Patent Publication Number: US-2004058081-A1

Title: Systems and methods for the deposition and curing of coating compositions

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This application is a division of U.S. application Ser. No. 09/682,831 filed Oct. 23, 2001, which is incorporated by reference herein. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
     [0002] The U.S. Government may have certain rights in this invention pursuant to National Institutes of Standards and Technology (NIST) contract number 70NANB9H3038. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0003] The present invention relates generally to systems and methods for generating combinatorial coating libraries and, more specifically, to systems and methods for depositing and curing substrate-supported chemical compositions.  
       [0004] Coatings are widely used in industry to enhance the functionality and add-on value of bulk materials. There are generally two types of functional coating materials: organic and inorganic coatings. Organic coating materials are widely used in industrial protective/decorative applications, such as automobile clear coatings, paints, etc. Other types of organic coatings include, for example, environmental barrier coatings, anticorrosive coatings, adhesive and release coatings, electric conductive/optic transparent coatings, scratch-resistant coatings, etc. The discovery of an advanced coating formulation promises significant value for a manufacturer.  
       [0005] The development of generic tools to accelerate the discovery process for various coating systems may be of even higher value for a manufacturer, however, as the search for and optimization of advanced coatings is more of an art than a science. The power of theoretical guidance in the search for and optimization of advanced coatings is limited, largely because of the complexity of a typical coating system and the multiplicity of quality requirements that must be met. Typically, industrial coating formulations must meet multiple functional requirements, and multiple compatible functional groups or blends are necessary to obtain a balanced formulation. In addition, the properties of a coating system depend not only on the formula/composition, but also on the coating application method and processing conditions. For example, the degree of thickness uniformity and surface roughness, which depend on the application method and processing conditions of a coating, are important in the quality and reproducibility of the coating. Further, different application methods and processing conditions, including, for example, the sequence of application of each layer of a multi-layer coating, exposure to ultraviolet (UV)/electron curing, and varying temperature/pressure, are highly important factors in determining the structure/composition of the final coating, impacting its functionality.  
       [0006] Thus, because of the multitude of variables that affect the production of a coating, most of the usable industrial coating systems developed to date have been the result of serendipitous trial-and-error experimental processes.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007] Therefore, there is a need for systems and methods that accelerate the rate at which functional coatings may be generated for various manufacturing applications. Further, there is a need for systems and methods that allow such coatings to be produced in a controlled manner, with variable compositions/thicknesses and curing parameters over the different regions of a single coating or a coating library.  
       [0008] In one embodiment, a system for creating a combinatorial coating library includes a coating system operatively coupled to at least one of a plurality of materials suitable for forming at least one coating layer on a surface of one or more substrates and a curing system operative to apply at least one of a plurality of curing environments to each of a plurality of regions associated with the at least one coating layer. The curing system includes a scanning mirror system having a mirrored surface positionable relative to an incoming radiation beam, wherein the mirrored surface is positionable to direct the incoming radiation beam to a selected one of the plurality of regions associated with the coating layer. The combinatorial coating library comprises a predetermined combination of at least one of the plurality of materials and at least one of the plurality of curing environments associated with each of the plurality of regions.  
       [0009] In another embodiment, a method for creating a combinatorial coating library includes selectively depositing at least one of a plurality of materials suitable for forming at least one coating layer on a surface of one or more substrates and selectively applying at least one of a plurality of curing environments to each of a plurality of regions associated with the at least one coating layer using a scanning mirror system having a mirrored surface positionable relative to an incoming radiation beam, wherein the mirrored surface is positionable to direct the incoming radiation beam to a selected one of the plurality of regions associated with the coating layer. The combinatorial coating library comprises a predetermined combination of at least one of the plurality of materials and at least one of the plurality of curing environments associated with each of the plurality of regions. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010]FIG. 1 is a schematic diagram of a system for the deposition and curing of coating compositions;  
     [0011]FIG. 2 is perspective view of a coating library generated by the system of FIG. 1;  
     [0012]FIG. 3 is a cross-sectional side view of one embodiment of the system of FIG. 1, utilizing a one-dimensional spin-coating method;  
     [0013]FIG. 4 is a cross-sectional side view of another embodiment of the system of FIG. 1, utilizing a two-dimensional spin-coating method;  
     [0014]FIG. 5 is a perspective view of a further embodiment of the system of FIG. 1, utilizing a dip-coating method;  
     [0015]FIG. 6 is cross-sectional side view of a spatially-addressable mask system;  
     [0016]FIG. 7 is a graphic representation of a wedge mask, a linearly-variable mask, a sinusoidally-variable mask, and a repeating mask;  
     [0017]FIG. 8 is a plot of the transmission characteristics of the mask of FIG. 7;  
     [0018]FIG. 9 is a perspective view of a scanning mirror system;  
     [0019]FIG. 10 is a perspective view of guided spatially-addressable curing system;  
     [0020]FIG. 11 is a cross-sectional side view of a thermal gradient curing system;  
     [0021]FIG. 12 is a perspective view of one embodiment of the system of FIG. 1, utilizing a plurality of coating and curing stations;  
     [0022]FIG. 13 is a perspective view of another embodiment of the system of FIG. 1, utilizing a plurality of spray coaters and curing sources; and  
     [0023]FIG. 14 is a block diagram of a method for the deposition and curing of coating compositions.  
