Radiation-curable cross-linked ribbon matrix material for bonding an array of coated optical glass fibers

A radiation-curable, cross-linked ribbon matrix material is suitable for covering an array of coated optical glass fibers. The matrix material contains at least one radiation-curable oligomer or monomer, and at least one chromophoric indicator selected so as to be susceptible to destruction of its chromophoric characteristic upon exposure to radiation and present in an amount which becomes substantially colorless when exposed to a level of radiation sufficient to cure the radiation-curable matrix material, wherein the at least one chromophoric indicator has a color that is distinguishable from a base color of the radiation-curable, optical glass fiber coating composition in cured form. A cable structure and a telecommunications system are also described.

FIELD OF THE INVENTION 
This invention relates to radiation-curable, optical glass fiber ribbon 
matrix material for bonding an array of optical glass fibers and to a 
method of controlling the cure thereof. More particularly the invention 
provides a ribbon matrix material having an effective amount of a 
chromophoric indicator component which will normally provide a visible 
color to the uncured composition but which will becomes colorless at the 
level of radiation for the desired cure of the coating composition. 
BACKGROUND OF THE INVENTION 
Optical glass fibers are generally coated with two superposed 
radiation-cured coatings, which together form a primary coating. The 
coating which is in direct contact with the glass is called the inner 
primary coating and the overlaying coating is called the outer primary 
coating. A plurality of these coated optical glass fibers may be assembled 
together and bonded with matrix material to form a ribbon of parallel 
coplanar coated optical fibers. Such a ribbon may typically contain 12 
coplanar optical fibers, but other numbers of fibers may be used to form a 
ribbon. The fibers may also be bundled into a circular or other shape of 
array forming a cylindrical or other shape of structure having an outer 
coating of ribbon matrix material. 
The inner primary coating is usually a relatively soft coating providing 
environmental protection to the glass fiber and resistance, inter alia, to 
the well-known phenomenon of microbending. Microbending in the coated 
fiber can lead to attenuation of the signal transmission capability of the 
coated fiber and is therefore undesirable. The outer primary coating, 
which is on the exposed surface of the coated fiber, is typically a 
relatively harder coating designed to provide a desired resistance to 
physical handling forces, such as those encountered when the fiber is 
cabled. 
Such primary coating systems are typically prepared from radiation-curable, 
optical glass fiber coating compositions (hereinafter referred to as 
"radiation-curable composition"). It is a characteristic of such systems 
that the curing proceeds upon exposure to a radiation source, typically a 
UV-radiation source, for a time sufficient to provide a full cure of the 
coating compositions at the level of intensity of such source. 
As the demand for coated optical glass fibers has increased, manufacturers 
must respond by adding more fiber drawing production lines and by 
attempting to increase the linear line speeds of the existing fiber 
drawing production lines. In the latter case, one factor which will 
determine the upper limit for the line speed will be the curing rate 
characteristics of the radiation-curable compositions, including the 
ribbon matrix material, for a given radiation source and intensity. 
If the line speed is increased to the extent that sufficient cure time for 
the radiation-curable composition, including the ribbon matrix material, 
is not provided, the radiation-curable composition will not have received 
a sufficient amount of radiation for complete cure, or cross-linking, of 
the radiation-curable composition. The production linear line speed is 
generally inversely related to the amount of radiation striking the 
optical glass fiber. That is, as the production line speed is increased 
the amount of radiation exposure to the radiation-curable composition 
during the production process will necessarily decrease for a given 
radiation source. Incomplete cure of the radiation-curable composition is 
undesirable and must be avoided because then the desired protective 
properties of the incompletely cured primary coating may not be achieved 
and/or the incompletely cured primary coating may retain tackiness (giving 
problems in subsequent handling) or a malodorous odor may be present, and 
there may also be an increase in the extractables (undesirable) in the 
supposedly-cured coating. 
Ribbon production as well as fiber production is therefore confronted with 
the problem that increases in production line speed are difficult to 
achieve without jeopardizing the cured coating quality. 
If the production line speed is increased without careful consideration and 
balancing of the associated reduction in radiation exposure, then the 
radiation-curable composition may be processed at a radiation exposure 
level less than required for the desired level of curing, which means that 
the cured primary coating or the ribbon matrix material may not be fully 
cured. However, if the line speed is conservatively adjusted downwards to 
ensure that an adequate cure is achieved, this means that the line 
production is correspondingly reduced at the expense of product 
throughput. 
