Abstract:
The present invention provides a filament with an easily removable protective coating as well as a method and apparatus for applying the protective coating to the filament during a draw process that can be easily removed with a reasonably benign solvent such as water, or if necessary, acetone or ethanol. The protective coating is water-soluble and can be easily dissolved in-line with a spooling process. The coating material may include a water-soluble “wax-like” material called Aquabond 65, distributed by Aquabond Technologies, as well as other grades of Aquabond such Aquabond 55 and Aquabond 85, which behave essentially the same but are dissolved at different temperatures.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application claims benefit to provisional patent application No. 60/629,006 (WFVA/CyVERA nos. 714-1.18/CV 75PR), filed Nov. 17, 2004, which is hereby incorporated by reference in their entirety.  
         [0002]     The following cases contain subject matter related to that disclosed herein and are incorporated herein by reference in their entirety: U.S. patent application Ser. No. 10/661,116 (CyVera Docket No. CV-0044), filed Sep. 12, 2003, entitled “Method of Manufacturing of a Diffraction grating-based identification Element”. 
     
    
     BACKGROUND OF INVENTION  
       [0003]     1. Technical Field  
         [0004]     The present invention relates to a method and apparatus for manufacturing a filament having an easily removed protective coating, as well as a method and apparatus for easily removing the protective coating from the filament.  
         [0005]     2. Description of Related Art  
         [0006]     Optical filament is typically manufacturer with a protective coating that protects the filament during its handling from the time it is manufactured to the time its is used in any particular application.  
         [0007]     When such filament is used to make microbeads, the fabrication of micro beads requires as a starting material a very small glass filament, approximately 28 microns in diameter. Before codes can be written into the filament the protective coating must be removed. For this, there are different known techniques, including thermal-mechanical, thermal, chemical-mechanical and chemical (e.g. sulphuric acid), for removing the protective coating from the filament.  
         [0008]     In particular, the thermal-mechanical process involved heating the coating to about 500 degrees C. while pulling it through a mechanical die, which physically strips the coating off the filament. The approach works on conventional filament sizes (125 um-65 um) with conventional coatings, such as a UV cured acrylate. However, due to the mechanical nature of the process, the filament was inevitably weakened. Moreover, this approach breaks down with filament smaller than 65 um. Since the target filament size for micro beads is 28 microns (um), this approach is not effective.  
         [0009]     The thermal ablation method may be used to remove the protective coating from the filament that is used to make microbeads. This method involves using superheated nitrogen (˜1000 degrees C.) to essentially evaporate the coating off the filament without ever needing to touch it with a die. Although this method essentially works in that it removed the coating, it has the disadvantage of having a slow speed combined with questions surrounding the effectiveness of the strip at the molecular level.  
         [0010]     In view of this, there is a need in the industry to remove the protective coating from the filament that overcomes the aforementioned disadvantages of the methods known in the art.  
       SUMMARY OF INVENTION  
       [0011]     The present invention provides a new and method and apparatus for applying a removable protective coating to the filament during a draw process that can be easily removed with a reasonably benign, and environmentally-friendly, solvent such as water, or if necessary, acetone or ethanol. The protective coating can be easily dissolved in-line with the spooling process.  
         [0012]     The material may include a water-soluble “wax-like” material called Aquabond 65, distributed by Aquabond Technologies, as well as other grades of Aquabond such Aquabond 55 and Aquabond 85, which behave essentially the same but are dissolved at different temperatures.  
         [0013]     Another material, which may be used for this application is called Crystalbond. However, this is soluble in acetone, which is more hazardous and therefore more expensive to work with.  
         [0014]     The present invention also relates to the method and Illumina, Inc. Proprietary apparatus for easily removing the protective coating with the reasonably benign, and environmentally-friendly, solvent, as well as the microbeads resulting from using all of these new techniques.  
