Abstract:
A laminar assembly including a first optically opaque layer defining a plurality of through-holes, a second optically opaque layer, an optically transparent inner layer between the inner surface of the first optically opaque layer and the inner surface of the second optically opaque layer, and a preprinted layer proximate the outer surface of at least one of the first and second optically opaque layers. The plurality of through-holes is at least partially filled with material from the optically transparent inner layer, and light is visibly transmitted in a single direction through the plurality of through-holes. Unidirectional opacity watermarks defined by the plurality of through-holes in the laminar assembly provide advantageous anti-counterfeiting measures, and are easy to view and authenticate, yet difficult to simulate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 61/881,230 entitled “UNIDIRECTIONAL OPACITY WATERMARK” and filed on Sep. 23, 2013, which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure is related to unidirectional opacity watermarks in information-bearing laminar assemblies. 
       BACKGROUND 
       [0003]    Forming watermarks in identification cards typically involves printing dark text or a dark image inside an opaque, white core. The process generally includes using two layers of white material, such as poly(vinyl chloride) or a poly(vinyl chloride) composite. In one example, a visual preprint is added on a first side of the first white layer, and the watermark is printed on the opposite side of the first white layer. The first white layer and the second white layer are fused together, with the watermark of the first white layer facing the second white layer, thereby embedding the watermark in the core of the identification card. When the identification card is held up to a strong light, or backlit, the watermark can be viewed through the front of the card and the back of the card. 
         [0004]    Other visible markings on the identification card (e.g., images, text, preprinted patterns) are usually opaque and therefore can interfere with viewing the watermark. For the watermark to be visible, the dark text or image is typically selected to have a large area, such that the watermark can be distinguished from the other visible markings on the identification card. Accordingly, edge definition and detail are generally difficult to attain with watermarks formed by this technology. 
       SUMMARY 
       [0005]    The unidirectional opacity watermark described herein is a security feature for information-bearing laminar assemblies. The unidirectional opacity watermark is visible when light is directed to a first side of the laminar assembly, but is not visible when light is directed to a second side of the laminar assembly. The unidirectional opacity watermark is not opaque, and can have edge definition and detail without requiring a large area. As such, the unidirectional opacity watermark provides advantageous anti-counterfeiting measures, and is easy to view and authenticate, yet difficult to simulate. 
         [0006]    In a first general aspect, a laminar assembly includes a first optically opaque layer defining a plurality of through-holes, a second optically opaque layer, an optically transparent inner layer between the inner surface of the first optically opaque layer and the inner surface of the second optically opaque layer, and a preprinted layer proximate the outer surface of at least one of the first and second optically opaque layers. The plurality of through-holes is at least partially filled with material from the optically transparent inner layer, and light is visibly transmitted in a single direction through the plurality of through-holes. 
         [0007]    In a second general aspect, a laminar assembly having a unidirectional opacity watermark is fabricated by forming a plurality of through-holes in a first optically opaque layer, positioning an optically transparent core layer between the first optically opaque layer and a second optically opaque layer to yield a stack of layers, and heating the stack of layers to fuse the optically transparent core layer between the first optically opaque layer and the second optically opaque layer, thereby yielding a fused assembly. The plurality of through-holes is at least partially filled with material from the optically transparent inner layer, and light is visibly transmitted in a single direction through the plurality of through-holes. 
         [0008]    In a third general aspect, authenticating a laminar assembly includes directing light toward a first side of the laminar assembly and visually inspecting a second side of the laminar assembly for a change in opacity of a portion of the second side of the laminar assembly, and directing light toward the second side of the laminar assembly and visually inspecting the first side of the laminar assembly for a change in opacity of a portion of the first side of the laminar assembly, wherein the second side of the laminar assembly is opposite the first side of the laminar assembly. A visibly detectable change in opacity of a portion of the first side of the laminar assembly or a portion of the second side of the laminar assembly, but not both, verifies authenticity of the laminar assembly. 
