Patent Publication Number: US-6221806-B1

Title: Diffusion resistant lenticular element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned U.S. patent application Ser. No. 09/404,093, filed of even date herewith pending, entitled “Process for Obtaining a Diffusion Resistant Lenticular Element”, of Tutt et al; and copending U.S. patent application Ser. No. 09/404,564, filed of even date herewith, pending entitled “Diffusion Resistant Lenticular Element”, of Tutt et al; the teachings of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the laser printing of stereoscopic, multiple images or motion images which will be used in conjunction with a lenticular element. 
     BACKGROUND OF THE INVENTION 
     Lenticular arrays or overlays are a known means to give images the appearance of depth or motion. A lenticular image is created using a transparent upper layer having narrow parallel lenticules (half cylindrical lenses) on the outer surface and an image containing substrate or lower layer which projects images through the lenticules. The two layers form a lenticular system wherein each image is selectively visible as a function of the angle from which the system is viewed. A depth image is a composite picture made by bringing together into a single composition a number of different parts of a scene viewed from different angles. When the lenticules are vertically oriented, each eye of a viewer will see different elements and the viewer will interpret the net result as depth of field. The viewer may also move his head with respect to the image thereby observing other views with each eye and enhancing the sense of depth. Each lenticule is associated with a plurality of image lines or an image line set and the viewer is supposed to see only one image line (or view slice) of each set with each eye for each lenticule. It is imperative that the line image sets be registered accurately with the lenticules, so that the proper picture is formed when the assembly is viewed. 
     This process can be used to generate a three-dimensional effect at a proper viewing distance or multiple images by viewing from different angles. When the lenticules are oriented horizontally, each eye receives the same image. In this case, the multiple images upon moving the lenticular can be used to generate the illusion of motion. For whichever orientation the lenticules are oriented, each of the viewed images is generated by lines from an image which has been interlaced substantially at the frequency of the lenticular array, number of lenticules per length and with the desired number of images. 
     One method of recording of linear images on a lenticular recording material is accomplished with a stereoscopic image recording apparatus (hereunder referred to simply as “a recording apparatus”) that relies upon optical exposure (printing). With this recording apparatus, original transmission images are projected from a light source. The light transmitted through the original images passes through the projection lenses of the recording apparatus to be focused on the lenticular recording material via a lenticular sheet. The original images are thereby exposed as linear images. 
     Another method of image recording uses scanning exposure which requires comparatively simple optics and yet has great flexibility in adapting to various image-processing operations and to alterations in the specifications of the lenticular sheet. 
     In the article entitled “Development of Motion Image Printer”, by H. Akahori et al., IS&amp;T 50th Annual Conference Proceedings, page 305, there is a disclosure of a printer for printing stereoscopic images using a thermal head and thermal dye transfer in registration with the lenticular material. The receiver sheet must be heated to achieve the necessary stability for registration of the images with the lenticular material. The resolution is six images on 100 DPI lenticular material with a 300 DPI thermal head. However, there is a problem with this method in that low resolution images are obtained, since heat transferred from the resistive head “spreads” through the support during printing. 
     EP 0 596 629A2 and EP 0 659 026A2 disclose a method and apparatus for directly printing on lenticular supports using lasers. This method generates an image in contact with the lenticular material. There is a problem with this method, however, in that the dyes can continue to migrate after transfer, resulting in unacceptable image ghosting (adjacent views bleeding through). 
     An object of this invention is to generate high resolution lenticular images which are resistant to thermal dye diffusion. It is another object of this invention to generate images efficiently with high abrasion resistance. 