     [0024]FIG. 15 is a schematic diagram of an experimental setup for the determination of the effect of temperature on the UV curing of coatings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0025] Referring to FIGS. 1 and 2, a system  10  for making an array of coated materials that form a coating library  11  includes a delivery mechanism  12  for delivering a plurality of materials  14  onto a surface  16  of a substrate  18  to form a coating  20 . The substrate surface  16  includes a plurality of predefined regions  22  that are positioned within a delivery area  23 . The delivery mechanism  12  is positioned to deliver the plurality of materials  14  to the delivery area  23 . Optionally, a mixer combines the plurality of materials  14  to form a mixture or combination of the plurality of materials  14 , with a controller  24  controlling the selection, quantity, and sequence of delivery of each of the plurality of materials  14  to the mixer such that the composition of the coating  20  may be varied, either incrementally or continuously, between each of the plurality of predefined regions  22  of the substrate surface  16  to form a coating library  11 . As such, each of the plurality of predefined regions  22  is coated with one of a plurality of predefined coatings. The plurality of predefined coatings may include a single layer coating of one of the plurality of materials  14  and a single layer coating of a combination of the plurality of materials  14 . Optionally, the plurality of predefined coatings may also include a multi-layer coating, where each layer is one of the plurality of materials  14 , and a multi-layer coating, where each layer is a combination of the plurality of materials  14 . Additionally, the system  10  may include a mask  26  in communication with the controller  24  to permit the delivery of the plurality of materials  14  to different combinations of the plurality of predefined regions  22  of the substrate surface  16 . The system  10  may also include a curing source  28  for curing the plurality of materials  14 , or combinations thereof, either as they are being delivered onto the substrate surface  16  or once they have been deposited on the substrate  18 . Further, the system  10  may include a testing device  30  for performing analytical tests on the coated substrate  18  or coating library  11  to determine the properties or characteristics of each of the plurality of predefined coatings. The mask  26  may be secured by a mounting device  32 , which optionally may movably position the mask  26  within the system  10 . Similarly, the substrate  18  may be secured by a holding device  34 , which preferably movably positions the substrate  18  within the system  10 . Thus, the present invention provides a system  10  and method for manufacturing a coating library  11  having an array of coatings  20  established from a plurality of materials  14  delivered onto a substrate  18 . Specific embodiments of this system  10  and method are discussed below.  
     [0026] The delivery mechanism  12  may be a single device or it may be a plurality of individual devices, each delivering the plurality of materials  14  onto the surface  16  of the substrate  18 . The position of the delivery mechanism  12  may be fixed within the system  10  relative to the delivery area  23  or it may be movable relative to the delivery area  23 . Preferably, the delivery mechanism  12  projects the plurality of materials  14  to the delivery area  23  in a vaporized/atomized or liquid form. Suitable examples of a delivery mechanism  12  include: a spray nozzle or gun of any type, such as an air, airless, thermal, ultrasonic, or hydraulic force spray nozzle or gun; a die/scraper casting head; an electron-beam evaporator; a sputtering device; a chemical vapor deposition device; an ink jet print head; a draw-down device, such as a wire-wound rod or a doctor-blade; and a linear coating head. The linear coating head may, for example, include one or more coating applicators, each having a supply inlet fluidly coupled to at least one of the plurality of materials  14  and each defining an elongate distribution channel with a length corresponding to a width of the substrate  18 . The linear coating head is preferably positioned at a suitable distance adjacent to the surface  16  of the substrate  18  to dispense a uniform thickness of the plurality of materials  14 , or a combination(s) thereof, onto the substrate  18 .  
     [0027] In one embodiment, the delivery mechanism  12  may also include a plurality of conventional liquid-handling devices (such as the Quadra 96 Model 230 Liquid Delivery System, Tomtec, Orange, Conn.). The liquid-handling devices, placed at predetermined positions adjacent to the surface  16  of one or more spinning substrates  18 , deliver the plurality of materials  14 , or combinations thereof, to the substrate(s)  18 . The spinning substrate(s)  18 , and the associated holding device  34  may be arranged in, for example, a one-dimensional array (see FIG. 3) or a two-dimensional array (see FIG. 4).  
