Abstract:
According to one exemplary embodiment, an apparatus for microreplication is disclosed. The apparatus includes a cooling unit that contains a bottom layer, a plurality of side walls, and an intermediate layer. The bottom layer has an outer perimeter, and the plurality of side walls surround the outer perimeter of the bottom layer. The intermediate layer is positioned between the bottom layer and an upper portion of the side walls. The intermediate layer may include a plurality of openings, which may either hold a device that dispenses cooling agents or be used for drainage of cooling agents. The method utilizes the apparatus after heating and pressing of a polymer film during microreplication.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from U.S. Provisional Application No. 61/418,153 filed Nov. 30, 2010, which is incorporated by herein by reference in its entirety. 
     
    
     SUMMARY OF THE INVENTION 
       [0002]    The present invention is in the field of manufacturing films containing microreplicated patterns in order to create a surface topography having a particular optical property. More particularly, the present invention is directed toward improving manufacturing efficiencies of certain microreplication processes. 
       BACKGROUND OF THE INVENTION 
       [0003]    Microreplication is a process where softened polymer film or an extruded material is brought into contact with a pressure nip such that an extrudate or softened film is pressed against a tool with fine patterning or a particular surface topography on it. The pattern or topography is reversely transferred onto the side of the material in contact with the tool. The foregoing process is widely used in roll to roll manufacturing methods to produce patterned or replicated products such as reflective materials, and other optical films. 
         [0004]    A typical microreplication process includes a heating means to soften the polymer material which may be provided as a film or extrudate, and then using heat and pressure to impress the pattern onto the polymer material, and then cooling the material to cool the patterned polymer before being rolled up, sheeted or otherwise collected. 
         [0005]    The manufacturing speed can be limited by the slowest process, which can be determined by any one of the steps (heating, pressing, cooling) mentioned above. With advancement in heating, such as through NIR, the cooling step then may become the bottle neck, i.e. the film does not get cooled fast enough so the production speed has to be lowered to provide sufficient time for the film to cool further. Currently, the cooling is conducted through the employment of cooling air, such as recirculating fans, blowers, chilled rollers, and the like. 
         [0006]    There are a number of prior methods to improve cooling of films or webs. One such example is to use heat conduction to remove heat from the film. It is well known that heat transfer coefficient of heat conduction is the order of magnitude higher than that of heat convection (by air). Cooling by conduction is commonly achieved by means of a continuous cooling belt, single or double. This type of equipment found broad implementation in pharmaceutical and food industries. Typically, such a thin metal belt (stainless steel or brass) is connected at its ends to form a closed loop. The belt is kept cooled by spraying chilled water or other cooling agent on the side of the belt opposite to the surface that requires cooling. Due to high heat transfer through the metal, heat is efficiently removed from the hot surface. In this process, it is critical to ensure a good contact between the hot and cold surfaces. In the event that there is an air gap between the surfaces of the cooling belt and the film being cooled, the heat transfer coefficient drops dramatically and cooling becomes inefficient. Exemplary manufacturers of such cooling equipment include Sandvik and BBA. 
         [0007]    Therefore, there is a need for an improvement for the cooling step in order to facilitate the production of the patterned product having a particular surface topography. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention. According to one exemplary embodiment, an apparatus for microreplication is are disclosed. The apparatus includes a cooling unit that contains a bottom layer, a plurality of side walls, and an intermediate layer. The bottom layer has an outer perimeter, and the plurality of side walls surround the outer perimeter of the bottom layer. The intermediate layer is positioned between the bottom layer and an upper portion of the side walls. The intermediate layer may include a plurality of openings, which may either hold a device that dispenses cooling agents or be used for drainage of cooling agents. The method utilizes the apparatus after heating and pressing of a polymer film during microreplication. 
