Patent Publication Number: US-8968629-B2

Title: Apparatus and method for producing two-sided patterned web in registration

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 12/837,826, filed Jul. 16, 2010, now allowed, which is a divisional of U.S. application Ser. No. 11/370,136, filed Mar. 6, 2006, now U.S. Pat. No. 7,767,273, which claims the benefit of U.S. Provisional Application No. 60/661,430, filed Mar. 9, 2005, the disclosure of which is incorporated by reference in their entirety herein. 
    
    
     TECHNICAL FIELD 
     The disclosure relates generally to the continuous casting of material onto a web, and more specifically to the casting of articles having a high degree of registration between the patterns cast on opposite sides of the web. In particular, the disclosure relates to casting patterns onto opposite sides of a web with a high degree of registration. 
     BACKGROUND 
     Many articles can be manufactured by applying a material that is at least temporarily in liquid form to opposite sides of a substrate. It is often the case that the material applied to the substrate is applied in a predetermined pattern. It is common in such cases for there to be at least a minimum requirement for registration between the patterns on opposite sides of the substrate. In some cases, it is necessary for the patterns on either side of a substrate to be aligned within very small tolerances. 
     A need remains, therefore, for improved techniques, apparatus and methods of producing two-sided substrates in which each side of the substrate bears a predetermined pattern in close registration with the predetermined pattern on the other side of the substrate. A need remains for improved techniques, apparatus and methods of reproducing closely registered microreplicated patterns on either side of a flexible, at least partially opaque web or substrate. 
     SUMMARY 
     The disclosure pertains generally to improved techniques, apparatus and methods of reproducing closely registered microreplicated patterns on either side of a flexible web or substrate. 
     Accordingly, an illustrative embodiment of the disclosure may be found in an assembly that includes an energy source adapted to provide curing energy. The assembly includes a first patterned roll having a number of regions that are opaque to the curing energy disposed on a substrate that is transparent to the curing energy. The opaque regions define a first pattern. The assembly includes a second patterned roll that define a second pattern. The second patterned roll can have a number of regions that are opaque to the curing energy disposed on a substrate that is transparent to the curing energy, where the opaque regions define a second pattern. 
     The assembly also includes means for rotating the first and second patterned rolls such that the first and second patterns are maintained in continuous registration to within 100 micrometers. In some instances, the first and second patterns are maintained in continuous registration to within 10 micrometers. 
     In some instances, the opaque regions block, scatter, absorb or reflect at least 98 percent of the curing energy incident upon the opaque regions. In some cases, the transparent substrates permit at least 25 percent of the curing energy incident upon the transparent substrates to pass through. In some cases, the substrates define an outer substrate surface, and the opaque regions extend radially outwardly from the outer substrate surface. In some instances, the opaque regions are located at a periphery of the substrate, and the transparent regions of the substrate extend inwardly from the periphery. 
     Another illustrative embodiment of the disclosure may be found in an apparatus that includes an energy source that is adapted to provide curing energy, a first patterned roll and a second patterned roll. The energy source may be adapted to provide ultraviolet light. The first patterned roll includes a number of regions that are opaque to the curing energy disposed on a substrate that is transparent to the curing energy. The opaque regions define a first raised pattern. The second patterned roll includes a number of regions that are opaque to the curing energy disposed on a substrate that is transparent to the curing energy. The opaque regions define a second raised pattern. 
     The apparatus also includes one or more feed rolls that are adapted to provide a web and to feed the web into contact with the first and second patterned rolls. In some embodiments, the web has first and second sides and can be opaque to the curing energy. A first dispenser is adapted to dispose a curable material onto the first side of the web or the first patterned roll before the web contacts the first patterned roll and a second dispenser is adapted to dispose a curable material onto the second side of the web or the second patterned roll before the web contacts the second patterned roll. 
     The apparatus also includes means for rotating the first and second patterned rolls such that the first and second raised patterns are imprinted in the curable material on the first and second sides of the web while the web is in continuous motion, and the first and second raised patterns are maintained in continuous registration on the first and second sides of the web to within 100 micrometers. In some instances, the first and second raised patterns are maintained in continuous registration to within 10 micrometers. 
     In some instances, the opaque regions block, scatter, absorb or reflect at least 98 percent of the curing energy incident upon the opaque regions. In some cases, the transparent substrates permit at least 10 percent of the curing energy incident upon the transparent substrates to pass through. In some instances, the web permits less than 2 percent of curing energy incident on the web to pass through the web. 
     In some instances, the transparent substrates may include a glass cylinder and may in particular cases include a quartz cylinder. The transparent substrates may be a polymeric cylinder such as a PMMA (poly methyl methacrylate) cylinder. The opaque regions may include materials such as chrome, copper, aluminum or epoxy. 
     The energy source may, in some instances, be adapted to provide curing energy that passes at least partially through the first patterned roll and/or at least partially through the second patterned roll. The energy source may include a first curing energy source disposed within the first patterned roll and a second curing energy source disposed within the second patterned roll. 
     Another illustrative embodiment of the disclosure may be found in a method of patterning an opaque web that has a first side and a second side. Curable material is disposed onto the opaque web, which is then directed into contact with a first patterned roll having a number of raised opaque regions disposed on a transparent substrate. Ultraviolet radiation is directed at least partially through the first patterned roll, thereby curing the curable material on the first side of the opaque web to form a first pattern. The opaque web is then directed into contact with a second patterned roll having a number of opaque regions disposed on a transparent substrate. Ultraviolet radiation is directed at least partially through the second patterned roll, thereby curing the curable material on the second side of the opaque web to form a second pattern. The first and second sides of the web are patterned while the web is in continuous motion such that the first and second patterns are maintained in continuous registration to within 100 micrometers. In some instances, the first and second patterns are maintained to within 10 micrometers. 