     [0028] Alternatively, referring to FIG. 5, in another embodiment the delivery mechanism  12  may include a plurality of wells  36  or other suitable containers in which the plurality of materials  14 , or combinations thereof, may be disposed. Liquids of the same or different compositions may be disposed within the plurality of wells  36  using, for example, a conventional liquid-handling device. A plurality of substrates  18 , each held by a substrate holder, are arranged vertically and immersed in the corresponding wells  36 . Upon removal of the substrate array  38 , each of the plurality of substrates  18  is dip-coated with a predetermined coating. This method is particularly useful for the coating of acoustic wave transducers used to measure variations in acoustic wave parameters as the amount of material deposited on each device or the viscoelastic properties of each coating vary. Each of the plurality of acoustic wave transducers may have a first acoustic wave parameter and a second acoustic wave parameter, the first acoustic wave parameter corresponding to a first amount of coating or viscoelastic property of the coating layer, the second acoustic wave parameter corresponding to a second amount of coating or viscoelastic property of the coating layer.  
     [0029] Referring again to FIGS. 1 and 2, the plurality of materials  14  may include organic materials in various states, such as vaporized/atomized and liquid materials. Suitable examples of said materials  14  include polymeric materials, oligomeric materials, and small molecules, where the small molecules may be individual monomers that react to form a coating. The plurality of materials  14  may include, but are not limited to, polymers and oligomeric materials such as polycarbonates, acrylics, silicones, cellulose esters, polyesters, alkyds, polyurethanes, polyethers, vinyl polymers, and the like, as well as monomers including acrylates, epoxies, polyisocyanates, polyols, thiols, unsaturated esters, silanes, substituted olefins, and the like. Preferably, the plurality of materials  14  provide organic polymeric materials, such as “architectural” materials having protective or decorative functionality, especially including thermoplastic or thermosetting polymers. Further, the plurality of materials  14  optionally may be vaporized or atomized, individually or in combination, and directed to or deposited onto the substrate  18 , with the vaporized/atomized material coalescing to form a continuous coating  20  if a sufficient amount of the material is delivered onto the substrate  18 . Alternatively, the plurality of materials  14  may be directed to or deposited onto the substrate  18  in a liquid form. Optionally, the material or combination of materials  14  may form a coating  20  having a plurality of layers, where the coating  20  may be a multi-functional coating having an overall function dictated by a predefined functional role of each layer. The plurality of materials  14  may be combined such that multiple organic materials are combined into a coating  20 . By providing these various combinations of the plurality of materials  14 , the interaction and compatibility of various combinations may be determined through the use of the testing device  30 .  
     [0030] The coating  20  is a material or a combination of materials deposited on the surface  16  of the substrate  18 . These materials  14  may remain as separate homogenous materials, or they may interact, react, diffuse, mix, or otherwise combine to form a new homogeneous material, a mixture, a composite, or a blend. In general, a coating  20  has a lateral measure, i.e. a measured length across the surface  16  of the substrate  18 , much greater than a thickness, i.e. a measure of the coating  20  normal to the surface  16  of the substrate  18 . Preferably, each layer of coating  20  is a thin-film layer. The coating  20  may vary in composition, preferably in an incremental or continuous manner, from one predefined region  22  to another to thereby form an array of coatings that define the plurality of predefined coatings of the coating library  11 . Each member of the array of coatings is distinguishable from the others based upon its location. Further, each member of the array of coatings may be processed under the same conditions and analyzed to determine its performance relative to functional or useful properties, and then compared with each of the other members of the array of coatings to determine its relative utility. Alternatively, each member of the array of coatings may be processed under different conditions and the processing methods may be analyzed to determine their performance relative to functional or useful properties, and then compared with each other to determine their relative utility.  
     [0031] Each of the plurality of predefined regions  22  is a fixed area on the surface  16  of the substrate  18  for receiving one or a combination of the plurality of materials  14  to form a coating  20 . Each of the predefined regions  22  may have any shape sufficient for receiving and analyzing the coating  20  deposited thereon, such as rectangular, linear, arcuate, circular, elliptical, combinations thereof, etc. Each of the predefined regions  22  typically has an area in the range of about 0.01 mm 2  to about 100 cm 2 , preferably in the range of about 1 mm 2  to about 10 cm 2 , and more preferably in the range of about 10 mm 2  to about 100 mm 2 . Other areas may be utilized, and the area of each predefined region  22  may be determined by the capability of the deposition and analytical devices, or by a preferred density of the coating library  11 , etc.  
     [0032] The substrate  18  is a rigid or semi-rigid material suitable for receiving and supporting the plurality of materials  14 . The substrate  18  has at least one substantially flat surface  16 , or surface otherwise capable of receiving the plurality of materials  14 , which includes the plurality of predefined regions  22 . This surface  16 , optionally, may have raised portions to physically separate each of the plurality of predefined regions  22 . The substrate  18  may be of any size and shape, but preferably is in an elongated shape, such as in a tape, film, web, or roll. A film, for example, may range in thickness from about 25 micrometers to about 1,250 micrometers. The substrate  18  may also be in a disk, plate, or spherical shape. The surface  16  of the substrate  18 , corresponding to the delivery area  23 , typically has an area in the range of about 1 mm 2  to about 1 m 2 , preferably in the range of about 50 mm 2  to about 750 cm 2 , and more preferably in the range of about 1 cm 2  to about 500 cm 2 .  
