OPTICAL FIBERS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S.

Provisional Application Serial No. 62/180,843 filed on June 17, 2015, the content of which is relied upon and incorporated herein by reference in its entirety.

BACKGROUND

Field

[0002] The present specification generally relates to optical fibers, and more particularly, to coatings for optical fibers and to curable compositions for use in coating optical fibers.

Technical Background

[0003] Optical fiber has acquired an increasingly important role in the field of telecommunications, frequently replacing existing copper wires. This trend has had a significant impact in all areas of telecommunications, greatly increasing the amount of data that is transmitted. Further increase in the use of optical fiber is foreseen, especially in metro and fiber- to-the-home applications, as local fiber networks are pushed to deliver an ever- increasing volume of audio, video, and data signals to residential and commercial customers. In addition, use of fiber in home and commercial premise networks for internal data, audio, and video communications has begun, and is expected to increase.

[0004] Optical fiber is typically made of glass or other transparent materials, and usually has a polymeric primary coating and a polymeric secondary coating. The primary coating (also known as an inner primary coating), is typically applied directly to the optical fiber, and when cured, forms a relatively soft, elastic, compliant material encapsulating the glass fiber. The primary coating serves as a buffer to cushion and protect the glass fiber during bending, cabling or spooling. The secondary coating (also known as an outer primary coating) is applied over the primary coating, and functions as a tough, protective outer layer that prevents damage to the optical fiber during processing, handling and use. [0005] When two or more optical fibers are spliced with one another, the primary and/or secondary coatings of the spliced optical fibers may be removed. Following splicing, the bare optical fiber is exposed to environmental conditions. Accordingly, a need exists for a method and material composition with which to re-coat the exposed portions of the optical fiber.

SUMMARY

[0006] According to one embodiment, a coated optical fiber may comprise a first coated optical fiber segment, a second coated optical fiber segment, and a splice-junction coating. The first coated optical fiber segment may comprise a first fiber segment and at least one coating disposed on the first fiber segment. The at least one coating may have been removed from an end portion of the first fiber segment (i.e., the first end portion). The second coated optical fiber segment may comprise a second fiber segment and at least one coating disposed on the second fiber segment. The at least one coating may have been removed from an end portion of the second fiber segment (i.e., the second end portion). The first end portion and the second end portion may abut one another end-to-end. The splice-junction coating may encapsulate the first end portion and the second end portion and contact at least one coating of the first coated optical fiber segment and the at least one coating of second coated optical fiber segment. The splice- junction coating may be a cured polymer product of a precursor composition. The precursor composition may comprise from 0 wt% to 1 wt% of total oligomers and at least 90 wt% of total monomers. A Young's modulus of the cured polymer product may be greater than or equal to 1800 MPa.

[0007] According to one embodiment, a coated optical fiber may comprise a first coated optical fiber segment, a second coated optical fiber segment, and a splice-junction coating. The first coated optical fiber segment may comprise a first fiber segment and at least one coating disposed on the first fiber segment. The at least one coating may have been removed from an end portion of the first fiber segment (i.e., the first end portion). The second coated optical fiber segment may comprise a second fiber segment and at least one coating disposed on the second fiber segment. The at least one coating may have been removed from an end portion of the second fiber segment (i.e., the second end portion). The first end portion and the second end portion may abut one another end-to-end. The splice-junction coating may encapsulate the first end portion and the second end portion and contact at least one coating of the first coated optical fiber segment and the at least one coating of second coated optical fiber segment. The splice- junction coating may be a cured polymer product of a precursor composition. The precursor composition may comprise 70 wt% to 90 wt% of an ethoxylated bisphenol A diacrylate, 10 wt% to 20 wt% of an epoxy acrylate formed by adding acrylate to bisphenol A diglycidylether, 2 wt% to 10 wt% of N- vinyl caprolactam, and 1 wt% to 5 wt% of a UV curable photo initiator.

[0008] In yet another embodiment, a method of re-coating an optical fiber at a splice junction may comprise providing a first coated optical fiber segment and providing a second coated optical fiber segment. The first coated optical fiber segment may comprise a first fiber segment and at least one coating disposed on the first fiber segment, wherein at least one coating has been removed from an end portion of the first fiber segment. The second coated optical fiber segment may comprise a second fiber segment and at least one coating disposed on the second fiber segment, wherein at least one coating has been removed from an end portion of the second fiber segment. The end portion of the first fiber segment and the end portion of the second fiber segment may abut one another end-to-end. The method may further comprise applying a coating composition to the first end portion and the second end portion to encapsulate the first end portion and second end portion. The coating composition may contact the at least one coating of the first coated optical fiber segment and the at least one coating of second coated optical fiber segment. The method may further comprise curing the coating composition to form a cured splice-junction coating having a Young's modulus of at least about 1800 MPa. The coating composition may comprise 0 wt% to 1 wt% of total oligomers and at least 90 wt% of total monomers.

[0009] Additional features and advantages of the methods and articles described herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0010] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 schematically depicts a cross-sectional axial view of a coated optical fiber, according to one or more embodiments shown and described herein;

[0012] FIG. 2 schematically depicts a cross-sectional length view of a re-coated optical fiber, according to one or more embodiments shown and described herein;

[0013] FIG. 3 schematically depicts the experimental testing apparatus used to determine splice-joint gap strength of a re-coated optical fiber, according to one or more embodiments shown and described herein;

[0014] FIG. 4 schematically depicts the experimental setup for determining butt-splice adhesion strength, according to one or more embodiments shown and described herein;

[0015] FIG. 5 graphically depicts experimental results for the splice joint gap strength of selected samples of splice-joint coatings, according to one or more embodiments shown and described herein; and

[0016] FIG. 6A and FIG 6B depict photographs of a non-gapped splice junction and a gapped splice junction, respectively, according to one or more embodiments shown and described herein.

