Optical waveguides – Optical transmission cable – Ribbon cable
Reexamination Certificate
2002-04-04
2002-12-24
Berman, Susan (Department: 1711)
Optical waveguides
Optical transmission cable
Ribbon cable
Reexamination Certificate
active
06498883
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to optical fibers embedded in ribbon matrix materials; to optical fiber ribbon arrays containing such matrix materials; and to processes for preparing same.
II. Description of the Prior Art
In certain applications, such as in short haul fiber-to-the-home uses, a single coated optical fiber may adequately transmit a signal from one point to the next. In most embodiments, however, a relatively large number of fibers are necessary to transmit a large volume of signals. For example, the telecommunications industry often requires aggregates of fibers spanning oceans or continents and containing dozens of individual fibers. Fibers are conveniently aggregated into cables, wherein large numbers of coated optical fibers are laid in parallel and are protected by a common sheathing material which may include fiberglass, steel tape and reinforced rubber cabling material.
When numerous individual coated optical fibers are aggregated into a cable, it is necessary to be able to identify each of the individual fibers. For example, when two cable segments are to be spliced together, it is necessary to splice together ends of each like optical fiber in order for a signal to convey properly. When only a few fibers are contained in a cable, identification is facilitated by coating each individual fiber with a characteristic color. Thereby, the splicer may simply match up green fiber to green fiber, red to red, and so forth.
When the cable contains one hundred or more fibers, however, it becomes difficult to impart a sufficient number of distinctive inks to color each fiber distinguishably. Thus, a geometric means of distinguishing the fibers is also used. For example, it is known to arrange the fibers in a number of layers or two-dimensional fiber arrays with each layer or array containing perhaps twelve ink-coated fibers of different colors. These. layers or arrays are stacked one atop the other to form three-dimensional structures known in the art as ribbons. The ribbons greatly facilitate matching up fibers when splicing.
The matrix material of the ribbons should, inter alia, have suitable glass transition temperature; cure rapidly; be non-yellowing; and have high thermal, oxidative and hydrolytic (moisture) stability. Further, the matrix material must possess solvent resistance, inasmuch as splicers typically remove residual matrix and coating material from stripped fibers using a solvent such as trichloroethane or ethanol or isopropanol or other commercially available solvent. Additionally, the matrix material must adhere sufficiently to the coated, colored optical fibers to prevent separation of the fibers during processing into cables, but not adhere so much as to remove the ink or other coloration from the individual fibers when the matrix material is stripped from the fibers to permit splicing. Removal of an ink layer from a fiber is referred to in the industry as “breakout failure.” It makes identification of the individual fibers nearly impossible. Also, the matrix material should be removable via thermal stripping at commonly-used stripping temperatures. Finally, the matrix and all underlying coatings contained within the ribbon should be removable in an intact tube, leaving a minimal amount of residue on the fibers.
Like individual fibers, individual ribbons are color-coded with inks, pigments or dyes. (Pigments are used in suspension; dyes are used in solution.) The prior art, however, offers ribbons that contain lower levels of pigment and are therefore too transparent, making color identification and differentiation difficult. Further, the pigments, dyes or inks in the color-coded optical fibers inside the ribbons tend to bleed, and prior art ribbons cannot adequately hide the bleed-through because they are insufficiently opaque.
The colors and opacity of the ribbons have been limited by the fact that pigments (or other colored materials) interfere with curing of the matrix material. Matrix material is typically cured when UV light is absorbed by photoinitiators in the matrix material. Pigments reduce the light that can be absorbed by the photoinitiator.
Incomplete cure causes many problems, including poor thermal strippability, reduced toughness, tackiness, odor and residual extractable material after curing. These problems have been addressed in the past by adding high levels of short-wavelength—absorbing photoinitiators, but this approach cannot be used in thicker films because high levels of these photoinitiators also reduce light penetration. Specifically, light absorption by photoinitiator in the upper layer of the film decreases the light reaching the bottom of the film, and inadequate cure at the bottom layer of the matrix profoundly affects ribbon performance. Of course, it helps to increase the curing time, but this slows production significantly.
Accordingly, there is a need in the art for matrix material that contains pigment, dyes, inks or other colored substances suitable to impart a variety of colors of sufficient opacity without thereby hampering cure, especially deep within the matrix film.
SUMMARY OF THE INVENTION
The invention provides: (1) a radiation-curable matrix material for affixing coated and colored optical fibers in a ribbon configuration containing at least two optical fibers, the matrix material exhibiting particular characteristics as defined below; (2) an optical fiber ribbon employing such matrix material and comprising a plurality of optical fibers in a fixed arrangement, preferably parallel to one another, within the cured matrix material; (3) a process for preparing an optical fiber ribbon using the aforesaid matrix material; and (4) a radiation-curable matrix composition including the same ingredients as the aforesaid matrix material and exhibiting similar characteristics.
Generally, the matrix material imparts sufficient opacity without causing problems with cure, strippability, adhesion to colored fibers, tackiness, odor, extractables and other requisite properties of matrix material. More specifically, after curing, the matrix material produces the following inside degrees of cure, hue angle ranges, minimum contrast ratios, lightness ranges and chroma values, measured as described below.
A 100 micron thick by 80 mm wide by 120 mm long sample of the matrix material exhibits an inside degree of cure of more than about 70 percent when cured with a radiation dose of about 0.2 J/cm
2
, preferably more than about 80 percent, most preferably more than about 85 percent. The values for degree of cure were determined by measuring, in samples of the matrix material as cured on glass plates about 6 mm thick, the percent reacted acrylate unsaturation (%RAU) via FTIR—ATR using a diamond crystal ATR attachment. By an inside degree of cure it is meant the degree of cure of a bottom surface of the sample after curing. The cured samples were 100 microns thick, 80 mm wide and 120 mm long. The acrylate analytical peak was 1410 cm
−1
and the reference peak was 1520 cm
−1
. For non-acrylated materials (i.e., vinyl or other functional groups capable of reacting with a free radical), an alternative method may be used, but more than about 70 percent of the total reactive groups should still undergo reaction at this cure dose.
A 25 micron thick by 75 mm wide by 180 mm long sample film of the cured matrix material exhibits a hue angle range which, when determined by means for spectrophotometrically analyzing, has the following values for each respectively colored matrix material: blue is about 230 to about 270; orange is about 55 to about 80; green is about 120 to about 185; brown is about 35 to about 80; slate is about 0 to about 360; white is about 0 to about 360; red is about 325 to about 50; black is about 0 to about 360; yellow is about 80 to about 120; violet is about 270 to about 325; rose is about 0 to about 22; and aqua is about 184 to about 230. Preferably, however, the 25 micron sample exhibits a hue angle range having the following values for each respectively
Berman Susan
Borden Chemical, Inc.
Stevens Davis Miller & Mosher LLP
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