salicylate,
[0061] p-t-butylphenyl salicylate
[0062] 2-(2'-hydroxy-5'-methylphenyl)benzotriazole,
[0063] 2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole,
[0064]
2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole
[0065] 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate, and
[0066] ethyl-2-cyano-3,3'-3,3'-diphenylacrylate.
[0067] A preferred example is 2-ethyl,2' ethoxyoxalamide (Sandovur
VSU). Another preferred example of a UV absorber which is
radiation-curable is 2-hydroxy-4-acryloxyethoxy benzophenone
(Cyasorb UV 416). Another preferred example is
2-(2'-hydroxy-5-methacryloxyethylphenyl)-2-benzotria- zole (Norbloc
7966).
[0068] The UV absorber preferably has strong absorption bands
between about 345 nm and 450 nm. It is important that the UV
absorption extend up to and, preferably, into the visible light
region (which begins at about 400 nm).
[0069] The amount of UV absorber can be about 0.01 wt. % to about
20 wt. %, and preferably, about 0.05 wt. % to about 5 wt. %, and
more preferably, about 0.1 wt. % to about 2 wt. %.
[0070] Surprisingly, the UV absorbers of the present invention,
when used in larger amounts, can be more effective than hindered
amine light stabilizers such as Tinuvin 292 to reduce the yellowing
rate.
[0071] In addition to the selection of the UV absorber, another
important aspect of the present invention is the selection of the
inner and outer primary coating photoinitiator system which
involves consideration of the cure speed of the photoinitiator, its
yellowing characteristics, its absorption spectra, and its amount.
The photoinitiator system should be selected to allow for rapid
production of optical fiber but also to not sacrifice substantial
non-yellowing character. In one coating, mixtures of
photoinitiators can provide the optimal amount of surface and
through cure and are preferred. Photoinitiators are preferred which
generate free radicals upon exposure to UV light.
[0072] Photoinitiators selected for use in the outer primary
coating layer should absorb radiation in a region that to the
extent possible does not substantially include the absorption range
of the UV absorbing compound in the outer primary coating
layer.
[0073] The total amount of photoinitiator in the inner or outer
primary coating is not particularly limited but will be sufficient,
for a given composition and application, to accelerate cure and
achieve the non-yellowing and fast cure speed advantages of the
present invention. The amount in one coating can be, for example,
about 0.1 wt. % to about 20 wt. %, and preferably, about 0.5 wt. %
to about 10 wt. %, and most preferably, about 1.0 wt. % to about
5.0 wt. %.
[0074] Mono- and bis-acyl phosphine oxide photoinitiators can be
used and have been disclosed in, for example, U.S. Pat. Nos.
5,534,559; 5,218,009; 5,399,770; and 4,792,632, which are hereby
incorporated by reference. Other photoinitiator types include those
disclosed in, for example, U.S. Pat. No. 4,992,524.
[0075] Examples of free radical-type photoinitiators include, but
are not limited to, the following:
[0076] hydroxycyclohexylphenylketone;
[0077] hydroxymethylphenylpropanone;
[0078] dimethoxyphenylacetophenone;
[0079] 2-methyl-1-[4-(methyl
thio)-phenyl]-2-morpholino-propanone-1;
[0080] 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one;
[0081] 1-(4-dodecyl-phenyl)-2-hydroxy-2-methylpropan-1-one;
[0082] 4-(2-hydroxyethoxy)phenyl-2(2-hydroxy-2-propyl)-ketone;
diethoxyphenyl acetophenone;
[0083] 2-hydroxy-2-methyl-1-phenyl-propan-1-one;
[0084] 2,4,6-trimethylbenzoyl diphenylphosphine oxide;
[0085] (2,6-dimethoxy benzoyl)-2,4,4 trimethylpentylphosphine
oxide,
[0086] 2-hydroxy-2-methyl-1-phenyl-propan-1-one; and mixtures of
these.
[0087] For an outer primary coating, a preferred photoinitiator
system is a mixture of 2,4,6-trimethyl benzoyl diphenyl phosphine
oxide and 1-hydroxycyclohexylphenyl ketone.
[0088] For an inner primary coating, a preferred photoinitiator
system is a mixture of
bis(2,6-dimethoxybenzoyl)2,4,4'-trimethylpentyl) phosphine oxide
and 2-hydroxy-2-methyl-1-phenyl-1-propanone.
[0089] Both inner and outer primary coatings generally comprise at
least one radiation-curable oligomer. The radiation-curable
oligomer can comprise an oligomer backbone, radiation-curable
end-capping groups, and linking groups which join the end-capping
groups to the oligomer backbone. For example, the radiation-curable
oligomer can be prepared by reaction of a backbone oligomeric
polyol compound, a polyisocyanate linking compound; and a
radiation-curable end-capping compound. Block copolymer and random
copolymer oligomer structures can be used.
[0090] The prior art discloses how to prepare suitable oligomers.
For example, oligomer synthesis can be carried out by methods
disclosed in, for example, U.S. Pat. No. 5,336,563, the complete
disclosure of which is hereby incorporated by reference. Outer
primary coatings are disclosed in, for example, U.S. Pat. Nos.
