The present invention relates to radiation-curable compositions useful when cured as matrix material for optical fiber ribbons; to optical fiber ribbons containing such matrix material; and to processes for preparing such matrix containing ribbons.
Optical glass fibers have revolutionized the telecommunications industry. The result has been a tremendous growth in demand for optical fibers which are free of many of the inherent defects of glass fibers.
Immediately after drawing, glass fibers are exceptionally strong and have very few intrinsic defects. However, such pristine fibers are very easily flawed by exposure to environmental conditions including dust and moisture. Therefore, there have been developed in the prior art numerous coatings which are minimally capable of protecting the underlying glass fiber from external harmful forces and which optimally possess proper-ties rendering them capable of obviating one or more of the various potential problems which may deleteriously effect optical fiber performance. Such properties include, inter alia, a glass transition temperature rendering the fiber useful over a large potential temperature use range; a higher refractive index than that of the fiber to refract any errant light signals away from the fiber; rapid cure, e.g., under ultraviolet irradiation; and high impermeability to moisture which may damage the coating or the fiber itself and may cause delamination of the two.
Additionally, the adhesion level between the fiber and the coating must be optimized so that the coating will remain adhered to the fiber during use but be easily stripped therefrom, with minimal damage to the integrity of the fiber and the coating, so that the fibers may be easily spliced in the field. Above all, the fiber coatings should display good thermal, oxidative and hydrolytic stability, to protect the underlying fiber over the long term, i.e., over twenty-five years"" time.
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. However, in most embodiments, a relatively large number of fibers are necessary to transmit a large volume of signals. For example, in the telecommunications industry, aggregates of fibers spanning oceans or continents and containing dozens of individual fibers may be required. 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 such as a layered arrangement 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 may be adequately made by having the coating of each individual fiber be a characteristic color; thus, the splicer may simply match up green fiber to green fiber, red to red, and so forth.
However, when the cable contains one hundred or more fibers, it may become impracticable to use a sufficient number of distinctive inks as to color each fiber distinguishably. Thus, a geometric means of distinguishing each fiber is used. For example, arranging the fibers in a number of layers, each layer containing perhaps twelve ink-coated fibers of different respective colors, will greatly facilitate the task of matching up fibers when splicing.
One practical way by which such spatial ordering of numerous fibers may be accomplished is to create two dimensional fiber arrays, wherein fibers are situated in a generally planar arrangement, within a given array, with the fibers in the array disposed in parallelism with each other. These arrays are stacked one atop another in a three dimensional structure.
Such arrays are known in the art as ribbons. For example, it is known to prepare a two-dimensional ribbon by forming a xe2x80x9csandwichxe2x80x9d of parallel coated optical fibers between two sheets of adhesive-coated Mylar tape, thus affixing the fibers in that configuration. This xe2x80x9csandwichxe2x80x9d provides structural integrity and a tack free exterior surface.
However, this arrangement is less than optimal because the tape occupies a substantial proportion of the total volume of the sandwich, so that when several xe2x80x9csandwichesxe2x80x9d are stacked to form a cable, an undesirably high proportion of the total cable volume is taken up by tape (rather than by optical fiber).
Thus it has been envisioned to prepare an optical fiber ribbon having a matrix material in which the optical fibers are embedded in the desired generally planar, parallel arrangement. This matrix material should, inter alias have suitable glass transition temperature; cure rapidly, be non-yellowing; and have high thermal, oxidative and hydrolytic (moisture) stability.
Additionally, the matrix material must be adherent enough to the coated, colored optical fibers to prevent separation of the fibers during processing into cables, but not so adherent as to remove the ink coloration from the individual ink-colored fibers when the matrix material is stripped from the fibers to permit splicing. Removal of the ink from a coated, colored optical fiber is referred to in the industry as xe2x80x9cbreakout failurexe2x80x9d; it makes identification of the individual fibers impossible.
