Abstract:
The present invention teaches apparatus and method for producing an indelible ink imprinted indicia particularly bar code labels and/or other identifying images. An ultraviolet light curable ink image is printed upon a selected substrate and passed through an ultraviolet radiation field wherein the combined infared and ultraviolet energy emitted by the UV light source, affects curing of the imprinted ink thereby producing an imprinted image having superior qualities.

Description:
RELATED APPLICATIONS 
   This application claims priority U.S. Provisional Patent Application Ser. No. 60/409,353 filed on Sep. 9, 2002 and is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a method and apparatus for imprinting an indelible ink image upon a selected substrate. Such indelible inked images are particularly desirable for use in imprinting any informational images, such as a scanable bar code, upon selected substrates that are exposed to unusually harsh environments as in industrial applications. Although the following discussion uses scanable bar codes as an example of the particular usefulness of the present invention, it is to be understood that the method and apparatus taught herein may be used on any suitable substrate and for the imprinting of other useful indicia such a sequential numbering, operating data, warning notices, etc. where long life legibility of the imprinted material is required. 
   Many devices exist for reading bar codes printed on packages and other objects. Bar codes may be printed on retail merchandise for product and price identification at the point of sale, warehouse inventory control, process control, and many other applications. 
   The basic principle employed in bar code reading devices is the detection of contrasting reflected light. A source of illumination such as a low a powered helium neon laser, produces a beam of light which is may be moved across the bar code imprint. Dark areas (bars) absorb laser light, whereas light areas (spaces) reflect light that is detected by a scanner. 
   Optics are typically used to expand the laser beam into a line of laser light and to move the expanded laser beam across the area containing the bar code. Without the use of optics, the laser beam would only appear as a point of light. This process is commonly referred to as “moving-beam scanning.” As the moving beam travels across the area to be scanned for a code, commonly called the scanning zone, the light and dark transition areas are detected and converted to a digital signal known as the code. A typical bar code consists of a defined number of light and dark transition areas having given ratios between the wide and narrow intervals. 
   Thus a scanable bar code consists of a series of solid parallel bars separated by open spaces. The bars and spaces are printed at either a full width or half width. The bars and spaces signify a bit pattern wherein wide spaces or bars are assigned a “one” while narrow spaces and bars are assigned a “zero” (or vice versa). 
   Prior art U.S. Pat. No. 3,728,677 employs a mirrored wheel having a polygonal periphery. Rotation of the mirrored wheel scans a laser beam across two azimuthally spaced mirrors, which deflect the beam downwardly to trace an “X” shaped pattern. 
   It is also known to use prisms and mirrors, or other apparatus, to turn the scanning beam direction of an optical code scanning system. For example see U.S. Pat. Nos. 3,663,800; 3,774,014; 3,800,282; 3,902,047; and 4,064,390. 
   U.S. Pat. No. 3,906,203 teaches scanning a bar code and measuring its interval widths by recording the time required to traverse each interval. The successive interval widths are then multiplied by a constant such as three, five, or eight. By storing and comparing the multiplied widths of successive scans, the scanner can determine whether the latest interval is about the same size as, or much smaller, or larger, than, the prior interval. 
   From the above description of bar codes, their formats and how they function, it is understandable that for a bar code system to function accurately it is desirable that the bar code, printed upon the object being scanned, contain clear undistorted set of dark and light parallel lines or bars. However, in many industrial applications and uses, the imprinted bar codes may be damaged by abrasion, chemicals, solvents and/or heat to the extent that the bar code or portions thereof maybe obliterated or otherwise unreadable. 
   Accordingly there is a need for a method and apparatus for imprinting a durable bar code that will resist the harsh environment of the industrial workplace. 
   SUMMARY OF THE INVENTION 
   In accord with the present invention a method and apparatus is taught by which a durable bar code, and/or any other printed material, may be applied to a suitable substrate material, which may then be adhesively affixed to or fastened by means of an alternative method to any product or article. 
   The Sony Chemical Corporation of America has developed a proprietary radiation-curable printing ink and a method of thermally transferring such ink from an ink ribbon to a selected substrate which is the subject of U.S. Pat. Nos. 6,476,840 and 5,729,272 incorporated herein by reference. 