         [0009]    In a fourth general aspect, a method of authenticating a laminar assembly includes directing light toward a first side of the laminar assembly and visually inspecting a second side of the laminar assembly for a change in opacity of a portion of the second side of the laminar assembly, and directing light toward the second side of the laminar assembly and visually inspecting the first side of the laminar assembly for a change in opacity of a portion of the first side of the laminar assembly, wherein the second side of the laminar assembly is opposite the first side of the laminar assembly. A visibly detectable change in opacity of a portion of the first side of the laminar assembly that differs in shape or position from a visibly detectable change in opacity of a portion of the second side of the laminar assembly verifies authenticity of the laminar assembly. 
         [0010]    Implementations of one or more of the above general aspects may independently include one or more of the following features. 
         [0011]    The preprinted layer is proximate the outer surface of the first optically opaque layer. 
         [0012]    The preprinted layer includes fixed or variable data or images or any combination thereof. 
         [0013]    The plurality of through-holes extends through the preprinted layer. 
         [0014]    The plurality of through-holes is arranged in the form of one or more fixed or variable images, shapes, designs, textual groupings, or any combination thereof. 
         [0015]    At least some of the plurality of through-holes are conical, frustoconical, or a combination thereof. 
         [0016]    The area of the opening of at least some of the through-holes at the inner surface of the first optically opaque layer exceeds the area of the opening of the through-holes at the outer surface of the first optically opaque layer. 
         [0017]    The area of the opening of at least some of the through-holes at the outer surface of the first optically opaque layer exceeds the area of the opening of the through-holes at the inner surface of the first optically opaque layer. 
         [0018]    At least some of the plurality of through-holes are cylindrical. 
         [0019]    The diameter of the opening of at least some of the through-holes at the outer surface of the first optically opaque layer, the inner surface of the first optically opaque layer, or both are in a range between 2 mil and 20 mil, or in a range between 4 mil and 10 mil. 
         [0020]    A longitudinal axis of at least some of the plurality of through-holes is perpendicular to the outer surface of the first optically opaque layer. 
         [0021]    A longitudinal axis of at least some of the plurality of through-holes is arranged at an angle between 45° and 90° with respect to the outer surface of the first optically opaque layer. 
         [0022]    A longitudinal axis of at least some of the plurality of through-holes is perpendicular to the outer surface of the first optically opaque layer. 
         [0023]    The optically transparent inner layer is an information-bearing layer. 
         [0024]    The optically transparent inner layer includes an electronic device, such as a microchip or UHF inlay. 
         [0025]    The plurality of through-holes are at least partially filled with material from the first optically opaque layer. 
         [0026]    Light directed toward the outer surface of the second optically opaque layer is transmitted through the plurality of through-holes in the first optically opaque layer, such that an outline formed by the plurality of through-holes is visible through the outer surface of the first optically opaque layer. 
         [0027]    Light directed toward the outer surface of the first optically opaque layer is not visibly transmitted through the laminar assembly. 
         [0028]    Diffuse or ambient light directed toward the outer surface of the second optically opaque layer is not visibly transmitted through the laminar assembly. 
         [0029]    The optically transparent inner layer is colored or colorless. 
         [0030]    The optically transparent inner layer includes an ultraviolet fluorescent material or fluorescing IR activated material. 
         [0031]    The laminar assembly is an identification card or a security document. 
         [0032]    The laminar assembly is a contactless smart card or a window card. 
         [0033]    The first optically opaque layer, the second optically opaque layer, the optically transparent inner layer, or any combination thereof comprises polycarbonate, polyester, poly(vinyl chloride), polystyrene, or a combination thereof. 
         [0034]    The laminar assembly includes a first optically transparent outer layer proximate the first optically opaque layer, and a second optically transparent outer layer proximate the second optically opaque layer. 
         [0035]    The laminar assembly includes 5 to 15 layers. 
         [0036]    The first optically transparent outer layer, the second optically transparent outer layer, or any combination thereof comprises polycarbonate. 
         [0037]    A thickness of the laminar assembly is in a range between 10 mil and 50 mil. 
         [0038]    A thickness of the first optically opaque layer is in a range between 2 mil and 8 mil. 
         [0039]    A thickness of the second optically opaque layer is in a range between 2 mil and 8 mil. 
         [0040]    A thickness of the optically transparent inner layer is in a range between 8 mil and 14 mil. 