4,522,465 and 4,514,037 to Bishop et al, the complete disclosures
of which are hereby incorporated by reference. U.S. Pat. No.
4,806,574 to Krajewski et al. also discloses methods for tailoring
the molecular architecture of the oligomer by, for example, use of
polyfunctional cores. U.S. Pat. No. 5,093,386 to Bishop et al. and
U.S. Pat. No. 4,992,524 to Coady et al. also disclose oligomer
synthetic strategies which can be used in the present
invention.
[0091] The number average molecular weight of the oligomer can be,
for example, about 750 g/mol to about 50,000 g/mol, and preferably,
about 1,000 g/mol to about 10,000 g/mole, and more preferably less
than about 5,000 g/mol. Molecular weight and its distribution can
be determined by gel permeation chromatography.
[0092] The oligomer can be present in amounts between about 5 wt. %
and about 95 wt. %, and preferably, between about 20 wt. % and
about 80 wt. %, and more preferably, between about 30 wt. % and
about 70 wt. % relative to the total composition.
[0093] The oligomer backbone can comprise, for example, polyether,
polycarbonate, polyester, or hydrocarbon repeat units, or
combinations thereof. Acrylated acrylics can be used. The backbone
structure in the oligomer can be derived from one or more
oligomeric polyol compounds having the above-noted repeat
units.
[0094] Polyether polyols which can help form the oligomer backbone
can be prepared by ring-opening polymerization of cyclic ethers, as
discussed in, for example, U.S. Pat. No. 4,992,524 to Coady et al.
Oligomers comprising polyether backbones can also be used as
disclosed in, for example, U.S. Pat. No. 5,538,791. Polyether-type
oligomers which are silicone modified are also disclosed in, for
example, EP Patent Publication No. 0,407,004 (A2).
[0095] Polyether repeat units can be based on, for example, C2-C6
alkyleneoxy repeat structures. Representative polyether structures
include ethyleneoxy, propyleneoxy, and tetramethyleneoxy repeat
units. Substituents such as methyl or ethyl or other alkyl or
substituted alkyl groups can be included off of the polyether
backbone to tailor properties.
[0096] Polycarbonate repeat unit structures can be, for example,
based on polyalkylcarbonate structures. Examples of polycarbonates
include those prepared by alcoholysis of diethylene carbonate with
C2-C12 alkylene diols such as, 1,4-butane-diol, 1,6-hexane diol,
1,12-dodecane diol, and the like. The polycarbonate structures in
an oligomer can be tailored by inclusion of polyether units.
[0097] In addition, hydrocarbon or polyolefin oligomer backbones
can be used as disclosed in, for example, U.S. Pat. Nos. 5,146,531
and 5,352,712. Unsaturated or saturated hydrocarbon polyols can be
used, although saturated ones are preferred. Hydrogenated
polybutadiene is a preferred example.
[0098] Polyester diols include the reaction products of
polycarboxylic acids, or their anhydrides, and diols. Acids and
anhydrides include, for example, phthalic acid, isophthalic acid,
terephthalic acid, trimellitic acid, succinic acid, adipic acid,
sebacic acid, malonic acid, and the like. Diols include, for
example, 1,4-butanediol, 1,8-octanediol, diethylene glycol,
1,6-hexane diol, dimethylol cyclohexane, and the like. Included in
this classification are the polycaprolactones. Polyester backbones,
however, are less preferred because they tend to cause hydrolytic
instability.
[0099] The oligomer also comprises linking units such as urethane
linkages formed by reaction of a polyol with a polyisocyanate. The
polyisocyanate linking group can either link the polyol backbone
compound to itself, another polyol backbone compound, or a
radiation-curable end group compound. Preferably, the
polyisocyanate linking group is a diisocyanate compound, although
higher order isocyanates can also be used such as, for example,
triisocyanates. For the inner primary coating, the polyisocyanate
is also preferably aliphatic although some aromatic polyisocyanates
can be included. In general, aromatic isocyanate compounds have
been associated with yellowing, although the person skilled in the
art can determine whether relatively small amounts of aromatic
groups can be tolerated in a given composition. Aromatic
isocyanates can be more readily used in an outer primary coating
because those coatings are generally less susceptible to
yellowing.
[0100] The polyisocyanate compound can have, for example, 4-20
carbon atoms. The molecular weight of the polyisocyanate can be
less than about 1,000 g/mol, and preferably, less than about 500
g/mol. Polymeric polyisocyanates can, in some cases, be useful.
[0101] Examples of diisocyanates include 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, polyethylene adipate terminated with TDI, and
tetramethylxylylene diisocyanate (TMXDI) respectively.
[0102] Urethane linkages in the oligomer can be generated with
known urethanation catalysts such as, for example, dibutyltin
dilaurate or diazabicyclooctane crystals.
[0103] The oligomer further comprises a radiation-curable
end-capping group. End-capping means that the oligomer contains a
terminal point on its molecular chain. The oligomer can have two to
four end-capping sites, but preferably has two sites. In general,
the oligomer can be formed from a monoethylenically unsaturated
compound of relatively low molecular weight less than, for example,
500 g/mol, and preferably, less than about 300 g/mol.
