Abstract:
A non-woven mono-component, mono-constituent poly lactic acid (PLA) web is disclosed. The web material is useful for production of tea bags and other infusion beverages. The nonwoven network of PLA fibers in mono-component, mono-constituent configuration provides infusion properties, strength and weight properties that surpass current beverage bags and pouches because of its unique composition and structure.

Description:
[0001]    The present application claims priority from U.S. provisional patent application 61/376,845 filed Aug. 25, 2010 and non-provisional patent application Ser. No. 12/971,505 filed Dec. 17, 2010. 
     
    
     BACKGROUND 
     Field 
       [0002]    The present invention relates to a melt-extrudable thermoplastic composition and to the preparation of nonwoven webs. The composition described is a non-woven fiber web made of a mono-component, mono-constituent polylactic acid (PLA) and more particularly made of PLA of a plurality of layers and having fibers with cross-sections in various structural configurations. 
         [0003]    As beverage fabrics presented in Noda (2002/0143116), Rose (203/0113411), Jordan (2005/0136155) as well as Ser. No. 12/971,505 have been produced there is still a need for improvement. 
         [0004]    In the United States, a cup of coffee is generally produced under atmospheric pressure with hot water flowing through the coffee grounds and through a filter. The resultant coffee is coloring the water from light grey to black, but still maintains a clarity. In Europe as well as most of the rest of the world, coffee is generally produced under a pressure greater than 1 atmosphere and the coffee is generally ground to finer particles. As a result, coffee is cloudy, stronger and has a “crema” or foam on the surface. Such coffee is sipped slowly to enjoy the enhanced flavor. 
         [0005]    In all cases, there is a need for a tortuous path for the water to flow through a filter that will allow a fast flow, but preventing any particles from flowing into the cup. It is believed that a tortuous path will allow more complete transfer of the coffee essence from the grounds to the liquid, while at the same time increasing the “crema”. 
         [0006]    Cellulosic “paper” products have an inverse relationship of weight with porosity. As cellulosic papers get higher than 30 gsm in weight, there porosity goes to zero and become impermeable. Further cellulose fibers swell on contact with water, further closing the pores of the paper. 
         [0007]    Therefore a need exists for improvement to the Ser. No. 12/971,505 invention. 
         [0008]    There is also a need for an infusion substrate, particularly for tea and coffee, which provides rapid infusion of hot water into the tea or coffee particles, while being strong enough to keep the particles within a bag or pouch made up in substantial part or wholly of such substrate. There is also a need for heat-sealable pouch for tobacco and tobacco products (i.e. snuff and chewing tobacco). 
         [0009]    Further, it is highly desirable that the substrate media be 100% bio-degradable and not contain any inert or non-biodegradable components. 
         [0010]    Further, it is highly desirable that the media, including all of the production scrap, be recyclable into itself. 
         [0011]    Significant development of Polylactic Acid (PLA) fiber was conducted by Cargill Inc. to make fibers from natural raw materials and resultant process and products are described in U.S. Pat. No. 6,506,873. 
         [0012]    Kimberly Clark mentions PLA in its U.S. Pat. No. 7,700,500, “Durable hydrophilic treatment for biodegradable polymer substrate.” 
         [0013]    U.S. Pat. No. 6,510,949 by Grauer et al teaches that hydrophilic substances may be impregnated, into filter paper to improve the water-wet ability and water absorption. 
         [0014]    Tea bags and coffee pouches traditionally have been made of paper and teabags suffer from slow infusion times and tend to float on the liquid surface. 
         [0015]    A new tea bag fabric from Japan has been made using a nylon knitted mesh, which provides rapid infusion, but requires a non-traditional sealing method, are expensive and are not biodegradable. 
         [0016]    Attempts have been made to produce a spun melt nonwoven from PL A, but it suffers from poor sealability and performance in automated packing machines. 
       SUMMARY 
       [0017]    The present invention provides a highly porous media of web form, divisible and fabricated into end product components (e.g. bags, pouches) or portions of the same that is produced from PLA, alone or with Co-PLA fibers, using a thermo bonded nonwoven manufacturing method. The media exhibits high efficiency for infusion of hot water into the coffee or tea (or other liquid as more broadly indicated above). The use of Synthetic Cellulosic fibers blended with proprietary PLA formula is disclosed. 
