Abstract:
Disclosed herein are imaging materials and methods of making imaging materials. The imaging systems disclosed herein may include a reflective layer disposed proximate to and beneath a laser imageable layer on an optical disc.

Description:
BACKGROUND  
       [0001]     Materials that produce color change upon stimulation with energy such as laser radiation may have possible applications in imaging. For example, such materials may be useful in allowing the laser labeling and imaging of optical discs such as DVDs, and blue laser discs. One method of performing laser labeling or imaging of an optical disc involves layering onto the disc an imaging composition that changes color upon the application of laser light. However, some of the laser radiation may not be absorbed by the imaging composition and may pass into the other layers of the disc. Thus, because of this wasted energy, imaging may take longer than expected. Additionally, the radiation may reflect off of internal layers of the optical disc and be absorbed by the laser labeling layer in undesirable locations, possibly causing fuzzy images. Because of the limited amount of energy available for the imaging, the desire to perform imaging quickly, and the desire to produce sharp images it may be advantageous for the laser imaging system to efficiently use the laser energy available for labeling, while minimizing or decreasing the laser energy that is wasted or not used to produce the color change or causes color change in undesirable locations. Such an efficient system may increase the shelf life and/or sharpness of the images created on the optical disc.  
       BRIEF SUMMARY  
       [0002]     Disclosed herein are imaging materials and methods of making imaging materials. The imaging systems disclosed herein may include a reflective layer disposed proximate to and below a laser imageable layer.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]     For a detailed description of exemplary embodiments of the invention, reference will now be made to the accompanying drawings in which:  
         [0004]      FIG. 1  shows a schematic cross-sectional drawing of an optical disc in accordance with embodiments of the present invention; and  
         [0005]      FIG. 2  shows a schematic cross-sectional drawing of an optical disc in accordance with embodiments of the present invention. 
     
    
     NOTATION AND NOMENCLATURE  
       [0006]     Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “optical disc” is defined to include any optical disc (e.g., DVD or blue laser disc) having a data recording side upon which data is recorded by a laser having a wavelength of 750 nm or less. By way of example only, data is recorded onto a DVD by a laser having a wavelength of about 650 nm and data is recorded onto a blue laser disc by a laser having a wavelength of between about 400 nm and about 500 nm.  
         [0007]     Additionally, spatially relative terms (e.g., lower, upper, below, above) are used herein for convenience. One of ordinary skill in the art will recognize that these terms are used merely for convenience and clarity and that the scope of the present invention will encompass any spatial configuration of the optical discs (by way of example only, upside-down, right-side-up, vertical, horizontal). By way of example only, when it is stated that one layer is “below” another in an optical disc, it is intended that the first layer is below the second layer when the optical disc is oriented with the label side pointing up. If the optical disc is turned data side up, the relative orientation of the layers has not changed.  
       DETAILED DESCRIPTION  
       [0008]     The following discussion is directed to various embodiments of the invention. Although one or more of these embodiments may be preferred, the embodiments disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that embodiment.  
         [0009]     Referring now to  FIG. 1 , there is shown an optical disc  200  comprising several layers: lower polycarbonate  260 , data layer  250 , data reflective layer  240 , upper polycarbonate layer  230 , imaging reflective layer  290 , protective layer  270 , and laser labeling layer  220 .  
         [0010]     Optical disc  200  (e.g., a recordable DVD) comprises two polycarbonate layers (lower and upper)  260  and  230 . In some embodiments, polycarbonate layers  260  and  230  are about 0.6 mm thick. Sandwiched between polycarbonate layers  260  and  230  is a data layer  250 , backed by data reflective layer  240 . To record data onto disc  200 , a laser is shown through lower polycarbonate layer  260  onto data layer  250 . The laser causes changes in data layer  240  which corresponds to the data being recorded.  