     SUMMARY OF THE INVENTION 
     These and other objects are achieved in accordance with this invention which relates to a diffusion resistant lenticular element comprising a first support having thereon a lenticular array, the element having thereon a protective element comprising a second support having thereon an adhesive layer of an acidic polymer having a Tg less than about 80° C., the adhesive layer of the protective element being on the side of the first support which does not contain the lenticular array, the adhesive layer containing a laser-induced, cationic dye image. 
     Another embodiment of the invention relates to a process of forming a diffusion resistant lenticular element comprising: 
     a) contacting at least one dye-donor element comprising a support having thereon a dye layer comprising an image dye in a binder having an infrared-absorbing material associated therewith, the image dye comprising a nonionic dye capable of being converted to a cationic dye by means of an acid, with a lenticular element comprising a first support having thereon a lenticular array on the opposite side thereof; 
     b) imagewise-heating the dye-donor element by means of a laser; 
     c) transferring a dye image to the first support of the lenticular element; 
     d) contacting the dye image with a protective element comprising a second support having thereon an adhesive layer of an acidic polymer having a Tg less than about 80° C., the adhesive layer of the protective element being in contact with the side of the first support which contains the dye image; and 
     e) heating the element to cause the nonionic dye to convert to a cationic dye which is mordanted in the adhesive layer and to cause the adhesive layer to adhere the protective element to the lenticular element. 
     By use of the invention, a high resolution lenticular image is generated efficiently which is resistant to thermal dye diffusion and has a high abrasion resistance. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As noted above, the lenticular element has thereon a protective element, the support of which may be either transparent or reflective. In addition, the support may have thereon a separate reflective layer. Examples of such supports include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; cellulose esters such as cellulose acetate; fluorine polymers such as poly(vinylidene fluoride) or poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, polypropylene or methylpentene polymers; and polyimides such as polyimide-amides and polyether-imides. The support generally has a thickness of from about 5 to about 200 μm. 
     As noted above, dyes useful in the invention are nonionic dyes capable of being converted to cationic dyes by means of an acid. A cationic dye diffuses much less readily than a nonionic dye due to electrostatic forces retarding movement. An example of an nonionic dye which converts to a cationic dye in the presence of an acid is the following (Since the chromophore is involved in the reaction, there is a color change indicating the state of the dye molecule):                    
     Examples of such dyes which may be used in the invention are of many classes. For example, the dye may be a deprotonated cationic dye which is capable of being reprotonated to a cationic dye having an N—H group which is part of a conjugated system. Additional examples of such dyes are disclosed in U.S. Pat. No. 5,523,274, the disclosure of which is hereby incorporated by reference, and include the following:                    
     Another class of dyes useful in the invention is a pendant basic dye capable of being protonated to a cationic dye, as disclosed in U.S. Pat. Nos. 5,512,532, 5,744,422, and 5,804,531, the disclosures of which are hereby incorporated by reference. An example of a pendant basic dye which converts to a cationic dye in the presence of an acid is the following:                    
     Additional examples of such dyes include the following:                    
     Another class of dyes useful in the invention is a lactone leuco dye capable of being protonated to a cationic dye, as disclosed in U.S. Pat. No. 5,830,823 and copending U.S. Ser. No. 08/996,388, the disclosures of which are hereby incorporated by reference. An example of a lactone leuco dye which converts to a cationic dye in the presence of an acid is the following:                    
     An additional example of such dyes includes the following:                    
