Patent Application
20140079367
The present invention relates to radiation curable coatings for optical fiber.
An optical fiber is a glass fiber that carries light along its length. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are also immune to electromagnetic interference.
Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fibers which support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those which can only support a single mode are called single-mode fibers (SMF). MMF generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. SMF are used for most communication links longer than 550 meters (1,800 ft).
Throughout this patent application, attenuation in fiber optics, also known as transmission loss, is defined as the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. Attenuation loss coefficients in optical fibers usually are reported using units of decibels per kilometer, abbreviated dB/km.
Attenuation is an important factor limiting the transmission of a digital signal across large distances. Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption.
In 1965, Charles K. Kao {one of three winners of the 2009 Nobel Prize in physics for “groundbreaking achievements concerning the transmission of light in fibers for optical communication”} and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), allowing optical fibers to be a practical medium for communication. They proposed that the attenuation in fibers available at the time was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. The crucial attenuation level of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. The achievement of such low attenuations ushered in optical fiber telecommunications and enabled the internet.
The following U.S. patent is incorporated by reference in its entirety: U.S. Pat. No. 6,014,488 issued on Jan. 11, 2000.
Microbends are sharp but microscopic curvatures in an 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. When present, microbends attenuate the signal transmission capability of the coated optical fiber. Thus for the success of a telecommunications network it is known each telecommunications system has a limit to the amount of tolerable increase in attenuation for optical fiber and that to avoid reaching that limit it is well to reduce microbending overall because reducing microbending, reduces the increase in attenuation.
One of the critical driving forces for the development of optical fiber coating technology is increased user demands on videos. For the existing technology of optical fiber coating, 2G network application is sufficient. However, the future networks, such as 3G, 4G, and IPTV, high definition television (HDTV), video conferencing and other high bandwidth applications will impose a higher requirement for the performance of optical fiber, therefore the requirement of performance of the optical fiber coating will become higher and higher.
In order to meet the huge demand of video applications on the internet, the telecommunication network of next generation requires the support of transmission of greater capacity, longer distance and broader spectral range, and the performance of the current generation of optical fibers G652 was developed for long haul straight alignment utility; therefore G562 is not suitable to meet the requirements of Fiber to the Home (FTTH) challenges.
As optical transport of communication signals migrates into homes and MDU's (Multiple Dwelling Units), optical glass fibers are encountering tighter bends, requiring optical fiber producers to offer G657 Macrobend resistant fibers. At the same time, increasing demands for bandwidth are putting strains on the available margin in deployed networks.
The first generation of radiation curable DeSolite Radiation curable Supercoatings™ (trademark of DSM IP Assets B.V.) for optical fiber are described and claimed in these U.S. patent applications, which are hereby incorporated by reference in their entirety: U.S. patent application Ser. No. 11/955,935, filed Dec. 13, 2007, published as US 20080226916 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,838, filed Dec. 13, 2007, published as US 20080241535 on Oct. 23, 2008; U.S. patent application Ser. No. 11/955,547, filed Dec. 13, 2007, published as US 20080226912 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,614, filed Dec. 13, 2007, published as US 20080226914 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,604, filed Dec. 13, 2007, published as US 20080226913 on Sep. 19, 2008;
U.S. patent application Ser. No. 11/955,721, filed Dec. 13, 2007, published as US 20080233397 on Sep. 25, 2008; U.S. patent application Ser. No. 11/955,525, filed Dec. 13, 2007, published as US 20080226911 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,628, filed Dec. 13, 2007, published as US 20080226915 on Sep. 19, 2008; and U.S. patent application Ser. No. 11/955,541, filed Dec. 13, 2007, published as US 20080226909 on Sep. 19, 2008.
U.S. patent application Ser. No. 11/955,541, filed Dec. 13, 2007, published on Sep. 18 2009 as US Published Patent Application 20080226909, entitled “D1381 RADIATION CURABLE SUPERCOATINGS FOR OPTICAL FIBER” describes and claims Radiation Curable Supercoatings for Optical Fiber as follows:
Supercoatings suitable for coating an optical fiber;
wherein the Supercoatings comprise at least two layers, wherein the first layer is a Primary Coating that is in contact with the outer surface of the optical fiber and the second layer is a Secondary Coating in contact with the outer surface of the Primary Coating,
wherein the cured Primary Coating on the optical fiber has the following properties after initial cure and after one month aging at 85° C. and 85% relative humidity:
wherein the cured Secondary Coating on the optical fiber has the following properties after initial cure and after one month aging at 85° C. and 85% relative humidity:
With the recent launch of the DeSolite Supercoatings™ line of Radiation curable Supercoatings for optical fiber, by DSM Desotech, see www.Supercoatings.com it has been reported that use of Supercoatings has great positive effect upon the microbending characteristics of the optical fiber. Thus using Supercoatings is known to reduce the amount of microbending in an optical fiber and reducing the amount of microbending reduces the amount of attenuation in the telecommunications network
As the demand for ever increasing bandwidth develops in the internet and current telecommunications devices, the demand for optical fiber that is attenuation resistant will also increase. Thus the demand for radiation curable Supercoatings will increase. As the demand for attenuation resistant optical fiber and radiation curable Supercoatings increases it would be desirable to have a method for selecting and formulating radiation curable Supercoatings for optical fiber.
The first aspect of the instant claimed invention is a method of formulating radiation curable Supercoatings for application to an optical fiber used in a telecommunications network, wherein said Supercoatings comprise at least two layers, the first layer being a primary coating that is in contact with the outer layer surface of the optical fiber and the second layer being a secondary coating in contact with the outer surface of the primary coating, wherein the cured primary coating on the optical fiber has the following properties after initial cure and after at least one month aging at 85° C. and 85% relative humidity:
The second aspect of the instant claimed invention is the Method of the first aspect, in which the Three-Dimensional Laced Methodology includes using a Multi-Layer Film Drawdown method to evaluate composite fused Primary Coating Layer and Secondary Coating Layer of Radiation curable Supercoatings.