         [0009]    It is an object of the present invention to provide for a system with a cooling belt for microreplication including a belt forming a loop around a first set of rollers, a second set of rollers that support the belt and a film and at least one nozzle for delivering at least one cooling agent wherein at least one nozzle is located underneath the belt and the film. 
         [0010]    It is yet another object of the present invention to provide for a system with a cooling belt for microreplication including a belt forming a loop around a first set of rollers that support the belt and a film and at least one nozzle for delivering at least one cooling agent wherein at least one nozzle is located underneath the belt and the film. 
         [0011]    Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description of the various embodiments and specific examples, while indicating preferred and other embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by referring to the following more detailed description of the presently preferred exemplary embodiments of the invention in conjunction with the accompanying drawings, of which: 
           [0013]      FIG. 1  is a schematic illustration of a cooling unit; 
           [0014]      FIG. 2   a - 2   b  are schematic illustrations of a design of a cooling unit; 
           [0015]      FIG. 3  is a schematic view of a cooling set up; and 
           [0016]      FIG. 4  shows an exemplary view of a microreplication set up. 
       
    
    
       [0017]    Unless otherwise indicated, the illustrations in the above figures are not necessarily drawn to scale. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The apparatuses and methods disclosed in this document are described in detail by way of examples and with reference to the figures. Unless otherwise specified, like numbers in the figures indicate references to the same, similar, or corresponding elements throughout the figures. It will be appreciated that modifications to disclosed and described examples, arrangements, configurations, components, elements, apparatuses, methods, materials, etc. can be made and may be desired for a specific application. In this disclosure, any identification of specific shapes, materials, techniques, arrangements, etc. are either related to a specific example presented or are merely a general description of such a shape, material, technique, arrangement, etc. Identifications of specific details or examples are not intended to be, and should not be, construed as mandatory or limiting unless specifically designated as such. Selected examples of apparatuses and methods are hereinafter disclosed and described in detail with reference made to figures. 
         [0019]    A cooling method of microreplication is disclosed. The cooling method employs heat conduction in cooling embossed polymer film. 
         [0020]      FIG. 1  provides an illustration of a cooling unit  110 . The cooling unit  110  includes a tank  106  and a set of nozzles  104 . The tank  106  has two side portions  106 - 1  and a bottom portion  106 - 2 . The set of nozzles  104  are connected by a feeding tube  105  that may either feed the set of nozzles  104  from a common source or individually. 
         [0021]    After heating, an embossed polymer film, or web,  102  is incrementally indexed forward, indicated by arrow M, over the cooling unit  110 . The embossed polymer film  102  has a backside  103  and a front side  101 . The front side  101  includes an embossed pattern from heating and pressing the embossed polymer film  102  and is not in contact with the cooling unit  110 , while the backside  103  of the embossed polymer film  102  is in contact with the cooling unit  110 . 
         [0022]    In cooling the embossed polymer film  102 , the set of nozzles  104  spray a cooling agent directly onto the backside  103  of the embossed polymer film  102 , and the tank  106  is used to collect the cooling agents once expelled from the nozzles  104  to either be recycled or disposed. A pumping and chilling system may also be used for delivery of the cooling agents. 
         [0023]    The cooling agent may include but is not limited to water, chilled water, water mixed with glycol, glycol, or water mixed with air. 
         [0024]    Each nozzle  104  is connected by the feeding tube  105  to a supply of cooling agents. The feeding tube  105  may either provide the cooling agents from one supply or from several independent supplies. When the feeding tube  105  feeds the nozzles  104  from independent supplies of cooling agents, different types of cooling agents may be provided at once. In addition, the nozzles  104  may be equipped with control valves that allow one type of agent to be utilized while other cooling agents are not in use. The control valves can be added to each nozzle  104 , or each roll of nozzles, or nozzles for a specific area. 