         [0041]    A thickness of the first and second optically transparent layers is in a range between 2 mil and 8 mil. 
         [0042]    A plurality of through-holes are formed via laser ablation, optionally CO 2  laser ablation or YAG laser ablation. 
         [0043]    The optically transparent inner layer comprises two or more layers. 
         [0044]    The plurality of through-holes is a first plurality of through-holes, the second optically opaque layer comprises a second plurality of through-holes, and light is visibly transmitted in a single direction through the second plurality of through-holes. 
         [0045]    The light is visibly transmitted through the second plurality of through-holes in a direction opposite the single direction light is visibly transmitted through the first plurality of through-holes. 
         [0046]    Unidirectional opacity watermarks described herein provide advantageous anti-counterfeiting measures. These unidirectional opacity watermarks are easy to view and authenticate, yet difficult to simulate. 
         [0047]    The details of one or more disclosed implementations are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages will become apparent from the description, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]      FIG. 1  depicts authentication of an information-bearing laminar assembly with a light source proximate a back side of the information-bearing laminar assembly. 
           [0049]      FIG. 2  depicts a unidirectional feature of a unidirectional opacity watermark. 
           [0050]      FIG. 3  depicts the behavior of a unidirectional opacity watermark in ambient light. 
           [0051]      FIG. 4  depicts the behavior of a unidirectional opacity watermark in reflected light. 
           [0052]      FIGS. 5A-5D  depict cross-sectional views of laminar assemblies having unidirectional opacity watermarks. 
           [0053]      FIG. 6  is a flowchart for a process for forming a laminar assembly with a unidirectional opacity watermark. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    The unidirectional opacity watermark described herein is a security feature for information-bearing laminar assemblies. The unidirectional opacity watermark, in the form of one or more fixed or variable images, shapes, designs, textual groupings, or any combination thereof, is visible when light is directed to a first side of the laminar assembly, but is not visible when light is directed to a second side of the laminar assembly. Information-bearing laminar assemblies include, for example, identification cards, contactless smart cards, “window” cards, passport data pages, and the like. A “fixed” image, shape, design, or textual grouping is generally the same for a multiplicity of laminar assemblies. A “variable” image, shape, design, or textual grouping is generally specific for a subset of laminar assemblies or for a single laminar assembly (e.g., the image, name, signature, birthday, or the like of an individual card bearer). 
         [0055]    Referring to  FIG. 1 , identification card  100  is shown as an example of an information-bearing laminar assembly. When light source  102  is positioned proximate first side  104  of identification card  100 , unidirectional opacity watermark  106  is visible to the unaided human eye from a second side  108  of the identification card. That is, unidirectional opacity watermark  106  is visible when backlit by a light source proximate (e.g., close to or in contact with) first side  104  of identification card  100 , such that light at close range is transmitted through the identification card, making the unidirectional opacity watermark visible via transmission. As depicted in  FIG. 1 , first side  104  corresponds to the back of identification card  100 , and second side  108  corresponds to the front side of the identification card. In other cases, however, the first side  104  corresponds to the front of identification card  100 , and the second side  108  corresponds to the back of the identification card. Authentication can be achieved under light (e.g., daytime) or dark (e.g. nighttime) conditions. Suitable light sources for backlighting the unidirectional opacity watermark  106  include, for example, incandescent lights, halogen lights, light-emitting diodes, flashlights, and the like. 
         [0056]    As depicted in  FIG. 1 , the unidirectional opacity watermark  106  is in the form of an image (i.e., an eagle). The color of the unidirectional opacity watermark  106  is influenced by the color of the light from the direct light source  102  and the color of one or more layers in the laminar assembly. In some cases, a layer in the laminar assembly includes a UV fluorescent material that fluoresces when irradiated with a UV light source. In certain cases, a layer in a laminar assembly includes fluorescing IR activated material. Thus, the unidirectional opacity watermark  106  can be white or another color, and is not limited to black or a dark color. The unidirectional opacity watermark  106 , typically in the form of one or more fixed or variable images, shapes, designs, textual groupings, or any combination thereof, can be crisp and detailed, and is easily seen (e.g., as light shining through the identification card) against the preprint  110  or variable printing  112  on the identification card  100 . 