The third aspect of the instant claimed invention is a Multi-Layer Film Drawdown Method comprising the steps of:
The fourth aspect of the instant claimed invention is a single-mode optical fiber coated with Supercoatings, wherein said Supercoatings comprise,
wherein the composition of the Primary Coating layer, prior to curing, is selected from the group consisting of the formulations of Examples 1PA2, 1PB3, 1PC1, 1PD5, 2Alpha, and 2Beta;
wherein the composition of the Secondary Coating layer, prior to curing, is selected from the group
consisting of the formulations of Examples 2SA4 and 2SB3 and 3SA1 and 5SA1.
The fifth aspect of the instant claimed invention is a multi-mode optical fiber coated with radiation curable coatings comprising a Primary Coating Layer and
wherein the composition of the Primary Coating layer, prior to curing, is selected from the group
consisting of the formulation of Example 1PD5; and
wherein the composition of the Secondary Coating layer, prior to curing, is selected from the group
consisting of the formulations of Examples 2SA4 and 2SB3 and 3SA1 and 5SA1.
The first aspect of the instant claimed invention is a method of formulating radiation curable Supercoatings for application to an optical fiber used in a telecommunications network, wherein said Supercoatings comprise at least two layers, the first layer being a primary coating that is in contact with the outer layer surface of the optical fiber and the second layer being a secondary coating in contact with the outer surface of the primary coating, wherein the cured primary coating on the optical fiber has the following properties after initial cure and after at least one month aging at 85° C. and 85% relative humidity:
and wherein the cured secondary coating on the optical fiber has the following properties after initial cure and after at least one month aging at 85° C. and 85% relative humidity:
said method comprising the steps of:
The first step in the process is determining the Maximum Acceptable Increase in Attenuation requirements for the telecommunications network where the optical fiber will be installed. Determining the attenuation requirements for the telecommunications network involves the design criteria for the Optical Fiber Network. Some considerations in the design include: an understanding of how much of the network is straight line installation of multi-mode optical fiber as compared to how much of the network is Fiber-to-the-Home (abbreviated FFTH) installation of single mode optical fiber. There are many other design criteria for an Optical Fiber network that are known to people of ordinary skill in the art of designing Optical Fiber Networks.
Specific Considerations in design of Optical Fiber Networks include the following:
It is currently known, that in contrast to traditional straight line optical fiber long haul networks, that FTTH applications have to work at least at three wavelengths:
There are several sources for the standards for attenuation in the telecommunications industry. One such standards setting organization is The Telecommunications Industry Association (TIA), which is the leading trade association representing the global information and communications technology (ICT) industries through such activities such as: Standards development, Providing Market Intelligence, Government affairs guidance, Certification of optical fiber and networks containing optical fiber and advice regarding World-wide environmental regulatory compliance. TIA's United States Technical Advisory Groups (USTAG) also participates in international standards-setting activities, such as the International Electrotechnical Commission (IEC).
Another source for the standards for attenuation in the telecommunications industry is the IEC. The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes international standards for all electrical, electronic and related technologies. These serve as a basis for national standardization and as references when drafting international tenders and contracts.
Telcordia is a U.S. based corporation that provides fiber optic media & components analysis & consulting services. They also write and keep a library of Generic Requirements for Optical Fiber.
All of these organizations have publicly available literature, reports and standards that are used by people of ordinary skill in the art of designing optical fiber networks.
Methods used to test for microbending sensitivity are described in IEC TR 62221, First Edition 10-2001. There are currently four test methods used to determine microbending sensitivity, which is reported in attenuation units of dB/km.
Method A—Expandable Drum calls for at least 400 m of fiber to be wound with minimal tension around an expandable drum with material of fixed roughness on the drum surface. Method B—Fixed-Diameter Drum calls for at least 400 m of fiber to be wound with 3N tension around a fixed-diameter drum with material of fixed roughness on the drum surface. Method C—Wire Mesh calls for application of wire mesh (under load) to the fiber under Test. Method D—Basketweave calls for 2.5 km of fiber to be applied to a fixed diameter drum via a “basketweave” wrap.
Of these four test methods, only Method D, specifically describes a procedure to measure the microbending sensitivity of fibers as a function of temperature and provides the microbending sensitivity over a wide temperature range and suggests that temperature cycling could include lower temperatures such as −60° C.
Throughout this patent application, microbending sensitivity using test Method D—Basketweave will be spoken of in terms of a dB/Km number, at a specified wavelength and temperature.
There are at least four different types of tests currently in use to test for Microbending Sensitivity with test results being reported in attenuation units of dB/km. Four specific Microbending Sensitivity test Methods are described in IEC TR 62221, First Edition 10-2001.
They are as follows:
Throughout this patent application, Method D measured Microbending Sensitivity will be discussed and reported in units of attenuation which will be spoken of in terms of a dB/Km number, at a specified wavelength and temperature. It is understood that whatever Microbending Sensitivity is given, that the number given is the Maximum Acceptable Increase in Attenuation permissible for that optical fiber in a given telecommunications network.
Of these four test methods, only Method D, specifically describes a procedure to measure the Microbending Sensitivity of fibers as a function of temperature and provides the Microbending Sensitivity over a wide temperature range and suggests that temperature cycling could include lower temperatures such as −60° C.
It is understood, within the industry, that it is unlikely that Optical Fibers in a telecommunications network would be routinely exposed to temperatures as low as −60° C. However, after recent field failures in China, it is also beginning to be understood that having a specification for Microbending Sensitivity for the optical fiber in a telecommunications network at room temperature of approximately 25° C. is not sufficient to protect a telecommunications network from having “dark fiber” develop over the course of a winter where the temperature is below freezing (0° C. or 32° F.) for extended periods of time.
