Patent Publication Number: US-2007122630-A1

Title: Co-extrusion or tandem extrusion of surface protection films

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Patent Application No. 60/734,502, filed Nov. 8, 2006 which is hereby fully incorporated by reference. 
    
    
     TECHNICAL FIELD  
      The present disclosure relates to protective films and more particularly, relates to method and apparatus for manufacturing polyurethane surface protective films.  
     BACKGROUND INFORMATION  
      Surface protection films may be made from polyurethane and may be used to protect land or marine craft exteriors from harsh environments and weathering. Polyurethane may be used in surface protection environments because, in part, of its high abrasion resistance, UV resistance, elongation, resistance to chemicals and fungus, and ease of fabrication. Surface protection polyurethane films are commonly known for their automotive applications, yet have recently found many useful applications in several other markets.  
      There currently exists several known methods for manufacturing polyurethane film on a flat die line for surface protection applications. One such method features an extruder  2 ,  FIG. 1 , (for example, fed from a hopper  3  or the like) that extrudes polyurethane  4  at a thickness between 4-12 mils onto a 0.5-3 mils polyester, polypropylene, or polyethylene carrier  5  which may be unwound from a roll  6 . The combination of the polyurethane  4  and carrier  5  may then wound onto a roll  9 . The exposed surface  7  (i.e., the non-carrier side) of the polyurethane  4  may be in contact with the backside  8  of the carrier  5  when wound onto the roll  9 .  
      This method suffers from several disadvantages. For example, the non-carrier surface  7  of the polyurethane  4  may develop imperfections and inconsistencies when wound onto the roll  9  because of uneven contact and pressure with backside of carrier  5 . Because the carrier  5  may be unrolled from a roll  6 , the carrier  5  may often have imperfections due to the winding of the roll  6 . The imperfections of the carrier  5  may then be transferred onto polyurethane  4 .  
      Another known method for manufacturing polyurethane film on a flat die line features an extruder  2 ,  FIG. 2 , (for example, fed from a hopper  3  or the like) which extrudes polyurethane  4  at a thickness between 4-12 mils onto a 0.5-3 mils polyester, polypropylene, or polyethylene carrier  5  (often unwound from a roll  6 ). A separate film  11  (for example, a film similar to the carrier  5 ) may be unwound from a roll  12  and introduced at the nip point  13  (the point  13  where the molten polyurethane  4  comes out of the die  14  and passes between two rolls  15 ). The second film  11  may be used to protect the non-carrier side  7  of the polyurethane  4  when wound onto roll  9 .  
      Unfortunately, introducing the separate film  11  may result in wrinkles and air pockets occasionally forming at the nip point  13 . These wrinkles and air pockets may cause imperfections in surface of polyurethane  4 . Additionally, any imperfections in introduced film  11  or the carrier  5  (e.g., due to the winding of the rolls  6 ,  12 ) may affect the polyurethane  4  surfaces.  
      Yet another known method for manufacturing polyurethane film on a flat die line features an extruder  2 ,  FIG. 3 , (for example, fed from a hopper  3  or the like) that extrudes polyurethane  4  at a thickness of between 4-12 mils between two very smooth chilled rolls  16 . An interleaf  17  (usually 0.5-2 mils polyethylene) may be unwound from a roll  18  and introduced before the polyurethane  4  is wound onto roll  9  but after the polyurethane  4  has crystallized in order to keep the material from blocking.  
      Unfortunately, winding two separate, unbonded films together (for example, in this case the interleaf  17  and the polyurethane film  4 ) may be difficult to do evenly due, in part, to the variations between the gauge, elongation, etc. properties of the two films  4 ,  17 . The winding process may result in wrinkles, air pockets, pressure marks, and other imperfections being created in the polyurethane  4  surfaces.  
      Accordingly, what is needed is an improved apparatus and method for manufacturing polyurethane film on a flat die line. The improved apparatus and method should preferably minimize the number of imperfections in the polyurethane film. Additionally, the improved apparatus and method should be economically viable.  
      It is important to note that the present disclosure is not intended to be limited to a system or method which must satisfy one or more of any stated objects or features of the invention. It is also important to note that the present disclosure is not limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present disclosure, which is not to be limited except by the following claims.  
     SUMMARY  
      According to one embodiment, the present disclosure features a surface protection film and a method of manufacturing the same. A first resin comprising a polyurethane and a second resin (for example, but not limited to, a polyester or a polypropylene) may be co-extruded through an AB feed block to form a co-extruded film having a first layer of the first resin and a second layer of the second resin. An exterior surface of the first resin of the co-extruded film may be placed onto a carrier film. The carrier film protects the exterior surface of the first layer and the second layer protects a second side of the first layer generally opposite the exterior surface. The carrier film and the second layer may optionally be substantially coextensive with the first layer.  