(Meth)acrylate compounds can be used in oligomer synthesis and
function to end-cap the oligomer and provide unsaturation suitable
for rapid radiation-cure, and in particular, ultraviolet light
radiation-cure. The (meth)acrylate is preferably selected to
maximize cure speed and allow for ready oligomer preparation.
Acrylate is most preferred. In addition, however, non-acrylate
systems such as vinyl ether and maleate can be used.
[0104] Hydroxyalkyl acrylate compounds can also be used, and
hydroxyethyl acrylate is a particularly preferred compound. Other
preferred examples include hydroxypropyl acrylate and hydroxybutyl
acrylate.
[0105] For the inner primary coating, the oligomer can be a block
copolymer oligomer prepared from a mixture of a polyether and a
polycarbonate. For example, a mixture of polyols can be used which
includes a (1) polyhexylcarbonate which also includes etheric
repeat units, and (2) polybutylene oxide. For the outer primary
coating, the polyol used to form the backbone is preferably a
polypropylene glycol or a copolymeric polyether based on
copolymerization of tetrahydrofuran and methyltetrahydrofuran.
[0106] For an outer primary coating, toluene diisocyanate is a
preferred example of a linking group compound from which the
oligomer is synthesized. For an inner primary coating, isophorone
diisocyanate (IPDI) is a preferred example of a linking group
compound.
[0107] Both inner and outer primary coatings further comprise at
least one liquid reactive diluent, or monomer diluent, which
functions to decrease the viscosity of the oligomer and tailor such
properties in the cured composition as refractive index, modulus,
and polarity. For example, aromatic diluents tend to raise the
refractive index and Tg of the material. Long chain aliphatic
diluents can soften the coating. Polar diluents can improve room
temperature mechanical properties by hydrogen bonding and can
increase solvent resistance. Preferably, formulations are tailored
to minimize water absorption because water generally has a
detrimental impact on fiber. Mixtures of diluents are preferred to
achieve the suitable balance of properties required for a given
application.
[0108] 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. More preferably, the radiation-curable functional group
forms free radicals during curing.
[0109] The total amount of diluent can be, for example, about 5 wt.
% to about 95 wt. %, and preferably, about 20 wt. % to about 80 wt.
%, and more preferably, about 30 wt. % to about 70 wt. %.
[0110] For example, the reactive diluent can be a monomer or
mixture of monomers having an acrylate or vinyl ether functionality
and an C.sub.4-C.sub.20 alkyl or polyether moiety. Particular
examples of preferred reactive diluents include:
[0111] hexylacrylate,
[0112] 2-ethylhexylacrylate,
[0113] isobornylacrylate,
[0114] decyl-acrylate,
[0115] laurylacrylate,
[0116] stearylacrylate,
[0117] 2-ethoxyethoxy-ethylacrylate,
[0118] laurylvinylether,
[0119] 2-ethylhexylvinyl ether,
[0120] N-vinyl formamide,
[0121] isodecyl acrylate,
[0122] isooctyl acrylate,
[0123] vinyl-caprolactam,
[0124] N-vinylpyrrolidone, and the like.
[0125] 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:
[0126] ethyleneglycolphenylether-acrylate,
[0127] polyethyleneglycolphenyletheracrylate,
[0128] polypropyleneglycolphenylether-acrylate, and
[0129] alkyl-substituted phenyl derivatives of the above monomers,
such as polyethyleneglycolnonylphenyl-etheracrylate.
[0130] The reactive diluent can also comprises a diluent having two
or more functional groups capable of polymerization. Particular
examples of such monomers include:
[0131] ethoxylated bisphenol-A-diacrylate--as available as SR 349A
monomer and supplied by Sartomer,
[0132] C2-Cl8 hydrocarbon-dioldiacrylates,
[0133] C.sub.4-C.sub.18 hydrocarbondivinylethers,
[0134] C.sub.3-C.sub.18 hydrocarbon triacrylates, and the polyether
analogues thereof, and the like, such as
1,6-hexanedioldiacrylate,
[0135] trimethylolpropane tri-acrylate,
[0136] hexanedioldivinylether,
[0137] triethylene-glycoldiacrylate,
[0138] pentaerythritol-triacrylate,
[0139] ethoxylated bisphenol-A diacrylate, and
[0140] tripropyleneglycol diacrylate.
[0141] A preferred diluent system for use in the outer primary
coatings in the present invention is a mixture of ethoxylated
nonylphenol acrylate and ethoxylated bisphenol A diacrylate. For an
inner primary coating, a preferred diluent system is a mixture of
ethoxylated nonylphenol acrylate and isodecyl acrylate.
[0142] Diluent molecular weight is not particularly limited but is
generally below about 1,000 g/mol so that it is a liquid. The
diluent, however, may itself contain some oligomeric character such
as repeating etheric groups like ethyleneoxy or propyleneoxy. In
this case, it may still be called a diluent.
[0143] The viscosity of the radiation-curable composition is
preferably less than about 12,000 cps but greater than about 2,000
cps, and preferably, between about 3,000 cps and about 10,000 cps
at ambient temperature. The viscosity is preferably stable over
time so that long shelf life for the uncured composition is
attained.