Because the amount of radiation exposure is equal to the radiation 
intensity multiplied by the exposure time, the desired or required 
production line speed could be achieved by increasing the radiation 
intensity. This would require larger radiation units, which could lead to 
problems and costs in designing and operating the production line. Even 
though adjustments in the radiation intensity or exposure can be made, 
there remain certain fundamental practical issues associated with a 
radiation curing lamp assembly which can affect the actual amount of 
radiation reaching a radiation-curable composition, such as a ribbon 
matrix material. 
Specifically, the amount of radiation striking the radiation-curable 
composition from, for instance, a UV-curing lamp system on a ribbon 
production line is not constant over the operative lifetime of the lamp 
and may be considered to be determined by the sum of the following: 
(1) reflectivity of lamp reflector system, 
(2) intensity of curing lamp output, and 
(3) surrounding enclosure of radiation-curable material. 
The reflector system's ability to reflect the radiation can vary during 
production runs due to: 
(1a) variability of reflector cleanliness, 
(1b) misalignment of reflector system with radiation-curable composition, 
(1c) solarization of the reflector system, 
(1d) the age of the lamp and system itself. 
The radiation curing UV lamp output typically changes in intensity as the 
bulb ages in use. Moreover, the wavelength distribution of lamp emission 
can change as a result of its aging during such use. 
When curing radiation-curable compositions such as ribbon matrix material, 
an elliptical reflector system containing a UV curing lamp is usually 
used. Such a system is shown in FIG. 1, (Prior Art). 
As shown in FIG. 1, the UV lamp shown at 5 is positioned at one focal point 
of the elliptical reflector system shown at 3. A clear center tube shown 
at 7 is positioned around the other focal point of the reflector system 
shown at 3. The optical glass fiber or ribbon shown at 9, having a liquid 
radiation-curable composition thereon, passes through the center tube 7. 
The clear center tube 7 is also flushed with an inert atmosphere such as 
nitrogen or argon gas to reduce the oxygen inhibition of polymerization. 
The clear center tube 7 also provides protection of the elliptical 
reflector system from contamination by the liquid coating as it is applied 
to the ribbon of optical fibers, e.g. by splattering. 
During the radiation curing production process, the inner surface of the 
clear center tube 7 may, over time, become contaminated with some of 
ribbon matrix material or its components. This contamination has the 
effect of thereby decreasing the amount of radiation which reaches the 
uncured coating on the ribbon array of optical glass fibers 9 after 
passage through the center tube 7. 
Thus, there is a need for some means to monitor and determine the level of 
cure of the ribbon matrix material during the prolonged operation of the 
coating line. Since, once installed, the line apparatus and its radiation 
source are not readily changed except by expensive shut-down of the 
(generally continuously operating) line itself, the amount of radiation 
actually striking the radiation-curable ribbon matrix material present on 
the array of optical glass fibers will necessarily vary, depending on the 
condition at any given point in time as a result of the above-described 
problems presented by the reflector system, lamp output, contaminated 
center tubes. 
It is accordingly difficult to confidently meet the demand for increased 
production line speeds while maintaining conditions which will assuredly 
provide optimum complete cure of the coating. At the present time, testing 
of the completeness of the ribbon matrix material cure is commonly done by 
off-line physical tests on specimens of the ribbon after it has been 
produced. 
What would be desirable is a system which would permit real time 
determination of the ribbon matrix cure level by indicator means. Knowing 
whether or not the required complete cure is achieved under the operating 
conditions will then inform the line operator of the need to make 
adjustments to line speed, lamp intensity (if possible) or replacement, or 
equipment cleaning, while not jeopardizing wasted production due to an 
inadequate coating cure. 
There has been no effective solution to the above described problems for 
the glass fiber ribbon technology, until the present invention. 