Furthermore, the matrix material must possess solvent resistance, inasmuch as, in the field, splicers typically remove residual matrix and coating material from stripped fibers using a solvent such as trichloroethane or ethanol. Matrix material on an unstrapped fiber should not absorb solvent and swell and thus compromise the integrity of ribbon.
It is an objective of the invention to provide an optical fiber ribbon having a plurality of distinguishably colored, optical fibers oriented in a generally planar, parallel arrangement and bonded in position by a matrix wherein the matrix has sufficient adhesion to the colored optical fibers so as to prevent separation during cabling but is not so adherent as to remove the color coating from the fibers when the matrix is stripped for splicing.
It is also an objective of the invention to provide a method by which the adhesion level of the cured matrix to the color distinguishing layer can be adjusted for more or less adhesion in the formulation of then matrix composition.
It is another objective of the invention to provide an optical fiber ribbon in which the matrix has an adhesion level within the range of about 0.02 to about 0.2 pounds per linear inch as measured by a T-peel test at specified conditions.
It is a further object of the invention to provide an optical fiber ribbon of color distinguished fibers in which the fibers are colored with an ink-containing vinylic coating and disposed within a matrix that can be stripped without removing the vinylic coating from the optical fibers.
A further objective of the invention is to provide a matrix composition that, when cured, has adequate cross-link density to resist swelling from solvent absorption.
Accordingly, the invention provides, in one embodiment, a radiation-curable matrix composition for affixing coated and ink-colored optical fibers in a ribbon configuration. The matrix composition generally comprises:
(a) from about 35 percent to about 98 percent by weight of an aliphatic polyester-based urethane acrylate;
(b) from about 0.5 percent to about 35 percent by weight of a monomer having a plurality of acrylate or methacrylate moieties per monomer molecule;
(c) from about 0.5 percent to about 20 percent by weight of an acrylate or methacrylate monomer having an alkyl moiety comprising from 7 to 18 carbon atoms; and (d) from about 0 percent to about 10 percent by weight of a photo initiator, all of the percentages by weight being based on the total weight of (a), (b), (c) and (d).
In preferred embodiments, the polyester-based urethane acrylate is silicone modified; and the matrix material additionally comprises a stabilizer, is ultraviolet curable and comprises at least about 1 percent by weight of the photo initiator.
In an alternate embodiment, the material includes from about 1 percent to about 30 percent of an adhesion increasing compound such as a polyester-based aliphatic urethane acrylate oligomer in addition to the alkyl containing acrylate-functional monomer (c).
In another embodiment, then, the invention is a process for adjusting the adhesive bond of a cured matrix material to glass optical fibers which are coated with a coating comprising a cured acrylate-or methacrylate-containing coating composition and colored by the application of inks of different respective colors for fiber identification, by incorporating into an uncured matrix material as described above a component that is capable of increasing the adhesive bond.
In another embodiment, the invention is an optical fiber ribbon assembly comprising a plurality of coated, colored optical fibers in a fixed relationship, e.g., a generally planar, generally parallel arrangement, and a radiation-cured matrix material bonding said fibers in said position within the matrix material. The matrix material has sufficient adhesion to the fibers to remain adhered thereto during use but is easily strippable therefrom. Specifically, the invention may be such an optical fiber ribbon wherein the matrix material is as described above.
In yet another embodiment, the invention is a process for preparing an optical fiber ribbon. The process comprises mechanically aligning the optical fibers in the desired (e.g., generally parallel) arrangement; applying about the fibers the matrix material described above; and curing the matrix material to secure the fibers in the desired arrangement, e.g., preferably with ultraviolet light or an electron beam.
In a still further embodiment, the invention is a coating composition for coating a substrate, the composition being as described above.
A radiation-curable composition for a matrix material has been devised to possess a number of important qualities rendering it useful for various applications, e.g., for affixing coated and inked optical fibers in a ribbon configuration. The matrix material has a number of properties making it particularly suitable for such end uses, these properties including moisture resistance; solvent resistance; thermal, oxidative and hydrolytic stability, and so forth.
