Patent Publication Number: US-6210054-B1

Title: Method for applying printer registration marks to linerless label stock

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to printer registration marks, and more specifically to a method for applying printer registration marks to linerless label stock. 
     2. Description of Related Art 
     Linerless media and labels are becoming increasingly popular in the label producing industry because of the many advantages over their linered counterparts. A linerless label stock is typically a continuous roll of direct thermal label or tag stock (e.g., paper, film, or combination) having a pressure sensitive (i.e., self-stick) adhesive on the backside without a silicone coated release liner. Linerless label stock is advantageous over traditional linered media since there is no release liner to dispose of, and as a result, a greater amount of media may be included in a same size roll as that of linered media. In view of the growing popularity of linerless media, methods to improve the production and throughput rates of linerless labels have become essential. 
     The linerless label stock is transported through a printing system including a printer such as a thermal transfer or direct thermal printer. In a thermal transfer printer, the linerless label stock is transferred through the print region of the printer along with a thermal transfer ribbon. The thermal transfer ribbon is impregnated with a thermally sensitive chemical that reacts in the presence of heat applied by print elements of the print region. The chemical is then transferred onto the linerless label stock in the form of printed indicia. In a direct thermal printer, the thermally sensitive chemical is impregnated directly into the linerless label stock, thereby eliminating the need for a separate thermal transfer ribbon. Both types of printing are collectively referred to herein as thermal printing. Under either method of thermal printing, the thermal printer creates the printed indicia by selectively controlling individual ones of the print elements. The printed indicia may take the form of individual labels provided on designated sections of the linerless label stock with a gap defined between adjacent ones of the labels. 
     Unlike linered labels that are pre-cut to size, the individual labels of linerless label stock must be separated after printing. Some printers for linerless media use an automatic rotary or guillotine type cutter knife mechanism to separate the labels from the continuous label stock. These cutter mechanisms can be costly and difficult to keep clean of adhesive residue. Other printers use a manual tear bar, which is a stationary blade that is used to cut the label stock by manually pulling the media across the tear bar. These tear bars do not always give a consistently clean tear across the label stock. Also, the tear bar may have a serrated knife that can pose a risk of serious injury to users of the printer. Thus, a preferred method to produce individual labels is to pre-cut a perforation line into the label stock. The perforation line allows for easy, clean separation of individual labels or tags. The perforation lines must be recognized by the printer so that the printed indicia can be aligned to the predetermined labels defined by the perforation lines without extending over the perforations lines. Thus, it is known to include printer registration marks onto a roll of linerless label stock disposed in correspondence with the perforation lines. The registration marks may be detected by optical sensors included within the printer used to print indicia upon the linerless label stock. 
     A known way to apply registration marks to linerless media is to print the marks onto the back of the label stock before the adhesive is applied to the label stock. Linerless media manufacturers typically apply the adhesive coating to large sheets of the media that are later cut down to the desired width dimensions of the linerless label stock and wound onto rolls or spindles. The adhesive coating equipment is generally large and expensive, and it is thus impractical for small scale label manufactures or printer end-users to perform. Another drawback of having registration marks pre-printed on the linerless media prior to applying the adhesive layer is that it limits the eventual printing of labels to the particular dimensions determined by the registration marks. An alternative method is to place registration marks on the facing surface of the label stock. This is undesirable because the registration marks have the potential to interfere with the printed indicia, such as barcodes, that are printed onto the labels. Thus, there is a need for a method to apply printer registration marks onto the backs of the linerless labels after the adhesive has been applied. 
     Therefore it is an object of this invention to provide a process for applying printer registration marks to linerless label stock so that the resulting labels can be produced in a fast, efficient manner. It is further an object of this invention to provide an economical process for applying printer registration marks onto linerless label stock. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a web of linerless label stock having a recording layer on a top surface and an adhesive layer on a bottom surface is provided with registration marks printed onto the adhesive layer. The linerless label stock further includes perforation lines in correspondence with the registration marks. The spacing between adjacent ones of the registration marks may be selected to correspond with desired width of the linerless labels. To process the linerless label stock, the web of linerless label stock is first sent through a flexographic printing system where registration marks are applied to the adhesive layer at constant intervals. After the registration marks are applied, the web of label stock passes through a die station that perforates the web in correspondence with the registration marks. The web is then wound up into finished rolls to be placed on a thermal printer. 