         [0015]     The present invention also has the following advantages, including minimizing the volume of reagent needed, providing easy to set up devices, and providing easy to scale up and down depending on the requirements of the application. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]     The drawing, which are not drawn to scale, include the following:  
         [0017]      FIG. 1  shows apparatus for applying a protective coating to a filament being drawn in a draw tower that is easily removable according to the present invention.  
         [0018]      FIG. 2 , including FIGS.  2 ( a ) and ( b ), show two graphs, one having break strain (% dl/length) plotted versus cumulative failure probability, the other having mean distance between failure (meters) plotted versus mean load (grams).  
         [0019]      FIG. 3  shows a method for removing or stripping the protective coating from a filament according to the present invention.  
         [0020]      FIG. 3   a  shows one or more alternative methods for removing or stripping the protective coating from a filament according to the present invention.  
         [0021]      FIG. 4  shows another method for removing or stripping the protective coating from a filament according to the present invention.  
         [0022]      FIG. 5  shows four photographs of the filament based on these new techniques, including  FIG. 5 ( a ) showing a filament having full coat; FIGS.  5 ( b ) and ( c ) showing a filament after stripping using the method in  FIG. 4 , and  FIG. 5 ( d ) showing a filament after stripping using the method in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
     FIG.  1 : Applying the Coating  
       [0023]      FIG. 1  shows a drawing tower generally indicated as  10  having a preform  12  arranged in a furnace  14 , in which a filament  16  of bare glass is drawn. In operation, the bare filament  16  is coated by passing it through a cup  18  that has a hole in the bottom and is filled with an Aquabond coating  20 . A heater  22  arranged in relation to the cup  18  provides heat to the cup  18  for maintaining it at a predetermined temperature. After the filament is coated with Aquabond  20 , the filament  16  with the Aquabond coating  20  thereon is taken-up on a wheel or spool  24 , as shown.  
         [0024]      FIG. 5 ( a ) shows a filament  16  having a full coating of Aquabond according to the present invention.  
         [0025]     In effect, the method involves applying the Aquabond coating  20  directly to the filament  16  during the draw process. Like other thermoplastic coatings the material transitions from a solid to a liquid at an elevated temperature. Aquabond 65 begins to soften at about 60 degrees C. and becomes watery at about 80 degrees C. To apply the Aquabond coating  20  to the filament  16 , the heated cup  18  with the small hole or die is used to establish the diameter of the coating material (&lt;about 100 microns works best). The optimal viscosity was achieved when the cup  18  was heated to about 70 degrees C. It was determined that once the filament  16  is drawn and spooled on a mandrel, it can be handled normally without risk of degrading its pristine strength.  
         [0026]      FIG. 2 ( a ) shows a graph of the failure statistics. Bare filament tends to be extremely fragile, to the extent that it will not stay intact while it is still on the spool. Handling such filament in long contiguous lengths is virtually impossible. A characteristic Weible plot will exhibit a long slow decay rolling off less than 1% strain. Conversely, high strength telecom style filament with an optimized robust coating will exhibit a very sharp roll off starting near 7%. Such a curve indicates that the probability of failure even at high tensile strains (greater than about 6%) is very low. The failure statistics for the Aquabond coated filament, not surprisingly, indicate that the coating is not as good at maintaining strength as filament with those coatings which are designed to not be easily removed. However, the relatively steep curve indicates that the coating is providing a significant level of protection against failure use to mechanical abrasion and attack from humidity.  
         [0027]      FIG. 1   a  shows, by way of example, a die/cup arrangement generally indicated as  30  having a die  32  arranged in a cup  34  for use according to the present invention. The cup  34  holds the coating material which is applied to the filament F as it passes through the arrangement. It has been determined by experimentation that the die size (D die ) to filament (D filament ) size is about 2:1 for the optimal application of the coating. This unique ratio results in self-centering forces causing the filament to pass through the center of the die  32  to increase the uniformity of the coating being applied to the filament F. In one embodiment, the die  32  is made from a silicon mold with a diameter (D die ) in a range of about 60-80 microns, and preferably about 75 microns, depending on the diameter (D filament ) of the filament.  