DETAILED DESCRIPTION

[0017] Reference will now be made in detail to embodiments of re-coated optical fibers and methods for re-coating optical fibers, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Generally, when coated optical fibers are spliced, the primary and secondary coatings of the optical fibers are removed. Upon splicing of the two optical fibers, a splice-junction coating (sometimes referred to herein as a "recoat") may be applied over the exposed portions of the optical fibers. This "patch" coating generally covers the area where the removed primary and secondary coatings were positioned, and fills in the gap between the coatings of the spliced optical fibers. The splice-junction coatings described herein adhere to the optical fibers as well as the secondary coatings of the optical fibers. Additionally, the splice- junction coatings described herein may have acceptable mechanical characteristics such that they protects the underlying optical fiber while being flexible enough to not break when the optical fiber is coiled or bent.

[0018] To achieve the desired mechanical characteristics, conventional splice-junction coating compositions generally contain urethane-based oligomers with monomers being introduced into the splice-junction coating composition as reactive diluents to lower the viscosity. Because conventional oligomeric components are, in general, much more expensive than the monomeric components, the use of oligomers in has the effect of increasing the cost of producing secondary coating compositions as well as the resulting optical fiber. Despite the relatively high cost of using oligomeric components, it is believed that there are no commercially viable splice-junction coating compositions that either contain a low concentration or are devoid of oligomeric components.

[0019] Specifically, oligomeric components are often used to tailor the desired properties of the splice-junction coating. The main role of the urethane acrylate oligomer in a splice-junction coating formulation is performance; depending on the oligomer type it can provide chemical resistance, heat resistance, water resistance, flexibility, hardness and/or enhanced adhesion. The structure of the urethane acrylate oligomer can be designed to achieve the desired properties of the pre-cured liquid coating and the resulting cured material. However, as described, urethane acrylate oligomers are a high cost component of the splice-junction coating formulation. It is desirable to formulate oligomer-free splice-junction coating formulations while maintaining suitable properties of the formulation and the resulting cured coatings.

[0008] Because of substantial cost savings in reducing the oligomer content of splice-junction coating compositions, the major constituent of the composition of the present splice-junction coating composition is the monomeric component and the minor, or even optional, constituent is the oligomeric component. In one embodiment, the composition of the splice-junction coatings described herein is devoid of an oligomeric component and the monomeric component is a combination of two or more monomers. The term "oligomer" is defined as the class of compounds including aliphatic and aromatic urethane (meth)acrylate oligomers, urea (meth)acrylate oligomers, polyester and polyether (meth)acrylate oligomers, acrylated acrylic oligomers, polybutadiene (meth)acrylate oligomers, polycarbonate (meth)acrylate oligomers, and melamine (meth)acrylate oligomers. Oligomers may be present in the splice-junction coatings described herein in amounts from about 0 wt % to about 1 wt%, such as substantially oligomer free splice-junction coatings.

[0020] According to embodiments of the present invention, an example of a coated optical fiber (non-spliced) is shown in the schematic cross-sectional axial view in FIG. 1. The coated optical fiber 100 has a lateral direction extending in the major length of the coated optical fiber 100 and an axial direction having a substantially circular cross-section, as shown in FIG. 1. Coated optical fiber 100 includes an optical fiber 110 (including a core 112 and a cladding 114) surrounded by primary coating 130 and secondary coating 120. As used herein in the context of the positioning of a coating, the term "surrounding" means that the underlying optical fiber or coating is at least surrounded in the axial direction by the outer, surrounding coating, where the terminal ends of the coated optical fiber are not necessarily surrounded by the coating layer in the lateral direction. For example, as shown in FIG. 1, the primary coating 130 surrounds the optical fiber 110 and the secondary coating 120 surrounds the primary coating 130. In embodiments, the primary coating 130 may be in direct contact with the optical fiber 110 and the secondary coating 120 may be in direct contact with the primary coating 120. However, embodiments containing interlayers positioned between the optical fiber 110 and the primary coating 130, and/or between the primary coating 130 and the secondary coating 120 are contemplated herein.

[0021] The optical fiber 110 (sometimes referred to as a fiber segment) may generally include a core 112 and a cladding 114. The core 112 and cladding 114 may comprise a wide variety of transparent materials, including glass, polymers, and the like. Generally, the core 112 and the cladding 114 are transparent materials where the cladding 114 has a lower refractive index than the core 112. The optical fiber 110 may be a single mode fiber, or a multimode fiber. The optical fiber 110 may be adapted for use as a data transmission fiber (e.g., SMF-28®, LEAF®, and METROCOR®, each of which is available from Corning Incorporated of Corning, NY). Alternatively, the optical fiber 110 may perform an amplification, dispersion compensation, or polarization maintenance function. It should be understood that that the coatings (i.e., primary coatings, secondary coatings, and splice-junction coatings) described herein are suitable for use with virtually any optical fiber for which protection from the environment is desired.