         [0018]    The fibers self bond at many cross over points through web heating and/or pressure applications in initial web production and/or subsequent steps. Disclosed is a melt-extruded thermoplastic non-woven web composition consisting of: a plurality of fiber layers made from a plurality of fibers that are blends of mono-component, mono-constituent polylactic acid (PLA) fibers. 
         [0019]    The polylactic acid (PLA) fiber have different deniers and blend percentages of high and low fibers having a melt flow temperature in a range of 145-175° C. and 105-165° C., respectively. Various layer combinations and sequences are also provided for within the purview of the invention. 
         [0020]    The present invention also provides a highly porous media of web form, divisible and fabricatable into end product components (e.g. bags, pouches) or portions of the same that is produced from PLA, alone or with Co-PLA fibers, using a thermo bonded nonwoven manufacturing method. The media exhibits high efficiency for infusion of hot water into the coffee or tea (or other liquid as more broadly indicated above). The fibers self bond at many cross over points through web heating and/or pressure applications in initial web production and/or subsequent steps. 
         [0021]    The web material of the invention is produced in a continual process that provides for controllable machine processing direction and cross machine direction properties that enhance the performance of the media. By controlling the % of the lower melt Co-PLA in an intimate blend of PLA and Co-PLA fibers, the thermo bonding strength can be controlled during web manufacture by fiber orientation, temperature setting, and time of exposure to heat. During bag or pouch manufacture, the strength of the sealing bond can be controlled by temperature, dwell time, and knife pressure. 
         [0022]    PLA and Co-PLA have specific gravity of 1.25, i.e. greater than water, which causes the bag or pouch to sink and to be submerged and be totally engulfed in the hot water. Further, PLA is naturally hydrophilic, without special treatment, which allows the water to flow quickly into the tea or coffee. 
         [0023]    The Co-PLA can be chosen with a melt point from 125° C. to 160° C. by varying the isomer content of the polymer. Thus it is possible to address the sealing requirements of various automated packaging machines. 
         [0024]    Not only is the media made from a renewable raw material, but the scrap fiber, nonwoven trim scrap, and the bag making scrap can be remelted, extruded into a pellet, and blended into the extrusion operation to make more fiber. It is from 100% renewable source and it is 100% recyclable. During the fiber manufacturing process, any “waste” fiber may be re-extruded into pellets and put back into the fiber process. During the nonwoven web production process, any startup or trim “waste” may be re-extruded into pellets and put back into the fiber process. During the infusion package manufacturing process, any trim, start-up, or other web “waste” may be re-extruded and put back into the fiber manufacture process. 
         [0025]    Unlike PET, nylon, and most papers, which contain latexes and synthetic fillers, the media of the present invention is 100% compostable. After hydrolysis at 98% humidity and 60 C or higher, PLA is readily consumed by microbes and its component atoms are converted for possible re-use in growing more corn, beets, rice or etc. for future conversion to PLA. 
         [0026]    The invention was produced in three weights: 16, 18 and 20 gsm (grams per square meter, but could be produced in a lighter or heavier weight). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIGS. 1A-1I  illustrate embodiments of fiber shapes that utilize the teachings of the present invention; 
           [0028]      FIGS. 2A-2I  illustrate one embodiments of layers; 
           [0029]      FIG. 3  illustrates three different fibers. Large diameter, smaller diameter and low melt forming fused bond points at 4× magnification; 
           [0030]      FIG. 4  illustrates another view of  FIG. 3  at 10× magnification showing low melt bond points and that the low melt fiber ceases to be a fiber; 
           [0031]      FIG. 5  is photomicroscope slide ( 1 ) at 40× magnification power showing an 18 gsm web with 30% (by weight) co-PLA/70% PLA which exhibited excellent strength and superb sealing characteristics. It should perform equally well at lighter weights from 12 to 20 gram per square meter (gsm); 
           [0032]      FIG. 6  is photomicroscope slide ( 2 ) showing an 16 gsm web with 10% co-PLA/90% PLA blend, which exhibited adequate strength but did not have enough low melt fiber to seal effectively; 
           [0033]      FIG. 7  is a drawing of a bi-component fiber with a high melt core (PLA @ 175° CM) and a low-melt sheath (Co-PLA @ 135° C.); 
           [0034]      FIG. 8  is a Microscope slide of 85/15% blend at 18 gsm-40 power; 
           [0035]      FIG. 9  is a Microscope slide of 80/20% blend at 18 gsm-40 power; 
           [0036]      FIG. 10  is a microscope slide of 80/20% blend at 18 gsm-100 power; 
           [0037]      FIG. 11  is a microscope slide of standard paper; and; 
           [0038]      FIG. 12  is a microscope slide of a Japanese made nylon fabric, and  FIG. 13  is Table I showing a comparison of paper airflow with PLA airflow and Graph A showing the relationship of breathability properties to GSM. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Nonwoven webs are porous, textile-like materials which are composed primarily or entirely of fibers assembled in flat sheet form. The tensile properties of such webs may depend on frictional forces or on a film-forming polymeric additive functioning as a binder. All or some of the fibers may be welded to adjacent fibers by a solvent or by the application of heat and pressure. 
