WO2018158739A1

WO2018158739A1 - Systems and methods for curing coatings on optical fibers

Info

Publication number: WO2018158739A1
Application number: PCT/IB2018/051340
Authority: WO
Inventors: Zhang DONGNAN
Original assignee: Shanghai Jenwhee Technology, Inc.
Priority date: 2017-03-03
Filing date: 2018-03-02
Publication date: 2018-09-07
Also published as: CN108686907A

Abstract

Curing lamp systems, LED bonding pad assemblies (1), and methods of producing coated optical fibers utilizing such curing lamp systems and/or LED bonding pad assemblies (1) wherein the power input per line is maintained below certain values and/or the energy density is maintained above certain values are described and claimed herein. Such curing lamps systems and their method of use include a plurality of light emitting diodes configured to yield the production of commercially viable coated optical fibers by maximizing radiant intensity while minimizing the power input. Also described and claimed are LED bonding pad assemblies (1) including at least one row (6) of non-contacting consecutive pads (12, 14), wherein at least one pad (12, 14) includes an elongate portion (26, 28) in various efficient configurations.

Description

Title: SYSTEMS AND METHODS FOR CURING COATINGS ON OPTICAL FIBERS Technical Field

Aspects of the disclosure generally relate to systems and methods for curing coatings on optical fibers. In particular, various aspects of the disclosure relate to devices, systems, and methods that use light emitting diodes (LEDs) to cure radiation curable coatings on optical fibers.

Cross-reference To Related Applications

This application claims priority to U.S. Provisional Application No.

62/466,625, filed March 3, 2017, and Chinese National Patent Application No. 201710230624.6, filed April 10, 2017, which are hereby incorporated by reference in its entirety as if full set forth herein.

Background

[0001] Optical fibers have been used in a variety of applications and have some advantages over other media. For example, data can be transmitted over optical fibers at a higher data rate than over wires. Optical fibers are also lighter and more flexible than wires. Thus, optical fibers are often used in the telecommunication industry for data transmission. However, if left unprotected, optical fibers are unsuitable for field use because of the fragility of the thin glass strand across which optical signals are

transmitted. In addition to their susceptibility to physical damage, uncoated optical fibers would also be negatively impacted by moisture contact. As a result, surface coatings are typically applied to optical fibers for protection and to ensure a high-level of performance.

[0002] Optical fibers are frequently coated with two or more superposed radiation-curable coatings immediately after the fiber is produced by drawing. The coating which directly contacts the optical fiber is called the "inner primary coating" and an overlaying coating is called the "outer primary coating." In some references, the inner primary coating is also called simply the "primary coating" and the outer primary coating is called a "secondary coating." Inner primary coatings are typically formulated to possess a significantly lower modulus than secondary coatings.

[0003] The relatively soft inner primary coating provides resistance to microbending which results in added attenuation of the signal transmission of the coated optical fiber and is therefore undesirable. Microbends are microscopic curvatures in the optical fiber involving local axial

displacements of a few micrometers and spatial wavelengths of a few millimeters. Microbends can be induced by thermal stresses and/or mechanical lateral forces. Coatings can provide lateral force protection that protect the optical fiber from microbending, but as coating thickness decreases the amount of protection provided decreases. The relationship between coatings and protection from lateral stress that leads to

microbending is discussed, for example, in D. Gloge, "Optical -fiber packaging and its influence on fiber straightness and loss", Bell System Technical Journal, Vol. 54, 2, 245 (1975); W. B. Gardner, "Microbending Loss in Optical Fibers", Bell System Technical Journal, Vol. 54, No. 2, p. 457 (1975); J. Baldauf, "Relationship of Mechanical Characteristics of Dual

Coated Single Mode Optical Fibers and Microbending Loss", IEICE Trans. Commun., Vol. E76-B, No. 4, 352 (1993); and K. Kobayashi, "Study of Microbending Loss in Thin Coated Fibers and Fiber Ribbons", IWCS, 386 (1993). The harder outer Primary coating, that is, the Secondary coating, provides resistance to handling forces such as those encountered when the coated fiber is ribboned and/or cabled.

[0004] Optical fiber secondary coating compositions generally comprise, before cure, a mixture of ethylenically-unsaturated compounds, often consisting of one or more oligomers dissolved or dispersed in liquid ethylenically-unsaturated diluents and photoinitiators. The coating composition is typically applied to the optical fiber in liquid form and then exposed to actinic radiation to effect cure.

[0005] Primary coatings preferably possess a higher refractive index than the cladding of the associated optical fiber, in order to allow them to strip errant optical signals away from the core of the optical fiber. Primary coatings should maintain adequate adhesion to the glass fiber during thermal and hydrolytic aging, yet (if needed) is capable of being strippable therefrom for splicing purposes. The primary coating typically has a thickness in the range of 20-50 μιη (e.g., about 25 or 32.5 μιη), thinner thickness in the range of 15-25 μιη for 200 μιη fibers.

[0006] The primary coating preferably has a thickness that is less than about 40 μιη. The primary coating is typically applied to the glass fiber and subsequently cured. Various additives that enhance one or more properties of the primary coating can also be present, including antioxidants, adhesion promoters, PAG compounds, photosensitizers, carrier surfactants, tackifiers, catalysts, stabilizers, surface agents, and optical brighteners.

[0007] Secondary coatings are the outer coating. The secondary coating is, for example, the polymerization product of a coating composition whose molecules become highly crosslinked when polymerized. In the embodiments described herein the secondary coating has a high in situ modulus (e.g., greater than about 800 MPa at 25 °C, more preferably from between about 1 GPa to about 3 GPa) and a high T_g (e.g., greater than about 50 °C). The in situ secondary modulus is preferably greater than about 1000 MPa.

Secondary coatings often possess a thickness that is less than about 40 μιη.

[0008] Fiber optic coatings, including the primary and secondary layers, are applied using one of two processes: wet-on-wet (WOW) and wet-on-dry (WOD). In the WOD process, the fiber passes first through a primary coating application, which is cured via exposure to ultraviolet (UV) radiation, then passes through a secondary coating application, which is subsequently cured by similar means. In the WOW process, the fiber passes through both the primary and secondary coating applications, whereupon the fiber proceeds to UV or UV-LED curing. In a wet-on-wet process, the curing lamps between primary and secondary coating application are omitted.

[0009] Radiant light energy is crucially used in the manufacture of radiation curable coatings for optical fibers. In particular, curing processes use radiant energy from UV lamps to cure optical fiber coatings. For decades, UV lamps with broadband mercury spectra were preferred in the industry, due to their high intensity and broad emission spectrum to ensure rapid and full cure of such radiation curable coatings. However, such UV- emitting "electrodeless" microwave lamps tend to be bulky, noisy, and exhibit poor energy efficiency.

[0010] Recently, however, curing systems utilizing UV-LED (light emitting diodes) lamps have begun to increase in popularity. LED-based curing systems offer substantial benefits over conventional mercury lamps. Advantages include reduced power consumption, a more compact design, instant on-off capability, longer lamp life, no substrate heating, reduced maintenance, and more environmental sustainability.

[0011] However, several drawbacks have limited the suitability and competitiveness of optical fiber coating processes utilizing LED-based curing systems. First, LED lamps typically produce less radiant energy density than conventional mercury lamps. Several LED lamps may be required to apply the requisite radiant energy to a coating where one or two

conventional lamps may suffice. Second, LED-based light sources tend to emit a shorter range of wavelengths than conventional lamps. A broader range of wavelengths allows the radiant energy to penetrate the coating at different depths and thereby yield a more uniform bulk cure. Increasing the radiant energy applied to the coating can compensate for having limited range of wavelengths but also results in increasing energy costs through increased power input requirements. [0012] The radiation curable coatings may exhibit multiple undesirable effects resulting from insufficient surface or bulk cure. For example, undercured primary coatings may exhibit poor coating adhesion on fiber with resulting lower fiber strip force (SF), weak mechanical properties (such as weak tensile strength and cavitation strength), and unstable

microbending attenuation levels, to name a few.

[0013] Similarly, undercured secondary coatings also results in multiple undesirable effects. For example, undercuring may cause a lower modulus of the protection layer on the fiber, thus resulting in poor mechanical protection. Undercured secondary coatings may readily deteriorate at ambient storage conditions because of the low chemical or moisture protection they afford.

[0014] When the percent surface cure of secondary coatings is poor, particularly when the surface cure degree is lower than even about 90 %, a tacky or high friction surface of the coating is generated. This creates winding and handling problems of the fiber and potentially leads to broken fibers during the cabling process.

[0015] Recent evolutionary improvements in process design and coating formulation have somewhat facilitated the historic drawbacks associated with an all-LED solution. However, even with these higher performance characteristics UV LED lamps do not consistently impart improved cure characteristics into photocurable compositions.

[0016] Along with the increased demand of optical fiber and market competition, modern optical fiber manufacturing requires the coating material able to be drawn at even higher drawing speeds, up to 2500 m/min or more. All else being equal, as so-called "draw speeds" continue to increase, the unit energy per time imparted upon the rapidly descending radiation curable coating proportionally decreases.

[0017] Radiation curable coatings suitable for competitive manufacturing processes require exposure to sufficient radiant energy while optical fibers are drawn at fast rates of speed through a curing lamp. The speed at which optical fibers can be cured during production depends the curing lamp being able to apply sufficient radiant energy to the radiation curable coating. However, increasing radiant energy output of LED-based lamps can cause problems, such as higher energy costs and increased heat generation that reduce the efficiency and service life of the lamp. Thus, there exists a need for an improved device, system, and method for curing optical fibers using LED-based curing systems. Brief Summary

[0018] The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosure. The summary is not an extensive overview of the disclosure. It is neither intended to identify key or critical elements of the disclosure nor to delineate the scope of the disclosure. The following summary merely presents some concepts of the disclosure in a simplified form as a prelude to the description below.

[0019] Aspects of the disclosure concern devices, systems, and methods relating to applying surface coatings on optical fiber using light emitting diodes.

[0020] In an embodiment, a device comprises a curing lamp system including more than one light emitting diodes (LEDs), the LEDs configured to apply radiant output to a surface of an optical fiber while the optical fiber is drawn through an exposure area at a predetermined rate of speed. The surface has a radiation curable coating that further includes at least an ethylenically-unsaturated compound. Further, the LEDs are configured such that, at the predetermined rate of speed of about 2500 meters per minute, a power input per line of the plurality of light emitting diodes is from about 3.5 kW to about 25 kW, or from about 4 kW to about 20 kW, or from about 5 kW to about 15 kW, or from about 6 kW to about 10 kW, or from about 5 kW to about 7 kW. In such an embodiment, the radiant output applied to the surface yields a coated optical fiber with a cured coating having a reacted acrylate unsaturation of at least about 90 %, more preferably at least about 95 %, and an in-situ modulus from about 1 GPa to about 3 GPa.

[0021] In a second embodiment, a method for producing a coated optical fiber includes the steps of coating an optical fiber with a radiation curable coating (itself further including an ethylenically-unsaturated compound), drawing the optical fiber through an exposure area of a curing lamp system including more than one light emitting diode at a predetermined rate of speed, and using the plurality of light emitting diodes to apply radiant output to a surface of the radiation curable coating. In such an embodiment, the power input per line of the plurality of hght emitting diodes is less than about 25 kW and the radiant output applied to the surface yields a coated optical fiber with a cured coating having a reacted acrylate unsaturation of at least about 90 %, more preferably at least about 95 %, and a modulus of between about 1 GPa to about 3 GPa.

[0022] In a third embodiment, a method for producing a coated optical fiber includes the steps of coating an optical fiber with a radiation curable secondary coating (itself further including an ethylenically-unsaturated compound), drawing the optical fiber through an exposure area of a curing lamp system having more than one hght emitting diode at a predetermined rate of speed, and applying, using the light emitting diodes, radiant output to a surface of the radiation curable secondary coating. In such an

embodiment, the light emitting diodes are configured such that an energy density of the radiant output at the radiation curable secondary coating is equal to or greater than about 26 W/cm².