Applicants have chosen to report Microbending Sensitivity as a change in attenuation from a baseline per the IEC procedure; this procedure requires the reporting of change in attenuation be reported at specific wavelengths and a temperature of −60° C. Applicants believe that reporting Microbending Sensitivity data at these extreme temperature conditions will provide a type of “worst case scenario” possibility for Microbending Sensitivity of the coated optical fiber in the field.
It is Applicants' position that if the Microbending Sensitivity properties of the Optical Fiber at the −60° C. level are deemed to be acceptable, then it is reasonable to assume that the performance of the Optical Fiber at room temperature, assuming the same level of mechanical stress, will also be acceptable.
Further to this point, at room temperature Microbending Sensitivity testing it may or may not be possible to identify the difference in Microbending Sensitivity between an Optical Fiber coated with a standard, “non-Supercoatings” coating, because neither Supercoatings or a non-Supercoatings is anywhere near their glass transition temperature (Tg) for the primary coating layer at room temperature.
The difference between an Optical Fiber coated with a standard “non-Supercoatings” coating and an Optical Fiber coated with Supercoatings shows up with Microbending Sensitivity testing at the extreme low temperatures because the standard “non-Supercoatings” Primary Layer exceeds its glass transition temperature at the extreme low temperatures and thus transitions from rubbery state to glassy state. Having the Primary Layer of an Optical Fiber coating being in the glassy state is known to cause an increase in Microbending Sensitivity. In contrast, the Tg of a Supercoatings Primary Layer is much lower and therefore the Primary Layer of Supercoatings remains in the rubbery phase which is better for Microbending Sensitivity.
Another way of explaining the difference between standard “non-Radiation curable Supercoatings” for Optical Fiber and Radiation curable Supercoatings for Optical Fiber is that the combination of fully cured, low modulus and low Tg coatings in the Primary Coating Layer and fully cured, high modulus, high Tg coatings in the Secondary Coating Layer of the Supercoatings leads to acceptable performance under the stress of either extreme temperature or mechanical stress or both temperature and mechanical stress with acceptable performance being gauged by the low level of Microbending Sensitivity which is reflected in the fiber having an acceptable increase in reported attenuation.
In current practice, it is understood that the Telecommunications network generally requests that Optical Fiber be supplied with a known maximum attenuation at 1310 nm and room temperature. This highest tolerable level of attenuation is known to people of ordinary skill in the art of design criteria for Telecommunications networks.
For Optical Fibers coated with Radiation curable Supercoatings, it is possible and desirable to report Microbending Sensitivity at three separate wavelengths and at a very cold (−60° C.) temperature. This data can then be used by the Network designer to understand the limits, and be able to predict failure modes for the network. It is applicants' position that a network containing Optical Fibers coated with standard, “non-Supercoatings” will have much less tolerance to the stress involved from the cable environment of temperature extremes and mechanical forces than will a network containing Optical Fibers coated with Radiation curable Supercoatings. Another factor is that it is believed that using Radiation curable Supercoatings to coat Optical Fiber will provide a Telecommunications network with sufficient data to be able to design without requiring the same “safety margin” as is built in with using standard “non-Radiation curable Supercoatings” to coat Optical Fiber.
The next step in the process is determining the Field Application Environment of the Supercoatings requirements for the telecommunications network where the optical fiber will be installed. The Field Application Environment involves the understanding of four factors:
Regarding element i): Optical Fiber is known to have standard grades for installation of long haul straight cable. Recently various grades of “bend resistant” Optical Fiber have been developed by Optical Fiber Suppliers such as Corning and Drake and OFS and YOFC and others. These bend resistant Optical Fibers are being deployed in Fiber to the Node (FTTX) and Fiber to the Home (FTTH) applications.
Details about standard grade and Microbend resistant Optical Fibers are available from the Suppliers own literature and websites.
Current commercial Optical Fiber available for sale include: Corning® InfiniCor® optical fibers, Corning® ClearCurve® OM2/OM3/OM4 multimode optical fiber, Corning® ClearCurve® single-mode optical fiber, Corning® SMF-28e® XB optical fiber, Corning® SMF-28® ULL optical fiber,
Corning® LEAF® optical fiber, Corning® Vascade® optical fibers and Corning® Specialty Fiber,
OFS AllWave® Zero Water Peak (ZWP) and newly introduced OFS AllWave FLEX ZWP Fibers, OFS LaserWave® Fibers, OFS Access ADVANTAGE™ System. OFS HCS®, OFS FiberWire®, and OFS PYROCOAT® brand technologies, YOFC HiBand GIMM fiber, YOFC High Temperature Fibre (HTF) Series, YOFC HiBand Graded-index Multimode Optical Fiber (50/125 & 62.5/125 um) and others.
Typically fiber to be deployed in straight line applications undergoes less stress, and less microbending than fiber to be deployed in FTTX and FTTH applications. Therefore, the selection of Radiation curable Supercoatings to be applied to fiber for FTTX and FTTH applications is crucial to the performance of FTTX and FTTH optical fiber. Accordingly, whenever the optical fiber to be coated is designated for FTTX and FTTH applications, the Supercoatings must be highly resistant to microbending.
Unique to formulating Supercoatings is just how much of the formulation requirements to achieve the six required properties are dependent upon the Mechanical aspects of the coating of an optical fiber. For example, it is possible to coat a standard grade of Optical Fiber with Supercoatings and obtain a Coated Optical Fiber with desired attenuation properties, but it is also possible to coat a “Bend-Resistant” premium grade of Optical Fiber with a standard, “non-Supercoatings”, and have the result be a coated optical fiber with unacceptable Microbending Sensitivity leading to the failure in achieving the system required tolerable level of attenuation. Therefore, in order to produce an optical fiber with the desired attenuation properties it is desirable, optionally even necessary, for the formulator of Supercoatings to have an understanding of the details of the optical fiber production process. These details include the type of glass, the processing temperature, the atmosphere surrounding the application of coating(s), the line speed, the type of radiation source, typically described as a “curing lamp”, and the location and number of curing lamps along the processing line and whether the secondary coating is applied over the primary coating wet on wet or wet on dry. These types of mechanical aspects to the glass processing have, in the past, not been of interest to the formulator of the Optical Fiber coatings because the formulator focused on the Optical Fiber coatings and the glass manufacturer focused on the glass. As stated previously, without an adequate amount of information about the processing of the glass, it is possible to coat a standard grade of Optical Fiber with Supercoatings and obtain a Coated Optical Fiber with desired Microbending Sensitivity properties, but it is also possible to coat a “Bend-Resistant” premium grade of Optical Fiber with a standard, non-Supercoatings, and have the result be a coated optical fiber without the desired Microbending Sensitivity properties.
