Abstract:
A method and apparatus for producing a lenticular plastic sheet from a material resin having a first surface and an opposite second surface employs a patterned chill roller having an outer surface defining a lenticular pattern thereon disposed adjacent and parallel to a nip roller so as to define a nip therebetween. A material resin is extruded onto the chill roller while in a molten state and begins to cool forming a sheet. Thereafter, the sheet passes into the nip so that the first surface of the sheet is in contact with the lenticular pattern of the chill roller. The lenticular pattern of the chill roller is subsequently transferred to the sheet.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a casting method for manufacturing plastic films, and more particularly, the present invention relates to a casting-type manufacturing method and the associated apparatus for producing lenticular sheets or film having lens arrays located thereon in selected areas. 
         [0003]    2. Description of the Related Art 
         [0004]    There are known methods of producing very thin lenticular sheets or film. Typically, these methods involve coating a clear UV formulation onto a carrier web and curing the resin through the carrier web while it is held against an engraved cylinder. Another method is by extrusion coating a molten resin between a patterned roll and a carrier film. Both of these methods produce a two layer lenticular sheet or film. Having two layers disadvantageously provides concerns relating to the effect of having two different refractive indices, clarity, the bond of one layer to another and overall manufacturing costs. 
         [0005]    Conventionally, there are also known methods of producing thin monolayer films such as through a circular die, known as “blown film,” Orientation and stretch of a flat film from a die can also produce very thin and stable film, such as Mylar, Celenar, etc. Disadvantageously, a uniform lenticular pattern cannot be put into these films as in both cases, the dimensions of the film changes drastically through the manufacturing process in order to compensate for gauge increase. 
         [0006]    In seeking to produce quality monolayer lenticular sheets, manufacturers have relied upon sheet extrusion methods. These methods are capable of producing lenticular sheets or film in thicknesses of about 7 mil to ¼ inch. Typically, the sheet extrusion process uses an extrusion die to meter a molten resin into a nip consisting of two metal rolls. To produce a lenticular pattern, at least one of the rolls is engraved with a desired inverse lenticular pattern. Once the sheet passes through the nip, it is typically pulled along a manufacturing line to cool. The distance pulled oftentimes reaches 30 or more feet. By pulling the sheets along the manufacturing line, they are undesirably necked or shrunk. This necking distorts the lineal lenticular pattern and decreases the overall quality. 
         [0007]    Accordingly, to overcome the various disadvantages in the art, manufacturers are looking for solutions which produce thin lenticular sheets or film which provide superior clarity and quality. In one solution, it would be desirable to provide a casting method of manufacture and apparatus for producing engraved lenticular sheets or film having lens arrays located in selected areas. Such a solution would be capable of producing lenticular sheets or film having thicknesses from about 3 mil (having about 300 or more lenses per inch) to about 15 mil (having about 75 or more lenses per inch). Further, such a solution would be capable of producing lenticular sheets or film that have improved stability and less shrinkage as those sheets or film produced by extrusion processes. Still further, such a solution would be capable of producing lenticular sheets or film which provide improved clarity of a final commercial product by rapidly cooling the same during manufacture. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    To achieve the foregoing and other objects, and in accordance with the purposes of the invention as embodied and broadly described herein, the present invention provides various embodiments of a manufacturing method for engraved lenticular sheet products, and more particularly, the present invention relates to a casting manufacturing method for producing engraved lenticular sheets having lens arrays located thereon in pre-selected areas. In various embodiments, the present invention provides cylinders operable for engraving thin, flexible webs having a variety of lens shapes for use with commercial products and/or the like. The present invention provides significant advantages over the prior art. 
         [0009]    According to one exemplary embodiment, a clear molten material resin which will form a layer of a lenticular sheet is contained in a reservoir. The reservoir is operable for feeding the molten material resin through a flange or opening and into a slot or flat die. The die is operable for extruding the material resin onto a chill roller and through a nip to form the lenticular sheet or film. In exemplary embodiments, the molten material resin wraps around the chill roller and through the nip before it is removed to idler rollers (not shown) or wind up rollers (not shown). Thus, by the time the lenticular sheet or film comes off the chill roller, it has reached substantially room temperature. Advantageously, by having the lenticular sheet or film reach room temperature prior to corning off the chill roller, maximum strength of the lenticular sheet or film is achieved. In exemplary embodiments, the chiller roller is positioned under the die with a nip roller positioned adjacent the chill roller. The molten material is extruded onto the chill roller and begins to cool such that it takes the form of the inverse lens pattern. In exemplary embodiments, the chill roller is positioned under the die at a distance from about 9 inches to about 3 feet. 
