Abstract:
A method for forming sunglass lenses with a predetermined optical gradient, namely a polarized gradient, transmissivity gradient or color gradient in which an ink jet printer is used to print a gradient pattern on an oriented sheet, with the ink jet printer being provided with a dye, in one embodiment a dichroic dye and in another embodiment an iodine dye. The printed oriented sheet is incorporated into a lens to provide the lens with the associated gradient.

Description:
FIELD OF INVENTION 
     This invention relates to the manufacture of sunglass lenses and more particularly to a method and apparatus for forming sunglass lenses with a predetermined polarization or color gradient in which the lenses are provided with the gradient through the utilization of inkjet printing. 
     BACKGROUND OF THE INVENTION 
     As described in U.S. Pat. No. 7,374,282 issued to Robert K. Tendler on May 20, 2008, it is desirable to provide sunglass lenses with a polarization gradient such that when one views the far field one looks at a polarized scene, whereas when one looks at the near field where a polarized display might be located one sees the polarized display without it being blackened by cross polarization. 
     As described in the aforementioned patent, one of the ways of providing for gradient polarization in which there is maximum polarization at the top of the lens and minimum polarization at the bottom of the lens is to provide differential stretching of the oriented material which is provided with a stain, such as iodine or a dichroic dye. This then provides the final structure with a gradient polarization characteristic. 
     However this type of technique is difficult to achieve and while there may be many other ways of providing for gradient polarization for a polarized sheet, there remains the problem in providing a true gradient polarized lens. Moreover there are problems in providing for gradient lenses in which the color or filter characteristics of the lens vary across the face of the lens. 
     It will be appreciated that if one can provide a gradient polarized lens with printable characteristics, it would be very easy to fashion specialty lenses having required specialized characteristics simply by printing. 
     As to printing to provide polarized films with either a transparency image or a printed image, inkjet printing has been used to produce 3-D viewable images by overprinting polarized material or films with dichroic dyes or other colorants. In one embodiment their 3-D imaging involves printing on one side of an oriented film with one image and an offset version of the same image on the opposite side of the film. When viewed stereoscopically with oppositely circularly polarized glasses, one sees a 3-D image of the artwork printed on the polarized film due to the offset in the images front and back. Inkjet printing of oriented substrates has been described in U.S. Pat. Nos. 5,552,182; 5,591,508; 5,758,036; 5,764,248; 6,013,123; and 6,347,851 issued to Julius J. Scarpetti, all incorporated herein by reference. It will be appreciated that nowhere in the Scarpetti patents is suggested providing a transparency involving an oriented substrate with a gradient pattern, either for providing a gradient polarization characteristic or for providing color filtering characteristics. 
     SUMMARY OF INVENTION 
     In order to provide sunglass lenses with a predetermined characteristics such as a gradient characteristic, in the subject invention when an oriented sheet is utilized in the formation of the polarizing layer for the sunglasses, this oriented sheet is imprinted utilizing an inkjet printer to provide a transparency, in one embodiment using transparent dichroic dyes, such that the oriented sheet is selectively stained with the dyes to provide a transparency with the required gradient. In one embodiment, the pattern of the inkjet-printed dyes provide both gradient transmissivity and gradient polarization due to the density of the dye dots on the oriented material. 
     The density of the inkjet dots on the material refers to either the size of the dots in terms of lines per inch, or in terms of the actual amount of material deposited in a given location by the inkjet printer. 
     In addition to being able to selectively pattern an oriented sheet with a selective pattern corresponding to a gradient matrix that is used to create a gradient polarized sheet, is possible to use the inkjet printer to also selectively deposit transparent dyes of various colors so that the finished lens has not only a gradient polarization effect but also gradient color. 
     It is in general possible to provide a gradient effect for sunglasses or in fact any optical lens by simply using the jet printer to print the particular colored dyes that are desired such that the lens itself takes on the gradient characteristic of the deposited dyes. In either case, inkjet printing provides the ability to pattern the lens at precise locations with the desired pattern so that for instance a predetermined portion of the lens can be provided with a different characteristic. 