Regarding element iii) the type, number of lights and positioning of lights along the draw tower manufacturing line that are used to cure the Supercoatings on the optical fiber; the use of conventional ultraviolet mercury arc lamps to emit ultraviolet light suitable to cure radiation curable coatings applied to optical fiber is well known. Ultraviolet arc lamps emit light by using an electric arc to excite mercury that resides inside an inert gas (e.g., Argon) environment to generate ultraviolet light which effectuates curing. Alternatively, microwave energy can also be used to excite mercury lamps in an inert gas medium to generate the ultraviolet light. Throughout this patent application, arc excited and microwave excited mercury lamp, plus various additives (ferrous metal, Gallium, etc.) modified forms of these mercury lamps are identified as mercury lamps. Conventional ultraviolet mercury arc lamps are the “state-of-the-art” when it comes to curing of radiation curable coatings for optical fiber.
However, the use of ultraviolet mercury lamps as a radiation source suffers from several disadvantages including environmental concerns from mercury and the generation of ozone as a by-product. Further, mercury lamps typically have lower energy conversion ratio, require warm-up time, generate heat during operation, and consume a large amount of energy when compared with Lights that are generated by Light Emitting Diodes “LED”.
Knowing what type of light is going to be used in the curing of the Radiation Curable Supercoatings is critical information because in the production of coated optical fiber, the heat generated by the UV mercury lamps can negatively impact the liquid coating in that if the coating is not formulated to avoid the presence of volatiles, those volatiles may be excited and deposit upon the quartz tube surface, blocking the UV rays from irradiating the liquid coating on the glass fiber which inhibits the curing of the liquid coating to a solid.
In contrast to ultraviolet mercury lamps, light emitting diodes (LEDs) are semiconductor devices which use the phenomenon of electroluminescence to generate light. LEDs consist of a semiconducting material doped with impurities to create a p-n junction capable of emitting light as positive holes join with negative electrons when voltage is applied. The wavelength of emitted light is determined by the materials used in the active region of the semiconductor. Typical materials used in semiconductors of LEDs include, for example, elements from Groups 13 (III) and 15 (V) of the periodic table. These semiconductors are referred to as III-V semiconductors and include, for example, GaAs, GaP, GaAsP, AlGaAs, InGaAsP, AlGaInP, and InGaN semiconductors. Other examples of semiconductors used in LEDs include compounds from Group 14 (IV-IV semiconductor) and Group 12-16 (II-VI). The choice of materials is based on multiple factors including desired wavelength of emission, performance parameters, and cost.
Early LEDs used gallium arsenide (GaAs) to emit infrared (IR) radiation and low intensity red light. Advances in materials science have led to the development of LEDs capable of emitting light with higher intensity and shorter wavelengths, including other colors of visible light and UV light. It is possible to create LEDs that emit light anywhere from a low of about 100 nm to a high of about 900 nm. Currently, known LED UV light sources emit light at wavelengths between about 300 and about 475 nm, with 365 nm, 390 nm and 395 nm being common peak spectral outputs. See textbook, “Light-Emitting Diodes” by E. Fred Schubert, 2nd Edition, © E. Fred Schubert 2006, published by Cambridge University Press.
LED lamps offer advantages over conventional mercury lamps in curing applications. For example, LED lamps do not use mercury to generate UV light and are typically less bulky than mercury UV are lamps. In addition, LED lamps are instant on/off sources requiring no warm-up time, which contributes to LED lamps' low energy consumption. LED lamps also generate much less heat, with higher energy conversion efficiency, have longer lamp lifetimes, and are essentially monochromatic emitting a desired wavelength of light which is governed by the choice of semiconductor materials employed in the LED.
Several manufacturers offer LED lamps for commercial curing applications. For example, Phoseon Technology, Summit UV Honle UV America, Inc., IST Metz GmbH, Jenton International Ltd., Lumios Solutions Ltd., Solid UV Inc., Seoul Optodevice Co., Ltd, Spectronics Corporation, Luminus Devices Inc., and Clearstone Technologies, are some of the manufacturers currently offering LED lamps for curing ink-jet printing compositions, PVC floor coating compositions, metal coating compositions, plastic coating composition, and adhesive compositions.
Regarding element iv) the line speed at which the Supercoatings will be applied, in D1381 RADIATION CURABLE SUPERCOATINGS FOR OPTICAL FIBER, U.S. patent application Ser. No. 11/955,541, filed Dec. 13, 2007, published on Sep. 18 2009 as US Published Patent Application 20080226909, entitled it is stated that a Supercoating may be applied to single-mode optical fiber at a line speed of between about 750 meters/minute to about 2100 meters/minute. As of the date of filing this patent application, Oct. 8, 2010, the optical fiber industry has now progressed to the point where it is possible to draw single-mode optical fiber at line speeds in excess of 2100 meters/minute. It is also possible to draw single-mode optical fiber at line speeds in excess of 2200 meters/minute. It is also possible to draw single-mode optical fiber at line speeds in excess of 2300 meters/minute. It is believed, without intending to be bound thereby that it may also be possible to draw single-mode optical fiber at line speeds in excess of 2350 meters/minute. It is believed, without intending to be bound thereby, that it may also be not possible to draw single-mode optical fiber at line speeds in excess of 2400 meters/minute.