     In some instances, disposing curable material onto the opaque web includes disposing curable material onto the first side of the web or first patterned roll prior to the first side of the web contacting the first patterned roll and disposing curable material onto the second side of the web or second patterned roll prior to the second side of the web contacting the second patterned roll. 
     Another illustrative embodiment of the disclosure may be found in a patterned roll that includes a curing energy transparent cylinder, a tie layer disposed on the curing energy transparent cylinder, and a number of curing energy opaque features disposed on the tie layer to form a pattern. The curing energy transparent cylinder permits at least 10 percent of curing energy light incident upon the cylinder to pass through the cylinder while the curing energy opaque features block at least 98 percent of curing energy light incident upon the curing energy opaque features. In some particular instances, the curing energy transparent cylinder includes quartz, the tie layer includes titanium, and the curing energy opaque feature includes chrome. 
     The above summary of the present disclosure is not intended to describe each disclosed embodiment or every implementation of the present disclosure. The Figures, Detailed Description and Examples which follow more particularly exemplify these embodiments. 
     DEFINITIONS 
     In the context of this disclosure, “registration,” means the positioning of structures on one surface of the web in a defined relationship to other structures on the opposite side of the same web. 
     In the context of this disclosure, “web” means a sheet of material having a fixed dimension in a first direction and either a predetermined or indeterminate length in a second direction that is orthogonal to the first direction. 
     In the context of this disclosure, “continuous registration,” means that at all times during rotation of first and second patterned rolls the degree of registration between structures on the rolls is better than a specified limit. 
     In the context of this disclosure, “microreplicated” or “microreplication” means the production of a microstructured surface through a process where the structured surface features retain an individual feature fidelity during manufacture, from product-to-product, that varies no more than about 100 micrometers. 
     In the context of this disclosure, “curing energy” refers to electromagnetic radiation having a particular wavelength or band of wavelengths suitable for curing a curable material. The phrase “curing energy” may be modified by a term identifying the wavelength or band of wavelengths. For example, “ultraviolet curing energy” refers to energy within a band of wavelengths that is considered to be ultraviolet and that is suitable for curing a particular material. The phrase “curable material”, when used in conjunction with “curing energy”, refers to a material that may be cured, polymerized or cross-linked when exposed to “curing energy”. 
     In the context of this disclosure, “opaque” refers to a material that blocks at least a significant amount of electromagnetic radiation of a particular wavelength or band of wavelengths. A material may be considered to be opaque to energy of a first wavelength, but not be opaque to energy of a second wavelength. A material that is “opaque” to energy of a particular wavelength may block at least 95 percent of the energy of that particular wavelength that is incident upon the material. An “opaque” material may block 98 percent or even more than 99 percent of the energy of that particular wavelength that is incident upon the material. 
     A material may be described as “opaque to curing energy”, meaning that the material blocks at least 95 percent of the curing energy (of a particular wavelength or band of wavelengths) incident upon the material. A material described as “opaque to ultraviolet energy” would block at least 95 percent of ultraviolet radiation incident upon the material. 
     A material such as a flexible web or substrate may be described as “opaque”, meaning that the flexible web or substrate blocks at least 95 percent of the electromagnetic energy of a particular wavelength or band of wavelengths incident upon the flexible web or substrate. A flexible web or substrate may be described as described as “opaque to curing energy”, meaning that the flexible web or substrate blocks at least 95 percent of the curing energy (of a particular wavelength or band of wavelengths) incident upon the flexible web or substrate. A flexible web or substrate described as “opaque to ultraviolet energy” would block at least 95 percent of ultraviolet radiation incident upon the flexible web or substrate. 
     As used within the context of this disclosure, “transparent” refers to a material that transmits, or permits passage, of at least a significant amount of electromagnetic radiation of a particular wavelength or band of wavelengths. A material may be considered to be transparent to energy of a first wavelength, but not be transparent to energy of a second wavelength. A material that is “transparent” to energy of a particular wavelength may transmit or permit passage at least 10 percent of the energy of that particular wavelength that is incident upon the material. A “transparent” material may transmit or permit passage of 25 percent or even more than 50 percent of the energy of that particular wavelength that is incident upon the material. 
     A material may be described as “transparent to curing energy”, meaning that the material transmits or permits passage of at least 10 percent of the curing energy (of a particular wavelength or band of wavelengths) incident upon the material. A material described as “transparent to ultraviolet energy” would transmit or permit passage of at least 10 percent of ultraviolet radiation incident upon the material. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic illustration of a casting apparatus in accordance with an embodiment of the disclosure; 
         FIG. 2  is a schematic illustration of a portion of the casting apparatus shown in  FIG. 1 ; 
         FIG. 3  is a partial illustration of a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 4-13  demonstrate an illustrative but non-limiting method of forming the patterned roll of  FIG. 3  in accordance with an embodiment of the disclosure; 
         FIGS. 14A-14E  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 15A-15D  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 16A-16D  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 17A-17C  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 18A-18C  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 19A-19D  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 20A-20E  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIGS. 21A-21D  demonstrate an illustrative but non-limiting method of forming a patterned roll in accordance with an embodiment of the disclosure; 
         FIG. 22  is a perspective view of a microreplication assembly in accordance with an embodiment of the disclosure; 
         FIG. 23  is a perspective view of a portion of the microreplication assembly of  FIG. 22 ; 
         FIG. 24  is a perspective view of a portion of the microreplication assembly of  FIG. 22 ; 
         FIG. 25  is a schematic illustration of a roll mounting arrangement in accordance with an embodiment of the disclosure; 
         FIG. 26  is a schematic illustration of a mounting arrangement for a pair of patterned roll in accordance with an embodiment of the disclosure; 
         FIG. 27  is a schematic illustration of a motor and roll arrangement in accordance with an embodiment of the disclosure; 
         FIG. 28  is a schematic illustration of structure for controlling the registration between rolls in accordance with an embodiment of the disclosure; 
         FIG. 29  is a schematic illustration of a control algorithm for controlling registration in accordance with an embodiment of the disclosure; and 
         FIG. 30  is a diagrammatic cross-sectional view of an article made in accordance with an embodiment of the disclosure; 
     
    
    
     While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the disclosure to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure. 