[0023] In a fourth embodiment, a device comprises an LED bonding pad assembly including a row of conductive pads configured for coupling a row of hght emitting diode (LED) dies having a plurality of consecutive pads. The plurality of consecutive pads include a first pad and a second pad with an elongate portion. In such an embodiment, the elongate portion protrudes from the second pad. Furthermore, in such an embodiment, the first pad is consecutive with the second pad, and the first pad does not directly contact the second pad.

[0024] In a fifth embodiment, an LED bonding pad assembly includes a row of conductive pads configured for coupling two rows of light emitting diode (LED) dies and having at least two consecutive pads. In such an embodiment, the consecutive pads themselves further have a first pad with a first notch in a front edge and a second pad with an elongate portion extending from a rear edge of the second pad. Furthermore, in such an embodiment, a distal end of the elongate portion extends within the first notch of the first pad, the first pad is consecutive with the second pad, and the first pad does not contact the second pad.

[0025] Further embodiments of the invention are described below.

Brief Description of the Drawings

[0026] A more complete understanding of the present disclosure and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features, and wherein:

[0027] FIG. 1A illustrates an embodiment of a row of bonding pads configured for configuring a row of LED dies in accordance with aspects of the present disclosure;

[0028] FIG. IB illustrates a top view of the bonding pads shown in FIG. 1A in accordance with aspects of the present disclosure;

[0029] FIG. 1C illustrates an embodiment of a row of LED dies coupled to the bonding pads shown in FIG. 1A in accordance with aspects of the present disclosure; [0030] FIG. ID illustrates a top view of an embodiment of a row of LED dies coupled to the bonding pads shown in FIG. 1A in accordance with aspects of the present disclosure;

[0031] FIG. 2A illustrates an embodiment of a row of bonding pads configured for coupling two rows of LED dies in accordance with aspects of the present disclosure;

[0032] FIG. 2B illustrates a top view of the bonding pads shown in FIG. 2A in accordance with aspects of the present disclosure;

[0033] FIG. 2C illustrates an embodiment of two rows of LED dies coupled to the row of bonding pads shown in FIG. 2A in accordance with aspects of the present disclosure;

[0034] FIG. 2D illustrates a top view of an embodiment of two rows of LED dies coupled to the row of bonding pads shown in FIG. 2A in

accordance with aspects of the present disclosure;

[0035] FIG. 3A illustrates an embodiment of a two row configuration of bonding pads for configuring four rows of LED dies in accordance with aspects of the present disclosure;

[0036] FIG. 3B illustrates a top view of the bonding pads shown in FIG. 3A in accordance with aspects of the present disclosure;

[0037] FIG. 3C illustrates an embodiment of four rows of LED dies coupled to the two rows of bonding pads shown in FIG. 3A in accordance with aspects of the present disclosure;

[0038] FIG. 3D illustrates a top view of an embodiment of four rows of LED dies coupled to the two rows of bonding pads shown in FIG. 3A in accordance with aspects of the present disclosure;

[0039] FIG. 3E illustrates an embodiment of a two row configuration of bonding pads for configuring six rows of LED dies in accordance with aspects of the present disclosure; [0040] FIG. 3F illustrates a top view of an embodiment of six rows of LED dies coupled to the two rows of bonding pads shown in FIG. 3E in

accordance with aspects of the present disclosure;

[0041] FIG. 4A illustrates an embodiment of a light source module in accordance with aspects of the present disclosure;

[0042] FIG. 4B illustrates an embodiment of a light source module in accordance with aspects of the present disclosure;

[0043] FIG. 5 illustrates an embodiment of a light source module and a corresponding light source housing in accordance with aspects of the present disclosure;

[0044] FIG. 6A is a front view of a light source module coupled to a corresponding light source housing in accordance with aspects of the present disclosure;

[0045] FIG. 6B is a side view of a light source module coupled to a corresponding light source housing in accordance with aspects of the present disclosure;

[0046] FIG. 7A is a cross-sectional view taken along line 7A of FIG. 6A showing aspects of a light source module coupled to a light source housing in accordance with aspects of the present disclosure;

[0047] FIG. 7B is a cross-sectional view taken along line 7B of FIG. 6B showing aspects of a light source module coupled to a light source housing in accordance with aspects of the present disclosure;

[0048] FIG. 8A is a top view of a curing lamp assembly in accordance with aspects of the present disclosure;

[0049] FIG. 8B is a top view of a curing lamp assembly in accordance with aspects of the present disclosure; and

[0050] FIG. 8C is a front view of a curing lamp assembly in accordance with aspects of the present disclosure. Detailed Description

[0051] In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration, various embodiments of the disclosure that may be practiced. It is to be understood that other embodiments may be utilized.

[0052] Several alternative embodiments and examples are described and illustrated herein. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. It is understood that the inventions may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. The terms "first," "second," etc., as used herein, are intended for illustrative purposes only and do not limit the embodiments in any way. In particular, these terms do not imply any order or position of the components modified by such terms. Terms such as "top," "bottom," etc., are relative terms that describe orientation relative to each other, but not imply orientation relative to any external object unless explicitly provided.

Additionally, the term "plurality," as used herein, indicates any number greater than one, either disjunctively or conjunctively, as necessary, up to an infinite number. Accordingly, while specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the inventions and aspects of the inventions described herein.

[0053] As used herein, "a standard processing protocol" means a standard method of manufacturing a coated optical fiber known to those of ordinary skill in the art to which this invention applies, including a process that is carried out at or near room temperature, and at about 50 % RH and standard atmospheric pressure; and wherein the "atmospheric" conditions inside quartz tube include the introduction of N2 at a flow rate of between 10-20 1/min.

[0054] In reference to FIGS. 1A through 3F, aspects of the present disclosure pertain to assemblies configured for arrangement of arrays of chip-on-board LEDs and components of such assemblies. As used herein, a chip-on-board (COB) LED means a plurality of light emitting diodes packaged together in a single chip. A single COB LED can be referred to herein as an LED die.

[0055] In accordance with examples disclosed herein, an assembly 1 can include a configuration of conductive bonding pads 2 that provides for close positioning of consecutive LED dies 4 placed on the bonding pads 2. In some examples, the bonding pads can be mounted on a non-conductive substrate 8 and be made of a suitable conductive material. According to multiple examples disclosed herein, the bonding pads 2 are arranged in a row 6 mounted on the substrate 8. A bonding pad can be of various shapes, including square, rectangular, or other shape.

[0056] A row 6 of conductive bonding pads 2 can include a plurality of consecutive pads having configurations and features, includes those described by example in the present disclosure. For example, for ease of reference, a pair of consecutive pads can include a first pad 12 and a second pad 14. In certain examples, a first pad 12 and a second pad 14 can each can include a front edge 16, read edge 18, first lateral side 20, and second lateral side 22. In certain examples, the first pad 12 and the second pad 14 are not in direct contact with each other. In certain examples, the first pad 12 and the second pad 14 can be positioned such that a front edge 16 of the first pad 12 is spaced from the rear edge 18 of the second pad 14 a distance ranging between about 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm.

[0057] Referring to examples illustrated in FIGS. 1A- 1D, the second pad 14 can include an elongate portion 26 that extends along at least a portion of the first lateral side 20 of the first pad 12. In addition, for example, the second pad 14 can include a second elongate portion 28 that extends along at least a portion of the second lateral side 22 of the first pad 14. In other examples, an elongate portion 26 can extend in a direction perpendicular to the lateral side 20 of the pad. As described in examples below, the elongate portions 26, 28 can be configured to receive wire bonding from LED dies positioned on the preceding pad 12.

[0058] Referring to examples illustrated in FIGS. 1C and ID, a plurality of LED dies 4 are coupled to the row 6 of conductive bonding pads 2 to form an array of LED dies in the form of a row 30. In certain examples, the LED dies 4 include at least one electrode on the bottom surface of the die and an at least one electrode on the top surface of the die. In an embodiment, an electrode on the bottom of the die can be the anode and an electrode on the top of the die can be cathode. In another embodiment, an electrode on the bottom of the die can be the cathode and an electrode on the top can be the anode.

[0059] A row 30 of LED dies 4 can include a plurality of consecutive dies having configurations and features in accordance with the examples present disclosure. For ease of reference, a pair of consecutive dies can include a first die 32 and a second die 34. In certain examples, a first die and a second die can each include a die front edge 42, die read edge 44, die first lateral side 46, and die second lateral side 48. In certain examples, a first die 32 can be electrically coupled to a first pad 12 by, for example, using a conductive adhesive or solder to couple the bottom electrode of the first die to the first pad 12. Similarly, in certain examples, a second die 34 can be electrically coupled to a second pad 14 in the same manner. In accordance with aspects of the present disclosure, the first die 32 can be electrically coupled to the second pad 14 by connecting a top electrode 36 of the first die 32 to an elongate portion 26 of the second pad 14 with a conductive element. In examples disclosed herein, the top electrode 36 of the first die 32 is bonded with conductive wire 38 to the elongate portion 26 of the second pad 14 to thereby connect the first die 32 and second die 34 in a series circuit. In other embodiments, a second top electrode 40 of the first die 32 is bonded with conductive wire 38 to the second elongate portion 28 of the second pad 14. In an example, the first die 32 and second die 3 and corresponding pads 12, 14 are positioned in substantially the same plane.

[0060] The example arrangement of conductive bonding pads and dies shown and described above allow the dies to be positioned closer to each other than they otherwise could be positioned using conventional bonding arrangements. In accordance with aspects of the present disclosure, the first die 32 and the second die 34 can be positioned such that a front edge 42 of the first die 32 is spaced from the rear edge 44 of the second die 34 a distance 50 ranging between 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm. As discussed below, decreasing distance between consecutive dies in accordance with aspects of the present disclosure results in an increase of the energy density per unit area applied to a workpiece. Such increase can improve performance and efficiency of unit operations utilizing radiant light energy, as described below by example in reference to using light emitting diodes in a curing lamp assembly for curing radiation curable coatings of optical fiber.

[0061] Referring to FIGS. 2A-3F, conductive bonding pads of the present disclosure can be configured to form arrays having a plurality of rows of LED dies. Referring to FIGS. 2A-3D, a first pad 12 can include a notch 52 defined in a front edge 16 of the pad 12. The notch 52 can divide the pad 12 into a first right portion 54 and a first left portion 56 positioned on opposing sides of the notch 52. A second pad 14 can be similarly configured to include a notch 52 dividing the second pad 14 into a second right portion 58 and a second left portion 60. The second pad 14 can include an elongate portion 26 extending from a rear edge 18 of the pad 14. A distal end 62 of the elongate portion can extend within the notch 50 of the first pad 12. As described above, the first pad 12 and the second pad 14 can be positioned such that a front edge 16 of the first pad 12 is spaced from the rear edge 18 of the second pad 14 a distance ranging between about 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm. A length 64 of pad 14 from a front edge to the distal end 62 can be about 1.14 mm.

[0062] Referring to FIGS. 2A-2D, in an embodiment, LED dies can be bonded to the first right and left portions 54, 56 and the second right and left portions 58, 60 to form two rows of LED dies. The dies can be bonded to the pads in a manner described above. In addition, an electrode from each of the dies positioned on the right and left portions 54, 56 can be electrically coupled to the elongate portion 26. The electrical coupling can be completed by wire bonding. Referring to FIGS. 3A-3D, two rows of conductive bonding pads having the features as shown and described in reference to FIGS.

2A-2D can be used to form an array of four rows of LED dies.