         [0010]    In exemplary embodiments, the nip roller is substantially cylindrical and is constructed by a rubber or polymeric material. The nip roller is operable for aiding in transferring the inverse lens pattern from the chill roller to the material resin. The nip roller may be positioned adjacent the chill roller such that it presses against the chill roller. In this case, material may flow through the nip because the surface of nip roller is not rigid. In other exemplary embodiments, the nip roller may be constructed from steel or chrome to impart a mirror or patterned finish. In this case, nip may be adjusted to provide a gap appropriate for the desired thickness of the lenticular sheet. 
         [0011]    In operation, the clear molten material resin is fed from the reservoir through the opening to the die. Thereafter, the die extrudes the clear molten material about the rotating chill roller. The molten material rotates about the chill roller and begins to cool, thereby taking the form of the inverse lens pattern engraved upon the chill roller. Further, the molten material passes through the nip formed by the chill roller and nip roller. The molten material resin solidifies along its path at an unspecified point and emerges as a lenticular sheet or film. The lenticular sheet is thereafter wound up by additional rollers or reverse printed with an image using any known method. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         [0012]    These and other features, aspects and advantages of the present invention are better understood when the following detailed description of the invention is read with reference to the accompanying drawing(s), in which: 
           [0013]      FIG. 1  is a perspective view of an exemplary casting manufacturing system for lenticular sheets or film constructed in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    The present invention will now be described more fully hereinafter with reference to the accompanying drawing(s) in which exemplary embodiments of the invention are shown. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These exemplary embodiments are provided so that this disclosure will be both thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numbers refer to like elements throughout the various drawing(s). 
         [0015]    The present invention provides various embodiments of a casting method of manufacture and apparatus for producing engraved lenticular sheets or film having lens arrays located in selected areas. As is well known and understood in the art, lenticular lens material utilizes rows of simple and commonly dome-shaped lenses or “lenticules.” It will be understood by those skilled in the art that any lens element may be used in accordance with the present invention either singularly or in combination such as, and without limitation, lineal, fresnel, dot (also known as integral or fly&#39;s eye), or prismatic. As used herein, the term “lenticular sheet” or “lenticular film” is intended to include any optical sheet, roll, film or material that is suitable for use in the printing arts and has a substantially transparent quality. Material compositions of such sheets or film may include, for example and without limitation, polyolefin, polycarbonate, polypropylene, polyester, polyethylene, polyvinylchloride, and polystyrene. All such material compositions are considered to be polymeric and are synonymous therewith. In one example, the lenticular sheet or film generally comprises a first, flat side and a second, lenticulated side including the lenticules forming the lens arrays 
         [0016]    Advantageously, by using the disclosed methods of manufacture and apparatus of the present invention, lenticular sheets or film can be produced having superior qualities over conventionally manufactured lenticular sheets or film. By way of example, the lenticular sheets or film of the present invention may be produced having thicknesses from about 3 mil (having about 400 or more lenses per inch) to about 15 mil (having about 100 or more lenses per inch). By way of another example, lenticular sheets or film produced by the disclosed methods and apparatus have improved stability and less shrinkage as those sheets or film produced by extrusion processes. By way of yet another example, since the lenticular sheets or film of the disclosed methods are rapidly cooled, overall clarity of the final product is improved. 
         [0017]    Referring now to  FIG. 1 , an exemplary embodiment of the present invention is illustrated in which a monolayer lenticular sheet  32  is produced. As illustrated, an engraved, substantially cylindrical chill roller  28  is provided and is central to the apparatus  10  and method of manufacture. It will be understood by those skilled in the art that the chill roller  28  may be any conventional type chill roller and in exemplary embodiments is provided with a relatively large diameter and is cooled with water flowing through a central core  27 . 
         [0018]    In accordance with one exemplary embodiment of the present invention, the lens arrays engraved on lenticular sheets or film are fabricated by first designing a cutting tool, such as a stylus, with a desired lens shape such that an inverse of the same can be transferred to the chill roller  28 . The cutting tool (not shown) is preferably made of a diamond or carbide, however, it will be understood by those skilled in the art that any hard material suitable for engraving cylinders may be used. The shape of the cutting tool is dictated by the desired visual effect, 
         [0019]    Once the cutting tool is designed, a desired inverse lens shape is engraved into pre-selected portions of the chill roller  28  using any known, conventional method of engraving, thereby forming a plurality of inverse lens arrays or patterns. In one exemplary embodiment, the chill roller  28  is placed in an engraving or CNC turning lathe which can accurately guide an engraving head, the cutting tool, across the surface of the roller  28 . Preferably, the engraving process includes the use of a programmable computer operable for directing the cutting action and placement of the cutting tool in both direction and depth such that bands of optimal lens patterns are transferred into the roller  28  which are areas where light from a scanning device will be deflected or reflected in a different direction from smooth adjacent unengraved areas on the roller  28 , or simply to scatter light. Each of the engraved bands of lenses can be just one cut or a series of engravings consisting of a frequency of up to 2000 cuts per inch or more. 