U.S. Pat. No. 5,302,627 is directed to the fabrication of printed circuit 
boards and similar electrical or electronic devices. This patent discloses 
a method for indicating a cure point of an ultraviolet radiation curable 
composition used with such devices. It does not disclose any use of the 
compositions as coatings for or ribbons for an array of optical glass 
fibers. Nor does it address the special problems of high speed 
continuously-operated glass fiber ribbon forming lines and the very 
critical requirements thereof. However, no definition of the cure point is 
provided. Furthermore, while this patent discloses that a dye can be used 
which becomes colorless upon exposure to ultraviolet radiation, no 
examples of such dyes are provided. All of the examples merely changed 
color upon exposure to ultraviolet radiation. This patent only teaches 
that the amount of dye used should be such that it does not inhibit the 
curing of the composition. One skilled in the art reading and 
comprehending this patent would not know how to prepare a 
radiation-curable composition which will provide instant real time visible 
feedback that the amount of radiation exposed to the radiation-curable 
composition is or is not sufficient to cure the radiation-curable 
composition to the desired level. 
Published Japanese Patent Application No. 1-204902 is directed to molding 
materials, paints and adhesives. This patent discloses a photosetting 
resin composition containing a photo-coloring compound which changes color 
upon exposure to light for finding the state of curing of the composition. 
It does not disclose any use of the compositions as coatings for optical 
glass fibers or as ribbon matrix material for arrays of fibers. Nor does 
it address the special problems of high speed continuously-operated glass 
fiber ribbon matrix forming lines and the very critical requirements for 
such production lines. While this patent discloses that a dye can be used 
which becomes colorless upon exposure to ultraviolet radiation, no 
examples of such dyes are provided. All of the examples merely changed 
color upon exposure to ultraviolet radiation. This patent only teaches 
that the amount of dye used should be 0.5 to 10 parts by weight. One 
skilled in the art reading and comprehending this patent would not know 
how to prepare a radiation-curable composition which will provide instant 
real time visible feedback that the amount of radiation exposed to the 
radiation-curable composition is or is not sufficient to cure the 
radiation-curable composition to the desired level. 
A process and apparatus for producing a bonded ribbon of coated fibers is 
described in U.S. Pat. Nos. 5,037,763 and 4,900,126, the entire 
disclosures of which patents are incorporated herein by reference. 
SUMMARY OF THE INVENTION 
This application is a continuation-in-part of Ser. No. 08/685,033, filed 
Jul. 22, 1996, the entire disclosure thereof being incorporated herein by 
reference. 
In view of the above described problems, an objective of the present 
invention is to provide a simple and effective real-time means to 
determine whether a radiation-curable ribbon matrix material applied to an 
array of optical glass fibers has been exposed to the required amount of 
radiation sufficient to reach the necessary level of cure. 
The array may be a ribbon or a bundle of coated optical fibers. A typical 
ribbon may be formed from a row of 12 or 16 fibers. A typical bundle may 
be a substantially circular array having a central fiber surrounded by a 
plurality of further fibers. Alternatively, the bundle may have other 
appropriate cross-sectional shapes such as square, trapezoid, etc. The 
terms "ribbon" and "bundle" as used herein are interchangeable and 
non-limiting. 
More particularly, this invention provides a technique whereby the optical 
glass fiber ribbon matrix material is provided with a chromophoric 
component which has the property of losing its visible light chromophoric 
functionality upon exposure to UV actinic radiation and does so at a 
minimal concentration level such as to coincide with the level of 
radiation exposure which is required to achieve cure of the ribbon matrix 
material itself during the operation of the production line. This 
invention thus requires two balanced selection steps: first, the selection 
of the suitable chromophoric component, and secondly the selection of the 
concentration of that component in the ribbon matrix material. At the same 
time, the desired protective characteristics of the ribbon matrix material 
itself must not be degraded by addition of the chromophoric entity. 
Surprisingly, this objective, and other objectives, are achieved by the 
following. 
The invention provides a radiation-curable, cross-linkable optical glass 
fiber ribbon matrix material including at least one radiation-curable 
oligomer or monomer; and 
at least one chromophoric indicator selected so as to be susceptible to 
destruction of its chromophoric characteristic upon exposure to actinic 
radiation and present in an amount which becomes substantially colorless 
when exposed to a level of radiation sufficient to cure said 
radiation-curable, optical glass fiber ribbon matrix material wherein said 
at least one chromophoric indicator has a color which is distinguishable 
from a base color of said radiation-curable, optical glass fiber ribbon 
matrix material in cured form. 