[0063] Referring to FIGS. 3E and 3F, in an embodiment, in the first row of pads 6 a first pad 12 can include a first notch 52 and a second notch 66 defined in a front edge 16 of pad 12. The notches 52, 66 can be positioned to divide the pad 12 into a first right portion 54, a first middle portion 68, and a first left portion 56. A second pad 14 can be similarly configured to include notches 52, 66 which divide the pad 14 into a second right portion 58, a second middle portion 70, and a second left portion 60. The second pad 14 can include a first elongate portion 26 that extends within the first notch 52 of the first pad 12 and a second elongate portion 72 that extends within the second notch 66 of the first pad 12. LED dies can be bonded to the first right, middle, and left portions 54, 68, 56 of pad 12 and the second right, middle, and left portions 58, 70, 60 of pad 14 to form three rows of LED dies. The dies can be bonded to the pads in a manner described above. In addition, an electrode from each of the dies positioned on the right and left portions 54, 56 can be electrically coupled to the elongate portions 26 and 72 respectively while an electrode from the die positioned on middle portion 68 can be coupled to elongate portion 26 and/or 27. The electrical coupling can be completed by wire bonding. Including a second row of pads 74 having the features described above can be used to form an array of six rows of LED dies as shown in FIG. 3F.

[0064] Aspects of the configurations of conductive bonding pads and arrays of LED dies described above can be incorporated in industrial lamps used for applying radiant light energy to a surface of a workpiece. In an embodiment, such lamps can be used to cure radiation curable coatings applied to optical fiber. Example aspects of a curing lamp assembly and examples of features thereof are disclosed herein in reference to FIGS.

4A-8C below.

[0065] Referring to FIGS. 4A and 4B, examples of a light source module 76 for use in a curing lamp is disclosed. The light source module can be configured to include array of LEDs 78 and an optical element 80 configured to focus radiant light energy emitted from the LEDs. The array of LEDs can be configured in the form of the arrays of LED dies disclosed above. The light source module 76 can include an outer shell configured for securing the optical element 80 and sealing the array 78 within the light source module 76. The light source module 76 can also include a heat exchanger 84. In an embodiment, the heat exchanger is a liquid cooled unit. Liquid coolant inlet 86 and outlet ports 88 can be included on the module 76. The light source module can also include an electrical connection port 90 for connection to a power supply port 92. [0066] Referring to FIG. 5, examples of a light source housing 94 and corresponding light source module 76 is disclosed. The light source module 76 can be detachably coupled to the light source housing 94. The light source module 76 can be secured to the housing 94 by, for example, screws 96. In certain examples, the combination of light source module 76 and housing 94 can be referred to as a lamp 96. In certain examples, one or more lamps configured to apply radiant output from the lamp to a workpiece can be referred to as a lamp assembly. Radiant output as used herein means radiant light energy emitted from a light source and focused to apply the radiant light energy to a workpiece.

[0067] Referring to FIG. 6 A, a front view of an example lamp 96 is disclosed. Referring to FIG. 6B a side view of an example lamp 96 is disclosed. FIG. 6B also illustrates an example exposure area 98. As used herein, an exposure area means the area to which light from a light source is focused in order to apply radiant output to a surface of a workpiece. The shape and size of the exposure area can be adjusted for the purposes of the application. In the context of curing of optical fibers, the exposure area is generally focused to cover a width greater than the width of an optical fiber 102 over a length of the fiber as the fiber is drawn in the longitudinal direction. An example of the longitudinal direction 100 as used herein is shown in FIG. 6B. In optical fiber coating processes, the fiber is typically surrounded by a glass tube (not shown). In an embodiment, the glass tube possesses a diameter of 20 mm or 25 mm.

[0068] Referring to FIGS. 7A and 7B, cross sectional views showing interior features of an example lamp 96 is disclosed. In an embodiment, an optical element includes a first lens 104 and a second lens 106. In an embodiment, the first lens 104 can be a plano-convex lens oriented such that the planar surface of the plano-convex lens is positioned proximate the array 78. In an embodiment, the second lens 106 can be a bi-convex lens. In an embodiment, either of the first lens or the second lens can be a Fresnel lens. In an embodiment, the lenses of the optical element can extend longitudinally over the length the array 78. In an embodiment, the lamp can include a rotational structure 110 configured to permit the lamp to rotate about an axis along a longitudinal direction, n addition, in an embodiment, the light source module and housing of a lamp can be configured to allow the module, housing, and/or lamp to be adjustable in a direction transverse to a longitudinal direction for increasing or decreasing a distance between the optical element and the workpiece.

[0069] Referring to FIGS. 8A-8C, an example of a curing lamp assembly is shown including three lamps 96. In other examples, a curing lamp assembly can include one or more lamps. The modules, housings, and/or lamps of the assembly can be spaced radially from and symmetrically around a central longitudinal axis of the exposure area. In FIG. 8A, the assembly is in the closed position and configured to apply radiant output to a surface of an optical fiber while the optical fiber is drawn through an exposure area. In FIGS. 8B and 8C, the assembly is in an open position, which allows access to the workpiece and/or light source modules for repairs and/or swapping of the modules. Light source modules may be swapped for various purposes, including providing light source modules with different optical properties to suit a particular application. One or more assemblies shown in FIGS. 8A-8C can be employed on a production line manufacturing coated optical fiber.

[0070] Table 1 below discloses performance data obtain for a curing lamp assembly in accordance with the present disclosure. Power input per line as used herein in the context of curing coatings of optical fibers means: power consumed by an identified component of a curing lamp assembly during operation of the curing lamp assembly on a production line manufacturing coated optical fiber. Irradiance at target means the energy density per area measured at the surface of the coated fiber. RAU% means percentage of reacted acrylate unsaturation in the secondary coating applied to the optical fiber. Modulus means modulus of elasticity of the coated fiber. TABLE 1

Number of Lamps 6

Drawing Speed (meters/min) 2500

Lamp Power Input Per Line Hour (kW) 1.2

Lamp Power Input Per Line Hour (kW) 7.2

Cooling System Power Input Per Line Hour

3.0

(kW)

Total Power Consumption Per Line (kW) 10.20

Irradiance at Target (W/cm²) > 30

RAU% of Coated Fiber 98 %

Modulus of Coated Fiber 1-3 GPa

[0071] In an embodiment, the coated fiber produced by the curing lamps system of the present invention, or by methods of curing using curing lamp systems according to the present invention, possesses a %RAU above about 80 %, more preferably above about 85 %, more preferably above about 90 %, more preferably above about 99 %, when tested according to an LED DSC method.

[0072] A method of LED-DSC is described below using a photo-DSC equipped with a LED lamp to cure coating samples for cure degree measurements. As coating processes utilizing monochromatic light sources (such as LEDs) are more prone to oxygen inhibition, the surface cure degree is particularly sensitive to the O2 content in the N2 purged air condition during the cure. The commonly used conveyer belt equipment for preparing regular film samples suffers from large variations on surface cure due to the difficulty of precisely controlling the O2 content in the associated open environment. The LED-DSC method as described below utilizing a photo-DSC equipment is superior in this respect in that it provides much better control with regards to atmospheric conditions in the sample chamber. This results in coating surface cure degree data wither levels of accuracy, repeatability and reproducibility.

Preparation of the Cured Film Samples from the LED-DSC Unit

[0073] From about 1.3 to about 1.7 mg of each sample was dropped at the center of a T130522 DSC Tzero pan. The pan was then moved onto the sample plate of a Q2000 DSC unit from TA Instruments. A lamp holder for the DSC unit was customized and built according to well-known methods from Somos^® NanoTool stereolithography resin in order to ensure proper fit of an Accucure ULM-2-395 model LED lamp from Digital Light Labs. The included LED external shutter was automatically triggered by connecting the "Event" outlet of the DSC to an Accure Photo Rheometer Ultraviolet Illumination & Measurement System.

[0074] Each liquid sample was gradually and uniformly wetted out to establish a film with a thickness of about 60 microns in the pan. These films were then cured by the LED lamp. The intensity of light and exposure time could be adjusted by the Accure Photo Rheometer Ultraviolet Illumination & Measurement System, while the curing temperature and N2 flow rate could be adjusted by the DSC unit. Under an N2 flow rate of approximately 50 ml/min, each sample was equilibrated at about 50 °C and isothermalized for approximately 5 mins, after which a 395 nm LED lamp with an intensity of about 50 mW/cm² was illuminated and remained on for about 6 seconds. The cured film was then carefully peeled off from the bottom of Tzero pan. Finally, the surface and bottom of the cured film were measured and the conversion was calculated as per the FTIR test method described herein.

[0075] Measurement of Surface and Bottom Cure of Film Samples by FTIR: The surface of the cured film was measured using a Nicolet 4700 FTIR Spectrometer from Thermo Electron Corp. Measurements were taken at the area under the reference peak from about 1485 cm ¹ to about 1570 cm⁴; the acrylate peak at 1407 cm⁴ was also measured. Peak area is determined using the baseline technique where a baseline is chosen to be tangent to absorbance minima on either side of the peak. The area under the peak and above the baseline is then determined. The integration limits for liquid and the cured sample are not identical but are similar, especially for the reference peak.

[0076] The ratio of the acrylate peak area to the reference peak were determined for both the liquid and the cured samples. Degree of cure, expressed as percent reacted acrylate unsaturation (%RAU), is calculated from the equation below:

% RAU = [(R_L - RF) X 100] / RL

where RL is the area ratio of the liquid sample and RF is the area ratio of the cured film.

[0077] It should be noted that the %RAU of the film samples cured by the LED-DSC method is expected to be substantially lower than the actual secondary coating surface cure on fiber under typical fiber drawing conditions cured by LED lamps. First, this occurs because the LED lamps utilized in actual draw towers for coating optical fibers possess a

significantly higher output intensity than the one used on LED-DSC unit. Also, the LED lamps which are custom-designed for fiber drawing processes are highly focused on small areas of an optical fiber therefore providing much higher irradiance than the lamp condition used in LED-DSC.

However, the relative trend of %RAU results of the series of film samples are expected to correlate well with the in-situ cure degree of coatings on fiber. The LED-DSC method is therefore a reliable laboratory test that can be used as an accurate proxy to predict the relative trend of secondary coating cure on fiber by typical fiber drawing processes equipped with LED lamps. In an embodiment, the lamp curing systems of the present invention are configured to yield a coated optical fiber with a coating possessing an in-situ modulus from about 1 GPa to about 3 GPa. Measurement of in-situ modulus.

[0078] From the coated fiber sample, strip about 2-3 cm length of coating tube as a complete piece out of the glass, where the coating tube contains both primary coating layer and secondary coating layer. This can be done by dipping the fiber together with the stripping tool clamping on the fiber into liquid N2; when taking the fiber out of the liquid N2 immediately strip the coating in a very rapid motion. The coating system should detach from the glass and come out as a whole piece of a hollow coating tube.

[0079] A Dynamic Mechanical Tester, such as RSA-G2 Solids Analyzer from TA Instruments, is used to measure the storage modulus of the coating tube at room condition at ~ 23 °C. Because secondary coating (at GPa level) is much higher modulus than the primary coating (at MPa level), the contribution from the primary coating layer can be ignored. Set the gap between the two grips to be the desired sample length, for example 11 mm used in our test. Select 'cylindrical' as the geometry type. Enter 11 mm for the sample length. Enter 0.16 mm for the diameter. This is calculated through transforming the hollow cylinder shape of the secondary coating layer into solid cylinder. If using the standard fiber geometry

62.5 / 92.5 / 122.5 μιη radius for glass / primary / secondary, the diameter for the solid cylinder is calculated as 2 x 122.5² — 92.5² = 161 μηι. Select

'Dynamic time sweep test'. Set the frequency to be 1.0 rad/sec, the strain to be 0.05 %, duration is 70 s, sampling rate is 0.1 pts/sec.