         [0040]    Nonwoven webs currently are employed in a variety of products such as diapers, napkins, sterilization wraps; medical drapes, such as surgical drapes and related items; medical garments, such as hospital gowns, shoe covers, and the like to name but a few. The nonwoven webs can be utilized as a single layer or as a component of a multilayered laminate or composite. When a multilayered laminate or composite is present, often each layer is a nonwoven web. Such multilayered structures are particularly useful for providing improved performance in strength properties. 
         [0041]    In order to improve the performance of a nonwoven-containing product, it sometimes is necessary to modify certain characteristics of the fibers of which the web is composed. A classic example is the modification of the hydrophobicity of fibers by a topical treatment of the web with a surfactant or through the use of a melt additive. 
         [0042]    The use of a topical treatment or melt additive has the draw back when the non-woven is used in the food industry or related to contact with human skin or human digestion. The present invention avoids the use of such surfactants and topical treatments and provides additional unexpected results. 
         [0043]    The diameter of fibers will affect the nesting or stacking of the fibers during web formation. Further, the percentage of low melt fibers will affect the density and porosity of the web. 
         [0044]    The ability to produce a web with multiple layers presents the ability to create webs of different porosity, thickness, and stiffness. Webs were produced with three layers A B A. All fibers were mono-component, mono-constituent PLA. 
         [0045]    It is within the purview of this invention that different layers, depending on the embodiment, contain different diameters, different ratios of high &amp; low melt, and different shapes as well as the weight of each layer. 
         [0046]    The A layers were produced with 50% 1.5 d×2″ High Melt (170° C.) PLA (PS 2650) and 50% 2.5 d×2″ Low Melt (130° C.) co-PLA (PS1801). 
         [0047]    The B layer (in the center) was produced with 75% 2.5 d×2″ High melt (170° C.) PLA (PS2650) and 25% 2.5 d×2″ Low melt (130° C.) Co-PLA (PS1801). Note that B has 2.5 d vs. 1.5 d high melt fibers which are about 2.5× greater in diameter and only 25% vs. 50% of the low melt. 
         [0048]    The fibers were blended separately and then fed into the card feeders. All cards were Hergerth 3 m wide roller cards with randomizing rolls. The first two cards produced the A layer and fed the layer onto a collecting apron. The next two cards produced the B layer and it onto the apron on top of the A layer. The final 2 cards produced the A layer and fed it onto the same apron on top of the B layer, creating a single web of A B A layers. 
         [0049]    The collective web was then delivered to a heated two roll calendar machine with the rolls heated by Hot Oil to a temperature of 150° C. 
         [0050]    The fabric weight was adjusted between 80 to 120 grams per square meter and a weight of 90 grams per square meter was chosen as having the best properties. 
         [0051]    The stiffness improved to fit the Senseo® brewing machines and produce an excellent cup of coffee without leaking around the edges. 
         [0052]    The porosity of the 90 gsm ABA web was tested against other weights of mono-component, mono-constituent PLA webs ranging from 16 to 90 gsm. The porosity was measured with a Frazer® air-permeometer and measured in liters/m 2 /second. Industry standard webs made from cellulose with either a Polyethylene or PLA bi-component fiber at 30% were compared by weight in the following table and graph: 
         [0053]    The net effect is that a 90 gsm web was obtained with excellent airflow or permeability, but the cellulosic web had virtually no airflow. 