The invention also provides a method of formulating a radiation-curable 
ribbon matrix material adapted for use on already coated optical glass 
fibers so as to provide a visual indication of a desired cure, said method 
comprising the steps of: 
providing a radiation-curable, optical glass fiber ribbon matrix material; 
measuring and determining a critical radiation dose level for said 
radiation-curable, optical glass fiber ribbon matrix material which is the 
minimum level of radiation sufficient to achieve a desired cure of said 
radiation-curable, optical glass fiber ribbon matrix material; 
selecting a chromophoric indicator having the characteristics of exhibiting 
a visible color while also having its chromophoric characteristics 
substantially destroyed upon exposure to actinic radiation; 
determining a concentration of a chromophoric indicator that exhibits a 
substantially colorless characteristic at said critical radiation dose 
level for curing of said ribbon matrix material; and 
incorporating at least said concentration of said chromophoric indicator 
into said uncured radiation-curable, optical glass fiber ribbon matrix 
material prior to application to a coated optical glass fiber. 
The invention further provides a ribbon matrix for coated optical glass 
fibers comprising: 
a plurality of coated optical glass fibers; and 
at least one radiation-cured ribbon matrix material containing a bleached 
chromophoric indicator, formulated from a radiation-curable ribbon matrix 
material having as essential elements: 
at least one radiation-curable oligomer or monomer; and 
at least one chromophoric indicator in an amount which becomes 
substantially colorless when exposed to an amount of radiation suitable 
for curing said radiation-curable, ribbon matrix material, wherein said at 
least one chromophoric indicator has a color which is distinguishable from 
a base color of said radiation-cured ribbon matrix material. 
The invention further provides an optical glass fiber cable structure 
including: 
(1) at least one coated optical glass fiber; and 
(2) a ribbon matrix material covering the at least one coated optical glass 
fiber, wherein 
the ribbon matrix material includes at least one radiation-cured material 
containing a bleached chromophoric indicator, the at least one 
radiation-cured matrix material being formulated from a radiation-curable 
cross-linkable matrix material having as essential elements: 
(i) at least one radiation-curable oligomer or monomer; and 
(ii) at least one chromophoric indicator in an amount which becomes 
substantially colorless when exposed to an amount of radiation suitable 
for curing said radiation-curable matrix material, wherein the at least 
one chromophoric indicator has a color which is distinguishable from a 
base color of said radiation-cured matrix material. 
Also provided is a telecommunications system including: an array of optical 
glass fibers coated with at least one radiation-cured ribbon matrix 
material containing a bleached chromophoric indicator, the at least one 
radiation-cured ribbon matrix material being formulated from a 
radiation-curable ribbon matrix material having as essential elements: 
at least one radiation-curable oligomer or monomer; and 
at least one chromophoric indicator in an amount which becomes 
substantially colorless when exposed to an amount of radiation suitable 
for curing said radiation-curable ribbon matrix material, wherein the at 
least one chromophoric indicator has a color which is distinguishable from 
a base color of the radiation-cured ribbon matrix material. 
The completeness of the cure of the matrix material can be determined by 
using an in-line calorimetric method to measure the chromophoric indicator 
.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Radiation-curable compositions usually exhibit the behavior shown in FIG. 
2. As shown in FIG. 2, as the amount of radiation to which a 
radiation-curable composition is exposed is increased, the amount of a 
specific physical or performance property of the cured material (measured 
as a percentage of the fully attainable value for the specific 
composition) correspondingly increases. This increase continues until the 
ultimate value of the measured physical or performance property is 
achieved. The ultimate value is defined as the maximum value of a physical 
or performance property, which cannot be exceeded by further exposure to 
radiation. Examples of measured physical or performance properties are 
modulus, glass transition temperature, hardness, surface adhesion, and 
remaining extractables. 
As shown in FIG. 2, once the measured physical property or performance 
property reaches the ultimate value, further exposure to radiation does 
not result in an increase in the measured property or performance. The 
lowest radiation dose which achieves the level of curing sufficient to 
provide the ultimate value is hereinafter referred to as the critical 
radiation dose "D.sub.c ", and can be easily obtained from the graph in 
FIG. 2. D.sub.c is used herein to represent minimum level of radiation 
exposure to fully cure the radiation-curable composition. By adjusting the 
radiation exposure in the fiber ribbon production line closely to the 
D.sub.c, and being able to determine in real time that the Dc is just 
being maintained to effect the desired full cure, the linear line speed 
can be maximized without jeopardizing the product quality. 
