Abstract:
An apparatus for laser marking indicia on a moving photosensitive web by impinging laser energy upon the moving web with a laser printer device. The laser printer device is provided with a nozzle element that concentrates beams of radiation onto the web with substantially reduced incidences of fog spots on the web. The nozzle element extends circumferentially, substantially around a laser beam tube and the predetermined optical path defined by laser beams emanating from the laser beam tube.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of laser marking systems. More particularly, the invention concerns an apparatus that uses laser energy for marking indicia on photosensitive web with a dramatic reduction in the occurrence of fog on the photosensitive web. 
     BACKGROUND OF THE INVENTION 
     Conventional edge marking in photographic film manufacturing involves printing some sort of identification indicia along the edge of film rolls during the finishing operation. Edge marked film has direct verification of roll identity, sheet identity and waste identity during all stages of the manufacturing process. Importantly, edge marked film provides accurate footage identification that enables operators to quickly identify, trace and remove film imperfections, thereby minimizing the amount of product waste. More generally, edge marked film increases process understanding by allowing process interactions to be more closely identified with their corresponding effect on the product. Traditional embossing marking techniques are being replaced by laser edge marking. Current mechanical embossing techniques (embossing wheels) are not programmable, generate poor quality marks and require excessive maintenance. Laser edge marking, on the other hand, is particularly advantageous in the industry because it provides a permanent record and can be read before and after film processing. 
     Advances in laser technology enabled the use of a dot matrix CO 2  laser marking system to be used to replace existing embossing technology. Off the shelf laser marking equipment will mark the film at required throughput rate, however, an unacceptable level of fog spots occurred. 
     Thus, a particular shortcoming of these advanced high powered laser systems used for edge marking photosensitive film is that they produce a by-product that impinges on the film surface. Laser energy by-products in the form of a plume of energized smoke and irradiated debris on the film surface is known to cause the localized fogging on the film. Experience has shown that localized fogging is not easily eliminated even when the film is immersed in a 99.8% nitrogen atmosphere. 
     More recent developments in laser technology enabled the development of high speed marking systems using short pulse lasers. Short pulse laser exposure on photosensitive film shows some promise in reducing the occurrences of fog spots. Our experience also indicates that an air jet directed at the laser impingement point on the film surface further reduce the occurrence of fog. Statistical methods have been employed to gain information on fog incidence reduction when laser marking photosensitive film. It has been experimentally proven that laser pulse width does not have a significant effect on fog. Importantly, however, our experience does suggest that laser peak power has a dramatic effect on the reduction of occurrences of fog spots by a factor of about 30. In addition, significant statistical benefits can be derived from an air jet that we believe can further reduce the incidences of fog spots by a factor of about 10. 
     Hence, laser marking without controlling peak power will result in 14% to 50% of the laser-generated dots of dot matrix characters to have fog spots around the dots. There are no present attempts known to the inventors to control peak power in laser edge marking devices because embossing techniques still remain prevalent in the industry and, more importantly, the fog spots remain a significant quality issue during the finishing process. 
     Therefore, a need persists for variable information to be permanently marked on die edge of each sheet of photosensitive web, such as photographic film, without significant incidences of fog spots on the surface of the film. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of die invention to provide an apparatus for laser marking indicia on a moving photosensitive web while substantially reducing the occurrence of deleterious fog spots on the photosensitive web. 
     It is another object of the invention to provide an apparatus for exposing a moving photosensitive web to laser energy while controlling the peak power of the laser energy. 
     Yet another object of the invention is to provide an apparatus for laser printing indicia on a photosensitive web by further directing a jet of air onto the laser energy impinged surface of the photosensitive web. 
     It is a feature of the invention that the apparatus for laser marking indicia on a moving photosensitive web has a nozzle element for reducing the incident of fog spots on the laser impinged photosensitive web. 
     To accomplish these and other objects and features and advantages of the invention, there is provided, in one aspect of the invention, an apparatus for marking indicia on a moving photosensitive web, comprising: 
     a source of laser energy; 
     laser printer means operably connected to said source of laser energy, said laser printer means being provided with: 
     a laser head; 
     a laser beam tube connected to said laser head, said laser beam tube having an active end; and, 
     a nozzle element structurally associated with said active end of said laser beam tube, said nozzle element comprising a chamber having a laser energy inlet end and a laser energy outlet end; an air jet member arranged in said chamber for directing a burst of air onto a laser beam impingeable surface; at least one lens arranged in said chamber for focusing each one of a plurality of laser beams passing through said chamber; a lens cleaning member arranged in said chamber proximate to said at least one lens; and, a vacuum port extending from said chamber, said vacuum port providing means for evacuating said chamber of smoke and debris generated during laser marking; and wherein said laser head has a plurality of lasers disposed therein for generating a plurality of laser beams, a lens arranged in said laser beam tube for focusing said each one of a plurality of laser beams along a predetermined optical path through said laser beam tube and into impinging contact with said moving photosensitive web thereby producing said indicia thereon. 