     [0033] The substrate  18  may be secured within the system  10  and positioned in the delivery area  23  by the holding device  34 . The holding device  34  may movably position the substrate  18  within the system  10 . Preferably, the holding device  34  may movably position the substrate  18  at a substantially constant rate. For example, for a substrate  18  in the form of an elongated tape, web, or roll, the holding device  34  may include a tape pay-out device and a tape take-up device that are both rotatable and which support the tape, possibly in combination with rollers, in the delivery area  23 . In another example, the holding device  34  may be a stage on which the substrate  18  is placed and secured, where the stage is connected to a motor or other actuator-type device that controls the position and movement of the stage relative to the delivery area  23 . As such, the controller  24  may control the movement of the holding device  34  to determine which of the plurality of predefined regions  22  of the surface  16  of the substrate  18  receive the plurality of materials  14 . For example, the controller  24  may move the holding device  34  such that predetermined ones of the plurality of predefined regions  22  are outside of the delivery area  23  and therefore do not receive the plurality of materials  14 .  
     [0034] The delivery area  23  is an area at a fixed position within the system  10 . The delivery area  23  may be of any shape and size and typically, but not necessarily, substantially corresponds in shape and size to the plurality of predefined regions  22  of the surface  16  of the substrate  18 . However, the plurality of predefined regions  22  of the surface  16  of the substrate  18  may be much larger or much smaller than the delivery area  23 . The fixed positioning of the delivery area  23  provides a known, constant locale for the system  10  to deliver the plurality of materials  14  onto the surface  16  of the substrate  18 .  
     [0035] The controller  24  is a computer system having inputs, outputs, a memory, and a processor for receiving, sending, storing, and processing signals and data to operate, monitor, record, and otherwise functionally control the operation of the system  10 . The controller  24  includes a computer system having an interface board for integrating all of the components of the system  10  and a motion controller for controlling the movements of the mask  26  and substrate  18 . The controller  24  may include a keyboard and a mouse for inputting data and commands, a video display for displaying information, and a printer for printing information. The controller  24  may include software, hardware, firmware, and other similar components and circuitry for operating the system  10 . The controller  24  may be a single device, or it may be a plurality of devices working in concert. The controller  24  is preferably in communication with all of the other components of the system  10 , including the plurality of materials  14 , the delivery mechanism  12 , the substrate  18 , the mask  26 , the curing source  28 , the testing device  30 , the mounting device  32 , and the holding device  34 , to coordinate the operations of the system  10 . For example, the controller  24  may control the selection, quantity, and sequence of delivery of each of the plurality of materials  14  to a mixer such that the composition of the coating  20  may be varied, either incrementally or continuously, between each of the plurality of predefined regions  22  of the substrate surface  16 . The controller  24  may also control the delivery of the plurality of materials  14  onto the substrate  18 , recording the exact combination of materials  14  that make up the coating  20  at each predefined region  22 . By controlling the delivery, the controller  24  may control one or more of the material volume, the combination of materials  14 , the projective power, the coating speed, the spacing between the delivery mechanism  12  and the substrate  18 , the masking, etc. Further, the controller  24  controls, synchronizes, combines, and records the delivery and curing of the delivered materials  14 , the testing of the coating library  11 , and the analysis of the test results.  
     [0036] The mask  26  is a material having one or more patterns of open areas and blocked areas, where the open areas allow delivery of the plurality of materials  14  and/or a curing medium onto the substrate  18  and the blocked areas prohibit the delivery. The pattern may be in any shape. The mask  26  is utilized to define the spatial variation of materials or processing conditions in the coating library. In a binary masking system, for example, the mask  26  includes a plurality of patterns that are sequentially arranged to allow delivery to alternating half areas on the surface  16  of the substrate  18 . The mask  26  may be positioned anywhere in between the plurality of materials  14  and/or curing source  28  and the substrate  18 , including positioned directly on top of and in contact with the substrate  18 , along the line of delivery of the materials  14  or curing medium. By increasing the spacing between the mask  26  and the substrate  18 , an effect called “shadowing” is produced which may be undesirable in some instances. In shadowing, the pattern of material  14  delivered to the substrate  18  is proportional to the pattern of the mask  26 , but larger, as the spacing between the mask  26  and the substrate  18  allows the delivered pattern to expand until it reaches the substrate  18 . The mask  26  may be formed of a rigid or semi-rigid material, or the mask  26  may be a chemical formed on the surface  16  of the substrate  18 . Preferably, the material of the mask  26  insures that the mask  26  is as flat as possible and resists bending and/or folding. Suitable examples of mask materials include: silicon, silicon oxide, and glass for rigid or relatively non-bendable materials; plastics, metals, and alloys for semi-rigid or relatively bendable materials in the form of sheets, films, or foils; and lithographic-polyacrylate (“PMMA”) and other chemical materials that form positive and negative chemical masks.  