[0022] In optical fiber 110 is surrounded by a primary coating 130. Primary coating 130 may comprise a polymer composition, such as a soft crosslinked polymer material having a low Young's modulus (e.g., less than about 5 MPa at 25° C) and a low glass transition temperature (e.g., less than about -10° C). The primary coating 130 may have a higher refractive index than the cladding 114 of the optical fiber 110 in order to allow it to strip errant optical signals away from the optical fiber core 112. The primary coating 130 should maintain adequate adhesion to the optical fiber 110 during thermal and hydro lytic aging, yet be strippable therefrom for splicing purposes. The primary coating 130 typically has a thickness in the range of 25-40 μηι (e.g. about 32.5 μηι). The primary coating 130 is typically applied to the glass fiber as a liquid and cured, as will be described in more detail hereinbelow. Curable compositions used to form primary coatings may be formulated using an oligomer (e.g., a polyether urethane acrylate), one or more monomer diluents (e.g. ether- containing acrylates), a photoinitiator, and other additives (e.g., antioxidants).

[0023] In the embodiment of coated optical fiber 100, the primary coating 130 is surrounded by a secondary coating 120. The secondary coating 130 may be formed from a cured polymeric material, and may typically have a thickness in the range of 20-35 μηι (e.g. about 27.5 μηι). The secondary coating may have sufficient stiffness to protect the optical fiber; may be flexible enough to be handled, bent, or spooled; may have a relatively small tackiness to enable handling and prevent adjacent convolutions on a spool from sticking to one another; may be resistant to water and chemicals such as optical fiber cable filling compound; and may have adequate adhesion to the coating to which it is applied (e.g., the primary coating 130). Secondary coating compositions may include oligomers, monomers, and other additives, and in some embodiments, may comprise a low concentration of oligomers (i.e., less than about 3%). Generally, the material of the secondary coating 120 has a relatively high Young's modulus, such as greater than about 1000 MPa, 1200 MPa, 1400 MPa, 1600 MPa, 1800 MPa, or even greater than about 2000 MPa.

[0024] In order to couple a coated optical fiber 100 to a device or to another coated optical fiber (sometimes referred to herein as "splicing" of optical fibers), it is typically necessary to strip the dual coating system (i. e., the primary coating 130 and secondary coating 120) off of a portion of the optical fiber 1 10. The splice-junction coatings described herein may be useful in recoating a stripped optical fiber, for example, at a splice joint or splice junction where two optical fibers and/or optical fiber connectors connect.

[0025] More specifically, and with reference to FIG. 2, the optical fiber 200 may be formed upon splicing a first coated optical fiber segment (including a fiber segment 110, primary coating 130, and secondary coating 120) and a second coated optical fiber segment 220 (including a fiber segment 1 10, primary coating 130, and secondary coating 120). The first coated optical fiber segment and the second coated optical fiber segment may be substantially identical in embodiments described herein (at least at their ends), and each may be representative of the coated optical fiber 100 of FIG. 1. Upon splicing the fiber segments 110, the segments are joined together at splice junction 240. The segments may be spliced together end-to-end, which is known as a "butt splice."

[0026] After creating the splice junction 240 (i. e., by placing the two butt ends together), the area around the splice junction 240 is coated with a splice-junction coating 230 so as to encapsulate the end sections (the areas near the splice junction 240) of the first segment 210 and second segment 220 and contact the coatings of the first and second optical fiber segments (i.e., primary coatings 130 and secondary coatings 120). This positioning of the splice-junction coating 230 allows for environmental protection to the optical fiber surface that was left exposed when the primary 130 and secondary 120 coatings were stripped. The splice-junction coating 230 may be between about 40 microns and about 260 microns in thickness, such as between about 40 microns and 125 microns. Generally, the splice-junction coating 230 is about the same thickness as the sum of the thicknesses of the primary coating 130 and the secondary coating 120 of the coated optical fiber segments. However, in some embodiments, the splice-junction coating 230 may be thicker than the combination of the primary coating 130 and the secondary coating 120 and some of the splice-junction coating 230 may be positioned on the outer surface of the secondary coating 120.

[0027] Generally, the splice-junction coating 230 is applied as a liquid precursor composition, and is then cured, forming the solid splice-junction coating 230. In embodiments described herein, the splice-junction coating 230 may be a cured polymer product of a precursor composition. The precursor composition of the splice-junction coating 230 may comprise a mixture of chemical components in varying ratios. As used herein, the weight percent (wt%) of a particular component refers to the amount introduced into the bulk composition, excluding other additives. The amount of other additives that are introduced into the bulk composition to produce a composition of the present disclosure is listed in parts per hundred (pph). For example, as used herein, an oligomer, monomer, and photoinitiator are combined to form the bulk composition such that the total weight percent of these components equals 100wt%. To this bulk composition, an amount of an additive, for example 1.0 pph of an antioxidant, is introduced in excess of the 100 wt% of the bulk composition.

[0028] In embodiments, curing of the precursor material, to form the splice-junction coating 230, may be achieved by exposure to radiation, such as ultraviolet radiation. In embodiments, LED lamps, mercury lamps, halogen lamps, and the like, may be utilized to cure the precursor material. Deposition of the precursor material and curing can take place in a recoat apparatus, such as a Vytran PTR-200 MRC recoater machine. Example recoat mold sizes are 250-270 microns and example radiation sources include four 10W halogen lamps.

[0029] In the precursor composition of the presently disclosed splice-junction coating 230, the monomeric component can include a single monomer or it can be a combination of two or more monomers. Although not required, it may be desirable that the monomeric component be a combination of two or more monomers when the composition is devoid of the oligomeric component. In embodiments, the monomeric component introduced into the composition of the present invention may include ethylenically unsaturated monomer(s). While the monomeric component may be present in an amount of 50 wt% or more, in some embodiments it may be present in an amount of about 75 wt% to about 99.2 wt%, about 80 wt% to about 99 wt%, or about 85 wt% to about 98 wt%, or at least about 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, or even at least about 95 wt%. As used herein, "total monomers" refers to the combination of all monomer compositions present in the splice-junction coating precursor.

