Background of the Invention In the typical process for the formation of lithographic printing plates, the sensitized web of lithographic plate stock is cut into individual plates and stacked prior to imaging. The individual plates are optionally separated by individual sheets of interleaving paper where needed to protect the integrity of the coating. To image the plates, each individual plate is picked up from the stack, the interleaving paper is removed when present, and the plate is transferred to the imaging device. The imaging device may be of the internal drum type, the external drum type or of the flat bed design. After positioning the plate in the imaging device, vacuum is typically employed to hold the plate securely in place. Once the image is formed, the vacuum is released and the plate is removed from the imaging device. United States Patent No. 5,619,246 discloses an apparatus for loading and unloading of individual plates into an imaging device. Where punched plates are desired, the individual plates are optionally punched prior to or subsequent to the imaging process as a discrete, separate operation. Such prior art processes require considerable material handling equipment and consume a lot of time.

Summary of the Present Invention The present invention simplifies the process and equipment for producing punched, imaged and sheeted printing plates. An object of the invention is to provide a web with registration holes and image the web prior to cutting the web into individual imaged plates. A web of material which is prepunched with registration holes is then imaged and sheeted (cut) in a continuous process. The web is advanced through the imaging step into a set of pull rolls and then passed to a sheeter where it is cut into discrete sheets. The punching is performed at a separate station or location prior to the imaging. The punched holes are utilized to assure registration and alignment in the imaging and sheeting operations. The web is preferably advanced under tension and tension and/or a vacuum may be used to hold the web flat during the operations. A modification of the invention involves imaging on the web as it is moving rather than stopping the web for imaging. The present invention thus simplifies the process of obtaining finished, imaged sheets, by combining several discrete process steps into a continuous process. Further, the time required to image individual sheets is reduced since the present invention allows the imageable web to be loaded into the imaging device as the already imaged area of the web is being removed. Since all operations are controlled with improved precision, the subsequent alignment and registration of the finished plates is greatly improved.

Brief Description of the Drawings Figure 1 is an illustration of a process line illustrating the method and the equipment for practicing the present invention.

Figure 2 is a top view of straight grain punched web according to the invention.

Figure 3 is another top view of a punched web showing a cross grain form of punching.

Figure 4 is an illustration of a process line showing an alternate embodiment of the present invention.

Description of the Preferred Embodiment The present invention relates to the imaging of any suitable web with an imageable surface where the desired resultant article is discrete, imaged sheets. In the preferred embodiment, the web of material is suitable for the formation of printing plates. The web will typically be a grained, anodized aluminum stock having a sensitized coating which is imageable by exposure to actinic radiation in the infrared, visible or ultraviolet wavelength ranges in a manner well known to those skilled in the art. The invention is particularly suited for but not limited to lithographic printing plates.

Figure 1 illustrates a web of imageable printing plate stock 12 coming off the unwind reel 14. The web in this instance is prepunched with registration holes. Examples are the holes 41 and notches 42 as shown in Figures 2 and 3. These holes and notches may be of any desired configuration and they may be straight grain punches as shown in Figure 2 (across the web) or cross grain punches as shown in Figure 3 (lengthwise along the edges of the web). The notches 42 are for registration on the printing press while the holes 41 are typically used for registration in the equipment for forming the bend in the ends of the plates for mounting on the press cylinder. The notches and holes, generally designated as holes hereinafter, are used for registration in the imaging system which provides a very accurate registration system on press. The registration holes can be prepunched during the web manufacture or at any other time or location.

The unwind reel 14 is driven by a controlled power source such as motor 16 with regenerative capabilities as known in the art. Such a device is capable of operating in reverse or of applying negative torque. A diameter sensing device 18 is used to provide a signal to the control system 20 representing the current diameter of the web on the unwind reel. Any suitably accurate distance-measuring device can be used. This

diameter is required by the control system to accurately calculate the proper revolutions per minute of the unwind reel and thus control the speed of the motor 16 to set the proper web speed. The control system 20 is merely a conventional type of timing sequencing and calculating device to control the various functions of the entire process as discussed later.

Web tension is created by the pull roll system 22 providing a forward pull on the web and the unwind reel 14 providing the back tension through the motor 16. Web tension is sensed by a linear variable-differential transformer (LVDT) transducer or a stain gauge or similar known tension sensing device 24 associated with the roll 26. For example, the pillow blocks for the journals of the roll 26 can be mounted on the transducers which will then produce a signal proportioned to the force of the web on the roll 26 and thus proportional to the web tension. Rolls 28 and 30 maintain a constant angle of wrap of the web around the roll 26. The tension feedback signal from 24 is utilized by control system 20 to determine the proper control parameters of speed and torque for motor 16 thereby insuring that the proper web tension is maintained.