         [0057]    The unidirectional opacity watermark is not visible through the first side  104  of identification card  100  when direct light source  102  is positioned proximate the second side  108  of the identification card. In  FIG. 2 , the “X” indicates that the unidirectional opacity watermark is not visible from the first side  104  of the identification card  100 . That is, neither the “X” nor the unidirectional opacity watermark is visible from the first side  104  of the identification card  100  when the second side  108  of the identification card is backlit.  FIG. 2 , however, shows where the opacity watermark would appear if it were visible from both sides of the identification card. 
         [0058]    Unidirectional opacity watermark  106  is not visible through the second side  108  of the identification card  100  when the light source  102  is an ambient light source, such as the sun. Similarly, unidirectional opacity watermark  106  is not visible in ambient interior lighting, such as incandescent or fluorescent lighting, when the light source is not proximate the first side  104  of the identification card  100 . In  FIG. 3 , the “X” indicates that the unidirectional opacity watermark is not visible from the second side  108  of the identification card  100 . That is, neither the “X” nor the unidirectional opacity watermark is visible from the second side  108  of the identification card  100  in the presence of ambient (i.e., no direct) light.  FIG. 3 , however, shows where the opacity watermark would appear if it were visible from the second side  108  under ambient light. 
         [0059]      FIG. 4  depicts identification card  100  in the presence of light sources  102  and  102 ′. The unidirectional opacity watermark is not visible in the presence of reflected light from light sources  102  and  102 ′. In  FIG. 4 , the “X” indicates that the unidirectional opacity watermark is not visible with ambient light reflecting on the second side  108  of the identification card  100 . That is, neither the “X” nor the unidirectional opacity watermark is visible from the second side  108  of the identification card  100  in the presence of ambient light reflecting on the second side  108  of the identification card  100 .  FIG. 4 , however, shows where the opacity watermark would appear if it were visible from the second side  108  in reflected light. 
         [0060]    Thus, as described with respect to  FIGS. 1-4 , a unidirectional opacity watermark can be created such that it is visible from the front of a laminar assembly when the back of the laminar assembly is backlit, but not visible from the back of the laminar assembly when the front of the laminar assembly is backlit. Similarly, a unidirectional opacity watermark can be created such that it is visible from the back of a laminar assembly when the front of the laminar assembly is backlit, but not visible from the front of the laminar assembly when the back of the laminar assembly is backlit. In some cases, the unidirectional opacity watermark is an image, as depicted in  FIGS. 1-4 . In certain cases, the unidirectional opacity watermark includes one or more fixed or variable images, shapes, designs, textual groupings, or any combination thereof. In some instances, the unidirectional opacity watermark may include information specific to the bearer (e.g., variable information such as name, birthdate, image, or the like) or information specific to the origin of type of laminar assembly (e.g., fixed information such as a state seal or flag, concentric circles, words or phrases, or the like). A unidirectional opacity watermark may overlap variable information, fixed information or both. In  FIGS. 1-4 , however, the unidirectional opacity watermark is not depicted as overlapping variable or fixed information for simplicity. 
         [0061]      FIGS. 5A-5D  depict examples of unidirectional laminar assemblies  500 ,  530 ,  540 , and  550 , respectively. The layers and materials of these laminar assemblies are generally described with respect to laminar assembly  500  depicted in  FIG. 5A   
         [0062]      FIG. 5A  depicts a cross-sectional view of a portion of a laminar assembly  500  including a unidirectional opacity watermark. Laminar assembly  500  includes optically transparent inner layer  502  between inner surface  504  of first optically opaque layer  506  and inner surface  508  of second optically opaque layer  510 . In some cases, optically transparent inner layer  502  includes two or more fused layers (e.g., as depicted in  FIG. 5B ). In certain cases, a microchip, UHF inlay, or other electronic information-bearing device is embedded in optically transparent inner layer  502  (e.g., as depicted in  FIG. 5B ). Unidirectional watermark  512  is defined by a plurality of through-holes  514  in first optically opaque layer  506 . At least one of first optically opaque layer  506  and second optically opaque layer  510  typically includes a preprinted layer  516  proximate (e.g., printed on) outer surface  518  or  520  of first optically opaque layer  506  or second optically opaque layer  510 , respectively. Preprinted layer  516  may include, for example, fixed or variable data or images. As depicted in  FIG. 5A , preprinted layer  516  is proximate outer surface  518  of first optically opaque layer  506 . Laminar assembly  500  may also include first optically transparent layer  522  and second optically transparent layer  524  proximate first optically opaque layer  506  and second optically opaque layer  510 , respectively. 