     DETAILED DESCRIPTION 
     Generally, the present disclosure pertains to producing two-sided microreplicated structures having a first microreplicated pattern on a first surface of a web and a second microreplicated pattern on a second surface of the web. The system generally includes a first patterning assembly and a second patterning assembly. Each respective assembly creates a microreplicated pattern on either a first or second surface of the web. A first pattern can be created on the first surface of the web and a second pattern can be created on the second surface of the web. 
     In some instances, the apparatus and methods discussed herein result in a web having a microreplicated structure on each opposing surface of the web that can be manufactured by continuously forming microreplicated structures on opposite surfaces of the web while keeping the microreplicated structures registered generally to within 100 micrometers of each other. In some instances, the microreplicated structures may remain registered within 50 micrometers. In some cases, the microreplicated structures may remain registered within 20 micrometers. In some instances, the microreplicated structures may remain registered within 10 micrometers or even within 5 micrometers. 
     The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the disclosure. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. 
     Casting Assembly 
       FIG. 1  illustrates an example casting apparatus  10  for producing a two-sided web  12  that includes registered microreplicated structures on opposing surfaces. In some instances, the casting apparatus  10  includes first and second coating means  16 ,  20 , a nip roller  14 , and first and second patterned rolls  18 ,  24 . In some instances, first coating means  16  may be a first extrusion die  16  while second coating means may be a second extrusion die  20 . In the illustrated embodiment, the first and second curable liquid is disposed on the web surface prior to passing through the first and second patterned rolls, respectively. In other embodiments, the first curable liquid is disposed on the first patterned roll and the second curable liquid is disposed on the second patterned roll, which is then transferred to the web from the patterned rolls. 
     Web  12  may be presented to the first extrusion die  16 , which dispenses a first curable liquid layer coating  22  onto the web  12 . Nip roller  14  presses first coating  22  into the first patterned roller  18 . In some cases, nip roller  14  can be a rubber covered roller. While on the first patterned roll  18 , the coating  22  is cured using an energy source  26  adapted to provide suitable curing energy. In some instances, energy source  26  may be adapted to provide ultraviolet light. The term “ultraviolet light” refers to light having a wavelength in a range from 200 to 500 nanometers or from 200 to 400 nanometers. 
     A second curable liquid layer  28  is coated on the opposite side of the web  12  using a second side extrusion die  20 . The second layer  28  is pressed into the second patterned tool roller  24  and the curing process repeated for the second coating layer  28 . Registration of the two coating patterns is achieved by maintaining the tool rollers  18 ,  24  in a precise angular relationship with one another, as will be described hereinafter. 
       FIG. 2  provides a closer view at first and second patterned rolls  44  and  46 . First and second patterned rolls  44 ,  46  may be considered as particular embodiments of patterned rolls  18 ,  24  as discussed with respect to  FIG. 1 . Other patterns are contemplated, as will be discussed in greater detail subsequently. First patterned roll  44  has a first pattern  42  for forming a microreplicated surface. Second pattern roll  46  has a second microreplicated pattern  50 . In the illustrated embodiment, first and second patterns  42 ,  50  are the same pattern. In other instances, the first and second patterns may be different. 
     As a web  30  passes over the first patterned roll  44 , a first curable liquid (not shown) on a first surface  32  may be cured by curing energy provided by an energy source  34  near a first region  36  on the first patterned roll  44 . A first microreplicated patterned structure  54  is formed on the first side  43  of the web  30  after the liquid is cured. The first patterned structure  54  is a negative of the pattern  42  on the first patterned roll  44 . After the first patterned structure  54  is formed, a second curable liquid  52  is dispensed onto a second surface  38  of the web  30 . To insure that the second liquid  52  is not cured prematurely, the second liquid  52  is isolated from the first energy source  34 , typically by locating the first energy source  34  so that energy emitted by the first energy source  34  does not fall on the second liquid  52 . If desired, the curing sources can be located inside their respective patterned rolls. As such, the opaque nature of web  30  can aid in preventing undesired curing. 
     After the first patterned structure  54  is formed, the web  30  continues along the first roll  44  until it enters a gap region  48  between the first and second patterned rolls  44 ,  46 . The second liquid  52  then engages the second pattern  50  on the second patterned roll  46  and is shaped into a second microreplicated structure, which is then cured by curing energy emitted by a second energy source  40 . As the web  30  passes into the gap  48  between first and second patterned rolls  44 ,  46 , the first patterned structured  54 , which is by this time substantially cured and bonded to the web  30 , restrains the web  30  from slipping while the web  30  begins moving into the gap  48  and around the second patterned roller  46 . This removes web stretching and slippages as a source of registration error between the first and second patterned structures formed on the web. 
     By supporting the web  30  on the first patterned roll  44  while the second liquid  52  comes into contact with the second patterned roll  46 , the degree of registration between the first and second microreplicated structures  54 ,  56  formed on opposite sides  32 ,  38  of the web  30  becomes a function of controlling the positional relationship between the surfaces of the first and second patterned rolls  44 ,  46 . The S-wrap of the web around the first and second patterned rolls  44 ,  46  and between the gap  48  formed by the rolls minimizes effects of tension, web strain changes, temperature, microslip caused by mechanics of nipping a web, and lateral position control. The S-wrap can maintain the web  30  in contact with each roll over a wrap angle of 180 degrees, though the wrap angle can be more or less depending on the particular requirements. 