The primary control of the registration in the process line is the pull roll system 22. The pull roll system 22 consists of two feed rolls 32 and 34 that are ground to a precisely controlled diameter. An optical encoder 36 is mounted on the pull roll drive motor 38 or one of the pull rolls. The optical encoder 36 determines the length of the web as the web advances to the next position and will feedback the position to the control system 20.

The feed rolls are conventional intermittently driven types of feed rolls which engage the web and intermittently move the web forward a predetermined distance equivalent to the size of one printing plate as set into the control system 20.

The punched web is fed to the imaging station generally designated 44. This comprises a platen 46 and an imager 48. The punched web 12 is fed onto the platen 46 and is stopped in the proper position by the position sensor 50, such as an optical sensor, which detects an appropriate

punched hole. This then provides for the indexing of the web to each successive position. The sensor 50 is ideally located within the imaging station 44 thus insuring the highest degree of accuracy in the imaging process. The control signal generated by position sensor 50 is used by control system 24 to identify the web stopping position and insure the accurate position of the punched hole in the imaging station 44. With the web 12 at a stationary position on the platen 46, the web is imaged by the imaging device 48 which, for example, might be any conventional laser or other imager. Upon completion of the imaging, the controller 20 again triggers the web to move forward the required amount ready for the next image.

The web 12 is maintained flat on the platen 46 by the web tension or by a vacuum which is drawn on the interface between the web and the platen by the vacuum pump 47. For example, the surface of the platen may contain a series of small holes connected with the vacuum pump 47 by appropriate channels. Also, a combination of web tension and vacuum may be used. A unique feature is that the vacuum need not be cycled on and off since the web can be moved across the platen in the direction perpendicular to the pull of the vacuum without releasing the vacuum.

Following the pull roll system 22 is a shear device 52 which cuts the web into individual plates. The shear device 52 is also controlled by the controller 20 and is preferably located an exact distance from the position sensor 50 that is a multiple of the desired plate length. Since the accuracy of the shear cut-off length is determined by this distance, the cutter is preferably located as close to the feed rolls as practical to minimize any accumulative errors. After cutting, the plates can be sent to a washing station which is not shown.

The imageable surface of the web 12 is on the upper surface as depicted in Figure 1. Since the imageable surface is often a coating which should be protected, the web may be rolled together with an interleaving web of paper 54 which is located between each layer of the web 12 on the

reel and protects the coating from the adjacent back-side of the web 12. As can be seen in Figure 1, this paper web 54 is separated from the printing plate web 12 as it is unreeled. The paper web can then merely be rolled onto the spool 56 for disposal or reuse. The rotation of the spool 56 is controlled by the control unit 20.

Another embodiment of the present invention is illustrated in Figure 4 and involves the imaging of the web 12 as it is continuously moving. In this embodiment, the pull roll system 58 continuously moves the web forward at a selected speed as controlled by the control system 20 and the drive motor 60. The imager 48 may be any conventional imaging device capable of imaging as the web is moving. For example, the imager could be an ink jet imager for the selective application of an imaging material. An additional example would be a modulated laser beam impinging on a rotating mirror, with the web passing under the laser raster pattern at a rate calibrated to the time for the mirror to complete a cycle.

The sensor 50, which can be located as desired, detects the registration holes as they pass by and activates the imager at the appropriate time.

In the Figure 4 embodiment, the web is continuously moving through the imager and the pull roll system 58. However, it is preferable, but not necessary, that the web be stopped for purposes of cutting the web into the individual printing plates at 52. Therefore, an intermittent feed roll system is used for feeding the web to the cutter 52. The system 64 maintains tension on the web by moving the roller 66 up and down thereby taking up the slack as the web is moving through pull roll system 58 and stopped in pull roll system 62.

There are a number of advantages of the present invention over the prior art. The imaging and cutting are performed as a continuous operation instead of as individual, discrete processing steps. This eliminates the time and equipment for the handling of individual plates between each step.

The time for imaging is reduced over the prior art since the web to be imaged can be fed into the imager as the already imaged region is being

removed. Further, the use of vacuum to hold the web during imaging is optional. In some applications, the web tension will be sufficient to secure the web in position on the flat surface of the platen. Where desirable, vacuum may be used, but since the web is transported along the imaging surface in a direction transverse to the pull of the vacuum, the vacuum need not be cycled on and off during the loading and unloading operations. Thus a time savings can be realized even where vacuum is employed. Also, where interleaving paper is used, the cumbersome handling of individual interleaving sheets is replaced by a simple rewind device for a continuous web of paper.

An additional advantage lies in the fact that the imaging and cutting are done with the use of the prepunched registration holes so as to assure alignment and registration with much greater precision than the prior art.

By imaging while maintaining a flat web and indexing the process for the imaging and sheeting operations from the prepunched holes, the finished plates can be prepared with a greatly improved registration when mounted on a press, resulting in a reduction of losses on start-up of the press. This alleviates the need for the costly and time consuming optical bending as is currently often used in the printing industry for registration.