         [0028]      FIG. 1   b  shows an alternative embodiment to that shown in  FIG. 1 . Similar elements are shown and described with similar reference numerals. The overall objective is to cool the coated filament in a reasonably short distance possible to keep the height/length of the overall draw tower to a minimum. In  FIG. 1   b , a variable speed capstan  26  is preferably arranged at a minimum distance D minimum  from the preform  12  so as to provide cooling and curing of the coating on the filament. The cooling time depends on the coating thickness and the temperature difference between the surrounding environment and the filament, and the cooling distance depends on the draw velocity of the filament and the cooling time. Alternatively, a cooling tube may be added to accelerate the cooling of the coating material on the filament. The capstan  26  may be independently controlled by a capstan controller (not shown).  
         [0029]     Embodiments are also envisioned in which multiple die/cup arrangements like element  30  used in an in-line technique for applying the protective coating to the filament  16 . This embodiment may include a series of arrangements  30  such as that shown in  FIG. 1   a . This approach randomizes the coating centering for a more even application of the coating.  
         [0030]      FIG. 1   c  shows a fiber F having the removable coating  20  and a substrate  21  in the form of a device.  
       Removal of the Coating  
       [0031]      FIG. 3  shows a method and apparatus generally indicated as  52  according to the present invention for easy removal of a protective coating  20  from a filament  16 , which is achieved by drawing the filament  16  off a spool  54  and through a 24 inch long Teflon tube  56  with hot water flowing through it, which is known herein as the hot aqueous stripping method. Although the present invention is described using a 24 inch long Teflon tube  56 , the scope of the invention is intended to include using other length tubes and tubes made from other materials. As shown, at either end of the tube  56  there are small diameter orifices  58 ,  60  (e.g. about 0.020″). Although the scope of the invention is not intended to be limited to any particular orifice diameter, it has been found through experimentation that the tighter the overall fit is between the small diameter orifices  58 ,  60  and the filament  16 , the better the overall method operates. A short distance from each end, two respective end ports  62 ,  64  are tied into the tube  56  to allow the flow of respective liquids into the tube  56 , and a center port  66  located in the middle of the tube  56  is arranged so that liquid can be removed from the tube  56 . Liquid is drawn in through the two end ports  58 ,  60  by applying a vacuum to the center port  66  using a vacuum pump  68  and collected in a tank  69 . This prevents liquid from flowing out the small orifices  58 ,  60  at the ends. This three-port configuration also enables the flow of two different liquids at the same time, but separated by a virtual boundary in the middle of the tube  56 .  
         [0032]     The process uses a hot aqueous solution of detergent  70  in a temperature range of about 65-100 degrees Celsius (preferably about 90 degrees C.) in one section generally indicated as  71  provided from a container  72  and pure hot water  74  also in a temperature range of about 65-100 degrees Celsius (preferably about 90 degrees C.) in another second section  75  provided from a container  76 . The aqueous solution detergent  70  is designed to dissolve the water-soluble coating, while the pure water is used to rinse or flush any residue in or from the detergent  70  and to remove undesirable entrained air. It has been found that linear draw rates exceeding 20 meters/minute have been achieved with the 24″ long tube  56  and modest water usage (less than 2 gallons/hour), although the scope of the invention is not intended to be limited to any particular draw rate. In principle, the system is scalable to nearly any linear feed rate, providing the length of the tube  56  is design to provide adequate dwell time in the hot aqueous solution  70 . In addition to being highly effective at cleaning the filament  16 , easy to use, environmentally friendly, and providing high throughput, this method produces very low residual tension on the filament  16 , which is particularly important when ultra fine diameter filament is used (less than 40 microns). As shown, after exiting the tube  56 , the stripped or bare filament  76  is wound on a take-up spool  80 .  
         [0033]      FIG. 5 ( d ) shows the bare or stripped filament using Aquaclean according to the method shown in  FIG. 3 .  