[0080] Load the coating tube sample vertically in the center between the two grips, tighten the bottom grip, then tighten the top grip while stretching the coating tube straight. The stretching force should be just sufficient to remove any slack however not to over stretch the coating sample. Set the initial axial force to be 10 g, then start the test. After test completed, analyze the data by taking average of all data points of the storage modulus E'. Because the contribution of the primary coating can be ignored, the resulted storage modulus E' is considered as the secondary coating in-situ modulus at RT. The procedure is repeated for at least three specimens. The average E' is then adjusted for actual geometry by multiplying a correction factor. The correction factor uses the actual fiber geometry measured by coating geometry tester such as 2402 Dark Field Coating Geometry System by Photon Kinetics. The correction factor is calculated as

(122.5² - 92.5²)/(R%^ctual - R*^ctual). The corrected E' is reported as the final result of the secondary in-situ modulus of this coated fiber sample.

Measurement of modulus ratio.

[0081] Take a section of coated fiber sample, such as lm length. Place on a glass plate and post cure under a UV processor, such as Convey Fusion System Model DRS-120N2Q with EPIQ 6000 11 mm 600 W/in microwave D lamp from Heraeus Noblelight American LLC, under N2 flow rate of 8 ft³/minute and cure dose of 1 J/cm². Under such condition or other equivalent conditions, the coating on fiber should reach full cure of 100 % RAU. The secondary coating in-situ modulus of this post cured fiber is measured according to the test method described in previous section, as E'max. Secondary coating modulus ratio R is defined as the ratio of secondary coating in-situ modulus of the original fiber E' to secondary coating in-situ modulus of the post cured fiber E'_max. R represents the level of bulk cure of the secondary coating on fiber. In an embodiment, lamp curing systems of the present invention are configured to yield a coated optical fiber with a cured coating having a modulus ratio of between about 0.5 to about 2, more preferably between about 0.75 to about 1.5, more preferably between about 0.9 to about 1.1, or between about 0.85 to about 0.95.

Measurement of Power Input

[0082] Power input was measured using methods well-known to those of ordinary skill in the art to which this invention applies. Measurement of Radiant Intensity

[0083] In general, the radiant intensity data is dependent upon two primary factors: distance from the light source surface and sample area size. Radiant intensity was measured using methods well-known to those of ordinary skill in the art to which this invention applies. Measurements are taken using a professional intensity meter, relying on peak intensity or have-wave integral energy measurement settings.

[0084] Curing lamp systems according to the present invention are configured to apply radiant output to a surface of an optical fiber while the optical fiber is drawn through an exposure area at a predetermined rate of speed, wherein the surface includes a radiation curable coating. In an embodiment, the radiation curable coating is specifically formulated or optimized for LED-based curing systems. Radiation curable optical fiber coatings formulated or optimized for LED-based curing systems are known. Such coatings are described in, for example, WO2016028668,

"Monochromatic Actinic Radiation Curable Coatings for Optical Fiber," assigned to DSM IP Assets, B.V.

[0085] Whether applied as a primary coating, a secondary coating, or some other variant of coating for use on an optical fiber (and whether utilized in processes incorporating LED-based or "traditional" curing systems), the radiation curable composition from which such a coating is derived typically possesses each of: one or more ethylenically unsaturated polymerizable compounds, namely reactive diluent monomers and/or

(typically urethane) acrylate oligomers, one or more photoinitiator

compounds, as well as one or more common additives. Each compositional constituent is described in turn below.

Ethylenically Unsaturated Polymerizable Compounds

[0086] The ethylenically unsaturated polymerizable compounds can contain one or more than one olefinic double bond. They may be low molecular weight (monomeric) or high molecular weight (oligomeric) compounds.

Reactive Diluent Monomers

[0087] Typical examples of lower molecular weight monomers containing one double bond are alkyl or hydroxyalkyl acrylates or methacrylates, for example methyl, ethyl, butyl, 2-ethylhexyl and 2 -hydroxy ethyl acrylate, isobornyl acrylate, and methyl and ethyl methacrylate. Further examples of these monomers are acrylonitrile, acrylamide, methacrylamide,

N-substituted (meth)acrylamides, vinyl esters such as vinyl acetate, styrene, alkylstyrenes, halostyrenes, N-vinylpyrrolidone, N-vinyl caprolactam, vinyl chloride and vinylidene chloride. Examples of monomers containing more than one double bond are ethylene glycol diacrylate, propylene glycol diacrylate, neopentyl glycol diacrylate, hexamethylene glycol diacrylate, bisphenol A diacrylate, 4,4'-bis(2-acryloyloxyethoxy)diphenylpropane, trimethylolpropane triacrylate, pent aery thritol triacrylate and

tetraacrylate, vinyl acrylate, divinyl benzene, divinyl succinate, diallyl phthalate, triallyl phosphate, triallyl isocyanurate or

tris (2 - acryloylethyl)isocy anur ate .

[0088] One or more of the aforementioned reactive diluent monomers can be employed in compositions according to the present invention in any suitable amount, and may be chosen singly or in combination of one or more of the types enumerated herein. In a preferred embodiment, the reactive diluent monomer component is present in an amount, relative to the entire weight of the composition, of from about 5 wt.% to about 90 wt.%, more preferably from about 10 wt.% to about 90 wt.%, more preferably from about 10 wt.% to about 80 wt.%., more preferably from about 10 wt.% to about 60 wt.%. Acrylate Oligomers

[0089] Generally, optical fiber coating materials comprise as an oligomer a urethane acrylate oligomer, comprising an acrylate group, urethane groups and a backbone. The backbone is derived from a polyol which has been reacted with a diisocyanate and hydroxyalkylacrylate.

[0090] Examples of suitable polyols are polyether polyols, polyester polyols, polycarbonate polyols, polycaprolactone polyols, acrylic polyols, and other polyols. These polyols may be used either individually or in

combinations of two or more. There are no specific limitations to the manner of polymerization of the structural units in these polyols. Each of random polymerization, block polymerization, or graft polymerization is acceptable.

[0091] Given as examples of the polyether polyols are polyethylene glycol, polypropylene glycol, polypropylene glycol-ethylene glycol copolymer, polytetramethylene glycol, polyhexamethylene glycol, polyheptamethylene glycol, polydecamethylene glycol, and polyether diols obtained by

ring-opening copolymerization of two or more ion-polymerizable cyclic compounds. Here, given as examples of the ion-polymerizable cyclic compounds are cyclic ethers such as ethylene oxide, isobutene oxide, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, dioxane, trioxane, tetraoxane, cyclohexene oxide, styrene oxide,

epichlorohydrin, isoprene monoxide, vinyl oxetane, vinyl tetrahydrofuran, vinyl cyclohexene oxide, phenyl glycidyl ether, butyl glycidyl ether, and glycidyl benzoate. Specific examples of combinations of two or more ion-polymerizable cyclic compounds include combinations for producing a binary copolymer such as tetrahydrofuran and 2-methyltetrahydrofuran, tetrahydrofuran and 3-methyltetrahydrofuran, and tetrahydrofuran and ethylene oxide; and combinations for producing a ternary copolymer such as a combination of tetrahydrofuran, 2-methyltetrahydrofuran, and ethylene oxide, a combination of tetrahydrofuran, butene-1 -oxide, and ethylene oxide, and the like. The ring-opening copolymers of these ion-polymerizable cyclic compounds may be either random copolymers or block copolymers.

[0092] Included in these polyether polyols are products commercially available under the trademarks, for example, PTMG1000, PTMG2000 (manufactured by Mitsubishi Chemical Corp.), PEG#1000 (manufactured by Nippon Oil and Fats Co., Ltd.), PTG650 (SN), PTG1000 (SN), PTG2000 (SN), PTG3000, PTGL1000, PTGL2000 (manufactured by Hodogaya

Chemical Co., Ltd.), PEG400, PEG600, PEG1000, PEG1500, PEG2000, PEG4000, PEG6000 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and Pluronics (by BASF).

[0093] Polyester diols obtained by reacting a polyhydric alcohol and a polybasic acid are given as examples of the polyester polyols. As examples of the polyhydric alcohol, ethylene glycol, polyethylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,6-hexanediol, 3-methyl- l,5-pentanediol, 1,9-nonanediol, 2-methyl-l,8-octanediol, and the like can be given. As examples of the polybasic acid, phthalic acid, dimer acid, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, adipic acid, sebasic acid, and the like can be given.

[0094] These polyester polyol compounds are commercially available under the trademarks such as MPD/IPA500, MPD/IPA1000, MPD/IPA2000, MPD/TPA500, MPD/TPA1000, MPD/TPA2000, Kurapol A- 1010, A-2010, PNA-2000, PNOA-1010, and PNOA-2010 (manufactured by Kuraray Co., Ltd.).

[0095] As examples of the polycarbonate polyols, polycarbonate of polytetrahydrofuran, poly(hexanediol carbonate), poly(nonanediol

carbonate), poly(3-methyl- l,5-pentamethylene carbonate), and the like can be given.

[0096] As commercially available products of these polycarbonate polyols, DN-980, DN-981 (manufactured by Nippon Polyurethane Industry Co., Ltd.), Priplast 3196, 3190, 2033 (manufactured by Unichema), PNOC-2000, PNOC-1000 (manufactured by Kuraray Co., Ltd.), PLACCEL CD220, CD210, CD208, CD205 (manufactured by Daicel Chemical Industries, Ltd.), PC-THF-CD (manufactured by BASF), and the like can be given.

[0097] Polycaprolactone diols obtained by reacting ε-caprolactone and a diol compound are given as examples of the polycaprolactone polyols having a melting point of 0 °C or higher. Here, given as examples of the diol compound are ethylene glycol, polyethylene glycol, polypropylene glycol, polypropylene glycol, tetramethylene glycol, polytetramethylene glycol, 1,2-polybutylene glycol, 1,6-hexanediol, neopentyl glycol,

1,4-cyclohexanedimethanol, 1,4-butanediol, and the like.

[0098] Commercially available products of these polycaprolactone polyols include PLACCEL 240, 230, 230ST, 220, 220ST, 220NP 1, 212, 210, 220N, 210N, L230AL, L220AL, L220PL, L220PM, L212AL (all manufactured by Daicel Chemical Industries, Ltd.), Rauccarb 107 (by Enichem), and the like.

[0099] As examples of other polyols ethylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, polyoxy ethylene bisphenol A ether, polyoxypropylene bisphenol A ether, polyoxy ethylene bisphenol F ether, polyoxypropylene bisphenol F ether, and the like can be given.

[0100] As these other polyols, those having a alkylene oxide structure in the molecule, in particular polyether polyols, are preferred. In an

embodiment, polyols containing polytetramethylene glycol and copolymer glycols of butyleneoxide and ethyleneoxide are particularly preferred.

[0101] The reduced number average molecular weight derived from the hydroxy! number of these polyols is usually from about 50 to about 15 000, and preferably from about 1000 to about 8000.

[0102] Given as examples of the polyisocyanate used for the oligomer are 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene

diisocyanate, 1,4-xylylene diisocyanate, 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate,

3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethylphenylene diisocyanate, 4,4'-biphenylene diisocyanate, 1,6-hexane diisocyanate, isophorone diisocyanate, methylene bis(4-cyclohexylisocyanate), 2,2,4-trimethylhexamethylene diisocyanate, bis(2-isocyanato-ethyl)fumarate, 6-isopropyl-l,3-phenyl diisocyanate, 4- diphenylpropane diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, tetramethyl xylylene diisocyanate, lysine isocyanate, and the like. These polyisocyanate compounds may be used either individually or in combinations of two or more. Preferred polyisocyanates are isophorone diisocyanate, 2,2,4-trimethyihexamethylene diisocyanate, 2,4-tolylene diisocyanate, and 2,6-tolylene diisocyanate.

[0103] Examples of the hydroxy! group -containing (meth)acrylate used in the oligomer, include, (meth)acrylates derived from (meth)acrylic acid and epoxy and (meth)acrylates comprising alkylene oxides, more in particular, 2-hydroxy ethyl (meth)acrylate, 2-hydroxypropylacrylate and

2-hydroxy-3-oxyphenyl(meth)acrylate. Acrylate functional groups are preferred over methacrylates.