         [0054]    Up to this point, only round, solid fibers of mono-component, mono-constituent PLA fibers were used. 
         [0055]    Fibers made in other shapes were investigated. The shapes included a triangle, mock hollow or “C” shaped, and ribbon or flat. (See  FIGS. 2A-2I ). 
         [0056]    These fibers were produced in the same manner as round. The molten polymer (PLA) was pumped by a metering pump through a metal spinneret. (Note: The low melt Co-PLA was not produced (but could be in the future) as they would melt, flow, and lose their shape). The fibers were air quenched and then drawn at their Tg of 60° C. at a ratio of 3.5:1 to obtain desired crystallinity. The fibers were crimped, heat set and cut to length. 
         [0057]    It was found that these shaped fibers do not affect the air flow, but improve the “crema” or foam in the finished cup of coffee. 
         [0058]    It was also learned that blending in synthetic cellulosic fibers, such as rayon, acetate, or Lyocell (Tencel®) solved a problem of heat effect on coffee and tea bag formation. Tencel® (generic name Lyocell) is a sustainable fabric regenerated from wood cellulose. Lyocell regenerated cellulose fiber is made from dissolving pulp (bleached wood pulp). It was developed and first manufactured for market development as Tencel® in the 1980s by Courtaulds Fibres. Standard forming machines (such as IMA or Cloud) do not have adequate heat controls to maintain a precise temperature over a wide range of running speeds. Hence, there were times when the mono-component, mono-constituent PLA fibers would melt, creating flaws in the pouch or pad. 
         [0059]    By blending in from 5 to 60% of the synthetic cellulosic fibers with the high and low melt PLA, there was a greater temperature range for pad formation available. Tencel® was found to be the easiest to blend with the PLA fibers. The net result was a fabric with higher strength at the melting point of the high melt PLA. While blending in the synthetic cellulose fibers negated the recyclability attribute, the end product was still suitable for tea and coffee pads, bags, or pouches. The fabric was still biodegradable and since Tencel® has a specific gravity compared to 1.24 for PLA, the blended fabric had equal or better ability to sink in the cup rather than float. 
         [0060]    Finally, hydrophilic finishes or lubricants were applied to the fibers during fiber production. These finishes were provided by Goulston Technologies, Inc. of Monroe N.C. These finishes were designed to meet FDA and German BfR requirements for food quality. Goulston finishes such as PS-11473, PS-10832, and PS 12062 were tried. All were heat set at 130° C. during the fiber production process to thoroughly bond them to the fibers. The heat-setting bonded the finishes so that they were not released into the boiling water (100-110° C.) used for Tea Bags, coffee pads, or other pouches. 
         [0061]    The water flow appeared to improve as the color of the water darkened at a much faster rate than PLA fibers made only with an anti-stat such as Goulston AS-23. These finishes were totally compatible to provide excellent carding and fabric formation. The hydrophilic properties and the 1.24 specific gravity of PLA, resulted in bags that would sink and wet out easily, resulting in a faster brew cycle. 
         [0062]    Another advantage of the invention is that since the pouch or bag is hydrophilic it sinks. This advantage is seen in a tea or coffee bag where most paper or other bags float on the top and give minimal diffusion of the coffee or tea contents. By having the bag sink diffusion of the contents is further given. Another advantage is as the non-woven web is exposed to water, it becomes clearer showing the contents of the bag or pouch. The bag or pouch has the benefits of using less contents such as coffee or tea leafs to accomplish the same strength of beverage. In addition diffusion time is decreased since the pore size is relatively maintained using the mono-component fiber. This invention is not limited to beverage pouches and can be utilized in any application that requires diffusion of contents through a pouch or bag. The advantages of biodegradation, recyclability, decreased amount of contents needed, decreased diffusion time, and clarity of the pouch is all realized in the present invention. 
         [0063]    In view of the disclosed description, it will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents. 