     Another class of dyes useful in the invention is a carbinol dye capable of being protonated to a cationic dye, as disclosed in U.S. Pat. No. 5,804,531, the disclosure of which is hereby incorporated by reference. An example of a carbinol dye which converts to a cationic dye in the presence of an acid is the following:                    
     As noted above, the adhesive layer of an acidic polymer used in the invention has a Tg less than about 80° C. If the Tg is greater than 80° C., then low or very little adhesion of the lenticular element to the protective element is obtained. Examples of acidic adhesive polymers useful in the invention include condensation polymers such as polyesters, polyurethanes, polycarbonates, etc.; addition polymers such as polystyrenes, vinyl polymers, etc.; and copolymers of more than one type of monomer covalently linked together, provided such polymeric material contains acid groups as part of the polymer chain. In a preferred embodiment of the invention, the acidic adhesive comprises an acrylic polymer, an olefinic polymer, an olefin acrylic copolymer, a sulfopolyester or a styrenic polymer. The adhesive layer can be used at a coverage of from about 0.1 to about 10 g/m 2 . 
     The dyes of the dye-donor element used in the invention can optionally be dispersed in a polymeric binder such as a cellulose derivative, e.g., cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate or any of the materials described in U.S. Pat. No. 4,700,207; polyvinyl butyrate; copolymers of maleic anhydride with vinyl ethers such as methyl vinyl ether; polycyanoacrylates; a polycarbonate; poly(vinyl acetate); poly(styrene-co-acrylonitrile); a polysulfone or a poly(phenylene oxide), gelatin, etc. The binder may be used at a coverage of from about 0.1 to about 5 g/m 2 . 
     Any material can be used as the support for the lenticular array of the invention provided it is dimensionally stable. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; cellulose esters such as cellulose acetate; fluorine polymers such as poly(vinylidene fluoride) or poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, polypropylene or methylpentene polymers; and polyimides such as polyimide-amides and polyether-imides. The support generally has a thickness of from about 50 to about 5000 μm. While the lenticular array may be provided on a separate support, generally the support and the array are in one integral element. 
     Infrared-absorbing materials which may be used in the invention include carbon black, cyanine infrared-absorbing dyes as described in U.S. Pat. No. 4,973,572, or other materials as described in the following U.S. Pat. Nos. 4,948,777; 4,950,640; 4,950,639; 4,948,776; 4,948,778; 4,942,141; 4,952,552; 5,036,040; and 4,912,083, the disclosures of which are hereby incorporated by reference. 
     A laser is used to transfer dye from the dye-donor element used in the invention. It is preferred to use a diode laser since it offers substantial advantages in terms of its small size, low cost, stability, reliability, ruggedness, and ease of modulation. 
     Lasers which can be used to transfer dye from dye-donors employed in the invention are available commercially. There can be employed, for example, Laser Model SDL-2420-H2 from Spectra Diode Labs, or Laser Model SLD 304 V/W from Sony Corp. 
     A thermal printer which uses the laser described above to form an image on a thermal print medium is described and claimed in U.S. Pat. No. 5,268,708, the disclosure of which is hereby incorporated by reference. 
     Spacer beads may be employed in a separate layer over the dye layer of the dye-donor element in the above-described laser process in order to separate the donor from the receiver during dye transfer, thereby increasing the uniformity and density of the transferred image. That invention is more fully described in U.S. Pat. No. 4,772,582, the disclosure of which is hereby incorporated by reference Alternatively, spacer beads may be employed in the receiving layer of the receiver as described in U.S. Pat. No. 4,876,235, the disclosure of which is hereby incorporated by reference. The spacer beads may be coated with a polymeric binder if desired. 
     As noted above, in the process of the invention, the lenticular element with the transferred dye is heated to cause the nonionic dye to convert to a cationic dye which is mordanted in the adhesive layer and to cause the adhesive layer to adhere the protective element to the lenticular element. This heating may be accomplished, for example by passing the element between a pair of heated rollers. Other methods of heating could also be used such as using a heated platen, use of pressure and heat, external heating, etc. 
    