         [0034]     In alternative embodiments, water may also be drawn from a tap or line having an in-line heater with the Aquabond metered into one line and provided to port  62  and the hot water alone provided to tap  64 . Moreover, instead of using the tank  69 , the liquid may be drawn from port  66  into a line and drawn from the tube  56 .  
         [0035]     Embodiments are also envisioned in which the tube  56  is heated to keep the liquid at a desired temperature consistent with that described herein.  
         [0036]     Embodiments are also envisioned in which multiple tubes like element  56  are used in an in-line technique for removing the protective coating from the filament. This embodiment may include a series of arrangements such as that shown in FIGS.  3  and/or  3   a , or a series of arrangement that may include a tube such as  56  having Aquabond cleaning, followed by a tube such as  56  having a hot water cleaning, etc. The scope of the invention is not intended to be limited to any particular type or kind of in-line arrangement that may be configured consistent with that shown and described herein.  
         [0037]     Embodiments are envisioned using a camera suitably arranged for inspecting the bare filament  76 . Such a camera may be viewed by an operator or inspector for evaluating quality control, or a camera signal from the camera may be fed to a suitable processing device for analyzing the image in the camera signal and adjusting the operation of the overall device based on the same, including but not limited to adjusting the draw rate of the filament being fed through the tube  56 , as well as the flow of the liquid to/from the tank  56 .  
         [0038]     Embodiments are also envisioned in which the protective of the filament is removed by steam cleaning, as well as other suitable techniques like chemical cleaning or gas cleaning, consistent with that described herein.  
         [0039]     Moreover, the scope of the invention is not intended to be limited to using a vacuum pump for drawing the liquid out of the tube  56 . For example, embodiments are envisioned using other type or kind of pumps for drawing the liquid out of the tube  56  either now known or later developed in the future, including but not limited to a diaphragm pump.  
         [0040]      FIG. 3   a  shows an alternative embodiment of the present invention in which the tube  56  also has a rumble strip  57  arranged in, or forming part of the interior surface of the tube  56 . By way of example, the rumble strip  57  may consist of a corrugated surface that helps to break up the laminar flow of the liquid in the tube  56 . As shown, the rumble strip  57  is arranged or forms part of the upper and lower interior surface; however, embodiments are envisioned in which the rumble strip  57  is circumferentially arranged about the interior surface as well.  FIG. 3   a  also shows an ultrasonic device  59  arranged in relation to the tube  56  which may be used to improve stripping efficiency and to keep the length of the tube  56  to a minimum.  
         [0041]     An embodiment of the present invention is also envisioned in which the tube  56  has a transparent top surface in order for an operator to look inside for contaminants.  
       The Graphs in FIGS.  2 ( a ) and ( b )  
       [0042]      FIG. 2 ( b ) illustrates the significance of maintaining a low working load. For the filament characterized by the failure statistics in  FIG. 2 ( a ), a predictive model was made to estimate the mean distance between failure for a range of working tensile loads. The graph in  FIG. 2 ( b ) shows that as the load (y-axis) decreases, the mean distance between failures increases. For example, the maximum usable operating load must be maintained less than 100 grams to achieve a mean distance of failure of greater than 600 meters.  
       FIG.  4 : Alternative Method—the Bath Method  
       [0043]      FIG. 4  shows a bath method generally indicated as  102  that was also developed as an alternative to the method shown in  FIG. 3 . The bath method involves drawing a filament such as  16  coated with Aquabond  20  from a supply spool  104  through a bath  106  having a hot aqueous detergent  108 . The hot aqueous detergent  108  strips the Aquabond  20  off the filament, resulting in a stripped filament  110  that is wound on a takeup spool  112 . As shown, the coated filament  16  is first drawn over a spool/wheel  114  before entering the bath  108 , drawn around a spool/wheel  116  in the bath  118  and over a spool/wheel  118 , then onto the takeup spool  112 .  