     Patterned Roll 
     In some instances, it may be useful to provide microreplicated patterns onto either side of a flexible web or substrate that is opaque, particularly, opaque to curing energy. In other instances, it may be useful to provide microreplicated patterns onto either side of a flexible web or substrate that is transparent, particularly, transparent to curing energy. When the web or substrate is opaque to the curing energy necessary to cure the materials applied to the web in liquid form, the materials cannot simply be cured by passing curing energy through the web or substrate to contact the liquid resin. In these cases, it may be useful to use a patterned roll that is transparent to a particular curing energy or includes portions that are transparent to curing energy. In some cases, only one patterned roll is transparent. 
       FIG. 3  is a partial illustration of an illustrative but non-limiting patterned roll and should not be considered as being to scale. Instead, the pattern has been exaggerated for clarity. Patterned roll can, as illustrated and as will be discussed in greater detail, may be formed by an additive method in which materials are deposited onto the surface of a transparent cylinder or other suitable shape. In some embodiments, it is believed that patterned roll may be formed using various subtractive methods in which material is removed from a transparent cylinder or other suitable shape. 
     Patterned roll includes a transparent cylinder  102  that can be formed of any suitable material. In some instances, transparent cylinder  102  is formed of a material that is transparent to the curing energy that will cure the curable material that will be applied to patterned roll. In some instances, as illustrated, transparent cylinder  102  can be made from a glass such as quartz. 
     As illustrated, in particular, patterned roll includes a quartz cylinder  102 . Quartz cylinder  102  may be of any suitable dimensions, although in some cases quartz cylinder  102  may have a length of 3 inches and a radius of 3 inches. Quartz cylinder  102  may be a substantially solid cylinder, or, as illustrated, quartz cylinder  102  may be a hollow cylinder. 
     In some cases, it may be useful to apply a thin tie layer  104  to the surface of the quartz cylinder  102 . This may assist subsequent materials in adhering or bonding to the quartz. In some instances, tie layer  104  is thin enough to not materially change the optical properties of the quartz cylinder  102 . At a minimum, tie layer  104  can be thin enough to remain transparent to curing energy. Tie layer  104  may be formed of any suitable material and using any suitable application technique. In some instances, tie layer  104  includes or consists of titanium and is applied via sputtering. 
     Once tie layer  104  has been formed, subsequent materials may be added to patterned roll. While particular processing steps are illustrated in  FIGS. 4-13 , and will be discussed in detail with respect to the Example, a variety of opaque materials may be applied to tie layer  104 . Suitable opaque materials include metals such as chrome, copper or aluminum, and curable polymers such as silicone and epoxy. Suitable materials may be applied and patterned using any suitable technique, such as sputtering, etching, and the like. 
     In the illustrated embodiment, the features of patterned roll have been formed in two steps. First, layers  106  have been deposited onto tie layer  104  and subsequently patterned. Layers  108  have been formed and patterned on top of layers  106 . Layers  106  and layers  108  may be formed of different materials or they may be formed of the same material. In some instances, layers  106  may be formed by sputtering a layer of chrome onto tie layer  104 . In some instances, layers  108  may be formed by plating chrome onto layers  106 . 
     In  FIG. 3 , the opaque features of patterned roll stand above the surface of quartz cylinder  102 . In some contemplated embodiments, such as those discussed with respect to  FIGS. 14-21 , the opaque features are actually closer to an outer surface of the substrate, while the transparent features actually penetrate the substrate. In either event, the opaque features may be considered as being farther from a radial center of patterned roll than are the transparent features. 
     In some instances, a patterned roll may be formed from either machinable or non-machinable transparent substrates. Several contemplated manufacturing techniques are described herein in  FIGS. 14-21 . It should be noted that in  FIGS. 14-21 , only a very small part of a transparent substrate is shown, for ease of illustration. While only a single transparent feature is shown for each potential manufacturing technique, it should be noted that of course a patterned roll will include a number of features. Moreover, it should be noted that a patterned roll will be cylindrical, while for ease of illustration and because only a very small part of the roll is shown,  FIGS. 14-21  appear rectangular. 
       FIGS. 14A-14E  illustrate a potential method of forming opaque features on a non-machinable transparent substrate that includes adding a machinable layer. In  FIG. 14A , a non-machinable, transparent, substrate  200  is provided. Examples of non-machinable, transparent substrates include glasses such as quartz. As shown in  FIG. 14B , a titanium tie layer  202  may be applied to substrate  200  using any suitable technique such as sputtering. A copper seed layer  204  may be sputtered onto titanium tie layer  202  as seen in  FIG. 14C . Additional copper may be plated onto copper seed layer  204  to form copper layer  206 , as seen in  FIG. 14D . 
       FIG. 14E  shows that copper layer  206  could be machined in any suitable manner to provide a transparent feature  208  positioned within copper layer  206 , which is of course opaque. In some instances, transparent feature  208  could be formed simply by a machining process such as micromilling, laser ablation, diamond turning or EDM processing. In some cases, additional processing such as a brief chemical etch may be useful in exposing transparent substrate  200  without damaging transparent substrate  200 . 
     In some instances, other materials may be used for the machinable layer  206 . For example, machinable layer  206  could be formed from an opaque epoxy or a machinable ceramic that could be coated in a “green” state and sintered after shaping. 
       FIGS. 15A-15D  illustrate another potential method of forming opaque features on a non-machinable transparent substrate  200  that includes adding a machinable layer. In  FIG. 15B , a transparent epoxy layer  210  may be added to the transparent substrate  200  to help protect the transparent substrate during subsequent machining. As seen in  FIG. 15C , an opaque epoxy layer  212  has been added on top of the transparent epoxy layer  210 . In  FIG. 15D , opaque epoxy layer  212  has been machined using any suitable technique to form transparent feature  214 . 