     A more complete understanding of the method for applying printer registration marks to linerless label stock will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings that will first be described briefly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged cross-section of linerless media; 
     FIG. 2 is block diagram of a linerless media converting process in accordance with the present invention; and 
     FIGS. 3A-3B are plan views of finished linerless label stock. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention satisfies the need for a process to apply printer registration marks onto linerless media without having to coat the media with adhesive after applying the marks. This is accomplished by applying the printer registration marks over the already present adhesive layer on the linerless label stock. In the detailed description that follows, like element numerals are used to describe like elements illustrated in one or more of the figures. 
     Referring first to FIG. 1, a cross-section of linerless label stock  10  in accordance with the present invention is shown. The linerless label stock  10  has two layers including an adhesive layer  14  and a recording layer  12 . As described above, the adhesive layer  14  is applied by adhesive coating equipment onto large sheets of the recording layer  12 . The recording layer  12  provides a surface onto which indicia may be printed, such as alphanumeric text, graphics, symbols, and barcodes. The top surface of the recording layer  12  may further be coated with a release material so that the adhesive layer  14  will not form a permanent bond to the recording layer  12  when the linerless label stock  10  is wound onto rolls. In the preferred embodiment, Fasson 10118 label stock is used. The linerless label stock  10  further includes registration marks  16  provided on the adhesive layer  14 . It should be appreciated that the side view of the linerless label stock  10  is not necessarily drawn to scale, but rather the dimensions of the registration marks  16  are distorted for ease of explanation of the present invention. 
     FIG. 2 shows a first embodiment of the process for applying registration marks, wherein an assembly  20  is set up for the preparation of the linerless label stock  10 . The initial web of linerless label stock  22 , including a recording layer  12  and an adhesive layer  14 , is sent through a sensor marking station  24  where the printer registration mark  16  is applied to the adhesive backside  14  of the label stock. The spacing between adjacent printer registration marks is selected to correspond with a desired size of the linerless labels that are ultimately produced. 
     The sensor marking station  24  may comprise a flexographic press, such as a Mark Andy 830 flexographic press. The label stock  10  is fed into the press such that the adhesive layer  14  is facing away from the central impression cylinder and die anvil. The idler and nip pressure rollers on the press are wrapped with silicone tape that can come into direct contact with the adhesive layer  14  without sticking. The ink used for this application is a water based black pigment system, preferably Wagers 20708 Eyemark Black. The optical density (OD) of the registration mark  16  is typically recommended to be no less than 1.2 OD to be compatible with the printer&#39;s reflective sensor. The size and location requirements of the registration mark  16  will depend on the specific printer model or other application method in addition to 10 sensor location. It should be appreciated that other methods of applying the registration marks could also be used, including offset, rotogravure, hot stamp, ink jet, or silk screen printing. 
     After the registration mark  16  has been applied to the label stock  10 , it is passed through a die station  26  which perforates the media in correspondence with each registration mark  16 . The perforation lines are cut across the width of the label stock and are formed by a perforating blade. The perforated label stock with registration marks  16  is then wound onto a finished roll  28  where it is stored for use on a printer such as a thermal printer. It should be appreciated that the perforation lines  18  may overlap with the registration marks  16  (as shown in FIG.  3 A), or the perforation lines  18  may be offset from the registration marks  16  by a predetermined distance (as shown in FIG.  3 B). 
     In the preferred embodiment, label stock 1.5 inches wide is used and a registration mark  16  is placed every 1.5 inches along the lengthwise dimension of the label stock. The minimum length of the registration mark  16 , for use with the preferred printer, is approximately 0.2 inches long in the machine direction (i.e., feed direction) and approximately 0.4 inches wide. It should be appreciated that the width of the registration mark  16  could span the entire label stock (e.g., 1.5 inches in the preferred embodiment); however, it is preferred to use the minimum width because it does not cover as much adhesive. This is important because the ink, when printed directly on the pressure sensitive adhesive, causes the loss of a significant amount of tack, creating a “dry edge” at the leading and trailing edges of a label which could cause adhesion problems. In addition, a smaller mark is generally preferred because there is less black ink showing through the label which decreases the background reflectance required for high symbol contrast on bar codes. 
     It should be appreciated that the order of the sensor marking station  24  and the die station  26  can also be reversed. This way, the label stock  10  is first perforated by the die station  26  and then the registration mark is applied by the sensor marking station  24 . The label stock is then wound into finish roll  28 . 
     Having thus described a preferred embodiment of a method and apparatus for applying printer registration marks to linerless label stock, it should be apparent to those skilled in the art that certain advantages of the aforementioned system have been achieved. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present invention. The invention is further defined by the following claims.