         [0044]     FIGS.  5 ( b ) and  5 ( c ) show a typical photograph of the filament  110  stripped with Aquaclean using this method. The visible residue  111  on the surface of the filament  102  was characteristic of this approach and led the inventors to develop the aforementioned improved method shown and described in relation to  FIG. 2 .  
       FIG.  6 : Trough Stripper  
       [0045]      FIG. 6  shows another embodiment generally indicated as  200  according to the present invention, wherein the filament  201  goes through 1, 2, 3 or more small tanks  202 ,  204  through a groove  206   a ,  206   b ,  208   a ,  208   b  on both end. A liquid in the form of a cleaning solution is pumped via tubes  209  inside the tanks  202 ,  204  and overflows into a secondary container  210  below. The overflow can be either on both end where the grooves  206   a ,  206   b ,  208   a ,  208   b  are, or all around as shown. In the secondary container  210  the liquid is drained by tubes  211  to a pump  212  where it is warmed/filtered and recirculated back to the upper container  202 ,  204 .  
         [0046]     Alternatively, the scope of the invention is intended to include a system having one of each arrangement to accommodate various properties of liquid, for instance if the liquid cannot bead up then the groove become necessary.  
         [0047]     This concept is designed to limit the amount of liquid used, and maximized the usage of liquid by using a re-circulation system. It minimizes the chemical waste and loss of heat.  
         [0048]     The quality of liquid can be monitored in the recirculation loop and a supply of fresh cleaning solution could be added replacing and pushing to waste partially “dirty” cleaning solution.  
       FIGS.  7   a ,  7   b ,  7   c : The Overflow Stripper  
       [0049]      FIGS. 7   a ,  7   b ,  7   c  show an embodiment of the invention generally indicated as  300 , wherein the cleaning solution is prepared in a tank  302 , then by a gravity feed, or with a pump (not shown), the liquid is pushed (see arrows  303 ) into the cleaning container  304  for cleaning the filament  301 . The level of liquid increase until it fills completely the small tank and starts to overflow (see arrows  305 ). Below the small tank is a secondary container  306  collecting the overflowed liquid. At one end a tube connected to a pump  308  brings the liquids back to the container  302  (or the pump).  
         [0050]      FIG. 7   c  shows an embodiment generally indicated as  400  in which one container  402  has Aquaclean for cleaning the filament  301  and the other container  404  has water, consistent with that described herein.  
       FIG.  8 : Surface Tension Stripper  
       [0051]      FIGS. 8   a ,  8   b  show an embodiment of the present invention generally indicated as  500 , using the concept of a meniscus stripper. Similar elements in  FIGS. 6 and 8   a  have similar reference numerals with the additional of  300  to the reference numerals in  FIG. 8   a . In  FIG. 8   a , the filament  501  goes through 1, 2, 3 or more small tanks  502 ,  504 . The cleaning solution is pumped via tubes  509  inside the tanks  502 ,  504  and overflows into a secondary container  510  below. However, in this embodiment, the filament  201  does not go through grooves as described in relation to  FIG. 6 , but instead surface tension of the liquid and the resulting beading up is conveniently use to allow the liquid to rise above the edge of the upper channel, and create a volume of liquid where the filament  201  can get cleaned. In the secondary container  510  the liquid is drained by tubes  211  to a pump  512  where it is warmed/filtered and recirculated back to the upper container  502 ,  504 .  
         [0052]      FIG. 8   b  shows an alternative embodiment generally indicated as  600 , where there is having an inlet  602  of liquid and an overflow on the other side. At the outlet, after the overflow the liquid is monitored for change of turbidity, or any optical change of the liquid. If the liquid properties change due to contamination or increase concentration by the material it is suppose to clean, then a system controlling the flow rate of liquid in the inlet, increase the flow rate to bring the cleaning liquid to what it should be. The filament  601  to be cleaned move from the left to the right and the liquid in the opposite direction, so the dirtiest liquid face the incoming filament  601  and the clean filament has the cleanest solution. The system can have sonic device  625  to help the cleaning, an infrared lamp  630  prior to it to fragilised/liquefied the coating of the filament, and a heater  635  to maintain the overall apparatus at a desired temperature. The edge of the liquid channel may be coated with Teflon  640  to allow the liquid to bead up and increase the usable volume of liquid. The apparatus can be closed by a lid (not shown) to minimize evaporation and change of concentration, dirt and dust contamination, potential exposure to the hot liquid by an operator, and to minimize overall heat loss.  