However, one property of the matrix composition of the present invention, which is a valuable property, is its controlled and optimized adhesion level, which allows it to remain adhered to the (fiber) substrate during use, yet be strippable without substantial damage to the substrate, when required. This property is regulated by adjusting or controlling the use of either of the adhesion-decreasing component (i.e., the alkyl acrylate or methacrylate) , or of the adhesion-increasing component (i.e., the polyester-based aliphatic urethane acrylate oligomer), or by a combination of the two, at appropriate levels to achieve the desired adhesion levels, in the range of 0.02 lb./in. to 0.20 lb/in.
The invention relates in part to a radiation curable matrix composition material, e.g., for affixing coated and inked optical fibers in a ribbon or other desired configuration. The cured matrix material should have, inter alia, the following properties: moisture resistance; solvent resistance; ease of stripping; resistance to breakout failure; low vocatives content; fast cure when irradiated; and long term thermal, oxidative and hydrolytic stability. It should be non-yellowing. It should also be resistant to failure during xe2x80x9ccablingxe2x80x9d. Cabling is the term used to describe a process of gathering a plurality of the ribbons together to form a cable.
The matrix material contains at least three basic ingredients, and, if envisioned for ultraviolet cure, at least four:
(a) a polyether-based urethane acrylate;
(b) a monomer having a plurality of acrylate or methacrylate groups;
(c) an alkyl acrylate or an alkyl methacrylate monomer; and
(d) optionally, for a U.V.-curable composition, a photoinitiator.
(A) The Polyether-Based Urethane Acrylate
The first ingredient is a specific urethane acrylate. Specifically, it is based on an aliphatic polyether polyol, which is reacted with an aliphatic polyisocyanate and acrylated.
In a preferred embodiment, this component is an oligomer which is silicone-modified, e.g., it may have silicone co-reacted into the polyether portion of the backbone. The silicone-modified alternative may provide the most desirable release characteristics vis-a-vis the ink (i.e., may exhibit less adhesion than the nonsilicone-containing urethane acrylate).
This component is chosen to possess good thermal and hydrolytic properties and a low glass transition temperature, and to be somewhat non-yellowing.
The polyether-based urethane acrylate comprises from about 35 percent to about 98 percent by weight of the matrix composition, based on the total weight of the (a) through (d) ingredients. Preferably, the (a) component comprises from about 53 percent to about 87.5 percent, and more preferably about 64 percent to about 80 percent by weight of the composition, based upon the total weight of the (a) through (d) ingredients. If less than about 35 percent by weight of this component is used, the release properties of the matrix may suffer. If more than about 98 percent by weight is used, the viscosity of the composition may be undesirably high and swelling may occur when the matrix is exposed to certain solvents which may be used in the field and which may be absorbed by the matrix, such as ethanol, trichloroethane or isopropyl alcohol.
Examples of suitable urethane acrylates (a) include but are not limited to Ebecryl 4842 (equivalent to Chempol 194842), which is a silicone-modified compound, and Ebecryl 19-6264, which is not silicone-modified, and which contains about 15% by weight of 1,6-hexanediol diacrylate as a reactive solvent, both from Radcure Specialties, Inc., Louisville, Ky.
(B) The Monomer Having A Plurality of Acrylate or Methacrylate Groups
The second component of the matrix material is a monomer having a plurality of acrylate or methacrylate moieties.