         [0063]    A thickness of laminar assembly  500  is typically in a range between 10 mil and 50 mil. A thickness of first optically opaque layer  506  is typically in a range between 4 mil and 8 mil. A thickness of the second optically opaque layer  510  is typically in a range between 2 mil and 6 mil. A thickness of the optically transparent inner layer  502  is typically in a range between 8 mil and 14 mil. A thickness of the first and second optically transparent layers  522  and  524  is typically in a range between 4 mil and 8 mil. In one example, first and second optically transparent layers  522  and  524  are 6 mil thick, first optically opaque layer  506  is 6 mil thick, second optically opaque layer  510  is 4 mil thick, and optically transparent inner layer  502  is 11 mil thick. Other embodiments may include additional layers, layers with different thicknesses, or a combination thereof. 
         [0064]    Layers of laminar assembly  500  are typically formed of polymeric material, such as polycarbonate, polyester, poly(vinyl chloride), polystyrene, or other material known in the construction of identification credentials. In one example, first and second optically transparent layers  522  and  524  are formed of clear polycarbonate LE. In another example, first optically opaque layer  506  is formed of white polycarbonate. First optically opaque layer  506  may have preprinted layer  516  on outer surface  518 . In yet another example, second optically opaque layer  510  is formed of white polycarbonate. Various types of polycarbonate are available, for example, from Saudi Basic Industries Corporation (Sabic). Optically transparent inner layer  502  may be formed of clear polycarbonate housing a UHF inlay, such as that available from ASK (Burlington, Vt.). 
         [0065]    The through-holes are typically formed via laser ablation (e.g., with a CO 2  or YAG laser) of first optically opaque layer  506  before layers of laminar assembly  500  are positioned proximate each other to form the assembly. Forming a pattern of laser-ablated microholes in identification cards is described in U.S. Pat. No. 6,752,432 and U.S. Pat. No. 7,086,666, both of which are incorporated herein by reference. In some cases, the laser on-time ranges from 200 ms to 500 ms at a variety of power settings. When preprinted layer  516  is on outer surface  518  of first optically opaque layer  506 , the through-holes are typically formed through preprinted layer  516  and extend through the entire thickness of the first optically opaque layer  506 . The through-holes are arranged in the form of one or more fixed or variable images, shapes, designs, textual groupings, or any combination thereof. In one example, the center-to-center distance between through-holes may be about 10 mil. This distance may vary, however, based on equipment, desired effect, diameter of through-holes, or arrangment of through-holes. With respect to  FIGS. 1-4 , the through-holes are arranged to form the outline of an eagle. 
         [0066]    As depicted in  FIG. 5A , through-holes  514  are conical (e.g., frustoconical, or having the shape of a frustrum), with the diameter (or area) of the opening at the inner surface  504  of the first optically opaque layer  506  exceeding the diameter (or area) of the opening at the outer surface  518  of the first optically opaque layer. In some cases, the diameter of the opening at the outer surface  518  is in a range of 2 mil to 20 mil or 4 mil to 10 mil, or 5% to 50% (e.g., 10% to 40% or 20% to 30%) of the diameter at the opening of the inner surface  504 . 
         [0067]    In certain cases, as depicted in  FIG. 5B , the diameter (or area) of the opening of the through-holes  534  defining unidirectional watermark  532  at the outer surface  518  of the first optically opaque  506  layer exceeds the diameter (or area) of the opening of the through-holes at the inner surface  504  of the first optically opaque layer  506 . The diameter of the opening at the inner surface  504  may be in a range of 2 mil to 20 mil or 4 mil to 10 mil, or 5% to 50% (e.g., 10% to 40% or 20% to 30%) of the diameter at the opening of the outer surface  518 .  FIG. 5B  also depicts multi-layer optically transparent inner layer  502 ′ with electronic device  536  embedded in one layer of the optically transparent inner layer. Electronic device  536  may be, for example, a microchip, UHF inlay, or other electronic information-bearing device. 
         [0068]    As depicted in  FIG. 5C , through-holes  544  of unidirectional watermark  542  of laminar assembly  540  are cylindrical, with a diameter in a range between 2 mil and 20 mil. It should be noted that when preprinted layer  516  is on outer surface  518  of first optically opaque layer  506 , it is desirable for the through-holes to have an area at the outer surface such that openings in the preprinted layer are not visible to the human eye, and the preprinted layer does not appear to be perforated. 