The next step in the process involves using a Three-Dimensional Laced Methodology Evaluation of candidate Radiation curable Supercoatings by evaluation of the Radiation curable Supercoatings Primary Layer and Secondary Layer. Historically Primary and Secondary coatings for optical fiber were formulated and reformulated according to a two-dimensional diagramed way of formulating.
In
The possible ways to change the coating are illustrated by the information contained in Table 1A, 1B, 1C, 1D, 1E, 2A, 2B, 2C, 2D, 2E, 1F, 2F, 1G, 2G, 1H, 2H, 1J, and 2J which summarize the state-of-the-art understanding of the ingredients that may or may not be used in formulating Primary and Secondary Radiation Curable Coatings for optical fiber with respect to creating formulations with physical properties of the Primary Coating Layers and Secondary Coating Layers on the Optical Fiber that meet the rigorous criteria of Supercoatings. In addition to the information in the Tables contained herein, additional information may be found in issued patents, published patent applications, scientific papers and other information commonly known to people of ordinary skill in the art of Radiation Curable Coatings for Optical Fiber.
In contrast to the “two-dimensional” approach illustrated in
The six necessary properties for Supercoatings for Optical Fiber are as follows:
The cured Primary Coating on the optical fiber has the following properties after initial cure and after one month aging at 85° C. and 85% relative humidity:
wherein the cured Secondary Coating on the optical fiber has the following properties after initial cure and after one month aging at 85° C. and 85% relative humidity:
Step ii) of the instant claimed invention, as illustrated in
The second aspect of the instant claimed invention is the Method of the first aspect of the instant claimed invention, in which the Three-Dimensional Laced Methodology includes using a Multi-Layer Film Drawdown method to evaluate composite fused Primary Coating Layer and Secondary Coating Layer of Radiation curable Supercoatings.
The third aspect of the instant claimed invention is a Multi-Layer Film Drawdown Method comprising the steps of:
The Multi-Layer Film Drawdown method flat plate substrate method for evaluation of layers of potential Radiation curable Supercoatings-Primary and Secondary Layers comprises the following steps:
1) For reference the general method for preparing drawdown films for UV curing is described by Szum et al., 43rd IWCS Proceedings (1994), p. 59.
2) The typical practice is to start with a clean single-thickness window-pane glass. One or more small daubs of test coatings are applied to the glass plate itself, or to an overlaid polyester sheet covering the glass plate, and drawn down with a Bird type calibrated bar to spread a coherent thin film of 25μ to 75μ. One such Bird type bar for the first layer has a film deposit height of 1.5 mils. These test coatings are most typically inner primary coatings.
3) Immediately after this first drawdown, a second drawdown is made over the top and wide enough to cover the edges of the first drawdown films. This second drawdown is also made with a Bird type bar calibrated to deposit a film of typically 75μ to 254μ. One such Bird type bar for the second layer has a film deposit height of 3.0 mils. The glass plate with the two drawdowns and the consequent composite films is exposed to suitable actinic radiation to achieve the desired degree of cure. This method is known as the wet-on-wet method.
4) A similar method known as wet-on-dry method, is conducted in the same manner as the wet-on-wet method described above; except the first drawdown films are exposed to actinic radiation to effectuate the cure of the Primary Coating Layer. After this radiant exposure the second drawdown is made and the plate is then further exposed to radiation to effectuate the cure of the Secondary Layer and the Primary Layer into a Fused Composite film.
5) This procedure results in the glass plate having upon its surface area cured composite films composed of a first layer of specified thickness and a second layer of a thickness calculated by the difference of the thickness of the first layer subtracted from the nominal thickness of the calibrated Bird type bar used for the second overcoating drawdown. These Fused Composite films are then suitable for typical testing related to the properties desirable in Radiation curable Supercoatings intended for optical fiber applications.
The method is used to apply some small dots of primary to a glass plate and drawdown with a 1 mil or 1.5 mil Bird Bar. While the primary is still uncured, a second drawdown of a colored secondary coating layer is made over the primary coating layer but with a 3 mil bar. The result is observed to be acceptably uniform as can be seen in
In practice, the Supercoatings Primary Layer is drawn down with a 1.5 mil bar, then a candidate for Supercoatings Secondary layer, observed as a brown layer, Example 3SA3 Color twoH, {Color 2HBrown} is drawn down over the Supercoatings Primary with a 3 mil bar. After this wet-on-wet application, the plate is exposed to radiation sufficient to effectuate the cure of both the Primary Coating Layer and the Secondary Coating Layer into a Fused Composite Film.
In
Follow-up analysis shows very little mixing of the layers during the dual-drawdown method.
It was surprising to discover that a simple w-o-w drawdown would leave both the bottom and top layers intact with their separate identities, and yet the two layers then fuse into a Fused Composite film during cure.
The lack of mixing of the layers is further illustrated in
These composite films are then suitable for typical testing related to the properties desirable in Radiation curable Supercoatings intended for optical fiber applications. Testing can include % RAU. This is especially of value when the Secondary layer is being applied wet over a wet Primary Coating Layer and it becomes critical that the cure rate of the Secondary layer is not faster than the cure rate of the Primary Coating layer because if the Secondary Coating cures faster than the primary coating then the Primary Coating may never cure to its desired % RAU because the optical transmission of cured Secondary Coating Layer is typically less than that of liquid, uncured Secondary Coating Layer.
An interesting observation is that with this new Method of Formulating Radiation curable Supercoatings for Optical Fiber it has been possible to formulate Radiation curable Supercoatings with the following enhanced functional Properties:
A % RAU that ranges now to an upper limit of about 100% for both the Primary Coating Layer and the Secondary Coating Layer.