[0104] The ratio of polyol, polyisocyanate, and hydroxyl group -containing (meth) acrylate used for preparing the urethane (meth)acrylate is

determined so that about 1.1 to about 3 equivalents of an isocyanate group included in the polyisocyanate and about 0.1 to about 1.5 equivalents of a hydroxy! group included in the hydroxyl group-containing (meth)acrylate are used for one equivalent of the hydroxyl group included in the glycol.

[0105] In the reaction of these three components, a urethanization catalyst such as copper naphthenate, cobalt naphthenate, zinc naphthenate, di-7 -butyl tin dilaurate, triethylamine, and

triethylenediamine-2-methyltriethyleneamine, is usually used in an amount from about 0.01 to about 1 wt.% of the total amount of the reactant. The reaction is carried out at a temperature from about 10 to about 90 °C, and preferably from about 30 to about 80 °C. [0106] The number average molecular weight of the urethane

(meth)acrylate used in the composition of the present invention is preferably in the range from about 600 to about 20 000 g/mol, and more preferably from about 2200 to about 10 000 g/mol. If the number average molecular weight of the urethane (meth)acrylate is less than about 100 g/mol, the resin composition tends to solidify; on the other hand, if the number average molecular weight is larger than about 20 000 g/mol, the viscosity of the composition becomes high, making handling of the composition difficult. Particularly preferred for inner primary coatings are oligomers having a number average molecular weight between about 2200 and about 5500 g/mol.

[0107] Other oligomers that can be used include polyester (meth)acrylate, epoxy (meth)acrylate, polyamide (meth)acrylate, siloxane polymer having a (meth)acryloyloxy group, a reactive polymer obtained by reacting

(meth)acrylic acid and a copolymer of glycidyl methacrylate and other polymerizable monomers, and the like. Particularly preferred are bisphenol A based acrylate oligomers such as alkoxylated bisphenol - A- diacrylate and diglycidyl -bisphenol -A-diacrylate.

[0108] Beside the above-described components, other curable oligomers or polymers may be added to the liquid curable resin composition of the present invention to the extent that the characteristics of the liquid curable resin composition are not adversely affected.

[0109] Preferred oligomers are polyether based acrylate oligomers, polycarbonate acrylate oligomers, polyester acrylate oligomers, alkyd acrylate oligomers and acrylated acrylic oligomers. More preferred are the urethane-containing oligomers thereof. Even more preferred are polyether urethane acrylate oligomers and urethane acrylate oligomers using blends of the above polyols, and particularly preferred are aliphatic polyether urethane acrylate oligomers. The term "aliphatic" refers to a wholly aliphatic polyisocyanate used. [0110] However, also urethane-free acrylate oligomers, such as

urethane-free acrylated acrylic oligomers, urethane-free polyester acrylate oligomers and urethane-free alkyd acrylate oligomers are also preferred. Examples of such high molecular weight (oligomeric) polyunsaturated compounds are acrylated epoxy resins, acrylated polyethers, and acrylated polyesters. Further examples of unsaturated oligomers are unsaturated polyester resins, which are usually prepared from maleic acid, phthalic acid and one or more diols and which have molecular weights of greater than about 500. Unsaturated oligomers of this type are also known as

prepolymers. Typical examples of unsaturated compounds are esters of ethylenically unsaturated carboxylic acids and polyols or polyepoxides, and polymers containing ethylenically unsaturated groups in the chain or in side groups, including unsaturated polyesters, polyamides and copolymers thereof, polybutadiene and butadiene copolymers, polyisoprene and isoprene copolymers, polymers and copolymers containing (meth)acryhc groups in side-chains, as well as mixtures of one or more than one such polymer.

Illustrative examples of unsaturated carboxylic acids are acrylic acid, methacrylic acid, crotonic acid, itaconic acid, cinnamic acid, unsaturated fatty acids such as linolenic acid or oleic acid. Suitable polyols are aromatic, aliphatic and cycloaliphatic polyols. Aromatic polyols are typically

hydroquinone, 4,4'-dihydroxydiphenyl, 2,2-bis(4-hydroxyphenyl) propane, as well as novolacs and cresols. Polyepoxides include those based on the cited polyols, for instance on the aromatic polyols and epichlorohydrin.

[0111] Further suitable polyols are polymers and copolymers which contain hydroxyl groups in the polymer chain or in side groups, for example polyvinyl alcohol and copolymers thereof or hydroxyalkyl polymethacrylates or copolymers thereof. Other suitable polyols are oligoesters carrying hydroxyl end groups. Illustrative examples of aliphatic and cycloaliphatic polyols are alkylenediols containing for example 2 to 12 carbon atoms, including ethylene glycol, 1,2- or 1,3-propanediol, 1,2-, 1,3-or 1,4-butanediol, pentanediol, hexanediol, octanediol, dodecanediol, diethylene glycol,

Methylene glycol, polyethylene glycols having molecular weights of for instance 200 to 1500, 1,3-cyclopentanediol, 1,2-, 1,3-or 1,4-cyclohexanediol, 1,4-dihydroxymethylcyclohexane, glycerol, ins(2-hydroxyethyl)amine, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol and sorbitol. The polyols may be esterified partially or completely with one or with different unsaturated carboxylic acids, in which case the free hydroxy! groups of the partial esters may be modified, for example etherified, or esterified with other carboxylic acids. Illustrative examples of esters are: trimethylolpropane triacrylate, trimethylolethane triacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, tetramethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, pentaerythritol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol diacrylate, dipentaerythritol triacrylate, dipentaerythritol tetraacrylate,

dipentaerythritol pentacrylate, dipentaerythritol hexacrylate,

tripentaerythritol octacrylate, pentaerythritol dimethacrylate,

pentaerythritol trimethacrylate, dipentaerythritol dimethacrylate, dipentaerythritol tetramethacrylate, tripentaerythritol octamethacrylate, pentaerythritol diitaconate, dipentaerythritol trisitaconate,

dipentaerythritol pentaitaconate, dipentaerythritol hexaitaconate, ethylene glycol diacrylate, 1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diitaconate, sorbitol triacrylate, sorbitol tetraacrylate, pentaerythritol-modified triacrylate, sorbitol tetramethacrylate, sorbitol pentacrylate, sorbitol hexacrylate, oligoester acrylates and methacrylates, glycerol di- and-triacrylate, 1,4-cyclohexanediacrylate, bisacrylates and bismethacrylates of polyethylene glycol having molecular weights of 200 to 1500 g/mol, or mixtures thereof. Polyfunctional monomers and oligomers are available for example from UCB Chemicals of Smyrna, Georgia, and

Sartomer of Exton, Pennsylvania. [0112] One or more of the aforementioned ethylenically unsaturated oligomers can be employed in compositions according to the present invention in any suitable amount, and may be chosen singly or in

combination of one or more of the types enumerated herein. In a preferred embodiment, the ethylenically unsaturated oligomer component is present in an amount, relative to the entire weight of the composition, of from about 5 wt.% to about 90 wt.%, more preferably from about 10 wt.% to about 90 wt.%, more preferably from about 10 wt.% to about 80 wt.%., more

preferably from about 10 wt.% to about 60 wt.%.

Photoinitiator s

[0113] In preferred embodiments, the liquid radiation curable resin for coating an optical fiber of the present invention includes a free-radical photoinitiator component. The photoinitiator is a compound that chemically changes due to the action of light or the synergy between the action of light and the electronic excitation of a sensitizing dye to produce at least one of a radical, an acid, and a base.

[0114] According to an embodiment of the present invention, the free-radical photoinitiator is an acylphosphine oxide photoinitiator.

Acylphosphine oxide photoinitiators are disclosed for example in U.S. Pat. Nos. 4324744, 4737593, 5942290, 5534559, 6020529, 6486228, and 6486226.

[0115] The acylphosphine oxide photoinititors are bisacylphosphine oxides (BAPO) or monoacylphosphine oxides (MAPO).

[0116] The bisacylphosphine oxide photoinitiators are of the formula I:

wherein R50 is C1-C12 alkyl, cyclohexyl or phenyl which is unsubstituted or is substituted by 1 to 4 halogen or Ci-Cs alkyl; R51 and R52 are each independently of the other Ci-Cs alkyl or Ci-Csalkoxy; R53 is hydrogen or Ci-Cs alkyl; and

R54 is hydrogen or methyl.

[0117] For example, R50 is C2-C 10 alkyl, cyclohexyl or phenyl which is unsubstituted or is substituted by 1 to 4 C 1-C4 alkyl, CI or Br. Another embodiment is where R50 is C3-C8 alkyl, cyclohexyl or phenyl which is unsubstituted or is substituted in the 2-, 3-, 4- or 2,5-positions by C1-C4 alkyl. For instance, R50 is C4-C 12 alkyl or cyclohexyl, R51 and R52 are each independently of the other Ci-Cs alkyl or Ci-Cs alkoxy and R53 is hydrogen or Ci-Cs alkyl. For instance, R51 and R52 are C1-C4 alkyl or C 1-C4 alkoxy and R53 is hydrogen or C 1-C4 alkyl. Another embodiment is where R51 and R52 are methyl or methoxy and R53 is hydrogen or methyl. For example R51, R52 and R53 are methyl. Another embodiment is where R51, R52 and R53 are methyl and R54 is hydrogen. Another embodiment is where R50 is C3-C8 alkyl. For example, R51 and R52 are methoxy, R53 and R54 are hydrogen and R50 is isooctyl. For instance R50 is isobutyl. For example R50 is phenyl. The present bisacylphosphine oxide photoinitiator is for example

bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (CAS# 162881-26-7) or is bis(2,4,6-trimethylbenzoyl)-(2,4-bis-pentyloxyphenyl)phosphine oxide.

[0118] The monoacylphosphine oxide photoinitiators are of the formula II:

in which

Ri and R2 independently of one another are C1-C12 alkyl, benzyl, phenyl which is unsubstituted or substituted from one to four times by halogen, Ci-Cs alkyl and/or Ci-Cs alkoxy, or are cyclohexyl or a group -COR3, or Ri is -OR4; R3 is phenyl which is unsubstituted or substituted from one to four times by Ci-Cs alkyl, Ci-Cs alkoxy, Ci-Cs alkylthio and/or halogen; and

R₄ is Ci-Cs alkyl, phenyl or benzyl. For example, Ri is -OR4. For example R2 is phenyl which is unsubstituted or substituted from one to four times by halogen, Ci-Cs alkyl and/or Ci-Cs alkoxy. For example R3 is phenyl which is unsubstituted or substituted from one to four times by Ci-Cs alkyl. For example, the present monoacylphosphine oxide is

2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (CAS# 84434-11-7) or 2,4,6-trimethylbenzoyldiphenylphosphine oxide (CAS# 127090-72-6).

[0119] Compositions according to the present invention may also employ further photoinitiators, for example oc-hydroxy ketone photoinitiators of the formula III:

where

R11 and R12 independently of one another are hydrogen, d-Ce alkyl, phenyl, Ci-C₆ alkoxy, OSiRi₆(Ri7)2 or -0(CH₂CH20)q-Ci-C₆ alkyl, or

R11 and R12, together with the carbon atom to which they are attached, form a cyclohexyl ring;

q is a number from 1 to 20;

R13 is OH, C1-C16 alkoxy or -O(CH₂CH2O)q-Ci-C₆ alkyl;

Ri4 is hydrogen, Ci-Cis alkyl, Ci-Ci2 hydroxyalkyl, Ci-Cis alkoxy,

-OCH2CH2-OR15, -CH=CH₂, -C(CH₃)=CH₂ or is

n is a number from 2 to 10;

Ri5 is hydrogen, -COCH=CH₂ or -COC(CH₃)=CH₂;

Ri6 and R17 independently of one another are Ci-Cs alkyl or phenyl; and G3 and G₄ independently of one another are end groups of the polymeric structure, preferably hydrogen or methyl.