     [0037] The mask  26  may be secured within the system  10  and positioned relative to the delivery area  23  by the mounting device  32 . The mounting device  32  may movably position the mask  26 . For example, for a mask  26  in the form of an elongated semi-rigid material having a plurality of patterns, the mounting device  32  may include a tape pay-out device and a tape take-up device that are both rotatable and that support the tape, possibly in combination with rollers, relative to the delivery area  23 . In another example, for a mask  26  in the form of a rigid material, the mounting device  32  may be a platform or other supporting structure connected to a motor or other actuator-type device that controls the position of the platform and mask  26  relative to the delivery area  23 . This allows one pattern or a number of patterns to be utilized to mask different predefined regions  22  of the substrate  18  by movement of the mask  26 . As such, the controller  24  may control the movement of the mounting device  32  to control the predefined regions  22  onto which the plurality of materials  14 , or combinations thereof, are delivered.  
     [0038] The curing source  28  is a device in communication with each of the plurality of materials  14  causing a reaction or solvent evaporation with one or a combination of the plurality of materials  14 . For example, the reaction may be a polymerization reaction, a cross-linking reaction, a small molecule reaction, an inorganic phase reaction, and other similar reactions appropriate for the delivered material(s)  14 . The curing source  28  accomplishes this by delivering a curing medium. The curing medium may be any form of energy or suitable material that interacts with the combination of the plurality of materials  14  forming the coating  20  to sufficiently cure the coating  20 . Suitable examples of curing environments preferably include those created by a curing source  28  selected from the group consisting of ultraviolet (UV) radiation, infrared (IR) radiation, thermal radiation, microwave radiation, visible radiation, narrow-wavelength radiation, laser light, and humidity. Suitable examples of a curing source  28  include, for example, a heating device in communication with the substrate  18 , a radiation device in communication with the delivered or deposited materials  14 , a microwave device, a plasma device, and combinations thereof. It may be desirable, for example, to combine radiative thermal energy with UV radiation or IR radiation to cure coatings  20  forming a coating library  11 .  
     [0039] The curing source  28  may be placed in communication with each of the plurality of materials  14  such that it causes the same reaction, or degree of reaction, in each of the predefined coatings in each of the plurality of predefined regions  22  or it may be placed such that it causes a different reaction, or degree of reaction, in each of the predefined coatings in each of the plurality of predefined regions  22 . In practice, this may be done, for example, by positioning the curing source  28  such that the plurality of materials  14  or predefined coatings in each of the plurality of predefined regions  22  are exposed to heat or radiation with, for example, a linearly varying intensity across the lateral direction, or width, of the substrate  18 .  
     [0040] The dose of the curing medium received by a particular coating composition is important because the amount of curing of a coating  20  may affect such coating characteristics as the physical, mechanical, chemical, morphological, optical, electrical, and biological performance characteristics of the coating  20 . The amount of curing may also affect the characteristics of a coating  20  with respect to the substrate  18 , such as the adhesion performance characteristics of the coating  20 . Coating characteristics affected by curing also include abrasion resistance, corrosion resistance, solvent resistance, translucence, haze, gloss, permeability, etc.  
     [0041] Referring to FIG. 6, one embodiment of a curing system incorporating a curing source  28  includes a spatially-addressable mask system  40 . The mask system  40  includes a curing source  28  spaced apart from a moving or stationary substrate  18  with a single coating  20  or a continuous or discrete coating library  11  deposited on its surface  16 . The curing source  28  is positioned to face the coated surface  16  of the substrate  18 . A spatial mask  26  is positioned between the curing source  28  and the coating  20  or coating library  11  such that the curing medium passes through the spatial mask  26  prior to being received by the coating  20  or coating library  11 . The spatial mask  26  preferably has an elongated surface having at least a length and a width, the transmission of the curing medium through the spatial mask  26  varying across the surface of the spatial mask  26 . The curing medium may be, for example, thermal, UV, visible, microwave, electron beam, laser radiation, or humidity. As such, the variable transmission characteristic of the spatial mask  26  acts to filter the dose of the curing medium across the coating  20  or coating library  11 , thereby providing variable, predetermined curing doses at each of the plurality of predefined regions  22 , enabling spatially-addressable curing. The performance characteristics of each of the plurality of coatings  20  of the coating library  11  may then be screened and analyzed to determine the desired amount or dose of a given curing medium associated with a desired level of a given performance characteristic.  
     [0042] The spatial mask  26  may include any material, component, or combination of materials or components that allow for the variable transmission of the curing medium across the coating library  11  along one or more spatial coordinates. Suitable examples of a spatial mask  26  include: a variable thickness wedge of quartz or glass; quartz or glass variably doped across its area with a material having lower transmissibility characteristics; a printed image on a slide or other optically transparent material; combinations thereof; and other suitable materials that variably attenuate a given curing medium within a spectral range of interest.  
