Patent Application
20070125254
The present invention relates in one embodiment to the printing industry and more specifically, relates to a method for mounting a printing plate in a circular manner in near perfect alignment more easily and inexpensively, thereby providing near perfect alignment of the resultant printed image.
The printing industry now nearly exclusively utilizes photographic or digitally imaged printing plates to produce a printed image. Although this invention is primarily aimed at Flexographic printing, it could be used for letterpress and offset printing, rotary screen printing as well as in any operation were it is desirable to wrap a flat planar item around a concave or convex (oval, a round, etc.) cylinder. In some instances, these “printing plates” are utilized only one time since the printed image will generally change with the printing job while in other instances, the printing plates will be re-used and are therefore saved.
Most printing presses utilize a circular drum (commonly called the “plate cylinder”) on which the printing plate is mounted. By rotating the plate cylinder and printing plate first in contact with ink and next in contact with the substrate to be printed (paper, plastic, foil, etc.), the image is transferred from the plate to the paper. In the offset lithography process, a transfer drum called the “blanket” is between the printing plate and the printed substrate.
When printing a one color product, proper alignment of the printing plate on the drum is important to maintain proper orientation to the substrate. When printing in multiple colors, the printing press must have one rotating drum and printing plate assembly for each color to be printed. In such cases, proper alignment (“registration”) of the printing plates on the drums is essential otherwise, the finished product will have improperly aligned images and colors in addition to improper alignment to the substrate.
In flexographic printing, the plate is usually attached to an expensive plate cylinder using double sided tape called “stickyback”. Stickyback has either a solid (usually rubber or polymer) core or foam core with adhesive applied to both sides. If a plate is to be used in a subsequent run of the same or similar product, it may be desirable to keep it mounted on the cylinder.
Since this would tie up that expensive cylinder making it not available for other jobs, an alternative has been employed where the plate is mounted on an intermediate shell or sleeve which slides on and off the plate cylinder. These sleeves are usually metal or some plastic or composite material. While less costly than plate cylinders, sleeves are still quite expensive. Many printers have cited the benefits of sleeve mounting, but do not use it because of the high sleeve cost per unit and because a large inventory of blank sleeves matched in diameter to the various sizes of plate cylinders in stock must be maintained to accommodate new jobs as they are scheduled.
The alignment accuracy of the plates is critical to high quality printing and minimizing waste due to mis-alignment or “mis-register”. Substrate and ink waste are usually large expenses to printing companies and they constantly try to minimize this waste. Lower waste also means shorter production time and thus reduced labor and overhead costs. A number of plate mounting systems are commercially available to mount plates directly on the cylinders or onto the sleeves. These systems generally utilize a method of alignment of two points on the surface of the plate, making the assumption that if all multiple images are in registration relative to two points, the entire composite multi color (or multi plate)image will be in registration. The systems generally use CCD cameras or microscopes to achieve this alignment. Some systems employ attachment points (holes or protrusions) which can be mechanically aligned. The same systems are used to mount plates on to plate cylinders or sleeves, so the current use of sleeves does nothing to improve the registration accuracy.
These systems have served the industry well, but they have some limitations. First, not all cylinders are exactly of the same diameter. Diametric differences can be introduced by the stickyback. Therefore, even if the leading or trailing edges or central region of the plates are aligned, there is no guarantee that the following and trailing portion are registered (aligned). Also, there is no way to assure that the individual who mounts the plates uses the same pressure, which can introduce variability.
Accordingly, what is needed is a new system and method for forming a printing plate mounted on a sleeve which is both highly accurate and inexpensive.
The present invention features a novel system and method for forming and adhering a photographic or digitally generated printing plate or other generally flat, planar object into a circular member that can then be inserted onto the drum of a printing press or other device. The invention assumes that the printing plate will have imaged thereon a minimum of one and preferably two or more alignment marks. These alignment marks ensure that the printing plate can be mounted in a circular manner with proper alignment between the marks to prevent image misalignment and image skew.
The present method provides, in addition to a printing plate, an adhesive member. The adhesive member, typically made of any combination of metal, polymer foam, solid polymer, rubber, etc, includes an adhesive layer on at least one side. In some embodiments, there maybe an adhesive layer on the second side as well. The adhesive member has approximately the same lateral dimensions as the printing plate, but may be thicker or thinner. In one embodiment, the piece of member may be provided as a flat, generally planar member having adhesive on at least one surface. In another preferred embodiment, the adhesive member may be provided at least somewhat “pre-formed” or bent into a generally circular form. The adhesive member may be a single or multilayered structure.
In one embodiment, the present invention begins by exposing at least a portion of the adhesive on one surface of the adhesive member and proximate a first edge of the adhesive sheet. The area immediate to the first edge is covered with a release layer that prevents sticking to the adhesive. Next, the photographic plate or other flat generally planar object is attached to the adhesive sheet proximate but not at the edge of the adhesive member. This attachment leaves a region of the adhesive sheet back from the edge to which nothing yet is attached. This dimension of edge can range from approximately ¼″ inch to 2″ inches in width, although this is not a limitation of the present invention.
The printing plate is secured to the remainder of the adhesive sheet. This now leaves a section of printing plate which has not yet been attached to the adhesive sheet because of the offset in the initial attachment point.