      According to another embodiment, the present disclosure features a surface protection film and a method of manufacturing the same comprising co-extruding a first resin of a polyurethane and a second resin (for example, but not limited to, a polyester or a polypropylene) through an ABA feed block. The co-extruded film may comprise a first layer of the first resin and a second and a third layer of the second resin substantially contacting a first and a second generally opposite exterior surface of the first layer. The second and third layers protect the first and the second exterior surfaces of the first layer such that the co-extruded film does not require a carrier film.  
      According to yet another embodiment, the present disclosure features a surface protection film and a method of manufacturing the same comprising extruding a first layer of a first resin of polyurethane and placing a first surface of the first layer onto a carrier film. A second layer of a second resin may be tandemly extruded with the first layer onto a second surface of the first layer generally opposite the first surface. The second layer protects the first surface of the first layer and the carrier film protects the second side of the first layer.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      These and other features and advantages of the present disclosure will be better understood by reading the following detailed description, taken together with the drawings wherein:  
       FIG. 1  is a block diagram showing one embodiment of the prior art methods of manufacturing polyurethane film on a flat die line;  
       FIG. 2  is a block diagram showing another embodiment of the prior art methods of manufacturing polyurethane film on a flat die line;  
       FIG. 3  is a block diagram showing yet another embodiment of the prior art methods of manufacturing polyurethane film on a flat die line;  
       FIG. 4  is a block diagram showing one embodiment of an apparatus for manufacturing polyurethane film on a flat die line according to one embodiment of the present disclosure;  
       FIG. 5  is a flow chart of one embodiment of the method of manufacturing polyurethane film using the apparatus shown in  FIG. 4 ;  
       FIG. 6  is a block diagram showing another embodiment of an apparatus for manufacturing polyurethane film on a flat die line according to one embodiment of the present disclosure;  
       FIG. 7  is a flow chart of one embodiment of the method of manufacturing polyurethane film using the apparatus shown in  FIG. 6 ;  
       FIG. 8  is a block diagram showing yet another embodiment of an apparatus for manufacturing polyurethane film on a flat die line according to one embodiment of the present disclosure; and  
       FIG. 9  is a flow chart of one embodiment of the method of manufacturing polyurethane film using the apparatus shown in  FIG. 8 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      According to one embodiment, the present disclosure features an apparatus  20 ,  FIG. 4 , and method  500 ,  FIG. 5 , for manufacturing polyurethane film that minimizes and/or reduces the number of imperfections in the polyurethane film. The apparatus  20  and method  500  may comprise an extruder  24  and a die  38  that receives a first and a second resin  30 ,  32  (for example, from a first and a second hopper  34 ,  36 , respectively) and co-extrudes a first and a second layer  33 ,  35  comprising the first and the second resins  30 ,  32 , respectively (act  510 ). The first resin  30  may comprise polyurethane or the like while the second resin  32  may comprise a polyester, polypropylene, or the like. The second resin  32  may be selected to have melt and flow temperature properties similar to those of the first resin  30 . The first and second resins  30 ,  32  may also be selected to have appropriate properties such that the resins  30 ,  32  may be peeled apart from each other. For example, the second resin may comprise a polyolefin (such as, but not limited to, high or low density polyethylene), any non-polar polymer, and any material that has been doped such that it substantially will peel apart from the first resin  30  (for example, but not limited to, adding silicon, Teflon®, wax, and/or the like).  
      The extruder  24  may include any extruder  24  and die  38  known to those skilled in the art capable of co-extruding the two resins  30 ,  32  and forming the first and second layers  33 ,  35  such as, but not limited to, an AB extruder  24  having a first and a second screw  26 ,  28  and a flat AB feed block die  38 . The first and second resins  30 ,  32  may be co-extruded such that a first surface  21  of the first layer  33  substantially contacts the second layer  35 . According to one embodiment, the first surface  21  of the first layer  33  may be substantially coextensive with the second layer  35 .  
      The co-extrusion  40  may be may be placed onto a carrier  42  such that a second surface  23  of the first layer  33  (i.e., the surface  23  of the first layer  33  generally opposite the first surface  21 ) substantially contacts the carrier  42  (act  520 ). According to one embodiment, the second surface  23  of the first layer  33  is substantially coextensive with the carrier  42 . The first layer  33  may be placed on the carrier  42  prior to the crystallization of the first resin  30 . The carrier  42  may include 0.5-3 mils polyester, polypropylene, or polyethylene, treated paper, or the like that may be unwound from a roll  41 .  
      Once the co-extrusion  40  has been placed on the carrier  42 , the combination  43  of the co-extrusion  40  and carrier  42  may be wound onto a roll  44  or cut into the desired shape and/or packaged (act  530 ).  