     [0043] For example, referring to FIGS. 7 and 8, the spatial mask  26  may include a wedge mask  42 , a linearly-variable mask  44 , a sinusoidally-variable mask  46 , and a repeating mask  48 . Referring to FIG. 7, the wedge mask  42  may include a quartz, borosilicate, or glass material having a variable thickness along a spatial coordinate, such as length or width. Referring to FIG. 8, the variable thickness of the wedge mask  42  serves as an exponential alternator of the curing medium, providing a transmission characteristic  50  that exponentially varies along the spatial coordinate.  
     [0044] Referring again to FIG. 7, the linearly-variable mask  44  includes a slide or optically transmissive material having a linearly varying pattern, such as ink or toner, deposited on one surface. Referring to FIG. 8, a linearly varying transmission characteristic  52  results from the attraction of the curing medium by the material pattern.  
     [0045] Referring again to FIG. 7, the sinusoidally-variable mask  46  is similar to the linearly-variable mask  44 , but with a sinusoidally varying material pattern. Referring to FIG. 8, a sinusoidally varying transmission characteristic  54  thereby results.  
     [0046] Referring again to FIG. 7, the repeating mask  48  includes a material pattern that varies in a step-wise fashion. Referring to FIG. 8, a step transmission characteristic  56  thereby results.  
     [0047] Although FIGS. 7 and 8 include longitudinally varying thicknesses or material patterns corresponding to transmission characteristics that vary along an associated longitudinal spatial coordinate, it is to be understood that variations may also occur laterally or along any other one or combinations of spatial coordinates.  
     [0048] In addition to providing variable curing across one or more spatial coordinates or dimensions, the use of a spatial mask  26  provides a controllable predetermined variation of the curing medium dosage across a coating library  11 . Further, the spatial mask  26  occupies only a small amount of physical space, making more efficient use of a given space and allowing for the use of bulkier curing sources  28 . Further, the spatial mask  26  may include polarization or filtering characteristics to channel the curing medium onto the coating library  11  so as to insure that a desired transmission characteristic is achieved for a given region of the coating library  11 .  
     [0049] Referring to FIG. 9, another embodiment of a spatially-addressable curing system incorporating a curing source  28  includes a scanning mirror system  60 . The scanning mirror system  60  includes a curing source  28 , such as a laser, that directs the curing medium to one or more scanning mirrors  62 , which re-direct the curing medium to one or more predetermined regions of the coating library  11 . The use of a narrow-wavelength curing source, such as a laser or similar radiation source, may provide high power over certain spectral ranges, power that may be unavailable using broad-band sources. Suitable scanning mirrors  62  include, but are not limited to, those scanning projectors utilized in, for example, laser shows (CATWEAZLE Pro, CATWEAZLE VX, and KillerCat available from MediaLas Laserproducts GmbH, Hechingen, Germany), industrial applications (model GS300s available from Laser and Motion Development Company, Union City, Calif.; X-Y scanner/3-dimensional profiler of concave surfaces and glass thickness meter available from Light Conversion Ltd., Vilnius, Lithuania), and research scanning systems (Institute for Computer Base Learning, Heriot-Watt University, Edinburgh EH14 4AS, UK). Suitable curing sources  28  include, but are not limited to, UV Lamp System Model EPIC 6000 from Fusion UV Systems, Inc., Gaithersburg, Md.; Pulsed UV Curing System Model RC-5000 from Xenon Corporation, Woburn, Mass.; UV-Visible Spot Cure System Model Novacure from EFOS, Mississauga, ON, CAN; and Spot Curing Source Model Flexicure from Macam Photometrics Ltd., Livingston Scotland. Optionally, the scanning mirror system  60  may be in communication with the controller  24  for controlling the timing and intensity of the curing medium delivered by the curing source  28  and for controlling the position/attitude of the scanning mirrors  62 .  
     [0050] Referring to FIG. 10, a further embodiment of a curing system incorporating a curing source  28  is a guided spatially-addressable curing system  66 . The guided system  66  includes a curing source  28 , such as a UV source, an IR source, a thermal source, a microwave source, or a humidity source, which provides a curing medium that is directed to individual spatial locations of the coated substrate  18  via dielectric or metal waveguides or tubes  68 . Preferably, the plurality of waveguides or tubes  68  each have a first end corresponding to one of the plurality of regions associated with the coated substrate  18  and a second end associated with the curing source  28 . For example, UV radiation may be directed to the coated substrate  18  using quartz or liquid-core waveguides. IR radiation may be directed to the coated substrate  18  using IR optical fibers. Hollow metal waveguides or tubes may be used to direct thermal radiation, microwave radiation, or humidity to the coated substrate  18 . The guided system  66  allows different regions of the coating  20  or coating library  11  to be cured using different curing techniques.  