         [0064]    A preferred embodiment of the invention was made, and is explained as follows, including all or most of its fibers in bi-component form and its production of mono-component PLA fiber made from Fiber Innovation Technologies (Type T811) was blended with core/sheath bi-component (BiCo) fibers with PLA in the Core and Co-PLA in the sheath. The core/sheath area ratio was 50/50%. Fibers were produced with a ratio between 80/20% and 20/80%. Other fiber producers such as Palmetto Synthetics and Foss Manufacturing Company can make these fibers. PLA fibers typically are made using lactic acid as the starting material for polymer manufacture. The lactic acid comes from fermenting various sources of natural sugars. These sugars can come from annually renewable agricultural crops such as corn or sugar beets. The polymer must be completely dried prior to extrusion to avoid hydrolysis. PLA is an aliphatic polyester and the helical nature of the PLA molecule makes it easier to crystallize than PET. The PLA can be extruded into a fiber using standard PET fiber equipment. 
         [0065]    In the case of the mono-component PLA fiber, the high temperature variant with a melt temperature of 175° C. is extruded into a fiber. The initial fiber is then drawn 3.5 times its length to get to the required 1.5 denier. It is then crimped and heat set to 140° C. to improve the crystallinity and stabilize the crimp. It is then cut to 1.5″ (38 mm). In the case of the Bi-CO fiber, a melt spinning line using the co-extrusion spinerettes made by Hills Inc, of Melbourne Fla. was used. The spinerettes of the line produced a fiber similar to  FIG. 3 . The higher melting (175° C.) PLA is in the core, while the lower melting Co-PLA (135° C.) is in the sheath. Generally, the low melt Co-PLA is fully amorphous, which makes it easier to melt and flow around the crystalline mono-component PLA fibers. The core PLA fiber remains and combines with (bonds to) the mono-PLA fiber at many cross-over points in the web for strength. A web comprising PLA fibers has two different melting points, 145 C-175 C and 105 C-165 C, respectively. The PLA fibers have a melting (softening) point of 145 C to 175 C and the Co-PLA fiber, mono-component is CoPLA with a melt temperature from 105 C to 165 C. 
         [0066]    The blend percentages were varied from 90% PLA/10% BiCo to 60% PLA/40% BiCo. The 70/30% produced the best fabric for strength and sealability. It is also possible to make a blend of crystalline PLA (175° C. melt point) and a mono-component fiber made from 100% Co-PLA (melt point between 135° and 165° C.) Blending is performed by weighing out the desired percentages of PLA and BiCo fibers either manually or with automated weigh feeders. The two fibers are layered on top of each other and fed into an opener which has feed rolls, feeding the fibers into a cylinder with teeth that pulls the clumps into individual fibers. The fibers are then blown into a blending bin to create a homogeneous mixture by first layering the fibers uniformly in the bin and then cross-cutting the layers with a spiked apron which feeds the fibers to a carding system. 
         [0067]    The carding system consists of two feeding hoppers. The first acts as a reserve holding bin to ensure continuous supply. The second feeding hopper has a continuous scale with a load cell that provides a set weight feed to the card. The card is a series of interacting cylinders covered with toothed wire that tears and combs the fibers into a parallel web. 
         [0068]    The fabric weights were varied from 12 to 20 gsm, with the 18 gsm chosen for testing. It is believed that the 16 gsm (not run) will provide the best characteristics. 
         [0069]    The production line was a Asselin-Thibeau line with 3 carding machines, each 2.3 meters wide. The web was run in a straight line and fed into a calendar with 460 mm diameter rolls heat with thermal oil at a temperature of 130° C. to 152° C. Line speeds were 40 meters per minute at a finished width of 2.0 meters. 
         [0070]    If a parallel web is desired, the fibers coming straight out of the carding system are combined with the other two cards and thermo-bonded. This generally results in a Machine Direction (MD)/Cross Machine Direction (CMD) strength ratio of 4:1. If a more balanced strength ratio is desired then a “randomizer” roll system may be added to one or more cards. The result can be MD/CMD strength ratio up to 1.5:1. 
         [0071]    By controlling the carding system and fiber orientation, the fibers can be aligned in a manner to control the apertures or openings in the web to enhance rapid infusion of the hot water. 
         [0072]    The rolls were slit to a width of 156 mm (6.14″) for the Tea Bag machine. 
         [0073]    The tea bag machine was a model ASK020 made by Miflex Masz. Two rolls were placed on the machine and centered on the mold. The correct amount of tea was deposited and the top and bottom sheet sealed automatically at a temperature of 135 C with a dwell time between 0.5 and 0.8 seconds, 
         [0074]    The present invention cuts easily on standard tea/coffee packaging machines with a simple knife device and creates minimal amount of lint or loose fibers. 