[0030] Ethylenically unsaturated monomers may contain various functional groups which enable their cross-linking. The ethylenically unsaturated monomers may be polyfunctional (i.e., each containing two or more functional groups), although monofunctional monomers may also be introduced into the composition. Therefore, the ethylenically unsaturated monomer can be a polyfunctional monomer, a monofunctional monomer, and mixtures thereof. Suitable functional groups for ethylenically unsaturated monomers used in accordance with the present splice- junction coatings 230 include, without limitation, acrylates, methacrylates, acrylamides, N- vinyl amides, styrenes, vinyl ethers, vinyl esters, acid esters, and combinations thereof (i.e., for polyfunctional monomers).

[0031] In general, individual monomers capable of about 80% or more conversion (i.e., when cured) may be more desirable than those having lower conversion rates. The degree to which monomers having lower conversion rates can be introduced into the composition depends upon the particular requirements (i.e., strength) of the resulting cured product. Typically, higher conversion rates will yield stronger cured products.

[0032] Suitable polyfunctional ethylenically unsaturated monomers include, without limitation, alkoxylated bisphenol A diacrylates such as ethoxylated bisphenol A diacrylate with ethoxylation being 2 or greater, such as ranging from 2 to about 30 (e.g. SR349 and SR601 available from Sartomer Company, Inc. West Chester, Pa. and Photomer 4025 and Photomer 4028, available from IMG Resins), and propoxylated bisphenol A diacrylate with propoxylation being 2 or greater, such as ranging from 2 to about 30; methylolpropane polyacrylates with and without alkoxylation such as ethoxylated trimethylolpropane triacrylate with ethoxylation being 3 or greater, such as ranging from 3 to about 30 (e.g., Photomer 4149, IMG Resins, and SR499, Sartomer Company, Inc.), propoxylated-trimethylolpropane triacrylate with propoxylation being 3 or greater, such as ranging from 3 to 30 (e.g., Photomer 4072, IMG Resins, and SR492, Sartomer), and ditrimethylolpropane tetraacrylate (e.g., Photomer 4355, IMG Resins); alkoxylated glyceryl triacrylates such as propoxylated glyceryl triacrylate with propoxylation being 3 or greater (e.g., Photomer 4096, IMG Resins and SR9020, Sartomer); erythritol polyacrylates with and without alkoxylation, such as pentaerythritol tetraacrylate (e.g., SR295, available from Sartomer Company, Inc. (West Chester, Pa.)), ethoxylated pentaerythritol tetraacrylate (e.g., SR494, Sartomer Company, Inc.), and dipentaerythritol pentaacrylate (e.g., Photomer 4399, IMG Resins, and SR399, Sartomer Company, Inc.); isocyanurate polyacrylates formed by reacting an appropriate functional isocyanurate with an acrylic acid or acryloyl chloride, such as tris-(2-hydroxyethyl) isocyanurate triacrylate (e.g., SR368, Sartomer Company, Inc.) and tris-(2-hydroxyethyl) isocyanurate diacrylate; alcohol polyacrylates with and without alkoxylation such as tricyclodecane dimethanol diacrylate (e.g., CD406, Sartomer Company, Inc.) and ethoxylated polyethylene glycol diacrylate with ethoxylation being 2 or greater, such as ranging from about 2 to 30; epoxy acrylates formed by adding acrylate to bisphenol A diglycidylether (4 up) and the like (e.g., Photomer 3016, IMG Resins); and single and multi-ring cyclic aromatic or non-aromatic polyacrylates such as dicyclopentadiene diacrylate and dicyclopentane diacrylate.

[0033] Some embodiments may utilize amounts of monofunctional ethylenically unsaturated monomers, which can be introduced to influence the degree to which the cured product absorbs water, adheres to other coating materials, or behaves under stress. Examples of monofunctional ethylenically unsaturated monomers include, without limitation, hydroxyalkyl acrylates such as 2-hydroxyethyl-acrylate, 2-hydroxypropyl-acrylate, and 2-hydroxybutyl-acrylate; long- and short-chain alkyl acrylates such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, amyl acrylate, isobutyl acrylate, t-butyl acrylate, pentyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate, lauryl acrylate, octadecyl acrylate, and stearyl acrylate; aminoalkyl acrylates such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, and 7-amino-3,7-dimethyloctyl acrylate; alkoxyalkyl acrylates such as butoxyethyl acrylate, phenoxyethyl acrylate (e.g., SR339, Sartomer Company, Inc.), and ethoxyethoxyethyl acrylate; single and multi-ring cyclic aromatic or non-aromatic acrylates such as cyclohexyl acrylate, benzyl acrylate, dicyclopentadiene acrylate, dicyclopentanyl acrylate, tricyclodecanyl acrylate, bomyl acrylate, isobornyl acrylate (e.g., SR423, Sartomer Company, Inc.), tetrahydrofiurfuryl acrylate (e.g., SR285, Sartomer Company, Inc.), caprolactone acrylate (e.g., SR495, Sartomer Company, Inc.), and acryloylmorpholine; alcohol-based acrylates such as polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, methoxyethylene glycol acrylate, methoxypolypropylene glycol acrylate, methoxypolyethylene glycol acrylate, ethoxydiethylene glycol acrylate, and various alkoxylated alkylphenol acrylates such as ethoxylated(4) nonylphenol acrylate (e.g., Photomer 4066, IMG Resins); acrylamides such as diacetone acrylamide, isobutoxymethyl acrylamide, Ν,Ν'-dimethyl-aminopropyl acrylamide, Ν,Ν-dimethyl acrylamide, N,N diethyl acrylamide, and t-octyl acrylamide; and acid esters such as maleic acid ester and fumaric acid ester. With respect to the long and short chain alkyl acrylates listed above, a short chain alkyl acrylate is an alkyl group with 6 or less carbons and a long chain alkyl acrylate is alkyl group with 7 or more carbons.

