Printing – Printing members – Plates
Reexamination Certificate
2001-06-25
2004-02-03
Funk, Stephen R. (Department: 2854)
Printing
Printing members
Plates
C101S376000
Reexamination Certificate
active
06684782
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a flexographic printing plate, more particularly a flexographic printing plate which can be mounted on a printing machine directly or via a sleeve, is excellent in printing characteristics and compressibility, and can be used repeatedly. The present invention also relates to a raw plate for producing the above-described flexographic printing plate.
BACKGROUND ART
The printing plate for flexography (hereinafter referred to as flexographic printing plate) has been of a photo-curable resin which is low in hardness and highly rubber-elasticity. However, it is not sufficiently elastic to give high-quality printed matter, when printed by a printing machine of low precision, causing several problems, e.g., distorted or uneven images.
One of the methods to solve the above problems is coating the flexographic printing plate with an elastic foam tape via a tackiness agent layer on the side on which a relief image is not formed (hereinafter referred to as back side), to impart elasticity to the plate.
However, this method may cause problems related to printing precision, because of high elasticity of foam tapes; for example, a foam tape may not uniformly impart elasticity in any case to the flexographic printing plate, and thickness uniformity of the flexographic printing plate mounted on the plate cylinder may be damaged by partial elongation or creases of the foam tape.
The other problems coming froma foam tape are separation or slippage of the flexographic printing plate from the tape during printing due to its insufficient tackiness, high cost of the tape, and insufficient strength of the tape for repeated use. These problems tend to hinder high-quality printing and push up the printing cost.
Another method puts a foam tape of high tackiness on a plate cylinder or sleeve, and thinly coats the back side of a flexographic printing plate with talc or a releasing spray agent to weaken tackiness of the foam tape to control tackiness of the plate at a low level to an extent not harmful to printing. The flexographic printing plate produced by this method can be separated more easily after printing, to prevent creases or damages of the expensive foam tape, allowing the tape to be repeatedly used to reduce the printing cost. However, it invariably involves the problems, e.g., slippage or separation of the flexographic printing plate during the printing period, resulting from difficulty in controlling a quantity of talc or a releasing spray agent to be spread over the plate. The foam tape on the tackiness agent layer, on which the flexographic printing plate is fixed, will be contaminated because of the repeated use. It naturally loses its tackiness, limiting stable cycles of reuse.
Therefore, the flexographic printing plate, inexpensive, high in workability and stably showing high printing repeatability has been in demand. The inventors of the present invention have developed, in order to solve the above problems, a novel flexographic printing plate, composed of a monolithically laminated photo-curable resin layer, an adhesive layer, a base having a barrier performance and an elastic foam layer, with the elastic foam layer having a separable surface, and applied for the patent (Japanese Patent Application No. 9-353631 specification).
This invention provides the flexographic printing plate having high printing repeatability, which allows the elastic foam component showing high printing repeatability to be used repeatedly. This flexographic printing plate, however, still needs a tackiness tape when mounted on the plate cylinder, although dispensing with a double-sided tackiness tape, which is expensive and difficult to reuse.
Fine, complex images on a flexographic printing plate have been generally printed with a compressive, elastic foam placed on the plate cylinder to have the image of high precision. The elastic foam used for the above flexographic printing is generally a thin foam tape or sheet with tackiness agent layers on both sides, and put on the back side of a flexographic printing plate or plate cylinder before printing. When it is put on the plate cylinder, however, the exposed tackiness tape hanging out of the flexographic printing plate is cut off or covered with a thin film, to prevent the troubles during the printing preparation or printing period, e.g., adhesion of the tape to the printed matter.
A foam tape is thin, and the foam itself is mechanically weak and easy to break. As a result, it takes a lot of time to uniformly put a large-sized foam tape on a plate cylinder or back side of a flexographic printing plate while preventing it from being stretched or slacked. A foam tape has been rarely reused repeatedly, because of low mechanical strength of the foam itself, as described above, to cause damages of the tape while it is being used, temporal changes of tackiness of the foam tape surface and problems associated with maintenance of the tape while it is being reused repeatedly.
Another method proposed so far puts reusable tackiness tape (or sheet) over the entire peripheral surface of a plate cylinder or sleeve, to utilize its tackiness for fixing a flexographic printing plate on the plate cylinder or sleeve. This method can recover tackiness of the tape (or sheet) for reuse of the tacky surface by cleaning it with a designated cleaning solution. It saves works and time for putting a double-sided tackiness tape, but involves some problems, resulting from insufficient elasticity of the tackiness tape (or sheet) for reproduction of printed images of high precision; the above-described elastic foam tape is made of a material having continuous and/or separate fine bubbles which decrease tape density to 0.1 to 0.6 g/cm
3
, and is also soft, whereas the tackiness film (or sheet) for this method should have a higher density and contain bubbles to only a limited extent or less, to be reusable semipermanently.
Moreover, the above-described method should provide the tacky surface over the entire surface of the plate cylinder, with the result that the tacky surface may be widely exposed, when the flexographic printing plate is small in size, to cause problems, e.g., tackiness of the printing medium to, and winding around, the plate cylinder during the printing preparation period, and contamination of the printed matter with adhered dust or foreign matter during the printing period. Therefore, it is necessary to cover the exposed tacky surface with a non-tacky material beforehand, to avoid the above problems. In addition, the tackiness agent layer put on a plate cylinder or sleeve is not allowed to have a joint which may appear on the printed matter. Fabrication of the tackiness agent layer needs special techniques, which inevitably pushes up the cost.
DISCLOSURE OF THE INVENTION
The inventors of the present invention have developed, after having studied to solve the problems involved in the characteristics of the elastic foams which are difficult to perform high-precision printing and mechanically weak, a flexographic printing plate of the present invention with an elastic layer combined with the flexographic printing plate to form a monolithic structure. The surface of the elastic layer combined with the flexographic printing plate is made tacky and rereleasable, to allow the flexographic printing plate to be attached to, and detached from, the plate cylinder without needing a tackiness tape, and to be reused repeatedly. These features reduce the flexographic printing plate cost.
The present invention provides a flexographic printing plate, composed of a photo-curable resin layer with one or more relief images thereon, a support layer having a barrier performance, an adhesive layer which adheres the photo-curable resin layer and the support layer to each other, and an elastic layer, with each of the photo-curable resin layer and the elastic layer serving as the outermost layer, wherein the elastic layer is provided with a rereleasable tacky surface.
The present invention also provides a raw plate for a flexographic printing plate, com
Kawamoto Tadashi
Kimura Toshiaki
Kusakawa Koichi
Suzuki Kenji
Asahi Kasei Kabushiki Kaisha
Dickstein Shapiro Morin & Oshinsky LLP.
Funk Stephen R.
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