This method permits the investigation of the properties of primary and secondary as a composite Supercoatings film in ways not available in the past. With this method it is now possible to conduct feasibility studies of Supercoatings Candidate Secondary Layers over Supercoatings Candidate Primary Layers for tensile properties, DMA characteristics, environmental durability, etc., with easily handled films instead of having to use the Draw Tower Simulator. There are many understood benefits of using the Multi-layer Film Drawdown method, including, but not limited to the following: the film drawdown takes away the line speed as a factor in coatings functionality to allow for more basic analysis; it also allows the formulator to evaluate the migration of materials from layer to layer during the wet on dry and wet on wet processing steps.
Another advantage of the Multi-Layer Film Drawdown method is that it is critical for both wet on wet processing and wet on dry processing that sufficient through cure is possible to cure the primary coating to the requisite percentage RAU when the coating is applied to wire or optical fiber. In practice, it is known that in Wet on dry processing, the primary coating may be undercured to achieve line speed with the expectations that the cure will be finished in the primary coating when the radiation is applied to the secondary coating. Therefore use of the Multi-Layer Film Drawdown method is helpful to simulate wet on wet application as compared to wet on dry application and testing the % RAU to determination of cure of primary through the secondary. The simulation allows the formulator to quickly evaluate the efficacy of different photoinitiators. This testing has already led to the hypothesis that for Radiation Curable Supercoatings for Optical Fiber, to achieve the very high levels of % RAU that are desired and required, it is believed, without intending to be bound thereby, to be better to have a different chemical type of photoinitiator in the Secondary Coating layer than in the Primary Coating layer. In this way, there will be two different photo initiated reactions taking place in the layers, rather than having one photoinitiator try to achieve the desired level of cure in both layers.
Another benefit of the Multi-layer film drawdown method is approximating the composite behavior of the cured secondary coating layer over the cured primary coating that can be correlated with Primary and Secondary characteristics that can be defined in SUPERCOATINGS. It is possible to evaluate the functional properties of each coating layer by analyzing film using solid film rheology testing, otherwise known as DMA (dynamic Mechanical Analysis)
The conclusion is that there is very little intermixing during the dual drawdown process, and that the method is useful in evaluating candidates for Supercoatings Primary Coating Layers and Supercoatings Secondary Coating Layers.
The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope.
The ingredients listed in these Examples have the following commercial names, are available from the listed source and have the indicated chemical composition.
The present invention is further illustrated with a number of examples.
In all of these examples, the process is as follows:
An optical fiber manufacturer wishes to apply a radiation curable Supercoatings to their Single Mode Optical Fiber.
The glass used in this Single Mode Optical Fiber is of the most modern type, able to resist Microbending.
The requested Microbending Sensitivity for optical fiber used in this network is reported at:
The radiation curable Radiation curable Supercoatings is applied Wet on Dry.
The curing lights available are: 600 w/10 inch D Lamps.
The number of curing lights are: 2 in the primary area and 4 after the secondary coating is applied-possibly up to 5 if needed.
The line speed at which the Supercoatings will be applied is about 1400 m/minute.
Four different formulators are given the task of working on potential Primary Coating Layers for this radiation curable Supercoatings.
Each Primary Coating Formulator selects the raw materials for their starting Oligomer, then the photoinitiator(s), antioxidant, one or more diluent monomers and other additives based on information available. In general, without intending to be bound thereby, the oligomer synthesis is carried out as follows:
Oligomers suitable for coating compositions of the invention are prepared by reaction of at least one polyether polyol, at least one diisocyanate, at least one hydroxyl terminated acrylate or (meth)acrylate, and optionally an alcohol. The following oligomer synthesis methods illustrate two different methods for synthesizing the oligomer. However, it will be appreciated by the skilled artisan that other synthesis methods also can be used so long as the oligomer comprises a urethane-backbone, with at least one terminal unsaturated group such as an alkenyl group or vinyl group.
Oligomer Synthesis—Method A is also known as an “outside-in” method that first reacts the isocyanate with hydroxyl terminated acrylate or methacrylate, followed by the reaction with polyol.
To a mixture of diisocyanate and inhibitor, HEA is added in a controlled manner so that the temperature does not exceed 40° C. The mixture is allowed to react at 40° C. for 2 h so that the desired NCO content is reached. Polyol and catalyst are then added, and the mixture is allowed to react at 80° C. for 2 h or longer, until the NCO content is not greater than 0.10.
Oligomer Synthesis—Method B is also known as an “inside-out” method that first reacts the isocyanate with polyol, followed by the reaction with hydroxyl terminated acrylate or methacrylate.
Catalyst is added to a mixture of diisocyanate, polyol and inhibitor. The mixture is allowed to react at 60° C. for 2 h, so that the desired NCO content is reached. Then, HEA is added, and the mixture is allowed to react at 85° C. for 1 h or longer, until the NCO content is not greater than 0.05.
Polyether polyols suitable for preparing oligomers in accordance with the invention preferably are selected from the group consisting of a polyethylene glycol and a polypropylene glycol. In an embodiment, the polyether polyol is a polypropylene glycol.
Catalysts for synthesizing urethane based oligomers for use in radiation curable coatings for optical fiber are known in the art. The catalyst is selected from the group consisting of copper naphthenate, cobalt naphthenate, zinc naphthenate, triethylamine, triethylenediamine, 2-methyltriethyleneamine, dibutyl tin dilaurate (DBTDL); metal carboxylates, including, but not limited to: organobismuth catalysts such as bismuth neodecanoate, CAS 34364-26-6; zinc neodecanoate, CAS 27253-29-8; zirconium neodecanoate, CAS 39049-04-2; and zinc 2-ethylhexanoate, CAS 136.53-8; sulfonic acids, including but not limited to dodecylbenzene sulfonic acid, CAS 27176-87-0; and methane sulfonic acid, CAS 75-75-2; amino or organo-base catalysts, including, but not limited to: 1,2-dimethylimidazole, CAS 1739-84-0; and diazabicyclo[2.2.2]octane (DABCO), CAS 280-57-9 (strong base); and triphenyl phosphine; alkoxides of zirconium and titanium, including, but not limited to zirconium butoxide, (tetrabutyl zirconate) CAS 1071-76-7; and titanium butoxide, (tetrabutyl titanate) CAS 5593-70-4; and ionic liquid phosphonium, imidazolium, and pyridinium salts, such as, but not limited to, trihexyl(tetradecyl)phosphonium hexafluorophosphate, CAS No. 374683-44-0; 1-butyl-3-methylimidazolium acetate, CAS No. 284049-75-8; and N-butyl-4-methylpyridinium chloride, CAS No. 125652-55-3; and tetradecyl(trihexyl) phosphonium.