The following example demonstrates a simple way to determine the D.sub.c 
required to achieve the ultimate value for the property of equilibrium 
modulus, according to this invention. FIG. 3 shows the graph of 
equilibrium modulus (MPas), (megapascals), versus the radiation dose 
(Joules/cm.sup.2). 
The ultimate value for the equilibrium modulus of this example material is 
0.6 MPas, at a critical radiation dose, D.sub.c, of 0.75 Joules/cm.sup.2. 
The D.sub.c can be easily read from the graph in FIG. 3, as shown at 1. 
The requirement for a production engineer is to produce a fully cured 
ribbon of an array of optical glass fibers and hence to ensure that the 
radiation-curable ribbon matrix material is always exposed to a radiation 
dosage of at least the D.sub.c, which here is 0.75 Joules/cm.sup.2. 
According to this invention, for determination of the level of adequate 
radiation cure of the radiation-curable ribbon matrix composition, i.e. 
that it has been exposed to at least the D.sub.c level of radiation, a 
chromophoric indicator is incorporated into that composition, the 
indicator having been selected so as to have the characteristic of 
substantially, and permanently, losing its chromophoric characteristic (at 
the concentration employed) upon exposure to that D.sub.c radiation level, 
so as to become essentially colorless in visible light. 
The use of such a chromophoric indicator according to the present invention 
is applicable to all radiation-curable, ribbon matrix material 
compositions. 
Examples of suitable radiation-curable compositions which may be used 
variously include those which are 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. 
Such radiation-curable compositions contain one or more radiation-curable 
oligomers or monomers having at least one functional group capable of 
polymerization when exposed to actinic radiation. Suitable 
radiation-curable oligomers or monomers are now well known and within the 
skill of the art. 
Commonly, the radiation-curable functionality used is ethylenic 
unsaturation, which can be polymerized through radical polymerization or 
cationic polymerization. Specific examples of suitable ethylenic 
unsaturation are groups containing acrylate, methacrylate, styrene, 
vinylether, vinyl ester, N-substituted acrylamide, N-vinyl amide, maleate 
esters, and fumarate esters. Preferably, the ethylenic unsaturation is 
provided by a group containing acrylate, methacrylate, or styrene 
functionality. 
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. 
The radiation-curable compositions may also contain a reactive diluent 
which is used to adjust the viscosity. The reactive diluent can be a low 
viscosity monomer containing having at least one functional group capable 
of polymerization when exposed to actinic radiation. This functional group 
may be of the same nature 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. 
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 such reactive diluents 
include: 
hexylacrylate, 
2-ethylhexylacrylate, 
isobornylacrylate, 
decyl-acrylate, 
laurylacrylate, 
stearylacrylate, 
2-ethoxyethoxy-ethylacrylate, 
laurylvinylether, 
2-ethylhexylvinyl ether, 
N-vinyl formamide, 
isodecyl acrylate, 
isooctyl acrylate, 
vinyl-caprolactam, 
N-vinylpyrrolidone, and the like. 
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: ethyleneglycolphenylether-acrylate, 
polyethyleneglycolphenyletheracrylate, 
polypropyleneglycolphenylether-acrylate, and alkyl-substituted phenyl 
derivatives of the above monomers, such as 
polyethyleneglycolnonylphenyl-etheracrylate. 
The reactive diluent can also comprise a diluent having two or more 
functional groups capable of polymerization. Particular examples of such 
monomers include: 
C.sub.2 -C.sub.18 hydrocarbon-dioldiacrylates, 
C.sub.4 -C.sub.18 hydrocarbondivinylethers, 
C.sub.3 -C.sub.18 hydrocarbon triacrylates, and the polyether analogues 
thereof, and the like, such as 
1,6-hexanedioldiacrylate, 
trimethylolpropanetri-acrylate, 
hexanedioldivinylether, 
triethylene-glycoldiacrylate, 
pentaerythritol-triacrylate, 
ethoxylated bisphenol-A diacrylate, and 
tripropyleneglycol diacrylate. 