       FIGS. 16A-D  illustrate another potential method of forming opaque features on a non-machinable transparent substrate  200  that includes adding a machinable layer. Transparent substrate  200  is shown in  FIG. 16A . In  FIG. 16B , a relatively thicker transparent epoxy layer  210  has been added atop transparent substrate  200 . A relatively thinner opaque epoxy layer  212  has been added on transparent epoxy layer  210  as shown in  FIG. 16C . In  FIG. 16D , the opaque epoxy layer  212  and the transparent epoxy layer  210  have been machined using any suitable technique to form transparent feature  216 . As an alternate, it may be feasible to machine transparent feature  216  into a transparent epoxy layer, then coat the tops of the transparent epoxy layer with an opaque epoxy layer. 
       FIGS. 17A-17C  illustrate a potential method of forming opaque features on a machinable transparent substrate.  FIG. 17A  shows a machinable transparent substrate  220  that can be formed of a machinable transparent polymer. In some instances, substrate  220  can be formed from PMMA (poly methyl methacrylate). In  FIG. 17B , an opaque coating  222  such as sputtered aluminum or copper has been added onto transparent substrate  220 . Alternatively, it is contemplated that opaque coating  222  could also be formed from an opaque epoxy or even an opaque filled epoxy. As shown in  FIG. 17C , a transparent feature  224  can be formed using any suitable machining technique. 
       FIGS. 18A-C  illustrate another potential method of forming opaque features on machinable transparent substrate  220 . In  FIG. 18B , transparent substrate  220  has been machined using any suitable technique to form transparent feature  226 . Subsequently, as shown in  FIG. 18C , the portions of transparent substrate  220  beyond transparent feature  226  may be coated with an opaque coating  228 . 
       FIGS. 19A-19D  illustrate a potential method of using a separately-created master mold to replicate raised features on a transparent substrate. The raised features can then be coated to be opaque. In  FIG. 19A , a master mold  230  can be cut from any suitable material using standard precision machining techniques. Master mold  230  can be seen to include protrusion  232 , which will ultimately form a transparent feature. 
     As seen in  FIG. 19B , master mold  230  can be filled with an opaque epoxy material  234  and then is applied to the surface of a desired substrate  236  such as quartz or PMMA as seen in  FIG. 19C . The epoxy can be allowed to cure, and then master mold  230  may be removed, as seen in  FIG. 19D , leaving substrate  236  having a transparent feature  238  with an opaque layer  234  on either side of the transparent feature  238 . 
       FIGS. 20A-20E  illustrate another potential method of using a separately-created master mold to replicate raised features on a transparent substrate. The raised features can then be coated to be opaque. In  FIG. 20A , a master mold  240  can be cut from any suitable material using standard precision machining techniques. Master mold  240  can be seen to include protrusion  242 , which will ultimately form a transparent feature. 
     As seen in  FIG. 20B , master mold  240  can be filled with a transparent epoxy material  244  and then is applied to the surface of a desired substrate  246  such as quartz or PMMA as seen in  FIG. 20C . The epoxy can be allowed to cure, and then master mold  240  may be removed, as seen in  FIG. 20D , leaving substrate  246  having a transparent feature  248 . As seen in  FIG. 20E , an opaque epoxy layer  250  can be applied to transparent epoxy layer  244  on either side of the transparent feature  248 . 
       FIGS. 21A-21D  illustrate another potential method of using a separately-created master mold to replicate raised features on a transparent substrate. The raised features can then be coated to be opaque. In  FIG. 21A , a master mold  252  can be cut from any suitable material using standard precision machining techniques. Master mold  252  can be seen to include protrusion  254 , which will ultimately form a transparent feature. 
     As seen in  FIG. 21B , master mold  252  has been imprinted directly into a machinable transparent substrate  256 . In  FIG. 21C , master mold  252  has been removed, leaving transparent substrate  256  including transparent feature  258 . As shown in  FIG. 21D , transparent substrate  256  can be coated with an opaque epoxy layer  258  on either side of transparent feature  258 . 
     Casting Apparatus 
     Referring now to  FIGS. 22-23 , an example embodiment of a system  110  including a roll to roll casting apparatus  120  is illustrated. In the depicted casting apparatus  120 , a web  122  is provided to the casting apparatus  120  from a main unwind spool (not shown). The exact nature of web  122  can vary widely, depending on the product being produced. However, the casting apparatus  120  is capable of handling a web  122  that is both flexible and transparent and/or opaque, as discussed previously. The web  122  is directed around various rollers  126  into the casting apparatus  120 . 
     Accurate tension control of the web  122  is beneficial in achieving optimal results, so the web  122  may be directed over a tension-sensing device (not illustrated). If an optional liner web is used to protect the web  122 , the liner web (not illustrated) can be separated at the unwind spool and directed onto a liner web wind-up spool (not shown). The web  122  can be directed via an idler roll to a dancer roller for precision tension control. Idler rollers can direct the web  122  to a position between nip roller  154  and first coating head  156 . 
     A variety of coating methods may be employed. In some embodiments, as illustrated, first coating head  156  is a die coating head. The web  122  then passes between the nip roll  154  and first patterned roll  160 . The first patterned roll  160  has a patterned surface  162 , and when the web  122  passes between the nip roller  154  and the first patterned roll  160  the material dispensed onto the web  122  by the first coating head  156  is shaped into a negative of patterned surface  162 . 
     While the web  122  is in contact with the first patterned roll  160 , material is dispensed from second coating head  164  onto the other surface of web  122 . In parallel with the discussion above with respect to the first coating head  156 , the second coating head  164  is also a die coating arrangement including a second extruder (not shown) and a second coating die (not shown). In some embodiments, the material dispensed by the first coating head  156  is a composition including a polymer precursor and intended to be cured to solid polymer with the application of curing energy such as ultraviolet radiation. 