         [0069]    In some embodiments, as depicted in  FIG. 5D , laminar assembly  550  includes unidirectional opacity watermarks having opposite directionality, so that a first unidirectional watermark  512  defined by through-holes  514  is visible through first optically transparent outer layer  522  when second transparent outer layer  524  is directly illuminated with a light source, and a second unidirectional watermark  552  defined by through-holes  554  is visible through second transparent outer layer  524  when first transparent outer layer  522  is directly illuminated with a light source. First unidirectional watermark  512  and second unidirectional opacity watermark  552  may be spatially separated from one another and may include different images, shapes, designs, or textual groupings. 
         [0070]    In some cases, as depicted in  FIGS. 5A-5D , a longitudinal axis of the through-holes is perpendicular to the outer surface of the first optically opaque layer  506 . In other cases, a longitudinal axis of the through-holes is arranged at an angle between 45° and 90° with respect to the outer surface of the first optically opaque layer  506 . In certain cases, through-holes in a unidirectional opacity watermark may have different sizes, shapes, and/or angular orientations with respect to the surface of the identification card. In various embodiments, the unidirectional opacity watermark is positioned to overlay or avoid certain fixed or variable preprinted items of the laminar assembly, or to avoid an embedded electronic device. 
         [0071]    With respect to  FIG. 5A , but generally applicable other embodiments, after through-holes  514  are formed in first optically opaque layer  506 , layers of laminar assembly  500  are aligned and fused together by processes generally known in the art. During fusing, material from optically transparent inner layer  502  and material from first optically opaque layer  506  fills or at least partially fills through-holes  514 . Thus, through-holes  514  are at least partially filled with a mixture of optically transparent (clear) and optically opaque (white) material, yielding lens-like structures. Thus, when a light source is placed proximate the laminar assembly  500  and travels in the direction of the arrows shown in  FIGS. 5A-5D , the light is effectively focused by the lens-like structures and is therefore visible at the first optically transparent outer layer  522 . However, when light travels in the direction opposite to that indicated by the arrows in  FIGS. 5A-5D , light is dispersed in optically transparent inner layer  502 , and is not visible at the second optically transparent outer layer  524 . Thus, what appears as a small illuminated (e.g., white) hole at the first optically transparent outer layer when the laminar assembly is directly illuminated at the second optically transparent outer layer, is a larger, diffuse white area that is not visible at the second optically transparent outer layer when the laminar assembly is directly illuminated at the first optically transparent outer layer. 
         [0072]      FIG. 6  is a flowchart showing process  600  for forming a laminar assembly having a unidirectional opacity watermark. In  602 , a plurality of through-holes is formed in a first optically opaque layer. In  604 , an optically transparent inner layer is positioned between the first optically opaque layer and a second optically opaque layer to yield a stack of layers. In  606 , the stack of layers is heated to fuse the optically transparent core layer between the first optically opaque layer and the second optically opaque layer, thereby yielding a laminar assembly including a unidirectional opacity watermark. In various embodiments, the stack of layers includes additional layers (e.g., up 15 layers) that are fused together. Additional layers may include, for example, laser sensitized clear polycarbonate, clear polycarbonate CORELAM, and the like. In some cases, a laser sensitized polycarbonate layer may be interposed between the first or second optically opaque layer the first or second optically transparent layer, respectively. A thickness of the laser sensitized polycarbonate layer may be in a range between 1 mil and 6 mil (e.g., 2 mil or 4 mil). In implementations having laser sensitized polycarbonate layers, the first or second optically transparent layer may have a thickness in a range between 1 mil and 5 mil (e.g., 2 mil). 
       EXAMPLE 
       [0073]    In one example, a laminar assembly with a unidirectional opacity watermark includes seven layers of polycarbonate, in the following order: 2 mil clear polycarbonate, 4 mil laser sensitized clear polycarbonate, 6 mil white printed polycarbonate into which the conical-shaped through-holes were laser-ablated; 12 mil clear polycarbonate CORELAM, 4 mil white polycarbonate, 2 mil laser sensitized clear polycarbonate, and 2 mil clear polycarbonate. 
         [0074]    Material for each layer was cut into 11 by 11.75 inch pieces. The layers were stacked in the sequence described above. Highly polished steel mirror plates were placed on opposite sides of the card material stack (i.e., contacting the 2 mil clear polycarbonate on each side). The material stack and plates were placed on the lower platen of a Tetrahedron Lab Press. The press cycle was initiated after closing the press. The press cycle consists of 3 steps which are executed automatically once the press is closed. The press cycle or process recipe is shown in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Process recipe. 
               