         [0025]    In addition, a flow rate at which the cooling agent is supplied may be varied. That is, two or more types of cooling agents may be supplied from the set of nozzles  104  to the backside  103  of the embossed polymer film  102 , either at the same flow rate or different flow rates so that temperature can be modified as is necessary to increase or decrease cooling rates in the cooling unit  110 . By individually feeding the cooling agents, different cooling agents may be used with one manufacturing process or with different manufacturing processes or materials. By allowing additional cooling agents to be used in different manufacturing processes, an entire system does not need to be purged when there is a changeover of materials or requirements for different processing applications. 
         [0026]    Another advantage of individually feeding the cooling agents, the temperature of the cooling agents can vary depending on the type of material that is used for cooling. For example, water used as the cooling agent can range from about 45° F. to about 55° F., while glycol when used as the cooling agent may have a temperature range of about 45° F. The feeding tube  105  can draw the cooling agent from one or more tanks depending on requirements, size and speed of the manufacturing operation. 
         [0027]    The cooling efficiency for a given set of nozzles  104  can be further improved by adjusting the distance between the nozzles  104  and the embossed polymer film  102 , or an angle at which the nozzles  104  are pointed towards the embossed polymer film  102 . 
         [0028]    The cooling unit  110  will be attached to the microreplication apparatus with water proof sealing. In addition, an air drying unit or air knife may be arranged downstream of the cooling unit to dry off and remove any residual cooling agent that remains on the embossed polymer film  102 . 
         [0029]      FIGS. 2   a  and  2   b  provides illustrations of the cooling unit&#39;s design.  FIG. 2   a  depicts a perspective view of a cooling unit  110 . The cooling unit  110  has a bottom layer  111 , a plurality of side walls  112  having both an upper portion and a lower portion. The bottom layer  111  has a specified area surrounded by an outer perimeter wherein the bottom layer  111  has both a top face and a bottom face. As shown in  FIG. 2   a , the outer perimeter of the bottom layer  111  is in a shape of a rectangle. If the bottom layer  112  is rectangular, then there are four side walls surrounding the outer perimeter of the bottom layer  112 . In addition to the rectangular shape of the bottom layer  111 , other geometric shapes may be utilized for the cooling unit  110  such as a square or hexagon. 
         [0030]    The cooling unit also includes an intermediate layer, or carrier tray,  113 . The intermediate layer  113  has a top side  115 , a bottom side  114  and an outer intermediate layer perimeter. Several holes  116 ,  117  and  118  are located on the intermediate layer  113 . The holes  116 ,  117  and  118  are of varying sizes to allow for a variety of sized nozzles  104  ( FIG. 1 ) to deliver cooling agents. The intermediate layer  113  is located in the space between the bottom layer  111  and below the top portion of the side walls  112  of the cooling unit  110 . The intermediate layer  113  is not in contact with the embossed polymer film  102 . The intermediate layer  113  is not in contact with the bottom layer  111  to allow for tubing or conduits to be arranged within the space defined by the intermediate layer  113  and the bottom layer  111 . 
         [0031]    To collect the cooling agent, the bottom layer  111  may have a drainage hole connected to a central drainage tubing. The central drainage tubing may also collect the spent cooling agent in a central reservoir. 
         [0032]      FIG. 2   b  provides a configuration of holes  116  and spacing of the intermediate layer  113 . As indicated, the holes  116  are evenly spaced and aligned. In addition to the holes  116 , the cooling unit  110  ( FIG. 2   a ) may contain collecting channels, or collecting grooves or collecting rows,  119  for collecting the cooling agents after the cooling agent have been expelled through the nozzles  104  ( FIG. 1 ), which are located in the holes  116 . In addition to the embodiment suggested by  FIG. 2   b , many configurations for the holes  116  and the collecting channels  119  may be arranged on the intermediate layer  113  to provide a uniform pattern of cooling. 