     Material that has been dispensed onto web  122  by the second coating head  164  is then brought into contact with second patterned roll  174  with a second patterned surface  176 . In parallel with the discussion above, in some embodiments, the material dispensed by the second coating head  164  is a composition including a polymer precursor and intended to be cured to solid polymer with the application of curing energy such as ultraviolet radiation. 
     At this point, the web  122  has had a pattern applied to both sides. A peel roll  182  may be present to assist in removal of the web  122  from second patterned roll  174 . In some instances, the web tension into and out of the casting apparatus is nearly constant. 
     The web  122  having a two-sided microreplicated pattern is then directed to a wind-up spool (not shown) via various idler rolls. If an interleave film is desired to protect web  122 , it may be provided from a secondary unwind spool (not shown) and the web and interleave film are wound together on the wind-up spool at an appropriate tension. 
     Referring to  FIGS. 22-24 , first and second patterned rolls are coupled to first and second motor assemblies  210 ,  220 , respectively. Support for the motor assemblies  210 ,  220  is accomplished by mounting assemblies to a frame  230 , either directly or indirectly. The motor assemblies  210 ,  220  are coupled to the frame using precision mounting arrangements. In the illustrated embodiment, for example, first motor assembly  210  is fixedly mounted to frame  230 . Second motor assembly  220 , which is placed into position when web  122  is threaded through the casting apparatus  120 , may need to be positioned repeatedly and therefore can be movable, both in the cross- and machine direction. Movable motor arrangement  220  may be coupled to linear slides  222  to assist in repeated accurate positioning, for example, when switching between patterns on the rolls. Second motor arrangement  220  also includes a second mounting arrangement  225  on the backside of the frame  230  for positioning the second patterned roll  174  side-to-side relative to the first patterned roll  160 . In some cases, second mounting arrangement  225  includes linear slides  223  allowing accurate positioning in the cross machine directions. 
     Referring to  FIG. 25 , a motor mounting arrangement is illustrated. A motor  633  for driving a tool or patterned roll  662  is mounted to the machine frame  650  and connected through a coupling  640  to a rotating shaft  601  of the patterned roller  662 . The motor  633  is coupled to a primary encoder  630 . A secondary encoder  651  is coupled to the tool to provide precise angular registration control of the patterned roll  662 . Primary  630  and secondary  651  encoders cooperate to provide control of the patterned roll  662  to keep it in registration with a second patterned roll, as will be described further hereinafter. 
     Reduction or elimination of shaft resonance is important as this is a source of registration error allowing pattern position control within the specified limits. Using a coupling  640  between the motor  633  and shaft  650  that is larger than general sizing schedules specify will also reduce shaft resonance caused by more flexible couplings. Bearing assemblies  660  are located in various locations to provide rotational support for the motor arrangement. 
     In the example embodiment shown, the tool roller  662  diameter can be smaller than its motor  633  diameter. To accommodate this arrangement, tool rollers may be installed in pairs, arranged in mirror image. In  FIG. 26 , two tool roller assemblies  610 ,  710  are installed as mirror images in order to be able to bring the two tool rollers  662 ,  762  together. Referring also to  FIG. 22 , the first motor arrangement is typically fixedly attached to the frame and the second motor arrangement is positioned using movable optical quality linear slides. 
     Tool roller assembly  710  is quite similar to tool roller assembly  610 , and includes a motor  733  for driving a tool or patterned roll  762  is mounted to the machine frame  750  and connected through a coupling  740  to a rotating shaft  701  of the patterned roller  762 . The motor  733  is coupled to a primary encoder  730 . A secondary encoder  751  is coupled to the tool to provide precise angular registration control of the patterned roll  762 . Primary  730  and secondary  751  encoders cooperate to provide control of the patterned roll  762  to keep it in registration with a second patterned roll, as will be described further hereinafter. 
     Reduction or elimination of shaft resonance is important as this is a source of registration error allowing pattern position control within the specified limits. Using a coupling  740  between the motor  733  and shaft  750  that is larger than general sizing schedules specify will also reduce shaft resonance caused by more flexible couplings. Bearing assemblies  760  are located in various locations to provide rotational support for the motor arrangement. 
     Because the features sizes on the microreplicated structures on both surfaces of a web are desired to be within fine registration of one another, the patterned rolls should be controlled with a high degree of precision. Cross-web registration within the limits described herein can be accomplished by applying the techniques used in controlling machine-direction registration, as described hereinafter. 
     For example, to achieve about 10 micrometers end-to-end feature placement on a 10-inch circumference patterned roller, each roller must be maintained within a rotational accuracy of ±32 arc-seconds per revolution. Control of registration becomes more difficult as the speed the web travels through the system is increased. 
     Applicants have built and demonstrated a system having 10-inch circular patterned rolls that can create a web having patterned features on opposite surfaces of the web that are registered to within 2.5 micrometers. Upon reading this disclosure and applying the principles taught herein, one of ordinary skill in the art will appreciate how to accomplish the degree of registration for other microreplicated surfaces. 
     Referring to  FIG. 27 , a schematic of a motor arrangement  800  is illustrated. Motor arrangement  800  includes a motor  810  including a primary encoder  830  and a drive shaft  820 . Drive shaft  820  is coupled to a driven shaft  840  of patterned roll  860  through a coupling  825 . A secondary, or load, encoder  850  is coupled to the driven shaft  840 . Using two encoders in the motor arrangement described allows the position of the patterned roll to be measured more accurately by locating the measuring device (encoder)  850  near the patterned roll  860 , thus reducing or eliminating effects of torque disturbances when the motor arrangement  800  is operating. 
     Apparatus Control 
     Referring to  FIG. 28 , a schematic of the motor arrangement of  FIG. 27 , is illustrated as attached to control components. In the example apparatus shown in  FIGS. 1-3 , a similar set-up would control each motor arrangement  210  and  220 . Accordingly, motor arrangement  900  includes a motor  910  including a primary encoder  930  and a drive shaft  920 . Drive shaft  920  is coupled to a driven shaft  940  of patterned roll  960  through a coupling  930 . A secondary, or load, encoder  950  is coupled to the driven shaft  940 . 