         [0020]    The shape of the engraving on each band of lens elements can be prismatic, lineal fresnel, lenticular or dot or any combination there of If the lens pattern is to be a dot repeating type of pattern, a vibrating tool or spinning tool holder is used. The shape of the engraving can be different on adjacent bands of lens elements, or different within the same band. Advantageously, by using the engraving process for the chill roller  28 , a variety of inverse lens patterns can be engraved into the roller  28 , thereby providing a variety of lens patterns embossed on the same sheet, including but without limitation, lens patterns having different shapes and lens patterns extending in different directions such as longitudinally and latitudinally from a certain axis. 
         [0021]    Subsequent to engraving the chill roller  28 , the chill roller  28  is placed into the lenticular system or process of manufacture  10  of the present invention. As stated above, in exemplary embodiments, the lenticular sheet material  32  is preferably plastic or polymeric. Further, it will be appreciated by those skilled in the art, that a variety of materials can be employed for the production of the lenticular sheets or film, for example and without limitation, acrylics, polystyrenes, polycarbonates, polyesters, polyolefins, polyvinyl chlorides and all such polymeric equivalent materials. 
         [0022]    As specifically shown in  FIG. 1 , a clear molten material resin  26  which will form a monolayer of the lenticular sheet  32  is contained in a reservoir  12 . It will be understood by those skilled in the art that while a method of manufacture of a monolayer is being described herein, multiple layers may be manufactured from the disclosed process. In such cases, additional reservoirs  14  and  16  may be provided and may contain the same or distinct material resins. The reservoir  12  is operable for feeding the molten material resin  26  through a flange or opening  18  and into a slot or flat die  24 . In exemplary embodiments, where a multilayered sheet is desired the molten material  26  is additionally fed from reservoirs  14  and  16  through openings  20  and  22 , respectively, to the die  24 . The die  24  is operable for extruding the material resin  26  onto the chill roller  28  and through a nip  29  to form the lenticular sheet or film  32 . In exemplary embodiments, the molten material resin  26  wraps around the chill roller  28  and through the nip  29  from about 180 degrees to about 300 degrees before it is removed to idler rollers (not shown) or wind up rollers (not shown). Thus, by the time the lenticular sheet or film  32  comes off the chill roller  28 , it has reached substantially room temperature. Advantageously, by having the lenticular sheet or film  32  reach room temperature prior to coming off the chill roller  28 , maximum strength of the lenticular sheet or film  32  is achieved. In exemplary embodiments, the chiller roller  28 , manufactured as described above, is positioned under the die  24  with a nip roller  30  positioned adjacent the chill roller  28 . The molten material  26  is extruded onto the chill roller  28  and begins to cool such that it takes the form of the inverse lens pattern. In exemplary embodiments, the chill roller  28  is positioned under the die  24  at a distance from about 9 inches to about 3 feet. 
         [0023]    In exemplary embodiments, the nip roller  30  is substantially cylindrical and is constructed by a rubber or polymeric material, such as Teflon®. The nip roller  30  may be positioned adjacent the chill roller  28  such that it presses against the chill roller  28 . The nip roller  30  is operable for aiding in transferring the inverse lens pattern from the chill roller  28  to the material resin  26 . In exemplary embodiments, the surface characteristic of the rubber or polymeric material which comprises the nip roller  30  is selected to impart a gloss like surface, and includes the use of very fine grain materials. In this case, material  26  may flow through the nip  29  because the surface of nip roller  30  is not rigid. In other exemplary embodiments, the nip roller  30  may be constructed from steel or chrome to impart a mirror or patterned finish. In this case, nip  29  may be adjusted to provide a gap appropriate for the desired thickness of the lenticular sheet  32 . In other exemplary embodiments, the nip roller  30  may have an engraved pattern on its periphery such that the lenticular sheet  32  has two sides with patterns. 