         [0033]      FIG. 3  depicts an exemplary cooling belt system  130 . The cooling belt system  130  includes the cooling unit  110 , a thin metal belt  120 , a first set of rollers  121  and a second set of rollers  125 . The thin metal belt  120  forms a continuous loop around the first set of rollers  121  and a second set of rollers  125 . The first set of roller  121  support the thin metal belt  120  as the thin metal belt  120  travels in the continuous loop. The second set of rollers  125  are contained within the cooling unit  110  and support the thin metal belt  120 , the embossed polymer film  102  and a set of nozzles  104  for delivering cooling agent. 
         [0034]    The thin metal belt  120  has a top side  123  and a bottom side  122 . The bottom side  122  of the thin metal belt  120  is in contact with the cooling belt system  130 , and the top side  123  of the thin metal belt  120  is in contact with the embossed polymer film  102 . 
         [0035]    The thin metal belt  120  initially makes contact with the embossed polymer film  102  after heating and pressing the embossed polymer film  102 . After initial contact, the thin metal belt  120  moves the embossed polymer film  102  forward, as indicated by arrow F, with the assistance of the first set of rollers  121  and the second set of rollers  125 . 
         [0036]    As a portion of the embossed polymer film  102  is on top of the thin metal belt  120  and moves forward in the F direction, the set of nozzles  104 , which are fed by the feeding tube  105 , spray cooling agents on the bottom side  122  of the thin metal belt  120 . 
         [0037]    The embossed polymer film  102  is preferably in contact or in close approximate contact with the thin metal belt  120  so as to not inhibit movement of the embossed polymer film  102  or otherwise deform an embossed pattern, or topography, which is located on the front side  101  ( FIG. 1 ) on the embossed polymer film  102 . Through conduction from the thin metal belt  120  to the embossed polymer film  102 , the embossed polymer film  102  will undergo a reduction in temperature, cooling from a molten state in which the embossed pattern is reduced to a lower temperature without destroying the embossed pattern. It is critical to ensure a good thermal contact between the embossed polymer film  102  and the thin metal belt  120  to provide for adequate cooling of the embossed polymer film  102 . 
         [0038]    In case there is an air gap between the thin metal belt  120  and the embossed polymer film  102 , the heat transfer coefficient drops dramatically and cooling becomes inefficient. 
         [0039]    Incrementally, the portion of the embossed polymer film  102  will be pulled over the cooling unit  110  in the F direction by the thin metal belt  120 , first set of rollers  121 , and the second set of rollers  125 . As the nozzles  104  continue to spray the thin metal belt  120 , the spent cooling agents are collected by the tank  106 . Once the portion of the embossed polymer film  102  reaches near an end of the cooling unit  110 , the embossed polymer film  102  continues forward and no longer is in contact with the thin metal belt  120 , which remains in its continuous loop. 
         [0040]    While a thin metal belt  120  has been described, it should be understood that other materials may be used in place of metal, such as a thermal blanket, polymeric or other material that have the ability to remove or wick away heat from a material. 
         [0041]    In addition, this embodiment displays four nozzles  104  in the cooling belt system  130 ; however, any number of nozzles  104  may be configured to the cooling belt system  130 . Also, the number of rollers or sets of rollers may be provided in any configuration without departing from the embodiment. 
         [0042]    Optionally, the cooling belt system  130  may be used on an opposite side of a microreplication tool or belt to ensure the close thermal contact between the embossed polymer film  102  and the metal belt  120 . 
         [0043]    In addition, the cooling belt system  130  may include a third set of rollers located above the cooling unit  110  that interfaces with the embossed polymer film  102 . The third set of rollers move at the same speed as the embossed polymer film  102  and exerts pressure on the embossed polymer film  102 . 
         [0044]      FIG. 4  is a schematic of a microreplication apparatus  131  with a microreplication cooling belt  140  and a microreplication belt  141  that includes patterns on a surface of the microreplication belt  141 . 