     Motor arrangement  900  communicates with a control arrangement  965  to allow precision control of the patterned roll  960 . Control arrangement  965  includes a drive module  966  and a program module  975 . The program module  975  communicates with the drive module  966  via a line  977 , for example, a SERCOS fiber network. The program module  975  is used to input parameters, such as set points, to the drive module  966 . Drive module  966  receives input 480 volt, 3-phase power  915 , rectifies it to DC, and distributes it via a power connection  973  to control the motor  910 . Motor encoder  912  feeds a position signal to control module  966  via line  972 . The secondary encoder  950  on the patterned roll  960  also feeds a position signal back to the drive module  966  via to line  971 . The drive module  966  uses the encoder signals to precisely position the patterned roll  960 . The control design to achieve the degree of registration is described in detail below. 
     In the illustrative embodiments shown, each patterned roll is controlled by a dedicated control arrangement. Dedicated control arrangements cooperate to control the registration between first and second patterned rolls. Each drive module communicates with and controls its respective motor assembly. 
     The control arrangement in the system built and demonstrated by Applicants include the following. To drive each of the patterned rolls, a high performance, low cogging torque motor with a high-resolution sine encoder feedback (512 sine cycles×4096 drive interpolation&gt;&gt;2 million parts per revolution) was used, model MHD090B-035-NG0-UN, available from Bosch-Rexroth (Indramat). Also the system included synchronous motors, model MHD090B-035-NG0-UN, available from Bosch-Rexroth (Indramat), but other types, such as induction motors could also be used. 
     Each motor was directly coupled (without gearbox or mechanical reduction) through an extremely stiff bellows coupling, model BK5-300, available from R/W Corporation. Alternate coupling designs could be used, but bellows style generally combines stiffness while providing high rotational accuracy. Each coupling was sized so that a substantially larger coupling was selected than what the typical manufacturers specifications would recommend. 
     Additionally, zero backlash collets or compressive style locking hubs between coupling and shafts are preferred. Each roller shaft was attached to an encoder through a hollow shaft load side encoder, model RON255C, available from Heidenhain Corp., Schaumburg, Ill. Encoder selection should have the highest accuracy and resolution possible, typically greater than 32 arc-sec accuracy. Applicants&#39; design, 18000 sine cycles per revolution were employed, which in conjunction with the 4096 bit resolution drive interpolation resulted in excess of 50 million parts per revolution resolution giving a resolution substantially higher than accuracy. The load side encoder had an accuracy of +/−2 arc-sec; maximum deviation in the delivered units was less than +/−1 arc-sec. 
     In some instances, each shaft may be designed to be as large a diameter as possible and as short as possible to maximize stiffness, resulting in the highest possible resonant frequency. Precision alignment of all rotational components is desired to ensure minimum registration error due to this source of registration error. 
     Referring to  FIG. 29 , identical position reference commands were presented to each axis simultaneously through a SERCOS fiber network at a 2 ms update rate. Each axis interpolates the position reference with a cubic spline, at the position loop update rate of 250 microsecond intervals. The interpolation method is not critical, as the constant velocity results in a simple constant times time interval path. The resolution is critical to eliminate any round off or numerical representation errors. Axis rollover is also addressed. In some cases, it is important that each axis&#39; control cycle is synchronized at the current loop execution rate (62 microsecond intervals). 
     The top path  1151  is the feed forward section of control. The control strategy includes a position loop  1110 , a velocity loop  1120 , and a current loop  1130 . The position reference  1111  is differentiated, once to generate the velocity feed forward terms  1152  and a second time to generate the acceleration feed forward term  1155 . The feed forward path  1151  helps performance during line speed changes and dynamic correction. 
     The position command  1111  is subtracted from current position  1114 , generating an error signal  1116 . The error  1116  is applied to a proportional controller  1115 , generating the velocity command reference  1117 . The velocity feedback  1167  is subtracted from the command  1117  to generate the velocity error signal  1123 , which is then applied to a PID controller. The velocity feedback  1167  is generated by differentiating the motor encoder position signal  1126 . Due to differentiation and numerical resolution limits, a low pass Butterworth filter  1124  is applied to remove high frequency noise components from the error signal  1123 . A narrow stop band (notch) filter  1129  is applied at the center of the motor—roller resonant frequency. This allows substantially higher gains to be applied to the velocity controller  1120 . Increased resolution of the motor encoder also would improve performance. The exact location of the filters in the control diagram is not critical; either the forward or reverse path are acceptable, although tuning parameters are dependent on the location. 
     A PID controller could also be used in the position loop, but the additional phase lag of the integrator makes stabilization more difficult. The current loop is a traditional PI controller; gains are established by the motor parameters. The highest bandwidth current loop possible will allow optimum performance. Also, minimum torque ripple is desired. 
     Minimization of external disturbances is important to obtain maximum registration. This includes motor construction and current loop commutation as previously discussed, but minimizing mechanical disturbances is also important. Examples include extremely smooth tension control in entering and exiting web span, uniform bearing and seal drag, minimizing tension upsets from web peel off from the roller, uniform rubber nip roller. In the current design, a third axis geared to the tool rolls is provided as a pull roll to assist in removing the cured structure from the tool. 
     Web Material 
     The web material can be any suitable material on which a microreplicated patterned structure can be created. A number of different materials may be used, depending on the ultimate use of the microreplicated patterned structure. If, for example, the microreplicated patterned structure will form a flexible circuit board, the web material may be a metallized polymeric film such as metallized KAPTON. 