         [0024]    In operation, the clear molten material resin  26  is fed from reservoir  12  through the opening  18  to die  24 . Thereafter, the die  24  extrudes the clear molten material  26  about the rotating chill roller  28  which rotates in the direction shown by arrow A. The molten material  26  rotates about the chill roller  28  and begins to cool, thereby taking the form of the inverse lens pattern engraved upon the chill roller  28 . Further, the molten material  26  passes through the nip  29  formed by the chill roller  28  and nip roller  30 , which is rotating in a direction shown by arrow B. The molten material resin  26  follows the path shown by arrows A, B, and C, solidifying at an unspecified point (not shown) along the path and emerging as a lenticular sheet or film  32 . The lenticular sheet  32  is thereafter wound up by additional rollers (not shown) or reverse printed. It will be understood by those skilled in the art that roller rotation means (not shown) are provided to cause the chill roller  28  and the nip roller  30  to rotate. The precise means employed to cause the rollers  28  and  30  to rotate are not critical to the invention, however. After coming off of tie chill roller  28 , the lenticular sheet or film  32  may be Corona treated or coated for ink adhesion. In exemplary embodiments, the lenticular sheet or film  32  may be identified with in line ink jet printing. In other exemplary embodiments, the lenticular sheet or film  32  may be provided with identifying or register marks. In still other exemplary embodiments, the lenticular sheet or film  32  may be reverse printed with a desired interlaced image by using known methods. 
         [0025]    As briefly mentioned above, if a multilayer lenticular sheet is desired, additional material  26  is stored in additional reservoirs  14  and  16 . The material  26  for the middle layer may be contained in reservoir  14  may be an adhesive layer. The specific material composition may vary. Further, the material  26  for the bottom layer may be contained in reservoir  16  and may be an adhesion layer. It will be understood by those skilled in the art that the lower layers are designed for cost reduction and adhesion to the final substrate in the final product, and need not be as hard as the top layer, as they are protected by the top layer. 
         [0026]    If such a multilayered sheet  32  is desired, it will be understood that in exemplary embodiments, the lenticular resin in reservoir  12  flows from the reservoir through lenticular resin opening  18 ; the adhesive material in reservoir  14  flows from the reservoir through opening  20 , and the adhesion material in reservoir  16  flows through opening  22 . The various material resins contact flow through a conduit (not shown) and enter the flat or slot die  24 . The compositions, temperature, pressure and flow rates may be selected so that little or no shear exists at the interfaces of the molten materials when they contact each other. Once in the die  24 , the composition material  26  is extruded through the die  24  and about the rotating chill roller  28 . Thereafter, the composition material  26  begins to cool and passes through the nip  29 . The inverse lens pattern of the chill roller  28  is impressed onto the sheet  32  and the surface characteristic of the nip roller  30  is impressed onto the opposing side of the sheet  32 . 
         [0027]    It is to be understood by those skilled in the art that, any number of layers from one to about five may be produced using the appropriate number of materials and extrusion means, with the number of layers and their composition being selected in accordance with the desired end use of the lenticular sheet  32 . (More than five layers are possible, and thus, this number should not be construed as a limitation on the invention; however, use of the preferred process and apparatus may, as a practical matter, become less convenient). It should be noted that, although the exemplary embodiments are described as providing a lenticular pattern, any pattern, lenticular or not, that directs rays of light to an appropriate predetermined portion of the sheet may be provided in accordance with the scope of the invention. It will also be understood by those skilled in the art that while the foregoing describes a method of manufacture whereby an image is reverse printed on the lenticular sheet  32  after coming off the chill roller  28 , an interlaced image or printed web may be fed from a source (not shown) into the nip  29  and over the nip roller  30  such that it is adhered to the lenticular sheet  32  directly. In such an instance, final product will be produced directly off the casting line. 
         [0028]    Once the lenticular sheet  32  is released, its edges can be trimmed to provide a uniform width and to remove irregular edges. It may also be desirable to remove the edges because the unequal shrinkage of the top and the bottom of the lenticular sheet  32  may subject the edges to additional stress, which could result in poorer optical quality at the edges of the material. In other exemplary embodiments, the lenticular sheet  32  is sheeted as opposed to rolling the product. 
         [0029]    The foregoing is a description of various embodiments of the invention that are provided here by way of example only. Although the apparatus and casting method for producing the engraved lenticular sheets or film has been described with reference to preferred embodiments and examples thereof, other embodiments and examples may perform similar functions and/or achieve similar results. All such equivalent embodiments and examples are within the spirit and scope of the present invention and are intended to be covered by the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.