The partially adhered printing plate and adhesive sheet are next rolled into a circular form and held in place in a printing plate mounting device. Using either a manual or automatic alignment process using equipment such as a microscope, camera, clamp, automated vision system or the like, the registration marks located on each end of the printing plate are properly aligned, the release sheet removed from proximate the first end, and finally the second end of the printing plate is adhered to the first end of the adhesive sheet thus forming a circular “sleeve” which can subsequently be mounted on a printing press drum. Using this method, each and every printing plate will be arranged in a circular format ready to be mounted on a printing press drum in perfect alignment thereby essentially eliminating misalignment or skew caused by improperly aligned printing plates.
These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein:
The present invention features a novel system and method for forming a photographically or digitally generated printing plate or other generally flat, planar object into a circular sleeve that can then be inserted onto the drum of a printing press or other device. The invention assumes that the printing plate 10,
Flexography is a “relief” printing process meaning that the image portion of the plate is raised above the “floor” of the plate (such as a rubber stamp). The “letterpress” method is also a relief printing process whereas offset lithography plates are essentially planar and rely on the chemistry of the printing area. The present invention applies equally well to all the above referenced printing technologies and to other areas of technology unrelated to printing.
The alignment or registration marks may be two-dimensional marks imaged on the surface of the printing plate or other generally flat, planar object to be aligned. The two-dimensional marks may include a specific design, such as a dot, cross hair mark or the like, to aid alignment. The alignment or registration marks 12 may also include three-dimensional marks protruding from the generally flat planar surface of the object to be aligned. The tops of these protrusions may also include an alignment aid such as a dot, crosshair mark or the like. The alignment marks 12 ensure that the printing plate can be mounted in a circular manner with proper alignment between the marks to prevent image misalignment and image skew. Although two marks are contemplated as a minimum, there are preferably provided four alignment marks. In addition, only one alignment mark or region having one or more alignment features may be provided, all without departing from the scope of the present invention.
The present method provides, in addition to a printing plate 10, an adhesive member 16,
The present invention begins by exposing at least a portion of the adhesive 17 on one surface 18 of the adhesive member 16. Typically, the one surface 18 will be covered by a thin silicone paper or similar release sheet 19. Alternatively, the one surface 18 of the adhesive member may covered by a release sheet in two sections; one larger sheet covering most of the surface 18 and the other, a smaller release sheet 19 disposed only in the region 24 of the adhesive member 16 that will not have the plate 10 attached to it at this time (much like the pull tabs used in printed toner cartridges.)
Next, the plate 10 is attached to the adhesive sheet 16 proximate but not directly at one edge 20 of the adhesive member 16. This attachment method leaves a region 24 of the adhesive sheet 16 back from the edge 20 to which nothing yet is attached. The dimension of the region 24 is preferably 1 inch although this dimension can range from approximately ¼ inch to 2 inches in width, however this is not a limitation of the present invention. This pre-assembly process will preferably be done on a cylinder because the final sleeve is cylindrical and the laminated construction described will resist significant bending although this is not a limitation on the invention.
The printing plate 10 is secured to the remainder of the adhesive sheet 16. This now leaves a section of printing plate 26 which has not yet been attached to the adhesive sheet 16 because of the offset 24 in the initial attachment point. The dimension of region 24 and 26 are generally the same. The partially adhered printing plate 10 and adhesive sheet 16 are next rolled into a circular form 30,
Using either a manual or automatic alignment process using, for example, micrometers 43 and using equipment such as a microscope, camera, automated vision system or the like, the one or more registration marks 12 located on or near each end of the printing plate 10 are properly aligned and finally the second end region 26 of the printing plate is adhered to the first end region 24 of the adhesive member 16 after removing release sheet 19, thus forming a cylindrical “sleeve” 30 which can subsequently be mounted on a printing press drum.
In the preferred embodiment, the adhesive member 16 is provided in a circular or at least partially circular form. This is particularly necessary when the adhesive member 16 is a multilayered structure including two or more layers. In that case, the multilayered adhesive member 16 must be assembled in a generally circular form otherwise the multilayered structure 16 will be too resistant to bending and will not be able to be formed in a circular manner once the generally flat planar object is adhered to it as one or more of the assemblies will “buckle” and not properly form.
In this and other embodiments, it will be desirable to pre-form the adhesive member 16 into a generally circular form before adhering the generally flat, planar object 10 to its surface, although the alignment methodology described above will work equally as well with a circular adhesive member 16. As those of ordinary skill in the art will know, other adhering methodologies may also be used without departing from the scope of the present invention.
Using this system and method, each and every generally flat, planar object with alignment marks such as printing plates will be arranged in a circular format ready to be mounted on a printing press drum in perfect alignment thereby essentially eliminating misalignment and/or skew caused by improperly aligned printing plates.
It is important to note that the present invention is not intended to be limited to a system or method which must satisfy one or more of any stated objects or features of the invention. It is also important to note that the present invention is not limited to the preferred, exemplary, or primary embodiment(s) described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by any allowed claims and their legal equivalents.
This application is related to U.S Patent Application No. 60/727,294 filed Oct. 17, 2005 entitled “System And Method For Mounting A Printing Plate Using Sleeves”, which is incorporated fully herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60727294 | Oct 2005 | US |