         [0011]     On the labeling side of optical disc  200  is deposited laser labeling layer  220  which comprises a laser imageable composition which changes color upon the application of laser energy. By way of example only, the composition may comprise an antenna for absorbing laser energy, a leuco dye, an activator, and a matrix such as, by way of example only, described in United States Patent Application Publication No. 2004/0146812. The laser labeling layer  220  may be about 0.5 μm to about 14μ thick and be deposited, for example, by sputter coating, silk screening, spin coating, offset printing, flexographic printing, pad printing, or any type of printing or deposition process which may deposit a substantially uniform layer. In some embodiments, the laser labeling layer  220  may be about 7 μm to about 8 μm thick. In other embodiments, the laser labeling layer  220  may be about 4 μm to about 7 μm and in yet other embodiments, the laser labeling layer  220  may be about 1 μm to about 4 μm thick.  
         [0012]     Beneath laser labeling layer  220  is imaging reflective layer  290 . In some embodiments, imaging reflective layer  290  may be closer than about 50 μm below laser labeling layer  220  and may be greater than about 40 nm thick. In still other embodiments, imaging reflective layer  290  may be about 30 nm to about 200 nm thick. It is not necessary that image reflective layer  290  be immediately adjacent or with only protective layer  270  between imaging reflective layer  290  and laser labeling layer  220 . In some embodiments, imaging reflective layer  290  may between about 0.5 μm to about 600 μm below laser labeling layer  220 . In still other embodiments, imaging reflective layer  290  may be between about 0.5 μm and about 200 μm, between about 0.5 μm and about 50 μm, or between about 0.5 μm and about 10 μm below laser labeling layer  220 . However, as imaging reflective layer  290  moves farther away from laser labeling layer  220 , the effectiveness of imaging reflective layer  290  may be decreased.  
         [0013]     Imaging reflective layer  290  may comprise any reflective coating capable of reflecting a substantial amount of the laser light  280  which is not absorbed by laser imageable layer  220  back up into laser imageable layer  220  where it has a second chance to cause a color change in laser imageable layer  220 . By way of example only, imaging reflective layer  290  may comprise sputter coated or vacuum deposited Ag, Al, Au, Al/Cu alloy, Ag/Al alloy, metallic Si, Cu, brass, Zn, or any other metal, alloy, or composition which reflects laser light. Vacuum deposition may comprise using resistive heating to vaporize the metal to coat a substrate (e.g., an optical disc). Sputter coating may comprise creating a voltage difference between the substrate and the metal to create a plasma. In some embodiments, imaging reflective layer  290  is covered by protective layer  270 . Protective layer  270  may be a lacquer which protects imaging reflective layer  270  from air and oxidation. By way of example only, acceptable lacquers may include spin coated UV curable acrylates such as Daicure Clear SD2200 or SD2407 (available from DIC Imaging Products U.S.A., Inc., Oak Creek, Wis.) and may be less than about 10 μm thick. In other embodiments, protective layer  270  may be about 4 μm to about 8 μm thick. In some embodiments the laser labeling layer may protect the reflective layer from oxidation and a separate protective layer may not be present.  
         [0014]     In operation, laser radiation  280  is directed imagewise to laser labeling layer  220  where it makes a mark. At least a portion of the laser radiation  280  that is not initially absorbed by laser labeling layer  220  reflects back up to laser labeling layer  220  and some of the reflected laser radiation is then absorbed to enhance the mark. Laser radiation  280  may be any laser radiation which makes a mark on laser labeling layer  220 . In some embodiments, the laser radiation may be of the same wavelength as the laser which writes data on the data layer  250  of the optical disc  200 . In some embodiments, the laser radiation may have a wavelength of about 780 nm, about 650 nm, or about 400 nm-500 nm.  
         [0015]     Referring now to  FIG. 2 , there is shown an optical disc  300  comprising several layers: lower polycarbonate layer  360 , data layer  350 , data reflective layer  340 , upper polycarbonate layer  330 , imaging reflective layer  370 , and laser labeling layer  320 .  
         [0016]     In the embodiments of  FIG. 2 , as in the embodiments of  FIG. 1 , optical disc  300  (e.g., a recordable DVD) comprises two polycarbonate layers (lower and upper)  360  and  330 . In some embodiments, polycarbonate layers  360  and  330  are about 0.6 mm thick. Sandwiched between polycarbonate layers  360  and  330  is a data layer  350 , backed by data reflective layer  340 . To record data onto disc  300 , a laser is shown through lower polycarbonate layer  360  onto data layer  350 . The laser causes changes in data layer  340  which corresponds to the data being recorded.  