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: 
epoxy-cyclohexane, 
phenylepoxyethane, 
1,2-epoxy-4-vinylcyclohexane, 
glycidylacrylate, 
1,2-epoxy-4-epoxyethyl-cyclohexane, 
diglycidylether of polyethylene-glycol, 
diglycidylether of bisphenol-A, and the like. 
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: 
diallylphthalate, 
triallyltri-mellitate, 
triallylcyanurate, 
triallylisocyanurate, and 
diallylisophthalate. 
For amine-ene systems, amine functional diluents that can be used include, 
for example: 
the adduct of trimethylolpropane, isophorondiisocyanate and 
di(m)ethylethanolamine, 
the adduct of hexanediol, isophoron-diisocyanate and dipropylethanolamine, 
and 
the adduct of trimethylol propane, tri-methylhexamethylenediisocyanate and 
di(m)ethylethanolamine. 
Other additives which can be used in the ribbon matrix composition include, 
but are not limited to, photoinitiators, catalysts, lubricants, wetting 
agents, release agents, antioxidants and stabilizers. The selection and 
use of such additives is within the skill of the art. 
Generally, according to the present invention, a specific concentration of 
the chromophoric indicator is incorporated within the desired 
radiation-curable ribbon matrix material composition. The chromophoric 
indicator is selected so as to display a color to the human eye prior to 
exposure to the radiation cure, e.g. a color having a wavelength in the 
range of about 400 to about 700 nm. During exposure to radiation, the 
chromophoric indicator changes from colored to substantially colorless, 
hereinafter referred to as bleaching. The color of the chromophoric 
indicator must be distinguishable from any desired base color of the cured 
ribbon matrix material so that a distinct color change can easily be seen 
prior to exposure of the radiation-curable ribbon matrix composition to 
the D.sub.c level of radiation. 
The concentration of the chromophoric indicator present within the 
radiation-curable composition can be adjusted so that the bleaching of the 
chromophoric indicator occurs at a radiation level which is substantially 
equal to or greater than the critical radiation dose D.sub.c for the 
radiation-curable composition. Thereby, the disappearance of the visible 
color serves as an indicator or a complete cure of the radiation-curable 
composition. Preferably, the concentration of the chromophoric indicator 
present in the radiation-curable composition is adjusted so that the 
bleaching of the chromophoric indicator occurs at a radiation level which 
is substantially equal to the critical radiation dose D.sub.c for the 
radiation-curable composition. 
Based on the disclosure herein, one skilled in the art will easily be able 
to select and to determine the concentration of chromophoric indicator 
which becomes substantially colorless at the radiation level "D.sub.c " 
required to fully cure the selected radiation-curable ribbon matrix 
composition. 
For a specific chromophoric indicator at a specific concentration, the 
amount of bleaching of the chromophoric indicator can be represented by 
the response curve shown in FIG. 4. This response curve can be easily 
determined and measured by one skilled in the art by exposing a specific 
concentration of the chromophoric indicator to varying levels of 
radiation, measuring the amount of bleaching that has occurred, and then 
plotting the results. The amount of radiation required to completely 
bleach the specific concentration of chromophoric indicator can be easily 
read from the graph, as shown at 10. 
Generally, an increase in the concentration of the chromophoric indicator 
will result in an increase in the amount of radiation required to bleach 
the chromophoric indicator. Different concentrations of the chromophoric 
indicator can then be tested in the same manner as above to determine the 
amounts of radiation required to completely bleach the different 
concentrations. The results can be plotted, as shown in FIG. 5 at number 
12, to make a concentration/radiation dose curve. This 
concentration/radiation dose curve can be used to easily determine the 
approximate concentration of the chromophoric indicator that will become 
colorless at the selected radiation dose level. For example, if the 
critical radiation dose D.sub.c of the radiation curable composition is 
0.75 Joules/cm.sup.2, the dose response curve can be used as shown by the 
dotted line to determine the concentration of chromophoric indicator that 
will be come colorless at this radiation dose level, shown at 14 in FIG. 
5. For this specific example, that concentration of the chromophoric 
indicator is about 1.25% by weight. The same type of radiation that will 
be used to cure the radiation-curable ribbon matrix material should be 
used to determine the concentration/radiation dose curve. 