     Central to the subject invention is the fact that one can utilize an inkjet printer to print transparent stains that result in films having transmissivity corresponding to the transmissivity of polarizing stains such as the iodine or dichroic dyes normally used to produce polarized films. This means and what is over printed on the substrate results in a transparent slide-like film having slide-like transmissivity, as supposed to opaque paint. It has been found that by using utilizing an inkjet printer and dichroic dyes one can deposit transparent staining in much the same way that stain is deposited on an oriented substrate when manufacturing standard polarized films for use in sunglasses; and that is by simply staining the oriented sheet by passing it through a staining bath. 
     Thus, rather than opaquely printing on a substrate with ink which is the manner in which most printers operate, in subject invention transparent dyes are used as well as regulating the amount of dye deposited to permit viewing through the stained substrate. Thus, the techniques described by Scarpetti for “painting” on polarized material so as to produce a 3-D image is rather used to stain an oriented substrate for producing a transparency with a gradient polarizing pattern that permits viewing through the stained substrate. 
     As a result, what is provided is a substrate which is over printed with either transparent iodine dyes or dichroic dyes to provide the substrate with a predetermined pattern. In one embodiment this results in a gradient polarized film having maximum polarization at the top of the lens and minimum polarization at the bottom of the lens. This provides the ability to view polarized displays when utilizing the sunglasses by peering downwardly through the relatively unpolarized portion of the sunglass lens so as to be able to view a polarized display. In addition because the density of the printing varies to zero towards the bottom of the lens, it is like viewing through plate glass when viewing a display. So not only is there no polarization effect, there is very little blockage of light when viewing through the bottom of the lens. This is equivalent to taking one&#39;s sunglasses off when viewing a display. Since there is no polarization effect when viewing a polarized display and since there is no blockage of light when utilizing the subject lenses, one can readily view a display without attenuation. This makes the displays as clear and bright as if viewed without sunglasses. 
     In summary, a method is provided for forming sunglass lenses with a predetermined optical gradient, namely a polarized gradient, transmissivity gradient or color gradient in which an ink jet printer is used to print a gradient pattern on an oriented sheet, with the ink jet printer being provided with a dye, in one embodiment a dichroic dye and in another embodiment an iodine dye. The printed oriented sheet is incorporated into a lens to provide the lens with the associated gradient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the subject invention better understood in connection Detailed Description in conjunction with Drawings of which: 
         FIG. 1  is a diagrammatic illustration of a front view of sunglasses having a gradient polarizer lens, also exhibiting gradient transmissivity; 
         FIG. 2  is a diagrammatic illustration of a sheet of polyvinyl alcohol stretched four times its length to provide an oriented sheet; 
         FIG. 3  is diagrammatic illustration of the bonding of a cellulose acetate substrate to the polyvinyl alcohol sheet of  FIG. 2 ; 
         FIG. 4  is a diagrammatic illustration of the overcoating of the structure of  FIG. 3  with a mordant; 
         FIG. 5  is an exploded view of the sandwiching of a gradient polarization shell between two glass caps laminated together to provide a lens; 
         FIG. 6  is a diagrammatic illustration of the completed lens of  FIG. 5 , showing a finished lens having a gradient polarization characteristic; 
         FIG. 7  is a diagrammatic illustration of the utilization of an inkjet printer provided with dichroic dye ink and an oriented sheet to provide a sheet with a gradient optical characteristic, namely gradient polarization; 
         FIG. 8  is a diagrammatic illustration of the printed sheet of  FIG. 7  dried by heating to cure the imprinted sheet; 
         FIG. 9  is a diagrammatic illustration of the molding of the sheet of  FIG. 8  into a curved cup shaped shell suitable for incorporating into a sunglass lens; 
         FIG. 10  is a diagrammatic illustration of the cutting of the cup shaped shell formed in  FIG. 9 ; 
         FIG. 11  is diagrammatic illustration of the gradient polarization shell that is the result of the cutting operation of  FIG. 10 ; and, 
         FIG. 12  is a flowchart showing the manufacture of a gradient polarization lens of  FIGS. 1-11  using an inkjet printing process. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to now to  FIG. 1 , a pair of sunglasses  10  is shown having lenses  12  and  14  with the gradient shading illustrating gradient polarization  16  and concomitant gradient transmissivity  18 . Here it can be seen that the gradient polarization is such that the upper portions of lenses  12  and  14  are heavily polarized at the top and lightly polarized at the bottom, whereas concomitantly the transmissivity of lenses  12  and  14  is greater at the bottom as compared to the top. In one embodiment the polarization percentage at the top is close to 100%, whereas at the bottom it is close to 0.04%. 
