Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-07-24
2003-04-22
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S286100, C430S287100, C430S281100, C430S306000, C430S905000, C430S907000, C430S910000
Reexamination Certificate
active
06551756
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to solvent-developable printing formulations useful for the manufacture of printing plates. In particular, the present invention provides formulations which exhibit markedly improved processing characteristics when deposited on a printing plate. In accordance with another aspect of the invention, there are provided methods for the preparation of said formulations and methods for use thereof.
BACKGROUND OF THE INVENTION
Flexographic printing is widely used in the production of newspapers and in the decorative printing of packaging media. In flexographic printing, a layer of a flexible printing medium is deposited onto a flexible substrate such as a thin sheet of steel, aluminum, or synthetic polymer, to form a printing plate. A relief pattern corresponding to the negative image to be printed is formed in the printing medium. The plate is then mounted on the printing press, and printing commences.
One type of printing medium is natural or synthetic rubber. This printing medium has excellent mechanical properties, but the preparation of a printing plate with a rubber printing medium is labor intensive and slow. A pattern plate and a matrix board are prepared, and rubber plates are then hot press molded. Molded rubber printing media are not practical for printing applications with short deadlines, such as newspapers. Due to the nature of the medium and imaging techniques described above, photosensitive printing plates have been developed to meet the demand for fast, inexpensive processing and long press runs.
The use of a photosensitive printing medium for the manufacture of flexographic printing plates is described in general terms as follows. The photosensitive printing material is coated onto the substrate to form the printing plate. The coated side is exposed with light through a photographic negative of the image to be printed, causing photopolymerization of the exposed portion of the printing medium, which then becomes physically hardened and resistant to solvent removal. The unexposed and therefore unhardened portion of the printing medium is removed by washing with solvent, leaving a relief pattern of the image to be printed. The printing plate is mounted on a press and printing commences.
Non-flexographic printing plates such as letterpress plates are also used for printing newspapers, shoppers, and books. Photosensitive resin compositions have been developed for use with non-flexographic printing applications for the same reasons disclosed above for flexographic applications. The use of photosensitive printing media for the manufacture of letterpress printing plates is essentially the same as described above for flexographic printing applications.
Photosensitive resin compositions employed for the preparation of conventional photosensitive resin plates are based on liquid unsaturated polyesters, polyvinyl alcohols, water soluble polyamides, cellulose acetate succinates, alcohol soluble polyamides, etc. Conventional photosensitive resin compositions currently play an adequate role in the manufacture of flexible printing plates. However, due to the rapid growth of the printing industry, there is an ever increasing demand for photosensitive resin formulations with improved processing characteristics. For example, the resin composition must maintain a good balance between mechanical properties such as tensile strength, elongation, and Young's modulus. Additionally, in order to increase manufacturing efficiency, the resin will desirably exhibit reduced tack for ease of handling before photopolymerization and will also desirably photopolymerize as quickly as possible when exposed to the light source.
Accordingly, there remains a need in the art for photosensitive resin formulations having improved chemical and physical properties. The present invention fulfills this need and further provides related advantages.
SUMMARY OF THE INVENTION
In accordance with the present invention, there are provided solvent-developable printing formulations having one or more improved processing characteristics such as reduced tack, increased image resolution, and/or improved mechanical properties, e.g., tensile strength, elongation. In addition, there are also provided methods for the preparation of said formulations and methods for use thereof.
A desirable characteristic of any printing medium is developability in water, rather than organic solvents. Water-developable formulations are desirable for reasons such as ease of handling, health of workers who are in contact therewith, safety, and avoidance of environmental pollution. Therefore, in accordance with a particular aspect of the invention there are provided water-developable formulations with improved processing characteristics comprising a photosensitive resin and a metal-containing additive. The formulation according to an alternate embodiment of the present invention is aqueous base and/or organic solvent developable.
Due to the improved processing characteristics provided by the formulations of the present invention, printing plates prepared employing invention formulations have excellent form stability, thereby enabling such plates to be handled without the need for excessive care. The increased image resolution provided by invention formulations leads to higher print quality. Once photopolymerized, printing plates of the invention have excellent physical properties, enabling their use in many very demanding commercial applications, e.g., commercial flexographic printing. Such applications require the photopolymerized resin to have excellent water resistance (so that exposure to water-based inks does not significantly alter resin properties), as well as high resilience (so that the physical contacting associated with the printing process does not significantly degrade resin properties). Photopolymerized formulations of the invention maintain a good balance between tensile strength, % elongation, and Young's modulus to 30%. Photopolymerization of invention formulations yields products with ink transfer characteristics considered acceptable by flexographic printing standards and demonstrates sufficient toughness for extended printing runs as required in such areas as telephone directory and comic section printing.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with the present invention, there are provided solvent-developable printing formulations comprising a photosensitive resin composition and a metal-containing additive. The metal-containing additive imparts improved processing characteristics to the resin, such as reduced tack, increased image resolution, and improved mechanical properties, (e.g., tensile strength, elongation) resulting in a markedly improved printing formulation.
Metal-containing additives contemplated for use in the practice of the present invention are coordination complexes of the formula M
+n
(Q)
m
, wherein M is a metal, n and m are integers from 1 to 4, and Q is an anionic ligand. The anionic ligand, Q, has the following structure:
(E—X)
y
—R
wherein:
E is NR
a
, PR
a
, O, or S, wherein R
a
is —H, optionally substituted C
1
to C
20
alkyl, or optionally substituted aryl,
X is optional and if present, is carbonyl, thiocarbonyl, SO
2
, or imine,
R is —H, optionally substituted C
1
-C
20
alkyl or alkenyl, or optionally substituted aryl, and
y is 1, 2, or 3.
Coordination complexes contemplated for use in the practice of the present invention include complexes of transition metals such as Mn, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, and the like. Presently preferred transition metals contemplated for use herein include Mn, Fe, Co, and Ni. Particularly preferred transition metals are Mn and Fe.
Coordination complexes contemplated for use in the practice of the present invention also include main group metals such as Cu, Ag, Au, Zn, Al, Ca, Mg, and the like. Presently preferred main group metals contemplated for use herein include Al, Zn, and Cu. Coordination complexes contemplated for use in the practice of the present invention also includ
Hu Yuxin
Jacobsen Nathan J.
Baxter Janet
Carmody & Torrance LLP
Lee Sin J.
Napp Systems Inc.
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