         [0045]    A first polymer film  136  is wound on a first roll of polymer film  135 . A second polymer film  138  may also be provided and wound on a second roll of polymer film  137 . The first polymer film  136  and the second polymer film  138  are pulled forward by a set of rollers  139  toward a heated roll  142  to start a microreplication process. 
         [0046]    The heated roll  142  is provided for heating up one or more of nip rolls  134 , the first polymer film  136  and the second polymer film  138 . The first polymer film  136  and the second polymer film  138  travel along the microreplication belt  141  as the nip rolls  134  interact with the first polymer film  136  and the second polymer film  138 . The nip rolls  134  provide pressure, which then provides a particular surface topography. The set of rollers  139  keep the first polymer film  136  and the second polymer film  138  moving and to maintain a sufficient tension. 
         [0047]    Once the first polymer film  136  and the second polymer film  138  travel along the hot roll  142  and the nip rolls  134 , the first polymer film  136  and the second polymer film  138  travel along the microreplication cooling belt  140 . The microreplication cooling belt  140  is provided for cooling the first polymer film  136  and the second polymer film  138 . 
         [0048]    The microreplication cooling belt  140  can be made of metal such as copper, nickel, aluminum or stainless steel and includes a set of rollers  144  that form a closed loop  143  to keep a consistent speed on the microreplication cooling belt  140 . The thickness of the microreplication cooling belt  140  can be from about 5 mils to about 25 mils with about 8 mils to about 10 mils being preferred. Multiple spray nozzles  104  may be arranged in an array under a bottom side of the microreplication cooling belt  140  and are fed by the feeding tube  105 . 
         [0049]    Once the first polymer film  136  and the second polymer film  138  travel along the microreplication cooling belt  140 , the first polymer film  136  and the second polymer film  138  is wound up at wind up roller  146 . 
         [0050]    To ensure good thermal contact between the first polymer film  136  and the second polymer film  138  and the microreplication cooling belt  140 , a plenum  145  can be used on a top side of the microreplication cooling belt  140 . Additional rolls such as  132  and  133  can be added to the set up to add a protective carrier film or a release liner to enable multilayer lamination on the production line. 
         [0051]    Through use of the microreplication cooling belt  140 , a peel temperature of the first polymer film  136  and the second polymer film  138 , when removed from the microreplication apparatus  131 , can be decreased when compared to a conventional microreplication manufacturing process enabling greater stability in collecting polymer film. 
         [0052]    The use of cooling agents can also be combined with the air cooling the microreplication apparatus  131  from a same side as the cooling agents, or from an opposite side as the cooling agents. The application of the air cooling and use of the cooling agents can occur simultaneously, substantially simultaneously or at different operational times of the microreplication process. For example, air cooling can occur before and after applying of the cooling agents or vice versa. Air cooling may also be applied to aid in the collection of the cooling agent in the channels as described above. 
         [0053]    In addition to the embodiments described, single polymer films or multiple polymer films may be utilized. 
         [0054]    The foregoing description and accompanying figures illustrate the principles, preferred embodiments and modes of operation of the invention. However, the invention should not be construed as being limited to the particular embodiments discussed above. Additional variations of the embodiments discussed above will be appreciated by those skilled in the art. 
         [0055]    Therefore, the above-described embodiments should be regarded as illustrative rather than restrictive. Accordingly, it should be appreciated that variations to those embodiments can be made by those skilled in the art without departing from the scope of the invention as defined by the following claims. It will thus be seen according to the present invention a highly advantageous process for producing microreplicated films has been provided. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiment, and that many modifications and equivalent arrangements may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products. 
         [0056]    It will thus be seen according to the present invention a highly advantageous method and apparatus for cooling embossed polymer film has been provided. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiment, and that many modifications and equivalent arrangements may be made thereof within the scope of the invention, which scope is to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products. 
         [0057]    The inventors hereby state their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of their invention as it pertains to any apparatus, system, method or article not materially departing from but outside the literal scope of the invention as set out in the following claims.