   By the present invention a substrate having printed thereon a bar code, and/or any other information bearing image, using inks curable by application of UV light is subjected to a combination of IR and UV energy whereby the ink, on the printed image, is cross-linked thereby producing a durable printed image. 
   Using an elliptical reflector the light energy from a UV light source is convergingly directed to a focal point. However by the present invention, the substrate having an image printed thereon, using a UV curable ink, is passed through the focused UV radiation zone above the reflected light&#39;s focal point. Thus the UV curable ink image printed upon the substrate is cured by being exposed to the combination of UV and IR energy emitted from the UV light source. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  presents a pictorial view of apparatus for processing a continuous roll of ink imprinted labels by the present invention. 
       FIG. 2  presents a pictorial view of apparatus for processing individual ink imprinted cut sheet labels by the present invention 
       FIG. 3  presents a schematic depiction of the apparatus illustrated in  FIG. 1 . 
       FIG. 4  presents a schematic depiction of the apparatus illustrated in  FIG. 2 . 
       FIG. 5  presents a schematic depiction of an additional embodiment of the present invention comprising a two step process. 
       FIG. 5A  generally presents a schematic depiction of the two step system as illustrated in  FIG. 5  wherein the UV energy source and its associated elliptical reflector has been replaced by a remote UV energy source and a liquid filled light guide. 
       FIG. 5B  schematically presents the system as illustrated in  FIG. 5A  wherein the thermal transfer printing apparatus and the UV curing apparatus have been combined into one printing unit. 
       FIG. 6  presents an isolated crossectional schematic of the UV ink curing system in accord with the present invention. 
       FIG. 7  presents an isolated crossectional view of an alternate embodiment of the elliptical reflector as illustrated in  FIGS. 3 ,  4 , and  5  comprising a two piece reflector that may be closed about the UV light source. 
       FIG. 8  presents a crossectional view of the two piece reflector illustrated in  FIG. 7  wherein the two halves of the elliptical reflector are rotated to enclose the UV light source. 
       FIG. 9  presents a flow chart of the method practiced by the present invention. 
       FIG. 10  presents an electrical schematic of the power supply for the apparatus illustrated in  FIGS. 1 and 2 . 
       FIG. 11  presents an electrical schematic for the embodiment illustrated in  FIG. 1 . 
       FIG. 12  presents an electrical schematic for the powering the UV energy source. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 and 3 , the apparatus  10  for practicing the present invention comprises a thermal transfer label printing station  12  and an ink curing station  14 . Within printing station  12  a continuous label carrier film  15  having blank, removable labels  16 , or any other printable substrate material, removably affixed thereto, is supplied from feed roll  21 . Print head  22  transfers ink from ink ribbon  18  upon labels  16  in a desired pattern as labels  16  pass thereby. Ink imprinted labels  19  then pass from printing station  12  and into curing station  14  wherein imprinted labels  19  are subjected to a focused, ultraviolet light emitted from an ultraviolet light source  25  focused by elliptical reflector  26 . The combined IR and UV radiation emitted from ultraviolet light source  25  causes curing of the radiation curable thermal ink imprinted image on labels  19  as discussed in more detail below. 
   For a more detailed description of the ink used and the process of thermally transferring an inked image from ribbon  18  to labels  16  the reader is referred to U.S. Pat. Nos. 5,729,272 and 6,476,840 both of which are incorporated herein by reference. 
   As carrier film  15 , having ink imprinted labels  19  thereon, pass through ink curing station  14 , carrier film  15  is supported upon and carried upon endless belt  30  driven by rotating drive rollers  32 A and  32 B by motor means not shown. A vacuum pump  31  is provided to maintain a negative pressure across tables  34 A and  34 B to draw carrier film  15  down upon the tables. As carrier film  15  and ink imprinted labels  19  pass through the radiation zone  32 , carrier film  15  is supported upon fixed tandem tables  34 A and  34 B. Tables  34 A and  34 B act to dimensionally fix the distance between UV light source  26  and ink imprinted labels  19  as they bass through the radiation zone  32 . It is to be noted that ink imprinted labels  19  are oriented to pass above the focal point  35  of the UV light reflected from elliptical reflector  26  as illustrated in  FIG. 3 . 