     The purpose of the subject technique to be able to manufacture a pair of sunglasses with a gradient polarization characteristic. In order to do so in one embodiment an inkjet process is employed. As described in  FIG. 2 , a polyvinyl alcohol sheet  20  is stretched to four times its length as illustrated by arrow  22  so as to provide an oriented sheet. 
     Referring to  FIG. 3 , sheet  20  is provided with a cellulose triacetate substrate  22  which is bonded to the bottom of the oriented sheet  20 . 
     Referring to  FIG. 4 , the polyvinyl alcohol oriented sheet  20  with cellulose triacetate substrate  22  bonded thereto is overcoated with a mordant as illustrated at  24 . 
     Referring to  FIG. 5 , when the structure of  FIG. 4  has been formed into a curved gradient polarization shell  30 , this shell is laminated between two glass caps  32  and  34 , with the lamination sandwiching the gradient polarization shell between the glass caps. 
     As illustrated in  FIG. 6 , the resulting laminate  40  is a finished lens in which gradient polarization of the lens is provided by the lamination of the gradient polarization shell between the glass caps. 
     How this is accomplished is shown in  FIG. 7  in which inkjet printer  50  is utilized to print over the coated and backed oriented sheet  52 , made printable by the mordant described above. The printer output is an over printed sheet  54  provided with a gradient optical characteristic in the form of a gradient polarization characteristic as illustrated at  56 . The printing is accomplished through the utilization of a dichroic dye which is patterned such that the upper portion of what is to be the lens is heavily dyed, whereas the base or bottom portion of the lens is virtually undyed, thus to give the aforementioned gradient optical characteristic. 
     As shown in  FIG. 8 , a sheet  54  from the printer  50  is then heated by a heater  58  to dry the dye and as illustrated in  FIG. 9 , the sheet  54  from the printer  50  is molded into the desired curvature of a shell illustrated at  56  such that the final structure of the sheet  54  is curved for instance to conform to the # 6  curvature of sunglass lenses. 
     Referring to  FIG. 10 , the molded sheet  54  of  FIG. 9  is cut as illustrated at  60  to provide a gradient polarized shell  62  as illustrated in  FIG. 11  to be laminate between two glass caps to finish the lens. 
     Referring now to  FIG. 12 , a flowchart  70  illustrates that as a first step  72  a sheet of polyvinyl alcohol of film is stretched to four times its length, followed as illustrated at  74  by bonding a cellulose triacetate substrate to the stretched sheet. Thereafter as illustrated  76 , the polyvinyl alcohol sheet is provided with a suitable mordant to produc a printable sheet. 
     Next, as illustrated at  78  a gradient optical density pattern is printed onto the sheet using an inkjet printer using a dichroic dye ink. The ink is dried as illustrated at  90 , with the sheet containing the printed optical density pattern. As illustrated at  92  the sheet containing the printed optical gradient density pattern is formed into a desired curvature shell, followed as illustrated at  94  by laminating the gradient density shell between two glass caps of a similar curvature to produce a lens blank. Thereafter as illustrated at  96  the lens blank is trimmed to the desired shape. 
     What will be seen is that a convenient method of providing a sunglass lens includes providing the prescribed gradient density pattern by utilizing an inkjet printer. The density gradient is controlled by the printing process to provide a selectable gradient pattern of the deposited dye onto the printable substrate. This pattern can provide for the required polarization of the sheet due to the interaction of the dye with the oriented substrate. 
     Note that while the subject invention has been described utilizing dichroic dyes, other dyes such as iodine dyes are suitable. Dichroic dyes are preferred because if heat is used in the molding process these dyes are less susceptible to the heat used in the molding process. 
     Moreover, note that the subject inkjet technique provides not only the requisite polarization but also the requisite colorization so that the sunglasses may be tinted as required for various sports and other activities. 
     While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications or additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.