The required amount of radiation to bleach the specific concentration of 
the chromophoric indicator in the radiation-curable composition may vary 
from the estimate provided by the concentration/radiation dose curve due 
to effects from the components in the radiation-curable composition. 
Therefore, the final concentration of the chromophoric indicator should be 
experimentally fine-tuned by measuring the amount of radiation required to 
bleach the chromophoric indicator in the desired radiation-curable 
composition and then increasing the concentration of the chromophoric 
indicator if the bleaching occurs at too low of a radiation dose or 
decreasing the concentration of the chromophoric indicator if the 
bleaching occurs at too high of a radiation dose. 
Suitable amounts of the chromophoric indicator have been found to be 
between about 0.05 and about 5% by weight of the total radiation-curable 
ribbon material composition. Preferably, the amount of chromophoric 
indicator is between about 0.1 and about 2% by weight. 
The chromophoric indicator can be any dye or pigment which bleaches or 
becomes colorless when exposed to radiation, in particular the type of 
radiation used to cure the radiation-curable ribbon matrix composition. 
For example, the chromophoric indicator can be an organic dye which 
becomes colorless upon exposure to UV radiation. 
Preferably, the chromophoric indicator is a polymeric dye. The term 
polymeric dye is used herein to represent those dyes having a polymeric 
(polyol) backbone into which at least one chromophoric molecular entity 
has been chemically incorporated. The polymeric dye preferably has 
molecular weight between about 1000 to about 2500, and more preferably 
about 1200 to about 2200. 
Examples of suitable polymeric dyes are disclosed in U.S. Pat. No. 
4,507,407, the complete disclosure of which is incorporated herein by 
reference. 
Commercial examples of suitable polymeric dyes presently include: 
Reactint Blue X3LV; 
Reactint Blue X17AB; 
Reactint Orange X38; 
Reactint Red X64; 
Reactint Violet X80LT; and 
Reactint Yellow X15, available from Milliken Chemicals. 
An advantage of using a polymeric dye is that the backbone can either 
become entangled within, or reacted with, the cross-linked ribbon matrix 
material composition. This significantly reduces or eliminates the 
possibility that the chromophoric indicator would contribute to cured 
material volatiles. 
The polymeric dye can be easily modified by incorporating into the 
polymeric backbone at least one functional group capable of polymerization 
exposed to radiation. The radiation-curable functional group can be any 
one of those described herein above. In this manner, the polymeric dye can 
be cross-linked with the radiation-curable oligomers and monomers present 
in the coating composition upon exposure to radiation. 
FIG. 6 shows schematically, the production of a ribbon assembly 42 of an 
array of coated optical fibers 40. Bonded ribbon 42 includes a plurality 
of coated optical fibers 36 each having a core, a cladding, and one or 
more layers fed from fiber suppliers 46. A planar array of optical fibers 
36 is embedded in radiation-curable matrix material by application of the 
matrix material in liquid form using applicator 52, for example, a coating 
die. The material is then directed past radiation curing apparatus 54, 
such as the apparatus shown in FIG. 1 herein, for curing the matrix 
material. The cured, bonded ribbon 42 then passes an in-line cure 
detection system 59 before being taken up on winding spool 56. In-line 
detection system 59 includes a color detection system for determining 
whether sufficient color shift of the chromophoric indicator has taken 
place, i.e., for determining calorimetrically whether cure of the matrix 
material is complete. This determination and corresponding in-line ability 
to monitor that cure is complete greatly reduces wastage of ribbon 
assemblies that include coated optical fibers. Details of methods for 
bonding optical fibers into a ribbon or other assembly are found in U.S. 
Pat. Nos. 5,037,763 and 4,900,126, the disclosures of which are 
incorporated herein by reference. 
The optical fiber ribbon may be visually inspected in-line at location 59, 
shown in FIG. 6, to determine whether the ribbon matrix material has been 
completely cured. A suitable wave-length sensitive calorimetric device may 
be used at this point. If the color of the cured ribbon matrix material 
containing the chromophoric indicator is the same as the base color 
(without chromophoric indicator) of a fully cured ribbon matrix material, 
then the ribbon matrix material has been exposed to sufficient actinic 
radiation to provide a complete cure. 