         [0075]    The web maintains its pore size during the infusion with hot liquids because the fibers do not swell. This enhances to flow of water into the tea or coffee, reducing the brewing time. 
         [0076]    Because the web fibers do not swell, the risk of gas pressure build up is eliminated and thus the risk of bag breakage and particle dispersion is eliminated. 
         [0077]    Using boiling water, the infusion time is reduced to one (1) minute 
         [0078]    When pressed, the infusion liquid completely leaves the container (bag or pouch), leaving a silky, translucent surface. 
         [0079]    Recycling of PLA is very easy, a depend on the place in the process. During fiber manufacture, all of the fibers from both spinning and drawing can be re-extruded to pellets by densifying the fiber scrap using an “Erema” or “Mechanic Moderne” recycling line (There are many others that will also work). The equipment will density the fibers and partially melt them to pre-dry to drive off any moisture. The dense particles are forced into a vented extruded to remove all of the moisture. The PLA is then fully melted and extruded and filtered to form pure amorphous pellets. The pellets can then be blended with virgin pellets to make new fiber. During the Thermo-Bond process, scrap fiber, edge trim, and defective fabric can be baled and shipped back to the recycling system described above. During the Tea-Bag process, the trimming scrap and “skeleton” scrap, especially from making round pouches, can be baled and reprocessed as described above. Finally, the tea bags can be composted after use and the PLA will turn back into sugars which can be used to make more PLA. 
         [0080]    The present invention may also be used as pouches for: lemonade, herbal sachets, soap powder, chemicals and chlorine for pools and spas, decontaminating liquids, coloring of liquids, dehumidifying chemicals, carriers for phase-change materials for heating or cooling, tobacco pouches, and all materials that can be placed in a heat/ultra sound activated scalable container, 
         [0081]    A further preferred embodiment comprises a tea bag material and end product made in whole or in part of a mono-component fiber with self bonding property to similar fibers or other to produce effective web material and effective end product. 
         [0082]    A preferred mono-component is co-PLA with a melt temperature of 135° C. Such a fiber was produced in a 1.3 denier×38 mm fiber. This produced a fiber which is 100% binder as opposed to a bi-component fiber, generally consisting of 50/50 PLA/Co-PLA. The Mono-component fiber was blended with standard PLA fiber in a ratio of 85% PLA/15% CoPLA. The blend was processed on a carded web line at 18 and 20 gsm. The result was a significantly stronger web than that produced with the bi-component fiber. The web was clearer and less opaque than the one with the Bi-co fiber. This is a very desirable attribute. 
         [0083]    In a second trial, the mono-component Co-PLA fiber was blended with the type 811 PLA fibers in a ratio of 80/20%. The web was produced in a weight of 18 and 20 gsm. The strength increased and the fabric was less opaque or more translucent. Rolls of both of the types were then slit to appropriate widths and processed on tea bag machines. A further advantage was that the PLA/CoPLA blend absorbed less water that the standard paper. While both the PLA and Standard paper weighed 18 gsm dry, the PLA reached 90 gsm when fully saturated with water, while the standard paper reached 200 gsm. 
         [0084]    A first trial was on a Fuso machine replacing an expensive nylon fabric. The tea bags formed well and the seams were stronger than those made with the nylon fabric. The 18 gsm with the 80/20 blend provided the best results. 
         [0085]    To improve strength, uniformity, and fiber distribution, one of the carding machines (out of 5) was modified by placing a randomizing unit on the doffer or take off rolls. On a standard card machine, the fiber orientation is generally 5:1 in the machine versus cross machine direction and can be optimized to 3.5:1. With the randomizing rolls, the orientation is about 1.5:1 for the card with the randomizer. The resultant composite web had an orientation of between 2:1 and 3:1. This was a significant improvement. The resultant webs showed no degradation of strength during wet conditions that standard tea bag paper exhibits. 
         [0086]    It will now be apparent to those skilled in the art that other embodiments, improvements, details, and uses can be made consistent with the letter and spirit of the foregoing disclosure and within the scope of this patent, which is limited only by the following claims, construed in accordance with the patent law, including the doctrine of equivalents.