All of these catalysts are commercially available.
In an embodiment, the catalyst is DBTDL or is an organobismuth catalyst such as “COSCAT 83” proprietary organobismuth catalyst, available from CosChem.
The choice of Photoinitiator is determined by:
There are two general classes of photoinitiators:
Type I: photoinitiators undergo a uni-molecular bond cleavage upon irradiation to yield free radicals
Type II: photoinitiators undergo a bimolecular reaction where the excited state of the photoinitiator interacts with a second molecule (a co-initiator) to generate free radicals.
UV photoinitiators of both Type I and Type II are available.
Two different formulators are given the task of working on potential Secondary Coating Layers for this radiation curable Supercoatings.
Each Secondary Coating Formulator selects the raw materials for their starting Oligomer, then the photoinitiator(s), antioxidant, one or more diluent monomers and other additives based on information available.
In selecting their raw materials, each Secondary Coating Formulator takes into account the following: TDI Type II is inexpensive, and is a fast reacting isocyanate. Further to the selection of TDI Type II for use in Secondary Coatings, group contribution theory (takes the characteristics of each part of the group and contributes) teaches that the aromatic group in the isocyanate contributes to high Tg and high modulus in the secondary, which is a technical reason why aromatic isocyanates would be favored for secondary coatings.
BHT Food Grade: Antioxidant scavenges free radicals (which is important because HEA (inhibited by methyl hydroquinone) can self-polymerize); therefore a synthetic chemist plans the synthesis to have the BHT in the reaction mixture before the HEA The scavenging reaction also requires the presence of oxygen—it is known that the oxygen in normal ambient air is typically sufficient for this purpose.
2-HEA (2-hydroxy ethyl acrylate) is a simple acrylate which historically has yielded very good cure rates in formulated radiation curable coatings for optical fiber. HBA (hydroxy butyl acrylate) or HPA (hydroxyl ethyl acrylate) are known to be not as reactive in the synthesis.
Both the Primary Coating Formulators and the Secondary Coating Formulators are aware of the following as they formulate; the polymerization of the secondary coating layer causes shrinkage of that layer and the shrinkage of the secondary coating layer puts pressure on the primary coating layer, whether the primary coating layer is already cured or is in the process of being cured when the secondary coating layer is being cured. Stress relaxation is a measure of the relief of stress on the primary caused by the shrinkage of the secondary coating as the secondary coating polymerizes. The temperature of the polymerization of the Secondary Coating Layer of a Supercoating has to be above the Tg for fast relief of that shrinkage. In formulating radiation Curable Supercoatings for Optical Fiber, it is assumed that the temperature of the polymerization of both the Primary and Secondary coating layer is well above their Tg's. If the polymerization temperature is below Tg, the stress relaxation is not as fast. If stress relaxation does not timely occur, the stress on the optical fiber can lead to unacceptable attenuation.
Wet on Wet processing has the potential for additional stress relaxation issues only because the fiber is being coated with two liquids before any polymerization occurs and both liquids are potentially cooler than the fiber, then there will be simultaneous polymerization taking place with dual heats of polymerization so as the curing takes place the temperature profile is uneven between the coating layers. Again, the formulators have to be aware of the fact that with the polymerization taking place simultaneously the difference in cross-link density is also a huge factor as there is much less cross-link-density in the primary coating as there is the secondary.
In the field of optical fiber manufacture it is known that the fiber cabler desires that the optical fiber is in a relaxed state before the optical fiber is manipulated further during the cabling process.
Thus, all formulators have to be aware that minimizing stress relaxation issues is critical, otherwise, the cabling operation will take longer as the cabler has to wait longer after the coatings are applied to the optical fiber to cable the optical fiber to allow for more stress relaxation to occur. It is known if the formulators misformulate such that the primary coating layer and the secondary coating layer don't relax properly and timely, it will be very, very difficult for the cabled optical fiber to not exceed the you never achieve the Maximum Acceptable Increase in Attenuation.
To enhance stress relaxation the formulators select materials that are more flexible in the secondary coating; however, these flexible materials must be selected in such a way that the additional flexibility does not negatively interfere with targeted physical properties of high Tg and high strength.
These Examples illustrate Formulator Alpha's candidate formulations for the candidate Primary Coating Layer of the Supercoatings.
These Examples illustrate Formulator Beta's candidate formulations for the Primary Coating Layer of the Supercoatings
These Examples illustrate Formulator Gamma's candidate formulations for the Primary Coating Layer of the Supercoatings.
Examples 2SA1-2SA5 illustrate Formulator Episilon's candidate formulations for the Secondary Coating Layer
These Examples illustrate Formulator Zeta's Candidate formulations for the Secondary Coating Layer of the Supercoatings
The results of the Multilayer Film Drawdown analysis show the most compatible potential combinations are:
An optical fiber manufacturer wishes to save energy costs by switching at least part of their curing lights over to LED lights. They decide to start the switch by changing their lights curing the primary coating to LED lights. Their current primary coating is Example 1PB3 (from Example 1).
The Single Mode Optical Fiber is of the most modern type, able to resist Microbending.
The requested Microbending Sensitivity for single mode optical fiber used in this network is reported at:
The Single Mode Optical Fiber is of the most modern type, able to resist Microbending
The radiation curable Radiation curable Supercoatings is applied Wet on Dry.