[0034] Another type of monomer that may be included in the precursor composition of the splice-junction coating 230 are N-vinyl amides. N-vinyl amides may provide curable compositions having decreased gel times. Such N-vinyl amides include N-vinyl lactam, N-vinyl pyrrolidinone and N-vinyl caprolactam. N-vinyl amides may be included in an amount of from about 0.1 wt% to about 40 wt%, from about 2 wt% to about 10 wt%, from about 5 wt% to about 10 wt%, from about 8wt% to about 10wt%, and in some embodiments from about 8.5 wt% to about 9.5 wt%. Without being bound by theory, it is believed that N-vinyl amides may promote hydrogen bonding between glass of an optical fiber 110 and the material of the cured splice- junction coating 230.

[0035] In one embodiment, the splice-junction coating 230 may be formed from a precursor composition comprising ethoxylated bisphenol A diacrylates, epoxy acrylates, and N-vinyl amides. For example, a splice-junction coating 230 may be formed from precursors comprising from 70 wt% to 90 wt% ethoxylated bisphenol A diacrylate monomers, from 10 wt% to 20 wt% epoxy acrylate monomers, and from 5 wt% to 10 wt% (i.e., from 6 wt% to 10 wt%, 7 wt% to 10 wt%, and 8 wt% to 10 wt%) N-vinyl amide monomers, such as N-vinyl caprolactam.

[0036] Many suitable monomers are either commercially available or readily synthesized using various reaction schemes. For example, most of the above-listed monofunctional monomers can be synthesized by reacting an appropriate alcohol or amide with an acrylic acid or acryloyl chloride. [0037] The precursor compositions for the splice-junction coatings 230 may also contain one or more polymerization initiator which is suitable to cause polymerization (i.e., curing) of the composition after its application to a glass fiber or previously coated glass fiber. Polymerization initiators suitable for use in the compositions of the present disclosure include thermal initiators, chemical initiators, electron beam initiators, microwave initiators, actinic-radiation initiators, and photoinitiators. For most acrylate-based coating formulations, conventional photoinitiators, such as the known ketonic photoinitiating and/or phosphine oxide additives, may be used. When used in the precursor compositions of the splice-junction coatings described herein, the photoinitiator may be present in an amount sufficient to provide ultraviolet curing. In embodiments, this includes about 0.5 wt% to about 10 wt%, about 1.5 wt% to about 7.5 wt%, about 1 wt% to about 5wt%, or about 2 wt% to about 4 wt% photoinitiator.

[0038] The photoinitiator, when used in a relatively small but effective amount to promote radiation cure, should provide reasonable cure speed without causing premature gelation of the coating composition. An example cure speed is any speed sufficient to cause substantial curing (i.e., greater than about 90%, such as about 95%) of the coating composition. As measured in a dose versus modulus curve, a cure speed for coating thicknesses of about 25-35 μπι is, e.g., less than 1.0 J/cm ² , such as less than 0.5 J/cm ² .

[0039] Suitable photoinitiators include, without limitation, 2,4,6- Trimethylbenzoyldiphenylphosphine oxide (e.g. Lucirin TPO), 1 -hydroxycyclohexylphenyl ketone (e.g.,; Irgacure 184 available from BASF), (2,6-diethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide (e.g. in commercial blends Irgacure 1800, 1850, and 1700, BASF), 2,2- dimethoxyl-2-phenyl acetophenone (e.g., Irgacure,651, BASF), bis(2,4,6- trimethylbenzoyl)phenyl phosphine oxide (e.g., Irgacure 819, BASF), (2,4,6- triiethylbenzoyl)diphenyl phosphine oxide (e.g., in commercial blend Darocur 4265, BASF), 2- hydroxy-2-methyl-l-phenylpropane-l-one (e.g., in commercial blend Darocur 4265, BASF), 1- Propanone, 2-methyl-l-[4-(methylthio)phenyl]-2-(4-morpholinyl) (e.g. Irgacure 907, BASF), isopropylthioxanthone (e.g., ITX, Rahn AG), and combinations thereof. Other photoinitiators are continually being developed and used in coating compositions on glass fibers. [0040] In addition to the above- described components, the precursor compositions of the splice-junction coatings described herein can optionally include an additive or a combination of additives. Suitable additives include, without limitation, antioxidants, catalysts, lubricants, low molecular weight non-crosslinking resins, adhesion promoters, and stabilizers. Some additives can operate to control the polymerization process, thereby affecting the physical properties (e.g., modulus, glass transition temperature) of the polymerization product formed from the composition. Others can affect the integrity of the polymerization product of the composition (e.g., protect against de-polymerization or oxidative degradation). An example antioxidant is thiodiethylene bis(3,5-di-tert-butyl)-4-hydroxyhydrocinnamate (e.g., Irganox 1035, available from BASF).