     [0051] Referring to FIG. 11, a still further embodiment of a curing system incorporating a curing source  28  is a thermal gradient curing system  72 . The thermal gradient system  72  includes a curing source  28 , such as a heater, attached to one end of an elongate heating element  74  The heating element  74  may have constant dimensions along its longitudinal direction, or length, or, optionally, may have variable dimensions along its longitudinal direction. The placement of the curing source  28  at one end of the heating element  74  provides an exponential, linear, or other decay profile in the temperature of the element  74  as a function of distance from the curing source  28  resulting in a thermal gradient in the longitudinal direction. This heating element  74  is placed adjacent to the coated substrate  18 , resulting in a variable temperature distribution across the coated substrate  18  and, therefore, variable curing conditions across the coated substrate  18 . Additionally, posts  76  and a weight  78  may be placed above and in contact with the coated substrate  18 , ensuring sufficient thermal communication between the coated substrate  18  and the heating element  74 .  
     [0052] Referring to FIGS. 12 and 13, various combinations of delivery mechanisms  12 , or coating applicators, and curing sources  28  may be utilized to deposit and cure multi-layer coatings. Referring to FIG. 12, in one embodiment, the substrate  18  may be in the form of an elongated tape, web, or roll. A plurality of delivery mechanisms  12  or coating applicators may be placed adjacent to the moving substrate  18  at predetermined positions. Each delivery mechanism  12  or coating applicator may be associated with a curing station including one or more curing sources  28 . Multi-layer coatings are produced as the substrate  18  moves through each of the coating/curing zones in series. Within each coating/curing zone, the substrate  18  preferably moves from a first position adjacent to a respective one of the plurality of delivery mechanisms  12  or coating applicators to a second position adjacent to a respective one of the plurality of curing stations. Referring to FIG. 13, in another embodiment, a plurality of delivery mechanisms  12 , such as spray coaters, may be positioned above below and adjacent to a stationary substrate  18 . Spatial masks  26  may also be utilized to mask the surfaces of the substrate  18  from radiation or other curing mediums delivered by curing sources  28  positioned above/below the substrate  18 . Multi-layer coatings are produced as the plurality of materials, or combinations thereof, are delivered onto the substrate  18  at predetermined times and sequentially cured.  
     [0053] Each of the plurality of curing environments, discussed above, may include one of a plurality of curing sources  28  and one of a plurality of curing characteristics. Each of the plurality of curing stations may be operatively coupled to substantially the same or a substantially different curing source  28  and each of the plurality of curing stations may apply substantially the same or a substantially different selected one of the plurality of curing characteristics to each of the plurality of regions associated with a respective coating layer.  
     [0054] Referring to FIG. 14, a method  80  for making an array of coated materials that form a coating library  11  includes providing a substrate  18  having a surface  16  with a plurality of predefined regions  22  (Block  82 ). Optionally, the substrate  18  is movable. The method  80  also includes providing a plurality of materials  14  for coating the substrate  18  (Block  84 ). The method  80  further includes delivering the plurality of materials  14 , or combinations thereof, to the surface  16  of the substrate  18  to form a predefined coating  20  on each of the plurality of predefined regions  22  of the substrate  18  (Block  86 ). The plurality of materials  14  are preferably delivered to the surface  16  of the substrate  18  in a vaporized/atomized or liquid state and the predefined coating  20  may, accordingly, be a thin film coating of at least one layer. The plurality of materials  14 , or combinations thereof, may be delivered to the surface  16  of the substrate  18  using, for example, the spray nozzle or gun, the linear coating head, the spin-coating, and the dip-coating systems described above. The method  80  preferably includes providing a curing source  28  for delivering a curing medium to each of the plurality of predefined regions  22  of the coated substrate (Block  88 ) and curing each of the plurality of predefined regions  22  of the coated substrate  18  using a selected one of a plurality of curing environments (Block  90 ). The curing source  28  may, for example, include the spatially-addressable mask system, the scanning mirror system, the guided spatially-addressable curing system, and the thermal gradient curing system, described above. A plurality of delivery mechanisms  12  and a plurality of curing sources  28  may be utilized, forming a single or multi-layer coating. The selective combination of the plurality of materials  14  and the plurality of curing environments associated with each of the plurality of predefined regions  22  of the surface  16  of the substrate  18  form a combinatorial library.  
     [0055] It is apparent that there has been provided, in accordance with the present invention, a system and method for the fabrication of coating libraries. This invention permits the manufacture of coating libraries having virtually infinite variations in composition and curing environment. While the present invention has been particularly shown and described in conjunction with preferred embodiments thereof, it will be appreciated that variations and modifications may be effected by persons of ordinary skill in the art without departing from the spirit or scope of the invention. Further, it is to be understood that the principles related to delivery mechanisms and the curing of combinations of materials described herein apply in a similar manner, where applicable, to all embodiments.  