   After curing of ink imprinted labels  19  within radiation zone  32 , the cured labels  23  are permitted to cool prior to being wrapped upon receiving roll  36 . Depending upon the exact configuration and structure of curing station  14  it may be preferred to provide covered exit and entrance conduits  38 A and  38 B respectively, as UV radiation shields. 
   Although  FIGS. 1 and 3  illustrates a continuous feed label curing system wherein blank labels are feed from supply roll  21 , imprinted with a UV curable ink, subjecting the imprinted UV curable ink to UV energy wherein the UV curable ink is fully cross-linked, and subsequently wound upon a receiving roll  36 ,  FIGS. 2 and 4  presents an alternate embodiment of the process wherein preprinted, cut sheet type labels  19 A may be separately feed into the ink curing station  14 A manually or by any other suitable mechanical means not shown. 
   Ink curing station  14 A generally comprises a porous web type endless belt  30  supported upon support tables  34 A and  34 B (similar as that illustrated in  FIG. 3 ). Ink imprinted labels  19 A are placed upon belt  30 , manually or by any suitable mechanized means, whereupon labels  19 A are passed through radiation zone  32  wherein the UV curable ink is fully cured. The fully cured labels  23 A may then be collected by any suitable means not shown. 
   A further embodiment of the process illustrated in  FIG. 5  may comprise a two step process wherein the ink imprinted labels, as they exit printing unit  12 , are received directly upon a receiving roll  24  as opposed to being directly feed into curing station  14 . The roll of ink imprinted labels  24  may then be feed into an ink curing station  14  at a later time. 
   Illustrated in  FIG. 5A  is a further alternative embodiment of the ink curing station identified as element  50 . In ink curing station  50  the UV light source  25  and its associated elliptical reflector  26 , illustrated in  FIG. 5 , has been replaced by a remote UV energy source  52  having a UV energy delivery medium such as a flexible, liquid filled light guide  54 . UV energy transmitted from remote source  52 , through light guide  54  is received within light discharge unit  62  and thereafter passed through an appropriate focusing lens  56  whereby a focused UV radiation field  58 , similar to radiation field  32  in  FIG. 5 , is directed to focal point  25 . 
   Similarly  FIG. 5B  presents an additional embodiment, of the present invention, wherein the thermal printing apparatus  22  and the UV curing apparatus has been combined into a unitary printing device  60 . Although the embodiment illustrated in  FIG. 5B  illustrates use of a remote UV energy source  52  and its associated light pipe  54 , it is to be understood that the  FIG. 5B  embodiment may also be structured to use the elliptical reflector  26  and UV light source  25  as illustrated in  FIG. 5 . 
   However, because of the remote location of UV energy source  52  and/or of the possibility the remote UV energy source may include an IR filter, it may be necessary to provide a preheater  59  to raise the temperature of the imprinted ink above ambient temperature to assist the curing process as described further below. 
   Although the above embodiment employing a remote UV energy source is described as being an alternate embodiment of the  FIG. 5  two step process, it is to be understood that the remote UV energy source described in  FIG. 5A  may also be used in place of the elliptical reflector embodiments illustrated in the other figures. 
   Referring now to  FIG. 6 , UV energy source  25  is positioned within elliptical reflector  26  such that the reflected UV light rays  38  are directed to a common focal point  35 . However, to affect curing of the imprinted UV curable ink it has been discovered preferable to pass ink imprinted labels  19  through the radiation field  32  above, and not through, focal point  35  as illustrated. The concentration of UV energy at focal point  35  has been found to be too intense and very likely to cause ignition of labels  19 . By passing ink imprinted labels  19  through radiation field  32 , above focal point  35 , the amount of UV energy, per surface area, of the label  19 , may be selectively chosen to labels  19 . 
   Since the UV energy imparted to and absorbed by the ink imprinted label, is dependent upon many variables, such as, the UV light  25 , surface area of the label, ink composition, ink color, line speed, substrate material parameters, etc., a quantitative value for the distance H above focal point  35  is not possible. The distance H must be determined qualitatively by empirical techniques for a given situation. 