This component, which may be difunctional or higher but which is preferably trifunctional, serves to increase the crosslink density of the cured coating and therefore to improve solvent resistance (by preventing absorption of solvent into the matrix) and to increase modulus. Examples of suitable components (b) include but are not limited to trimethylolpropane triacrylate; trimethylolpropane trimethacriylate; pentaerythritol triacrylate; pentaerythritol trimethacriylate; pentaerythritol tetraacrylate; pentaerythritol tetra methacrylate; trimethylolpropane propoxylate triacrylate; trimethylolpropane propoxylate trimethacriylate; trimethylolpropane ethoxylate triacrylate; trimethylolpropane ethoxylate trimethacriylate; glycerol propoxytriacrylate; glycerol propoxytrimethacrylate; dipentaerythritol monohydroxy pentaacrylate; dipentaerythritol monohydroxy pentamethacrylate; C6-C12 hydrocarbon diol diacrylates; C6-C12 hydrocarbon diol dimethacrylates; and mixtures thereof A preferred component (b) is trimethylolpropane triacrylate.
The monomer having a plurality of acrylate or methacrylate functionalities comprises from about 0.5 percent to about 35 percent by weight of the composition, based on the total weight of (a), (b), (c) and (d). Preferably, it comprises from about 10 percent to about 25 percent, and more preferably from about 15 percent to about 21 percent by weight of the composition, again based on total weight of (a) through (d). If less than about 0.5 percent by weight of component (b) is used, insufficient crosslink density, low modulus and poor solvent resistance may result; if more than about 35 percent is used, the cured composition may shrink to such an extent that adhesion may suffer (i.e., the matrix material may shrink away from the coated and inked optical fibers).
(C) The Alkyl Acrylate or Alkyl Methacrylate Monomer
The third component of the matrix material is an acrylate or methacrylate monomer having an alkyl moiety comprising from 7 to 18 carbon atoms.
One of the key features of the present invention is its optimized adhesion level, i.e., it has a high enough adhesion level to remain adhered under virtually all use conditions yet low enough to render it easily strippable for splicing. Further, the adhesion level of the matrix to the coated and inked fibers is variable, as discussed in further detail herein below, to meet different use conditions.
This third component (c) is instrumental in conferring release properties to the matrix material vis-a-vis the coated, inked optical fibers. As discussed above, it is necessary that a field worker is able to peel away the matrix material without removing the ink which identifies the underlying coated optical fibers, in order to splice the fibers together correctly. Furthermore, the inclusion of this third component increases the hydrolytic stability of the matrix material relative to that of the composition not including it. Thus, even in an embodiment, discussed infra wherein increased (rather than decreased) adhesion is required, this adhesion decreasing component should be used in addition to a further component that is capable of overriding this adhesion decreasing property, the adhesion-increasing component replacing a portion of the polyether urethane acrylate component (a).
In either embodiment, the adhesion level of matrix material to ink should fall within the range of between about 0.02 pounds per linear inch (lb./in.) and about 0.20 lb./in.; preferably between about 0.04 lb./in. and about 0.15 lb./in.; and more preferably between about 0.06 lb./in. and about 0.10 lb./in., as measured on a one-inch wide sample by a T-peel test, using an Instron, model 1122, at 23xc2x0 C., with a 10 mm/min crosshead speed.
Examples of such monomers include but are not limited to stearyl acrylate; stearyl methacrylate; isooctyl acrylate; isooctyl methacrylate; lauryl acrylate; lauryl methacrylate; C14 to C15 hydrocarbon diol diacrylates; C14 to C15 hydrocarbon diol dimethacrylates; caprolactone acrylate; caprolactone methacrylate; decyl acrylate; decyl methacrylate; isodecyl acrylate; isodecyl methacrylate; isobornyl acrylate; isobornyl methacrylate; and mixtures thereof. Of the above, those having straight chain alkyl groups of from 12 to 18 carbon atoms are preferred. Particularly preferred is stearyl acrylate, such as Sartomer SR-257 stearyl acrylate from the Sartomer Company of West Chester, Pa.
The alkyl-functional acrylate or methacrylate monomer (c) comprises from about 0.5 percent to about 20 percent by weight of the matrix material composition, based on the total of the weights of components (a) through (d). Preferably, it comprises from about 1 to about 14 percent by weight and more preferably about 3 to about 8 percent by weight of the composition, based on the total weight at (a) (b), (c) and (d) . As mentioned supra. if less than about 0.5 percent by weight of this component is used, hydrolytic stability may suffer. If more than 20 percent is used, crosslink density may be undesirably low, causing swelling of the matrix material due to solvent absorption when exposed to solvent in the field.