         [0017]     On the labeling side of optical disc  300  is deposited laser labeling layer  320  which comprises a laser imageable composition which changes color upon the application of laser energy. By way of example only, the composition may comprise an antenna for absorbing laser energy, a leuco dye, an activator, and a matrix such as, by way of example only, described in United States Patent Application Publication No. 2004/0146812. Laser labeling layer  320  may be about 7 μm to about 8 μm thick and be deposited, for example, by sputter coating, silk screening, or spin coating.  
         [0018]     Beneath laser labeling layer  320  is imaging reflective layer  370 . In some embodiments, imaging reflective layer  370  may be less than 50 μm below laser labeling layer  320  and may be greater than about 40 nm thick. In still other embodiments, imaging reflective layer  370  may be about 70 nm thick. It is not necessary that image reflective layer  370  be immediately adjacent to laser labeling layer  320 . In some embodiments, imaging reflective layer may be between about 0.5 μm to about 600 μm below laser labeling layer  320 . In still other embodiments, imaging reflective layer  290  may be between about 0.5 μm and about 200 μm, between about 0.5 μm and about 50 μm, or between about 0.5 μm and about 10 μm below laser labeling layer  220 . However, as imaging reflective layer  370  moves farther away from laser labeling layer  320 , the effectiveness of imaging reflective layer  370  may be decreased.  
         [0019]     Imaging reflective layer  370  may comprise a lacquer containing suspended metal flakes which reflect light that is not absorbed by laser imageable layer  320  back up into laser imageable layer  320  where it has a second chance to cause a color change in laser imageable layer  320 . By way of example only, imaging reflective layer  370  may comprise a paste/lacquer containing aluminum flakes (called “silver paste”); copper flakes (called “gold paste”); brass flakes (called “bronze paste”); or Ag, Cu, or Zn suspended in a paste or lacquer. In some embodiments, the “silver paste” may be Eckart SP8700 UV-curable lacquer (available from Eckart America L.P., Louisville, Ky.). In other embodiments, imaging reflective layer  370  may comprise solvent-based undercoats such as Eckart SX9102 (metal flakes suspended in propylene glycol and butoxyl ethanol).  
         [0020]     In operation, laser radiation  380  is directed imagewise to laser labeling layer  320  where it makes a mark. At least a portion of the laser radiation  380  that is not initially absorbed by laser labeling layer  320  reflects back up to laser labeling layer  320  and some of the reflected laser radiation is then absorbed to enhance the mark. Laser radiation  380  may be any laser radiation which makes a mark on laser labeling layer  320 . In some embodiments, the laser radiation may be of the same wavelength as the laser which writes data on the data layer  350  of the optical disc  300 . In some embodiments, the laser radiation may have a wavelength of about 780 nm, about 650 nm, or about 400 nm-500 nm.  
       EXAMPLES  
     Example 1  
       [0021]     A 50 nm to 100 nm thick reflective layer of Al was sputter coated onto a DVD. The reflective layer was then spin coated with Daicure SD2200 protective lacquer and cured for 1-3 seconds. An 8 μm laser labeling layer was screen printed over the cured lacquer and reflective layer. After the laser labeling layer was cured, a mark was made using a 38.25 mW/780 nm laser. In measuring shelf life over the course of 48 hours at 30% relative humidity the disc having a reflective layer performed better than marks made on DVDs which did not include a reflective layer. After 48 hours, the optical density of DVD with the Al undercoat had faded about 33% less than the mark on the uncoated DVD.  
       Example 2  
       [0022]     A reflective layer of UV curable Eckart SP8700 “silver paste” was screen printed onto a DVD and cured for 1 to 3 seconds. An 8 μm laser labeling layer was screen printed over the cured lacquer and reflective layer. After the laser labeling layer was cured, a mark was made using a 38.25 mW/780 nm laser. In measuring shelf life over the course of 48 hours at 30% relative humidity the disc having a reflective layer performed better than marks made on DVDs which did not include a reflective layer. After 48 hours, the optical density of DVD with the silver paste undercoat had faded about 10% less than the mark on the uncoated DVD.  
         [0023]     The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.