[0144] The inner and outer primary coating compositions can further
comprise additives which are conventional in the optical fiber
coating art. Suitable additives are disclosed in, for example, the
aforementioned U.S. Pat. Nos. 5,336,563, 5,093,386, 4,992,524, and
5,146,531.
[0145] For example, adhesion promoters such as organofunctional
silanes can be used in the inner primary coatings. Acrylate-,
amino-, or mercapto-functional silane can be employed in amounts of
about 0.1 wt. % to about 5 wt. %, and preferably, between about 0.3
wt. % and about 3 wt. %. Mercaptopropyltrimethoxy silane is a
preferred example of a silane adhesion promoter.
[0146] Other suitable additives include thermal antioxidants such
as hindered phenols or hindered amine light stabilizers. A
preferred type of thermal antioxidant for both primary and
secondary coatings is a thiodiethylene cinnamate derivative,
Irganox 1035 available from Ciba-Geigy. The thermal antioxidant can
be present, for example, in amounts between about 0.1 wt. % and
about 1 wt. %.
[0147] Shelf stabilizers and slip agents can be important
additives. For example, butylated hydroxy toluene and phenothiazine
are commonly used stabilizing additives. Additives are also useful
to tailor the handling characteristics of coated optical fiber. For
example, slip agents and friction adjusting additives are useful in
the outer primary coating. Still other additives or components
which may appear in the final coating include pigments, catalysts,
lubricants, wetting agents, and leveling agents.
[0148] Conventional colorants, dyes, and pigments can be used
having conventional colors. Pigments are preferred over dyes
because dye color tends to fade with time. Colorants are preferably
stable to ultraviolet radiation, and pigments are in the form of
small particles. Particle size can be reduced by milling.
[0149] The colored material can comprise oligomers, monomers and
diluents, photoinitiators, stabilizers, and additives, as disclosed
herein for substantially colorless coatings but adapted to be a
printing ink binder, a colored outer primary coating, a colored
matrix material, or the like.
[0150] Pigments can be conventional inorganic or organic pigments
as disclosed in, for example, Ullmann's Encyclopedia of Industrial
Chemistry, 5th Ed., Vol. A22, VCH Publishers (1993), pages 154-155,
the complete disclosure of which is hereby incorporated by
reference. The pigment can be selected based on, for example,
whether the composition is a printing ink or secondary coating.
Printing inks will be more heavily pigmented.
[0151] General classes of suitable colorants include, among others,
inorganic white pigments; black pigments; iron oxides; chromium
oxide greens; iron blue and chrome green; violet pigments;
ultramarine pigments; blue, green, yellow, and brown metal
combinations; lead chromates and lead molybdates; cadmium pigments;
titanate pigments; pearlescent pigments; metallic pigments; monoazo
pigments; disazo pigments; disazo condensation pigments;
quinacridone pigments; dioxazine violet pigment; vat pigments;
perylene pigments; thioindigo pigments; phthalocyanine pigments;
and tetrachloroisoindolinones; azo dyes; anthraquinone dyes;
xanthene dyes; and azine dyes.
[0152] More in particular, suitable inorganic pigments for printing
inks include, for example, titanium dioxide, iron oxide, iron
silicate, iron cyan blue (or Prussian blue), aluminum powder,
cooper-zinc allow powder, and carbon black. Suitable organic
pigments for printing inks include, for example, diarylide yellow,
diarylide orange, naphthol AS red, Rubin 4 B calcium salt, salts of
basic dyes, phthalocyanine blue, reflex blue, phthalocyanine green,
and polycyclic pigments. Fluorescent pigments can be used.
[0153] The amount of the colorant, pigment, or dye is also
conventional and will be determined by such factors as the shade,
coloring strength, and fastness of the colorant as well as the
dispersibility, rheological properties, and transparency. Also,
printing inks are generally more heavily pigmented than outer
primary coatings. The amount can be that which is sufficient to
impart the required color, and more than that is not generally
preferred. The amount of colorant can be, for example, between
about 0 wt. % and about 25 wt. %, and preferably, about 0.25 wt. %
and about 15 wt. %, and more preferably, between about 0.5 wt. %
and about 5 wt. %.
[0154] In a preferred embodiment for the present invention, an
outer primary coating composition is formulated from a combination
of pre-mixture ingredients comprising
[0155] about 20 wt. % to about 40 wt. % of a radiation-curable
oligomer, wherein the oligomer is prepared from hydroxyethyl
acrylate, toluene diisocyanate, and a polyether polyol compound
having molecular weight of about 750 g/mol to about 2,000
g/mol,
[0156] about 40 wt. % to about 80 wt. % of ethoxylated
bisphenol-A-diacrylate,
[0157] about 3 wt. % to about 20 wt. % of ethoxylated nonylphenol
acrylate,
[0158] about 2 wt. % to about 4 wt. % of a photoinitiator system
which includes at least one phosphine oxide type compound, and an
effective amount of UV-absorber such as UV 416. In this preferred
embodiment, an effective amount of antioxidant is also present.