(D) The Photoinitiator
The fourth component of the matrix material is a photoinitiator. The necessity for this component depends on the envisioned mode of cure of the matrix material: if it is to be ultraviolet cured, a photoinitiator is needed; if it is to be cured by an electron beam, the material may comprise substantially no photoinitiator.
In the ultraviolet cure embodiment, the photoinitiator, when used in a small but effective amount to promote radiation cure, must provide reasonable cure speed without causing premature gelation of the matrix composition. Further, it must not interfere with the optical clarity of the cured matrix material. Still further, the photoinitiator must itself be thermally stable, non-yellowing, and efficient.
Suitable photoinitiators include, but are not limited to, the following: hydroxycylohexylphenyl ketone; hydroxymethylphenylpropanone; dimethoxyphenylacetophenone; 2-methyl-1-[4-(methyl thio) phenyl]-2-morpholinopropanone-1; 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one; 1-(4dodecylphenyl)-2-hydroxy-2-methylpropan-1-one; 4-(2-hydroxyethoxy) phenyl-(2-hydroxy-2-propyl) ketone; diethoxyacetophenone; 2,2-di-sec-butoxyacetophenone; diethoxy-phenyl acetophenone; and mixtures of these.
The photoinitiator comprises from about 0 percent to about 10 percent by weight of the composition, based upon the weight of composition of the (a) through (d) ingredients (o percent representing the electron beam curable embodiment). In the ultraviolet curable embodiment, the photoinitiator comprises from about 1 percent to about 10 percent by weight of the composition, based on (a) through (d). Preferably, the amount of photoinitiator, when used, is from about 1.5 percent to about 8.0 percent, and more preferably from about 2.0 percent to about 7.0 percent by weight, based upon the total weight of the (a) through (d) ingredients. A particularly preferred photoinitiator is hydroxycylcohexylphenyl ketone, such as is supplied by Ciba-Geigy Corp., Ardsley, N.Y., as Irgacure 184.
The photoinitiator should be chosen such that cure speed, as measured in a dose versus modulus curve, of less than 1.0 J/cm2 , and preferably less than 0.5 J/cm2, is required, when the photoinitiator is used in the designated amount.
The curable composition used to make the matrix material may also comprise one or more optional ingredients, discussed infra.
(E) Component Capable of Increasing Adhesion
As discussed above, a controlled adhesion level is an important parameter of the present invention. The adhesion level should again lie within the range of between about 0.02 lb./in. and about 0.20 lb./in., preferably between about 0.04 lb./in. and about 0.15 lb./in., and more preferably between about 0.06 lb./in. and about 0.10 lb./in. as measured by T-peel test, as described, supra. Functionally, this means that the matrix material is adherent enough to the coated and inked optical fibers so as not to separate therefrom under normal use conditions, yet releasable enough to separate easily from the coated, inked fibers clearly and without removing a substantial amount of ink therefrom during, for example, splicing operations.
In order to attain this desired amount of adhesion, it may be necessary to incorporate an agent capable of increasing the adhesion level of the matrix to a coated and inked optical fiber relative to the composition not incorporating it. This higher adhesion level might be necessary, for example, when an ink having relatively poor adhesion to the matrix material is used. This adhesion-increasing additive may be used in addition to or in lieu of a portion of the polyether-based urethane acrylate component (a).
The invention thus further comprises a process for adjusting the adhesive bond of a cured matrix material to coated and inked glass optical fibers by incorporating such adhesion-increasing component into the uncured matrix material.
When used, the adhesion-increasing component preferably comprises from about 1 to about 30 percent by weight, based on the total weight of components (a), (b), (c) and (d) only.