   In the configuration illustrated in  FIG. 6  wherein imprinted labels  19  are passed through radiation zone  32  above focal point  35  the UV curable ink imprinted upon the label substrate is dry and at ambient temperature. In order to effectively cross-link the UV curable ink imprinted upon labels  19  it is preferable to elevate the imprinted ink substantially above ambient temperature so that the UV energy may affect cross-linking of the ink composition. In the process configuration as illustrated in  FIG. 6  the inherent IR energy accompanying the UV energy from UV light source  25  has been found to adequately elevate the imprinted ink temperature for this purpose. Here again quantitative values relating to the configuration illustrated in  FIG. 6  are not feasible for reasons stated immediately above. However one must optimize the amount of IR and UV energy, per surface area of label  19 , by experimentation considering all variables affecting the substrate and the ink printed thereon. 
   Alternatively one may consider passing an ink imprinted substrate  19 A through the extended radiation field  41  at a distance L beyond focal point  35 . However since IR energy decreases more quickly than UV energy as a function of distance from its source, optimizing the level of IR and UV energy received upon imprinted substrate  19 A from UV light source  25  becomes a problem without adding means for preheating the imprinted ink on substrate  19 A as it approaches radiation field  41 . Such a preheating device  42  is schematically illustrated in  FIG. 6 . Preheater  42  may comprise a thermal convection heater, an IR heater, or any other suitable heating means. However, now one must optimize both the IR and UV energy received by substrate  19 A and the energy received from preheater  42 . 
   It is to be also considered that a preheater, such as preheater  42  my also be used to preheat substrate  19  in  FIG. 6 . 
   It is to be understood that because of the massive heat generation by the UV light source  25  within the close confines of the apparatus as schematically illustrated herein it is necessary to provide adequate circulating cooling air within the UV apparatus schematically illustrated as cooling fan  22  in  FIGS. 1 through 5 . 
   Referring now to  FIGS. 7 and 8 , a two piece elliptical reflector  50  is illustrated. As illustrated, elliptical reflector  50  generally comprises a left half  52  and a right half  54 . Each reflector half,  52  and  54  may be pivoted about pivot points  62  and  64  respectively whereby reflector halves  52  and  54  may be rotated so as to act as shutters that enclose UV light source  25  as illustrated in  FIG. 8 . 
   Having operable shutters that may be closed about UV light source  25  is particularly useful when the operator desires to stop the machine throughput but does not desire to totally turn off UV light source  25 , or if the desired line speed is otherwise sensed to diminish or stop for unanticipated causes. By closing shutters  52  and  54 , about UV light  25 , IR and UV radiation is prevented from reaching labels  19  and possibly causing the labels to catch fire within the machine. Similarly should the operator need to stop the machine for maintenance and/or substrate change over, the operator may reduce the power to UV light  25  to a lower level without completely turning the UV light off whereby less time will be necessary for restart. 
     FIG. 9  presents a flow chart of the method steps performed by the apparatus illustrated in  FIGS. 1 and 3  in accord with the present invention. The process begins by first preparing a suitable substrate upon which the imprinted image is desired which generally, but not necessarily, comprises a continuous roll of paper labels or cut sheet paper stock. Next an UV curable ink imprinted image is printed upon the chosen substrate. It is then preferred to raise the temperature of the imprinted ink to a level above ambient temperature thereby causing the ink to flow slightly and more securely adhere to the substrate followed immediately by subjecting the softened ink to an UV radiation field whereby the softened ink is caused to cross-link into a hardened, durable substance. These two steps may be performed separately or may be preformed simultaneously. After curing of the ink is accomplished, the imprinted ink is permitted to cool and subsequently collected on a receiving roll or any other appropriate device. 
     FIG. 10  presents an electrical schematic of the 120 volt power supply for the apparatus illustrated in  FIGS. 1 and 2 . Since the electrical schematic of  FIG. 10  is self explanatory, no further explanation is deemed necessary here. 
     FIG. 11  presents an electrical schematic for the embodiment illustrated in  FIG. 1 . Again as the electrical schematic in  FIG. 11  is self explanatory, no further explanation is deemed necessary here. 
     FIG. 12  presents an electrical schematic for the powering the UV energy source. Since the electrical schematic of  FIG. 12  is self explanatory, no further explanation is deemed necessary here. 
   Although the invention has been described in detail with reference to the illustrated embodiments, variations and modifications exist within the scope and spirit of the invention as described and defined in the following claims.