[0159] In another preferred embodiment, an inner primary coating
was formulated from pre-mixture ingredients comprising:
[0160] about 30 wt. % to about 70 wt. % of a radiation-curable
oligomer, wherein the oligomer is prepared from (i) hydroxyethyl
acrylate, (ii) isophorone diisocyanate, and (iii) a polyether
polyol compound, a polycarbonate polyol compound, or a mixture
thereof, wherein the oligomer has a molecular weight of about 750
g/mol to about 3,000 g/mol,
[0161] about 5 wt. % to about 40 wt. % of ethoxylated nonyl phenol
acrylate,
[0162] about 5 wt. % to about 30 wt. % of isodecyl acrylate,
[0163] about 2 wt. % to about 4 wt. % of a photoinitiator system
which includes at least one phosphine oxide type compound,
[0164] about 0.3 wt. % to about 3 wt. % of an organofunctional
silane adhesion promoter, which preferably is
mercaptopropyltrimethoxy silane, and
[0165] an effective amount of UV-absorber such as UV 416. In this
preferred embodiment, an effective amount of antioxidant is also
present.
[0166] In addition to fast-cure speed and non-yellowing, other
properties are also important. For example, the inner primary
coating must have adequate adhesion to the fiber, even in moist
conditions. However, the inner primary coating should also allow
for a clean strip from the fiber in both fiber stripping and ribbon
stripping processes. Both inner and outer primary coatings should
be formulated to have resistance to moisture.
[0167] Cure speed for an outer primary coating should be less than
about 1.0 J/cm.sup.2, and preferably less than about 0.5
J/cm.sup.2, and more preferably less than about 0.4 J/cm.sup.2,
wherein cure speed here means the dose at which modulus has reached
95% of its maximum value. Cure speed for an inner primary coating
is also preferably less than about 1.0 J/cm.sup.2.
[0168] Conventional optical fiber production methods can be used to
prepare coated fiber. Such methods are disclosed in, for example,
U.S. Pat. No. 4,962,992, which is hereby incorporated by
reference.
[0169] The invention will be further illustrated with the following
non-limiting examples. Unless otherwise indicated, percentages are
weight percent and are with respect to the weight of the total
composition.
EXAMPLE 1
[0170] Formulation of an Outer Primary Coating
[0171] A radiation-curable outer primary coating formulation is
prepared from the pre-mixture ingredients summarized in Table
I:
1 TABLE I INGREDIENTS AMOUNTS (wt. %) H-T-PPG1025-T-H.sup.1 32.0
ethoxylated bisphenol-A- 56.50 diacrylate ethoxylated nonylphenol
7.00 acrylate 2-hydroxy-4- 0.5 acryloxyethoxy benzophenone (UV 416)
2,4,6-trimethyl benzoyl 0.5 diphenyl phosphine oxide 1-hydroxy
cyclohexyl 2.50 phenyl ketone thiodiethylene bis-(3,5- 0.5
di-tert-butyl-4- hydroxy)hydrocinnamate Ebecryl 170 0.5
.sup.1urethane acrylate oligomer prepared from (I)
hydroxyethylacrylate (H), (II) toluene diisocyanate (T), and (III)
polypropylene glycol diol with molecular weight of about 1,025 (PPG
1025).
[0172] The composition is expected to have both substantial
non-yellowing behavior and fast cure speed.
EXAMPLE 2
[0173] Formulation of Inner Primary Coatings
[0174] A control inner primary coating composition without UV
absorber was formulated from the pre-mixture ingredients summarized
in Table II:
2 TABLE II INGREDIENTS AMOUNTS H-(T-PTGL2000).sub.2-T-H.sup.1 50
ethoxylated nonyl phenol acrylate 20.4 lauryl acrylate 7 vinyl
caprolactam 6 isobornyl acrylate 13.7 2,4,6-trimethylbenzoyl
diphenyl phosphine 1.5 oxide Irganox 1035 0.3 diethyl amine 0.1
mercaptopropyl trimethoxy silane 1.0 .sup.1urethane acrylate
oligomer prepared from hydroxyethyl acrylate (H), toluene
diisocyanate (T), and a copolymer of THF and methyl-THF having
molecular weight of about 2,000 (PTG-L 2,000).
[0175] The control formulation of Table II, which did not comprise
UV-absorber, was further formulated into several additional
compositions by the addition of additive so that the newly
formulated compositions' concentration of additive was 0.5 wt. %
(and 99.5 wt. % of composition in Table II).
[0176] The additive for composition A was Norblock 7966
[2-(2'-hydroxy-5-methacryloxyethylphenyl)-2H-benzotriazole]; for
composition B was Sanduvor VSU (2-ethyl,2'-ethoxy-oxalamide), and
for composition C was Tinuvin 292 (which is a hindered amine light
stabilizer).
[0177] The three formulations, A-C, which each contained one
additive, and the control formulation of Table II were converted to
3 mil films and cured by UV light (1.0 J/cm under N.sub.2 at 8 cfm
with Fusion D lamp). The yellowness index was measured as a
function of aging time under QUV conditions, and the results are
shown in FIG. 1. Data was taken at 0, 1, 2, 3, 4, 6, and 8 weeks.
The data showed surprisingly that Sandovur VSU was most effective
for reducing the rate of yellowing.