     It is, therefore, an advantageous effect of the present invention that laser edge markings on photosensitive web can be accomplished with an apparatus that is easy to operate, simple and cost effective to produce and that substantially reduces the occurrence of fog spots on the photosensitive web. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein identical reference numerals have been used, where possible, to designate identical features that are common to the figures, and wherein: 
     FIG. 1 is a schematic diagram of a laser edge marking system of the invention; 
     FIG. 2 a  is a front elevational view of the laser head showing an attenuating member therein; 
     FIG. 2 b   1  is an enlarged view of the mesh screen depicted in FIG. 2 b;    
     FIG. 2 b  is a top elevational view of the mesh screen; 
     FIG. 2 c  is an isometric view of the beam splitter; 
     FIG. 3 is a graph of tie relationship between focus position effect (inversely proportional to peak power) on fog spots formed on the photosensitive film; 
     FIGS. 4 and 5 show the effects of an attenuating screen of the invention on incidents of fog spots; and, 
     FIG. 6 is an isometric view of the nozzle element used in the apparatus of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and in particular to FIG. 1, the apparatus  10  according to the principles of the invention for printing indicia on a moving laser impingeable surface, such as a moving photosensitive web  1 , is illustrated. According to FIG. 1, apparatus  10  has a source  12  of laser energy for producing a range of laser power. A laser printer means  14  is operably connected to the source  12  of laser energy. 
     Referring to FIG. 1, laser printer means  14 , preferably a Domino DDC2 Digital Laser Coder, manufactured by Domino Lasers, Inc. of Gurnee, Ill., is provided with laser head  16  and a laser beam tube  18  structurally associated with the laser head  16 . Laser beam tube  18  has an active end  20  positioned proximate to the moving photosensitive web  1  and a plurality of lasers  22  disposed in die laser beam tube  18  for generating a plurality of laser beams. Importantly, a nozzle clement  40 , described more fully below, is structurally associated with the active end of the beam tube  18 , as shown in FIGS. 1 and 2 a.    
     According to FIG. 2 a , in the preferred apparatus  10 , seven lasers  22  are employed, each being a medium power CO 2  laser that operates at about 30 watts maximum power. Each laser  22  corresponds to a row of dots in a dot matrix character. This type of laser  22  has enough power to mark small characters or indicia into photosensitive materials, for example emulsion coated film. At least one lens  49  is arranged in the laser beam tube  18  for focusing each one of the plurality of laser beams along a predetermined optical path  23  and into impinging contact with the laser impingeable material, such as photosensitive web  1  thereby producing indicia thereon. 
     Referring to FIGS. 2 a - 2   c , means for controlling peak power, preferably a laser beam attenuating member  26  (FIG. 2 a ), is disposed in the optical path  23  for attenuating the laser beams passing through the laser beam tube  18 . In the preferred embodiment, attenuating member  26  is a metallic mesh screen  30  (FIG. 2 b ) arranged in the laser beam tube  18 . Preferably, metallic mesh screen  30  is made of materials selected from the group consisting of brass, steel, copper and metal alloys. We consider copper to be most preferred because it has more suitable thermal conductivity and reflective characteristics of the wavelengths contemplated by the invention. Moreover, the mesh screen  30  has a plurality of openings  32 . Openings  32  each have a wire diameter in the range of from about 0.00025 inches (0.000635 cm) to about 0.025 inches (0.0635 cm) and a clear opening having a dimension in the range from about 0.001 inches (0.00254 cm) to about 0.100 inches (0.254 cm). In the preferred embodiment, mesh screen  30  has clear opening dimension of 0.055 inches (0.140 cm), and a wire diameter of 0.016 inches (0.041 cm). 
     As shown in FIG. 2 c , alternatively, attenuating member  26  may include at least one beam splitter  27  arranged along the optical path in the beam tube  18 . Moreover, attenuating member  26  may include a neutral density filter (not shown). 
     Referring to FIGS. 2 a  and  6 , nozzle element  40  has a preferably generally cylindrical shaped chamber  42  with a laser energy inlet end  44  and a laser energy outlet end  46 . Inlet end  44  is adaptable to any laser energy output device, such as a laser marking system for marking indicia on photosensitive web. Laser energy outlet end  46  is configured to focus beams of radiation onto a moving photosensitive web material  1  and to be spaced proximate to the moving photosensitive web material  1 . Preferably, laser energy outlet end  46  has a generally conical shape for concentrating the vacuum nearest the photosensitive web material  1  and, a generally conical lip  47  for concentrating the air surrounding lens  49 . 