     [0056] In one working example, the effect of temperature on the UV curing of coatings was determined. In the past, fluorescent dyes have been used to monitor a variety of curing processes. Such environmentally sensitive dyes, however, have not typically been used to study temperature-induced effects in the UV curing of coatings as the fluorescence of such dyes exhibit temperature dependence. This investigation permitted the decoupling of temperature and radiation effects in the UV curing of coating formulations.  
     [0057] The studied coating formulation was an acrylated aliphatic urethane oligomer (Ebecryl 8804, UCB Chemicals Corp., North Augusta, S.C.). The fluorophore used was 4,4′-bis(2-benzoxazolyl)-stilbene (Aldrich Chemical Company, Inc., Milwaukee, Wis.). The fluorophore was incorporated into the uncured coating formulation by dissolving it in chloroform and mixing the solution with a 30% wt. solution of the acrylated aliphatic urethane oligomer in methoxypropanol. About 10 μl of the resulting solution was disposed within standard aluminum plates (5-mm diameter, 1-mm depth) used in differential scanning calorimetry instruments. The solvents were allowed to evaporate, keeping the solutions at room temperature for about 20 hours. The resulting coating had a uniform thickness. The concentration of the fluorophore in the final formulation was about 10 −4 M.  
     [0058] Seven samples with coating formulations were arranged on a gradient heater. The curing temperature of each sample is shown in Table 1.  
               TABLE 1                          Curing Temperatures of Coating Samples                             Sample Position   Curing Temperature (degrees C.)                                         1   26           2   42           3   56           4   70           5   85           6   100           7   115                      
 
     [0059]FIG. 15 is a schematic diagram of the experimental setup  100  for the determination of the effect of temperature on the UV curing of coatings. Fluorescence measurements were carried out using a nitrogen laser and a portable spectrofluorometer. The laser (emission wavelength-337.1 nm) was operated with a 20-Hz repetition rate with a maximum average power of about 50 mW, maximum energy per pulse of about 2.8 mJ and pulse width of about 800 ps. The spectrofluorometer (Model ST2000, Ocean Optics, Inc., Dunedin, Fla.) was equipped with a 200-μm slit, 600-grooves/mm grating blazed at 400 nm and covering the spectral range from about 250 nm to about 800 nm with efficiency greater than 30%, and a linear CCD-array detector. Light from the laser was focused into one arm of a “six-around-one” bifurcated fiber-optic reflection probe 102 (Model R400-7-U/VIS, Ocean Optics, Inc.). Emission light from the sample array  104  was collected when the common end of the fiber-optic probe  102  was positioned near a sample at about a 45-degree angle to the normal to the surface. The second arm of the probe  102  was coupled to a spectrometer. Excitation light was blocked from entering the spectrometer using a long-pass optical filter. The common end of the fiber-optic probe  102  was arranged on an X-Y translation stage and data acquisition was achieved with a computer using a program written in LabVIEW (National Instruments, Austin, Tex.). The program provided adequate control of the data acquisition parameters and real-time communication with the translation stage. Processing of the collected spectra was performed using KaleidaGraph (Synergy Software, Reading, Pa.) and Matlab (The Mathworks, Inc., Natick, Mass.). For the evaluation of curing conditions, an intensity ratio at two wavelengths of the fluorescence emission spectra of the fluorophore (432 nm and 488 nm) was calculated as the I 488 /I 432  ratio after a baseline subtraction.  
     [0060] Curing of the coating formulations was performed using a UV-visible Spot Cure System (Model Novacure, EFOS, Mississauga, ON, CAN). The system was equipped with a high-pressure 100-W Hg vapor short arc lamp. The light from the source  106  was coupled into an extended spectral range liquid-core optical waveguide (8-mm diameter, 1-m length) and a 10-cm long fiber-optic line spreader, which converted the round light beam propagating in the waveguide into a 10-cm long, 2-mm wide light line. Curing was accomplished in the air by periodic exposure of the coatings to the UV-visible radiation for about 60 sec every 200 sec. Illumination was performed by positioning the fiber-optic line spreader at about a 45-degree angle to the surface of the coatings at a distance of about 5 mm. Four replicate measurements of fluorescence spectra were performed between pulses of curing radiation.  
     [0061] The curing rate of the coating samples was found to have a strong temperature dependence and, at an advanced phase of the curing experiment, the formulations exhibited different degrees of curing which were proportional to formulation temperature. An additional curing mechanism was found to be present at curing temperatures above about 70 degrees C.  
     [0062] It is apparent that there has been provided, in accordance with the present invention, a system and method for the fabrication of coating libraries. This invention permits the manufacture of coating libraries having virtually infinite variations in composition and curing environment. While the present invention has been particularly shown and described in conjunction with preferred embodiments and examples thereof, it will be appreciated that variations and modifications may be effected by persons of ordinary skill in the art without departing from the spirit or scope of the invention. Further, it is to be understood that the principles related to delivery mechanisms and the curing of combinations of materials described herein apply in a similar manner, where applicable, to all embodiments.