EXAMPLE 3
[0178] Formulation of Inner Primary Coatings
[0179] Inner primary coatings were formulated according to Table
III:
3 TABLE III INGREDIENTS A B H-(I-PTGL2000).sub.2-I-H 51.60 --
H-(I-PPG1025).sub.1.06-(I- -- 56 PERMANOLKM10- 1733).sub.1.14-I-H
CH.sub.2.dbd.CHCO(OCH.sub.2CH.sub.2).sub.4OC.sub.6 20.87 25.5
H.sub.4C.sub.9H.sub.19 LAURYL ACRYLATE 7.007 -- ISODECYL ACRYLATE
-- 14 IRGACURE 1700 -- 3 PHENOXYETHYL ACRYLATE 11.712 --
N-VINYLPYRROLIDONE 4.504 -- IRGACURE 184 3 -- IRGANOX 1035 0.3 0.5
mercaptopropyl 1.001 1.00 trimethoxy silane
[0180] To 99.5% by wt. of each of the above compositions was added
0.5% by wt. SANDOVUR VSU. Film samples were prepared by coating and
curing 10 mil films at 1.0 J/cm.sup.2, under a D-lamp (Fusion) in
the presence of N.sub.2 and color change was measured at 0, 1, 4,
7, 14 and 28 days. Yellowness Index (YI) was calculated as
described below, and delta E values estimated from the yellowness
index. The results are provided in FIG. 2. Cured coating
compositions containing 0.5% by wt SANDOVUR VSU consistently gave
lower yellowness index and delta E values over a period of 28 days
than the same compositions containing no UV absorbing compound.
[0181] In addition, the effect of the UV-absorber, Sandovur VSU
(0.5 wt. %), on the cure speed (measured by FT-IR measurements) of
composition 3B is illustrated in FIG. 3. The data show that cure
speed, although made slower, is not substantially impaired, and
fast cure speed can be obtained despite the presence of the UV
absorber which retards yellowing.
EXAMPLE IV
[0182] Cure of Inner Primary Coating Together with Outer Primary
Coating Having UV Stabilizer Therein
[0183] Two outer primary coating compositions were formulated from
the following pre-mixture ingredients summarized in Table IV:
4 TABLE IV COMPONENTS 4-A 4-B H-T-PTMG650-T-H.sup.1 37.0 37.40
Photomer 3016, 25.0 28.23 bisphenol-A-epoxy diacrylate
tetraethyleneglycol diacrylate -- 21.28 triethyleneglycol
diacrylate -- 3.45 trimethylolpropane triacrylate -- 6.36
hexanediol diacrylate 10.5 -- isobornyl acrylate 12.0 --
phenoxyethyl acrylate 11.0 -- benzophenone -- 1.49
2,2-dimethoxy-2-phenylacetophenon- e, -- 0.73 Irgacure 651
1-hydroxycyclohexyl phenyl ketone, 1.0 Irgacure 184
2,4,6-trimethylbenzoyl diphenylphosphine 2.0 oxide, Lucirin TPO
benzil -- 0.5 diethylamine -- 0.60 phenothiazine -- 0.01
thiodiethylene bis(3,5-di-tert-butyl-4- 0.5 --
hydroxy)hydrocinnamate 2-hydroxy-4-n-octoxybenzophenone -- 0.01
2-hydroxy-4-acryloyloxye- thoxy 0.5 -- benzophenone DC 57, silicone
0.2 0.07 DC 190, silicone 0.3 0.13 N-[2-(vinylbenzoamino)-ethyl]-3-
-- 0.19 aminopropyltrimethoxysilane, 40% in MeOH .sup.1urethane
acrylate oligomer prepared from hydroxyethyl acrylate (H), toluene
diisocyanate (T), and polytetramethylene glycol having molecular
weight of about 650 (PTMG 650).
[0184] The formulation 4B included less UV absorber and did not
comprise a fast cure phosphine oxide photoinitiator.
[0185] In addition, four inner primary coating compositions 4C-F
were formulated from pre-mixture ingredients which are summarized
below in Tables V and VI:
5 TABLE V COMPONENTS 4-C 4-D H-I-(PermanolKM101733-I).sub.2.7-H --
45.49 H-I-(PTGL2000).sub.2-I-H 52.7 -- ethoxylated nonylphenol
acrylate 15.0 33.83 Isodecyl acrylate 7.0 -- isobornyl acrylate
14.0 -- vinyl caprolactam 7.0 -- octyldecyl acrylate 11.37
tripropyleneglycol diacrylate -- 1.96 phenoxyethyl acrylate -- 3.92
trimethylbenzoyl diphenylphosphine -- 1.96 oxide
1-hydroxycyclohexyl phenyl ketone 3.0 -- ethylene
bis(oxyethylene)bis(3- -- 4.0 tert-butyl-4-hydroxy-5-
methylhydrocinnamate) thiodiethylene bis(3,5-di-tert- 0.3 --
butyl-4-hydroxy)hydrocinnamate mercaptopropyl trimethoxy silane 1.0
0.98
[0186]
6 TABLE VI Ingredients 4-E 4-F H-(I-PTGL2000).sub.2-I-H 52.7 52.7
ethoxylated 15.0 15.0 nonylphenol acrylate isodecyl 7.0 7.0
acrylate isobornyl 14.0 10.0 acrylate vinyl 7.0 7.0 caprolactam
tripropylene -- 4.0 glycol diacrylate Lucirin TPO 2.0 2.0 Irgacure
184 1.0 1.0 Irganox 1035 0.3 0.3 mercaptopropyl 1.0 1.0
trimethoxysilane
[0187] Tests were carried out to test the curing of the four inner
primary coatings (Tables V and VI) under the outer primary coatings
(Table IV). These tests simulated a wet-on-wet optical fiber
coating and cure process. Four samples comprising films of both
inner and outer primary coatings were tested for yellowing and cure
speed behavior:
7 sample inner primary/ outer primary 1 4-D/ 4-B 2 4-C/ 4-A 3 4-E/
4-A 4 4-F/ 4-A
[0188] Based on visual observation of the stickiness of the
coatings, inner primary coating composition in sample 3 cured more
quickly than the inner primary composition in sample 2. This
difference in cure speed can be attributed to the phosphine oxide
photoinitiator present in the inner primary composition of sample 3
which provides fast cure speed despite the presence of the UV
absorber in the outer primary coating.