[0120] -Hydroxy ketone photoinitiators that are of interest are those in which R11 and R12 independently of one another are hydrogen, Ci-Ce alkyl or phenyl or Rn and R12, together with the carbon atom to which they are attached, form a cyclohexyl ring, R13 is OH, and R14 is hydrogen,

C1-C12 alkyl, C1-C12 alkoxy, -OCH2CH2OR15, -C(CH₃)=CH₂ or is

c— O ?

H₃C- -C-CH, H-C-C- -CH,

i ^{3 3} I

OH OH

[0121] For example, suitable as the -hydroxy ketone photoinitiators are those in which Rn and R12 independently of one another are methyl or ethyl or Rn and R12, together with the carbon atom to which they are attached, form a cyclohexyl ring, R13 is hydrogen and R14 is hydrogen, C1-C4 alkyl, C1-C4 alkoxy or -OCH2CH2OH. Interesting also are compounds, wherein

[0122] For instance, suitable a-hydroxy ketone photoinitiators are oc-hydroxycyclohexyl phenyl ketone, 2 -hydroxy-2 -methyl- 1-phenylpropanone, 2 -hydroxy-2 -methyl- l-(4-isopropylphenyl) propanone,

2-hydroxy-2-methyl-l-(4-dodecylphenyl)propanone,

2 -hydroxy- 1 -{4- [4-(2 -hydroxy-2 -methyl-propionyl)-benzyl] -phenyl} -2 -methyl- prop an- 1 -one and

2 -hydroxy-2 -methyl- 1 - [(2 -hydroxy ethoxy)phenyl]prop anone .

[0123] The present α-hydroxy ketone photoinitiator is for example a-hydroxycyclohexylphenyl ketone or 2 -hydroxy-2 -methyl- 1 -phenyl - 1-propanone. Straight or branched chain alkyl is for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec -butyl, feri-butyl, pentyl, isopentyl, isooctyl, hexyl, heptyl, octyl, nonyl, decyl or dodecyl. Likewise alkoxy or alkylthio are of the same straight or branched chains.

[0124] Photoinitiators according to the present invention may be employed singularly or in combination of one or more as a blend. Suitable photoinitiator blends (PI blends) are for example disclosed in U.S. Pat. No. 6,020,528 and U.S. Pat. app. No. 60/498,848. The present PI (photoinitiator) blends are for example a mixture of bis(2,4,6-trimethylbenzoyl)

phenylphosphine oxide (CAS# 162881-26-7) and

2,4,6-trimethylbenzoylethoxyphenylphosphine oxide (CAS# 84434-11-7) in ratios by weight of about 1: 11, 1: 10, 1:9, 1:8 or 1:7.

[0125] Another especially suitable PI blend is a mixture of

bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide,

2,4,6-trimethylbenzoylethoxyphenylphosphine oxide and

2-hydroxy-2-methyl-l-phenyl-l-propanone (CAS# 7473-98-5) in weight ratios of for instance about 3: 1:15 or 3: 1:16 or 4: 1: 15 or 4: 1: 16. Another suitable PI blend is a mixture of bis(2,4,6-trimethylbenzoyl)

phenylphosphine oxide and 2-hydroxy-2-methyl-l-phenyl-l-propanone in weight ratios of for instance about 1:3, 1:4 or 1:5. The present acylphosphine oxide PI or PI blend is present in the radiation-curable compositions from about 0.2 to about 10 % by weight, based on the weight of the composition. For instance, the PI or PI blend is present from about 0.5 to about 8 %, about 1 to about 7 %, or about 2, 3, 4, 5 or 6 % by weight based on the weight of the radiation-curable composition.

[0126] Other suitable photoinitiators according to this invention are for or example, other mono- or bisacylphosphinoxides such as

diphenyl-2,4,6-trimethylbenzoylphosphine oxide or

bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphineoxide;

oc-hydroxyketones, such as 1-hydroxycyclohexylphenylketone or

2 -hydroxy- 1 - [4-(2 -hy droxyethoxy)phenyl] -2 -methyl- 1 -propanone;

-aminoketones, such as

2-methyl-l-[4-(methylthio)phenyl]-2-(4-morpholinyl)-l-propanone,

2-benzyl-2-(dimethylamino)-l-[4-(4-morpholinyl)phenyl]-l-butanone, 2-(4-methylbenzyl-2-(dimethylamino)-l-[4-(4-morpholinyl)phenyl]- 1-butanone or 2-benzyl-2-(dimethylamino)-l-[3,4-dimethoxyphenyl]- 1- butanone; benzophenones, such as benzophenone,

2,4,6-trimethylbenzophenone, 4-methylbenzophenone,

2- methylbenzophenone, 2-methoxycarbonylbenzophenone,

4,4'-bis(chloromethyl)-benzophenone, 4-chlorobenzophenone,

4-phenylbenzophenone, 4,4'-bis(dimethylamino)-benzophenone,

4,4'-bis(diethylamino)benzophenone, methyl-2-benzoylbenzoate,

3,3'-dimethyl-4-methoxybenzophenone,

4-(4-methylphenylthio)benzophenone,

2,4,6-trimethyl-4'-phenyl-benzophenone or

3-methyl-4'-phenyl-benzophenone; ketal compounds, for example

2,2-dimethoxy- l,2-diphenyl-ethanone; and monomeric or dimeric phenylglyoxylic acid esters, such as methylphenylglyoxylic acid ester,

5,5'-oxo-di(ethyleneoxydicarbonylphenyl) or l,2-(benzoylcarboxy)ethane.

[0127] Other suitable photoinitiators employed according to this invention, with or without acylphosphine oxide photoinitiators, are for example oxime esters as disclosed in U.S. Pat. No. 6,596,445. A suitable oxime ester photoinitiator is for example:

[0128] Another class of suitable photoinitiators according to this invention, with or without acylphosphine oxide photoinitiators, are for example phenyl glyoxalates, for example as disclosed in U.S. Pat. No. 6,048,660. For example phenyl glyoxalates of the formula:

[0129] wherein Y is C1-C12 alkylene, cyclohexylene, C2-C40 alkylene interrupted one or more times by cyclohexylene, O, S, or NR30, and R30 hydrogen, C 1-C 12 alkyl or phenyl, preferably Y is CH2CH2-O-CH2CH2. [0130] Without wishing to be bound by any theory, it is believed that the number of conjugated double-bonds in any single free-radical photoinitiator molecule can significantly contribute to the yellowing effect produced therefrom. Further, inventors have discovered that sulfur-containing photoinitiators tend also to produce undesirable yellowing effects. In an embodiment of the invention, therefore, the free-radical photoinitiator component has an average of not more than 12 conjugated double-bonds in any single molecule. In another embodiment of the invention, the free- radical photoinitiator component is also free of sulfur atoms.

[0131] One or more of the aforementioned free-radical photoinitiators can be employed in compositions according to the present invention in any suitable amount, and may be chosen singly or in combination of one or more of the types enumerated herein. In a preferred embodiment, the free-radical photoinitiator component is present in an amount, relative to the entire weight of the composition, of from about 0.1 wt.% to about 10 wt.%, more preferably from about 0.1 wt.% to about 5 wt.%, more preferably from about 1 wt.% to about 5 wt.%.

Additives

[0132] Additives are also typically added to optical fiber coatings to achieve certain desirable characteristics such as improved shelf life, improved coating oxidative and hydrolytic stability, and the like. There are many different types of desirable additives, and the invention discussed herein is not intended to be limited by these, nevertheless they are included in the envisioned embodiments since they have desirable effects.

[0133] Examples of these are thermal inhibitors, which are intended to prevent premature polymerization, examples being hydroquinone, hydroquinone derivatives, p-methoxyphenol, beta-naphthol or sterically hindered phenols, such as 2,6-di(teri-butyl)-/?-cresol. The shelf life in the dark can be increased, for example, by using copper compounds, such as copper naphthenate, copper stearate or copper octoate, phosphorus compounds, for example triphenylphosphine, tributylphosphine, triethyl phosphite, triphenyl phosphite or tribenzyl phosphite, quaternary ammonium compounds, such as tetramethylammonium chloride or trimethylbenzylammonium chloride.

[0134] In order to keep out atmospheric oxygen during the

polymerization, paraffin or similar waxlike substances can be added; these migrate to the surface on commencement of the polymerization because of their low solubility in the polymer, and form a transparent surface layer which prevents the ingress of air. It is likewise possible to apply an oxygen barrier layer.

[0135] Light stabilizers which can be added are UV absorbers, for example well known commercial UV absorbers of the

hydroxyphenylbenzotriazole, hydroxyphenyl-benzophenone, oxalamide or hydroxyphenyl-s-triazine type. It is possible to use individual such compounds or mixtures thereof, with or without the use of sterically hindered relatively non-basic amine light stabilizers (HALS). Sterically hindered amines are for example based on 2,2,6,6-tetramethylpiperidine.

UV absorbers and sterically hindered amines are for example:

[0136] 2-(2-Hydroxyphenyl)-2H-benzotriazoles, for example known commercial hydroxyphenyl-2H-benzotriazoles and benzotriazoles as disclosed in, United States Patent Nos. 3,004,896; 3,055,896; 3,072,585;

3,074,910; 3, 189,615; 3,218,332; 3,230, 194; 4, 127,586; 4,226,763; 4,275,004;

4,278,589; 4,315,848; 4,347, 180; 4,383,863; 4,675,352; 4,681,905; 4,853,471; 5,268,450; 5,278,314; 5,280, 124; 5,319,091; 5,410,071; 5,436,349; 5,516,914;

5,554,760; 5,563,242; 5,574, 166; 5,607,987; 5,977,219 and 6, 166,218 such as

2-(2-hydroxy-5-methylphenyl)-2H-benzotriazole,

2 - (3 , 5 - di- i-butyl-2 -hy droxyphenyl) -2H-benzotriazole,

2-(2-hydroxy-5-i-butylphenyl)-2H-benzotriazole,

2-(2-hydroxy-5-i-octylphenyl)-2H-benzotriazole, 5-chloro-2-(3,5-di-i-butyl-2-hydroxyphenyl)-2H-benzotriazole,

5-chloro-2-(3-i-butyl-2-hydroxy-5-methylphenyl)-2H-benzotriazole,

2-(3-sec-butyl-5-i-butyl-2-hydroxyphenyl)-2H-benzotriazole,

2-(2-hydroxy-4-octyloxyphenyl)-2H-benzotriazole,

2-(3,5-di-i-amyl-2-hydroxyphenyl)-2H-benzotriazole,

2-(3,5-bis-a-cumyl-2-hydroxyphenyl)-2H-benzotriazole,

2-(3-i-butyl-2-hydroxy-5-(2-(Q-hydroxy-octa-(ethyleneoxy)carbonyl-ethyl)-, phenyl)-2H-benzotriazole, 2-(3-dodecyl-2-hydroxy-5-methylphenyl)- 2H-benzotriazole, 2-(3-i-butyl-2-hydroxy-5-(2-octyloxycarbonyl)ethylphenyl)- 2H-benzotriazole, dodecylated 2-(2-hydroxy-5-methylphenyl)-

2H-benzotriazole, 2-(3-i-butyl-2-hydroxy-5-(2-octyloxycarbonylethyl)phenyl)-

5-chloro-2H-benzotriazole, 2-(3-teri-butyl-5-(2-(2-ethylhexyloxy)- carbonylethyl)-2-hydroxyphenyl)-5-chloro-2H-benzotriazole,

2 - (3 - i-butyl-2 -hy droxy-5 - (2 -methoxycarbonylethyl)phenyl)- 5 -chloro- 2H-benzotriazole, 2-(3-i-butyl-2-hydroxy-

5-(2-methoxycarbonylethyl)phenyl)-2H-benzotriazole,

2-(3-i-butyl-5-(2-(2-ethylhexyloxy)carbonylethyl)-2-hydroxyphenyl)- 2H-benzotriazole, 2-(3-i-butyl-2-hydroxy- 5-(2-isooctyloxycarbonylethyl)phenyl-2H-benzotriazole,