[0041] Embodiments described herein may include an adhesion promoter in the splice- junction coating curable precursor composition. In one embodiment, an adhesion promoter is present in the precursor curable composition in an amount from about 0.02 to about 10 parts per hundred (pph), from about 0.05 to about 4 parts per hundred, or from about 0.1 to about 2 parts per hundred. In some embodiments, the adhesion promoter is present in an amount from about 0.5 to about 1.5 pph. Suitable adhesion promoters include alkoxysilanes, organotitanates, and zirconates. Example adhesion promoters include, without limitation, 3- mercaptopropyltrialkoxysilane (e.g., 3-MPTMS, available from Gelest (Tullytown, Pa.)); bis(trialkoxysilylethyl)benzene, acryloxypropyltrialkoxysilane (e.g., (3-acryloxypropyl)- trimethoxysilane, available from Gelest), methacryloxypropyltrialkoxysilane, vinyltrialkoxysilane, bis(trialkoxysilylethyl)hexane, allyltrialkoxysilane, styrylethyltrialkoxysilane, and bis(trimethoxysilylethyl)benzene (available from United Chemical Technologies (Bristol, Pa.)).

[0042] Other suitable additives to the precursor composition may include slip additives and coloring agents. A slip additive may be present in an amount from about 0.1 wt% to about 3 wt%. Slip additives may improve processability of the recoat in its liquid and/or cured state, providing improved properties including but not limited to increased mold slip, mar resistance, and wetting. An example slip additive is a silicone-ethylene oxide/propylene oxide copolymer (e.g., Xiamoter OFX-0190 Fluid, formerly DC190, Dow Corning). Other example slip agents include an organo-modified silicone acrylate or silicone polyether acrylates (commercially available as TegoRad 2200N, TegoRad 2100, TegoRad 2300, TegoRad 2500, TegoRad 2700, or Tegorad 2200 from Goldschmidt Chemical Co., (Hopewell, Va.)) and polyethylenepolypropyleneglycol glyceryl ether (commercially available as Acclaim 4220 from Lyondel, formerly known as Arco Chemicals, (Newtowne Square, Pa.)). A suitable coloring agent may be a whitening agent such as a fluorescent whitening agent such as 2,5- thiophenediylbis(5-tert-butyl-l,3-benzoxazole) (e.g., BASF Tinopal OB).

[0043] Other materials that may be utilized as splice-junction coatings 230 are described in US Application No. 61/652538 Filed on May 29, 2012 Entitled "SECONDARY COATING

COMPOSITION FOR OPTICAL FIBERS" the teachings of which are incorporated herein by reference. For example, the compositions of secondary coatings of US Application No.

13/803498 Filed on March 14, 2013 may be utilized as splice junction coatings 230. In embodiments, the material of the splice-junction coating 230 may have a relatively high Young's modulus, such as greater than about 1000 MPa, 1200 MPa, 1400 MPa, 1600 MPa, 1800 MPa, 2000 MPa, or even greater than about 2200 MPa. The Young's modulus of the splice-junction coating 230 material may be greater than the Young's modulus of the secondary coating by about 50 MPa, 100 MPa, or even 150 MPa.

[0044] The splice-junction coatings 230 described herein may have enhanced performance as recoat materials. For example, some conventional recoats will form gaps when a tensile force is placed on the ends of the coated optical fibers that are spliced. The tensile force (pulling in opposite directions on the ends of the spliced optical fibers) may cause a gap to form between the splice-junction coating 230 and the secondary coating 120, causing at least a part of the optical fiber to be exposed at the gap. FIG. 3 depicts the tensile load applied on the spliced optical fiber 200, where an upward force (F) causes a tensile force on the portions of the spliced optical fiber 200 adjacent the splice-junction coating 230 at the splice junction 240.

[0045] In embodiments of the presently described splice-junction coatings, a gap may form between the splice-junction coating and at least one coating of the first coated optical fiber segment less than about 20%, less than about 10%, or even less than about 5% of the time (described herein sometimes a "gap rate") when under a tensile stress of about 350 kpsi, about 375 kpsi, or even about 400 kpsi. In some embodiments, a gap may not form between the splice- junction coating and the at least one coating of the first coated optical fiber segment under a tensile stress of about 350 kpsi, about 375 kpsi, or even about 400 kpsi. The splice-junction gapping rate can be determined based on the experimental process described in Example 4, below.

[0046] It should now be understood that the presently described splice-junction coating compositions and methods for applying splice-junction coatings may exhibit enhanced coating characteristics, such as high adhesion and non-gapping. Additionally, the splice-junction coatings contain low amounts of oligomer or no oligomers at all, and may have a relatively high Young's modulus, such as greater than about 1800 MPa.

[0047] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

EXAMPLES

[0048] The following examples are provided to illustrate embodiments of the present invention, but they are not intended to limit its scope.

Example 1 - Preparation of Splice- Junction Coatings

[0049] The compositions of Examples 1-5 of the present invention were prepared with the listed components using commercial blending equipment. The monomer, photo initiator and other additive components were weighed and then introduced into a heated kettle and blended together at a temperature within the range of from about 50 °C to 65 °C. Blending was continued until a homogenous mixture was obtained.