Suitable adhesion-increasing components include, but are not limited to, polyester-based aliphatic urethane acrylate oligomers, commercially available examples of which include Cargill 1512 oligomer, from Cargill, Inc., Minneapolis, Minn., and Ebecryl 284, from Radcure Specialties, Inc., Louisville, Ky.
(F) Stabilizers
Another optional class of components includes various stabilizers. To improve shelf life (storage stability) of the uncured coating, as well as to increase thermal and oxidative stability of the cured coating, one or more stabilizers may be included in the composition. Examples of suitable stabilizers include tertiary amines such as diethylethanolamine and trihexylamine; hindered amines; organic phosphates; hindered phenols; antioxidants; mixtures thereof; and the like. Some particular examples of antioxidants which can be used include octadecyl-3-(3xe2x80x2,5xe2x80x2-di-tert-butyl-4xe2x80x2-hydroxyphenyl) propionate; thiodiethylene bis (3,5-di-tert-butyl-4-hydroxy) hydrocinnamate; and tetrakis [methylene (3,5di-tert-butyl-4-hydroxyhydrocinnamate)] methane.
When a stabilizer is used, it may be incorporated in an amount from about 0.1 percent to about 3.0 percent, based on the weight of the (a) through (d) ingredients. Preferably, it is included in the range from about 0.25 percent to about 2.0 percent by weight, and more preferably in the range from about 0.5 percent to about 1.5 percent by weight, based on the total weight of the (a) through (d) ingredients. Desirable properties of a stabilizer include non-migration (probably enhanced by low polarity). A preferred stabilizer is thiodiethylene bis (3,5-di-tert-butyl-4xe2x80x2-hydroxy) hydrocinnamate, such as Irganox 1035, from Ciba-Geigy Corporation, Ardoloy, N.Y.
The matrix composition should have a viscosity of about 5,000 to about 9,000 cps at 23xc2x0 C., and a fast cure. The cured matrix material should have a modulus of over about 1,000 psi, a glass transition temperature of less than about xe2x88x9240xc2x0 C. (onset), low surface tack, and high thermal and hydrolytic stability.
The invention further relates to an optical fiber ribbon assembly. The ribbon assembly generally comprises a plurality of coated, inked optical fibers held in a fixed relationship, e.g., in a parallel and planar or other prescribed arrangement, and a radiation curable matrix material, in which the fibers are embedded, the matrix bonding the fibers in the desired arrangement. The matrix material has sufficient adhesion to the fibers to remain adhered thereto during use but is easily strippable therefrom without substantially damaging the integrity of an ink layer on the coated optical fibers. The optical fibers which are part of the ribbon are those known in the art which are singly or dually coated before being bonded in the matrix material, and which contain an ink layer on their surf ace, rendering each distinguishable from other fibers in the ribbon. The optical fibers which are coated may comprise, for example, a glass core and a glass cladding layer. The core, for example, may comprise silica doped with oxides of germanium or phosphorus and the cladding, a pure or doped silicate such as a fluorosilicate. Alternately, the fibers may comprise a polymer clad silica glass core. Examples of such polymer cladding include organosiloxanes such as polydimethylsiloxane or a fluorinated acrylic polymer.
The fiber coatings are of the type known in the art and preferably are radiation, e.g., ultraviolet light, cured. The coating compositions may comprise a single or a dual layer and often contain cured acrylate or methacrylate components such as urethane diacrylates. A suitable secondary coating, for example, may comprise an aromatic polyester urethane acrylate; vinyl pyrrolidone; ethoxyethoxyethylacrylate; a photoinitiator; and stabilizer.
