Patent Publication Number: US-8114811-B2

Title: Printable adhesive label

Description:
TECHNICAL FIELD 
     A label, method of printing and method of manufacture described herein relates generally to improvements to printable labels. More particularly, the invention relates to improvement to labels used in harsh environments. 
     BACKGROUND 
     A label used in a hazardous environment can come into contact with harsh chemicals, abrasive materials and other elements that will degrade the readability of the label. Labels uses in such hazardous conditions typically have a protective layer applied to the exterior surface of the label to protect the label from the hazardous environment. Currently, labels used in hazardous environments are printed using standard printing processes (i.e., thermal, ink jet or laser) and then in a separate step, they are laminated with a transparent layer to protect the labels from hazardous conditions. The lamination step, while effective, is time consuming and adds expense to the label. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following description taken in conjunction with the accompanying drawings in which like reference characters designate the same or similar parts throughout the several views and wherein: 
         FIG. 1  is a front view of a printable multilayer sheet in accordance with an exemplary embodiment of a label used in a hazardous environment; 
         FIG. 2  is a cross-sectional view of a portion of the printable multilayer sheet of  FIG. 1 ; and 
         FIG. 3  is a high-level block diagram of a thermal printer printing on a printable multilayer sheet. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous details are set forth to provide an understanding of the claimed invention. However, it will be understood by those skilled in the art that the claimed invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
     Illustrated in  FIG. 1  is a front view of label  10 . Label  10  is made from a portion of a printable multilayer sheet designed for use in hazardous environments. Information, including text and/or graphics, can be printed on the label  10  and the information is visible through the front surface of the label  10 . In addition, the label  10  can be applied to numerous surfaces using a pressure sensitive adhesive that is part of the label  10 . In this embodiment, basic Material Safety Data Sheet (MSDS) information for a hazardous chemical is printed on label  10 . The information printed on label  10  relates to hydrochloric acid (HCL) and the label  10  can be attached to any surface (i.e., the surface of a container of HCL or a storage area where a container of HCL is stored). 
       FIG. 2  illustrates a cross-section of a portion of label  10 . The top layer is a transparent protective laminate  20  that is able to withstand harsh chemical and abrasive environments. In some embodiments, the protective laminate also blocks ultra-violet light which can degrade the readability of the information printed on the label  10 . Illustrative examples of suitable materials for the protective laminate include polyester, polypropylene and cellulose acetate films. However, any clear or nearly clear material that protects the underling label is a candidate for use as a protective laminate  20 . This embodiment utilizes thermal printing techniques therefore good heat transfer through protective laminate  20  is required. This is achieved by using a protective laminate  20  that is not only clear but also thin with acceptable thermal conductive. A polyester protective laminate  20  having a thickness in the range of 1 to 2 mils is suitable. However, in other embodiments, using a protective laminate  20  with different thermal characteristics or changing the thermal characteristics of the printing device or the printing speed allows different thicknesses of protective laminates  20  to be used. In some cases, a thicker protective laminate  20  is required to properly protect the label from a harsh environment so other parameters must be adjusted to compensate for the thicker protective laminate  20 . 
     Continuing with  FIG. 2 , a thermosensitive image-forming adhesive layer  25  is permanently bonded or laminated to the bottom surface of the protective laminate  20 . The thermosensitive image-forming adhesive layer  25  is a composition of a pressure sensitive adhesive compound and a thermosensitive image compound. The pressure sensitive adhesive provides the adhesive force to attach the label  10  to a surface after pressure is applied to the top surface of the label  10 . The thermosensitive image compound changes color when exposed to heat and thus creates a readable label  10 . A standard thermosensitive image compound is comprised of thermally active dyes, reactants and fillers. However, when combined with the pressure sensitive adhesive, the adhesive replaces all or part of the fillers used in the standard thermosensitive compound. An illustrative example of a formula for the composition of the thermosensitive image-forming adhesive layer  25  is 15 parts dye, 20 parts reactant and 65 parts adhesive compound. However, it should be noted that this formula will change based on the characteristics of the components uses in the compounds. 
       FIG. 2  also shows a release layer  30  that is positioned over the thermosensitive image-forming adhesive layer  25 . It is releasably bonded to the thermosensitive image-forming adhesive layer  25 . The release layer  30  may have a release agent, such as silicone, coated there between to permit removal from the label  10  by being peeled the release layer  30  away from the thermosensitive image-forming adhesive layer  25 . 
     Referring now to  FIG. 3 , there is presented a high-level block diagram of a thermal printer  300  comprising a print head assembly  350  and a printable multilayer sheet  10 . The thermal print head assembly  350  is comprised of two opposed feed rollers  310 ,  320  that pull the printable multilayer sheet  10  through the thermal print head assembly  350 . The assembly  350  also is comprised of a thermal print head  340  and an opposing platen  330  where the printable multilayer sheet  10  is pulled between the two by the feed rollers  310 ,  320 . The printable multilayer sheet  10  is feed through the thermal print head assembly  350  configured so that the transparent protective layer  20  is pressed against the print head  340 . 
     To print a pattern containing text, graphic or an image on the printable multilayer sheet  10 , a section of the printable multilayer sheet  10  is feed through the thermal print head assembly  350 . Based on the desired pattern, the print head  340  selectively generates heat in selected areas on the surface of the transparent protective layer  20 . The heat is conducted through the transparent protective layer  20  to the thermosensitive image-forming adhesive layer  25  causing thermally active dye in the heated area of the thermosensitive image-forming adhesive layer  25  to change color. This process is repeated until the desired pattern is imaged on the surface of the thermosensitive image-forming adhesive layer  25 . Since the transparent protective layer  20  is transparent, it permits the pattern to be viewed while protecting the thermosensitive image-forming adhesive layer  25  from adverse conditions that would negatively impact the readability of the pattern. The printable multilayer sheet  10  can be cut or separated into smaller labels, each containing a pattern. Printable multilayer sheets  10  can be manufactured in different sizes and length depending on the type printer being used or the desired label. 
     Once a label  10  has been printed, it can be attached to a desired surface by peeling the release liner  30  off the bottom surface of the thermosensitive image-forming adhesive layer  25 , placing the bottom surface of the thermosensitive image-forming adhesive layer  25  against the desired surface and applying temporary pressure to the front surface  20  of the label  10 . 
     The present embodiment uses thermal printing techniques to illustrate the invention however, other embodiments are based on different printing techniques such as light diode technology. Light diode technology uses light to activate a component, similar to a thermal dye. A light receptive dye is placed in the adhesive layer in place of the thermal dye. Light from a diode passing through the clear protective layer activates the light receptive dye causing it to change color similar to heat causing the thermal dye to change color. 
     In another embodiment, the release layer  30  and thermosensitive image-forming adhesive layer  25  are sufficiently thin for a printer to print through the release layer  30  to the thermosensitive image-forming adhesive layer  25  causing the thermally active dyes to change color and be visible through the transparent protective layer  20 . The thermosensitive image-forming adhesive layer  25  must be sufficiently thin so that the heat causes the thermally active dyes to completely change color through the entire thickness of the thermosensitive image-forming adhesive layer  25 . Otherwise, the pattern will not visible from the front side of the label  10 . In this embodiment, a mirror image of the pattern to be viewed is printed through the release layer  30  (backside of the label  10 ) and the pattern is properly viewed through the transparent protective layer  20  (front side of the label  10 ). 
     While the invention is disclosed in the context of thermal printing on a printable multilayer sheet or label, it will be recognized that a wide variety of implementations may be employed by a person of ordinary skill in the art consistent with the above discussion and the claims, which follow below.