Sample A - Oligomer Free Splice- Junction Coating Composition

SR601 82 wt%

Photomer 3016 15 wt%

Lucirin TPO 1.5 wt%

Irgacure 184 1.5 wt% Irganox 1035 0.5 pph

Sample B - Oligomer Free Splice-Junction Coating Composition

SR601 74.5 wt%

Photomer 3016 13.6 wt%

N-vinylcaprolactam 9.1 wt%

Lucinn TPO 1.4 wt%

Irgacure l 84 1.4 wt%

Irganox 1035 0.5 pph

Sample C - Oligomer Free Splice-Junction Coating Composition

SR601 82 wt%

Photomer 3016 15 wt%

Lucinn TPO 1.5 wt%

Irgacure l84 1.5 wt%

Irganox 1035 0.5 pph

(3-acryloxypropyl)trimethoxysilane 1 pph

Sample D - Oligomer Free Splice-Junction Coating Composition

SR601 74.5 wt%

Photomer 3016 13.6 wt%

N-vinylcaprolactam 9.1 wt%

Lucinn TPO 1.4 wt%

Irgacure l 84 1.4 wt%

Irganox 1035 0.5 pph

Dow Corning 190 0.5 pph

Sample E - Oligomer Free Splice-Junction Coating Composition

SR601 74.5 wt%

Photomer 3016 13.6 wt%

N-vinylcaprolactam 9.1 wt% Lucinn TPO 2.8 wt%

Irganox 1035 0.5 pph

Sample F - Oligomer Free Splice-Junction Coating Composition

SR601 74.5 wt%

Photomer 3016 13.6 wt%

N-vinylcaprolactam 9.1 wt%

Irgacure 819 2.8 wt%

Irganox 1035 0.5 pph

Sample G - Oligomer Free Splice-Junction Coating Composition

SR601 74.5 wt%

Photomer 3016 13.6 wt%

N-vinylcaprolactam 9.1 wt%

Lucinn TPO 2.8 wt%

Irganox 1035 0.5 pph

Sample H - Oligomer Free Splice-Junction Coating Composition

SR601 74.5 wt%

Photomer 3016 13.6 wt%

N-vinylcaprolactam 9.1 wt%

Irgacure 819 2.8 wt%

Irganox 1035 0.5 pph

Dow Corningl90 0.5 pph

Sample I - Oligomer Free Splice-Junction Coating Composition

SR601 82 wt%

Photomer 3016 15 wt%

Lucirin TPO 3 wt%

Irganox 1035 0.5 pph Sample J - Oligomer Free Splice- Junction Coating Composition

SR601 82 wt%

Photomer 3016 15 wt%

Lucirin TPO 3 wt%

Irganox 1035 0.5 pph

Tinopal OB 0.05 pph

Sample K - Oligomer Free Splice-Junction Coating Composition

SR601 82 wt%

Photomer 3016 15 wt%

Lucirin TPO 3 wt%

Irganox 1035 0.5 pph

Dow Corning 190 0.5 pph

Sample L - Oligomer Free Splice-Junction Coating Composition

SR601 monomer 82 wt%

Photomer 3016 15 wt%

Lucirin TPO 2.25 wt%

ITX 0.75 wt%

Irganox 1035 0.5 pph

Sample M - Oligomer Free Splice-Junction Coating Composition

SR601 82 wt%

Photomer 3016 15 wt%

ITX 0.75 wt%

Irgacure 907 2.25 wt%

Sample N - Oligomer Free Splice-Junction Coating Composition

SR601 78.8 wt%

Photomer 3016 14.4 wt%

N-vinylcaprolactam 3.8 wt% Lucirin TPO 3 wt%

Irganox 1035 0.5 pph

Dow Corningl90 0.5 pph

Sample O - Oligomer Free Splice-Junction Coating Composition

SR601 80.4 wt%

Photomer 3016 14.7 wt%

N-vinylcaprolactam 2 wt%

Lucirin TPO 2.9 wt%

Irganox 1035 0.5 pph

Dow Corningl90 0.5 pph

Sample P - Oligomer Free Splice-Junction Coating Composition

SR601 monomer 75.5 wt%

Photomer 3016 13.8 wt%

N-vinylcaprolactam 9.2 wt%

Lucirin TPO 1.5 wt%

Irganox 1035 0.5 pph

Dow Corning 190 0.5 pph

Sample Q - Oligomer Free Splice-Junction Coating Composition

SR601 /Photomer 4028 ethoxylated (4)bisphenol A monomer 72 wt%

SR9038 ethoxylated (30)bisphenol A monomer 10 wt%

Photomer 3016 15 wt%

Lucirin TPO 1.5 wt%

Irgacure l84 1.5 wt%

Irganox 1035 0.5 pph

Sample R - Oligomer Free Splice-Junction Coating Composition

SR601 /Photomer 4028 ethoxylated (4) bisphenol A monomer 72 wt%

SR9038 ethoxylated (30) bisphenol A monomer 10 wt% Photomer 3016 15 wt%

Lucirin TPO 1.5 wt%

Irgacure l 84 1.5 wt%

Irganox 1035 0.5 pph

Dow Corning 190 1.0 pph

Sample S - Oligomer-Containing Splice-Junction Coating Composition (Comparative)

Photomer 6008 Urethane acrylate oligomer 20 wt%

Photomer 4028 Ethoxylated Bisphenol A diacrylate 77 wt%

Irgacure l 84 1.5 wt%

Irgacure 819 1.5 wt%

Irganox 1035 0.5 pph

BLANKOPHOR KLA Additive 0.1 pph

Example 2 - Tensile Properties of Splice- Junction Coatings

[0050] Oligomer free splice-junction coating compositions were used to make rod samples for tensile testing. Rods were prepared by injecting the curable compositions into Teflon® tubing having an inner diameter of about 0.025". The samples were cured using a Fusion D bulb at a dose of about 2.4 J/cm ² (measured over a wavelength range of 225-424 nm by a Light Bug model IL390 from International Light). After curing, the Teflon® tubing was stripped away. The cured rods were allowed to condition overnight at 23 °C and 50% relative humidity. Properties such as Young's modulus, tensile strength, and percent elongation at break were measured using a tensile testing instrument (e.g., a Sintech MTS Tensile Tester, or an Instron Universal Material Test System) on the defect-free secondary rod samples with a gauge length of 51 mm, and a test speed of 250 mm/min. The physical properties were determined as an average of at least five samples, with outlying data points or obviously defective samples being excluded from the average.