[0189] In addition, yellowing behavior (yellowness index) was
measured under fluorescent aging conditions.
[0190] The results are shown in FIGS. 4-7. The coating system
having the least amount of UV absorber in the outer primary
coating, sample 1, showed the greatest color change (yellowing).
Hence, compositions of sample 1 showed unacceptable yellowing and
did not provide a combination of fast cure and substantial
non-yellowing which the present invention provides. The coating
system of sample 3 showed the least color change.
EXAMPLE 5
[0191] Effect on Cure Speed of Outer Primary Coating
[0192] A base formulation, which did not comprise UV absorber, was
formulated according to Table VII.
8 TABLE VII INGREDIENTS AMOUNTS (wt. %) H-T-PTGL1000-T-H.sup.1 32.3
ethoxylated bisphenol-A- 56.0 diacrylate ethoxylated nonylphenol
8.2 acrylate diphenyl 2,4,6-trimethyl 1.0 benzoyl phosphine oxide
1-hydroxy cyclohexyl 2.0 phenyl ketone thiodiethylene bis-(3,5- 0.5
di-tert-butyl-4- hydroxy)hydrocinnamate .sup.1urethane acrylate
oligomer prepared from (I) hydroxyethylacrylate (H), (II) toluene
diisocyanate (T), and (III) PTGL1000 which is a polyether copolymer
diol having repeat units of tetramethylene glycol and
methyltetramethylene glycol and having molecular weight of about
1,000.
[0193] This base formulation was further formulated with different
UV absorbers in different amounts according to Table VIII. Samples
incorporating different UV absorbing agents were prepared by
coating and curing 3 mil Mylar films at 0.2, 0.3, 0.5, 0.75, 1.0
and 2.0 J/cm.sup.2, under a D-lamp (Fusion) in the presence of
N.sub.2.
[0194] Cure speed was measured by dose-modulus curves, and the
results are presented in Table VIII, shown below:
9TABLE VIII Ingre- Sample Sample Sample Sample Sample dient 5-A 5-B
5-C 5-D 5-E Base 100 99.5 99.5 99 99.04 UV 416 -- 0.5 -- -- 0.96 UV
531 -- -- 0.5 1.0 -- Cure 0.35 0.43 0.36 0.42 0.51 Speed**,
J/cm.sup.2 **Dose at 95% of ultimate modulus
[0195] CYASORB UV 531 reduced cure speed of the base formulation
less than CYASORB UV 416, and concentrations of about 0.5 wt % UV
absorber reduced cure speed less than concentrations of about 1.0
wt %.
[0196] Test Procedures:
[0197] Yellowness Index
[0198] Yellowness Index was calculated by UV-VIS spectroscopy.
Yellowness index is measured as the average absorbance over the
350-450 nm UV spectral region, calculated at a 0.1 mm film
thickness.
[0199] A specimen from a prepared coating film is cut and should be
at least 0.5".times.1.0" in size. The seam region is set between
350-450 nm at a speed of 60 nm/min. When placing the film in the
sample holder, care should be taken to avoid wrinkling of the film.
The film should be as smooth as possible before seaming. The
spectrum should be collected at data point per nm. The coating film
thickness in mm should be measured with a micrometer by taking the
average of at least three different readings in the area of the
film that was covering the hole in the sample holder.
[0200] The average absorbance (A.sub.Avg) for the region scanned in
the spectrum is calculated by scanning the absorbance at each
measured wavelength and dividing by the number of data points.
Yellowness index is calculated by adjusting the average absorbance
to a film thickness of 0.10 mm according to the following equation:
1 YI = A Avg .times. 0.1 T
[0201] when
[0202] YI=yellowness index
[0203] A.sub.Avg=average absorbance
[0204] T=film thickness in mm.
[0205] Cure Speed by FTIR
[0206] Cure speed in the present invention can be measured by FTIR.