      It should be noted that the second resin  32  may form a film/layer that protects the first side  21  of the first resin  30  from the back of carrier  42  when wound, thereby minimizing the number and frequency of imperfections introduced into the first layer  33 . Additionally, the apparatus  20  and method  500  reduces and/or eliminates wrinkles, air pockets, and blemishes that are formed when introducing a separate, crystallized film at the nip. When the co-extruded, second layer  35  is removed, the first layer  33  is left with a smooth, clean surface. As a result, the first layer  33  may be protected on a first side  21  by the second layer  35  and on the second, opposite side  23  by the carrier  42 .  
      According to an alternative embodiment, the present disclosure features an apparatus  50 ,  FIG. 6 , and method  700 ,  FIG. 7 , for manufacturing polyurethane film that minimizes and/or reduces the number of imperfections in the polyurethane film. The system  50  may comprise an ABA extruder  74  that may extrude an ABA film  54  from a die  78  (act  710 ). The ABA extruder  74  may include any extruder known to those skilled in the art for creating an ABA film such as, but not limited to, an ABA extruder  74  having two separate screws  26 ,  28  and an ABA feed block die  78  fed by two separate hoppers  34 ,  36 , respectively.  
      The ABA film  54  may comprise a first layer  51  of a first resin  30  and second and third layer  52 ,  53  of a second resin  32 . The first resin  30  may comprise polyurethane or the like and the second resin  32  may comprise polyester, polypropylene, or the like. A first and a second surface  61 ,  62  of the first layer  51  may substantially contact the second and third layers  52 ,  53 , respectively, such that the first layer  51  may be “sandwiched” between the second and third layers  52 ,  53 . According to one embodiment, the first and second surfaces  61 ,  62  of the first layer  51  may be substantially coextensive with the second and third layers  52 ,  53 . The ABA film  54  may then be wound onto a roll  44  or cut into the desired shape and/or packaged (act  720 ).  
      The second and third layers  52 ,  53  of the second resin  32  may protect both sides  61 ,  62  of the first layer  51  of the first resin  30 . In use, the second and third layers  52 ,  53  may simply be removed from the first layer  51  thereby reducing or eliminating the imperfection in the surfaces  61 ,  62  of the first layer  51 . As a result, the ABA film  54  may be manufactured without the need of a carrier.  
      According to a further embodiment, the present disclosure features an apparatus  80 ,  FIG. 8 , and method  900 ,  FIG. 9 , for manufacturing polyurethane film on a flat die line that minimizes and/or reduces the number of imperfections in the polyurethane film comprising the tandem extrusion of a first and a second layer  81 ,  83  one right after the other, onto the same web  90 . The first layer  81  may comprise a first resin  30  (for example, polyurethane or the like having a thickness of approximately 2-12 mils) that may be formed by a first extruder  86  and die  82  fed from a first hopper  34 . The first layer  81  may be extruded onto a carrier  42  (which may be unwound from a roll  41 ) such that a first surface  95  of the first layer  81  may substantially contact the carrier  42  (act  910 ). The second layer  83  may comprise a second resin  32  (for example, polyethylene, polypropylene, or the like having a thickness of approximately 0.5-3 mils) that may be formed from a second extruder  88  and die  84  (act  920 ).  
      The second layer  83  may be extruded and placed onto the second surface  97  of the first layer  81  after the first resin  30  has cooled and crystallized. The first and second layers  81 ,  83  may optionally be substantially coextensive. The tandem extrusion  90  may then wound onto a roll  44  or cut and packaged (act  930 ).  
      The first and the second surfaces  95 ,  97  of the first layer  81  may thus be protected by the carrier  42  and the second layer  83 , respectively. Specifically, the second layer  83  protects the second surface  97  of the first layer  81  from the exterior surface  96  of carrier  42  when wound. Additionally, tandem extrusion of the first and second resins  30 ,  32  substantially reduces or eliminates wrinkles, air pockets, and blemishes that may be formed when introducing a separate, crystallized film. Moreover, when the tandemly extruded second layer  83  is removed, the first layer  81  may be left with a smooth, clean surface  97 .  
      Furthermore, the first and second resins  30 ,  32  may have two very different melt flow temperatures and properties. In co-extrusion, the two materials  30 ,  32  should have similar melt flow temperatures and properties since they are coming out of the same die at similar temperatures. However, because two separate dies  82 ,  84  are used in tandem extrusion, this is not a limitation.  
      According, the present disclosure features novel and non-obvious apparatus and methods of manufacturing protective films. The apparatus and methods according to the present disclosure reduce or eliminate the number and frequency of imperfections in the protective films. Additionally, the apparatus and methods are commercially viable on a large or small scale.  
      The foregoing description is provided to illustrate and explain the present disclosure. However, the description hereinabove should not be considered to limit the scope of the invention set forth in the claims appended here to.  
      As mentioned above, the present disclosure is not intended to be limited to a system or method which must satisfy one or more of any stated or implied object or feature of the invention and should not be limited to the preferred, exemplary, or primary embodiment(s) described herein. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as is suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the claims when interpreted in accordance with breadth to which they are fairly, legally and equitably entitled.