    
     The following examples are provided to illustrate the invention. 
     EXAMPLES 
     Example 1 
     Dye Donor Element 
     The donor element was coated with a laydown of 0.22 g/m 2  carbon black, Cabot Black Pearls 700® (Cabot Corp.), 0.54 g/m 2  polyvinylbutyral, (Butvar® 76, Monsanto Co.), 0.01 g/m 2  Fluorad FC 431® surfactant (3M Co.), 0.02 g/m 2  crosslinked polydivinylbenzene beads, 5.4 μm, and 0.54 g/m 2  of Dye 1 (illustrated above) from methyl isobutyl ketone on a 104 μm thick poly(ethylene terephthalate) support. 
     Protective Element 1 of the Invention 
     A 36 μm thick poly(ethylene terephthalate) support was coated with an aqueous coating of 3.22 g/m 2  of the ammonia salt of poly{isophthalic acid-co- 5- sulfoisophthalic acid (90:10 molar ratio)-diethylene glycol (100 molar ratio)}, MW=20,000 (ammonium salt of AQ29D, Eastman Chemical Co.) and 0.02 g/m 2  Dispex N-40® surfactant (Ciba Specialty Chemicals). 
     Protective Element 2 of the Invention 
     A 104 μm thick poly(ethylene terephthalate) support was coated with ethylene/acrylic acid (15% acrylic acid) copolymer (3.24 g/m 2 ) (Scientific Polymer Products Inc.) from tetrahydrofuran. 
     Control 1 Protective Element 
     A 104 μm thick poly(ethylene terephthalate) support was coated with poly(vinyl butyral), (Butvar® 76, Monsanto Co.), (3.24 g/m 2 ) from acetone. This adhesive material has a low Tg, but is not an acidic polymer. 
     Control 2 Protective Element 
     A 104 μm thick poly(ethylene terephthalate) support was coated with an aqueous coating of acrylic acid (3.24 g/m 2 ). This material is an acidic polymer, but has a high Tg. 
     Lenticular Array 
     A polycarbonate lenticular material which consisted of cylindrical lenses on one face and a flat rear face was used. This lenticular material had a pitch of 1.973 lines/mm and a thickness of 1.27 mm. The lens curvature was such that focus was on the rear of the lenticular material. 
     Printing 
     A dye-donor element was placed dye side to flat rear side of the lenticular array and vacuum was applied to hold the donor to the array. Printing was accomplished using an SDL 23-S9781 1 watt c-mount laser diode (Spectra Diode Labs, Inc.). Approximately 700 mw was delivered to the element in a spot approximately 13 μm by 80 μm using the technique of beam folding as disclosed in copending application U.S. Ser. No. 09/175,735 of Kessler, filed Oct. 20, 1998. Scanning of the spot was accomplished using a galvanometer with the beam oriented with the long axis parallel to the scan direction as described in the copending application U.S. Ser. No. 09/128,077, of Kessler et al., filed Aug. 3, 1998. Dwell time was approximately 9 microseconds. 
     A target image was written onto the back of the donor causing the donor dye to be transferred to the lenticular material. The resulting image was magenta. 
     Mordanting of the dyes and lamination of the protective support with mordanting layer was accomplished by passing the card through a laminator with the protective support in contact with the flat side of the lenticular array. The lamination was conducted with a feed rate of 0.36 cm/sec at a temperature of 133° C. The laminator was a modified GMP Co. LTD (Kyoungki-Do, Korea) laminator model Passport-175LSI. The modification was to adjust the gap thickness to accommodate the 1270 μm lenticular material and the lower roller heating was disabled. 
     The adhesion was evaluated by attempting to separate the lenticular element from the protective element and is listed in the Table as either Yes or No. 
     Mordanting was indicated in the Table by noting whether or not there was a color change from magenta to cyan (see above). The following results were obtained: 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE  
               
               
                   
                   
               
               
                   
                   
                 Polymer Tg 
                   
                   
               
               
                   
                 Protective Element 
                 (° C.) 
                 Adhesion 
                 Mordanted 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Invention 1 
                 20 
                 Yes 
                 Yes 
               
               
                   
                 Invention 2 
                 9 
                 Yes 
                 Yes 
               
               
                   
                 Control 1 
                 67 
                 Yes 
                 No 
               
               
                   
                 Control 2 
                 106 
                 No 
                 Yes 
               
               
                   
                   
               
            
           
         
       
     
     The above results show that while Control 1 had good adhesion, it did not function as a mordant, and that while Control 2 functioned as a mordant, it did not have good adhesion. However, the acidic adhesive materials used in the invention had both good adhesion as well as good mordanting. 
     The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.