This method is applicable to coating systems that cure by loss of
double bonds when exposed to ultraviolet light. Samples are
prepared by placement of a drop of thoroughly mixed coating in the
center of an NaCl disc. A second NaCl disc is placed on top of the
coating drop such that the coating spreads evenly to the edge of
the spacer. Care should be taken to ensure that no air bubbles are
present in the coating layer. An FTIR spectrum of the uncured
coating is obtained. The net absorbance of the unsaturation band
from the peak minimum to the peak maximum is measured. The peak
maximum should be in the 1.0-1.2 angstrom range. The absorbance
will depend on the peak minimum. This step is repeated twice and
the three values for net absorbance averaged. The averaged value is
used for a target for analyses for a particular coating system. The
coating thickness is adjusted by tightening the demountable cell
holder screws until the net absorbance of the unsaturation band is
within .+-.0.05 angstroms of the averaged value of the net
absorbance. Spectra should be collected sequentially until the net
absorbance value stabilizes, e.g., does not vary by more than
.+-.5% on a relative basis for success of spectrum. The coating is
then exposed to a 0.5 second pulse from the UV lamp source, then a
second FTIR spectrum is immediately collected. This step is
repeated until the coating has been exposed for a total time of 5.0
seconds, performing each successive exposure and FTIR measurement
as quickly as possible.
[0207] All spectra obtained should be converted from transmission
to absorbance. For each spectrum, the net area under the
unsaturation band is determined. For acrylate based coatings, the
percent reacted acrylate unsaturation (% RAU) for each exposure is
as follows: 2 % RAU = A ( liq ) - A ( exposed ) A ( liq ) .times.
100
[0208] where A.sub.(liq) equals the net area of the 810 cm.sup.-1
band for the liquid coating and A.sub.(exposed) equals the net area
of the 810 cm.sup.-1 band after exposure. The average % RAU for the
triplicate analysis is determined for each time exposure and time
of exposure v. % RAU for both the sample and the control is
plotted.
[0209] Dose-Modulus Curves
[0210] Cure speed can also be measured by dose-modulus curves, as
shown in FIGS. 8-12, for Examples 5A-5E, respectively (see Table
VIII). Modulus measurements are secant modulus measurements which
are described further below. Cure speed is the dose at which 95% of
the maximum modulus was attained.
[0211] Tensile Testing
[0212] The tensile strength 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 generally followed, with the following modifications.
[0213] 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.degree. C. and 50.+-.5% relative humidity
for a minimum of sixteen hours prior to testing.
[0214] 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.
[0215] 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.
[0216] 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 test specimen after removal from the substrate.
[0217] 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 deviates from the average by more than 10% relative, the
test specimen was discarded. All specimens came from the same
plate.
[0218] The appropriate load cell was determined by using the
following equation:
[A.times.145].times.0.0015=C
[0219] Where: A=Product's maximum expected tensile strength (MPa);
145=Conversion Factor from MPa to psi; 0.00015=approximate
cross-sectional area (in.sub.2) of test specimens; and C=lbs. The 2
pound load cell was used for materials where C=1.8 lbs. The 20
pound load cell was used for materials where 1.8 (C<18 lbs). If
C>19, a higher capacity load cell was required.
[0220] 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
approximately 20 psi (1.5 Kg/cm) for primary optical fiber coatings
and other very soft coatings; set approximately 40 psi (3
Kg/cm.sup.2) for optical fiber single coats; and set 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.
[0221] 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.
[0222] The temperature near the Instron Instrument was measured and
the humidity was measured at the location of the humidity gage.
This was done just before beginning measurement of the first test
specimen.
[0223] Specimens were only analyzed if the temperature was within
the range 23.+-.1.0.degree. C. and the relative humidity was within
50.+-.5%. The temperature was verified as being within this range
for each test specimen. The humidity value was verified only at the
beginning and the end of testing a set of specimens from one
plate.
[0224] Each test specimen was tested by suspending it into 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.
[0225] The sample number was entered and sample dimensions into the
data system, following the instructions provided by the software
package.
[0226] The temperature and humidity were measured after the last
test specimen from the current drawdown was tested.
[0227] The calculation of tensile properties was performed
automatically by the software package.
[0228] The values for tensile strength, % elongation, and secant
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.
[0229] Delta E
[0230] The color aging behavior (delta E) of the cured films can be
measured by conventional methods as disclosed in the publication
entitled "A Measurement of the Contribution of UV Cured Coatings
and Ink Binders Towards Color Change of UV Cured Inks" by D. M.
Szum in Radtech Europe '93 Conference Proceedings (papers presented
at the Radtech Europe Conference held May 2-6, 1993), the complete
disclosure of which is hereby incorporated by reference. This
publication discloses measurements which were performed on three
layer samples, whereas the samples of the present invention were
single layers. The measurement involves a mathematical
manipulation, FMC-2.
[0231] Yellowing measurements can be carried out with film samples
about 2.times.2 inches square. Color measurement data was obtained
from a Macbeth Series 1500 Color Measurement System (Model 2020).
The colorimeter was calibrated and set to the following
parameters:
[0232] Illuminant: D for Primary and Secondary Illuminants
[0233] Color Difference: FMC-2
[0234] Mode: 2, COL
[0235] Area of Measurement: Large Area View
[0236] Specular Component: Excluded (SCE)
[0237] UV filter: Included
[0238] Background: White calibration standard.
[0239] Also, delta E measurements can be correlated with yellowness
index measurements, and calibration plots can be prepared which
allow one to estimate delta E based on yellowness index.
* * * * *