The type of curing lights for the primary coating are: The optical fiber manufacturer wants the flexibility of working with any LED lamp at 395 nm with a power of at least 4 W/cm2. For purposes of this Example, the LED Lamp chosen is a 8 W/cm2 LED unit with a peak emission at 395 nm. This type of LED lamp is available from Phoseon as an RX Fireline LED unit.
The number of curing lights are: from 1 to 3 in the Primary Coatings area,
The type of curing lights for the secondary coating are: 600 w/10 inch D Lamps
The number of curing lights: 3 in the Secondary Coatings Area
The line speed at which the Supercoatings will be applied is approximately 1300 m/min.
Therefore the fourth aspect of the instant claimed invention is a single-mode optical fiber coated with Supercoatings, wherein said Supercoatings comprise,
Primary Coating Layer and a Secondary Coating Layer,
wherein the composition of the Primary Coating layer, prior to curing, is selected from the group consisting of the formulations of Examples 1PA2, 1PB3, 1PC1, 2Alpha, 2Beta; and wherein the composition of the Secondary Coating layer, prior to curing, is selected from the group consisting of the formulations of Examples 2SA4 and 2SB3 and 5SA1.
An optical fiber manufacturer—wishes to apply a radiation curable Supercoatings for their Single Mode Optical Fiber. The Single Mode Optical Fiber is of the most modern type, able to resist Microbending.
The requested Microbending Sensitivity for single mode optical fiber used in this network is reported at:
The Single Mode Optical Fiber is of the most modern type, able to resist Microbending
The radiation curable Radiation curable Supercoatings is applied Wet on Wet.
The Secondary Coating is a Colored Secondary, wherein the clear Secondary Base Coat is mixed in line with a Color Concentrate.
The type of curing lights are: Proprietary Lamps with a metal halide spectrum similar to Fusion D lamps
The number of curing lights is: 3 lamps/20 inch.
The line speed at which the Supercoatings will be applied is approximately 1700 meters/minute.
For the Primary Coating Layer an Oligomer is selected, along with a photoinitiator, antioxidant, two diluent monomers and other additives based on information available. For the Secondary Coating Layer an Oligomer Blend is selected, along with a photoinitiator, antioxidant, two diluent monomers and other additives based on information available to formulate a Clear Secondary Coating. Colorants are formulated to add to the Clear Secondary Coating during in-line mixing. In addition to running the Primary coating and Secondary coating on the Draw tower Simulator operating at 1625 meters/minute, the Multilayer Film DrawDown test method is used to create Supercoatings Film of a Primary Coating Layer with an overcoat of Clear Secondary Coating Layer. The film is removed from the substrate and tested for the properties in Supercoatings.
In addition to using the Multilayer Film DrawDown test method to create Supercoatings Film of a Primary Coating Layer with an overcoat of Clear Secondary Coating Layer, a Multilayer Film DrawDown is made of a Primary Coating Layer and a Colored Secondary made of the Clear Secondary Coating and Colorant.
Example 3 continued
Oligomer M3 is an Oligomer. The ingredients combined to make Oligomer M3 include the following:
+Total Colorant:
@Total Dry Pigment:
An optical fiber manufacturer wishes to apply a radiation curable Supercoatings for their MULTI-Mode Optical Fiber. The MULTI-Mode Optical Fiber is of the most modern type, able to resist Microbending.
The requested Microbending Sensitivity for single mode optical fiber used in this network is as of this writing, still under investigation at 850 nm and 1300 nm. As details develop more Microbending Sensitivity testing will be done.
The MULTI-Mode Optical Fiber is of the most modern type, able to resist Microbending
The radiation curable Secondary Coating is applied Wet on Wet Primary Coating.
The line speed at which the Primary Coating and Secondary Coating will be applied is about 200 meters/minute.
The type of curing lights are 600 w/D Lamps.
The number of curing lights are: 3 in the Primary Coatings area, 3 in the Secondary Coatings Area
For the Primary Coating Layer an Oligomer is selected, along with a photoinitiator, antioxidant, two diluent monomers and other additives based on information available to make a Multi-Mode Coating. For the Secondary Coating Layer an Oligomer Blend is selected, along with a photoinitiator, antioxidant, two diluent monomers and other additives based on information available to formulate a Clear Secondary Coating for Multi-Mode Coating.
These Examples illustrate Formulator Delta's formulations for the Primary Coating Layer
The fifth aspect of the instant claimed invention is a multi-mode optical fiber coated with radiation
curable coatings comprising a Primary Coating Layer and a Secondary Coating Layer
wherein the composition of the Primary Coating layer, prior to curing, is selected from the group
consisting of the formulation of Example 4PD5; and
wherein the composition of the Secondary Coating layer, prior to curing, is selected from the group
consisting of the formulations of Examples 2SA4 and 2SB3.
This Supercoatings Secondary is formulated from an existing Supercoatings Secondary to meet the needs of a customer that is requesting a product with a higher refractive index to enable them to use installed equipment to ascertain concentricity in their finished coated fiber. The changes from the earlier coating are as follows:
Oligomer M3 is an Oligomer. The ingredients combined to make Oligomer M3 include the following:
This shows the combination of Primary Coating and Secondary Coating in each of the listed Supercoatings.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
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.
An embodiment embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those an embodiment embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend 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.
This patent application claims priority to U.S. Provisional Patent Application 61/272,596, filed Oct. 9, 2009 and to U.S. Provisional Patent Application 61/250,329, filed Oct. 9, 2009, U.S. Provisional Patent Application 61/287,567, filed Dec. 17, 2009 and U.S. Provisional Patent Application 61/363,965, filed Jul. 13, 2010, which are all incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61272596 | Oct 2009 | US | |
| 61250329 | Oct 2009 | US | |
| 61287567 | Dec 2009 | US | |
| 61363965 | Jul 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13388726 | Feb 2012 | US |
| Child | 13797908 | US |