2,2'-methylene-bis(4-i-octyl-(6-2H-benzotriazol-2-yl)phenol),

2 - (2 -hy droxy-3 - -cumyl- 5 - i-octylphenyl) -2H-benzotriazole,

2-(2-hydroxy-3-i-octyl-5-a-cumylphenyl)-2H-benzotriazole,

5-fluoro-2-(2-hydroxy-3,5-di-a-cumylphenyl)-2H-benzotriazole,

5-chloro-2-(2-hydroxy-3,5-di-a-cumylphenyl)-2H-benzotriazole,

5-chloro-2-(2-hydroxy-3-a-cumyl-5-i-octylphenyl)-2H-benzotriazole,

2 - (3 - i-butyl-2 -hy droxy-5 - (2 -isooctyloxycarbonylethyl)phenyl) -5 -chloro- 2H-benzotriazole, 5-trifluoromethyl-2-(2-hydroxy-3-a-cumyl- 5-i-octylphenyl)-2H-benzotriazole, 5-trifluoromethyl-2-(2-hydroxy- 5-i-octylphenyl)-2H-benzotriazole, 5-trifluoromethyl-2-(2-hydroxy- 3,5-di-i-octylphenyl)-2H-benzotriazole, methyl 3-(5-trifluoromethyl- 2H-benzotriazol-2-yl)-5-i-butyl-4-hydroxyhydrocinnamate,

5-butylsulfonyl-2-(2-hydroxy-3-a-cumyl-5-i-octylphenyl)-2H-benzotriazole, 5-trifluoromethyl-2-(2-hydroxy-3-a-cumyl-5-i-butylphenyl)-2H-benzotriazole, 5-trifluoromethyl-2-(2-hydroxy-3,5-di-i-butylphenyl)-2H-benzotriazole, 5-trifluoromethyl-2-(2-hydroxy-3,5-di-a-cumylphenyl)-2H-benzotriazole, 5-butylsulfonyl-2-(2-hydroxy-3,5-di-i-butylphenyl)-2H-benzotriazole and 5-phenylsulfonyl-2-(2-hydroxy-3,5-di-i-butylphenyl)-2H-benzotriazole.

[0137] 2-Hydroxybenzophenones, for example the 4-hydroxy, 4-methoxy, 4-octyloxy, 4-decyloxy, 4-dodecyloxy, 4-benzyloxy, 4,2',4'-trihydroxy and 2'-hydroxy-4,4'-dimethoxy derivatives.

Esters of substituted and unsubstituted benzoic acids, as for example

4-teri-butylphenyl salicylate, phenyl salicylate, octylphenyl salicylate, dibenzoyl resorcinol, bis(4-feri-butylbenzoyl) resorcinol, benzoyl resorcinol, 2,4-di-feri-butylphenyl 3,5-di-teri-butyl-4-hydroxybenzoate, hexadecyl 3,5-di-feri-butyl-4-hydroxybenzoate, octadecyl

3,5-di-feri-butyl-4-hydroxybenzoate, 2-methyl-4,6-di-feri-butylphenyl, 3,5-di-feri-butyl-4-hydroxybenzoate.

[0138] In an embodiment, the radiation curable coating is a so-called Supercoating. Supercoatings are latest- generation optical fiber coatings that are formulated to provide low light signal attenuation over a broad temperature range, are fast curing even under LED conditions. An example of a Supercoating is a Desolite Supercoating^®, available from DSM. In an embodiment, the Supercoating is DS-2045, available from DSM.

[0139] As used herein, an "LED Secondary Supercoating" means a composition comprising, relative to the weight of the entire composition: (a) about 29.95 wt.% of a urethane acrylate oligomer further comprising, relative to the weight of the entire weight of the urethane acrylate oligomer: (b) about 22.47 wt.% of TDI Type II (an 80/20 blend of 2,4- and 2,6- isomer of toluene diisocyanate, available from BASF);

(c) about 0.07 wt.% of BHT Food Grad (e (2,6-di-feri-butyl-4-methylphenol, available from Fitz. Chemical);

(d) about 13.99 wt.% of 2-HEA (hydroxyethyl acrylate, available from

BASF);

(e) about 0.07 wt.% of a dibutyltin dilaurate catalyst; and

(f) about 63.4 wt.% of a propylene glycol, MW 1000 (Pluracol P1010,

available from BASF);

(g) about 39.85 wt.% of an epoxy diacrylate diluent monomer (CN 110,

available from Sartomer);

(h) about 7.4 wt.% of SR-506A (isobornyl acrylate, available from Sartomer);

(i) about 8.4 wt.% of SR 339C (PEA)

(j) about 5.9 wt.% of SR306F (TPGDA)

(k) about 4.5 wt.% of SR238 monomer;

(1) about 3 wt.% of 2,4,6-trimethyl benzoyl diphenyl phosphine oxide

photoinitiator (TPO, available from Chitech);

(m) about 0.5 wt.% of Irganox 1035 antioxidant;

(n) about 0.33 wt.% of DC- 190 surfactant; and

(o) about 0.17 wt.% of DC-57 additive.

[0140] Unless otherwise specified, the term wt.% means the amount by mass of a particular constituent relative to the entire liquid radiation curable composition for additive fabrication into which it is incorporated.

[0141] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0142] Preferred embodiments of this invention are described herein, including the best mode known to the inventor for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as

appropriate, and the inventor intends for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.

[0143] While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made therein without departing from the spirit and scope of the claimed

invention.

Claims

A curing lamp system comprising:

(a) a plurality of light emitting diodes, the plurality of light emitting

diodes configured to apply radiant output to a surface of an optical fiber while the optical fiber is drawn through an exposure area at a predetermined rate of speed, wherein;

(b) the surface comprises a radiation curable coating;

(c) the radiation curable coating comprises an ethylenically-unsaturated compound; and

(d) the plurality of light emitting diodes are further configured such that, at the predetermined rate of speed of about 2500 meters per minute under a standard processing protocol and a power input per line of the plurality of light emitting diodes is from about 3.5 kW to about 25 kW, or from about 4 kW to about 20 kW, or from about 5 kW to about 15 kW, or from about 6 kW to about 10 kW, or from about 5 kW to about 7 kW, the radiant output applied to the surface yields a coated optical fiber with a cured coating having a reacted acrylate

unsaturation of at least about 90 %, more preferably at least about 95 %, and an in-situ modulus from about 1 GPa to about 3 GPa.

2. The curing lamp system of claim 1, wherein the plurality of light emitting diodes are configured such that energy density of the radiant output at the surface of the optical fiber is equal to or greater than about 20 W/cm², more preferably greater than or equal to about 26 W/cm², more preferably greater than or equal to 30 about W/cm²; and less than about 60 W/cm², or less than about 50 W/cm², or less than about 40 W/cm².

3. The curing lamp system of claims 1 or 2, wherein the radiant output applied to the surface yields a coated optical fiber with a cured coating having a modulus ratio of between about 0.5 to about 2, more preferably between about 0.75 to about 1.5, more preferably between about 0.9 to about 1.1, or between about 0.85 to about 0.95, and wherein the radiation curable coating comprises an LED Secondary Supercoating.

4. The curing lamp system of any of claims 1-3, wherein the plurality of light emitting diodes are further configured to be spaced at least 10 mm, or at least 12.5 mm from a center of the coated optical fiber.

5. The curing lamp system of any one of claims 1-4, wherein the plurality of light emitting diodes comprises a first array, and wherein the curing lamp system further comprises a first light source module comprising the first array and a first optical element, wherein:

(a) the first array comprises a first row of light emitting diodes; and (b) the first optical element is configured to focus light emitted from the first array toward the exposure area.

6. The curing lamp system of claim 5, wherein the first row is oriented along a first axis configured to be parallel to a longitudinal axis of the optical fiber at least while the optical fiber is drawn through the exposure area.

7. The curing lamp system of claims 5 or 6, wherein the first optical element comprises:

a first lens positioned proximate the first row; and

a second lens positioned in between the optical path of the first lens and the exposure area.

8. The curing lamp system of claim 7, wherein:

the first lens is at least one of: (a) a first plano-convex lens oriented such that a planar surface of the plano-convex lens is proximate the first row;

(b) a first bi-convex lens; and

(c) a first Fresnel lens; and

the second lens is at least one of a second bi-convex lens, a second bi-convex lens, and a second Fresnel lens.

9. The curing lamp system of claim 8 wherein the first lens and the second lens extend longitudinally along a length of the first row.

10. The curing lamp system of any of claims 5-9, wherein:

the first row comprises a plurahty of consecutive dies comprising a first die and a second die; wherein a distance between the first die and the second die is between about 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm.

11. The curing lamp system of claim 10, wherein the first die is positioned coplanar with the second die.

12. The curing lamp system of any of claims 5-11, wherein the first row comprises a plurality of consecutive dies comprising:

(a) a first die comprising a first top electrode on a top surface of the first die and a first bottom electrode on a bottom surface of the first die, wherein the first bottom electrode of the first die is electrically coupled to a first conductive bonding pad, and wherein the first conductive bonding pad is mounted on a substrate; and

(b) a second die comprising a second top electrode on a top surface of the second die and a second bottom electrode on a bottom surface of the second die, wherein the second bottom electrode of the second die is electrically coupled to a second conductive bonding pad, and wherein the second conductive bonding pad is mounted on the substrate; and wherein the second conductive bonding pad includes an elongate portion that extends alongside at least a portion of a first lateral side of the first die, and wherein the first top electrode of the first die is electrically coupled to the elongate portion of the second conductive bonding pad.

13. The curing lamp system of claim 12 wherein the second

conductive bonding pad further comprises a second elongate portion that extends alongside at least a portion of a second lateral side of the first die, and wherein the first die further comprises a plurahty of first top electrodes and at least one of the plurality of first top electrodes is electrically coupled to the second elongate portion.

14. The curing lamp system of claim 12 or 13, wherein the plurality of consecutive dies comprises at least ten consecutive dies having nine pairs of the first and second dies.

15. The curing lamp system of any of claims 12-14, wherein the first row further comprises a multiple of the plurality of consecutive dies.

16. The curing lamp system of any of claims 12-15, wherein the first array further comprises a second row of light emitting diodes, wherein the second row is configured to extend alongside the first row and comprises a second plurality of consecutive dies comprising:

(a) a third die comprising a third top electrode on a top surface of the third die and a third bottom electrode on a bottom surface of the third die, wherein the third top electrode of the third die is electrically coupled to the elongate portion of the second conductive bonding pad, wherein the third bottom electrode of the third die is electrically coupled to the first conductive bonding pad; and

a fourth die comprising a fourth top electrode on a top surface of the fourth die and a fourth bottom electrode on a bottom surface of the fourth die, wherein the fourth bottom electrode of the fourth die is electrically coupled to the second conductive bonding pad; and wherein the third die is positioned:

(i) coplanar with the fourth die and within a distance of about 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm from the fourth die; and

(ii) alongside the elongate portion of the second conductive bonding pad such that the elongate portion is between the third die and the first die.

17. The curing lamp system of any of claims 5-16, wherein the first light source module further comprises a heat exchanger configured to transfer heat away from the first array.

18. The curing lamp system of any of claims 5-17, wherein the first light source module is detachably coupled to a first light source housing, and the first light source housing is configured to rotate about a second axis along a longitudinal direction between a first position and a second position.

19. The curing lamps system of claim 18, wherein the second substantially parallel to the first axis.

20. The curing lamp system of claims 18 or 19, wherein the second axis is substantially parallel to the longitudinal axis of the optical fiber at least while the optical fiber is drawn through the exposure area.

21. The curing lamp system of any of claims 17-20, wherein the first light source module and the first light source housing are configured such that a position of the first light source module within the first light source housing is adjustable, in a direction transverse to a longitudinal direction, for increasing or decreasing a distance between the first light source module and the exposure area.