             
          
           
               
                   
                   
                 Temperature (° F.) 
                 Pressure (psi) 
                 Dwell time 
               
               
                   
                   
               
             
          
           
               
                   
                 Step 1 
                 315 
                 16 
                 30 sec 
               
               
                   
                 Step 2 
                 360 
                 370 
                 5 min 
               
               
                   
                 Step 3 
                 80 
                 370 
                 1 min 
               
               
                   
                   
               
             
          
         
       
     
         [0075]    Once the press were closed, the platen heaters were turned on and the platens were heated to the specified temperature of each step. If the temperature needed to decrease as in Step 3, water was circulated through the platens. The platen pressure was also increased to the level specified in the process step. Once the specified values of temperature and pressure were reached, the process was held at that level for the amount of time specified as dwell time for that step. On completion of the dwell time, the next step was initiated until the last process step was executed and reached and the specified dwell time has expired. 
         [0076]    On completion of the final process step, the pressure went to zero, causing the lower platen to descend to the starting or open position. The material and mirror plate package were removed from the press. The mirror plates were then removed from the fused polycarbonate material stack. The fused material stack was then cut into 15 ID1 sized cards, each containing a unidirectional opacity watermark feature. 
         [0077]    Further modifications and alternative embodiments of various aspects will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only. It is to be understood that the forms shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description.