As discussed herein above, in order for the optical fiber ribbons to be spliced in a reasonably easy manner, it is desirable to identify the individual fibers by color coding them. It is possible to add a coloring agent to the outermost fiber coating layer; however, this is impractical because the coating will impart its color to the apparatus used to apply it, requiring numerous sets of drawing and coating apparatuses to accommodate each color of ink used. Thus, it is more efficacious to ink over the optical fiber coating or coatings ink-containing layers of different colors, for individual fiber identification, by any means known in the art. The applied ink composition may be variable in nature but generally is vinylic and may comprise, for example, one or more organic or inorganic pigments; a vinyl copolymer; synthetic silica; and an organic solvent. As implied, supra, the precise nature of the ink composition will dictate the amounts and nature of the adhesion-affecting components in the matrix.
The matrix composition which bonds the fibers is of the type which constitutes the present invention, i.e., one which comprises:
(a) from about 35 percent to about 98 percent by weight of an aliphatic polyether-based urethane acrylate;
(b) from about 0.5 percent to about 35 percent by weight of a monomer having a plurality of acrylate or methacrylate moieties;
(c) from about 0.5 percent to about 20 percent by weight of an acrylate or methacrylate monomer having an alkyl moiety comprising from 7 to 18 carbon atoms; and (d) from about 0 percent to about 10 percent by weight of a photoinitiator, all of said percentages by weight being based on total weight of (a), (b), (c) and (d).
One kind of ribbon structure, and a cable made from such ribbon, is described in U.S. Pat. No. 3,411,010 to Gendhr et al., which is incorporated herein by reference.
The invention comprises, in a further aspect, a process for preparing an optical fiber ribbon. Broadly, the process comprises mechanically arranging coated and inked fibers in a desired (i.e., generally planar and generally parallel) configuration; applying a matrix material composition about the fibers; and curing.
A suitable but non-limitative means for applying the matrix material to the fibers is as follows. Optical fibers which have been coated and inked over in the manner described herein above or in any manner known in the art may be used. The optical fibers may be mechanically arranged in the desired configuration (e.g., in a generally parallel, generally planar disposition relative to each other). The fibers may be held in the desired configuration, for example, by taping or otherwise holding the ends together. The matrix material may be applied about the fibers by any conventional means, i.e., by dipping the fibers into a vat of the material or pouring the material thereupon. Once the matrix has been applied substantially uniformly about the fibers, it may be radiation cured, preferably either by ultraviolet light irradiation or via electron beam. Optionally, the composite may be flipped over, more matrix material applied thereto, and the matrix again cured as above. The resulting ribbon contains the fibers bonded and secured in the desired disposition (i.e., generally parallel and generally planar). The adhesive bond of the cured matrix material to the coated and inked fibers may be adjusted by incorporation into the uncured compositions of a component capable of increasing the adhesive bond of the type discussed, supra, e.g., a polyester-based aliphatic urethane acrylate oligomer.
Although the matrix composition has been exemplified herein above for use as a matrix material for coated and inked optical fibers, it should be understood to be useful in any embodiment where it is desired to coat or bind a substrate (e.g., a flexible substrate) wherein the coating has an optimized adhesion level to the substrate and particularly an ink-covered substrate. Examples of such substrates include, but are not limited to, glass, metal or plastic. For example, composition may be used as a release coating for a glass or plastic substrate having a logo printed thereon, as may be used in electronics or other industries, to identify a supplier, or in any embodiment where it is desired to temporarily protect a printed surface. For example, a logo may be protected during shipping with such a release coating, which coating may be removed by the customer. Thus, the invention, stated more broadly, is a radiation curable coating composition for coating a substrate, the coating composition comprising:
(a) from about 35 percent to about 98 percent by weight of an aliphatic polyether-based urethane acrylate;
(b) from about 0.5 percent to about 35 percent by weight of a monomer having a plurality of acrylate or methacrylate moieties;
(c) from about 0.5 percent to about 20 percent by weight of an acrylate or methacrylate monomer having an alkyl moiety comprising from 7 to 18 carbon atoms; and (d) from about 0 percent to about 10 percent by weight of a photoinitiator, all of the percentages by weight being based on total weight of (a), (b), (c) and (d).