22. The curing lamp system of any of claims 4-15, wherein the plurality of light emitting diodes further comprises:

(a) a second array, wherein the second array comprises a second row of light emitting diodes and wherein the second optical element is configured to focus light emitted from the second array toward the exposure area; and

(b) a third array, wherein the third array comprises a third row of light emitting diodes and wherein the third optical element is configured to focus light emitted from the third array toward the exposure area; the curing lamp system further comprises:

(c) a second light source module comprising the second array and a

second optical element; and

(d) a third light source module comprising the third array and a third optical element;

the first, second, and third light source modules are:

(e) positioned radially around the exposure area; and

(f) configured to apply at least a portion of the radiant output over a circumference of the surface of the optical fiber drawn through the exposure area.

23. The curing lamp system of claim 22 wherein the first, second, and third light source modules are further spaced radially from and

symmetrically around a central longitudinal axis of the exposure area.

24. The curing lamp system of claim 23, wherein the first light source module:

(a) further comprises a first heat exchanger configured to transfer heat away from the first array; and

(b) is detachably coupled to a first light source housing configured to

rotate about a first axis along a longitudinal direction between:

(i) a first position configured to direct light emitted from the first array toward the exposure area; and

(ii) a second position configured to facilitate detachment of the first light source module from the first light source housing; and the second light source module:

(c) further comprises a second heat exchanger configured to transfer heat away from the second array; and

(d) is detachably coupled to a second light source housing configured to rotate about a second axis along the longitudinal direction between:

(iii) a third position configured to direct light emitted from the second array toward the exposure area; and

(iv) a fourth position configured to facilitate detachment of the second light source module from the second light source housing.

25. A method of producing a coated optical fiber comprising:

(a) coating an optical fiber with a radiation curable coating, wherein the radiation curable coating comprises an ethylenically-unsaturated compound; (b) drawing the optical fiber through an exposure area of a curing lamp system at a predetermined rate of speed, the curing lamp system comprising a plurality of light emitting diodes;

(c) applying, using the plurality of light emitting diodes, radiant output to a surface of the radiation curable coating;

(d) wherein power input per line of the plurality of light emitting diodes is less than about 25 kW and the radiant output applied to the surface yields a coated optical fiber with a cured coating having a reacted acrylate unsaturation of at least about 90 %, more preferably at least about 95 %, and a modulus of between about 1 GPa to about 3 GPa.

26. The method of claim 25, wherein the power input per line of the plurality of light emitting diodes is between about 3.5 kW to about 25 kW, from about 4 kW to about 20 kW, or from about 5 kW to about 15 kW, or from about 6 kW to about 10 kW, or from about 5 kW to about 7 kW.

27. The method of claims 25 or 26, wherein the radiant output applied to the surface yields a coated optical fiber with a cured coating having a modulus ratio of between about 0.5 to about 2, more preferably between about 0.75 to about 1.5, more preferably between about 0.9 to about 1.1, or between about 0.85 to about 0.95.

28. The method of any of claims 25-27, wherein the predetermined rate of speed is between about 1500 to about 3500 meters per minute, more preferably from about 2000 to about 3000 meters per minute, or from about 2400 to about 2800 meters per minute.

29. The method of any of claims 25-28, wherein the plurality of light emitting diodes are configured such that energy density of the radiant output at the surface of the optical fiber is equal to or greater than 26 W/cm², more preferably equal or greater than 30 W/cm², and less than about 50 W/cm².

30. The method of any of claims 25-28, wherein the plurality of light emitting diodes are configured such that energy density of the radiant output at the surface of the optical fiber is between about 25 W/cm² and about 35 W/cm².

31. The method of any of claims 25-30, wherein the plurality of light emitting diodes comprises a first array and wherein the curing lamp system comprises a first light source module comprising the first array and a first optical element;

(a) wherein the first array comprises a first row of light emitting diodes and wherein the first optical element is configured to focus light emitted from the first array toward the exposure area; and

(b) wherein the first row comprises a plurality of consecutive dies

comprising a first die and a second die, wherein the first die is positioned coplanar with the second die and a distance between the first die and the second die is between about 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm.

32. The method of claim 31, wherein the first die comprises a first top electrode on a top surface of the first die and a first bottom electrode on a bottom surface of the first die, wherein the first bottom electrode of the first die is electrically coupled to a first conductive bonding pad, and wherein the first conductive bonding pad is mounted on a substrate; and (a) the second die comprises a second top electrode on a top surface of the second die and a second bottom electrode on a bottom surface of the second die, wherein the second bottom electrode of the second die is electrically coupled to a second conductive bonding pad, and wherein the second conductive bonding pad is mounted on the substrate; and

(b) wherein the second conductive bonding pad includes an elongate

portion that extends alongside a first lateral side of the first die, and the first top electrode of the first die is electrically coupled to the elongate portion of the second conductive bonding pad.

33. A method of producing a coated optical fiber comprising the steps of:

(a) coating an optical fiber with a radiation curable secondary coating, the radiation curable secondary coating comprising an

ethylenically-unsaturated compound;

(b) drawing the optical fiber through an exposure area of a curing lamp system at a predetermined rate of speed, the curing lamp system comprising a plurality of light emitting diodes;

(c) applying, using the plurality of light emitting diodes, radiant output to a surface of the radiation curable secondary coating;

(d) wherein the plurahty of light emitting diodes are configured such that an energy density of the radiant output at the radiation curable secondary coating is equal to or greater than about 26 W/cm².

34. The method of claim 33, wherein the predetermined rate of speed is between about 1500 to about 3500 meters per minute, more preferably from about 2000 to about 3000 meters per minute, more preferably from about 2400 to about 2800 meters per minute, and the radiant output applied to the surface yields a coated optical fiber with a cured secondary coating having a reacted acrylate unsaturation of at least 90 %, more preferably at least 95 %, and an in-situ modulus from about 1 GPa to about 3 GPa.

35. The method of claim 33 or 34, wherein the radiant output applied to the surface yields a coated optical fiber with a cured secondary coating having a modulus ratio of between about 0.5 to about 2, more preferably between about 0.75 to about 1.5, more preferably between about 0.9 to about 1.1, or between about 0.85 to about 0.95.

36. The method of any of claims 33-35, wherein power input per line of the plurality of light emitting diodes is less than about 25 kW.

37. The method of any of claims 33-36, wherein power input per line of the plurality of light emitting diodes is between about 3.5 kW to about 25 kW, or from about 4 kW to about 20 kW, or from about 5b kW to about 15 kW, or from about 6 kW to about 10 kW, or from about 5 kW to about 7 kW.

38. The method of any of claims 33-37, wherein the plurality of light emitting diodes comprises a first array and wherein the curing lamp system comprises a first light source module comprising the first array and a first optical element;

(a) wherein the first array comprises a first row of light emitting diodes and wherein the first optical element is configured to focus light emitted from the first array toward the exposure area;

(b) wherein the first row comprises a plurality of consecutive dies

comprising:

(i) a first die comprising a first top electrode on a top surface of the first die and a first bottom electrode on a bottom surface of the first die, wherein the first bottom electrode of the first die is electrically coupled to a first conductive bonding pad, and wherein the first conductive bonding pad is mounted on a substrate; and (ii) a second die comprising a second top electrode on a top surface of the second die and a second bottom electrode on a bottom surface of the second die, wherein the second bottom electrode of the second die is electrically coupled to a second conductive bonding pad, and wherein the second conductive bonding pad is mounted on the substrate; and

(c) wherein the second conductive bonding pad includes an elongate portion that protrudes from a lateral side of the second conductive bonding pad, and the first top electrode of the first die is electrically coupled to the elongate portion of the second conductive bonding pad.

39. The method of claim 37 or 38, wherein the energy density of the radiant output at the surface of the optical fiber is between about 26 W/cm² and about 35 W/cm².

An LED bonding pad assembly comprising:

a row of conductive pads, configured for coupling a row of light emitting diode (LED) dies and comprising a plurality of consecutive pads, the plurality of consecutive pads comprising:

(i) a first pad; and

(ii) a second pad comprising an elongate portion, wherein the

elongate portion protrudes from the second pad;

(iii) wherein the first pad is consecutive with the second pad, and the first pad does not directly contact the second pad.

41. The LED bonding pad assembly of claim 40, wherein the elongate portion of the second pad extends along at least a portion of a first lateral side of the first pad.

42. The LED bonding pad assembly of claim 41, wherein the second pad further comprises a second elongate portion that extends along at least a portion of a second lateral side of the first pad.

43. The LED bonding pad assembly of claim 42, wherein the row of LED dies comprises a plurality of consecutive dies comprising:

(a) a first die comprising a first top electrode on a top surface of the first die and a first bottom electrode on a bottom surface of the first die, wherein the first bottom electrode of the first die is electrically coupled to the first pad; and

(b) a second die comprising a second top electrode on a top surface of the second die and a second bottom electrode on a bottom surface of the second die, wherein the second bottom electrode of the second die is electrically coupled to the second pad; and

the first top electrode is electrically coupled to the elongate portion of the second pad.

44. The LED bonding pad assembly of claim 43, wherein the first top electrode is electrically coupled to the elongate portion of the second pad by wire bonding.

45. The LED bonding pad assembly of claim 43 or 44, wherein the second pad further comprises a second elongate portion that extends along at least a portion of a second lateral side of the first pad, and wherein the first die further comprises a plurality of first top electrodes and at least one of the plurality of first top electrodes is electrically coupled to the second elongate portion.

An LED bonding pad assembly comprising: (a) a row of conductive pads, configured for coupling two rows of light emitting diode (LED) dies and comprising a plurality of consecutive pads, the plurality of consecutive pads comprising:

(i) a first pad comprising a first notch in a front edge of the first pad; and

(ii) a second pad comprising an elongate portion extending from a rear edge of the second pad, wherein a distal end of the elongate portion extends within the first notch of the first pad; and

(iii) wherein the first pad is consecutive with the second pad, and the first pad does not contact the second pad.

47. The assembly of claim 46, further comprising:

(a) a first row of LED dies comprising a plurality consecutive dies

comprising:

(i) a first die comprising a first top electrode on a top surface of the first die and a first bottom electrode on a bottom surface of the first die, wherein the first bottom electrode of the first die is electrically coupled to the first pad; and

(ii) a second die comprising a second top electrode on a top surface of the second die and a second bottom electrode on a bottom surface of the second die, wherein the second bottom electrode of the second die is electrically coupled to the second pad; and the first top electrode is electrically coupled to the elongate portion of the second pad; and

(b) wherein a second row of LED dies comprises a second plurality

consecutive dies comprising:

(iii) a third die comprising a third top electrode on a top surface of the third die and a third bottom electrode on a bottom surface of the third die, wherein the third bottom electrode of the third die is electrically coupled to the first pad and positioned alongside the elongate portion of the second pad such that the elongate portion is between the third die and the first die, and wherein the third top electrode of the third die is electrically coupled to the elongate portion; and

(iv) a fourth die comprising a fourth top electrode on a top surface of the fourth die and a fourth bottom electrode on a bottom surface of the fourth die, wherein the fourth bottom electrode of the fourth die is electrically coupled to the second pad.

48. The assembly of claim 47, wherein the first pad further comprises a second notch in the front edge of the first pad, the second pad having a second elongate portion extending from a read edge of the second pad, and wherein a second distal end of the second elongate portion extends within the second notch of the first pad.

49. The assembly of claims 47 or 48, wherein the front edge of the first pad is spaced from the rear edge of the second pad between about 0.005 mm to about 1 mm, more preferably from about 0.01 mm to about 0.6 mm, or from about 0.01 mm to about 0.5 mm, or from about 0.2 mm to about 0.4 mm.

50. The assembly of any of claims 47-49 wherein a length from a front edge of the second pad to the distal end of the elongate portion of the second pad is about 1.14 mm.