         [0053]     An Infrared devise  650  can be added if it is required to increase the speed of the cleaning and if the overflow system cannot keep up in removing the filament coating. It is also possible to use much higher temperature acceptable by the cleaning solution.  
         [0054]     The sonic device  625  can be added to maximize the cleaning efficiency  
       Applications  
       [0055]     Microbeads made using the aforementioned techniques may be used in many different applications, including those set forth in the following cases, which are incorporated herein by reference in their entirety: U.S. patent application Ser. No. 10/661,234 (CyVera Docket No. CV-0038A), filed Sep. 12, 2003, entitled “Diffraction Grating-Based Optical Identification Element”; U.S. patent application Ser. No. 10/661,031 (CyVera Docket No. CV-0039A) filed Sep. 12, 2003, entitled “Diffraction Grating-Based Encoded Micro-particles for Multiplexed Experiments”; U.S. patent application Ser. No. 10/661,082 (CyVera Docket No. CV-0040), filed Sep. 12, 2003, entitled “Method and Apparatus for Labeling Using Diffraction Grating-Based Encoded Optical Identification Elements”; U.S. patent application Ser. No. 10/661,115 (CyVera Docket No. CV-0041), filed Sep. 12, 2003, entitled “Assay Stick”; U.S. patent application Ser. No. 10/661,836 (CyVera Docket No. CV-0042), filed Sep. 12, 2003, entitled “Method and Apparatus for Aligning Microbeads in order to Interrogate the Same”; U.S. patent application Ser. No. 10/661,254 (CyVera Docket No. CV-0043), filed Sep. 12, 2003, entitled “Chemical Synthesis Using Diffraction Grating-based Encoded Optical Elements”; U.S. patent application Ser. No. 10/661,116 (CyVera Docket No. CV-0044), filed Sep. 12, 2003, entitled “Method of Manufacturing of a Diffraction grating-based identification Element”; and U.S. patent application Ser. No. 10/763,995 (CyVera Docket No. CV-0054), filed Jan. 22, 2004, entitled, “Hybrid Random Bead/Chip Based Microarray”, US Provisional Patent Applications, Ser. Nos. 60/609,583, 60/610,059 and 60/609,712, all filed Sep. 13, 2004 (CV-0082PR, 83PR and 84PR); U.S. Provisional Patent Application Ser. Nos. 60/611,205, 60/610,910, 60/610,833, 60/610,829, 60/610,928, all filed Sep. 17, 2004 (CV-0085PR, 86PR, 87PR, 88PR and 89PR); U.S. Provisional Patent Application Ser. No. 60/611,676, filed Sep. 20, 2004 (CV-0091PR); and U.S. patent application Ser. No. 10/956,791, filed Oct. 1, 2004 (CV-0092 US).  
       SCOPE OF THE INVENTION  
       [0056]     The dimensions and/or geometries for any of the embodiments described herein are merely for illustrative purposes and, as such, any other dimensions and/or geometries may be used if desired, depending on the application, size, performance, manufacturing requirements, or other factors, in view of the teachings herein.  
         [0057]     It should be understood that, unless stated otherwise herein, any of the features, characteristics, alternatives or modifications described regarding a particular embodiment herein may also be applied, used, or incorporated with any other embodiment described herein. Also, the drawings herein are not drawn to scale.  
         [0058]     Although the invention has been described and illustrated with respect to exemplary embodiments thereof, the foregoing and various other additions and omissions may be made therein and thereto without departing from the spirit and scope of the present invention.  
         [0059]     Moreover, the invention comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth.  
         [0060]     It will thus be seen that the objects set forth above, and those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.