[0051] Results are shown in Table 1. The standard deviation values shown in Table 1 represent the determined standard deviation of the measured property in the column to the immediate left. As used herein, tensile properties of coatings, including primary, secondary, and splice-junction coatings were measured under these experimental parameters.

Table 1

Example 3 - Viscosity of Precursor Compositions

[0052] For testing viscosity, a Brookfield CAP2000 (with a spindle #4 cone and plate at a speed of 200 rpm at 25 °C, 400 rpm at 35 °C, and 800 rpm at 45 °C) viscometer was used. A volume of the composition (i.e., 124 μΐ) was placed on the center of the plate and then heated to either 25°C, 35°C, or 45°C. After reaching the desired temperature, viscosity readings were obtained from the viscometer. Viscosity results for the uncured liquid coatings are listed in Table 2.

Table 2

Example 4 - Joint Gap Failure

[0053] Joint gap failure tests were conducted for several splice-junction coating compositions. Splice-joint coating compositions were applied to spliced optical fibers. Constituent fibers were prepared for application of splice-junction coatings (i.e., recoating) by performing a window strip of about 10 mm in length on the optcal fiber to simulate a spliced region using a Miller strip tool. The constituent fiber used was targeted for a 195/250 μηι geometry (secondary coating thickness of about 27μηι). The secondary coating was the formulation of Sample R, above. The window-stripped region of the fiber was placed into the mold of a Vytran PTR-200 MRC recoater (250-270 micron mold size) and fiber ends were held in place using vacuum chucks. The splice-junction coating was injected into the mold and cured at maximum exposure (four 60W halogen bulbs on for 60 seconds) to ensure full cure. The sample was removed from the mold for testing with about 1 meter of fiber on either end of the recoated window-strip region.

[0054] To determine joint gap failure, a tensile load was applied as shown in FIG. 3. An MTS tensile tester equipped with a 28.1 lb. load cell was used to pull the samples to failure. Samples were mounted such that the window-strip region was under an axial load, with fiber ends secured on the mandrel mounted to the tensile tester load cell. The test was run at a test speed of 15 mm/min. Image capturing devices were mounted to continuously monitor the recoat-constituent fiber interface, recorded as a video. The force was also continuously monitored. Each interface was observed throughout testing. If a failure in adhesion between the recoat and constituent fiber interface was seen, the load at failure was recorded and is reported as the joint-gap stress. For samples where no interfacial failure was observed, the break stress is reported. No fewer than 6 and as many as 16 samples were tested for each recoat material. The average value of the sample set is reported with 95% confidence intervals in FIG. 5. FIG. 6 A shows a non-gapped optical fiber and FIG. 6B shows a gapped optical fiber.

[0055] Specifically, the bar graph of FIG. 5 is directed to the splice-junction coatings of Sample S (ref. no. 510), Sample Q (ref. no. 520), Sample A (ref. no. 530), Sample B (ref. no. 540), and Sample C (ref. no. 550). The bar on the left for each sample depicts the average tensile load when the spliced optical fiber failed (without gapping), and the bar the right depicts the average tensile load when gapping occured. No gapping occurred for Sample B and Sample C (no right side bar shown in FIG. 5). Sample S gapped 70% of the time, Sample Q gapped 16% of the time, and Sample A gapped only 13% of the time.

Example 5 - Butt-Splice Adhesion Strength [0056] Adhesion strength was measured by the "butt-splice adhesion strength test," described below. To prepare a sample for testing, a 10 inch piece of constituent fiber was cleaved in half. The resulting 5-inch fibers were placed into the mold of a Vytran PTR-200 MRC recoater, such that the cleaved ends were approximately 1 inch apart in the mold and the opposite ends were held in the vacuum v-groove of the fiber holding fixture (250-270 micron mold size). The desired splice-junction coating material was injected into the mold and cured at maximum exposure (four 10W halogen bulbs for 60 seconds) to ensure full cure. Referring to FIG. 4, the recoat section was then cut in half to obtain two specimens with half inch length of cured recoat 260 adhered to a 5-inch piece of constituent fiber that includes an optical fiber 110, primary coating 130 and secondary coatings 120. This was carried out 5 times to obtain 10 specimens. The constituent fiber used was targeted for a 195/250 μιη geometry (secondary coating thickness of about 27μηι). The composition of Sample R formulation was used as the secondary coating 120.

[0057] An MTS tensile tester equipped with an Interface 1.1 lb load cell and fiber gripping fixtures was used to pull the samples to failure. The test was run at a test speed of 5 mm/min. The peak force was measured and recorded. The average and standard deviation of the 10 specimens were reported as the adhesive strength of the recoat material to the constituent fiber. Table 3 reports experimnetal butt-adhesion strength values for various sample materials utilzed as the recoat material. Secondary coating materials are also listed. As Young's modulus of the secondary coating was increased, adhesive strength decreased, as is shown in the samples with recoat materials of Sample S. However, adhesive strength was increased with incorporation of specific recoat compositions such as Sample A and Sample Q.

Table 3

[0058] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.