     Referring to FIGS. 2 a  and  6 , an air jet member  48  is arranged in the chamber  42  near the outlet end  46 . Air to air jet member  48  may be supplied by any general source (not shown). Air jet member  48  is configured for directing a burst of air onto a laser beam impingeable surface, such as a photosensitive web material  1  positioned proximate to the air jet member  48 . 
     Referring to FIG. 2 a , chamber  42  may have at least one lens  49  arranged therein for focusing each one of a plurality of laser beams passing through the chamber  42 . Lens  49  is preferably a short focal length zinc selenide lens. Lens  49  may be mounted in any one of a variety of ways in chamber  42 , for instance using a typical lens mount (not shown). 
     Referring to FIGS. 2 a  and  6 , a lens cleaning member  50  is arranged in the chamber  42  proximate the lens  49 . Nozzle element  40  was developed to keep the lens  49  clean, prevent plume and draw away vapors associated with impinging laser energy. In the preferred embodiment, lens cleaning member  50  is a positive air flow pattern surrounding the lens  49  that shields the lens  49  from particulate matter. Alternatively, lens cleaning member  50  may be a burst of air directed at the lens  49  (not shown). 
     Turning again to FIGS. 2 a  and  6 , chamber  42  further has a vacuum inlet port  52  and a vacuum outlet port  54  in fluid communication with the chamber  42 . Vacuum outlet port  54  provides means for evacuating the chamber  42  of smoke and debris generated during laser marking. To concentrate vacuum at a predetermined location, vacuum inlet port  52  preferably has a generally conical shape. Affluence generated by the marking process without vacuum resulted in no detection of cyanide, sulfur dioxide, hydrochloric acid, or carbon monoxide. Carbon dioxide could be detected but the level was below exposure limits. Mercury, silver and aldehydes vapors were adequately removed by the Fumex FA2 fume extraction machine. 
     Vacuum outlet port  54 , is connected to a source of vacuum (not shown), and provides a means for receiving such particulates that are collected through vacuum inlet port  52 . 
     FIG. 2 a  illustrates nozzle element  40  adapted to a laser beam tube  18  having a plurality of lasers  22  therein. Laser beam tube  18  is preferably the output end of a laser marking system  10  (only partially shown). 
     Preferably, nozzle clement  40  is made from any structurally rigid material such as any metallic material. We prefer using aluminum because it is light-weight and can be easily formed. 
     Referring to FIG. 3, peak power of each of the plurality of lasers  22  was determined to be a primary factor controlling the incidences of fog spots occurring on the photosensitive web material  1  after impingement by laser energy. According to FIG. 3, we observed that the incidences of fog spots decreased as the focus position of the lens  49  moved further out of focus. This corresponded to an effective reduction in peak power that enabled the inventors to select controlling peak power for minimizing the incidences of fog spots. 
     Referring to FIGS. 4 and 5, performance of mesh screens  30  used as laser beam attenuating member  26  in the apparatus  10  of the invention are illustrated. According to both FIGS. 4 and 5, the incidences of fog spots are well below expected levels generally experienced in the industry. 
     In another embodiment of the invention, a method of controlling peak power of a laser marking apparatus  10  (FIG. 1) adapted for marking predetermined indicia  2  on a moving photosensitive web material  1  comprises the steps of providing a source  12  of laser energy. A laser printing means  14  (described above) is structurally connected to the source  12  of laser energy which has a laser head  16 , a laser beam tube  18  connected to the laser head  16 . As indicated above, the laser beam tube  18  has an active end  20  and a nozzle element  40  arranged on the active end  20  positioned proximate to the moving photosensitive web material  1 . A plurality of lasers  22  is disposed in the laser head  16  for generating a plurality of laser beams. A lens  49  is arranged in the laser beam tube  18 , preferably near the active end  20 , for focusing each one of the plurality of laser beams along a predetermined optical path  23  (FIG. 2 a ) and into impinging contact with the moving photosensitive web material  1  thereby producing indicia  2  thereon. 
     Further, the source  12  of laser energy is activated so as to energize each one of the plurality of lasers  22  for impinging laser beams forming predetermined indicia  2  on the moving photosensitive web material  1 . Importantly, the peak power to each one of the plurality of lasers  22  is controlled, as described above, for minimizing fog spots on the photosensitive web material  1 . 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     PARTS LIST 
       1  photosensitive web material 
       2  indicia 
       10  apparatus of the invention 
       12  source of laser energy 
       14  printer means 
       16  laser head 
       18  laser beam tube 
       20  active end of laser beam tube  18   
       22  lasers 
       23  optical path 
       26  means for controlling peak power or laser beam attenuating member 
       27  beam splitter 
       30  metallic mesh screen 
       32  openings in metallic mesh screen  30   
       40  nozzle element 
       42  chamber 
       44  laser energy inlet end 
       46  laser energy outlet end 
       47  lip 
       48  air jet member 
       49  lens 
       50  lens cleaning member 
       52  vacuum inlet port 
       54  vacuum outlet port