     Coating Material 
     The liquid from which the microreplicated structures are created can be a curable photocurable material, such as acrylates curable by UV light. One of ordinary skill in the art will appreciate that other coating materials can be used, for example, polymerizable material, and selection of a material will depend on the particular characteristics desired for the microreplicated structures. For example, if a flexible circuit board is being made, the coating material may include a conductive or insulating polymer. In some embodiments, the coating material includes an electroplate masking material and/or nonconductive or insulating polymers. 
     Examples of coating means that useful for delivering and controlling liquid to the web or patterned roll are, for example, die or knife coating, coupled with any suitable pump such as a syringe or peristaltic pump. One of ordinary skill in the art will appreciate that other coating means can be used, and selection of a particular means will depend on the particular characteristics of the liquid to be delivered to the web or patterned roll. 
     Examples of curing energy sources are infrared radiation, ultraviolet radiation, visible light radiation, or microwave. One of ordinary skill in the art will appreciate that other curing sources can be used, and selection of a particular web material/curing source combination will depend on the particular article (having microreplicated structures in registration) to be created. 
     Microreplicated Article 
       FIG. 30  schematically illustrates a contemplated coated microreplicated article  1200  formed according to the methods and using the apparatus described herein. Article  1200  includes a flexible opaque web  1202  and a number of schematic elements disposed on either side of opaque web  1202 . Element  1204  is disposed opposite element  1206 . Similarly, element  1208 , element  1212  and element  1216  are disposed opposite element  1210 , element  1214  and element  1218 , respectively. It should be noted that these elements can be considered as generically representing a number of different potential elements. These elements may be circuitry, for example. In some embodiments, the microreplicated pattern includes an electroplate mask that can pass through an additive circuit plating step. 
     In some embodiments, such as that illustrated, there may be little or no lands between adjacent elements. For example, there may be little or no coated material remaining on opaque web  1202  between element  1204  and element  1208 . This may have advantages if, for example, the coated material is an electrically conductive material or an electroplate mask. In some embodiments, an additional washing step can remove uncured material from the microreplicated pattern to produce a microreplicated features having no land areas and separated from one another. In other instances, article  1202  may include lands, i.e. coated material remaining on opaque web  1202  between adjacent elements. 
     EXAMPLE 
       FIGS. 4-13  illustrate an additive process for forming a patterned roll much like patterned roll of  FIG. 3 . Quartz tubes 3 inches long and 3 inches in radius were cleaned with water, acetone and methyl ethyl ketone (MEK), and were then placed under a UV lamp for 15 minutes. The quartz tubes were then mounted on a rotating table in a high vacuum sputter chamber, and the pressure within the chamber was slowly reduced to 1×10 −6  Torr over a period of one hour. A strip of chrome plated steel previously mounted within the chamber was electrically connected to an arc welder. The arc welder passed a current through the metal strip and the metal strip was thus heated to red hot. The rotating quartz tubes were washed by the resulting IR radiation for 10 minutes. 
     Once the quartz tubes were cleaned, a quartz cylinder  102  as seen in  FIG. 4  was sputtered with a thin layer  104  of chrome, which acts as an adhesion layer between the quartz and the nickel layer to follow. 
     Next, and as shown schematically in  FIG. 5 , a nickel metallization layer  110  was sputtered onto the chrome tie layer  104 . 
     Next, and as shown schematically in  FIG. 6 , a protective copper layer  112  was applied over the nickel metallization layer  110 . The copper layer  112  was a sacrificial layer that was intended to protect the nickel layer  110  from contamination and oxidation during subsequent processing steps. 
     Next, and as shown schematically in  FIG. 7 , a photoresist (SC Resists, Arch Semiconductor Photopolymers Company) layer  114  has been added on top of the copper layer  112 . The height of the photoresist layer  114  ultimately sets the height of the features being formed on quartz cylinder  102 . In the Example, the photoresist layer  114  was formed to be 50 micrometers thick, and was softbaked at 115 degrees Celsius for 30 seconds prior to exposure. 
     Next, and as shown schematically in  FIG. 8 , the photoresist layer  114  was patterned by shining light in a desired pattern onto the photoresist layer  114 . Consequently, the photoresist layer  114  now has portions  116  that will remain, and portions  118  that will be removed after developing. 
     Next, and as shown schematically in  FIG. 9 , the photoresist was developed. After sitting for at least 30 minutes, the photoresist was subjected to a post exposure bake at 115 degrees Celsius for 1 minute. The photoresist was then developed via exposure to developing solution for 30 to 60 seconds. Consequently, resist portions  116  remain on copper layer  112  while resist portions  118  have been removed. 
     Next, and as shown schematically in  FIG. 10 , the exposed portions of copper layer  112  were removed in an etching process. Sodium persulfate was used to remove the exposed copper because sodium persulfate reacts quickly with copper but slowly with the chrome underlying the copper, as it is desirable to keep the chrome layer as thick as possible. 
     Next, and as shown schematically in  FIG. 11 , chrome sections  120  were plated onto the freshly exposed chrome layer  110 , in between resist regions  116 . Chrome sections  120  were plated using low current densities on the order of 1 mA/17 mm 2 . As the current density increases, even at levels as low as 20 mA/17 mm 2 , either internal stress was high, causing the chrome to peel off, or severe pitting occurred. The geometry of chrome sections  120  were determined by resist regions  116 . 
     Next, and as shown schematically in  FIG. 12 , the remaining cured photoresist, in resist regions  116 , were removed using a basic solution. Finally, and as shown schematically in  FIG. 13 , the remaining copper layer  112  was removed using a sodium persulfate bath as discussed above. The resulting patterned roll has opaque regions corresponding to nickel  110  and chrome sections  120 , and transparent regions corresponding to where tie layer  104  is not covered by opaque material. 
     The disclosure should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the disclosure as set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the disclosure can be applicable will be readily apparent to those of skill in the art upon review of the instant specification.