Alternatively, the optical fiber ribbon may be visually inspected at 
winding spool 56, shown in FIG. 6, to determine whether the ribbon matrix 
material has been completely cured. If the color of the cured ribbon 
matrix material containing a chromophoric indicator is the same as the 
base color (without chromophoric indicator) of a fully cured ribbon matrix 
material, then the ribbon matrix material has been exposed to sufficient 
actinic radiation to provide a complete cure. 
FIGS. 7-11, in which like numerals represent like parts, illustrate various 
ribbon assemblies that can be formed using ribbon matrix material 
according to the invention. Ribbon assembly 42 shown in each of FIGS. 7-11 
is formed of an array of individual optical fibers 21 each surrounded by 
at least one coating 36, the array of optical fibers being joined together 
into a ribbon by ribbon matrix material 45. FIG. 7 shows a ribbon 
assembly. FIG. 8 shows edge bonding of the coated fibers forming the 
ribbon assembly. FIGS. 9-11 show arrays of optical fibers respectively 
having substantially rectilinear, trapezoid and circular cross-sectional 
shapes. 
The figures illustrate non-limiting examples of assemblies of bonded 
fibers. The ribbon matrix material may be of lesser thickness than the 
outer diameter of the coated glass fiber (FIG. 8), of substantially the 
same thickness, or of greater thickness than the outer diameter of the 
coated glass fiber (FIG. 7). Any of these configurations of the ribbon 
matrix material with respect to the coated optical glass fibers may be 
used with other arrays of fibers, such as those shown in FIGS. 9-11. 
The invention is not limited to the ribbon matrix material having a 
chromophoric indicator as already discussed. In the event it is desired to 
produce a color-coated ribbon matrix for the optical glass fibers, it will 
then be appropriate to employ a chromophoric indicator having the 
characteristic of exhibiting a color which will sufficiently modify the 
desired ribbon color so as to be readily detected by a shift in the tint 
or hue of the resulting combination of chromophores under the condition 
that the chromophoric indicator has received insufficient radiation to 
induce sufficient shift in the tint or hue thereof. 
If a wave-length sensitive device is used to determine whether the color 
indicator has been bleached (i.e., whether the ribbon matrix material has 
been completely cured), the device can be used to send a signal to the 
operator (manual or automated) of the ribbon matrix production line. For 
example, the wave-length sensitive device can be connected to a controller 
for the radiation intensity such that when the color indicator is 
insufficiently bleached, the radiation intensity can be adjusted by the 
wave-length sensitive device to provide the level of bleaching desired. 
Alternatively, by connecting the wave-length sensitive device to a 
controller for the line speed of the ribbon matrix production line, the 
wave-length sensitive device can signal an adjustment of the line speed to 
the maximum speed which will still achieve a complete cure. 
The coated optical glass fibers made according to this invention can be 
used to make cable structures and for telecommunication systems. Such 
telecommunication systems typically include cables containing optical 
glass fibers, transmitters, receivers, and switches. The cables containing 
ribbons or bundles of optical glass fibers are the fundamental connecting 
units of telecommunication systems. 
The ribbons or bundles of coated optical glass fibers made according to 
this invention can be adapted for enclosure within a cable structure. The 
cable structure can be buried under ground or water for long distance 
connections, such as between cities. Alternatively, the ribbons or bundles 
of coated optical glass fibers can be adapted for use in local area 
networks, such as for connecting offices in high rise buildings, 
residential subdivisions, and the like. 
The present invention will be further described by the following 
non-limiting example. 
EXAMPLE 
1 wt % of Reactint X38 Orange (Milliken Chemicals) was added to the 
following composition: 
40-60 wt % urethane acrylate oligomer; 
35-55 wt % mono functional acrylate; 
2-4 wt % photoinitiator; and 
0.75-1.5 wt % additive. 
The critical dose of radiation D.sub.c for the composition is 1.0 
Joule/cm.sup.2. 
The mixture was exposed to 1.0 Joule/cm.sup.2 of UV radiation. The orange 
color was not completely bleached at this radiation level. Therefore, the 
composition was then exposed to another 1.0 Joule/cm.sup.2, which 
completely bleached the orange dye. 
While the invention has been described in detail with respect to certain 
embodiments thereof, variations and modifications may be made without 
departing from the spirit and scope of the invention.